2019 International Solid Freeform Fabrication Symposium

Permanent URI for this collectionhttps://hdl.handle.net/2152/89836

Proceedings for the 2019 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Thirtieth Annual International Solid Freeform Fabrication (SFF) Symposium – An Additive Manufacturing Conference, held at The University of Texas in Austin on August 12-14, 2019, was attended by 701 researchers from 25 countries. The number of oral and poster presentations increased to 557 this year. The meeting was held on the Hilton Austin in the downtown area. The meeting consisted of a Monday morning plenary, 64 parallel technical sessions and a poster session.

The recipient of the International Outstanding Young Researcher in Freeform and Additive Manufacturing Award was Dr. Xiaoyu (Rayne) Zheng from Virginia Tech University. Dr. Olaf Diegel from the University of Auckland in New Zealand won the International Freeform and Additive Manufacturing Excellence (FAME) Award.

There are 197 papers in the conference proceedings. Papers marked "REVIEWED" in the title area were peer reviewed by two external reviewers. We have sequentially numbered the pages of the papers to facilitate citation. Manuscripts for this and all preceding SFF Symposia are available for free download below and at the conference website: http://sffsymposium.engr.utexas.edu/archive.

Nine materials-related papers were selected as best papers for inclusion in the journal JOM under the aegis of The Minerals, Metals & Materials Society (TMS). Two of these papers were substantially improved for the journal with the original also appearing in this proceedings. Seven were moved with only minor modification; these do not appear in the proceedings. The abstracts of these nine papers appear in the proceedings immediately before the first article. The special issue of JOM was published in the March 2020 issues of JOM.

A student lunch and panel discussion was provided on August 13th, 2019. A panel discussion with a focus on navigating the transition into career positions in the AM field was conducted with ample opportunities for the students to ask questions. The panel featured four recent PhD graduates working in the field of AM in academia, industry, and a national lab. The panel included, (1) Dr. David Epsalin (Assistant Professor - University of Texas at El Paso and Director of Research at the W.M. Keck Center for 3D Innovation), (2) Ben Fulcher (EOS North America), (3) Dr. Brian Gierra (Principle Investigator at Lawrence Livermore National Laboratory) and (4) Dr. Joy Gockel (Assistant Professor in Mechanical and Materials Engineering at Wright State University). The luncheon was attended by approximately 200 students.

The editors would like to thank the Organizing Committee, the session chairs, the attendees for their enthusiastic participation, and the speakers both for their significant contribution to the meeting and for the relatively prompt delivery of the manuscripts comprising this volume. We are grateful to TMS conference management staff for their significant contributions to the meeting planning and proceedings production, particularly Trudi Dunlap, Jennifer Booth, and Kelcy Wagner. We look forward to the continued close cooperation of the additive manufacturing community in organizing the Symposium. We also want to thank the Office of Naval Research (N00014-19-1-2678) and the National Science Foundation (CMMI-1934397) for supporting this meeting financially. The meeting was co-organized by the Mechanical Engineering Department/Lab for Freeform Fabrication under the aegis of the Advanced Manufacturing and Design Center at the University of Texas at Austin. The 2020 SFF Symposium is set for August 17-19, 2020 at the Hilton Austin Hotel in Austin, Texas, USA.

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Now showing 1 - 20 of 197

Printed Materials and Their Effects on Quasi-Optical Millimeter Wave Guide Lens Systems
(University of Texas at Austin, 2019) Foster, Diana; Corey, Chris; Fisher, Chris; Smith, Caitlin; Paolella, Arthur
This study of 3D printed quasi-optical (Q-O) millimeter wave guide lens systems is presented in three phases: the characterization of 3D printed materials for radio frequency (RF) applications and systems; the development and demonstration of 3D printing technology for RF systems; and the design process, simulation, fabrication, and testing of RF lens systems. The first phase explores the ability to print high-quality materials with fine resolution and the determination of each material’s dielectric constant and loss tangent. The second phase details the development of dual biconvex shaped lens systems and the resulting test data. The third phase combines the former stages’ results to model, print, and test a set of lenses pre-aligned with an integrated support structure. These lens systems were tested up to 100 GHz with demonstrated focusing gain of 22.1 dB.
A Low-Cost Approach for Characterizing Melt Flow Properties of Filaments Used in Fused Filament Fabrication Additive Manufacturing
(University of Texas at Austin, 2019) Chen, Jingdong; Smith, Douglas E.
Users of Fused Filament Fabrication (FFF) can choose from a wide variety of new materials as filament producers continue to introduce new polymer and polymer composite filament into the marketplace. This paper describes a low-cost device capable of measuring the rheological properties of off-the-shelf polymer filament. In this approach, measurements are taken during filament extrusion which are combined with a pressure drop model based on simple shear flow within the FFF nozzle to perform inverse analysis that computes parameters for the power law generalized Newtonian fluid (GNF) model. The applicability of our FFF-filament rheometer is demonstrated with four commercially available polymer filaments by comparing the results to those obtained from a commercial rotational rheometer. A filament characterization approach similar to Melt Flow Index (MFI) is also proposed to assess the extrusion characteristics of materials specific to FFF.
Mechanical Behavior of Additively-Manufactured Gyroid Lattice Structure under Different Heat Treatments
(University of Texas at Austin, 2019) Sereshk, Mohammad Reza Vaziri; Shrestha, Rakish; Lessel, Brandon; Phan, Nam; Shamsaei, Nima
Gyroid lattice structures, known for high stiffness and specific strength, are gaining attention for their energy absorption ability. However, energy absorption and strength of the gyroids are two desired properties, which vary contradictory. This study investigates manipulating properties on lattices using post-processing operation instead of modifying dimensions with consequent changes in weight and production cost. The challenge is that a particular post-processing heat treatment may improve one property, while it may be detrimental to other ones. The compressive properties of 17-4 PH stainless steel gyroid lattice structures fabricated using laser beam powder bed fusion (LB-PBF) method is investigated. Compressive properties such as load bearing capacity, crashing strength, and energy absorption are determined and the trends in their variation are discussed. Based on the experimental results, heat treating lattices with CA H900 procedure improves energy absorption and strength considerably, while increases crashing force, as well.
Electrical and Mechanical Properties of Fused Filament Fabrication of Polyamide 6 / Nanographene Filaments at Different Annealing Temperatures
(University of Texas at Austin, 2019) Tate, J.S.; Brushaber, R.P.; Danielsen, E.; Kallagunta, H.; Navale, S.V.; Arigbabowo, O.; Shree, S.; Yaseer, A.
Polyamide 6 (PA 6) nanographene composites are viable engineered nanocomposite materials with high potential for electrostatic discharge applications. This can be attributed to the ability of the nanographene particles in reducing the electrical resistivity of the parent polyamide 6 and in turn creating a conductive network for a controllable discharge of static electricity. In addition, PA 6 nanographene composites can also exploit the good mechanical properties of the parent polyamide 6, a structural thermoplastic ideal for 3D printing via fused filament fabrication (FFF). Hence, 3, 5, and 7 wt.% of NGP were blended with PA6 using co-rotating twin screw extruder to produce 1.75mm diameter for FFF using Lulzbot TAZ 6 3D printer. Scanning Electron Microscopy (SEM) was used to evaluate the degree of exfoliation of the nanographene and tensile and electrical resistivity test samples were manufactured via fused filament fabrication. The polyamide 6 nanographene composites were further subjected to annealing treatment at 80ºC, 140ºC, 200ºC and a comparison study was carried out on the observed tensile properties and electrical resistivity values of both annealed and not annealed treated.
Frequency Inspection of Additively Manufactured Parts for Layer Defect Identification
(University of Texas at Austin, 2019) Allen, Aimee; Johnson, Kevin; Blough, Jason; Barnard, Andrew; Hartwig, Troy; Brown, Ben; Soine, David; Cullom, Tristan; Bristow, Douglas; Landers, Robert; Kinzel, Edward
Additive manufactured (AM) parts are produced at low volume or with complex geometries. Identifying internal defects is difficult as current testing techniques are not optimized for AM processes. The goal of this paper is to evaluate defects on multiple parts printed on the same build plate. The technique used was resonant frequency testing with the results verified through Finite Element Analysis. From these tests, it was found that the natural frequencies needed to detect the defects were higher than the excitation provided by a modal hammer. The deficiencies in this range led to the development of other excitation methods. Based on these results, traditional methods of resonant part inspection are not sufficient, but special methods can be developed for specific cases.
Ultrasonic Embedding of Continuous Carbon Fiber into 3D printed Thermoplastic Parts
(University of Texas at Austin, 2019) Billah, Kazi Md Masum; Coronel, Jose L. Jr.; Chacon, Sarah; Wicker, Ryan B.; Espalin, David
A novel multimaterial fabrication process was developed to embed continuous bundles of carbon fiber (CF) into polycarbonate (PC) substrates using ultrasonic energy. Continuous CF possesses superior reinforcement properties compared to that of chopped or short fibers. In this research, dry continuous CF bundles were impregnated with a PC solution prior to embedding. Three printing raster orientations were studied (0°, 45°, and 90°), where three layers of CCF were embedded within each test specimen. Characterizations including tensile, flexural, and dynamic mechanical analysis were carried out to investigate reinforcement related properties. Results showed an increase in ultimate tensile strength between neat PC (37 MPa) and CF reinforced specimens (141 MPa). An automated ultrasonic embedding process allowed for the selective deposition of CF, regardless of the raster orientation. Future development of continuous CF reinforced parts could enable smart part fabrication, with applications in structural health monitoring, microwave shielding, and thermal management.
Fatigue Behavior of Additive Manufactured 304L Stainless Steel Including Surface Roughness Effects
(University of Texas at Austin, 2019) Lee, Seungjong; Pegues, Jonathan; Shamsaei, Nima
The fatigue behavior of additive manufactured parts in the as-built surface condition is typically dominated by the surface roughness. However, the fatigue behavior of 304L stainless steel fabricated by laser beam powder bed fusion shows less sensitivity to surface roughness under strain-controlled loading conditions than other additive manufactured materials. Under force-controlled conditions, however, the high cycle fatigue resistance is much lower for the as-built surface condition than the machined one. This study investigates the underlying mechanisms responsible for fatigue failure for each condition (i.e. strain-controlled or force-controlled). The corresponding cyclic deformation behavior was characterized, and a thorough fractography analysis was performed to identify the features responsible for crack initiation. Results indicate that the crack initiation features in both loading conditions are similar, and that the reduced high cycle fatigue resistance for force-controlled fatigue loading compared to strain-controlled one is related to differences in the cyclic deformation behavior of the material.
Effects of Particle Size Distribution on Surface Finish of Selective Laser Melting Parts
(University of Texas at Austin, 2019) Lim, J.H.; Khan, N.A.
Metal parts produced by Selective Laser Melting (SLM) usually exhibit poor surface finish compared to conventional manufacturing processes. There is a growing need for parts to have good surface quality in the as-built condition to minimise post-processing costs and reduce lead time. There are many studies done on the effects of processing parameters on surface finish but very little on the influence of powder characteristics. This study aims to investigate the effects of Particle Size Distribution (PSD) on surface finish of AM parts by printing coupons with Inconel 625 powders of varying PSD. It was found that roughness of internal surfaces was mainly caused by the presence of partially sintered particles. Whilst a smaller particle mean size and wider particle size range are preferred for better surface finish, a powder that is too fine may result in poor flowability affecting its processability in terms of layering and powder bed quality.
A Multi-Scale Computational Model to Predict the Performance of Cell Seeded Scaffolds with Triply Periodic Minimal Surface Geometries
(University of Texas at Austin, 2019) Lehder, E.F.; Ashcroft, I.A.; Wildman, R.D.; Maskery, I.; Cantu, L.R.
Bone scaffolds are required to replace the painful and dangerous process of bone grafting, currently the gold standard for treating open bone fractures. Tissue engineering scaffolds work best when there is a high amount of surface area for biological cells to attach. Triply Periodic Minimal Surface (TPMS) geometries offer high ratios of surface area per volume. However, it is not yet clear which TPMS cell type would yield the fastest bone growth rate. In this study, we used a three-dimensional multi-scale model to predict the performance of scaffolds with four TPMS unit cell types (Primitive, Gyroid, Diamond and Lidinoid). At the micro-scale, the model simulates curvature-dependent tissue growth, while at the macro-scale the model uses FEA to ensure the construct stiffness is acceptable. The Lidinoid unit cell type was found to yield the most bone growth after 40 days while also ensuring an acceptable scaffold stiffness.
Implementation of 3D Printer in the Hands-On Material Processing Course: An Educational Paper
(University of Texas at Austin, 2019) Silwal, B.
Manufacturing equipment and technology will continue to be an integral part of engineering education. Using advanced and modern equipment and technology not only emphasizes hands-on activity-based teaching and learning, but it also makes the educator and the program competitive. There are many advantages to implementing 3-d printers in engineering education; however, there are also some challenges. In this paper, a two-year implementation of 3-d printers in a traditional material processing undergraduate engineering course has been presented and discussed.
Conceptual Design for Additive Manufacturing: Lessons Learned from an Undergraduate Course
(University of Texas at Austin, 2019) Thompson, Scott M.
Design for additive manufacturing (DfAM) guidelines continue to emerge and evolve as various additive manufacturing (AM) technologies, and the knowledge of their associated end-users/designers, matures. This work summarize important pedagogical and technical lessons learned from the conceptual re-design of several, diverse parts/assemblies submitted by ~50 undergraduate students cognizant of recent DfAM strategies and guidelines. All students were enrolled in a traditional, semester-long metals AM course designed by the author herein. Students were instructed to select an existing, metallic product and provide a conceptual redesign of that product for subsequent, effective laser-powder bed fusion (L-PBF). Students were instructed that the redesigned concept should have enhanced functionality/specifications and consist of features (e.g. thin walls, bore diameters, etc.) that can be fabricated with minimal risk via current L-PBF systems. The presented results include the types of parts that attract an ‘AM redesign’ effort and the most popular AM-enabled detailed design decisions made. To encourage a more detail-inspired design, DfAM topics were presented ‘backwards’; from post-manufacturing considerations to conceptual design while considering emerging design rules and heuristics. Results indicate that students can become preoccupied with DfAM rules to a point where the design failure modes are not properly accounted for.
Dynamic Defect Detection in Additively Manufactured Parts using FEA Simulation
(University of Texas at Austin, 2019) Johnson, Kevin; Allen, Aimee; Blough, Jason; Barnard, Andrew; Labyak, David; Hartwig, Troy; Brown, Ben; Soine, David; Cullom, Tristan; Kinzel, Edward; Bristow, Douglas; Landers, Robert
The goal of this paper is to evaluate internal defects in additively manufactured (AM) parts using FEA simulation. The resonant frequencies of parts are determined by the stiffness and mass involved in the mode shape at each resonant frequency. Voids in AM parts will change the stiffness and mass therefore shift the resonant frequencies from nominal. This paper will investigate the use of FEA to determine how much a void size, shape, and location will change the resonant frequencies. Along with where the optimal input and response locations are in order to find these frequency changes. The AM part evaluated in this work includes a common tensile bar and hammer shaped part evaluated individually and as a set of parts that are still attached to the build plate.
Thermal Analysis of Thermoplastic Materials Filled with Chopped Fiber for Large Area 3D Printing
(University of Texas at Austin, 2019) Billah, Kazi Md Masum; Lorenzana, Fernando A.R.; Martinez, Nikki L.; Chacon, Sarah; Wicker, Ryan B.; Espalin, David
At room temperature, material extrusion, in the context of large area fabrication, requires thermally stable materials and, as a result, fillers are included to tailor the thermal behavior. This research investigated the thermophysical properties of neat ABS and short carbon fiber (CF) reinforced ABS. Thermogravimetric analysis, differential scanning calorimetry, and thermomechanical analysis were carried out to determine the thermophysical properties. The addition of CF (20 wt. %) to an ABS matrix caused the glass transition temperature to change slightly (110 °C to 105 °C). Also, the CF within the ABS matrix reduced the thermal stability by decreasing the degradation on set temperature by (323 °C to 253 °C). Thermal deformation analysis showed that large area pellet extruded AM machine produces highly anisotropic materials. Thermomechanical analysis results showed that the coefficient of thermal expansion (CTE) reduced 4 times in the perpendicular to the extruded direction. The dataset and knowledge from the thermal analysis can be useful to design optimized printing parameters for highly filled thermoplastics used in large area 3D printing machines.
Influence of Powder Particle Size Distribution on the Printability of Pure Copper for Selective Laser Melting
(University of Texas at Austin, 2019) Sinico, M.; Cogo, G.; Benettoni, M.; Calliari, I.; Pepato, A.
This work investigates the use of fine Cu powder, with ~ 20 vol% smaller than 15 μm size, for the selective laser melting process. Cubes reaching > 98 % density are produced at relative low laser output (175 W) and characterized. After the selection of a proper combination of laser scan parameters, the properties of fabricated parts are briefly studied through profilometry and tensile tests. Finally, a voluminous demo component for high-energy physics is manufactured to stress-test the employed SLM machine. Even though unmolten particles and lack of fusion defects are still present in the produced specimens, the investigated approach confirms that powder selection can have a huge influence on the processability of materials with high reflectivity towards near-infrared irradiation.
Experimental Investigation of Fluid-Particle Interaction in Binder Jet 3D Printing
(University of Texas at Austin, 2019) Wagner, Joshua J.; Shu, Hang; Kilambi, Rahul; Higgs, C. Fred III
Wide-scale adoption of binder jet 3D printing for mission-critical components in aerospace, biomedical, defense, and energy applications requires improvement in mechanical properties and performance characteristics of end-use components. Increased fidelity may be achieved with better understanding of the interfacial physics and complex fluid-particle interactions fundamental to the process. In this work, an experimental testing apparatus and procedure is developed to investigate the fluid and particle dynamics occurring upon impact of jetted binder droplets onto a powder bed. High-speed, microscopic imaging is employed to capture short time-scale phenomena such as ballistic particle ejection, capillary flow, and particle clustering. The effects of different process parameters (e.g., translational printhead velocity, jetting frequency, and impact velocity) on the dynamics of Inconel powder are studied. These experiments reveal that the fluid-particle interaction is significantly affected by a combination of printing parameters, ultimately governing the quality and performance of binder jet 3D printed components.
Electroforming Process to Additively Manufactured Microscale Structures
(University of Texas at Austin, 2019) Patel, Krish; McNamee, Amelia; Silwal, Bishal
Electroforming is a metal forming process that forms parts through electrodeposition. The overall study and production of the copper mandrel were conducted by examining the growth and depth of the depositions at macroscopic levels. The study of the plating constant for a copper plate in copper sulfate was performed via the production of copper mandrels. Each mandrel was produced by performing multiple experiments and qualitatively and quantitatively examining the resultant depositions and the initial and final states of the experiment. The results were measured based on variations of current and voltage duration in the bath cycle, time duration, solution concentration, and change in mass of both the anode and cathode. The variables such as plating constant and direct current distribution are determined. It seems the rate at which the structure can be fabricated depends on the type of electrolytes used and the parts that are deposited can be scalable.
Analysis of the Shielding Gas Dependent L-PBF Process Stability by Means of Schlieren and Shadowgraph Techniques
(University of Texas at Austin, 2019) Hoppe, B.; Enk, S.; Schleifenbaum, J.H.
Ensuring a robust and reproducible Laser Powder Bed Fusion (L-PBF) process depends on the design of the shielding gas flow in the corresponding manufacturing system. The gas flow assures the removal of particles from the process zone that emerge from the interaction with the laser irradiation. Minor disturbances may influence the stability of the L-PBF-Process and cause defects in final parts produced. The objective of this work comprises visualizing the convection processes and particle dynamics to analyze their influence on process stability. Therefore, a high speed camera based Schlieren and Shadowgraph setup is used to visualize convection flows as well as trajectories of metallic condensate and particles with up to 10,568 fps. This arrangement allowed investigating the influence of shielding gas flow conditions on single melt tracks. Corresponding results and studies on the interaction between laser irradiation and particles in varying shielding gas flow conditions are contents of this work.
Manufacturing and Application of PA11-Glass Fiber Composite Particles for Selective Laser Sintering
(University of Texas at Austin, 2019) Dechet, Maximilian A.; Lanzl, Lydia; Werner, Yannick; Drummer, Dietmar; Bück, Andreas; Peukert, Wolfgang; Schmidt, Jochen
Selective laser sintering (SLS), a powder-based additive manufacturing technology, employs micronsized polymer particles, which are selectively fused by a laser. SLS yields excellent part qualities with good mechanical properties. However, a persistent challenge in this layer-by-layer process is a reduction of mechanical properties in the z-direction. This is often caused by insufficient layer adhesion. One way to strengthen the layer adhesion in z-direction is the incorporation of glass fibers, which exceed from one layer into another. However, most commercially available glass-fiber enhanced materials are dry blends of the polymer powders and the fibers. In order to enhance the isotropic mechanical properties of parts manufactured via selective laser sintering, the manufacturing of glass fiber-filled PA11 particles is shown in this contribution. We present a single-pot approach to produce glass fiber-filled polyamide 11 (PA11) composite particles. The particles are manufactured via liquid-liquid phase separation and precipitation [1] (also known as solution-dissolution process) from ethanol glass fiber dispersions. Bulk polymer material of PA11 is directly converted to composite microparticles in a single process. The produced particles are characterized regarding their size and morphology. The amount of glass fibers in the bulk is assessed via thermogravimetric analysis and the effect of the fibers on the processing window is investigated via differential scanning calorimetry (DSC). As a proof of concept, the powder is employed in the SLS process to produce glass fiber-enhanced test specimens for mechanical testing.
Modelling for the Tensile Fracture Characteristic of Cellular Structures under Tensile Load with Size Effect
(University of Texas at Austin, 2019) Wu, Yan; Yang, Li
In the unit cell-based design of cellular structures, an important issue is the effect of the cellular pattern size (i.e. the number of unit cell numbers along different orientations) on their mechanical properties. Among these properties, the fracture properties are of great importance for a broad range of applications but have been rarely investigated. In this work the size effects on the fracture characteristic (including failure initiation, crack propagation and failure patterns) of the BCC, octet-truss, auxetic and octahedral structures under tensile loadings were analyzed based analytical models. It was found that for the fracture of the cellular structures there exist significant coupling effects between the unit cell topology and the cellular pattern size. The results also clearly suggested the importance of dedicating more design attentions to the boundaries of the cellular structures during their fracture designs. This study provides additional insights into the design considerations for the fracture properties of the cellular structures.
Compressive Response of Strut-Reinforced Kagome with Polyurethane Reinforcement
(University of Texas at Austin, 2019) Gautam, Rinoj; Sridharan, Vijay Shankar; Teh, Wee Lee; Idapalapati, Sridhar
Lattice structures find immense application in lightweight structures for their high specific strength, modulus, and energy absorption. Strut-reinforced Kagome (SRK) structures provide better compressive performance compared to many existing lattice structures. In this study, the performance of acrylonitrile butadiene styrene (ABS) SRK lattice structures, fabricated by fused deposition modeling, under compression loading is investigated. Further, SRK structures were filled with different polyurethane in the empty space and their effect on the compressive performance was examined. The SRK structure demonstrated abrupt failure at the joints in the vicinity of face sheet, thereby reducing the energy absorption of the structure. The SRK with flexible foam (low-density polyurethane foam) had no significant effect on peak failure load and moduli, whereas energy absorption per unit mass was higher by 16.5%. The SRK with the rigid foam (high-density foam) displayed not only the better energy absorption per unit mass (116%) but also different failure behavior than SRK only.

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