2012 International Solid Freeform Fabrication Symposium

Permanent URI for this collectionhttps://hdl.handle.net/2152/88315

Proceedings for the 2012 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Twenty-Third Annual International Solid Freeform Fabrication (SFF) Symposium – An Additive Manufacturing Conference, held at The University of Texas in Austin on August 6-8, 2012, was attended by 170 researchers from 13 countries. A two-morning special session on “Societal Impacts” emphasized the integration of additive manufacturing into culture and society. Terry Wohlers (Wohlers Associates) presented a keynote to start the session. Of special interest were a number of talks from China organized by Professor Wei Sun who currently holds joint appointments at Drexel University and Tsinghua University in Beijing. Other presentations summarized activity in the US and United Kingdom. Brent Stucker (University of Louisville) talked about international trends including standards development. Dr. Ian Gibson from the University of Singapore closed out the session with a 20-year perspective on the development of AM with a personal bent.

This year’s best oral presentation was entitled, “Observation and Numerical Simulation of Melt Pool Dynamic and Beam Powder Interaction During Selective Electron Beam Melting”, authored by Thorsten Scharowsky, Andreas Bauereiβ, Robert F. Singer and Carolin Körner from the Friedrich Alexander Universität Erlangen. Selection is based on the overall quality of the paper, the presentation and discussion at the meeting, the significance of the work and the manuscript submitted to the proceedings. Selected from 107 oral presentations, the associated manuscript appears on Page 815. The best poster presentation selected from 18 posters was given by Andrew Johnson, Dr. Guy Bingham and Dr. Candice Majewski from the University of Sheffield and Loughborough University. Titled, “Establishing the Performance Requirements for Stab Resistant Additive Manufactured Body Armour (AMBA)”, the article appears on Page 297 of this Proceedings.

The recipient of the International Outstanding Young Researcher in Freeform and Additive Manufacturing Award was Dr. Christopher Williams, an assistant professor with joint appointments in the Departments of Mechanical Engineering and Engineering Education at Virginia Tech in the United States. Dr. Jean-Pierre Kruth won the International Freeform and Additive Manufacturing Excellence (FAME) Award. He is a professor at the Katholieke Universitaet Leuven in Belgium.

The editors would like to extend a warm “Thank You” to Rosalie Foster for her detailed handling of the logistics of the meeting, as well as her excellent performance as registrar and problem solver during the meeting. We 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 (N00014-10-1-0528) and the National Science Foundation (#CMMI-1230744) for supporting this meeting financially. The meeting was co- organized by The University of Connecticut at Storrs, and the Mechanical Engineering Department and the Lab for Freeform Fabrication at The University of Texas at Austin.

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2012 International Solid Freeform Fabrication Symposium Table of Contents
(2012) Laboratory for Freeform Fabrication and University of Texas at Austin
Effects of Processing on Microstructure and Mechanical Properties of Ti-6Al-4V Fabricated using Electron Beam Melting (EBM): Orientation and Location
(2012) Hrabe, Nikolas; Kircher, Ryan; Quinn, Timothy
Electron beam melted (EBM) titanium alloy (Ti-6Al-4V) samples were built and characterized (qualitative prior-β grain size, quantitative α lath thickness, monotonic tensile, Vickers microhardness) to determine the effect of location and orientation on microstructure and properties. Samples of vertical orientation, compared to horizontal, were found to have 30% lower elongation. Orientation within the x-y plane as well as location were found to have less than 3 % effect on mechanical properties, and it is possible a second order effect of thermal mass contributed to these results.
Controlling the Quality of Laser Sintered Parts Along the Process Chain
(University of Texas at Austin, 2012-08-22) Rüsenberg, S.; Weiffen, R.; Knoop, F.; Schmid, H.-J.
The quality of laser sintered parts, in this work, manufactured by polymer laser sintering by using an EOSINT P395 Laser Sintering system, depends on several steps along the process chain. The first step is the characterization of the powder quality, whereas the rheological and physical investigations of nylon 12 powder are shown. By changing some important influencing factors, for example the powder ratio, the powder ageing and the moisture content, the influence on mechanical and physical properties, density and porosity, are investigated. The composition of the used powder is known. The previous process (storage conditions, etc.) as well as the laser sintering process (regarding energy density, temperature, etc.) is kept constant for the duration of this work. Regarding the post process in this work the cooling down phase is investigated as well. With an automatically blasting system it is possible to keep the post process parameters blasting distance and blasting time, constant. All of the tests will be performed using dry and conditioned test specimens. This work is showing the dependence on mechanical, rheological and physical parameters by varying important influencing factors along the laser sintering process quality chain.
Characterisation of Metal Deposition During Additive Manufacturing of Ti-6Al-4V by Arc-Wire Methods
(University of Texas at Austin, 2012) Hoye, N.P.; Appel, E.C.; Cuiuri, D.; Li, H.
This study considers the use of the gas tungsten arc (GTA) welding process in conjunction with ‘cold’ wire addition to give layer-wise build-up of thin walled structures, simulating those commonly found in aerospace applications, which may in the future be manufactured by additive means. Taguchi DOE and multiple regression analysis methods have been applied to quantitatively establish relationships between common process parameters including arc length, arc current, travel speed and wire feed speed and resulting weld bead geometries and actual metal deposition rates. Mathematical expressions for build-up height, thickness and surface roughness are presented and evaluated against experimental data, with observations related to physical phenomena.
Thermography for Monitoring the Selective Laser Melting Process
(University of Texas at Austin, 2012-08-22) Krauss, H.; Eschey, C.; Zaeh, M.F.
A lot of strategies exist to monitor and control additive layer manufacturing processes. Basically one can distinguish between coaxially monitoring the process zone and monitoring the complete layer currently being built. Since Selective Laser Melting is a thermal process, a lot of information about the process and in consequence about the resulting part quality can be gathered by monitoring the temperature distribution of a complete layer and its temporal evolution. It depends on the geometrical configuration of parts being built and the quality of the powder layer deposition. In this paper, process errors originating from insufficient heat dissipation are investigated as well as the limits for detecting pores and other irregularities by observation of the temperature distribution.
An Investigation of the Effects of Quantum Dot Nanoparticles on Photopolymer Resin for Use in PolyJet Direct 3D Printing
(University of Texas at Austin, 2012-08-15) Elliott, A.M.; Ivanova, O.S.; Williams, C.B.; Campbell, T.A.
The addition of quantum dot (QD) nanoparticles to additive manufacturing (AM) media provides the opportunity to create artifacts with complex geometry that also have unique optical characteristics. However, the addition of nanoparticles can significantly alter the rheology of a material and make it difficult to process in an AM context. In this study, quantum dots were added to a photopolymer resin in varying mass ratios to photopolymer, and their effects on the viscosity, surface tension, and jetting ability of the suspension were investigated. Results show that printability was not significantly affected by the presence of quantum dots in mass concentrations less than or equal to 0.5%. The nanosuspensions were deposited via inkjet to demonstrate the feasibility of creating optically-unique artifacts.
Error Detection in Laser Beam Melting Systems by High Resolution Imaging
(University of Texas at Austin, 2012-08-15) Kleszczynski, S.; zur Jacobsmühlen, J.; Sehrt, J.T.; Witt, G.
Laser Beam Melting as a member of Additive Manufacturing processes allows the fabrication of three-dimensional metallic parts with almost unlimited geometrical complexity and very good mechanical properties. However, its potential in areas of application such as aerospace or medicine has not yet been exploited due to the lack of process stability and quality management. For that reason samples with pre-defined process irregularities are built and the resulting errors are detected using high-resolution imaging. This paper presents an overview of typical process errors and proposes a catalog of measures to reduce process breakdowns. Based on this systematical summary a future contribution to quality assurance and process documentation is aspired.
Efforts to Reduce Part Bed Thermal Gradients During Laser Sintering Processing
(University of Texas at Austin, 2012-08-15) Yuan, Mengqi; Bourell, David
Part bed surface thermal gradients (x-y plane) are usually present in laser sintering (LS) fabricators. The purpose of this study was to investigate various means to reduce these thermal gradients. Several experiments were conducted using a FLIR™ infrared camera to examine the thermal profile of the part bed during the LS operation. Experiments included thermal profile characterization of the part bed with different nitrogen shielding gas flow rates, assessment of the proper experimental settings, and a temperature profile record of the part bed from the warm-up to the cool-down stage. A series of experiments were conducted using the laser as a heat source to preheat part bed surface cold spots to decrease the thermal gradients, which effect was limited by the natural low thermal conductivity of nylon 12 powder and large heat convection. Moreover, manifolds were mounted below the piston to provide warm nitrogen down draft flow during the LS operation.
Integration of a Thermal Imaging Feedback Control System in Electron Beam Melting
(University of Texas at Austin, 2012-08-15) Rodriguez, Emmanuel; Medina, Francisco; Espalin, David; Terrazas, Cesar; Muse, Dan; Henry, Chad; MacDonald, Eric; Wicker, Ryan B.
A thermal imaging system using an infrared (IR) camera was incorporated in the fabrication process of an Arcam A2 Electron Beam Melting system to provide layer-by-layer feedback and ensure quality and defect free products. Using the IR camera, build chamber surface temperature profiles were imaged and analyzed, providing information used to modify build settings for the next build layer. Individual part temperatures were also monitored and modified to achieve a more uniform bed temperature. The thermal imaging information can also be used as a quality control tool to detect imperfections during the build. Results from the integration of the camera in the system as well as use of the thermal images in process monitoring and control is described.
Combined Build-Time, Energy Consumption and Cost Estimation for Direct Metal Laser Sintering
(University of Texas at Austin, 2012-08-15) Baumers, M.; Tuck, C.; Wildman, R.; Ashcroft, I.; Rosamond, E.; Hague, R.
As a single-step process, Additive Manufacturing (AM) affords full measurability with respect to process energy inputs and production cost. However, the parallel character of AM (allowing the contemporaneous production of multiple parts) poses a number of problems for the estimation of resource consumption. A novel combined estimator of build-time, energy consumption and production cost is presented for the EOSINT M270 Direct Metal Laser Sintering system. It is demonstrated that the quantity and variety of parts demanded and the resulting ability to utilize the available machine capacity impact process efficiency, both in energy and in financial terms.
A Designer's Guide for Dimensioning and Tolerancing SLS Parts
(University of Texas at Austin, 2012) Seepersad, Carolyn Connor; Govett, Tyler; Kim, Kevin; Lundin, Michael; Pinero, Daniel
Because additive manufacturing (AM) is a relatively novel industry, with the first commercial machines introduced in the late 1980s, many designers are unaware of the capabilities of AM technologies. Many engineers also find it difficult to utilize AM because of a lack of “Design for AM” knowledge in the public domain. Reliable information on material properties, dimensions and tolerances, and other process-related specifications is often scattered throughout the literature, if it is publicly available at all. The objective of the research reported in this paper is to begin to create a designer's guide for dimensioning and tolerancing parts that are additively manufacturing using selective laser sintering (SLS) technology. The guide is based on a series of experiments designed to determine the limiting feature sizes for various types of features fabricated in commercially available SLS machines. The features include slits, holes, letters, mating gears, and shafts built in a preassembled state. The impact of part thickness, orientation, clearance, and dimensions on the resolvability of features is examined. Results are reported in a series of matrices that relate realizable feature sizes to other important variables such as part thickness.
Proposal for a Standardized Test Artifact for Additive Manufacturing Machines and Processes
(University of Texas at Austin, 2012-08-15) Moylan, Shwan; Slotwinski, John; Cooke, April; Jurrens, Kevin; Donmez, M. Alkan
Historically, standardized test parts are used to quantitatively evaluate the performance of a machine or process. While several different additive manufacturing (AM) test parts have been developed in the past, there are no current standard test parts. This paper reviews existing AM test parts, discusses the purposes of the studies, and describes important features and characteristics found in these test parts. A new test part intended for standardization is proposed. This part incorporates the most useful features seen in previous test parts. These features are designed to highlight process capabilities and test machine accuracy. The design has been validated through builds by several AM processes.
First Steps Towards Collaboratively Edited Design for Additive Manufacturing Knowledge
(University of Texas at Austin, 2012-08-18) Doubrovski, E.L.; Verlinden, J.C.; Horvath, I.
Despite the broad coverage concerning the technological challenges, little research has been performed on the methods that enable designers to deal with Additive Manufacturing. At present, the challenge is to generate Design for Additive Manufacturing knowledge which goes beyond traditional solutions and to ensure that this knowledge is complete, correct and up to date. This paper reports on the employment of a wiki environment to support open-ended knowledge management. We applied this solution in an undergraduate prototyping course focused on exploring visual properties using AM structures. The results of the 32 students encompass unexpected designs while the knowledge on the wiki encompassed i) AM processes, ii) procedures, iii) artifacts. This forces us to rethink what should constitute DfAM.
Examining Variability in the Mechanical Properties of Parts Manufactured via PolyJet Direct 3D Printing
(University of Texas at Austin, 2012-08-15) Barclift, Michael W.; Williams, Christopher B.
In Objet’s PolyJet process, part layers are created by selectively inkjetting photopolymers onto a build substrate and then cured with ultraviolet lamps. With an eye towards using PolyJet as a manufacturing process to fabricate end-use products, the authors examine the sensitivity of part material properties to variation in process parameters. Specifically, a design of experiments is conducted using a full-factorial design to analyze the effects of three parameters on the specimens’ tensile strength and tensile modulus: the in-build plane part orientation (X-Y), the out-of-build plane part orientation (Z), and the distance between specimens. Results show that part spacing has the largest effect on the tensile strength, but the three parameters produced no statistically significant effects on the tensile modulus. Orienting specimens in XZ orientation with minimal part spacing resulted in the highest tensile strength and modulus. Whereas, orienting specimens in the YZ orientation at the farthest part spacing led to the lowest mechanical properties.
Ceramic-Polymer Additive Manufacturing System for Ultrasound Transducers
(University of Texas at Austin, 2012) Cheverton, Mark; Singh, Prabhjot; Smith, Scott; Chan, Kwok Pong
A modified multi-layer lithography process is used to additively manufacture highresolution netshape ceramic structures by photopolymerizing a ceramic-polymer slurry using structured light patterns. This paper will discuss the development of a low-cost, high speed manufacturing process method for the fabrication of piezoelectric ceramic transducer elements in the 1-25 MHz frequency range. The key considerations in the development of the process including the selection and optimization of slurry materials for the deposition of PZT 5H materials, optical exposure parameters, debinding/sintering profiles, process monitoring, and post manufacturing processing. Ongoing work includes improvements to the materials properties, improved throughput and geometric fidelity.
Fast Recoating Methods for the Projection-based Stereolithography Process in Micro- and Macro-Scales
(University of Texas at Austin, 2012) Pan, Yayue; Chen, Yong; Zhou, Chi
The purpose of this paper is to present a recoating method for the development of a direct digital manufacturing (DDM) process that can be an order of magnitude faster than other currently available DDM processes. In the mask-image-projection-based Stereolithography (MIP-SL) process, projection light controlled by a Digital Micromirror Device (DMD) can quickly cure liquid photopolymer resin in a whole area; a fast recoating method is required for achieving truly high-speed fabrication. We investigate the bottom-up projection system in the MIP-SL process. For the macro-scale MIP-SL process, a two-way linear motion approach has been developed for the quick spreading of liquid resin into uniform thin layers. In comparison, a direct pull-up motion can be used in the micro-scale MIP-SL process. The system design and related settings for achieving a fabrication speed of a few seconds per layer are presented. Additionally, the hardware, software, and material setups for fabricating three-dimensional (3D) digital models are presented. Experimental studies using the developed testbed have been performed to verify the effectiveness and efficiency of the presented fast MIP-SL process.
Fused Deposition Modeling of Metals
(University of Texas at Austin, 2012-08-22) Mireles, Jorge; Espalin, David; Roberson, David; Zinniel, Bob; Medina, Francisco; Wicker, Ryan
Studies have been conducted to improve previous work performed in developing a Fused Deposition Modeling for metals (FDMm) system used for applications in electronics and fabrication of 3-dimensional metallic structures. A FDM 3000 system was modified to achieve controlled deposition of eutectic Bi58Sn42 and non-eutectic Sn60Bi40 materials. Toolpath command modifications were required to achieve controlled deposition of metals. Results are presented which include a redesigned metal deposition head, computer modeling of fluid flow, and finally examples of the successful deposition of metal alloys. Additionally, FDMm-fabricated metal samples were prepared and analyzed using optical and scanning electron microscopy. Controlled deposition of metals using FDMm allows for parts that can be used for jigs and fixtures, electroforming mandrels, encapsulation molds, dies, electronic joining applications, as well as printing 3-dimensional electronic circuitry.
Multi-Material, Multi-Technology FDM System
(University of Texas at Austin, 2012-08-15) Espalin, David; Ramirez, Jorge; Medina, Francisco; Wicker, Ryan
A multi-material, multi-technology FDM system was developed and constructed to enable the production of novel thermoplastic parts. Two legacy FDM systems were modified and installed onto a single manufacturing system to allow the strategic, spatially controlled thermoplastic deposition of multiple materials during the same build. Additionally, a build process variation utilizing more than two extrusions tips was employed to deposit thermoplastic materials using variable layer thicknesses and road widths. The hardware and control software is discussed as well as the potential applications of multi-material polymeric parts. Benefits of multiple material FDM include: 1) achieving aesthetic requirements by using polymers of different colors, and 2) attaining desired properties (e.g., bulk tensile/compressive/flexural strength, weight, thermal conductivity) by strategically combining layers and regions within layers of polymers that display different properties. Parts produced using the build process variation exhibited internal road with 1200 ± 39µm road width and 497 ± 11µm layer height while the contours measured 269 ± 18µm road width and 133 ± 3µm layer thickness. Additionally, for a 50.8mm by 50.8mm square section (25.4mm tall), the build process variation required 4.0 hours to build while the original strategy required 6.2 hours constituting a 35% reduction in build time.
Remanufacture of Turbine Blades by Laser Cladding, Machining and In-Process Scanning in a Single Machine
(University of Texas at Austin, 2012-08-16) Jones, Jason; McNutt, Phil; Tosi, Riccardo; Perry, Clinton; Wimpenny, David
Remanufacturing is one of the most efficient ways of recycling worn parts because it consumes only a fraction of the energy, cost, and material required for new parts. Remanufacture of engineering components typically entails serial labor intensive and operator skill sensitive processes, often requiring parts to move between manufacturers and subcontractors. Unfortunately the logistics and quality assurance measures required for effective remanufacturing currently restrict its implementation primarily to high value components (e.g. turbine blades, blisks, etc.). This research reports progress toward an integrated production system which combines laser cladding, machining and in-process scanning in a single machine for flexible and lean remanufacturing.
Observation and Numerical Simulation of Melt Pool Dynamic and Beam Powder Interaction During Selective Electron Beam Melting
(University of Texas at Austin, 2012) Scharowsky, T.; Baureiβ, A.; Singer, R.F.; Körner, C.
Selective electron beam melting (SEBM) is an additive manufacturing method used to produce complex parts in a layer-by-layer process utilizing Ti6Al4V powder. To improve the very good properties of built parts even more and to use the full capacity of the process, the fundamental understanding of the beam powder interaction is of essential relevance. Numerical simulations and observation with a high speed camera of powder melting show the strong melt pool dynamic and its lateral extent clearly. Furthermore, the immediate effect of beam parameters, e.g. beam current and velocity, on the melting behavior of the powder can be resolved in time steps of a few milliseconds.

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