2017 International Solid Freeform Fabrication Symposium

Permanent URI for this collectionhttps://hdl.handle.net/2152/89792

Proceedings for the 2017 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.>

The Twenty-Eighth Annual International Solid Freeform Fabrication (SFF) Symposium – An Additive Manufacturing Conference, held at The University of Texas in Austin on August 7-9, 2017, was attended by 654 researchers from 20 countries. The number of oral and poster presentations increased to 473 this year. The meeting was held on the Hilton Austin in the downtown area. The meeting consisted of a Monday morning plenary, 50 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. Allison Beese from Penn State University. Dr. Ian Gibson form Deakin University in Australia won the International Freeform and Additive Manufacturing Excellence (FAME) Award.

There are 231 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.

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 (N00014-17-1-2471) and the National Science Foundation (CMMI-1639406) 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 2018 SFF Symposium is set for August 13-15, 2018 in Austin, Texas USA.

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Now showing 1 - 20 of 221

Design Optimisation of a Thermoplastic Splint
(University of Texas at Austin, 2017) Fitzpatrick, Angus; Mohammed, Mazher; Collins, Paul; Gibson, Ian
Following partial hand amputation, a post-surgery orthosis is required to hold the remaining ligaments and appendages of the patient in a fixed position to aid recovery. This type of orthosis is traditionally handmade and fabricated using laborious and qualitative techniques, which would benefit from the enhancements offered by modern 3D technologies. This study investigated the use of optical laser scanning, Computer Aided Design (CAD) and Material Extrusion (ME) additive manufacturing to manufacture a polymeric splint for use in post-surgical hand amputation. To examine the efficacy of our techniques, we take an existing splint from a patient and use this as the template data for production. We found this approach to be a highly effective means of rapidly reproducing the major surface contours of the orthosis while allowing for the introduction of advanced design features for improved aesthetics, alongside reduced material consumption. Our demonstrated techniques resulted in a more lightweight and lower cost device, while the design and manufacturing elements afford greater flexibility for orthosis customisation. Ultimately, this approach provides an optimized and complete methodology for orthosis production.
Multiscale Analysis of Cellular Solids Fabricated by EBM
(University of Texas at Austin, 2017) Arrieta, Edel; Mireles, Jorge; Stewart, Calvin; Carrasco, Cesar; Wicker, Ryan B.
Additive Manufacturing technologies such as Electron Beam Melting are empowering individuals to develop novelty materials by introducing hierarchical levels into solids. Features from the introduced architectures and the manufacturing technology grant these metamaterials with mechanical performances not commonly seen in standard solids. Thus, the response of cellular metals can now be manipulated. In general, the reported research on lattices focuses on very specific topics such as microstructure, geometry and orientation, giving the impression of isolated knowledge. However, the response of these metamaterials is the result of a complex multiscale interaction between these and other factors ranging from the microstructure of the constitutive solid, up to the cell topology. Intended as a one-stop introductory document for a new branch of material designers, the major factors affecting the response of cellular metals are identified, classified and merged into a multiscale discussion supported with evidence from a series of experiments including ASTM standard tests of EBM Ti-6Al-4V standard and lattice specimens, accompanied by failure analysis. The testing features digital image correlation (DIC) for measuring deformations, strain fields, as well as Poisson and shear effects, becoming a critical tool for the advanced characterization of specimens, especially those with complex geometries that normally would require specific instrumentation. Among these multiple determinants; microstructure, manufacturing orientation, manufacturing process, Maxwell’s stability criterion, and other geometrical features are discussed for the comprehensive understanding of two lattice designs presented herein. Lastly, Illustrative examples of how the stress-strain curves are helpful in diagnosing design features to start reverse engineering processes, and a summary of the determinants effects are included.
Predicting Sharkskin Instability in Extrusion Additive Manufacturing of Reinforced Thermoplastics
(University of Texas at Austin, 2017) Kishore, Vidya; Ajinjeru, Christine; Liu, Peng; Lindahl, John; Hassen, Ahmed; Kunc, Vlastimil; Duty, Chad
The development of large scale extrusion additive manufacturing systems such as the Big Area Additive Manufacturing (BAAM) system has enabled faster printing with throughput as high as 50 kg/h and the use of a variety of thermoplastics and composites with filler loading as high as 50%. The combination of high throughput and heavy reinforcements can give rise to a phenomenon known as “sharkskin” instability, which refers to extrudate surface distortions typically in the form of roughness or mattness, and is commonly observed in traditional extrusion processes. The onset of this instability depends upon the viscoelastic properties of the material and processing parameters such as throughput, shear rate, extruder die geometry, and temperature. For printed parts, such instabilities are undesirable and detrimental to mechanical properties. This work examines the effect of process parameters on the rheological properties of BAAM thermoplastics and composites to predict the occurrence of sharkskin during printing.
Tensile Mechanical Properties of Polypropylene Composites Fabricated by Material Extrusion
(University of Texas at Austin, 2017) Watanabe, Narumi; Shofner, Meisha L.; Rosen, David W.
In the material extrusion additive manufacturing process, a thin filament of material is deposited in a layer-by-layer manner to fabricate a three dimensional part. The filament deposition pattern can result in voids and incomplete bonding between adjacent filaments in a part, which leads to reduced mechanical properties. Further, the layer-by-layer deposition procedure typically results in mechanical property anisotropy, with higher properties in the layer compared to those across layers. The study reported in this paper explored various polypropylene composite formulations to address these issues: low residual stress and warpage, good mechanical properties, and reduced anisotropy. The reduction in anisotropy will be the focus of this paper as a function of thermal properties and process variable settings. A series of process simulation models was developed to explore ranges of thermal properties and process settings, which provided insights into tensile specimen behaviors. Results demonstrate that anisotropy can be reduced almost completely if the material can be formulated to have low crystallinity, low coefficient of thermal expansion, and moderate to high thermal conductivity (for a polymer).
Fiber-Fed Laser-Heated Process for Printing Transparent Glass
(University of Texas at Austin, 2017) Hostetler, John M.; Goldstein, Jonathan T.; Bristow, Douglas; Landers, Robert; Kinzel, Edward C.
This paper presents the Additive Manufacturing (AM) of glass using a fiber-fed process. Glass fiber with a diameter of 100 μm is fed into a laser generated melt pool. A CO2 laser beam is focused on the intersection between the fiber and the work piece which is positioned on a four-axis computer controlled stage. The laser energy at λ=10.6 μm is directly absorbed by the silica and locally heats the glass above the working point. By carefully controlling the laser power, scan speed, and feed rate, bubble free shapes can be deposited including trusses and basic lenses. Issues unique to the process are discussed, including the thermal breakdown of the glass, buckling of the fiber against an inadequately heated stiff molten region, and dimensional control when depositing viscous material.
Multisystem Modeling and Optimization of Solar Sintering System
(University of Texas at Austin, 2017) Morris, C.; Debeau, D.; Dressler, A.; Seepersad, C.C.
In developing countries, the production of building materials such as tile and brick, require large amounts of non-renewable energy and/or time to produce. Previous work has shown that solar sintering machines are capable of producing ceramic parts in a viable amount of time using only solar energy. The systems focus sunlight on a bed of sand where the intensity is sufficient for sintering. Then by moving the sand bed, parts of complex geometry are formed. This study aims to identify optimal operating parameters for the solar sintering system by solving a multi-objective, multisystem model. The subsystems considered are the dynamics of the sand bed, optics of focusing sunlight, and heating of the sand bed. To reduce the computational expense, a Kriging surrogate model was employed to model the heating of the sand bed. Finally by performing a tradeoff analysis of production time and part quality, candidate operating parameters were identified.
Thermal Modeling of 304L Stainless Steel Selective Laser Melting
(University of Texas at Austin, 2017) Li, Lan; Lough, Cody; Replogle, Adriane; Bristow, Doug; Landers, Robert; Kinzel, Edward
This paper describes the continuum thermal modeling of the Selective Laser Melting (SLM) process for 304L stainless steel using Abaqus. Temperature dependent thermal properties are obtained from literature and incorporated into the model capturing the change from powder to fully dense stainless steel. The thermal model predicts the temperature history for multi-track scans under different process parameters (laser power, effective scanning speed, hatch spacing) which is used to extract the melt-pool size, solidification rate, and temperature gradients. These are compared to experimental results obtained from a Renishaw AM250 in terms of the melt pool size, grain structure, and cell spacing. These experimental results are used to tune unknown simulation parameters required by the continuum model including the optical penetration depth and thermal conductivity multiplier for the molten region. This allows the model to yield predictive simulations of melt pool size and solidification structure of SLM 304L stainless steel.
A Trade-Off Analysis of Recoating Methods for Vat Photopolymerization of Ceramics
(University of Texas at Austin, 2017) Hafkamp, Thomas; van Baars, Gregor; de Jager, Bram; Etman, Pascal
Technical ceramic parts can be produced by curing ceramic-filled resins in the vat photopolymerization (stereolithography) process. Scaling up to larger ceramic product sizes and higher product quality calls for the integration of more sensing, actuation and closed-loop control solutions while taking a systems engineering approach. This paper gives a comprehensive overview of methods to deposit a layer of (ceramic-filled) resin, better known as recoating. The aim of this work is to perform a trade-off analysis of recoating methods to enable the selection of the method that best meets the requirements for scaling up the printable object size in the ceramic vat photopolymerization process.
An Investigation of Anisotropy off 3D Periodic Cellular Structure Designs
(University of Texas at Austin, 2017) Yang, Li
In the design of periodic cellular structures, there exist various isotropic unit cell designs that possess identical theoretical mechanical properties along three or multiple principal symmetry directions. Although such definition of “isotropy” differs from the traditional definition that is used for solid materials, it is often considered to represent the equivalent design implications in many applications. In this study, the mechanical properties of various 2D and 3D periodic cellular structures under uniaxial stress along different non-principal directions were investigated. The relationships between the cellular unit cell geometries, structural size, loading orientation and the mechanical properties of the cellular structures made of perfect elastic-plastic material were discussed, which provide insights into the future design of cellular structures when utilizing homogenization treatments.
ORNL Slicer 2: A Novel Approach for Additive Manufacturing Tool Path Planning
(University of Texas at Austin, 2017) Roschli, Alex; Messing, Andrew; Borish, Michael; Post, Brian K.; Love, Lonnie J.
ORNL Slicer is the first software designed to generate machine instructions, or tool paths, from CAD files for large-scale 3D printing of metals and polymers. The software was revolutionary because it allowed for slicing of models reaching 20 feet long, generating millions of lines of G-Code in seconds. The structure of the first ORNL Slicer had limitations in its framework, which has led to the development of ORNL Slicer 2. In the second version of the slicer, the process is modularized with individual layers being divided into regions, smarter infill patterns, and traversals are generated based upon stress, thermal, and other models. The new software has also been structured to allow for slicing and reslicing based on machine feedback during the printing process.
Computer Integration for Geometry Generation for Product Optimization with Additive Manufacturing
(University of Texas at Austin, 2017) Reiher, T.; Vogelsang, S.; Koch, R.
Designing parts for additive manufacturing (AM) offers a broad range of geometrical and functional potentials. On the one hand the manufacturing technology offers the possibility of manufacturing highly complex freeform shapes, often referred to as bionic shapes. By use of these, perfect force fluxes without stress risings due to imperfect notches are realizable, getting the most value of used material. On the other hand these complex structures require a reliable geometry representation in compatible CAD-files. Conventional CAD systems were developed to generate geometries that are manufacturable with conventional machining. These are not capable of representing the high complex designs for AM. Especially for geometries generated by CAE like from topology optimization the conventional CAD systems fail to take advantage of the combination of CAE and AM. This paper explains why there is a lack of compatibility of well-known CAD systems with the potentials of AM. Therefore the AM-side of the problem is described by showing some potentials of AM and the need of high complex structures for this manufacturing technology. For the other side of the problem conventional methodologies for geometry representation of CAD systems are described and their limitations with regard to AM are worked out. Finally a voxel based geometry representation is presented as a solution for computer aided geometry generation of high complex AM–structures.
Defects Classification of Laser Metal Deposition Using Acoustic Emission Sensor
(University of Texas at Austin, 2017) Gaja, Haythem; Liou, Frank
Laser metal deposition (LMD) is an advanced additive manufacturing (AM) process used to build or repair metal parts layer by layer for a range of different applications. Any presence of deposition defects in the part produced causes change in the mechanical properties and might cause failure to the part. In this work, defects monitoring system was proposed to detect and classify defects in real time using an acoustic emission (AE) sensor and an unsupervised pattern recognition analysis. Time domain and frequency domain, and relevant descriptors were used in the classification process to improve the characterization and the discrimination of the defects sources. The methodology was found to be efficient in distinguishing two types of signals that represent two kinds of defects. A cluster analysis of AE data is achieved and the resulting clusters correlated with the defects sources during laser metal deposition.
A Floor Power Module for Cooperative 3D Printing
(University of Texas at Austin, 2017) Currence, Jacob; Morales-Ortega, Rolando; Steck, Jason; Zhou, Wenchao
Cooperative 3D printing is an emerging technology that utilizes multiple printhead-carrying mobile robots to work simultaneously to 3D print or assemble products on a factory floor, which can provide the scalability, increased printing capability, and reduced human intervention for 3D printing to potentially become a mainstream digital manufacturing technology. However, powering the mobile printers for them to span entire factory floors poses an issue. Traditional cords are not an option due to restricting free movement across long distances. On-board batteries would waste energy due to additional weight and the need to recharge could interrupt ongoing print jobs and increase printing time. In this paper, we present an electrified floor to power the mobile printers wirelessly. First, we designed a floor module with stainless steel conductive strips in a concrete base and a brush that is carried by the mobile robots to make sure it never loses contact with the electrified floor while in motion. Then we designed a circuit to sort the polarity of the current from the floor based on the power requirements of the robot. A prototype of the floor power module was then developed and tested with a mobile 3D printer. Results show the developed floor power supply can power the mobile 3D printers effectively. This development will potentially enable an autonomous factory equipped with thousands of mobile 3D printers powered wireless by the factory floor.
Reactive Inkjet Printing Approach Towards 3D Silicone Elastomeric Structures Fabrication
(University of Texas at Austin, 2017) Foerster, A.; Wildman, R.; Hague, R.; Tuck, C.
Production of 3D silicone structures with tailored architectures has a wide number of applications including soft robotics and stretchable electronics. This work investigates a method based on a reactive inkjet printing approach to produce 3D silicone structures. Printing parameters including pressure and temperature for jetting SE1700 ink to produce silicone structures were optimised. Additives, silicone oil and vinyl terminated polydimethylsiloxane were added to the main SE1700 formula to evaluate mechanical properties of the final parts. Characterisation was performed to understand the change in a sample’s properties in relation to different formulations. Silicone structures with different porosities were printed and the mechanical properties were investigated. It has been demonstrated that 3D silicone structures can be produced using reactive inkjet printing approach. The presented method allowed tailoring of the mechanical properties of silicones without increasing the viscosity properties of the base material by adjusting the silicone formula and using different structures.
Influence of Process Time and Geometry on Part Quality of Low Temperature Laser Sintering
(University of Texas at Austin, 2017) Yamauchi, Yuki; Niino, Toshiki; Kigure, Takashi
The authors are developing a novel laser sintering process that prevents parts from warping by anchoring them to a rigid base plate. Since the powder bed temperature of the process is normally lower than in the standard process, the laser is required to supply more energy in the novel process, namely low temperature process. Accordingly, the part quality is more sensitive to laser parameters. Additionally, accumulation and dispersion of energy which is supplied by the laser through layers plays an important role in the consolidation of the powder. Thus, in low temperature process, parameter relating part geometry and time affects the part quality more than in standard high temperature process. In this research, the influence of part size and process time per layer on the density of parts as a primary index of part quality is investigated. Density decreases as the process time per layer increases. With respect to part size, density increases as parts become larger.
Geometrical Accuracy of Holes and Cylinders Manufactured with Fused Deposition Modeling
(University of Texas at Austin, 2017) Knoop, F.; Schoeppner, V.
A widely used Additive Manufacturing (AM) technology is Fused Deposition Modeling (FDM) to create prototypes and end-use parts with close-to-production thermoplastics. For their use as a final product, it is necessary that additively manufactured parts strictly adhere to the geometrical requirements of the technical drawing. In this paper, the holes and cylinders of the cylindrical elements are investigated in terms of achievable geometrical accuracy. For this purpose, different test specimens that allow a measurement of inner and outer diameters from 3 to 80 mm were designed. All specimens were measured with a coordinate measuring machine (CMM) to evaluate deviations from the nominal dimension and form deviations. The measuring method includes a scanning of the surface to record the course of dimensional deviations over the diameter. Thus, it was possible to visualize how deviations on cylindrical elements manufactured in FDM occur. In order to counteract these deviations and to improve the dimensional accuracy, different shrink factors and filling patterns were investigated. Consequently, an improvement of the dimensional accuracy was achieved.
Hypervelocity Impact of Additively Manufactured A356/316L Interpenetrating Phase Composites
(University of Texas at Austin, 2017) French, M.R.; Yarberry, W.A. III; Pawlowski, A.E.; Shyam, A.; Splitter, D.A.; Elliott, A.M.; Carver, J.K.; Cordero, Z.C.
We have examined the hypervelocity impact response of targets made from monolithic A356 and 316L stainless steel, as well as an additively manufactured A356/316L interpenetrating phase composite. 1.9 mm diameter spherical projectiles made from 2017 aluminum were fired at velocities of 5.9-6.1 km/s, allowing for the observation of multiple types of macro- and microstructural damage within each target. The macroscopic cratering damage to the A356/316L composite resembles that of the A356, but observations of both the cross section and the microstructural damage suggest that the A356/316L composite may be more resistant to spalling than A356 shielding with the same areal density.
Effect of Process Parameters and Shot Peening on Mechanical Behavior of ABS Parts Manufactured by Fused Filament Fabrication (FFF)
(University of Texas at Austin, 2017) Kanger, Cody; Hadidi, Haitham; Akula, Sneha; Sandman, Chandler; Quint, Jacob; Alsunni, Mahdi; Underwood, Ryan; Slafter, Cody; Sonderup, Jason; Spilnek, Mason; Casias, John; Rao, P.; Sealy, M.P.
The goal of this research was to understand how shot peening affected the tensile strength and elongation of ABS polymer parts between three process parameters: layer height, infill angle, and outer shell quantity. Experiments were conducted using a Hyrel 30M fused filament fabrication (FFF) printer to produce ASTM 638D-IV samples. This is an important area of research because 3D printed polymers have typically been limited to prototyping applications due to low strengths and stiffness. Traditional means of improving a polymer’s mechanical properties are changing the structural or chemical makeup. However, shot peening, a surface treatment commonly used to improve mechanical properties of metals, was hypothesized to have a statistically significant effect on the tensile strength and elongation of polymer parts. Results showed that shot peening had a significant effect on decreasing the tensile strength. Although not statistically significant, samples did show an increase in elongation after shot peening.
The Effect of Process Parameters and Mechanical Properties of Direct Energy Deposited Stainless Steel 316
(University of Texas at Austin, 2017) Izadi, Mojtaba; Farzaneh, Aidin; Gibson, Ian; Rolfe, Bernard
Process parameters in Direct Energy Deposition (DED) Additive Manufacturing are playing an important role in order to fabricate desired parts. In this research, we studied the effect of 3 process parameters, namely laser power, scan speed and powder feed rate. Based on variation of these parameters, we examined macrostructure and mechanical properties of stainless steel 316 fabricated parts, employing an orthogonal L9 array using the Taguchi technique. The results showed laser power to be the most effective factor whereas scan speed and powder feed rate were respectively less effective. In addition, effect of height of deposition was also considered. The results indicated change in macrostructure with increasing height. Finally, validation of a previously defined energy density equation for the DED process was studied. The results clearly showed the current energy density equation cannot fully represent a relation between input energy and output geometry, macrostructure, and mechanical properties.
A Post-Processing Procedure for Level Set Based Topology Optimization
(University of Texas at Austin, 2017) Xian, Y.; Rosen, D.W.
This paper addresses two issues: 1. Topology optimization yields designs that may require support structures if additively manufactured, which increase material and clean-up costs. 2. Topologically optimized designs consist of discretized geometry which makes subsequent engineering difficult, hence the increasing need to somehow render TO results to parameterized CAD models. This paper presents a procedure that, after a standard level set based topology optimization, firstly identifies certain regions on the part boundary that may require support materials or may cause staircase effect during 3D printing, then replaces these boundary segments with similar-shaped printable design features. Additionally, other boundary regions are fitted with simple geometric entities, so that the part boundary can be completely defined by geometric parameters of design primitives.

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