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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2019 International Solid Freeform Fabrication Symposium Table of Contents
(2019) Laboratory for Freeform Fabrication and University of Texas at Austin
Additive Manufactured Lightweight Vehicle Door Hinge with Hybrid Lattice Structure
(University of Texas at Austin, 2019) Aydin, I.; Akarcay, E.; Gumus, O.F.; Yelek, H.; Engin, C.B.
Investigating the Production of Gradient Index Optics by Modulating Two-Photon Polymerisation Fabrication Parameters
(University of Texas at Austin, 2019) Woods, E.; Fromhold, M.; Wildman, R.; Tuck, C.
Two-photon polymerisation (TPP) is an additive manufacturing technique allowing the fabrication of arbitrary 3D geometries with sub-micron features. As such, TPP is a promising technique for fabricating optical metamaterials. The electromagnetic (EM) properties of metamaterials arise from their geometrical structure rather than their material constituents alone. By introducing variations across the unit cells of a metamaterial spatially varying EM properties can be created. In this way, gradient index (GRIN) optics can be produced which are useful for reducing coupling losses and creating compact optical systems. This work looks at modulating fabrication parameters to achieve geometrical variations. Line widths of IP-L 780 are measured on an array of lines fabricated at different laser powers and scan speeds. Proof of concept woodpile structures are also fabricated where laser power is changed for individual lines in the structure resulting in geometrical changes. Changing fabrication parameters along a single scan line is also investigated.
Design, Modeling and Characterization on Triply Periodic Minimal Surface Heat Exchangers with Additive Manufacturing
(University of Texas at Austin, 2019) Peng, Hao; Gao, Feng; Hu, Wenjing
Next-generation power plants will generate heated fluids at significantly higher temperatures than current-generation power plants, which challenges the state-of-the-art heat exchanger design. In this study triply periodic minimal surfaces were combined with additive manufacturing for next-generation heat exchanger design. Triply periodic minimal surfaces separate three-dimensional space into two interpenetrating channels, creating high surface area to volume ratios and low hydrodynamic resistance. Parametric design of triply periodic minimal surface heat exchanger is straightforward because they are governed by simple implicit functions with parameters such as periodic length and offset parameter. In this study a design workflow was developed to streamline the design of triply periodic minimal surface heat exchangers and a numerical model was developed to optimize triply periodic minimal surface heat exchanger design for optimal performance. Finally, the optimized triply periodic minimal surface heat exchanger was printed with EOS M290 DMLS machine and the performance was tested by experiment.
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.
In-Plane Pure Shear Deformation of Cellular Materials with Novel Grip Design
(University of Texas at Austin, 2019) Conway, K.M.; Kulkarni, S.S.; Smith, B.A.; Pataky, G.J.; Mocko, G.M.; Summers, J.D.
Cellular materials are popular due to their high specific strength, but their in-plane shear behavior is not well understood. Current experimental methods are limited due to the lack of pure shear loading as common arcan-style grips have not been adjusted for cellular materials. A significant concern is a mixture of shear loading with grip induced tension. While in bulk materials the tensile force can be assumed negligible, it has a significant impact on the deformation behavior of cellular materials. In this study, finite element modeling simulations were used to demonstrate that using a new sliding grip design reduced grip induced tension on cellular materials. Experimental studies were performed on honeycomb cellular materials with traditional and newlydeveloped grips to calculate and compare the shear strength and ductility of honeycomb cellular materials. The study concluded that traditional grips overestimate the shear strength of honeycomb cellular materials and honeycomb cellular materials in pure shear with limited grip induced tension has significantly lower strength and ductility due to the early formation of plastic hinges.
Compressive Properties Optimization of a Bio-Inspired Lightweight Structure Fabricated via Selective Laser Melting
(University of Texas at Austin, 2019) Meng, Liang; Wang, Zemin; Zeng, Xiaoyan
Compressive properties optimization of a bio-inspired lightweight structure is developed by Response Surface Methodology (RSM) and Non-dominated Sorting Genetic Algorithm II (NSGA-II). Multi-layered bio-inspired structures of a Ti6Al4V alloy are designed and fabricated by Selective Laser Melting. The results show that the optimized structure parameters of bio-inspired structures can be obtained by RSM and NSGA-II. The relative error rate of experimental results and response values is less than 10%. Moreover, increasing the number of layers cannot effectively improve energy absorption (EA) and specific energy absorption (SEA) for multi-layered bio-inspired structures. The damage process of bio-inspired structures with different core-arranged configurations fails layer by layer. The load-displacement curves and damage process of FE simulations are consistent with the experimental results.
Fast and Simple Printing of Graded Auxetic Structures
(University of Texas at Austin, 2019) Carton, M.A.; Ganter, M.
One of the great promises of additive manufacturing is the ability to build parts with volumetrically graded parameters that would be difficult or impossible with traditional manufacturing. This paper presents a method of procedural generation and unsupported fabrication of 2D objects patterned with functionally graded auxetic (negative Poisson’s ratio) cellular structures using commercially available FDM printers. Several types of two-dimensional auxetic pattern are fabricated. The resulting printed objects exhibit a graded response to load, deforming corresponding to local patterning. Deformation is studied using imaging of loaded structures and applications in several areas are considered.
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.
Effects of Unit Cell Size on the Mechanical Performance of Additive Manufactured Lattice Structures
(University of Texas at Austin, 2019) Soltani-Tehrani, Arash; Lee, Seungjong; Sereshk, Mohammad Reza Vaziri; Shamsaei, Nima
Lattice structures are generated through the repetition of smaller structures, defined as unit cells. These structures are popular alternatives for bone implants due to the potential to adjust the stiffness. However, in some applications, there are volume and mass constraints that cannot be exceeded. Therefore, to match the lattice structure’s stiffness to that of the natural bone, unit cell sizes should be altered. In this study, the effects of different unit cell sizes, on the compression behavior of lattice structures fabricated from 316L stainless steel (SS) via laser beam powder bed fusion (LB-PBF) are studied through finite element analysis (FEA) while the volume and mass are kept constant and results of which, are validated by experiments. It was found that energy absorption capability and stiffness of lattice structures can increase with decreasing the size while the volume and mass are kept constant. The lattice structure with smaller unit cell dimensions tolerated a relatively higher maximum force for the same amount of displacement.
Permeability Analysis of Polymeric Porous Media Obtained by Material Extrusion Additive Manufacturing
(University of Texas at Austin, 2019) Shigueoka, M.O.; de M. Junqueira, S.L.; Alves, T.A.; Volpato, N.
Porous media (PM) are used in many applications, and their geometry and hydraulic properties are essential in flow analysis, especially in geology (oil and gas) and medical (tissue engineering) applications. Additive Manufacturing (AM) enables the production of planned porosity and the material extrusion AM allows working with process parameters to produce lattice type geometries, without the need to have a 3D model of the internal porous structure. This work presents a preliminary study on the permeability of some PM designs obtained in PLA using an in-house process-planning software. Two main filling variations of the raster strategies were studied, one considering the displacement of staggered layers and the other involving a new joined filaments proposal. The permeability obtained experimentally is compared with numerical outputs. The results indicate that both filling strategies influence the PM permeability, but this was more significant with the joined filaments approach.
Impact Energy Absorption Ability of Thermoplastic Polyurethane (TPU) Cellular Structures Fabricated via Powder Bed Fusion
(University of Texas at Austin, 2019) Wu, Y.; Hermes, J.; Verbelen, L.; Yang, L.
In this study, experimental based investigation was carried out with various cellular structure designs realized using a developmental thermoplastic polyurethane (TPU) fabricated by powder bed fusion process, in the attempt to evaluate the effectiveness of impact energy absorption design with cellular structures when combined with favorable materials. Various cellular designs including the re-entrant auxetic, double-arrow auxetic, octet-truss, BCC, octahedral, diamond and double bow-tie were designed and evaluated. Pendulum-rebound resilience testing and drop-weight impact testing were carried out with each designs, and the effective energy absorption capabilities of these designs were compared. The results from this study provide some initial insights into the design of TPU-based cellular structures for energy absorption applications that could benefit the establishment of more comprehensive knowledge base in this area.
Effective Elastic Properties of Additively Manufactured Metallic Lattice Structures: Unit-Cell Modeling
(University of Texas at Austin, 2019) Fashanu, O.; Murphy, D.; Spratt, M.; Newkirk, J.; Chandrashekhara, K.
Lattice structures are lightweight materials, which exhibit a unique combination of properties such as air and water permeability, energy and acoustic absorption, low thermal conductivity, and electrical insulation. In this work, unit-cell homogenization was used to predict the effective elastic moduli of octet-truss (OT) lattice structures manufactured using selective laser melting (SLM). OT structures were manufactured using a Renishaw AM 250 SLM machine with various relative densities. Compression test was carried out at strain rate 5 × 10-3 m-1 using an MTS frame. Finite element analysis was used in the determination of the OT’s effective elastic properties. Results from the finite element analysis were validated using experiments. It was observed that the finite element predictions were in good agreement with the experimental results.
The Effect of Cell Size and Surface Roughness on the Compressive Properties of ABS Lattice Structures Fabricated by Fused Deposition Modeling
(University of Texas at Austin, 2019) Mason, L.; Leu, M.C.
Researchers looking to improve the surface roughness of acrylonitrile butadiene styrene (ABS) parts fabricated by fused deposition modeling (FDM) have determined that acetone smoothing not only achieves improved surface roughness but increases compressive strength as well. However, the sensitivity of ABS parts to acetone smoothing has not been explored. In this study we investigated FDM-fabricated ABS lattice structures of various cell sizes subjected to cold acetone vapor smoothing to determine the combined effect of cell size and acetone smoothing on the compressive properties of the lattice structures. The acetone-smoothed specimens performed better than the as-built specimens in both compression modulus and maximum load, and there was a decrease in those compressive properties with decreasing cell size. The difference between as-built and acetone-smoothed specimens was found to increase with decreasing cell size for the maximum load.
A Computational and Experimental Investigation into Mechanical Characterizations of Strut-Based Lattice Structures
(University of Texas at Austin, 2019) Sereshk, Mohammad Reza Vaziri; Triplett, Kevin; St. John, Christopher; Martin, Keith; Gorin, Shira; Avery, Alec; Byer, Eric; St Pierre, Conner; Soltani-Tehrani, Arash; Shamsaei, Nima
Strut-based lattices are widely used in structural components for reducing weight. Additive manufacturing has provided a unique opportunity to fabricate such complex geometries. In addition to the unit cell type, the strut size and shape can significantly affect the mechanical properties achieved. Therefore, furnishing a lattice structure library may help in selecting the appropriate combination of lattice types and dimensions for targeted mechanical performance for a specific application. This study presents a method for determination of mechanical properties, including strength and stiffness, for lattice structures. Finite element (FE) simulations are used as the main tool and the results of which are to be verified by mechanical testing of samples fabricated using the laser beam powder bed fusion (LB-PBF) process. Proper lattices with the stiffness matched with associated bone were determined. However, the result indicated that lattices made from 316L SS are not strong enough for bone implants. The proposed procedure can be used for other unit cells of interest due to its generality.
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.
Compressive and Bending Performance of Selectively Laser Melted AlSi10Mg Structures
(University of Texas at Austin, 2019) Murphy, D.; Fashanu, O.; Spratt, M.; Newkirk, J.; Chandrashekhara, K.
Selective laser melting (SLM) is a widely used additive manufacturing technique that effectively manufactures complex geometries such as cellular structures. However, challenges such as anisotropy and mechanical property variation are commonly found due to process parameters. In a bid to utilize this method for the commercial production of cellular structures, it is important to understand the behavior of a material under different loading conditions. In this work, the behavior of additively manufactured AlSi10Mg under compression, bending, and tension loads was investigated. Vertical and horizontal build directions are compared for each type of loading. Specimens were manufactured using the reduced build volume (RBV) chamber of the Renishaw AM 250 SLM machine.
Surface Roughness Characterization in Laser Powder Bed Fusion Additive Manufacturing
(University of Texas at Austin, 2019) Eidt, Wesley; Tatman, Eric-Paul; McCarther, Josiah; Kastner, Jared; Gunther, Sean; Gockel, Joy
Failure Detection of Fused Filament Fabrication via Deep Learning
(University of Texas at Austin, 2019) Zhang, Zhicheng; Fidan, Ismail
Additive Manufacturing (AM) is used in several fields and its utilization is growing sharply in almost every aspect of daily life. The focus of the current studies in the AM field is generally focused on the development of new technologies and materials. In addition, there is a limited number of research studies on the troubleshooting aspects of the AM processes. For the most commonly used Fused Filament Fabrication (FFF) process, the waste of material and time due to the printing errors are still an unsolved problem. The typical errors such as nozzle jamming and layer mis-alignment are inevitable during the printing process, and thus cause the failure of printing. It is a challenging task to clearly understand the physical behavior of FFF process with uncertainty, due to the phase transition and heterogeneity of the materials. Therefore, to detect the printing error, this research proposes a deep learning (DL) based printing failure detection technique. In this study, DL is utilized to monitor the printing process, and detect its failures. This newly developed DL framework was beta-tested with a commercially available FFF setup. The beta testing results showed that this technique could effectively detect printing failures with high accuracy.
Fatigue Performance of Additively Manufactured Stainless Steel 316L for Nuclear Applications
(University of Texas at Austin, 2019) Beard, William; Lancaster, Robert; Adams, Jack; Buller, Dane
Additive manufacturing (AM) is a rapidly growing technology which is extending its influence into many industrial sectors such as aerospace, automotive and marine. Recently the nuclear sector has considered AM in the production of nuclear reactor components due to its possible advantages over conventional manufacturing routes. This includes considerable cost savings due to less material wastage, the ability to produce complex near net shape components that conventional manufacturing processes are unable to achieve and a reduced manufacturing time. Initially, Stainless Steel 316L (SS316L) manufactured by laser powder bed fusion (LPBF) has been identified as a potential candidate. However, due to the transient nature of the microstructure it is now of fundamental importance to assess and understand the mechanical behaviour of the LPBF material. This paper will highlight some of the recent research at Swansea University in investigating the variation on the fatigue characteristics between wrought SS316L and LPBF processed SS316L material. This will include an extensive microstructural and fractographic investigation. As LPBF material looks to replace conventionally manufactured equivalents, an understanding of how build integrity and orientation affects the mechanical properties of AM material is critical. Wrought and vertical LPBF material are to be assessed to understand how the microstructure controls the fatigue performance of LPBF SS316L material.

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