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Publisher: Elsevier   (Total: 3181 journals)

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Showing 1 - 200 of 3181 Journals sorted alphabetically
Academic Pediatrics     Hybrid Journal   (Followers: 39, SJR: 1.655, CiteScore: 2)
Academic Radiology     Hybrid Journal   (Followers: 26, SJR: 1.015, CiteScore: 2)
Accident Analysis & Prevention     Partially Free   (Followers: 105, SJR: 1.462, CiteScore: 3)
Accounting Forum     Hybrid Journal   (Followers: 28, SJR: 0.932, CiteScore: 2)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 42, SJR: 1.771, CiteScore: 3)
Achievements in the Life Sciences     Open Access   (Followers: 7)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 6)
Acta Astronautica     Hybrid Journal   (Followers: 444, SJR: 0.758, CiteScore: 2)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 2)
Acta Biomaterialia     Hybrid Journal   (Followers: 30, SJR: 1.967, CiteScore: 7)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription   (Followers: 3)
Acta de Investigación Psicológica     Open Access   (Followers: 3)
Acta Ecologica Sinica     Open Access   (Followers: 11, SJR: 0.18, CiteScore: 1)
Acta Histochemica     Hybrid Journal   (Followers: 5, SJR: 0.661, CiteScore: 2)
Acta Materialia     Hybrid Journal   (Followers: 319, SJR: 3.263, CiteScore: 6)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.504, CiteScore: 1)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.542, CiteScore: 1)
Acta Oecologica     Hybrid Journal   (Followers: 12, SJR: 0.834, CiteScore: 2)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription  
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 2, SJR: 0.307, CiteScore: 0)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 2, SJR: 1.793, CiteScore: 6)
Acta Poética     Open Access   (Followers: 4, SJR: 0.101, CiteScore: 0)
Acta Psychologica     Hybrid Journal   (Followers: 26, SJR: 1.331, CiteScore: 2)
Acta Sociológica     Open Access   (Followers: 1)
Acta Tropica     Hybrid Journal   (Followers: 6, SJR: 1.052, CiteScore: 2)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 3, SJR: 0.374, CiteScore: 1)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 2)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 3, SJR: 0.344, CiteScore: 1)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 1)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 7, SJR: 0.19, CiteScore: 0)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 3)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 8)
Acute Pain     Full-text available via subscription   (Followers: 15, SJR: 2.671, CiteScore: 5)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.53, CiteScore: 4)
Addictive Behaviors     Hybrid Journal   (Followers: 18, SJR: 1.29, CiteScore: 3)
Addictive Behaviors Reports     Open Access   (Followers: 9, SJR: 0.755, CiteScore: 2)
Additive Manufacturing     Hybrid Journal   (Followers: 11, SJR: 2.611, CiteScore: 8)
Additives for Polymers     Full-text available via subscription   (Followers: 23)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 188, SJR: 4.09, CiteScore: 13)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 12, SJR: 1.167, CiteScore: 4)
Advanced Powder Technology     Hybrid Journal   (Followers: 17, SJR: 0.694, CiteScore: 3)
Advances in Accounting     Hybrid Journal   (Followers: 9, SJR: 0.277, CiteScore: 1)
Advances in Agronomy     Full-text available via subscription   (Followers: 17, SJR: 2.384, CiteScore: 5)
Advances in Anesthesia     Full-text available via subscription   (Followers: 30, SJR: 0.126, CiteScore: 0)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 2)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 12, SJR: 0.992, CiteScore: 1)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 12, SJR: 1.551, CiteScore: 4)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 24, SJR: 2.089, CiteScore: 5)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 15, SJR: 0.572, CiteScore: 2)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.61, CiteScore: 7)
Advances in Botanical Research     Full-text available via subscription   (Followers: 2, SJR: 0.686, CiteScore: 2)
Advances in Cancer Research     Full-text available via subscription   (Followers: 34, SJR: 3.043, CiteScore: 6)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 9, SJR: 1.453, CiteScore: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 1.992, CiteScore: 5)
Advances in Cell Aging and Gerontology     Full-text available via subscription   (Followers: 5)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 14)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 29, SJR: 0.156, CiteScore: 1)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 11, SJR: 0.713, CiteScore: 1)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 10, SJR: 1.316, CiteScore: 2)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 26, SJR: 1.562, CiteScore: 3)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 20, SJR: 1.977, CiteScore: 8)
Advances in Computers     Full-text available via subscription   (Followers: 14, SJR: 0.205, CiteScore: 1)
Advances in Dermatology     Full-text available via subscription   (Followers: 15)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 13)
Advances in Digestive Medicine     Open Access   (Followers: 12)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 7)
Advances in Drug Research     Full-text available via subscription   (Followers: 26)
Advances in Ecological Research     Full-text available via subscription   (Followers: 44, SJR: 2.524, CiteScore: 4)
Advances in Engineering Software     Hybrid Journal   (Followers: 29, SJR: 1.159, CiteScore: 4)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 8)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 52, SJR: 5.39, CiteScore: 8)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 1)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 9)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 67, SJR: 0.591, CiteScore: 2)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 17)
Advances in Genetics     Full-text available via subscription   (Followers: 21, SJR: 1.354, CiteScore: 4)
Advances in Genome Biology     Full-text available via subscription   (Followers: 11, SJR: 12.74, CiteScore: 13)
Advances in Geophysics     Full-text available via subscription   (Followers: 7, SJR: 1.193, CiteScore: 3)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 26, SJR: 0.368, CiteScore: 1)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 11, SJR: 0.749, CiteScore: 3)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 26)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 3, SJR: 0.193, CiteScore: 0)
Advances in Immunology     Full-text available via subscription   (Followers: 37, SJR: 4.433, CiteScore: 6)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 10, SJR: 1.163, CiteScore: 2)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 2, SJR: 1.938, CiteScore: 3)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 6, SJR: 0.176, CiteScore: 0)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 3)
Advances in Life Course Research     Hybrid Journal   (Followers: 9, SJR: 0.682, CiteScore: 2)
Advances in Lipobiology     Full-text available via subscription   (Followers: 1)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 8)
Advances in Marine Biology     Full-text available via subscription   (Followers: 21, SJR: 0.88, CiteScore: 2)
Advances in Mathematics     Full-text available via subscription   (Followers: 15, SJR: 3.027, CiteScore: 2)
Advances in Medical Sciences     Hybrid Journal   (Followers: 8, SJR: 0.694, CiteScore: 2)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 6)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 5, SJR: 1.158, CiteScore: 3)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 25)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 8)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 7, SJR: 0.182, CiteScore: 0)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 5)
Advances in Oncobiology     Full-text available via subscription   (Followers: 2)
Advances in Organ Biology     Full-text available via subscription   (Followers: 2)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 18, SJR: 1.875, CiteScore: 4)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.174, CiteScore: 0)
Advances in Parasitology     Full-text available via subscription   (Followers: 5, SJR: 1.579, CiteScore: 4)
Advances in Pediatrics     Full-text available via subscription   (Followers: 27, SJR: 0.461, CiteScore: 1)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 19)
Advances in Pharmacology     Full-text available via subscription   (Followers: 17, SJR: 1.536, CiteScore: 3)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 0.574, CiteScore: 1)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.109, CiteScore: 1)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 10)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 6)
Advances in Porous Media     Full-text available via subscription   (Followers: 5)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 19)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 20, SJR: 0.791, CiteScore: 2)
Advances in Psychology     Full-text available via subscription   (Followers: 68)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 6, SJR: 0.371, CiteScore: 1)
Advances in Radiation Oncology     Open Access   (Followers: 2, SJR: 0.263, CiteScore: 1)
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 3, SJR: 0.101, CiteScore: 0)
Advances in Space Biology and Medicine     Full-text available via subscription   (Followers: 6)
Advances in Space Research     Full-text available via subscription   (Followers: 424, SJR: 0.569, CiteScore: 2)
Advances in Structural Biology     Full-text available via subscription   (Followers: 5)
Advances in Surgery     Full-text available via subscription   (Followers: 13, SJR: 0.555, CiteScore: 2)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 38, SJR: 2.208, CiteScore: 4)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 20)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 15)
Advances in Virus Research     Full-text available via subscription   (Followers: 6, SJR: 2.262, CiteScore: 5)
Advances in Water Resources     Hybrid Journal   (Followers: 54, SJR: 1.551, CiteScore: 3)
Aeolian Research     Hybrid Journal   (Followers: 6, SJR: 1.117, CiteScore: 3)
Aerospace Science and Technology     Hybrid Journal   (Followers: 385, SJR: 0.796, CiteScore: 3)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.42, CiteScore: 2)
African J. of Emergency Medicine     Open Access   (Followers: 6, SJR: 0.296, CiteScore: 0)
Ageing Research Reviews     Hybrid Journal   (Followers: 12, SJR: 3.671, CiteScore: 9)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 483, SJR: 1.238, CiteScore: 3)
Agri Gene     Hybrid Journal   (Followers: 1, SJR: 0.13, CiteScore: 0)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 18, SJR: 1.818, CiteScore: 5)
Agricultural Systems     Hybrid Journal   (Followers: 32, SJR: 1.156, CiteScore: 4)
Agricultural Water Management     Hybrid Journal   (Followers: 45, SJR: 1.272, CiteScore: 3)
Agriculture and Agricultural Science Procedia     Open Access   (Followers: 4)
Agriculture and Natural Resources     Open Access   (Followers: 3)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 58, SJR: 1.747, CiteScore: 4)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.589, CiteScore: 3)
Air Medical J.     Hybrid Journal   (Followers: 8, SJR: 0.26, CiteScore: 0)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.19, CiteScore: 0)
Alcohol     Hybrid Journal   (Followers: 12, SJR: 1.153, CiteScore: 3)
Alcoholism and Drug Addiction     Open Access   (Followers: 12)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 2, SJR: 0.604, CiteScore: 3)
Alexandria J. of Medicine     Open Access   (Followers: 1, SJR: 0.191, CiteScore: 1)
Algal Research     Partially Free   (Followers: 11, SJR: 1.142, CiteScore: 4)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 2)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.504, CiteScore: 1)
Allergology Intl.     Open Access   (Followers: 5, SJR: 1.148, CiteScore: 2)
Alpha Omegan     Full-text available via subscription   (SJR: 3.521, CiteScore: 6)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 11, SJR: 0.201, CiteScore: 1)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 54, SJR: 4.66, CiteScore: 10)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 6, SJR: 1.796, CiteScore: 4)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 6, SJR: 1.108, CiteScore: 3)
Ambulatory Pediatrics     Hybrid Journal   (Followers: 5)
American Heart J.     Hybrid Journal   (Followers: 58, SJR: 3.267, CiteScore: 4)
American J. of Cardiology     Hybrid Journal   (Followers: 66, SJR: 1.93, CiteScore: 3)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 47, SJR: 0.604, CiteScore: 1)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 13)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 14, SJR: 1.524, CiteScore: 3)
American J. of Human Genetics     Hybrid Journal   (Followers: 37, SJR: 7.45, CiteScore: 8)
American J. of Infection Control     Hybrid Journal   (Followers: 29, SJR: 1.062, CiteScore: 2)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 36, SJR: 2.973, CiteScore: 4)
American J. of Medicine     Hybrid Journal   (Followers: 50)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3, SJR: 1.967, CiteScore: 2)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 266, SJR: 2.7, CiteScore: 4)
American J. of Ophthalmology     Hybrid Journal   (Followers: 66, SJR: 3.184, CiteScore: 4)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 5, SJR: 0.265, CiteScore: 0)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.289, CiteScore: 1)
American J. of Otolaryngology     Hybrid Journal   (Followers: 25, SJR: 0.59, CiteScore: 1)
American J. of Pathology     Hybrid Journal   (Followers: 32, SJR: 2.139, CiteScore: 4)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 28, SJR: 2.164, CiteScore: 4)
American J. of Surgery     Hybrid Journal   (Followers: 39, SJR: 1.141, CiteScore: 2)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.767, CiteScore: 1)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 7)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.144, CiteScore: 3)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 67, SJR: 0.138, CiteScore: 0)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 25, SJR: 0.411, CiteScore: 1)
Anales de Cirugia Vascular     Full-text available via subscription   (Followers: 1)
Anales de Pediatría     Full-text available via subscription   (Followers: 3, SJR: 0.277, CiteScore: 0)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription  
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 5, SJR: 4.849, CiteScore: 10)
Analytica Chimica Acta     Hybrid Journal   (Followers: 44, SJR: 1.512, CiteScore: 5)
Analytica Chimica Acta : X     Open Access  
Analytical Biochemistry     Hybrid Journal   (Followers: 211, SJR: 0.633, CiteScore: 2)
Analytical Chemistry Research     Open Access   (Followers: 13, SJR: 0.411, CiteScore: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 14)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 2)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 25, SJR: 0.683, CiteScore: 2)
Angiología     Full-text available via subscription   (SJR: 0.121, CiteScore: 0)
Angiologia e Cirurgia Vascular     Open Access   (Followers: 1, SJR: 0.111, CiteScore: 0)
Animal Behaviour     Hybrid Journal   (Followers: 227, SJR: 1.58, CiteScore: 3)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 7, SJR: 0.937, CiteScore: 2)
Animal Reproduction Science     Hybrid Journal   (Followers: 7, SJR: 0.704, CiteScore: 2)

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Similar Journals
Journal Cover
Additive Manufacturing
Journal Prestige (SJR): 2.611
Citation Impact (citeScore): 8
Number of Followers: 11  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 2214-8604
Published by Elsevier Homepage  [3181 journals]
  • Correlation between forming quality and spatter dynamics in laser powder
           bed fusion
    • Abstract: Publication date: Available online 19 November 2019Source: Additive ManufacturingAuthor(s): Jie Yin, Dengzhi Wang, Liangliang Yang, Huiliang Wei, Peng Dong, Linda Ke, Guoqing Wang, Haihong Zhu, Xiaoyan ZengAbstractLaser powder bed fusion (LPBF) has broad application prospects due to its high fabrication accuracy and excellent performance, but the dynamic mechanical properties of LPBF components are relatively low due to defects of the melt track such as protrusions and depressions, whose generation mechanisms remain unclear. In this work, we investigate the correlation between the ex situ melt track properties and in situ high-speed high-resolution characterization. We correlate the protrusion of the starting position of the melt track with the droplet ejection behaviour and backward surging melt. We also reveal that the inclination angles of the depression walls are consistent with the ejection angles of the backward-ejected spatter. Furthermore, we quantify the vapour recoil pressure by in situ characterization of the deflection of the typical forward-ejected spatter. Our results clarify the intrinsic correlation of the melt track properties, which is important for the stable formation of LPBF with few defects.
       
  • Al–Cu Alloy Fabricated by Novel Laser-TIG Hybrid Additive
           Manufacturing
    • Abstract: Publication date: Available online 19 November 2019Source: Additive ManufacturingAuthor(s): Dongjiang Wu, Dehua Liu, Fangyong Niu, Qiuyu Miao, Kai Zhao, Bokai Tang, Guijun Bi, Guangyi MaOwing to its high strength to weight ratio, Al–Cu alloy is extensively used in the aeronautic and aerospace industries. However, there are some shortcomings in the additive manufacturing of Al–Cu alloy, such as cracks and poor strength. In this work, Al–Cu (2219-Al) specimens with excellent mechanical properties were fabricated by laser-TIG hybrid additive manufacturing. From microstructural studies, the average grain size in the laser zone (LZ) decreased to 14.4 μm, which was approximately 40.3% smaller than that in the arc zone (AZ). A {100} texture could be observed along the deposition direction. Under the influence of laser stirring, Cu in the LZ was distributed more uniformly than in the AZ. An incoherent θ phase, at the nanoscale, was discovered in both the AZ and the LZ. Its crystal orientation relationship was described as [110]α∥[002]θ, (110)α∥(002)θ between the α-Al matrix and the θ phase. The semi-coherent θ′ phase was observed in the LZ. Meanwhile, the θ′ phase characterized a good coherent relationship with the α-Al matrix, which resulted in low phase boundary energy. Furthermore, the deposited specimens exhibited a yield strength of 155.5 ± 7.9 MPa and an ultimate tensile strength of 301.5 ± 16.7 MPa, with an elongation of 12.8 ± 2.8%. These mechanical properties were higher than in specimens fabricated by TIG, CMT and SLM methods. The improved properties were predominately related to the smaller size of eutectics, the uniform distribution of Cu and the semi-coherent θ′ phases in the LZ. The combined effect of laser and arc can yield components with excellent mechanical properties, promoting the material for an expansive range of applications.Graphical Graphical abstract for this article
       
  • Laser-based powder bed fusion of alumina toughened zirconia
    • Abstract: Publication date: Available online 18 November 2019Source: Additive ManufacturingAuthor(s): Fabrizio Verga, Mario Borlaf, Laura Conti, Kevin Florio, Marc Vetterli, Thomas Graule, Manfred Schmid, Konrad WegenerAbstractAlumina toughened zirconia (ATZ) parts were produced via a laser-based powder bed fusion technology using a conventional Nd-YAG continuous wave laser. The powder was produced using a spray drying process and the laser matter interaction was enhanced by a binder pyrolysis. A processing window led to part densities of over 90%. Thermal post-processing to further increase the part density was investigated using dilatometry. The microstructure was analysed using X-ray powder diffraction measurements. The mechanical properties were assessed using a four-point bending test on ten specimens, reaching a bending strength of 31 ± 11 MPa.
       
  • Binder Jetting Additive Manufacturing of Copper Foam Structures
    • Abstract: Publication date: Available online 18 November 2019Source: Additive ManufacturingAuthor(s): Hadi Miyanaji, Da Ma, Mark A. Atwater, Kristopher A. Darling, Vincent H. Hammond, Christopher B. WilliamsIn Binder jetting additive manufacturing (BJAM), the part geometry is generated via a binding agent during printing and structural integrity is imparted during sintering at a later stage. This separation between shape generation and thermal processing allows the sintering process to be uniquely controlled and the final microstructural characteristics to be tailored. The separation between the printing and consolidation steps offers a unique opportunity to print responsive materials that are later “activated” by temperature and/or environment. This may allow a new paradigm in multi-scale, multifunctional materials. This concept is preliminarily demonstrated using a foaming copper feedstock, such that the copper is printed, sintered and then foamed via intraparticle expansion in separate steps. The integration of foaming feedstock in BJAM could allow for creation of ultra-lightweight structures that offer hierarchical porosity, graded density, and/or tailored absorption properties. This work investigates processing protocol for copper foam structures to achieve the highest porosity. The copper feedstock was prepared by distributing copper oxides through the copper matrix via mechanical milling, and that powder was then printed into a green geometry through BJAM. The printed green parts were then heat treated using different thermal cycles to investigate the porosity evolution relative to various heating conditions. The heat treated parts were then examined for their resulting properties including porosity, microstructural evolution, and volumetric shrinkage. Parts that were initially sintered in air and then annealed in a hydrogen atmosphere led to higher porosity compared to those sintered in hydrogen alone. It was also found that the annealing of parts at 600 °C for 2 hours resulted in the highest final porosity (59%) and the lowest volumetric shrinkage of 5%. Anisotropy in linear shrinkage in X, Y, and Z direction was also observed in the heat treated parts with the largest linear shrinkage occurring in the Z direction.Graphical abstractGraphical abstract for this article
       
  • Laser opto-ultrasonic dual detection for simultaneous compositional,
           structural, and stress analyses for wire + arc additive manufacturing
    • Abstract: Publication date: Available online 18 November 2019Source: Additive ManufacturingAuthor(s): Yuyang Ma, Zhenlin Hu, Yun Tang, Shixiang Ma, Yanwu Chu, Xin Li, Wei Luo, Lianbo Guo, Xiaoyan Zeng, Yongfeng LuAbstractThe complex, nonequilibrium physical, chemical, and metallurgical nature of additive manufacturing (AM) tends to lead to uncontrollable and unpredictable material and structural properties. Therefore, real-time monitoring of AM is of great significance. However, current AM relies on separate postprocess analyses, which are usually destructive, costly, and time-consuming. In this study, we investigated a laser opto-ultrasonic dual (LOUD) detection approach for simultaneous and real-time detection of elemental compositions, structural defects, and residual stress in aluminium (Al) alloy components during wire + arc additive manufacturing (WAAM) processes. In this approach, a pulsed-laser beam was used to excite the surfaces of Al alloy samples to generate ultrasound and optical spectra. As a result, the compositional information can be obtained from the optical spectra, while the structural defects and residual stress distributions can be extracted from the ultrasonic signals. The silicon (Si) and copper (Cu) compositions obtained from optical spectral analyses are consistent with those obtained from the electron-probe microanalyses (EPMA). The 1 mm blowhole and the residual stress distribution of the sample were detected by the ultrasonic signals in the LOUD detection, which shows consistency with the conventional ultrasonic testing (UT). Both results indicate that the LOUD detection holds the promising of becoming an effective testing method for AM processes to ensure quality control and process feedback.
       
  • Linking pyrometry to porosity in additively manufactured metals
    • Abstract: Publication date: Available online 17 November 2019Source: Additive ManufacturingAuthor(s): John A. Mitchell, Thomas A. Ivanoff, Daryl Dagel, Jonathan D. Madison, Bradley JaredAbstractPorosity in additively manufactured metals can reduce material strength and is generally undesirable. Although studies have shown relationships between process parameters and porosity, monitoring strategies for defect detection and pore formation are still needed. In this paper, instantaneous anomalous conditions are detected in-situ via pyrometry during laser powder bed fusion additive manufacturing and correlated with voids observed using post-build micro-computed tomography. Large two-color pyrometry data sets were used to estimate instantaneous temperatures, melt pool orientations and aspect ratios. Machine learning algorithms were then applied to processed pyrometry data to detect outlier images and conditions. It is shown that melt pool outliers are good predictors of voids observed post-build. With this approach, real time process monitoring can be incorporated into systems to detect defect and void formation. Alternatively, using the methodology presented here, pyrometry data can be post processed for porosity assessment.
       
  • Digital image correlation for microstructural analysis of deformation
           pattern in additively manufactured 316L thin walls
    • Abstract: Publication date: January 2020Source: Additive Manufacturing, Volume 31Author(s): Yanis Balit, Eric Charkaluk, Andrei ConstantinescuIn additive manufacturing, the process parameters have a direct impact on the microstructure of the material and consequently on the mechanical properties of the manufactured parts. The purpose of this paper is to explore this relation by characterizing the local microstructural response via in situ tensile test under a scanning electron microscope (SEM) combined with high resolution digital image correlation (HR-DIC) and Electron Backscatter Diffraction (EBSD) maps. The specimens under scrutiny were extracted from bidirectionally-printed single-track thickness 316L stainless steel walls built by directed energy deposition. The morphologic and crystallographic textures of the grains were characterized by statistical analysis and associated with the particular heat flow pattern of the process. Grains were sorted according to their size into large columnar grains located within the printed layer and small equiaxed grains located at the interfaces between successive layers. In situ tensile experiments were performed with a loading direction either perpendicular or along the printing direction and exhibit different mechanisms of deformation. A statistical analysis of the average deformation per grain indicates that for a tensile loading along the building direction, small grains deform less than the large ones. In addition, HR-DIC combined with EBSD maps showed strain localization situated at the interface between layers in the absence of small grains either individual or in clusters. For tensile loads along the printing direction, the strain localization was present in several particular large grains. These observations permit to justify the differences in yield and ultimate strength noticed during macroscopic tensile tests for both configurations. Moreover, they indicate that an optimization of the process parameters could trigger the control of microstructure and consequently the macroscopic mechanical behavior.Graphical abstractGraphical abstract for this article
       
  • Additive Manufacturing of Functionally Graded Metallic Materials Using
           Laser Metal Deposition
    • Abstract: Publication date: Available online 16 November 2019Source: Additive ManufacturingAuthor(s): Lei Yan, Yitao Chen, Frank LiouAbstractFunctionally graded materials (FGMs) have attracted much research interest in the industry due to their graded material properties, which result from gradually distributed compositions or structures. In recent years, metallic FGMs have been widely studied, and additive manufacturing (AM) has become an important approach to build metallic FGMs. This paper aims to provide an overview of the research progress in metallic FGMs fabricated by laser metal deposition (LMD), an AM process that is widely used in metallic materials. Firstly, the unique material properties and advantages of FGMs are introduced. Then, typical recent findings in transition path design, fabrication, and characterization for different types of metallic FGMs via LMD are summarized and discussed. Finally, challenges in fabricating metallic FGMs via LMD are discussed, and other related aspects in the area of FGMs such as model representation and numerical simulation are proposed for further investigation.
       
  • Extended finite element method (XFEM) modeling of fracture in additively
           manufactured polymers
    • Abstract: Publication date: Available online 14 November 2019Source: Additive ManufacturingAuthor(s): R. Ghandriz, K. Hart, J. LiAbstractThe fracture of additively manufactured polymer materials with various layer orientations is studied using the extended finite element method (XFEM) in an anisotropic cohesive zone model (CZM). The single edge notched bending (SENB) specimens made of acrylonitrile-butadiene-styrene (ABS) materials through fused filament fabrications with various crack tip/layer orientations are considered. The XFEM coupled with anisotropic CZM is employed to model the brittle fracture (fracture between layers), ductile fracture (fracture through layers), as well as kinked fracture behaviors of ABS specimens printed with vertical, horizontal, and oblique layer orientations, respectively. Both elastic and elastoplastic fracture models, coupled with linear or exponential traction-separation laws, are developed for the inter-layer and cross-layer fracture, respectively. For mixed inter-/cross- layer fracture, an anisotropic cohesive zone model is developed to predict the kinked crack propagations. Two crack initiation and evolution criteria are defined to include both crack propagation between layers (weak plane failure) and crack penetration through layers (maximum principal stress failure) that jointly determine the zig-zag crack growth paths. The anisotropic cohesive zone model with XFEM developed in this study is able to capture different fracture behaviors of additively manufactured ABS samples with different layer orientations.
       
  • Revisiting solidification microstructure selection maps in the frame of
           additive manufacturing
    • Abstract: Publication date: Available online 14 November 2019Source: Additive ManufacturingAuthor(s): P. Mohammadpour, A. Plotkowski, A.B. PhillionAbstractUnderstanding microstructural development in additive manufacturing under highly non-equilibrium cooling conditions and the consequent effects on mechanical properties of the final component is critical for accelerating industrial adoption of these manufacturing techniques. In this study, simple but effective theoretical solidification models are recalled to evaluate their ability to predict of microstructural features in additive manufacturing applications. As a case study, the resulting solidification microstructure selection maps are created to predict the stable growth modality and the columnar to equiaxed transition (CET) of an Al-10Si-0.5Mg alloy processed via Selective Laser Melting. The potential of this method in microstructural predictions for additively manufactured products, as well as outstanding challenges and limitations, are discussed.
       
  • Additive manufacturing of magnetic materials
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): E.A. Périgo, J. Jacimovic, F. García Ferré, L.M. ScherfAbstractTechniques that use the layer-by-layer manufacturing concept have triggered novel research topics related to the processing of functional magnetic materials (FMMs). In this article, we focus on four FMM classes due to their technical relevance for energy conversion, harvesting, transmission, and sensing/actuation. Permanent magnets, soft magnetic materials, magnetocaloric compounds, and magnetic shape memory alloys are reviewed in terms of functionality and performance limits. Relationships among printing techniques and/or conditions, microstructure and performance are highlighted. Additively manufactured hard magnets are the closest to commercial/industrial application.
       
  • Fast solution strategy for transient heat conduction for arbitrary scan
           paths in additive manufacturing
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): Alexander J. Wolfer, Jeremy Aires, Kevin Wheeler, Jean-Pierre Delplanque, Alexander Rubenchik, Andy Anderson, Saad KhairallahAbstractA unique and efficient semi-analytic method is presented for quickly predicting the three-dimensional thermal field produced by conduction from a heat source moving along an arbitrary path. A Green's function approach is used to decouple the solution at each time step into the analytical source contribution and a conduction contribution. The latter is solved numerically using efficient Gaussian convolution algorithms. This decoupling allows for boundary conditions on side boundaries to be satisfied numerically and lowers computational expenses by allowing calculations to be localized around the heat source. The thermal field resulting from arbitrary scan paths is constructed using analytical solutions for elementary linear segments. With focus on efficiency, a novel approach is used to store the calculated analytical line solutions for reuse on multiple other path segments. The results of various scan patterns are presented and successfully verified against finite element simulations. The computational times of predictions are shown to be faster than the corresponding finite element simulation by an order of magnitude with less than 1% average error. Given its ability to quickly predict the thermal history and changes in melt pool geometry due to arbitrary scan paths, this method provides a potentially powerful tool for exploration and optimization of laser powder bed fusion processes.
       
  • Research on large-scale additive manufacturing based on multi-robot
           collaboration technology
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): Hongyao Shen, Lingnan Pan, Jun QianAbstractAdditive manufacturing is considered a promising technology for many applications, such as in the construction industry. However, the size of a design is constrained by the chamber volume of the 3D printer, and large-scale additive manufacturing technology with flexible equipment is still unproven. This paper proposes a large-scale 3D printing system composed of multiple robots working in collaboration. For this flexible and extensible 3D printing system, the influences of the multi-robot layout on the maximum reachable area and the geometry adaptability are discussed. Furthermore, a printer task optimized scheduling algorithm based on efficiency egalitarianism is proposed in this paper, and a robot interference avoidance strategy is designed by dividing the printing layer into several safe areas and interference areas. Collaborative printing experiments are implemented on the multi-robot platform, and the results show that the efficiency improvement with four robots exceeds 73 % compared with a general printing method.
       
  • Fast micron-scale 3D printing with a resonant-scanning two-photon
           microscope
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): Benjamin W. Pearre, Christos Michas, Jean-Marc Tsang, Timothy J. Gardner, Timothy M. OtchyAbstract3D printing allows rapid fabrication of complex objects from digital designs. One 3D-printing process, direct laser writing, polymerises a light-sensitive material by steering a focused laser beam through the shape of the object to be created. The highest-resolution direct laser writing systems use a femtosecond laser, steered using mechanised stages or galvanometer-controlled mirrors, to effect two-photon polymerisation. Here we report a new high-resolution direct laser writing system that employs a resonant mirror scanner to achieve a significant increase in printing speed over current methods while maintaining resolution on the order of a micron. This printer is based on a software modification to a commercially available resonant-scanning two-photon microscope. We demonstrate the complete process chain from hardware configuration and control software to the printing of objects of approximately 400 × 400 × 350 μm, and validate performance with objective benchmarks. Released under an open-source license, this work makes micron-scale 3D printing available at little or no cost to the large community of two-photon microscope users, and paves the way toward widespread availability of precision-printed devices.
       
  • “Implications of lattice structures on economics and productivity of
           metal powder bed fusion”
    • Abstract: Publication date: Available online 13 November 2019Source: Additive ManufacturingAuthor(s): Inigo FloresThe cost-effectiveness of metal powder bed fusion (PBF) systems in high-throughput production are dominated by the high cost of metallic powder materials. Metal PBF technologies become more competitive in production scenarios when Design for Additive Manufacturing (DfAM) is integrated to embed functionality through shape complexity, weight, and material reduction through topology optimization and lattice structures.This study investigates the value of DfAM in terms of unit cost and manufacturing time reduction. Input design parameters, such as lattice design-type, part size, volume fraction, material type and production volumes are included in a Design-of-Experiment to model their impact. The performance variables for cost and manufacturing time were assessed for two scenarios: (i) outsourcing scenario using an online quotation system, and (ii) in-house scenario utilizing a decision support system (DSS) for metal PBF.The results indicate that the size of the part and the lattice volume fraction are the most significant parameters that contribute to time and cost savings. This study shows that full utilization of build platforms by volume-optimized parts, high production volumes, and reduction of volume fraction lead to substantial benefits for metal PBF industrialization. Integration of DfAM and lattice designs for lightweight part production can decrease the unit cost of production down to 70.6% and manufacturing time can be reduced significantly down to 71.7% depending on the manufacturing scenarios and design constraints when comparing to solid infill designs. The study also provides a case example of a bracket design whose cost is reduced by 53.7%, manufacturing time is reduced by 54.3 %, and the overall weight is reduced significantly with the use of lattices structures and topology optimization.Graphical abstractGraphical abstract for this article
       
  • Efficient generation strategy for hierarchical porous scaffolds with
           freeform external geometries
    • Abstract: Publication date: Available online 11 November 2019Source: Additive ManufacturingAuthor(s): Jiawei Feng, Jianzhong Fu, Ce Shang, Zhiwei Lin, Xiaomiao Niu, Bin LiAbstractThe external geometry design and manipulation of internal porosity distribution according to the actual application demands are the main challenges of scaffold generation; moreover, computational efficiency is a key factor that should be considered. This paper proposes efficient generation strategies for constructing internal porous architectures by using triply periodic minimal surfaces (TPMSs) and external freeform shapes through T-spline surfaces. After discretizing the geometries as slicing contours, TPMSs can be efficiently extracted using the intersection-interpolation method in 2D space, and then be offset as infill areas of sheet solids. Based on the proposed fractal sheet TPMSs, hierarchical scaffolds are further generated using the refined constrained Delaunay triangulation method to construct multiscale pores. The porosity features can be conveniently controlled in 2D space according to the actual computed tomography images. Eventually, the resulting infill areas can be directly fabricated as scaffolds by additive manufacturing technology. Several experimental instances validate the effectiveness and efficiency of the proposed strategies.
       
  • Expanding capabilities of additive manufacturing through use of robotics
           technologies: A survey
    • Abstract: Publication date: Available online 11 November 2019Source: Additive ManufacturingAuthor(s): Prahar M. Bhatt, Rishi K. Malhan, Aniruddha V. Shembekar, Yeo Jung Yoon, Satyandra K. GuptaAbstractRobots are versatile machines that can perform complex manipulation operations. Recent advances in industrial robotics make robots useful in a wide variety of manufacturing processes. Several recent efforts have demonstrated how robots can be used in additive manufacturing (AM) processes. This paper surveys the work focused on expanding the functional capabilities of AM processes using robots. We identify the following main capabilities realized by performing AM using robots: (1) multi-directional fabrication, (2) conformal deposition, (3) assembling prefabricated components in AM, (4) supportless AM, and (5) large-scale AM. We classify the recent literature in this area in terms of mechanisms, kinematic degrees of freedom (DOF) of the system, types of AM process, and materials. Finally, we discuss the limitations of the current work and the opportunities for future research in this area.
       
  • Automated non-destructive inspection of Fused Filament Fabrication
           components using Thermographic Signal Reconstruction
    • Abstract: Publication date: Available online 11 November 2019Source: Additive ManufacturingAuthor(s): Joshua E. Siegel, Maria F. Beemer, Steven M. ShepardAbstractManufacturers struggle to produce low-cost, robust and intricate components in small batches. Additive processes like Fused Filament Fabrication (FFF) inexpensively generate such complex geometries, but potential defects may limit these components’ viability in critical applications. We present a high-accuracy, high-throughput and low-cost approach to automated non-destructive testing (NDT) for FFF interlayer delamination. This Artificially Intelligent (AI) approach utilizes Flash Thermography (FT) data processed with Thermographic Signal Reconstruction (TSR). A Deep Neural Network (DNN) attains 95.4% per-pixel accuracy when differentiating four delamination severities 5 mm below the surface in PolyLactic Acid (PLA) widgets, and 98.6% accuracy in differentiating acceptable from unacceptable states for the same components. Automation supports time- and cost-efficient inspection for delamination defects in 100% of widgets, supporting FFF's use in critical and lot-size one applications.
       
  • Load Path Visualization and Fiber Trajectory Optimization for Additive
           Manufacturing of Composites
    • Abstract: Publication date: Available online 11 November 2019Source: Additive ManufacturingAuthor(s): Takuya Suzuki, Shinya Fukushige, Mitsuyoshi TsunoriAbstractA methodology of fiber trajectory optimization is proposed for Additive Manufacturing of composites. The present method aligns fiber with a physically-determined load path to simultaneously increase the stiffness and strength of the composite structures. The fiber trajectories of the open-hole panel and Payload Attach Fitting (PAF) were determined. In the case of open-hole panel, the deformation and the failure index were decreased by 8% and 55% compared to those obtained by the unidirectional structure. In the case of PAF, the decrease in failure index was 76%, but the reduction of deformation was not significant (6%). The present method also identified the structural members that did not contribute to strength and rigidity, which in turn realized the appropriate weight savings and increased the specific strength and specific stiffness.
       
  • Chemical composition and degradation products in additively manufactured
           methacrylates for dental devices
    • Abstract: Publication date: Available online 11 November 2019Source: Additive ManufacturingAuthor(s): Frank Alifui-Segbaya, Jasper Bowman, Alan R. White, Ismail Fidan, Robert M. Love, Roy GeorgeAbstractIn additive manufacturing (AM) or three-dimensional printing (3DP), crosslinked polymers can be synthesized from multifunctional monomers and telechelic oligomers by photochemical reactions, so liquid to solid phase change takes place within a fraction of a second at ambient temperature. Despite the potentials of AM or 3DP offering speed, biocompatibility is an issue of concern due to the complexities of the manufacturing process including postprocessing. For instance, photochemical reactions rarely proceed to completion hence could lead to accumulation of residual monomer and degradation products, and consequently cause local and systemic side effects in high doses. In this novel study, we evaluate an array of commercially available and proprietary methacrylates for dental devices i.e., denture bases (>60% Bis-EMA and 15-25% proprietary methacrylic oligomer), orthodontic appliances (>70% proprietary methacrylic oligomer,
       
  • Behavior of yttria-stabilized zirconia (YSZ) during Laser Direct Energy
           Deposition of an Inconel 625-YSZ Cermet
    • Abstract: Publication date: Available online 10 November 2019Source: Additive ManufacturingAuthor(s): Harish Rao, Richard P. Oleksak, Kory Favara, Arshad Harooni, Bhaskar Dutta, David MauriceAbstractThermal barrier coatings (TBC) are regularly used today to protect and extend the service life of several superalloys which are extensively used in high temperature applications. The existing TBCs are typically between 0.1 to 0.5 mm in thickness, are deposited on metal substrates using plasma spray or electron beam vapor deposition, and can reduce temperatures at the substrate surface by up to 300 °C. For greater temperature reductions there is a need for thicker TBCs. The building of thick TBCs has to date been stymied by poor adhesion, and cracking during deposition. It has been suggested that a functionally graded approach may reduce the residual stresses which result in these defects. To date there have been few reports on the deposition of ceramic or cermet coatings using laser AM and none have reported on the phase stability of ceramic particles post-deposition. This paper is a first report on the phase stability of ceramic particles following the compositional segregation of elements during deposition using a powder feed additive manufacturing process. Functionally graded (FG), thick TBCs (>3 mm) consisting of Inconel 625 (IN625) and yttria-partially stabilized zirconia (8YSZ) were deposited on an A516 steel substrate via laser direct energy deposition (LDED). Good interfaces were observed between the bond coat (BC) and first cermet layer and between the graded cermet layers. However, cermet layers deposited with 10 wt.% or more YSZ developed a thin layer of YSZ on the surface. The thin layer of YSZ greatly hindered additional deposition of new cermet layers. In cermet layers that did exhibit good interfaces, fine, re-solidified, YSZ particles were homogenously distributed within the Inconel 625 matrix. The YSZ particles exhibited a tetragonal lattice structure and were depleted of yttrium. In contrast, the thin YSZ layer formed on a cermet surface showed no yttrium depletion.
       
  • In-situ areal inspection of powder bed for electron beam fusion system
           based on fringe projection profilometry
    • Abstract: Publication date: Available online 8 November 2019Source: Additive ManufacturingAuthor(s): Yue Liu, Liam Blunt, Zonghua Zhang, Hussein Abdul Rahman, Feng Gao, Xiangqian JiangAbstractAdditive manufacturing (AM) techniques provide significant advantages over conventional subtractive manufacturing techniques in terms of the wide range of part geometry that can be obtained. Powder delivery is a process that occurs thousands of times during AM build process, consequently assessment of delivery quality would be advantageous in the process and provide feedback for process control. This paper presents an in-situ quantitative inspection technique for assessing the whole of the powder bed post raking, by using fringe projection profilometry. In order to increase accuracy and traceability of the inspection technique, an accepted fringe projection method, is enhanced using a novel surface fitting algorithm employed to reduce the influence of phase error and random noise during calibration. A simulation was conducted to verify the accuracy of the proposed system calibration. The proposed in-situ inspection technique has been applied in an Electron Beam Powder Bed Fusion (PBF-EB) machine, also known as Electron Beam Melting (EBM). Some examples of melting edge swelling and excessive powder delivery due to rake damage during a real part build are used to demonstrate the system capability on the actual EBM machine. A build process with presented fringe projection system is reported in this paper. Experimental results demonstrate that powder defects can be efficiently inspected which is represent as a feedback information in a build process with the proposed technique, and the inspection accuracy is consistent with the simulation results.
       
  • Integrated Laser-Based Powder Bed Fusion and Fused Filament Fabrication
           for Three-Dimensional Printing of Hybrid Metal/Polymer Objects
    • Abstract: Publication date: Available online 8 November 2019Source: Additive ManufacturingAuthor(s): Yuan-Hui Chueh, Chao Wei, Xiaoji Zhang, Lin LiAbstractTo produce complex functional devices while eliminating the need for assembly calls for a multi-material additive manufacturing technology. This paper presented a 3D-printing system that integrated fused filament fabrication (FFF) and laser-based powder bed fusion (PBF) to produce hybrid metal and polymer components. The design and operation procedure of the system were introduced. PBF-printed metal and FFF-printed polymer, both of which differ in material properties, were joined through PBF-printed interlocking structures, with their joining strength enhanced by laser heating. The mechanisms and scientific rationale that governed metal/polymer joining were discussed. Tensile and shear tests confirmed good joint strength of the printed metal/polymer components, which were created without adhesives. In addition, metal powder deposition onto the top of polymer substrates through laser melting was demonstrated. Layers of copper (Cu10Sn) were successfully deposited onto the top of a PLA/SS 316 L composite substrate; however, their joint strength remained a problem to resolve. Finally, several 3D components consisting of hybrid stainless steel (SS 316 L), copper (Cu10Sn) and polymer (PLA, PET) were successfully printed and their potential applications were discussed.
       
  • Highly loaded fiber filled polymers for material extrusion: A review of
           current understanding
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): Jacob J. Fallon, Steven H. McKnight, Michael J. BortnerAbstractThis review documents the current state of the art of highly filled (HF) polymer composite systems used in additive manufacturing (AM), with a core focus on short and continuous fiber filled composites for use in material extrusion (MatEx) AM. Current state of the art composite materials systems have been succesfully incorporated into the MatEx process with loading percentages up to approximately 45 vol. %. Further increasing the loading percentage would afford significant mechanical improvements that could enable structural performance, however there are currently a number of limitations that need to be addressed. Viscosity limitations associated with MatEx processing of HF composites originate from the low processing pressure inherent to filament feed MatEx processes. Restrictive hot end nozzle geometries (high volume contractions) increase required processing pressure and potential for nozzle clogging failures. The increased viscosity of the HF composite reduces interlayer contact and adhesion during the printing process, resulting in increased void spacing. Mechanical limitations of HF composites processed using MatEx are also reviewed. Flow induced fiber orientation and its influence on viscosity and mechanical anisotropy are investigated. Fiber breakage as well as strain to break limitations are reviewed. Lastly, the geometric packing limitations of fibers within a circular bound nozzle are reviewed. This review takes an in-depth look at recent advances in addressing these challenges, and discusses opportunities for realizing MatEx processing of HF composite systems with significantly improved performance.
       
  • Characterization of lattice defects and tensile deformation of biomedical
           Co29Cr9W3Cu alloy produced by selective laser melting
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): Yanjin Lu, Chunguang Yang, Yujing Liu, Ke Yang, Jinxin LinAbstractIn this study, novel biomedical Co29Cr9W3Cu samples were fabricated using selective laser melting (SLM) technology. In order to better understand the formation of the lattice defects during the melting process, and the tensile deformation mechanism of the SLM-produced Co29Cr9W3Cu samples, the microstructures of the samples before and after tensile deformation were observed using a scanning electron microscope (SEM), a transmission electron microscope (TEM), and an electron back-scattered diffraction (EBSD), respectively. The SEM morphology indicated that the non-equilibrium structure of the SLM-produced Co29Cr9W3Cu samples contained cellular and columnar subgrains. The TEM observation and EBSD analysis showed that the accumulated residual stress during the SLM process predominated in the overlapping regions between the adjacent scanning tracks, which consequently induced a larger number of the lattice defects, such as dislocations and overlapping stacking faults. The analysis of the tensile deformation revealed that the main plastic deformation was caused by the strain-induced martensitic transformation effect in the SLM-produced Co29Cr9W3Cu samples.
       
  • Laser powder bed fusion of Ni-Mn-Ga magnetic shape memory alloy
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): Ville Laitinen, Alexei Sozinov, Andrey Saren, Antti Salminen, Kari UllakkoAbstractAdditive manufacturing (AM) has gone through major developments in the past decade, enabling the rapid manufacture of complex geometries from traditional engineering materials. This study aims to facilitate the development and additive manufacturing of a new generation of fast and simple digital components with integrated magnetic shape memory (MSM) alloy sections that can be actuated by an external magnetic field. Here, we employ a systematic design of experiments (DoE) approach for investigating laser powder bed fusion (L-PBF) of a Ni-Mn-Ga based MSM alloy. The effects of the applied process parameters on the chemical composition and relative density are determined, and detailed investigations are conducted on the microstructural properties of the as-deposited material obtained using optimized parameters. The results show that although the L-PBF of Ni-Mn-Ga is characterized by an ever-present loss of Mn, deposition of Ni-Mn-Ga with a high relative density of 98.3% and a minimal loss of Mn at ∼1.1 at.% is feasible. The material produced in this manner was compositionally near homogenous and, in as-deposited condition, consisted of a mixture of 14 M and non-modulated (NM) martensites. However, combined measurements by the low-field ac magnetic susceptibility method (LFMS) and DSC revealed that the phase transformation of the as-deposited material from martensite to austenite, and vice versa, was broad and occurred in a paramagnetic state. Inspection by SEM revealed a layered microstructure with a stripe-like surface relief that originated from the presence of martensitic twins within the sample. Additionally, AFM and MFM measurements showed that in as-deposited Ni-Mn-Ga, there exists a weak MFM contrast that can be attributed to the twinned martensite having magnetic anisotropy. Overall, L-PBF shows high potential for the production of functional Ni-Mn-Ga based MSM alloys.
       
  • Surface finishing on IN625 additively manufactured surfaces by combined
           ultrasonic cavitation and abrasion
    • Abstract: Publication date: Available online 6 November 2019Source: Additive ManufacturingAuthor(s): K.L. Tan, S.H. YeoAbstractThe poor and non-uniform surface quality of parts produced by powder bed fusion (PBF) processes remains a huge limitation in additive manufacturing. Here we show that ultrasonic cavitation abrasive finishing (UCAF) could improve the surface integrity of PBF surfaces built at various orientations – 0°, 45° and 90°. Average surface roughness, Ra, was reduced from as high as 6.5 µm on side surfaces (90°) to 3.8 µm. Surface morphological observations showed extensive removals of surface irregularities and peak reduction on sloping (45°) and side surfaces. The micro-hardness of the first 100 µm of the surface layer was enhanced up to 15 % post-UCAF. Dimensional changes were minimal and uniquely dependent on the initial surface characteristics. A parametric study further showed the effect of abrasive size, abrasive concentration, ultrasonic amplitude and working gap on UCAF’s performance. A moderate abrasive size at 12.5 µm and concentration level at 5 wt% resulted in the lowest final Ra; as the two dominant material removal mechanisms – direct cavitation erosion and micro-abrasive impacts – were balanced. Finally, UCAF was demonstrated to result in 20 % Ra improvement of internal surfaces of a 3 mm diameter channel.
       
  • In-situ full-field mapping of melt flow dynamics in laser metal additive
           manufacturing
    • Abstract: Publication date: Available online 6 November 2019Source: Additive ManufacturingAuthor(s): Qilin Guo, Cang Zhao, Minglei Qu, Lianghua Xiong, S. Mohammad H. Hojjatzadeh, Luis I. Escano, Niranjan D. Parab, Kamel Fezzaa, Tao Sun, Lianyi ChenAbstractMelt flow plays a critical role in laser metal additive manufacturing, yet the melt flow behavior within the melt pool has never been explicitly presented. Here, we report in-situ characterization of melt-flow dynamics in every location of the entire melt pool in laser metal additive manufacturing by populous and uniformly dispersed micro-tracers through in-situ high-resolution synchrotron x-ray imaging. The location-specific flow patterns in different regions of the melt pool are revealed and quantified under both conduction mode and depression mode. The physical processes at different locations in the melt pool are identified. The full-field melt-flow mapping approach reported here opens the way to study the detailed melt-flow dynamics under real additive manufacturing conditions. The results obtained provide crucial insights into laser additive manufacturing processes and are critical for developing reliable high-fidelity computational models.
       
  • Influence of particle morphology and size distribution on the powder
           flowability and laser powder bed fusion manufacturability of Ti-6Al-4V
           alloy
    • Abstract: Publication date: Available online 6 November 2019Source: Additive ManufacturingAuthor(s): Salah Eddine Brika, Morgan Letenneur, Christopher Alex Dion, Vladimir BrailovskiAbstractLaser powder bed fusion (LPBF) additive manufacturing technology is sensitive to variations in powder particle morphology and size distribution. However, the absence of a clear link between the powder characteristics and the LPBF performances complicates the development, selection and quality control of LPBF powder feedstock. In this work, three Ti-6Al-4 V powder lots produced by two different techniques, namely, plasma atomization and gas atomization, were selected and characterized. Following the micro-computed tomography analysis of the powder particles’ morphology, size and density, the flowability of these powder lots was concurrently evaluated using Hall and Gustavsson flowmeters and an FT4 powder rheometer. Using established rheology-based criteria, a figure of merit was proposed to quantify the overall powder suitability for the LPBF process. Next, the same three powder lots were used to 3D-print and post-process a series of testing specimens with different layer thicknesses and build orientations, in order to establish a correlation between the powder characteristics and the geometric and mechanical properties of a final product. This study demonstrates that the use of highly spherical powders with a limited amount of fine particles promotes their flowability and yields LPBF components with improved mechanical and geometric characteristics.
       
  • Microstructural investigation and mechanical behavior of a two-material
           component fabricated through selective laser melting of AlSi104Mg on an
           Al-Cu-Ni-Fe-Mg cast alloy substrate
    • Abstract: Publication date: Available online 6 November 2019Source: Additive ManufacturingAuthor(s): Amir Hadadzadeh, Babak Shalchi Amirkhiz, Sajad Shakerin, Josh Kelly, Jian Li, Mohsen MohammadiAbstractA hybrid-part made of two materials was fabricated by selective laser melting (SLM) of AlSi10Mg on an Al-Cu-Ni-Fe-Mg cast alloy substrate. The microstructure of the two-material component and the interface is investigated using multi-scale characterization techniques including optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The microstructure of SLM-AlSi10Mg consists of fine cellular dendrites and columnar grains, developed along the building direction, where the substrate cast alloy is featured by large equiaxed grains. OM and SEM studies of the interface show a sound metallurgical bonding as a result of the melting of AlSi10Mg powder and partial melting of the cast substrate assisted by the circulate flows and Marangoni convection. The circulate flows cause complex phenomena at the interface, which lead to the dilution of alloying elements and a variation in the microstructure of the first consolidated layer of SLM-AlSi10Mg (as a result of variation in thermal gradient and solidification rate). TEM investigations of the interface reveal segregation of alloying elements at the interdendritic regions after solidification. Moreover, no precipitate is formed on top of the interface, due to the rapid solidification and dilution of the alloying elements. EBSD analysis of the interface shows substantial differences in the grain structure of SLM-AlSi10Mg and the cast substrate, in terms of size and morphology. Mechanical properties of the hybrid material are studied afterwards using Vickers microhardness measurements, nanoindentation and quasi-static uniaxial tensile tests. The SLM-AlSi10Mg side of the hybrid-part possesses better performance, mainly due to its finer and hierarchical microstructure.
       
  • Development of a Cooperative System for Wire and Arc Additive
           Manufacturing and Machining
    • Abstract: Publication date: Available online 5 November 2019Source: Additive ManufacturingAuthor(s): Hideaki Nagamatsu, Hiroyuki Sasahara, Yuusuke Mitsutake, Takeshi HamamotoAbstractWire and arc additive manufacturing (WAAM), which is an additive manufacturing (AM) process that uses metal materials, has a higher fabricated volume per unit time but a lower fabricated shape accuracy compared with other methods. With this process, the surface roughness of fabricated objects is several hundred micrometers or more, and a finishing process is necessary. However, the fabricated objects after finishing can have uncut areas or can be overcut during the finishing process owing to the large difference between the target and actual fabricated shapes. Therefore, the objective of this study is to develop a cooperative system for WAAM and machining that includes a process that measures the shape of the fabricated object. First, the three-dimensional (3-D) shape of the fabricated object was measured by structure from motion (SfM) and compared with the 3-D computer-aided design (CAD) data. Second, the original design was modified, and the amount of material removed during finish cutting was optimized with the developed software. Finally, the fabricated hollow object was finished by milling to obtain a uniform wall thickness without any defects. A 3-D fabricated object was measured by SfM, and it was observed that the measurement accuracy was sufficiently high for the requirements of the system. In addition, a fabricated hollow quadrangular pyramid with a closed shape was machined with a computer numerical control (CNC) machine tool with the modification of the work origin. As a result, the amount of material removed during finish cutting was optimized, and the inclined wall thickness was uniform compared with that without modification. In addition, a hollow turbine blade with a freeform shape was successfully finished without any defects.
       
  • Strong and light cellular silicon carbonitride – Reduced graphene oxide
           material with enhanced electrical conductivity and capacitive response
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): J.J. Moyano, J. Mosa, M. Aparicio, D. Pérez-Coll, M. Belmonte, P. Miranzo, M.I. OsendiSteady graphene oxide (GO) scaffolds created by direct ink writing are used to develop a silicon carbonitride (SiCN) -graphene oxide hybrid material through a preceramic polymer route. For achieving mechanically stable GO scaffolds, the drying method is critical as the ink contains about 5 wt.% of GO, 10 wt.% of polyelectrolytes and 85 wt.% of water. The liquid preceramic polymer (polysilazane type) quickly infiltrates the 3D scaffolds, under vacuum conditions, entirely covering the GO network creating a replica of the original scaffold. The hybrid cellular structure -once thermally treated for GO reduction and ceramic conversion- consists of a network of reduced GO (∼10 wt.%) embedded in an amorphous SiCN matrix following the designed architecture. The 3D hybrid structures show notable electrical conductivity (890 S m−1 at room temperature), thermal stability and considerable strength, about 20 times higher than the single GO scaffold. The structures are tested as electrodes for supercapacitors, reaching a gravimetric capacitance of 39 F g−1 that remains stable after 7000 charge/discharge cycles.Graphical abstractGraphical abstract for this article
       
  • Keyhole-induced porosities in Laser-based Powder Bed Fusion (L-PBF) of
           Ti6Al4V: High-fidelity modelling and experimental validation
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): Mohamad Bayat, Aditi Thanki, Sankhya Mohanty, Ann Witvrouw, Shoufeng Yang, Jesper Thorborg, Niels Skat Tiedje, Jesper Henri HattelAbstractMetal additive manufacturing, despite of offering unique capabilities e.g. unlimited design freedom, short manufacturing time, etc., suffers from raft of intrinsic defects. Porosity is of the defects which can badly deteriorate a part’s performance. In this respect, enabling one to observe and predict the porosity during this process is of high importance. To this end, in this work a combined numerical and experimental approach has been used to analyze the formation, evolution and disappearance of keyhole and keyhole-induced porosities along with their initiating mechanisms, during single track L-PBF of a Ti6Al4V alloy. In this respect, a high-fidelity numerical model based on the Finite Volume Method (FVM) and accomplished in the commercial software Flow-3D is developed. The model accounts for the major physics taking place during the laser-scanning step of the L-PBF process. To better simulate the actual laser-material interaction, multiple reflection with the ray-tracing method has been implemented along with the Fresnel absorption function. The results show that during the keyhole regime, the heating rises dramatically compared to the shallow-depth melt pool regime due to the large entrapment of laser rays in the keyhole cavities. Also a detailed parametric study is performed to investigate the effect of input power on thermal absorptivity, heat transfer and melt pool anatomy. Furthermore, an X-ray Computed Tomography (X-CT) analysis is carried out to visualize the pores formed during the L-PBF process. It is shown, that the predicted shape, size and depth of the pores are in very good agreement with those found by either X-CT or optical and 3D digital microscopic images.
       
  • Liquid-Absorbing System-Assisted Intersecting Jets Printing of Soft
           Structures from Reactive Biomaterials
    • Abstract: Publication date: Available online 4 November 2019Source: Additive ManufacturingAuthor(s): Shinichi Sakurada, Marc Sole-Gras, Kyle Christensen, David B. Wallace, Yong HuangAbstractTraditional three-dimensional (3D) bioprinting techniques of reactive materials usually include a mixing step of reactive agents prior to deposition, leading to potential changes in the rheological and biocompatibility properties of the resulting ink. During intersecting jets printing, reactive materials are dispensed separately, colliding and mixing with each other in air before landing on a previously deposited layer. While this enables reactive material printing using a printing-then-mixing approach, the resulting excess fluid may compromise the printing quality and accuracy. This study aims to improve the performance of intersecting jets–based reactive material printing by introducing a stainless-steel wire mesh and fibrous tissue paper–based liquid-absorbing system, which functions as a method to remove the excess resultant liquid from the printing zone. The proposed stainless-steel wire mesh and tissue paper-based liquid absorbing system effectively absorbs the excess liquid resulted during the printing process which enables higher-resolution and denser depositions of soft structures. By selecting a proper wire mesh, the proposed liquid-absorbing system can absorb up to 65-90% of the excess liquid (water herein) resulting from printing aqueous reactive sodium alginate and calcium chloride inks, which are selected as model materials in this study. By controlling the tilt angles of intersecting jets, the incident angle of post-collision droplets is desirable to be less than 14º to avoid droplet bouncing on the top of a previously deposited layer during 3D bioprinting. Using the liquid-absorbing system, different 3D structures have been successfully printed using intersecting jets printing. For tubular alginate constructs printed in air from sodium alginate and calcium chloride inks, a 2.5 height-diameter ratio can be achieved. The proposed printing technology does not influence the post-printing cell viability while printing 3T3 cells, demonstrating its promising potential for bioprinting applications.
       
  • Characterization of Laser Spatter and Condensate Generated during the
           Selective Laser Melting of 304L Stainless Steel Powder
    • Abstract: Publication date: Available online 4 November 2019Source: Additive ManufacturingAuthor(s): Austin T. Sutton, Caitlin S. Kriewall, Ming C. Leu, Joseph W. Newkirk, Ben BrownThe selective laser melting process, commonly referred to as laser powder-bed fusion (L-PBF), is an Additive Manufacturing (AM) technique that uses a laser to fuse successive layers of powder into near fully dense components. Due to the large energy input from the laser during processing, vaporization causes instabilities in the melt pool leading to the formation of laser spatter and condensate, collectively known as heat-affected powder. Since heat-affected powder settles into the powder bed, the properties of the unconsolidated powder may be altered compromising its reusability. In this study, characterization of 304 L heat-affected powder was performed through particle size and shape distribution measurements, energy-dispersive spectroscopy, Raman spectroscopy, inert gas fusion, metallography, and x-ray diffraction. The results show morphological, chemical, and microstructural differences between the virgin powder and heat-affected powder formed during processing which aid in the understanding of laser spatter and condensate that form in the L-PBF process.Graphical Graphical abstract for this article
       
  • Microstructures and properties of SLM-manufactured Cu-15Ni-8Sn alloy
    • Abstract: Publication date: Available online 2 November 2019Source: Additive ManufacturingAuthor(s): Jibing Wang, X.L. ZHOU, Jinghao Li, Mathieu Brochu, Yaoyao Fiona ZhaoAbstractEasily segregated Cu-15Ni-8Sn alloy bulk material was fabricated using a selective laser melting (SLM) process. The microstructure of SLM-manufactured Cu-15Ni-8Sn alloy was investigated using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Differences in the microstructures and elemental segregation of gas-atomized alloy powder, cast ingots, and SLM-manufactured samples were analyzed. The statistical average grain size of the SLM-manufactured Cu-15Ni-8Sn alloy was 4.03 μm. Microstructures of the SLM-manufactured sample were mainly composed of epitaxially grown slender cellular structures with submicron widths. Microsegregation was detected by TEM, and 80- to 200-nm Sn-enriched precipitates were dispersed between cellullar structures. Many dislocations and dislocation tangles appeared around the precipitates. An EBSD test revealed that most local misorientations within 3 degrees were concentrated in fusion line regions. Compared with cast ingots, the yield strength Rp0.2, ultimate tensile strength Rm, elongation A, and elastic modulus E of the SLM-manufactured sample increased by 67%, 24.6%, 360%, and 7%, respectively. Moreover, the SLM-manufactured Cu-15Ni-8Sn alloy could be directly aged at 350℃ for 12 hours, reaching Rm=991.1 MPa and A=3%, with no need for solid solution treatment or cold working.
       
  • 3-D Printed Porous Cellulose Acetate Tissue Scaffolds for Additive
           Manufacturing
    • Abstract: Publication date: Available online 1 November 2019Source: Additive ManufacturingAuthor(s): Hanxiao Huang, Derrick Dean
       
  • Functional Bimetallic Joints of Ti6Al4V to SS410
    • Abstract: Publication date: Available online 1 November 2019Source: Additive ManufacturingAuthor(s): Onuike Bonny, Bandyopadhyay AmitBimetallic structures provide a unique solution to achieve site-specific functionalities and enhanced-property capabilities in engineering structures but suffer from bonding compatibility issues. Materials such as titanium alloy (Ti6Al4 V) and stainless steel (SS410) have distinct attractive properties but are impossible to reliably weld together using traditional processes. To this end, a laser-based directed energy deposition (DED) system was used to fabricate bimetallic joint of Ti6Al4 V and SS410 keeping niobium (Nb) as a diffusion barrier layer. Both shear and compression tests were used to characterize the joint’s strength, and compared with the base materials. The bimetallic-joint shear and compressive yield strengths were 419 ± 3 MPa (∼ 114 % of SS410) and 560 ± 4 MPa (∼ 169 % of SS410), respectively. The increase in interfacial shear and compressive yield strengths over the base material indicates strong metallurgical bonding between the base materials and the interlayer, Nb. Proof-of-concept part for direct application of the bimetallic joint was demonstrated by welding base metals, end-to-end, to the joint. The interfacial microstructures, elemental diffusion and phases, including failure modes were examined using secondary and backscatter electron imaging, X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The bimetallic-joint interfaces were free from brittle intermetallic compounds such as FeTi and Fe2Ti that are generally responsible for weak bond strength.Graphical abstractGraphical abstract for this article
       
  • Effects of laser additive manufacturing on microstructure and
           crystallographic texture of austenitic and martensitic stainless steels
    • Abstract: Publication date: Available online 1 November 2019Source: Additive ManufacturingAuthor(s): F. Khodabakhshi, M.H. Farshidianfar, A.P. Gerlich, M. Nosko, V. Trembošová, A. KhajepourAbstractPowder-fed laser additive manufacturing (LAM) based on directed energy deposition (DED) technology is used to produce S316-L austenitic, and S410-L martensitic stainless steel structures by 3D-printing through a layer-upon-layer fashion. The microstructural features and crystallographic textural components are studied via electron backscattering diffraction (EBSD) analysis, hardness indentation and tensile testing. The results are compared with commercial rolled sheets of austenitic and martensitic stainless steels. A well-developed direction solidification texture (with a J-index of ∼11.5) is observed for the austenitic structure produced by the LAM process, compared to a J-index of ∼2.0 for the commercial austenitic rolled sheet. Such a texture in the LAM process is caused by equiaxed grain formation in the middle of each layer followed by columnar growth during layer-upon-layer deposition. A quite strong preferred orientation (J-index of 17.5) is noticed for martensitic steel developed by LAM. Large laths of martensite exhibit a dominant textural component of {011} in the α-phase, which is mainly controlled by transformation during layer-by-layer deposition. On the other hand, the martensitic commercial sheet consists of equiaxed grains without any preferred orientation or completely random orientations. In the case of the austenitic steel, mechanical properties such as tensile strength, hardness and ductility were severely deteriorated during the LAM deposition. A ductility loss of about 50% is recorded compared to the commercially rolled sheets that is attributed to the cast/solidified structure. However, LAM manufacturing of martensitic stainless steel structures leads to a considerably enhanced mechanical strength (more than double) at the expense of reduced ductility, because of martensitic phase transformations under higher cooling rates.
       
  • Towards digital metal additive manufacturing via high-temperature
           drop-on-demand jetting
    • Abstract: Publication date: Available online 31 October 2019Source: Additive ManufacturingAuthor(s): Marco Simonelli, Nesma Aboulkhair, Mircea Rasa, Mark East, Chris Tuck, Ricky Wildman, Otto Salomons, Richard HagueAbstractDrop-on-demand jetting of metals offers a fully digital manufacturing approach to surpass the limitations of the current generation powder-based additive manufacturing technologies. However, research on this topic has been restricted mainly to near-net shaping of relatively low melting temperature metals. Here it is proposed a novel approach to jet molten metals at high-temperatures (>1000 °C) to enable the direct digital additive fabrication of micro- to macro-scale objects. The technique used in our research – “MetalJet” - is discussed by studying the ejection and the deposition of two example metals, tin and silver. The applicability of this new technology to additive manufacturing is evaluated through the study of the interface formed between the droplets and the substrate, the inter-droplets bonding, the microstructure and the geometrical fidelity of the printed objects. The research shows that the integrity of the samples (in terms of density as well as metallurgy) varies dramatically in the two investigated materials due to the different conditions that are required to melt the interface of the stacked droplets. Nevertheless the research shows that by a careful choice of the jetting strategy and sintering treatments 3D structures of various complexity can be formed. This research paves the way towards the next generation metal additive manufacturing where various printing resolutions and multi-material capabilities could be used to obtain functional components for applications in printed electronics, medicine and the automotive sectors.
       
  • On the effect of the thermal cycle during the directed energy deposition
           application to the in-situ production of a Ti-Mo alloy functionally graded
           structure
    • Abstract: Publication date: Available online 31 October 2019Source: Additive ManufacturingAuthor(s): N. Kang, X. Lin, M. El Mansori, Q.Z. Wang, J.L. Lu, C. Coddet, W.D. HuangIn this work, almost dense (over 99.8%) Ti-Mo alloy samples were manufactured by directed energy deposition (DED) from a mixture of pure Ti and pure Mo (7.5 wt.%) powders. As a consequence of thermal accumulation and in-situ heat treating during the DED process, as-deposited samples present a graded microstructure along the building direction along with a phase transition from hcp-α Ti to bbc-β Ti. Mechanical properties were determined by tensile tests from flat samples harvested at different altitude positions. As altitude increases from the base plate, yield strength decreases from 681 MPa to 579 MPa and ultimate tensile strength from 791 MPa to 686 MPa. Elongation of the as-deposited material increases from 10% to 25% while the Young’s modulus keeps a low value of 105 GPa for the entire DEDed sample.Graphical abstractGraphical abstract for this article
       
  • Fabrication of Low Dielectric Constant Composite Filaments for use in
           Fused Filament Fabrication 3D Printing
    • Abstract: Publication date: Available online 28 October 2019Source: Additive ManufacturingAuthor(s): Paul Parsons, Zachary Larimore, Faheem Muhammed, Mark MirotznikAbstractIn this paper we describe a method for creating flexible composite filaments with dielectric constants below 2.0 over a wide frequency band (i.e. 18 - 40 GHz). We demonstrate that a low dielectric constant composite filament, useful for FFF printing, can be manufactured by combining a base thermoplastic polymer with hollow microspheres and a plasticizer. Experimental results are provided for filaments made from two different base polymers (i.e. ABS and HDPE) and varying volume fractions of hollow microspheres. We also describe an effective media model to predict the dielectric properties of the composite filaments as a function of the properties of the constituent materials (e.g. base polymer, hollow microspheres) and their relative volume fractions within the composite filament. Experimental test samples were printed using the new low-K filaments and experimental characterization results are provided that validate this approach.
       
  • 3D Printed Optics with a Soft and Stretchable Optical Material
    • Abstract: Publication date: Available online 25 October 2019Source: Additive ManufacturingAuthor(s): Edidiong Nseowo Udofia, Wenchao ZhouWaveguides are important optical elements for sensing, illumination, artistic displays, integrated optical circuits, as well as teaching aids for demonstrating important optical phenomena. However, despite the high demand, most optical materials are difficult to fabricate into desired shapes using state-of-the-art manufacturing technologies. This paper presents a novel method for 3D printing customizable optics with a soft and stretchable (over 100% elastic strains) thermoplastic polymer. To showcase the versatility of this approach, several applications were demonstrated, including unique artistic illumination, caustic patterns, beam splitter and combiner on both planar and 3D conformal surfaces, and optical encoder. The printed waveguides exhibit an outstanding optical transparency of more than 98% and an optical loss of less than 0.22 dBcm-1. The simplicity of the fabrication process, low-cost, excellent optical properties, and flexibility provide an attractive pathway for fabricating integrated optical devices and new opportunities for controlling light.Graphical abstractGraphical abstract for this articleFigure: (a) Photograph showing high level of transparency of as-printed object, and (b) Caustic patterns of (a) produced by illumination from a suspended overhead green LED. (c) As-printed waveguide splitter and combiner circuit on a 3D printed dome surface, and (d) Top view of lighted circuited. (e) Pattern of our group name “AM3 Lab” on a black paper substrate, and (f) Lighted with different LEDs.
       
  • Simulation of Melt Pool Behaviour during Additive Manufacturing:
           Underlying Physics and Progress
    • Abstract: Publication date: Available online 25 October 2019Source: Additive ManufacturingAuthor(s): Peter S. Cook, Anthony B. MurphyAbstractReliable computational models of metal additive manufacturing will assist in optimising part quality, and are likely to play a role in component qualification. A key component of these models will be a detailed simulation of flow and heat transfer in and around the melt pool formed as the powder bed is melted. This paper reviews the burgeoning literature concerning melt pool simulation. The physical theory underlying the current benchmark models is first presented and the main approximations and assumptions discussed. The individual capabilities of the leading simulation groups around the world are listed in detail. Publications by less prominent research groups are also summarised. Finally, the overall status of melt pool simulation and the implications for model development are discussed.
       
  • Influence of Solidification Cell Structure on the Martensitic
           Transformation in Additively Manufactured Steels
    • Abstract: Publication date: Available online 24 October 2019Source: Additive ManufacturingAuthor(s): Felicity S.H.B. Freeman, Jo Sharp, Jiawei Xi, Iain ToddA key feature when using martensitic steels is the proportion of retained austenite present in the final component. Martensitic steels manufactured by laser powder-bed fusion (LPBF) have been shown to have more retained austenite than when conventionally manufactured. The LPBF microstructure is characterised by small grains containing ultrafine solidification cells (
       
  • Ultrasound-Assisted 3D Printing of Continuous Fiber-Reinforced
           Thermoplastic (FRTP) Composites
    • Abstract: Publication date: Available online 24 October 2019Source: Additive ManufacturingAuthor(s): Jing Qiao, Yingrui Li, Longqiu LiAbstractInvestigation of manufacturing continuous fiber reinforced thermoplastic polymer composites (CFRTPCs) through 3D printing technologies has attracted great attention in the past few years due to excellent properties of CFRTPCs, such as high strength-to-weight ratio and stiffness. It is found that the properties of CFRTPCs are affected not only by the properties of the individual parent materials but also by interfacial characteristics. Modification of the interface is a great method to improve the wettability between fiber and polymer and hence the mechanical properties of CFRTPCs. In this work, an ultrasound-assisted 3D printing device for CFRTPCs is developed. The changes of surface profile and chemical structure of carbon fiber and carbon fiber prepreg after ultrasonic treatment are studied. The effects of ultrasonic processing parameters on the microstructure and mechanical properties of CFRTPCs are provided. It is found that the tensile and flexural strength of composite materials are improved by 34% and 29%, respectively, compared with untreated material by using the ultrasonic amplitude of 40 μm, resin solution mass fraction of 10%, processing speed of 15 mm/s.
       
  • Processing Parameter Correlations in Material Extrusion Additive
           Manufacturing
    • Abstract: Publication date: Available online 23 October 2019Source: Additive ManufacturingAuthor(s): Daniel J. Braconnier, Robert E. Jensen, Amy M. PetersonAbstractProcessing-structure-property relationships in material extrusion additive manufacturing are complex, non-linear, and poorly understood. In this work, we designed an informatics workflow for the collection of high pedigree data from each stage of the fused filament fabrication (FFF) printing process. In conjunction with a design of experiments, we applied the workflow to investigate the influences of processing parameters on weld strength across three commercially available FFF printers. Environmental, material, and print conditions that may impact performance were monitored to ensure that relevant data were collected in a consistent manner. Acrylonitrile butadiene styrene (ABS) filament was used to print ASTM D638-14 Type V tensile bars. Data were analyzed using multivariate statistical techniques, including principal component analysis. The magnitude of the effects of extrusion temperature, layer thickness, print bed temperature, and print speed on the tensile properties of the final print were determined. The results demonstrated that printer selection is important and changes the impact of print parameters.
       
  • In situ thermography for laser powder bed fusion: Effects of layer
           temperature on porosity, microstructure and mechanical properties
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): Richard J. Williams, Alessandro Piglione, Tobias Rønneberg, Connor Jones, Minh-Son Pham, Catrin M. Davies, Paul A. HooperAbstractIn laser powder bed fusion (LPBF) the surface layer temperature is continually changing throughout the build process. Variations in part geometry, scanned cross-section and number of parts all influence the thermal field within a build. Process parameters do not take these variations into account and this can result in increased porosity and differences in local microstructure and mechanical properties, undermining confidence in the structural integrity of a part. In this paper a wide-field in situ infra-red imaging system is developed and calibrated to enable measurement of both solid and powder surface temperatures across the full powder bed. The influence of inter-layer cooling time is investigated using a build scenario with cylindrical components of differing heights. In situ surface temperature data are acquired throughout the build process and are compared to results from porosity, microstructure and mechanical property investigations. Changes in surface temperature of up to 200 °C are attributed to variation in inter-layer cooling time and this is found to correlate with density and grain structure changes in the part. This work shows that these changes are significant and must be accounted for to improve the consistency and structural integrity of LPBF components.
       
  • Development of a combined analytical and experimental approach for the
           determination of the cohesive strength between material extrusion layers
           using the true area of contact
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): Thao Thi Phuong Phan, The Quang Phan, Ahmed Sherif El-GizawyMaterial Extrusion (ME) is a type of Additive Manufacturing (AM) process that creates parts by depositing polymer filaments in successive layers. The strength of ME products depends on both the cohesive strength between layers and between rasters. The raster gap is the most significant process factor affecting the strength of ME built parts. Standard tensile tests with a dog-bone shaped specimens are not suitable to determine the strength between layers of the ME built parts. A new model is introduced to predict the cohesive strength between layers using the true area of contact which can be obtained from the apparent values taken from mini three-point bending tests. The accuracy of the introduced model was verified by comparing its bending test results with different build parameters, the applicability and promise of the introduced model were confirmed.Graphical abstractGraphical abstract for this article
       
  • Enhancing the interlayer tensile strength of 3D printed short carbon fiber
           reinforced PETG and PLA composites via annealing
    • Abstract: Publication date: Available online 22 October 2019Source: Additive ManufacturingAuthor(s): Sunil Bhandari, Roberto A. Lopez-Anido, Douglas J. GardnerAbstractPrevious studies have shown that 3D printed composites exhibit an orthotropic nature with inherently lower interlayer mechanical properties. This research work is an attempt to improve the interlayer tensile strength of extrusion-based 3D printed composites. Annealing was identified as a suitable post-processing method and was the focus of this study. Two distinct thermoplastic polymers, which are common in 3D printing, were selected to study the enhancement of interlayer tensile strength of composites by additive manufacturing: a) an amorphous polyethylene terephthalate-glycol (PETG), and b) a semi-crystalline poly (lactic acid) (PLA). It was determined that short carbon fiber reinforced composites have lower interlayer tensile strength than the corresponding neat polymers in 3D printed parts. This reduction in mechanical performance was attributable to an increase in melt viscosity and the consequential slower interlayer diffusion bonding. However, the reduction in interlayer tensile strength could be recovered by post-processing when the annealing temperature was higher than the glass transition temperature of the amorphous polymer. In the case of the semi-crystalline polymer, the recovery of the interlayer tensile strength was only observed when the annealing temperature was higher than the glass transition temperature but lower than the cold-crystallization temperature. This study utilized rheological and thermal analysis of 3D printed composites to provide a better understanding of the interlayer strength response and, therefore, overcome a mechanical performance limitation of these materials.
       
  • Production and characterization of PEEK/IF-WS2 nanocomposites for Additive
           Manufacturing: simultaneous improvement in processing characteristics and
           material properties
    • Abstract: Publication date: Available online 16 October 2019Source: Additive ManufacturingAuthor(s): Atefeh Golbang, Eileen Harkin-Jones, Marcin Wegrzyn, Gavin Campbell, Edward Archer, Alistair McIlhaggerAbstractSuccessful printing of high-performance material with suitable properties using additive manufacturing methods such as Fused Filament Fabrication (FFF) can create many advanced applications in industries. However, the high viscosity of high-performance polymers causes complications during the FFF process and reduces the final print quality. To overcome this challenge, Inorganic Fullerene Tungsten Sulphide (IF-WS2) nanoparticles are applied in this study to enhance the flowability of poly-ether-ketone-ketone (PEEK) without compromising its mechanical and thermal properties. In the first step, different loadings of IF-WS2 nanoparticles are melt compounded with PEEK and the nanocomposites are characterized. SEM and EDX images of fractured surfaces indicate that a good dispersion of nanoparticles is achieved without any pre-treatment or pre-dispersion. A reduction in melt viscosity of 25%, and a simultaneous growth in storage modulus, crystallization and degradation temperature of about 60%, 53% and 100 °C is found with addition of 2 wt% IF-WS2 to PEEK, respectively. This great achievement is mainly ascribed to the unique characteristics of IF-WS2 nanoparticles, acting as both reinforcing and lubricating agents, indicated by a reduction in coefficient of friction. There is no significant increase of crystallization and melting temperatures with the addition of IF-WS2 nanoparticles, which is beneficial in the FFF process. In the second step, the PEEK nanocomposite filaments are printed via FFF. The print quality and mechanical properties of the printed PEEK are also improved with the incorporation of IF-WS2 nanoparticles. Hence, incorporation of IF-WS2 nanoparticles into PEEK via melt compounding is an effective approach for the development of suitable high-performance engineering materials for FFF.
       
  • Heterogeneous Sensor-based Condition Monitoring in Directed Energy
           Deposition
    • Abstract: Publication date: Available online 16 October 2019Source: Additive ManufacturingAuthor(s): Mohammad Montazeri, Abdalla R. Nassar, Christopher B. Stutzman, Prahalada RaoAbstractThe objective of this work is to detect in situ the occurrence of lack-of-fusion defects in titanium alloy (Ti-6Al-4 V) parts made using directed energy deposition (DED) additive manufacturing (AM). We use data from two types of in-process sensors, namely, a spectrometer and an optical camera which are integrated into an Optomec MR-7 DED machine. Both sensors are focused on capturing the dynamic phenomena around the melt pool region. To detect lack-of-fusion defects, we fuse (combine) the data from the in-process sensors invoking the concept of Kronecker product of graphs. Subsequently, we use the features derived from the graph Kronecker product as inputs to a machine learning algorithm to predict the severity (class or level) of average length of lack-of-fusion defects within a layer, which is obtained from offline X-ray computed tomography of the test parts. We demonstrate that the severity of lack-of-fusion defects is classified with statistical fidelity (F-score) close to 85% for a two-level classification scenario, and approximately 70% for a three-level classification scenario. Accordingly, this work demonstrates the use of heterogeneous in-process sensing and online data analytics for in situ detection of defects in DED metal AM process.
       
  • Understanding the process-microstructure correlations for tailoring the
           mechanical properties of L-PBF produced austenitic advanced high strength
           steel
    • Abstract: Publication date: Available online 15 October 2019Source: Additive ManufacturingAuthor(s): Patrick Köhnen, Maike Létang, Maximilian Voshage, Johannes Henrich Schleifenbaum, Christian HaaseIn this work, the additive manufacturing technique of laser powder bed fusion (L-PBF) was used to build up X30Mn21 austenitic advanced high strength steel (AHSS) samples. Different L-PBF process parameters were used to understand the correlation between process, microstructure, texture, and mechanical properties. The influence of build platform preheating (200 °C - 800 °C), laser speed (550 mm/s - 950 mm/s) and scan strategy (bidirectional continuous and Mark&Sleep (M&S)) on grain size, grain morphology, size of solidification cells, dislocation density, and texture was studied. Local solidification parameters in the melt pool e.g. cooling rates, temperature gradients and solidification velocities were simulated by a FEM heat flow model and correlated with the solidification microstructure. By using SEM/EBSD analysis and tensile testing, the mechanical properties of the AHSS were assessed by considering microstructural aspects. It was found that AHSS, produced with higher laser speeds and an alternative M&S scan strategy, revealed a reduced grain size and texture intensity This was attributed to a partial columnar to equiaxed transition (CET), as well as a significantly increased density of geometrically necessary dislocations. Preheating of the build platform promoted columnar grain growth with a more pronounced texture, low dislocation densities, and reduced yield strength. The influence of cooling rate, temperature gradient and solidification velocity on microstructural and textural evolution are discussed based on fundamental solidification theories.Graphical abstractGraphical abstract for this article
       
  • Additive manufacturing of high-strength crack-free Ni-based Hastelloy X
           superalloy
    • Abstract: Publication date: Available online 15 October 2019Source: Additive ManufacturingAuthor(s): Quanquan Han, Yuchen Gu, Rossitza Setchi, Franck Lacan, Richard Johnston, Sam L. Evans, Shoufeng YangLaser powder bed fusion (LPBF) is a proven additive manufacturing (AM) technology for producing metallic components with complex shapes using layer-by-layer manufacture principle. However, the fabrication of crack-free high-performance Ni-based superalloys such as Hastelloy X (HX) using LPBF technology remains a challenge because of these materials’ susceptibility to hot cracking. This paper addresses the above problem by proposing a novel method of introducing 1 wt.% titanium carbide (TiC) nanoparticles. The findings reveal that the addition of TiC nanoparticles results in the elimination of microcracks in the LPBF-fabricated enhanced HX samples; i.e. the 0.65% microcracks that were formed in the as-fabricated original HX were eliminated in the as-fabricated enhanced HX, despite the 0.14% residual pores formed. It also contributes to a 21.8% increase in low-angle grain boundaries (LAGBs) and a 98 MPa increase in yield strength. The study revealed that segregated carbides were unable to trigger hot cracking without sufficient thermal residual stresses; the significantly increased subgrains and low-angle grain boundaries played a key role in the hot cracking elimination. These findings offer a new perspective on the elimination of hot cracking of nickel-based superalloys and other industrially relevant crack-susceptible alloys. The findings also have significant implications for the design of new alloys, particularly for high-temperature industrial applications.Graphical abstractGraphical abstract for this article
       
  • Influence of resin infiltrants on mechanical and thermal performance in
           plaster binder jetting additive manufacturing
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): Timothy J. Ayres, Santosh R. Sama, Sanjay B. Joshi, Guha P. ManogharanAbstractPlaster Binder Jetting (BJ) is one of the major Additive Manufacturing (AM) technologies which has been in use since the 1990s. It has many advantages such as the ability to print in full color CMY(K), no support structures, and is relatively faster and less expensive when compared to other AM technologies. Since there is no phase transformation (e.g. powder to molten pool in powder bed fusion, directed energy deposition), BJ does not require support structures and enables higher packing density in the build volume. However, relatively lower mechanical strength when compared to other AM processes has mostly limited it to non-functional applications such as prototyping. This paper investigates novel methods to improve the mechanical and temperature performance of plaster BJ additive manufactured parts via improved infiltration processes and incorporation of infiltrants with higher strength. Potential applications include functional end use products, including tooling, jigs and fixtures for higher temperature applications. Three 2-part epoxy resin systems were evaluated as infiltrants in comparison to epoxy and cyanoacrylate (CA) resins recommended by the original equipment manufacturer (OEM). Multiple impregnation methods including hot and wet vacuum were evaluated on their infiltration effectiveness. The best impregnation method was then used to prepare tensile, flexural and compressive samples for additional evaluation of each resin. Statistical analysis was conducted to analyze and compare the data. Both resins and infiltrated samples were individually evaluated using Differential Scanning Calorimetry (DSC) to determine glass transition temperatures and other thermal events. Infiltrated specimens of the best performing resins were evaluated for Heat Deflection Temperature (HDT) performance utilizing Dynamic Mechanical Analysis (DMA). It was found that infiltration is anisotropic, with the higher penetration depth from the sides (between layers) than top and bottom (across layers). Vacuum impregnation resulted in the highest infiltration depth by fully impregnating the 25 mm cubic samples. The best performing epoxy showed a 10% increase in mechanical strength over the OEM epoxy at 76% reduction in cost. The OEM cyanoacrylate had the lowest mechanical strength across all tests. DSC analysis revealed that the plaster and gypsum base material will start to dehydrate above 100 °C and will ultimately limit the parts’ high temperature capabilities. The OEM epoxy showed the highest HDT.
       
  • Multiscale ceramic components from preceramic polymers by hybridization of
           vat polymerization-based technologies
    • Abstract: Publication date: Available online 14 October 2019Source: Additive ManufacturingAuthor(s): Johanna Schmidt, Laura Brigo, A. Gandin, Martin Schwentenwein, Paolo Colombo, Giovanna BrusatinAbstractA novel approach to fabricate ceramic structures at multiple scales in a single component, based on the hybridization of additive manufacturing technologies, was developed by combining 3D macro-stereolithography (Digital Light Processing, DLP) with two-photon lithography (2 PL), to produce cm-sized sample geometries with sub-µm surface features. The preceramic structures in the sub-µm scale were realized by 2 PL directly on easily manageable DLP macro-sized samples of the same ceramic composition. In this way, preceramic structures presenting both features typical of DLP printers (with a minimum size of around 50 µm) and features well below their resolution limit were realized. We report here, for the first time, the realization of polymer-derived ceramic SiOC ceramic components structured in 3D across several length scales (with micron and mesoscale 3D features), produced by pyrolysis at 1000 °C of preceramic parts, without shape distortion during the pyrolysis step.
       
  • Enabling direct writing of an epoxy resin with thermo-activated organic
           thixotropes
    • Abstract: Publication date: Available online 13 October 2019Source: Additive ManufacturingAuthor(s): Ruel McKenzie, Hilmar KoernerAbstractDirect writing a thermosetting resin typically requires a rheological modifier or peripheral reaction rate-modulating equipment to enable shape fidelity during parts fabrication. This work describes the processing and characterization of low molecular weight diamide-based derivatives of hydroxystearic acid to facilitate direct writing of an epoxy resin. These low molecular weight gelators (LMWG) are thermally activated to produce sufficient yield stress for self-supporting, reactive, physical gels. These organic gelators are semi-crystalline and enable two modes of processing to produce form-stable resin formulations – cold processing and melt processing. Physical gelation occurs by assembly of the LMWG into supramolecular morphologies [1] that vary by mode of processing. Flow of the form-stable epoxy resin is induced by yielding of the physical gel structure. When the physical gel is cured at temperatures below the melt transition of the organic gelator, the network structure likely kinetically traps the organic gelator in a metastable state. Recrystallization of the kinetically trapped organic gelator is impeded when the network is post-cured above the melt transition temperature of the organic gelator. The use of low molecular weight agents that physically gel by thermal activation, generates low viscosity solution processability and suggests that this platform may be suitable for high solids loading applications amenable to direct writing.
       
  • Numerical verification of an octree mesh coarsening strategy for
           simulating additive manufacturing processes
    • Abstract: Publication date: Available online 12 October 2019Source: Additive ManufacturingAuthor(s): Chao Li, Erik R. Denlinger, Michael F. Gouge, Jeff E. Irwin, Pan MichalerisAbstractThermo-mechanical finite element modeling of additive manufacturing processes, such as Directed Energy Deposition and Laser Powder Bed Fusion, has been widely applied for the prediction and mitigation of part distortion. However, as the size of modeled geometries gets larger, the number of nodes and elements required in the finite element mesh increases significantly. Because runtime will increase as more nodes are added, it is not practical to conduct full simulations of large builds using standard static meshes. Advanced meshing strategy is required to reduce the run time and to retain the accuracy of the prediction. In this work, a mesh coarsening strategy is evaluated for predicting temperature, distortion, and residual stress in additive manufacturing, aiming to achieve feasible run times with reasonable accuracy on large builds. Directed Energy Deposition of thin wall geometries built from Inconel® 625 and Ti6Al4V is used as a reference and models with 2 levels of Octree mesh coarsening are investigated. The thermal history, in situ distortion, residual stress, and run times are compared with previously experimentally validated static mesh results. Two levels of mesh coarsening is found to be the most effective case for both materials reducing the computational time by 75 % while reporting less than 2.5 % error for the peak distortion and negligible error for the thermal history difference as compared to the static mesh. Keeping two fine layers of elements underneath the heat source is found to be the most efficient in terms of prediction accuracy and run time.Keywords: Additive manufacturing; Thermo-mechanical modeling; Distortion; Octree mesh coarsening
       
  • Additive manufacturing in construction: A review on processes,
           applications, and digital planning methods
    • Abstract: Publication date: Available online 9 October 2019Source: Additive ManufacturingAuthor(s): Alexander Paolini, Stefan Kollmannsberger, Ernst RankAbstractThe application of additive manufacturing (AM) in construction has been increasingly studied in recent years. Large robotic arm- and gantry-systems have been created to print building parts using aggregate-based materials, metals, or polymers. Significant benefits of AM are the automation of the production process, a high degree of design freedom, and the resulting potential for optimization. However, the building components and 3D-printing processes need to be modeled appropriately. In this paper, the current state of AM in construction is reviewed. AM processes and systems as well as their application in research and construction projects are presented. Moreover, digital methods for planning 3D-printed building parts and AM processes are described.
       
  • Ply and interlaminar behaviours of 3D printed continuous carbon
           fibre-reinforced thermoplastic laminates; effects of processing conditions
           and microstructure
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): M. Iragi, C. Pascual-González, A. Esnaola, C.S. Lopes, L. AretxabaletaAbstractTaking advantage of an extended design and manufacturing space for composites, the technology of fused filament fabrication (FFF) of continuous fibre-reinforced thermoplastics shows great potential for the production of the next generation of lightweight structural parts. This process still has room for development. Moreover, knowledge of the mechanical behaviour of the resulting 3D printed composites is still limited. In this work, the intra- and inter-laminar behaviours of carbon fibre/polyamide printed laminates were extensively characterised to determine ply elastic and strength properties, as well as interface strength and fracture characteristics. Moreover, the effects of eventual production defects on these properties were analysed, putting in evidence some of the present shortcomings of the FFF process. Such defects include non-homogeneous fibre distribution, large amounts of intra- and interlaminar voids, and weak interlayer bonding, which are likely to be due to insufficient thermo-mechanical consolidation of the material during the FFF process, and have significant influence on the matrix-dominated mechanical properties. As a result, the transverse and interlaminar properties were found to be lower than those obtained through hot compression moulding of carbon fibre/polyamide laminates. Besides highlighting possible process improvements, the mechanical characterisation carried out in this work promises a significant contribution to the abilities of designing and simulating general 3D printed composite parts.
       
  • High-fidelity and high-efficiency additive manufacturing using tunable
           pre-curing digital light processing
    • Abstract: Publication date: Available online 7 October 2019Source: Additive ManufacturingAuthor(s): Yang Li, Qijiang Mao, Xiaokeng Li, Jun Yin, Yifang Wang, Jianzhong Fu, Yong HuangAbstractTo improve printing fidelity, reducing the slice thickness to eliminate the staircase effect is of great importance for digital light processing (DLP) technology. However, using a thinner slice printing model leads to a longer total printing time in the conventional DLP approach, which significantly reduces printing efficiency. In this work, a tunable pre-curing DLP approach was developed where the relationship between the forming layer thickness and ultraviolet (UV) exposure time is theoretically analyzed, and the curing process of photo-curable solutions is divided into two sub-processes: pre-curing and further curing. In the pre-curing process, the photo-curable solution is initially pre-cured and kept at the pre-gelled state due to continuous UV exposure during subsequent DLP printing. Then, the pre-cured photo-curable solution is quickly cured to form a designed thickness in each printing cycle. Also, the UV absorbing agent is added to the photo-curable hydrogel solutions to regulate the pre-curing process. Using a 10 μm slice for DLP printing, the total printing time of the tunable pre-curing DLP is approximately 5.6% of the conventional DLP, and the staircase effect on the surface is significantly eliminated using 10 μm slice tunable pre-curing DLP approach, which leads to a better printing fidelity. Thus, both printing fidelity and efficiency are significantly and simultaneously improved by the tunable pre-curing DLP approach. Moreover, the reduction of UV exposure time and slice thickness is beneficial for cell viability during DLP bioprinting of thick bulk structures, which is demonstrated by the printing of PC12 cell-laden gelatin methacrylate (GelMA) bioinks. Using the tunable pre-curing DLP approach, the PC12 cells achieved higher cell viability (90.2 ± 6.1%) and better cell morphology than the conventional DLP approach (54.5 ± 4.8%). The tunable pre-curing DLP approach provides a promising alternative to extend the application of DLP printing greatly.
       
  • Influence of process parameters on the correlation between in-situ process
           monitoring data and the mechanical properties of Ti-6Al-4V non-stochastic
           cellular structures
    • Abstract: Publication date: Available online 5 October 2019Source: Additive ManufacturingAuthor(s): Darragh S. Egan, Denis P. DowlingAbstractSelective Laser Melting (SLM) facilitates the formation of complex, stochastic or non-stochastic, metallic cellular structures. There is a high level of interest in these structures recently, particularly due to their high strength to weight ratios and osteoconductive properties. While the ability to in-situ monitor the SLM process is of key importance for future quality control methods.In this work lattice structures were fabricated, using the single exposure scanning strategy, on a Renishaw 500M SLM machine. The build process was also monitored using a co-axial in-situ process monitoring system.It was found that by increasing the energy input, through increasing the laser power and/or exposure time, the lattice strut diameters, within the 1.5 mm diamond unit cells, increased from 119 to 293 µm, resulting in the major pore diameter decreasing from 1,106 to 932 µm. The effect of systematically altering the laser beam spot size on the cellular structures was also evaluated. It was observed that by doubling the laser beam spot size, that there was a 17 % reduction in strut diameter and a 22 % reduction in mechanical strength of the structures. It was also observed that at constant energy input levels, the lattice structures created using a focused laser exhibited an 81% lower mechanical strength than the structures created using a de-focused laser. Thus, demonstrating that the mode of energy input is critical to achieving the desired strength in these structures.Based on the outputs from the in-situ monitoring system, a broadly linear correlation was obtained between the laser input energy, the associated process monitoring data generated and the mechanical strength of the lattice structures.
       
  • Elevated Temperature Corrosion Resistance of Additive Manufactured Single
           Phase AlCoFeNiTiV0.9Sm0.1 and AlCoFeNiV0.9Sm0.1 HEAs in a simulated Syngas
           Atmosphere
    • Abstract: Publication date: Available online 4 October 2019Source: Additive ManufacturingAuthor(s): Sayan Sarkar, Prashant K. Sarswat, Michael L. FreeABSTRACTHigh entropy alloys have attracted great interest due to their great stability and exceptional mechanical properties. Due to growing demand of novel engineering materials, which can endure harsh corrosive atmospheres, HEAs have been studied extensively to meet the demands of challenging industrial environments. Current manufacturing techniques of HEAs include arc-melting or spark plasma sintering, which are limited by factors such as high energy, grain refinement, alloying, and size limitations. In this study we report elevated temperature corrosion behavior of two new HEAs AlCoFeNiTiV0.9Sm0.1 and AlCoFeNiV0.9Sm0.1, produced by laser-based additive manufacturing, which offers high freedom of design, fast prototyping, and rapid quenching rates that are ideal for many industrial applications. These alloys were tested in corrosive syngas at elevated temperatures to explore their applicability in such harsh environments. Phase analysis results indicated the presence of a single FCC phase in these HEAs with no major surface cracks after enduring such corrosive atmospheres. These alloys exhibited good corrosion resistance as revealed by electrochemical testing methods. CALPHAD and DFT simulations were also performed to reveal the phase stability and crystal structures to further corroborate our experimental results.
       
  • Pore formation and evolution in wire + arc additively manufactured 2319 Al
           alloy
    • Abstract: Publication date: Available online 4 October 2019Source: Additive ManufacturingAuthor(s): Jianglong Gu, Minjie Gao, Shouliang Yang, Jing Bai, Jialuo Ding, Xuewei FangGiven its detrimental influence on mechanical properties, porosity defect is a major problem for wire + arc additively manufactured (WAAM) Al components. We performed X-ray computed tomography, optical microscopy, and scanning electron microscopy to observe the spatial distribution, size, and shape of micropores and reveal their formation and evolution mechanisms during the deposition and heat treatment of the WAAM 2319 Al alloys. Key findings demonstrated that thehydrogenmicropores and solidification microvoids existed in as-deposited alloys. The amounts and morphologies of hydrogen micropores and solidification microvoids varied from the top, middle, and bottom of the wall sample because of the distinct microstructure and second-phase distribution in each section. After the heat treatment, a significant variation in micropores involving three main evolution mechanisms, namely, hydrogen micropore precipitation, phase particle dissolution, and micropore growth, was observed. The hydrogen content analysis verifies that the evolution of micropores from each section of the wall was dominated by different mechanisms. Results of this research may provide a solid foundation for the safe application of WAAM Al alloy structures.Graphical Graphical abstract for this article
       
  • Powder bed properties modelling and 3D thermo-mechanical simulation of the
           additive manufacturing Electron Beam Melting process
    • Abstract: Publication date: Available online 4 October 2019Source: Additive ManufacturingAuthor(s): Manuela Galati, Anders Snis, Luca IulianoIn this work, an improved but still rather simple computational analysis is presented for a more detailed prediction of Electron Beam Melting (EBM) process outcomes. A fully coupled thermomechanical analysis is developed in which nonlinearities due to the variation of material properties when the material melts are included. A new analytical approach is developed to emulate the volume variation of the powder bed during heating and melting. Particularly, the expansion of the powder particles and the porosity reduction within the powder bed are considered simultaneously. The thermal expansion and the shrinkage of solid material during heating and cooling and the stress formation within the solid material are also modelled. The model can predict the geometrical transformation of the powder into solid material in an efficient way. A comparison between experimental and simulated cross-sectional areas of melted single lines is presented. Both continues line melting and fractional line melting, multi beam melting, are considered. The model shows a good ability to provide consistent and accurate forecasts. The maximum deviations between experimental and numerical results are approximately 15% for the height and 5% for the width of the melted lines, respectively. A comparison with a pure thermal model is also included, and benefits and differences between the two models are discussed.Graphical abstractGraphical abstract for this article
       
  • Directed energy deposition and characterization of high-carbon high speed
           steels
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): N. Ur Rahman, L. Capuano, S. Cabeza, M. Feinaeugle, A. Garcia-Junceda, M.B. de Rooij, D.T.A. Matthews, G. Walmag, I. Gibson, G.R.B.E. RömerDirected energy deposition (DED) of two high-carbon high speed steel alloys Febal-C-Cr-Mo-V and Febal−x-C-Cr-Mo-V-Wx was performed by using a 4 kW Nd:YAG laser source. The purpose of additive manufacturing was design and evaluation of thermally stable – high temperature wear resistant alloys. High temperature (500 °C) pin-on-disc tests were conducted to investigate the effect of carbides phase fraction on friction and wear. Strain scanning of the powder and additively manufactured materials was carried out by Neutron diffraction.Microstructures of both alloys consisted of a martensitic matrix with networks of primary and eutectic carbides. Micro-hardness (0.5 HV) measurement of all multilayer laser deposits, showed a micro-hardness greater than 700 HV, with no detrimental effect of repetitive laser thermal cycling. Febal−x-C-Cr-Mo-V-Wx showed a better high temperature wear resistance due to greater phase fraction of VC and Mo2C carbides. Fracture surfaces of post-heat treated tensile samples of Febal-C-Cr-Mo-V and Febal−x-C-Cr-Mo-V-Wx revealed brittle failures with minimal plasticity. Neutron strain mapping of the metal powders and the additively manufactured materials resulted in a weak diffraction signal and peak widening effect. These results could be explained either by an effect of strong crystallographic texture in the bulk or by the presence of nano- or semi-crystalline phases.Graphical abstractGraphical abstract for this article
       
  • Modelling of the capillarity effect in Multi Jet Fusion technology
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): Mattia Mele, Giampaolo Campana, Gian Luca MontiAbstractMulti Jet Fusion is a powder-based Additive Manufacturing technology patented by Hewlett-Packard Inc. It is characterised by the use of lamps instead of lasers to heat and melt polymers and by fusing and detailing agents that are jetted on the polymeric particles to modify and to control their heat absorption and thus selectively melt them. The high production rate and excellent mechanical properties of the manufactured parts, even in comparison with Laser Sintering, together with the overall product quality make this technology effective for a production of small series of end-parts rather than functional prototypes.In the present paper, the so-called capillarity effect is investigated. Capillarity derives from the interaction between the detailing and the fusing agents during the layer-based part building and it determines a deviation of the upper planar geometries when close to the border edges between the molten material and the powder bed.A model for the estimation of the capillarity effect is here proposed by adopting the free liquid meniscus theory. A benchmark geometry was designed to be affected by the capillarity effect and then manufactured by the MJF process. Values of the contact angle and of the characteristic length of the capillary, which are necessary to implement the analytical model, were obtained by experimental measurements made on the benchmark geometry.As a result the capillarity effect showed a dependence on the border edge orientation. The comparison between calculated shapes of the plane affected by the capillarity effect through the analytical model was in accordance with the experimental measurements thus allowing a reliable prediction to be made.
       
  • Multi-scale microstructural development and mechanical properties of a
           selectively laser melted beta titanium alloy
    • Abstract: Publication date: Available online 29 September 2019Source: Additive ManufacturingAuthor(s): Chunlei Qiu, Liu QiAbstractA β titanium alloy, Ti-10V-2Fe-3Al, was selectively laser melted under a modulated pulsed laser mode with different processing conditions. The as-fabricated samples were examined using a range of characterization techniques and properties evaluated through tensile testing. It was shown that with a small powder layer thickness (30 μm), a low laser power and a short exposure time (i.e., low energy density) led to development of fine β columnar grains and widespread cell structures whereas increased laser power and exposure time (i.e., high energy density) resulted in pronounced grain growth, increased texture and significantly decreased cell structures. Increasing powder layer thickness effectively promoted the columnar-to-equiaxed grain transition (CET), leading to a greatly reduced texture and a hybrid microstructure which consists of small and chunky equiaxed grains together with a small number of large columnar grains. Athermal ω precipitates were observed in all the as-fabricated samples. In the samples made with high energy densities, α laths which tend to constitute a grid-like structure were observed. The samples with the finest columnar grains showed both high strengths and good ductility thanks to full plastic deformation through both slipping and twinning. The samples with the hybrid grain structure, however, exhibited a highly limited or no ductility due to intergranular fracturing. The α-containing samples which also have coarse grains all failed in a cleavage fracture mode and exhibited almost no ductility. Transmission electron microscopy study revealed that the α-demarcated grid structure tended to confine plastic deformation within the β matrix and suppress the macroscopic plastic deformation throughout the samples.
       
  • A review of mechanical properties of additively manufactured Inconel 718
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): E. Hosseini, V.A. PopovichAbstractInconel 718 is one of the most commonly employed alloys for metal additive manufacturing (MAM) and has a wide range of applications in aircraft, gas turbines, turbocharger rotors, and a variety of other corrosive and structural applications involving temperatures of up to ∼700 °C. Numerous studies have investigated different aspects of the mechanical behaviour of additively manufactured (AM) Inconel 718. This study analyses the observations from more than 170 publications to provide an unbiased engineering overview for the mechanical response of AM Inconel 718 (and its variations and spread among different reports). First, a brief review of the microstructural features of AM Inconel 718 is presented. This is followed by a comprehensive summary of tensile strength, hardness, fatigue strength, and high-temperature creep behaviour of AM Inconel 718 for different types of MAM techniques and for different process and post-process conditions.
       
  • Towards Out-of-Chamber Damage-Free Fabrication of Highly Conductive
           Nanoparticle-Based Circuits inside 3D Printed Thermally Sensitive Polymers
           
    • Abstract: Publication date: Available online 26 September 2019Source: Additive ManufacturingAuthor(s): Md Naim Jahangir, Jeremy Cleeman, Hyun-Jun Hwang, Rajiv MalhotraAbstractCombining metal nanoparticle (NP) printing and additive manufacturing has high potential for integration of 3D conductive elements and electronic devices inside objects. Current processes used to achieve desired electrical resistivity of the printed NP circuits entail a compromise between resistivity, throughput, and thermal damage of the structure. We aim to break this tradeoff. We explore the mechanisms underlying the combination of Fused Filament Fabrication (FFF) of Acrylonitrile Butadiene Styrene (ABS) and Polylactide (PLA) polymer structures, printing of silver NPs (mixed nanowires and nanospheres), and out-of-chamber Intense Pulsed Light (IPL) sintering of the printed circuits. IPL of only-nanosphere based circuits on the FFF-made structure thermally damages the polymer without any resistivity reduction. In a significant advance, the addition of nanowires achieves a resistivity several times lesser than the state-of-the-art (13.1 µΩ-cm or 8 x bulk silver) without any thermal damage and within 0.75 seconds of IPL. Electromagnetic analysis and Molecular Dynamics simulations show that nanowire addition concurrently reduces IPL temperature and accelerates the kinetics of resistivity reduction. Subsequent FFF over the post-IPL conductive pattern causes a non-monotonic change in resistivity, surprisingly effecting a resistivity reduction down to 11.8 µΩ-cm. The mechanisms underlying this observation are discussed. The developed approach is used to demonstrate multilayer sensing of internal temperature and a light sensing circuit with embedded interconnects. Finally, we discuss how these insights may guide the creation of a machine tool that creates a seamless form of the proposed process.
       
  • Healing cracks in Selective Laser Melting by 3D Laser Shock Peening
    • Abstract: Publication date: Available online 24 September 2019Source: Additive ManufacturingAuthor(s): Nikola Kalentics, Navid Sohrabi, Hossein Ghasemi Tabasi, Seth Griffiths, Jamasp Jhabvala, Christian Leinenbach, Andreas Burn, Roland E. LogéSelective Laser Melting (SLM) of Ni-based superalloys such as CM247LC is prone to weld-cracking. This paper investigates how to suppress cracks by repeatedly applying Laser Shock Peening (LSP) during the building phase of SLM. Samples made of CM247LC were processed with different LSP parameters, and the influence on bulk crack density has been quantified. It was observed that for all chosen conditions, a significant decrease of up to 95% could be achieved, demonstrating the potential of the new hybrid 3D LSP method in improving SLM processability of alloys sensitive to cracking.Graphical abstractGraphical abstract for this article
       
  • Fabrication of poly(lactic acid)/Ti composite scaffolds with enhanced
           mechanical properties and biocompatibility via fused filament fabrication
           (FFF)–based 3D printing
    • Abstract: Publication date: Available online 20 September 2019Source: Additive ManufacturingAuthor(s): Jina Lee, Hyun Lee, Kwang-Hee Cheon, Cheonil Park, Tae-Sik Jang, Hyoun-Ee Kim, Hyun-Do JungAbstractIdeal bone substitutes should ensure good integration with bone tissue and are therefore required to exhibit good mechanical stability and biocompatibility. Consequently, the high elastic modulus (similar to that of bone), thermoplasticity, and biocompatibility of poly(lactic acid) (PLA) make it well suited for the fabrication of such substitutes by fused filament fabrication (FFF)-based 3D printing. However, the demands of present-day applications require the mechanical and biological properties of PLA to be further improved. Herein, we fabricated PLA/Ti composite scaffolds by FFF-based 3D printing and used thermogravimetric analysis to confirm the homogenous dispersion of Ti particles in the PLA matrix at loadings of 5–20 vol%. Notably, the thermal stability of these composites and the crystallization temperature/crystallinity degree of PLA therein decreased with increasing Ti content, while the corresponding glass transition temperature and melting temperature concomitantly increased. The compressive and tensile strengths of PLA/Ti composites increased with Ti increasing loading until it reached 10 vol% and were within the range of real bone values, while the impact strengths of the above composites significantly exceeded that of pure PLA. The incorporation of Ti resulted in enhanced in vitro biocompatibility, promoting the initial attachment, proliferation, and differentiation of pre-osteoblast cells, which allowed us to conclude that the prepared PLA/Ti composite scaffolds with enhanced mechanical and biological properties are promising candidates for bone tissue engineering applications.
       
  • Effect of trace lanthanum hexaboride on the phase, grain structure, and
           texture of electron beam melted Ti-6Al-4V
    • Abstract: Publication date: Available online 19 September 2019Source: Additive ManufacturingAuthor(s): Min Liu, Shichao Liu, Wei Chen, Chao Chen, Yaping Lv, Xiaoyong Zhang, Pengfei Lei, Yongcheng Lin, Kechao ZhouAbstractThis study investigated the effect of trace lanthanum hexaboride (LaB6) addition on the microstructure and mechanical properties of an electron beam melting (EBM) processed Ti-6Al-4V component. LaB6 exhibited a significant effect on the grain structure, phase, and texture of the EBM-processed Ti-6Al-4V alloys. Although prior-β columnar grains were observed in both Ti-6Al-4V and LaB6-modified Ti-6Al-4V (Ti-6Al-4V-LaB6), the width of the columnar grains decreased significantly with LaB6 addition. Alternating acicular α′ martensite and acicular α laths were distributed in the Ti-6Al-4V, whereas refined lamellar α + β structures were observed in the Ti-6Al-4V-LaB6. The texture intensity of α and β phases was also reduced in Ti-6Al-4V-LaB6. We propose that the addition of LaB6 provided a large amount of heterogenous nucleation sites for solidification and α phase formation. Consequently, high tensile strength with considerable elongation was achieved in the EBM-processed Ti-6Al-4V modified by trace LaB6 addition.
       
  • Spectral Diagnosis of Wire Arc Additive Manufacturing of Al Alloys
    • Abstract: Publication date: Available online 19 September 2019Source: Additive ManufacturingAuthor(s): Chen Zhang, Ming Gao, Cong Chen, Xiaoyan ZengAbstractOnline nondestructive testing for quality control is a critical direction for research in additive manufacturing in the future. In this study, for the first time, optical emission spectroscopy was employed to probe the arc characteristics in the wire arc additive manufacturing (WAAM) of an Al alloy and to detect its structural features. The arc characteristics, such as spectral intensity, electron density, and electron temperature, were calculated based on the atomic emission spectral lines. The resulting structural features of the deposited layers, namely the forming width, composition, grain size, and porosity defects, were analyzed, and a correlation between the arc characteristics and the structural features was proposed. The arc cathode size, which changed with the number of deposited layers, controlled the arc energy distribution. Hence, the forming width had an approximately linear relation with the spectral intensity of Mg (a constituent of the alloy used for the wire feed) and the electron density. The porosity in the alloy was observed to be caused by H, which was a dominant pollutant in the process. Furthermore, the correlation between the porosity and H spectral intensity was observed to be approximately linear. However, no significant correlation between the grain size and the spectrum was noticeable. The results from this study establish the applicability of spectral diagnosis of the forming size and the porosity in WAAM.
       
  • Effects of process parameters on porosity in laser powder bed fusion
           revealed by X-ray tomography
    • Abstract: Publication date: Available online 19 September 2019Source: Additive ManufacturingAuthor(s): Anton du PlessisThis paper reports on X-ray tomography of a series of coupon samples (5 mm cubes) produced under different process parameters, for laser powder bed fusion of Ti6Al4V. Different process parameters result in different pore formation mechanisms, each with characteristic pore sizes, shapes and locations within the 5 mm cube samples. While keyhole pores, lack of fusion pores and metallurgical pores have been previously identified and illustrated using X-ray tomography, this work extends beyond prior work to show how each of these not only exist in extreme situations but how they vary in size and shape in the transition regimes. It is shown how keyhole mode porosity increases gradually with increasing power, and how this depends on the scan speed. Similarly, lack of fusion pores are shown to occur following scan tracks in situations of poor hatch overlap, or a similar but different distribution of lack of fusion porosity due to large layer height spacing, showing respectively vertical and horizontal lack of fusion pore morphologies. Increased spacing between hatch scan tracks and contour scan tracks is demonstrated to form a near-surface porosity similar to that previously reported for slowing at the end of scan tracks which can cause keyhole mode porosity. Insights from 3D images allow improvements in parameter choices for optimized density of parts produced by laser powder bed fusion, and generally allow a better understanding of the porosity present in additively manufactured parts.Graphical Graphical abstract for this article
       
  • Evaluating the coefficient of thermal expansion of additive manufactured
           AlSi10Mg using microwave techniques
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): Richard Gumbleton, Jerome A. Cuenca, Georgina M. Klemencic, Nick Jones, Adrian PorchAbstractIn this paper we have used laser powder bed fusion (PBF) to manufacture and characterize metal microwave components. Here we focus on a 2.5 GHz microwave cavity resonator, manufactured by PBF from the alloy AlSi10Mg. Of particular interest is its thermal expansion coefficient, especially since many microwave applications for PBF produced components will be in satellite systems where extreme ranges of temperature are experienced. We exploit the inherent resonant frequency dependence on cavity geometry, using a number of TM cavity modes, to determine the thermal expansion coefficient over the temperature range 6–450 K. Our results compare well with literature values and show that the material under test exhibits lower thermal expansion when compared with a bulk aluminium alloy alternative (6063).
       
  • Overmelting and closing of thin horizontal channels in AlSi10Mg samples
           obtained by selective laser melting
    • Abstract: Publication date: December 2019Source: Additive Manufacturing, Volume 30Author(s): Y. Solyaev, L. Rabinskiy, D. TokmakovAbstractThis paper presents the results of numerical simulations and experimental tests on AlSi10Mg samples, having thin cylindrical channels built in the horizontal direction, using selective laser melting technology. The thermal state of the samples with channels of varying diameters is investigated by employing a simplified part-scale transient model that takes into consideration the overmelting effects through the change of the materials properties related with phase transition effects in the melted area of the sample. Comparison of simulation results and computing tomography of experimental samples reveal that the final cross section geometry of thin channels can be predicted and evaluated by the proposed model. Namely, it is found that the unsupported down-skin area of the channels is processed with formation of protrusions due to presence of the low conductive powder bed under the melted metal layer. This powder area overheated during laser action and melted together with desirable solid region of the model. Overmelting effects lead to the total closing of the channels with diameter less than 200 μm, partial closing of the channels of diameters 0.2-1 mm, and distortion of the cross section of larger channels. Possible approaches of adjusting the geometry of a channel are studied, considering the teardrop and enlarged shapes of the cross sections, which could help obtain a predefined cylindrical shape of the channels.
       
  • Investigation of Dynamic Fracture Behavior of Additively Manufactured
           Al-10Si-Mg Using High-speed Synchrotron X-ray Imaging
    • Abstract: Publication date: Available online 16 September 2019Source: Additive ManufacturingAuthor(s): Niranjan D. Parab, Lianghua Xiong, Qilin Guo, Zherui Guo, Cody Kirk, Yizhou Nie, Xianghui Xiao, Kamel Fezza, Wesley Everheart, Weinong W. Chen, Lianyi Chen, Tao SunAbstractThe dynamic tensile properties of additively manufactured (AM) and cast Al-10Si-Mg alloy were investigated using high-speed synchrotron X-ray imaging coupled with a modified Kolsky bar apparatus. A controlled tensile loading (strain rate ≈ 750 s-1) was applied using the Kolsky bar apparatus and the deformation and fracture behavior were recorded using the high-speed X-ray imaging setup. The CT and high-speed imaging results worked together to identify the location of the critical flaw and to capture the dynamics of crack propagation. In all experiments, the critical flaw was located on the surface of each specimen. The AM specimens showed significantly higher crack propagation speed, yield strength, ultimate tensile strength, strain hardening coefficient, and yet lower ductility compared to the cast specimens under dynamic tension. Although the strength values were higher for the AM specimens, the critical mode I stress intensity factors were comparable for both specimens. The microstructures of the samples were characterized by synchrotron X-ray computed tomography (CT) and scanning electron microcopy. The correlation between the dynamic fracture behavior of the samples and the microstructure of the samples is analyzed and discussed.
       
  • Additive manufacturing of CMSX-4 Ni-base superalloy by Selective Laser
           Melting: Influence of processing parameters and heat treatment
    • Abstract: Publication date: Available online 16 September 2019Source: Additive ManufacturingAuthor(s): Inmaculada Lopez-Galilea, Benjamin Ruttert, Junyang He, Thomas Hammerschmidt, Ralf Drautz, Baptiste Gault, Werner TheisenAbstractSelective laser melting (SLM) provides an economic approach to manufacturing Ni-base superalloy components for high-pressure gas turbines as well as repairing damaged blade sections during operation. In this study, two advanced processing routes are combined: SLM, to fabricate small specimens of the nonweldable CMSX-4, and hot isostatic pressing (HIP) with a rapid cooling rate as post-processing to heal defects while the target γ/γ´ microstructure is developed. An initial parametric study is carried out to investigate the influence of the SLM process parameters on the microstructure and defects occurring during SLM. Special emphasis is placed on understanding and characterizing the as-built SLM microstructures by means of high-resolution characterization techniques. The post-processing heat treatment is then optimized with respect to segregation and the γ/γ´ microstructure.
       
  • Microstructural evolution and corrosion behaviors of Inconel 718 alloy
           produced by selective laser melting following different heat treatments
    • Abstract: Publication date: Available online 16 September 2019Source: Additive ManufacturingAuthor(s): Shuncun Luo, Wenpu Huang, Huihui Yang, Jingjing Yang, Zemin Wang, Xiaoyan ZengThe microstructures and corrosion resistances of Inconel 718 alloy prepared by selective laser melting (SLM), SLM following various heat treatments, and conventional rolling are studied. Results show that only Nb element is enriched in interdendritic regions while Fe element is abundant in dendritic trunks for the as-built Inconel 718 alloy. After solution annealing treatment, incomplete recrystallization is observed and distortion energy is released. Increasing the solution annealing temperature from 980 °C to 1020 °C (ST1˜ST3), the morphologies of δ phases turn from needle-like into short platelet shape, which reduces the anodic current density and improves the corrosion resistance compared to other heat-treated samples in 3.5 wt% NaCl solution. Corrosion morphology observation shows that obvious cracking of surface passive film occurs for the SLM, solution annealing plus double aging (SA) and rolled samples, while corrosion pits and micro-cracks appear at the δ phase boundaries of solution-annealed (ST1˜ST3) samples. The surface passive film is smooth for the rolled sample. The corrosion resistance of samples obtained by different processes follows in the order of rolled> ST3> ST2> ST1> SA> SLM. The galvanic coupling effect causes the formation of corrosion pits or cracks between γ matrix and second phases. The high interface energy and lattice misfit may provide driving forces for the preferential dissolution of γ matrix rather than second phases. The inferior corrosion resistance of the as-built Inconel 718 alloy can be significantly improved through solution annealing treatment at 1020 °C.Graphical abstractGraphical abstract for this article
       
  • Effect of powder chemical composition on the as-built microstructure of
           17-4 PH stainless steel processed by selective laser melting
    • Abstract: Publication date: Available online 16 September 2019Source: Additive ManufacturingAuthor(s): Swathi Vunnam, Abhinav Saboo, Chantal Sudbrack, Thomas L. StarrSelective laser melting (SLM) processed stainless steel usually exhibits an inhomogeneous microstructure in the as-built condition. The effect of powder chemical composition on the microstructural evolution of SLM processed 17-4 PH in the as-built condition was studied. A path to achieve a fully martensitic 17-4 PH component in the as-built condition by fine-tuning the alloy composition without any post-built heat treatments was demonstrated. The as-built 17-4 PH phase transformation from δ ferrite to austenite (γ) and subsequently to martensite (α’) was governed by the concentrations of ferrite and austenite stabilizing elements as represented by a chromium to nickel equivalent (Creq/Nieq) value. Electron backscatter diffraction (EBSD) analysis revealed that increase in the WRC-1992 equations based Creq/Nieq value to ≥ 2.65 resulted in coarse δ ferrite grains with a preferential crystal orientation along the build direction. Epitaxial growth of semi-circular and columnar δ ferrite grains accompanied by a marginal volume fraction of retained austenite and transformed martensitic phases was observed. Retained austenite and transformed martensitic phases exhibited a fine grain structure preferentially along the coarse ferrite grain boundaries. Decreasing the Creq/Nieq value to 2.36 induced δ ferrite grain refinement with a significant amount of transformed martensite in the as-built condition. EBSD phase composition analysis along with thermodynamic equilibrium modeling implies that a lower Creq/Nieq value promotes martensite formation resulting in a less retained δ ferrite in the as-built condition.Graphical abstractGraphical abstract for this article
       
  • Microstructural evolution and mechanical behavior of nickel aluminum
           bronze Cu-9Al-4Fe-4Ni-1Mn fabricated through wire-arc additive
           manufacturing
    • Abstract: Publication date: Available online 13 September 2019Source: Additive ManufacturingAuthor(s): C. Dharmendra, A. Hadadzadeh, B.S. Amirkhiz, G.D. Janaki Ram, M. MohammadiAs a step forward toward the development of the next generation of nickel aluminum bronze (NAB) components using wire-arc additive manufacturing (WAAM), square bars were printed in the vertical direction. The as-built microstructure was characterized using multi-scale electron microscopy techniques, where the differences in phase formation were compared to the reference cast-NAB based on the solidification characteristics. The as-cast microstructure typically consists of Cu-rich α-matrix, and four types of intermetallic particles referred to as κ-phases. In the WAAM-NAB, the formation of κI was suppressed due to high cooling rates. The microstructure was finer and the volume fraction of intermetallic particles was significantly lower than that of the cast-NAB. Based on energy dispersive spectroscopy (EDS) technique and diffraction pattern analysis using transmission electron microscopy (TEM), the phases formed in the interdendritic regions were identified as κII (globular Fe3Al) and κIII (lamellar NiAl), whereas numerous fine (5-10 nm) Fe-rich κIV particles were precipitated uniformly within the α-matrix. Electron backscatter diffraction analysis revealed weak texture on both parallel and perpendicular planes to the building direction with (100) poles rotated away from the build direction. The WAAM-NAB sample exhibited considerably higher yield strength (˜88 MPa) and elongation (˜10%) than the cast-NAB, but the gain in the ultimate tensile strength was marginal.Graphical abstractGraphical abstract for this article
       
  • Laboratory X-ray tomography for metal additive manufacturing: round robin
           test
    • Abstract: Publication date: Available online 13 September 2019Source: Additive ManufacturingAuthor(s): Anton du Plessis, Stephan G. le Roux, Jess Waller, Philip Sperling, Nils Achilles, Andre Beerlink, Jean-François Métayer, Mirko Sinico, Gabriel Probst, Wim Dewulf, Florian Bittner, Hans-Josef Endres, Marian Willner, Ágota Drégelyi-Kiss, Tomas Zikmund, Jakub Laznovsky, Jozef Kaiser, Pascal Pinter, Stefan Dietrich, Elena LopezAbstractThis paper reports on the results of a round robin test conducted by ten X-ray micro computed tomography (micro-CT) laboratories with the same three selected titanium alloy (Ti6Al4V) laser powder bed fusion (L-PBF) test parts. These parts were a 10-mm cube, a 60-mm long and 40-mm high complex-shaped bracket, and a 15-mm diameter rod. Previously developed protocols for micro-CT analysis of these parts were provided to all participants, including suggested scanning parameters and image analysis steps. No further information on the samples were provided, and they were selected from a variety of parts from a previous different type of round robin study where various L-PBF laboratories provided identical parts for micro-CT analysis at one laboratory. In this new micro-CT round robin test which involves various micro-CT laboratories, parts from the previous work were selected such that each part had a different characteristic flaw type, and all laboratories involved in the study analyzed the same set of parts. The 10-mm cube contained subsurface pores just under its top surface (relative to build direction), and all participants could positively identify this. The complex bracket had contour pores around its outer vertical sides, and was warped with two arms deflected towards one another. Both of these features were positively identified by all participants. The 15-mm diameter rod had a layered stop/start flaw, which was also positively identified by all participants. Differences were found among participants for quantitative evaluations, ranging from no quantitative measurement made, to under and overestimation of the values in all analyses attempted. This round robin provides the opportunity to highlight typical causes of errors in micro-CT scanning and image analysis as applied to additively manufactured parts. Some workflow variations, sources of error and ways to increase the reproducibility of such analysis workflows are discussed. The ultimate aim of this work is to advance the efficient use of micro-CT facilities for process optimization and quality inspections for additively manufactured products. The results provide confidence in the use of laboratory micro-CT but also indicate the need for further development of standards, protocols and image analysis workflows for quantitative assessment, especially for direct and quantitative comparisons between different laboratories.
       
  • 3D Printed High Functional Density Packaging Compatible Out-of-Plane
           Antennas
    • Abstract: Publication date: Available online 12 September 2019Source: Additive ManufacturingAuthor(s): Mohd Ifwat Mohd Ghazali, Saranraj Karuppuswami, Amanpreet Kaur, Premjeet ChahalAbstractThis paper demonstrates a simple, low-cost additive manufacturing technique for fabricating structures compatible with high-density packaging solutions. Leveraging the third dimension (z-axis), several out-of-plane (non-planar) antennas that are compatible with multi-layer integration are presented, including an elevated vertical mount patch antenna, an air-gap based E-Patch antenna, a monopole with a corner reflector, and a vertical Yagi-Uda antenna. A T-line resonator is characterized to understand the transmission line losses associated with the vertical bends. Details of the simulation, fabrication, and measurements are presented. Simulations are carried out using ANSYS High-Frequency Structure Simulator (HFSS®), and structures are fabricated using a polyjet printing process. The measured results are in good agreement with the simulation results, and overall a good performance is achieved for all the antenna designs. For example, the elevated vertical mount patch shows a gain of 3.62 dBi (center frequency of 5.4 GHz), and the air-gap E-patch antenna shows a gain of 6 dBi at 2.4 GHz and 10 dB bandwidth of 4.9 GHz. The vertical monopole antenna with a corner reflector shows a peak gain of 7.3 dBi at 6 GHz, and the Yagi-Uda antenna shows a forward gain of 6 dBi at 5 GHz.
       
  • Parametric Analysis to Quantify Process Input Influence on the Printed
           Densities of Binder Jetted Alumina Ceramics
    • Abstract: Publication date: Available online 9 September 2019Source: Additive ManufacturingAuthor(s): Edgar Mendoza Jimenez, Daming Ding, Laisuo Su, Aparna R. Joshi, Aarti Singh, B. Reeja-Jayan, Jack BeuthAbstractBinder jetting, a commercial additive manufacturing process that selectively deposits a liquid binder onto a powder bed, can become a viable method to additively manufacture ceramics. However, the effects of process parameters/inputs on printing outputs (e.g. part density and geometric resolution) have not been investigated and no methodical approach exists for the process development of new materials. In this work, a parametric study consisting of 18 experiments with unique process input combinations explores the influence of seven process inputs on the relative densities of as-printed (green) alumina (Al2O3) parts. Sensitivity analyses compare the influence of each input on green densities. Multivariable linear and Gaussian process regressions provide models for predicting green densities as a function of binder jetting process inputs. The parametric study reveals that two process inputs, namely recoat speed and oscillator speed, significantly influence green densities. The multivariable linear and Gaussian process regression models indicate that the green densities of alumina builds can be increased by decreasing the recoat speed and increasing the oscillator speed. The Gaussian process regression model further suggests that the green densities have nonlinear dependence on the rest of the process parameters. Separate prints were performed at process input combinations different than those of the parametric study to validate the green density models. The models produced can assist operators in selecting process inputs that will result in a desired green density, allowing for the control of porosity in printed parts with a high degree of accuracy. The methodology reported in this study can be leveraged for other powder systems and machines to predict and control the porosity of binder jetted parts for applications such as filters, bearings, electronics, and medical implants.
       
  • Fused filament fabrication, debinding and sintering as a low cost additive
           manufacturing method of 316L Stainless Steel
    • Abstract: Publication date: Available online 9 September 2019Source: Additive ManufacturingAuthor(s): Yvonne Thompson, Joamin Gonzalez-Gutierrez, Christian Kukla, Peter FelferAbstractBy using filaments comprising metal or ceramic powders and polymer binders, solid metal and ceramic parts can be created by combining low-cost fused filament fabrication (FFF) with debinding and sintering. In this work, we explored a fabrication route using a FFF filament filled with 316 L steel powder at 55 vol.-%. We investigated the printing, debinding and sintering parameters and optimized them with respect to the mechanical properties of the final part. Special focus was placed on debinding and sintering in order to obtain components of low residual porosity. Solvent debinding of the printed green bodies created an internal network of interconnected pores and was followed by thermal debinding. Thermal debinding allowed for complete removal of the remaining binder and produced mechanically stable brown parts. Sintering at 1360 °C provided densification of the parts and generated nearly isotropic linear shrinkage of about 20 %. Using optimized parameters, it was possible to fabricate 316 L steel components with a density greater than 95 % via the material extrusion additive manufacturing, debinding and sintering route, with achievable deflections in a 3-point bending test similar to rolled sheet material, albeit at lower strength.
       
  • Analytical modeling and experimental validation of powder stream
           distribution during direct energy deposition
    • Abstract: Publication date: Available online 7 September 2019Source: Additive ManufacturingAuthor(s): Zhichao Liu, Hong-Chao Zhang, Shitong Peng, Hoyeol Kim, Dongping Du, Weilong CongAbstractAs an important factor during direct energy deposition (DED) additive manufacturing process, powder stream distribution will not only affect the deposition rate, but also the powder-gas and power-powder interactions, and thus the consequent quality and property of the fabricated part. This paper created an analytical model to illustrate the powder stream distribution under the four-jet nozzles in the DED. To validate the proposed model, weight measurement method was used to track the powder stream distributions at different positions under the nozzle. Additionally, the effects of the input variables, including powder flow rate, gas flow rate and particle size, on the powder stream distribution were also analyzed. The results suggest a relatively good agreement between the modelling and experimental measurements. At the end, the powder deposition efficiency (PDE) was estimated based on the simulation results.
       
  • Production of net-shape Mn-Al permanent magnets by electron beam melting
    • Abstract: Publication date: Available online 6 September 2019Source: Additive ManufacturingAuthor(s): I.A. Radulov, V.V. Popov, A. Koptyug, F. Maccari, A. Kovalevsky, S. Essel, J. Gassmann, K.P. Skokov, M. BambergerAbstractThe main goal of this work is the adoption of additive manufacturing for the production of inexpensive rare-earth free MnAl-based permanent magnets. The use of more advanced binder-free additive manufacturing technique such as Electron Beam Melting (EBM) allows obtaining fully-dense magnetic materials with advanced topology and complex shapes. We focus on the feasibility of controlling the phase formation in additively manufactured Mn-Al alloys by employing post-manufacturing heat treatment. The as-manufactured EBM samples contain 8% of the desired ferromagnetic τ-MnAl phase. After the optimized annealing treatment, the content of the τ-phase was increased to 90%. This sample has a coercivity value of 0.15 T, which is also the maximum achieved in conventionally produced binary MnAl magnets. Moreover, the EBM samples are fully dense and have the same density as the samples produced by conventional melting density.
       
  • Thermal Conductivity of TPMS Lattice Structures Manufactured via Laser
           Powder Bed Fusion
    • Abstract: Publication date: Available online 5 September 2019Source: Additive ManufacturingAuthor(s): S. Catchpole-Smith, R.R.J. Sélo, A.W. Davis, I.A. Ashcroft, C.J. Tuck, A. ClareAbstractLattice structures can add value to high-performance components manufactured by laser powder bed fusion due to their high specific strength and stiffness. A further use of lattice structures is in thermo-mechanical applications, where the high surface area of the lattice may aid heat transfer. However, little characterisation of lattices under thermal loading is currently available in the literature. In this study, a custom-built test rig was used to characterise the thermal conduction for three triply periodic minimal surface lattice types, namely: gyroid, diamond and Schwarz primitives, with unit cell size and volume fraction being varied.Results show that thermal conductivity is primarily a function of the material properties and volume fraction of the sample. However, some effects of the geometry, such as surface area to volume ratio, can be used to explain slight differences in the measured conductivity. The Schwarz primitive unit cell consistently gave the highest conductivity, with diamond and gyroid unit cells being marginally lower. Larger cell sizes typically gave higher conductivity than smaller cells, which can be attributed to greater intra-cell convective heat transfer and better interface coupling with the testing apparatus.The experimental results are used to derive equations that allow samples with a specified thermal conductivity to be designed, thus demonstrating how a component may be manufactured with a custom thermal profile by varying the volume fraction of the lattice.
       
  • Part Geometry and Conduction-based Laser Power Control for Powder Bed
           Fusion Additive Manufacturing
    • Abstract: Publication date: Available online 4 September 2019Source: Additive ManufacturingAuthor(s): Ho Yeung, Brandon Lane, Jason FoxAbstractLaser powder bed fusion (LPBF) uses a focused, high power laser to repeatedly scan geometric patterns on thin layers of metal powder, which build up to a final, solid three-dimensional (3D) part. This process is somewhat limited in that the parts tend to have poorer surface finish (compared to machining or grinding) and distortion due to residual stress, as well as multiple other deficiencies. Typical laser scan strategies are relatively simple and use constant laser power levels. This elicits local variations in the melt pool size, shape, or temperature, particularly near sharp geometric features or overhang structures due to the relatively higher thermal conductivity of solid metal compared to metal powder. In this paper, we present a new laser power control algorithm, which scales the laser power to a value called the geometric conductance factor (GCF). The GCF is calculated based on the amount of solid vs. powder material near the melt pool. The algorithm for calculating GCF is presented along with some basic examples for clarification. Then, we detail the hardware and software implementation on the National Institute of Standards and Technology (NIST) additive manufacturing metrology testbed (AMMT), which includes co-axial melt pool monitoring using a high-speed camera. Six parts were fabricated out of nickel superalloy 625 (IN625) with the same nominal laser power, but with varying GCF algorithm parameters. We demonstrate the effect of tailored laser power on reducing the variability of melt pool intensity measured throughout the 3D build. Finally, we contrast the difference between the ‘optimized’ part vs. the standard build parameters, including the deflection of the final part top surface near the overhang and the variation of surface finish on the down-facing surfaces. Ultimately, the improvements to the in-situ process monitoring and part qualities demonstrate the utility and future potential tuning and optimizing more complex laser scan strategies.
       
  • Additive Biomanufacturing of Scaffolds for Breast Reconstruction
    • Abstract: Publication date: Available online 4 September 2019Source: Additive ManufacturingAuthor(s): Mina Mohseni, Onur Bas, Nathan J. Castro, Beat Schmutz, Dietmar W. HutmacherAbstractLimitations for the current clinical treatment strategies for breast reconstruction have prompted researchers and bioengineers to develop unique techniques based on tissue engineering and regenerative medicine (TE&RM) principles. Recently, scaffold-guided soft TE has emerged as a promising approach due to its potential to modulate the process of tissue regeneration. Herein, we utilized additive biomanufacturing (ABM) to develop an original design-based concept for scaffolds which can be applied in TE-based breast reconstruction procedures. The scaffold design addresses biomechanical and biological requirements for medium to large-volume regeneration with the potential of customization. The model is composed of two independent structural components. The external structure provides biomechanical stability to minimize load transduction to the newly formed tissue while the internal structure provides a large pore and fully interconnected pore architecture to facilitate tissue regeneration. A methodology was established to design, optimize and 3D print the external structure with customized biomechanical properties. The internal structure was also designed and printed with a gradient of pore size and a channel structure to facilitate lipoaspirated fat delivery and entrapment. A fused filament fabrication-based printing strategy was employed to print two structures as a monolithic breast implant.
       
  • 3D printed architected hollow sphere foams with low-frequency phononic
           band gaps
    • Abstract: Publication date: Available online 3 September 2019Source: Additive ManufacturingAuthor(s): Olivia McGee, Huan Jiang, Feng Qian, Zian Jia, Lifeng Wang, Han Meng, Dimitrios Chronopoulos, Yanyu Chen, Lei ZuoAbstractWe experimentally and numerically investigate elastic wave propagation in a class of lightweight architected materials composed of hollow spheres and binders. Elastic wave transmission tests demonstrate the existence of vibration mitigation capability in the proposed architected foams, which is validated against the numerically predicted phononic band gap. We further describe that the phononic band gap properties can be significantly altered through changing hollow sphere thickness and binder size in the architected foams. Importantly, our results indicate that by increasing the stiffness contrast between hollow spheres and binders, the phononic band gaps are broadened and shifted toward a low-frequency range. At the threshold stiffness contrast of 50, the proposed architected foam requires only a volume fraction of 10.8% while exhibiting an omnidirectional band gap size exceeding 130%. The proposed design paradigm and physical mechanisms are robust and applicable to architected foams with other topologies, thus providing new opportunities to design phononic metamaterials for low-frequency vibration control.
       
  • Direct-write Printed Broadband Inductors
    • Abstract: Publication date: Available online 3 September 2019Source: Additive ManufacturingAuthor(s): Yuan Gu, Donghun Park, Stephen Gonya, Joseph Jendrisak, Siddhartha Das, D.R. HinesAbstractThe capability to additively manufacture fully-functioning electronic circuits is a frontier in 3D-printed electronics that will afford unprecedented scalability, miniaturization, and conformability of electronic circuits. The printed passives, such as resistors, capacitors, and inductors, however, are rarely capable of performances comparable to that of the commercially available versions. In this paper, we report a novel procedure that employs three-dimensional (3D) additive manufacturing techniques to fabricate high-frequency, tapered-solenoid type inductors for RF applications capable of wide bandwidth performance. The design includes a polymer support structure to reduce the parasitic capacitance between the inductor and the substrate, a tapered solid core, and conducting windings. Each design component is printed using aerosol-jet (AJ) printing methods on a grounded coplanar waveguide such that the small end of the conical-shaped inductor is connected to the transmission line and the base of the inductor is connected to ground. Two types of solid-core inductors were fabricated: one with a printed polymer core and another with a non-printed iron core. Scattering parameter measurements establish that the polymer and iron-core inductors, combined with a 45º-polymer support structure, can achieve usable bandwidths up to 18 GHz and 40 GHz, respectively, with low insertion loss. 3D model and circuit model simulations were also carried out to study inductor performance in terms of self-resonance and insertion loss.
       
  • Rapid cooling of laser sintered part cakes using airflow through cracks
    • Abstract: Publication date: Available online 29 August 2019Source: Additive ManufacturingAuthor(s): Ryuichi Kobayashi, Yuki Yamauchi, Seiji Koganei, Takashi KigureAbstractIn polymer laser sintering, the generated part cake is a large mass of powder, and the part cake is heated to nearly its melting point. Accelerating this cooling process would allow the quick harvesting of the parts. Here we propose a method that promotes the cooling of the part cake using injected air into the cracks formed inside the part cake. Further, a system was designed and experimentally tested to inject air into the bottom of the fabricated part cake. The results denoted that the internal temperature of the part cake reached the glass transition point 17 hours earlier than it did by natural cooling without airflow. Furthermore, the airflow did not result in any significant deformation or adversely affect the mechanical properties of parts. In addition, the heat transfer coefficient of the crack was estimated using the finite element method and was used to evaluate the cooling enhancement limit based on a parametric study. Thus, we concluded that the airflow through the cracks facilitated the rapid cooling of the part cakes, reducing the production time required for polymer laser sintering.
       
  • Design and Additive Manufacture of Functionally Graded Structures Based on
           Digital Materials
    • Abstract: Publication date: Available online 29 August 2019Source: Additive ManufacturingAuthor(s): Inigo FloresABSTRACTVoxel-based multimaterial jetting additive manufacturing allows fabrication of digital materials (DMs) at meso-scale (˜1 mm) by controlling the deposition patterns of soft elastomeric and rigid glassy polymers at the voxel-scale (˜90 μm). The digital materials can then be used to create heterogeneous functionally graded material (FGM) structures at macro-scale (˜10 mm) programmed to behave in a predefined manner. This offers huge potential for design and fabrication of novel and complex bespoke mechanical structures.This paper presents a complete design and manufacturing workflow that simultaneously integrates material design, structural design, and product fabrication of FGM structures based on digital materials. This is enabled by a regression analysis of the experimental data on mechanical performance of the DMs i.e., Young’s modulus, tensile strength and elongation at break. This allows us to express the material behavior simply as a function of the microstructural descriptors (in this case, just volume fraction) without having to understand the underlying microstructural mechanics while simultaneously connecting it to the process parameters.Our proposed design and manufacturing approach is then demonstrated and validated in two series of design exercises to devise complex FGM structures. First, we design, computationally predict and experimentally validate the behavior of prescribed designs of FGM tensile structures with different material gradients. Second, we present a design automation approach for optimal FGM structures. The comparison between the simulations and the experiments with the FGM structures shows that the presented design and fabrication workflow based on our modeling approach for DMs at meso-scale can be effectively used to design and predict the performance of FGMs at macro-scale.Graphical Graphical abstract for this article
       
  • Real-time feedback controlled conversion in vat photopolymerization of
           ceramics: a proof of principle
    • Abstract: Publication date: Available online 8 July 2019Source: Additive ManufacturingAuthor(s): Thomas Hafkamp, Gregor van Baars, Bram de Jager, Pascal EtmanTechnical ceramics for high-performance applications can be additively manufactured using vat photopolymerization technology. This technology faces two main challenges: increasing ceramic product size and improving product quality. The integration of process control strategies into AM equipment is expected to play a key role in tackling these challenges. This work demonstrates the feasibility of real-time and in-situ feedback control of the light-initiated polymerization reaction that lies at the core of vat photopolymerization technology. To prove the principle, a single-layer experimental setup was developed in which the degree of conversion was measured by infrared spectroscopy. Experimental data obtained from this setup was used to develop a control-oriented process model and identify its parameters. A material perturbation was applied by adding an inhibitor and the case with and without feedback control were compared. The results show that the feedback controller successfully compensated for the material perturbation and reached the same final conversion value as the unperturbed case. This result can be considered a fundamental step towards additive manufacturing of defect-free ceramic parts using in-line process control.Graphical abstractGraphical abstract for this article
       
  • High-fidelity 3D Printing using Flashing Photopolymerization
    • Abstract: Publication date: Available online 19 August 2019Source: Additive ManufacturingAuthor(s): Shangting You, Pengrui Wang, Jacob Schimelman, Henry H. Hwang, Shaochen ChenAbstractPhotopolymerization-based 3D printing has emerged as a promising technique to fabricate 3D structures. However, during the printing process, polymerized materials such as hydrogels often become highly light-scattering, thus perturbing incident light distribution and thereby deteriorating the final print resolution. To overcome this scattering-induced resolution deterioration, we developed a novel method termed flashing photopolymerization (FPP). Our FPP approach is informed by the fundamental kinetics of photopolymerization reactions, where light exposure is delivered in millisecond-scale ‘flashes’, as opposed to continuous light exposure. During the period of flash exposure, the prepolymer material negligibly scatters light. The material then polymerizes and opacifies in absence of light, therefore the exposure pattern is not perturbed by scattering. Compared to the conventional use of a continuous wave (CW) light source, the FPP fabrication resolution is improved. FPP also shows little dependency on the exposure, thus minimizing trial-and-error type optimization. Using FPP, we demonstrate its use in generating high-fidelity 3D printed constructs.
       
  • Processing of Gas-nitrided AISI 316L Steel Powder by Laser Powder Bed
           Fusion – Microstructure and Properties
    • Abstract: Publication date: Available online 19 August 2019Source: Additive ManufacturingAuthor(s): J. Boes, A. Röttger, L. Becker, W. TheisenAbstractThis work investigated the processing of high nitrogen-alloyed austenitic stainless steels by laser powder bed fusion (L-PBF). Prior to L-PBF processing, the AISI 316 L steel powder was nitrided at a temperature of 675° in a 3 bar nitrogen atmosphere, thus achieving a N content of 0.58 mass-%. By mixing nitrided 316 L powder with untreated 316 L powder, two different powder mixtures were obtained with 0.065 mass-% and 0.27 mass-% nitrogen, respectively. After nitriding and mixing, the powder was characterized in terms of its flow properties and chemical composition. The nitrided steel powder was then processed by L-PBF, and the microstructure as well as the chemical composition were investigated by means of scanning electron microscopy and carrier gas hot extraction. It was shown that nitriding of steel powders in an N2 atmosphere can be used to significantly increase the nitrogen content of the powder without impairing its flow properties. With increasing nitrogen content of the powder, the porosity within the L-PBF built specimens increased. However, both the yield strength and the tensile strength were greatly improved without a marked reduction in the elongation at fracture of the respective steels. This work shows that nitrogen-alloyed austenitic stainless steels can be processed by L-PBF and the mechanical properties can be improved.
       
  • Effects of Amylose Content on the Mechanical Properties of
           Starch-Hydroxyapatite 3D Printed Bone Scaffolds
    • Abstract: Publication date: Available online 6 August 2019Source: Additive ManufacturingAuthor(s): Caitlin Koski, Susmita BoseRecent efforts in the bone and tissue engineering field have been made to create resorbable bone scaffolds that mimic the structure and function of natural bone. While enhancing mechanical strength through increased ceramics loading has been shown for sintered parts, few studies have reported that the crosslinked polymer provides strength for the composite parts without post processing. The objective of this study is to assess the effect of amylose content on the mechanical and physical properties of starch-hydroxyapatite (HA) composite scaffolds for bone and tissue engineering applications. Starch-HA composite scaffolds utilizing corn, potato, and cassava sources of gelatinized starch were fabricated through the utilization of a self-designed and built solid freeform fabricator (SFF). It was hypothesized that the mechanical strength of the starch-HA scaffolds would increase with increasing amylose content based on the botanical source and weight percentage added. Overall, compressive strengths of scaffolds were achieved up to 12.49 + 0.22 MPa, through the implementation of 5.46 wt% corn starch with a total amylose content of 1.37%. The authors propose a reinforcement mechanism through a matrix of gelled starch particles and interlocking of hydroxyl-rich amylose with hydroxyapatite through hydrogen bonding. XRD, FTIR, and FESEM were utilized to further characterize these scaffold structures, ultimately elucidating amylose as a biologically relevant reinforcement phase of resorbable bone scaffolds.Graphical Graphical abstract for this article
       
 
 
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