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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2017 International Solid Freeform Fabrication Symposium Table of Contents
(2017) Laboratory for Freeform Fabrication and University of Texas at Austin
3-Dimensional Cellular Automata Simulation of Grain Structure in Metal Additive Manufacturing Process
(University of Texas at Austin, 2017) Li, Xuxiao; Tan, Wenda
Distinct grain structures have been observed in Metal Additive Manufacturing (MAM) processes. These grain structures feature columnar grains which occasionally mix with equiaxed grains. The occurrence of these grain structures is not yet fully understood. In this work, direct laser deposition process is studied as a typical MAM process. A finite volume model is first implemented to obtain the thermal history. Next, the thermal history is fed into a Cellular Automata (CA) model to simulate the epitaxial and competitive growth through which the columnar grains are formed. Nucleation is included in the model to predict the generation of equiaxed grains, and is characterized by two nucleation parameters, the nucleation density and the critical undercooling. The simulation results show that both the nucleation parameters and process parameters can significantly affect the grain structure. The simulated grain structures examined on different planes can be significantly different, revealing the complexity of the 3-dimensional grain structures in MAM processes.
316L Powder Reuse for Metal Additive Manufacturing
(University of Texas at Austin, 2017) Sartin, B.; Pond, T.; Griffith, B.; Everhart, W.; Elder, L.; Wenski, E.; Cook, C.; Wieliczka, D.; King, W.; Rubenchik, A.; Wu, S.; Brown, B.; Johnson, C.; Crow, J.
Metal additive manufacturing via laser powder bed fusion is challenged by low powder utilization. The ability to reuse metal powder will improve the process efficiency. 316L powder was reused twelve times during this study, completing thirty-one builds over one year and collecting 380 powder samples. The process, solidified samples, and powder were analyzed to develop an understanding of powder reuse implications. Solidified sample characteristics were affected more by slight process variations than by cycling of the powder. While a small percentage of powder was greatly affected by processing, the bulk powder only observed a slight increase in powder size.
3D Bioprinting of Scaffold Structure Using Micro-Extrusion Technology
(University of Texas at Austin, 2017) Xing, Juan; Luo, Xianli; Bermudez, Juliana; Moldthan, Matthew; Li, Bingbing
Scaffold-based techniques are a vital assistance tool to support main structure and enhance the resolution of target structure. In this study, a custom-made micro-extrusion bioprinting system was built and utilized to fabricate different scaffold structures such as log-pile scaffold and two-ring scaffold. This approach showed tremendous potential because of its ability to produce microscale channels with almost any shape. We were able to fabricate these scaffolds by using a custom-made 3D bioprinter to print hydrogel solution, mostly composed of Pluronic F-127, then wash away hydrogen by phosphate buffer saline (PBS) after crosslinking of main structure. We were able to achieve the desired scaffold structure by feeding G-codes data into user interface (Pronterface) and then translating that model into a program that utilizes a customized programming language, which instructs the microfabrication printer nozzles to dispense the hydrogel at specific locations. This fundamental study will be used to print increasingly viable and complex tissue shapes with living cells.
5-Axis Slicing Methods for Additive Manufacturing Process
(University of Texas at Austin, 2017) Kapil, Sajan; Negi, Seema; Joshi, Prathamesh; Sonwane, Jitendra; Sharma, Arun; Bhagchandani, Ranjeet; Karunakaran, K.P.
In metallic Additive Manufacturing (AM) processes such as Hybrid Layered Manufacturing (HLM), it is difficult to remove the support material used for realizing the overhanging/undercut features. Multi-axis kinematics can be used to eliminate the requirement of the support mechanism. In this work, two slicing methods have been proposed which utilize the benefits of multi-axis kinematics to eliminate the support mechanism. In the first method, planar slicing is used and the overhanging/undercut features are realized while keeping the growth of the component in the conventional Z-direction. In the second method, non-planar slicing is used, and the growth of the component need not necessarily be in the Z-direction; it can also be conformal to the selected feature of the component. Both these methods are explained through a case study of manufacturing an impeller by the HLM process.
Active - Z Printing: A New Approach to Increasing 3D Printed Part Strength
(University of Texas at Austin, 2017) Khurana, Jivtesh B.; Dinda, Shantanab; Simpson, Timothy W.
Research suggests that topology and build parameters in Fused Filament Fabrication (FFF) play a vital role in determining mechanical properties of parts produced by this technique. In particular, the use of 2D layers printed parallel to the build surface produces high anisotropy in parts making them the weakest when loaded perpendicular to the layer interfaces. We investigate a novel approach that uses non-planar 3D layer shapes - Active Z printing, to improve mechanical strength through alignment of localized stress tensors parallel to the deposition paths. Sinusoidal layer shapes are used with varying amplitude, frequency, and orientation. Design of experiments is performed to correlate effect of varying shape and orientation of sinusoidal layer shapes on flexural strength of parts. Based on this, the results are used to decide parameters to be studied further and characterize their effect on the strength of parts.
Additive Fabrication of Polymer-Ceramic Composite for Bone Tissue Engineering
(University of Texas at Austin, 2017) Ramesh, S.; Eldakroury, M.; Rivero, I.V.; Frank, M.C.
The objective of this study is to manufacture chitosan-based biocomposite 3-D scaffolds through additive fabrication for promoting the regeneration of bone defects. Additive manufacturing has enabled the production of effective scaffolds by overcoming traditional limitations such as suboptimal distribution of cells, and poor control over scaffold architecture. In this study, cryomilled biocomposites comprising of poly (lactic) acid (PLA), chitosan (CS) and tricalcium phosphate (TCP) provided the basis for the generation of hydrogels, which were then utilized for the fabrication of scaffolds with orthogonal (0, 90) geometry. Rheological studies were conducted using a rotational rheometer to identify the ideal hydrogel concentration for the continuous production of scaffolds. The scaffolds were fabricated using a 3-axis computerized numerical control (CNC) which was modified to function as a customized bioplotter. Scanning electron microscopy (SEM) was used to observe the morphology of the bioplotted scaffolds. Finally, a short-term stability (14 days) study was conducted to analyze the in vitro degradation behavior of the scaffolds in phosphate buffer saline (PBS).
Additive Manufacturing of High-Entropy Alloys - A Review
(University of Texas at Austin, 2017) Cui, Wenyuan; Zhang, Xinchang; Liou, Frank
High-entropy alloys have attracted increasingly interest due to their unique compositions, microstructures and mechanical properties. Additive manufacturing has been recognized as a promising technology to fabricate the high-entropy alloys in the recent years. The purpose of this paper is to review the current research progress in high-entropy alloys by additive manufacturing process. It will first highlight the important theory of the high-entropy alloys. The next aspect is to summarize current additive manufacturing methods applied for the high entropy alloys. At last, the correlation between the microstructures and the mechanical properties of the high-entropy alloys will be examined and discussed.
Additive Manufacturing Utilizing Stock Ultraviolet Curable Silicone
(University of Texas at Austin, 2017) Porter, Daniel A.; Cohen, Adam L.; Krueger, Paul S.; Son, David
Extrude and Cure Additive Manufacturing (ECAM) is a method that enables 3D printing (3DP) of common thermoset materials. Ultraviolet (UV)-curable silicone is an example of a thermoset material with a large number of industrial and medical applications. 3D printed silicone prototype parts are obtained using a custom high pressure ram, valve, and UV exposure system. This paper will address issues with printing stock UV curable silicone such as electrostatic repulsion, in-nozzle curing, and extrudate slumping. One solution that addresses two issues is adding carbon black (CB) to the mixture to reduce electrostatic repulsion while also inhibiting UV cure depth, hence preventing material from curing in the nozzle. Evidence shows that too much carbon black can be detrimental to the structural stiffness of the resulting part.
Additively Manufactured Conformal Negative Stiffness Honeycombs
(University of Texas at Austin, 2017) Debeau, D.A.; Seepersad, C.C.
This study investigates the static and dynamic mechanical performance of conformal negative stiffness honeycomb structures. Negative stiffness honeycombs are capable of elastically absorbing a static or dynamic mechanical load at a predefined force threshold and returning to their initial configuration after the load is released. Most negative stiffness honeycombs rely on mechanical loading that is orthogonal to the base of the structure. In this study, a more three dimensional design is presented that allows the honeycomb to conform to complex surfaces and protect against impacts from multiple directions. The conformal designs are additively manufactured in nylon and stainless steel and subjected to quasi-static mechanical loading and dynamic mechanical impact tests that demonstrate their impact protection capabilities.
Aluminum Matrix Syntactic Foam Fabricated with Additive Manufacturing
(University of Texas at Austin, 2017) Spratt, M.; Newkirk, J.; Chandrashekhara, K.
Syntactic foams are lightweight structural composites with hollow reinforcing particles embedded in a soft matrix. These materials have applications in transportation, packaging, and armor due to properties such as relatively high specific stiffness, acoustic dampening, and impact absorption. Aluminum matrices are the most widely studied of metal matrix syntactic foams, but there is little to no research in regards to processing the foams with additive manufacturing. It is theorized that the fast cooling rates and limited kinetic energy input of additive could reduce two issues commonly associated with processing syntactic foams: microsphere flotation in the melt and microsphere fracture during processing. In this study, 4047 aluminum blended with glass particles was deposited on a 4047 Al substrate using an additive process. Characterization of the foams include mechanical testing and microstructural analysis.
Analysis of Hybrid Manufacturing Systems Based on Additive Manufacturing Technology
(University of Texas at Austin, 2017) Cunico, Marlon Wesley Machado
Along the last year, additive manufacturing technologies has been proving to be a real game changer in several market segments. Nevertheless, the main foundation of production and flexible manufacturing systems generally considers classical technologies. For that reason, the present work aim to propose and investigate manufacturing systems which includes additive manufacturing technologies as part of the main or secondary production flow. As result, it was identified that several marketing segments, types of components and different annual volumes tend to be better attended by hybrid flexible manufacturing systems which includes additive manufacturing technologies.
Analytical and Experimental Characterization of Anisotropic Mechanical Behaviour of Infill Building Strategies for Fused Deposition Modelling Objects
(University of Texas at Austin, 2017) Cunico, Marlon Wesley Machado
As consequence of the 3d printing extraordinary rising along the last years, product development fields are facing new challenges. In addition, it is notary that low cost additive manufacturing, as such fused filament fabrication (FFF), result in objects with anisotropic mechanical behaviour. Nevertheless, there is still lacking studies that highlight a proper specification of those mechanical proprieties. For that reason, the main goal of this work is to present a mechanical characterization of anisotropic behaviour of FFF objects as a function of infill strategy using a finite element method. In this work, the main effect of building parameters were investigated in addition the identification of generalized elasticity and failure mode formulations. By the end, the general recommendation for objects building was sketched in order to support new strength based developments.
The Application of Composite Through-Thickness Assessment to Additively Manufactured Structures
(University of Texas at Austin, 2017) Bitar, Isam S.; Aboulkhair, Nesma T.; Leach, Richard
This study looks into the applicability of through-thickness assessment to additive manufacturing (AM) carbon-fibre reinforced polymers (CFRPs). The study utilised a material extrusion printer that uses fused filament fabrication and composite filament fabrication technologies to manufacture functionally-graded polymer and composite polymer parts. The matrix material of choice was nylon 6. Samples were printed exploring a range of reinforcement volume content. In summary, this study presents an assessment of the applicability of through-thickness testing to AM CFRP specimens and provides a performance comparison between AM composite through-thickness properties and the properties of equivalent CM CFRP specimens.
Applied Solvent-Based Slurry Stereolithography Process to Fabricate High-Performance Ceramic Earrings with Exquisite Details
(University of Texas at Austin, 2017) Wang, Jia-Chang; Dommati, Hitesh
This paper discusses the application of Slurry based Stereolithography additive manufacturing process in the fabrication of complex earring models without any support structures requirement, using High-Performance Ceramic (HPC) materials. The earring model chosen in this study is a Rose flower with blossomed petals. The petals have edge thickness in microns and extreme overhangs with a custom text and logo on the bottom. Using any other ceramic additive manufacturing process, it requires support structures to build this model. The support removal in such minute structures is not easy and not always successful. Using Solvent based Slurry Stereolithography (3S) process, models with the micron details and overhangs can be easily built. This is enabling the neat and clean post-processing procedure to maintain the exquisite details and also gain high surface quality. The ceramic material used in this application is alumina. With some additives, it will show in different colors like sapphire. The resultant flowers are vividly shown in white, pink, green, and blue. In this study, it is also discussed about the slurry process, Stereolithography system, and proven applications of the 3S process.
Approaching Rectangular Extrudate in 3D Printing for Building and Construction by Experimental Iteration of Nozzle Design
(University of Texas at Austin, 2017) Lao, Wenxin; Li, Mingyang; Masia, Lorenzo; Tan, Ming Jen
In Extrusion based 3D Printing technology, the voids could be reduced and the surface finish of printed parts could be improved with extrudate shape optimization. For large-scale 3D Printing technology like 3D Printing for Building and Construction, reducing printed layer height would increase the fabrication time drastically, while having few effect on voids reduction and surface finish improvement. In this paper, an iterative experimental approach to achieve the optimized nozzle design for rectangular shaped extrudate was proposed. Two nozzle prototypes were manufactured by Fused Deposition Method and implemented for experimental tests, then a new nozzle design was created based on the experimental extrudate shapes. This process iterated until a good rectangular extrudate shape was obtained. Printing tests were conducted with the optimized nozzle, which showed the designed nozzle could help to eliminate the voids among the printed parts and guarantee good surface finish without losing the speed of printing.
Areal Surface Characterization of Laser Sintered Parts for Various Process Parameters
(University of Texas at Austin, 2017) Delfs, P.; Schmid, H.-J.
Laser sintered polymer parts consist of rough surfaces due to the layered manufacturing and adherence of incomplete molten particles. The absolute roughness depend on various process parameters like build angle, spatial position, build temperature, exposure order and layer time. Analyses with the help of several areal roughness values of DIN EN ISO 25178-2 considering these parameters are introduced in this paper. Multiple build jobs with 120 µm layer thickness and PA2200 powder were built on an EOS P396 machine using the same build job design with varying process parameters. An individual sample part was designed to receive lots of surface topography information with optical 3D measurements. The results show roughness dependencies for 0° to 180° build angles in 15° steps and eleven distributed in-plane and three axial direction positions depending on different build temperatures, reversed exposure order and layer times. Limitations of the varied parameters are finally derived for the manufacturing of improved surface qualities.
Big Area Additive Manufacturing Application in Wind Turbine Molds
(University of Texas at Austin, 2017) Post, Brian K.; Richardson, Bradley; Lind, Randall; Love, Lonnie J.; Lloyd, Peter; Kune, Vlastimil; Rhyne, Breanna J.; Roschli, Alex; Hannan, Jim; Nolet, Steve; Veloso, Kevin; Kurup, Parthiv; Remo, Timothy; Jenne, Dale
Tooling is a primary target for current additive manufacturing (AM), or 3D printing, technology because of its rapid prototyping capabilities. Molds of many sizes and shapes have been produced for a variety of industries. However, large tooling remained out of reach until the development of large-scale composite AM manufacturing processes like the Big Area Additive Manufacturing (BAAM) system. The Department of Energy’s Oak Ridge National Laboratory (ORNL) worked with TPI Composites to use the BAAM system to fabricate a wind turbine blade mold. The fabricated wind turbine blade mold was produced in 16 additively manufactured sections, was 13 meters long, had heating channels integrated into the design, and was mounted into a steel frame post fabrication. This research effort serves as a case study to examine the technological impacts of AM on wind turbine blade tooling and evaluate the efficacy of this approach in utility scale wind turbine manufacturing.
Binder Jet Additive Manufacturing of Stainless Steel - Tricalcium Phosphate Biocomposite for Bone Scaffold and Implant Applications
(University of Texas at Austin, 2017) Agarwal, Kuldeep; Vangapally, Sairam; Sheldon, Alexander
Scaffolds are 3D biocompatible structures that mimic the extracellular matrix properties (mechanical support, cellular activity and protein production) of bones and provide place for cell attachment and bone tissue formation. Their performance depends on chemistry, pore size, pore volume, and mechanical strength. Recently, additive manufacturing (AM) has been used as a means to produce these scaffolds. This paper explores a new biocomposite manufactured using Binder Jet AM process. Stainless steel and tricalcium phosphate are combined to form a composite and used in different volume fractions to produce parts with varying densities. Layer thickness, sintering time and sintering temperature are varied to study the effect of process parameters on the microstructure, dimensions and mechanical properties of the resulting structure. It is found that the resulting biocomposite can be tailored by varying the process to change its properties and mimic the properties of scaffolds in bone tissue applications.
Binderless Jetting: Additive Manufacturing of Metal Parts via Jetting Nanoparticles
(University of Texas at Austin, 2017) Bai, Yun; Williams, Christopher B.
Binder Jetting AM has been used to fabricate metal parts by first jetting a binder into powder bed; the resulting green part is then thermally post-processed wherein the binder is removed and the metal particles are sintered. In this work, the authors replace conventionally-used polymeric binders with nanoparticle suspensions as a means for binding metal powder bed particles together. After being deposited into the powder particles’ interstices, the jetted nanoparticles are sintered at a low temperature via a heated powder bed to provide strength to the printed green part. Regions of the powder bed that do not receive the jetted nanoparticle suspension remain as loose powder as the sintering temperature of the nanoparticles is significantly lower than the larger powder bed particles. The concept of printing metal by jetting a nanoparticle binder made of the same material is demonstrated in the context of copper through printing copper parts with satisfactory green strength.

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