2016 International Solid Freeform Fabrication Symposium

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https://hdl.handle.net/2152/89344

Proceedings for the 2016 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Twenty-Seventh Annual International Solid Freeform Fabrication (SFF) Symposium – An Additive Manufacturing Conference, held at The University of Texas in Austin on August 8-10, 2016, was attended by 544 researchers from 19 countries. The number of oral and poster presentations increased to 424 this year. The meeting was held on the campus of The University of Texas at Austin in the AT&T Executive Education and Conference Center. The meeting consisted of a Monday morning plenary, 40 parallel technical sessions and a poster session.

The conference attendance is growing rapidly, clearly reflective of the interest at large in the area.

The recipient of the International Outstanding Young Researcher in Freeform and Additive Manufacturing Award was Dr. Li Yang from The University of Louisville. Dr. Brent Stucker from 3DSIM, LLC won the International Freeform and Additive Manufacturing Excellence (FAME) Award.

There are 197 papers in this conference proceedings volume. Papers marked “REVIEWED” on the first page heading were peer reviewed by two external reviewers. Papers have been placed in topical order and numbered sequentially 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.

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 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 (N00014-16-1-3004) and the National Science Foundation (CMMI-1639406) for supporting this meeting financially. The meeting was co-organized by The University of Connecticut at Storrs, and 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.

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2016 International Solid Freeform Fabrication Symposium Table of Contents
(2016) Laboratory for Freeform Fabrication and University of Texas at Austin
Finishing of Additively Manufactured Metal Parts by Abrasive Flow Machining
(University of Texas at Austin, 2016) Wang, Xuanping; Li, Shichong; Fu, Youzhi; Gao, Hang
Surface finishing is still a crucial challenge in metal Additive Manufacturing (AM) as the as-built surface roughness is difficult to fulfill service requirements, due to staircase effect, balling effect inherent to AM. Abrasive flow machining (AFM) is a non-conventional finishing technique that offers better accuracy and efficiency for parts with difficult-to-access structures, and the application of AFM to finishing metal parts of AM process is discussed in this paper. The aluminum and titanium grilles by selective laser melting are taken to explore the finishing effect of outer and inner surfaces. The AFM process parameters of abrasive grits sizes, abrasive media viscosity, and tooling designs are optimized to implement effective material removal from the outer and inner surfaces. The results show that the AM grille parts with non-trial internal structures can be finished efficiently and consistently by AFM.
3D Printing in the Wild: A Preliminary Investigation of Air Quality in College Maker Spaces
(University of Texas at Austin, 2016) McDonnell, Bill; Jimenez Guzman, Xavier; Dolack, Matthew; Simpson, Timothy W.; Cimbala, John M.
Additive manufacturing is a popular method for prototyping and manufacturing custom parts, especially on college campuses. While there is widespread use of 3D printers as part of many engineering classwork, there is little regulation or knowledge regarding emissions. Many plastics, including polycarbonates, ABS, and PLA are known to emit high counts of volatile organic compounds (VOCs) and particulate matters (PMs). This study focuses on VOC and PM counts in several natural environments and dedicated “maker spaces” on a large college campus to gauge the exposure that students and operators experience. Emissions were measured using a photoionization detector and two particle sizers. The photoionization detector measured total VOCs, and the particle size counters measured both total nanoparticles and individual micro-particles based on relative particle diameter. Measurements were taken in hourly increments and then analyzed to determine the degree with which desktop printers emitted VOCs and PM. Our data can be used to determine whether additional ventilation or filtration is needed when 3D printing “in the wild” to enhance operator and bystander safety.
A Model for Residual Stress and Part Warpage Prediction in Material Extrusion with Application to Polypropylene
(University of Texas at Austin, 2016) Watanabe, N.; Shofner, M.L.; Treat, N.; Rosen, D.W.
The layer-by-layer fabrication procedure causes residual stresses to accumulate due to the repetition of heating and cooling during the material extrusion process. In this study, residual stress and part warpage of a polypropylene copolymer are investigated. The effects of adjusting process variable settings, such as deposition temperature, deposition speed, and layer height, on part warpage are analyzed computationally and experimentally. Material extrusion process simulation models that are capable of predicting the temperature distributions, deposited filament shapes, and residual stresses of fabricated parts have been developed. These models are used to predict the warpages and deformations of the fabricated parts; these predictions are compared with experimental results to evaluate the models’ efficacy. Insights are gained on the effects of particulate inclusions on the residual stress and warpage behaviors of polypropylene copolymer.
Complex Functional Surface Design for Additive Manufacturing
(University of Texas at Austin, 2016) Morris, S.J.; Dudman, J.P.R.; Körner, L.; Melo, P.; Newton, L.H.; Clare, A.T.
This paper presents a new methodology for the creation of advanced surfaces which can be produced by Additive Manufacturing (AM) methods. Since there is no cost for enhanced complexity, AM allows for new capabilities in surface design. Micro-scale surface features with varying size, shape and pitch can be manufactured by Two-Photon Polymerisation (2PP). Computer-Aided Design (CAD) tools allowing for this variation to be incorporated into the surface design are only just emerging. With the presented methodology, surfaces are created from a single feature design. Variation is applied to the surface features through algorithmic design tools, allowing for arrays of hundreds of unique features can be created by non-CAD experts. The translation of these algorithmic expressions from CAD to a physical surface is investigated. Using the proposed methodology, 2PP is used to create quasi stochastic surfaces for the purpose of enhancing the biointegration of medical implants against current state-of-the-art.
Flammability of 3-D Printed Polymers – Composition and Geometry Factors
(University of Texas at Austin, 2016) Kraft, Stefan M.; Lattimer, Brian Y.; Williams, Christopher B.
The focus of this paper is to evaluate the comparative flammability of additively manufactured (AM) and conventionally molded polymers. Flammability of objects is dependent on two main factors: material composition and object geometry. To evaluate effects of material composition, experiments on polymer samples made via conventional molding and via AM were performed using an ASTM E1354 cone calorimeter to measure and compare material ignitability and heat release rate. ULTEM™ (amorphous thermoplastic polyetherimide) and PPSF/PPSU (polyphenylsulfone) heat release rates were about 10 times lower than ABS (acrylonitrile butadiene styrene). This was in part due to the large char layer formed by these materials during burning. Comparisons between conventional molded and AM materials revealed slight differences in heat release rate. Additively manufactured ABS sheets had about a 17% higher mean average heat release rate (MAHRR). Conversely, the characterization of ULTEM 9085™ sheets revealed the MAHRR of the AM samples were 13% lower than the molded samples. This is attributed to additives in the material used for extrusion AM as well as the build process itself. Effects of geometry were assessed using material cribs, which were composed of layers of rectangular prisms separated by air gaps, with prisms on consecutive layers being orthogonal. Cribs were constructed with three to ten prisms per layer to evaluate the effects of varying the internal material surface area. Below a specific threshold, the burning mass loss rate per unit area of the cribs decreased with an increase in internal material surface area; this agrees with trends predicted using a theoretical model previously developed for wood cribs.
Production-Integrated Markings for Traceability of AM Parts in the Context of Industry 4.0
(University of Texas at Austin, 2016) Jahnke, U.; Bornefeld, P.A.; Koch, R.
Traceability is often mentioned as one fundamental requirement to reach the vision of Industry 4.0, the next industrial revolution. As Additive Manufacturing (AM) is a technology with high relevance in the scope of Industry 4.0 this paper focuses on production-integrated markings for traceability of additively manufactured parts. Even industries that are not focusing on products with critical functionality using markings for quality management and liability exclusion can benefit a lot from identifiability of products. Markings can be understood as a kind of individualization of parts. As individualization does not increase production costs when using AM and the effort for integration of markings can be minimized by software in particular for high batch production, product marking should be an obligatory process step. This paper comprises various applications that can be achieved due to markings as well as different ways to embed a marking at least partly automatically.
Design and Fabrication of Functionally Graded Components by Selective Laser Melting
(University of Texas at Austin, 2016) Sun, C.N.; Choy, S.Y.; Leong, K.F.; Wei, J.
The control of structure formation of additive manufacturing simplifies the fabrication of functionally graded components (FGC), which changes in the physical properties can be achieved via structural design. In this research, selective laser melting (SLM) technology was used to fabricate structures with gradient lattice designs. The structure was varied in strut thickness continuously and linearly in single direction for cubic and honeycomb unit cells. Results showed that the complex design was successfully built and achieved nearly full-dense strut. Compression test results showed that the stress-strain curves of both cubic and honeycomb lattice structures oscillate with multiple peak loads, suggesting ductile characteristics. However, lattice structures with graded thickness tend to oscillate upward as the strut diameter increases.
Investigating the Links Between the Process Parameters and Their Influence on the Aesthetic Evaluation of Selective Laser Melted Parts
(University of Texas at Austin, 2016) Galimberti, G.; Doubrovski, E.L.; Guagliano, M.; Previtali, B.; Verlinden, J.C.
This study is a precursor to gaining a deeper understanding of how each parameter of the Additive Manufacturing (AM) process influences the aesthetic properties of 3D printed products. Little research has been conducted on this specific aspect of AM. Using insights from the work presented in this paper, we intend to develop design support tools to give the designer more control over the printed products in terms of aesthetics. In this initial work, we fabricated samples using Selective Laser Melting (SLM) technology, and investigated the parameters geometry, building strategy, and post-processing. We asked participants to evaluate the visual and physical interaction with the manufactured samples. Results show that, in addition to geometry and post-processing, the aesthetic evaluation can also be strongly influenced by the SLM process’ building strategy. This understanding will enable us to develop tools to give designers more control over the part’s aesthetic appearance. In addition, we present a systematic procedure and setup to evaluate the aesthetic appearance of products manufactured using AM.
Optimisation of Substrate Angles for Three Dimensional Inkjet Printing of Multi-Functional and Multi-Material Parts
(University of Texas at Austin, 2016) Vaithilingam, Jayasheelan; Laoboonmee, Kasidis; Saleh, Ehab; Hague, Richard J.M.; Wildman, Ricky D.; Tuck, Christopher J.
Three dimensional (3D) inkjet printing of multiple materials is being explored widely to fabricate multi-functional parts such as the printing of strain gauges and heating elements embedded within a component. Although dielectrics and conductive materials can be inkjet-printed together, there is a difference in their layer thicknesses. Inkjet printed conductive materials require sintering at temperatures of around 150°C to form a conductive network. Exposing the dielectric materials which may be sensitive to prolonged heat exposure could affect their material properties. Hence, optimisation of conductive routes within the structural material is essential. It is envisaged that printing of structural materials at an angle to a certain height/layers and then printing a few layers (~ 10 layers) of conductive material on to the top surface will enable faster fabrication and reduced exposure of the dielectric material to heat. To compliment this aim, in this study, dielectric substrates were printed at different angles and the conductivity of the tracks were assessed. Surface morphology of the printed tracks showed misplacement of droplets for angles above 15° due to the influence of print height. The printed tracks remained conductive up to 65°; however above 50°, the tracks were highly resistive (> 150KΩ). The optimal angle to obtain conductive tracks with the highest print resolution was 15° and it was greatly influenced by the print height. Further study is required to optimise the substrate angle by using a constant print height and varying the slope length.
Folding Endurance Appraisal for Thermoplastic Materials Printed in Fusion Deposition Technology
(University of Texas at Austin, 2016) Balderrama-Armendariz, Cesar O.; MacDonald, Eric; Valadez, Esdras D.; Espalin, David
The anisotropic behavior of the fusion deposition modeling (FDM) machines could change the mechanical properties of the materials in the layer by layer technology. In general, the tensile, compressive and flexural strength are decreased against molded plastics. Some lasting products need the iteration of low flexural strength and high elongation to obtain an effective flexibility to bend in repetitive movements. The present work provides an analysis of the capacity of several selected thermoplastics materials such as Nylon (PA), Polyethylene Terephthalate (PETG), Polylactide (PLA), Polyurethane (TPU) and Polypropylene (PP) in order to test the maximal load capacity and the number of folding cycles sustained in perpendicular direction of movement. Results demonstrate that those of similar to injected molded products, PP and TPU materials surpass one million of cycles in the folding test. Yet, in axial load they have lower strength against the other considered materials.
Effect of Sparse-Build Internal Structure on Performance of Fused Deposition Modeling Tools Under Pressure
(University of Texas at Austin, 2016) Meng, S.; Mason, L.; Taylor, G.; Wang, X.; Leu, M.C.; Chandrashekhara, K.
Two different approaches to design a sparse-build tool for fabrication by the fused deposition modeling (FDM) process are compared. One approach uses a 2D lattice structure and the other approach is inspired by topology optimization. Ultem 9085 is used as the material, and the amount of material used to build the tool is kept constant to ensure a fair comparison. A solid tool is also included in the comparison. The performance of the tool under uniform pressure is simulated using finite element analysis (FEA) and the accuracy of the FEA results is verified by comparing them with experimentally measured data for a similar tool. The build material, support material, build time, maximum displacement, and maximum von Mises stress are compared for the three build approaches, with an emphasis on the pros and cons of each sparse-build tool with regards to performance under uniform pressure and fabrication by FDM.
Development of Novel Tapered Pin Fin Geometries for Additive Manufacturing of Compact Heat Exchangers
(University of Texas at Austin, 2016) Cohen, Julien; Bourell, David L.
Pin fin arrays are widely used to enhance forced convection heat transfer across various industries, finding application in turbine blade trailing edges, electronics cooling, and broadly for compact heat exchange. Fin shape greatly affects flow separation and turbulence generation, and optimizing performance relies on this balance between increased heat transfer and increased pressure loss along the array. Straight circular and elliptical fins are well-characterized in the literature, and there exist a scant few studies on tapered configurations with conventional cross-sections. Recent works have investigated straight pin fins with more complex shapes. Tapered, complex fin geometries represent an avenue for overall performance gains, but manufacturing them is difficult and time-consuming using traditional machining processes. The unique capabilities of additive manufacturing now allow their economical fabrication in an increasing number of fully-dense engineering materials. This work compares 21 pin fin arrays of varying fin cross-section, taper angle, taper profile, and array patterns using experimental and computational methods.
Surface Scanning Methods and Large-Scale FDM Printing for the Replication of Watercraft Layup Tooling
(University of Texas at Austin, 2016) Nuttall, D.W.; Elliott, A.M.; Post, B.K.; Love, L.J.
The manufacturing of tooling for large, contoured surfaces for fiber-layup applications requires significant effort, with traditional methods for the auto industry using hand sculpted clay, and the marine pleasure-craft industry typically creating forms from foam lay-up, then hand cut or machined down from a billet. Oak Ridge National Lab’s Manufacturing Demonstration Facility (ORNL MDF) collaborated with Magnum Venus Products to develop a process for reproducing legacy whitewater adventure craft via digital scanning and large scale 3-D Printing molds. The process entailed scanning a legacy canoe, converting to CAD, additively manufacturing the mold, and subtractively finishing the transfer surfaces. The outlined steps were performed on a specific canoe geometry, with intent to develop energy efficient, marketable processes for replicating complex shapes related to watercraft, and provide products for demonstration to the composites industry. It is anticipated that developing this process to manufacture tooling for complex contoured surfaces will have direct applicability to the sports/pleasure craft industry, naval and other watercraft, as well as bathrooms and large trucks.
Impact of Vapor Polishing on Surface Roughness and Mechanical Properties for 3D Printed ABS
(University of Texas at Austin, 2016) Neff, Clayton; Trapuzzano, Matthew; Crane, Nathan B.
Additive manufacturing (AM) is useful when creating complex geometric models and prototypes. However, a well-known drawback is the fact that parts produced by AM methods typically have lower strength and higher surface roughness than traditionally-formed parts. To compensate for this, the surface finish is commonly improved by mechanical finishing or some type of coating. Another widely used surface treatment for ABS components is vapor polishing. In this process, the part is exposed to a solvent vapor that partially dissolves a surface layer and enables smoothing through surface tension-driven flow; it is known to decrease the surface roughness. However, little work has been reported quantifying the surface roughness change or on the mechanical impacts of this processing method. This work compares the strength, ductility and surface finish of vapor-polished ABS tensile specimens of varying thicknesses (1 mm, 2mm, and 4 mm). Results show that elongation at break is improved, while the modulus of elasticity is reduced in thin specimens. The tensile strength is largely unchanged. The power spectral density for roughness features larger than 20 µm were reduced 10X.
Performance of Sulfur Concrete in Planetary Applications of Contour Crafting
(University of Texas at Austin, 2016) Yuan, Xiao; Zhang, Jing; Zahiri, Behnam; Khoshnevis, Behrokh
Sulfur concrete is a high potential composite material which meets NASA’s ISRU (In-Situ Resource Utilization) requirements for some Lunar and most Martian structure construction by means of Contour Crafting (CC). The performance of sulfur concrete is sensitive to its ingredients and to the variables in the thermal process used for applying the material. The sulfur concrete extrusion process is implemented on a mini-scale auger extruder and a novel full-scale extruder. An experiment is designed to study the factors that influence the workability of sulfur concrete. The research result may be instrumental for improving the workability of sulfur concrete, which also has significant terrestrial applications.
Investigation the Additive Manufacture of Extra-Terrestrial Materials
(University of Texas at Austin, 2016) Goulas, Athanasios; Southcott-Engstrøm, Daniel; Friel, Ross J.; Harris, Russell A.
The Powder Bed Fusion (PBF) additive manufacturing process category, consists of a group of key enabling technologies allowing the fabrication of both intrinsic and complex structures for a series of applications, including aerospace and astronautics. The purpose of this investigation was to explore the potential application of in-space additive manufacturing/3D printing, for onsite fabrication of structures and parts, using the available extra-terrestrial natural resources as feedstock. This study was carried out by using simulants of terrestrial origin, mimicking the properties of those respective materials found extra-terram (in space). An investigation was conducted through material characterisation, processing and by powder bed fusion, and resultant examination by analytical techniques. The successful realisation of this manufacturing approach in an extra-terrestrial environment could enable a sustainable presence in space by providing the ability to build assets and tools needed for long duration/distance missions in deep space.
Selectively Anodised Aluminum Foils as an Insulating Layer for Embedding Electronic Circuitry in a Metal Matrix via Ultrasonic Additive Manufacturing
(University of Texas at Austin, 2016) Bournias-Varotsis, A.; Friel, R.J.; Harris, R.A.; Engstrom, D.
Ultrasonic Additive Manufacturing (UAM) is a hybrid Additive Manufacturing (AM) process that involves layer-by-layer ultrasonic welding of metal foils and periodic machining to achieve the desired shape. Prior investigative research has demonstrated the potential of UAM for the embedding of electronic circuits inside a metal matrix. In this paper, a new approach for the fabrication of an insulating layer between an aluminium (Al) matrix and embedded electronic interconnections is presented. First, an Anodic Aluminium Oxide (AAO) layer is selectively grown onto the surface of Al foils prior to bonding. The pre-treated foils are then welded onto a UAM fabricated aluminium substrate. The bonding step can be repeated for the full encapsulation of the electronic interconnections or components. This ceramic AAO insulating layer provides several advantages over the alternative organic materials used in previous works.
Design and Simulation of 3D Printed Air-Cooled Heat Exchangers
(University of Texas at Austin, 2016) Felber, R.A.; Rudolph, N.; Nellis, G.F.
The use of material extrusion with conductive fillers is explored for air-cooled heat exchangers. A general overview of the manufacturing tasks, design criteria, printability constraints, and modeling techniques is given, along with experimental data from prototype testing. The first sub-scale prototype design is an air-water crossflow heat exchanger designed to transfer around 100 Watts. It was printed with unfilled conventional ABS and the air channels designed with an array of round pin fins to enhance heat transfer. The prototype was also CT-scanned for inspection of the printed pin fin shapes.
Product Optimization with and for Additive Manufacturing
(University of Texas at Austin, 2016) Reiher, T.; Koch, R.
Additive Manufacturing offers a great potential for the optimization of products. Therefore different approaches are feasible to exploit these potentials for elaborating optimal solutions. For example these include optimization of weight or stiffness of structural components as well as the integration of functions and other entities of assemblies. Note, however, that additive manufacturing processes have process specific limitations. Products, components and assemblies, as well as procedures for the design and production preparation must be optimized with regard to a successful additive manufacturing. The use of already known tools for the optimization and design needs to be reconsidered and adapted to the additive manufacturing. This also includes the production planning with component orientation in build chamber as well as a necessary quality management system. This paper shows several ways for product optimization with additive manufacturing, often based on topology optimization, and procedures for information gathering, decision making and shape determination for part optimization for Additive Manufacturing.

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