2006 International Solid Freeform Fabrication Symposium

Permanent URI for this collectionhttps://hdl.handle.net/2152/80069

Proceedings for the 2006 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Seventeenth Solid Freeform Fabrication (SFF) Symposium, held at The University of Texas in Austin on August 14-16, 2006, was attended by 101 national and international researchers from ten countries. Papers addressed SFF issues in computer software, machine design, materials synthesis and processing, and integrated manufacturing. The diverse domestic and foreign attendees included industrial users, SFF machine manufacturers, university researchers and representatives from the government. The Symposium organizers look forward to its being a continuing forum for technical exchange among the expanding body of researchers involved in SFF.

The Symposium was again organized in a manner to allow the multi-disciplinary nature of the SFF research to be presented coherently, with various sessions emphasizing process development, design tools, modeling and control, process parameter optimization, applications and materials. We believe that documenting the changing state of SFF art as represented by these Proceedings will serve both those presently involved in this fruitful technical area as well as new researchers and users entering the field.

This year’s best oral presentation, “Repeatability Analysis of 304L Deposition by the LENS® Process”, was given by David Gill from Sandia National Laboratories-New Mexico, (co-authors John Smugeresky and Clinton J. Atwood). Selection was 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 over 60 oral presentations, his presentation appears on Page 770 of this Proceedings. The best poster presentation selected from 14 posters was given by Hongyi Yang of the University of London (co-authors Xiaopeng Chi, Shoufeng Yang and Julian R. G. Evans). The paper title was, “Direct Extrusion Freeforming of Ceramic Pastes”. The article appears on Page 304.

The editors would like to extend a warm “Thank You” to Rosalie Foster for her detailed handling of the logistics of the meeting and the Proceedings, as well as her excellent performance as registrar and problem solver during the meeting. We are grateful to Bryan Blackmur and Cindy Pflughoft who helped with Proceedings production. We would like to thank the Organizing Committee, the session chairs, the attendees for their enthusiastic contributions, 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 SFF community in organizing the Symposium. We also want to thank the Naval Research Laboratory and the National Science Foundation (DMI- 0621169s) for supporting this meeting financially. The meeting was co-organized by the University of Connecticut at Storrs, and the Mechanical Engineering Department, Laboratory for Freeform Fabrication and the Texas Materials Institute at The University of Texas at Austin.


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    2006 International Solid Freeform Fabrication Symposium Table of Contents
    (2006) Laboratory for Freeform Fabrication and University of Texas at Austin
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    Selective Infrared Sintering of Polymeric Powders using Radiant IR Heating & Ink Jet Printing
    (2006-09-14) Wimpenny, David Ian; Banerjee, Soumya
    Established methods of rapid prototyping by sintering polymeric powders have predominantly focused on the use of lasers to selectively heat the polymeric particles together to form fused layers. Although effective, this route requires the laser to draw in the entire cross section of the slice and this limits the speed of the process, particularly for the production of thick walled parts. The use of IR radiant lamps to fuse an entire layer simultaneously has been explored by several groups and is now the basis of at least one commercially available process (Speed Part). An alternative route, developed by the Rapid Prototyping & Manufacturing Group (RPMG) at DeMonfort University, where areas of the powder bed are selectively treated to promote absorption by particular IR radiation will be described in this paper. The advantages of this approach and the limitations which must be overcome through further research will be fully discussed.
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    Repeatability Analysis of 304L Deposition by the LENS® Process
    (2006) Gill, David; Smugeresky, John; Atwood, Clinton J.
    Sandia National Laboratories is currently engaging in an effort to qualify Laser Engineered Net Shaping™ (LENS®) as a repair and modification process for high rigor metal components. As part of that effort, the LENS team has conducted a process repeatability test to help identify variation within the system. This test utilized 304L stainless steel which is a commonly used material at Sandia. Over the course of 12 weeks, 3/8”x3/8”x2” towers were built in sets of 3 with a total of 30 towers completed. A random sampling of 10 of these towers (1 from each set of 3) had been identified before depositing the towers, and these towers were used for tensile testing and metallographic testing. The testing showed the ultimate and yield strengths of all samples to be well above those of annealed 304L. This is expected because of the rapid melt pool solidification present in the LENS process and the resulting grain refinement. The ductility, which usually remains on par with annealed 304L, was found to be lower. The final cause of this loss of ductility was determined to be inter-layer separation due to loose wires in the closed loop melt pool control system.
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    Reduction of Machine Tool Times Through a Software/Hardware Integrated Solution
    (2006) Bevan, D. R.; Mouton, S. A.
    Toolmaking is an industry that creates metal moulds, generally of durable tool steels, for producing vacuum-formed and injection moulded plastic parts, which are used in thousands of everyday items such as mobile phones. At present toolmaking is labour intensive with each machining operation requiring manual supervision. The FASTOOL project was a European Union funded collaboration that was aimed at reducing the manpower content of mould toolmaking, and extending the working day. This paper focuses on one element which utilised specially created scheduling and control software that operated an automated overhead gantry system and could remotely start the workshop machines. The software was completely object oriented which allows future proofing by creating new objects for new machines. The results demonstrate that this manufacturing process can be automated, leading to better working conditions for employees and an increase in efficiency and profitability.
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    Process Parameters Optimization for Ultrasonically Consolidated Fiber-Reinforced Metal Matrix Composites
    (2006-09-14) Yang, Y.; Janaki Ram, G. D.; Stucker, B. E.
    As an emerging rapid prototyping technology, Ultrasonic Consolidation (UC) has been used to successfully fabricate metal matrix composites (MMC). The intent of this study is to identify the optimum combination of processing parameters, including oscillation amplitude, welding speed, normal force, operating temperature and fiber orientation, for manufacture of long fiber-reinforced MMCs. The experiments were designed using the Taguchi method, and an L25 orthogonal array was utilized to determine the influences of each parameter. SiC fibers of 0.1mm diameter were successfully embedded into an Al 3003 metal matrix. Two methods were employed to characterize the bonding between the fiber and matrix material: optical/electron microscopy and push-out tests monitored by an acoustic emission (AE) sensor. SEM images and data from push-out tests were analyzed and optimum combinations of parameters were achieved.
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    Principles of Laser Micro Sintering
    (2006-09-14) Regenfuss, P.; Streek, A.; Hartwig, L.; Klötzer, S.; Brabant, Th.; Horn, M.; Ebert, R.; Exner, H.
    Laser Micro Sintering was introduced to the international community of freeform fabrication engineers in 2003 and has since been employed for a variety of applications. It owes its unique features to certain effects of q-switched pulses that formerly had been considered detrimental in selective laser sintering. Besides sub-micrometer sized powders also materials with grain sizes of 1-10 micrometers can be sintered. Surface and morphology of the product are influenced by grain size and process environment. First results have been achieved with processing ceramic materials. A comprehensive overview of the process and the features is given supported by experimental evidence. Routes of further development are indicated.
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    Practical Issues in the Application of Direct Metal Laser Sintering
    (2006) Jacobson, D. M.; Bennett, G.
    Direct Metal Laser Sintering (DMLS) was introduced to meet the objective of producing metal parts directly from CAD data. CRDM has accumulated six years of experience in applying this technique, mostly to prototyping parts for evaluation. For some applications, such as blow moulds, porosity generated in DMLS has proved to be beneficial, but for others a concession on tolerances or finish are necessary and/or complementary operations are required, which add to manufacturing time and cost. This paper examines such issues through some well chosen examples of parts to demonstrate both the strengths and weaknesses of the DMLS process.
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    Mechanical Behavior of SLS Components in Relation to the Build Orientation During the Sintering Process as Measured by ESPI
    (2006) Amado-Becker, Felipe; Díaz, Richard A.; Ramos-Grez, Jorge
    Selective Laser Sintering (SLS) allows producing real parts from CAD data from materials with different characteristics compared to the final model, presenting dissimilar mechanical properties between the prototype and the product. The purpose of this work is to correlate the mechanical behavior of beam-type specimens produced by SLS with build orientation angle used as a process parameter, also attempting to demonstrate how this parameter affects the accuracy of the Empirical Similitude Method (ESM). ESM presents itself as a valuable tool when creating scale models with SLS, specifically in the framework of evolutionary product design. More specifically, the Young modulus variation of test specimens of well-known dimensions and material (DuraformTM PA2 ), will be characterized by loading them within the elastic range. The resulting elastic deformations will be measured using the technique of Electronic Speckle Pattern Interferometry (ESPI) for small deformations in an out-of-plane configuration, contrasting these results with the elastic theory of deformations. As a main result, it was found that there exists a linear correlation between the build angle and the elastic modulus of the parts. Secondly, it was demonstrated empirically that the ESM predicts better the mechanical response of the part than TSM. Moreover, a 30% error reduction can be achieved within the ESM when using the build orientation angle as a process parameter.
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    Localized Preheating Approaches for Reducing Residual Stress in Additive Manufacturing
    (2006) Aggarangsi, Pruk; Beuth, Jack L.
    Uniform preheating can be used to limit residual stress in the solid freeform fabrication of relatively small parts. However, in additive manufacturing processes, where a feature is deposited onto a much larger part, uniform preheating of the entire assembly is typically not practical. This paper considers localized preheating to reduce residual stresses, building on previous work using a defined thermal gradient through the part depth as a metric for predicting maximum final residual stress. The building of thinwalled structures is considered. Two types of localized preheating approaches are compared, appropriate for use in laser- or electron beam-based additive manufacturing processes. In evaluating the effectiveness of each approach, a simplified thermomechanical model is used that can be related directly to analytical thermomechanical models for thermal stresses in unconstrained thin plates. Results are presented showing that one of the methods yields temperature profiles likely to yield reduced residual stresses at room temperature. Mechanical model results confirm this, showing a significant reduction in maximum stress values. A more complete thermomechanical simulation of thin wall fabrication is used to verify the trends seen in the simplified model results.
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    Improving Linear Weld Density in Ultrasonically Consolidated Parts
    (2006-09-14) Ram, G. D. Janaki; Yang, Y.; George, J.; Robinson, C.; Stucker, B. E.
    Ultrasonic consolidation is a novel additive manufacturing process with immense potential for fabrication of complex shaped three-dimensional metallic objects from metal foils. The proportion of bonded area to unbonded area along the layer interface, termed linear weld density (LWD), is perhaps the most important quality attribute of ultrasonically consolidated parts. Part mechanical properties largely depend on LWD and a high level of LWD must be ensured in parts intended for load-bearing structural applications. It is therefore necessary to understand what factors influence LWD or defect formation and devise methods to enhance bond formation during ultrasonic consolidation. The current work examines these issues and proposes strategies to ensure near 100% LWD in ultrasonically consolidated aluminum alloy 3003 parts. The work elucidates the effects of various process parameters on LWD and a qualitative understanding of the effects of process parameters on bond formation during ultrasonic consolidation is presented. The beneficial effects of using elevated substrate temperatures and its implications on overall manufacturing flexibility are discussed. A preliminary understanding of defect morphologies and defect formation is presented, based on which a method (involving surface machining) for minimizing defect incidence during ultrasonic consolidation is proposed and demonstrated. Finally, trade-offs between part quality and build time are discussed.
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    High Speed Sintering – Continuing Research into a New Rapid Manufacturing Process
    (2006) Thomas, Helen R.; Hopkinson, Neil; Erasenthiran, Poonjolai
    High Speed Sintering (HSS) is an emerging layer manufacturing technique aiming to break into the lucrative field of Rapid Manufacturing (RM). The process is likened to Selective Laser Sintering (SLS), however, instead of a laser dictating the sintered cross sectional area of each layer, the desired area is first printed using a Radiation Absorbing Material (RAM) and then sintered using an inexpensive infrared lamp. This paper begins by describing the sintering process in more detail and then outlining the overall manufacturing cycle. It then continues by describing the experiments performed to investigate the current problem concerning the hardness of excess powder within the powder bed. This problem arose due to the continual exposure of the whole bed to infrared radiation from the lamp. The experiments showed that as the power of the IR lamp increased, the hardness of the bed also increased. Furthermore, at higher IR power levels it was found the excess powder produced a solid tile which could only be broken down by a glass bead blaster.
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    Fab@Home: The Personal Desktop Fabricator Kit
    (2006) Malone, Evan; Lipson, Hod
    Solid freeform fabrication has the potential to revolutionize manufacturing, perhaps even to allow consumers to customize and manufacture goods cost-effectively in their own home. At present, the florescence of the technology is limited by a “chicken and egg” paradox. There is insufficient consumer demand and too narrow a range of applications for SFF systems to allow mass production to reduce their cost and complexity. At the same time, consumer applications for, demand for, and indeed awareness of SFF technology is limited by its high cost and complexity. We posit that just as the personal computer revolution was spurred by development of computer kits, getting SFF technology into the hands of hobbyists and hackers will simultaneously generate applications for, and improvements to it. To this end, we have developed the Fab@Home personal SFF kit, and are developing a user-group website to promote exchange of ideas and improvements. The designs and software for Fab@Home will be freely distributed, and constructing a first generation kit should cost roughly $2000. The kit design and a working unit will be presented, along with our experience deploying a unit for public use.
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    Exploiting the Design Freedom of RM
    (2006) Watts, D. M.; Hague, R. J.
    This paper details how Rapid Manufacturing (RM) can overcome the restrictions imposed by the inherent process limitations of conventional manufacturing techniques and become the enabling technology in fabricating optimal products. A new design methodology capable of exploiting RM’s increased design freedom is therefore needed. Inspired by natural world structures of trees and bones, a multi-objective, genetic algorithm based topology optimisation approach is presented. This combines multiple unit cell structures and varying volume fractions to create a heterogeneous part structure which exhibits a uniform stress distribution.
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    Expanding Rapid Prototyping for Electronic Systems Integration of Arbitrary Form
    (2006-09-14) Lopes, Amit; Navarrete, Misael; Medina, Francisco; Palmer, Jeremy; MacDonald, Eric; Wicker, Ryan
    An innovative method for rapid prototyping (RP) of electronic circuits with components characteristic of typical electronics applications was demonstrated using an enhanced version of a previously developed hybrid stereolithography (SL) and direct write (DW) system, where an existing SL machine was integrated with a three-axis DW fluid dispensing system for combined arbitrary form electronic systems manufacturing. This paper presents initial efforts at embedding functional electronic circuits using the hybrid SL/DW system. A simple temperature-sensitive circuit was selected, which oscillated an LED at a frequency proportional to the temperature sensed by the thermistor. The circuit was designed to incorporate all the required electronic components within a 2.5” x 2” x 0.5” SL part. Electrical interconnects between electronic components were deposited on the SL part with a DW system using silver conductive ink lines. Several inks were deposited, cured, and tested on a variety of SL resin substrates, and the E 1660 ink (Ercon Inc, Wareham, MA) was selected due to its measured lowest average resistivity on the SL substrates. The finished circuit was compared with Printed Circuit Board (PCB) technology for functionality. The electronic components used here include a low voltage battery, LM 555 timer chip, resistors, a thermistor, capacitors, and Light Emitting Diodes (LEDs). This circuit was selected because it (1) represented a simple circuit combining many typically used electronic components and thus provided a useful demonstration for integrated electronic systems manufacturing applicable to a wide variety of devices, and (2) provided an indication of the parasitic resistances and capacitances introduced by the fabrication process due to its sensitivity to manufacturing variation. The hybrid technology can help achieve significant size reductions, enable systems integration in atypical forms, a natural resistance to reverse engineering and possibly increase maximum operating temperatures of electronic circuits as compared to the traditional PCB process. This research demonstrates the ability of the hybrid SL/DW technology for fabricating combined electronic systems for unique electronics applications in which arbitrary form is a requirement and traditional PCB technology cannot be used.
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    Dry Powder Microfeeding System for Solid Freeform Fabrication
    (2006) Lu, Xuesong; Yang, Shoufeng; Chen, Lifeng; Evans, Julian R. G.
    Second generation SFF techniques allow both composition and shape to be downloaded directly from a computer file so that 3D functionally graded materials (FGM) can be assembled. Methods for multi-material deposition are also needed in combinatorial research, colour management and pharmaceutical dosing. In this work, computer-controlled microfeeding systems using ultrasonic vibration of a capillary were built. A wide range of stable flow rate control and switching control were achieved in the acoustic vibration system, and uniform powder doses were obtained in the ultrasonic system. The experimental results show that the nozzle diameter, transmission fluid depth, waveforms, voltage amplitude, frequency and oscillation duration all influence the dose mass. Among these factors, the nozzle diameter, voltage amplitude and oscillation duration can be used to control the dose mass. Raster printing of patterns with various resolution and dot size are demonstrated.
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    Development of an Automated Multiple Material Stereolithography Machine
    (2006) Inamdar, Asim; Magana, Marco; Medina, Frank; Grajeda, Yinko; Wicker, Ryan
    An automated Multiple Material Stereolithography (MMSL) machine was developed by integrating components of a 3D Systems 250/50 stereolithography (SL) machine in a separate stand-alone system and adapting them to function with additional components required for MMSL operation. We previously reported retrofitting a 250/50 SL machine with multiple vats to accommodate multiple material fabrication for building a wide variety of multi-material models (Wicker et al., 2004). In the MMSL retrofit, spatial constraints limited the multiple vats located circumferentially on a vertical rotating vat carousel to cross-sectional areas of approximately 4.5-inches by 4.5-inches. The limited build size of the retrofitted 250/50 motivated the full development of a new system with multiple material build capabilities comparable to the build envelope of the original 250/50 machine. The new MMSL machine required fabrication of a large system frame, incorporating various 250/50 components and software, and adding a variety of new components and software. By using many existing components and software, the previous engineering development of 3D Systems could be directly applied to this new technology. Components that were transferred from an existing 250/50 to the MMSL machine included the complete optical system (including the optics plate with laser, mirrors, beam expander, scanning mirrors, and focusing lens), the rim assembly (including the laser beam profilers), the associated controllers (computer system, scanning mirror controller, power supply-vat controller) and the wiring harness. In addition to the new frame, the MMSL machine required the development of a new rotating vat carousel system, platform assembly, multi-pump filling/leveling system, and a custom LabVIEW® control system to provide automated control over the MMSL process. The overall operation of the MMSL system was managed using the LabVIEW® program, which also included controlling a new vat leveling system and new linear and rotational stages, while the 3D Systems software (Buildstation 4.0) was retained for controlling the laser scanning process. As a demonstration of MMSL technology, simple multi material parts were fabricated with vertically and horizontally oriented interfaces. The fully functional MMSL system offers enormous potential for fabricating a wide variety of multiple material functional devices.
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    Determination of Transformation Matrix in a Hybrid Multi-Axis Laser-Aided Manufacturing System and its Practical Implementation
    (2006) Vijayan, Ajay Panackal Padathu; Sparks, Todd; Ruan, Jianzhong; Liou, Frank
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    Design and Freeform Fabrication of Deployable Structures with Lattice Skins
    (2006) Maheshwaraa, Uma; Tradd, Catherine; Bourell, David; Seepersad, Carolyn Conner
    Frontier environments—such as battlefields, hostile territories, remote locations, or outer space—drive the need for lightweight, deployable structures that can be stored in a compact configuration and deployed quickly and easily in the field. We introduce the concept of lattice skins to enable the design, solid freeform fabrication (SFF), and deployment of customizable structures with nearly arbitrary surface profile and lightweight multi-functionality. Using Duraform FLEX® material in a selective laser sintering machine, large deployable structures are fabricated in a nominal build chamber by either virtually collapsing them into a condensed form or decomposing them into smaller parts. Before fabrication, lattice sub-skins are added strategically beneath the surface of the part. The lattices provide elastic energy for folding and deploying the structure or constrain expansion upon application of internal air pressure. Nearly arbitrary surface profiles are achievable and internal space is preserved for subsequent usage. In this paper, we present the results of a set of experimental and computational models that are designed to provide proof of concept for lattice skins as a deployment mechanism in SFF and to demonstrate the effect of lattice structure on deployed shape.
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    Automation of a Hybrid Manufacturing System Through Tight Integration of Software and Sensor Feedback
    (2006-09-14) Stroble, J. K.; Landers, R. G.; Liou, F. W.
    This paper presents a framework for the automation of the Laser Aided Manufacturing Process (LAMP) lab at the University of Missouri-Rolla. The groundwork for the proposed system involves the integration of the LabVIEW software package and a PXI-8195 real time controller with several sensors and actuators. The incorporation of all key control parameters into one virtual instrument will help achieve the goal of an automated hybrid system. To achieve this goal, a five-phase plan, which will be further discussed in the paper, has been developed. The first phase of this plan, which includes the deposition of a thin walled structure without DNC communication between LabVIEW and the CNC has been achieved, and will be the focus of this paper
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    Approach Tolerance in the Assemblies of Evolutionary Hybrid Prototypes
    (2006-09-14) Rivette, M.; Mognol, P.; Hascoet, JY.
    A new answer is proposed to replace the traditional “one shot” prototype (manufactured in one piece with one process): the hybrid rapid prototype. It is used to highly reduce time, cost and increase reactivity during the development times of new products. The part is decomposed in several components which can quickly be changed and can be manufactured with a process the most adapted. The main objective of the presented method is to propose an available technological assembly between the different components of the part in the respect of technological and topological function, and initial tolerance. Using a graph of representation, fuzzy logic and a tolerance point of view, some entities are associated with a CIA (Assembly Identity Card) in accordance with evolutionary and manufacturing analysis. This work will be illustrated by an industrial tooling for plastic injection.