2021 International Solid Freeform Fabrication Symposium
Permanent URI for this collectionhttps://hdl.handle.net/2152/90484
Proceedings for the 2021 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.
The Thirty-second Annual International Solid Freeform Fabrication (SFF) Symposium – An Additive Manufacturing Conference, was held on August 2-4, 2021. For the first, and hopefully the last, time, the meeting was held virtually. At the time of the conference, Texas and the United States was at the height of the initial Delta COVID-19 variant surge. There were 465 registrants from 16 countries, including 167 students. The total number of oral and poster presentations was 403. The meeting consisted of a Monday morning plenary, 56 parallel technical sessions and a poster session. The organizers provided opportunities for networking and live interaction. There were a number of advantages to the virtual format, including elimination of parallel session time conflicts and reduced meeting cost. However, the consensus was that the in-person meeting format is strongly preferred.
The recipient of the 2021 International Outstanding Young Researcher in Freeform and Additive Manufacturing Award was Dr. Joy Gockel from the Colorado School of Mines. Dr. Ola Harrysson from North Carolina State University won the International Freeform and Additive Manufacturing Excellence (FAME) Award. There are 140 papers in this 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: https://www.sffsymposium.org/; select the “Proceedings Archive” pull-down menu item.
Thirteen materials-related papers were selected as best papers for inclusion in the journal JOM under the aegis of The Minerals, Metals & Materials Society (TMS). Five of these papers were substantially improved for the journal with the original also appearing in this proceedings. Eight were moved with only minor modification; these do not appear in the proceedings. The abstracts of these eight papers appear in the proceedings with a note referring the reader to the JOM full article. These thirteen outstanding papers are notated in the Proceedings Table of Contents and were published in the March 2022 issue of JOM.
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 Marini. We look forward to the continued close cooperation of the additive manufacturing community in organizing the Symposium. We also want to thank the National Science Foundation (CMMI-2005490) for supporting this meeting financially by providing 161 student registration fee waivers. The meeting was organized within the Mechanical Engineering Department and the Center for Additive Manufacturing and Design Innovation (CAMDI) at The University of Texas at Austin. The 2022 SFF Symposium is planned to be in person on July 25-27, 2022 at the HiltonAustin Hotel inAustin, Texas USA. The conference website will become active in mid-January 2022.
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Item 2021 International Solid Freeform Fabrication Symposium Table of Contents(2021) Laboratory for Freeform Fabrication and University of Texas at AustinItem Abrasive Flow Machining of Additively Manufactured Titanium: Thin Walls and Internal Channels(University of Texas at Austin, 2021) Jalui, S.S.; Spurgeon, T.J.; Jacobs, E.R.; Chatterjee, A.; Stecko, T.; Manogharan, G.P.Metal additive manufacturing using Laser-Powder Bed Fusion (L-PBF) technique has enabled the metal manufacturing industry to use design tools with increased flexibility such as freeform internal channel geometries that benefit thermofluidic applications such as heat exchangers. A primary drawback of the L-PBF process is the as-built surface roughness, which is a critical factor in such surface-fluidic applications. In addition, complex internal channel geometries cannot be post-processed through traditional finishing and polishing methods, and require advanced finishing processes such as Abrasive Flow Machining (AFM). In this original study, the effects of AM design including geometrical changes at the inlets, internal channel and wall thickness of thin features are experimentally studied on Ti64 L-PBF parts. A novel surface roughness inspection technique using micro-CT data is also presented. The internal channels with larger dimensions underwent 40% improvement in surface roughness with no statistically significant change in diameter whereas the channels with smaller dimensions and bends had a 38% improvement in surface roughness accompanied by a 6% increase in diameter. While there was as much as 30% improvement in surface roughness values, the thin walls less than 0.4 mm in dimension were deformed under the AFM pressure after just 5 cycles.Item Accelerated Corrosion Behavior of Additive Manufactured WE43 Magnesium Alloy(University of Texas at Austin, 2021) Karunakaran, Rakeshkumar; Ortgies, Sam; Green, Ryan; Barelman, William; Kobler, Ian; Sealy, MichaelMagnesium alloys are capable of withstanding the high temperatures and pressures needed in oil and gas fracking operations followed by rapid and complete dissolution in days. Dissolvable magnesium plugs are used in fracking to enable longer lateral wellbores by eliminating mill-outs and the associated debris clogging. To increase extraction efficiency, the key technical challenge is determining how to increase the strength of a high corrosion rate magnesium device that enables higher pressures while maintaining high corrosion rates. Topologically modified dissolvable plugs fabricated by additive manufacturing is proposed as a solution to fabricate high strength and high corrosion rate fracture plugs. Corrosion of magnesium is dependent on surface area exposed to corrosive media and is easily manipulated by additive manufacturing. This study highlights the development of optimal powder bed fusion process parameters for WE43 magnesium alloy and investigates the corrosion behavior of printed WE43 in a salt solution concentrated with sodium bicarbonate to initiate highly accelerated corrosion. Printed WE43 corroded three times faster than an as-rolled sample and was driven by the mechanical and materials properties formed by printing.Item Adaptive Voxelization for Rapid Projection Generation in Computed Axial Lithography(University of Texas at Austin, 2021) Coulson, Kevin; Toombs, Joseph; Gu, Magnus; Taylor, HaydenComputed axial lithography (CAL) is a tomographic additive manufacturing technology that offers exceptionally fast printing in a wide range of materials. CAL involves pre-computing a sequence of light patterns to be projected into a photopolymer. For a uniform spatial discretization of the target geometry, computational time scales inversely with the cube of the discretization pitch, which makes it challenging to exploit the full space-bandwidth product of available spatial light modulators. This work introduces an adaptive voxelization approach to reduce computational expense. Using one of several proposed mesh-based complexity analyses, a CAD model is recursively subdivided into stacked sub-meshes of varying voxel resolution. These complexity methods can be tailored to emphasize complexity in particular regions. Each sub-mesh is then independently voxelized before projections are generated and optimized in parallel. On a four-core CPU, this method results in a 2 − 6 × speedup with applications in high-precision CAL and other voxel-based additive manufacturing computations.Item Additive Manufacturing of Cu on 316L Stainless Steel via Inconel 718 Intermediate Layers(University of Texas at Austin, 2021) Zhang, Xinchang; Pan, Tan; Chen, Yitao; Liou, FrankJoining of dissimilar materials is becoming increasingly prevalent to combine differing material properties to enhance product design flexibility and performance. In this study, pure copper was built on 316L stainless steel (SS316L) by laser-based additive manufacturing technology in which copper was deposited layer-by-layer on SS316L with Inconel 718 intermediate layers. The goal is to fabricate multi-metallic structures with improved thermal conductivity. The direct joining of Cu on SS316L would result in porosities at the interface and the consequent poor mechanical properties, which could be addressed by Inconel 718 intermediate layers. The microstructure, chemical composition, tensile properties, and micro-hardness were characterized in the dissimilar materials using scanning electron microscopy, energy dispersive spectroscopy, tensile test with digital image correlation technique, and hardness tester. Results confirm excellent bonding when Inconel 718 intermediate layers are introduced.Item Additive Manufacturing of Si-SiC Cermets for Combustion Device Applications(University of Texas at Austin, 2021) Radyjowski, P.P.; Bourell, D.L.; Kovar, D.; Ellzey, J.L.Traditional manufacturing methods for high-temperature devices are time intensive and limited to simple shapes. Additive manufacturing (AM) reduces lead times and opens the design space to more complex geometries. Indirect laser sintering of siliconized silicon carbide (Si-SiC) cermets was evaluated for creating devices compatible with combustion environments. Heat recirculating combustors especially benefit from geometric flexibility. Si-SiC process improvements are presented for the production of cermet combustors. The effect of flame on the material was studied by directly exposing samples to hot combustion products at 1000°C and 1260°C for 10 hours. Subsequently, three experimental Si-SiC combustors were manufactured and fired to evaluate the practical aspects of cermet applications. Each device was operated for 70 hours under excess-air methane flames with solid temperatures up to 1405°C. The surface oxidation and phase changes were assessed. Operating temperatures between 1200°C and 1350°C reduce damage to the material and give a promise of long-term, high-temperature operation.Item Additive OS: An Open-Source Platform for Additive Manufacturing Data Management & IP Protection(University of Texas at Austin, 2021) Diewald, Evan P.The additive manufacturing (AM) digital thread presents unique challenges for data management and security. While proprietary software packages solve many issues, they can be expensive and lacking in customization. Additive OS is an open-source platform for importing, sharing, organizing, and querying AM data. Man-in-the-middle attacks, secure print licensing, and IP theft are addressed using custom smart contracts, ontology is preserved with a NoSQL database and directed acyclic graph (DAG) representations, and peer-to-peer content delivery facilitates low-latency file transfer. The application includes a browser-based graphical user interface, but developers can access the underlying API to invoke sophisticated queries, add functionality, or run the lightweight client on low-resource hardware.Item Additively Manufactured Hastelloy-X: Effect of Post-Process Heat Treatment on Microstructure and Mechanical Properties(University of Texas at Austin, 2021) Muhammad, Muztahid; Ghiaasiaan, Reza; Gradl, Paul R.; Schobel, Andre; Godfrey, Donald; Shao, Shuai; Shamsaei, NimaIn this study, the effect of post-process heat treatment on the microstructure and mechanical properties of Hastelloy-X superalloy fabricated via two different additive manufacturing technologies, namely, laser beam powder bed fusion (LB-PBF) and laser powder directed energy deposition (LP-DED), is investigated. Microstructure was examined using scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) analysis, while mechanical properties were evaluated by macro-hardness testing using the Rockwell B method. Microstructure of the alloys was studied thoroughly after several heat treatments that involve stress-relieving (at 1066°C for 1.5 hours), hot isostatic pressing (HIP at 1163°C for 3 hours under 103 MPa pressure), and/or solution treatment (at 1177°C for 3 hours). The results revealed that, for both LB-PBF and LP-DED Hastelloy-X, the post-process heat treatments resulted in uniform grain structure as well as partial dissolution of carbides, although they have different grain sizes.Item Additively Manufactured Haynes 230 by Laser Powder Directed Energy Deposition (LP-DED): Effect of Heat Treatment on Microstructure and Tensile Properties(University of Texas at Austin, 2021) Muhammad, Muztahid; Ghiaasiaan, Reza; Gradl, Paul R.; Shao, Shuai; Shamsaei, NimaThe microstructure and tensile mechanical properties of Haynes 230 fabricated through laser powder directed energy deposition (LP-DED) were investigated, varying temperature heat treatments between 900°C to 1177°C following deposition. Scanning electron microscopy (SEM) was employed for microstructural analysis, whilst tensile testing was utilized to evaluate the room temperature mechanical properties of the alloy. In an as-deposited state, the initial microstructure consisted of cellular γ and M6C/M23C6 carbides. The cellular regions seem to be fully dissolved upon solutionizing at 1177°C for 3 hours. Following post-deposition heat-treatments, the carbides were observed to precipitate and grow along the grain boundaries as well as in the interior of grains. Solutionizing at 1177°C for 3 hours following stress-relieving yielded better ductility and had an insignificant effect on the strength.Item Analyzing Remelting Conditions based on In-Situ Melt Pool Data Fusion for Overhang Building in Powder Bed Fusion Process(University of Texas at Austin, 2021) Yang, Zhuo; Lu, Yan; Lane, Brandon; Kim, Jaehyuk; Ndiaye, Yande; Krishnamruty, SundarCoaxial melt pool monitoring (MPM) images provide in-depth insights into the building process of laser powder bed fusion additive manufacturing. An in-situ MPM image captures the independent melting condition at specific positions within each build layer. However, identifying material defects such as horizontal lack-of-fusion using individual, discontinuous MPM images poses multiple challenges. This paper builds upon the authors’ previous work on data registration and data fusion to analyze material remelting conditions based on co-axial MPM images. MPM data are fused to formulate layerwise remelting ‘maps’ to evaluate printing quality. A 3D part with various overhang features was built to verify the method. A regular layer with solid support from the previous layers has around 30 % remelting ratio for the given laser scan conditions. In contrast, overhang regions remelted at about 10 % with the same process setting, whichis too low to provide sufficient material fusion, resulting in lack-of-fusion between melting tracks. The negative impact in remelting would not immediately disappear in subsequent layers following the overhang regions. Results shows three additional layers are required to fully recover the remelting condition back to normal. The remelting results from MPM are also visible within layerwise optical images of the same surface.Item The Anisotropic Yield Surface of Cellular Materials(University of Texas at Austin, 2021) Conway, Kaitlynn M.; Romanick, Zachary; Cook, Lea M.; Morales, Luis A.; Despeaux, Jonathan D.; Ridlehuber, Marcus L.; Fingar, Christian; Doctor, Daquan; Pataky, Garrett J.Mechanical metamaterials are often limited in engineering applications because of uncertainty in their deformation behavior. This uncertainty necessitates large factors of safety and behavior assumptions to be included in mechanical metamaterial designs, detracting from the largest benefit of metamaterials: their ultralight weight. In this study, a yield envelope was created for both a bending dominated and a stretching dominated cellular material topology to improve the understanding of the response of cellular materials under various load types and orientations. Experimental studies revealed that the shear strength of a cellular material is significantly less than that predicted by the Mohr’s criterion, necessitating a modification of the Mohr’s yield criterion for cellular materials. Both topologies experienced tension-compression anisotropy and anisotropy dependent on the topology orientation during loading with the stretching dominated topology experiencing the largest anisotropies.Item Applied Viscous Thread Instability for Manufacturing 3D Printed Foams(University of Texas at Austin, 2021) Emery, B.; Revier, D.L.; Lipton, J.I.Traditional foams are fabricated via stochastic chemical processes that yield homogeneous material properties. Foams can exhibit a wide range of material properties by varying process controls allowing them to be used in many industrial and commercial applications. Previously, additive manufacturing could only produce foam approximations in the form of traditional lattice infill. Our work employs viscous thread printing (VTP) of thermoplastic polyurethane (TPU) on a fused filament fabrication (FFF) printer, exploiting the semi-viscous nature of extruded filament to coil producing a new type of printed foam. Specimens were tested under compression to determine uniformity along principal axes and behavior under strain when compared to infill patterns, such as grid and cubic. This work establishes that VTP as applied to TPU can be used to manufacture programmable stiffness foams as a function of density, suited to a variety of needs and should be considered as an alternative to traditional foams and other printed lattice geometries.Item Automated Anomaly Detection of Laser-Based Additive Manufacturing Using Melt Pool Sparse Representation and Unsupervised Learning(University of Texas at Austin, 2021) Zhao, Xiyue; Imandoust, Aidin; Khanzadeh, Mojtaba; Imani, Farhad; Bian, LinkanAdvanced thermal imaging is increasingly invested in direct energy deposition (DED) additive manufacturing (AM) to cope with information visibility of melt pool and tackle process inconsistency. However, there are key challenges regarding the feasibility of current image-guided monitoring methodologies in the DED process. First, high-resolution thermal images consist of millions of pixels captured by hundreds of frames lead to the curse of dimensionality in analysis. Second, the presence of various exogenous noise, ill-structured data, and significant cluster imbalance limit the capability of the current methodologies to perform real-time monitoring. The objective of this research is to advance the frontier of melt pool monitoring in DED process by designing an automated and unsupervised anomaly detection on high-dimensional thermal image data. Specifically, we develop a variational autoencoder to generate a low-dimensional representation of each input thermal image data. A Gaussian mixture model and K-Mean clustering are integrated with the generative model to split latent space into homogenous regions and detect anomalies. Experimental results show that the proposed methodology is highly effective in detecting defective melt pools with accuracy up to 94.52% and a false alarm rate of less than 2.1%.Item Bayesian Process Optimization for Additively Manufactured Nitinol(University of Texas at Austin, 2021) Ye, Jiafeng; Yasin, Mohammad Salman; Muhammad, Muztahid; Liu, Jia; Vinel, Aleksandr; Slvia, Daniel; Shamsaei, Nima; Shao, ShuaiAdditively manufactured nitinol enables the design and rapid prototyping of the shape memory alloy with great flexibility and cost-effectiveness in various applications. To achieve high-density fabrication of nitinol, we utilize a Gaussian process-based Bayesian optimization method to efficiently optimize process parameters of the laser beam-powder bed fusion (LB-PBF) process in this work. Specifically, Gaussian process regression is applied to formulate a surrogate model between the critical process parameters (i.e., laser power, scanning speed) and the residual porosity of the nitinol samples. Then Bayesian optimization is integrated to successively explore the design space to search for the optimal process parameters. These two methods are integrated to find the global optimum iteratively. Compared with the traditional trial-and-error methods, the proposed method can quickly find the optimal process parameter for the high-quality nitinol samples, especially with many process parameters, and accelerate the innovations with nitinol in additive manufacturing.Item Bimetallic Castings for Wear Performance through Infiltration of Additive Manufactured Metal Lattice Structures(University of Texas at Austin, 2021) Liggett, J.C.; Snelling, D.A.; Xu, M.; Myers, O.J.; Thompson, S.M.High chromium white iron is an alloy frequently employed in the production of abrasion resistive wear components. Ground engaging components for mining or earthmoving frequently require such materials, as well as slurry pumps for mining applications. Although high chromium white iron alloy demonstrates excellent wear performance due to the formation of chromium carbides, it is brittle and lacks toughness. Impact resistance is often of great importance for ground engaging wear components; hence, this study will investigate a method by which high chromium white iron wear components may be reinforced by the formation of a bimetallic composite. In this research, an additively manufactured lattice structure of 316L stainless steel is infiltrated with high chromium white iron via the metal casting process. This procedure results in a bimetallic casting of reinforced white iron. Complete infiltration and metallurgical diffusion bonding were observed between the two alloys, validating this method as a means of reinforcing high chromium white iron castings for applications requiring high abrasion and impact resistance.Item Challenges during laser Powder Bed Fusion of a Near-Alpha Titanium Alloy - Ti-6242Si(University of Texas at Austin, 2021) Patel, Sagar; Keshavarz, Mohsen; Vlasea, MihaelaTi-6Al-2Sn-4Zr-2Mo-Si (Ti-6242Si) is a near-α phase titanium alloy that has a greater strength up to 565 °C compared to the workhorse Ti-6Al-4V alloy with a typical service temperature of up to 400 °C. While there is a wealth of literature to help understand the laser powder bed fusion (LPBF) of Ti-6Al-4V, only a few research articles about LPBF of Ti-6242Si are available in the open literature. In this work, LPBF processing diagrams and temperature prediction models were used to investigate the impact of process parameters such as laser power, scan speed, and beam spot radius on macroscale characteristics of the builds such as density and surface roughness. The use of processing diagrams allowed for exploration of density ranges between 99.55-99.98 %, and surface roughness, Sa, ranges between 8-16 μm in Ti-6242Si processed by LPBF. Cracking in Ti-6242Si manufactured by LPBF is reported for the first time. Cracking during LPBF of Ti-6242Si was observed to strongly depend upon the predicted melting mode (conduction, transition, and keyhole) for a given set of LPBF process parameters.Item Characterizing Internal Porosity of 3D-Printed Fiber Reinforced Materials(University of Texas at Austin, 2021) Mattingly, Frye L.; Franc, Alan; Kunc, Vlastimil; Duty, ChadAs the functional requirements for 3D printed parts become more demanding, the use of fiber reinforced materials in material extrusion printers is increasingly common. Although fiber-reinforced thermoplastics offer higher stiffness and strength, the internal volume of the extruded material often has a high degree of porosity which can negatively impact mechanical properties. This research surveys the internal porosity present across a range of material extrusion additive manufacturing platforms, primarily those involving a single screw extruder, such as the Big Area Additive Manufacturing (BAAM) system. The porosity within the volume of an extruded bead was quantified through image analysis of cross sectional micrographs. The impact of extrusion rate, transient vs steady state flow, multiple hardware configurations, and material conditions were evaluated. Across the five systems studied porosities ranged from 0.1% to 18.4% with the greatest reductions in porosity coming from two systems that added a vent to the extruder barrel which lowered porosity 64% in one case and 98% in the other.Item Characterizing the Internal Morphology of Transition Regions in Large-Scale Extrusion Deposition Additive Manufacturing(University of Texas at Austin, 2021) Brackett, James; Hussein, Zaky; Charles, Elijah; Smith, Tyler; Hassen, Ahmed; Kim, Seokpum; Kunc, Vlastimil; Duty, ChadA dual-hopper feed system that was developed for the Big Area Additive Manufacturing (BAAM) system allows for transitioning between different materials while maintaining continuous deposition. This technique creates a step-change in material feedstock by switching the pellet feeding system to alternate which hopper is currently supplying material, allowing for multi-material construction. The step-change in feedstock material produces a transition region that is characterized by a compositional gradient and blended internal morphology. Initial cross-sectional imaging of the transition region revealed a non-homogenous blend of materials with distinct domains of each material, likely due to incomplete mixing within the screw. This study used a carbon fiber reinforced acrylonitrile butadiene styrene (CF-ABS) and an unfilled ABS to characterize the internal structure and to correlate it to mechanical performance by tracking microhardness across cross-sections of the transition region.Item A Comparative and Experimental Study on the Effect of Heat Treatment Cycles for PBF Ti6Al4V(University of Texas at Austin, 2021) Karasoglu, M.; Yasa, E.; Tan, E.; Yağmur, A.Powder bed fusion (PBF) presents the highest level of technological maturity and industrialization level for metallic materials among other Additive Manufacturing technologies. The advantages of high geometrical complexity, ability to produce internal cavities, reduced lead time and buy-to-fly ratio enables a wide range of application areas from aerospace to biomedical. Laser-PBF and Electron-PBF present different limitations and opportunities while they can both build from Ti6Al4V powder. The performance of the E-PBF and L-PBF parts highly depends on the resulting microstructures and differs significantly due to various mechanisms such as preheating temperatures and processing environment. Moreover, the obtained material properties generally necessitate heat treatments for reducing residual stresses, enhancing mechanical properties and changing the microstructure. This study aims to investigate the effect of the same heat treatment cycles on the E-PBF and L-PBF microstructure evolution and microhardness by a comparative experimental work with several combinations of exposure durations, temperatures and cooling rates.Item A Comparative Study on the Microstructure and Texture Evolution of L-PBF and LP-DED 17-4 PH Stainless Steel during Heat Treatment(University of Texas at Austin, 2021) Nezhadfar, P.D.; Gradl, Paul R.; Shao, Shuai; Shamsaei, NimaThis study aims to characterize the microstructure and crystallographic texture of 17-4 PH stainless steel (SS) manufactured with laser powder directed energy deposition (LP-DED) and laser powder bed fusion (L-PBF), in both non-heat treated and heat treated conditions. It is found that the non-heat treated LP-DED 17-4 PH SS possesses coarse columnar ferrite grains decorated with Widmanstätten ferrite grains, whereas the L-PBF counterpart has very fine and mostly equiaxed ferrite grains along with lath martensite. An identical stress relief (SR) temperature is obtained for both the L-PBF and LP-DED 17-4 PH SS samples based on the phase diagrams generated using Thermo-Calc. software. The SR step prior to CA-H1025 heat treatment resulted in texture weakening and slightly refined the grain structure. The non-heat treated L-PBF 17-4 PH SS sample possesses strong cube and γ-fiber textures, while the texture transfers to weaker γ-fiber components after performing SR-CA-H1025 heat treatment.