2021 International Solid Freeform Fabrication Symposium

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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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Now showing 1 - 20 of 142
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    2021 International Solid Freeform Fabrication Symposium Table of Contents
    (2021) Laboratory for Freeform Fabrication and University of Texas at Austin
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    Effects of Centrifugal Disc Finishing for Surface Improvements in Additively Manufactured Gears
    (University of Texas at Austin, 2021) Fan, Foxian; Soares, Nicholas; Jalui, Sagar; Isaacson, Aaron; Savla, Aditya; Manogharan, Guha; Simpson, Tim
    Additive Manufacturing (AM) is well suited to rapidly produce complex and customized geometries economically for low production runs. However, there is an inherent need for post-AM machining and surface finishing in most metal AM applications. Centrifugal Disc Finishing (CDF) is a media-based mass finishing process that can be employed to improve surface finish of external surfaces of AM parts with complex geometry. This original study aims to understand the influence of CDF processing conditions on Ti64 gear teeth fabricated via Powder Bed Fusion (PBF). A detailed statistical analysis is conducted to analyze the effectiveness of CDF to improve surface roughness of different build surfaces of the AM gear teeth. In addition, both contact profilometer and X-ray Computer Tomography (CT) techniques are applied to evaluate its effectiveness to measure CDF and AM surface finishing. Findings from this study on CDF of gear AM will benefit metal AM community by better understanding the impact of CDF processing conditions for surface improvements in mass finishing of metal AM parts.
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    The Role of Interface in Additively Manufactured Interpenetrating Composites
    (University of Texas at Austin, 2021) Allen, J.; Cheng, J.; Hu, X.; Splitter, D.A.; Gussev, M.; Shyam, A.
    Additively Manufactured Interpenetrating Composites (AMIPCs) are a relatively new metal-metal chain composite in development for use in high energy absorption systems. In this system, reinforcing phase of additively manufactured continuous lattice configurations 316L austenitic stainless-steel is in melt infiltrated with a matrix phase of A356 aluminum-silicon casting alloy. Measurements and observations of this material system have shown that weakly bonded or open/porous interface between the reinforcement and matrix phases exhibits dramatically different mechanical properties of AMIPCs, which is not currently well understood. In this work, Finite Element Models (FEM) are used to model the effects of interfaces between the composite phases. Mechanical tensile tests measurements of various composite volume fractions and varying degrees of casting infiltration are also examined and used to show consistency with the FEM results. The outcome provides insight into material design criteria and performance predictions for new hybrid material systems with exceptional damage tolerance.
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    Mechanical Interface for Iterative Hybrid Additive and Subtractive Manufacturing
    (University of Texas at Austin, 2021) Weflen, E.D.; Ginther, M.C.; Eldakroury, M.A.; Frank, M.C.
    Additive and subtractive manufacturing systems for in-envelope production of large objects face challenges with respect to reach and access of cutting tools. One approach to overcoming this is iteratively alternate between additive and subtractive processes. However, polymer objects require cooling before machining, resulting in poor thermal welding when the subsequent polymer layer is deposited. This paper describes a method to enable iterative processing for in-envelope hybrid manufacturing that uses a mechanical bond to transition back to additive deposition after machining. This is accomplished using an AMBIT screw-extrusion head to additively manufacture a section of the object within a 5-axis machining center. After the object is machined, a dovetail cutting tool forms undercut geometry in the interface where plastic extrusion will resume. Upon polymer solidification, a mechanical interlock is formed. This work evaluates several undercut geometries for mechanical performance. This iterative approach to hybrid additive/subtractive manufacturing reduces machining complexity while maintaining structural integrity.
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    Effects of In-Situ Mechanical and Chemical Polishing on Surface Topography of Additively Manufactured Fiber-Reinforced Polymers
    (University of Texas at Austin, 2021) Nigam, Aman; Tai, Bruce L.
    Additive manufacturing of fiber-reinforced polymers (FRPs) has revolutionized fused filament fabrication (FFF) by producing polymeric parts with enhanced mechanical properties. However, FFF suffers from poor surface quality and dimensional accuracy, particularly for FRPs, due to their abrasive and rheological nature. This examines an in-situ polishing scheme for FRPs in the FFF configuration. Glass-fiber-reinforced Nylon was used as the study material. Three polishing schemes, mechanical, chemical, and a combined thereof, were adopted along with various parameters in each case. The results show significant surface improvements in all cases, and the combined process can further reduce the Ra value to around 2 μm and the dimensional error to 0.2 mm and less. The combined process also enhances surface uniformity (i.e., similar Ra in all directions). In particular, with the combined approach, the in-situ polishing scheme is expected to improve the quality of 3D printed FRPs significantly.
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    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.
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    Mechanical Behavior of ABS after Interlayer Ultrasonic Peening Printed by Fused Filament Fabrication
    (University of Texas at Austin, 2021) Guivier, Manon; Kuebler, Jesse; Swanson, Trevor; Lawson, Christopher; Fernandez-Ballester, Lucia; Negahban, Mehrdad; Sealy, Michael P.
    Hybrid additive manufacturing brought new opportunities to improve the mechanical properties of materials by secondary processing of individual layers during printing. Previous work demonstrated interlayer shot peening during printing by fused filament fabrication (FFF) affected mechanical behavior while inadvertently imparting debris contamination from pulverized beads. The encouraging results motivated a study on the use of contamination free ultrasonic peening (UP) as an alternative interlayer surface treatment. Ultrasonic peening of FFF printed Acrylonitrile Butadiene Styrene (ABS) was studied in order to compare the effects on mechanical properties between ultrasonic peening and previously studied shot peening, different print orientations, and different interlayer peening frequencies. Two different layer peening frequencies (L4 and L8) were compared to an as-printed control (L0). Two orientations for each layer peening frequency were chosen for comparison. Tensile tests were conducted in order to observe the influence of interlayer UP on tensile strength of ABS parts.
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    Static Liquid Interface to Reduce Support Structure Necessity in Top-Down Stereolithography
    (University of Texas at Austin, 2021) Mulka, Nicholas; Goyal, Tarun; Jariwala, Amit; Rosen, David
    Stereolithography (SLA) 3D printing is a vat photopolymerization additive manufacturing process that utilizes photocurable resin, which requires sacrificial supporting structures on part overhangs, increasing material waste and post-processing time. This study details a novel process for conducting top-down SLA 3D printing from a thin resin layer located above a static immiscible supporting fluid, which reduces or eliminates the need for solid supports. The support fluid prevents deflection from buoyant and gravitational forces on thin overhangs from anchored parts due to minute density differences between the supporting fluid and cured resin, while reducing the volume of resin necessary to print compared to traditional top-down SLA. Using this process, we have experimentally demonstrated printed geometry with overhangs of up to 90 degrees. Additionally, necessary material properties of both fluids and process parameters of the system have been identified for the system’s feasibility and broader adaptation.
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    Laser Powder Bed Fusion of Stainless Steel 316L Using a Flexible Dual Fiber Laser Array
    (University of Texas at Austin, 2021) Lantzsch, T.; Westphalen, T.; Tenbrock, C.; Traub, M.; Haefner, C.L.
    In recent years, Laser Powder Bed Fusion (LPBF) has become an industrially established manufacturing technique. State-of-the-art LPBF machines feature a combination of fiber lasers and galvanometer scanners due to their high dynamic and excellent focusability. To increase the productivity of LPBF machines the number of laser scanner systems (LSS) is multiplied, which causes an almost linear increase of machine costs. In this study a flexible optical system which allows the combination of two fiber lasers with a single galvanometer scanner is developed and integrated into a LPBF lab machine to scale the productivity within one scan field. The resulting machine is characterized and used for the manufacturing of test specimen out of stainless steel AISI 316L. The manufactured specimens are analyzed in terms of melt pool formation via high-speed videography as well as resulting part density and build-up rate. The obtained results are compared with state-of-the-art LPBF-machines.
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    Multi-track Geometry Prediction in Powder Fed Laser Additive Manufacturing Using Machine Learning
    (University of Texas at Austin, 2021) Botelho, L.; van Blitterswijk, R.H.; Khajepour, A.
    Laser additive manufacturing (LAM) allows for complex geometries to be fabricated without the limitations of conventional manufacturing. However, LAM is highly sensitive to small disturbances, resulting in variation in the geometry of the produced layer (clad). Therefore, in this research a monitoring algorithm is discussed with the capability of predicting the geometry of multiple tracks of added material. Though imaging can be used to measure the geometry of the melt pool during LAM, the appearance of the melt pool changes in multi-track processes due to the previous layers causing measurement errors. Hence, a machine learning algorithm may be able to accommodate for the changing melt pool appearance to improve accuracy. Images can be captured during LAM with visible-light and infrared sensors which may provide sufficient information for the geometry to be predicted. A convolutional neural network (CNN) can then use these images to estimate the geometry (height and width) during LAM processes.
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    Multiple-Material Powder Bed Fusion Machine Development: Reducing Cross-Contamination between Materials
    (University of Texas at Austin, 2021) Snarr, Scott E.; Najera, Andres; Beaman, Joseph Jr.; Haas, Derek
    Powder bed fusion is an additive manufacturing technology capable of producing fully dense, high strength parts with complex geometries. However, it is currently only able to fabricate parts comprised of a single material. Multiple-material capabilities would allow for an added level of design complexity and the matching of material properties to the functional requirements of a part. In order to achieve this, a full redesign of the current powder deposition system is required. Previous attempts to implement multiple-material powder deposition systems encountered issues with controlling the dimensional accuracy in the build direction and cross-contamination between materials. This research integrates an angled blade leveling mechanism along with a nozzle-based powder deposition system to solve these problems. A design of experiments was run to identify significant leveling parameters and to quantify material cross-contamination. A deposition and leveling system that creates a uniform height multiple-material powder bed with no significant cross-contamination of materials is demonstrated.
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    Vibration-Actuated Powder Dispensing for Directed Energy Deposition Systems
    (University of Texas at Austin, 2021) Greeley, Andrew; Cormier, Denis
    Users of powder-fed directed energy deposition system often face several challenges associated with conventional powder delivery sub-systems. In addition to the high cost of wasted powder, it can be difficult to plan for the amount of material being deposited when some of the dispensed powder is not captured in the melt pool. This work studies the effectiveness of a vibration-actuated powder dispensing system using a nozzle with a small capillary opening. The opening is sized so that particle contact forces arrest powder flow when the vibration actuator is turned off. The relative effects of vibration frequency, vibration acceleration, nozzle size and nozzle inclination are compared with the goal of having the output mass flow rate monotonically change with one of these parameters. For the materials and parameters explored in this study, nozzle inclination is found to have the largest effect on mass flow rate output and has the desired monotonically changing relationship.
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    Material Characterization of Diversity Aggregated Cementitious Materials Produced with a Modular Lightweight Additive Manufacturing Extrusion System
    (University of Texas at Austin, 2021) Nodehi, Mehrab; Asiabanpour, Bahram; Omer, Liam; Ozbakkaloglu, Togay
    Applications of additive manufacturing in the construction industry started three decades ago with the first patent and prototype of the contour crafting process. Since then, its obvious benefits in reducing labor cost, construction waste while improving efficiency and flexibility have led to the development of several large-scale commercial machines in this field. However, proper lab-scale machines for training experts in automated construction and research-based activities such as material optimizations for civil and structural engineers are not available. The only available small-scale apparatus in AM-based construction is limited to a minimal list of materials and properties. Those machines are not capable of fabricating samples from cementitious materials with a variety of aggregate sizes. This paper compares two low-cost, modular AM-based construction systems capable of extruding a wide variety of cementitious materials with diverse aggregate sizes. The systems are capable of controlled extrusion with a variety of cross-section forms. The system can be attached to a robotic arm, CNC machine, or other programmable machines. As a proof-of-concept, the developed system is utilized to fabricate cement mortar with larger aggregate sizes with different materials mixture ratios. Mechanical performance of the resulting additively manufactured cementitious parts is examined and compared.
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    Geometrical Analysis of Simple Contours Deposited by a 3D Printing Hexacopter
    (University of Texas at Austin, 2021) Nettekoven, Alexander; Franken, Nicholas; Topcu, Ufuk
    Current limitations in vertical and horizontal mobility for ground robots in 3D printing of medium to large-scale objects have recently led to the development of a 3D printing hexacopter testbed at the University of Texas at Austin. This testbed can fly to a desired location and deposit polylactic acid on flat surfaces. A previous study has shown the feasibility of this approach but has not yet quantified the testbed’s printing capabilities. In this paper, we quantify the printing capabilities. We print square contours of different sizes and quantify the printed results based on their geometric dimensions. We also quantify the testbed’s trajectory tracking to assess the testbed’s positioning accuracy during printing. In quantifying the testbed, we lay the groundwork for using aerial robots in printing applications of medium to large-scale objects, such as concrete printing.
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    Review of Current Problems and Developments in Large Area Additive Manufacturing (LAAM)
    (University of Texas at Austin, 2021) Crisp, Tyler G.; Weaver, Jason M.
    Large Area Additive Manufacturing (LAAM), also known as Big Area Additive Manufacturing (BAAM), is a screw extrusion, pellet-fed additive manufacturing technology. The large build area, rapid build speed, and inexpensive pelletized feedstock of LAAM are major advantages over conventional AM methods. LAAM has a large variety of applications in areas including energy, automotive, aerospace, high volume production, and composite molds. However, LAAM is not without its challenges. The largest challenges LAAM faces include mechanical properties, uniformity and precision, and predictability of composite material properties. The goal of this paper is to present current research regarding challenges in LAAM, methods of addressing those challenges, developments, and applications, as well to highlight further research to be done.
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    Variable Extrusion Width for Interlocking Features in Fused Filament Fabrication 3D Printing
    (University of Texas at Austin, 2021) Habbal, Osama; Ayoub, Georges; Pannier, Christopher
    Following from developments in continuously variable extrusion width in fused filament fabrication additive manufacturing, this work explores the combination of in-plane bead width variation with bead trajectory variation as a technique to improve in-plane strength in polymer material extrusion additive manufacturing. Sinusoidal in-plane waveforms are used for the extruder trajectory instead of maintaining a straight line. The varied bead width, in conjunction with the non-straight bead trajectory, reduces anisotropy of strength within the layer. The findings apply to fully dense infill of single layers, commonly called horizontal perimeters in common slicing/toolpath planning computer programs. Experimental tensile testing results show a 48.6% reduction in anisotropy of tensile strength driven by 43% and 29% increases in the ultimate tensile strength in the 0° and 45° orientations, respectively. However, this comes at the cost of 99.6% reduction in toughness in the 90° orientation. We also present the principal concept behind the machine code generating script, that allows for the increase and decrease of the extruded bead width continuously along the extruded bead.
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    Feasibility Study of Large-Format, Freeform 3D Printing for On-Orbit Additive Manufacturing
    (University of Texas at Austin, 2021) Jonckers, D.; Tauscher, O.; Stoll, E.; Thakur, A.
    Large scale, on-orbit additive manufacturing (AM) and assembly is being considered as a modular and resource saving approach to facilitate permanent human presence in space. To realise this, a novel AM approach to freeform fabricate large, functional structures in space has been developed. Combining the reach of a free-flying CubeSat with a collaborative robotic arm and a 3D printer, large support-free thermoplastic structures can be manufactured beyond the size of the setup itself. The feasibility of the proposed fabrication approach was established using the Experimental Lab for Proximity Operations and Space Situational Awareness (ELISSA) system, where a modified fused filament fabrication setup was mounted on a free-flyer to 3D print free-standing structures. Using a continuous navigation path incorporating an infinite fabrication loop, over 70 centimetre long, support-free trusses were produced to well demonstrate the potential of the proposed method in boundless direct printing of complex structures, independent of gravity or printing orientation.
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    A Triz-Based Analysis of the Fundamental Limits of Fused Filament Fabrication
    (University of Texas at Austin, 2021) Weaver, J.M.; Patternson, C.
    Each category of additive manufacturing (AM) has specific fundamental limitations bounded by the physics and material properties involved. For example, the speed of fused filament fabrication (FFF) processes is bounded by how quickly thermoplastics can be melted, deposited, and resolidified while retaining material properties and dimensional accuracy. Incremental improvements approaching these theoretical limits will continue to occur, but more radical changes are necessary to completely overcome the current constraints. This paper considers some of the fundamental limits bounding FFF processes and investigates possible avenues for future research to overcome these limits. The framework for this analysis is the “Theory of Inventive Problem Solving” (TRIZ), a formalized problem solving and ideation tool that generalizes design-specific problems into contradicting engineering parameters, then suggests universal design principles based on analogy to solutions in other systems and patents. TRIZ has been used in many fields successfully, including the design of parts to be more manufacturable through AM, but literature on its application to additive manufacturing processes themselves is limited. Two case studies are shared demonstrating how TRIZ-based analysis can lead to radical improvements in FFF and other AM technologies.
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    Design and Implementation of Laser Powder Bed Fusion Additive Manufacturing Testbed Control Software
    (University of Texas at Austin, 2021) Yeung, Ho; Hutchinson, Keely; Lin, Dong
    The National Institute of Standards and Technology developed a facility titled the Additive Manufacturing Metrology Testbed to advance the research in laser powder bed fusion (LPBF) processes. The testbed adopted an open control architecture which allows full access to all key process parameters. Although LPBF control is a very important topic, very little literature can be found on how this is implemented. This paper reviews the testbed control software design and implementation. Scan path planning, galvo motion control, and laser power control are detailed with select highlights. Comparison with commercial machine control software is made, and recent experiments utilizing the advanced features of the testbed control software are also discussed.