for Journals by Title or ISSN
for Articles by Keywords
help

Publisher: Elsevier   (Total: 3161 journals)

 A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z  

        1 2 3 4 5 6 7 8 | Last   [Sort by number of followers]   [Restore default list]

Showing 1 - 200 of 3161 Journals sorted alphabetically
A Practical Logic of Cognitive Systems     Full-text available via subscription   (Followers: 9)
AASRI Procedia     Open Access   (Followers: 15)
Academic Pediatrics     Hybrid Journal   (Followers: 35, SJR: 1.655, CiteScore: 2)
Academic Radiology     Hybrid Journal   (Followers: 24, SJR: 1.015, CiteScore: 2)
Accident Analysis & Prevention     Partially Free   (Followers: 96, SJR: 1.462, CiteScore: 3)
Accounting Forum     Hybrid Journal   (Followers: 27, SJR: 0.932, CiteScore: 2)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 37, SJR: 1.771, CiteScore: 3)
Achievements in the Life Sciences     Open Access   (Followers: 5)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 7)
Acta Astronautica     Hybrid Journal   (Followers: 421, SJR: 0.758, CiteScore: 2)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 2)
Acta Biomaterialia     Hybrid Journal   (Followers: 28, SJR: 1.967, CiteScore: 7)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription   (Followers: 2)
Acta de Investigación Psicológica     Open Access   (Followers: 3)
Acta Ecologica Sinica     Open Access   (Followers: 10, SJR: 0.18, CiteScore: 1)
Acta Haematologica Polonica     Free   (Followers: 1, SJR: 0.128, CiteScore: 0)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.661, CiteScore: 2)
Acta Materialia     Hybrid Journal   (Followers: 276, SJR: 3.263, CiteScore: 6)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.504, CiteScore: 1)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.542, CiteScore: 1)
Acta Oecologica     Hybrid Journal   (Followers: 12, SJR: 0.834, CiteScore: 2)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription  
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 3, SJR: 0.307, CiteScore: 0)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 1, SJR: 1.793, CiteScore: 6)
Acta Poética     Open Access   (Followers: 4, SJR: 0.101, CiteScore: 0)
Acta Psychologica     Hybrid Journal   (Followers: 27, SJR: 1.331, CiteScore: 2)
Acta Sociológica     Open Access   (Followers: 1)
Acta Tropica     Hybrid Journal   (Followers: 6, SJR: 1.052, CiteScore: 2)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 3, SJR: 0.374, CiteScore: 1)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 2)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 3, SJR: 0.344, CiteScore: 1)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 1)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 6, SJR: 0.19, CiteScore: 0)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 3)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 8)
Acute Pain     Full-text available via subscription   (Followers: 14, SJR: 2.671, CiteScore: 5)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.53, CiteScore: 4)
Addictive Behaviors     Hybrid Journal   (Followers: 17, SJR: 1.29, CiteScore: 3)
Addictive Behaviors Reports     Open Access   (Followers: 8, SJR: 0.755, CiteScore: 2)
Additive Manufacturing     Hybrid Journal   (Followers: 11, SJR: 2.611, CiteScore: 8)
Additives for Polymers     Full-text available via subscription   (Followers: 23)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 167, SJR: 4.09, CiteScore: 13)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 12, SJR: 1.167, CiteScore: 4)
Advanced Powder Technology     Hybrid Journal   (Followers: 17, SJR: 0.694, CiteScore: 3)
Advances in Accounting     Hybrid Journal   (Followers: 8, SJR: 0.277, CiteScore: 1)
Advances in Agronomy     Full-text available via subscription   (Followers: 15, SJR: 2.384, CiteScore: 5)
Advances in Anesthesia     Full-text available via subscription   (Followers: 28, SJR: 0.126, CiteScore: 0)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 2)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 10, SJR: 0.992, CiteScore: 1)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 11, SJR: 1.551, CiteScore: 4)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 24, SJR: 2.089, CiteScore: 5)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 14, SJR: 0.572, CiteScore: 2)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.61, CiteScore: 7)
Advances in Botanical Research     Full-text available via subscription   (Followers: 2, SJR: 0.686, CiteScore: 2)
Advances in Cancer Research     Full-text available via subscription   (Followers: 33, SJR: 3.043, CiteScore: 6)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 9, SJR: 1.453, CiteScore: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 1.992, CiteScore: 5)
Advances in Cell Aging and Gerontology     Full-text available via subscription   (Followers: 4)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 13)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 28, SJR: 0.156, CiteScore: 1)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, SJR: 0.713, CiteScore: 1)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 10, SJR: 1.316, CiteScore: 2)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 26, SJR: 1.562, CiteScore: 3)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 20, SJR: 1.977, CiteScore: 8)
Advances in Computers     Full-text available via subscription   (Followers: 14, SJR: 0.205, CiteScore: 1)
Advances in Dermatology     Full-text available via subscription   (Followers: 15)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 12)
Advances in Digestive Medicine     Open Access   (Followers: 9)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 7)
Advances in Drug Research     Full-text available via subscription   (Followers: 25)
Advances in Ecological Research     Full-text available via subscription   (Followers: 44, SJR: 2.524, CiteScore: 4)
Advances in Engineering Software     Hybrid Journal   (Followers: 29, SJR: 1.159, CiteScore: 4)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 8)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 46, SJR: 5.39, CiteScore: 8)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 1)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 9)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 60, SJR: 0.591, CiteScore: 2)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 17)
Advances in Genetics     Full-text available via subscription   (Followers: 19, SJR: 1.354, CiteScore: 4)
Advances in Genome Biology     Full-text available via subscription   (Followers: 10, SJR: 12.74, CiteScore: 13)
Advances in Geophysics     Full-text available via subscription   (Followers: 6, SJR: 1.193, CiteScore: 3)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 24, SJR: 0.368, CiteScore: 1)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 12, SJR: 0.749, CiteScore: 3)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 23)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 2, SJR: 0.193, CiteScore: 0)
Advances in Immunology     Full-text available via subscription   (Followers: 36, SJR: 4.433, CiteScore: 6)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 10, SJR: 1.163, CiteScore: 2)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 2, SJR: 1.938, CiteScore: 3)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 6, SJR: 0.176, CiteScore: 0)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 3)
Advances in Life Course Research     Hybrid Journal   (Followers: 8, SJR: 0.682, CiteScore: 2)
Advances in Lipobiology     Full-text available via subscription   (Followers: 1)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 8)
Advances in Marine Biology     Full-text available via subscription   (Followers: 18, SJR: 0.88, CiteScore: 2)
Advances in Mathematics     Full-text available via subscription   (Followers: 11, SJR: 3.027, CiteScore: 2)
Advances in Medical Sciences     Hybrid Journal   (Followers: 7, SJR: 0.694, CiteScore: 2)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 4, SJR: 1.158, CiteScore: 3)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 23)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 8)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 7, SJR: 0.182, CiteScore: 0)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 4)
Advances in Oncobiology     Full-text available via subscription   (Followers: 2)
Advances in Organ Biology     Full-text available via subscription   (Followers: 2)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 17, SJR: 1.875, CiteScore: 4)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.174, CiteScore: 0)
Advances in Parasitology     Full-text available via subscription   (Followers: 5, SJR: 1.579, CiteScore: 4)
Advances in Pediatrics     Full-text available via subscription   (Followers: 25, SJR: 0.461, CiteScore: 1)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 12)
Advances in Pharmacology     Full-text available via subscription   (Followers: 16, SJR: 1.536, CiteScore: 3)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 0.574, CiteScore: 1)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.109, CiteScore: 1)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 10)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 5)
Advances in Porous Media     Full-text available via subscription   (Followers: 5)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 19)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 20, SJR: 0.791, CiteScore: 2)
Advances in Psychology     Full-text available via subscription   (Followers: 65)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 6, SJR: 0.371, CiteScore: 1)
Advances in Radiation Oncology     Open Access   (Followers: 1, SJR: 0.263, CiteScore: 1)
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 3, SJR: 0.101, CiteScore: 0)
Advances in Space Biology and Medicine     Full-text available via subscription   (Followers: 6)
Advances in Space Research     Full-text available via subscription   (Followers: 403, SJR: 0.569, CiteScore: 2)
Advances in Structural Biology     Full-text available via subscription   (Followers: 5)
Advances in Surgery     Full-text available via subscription   (Followers: 12, SJR: 0.555, CiteScore: 2)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 34, SJR: 2.208, CiteScore: 4)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 18)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 14)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 2.262, CiteScore: 5)
Advances in Water Resources     Hybrid Journal   (Followers: 47, SJR: 1.551, CiteScore: 3)
Aeolian Research     Hybrid Journal   (Followers: 6, SJR: 1.117, CiteScore: 3)
Aerospace Science and Technology     Hybrid Journal   (Followers: 358, SJR: 0.796, CiteScore: 3)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.42, CiteScore: 2)
African J. of Emergency Medicine     Open Access   (Followers: 6, SJR: 0.296, CiteScore: 0)
Ageing Research Reviews     Hybrid Journal   (Followers: 11, SJR: 3.671, CiteScore: 9)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 463, SJR: 1.238, CiteScore: 3)
Agri Gene     Hybrid Journal   (Followers: 1, SJR: 0.13, CiteScore: 0)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 17, SJR: 1.818, CiteScore: 5)
Agricultural Systems     Hybrid Journal   (Followers: 31, SJR: 1.156, CiteScore: 4)
Agricultural Water Management     Hybrid Journal   (Followers: 42, SJR: 1.272, CiteScore: 3)
Agriculture and Agricultural Science Procedia     Open Access   (Followers: 4)
Agriculture and Natural Resources     Open Access   (Followers: 3)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 57, SJR: 1.747, CiteScore: 4)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.589, CiteScore: 3)
Air Medical J.     Hybrid Journal   (Followers: 6, SJR: 0.26, CiteScore: 0)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.19, CiteScore: 0)
Alcohol     Hybrid Journal   (Followers: 12, SJR: 1.153, CiteScore: 3)
Alcoholism and Drug Addiction     Open Access   (Followers: 11)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 1, SJR: 0.604, CiteScore: 3)
Alexandria J. of Medicine     Open Access   (Followers: 1, SJR: 0.191, CiteScore: 1)
Algal Research     Partially Free   (Followers: 10, SJR: 1.142, CiteScore: 4)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 2)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.504, CiteScore: 1)
Allergology Intl.     Open Access   (Followers: 5, SJR: 1.148, CiteScore: 2)
Alpha Omegan     Full-text available via subscription   (SJR: 3.521, CiteScore: 6)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 10, SJR: 0.201, CiteScore: 1)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 52, SJR: 4.66, CiteScore: 10)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 4, SJR: 1.796, CiteScore: 4)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 4, SJR: 1.108, CiteScore: 3)
Ambulatory Pediatrics     Hybrid Journal   (Followers: 6)
American Heart J.     Hybrid Journal   (Followers: 56, SJR: 3.267, CiteScore: 4)
American J. of Cardiology     Hybrid Journal   (Followers: 59, SJR: 1.93, CiteScore: 3)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 44, SJR: 0.604, CiteScore: 1)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 11)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 13, SJR: 1.524, CiteScore: 3)
American J. of Human Genetics     Hybrid Journal   (Followers: 34, SJR: 7.45, CiteScore: 8)
American J. of Infection Control     Hybrid Journal   (Followers: 28, SJR: 1.062, CiteScore: 2)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 35, SJR: 2.973, CiteScore: 4)
American J. of Medicine     Hybrid Journal   (Followers: 48)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3, SJR: 1.967, CiteScore: 2)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 225, SJR: 2.7, CiteScore: 4)
American J. of Ophthalmology     Hybrid Journal   (Followers: 66, SJR: 3.184, CiteScore: 4)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 5, SJR: 0.265, CiteScore: 0)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.289, CiteScore: 1)
American J. of Otolaryngology     Hybrid Journal   (Followers: 25, SJR: 0.59, CiteScore: 1)
American J. of Pathology     Hybrid Journal   (Followers: 28, SJR: 2.139, CiteScore: 4)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 29, SJR: 2.164, CiteScore: 4)
American J. of Surgery     Hybrid Journal   (Followers: 38, SJR: 1.141, CiteScore: 2)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.767, CiteScore: 1)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 7)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.144, CiteScore: 3)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 63, SJR: 0.138, CiteScore: 0)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 19, SJR: 0.411, CiteScore: 1)
Anales de Cirugia Vascular     Full-text available via subscription   (Followers: 1)
Anales de Pediatría     Full-text available via subscription   (Followers: 3, SJR: 0.277, CiteScore: 0)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription  
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 5, SJR: 4.849, CiteScore: 10)
Analytica Chimica Acta     Hybrid Journal   (Followers: 43, SJR: 1.512, CiteScore: 5)
Analytical Biochemistry     Hybrid Journal   (Followers: 188, SJR: 0.633, CiteScore: 2)
Analytical Chemistry Research     Open Access   (Followers: 12, SJR: 0.411, CiteScore: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 13)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 2)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 23, SJR: 0.683, CiteScore: 2)
Angiología     Full-text available via subscription   (SJR: 0.121, CiteScore: 0)
Angiologia e Cirurgia Vascular     Open Access   (Followers: 1, SJR: 0.111, CiteScore: 0)
Animal Behaviour     Hybrid Journal   (Followers: 205, SJR: 1.58, CiteScore: 3)

        1 2 3 4 5 6 7 8 | Last   [Sort by number of followers]   [Restore default list]

Journal Cover
Additive Manufacturing
Journal Prestige (SJR): 2.611
Citation Impact (citeScore): 8
Number of Followers: 11  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 2214-8604
Published by Elsevier Homepage  [3161 journals]
  • One-step Electrodeposition of Copper on Conductive 3D Printed
           Objects
    • Abstract: Publication date: Available online 19 March 2019Source: Additive ManufacturingAuthor(s): Myung Jun Kim, Mutya A. Cruz, Shengrong Ye, Allen L. Gray, Gabriel L. Smith, Nathan Lazarus, Christopher J. Walker, Hjalti H. Sigmarsson, Benjamin J. Wiley 3D printing with electrically conductive filaments enables rapid prototyping and fabrication of electronics, but the performance of such devices can be limited by the fact that the most conductive thermoplastic-based filaments for 3D printing are 3750 times less conductive than copper. This study explores the use of one-step electrodeposition of copper onto electrically conductive 3D printed objects as a way to improve their conductivity and performance. Comparison of three different commercially-available conductive filaments demonstrates that only the most conductive commercially available filament could enable one-step electrodeposition of uniform copper films. Electrodeposition improved the electrical conductivity and the ampacity of 3D printed traces by 94 and 17 times respectively, compared to the as-printed object. The areal surface roughness of the objects was reduced from 9.3 to 6.9 μm after electrodeposition, and a further reduction in surface roughness to 3.9 μm could be achieved through the addition of organic additives to the electrodeposition bath. Copper electrodeposition improved the quality factor of a 3D printed inductor by 1740 times and the gain of a 3D printed horn antenna by 1 dB. One-step electrodeposition is a fast and simple way to improve the conductivity and performance of 3D printed electronic components.Graphical abstractGraphical abstract for this article
       
  • Vision-Based Inspection System for Cladding Height Measurement in Direct
           Energy Deposition (DED)
    • Abstract: Publication date: Available online 19 March 2019Source: Additive ManufacturingAuthor(s): Hsu-Wei Hsu, Yu-Lung Lo, Min-Hsun Lee A vision-based inspection system based on three digital cameras is proposed for measuring the cladding height in the Direct Energy Deposition (DED) process. To improve the accuracy of the cladding height measurements, an image processing technique is applied to remove the undesirable zone from the binary image. Furthermore, since the unit length in the captured images is different to that in the world coordinate framework, a calibration bar method is designed to transform the pixel value to the real size. In the proposed approach, a calibration bar method is employed to compensate for the Field-of-View (FOV) and perspective effects in the trinocular system. An image-processing technique is then employed to isolate the laser nozzle and melt pool in the captured images. Finally, the cladding height is estimated based on the distance between the tip of the laser nozzle and the centroid of the melt pool. The validity of the proposed approach is demonstrated by comparing the inspection results for the cladding height of a horseshoe component with the measurements obtained using a 3-D scanner. The maximum estimation error is found to be just 4.2% Overall, the results confirm that the proposed trinocular vision-based system provides a rapid, convenient and accurate means of determining the cladding height in the DED process.
       
  • Introduction of ternary alloying element in wire arc additive
           manufacturing of titanium aluminide intermetallic
    • Abstract: Publication date: Available online 15 March 2019Source: Additive ManufacturingAuthor(s): Jun Wang, Zengxi Pan, Liangliang Wei, Shuai He, Dominic Cuiuri, Huijun Li In order to introduce vanadium as a ternary alloying element during the wire arc additive manufacturing (WAAM) of titanium aluminide intermetallic alloys, alloy and elemental wire consumables (Ti6Al4V and Al wires, respectively) were used with the WAAM process. A crack-free TiAl bulk with nominal chemical composition of Ti45Al2.2 V was successfully fabricated for the first time through dynamic in situ alloying using WAAM method. The experimental results showed that the introduction of V from Ti6Al4V alloy does not change the flat features of lamellar interface and also does not alter the phase composition of the resultant TiAl alloy. The fabricated Ti45Al2.2 V alloy consists of lamellar colonies and γ interdendritic phase in the top region, fully lamellar structure with unclear grain boundaries in the band regions and large equiaxed α2 with fine γ laths precipitated at grain boundaries in the layers. The microhardness and tensile properties were greatly increased by introducing V due to the general absence of interdendritic γ phase and the V ductilization effect. In addition, the influences of two-step post-heat treatments on the microstructure and mechanical properties are analysed. Results indicate that the microstructure and mechanical properties of the fabricated alloy can be considerably modified after applying different solution treatment temperatures.
       
  • Simple Method to Construct Process Maps for Additive Manufacturing Using
           Support Vector Machine
    • Abstract: Publication date: Available online 14 March 2019Source: Additive ManufacturingAuthor(s): Kenta Aoyagi, Hao Wang, Akihiko Chiba, Hideki Sudo We propose a simple method to construct a process map for additive manufacturing using a support vector machine. By observing the surface of the built parts and classifying them into two classes (good or bad), this method enables a process map to be constructed in order to predict a process condition that is effective at fabricating a part with low pore density. This proposed method is demonstrated in a biomedical CoCr alloy system. We show that the proposed method is effective at reducing the number of experiments necessary to tailor an optimized process condition. This study also shows that the value of a decision function in a support vector machine has a physical meaning (at least in the proposed method) and is a semi-quantitative guideline for porosity density of parts fabricated by additive manufacturing.
       
  • Thermal simulation and phase modeling of bulk metallic glass in the powder
           bed fusion process
    • Abstract: Publication date: Available online 14 March 2019Source: Additive ManufacturingAuthor(s): Johan Lindwall, Victor Pacheco, Martin Sahlberg, Andreas Lundbäck, Lars-Erik Lindgren One of the major challenges with the powder bed fusion process (PBF) and formation of bulk metallic glass (BMG) is the development of process parameters for a stable process and a defect-free component. The focus of this study is to predict formation of a crystalline phase in the glass forming alloy AMZ4 during PBF. The approach combines a thermal finite element model for prediction of the temperature field and a phase model for prediction of crystallization and devitrification. The challenge to simulate the complexity of the heat source has been addressed by utilizing temporal reduction in a layer-by-layer fashion by a simplified heat source model. The heat source model considers the laser power, penetration depth and hatch spacing and is represented by a volumetric heat density equation in one dimension. The phase model is developed and calibrated to DSC measurements at varying heating rates. It can predict the formation of crystalline phase during the non-isothermal process. Results indicate that a critical location for devitrification is located a few layers beneath the top surface. The peak is four layers down where the crystalline volume fraction reaches 4.8% when 50 layers are built.
       
  • Role of Compatibilizer in 3D Printing of Polymer Blends
    • Abstract: Publication date: Available online 12 March 2019Source: Additive ManufacturingAuthor(s): Matthew E. Spreeman, Holly A. Stretz, Mark Dadmun For additive manufacturing interfacial adhesion (bead-bead) remains an important issue affecting uniformity of mechanical properties. The present work examined the role a compatibilizer would play when used in fused filament fabrication (FFF) printing. Poly(styrene-maleic anhydride) (SMA) compatiblizer was mixed in varying compositions in blends of polyamide/poly(acrylonitrile-butadiene-styrene) (PA/ABS) to improve interfacial adhesion. Both small and large-scale 3-D component properties were examined. The mechanical property anisotropy ratio, an indication of bead-bead adhesive strength (defined as a property measured along the z axis versus the x axis) is representative of adhesive strength. Large-scale (big area additive manufacturing, BAAM) tests (flexural properties) showed 62% improvement in the anisotropy ratio for modulus, 77% improvement in the anisotropy ratio of the strength, 56% improvement in the anisotropy ratio of elongation at break, and 55% improvement of the anisotropy ratio of the Charpy impact strength over the control PA values. Thus, use of compatibilized polymer blends can provide customized materials without the need for new chemistry. Addition of maleic anhydride-compatibilized ABS improved PA blend bead-bead adhesion.Graphical abstractGraphical abstract for this article
       
  • Design against Distortion for Additive Manufacturing
    • Abstract: Publication date: Available online 11 March 2019Source: Additive ManufacturingAuthor(s): Anas Yaghi, Sabino Ayvar-Soberanis, Shanmukha Moturu, Ravi Bilkhu, Shukri Afazov This paper presents the methodology and findings of a novel piece of research with the purpose of understanding and mitigating distortion caused by the combined processes of additive manufacturing (AM) and post machining to final specifications. The research work started with the AM building of a stainless steel 316 L industrial impeller that was then machined by removing around 0.5 mm from certain surfaces of the impeller’s blades and hub. Distortion and residual stresses were experimentally measured.The manufacture of the impeller by AM and then machining was numerically simulated by applying the finite element (FE) method. Distortion and residual stresses were simulated and validated. The FE distortion was then used in a numerical procedure to reverse distortion directions in order to produce a new impeller with mitigated distortion. The results have shown that distortions in the new impeller, on average, have reduced to less than 50% of the original non-compensated values.
       
  • A novel approach for understanding laser sintering of polymers
    • Abstract: Publication date: Available online 11 March 2019Source: Additive ManufacturingAuthor(s): D. Drummer, S. Greiner, M. Zhao, K. Wudy Selective laser sintering (LS) of thermoplastic powders allows for the construction of complex parts with higher mechanical properties and durability compared to other additive manufacturing methods. According to the current model of isothermal laser sintering, semi-crystalline thermoplastics need to be processed within a certain temperature range, resulting in the simultaneous presence of the material both in a molten and solid state, which is present during part building. Based on this process model, high cycle times ranging from hours to days are a thought to be a necessity to avoid warpage.In this paper, the limited validity of the model of isothermal laser sintering was shown by various experiments, as ongoing solidification could be detected a few layers below the powder bed surface. The results indicate that crystallization and material solidification is initiated at high temperatures and further progresses throughout part build-up in z-direction. Therefore, a process-adapted material characterization was performed to identify the isothermal crystallization kinetics at processing temperature and to track changes of the material state over time. A dual approach on measuring surface temperatures by infrared thermography and additional thermocouple measurements in z-direction was performed to identify further influences on the material solidification. A model experiment revealed that a few millimeters below the surface, components produced by LS are already solidified. Based on these results, the authors present an enhanced process model of isothermal laser sintering, which considers material solidification in z-direction during part build-up. In addition, a new processing strategy is derived to increase the efficiency of LS processes significantly.Graphical abstractGraphical abstract for this article
       
  • On Utilizing Topology Optimization to Design Support Structure to Prevent
           Residual Stress Induced Build Failure in Laser Powder Bed Metal Additive
           Manufacturing
    • Abstract: Publication date: Available online 9 March 2019Source: Additive ManufacturingAuthor(s): Lin Cheng, Xuan Liang, Jiaxi Bai, Qian Chen, John Lemon, Albert To Metal additive manufacturing (AM) as an emerging manufacturing technique has been gradually accepted to manufacture end-use components. However, one of the most critical issues preventing its broad applications is build failure resulting from residual stress accumulation in manufacturing process. The goal of this work is to investigate the feasibility of using topology optimization to design support structure to mitigate residual stress induced build failure. To make topology optimization computationally tractable, the inherent strain method is employed to perform fast prediction of residual stress in an AM build. Graded lattice structure optimization is utilized to design the support structure due to the open-celled and self-supporting nature of periodic lattice structure. The objective for the optimization is to minimize the mass of sacrificial support structure under stress constraint. By limiting the maximum stress under the yield strength, cracking resulting from residual stress can be prevented. To show the feasibility of the proposed method, the support structure of a double-cantilever beam and a hip implant is designed, respectively. The support structure after optimization can achieve a weight reduction of approximately 60%. The components with optimized support structures no longer suffer from stress-induced cracking after the designs are realized by AM, which proves the effectiveness of the proposed method.
       
  • Influence of mixed isotropic fiber angles and hot press on the mechanical
           properties of 3D printed composites
    • Abstract: Publication date: Available online 8 March 2019Source: Additive ManufacturingAuthor(s): Hui Mei, Zeeshan Ali, Yuekai Yan, Ihtisham Ali, Laifei Cheng This paper aims to study the mechanical properties of mixed isotropic carbon fiber 3D printed composites and further investigates the influence of hot press on the [0°/45°/90°]2 fiber angles composite with varying temperature, pressure and time. Tensile tests, autoclave treatment and microstructural observation were utilized to characterize the composites. Results revealed that the [0°/45°/90°]2 performed the highest tensile strength of 79 MPa and modulus of 3.51 GPa, compared to [30°/45°/60°]2 and [15°/45°/75°]2. This is due to the fibers along the tensile axis angle that bears maximum load in longitudinal direction. At 200 °C temperature, the hot pressed composites presented the highest tensile strength of 98 MPa and modulus of 3.93 GPa than non-hot pressed. Increased temperature caused better interface wettability between fibers and matrix. At 200 kPa pressure, the hot pressed composites showed the highest tensile strength of 100 MPa and modulus of 4.06 GPa than non-hot pressed. Further increased pressure resulted in lower tensile strength and modulus, as the material became stiffer pushing more matrix material to side leaving numerous fibers unbounded by the matrix. For 30 minutes withholding time, the hot pressed composites indicated the highest tensile strength of 106 MPa and modulus of 4.27 GPa than non-hot pressed. Increased time caused strongest interface bonding by removing the air gaps induced during printing between fibers and matrix. Results revealed that hot press significantly improved the mechanical properties of carbon fiber 3D printed composites.
       
  • Z-Pinning Approach for 3D Printing Mechanically Isotropic Materials
    • Abstract: Publication date: Available online 7 March 2019Source: Additive ManufacturingAuthor(s): Chad Duty, Jordan Failla, Seokpum Kim, Tyler Smith, John Lindahl, Vlastimil Kunc Conventional 3D printing approaches are restricted to building up material in a layer-by-layer format, which is more appropriately considered “2.5-D” printing. The layered structure inherently results in significant mechanical anisotropy in printed parts, causing the tensile strength in the build direction (z-axis) to be only a fraction of the in-plane strength – a decrease of 50-75% is common. In this study, a novel “z-pinning” approach is described that allows continuous material to be deposited across multiple layers within the volume of the part. The z-pinning process is demonstrated using a Fused Filament Fabrication (FFF) printer for polylactic acid (PLA) and carbon fiber reinforced PLA. For both materials, z-pinning increased the tensile strength and toughness in the z-direction by more than a factor of 3.5. Direct comparisons to tensile strength in the x-axis showed a significant decrease in mechanical anisotropy as the volume of the pin was increased relative to the void in the rectilinear grid structure. In fact, the PLA sample with the largest pin volume demonstrated mechanically isotropic properties within the statistical uncertainty of the tests. Tensile test results were also analyzed relative to the functional area resisting deformation for each sample.
       
  • Compulsively Constricted WAAM with Arc Plasma and Droplets Ejected from a
           Narrow Space
    • Abstract: Publication date: Available online 2 March 2019Source: Additive ManufacturingAuthor(s): Wenqiang Liu, Chuanbao Jia, Meng Guo, Jinqiang Gao, Chuansong Wu In order to realize oriented wire and arc additive manufacturing (WAAM) featured by low heat input and small droplets, a novel compulsively constricted WAAM (CC-WAAM) method was proposed and investigated in this paper. The arc burned between a metallic wire and a tungsten electrode in a narrow-space nozzle. The proposed technology could provide compulsive constriction for arc plasma and liquid metal droplets using a cubic boron nitride (CBN) ceramic nozzle. The surrounding arc was ejected out of the nozzle and offered extra heating and a good shielding environment during the whole manufacturing process. The arc and metal transfer behaviors could be improved for better performance and higher quality. The economic and efficient new method is expected to solve the challenges faced by traditional WAAM such as excessive heat input and poor geometrical accuracy. Preliminary experiments showed that the two AM layers produced by the novel method had homogeneous microstructure distribution and fine grains. The geometrical dimensions of each layer can be effectively controlled by regulating the travel speed of the torch. The wide-range adjustable heat input can effectively control the state of the metallic formation, making it possible to realize an accurate control of the microstructure and properties.Graphical abstractGraphical abstract for this article
       
  • Multi-scale Design and Fabrication of the Trabeculae Pavilion
    • Abstract: Publication date: Available online 2 March 2019Source: Additive ManufacturingAuthor(s): Roberto Naboni, Luca Breseghello, Anja Kunic Building on a large scale with Additive Manufacturing (AM) is one of the biggest manufacturing challenges of our time. In the last decade, the proliferation of 3D printing has allowed architects and engineers to imagine and develop constructions that can be produced additively. However, questions about the convenience of using this technology, and whether additive large-scale constructions can be feasible, efficient and sustainable are still open. In this research 3D printing is considered not as a question, but as an answer to the increasing scarcity of material resources in the construction industry. This paper illustrates the overarching process from concept to the realisation of the Trabeculae Pavilion, a load-responsive architecture that is entirely designed and optimized for 3D printing, using Fused Filament Fabrication (FFF) - one of the most cost-effective additive techniques of production. The research methodology is based on a multi-scale computational workflow that integrates several aspects, such as material testing, bio-inspired design algorithms, multi-criteria optimization, and production management. The work culminates in the construction process of a full-scale architectural prototype; an anticlastic shell that features a cellular structure with increased material and structural efficiency.
       
  • Analysis of material aging and the influence on the mechanical properties
           of polyamide 12 in the Multi Jet Fusion process
    • Abstract: Publication date: Available online 2 March 2019Source: Additive ManufacturingAuthor(s): Julius Riedelbauch
       
  • Mechanical and Material Properties of Castings produced via 3d printed
           molds
    • Abstract: Publication date: Available online 2 March 2019Source: Additive ManufacturingAuthor(s): Dean Snelling, Christopher Williams, Alan Druschitz Additive manufacture of sand molds via binder jetting enables the casting of complex metal geometries. Various material systems have been created for 3D printing of sand molds; however, a formal study of the materials’ effects on cast products has not yet been conducted. In this paper the authors investigate potential differences in material properties (microstructure, porosity, mechanical strength) of A356 – T6 castings resulting from two different commercially available 3D printing media. In addition, the material properties of cast products from traditional “no-bake” silica sand is used as a basis for comparison of castings produced by the 3D printed molds.
       
  • Pilot Feedback Electronic Imaging at Elevated Temperatures and its
           Potential for In-Process Electron Beam Melting Monitoring
    • Abstract: Publication date: Available online 1 March 2019Source: Additive ManufacturingAuthor(s): Hay Wong, Derek Neary, Eric Jones, Peter Fox, Chris Sutcliffe Electron Beam Melting (EBM) is an increasingly used Additive Manufacturing (AM) technique employed by many industrial sectors, including the medical device and aerospace industries. The application of this technology is, however, challenged by the lack of process monitoring and control system that underpins process repeatability and part quality reproducibility. An electronic imaging system prototype has been developed to serve as an EBM monitoring equipment, the capabilities of which have been verified at room temperature and at 320 + 10 °C. Nevertheless, in order to fully assess the applicability of this technique, electronic imaging needs to be conducted at a range of elevated temperatures to fully understand the influence of temperature on electronic image quality. Building on top of the previous electronic imaging trials at room temperature, this paper disseminates the essential step changes to allow high temperature electronic imaging: (1) modification of a signal amplifier to deal with high electron beam current during electron beam heating, and (2) design of an open-source electron beam heating algorithm to maximise flexibility for user-defined heating strategy. In this paper, electronic imaging pilot trials at elevated temperatures, ranging from room temperature to 650°C, were carried out. Image quality measure Q of the digital electron images was evaluated, and the influence of temperature was investigated. In this study, raw electronic images generated at higher temperatures had greater Q values, i.e. better global image quality. It has been demonstrated that, for temperatures between 30°C-650°C, the influence of temperature on electronic image quality was not adversely affecting the visual clarity of image features. It is thus envisaged that the prototype has a potential to contribute to in-process EBM monitoring, and this paper has served as a crucial precursor to the ultimate goal of carrying out electronic imaging under real EBM building condition.
       
  • An overview of residual stresses in metal powder bed fusion
    • Abstract: Publication date: Available online 1 March 2019Source: Additive ManufacturingAuthor(s): Jamison L. Bartlett, Xiaodong Li Metal additive manufacturing (AM) has garnered tremendous research and industrial interest in recent years; in the field, powder bed fusion (PBF) processing is the most common technique, with selective laser melting (SLM) dominating the landscape followed by electron beam melting (EBM). Through continued process improvements, these methods are now often capable of producing high strength parts with static strengths exceeding their conventionally manufactured counterparts. However, PBF processing also results in large and anisotropic residual stresses (RS) that can severely affect fatigue properties and result in geometric distortion. The dependence of RS formation on processing variables, material properties and part geometry has made it difficult to predict efficiently and has hindered widespread acceptance of AM techniques. Substantial investigations have been conducted with regards to RS in PBF processing, which have illuminated a number of important relationships, yet a review encompassing this information has not been available. In this review, we survey and assemble the knowledge existing in the literature regarding RS in PBF processes. A discussion of background mechanics for RS development in AM is provided along with methods of measurement, highlighting the anisotropic nature of the stress fields. We then review modeling efforts and in-process experimental measurements made to advance process understanding, followed by a thorough analysis and summary of the known relationships of both material properties and processing variables to resulting RS. The current state of knowledge and future research needs for the field are discussed.
       
  • Micromechanical Modeling of Irreversible Thermal Strain
    • Abstract: Publication date: Available online 27 February 2019Source: Additive ManufacturingAuthor(s): Tone D’Amico, Connor Barrett, Joseph Presing, Amy M. Peterson Warping and delamination in material extrusion additive manufacturing (MatEx) parts are well documented and irreversible thermal strain (ITε) has also recently been reported. As parts are built up as a collection of roads, they are analogous to fiber reinforced composites. However, the lack of bonding between the matrix, air, and the reinforcing phase, polymer roads, necessitates the development of a micromechanical model for these parts. In this work, a micromechanical model for MatEx parts is developed to describe bulk part behavior that incorporates void fraction, road morphology, and bonding between and within layers. Previous work suggested ITε occurred within roads. Combining stress accumulation within roads with the micromechanical model successfully predicted ITε and provided a rationale for ITε dependence on both layer thickness and raster angle. These results show ITε can be predicted and, therefore, controlled, making MatEx part annealing more feasible and opening the possibility of one-way shape memory in parts. Additionally, the micromechanical model developed can be used to explain bonding limitations in MatEx based on road and bond geometry.
       
  • Real-time process monitoring of core shifts during metal casting with
           wireless sensing and 3D sand printing
    • Abstract: Publication date: Available online 26 February 2019Source: Additive ManufacturingAuthor(s): Jason Walker, Andrew Prokop, Chad Lynagh, Brian Vuksanovich, Brett Conner, Kirk Rogers, Jerry Thiel, Eric MacDonald In this work, real-time in-process monitoring of core motion in metal castings is demonstrated though the use of two emerging technologies. 3D sand printing (3DSP) is a binder jetting additive manufacturing process that is quickly manifesting itself as a technological disrupter in the metal casting industry. Based on its direct digital manufacturing principle, 3DSP enables complex mold and core design freedom that has been previously unavailable to foundry engineers. In addition, the miniaturization and affordability of electronics and sensing equipment is rapidly accelerating. Here, these two shifting paradigms are leveraged together. An experimental casting and mold were designed in this research to demonstrate and evaluate wireless sensing of core shifts. With the use of 3D sand printing, precisely sized and located pockets were manufactured inside of cores. Miniature wireless Bluetooth sensors capable of measuring acceleration and rotation were then embedded inside the cores. From these, high fidelity data was captured wirelessly from the sensors during the casting process. With strategically designed core prints designed to allow varying levels of core motion, it is shown that core shifts can be measured and discriminated during casting in real time.
       
  • Heterogeneous Materials Design in Additive Manufacturing: Model
           Calibration and Uncertainty-Guided Model Selection
    • Abstract: Publication date: Available online 25 February 2019Source: Additive ManufacturingAuthor(s): David Garcia, Ziling Wu, Jee Yun Kim, Hang Z. Yu, Yunhui Zhu Multi-material additive manufacturing enables high-performance heterogeneous design at the mesoscale, through which bulk parts can be engineered to adapt to complex loading conditions. The optimization of multi-material parts relies on accurate forward prediction, which is challenging to achieve owing to the complex processing conditions in additive manufacturing and the resultant uncertainties in material properties. To address these limitations, here we present a new model calibration and model selection framework based on the high dimensional, local-scale deformation data. By matching the pixel-level deformation data from digital image correlation experiments and constitutive modeling, the presented framework enables more accurate prediction and significant reduction of the prediction uncertainties, as compared to the single material calibration approach that is widely used in additive manufacturing. In turn, this enables quantitative comparison of the candidate models, so the most accurate and computationally efficient constitutive model can be selected for forward prediction in heterogeneous material design. The advantages of the framework are demonstrated using a multi-polymer system manufactured by dual-extrusion additive manufacturing, which consists of two constituent materials with dramatically different deformation behaviors.
       
  • Introduction to the Design Rules for Metal Big Area Additive Manufacturing
    • Abstract: Publication date: Available online 25 February 2019Source: Additive ManufacturingAuthor(s): Clayton Greer, Andrzej Nycz, Mark Noakes, Brad Richardson, Brian Post, Thomas Kurfess, Lonnie Love Wire feed metal additive manufacturing offers advantages, such as large build volumes and high build rates, over powder bed and blown powder techniques, but it has its own disadvantages, i.e., lower feature resolution and bead morphology control issues. A new wire feed metal additive manufacturing process called Metal Big Area Additive Manufacturing (mBAAM) uses a Gas Metal Arc Weld system on an articulated robot arm to increase build volume and deposition rate in comparison to powder bed techniques. The high deposition rate implies a low-resolution process; therefore, parts designed for mBAAM must incorporate the use of machining to achieve certain features. This paper presents an introduction to how design rules, such as overhang constraint, large weld bead thickness, and support structure, for mBAAM interact in the context of an excavator arm case study, which was designed using topology optimization.
       
  • Multiscale study of different types of interface of a buffer material in
           powder-based directed energy deposition: example of Ti6Al4V/Ti6Al4V - Mo /
           Mo - Inconel 718
    • Abstract: Publication date: Available online 23 February 2019Source: Additive ManufacturingAuthor(s): Amélie Thiriet, Catherine Schneider-Maunoury, Pascal Laheurte, Didier Boisselier, Laurent WeissABSTRACTWhen it is difficult to deposit a material A on a material B, it is possible to create a Functionally Graded Material (FGM) using a buffer material between them to avoid the appearance of defects. The literature shows that it is very difficult, nay impossible, to have an efficient metallurgical bond between Ti6Al4V and Inconel-Mo alloys without cracks, porosities or delamination. A buffer material is therefore needed (here 25% Ti6Al4V – 75% Mo) and the fine analysis of the two interfaces thus created makes it possible to define the relevance of the choice of the buffer. Moreover, the understanding of the phenomena taking place at the interface allows the preservation of the structural integrity of a FGM made by additive manufacturing. CLAD® powder-based directed energy deposition allows the building of parts containing FGM and/or buffer materials directly during the process. The study of the interfaces at both sides of the buffer material is essential. In this paper, the first interface 100 Ti6Al4V / 25 Ti6Al4V – 75 Mo (in wt%) is smooth, suggesting that there has been diffusion between both alloys. The second one, 25 Ti6Al4V – 75 Mo / 30 Inconel 718 – 70 Mo, contains numerous exotic structures between both alloys. For such a sharp interface, we show in this paper that a microscopic study is not sufficient, but a finer scale is necessary to have a good metallurgical insight. Thus, EDS, TKD and X-ray crystallography were performed right on this interface and revealed three main structures: a hexagonal matrix, a cubic structure and an ordered hexagonal one. The hexagonal matrix appears to consist of Ni3Ti and the ordered hexagonal one of NiMo.
       
  • A method for predicting geometric characteristics of polymer deposition
           during fused-filament-fabrication
    • Abstract: Publication date: Available online 23 February 2019Source: Additive ManufacturingAuthor(s): Michael Hebda, Claire McIlroy, Ben Whiteside, Fin Caton-Rose, Phil Coates In recent years 3D printing has gained popularity amongst industry professionals and hobbyists alike, with many new types of Fused Filament Fabrication (FFF) apparatus types becoming available on the market. A massively overlooked component of FFF is the requirement for a simple method to calculate the geometries of polymer depositions extruded during the FFF process. Manufacturers have so far achieved adequate methods to calculate tool-paths through so called slicer software packages which calculate the required velocities of extrusion from prior knowledge and data. Presented here is a method for obtaining a series of equations for predicting height, width and cross-sectional area values for given processing parameters within the FFF process for initial laydown on to a glass surface.
       
  • Additive Manufacturing of Ceramics from Preceramic Polymers: A Versatile
           Stereolithographic Approach Assisted by Thiol-Ene Click Chemistry
    • Abstract: Publication date: Available online 22 February 2019Source: Additive ManufacturingAuthor(s): Xifan Wang, Franziska Schmidt, Dorian Hanaor, Paul H. Kamm, Shuang Li, Aleksander Gurlo Here we introduce a versatile stereolithographic route to produce three different kinds of Si-containing thermosets that yield high performance ceramics upon thermal treatment. Our approach is based on a fast and inexpensive thiol-ene free radical addition that can be applied for different classes of preceramic polymers with carbon-carbon double bonds. Due to the rapidity and efficiency of the thiol-ene click reactions, this additive manufacturing process can be effectively carried out using conventional light sources on benchtop printers. Through light initiated cross-linking, the liquid preceramic polymers transform into stable infusible thermosets that preserve their shape during the polymer-to-ceramic transformation. Through pyrolysis the thermosets transform into glassy ceramics with uniform shrinkage and high density. The obtained ceramic structures are nearly fully dense, have smooth surfaces, and are free from macroscopic voids and defects. A fabricated SiOC honeycomb was shown to exhibit a significantly higher compressive strength to weight ratio in comparison to other porous ceramics.Graphical abstractGraphical abstract for this articleSchematic representation of the stereolithographic additive manufacturing of preceramic polymers into intricately patterned thermosets assisted by thiol-ene click chemistry and their subsequent conversion into ceramics
       
  • Binder Jetting of the AlCoCrFeNi Alloy
    • Abstract: Publication date: Available online 20 February 2019Source: Additive ManufacturingAuthor(s): Dennis Karlsson, Greta Lindwall, Andreas Lundbäck, Mikael Amnebrink, Magnus Boström, Lars Riekehr, Mikael Schuisky, Martin Sahlberg, Ulf Jansson High density components of an AlCoCrFeNi alloy, often described as a high-entropy alloy, were manufactured by binder jetting followed by sintering. Thermodynamic calculations using the CALPHAD approach show that the high-entropy alloy is only stable as a single phase in a narrow temperature range below the melting point. At all other temperatures, the alloy will form a mixture of phases, including a sigma phase, which can strongly influence the mechanical properties. The phase stabilities in built AlCoCrFeNi components were investigated by comparing the as-sintered samples with the post-sintering annealed samples at temperatures between 900 °C and 1300 °C. The as-sintered material shows a dominant B2/bcc structure with additional fcc phase in the grain boundaries and sigma phase precipitating in the grain interior. Annealing experiments between 1000 °C and 1100 °C inhibit the sigma phase and only a B2/bcc phase with a fcc phase is observed. Increasing the temperature further suppresses the fcc phase in favor for the B2/bcc phases. The mechanical properties are, as expected, dependent on the annealing temperature, with the higher annealing temperature giving an increase in yield strength from 1203 MPa to 1461 MPa and fracture strength from 1996 MPa to 2272 MPa. This can be explained by a hierarchical microstructure with nano-sized precipitates at higher annealing temperatures. The results enlighten the importance of microstructure control, which can be utilized in order to tune the mechanical properties of these alloys. Furthermore, an excellent oxidation resistance was observed with oxide layers with a thickness of less than 5 µm after 20 h annealing at 1200 °C, which would be of great importance for industrial applications.
       
  • All-printed Multilayer High Voltage Capacitors with Integrated Processing
           Feedback
    • Abstract: Publication date: Available online 19 February 2019Source: Additive ManufacturingAuthor(s): James O. Hardin, Christopher A. Grabowski, Matthew Lucas, Michael F. Durstock, J. Daniel Berrigan Template-free 3D printing of electronic devices has the potential to broaden electronics integration to include complex integrated form factors, but success requires precise, adaptive control over materials processing. The development of such manufacturing technologies requires exploration of new combinations of ink sets, printing techniques, and automation strategies. In this work, solution-cast direct-write (SC-DW) was used to print poly(methyl methacrylate) (PMMA) dielectric films with breakdown fields of 790 V/µm, similar to commercially available biaxial-oriented polypropylene (BOPP) films. Furthermore, a complementary composite ink for printing conductive features was developed with conductivities of ˜10,000 S cm-1. A closed-loop feedback system that links deposition with characterization to enable µm-precision deposition for over 20 h without human involvement. This closed-loop control scheme led to both single- and double-layer high-voltage capacitors to be 3D printed with capacitances as large as 314 pF (at 1 kHz) and breakdown voltages over 1,000 V, which is significant step towards repeatable template-free, 3D printing of electronics for rapid prototyping of multifunctional devices.Graphical abstractGraphical abstract for this articleA process for 3D printing multimaterial, multilayer electronics with high performance is demonstrated using high voltage capacitors as a model system. Dielectric and conductive materials are characterized independently then combined together into a functional device which is then characterized. The resulting capacitors have excellent capacitance, (322 pF) and breakdown voltage (1,000 V) relative to literature.
       
  • Synchronized Multi-Spot Scanning Strategies for the Laser Powder Bed
           Fusion Process
    • Abstract: Publication date: Available online 19 February 2019Source: Additive ManufacturingAuthor(s): Chun-Yu Tsai, Chung-Wei Cheng, An-Chen Lee, Mi-Ching Tsai The laser powder bed fusion (LPBF) process can produce parts with complex internal geometries that cannot be easily manufactured using a material removal process. However, owing to the different heat transfer efficiencies of a laser melting process, the optimal process parameters are limited to a small range. This study used galvanometric scanner technology and a diffractive optical element (DOE) to build an experimental multi-spot LPBF system. Adjustable characteristics were the angle and the lateral distance between spots. An adjustable multi-spot method was used to modulate the temperature field on the powder bed and enhance the processing quality and throughput. The results from the synchronized three-spot method using different scanning strategies improved the layer surface roughness Ra by 3.2 μm. Moreover, the scanning time was decreased by 38.1% of the single-spot method.
       
  • Modification of Mechanical Properties and Resolution of Printed
           Stereolithographic Objects through RAFT Agent Incorporation
    • Abstract: Publication date: Available online 18 February 2019Source: Additive ManufacturingAuthor(s): Brian J. Green, C. Allan Guymon Stereolithography (SL) is an additive manufacturing technique that uses light to cure liquid resins into thin layers and fabricate 3-dimensional objects layer by layer. SL is of high interest for small-volume manufacturing and rapid prototyping because of its ability to relatively quickly create objects with intricate 100 µm or smaller features. However, widespread adoption of SL faces a number of obstacles including unsuitable thermomechanical properties, anisotropic properties, and limited resolution and fidelity. In this work, we incorporate a reversible addition-fragmentation chain transfer (RAFT) agent into a glassy acrylate formulation to modify mechanical properties and improve resolution of objects printed using digital light processing (DLP) SL. Incorporating a small amount of a trithiocarbonate RAFT agent into the formulation leads to increased elongation and toughness accompanied by a small decrease in tensile modulus. To determine anisotropic properties of DLP SL, samples were printed in “horizontal” or “vertical” directions, where the long axis of the sample was printed in the x-axis or z-axis, respectively. RAFT samples printed in a vertical orientation exhibit a higher modulus than non-RAFT controls prior to post-cure in addition to a similar modulus with increased toughness upon UV post-cure due to the living/controlled nature of RAFT polymerization. Furthermore, incorporating a RAFT agent into the formulation allows significantly higher fidelity printing of a broad range of positive and negative features as small as 100 µm. The RAFT formulation allows objects to be printed with significantly better fidelity than non-RAFT formulations, even when a radical scavenger is incorporated to mimic reaction rates observed from the RAFT formulation. Additionally, the RAFT agent significantly increases the critical energy parameter determined from the SL working curve, indicating an increase in gel point conversion. This work demonstrates the benefits of using controlled/living polymerization in a highly cross-linked acrylate system to improve toughness, modify anisotropic properties, and print high-fidelity features with enhanced properties in 3D printed materials.
       
  • Additively manufactured 316L stainless steel with improved corrosion
           resistance and biological response for biomedical applications
    • Abstract: Publication date: Available online 16 February 2019Source: Additive ManufacturingAuthor(s): M.J.K. Lodhi, K.M. Deen, M.C. Greenlee-Wacker, Waseem Haider Enhancing the corrosion resistance and improving the biological response to 316 L stainless steel is a long-standing and active area of biomedical research. Here, we analyzed the structure and corrosion tendency of selective laser melted-additively manufactured (AM) 316 L stainless steel (AM 316L SS) and its wrought counterpart. SEM analysis showed a fine (500–800 nm) interconnected sub-granular structure for the AM 316L SS, but a polygonal coarse-grained structure for the wrought sample. Relative to the wrought sample, the AM 316L SS also exhibited a higher charge transfer resistance (approx. one order of magnitude) and higher breakdown potential (˜1000 mV vs. SCE) when tested in biological electrolytes, which included human serum, PBS, and 0.9 M NaCl. A higher pitting resistance (extended passive region) and improved stability of the AM 316L SS was attributed to its dense structure of oxide film and refined microstructure. Finally, material compatibility with pre-osteoblasts was analyzed. Large cytoplasmic extension of osteoblast cells and retention of stiller morphology was observed when cells were cultured on the AM 316L SS as compared to its wrought counterpart, suggesting that the AM 316L SS was a better substrate for cell spreading and differentiation. The differentiation of cultured cells was further validated by western blot for Runx2. Runx2, an anti–proliferative marker indicative of differentiation, was equivalent in cells cultured on either samples, but overall more cells were present on the AM 316L SS. Given its higher corrosion resistance and ability to support osteoblast adherence, spreading and differentiation, the AM 316L SS has potential for use in the biomedical industry.
       
  • Selective Laser Sintering and Multi Jet Fusion: process-induced
           modification of the raw materials and analyses of parts performance
    • Abstract: Publication date: Available online 14 February 2019Source: Additive ManufacturingAuthor(s): Francesco Sillani, Rob G. Kleijnen, Marc Vetterli, Manfred Schmid, Konrad Wegener Additive Manufacturing (AM) is a rapidly expanding framework of production technologies evolving in different directions, following the needs of different industries. Among powder bed fusion technologies, one of the main branches of AM, Selective Laser Sintering (SLS) is the second oldest one. In the last few years, a direct rival has emerged: Multi Jet Fusion (MJF). The purpose of this work is to compare these processes throughout a systematic analysis of powder and final parts made of commercially available polyamide 12 (PA12). Differences have been spotted both on the molecular and powder scale, with end capping of the MJF feedstock together with different thermal properties of the new and recycled materials. On the other hand, flowing properties are similar among the two virgin and recycled powders, with only a significant change in the fraction of fines for SLS material. The parts produced through SLS exhibit higher Young's modulus but lower elongation at break and ultimate tensile strength if compared to the ones obtained using MJF. This confirms once more that the occurrence of postcondensation has a profound influence on the final properties. Also Charpy impact strength according to ISO 179 has been tested, confirming the literature data for SLS, but also showing higher strength in the out-of-plane direction for un-notched specimens coming from MJF. Finally, the evaluation of advanced area roughness parameters such as surface roughness, skewness and kurtosis according to ISO 25178 allows the ascertainment of subtle differences arising in parts with different positioning on the build platform, possibly due to the inks employed in the MJF process.
       
  • Estimation of Part-to-Powder Heat Losses as Surface Convection in Laser
           Powder Bed Fusion
    • Abstract: Publication date: Available online 12 February 2019Source: Additive ManufacturingAuthor(s): Chao Li, Michael F. Gouge, Erik R. Denlinger, Jeff E. Irwin, Pan Michaleris Thermal modeling of additive manufacturing processes such as Laser Powder Bed Fusion is able to calculate a thermal history of a build. This simulated thermal history can in turn be used as an input to further simulate temperature related characteristics such as residual stress, distortion, microstructure, lack of fusion porosity, and hot spots. In order to estimate the heat loss to the powder bed during the process, convective heat transfer is widely used as thermal boundary condition in finite element modeling of Laser Powder Fusion processes. However, this convection coefficient is usually selected based on empirical estimation or model tuning. In this work, FEA models of the part and surrounding powder are used as a reference to determine the surface convection BC's for modeling the part only. Seven types of commonly used AM materials with a wide range of thermal conductivities were studied for better testing of the conductivity dependency of the convection coefficient. The convection coefficient values, which predict similar thermal history as the powder model, are found to be a function of thermal conductivity of the deposited material and the cross-sectional thickness of the part feature. A new thickness dependent convection boundary condition is proposed and found to be capable of predicting much closer thermal history to the powder model. These newly developed boundary conditions improve the peak temperature prediction accuracy by 36% while running in 1/4th of the time as the powder model.
       
  • Automatic Fault Detection for Laser Powder-Bed Fusion using
           Semi-Supervised Machine Learning
    • Abstract: Publication date: Available online 11 February 2019Source: Additive ManufacturingAuthor(s): Ikenna A. Okaro, Sarini Jayasinghe, Chris Sutcliffe, Kate Black, Paolo Paoletti, Peter L. Green Risk-averse areas such as the medical, aerospace and energy sectors have been somewhat slow towards accepting and applying Additive Manufacturing (AM) in many of their value chains. This is partly because there are still significant uncertainties concerning the quality of AM builds.This paper introduces a machine learning algorithm for the automatic detection of faults in AM products. The approach is semi-supervised in that, during training, it is able to use data from both builds where the resulting components were certified and builds where the quality of the resulting components is unknown. This makes the approach cost efficient, particularly in scenarios where part certification is costly and time consuming.The study specifically analyses Laser Powder-Bed Fusion (L-PBF) builds. Key features are extracted from large sets of photodiode data, obtained during the building of 49 tensile test bars. Ultimate tensile strength (UTS) tests were then used to categorise each bar as ‘faulty’ or ‘acceptable’. Using a variety of approaches (Receiver Operating Characteristic (ROC) curves and 2-fold cross-validation), it is shown that, despite utilising a fraction of the available certification data, the semi-supervised approach can achieve results comparable to a benchmark case where all data points are labelled. The results show that semi-supervised learning is a promising approach for the automatic certification of AM builds that can be implemented at a fraction of the cost currently required.
       
  • Comparison of the fatigue strength between additively and conventionally
           fabricated tool steel 1.2344
    • Abstract: Publication date: Available online 10 February 2019Source: Additive ManufacturingAuthor(s): R. Dörfert, J. Zhang, B. Clausen, H. Freiße, J. Schumacher, F. Vollertsen The residual porosity and surface roughness of metal materials generated via additive manufacturing are generally regarded as the major influence factors on the fatigue strength. The mechanical properties of specimens out of tool steel 1.2344 were investigated. Tensile strength and hardness achieved results in the range of conventionally fabricated parts, whereas a significantly lower fatigue strength was observed. Cracks were induced by the present cavities as well as in the steel matrix. Further investigations of the oxygen content showed a high oxygen content of 570 ppm homogeneously distributed inside the specimens potentially limiting the strength of the matrix itself.Graphical Graphical abstract for this article
       
  • Residual stress and distortion of rectangular and S-shaped Ti-6Al-4V parts
           by Directed Energy Deposition: Modelling and experimental calibration
    • Abstract: Publication date: March 2019Source: Additive Manufacturing, Volume 26Author(s): Xufei Lu, Xin Lin, Michele Chiumenti, Miguel Cervera, Yunlong Hu, Xianglin Ji, Liang Ma, Haiou Yang, Weidong Huang Residual stresses and distortion in Additive Manufactured (AM) parts are two key obstacles which seriously hinder the wide application of this technology. Nowadays, understanding the thermomechanical behavior induced by the AM process is still a complex task which must take into account the effects of both the process and the material parameters, the microstructure evolution as well as the pre-heating strategy. One of the challenges of this work is to increase the complexity of the geometries used to study the thermomechanical behavior induced by the AM process. The reference geometries are a rectangular and a S-shaped structures made of 44-layers each. The samples have been fabricated by Directed Energy Deposition (DED). In-situ thermal and distortion histories of the substrate are measured in order to calibrate the 3D coupled thermo-mechanical model. Once the numerical results showed a good agreement with the temperature measurements, the validated model has been used to predict the residual stresses and distortions. Different process parameters have been analyzed to study their sensitivity to the process assessment. Different preheating strategies have been also analyzed to check their effectiveness on the mitigation of both distortions and residual stresses. Finally, some simplifications of the actual scanning sequence are proposed to reduce the computational cost without loss of the accuracy of the simulation framework.
       
  • A Robotic Cell for Performing Sheet Lamination-based Additive
           Manufacturing
    • Abstract: Publication date: Available online 6 February 2019Source: Additive ManufacturingAuthor(s): Prahar M. Bhatt, Ariyan M. Kabir, Max Peralta, Hugh A. Bruck, Satyandra K. Gupta Many applications require structures composed of layers of heterogeneous materials and prefabricated components embedded between the layers. The existing additive manufacturing process based on layered object manufacturing is not able to handle multiple layer materials and cannot embed prefabricated components. Moreover, the existing process imposes restrictions on the material options. This significantly limits the type of heterogeneous structures that can be manufactured using traditional additive manufacturing. This paper presents an extension of sheet lamination object manufacturing process by using a robotic cell to perform the sheet manipulation and handling. It makes the following three advances: (1) enabling the use of multi-material layers and inclusion of prefabricated components between the layers, (2) developing an algorithmic foundation to facilitate automated generation of robot instructions, and (3) identifying the relevant process constraints related to speed, accuracy, and strength. We demonstrate the system capabilities by using three case studies.
       
  • Calibration of galvanometric scan heads for additive manufacturing with
           machine assembly defects consideration
    • Abstract: Publication date: Available online 5 February 2019Source: Additive ManufacturingAuthor(s): K. Godineau, S. Lavernhe, C. Tournier The calibration of additive manufacturing machines using scanning heads in processes such as Laser Powder Bed Fusion (LPBF) and vat photopolymerization is an iterative and time-consuming process often based on limited physical models. Indeed, the relationship between the laser spot position in the work plane and the actuators position (galvanometers) is achieved by interpolating correction tables experimentally determined. In this paper, representative geometrical models of the real system are established in order to reduce the time required to obtain the final correction tables. For this purpose, a geometrical model is developed with assembly defects consideration. This model is used in a process of defects identification to obtain a virtual machine representative of the real system and thus directly generates the final correction tables. The geometrical model thereby developed is used to quantify the impact of assembly defects on the laser spot position, to compensate them and to reduce the calibration time of an additive manufacturing machine.
       
  • Effect of Wire and Arc Additive Manufacturing (WAAM) Process Parameters on
           Bead Geometry and Microstructure
    • Abstract: Publication date: Available online 1 February 2019Source: Additive ManufacturingAuthor(s): Malcolm Dinovitzer, Xiaohu Chen, Jeremy Laliberte, Xiao Huang, Hanspeter Frei This paper discusses the effects of process parameters in TIG based WAAM for specimens created using Hastelloy X alloy (Haynes International) welding wire and 304 stainless-steel plate as the substrate. The Taguchi method and ANOVA were used to determine the effects of travel speed, wire feed rate, current, and argon flow rate on the responses including bead shape and size, bead roughness, oxidation levels, melt through depth, and the microstructure. Travel speed and current were found to have the largest effect on the responses. Increasing travel speed or decreasing current caused a decrease in melt through depth and an increase in roughness. Printing strategies were tested using specimens of multiple layers and no significant difference was found between printing layers in the same direction and printing layers in alternating directions. No observable interface between the layers was present suggesting a complete fusion between layers with no oxidation. Three distinct zones were identified within the three- and eight-layer samples. The zones were characterized by the size and distribution of the molybdenum carbide formations within the matrix grain formations.
       
  • Improvement in build-direction thermal conductivity in extrusion-based
           polymer additive manufacturing through thermal annealing
    • Abstract: Publication date: Available online 31 January 2019Source: Additive ManufacturingAuthor(s): Hardikkumar Prajapati, Divya Chalise, Darshan Ravoori, Robert M. Taylor, Ankur Jain While additive manufacturing offers significant advantages compared to traditional manufacturing technologies, deterioration in thermal and mechanical properties compared to properties of the underlying materials is a serious concern. In the context of polymer extrusion based additive manufacturing, post-process approaches, such as thermal annealing have been reported for improving mechanical properties based on reptation of polymer chains and enhanced filament-to-filament adhesion. However, there is a lack of similar work for improving thermal properties such as thermal conductivity. This paper reports significant enhancement in build-direction thermal conductivity of polymer extrusion based parts as a result of thermal annealing. Over 150% improvement is observed when annealed at 135 °C for 96 hours. The effect of annealing temperature and time on thermal conductivity enhancement is investigated through experiments. A theoretical model based on Arrhenius kinetics for neck growth and a heat transfer model for the consequent impact on inter-layer thermal contact resistance is developed. Predicted thermal conductivity enhancement is found to be in good agreement with experimental data for a wide range of annealing temperature and time. The theoretical model may play a key role in developing practical thermal annealing strategies that account for the multiple constraints involved in annealing of polymer parts. This work may facilitate the use of polymer extrusion additive manufacturing for parts that are required to withstand thermal loads.
       
  • Heat Source Management in Wire-Arc Additive Manufacturing Process for
           Al-Mg and Al-Si Alloys
    • Abstract: Publication date: Available online 30 January 2019Source: Additive ManufacturingAuthor(s): Kohei Oyama, Spyros Diplas, Mohammed M'hamdi, Anette E. Gunnæs, Amin S. Azar Modelling of wire-arc additive manufacturing process is an effective way for adapting the optimum parameters as well as understanding and managing the sequences of layer-by-layer deposition. Some of these parameters such as toolpath, deposition intervals and heat source power play important roles in improving the process viability and cost efficiency. In this article, we have studied Al-5Mg, Al-3Si alloys as demonstrators, from both experimental and modelling perspectives, to benchmark different deposition parameters and provided guidelines for optimising the process conditions. Physical values such as total distortion and residual stress were selected as indicators for the manufacturability of the structure. The simulations were performed by the Simufact Welding software, that is outfitted with the MARC solver and the experiments were executed in a robotic cell. We have introduced a method for optimising the process parameters based on the heat source power modification and selection of unique parameters for each deposition layer. This was performed by monitoring the evolution of the molten pool size and geometry when building a wall structure. The results suggest that achieving an uninterrupted deposition process entails modification of the heat input for each layer. Thus, a simple analytical method was proposed to estimate the heat input reduction coefficient for a wall structure as a function of molten pool geometry and the height at which, the new layer is being deposited. It was also shown that a generic selection of parameters for aluminium alloys may impair the eventual quality for some of the alloys due to their inherent physical properties such as high temperature flowability.
       
  • High-temperature mechanical properties of alloy 718 produced by laser
           powder bed fusion with different processing parameters
    • Abstract: Publication date: Available online 30 January 2019Source: Additive ManufacturingAuthor(s): Alexandra Hilaire, Eric Andrieu, Xinhua Wu The laser powder bed fusion (LPBF) process produces complex microstructures and specific defects. To build structural components with an acceptable mechanical integrity, optimization of the processing parameters is required. In addition, the evolution of defects under service conditions should be investigated. In this study, the nickel-based alloy 718 was studied in the as-built metallurgical state. Laser processing parameters such as the laser power, scanning speed, and hatch spacing were modified to evaluate their effects on the porosity, microstructure, and mechanical properties at high temperatures. The porosity and pore shape were evaluated using relative density measurements and image analysis. Moreover, the effects of the microstructure and defects on the tensile properties and damaging processes at 650 °C were investigated in air. The results revealed that the loading direction is critical to the mechanical integrity of the alloy, due to the specific orientation of the microstructural interfaces and defects. In addition, from observations of the fracture surfaces, inter-dendritic phases were found to act as crack initiation sites. A tensile test was conducted in vacuum at 650 °C and 2.10-4 s-1, and the results indicated that damage processes were not affected by oxidation when the experiments were carried out in air.
       
  • New approach to evaluate 3D laser printed parts in powder bed fusion-based
           additive manufacturing in-line within closed space
    • Abstract: Publication date: Available online 30 January 2019Source: Additive ManufacturingAuthor(s): Michael Kalms, Ryuichi Narita, Claus Thomy, Frank Vollertsen, Ralf B. Bergmann Additive manufacturing that allows layer by layer shaping of complex structures is of rapidly increasing interest in production technology. A particularly rapid prototyping technique of additive manufacturing is laser beam melting (LBM). This 3D printing method is based on a powder bed fusion technique, using a high-powered laser to melt and consolidate metallic powders. The process needs a tightly controlled atmosphere of inert gas, which requires a confined space of a building chamber. This and more process related factors like elevated temperatures, laser radiation or the resulting light intensity caused by the melting of metals, make a closed-loop quality control very ambitious. In this paper, we propose a new in-process approach for quality control with high precision metrology based on structured light. The precise layer by layer dimensional measurement of both the printed part and the powder deposition, allows for process assessment in- or off-line.
       
  • Tensile properties and failure behavior of chopped and continuous carbon
           fiber composites produced by Additive Manufacturing
    • Abstract: Publication date: Available online 29 January 2019Source: Additive ManufacturingAuthor(s): Juan Naranjo Lozada, Horacio Ahuett-Garza, Pedro Orta Castañón, Wilco M.H. Verbeeten, Daniel Sáiz González The use of additive manufacturing (AM) is rapidly expanding in many industries mostly because of the flexibility to manufacture complex geometries. Recently, a family of technologies that produce fiber reinforced components has been introduced, widening the options available to designers. AM fiber reinforced composites are characterized by the fact that process related parameters such as the amount of reinforcement fiber, or printing architecture, significantly affect the tensile properties of final parts. To find optimal structures using new AM technologies, guidelines for the design of 3D printed composite parts are needed. This paper presents an evaluation of the effects that different geometric parameters have on the tensile properties of 3D printed composites manufactured by fused filament fabrication (FFF) out of continuous and chopped carbon fiber reinforcement. Parameters such as infill density and infill patterns of chopped composite material, as well as fiber volume fraction and printing architecture of continuous fiber reinforcement (CFR) composites are varied. The effect of the location of the initial deposit point of reinforcement fibers on the tensile properties of the test specimens is studied. Also, the effect that the fiber deposition pattern has on tensile performance is quantified. Considering the geometric parameters that were studied, a variation of the Rule of Mixtures (ROM) that provides a way to estimate the elastic modulus of a 3D printed composite is proposed. Findings may be used by designers to define the best construction parameters for 3D printed composite parts.
       
  • Design and direct additive manufacturing of three-dimensional surface
           micro-structures using material jetting technologies
    • Abstract: Publication date: Available online 28 January 2019Source: Additive ManufacturingAuthor(s): Jessirie Dilag, Tiffany Chen, Sheng Li, Stuart A. Bateman The ability to directly print 3D microstructures across the surface of large dimension substrates opens up numerous possibilities not feasible with conventional 2D or 2.5D printing or coating techniques. Demonstrated herein is a method to print 3D microstructures onto clear poly(methyl methacrylate) (PMMA) plates using material jetting technologies. Contact angle and profilometry analysis indicated that the VeroCyan™ photopolymer had enhanced wetting of the PMMA surface leading to greater droplet spreading affecting the geometries printed compared to VeroCyanTM integrated models. Strategies to manipulate the interfacial interactions and hence adhesion of the VeroCyan™ photopolymer were investigated by varying PMMA surface free energy through physio-chemical and chemical techniques including (i) corona discharge, followed by post-treatments with 3-(trimethoxysilyl)propyl methacrylate, polyethyleneimine graft chemicals, and (ii) plasma treatments with air and plasma polymerisation of 1,7-octadiene. The surface chemistry and wetting behaviour played a crucial role in influencing interfacial interactions with the VeroCyan™ photopolymer hence its adhesion to the PMMA surface.Graphical Graphical abstract for this article
       
  • Laser strip cladding for large area metal deposition
    • Abstract: Publication date: Available online 28 January 2019Source: Additive ManufacturingAuthor(s): Jari Tuominen, Marc Kaubisch, Sebastian Thieme, Jonne Näkki, Steffen Nowotny, Petri Vuoristo Directed energy deposition (DED) processes rely frequently on metallic powder and wire feedstock materials. Several grades of metallic strips are, however, commercially available but not yet largely utilized in DED. This paper introduces newly developed laser strip cladding process, which can be used for surfacing, repair and additive manufacturing. Cladding tests consisted of single-layer single- and multi-bead tests on planar and round bar type base materials using a 30 mm wide solid Alloy 625 strip. The results showed that with 8 kW laser power 34 mm wide and ˜2 mm thick single beads on steel can be produced with low dilution and fusion bond with high deposition (8 kg/h) rates. In multi-bead tests coverage rates of 0.45 m2/h were reached. Corrosion performance of clad deposit was influenced by inhomogeneous distribution of intermixed iron from the base material on test surface. In addition to high productivity, the developed process takes the advantage of the large build volume (>1 m3) and complete material utilization as well as the clean process conditions.
       
  • Additive manufacturing of zirconia parts by fused filament fabrication and
           solvent debinding: Selection of binder formulation
    • Abstract: Publication date: Available online 28 January 2019Source: Additive ManufacturingAuthor(s): Santiago Cano, Joamin Gonzalez-Gutierrez, Janak Sapkota, Martin Spoerk, Florian Arbeiter, Stephan Schuschnigg, Clemens Holzer, Christian Kukla The material extrusion additive manufacturing technique known as fused filament fabrication (FFF) is an interesting method to fabricate complex ceramic parts whereby feedstocks containing thermoplastic binders and ceramic powders are printed and the resulting parts are subjected to debinding and sintering. A limiting factor of this process is the debinding step, usually done thermally. Long thermal cycles are required to avoid defects such as cracks and blisters caused by trapped pyrolysis products. The current study addresses this issue by developing a novel FFF binder formulation for the production of zirconia parts with an intermediate solvent debinding step. Different unfilled binder systems were evaluated considering the mechanical and rheological properties required for the FFF process together with the solvent debinding performance of the parts. Subsequently, the same compounds were used in feedstocks filled with 47 vol.% of zirconia powder, and the resulting morphology was studied. Finally, the most promising formulation, containing zirconia, styrene-ethylene/butylene-styrene copolymer, paraffin wax, stearic acid, and acrylic acid-grafted high density polyethylene was successfully processed by FFF. After solvent debinding, 55.4 wt.% of the binder was dissolved in cyclohexane, creating an interconnected porosity of 29 vol.% that allowed a successful thermal debinding and subsequent pre-sintering.Graphical abstractGraphical abstract for this article
       
  • Hygromechanical properties of 3D printed continuous carbon and glass fibre
           reinforced polyamide composite for outdoor structural applications
    • Abstract: Publication date: Available online 23 January 2019Source: Additive ManufacturingAuthor(s): G. Chabaud, M. Castro, C Denoual, A. Le Duigou The additive manufacturing of structural composites is a disruptive technology currently limited by its moderate mechanical properties. Continuous fibre reinforcements have recently been developed to create high performance composites and open up encouraging prospects. However, to increase their use, deeper understanding of the relationship between process and induced properties remains necessary. In addition, to apply these materials to engineering applications, it is of high importance to evaluate the effect of environmental conditions on their mechanical performances, particularly when moisture-sensitive polymer is used (PolyAmide PA for instance) which is currently lacking in the literature.This present article aims to investigate in more detail the relationship between the process, the mechanical behaviour and the induced properties of continuous carbon and glass fibres reinforced with a polyamide matrix manufactured using a commercial 3D printer. In addition, their hygromechanical behaviour linked to moisture effect is investigated through sorption, hygroexpansion and mechanical properties characterization on a wide range of relative humidity (10-98% Relative Humidity RH).The printing process induces an original microstructure with multiscale singularities (intra/inter beads porosity and filament loop). Longitudinal tensile performance shows that the reinforcing mechanism is typical of composite laminates for glass and carbon. However, the rather poor transverse properties are not well fitted by the Rule Of Mixture (ROM), thus underlining the specificity of the printing-induced microstructure and an anisotropic behaviour in the material.Non-negligible (5-6%) moisture uptake is observed at 98% RH, as well as orthotropic hygroscopic expansion of PA/carbon and PA/glass composites. The consequences of various moisture contents on mechanical properties are studied, showing a reduction of PA/carbon stiffness and strength of 25 and 18 % in the longitudinal direction and 45 and 70% in the transverse direction. For PA/glass composites, we obtain a reduction in strength of 25 % in the longitudinal direction, along with a 80% reduction of stiffness and 45% in strength in the transverse direction. A wetting/drying cycle underlines reversible phenomena in the longitudinal direction and mainly non-reversible degradation in the transverse direction.
       
  • Compatibility in microstructural optimization for additive manufacturing
    • Abstract: Publication date: March 2019Source: Additive Manufacturing, Volume 26Author(s): Eric Garner, Helena M.A. Kolken, Charlie C.L. Wang, Amir A. Zadpoor, Jun Wu Microstructures with spatially-varying properties such as trabecular bone are widely seen in nature. These functionally graded materials possess smoothly changing microstructural topologies that enable excellent micro and macroscale performance. The fabrication of such microstructural materials is now enabled by additive manufacturing (AM). A challenging aspect in the computational design of such materials is ensuring compatibility between adjacent microstructures. Existing works address this problem by ensuring geometric connectivity between adjacent microstructural unit cells. In this paper, we aim to find the optimal connectivity between topology optimized microstructures. Recognizing the fact that the optimality of connectivity can be evaluated by the resulting physical properties of the assemblies, we propose to consider the assembly of adjacent cells together with the optimization of individual cells. In particular, our method simultaneously optimizes the physical properties of the individual cells as well as those of neighbouring pairs, to ensure material connectivity and smoothly varying physical properties. We demonstrate the application of our method in the design of functionally graded materials for implant design (including an implant prototype made by AM), and in the multiscale optimization of structures.
       
  • Skeleton arc additive manufacturing with closed loop control
    • Abstract: Publication date: Available online 15 January 2019Source: Additive ManufacturingAuthor(s): S. Radel, A. Diourte, F. Soulié, O. Company, C. Bordreuil Wire Arc Addtive Manufacturing (WAAM) is a promising direct energy deposition technology to produce high-value material components with a low buy-to-fly ratio. WAAM is able to produce thin-walled structures of large scale and also truss structures without any support. To manufacture complex parts, process reliability and repeatability are still a necessity and this often leads to long developing times. In this paper, a method is proposed to automatically manufacture complex truss structures with point by point arc additive manufacturing and a six axis robot. Computer aided manufacturing (CAM) software is designed to manage (i) material deposition at intersections and (ii) collisions between the part under construction and the torch. Because it is difficult to model the deposition process, the bead geometry is monitored using video imaging. Image treatment program detects the contour of the deposit and computes its current position. With this position, the CAM software corrects the geometry of the part for future deposition. Simple case studies are tested to validate the algorithm. Two solid free form geometries designed by topology optimization are manufactured with this skeleton arc additive manufacturing process.
       
  • In-Situ Monitoring of Polymer Flow Temperature and Pressure in Extrusion
           Based Additive Manufacturing
    • Abstract: Publication date: Available online 15 January 2019Source: Additive ManufacturingAuthor(s): David A. Anderegg, Hunter A. Bryant, Devante C. Ruffin, Stephen M. Skrip, Jacob J. Fallon, Eric L. Gilmer, Michael J. Bortner We demonstrate a novel Fused Filament Fabrication (FFF) nozzle design to enable measurements of in-situ conditions inside FFF nozzles, which is critical to ensuring that the polymer extrudate is flowing at appropriate temperature and flow rate during the part build process. Testing was performed with ABS filament using a modified Monoprice Maker Select 3D printer. In-situ measurements using the printer’s default temperature control settings showed an 11 °C decrease in temperature and significant fluctuation in pressure during printing as well as fluctuations while idle of ± 2 °C and ±14 kPa. These deviations were eliminated at lower flow rates with a properly calibrated proportional–integral–derivative (PID) system. At the highest tested flow rates, decreases in melt temperature as high as 6.5 °C were observed, even with a properly calibrated PID, providing critical insight into the significance of flow rate and PID calibration on actual polymer melt temperature inside the FFF nozzle. Pressure readings ranging from 140-6900 kPa were measured over a range of filament feed rates and corresponding extrusion flow rates. In-situ pressure measurements were higher than theoretical predictions using a power-law fluid model, suggesting that the assumptions used for theoretical calculations may not be completely capturing the dynamics in the FFF liquefier. Our nozzle prototype succeeded in measuring the internal conditions of FFF nozzles, thereby providing a number of important insights into the printing process which are vital for monitoring and improving FFF printed parts.
       
  • Controlled dissolution of freeform 3D printed carbohydrate glass scaffolds
           in hydrogels using a hydrophobic spray coating
    • Abstract: Publication date: Available online 27 December 2018Source: Additive ManufacturingAuthor(s): M.C. Gryka, T.J. Comi, R.A. Forsyth, P.M. Hadley, S. Deb, R. Bhargava Freeform 3D printing combined with sacrificial molding promises to lead advances in production of highly complex tubular systems for biomedical applications. Here we leverage a purpose-built isomalt 3D printer to generate complex channel geometries in hydrogels which would be inaccessible with other techniques. To control the dissolution of the scaffold, we propose an enabling technology consisting of an automated nebulizer coating system which applies octadecane to isomalt scaffolds. Octadecane, a saturated hydrocarbon, protects the rigid mold from dissolution and provides ample time for gels to set around the sacrificial structure. With a simplified model of the nebulizer system, the robotic motion was optimized for uniform coating. Using a combination of stimulated Raman scattering (SRS) microscopy and X-ray computed tomography, the coating was characterized to assess surface roughness and consistency. Colorimetric measurements of dissolution rates allowed optimization of sprayer parameters, yielding a decrease in dissolution rates by at least 4 orders of magnitude. High fidelity channels are ensured by surfactant treatment of the coating, which prevents bubbles from clinging to the surface. Spontaneous Raman scattering microspectroscopy and white light microscopy indicate cleared channels are free of octadecane following gentle flushing. The capabilities of the workflow are highlighted with several complex channel architectures including helices, blind channels, and multiple independent channels within polyacrylamide hydrogels of varying stiffnesses.Graphical abstractGraphical abstract for this article
       
  • The effect of post-processing operations on surface characteristics of
           316L stainless steel produced by selective laser melting
    • Abstract: Publication date: Available online 24 December 2018Source: Additive ManufacturingAuthor(s): Yusuf Kaynak, Ozhan Kitay Metal additive manufacturing is an emerging method to fabricate components used in the aerospace and biomedical industries. However, one of the significant challenges in this approach is the surface quality of the fabricated components. After metal additive manufacturing operations, post-processing is essential to meet the expected surface quality. This study presents the surface characteristics of as-built specimens manufactured by selective laser melting (SLM), where improvement of the surface can be achieved by post-processing operations. The post-processing operations in focus are finish machining (FM), vibratory surface finishing (VSF) and drag finishing (DF) operations. Surface topography, average surface roughness, microhardness, microstructure and XRD analysis have been carried out to examine the surface characteristics resulting from the post-processing operations. This study demonstrates that the drag finishing operation can be used for post-processing to meet the surface quality requirement of SLM manufactured parts.
       
  • Insight into the mechanisms of columnar to equiaxed grain transition
           during metallic additive manufacturing
    • Abstract: Publication date: Available online 24 December 2018Source: Additive ManufacturingAuthor(s): Pengwei Liu, Zhuo Wang, Yaohong Xiao, Mark F. Horstemeyer, Xiangyang Cui, Lei Chen The columnar to equiaxed transition (CET) of grain structures associated with processing conditions has been observed during metallic additive manufacturing (AM). However, the formation mechanisms of these grain structures have not been well understood under rapid solidification conditions, especially for AM of superalloys. This paper aims to uncover the underlying mechanisms that govern the CET of AM metals, using a well-tested multiscale phase-field model where heterogeneous nucleation, grain selection and grain epitaxial growth are considered. Using In718 as an example, the simulated results show that the CET is critically controlled by the undercooling, involving constitutional supercooling, thermal and curvature undercoolings in the melt pool, which dictates the extent of heterogeneous nucleation with respect to the grain epitaxial growth during rapid solidification.Graphical abstractGraphical abstract for this article
       
  • Microstructure and mechanical behavior of an additive manufactured (AM)
           WE43-Mg alloy
    • Abstract: Publication date: Available online 23 December 2018Source: Additive ManufacturingAuthor(s): Sindhura Gangireddy, Bharat Gwalani, Kaimiao Liu, Eric J. Faierson, Rajiv S. Mishra Magnesium alloys are highly attractive in aerospace and auto industries due to their high strength-to-weight ratio. Additive manufacturing of Mg alloys can further save cost from materials and machining time. This paper investigates the microstructure and dynamic mechanical behavior of WE-43 Mg alloy built through the powder bed fusion process. Samples from four different combinations of processing parameters were built. These builds were studied in both as-built and hot isostatically pressed conditions. The resultant complex microstructures were studied under scanning and transmission electron microscopes while their dynamic mechanical behavior was evaluated using a split-Hopkinson pressure bar testing system. Effects of initial porosity and microstructural evolution during HIP treatment on mechanical response are discussed.
       
  • Integrating Digital Image Correlation in Mechanical Testing for the
           Materials Characterization of Big Area Additive Manufacturing Feedstock
    • Abstract: Publication date: Available online 23 December 2018Source: Additive ManufacturingAuthor(s): Kevin Schnittker, Edel Arrieta, Xavier Jimenez, David Espalin, Ryan B. Wicker, David A. Roberson To enable the advancement of large-scale additive manufacturing processes, it is necessary to establish and standardize methodologies to characterize the mechanical properties of printed test coupons. Due to the large size of the print beads, conventional test standards are inadequate. The focus of this study was to determine the feasibility of using Digital image correlation (DIC) technology as a key enabler for robust data collection of strain measurements of large 3D printed parts. To incorporate the DIC measurements, a novel method was developed to prepare large 20% (by wt.) glass filled ABS test coupons for adequate contrast. Through this technique, Poisson's ratio and elastic modulus were measured and stress strain curves were generated. The data produced by DIC correlated well with failure analysis performed on spent test coupons. Additionally, fracture surface analysis of the specimens revealed poor adhesion among the ABS matrix and glass fibers. This matrix/fiber debonding demonstrated the need for improved printing parameters to maximize tensile strength. Finally, critical length analysis of the fibers revealed them to be dimensionally inadequate.
       
  • Effect of Structural Support on Microstructure of Nickel Base Superalloy
           Fabricated By Laser-Powder Bed Fusion Additive Manufacturing
    • Abstract: Publication date: Available online 23 December 2018Source: Additive ManufacturingAuthor(s): Hyeyun Song, Tom McGaughy, Alber Sadek, Wei Zhang INCONEL® 718 cubes with and without structural support were built by laser-powder bed fusion (L-PBF) additive manufacturing. The effect of support on the as-built microstructure was studied based on the microstructural characteristics and micro-hardness variations. Specifically, the microstructure was examined by optical microscopy, and scanning and transmission electron microscopy. The precipitates were identified via selected area diffraction supplemented by high-resolution energy dispersive X-ray spectroscopy. Micro-hardness distributions on cross sections parallel and perpendicular to the build direction were mapped. In addition, analytical equations, taking into account various laser processing parameters, material properties and support geometries, were developed to calculate the heat build-up and cooling conditions during L-PBF. The results of microstructure characterization and analytical calculation showed a marginal effect of the support on the local microstructure and hardness due to the low heat input in L-PBF. Moreover, the comprehensive set of microstructure data is useful for future work of modelling processing-microstructure relation as well as optimizing post-fabrication heat treatment.Graphical abstractGraphical abstract for this article
       
  • Effect of process parameters on melt pool geometry and microstructure
           development for electron beam melting of IN718: a systematic single bead
           analysis study
    • Abstract: Publication date: Available online 23 December 2018Source: Additive ManufacturingAuthor(s): Xiao Ding, Yuichiro Koizumi, Daixiu Wei, Akihiko Chiba To understand the fundamentals of microstructure formation in an electron beam melting (EBM) additive-manufacturing process, which is classified as a type of electron beam powder bed fusion (EB-PBF) in ISO562910/ASTM-F42, single bead experiments were conducted by using an electron beam to scan an IN718 plate, using various combinations of power and scan speed, focusing on the relationship between (i) the beam irradiation level, (ii) the melt pool geometry, and (iii) the solidification microstructure. The width and depth of the melt pool increases almost linearly with the line energy. Elongated grains, which are generally called “columnar grains” were observed in almost the entire cross-section of the beads regardless of the process parameters. Temporal evolution of the temperature distribution for the single bead experiments was simulated by finite element analysis (FEA) with thermal conduction and recoalescence taken into account. The surface heat source model used in the simulation was modified to cause the geometry of the simulated melt pool to align with that which was observed experimentally. The distributions of the temperature gradient (G) and solidification rate (R) on the solidification interface were evaluated from the simulation results. The distributions of the microstructures were constructed from the distributions of G and R, as obtained from a solidification map in the literature. Contrary to the experimental observations, the constructed microstructure consisted mostly of equiaxed and mixed grains. The reasons for this contradiction are discussed.
       
  • Creating 3D Printed Magnetic Devices with Ferrofluids and Liquid Metals
    • Abstract: Publication date: Available online 21 December 2018Source: Additive ManufacturingAuthor(s): Nathan Lazarus, Sarah S. Bedair, Gabriel L. Smith Combining electrical and magnetic materials in the same part has been a challenge in 3D printing due to difficulties co-printing complex materials in many additive manufacturing processes. Past 3D printed inductors and other similar magnetic devices have therefore either lacked the magnetic materials necessary for improved performance, or required sintering at high temperatures for extended periods, beyond the capability of most 3D printable polymers. In this work, we demonstrate a room temperature process for incorporating conductive and magnetic materials into the same 3D printed device. A multi-stage fabrication process based on 3D printing followed by fill with magnetic and conductive fluids is proposed. Multi-layer microfluidic channels for magnetic passives are first printed in a stereolithography process. The microfluidic systems are then filled with room temperature liquid metal, a gallium alloy liquid at room temperature, and ferrofluid to create inductors, transformers and wireless power coils. Through the addition of ferrofluid as a magnetic material, increases in inductance density by nearly a factor of three were demonstrated, in addition to coupling improvements for transformer and wireless power coils compared to the devices before magnetic fill.
       
  • Fracture Toughness of Additively Manufactured Carbon Fiber Reinforced
           Composites
    • Abstract: Publication date: Available online 17 December 2018Source: Additive ManufacturingAuthor(s): Easir Arafat Papon, Anwarul Haque In this paper, the fracture properties (stress intensity factor and energy release rate) of additively manufactured (AM) polylactic acid (PLA) and its short carbon fiber (CF) reinforced composites have been studied. The effects of CF reinforcement, nozzle geometry and bead lay-up orientations in fracture properties, void contents, and interfacial bonding were studied. The fused deposition modeling (FDM) based AM specimens using both circular and square shaped nozzle were printed and compared with the conventional compression molded (CM) samples. Compact tension (CT) specimens with different CF concentrations (0 wt.%, 3 wt. %, 5 wt.%, 7 wt.% and 10 wt.%) were printed with two bead lay-up orientations ( 450/-450 and 00/900 ) using PLA and CF/PLA composite filaments. The results show significant improvement in fracture toughness and fracture energy for CF/PLA composites in comparison to neat PLA. The fracture toughness was increased by 42% for 00/900 and 38% for 450/-450 bead orientations, respectively with 5 % CF loading. The increase in fracture energy was observed to be about 77% for 00/900 and 88% for 450/-450 layer orientations, respectively for the same fiber reinforcement (5 wt. %). Such improvement in fracture properties is expected to be higher for all 900 bead orientations. The samples printed by square-shaped nozzle showed some enhancement in fracture toughness with less inter-bead voids and larger bonded areas in comparison to the circular-shaped nozzle. Although the fracture toughness showed very negligible differences between 00/900 and 450/-450 specimens, distinguishable variation may be seen in the case of 00 and 900 bead orientations. The crack propagation path and fracture mechanisms were studied using optical microscopy (OM) and scanning electron microscopy (SEM) examinations. Fractography revealed different modes of failure with a very high fiber orientation along the printing direction and a relatively higher void contents for 7 and 10 wt. % fiber reinforcement.
       
  • Molten Pool Behavior and Effect of Fluid Flow on Solidification Conditions
           in Selective Electron Beam Melting (SEBM) of a Biomedical Co-Cr-Mo Alloy
    • Abstract: Publication date: Available online 4 December 2018Source: Additive ManufacturingAuthor(s): Yufan Zhao, Yuichiro Koizumi, Kenta Aoyagi, Daixiu Wei, Kenta Yamanaka, Akihiko Chiba Selective electron beam melting (SEBM) is a type of additive manufacturing (AM) that involves multiple physical processes. Because of its unique process conditions compared to other AM processes, a detailed investigation into the molten pool behavior and dominant physics of SEBM is required. Fluid convection involves mass and heat transfer; therefore, fluid flow can have a profound effect on solidification conditions. In this study, computational thermal-fluid dynamics simulations with multi-physical modeling and proof-of-concept experiments were used to analyze the molten pool behavior and resultant thermal conditions related to solidification. The Marangoni effect of molten metal primarily determines fluid behavior and is a critical factor affecting the molten pool instability in SEBM of the Co–Cr–Mo alloy. The solidification parameters calculated from simulated data, especially the solidification rate, are sensitive to the local fluid flow at the solidification front. Combined with experimental analysis, the results presented herein indicate that active fluid convection at the solidification front increase the probability of new grain formation, which suppresses the epitaxial growth of columnar grains.
       
  • Predictive process parameter selection for Selective Laser Melting
           Manufacturing: applications to high thermal conductivity alloys
    • Abstract: Publication date: Available online 3 December 2018Source: Additive ManufacturingAuthor(s): Priyanshu Bajaj, Jonathan Wright, Iain Todd, Eric A. Jägle There is growing interest in Laser Powder Bed Fusion (L-PBF) or Selective Laser Melting (SLM) manufacturing of high conductivity metals such as copper and refractory metals. SLM manufacturing of high thermal conductivity metals is particularly difficult. In case of refractory metals, the difficulty is amplified because of their high melting point and brittle behaviour. Rapid process development strategies are essential to identify suitable process parameters for achieving minimum porosities in these alloys, yet current strategies suffer from several limitations. We propose a simple approach for rapid process development using normalized process maps. Using plots of normalized energy density vs. normalized hatch spacing, we identify a wide processability window. This is further refined using analytical heat transfer models to predict melt pool size. Final optimization of the parameters is achieved by experiments based on statistical Design of Experiments concepts. In this article we demonstrate the use of our proposed approach for development of process parameters (hatch spacing, layer thickness, exposure time and point distance) for SLM manufacturing of molybdenum and aluminium. Relative densities of 97.4% and 99.7% are achieved using 200 W pulsed laser and 400 W continuous laser respectively, for molybdenum and aluminium, demonstrating the effectiveness of our approach for SLM processing of high conductivity materials.Graphical abstractGraphical abstract for this article
       
 
 
JournalTOCs
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
Email: journaltocs@hw.ac.uk
Tel: +00 44 (0)131 4513762
Fax: +00 44 (0)131 4513327
 
About JournalTOCs
API
Help
News (blog, publications)
JournalTOCs on Twitter   JournalTOCs on Facebook

JournalTOCs © 2009-