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Publisher: Elsevier   (Total: 3031 journals)

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Showing 1 - 200 of 3031 Journals sorted alphabetically
AASRI Procedia     Open Access   (Followers: 15)
Academic Pediatrics     Hybrid Journal   (Followers: 20, SJR: 1.402, h-index: 51)
Academic Radiology     Hybrid Journal   (Followers: 16, SJR: 1.008, h-index: 75)
Accident Analysis & Prevention     Partially Free   (Followers: 79, SJR: 1.109, h-index: 94)
Accounting Forum     Hybrid Journal   (Followers: 22, SJR: 0.612, h-index: 27)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 27, SJR: 2.515, h-index: 90)
Achievements in the Life Sciences     Open Access   (Followers: 4)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 5, SJR: 0.338, h-index: 19)
Acta Astronautica     Hybrid Journal   (Followers: 302, SJR: 0.726, h-index: 43)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 3)
Acta Biomaterialia     Hybrid Journal   (Followers: 25, SJR: 2.02, h-index: 104)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription  
Acta de Investigación Psicológica     Open Access   (Followers: 2)
Acta Ecologica Sinica     Open Access   (Followers: 8, SJR: 0.172, h-index: 29)
Acta Haematologica Polonica     Free   (SJR: 0.123, h-index: 8)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.604, h-index: 38)
Acta Materialia     Hybrid Journal   (Followers: 195, SJR: 3.683, h-index: 202)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.615, h-index: 21)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.442, h-index: 21)
Acta Oecologica     Hybrid Journal   (Followers: 9, SJR: 0.915, h-index: 53)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription   (Followers: 1)
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 3, SJR: 0.311, h-index: 16)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 2)
Acta Poética     Open Access   (Followers: 4)
Acta Psychologica     Hybrid Journal   (Followers: 21, SJR: 1.365, h-index: 73)
Acta Sociológica     Open Access  
Acta Tropica     Hybrid Journal   (Followers: 5, SJR: 1.059, h-index: 77)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 4)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 3)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 3, SJR: 0.383, h-index: 19)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 2)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 5, SJR: 0.141, h-index: 3)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 4, SJR: 0.112, h-index: 2)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 4)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.967, h-index: 57)
Addictive Behaviors     Hybrid Journal   (Followers: 15, SJR: 1.514, h-index: 92)
Addictive Behaviors Reports     Open Access   (Followers: 5)
Additive Manufacturing     Hybrid Journal   (Followers: 7, SJR: 1.039, h-index: 5)
Additives for Polymers     Full-text available via subscription   (Followers: 20)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 119, SJR: 5.2, h-index: 222)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 11, SJR: 1.265, h-index: 53)
Advanced Powder Technology     Hybrid Journal   (Followers: 16, SJR: 0.739, h-index: 33)
Advances in Accounting     Hybrid Journal   (Followers: 8, SJR: 0.299, h-index: 15)
Advances in Agronomy     Full-text available via subscription   (Followers: 15, SJR: 2.071, h-index: 82)
Advances in Anesthesia     Full-text available via subscription   (Followers: 24, SJR: 0.169, h-index: 4)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 3)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 6, SJR: 1.054, h-index: 35)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 10, SJR: 0.801, h-index: 26)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 21, SJR: 1.286, h-index: 49)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 16, SJR: 3.31, h-index: 42)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.277, h-index: 43)
Advances in Botanical Research     Full-text available via subscription   (Followers: 3, SJR: 0.619, h-index: 48)
Advances in Cancer Research     Full-text available via subscription   (Followers: 26, SJR: 2.215, h-index: 78)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 9, SJR: 0.9, h-index: 30)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 2.139, h-index: 42)
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: 24, SJR: 0.183, h-index: 23)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, SJR: 0.665, h-index: 29)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 8, SJR: 1.268, h-index: 45)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 28, SJR: 0.938, h-index: 33)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 18, SJR: 2.314, h-index: 130)
Advances in Computers     Full-text available via subscription   (Followers: 16, SJR: 0.223, h-index: 22)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 11)
Advances in Digestive Medicine     Open Access   (Followers: 4)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 5)
Advances in Drug Research     Full-text available via subscription   (Followers: 22)
Advances in Ecological Research     Full-text available via subscription   (Followers: 39, SJR: 3.25, h-index: 43)
Advances in Engineering Software     Hybrid Journal   (Followers: 25, SJR: 0.486, h-index: 10)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 7)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 38, SJR: 5.465, h-index: 64)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 3)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 8)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 41, SJR: 0.674, h-index: 38)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 14)
Advances in Genetics     Full-text available via subscription   (Followers: 15, SJR: 2.558, h-index: 54)
Advances in Genome Biology     Full-text available via subscription   (Followers: 11)
Advances in Geophysics     Full-text available via subscription   (Followers: 6, SJR: 2.325, h-index: 20)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 18, SJR: 0.906, h-index: 24)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 0.497, h-index: 31)
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: 0.396, h-index: 27)
Advances in Immunology     Full-text available via subscription   (Followers: 33, SJR: 4.152, h-index: 85)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 1.132, h-index: 42)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 3, SJR: 1.274, h-index: 27)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 4)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 4)
Advances in Life Course Research     Hybrid Journal   (Followers: 7, SJR: 0.764, h-index: 15)
Advances in Lipobiology     Full-text available via subscription   (Followers: 1)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 8)
Advances in Marine Biology     Full-text available via subscription   (Followers: 16, SJR: 1.645, h-index: 45)
Advances in Mathematics     Full-text available via subscription   (Followers: 10, SJR: 3.261, h-index: 65)
Advances in Medical Sciences     Hybrid Journal   (Followers: 5, SJR: 0.489, h-index: 25)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 4, SJR: 1.44, h-index: 51)
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: 10)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 6, SJR: 0.324, h-index: 8)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 3)
Advances in Oncobiology     Full-text available via subscription   (Followers: 3)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 15, SJR: 2.885, h-index: 45)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.148, h-index: 11)
Advances in Parasitology     Full-text available via subscription   (Followers: 7, SJR: 2.37, h-index: 73)
Advances in Pediatrics     Full-text available via subscription   (Followers: 20, SJR: 0.4, h-index: 28)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 14)
Advances in Pharmacology     Full-text available via subscription   (Followers: 13, SJR: 1.718, h-index: 58)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 7, SJR: 0.384, h-index: 26)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.248, h-index: 11)
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: 4)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 18)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 17, SJR: 1.5, h-index: 62)
Advances in Psychology     Full-text available via subscription   (Followers: 56)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 5, SJR: 0.478, h-index: 32)
Advances in Radiation Oncology     Open Access  
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 1, SJR: 0.1, h-index: 2)
Advances in Space Research     Full-text available via subscription   (Followers: 332, SJR: 0.606, h-index: 65)
Advances in Structural Biology     Full-text available via subscription   (Followers: 7)
Advances in Surgery     Full-text available via subscription   (Followers: 6, SJR: 0.823, h-index: 27)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 28, SJR: 1.321, h-index: 56)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 14)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 12)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 1.878, h-index: 68)
Advances in Water Resources     Hybrid Journal   (Followers: 42, SJR: 2.408, h-index: 94)
Aeolian Research     Hybrid Journal   (Followers: 5, SJR: 0.973, h-index: 22)
Aerospace Science and Technology     Hybrid Journal   (Followers: 303, SJR: 0.816, h-index: 49)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.318, h-index: 36)
African J. of Emergency Medicine     Open Access   (Followers: 4, SJR: 0.344, h-index: 6)
Ageing Research Reviews     Hybrid Journal   (Followers: 7, SJR: 3.289, h-index: 78)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 389, SJR: 1.385, h-index: 72)
Agri Gene     Hybrid Journal  
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 15, SJR: 2.18, h-index: 116)
Agricultural Systems     Hybrid Journal   (Followers: 29, SJR: 1.275, h-index: 74)
Agricultural Water Management     Hybrid Journal   (Followers: 36, SJR: 1.546, h-index: 79)
Agriculture and Agricultural Science Procedia     Open Access  
Agriculture and Natural Resources     Open Access   (Followers: 1)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 48, SJR: 1.879, h-index: 120)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.434, h-index: 14)
Air Medical J.     Hybrid Journal   (Followers: 3, SJR: 0.234, h-index: 18)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.285, h-index: 3)
Alcohol     Hybrid Journal   (Followers: 9, SJR: 0.922, h-index: 66)
Alcoholism and Drug Addiction     Open Access   (Followers: 5)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 1, SJR: 0.436, h-index: 12)
Alexandria J. of Medicine     Open Access  
Algal Research     Partially Free   (Followers: 7, SJR: 2.05, h-index: 20)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 3)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.46, h-index: 29)
Allergology Intl.     Open Access   (Followers: 5, SJR: 0.776, h-index: 35)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 6, SJR: 0.158, h-index: 9)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 45, SJR: 4.289, h-index: 64)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 5)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 3)
American Heart J.     Hybrid Journal   (Followers: 45, SJR: 3.157, h-index: 153)
American J. of Cardiology     Hybrid Journal   (Followers: 47, SJR: 2.063, h-index: 186)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 34, SJR: 0.574, h-index: 65)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 6, SJR: 1.091, h-index: 45)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 14, SJR: 1.653, h-index: 93)
American J. of Human Genetics     Hybrid Journal   (Followers: 32, SJR: 8.769, h-index: 256)
American J. of Infection Control     Hybrid Journal   (Followers: 25, SJR: 1.259, h-index: 81)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 31, SJR: 2.313, h-index: 172)
American J. of Medicine     Hybrid Journal   (Followers: 48, SJR: 2.023, h-index: 189)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 173, SJR: 2.255, h-index: 171)
American J. of Ophthalmology     Hybrid Journal   (Followers: 51, SJR: 2.803, h-index: 148)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 2)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.249, h-index: 88)
American J. of Otolaryngology     Hybrid Journal   (Followers: 22, SJR: 0.59, h-index: 45)
American J. of Pathology     Hybrid Journal   (Followers: 23, SJR: 2.653, h-index: 228)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 21, SJR: 2.764, h-index: 154)
American J. of Surgery     Hybrid Journal   (Followers: 32, SJR: 1.286, h-index: 125)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 13, SJR: 0.653, h-index: 70)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 5)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.066, h-index: 51)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 52, SJR: 0.124, h-index: 9)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 3)
Anales de Cirugia Vascular     Full-text available via subscription  
Anales de Pediatría     Full-text available via subscription   (Followers: 2, SJR: 0.209, h-index: 27)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription   (SJR: 0.104, h-index: 3)
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 2, SJR: 2.577, h-index: 7)
Analytica Chimica Acta     Hybrid Journal   (Followers: 38, SJR: 1.548, h-index: 152)
Analytical Biochemistry     Hybrid Journal   (Followers: 152, SJR: 0.725, h-index: 154)
Analytical Chemistry Research     Open Access   (Followers: 7, SJR: 0.18, h-index: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 10)
Anesthésie & Réanimation     Full-text available via subscription  
Anesthesiology Clinics     Full-text available via subscription   (Followers: 21, SJR: 0.421, h-index: 40)
Angiología     Full-text available via subscription   (SJR: 0.124, h-index: 9)
Angiologia e Cirurgia Vascular     Open Access  
Animal Behaviour     Hybrid Journal   (Followers: 141, SJR: 1.907, h-index: 126)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 5, SJR: 1.151, h-index: 83)
Animal Reproduction Science     Hybrid Journal   (Followers: 5, SJR: 0.711, h-index: 78)
Annales d'Endocrinologie     Full-text available via subscription   (SJR: 0.394, h-index: 30)
Annales d'Urologie     Full-text available via subscription  
Annales de Cardiologie et d'Angéiologie     Full-text available via subscription   (SJR: 0.177, h-index: 13)
Annales de Chirurgie de la Main et du Membre Supérieur     Full-text available via subscription  
Annales de Chirurgie Plastique Esthétique     Full-text available via subscription   (Followers: 2, SJR: 0.354, h-index: 22)
Annales de Chirurgie Vasculaire     Full-text available via subscription   (Followers: 1)

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Journal Cover Additive Manufacturing
  [SJR: 1.039]   [H-I: 5]   [7 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 2214-8604
   Published by Elsevier Homepage  [3031 journals]
  • Tensile Strength of Commercial Polymer Materials for Fused Filament
           Fabrication 3D Printing
    • Authors: Nagendra G. Tanikella; Ben Wittbrodt; Joshua M. Pearce
      Pages: 40 - 47
      Abstract: Publication date: Available online 18 March 2017
      Source:Additive Manufacturing
      Author(s): Nagendra G. Tanikella, Ben Wittbrodt, Joshua M. Pearce
      3D printing functional parts with known mechanical properties is challenging using variable open source 3D printers. This study investigates the mechanical properties of 3D printed parts using a commercial open-source 3D printer for a wide range of materials. The samples are tested for tensile strength following ASTM D638. The results are presented and conclusions are drawn about the mechanical properties of various fused filament fabrication materials. The study demonstrates that the tensile strength of a 3D printed specimen depends largely on the mass of the specimen, for all materials. Thus, to solve the challenge of unknown print quality on mechanical properties of a 3D printed part a two step process is proposed, which has a reasonably high expectation that a part will have tensile strengths described in this study for a given material. First, the exterior of the print is inspected visually for sub-optimal layers. Then, to determine if there has been under-extrusion in the interior, the mass of the sample is measured. This mass is compared to the theoretical value using densities for the material and the volume of the object. This two step process provides a means to assist low-cost open-source 3D printers expand the range of object production to functional parts.

      PubDate: 2017-03-22T10:27:33Z
      DOI: 10.1016/j.addma.2017.03.005
      Issue No: Vol. 15 (2017)
  • Automated manufacturing and processing of fiber-reinforced polymer (FRP)
           composites: An additive review of contemporary and modern techniques for
           advanced materials manufacturing
    • Authors: Jolie Frketic; Tarik Dickens; Subramanian Ramakrishnan
      Pages: 69 - 86
      Abstract: Publication date: March 2017
      Source:Additive Manufacturing, Volume 14
      Author(s): Jolie Frketic, Tarik Dickens, Subramanian Ramakrishnan
      High throughput automated techniques are nowadays playing a key role in polymer composite manufacturing in a number of industries such as automotive and aerospace. There is a need to produce high volume parts efficiently. Automated manufacturing methods such as automated tape layup and automated fiber placement can produce composite parts efficiently, and with the advent of additive manufacturing the complexity of these components are increasing. This paper will review contemporary composite manufacturing methods filament winding, automated tape layup, and automated fiber placement, and the newer automation techniques of robotic pick-and-place and continuous tow shearing. It also addresses recent advances in composite additive manufacturing using vat photopolymerization, binder jetting, material extrusion, sheet lamination and powder bed fusion. Methods, materials and testing results of the manufactured components will be discussed.

      PubDate: 2017-01-31T17:48:13Z
      DOI: 10.1016/j.addma.2017.01.003
      Issue No: Vol. 14 (2017)
  • A novel freeform extrusion fabrication process for producing solid ceramic
           components with uniform layered radiation drying
    • Authors: Amir Ghazanfari; Wenbin Li; Ming C. Leu; Gregory E. Hilmas
      Abstract: Publication date: Available online 15 April 2017
      Source:Additive Manufacturing
      Author(s): Amir Ghazanfari, Wenbin Li, Ming C. Leu, Gregory E. Hilmas
      An extrusion-based additive manufacturing process, called the Ceramic On-Demand Extrusion (CODE) process, for producing three-dimensional ceramic components with near theoretical density is introduced in this paper. In this process, an aqueous paste of ceramic particles with a very low binder content (<1vol%) is extruded through a moving nozzle at room temperature. After a layer is deposited, it is surrounded by oil (to a level just below the top surface of most recent layer) to preclude non-uniform evaporation from the sides. Infrared radiation is then used to partially, and uniformly, dry the just-deposited layer so that the yield stress of the paste increases and the part maintains its shape. The same procedure is repeated for every layer until part fabrication is completed. Several sample parts for various applications were produced using this process and their properties were obtained. The results indicate that the proposed method enables fabrication of large, dense ceramic parts with complex geometries.

      PubDate: 2017-04-19T01:36:29Z
      DOI: 10.1016/j.addma.2017.04.001
  • Strengthening of ferrous binder jet 3D printed components through bronze
    • Authors: Zachary C. Cordero; Derek H. Siddel; William H. Peter; Amelia M. Elliott
      Abstract: Publication date: Available online 8 April 2017
      Source:Additive Manufacturing
      Author(s): Zachary C. Cordero, Derek H. Siddel, William H. Peter, Amelia M. Elliott
      Net-shape 98% dense objects have been fabricated from a rapidly solidified ferrous powder using binder jet 3D printing and molten bronze infiltration. X-ray diffraction, scanning electron microscopy, and differential thermal analysis were used to characterize the structural evolution of the powder feedstock during an infiltration heating cycle. Microindentation and bend tests were performed on the infiltrated material to evaluate its mechanical properties. It was found that infiltration improved the strength of the sintered preforms by eliminating the stress concentration points at interparticle necks.

      PubDate: 2017-04-12T01:05:04Z
      DOI: 10.1016/j.addma.2017.03.011
  • 3D−printed cellular structures for bone biomimetic implants
    • Authors: Sakkadech Limmahakhun; Adekunle Oloyede; Kriskrai Sitthiseripratip; Yin Xiao; Cheng Yan
      Abstract: Publication date: Available online 3 April 2017
      Source:Additive Manufacturing
      Author(s): Sakkadech Limmahakhun, Adekunle Oloyede, Kriskrai Sitthiseripratip, Yin Xiao, Cheng Yan
      The use of porous cellular structures in bone tissue engineering can provide mechanical and biological environments closer to the host bone. However, poor internal architectural designs may lead to catastrophic failure. In this work, 192 open-porous cellular structures were fabricated using 3D printing (3DP) techniques. The mechanical and biological behavior of four 3D internal structures (octahedral, pillar octahedral, cubic and truncated octahedral) was investigated. It was found that the pillar octahedral shape has not only greater stiffness and strength under compression, shear and torsion but increased rate of pre-osteoblastic cell proliferation. We believe bone implants can be fabricated using 3DP techniques and their mechanical and biological performance can be tailored by modifying the internal architectures.

      PubDate: 2017-04-05T03:36:21Z
      DOI: 10.1016/j.addma.2017.03.010
  • Additive Technology of Soluble Mold Tooling for Embedded Devices in
           Composite Structures: A Study on Manufactured Tolerances
    • Authors: Madhuparna Roy; Tarik J. Dickens
      Abstract: Publication date: Available online 31 March 2017
      Source:Additive Manufacturing
      Author(s): Madhuparna Roy, Tarik J. Dickens
      Composite textiles have found widespread use and advantages in various industries and applications. The constant demand for high-quality products and services requires companies to minimize their manufacturing costs, and delivery time in order to compete in general and niche marketplaces. Creation of molding and tooling options for advanced composites encompasses a large portion of fabrication time, making it a costly process and a restraining factor. This research discusses a preliminary investigation into the use and control of soluble polymer compounds and additive manufacturing to fabricate sacrificial molds. These molds suffer from dimensional errors due to several factors, which have also been characterized. The basic soluble mold of a composite is 3D printed to meet the desired dimensions and geometry of holistic structures or spliced components. The time taken to dissolve the mold depends on the rate of agitation of the solvent. This process is steered towards enabling the implantation of optoelectronic devices within the composite to provide a sensing capability for structural health monitoring. The shape deviation of the 3D printed mold is also studied and compared to its original dimensions to optimize the dimensional quality to produce dimensionally accurate parts of up to 0.02% error.

      PubDate: 2017-04-05T03:36:21Z
      DOI: 10.1016/j.addma.2017.03.012
  • Microstructure and physical properties of a Ni/Fe-based superalloy
           processed by Selective Laser Melting
    • Authors: Alexey Domashenkov; Anna Plotnikova; Igor Movchan; Philippe Bertrand; Nathalie Peillon; Benjamin Desplanques; Sebastien Saunier; Christophe Desrayaud
      Abstract: Publication date: Available online 19 March 2017
      Source:Additive Manufacturing
      Author(s): Alexey Domashenkov, Anna Plotnikova, Igor Movchan, Philippe Bertrand, Nathalie Peillon, Benjamin Desplanques, Sebastien Saunier, Christophe Desrayaud
      In this work, 3D cubic test specimens were manufactured by Selective Laser Melting (SLM) from commercially available Ni/Fe-based superalloy powder, and were further subjected to heat treatment. The evolution of their microstructure, phase composition and microhardness was analysed in relation to the applied heat-treatment procedure Parametric study of the SLM process allows determination of a suitable parametric set for obtaining of 3D objects from the Ni/Fe-based single-crystal superalloy Thymonel-2, with the resulting porosity of 0.35%. The manufactured 3D specimens were subjected to three different heat-treatment procedures. The microstructure and the phase composition of the as-manufactured and the heat-treated samples were analysed in order to study the microstructure-microhardness correlation of Thymonel-2. XRD analysis of the as-manufactured samples reveals the presence of the fcc γ-(Fe, Ni) phase only. The literature reports a considerable amount of γ′ phase in Ni/Fe-based superalloys processed by conventional metallurgy. The absence of the γ′ can be explained by extremely high cooling rates during SLM which prevents precipitation. Micrographic examination of the SLM-manufactured specimens shows a fully dendritic microstructure. Post heat-treatment of the specimens leads to significant changes in microstructure and the resulting 30–90% increase in microhardness. Recommendations on SLM strategy and post heat-treatment of Thymonel-2 are provided.
      Graphical abstract image

      PubDate: 2017-03-22T10:27:33Z
      DOI: 10.1016/j.addma.2017.03.008
  • Rate limits of additive manufacturing by fused filament fabrication and
           guidelines for high-throughput system design
    • Authors: Jamison Go; Scott N. Schiffres; Adam G. Stevens; A. John Hart
      Abstract: Publication date: Available online 16 March 2017
      Source:Additive Manufacturing
      Author(s): Jamison Go, Scott N. Schiffres, Adam G. Stevens, A. John Hart
      While additive manufacturing (AM) advances rapidly towards new materials and applications, it is vital to understand the performance limits of AM process technologies and to overcome these limits via improved machine design and process integration. Extrusion-based AM (i.e., fused filament fabrication, FFF) is compatible with a wide variety of thermoplastic polymer and composite materials, and can be deployed across a wide range of length scales. However, the build rate of both desktop and professional FFF systems is comparable (∼10’s of cm3/hr at ∼0.2mm layer thickness), suggesting that fundamental aspects of the machine design and process physics limit system performance. We determine the rate limits to FFF by analysis of machine modules: the filament extrusion mechanism, the heater and nozzle, and the motion system. We determine, by direct measurements and numerical analysis, that FFF build rate is influenced by the coincident module-level limits to traction force exerted on the filament, conduction heat transfer to the filament core, and gantry velocity for positioning the printhead. Our findings are validated by direct measurements of build rate versus part complexity using desktop FFF systems. Last, we study the scaling of the rate limits using finite element simulations of thermoplastic flow through the extruder. We map the scaling of extrusion force, polymer exit temperature, and average printhead velocity onto a unifying trade-space of build rate versus resolution. This approach validates the build rate performance of current FFF systems, and suggests that significant enhancements in FFF build rate with targeted quality specifications are possible via mutual improvements to the extrusion and heating mechanism along with high-speed motion systems.

      PubDate: 2017-03-17T12:56:18Z
      DOI: 10.1016/j.addma.2017.03.007
  • Design of a 3D printer head for additive manufacturing of sugar glass for
           tissue engineering applications
    • Authors: André Bégin-Drolet; Marc-André Dussault; Stephanie A. Fernandez; Jeanne Larose-Dutil; Richard L. Leask; Corinne A. Hoesli; Jean Ruel
      Abstract: Publication date: Available online 16 March 2017
      Source:Additive Manufacturing
      Author(s): André Bégin-Drolet, Marc-André Dussault, Stephanie A. Fernandez, Jeanne Larose-Dutil, Richard L. Leask, Corinne A. Hoesli, Jean Ruel
      Additive manufacturing is now considered as a new paradigm that is foreseen to improve progress in many fields. The field of tissue engineering has been facing the need for tissue vascularization when producing thick tissues. The use of sugar glass as a fugitive ink to produce vascular networks through rapid casting may offer the key to vascularization of thick tissues produced by tissue engineering. Here, a 3D printer head capable of producing complex structures out of sugar glass is presented. This printer head uses a motorized heated syringe fitted with a custom made nozzle. The printer head was adapted to be mounted on a commercially available 3D printer. A mathematical model was derived to predict the diameter of the filaments based on the printer head feed rate and extrusion rate. Using a 1mm diameter nozzle, the printer accurately produced filaments ranging from 0.3mm to 3.2mm in diameter. One of the main advantages of this manufacturing method is the self-supporting behaviour of sugar glass that allows the production of long, horizontal, curved, as well as overhanging filaments needed to produce complex vascular networks. Finally, to establish a proof of concept, polydimethylsiloxane was used as the gel matrix during the rapid casting to produce various “vascularized” constructs that were successfully perfused, which suggests that this new fabrication method can be used in a number of tissue engineering applications, including the vascularization of thick tissues.

      PubDate: 2017-03-17T12:56:18Z
      DOI: 10.1016/j.addma.2017.03.006
  • Use of Space-Filling Curves for Additive Manufacturing of Three
           Dimensionally Varying Graded Dielectric Structures Using Fused Deposition
    • Authors: Zachary Larimore; Sarah Jensen; Paul Parsons; Brandon Good; Kelsey Smith; Mark Mirotznik
      Abstract: Publication date: Available online 16 March 2017
      Source:Additive Manufacturing
      Author(s): Zachary Larimore, Sarah Jensen, Paul Parsons, Brandon Good, Kelsey Smith, Mark Mirotznik
      In this paper the authors present a novel design tool for realizing dielectric structures with spatially varying electromagnetic properties via additive manufacturing (AM). To create tool paths ideal for AM processes, space-filling curves were utilized. Using fused deposition modeling (FDM), spatially varying structures were printed that produced a spatially varying relative permittivity. A wide range of varying fill fractions were printed and evaluated, demonstrating good agreement between the simulated and measured results. Furthermore, the authors verified that this design tool can be applied to practical structures by designing, printing and testing a gradient index flat lens.

      PubDate: 2017-03-17T12:56:18Z
      DOI: 10.1016/j.addma.2017.03.002
  • Comparisons of laser powder bed fusion additive manufacturing builds
           through experimental in situ distortion and temperature measurements
    • Authors: Alexander J. Dunbar; Erik R. Denlinger; Michael F. Gouge; Timothy W. Simpson; Pan Michaleris
      Abstract: Publication date: Available online 16 March 2017
      Source:Additive Manufacturing
      Author(s): Alexander J. Dunbar, Erik R. Denlinger, Michael F. Gouge, Timothy W. Simpson, Pan Michaleris
      In situ experimental measurements of the laser powder bed fusion build process are completed with the goal gaining insight into the evolution of distortion in the powder bed fusion build process. Utilizing a novel enclosed instrumented system, five experimental builds are performed. Experimental builds compare materials: Ti-6Al-4V and Inconel® 718, differing build geometries, and manufacturing machines: EOS M280 and Renishaw AM250. A combination of in situ measurements of distortion and temperature and post-build measurements of final part geometry are used to compare and contrast the different experiments. Experimental results show that builds completed using Inconel® 718 distort between 50%-80% more relative to Ti-6Al-4V depending on substrate size and build geometry. The experimental build completed on the Renishaw AM250 distorted 10.6% more in the Z direction when compared with the identical build completed on the EOS M280 machine. Comparisons of post-build XY cross-sectional area show a 0.3% contraction from the predefined build geometry for the Renishaw AM250 as compared with the 4.5% contraction for the part built using the EOS M280. Recommendations and future work are also discussed.

      PubDate: 2017-03-17T12:56:18Z
      DOI: 10.1016/j.addma.2017.03.003
  • Selective laser melting of pure Zn with high density for biodegradable
           implant manufacturing
    • Authors: Ali Gökhan Demir; Lorenzo Monguzzi; Barbara Previtali
      Abstract: Publication date: Available online 16 March 2017
      Source:Additive Manufacturing
      Author(s): Ali Gökhan Demir, Lorenzo Monguzzi, Barbara Previtali
      Zinc and its alloys constitute the new generation of biodegradable metallic materials for biomedical implants. Biodegradable implants of Zn, customized for the specific patient can be potentially realised through additive manufacturing processes. However, Zn is characterized by low melting and boiling points, resulting in high porosity in the build parts. In this work, the selective laser melting (SLM) of pure Zn powder is studied to improve part density. A flexible prototype SLM system was used to determine process feasibility under different atmospheric conditions. Working in a closed chamber under inert gas was found to be inadequate. Process stability was obtained in an open chamber with an inert gas jet flow over the powder bed. The effect of laser process parameters and powder size was studied in this condition. Part density over 99% was achieved in optimal processing conditions.

      PubDate: 2017-03-17T12:56:18Z
      DOI: 10.1016/j.addma.2017.03.004
  • Analysis of the material properties involved in laser sintering of
           thermoplastic polyurethane
    • Authors: Leander Verbelen; Sasan Dadbakhsh; Michael Van den Eynde; Dieter Strobbe; Jean-Pierre Kruth; Bart Goderis; Peter Van Puyvelde
      Abstract: Publication date: Available online 2 March 2017
      Source:Additive Manufacturing
      Author(s): Leander Verbelen, Sasan Dadbakhsh, Michael Van den Eynde, Dieter Strobbe, Jean-Pierre Kruth, Bart Goderis, Peter Van Puyvelde
      As laser sintering is increasingly being used for the production of actual end-use parts, there is considerable interest in developing materials that would enable new applications for this technique. Considering their properties and current applications, elastomeric polymers such as thermoplastic polyurethanes (TPU) have a very high potential in this regard. This study investigates the material properties that are involved in TPU sintering through the analysis of four distinct TPU grades. Examined parameters include powder flow, rheology of the melt and shrinkage and hardening behavior. It is found that, even though the particle morphology is not optimum, smooth and dense powder layers can be deposited for the investigated powders. Low melt viscosity and low shrinkage upon hardening further enable these materials to be easily processed into functional parts. Remaining issues, however, are part porosity and material degradation. The findings in this study provide clear links between material properties and behavior during laser sintering, and result in guidelines for future selection of TPU grades.
      Graphical abstract image

      PubDate: 2017-03-04T18:39:08Z
      DOI: 10.1016/j.addma.2017.03.001
  • Flaw Detection in Powder Bed Fusion Using Optical Imaging
    • Authors: Mostafa Abdelrahman; Edward W. Reutzel; Abdalla R. Nassar; Thomas L. Starr
      Abstract: Publication date: Available online 21 February 2017
      Source:Additive Manufacturing
      Author(s): Mostafa Abdelrahman, Edward W. Reutzel, Abdalla R. Nassar, Thomas L. Starr
      Lack-of-fusion flaws can occur in powder bed fusion (PBF) additive manufacturing of metal components. This paper demonstrates a method for detecting such flaws by monitoring the fabrication of every layer before and after laser scanning with high resolution optical imaging. A binary template is created from the sliced 3D model of the part. Using this template the optical image data is indexed to the part geometry. The indexed image data is used to detect anomalies in the powder layer before laser scanning and in the solidified material after scanning. Lack-of-fusion defects are identified from optical data by correlating multiple images with different lighting conditions and from multiple layers. To test the algorithms intentional defects are created inside a test part at different locations and are successfully detected with a high true positive rate.

      PubDate: 2017-02-24T18:33:16Z
      DOI: 10.1016/j.addma.2017.02.001
  • Melt Pool Simulation for the Evaluation of Process Parameters in Selective
           Laser Melting
    • Authors: Thorsten Heeling; Michael Cloots; Konrad Wegener
      Abstract: Publication date: Available online 16 February 2017
      Source:Additive Manufacturing
      Author(s): Thorsten Heeling, Michael Cloots, Konrad Wegener
      With increasing industrial interest and significance of the selective laser melting the importance for profound process knowledge increases so that new materials can be qualified faster. Also it is the basis for an educated evaluation of possible process innovations. Therefore a 3D numerical model for the selective laser melting process is presented that allows a detailed look into the process dynamics at comparably low calculation effort. It combines a finite difference method with a combined level set volume of fluid method for the simulation of the process and starts with a homogenized powder bed in its initial configuration. The model uses a comprehensive representation of various physical effects like dynamic laser power absorption, buoyancy effect, Marangoni effect, capillary effect, evaporation, recoil pressure and temperature dependent material properties. It is validated for different process parameters using cubic samples of stainless steel 316L and nickel-based superalloy IN738LC. The results show the significance of evaporation and its related recoil pressure for a feasible prediction of the melt pool dynamics. Furthermore a possible way to reduce the times and costs for material qualification by using the simulation model to predict possible process parameters and therefore to reduce the necessary experimental effort for material qualification to a minimum is shown.

      PubDate: 2017-02-18T10:40:24Z
      DOI: 10.1016/j.addma.2017.02.003
  • Mechanical Properties of Additive Manufactured Nickel Alloy 625
    • Authors: By Harvey Hack; Richard Link; Erik Knudsen; Brad Baker; Scott Olig
      Abstract: Publication date: Available online 13 February 2017
      Source:Additive Manufacturing
      Author(s): By Harvey Hack, Richard Link, Erik Knudsen, Brad Baker, Scott Olig
      The mechanical, metallurgical and corrosion properties of Alloy 625 produced using the laser powder bed fusion (L-PBF) manufacturing process were investigated and compared with typical performance of the alloy produced using conventional forging processes. Test specimens were produced near net shape along with several demonstration pieces that were produced to examine the geometric complexity that could be achieved with the process. The additively manufactured specimens exhibited strength, fracture toughness and impact toughness that was equal to or better than properties typically achieved for wrought product. There was no evidence of stress corrosion cracking susceptibility in 3.5% NaCl solution at stress intensities up to 70 ksi-in1/2 after 700hours exposure. The microstructure was equiaxed in the plane of the powder bed build platform (X-Y) and exhibited a columnar shape in the Z direction although there was not any significant evidence of anisotropy in the mechanical properties.

      PubDate: 2017-02-18T10:40:24Z
      DOI: 10.1016/j.addma.2017.02.004
  • Fractal Scan Strategies for Selective Laser Melting of
           ‘Unweldable’ Nickel Superalloys
    • Authors: S. Catchpole-Smith; N. Aboulkhair; L. Parry; C. Tuck; I.A. Ashcroft; A. Clare
      Abstract: Publication date: Available online 12 February 2017
      Source:Additive Manufacturing
      Author(s): S. Catchpole-Smith, N. Aboulkhair, L. Parry, C. Tuck, I.A. Ashcroft, A. Clare
      The high thermal gradients experienced during manufacture via selective laser melting commonly result in cracking of high γ/γ′ Nickel based superalloys. Such defects cannot be tolerated in applications where component integrity is of paramount importance. To overcome this, many industrial practitioners make use of hot isostatic pressing to ‘heal’ these defects. The possibility of such defects re-opening during the component life necessitates optimisation of SLM processing parameters in order to produce the highest bulk density and integrity in the as-built state. In this paper, novel fractal scanning strategies based upon mathematical fill curves, namely the Hilbert and Peano-Gosper curve, are explored in which the use of short vector length scans, in the order of 100μm, is used as a method of reducing residual stresses. The effect on cracking observed in CM247LC superalloy samples was analysed using image processing, comparing the novel fractal scan strategies to more conventional ‘island’ scans. Scanning electron microscopy and energy dispersive X-ray spectroscopy was utilised to determine the cracking mechanisms. Results show that cracking occurs via two mechanisms, solidification and liquation, with a strong dependence on the laser scan vectors. Through the use of fractal scan strategies, bulk density can be increased by 2±0.7% when compared to the ‘island’ scanning, demonstrating the potential of fractal scan strategies in the manufacture of typically ‘unweldable’ nickel superalloys.

      PubDate: 2017-02-18T10:40:24Z
      DOI: 10.1016/j.addma.2017.02.002
  • A review of defect modeling in laser material processing
    • Authors: Chong Teng; Deepankar Pal; Haijun Gong; Kai Zeng; Kevin Briggs; Nachiket Patil; Brent Stucker
      Abstract: Publication date: Available online 30 January 2017
      Source:Additive Manufacturing
      Author(s): Chong Teng, Deepankar Pal, Haijun Gong, Kai Zeng, Kevin Briggs, Nachiket Patil, Brent Stucker
      Thermomechanical modeling of laser material processing in general, and defect modeling in particular, has raised attention in both academia and industry for the last twenty years. Additive manufacturing (aka, 3D printing) is increasingly studied and utilized by researchers and engineers. Defects created during a part building process are costly to identify and could cause premature part failure, and thus numerous studies and research projects have been conducted in order to predict and analyze defects in laser material processing. The available information for defect modeling is scattered widely in the literature and mostly dedicated to very small and specific areas of focus, making it difficult for others to follow, even though the quantity of information is not small. In this work, a review of defect modeling which focuses specifically on the defect types existing in additive manufacturing industry has been carried out, including over 140 referenced articles.

      PubDate: 2017-02-18T10:40:24Z
      DOI: 10.1016/j.addma.2016.10.009
  • Fabrication and Characterization of a Functionally Graded Material from
           Ti-6Al-4 V to SS316 by Laser Metal Deposition
    • Authors: Wei Li; Sreekar Karnati; Caitlin Kriewall; Frank Liou; J. Newkirk; Karen M. Brown Taminger; William J. Seufzer
      Abstract: Publication date: Available online 4 February 2017
      Source:Additive Manufacturing
      Author(s): Wei Li, Sreekar Karnati, Caitlin Kriewall, Frank Liou, J. Newkirk, Karen M. Brown Taminger, William J. Seufzer
      In this study, laser metal deposition (LMD) was employed to explore a new fabrication process for producing a functionally graded material (FGM) from Ti-6Al-4V to SS316. A transition composition route was introduced (Ti-6Al-4V→V→Cr→Fe→SS316) to avoid the intermetallic phases between Ti-6Al-4V and SS316. A thin wall sample was fabricated via LMD by following the transition composition route. Microstructure characterization and composition distribution analyses were performed by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The SEM images depicted the microstructural morphology of the FGM sample. The element gradient distribution determined by the EDS results may reflect the FGM transition composition route design. X-ray diffraction tests were conducted and the results demonstrated that the generation of intermetallic phases effectively avoided following the composition route. The Vickers hardness test was used to determine the Vickers hardness number (VHN) distribution from Ti-6Al-4V to SS316. The VHN results showed that no significant formation of hard brittle phases occurred in the LMD procedure.

      PubDate: 2017-02-06T10:25:42Z
      DOI: 10.1016/j.addma.2016.12.006
  • Experimental and Theoretical Modeling of Behavior of 3D-Printed Polymers
           Under Collision with a Rigid Rod
    • Authors: Kamran Kardel; Hamid Ghaednia; Andres L. Carrano; Dan B. Marghitu
      Abstract: Publication date: Available online 24 January 2017
      Source:Additive Manufacturing
      Author(s): Kamran Kardel, Hamid Ghaednia, Andres L. Carrano, Dan B. Marghitu
      The behavior of five different 3D-printed polymers has been analyzed both theoretically and experimentally under low-speed collision conditions. The impact of a rigid rod with a flat specimen fabricated of 3D-printed materials was analyzed. An experimental setup has been designed in order to capture the motion of the rod during the impact using a high-speed camera. Image processing algorithms were developed to estimate the velocity before and after the impact as well as the coefficient of restitution. Also, permanent deformations after the impact were scanned with an optical profilometer. In this work, a theoretical formulation for the contact force during the impact is proposed. The impact was divided into two phases, compression and restitution, in which materials considered elastic-plastic in the first and fully elastic in the second one. The experimental results are used to measure the damping coefficient. Results show a good correlation between the proposed formulation for the contact force and the behavior of materials.

      PubDate: 2017-01-31T17:48:13Z
      DOI: 10.1016/j.addma.2017.01.004
  • Numerical modeling of the thermal behavior and residual stress in the
           direct metal laser sintering process of titanium alloy products
    • Authors: Xinran Zhao; Akshay Iyer; Patcharapit Promoppatum; Shi-Chune Yao
      Abstract: Publication date: Available online 20 January 2017
      Source:Additive Manufacturing
      Author(s): Xinran Zhao, Akshay Iyer, Patcharapit Promoppatum, Shi-Chune Yao
      In this paper the heat transfer and residual stress evolution in the direct metal laser sintering process of the additive manufacturing of titanium alloy products are studied. A numerical model is developed in a COMSOL multiphysics environment considering the temperature-dependent material properties of TiAl6V4. The thermo-mechanical coupled simulation is performed. 3-D simulation is used to study single-layer laser sintering. A 2-D model is used to study the multi-layer effects of additive manufacturing. The results reveal the behavior of the melt pool size, temperature history, and change of the residual stresses of a single layer and among the multiple layers of the effects of the change of the local base temperature and laser power etc. The result of the simulation provides a better understanding of the complex thermo-mechanical mechanisms of laser sintering additive manufacturing processes.

      PubDate: 2017-01-23T19:18:11Z
      DOI: 10.1016/j.addma.2016.10.005
  • Characterization of the strength of support structures used in powder bed
           fusion additive manufacturing of Ti-6Al-4V
    • Authors: Lourdes D. Bobbio; Shipin Qin; Alexander Dunbar; Panagiotis Michaleris; Allison M. Beese
      Abstract: Publication date: Available online 19 January 2017
      Source:Additive Manufacturing
      Author(s): Lourdes D. Bobbio, Shipin Qin, Alexander Dunbar, Panagiotis Michaleris, Allison M. Beese
      Support structures are required in powder bed fusion (PBF) additive manufacturing of metallic components with overhanging structures in order to reinforce and anchor the part, preventing warping during fabrication. In this study, we fabricated and tested the tensile structural strength of support structures with four different 2-dimensional lattice geometries by fabricating samples composed of solid material on the bottom, followed by support material in the middle, followed by solid material on the top. The support structure regions were fabricated with a lower linear heat input than the solid material, providing deliberate geometrical stress concentrations to enable the removal of support material after processing. These samples were subjected to tension in the vertical direction to measure the strengths of the support structure-solid material interfaces. Two strengths were computed: an effective structural strength defined as the total force that the structure withstood normalized by the full cross-sectional area, and a ligament structural strength, defined as the effective structural strength normalized by the density of the solid material, thereby ignoring the volume of the surrounding powder and voids that do not contribute to the strength of the lattice. The effective structural strength was 14-32% of the strength of fully dense Ti-6Al–4V made by PBF and the ligament structural strength was 34-49% of the strength of fully dense material. These interface strengths are lower than that of fully-dense material due to the stress concentrations at the support structure-solid material interfaces, not any intrinsic difference in the intrinsic strength of support structure versus solid material. These results can be used to tailor the support structure geometry to balance sufficient anchoring strength during fabrication and ease of part removal and subsequent machining during post-processing.

      PubDate: 2017-01-23T19:18:11Z
      DOI: 10.1016/j.addma.2017.01.002
  • Modelling energy source and powder properties for the development of a
           thermal FE model of the EBM additive manufacturing process
    • Authors: Manuela Galati; Luca Iuliano; Alessandro Salmi; Eleonora Atzeni
      Abstract: Publication date: Available online 11 January 2017
      Source:Additive Manufacturing
      Author(s): Manuela Galati, Luca Iuliano, Alessandro Salmi, Eleonora Atzeni
      The combination of additive manufacturing principles and electron beam (EB) technology allows complex metal parts, featuring excellent quality material, to be produced, whenever traditional methods are expensive or difficult to apply. Today, the optimization of process parameters, for a given metal powder, is generally attained through an empirical trial and error approach. Process simulation can be used as a tool for decision-making and process optimization, since a virtual analysis can help to facilitate the possibility of exploring “what if” scenarios. In this work, a new type of modelling has been introduced for energy source and powder material properties and it has been included in a thermal numerical model in order to improve the effectiveness and reliability of Electon Beam Melting (EBM) FE simulation. Several specific subroutines have been developed to automatically calculate the powder properties as temperature functions, and to consider the position of the beam during scanning as well as the material state changes from powder to liquid in the melting phase and from liquid to solid during cooling. A comparison of the numerical results and experimental data taken from literature has shown a good forecasting capability. The average deviations of the simulation from an experimental scan line width have been found to be below about 15%.

      PubDate: 2017-01-16T03:37:49Z
      DOI: 10.1016/j.addma.2017.01.001
  • Prediction of lack-of-fusion porosity for powder bed fusion
    • Authors: Ming Tang; P.Chris Pistorius; Jack L. Beuth
      Abstract: Publication date: Available online 5 January 2017
      Source:Additive Manufacturing
      Author(s): Ming Tang, P.Chris Pistorius, Jack L. Beuth
      A geometry-based simulation is used to predict porosity caused by insufficient overlap of melt pools (lack of fusion) in powder bed fusion. The inputs into the simulation are hatch spacing, layer thickness, and melt pool cross-sectional area. Melt pool areas used in the simulations can be obtained from experiments, or estimated with the analytical Rosenthal equation. The necessary material constants, including absorptivity for laser-based melting, have been collated for alloy steels, aluminum alloys and titanium alloys. Comparison with several data sets from the literature shows that the simulations correctly predict process conditions at which lack-of-fusion porosity becomes apparent, as well as the rate at which porosity increases with changes in process conditions such as beam speed, layer thickness and hatch spacing.
      Graphical abstract image

      PubDate: 2017-01-06T12:30:06Z
      DOI: 10.1016/j.addma.2016.12.001
  • Closed Loop Control of Slippage during Filament Transport in Molten
           Material Extrusion
    • Authors: Gabriel Pieter Greeff; Meinhard Schilling
      Abstract: Publication date: Available online 28 December 2016
      Source:Additive Manufacturing
      Author(s): Gabriel Pieter Greeff, Meinhard Schilling
      In the quest to achieve functional 3D printed parts with open source machines and tools it is required to study all the error sources. Flow control is a major contributor to accuracy of parts manufactured additively with material extrusion and a precise filament feed rate is therefore essential. Filament slippage is measured in this work. The speed difference between filament feed gear speed and filament speed is measured with a cost effective, automated setup, using a low cost USB microscope video camera and image processing. The filament width is also measured simultaneously, allowing for real time volumetric flow rate estimation. Extrusion temperature and feed rate are found to influence the amount of slippage. Significantly, the amount of slippage varies dynamically and therefore cannot be fully corrected for statically. Proof of concept closed loop control of the extruder is also implemented and reduces the amount of slippage considerably.

      PubDate: 2017-01-06T12:30:06Z
      DOI: 10.1016/j.addma.2016.12.005
  • Effective Liquid Conductivity for Improved Simulation of Thermal Transport
           in Laser Beam Melting Powder Bed Technology
    • Authors: Leila Ladani; John Romano; William Brindley; Sergei Burlatsky
      Abstract: Publication date: Available online 28 December 2016
      Source:Additive Manufacturing
      Author(s): Leila Ladani, John Romano, William Brindley, Sergei Burlatsky
      An effective liquid conductivity approach has been developed to describe the convective transport modes existing within the melt pool in powder bed additive manufacturing processes. A first principles approach is introduced to derive an effective conductive transport mode that encompasses conduction and advection within the melt pool. A modified Bond number was calculated by comparing surface tension forces with viscous forces within the melt pool region. It was determined, due to the small size scale of melt pools in powder bed processes, that the surface tension gradient driven flow, or the Marangoni effect, is the dominant mass transport phenomenon within the melt pool. Validation was conducted by comparing simulation melt pool widths and depths against experimental measurements for Inconel 718 built at beam powers of 150W, 200W and 300W and a scan speed of 200mm/s. By introducing the effective liquid conductivity, simulated melt pool widths were up to 50% closer to experimental widths and simulated melt pool depths were up to 80% closer to experimental measurements. Analytic temperature profiles and melt pool dimensions are compared between Ti6Al4V, Stainless Steel 316L, Aluminum 7075 and Inconel 718 built with similar process parameters, while including effective liquid conductivity. The reasons for differences in temperature and melt pool geometry are discussed.

      PubDate: 2017-01-06T12:30:06Z
      DOI: 10.1016/j.addma.2016.12.004
  • Influence of processing and orientation print effects on the mechanical
           and thermal behavior of 3D-Printed ULTEM® 9085 Material
    • Authors: R.J. Zaldivar; D.B. Witkin; T. McLouth; D.N. Patel; K. Schmitt; J.P. Nokes
      Pages: 71 - 80
      Abstract: Publication date: January 2017
      Source:Additive Manufacturing, Volume 13
      Author(s): R.J. Zaldivar, D.B. Witkin, T. McLouth, D.N. Patel, K. Schmitt, J.P. Nokes
      In this paper, we investigate the print orientation effects on the macrostructure, the mechanical and thermal properties, and the strain field behavior of ULTEM® 9085 using a Stratasys Fused deposition modeling (FDM) 400 Printer. The tensile strength, failure strain, Poisson’s ratio, coefficient of thermal expansion and modulus were all shown to vary significantly depending on the build orientation of identical dogbones. FDM parts ranged in strength from 46 to 85% of strengths attainable from comparable injection-molded parts. The coefficient of variation (CV) increased from 2 to 13% as the primary layer orientation deviated from the primary load direction. CAT scan and SEM were employed to relate the corresponding macrostructure to the mechanical response of the material along the parts’ 3-primary directions, using digital image correlation (DIC). The fracture surfaces of these parts further suggest that 3D FDM materials behave more like laminated composite structures than isotropic cast resins and therefore design allowables should reflect actual part build configurations.

      PubDate: 2016-12-04T09:21:13Z
      DOI: 10.1016/j.addma.2016.11.007
      Issue No: Vol. 13 (2016)
  • Preparing industry for additive manufacturing and its applications:
    • Authors: Timothy W. Simpson; Christopher B. Williams; Michael Hripko
      Pages: 166 - 178
      Abstract: Publication date: January 2017
      Source:Additive Manufacturing, Volume 13
      Author(s): Timothy W. Simpson, Christopher B. Williams, Michael Hripko
      Accompanying the increasing advances and interest in Additive Manufacturing (AM) technologies is an increasing demand for an industrial workforce that is knowledgeable about the technologies and how to apply them to solve real-world problems. As a step towards addressing this knowledge gap, a workshop was held at the National Science Foundation (NSF) to discuss the educational needs to prepare industry for AM and its use in different fields. The workshop participants – 66 representatives from academia, industry, and government – identified several key educational themes: (1) AM processes and process/material relationships, (2) engineering fundamentals with an emphasis on materials science and manufacturing, (3) professional skills for problem solving and critical thinking, (4) design practices and tools that leverage the design freedom enabled by AM, and (5) cross-functional teaming and ideation techniques to nurture creativity. This paper summarizes the industry speakers and presentations from the workshop, along with several new educational partnerships identified by small working groups. Based on the presentations and partnerships, the following recommendations are offered to advance the AM workforce. First, ensure that all AM curricula provide students with an understanding of (i) AM and traditional manufacturing processes to enable them to effectively select the appropriate process for product realization; (ii) the relationships between AM processes and material properties; and (iii) “Design for AM”, including computational tools for AM design as well as frameworks for process selection, costing, and solution generation that take advantage of AM capabilities. Second, establish a national network for AM education that, by leveraging existing “distributed” educational models and NSF’s Advanced Technology Education (ATE) Programs, provides open source resources as well as packaged activities, courses, and curricula for all educational levels (K-Gray). Third, support K-12 educational programs in STEAM (STEM plus the arts) and across all formal and informal learning environments in order to learn the unique capabilities of AM while engaging students in hands-on, tactile, and visual learning activities to prepare them for jobs in industry while learning how to think differently when designing for AM. Fourth, provide support for collaborative and community-oriented maker spaces that promote awareness of AM among the public and provide AM training programs for incumbent workers in industry and students seeking alternative pathways to gain AM knowledge and experience. Recommendations for scaling and coordination across local, regional, and national levels are also discussed to create synergies among the proposed activities and existing efforts.

      PubDate: 2016-12-27T06:08:34Z
      DOI: 10.1016/j.addma.2016.08.002
      Issue No: Vol. 13 (2016)
  • Understanding the effect of laser scan strategy on residual stress in
           selective laser melting through thermo-mechanical simulation
    • Authors: L. Parry; I.A. Ashcroft; R.D. Wildman
      Pages: 1 - 15
      Abstract: Publication date: October 2016
      Source:Additive Manufacturing, Volume 12, Part A
      Author(s): L. Parry, I.A. Ashcroft, R.D. Wildman
      Selective laser melting (SLM) is an attractive technology, enabling the manufacture of customised, complex metallic designs, with minimal wastage. However, uptake by industry is currently impeded by several technical barriers, such as the control of residual stress, which have a detrimental effect on the manufacturability and integrity of a component. Indirectly, these impose severe design restrictions and reduce the reliability of components, driving up costs. This paper uses a thermo-mechanical model to better understand the effect of laser scan strategy on the generation of residual stress in SLM. A complex interaction between transient thermal history and the build-up of residual stress has been observed in the two laser scan strategies investigated. The temperature gradient mechanism was discovered for the creation of residual stress. The greatest stress component was found to develop parallel to the scan vectors, creating an anisotropic stress distribution in the part. The stress distribution varied between laser scan strategies and the cause has been determined by observing the thermal history during scanning. Using this, proposals are suggested for designing laser scan strategies used in SLM.

      PubDate: 2016-06-13T04:04:31Z
      DOI: 10.1016/j.addma.2016.05.014
      Issue No: Vol. 12 (2016)
  • MRI monitoring and non-destructive quality measurement of polymeric
           patterns manufactured via stereolithography
    • Authors: Evgeny V. Morozov; Mikhail M. Novikov; Vyacheslav M. Bouznik
      Pages: 16 - 24
      Abstract: Publication date: October 2016
      Source:Additive Manufacturing, Volume 12, Part A
      Author(s): Evgeny V. Morozov, Mikhail M. Novikov, Vyacheslav M. Bouznik
      The use of Magnetic Resonance Imaging (MRI) for monitoring, studying and performing output quality measurements of the acrylate-based polymeric patterns manufactured using stereolithography (SL) was introduced in this work. The effects of build parameters and humid environment on sample homogeneity, distribution of crosslink density, stability and defect formation were examined. The spatial resolution of the method was found to be sufficient to identify patterns according to the build parameters used and to detect specific hatch-predicted crosslink density variations. Qualitative information obtained using MRI visualisation was supplemented by quantitative measurements of Nuclear Magnetic Resonance (NMR) relaxation times and 1H NMR spectra. NMR spectroscopy confirmed the identity of the chemical composition among the patterns and showed that the crosslink density variation observed via spatially resolved T2-profiles stems from the difference of the build parameters. Different types of defects in the samples were observed and classified; some defects originated from local matrix continuity failures (partially cured resin trapping within the polymer or bubbles formation), while other defects were found in the form of bulk layering. MRI visualisation coupled with relaxometry and 1H spectroscopy of patterns during their interaction with humidity allowed tracking water distribution inside the sample and observing effects of swelling, fracturing and chemical decomposition. It was found that the initial inhomogeneous structure of the specimen has a crucial role in subsequent fracturing due to non-uniform expansion of the swollen parts. As a result, the approach presented in this work improves the output quality control and current testing techniques, provides insight how physical properties of the 3D parts are affected by different technical parameters, and eventually can help the use of SL technologies for a variety of applications.

      PubDate: 2016-06-13T04:04:31Z
      DOI: 10.1016/j.addma.2016.05.015
      Issue No: Vol. 12 (2016)
  • Simulation of additive manufacturing using coupled constitutive and
           microstructure models
    • Authors: Lars-Erik Lindgren; Andreas Lundbäck; Martin Fisk; Robert Pederson; Joel Andersson
      Pages: 144 - 158
      Abstract: Publication date: October 2016
      Source:Additive Manufacturing, Volume 12, Part B
      Author(s): Lars-Erik Lindgren, Andreas Lundbäck, Martin Fisk, Robert Pederson, Joel Andersson
      The paper describes the application of modeling approaches used in Computational Welding Mechanics (CWM) applicable for simulating Additive Manufacturing (AM). It focuses on the approximation of the behavior in the process zone and the behavior of the solid material, particularly in the context of changing microstructure. Two examples are shown, one for the precipitation hardening Alloy 718 and one for Ti-6Al-4V. The latter alloy is subject to phase changes due to the thermal cycling.

      PubDate: 2016-11-27T15:08:06Z
      DOI: 10.1016/j.addma.2016.05.005
      Issue No: Vol. 12 (2016)
  • 3D printing of tough hydrogel composites with spatially varying materials
    • Authors: Shannon E. Bakarich; Robert Gorkin; Reece Gately; Sina Naficy; Marc in het Panhuis; Geoffrey M. Spinks
      Abstract: Publication date: Available online 23 December 2016
      Source:Additive Manufacturing
      Author(s): Shannon E. Bakarich, Robert Gorkin, Reece Gately, Sina Naficy, Marc in het Panhuis, Geoffrey M. Spinks
      Biofabrication is the process of transforming materials into systems that reproduce biological structure and function. Previous attempts to create biomimetic systems have often used single materials shaped into limited configurations that do not mimic the heterogeneous structure and properties of many biological tissues. The identification of new bio-inspired materials alongside the development of appropriate fabrication techniques is the key to overcoming the challenge of replicating the functional gradients of these heterogeneous tissues. This paper presents a new extrusion-based gradient printing system that utilizes custom software to control the rates at which two inks are dispensed through a mixing nozzle. The printer was used to fabricate a range of composite materials containing varying blends of a tough alginate/poly(acrylamide) ionic covalent entanglement hydrogel and an acrylated urethane based UV-curable adhesive material. The hard adhesive material acted as particulate reinforcement within the matrix of composites printed with a large hydrogel volume fraction. The composite materials were characterized mechanically and their performance could be modeled with standard composite theory. The platform of a 3D printer allowed these composite materials to be fabricated directly with a smooth and continuous gradient of modulus between the soft hydrogel and harder acrylated urethane material, such as may be useful in the development of bio-inspired structures such as artificial tendons.

      PubDate: 2016-12-27T06:08:34Z
      DOI: 10.1016/j.addma.2016.12.003
  • Improving Dimensional Accuracy in EBM using Beam Characterization and
           Trajectory Optimization
    • Authors: Vignat Villeneuve; Dendievel
      Abstract: Publication date: Available online 16 December 2016
      Source:Additive Manufacturing
      Author(s): N. Béraud, F. Vignat, F. Villeneuve, R. Dendievel
      Managing the dimensional accuracy of parts produced by the Electron Beam Melting process is a challenge. For small dimensions, as in lattice structures (strut diameters), accuracy becomes even more important and geomtric quality is linked to mechanical properties. The dimensional quality of parts produced by EBM can be influenced by many process parameters. Simulating the process can help the machine user to choose the best process parameters and improve build dimensional accuracy. The work presented here is based on a method for linking process parameters with beam parameters. Once linked, both sets of parameters are then integrated into a full simulation of the process in order to make trajectory optimization possible. First, this paper explains how the finite element model described in the literature can be improved to simulate the multilayer EBM process. It then describes how this simulation is used to develop a method to characterize the machine beam and determine the link between the focus current and the beam diameter. Finally, it shows how this simulation can be applied to a built shape (vertical strut) hence demonstrating improved accuracy of the produced part.

      PubDate: 2016-12-18T06:33:10Z
  • Infrared preheating to improve interlayer strength of big area additive
           manufacturing (BAAM) components
    • Authors: Vidya Kishore; Christine Ajinjeru; Andrzej Nycz; Brian Post; John Lindahl; Vlastimil Kunc; Chad Duty
      Abstract: Publication date: Available online 2 December 2016
      Source:Additive Manufacturing
      Author(s): Vidya Kishore, Christine Ajinjeru, Andrzej Nycz, Brian Post, John Lindahl, Vlastimil Kunc, Chad Duty
      The Big Area Additive Manufacturing (BAAM) system can print structures on the order of several meters at high extrusion rates, thereby having the potential to significantly impact automotive, aerospace and energy sectors. The functional use of such parts, however, may be limited by mechanical anisotropy, in which the strength of printed parts across successive layers in the build direction (z-direction) can be significantly lower than the corresponding in-plane strength (x-y directions). This has been primarily attributed to poor bonding between printed layers since the lower layers cool below the glass transition temperature (Tg) before the next layer is deposited. Therefore, the potential of using infrared heating is considered for increasing the surface temperature of the printed layer just prior to deposition of new material to improve the interlayer strength of the components. This study found significant improvements in bond strength for the deposition of acrylonitrile butadiene styrene (ABS) reinforced with 20% chopped carbon fiber when the surface temperature of the substrate material was increased from below Tg to close to or above Tg using infrared heating.

      PubDate: 2016-12-04T09:21:13Z
      DOI: 10.1016/j.addma.2016.11.008
  • Effects of in-situ poling and process parameters on fused filament
           fabrication printed PVDF sheet mechanical and electrical properties
    • Authors: Daniel Porter; Trung V.T. Hoang Thomas Berfield
      Abstract: Publication date: Available online 29 November 2016
      Source:Additive Manufacturing
      Author(s): Daniel A. Porter, Trung V.T. Hoang, Thomas A. Berfield
      Polyvinylidene fluoride (PVDF) is a polymer prized for its unique material properties, including a high resistance to corrosive acids such as HCL and HF and its piezoelectric potential based on the proper microstructure arrangement. In this work, the effects of fused filament fabrication (FFF) routine parameters on printed PVDF film properties were investigated using a variety of experimental methods. The influence of in-fill angle (0°, 45°, and 90°) on the effective Young’s Modulus, Poisson’s ratio, and yield strength were evaluated using tensile testing and a digital image correlation (DIC) analysis. The phase content, in particular the β-phase amount, within the semi-crystalline PVDF films was determined as a function of processing parameters using the FTIR method. Considered parameters included the extrusion temperature, horizontal speed, in-situ applied hot end voltage, and bed material. Results showed that higher β-phase content was associated with lower extrusion temperatures, faster extrusion rates, and higher hot end voltages. While all “as printed” films demonstrated little to no measurable piezoelectricity, PVDF films printed with a high β-phase content and subjected to a post-printing corona poling procedure showed a small, but consistent piezoelectric response. Based on a static deflection cantilever beam experiment, the d31 coefficient of the poled specimens was estimated at 1.19 pm/V.

      PubDate: 2016-12-04T09:21:13Z
  • Hot Isostatic Pressing of IN718 Components Manufactured by Selective Laser
    • Authors: W. Tillmann; C. Schaak; J. Nellesen; M. Schaper; M.E. Aydinöz; K.-P. Hoyer
      Abstract: Publication date: Available online 27 November 2016
      Source:Additive Manufacturing
      Author(s): W. Tillmann, C. Schaak, J. Nellesen, M. Schaper, M.E. Aydinöz, K.-P. Hoyer
      Selective laser melting and other additive manufacturing (AM) techniques have recently attracted substantial interest of both researchers and the processing industry. The freedom of design leads to completely new possibilities for constructions and, thus, to entirely new products. In the selective laser melting (SLM) process, the components are produced layer-wise using a laser beam. SLM is a powder bed based AM process and is characterized by the complete melting of the utilized powder material. Employing SLM, complex three-dimensional parts and light weight structures can be produced directly from 3D CAD data. However, although SLM is a very promising technology, there are still challenges to solve. In the present study, a close look is taken at the porosity. Under cyclic loading, pores can act as stress raisers and lead to premature crack initiations, which reduce the fatigue strength of the material. Hot isostatic pressing (HIP) offers the possibility to reduce the porosity. HIP combines high pressure and high temperature to produce materials with superior properties. The influence of the HIP process parameters on the density and microstructure of IN718 SLM components is investigated by means of micro X-ray computed tomography and scanning electron microscopy. The results of the experiments show that the majority of pores can be densified by means of HIP. On the other hand, some pores cannot be densified. The reason for this is seen in entrapped argon gas from the SLM process.

      PubDate: 2016-12-04T09:21:13Z
      DOI: 10.1016/j.addma.2016.11.006
  • Selective laser melting of HY100 steel: Process parameters, microstructure
           and mechanical properties
    • Authors: J.J.S. Dilip; G.D. Janaki Ram; Thomas L. Starr; Brent Stucker
      Abstract: Publication date: Available online 17 November 2016
      Source:Additive Manufacturing
      Author(s): J.J.S. Dilip, G.D. Janaki Ram, Thomas L. Starr, Brent Stucker
      Selective Laser Melting (SLM) of a high strength low alloy steel HY100 is considered in the present investigation. The current work describes (i) optimization of SLM process parameters for producing fully dense parts in HY100 steel and (ii) the effects of post-processing heat treatment on the microstructure and mechanical properties. Samples have been fabricated by SLM using different combinations of laser power, laser scan speed, and hatch spacing. Fully dense samples were achieved at an energy density of 65J/mm3. Microstructures of the as-built and heat treated samples were investigated using optical and scanning electron microscopes, X-ray diffraction, and electron backscattered diffraction techniques. The as-built sample showed fully martensitic microstructure with alternate bands of untempered (hard) and auto-tempered (soft) regions. The as-built parts are unsuitable for direct application due to untempered, hard and brittle martensite microstructure. The as-built parts were subjected to post-processing heat treatments (“direct temper” and “quench and temper”). The direct tempered samples exhibited higher yield strength and ultimate strength than the quench and temper ones. Noticeable amounts of anisotropy with respect to the build orientation, especially in tensile elongation, were observed in the direct tempered samples due to in-homogenous microstructure. Quench and temper treatment of the parts resulted in recrystallized grains with uniform microstructure. The current investigation shows that quench and temper at 650°C is an optimum post processing treatment for HY100 SLM parts as it manifests desired strength with good tensile elongation.

      PubDate: 2016-11-20T15:27:52Z
      DOI: 10.1016/j.addma.2016.11.003
  • Predictive modeling and optimization of multi-track processing for laser
           powder bed fusion of nickel alloy 625
    • Authors: Luis E. Criales; Yiğit M. Arısoy; Brandon Lane; Shawn Moylan; Alkan Donmez; Tuğrul Özel
      Abstract: Publication date: Available online 14 November 2016
      Source:Additive Manufacturing
      Author(s): Luis E. Criales, Yiğit M. Arısoy, Brandon Lane, Shawn Moylan, Alkan Donmez, Tuğrul Özel
      This paper presents an integrated physics-based and statistical modeling approach to predict temperature field and meltpool geometry in multi-track processing of laser powder bed fusion (L-PBF) of nickel 625 alloy. Multi-track laser processing of powder material using L-PBF process has been studied using 2-D finite element simulations to calculate temperature fields along the scan and hatch directions for three consecutive tracks for a moving laser heat source to understand the heating and melting process. Based on the predicted temperature fields, width, depth and shape of the meltpool is determined. Designed experiments on L-PBF of nickel alloy 625 powder material are conducted to measure the relative density and meltpool geometry. Experimental work is reported on the measured density of built coupons and meltpool size. Statistically-based predictive models using response surface regression for relative density, meltpool geometry, peak temperature, and time above melting point are developed and multi-objective optimization studies are conducted by using genetic algorithm and swarm intelligence.

      PubDate: 2016-11-20T15:27:52Z
      DOI: 10.1016/j.addma.2016.11.004
  • Finite element simulations of temperature distribution and of
           densification of a titanium powder during metal laser sintering
    • Authors: L. Dong; J.P.M. Correia; N. Barth; S. Ahzi
      Abstract: Publication date: Available online 12 November 2016
      Source:Additive Manufacturing
      Author(s): L. Dong, J.P.M. Correia, N. Barth, S. Ahzi
      Metal Laser Sintering (LS) is a powder bed fusion process that can be used to produce manufactured parts of complex shapes directly from metallic powders. One of the major problems of such powder bed fusion processes is that during the continuous movement of the laser beam, temperature distribution becomes inhomogeneous and instable in the powder. It leads to greater residual stresses in the solidified layer. Thus, temperature analyses must be performed to better understand the heating-cooling process of the powder bed as well as the interactions of different laser scanning paths within a sintering pattern. A transient 3D Finite Element (FE) model of the LS process has been developed with the commercial FE code ABAQUS. The model takes into account the different physical phenomena involved in this powder bed fusion technology (including thermal conduction, radiation and convection). A moving thermal source, modeling the laser scan, is implemented with the user scripting subroutine DFLUX in this FE code. The material’s thermal behavior is also defined via the subroutine UMATHT. As the material properties change due to the powder bed fusion process, the model takes it into account. In this way, the calculation of a temperature-dependent behavior is undertaken for the packed powder bed, within its effective thermal conductivity and specific heat. Furthermore, the model accounts for the latent heat due to phase change of the metal powder. Finally, a time- and temperature-dependent formulation for the material’s density is also computed, which is then integrated along with the other thermal properties in the heat equation. FE simulations have been applied to the case of titanium powder and show predictions in good agreement with experimental results. The effects of process parameters on the temperature and on the density distribution are also presented.

      PubDate: 2016-11-13T17:27:14Z
      DOI: 10.1016/j.addma.2016.11.002
  • Effect of building direction on the microstructure and tensile properties
    • Authors: Mitsuharu Todai; Takayoshi Nakano; Tianqi Liu; Hiroyuki Y. Yasuda; Koji Hagihara; Ken Cho; Minoru Ueda; Masao Takeyama
      Abstract: Publication date: Available online 10 November 2016
      Source:Additive Manufacturing
      Author(s): Mitsuharu Todai, Takayoshi Nakano, Tianqi Liu, Hiroyuki Y. Yasuda, Koji Hagihara, Ken Cho, Minoru Ueda, Masao Takeyama
      This paper clarified a novel strategy to improve the tensile properties of the Ti-48Al-2Cr-2Nb alloys fabricated by electron beam melting (EBM), via the finding of the development of unique layered microstructure composed of the two-layers of “lamellar-structured γ/α2 fine grains and fine γ grains layer” and “coarse γ grains layer”. It was clarified that the mechanical properties of the alloy fabricated by EBM can be controlled by varying an angle θ between EBM-building directions and stress loading direction. At room temperature, the yield strength exhibits high values more than 550MPa at all the loading orientations investigated (θ=0, 45 and 90°). In addition, the elongation at θ=45° was surprisingly larger than 2%, owing to the development of unique layered microstructure. The anisotropy of the yield strength decreased with increasing temperature. All the examined alloys exhibited a brittle-ductile transition temperature of approximately 750°C and the yield strength and tensile elongation at 800°C were over 350MPa and 40%, respectively. By the detailed observation of the microstructure, formation mechanism of the unique layered microstructure was found to be closely related to the repeated local heat treatment effect during the EBM process, and thus its control is further possible by the tuning-up of the process parameters. The results demonstrate that the EBM process enables not only the fabrication of TiAl products with complex shape but also the control of the tensile properties associated with the peculiar microstructure formed during the process.
      Graphical abstract image

      PubDate: 2016-11-13T17:27:14Z
      DOI: 10.1016/j.addma.2016.11.001
  • A voxel-based method of constructing and skinning conformal and
           functionally graded lattice structures suitable for additive manufacturing
    • Authors: A.O. Aremu; J.P.J. Brennan-Craddock; A. Panesar; I.A. Ashcroft; R.J.M. Hague; R.D. Wildman; C. Tuck
      Abstract: Publication date: Available online 9 November 2016
      Source:Additive Manufacturing
      Author(s): A.O. Aremu, J.P.J. Brennan-Craddock, A. Panesar, I.A. Ashcroft, R.J.M. Hague, R.D. Wildman, C. Tuck
      Additive Manufacturing (AM) enables the production of geometrically complex parts that are difficult to manufacture by other means. However, conventional CAD systems are limited in the representation of such parts. This issue is exacerbated when lattice structures are combined or embedded within a complex geometry. This paper presents a computationally efficient, voxel-based method of generating lattices comprised of practically any cell type that can conform to an arbitrary external geometry. The method of conforming involves the tessellation and trimming of unit cells that can leave ‘hanging’ struts at the surface, which is a possible point of weakness in the structure. A method of joining these struts to form an external two dimensional lattice, termed a ‘net-skin’ is also described. Traditional methods of manufacturing lattice structures generally do not allow variation of cell properties within a structure; however, additive manufacturing enables graded lattices to be generated that are potentially more optimal. A method of functionally grading lattices is, therefore, also described to take advantage of this manufacturing capability.

      PubDate: 2016-11-13T17:27:14Z
      DOI: 10.1016/j.addma.2016.10.006
  • Influences of processing parameters on surface roughness of Hastelloy X
           produced by selective laser melting
    • Authors: Yang Tian; Dacian Tomus; Paul Rometsch; Xinhua Wu
      Abstract: Publication date: Available online 8 November 2016
      Source:Additive Manufacturing
      Author(s): Yang Tian, Dacian Tomus, Paul Rometsch, Xinhua Wu
      Selective laser melting (SLM) technology is a layer-wise powder-based additive manufacturing method capable of building 3D components from their CAD models. This approach offers enormous benefits for generating objects with geometrical complexity. However, due to the layer-wise nature of the process, surface roughness is formed between layers, thus influenced by layer thickness and other processing parameters. In this study, systematic research has been carried out to study the influence of processing parameters on surface roughness in Hastelloy X alloy. All samples were manufactured using an EOSINT M 280 machine. Laser power, scan speed, layer thickness and sloping angle of a surface were systematically varied to understand their effects on surface roughness. The arithmetic average roughness, Ra, was measured using a surface roughness tester, and optimum conditions for achieving the lowest roughness for both up-skin surfaces and down-skin surfaces have been obtained. The formation mechanism for the roughness on these two types of surfaces has been studied. Computer simulation was also used to understand thermal profiles at those two surfaces and their resultant influence on surface roughness. The simulated result has been found to be consistent with the measured result. Contour scan and skywriting scan strategies were found to be helpful for reducing the surface roughness.

      PubDate: 2016-11-13T17:27:14Z
      DOI: 10.1016/j.addma.2016.10.010
  • Simulation of grain structure evolution during powder bed based additive
    • Authors: Abha Rai; H. Helmer; Carolin Körner
      Abstract: Publication date: Available online 5 November 2016
      Source:Additive Manufacturing
      Author(s): Abha Rai, H. Helmer, Carolin Körner
      A lattice Boltzmann (LB) method to simulate melt pool dynamics and a cellular automaton (CA) to simulate the solidification process are coupled to predict the microstructure evolution during selective electron beam melting (SEBM). The resulting CALB model takes into account powder related stochastic effects, energy absorption and evaporation, melt pool dynamics and solidification microstructure evolution. Several physical phenomena are observed during grain solidification, e.g., initial grain selection starting at the base plate, grain boundary perturbation, grain nucleation due to unmolten powder particles in the bulk, grain penetration from the surface of the part or grain alignment dependent on the beam scanning strategy. Aim of the present work is to apply the CALB model to qualitatively examine the aforementioned phenomena. The effect of process parameters on the final grain structure and texture evolution is presented.

      PubDate: 2016-11-06T17:15:03Z
      DOI: 10.1016/j.addma.2016.10.007
  • Additive Manufacturing of 3D Structures with Non-Newtonian Highly Viscous
           Fluids: Finite Element Modeling and Experimental Validation
    • Authors: Farzad Liravi; Robin Darleux; Ehsan Toyserkani
      Abstract: Publication date: Available online 28 October 2016
      Source:Additive Manufacturing
      Author(s): Farzad Liravi, Robin Darleux, Ehsan Toyserkani
      Additive manufacturing (AM) of highly viscous materials, e.g., polysiloxane (silicone) has gained attention in academia and different industries, specifically the medical and healthcare sectors. Different AM processes including micro-syringe nozzle dispensing systems have demonstrated promising results in the deposition of highly viscous materials. This contact-based 3D printing system has drawbacks such as overfilling of material at locations where there is a change in the direction of the trajectory, thereby reducing the printing quality. Modeling the continuous flow of a highly viscous polysiloxane in the nozzle dispensing AM system using finite element analysis will be the first step to solve this overfilling phenomenon. The results of simulation can be used to predict the required variation in the value of pressure before the nozzle reaches a corner. The level-set method is employed for this simulation, and the results are validated by comparing the flow profile and geometrical parameters of the model with those of the experimental trials of the dispensing of polysiloxane. Comparisons show that the model is able to predict the location of the droplet before it reaches the substrate, as well as the height of the droplet generated on the substrate accurately. To predict the width of the droplet, adjustment factors need to be considered in calculations based on the value of the pressure.

      PubDate: 2016-10-29T17:03:52Z
      DOI: 10.1016/j.addma.2016.10.008
  • Assessing the capability of in-situ nondestructive analysis during layer
           based additive manufacture
    • Authors: Matthias Hirsch; Rikesh Patel; Wenqi Li; Guangying Guan; Richard K. Leach; Steve D. Sharples; Adam T. Clare
      Abstract: Publication date: Available online 20 October 2016
      Source:Additive Manufacturing
      Author(s): Matthias Hirsch, Rikesh Patel, Wenqi Li, Guangying Guan, Richard K. Leach, Steve D. Sharples, Adam T. Clare
      Unlike more established subtractive or constant volume manufacturing technologies, additive manufacturing methods suffer from a lack of in-situ monitoring methodologies which can provide information relating to process performance and the formation of defects. In-process evaluation for additive manufacturing is becoming increasingly important in order to assure the integrity of parts produced in this way. This paper addresses the generic performance of inspection methods suitable for additive manufacturing. Key process and measurement parameters are explored and the impacts these have upon production rates are defined. Essential working parameters are highlighted, within which the spatial opportunity and temporal penalty for measurement allow for comparison of the suitability of different nondestructive evaluation techniques. A new method of benchmarking in-situ inspection instruments and characterising their suitability for additive manufacturing processes is presented to act as a design tool to accommodate end user requirements. Two inspection examples are presented: spatially resolved acoustic spectroscopy and optical coherence tomography for scanning selective laser melting and selective laser sintering parts, respectively. Observations made from the analyses presented show that the spatial capability arising from scanning parameters affects the temporal penalty and hence impact upon production rates. A case study, created from simulated data, has been used to outline the spatial performance of a generic nondestructive evaluation method and to show how a decrease in data capture resolution reduces the accuracy of measurement.
      Graphical abstract image

      PubDate: 2016-10-22T18:04:14Z
      DOI: 10.1016/j.addma.2016.10.004
  • Impact of chemical finishing on laser-sintered nylon 12 materials
    • Authors: N.B. Crane; Qi Ni; A. Ellis; N. Hopkinson
      Abstract: Publication date: Available online 17 October 2016
      Source:Additive Manufacturing
      Author(s): N.B. Crane, Qi Ni, A. Ellis, N. Hopkinson
      Additive Manufacturing offers many potential benefits including reduced tooling costs and increased geometric freedom. However, the surface quality of the parts is typically below that of conventionally-processed materials. This paper evaluates a new chemical post-processing method to reduce the roughness of laser-sintered Nylon 12 components. This process is called the PUSh™ process. The treatment reduced the surface roughness of sample parts from 18μm to 5μm Ra and largely eliminated roughness with length scales below 500μm. Treatment did not affect the flexural modulus, flexural strength, or dimensions of 3.2mm thick bending specimens, but it did significantly impact the mechanical properties of thin tensile specimens that are one to eight layers thick. The post processing reduced the breaking force of the samples, but it increased the ultimate tensile strength and elongation at break. The impact was largest on the thinnest parts. Significant sample shrinkage (12–20%) and weight gain (3.7–7%) from treatment was also observed in the tensile specimens. The results show that the PUSh™ process dramatically increases surface smoothness and elongation at break in thin specimens. It decreases the surface strength, but effects are negligible in larger samples.

      PubDate: 2016-10-22T18:04:14Z
      DOI: 10.1016/j.addma.2016.10.001
  • Evaluation of bioprinter technologies
    • Authors: Ibrahim T. Ozbolat; Kazim K. Moncal; Hemanth Gudapati
      Abstract: Publication date: Available online 15 October 2016
      Source:Additive Manufacturing
      Author(s): Ibrahim T. Ozbolat, Kazim K. Moncal, Hemanth Gudapati
      Since the first printing of biologics with cytoscribing as demonstrated by Klebe in 1986, three dimensional (3D) bioprinting has made a substantial leap forward, particularly in the last decade. It has been widely used in fabrication of living tissues for various application areas such as tissue engineering and regenerative medicine research, transplantation and clinics, pharmaceutics and high-throughput screening, and cancer research. As bioprinting has gained interest in the medical and pharmaceutical communities, the demand for bioprinters has risen substantially. A myriad of bioprinters have been developed at research institutions worldwide and several companies have emerged to commercialize advanced bioprinter technologies. This paper prefaces the evolution of the field of bioprinting and presents the first comprehensive review of existing bioprinter technologies. Here, a comparative evaluation is performed for bioprinters; limitations with the current bioprinter technologies are discussed thoroughly and future prospects of bioprinters are provided to the reader.

      PubDate: 2016-10-22T18:04:14Z
      DOI: 10.1016/j.addma.2016.10.003
  • 3D inkjet-printed UV-curable inks for multi-functional electromagnetic
    • Authors: Ehab Saleh; Peter Woolliams Bob Clarke Andrew Gregory Steve Greedy
      Abstract: Publication date: Available online 14 October 2016
      Source:Additive Manufacturing
      Author(s): Ehab Saleh, Peter Woolliams, Bob Clarke, Andrew Gregory, Steve Greedy, Chris Smartt, Ricky Wildma, Ian Ashcroft, Richard Hague, Phill Dickens, Christopher Tuck
      Inkjet printing of multiple materials is usually processed in multiple steps due to various jetting and curing/sintering conditions. In this paper we report on the development of all inkjet-printed UV-curable electromagnetic responsive inks in a single process, and the electromagnetic characterization of the developed structure. The ink consists of iron oxide (Fe3O4) nanoparticles (nominal particle size 50–100nm) suspended within a UV curable matrix resin. The viscosity and surface tension of the inks were tuned to sit within the inkjet printability range. Multiple layers of the electromagnetic active ink were printed alongside passive UV-curable ink in a single manufacturing process to form a multi-material waffle shape. The real permittivity of the cured passive ink, active ink and waffle structure at a frequency of 8–12GHz were 2.25, 2.73 and 2.65F/m, respectively. This shows the potential of additive manufacturing (AM) to form multi-material structures with tunable electromagnetic properties.

      PubDate: 2016-10-15T14:42:42Z
  • Feasibility of In Situ Controlled Heat Treatment (ISHT) of Inconel 718
           During Electron Beam Melting Additive Manufacturing
    • Authors: W.J. Sames; K.A. Unocic; G.W. Helmreich; M.M. Kirka; F. Medina; R.R. Dehoff; S.S. Babu
      Abstract: Publication date: Available online 7 October 2016
      Source:Additive Manufacturing
      Author(s): W.J. Sames, K.A. Unocic, G.W. Helmreich, M.M. Kirka, F. Medina, R.R. Dehoff, S.S. Babu
      A novel technique was developed to control the microstructure evolution in Alloy 718 processed using Electron Beam Melting (EBM). In situ solution treatment and aging of Alloy 718 was performed by heating the top surface of the build after build completion scanning an electron beam to act as a planar heat source during the cool down process. Results demonstrate that the measured hardness (478±7 HV) of the material processed using in situ heat treatment similar to that of peak-aged Inconel 718. Large solidification grains and cracks formed, which are identified as the likely mechanism leading to failure of tensile tests of the in situ heat treatment material under loading. Despite poor tensile performance, the technique proposed was shown to successively age Alloy 718 (increase precipitate size and hardness) without removing the sample from the process chamber, which can reduce the number of process steps in producing a part. Tighter controls on processing temperature during layer melting to lower process temperature and selective heating during in situ heat treatment to reduce over-sintering are proposed as methods for improving the process.

      PubDate: 2016-10-08T13:37:12Z
      DOI: 10.1016/j.addma.2016.09.001
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