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Publisher: Elsevier   (Total: 3042 journals)

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Showing 1 - 200 of 3042 Journals sorted alphabetically
AASRI Procedia     Open Access   (Followers: 15)
Academic Pediatrics     Hybrid Journal   (Followers: 20, SJR: 1.402, h-index: 51)
Academic Radiology     Hybrid Journal   (Followers: 17, SJR: 1.008, h-index: 75)
Accident Analysis & Prevention     Partially Free   (Followers: 81, SJR: 1.109, h-index: 94)
Accounting Forum     Hybrid Journal   (Followers: 23, SJR: 0.612, h-index: 27)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 27, SJR: 2.515, h-index: 90)
Achievements in the Life Sciences     Open Access   (Followers: 4)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 5, SJR: 0.338, h-index: 19)
Acta Astronautica     Hybrid Journal   (Followers: 328, SJR: 0.726, h-index: 43)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 3)
Acta Biomaterialia     Hybrid Journal   (Followers: 25, SJR: 2.02, h-index: 104)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription  
Acta de Investigación Psicológica     Open Access   (Followers: 2)
Acta Ecologica Sinica     Open Access   (Followers: 8, SJR: 0.172, h-index: 29)
Acta Haematologica Polonica     Free   (SJR: 0.123, h-index: 8)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.604, h-index: 38)
Acta Materialia     Hybrid Journal   (Followers: 206, SJR: 3.683, h-index: 202)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.615, h-index: 21)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.442, h-index: 21)
Acta Oecologica     Hybrid Journal   (Followers: 9, SJR: 0.915, h-index: 53)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription   (Followers: 1)
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 3, SJR: 0.311, h-index: 16)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 2)
Acta Poética     Open Access   (Followers: 4)
Acta Psychologica     Hybrid Journal   (Followers: 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: 3)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.967, h-index: 57)
Addictive Behaviors     Hybrid Journal   (Followers: 15, SJR: 1.514, h-index: 92)
Addictive Behaviors Reports     Open Access   (Followers: 5)
Additive Manufacturing     Hybrid Journal   (Followers: 7, SJR: 1.039, h-index: 5)
Additives for Polymers     Full-text available via subscription   (Followers: 20)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 128, SJR: 5.2, h-index: 222)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 11, SJR: 1.265, h-index: 53)
Advanced Powder Technology     Hybrid Journal   (Followers: 16, SJR: 0.739, h-index: 33)
Advances in Accounting     Hybrid Journal   (Followers: 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: 10, SJR: 0.801, h-index: 26)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 20, 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: 24, SJR: 0.183, h-index: 23)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, SJR: 0.665, h-index: 29)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 10, SJR: 1.268, h-index: 45)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 28, SJR: 0.938, h-index: 33)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 18, SJR: 2.314, h-index: 130)
Advances in Computers     Full-text available via subscription   (Followers: 16, SJR: 0.223, h-index: 22)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 11)
Advances in Digestive Medicine     Open Access   (Followers: 4)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 5)
Advances in Drug Research     Full-text available via subscription   (Followers: 22)
Advances in Ecological Research     Full-text available via subscription   (Followers: 40, 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: 40, SJR: 5.465, h-index: 64)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 3)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 8)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 48, SJR: 0.674, h-index: 38)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 15)
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: 12)
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: 21, SJR: 0.906, h-index: 24)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 0.497, h-index: 31)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 25)
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: 4)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 4)
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: 16, SJR: 1.645, h-index: 45)
Advances in Mathematics     Full-text available via subscription   (Followers: 10, SJR: 3.261, h-index: 65)
Advances in Medical Sciences     Hybrid Journal   (Followers: 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: 25, 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: 7, SJR: 0.384, h-index: 26)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.248, h-index: 11)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 8)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 5)
Advances in Porous Media     Full-text available via subscription   (Followers: 4)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 18)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 19, SJR: 1.5, h-index: 62)
Advances in Psychology     Full-text available via subscription   (Followers: 59)
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: 2, SJR: 0.1, h-index: 2)
Advances in Space Research     Full-text available via subscription   (Followers: 340, 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: 6, 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: 15)
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: 309, 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: 400, 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: 38, 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: 50, 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: 9, SJR: 0.922, h-index: 66)
Alcoholism and Drug Addiction     Open Access   (Followers: 6)
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)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 7, 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: 5)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 3)
American Heart J.     Hybrid Journal   (Followers: 48, SJR: 3.157, h-index: 153)
American J. of Cardiology     Hybrid Journal   (Followers: 44, SJR: 2.063, h-index: 186)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 36, SJR: 0.574, h-index: 65)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 6, SJR: 1.091, h-index: 45)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 16, SJR: 1.653, h-index: 93)
American J. of Human Genetics     Hybrid Journal   (Followers: 30, SJR: 8.769, h-index: 256)
American J. of Infection Control     Hybrid Journal   (Followers: 24, SJR: 1.259, h-index: 81)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 34, SJR: 2.313, h-index: 172)
American J. of Medicine     Hybrid Journal   (Followers: 46, 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: 179, SJR: 2.255, h-index: 171)
American J. of Ophthalmology     Hybrid Journal   (Followers: 55, SJR: 2.803, h-index: 148)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 2)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.249, h-index: 88)
American J. of Otolaryngology     Hybrid Journal   (Followers: 23, SJR: 0.59, h-index: 45)
American J. of Pathology     Hybrid Journal   (Followers: 24, SJR: 2.653, h-index: 228)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 21, SJR: 2.764, h-index: 154)
American J. of Surgery     Hybrid Journal   (Followers: 33, 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: 55, SJR: 0.124, h-index: 9)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 9)
Anales de Cirugia Vascular     Full-text available via subscription  
Anales de Pediatría     Full-text available via subscription   (Followers: 2, SJR: 0.209, h-index: 27)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription   (SJR: 0.104, h-index: 3)
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 2, SJR: 2.577, h-index: 7)
Analytica Chimica Acta     Hybrid Journal   (Followers: 38, SJR: 1.548, h-index: 152)
Analytical Biochemistry     Hybrid Journal   (Followers: 160, 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  
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: 153, SJR: 1.907, h-index: 126)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 5, SJR: 1.151, h-index: 83)
Animal Reproduction Science     Hybrid Journal   (Followers: 5, SJR: 0.711, h-index: 78)
Annales d'Endocrinologie     Full-text available via subscription   (SJR: 0.394, h-index: 30)
Annales d'Urologie     Full-text available via subscription  
Annales de Cardiologie et d'Angéiologie     Full-text available via subscription   (SJR: 0.177, h-index: 13)
Annales de Chirurgie de la Main et du Membre Supérieur     Full-text available via subscription  
Annales de Chirurgie Plastique Esthétique     Full-text available via subscription   (Followers: 2, SJR: 0.354, h-index: 22)
Annales de Chirurgie Vasculaire     Full-text available via subscription   (Followers: 1)

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Journal Cover Additive Manufacturing
  [SJR: 1.039]   [H-I: 5]   [7 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 2214-8604
   Published by Elsevier Homepage  [3042 journals]
  • Three-dimensional finite element thermomechanical modeling of additive
           manufacturing by selective laser melting for ceramic materials
    • Authors: Qiang Chen; Gildas Guillemot; Charles-André Gandin; Michel Bellet
      Pages: 124 - 137
      Abstract: Publication date: August 2017
      Source:Additive Manufacturing, Volume 16
      Author(s): Qiang Chen, Gildas Guillemot, Charles-André Gandin, Michel Bellet
      A model for additive manufacturing by selective laser melting of a powder bed with application to alumina ceramic is presented. Based on Beer–Lambert law, a volume heat source model taking into account the material absorption is derived. The level set method is used to track the shape of deposed bead. An energy solver is coupled with thermodynamic database to calculate the melting-solidification path. Shrinkage during consolidation from powder to liquid and compact medium is modeled by a compressible Newtonian constitutive law. A semi-implicit formulation of surface tension is used, which permits a stable resolution to capture the liquid/gas interface. The influence of different process parameters on temperature distribution, melt pool profiles and bead shapes is discussed. The effects of liquid viscosity and surface tension on melt pool dynamics are investigated. Three dimensional simulations of several passes are also presented to study the influence of the scanning strategy.

      PubDate: 2017-06-12T15:19:52Z
      DOI: 10.1016/j.addma.2017.02.005
      Issue No: Vol. 16 (2017)
       
  • Mechanical strength of welding zones produced by polymer extrusion
           additive manufacturing
    • Authors: Chelsea S. Davis; Kaitlyn E. Hillgartner; Seung Hoon Han; Jonathan E. Seppala
      Pages: 162 - 166
      Abstract: Publication date: August 2017
      Source:Additive Manufacturing, Volume 16
      Author(s): Chelsea S. Davis, Kaitlyn E. Hillgartner, Seung Hoon Han, Jonathan E. Seppala
      As more manufacturing processes and research institutions adopt customized manufacturing as a key element in their design strategies and finished products, the resulting mechanical properties of parts produced through additive manufacturing (AM) must be characterized and understood. In polymer extrusion (PE), the most recently extruded polymer filament must bond to the previously extruded filament via polymer diffusion to form a “weld”. The strength of the weld limits the performance of the manufactured part and is controlled through processing conditions. Understanding the role of processing conditions, specifically extruder velocity and extruder temperature, on the overall strength of the weld will allow optimization of PE-AM parts. Here, the fracture toughness of a single weld is determined through a facile “trouser tear” Mode III fracture experiment. The actual weld thickness is observed directly by optical microscopy (OM) characterization of cross sections of PE-AM samples. Representative data of weld strength as a function of printing parameters on a commercial 3D printer demonstrates the robustness of the method.
      Graphical abstract image

      PubDate: 2017-06-23T07:27:00Z
      DOI: 10.1016/j.addma.2017.06.006
      Issue No: Vol. 16 (2017)
       
  • Tensile Strength of Commercial Polymer Materials for Fused Filament
           Fabrication 3D Printing
    • Authors: Nagendra G. Tanikella; Ben Wittbrodt; Joshua M. Pearce
      Pages: 40 - 47
      Abstract: Publication date: Available online 18 March 2017
      Source:Additive Manufacturing
      Author(s): Nagendra G. Tanikella, Ben Wittbrodt, Joshua M. Pearce
      3D printing functional parts with known mechanical properties is challenging using variable open source 3D printers. This study investigates the mechanical properties of 3D printed parts using a commercial open-source 3D printer for a wide range of materials. The samples are tested for tensile strength following ASTM D638. The results are presented and conclusions are drawn about the mechanical properties of various fused filament fabrication materials. The study demonstrates that the tensile strength of a 3D printed specimen depends largely on the mass of the specimen, for all materials. Thus, to solve the challenge of unknown print quality on mechanical properties of a 3D printed part a two step process is proposed, which has a reasonably high expectation that a part will have tensile strengths described in this study for a given material. First, the exterior of the print is inspected visually for sub-optimal layers. Then, to determine if there has been under-extrusion in the interior, the mass of the sample is measured. This mass is compared to the theoretical value using densities for the material and the volume of the object. This two step process provides a means to assist low-cost open-source 3D printers expand the range of object production to functional parts.

      PubDate: 2017-03-22T10:27:33Z
      DOI: 10.1016/j.addma.2017.03.005
      Issue No: Vol. 15 (2017)
       
  • 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
       
  • Compressive Properties of Ti-6Al-4V Lattice Structures Fabricated by
           Selective Laser Melting: Design, Orientation and Density
    • Authors: Sing Ying Choy; Chen-Nan Sun; Kah Fai Leong; Jun Wei
      Abstract: Publication date: Available online 30 June 2017
      Source:Additive Manufacturing
      Author(s): Sing Ying Choy, Chen-Nan Sun, Kah Fai Leong, Jun Wei
      Lattice structures have been intensively researched for their light-weight properties and unique functions in specific applications such as for impact protection and biomedical-implant. The advancement of additive manufacturing simplifies the fabrication of lattice structures as opposed to conventional manufacturing and this opens doors to create more designs. There are ample research opportunities to explore the mechanical performance of the lattice structures fabricated by this technology specific to each design. This study filled the research gap by investigating the deformation behaviour and compressive properties of Ti-6Al-4V lattice structures fabricated by a powder bed fusion method from the aspects of design, orientation and density. The results were compared between cubic and honeycomb unit designs, between two orientations and across five different densities. Results showed that both cubic and honeycomb lattice deformed in a layer-by-layer manner for the first tested orientation, where vertical struts were parallel to the compression direction. In the second tested orientation, where lattice struts were angled with respect to the direction of compression, the deformation behaviour was observed as a single diagonal shear band. As the density of the structure increased, the deformation pattern shifted towards diagonal crack similar to a solid part. Honeycomb lattice structure had the highest density efficiency for energy absorption in both orientations and for first maximum compressive strength in the second orientation. Change of orientation significantly affected the efficiency in plateau stress for cubic lattice structure, and compressive property values for honeycomb lattice structure. Comparative studies showed that the first maximum compressive strength and energy absorption of the lattice structures in the first orientation were higher than most of the lattice designs from other literature.

      PubDate: 2017-07-03T14:00:20Z
      DOI: 10.1016/j.addma.2017.06.012
       
  • Multi-branched Benzylidene Ketone based Photoinitiators for Multiphoton
           Fabrication
    • Authors: F. Zhang; Q. Hu; A. Castañon; Y. He; Y. Liu; B.T. Paul; C.J. Tuck; R.J.M. Hague; R.D. Wildman
      Abstract: Publication date: Available online 23 June 2017
      Source:Additive Manufacturing
      Author(s): F. Zhang, Q. Hu, A. Castañon, Y. He, Y. Liu, B.T. Paul, C.J. Tuck, R.J.M. Hague, R.D. Wildman
      In this article, we report the synthesis of a series of multi-branched benzylidene (BI) ketone-based photo-initiators for two-photon polymerisation based 3D printing/additive manufacturing. Resins prepared by the addition of 1wt.% of these initiators were processed in a commercial 2 photon polymerisation system to fabricate 3D woodpile structures, the qualities of which were examined to determine the efficiencies of the initiators. The results showed that compared to commercial initiator Irgacure 369, the four-branched initiator 4-BI exhibited excellent performance with higher writing speeds and broader ideal processing windows. The successful fabrication of complex 3D structures at high writing speeds (up to 100mm/s) indicated that the four-branched initiator 4-BI could potentially increase the fabrication efficiency and hence become a promising initiator for two-photon polymerisation.

      PubDate: 2017-06-23T07:27:00Z
      DOI: 10.1016/j.addma.2017.06.008
       
  • An open-architecture metal powder bed fusion system for in-situ process
           measurements
    • Authors: P. Bidare; R.R.J. Maier; R.J. Beck; J.D. Shephard; A.J. Moore
      Abstract: Publication date: Available online 17 June 2017
      Source:Additive Manufacturing
      Author(s): P. Bidare, R.R.J. Maier, R.J. Beck, J.D. Shephard, A.J. Moore
      We report the design of a metal powder bed fusion system for in-situ monitoring of the build process during additive manufacture. Its open-architecture design was originally determined to enable access for x-rays to the melt pool, but it also provides access to the build area for a range of other in-situ measurement techniques. The system is sufficiently automated to enable single tracks and high-density, multiple layer components to be built. It is easily transportable to enable measurements at different measurement facilities and its modular design enables straightforward modification for the specific measurements being made. We demonstrate that the system produces components with >99% density. Hence the build conditions are representative to observe process fundamentals and to develop process control strategies.

      PubDate: 2017-06-23T07:27:00Z
      DOI: 10.1016/j.addma.2017.06.007
       
  • Anisotropy of Thermal Conductivity in 3D Printed Polymer Matrix Composites
           for Space Based Cube Satellites
    • Authors: Corey Shemelya; Angel De La Rosa; Angel R. Torrado; Kevin Yu; Jennifer Domanowski; Peter J. Bonacuse; Richard E. Martin; Michael Juhasz; Frances Hurwitz; Ryan B. Wicker; Brett Conner; Eric MacDonald; David A. Roberson
      Abstract: Publication date: Available online 17 June 2017
      Source:Additive Manufacturing
      Author(s): Corey Shemelya, Angel De La Rosa, Angel R. Torrado, Kevin Yu, Jennifer Domanowski, Peter J. Bonacuse, Richard E. Martin, Michael Juhasz, Frances Hurwitz, Ryan B. Wicker, Brett Conner, Eric MacDonald, David A. Roberson
      Polymer extrusion three dimensional (3D) printing, such as fused deposition modeling (FDM), has recently garnered attention due to its inherent process flexibility and rapid prototyping capability. Specifically, the addition of electrical components and interconnects into a 3D printing build sequence has received heavy interest for space applications. However, the addition of these components, along with the thermal load associated with space-based applications, may prove problematic for typical thermally insulating 3D printed polymer structures. The work presented here addresses thermally conductive polymer matrix composites (specifically, graphite, carbon fiber, and silver in an acrylonitrile butadiene styrene polymer matrix) to identify the effect of composite geometry and print direction on thermal anisotropic properties. The work also examines the effect of these composites on print quality, mechanical tensile properties, fracture plane analysis, micrograph imaging, and cube satellite thermal analysis. The thermal conductivity of 3D printed material systems in this work may enable the production of thermally stable 3D printed structures, supports, and devices. Key results of this work include anisotropic thermal conductivity for 3D printed structures related to print direction and filler morphology meaning that thermal conductivity can be controlled through a combination of print raster direction and material design. When the materials analyzed in this work are incorporated with other active cooling systems, space-based 3D printed applications can then be designed to incorporate increasing thermal loads, opening a new door to producing space-ready 3D printed structures.

      PubDate: 2017-06-23T07:27:00Z
      DOI: 10.1016/j.addma.2017.05.012
       
  • Bending Behaviors of 3D-printed Bi-material Structure: Experimental Study
           and Finite Element Analysis
    • Authors: Yi-Tang Kao; Ying Zhang; Jyhwen Wang; Bruce L. Tai
      Abstract: Publication date: Available online 16 June 2017
      Source:Additive Manufacturing
      Author(s): Yi-Tang Kao, Ying Zhang, Jyhwen Wang, Bruce L. Tai
      This paper investigates the bending behaviors of a bi-material structure (BMS) using both experimental and numerical methods The BMS is a composite material built by a 3D-printed, open-cellular brittle plaster structure filled with a silicone elastomer. The composition and configuration of the two materials determine the overall mechanical properties. Four-point bending test results show a non-linear elastic property, enhanced strength and toughness of BMS samples compared to either material phase alone. Such behavior is believed to be a result of delayed microcrack propagation in the brittle phase and a hardening effect of elastomer. In the numerical study, finite element analysis (FEA) is employed to verify these hypotheses. The FEA incorporates a brittle cracking material model for the plaster and a hyperelastic model for the silicone. The brittle cracking model enables the estimation of element degradation as a result of crack development and thus eliminates the need for the extremely refined mesh. Simulation result confirms the non-linear elastic transition and crack-induced material degradation and visualizes the silicone strengthening mechanism that can avoid rapid structural rupture.

      PubDate: 2017-06-17T07:25:40Z
      DOI: 10.1016/j.addma.2017.06.005
       
  • Poly-l-lactic Acid: Pellets to Fiber to Fused Filament Fabricated
           Scaffolds, and Scaffold Weight Loss Study
    • Authors: Prashanth Ravi; Panos S. Shiakolas; Tré R. Welch
      Abstract: Publication date: Available online 15 June 2017
      Source:Additive Manufacturing
      Author(s): Prashanth Ravi, Panos S. Shiakolas, Tré R. Welch
      Poly-l-lactic acid (PLLA) is a bioresorbable polymer used in a variety of biomedical applications. Many 3D printers employ the fused filament fabrication (FFF) approach with the ubiquitous low-cost poly-lactic acid (PLA) fiber. However, use of the FFF approach to fabricate scaffolds with medical grade PLLA polymer remains largely unexplored. In this study, high molecular weight PL-32 pellets were extruded into ∼1.7mm diameter PLLA fiber. Melt rheometric data of the PLLA polymer was analyzed and demonstrated pseudo-plastic behavior with a flow index of n=0.465 (<1). Differential scanning calorimetry (DSC) was conducted using samples from the extruded fiber to obtain thermal properties. DSC of the 3D printed struts was also analyzed to assess changes in thermal properties due to FFF. The DSC and rheometric analysis results were subsequently used to define appropriate FFF process parameters. Constant porosity scaffolds were FFF 3D printed with 4 distinct laydown patterns; 0/90° rectilinear (control), 45/135° rectilinear, Archimedean chords, and honeycomb using the in-house developed custom multi-modality 3D bioprinter (CMMB). The effect of laydown pattern on scaffold bulk erosion (weight loss) was studied by immersion in phosphate-buffered saline (PBS) over a 6-month period and measured monthly. A repeated measures analysis of variance (ANOVA) was performed to identify statistically significant differences between mean percent weight loss of the four laydown patterns at each time point (1-6 months). The resulting data follows distinct temporal trends, but no statistically significant differences between means at individual time points were found. Cross-sectional scanning electron microscope (SEM) images of the 6-month degraded scaffolds showed noticeable structural deterioration. The study demonstrates successful processing of PLLA fiber from PL-32 pellets and FFF-based 3D printing of bioresorbable scaffolds with pre-defined laydown patterns using medical grade PLLA polymer which could prove beneficial in biomedical applications.

      PubDate: 2017-06-17T07:25:40Z
      DOI: 10.1016/j.addma.2017.06.002
       
  • Fabrication of Continuous Carbon, Glass and Kevlar fibre reinforced
           polymer composites using Additive Manufacturing
    • Authors: Andrew N. Dickson; James N. Barry; Kevin A. McDonnell; Denis P. Dowling
      Abstract: Publication date: Available online 15 June 2017
      Source:Additive Manufacturing
      Author(s): Andrew N. Dickson, James N. Barry, Kevin A. McDonnell, Denis P. Dowling
      This study evaluated the performance of continuous carbon, Kevlar and glass fibre reinforced composites manufactured using the fused deposition modelling (FDM) additive manufacturing technique. These nylon composites were fabricated using a Markforged Mark One 3D printing system. The mechanical performance of the composites was evaluated both in tension and flexure. The influence of fibre orientation, fibre type and volume fraction on mechanical properties were also investigated. The results were compared with that of both non-reinforced nylon control specimens, and known material property values from literature. It was demonstrated that of the fibres investigated, those fabricated using carbon fibre yielded the largest increase in mechanical strength. Its tensile strength values were up to 6.3 times that obtained with the non-reinforced nylon polymer. As the carbon and glass fibre volume fraction increased so too did the level of air inclusion in the composite matrix, which impacted on mechanical performance. As a result, a maximum efficiency in tensile strength was observed in glass specimen as fibre content approached 18%, with higher fibre contents (up to 33%), yielding only minor increases in strength.

      PubDate: 2017-06-17T07:25:40Z
      DOI: 10.1016/j.addma.2017.06.004
       
  • Investigation of Mechanical Anisotropy of the Fused Filament Fabrication
           Process via Customized Tool Path Generation
    • Authors: Carsten Koch; Luke Van Hulle; Natalie Rudolph
      Abstract: Publication date: Available online 15 June 2017
      Source:Additive Manufacturing
      Author(s): Carsten Koch, Luke Van Hulle, Natalie Rudolph
      To aid in the transition of 3D printed parts from prototypes to functional products it is necessary to investigate the mechanical anisotropy induced by the Fused Filament Fabrication (FFF) process. Since the mechanical properties of an FFF part are most greatly affected by the bead orientation and printed density, or solidity ratio, techniques to precisely control these variables are required. An open source Python program, SciSlice, was developed to create the desired tool paths/layer orientations and convert them into machine commands (e.g. G-Code). SciSlice was then used to develop tool paths which either directly printed tensile specimens or printed sheets from which specimens could be water-jet cut. The effects of proper bed leveling and feed wheel adjustment are noted and a careful analysis of both bead orientation and solidity ratio are presented. Printing artifacts related to turns made at the part edges are discussed having been found to have strong effects on the measure strength in the weakest orientation. Finally, it is shown that with proper bead orientation, low layer heights, and a maximum solidity ratio, tensile strengths within 3% of injection molded parts are achievable.

      PubDate: 2017-06-17T07:25:40Z
      DOI: 10.1016/j.addma.2017.06.003
       
  • A Tripropylene Glycol Diacrylate-based polymeric support ink for material
           jetting
    • Authors: Yinfeng He; Fan Zhang; Ehab Saleh; Jayasheelan Vaithilingam; Nesma Aboulkhair; Belen Begines; Chris J. Tuck; Richard J.M. Hague; Ian Ashcroft; Ricky D. Wildman
      Abstract: Publication date: Available online 12 June 2017
      Source:Additive Manufacturing
      Author(s): Yinfeng He, Fan Zhang, Ehab Saleh, Jayasheelan Vaithilingam, Nesma Aboulkhair, Belen Begines, Chris J. Tuck, Richard J.M. Hague, Ian Ashcroft, Ricky D. Wildman
      Support structures and materials are indispensable components in many Additive Manufacturing (AM) systems in order to fabricate complex 3D structures. For inkjet-based AM techniques (known as Material Jetting), there is a paucity of studies on specific inks for fabricating such support structures. This limits the potential of fabricating complex 3D objects containing overhanging structures. In this paper, we investigate the use of Tripropylene Glycol Diacrylated (TPGDA) to prepare a thermally stable ink with reliable printability to produce removable support structures in an experimental Material Jetting system. The addition of TGME to the TPGDA was found to considerably reduce the modulus of the photocured structure from 575MPa down to 27MPa by forming micro-pores in the cured structure. The cured support structure was shown to be easily removed following the fabrication process. During TG-IR tests the T5% temperature of the support structure was above 150°C whilst the majority of decomposition happened around 400°C. Specimens containing overhanging structures (gate-like structure, propeller structure) were successfully manufactured to highlight the viability of the ink as a support material.

      PubDate: 2017-06-17T07:25:40Z
      DOI: 10.1016/j.addma.2017.06.001
       
  • Prospective study on the integration of additive manufacturing to building
           industry- Case of a French construction company.
    • Authors: Imane Krimi; Zoubeir Lafhaj; Laure Ducoulombier
      Abstract: Publication date: Available online 24 May 2017
      Source:Additive Manufacturing
      Author(s): Imane Krimi, Zoubeir Lafhaj, Laure Ducoulombier
      The objective of this paper is to present a reflection on the use of Additive manufacturing in construction. In this research examples from manufacturing industries are presented. Some Advantages of additive manufacturing in industry were identified. Relevant cases used to promote AM for construction are: building rate improvement and schedules shortening. This study investigated these advantages in three parts. Firstly, a comparison between construction and manufacturing industry was presented. Secondly, Design and Building rate for construction were studied using data from a French construction company. Finally a comparison was made between conventional processes and Additive manufacturing. Conventional processes included prefabrication and casting on site. Results showed that pre-casting may be faster than AM in some cases. Time saving is not necessary the best advantage from applying additive manufacturing to construction.

      PubDate: 2017-05-29T05:18:46Z
      DOI: 10.1016/j.addma.2017.04.002
       
  • SYNCHRONIZED MATERIAL DEPOSITION RATE CONTROL WITH PATH VELOCITY ON FUSED
           DEPOSITION MACHINES
    • Authors: Deniz Sera Ertay; Alexander Yuen; Yusuf Altintas
      Abstract: Publication date: Available online 24 May 2017
      Source:Additive Manufacturing
      Author(s): Deniz Sera Ertay, Alexander Yuen, Yusuf Altintas
      Additive manufacturing (AM) technologies are used in three dimensional (3D) printing of parts using thermo-plastic extruders, or laser and electron beam based metal deposition methods This paper presents an integrated methodology for planning of tangential path velocity, material deposition rate and temperature control of the extruded material which is deposited along curved paths. The tangential velocity along the path is smoothed and optimized while respecting the heater’s and extruder’s capacities, as well as the feed drives’ jerk, acceleration and velocity limits. The extrusion rate is controlled proportional to the tangential path velocity while keeping the temperature of the deposited thermo-plastic material at the desired temperature by adaptively controlling current supply to the heater. The experimentally proven algorithm leads to more uniform material deposition at sharp curvatures and resulting improved dimensional accuracy of printed parts. The proposed methodology can be extended to laser and electron beam based metal printing applications.

      PubDate: 2017-05-29T05:18:46Z
      DOI: 10.1016/j.addma.2017.05.011
       
  • Wire and Arc Additive Manufactured Steel: Tensile and Wear Properties
    • Authors: C.V. Haden; G.S. Zeng; F.M. Carter; C. Ruhl; B.A. Krick; D.G. Harlow
      Abstract: Publication date: Available online 23 May 2017
      Source:Additive Manufacturing
      Author(s): C.V. Haden, G.S. Zeng, F.M. Carter, C. Ruhl, B.A. Krick, D.G. Harlow
      The present study systematically investigated the mechanical properties of wire-based (wire and arc additive manufacturing, known as WAAM) deposition of steel metals, both stainless steel 304 and mild steel ER70S. Graded material properties of stainless steel 304 were observed for wear and hardness in the direction of deposition and in Z height, due to variations in local thermal histories of the metal. Wear rates decreased significantly (p=5.6×10−12 by one-way ANOVA) along the length of the deposited material, from μ=2.62×10−5 mm3/N · m and σ=2.32×10−6 mm3/N · m, to μ=0.63mm3/N · m and σ=3.08×10−6 mm3/N · m, whereas microhardness values increased significantly (p∼0 by one-way ANOVA) along the same path from μ=202.3 HV and σ=5.82 HV to 210.9 HV and σ=5.91 HV. The yield and ultimate strength, however, were not found to be statistically significantly different (p=0.55) along the direction of deposition for SS304. During wear testing, a grain refinement was observed directly beneath the wear scar in these materials in a focused ion beam channel observed under scanning electron microscopy. Additionally, no significant difference in yield strength was observed in printed mild steel (ER70S) between vertical and horizontal specimens. The observed graded mechanical properties in stainless steel 304 allow the opportunity for varying the processing conditions to design parts with locally optimized or functionally graded mechanical properties.

      PubDate: 2017-05-24T01:18:19Z
      DOI: 10.1016/j.addma.2017.05.010
       
  • Design Framework for Multifunctional Additive Manufacturing: Coupled
           Optimization Strategy for Structures with embedded functional Systems
    • Authors: Ajit Panesar; Ian Ashcroft; David Brackett; Ricky Wildman; Richard Hague
      Abstract: Publication date: Available online 23 May 2017
      Source:Additive Manufacturing
      Author(s): Ajit Panesar, Ian Ashcroft, David Brackett, Ricky Wildman, Richard Hague
      The driver for this research is the development of multi-material additive manufacturing processes that provide the potential for multi-functional parts to be manufactured in a single operation. In order to exploit the potential benefits of this emergent technology, new design, analysis and optimization methods are needed. This paper presents a method that enables in the optimization of a multifunctional part by coupling both the system and structural design aspects. This is achieved by incorporating the effects of a system, comprised of a number of connected functional components, on the structural response of a part within a structural topology optimization procedure. The potential of the proposed method is demonstrated by performing a coupled optimization on a cantilever plate with integrated components and circuitry. The results demonstrate that the method is capable of designing an optimized multifunctional part in which both the structural and system requirements are considered.

      PubDate: 2017-05-24T01:18:19Z
      DOI: 10.1016/j.addma.2017.05.009
       
  • 316L stainless steel mechanical and tribological behavior − a comparison
           between selective laser melting, hot pressing and conventional casting
    • Authors: F. Bartolomeu; M. Buciumeanu; E. Pinto; N. Alves; O. Carvalho; F.S. Silva; G. Miranda
      Abstract: Publication date: Available online 23 May 2017
      Source:Additive Manufacturing
      Author(s): F. Bartolomeu, M. Buciumeanu, E. Pinto, N. Alves, O. Carvalho, F.S. Silva, G. Miranda
      This work presents a comprehensive study on the influence of three different processing technologies (Selective Laser Melting, Hot Pressing and conventional casting) on the microstructure, mechanical and wear behavior of an austenitic 316L Stainless Steel. A correlation between the processing technologies, the obtained microstructure and the mechanical and wear behavior was achieved. The results showed that the highest mechanical properties and tribological performance were obtained for 316L SS specimens produced by Selective Laser Melting, when compared to Hot Pressing and conventional casting. The high wear and mechanical performance of 316L Stainless Steel fabricated by Selective Laser Melting are mainly due to the finer microstructure, induced by the process. In this sense, Selective Laser Melting seems a promising method to fabricate customized 316L SS implants with improved mechanical and wear performance.

      PubDate: 2017-05-24T01:18:19Z
      DOI: 10.1016/j.addma.2017.05.007
       
  • Tailoring residual stress profile of Selective Laser Melted parts by Laser
           Shock Peening
    • Authors: Nikola Kalentics; Eric Boillat; Patrice Peyre; Snežana Ćirić-Kostić; Nebojša Bogojević; Roland E. Logé
      Abstract: Publication date: Available online 23 May 2017
      Source:Additive Manufacturing
      Author(s): Nikola Kalentics, Eric Boillat, Patrice Peyre, Snežana Ćirić-Kostić, Nebojša Bogojević, Roland E. Logé
      The paper describes a new approach in controlling and tailoring residual stress profile of parts made by Selective Laser Melting (SLM). SLM parts are well known for the high tensile stresses in the as − built state in the surface or subsurface region. These stresses have a detrimental effect on the mechanical properties and especially on the fatigue life. Laser Shock Peening (LSP) as a surface treatment method was applied on SLM parts and residual stress measurements with the hole − drilling method were performed. Two different grades of stainless steel were used: a martensitic 15-5 precipitation hardenable PH1 and an austenitic 316L. Different LSP parameters were used, varying laser energy, shot overlap, laser spot size and treatments with and without an ablative medium. For both materials the as-built (AB) residual stress state was changed to a more beneficial compressive state. The value and the depth of the compressive stress was analyzed and showed a clear dependence on the LSP processing parameters. Application of LSP on SLM parts showed promising results, and a novel method that would combine these two processes is proposed. The use of LSP during the building phase of SLM as a “3D LSP” method would possibly give the advantage of further increasing the depth and volume of compressive residual stresses, and selectively treating key areas of the part, thereby further increasing fatigue life.

      PubDate: 2017-05-24T01:18:19Z
      DOI: 10.1016/j.addma.2017.05.008
       
  • 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
       
  • Thermomechanical model development and in situ experimental validation of
           the Laser Powder-Bed Fusion Process
    • Authors: Erik R. Denlinger; Michael Gouge; Jeff Irwin; Pan Michaleris
      Abstract: Publication date: Available online 4 May 2017
      Source:Additive Manufacturing
      Author(s): Erik R. Denlinger, Michael Gouge, Jeff Irwin, Pan Michaleris
      A three-dimensional finite element model is developed to allow for the prediction of temperature, residual stress, and distortion in multi-layer Laser Powder-Bed Fusion builds. Undesirable residual stress and distortion caused by thermal gradients are a common source of failure in AM builds. A non-linear thermoelastoplastic model is combined with an element coarsening strategy in order to simulate the thermal and mechanical response of a significant volume of deposited material (38 layers and 91 mm3). It is found that newly deposited layers experience the greatest amount of tensile stress, while layers beneath are forced into compressive stress. The residual stress evolution drives the mechanical response of the workpiece. The model is validated by comparing the predicted in situ and post process distortion to experimental measurements taken on the same geometry. The model accurately predicts the distortion of the workpiece (5 % error).

      PubDate: 2017-05-08T10:44:05Z
      DOI: 10.1016/j.addma.2017.05.001
       
  • 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
           Fusion
    • 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
           Component
    • 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
       
  • A novel freeform extrusion fabrication process for producing solid ceramic
           components with uniform layered radiation drying
    • Authors: Amir Ghazanfari; Wenbin Li; Ming C. Leu; Gregory E. Hilmas
      Abstract: Publication date: Available online 15 April 2017
      Source:Additive Manufacturing
      Author(s): Amir Ghazanfari, Wenbin Li, Ming C. Leu, Gregory E. Hilmas
      An extrusion-based additive manufacturing process, called the Ceramic On-Demand Extrusion (CODE) process, for producing three-dimensional ceramic components with near theoretical density is introduced in this paper. In this process, an aqueous paste of ceramic particles with a very low binder content (<1vol%) is extruded through a moving nozzle at room temperature. After a layer is deposited, it is surrounded by oil (to a level just below the top surface of most recent layer) to preclude non-uniform evaporation from the sides. Infrared radiation is then used to partially, and uniformly, dry the just-deposited layer so that the yield stress of the paste increases and the part maintains its shape. The same procedure is repeated for every layer until part fabrication is completed. Several sample parts for various applications were produced using this process and their properties were obtained. The results indicate that the proposed method enables fabrication of large, dense ceramic parts with complex geometries.

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

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

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

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

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

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

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

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

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

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

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

      PubDate: 2017-02-24T18:33:16Z
      DOI: 10.1016/j.addma.2017.02.001
       
  • Fractal Scan Strategies for Selective Laser Melting of
           ‘Unweldable’ Nickel Superalloys
    • Authors: S. Catchpole-Smith; N. Aboulkhair; L. Parry; C. Tuck; I.A. Ashcroft; A. Clare
      Abstract: Publication date: Available online 12 February 2017
      Source:Additive Manufacturing
      Author(s): S. Catchpole-Smith, N. Aboulkhair, L. Parry, C. Tuck, I.A. Ashcroft, A. Clare
      The high thermal gradients experienced during manufacture via selective laser melting commonly result in cracking of high γ/γ′ Nickel based superalloys. Such defects cannot be tolerated in applications where component integrity is of paramount importance. To overcome this, many industrial practitioners make use of hot isostatic pressing to ‘heal’ these defects. The possibility of such defects re-opening during the component life necessitates optimisation of SLM processing parameters in order to produce the highest bulk density and integrity in the as-built state. In this paper, novel fractal scanning strategies based upon mathematical fill curves, namely the Hilbert and Peano-Gosper curve, are explored in which the use of short vector length scans, in the order of 100μm, is used as a method of reducing residual stresses. The effect on cracking observed in CM247LC superalloy samples was analysed using image processing, comparing the novel fractal scan strategies to more conventional ‘island’ scans. Scanning electron microscopy and energy dispersive X-ray spectroscopy was utilised to determine the cracking mechanisms. Results show that cracking occurs via two mechanisms, solidification and liquation, with a strong dependence on the laser scan vectors. Through the use of fractal scan strategies, bulk density can be increased by 2±0.7% when compared to the ‘island’ scanning, demonstrating the potential of fractal scan strategies in the manufacture of typically ‘unweldable’ nickel superalloys.

      PubDate: 2017-02-18T10:40:24Z
      DOI: 10.1016/j.addma.2017.02.002
       
  • Experimental and Theoretical Modeling of Behavior of 3D-Printed Polymers
           Under Collision with a Rigid Rod
    • Authors: Kamran Kardel; Hamid Ghaednia; Andres L. Carrano; Dan B. Marghitu
      Abstract: Publication date: Available online 24 January 2017
      Source:Additive Manufacturing
      Author(s): Kamran Kardel, Hamid Ghaednia, Andres L. Carrano, Dan B. Marghitu
      The behavior of five different 3D-printed polymers has been analyzed both theoretically and experimentally under low-speed collision conditions. The impact of a rigid rod with a flat specimen fabricated of 3D-printed materials was analyzed. An experimental setup has been designed in order to capture the motion of the rod during the impact using a high-speed camera. Image processing algorithms were developed to estimate the velocity before and after the impact as well as the coefficient of restitution. Also, permanent deformations after the impact were scanned with an optical profilometer. In this work, a theoretical formulation for the contact force during the impact is proposed. The impact was divided into two phases, compression and restitution, in which materials considered elastic-plastic in the first and fully elastic in the second one. The experimental results are used to measure the damping coefficient. Results show a good correlation between the proposed formulation for the contact force and the behavior of materials.

      PubDate: 2017-01-31T17:48:13Z
      DOI: 10.1016/j.addma.2017.01.004
       
  • Characterization of the strength of support structures used in powder bed
           fusion additive manufacturing of Ti-6Al-4V
    • Authors: Lourdes D. Bobbio; Shipin Qin; Alexander Dunbar; Panagiotis Michaleris; Allison M. Beese
      Abstract: Publication date: Available online 19 January 2017
      Source:Additive Manufacturing
      Author(s): Lourdes D. Bobbio, Shipin Qin, Alexander Dunbar, Panagiotis Michaleris, Allison M. Beese
      Support structures are required in powder bed fusion (PBF) additive manufacturing of metallic components with overhanging structures in order to reinforce and anchor the part, preventing warping during fabrication. In this study, we fabricated and tested the tensile structural strength of support structures with four different 2-dimensional lattice geometries by fabricating samples composed of solid material on the bottom, followed by support material in the middle, followed by solid material on the top. The support structure regions were fabricated with a lower linear heat input than the solid material, providing deliberate geometrical stress concentrations to enable the removal of support material after processing. These samples were subjected to tension in the vertical direction to measure the strengths of the support structure-solid material interfaces. Two strengths were computed: an effective structural strength defined as the total force that the structure withstood normalized by the full cross-sectional area, and a ligament structural strength, defined as the effective structural strength normalized by the density of the solid material, thereby ignoring the volume of the surrounding powder and voids that do not contribute to the strength of the lattice. The effective structural strength was 14-32% of the strength of fully dense Ti-6Al–4V made by PBF and the ligament structural strength was 34-49% of the strength of fully dense material. These interface strengths are lower than that of fully-dense material due to the stress concentrations at the support structure-solid material interfaces, not any intrinsic difference in the intrinsic strength of support structure versus solid material. These results can be used to tailor the support structure geometry to balance sufficient anchoring strength during fabrication and ease of part removal and subsequent machining during post-processing.

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

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

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

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

      PubDate: 2017-01-06T12:30:06Z
      DOI: 10.1016/j.addma.2016.12.004
       
 
 
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