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Publisher: Elsevier   (Total: 3161 journals)

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Showing 1 - 200 of 3161 Journals sorted alphabetically
A Practical Logic of Cognitive Systems     Full-text available via subscription   (Followers: 9)
AASRI Procedia     Open Access   (Followers: 15)
Academic Pediatrics     Hybrid Journal   (Followers: 35, SJR: 1.655, CiteScore: 2)
Academic Radiology     Hybrid Journal   (Followers: 24, SJR: 1.015, CiteScore: 2)
Accident Analysis & Prevention     Partially Free   (Followers: 98, SJR: 1.462, CiteScore: 3)
Accounting Forum     Hybrid Journal   (Followers: 27, 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: 418, 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: 266, SJR: 3.263, CiteScore: 6)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.504, CiteScore: 1)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.542, CiteScore: 1)
Acta Oecologica     Hybrid Journal   (Followers: 12, SJR: 0.834, CiteScore: 2)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription  
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 3, 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: 6, 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: 14, 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: 8, 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: 163, 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: 8, SJR: 0.277, CiteScore: 1)
Advances in Agronomy     Full-text available via subscription   (Followers: 15, 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: 33, 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: 13)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 27, 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: 19, 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: 12)
Advances in Digestive Medicine     Open Access   (Followers: 9)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 7)
Advances in Drug Research     Full-text available via subscription   (Followers: 25)
Advances in Ecological Research     Full-text available via subscription   (Followers: 44, SJR: 2.524, CiteScore: 4)
Advances in Engineering Software     Hybrid Journal   (Followers: 28, 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: 46, 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: 60, SJR: 0.591, CiteScore: 2)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 16)
Advances in Genetics     Full-text available via subscription   (Followers: 18, 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: 8, 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: 3)
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: 24, 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: 65)
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: 404, 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: 34, SJR: 2.208, CiteScore: 4)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 18)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 14)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 2.262, CiteScore: 5)
Advances in Water Resources     Hybrid Journal   (Followers: 47, SJR: 1.551, CiteScore: 3)
Aeolian Research     Hybrid Journal   (Followers: 6, SJR: 1.117, CiteScore: 3)
Aerospace Science and Technology     Hybrid Journal   (Followers: 351, 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: 465, 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: 42, 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: 57, 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: 1, SJR: 0.604, CiteScore: 3)
Alexandria J. of Medicine     Open Access   (Followers: 1, SJR: 0.191, CiteScore: 1)
Algal Research     Partially Free   (Followers: 10, 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: 53, SJR: 3.267, CiteScore: 4)
American J. of Cardiology     Hybrid Journal   (Followers: 58, 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: 10)
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: 221, 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: 28, SJR: 2.139, CiteScore: 4)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 29, SJR: 2.164, CiteScore: 4)
American J. of Surgery     Hybrid Journal   (Followers: 38, 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: 18, 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: 42, SJR: 1.512, CiteScore: 5)
Analytical Biochemistry     Hybrid Journal   (Followers: 186, 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: 12)
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: 203, SJR: 1.58, CiteScore: 3)

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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  [3161 journals]
  • 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.
       
  • Estimation of Part-to-Powder Heat Losses as Surface Convection in Laser
           Powder Bed Fusion
    • Abstract: Publication date: Available online 12 February 2019Source: Additive ManufacturingAuthor(s): Chao Li, Michael F. Gouge, Erik R. Denlinger, Jeff E. Irwin, Pan Michaleris Thermal modeling of additive manufacturing processes such as Laser Powder Bed Fusion is able to calculate a thermal history of a build. This simulated thermal history can in turn be used as an input to further simulate temperature related characteristics such as residual stress, distortion, microstructure, lack of fusion porosity, and hot spots. In order to estimate the heat loss to the powder bed during the process, convective heat transfer is widely used as thermal boundary condition in finite element modeling of Laser Powder Fusion processes. However, this convection coefficient is usually selected based on empirical estimation or model tuning. In this work, FEA models of the part and surrounding powder are used as a reference to determine the surface convection BC's for modeling the part only. Seven types of commonly used AM materials with a wide range of thermal conductivities were studied for better testing of the conductivity dependency of the convection coefficient. The convection coefficient values, which predict similar thermal history as the powder model, are found to be a function of thermal conductivity of the deposited material and the cross-sectional thickness of the part feature. A new thickness dependent convection boundary condition is proposed and found to be capable of predicting much closer thermal history to the powder model. These newly developed boundary conditions improve the peak temperature prediction accuracy by 36% while running in 1/4th of the time as the powder model.
       
  • 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
       
  • Residual stress and distortion of rectangular and S-shaped Ti-6Al-4V parts
           by Directed Energy Deposition: Modelling and experimental calibration
    • Abstract: Publication date: March 2019Source: Additive Manufacturing, Volume 26Author(s): Xufei Lu, Xin Lin, Michele Chiumenti, Miguel Cervera, Yunlong Hu, Xianglin Ji, Liang Ma, Haiou Yang, Weidong Huang Residual stresses and distortion in Additive Manufactured (AM) parts are two key obstacles which seriously hinder the wide application of this technology. Nowadays, understanding the thermomechanical behavior induced by the AM process is still a complex task which must take into account the effects of both the process and the material parameters, the microstructure evolution as well as the pre-heating strategy. One of the challenges of this work is to increase the complexity of the geometries used to study the thermomechanical behavior induced by the AM process. The reference geometries are a rectangular and a S-shaped structures made of 44-layers each. The samples have been fabricated by Directed Energy Deposition (DED). In-situ thermal and distortion histories of the substrate are measured in order to calibrate the 3D coupled thermo-mechanical model. Once the numerical results showed a good agreement with the temperature measurements, the validated model has been used to predict the residual stresses and distortions. Different process parameters have been analyzed to study their sensitivity to the process assessment. Different preheating strategies have been also analyzed to check their effectiveness on the mitigation of both distortions and residual stresses. Finally, some simplifications of the actual scanning sequence are proposed to reduce the computational cost without loss of the accuracy of the simulation framework.
       
  • A Robotic Cell for Performing Sheet Lamination-based Additive
           Manufacturing
    • 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.
       
  • Calibration of galvanometric scan heads for additive manufacturing with
           machine assembly defects consideration
    • Abstract: Publication date: Available online 5 February 2019Source: Additive ManufacturingAuthor(s): K. Godineau, S. Lavernhe, C. Tournier The calibration of additive manufacturing machines using scanning heads in processes such as Laser Powder Bed Fusion (LPBF) and vat photopolymerization is an iterative and time-consuming process often based on limited physical models. Indeed, the relationship between the laser spot position in the work plane and the actuators position (galvanometers) is achieved by interpolating correction tables experimentally determined. In this paper, representative geometrical models of the real system are established in order to reduce the time required to obtain the final correction tables. For this purpose, a geometrical model is developed with assembly defects consideration. This model is used in a process of defects identification to obtain a virtual machine representative of the real system and thus directly generates the final correction tables. The geometrical model thereby developed is used to quantify the impact of assembly defects on the laser spot position, to compensate them and to reduce the calibration time of an additive manufacturing machine.
       
  • Effect of Wire and Arc Additive Manufacturing (WAAM) Process Parameters on
           Bead Geometry and Microstructure
    • Abstract: Publication date: Available online 1 February 2019Source: Additive ManufacturingAuthor(s): Malcolm Dinovitzer, Xiaohu Chen, Jeremy Laliberte, Xiao Huang, Hanspeter Frei This paper discusses the effects of process parameters in TIG based WAAM for specimens created using Hastelloy X alloy (Haynes International) welding wire and 304 stainless-steel plate as the substrate. The Taguchi method and ANOVA were used to determine the effects of travel speed, wire feed rate, current, and argon flow rate on the responses including bead shape and size, bead roughness, oxidation levels, melt through depth, and the microstructure. Travel speed and current were found to have the largest effect on the responses. Increasing travel speed or decreasing current caused a decrease in melt through depth and an increase in roughness. Printing strategies were tested using specimens of multiple layers and no significant difference was found between printing layers in the same direction and printing layers in alternating directions. No observable interface between the layers was present suggesting a complete fusion between layers with no oxidation. Three distinct zones were identified within the three- and eight-layer samples. The zones were characterized by the size and distribution of the molybdenum carbide formations within the matrix grain formations.
       
  • Improvement in build-direction thermal conductivity in extrusion-based
           polymer additive manufacturing through thermal annealing
    • Abstract: Publication date: Available online 31 January 2019Source: Additive ManufacturingAuthor(s): Hardikkumar Prajapati, Divya Chalise, Darshan Ravoori, Robert M. Taylor, Ankur Jain While additive manufacturing offers significant advantages compared to traditional manufacturing technologies, deterioration in thermal and mechanical properties compared to properties of the underlying materials is a serious concern. In the context of polymer extrusion based additive manufacturing, post-process approaches, such as thermal annealing have been reported for improving mechanical properties based on reptation of polymer chains and enhanced filament-to-filament adhesion. However, there is a lack of similar work for improving thermal properties such as thermal conductivity. This paper reports significant enhancement in build-direction thermal conductivity of polymer extrusion based parts as a result of thermal annealing. Over 150% improvement is observed when annealed at 135 °C for 96 hours. The effect of annealing temperature and time on thermal conductivity enhancement is investigated through experiments. A theoretical model based on Arrhenius kinetics for neck growth and a heat transfer model for the consequent impact on inter-layer thermal contact resistance is developed. Predicted thermal conductivity enhancement is found to be in good agreement with experimental data for a wide range of annealing temperature and time. The theoretical model may play a key role in developing practical thermal annealing strategies that account for the multiple constraints involved in annealing of polymer parts. This work may facilitate the use of polymer extrusion additive manufacturing for parts that are required to withstand thermal loads.
       
  • Heat Source Management in Wire-Arc Additive Manufacturing Process for
           Al-Mg and Al-Si Alloys
    • Abstract: Publication date: Available online 30 January 2019Source: Additive ManufacturingAuthor(s): Kohei Oyama, Spyros Diplas, Mohammed M'hamdi, Anette E. Gunnæs, Amin S. Azar Modelling of wire-arc additive manufacturing process is an effective way for adapting the optimum parameters as well as understanding and managing the sequences of layer-by-layer deposition. Some of these parameters such as toolpath, deposition intervals and heat source power play important roles in improving the process viability and cost efficiency. In this article, we have studied Al-5Mg, Al-3Si alloys as demonstrators, from both experimental and modelling perspectives, to benchmark different deposition parameters and provided guidelines for optimising the process conditions. Physical values such as total distortion and residual stress were selected as indicators for the manufacturability of the structure. The simulations were performed by the Simufact Welding software, that is outfitted with the MARC solver and the experiments were executed in a robotic cell. We have introduced a method for optimising the process parameters based on the heat source power modification and selection of unique parameters for each deposition layer. This was performed by monitoring the evolution of the molten pool size and geometry when building a wall structure. The results suggest that achieving an uninterrupted deposition process entails modification of the heat input for each layer. Thus, a simple analytical method was proposed to estimate the heat input reduction coefficient for a wall structure as a function of molten pool geometry and the height at which, the new layer is being deposited. It was also shown that a generic selection of parameters for aluminium alloys may impair the eventual quality for some of the alloys due to their inherent physical properties such as high temperature flowability.
       
  • High-temperature mechanical properties of alloy 718 produced by laser
           powder bed fusion with different processing parameters
    • Abstract: Publication date: Available online 30 January 2019Source: Additive ManufacturingAuthor(s): Alexandra Hilaire, Eric Andrieu, Xinhua Wu The laser powder bed fusion (LPBF) process produces complex microstructures and specific defects. To build structural components with an acceptable mechanical integrity, optimization of the processing parameters is required. In addition, the evolution of defects under service conditions should be investigated. In this study, the nickel-based alloy 718 was studied in the as-built metallurgical state. Laser processing parameters such as the laser power, scanning speed, and hatch spacing were modified to evaluate their effects on the porosity, microstructure, and mechanical properties at high temperatures. The porosity and pore shape were evaluated using relative density measurements and image analysis. Moreover, the effects of the microstructure and defects on the tensile properties and damaging processes at 650 °C were investigated in air. The results revealed that the loading direction is critical to the mechanical integrity of the alloy, due to the specific orientation of the microstructural interfaces and defects. In addition, from observations of the fracture surfaces, inter-dendritic phases were found to act as crack initiation sites. A tensile test was conducted in vacuum at 650 °C and 2.10-4 s-1, and the results indicated that damage processes were not affected by oxidation when the experiments were carried out in air.
       
  • New approach to evaluate 3D laser printed parts in powder bed fusion-based
           additive manufacturing in-line within closed space
    • Abstract: Publication date: Available online 30 January 2019Source: Additive ManufacturingAuthor(s): Michael Kalms, Ryuichi Narita, Claus Thomy, Frank Vollertsen, Ralf B. Bergmann Additive manufacturing that allows layer by layer shaping of complex structures is of rapidly increasing interest in production technology. A particularly rapid prototyping technique of additive manufacturing is laser beam melting (LBM). This 3D printing method is based on a powder bed fusion technique, using a high-powered laser to melt and consolidate metallic powders. The process needs a tightly controlled atmosphere of inert gas, which requires a confined space of a building chamber. This and more process related factors like elevated temperatures, laser radiation or the resulting light intensity caused by the melting of metals, make a closed-loop quality control very ambitious. In this paper, we propose a new in-process approach for quality control with high precision metrology based on structured light. The precise layer by layer dimensional measurement of both the printed part and the powder deposition, allows for process assessment in- or off-line.
       
  • Tensile properties and failure behavior of chopped and continuous carbon
           fiber composites produced by Additive Manufacturing
    • Abstract: Publication date: Available online 29 January 2019Source: Additive ManufacturingAuthor(s): Juan Naranjo Lozada, Horacio Ahuett-Garza, Pedro Orta Castañón, Wilco M.H. Verbeeten, Daniel Sáiz González The use of additive manufacturing (AM) is rapidly expanding in many industries mostly because of the flexibility to manufacture complex geometries. Recently, a family of technologies that produce fiber reinforced components has been introduced, widening the options available to designers. AM fiber reinforced composites are characterized by the fact that process related parameters such as the amount of reinforcement fiber, or printing architecture, significantly affect the tensile properties of final parts. To find optimal structures using new AM technologies, guidelines for the design of 3D printed composite parts are needed. This paper presents an evaluation of the effects that different geometric parameters have on the tensile properties of 3D printed composites manufactured by fused filament fabrication (FFF) out of continuous and chopped carbon fiber reinforcement. Parameters such as infill density and infill patterns of chopped composite material, as well as fiber volume fraction and printing architecture of continuous fiber reinforcement (CFR) composites are varied. The effect of the location of the initial deposit point of reinforcement fibers on the tensile properties of the test specimens is studied. Also, the effect that the fiber deposition pattern has on tensile performance is quantified. Considering the geometric parameters that were studied, a variation of the Rule of Mixtures (ROM) that provides a way to estimate the elastic modulus of a 3D printed composite is proposed. Findings may be used by designers to define the best construction parameters for 3D printed composite parts.
       
  • 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.
       
  • Additive manufacturing of zirconia parts by fused filament fabrication and
           solvent debinding: Selection of binder formulation
    • Abstract: Publication date: Available online 28 January 2019Source: Additive ManufacturingAuthor(s): Santiago Cano, Joamin Gonzalez-Gutierrez, Janak Sapkota, Martin Spoerk, Florian Arbeiter, Stephan Schuschnigg, Clemens Holzer, Christian Kukla The material extrusion additive manufacturing technique known as fused filament fabrication (FFF) is an interesting method to fabricate complex ceramic parts whereby feedstocks containing thermoplastic binders and ceramic powders are printed and the resulting parts are subjected to debinding and sintering. A limiting factor of this process is the debinding step, usually done thermally. Long thermal cycles are required to avoid defects such as cracks and blisters caused by trapped pyrolysis products. The current study addresses this issue by developing a novel FFF binder formulation for the production of zirconia parts with an intermediate solvent debinding step. Different unfilled binder systems were evaluated considering the mechanical and rheological properties required for the FFF process together with the solvent debinding performance of the parts. Subsequently, the same compounds were used in feedstocks filled with 47 vol.% of zirconia powder, and the resulting morphology was studied. Finally, the most promising formulation, containing zirconia, styrene-ethylene/butylene-styrene copolymer, paraffin wax, stearic acid, and acrylic acid-grafted high density polyethylene was successfully processed by FFF. After solvent debinding, 55.4 wt.% of the binder was dissolved in cyclohexane, creating an interconnected porosity of 29 vol.% that allowed a successful thermal debinding and subsequent pre-sintering.Graphical abstractGraphical abstract for this article
       
  • Hygromechanical properties of 3D printed continuous carbon and glass fibre
           reinforced polyamide composite for outdoor structural applications
    • Abstract: Publication date: Available online 23 January 2019Source: Additive ManufacturingAuthor(s): G. Chabaud, M. Castro, C Denoual, A. Le Duigou The additive manufacturing of structural composites is a disruptive technology currently limited by its moderate mechanical properties. Continuous fibre reinforcements have recently been developed to create high performance composites and open up encouraging prospects. However, to increase their use, deeper understanding of the relationship between process and induced properties remains necessary. In addition, to apply these materials to engineering applications, it is of high importance to evaluate the effect of environmental conditions on their mechanical performances, particularly when moisture-sensitive polymer is used (PolyAmide PA for instance) which is currently lacking in the literature.This present article aims to investigate in more detail the relationship between the process, the mechanical behaviour and the induced properties of continuous carbon and glass fibres reinforced with a polyamide matrix manufactured using a commercial 3D printer. In addition, their hygromechanical behaviour linked to moisture effect is investigated through sorption, hygroexpansion and mechanical properties characterization on a wide range of relative humidity (10-98% Relative Humidity RH).The printing process induces an original microstructure with multiscale singularities (intra/inter beads porosity and filament loop). Longitudinal tensile performance shows that the reinforcing mechanism is typical of composite laminates for glass and carbon. However, the rather poor transverse properties are not well fitted by the Rule Of Mixture (ROM), thus underlining the specificity of the printing-induced microstructure and an anisotropic behaviour in the material.Non-negligible (5-6%) moisture uptake is observed at 98% RH, as well as orthotropic hygroscopic expansion of PA/carbon and PA/glass composites. The consequences of various moisture contents on mechanical properties are studied, showing a reduction of PA/carbon stiffness and strength of 25 and 18 % in the longitudinal direction and 45 and 70% in the transverse direction. For PA/glass composites, we obtain a reduction in strength of 25 % in the longitudinal direction, along with a 80% reduction of stiffness and 45% in strength in the transverse direction. A wetting/drying cycle underlines reversible phenomena in the longitudinal direction and mainly non-reversible degradation in the transverse direction.
       
  • Compatibility in microstructural optimization for additive manufacturing
    • Abstract: Publication date: March 2019Source: Additive Manufacturing, Volume 26Author(s): Eric Garner, Helena M.A. Kolken, Charlie C.L. Wang, Amir A. Zadpoor, Jun Wu Microstructures with spatially-varying properties such as trabecular bone are widely seen in nature. These functionally graded materials possess smoothly changing microstructural topologies that enable excellent micro and macroscale performance. The fabrication of such microstructural materials is now enabled by additive manufacturing (AM). A challenging aspect in the computational design of such materials is ensuring compatibility between adjacent microstructures. Existing works address this problem by ensuring geometric connectivity between adjacent microstructural unit cells. In this paper, we aim to find the optimal connectivity between topology optimized microstructures. Recognizing the fact that the optimality of connectivity can be evaluated by the resulting physical properties of the assemblies, we propose to consider the assembly of adjacent cells together with the optimization of individual cells. In particular, our method simultaneously optimizes the physical properties of the individual cells as well as those of neighbouring pairs, to ensure material connectivity and smoothly varying physical properties. We demonstrate the application of our method in the design of functionally graded materials for implant design (including an implant prototype made by AM), and in the multiscale optimization of structures.
       
  • Skeleton arc additive manufacturing with closed loop control
    • Abstract: Publication date: Available online 15 January 2019Source: Additive ManufacturingAuthor(s): S. Radel, A. Diourte, F. Soulié, O. Company, C. Bordreuil Wire Arc Addtive Manufacturing (WAAM) is a promising direct energy deposition technology to produce high-value material components with a low buy-to-fly ratio. WAAM is able to produce thin-walled structures of large scale and also truss structures without any support. To manufacture complex parts, process reliability and repeatability are still a necessity and this often leads to long developing times. In this paper, a method is proposed to automatically manufacture complex truss structures with point by point arc additive manufacturing and a six axis robot. Computer aided manufacturing (CAM) software is designed to manage (i) material deposition at intersections and (ii) collisions between the part under construction and the torch. Because it is difficult to model the deposition process, the bead geometry is monitored using video imaging. Image treatment program detects the contour of the deposit and computes its current position. With this position, the CAM software corrects the geometry of the part for future deposition. Simple case studies are tested to validate the algorithm. Two solid free form geometries designed by topology optimization are manufactured with this skeleton arc additive manufacturing process.
       
  • In-Situ Monitoring of Polymer Flow Temperature and Pressure in Extrusion
           Based Additive Manufacturing
    • Abstract: Publication date: Available online 15 January 2019Source: Additive ManufacturingAuthor(s): David A. Anderegg, Hunter A. Bryant, Devante C. Ruffin, Stephen M. Skrip, Jacob J. Fallon, Eric L. Gilmer, Michael J. Bortner We demonstrate a novel Fused Filament Fabrication (FFF) nozzle design to enable measurements of in-situ conditions inside FFF nozzles, which is critical to ensuring that the polymer extrudate is flowing at appropriate temperature and flow rate during the part build process. Testing was performed with ABS filament using a modified Monoprice Maker Select 3D printer. In-situ measurements using the printer’s default temperature control settings showed an 11 °C decrease in temperature and significant fluctuation in pressure during printing as well as fluctuations while idle of ± 2 °C and ±14 kPa. These deviations were eliminated at lower flow rates with a properly calibrated proportional–integral–derivative (PID) system. At the highest tested flow rates, decreases in melt temperature as high as 6.5 °C were observed, even with a properly calibrated PID, providing critical insight into the significance of flow rate and PID calibration on actual polymer melt temperature inside the FFF nozzle. Pressure readings ranging from 140-6900 kPa were measured over a range of filament feed rates and corresponding extrusion flow rates. In-situ pressure measurements were higher than theoretical predictions using a power-law fluid model, suggesting that the assumptions used for theoretical calculations may not be completely capturing the dynamics in the FFF liquefier. Our nozzle prototype succeeded in measuring the internal conditions of FFF nozzles, thereby providing a number of important insights into the printing process which are vital for monitoring and improving FFF printed parts.
       
  • Controlled dissolution of freeform 3D printed carbohydrate glass scaffolds
           in hydrogels using a hydrophobic spray coating
    • Abstract: Publication date: Available online 27 December 2018Source: Additive ManufacturingAuthor(s): M.C. Gryka, T.J. Comi, R.A. Forsyth, P.M. Hadley, S. Deb, R. Bhargava Freeform 3D printing combined with sacrificial molding promises to lead advances in production of highly complex tubular systems for biomedical applications. Here we leverage a purpose-built isomalt 3D printer to generate complex channel geometries in hydrogels which would be inaccessible with other techniques. To control the dissolution of the scaffold, we propose an enabling technology consisting of an automated nebulizer coating system which applies octadecane to isomalt scaffolds. Octadecane, a saturated hydrocarbon, protects the rigid mold from dissolution and provides ample time for gels to set around the sacrificial structure. With a simplified model of the nebulizer system, the robotic motion was optimized for uniform coating. Using a combination of stimulated Raman scattering (SRS) microscopy and X-ray computed tomography, the coating was characterized to assess surface roughness and consistency. Colorimetric measurements of dissolution rates allowed optimization of sprayer parameters, yielding a decrease in dissolution rates by at least 4 orders of magnitude. High fidelity channels are ensured by surfactant treatment of the coating, which prevents bubbles from clinging to the surface. Spontaneous Raman scattering microspectroscopy and white light microscopy indicate cleared channels are free of octadecane following gentle flushing. The capabilities of the workflow are highlighted with several complex channel architectures including helices, blind channels, and multiple independent channels within polyacrylamide hydrogels of varying stiffnesses.Graphical abstractGraphical abstract for this article
       
  • The effect of post-processing operations on surface characteristics of
           316L stainless steel produced by selective laser melting
    • Abstract: Publication date: Available online 24 December 2018Source: Additive ManufacturingAuthor(s): Yusuf Kaynak, Ozhan Kitay Metal additive manufacturing is an emerging method to fabricate components used in the aerospace and biomedical industries. However, one of the significant challenges in this approach is the surface quality of the fabricated components. After metal additive manufacturing operations, post-processing is essential to meet the expected surface quality. This study presents the surface characteristics of as-built specimens manufactured by selective laser melting (SLM), where improvement of the surface can be achieved by post-processing operations. The post-processing operations in focus are finish machining (FM), vibratory surface finishing (VSF) and drag finishing (DF) operations. Surface topography, average surface roughness, microhardness, microstructure and XRD analysis have been carried out to examine the surface characteristics resulting from the post-processing operations. This study demonstrates that the drag finishing operation can be used for post-processing to meet the surface quality requirement of SLM manufactured parts.
       
  • Insight into the mechanisms of columnar to equiaxed grain transition
           during metallic additive manufacturing
    • Abstract: Publication date: Available online 24 December 2018Source: Additive ManufacturingAuthor(s): Pengwei Liu, Zhuo Wang, Yaohong Xiao, Mark F. Horstemeyer, Xiangyang Cui, Lei Chen The columnar to equiaxed transition (CET) of grain structures associated with processing conditions has been observed during metallic additive manufacturing (AM). However, the formation mechanisms of these grain structures have not been well understood under rapid solidification conditions, especially for AM of superalloys. This paper aims to uncover the underlying mechanisms that govern the CET of AM metals, using a well-tested multiscale phase-field model where heterogeneous nucleation, grain selection and grain epitaxial growth are considered. Using In718 as an example, the simulated results show that the CET is critically controlled by the undercooling, involving constitutional supercooling, thermal and curvature undercoolings in the melt pool, which dictates the extent of heterogeneous nucleation with respect to the grain epitaxial growth during rapid solidification.Graphical abstractGraphical abstract for this article
       
  • Microstructure and mechanical behavior of an additive manufactured (AM)
           WE43-Mg alloy
    • Abstract: Publication date: Available online 23 December 2018Source: Additive ManufacturingAuthor(s): Sindhura Gangireddy, Bharat Gwalani, Kaimiao Liu, Eric J. Faierson, Rajiv S. Mishra Magnesium alloys are highly attractive in aerospace and auto industries due to their high strength-to-weight ratio. Additive manufacturing of Mg alloys can further save cost from materials and machining time. This paper investigates the microstructure and dynamic mechanical behavior of WE-43 Mg alloy built through the powder bed fusion process. Samples from four different combinations of processing parameters were built. These builds were studied in both as-built and hot isostatically pressed conditions. The resultant complex microstructures were studied under scanning and transmission electron microscopes while their dynamic mechanical behavior was evaluated using a split-Hopkinson pressure bar testing system. Effects of initial porosity and microstructural evolution during HIP treatment on mechanical response are discussed.
       
  • Integrating Digital Image Correlation in Mechanical Testing for the
           Materials Characterization of Big Area Additive Manufacturing Feedstock
    • Abstract: Publication date: Available online 23 December 2018Source: Additive ManufacturingAuthor(s): Kevin Schnittker, Edel Arrieta, Xavier Jimenez, David Espalin, Ryan B. Wicker, David A. Roberson To enable the advancement of large-scale additive manufacturing processes, it is necessary to establish and standardize methodologies to characterize the mechanical properties of printed test coupons. Due to the large size of the print beads, conventional test standards are inadequate. The focus of this study was to determine the feasibility of using Digital image correlation (DIC) technology as a key enabler for robust data collection of strain measurements of large 3D printed parts. To incorporate the DIC measurements, a novel method was developed to prepare large 20% (by wt.) glass filled ABS test coupons for adequate contrast. Through this technique, Poisson's ratio and elastic modulus were measured and stress strain curves were generated. The data produced by DIC correlated well with failure analysis performed on spent test coupons. Additionally, fracture surface analysis of the specimens revealed poor adhesion among the ABS matrix and glass fibers. This matrix/fiber debonding demonstrated the need for improved printing parameters to maximize tensile strength. Finally, critical length analysis of the fibers revealed them to be dimensionally inadequate.
       
  • Effect of Structural Support on Microstructure of Nickel Base Superalloy
           Fabricated By Laser-Powder Bed Fusion Additive Manufacturing
    • Abstract: Publication date: Available online 23 December 2018Source: Additive ManufacturingAuthor(s): Hyeyun Song, Tom McGaughy, Alber Sadek, Wei Zhang INCONEL® 718 cubes with and without structural support were built by laser-powder bed fusion (L-PBF) additive manufacturing. The effect of support on the as-built microstructure was studied based on the microstructural characteristics and micro-hardness variations. Specifically, the microstructure was examined by optical microscopy, and scanning and transmission electron microscopy. The precipitates were identified via selected area diffraction supplemented by high-resolution energy dispersive X-ray spectroscopy. Micro-hardness distributions on cross sections parallel and perpendicular to the build direction were mapped. In addition, analytical equations, taking into account various laser processing parameters, material properties and support geometries, were developed to calculate the heat build-up and cooling conditions during L-PBF. The results of microstructure characterization and analytical calculation showed a marginal effect of the support on the local microstructure and hardness due to the low heat input in L-PBF. Moreover, the comprehensive set of microstructure data is useful for future work of modelling processing-microstructure relation as well as optimizing post-fabrication heat treatment.Graphical abstractGraphical abstract for this article
       
  • Effect of process parameters on melt pool geometry and microstructure
           development for electron beam melting of IN718: a systematic single bead
           analysis study
    • Abstract: Publication date: Available online 23 December 2018Source: Additive ManufacturingAuthor(s): Xiao Ding, Yuichiro Koizumi, Daixiu Wei, Akihiko Chiba To understand the fundamentals of microstructure formation in an electron beam melting (EBM) additive-manufacturing process, which is classified as a type of electron beam powder bed fusion (EB-PBF) in ISO562910/ASTM-F42, single bead experiments were conducted by using an electron beam to scan an IN718 plate, using various combinations of power and scan speed, focusing on the relationship between (i) the beam irradiation level, (ii) the melt pool geometry, and (iii) the solidification microstructure. The width and depth of the melt pool increases almost linearly with the line energy. Elongated grains, which are generally called “columnar grains” were observed in almost the entire cross-section of the beads regardless of the process parameters. Temporal evolution of the temperature distribution for the single bead experiments was simulated by finite element analysis (FEA) with thermal conduction and recoalescence taken into account. The surface heat source model used in the simulation was modified to cause the geometry of the simulated melt pool to align with that which was observed experimentally. The distributions of the temperature gradient (G) and solidification rate (R) on the solidification interface were evaluated from the simulation results. The distributions of the microstructures were constructed from the distributions of G and R, as obtained from a solidification map in the literature. Contrary to the experimental observations, the constructed microstructure consisted mostly of equiaxed and mixed grains. The reasons for this contradiction are discussed.
       
  • Creating 3D Printed Magnetic Devices with Ferrofluids and Liquid Metals
    • Abstract: Publication date: Available online 21 December 2018Source: Additive ManufacturingAuthor(s): Nathan Lazarus, Sarah S. Bedair, Gabriel L. Smith Combining electrical and magnetic materials in the same part has been a challenge in 3D printing due to difficulties co-printing complex materials in many additive manufacturing processes. Past 3D printed inductors and other similar magnetic devices have therefore either lacked the magnetic materials necessary for improved performance, or required sintering at high temperatures for extended periods, beyond the capability of most 3D printable polymers. In this work, we demonstrate a room temperature process for incorporating conductive and magnetic materials into the same 3D printed device. A multi-stage fabrication process based on 3D printing followed by fill with magnetic and conductive fluids is proposed. Multi-layer microfluidic channels for magnetic passives are first printed in a stereolithography process. The microfluidic systems are then filled with room temperature liquid metal, a gallium alloy liquid at room temperature, and ferrofluid to create inductors, transformers and wireless power coils. Through the addition of ferrofluid as a magnetic material, increases in inductance density by nearly a factor of three were demonstrated, in addition to coupling improvements for transformer and wireless power coils compared to the devices before magnetic fill.
       
  • Tandem metal inert gas process for high productivity wire arc additive
           manufacturing in stainless steel
    • Abstract: Publication date: January 2019Source: Additive Manufacturing, Volume 25Author(s): Filomeno Martina, Jialuo Ding, Stewart Williams, Armando Caballero, Gonçalo Pardal, Luisa Quintino This study investigates the feasibility of achieving high deposition rate using wire + arc additive manufacturing in stainless steel to reduce lead time and cost of manufacturing. The pulse MIG welding technique with a tandem torch was used for depositing martensitic stainless steel 17-4 pH. The mechanical and metallurgical properties of the manufactured component were analysed to evaluate the limitations and the extent to which the rate of deposition reaches a maximum without any failure or defect being evident in the manufactured component. Deposition rate of 9.5 kg/h was achieved. The hardness was matched for the as deposited condition.
       
  • Fracture Toughness of Additively Manufactured Carbon Fiber Reinforced
           Composites
    • Abstract: Publication date: Available online 17 December 2018Source: Additive ManufacturingAuthor(s): Easir Arafat Papon, Anwarul Haque In this paper, the fracture properties (stress intensity factor and energy release rate) of additively manufactured (AM) polylactic acid (PLA) and its short carbon fiber (CF) reinforced composites have been studied. The effects of CF reinforcement, nozzle geometry and bead lay-up orientations in fracture properties, void contents, and interfacial bonding were studied. The fused deposition modeling (FDM) based AM specimens using both circular and square shaped nozzle were printed and compared with the conventional compression molded (CM) samples. Compact tension (CT) specimens with different CF concentrations (0 wt.%, 3 wt. %, 5 wt.%, 7 wt.% and 10 wt.%) were printed with two bead lay-up orientations ( 450/-450 and 00/900 ) using PLA and CF/PLA composite filaments. The results show significant improvement in fracture toughness and fracture energy for CF/PLA composites in comparison to neat PLA. The fracture toughness was increased by 42% for 00/900 and 38% for 450/-450 bead orientations, respectively with 5 % CF loading. The increase in fracture energy was observed to be about 77% for 00/900 and 88% for 450/-450 layer orientations, respectively for the same fiber reinforcement (5 wt. %). Such improvement in fracture properties is expected to be higher for all 900 bead orientations. The samples printed by square-shaped nozzle showed some enhancement in fracture toughness with less inter-bead voids and larger bonded areas in comparison to the circular-shaped nozzle. Although the fracture toughness showed very negligible differences between 00/900 and 450/-450 specimens, distinguishable variation may be seen in the case of 00 and 900 bead orientations. The crack propagation path and fracture mechanisms were studied using optical microscopy (OM) and scanning electron microscopy (SEM) examinations. Fractography revealed different modes of failure with a very high fiber orientation along the printing direction and a relatively higher void contents for 7 and 10 wt. % fiber reinforcement.
       
  • Characterization of process–deformation/damage property relationship of
           fused deposition modeling (FDM) 3D-printed specimens
    • Abstract: Publication date: Available online 15 December 2018Source: Additive ManufacturingAuthor(s): Tomas Webbe Kerekes, Hyoungjun Lim, Woong Yeol Joe, Gun Jin Yun In this paper, we investigated the process variable effects on the damage and deformational behavior of fused deposition modeling (FDM) three-dimensional (3D)-printed specimens by performing tensile tests and inverse identification analyses. A characterization of the effects of different parametric variations of 3D-printed specimens on fracture properties are a matter of considerable significance that are often overlooked. By combining the infill density and the layer thickness options that are available in the 3D printer machine, six groups with different structural configurations can be obtained. The data and images obtained from experiments are employed to investigate the failure mechanism of 3D-printed specimens and demonstrate the relationship that exists between structural variations and fracture mechanical properties. On the basis of experimental results, a Gurson-type porous plasticity model was used within a 3D continuum finite element model to characterize the process–damage parameter relationship through an inverse identification process.
       
  • New Actuation Waveform Design of DoD Inkjet Printer forSingle and
           Multi-Drop Ejection Method
    • Abstract: Publication date: Available online 14 December 2018Source: Additive ManufacturingAuthor(s): Oke Oktavianty, Tadayuki Kyoutani, Shigeyuki Haruyama, Ken Kaminishi The development of a variety of inkjet technologies to improve the print quality has been attempted over the past few decades. In recent years, binary technology has mostly been used instead of grey-scale technology. The development of amulti-drop ejection method for use in a grey-scale technique with a clear spherical droplet, and without a satellite or ligament occurring, has become a significant challenge in inkjet printer technology. In this study, we create a new actuation waveform for both single and multi-drop ejection methods. The design process uses a conceptual model based on the wave superposition principle. A good performance in terms of the droplet shape without the occurrence of a satellite, a ligament, or weeping has been achieved for up to five main pulses,thereby generating five different droplet sizes from the same nozzle. This is a radical improvement, particularly for a multi-drop ejection method, thereby enhancing the print quality.
       
  • NOVEL SPRUE DESIGNS IN METAL CASTING via 3D SAND-PRINTING
    • Abstract: Publication date: Available online 12 December 2018Source: Additive ManufacturingAuthor(s): Santosh Reddy Sama, Tony Badamo, Paul Lynch, Guha Manogharan The opportunity to improve the quality of metal castings by allowing fabrication of complex gating systems via 3D Sand-Printing (3DSP) has been recently established. Among the different components of a gating system (often called rigging), sprue design offers a major opportunity to exploit the unlimited geometric freedom offered by 3DSP process. In this study, conventional principles of casting hydrodynamics is advanced by validated novel numerical models novel sprue designs to improve melt flow control. Computational flow simulations demonstrate that conical-helix sprue satisfy the critical velocity condition by reducing the ingate velocity below 0.5 m/s. Multiple approaches to integrate 3DSP into conventional manufacturing to fabricate complex gating systems through “Hybrid Molding” are presented. 3DSP molds featuring two optimized sprue profiles and benchmark straight sprue are fabricated to pour 17-4 stainless steel. Computed tomography scans (CT) shows that parabolic sprue casting (PSC) and conical-helix sprue casting (CHSC) reduced overall casting defects by 56% and 99.5% respectively when compared to straight sprue casting (SSC). Scanning electron microscopy (SEM) analysis confirms the presence of globular oxide inclusions and that PSC and CHSC exhibits 21% and 35% reduced inclusion when compared to the SSC. Three point flexural testing reveals that CHSC and PSC exhibits an increase of 8.4% and 4.1% respectively in average ultimate flexural strength than SSC. The findings from this study demonstrate that numerically optimized gating systems that can only be fabricated via 3DSP have the potential to significantly improve both mechanical and metallurgical performance of sand castings.Graphical abstractGraphical abstract for this article
       
  • On the microstructure, mechanical properties and wear resistance of an
           additively manufactured Ti64/metallic glass composite
    • Abstract: Publication date: Available online 10 December 2018Source: Additive ManufacturingAuthor(s): Xiao-Jun Shen, Cheng Zhang, Yan-Ge Yang, Lin Liu Selective laser melting (SLM) provides flexibility in creating novel metal-matrix composites (MMCs) with unique microstructures and enhanced mechanical properties over conventionally manufactured MMGs. In this study, a Zr-based metallic glass (MG) decorated Ti6Al4V (Ti64) composite with a unique hybrid nanostructure and enhanced mechanical properties and wear resistance was fabricated using SLM. The results revealed that a near-full dense and crack-free Ti-based composite was produced, with its reinforcements consisting of ultrafine β dendrites set with partially crystallized MG nanobands uniformly distributed along the boundaries of the melt pool. The addition of MG significantly affected the solidification behavior of the Ti-liquid because of its higher dynamic viscosity and density as well as compositional effect on the phase stability. With such a unique nanostructured reinforcement, the Ti64/MG composite exhibited an enhanced yield strength (>1 GPa) with reasonable ductility and fracture toughness. On the basis of the result of a theoretical analysis, we attributed the main strengthening mechanism to Orowan strengthening. The wear resistance was also much improved in the Ti64/MG composite, arising from the higher hardness of the nanostructured reinforcement and the formation of a more protective tribo-oxide layer during sliding. The confinement of the 3D distributed reinforcement phase played a crucial role in preventing the delamination of the tribo-layer on the matrix. This work opens a pathway to the design of novel additively manufactured MMCs with outstanding mechanical properties.Graphical abstractGraphical abstract for this article
       
  • Reactive material jetting of polyimide insulators for complex circuit
           board design
    • Abstract: Publication date: January 2019Source: Additive Manufacturing, Volume 25Author(s): Fan Zhang, Ehab Saleh, Jayasheelan Vaithilingam, You Li, Christopher J. Tuck, Richard J.M. Hague, Ricky D. Wildman, Yinfeng He Polyimides are a group of high performance thermal stable dielectric materials used in diverse applications. In this article, we synthesized and developed a high-performance polyimide precursor ink for a Material Jetting (MJ) process. The proposed ink formulation was shown to form a uniform and dense polyimide film through reactive MJ utilising real-time thermo-imidisation process. The printed polyimide film showed a permittivity of 3.41 and degradation temperature around 500 °C, both of which are comparable to commercially available polyimide films. Benefiting from the capability of being able to selectively deposit material through MJ, we propose the use of such a formulation to produce complex circuit board structures by the co-printing of conductive silver tracks and polyimide dielectric layers. By means of selectively depositing 4 μm thick patches at the cross-over points of two circuit patterns, a traditional double-sided printed circuit board (PCB) can be printed on one side, providing the user with higher design freedom to achieve a more compact high performance PCB structure.Graphical abstractGraphical abstract for this article
       
  • First Demonstration of Additive Manufacturing of Cutting Tools using
           Directed Energy Deposition System: Stellite™-Based Cutting Tools
    • Abstract: Publication date: January 2019Source: Additive Manufacturing, Volume 25Author(s): Kellen D. Traxel, Amit Bandyopadhyay Machine-tool concepts are becoming increasingly complex to meet the demanding requirements of advanced applications. This raises per-tool costs for manufacturers and end users, motivating the development of novel, innovative fabrication methods for these tools. Our objective herein is to investigate laser-based additive manufacturing to fabricate application-optimized machine-tools that perform comparably to commercially-available products. To demonstrate this technology, multi-layer Stellite™ (Co-Cr-W superalloy) structures were deposited on a stainless-steel substrate via directed energy deposition technique to be used as a tool for cutting applications requiring high-temperature strength and ductility, an area where conventional carbide and high-speed steel tools are challenged. The as-printed structures were free of large-scale defects and voids, and were further characterized and compared to commercial Blackalloy 525 barstock (B525), a Co-Cr-W alloy tool of similar composition. The Stellite™ contained mostly Co-rich (α-phase) dendrites, as well as inter-dendritic Cr7C3 and Cr23C6 phases. The B525 composition consisted of a range of lamellar-eutectic microstructure comprised of Co-phase with W6C reinforcement. In reciprocating wear testing, Stellite™ 6 maintained a steady-state COF within 20% of B525 (0.36 ± 0.01 vs. 0.30 ± 0.01), and final wear rate as low as 38% difference from B525 (5.14*10−6 ± 4.58*10−7Nmm3 vs. 3.20*10−6 ± 4.99*10-7Nmm3). During a turning operation of SS304L, the Stellite™ 6 tool demonstrated consistent chip formation and more consistent rake-face and cratering wear in comparison to the B525 tool, indicating its adequacy for service in this application. Our results demonstrate for the first time that directed-energy-deposition can be utilized to fabricate advanced cutting tool concepts for job-specific applications.Graphical abstractGraphical abstract for this article
       
  • Hybrid manufacturing—Locating AM hubs using a two-stage facility
           location approach
    • Abstract: Publication date: January 2019Source: Additive Manufacturing, Volume 25Author(s): Danielle Strong, Michael Kay, Brett Conner, Thomas Wakefield, Guha Manogharan Hybrid Manufacturing is defined as the integration of Additive Manufacturing (AM), specifically metal AM, with traditional manufacturing post-processing such as heat treatment and machining. Hybrid AM enables Small and Medium Enterprises (SME) who can offer post-processing services to integrate into the growing AM supply chain. Most near-net metal AM parts require heat treatment processes (e.g. residual stress relieving/annealing) before machining to achieve final engineering specification. This research investigates a two-stage facility model to optimize the locations and capacities for new metal AM hubs which require two sequential post-processing services: heat treatment and machining. Using North American Industry Classification System (NAICS) data for machine shops and heat treatment facilities in the U.S., a p-median location model is used to determine the optimal locations for AM hub centers based on: (1) geographical data, (2) demand and (3) fixed and operational costs of hybrid-AM processing. Results from this study have identified: (a) candidate US counties to locate metal AM hubs, (b) total cost (fixed, operational and transportation), (c) capacity utilization of the AM hubs and (d) demand assignments across machine shops – heat treatment facilities – AM hubs. It was found that 2-stage p-Median model identified 22 A M hub locations as the initial sites for AM hubs which grows to 35 A M hubs as demand increases. It was also found that relatively fewer number of heat treatment facilities than machine shops resulted in a more concentrated locations of AM hubs. In addition, transportation costs were not adversely affected by the inclusion of as-build plates and showed that including heat treatment facilities as part of the hybrid AM supply chain will be mutually beneficial to all stakeholders of metal hybrid AM supply chain, i.e. AM → Heat treatment → Machining.Graphical abstractGraphical abstract for this article
       
  • Mesoscale multi-physics simulation of rapid solidification of Ti-6Al-4V
           alloy
    • Abstract: Publication date: Available online 7 December 2018Source: Additive ManufacturingAuthor(s): Dehao Liu, Yan Wang Powder bed fusion is a recently developed additive manufacturing (AM) technique for alloys, which builds parts by selectively melting metallic powders with a high-energy laser or electron beam. Nevertheless, there is still a lack of fundamental understanding of the rapid solidification process for better quality control. To simulate the microstructure evolution of alloys during the rapid solidification, in this research, a mesoscale multi-physics model is developed to simultaneously consider solute transport, phase transition, heat transfer, latent heat, and melt flow. In this model, the phase-field method simulates the dendrite growth of alloys, whereas the thermal lattice Boltzmann method models heat transfer and fluid flow. The phase-field method and the thermal lattice Boltzmann method are tightly coupled. The simulation results of Ti-6Al-4 V show that the consideration of latent heat is necessary because it reveals the details of the formation of secondary arms and provides more realistic kinetics of dendrite growth. The proposed multi-physics simulation model provides new insights into the complex solidification process in AM.Graphical abstractGraphical abstract for this article
       
  • Experiments and simulations on solidification microstructure for Inconel
           718 in powder bed fusion electron beam additive manufacturing
    • Abstract: Publication date: Available online 5 December 2018Source: Additive ManufacturingAuthor(s): G.L. Knapp, N. Raghavan, A. Plotkowski, T. DebRoy Previous research on the powder bed fusion electron beam additive manufacturing of Inconel 718 has established a definite correlation between the processing conditions and the solidification microstructure of components. However, the direct role of physical phenomena such as fluid flow and vaporization on determining the solidification morphology have not been investigated quantitatively. Here, we investigate the transient and spatial evolution of the fusion zone geometry, temperature gradients, and solidification growth rates during pulsed electron beam melting of the powder bed with a focus on the role of key physical phenomena. The effect of energy density during pulsing, which relates to the amount of heating of the build area during processing, on the columnar-to-equiaxed transition of the solidification structure was studied both experimentally and theoretically. Predictions and evaluation of the role of heat transfer and fluid flow was established using existing solidification theories combined with transient, three-dimensional numerical heat transfer and fluid flow modeling. Metallurgical characteristics of the alloy’s solidification are extracted from the transient temperature fields, and microstructure is predicted and validated using optical images and electron backscattered diffraction data from the experimental results. Simulations show that the pure liquid region solidified quickly, creating a large two-phase, mushy region that exists during the majority of solidification. While conductive heat transfer dominates in the mushy region, both the pool geometry and the solidification parameters are affected by convective heat transfer. Finally, increased energy density during processing is shown to increase the time of solidification, lowering temperature gradients and increasing the probability of equiaxed grain formation.Graphical abstractGraphical abstract for this article
       
  • A Discrete Source Model of Powder Bed Fusion Additive Manufacturing
           Thermal History
    • Abstract: Publication date: Available online 4 December 2018Source: Additive ManufacturingAuthor(s): Edwin J. Schwalbach, Sean P. Donegan, Michael G. Chapman, Kevin J. Chaput, Michael A. Groeber Significant attention has been focused on modeling of metallic additive manufacturing (AM) processes, with the initial aim of predicting local thermal history, and ultimately structure and properties. Existing models range greatly in physical complexity and computational cost, and the implications of various simplifying assumption often go unassessed. In the present work, we first formulate a fast acting Discrete Source Model (DSM) capable of handling the complex processing often encountered in metal powder bed fusion AM. We then assess implications of the source representation, details of the numeric implementation, as well as effects of boundary conditions and thermophysical parameters. We verify the DSM implementation against simple numerical thermal predictions, calibrate it with single track deposit experiments, validate outputs against multitrack deposits, and finally quantify the scaling performance. The DSM is an effective means of quickly generating an estimate of the local thermal history induced by complex scan strategies when combined with arbitrary component geometry. While a number of approximations limit its quantitative accuracy, the inexpensive nature and ability to treat complex processing plans suggests it will be useful for screening and identification of regions experiencing anomalous thermal history. Such a capability is necessary to direct usage of higher fidelity, more expensive models and experimental resources.
       
  • Molten Pool Behavior and Effect of Fluid Flow on Solidification Conditions
           in Selective Electron Beam Melting (SEBM) of a Biomedical Co-Cr-Mo Alloy
    • Abstract: Publication date: Available online 4 December 2018Source: Additive ManufacturingAuthor(s): Yufan Zhao, Yuichiro Koizumi, Kenta Aoyagi, Daixiu Wei, Kenta Yamanaka, Akihiko Chiba Selective electron beam melting (SEBM) is a type of additive manufacturing (AM) that involves multiple physical processes. Because of its unique process conditions compared to other AM processes, a detailed investigation into the molten pool behavior and dominant physics of SEBM is required. Fluid convection involves mass and heat transfer; therefore, fluid flow can have a profound effect on solidification conditions. In this study, computational thermal-fluid dynamics simulations with multi-physical modeling and proof-of-concept experiments were used to analyze the molten pool behavior and resultant thermal conditions related to solidification. The Marangoni effect of molten metal primarily determines fluid behavior and is a critical factor affecting the molten pool instability in SEBM of the Co–Cr–Mo alloy. The solidification parameters calculated from simulated data, especially the solidification rate, are sensitive to the local fluid flow at the solidification front. Combined with experimental analysis, the results presented herein indicate that active fluid convection at the solidification front increase the probability of new grain formation, which suppresses the epitaxial growth of columnar grains.
       
  • Invited review article: Where and how 3D printing is used in teaching and
           education
    • Abstract: Publication date: January 2019Source: Additive Manufacturing, Volume 25Author(s): Simon Ford, Tim Minshall The emergence of additive manufacturing and 3D printing technologies is introducing industrial skills deficits and opportunities for new teaching practices in a range of subjects and educational settings.In response, research investigating these practices is emerging across a wide range of education disciplines, but often without reference to studies in other disciplines. Responding to this problem, this article synthesizes these dispersed bodies of research to provide a state-of-the-art literature review of where and how 3D printing is being used in the education system. Through investigating the application of 3D printing in schools, universities, libraries and special education settings, six use categories are identified and described: (1) to teach students about 3D printing; (2) to teach educators about 3D printing; (3) as a support technology during teaching; (4) to produce artefacts that aid learning; (5) to create assistive technologies; and (6) to support outreach activities. Although evidence can be found of 3D printing-based teaching practices in each of these six categories, implementation remains immature, and recommendations are made for future research and education policy.
       
  • Qualification of channels produced by laser powder bed fusion: Analysis of
           cleaning methods, flow rate and melt pool monitoring data
    • Abstract: Publication date: January 2019Source: Additive Manufacturing, Volume 25Author(s): T. Kolb, A. Mahr, F. Huber, J. Tremel, M. Schmidt Laser powder bed fusion, is an additive manufacturing technology that is used in industry for rapid prototyping and manufacturing of aftermarket products, molds and special machine parts. Quality assurance and process stability still require improvement until this technology is ready for large scale serial production. Scan strategies and parameter sets for manufacturing are often fixed when certification processes are finished. Thus, it is important to test the manufacturability of specific design features such as inner channels. In the following we will present the qualification of inner channels in different test parts for the aluminum alloy AlSi10Mg and the stainless steel 1.4542. The testing includes different cleaning methods and air flow rate measurements. Additionally, we will compare such parts and LPBF specific problems to observations with a coaxial melt pool monitoring system.
       
  • Mechanical vibration bandgaps in surface-based lattices
    • Abstract: Publication date: January 2019Source: Additive Manufacturing, Volume 25Author(s): Waiel Elmadih, Wahyudin P. Syam, Ian Maskery, Dimitrios Chronopoulos, Richard Leach In this paper, the phonon dispersion curves of several surface-based lattices are examined, and their energy transmission spectra, along with the corresponding bandgaps are identified. We demonstrate that these bandgaps may be controlled, or tuned, through the choice of cell type, cell size and volume fraction. Our results include two findings of high relevance to the designers of lattice structures: (i) network and matrix phase gyroid lattice structures develop bandgaps below 15 kHz while network diamond and matrix diamond lattices do not, and (ii) the bandwidth of a bandgap in the network phase gyroid lattice can be tuned by adjusting its volume fraction and cell size.
       
  • Mechanical and corrosion properties of CoCrFeNiTi-based high-entropy alloy
           additive manufactured using selective laser melting
    • Abstract: Publication date: January 2019Source: Additive Manufacturing, Volume 25Author(s): Tadashi Fujieda, Meichuan Chen, Hiroshi Shiratori, Kosuke Kuwabara, Kenta Yamanaka, Yuichiro Koizumi, Akihiko Chiba, Seiichi Watanabe The effectiveness of applying selective laser melting (SLM) to a CoCrFeNiTi-based high-entropy alloy was compared with that of using electron beam melting (EBM). The higher solidification rate during SLM promoted a fine uniform microstructure with no visible segregation, which led to superior tensile properties (yield strength: 773.0 ± 4.2 MPa, ultimate tensile strength: 1178.0 MPa, elongation: 25.8 ± 0.6%) and a higher pitting potential (0.88 ± 0.03 V versus Ag/AgCl in a 3.5% NaCl solution at 353 K) in comparison to the EBM specimens (743.4 ± 11.6, 932.2 ± 4.8 MPa, 4.0 ± 0.2%, and 0.50 ± 0.04 V versus Ag/AgCl, respectively). The effect of a solution treatment on the tensile properties and pitting-corrosion resistance of the SLM specimens was then examined. The effect of the solution treatment on these properties depended on the cooling method used during the treatment. In particular, the tensile properties and pitting-corrosion resistance improved as a result of water quenching. On the other hand, the properties of the solution-treated specimens depended on the size and volume fraction of very fine-ordered particles, with diameters of tens of nanometers that contained Ni and Ti. The as-built and solution-treated SLM specimens exhibited excellent tensile strength and exceptional pitting-corrosion resistance; they had higher tensile strength and pitting-corrosion resistance than the conventional high-corrosion-resistant alloys.Graphical abstractGraphical abstract for this article
       
  • Computational mechanical characterization of geometrically transformed
           Schwarz P lattice tissue scaffolds fabricated via two photon
           polymerization (2PP)
    • Abstract: Publication date: January 2019Source: Additive Manufacturing, Volume 25Author(s): Adi Z. Zabidi, Shuguang Li, Reda M. Felfel, Kathryn G. Thomas, David M. Grant, Donal McNally, Colin Scotchford Schwarz P unit cell-based tissue scaffolds comprised of poly(D,L-lactide-co- ε -caprolactone)(PLCL) fabricated via the additive manufacturing technique, two-photon polymerisation (2 P P) were found to undergo geometrical transformations from the original input design. A Schwarz P unit cell surface geometry CAD model was reconstructed to take into account the geometrical transformations through CAD modeling techniques using measurements obtained from an image-based averaging technique before its implementation for micromechanical analysis. Effective modulus results obtained from computational mechanical characterization via micromechanical analysis of the reconstructed unit cell assigned with the same material model making up the fabricated scaffolds demonstrated excellent agreement with a small margin of error at 6.94% from the experimental mean modulus (0.69 ± 0.29 MPa). The possible sources for the occurrence of geometrical transformations are discussed in this paper. The inter-relationships between different dimensional parameters making up the Schwarz P architecture and resulting effective modulus are also assessed and discussed. With the ability to accommodate the geometrical transformations, maintain efficiency in terms of time and computational resources, micromechanical analysis has the potential to be implemented in tissue scaffolds with a periodic microstructure as well as other structures outside the field of tissue engineering in general.Graphical abstractGraphical abstract for this article
       
  • Enriched analytical solutions for additive manufacturing modeling and
           simulation
    • Abstract: Publication date: January 2019Source: Additive Manufacturing, Volume 25Author(s): John C. Steuben, Andrew J. Birnbaum, John G. Michopoulos, Athanasios P. Iliopoulos Recent developments in additive manufacturing (AM) technologies involving heat and mass deposition have exposed the need for computationally efficient modeling of thermal field histories. This is due to the effect of such histories on resulting morphologies and quantities of interest, such as micro- and meso-structure, residual strains and stresses, as well as on material and structural properties and associated functional performance at the macro-scale. Limiting undesirable manifestations of these phenomena has motivated the development of both feed-forward and feedback loop control methodologies. However, up to now the computational cost of existing methods for predicting thermal fields and associated aspects, have allowed only feed-forward control methods. Consequently, in this paper, analytic solutions are enriched and then used to model the thermal aspects of AM, in a manner that demonstrates both high computational performance and fidelity required to enable “in the loop” use for feedback control of AM processes. It is first shown that the utility of existing analytical solutions is limited due to their underlying assumptions, some of which are their derivation based on a homogeneous semi-infinite domain and temperature independent material properties among others. These solutions must therefore be enriched in order to capture the actual thermal physics associated with the relevant AM processes. Enrichments introduced herein include the handling of strong nonlinear variations in material properties due to their dependence on temperature, finite non-convex solution domains, behavior of heat sources very near domain boundaries, and mass accretion coupled to the thermal problem. The enriched analytic solution method (EASM) that implements these enrichments is shown to produce results equivalent to those of numerical methods (such as Finite Elements and Finite Differences) that require six orders of magnitude greater computational cost.
       
  • 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
       
  • Additive laser metal deposition onto silicon
    • Abstract: Publication date: January 2019Source: Additive Manufacturing, Volume 25Author(s): Arad Azizi, Matthias A. Daeumer, Scott N. Schiffres By employing selective laser melting (SLM), we demonstrate how Sn3Ag4Ti alloy can robustly bond to silicon via additive manufacturing. With this technology, heat removal devices (e.g., vapor chamber evaporators, heat pipes, micro-channels) can be directly printed onto the electronic package without using thermal interface materials. This has the advantage of keeping the current microprocessor about 10 °C cooler by eliminating two thermal interface materials. This reduces operating temperature, saving power and reducing electronic-waste. The bonding of common metal alloys used in additive manufacturing onto silicon is relatively weak and generally possesses high contact angles (poor wetting and interfacial strength). By using the proper interlayer material, wettability and reactivity with the silicon substrate increase drastically. Unlike conventional dissimilar material brazing that can take tens of minutes to form a strong bond, this study demonstrates how this kinetic limitation can be overcome to form a good bond in sub-milliseconds via intense laser heating. The mechanism for rapid bonding lies in using an alloy that can form a strong intermetallic bond to the substrate at a low temperature, and exposing the sample multiple times to give sufficient diffusion time for a strong bond. Bonding of Sn3Ag4Ti to silicon occurs through the formation of a thin (∼μm) titanium-silicide interfacial layer that makes the silicon wettable to the Sn3Ag4Ti. These printed parts are mechanically resistant to thermal cycling, with no mechanical failures visible after over a week of continuous thermal cycling (−40 °C and 130 °C).Graphical abstractGraphical abstract for this article
       
  • Prediction of lack of fusion porosity in selective laser melting based on
           melt pool monitoring data
    • Abstract: Publication date: January 2019Source: Additive Manufacturing, Volume 25Author(s): Sam Coeck, Manisha Bisht, Jan Plas, Frederik Verbist Selective laser melting is already established as a commercial production technique. Some high-end users are, however, struggling with the complexity, consistency and cost associated with the qualification of high-end products built using the technique. In-situ process monitoring is a promising means to accommodate this issue, but quantitative correlations between monitoring signals and actual part defects have been lacking. In this paper, results are presented that have been obtained with an off-axis melt pool monitoring system on a 3D Systems ProX DMP 320 using Ti-6Al-4 V ELI. The focus is on the development of a method for predicting the presence and location of lack of fusion porosities as they can have a large impact on part quality and are not always easily detected post-build. The processed signals from the monitoring system are shown to have a high degree of correlation with the presence of lack of fusion porosities as measured by CT scans. A prediction sensitivity of 90% for lack of fusion events in the range of pores having a volume greater than 0.001 mm3, roughly equivalent to 160 μm in diameter, was obtained.
       
  • New aspects about the search for the most relevant parameters optimizing
           SLM materials
    • Abstract: Publication date: January 2019Source: Additive Manufacturing, Volume 25Author(s): Tatiana Mishurova, Katia Artzt, Jan Haubrich, Guillermo Requena, Giovanni Bruno While the volumetric energy density is commonly used to qualify a process parameter set, and to quantify its influence on the microstructure and performance of additively manufactured (AM) materials and components, it has been already shown that this description is by no means exhaustive. In this work, new aspects of the optimization of the selective laser melting process are investigated for AM Ti-6Al-4V. We focus on the amount of near-surface residual stress (RS), often blamed for the failure of components, and on the porosity characteristics (amount and spatial distribution). First, using synchrotron x-ray diffraction we show that higher RS in the subsurface region is generated if a lower energy density is used. Second, we show that laser de-focusing and sample positioning inside the build chamber also play an eminent role, and we quantify this influence. In parallel, using X-ray Computed Tomography, we observe that porosity is mainly concentrated in the contour region, except in the case where the laser speed is small. The low values of porosity (less than 1%) do not influence RS.
       
  • Areal topography measurement of metal additive surfaces using focus
           variation microscopy
    • Abstract: Publication date: January 2019Source: Additive Manufacturing, Volume 25Author(s): Lewis Newton, Nicola Senin, Carlos Gomez, Reinhard Danzl, Franz Helmli, Liam Blunt, Richard Leach In this work, the performance of a focus variation instrument for measurement of areal topography of metal additive surfaces was investigated. Samples were produced using both laser and electron beam powder bed fusion processes with some of the most common additive materials: Al-Si-10Mg, Inconel 718 and Ti-6Al-4V. Surfaces parallel and orthogonal to the build direction were investigated. Measurement performance was qualified by visually inspecting the topographic models obtained from measurement and quantified by computing the number of non-measured data points, by estimating local repeatability error in topography height determination and by computing the value of the areal field texture parameter Sa. Variations captured through such indicators were investigated as focus variation-specific measurement control parameters were varied. Changes in magnification, illumination type, vertical resolution and lateral resolution were investigated. The experimental campaign was created through full factorial design of experiments, and regression models were used to link the selected measurement process control parameters to the measured performance indicators. The results indicate that focus variation microscopy measurement of metal additive surfaces is robust to changes of the measurement control parameters when the Sa texture parameter is considered, with variations confined to sub-micrometre scales and within 5% of the average parameter value for the same surface and objective. The number of non-measured points and the local repeatability error were more affected by the choice of measurement control parameters. However, such changes could be predicted by the regression models, and proved consistent once material, type of additive process and orientation of the measured surface are set.
       
  • Three-dimensional grain growth during multi-layer printing of a
           nickel-based alloy Inconel 718
    • Abstract: Publication date: Available online 28 November 2018Source: Additive ManufacturingAuthor(s): H.L. Wei, G.L. Knapp, T. Mukherjee, T. DebRoy Heterogeneous grain structure is a source of the inhomogeneity in structure and properties of the metallic components made by multi-layer additive manufacturing (AM). During AM, repeated heating and cooling during multi-layer deposition, local temperature gradient and solidification growth rate, deposit geometry, and molten pool shape and size govern the evolution of the grain structure. Here the effects of these causative factors on the heterogeneous grain growth during multi-layer laser deposition of Inconel 718 are examined by a Monte Carlo method based grain growth model. It is found that epitaxial columnar grain growth occurs from the substrate or previously deposited layer to the curved top surface of the deposit. The growth direction of these columnar grains is controlled by the molten pool shape and size. The grains in the previously deposited layers continue to grow because of the repeated heating and cooling during the deposition of the successive layers. Average longitudinal grain area decreases by approximately 80 % when moving from the center to the edge of the deposit due to variable growth directions dependent on the local curvatures of the moving molten pool. The average horizontal grain area increases with the distance from the substrate, with a 20 % increase in the horizontal grain area in a short distance from the third to the eighth layer, due to competitive solid-state grain growth causes increased grain size in previous layers.Graphical abstractGraphical abstract for this article
       
  • Characterisation of porosity, density, and microstructure of directed
           energy deposited stainless steel AISI 316L
    • Abstract: Publication date: January 2019Source: Additive Manufacturing, Volume 25Author(s): Zhi’En Eddie Tan, John Hock Lye Pang, Jacek Kaminski, Helene Pepin Directed Energy Deposition (DED) was used to form a Stainless Steel AISI 316 L steel block component on a Mild Steel S235JR substrate. Porosity, density, and defect were characterised at 4 localities within the DED component by microscopy and x-ray tomography. Three-dimensional (3D) reconstruction of the x-ray tomographic image sequences focused at select porosities is presented. The element composition and Vickers microhardness measurements were taken at the fusion lines and track body locations to characterise the differences in materials and mechanical properties at the 2 locations. Lastly, an element mapping analysis was conducted to determine the solidification mode for the DED component. Sources for defects were proposed based on the characteristics of the porosity analysis and conclusions were made about the solidification behaviour of the DED component.
       
  • Designing for Big Area Additive Manufacturing
    • Abstract: Publication date: January 2019Source: Additive Manufacturing, Volume 25Author(s): Alex Roschli, Katherine T. Gaul, Alex M. Boulger, Brian K. Post, Phillip C. Chesser, Lonnie J. Love, Fletcher Blue, Michael Borish Additive manufacturing (AM), more commonly referred to as 3D printing, is revolutionizing the manufacturing industry. With any new technology comes new rules and guidelines for the optimal use of said technology. Big Area Additive Manufacturing (BAAM), developed by Cincinnati Incorporated and Oak Ridge National Laboratory’s Manufacturing Demonstration Facility, requires a host of new design parameters compared to small-scale 3D printing to create large-scale parts. However, BAAM also creates new possibilities in material testing and various applications in the manufacturing industry. Most of the design constraints of small-scale polymer 3D printers still apply to BAAM. Beyond those constraints, new rules and limitations exist because BAAM’s large-scale system significantly changes the thermal properties associated with small-scale AM. This work details both physical and software-related design considerations for additive manufacturing. After reading this guide, one will have a better understanding of slicing software’s capabilities and limitations, different physical characteristics of design and how to apply them appropriately for AM, and how to take the inherent nature of AM into consideration during the design process.
       
  • Interference fit of material extrusion parts
    • Abstract: Publication date: Available online 22 November 2018Source: Additive ManufacturingAuthor(s): L. Bottini, A. Boschetto Material extrusion is an Additive Manufacturing process able to fabricate a physical object directly from a virtual model using layer by layer deposition of a thermoplastic filament extruded by a nozzle. The fabrication of functional components implies the need for the assembly with other parts with different properties in terms of material and surface quality. One of the most used assembly method involving plastic materials is the interference fit. It consists of fastening elements in which the two parts are pushed together, by means of a fit force, and no other fastener is necessary. It requires the accurate design of the interference, typically carried out by the designers through diagrams and theoretical formulations supplied by the material manufacturers. At present no theory has been provided for material extrusion parts due to the anisotropic behavior: the mesostructure, the surface roughness and the dimensional deviations mainly depend upon the build orientation.In this work the effects of the surface morphology and the interference grade on the assembly and disassembly forces in an interference fit joint are investigated. For the purpose, a design of experiment with a factorial plan has been carried out. The coupling behavior and the maximum forces are discussed. A new variable namely the real interference has been introduced and a relationship between this variable and the assembly force has been found. Through this model it is possible to know in advance the force necessary to assemble a material extrusion part with an assigned interference grade.
       
  • Microstructure modelling of laser metal powder directed energy deposition
           of Alloy 718
    • Abstract: Publication date: Available online 22 November 2018Source: Additive ManufacturingAuthor(s): Chamara Kumara, Andreas Segerstark, Fabian Hanning, Nikhil Dixit, Shrikant Joshi, Johan Moverare, Per Nylén A multi-component and multi-phase-field modelling approach, combined with transformation kinetics modelling, was used to model microstructure evolution during laser metal powder directed energy deposition of Alloy 718 and subsequent heat treatments. Experimental temperature measurements were utilised to predict microstructural evolution during successive addition of layers. Segregation of alloying elements as well as formation of Laves and δ phase was specifically modelled. The predicted elemental concentrations were then used in transformation kinetics to estimate changes in Continuous Cooling Transformation (CCT) and Time Temperature Transformation (TTT) diagrams for Alloy 718. Modelling results showed good agreement with experimentally observed phase evolution within the microstructure. The results indicate that the approach can be a valuable tool, both for improving process understanding and for process development including subsequent heat treatment.
       
  • Deformation of honeycomb cellular structures manufactured with Laser
           Engineered Net Shaping (LENS) technology under quasi-static loading:
           experimental testing and simulation
    • Abstract: Publication date: Available online 19 November 2018Source: Additive ManufacturingAuthor(s): Paweł Baranowski, Paweł Płatek, Anna Antolak-Dudka, Marcin Sarzyński, Michał Kucewicz, Tomasz Durejko, Jerzy Małachowski, Jacek Janiszewski, Tomasz Czujko The paper presents a methodology investigation of honeycomb cellular structures deformation process in quasi-static compression tests. Two honeycomb topologies with different elementary cells were designed and manufactured from Ti-6Al-4 V alloy powder with the use of Laser Engineered Net Shaping (LENS) system and compressed using a universal strength machine. To simulate the deformation process with LS-Dyna software, the mechanical properties of the material were assessed and correlated. An elasto-visco-plastic material model (Mat_Plasticity_With_Damage) was used for predicting the material behavior. The results of experimental tests and numerical simulations were compared. A reasonable agreement between deformation, failure and force histories was obtained. Additionally, both the topologies were compared for their energy absorption capabilities. The validated numerical modelling with the adopted constitutive model will be used in the further studies to analyze different cellular structures topologies subjected to dynamic loading.
       
  • Visible light 3D printing with epoxidized vegetable oils
    • Abstract: Publication date: Available online 19 November 2018Source: Additive ManufacturingAuthor(s): Diego Savio Branciforti, Simone Lazzaroni, Chiara Milanese, Marco Castiglioni, Ferdinando Auricchio, Dario Pasini, Daniele Dondi Stereolithography is a 3D printing technique in which a liquid monomer is photopolymerized to produce a solid object. The most widely used materials usually belong to the family of acrylate monomers, and photopolymerization occurs through a radical pathway. Photoinitiators can absorb UV or (less often) visible light, producing radicals for direct decomposition or hydrogen abstraction. Due to the toxicity of acrylates, vegetable oil-derived monomers were used in this study. In fact, vegetable oils contain unsaturations, and thus, they can be exploited as monomers. In particular, linseed oil, tung oil or edible oils (soybean, sunflower or corn) could be good candidates as raw materials. Unfortunately, the photoinduced radical polymerization of these oils either does not occur or is too slow for 3D printing applications. For this reason, the oils were modified as epoxides. Epoxides are monomers that are more reactive than natural oils, and they can be polymerized via a cationic mechanism. The aim of this work was to exploit visible light generated by a common digital projector (like those used in classrooms) as a light source. Since the tested photoacid generators working under visible light are ineffective for the polymerization of epoxidized oils, a multi-component photo-initiating mixture was used.Graphical abstractGraphical abstract for this articleVegetable oil epoxides, together with curcumin and visible light could replace acrylates from 3D printing
       
  • Novel Plasma Treatment for Preparation of Laser Sintered Nanocomposite
           parts
    • Abstract: Publication date: Available online 19 November 2018Source: Additive ManufacturingAuthor(s): Alaa Almansoori, Kerry J. Abrams, Ammar D. Ghali Al-Rubaye, Candice Majewski, Cornelia RodenburgABSTRACTPolymer Laser Sintering (LS) is a well-known Additive Manufacturing process, capable of producing highly complex geometries with little or no cost penalty. However, the restricted range of materials currently available for this process has limited its applications. Whilst it is common to modify the properties of standard LS polymers with the inclusion of fillers e.g. nanoclays, achieving effective dispersions can be difficult. The work presented here investigates the use of plasma treatment as a method of enhancing dispersion with an expectation of improving consistency and surface quality of laser sintered nanocomposite parts. To enable the preparation of polyamide 12 nanocomposite powder for applications in LS, plasma surface modification using Low Pressure Air Plasma Treatment was carried out on two nanoclays: Cloisite 30B (C30B) and Nanomer I.34TCN (I.34TCN). Plasma treatment strongly reduced the aggregation of the nanoclay (C30B and I.34TCN) particles, and powders displayed higher decomposition temperatures than those without plasma treatment. LS parts from neat polyamide 12, untreated I.34TCN and plasma treated I.34TCN composites were successfully produced with different complex shapes. The presence of well dispersed plasma treated nanoclays was observed and found to be essential for an improved surface quality of LS fabricated which was achieved only for plasma treated I.34TCN. Likewise, some mechanical properties could be improved above that of PA12 by incorporation of treated I.34TCN. For example, the elastic modulus of plasma treated composites was higher than that of polyamide 12 and the untreated composite. In the case of the ultimate strain, the plasma treated composite performed better than untreated and results had a reduced variation between samples. This illustrates the feasibility of the use of plasma treatments on nanoclays to improve the properties of LS parts, even though further studies will be required to exploit the full potential.
       
  • The Influence of Forced-Air Cooling on a 3D Printed Part Manufactured by
           Fused Filament Fabrication
    • Abstract: Publication date: Available online 15 November 2018Source: Additive ManufacturingAuthor(s): Chun-Ying Lee, Chung-Yin Liu The dimensional quality and mechanical properties of a fused filament fabrication (FFF)-printed 3D model are influenced by several process parameters. A forced-air cooling system that moves along with the print head was designed and installed on a commercial 3D FFF printer to control the cooling of the printed model. The quality of the printed polylactide (PLA) model, including the dimensions and mechanical properties, was investigated for different cooling air velocities. It was found that the cooling air velocity had different influences on the dimensional quality and mechanical strength of the printed model. More specifically, higher cooling speeds generated better geometric accuracy but lower mechanical strength. With the highest and lowest cooling air speeds of 5 m/s and 0 m/s, respectively, the tensile strengths of the printed models differed by 4-fold. In order to determine a suitable cooling air velocity setting for each specific printing material, a design model was proposed. The determined printing parameters were employed in the fabrication of a Rubik’s cube, as an example. The assembled cube demonstrated satisfactory performance both in the dimensional quality and in the mechanical function. Therefore, the cooling air velocity can be employed as an additional control parameter in 3D printing for a specified model.
       
  • Selective laser melting of typical metallic materials: An effective
           process prediction model developed by energy absorption and consumption
           analysis
    • Abstract: Publication date: Available online 13 November 2018Source: Additive ManufacturingAuthor(s): Y.H. Zhou, Z.H. Zhang, Y.P. Wang, G. Liu, S.Y. Zhou, Y.L. Li, J. Shen, M. Yan Selective laser melting (SLM) is a laser-based additive manufacturing technique that can fabricate parts with complex geometries and sufficient mechanical properties. However, the optimal SLM process windows of metallic materials are difficult to predict, especially when exploring new metallic materials. In this paper, a universal and simplified model has been proposed to predict the energy density suitable for SLM of a variety of metallic materials including Ti and Ti alloys, Al alloy, Ni-based superalloy and steel, on the basis of the relationship between energy absorption and consumption during SLM. Several important but easily overlooked factors, including the surface structure of metallic powder, porosity of powder bed, vaporization and heat loss, were considered to improve the accuracy of the model. Results show that, to achieve near-full density parts, the energy absorption (Qa) by the local powder bed should be approximately 3–8 times greater than the energy consumption (Qc), and this finding applies to all materials investigated. The value of Qa/Qc highly depends on material properties, particularly laser absorptivity, latent heat of melting and specific heat capacity. Experiments on high-entropy alloy (CrMnFeCoNi) and Hastelloy X alloy, new metallic materials for SLM, have been further conducted to verify the model. Results confirm that the model can predict suitable laser energy densities needed for processing the various metallic materials without tedious trial and error experiments. Indications and uncertainty of the model have also been analyzed.Graphical abstractGraphical abstract for this article
       
  • Geometrical effects on residual stress in selective laser melting
    • Abstract: Publication date: Available online 25 September 2018Source: Additive ManufacturingAuthor(s): L.A. Parry, I.A. Ashcroft, R.D. Wildman Selective laser melting is an increasingly attractive technology for the manufacture of complex and low volume / high value metal parts. However, the inevitable residual stresses that are generated can lead to defects or build failure. Due to the complexity of this process, efficient and accurate prediction of residual stress in large components remains challenging. For the development of predictive models of residual stress, knowledge on their generation is needed. This study investigates the geometrical effect of scan strategy on residual stress development. It was found that the arrangement of scan vectors due to geometry, heavily influenced the thermal history within a part, which in turn significantly affected the transverse residual stresses generated. However, irrespective of the choice of scanned geometry and the thermal history, the higher magnitude longitudinal stresses had consistent behaviour based on the scan vector length. It was shown that the laser scan strategy becomes less important for scan vector length beyond 3 mm. Together, these findings, provide a route towards optimising scan strategies at the meso-scale, and additionally, developing a model abstraction for predicting residual stress based on scan vectors alone.
       
  • The Effect of SLM Process Parameters on Density, Hardness, Tensile
           Strength and Surface Quality of Ti-6Al-4V
    • Abstract: Publication date: Available online 5 September 2018Source: Additive ManufacturingAuthor(s): Amir Mahyar Khorasani, Ian Gibson, Umar Shafique Awan, Alireza Ghaderi In this paper, we printed Ti-6Al-4 V SLM parts based on Taguchi design of experiment and related standards to measure and compare hardness with different mechanical properties that were obtained in our previous research such as density, strength, elongation, and average surface. Then the effect of process parameters comprising laser power, scan speed, hatch space, laser pattern angle coupling, along with heat treatment as a post-process, in relation to hardness was analysed. The relation of measured factors with each other was also studied and related mechanisms were discussed in depth. The original contribution in this paper is in producing a large and precise dataset and the comparison with mechanical properties. Another contribution is related to the analysis of process parameters in relation to hardness and explaining them by rheological phenomena. The results showed an interesting similarity between hardness and density which is highly related to the formation of the melting pool and porosities within the process.
       
  • Using Machine Learning to identify In-Situ Melt Pool Signatures Indicative
           of Flaw Formation in a Laser Powder Bed Fusion Additive Manufacturing
           Process
    • Abstract: Publication date: Available online 11 November 2018Source: Additive ManufacturingAuthor(s): Luke Scime, Jack Beuth Because many of the most important defects in Laser Powder Bed Fusion (L-PBF) occur at the size and timescales of the melt pool itself, the development of methodologies for monitoring the melt pool is critical. This works examines the possibility of in-situ detection of keyholing porosity and balling instabilities. Specifically, a visible-light high speed camera with a fixed field of view is used to study the morphology of L-PBF melt pools in the Inconel 718 material system. A scale-invariant description of melt pool morphology is constructed using Computer Vision techniques and unsupervised Machine Learning is used to differentiate between observed melt pools. By observing melt pools produced across process space, in-situ signatures are identified which may indicate flaws such as those observed ex-situ. This linkage of ex-situ and in-situ morphology enabled the use of supervised Machine Learning to classify melt pools observed (with the high speed camera) during fusion of non-bulk geometries such as overhangs.
       
  • Recycled polypropylene blends as novel 3D printing materials
    • Abstract: Publication date: Available online 8 November 2018Source: Additive ManufacturingAuthor(s): Nicole E. Zander, Margaret Gillan, Zachary Burckhard, Frank Gardea Consumer-grade plastics can be considered a low-cost and sustainable feedstock for fused filament fabrication (FFF) additive manufacturing processes. Such materials are excellent candidates for distributed manufacturing, in which parts are printed from local materials at the point of need. Most plastic waste streams contain a mixture of polymers, such as water bottles and caps comprised of polyethylene terephthalate (PET) and polypropylene (PP), and complete separation is rarely implemented. In this work, blends of waste PET, PP and polystyrene (PS) were processed into filaments for 3D printing. The effect of blend composition and styrene ethylene butylene styrene (SEBS) compatibilizer on the resulting mechanical and thermal properties were probed. Recycled PET had the highest tensile strength at 35 ± 8 MPa. Blends of PP/PET compatibilized with SEBS and maleic anhydride functionalized SEBS had tensile strengths of 23 ± 1 MPa and 24 ± 1 MPa, respectively. The non-compatibilized PP/PS blend had a tensile strength of 22 ± 1 MPa. PP/PS blends exhibited reduced tensile strength to ca. 19 ± 1-3 MPa with the addition of SEBS. Elongation to failure was generally improved for the blended materials compared to neat recycled PET and PS. The glass transition was shifted to higher temperatures for all of the blends except the 50-50 wt. % PP/PET blend. Crystallinity was decreased for the blends, but was highest in the 75-25 wt. % PP/PS and the 50-50 wt. % PP/PET blend with SEBS-maleic anhydride. Solvent extraction of the dispersed phase revealed polypropylene was the matrix phase in both the 50-50 wt. % PP/PET and PP/PS blends.Graphical abstractGraphical abstract for this article
       
  • terial_Spec_Sheets/MSS_PJ_PJMaterialsDataSheet_051Digital Design and
           Nonlinear Simulation for Additive Manufacturing of Soft Lattice Structures
           
    • Abstract: Publication date: Available online 6 November 2018Source: Additive ManufacturingAuthor(s): O. Weeger, N. Boddeti, S.-K. Yeung, S. Kaijima, M.L. Dunn Lattice structures are frequently found in nature and engineering due to their myriad attractive properties, with applications ranging from molecular to architectural scales. Lattices have also become a key concept in additive manufacturing, which enables precise fabrication of complex lattices that would not be possible otherwise. While design and simulation tools for stiff lattices are common, here we present a digital design and nonlinear simulation approach for additive manufacturing of soft lattices structures subject to large deformations and instabilities, for which applications in soft robotics, healthcare, personal protection, energy absorption, fashion and design are rapidly emerging. Our framework enables design of soft lattices with curved members conforming to freeform geometries, and with variable, gradually changing member thickness and material, allowing the local control of stiffness. We model the lattice members as 3D curved rods and using a spline-based isogeometric method that allows the efficient simulation of nonlinear, large deformation behavior of these structures directly from the CAD geometries. Furthermore, we enhance the formulation with a new joint stiffening approach, which is based on parameters derived from the actual node geometries. Simulation results are verified against experiments with soft lattices realized by PolyJet multi-material polymer 3D printing, highlighting the potential for simulation-driven, digital design and application of non-uniform and curved soft lattice structures.
       
  • Evidence of austenite by-passing in a stainless steel obtained from laser
           melting additive manufacturing
    • Abstract: Publication date: Available online 6 November 2018Source: Additive ManufacturingAuthor(s): Michella Alnajjar, Frédéric Christien, Krzysztof Wolski, Cedric Bosch Microstructural characterization was carried out on AISI 17-4 PH stainless steel fabricated by selective laser melting (SLM) in an argon environment. Conventionally, this steel exhibits a martensitic structure with a small fraction of δ ferrite. However, the combined findings of x-ray diffraction and electron backscatter diffraction (EBSD) proved that SLM-ed 17-4 PH steel has a fully ferritic microstructure, more specifically  δ ferrite. The microstructure consists of coarse ferritic grains elongated along the build direction, with a pronounced solidification crystallographic texture. These results were associated to the high cooling and heating rates experienced throughout the SLM process that suppressed the austenite formation and produced a “by-passing” phenomenon of this phase during the numerous thermal cycles. Furthermore, the energy-dispersive X-ray spectroscopy (EDS) measurements revealed a uniform distribution of elements without any dendritic structure. The extremely high cooling kinetics induced a diffusionless solidification, resulting in a homogeneous elemental composition. It was also found that the ferritic SLM-ed material can be transformed to martensite again by re-austenitization at 1050 °C followed by quenching.Graphical abstractGraphical abstract for this article
       
  • Aging effects of polyamide 12 in selective laser sintering: Molecular
           weight distribution and thermal properties
    • Abstract: Publication date: Available online 6 November 2018Source: Additive ManufacturingAuthor(s): Katrin Wudy, Dietmar Drummer The material aging in selective laser sintering SLS of polyamide 12 is one challenge, which has to be overcome for implementation of this technique in serial production. High temperatures and along going processing times lead to chemical and physical aging effects of the supporting partcake material. Resulting aging mechanisms are not understood up to now. The investigations in this study aims at the influence of processing time and temperature on molecular changes and thermal properties of polyamide 12 partcake material in selective laser sintering. The focus of the investigations lays on the global heat exposure of the of the bulk material und thus on global material changes. Gel permeation chromatography analysis was used to determine the molecular weight distribution and changes of polymer structure. The Mark-Houwink plot exhibits a linear chain growth, which is a hint for a resulting solid state polycondensation. With increasing build time and build chamber temperature the average molecular weight is rising, whereby the influence of build time is more significant. The rise of chain length leads to a reduction of crystallization temperature, which was detected by DSC.Graphical abstractGraphical abstract for this article
       
  • Effects of Cold Plasma Treatment on Interlayer Bonding Strength in FFF
           Process
    • Abstract: Publication date: Available online 6 November 2018Source: Additive ManufacturingAuthor(s): Chin-Cheng Shih, Matthew Burnette, David Staack, Jyhwen Wang, Bruce L. Tai Fused Filament Fabrication (FFF) is the most popular additive manufacturing method because of its numerous capabilities and relatively low cost. This comes with a trade off as FFF printed parts are typically weak in the layer deposition direction due to insufficient interlayer bonding. This research adopts the method of cold plasma treatment and investigates the potential enhancement of interlayer bonding by altering the printed surface prior to the deposition of the next layer. Polylactic acid (PLA) is used as the printing material, due to its ubiquity in industry. The bonding strength is measured by the shear bond strength test. The results show that bond strength improved over 100% with 30 s of treatment and over 50% with 300 s of treatment. A mechanically polished surface is also included in the comparison for the high surface wettability, but the result shows no improvement. This indicates that wettability may not be the dominant mechanism for enhanced bonding after treatment.
       
  • Reducing the Roughness of Internal Surface of an Additive Manufacturing
           Produced 316 Steel Component by Chempolishing and Electropolishing
    • Abstract: Publication date: Available online 6 November 2018Source: Additive ManufacturingAuthor(s): Pawan Tyagi, Tobias Goulet, Christopher Riso, Robert Stephenson, Nitt Chuenprateep, Justin Schlitzer, Cordell Benton, Francisco Garcia-Moreno Surface roughness of an as produced AM component is very high, which prohibits the direct utilization of additively manufactured (AM) components for the intended applications. Reducing surface roughness is exponentially more challenging for the internal surfaces of an AM component. This paper reports our research in the area of postprocessing of interior surfaces of an AM component. We have investigated electropolishing and chemical polishing (chempolishing) methods to reduce the surface roughness of the internal surface. We found that chempolishing was effective in simultaneously reducing the internal and external surface roughness of 316 steel AM components. Chempolishing is found suitable for any complicated AM shape and geometry. Our electropolishing methodology was effective in reducing the surface roughness of the internal or external surfaces provided that a counter electrode could be positioned in the proximity of the surface to be polished. We have performed optical profilometry, scanning electron microscopy, and contact angle measurement study to investigate the difference between electropolishing and chemical polishing methods.
       
  • Mechanical Properties of Hexagonal Lattice Structures Fabricated Using
           Continuous Liquid Interface Production Additive Manufacturing
    • Abstract: Publication date: Available online 3 November 2018Source: Additive ManufacturingAuthor(s): Davis J. McGregor, Sameh Tawfick, William P. King Additive manufacturing (AM) is a key enabler for architectured lattice materials, because of the geometric complexity of parts that can be produced. Recent advancements in AM have enabled rapid production speeds, high spatial resolution, and a variety of engineering polymers. An open question remains whether production grade AM can accurately and repeatably produce lattice parts. This study presents design, production, and mechanical property testing of hexagonal lattice parts manufactured using continuous liquid interface production (CLIP) based AM. We printed and tested 84 parts, in three polymer materials having relative density ranging from 0.06 to 0.23. Lattice wall structures were reliably printed when truss aspect ratio was in the range 5 to 20 and wall thicknesses are 0.35 or 0.5 mm. The printed lattice parts, each comprising hundreds of slender walls, were measured using high resolution optical scanning. The images were analyzed to evaluate the difference between the printed parts and their designs, and the effect of geometric deviations on the mechanical behavior. The measured elastic moduli of the printed parts are close to the values expected from the materials specifications. The strength of all printed parts deviates by 7% from the behavior predicted from the scanned geometry. The failure mode of the printed structures depends upon the material and part geometry. To our knowledge, this is the largest study on the accuracy and performance of AM lattice parts, and the first study of its type for lattice parts made using CLIP.
       
  • Evolution of 316L Stainless Steel Feedstock Due to Laser Powder Bed Fusion
           Process
    • Abstract: Publication date: Available online 2 November 2018Source: Additive ManufacturingAuthor(s): Michael J. Heiden, Lisa A. Deibler, Jeff M. Rodelas, Josh R. Koepke, Dan J. Tung, David J. Saiz, Bradley H. Jared
       
  • Investigation on the mode of failures and fatigue life of laser-based
           powder bed fusion produced stainless steel parts under variable amplitude
           loading conditions
    • Abstract: Publication date: Available online 2 November 2018Source: Additive ManufacturingAuthor(s): Sagar Sarkar, Cheruvu Siva Kumar, Ashish Kumar Nath Additive Manufacturing (AM) is a method of joining metal/non-metals or composites layer by layer using different energy sources. Among the various AM processes, laser-based powder bed fusion (LPBF) is very popular, in which geometrically complex structures can be manufactured directly from CAD models. One of the least investigated areas in LPBF is the fatigue property of LPBF produced stainless steel parts, which find a variety of engineering and medical applications. In actual service conditions, many engineering components undergo variable cyclic loadings. Therefore, in order to widen industrial applications of LPBF process, effects of variable amplitude loading under both zero and tensile mean stresses on the fatigue life of LPBF produced 15-5 precipitation hardened stainless steel parts have been examined in the present study. Further, different modes of failure, effects of load sequences on fatigue life and the cumulative damage during the process have also been studied. For a typical case under tensile mean stress, results showed that the number of cycles to failure with low to high loading sequence was almost double of that with the sequence reversed. Also, the cumulative damage was more in the first case than that of the second case. Fracture surfaces were studied using Scanning Electron Microscopy to investigate the mode of failures and completely different fracture surface morphologies for these two cases explain the observed difference in number of cycles to failure with the reversal of the load sequence.
       
  • Implications of modeling approaches on the fatigue behavior of cellular
           solids
    • Abstract: Publication date: Available online 2 November 2018Source: Additive ManufacturingAuthor(s): Gianpaolo Savio, Stefano Rosso, Andrea Curtarello, Roberto Meneghello, Gianmaria Concheri According to recent studies, a new paradigm in the geometric modeling of lattice structures based on subdivision surfaces for additive manufacturing overcomes the critical issues on CAD modeling highlighted in the literature, such as scalability, robustness, and automation. In this work, the mechanical behavior of the subdivided lattice structures was investigated and compared with the standard lattices. Five types of cellular structures based on cubic cell were modeled: struts based on squared or circular section, with or without fillets and cell based on the subdivision approach. Sixty-five specimens were manufactured by selective laser sintering technology in polyamide 12 and tensile and fatigue tests were performed. Furthermore, numerical analyses were carried out in order to establish the stress concentration factors.Results show that subdivided lattice structures, at the same resistant area, improve stiffness and fatigue life and reduce stress concentration while opening new perspectives in the development of lattice structures for additive manufacturing technologies and applications.Graphical abstractGraphical abstract for this article
       
  • Planar Deposition Flow Modeling of Fiber Filled Composites in Large Area
           Additive Manufacturing
    • Abstract: Publication date: Available online 1 November 2018Source: Additive ManufacturingAuthor(s): Blake P. Heller, Douglas E. Smith, David A. Jack The rapid transition of the Fused Filament Fabrication (FFF) Additive Manufacturing (AM) process from small scale prototype models to large scale polymer deposition has been driven, in part, by the addition of short carbon fibers to the polymer feedstock. The addition of short carbon fibers improves both the mechanical and thermal properties of the printed beads. The improvements to the anisotropic mechanical and thermal properties of the polymer feedstock are dependent on the spatially varying orientation of short carbon fibers which is itself a function of the velocity gradients in the flow field throughout the nozzle and in the extrudate during deposition flow. This paper presents a computational approach for simulating the deposition flow that occurs in the Large Area Additive Manufacturing (LAAM) process and the effects on the final short fiber orientation state in the deposited polymer bead and the resulting bead mechanical and thermal properties. The finite element method is used to evaluate Stokes flow for a two-dimensional planar flow field within a Strangpresse Model 19 LAAM polymer deposition nozzle. A shape optimization method is employed to compute the shape of the polymer melt flow free surface below the nozzle exit as the bead is deposited on a moving print platform. Three nozzle configurations are considered in this study. Fiber orientation tensors are calculated throughout the fluid domain using the Folgar-Tucker fiber interaction model. The effective bulk mechanical properties, specifically the longitudinal and transverse moduli, and the coefficient of thermal expansion, are also calculated for the deposited bead based on the spatially varying fiber orientation tensors. Fiber orientation is found to be highly aligned along the deposition direction of the resulting bead and the computed properties through the thickness of the bead are found to be affected by nozzle height during deposition.
       
  • Plastic Anisotropy of Additively Manufactured Maraging Steel: Influence of
           the Build Orientation and Heat Treatments
    • Abstract: Publication date: Available online 31 October 2018Source: Additive ManufacturingAuthor(s): Barry Mooney, Kyriakos I. Kourousis, Ramesh Raghavendra This experimental study investigates the combined effect of the three primary Additive Manufacturing (AM) build orientations (0∘, 45∘, and 90∘) and an extensive array of heat treatment plans on the plastic anisotropy of maraging steel 300 (MS1) fabricated on the EOSINT M280 Direct Metal Laser Sintering (DMLS) system. The alloy's microstructure, hardness, tensile properties and plastic strain behaviour have been examined for various strengthening heat-treatment plans to assess the influence of the time and temperature combinations on plastic anisotropy and mechanical properties (e.g. strength, ductility). A comprehensive visual representation of the material's overall mechanical properties, for all three AM build orientations, against the various heat treatment plans is offered through time - temperature contour maps. Considerable plastic anisotropy has been confirmed in the as-built condition, which can be reduced by aging heat-treatment, as verified in this study. However, it has identified that a degree of transverse strain anisotropy is likely to remain due to the AM alloy's fabrication history, a finding that has not been previously reported in the literature. Moreover, the heat treatment plan (6h at 490∘C) recommended by the DMLS system manufacturer has been found not to be the optimal in terms of achieving high strength, hardness, ductility and low anisotropy for the MS1 material. With the use of the comprehensive experimental data collected and analysed in this study, and presented in the constructed contour maps, the alloy's heat treatment parameters (time, temperature) can be tailored to meet the desired strength/ductility/anisotropy design requirements, either for research or part production purposes.
       
  • Laser metal deposition of compositionally graded TiZrNbTa refractory
           high-entropy alloys using elemental powder blends
    • Abstract: Publication date: Available online 31 October 2018Source: Additive ManufacturingAuthor(s): Henrik Dobbelstein, Evgeny L. Gurevich, Easo P. George, Andreas Ostendorf, Guillaume Laplanche In the present study, laser metal deposition (LMD) was used to produce compositionally graded refractory high-entropy alloys (HEAs) for screening purposes by in-situ alloying of elemental powder blends. A compositional gradient from Ti25Zr50Nb0Ta25 to Ti25Zr0Nb50Ta25 is obtained by incrementally substituting Zr powder with Nb powder. A suitable strategy was developed to process the powder blend despite several challenges such as the high melting points of the refractory elements and the large differences in melting points among them. The influence of the LMD process on the final chemical composition was analyzed in detail and the LMD process was optimized to obtain a well-defined compositional gradient. Microstructures, textures, chemical compositions and mechanical properties were characterized using SEM, EBSD, EDX, and microhardness testing, respectively. Compositions between Ti25Zr0Nb50Ta25 and Ti25Zr25Nb25Ta25 were found to be single-phase bcc solid solutions with a coarse grain microstructure. Increasing the Zr to Nb ratio beyond the equiatomic composition results in finer and harder multiphase microstructures. The results shown in the present study clearly show for the first time that LMD is a suitable processing tool to screen HEAs over a range of chemical compositions.
       
  • In situ multi-elemental analysis by laser induced breakdown spectroscopy
           in additive manufacturing
    • Abstract: Publication date: Available online 31 October 2018Source: Additive ManufacturingAuthor(s): Vasily N. Lednev, Pavel A. Sdvizhenskii, Roman D. Asyutin, Roman S. Tretyakov, Mikhail Ya. Grishin, Anton Ya. Stavertiy, Sergey M. Pershin The feasibility of in situ quantitative multi-elemental analysis during the additive manufacturing process has been demonstrated for the first time using laser induced breakdown spectroscopy (LIBS). The coaxial laser cladding technique was utilized for the production of highly wear-resistant coatings (nickel alloy reinforced with tungsten carbide grains). High-quality production as well as gradient composition coating synthesis required an online technique for quantitative elemental analysis. A low-weight, compact LIBS probe was designed to equip the laser cladding head installed at an industrial robot. Hot solidified clad as well as a melt pool surface was sampled by the LIBS probe but meaningful analytical results were achieved only for the latter case due to non-uniform distribution of tungsten carbide grains in the upper surface layer. No effect was observed for the laser ablation at the melt pool on the clad properties by optical microscopy and scanning electron microscopy studies. On-line LIBS quantitative analysis of key components (carbon and tungsten) was achieved during the synthesis of highly wear-resistant coatings and obtained results were in good agreement with offline analysis obtained by electron energy dispersive X-ray spectroscopy, X-ray fluorescence spectroscopy, and the combustion infrared absorption method.
       
  • Influence of printing parameters on the stability of deposited beads in
           fused filament fabrication of poly(lactic) acid
    • Abstract: Publication date: Available online 31 October 2018Source: Additive ManufacturingAuthor(s): Shahriar Bakrani Balani, France Chabert, Valérie Nassiet, Arthur Cantarel Fused filament fabrication (FFF) is one of the various types of additive manufacturing processes. Similar to other types, FFF enables free-form fabrication and optimised structures by using polymeric filaments as the raw material. This work aims to optimise the printing conditions of the FFF process based on reliable properties, such as printing parameters and physical properties of polymers. The selected polymer is poly(lactic) acid (PLA), which is a biodegradable thermoplastic polyester derived from corn starch and is one of the most common polymers in the FFF process. Firstly, the maximum inlet velocity of the filament in the liquefier was empirically determined according to process parameters, such as feed rate, nozzle diameter and dimensions of the deposited segment. Secondly, the rheological behaviour of the PLA, including the velocity field, shear rate and viscosity distribution in the nozzle, was determined via analytical study and numerical simulation. Our results indicated the variation in the shear rate according to the diameter of the nozzle and the inlet velocity. The shear rate attained its maximum value near the internal wall at high inlet velocities and smaller diameters. Finally, the distribution of the viscosity along the radius of the nozzle was obtained. At high inlet velocity, several defects appeared at the surface of the extrudates. At the highest shear rates, the extrudates underwent severe deformation. The defects predicted via numerical simulation were reasonably consistent with that observed from an optical microscope. Hence, these results are effective for selecting the printing parameters (i.e. nozzle diameter, feed rate and layer height) to improve the quality of the manufactured parts.
       
  • Powder bed fusion metrology for additive manufacturing design guidance
    • Abstract: Publication date: Available online 28 October 2018Source: Additive ManufacturingAuthor(s): Jared Allison, Conner Sharpe, Carolyn Conner Seepersad Design for additive manufacturing (DFAM) guidelines are important for helping designers avoid iterations and leverage the design freedoms afforded by additive manufacturing (AM). Comprehensive design guidelines should incorporate a variety of features of interest to designers, and given the wide variety of AM processes and their associated capabilities and limitations, those guidelines may need to be process- or even machine-specific. One way to generate detailed DFAM guidelines is to implement a metrology study focused on a strategically designed test part. This paper describes how quantitative design guidelines are compiled for a polymer selective laser sintering (SLS) process via a metrology study. As part of the metrology study, a test part is designed to focus specifically on geometric resolution and accuracy of the polymer SLS process. The test part is compact, allowing it to be easily inserted into existing SLS builds and therefore eliminating the need for dedicated metrology builds. To build a statistical foundation upon which design guidelines can be compiled, multiple copies of the test part are fabricated within existing commercial builds in a factorial study with materials, build orientations, and locations within the build chamber as control factors. Design guidelines are established by measuring and analyzing the as-built test parts. The guidelines are summarized in this paper and documented in a publicly accessible, online web tool.
       
  • In-situ Monitoring of Laser-based PBF via off-axis Vision and Image
           Processing Approaches
    • Abstract: Publication date: Available online 28 October 2018Source: Additive ManufacturingAuthor(s): Yingjie Zhang, Jerry Y H Fuh, Dongsen Ye, Geok Soon Hong With the development of powder bed fusion (PBF) additive manufacturing technique for functional parts production, process monitoring and diagnosis is highly demanded to ensure its process reliability and repeatability. An off-axis vision monitoring method using high-speed camera is proposed in this paper. An optical filter with 350 nm-800 nm cut-off was used to enhance the image contrast between the plume and the melt pool. A new image processing method was designed to extract features from the melt pool, plume and spatters, respectively. Kalman filter tracking was used to pinpoint the exact melt pool position, and image segmentation algorithm was developed to segment the melt pool, plume and spatters from each other; a new tracking method was utilized to remove the spatters generated in the previous frame. After image processing, the features of melt pool intensity, plume area, plume orientation, spatter number, spatter area, spatter orientation and spatter velocity were extracted and their correlations with the scanning quality were investigated. The results indicated that these features were potential indicators for scanning quality assessment. The proposed method could be used to further study the characteristics of plume and spatter and to explore the diagnosis performance based on the fusion of melt pool, plume and spatter information. It provides a promising means for in-situ monitoring and control of PBF process.
       
  • Epoxy Infiltrated 3D Printed Ceramics for Composite Tooling Applications
    • Abstract: Publication date: Available online 23 October 2018Source: Additive ManufacturingAuthor(s): Michael Maravola, Brett Conner, Jason Walker, Pedro Cortes The use of additive manufacturing (AM) provides an opportunity to fabricate composite tooling molds in a rapidly and cost effectively manner. This work has shown the use of a polymer based infiltrated ceramics produced via binder jetting for producing composite tooling molds. Here, molds based on silica sand as well as zircon sand have been printed on a S-Max 3D printer unit and subsequently impregnated with an epoxy system for yielding functional molds in the range of autoclave temperatures around 150-177 °C. The mechanical properties of the infiltrated 3D printed materials have been investigated and it was observed that the polymer-infiltrated systems resulted in a compressive and flexural strength one order of magnitude higher than the non-infiltrated printed ceramic material. A thermal analysis was also performed on both the infiltrated and non-infiltrated printed samples, and it was recorded that the incorporation of the polymer resulted in a larger coefficient of thermal expansion on the infiltrated systems. Here, a carbon fiber reinforced composite was manufactured with the infiltrated composite tooling molds printed in the S-Max unit, and it was observed that the assembled molds are capable of producing a successful composite material. The present work has demonstrated that a binder jetting process, is a feasible technology for producing thermostable low cost composite tooling molds.
       
 
 
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