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Showing 1 - 200 of 3043 Journals sorted alphabetically
AASRI Procedia     Open Access   (Followers: 15)
Academic Pediatrics     Hybrid Journal   (Followers: 22, SJR: 1.402, h-index: 51)
Academic Radiology     Hybrid Journal   (Followers: 21, SJR: 1.008, h-index: 75)
Accident Analysis & Prevention     Partially Free   (Followers: 84, SJR: 1.109, h-index: 94)
Accounting Forum     Hybrid Journal   (Followers: 25, SJR: 0.612, h-index: 27)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 30, 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: 348, 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   (Followers: 1)
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: 252, 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: 10, 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: 23, SJR: 1.365, h-index: 73)
Acta Sociológica     Open Access  
Acta Tropica     Hybrid Journal   (Followers: 6, 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: 4, 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)
Acute Pain     Full-text available via subscription   (Followers: 13)
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: 21)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 135, 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: 17, SJR: 0.739, h-index: 33)
Advances in Accounting     Hybrid Journal   (Followers: 9, 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: 25, 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: 11, SJR: 0.801, h-index: 26)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 22, 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: 25, 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: 26, 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: 9, SJR: 1.268, h-index: 45)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 29, 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 Dermatology     Full-text available via subscription   (Followers: 12)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 11)
Advances in Digestive Medicine     Open Access   (Followers: 6)
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: 41, 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: 41, SJR: 5.465, h-index: 64)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 3)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 50, SJR: 0.674, h-index: 38)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 16)
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: 22, SJR: 0.906, h-index: 24)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 0.497, h-index: 31)
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: 35, 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: 6)
Advances in Life Course Research     Hybrid Journal   (Followers: 8, SJR: 0.764, h-index: 15)
Advances in Lipobiology     Full-text available via subscription   (Followers: 2)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 9)
Advances in Marine Biology     Full-text available via subscription   (Followers: 15, 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: 6, 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: 22)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 10)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 7, SJR: 0.324, h-index: 8)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 4)
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: 24, SJR: 0.4, h-index: 28)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 13)
Advances in Pharmacology     Full-text available via subscription   (Followers: 15, SJR: 1.718, h-index: 58)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 8, 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: 17)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 20, SJR: 1.5, h-index: 62)
Advances in Psychology     Full-text available via subscription   (Followers: 61)
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: 3, SJR: 0.1, h-index: 2)
Advances in Space Research     Full-text available via subscription   (Followers: 353, SJR: 0.606, h-index: 65)
Advances in Structural Biology     Full-text available via subscription   (Followers: 8)
Advances in Surgery     Full-text available via subscription   (Followers: 7, SJR: 0.823, h-index: 27)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 30, SJR: 1.321, h-index: 56)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 17)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 13)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 1.878, h-index: 68)
Advances in Water Resources     Hybrid Journal   (Followers: 43, 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: 326, 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: 5, SJR: 0.344, h-index: 6)
Ageing Research Reviews     Hybrid Journal   (Followers: 8, SJR: 3.289, h-index: 78)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 405, 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: 30, SJR: 1.275, h-index: 74)
Agricultural Water Management     Hybrid Journal   (Followers: 39, 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: 54, 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: 5, 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: 10, SJR: 0.922, h-index: 66)
Alcoholism and Drug Addiction     Open Access   (Followers: 8)
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: 8, 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: 4, SJR: 0.776, h-index: 35)
Alpha Omegan     Full-text available via subscription   (SJR: 0.121, h-index: 9)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 8, SJR: 0.158, h-index: 9)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 48, SJR: 4.289, h-index: 64)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 6)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 5)
American Heart J.     Hybrid Journal   (Followers: 49, 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: 39, SJR: 0.574, h-index: 65)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 8, SJR: 1.091, h-index: 45)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 15, SJR: 1.653, h-index: 93)
American J. of Human Genetics     Hybrid Journal   (Followers: 31, 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: 32, SJR: 2.313, h-index: 172)
American J. of Medicine     Hybrid Journal   (Followers: 45, 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: 250, SJR: 2.255, h-index: 171)
American J. of Ophthalmology     Hybrid Journal   (Followers: 57, SJR: 2.803, h-index: 148)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 5)
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: 25, SJR: 0.59, h-index: 45)
American J. of Pathology     Hybrid Journal   (Followers: 26, SJR: 2.653, h-index: 228)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 22, SJR: 2.764, h-index: 154)
American J. of Surgery     Hybrid Journal   (Followers: 34, SJR: 1.286, h-index: 125)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, 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: 57, SJR: 0.124, h-index: 9)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 11)
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: 4, SJR: 2.577, h-index: 7)
Analytica Chimica Acta     Hybrid Journal   (Followers: 37, SJR: 1.548, h-index: 152)
Analytical Biochemistry     Hybrid Journal   (Followers: 167, SJR: 0.725, h-index: 154)
Analytical Chemistry Research     Open Access   (Followers: 8, SJR: 0.18, h-index: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 11)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 1)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 22, 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: 160, 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   (Followers: 1, 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  [3043 journals]
  • Effects of thermal cycles on the microstructure evolution of Inconel 718
           during selective laser melting process
    • Authors: Xiaoqing Wang; Kevin Chou
      Pages: 1 - 14
      Abstract: Publication date: December 2017
      Source:Additive Manufacturing, Volume 18
      Author(s): Xiaoqing Wang, Kevin Chou
      A staircase Inconel 718 block was fabricated to investigate the effects of the thermal cycles on the microstructure evolution in the selective laser melting (SLM) part using optical scope (OM), scanning electron microscope (SEM), and electron backscatter diffraction (EBSD). The laser beam scanning strategy was clearly shown in the part under OM, including laser scanning pattern and hatch spacing. The Y-plane (side surface) was characterized by elongated colonies of cellular dendrites with an average cell spacing of 0.511∼0.845μm. In addition, Laves phase was observed in the inter-layers and inter-cellular regions. Under the continuing effects of the thermal cycles, the fraction of the Laves-phase showed a significant drop with their morphology changing from coarse and interconnected particles to discrete Laves phase. This is attributed to the reheating process as Laves phase can be dissolved at a proper heat treatment. In terms of the width of the cellular dendrites, the longer the thermal cycle period is, the coarser the elongated grains are. Due to the preferred orientation of the crystal, the Y-plane and Z-plane had a strong texture of < 1 0 1> and < 0 0 1>, respectively. With the repeating thermal cycle period elongating, the maximum intensity of the texture, together with the fraction of larger grains and the high misorientation angles, increased. At the same height, there was no significant changes with the grains size, but the fraction of the high misorientation angles (>15°) increased with the subsequent building of the part. Moreover, the area fraction of the porosity was below 0.2%, with no remarkable effects found from the thermal cycles and the build height.

      PubDate: 2017-09-10T11:51:53Z
      DOI: 10.1016/j.addma.2017.08.016
      Issue No: Vol. 18 (2017)
  • The Impact of Print Orientation and Raster Pattern on Fracture Toughness
           in Additively Manufactured ABS
    • Authors: Tait D. McLouth; Joseph V. Severino; Paul M. Adams; Dhruv N. Patel; Rafael J. Zaldivar
      Pages: 103 - 109
      Abstract: Publication date: Available online 21 September 2017
      Source:Additive Manufacturing
      Author(s): Tait D. McLouth, Joseph V. Severino, Paul M. Adams, Dhruv N. Patel, Rafael J. Zaldivar
      Fused deposition modeling (FDM) has been gaining industrial interest due to its potential to simplify and lower the cost of complex manufacturing. To better understand the mechanical response of these materials—due to potential integration of FDM parts into structural components—compact tension samples of acrylonitrile butadiene styrene (ABS) were printed in three orthogonal orientations to analyze how the fracture toughness varied with mesostructure. Furthermore, in each of these orientations the raster pattern was either an alternating +45/−45° or a 0/90° pattern. When the alignment of extruded filament layers changed from parallel to perpendicular with respect to the crack plane, a 54% increase in fracture toughness was observed. However, the raster pattern only had a significant effect in one of the print orientations; the fracture toughness decreased by 11% when a 0/90° pattern was used in place of a +45/−45° pattern in layers oriented perpendicularly to the crack plane. The orientation of individual tracks of deposited material with respect to the crack tip appeared to have the most pronounced role in altering the fracture toughness of FDM ABS. This research provides useful information and insight to future designers determining how processing affects the crack stability of these new materials used for space hardware

      PubDate: 2017-09-28T02:18:11Z
      DOI: 10.1016/j.addma.2017.09.003
      Issue No: Vol. 18 (2017)
  • Slicer and process improvements for open-source GMAW-based metal 3-D
    • Authors: Yuenyong Nilsiam; Paul Sanders; Joshua M. Pearce
      Pages: 110 - 120
      Abstract: Publication date: December 2017
      Source:Additive Manufacturing, Volume 18
      Author(s): Yuenyong Nilsiam, Paul Sanders, Joshua M. Pearce
      Low-cost gas metal arc welding (GMAW)-based 3-D printing has proven effective at additive manufacturing steel and aluminum parts. Early success, however, was based on hand-writing G-code, which is inadequate for the majority of potential users. To enable automated slicing a 3-D model and generating G-code for an acceptable path for GMAW 3-D printing, this paper reports on upgrading of the free and open source CuraEngine. The new slicer, MOSTMetalCura, provides the following novel abilities necessary for GMAW 3-D printing: i) change the perimeter metric from width to track count, ii) avoid movement that overlaps previous weld beads, iii) have infill start immediately after the perimeter finished and in the direction that eliminates translations, iv) add a variable pause between layers to allow for substrate cooling, v) configure GPIO pins to turn on/off the welder, and vi) set optimized wire feed speed and voltage of the welder based on printing speed, layer height, filament diameter, and tool track width. The process for initiating these changes are detailed and the new slicer is used to help improve the function of the printer for ER70S-6 steel. To find the printing function with the smallest bead width based on volume of material, the line width, layer height, and printing speed are varied to provide wire feed speed calculated by MOSTMetalCura, then the settings are used to print 3-D models. The results of 3-D printing three case study objects of increasing geometric complexity using the process methodology improvements presented, which show resolution of 1mm bead widths.
      Graphical abstract image

      PubDate: 2017-10-12T13:48:19Z
      DOI: 10.1016/j.addma.2017.10.007
      Issue No: Vol. 18 (2017)
  • Multiphysical modeling of the heating phase in the polymer powder bed
           fusion process
    • Authors: Liu Xin; M’hamed Boutaous; Shihe Xin; Dennis A. Siginer
      Pages: 121 - 135
      Abstract: Publication date: December 2017
      Source:Additive Manufacturing, Volume 18
      Author(s): Liu Xin, M’hamed Boutaous, Shihe Xin, Dennis A. Siginer
      A numerical framework based on a modified Monte Carlo ray-tracing method and the Discrete Element Method (DEM) is developed to predict the physical behavior of discrete particles during the Powder Bed Fusion (SLS) process. A comprehensive model coupling all major aspects of the underlying physics and the corresponding numerical framework, accounting for radiative heat transfer, heat conduction, sintering and granular dynamics among others, is developed. In particular, the effect of scattering on the laser-particle interaction is investigated and accounted for in the numerical framework. The spatially and temporally varying distribution of heat and displacement within the additively manufactured object are captured in detail. The model is validated through the comparison of simulated results with existing experimental results in the literature.
      Graphical abstract image

      PubDate: 2017-10-12T13:48:19Z
      DOI: 10.1016/j.addma.2017.10.006
      Issue No: Vol. 18 (2017)
  • The effect of anisotropy on the optimization of additively manufactured
           lattice structures
    • Authors: Tino Stanković; Jochen Mueller; Kristina Shea
      Pages: 67 - 76
      Abstract: Publication date: October 2017
      Source:Additive Manufacturing, Volume 17
      Author(s): Tino Stanković, Jochen Mueller, Kristina Shea
      The build orientation is one the most influential factors on material properties in additively manufactured parts. Advanced applications, such as lattice structures optimized for lightweight, often rely on small safety margins and are, hence, particularly affected, but research has not gone far beyond the pure empirical characterization. The focus of this paper is to investigate in detail the influence of anisotropy induced through fabrication on the mechanical performance and build orientation of whole structures when subject to optimization. First, a material property model for both compression and tension states is formulated. Then, the Generalized Optimality Criteria method is extended for fixed topology lattice structures with respect to constraints in displacement, stress, and Euler buckling. The two latter are formulated as local constraints that are handled in combination with Fully-Stressed Design recursion. The results reveal significant safety threads likely leading to premature failure when using properties from one-directional tests, as is so far the case, rather than the full anisotropy model developed herein. If used inversely, the algorithm yields the optimal orientation of a structure on the build platform, allowing further weight reduction while maintaining the mechanical properties.

      PubDate: 2017-10-12T13:48:19Z
      DOI: 10.1016/j.addma.2017.07.004
      Issue No: Vol. 17 (2017)
  • Polymer recycling in an open-source additive manufacturing context:
           Mechanical issues
    • Authors: Fabio A. Cruz Sanchez; Hakim Boudaoud; Sandrine Hoppe; Mauricio Camargo
      Pages: 87 - 105
      Abstract: Publication date: October 2017
      Source:Additive Manufacturing, Volume 17
      Author(s): Fabio A. Cruz Sanchez, Hakim Boudaoud, Sandrine Hoppe, Mauricio Camargo
      Nowadays, the low recycling rate of polymers is still a challenge to humankind due to energy, economic and logistical issues. In the context of additive manufacturing, there is an exponential use of thermoplastic materials in the industrial and public open-source additive manufacturing sector, leading to an increase in global polymer consumption and waste generation. However, the coupling of the open-source 3D printers with polymer processing could potentially offer the basis for a new paradigm of distributed recycling process. It could be a complementary alternative to the traditional paradigm of centralized recycling of polymers, which is often uneconomical and energy intensive due to transportation embodied energy. In order to achieve this goal, a first step is to prove the technical feasibility to recycle thermoplastic material intended for open-source 3D printing feedstock. The contribution of the present study is twofold: first, a general methodology to evaluate the recyclability of thermoplastics used as feedstock in open-source 3D printing machines is proposed. Then, the proposed methodology is applied to the recycling study of polylactic acid (PLA) material addressed to the fused filament fabrication (FFF) technique, which is currently the most widely used. The main results of this application contribute to the understanding of the influence of the material's physico-chemical degradation on its mechanical properties as well as its potential distributed recyclability.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.05.013
      Issue No: Vol. 17 (2017)
  • The origins for tensile properties of selective laser melted aluminium
           alloy A357
    • Authors: Jeremy H. Rao; Yong Zhang; Xiya Fang; Yu Chen; Xinhua Wu; Chris H.J. Davies
      Pages: 113 - 122
      Abstract: Publication date: October 2017
      Source:Additive Manufacturing, Volume 17
      Author(s): Jeremy H. Rao, Yong Zhang, Xiya Fang, Yu Chen, Xinhua Wu, Chris H.J. Davies
      In this work the tensile behaviour of selective laser melted (SLMed) aluminium alloy A357 in the as-fabricated and heat-treated states is explained using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and transmission electron backscatter diffraction (t-EBSD). The as-built sample has an ultrafine microstructure, with high residual stresses and non-equilibrium solid solute concentration of Si in the supersaturated Al matrix. Consequently, the tensile properties of the SLMed Al alloy A357 are comparable or better than traditional cast counterparts. The Al grains in the SLMed alloy consist of sub-micron sized Al cells, and both high angle and low angle boundaries are initially occupied by eutectic nano-sized Si particles, which are beneficial for strength but detrimental for ductility. With subsequent solution heat treatment, the Si particles on the low angle cell boundaries (LACBs) dissolve while those at the high angle grain boundaries (HAGBs) coarsen. Simultaneously internal stresses decrease, as does solute content in the matrix. The evolution of these microstructural features explains the improved tensile ductility (at its maximum >23%) and reduced tensile strength for the heat treated SLMed aluminium alloy A357 samples.
      Graphical abstract image

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.007
      Issue No: Vol. 17 (2017)
  • Residual stress measurements on AISI 316L samples manufactured by
           selective laser melting
    • Authors: Thomas Simson; Andreas Emmel; Anja Dwars; Juliane Böhm
      Pages: 183 - 189
      Abstract: Publication date: October 2017
      Source:Additive Manufacturing, Volume 17
      Author(s): Thomas Simson, Andreas Emmel, Anja Dwars, Juliane Böhm
      This paper aims to understand the formation and the effect of residual stress on selective laser melting (SLM) parts. SLM is a powder bed based additive manufacturing (AM) process and can be compared to a laser welding process. Due to the high temperature gradients and the densification ratio, which are characteristic of this process, residual stresses occur. The investigation of residual stress is performed using X-ray diffraction (XRD) for samples made of austenitic stainless steel AISI 316L (EN 1.4404). This research examines residual stress at different depths and at two outer surfaces. For the measurement of stresses at different depths, the samples’ surface layers were removed by electropolishing. At sufficiently large distances from the top surface, the stresses in the area of the edge layer initially increase strongly and then decline again. The value and orientation of the resulting main stress components are dependent on the examined layer. At the top surface, the residual stresses are higher in scan direction than in perpendicular direction. In contrast, at the lateral surface the maximum main stress is perpendicular to the scan and parallel to the building direction. These two cases can be described very well by the two mechanisms in SLM, namely the temperature gradient mechanism (TGM) and the cool-down phase. It is also shown that at samples with a relative structural density of >99%, the residual stress values are independent of the applied energy density.

      PubDate: 2017-09-16T12:00:18Z
      DOI: 10.1016/j.addma.2017.07.007
      Issue No: Vol. 17 (2017)
  • Experimental investigation of creep deformation of part processed by fused
           deposition modeling using definitive screening design
    • Authors: Omar Ahmed Mohamed; Syed Hasan Masood; Jahar Lal Bhowmik
      Abstract: Publication date: Available online 10 October 2017
      Source:Additive Manufacturing
      Author(s): Omar Ahmed Mohamed, Syed Hasan Masood, Jahar Lal Bhowmik
      Fused deposition modeling (FDM) is shown to be a future-oriented technology. In this study, short-term creep deformation of PC-ABS parts created by FDM under different fabrication conditions was investigated using a recently innovative class of experimental design − definitive screening design (DSD) − along with graphical analysis. Short-term creep experiments were conducted at prescribed combinations of FDM operating conditions, namely layer thickness, air gap, raster angle, build orientation, road width and number of contours, as per DSD matrix. The results have shown that layer thickness, number of contours, raster angle and build orientation have a major effect on the creep rate of the parts. However, road width and air gap have least impact on the creep rate of FDM processed prototypes.

      PubDate: 2017-10-12T13:48:19Z
      DOI: 10.1016/j.addma.2017.10.013
  • Vacuum-filling of liquid metals for 3D printed RF antennas
    • Authors: Vivek Bharambe; Dishit P. Parekh; Collin Ladd; Khalil Moussa; Michael D. Dickey; Jacob J. Adams
      Abstract: Publication date: Available online 10 October 2017
      Source:Additive Manufacturing
      Author(s): Vivek Bharambe, Dishit P. Parekh, Collin Ladd, Khalil Moussa, Michael D. Dickey, Jacob J. Adams
      This paper describes a facile method to fabricate complex three-dimensional (3D) antennas by vacuum filling gallium-based liquid metals into 3D printed cavities at room temperature. To create the cavities, a commercial printer co-prints a sacrificial wax-like material with an acrylic resin. Dissolving the printed wax in oil creates cavities as small as 500μm within the acrylic monolith. Placing the entire structure under vacuum evacuates most of the air from these cavities through a reservoir of liquid metal that covers a single inlet. Returning the assembly to atmospheric pressure pushes the metal from the reservoir into the cavities due to the pressure differential. This method enables filling of the closed internal cavities to create planar and curved conductive 3D geometries without leaving pockets of trapped air that lead to defects. An advantage of this technique is the ability to rapidly prototype 3D embedded antennas and other microwave components with metallic conductivity at room temperature using a simple process. Because the conductors are liquid, they also enable the possibility of manipulating the properties of such devices by flowing metal in or out of selected cavities. The measured electrical properties of fabricated devices match well to electromagnetic simulations, indicating that the approach described here forms antenna geometries with high fidelity. Finally, the capabilities and limitations of this process are discussed along with possible improvements for future work.

      PubDate: 2017-10-12T13:48:19Z
      DOI: 10.1016/j.addma.2017.10.012
  • Finite Element Mesh Coarsening for Effective Distortion Prediction in Wire
           Arc Additive Manufacturing
    • Authors: Filippo Montevecchi; Giuseppe Venturini; Niccolò Grossi; Antonio Scippa; Gianni Campatelli
      Abstract: Publication date: Available online 9 October 2017
      Source:Additive Manufacturing
      Author(s): Filippo Montevecchi, Giuseppe Venturini, Niccolò Grossi, Antonio Scippa, Gianni Campatelli
      WAAM (Wire Arc Additive Manufacturing) is a metal AM (Additive Manufacturing) technology that allows high deposition rates and the manufacturability of very large components, compared to other AM technologies. Distortions and residual stresses affecting the manufactured parts represent the main drawbacks of this AM technique. FE (Finite Element) modeling could represent an effective tool to tackle such issues, since it can be used to optimize process parameters, deposition paths and to test alternative mitigation strategies. Nevertheless, specific modeling strategies are needed to reduce the computational cost of the process simulation, such as reducing the number of elements used in discretizing the model. This paper presents an alternative technique to reduce the number of elements required to discretize the substrates of WAAM workpieces. The proposed technique is based on dividing the substrate in several zones, separately discretized and then connected by means of a double sided contact algorithm. This strategy allows to achieve a significant reduction of the number of elements required, without affecting their quality parameters. The geometry and dimension of the mesh zones are identified through a dedicated algorithm that allows to achieve an accurate temperature prediction with the minimum element number. The effectiveness of the proposed technique was tested by means of both numerical and experimental validation tests.

      PubDate: 2017-10-12T13:48:19Z
      DOI: 10.1016/j.addma.2017.10.010
  • Assessing the effect of TIG alternating current time cycle on aluminium
           wire + arc additive manufacture
    • Authors: K.F. Ayarkwa; S.W. Williams; J. Ding
      Abstract: Publication date: Available online 9 October 2017
      Source:Additive Manufacturing
      Author(s): K.F. Ayarkwa, S.W. Williams, J. Ding
      The effect of electrode positive time cycle (% EP) of the alternating current TIG process has been investigated for aluminium wire+arc additive manufacture of linear walls. The study considered the effect on oxide removal, linear wall dimensions, microstructure, mechanical properties as well as the effect on electrode wear. The results showed that the effective wall width was minimum at 20%EP with a corresponding maximum in layer height. It was also observed that increasing the % EP increased the electrode wear rate, which in turn affected the arc stability. Microstructure analysis showed a noticeable increase in the grain size for higher % EP. The study also showed that % EP had no significant effect on mechanical properties. From a heat input analysis, a direct correlation was observed between the arc voltage and the % EP. The study also indicated that there could be other contributing factors to wall dimensions. For aluminium wire+arc additive manufacture of linear walls, minimum cleaning ranged between 10%EP and 20%EP.

      PubDate: 2017-10-12T13:48:19Z
      DOI: 10.1016/j.addma.2017.10.005
  • Measuring UV Curing Parameters of Commercial Photopolymers used in
           Additive Manufacturing
    • Authors: Joe Bennett
      Abstract: Publication date: Available online 9 October 2017
      Source:Additive Manufacturing
      Author(s): Joe Bennett
      A testing methodology was developed to expose photopolymer resins and measure the cured material to determine two key parameters related to the photopolymerization process: Ec (critical energy to initiate polymerization) and Dp (penetration depth of curing light). Five commercially available resins were evaluated under exposure from 365nm and 405nm light at varying power densities and energies. Three different methods for determining the thickness of the cured resin were evaluated. Caliper measurements, stylus profilometry, and confocal laser scanning microscopy showed similar results for hard materials while caliper measurement of a soft, elastomeric material proved inaccurate. Working curves for the five photopolymers showed unique behavior both within and among the resins as a function of curing light wavelength. Ec and Dp for the five resins showed variations as large as 10x. Variations of this magnitude, if unknown to the user and not controlled for, will clearly affect printed part quality. This points to the need for a standardized approach for determining and disseminating these, and perhaps, other key parameters.

      PubDate: 2017-10-12T13:48:19Z
      DOI: 10.1016/j.addma.2017.10.009
  • Impact of intermediate UV curing and yield stress of 3D printed
           poly(ethylene glycol) diacrylate hydrogels on interlayer connectivity and
           maximum build height
    • Authors: Adrian Hiller; Kirsten Borchers E.M. Tovar Alexander Southan
      Abstract: Publication date: Available online 6 October 2017
      Source:Additive Manufacturing
      Author(s): Adrian Hiller, Kirsten Borchers, Günter E.M. Tovar, Alexander Southan
      Extrusion-based 3D printing of photo-curable hydrogel materials can be used for the generation of complex objects layer by layer without the need for molds. Photo-curing often is the final step of the 3D printing process, fixing the shape of the generated object. However, the fabricated objects have to support themselves before curing, limiting the size of the objects. In this contribution, intermediate curing after completing each individual layer with poly(ethylene glycol) diacrylate as a radically curing hydrogel system was investigated compared with single curing of the whole structure after complete layered deposition, and its effect on the mechanical properties and achievable object size was assessed. Defect-free hydrogel samples for mechanical testing were obtained with an optimized washing/swelling protocol. It was found that hydrogel objects cured after completion without intermediate curing steps had the highest fracture stresses and compression at break with 32.5 N cm−2 and 44%, respectively. With increasing intermediate curing time, both the fracture stress and the compression at break decreased down to 7.8 N cm−2 and 26%, respectively, for 5s intermediate curing. Long intermediate curing times between the layers lead to preferred crack formation parallel to the layers due to decreased chemical bonding. However, the formation of higher hydrogel objects than enabled by the yield stress of the hydrogel was only possible with intermediate curing due to the better self-support of partially cured objects.

      PubDate: 2017-10-06T11:27:37Z
  • Natural Frequency Optimization of 3D Printed Variable-Density Honeycomb
           Structure via a Homogenization-Based Approach
    • Authors: Xue Wang; Pu Zhang; Stephen Ludwick; Eric Belski; Albert C. To
      Abstract: Publication date: Available online 2 October 2017
      Source:Additive Manufacturing
      Author(s): Xue Wang, Pu Zhang, Stephen Ludwick, Eric Belski, Albert C. To
      It is well-known that the effective mechanical properties of cellular structures can be tuned by varying its relative density. With the advancement of 3D printing, variable-density cellular structures can be fabricated with high precision using this emerging manufacturing technology. Taking advantage of this unique ability to fabricate variable-density cellular structure, an efficient homogenization-based topology optimization method for natural frequency optimization is presented in this work. The method is demonstrated using a cantilevered plate with a honeycomb structure and is validated by detailed finite element analysis and experiment. It is shown that the optimal design can be fabricated by 3D printing and shows significant enhancement in natural frequency and reduction in weight.

      PubDate: 2017-10-06T11:27:37Z
      DOI: 10.1016/j.addma.2017.10.001
  • 3D Printing Electronic Components and Circuits with Conductive
           Thermoplastic Filament
    • Authors: Patrick F. Flowers; Christopher Reyes; Shengrong Ye; Myung Jun Kim; Benjamin J. Wiley
      Abstract: Publication date: Available online 2 October 2017
      Source:Additive Manufacturing
      Author(s): Patrick F. Flowers, Christopher Reyes, Shengrong Ye, Myung Jun Kim, Benjamin J. Wiley
      This work examines the use of dual-material fused filament fabrication for 3D printing electronic components and circuits with conductive thermoplastic filaments. The resistivity of traces printed from conductive thermoplastic filaments made with carbon-black, graphene, and copper as conductive fillers was found to be 12, 0.78, and 0.014ohmcm, respectively, enabling the creation of resistors with values spanning 3 orders of magnitude. The carbon black and graphene filaments were brittle and fractured easily, but the copper-based filament could be bent at least 500 times with little change in its resistance. Impedance measurements made on the thermoplastic filaments demonstrate that the copper-based filament had an impedance similar to a copper PCB trace at frequencies greater than 1MHz. Dual material 3D printing was used to fabricate a variety of inductors and capacitors with properties that could be predictably tuned by modifying either the geometry of the components, or the materials used to fabricate the components. These resistors, capacitors, and inductors were combined to create a fully 3D printed high-pass filter with properties comparable to its conventional counterparts. The relatively low impedance of the copper-based filament enable its use to 3D print a receiver coil for wireless power transfer. We also demonstrate the ability to embed and connect surface mounted components in 3D printed objects with a low-cost ($1,000 in parts), open source dual-material 3D printer. This work thus demonstrates the potential for FFF 3D printing to create complex, three-dimensional circuits composed of either embedded or fully-printed electronic components.

      PubDate: 2017-10-06T11:27:37Z
      DOI: 10.1016/j.addma.2017.10.002
  • Location Specific Solidification Microstructure Control in Electron Beam
           Melting of Ti-6Al-4V
    • Authors: Sneha P. Narra; Ross Cunningham; Jack Beuth; Anthony D. Rollett
      Abstract: Publication date: Available online 2 October 2017
      Source:Additive Manufacturing
      Author(s): Sneha P. Narra, Ross Cunningham, Jack Beuth, Anthony D. Rollett
      Relationships between prior beta grain size in solidified Ti-6Al-4V and melting process parameters in the Electron beam melting (EBM) process are investigated. Samples were built by varying a machine-dependent proprietary speed function to cover the process space. Optical microscopy was used to measure the prior beta grain widths and assess the number of prior beta grains present in a melt pool in the raster region of the build. Despite the complicated evolution of beta grain sizes in solid parts, beta grain width scales with melt pool width. The resulting understanding of the relationship between primary machine variables and prior beta grain widths is a key step toward enabling the location specific control of as-built microstructure in the EBM process. Control of grain width in separate specimens and within a single specimen is demonstrated.

      PubDate: 2017-10-06T11:27:37Z
      DOI: 10.1016/j.addma.2017.10.003
  • Numerical modelling and experimental validation in Selective Laser Melting
    • Authors: Michele Chiumenti; Eric Neiva; Emilio Salsi; Miguel Cervera; Santiago Badia; Joan Moya; Zhuoer Chen; Caroline Lee; Christopher Davies
      Abstract: Publication date: Available online 22 September 2017
      Source:Additive Manufacturing
      Author(s): Michele Chiumenti, Eric Neiva, Emilio Salsi, Miguel Cervera, Santiago Badia, Joan Moya, Zhuoer Chen, Caroline Lee, Christopher Davies
      In this work a finite-element framework for the numerical simulation of the heat transfer analysis of additive manufacturing processes by powder-bed technologies, such as Selective Laser Melting, is presented. These kind of technologies allow for a layer-by-layer metal deposition process to cost-effectively create, directly from a CAD model, complex functional parts such as turbine blades, fuel injectors, heat exchangers, medical implants, among others. The numerical model proposed accounts for different heat dissipation mechanisms through the surrounding environment and is supplemented by a finite-element activation strategy, based on the born-dead elements technique, to follow the growth of the geometry driven by the metal deposition process, in such a way that the same scanning pattern sent to the numerical control system of the AM machine is used. An experimental campaign has been carried out at the Monash Centre for Additive Manufacturing using an EOSINT-M280 machine where it was possible to fabricate different benchmark geometries, as well as to record the temperature measurements at different thermocouple locations. The experiment consisted in the simultaneous printing of two walls with a total deposition volume of 107cm3 in 992 layers and about 33,500s build time. A large number of numerical simulations have been carried out to calibrate the thermal FE framework in terms of the thermophysical properties of both solid and powder materials and suitable boundary conditions. Furthermore, the large size of the experiment motivated the investigation of two different model reduction strategies: exclusion of the powder-bed from the computational domain and simplified scanning strategies. All these methods are analysed in terms of accuracy, computational effort and suitable applications.

      PubDate: 2017-09-28T02:18:11Z
      DOI: 10.1016/j.addma.2017.09.002
  • Efficient predictive model of part distortion and residual stress in
           selective laser melting
    • Authors: C. Li; J.F. Liu; X.Y. Fang; Y.B. Guo
      Abstract: Publication date: Available online 21 September 2017
      Source:Additive Manufacturing
      Author(s): C. Li, J.F. Liu, X.Y. Fang, Y.B. Guo
      Selective laser melting (SLM) is a promising technology to manufacture functional (end-use) metal parts with complex geometry directly from CAD data. The process induced high tensile residual stress and part distortion due to the non-uniform heat input during a SLM process would detrimentally affect the part performance. However, it is extremely challenging to predict distortion of a practical SLMed part if each single track is taken into account by using the conventional modeling methods The complex multiphysics phenomenon such as fluid flow in the melt pool, phase transformation during cooling, and resulted anisotropic properties further complicate this issue. In this study, a temperature-thread multiscale modeling approach has been developed to effectively predict residual stress and part distortion of a twin cantilever. An equivalent body heat flux has been proposed from the microscale laser scan model and imported as the “temperature-thread” to the subsequent mesoscale layer hatch model. The hatched layer is then heated up by the equivalent body heat flux and used as a basic unit to build up the macroscale part in a layer by layer fashion. The thermal history and residual stress fields of the twin cantilever during the SLM process were simulated. The predicted cantilever distortion agrees with the measured data with a reasonable accuracy.
      Graphical abstract image

      PubDate: 2017-09-28T02:18:11Z
      DOI: 10.1016/j.addma.2017.08.014
  • Topology optimization for additivemanufacturing: accounting for overhang
           limitations using a virtual skeleton
    • Authors: Yoram Mass; Oded Amir
      Abstract: Publication date: Available online 14 September 2017
      Source:Additive Manufacturing
      Author(s): Yoram Mass, Oded Amir
      This article proposes a new method for reducing the amount of support material required for 3-D printing of complex designs generated by topology optimization. This procedure relies on solving sequentially two structural optimization problems – the first on a discrete truss-based model and the second on a continuum-based model. In the optimization of the discrete model, the maximum overhang limitation is imposed based on geometrical parameters. The optimized discrete pattern is then projected on to the continuum so that it influences the material distribution in the continuum optimization. The method is explained and investigated on a set of test cases in 2-D and subsequently demonstrated on examples in 3-D. Numerical results indicate that the designs obtained by this approach exhibit improved printability as they have fewer overhanging features. In some cases, practically no supporting material will be required for printing the optimized design.

      PubDate: 2017-09-16T12:00:18Z
      DOI: 10.1016/j.addma.2017.08.001
  • Ultrafast 3D High Precision Print of Micro Structures for Optical
           Instrument Calibration Procedures
    • Authors: Felix Ströer; Julian Hering; Matthias Eifler; Indek Raid; Georg von Freymann; Jörg Seewig
      Abstract: Publication date: Available online 9 September 2017
      Source:Additive Manufacturing
      Author(s): Felix Ströer, Julian Hering, Matthias Eifler, Indek Raid, Georg von Freymann, Jörg Seewig
      Multi-photon polymerization, like the so-called direct laser writing (DLW) technique allows for flexible additive manufacturing of three-dimensional ultra-precise structures on the micro- and nanoscale. A possible application for DLW is the manufacturing of measurement standards for calibration procedures of optical measurement instruments. This requires flexible and high precision manufacturing of individualized geometries with high quality surfaces. However, many of the process parameters in DLW have to be selected based on experience and previous knowledge. In this article, the influence of DLW process parameters on the micro-geometry and surface roughness produced are systematically studied, and optimized in terms of printing speed and manufacturing accuracy. Resulting microstructures are being evaluated with different measurement techniques, i. e., a stylus instrument, SEM and AFM. Based on optimized process parameters, a new measurement standard for the novel interferometric measurement instrument Ellipso-Height-Topometer is manufactured and examined as a case study. As a result, it can be shown, that DLW is able to manufacture ultra-precise micro geometries in a very flexible and very fast way and satisfies the tolerances for manufacturing of the designed measurement standard.

      PubDate: 2017-09-10T11:51:53Z
      DOI: 10.1016/j.addma.2017.09.001
  • On the effect of throughout layer thickness variation on properties of
           additively manufactured cellular titanium structures
    • Authors: Esmat Sheydaeian; Zachary Fishman; Mihaela Vlasea; Ehsan Toyserkani
      Abstract: Publication date: Available online 8 September 2017
      Source:Additive Manufacturing
      Author(s): Esmat Sheydaeian, Zachary Fishman, Mihaela Vlasea, Ehsan Toyserkani
      Over the past two decades, additive manufacturing has opened a new window of opportunities in fabricating complex porous matrix structures such as cellular solids. Several factors including design, material and process parameters can selectively be varied to tailor the porous properties of products based on the intended application. This article addresses the effect of variable throughout layer thickness configuration in the binder-jet additive manufacturing of titanium structures for orthopedic applications. Two layer thicknesses of 80 and 150μm are selectively controlled inside of each titanium sample with four different configurations. Several studies were performed, including shrinkage analysis, porosity measurements, and mechanical compression tests to quantify the effect of layer thickness on part quality and mechanical properties. The results of the porosity measurement revealed that there is about 5% variation among the samples with different layer thickness configuration. Bulk porosity values obtained from micro computed tomography (μCT) scan data placed the bulk porosity of the samples combining more than one layer thickness, in between of the results for control specimens, which were manufactured by applying a single layer thickness throughout the samples. Mechanical properties did not show any significant variation, which is attributed to the low range of the porosity deviation (less than 5%). The highest Young’s modulus of 3.50±0.4GPa and yield stress of 175±25MPa were obtained from analysis of the data achieved from the compression test.

      PubDate: 2017-09-10T11:51:53Z
      DOI: 10.1016/j.addma.2017.08.017
  • Digital light processing 3D printing of conductive complex structures
    • Authors: Quanyi Mu; Lei Wang; Conner K. Dunn; Xiao Kuang; Feng Duan; Zhong Zhang; H. Jerry Qi; Tiejun Wang
      Abstract: Publication date: Available online 6 September 2017
      Source:Additive Manufacturing
      Author(s): Quanyi Mu, Lei Wang, Conner K. Dunn, Xiao Kuang, Feng Duan, Zhong Zhang, H. Jerry Qi, Tiejun Wang
      3D printing has gained significant research interest recently for directly manufacturing 3D components and structures for use in a variety of applications. In this paper, a digital light processing (DLP®) based 3D printing technique was explored to manufacture electrically conductive objects of polymer nanocomposites. Here, the ink was made of a mixture of photocurable resin with multi-walled carbon nanotubes (MWCNTs). The concentrations of MWCNT as well as the printing parameters were investigated to yield optimal conductivity and printing quality. We found that 0.3wt% loading of MWCNT in the resin matrix can provide the maximum electrical conductivity of 0.027S/m under the resin viscosity limit that allows high printing quality. With electric conductivity, the printed MWCNT nanocomposites can be used as smart materials and structures with strain sensitivity and shape memory effect. We demonstrate that the printed conductive complex structures as hollow capacitive sensor, electrically activated shape memory composites, stretchable circuits, showing the versatility of DLP® 3D printing for conductive complex structures. In addition, mechanical tests showed that the addition of MWCNT could slightly increase the modulus and ultimate tensile stress while decreasing slightly the ultimate stretch, indicating that the new functionality is not obtained at the price of sacrificing mechanical properties.

      PubDate: 2017-09-10T11:51:53Z
      DOI: 10.1016/j.addma.2017.08.011
  • Continuous lattice fabrication of ultra-lightweight composite structures
    • Authors: Martin Eichenhofer; Joanna C.H. Wong; Paolo Ermanni
      Abstract: Publication date: Available online 1 September 2017
      Source:Additive Manufacturing
      Author(s): Martin Eichenhofer, Joanna C.H. Wong, Paolo Ermanni
      This paper introduces continuous lattice fabrication (CLF) – a novel additive manufacturing (AM) technique invented for fiber-reinforced thermoplastic composites – and demonstrates its ability to exploit anisotropic material properties in digitally fabricated structures. In contrast to the layer-by-layer approaches employed in most AM processes, CLF enables the directed orientation of the fibers in all spatial coordinates, that is in the x-, y-, and z-directions. Based on a serial pultrusion and extrusion approach, CLF consolidates commingled yarns in situ and allows for the continuous deposition of high fiber volume fraction (>50%) materials along a programmable trajectory without the use of molds or sacrificial layers by exploiting the high viscosities of fiber-filled polymer melts. The capacity of CLF to produce high-performance structural components is demonstrated in the fabrication of an ultra-lightweight load-bearing lattice structure with outstanding stiffness-to-density and strength-to-density performance (compression modulus of 13.2MPa and compressive strength of 0.20MPa at a core density of 9mg/cm3). This digital fabrication method enables new approaches in load-tailored design, including the possibility to build freeform structures, which have previously been overlooked due to difficulties and limitations in modern fiber composite manufacturing capabilities.
      Graphical abstract image

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.013
  • Additive Manufacturing of Multifunctional Reactive Materials
    • Authors: Trevor J. Fleck; Allison K. Murray; I. Emre Gunduz; Steven F. Son; George T.-C Chiu; Jeffrey F. Rhoads
      Abstract: Publication date: Available online 1 September 2017
      Source:Additive Manufacturing
      Author(s): Trevor J. Fleck, Allison K. Murray, I. Emre Gunduz, Steven F. Son, George T.-C Chiu, Jeffrey F. Rhoads
      This paper demonstrates the ability to 3D print a fluoropolymer based energetic material which could be used as part of a multifunctional reactive structure. The work presented lays the technical foundation for the 3D printing of reactive materials using fusion based material extrusion. A reactive filament comprising of a polyvinylidene fluoride (PVDF) binder with 20% mass loading of aluminum (Al) was prepared using a commercial filament extruder and printed using a Makerbot Replicator 2X. Printing performance of the energetic samples was compared with standard 3D printing materials, with metrics including the bead-to-bead adhesion and surface quality of the printed samples. The reactivity and burning rates of the filaments and the printed samples were comparable. Differential scanning calorimetry and thermal gravimetric analysis showed that the onset temperature for the reactions was above 350°C, which is well above the operation temperature of both the filament extruder and the fused deposition printer.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.008
  • A systematic study on numerical simulation of electrified jet printing
    • Authors: A. Rahmat; B. Koc; M. Yildiz
      Abstract: Publication date: Available online 31 August 2017
      Source:Additive Manufacturing
      Author(s): A. Rahmat, B. Koc, M. Yildiz
      In this paper, a numerical model based on a systematic study of electrified jet printing is presented. The Volume of Fluid (VOF) method which suits for modeling multiphase flows with a continuous interface is used. The surface tension force is calculated with the Continuum Surface Force (CSF) method and the electric forces are added to the momentum equation by taking the divergence of the Maxwell stress tensor. A systematic study is carried out by introducing three dimensionless numbers, namely Reynolds, Electro-Weber and Weber numbers. Employing these dimensionless numbers, the number of effective parameters is reduced, and a relative comparison of the importance of competing forces on the process becomes possible. It is observed that the electric forces contribute to the formation of the jet by acting on its tip, and by pulling the jet towards the deposition surface. The results show that an increase in Reynolds and Electro-Weber numbers both lead to form a thinner jet. It is also observed that further increase in Electro-Weber and Reynolds numbers leads to the formation of an unstable jet.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.004
  • Partitioning of Laser Energy during Directed Energy Deposition
    • Authors: Frederick Lia; Joshua Park; Jay Tressler; Richard Martukanitz
      Abstract: Publication date: Available online 30 August 2017
      Source:Additive Manufacturing
      Author(s): Frederick Lia, Joshua Park, Jay Tressler, Richard Martukanitz
      An energy balance that describes the transfer of energy is proposed for the laser-based directed energy deposition process. The partitioning of laser energy was experimentally measured and accurately validated using a special process calorimeter for Ti-6Al-4V and Inconel 625™ alloys. The total energy provided by the laser was partitioned as: the energy directly absorbed by the substrate, the energy absorbed by the powder stream and deposited onto the substrate, the energy reflected from the substrate surface, and the energy reflected or absorbed and lost from the powder stream. Titanium alloy Ti-6Al-4V showed higher overall or bulk absorption than the Inconel 625™ alloy. Processing with powder resulted in lower laser energy absorption within the substrate than without powder, due to the “shadowing” effect of the powder stream within the beam and loss of energy representing unfused powder. During processing at a laser power of approximately 1kW the total energy absorbed during the deposition process was found to be 42% for the Ti-6Al-4V alloy and 37% for the Inconel 625™ alloy. Under these conditions 14% of the total energy was lost by the Ti-6Al-4V unfused powder; whereas only 11% was lost by the Inconel 625™ powder.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.012
  • On characterization of separation force for resin replenishment
           enhancement in 3D printing
    • Authors: D. Gritsenko; A.A. Yazdi; Y. Lin; V. Hovorka; Y. Pan; J. Xu
      Abstract: Publication date: Available online 30 August 2017
      Source:Additive Manufacturing
      Author(s): D. Gritsenko, A.A. Yazdi, Y. Lin, V. Hovorka, Y. Pan, J. Xu
      Additive Manufacturing (AM), which is also referred to as 3D Printing, is a class of manufacturing techniques that fabricate three dimensional (3D) objects by accumulating materials. Constrained Surface based Stereolithography is one of the most widely used AM techniques. In the process, a thin layer of liquid photosensitive resin is constrained between a constrained surface and the platform or part. The light penetrates the transparent constrained surface and cures that layer of liquid polymer. Then the platform is moved up to separate the newly cured layer to let new liquid resin fill into the gap and get cured. The separation of newly cured layer from the constrained surface is a grand challenge that limits the printable size and printing speed in this manufacturing technique. Numerous experimental work has been performed to understand how to reduce the separation force in the process. In this paper we study a new design of constrained surface with radial groove texture that significantly influences the effectiveness of reduction of the separation force and hence the manufacturing capability via theoretical modeling. In particular, we investigate an influence of grooves shape, grooves depth and the number of grooves on the separation force. The proposed model is validated with numerical simulations demonstrating an excellent agreement. We demonstrate the possibility of drastic reduction of the separation force (up to 112%) via surface texturing of the permeable window for continuous 3D printing.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.010
  • Study of Moineau-based pumps for the volumetric extrusion of pellets
    • Authors: Enrique Canessa; Marco Baruzzo; Carlo Fonda
      Abstract: Publication date: Available online 30 August 2017
      Source:Additive Manufacturing
      Author(s): Enrique Canessa, Marco Baruzzo, Carlo Fonda
      A volumetric, mini extruder for pellets or granules of recycled plastic that can be used in a RepRap FDM 3D printer for rapid prototyping is discussed. It combines a rotor of a Moineau progressing cavity pump coupled with an Auger screw, both contained inside a stator at high temperatures. The steer Auger portion is added to increase the pressure inside a helix stator container of n-lobes as a helical rotor is turned. A novel, alternative multi-layer Moineau-based pump −easier to build, implement and clean– is also introduced to extrude a quantity of viscous material in vertical direction.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.015
  • Electron beam melted scaffolds for orthopedic applications
    • Authors: Ibrahim Eldesouky; Ola Harrysson; Harvey West; Hassan Elhofy
      Abstract: Publication date: Available online 26 August 2017
      Source:Additive Manufacturing
      Author(s): Ibrahim Eldesouky, Ola Harrysson, Harvey West, Hassan Elhofy
      Ti6Al4 V porous scaffolds of two unit cell geometries (reentrant and cubic) were investigated as candidates for load-bearing biomedical applications. Samples were fabricated using an Arcam A2 electron beam melting (EBM) machine and evaluated for geometric deviation from the original CAD design using a digital optical microscope. The mass and bounding volume of each sample were also measured to calculate the resulting relative density. The scaffolds were loaded in compression in the build direction to determine the relative modulus of elasticity and ultimate compressive load. Experimental results were used to calculate the Gibson and Ashby relation parameters for the studied unit cell geometries. The results suggest that samples with the cubic unit cell geometries, with struts oriented at an angle of 45° to the loading direction, exhibited higher stiffness than samples with the reentrant unit cell geometry at equivalent relative densities. A cubic scaffold is verified to withstand high compressive loads (more than 71kN) while having an approximate pore size in the range of 0.6mm. These characteristics demonstrate its suitability for load bearing biomedical implants.
      Graphical abstract image

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.005
  • Anisotropic Mechanical Properties of Oriented Carbon Fiber Filled Polymer
           Composites Produced with Fused Filament Fabrication
    • Authors: Delin Jiang; Douglas E. Smith
      Abstract: Publication date: Available online 26 August 2017
      Source:Additive Manufacturing
      Author(s): Delin Jiang, Douglas E. Smith
      Fused Filament Fabrication (FFF) is a widely used Additive Manufacturing (AM) technique. Recently, mechanical properties of plastic FFF parts have been enhanced by adding short carbon fibers to the thermoplastic polymer filament to form a carbon fiber filled (CFF) polymer composite. Unfortunately, improvements to the material properties of commercially available CFF filament are not well understood. This paper presents a study of CFF FFF parts produced on desktop 3D printers using commercially available filament. Tensile test samples fabricated with CFF polymer composite and unfilled polymer were printed and then tested following ASTM D3039M. Test bars were printed with FFF bead orientations aligned with the direction of the applied load at 0degree, and also at 45 degrees, ±45 degrees, and normal to the loading axis at 90 degrees. The filament considered here was purchased from filament suppliers and included both CFF and unfilled PLA, ABS, PETG and Amphora. Results for tensile strength and tensile modulus show that CFF coupons in general yield higher tensile modulus at all print orientations and higher tensile strength at 0degree print orientation. The addition of carbon fiber was shown to decrease tensile strength for some materials when printed with beads not aligned with the loading direction. Additionally, CFF samples are evaluated for fiber length distribution (FLD) and fiber weight fraction, where it was found that the filament extrusion process contributes very little to fiber breakage. Finally, fracture surfaces evaluated under SEM show that voids between the beads are reduced with CFF coupons, and poor interfacial bonding between fibers and polymer become a prominent failure mechanism.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.006
  • Geometric Characterization of Additively Manufactured Polymer Derived
    • Authors: Jacob M. Hundley; Zak C. Eckel; Emily Schueller; Kenneth Cante; Scott M. Biesboer; Brennan D. Yahata; Tobias A. Schaedler
      Abstract: Publication date: Available online 26 August 2017
      Source:Additive Manufacturing
      Author(s): Jacob M. Hundley, Zak C. Eckel, Emily Schueller, Kenneth Cante, Scott M. Biesboer, Brennan D. Yahata, Tobias A. Schaedler
      The high hardness, melting temperature and environmental resistance of most ceramic materials makes them well-suited for propulsion, tribilogical and protective applications. However, these same attributes pose difficulties for manufacturing and machining of ceramics and ultimately limit the achievable design space of these materials. Recently, a new class of preceramic photopolymers has been developed that enables additive manufacturing of ceramics using commercially available stereolithography systems. By consolidating preceramic monomers via layer-wise exposure to ultraviolet light and subsequently pyrolyzing under an inert atmosphere to form a ceramic, this method allows for complex geometry parts that cannot be produced with traditional sintering, pressing or vapor infiltration processes. In order to retain geometric fidelity and generate flaw-free microstructures, volumetric and gravimetric changes during the polymer-to-ceramic conversion must be quantified. To this end, we present x-ray micro-computed tomography (micro-CT) measurements of the dimensional stability and uniformity of additively manufactured silicon-based ceramics as a function of geometry and processing conditions.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.009
  • Effect of powder oxidation on the impact toughness of electron beam
           melting Ti-6Al-4V
    • Authors: W.A. Grell; E. Solis-Ramos; E. Clark; E. Lucon; E.J. Garboczi; P.K. Predecki; Z. Loftus; M. Kumosa
      Abstract: Publication date: Available online 25 August 2017
      Source:Additive Manufacturing
      Author(s): W.A. Grell, E. Solis-Ramos, E. Clark, E. Lucon, E.J. Garboczi, P.K. Predecki, Z. Loftus, M. Kumosa
      Powder quality in additive manufacturing (AM) electron beam melting (EBM) of Ti-6Al-4V components is crucial in determining the critical material properties of the end item. In this study, we report on the effect of powder oxidation on the Charpy impact energy of Ti-6Al-4V parts manufactured using EBM. In addition to oxidation, the effects on impact energy due to hot isostatic pressing (HIP), specimen orientation, and EBM process defects were also investigated. This research has shown that excessive powder oxidation (oxygen mass fraction above 0.25% and up to 0.46%) dramatically decreases the impact energy. It was determined that the room temperature impact energy of the parts after excessive oxidation was reduced by about seven times. We also report that HIP post-processing significantly increases the impact toughness, especially for specimens with lower or normal oxygen content. The specimen orientation effect was found to be more significant for low oxidation levels.

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.002
  • In situ real time defect detection of 3D printed parts
    • Authors: Oliver Hammond; Xiaodong Li
      Abstract: Publication date: Available online 25 August 2017
      Source:Additive Manufacturing
      Author(s): Oliver Hammond, Xiaodong Li
      Additive manufacturing (AM) allows for the production of custom parts with previously impractical internal features, but comes with the additional possibility of internal defects due to print error, residual stress buildup, or cyber-attack by a malicious actor. Conventional post process analysis techniques have difficulty detecting these defects, often requiring destructive tests that compromise the integrity (and thus the purpose) of the part. Here, we present a “certify-as-you-build” quality assurance system with the capability to monitor a part during the print process, capture the geometry using three-dimensional digital image correlation (3D-DIC), and compare the printed geometry with the computer model to detect print errors in situ. A test case using a fused filament fabrication (FFF) 3D printer was implemented, demonstrating in situ error detection of localized and global defects.
      Graphical abstract image

      PubDate: 2017-09-04T03:24:05Z
      DOI: 10.1016/j.addma.2017.08.003
  • Thermal analysis of additive manufacturing of large-scale thermoplastic
           polymer composites
    • Authors: Brett G. Compton; Brian K. Post; Chad E. Duty; Lonnie Love; Vlastimil Kunc
      Abstract: Publication date: Available online 30 July 2017
      Source:Additive Manufacturing
      Author(s): Brett G. Compton, Brian K. Post, Chad E. Duty, Lonnie Love, Vlastimil Kunc
      The incremental deposition process utilized by most additive manufacturing (AM) technologies presents significant challenges related to residual stresses and warping which arise from repeated deposition of hot material onto cooler material. These issues are magnified at larger scale, where even a small thermal strain can correspond to several millimeters of deformation. In this work we investigate the thermal evolution in thin walls of carbon fiber/acrylonitrile butadiene styrene (CF/ABS) composite materials fabricated via Big Area Additive Manufacturing (BAAM). We measure the thermal evolution of composite parts during the build process using infrared imaging, and develop a simple 1D transient thermal model to describe the build process. The model predictions are in excellent agreement with the observed temperature profiles and from the results we develop criteria to guide deposition parameter selection to minimize the likelihood of cracking during printing.

      PubDate: 2017-08-04T12:05:36Z
      DOI: 10.1016/j.addma.2017.07.006
  • Functionally graded Ti6Al4V-Mo alloy manufactured with DED-CLAD®
    • Authors: Catherine Schneider-Maunoury; Laurent Weiss; Philippe Acquier; Didier Boisselier; Pascal Laheurte
      Abstract: Publication date: Available online 29 July 2017
      Source:Additive Manufacturing
      Author(s): Catherine Schneider-Maunoury, Laurent Weiss, Philippe Acquier, Didier Boisselier, Pascal Laheurte
      This paper presents the results of functionally graded Ti6Al4V-Mo alloy manufactured with directed energy deposition called CLAD® (Construction Laser Additive Direct) process. Single track width sample with five gradients of composition, from 0 to 100wt.%Mo, was manufactured using a coaxial nozzle. Both Ti6Al4V and Mo ratios were modified with a 25wt.% increase or decrease in the chemical composition of each gradient. A two-powder feeder was used to input the correct ratio of each powder, so as to obtain the desired chemical composition. XRD analysis allowed to define the phases present in each deposition, as well as the lattice parameter. SEM observations showed microstructural evolution from 25wt%Mo on, namely where the β-phase becomes dominant. Moreover, dendrites appear from 50wt.%Mo on. Microhardness analysis revealed variation along the deposition depending on the chemical composition. The homogeneity of the powder mixture under laser beam was highlighted thanks to tomography on the manufactured samples, which validates the processability of functionally graded material (FGM) by CLAD® process.

      PubDate: 2017-08-04T12:05:36Z
      DOI: 10.1016/j.addma.2017.07.008
  • On the Development of Antenna Feed Array for Space Applications by
           Additive Manufacturing Technique
    • Authors: S.S. Gill; Hemant Arora; Jidesh; Viren Sheth
      Abstract: Publication date: Available online 24 July 2017
      Source:Additive Manufacturing
      Author(s): S.S. Gill, Hemant Arora, Jidesh, Viren Sheth
      Space agencies are looking for advanced technologies to build light weight and stiff payload components to bear space environment and launch loads. Additive manufacturing (AM) techniques like Direct Metal Laser Sintering (DMLS) is one of the suitable option which can be explored for space applications. This paper highlights the development process of Antenna Feed Array (AFA) using DMLS as an Additive Manufacturing (AM) technique. A high efficiency horn element is used in the array. Such horns are preferred for this development as they are the prime choice for feed elements in High Throughput satellites (HTS) that employ Multibeam Antennas. A brief description of Multibeam antennas along with the RF design process for the high efficiency horn is presented. In the development process, certain design rules of AM are adopted based on consideration to produce self-sustaining structures. AFA realized by DMLS is evaluated by functional testing, vibration testing for space qualification test levels. Test results shows its structural intactness which proves its space worthiness. Procedures are very well established for further development of space payload components.

      PubDate: 2017-07-26T06:45:46Z
      DOI: 10.1016/j.addma.2017.06.010
  • Distortion Prediction and Compensation in Selective Laser Melting
    • Authors: Shukri Afazov; Willem A.D. Denmark; Borja Lazaro Toralles; Adam Holloway; Anas Yaghi
      Abstract: Publication date: Available online 23 July 2017
      Source:Additive Manufacturing
      Author(s): Shukri Afazov, Willem A.D. Denmark, Borja Lazaro Toralles, Adam Holloway, Anas Yaghi
      This paper presents a new approach for modelling additive layer manufacturing at component scale. The approach is applied to powder-bed selective laser melting (SLM) and validated, where the mechanical behaviour of macro-scale industrial components has been predicted and compared with experimental results. The novelty of the approach is based on using a calibrated analytical thermal model to derive functions that are implemented in a structural finite element analysis (FEA). The computational time for a complete analysis has been reduced from many days to less than three hours for a 3D blade component with a height of 80mm. The induced distortion in SLM has been compensated for by modifying the initial geometry using FE predicted distortion. A newly developed distortion compensation method, based on optical 3D scan measurements, has also been implemented. The two distortion compensation methods have been experimentally validated. In summary, the research presented in this paper shows that the mitigation of distortion in SLM is now possible on industrial macro-scale components.

      PubDate: 2017-07-26T06:45:46Z
      DOI: 10.1016/j.addma.2017.07.005
  • Hierarchical structures of stainless steel 316L manufactured by Electron
           Beam Melting
    • Authors: Lars-Erik Rännar; Andrey Koptyug; Jon Olsén; Kamran Saeidi; Zhijian Shen
      Abstract: Publication date: Available online 22 July 2017
      Source:Additive Manufacturing
      Author(s): Lars-Erik Rännar, Andrey Koptyug, Jon Olsén, Kamran Saeidi, Zhijian Shen
      One of the serious obstacles preventing wide industrial use of additive manufacturing (AM) in metals and alloys is a lack of materials available for this technology. It is particularly true for the Electron Beam Melting (EBM®) process, where only a few materials are commercially available, which significantly limits the use of the method. One of the dominant trends in AM today is developing processes for technological materials already widely used by other methods and developed for other industrial applications, gaining further advantages through the unique value added by additive manufacturing. Developing new materials specifically for additive manufacturing that can utilize the properties and specifics of the method in full is still a research and development subject, and such materials are yet far from full scale industrial usage. Stainless steels are widely used in industry due to good mechanical properties, corrosion resistance and low cost of material. Hence, there is potentially a market for this material and one possible business driver compared with casting for example is that lead times could be cut drastically by utilizing an additive approach for one-off or small series production. This paper presents results from the additive manufacturing of components from the known alloy 316L using EBM®. Previously the samples of 316L were made by laser-based AM technology. This work was performed as a part of the large project with the long term aim to use additively manufactured components in a nuclear fusion reactor. Components and test samples successfully made from 316L stainless steel using EBM® process show promising mechanical properties, density and hardness compared to its counterpart made by powder metallurgy (hot isostatic pressing, HIP). As with the other materials made by EBM® process, 316L samples show rather low porosity. Present paper also reports on the hierarchical microstructure features of the 316L material processed by EBM® characterized by optical and electron microscopy.

      PubDate: 2017-07-26T06:45:46Z
      DOI: 10.1016/j.addma.2017.07.003
  • Algorithm-driven design of fracture resistant composite materials realized
           through additive manufacturing
    • Authors: Grace X. Gu; Susan Wettermark; Markus J. Buehler
      Abstract: Publication date: Available online 20 July 2017
      Source:Additive Manufacturing
      Author(s): Grace X. Gu, Susan Wettermark, Markus J. Buehler
      Fracture, the breakdown of materials as cracks advance, is one of the most intriguing materials phenomena; it can happen even to very tough biological tissues including tendons, skin, bone and teeth, materials whose critical physiological functions can be compromised by structural irregularities. It has been suggested that creating composites by mixing heterogeneous constituents of contrasting material properties can yield designs that can better adapt to stress concentration, leading to synthetic materials with higher toughness than their constituents. Here, an optimization algorithm is used to assess material fracture resistance in the presence of a crack. The analysis is further extended through experiments that involve the use of additive manufacturing. Optimal solutions are composed solely of soft and stiff material elements, and are compared to various benchmarks. Multi-material three-dimensional-printing (3D-printing) is used to create material samples. Experimental results and mechanical testing show that an algorithmic design coupled with 3D-printing technology can generate morphologies of composites more than 20 times tougher than the stiffest base material, and more than twice as strong as the strongest base material. Direct comparison of strain fields around cracks shows excellent agreement between simulation and experiment. The results suggest that the systematic use of microstructure optimization to generate enhanced fracture resistance constitutes a new materials design paradigm.

      PubDate: 2017-07-26T06:45:46Z
      DOI: 10.1016/j.addma.2017.07.002
  • The Extrusion-based Additive Manufacturing of Moisture-Cured Silicone
           Elastomer with Minimal Void for Pneumatic Actuators
    • Authors: Jeffrey Plott; Albert Shih
      Abstract: Publication date: Available online 15 July 2017
      Source:Additive Manufacturing
      Author(s): Jeffrey Plott, Albert Shih
      The extrusion-based additive manufacturing (AM) of moisture-cured silicone elastomer with minimal voids and high strength, elongation, and fatigue life is presented. Due to the soft nature and extended cure time of moisture-cured silicone, AM is technically challenging. When each layer is deposited, it can compress and deform previous layers. This compression is exploited to prevent void formation in silicone AM. This research aims to explore process parameters for voidless silicone AM of solid and thin-wall structures for pneumatic actuators. Experiments were performed to study effects of flowrate, layer height, and distance between adjacent silicone lines on the solid and thin-wall vertical layer deformation and void generation. The results were then applied in AM of two thin-walled hollow silicone pneumatic parts: the sphere-like balloons and finger pneumatic actuators. The sphere-like balloons exhibited diametric expansion between 152 and 207% with burst stress between 1.46 and 2.55MPa (which is comparable to the base material properties) while the pneumatic finger actuators were able to fully articulate over 30,000 cycles before failure.

      PubDate: 2017-07-19T03:20:04Z
      DOI: 10.1016/j.addma.2017.06.009
  • Investigation of pore structure in cobalt chrome additively manufactured
           parts using X-ray computed tomography and three-dimensional image analysis
    • Authors: F.H. Kim; S.P. Moylan; E.J. Garboczi; J.A. Slotwinski
      Abstract: Publication date: Available online 15 July 2017
      Source:Additive Manufacturing
      Author(s): F.H. Kim, S.P. Moylan, E.J. Garboczi, J.A. Slotwinski
      Pore structures of additively manufactured metal parts were investigated with X-ray Computed Tomography (XCT). Disks made of a cobalt-chrome alloy were produced using laser-based powder bed fusion (PBF) processes. The additive manufacturing processing parameters (scan speed and hatch spacing) were varied in order to have porosities varying from 0.1% to 70% so as to see the effects of processing parameters on the formation of pores and cracks. The XCT images directly show three-dimensional (3D) pore structure, along with cracks. Qualitative visualization is useful; however, quantitative results depend on accurately segmenting the XCT images. Methods of segmentation and image analysis were carefully developed based, as much as possible, on aspects of the images themselves. These enabled quantitative measures of porosity, including how porosity varies in and across the build direction, pore size distribution, how pore structure varies between parts with similar porosity levels but different processing parameters, pore shape, and particle size distribution of un-melted powder trapped in pores. These methods could possibly serve as the basis for standard segmentation and image analysis methods for metallic additively manufactured parts, enabling accurate and reliable defect detection and quantitative measures of pore structure, which are critical aspects of qualification and certification.

      PubDate: 2017-07-19T03:20:04Z
      DOI: 10.1016/j.addma.2017.06.011
  • Effect of minor alloying elements on crack-formation characteristics of
           Hastelloy-X manufactured by selective laser melting
    • Authors: Dacian Tomus; Paul A. Rometsch; Martin Heilmaier; Xinhua Wu
      Abstract: Publication date: Available online 9 May 2017
      Source:Additive Manufacturing
      Author(s): Dacian Tomus, Paul A. Rometsch, Martin Heilmaier, Xinhua Wu
      Two batches of pre-alloyed Hastelloy-X powder with different Si, Mn and C contents were used to produce specimens by Selective Laser Melting (SLM). Cracks with various morphologies were found in some of the parts. Two major reasons that control crack formation and propagation were considered: (i) internal strain accumulation due to the thermal cycling that is characteristic to SLM processing; (ii) crack formation and propagation during solidification. This phenomenon, known as hot tearing, is frequently found in conventional casting and is dependent on chemical composition. Using thermodynamic software simulation, the temperature vs fraction of solid curves was used to determine hot tearing sensitivity as a function of Si, Mn and C content. It was found that low Si and C contents help in avoiding crack formation whereas cracking propensity was relatively independent of Mn concentration. Hence, the cracking mechanism during SLM is believed to be as follows: crack initiation is mainly induced during solidification and is dependent on the content of minor alloying elements such as Si and C, whereas crack propagation predominantly occurs during thermal cycling. If microstructures free of micro-cracks after solidification can be generated with optimised SLM parameters, these manufactured parts can sustain the internal strain level and, thus, crack formation and propagation can be avoided.

      PubDate: 2017-05-13T10:52:10Z
      DOI: 10.1016/j.addma.2017.05.006
  • Quantitative texture prediction of epitaxial columnar grains in additive
           manufacturing using selective laser melting
    • Authors: Jian Liu; Albert C. To
      Abstract: Publication date: Available online 5 May 2017
      Source:Additive Manufacturing
      Author(s): Jian Liu, Albert C. To
      Metal additive manufacturing (AM) such as selective laser melting (SLM) has the powerful capability to produce very different microstructural features, hence different mechanical properties in metals using the same feedstock material but different values of process parameters. However, the relation between processing-microstructure is mostly investigated by experiments, which is expensive and time-consuming since the parameter space is quite large. The lack of a reliable theoretical model of the processing-microstructure relationship of AM material is preventing AM technology from being widely adopted by the manufacturing community. Hence, the goal of this work is to establish the link between the microstructure (texture) and the process parameters (laser power, scanning speed, preheat and scanning strategy) of a metal SLM process. To achieve the above goal, a quantitative semi-empirical method is proposed to predict the texture of the epitaxial columnar grains grown from polycrystal substrates. Combined with the melt pool prediction by the Rosenthal solution, the processing and microstructure were linked together quantitatively. The proposed method is used to estimate the texture evolution with the number of layers for EOS-DMLS-processed AlSi10Mg (unidirectional scanning direction in one layer and no rotation of scanning direction between layers). The texture reaches a steady state after five layers, and the steady state texture has similar pattern and intensity to that obtained from the experiment using the same process parameter values and scanning strategy.

      PubDate: 2017-05-08T10:44:05Z
      DOI: 10.1016/j.addma.2017.05.005
  • Sub-wavelength Lithography of Complex 2D and 3D Nanostructures without
           Two-photon Dyes
    • Authors: Raghvendra P Chaudhary; Arun Jaiswal; Govind Ummethala; Suyog R Hawal; Sumit Saxena; Shobha Shukla
      Abstract: Publication date: Available online 3 May 2017
      Source:Additive Manufacturing
      Author(s): Raghvendra P Chaudhary, Arun Jaiswal, Govind Ummethala, Suyog R Hawal, Sumit Saxena, Shobha Shukla
      One-photon or two photon absorption by dye molecules in photopolymers enable direct 2D & 3D lithography of micro/nano structures with high spatial resolution and can be used effectively in fabricating artificially structured nanomaterials. However, the major bottleneck in unleashing the potential of this useful technique is the indispensable usage of dyes that are expensive, highly toxic and usually insoluble in commercially available photopolymers. Here we report a simple, inexpensive and one-step technique for direct-writing of micro/nanostructures, with sub-wavelength resolution at high speeds without using any one photon or two photon absorbing dye. We incorporated large amount (20 weight %) of inexpensive photoinitiator, which has not been done to best of our knowledge, into the photopolymer and utilized its two-photon absorbing property for sub-wavelength patterning. Complex 2D patterns and 3D meshes were fabricated with sub-micron resolution, in commercially available liquid photopolymer to show the impact/versatility of this technique.

      PubDate: 2017-05-08T10:44:05Z
      DOI: 10.1016/j.addma.2017.05.003
  • On the use of spatter signature for in-situ Monitoring of Laser Power Bed
    • Authors: Giulia Repossini; Vittorio Laguzza; Marco Grasso; Bianca Maria Colosimo
      Abstract: Publication date: Available online 3 May 2017
      Source:Additive Manufacturing
      Author(s): Giulia Repossini, Vittorio Laguzza, Marco Grasso, Bianca Maria Colosimo
      In-situ monitoring of metal additive manufacturing (AM) processes is a key issue to determine the quality and stability of the process during the layer-wise production of the part. The quantities that can be measured via in-situ sensing can be referred to as “process signatures”, and can represent the source of information to detect possible defects. Most of the literature on in-situ monitoring of Laser Power Bed Fusion (LPBF) processes focuses on the melt-pool, laser track and layer image as source of information to detect the onset of possible defects. Up to our knowledge, this paper represents a first attempt to investigate the suitability of including spatter-related information to characterize the LPBF process quality. High-speed image acquisition, coupled with image segmentation and feature extraction, is used to estimate different statistical descriptors of the spattering behaviour along the laser scan path. A logistic regression model is developed to determine the ability of spatter-related descriptors to classify different energy density conditions corresponding to different quality states. The results show that by including spatters as process signature driver, a significant increase of the capability to detect under-melting and over-melting conditions is observed. This is why future research on spatter signature analysis and modelling is highly encouraged to improve the effectiveness of in-situ monitoring tools.

      PubDate: 2017-05-08T10:44:05Z
      DOI: 10.1016/j.addma.2017.05.004
  • Finite Element Simulation and Experimental Validation of Distortion and
           Cracking Failure Phenomena in Direct Metal Laser Sintering Fabricated
    • Authors: Yi Zhang; Jing Zhang
      Abstract: Publication date: Available online 3 May 2017
      Source:Additive Manufacturing
      Author(s): Yi Zhang, Jing Zhang
      A new one-way coupled thermal-mechanical finite element based model of direct metal laser sintering (DMLS) is developed to simulate the process, and predict distortion and cracking failure location in the fabricated components. The model takes into account the layer-by-layer additive manufacturing features, solidification and melting phenomena. The model is first validated using experimental data, then model is applied to a DMLS fabricated component. The study shows how the stress distribution at the support-solid interface is critical to contributing to cracking and distortion. During the DMLS process, thermal stress at the support-solid interface reaches its maximum during the printing process, particularly when the first solid layer is built above the support layer. This result suggests that cracking at the interface may occur during the printing process, which is consistent with experimental observation. Using a design parametric study, a thick and low-density porous layer is found to reduce residual stress and distortion in the built component. The developed finite element model can be used to future design and optimize DMLS process.

      PubDate: 2017-05-08T10:44:05Z
      DOI: 10.1016/j.addma.2017.05.002
  • Compressive failure modes and energy absorption in additively manufactured
           double gyroid lattices
    • Authors: I. Maskery; N.T. Aboulkhair; A.O. Aremu; C.J. Tuck; I.A. Ashcroft
      Abstract: Publication date: Available online 3 May 2017
      Source:Additive Manufacturing
      Author(s): I. Maskery, N.T. Aboulkhair, A.O. Aremu, C.J. Tuck, I.A. Ashcroft
      Lattice structures are excellent candidates for lightweight, energy absorbing applications such as personal protective equipment. In this paper we explore several important aspects of lattice design and production by metal additive manufacturing, including the choice of cell size and the application of a post-manufacture heat treatment. Key results include the characterisation of several failure modes in double gyroid lattices made of Al-Si10-Mg, the elimination of brittle fracture and low-strain failure by the application of a heat treatment, and the calculation of specific energy absorption under compressive deformation (16×106 J m−3 up to 50% strain). These results demonstrate the suitability of double gyroid lattices for energy absorbing applications, and will enable the design and manufacture of more efficient lightweight parts in the future.

      PubDate: 2017-05-08T10:44:05Z
      DOI: 10.1016/j.addma.2017.04.003
  • Microstructured Monofilament via Thermal Drawing of Additively
           Manufactured Preforms
    • Authors: P.M. Toal; L.J. Holmes; R.X. Rodriguez; E.D. Wetzel
      Abstract: Publication date: Available online 29 April 2017
      Source:Additive Manufacturing
      Author(s): P.M. Toal, L.J. Holmes, R.X. Rodriguez, E.D. Wetzel
      A process is presented for the rapid production of microstructured monofilaments via thermal drawing of additively manufactured polymer preforms. Preforms are produced wholly, or in part, via fused filament fabrication of acrylonitrile-butadiene-styrene (ABS) and polycarbonate materials. The preforms are heated and drawn under tension to convert the preforms into lengths of monofilament that closely reproduce the geometric structure of the parent preform. Example monofilaments include “microprinted” monofilaments that contain an arbitrary image embedded in the monofilament cross section; microfluidic monofilaments in which flow channels are formed by combining optically transparent and opaque materials; dual-material monofilaments that combine ABS and polycarbonate into a regular spoked geometry with five-fold symmetry; and a microfluidic preform co-drawn with glass optical fiber, allowing both fluid and light transmission through the monofilament. The primary advantages of this monofilament fabrication technique include short lead times; minimal investment in materials and equipment; a means of directly combining multiple materials into a single monofilament, even if the material components have different thermorheological properties; and the ability to create arbitrary and complex geometries.

      PubDate: 2017-05-03T14:38:20Z
      DOI: 10.1016/j.addma.2017.03.009
  • 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
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