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Publisher: Elsevier   (Total: 3159 journals)

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Showing 1 - 200 of 3159 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: 32, SJR: 1.655, CiteScore: 2)
Academic Radiology     Hybrid Journal   (Followers: 22, SJR: 1.015, CiteScore: 2)
Accident Analysis & Prevention     Partially Free   (Followers: 90, SJR: 1.462, CiteScore: 3)
Accounting Forum     Hybrid Journal   (Followers: 25, SJR: 0.932, CiteScore: 2)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 34, 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: 408, SJR: 0.758, CiteScore: 2)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 2)
Acta Biomaterialia     Hybrid Journal   (Followers: 27, 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: 8, 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: 246, 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: 10, SJR: 0.834, CiteScore: 2)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription  
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 2, SJR: 0.307, CiteScore: 0)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 1, SJR: 1.793, CiteScore: 6)
Acta Poética     Open Access   (Followers: 4, SJR: 0.101, CiteScore: 0)
Acta Psychologica     Hybrid Journal   (Followers: 28, 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: 6)
Acute Pain     Full-text available via subscription   (Followers: 15, SJR: 2.671, CiteScore: 5)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.53, CiteScore: 4)
Addictive Behaviors     Hybrid Journal   (Followers: 16, SJR: 1.29, CiteScore: 3)
Addictive Behaviors Reports     Open Access   (Followers: 8, SJR: 0.755, CiteScore: 2)
Additive Manufacturing     Hybrid Journal   (Followers: 9, SJR: 2.611, CiteScore: 8)
Additives for Polymers     Full-text available via subscription   (Followers: 22)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 143, SJR: 4.09, CiteScore: 13)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 11, SJR: 1.167, CiteScore: 4)
Advanced Powder Technology     Hybrid Journal   (Followers: 16, 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: 12, 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: 22, 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: 30, SJR: 3.043, CiteScore: 6)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 7, 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: 3)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 12)
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: 28, 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: 11)
Advances in Digestive Medicine     Open Access   (Followers: 9)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 5)
Advances in Drug Research     Full-text available via subscription   (Followers: 24)
Advances in Ecological Research     Full-text available via subscription   (Followers: 43, SJR: 2.524, CiteScore: 4)
Advances in Engineering Software     Hybrid Journal   (Followers: 27, SJR: 1.159, CiteScore: 4)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 7)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 44, 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: 54, 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: 16, SJR: 1.354, CiteScore: 4)
Advances in Genome Biology     Full-text available via subscription   (Followers: 8, 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: 21, SJR: 0.368, CiteScore: 1)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 11, SJR: 0.749, CiteScore: 3)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 22)
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: 9)
Advances in Marine Biology     Full-text available via subscription   (Followers: 14, 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: 6, 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: 21)
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: 1)
Advances in Organ Biology     Full-text available via subscription   (Followers: 1)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 16, 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: 10)
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: 8)
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: 18)
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: 63)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 6, SJR: 0.371, CiteScore: 1)
Advances in Radiation Oncology     Open Access   (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: 5)
Advances in Space Research     Full-text available via subscription   (Followers: 396, 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: 10, SJR: 0.555, CiteScore: 2)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 31, 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: 13)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 2.262, CiteScore: 5)
Advances in Water Resources     Hybrid Journal   (Followers: 46, SJR: 1.551, CiteScore: 3)
Aeolian Research     Hybrid Journal   (Followers: 6, SJR: 1.117, CiteScore: 3)
Aerospace Science and Technology     Hybrid Journal   (Followers: 336, 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: 445, SJR: 1.238, CiteScore: 3)
Agri Gene     Hybrid Journal   (SJR: 0.13, CiteScore: 0)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 16, SJR: 1.818, CiteScore: 5)
Agricultural Systems     Hybrid Journal   (Followers: 32, SJR: 1.156, CiteScore: 4)
Agricultural Water Management     Hybrid Journal   (Followers: 43, SJR: 1.272, CiteScore: 3)
Agriculture and Agricultural Science Procedia     Open Access   (Followers: 1)
Agriculture and Natural Resources     Open Access   (Followers: 2)
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: 11, SJR: 1.153, CiteScore: 3)
Alcoholism and Drug Addiction     Open Access   (Followers: 9)
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: 9, SJR: 0.201, CiteScore: 1)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 50, 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: 50, SJR: 3.267, CiteScore: 4)
American J. of Cardiology     Hybrid Journal   (Followers: 54, 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: 14, 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: 28, SJR: 1.062, CiteScore: 2)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 34, SJR: 2.973, CiteScore: 4)
American J. of Medicine     Hybrid Journal   (Followers: 45)
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: 202, SJR: 2.7, CiteScore: 4)
American J. of Ophthalmology     Hybrid Journal   (Followers: 63, 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: 27, SJR: 2.139, CiteScore: 4)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 28, SJR: 2.164, CiteScore: 4)
American J. of Surgery     Hybrid Journal   (Followers: 37, 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: 6)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.144, CiteScore: 3)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 62, SJR: 0.138, CiteScore: 0)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 16, SJR: 0.411, CiteScore: 1)
Anales de Cirugia Vascular     Full-text available via subscription  
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: 40, SJR: 1.512, CiteScore: 5)
Analytical Biochemistry     Hybrid Journal   (Followers: 173, SJR: 0.633, CiteScore: 2)
Analytical Chemistry Research     Open Access   (Followers: 10, SJR: 0.411, CiteScore: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 11)
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: 190, 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: 9  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 2214-8604
Published by Elsevier Homepage  [3159 journals]
  • Split Hopkinson pressure bar tests for investigating dynamic properties of
           additively manufactured AlSi10Mg alloy by selective laser melting
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Bar Nurel, Moshe Nahmany, Nachum Frage, Adin Stern, Oren Sadot Dynamic properties of additively manufactured AlSi10Mg alloy by selective laser melting (AM–SLM-processed) have been investigated using the split Hopkinson pressure bar (SHPB) system. Additive manufacturing (AM) processes have attracted increased attention over the past three decades, and AlSi10Mg is an alloy commonly used in AM processes. AlSi10Mg is a widely used material, and has been a subject of extensive investigations concerning its microstructure, quasi-static properties, and post-processing. Nonetheless, dynamic mechanical properties of this alloy are yet to be explored over a wide range of strain rates. Dynamic properties of X- and Z-oriented AlSi10Mg alloy samples in the as-built and T5 heat-treated (T5-HT) states were investigated using SHPB under strain rates varying over a range of 700–7900 s−1. The investigation revealed an important dependence of dynamic properties of the said alloy on build orientation when subjected to strain rates range of the order of 1000–3000 s−1. At values of strain rate above and below this range, the observed dependency no longer existed. In addition, dependency of dynamic properties of the alloy on its thermal state (as-built versus T5-HT state) was investigated for the first time along with detection of no-strain-rate sensitivity of the AM-SLM-processed AlSi10Mg alloy. A pronounced ellipticity was observed in most samples, thereby reflecting the anisotropic nature of the alloy. Fractography and optical microscopy analyses revealed differences between fracture morphologies observed in the as-built and T5-HT samples. Cracks observed were predominantly of the radial type (with minor circumferential cracks) under the brittle fracture mode in as-built samples. In contrast, T5-HT samples mainly demonstrated the ductile mode of deformation.
       
  • Effect of oxygen content in new and reused powder on microstructural and
           mechanical properties of Ti6Al4V parts produced by Directed Energy
           Deposition
    • Abstract: Publication date: Available online 10 August 2018Source: Additive ManufacturingAuthor(s): Jean Nicolas Rousseau, Alexandre Bois-Brochu, Carl Blais Some AM processes such as directed energy deposition (DED) have typical powder usage efficiencies ranging between 40 and 80 %. Since, for a given alloy, powder cost is proportional to its purity, choosing a less expensive powder or reusing powders is interesting for economical and environmental reasons. The work summarized below studied the effect of oxygen content in Ti6Al4V powders on mechanical properties of AM parts fabricated by DED. Three different powders with increasing oxygen content were used to produce specimens and characterize its effect on microstructure and tensile properties before and after heat treatment. Our results show that no clear oxygen pick up was measured from either powder recycling or during printing of parts. Only coarsening of the particle size distribution and the presence of fragmented particles was observed for the recycled powder. Comparing the chemistry of parts vs that of powder feedstock it was determined that for all the tests, the Al content was slightly lower in the parts and that no significant loss of vanadium was noted when printing with new (fresh) powders. On the other hand, V loss was significant in parts made with recycled powders, although still leaving them within acceptable chemistry to respect their original grade 5 classification.
       
  • Additive manufacturing of ceramic nanopowder by direct coagulation
           printing
    • Abstract: Publication date: October 2018Source: Additive Manufacturing, Volume 23Author(s): Tucker J. Hensen, Trevor G. Aguirre, Corson L. Cramer, Austin S. Wand, Kaka Ma, David A. Prawel, John D. Williams, Troy B. Holland This work investigates the feasibility of a binderless, extrusion-based additive manufacturing approach to fabricate alumina (Al2O3) parts from nanopowder. Traditional manufacture of ceramics with subtractive methods is limited due to their inherent hardness and brittleness, inevitably leading to ceramic parts with less-than-optimal geometries for the specific application. With an additive manufacturing approach, ceramic parts with complex 3D geometries, including overhangs or hollow enclosures, become possible. These complex ceramic parts are highly valuable in heat exchanger, condenser, biomedical implant, chemical reactant vessel, and electrical isolation applications. This research employed direct coagulation of alumina nanopowder slurries with the polyvalent salt tri-ammonium citrate providing the solidification mechanism in an extrusion-based printing process. The viscosity of the slurries was adjusted from ∼35 Pa-s to ∼1000 Pa-s by adjusting pH from ∼9 to ∼4, resulting in a paste that is suitable for extrusion, which retains near-net geometry. It was shown that the direct coagulation approach can be used to create a suspension with tuneable flow characteristics and coagulation rate, and a mechanism describing the process was proposed. The direct coagulation printing (DCP) method is described in detail, including how slurry is extruded, solidified, and printed in complex geometries, and sintered to full density. Parts were printed with a sintered resolution of 450 μm and green densities as high as 65%. After sintering at 1550 °C for up to 2 h, parts were shown to be fully dense (>97%) with an average grain size of ∼2 μm. Mechanical properties were characterized with a comparison to different materials and methods from literature, showing hardness and flexural modulus up to ∼1800 HV and 400 GPa, respectively.Graphical abstractGraphical abstract for this article
       
  • laser sintering process oF Ceramic powders: the effect of particle size on
           the mechanical properties of sintered layers
    • Abstract: Publication date: Available online 9 August 2018Source: Additive ManufacturingAuthor(s): Daniele Sofia, Diego Barletta, Massimo Poletto Selective Laser Sintering (SLS) of ceramic powders is studied in order to understand how the initial material properties and the process conditions affect the degree of sintering/melting and the mechanical properties of the sintered material. Unimodal powder samples of different narrow particle size distributions between 16 and 184 μm were sintered with a 40 W CO2 laser, using laser scan speeds of either 50 or 100 mm s-1 and, in both cases, a scanning energy of 160 J m-1. The sintered material was studied by means of optical and SEM microphotography and characterized in terms of bulk density and tensile strength. The Rumpf approach to relate interparticle forces to the strength of powder agglomerates was used in this work to estimate the average strength of the sintered interparticle contacts starting from the tensile strength of specimens. In turn, the average strength of the neck contact was used to estimate the size of the neck of fused material between two sintered particles. These data coupled with the Frenkel model for particle sintering allowed an estimate of the sintering temperature for the different experimental conditions tested. The temperatures found are consistent with the glass transition temperature of the material used. The effect of particle size and scanning speed is assessed and discussed.
       
  • An implementation of real-time feedback control of cured part height in
           Exposure Controlled Projection Lithography with in-situ interferometric
           measurement feedback
    • Abstract: Publication date: Available online 9 August 2018Source: Additive ManufacturingAuthor(s): Xiayun Zhao, David W. Rosen Exposure Controlled Projection Lithography (ECPL) is an in-house additive manufacturing process that can cure microscale photopolymer parts on a stationary transparent substrate with a time sequence of patterned ultraviolet beams delivered from underneath. An in-situ interferometric curing monitoring and measurement (ICM&M) system has been developed to measure the ECPL process output of cured height profile. This study develops a real-time feedback control system that utilizes an empirical process model and an online ICM&M feedback to automatically and accurately cure a part with targeted height. Due to the nature of photopolymerization, the total height of an ECPL cured part is divided into exposure cured height and dark cured height. The exposure cured height is controlled by a closed-loop feedback on-off controller. The dark cured height is compensated by an empirical process model obtained from the ICM&M measurements for a series of cured parts. A parallel computing software application is developed to implement the real-time measurement and control simultaneously. The experimental results directly validate the ICM&M system’s real-time capability in capturing the process dynamics and in sensing the process output. Meanwhile, it evidently demonstrates the feedback control system’s satisfactory performance in achieving the setpoint of total height, despite the presence of ECPL process uncertainties, ICM&M noises and computing interruptions. A comprehensive error analysis is reported, implying a promising submicron control with enhanced hardware. Generally, the study establishes a paradigm of improving additive manufacturing with a real-time closed-loop measurement and control system.
       
  • Texture Analysis of Additively Manufactured Ti-6Al-4V using Neutron
           Diffraction
    • Abstract: Publication date: Available online 9 August 2018Source: Additive ManufacturingAuthor(s): A. Pesach, E. Tiferet, S.C. Vogel, M. Chonin, A. Diskin, L. Zilberman, O. Rivin, O. Yeheskel, E.N. Caspi This study presents a detailed characterization of room temperature bulk microstructure and texture of additively manufactured Ti-6Al-4 V alloy samples with the neutron time-of-flight diffractometer HIPPO. A comparison is made between samples that were manufactured by two different methods utilizing selective laser melting and electron beam melting. Analysis of the orientation distribution function shows a dependency upon the particular fabrication technique used as well as on the location within the built body and orientation relative to the build direction. It is shown that the texture components strength in the hexagonal phase depends on the relative tilt angle between the build direction and that the overall texture of samples prepared with the electron beam method is weaker than those prepared with the selective laser melting. Such knowledge on the bulk microstructure allows to optimize additive manufacturing process parameters.
       
  • Nozzle Clogging Factors During Fused Filament Fabrication of Spherical
           Particle Filled Polymers
    • Abstract: Publication date: Available online 7 August 2018Source: Additive ManufacturingAuthor(s): Tobias Beran, Tom Mulholland, Frank Henning, Natalie Rudolph, Tim A. Osswald Fused filament fabrication with reinforced or filled polymers provides improved material properties compared to ordinary feedstock. A current limitation of these materials is the occurrence of nozzle clogging at higher filler contents. In this work, an experiment is designed to identify the factors causing nozzle clogging. Glass sphere-filled polycarbonate is investigated by varying nozzle and filler diameters, the resin viscosity, the filler content, and the extrusion pressure. Equations identifying nozzle clogging and intermittent clogging conditions are provided. Based on these results, a model for the clogging of sphere-filled polymers is proposed. Last, a mathematical model is derived, which approximates the printability of filled polymers without the preparation of composites. This model is based on the nozzle geometry, the filler type and content, the resin viscosity, and the printer’s maximum extrusion force.
       
  • Simulation of Buckling of Internal Features during Selective Laser
           Sintering of Metals
    • Abstract: Publication date: Available online 7 August 2018Source: Additive ManufacturingAuthor(s): Luis S. Santos, Satyandra K. Gupta, Hugh A. BruckABSTRACTAdditive manufacturing (AM) processes, such as Selective Laser Sintering (SLS), have enabled the fabrication of geometrically complicated designs. However, undesired distortions due to thermally-induced residual stresses may lead to loss of tolerance or failure of the part. One potential failure mode is buckling, particularly when realizing high aspect ratio features, like for infill, to minimize weight. In this paper, we address distortions and part failures due to buckling by using a finite element model to predict residual stress distributions and sintering induced distortions. Initially, we conduct a transient thermal simulation to determine the Heat Affected Zone (HAZ), which is then used in the thermomechanical simulation. In addition, we imposed perturbations on the mechanical mesh based on the buckling eigenmodes. Finally, a thermomechanical viscoplastic analysis was performed layer-by-layer to obtain the final residual stress state and subsequent distortions that occur after cooling down to ambient temperature. A model was used to describe the evolution of porosity due to laser sintering, and then a model of the effects of porosity on the viscoplastic constitutive properties of the sintered material was used in the thermomechanical simulation. Modeling results are compared against experimental specimens using a Durelli (aka, Theta) specimen geometry fabricated with a 3D Systems ProX 200 Selective Laser Sintering (SLS) machine. The geometry of the specimen represents an internal feature with a high aspect ratio that is prone to buckling, and the dimensions were modified based on the simulation results to confirm the ability of the modeling approach to provide accurate mitigation of buckling-induced distortions.
       
  • Investigation of process-structure-property relationships in polymer
           extrusion based additive manufacturing through in situ high speed imaging
           and thermal conductivity measurements
    • Abstract: Publication date: October 2018Source: Additive Manufacturing, Volume 23Author(s): Darshan Ravoori, Lorenzo Alba, Hardikkumar Prajapati, Ankur Jain Additive manufacturing has gained significant research attention due to multiple advantages over traditional manufacturing technologies. A fundamental understanding of the relationships between process parameters, microstructure and functional properties of built parts is critical for optimizing the additive manufacturing process and building parts with desired properties. This is also critical for a multi-functional part where the process needs to be optimized with respect to disparate performance requirements such as mechanical strength and thermal conductivity. This paper presents in situ high speed imaging and build-direction thermal conductivity measurements of polymer extrusion based additively manufactured parts in order to understand the effect of process parameters such as raster speed, infill percentage and layer height on build-direction thermal conductivity. Measurements of thermal conductivity using a one-dimensional heat flux method are correlated with in situ process images obtained from a high speed camera as well as cross section images of the built part. Results indicate strong dependence of build-direction thermal conductivity on raster speed, layer thickness and infill percentage, which is corroborated by high speed imaging of the printing process at different values of these process parameters. Key trade-offs between process throughput and thermal properties are also identified. In addition to enhancing our fundamental understanding of polymer extrusion based additive manufacturing and its influence on thermal properties of built parts, results presented here may facilitate process optimization towards parts with desired thermal and multi-functional properties.
       
  • The influence of post-production heat treatment on the multi-directional
           properties of nickel-aluminum bronze alloy fabricated using wire-arc
           additive manufacturing process
    • Abstract: Publication date: Available online 6 August 2018Source: Additive ManufacturingAuthor(s): Chen Shen, Zengxi Pan, Donghong Ding, Lei Yuan, Ning Nie, Dongzhi Luo, Dominic Cuiuri, Stephen van Duin, Huijun Li In this paper, a nickel-aluminum bronze alloy component is built using wire-arc additive manufacturing process. In order to investigate the influence of anisotropy introduced by the wire-arc additive manufacturing process, the layer-by-layer manufactured components with different post-production heat treatments are characterized by optical and scanning electron microscopy morphologies, X-ray diffraction and mechanical tests in longitudinal, transverse and normal directions. The experimental results show that the deposit exhibits higher strengths in the longitudinal and transverse direction than in the normal direction. Also, the ductility of the alloy is significantly improved with the designed quenching and tempering method, and competitive mechanical properties are achieved when tempering temperature reaches 650 °C. In addition, the anisotropy in the additively manufactured alloy can be effectively modified by the quenching and tempering heat treatments.Graphical abstractGraphical abstract for this article
       
  • Microstructure and mechanical properties of X65MoCrWV3-2 cold-work tool
           steel produced by selective laser melting
    • Abstract: Publication date: Available online 4 August 2018Source: Additive ManufacturingAuthor(s): J. Boes, A. Röttger, C. Mutke, C. Escher, W. Theisen In this study, martensitic cold-work tool steel X65MoCrWV3-2 was processed by selective laser melting (SLM) by varying the laser scanning parameters and baseplate preheating temperatures. Porosity as well as crack density of the SLM-densified steel were determined by quantitative image analysis. The resulting microstructure and the associated local mechanical properties were characterized, and the hardness-tempering behavior of the SLM-densified steel was compared to the behavior of the conventionally manufactured X65MoCrWV3-2 steel in the cast and hot-formed condition. Regardless of the preheating temperature, SLM-densified X65MoCrWV3-2 possesses a porosity of less than 0.5 vol.-%. The crack density was reduced significantly by means of a higher preheating temperature. The microstructure after SLM densification shows a fine, equiaxed cellular-dendritic subgrain structure, superimposed by lath- or needle-like martensite. The martensite morphology appeared to be finer at a lower preheating temperature, whereas the observed subgrain structure did not seem to be influenced by the preheating temperatures. Microhardness measurements indicated tempering effects in first solidified layers caused by the densification of subsequently deposited layers. Peak hardness after tempering of the SLM-densified steel was found to be higher compared to the maximum hardness in the X65MoCrWV3-2 steel in the cast condition.
       
  • Effects of heat accumulation on microstructure and mechanical properties
           of Ti6Al4V alloy deposited by wire arc additive manufacturing
    • Abstract: Publication date: Available online 4 August 2018Source: Additive ManufacturingAuthor(s): Bintao Wu, Zengxi Pan, Donghong Ding, Dominic Cuiuri, Huijun LiABSTRACTComplex thermal behaviour during fabrication plays an import role in the geometrical formation and mechanical properties of Ti6Al4V components manufactured using Wire Arc Additive Manufacturing (WAAM) technology. In this study, through in-situ temperature measurement, the heat accumulation and thermal behaviour during the gas tungsten wire arc additive manufacturing (GT-WAAM) process are presented. The effects of heat accumulation on microstructure and mechanical properties of additively manufactured Ti6Al4V parts were studied by means of optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and standard tensile tests, aiming to explore the feasibility of fabricating Ti6Al4V parts by GT-WAAM using localized gas shielding. The results show that due to the influences of thermal accumulation, the layer’s surface oxidation, microstructural evolution, grain size, and crystalline phase vary along the building direction of the as-fabricated wall, which creates variations in mechanical properties and fracture features. It has also been found that it is necessary to maintain the process interpass temperature below 200 °C to ensure an acceptable quality of Ti6Al4V part fabricated using only localized gas shielding in an otherwise open atmosphere. This research provides a better understanding of the effects of heat accumulation on targeted deposition properties during the WAAM process, which will benefit future process control, improvement, and optimization.
       
  • Energy absorption characteristics of metallic triply periodic minimal
           surface sheet structures under compressive loading
    • Abstract: Publication date: Available online 4 August 2018Source: Additive ManufacturingAuthor(s): Lei Zhang, Stefanie Feih, Stephen Daynes, Shuai Chang, Michael Yu Wang, Jun Wei, Wen Feng Lu Designing metallic cellular structures with triply periodic minimal surface (TPMS) sheet cores is a novel approach for lightweight, multi-functional structural applications. Different from current honeycombs and lattices, TPMS sheet structures are composed of continuous and smooth shells, allowing for large surface areas and continuous internal channels. In this paper, we investigate the mechanical properties and energy absorption abilities of three types of TPMS sheet structures (Primitive, Diamond, and Gyroid) fabricated by selective laser melting (SLM) with 316 L stainless steel and classify their failure mechanisms and printing accuracy with the help of numerical analysis. The results reveal that the properties and deformation mechanisms strongly depend on the unit cell geometry. TPMS sheet structures are found to exhibit superior stiffness, plateau stress and energy absorption ability compared to body-centred cubic lattices, with Diamond-type sheet structures performing best. Linear and post-yielding mechanical behaviour of TPMS sheet structures as predicted by explicit finite element models is in good agreement with experimental results. The simulation results also show that Diamond and Gyroid sheet structures display relatively uniform stress distributions across all lattice cells under compression, leading to stable collapse mechanisms and desired energy absorption performance. In contrast, P-type structures display rapid diagonal shear band development followed by localized wall buckling. Lastly, an energy absorption diagram is developed to facilitate a systematic way to select optimal densities of TPMS structures for energy absorbing applications.
       
  • On the influence of laser defocusing in Selective Laser Melting of 316L
    • Abstract: Publication date: Available online 4 August 2018Source: Additive ManufacturingAuthor(s): Jitka Metelkova, Yannis Kinds, Karolien Kempen, Charlotte de Formanoir, Ann Witvrouw, Brecht Van Hooreweder Despite its many benefits, Selective Laser Melting's (SLM) relatively low productivity compared to deposition-based additive manufacturing techniques is a major drawback. Increasing the laser beam diameter improves SLM's build rate, but causes loss of precision. The aim of this study is to investigate laser beam focus shift, or “defocus”, using a dynamic focusing unit, in order to increase the laser spot size. When applied to the SLM process, focus shift can be integrated into a “hull-core” strategy. This involves scanning the core with a high productivity parameter set using defocus while enabling return to the focused smaller spot size position for hull scanning. To assess the process stability, single line scans were made from 316L stainless steel powder. The consolidated melt pool morphology was analyzed and correlated with the process parameters comprising laser power, scanning speed and defocus distance. In order to link the melt pool morphology with the heat input, Volumetric Energy Density, Normalized Enthalpy and Rosenthal equation were considered. The suitability of using the Normalized Enthalpy as a design parameter to predict the melt pool depth and Rosenthal equation to predict its width was highlighted. This study shows that within a single laser setup, implementing defocus can lead to a potential productivity increase by 840 %, i.e. to 18.8 mm3/s.Graphical abstractGraphical abstract for this article
       
  • Columnar to equiaxed transition during direct metal laser sintering of
           AlSi10Mg alloy: effect of building direction
    • Abstract: Publication date: Available online 2 August 2018Source: Additive ManufacturingAuthor(s): Amir Hadadzadeh, Babak Shalchi Amirkhiz, Jian Li, Mohsen Mohammadi In the current study, cylindrical samples of AlSi10Mg alloy were fabricated using direct metal laser sintering (DMLS) technique in vertical and horizontal directions. The microstructure of the samples was analyzed using scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. It was observed that, by changing the building direction from vertical to horizontal, columnar to equiaxed transition (CET) occurred in the alloy. While 75% of the grains in the vertical sample were columnar, by changing the direction to horizontal, 49% of the grains evolved with columnar shape and 51% of them were equiaxed. Moreover, the texture of DMLS-AlSi10Mg alloy changed due to CET. While {001} fiber texture evolved in the vertical sample, the direction tilted away from the building direction in the horizontal one. Using the fundamentals of solidification and constitutional undercooling, the solidification behavior of AlSi10Mg alloy during DMLS process was modeled. It was observed that, the determinant parameter in CET during DMLS of AlSi10Mg alloy is the angle between the nominal growth rate and direction of the growing dendrite, which is controlled by the geometry and building direction of the sample. Further TEM studies confirmed that, CET alters the shape and coherency of Si precipitates and dislocation density inside the α-Al dendrites in DMLS-AlSi10Mg alloy.
       
  • 3D printed hierarchically-porous microlattice electrode materials for
           exceptionally high specific capacity and areal capacity lithium ion
           batteries
    • Abstract: Publication date: October 2018Source: Additive Manufacturing, Volume 23Author(s): Mohammad Sadeq Saleh, Jie Li, Jonghyun Park, Rahul Panat Despite the enormous potential of additive manufacturing in fabricating three-dimensional battery electrodes, the structures realized through this technology are mainly limited to the interdigitated geometries due to the nature of the manufacturing process. This work reports a major advance in 3D batteries, where highly complex and controlled 3D electrode architectures with a lattice structure and a hierarchical porosity are realized by 3D printing. Microlattice electrodes with porous solid truss members (Ag) are fabricated by Aerosol Jet 3D printing that leads to an unprecedented improvement in the battery performance such as 400% increase in specific capacity, 100% increase in areal capacity, and a high electrode volume utilization when compared to a thin solid Ag block electrode. Further, the microlattice electrodes retain their morphologies after 40 electrochemical cycles, demonstrating their mechanical robustness. These results indicate that the 3D microlattice structure with a hierarchical porosity enhances the electrolyte transport through the electrode volume, increases the available surface area for electrochemical reaction, and relieves the intercalation-induced stress; leading to an extremely robust high capacity battery system. Results presented in this work can lead to new avenues for improving the performance of a wide range of electrochemical energy storage systems.Graphical abstractGraphical abstract for this article
       
  • Micromechanical analysis of the effective properties of lattice structures
           in additive manufacturing
    • Abstract: Publication date: October 2018Source: Additive Manufacturing, Volume 23Author(s): José Souza, Alexander Großmann, Christian Mittelstedt Lightweight design is an area of mechanical engineering that becomes increasingly important in many industries, as they pursue reduced mass and more efficient parts. A special class of materials for load-bearing structures are metallic cellular materials with cubic unit cells, which can be manufactured conveniently through laser beam melting (LBM). Such materials exhibit a rather complex microstructure and can be analysed using analytical and numerical methods wherein the determination of properties such as relative density, effective elastic and yield strength properties is of special interest. This paper addresses closed-form analytical methods based on beam theories for the determination of the effective properties of additively manufactured microstructures such as lattices, and a comparison with experimental results [1], [2] which leads to excellent agreements for relative densities lower than 40%, although results reveal a great dependency on the manufacturing strategy. Lastly, a classification concerning the topology of the cellular units is presented as well in order to help the engineer choose appropriate geometries for specific application purposes. In conclusion, this structural concept may be applied in many fields such as bioengineering and in functional graded materials as they are applied in lightweight engineering.
       
  • Chemical Compatibility of Fused Filament Fabrication-based 3-D Printed
           Components with Solutions Commonly Used in Semiconductor Wet Processing
    • Abstract: Publication date: Available online 30 July 2018Source: Additive ManufacturingAuthor(s): Ismo T.S. Heikkinen, Christoffer Kauppinen, Zhengjun Liu, Sanja M. Asikainen, Steven Spoljaric, Jukka V. Seppälä, Hele Savin, Joshua M. Pearce 3-D printing shows great potential in laboratories for making customized labware and reaction vessels. In addition, affordable fused filament fabrication (FFF)-based 3-D printing has successfully produced high-quality and affordable scientific equipment, focusing on tools without strict chemical compatibility limitations. As the additives and colorants used in 3-D printing filaments are proprietary, their compatibility with common chemicals is unknown, which has prevented their widespread use in laboratory chemical processing. In this study, the compatibility of ten widely available FFF plastics with solvents, acids, bases and solutions used in the wet processing of semiconductor materials is explored. The results provide data on materials unavailable in the literature and the chemical properties of 3-D printable plastics that were, are in line with literature. Overall, many 3-D printable plastics are compatible with concentrated solutions. Polypropylene emerged as a promising 3-D printable material for semiconductor processing due to its tolerance of strongly oxidizing acids, such as nitric and sulfuric acids. In addition, 3-D printed custom tools were demonstrated for a range of wet processing applications. The results show that 3-D printed plastics are potential materials for bespoke chemically resistant labware at less than 10% of the cost of such purchased tools. However, further studies are required to ascertain if such materials are fully compatible with clean room processing.
       
  • Strengthening mechanisms in direct metal laser sintered AlSi10Mg:
           Comparison between virgin and recycled powders
    • Abstract: Publication date: Available online 30 July 2018Source: Additive ManufacturingAuthor(s): Amir Hadadzadeh, Carter Baxter, Babak Shalchi Amirkhiz, Mohsen Mohammadi Rod shaped samples of AlSi10Mg additively manufactured using recycled powder through direct metal laser sintering (DMLS) process showed higher quasi-static uniaxial tensile strength in both horizontal and vertical build directions than those of cast counterpart alloy. In addition, they offered mechanical properties within the range of other additively manufactured counterparts. TEM showed that the microstructure of the as-built samples comprised of cell-like structures featured by dislocation networks and Si precipitates. HRTEM studies revealed the semi-coherency characteristics of the Si precipitates. After deformation, the dislocation density increased as a result of generation of new dislocations due to dislocation motion. The dislocations bypassed the precipitates by bowing around them and penetrating the semi-coherent precipitates. Strengthening of recycled DMLS-AlSi10Mg alloys manufactured in both directions was attributed to Orowan mechanism (due to existence of Si precipitates), Hall-Petch effect (due to eutectic cell walls), and dislocation hardening (due to pre-existing dislocation networks). Due to the slightly different microstructure, the contribution of each strengthening mechanism was slightly different in identical samples made with virgin powder.
       
  • Predictive model for porosity in powder-bed fusion additive manufacturing
           at high beam energy regime
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): G. Vastola, Q.X. Pei, Y.-W. Zhang Process consistency and control are bottleneck issues to wider insertion of powder-bed fusion additive manufacturing in the industrial shopfloor. Of particular interest is the porosity of the components, which remains the limiting factor to high-cycle fatigue performance. Recent experiments have shown that, with increasing energy density, a surge in porosity is seen in selectively laser melted metals. In this high-energy density regime, porosity must originate from mechanisms that are different from the well-known incomplete melting in the low energy density regime. To shed light on this interesting phenomenon, this paper first discusses the mechanism of bubble formation in the melt pool and possible trapping during the solidification, and then formulates a predictive model for porosity in this regime. To compare with experimental results, we perform computer modeling and simulations which have been fully validated by experiments to determine the parameters in the model. We show that the model predictions are in good qualitative and quantitative agreement with the experimental measurements. Hence, the proposed model can be used as a tool to predict the porosity, and further to control and possibly reduce porosity in laser powder-bed fusion additive manufacturing, paving the way for its wider adoption in manufacturing shopfloors.Graphical abstractGraphical abstract for this article
       
  • Microstructure and micro-texture evolution of additively manufactured
           β-Ti alloys
    • Abstract: Publication date: Available online 26 July 2018Source: Additive ManufacturingAuthor(s): S.A. Mantri, R. Banerjee This study focuses on the microstructural evolution in additively manufactured (AM) β titanium alloys due to solid-state phase transformations occurring during the reheating of previously deposited layers, directly influencing the uniformity of microstructure across the entire build. During the AM of titanium alloys of a wide variety of compositions, including α + β alloys such as Ti-6Al-4 V, and β alloys, when the laser or electron beam hits the sample, the grains in the previously deposited topmost layers either re-melt or transform into the β phase. Subsequently, during the cooling cycle, depending on the alloy composition, second-phase precipitation may occur within these layers via solid-state precipitation. The present study compares two binary β -Ti alloys, Ti-12Mo and Ti-20 V, that have been processed using laser engineered net shaping (LENS™), a directed energy deposition technique for AM. Compared to Ti-V, which exhibited grains of only the β phase in the as-built condition, the less β stabilized Ti-Mo had extensive second-phase α precipitation within the build. The location within the LENS™ build played a pivotal role in determining the size scale, area fraction, and morphology of the α precipitates. These changes have been attributed to the different thermal cycles experienced during the deposition process. Irrespective of the alloy composition, columnar grains were observed in the depositions with a strong [001]β texture along the build direction. In the Ti-12Mo alloy, wherein second phase α precipitation takes place, there was no significant α texturing, with all twelve variants forming.
       
  • Large-format Polymeric Pellet-Based Additive Manufacturing for the Naval
           Industry
    • Abstract: Publication date: Available online 25 July 2018Source: Additive ManufacturingAuthor(s): Daniel Moreno Nieto, Victor Casal López, Sergio Ignacio Molina Polymeric Pellet-Based Additive Manufacturing (PPBAM) systems are increasing in the field of 3D printing as a result of the evolution of additive technologies as their development process consolidates and expands. New opportunities for industrial integration of additive manufacturing (AM) technologies are identified, including AM of large polymeric parts. The PPBAM process consists of adapting a pellet-fed extrusion mechanism to a displacement system, either a Cartesian mechanism or a robotic arm system, building parts in a multi-layered approach. This use is justified by the extruded filament sizes required and the material costs when facing large-format prints. In this article, a pellet extrusion based printer prototype is presented together with a case study. The case study consists of the development of a two cubic meter capacity plastic part for the naval industry with a topology optimization design approach and material selection and validation methodology for a large-volume pellet based extrusion system. Two functional prototypes were developed with the selected materials from the explained methodology a PLA and a flame retardant ABS, and post processed to full fill the actual product´s specifications.
       
  • Thickness dependency of mechanical properties of laser-sintered polyamide
           lightweight structures
    • Abstract: Publication date: October 2018Source: Additive Manufacturing, Volume 23Author(s): David Tasch, Anna Mad, Robert Stadlbauer, Martin Schagerl Laser sintering (LS), as an additive manufacturing process for production of polymer structures, provides the possibility of directly manufacturing personalized, structural motorcycle components for motor sports. To create such lightweight structures, the wall thickness and position limits of the LS systems need to be investigated in detail. Appearing process-related flaws such as different amounts of crystallinity, surface roughness, and defects such as pores exhibit dimensions similar to the wall thickness. To study the process-related effects on the mechanical properties of 450 tensile test specimens in z-direction, the build areas of two LS systems were screened and a detailed wall thickness investigation was conducted. In addition, dynamic mechanical analysis, differential scanning calorimetry, and scanning electron microscopy for several wall thicknesses similar to the spot size were conducted. The investigations showed that the Young's moduli and ultimate tensile strengths of the produced specimens of the two commercial EOS systems, P396 and P770, are similar and evenly distributed. However, distinct differences were found in elongation at break. The scattering of mechanical properties is more in the specimens produced by P770 than in those produced by P396. The Poisson's ratio does not vary between thin- and thick-walled structures. Furthermore, structures with a thickness below 1 mm showed distinctive losses in stiffness, ultimate tensile strength, and elongation at break.
       
  • An Overview of Functionally Graded Additive Manufacturing
    • Abstract: Publication date: Available online 11 July 2018Source: Additive ManufacturingAuthor(s): Giselle Hsiang Loh, Eujin Pei, David Harrison, Mario D. Monzón Functionally Graded Additive Manufacturing (FGAM) is a layer-by-layer fabrication process that involves gradationally varying the material organisation within a component to achieve an intended function. FGAM establishes a radical shift from contour modelling to performance modelling by having the performance-driven functionality built directly into the material. FGAM can strategically control the density and porosity of the composition or can combine distinct materials to produce a seamless monolithic structure. This paper presents a state-of-art conceptual understanding of FGAM, covering an overview of current techniques that can enable the production of FGAM parts as well as identify current technological limitations and challenges. The possible strategies for overcoming those barriers are presented and recommendations on future design opportunities are discussed.
       
  • Experimental and Analytical Investigation of Mechanical Behavior of
           Laser-Sintered Diamond-Lattice Structures
    • Abstract: Publication date: Available online 11 July 2018Source: Additive ManufacturingAuthor(s): Clayton Neff, Neil Hopkinson, Nathan B. Crane Typically, additive manufacturing (AM) processes are limited to a single material per build while many products benefit from the integration of multiple materials with varied properties. To achieve the benefits of multiple materials, the geometric freedom of AM could be used to build internal structures that emulate a range of different material properties such as stiffness, Poisson’s ratio, and elastic limit using only a single build material. This paper examines a wide range of properties that can be achieved using diamond lattice structures manufactured from Nylon 12 with a commercial laser sintering (LS) process. Stiffness and energy absorption were measured for all lattices and the stiffness response was compared to finite element analysis (FEA). Simulation shows agreement with experimental results over a stiffness range of four orders of magnitude once a correction factor is applied. Experimental results also show a wide range of energy absorption for diamond lattice structures and a significant increase in the effective elastic limit of the build material, which compensates for the low ductility of many AM materials. The elastic limit decreases with an increasing t/L ratio meanwhile the degradation under cyclic loading is relatively independent of the t/L ratio. Extrapolating this data into lattice structures made from metal, these same structures could mimic a wide range of “fully” dense and porous materials with just the use of a single material. Since the diamond lattice is a cellular structure, the voids can also be filled with other materials or structures to add secondary control of embedded functions such as energy storage and sensing.
       
  • Multi-Material 3D Printing: the Relevance of Materials Affinity on the
           Boundary Interface Performance
    • Abstract: Publication date: Available online 11 July 2018Source: Additive ManufacturingAuthor(s): L.R. Lopes, A.F. Silva, O.S. Carneiro Multi-material extrusion in 3D printing is gaining attention due to a wide range of possibilities that it provides, specially driven by the commercial availability of a large variety of non-conventional filament materials. As a result, one can print models that are not limited to aesthetics purposes but can now also provide larger functionality, and therefore with mechanical performance tuned according to their purpose. With this in mind, this paper addresses the mechanical performance of multi-material printed objects, specially focused on the interface zone generated between the different materials at their geometrical boundaries. Tensile test specimens were designed and printed in three types: (A) a single-material specimen printed by a single extrusion head; (B) a single-material but multi-section specimen printed in a zebra-crossing structure by two extrusion heads; and (C) a multi-material specimen printed with two materials in a zebra-crossing pattern. The materials considered were PLA, TPU and PET. The comparison of the mechanical performance between Type-A and -B specimens demonstrated the negative influence of the presence of a geometrical boundary interface between the same material. On the other hand, the comparison between Type-B and -C demonstrated how the previous performance loss was yet more drastic when the lack of chemical affinity between the materials was present. The methodology proposed to assess the quality of the pairs of materials selected is innovative, and enabled to depict the importance of the boundary design in multi-material printing techniques.
       
  • Impact of Extended Sintering Times on Mechanical Properties in PA-12 Parts
           Produced by Powderbed Fusion Processes
    • Abstract: Publication date: Available online 10 July 2018Source: Additive ManufacturingAuthor(s): Garrett Craft, Justin Nussbaum, Nathan Crane, J.P. Harmon Additive Manufacturing provides many advantages in reduced lead times and increased geometric freedom compared to traditional manufacturing methods, but material properties are often reduced. This paper considers powder bed fusion of polyamide 12 (PA12, Nylon 12) produced by three different processes: laser sintering (LS), multijet fusion (MJF)/high speed sintering (HSS), and large area projection sintering (LAPS). While all utilize similar PA12 materials, they are found to differ significantly in mechanical properties especially in elongation to break. The slower heating methods (MJF/HSS and LAPS) produce large elongation at break with the LAPS process showing 10x elongation and MJF/HSS exhibiting 2.5x the elongation when compared to commercial LS samples. While there are small differences in crystallinity between these samples, the difference may be attributed to changes in the heating and cooling rates of the LAPS samples.
       
  • Additive manufacturing of Ti-45Al-4Nb-C by selective electron beam melting
           for automotive applications
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): V. Juechter, M.M. Franke, T. Merenda, A. Stich, C. Körner, R.F. Singer Selective electron beam melting (SEBM) is shown to be a viable production route for titanium aluminides components. Fully dense and crack free parts can be produced. In the present paper a titanium aluminide alloy Ti-45Al-4Nb-C was investigated and the complete processing chain was developed, i.e. starting from the determination of the processing window, the evaluation of corresponding material properties for cube like specimens and finally the production of turbocharger wheels. The material properties were optimized by adjusting scanning strategy as well as heat treatment with particular consideration of the application to turbocharger wheels. The issue of dimensional accuracy and the feasibility of joining will be discussed and a proof test is performed.
       
  • Simulating image-guided in situ bioprinting of a skin graft onto
           a phantom burn wound bed
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Houzhu Ding, Robert C. Chang Deep skin thermal wounds require skin excision and engraftment. Clinical treatment for deep skin wounds is the use of autologous split-thickness skin grafts. However, timely coverage of large-area burn wounds remains a significant challenge. Engineered skin tissue constructs aim to overcome the limitations of traditional clinical intervention. In this study, an in situ bioprinting-based methodological workflow is advanced to directly fabricate a custom engineered skin graft onto a skin burn phantom. To illustrate this modular approach, a burn phantom is first created by mold casting gelatin-alginate hydrogel material to simulate a burn wound bed with arbitrary 2D shape and uniform depth. The cast hydrogel phantom is then placed on the printer platform to host the to-be-printed skin graft. Next, a color image-based module is proposed to extract the contour of the burn wound. This is followed by implementing a contour calibration process based on fiducial markers to yield the real dimension and pose of the burn phantom. A new directed toolpath generation algorithm is detailed to generate a burn-specific toolpath for the microextrusion-based bioprinting process. Based on this method, the bioprinted cell-laden gelatin-alginate hydrogel filaments are precisely arranged in a meshed pattern that is bound by the burn phantom contour. Internal geometries defined by the filament and pore dimensional characteristics of the printed construct design can be controlled to promote cell viability, proliferation, and nutrient delivery. Printed cell-laden multi-layered constructs are evaluated for single filament and pore dimensional precision, alignment of filaments between layers, and positional accuracy of the filaments within the extracted contour. Finally, a 24-hour time course incubation study reveals that the printed constructs preserve their structural properties while cells proliferate and maintain their spatial positioning.
       
  • The development of a strategy for direct part reuse using additive and
           subtractive manufacturing technologies
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Van Thao Le, Henri Paris, Guillaume Mandil In recent years, combining additive and subtractive manufacturing technologies has attracted much attention from both industrial and academic sectors. Due to consolidated benefits of individual techniques, this combination provides new possibilities to manufacture products, and develop new strategies for recovering products at their end-of-life stage. This paper aims to develop a direct material reuse strategy based on such technique combination. The principle of the strategy is to manufacture new parts (or final parts) directly from end-of-life parts (or existing parts) without involving the material recycling phase. In this paper, a systematic methodology is proposed to develop the strategy. Firstly, the good mechanical characteristics of parts obtained by the strategy are confirmed. Thereafter, the design of process planning for combining additive and subtractive manufacturing processes is focused. This allows achieving the geometry and quality of final part from the existing part. The methodology for process planning design is developed in two major steps using the manufacturing feature concept, the knowledge of manufacturing processes, technological requirements, and available resources. In the first step, manufacturing features (i.e. machining and additive manufacturing features) are extracted from the information of the existing and final parts. In the second step, the process planning is generated from extracted features by respecting the relationships of features and the manufacturing precedence constraints. Finally, a case study is used to illustrate the proposed methodology.
       
  • Epitaxial deposition of nickel-based superalloy René 142 through
           scanning laser epitaxy (SLE)
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Amrita Basak, Ranadip Acharya, Suman Das Single-pass depositions of columnar René 142 on investment cast single-crystal (SX) René N5 substrates having [100] and [001] primary dendrite growth directions were obtained through scanning laser epitaxy (SLE), a laser powder bed fusion (LPBF)-based additive manufacturing (AM) process. The microstructure and the microhardness properties of the René 142 deposits were investigated through high-resolution optical microscopy (HR-OM), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), x-ray diffraction (XRD), electron backscatter diffraction (EBSD), and micro-hardness measurements. HR-OM investigations revealed the capability of SLE in depositing more than 1000 μm of columnar René 142 in a single pass. SEM investigations demonstrated that the primary γ/γ′ precipitates in the deposit region were 90% finer in size compared to the substrate. XRD investigation revealed the presence of a strong [200] peak and EBSD analysis confirmed SX René 142 growth. Microhardness measurements showed an increase in the hardness values by ∼10% in the deposit region compared to the cast substrate. The results showed that the SLE process has tremendous potential in producing epitaxial deposits of nickel-based superalloys and, therefore, the findings reported in this work can pave ways to fabricate components with dissimilar-chemistry high-γ′ nickel-based superalloys using an LPBF-based AM process.
       
  • Early detection of fracture failure in SLM AM tension testing with
           Talbot-Lau neutron interferometry
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Adam J. Brooks, Hong Yao, Jumao Yuan, Omoefe Kio, Caroline G. Lowery, Henning Markötter, Nikolay Kardjilov, Shengmin Guo, Leslie G. Butler Tensile stress in selective laser melted (SLM) stainless steel 316 (SS316) bars was studied with neutron imaging methods for measurement of attenuation, scattering, and diffraction. The hypotheses for stress failure includes modifications to both the grain structure and residual porosity. Neutron Bragg edge imaging showed a change in crystallographic structure and/or texture at a pre-existing fracture, but did not provide evidence for presumptive crack formation. A Talbot-Lau grating-based neutron interferometer yielded better than 100 μm spatial resolution for the attenuation images and was tuned to an autocorrelation scattering length of 1.97 μm for the dark-field (scattering) images. The interferometry imaging was performed with samples parallel and perpendicular to the linear grating, allowing assessment of scattering along and perpendicular to the additive manufacturing build direction. In the 3D tomography dark-field volume of a tensile stressed bar, features were observed that suggested possible sites of crack formation. The features were quantified with line probes and found to be reproducible over three tomography experiments. After imaging, the half-stressed bar was pulled to failure; the fracture point is correlated with a feature in the line probe having enhanced neutron scattering. Neutron interferometry, particularly the dark-field imaging modality, emerges as a powerful non-destructive method for detecting early crack formation in additive manufactured components.
       
  • Feature based three axes computer aided manufacturing software for wire
           arc additive manufacturing dedicated to thin walled components
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Giuseppe Venturini, Filippo Montevecchi, Francesco Bandini, Antonio Scippa, Gianni Campatelli WAAM (Wire-Arc-Additive-Manufacturing) is a metal additive manufacturing process using arc welding to create large components with high deposition rate. The workpiece quality and the process productivity are strongly dependent both on the process parameters (wire feed speed, voltage and current) and on the selected deposition path. Currently, the CAM (Computer-Aided-Manufacturing) software dedicated to WAAM rely on a multi-pass strategy to create the component layers, i.e. each layer is built overlapping multiple welding passes. However, since WAAM can create wide layers, a single pass strategy can improve the process efficiency when dealing with thin walled components. This paper proposes CAM software dedicated to WAAM, using a single pass strategy. The proposed solution uses a midsurface representation of the workpiece as input, to generate the deposition toolpath. A feature recognition module is proposed, to identify the critical features of the part, such as free end walls, t-crossings, direct-crossings and isolated tubulars. A specific strategy is developed and proposed for each one of the selected features, with the aim of minimizing the geometrical errors and to ensure the required machining allowances for the subsequent finishing operations. The effectiveness of the proposed strategy is verified manufacturing a test case.
       
  • Isotropic Ti–6Al–4V lattice via topology optimization and
           electron-beam melting
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Akihiro Takezawa, Kazuo Yonekura, Yuichiro Koizumi, Xiaopeng Zhang, Mitsuru Kitamura Electron-beam melting (EBM) exhibits advantages over other metal-additive manufacturing techniques owing to its low residual stress, rapid fabrication speed, and high energy efficiency. However, in EBM, metal powder is preheated and sintered to stabilize the temperature gradient and powder position during melting with a high-power electron beam. When making a lattice structure by EBM, a certain size of the powder-removing hole is required to remove the sintered remaining metal powder from the lattice. However, a large powder-removing hole can reduce the lattice mechanical performance. We conducted topology optimization to derive an optimal lattice structure shape with high isotropic stiffness assuming fabrication by EBM and minimizing the performance reduction owing to fixed large powder-removing holes. The optimized structure was fabricated via the EBM of a Ti–6Al–4V alloy. The optimal lattice structure achieved 83% of the performance of the Hashin–Shtrikman upper bound in numerical simulations, but an approximate 20% stiffness reduction was observed in the experiments. The isotropy was high with an error in Young's modulus and a strength of less than 9% and 6%, respectively. These results are discussed based on numerical and experimental results.
       
  • Octree data structure for support accessibility and removal analysis in
           additive manufacturing
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Rutuja Samant, Rajit Ranjan, Kunal Mhapsekar, Sam Anand Metal Additive Manufacturing (AM) processes have made it possible to build parts with complex geometric features by adopting a layer-by-layer approach. However, additional support structures are needed to support overhanging surfaces and reduce distortion that may occur in these parts. This increases the overall build time of the part and leads to additional post processing efforts for removal of support structures. Often, removal of these supports becomes difficult due to complex part features that may interfere with support removal. Further, support structures have a detrimental effect on the surface finish on the areas of the part that come in contact with the supports. Thus, minimizing the need for support structures and ensuring its maximum removal is essential for an efficient part build in AM. Part build orientation is the main parameter that influences the need for support structures to build a part. This paper presents an approach to identify the best build orientation for a part such that the overall part build time is minimized while ensuring maximum removal of supports and minimizing the contact area between the part surface and supports. A hierarchical octree data structure has been used to analyze support accessibility and the area of support in contact with part. In addition, this paper also focuses on identification of optimal number/direction of part set-ups required to remove the maximum possible support structures from a part. A 2D setup map highlighting the feasible directions of setups for support removal has also been presented. The results of these analyses have been presented with the help of four sample parts.
       
  • Voids and tensile properties in extrusion-based additive manufacturing of
           moisture-cured silicone elastomer
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Jeffrey Plott, Xiaoqing Tian, Albert J. Shih The tensile strength and strain properties as well as failure modes in silicone dumbbell specimens fabricated by extrusion-based additive manufacturing are investigated. Effects of process parameters, specifically the infill direction (0°, ±45°, and 90° relative to the tensile direction) and adjacent line spacing on the void formation and ultimate tensile strength are studied and compared to the baseline of stamped silicone specimens. The additive manufactured specimens with ±45° and 90° infill direction and either the minimal or small void extrusion configuration had the strongest ultimate tensile strength (average ranged from 1.44 to 1.51 MPa). This strength is close to that of the sheet stamped specimens which have an average ultimate tensile strength of 1.63 MPa. As the void size became larger and more elongated in shape, the average ultimate tensile strength significantly reduced to 1.15 and 0.90 MPa for specimens with ±45° and 90° infill direction, respectively. Counterintuitively, specimens with 0° infill direction were consistently the worst performing due to the tangency voids and poor edge surface finish resulting from the toolpath. We show that, to maximize ultimate tensile strength of silicone parts made by extrusion-based additive manufacturing, it is important to select process parameters which minimize the elongated voids, infill tangency voids, and surface edges. If these conditions can be achieved, the infill direction does not play a significant role in tensile strength of the tensile specimen.
       
  • Thermal near infrared monitoring system for electron beam melting with
           emissivity tracking
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): N. Boone, C. Zhu, C. Smith, I. Todd, J.R. Willmott This paper presents the design of a high speed, high resolution silicon based thermal imaging instrument and its application to thermally image the temperature distributions of an electron beam melting additive manufacturing system. Typically, thermal images are produced at mid or long wavelengths of infrared radiation. Using the shorter wavelengths that silicon focal plane arrays are sensitive to allows the use of standard windows in the optical path. It also affords fewer modifications to the machine and enables us to make use of mature silicon camera technology. With this new instrument, in situ thermal imaging of the entire build area has been made possible at high speed, allowing defect detection and melt pool tracking. Melt pool tracking was used to implement an emissivity correction algorithm, which produced more accurate temperatures of the melted areas of the layer.
       
  • The influence of aging temperature and aging time on the mechanical and
           
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Shuo Yin, Chaoyue Chen, Xingchen Yan, Xiaohua Feng, Richard Jenkins, Peter O'Reilly, Min Liu, Hua Li, Rocco Lupoi Selective laser melting (SLM) is an additive manufacturing and 3D printing technology which offers flexibility in geometric design and rapid production of complex structures. Maraging steels have high strength and good ductility, and therefore have been widely used in aerospace and tooling sectors for many years. This work aims to study the influence of aging temperature and aging time on the microstructure, mechanical property (hardness, strength and ductility) and tribological property of SLM maraging 18Ni-300 steel. The results reveal that the aging conditions had a significant impact on the strength and wear-resistance of the SLM maraging steel. The optimal aging conditions for the SLM maraging steel produced in this work were 490 °C for 3 h under which strength and wear-resistance were maximised. Lower or higher aging temperature led to under-aging or over-aging phenomena, reducing the strength and wear-resistance performance. Shorter or longer aging time also resulted in the decrease of strength and wear-resistance performance of the SLM maraging steel as compared with the optimal conditions. The variation of the mechanical and tribological properties is primarily due to changes in phase compositions and microstructures of the SLM maraging steels.
       
  • Parametric studies on bending stiffness and damping ratio of Sandwich
           structures
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Rohit Rajpal, Lijesh K.P, K.V. Gangadharan Sandwich structures are extensively used in aviation industries to reduce the overall weight of the system. Although the mechanical behavior of these structures has been widely studied, the performance of core shape in vibration response has been minimally explored. This study focuses on understanding the various influences of sandwich structures considering the following parameters: (i) nature of core shape, (ii) number of infill shapes, and (iii) orientation of cores, which affect the dynamic behavior of sandwich structures. Nine sandwich structures comprising three different core shapes, hexagon, triangle, and square shapes, in three different orientations, namely 0°, 45°, and 90°, were considered for the present study. These structures in the beginning were put by modal analysis using finite element method (FEM). All the nine structures were printed using the fused deposition method to validate the FEM findings, while the DEWE soft data acquisition system was used to estimate the modal parameters (i) natural frequency and (ii) damping ratio. Natural frequency and damping ratio were estimated using FRF and Nyquist circle plot, respectively. This study demonstrates that although the square core orientated at 0° exhibited superior stiffness in bending loads, the hexagonal core orientated at 0° displayed an admirable combination of both stiffness and damping properties.
       
  • Residual stress evaluation in selective-laser-melting additively
           manufactured titanium (Ti-6Al-4V) and inconel 718 using the contour method
           and numerical simulation
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Bilal Ahmad, Sjoerd O. van der Veen, Michael E. Fitzpatrick, Hua Guo Residual stresses play an important role for the structural integrity of engineering components. In this study residual stresses were determined in titanium alloy (Ti-6Al-4V) and Inconel 718 samples produced using selective-laser-melting (SLM) additive manufacturing. The contour method and a numerical simulation approach (inherent-strain-based method) were used to determine the residual stress distributions. The inherent-strain-based method reduces the computational time compared to weakly-coupled thermo-mechanical simulations. Results showed the presence of high tensile residual stresses at and near the surface of both titanium and Inconel alloys samples, whereas compressive residual stresses were seen at the center region. A good agreement was seen between the results obtained from contour method and the numerical simulation, particularly 1 mm below the surface of the samples.
       
  • Laser sintering of nano-hydroxyapatite coated polyamide 12 powders
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): D. Hui, R.D. Goodridge, C.A. Scotchford, D.M. Grant As part of a larger study on the laser sintering (LS) of nano-composite structures for biomedical applications, a wet mixing method was used to coat Polyamide 12 (PA12) particles with nano-hydroxyapatite (nHA). The addition of nHA significantly affected powder processability due to laser absorption and heat transfer effects which led to part warping. This phenomenon has not been reported in other studies investigating LS of polymer/HA and nHA powders. Nano-composites containing 0.5–1.5 wt% nHA were successfully produced and tensile testing showed that 0.5 wt% nHA provided the greatest reinforcement with a 20% and 15% increase in modulus and strength respectively. However, the elongation at break had significantly declined which was likely due to the formation of nHA aggregates at the sintering borders following the processing of the coated powders despite being initially well dispersed on the particle surface.
       
  • Melt pool temperature and cooling rates in laser powder bed fusion
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Paul A. Hooper In laser powder bed fusion, melt pool dynamics and stability are driven by the temperature field in the melt pool. If the temperature field is unfavourable defects are likely to form. The localised and rapid heating and cooling in the process presents a challenge for the experimental methods used to measure temperature. As a result, understanding of these process fundamentals is limited. In this paper a method is developed that uses coaxial imaging with high-speed cameras to give both the spatial and temporal resolution necessary to resolve the surface temperature of the melt pool. A two wavelength imaging setup is used to account for changes in emissivity. Temperature fields are captured at 100 kHz with a resolution of 20 μm during the processing of a simple Ti6Al4V component. Thermal gradients in the range 5–20 K/μm and cooling rates in range 1–40 K/μs are measured. The results presented give new insight into the effect of parameters, geometry and scan path on the melt pool temperature and cooling rates. The method developed here provides a new tool to assist in optimising scan strategies and parameters, identifying the causes of defect prone locations and controlling cooling rates for local microstructure development.Graphical abstractGraphical abstract for this article
       
  • Mechanical properties and microstructures in zirconium deposited by
           injected powder laser additive manufacturing
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Arshad Harooni, Mehrdad Iravani, Amir Khajepour, J. Mitch King, Ahmed Khalifa, Adrian P. Gerlich The use of laser additive manufacturing based on melting of injected zirconium powder under localized shielding was evaluated in terms of microstructures and mechanical properties of thin wall structures. The material was characterized in both the laser travel and the build directions. The microstructures, tensile properties and fracture behavior were assessed for deposits made using as-received and recycled powder. Electron backscattered diffraction and transmission electron microcopy revealed a fine structure of Zr-α laths with nano-scale iron-rich precipitates at the lath interfaces. The properties of the fabricated components, which were made using new as-received powder were comparable to a Zr-2.5Nb alloy substrate, with yield strengths of over 569 MPa and uniform strains up to the ultimate tensile stress ranging from 8.5 to 9.9%. However, when recycled powder was used, the ductility dropped with total strains to failure of 1.0–7.5%, as a result of porosity and unmelted powder particles serving as brittle inclusions in the deposited material.
       
  • Characterization of magnetic particle alignment in photosensitive polymer
           resin: A preliminary study for additive manufacturing processes
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Balakrishnan Nagarajan, Alejandro Federico Eufracio Aguilera, Michael Wiechmann, Ahmed Jawad Qureshi, Pierre Mertiny Material jetting 3D printing is an additive manufacturing technique that allows producing complex parts without tooling and minimum material wastage. In this study, orientation control of randomly shaped, anisotropic hard magnetic ferrite particles is demonstrated for material jetting-based additive manufacturing processes using a developed particle alignment configuration. Strontium ferrite and PR-48 photosensitive resin were used as the base materials. An automated experimental setup with two neodymium permanent cube magnets capable of generating a dipolar magnetic field was built to align magnetic particles in the resin. Particle alignment was characterized for directionality using images obtained through real time optical microscopy. The orientation of magnetic particles was observed to be dependent on the distance of separation between the cube magnets and the magnetization time. X-ray diffraction was used to indicate the c-axis alignment of the hexagonal strontium ferrite particles in the cured specimens. The influence of process parameters on particle orientation was evaluated, employing a full factorial experiment analysis. This fundamental research serves as a basis for constructing and optimizing the magnetic particle alignment setup for additive manufacturing processes.
       
  • Role of scan strategies on thermal gradient and solidification rate in
           electron beam powder bed fusion
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Y.S. Lee, M.M. Kirka, R.B. Dinwiddie, N. Raghavan, J. Turner, R.R. Dehoff, S.S. Babu Local microstructure control in electron beam powder bed fusion (EB-PBF) is of great interest to the additive manufacturing community to realize complex part geometry with targeted performance. The local microstructure control relies on having a detailed understanding of local melt pool physics (e.g., 3-D melt pool shape as well as spatial and temporal variations of thermal gradient (G) and solidification rate (R)). In this research, a new scan strategy referred to as ghost beam is numerically evaluated as a candidate to achieve the targeted G and R of IN718 alloy. The boundary conditions for simulations, including the speed (490 mm/s) and spatial locations of the beam within a given layer, are obtained by using series of snapshot images, recorded at 12,000 frames per second, using a high-speed camera. The heat transfer simulations were performed using TRUCHAS an open-source software deployed within a high-performance computational infrastructure. The simulation results showed that reheating at short beam on-time and time delay decreases both G and R. Local variation of R at the center of the melt pool trailing edge showed periodic temporal fluctuations. Finally, the ghost beam scan strategy was compared to other existing raster and spot scan strategies.
       
  • Interlayer fracture toughness of additively manufactured unreinforced and
           carbon-fiber-reinforced acrylonitrile butadiene styrene
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Devin Young, Nelson Wetmore, Michael Czabaj This study presents development of a test method for characterization of interlayer, mode-I fracture toughness of fused filament fabrication (FFF) materials using a modified double cantilever beam (DCB) test. This test consists of DCB specimen fabricated from using unidirectional FFF layers, an 8 μm Kapton starter crack inserted in the midplane during the printing process, and reinforcing glass/epoxy doublers to prevent DCB arm failure during loading. DCB specimens are manufactured with a commercially available 3D printer using unreinforced Acrylonitrile Butadiene Styrene (ABS) and chopped carbon-fiber-reinforced ABS (CF-ABS) filaments. To examine the effect of the FFF printing process on fracture toughness, additional ABS and CF-ABS specimens are hot-press molded using the filament material, and tested with the single end notch bend (SENB) specimen configuration. The fracture toughness data from DCB and SENB tests reveal that the FFF process significantly lowers the mode-I fracture toughness of ABS and CF-ABS. For both materials, in situ thermal imaging and post-mortem fractography shows, respectively, rapid cool-down of the rasters during filament deposition and presence of voids between adjacent raster roads; both of which serve to reduce fracture toughness. For CF-ABS specimens, fracture toughness is further reduced by inclusion of poorly wetted chopped carbon fibers. Although this study did not attempt to optimize the fracture performance of FFF specimens, the results demonstrate that the proposed methodology is suitable for design and optimization of FFF processes for improved interlayer fracture performance.
       
  • High-speed imaging and process characterization of coaxial laser metal
           wire deposition
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Maurizio Motta, Ali Gökhan Demir, Barbara Previtali In this work, coaxial laser metal wire deposition (LMWD) process is studied, with particular attention to defect formation mechanisms and the establishment of stable processing conditions. The coaxial LMWD of AISI 308 stainless steel wire was carried out by a multi-mode fiber laser delivered to an industrial coaxial LMWD deposition head. The continuous mechanical connection with the deposition region requires further attention to the process dynamics, which may alter the deposition precision and continuity. Accordingly, this work presents a systematic analysis of how the defects are formed at single and multiple layer deposition conditions. High-speed imaging is employed to reveal the process dynamics as a diagnostics aid. The process stability is determined initially at single layer condition, providing a correct match between the melting position and rate of the wire. At multiple layer deposition, the thermal load is managed to achieve high-aspect ratio components. At the stable conditions, the process is benchmarked for porosity, surface roughness, and deposition rates.
       
  • Role of heat treatment and build orientation in the microstructure
           sensitive deformation characteristics of IN718 produced via SLM additive
           manufacturing
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Michael D. Sangid, Todd A. Book, Diwakar Naragani, John Rotella, Priya Ravi, Alexander Finch, Peter Kenesei, Jun-Sang Park, Hemant Sharma, Jonathan Almer, Xianghui Xiao The benefits of additive manufacturing have been well documented, but prior to these materials being used in critical applications, the deformation mechanisms must be properly characterized. In this work, the role of heat treatment and build orientation of selective laser melting IN718 is investigated through detailed characterization. The microstructure of this material is probed through a combination of electron microscopy to identify the precipitate structure, electron backscatter diffraction to quantify the grain-level features, and synchrotron-based X-ray microcomputed tomography to detect porosity. A high degree of porosity is observed spatially near the free surface of the part, where the contour during the build process meets the interior hatch. Further, microstructure based deformation mechanisms are explored through digital image correlation relative to the grain features after monotonic and cyclic loading and in situ high-energy X-ray diffraction to identify the lattice strain evolution in these materials. Demarcations between the behaviors of the as-built versus post-processed materials are discussed; specifically, in terms of anisotropy with respect to build direction and values of the strength properties, based on the grain morphology, coherent twin formation, and precipitate structure. Lastly, the presence of dislocation sub-structures within the grains is observed to homogenize deformation within the as-built sample, while strain partitioning is observed during loading of the post-processed sample.Graphical abstractGraphical abstract for this article
       
  • Additive manufacturing-driven mold design for castings
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Jinwu Kang, Haolong Shangguan, Chengyang Deng, Yongyi Hu, Jihao Yi, Xiang Wang, Xiaochuan Zhang, Tao Huang The advance of additive manufacturing drives the design of molds for castings. In the present study, a type of skeletal mold for castings was proposed, which includes two structures, lattice-shell and rib enforced shell. The shell forms the cavity for a casting and the surrounding ribs or lattices support and enforce the shell. This type of mold structure design results in fast and uniform cooling of a casting, which can improve production efficiency and reduce the deformation and residual stress of a casting. In addition, it provides more space and flexibility to adjust the cooling conditions of interested locations of a casting. The thickness of the shell can be varied according to the local geometries of a casting. The support is designed based on the hydrostatic pressure before solidification and the weight after solidification. An air pocket (hollow structure) in the shell was designed for the riser to postpone its solidification and then facilitate shrinkage feeding. The experimental results revealed that the new design of sand molds saved at least 60% sand and shortened the shakeout time by at least 20%. Local hollow structure prolonged its solidification process by approximately 15%.Graphical abstractGraphical abstract for this article
       
  • Design, testing, and mechanical behavior of additively manufactured casing
           with optimized lattice structure
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Matthew E. Lynch, Matthew Mordasky, Lin Cheng, Albert To Additively manufactured internal lattice structures offer a unique approach to lightweight components and adding multi-functionality. Design methods for parts based on lattices are emerging and include a family of topology optimization schemes for tailoring local cell density to service loadings. In order to gain confidence, these methods must be validated in a controlled manner. In this paper, we report optimization, analysis, manufacturing, and mechanical test validation of a casing-like test article. The test article was optimized using a stress-based homogenized topology optimization approach and achieved a 53% weight reduction versus a solid, fully-dense casing with the same form factor. The optimized geometry was studied with high-fidelity finite element analysis and then additively manufactured. Mechanical testing was performed and demonstrated good correlation between the homogenized finite element model used for optimization, the high-fidelity finite element model, and experimental results. The findings validate the optimization approach for the particular use and load case and start to build confidence in the approach as an accepted method.
       
  • Direct laser fabrication of meso-scale 2D and 3D architectures with
           micrometric feature resolution
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Angelo Accardo, Rémi Courson, Roberto Riesco, Vincent Raimbault, Laurent Malaquin The realization of 2D and 3D meso-scale architectures is an area of research involving a wide range of disciplines ranging from materials science, microelectronics, phononics, microfluidics to biomedicine requiring millimeter to centimeter-sized objects embedding micrometric features. In the recent years, several technologies have been employed to provide optimal features in terms of object size flexibility, printing resolution, large materials library and fabrication speed. In this work, we report a fully customizable single-photon absorption 3D fabrication methodology based on direct laser fabrication. To validate this approach and highlight the versatility of the setup, we have fabricated a comprehensive ensemble of 2D and 3D designs with potential applications in biomimetics, 3D scaffolding and microfluidics. The high degree of tunability of the reported fabrication system allows tailoring the laser power, slicing and fabrication speed for each single area of the design. These unique features enable a rapid prototyping of millimeter to centimeter-sized objects involving 3D architectures with true freestanding subunits and micrometric feature reproducibility. The presented strategy fills indeed the current technological gap related to the development of meso-scale architectures required in multidisciplinary fields of research.Graphical abstractGraphical abstract for this article
       
  • Effect of energy per layer on the anisotropy of selective laser melted
           AlSi12 aluminium alloy
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): R. Rashid, S.H. Masood, D. Ruan, S. Palanisamy, R.A. Rahman Rashid, J. Elambasseril, M. Brandt The anisotropy in the tensile properties of AlSi12 alloy fabricated using selective laser melting (SLM) additive manufacturing process was investigated. The tensile samples were printed in three different orientations, horizontal (H - 0°), inclined (I - 45°), and vertical (V - 90°), and found to exhibit yield strength between 225 MPa and 263 MPa, tensile strength between 260 MPa and 365 MPa, and ductility between 1 and 4%, showing distinct fracture patterns. It was established that the build orientation had insignificant effect on the microstructural characteristics of the SLM-printed samples, while XRD phase analysis showed variations in the Al (111) and Al (200) peak intensities. Consequently, the anisotropy in the mechanical properties of the SLM-printed AlSi12 samples was attributed to the differences in their relative density. Although the energy density was kept constant when printing the samples along different orientations, the “energy per layer” was found to be different owing to the variation in the printing area along the build direction. Further investigation on the effect of printing area, and correspondingly energy per layer, on the relative density was carried out. It was found that energy per layer in the range of 504–895 J yielded ≥99.8% relatively dense AlSi12 SLM-printed samples. This study puts forth a new idea that the density of the SLM-printed samples could be controlled using energy per layer as an input process parameter.
       
  • A pragmatic part scale model for residual stress and distortion prediction
           in powder bed fusion
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Richard J. Williams, Catrin M. Davies, Paul A. Hooper Parts manufactured by laser powder bed fusion contain significant residual stress. This stress causes failures during the build process, distorts parts and limits in-service performance. A pragmatic finite element model of the build process is introduced here to predict residual stress in a computationally efficient manner. The part is divided into coarse sections which activate at the melting temperature in an order that imitates the build process. Temperature and stress in the part are calculated using a sequentially coupled thermomechanical analysis with temperature dependent material properties. The model is validated against two sets of experimental measurements: the first from a bridge component made from 316L stainless steel and the second from a cuboidal component made from Inconel 718. For the bridge component the simulated distortion is within 5% of the experimental measurement when modelled with a section height of 0.8 mm. This is 16 times larger than the 50 μm layer height in the experimental part. For the cuboid component the simulated distortion is within 10% of experimental measurement with a section height 10 times larger than the experiment layer height. These results show that simulation of every layer in the build process is not required to obtain accurate results, reducing computational effort and enabling the prediction of residual stress in larger components.
       
  • Processing and characterization of crack-free aluminum 6061 using
           high-temperature heating in laser powder bed fusion additive manufacturing
           
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Syed Z. Uddin, Lawrence E. Murr, Cesar A. Terrazas, Philip Morton, David A. Roberson, Ryan B. Wicker During solidification of many so-called high-performance engineering alloys, such as 6000 and 7000 series aluminum alloys, which are also unweldable autogenously, volumetric solidification shrinkage and thermal contraction produces voids and cracks. During additive manufacturing processing, these defects can span the length of columnar grains, as well as intergranular regions. In this research, laser powder bed fusion (LPBF) of aluminum alloy (AA) 6061 used powder bed heating at 500 °C in combination with other experimentally determined processing parameters to produce crack-free components. In addition, melt-pool banding, which is a normal solidification feature in LPBF, was eliminated, illustrating solidification process modification as a consequence of powder bed heating. Corresponding microindentation hardness and tensile testing of the as-fabricated AA6061 components indicated an average Vickers hardness of HV 54, and tensile yield, ultimate strength, and elongation values of 60 MPa, 130 MPa, and 15%, respectively. These mechanical properties and those of heat treated parts showed values comparable to annealed and T6 heat treated wrought products, respectively. X-ray diffraction and optical microscopy revealed columnar grain growth in the build direction with the as-fabricated, powder-bed heated product microstructure characterized by [100] textured, elongated grains (∼ 25 μm wide by 400 μm in length), and both intragranular and intergranular, noncoherent Al-Si-O precipitates which did not contribute significantly to the mechanical properties. The results of this study are indicative that powder bed heating may be used to assist with successful fabrication of AA6061 and other alloy systems susceptible to additive manufacturing solidification cracking.
       
  • Metastable carbides and their impact on recrystallisation in IN738LC
           processed by selective laser melting
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): O.M.D.M. Messé, R. Muñoz-Moreno, T. Illston, S. Baker, H.J. Stone Selective laser melting of nickel based superalloys opens up new possibilities for gas turbine engine manufacturers; namely, efficient production of low component volumes, decreased component cost through reduced post-machining procedures and access to new component geometries that cannot be fabricated by conventional processing methods. However, processing high performance nickel-based superalloys components via additive manufacturing, without the occurrence of defects, is challenging and requires a better understanding of the resulting microstructure, especially as different compositions can lead to significant changes in the microstructure obtained. In addition, carefully selected post-processing heat-treatments are required to alter the microstructure and attain the required mechanical properties. In this study, the microstructure of the nickel base superalloy IN738LC has been characterised in the as-deposited and stress relieved heat-treated states, as well as following high temperature heat treatments. The data acquired highlights the influence of the stress relief step on the recrystallisation temperature and its relation with the distribution of carbide particles present in the alloy's microstructure.
       
  • Mechanical properties of Sn63Pb37 components by fused coating technology
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Guangxi Zhao, Zhengying Wei, Jun Du, Ruwei Geng, Siyuan Xu The fused coating process is a new material jetting additive manufacturing technology that proposes to solve the problem of high cost, low efficiency and high material requirements of laser-based process and electron beam process. The structure and operating principles of the fused coating machine are explained in this paper. Sn63Pb37 is taken as the experimental material because of its low melting temperature, small surface tension coefficient and high viscosity. Tensile test specimens were made both parallel and perpendicular to the forming trajectory. Tensile strengths were measured and the corresponding fractographies were observed. It is found that large plastic deformation has occurred before the fracture, and the plasticity of fused components that the tensile direction parallel to the forming trajectory, is higher. The densification degree of fused coating component is measured by the drainage method. The average value is up to 99.78% which indicates that the internal structure is indistinguishable from extruded Sn63Pb37. The Vickers hardness of the fused coated component and raw casted material were tested by 5 points respectively, the results showed that the average Vickers hardness of the fused coating component is 14.6% higher than the casted one.
       
  • Evaluation of the mechanical performance of polymer parts fabricated using
           a production scale multi jet fusion printing process
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Heather J. O’Connor, Andrew N. Dickson, Denis P. Dowling Additive manufacturing (AM) is rapidly becoming one of the most popular manufacturing techniques for short run part production and rapid prototyping. AM encompasses a range of technologies, including powder bed fusion (PBF) process. The purpose of this paper is to evaluate and benchmark the mechanical performance of polyamide 12 (PA12) parts, fabricated using a production scale powder bed fusion printing process (HP Multi Jet Fusion printing process). This system has a build volume is 380 × 254 × 350 mm. The printed polymer parts were examined to determine their hydrophobicity, morphology, porosity and roughness. Chemical and thermal properties of the PA12 parts were also evaluated using attenuated total reflection infrared spectroscopy (ATR FT-IR), x-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC). The study highlights the influence of build orientation on the tensile (ISO 527-1:2012) and flexural (ISO 178:2010) properties. In terms of tensile strength, the parts exhibited isotropic behaviour with a maximum tensile strength of 49 MPa. In terms of flexural testing, the build orientations had a significant effect on the strength of the printed part. The Z orientation exhibited a 40% higher flexural strength, when compared to that of the X orientation. The maximum flexural strength observed was 70 MPa. The results of this rapid, production scale AM study are compared with previous studies that detail the mechanical performance of PA12, fabricated using PBF processes, such as selective laser sintering.
       
  • Realizing a full volume component by in-situ welding during electron beam
           melting process
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Pan Wang, Mui Ling Sharon Nai, Wai Jack Sin, Shenglu Lu, Baicheng Zhang, Jiaming Bai, Jie Song, Jun Wei As one of the powder-bed-fusion additive manufacturing processes, electron beam melting (EBM) is able to produce metal parts directly. Many small volume components with high quality have been fabricated using the EBM technology. However, there are only few reports on the EBM fabrication of medium-sized components. One of the reasons is the lack of energy issue when the scan length is too long, which results in the generation of lack of fusion pores. This, in turn, drastically degrades the mechanical properties of the EBM printed parts. Here, we firstly report an in-situ welding process to overcome the lack of energy issue caused by the long scan length during EBM process. After the investigation of the corresponding microstructure, microhardness and tensile properties, it is revealed that the in-situ welding zone is fully joined and the mechanical properties of the in-situ welded part are comparable to that of the wrought counterpart. This implies that medium-sized components can be successfully fabricated using the EBM, with no compromise on the mechanical properties.
       
  • Observations of particle-melt pool impact events in directed energy
           deposition
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): James C. Haley, Julie M. Schoenung, Enrique J. Lavernia In the rapidly growing field of Additive Manufacturing (AM), the Laser Directed Energy Deposition (L-DED) process is the focus of intense technical attention due to its potential to generate high quality components with location specific composition and microstructural control. Despite the variety of experimental and modelling efforts devoted to the subject, no studies directly observe the interactions between individual powder particles and the liquid pool of metal at a high enough temporal frequency to characterize these discrete contact events. The frequency and nature of these powder-pool impingements govern overall process behavior, and are a poorly quantified fundamental building block of L-DED. In this work, we report novel results in which the melt pool is imaged at up to 200,000 frames per second, with pixel resolution of up to 3.6 μm. Video images reveal that particles often impact and float on the surface of the melt pool for several hundreds of microseconds before melting into it. Further incoming particles were observed to rebound from the melt pool by these floating particles. Through modelling this process analytically, particle self-shielding is shown to impose unavoidable upper limits on overall powder capture efficiency for the L-DED process.
       
  • Multi-functional flexible carbon fiber composites with controlled fiber
           alignment using additive manufacturing
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Ali Anwer, Hani E. Naguib This paper details a novel study and manufacturing approach of fiber alignment in flexible hybrid carbon fiber composites using Material extrusion. Varying carbon fiber volume fractions from 0 to 4 vol % was melt blended with a masterbatch of TPU + 10 wt% MWCNT followed by extrusion. The final extrudate was then filament wound onto a spool and two different filament layout orientations, 0° and 45°, were printed to compare their mechanical properties to validate the effect of fiber alignment during the printing process for these flexible fiber composites. The 0° printed composites exhibited up to 34% improvement in stiffness as compared to the 45° composite. To validate this fiber orientation, the flexible composite was textured using fiber-debonding and pullout phenomenon and the surfaces were visually and quantifiably characterized using SEM images and surface roughness respectively. To further elucidate the fiber alignment as indicated by the surface roughness, a water contact angle hydrophobicity test was conducted to prove that the 0° printed composite showed higher contact angle as compared with the 45° orientation, confirming greater entrapment due to fiber alignment at the surface. These composites are expected to find future potential in high strength and surface texturing applications.
       
  • Simulation and validation of three dimension functionally graded materials
           by material jetting
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Eduardo Salcedo, Dongcheon Baek, Aaron Berndt, Jong Eun Ryu The goal of this work is to validate the material models for parts created with a Material Jetting 3-dimensional printer through the comparison of Finite Element Analysis (FEA) simulations and physical tests. The strain maps generated by a video extensometer for multi-material samples are compared to the FEA results based on our material models. Two base materials (ABS-like and rubber-like) and their composites are co-printed in the graded tensile test samples. The graded islands are embedded in the rubber-like test specimens. The simulations were conducted utilizing previously fitted material models, a two-parameter Mooney-Rivlin model for the elastic materials (Tango Black+, DM95, and DM60) and a bilinear model for the rigid material (Vero White+). The results show that the simulation results based on our material models can predict the deformation behaviors of the multi-material samples during a uniaxial tensile test. Our simulation results are able to predict the maximum strain in the matrix material (TB+) within 5% error. Both global deformation pattern and local strain level confirm the validity of the simulated material models.Graphical abstractGraphical abstract for this article
       
  • Direct write fabrication of high-density parallel silver interconnects
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Alan Shen, Dustin Caldwell, Anson W.K. Ma, Sameh Dardona This study investigates the suitability of direct write (DW) technology for the fabrication of high-resolution wear sensors. We demonstrate the production of high-density parallel interconnect traces and provide recommendations for processing conditions to minimize line width and line spacing based on DW ink rheology. To create parallel silver lines with 50 μm center-to-center spacing and 15 μm line width on alumina substrates, we used an nScrypt DW system and sintered the lines at 625 °C in air. The sintered lines exhibited an electrical resistivity of 5.29 × 10−8 Ω m (about three times bulk silver resistivity reported in the literature) with a standard deviation of 3.68 × 10-9 Ω m (ca. 7% variation). To determine the conditions needed to consistently create fine conductive lines, we simulated the volumetric flow rate and analyzed the effects on line geometry of several printing parameters including valve opening, dispensing gap, and substrate translation speed. Our results indicate decreasing the valve opening, decreasing the dispensing gap, and/or increasing the translation speed of the substrate reduces the resultant printing flow rate and cross-sectional area of DW lines. For a fixed valve opening and dispensing gap, we also observed broken lines due to overstretching of the inks at exceedingly high substrate translation speeds.
       
  • The effect of multi-beam strategies on selective laser melting of
           stainless steel 316L
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Thorsten Heeling, Konrad Wegener With increasing industrial application of additive manufacturing technologies, such as selective laser melting, the requirements concerning the processes’ capabilities like productivity, robustness, part quality and the range of processable materials are increasing as well. But due to high cooling rates, high thermal gradients and a layer-wise processing, parts produced by selective laser melting are subject to different kinds of defects. These defects commonly lead to high porosity, distortion, cracking and rough surfaces. But when a second beam is used to heat the vicinity of the melt pool a homogenization of the temperature field, a reduction of the cooling speeds within the melt pool and in its vicinity as well as an improved wetting behavior is possible. A proof of concept is shown, discussing general trends and possibilities, like increased surface qualities or dense microstructures with low amounts of remelting, when these strategies are elaborated.
       
  • Projection based light-directed electrophoretic deposition for additive
           manufacturing
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Jeronimo Mora, Jessica K. Dudoff, Bryan D. Moran, Joshua R. DeOtte, Wyatt L. Du Frane, Joshua D. Kuntz, Andrew J. Pascall Electrophoretic deposition (EPD) is a widely used industrial coating technique for depositing polymer, ceramic, and metal thin films. Recently, there has been interested in using EPD for additive manufacturing using reconfigurable electrodes. Here, we report the first projector-based light-directed electrophoretic deposition (EPD) system that uses projected digital masks to dynamically control the electric field, eliminating the need for physical photomasks. We demonstrate a resolution limit of 10 μm for the deposited feature, which corresponds to the limits of the optical system. Furthermore, the first 3D overhanging structure made with EPD is presented, which points to the ability to create architected cellular materials. These improvements open the possibility for EPD to be a true 3D additive manufacturing technique.
       
  • Improvement of the bridge curvature method to assess residual stresses in
           selective laser melting
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Sabine Le Roux, Mehdi Salem, Anis Hor In the Selective Laser Melting (SLM) process, residual stresses are a major problem because they impact the dimensional accuracy and mechanical properties of the manufactured parts. A new methodology, based on distortion measurements using the bridge curvature method (BCM), is developed for the quantitative assessment of residual stresses. The bending of the surface of the released specimen is approximated by a quadratic polynomial and quantitative criteria are determined on both profiles and surface topographies measured by non-contact 3D optical microscopy. The accuracy of the method is evaluated by a statistical analysis using repeatability tests. Focus variation microscopy (FVM) measurements show better repeatability than extended field confocal microscopy. Compared to the 2D measurements generally reported in the literature, 3D characterization provides relevant information as the orientation of the main distortion, which may help to highlight the effect of SLM process parameters. In fact, the flatness parameters and curvature attributes measured on surface topographies are much more robust and repeatable than the distortion magnitude measured on isolated profiles. In particular, 3D analysis helps to show that the distortions are maximum perpendicular to the path of the laser.
       
  • A physical modeling and predictive simulation of the laser cladding
           process
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Florian Wirth, Konrad Wegener A 3D finite element simulation model of the laser cladding process has been developed taking into account heat transfer, fluid flow, surface tension and free surface movement. All input parameters and data, which are independent of the process parameters but depend only on the material and machine properties, have been obtained from measurements. Thereby the melt pool and the resulting surface contour can be simulated without compromising assumptions or calibration, because the machine parameters are the only variable input parameters of the model. Thus, the model can easily be transferred to other material combinations or other machines. For the surface contour calculation a modified height function method is applied. The model surface follows this contour as an arbitrary Lagrangian Eulerian (ALE) method is used allowing for mesh deformations. The model was implemented using the commercial finite element software COMSOL Multiphysics and validated by comparing the simulation results with caloric measurements of the effective heat input and metallographic cross sections from experiments, where the nickel-base alloy MetcoClad® 625 in powder form was deposited on structural steel S235JRC + C and the process parameters of laser power, feed speed, laser beam spot size and powder mass flow were varied within a range of at least 50% of their mean value each. The maximum deviation of the simulation results compared to the experimental data regarding track geometry is 14% for the parameter sets without weld defects so that these parameter sets could be industrially applied, whereas the average deviation of track width and height is below 5.1%. Moreover, the maximum difference of the simulated absorptivity compared to the measurement results is 6.9%, while the average difference is only 1.7%, meaning the model shows a high predictive capability especially regarding the heat input.
       
  • Correlation of selective laser melting-melt pool events with the tensile
           properties of Ti-6Al-4V ELI processed by laser powder bed fusion
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Manisha Bisht, Nachiketa Ray, Frederik Verbist, Sam Coeck In this study, we present the first results of a newly developed melt pool monitoring tool for selective laser melting, called DMP-meltpool. A manual data analysis method is given, and the events indicated by the analysis (DMP-meltpool events) are shown to correlate to the static tensile properties of the samples built. These events indicate the probability of material discontinuities (defects) in the metal additive manufacturing (AM) parts. In order to do so, cylindrical bars of Ti-6Al-4V ELI were built and monitored using DMP-meltpool. The tensile properties of the printed cylinders were correlated with the events detected by DMP-meltpool. An inverse relation between plastic elongation and the DMP-meltpool event density was observed. These results show that DMP-meltpool can be used to predict the quality of AM parts by detecting variations in the signals and tagging these events throughout the build as defects. Thus the technique can be employed for first stage in-line quality control of AM parts and for sorting out parts with potential defects non-destructively. The DMP-meltpool events could have significant correlations with other mechanical properties (like fatigue, hardness, fracture toughness, and crack propagation) since such properties are influenced by defects originating from the process instabilities.
       
  • The influence of laser parameters, scanning strategies and material on the
           fatigue strength of a stochastic porous structure
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Shaaz Ghouse, Sarat Babu, Kenneth Nai, Paul A. Hooper, Jonathan R.T. Jeffers Additive manufactured (AM) porous materials behave quantitatively and qualitatively differently in fatigue than bulk materials, and the relationships normally used for the fatigue design of continuous bulk materials are not applicable to AM porous materials particularly for low stiffness applications.This study investigated how the manufacturing methods and the material used during powder bed fusion affects the compressive strength and high cycle fatigue strength of a stochastic porous material for a given stiffness. Specimens were manufactured using varying laser parameters, 3 scan strategies (Contour, Points, Pulsing) and 4 materials. The materials investigated were two titanium alloys: commercially pure grade 2 (CP-Ti) and Ti6Al4V ELI, commercially pure tantalum (Ta) and a titanium-tantalum alloy (Ti-30Ta).The trends observed during fatigue testing for monolithic metals and statically for solid and porous AM materials were not always indicative of the high cycle fatigue behaviour of porous AM materials. Unlike their solid counterparts, porous tantalum and the titanium-tantalum alloy had the greatest fatigue strength for a given stiffness, 8% greater than CP-Ti and 19% greater than Ti6Al4V ELI. Optimisation of the laser parameters and scan strategies was found to also increase the fatigue strength for a given stiffness of porous AM materials by 7–8%.
       
  • Absorption cross-sections of Disperse Orange 13 and Irgacure 784
           determined with mask projection vat photopolymerization
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Pekka Lehtinen, Matti Kaivola, Jouni Partanen It is necessary to understand the photoinitiated curing process, which occurs in vat photopolymerization resins during exposure, to develop high quality end products. Usually a curable resin contains photosensitizers, crosslinkable monomers and neutral absorbers, which have different roles in the curing process. The photosensitizer initiates the process by absorbing a photon and creating a chain initiator species, which causes the monomers to polymerize, crosslink and form a solid shape. While a photoinitiator is essential to achieve curing, a neutral absorber is required to control the cure depth. Short cure depth results in thin layers and high resolution end products, whereas large cure depth increases manufacturing speed. Thus, information about the absorptive properties of both the initiator and the absorber is crucial for the development of additive manufacturing techniques that are based on photoinitiated curing. To investigate these absorptive properties, a working curve method is applied with a mask projection vat photopolymerization apparatus to determine the absorption cross-sections of Irgacure 784 and Disperse Orange 13 and compare the results to ones obtained with spectrophotometry. With both methods, the results for each substance are within the same order of magnitude, but photobleaching seems to affect the vat photopolymerization results.
       
  • Environmentally benign metallization of material extrusion technology 3D
           printed acrylonitrile butadiene styrene parts using physical vapor
           deposition
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Justin White, Christopher Tenore, Austin Pavich, Ryan Scherzer, Stephen Stagon Metallization has been widely used to enhance the aesthetics and performance of injection molded plastic parts, but the techniques have not been widely extended to 3D printed parts due to intrinsic differences in surface chemistry and morphology. Here, we investigate direct metallization of acrylonitrile butadiene styrene (ABS) 3D printed thermoplastic parts using low cost environmentally benign surface preparations and physical vapor deposition (PVD) to avoid the use of preparation with toxic chromic acid. Fourier transform infrared (FTIR) spectra are gathered for each surface preparation method prior to metallization. The metallized parts are then characterized for thin film adhesion, electrical resistivity, and optical reflectivity. Additionally, each part is imaged using a scanning electron microscope (SEM) post-metallization. The results show that surface preparation with solvent results in a smooth and aesthetically pleasing surface, but metallic film adhesion is poor. Conversely, when 2000 grit sandpaper is used to mechanically prepare the surfaces, the resulting films have poor electrical conductivity and optical reflectance, but excellent adhesion. Atmospheric plasma treatment of the parts results in the highest overall performance, with superior adhesion strength and optical reflectivity and low electrical resistivity. Electron microscopy and FTIR reveal that the high adhesion resulting from atmospheric plasma is caused by modification surface morphology, but not surface chemical termination. The results indicate that direct metallization of 3D printed ABS is a viable method for creating metallized parts with high performance and an aesthetically pleasing appearance and that the use of chromic acid in surface preparation is not necessary.
       
  • Microstructure and performance evolution and underlying thermal mechanisms
           of Ni-based parts fabricated by selective laser melting
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Dongdong Gu, Qimin Shi, Kaijie Lin, Lixia Xi This work presented a comprehensive study of microstructural evolution, microhardness and quantitative thermodynamic analysis within the molten pool during Selective Laser Melting (SLM) of Inconel 718 parts. Microstructures and corresponding microhardness of different zones within the molten pool experienced the following evolution: fine cellular dendrites or equiaxed grains on the top surface (387HV); columnar dendrites with single direction of grain growth at the bottom (337HV); columnar dendrites with multiple directions of grain growth at the edge of the molten pool (340HV-350HV); microstructures between cellular and columnar grains around the center of the molten pool (363HV). The impact of Gaussian-distributed laser energy and relatively weak thermal conductivity and convection of Inconel 718 contributed to the variation of temperature gradient at different zones within the molten pool. The formation of different kinds of microstructures in the molten pool was controlled by the temperature gradient (which determined the direction of grain growth) and the cooling rate (which determined the size of grain growth). The variation of microhardness within the molten pool was ascribed to the number of grain boundaries and the stress characteristics of different kinds of microstructures under mechanical load. The zones with fine cellular grains had elevated mechanical performance due to the superior capability to endure the load. This work hopefully provides scientific and theoretical support for SLM-processed Inconel 718 parts with favorable properties.Graphical abstractGraphical abstract for this article
       
  • A challenge for enhancing the dimensional accuracy of a low-cost 3D
           printer by means of self-replicated parts
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): P. Minetola, M. Galati Owing to the lack of optimization, the dimensional accuracy of low-cost 3D printers is quite limited. In order to enhance the performances of a Prusa i3 3D printer, an optimization challenge was assigned to the students of the Specializing Master in Industrial Automation of the Politecnico di Torino. The enhancements were applied to four printers by manufacturing new self-replicated parts by means of the same 3D printers. Finally, a benchmarking activity was used to check and validate the results of the optimization activities. The benchmarking involved the fabrication of replicas of an innovative reference artifact by means of the modified printers. A coordinate measuring machine (CMM) was then used to inspect the dimensions of the replicas. Measures were used to compare the performances of the four optimized printers in terms of dimensional accuracy using ISO IT grades. The form errors of the geometrical features of the replicas were also evaluated according to the GD&T system. The benchmarking results show that the most effective modifications to the original printer were those related to the improvement of the structure stiffness and chatter reduction.Graphical abstractGraphical abstract for this article
       
  • Accuracy in dental surgical guide fabrication using different 3-D printing
           techniques
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Mamta Juneja, Niharika Thakur, Dinesh Kumar, Ankur Gupta, Babandeep Bajwa, Prashant Jindal Accuracy in dental prosthesis plays a significant role. Surgical guides are widely used for accurate positioning of dental implants. Designing of guides using modern software is useful in achieving precision; however, translation of these images into actual fabricated parts can be achieved using Three-dimensional (3-D) printing. Conventionally, guides were fabricated using vacuum forming technique which leads to several dimensional inaccuracies. Computed Tomography (CT) images of patients with missing teeth are modeled to design surgical guide using Computer Aided Design (CAD) / Computer Aided Manufacturing (CAM) software which is then combined with surface scan files in Standard Tessellation Language (STL) formats to design the guide. In this work, surgical guides have been 3-D printed using different technologies like Material Jetting technology (MJT), Vat photopolymerization (VP) and Material extrusion (ME). Depth, diameter, Area and Volume of the printed guides have been calculated using vernier caliper and scan measurements. These dimensions have then been compared with the dimensions obtained from software modeled images. Least error has been found for the guides fabricated using MJT. The experimental work in this paper, hence, suggests MJT be the most preferred printing technique due to its superior accuracy for printing dental prosthesis like aligners, implants, and crowns, etc.
       
  • Mesostructure and porosity effects on the thermal conductivity of
           additively manufactured interpenetrating phase composites
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Abdel R. Moustafa, Ralph B. Dinwiddie, Alexander E. Pawlowski, Derek A. Splitter, Amit Shyam, Zachary C. Cordero We have investigated the relationship between structure and thermal conductivity in additively manufactured interpenetrating A356/316L composites. We used X-ray microcomputed tomography to characterize the pore structure in as-fabricated composites, finding microporosity in both constituents as well as a 50 μm thick layer of interfacial porosity separating the constituents. We measured the thermal conductivity of a 43 vol% 316L composite to be 53 Wm−1K−1, which is significantly less than that predicted by a simple rule-of-mixtures approximation, presumably because of the residual porosity. Motivated by these experimental results we used periodic homogenization theory to determine the combined effects of porosity and unit cell structure on the effective thermal conductivity. This analysis showed that in fully dense composites, the topology of the constituents has a weak effect on the thermal conductivity, whereas in composites with interfacial porosity, the size and structure of the unit cell strongly influence the thermal conductivity. We also found that an approximation formula of the strong contrast expansion method gives excellent estimates of the effective thermal conductivity of these composites, providing a powerful tool for designing functionally graded composites and for identifying mesostructures with optimal thermal conductivity values.
       
  • Experimental analysis of metal/plastic composites made by a new hybrid
           method
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Javaid Butt, Hassan Shirvani The purpose of this paper is to identify the key elements of a new hybrid process to produce high quality metal/plastic composites. The process is a combination of Fused Deposition Modelling (FDM), vacuum forming and CNC machining. The research aims to provide details of the proposed hybrid process, equipment used, and the experimental results of the composites produced. The research has been separated into three study areas. In the first, the hybrid process has been defined as a whole whereas the second area deals with the breakdown of steps to produce the metal/plastic composites. The third area explains the varied materials used for the production and testing of the composites. Composites have been made by joining copper (99.99% pure) mesh with ABS (acrylonitrile butadiene styrene). Strain measurement has been carried out on Cu/ABS sample to analyse the effect of metal mesh and to verify the effectiveness of the hybrid process. The resulting composites (Cu/ABS) have also been subjected to tensile loading with different layers of metal mesh, followed by microstructural analysis and comparative studies to serve as a proof of the methodology. The results show that the proposed hybrid process is very effective in producing metal/plastic composites with lower strain values compared to the parent plastic indicating a lower level of deformation due to interlocking of the metal and plastic layers. This effect has been reinforced by the tensile testing where the composites showed higher fracture load values compared to the parent plastic. Microstructural analysis shows the layer of metal mesh sandwiched between ABS layers indicating the existence of a bond holding the layers of metal and plastic together. These results demonstrate the capabilities and effectiveness of the proposed process that has shown promising results under tensile and static loading.
       
  • Effect of laser focus shift on surface quality and density of Inconel 718
           parts produced via selective laser melting
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Glenn E. Bean, David B. Witkin, Tait D. McLouth, Dhruv N. Patel, Rafael J. Zaldivar Selective laser melting (SLM) is a method of laser powder bed fusion additive manufacturing (AM) currently being pursued in numerous industries, including space launch and space flight. In this study we performed an extensive parameter development investigation to better understand the effect of laser parameters on surface roughness, density, and porosity of SLM Inconel 718 parts. Laser energy density was varied via laser focus shift, and the effects on porosity in both as-printed and post-HIP treated states were analyzed. Tensile testing was also conducted to investigate the effect of processing conditions on the mechanical properties of SLM 718. It was found that for these laser parameters, while the material met ultimate tensile strength and yield strength requirements per AMS 5662, the strain-to-failure was reduced with negative focus shift due to increases in porosity levels. It was also found that while correlations were observed between surface roughness, density, and porosity within the laser focus shift range investigated, porosity measurement appears to be the clearest indicator of build quality for AM processed 718.
       
  • Complex flow and temperature history during melt extrusion in material
           extrusion additive manufacturing
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Fang Peng, Bryan D. Vogt, Miko Cakmak 3D printing using the materials extrusion additive manufacturing (ME-AM) process is highly nonisothermal. In this process, a solid polymer filament is mechanically drawn into a heated hot end (liquefier) where the polymer is ideally melted to a viscous liquid. This melt is extruded through an orifice using applied pressure of the solid filament that is continuously being drawn into the extruder. The extruded filament melt is deposited to build up the desired part. The poor thermal conductivity of most polymers inevitably leads to temperature gradients, in both the radial and axial directions. Here we quantify the temperature evolution of the polymer filament in axial direction using embedded fine thermocouples as a function of process parameters. Information about the radial gradients is obtained by introducing dye markers within the filament through understanding the flow behavior through the extruder by the deformation of the dye from a linear to pseudo parabolic profile. The polymer is heated above the glass transition temperature for less than 30 s for reasonable print conditions with the center of the filament remaining cooler than the liquefier temperature throughout the process. These process measurements provide critical data to enable improved simulation and modeling of the ME-AM process and the properties of the printed parts.
       
  • Finite element analysis of thermoplastic polymer extrusion 3D printed
           material for mechanical property prediction
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Sunil Bhandari, Roberto Lopez-Anido A space frame lattice and shell finite element model was created to predict the linearly elastic response of test coupons made with a modified polyetherimide (PEI) material. This approach was employed because it provides an efficient procedure to design and optimize 3D printed parts. The modeled coupons were 3D printed by extrusion of molten thermoplastic polymer. The finite element model was verified by comparing the predicted values of elastic modulus, shear modulus, and Poisson’s ratio in two material directions with the corresponding values obtained from quasi-static mechanical experiments. The values obtained for the moduli and the Poisson’s ratios from the finite element model matched closely with those obtained from the experiments.
       
  • An investigation into 3D printing of fibre reinforced thermoplastic
           composites
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): L.G. Blok, M.L. Longana, H. Yu, B.K.S. Woods Fused filament fabrication (FFF) is a 3D printing technique which allows layer-by-layer build-up of a part by the deposition of thermoplastic material through a nozzle. The technique allows for complex shapes to be made with a degree of design freedom unachievable with traditional manufacturing methods. However, the mechanical properties of the thermoplastic materials used are low compared to common engineering materials. In this work, composite 3D printing feedstocks for FFF are investigated, wherein carbon fibres are embedded into a thermoplastic matrix to increase strength and stiffness. First, the key processing parameters for FFF are reviewed, showing how fibres alter the printing dynamics by changing the viscosity and the thermal profile of the printed material. The state-of-the-art in composite 3D printing is presented, showing a distinction between short fibre feedstocks versus continuous fibre feedstocks. An experimental study was performed to benchmark these two methods. It is found that printing of continuous carbon fibres using the MarkOne printer gives significant increases in performance over unreinforced thermoplastics, with mechanical properties in the same order of magnitude of typical unidirectional epoxy matrix composites. The method, however, is limited in design freedom as the brittle continuous carbon fibres cannot be deposited freely through small steering radii and sharp angles. Filaments with embedded short carbon microfibres (∼100 μm) show better print capabilities and are suitable for use with standard printing methods, but only offer a slight increase in mechanical properties over the pure thermoplastic properties. It is hypothesized that increasing the fibre length in short fibre filament is expected to lead to increased mechanical properties, potentially approaching those of continuous fibre composites, whilst keeping the high degree of design freedom of the FFF process.
       
  • Evaluation of compressive and flexural properties of continuous fiber
           fabrication additive manufacturing technology
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Miguel Araya-Calvo, Ignacio López-Gómez, Nicolette Chamberlain-Simon, José Luis León-Salazar, Teodolito Guillén-Girón, Juan Sebastián Corrales-Cordero, Olga Sánchez-Brenes This study focuses on the characterization of additive manufacturing technology based on composite filament fabrication (CFF). CFF utilizes a similar method of layer by layer printing as fused filament fabrication but is also capable of reinforcing parts with layers of various continuous fibers into a polymer matrix. Due to the orthotropic characteristics of additive manufacturing based on fused filament fabrication, 3D printed parts may present different mechanical behavior under different orientations of stress. Furthermore, technologies such as CFF allow a range of configurations to fabricate and reinforce the parts. In this study, mechanical characterization of polyamide 6 (PA6) reinforced with carbon fiber was conducted by design of experiment as a statistical method, to investigate the effect of reinforcement pattern, reinforcement distribution, print orientation and percentage of fiber on compressive and flexural mechanical properties. CFF technology 3D print stronger parts than conventional additive manufacturing technologies. Maximized compressive response was achieved with a 0.2444 Carbon Fiber volume ratio, concentric and equidistant reinforcement configuration, resulting in a compressive modulus of 2.102 GPa and a stress at proportional limit of 53.3 MPa. Maximized flexural response was achieved with 0.4893 Carbon Fiber volume ratio, concentric reinforcement and perpendicular to the applied force, resulting in a flexural modulus of 14.17 GPa and a proportional limit of 231.1 MPa.
       
  • Electrochemical behavior of AISI316L stainless steel parts produced by
           laser-based powder bed fusion process and the effect of post annealing
           process
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Ali Hemmasian Ettefagh, Shengmin Guo This paper presents the investigation of the corrosion behavior of AISI316L samples prepared by laser-based powder bed fusion additive manufacturing (AM) method. Both AM and conventional stainless steel 316L samples were examined in NaCl 3.5% solution before and after the annealing process using Tafel curves, Electrochemical Impedance Spectroscopy, and X-ray diffraction. The results indicate that the AM parts have an improved corrosion behavior than the conventional wrought samples. Besides, the heat treatment process is found to further decrease the corrosion rate of the AM parts through the relieving of the residual stress. In contrast, the post annealing induced improvement to corrosion resistance for the wrought samples is due to the elimination of martensite phase which almost always exists after the plastic deformation during their production process.
       
  • Computed tomography metrological examination of additive manufactured
           acetabular hip prosthesis cups
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Nadia Kourra, Jason M. Warnett, Alex Attridge, Greg Dibling, James McLoughlin, Sarah Muirhead-Allwood, Richard King, Mark A. Williams Additive manufacturing (AM) is uniquely suitable for healthcare applications due to its design flexibility and cost effectiveness for creating complex geometries. Successful arthroplasty requires integration of the prosthetic implant with the bone to replace the damaged joint. Bone-mimetic biomaterials are utilised due to their mechanical properties and porous structure that allows bone ingrowth and implant fixation. The predictability of predetermined interconnected porous structures produced by AM ensures the required shape, size and properties that are suitable for tissue ingrowth and prevention of the implant loosening. The quality of the manufacturing process needs to be established before the utilisation of the parts in healthcare. This paper demonstrates a novel examination method of acetabular hip prosthesis cups based on X-ray computed tomography (CT) and image processing. The method was developed based on an innovative hip prosthesis acetabular cup prototype with a prescribed non-uniform lattice structure forming struts over the surface, with the interconnected porosity encouraging bone adhesion. This non-destructive, non-contact examination method can provide information of the interconnectivity of the porous structure, the standard deviation of the size of the pores and struts, the local thickness of the lattice structure in its size and spatial distribution. In particular, this leads to easier identification of weak regions that could inhibit a successful bond with the bone.
       
  • Fire resistance of additively manufactured water filled polymer parts
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Hadley Brooks, Chris Wright, Stephen Harris, Andrew Fsadni This paper introduces the concept of additively manufactured (AM) water filled parts (WFPs). By combining the energy absorbing properties of water with polymers, it is possible to significantly improve the time to ignition of AM parts with open internal structures. Theory relating the flame temperature to the maximum wall temperature of WFPs is developed. A range of water-polymer configurations are presented as a basis for WFP designs. Three separate thermal experiments were conducted to test different aspects of the WFPs. The time to ignition for cone calorimetry samples was extended 794% over plain photopolymers. Case studies were used to demonstrate the effectiveness of WFPs with complex shapes. The results of thermo-fluid finite element simulations showed good agreement with experimental observations and provide a useful tool for the evaluation and optimisation of WFP designs. The fire resistance of thin walled structures with internal water volumes was found to be significantly improved. The water filling strategy was found to be more effective than adding intumescent coatings. Finally further work and recommendations are discussed.Graphical abstractGraphical abstract for this article
       
  • Effects of atomizing media and post processing on mechanical properties of
           17-4 PH stainless steel manufactured via selective laser melting
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Somayeh Pasebani, Milad Ghayoor, Sunil Badwe, Harish Irrinki, Sundar V. Atre Water-atomized and gas-atomized 17-4 PH stainless steel powder were used as feedstock in selective laser melting process. Gas atomized powder revealed single martensitic phase after printing and heat treatment independent of energy density. As-printed water atomized powder contained dual martensitic and austenitic phase regardless of energy density. The H900 heat treatment cycle was not effective in enhancing mechanical properties of the water-atomized powder after laser melting. However, after solutionizing at 1315ºC and aging at 482 °C fully martensitic structure was observed with hardness (40.2 HRC), yield strength (1000 MPa) and ultimate tensile strength (1261 MPa) comparable to those of gas atomized (42.7 HRC, 1254 MPa and 1300 MPa) and wrought alloy (39 HRC, 1170 MPa and 1310 MPa), respectively. Improved mechanical properties in water-atomized powder was found to be related to presence of finer martensite and higher volume fraction of fine Cu-enriched precipitates. Our results imply that water-atomized powder is a promising cheaper feedstock alternative to gas-atomized powder.
       
  • Effects of pore distribution and chemistry on physical, mechanical, and
           biological properties of tricalcium phosphate scaffolds by binder-jet 3D
           printing
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Dongxu Ke, Susmita Bose Porous tricalcium phosphate (TCP) scaffolds are becoming more and more important for treating musculoskeletal diseases. With the maturation of 3D printing (3DP) technology in the past two decades, porous TCP scaffolds can also be easily prepared with complex design and high dimensional accuracy. However, the mechanical and biological properties of porous TCP scaffolds prepared by 3D printing still need improvements. In this study, novel 3D printed TCP and MgO/ZnO-TCP scaffolds were prepared by an binder-jet 3D printer. Scaffolds had a dense core and porous surface feature with a designed pore size of 500 μm and a designed porosity of 18%. After printing, scaffolds were sintered in a muffle furnace at 1250 °C. The presence of MgO and ZnO increased the surface area of TCP from 1.18 ± 0.01 m2/g to 2.65 ± 0.02 m2/g, the bulk density from 37.89 ± 0.83% to 50.82 ± 1.10%, and the compressive strength from 17.94 ± 1.65 MPa to 27.46 ± 2.63 MPa. Enhanced osteoblast proliferation was shown in doped 3D printed TCP scaffolds compared to the pure 3DP TCP. In addition, the use of 3D printing as well as dense core and porous surface design enhanced the surface roughness and osteoblast proliferation of TCP scaffolds. This novel 3D printed MgO/ZnO-TCP scaffold shows enhanced mechanical and biological properties, which is promising for orthopedic and dental applications.Graphical abstractGraphical abstract for this article
       
  • Selective laser melting of tungsten carbide reinforced maraging steel
           composite
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Nan Kang, Wenyou Ma, Lorène Heraud, Mohamed El Mansori, Fuhai Li, Min Liu, Hanlin Liao In this work, tungsten carbide (WC) reinforced maraging steel matrix composites were in-situ manufactured by selective laser melting (SLM) from powder mixture. The SLM processed samples presented high relative density (over 99%) with a homogenous distribution of WC. The as-fabricated surface quality of SLM processed samples was improved significantly by the addition of WC. Focused ion beam and transmission electron microscopy were employed to characterize the interfacial properties between tungsten carbide and steel matrix. The elemental analysis indicates that metallurgical bonding appears at interfacial region due to the diffusion. Tensile behavior of SLM processed maraging steel was different from their composite with several WC contents.Graphical abstractGraphical abstract for this article
       
  • 3D printing of extremely viscous materials using ultrasonic vibrations
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): I.E. Gunduz, M.S. McClain, P. Cattani, G.T.-C. Chiu, J.F. Rhoads, S.F. Son Heterogeneous materials used in biomedical, structural and electronics applications contain a high fraction of solids (>60 vol.%) and exhibit extremely high viscosities (μ > 1000 Pa s), which hinders their 3D printing using existing technologies. This study shows that inducing high-amplitude ultrasonic vibrations within a nozzle imparts sufficient inertial forces to these materials to drastically reduce effective wall friction and flow stresses, enabling their 3D printing with moderate back pressures (
       
  • Study of the spatter distribution on the powder bed during selective laser
           melting
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Ahmad Bin Anwar, Quang-Cuong Pham In Selective Laser Melting (SLM), inert gas is pumped into the chamber to eliminate the deleterious by-products, which includes spatter. Despite this, traces of spatter on the powder bed have always been observed. Earlier research mainly focussed on the formation and characterization of spatter particles that were freshly ejected from the melt pool. However, in this study, the quantification of the spatter distribution on the powder bed was performed, following their transport by the inert gas flow which was varied at two gas pump settings (60 and 67%). Image processing for spatter detection based on contrast was first conducted. The sieved out spatter particles were quantified by precision weighing of mass. Optical microscopy was then utilised for size determination. The majority of spatter particles were originally distributed along the −x direction, as observed from the top down images taken. It was found that spatter was generally transported in the −x direction with the mass and size gradually decreasing with distance from the scanned regions. However, increasing the gas flow velocity did not correspond to a lesser mass distribution. Computations on the Stk number revealed that at the gas pump setting of 67%, spatter particles of greater size were deposited earlier on the powder bed, suggesting that increasing the gas flow velocity to a large extent would increase the likelihood of powder bed contamination. The forward extrapolation of the exponential Stk number trendlines also elucidated the reason for the limitations on the width of the powder bed in machines designed by SLM Solutions.Graphical abstractGraphical abstract for this article
       
  • Microstructure and mechanical characteristics of surface oxide
           dispersion-strengthened Zircaloy-4 cladding tube
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Hyun-Gil Kim, Il-Hyun Kim, Yang-Il Jung, Dong-Jun Park, Jung-Hwan Park, Jae-Ho Yang, Yang-Hyun Koo To increase the mechanical strength of Zircaloy-4 cladding at high temperatures, partial oxide dispersion-strengthened (ODS) treatment of the cladding tube surface was achieved by using laser processing technology. The microstructural characteristics and stability of the ODS layer formed on the Zircaloy-4 cladding surface were analyzed at temperatures up to 1000 °C. Ring tensile and loss-of-coolant accident (LOCA) simulation tests were performed to evaluate the mechanical properties of the surface ODS treated Zircaloy-4 cladding tube. The formation and uniform distribution of Y2O3 particles formed in the Zr matrix were identified, and the stability of the particles was confirmed up to 1000 °C. When compared to the reference Zircaloy-4 cladding tube, the surface ODS treated Zircaloy-4 cladding tube showed improved mechanical properties at both room temperature and 500 °C, as well as under LOCA simulation conditions.
       
  • Selectively-deposited energetic materials: A feasibility study of the
           piezoelectric inkjet printing of nanothermites
    • Abstract: Publication date: August 2018Source: Additive Manufacturing, Volume 22Author(s): Allison K. Murray, Whitney A. Novotny, Trevor J. Fleck, I. Emre Gunduz, Steven F. Son, George T.-C Chiu, Jeffrey F. Rhoads This work investigated the utility of three piezoelectric inkjet printers as energetic material deposition systems, focusing on the ability of each system to achieve the seamless integration of energetic material into small-scale electronic devices. Aluminum copper (II) oxide nanothermite was deposited using the three deposition systems. The printers were evaluated based on their robustness to energetic ink solids loading, drop formation reliability, drop quality degradation over time, and the energetic performance of the deposited material. These metrics correlate to the feasibility of a deposition system to successfully achieve high sample throughput while maintaining the energetic performance of the printed material. After initial system testing, the PipeJet P9 500 μm pipe was used to demonstrate the successful deposition of nanothermite in varying geometric patterns with micrometer precision. From these samples, preliminary propagation speed measurements were obtained, which showed a correlation between the printed line widths and burning rates.
       
  • Selective laser melting of rare earth element Sc modified aluminum alloy:
           Thermodynamics of precipitation behavior and its influence on mechanical
           properties
    • Abstract: Publication date: Available online 10 July 2018Source: Additive ManufacturingAuthor(s): Han Zhang, Dongdong Gu, Jiankai Yang, Donghua Dai, Tong Zhao, Chen Hong, Andres Gasser, Reinhart Poprawe The interest of selective laser melting (SLM) Al-based alloys for lightweight applications, especially the rare earth element Sc modified Al-Mg alloy, is increasing. In this work, high-performance Al-Mg-Sc-Zr alloy was successfully fabricated by SLM. The phase identification, densification behavior, precipitate distribution and mechnical properties of the as-fabricated parts at a wide range of processing parameters were carefully characterized. Meanwhile, the evolution of nanoprecipitation behavior under various scan speeds is revealed and TEM analysis of precipitates shows that a small amount of spherical nanoprecipitates Al3(Sc,Zr) were embedded at the bottom of the molten pool using a low scan speed. While no precipitates were found in the matrix using a relatively high scan speed due to the combined effects of the variation of Marangoni convection vector, ultrashort lifetime of liquid and the rapid cooling rate. An increased hardness and a reduced wear rate of 94 HV0.2 and 1.74 × 10-4 mm3N-1 m-1 were resultantly obtained respectively as a much lower scan speed was applied. A relationship between the processing parameters, the surface tension, the convection flow, the precipitation distribution and the resultant mechanical properties has been well established, demonstrating that the high-performance of SLM-processed Al-Mg-Sc-Zr alloy could be tailored by controlling the distribution of nanoprecipitates.
       
  • Determination of the Effect of Scan Strategy on Residual Stress in Laser
           Powder Bed Fusion Additive Manufacturing
    • Abstract: Publication date: Available online 9 July 2018Source: Additive ManufacturingAuthor(s): J. Robinson, I. Ashton, P. Fox, E. Jones, C. Sutcliffe Any literature investigation of Laser Powder Bed Fusion (L-PBF) manufacturing of metal parts would reveal that the development of internal stresses is a serious limitation in the application of this technology. Researchers have used a variety of different methods to quantify this stress and investigate scanning strategies aimed at reducing or distributing this stress more evenly in the part. The most common methods used to assess the levels of stress in parts are deflection based. These techniques provide a rapid method to give a quantitative comparison of scan strategies and parameters. Although studies have calculated the levels of stress relieved by the measured deflection, these studies often neglect the stresses that remain in the part after release. This study shows that these stresses can still be considerable. Non-destructive diffraction based methods can be used to calculate the profile of stress in a part but these are often prohibitively expensive or difficult to use on a large scale. This study presents a methodology which combines deflection based methods with either the hole drilling or contour methods. Results show that these experiments can be completed in a cost effective manner, with standard lab based equipment to generate a through thickness measurement of residual stress.
       
  • On the multiphysics modeling challenges for metal additive manufacturing
           processes
    • Abstract: Publication date: Available online 30 June 2018Source: Additive ManufacturingAuthor(s): John G. Michopoulos, Athanasios P. Iliopoulos, John C. Steuben, Andrew J. Birnbaum, Samuel Lambrakos In order to establish modeling and simulation (M&S) in support of Additive Manufacturing Processes (AMP) process control for tailoring functional component performance by design, a methodology is introduced for identifying relevant M&S challenges. This exercise is meant to spur research addressing the specific issue of tailoring functional component performance by design, as well as AMP-related process optimization more generally. A composition abstraction that connects process control with functional performance of the multiscale modeling processes is presented, from both the forward and inverse analysis perspectives. A brief ontology is introduced that describes the ordering of dependency and membership of all components of a model, which serves the purpose of isolating potential challenge areas. An application space where this ontology unfolds is also presented to further elucidate the complexity of the potential challenges. Certain features of AMPs that are usually ignored by the community during modeling are a specific focus. Furthermore, two semantically reduced modeling approaches involving continuum abstractions for the computational domains are presented. The solutions of the relevant system of coupled partial differential equations are used to demonstrate both the positive and negative implications of a series of assumptions routinely made in M&S of AMPs. Finally, a discrete element method model is presented to highlight the challenges introduced by the specific nature of this approach. A closing section highlights the most important lessons learned.
       
  • A numerical and experimental investigation of convective heat transfer
           during laser-powder bed fusion
    • Abstract: Publication date: Available online 30 June 2018Source: Additive ManufacturingAuthor(s): Mohammad Masoomi, Jonathan W. Pegues, Scott M. Thompson, Nima Shamsaei Parts fabricated using additive manufacturing (AM) methods, such as laser-powder bed fusion (L-PBF), receive highly localized heat fluxes from a laser within a purged, inert environment during manufacture. These heat fluxes are used for melting metal powder feedstock, while remaining energy is transferred to the solidified part and adjoining gas environment. Using computational fluid dynamics (CFD), the local heat transfer between the adjoining shielding gas, laser-induced melt pool and surrounding heat affected zone is estimated. Simulations are performed for the L-PBF of a single layer of Ti-6Al-4 V. Local temperature, temperature gradients, temperature time-rates-of-change (including cooling rates), as well as dimensionless numbers descriptive of important thermophysics, are provided in order to quantify local convective heat transfer for various laser/gas motion directions. Results demonstrate that L-PBF track heat transfer is highly dependent on relative gas/laser direction which can impact the prior β grain sizes in Ti-6Al-4 V material by up to 10%. It is found that when the laser and gas are moving in the same direction, convection heat transfer is the highest and a ‘leading thermal boundary layer’ exists in front of the laser which is capable of preheating downstream powder for a possible reduction in residual stress formation along the track. Presented results can aid ongoing L-PBF modeling efforts and assist manufacturing design decisions (e.g. scan strategy, laser power, scanning speed, etc.) – especially for cases where homogeneous or controlled material traits are desired.
       
  • Nondestructive ultrasonic evaluation of additively manufactured AlSi10Mg
           samples
    • Abstract: Publication date: Available online 28 June 2018Source: Additive ManufacturingAuthor(s): T. Sol, S. Hayun, D. Noiman, E. Tiferet, O. Yeheskel, O. TevetABSTRACTPulse-echo ultrasonic method was carried out to investigate possible anisotropy in selective laser melting additively manufactured (AM) AlSi10Mg samples. Three types of ultrasonic analyses were employed: time of flight (TOF) sound velocity measurement, frequency depended attenuation and exponential fitted attenuation. Analysis of the transverse waves TOF sound velocity as a function the oscillation angle relative to the build direction reveals that the AM AlSi10Mg material has anisotropy in both transverse wave velocity and attenuation with respect to the build direction. Such an anisotropy is with symmetry around the build direction. Three transverse wave velocity zones were identified, low-velocity zone, where the transverse oscillation direction perpendicular to the build direction, high-velocity zone where the transverse oscillation direction parallel to the build direction and a transition zone. This behavior held even after heat treatments. The transverse velocity and the frequency depended attenuation seems to be sensitive tools that enable detection of subtle changes in AM products.
       
  • Q2: Improving Printing Orientation for Fused Deposition Modeling Printers
           by Analyzing Connected Components
    • Abstract: Publication date: Available online 27 June 2018Source: Additive ManufacturingAuthor(s): Jorge A. García Galicia, Bedrich Benes The spatial orientation of an object on a 3D printing plate is a significant contributor to its printing time. Thus, the speed of the 3D printing processes can generally be Q2: increased by using time-efficient object orientations. This paper presents a novel method for Q2: speeding-up printing processes that employs maximally efficient orientations. This method finds an orientation for the object that minimizes the number of disconnected components and the distance between the disconnected components that remain, thereby minimizing the time needed for the printer head to traverse empty areas. The method also considers the height of the printed object, its trapped volume, and the number of connected components in each layer. Our novel Q2: algorithm considers all four criteria, each weighted according to printer-specific and experimentally-obtained parameters. Preliminary trials demonstrate that this methodology can decrease printing times Q5: on fused deposition printers to 45% of that of current state of the art Q2: algorithms.
       
  • Control of Residual Stress and Distortion in Aluminium Wire + Arc Additive
           Manufacture with Rolling
    • Abstract: Publication date: Available online 25 June 2018Source: Additive ManufacturingAuthor(s): J.R. Hönnige, P.A. Colegrove, S. Ganguly, E. Eimer, S. Kabra, S. Williams Rolling can control residual stress and distortion in aluminium Wire + Arc Additively Manufactured (WAAM) walls. It was applied both vertically to each deposited layer (inter-pass) and to the side of the wall after deposition is completed. Distortion was virtually eliminated with the vertical inter-pass method (unlike other metals) and inverted with side rolling. Neutron diffraction stress measurements show that the deposited wall contains constant tensile residual stresses along the build direction that reach the flow strength of the alloy in longitudinal direction. Vertical inter-pass rolling eliminates the distortion, but produces a multi-directional stress field, with hydrostatic compressive stresses approximately 2 mm below the top surface and hydrostatic tension 5-10 mm below the surface. Side rolling was even more effective in stress and distortion control and produced fairly uniform longitudinal compressive stresses along the wall height. An interesting by-product of the neutron diffraction measurements is the observation of a significantly larger FCC aluminium unit cell in the inter-pass rolled walls. This is a result of less copper in solid solution with the aluminium matrix, indicating greater precipitation which could have contributed to the material’s improved strength.Graphical abstractGraphical abstract for this article
       
  • Density variation in binder jetting 3D-printed and sintered Ti-6Al-4V
    • Abstract: Publication date: Available online 21 June 2018Source: Additive ManufacturingAuthor(s): Erica Stevens, Samantha Schloder, Eric Bono, David Schmidt, Markus Chmielus Binder jet printing is one additive manufacturing technique utilized in today’s industry that uses an adhesive to bind powders together selectively in a bed. Post-printing processes are necessary for binder jet printed parts to increase key properties in materials such as density, but the full effects of this post-processing are not yet well understood. This study aims to enhance the understanding of how the process of sintering can affect the density evolution of a Ti-6Al-4 V binder jet printed part. Results show that the density is lower at the edges of the part and higher in regions of significant topological curvature, likely due to variations originating from the printing process that are propagated. These printing process effects can be due to binder- or powder-related occurrences, which are described in relation to the obtained results. Binder effects include high-velocity impact, particle disruption, and excessive spreading. Powder effects include printhead and recoater speed, satellite particles, and changing pressure throughout the powder bed. These factors affected the coordination number of particles in the green part, and caused sintering to progress more slowly in certain areas.Graphical abstractGraphical abstract for this article
       
  • Experimental determination of cooling rates in selectively laser-melted
           eutectic Al-33Cu
    • Abstract: Publication date: Available online 21 May 2018Source: Additive ManufacturingAuthor(s): Simon Pauly, Pei Wang, Uta Kühn, Konrad Kosiba The cooling rates inherent to selective laser melting (SLM) were experimentally determined by processing the eutectic Al-33Cu (wt.%) alloy. Two different parameter sets yielding an identical volumetric energy density were employed to produce the samples. Based on the average spacing of the Al and CuAl2 lamellae, the cooling rates in different parts of the SLM specimens were estimated. At a high laser power (300 W) the cooling rate amounts to 104 K/s and at the lower laser power (200 W) to 105 K/s. The present approach proves to be useful for exploring the thermal history of additively manufactured metallic components.Graphical abstractGraphical abstract for this article
       
 
 
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