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Publisher: Elsevier   (Total: 3160 journals)

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Showing 1 - 200 of 3160 Journals sorted alphabetically
Academic Pediatrics     Hybrid Journal   (Followers: 37, SJR: 1.655, CiteScore: 2)
Academic Radiology     Hybrid Journal   (Followers: 25, SJR: 1.015, CiteScore: 2)
Accident Analysis & Prevention     Partially Free   (Followers: 97, SJR: 1.462, CiteScore: 3)
Accounting Forum     Hybrid Journal   (Followers: 28, SJR: 0.932, CiteScore: 2)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 37, SJR: 1.771, CiteScore: 3)
Achievements in the Life Sciences     Open Access   (Followers: 5)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 7)
Acta Astronautica     Hybrid Journal   (Followers: 428, SJR: 0.758, CiteScore: 2)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 2)
Acta Biomaterialia     Hybrid Journal   (Followers: 28, SJR: 1.967, CiteScore: 7)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription   (Followers: 2)
Acta de Investigación Psicológica     Open Access   (Followers: 3)
Acta Ecologica Sinica     Open Access   (Followers: 10, SJR: 0.18, CiteScore: 1)
Acta Haematologica Polonica     Free   (Followers: 1, SJR: 0.128, CiteScore: 0)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.661, CiteScore: 2)
Acta Materialia     Hybrid Journal   (Followers: 289, SJR: 3.263, CiteScore: 6)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 6, 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: 1, SJR: 1.793, CiteScore: 6)
Acta Poética     Open Access   (Followers: 4, SJR: 0.101, CiteScore: 0)
Acta Psychologica     Hybrid Journal   (Followers: 27, 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: 17, 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: 175, 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: 16, SJR: 2.384, CiteScore: 5)
Advances in Anesthesia     Full-text available via subscription   (Followers: 28, 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: 10, SJR: 0.992, CiteScore: 1)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 11, 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: 14, 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: 32, 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: 4)
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: 28, SJR: 0.156, CiteScore: 1)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, 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: 11)
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: 43, 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: 49, 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: 61, 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: 20, SJR: 1.354, CiteScore: 4)
Advances in Genome Biology     Full-text available via subscription   (Followers: 10, SJR: 12.74, CiteScore: 13)
Advances in Geophysics     Full-text available via subscription   (Followers: 6, SJR: 1.193, CiteScore: 3)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 24, SJR: 0.368, CiteScore: 1)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 12, SJR: 0.749, CiteScore: 3)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 23)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 2, SJR: 0.193, CiteScore: 0)
Advances in Immunology     Full-text available via subscription   (Followers: 36, 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: 8, 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: 18, SJR: 0.88, CiteScore: 2)
Advances in Mathematics     Full-text available via subscription   (Followers: 11, SJR: 3.027, CiteScore: 2)
Advances in Medical Sciences     Hybrid Journal   (Followers: 7, SJR: 0.694, CiteScore: 2)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 4, SJR: 1.158, CiteScore: 3)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 23)
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: 4)
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: 17, 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: 25, SJR: 0.461, CiteScore: 1)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 12)
Advances in Pharmacology     Full-text available via subscription   (Followers: 16, SJR: 1.536, CiteScore: 3)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 8, 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: 5)
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: 66)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 6, SJR: 0.371, CiteScore: 1)
Advances in Radiation Oncology     Open Access   (Followers: 1, 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: 414, 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: 12, SJR: 0.555, CiteScore: 2)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 35, SJR: 2.208, CiteScore: 4)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 19)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 15)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 2.262, CiteScore: 5)
Advances in Water Resources     Hybrid Journal   (Followers: 49, SJR: 1.551, CiteScore: 3)
Aeolian Research     Hybrid Journal   (Followers: 6, SJR: 1.117, CiteScore: 3)
Aerospace Science and Technology     Hybrid Journal   (Followers: 363, 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: 11, SJR: 3.671, CiteScore: 9)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 471, SJR: 1.238, CiteScore: 3)
Agri Gene     Hybrid Journal   (Followers: 1, SJR: 0.13, CiteScore: 0)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 17, SJR: 1.818, CiteScore: 5)
Agricultural Systems     Hybrid Journal   (Followers: 31, SJR: 1.156, CiteScore: 4)
Agricultural Water Management     Hybrid Journal   (Followers: 43, 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: 6, 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: 11)
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: 10, SJR: 0.201, CiteScore: 1)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 52, SJR: 4.66, CiteScore: 10)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 4, SJR: 1.796, CiteScore: 4)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 4, SJR: 1.108, CiteScore: 3)
Ambulatory Pediatrics     Hybrid Journal   (Followers: 6)
American Heart J.     Hybrid Journal   (Followers: 57, SJR: 3.267, CiteScore: 4)
American J. of Cardiology     Hybrid Journal   (Followers: 62, SJR: 1.93, CiteScore: 3)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 44, SJR: 0.604, CiteScore: 1)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 11)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 13, SJR: 1.524, CiteScore: 3)
American J. of Human Genetics     Hybrid Journal   (Followers: 34, 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: 35, SJR: 2.973, CiteScore: 4)
American J. of Medicine     Hybrid Journal   (Followers: 48)
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: 232, 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: 29, 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: 63, SJR: 0.138, CiteScore: 0)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 20, 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: 200, SJR: 0.633, CiteScore: 2)
Analytical Chemistry Research     Open Access   (Followers: 12, 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: 23, 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: 207, SJR: 1.58, CiteScore: 3)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 6, SJR: 0.937, 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  [3160 journals]
  • Infiltration studies of additive manufacture of WC with Co using binder
           jetting and pressureless melt method
    • Abstract: Publication date: August 2019Source: Additive Manufacturing, Volume 28Author(s): Corson L. Cramer, Peeyush Nandwana, Richard A. Lowden, Amy M. Elliott Additive manufacturing (AM) of tungsten carbide-cobalt (WC-Co) is explored starting with WC preforms shaped with binder jet additive manufacturing (BJAM) followed by melt infiltration of Co. The research objective is to demonstrate the ability to net-shape WC-Co composites through BJAM of a WC preform followed by backfilling with cobalt via pressureless infiltration. This method also has the potential to minimize shrinkage and grain growth compared to other AM techniques. The effects of sintering, Co content, and infiltration time on the net shaping and properties of processed composites are shown. The best shaped material had an average grain size of 5.1 μm, 32 vol.% Co, density of 98.54% theoretical, fracture toughness of 23.2 MPa m1/2, and hardness of 9.0 GPa. Data presented illustrates that the proposed approach results in favorable ceramic-metal (cermet) properties and is viable for fabricating cermets of other material combinations. Successful AM of cermets provides complex geometries, high throughout, and low costs.
  • The Effect of Process Parameters on Residual Stress Evolution and
           Distortion in the Laser Powder Bed Fusion of Ti-6Al-4V
    • Abstract: Publication date: Available online 23 May 2019Source: Additive ManufacturingAuthor(s): N.C. Levkulich, S.L. Semiatin, J.E. Gockel, J.R. Middendorf, A.T. DeWald, N.W. KlingbeilABSTRACTLaser powder bed fusion (LPBF) is a popular additive manufacturing (AM) process that has shown promise in fabricating novel components that can be utilized for a wide variety of applications. However, one of the main drawbacks of LPBF is that it produces large thermal gradients and fast cooling rates during the solidification of each layer, which can lead to large levels of residual stress/distortion, sometimes resulting in build failure/rejection. In the present work, several experimental techniques (x-ray diffraction, hole drilling, contour method, and laser line profilometry) were utilized to establish the effect of LPBF process parameters (scan speed, laser power, build height, build plan area, and substrate condition) on residual stress evolution and distortion. X-ray diffraction and hole-drilling measurements were performed on the surfaces of the LPBF deposits and substrates, while bulk residual stresses were measured using the contour method. In addition, a laser line profilometer was used to measure the distortion after fabrication. The results obtained by the non-destructive and destructive measurement techniques suggested that process parameters greatly influence the development of residual stress and distortion throughout the LPBF deposit and the substrate. Furthermore, the experimental results in this work provide a valuable foundation for future modeling and simulation of the evolution of residual stress and distortion.
  • In situ Monitoring of Material Jetting Additive Manufacturing Process via
           Impedance Based Measurements
    • Abstract: Publication date: Available online 22 May 2019Source: Additive ManufacturingAuthor(s): Logan D. Sturm, Mohammed I. Albakri, Pablo A. Tarazaga, Christopher B. WilliamsABSTRACTIn this paper, the authors explore the use of impedance-based monitoring techniques for in-situ detection of additive manufacturing build defects. By physically coupling a piezoceramic (PZT) sensor to the part being fabricated, the measured electrical impedance of the PZT can be directly linked to the mechanical impedance of the part. It is hypothesized that one can detect build defects in geometry or material properties in-situ by comparing the signatures collected during printing of parts with that of a defect-free control sample. In this paper, the authors explore the layer-to-layer sensitivity for both PZT sensors embedded into printed parts and for a fixture-based PZT sensor. For this work, this concept is evaluated in context of material jetting. A set of control samples is created and used to establish a baseline signature. (e.g., internal voids) are fabricated and their layer-to-layer signatures are compared to a control sample. Using this technique, the authors demonstrate an ability to track print progress and detect defects as they occur. For embedded sensors the defects were detectable at 2.28% of the part volume (95.6 mm3) and by fixture-based sensors when it affected 1.38% of the part volume.
  • Fabrication and durability testing of a 3D printed façade for desert
    • Abstract: Publication date: Available online 22 May 2019Source: Additive ManufacturingAuthor(s): Giulia Grassi, Sonia Lupica Spagnolo, Ingrid Paoletti The use of 3D printing in architecture has grown tremendously over the last decade thanks to its strong reputation as a versatile, cheap and fast technology. However, its ability to maintain its initial performances over time cannot be taken for granted. Its durability, in fact, depends on several factors (above all design accuracy, quality of materials and environmental aggressiveness), which may lead or contribute to rapid performance decay over time. With this in mind, the paper describes the design-to-production process for a façade shading system using additive manufacturing and the associated testing campaign to assess the feasibility of the design and durability of materials. The aim of the project was to create a second skin for an overlay pavilion at Expo 2020 in Dubai with a façade design that evokes desert dunes. Horizontal lamellas, with a complex curved geometry, were generated using computational design optimised for additive manufacturing. In order to select the most suitable 3D-printable material, tests were conducted on different polymers in a climatic chamber at Politecnico di Milano to monitor material performances over time at high temperatures such as the ones in Dubai. The data gathered from these tests was crucial to the correct design of the façade manufacturing process.
  • Microwave dielectric properties of zirconia fabricated using NanoParticle
    • Abstract: Publication date: May 2019Source: Additive Manufacturing, Volume 27Author(s): Yongduk Oh, Vivek Bharambe, Bhargavi Mummareddy, John Martin, Jeremy McKnight, Martin A. Abraham, Jason M. Walker, Kirk Rogers, Brett Conner, Pedro Cortes, Eric MacDonald, Jacob J. Adams Additive manufacturing of ceramics has been actively investigated with the objective of fabricating complex structures that compete in terms of material performance with traditionally manufactured ceramics but with the benefit of increased geometric freedom. More specifically, zirconia provides high fracture toughness and thermal stability. In addition, its dielectric permittivity may be the highest among materials available for 3D printing, and may enable the next generation of complex electromagnetic structures. NanoParticle Jetting™ is a new material jetting process for selectively depositing nanoparticles and is capable of printing zirconia. Dense, fine-featured parts can be manufactured with layer thicknesses as small as 10 μm and jetting resolution of 20 μm after a final sintering step. For this study, 3D printed zirconia using NanoParticle Jetting™ was characterized in terms of chemistry, density, crystallography, sintering shrinkage and dielectric properties as a foundation for developing high performance radio frequency (RF) components. The experimental results indicate a yttria-stabilized ZrO2 structure exhibiting a bulk relative permittivity of 23 and a loss tangent of 0.0013 at microwave frequencies. A simple zirconia dielectric resonator antenna is measured, confirming the measured dielectric properties and illustrating a practical application of this material.
  • Interrupted fatigue testing with periodic tomography to monitor porosity
           defects in wire + arc additive manufactured Ti-6Al-4V
    • Abstract: Publication date: Available online 1 May 2019Source: Additive ManufacturingAuthor(s): Romali Biswal, Xiang Zhang, Muhammad Shamir, Abdullah Al Mamun, Mustafa Awd, Frank Walther, Abdul Khadar Syed Porosity defects remain a challenge to the structural integrity of additive manufactured materials, particularly for parts under fatigue loading applications. Although the wire + arc additive manufactured Ti-6Al-4 V builds are typically fully dense, occurrences of isolated pores may not be completely avoided due to feedstock contamination. This study used contaminated wires to build the gauge section of fatigue specimens to purposely introduce spherical gas pores in the size range of 120 to 250 micrometres. Changes in the defect morphology were monitored via interrupted fatigue testing with periodic X-ray computed tomography (CT) scanning. Prior to specimen failure, the near surface pores grew by approximately a factor of 2 and tortuous fatigue cracks were initiated and propagated towards the nearest free surface. Elastic-plastic finite element analysis showed cyclic plastic deformation at the pore root as a result of stress concentration; consequently for an applied tension-tension cyclic stress (stress ratio 0.1), the local stress at the pore root became a tension-compression nature (local stress ratio −1.0). Fatigue life was predicted using the notch fatigue approach and validated with experimental test results.
  • Direct Ink Writing of Three Dimensional Ti2AlC Porous
    • Abstract: Publication date: Available online 20 May 2019Source: Additive ManufacturingAuthor(s): Hamada Elsayed, Anna Chmielarz, Marek Potoczek, Tobias Fey, Paolo Colombo In this work, the Direct Ink Writing (DIW) technique was used to produce three-dimensional Ti2AlC ceramic components with high, uniform porosity. Suitable formulations were developed, with appropriate rheological properties for extruding thin filaments through a nozzle with a diameter of 810 µm. The main rheological properties of the inks were investigated to evaluate their behavior and flowability during the printing process. Porous Ti2AlC lattices were fabricated, in selected conditions, with uniform pore size and good interconnectivity, and sintered at 1400 °C in Ar. Total porosity ranged from ∼44 to ∼63 vol%, and the mechanical strength ranged from ∼43 to 83 MPa. The influence of the ink composition and heat-treatment conditions on the phase composition of the 3D porous structures was also evaluated.
  • Reinforcement of material extrusion 3D printed polycarbonate using
           continuous carbon fiber
    • Abstract: Publication date: Available online 20 May 2019Source: Additive ManufacturingAuthor(s): M.N. Jahangir, K.M.M. Billah, Y. Lin, D.A. Roberson, R.B. Wicker, D. Espalin Additive manufacturing (AM) technologies are capable of fabricating custom parts with complex geometrical shapes in a short period of time relative to traditional fabrication processes that require expensive tooling and several post processing steps. Material extrusion AM, known commercially as Fused Filament Fabrication (FFF) technology, is a widely used polymer AM process, however, the effects of inherent porosity on mechanical strength continues to be researched to identify strength improvement solutions. To address the effect of porosity and layer adhesion on mechanical properties (which can sometimes result in 27-35 % lower ultimate tensile strength when compared to plastic injection molding), an approach was employed to reinforce 3D printed polycarbonate (PC) parts with continuous carbon fiber (CF) bundles. ASTM D638 Type I specimens were fabricated with printing interruptions to manually place and embed CF bundles. Specimens contained either one, two, or three layers of embedded CF bundles. Results demonstrated a maximum of 77 % increase in tensile yield strength when PC was reinforced with three CF bundles and micrographs showed multiple regions with zero porosity due to the CF inclusion. PC with three bundles of CF (modulus of 3.36 GPa) showed 85 % higher modulus of elasticity than the neat PC specimens (modulus of 1.82 GPa). The manual placement of CF and its impact on mechanical properties motivated the development of an automated selective deposition method using an ultrasonic embedding apparatus. Substantial technology development towards the embedding process of continuous carbon fiber bundles using ultrasonic energy was achieved in an automated fashion which is complementary of digital manufacturing and novel when compared to other existing processes.
  • An Inherent Strain Based Multiscale Modeling Framework for Simulating
           Part-scale Residual Deformation for Direct Metal Laser Sintering
    • Abstract: Publication date: Available online 20 May 2019Source: Additive ManufacturingAuthor(s): Qian Chen, Xuan Liang, Devlin Hayduke, Jikai Liu, Lin Cheng, Jason Oskin, Ryan Whitmore, Albert C. To Residual distortion is a major technical challenge for laser powder bed fusion (LPBF) additive manufacturing (AM), since excessive distortion can cause build failure, cracks and loss in structural integrity. However, residual distortion can hardly be avoided due to the rapid heating and cooling inherent in this AM process. Thus, fast and accurate distortion prediction is an effective way to ensure manufacturability and build quality. This paper proposes a multiscale process modeling framework for efficiently and accurately simulating residual distortion and stress at the part-scale for the direct metal laser sintering (DMLS) process. In this framework, inherent strains are extracted from detailed process simulation of micro-scale model based on the recently proposed modified inherent strain model. The micro scale detailed process simulation employs the actual parameters of the DMLS process such as laser power, velocity, and scanning path. Uniform but anisotropic strains are then applied to the part in a layer-by-layer fashion in a quasi-static equilibrium finite element analysis, in order to predict residual distortion/stress for the entire AM build. Using this approach, the total computational time can be significantly reduced from potentially days or weeks to a few hours for part-scale prediction. Effectiveness of this proposed framework is demonstrated by simulating a double cantilever beam and a canonical part with varying wall thicknesses and comparing with experimental measurements which show very good agreement.
  • Extrusion Control for High Quality Printing on Big Area Additive
           Manufacturing (BAAM) Systems
    • Abstract: Publication date: Available online 19 May 2019Source: Additive ManufacturingAuthor(s): Phillip Chesser, Brian Post, Alex Roschli, Charles Carnal, Randall Lind, Michael Borish, Lonnie Love Big Area Additive Manufacturing (BAAM) is a large format additive manufacturing (AM) process. The size scale has enabled many new applications for AM. However, at this scale, lack of high print resolution and extruder flowrate control lead to potentially significant geometric deviations in the printed part. This paper examines strategies to improve geometric quality in BAAM parts. Multi-resolution printing, extrusion diversion, and feedforward extruder control are examined herein. These methods were all found to be effective in mitigating phenomena detrimental to geometric part quality on the BAAM process.
  • New scanning strategy to reduce warpage in additive manufacturing
    • Abstract: Publication date: Available online 18 May 2019Source: Additive ManufacturingAuthor(s): Davi Leão Ramos, Fawzi Belblidia, Johann Sienz This paper proposes a novel geometric based scanning strategy adopted in the selective laser melting (SLM) manufacturing technology aimed at reducing the level of residual stresses generated during the build-up process. A set of computer simulations of the build, based on different scans strategies, including temperature dependent material properties, and a moving heat flux, were performed. The research novelty explores intermittent scan strategies in order to analyze the effect of reduction on heat concentration on the residual stress and deformation. Coupled thermal-structural computations revealed a significant stress and warpage reduction on the proposed scanning scheme. Different powder material properties were investigated and the computational model was validated against published numerical and experimental studies.
  • Method to optimize an additively-manufactured functionally-graded lattice
           structure for effective liquid cooling
    • Abstract: Publication date: August 2019Source: Additive Manufacturing, Volume 28Author(s): Akihiro Takezawa, Xiaopeng Zhang, Masaki Kato, Mitsuru Kitamura The development of cooling devices is important for many industrial products, and the lattice structure fabricated by additive manufacturing is expected to be useful for effective liquid cooling. However, lattice density should be carefully designed for an effective arrangement of coolant flow. In this research, we optimize the lattice density distribution using a lattice structure approximation and the gradient method. Fluid flow is approximated by deriving effective properties from the Darcy–Forchheimer law and analyzing the flow according to the Brinkman–Forchheimer equation. Thermal conduction and convection are also approximated as a weakly coupled problem. We use a simple basic lattice shape composed of pillars, optimizing only its density distribution by setting the pillar diameter as the design variable. Steady-state pressure and temperature reductions are treated as multi-objective functions. Through 2D and 3D numerical studies, we discuss the validity and limitations of the proposed method. Although observable errors in accuracy exist between the results obtained from the optimization and full scale models, relative performance optimization was considered successful.
  • Spatially resolved acoustic spectroscopy for integrity assessment in
           wire–arc additive manufacturing
    • Abstract: Publication date: August 2019Source: Additive Manufacturing, Volume 28Author(s): Paul Dryburgh, Don Pieris, Filomeno Martina, Rikesh Patel, Steve Sharples, Wenqi Li, Adam T. Clare, Stewart Williams, Richard J. Smith Wire–arc additive manufacturing (WAAM) is an emergent method for the production and repair of high value components. Introduction of plastic strain by inter-pass rolling has been shown to produce grain refinement and improve mechanical properties, however suitable quality control techniques are required to demonstrate the refinement non-destructively. This work proposes a method for rapid microstructural assessment of Ti–6Al–4V, with limited intervention, by measuring an acoustic wave generated on the surface of the specimens. Specifically, undeformed and rolled specimens have been analysed by spatially resolved acoustic spectroscopy (SRAS), allowing the efficacy of the rolling process to be observed in velocity maps. The work has three primary outcomes (i) differentiation of texture due to rolling force, (ii) understanding the acoustic wave velocity response in the textured material including the underlying crystallography, (iii) extraction of an additional build metric such as layer height from acoustic maps and further useful material information such as minimum stiffness direction. Variations in acoustic response due to grain refinement and crystallographic orientation have been explored. It has been found that the limited α-variants which develop within prior-β grains lead to distinctive acoustic slowness surfaces. This allowed prior-β grains to be resolved. A basic algorithm has been proposed for the automated measurement, which could be used for in-line closed loop control. The practicality and challenges of applying this approach in-line with fabrication are also discussed.Graphical abstractGraphical abstract for this article
  • Heat Retention Modeling of Large Area Additive Manufacturing
    • Abstract: Publication date: Available online 15 May 2019Source: Additive ManufacturingAuthor(s): Kyosung Choo, Brian Friedrich, Tim Daugherty, Austin Schmidt, Clark Patterson, Martin A. Abraham, Brett Conner, Kirk Rogers, Pedro Cortes, Eric MacDonald Large Area Additive Manufacturing now enables the fabrication of structures that are dramatically more substantial than those produced with standard 3D printing. Because the use of support structure is generally not appropriate when printing at these scales, understanding the limits of overhanging feature angles is necessary to establish the economic case for the use of large 3D printing. Additionally, understanding the physics of the process is paramount to avoiding expensive failed prints. Rapid sequential layers can result in slumping as the structure retains excessive heat when the next layer is printed. In this study, the thermal profiles of large printed parts have been experimentally measured and mathematically modeled in order to assist in the decision of whether a delay between layers is required to avoid slumping of overhanging features. The model can be used to insert additional dwell times after each layer so that the next layer of printing initiates after the previous layer is sufficiently cool such that the existing structure is appropriately solidified. Inputs to the model include the feedstock material, the number of beads in the overhanging wall, the angle of overhang and the threshold of failure represented as out-of-plane displacement from the intended geometry. The proposed thermal model can then be used with slicing software to insert pauses a priori, or can be leveraged during the print in conjunction with infrared imaging in order to provide in situ process control to improve quality and yield.
  • Quality control of AlSi10Mg produced by SLM: metallography versus CT scans
           for critical defect size assessment
    • Abstract: Publication date: Available online 15 May 2019Source: Additive ManufacturingAuthor(s): S. Romano, A. Abel, J. Gumpinger, A.D. Brandão, S. Beretta While the adoption of metal additive manufacturing (AM) is growing exponentially owing to its wide range of potential applications, its application to safety-critical and structural parts is significantly impeded by the lack of standards. Quality assessment of AM products is a crucial requirement, as the AM process induces internal defects that can have detrimental effects on the fatigue resistance.By evaluating the defect distribution, it is possible to perform a fracture mechanics assessment to estimate the fatigue strength and service lifetime of AM materials. This strategy has been successfully applied to selective laser-melted AlSi10Mg by performing X-ray micro-computed tomography (µCT) and applying suitable statistical methods (i.e., statistics of extremes). However, it remains unclear whether complex and expensive nondestructive inspection methods (e.g., µCT) are necessary and whether simpler and more conventional approaches (i.e., microscopy of polished sections (PSs), as prescribed by ASTM E2283) would provide equivalent information for the estimation of internal defects.In this study, the size of the most detrimental defect was estimated by performing both light microscopy on PSs and µCT on three batches of fatigue specimens characterized by different internal porosities. The results showed that both techniques were able to pinpoint a significant difference in the prospective largest defect in a material volume corresponding to the gauge section of a specimen. However, extrapolation of the critical defect size for fatigue failure using PS data was less accurate and less conservative than that using CT data. An evaluation of the techniques with regard to time and cost indicated that µCT allowed the investigation of larger sample volumes and the reduction of both man hours and cost.Graphical abstractGraphical abstract for this article
  • Single-operation, multi-phase additive manufacture of electro-chemical
           double layer capacitor devices
    • Abstract: Publication date: Available online 14 May 2019Source: Additive ManufacturingAuthor(s): Lukas Fieber, Jack D. Evans, Chun Huang, Patrick S. Grant additive manufacturing (AM) may offer a flexible, cost-effective approach to address conventional manufacturing limitations, such as time-consuming, high work-in-progress, multi-step assembly. In principle AM can also allow more novel geometric or even bespoke designs of structural and functional products. However, in terms of energy storage devices such as batteries and supercapacitors, the benefits of AM have not yet been explored to any significant extent. In this paper, a hybrid-AM system, combining low-cost (FDM) and direct ink writing (DIW) techniques, has been designed to fabricate supercapacitors (electro-chemical double layer capacitors, EDLCs) in a single, automated operation. The inherent flexibility of the AM process provided an opportunity to address restrictions in geometric form factor associated with conventional planar supercapacitor manufacturing approaches. Functioning, ring-shaped EDLC devices were manufactured in a single, multi-material operation comprising symmetric activated carbon electrodes in a 1M (KOH) electrolyte hydrogel. Gravimetric and areal electrode capacitances were 116.4±0.6 Fg−1 and 599.2±0.30mF cm−2 at 10mVs−1, with a columbic efficiency of 99.6±0.4% in the as-printed condition. The work aims to accelerate progress towards monolithic integration of energy storage devices in product manufacture, offering an alternative fabrication process for applications with irregular volume/shape and mass-customization requirements.Graphical abstractGraphical abstract for this article
  • Resolution, energy and time dependency on layer scaling in finite element
           modelling of laser beam powder bed fusion additive manufacturing
    • Abstract: Publication date: Available online 11 May 2019Source: Additive ManufacturingAuthor(s): Wenyou Zhang, Mingming Tong, Noel M. HarrisonABSTRACTThe Laser Beam Powder Bed Fusion (PBF-LB) category of Additive Manufacturing (AM) is currently receiving much attention for computational process modelling. Major challenges exist in how to reconcile resolution, energy and time in a real build, with the practical limitations of resolution (layer height and mesh resolution), energy (heat format and magnitude) and time (heating and cooling step times) in the computational space. A novel thermomechanical PBF-LB process model including an efficient powder-interface heat loss mechanism was developed. The effect of variations in layer height (layer scaling), energy and time on the temperature and stress evolution was investigated. The influence of heating step time and cooling step time was characterised and the recommended ratio of element size to layer scaling was presented, based on a macroscale 2D model. The layer scaling method was effective when scaling up to 4 times the layer thickness and appropriately also scaling the cooling step time. This research provides guidelines and a framework for layer scaling for finite element modelling of the PBF-LB process.
  • Internal pores in DED Ti-6.5Al-2Zr-Mo-V alloy and their influence on crack
           initiation and fatigue life in the mid-life regime
    • Abstract: Publication date: Available online 10 May 2019Source: Additive ManufacturingAuthor(s): Xiaofan He The present work aims to investigate the mechanism of crack initiation induced by internal pores, which are inevitable in additive manufacturing (AM), and the influence of internal pores on the fatigue performance of directed energy deposited (DED) Ti-6.5Al-2Zr-Mo-V. After fatigue test under constant amplitude alternating stress at three stress levels, thirty-one pieces of DED Ti-6.5Al-2Zr-Mo-V specimens were found that cracks initiating from internal pores. Scanning electron microscope (SEM) and its accessories, such as energy dispersive spectrometry (EDS) and electron backscattered diffraction (EBSD), were used to analyze the characteristics of pore defects and clarify the mechanism of crack initiation. The results show that the specificity of the microstructure affected by the DED process and pore defects, such as segregation of Al and the existence of incomplete grain boundaries, are the main causes of crack initiation. Then, the crack initiation modes were divided into three types, and a classification model was established that can make the effect of pore defects on fatigue life clearer and more intuitive.
  • Biodegradation-affected fatigue behavior of additively manufactured porous
    • Abstract: Publication date: Available online 10 May 2019Source: Additive ManufacturingAuthor(s): Y. Li, H. Jahr, X-Y. Zhang, M.A. Leeflang, W. Li, B. Pouran, F.D. Tichelaar, H. Weinans, J. Zhou, A.A. Zadpoor Additively manufactured (AM) biodegradable metals with topologically ordered porous structures hold unprecedented promise as potential bone substitutes. The first reports on this type of biomaterials have just recently appeared in the literature. There is, however, no information available in the literature regarding their mechanical performance under cyclic loading or the interactions between biodegradation and cyclic loading. We therefore used selective laser melting (SLM) to fabricate porous magnesium alloy (WE43) scaffolds based on diamond unit cells. The microstructure of the resulting material was examined using electron back-scattered diffraction, scanning transmission electron microscopy, and X-ray diffraction. The fatigue behaviors of the material in air and in revised simulated body fluid (r-SBF) were evaluated and compared. Biodegradation decreased the fatigue strength of the porous material from 30% to 20% of its yield strength. Moreover, cyclic loading significantly increased its biodegradation rate. The mechanistic aspects of how biodegradation and cyclic loading interacted with each other on different scales were revealed as well. On the micro-scale, cracks initiated at biodegradation pits and propagated transgranularly. In addition, dislocations became more tangled after the fatigue tests. On the macro-scale, cracks preferred initiating at the strut junctions where tensile stress concentrations were present, as revealed by the finite element analysis of the porous material under compressive loading. Most of the cracks initiated in the struts were positioned on the periphery of the specimens. Furthermore, the biodegradation pattern was found to be location-dependent with more localized biodegradation occurring in the center of the specimens. Further improvements in the biodegradation-affected fatigue performance of the AM porous Mg alloy may therefore be realized by optimizing both the topological design of the porous structure and the laser-processing parameters that determine the microstructure of the SLM porous material.
  • Bagasse – a major agro-industrial residue as potential resource for
           nanocellulose inks for 3D printing of wound dressing devices
    • Abstract: Publication date: Available online 10 May 2019Source: Additive ManufacturingAuthor(s): Gary Chinga-Carrasco, Nanci V. Ehman, Daniel Filgueira, Jenny Johansson, María E. Vallejos, Fernando E. Felissia, Joakim Håkansson, María C. Area Sugarcane bagasse, an abundant residue, is usually burned as an energy source. However, provided that appropriate and sustainable pulping and fractionation processes are applied, bagasse can be utilized as a main source of cellulose nanofibrils (CNF). We explored in this study the production of CNF inks for 3D printing by direct-ink-writing technology. The CNF were tested against L929 fibroblasts cell line and we confirmed that the CNF from soda bagasse fibers were found not to have a cytotoxic potential. Additionally, we demonstrated that the alginate and Ca2+ caused significant dimensional changes to the 3D printed constructs. The CNF-alginate grids exhibited a lateral expansion after printing and then shrank due to the cross-linking with the Ca2+. The release of Ca2+ from the CNF and CNF-alginate constructs was quantified thus providing more insight about the CNF as carrier for Ca2+. This, combined with 3D printing, offers potential for personalized wound dressing devices, i.e. tailor-made constructs that can be adapted to a specific shape, depending on the characteristics of the wound healing treatment.
  • Corrosion behavior of additively manufactured Ti-6Al-4V parts and the
           effect of post annealing
    • Abstract: Publication date: Available online 9 May 2019Source: Additive ManufacturingAuthor(s): Ali Hemmasian Ettefagh, Congyuan Zeng, Shengmin Guo, Jonathan Raush This paper evaluates the corrosion behavior of Ti-6Al-4V alloy parts produced by laser-based powder bed fusion additive manufacturing (AM). The effect of post annealing heat treatment on the corrosion resistance of AM parts is studied by comparing the heat treated samples with cold rolled commercial titanium alloy samples. The results obtained via corrosion tests show that the corrosion rate of as-fabricated AM parts is almost sixteen times worse than the commercial grade samples. The accelerated rate was due to the presence of non-equilibrium phases and can be ameliorated by a proper post heat treatment process at 800°C for 2 hours. The proposed heat treatment makes the corrosion behavior of AM parts comparable to the commercial grade samples, due to the stress relief of the martensitic phase and formation of BCC phase of β Ti-6Al-4V which has a higher corrosion resistance. CALculation of PHAse Diagrams (CALPHAD) method was used to identify the equilibrium phases.
  • Process Development and Impact of Intrinsic Heat Treatment on the
           Mechanical Performance of Selective Laser Melted AISI 4140
    • Abstract: Publication date: Available online 9 May 2019Source: Additive ManufacturingAuthor(s): James Damon, Robin Koch, Daniel Kaiser, Gregor Graf, Stefan Dietrich, Volker Schulze The low alloy steel AISI 4140 (German grade 42CrMo4) is one of the most frequently used Quench&Tempering (Q&T) steels with a wide range of applicability. Until now, commercially available iron powders for additive manufacturing can be summed up by their low amount of carbon. Fusion welding of Q&T steels often leads to cracks due to brittle martensitic transformation and the associated volume change. Therefore, the selection of appropriate process parameters in laser powder bed fusion (LPBF) plays a key role for the final material properties and is achieved through utilization of a new process development strategy and evaluation of microstructural features of test cubes. In this work tensile specimens were successfully produced with optimal process parameters and mechanical tests of additively built samples indicate mechanical performance comparable with a 450°C tempered state of conventionally cast material. By correlating the measured mechanical properties of LPBF samples to those of a conventional Q&T state, an estimation of the intrinsic heat treatment during LPBF was carried out using an inverse transient Hollomon-Jaffe approach. This analysis indicates that a rapid reheating rate of 103 − 105°C/s to ≈700 − 800°C of the previous built layers is the determinant for the low hardness found in the LPBF process of AISI 4140. This is also in accordance with the finely dispersed carbide precipitates in the as built condition. Furthermore, the effect of bed pre-heating on the final material tempering state was found to be negligible. This shows the importance of a balanced match between LPBF process parameters and subsequent application demands as well as necessary postprocessing steps.
  • On microstructural homogenization and mechanical properties optimization
           of biomedical Co-Cr-Mo alloy additively manufactured by using electron
           beam melting
    • Abstract: Publication date: Available online 8 May 2019Source: Additive ManufacturingAuthor(s): Daixiu Wei, Ainiwaer Anniyaer, Yuichiro Koizumi, Kenta Aoyagi, Makoto Nagasako, Hidemi Kato, Akihiko Chiba The electron beam melting (EBM), a layer-by-layer additive manufacturing (AM) technique, has been recently utilized for fabricating metallic components with complex shape and geometry. However, the inhomogeneity in microstructures and mechanical properties are the main drawbacks constraining the serviceability of the EBM-built parts. In the present study, we found remarkable microstructural inhomogeneity along build direction in the EBM-built Co-based alloy, owing to the competitive grain growth and subsequent isothermal γ-fcc → ε-hcp phase transformation, which affects the corresponding tensile properties significantly. Then, we succeeded in eliminating the inhomogeneities, modifying the phase structures and refining grain sizes via comprehensive post-production heat treatment regimes, which provides a valuable implication for improving the reliabilities of AM-built metals and alloys. The Co-based alloy can be selectively transformed into predominant ε or predominant γ phase by the regime, and the grains were refined to 1/10 of the initial sizes by repeated heat treatment. Finally, we investigated the tensile properties and fracture behaviors of the alloy before and after each heat treatment. The γ → ε strain-induced martensitic transformation is the major deformation mode of the γ phase, meanwhile the formation of stripped ε phase at {111}γ habit planes contributed to a good combination of strength and ductility. Nevertheless, the ε phase was deformed mainly by (0001)ε ε basal and {1 1¯00 }ε ε prismatic slip systems, exhibiting very limited ductility and strength. In addition, the ε grains act as secondary hardening factor in the samples consisting of dual γ/ε phase, leading to a non-uniform deformation behavior.Graphical abstractGraphical abstract for this article
  • Room Temperature Extrusion 3D Printing of Polyether Ether Ketone Using a
           Stimuli-Responsive Binder
    • Abstract: Publication date: Available online 6 May 2019Source: Additive ManufacturingAuthor(s): Chang-Uk Lee, Johanna Vandenbrande, Adam E. Goetz, Mark A. Ganter, Duane W. Storti, Andrew J. Boydston We report our efforts toward 3D printing of polyether ether ketone (PEEK) at room temperature by direct-ink write technology. The room-temperature extrusion printing method was enabled by a unique formulation comprised of commercial PEEK powder, soluble epoxy-functionalized PEEK (ePEEK), and fenchone. This combination formed a Bingham plastic that could be extruded using a readily available direct-ink write printer. The initial green body specimens were strong enough to be manipulated manually after drying. After printing, thermal processing at 230 °C resulted in crosslinking of the ePEEK components to form a stabilizing network throughout the specimen, which helped to preclude distortion and cracking upon sintering. A final sintering stage was conducted at 380 °C. The final parts were found to have excellent thermal stability and solvent resistance. The Tg of the product specimens was found to be 158 °C, which is 13 °C higher than commercial PEEK as measured by DSC. Moreover, the thermal decomposition temperature was found to be 528 °C, which compares well against commercial molded PEEK samples. Chemical resistance in trifluoroacetic acid and 8 common organic solvents, including CH2Cl2 and toluene, were also investigated and no signs of degradation or weight changes were observed from parts submerged for 1 week in each solvent. Test specimens also displayed desirable mechanical properties, such as a Young’s modulus of 2.5 GPa, which corresponds to 63% of that of commercial PEEK (reported to be 4.0 GPa).
  • Reducing residual stress by selective large-area diode surface heating
           during laser powder bed fusion additive manufacturing
    • Abstract: Publication date: Available online 6 May 2019Source: Additive ManufacturingAuthor(s): John D. Roehling, William L. Smith, Tien T. Roehling, Bey Vrancken, Gabriel M. Guss, Joseph T. McKeown, Michael R. Hill, Manyalibo J. Matthews High residual stresses are typical in additively manufactured metals and can reach levels as high as the yield strength, leading to distortions and even cracks. Here, an in situ method for controlling residual stress during laser powder bed fusion additive manufacturing was demonstrated. By illuminating the surface of a build with homogeneously intense, shaped light from a set of laser diodes, the thermal history was controlled thereby reducing the residual stress in as-built parts. 316L stainless steel bridge-shaped parts were built to characterize the effect of in situ annealing on the residual stress. A reduction in the overall residual stress value of up to 90% was realized without altering the as-built grain structure (no grain growth). Some annealing effects on the cellular-dendritic solidification structure (patterns of higher solute content) occurred in areas that experienced prolonged exposure to elevated temperature. A comparison of the in situ process to conventional post-build annealing demonstrated equivalent stress reduction compared to rule-of-thumb thermal treatments. Use of this method could reduce or remove the need for post processing to remove residual stresses.Graphical abstractGraphical abstract for this article
  • Inter-layer bonding characterisation between materials with different
           degrees of stiffness processed by fused filament fabrication
    • Abstract: Publication date: Available online 4 May 2019Source: Additive ManufacturingAuthor(s): A. Khudiakova, F. Arbeiter, M. Spoerk, M. Wolfahrt, D. Godec, G. Pinter One of the main benefits of material extrusion additive manufacturing, also known as fused filament fabrication (FFF) or 3D printing, is the flexibility in terms of printing materials. Locally reinforced components can be easily produced by selectively combining reinforced with unfilled tough thermoplastics. However, such multi-material composites usually lack sufficient weld strength in order to be able to withstand operation loads. The present study attempts to close this gap by characterising the cohesion between the strands of two materials with different stiffness, namely neat PLA and short carbon fibre reinforced PLA (CF-PLA), produced by FFF using advanced fracture mechanical techniques. The full set of engineering constants of both materials were obtained under the assumption of transverse isotropy from tensile tests in combination with digital image correlation. Double cantilever beam (DCB) and cracked round bar (CRB) tests were used to determine the critical energy release rate (GIc). Both tests were in good correlation with each other and revealed that the interlayer PLA/CF-PLA bonding was at least as tough as the interlayer CF-PLA/CF-PLA bonding.
  • 3D printing of high density polyethylene by fused filament fabrication
    • Abstract: Publication date: Available online 4 May 2019Source: Additive ManufacturingAuthor(s): Carl G. Schirmeister, Timo Hees, Erik H. Licht, Rolf Mülhaupt Polyolefin thermoplastics like high density polyethylene (HDPE) are the leaders in terms of world-scale plastics’ production, environmentally benign polymerization processes, recycling, and sustainability. However, additive manufacturing of HDPE by means of fused deposition modeling (FDM) also known as fused filament fabrication (FFF) has been problematic owing to its massive shrinkage, voiding and warpage problems accompanied by its poor adhesion to common build plates and to extruded HDPE strands. Herein we overcome these problems and improve Young’s modulus, tensile strength and surface quality of 3D printed HDPE by varying 3D printing parameters like temperature and diameter of the nozzle, extrusion rate, build plate temperature, and build plate material. Both nozzle diameter and printing speed affect surface quality but do not impair mechanical properties. Particularly, an extrusion rate gradient prevents void formation. For the first time additive manufactured HDPE and injection-molded HDPE exhibit similar mechanical properties with exception of elongation at break. Excellent fusion of the extruded polymer strands and the absence of anisotropy are achieved, as verified by microscopic imaging and measuring the tensile strength parallel and perpendicular to the 3D printing direction.
    • Abstract: Publication date: Available online 4 May 2019Source: Additive ManufacturingAuthor(s): Gerardo A. Mazzei Capote, Natalie M. Rudolph, Paul V. Osswald, Tim A. Osswald Fused Filament Fabrication (FFF) is the most widely available Additive Manufacturing technology. Offering the possibility of producing complex geometries in a compressed product development cycle and in a plethora of materials, it comes as no surprise that FFF is attractive to multiple industries, including the automotive and aerospace segments. However, the high anisotropy of parts developed through this technique implies that failure prediction is extremely difficult -a requirement that must be satisfied to guarantee the safety of the final user. This work applies a criterion that incorporates stress interactions to define a 3D failure envelope that could prove an invaluable tool in formalizing the embrace of FFF in industry. Tensile, compressive and torsion tests were executed on coupons developed in a traditional FFF printer, as well as a customized, 6-axis robotic printer necessary to produce specimens in out of ordinary orientations. These tests were used to calculate the parameters of the mathematical function that describe the failure envelope. Mechanical tests clearly showed significant difference between tensile, compressive and shear strengths. The calculated envelope shows strong interactions between axial loads, and a considerable interaction between shear stresses and loads applied in directions parallel and perpendicular to the beads.
  • The Re-usability of Heat-exposed Poly (ethylene terephthalate) Powder for
           Laser Sintering
    • Abstract: Publication date: Available online 4 May 2019Source: Additive ManufacturingAuthor(s): Hao Gu, Zahir Bashir, Lanti Yang Selective laser sintering, also called laser sintering (LS), is an additive manufacturing process that requires micronized plastic powder. Recently, we showed poly (ethylene terephthalate (PET) powder is a suitable material for LS, with a comparable printing performance as the current front-runner, polyamide 12 (PA12). However, the LS process, by its nature, leaves unused powder that has been exposed to heat for prolonged time, and this powder may not be fully re-usable due to degradation.In this work, the re-use potential of heat-exposed PET powder is established. This is a matter of crucial importance as powders suitable for LS are very expensive, and the powder left after a building episode has to be re-used. Heat-exposed PA12 has to be blended or refreshed with virgin powder, to avoid printing defects. In contrast, heat-exposed PET powder, after 96 h at 210 °C, could be used, without refreshing with a portion of virgin powder. The printed articles from heat-exposed powders were as good as those from the fresh powder. There was no cross-linking and there was only a minor increase in the molecular weight of the powder after 96 h, at 210 °C.
  • 3D printing of nano-scale Al2O3-ZrO2 eutectic ceramic: Principle analysis
           and process optimization of pores
    • Abstract: Publication date: August 2019Source: Additive Manufacturing, Volume 28Author(s): Shuai Yan, Yunfei Huang, Dake Zhao, Fangyong Niu, Guangyi Ma, Dongjiang Wu Pores are common defects in the process of directed laser deposition (DLD) which not only greatly reduce the fracture toughness of ceramic materials, but also lead to the failure of shaped parts. In this paper, the formation mechanism of pores was analyzed and the effects of laser power, feeding rate, scanning speed and ultrasonic power on pores were investigated. Transmission electron microscope, scanning electron microscopy observation and X-ray diffraction analysis were carried out for sample microstructure and phase composition respectively. The relative density of samples was measured by the progressive focused ion beam and the porosity was calculated by image processing software Image. The results show that the pores are divided into gas holes and shrinkage cavities. The appearance of circular gas holes with smooth inner walls are caused by the feeding method by gas forced blowing, the gas mixed with powder itself, and the gas in the molten pool formed by gasification of low-melting impurities and alumina/zirconia during laser processing. The gas holes are evenly distributed in the cross-section of the thin-walled specimen parallel to the scanning speed. As the temperature changes drastically, the material around the melt solidifies first, the melt will be attached to the solidified material to shrink, so that the melt can not be filled as a solid and finally the shrinkage cavities are formed. Generally the shrinkage cavities are irregular and the pore wall is relatively rough, mainly concentrated on the top of thin-walled samples. The laser power has the greatest influence on the pores, which has the greatest effect on the porosity but little effect on the shrinkage cavities. After attaching the ultrasound, the gas holes are mainly distributed on the top of the sample, and the shrinkage cavities almost disappear due to acoustic streaming effect of ultrasonic. When the ultrasonic power is 180 W, the porosity reaches a minimum of 0.1±0.05% and the relative density is 99.9±0.1%.
  • Design of laser parameters for selectively laser melted maraging steel
           based on deposited energy density
    • Abstract: Publication date: Available online 2 May 2019Source: Additive ManufacturingAuthor(s): Asuka Suzuki, Ryoya Nishida, Naoki Takata, Makoto Kobashi, Masaki Kato In this study, the effects of laser power and scan speed on the relative density, melt pool depth, and Vickers hardness of selectively laser melted (SLM) maraging steel were systematically investigated. The change in these structural parameters and hardness could not always be clarified by the volumetric energy density, which is widely used in the SLM processes. The deposited energy density, wherein the thermal diffusion length is used as a heat-distributed depth, can express the change in these structural parameters and the hardness with one curve. To clarify the effect of the laser parameters, the deposited energy should be used instead of the volumetric energy density. Thus, this study provides a new insight on the selection of the laser condition for SLM-fabricated materials.Graphical abstractGraphical abstract for this article
  • Additively manufactured calcium phosphate reinforced CoCrMo alloy:
           Bio-tribological and biocompatibility evaluation for load-bearing implants
    • Abstract: Publication date: Available online 2 May 2019Source: Additive ManufacturingAuthor(s): Amit Bandyopadhyay, Anish Shivaram, Murat Isik, Jose D. Avila, William S. Dernell, Susmita Bose Cobalt-chromium-molybdenum (CoCrMo) alloys are widely used in load-bearing implants; specifically, in hip, knee, and spinal applications due to their excellent wear resistance. However, due to in vivo corrosion and mechanically assisted corrosion, metal ion release occurs and accounts for poor biocompatibility. Therefore, a significant interest to find an alternative to CoCrMo alloy exists. In the present work we hypothesize that calcium phosphate (CaP) will behave as a solid lubricant in CoCrMo alloy under tribological testing, thereby minimizing wear and metal ion release concerns associated with CoCrMo alloy. CoCrMo-CaP composite coatings were processed using laser engineered net shaping (LENS™) system. After LENS™ processing, CoCrMo alloy was subjected to laser surface melting (LSM) using the same LENS™ set-up. Samples were investigated for microstructural features, phase identification, and biocompatibility. It was found that LSM treated CoCrMo improved wear resistance by 5 times. CoCrMo-CaP composites displayed the formation of a phosphorus-based tribofilm. In vitro cell-material interactions study showed no cytotoxic effect. Sprague-Dawley rat and rabbit in vivo study displayed increased osteoid formation for CoCrMo-CaP composites, up to 2 wt.% CaP. Our results show that careful surface modification treatments can simultaneously improve wear resistance and in vivo biocompatibility of CoCrMo alloy, which can correlate to a reduction of metal ion release in vivo.Graphical abstractGraphical abstract for this article
  • Direct comparison of additively manufactured porous Titanium and Tantalum
           implants towards in vivo osseointegration
    • Abstract: Publication date: Available online 1 May 2019Source: Additive ManufacturingAuthor(s): Amit Bandyopadhyay, Indranath Mitra, Anish Shivaram, Nairanjana Dasgupta, Susmita Bose Material properties of implants such as volume porosity and nanoscale surface modification have been shown to enhance cell-material interactions in vitro and osteoconductivity in vivo. Porous tantalum (Ta) and titanium (Ti) coatings are widely used for non-cemented implants, which are fabricated using different processing routes. In recent years, some of those implants are being manufactured using additive manufacturing. However, limited knowledge is available on direct comparison of additively manufactured porous Ta and Ti structures towards early stage osseointegration. In this study, we have fabricated porous Ta and Ti6Al4V (Ti64) implants using laser engineered net shaping (LENS™) with similar volume fraction porosity to compare the influence of surface characteristics and material chemistry on in vivo response using a rat distal femur model for 5 and 12 weeks. We have also assessed whether surface modification on Ti64 can elicit similar in vivo response as porous Ta in a rat distal femur model for 5 and 12 weeks. The harvested implants were histologically analyzed for osteoid surface per bone surface. Field emission scanning electron microscopy (FESEM) was done to assess the bone-implant interface. The results presented here indicate comparable performance of porous Ta and surface modified porous Ti64 implants towards early stage osseointegration at 5 weeks post implantation through seamless bone-material interlocking. However, a continued and extended efficacy of porous Ta is found in terms of higher osteoid formation at 12 weeks post-surgery.Graphical abstractGraphical abstract for this article
  • On Microstructure and Early Stage Corrosion Performance of Heat Treated
           Direct Metal Laser Sintered AlSi10Mg
    • Abstract: Publication date: Available online 29 April 2019Source: Additive ManufacturingAuthor(s): Mehran Rafieazad, Mohsen Mohammadi, Ali M. Nasiri This study examines the impact of low-temperature heat-treatment on the microstructure and corrosion performance of direct metal laser sintered (DMLS)-AlSi10Mg alloy. Differential scanning calorimetry (DSC) was used to determine the phase(s) transition temperatures in the alloy. Two exothermic phenomena were detected and associated with the Mg2Si precipitation and Si phase precipitation in the as-printed alloy. Based on DSC results, thermal-treatments including below and above the active Si precipitation temperature at 200 °C and 300 °C, respectively, and 350 °C as an upper limit temperature for 3 h were applied to the as-printed samples. Scanning electron microscopy and X-ray diffraction analysis confirmed that heat-treatment from 200 °C to 350 °C promotes the homogeneity of the microstructure, characterized by uniform distribution of eutectic Si in α-Al matrix. To investigate the impact of the applied heat-treatment cycles on corrosion resistance of DMLS-AlSi10Mg at early stage of immersion, anodic polarization testing and electrochemical impedance spectroscopy were performed in aerated 3.5 wt.% NaCl solution. The results revealed more uniformly distributed pitting attack on the corroded surfaces by increasing the heat-treatment temperature up to 300 °C, attributed to the more protective nature of the spontaneously air-formed passive layer on the surface of the alloy at initial immersion time. Further increase of the heat treatment temperature to 350 °C induced severe localized corrosion attacks near the coarse Si particles, ascribed to the increased potential difference between the coalesced Si particles and aluminum matrix galvanic couple. In comparison, the corrosion of the as-printed and 200 °C heat treated samples was characterized by a penetrating selective attack along the melt pool boundaries, leading to a higher corrosion current density and an active surface at early exposure, associated with the weakness of the existing passive film on their surfaces.
  • Technology cost drivers for a potential transition to decentralized
    • Abstract: Publication date: Available online 27 April 2019Source: Additive ManufacturingAuthor(s): Jaime Bonnín Roca, Parth Vaishnav, Rianne E. Laureijs, Joana Mendonça, Erica R.H. Fuchs Popular dialogue around additive manufacturing (AM) often assumes that AM will cause a move from centralized to distributed manufacturing. However, distributed configurations can face additional hurdles to achieve economies of scale. We combine a Process-Based Cost Model and an optimization model to analyze the optimal location and number of manufacturing sites, and the tradeoffs between production, transportation and inventory costs. We use as a case study the commercial aviation maintenance market and a titanium jet engine bracket as an exemplar of a class of parts that are not flight-critical. We run our analysis for three different scenarios, one corresponding to the current state of the technology, and two which represent potential improvements in AM technology. Our results suggest that the cost-minimizing number of manufacturing locations does not vary significantly when taking into account a range of plausible improvements in the technology. In this case, distributed manufacturing is only favorable for a set of non-critical components that can be produced on the same equipment with minimal certification requirements and whose annual demand is in the tens of thousands. Distributed manufacturing is attractive at lower volumes for components that require no hot isostatic pressing.
  • Magnetically Navigable 3D Printed Multifunctional Microdevices for
           Environmental Applications
    • Abstract: Publication date: Available online 25 April 2019Source: Additive ManufacturingAuthor(s): Roberto Bernasconi, Elena Carrara, Marcus Hoop, Fajer Mushtaq, Xiangzhong Chen, Bradley J. Nelson, Salvador Pané, Caterina Credi, Marinella Levi, Luca Magagnin Microrobotic prototypes for water cleaning are produced combining stereolithography 3D printing and wet metallization. Different metallic layers are deposited on 3D printed parts using both electroless and electrolytic deposition to impart required functionalities. In particular, by exploiting the flexibility and versatility of electrolytic codeposition, pollutants photodegradation and bacteria killing are for the first time combined on the same device by coating it with a composite nanocoating containing titania nanoparticles in a silver matrix. The microstructure of the microrobots thus obtained is fully characterized and they are successfully actuated by applying rotating magnetic fields. From the water cleaning point of view, devices show evident photocatalytic activity towards water pollutants and antimicrobial activity for gram negative bacteria.
  • Measurement of Actual Powder Layer Height and Packing Density in a Single
           Layer in Selective Laser Melting
    • Abstract: Publication date: Available online 24 April 2019Source: Additive ManufacturingAuthor(s): Tim Marten Wischeropp, Claus Emmelmann, Milan Brandt, Aaron Pateras For a detailed numerical analysis of laser–material interactions and melt pool dynamics in selective laser melting (SLM), it is important to consider correct powder layer height and packing density in a single layer. Thus far, most experts assume that the powder layer height, which is equal to the leveling height of the build platform divided by the packing density of the powder bed, reaches a steady state after several layers. However, this assumption neglects the fact that a certain amount of powder is deposited (e.g., by spatter), and therefore, does not contribute to the molten powder layer height and that the packing density in a single layer is smaller than in “bulk.” To determine the actual powder layer height and packing density in a single layer, experiments are conducted using two different materials (SS 17-4 PH and Ti6Al4V) and layer heights (30 and 50 µm). The results reveal that the powder layer height is between 4 and 5.5 times the leveling height of the build platform and is, therefore, significantly larger than that assumed thus far. This is an important finding to consider when one investigates the details of the laser–material interaction and melting process in SLM, e.g., by numerical simulations. The measured packing density varies by approximately 50%.
  • Non-equilibrium Microstructure, Crystallographic Texture and Morphological
           Texture Synergistically Result in Unusual Mechanical Properties of 3D
           Printed 316L Stainless Steel
    • Abstract: Publication date: Available online 22 April 2019Source: Additive ManufacturingAuthor(s): Sumit Bahl, Sumeet Mishra, K.U. Yazar, Immanuel Raju Kola, Kaushik Chatterjee, Satyam Suwas Mechanisms underlying the evolution of texture and microstructure during selective laser melting (SLM) and their combined effects on the mechanical response of 316 L stainless steel are presented. Long columnar grains with a fiber texture build direction (BD) evolved in the SLM printed material. Fiber texture was stronger in the horizontal build compared to the vertical build. Use of bidirectional scanning strategy enforced epitaxial growth of grains across melt pools present within a single printed layer. BD texture evolved as a consequence of maintaining the balance between epitaxy and growth of [100] along maximum thermal gradient. High dislocation density and not grain size effect of the ultra-fine cellular structure, imparted high strength to 316L. Lower average Schmid factor and smaller effective grain size in the horizontal build by virtues of crystallographic and morphological textures, respectively, imparted higher yield strength than the vertical build. The horizontal build demonstrated higher strain hardening rate in the early stages of deformation compared to the vertical build due to higher crystallographic texture dependent twinning. However, the higher rate of dislocation annihilation led to a continuous decline in the strain hardening rate of the horizontal build. In contrast, a stable strain hardening rate was maintained in the vertical build, which led to higher ductility than the horizontal build. In summary, the roles of non-equilibrium microstructure and texture (crystallographic and morphological) in regulating mechanical properties elucidated here, can be utilized in designing additively manufactured structural components of 316 L stainless steel.
  • On The Development Of Powder Spreadability Metrics And Feedstock
           Requirements For Powder Bed Fusion Additive Manufacturing
    • Abstract: Publication date: Available online 22 April 2019Source: Additive ManufacturingAuthor(s): Zackary Snow, Richard Martukanitz, Sanjay Joshi Existing powder feedstock metrics for powder bed fusion (PBF) additive manufacturing (AM) are related to packing efficiency and flowability, and newer techniques, such as powder rheometry and dynamic avalanche testing, have received recent attention in the literature. To date, however, no powder characterization technique is able to predict the spreadability of AM feedstock. In fact, no such spreadability metrics exist. This study endeavored to establish viable powder spreadability metrics through the development of a spreadability testing rig that emulates the recoating conditions present in commercial PBF AM systems. As no metrics for spreadability currently exist, four potential metrics were evaluated in a 3∙23 split plot experimental design. These four metrics were: (1) the percentage of the build plate covered by spread powder, (2) the rate of powder deposition, (3) the average avalanching angle of the powder, and (4) the rate of change of the avalanching angle. Three samples of gas atomized, Al-10Si-0.5 Mg PBF powder representing differing degrees of quality were used as the levels of the powder quality input variable. As no powder quality metrics have been shown to be indicative of powder spreadability in PBF, various bulk powder characteristics were used as the powder quality indicator during ANOVA. Of the four metrics tested, the average avalanching angle, while statistically dependent of the powders angle of repose, showed poor correlation with experimental data. The remaining three metrics, however, were all found to have a statistically significant dependence on the angle of repose. Increasing the angle of repose resulted in significantly worse powder spreading, i.e. poor build plate coverage and powder clumping, as measured by the viable spreading metrics. Other processing parameters, such as the recoating speed and the recoater blade material were shown to also influence the spread quality.
  • Approach to Qualification using E-PBF In-situ Process Monitoring in
    • Abstract: Publication date: Available online 20 April 2019Source: Additive ManufacturingAuthor(s): S. Yoder, P. Nandwana, V. Paquit, M. Kirka, A. Scopel, R.R. Dehoff, S.S. Babu Traditional design and qualification methodologies for parts manufactured by traditional methods are being applied to Additive Manufacturing (AM) without understanding the nuances of the machines. While mapping process variables and tracking build data is helpful, some variables such as build geometry, support structure, and part melt order have not been researched in depth. Changing these variables can result in significant variations in material properties and defect structure such that the process appears to be unreliable compared to traditional manufacturing. Therefore, this research focuses on the need to understand the effects of overlooked variables such as melt order and nested geometry on the distribution of defects and bulk material properties in Ti-6Al-4 V alloy builds manufactured using the Arcam AB ® electron beam powder bed fusion process1. This study collected and analyzed process log data and near infrared (NIR) images for every layer to correlate trends in porosity formation and mechanical performance. The location of pores, while naturally stochastic, is heavily influenced by the cross-sectional area as detected by NIR images and correlates with the failure sites from uniaxial testing.
  • Cellulose Nanocrystals Support Material for 3D Printing Complexly Shaped
           Structures via Multi-Materials-Multi-Methods Printing
    • Abstract: Publication date: Available online 17 April 2019Source: Additive ManufacturingAuthor(s): Vincent Chi-Fung Li, Xiao Kuang, Craig M. Hamel, Devin Roach, Yulin Deng, H. Jerry Qi To fabricate highly complex structures, sacrificial support material is usually needed. However, traditional petroleum-based support materials are un-sustainable, non-recyclable, and difficult to be completely removed from the target structure after 3D processing. Instead, cellulose nanocrystals (CNC) gel could serves as an interesting 3D printing support material due to its sustainability, renewability, and potential recyclability. Since CNCs are highly dispersible in water as nanoparticles and are also not UV sensitive, it has less absorption or bondability with other UV curable polymer matrices. This allows them to be completely washed out by water, which offers a green and efficient method to remove the CNC support material during post processing. In addition, with increasing needs for more intricate structures, combining different 3D printing strategies into a hybrid 3D printing platform can be highly beneficial. In this work, a multi-materials-multi-methods (M4) printer with dual direct-ink-write (DIW) and DIW-inkjet printing capability was used to fabricate various complex structures while using CNC as support material. After 3D printing, water was used to remove the CNC support structure. Even in a highly confined environment, such as the inside of a balloon structure, CNC support material was still easily removed. The potential of using sustainable CNC support material and M4 hybrid 3D printing strategies to fabricate different complex structures was demonstrated. Since CNC gel is derived from forestry products and is entirely water based, the 3D printing process was also made more environmentally friendly, sustainable, and potentially recyclable.
  • Fatigue Behavior of Additive Manufactured 316L Stainless Steel Parts:
           Effects of Layer Orientation and Surface Roughness
    • Abstract: Publication date: Available online 16 April 2019Source: Additive ManufacturingAuthor(s): Rakish Shrestha, Jutima Simsiriwong, Nima Shamsaei The effects of layer orientation and surface roughness on the mechanical properties and fatigue life of 316 L stainless steel (SS) fabricated via a laser beam powder bed fusion (LB-PBF) additive manufacturing process were investigated. Quasi-static tensile and uniaxial fatigue tests were conducted on LB-PBF 316 L SS specimens fabricated in vertical and diagonal directions in their as-built surface condition, as well as in horizontal, vertical, and diagonal directions where the surface had been machined to remove any effects of surface roughness. In the machined condition, horizontally built LB-PBF specimens possessed higher fatigue resistance, followed by vertically built specimens, while the lowest fatigue resistance was obtained for diagonal specimens. Similarly, in the as-built condition, vertical specimens demonstrated better fatigue resistance when compared to diagonal specimens. Furthermore, the detrimental effects of surface roughness on fatigue life of LB-PBF 316 L SS specimens was not significant, which may be due to the presence of large internal defects in the specimens. Anisotropy of LB-PBF 316 L SS specimens was attributed to the variation in layer orientation, affecting defects’ directionality with respect to the loading direction. These defect characteristics can significantly influence the stress concentration and, consequently, fatigue behavior of additive manufactured parts. Therefore, the elastic-plastic energy release rates, a fracture mechanics-based concept that incorporates size, location, and projected area of defects on the loading plane, were determined to correlate the fatigue data and acceptable results were achieved.
  • Role of hierarchical microstructure of additively manufactured AlSi10Mg on
           dynamic loading behavior
    • Abstract: Publication date: Available online 16 April 2019Source: Additive ManufacturingAuthor(s): Amir Hadadzadeh, Babak Shalchi Amirkhiz, Akindele Odeshi, Jian Li, Mohsen Mohammadi Microstructure of an additively manufactured AlSi10Mg through direct metal laser sintering (DMLS) process is studied using multi-scale characterization techniques including scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. The microstructure of DMLS-AlSi10Mg consists of hierarchical characteristics, spanning three order of magnitude, where nanometer sized to sub-millimeter scaled features exists in the structure. These characteristics included grain and cell structures, nanoscale Si precipitates and pre-existing dislocation networks. Dynamic mechanical behavior of the material is studied using a Split Hopkinson Pressure Bar apparatus over a range of strain rates varying between 800 s-1 and 3200 s-1. Investigation of the deformed microstructures reveals the role of hierarchical microstructure on the dynamic behavior of the material. The high strain-rate deformation is accommodated by dynamic recovery (DRV) process, where low angle grain boundaries evolve due to the generation of dislocations, evolution of dislocation networks, and annihilation of dislocations. Both cell walls and Si precipitates contribute to impeding the dislocation motion and development of dislocation networks. At high strain rates, dislocation networks evolve in the nanoscale DRVed subgrains.
  • Silicone rheological behavior modification for 3D printing: evaluation of
           yield stress impact on printed object properties
    • Abstract: Publication date: Available online 15 April 2019Source: Additive ManufacturingAuthor(s): Edwin-Joffrey Courtial, Clément Perrinet, Arthur Colly, David Mariot, Jean-Marc Frances, René Fulchiron, Christophe Marquette Silicone-based materials are commonly used in medical applications such as pre-surgery models or implants, leading to interesting biomimetic mechanical properties. Emergence of 3D printing and particularly liquid deposition modelling (LDM) has shown that specific rheological behaviors, particularly yield stress characters, were required to achieve efficient LDM. Unfortunately, standard silicone formulations seldom present such behaviors and are then proved to have low applicability in LDM-based 3D printing.In the present study, polyethylene glycol of different lengths were added as yield stress agents in a bi-component silicone and were demonstrated to operate a drastic improvement of the material rheological behaviors, without significant impact on the final mechanical properties of the material. An interesting relationship was demonstrated between dynamic yield stress values and reachable 3D geometries (the higher σys, the more complex the 3D printed shape can be) but the study also revealed that it is not the only key factor to ensure the printability of viscoelastic materials when highly complex geometries are seek; tack and melt strength have also to be investigated.
  • Print time vs. elapsed time: A temporal analysis of a continuous printing
           operation for additive constructed concrete
    • Abstract: Publication date: Available online 13 April 2019Source: Additive ManufacturingAuthor(s): Brandy Diggs-McGee, Eric Kreiger, Megan Kreiger, Mike Case In additive construction, ambitious goals to fabricate a concrete building in less than 24 hours are attempted. In the field, this goal relies on a metric of print time to make this conclusion, which excludes rest time and delays. The task to complete a building in 24 hours was put to the test with the first attempt at a fully continuous print of a structurally reinforced additively constructed concrete (ACC) building. A time series analysis was performed on the events during the construction of a 512 ft2 (16’x32’x9.25’) building to explore the effect of delays on the completion time. This analysis included a study of the variation in comprehensive layer print times, expected trends and forecasting for what is expected in future prints of similar types. Furthermore, the study included a determination and comparison of print time, elapsed time and construction time, as well as a look at the effect of environmental conditions on the delay events. Upon finishing, the analysis concluded that the 3D-printed building was completed in 14-hours of print time, 31.2-hours elapsed time, or a total of 5 days of construction time. This emphasizes that reports on newly 3D-printed constructions need to provide a definition of time that includes all possible duration periods to communicate realistic capabilities of this new technology.
  • Numerical/experimental strategies to infer enhanced liquid thermal
           conductivity and roughness in laser powder-bed fusion processes
    • Abstract: Publication date: Available online 13 April 2019Source: Additive ManufacturingAuthor(s): S. Ancellotti, V. Fontanari, A. Molinari, E. Iacob, P. Bellutti, V. Luchin, G. Zappini, M. Benedetti Modelling the thermal behaviour of the melt pool produced in Laser Powder-Bed Fusion (L-PBF) processes is not an easy task, as many complex non-linear thermal phenomena are involved. An effective way to make the computational cost of these analyses affordable is to model powder and molten metal as continuous media, wherein all the heat transfer modes occurring in the liquid are simulated as lumped fictitious heat conduction. The augmentation factor used to enhance the thermal conductivity of the liquid is in general calibrated through experimental estimations of the melt pool size. The present work is aimed at devising a robust method for the calibration of such thermal parameters. A specific point of novelty of the present paper is the definition of a method to correlate surface roughness and numerically predicted melting pool size. This strategy is able to predict with good accuracy the roughness of L-PBF fabricated parts and could pave the way for calibration strategies based on roughness measurements. For this purpose, a 3-factor, 3-level Design of Experiment (DoE) has been carried out to investigate melting pool size and roughness by changing the machine process parameters: laser power, hatch distance, time exposure. In this way, the calibration of the thermal properties is made less sensitive to the large uncertainty usually affecting the melt pool size measurements and the range of applicability of the thermal model is explored over a broad spectrum of L-PBF process parameters. Anisotropic and isotropic enhanced thermal conductivity approaches are applied in combination with a laser source modelled either as a 2D or 3D heat source, respectively. The latter approach proved to be more accurate and robust against experimental uncertainties.
  • Bond Strength Measurement for Additively Manufactured Inconel 718- GRCop84
           Copper Alloy Bimetallic Joints
    • Abstract: Publication date: Available online 9 April 2019Source: Additive ManufacturingAuthor(s): Bonny Onuike, Amit Bandyopadhyay To benefit from the fascinating properties of multi-material structures, the interfacial joint should exhibit good mechanical strength. Evaluating the shear strength of a bimetallic joint via conventional methods is usually complex, and in most cases produces unreliable data due to induced bending stress among others. In this work, a novel single-shear test device was designed and fabricated to measure shear strength of bimetallic joints. The device was first standardized by shearing standard materials, and the results were in good agreement with published data. Subsequently, the shear strength of Inconel 718/copper alloy (GRCop-84) bimetallic joint built via laser engineered net shaping (LENS™) was evaluated. Compression test on the bimetallic joint was carried out as well for mechanical characterization. Both shear and compressive yield strengths of bimetallic joints were compared with the base materials in addition to influence of thermal cycling on the joint strength. Inconel 718/GRCop-84 bimetallic-joint shear strength was 220 ± 18 MPa and 231 ± 27 MPa for as-printed sample and after thermal cycling, respectively. Likewise, the bimetallic yield strength after compression test was 232 ± 3 MPa and 337 ± 15 MPa. No cracking through or along the interface was observed even after thermal cycling, which indicates no thermal degradation at the bimetallic interfacial joint. Increase in compressive yield strength after thermal cycling could be attributed to precipitation of Cr2Nb particles in GRCop-84 matrix along with strengthening due to gamma phases in Inconel 718. Scanning electron microscopy (SEM) and backscatter electron imaging were used to examine the interfacial microstructures and failure modes. EDS was used as well to analyze the interface elemental composition. The development of the single-shear test device can provide an added opportunity to effectively evaluate mechanical behavior, reliability and performance of additively manufactured multi-material structures through bond strength analysis.
  • Effect of Process Parameters and Electropolishing on the Surface Roughness
           of Interior Channels in Additively Manufactured Nickel Titanium Shape
           Memory Alloy Actuators
    • Abstract: Publication date: Available online 8 April 2019Source: Additive ManufacturingAuthor(s): Jacob Mingear, Bing Zhang, Darren Hartl, Alaa Elwany Recently, laser-powder bed fusion (L-PBF) has been utilized to produce a NiTi shape memory alloy actuator with embedded channels for liquid metal forced fluid convection to increase actuator heat transfer rates. To enable further increases in performance, it is critical to characterize and control the surface quality of fully interior channels which have higher surface roughness compared to exterior top surfaces. This work utilizes a design of experiments methodology by varying laser power, scan speed, hatch space, scan pattern, channel orientation, and channel diameter on the as-fabricated surface roughness of the overhangs and walls of interior channels in NiTi. To enable post-process increases in surface quality, the channels are subjected to an electropolishing treatment and further characterized. Internal channel surfaces are characterized using optical profilometry and SEM imaging. It is concluded that channel orientation plays a prominent role in determining the surface roughness of as-fabricated interior channels, and a lower laser energy density results in the highest reduction in surface roughness after an electropolishing treatment.
  • A lightweight electromagnetic actuator for high voltage DC power grids
    • Abstract: Publication date: Available online 6 April 2019Source: Additive ManufacturingAuthor(s): F. García Ferré, A. Johansson, L. Herrmann, J. Korbel, T. Erford, U. Riechert High voltage direct current (HVDC) is a highly efficient alternative for transmitting large amounts of electricity over long distances, and holds great potential to enable stronger, smarter and greener power grids based on renewable energy sources. However, efficient management of HVDC grids calls for robust switchgear technology, which is still under development. In particular, fast switching speed is paramount to limit peak fault current and energy loss in hybrid HVDC circuit breakers (HHBs). In such breakers, the switching speed depends on the mass of the moving parts. Therefore, lightweight is paramount.Here, a lightweight electromagnetic actuator for HHBs is conceived using Design for Additive Manufacturing (DfAM) tools, including topology optimization and free-shape design. A prototype is manufactured by selective laser melting (SLM) of alloy Ti-6Al-4 V. The prototype weighs 25% less than the actuator designed and manufactured using traditional methods (i.e. CAD, milling) and materials (i.e. Al alloys). The performance of the actuator in service is simulated by transient modal mechanical analyses using finite element methods. The results show that the high strength of the material selected, combined with the bionic geometry designed and the resulting lightweight, allow the actuator to withstand the extreme accelerations of the HHB (3000 g) without yielding, enabling ultra-fast switching –namely, below 1 ms.
  • Green Fab Lab Applications of Large-Area Waste Polymer-based Additive
    • Abstract: Publication date: Available online 6 April 2019Source: Additive ManufacturingAuthor(s): Dennis J. Byard, Aubrey L. Woern, Robert B. Oakley, Matthew J. Fiedler, Samantha L. Snabes, Joshua M. Pearce Fab labs, which offer small-scale distributed digital fabrication, are forming a Green Fab Lab Network, which embraces concepts of an open source symbiotic economy and circular economy patterns. With the use of industrial 3D printers capable of fused particle fabrication/ fused granular fabrication (FPF/FGF) printing directly from waste plastic streams, green fab labs could act as defacto recycling centers for converting waste plastics into valuable products for their communities. Clear financial drivers for this process have not been studied in the past. Thus, in this study the Gigabot X, an open source industrial 3D printer, which has been shown to be amenable to a wide array of recyclables for FPF/FGF 3D printing, is used to evaluate this economic potential. An economic life cycle analysis of the technology is completed comprised of three cases studies using FPF for large sporting equipment products. Sensitivities are run on the electricity costs for operation, materials costs from various feed stocks and the capacity factors of the 3D printers. The results showed that FPF/FGF 3D printing is capable of energy efficient production of a wide range of large high-value sporting goods products. In all cases, a substantial economic savings was observed when comparing the materials and energy related costs to commercial goods (even for customized goods). Using locally-sourced shredded plastic represented not only the best environmental option, but also the most economic. For the case study products analyzed even the lowest capacity factor (starting only one print per week) represented a profit when comparing to high-end value products. For some products the profit potential and return on investment was substantial (e.g. over 1000%) for high capacity use of a Gigabot X. The results clearly show that open source industrial FPF/FGF 3D printers have significant economic potential when used as a distributed recycling/manufacturing system using recyclable feed stocks in the green fab lab context.
  • A review of the fatigue behavior of 3D printed polymers
    • Abstract: Publication date: Available online 6 April 2019Source: Additive ManufacturingAuthor(s): Lauren Safai, Juan Sebastian Cuellar, Gerwin Smit, Amir A. Zadpoor As additive manufacturing of polymeric materials is becoming more prevalent throughout industry and research communities, it is important to ensure that 3D printed parts are able to withstand mechanical and environmental stresses that occur when in use, including the sub-critical cyclic loads that could result in fatigue crack propagation and material failure. There has so far been only limited research on the fatigue behavior of 3D printed polymers to determine which printing or material parameters result in the most favorable fatigue behavior. To better understand the effects of the printing technique, printing materials, and printing parameters on the fatigue behavior of 3D printed materials, we present here an overview of the data currently available in the literature including fatigue testing protocols and a quantitative analysis of the available fatigue data per type of the AM technology. The results of our literature review clearly show that, due to the synergism between printing parameters and the properties of the printed material, it is challenging to determine the best combination of variables for fatigue resistance. There is therefore a need for more experimental and computational fatigue studies to understand how the above-mentioned material and printing parameters affect the fatigue behavior.
  • Evaluation of a thermomechanical model for prediction of residualstress
           during laser powder bed fusion of Ti-6Al-4V
    • Abstract: Publication date: Available online 2 April 2019Source: Additive ManufacturingAuthor(s): R.K. Ganeriwala, M. Strantza, W.E. King, B. Clausen, T.Q. Phan, L.E. Levine, D.W. Brown, N.E. Hodge The build-up of residual stresses in a part during laser powder bed fusion provides a significant limitation to the adoption of this process. These residuals stresses may cause a part to fail during a build or fall outside the specified tolerances after fabrication. In the present work a thermomechanical model is used to simulate the build process and calculate the residual stress state for Ti-6Al-4V specimens built with continuous and island scan strategies. A layer agglomeration, or lumping, approach is used to speed up the computations. A material model is developed to naturally capture the strain-rate dependence and annealing behavior of Ti-6Al-4V at elevated temperatures. Results from the thermomechanical simulations showed good agreement with synchrotron X-ray diffraction measurements used to determine the residual elastic strains in these parts. However, the experimental measurements showed higher residual strains for the specimen built with an island scan strategy; a trend not fully captured by the simulations. Parameter studies were performed to fully understand the advantages and limitations of the current simulation methodology. Reasons for both the computational and experimental findings are discussed.
  • 3D printing for construction based on a complex wall of polymer-foam and
    • Abstract: Publication date: Available online 2 April 2019Source: Additive ManufacturingAuthor(s): Benoit Furet, Philippe Poullain, Sébastien Garnier The objective of this paper is to present a new advanced Additive Manufacturing (AM) process for the construction of concrete structures: Batiprint3dTM. The proposed advanced technology consists of creating a complex wall of 3D-printed materials using a mobile and polyarticulated robot: two polymer-foam printed walls are used to encase a subsequent third wall made of concrete. Once the walls were in place, the foam is maintained to provide both an internal and external insulation to the house without requiring thermal bridges. This technique of the complex wall with 3D-printed composite foam/concrete material is similar to the use of expansive-foam formwork (FW) filled by concrete or Insulated Concrete Forms (ICF) but in that case printed directly on site. By using 3D printing for the foam and extrusion of the concrete with the same robotic system, the technique creates jointly both the structure and thermal elements of the building. In the first part of this paper the composite foam/concrete 3D printing method and optimized process parameters are présented. Polyurethane (PU) foam has weak mechanical properties and the filling of the internal void with concrete can yield in high deformations and even failure of the FW, it is therefore necessary to control this phenomenon. For that, an experimental study has been conducted to determine a filling procedure capable of minimizing the deformations. The results show that spacers between the two foam walls can allow for wall heights of poured concrete up to 50 cm. The problems solved, it was decided to experiment in full scale this new walls 3D printing method with the construction of YhnovaTM, a real 95m² social housing. This technology Batiprint3dTM have been used, it is possible now to propose a synthesis of the impacts of this new advanced technology for construction.
  • A novel strategy to fabricate thin 316L stainless steel rods by continuous
           directed energy deposition in Z direction
    • Abstract: Publication date: Available online 31 March 2019Source: Additive ManufacturingAuthor(s): Fei Weng, Shiming Gao, Jingchao Jiang, JianJian Wang, Ping Guo Thin 316L stainless steel rods were fabricated by continuous directed energy deposition in Z direction. The process parameters (laser power, scan velocity, and powder feeding rate) were carefully selected to obtain a stable deposition process and the effects of powder feeding rate and scan velocity were studied. A preliminary study on microstructure and tensile properties of the specimens was carried out. Results indicated that the specimen showed superior austenite/ferrite (γ/δ) dual phase microstructure, high strength (608.24 MPa), and good plastic deformation capacity (65.08% shrinkage rate) when setting the laser power at 45.2 W, powder feeding rate at 2.81 g/min, and scan velocity at 0.5 mm/s. The technique reported in this paper is expected to lay the foundation for the deposition of wire or frame structures more efficiently than traditional layer-by-layer directed energy deposition.Graphical abstractGraphical abstract for this article
  • Wire and arc additive manufacturing of HSLA steel: Effect of Thermal
           Cycles on Microstructure and Mechanical Properties
    • Abstract: Publication date: Available online 30 March 2019Source: Additive ManufacturingAuthor(s): Tiago A. Rodrigues, V. Duarte, Julian A. Avila, Telmo G. Santos, R.M Miranda, J.P Oliveira Wire and arc additive manufacturing (WAAM) is a viable technique for the manufacture of large and complex dedicated parts used in structural applications. High-strength low-alloy (HSLA) steels are well-known for their applications in the tool and die industries and as power-plant components. The microstructure and mechanical properties of the as-built parts are investigated, and are correlated with the thermal cycles involved in the process. The heat input is found to affect the cooling rates, interlayer temperatures, and residence times in the 800–500 °C interval when measured using an infrared camera. The microstructural characterization performed by scanning electron microscopy reveals that the microstructural constituents of the sample remain unchanged. i.e., the same microstructural constituents—ferrite, bainite, martensite, and retained austenite are present for all heat inputs. Electron backscattered diffraction analysis shows that no preferential texture has been developed in the samples. Because of the homogeneity in the microstructural features of the as-built parts, the mechanical properties of the as-built parts are found to be nearly isotropic. Mechanical testing of samples shows excellent ductility and high mechanical strength. This is the first study elucidating on the effect of thermal cycles on the microstructure and mechanical properties during WAAM of HSLA steel.Graphical abstractGraphical abstract for this article
  • Parallel Electrostatic Grippers for Layered Assembly
    • Abstract: Publication date: Available online 27 March 2019Source: Additive ManufacturingAuthor(s): Joni Mici, Jang Won Ko, Jared West, Jeffrey Jaquith, Hod Lipson Layered Assembly is a voxel-based additive manufacturing method in which premanufactured voxels serve as the feedstock for producing multi-material parts. The parallel placement of voxels necessary for Layered Assembly is carried out by electroadhesion—a type of astrictive prehension, which is an elegant, scalable, low-power, solid-state, and epoxy-free grasping method with numerous applications. In the present work, 2 × 2 arrays of electroadhesive grippers were designed in both comb- and spiral-shaped electrode geometries. Electrodes were nominally designed for grasping voxels of 3 × 3 mm cross-section. Electrostatic field simulations were performed in COMSOL Multiphysics for both single electrodes, and 2 × 2 electrode arrays. The selective gripping capability of the electrode arrays was tested at voltages in the 75–800 V range and applied to both polymer and metallic voxels. A comparison of voxel performance in terms of geometry revealed that comb-shaped voxels were superior, due to ≈100% reliability when operating in the 600–800 V range.
  • Metallurgical and Mechanical Assessment of Hybrid Additively-Manufactured
           Maraging Tool Steels via Selective Laser Melting
    • Abstract: Publication date: Available online 26 March 2019Source: Additive ManufacturingAuthor(s): H. Azizi, R. Ghiaasiaan, R. Prager, M.H. Ghoncheh, Khaled Abu Samk, Ante Lausic, Wes Byleveld, A.B. Phillion A complete metallurgical and mechanical assessment of additively-manufactured maraging tool steels has been undertaken, beginning with the initial powder and ending at hybrid builds. The effect of powder recycling on powder characteristics is investigated using flowability, size distribution, and density measurements. Virgin and re-used powder have similar characteristics in terms of size distribution and chemical and phase homogeneity, but no flowability. A microstructural characterization of the as-built and heat-treated samples is undertaken, showing the phase evolution, and the formation of porosity between build layers. The age-hardening response of the alloy at 490 °C and 650 °C is demonstrated to be similar to the material in the wrought condition. Finally, hybrid build scenarios are examined – maraging steel powder deposited onto C300 maraging steel, as well as H13 tool steel substrates – using digital image correlation. In both cases, the interface remains coherent without any sign of de-bonding during tensile deformation. In the case of the maraging steel powder / C300 substrate, the deformation is homogeneous throughout until failure localizes away from the interface. In the case of the maraging steel powder / H13 substrate, the deformation is predominantly within the substrate until failure localizes at the interface. A heat treatment strategy for the maraging steel powder / H13 tool steel substrate is proposed.
    • Abstract: Publication date: Available online 25 March 2019Source: Additive ManufacturingAuthor(s): Michael Robinson, Shwe Soe, Richard Johnston, Rhosslyn Adams, Benjamin Hanna, Roy Burek, Graham McShane, Rafael Celeghini, Marcilio Alves, Peter Theobald Additive manufacturing (AM) enables production of geometrically-complex elastomeric structures. The elastic recovery and strain-rate dependence of these materials means they are ideal for use in dynamic, repetitive mechanical loading. Their process-dependence, and the frequent emergence of new AM elastomers, commonly necessitates full material characterisation; however, accessing specialised equipment means this is often a time-consuming and expensive process. This work presents an innovative equi-biaxial rig that enables full characterisation via just a conventional material testing machine (supplementing uni-axial tension and planar tension tests). Combined with stress relaxation data, this provides a novel route for hyperelastic material modelling with viscoelastic components. This approach was validated by recording the force-displacement and deformation histories from finite element modelling a honeycomb structure. These data compared favourably to experimental quasistatic and dynamic compression testing, validating this novel and convenient route for characterising complex elastomeric materials. Supported by data describing the potential for high build-quality production using an AM process with low barriers to entry, this study should serve to encourage greater exploitation of this emerging manufacturing process for fabricating elastomeric structures within industrial communities.
  • Experimentally validated predictions of thermal history and microhardness
           in laser-deposited Inconel 718 on carbon steel
    • Abstract: Publication date: Available online 23 March 2019Source: Additive ManufacturingAuthor(s): Sarah J. Wolff, Zhengtao Gan, Stephen Lin, Jennifer L. Bennett, Wentao Yan, Gregory Hyatt, Kornel F. Ehmann, Gregory J. Wagner, Wing Kam Liu, Jian Cao Process−property relationships in additive manufacturing (AM) play critical roles in process control and rapid certification. In laser-based directed energy deposition, powder mass flow into the melt pool influences the cooling behavior and properties of a built part. This study develops predictive computational models that provide the microhardness of AM components processed with miscible dissimilar alloys, and then investigates the influence of varying process parameters on properties in experiments and modeling. Experimentally-determined clad dilution and microhardness results of Ni-based superalloy Inconel 718 clads deposited onto 1045 carbon steel substrates are compared to the values from a computational thermo-fluid dynamics (CtFD) model. The numerical model considers the fluidic mechanisms of molten metal during powder deposition and the resulting transient melt pool geometry changes. The model also handles the change in thermal-physical properties caused by the composition mixture between the powder and substrate materials in the melt pool. Based on the computed temperature and velocity distributions in the melt pool, cooling rate, dilution of the melt pool and microhardenss are evaluated. The capability to predict thermal histories in such models is calibrated and validated with experimental thermal imaging and microstructures of additive manufactured clads. In addition, the roles of cooling rate and alloy composition on the microhardness are examined. The results show that variation in microhardness is dominated by composition mixture between the powder and substrate materials, rather than cooling behavior or dendrite arm spacing at liquid-solid interface in laser deposited Inconel 718 on AISI 1045 carbon steel.
  • Microstructure and Corrosion Properties of Sensitized Laser Powder Bed
           Fusion Printed Inconel 718 to Dissolve Support Structures in a
           Self-Terminating Manner
    • Abstract: Publication date: Available online 22 March 2019Source: Additive ManufacturingAuthor(s): Christopher S. Lefky, Thomas G. Gallmeyer, Senthamilaruvi Moorthy, Owen J. Hildreth This manuscript expands the existing framework for single-material laser powder bed fusion printed dissolvable supports to Inconel 718 (IN718). Prior work with stainless steel leveraged a sensitization heat treatment using sodium hexacyanoferrate to precipitate chromium carbides over the top 100 µm to 200 µm of material, decreasing the corrosion resistance within this top layer relative to the bulk material. The component is then etched at an anodic potential with a high selectivity toward the “sensitized” surface over the base component material. This creates an etching process that self-terminates once the sensitized layer is removed. Since supports are typically less than 200 µm thick, they are completely sensitized and dissolved. Additionally, the surface roughness of the component is often improved once the sensitized region is removed. In this work, two different sensitization heat schedules were investigated: 750 °C for 24 h to understand the impact of preferential chromium carbide precipitation and 1050 °C for 8 h to understand the impact of primary carbide precipitations. At 1050 °C, the formation of a protective oxide scale inhibits material removal in an electrolyte of 0.48 M HNO3. At 750 °C, 70 µm of material is removed after quenching to avoid the precipitation of corrosion resistant oxides. This manuscript investigates the effect of targeting different carbide precipitation regimes and oxides to produce an ideal microstructure for dissolvable supports post-sensitization. To demonstrate the utility of the process, the supports from a mock IN718 turbine blade were removed using this process.
  • Additive manufacturing of soft magnetic materials and components
    • Abstract: Publication date: Available online 20 March 2019Source: Additive ManufacturingAuthor(s): D. Goll, D. Schuller, G. Martinek, T. Kunert, J. Schurr, C. Sinz, T. Schubert, T. Bernthaler, H. Riegel, G. Schneider Additive manufacturing of soft magnetic materials and components based on laser powder bed fusion (L-PBF) offer new opportunities for soft magnetic core materials in efficient energy converters. For more favorable material compositions like FeSi6.7 (strategy 1) with larger electrical resistivity and close-to-zero magnetostriction a maximum permeability of µmax = 31000, minimum coercivity of Hc = 16 A/m and hysteresis losses of 0.7 W/kg at 1 T and 50 Hz have been realized. To further reduce eddy current losses significantly, novel topological structures like inner slits (strategy 2) and multilayered structures of alternating layers of electrically insulating material and soft magnetic material (strategy 3) are suggested. Feasibility, functionality and potential of the different strategies (and combinations thereof) are discussed based on first prototypes and supporting simulations. The results are compared to conventional electrical steel and SMC (soft magnetic composites).
  • Understanding the Microstructure and Mechanical Properties of Ti-6Al-4V
           and Inconel 718 Alloys Manufactured by Laser Engineered Net Shaping
    • Abstract: Publication date: Available online 20 March 2019Source: Additive ManufacturingAuthor(s): Yuwei Zhai, Diana A. Lados, Eric J. Brown, Gregory N. Vigilante Laser Engineered Net Shaping (LENS®) is a metal Additive Manufacturing (AM) technique that carries great potential for the fabrication and repair of high-integrity structural and engine components. Confident application of the LENS technique requires a fundamental understanding of the microstructure and properties of the fabricated materials, as well as their correlations to processing conditions. In this study, two alloys fabricated by LENS, Ti-6Al-4 V and Inconel 718, were examined and compared to their wrought counterparts. The differences between low and high laser power fabrications, as well as the effects of various post-LENS heat treatments were systematically investigated and discussed. The interfacial bond strength between LENS depositions and substrates were also evaluated for repair purposes.
  • One-step Electrodeposition of Copper on Conductive 3D Printed
    • Abstract: Publication date: Available online 19 March 2019Source: Additive ManufacturingAuthor(s): Myung Jun Kim, Mutya A. Cruz, Shengrong Ye, Allen L. Gray, Gabriel L. Smith, Nathan Lazarus, Christopher J. Walker, Hjalti H. Sigmarsson, Benjamin J. Wiley 3D printing with electrically conductive filaments enables rapid prototyping and fabrication of electronics, but the performance of such devices can be limited by the fact that the most conductive thermoplastic-based filaments for 3D printing are 3750 times less conductive than copper. This study explores the use of one-step electrodeposition of copper onto electrically conductive 3D printed objects as a way to improve their conductivity and performance. Comparison of three different commercially-available conductive filaments demonstrates that only the most conductive commercially available filament could enable one-step electrodeposition of uniform copper films. Electrodeposition improved the electrical conductivity and the ampacity of 3D printed traces by 94 and 17 times respectively, compared to the as-printed object. The areal surface roughness of the objects was reduced from 9.3 to 6.9 μm after electrodeposition, and a further reduction in surface roughness to 3.9 μm could be achieved through the addition of organic additives to the electrodeposition bath. Copper electrodeposition improved the quality factor of a 3D printed inductor by 1740 times and the gain of a 3D printed horn antenna by 1 dB. One-step electrodeposition is a fast and simple way to improve the conductivity and performance of 3D printed electronic components.Graphical abstractGraphical abstract for this article
  • Vision-Based Inspection System for Cladding Height Measurement in Direct
           Energy Deposition (DED)
    • Abstract: Publication date: Available online 19 March 2019Source: Additive ManufacturingAuthor(s): Hsu-Wei Hsu, Yu-Lung Lo, Min-Hsun Lee A vision-based inspection system based on three digital cameras is proposed for measuring the cladding height in the Direct Energy Deposition (DED) process. To improve the accuracy of the cladding height measurements, an image processing technique is applied to remove the undesirable zone from the binary image. Furthermore, since the unit length in the captured images is different to that in the world coordinate framework, a calibration bar method is designed to transform the pixel value to the real size. In the proposed approach, a calibration bar method is employed to compensate for the Field-of-View (FOV) and perspective effects in the trinocular system. An image-processing technique is then employed to isolate the laser nozzle and melt pool in the captured images. Finally, the cladding height is estimated based on the distance between the tip of the laser nozzle and the centroid of the melt pool. The validity of the proposed approach is demonstrated by comparing the inspection results for the cladding height of a horseshoe component with the measurements obtained using a 3-D scanner. The maximum estimation error is found to be just 4.2% Overall, the results confirm that the proposed trinocular vision-based system provides a rapid, convenient and accurate means of determining the cladding height in the DED process.
  • Introduction of ternary alloying element in wire arc additive
           manufacturing of titanium aluminide intermetallic
    • Abstract: Publication date: Available online 15 March 2019Source: Additive ManufacturingAuthor(s): Jun Wang, Zengxi Pan, Liangliang Wei, Shuai He, Dominic Cuiuri, Huijun Li In order to introduce vanadium as a ternary alloying element during the wire arc additive manufacturing (WAAM) of titanium aluminide intermetallic alloys, alloy and elemental wire consumables (Ti6Al4V and Al wires, respectively) were used with the WAAM process. A crack-free TiAl bulk with nominal chemical composition of Ti45Al2.2 V was successfully fabricated for the first time through dynamic in situ alloying using WAAM method. The experimental results showed that the introduction of V from Ti6Al4V alloy does not change the flat features of lamellar interface and also does not alter the phase composition of the resultant TiAl alloy. The fabricated Ti45Al2.2 V alloy consists of lamellar colonies and γ interdendritic phase in the top region, fully lamellar structure with unclear grain boundaries in the band regions and large equiaxed α2 with fine γ laths precipitated at grain boundaries in the layers. The microhardness and tensile properties were greatly increased by introducing V due to the general absence of interdendritic γ phase and the V ductilization effect. In addition, the influences of two-step post-heat treatments on the microstructure and mechanical properties are analysed. Results indicate that the microstructure and mechanical properties of the fabricated alloy can be considerably modified after applying different solution treatment temperatures.
  • Simple Method to Construct Process Maps for Additive Manufacturing Using
           Support Vector Machine
    • Abstract: Publication date: Available online 14 March 2019Source: Additive ManufacturingAuthor(s): Kenta Aoyagi, Hao Wang, Akihiko Chiba, Hideki Sudo We propose a simple method to construct a process map for additive manufacturing using a support vector machine. By observing the surface of the built parts and classifying them into two classes (good or bad), this method enables a process map to be constructed in order to predict a process condition that is effective at fabricating a part with low pore density. This proposed method is demonstrated in a biomedical CoCr alloy system. We show that the proposed method is effective at reducing the number of experiments necessary to tailor an optimized process condition. This study also shows that the value of a decision function in a support vector machine has a physical meaning (at least in the proposed method) and is a semi-quantitative guideline for porosity density of parts fabricated by additive manufacturing.
  • Thermal simulation and phase modeling of bulk metallic glass in the powder
           bed fusion process
    • Abstract: Publication date: Available online 14 March 2019Source: Additive ManufacturingAuthor(s): Johan Lindwall, Victor Pacheco, Martin Sahlberg, Andreas Lundbäck, Lars-Erik Lindgren One of the major challenges with the powder bed fusion process (PBF) and formation of bulk metallic glass (BMG) is the development of process parameters for a stable process and a defect-free component. The focus of this study is to predict formation of a crystalline phase in the glass forming alloy AMZ4 during PBF. The approach combines a thermal finite element model for prediction of the temperature field and a phase model for prediction of crystallization and devitrification. The challenge to simulate the complexity of the heat source has been addressed by utilizing temporal reduction in a layer-by-layer fashion by a simplified heat source model. The heat source model considers the laser power, penetration depth and hatch spacing and is represented by a volumetric heat density equation in one dimension. The phase model is developed and calibrated to DSC measurements at varying heating rates. It can predict the formation of crystalline phase during the non-isothermal process. Results indicate that a critical location for devitrification is located a few layers beneath the top surface. The peak is four layers down where the crystalline volume fraction reaches 4.8% when 50 layers are built.
  • Role of Compatibilizer in 3D Printing of Polymer Blends
    • Abstract: Publication date: Available online 12 March 2019Source: Additive ManufacturingAuthor(s): Matthew E. Spreeman, Holly A. Stretz, Mark Dadmun For additive manufacturing interfacial adhesion (bead-bead) remains an important issue affecting uniformity of mechanical properties. The present work examined the role a compatibilizer would play when used in fused filament fabrication (FFF) printing. Poly(styrene-maleic anhydride) (SMA) compatiblizer was mixed in varying compositions in blends of polyamide/poly(acrylonitrile-butadiene-styrene) (PA/ABS) to improve interfacial adhesion. Both small and large-scale 3-D component properties were examined. The mechanical property anisotropy ratio, an indication of bead-bead adhesive strength (defined as a property measured along the z axis versus the x axis) is representative of adhesive strength. Large-scale (big area additive manufacturing, BAAM) tests (flexural properties) showed 62% improvement in the anisotropy ratio for modulus, 77% improvement in the anisotropy ratio of the strength, 56% improvement in the anisotropy ratio of elongation at break, and 55% improvement of the anisotropy ratio of the Charpy impact strength over the control PA values. Thus, use of compatibilized polymer blends can provide customized materials without the need for new chemistry. Addition of maleic anhydride-compatibilized ABS improved PA blend bead-bead adhesion.Graphical abstractGraphical abstract for this article
  • Design against Distortion for Additive Manufacturing
    • Abstract: Publication date: Available online 11 March 2019Source: Additive ManufacturingAuthor(s): Anas Yaghi, Sabino Ayvar-Soberanis, Shanmukha Moturu, Ravi Bilkhu, Shukri Afazov This paper presents the methodology and findings of a novel piece of research with the purpose of understanding and mitigating distortion caused by the combined processes of additive manufacturing (AM) and post machining to final specifications. The research work started with the AM building of a stainless steel 316 L industrial impeller that was then machined by removing around 0.5 mm from certain surfaces of the impeller’s blades and hub. Distortion and residual stresses were experimentally measured.The manufacture of the impeller by AM and then machining was numerically simulated by applying the finite element (FE) method. Distortion and residual stresses were simulated and validated. The FE distortion was then used in a numerical procedure to reverse distortion directions in order to produce a new impeller with mitigated distortion. The results have shown that distortions in the new impeller, on average, have reduced to less than 50% of the original non-compensated values.
  • A novel approach for understanding laser sintering of polymers
    • Abstract: Publication date: Available online 11 March 2019Source: Additive ManufacturingAuthor(s): D. Drummer, S. Greiner, M. Zhao, K. Wudy Selective laser sintering (LS) of thermoplastic powders allows for the construction of complex parts with higher mechanical properties and durability compared to other additive manufacturing methods. According to the current model of isothermal laser sintering, semi-crystalline thermoplastics need to be processed within a certain temperature range, resulting in the simultaneous presence of the material both in a molten and solid state, which is present during part building. Based on this process model, high cycle times ranging from hours to days are a thought to be a necessity to avoid warpage.In this paper, the limited validity of the model of isothermal laser sintering was shown by various experiments, as ongoing solidification could be detected a few layers below the powder bed surface. The results indicate that crystallization and material solidification is initiated at high temperatures and further progresses throughout part build-up in z-direction. Therefore, a process-adapted material characterization was performed to identify the isothermal crystallization kinetics at processing temperature and to track changes of the material state over time. A dual approach on measuring surface temperatures by infrared thermography and additional thermocouple measurements in z-direction was performed to identify further influences on the material solidification. A model experiment revealed that a few millimeters below the surface, components produced by LS are already solidified. Based on these results, the authors present an enhanced process model of isothermal laser sintering, which considers material solidification in z-direction during part build-up. In addition, a new processing strategy is derived to increase the efficiency of LS processes significantly.Graphical abstractGraphical abstract for this article
  • On Utilizing Topology Optimization to Design Support Structure to Prevent
           Residual Stress Induced Build Failure in Laser Powder Bed Metal Additive
    • Abstract: Publication date: Available online 9 March 2019Source: Additive ManufacturingAuthor(s): Lin Cheng, Xuan Liang, Jiaxi Bai, Qian Chen, John Lemon, Albert To Metal additive manufacturing (AM) as an emerging manufacturing technique has been gradually accepted to manufacture end-use components. However, one of the most critical issues preventing its broad applications is build failure resulting from residual stress accumulation in manufacturing process. The goal of this work is to investigate the feasibility of using topology optimization to design support structure to mitigate residual stress induced build failure. To make topology optimization computationally tractable, the inherent strain method is employed to perform fast prediction of residual stress in an AM build. Graded lattice structure optimization is utilized to design the support structure due to the open-celled and self-supporting nature of periodic lattice structure. The objective for the optimization is to minimize the mass of sacrificial support structure under stress constraint. By limiting the maximum stress under the yield strength, cracking resulting from residual stress can be prevented. To show the feasibility of the proposed method, the support structure of a double-cantilever beam and a hip implant is designed, respectively. The support structure after optimization can achieve a weight reduction of approximately 60%. The components with optimized support structures no longer suffer from stress-induced cracking after the designs are realized by AM, which proves the effectiveness of the proposed method.
  • Influence of mixed isotropic fiber angles and hot press on the mechanical
           properties of 3D printed composites
    • Abstract: Publication date: Available online 8 March 2019Source: Additive ManufacturingAuthor(s): Hui Mei, Zeeshan Ali, Yuekai Yan, Ihtisham Ali, Laifei Cheng This paper aims to study the mechanical properties of mixed isotropic carbon fiber 3D printed composites and further investigates the influence of hot press on the [0°/45°/90°]2 fiber angles composite with varying temperature, pressure and time. Tensile tests, autoclave treatment and microstructural observation were utilized to characterize the composites. Results revealed that the [0°/45°/90°]2 performed the highest tensile strength of 79 MPa and modulus of 3.51 GPa, compared to [30°/45°/60°]2 and [15°/45°/75°]2. This is due to the fibers along the tensile axis angle that bears maximum load in longitudinal direction. At 200 °C temperature, the hot pressed composites presented the highest tensile strength of 98 MPa and modulus of 3.93 GPa than non-hot pressed. Increased temperature caused better interface wettability between fibers and matrix. At 200 kPa pressure, the hot pressed composites showed the highest tensile strength of 100 MPa and modulus of 4.06 GPa than non-hot pressed. Further increased pressure resulted in lower tensile strength and modulus, as the material became stiffer pushing more matrix material to side leaving numerous fibers unbounded by the matrix. For 30 minutes withholding time, the hot pressed composites indicated the highest tensile strength of 106 MPa and modulus of 4.27 GPa than non-hot pressed. Increased time caused strongest interface bonding by removing the air gaps induced during printing between fibers and matrix. Results revealed that hot press significantly improved the mechanical properties of carbon fiber 3D printed composites.
  • Z-Pinning Approach for 3D Printing Mechanically Isotropic Materials
    • Abstract: Publication date: Available online 7 March 2019Source: Additive ManufacturingAuthor(s): Chad Duty, Jordan Failla, Seokpum Kim, Tyler Smith, John Lindahl, Vlastimil Kunc Conventional 3D printing approaches are restricted to building up material in a layer-by-layer format, which is more appropriately considered “2.5-D” printing. The layered structure inherently results in significant mechanical anisotropy in printed parts, causing the tensile strength in the build direction (z-axis) to be only a fraction of the in-plane strength – a decrease of 50-75% is common. In this study, a novel “z-pinning” approach is described that allows continuous material to be deposited across multiple layers within the volume of the part. The z-pinning process is demonstrated using a Fused Filament Fabrication (FFF) printer for polylactic acid (PLA) and carbon fiber reinforced PLA. For both materials, z-pinning increased the tensile strength and toughness in the z-direction by more than a factor of 3.5. Direct comparisons to tensile strength in the x-axis showed a significant decrease in mechanical anisotropy as the volume of the pin was increased relative to the void in the rectilinear grid structure. In fact, the PLA sample with the largest pin volume demonstrated mechanically isotropic properties within the statistical uncertainty of the tests. Tensile test results were also analyzed relative to the functional area resisting deformation for each sample.
  • Compulsively Constricted WAAM with Arc Plasma and Droplets Ejected from a
           Narrow Space
    • Abstract: Publication date: Available online 2 March 2019Source: Additive ManufacturingAuthor(s): Wenqiang Liu, Chuanbao Jia, Meng Guo, Jinqiang Gao, Chuansong Wu In order to realize oriented wire and arc additive manufacturing (WAAM) featured by low heat input and small droplets, a novel compulsively constricted WAAM (CC-WAAM) method was proposed and investigated in this paper. The arc burned between a metallic wire and a tungsten electrode in a narrow-space nozzle. The proposed technology could provide compulsive constriction for arc plasma and liquid metal droplets using a cubic boron nitride (CBN) ceramic nozzle. The surrounding arc was ejected out of the nozzle and offered extra heating and a good shielding environment during the whole manufacturing process. The arc and metal transfer behaviors could be improved for better performance and higher quality. The economic and efficient new method is expected to solve the challenges faced by traditional WAAM such as excessive heat input and poor geometrical accuracy. Preliminary experiments showed that the two AM layers produced by the novel method had homogeneous microstructure distribution and fine grains. The geometrical dimensions of each layer can be effectively controlled by regulating the travel speed of the torch. The wide-range adjustable heat input can effectively control the state of the metallic formation, making it possible to realize an accurate control of the microstructure and properties.Graphical abstractGraphical abstract for this article
  • Multi-scale Design and Fabrication of the Trabeculae Pavilion
    • Abstract: Publication date: Available online 2 March 2019Source: Additive ManufacturingAuthor(s): Roberto Naboni, Luca Breseghello, Anja Kunic Building on a large scale with Additive Manufacturing (AM) is one of the biggest manufacturing challenges of our time. In the last decade, the proliferation of 3D printing has allowed architects and engineers to imagine and develop constructions that can be produced additively. However, questions about the convenience of using this technology, and whether additive large-scale constructions can be feasible, efficient and sustainable are still open. In this research 3D printing is considered not as a question, but as an answer to the increasing scarcity of material resources in the construction industry. This paper illustrates the overarching process from concept to the realisation of the Trabeculae Pavilion, a load-responsive architecture that is entirely designed and optimized for 3D printing, using Fused Filament Fabrication (FFF) - one of the most cost-effective additive techniques of production. The research methodology is based on a multi-scale computational workflow that integrates several aspects, such as material testing, bio-inspired design algorithms, multi-criteria optimization, and production management. The work culminates in the construction process of a full-scale architectural prototype; an anticlastic shell that features a cellular structure with increased material and structural efficiency.
  • Analysis of material aging and the influence on the mechanical properties
           of polyamide 12 in the Multi Jet Fusion process
    • Abstract: Publication date: Available online 2 March 2019Source: Additive ManufacturingAuthor(s): Julius Riedelbauch
  • Mechanical and Material Properties of Castings produced via 3d printed
    • Abstract: Publication date: Available online 2 March 2019Source: Additive ManufacturingAuthor(s): Dean Snelling, Christopher Williams, Alan Druschitz Additive manufacture of sand molds via binder jetting enables the casting of complex metal geometries. Various material systems have been created for 3D printing of sand molds; however, a formal study of the materials’ effects on cast products has not yet been conducted. In this paper the authors investigate potential differences in material properties (microstructure, porosity, mechanical strength) of A356 – T6 castings resulting from two different commercially available 3D printing media. In addition, the material properties of cast products from traditional “no-bake” silica sand is used as a basis for comparison of castings produced by the 3D printed molds.
  • Pilot Feedback Electronic Imaging at Elevated Temperatures and its
           Potential for In-Process Electron Beam Melting Monitoring
    • Abstract: Publication date: Available online 1 March 2019Source: Additive ManufacturingAuthor(s): Hay Wong, Derek Neary, Eric Jones, Peter Fox, Chris Sutcliffe Electron Beam Melting (EBM) is an increasingly used Additive Manufacturing (AM) technique employed by many industrial sectors, including the medical device and aerospace industries. The application of this technology is, however, challenged by the lack of process monitoring and control system that underpins process repeatability and part quality reproducibility. An electronic imaging system prototype has been developed to serve as an EBM monitoring equipment, the capabilities of which have been verified at room temperature and at 320 + 10 °C. Nevertheless, in order to fully assess the applicability of this technique, electronic imaging needs to be conducted at a range of elevated temperatures to fully understand the influence of temperature on electronic image quality. Building on top of the previous electronic imaging trials at room temperature, this paper disseminates the essential step changes to allow high temperature electronic imaging: (1) modification of a signal amplifier to deal with high electron beam current during electron beam heating, and (2) design of an open-source electron beam heating algorithm to maximise flexibility for user-defined heating strategy. In this paper, electronic imaging pilot trials at elevated temperatures, ranging from room temperature to 650°C, were carried out. Image quality measure Q of the digital electron images was evaluated, and the influence of temperature was investigated. In this study, raw electronic images generated at higher temperatures had greater Q values, i.e. better global image quality. It has been demonstrated that, for temperatures between 30°C-650°C, the influence of temperature on electronic image quality was not adversely affecting the visual clarity of image features. It is thus envisaged that the prototype has a potential to contribute to in-process EBM monitoring, and this paper has served as a crucial precursor to the ultimate goal of carrying out electronic imaging under real EBM building condition.
  • Micromechanical Modeling of Irreversible Thermal Strain
    • Abstract: Publication date: Available online 27 February 2019Source: Additive ManufacturingAuthor(s): Tone D’Amico, Connor Barrett, Joseph Presing, Amy M. Peterson Warping and delamination in material extrusion additive manufacturing (MatEx) parts are well documented and irreversible thermal strain (ITε) has also recently been reported. As parts are built up as a collection of roads, they are analogous to fiber reinforced composites. However, the lack of bonding between the matrix, air, and the reinforcing phase, polymer roads, necessitates the development of a micromechanical model for these parts. In this work, a micromechanical model for MatEx parts is developed to describe bulk part behavior that incorporates void fraction, road morphology, and bonding between and within layers. Previous work suggested ITε occurred within roads. Combining stress accumulation within roads with the micromechanical model successfully predicted ITε and provided a rationale for ITε dependence on both layer thickness and raster angle. These results show ITε can be predicted and, therefore, controlled, making MatEx part annealing more feasible and opening the possibility of one-way shape memory in parts. Additionally, the micromechanical model developed can be used to explain bonding limitations in MatEx based on road and bond geometry.
  • Real-time process monitoring of core shifts during metal casting with
           wireless sensing and 3D sand printing
    • Abstract: Publication date: Available online 26 February 2019Source: Additive ManufacturingAuthor(s): Jason Walker, Andrew Prokop, Chad Lynagh, Brian Vuksanovich, Brett Conner, Kirk Rogers, Jerry Thiel, Eric MacDonald In this work, real-time in-process monitoring of core motion in metal castings is demonstrated though the use of two emerging technologies. 3D sand printing (3DSP) is a binder jetting additive manufacturing process that is quickly manifesting itself as a technological disrupter in the metal casting industry. Based on its direct digital manufacturing principle, 3DSP enables complex mold and core design freedom that has been previously unavailable to foundry engineers. In addition, the miniaturization and affordability of electronics and sensing equipment is rapidly accelerating. Here, these two shifting paradigms are leveraged together. An experimental casting and mold were designed in this research to demonstrate and evaluate wireless sensing of core shifts. With the use of 3D sand printing, precisely sized and located pockets were manufactured inside of cores. Miniature wireless Bluetooth sensors capable of measuring acceleration and rotation were then embedded inside the cores. From these, high fidelity data was captured wirelessly from the sensors during the casting process. With strategically designed core prints designed to allow varying levels of core motion, it is shown that core shifts can be measured and discriminated during casting in real time.
  • Heterogeneous Materials Design in Additive Manufacturing: Model
           Calibration and Uncertainty-Guided Model Selection
    • Abstract: Publication date: Available online 25 February 2019Source: Additive ManufacturingAuthor(s): David Garcia, Ziling Wu, Jee Yun Kim, Hang Z. Yu, Yunhui Zhu Multi-material additive manufacturing enables high-performance heterogeneous design at the mesoscale, through which bulk parts can be engineered to adapt to complex loading conditions. The optimization of multi-material parts relies on accurate forward prediction, which is challenging to achieve owing to the complex processing conditions in additive manufacturing and the resultant uncertainties in material properties. To address these limitations, here we present a new model calibration and model selection framework based on the high dimensional, local-scale deformation data. By matching the pixel-level deformation data from digital image correlation experiments and constitutive modeling, the presented framework enables more accurate prediction and significant reduction of the prediction uncertainties, as compared to the single material calibration approach that is widely used in additive manufacturing. In turn, this enables quantitative comparison of the candidate models, so the most accurate and computationally efficient constitutive model can be selected for forward prediction in heterogeneous material design. The advantages of the framework are demonstrated using a multi-polymer system manufactured by dual-extrusion additive manufacturing, which consists of two constituent materials with dramatically different deformation behaviors.
  • Introduction to the Design Rules for Metal Big Area Additive Manufacturing
    • Abstract: Publication date: Available online 25 February 2019Source: Additive ManufacturingAuthor(s): Clayton Greer, Andrzej Nycz, Mark Noakes, Brad Richardson, Brian Post, Thomas Kurfess, Lonnie Love Wire feed metal additive manufacturing offers advantages, such as large build volumes and high build rates, over powder bed and blown powder techniques, but it has its own disadvantages, i.e., lower feature resolution and bead morphology control issues. A new wire feed metal additive manufacturing process called Metal Big Area Additive Manufacturing (mBAAM) uses a Gas Metal Arc Weld system on an articulated robot arm to increase build volume and deposition rate in comparison to powder bed techniques. The high deposition rate implies a low-resolution process; therefore, parts designed for mBAAM must incorporate the use of machining to achieve certain features. This paper presents an introduction to how design rules, such as overhang constraint, large weld bead thickness, and support structure, for mBAAM interact in the context of an excavator arm case study, which was designed using topology optimization.
  • Multiscale study of different types of interface of a buffer material in
           powder-based directed energy deposition: example of Ti6Al4V/Ti6Al4V - Mo /
           Mo - Inconel 718
    • Abstract: Publication date: Available online 23 February 2019Source: Additive ManufacturingAuthor(s): Amélie Thiriet, Catherine Schneider-Maunoury, Pascal Laheurte, Didier Boisselier, Laurent WeissABSTRACTWhen it is difficult to deposit a material A on a material B, it is possible to create a Functionally Graded Material (FGM) using a buffer material between them to avoid the appearance of defects. The literature shows that it is very difficult, nay impossible, to have an efficient metallurgical bond between Ti6Al4V and Inconel-Mo alloys without cracks, porosities or delamination. A buffer material is therefore needed (here 25% Ti6Al4V – 75% Mo) and the fine analysis of the two interfaces thus created makes it possible to define the relevance of the choice of the buffer. Moreover, the understanding of the phenomena taking place at the interface allows the preservation of the structural integrity of a FGM made by additive manufacturing. CLAD® powder-based directed energy deposition allows the building of parts containing FGM and/or buffer materials directly during the process. The study of the interfaces at both sides of the buffer material is essential. In this paper, the first interface 100 Ti6Al4V / 25 Ti6Al4V – 75 Mo (in wt%) is smooth, suggesting that there has been diffusion between both alloys. The second one, 25 Ti6Al4V – 75 Mo / 30 Inconel 718 – 70 Mo, contains numerous exotic structures between both alloys. For such a sharp interface, we show in this paper that a microscopic study is not sufficient, but a finer scale is necessary to have a good metallurgical insight. Thus, EDS, TKD and X-ray crystallography were performed right on this interface and revealed three main structures: a hexagonal matrix, a cubic structure and an ordered hexagonal one. The hexagonal matrix appears to consist of Ni3Ti and the ordered hexagonal one of NiMo.
  • A method for predicting geometric characteristics of polymer deposition
           during fused-filament-fabrication
    • Abstract: Publication date: Available online 23 February 2019Source: Additive ManufacturingAuthor(s): Michael Hebda, Claire McIlroy, Ben Whiteside, Fin Caton-Rose, Phil Coates In recent years 3D printing has gained popularity amongst industry professionals and hobbyists alike, with many new types of Fused Filament Fabrication (FFF) apparatus types becoming available on the market. A massively overlooked component of FFF is the requirement for a simple method to calculate the geometries of polymer depositions extruded during the FFF process. Manufacturers have so far achieved adequate methods to calculate tool-paths through so called slicer software packages which calculate the required velocities of extrusion from prior knowledge and data. Presented here is a method for obtaining a series of equations for predicting height, width and cross-sectional area values for given processing parameters within the FFF process for initial laydown on to a glass surface.
  • Additive Manufacturing of Ceramics from Preceramic Polymers: A Versatile
           Stereolithographic Approach Assisted by Thiol-Ene Click Chemistry
    • Abstract: Publication date: Available online 22 February 2019Source: Additive ManufacturingAuthor(s): Xifan Wang, Franziska Schmidt, Dorian Hanaor, Paul H. Kamm, Shuang Li, Aleksander Gurlo Here we introduce a versatile stereolithographic route to produce three different kinds of Si-containing thermosets that yield high performance ceramics upon thermal treatment. Our approach is based on a fast and inexpensive thiol-ene free radical addition that can be applied for different classes of preceramic polymers with carbon-carbon double bonds. Due to the rapidity and efficiency of the thiol-ene click reactions, this additive manufacturing process can be effectively carried out using conventional light sources on benchtop printers. Through light initiated cross-linking, the liquid preceramic polymers transform into stable infusible thermosets that preserve their shape during the polymer-to-ceramic transformation. Through pyrolysis the thermosets transform into glassy ceramics with uniform shrinkage and high density. The obtained ceramic structures are nearly fully dense, have smooth surfaces, and are free from macroscopic voids and defects. A fabricated SiOC honeycomb was shown to exhibit a significantly higher compressive strength to weight ratio in comparison to other porous ceramics.Graphical abstractGraphical abstract for this articleSchematic representation of the stereolithographic additive manufacturing of preceramic polymers into intricately patterned thermosets assisted by thiol-ene click chemistry and their subsequent conversion into ceramics
  • Binder Jetting of the AlCoCrFeNi Alloy
    • Abstract: Publication date: Available online 20 February 2019Source: Additive ManufacturingAuthor(s): Dennis Karlsson, Greta Lindwall, Andreas Lundbäck, Mikael Amnebrink, Magnus Boström, Lars Riekehr, Mikael Schuisky, Martin Sahlberg, Ulf Jansson High density components of an AlCoCrFeNi alloy, often described as a high-entropy alloy, were manufactured by binder jetting followed by sintering. Thermodynamic calculations using the CALPHAD approach show that the high-entropy alloy is only stable as a single phase in a narrow temperature range below the melting point. At all other temperatures, the alloy will form a mixture of phases, including a sigma phase, which can strongly influence the mechanical properties. The phase stabilities in built AlCoCrFeNi components were investigated by comparing the as-sintered samples with the post-sintering annealed samples at temperatures between 900 °C and 1300 °C. The as-sintered material shows a dominant B2/bcc structure with additional fcc phase in the grain boundaries and sigma phase precipitating in the grain interior. Annealing experiments between 1000 °C and 1100 °C inhibit the sigma phase and only a B2/bcc phase with a fcc phase is observed. Increasing the temperature further suppresses the fcc phase in favor for the B2/bcc phases. The mechanical properties are, as expected, dependent on the annealing temperature, with the higher annealing temperature giving an increase in yield strength from 1203 MPa to 1461 MPa and fracture strength from 1996 MPa to 2272 MPa. This can be explained by a hierarchical microstructure with nano-sized precipitates at higher annealing temperatures. The results enlighten the importance of microstructure control, which can be utilized in order to tune the mechanical properties of these alloys. Furthermore, an excellent oxidation resistance was observed with oxide layers with a thickness of less than 5 µm after 20 h annealing at 1200 °C, which would be of great importance for industrial applications.
  • All-printed Multilayer High Voltage Capacitors with Integrated Processing
    • Abstract: Publication date: Available online 19 February 2019Source: Additive ManufacturingAuthor(s): James O. Hardin, Christopher A. Grabowski, Matthew Lucas, Michael F. Durstock, J. Daniel Berrigan Template-free 3D printing of electronic devices has the potential to broaden electronics integration to include complex integrated form factors, but success requires precise, adaptive control over materials processing. The development of such manufacturing technologies requires exploration of new combinations of ink sets, printing techniques, and automation strategies. In this work, solution-cast direct-write (SC-DW) was used to print poly(methyl methacrylate) (PMMA) dielectric films with breakdown fields of 790 V/µm, similar to commercially available biaxial-oriented polypropylene (BOPP) films. Furthermore, a complementary composite ink for printing conductive features was developed with conductivities of ˜10,000 S cm-1. A closed-loop feedback system that links deposition with characterization to enable µm-precision deposition for over 20 h without human involvement. This closed-loop control scheme led to both single- and double-layer high-voltage capacitors to be 3D printed with capacitances as large as 314 pF (at 1 kHz) and breakdown voltages over 1,000 V, which is significant step towards repeatable template-free, 3D printing of electronics for rapid prototyping of multifunctional devices.Graphical abstractGraphical abstract for this articleA process for 3D printing multimaterial, multilayer electronics with high performance is demonstrated using high voltage capacitors as a model system. Dielectric and conductive materials are characterized independently then combined together into a functional device which is then characterized. The resulting capacitors have excellent capacitance, (322 pF) and breakdown voltage (1,000 V) relative to literature.
  • Synchronized Multi-Spot Scanning Strategies for the Laser Powder Bed
           Fusion Process
    • Abstract: Publication date: Available online 19 February 2019Source: Additive ManufacturingAuthor(s): Chun-Yu Tsai, Chung-Wei Cheng, An-Chen Lee, Mi-Ching Tsai The laser powder bed fusion (LPBF) process can produce parts with complex internal geometries that cannot be easily manufactured using a material removal process. However, owing to the different heat transfer efficiencies of a laser melting process, the optimal process parameters are limited to a small range. This study used galvanometric scanner technology and a diffractive optical element (DOE) to build an experimental multi-spot LPBF system. Adjustable characteristics were the angle and the lateral distance between spots. An adjustable multi-spot method was used to modulate the temperature field on the powder bed and enhance the processing quality and throughput. The results from the synchronized three-spot method using different scanning strategies improved the layer surface roughness Ra by 3.2 μm. Moreover, the scanning time was decreased by 38.1% of the single-spot method.
  • Modification of Mechanical Properties and Resolution of Printed
           Stereolithographic Objects through RAFT Agent Incorporation
    • Abstract: Publication date: Available online 18 February 2019Source: Additive ManufacturingAuthor(s): Brian J. Green, C. Allan Guymon Stereolithography (SL) is an additive manufacturing technique that uses light to cure liquid resins into thin layers and fabricate 3-dimensional objects layer by layer. SL is of high interest for small-volume manufacturing and rapid prototyping because of its ability to relatively quickly create objects with intricate 100 µm or smaller features. However, widespread adoption of SL faces a number of obstacles including unsuitable thermomechanical properties, anisotropic properties, and limited resolution and fidelity. In this work, we incorporate a reversible addition-fragmentation chain transfer (RAFT) agent into a glassy acrylate formulation to modify mechanical properties and improve resolution of objects printed using digital light processing (DLP) SL. Incorporating a small amount of a trithiocarbonate RAFT agent into the formulation leads to increased elongation and toughness accompanied by a small decrease in tensile modulus. To determine anisotropic properties of DLP SL, samples were printed in “horizontal” or “vertical” directions, where the long axis of the sample was printed in the x-axis or z-axis, respectively. RAFT samples printed in a vertical orientation exhibit a higher modulus than non-RAFT controls prior to post-cure in addition to a similar modulus with increased toughness upon UV post-cure due to the living/controlled nature of RAFT polymerization. Furthermore, incorporating a RAFT agent into the formulation allows significantly higher fidelity printing of a broad range of positive and negative features as small as 100 µm. The RAFT formulation allows objects to be printed with significantly better fidelity than non-RAFT formulations, even when a radical scavenger is incorporated to mimic reaction rates observed from the RAFT formulation. Additionally, the RAFT agent significantly increases the critical energy parameter determined from the SL working curve, indicating an increase in gel point conversion. This work demonstrates the benefits of using controlled/living polymerization in a highly cross-linked acrylate system to improve toughness, modify anisotropic properties, and print high-fidelity features with enhanced properties in 3D printed materials.
  • Additively manufactured 316L stainless steel with improved corrosion
           resistance and biological response for biomedical applications
    • Abstract: Publication date: Available online 16 February 2019Source: Additive ManufacturingAuthor(s): M.J.K. Lodhi, K.M. Deen, M.C. Greenlee-Wacker, Waseem Haider Enhancing the corrosion resistance and improving the biological response to 316 L stainless steel is a long-standing and active area of biomedical research. Here, we analyzed the structure and corrosion tendency of selective laser melted-additively manufactured (AM) 316 L stainless steel (AM 316L SS) and its wrought counterpart. SEM analysis showed a fine (500–800 nm) interconnected sub-granular structure for the AM 316L SS, but a polygonal coarse-grained structure for the wrought sample. Relative to the wrought sample, the AM 316L SS also exhibited a higher charge transfer resistance (approx. one order of magnitude) and higher breakdown potential (˜1000 mV vs. SCE) when tested in biological electrolytes, which included human serum, PBS, and 0.9 M NaCl. A higher pitting resistance (extended passive region) and improved stability of the AM 316L SS was attributed to its dense structure of oxide film and refined microstructure. Finally, material compatibility with pre-osteoblasts was analyzed. Large cytoplasmic extension of osteoblast cells and retention of stiller morphology was observed when cells were cultured on the AM 316L SS as compared to its wrought counterpart, suggesting that the AM 316L SS was a better substrate for cell spreading and differentiation. The differentiation of cultured cells was further validated by western blot for Runx2. Runx2, an anti–proliferative marker indicative of differentiation, was equivalent in cells cultured on either samples, but overall more cells were present on the AM 316L SS. Given its higher corrosion resistance and ability to support osteoblast adherence, spreading and differentiation, the AM 316L SS has potential for use in the biomedical industry.
  • Selective Laser Sintering and Multi Jet Fusion: process-induced
           modification of the raw materials and analyses of parts performance
    • Abstract: Publication date: Available online 14 February 2019Source: Additive ManufacturingAuthor(s): Francesco Sillani, Rob G. Kleijnen, Marc Vetterli, Manfred Schmid, Konrad Wegener Additive Manufacturing (AM) is a rapidly expanding framework of production technologies evolving in different directions, following the needs of different industries. Among powder bed fusion technologies, one of the main branches of AM, Selective Laser Sintering (SLS) is the second oldest one. In the last few years, a direct rival has emerged: Multi Jet Fusion (MJF). The purpose of this work is to compare these processes throughout a systematic analysis of powder and final parts made of commercially available polyamide 12 (PA12). Differences have been spotted both on the molecular and powder scale, with end capping of the MJF feedstock together with different thermal properties of the new and recycled materials. On the other hand, flowing properties are similar among the two virgin and recycled powders, with only a significant change in the fraction of fines for SLS material. The parts produced through SLS exhibit higher Young's modulus but lower elongation at break and ultimate tensile strength if compared to the ones obtained using MJF. This confirms once more that the occurrence of postcondensation has a profound influence on the final properties. Also Charpy impact strength according to ISO 179 has been tested, confirming the literature data for SLS, but also showing higher strength in the out-of-plane direction for un-notched specimens coming from MJF. Finally, the evaluation of advanced area roughness parameters such as surface roughness, skewness and kurtosis according to ISO 25178 allows the ascertainment of subtle differences arising in parts with different positioning on the build platform, possibly due to the inks employed in the MJF process.
  • Automatic Fault Detection for Laser Powder-Bed Fusion using
           Semi-Supervised Machine Learning
    • Abstract: Publication date: Available online 11 February 2019Source: Additive ManufacturingAuthor(s): Ikenna A. Okaro, Sarini Jayasinghe, Chris Sutcliffe, Kate Black, Paolo Paoletti, Peter L. Green Risk-averse areas such as the medical, aerospace and energy sectors have been somewhat slow towards accepting and applying Additive Manufacturing (AM) in many of their value chains. This is partly because there are still significant uncertainties concerning the quality of AM builds.This paper introduces a machine learning algorithm for the automatic detection of faults in AM products. The approach is semi-supervised in that, during training, it is able to use data from both builds where the resulting components were certified and builds where the quality of the resulting components is unknown. This makes the approach cost efficient, particularly in scenarios where part certification is costly and time consuming.The study specifically analyses Laser Powder-Bed Fusion (L-PBF) builds. Key features are extracted from large sets of photodiode data, obtained during the building of 49 tensile test bars. Ultimate tensile strength (UTS) tests were then used to categorise each bar as ‘faulty’ or ‘acceptable’. Using a variety of approaches (Receiver Operating Characteristic (ROC) curves and 2-fold cross-validation), it is shown that, despite utilising a fraction of the available certification data, the semi-supervised approach can achieve results comparable to a benchmark case where all data points are labelled. The results show that semi-supervised learning is a promising approach for the automatic certification of AM builds that can be implemented at a fraction of the cost currently required.
  • Comparison of the fatigue strength between additively and conventionally
           fabricated tool steel 1.2344
    • Abstract: Publication date: Available online 10 February 2019Source: Additive ManufacturingAuthor(s): R. Dörfert, J. Zhang, B. Clausen, H. Freiße, J. Schumacher, F. Vollertsen The residual porosity and surface roughness of metal materials generated via additive manufacturing are generally regarded as the major influence factors on the fatigue strength. The mechanical properties of specimens out of tool steel 1.2344 were investigated. Tensile strength and hardness achieved results in the range of conventionally fabricated parts, whereas a significantly lower fatigue strength was observed. Cracks were induced by the present cavities as well as in the steel matrix. Further investigations of the oxygen content showed a high oxygen content of 570 ppm homogeneously distributed inside the specimens potentially limiting the strength of the matrix itself.Graphical Graphical abstract for this article
  • A Robotic Cell for Performing Sheet Lamination-based Additive
    • Abstract: Publication date: Available online 6 February 2019Source: Additive ManufacturingAuthor(s): Prahar M. Bhatt, Ariyan M. Kabir, Max Peralta, Hugh A. Bruck, Satyandra K. Gupta Many applications require structures composed of layers of heterogeneous materials and prefabricated components embedded between the layers. The existing additive manufacturing process based on layered object manufacturing is not able to handle multiple layer materials and cannot embed prefabricated components. Moreover, the existing process imposes restrictions on the material options. This significantly limits the type of heterogeneous structures that can be manufactured using traditional additive manufacturing. This paper presents an extension of sheet lamination object manufacturing process by using a robotic cell to perform the sheet manipulation and handling. It makes the following three advances: (1) enabling the use of multi-material layers and inclusion of prefabricated components between the layers, (2) developing an algorithmic foundation to facilitate automated generation of robot instructions, and (3) identifying the relevant process constraints related to speed, accuracy, and strength. We demonstrate the system capabilities by using three case studies.
  • Design and direct additive manufacturing of three-dimensional surface
           micro-structures using material jetting technologies
    • Abstract: Publication date: Available online 28 January 2019Source: Additive ManufacturingAuthor(s): Jessirie Dilag, Tiffany Chen, Sheng Li, Stuart A. Bateman The ability to directly print 3D microstructures across the surface of large dimension substrates opens up numerous possibilities not feasible with conventional 2D or 2.5D printing or coating techniques. Demonstrated herein is a method to print 3D microstructures onto clear poly(methyl methacrylate) (PMMA) plates using material jetting technologies. Contact angle and profilometry analysis indicated that the VeroCyan™ photopolymer had enhanced wetting of the PMMA surface leading to greater droplet spreading affecting the geometries printed compared to VeroCyanTM integrated models. Strategies to manipulate the interfacial interactions and hence adhesion of the VeroCyan™ photopolymer were investigated by varying PMMA surface free energy through physio-chemical and chemical techniques including (i) corona discharge, followed by post-treatments with 3-(trimethoxysilyl)propyl methacrylate, polyethyleneimine graft chemicals, and (ii) plasma treatments with air and plasma polymerisation of 1,7-octadiene. The surface chemistry and wetting behaviour played a crucial role in influencing interfacial interactions with the VeroCyan™ photopolymer hence its adhesion to the PMMA surface.Graphical Graphical abstract for this article
  • Laser strip cladding for large area metal deposition
    • Abstract: Publication date: Available online 28 January 2019Source: Additive ManufacturingAuthor(s): Jari Tuominen, Marc Kaubisch, Sebastian Thieme, Jonne Näkki, Steffen Nowotny, Petri Vuoristo Directed energy deposition (DED) processes rely frequently on metallic powder and wire feedstock materials. Several grades of metallic strips are, however, commercially available but not yet largely utilized in DED. This paper introduces newly developed laser strip cladding process, which can be used for surfacing, repair and additive manufacturing. Cladding tests consisted of single-layer single- and multi-bead tests on planar and round bar type base materials using a 30 mm wide solid Alloy 625 strip. The results showed that with 8 kW laser power 34 mm wide and ˜2 mm thick single beads on steel can be produced with low dilution and fusion bond with high deposition (8 kg/h) rates. In multi-bead tests coverage rates of 0.45 m2/h were reached. Corrosion performance of clad deposit was influenced by inhomogeneous distribution of intermixed iron from the base material on test surface. In addition to high productivity, the developed process takes the advantage of the large build volume (>1 m3) and complete material utilization as well as the clean process conditions.
  • Predictive process parameter selection for Selective Laser Melting
           Manufacturing: applications to high thermal conductivity alloys
    • Abstract: Publication date: Available online 3 December 2018Source: Additive ManufacturingAuthor(s): Priyanshu Bajaj, Jonathan Wright, Iain Todd, Eric A. Jägle There is growing interest in Laser Powder Bed Fusion (L-PBF) or Selective Laser Melting (SLM) manufacturing of high conductivity metals such as copper and refractory metals. SLM manufacturing of high thermal conductivity metals is particularly difficult. In case of refractory metals, the difficulty is amplified because of their high melting point and brittle behaviour. Rapid process development strategies are essential to identify suitable process parameters for achieving minimum porosities in these alloys, yet current strategies suffer from several limitations. We propose a simple approach for rapid process development using normalized process maps. Using plots of normalized energy density vs. normalized hatch spacing, we identify a wide processability window. This is further refined using analytical heat transfer models to predict melt pool size. Final optimization of the parameters is achieved by experiments based on statistical Design of Experiments concepts. In this article we demonstrate the use of our proposed approach for development of process parameters (hatch spacing, layer thickness, exposure time and point distance) for SLM manufacturing of molybdenum and aluminium. Relative densities of 97.4% and 99.7% are achieved using 200 W pulsed laser and 400 W continuous laser respectively, for molybdenum and aluminium, demonstrating the effectiveness of our approach for SLM processing of high conductivity materials.Graphical abstractGraphical abstract for this article
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
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