2002 International Solid Freeform Fabrication Symposium

Permanent URI for this collectionhttps://hdl.handle.net/2152/76041

Proceedings for the 2002 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Thirteenth Solid Freeform Fabrication (SFF) Symposium, held at The University of Texas in Austin on August 5-7, 2002, was attended by over 110 national and international researchers. 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 modeling, process development, 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.

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 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 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 Office of Naval Research (N00014-02-1-0646) and the National Science Foundation (DMI-0233930) 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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    2002 International Solid Freeform Fabrication Symposium Table of Contents
    (2002) Laboratory for Freeform Fabrication and University of Texas at Austin
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    Advancements in the SIS Process
    (2003) Asiabanpour, Bahram; Khoshnevis, Behrokh; Palmer, Kurt; Mojdeh, Mehdi
    Selective Inhibition of Sintering (SIS) is a new layer-based rapid prototyping process. This paper reports the progress in research and development of the SIS process. Specific printer path generation method, experimentation with various powder and inhibitor materials, and systematic models leading to optimum performance given various factors affecting part strength, surface quality, and dimensional accuracy are presented.
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    Digital Micromirror Device Based Microstereolithography for Micro Structures of Transparent Photopolymer and Nanocomposites
    (2003) Hadipoespito, George W.; Yang, Yong; Choi, Hongseok; Ning, Guoqing; Li, Xiaochun
    This paper describes a Digital Micromirror Device (DMD) based ultraviolet (UV) microstereolithography (µ-SL) system developed for rapid prototyping and manufacturing of micro 3D structures. Characterization experiments show that the developed the DMD-based imaging system irradiates an entire photopolymer layer at once, providing reasonable curing speed and good resolution at a low cost. 2D and 3D micro parts were fabricated. High frequency ultrasonic vibration (above 20 kHz) was experimented and verified that it can be used to significantly decrease the leveling time of viscous photopolymer. Furthermore, micro parts were also fabricated in nanocomposites, which were obtained by ultrasonic mixing of the transparent photopolymer and nano-sized ceramic particles. High quality micro models fabricated by this novel process could be used for micro scale investment casting, tooling, devices, and medical applications.
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    Process Planning for Solid Freeform Fabrication Based on Laser-Additive Multi-axis Deposition
    (2003) Dwivedi, Rajeev; Kovacevic, Radovan
    This paper describes a new approach for rapid prototyping based on volumetric skeletonization. Contrary to most of the popular techniques for Solid Freeform Fabrication (SSF) based on 2-1/2 -axis layering as planar slices, this approach suggests the growth of the component along all three coordinate axes. While this approach offers many advantages in terms of the elimination of the support structures for the reduction of the staircase effects and the elimination of various post processes for the functional parts, this approach also offers challenges towards process planning. For various complicated shapes it may not be possible to generate the required shape using this approach; however, a hybrid approach which also incorporates the deposition by layers, may offer an optimum solution. Preliminary results are based on the successful laser-based additive deposition along multiple g-vectors. The material properties and the problems of possible porosities are still to be investigated. Advantages, process planning, applications, experimental results, and the challenges of this new method are the subject of this paper.
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    A Study on Effects of Process Parameters in Rapid Freeze Prototyping
    (2002) Bryant, Frances D.; Sui, Guanghua; Leu, Ming C.
    Rapid Freeze Prototyping (RFP) is a relatively new solid freeform fabrication process, which builds a three-dimensional part according to a CAD model by depositing and freezing water droplets layer by layer. A study on the effects of RFP process parameters including the nozzle scanning speed, droplet size, and droplet frequency in building ice parts with a single-nozzle work head is made. Presented in this paper are the results of this study which indicate that these process parameters determine the ice layer thickness and ice line width, which in turn determine the surface roughness and the waiting time required after depositing each layer of water (i.e. between successive layers) during the ice part building process.
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    Motion Planning for Cladding Operations in a 5-Axis LENS� Machine
    (2002) Jouaneh, Musa
    This paper presents a motion planning approach for some basic part shapes that require 5-axis motion control in a LENS machine. The paper discusses an approach that allows a cladding layer to be deposited on a cylindrical or a semi-spherical part for re-build operations. For cylindrical parts, the deposited layer could take the form of a tube, a spiral, or stepped/tappered tube. The approach allows arbitrary values for the parameters of these layers, and automatically translates the part parameters into a motion control program to run the LENS machine. The developed methodology was tested on an Optomec 850 machine, and the results were successful.
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    Experimental and Numerical Study on the Flow of Fine Powders from Small-Scale Hoppers Applied to SLS Multi-Material Deposition-Part I
    (2002) Santosa, James; Jing, Dejun; Das, Suman
    We present experimental guidelines for the delivery of powders under 100µm through hopper-nozzle orifice diameters on the order of 1mm. Small-scale hoppers will be incorporated into an SLS powder deposition system for creating thin layers of multiple powdered materials in a patterned bed. This is a preliminary investigation on the flow behavior for selected orifice diameters and particle sizes under gravity or low pressure-assisted flow conditions. A method for numerically modeling the gas-particle behavior in hopper-nozzles is presented and conditions for achieving continuous mass flow rates are demonstrated.
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    Design of Thermal Environment in Plastic Injection Mold Based on Evaluation of Resin Cooling Uniformity
    (2002) Gao, Feng; Koresawa, Hiroshi; Narahara, Hiroyuki; Suzuki, Hiroshi
    Thermal state in plastic injection molds greatly influences the molding quality of products. This paper discusses the optimum design of thermal environment in the molds by observing and estimating the cooling uniformity of resin. Numerical analysis based on unsteady heat transfer is conducted to confirm the utility of the proposed evaluation method, and case studies show the comparison results of resin deformations under different cooling systems conditions and the improved designs.
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    Study of the Heating-and-Pressing Separation Process of Laminated Object Manufacturing (LOM)
    (2002) Liao, Y.S.; Li, H.C.; Chiu, Y.Y.
    To improve hot-pressing process currently employed by the laminated object manufacturing (LOM), an innovated heating-and-pressing separation system is proposed, and heat transfer problems of this system is investigated. A thermal model is first established. It is solved numerically by the finite element method (FEM) software ANSYS, and verified by experiments. According to the numerical solution under various operating conditions, it is suggested that if the temperature and the moving speed of the heater are both increased, the depth of the heat affected laminates will be reduced. The processing time will be shortened and the manufacture efficiency will be promoted. Through analysis, it is concluded that, to obtain finished parts of high quality, the appropriate distance between the roller and the heater can be determined.
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    An Integrated Approach to Finish Machining of RP Parts
    (2002) Stucker, Brent; Qu, Xiuzhi
    An integrated approach to finish machining of RP parts and tools has been developed at the University of Rhode Island. Pre-processing operations, including surface offsets to add machining stock, and post-processing operations, including CNC tool-path generation, have been combined into one integrated set of software algorithms to make possible the effective finishing of near-net parts and tools from RP. An in-depth description of the uniquely developed STL vertex offset algorithm will be explored as well as an automatic method for adaptive raster milling, sharp edge contour machining and hole drilling from STL files. The time involved and surface finish benefits of the developed methodology will be compared to alternative approaches.
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    A Statistical Model of Laser Surface Finishing Using Design of Experiments and ANOVA
    (2002) Murphy, J.; Lappo, K.; Wood, K.; Beaman, J.
    In previous work, laser polishing indirect-SLS metal parts was achieved using a Nd:YAG laser raster scanned at high speed. This work showed surface roughness could effectively be reduced by means of shallow surface melting. Surface area roughness data, Ra, was obtained by line profilometry measurements of the polished samples according to a modified procedure based on the ASME standard for surface texture measurements. A Design of Experiments (DOE) was conducted to better understand the effects of processing parameters such as laser beam power, scan time, and scan line density on the surface roughness. The DOE consisted of a multi-level test for each variable and included one replicate. ANOVA was used to determine the significance of each variable and the interactions between variables. Three reduced order models were derived, but large variations in absorptivity in the experiment resulted in large errors and inaccurate models. The data did show the average reduction in roughness over all the trails was about 20%, however several trials resulted in roughness reductions of over 50%. Future work will concentrate on reducing the absorptivity noise to produce more accurate models.
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    Stereolithography Process Resolution
    (2002) Sager, Benay; Rosen, David
    To build smaller parts in StereoLithography (SL) and detect some build errors before fabrication, a good understanding of process resolution is needed. A categorization of resolution factors into process-inherent and software-induced categories is presented in the paper. Results from several experiments testing different aspects of SL resolution illustrate the effects of these factors. A method based on offsetting algorithms is presented to determine as-built part crosssections and aid detection of possible build errors. A method that will enhance build resolution of SL parts is proposed.
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    Investigation of Part Accuracy and Surface Roughness in Rapid Freeze Prototyping Based Investment Casting
    (2002) Liu, Qingbin; Leu, Ming C.; Schmitt, Stephen M.
    The study as described in this paper is aimed at investigating the dimensional accuracy and surface finish of metal parts made by investment casting with ice patterns generated by rapid freeze prototyping. The process of investment casting with ice patterns is described and contrast with conventional investment casting with wax patterns is made. The selection of binder material for ceramic slurries and the need for an interface agent to separate the ice pattern from the ceramic slurry in the mold making process are discussed. The accuracy and surface finish of ice patterns and of the metal castings are presented and discussed. The parts used in this investigation include cylinders with vertical and slant walls and a turbine impeller.
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    Surface Characterization of Laser Polished Indirect-SLS Parts
    (2002) Ramos, Jorge A.; Bourell, David L.; Beaman, Joseph J.
    Surface analysis was performed on laser polished indirect-SLS samples made from 420 stainless steel sintered powder - bronze infiltrated. The goal was to determine variations from the as-received condition in surface chemical composition, morphological structure, presence of contaminants as well as the formation of new phases. Comprehensive characterization of the laser polished surfaces was performed using scanning electron microscopy (SEM), energy dispersive spectrochemical analysis (EDS), x-ray diffraction analysis (XRD) and Vickers hardness. A large quantity of carbon (i.e. > 29 wt%) was present on the as-received surface mostly from the polymer binder present in the green part. Although surface-shallow-melting is the principal mechanism for the roughness reduction of the as-received surface, the chemical composition of the latter after processing changed to a higher carbon and oxygen content and a lower copper content. Additionally, clusters were formed periodically over the polished surface consisting of Fe, Cr, Si and Al oxides. The surface analysis demonstrated that the laser polished surfaces differ significantly more from a morphological rather than a microstructural perspective.
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    Characterization of Selective Laser Sintering™ Materials to Determine Process Stability
    (2002) Gornet, T.J.; Davis, K.R.; Starr, T.L.; Mulloy, K.M.
    The Selective Laser Sintering (SLS) process has proved to be an excellent method for prototyping functional parts out of engineering thermoplastics such as polyamides. However, the material undergoes physical and chemical changes due to repeated heating cycles in the SLS equipment. This causes variations in powder characteristics and performance in the SLS process. With the increased utilization of SLS for direct manufacturing it is necessary to develop a characterization and testing system that can determine powder fitness to ensure process stability and part quality. Current powder recycling methodologies use an average virgin-to-used powder mixture. In a new approach, a testing mechanism to deliver a numerical, measurable material characterization will be discussed. Experimental results of repeated reuse of material and its resulting physical effects on mechanical properties, shrinkage, and chemical tests will be presented. A definitive testing and measurement process control will be shown to improve process stability and thus part quality and consistency.
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    Selective Laser Sintering of SiC/Polyamide Matrix Composites
    (2002) Gill, Toby; Hon, Bernard
    This paper presents an experimental study into the production of particulate Silicon Carbide/Duraform Polyamide matrix composites via the selective laser sintering (SLS) process. FEPA standard SiC grits, F240 and F360, were each individually blended with the commercially available Duraform Polyamide, to produce blend compositions of 50 and 60 volume percent SiC for direct SLS processing. A full factorial experimental approach was applied to examine the effects and interactions of laser power, scan speed, scan spacing and layer thickness, with regards to the mechanical and physical properties of sintered parts. Analysis of parameter interactions and individual main effects as well as Pareto analysis for all parameter combinations are presented for the responses of part porosity and strength.
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    Morphology of Direct SLS-Processed Stainless Steel Layers
    (2002) Taylor, C. Martin; Childs, T.H.C.; Hauser, C.
    This paper discusses work done to analyse the shape of stainless steel layers generated by direct selective laser sintering (SLS). Laser power, scan spacing and scanning speed have been varied, to investigate their effect on geometry. The relationship between scanning parameters and the qualities of sintered parts (dimensional uniformity, porosity and scanned track shape) is described. A PC-based finite element code, developed to simulate SLS, has been modified to match the conditions of experiments discussed above. A comparison is made between computer-generated and experimentally-generated parts.
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    System Integration and Real-Time Control Architecture of a Laser Aided Manufacturing Process
    (2002) Boddu, Mallikharjuna R.; Landers, Robert G.; Musti, Srinivas; Agarwal, Sanjeev; Ruan, JianZhong; Liou, Frank W.
    This paper discusses a hybrid deposition–removal manufacturing system being developed at the University of Missouri–Rolla. The system consists of a laser system, five–axis CNC machining center, and powder feeder system. A description of the control software, real–time control architecture, and integration of various subsystems to build the hybrid system is given. The interaction of the real–time controller with various sensors and subsystems to monitor and regulate the process is presented. The communication between integrated process planning for the system and real–time control is also discussed in this paper.
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    The Study of On-Line Waste Material Removal Procedures for Bridge Laminated Object Manufacturing (LOM) Process
    (2002) Chiu, Y.Y.; Liao, Y.S.; Hou, C.C.
    Focusing on the drawbacks inhered in the laminated object manufacturing (LOM), a new Bridge-LOM process and its associated building algorithm are proposed in this paper. The proposed Bridge-LOM process starts with the construction of the bridge structures to link a stack of 2-D geometry contours to the outer frame based on the proposed bridge building algorithm. Afterwards, laser is directed to cut along the contours, and then the upper pressing head is pushed down and the layers are bonded. This is followed by spraying some adhesive on the top of bonded layers. The procedures of cutting, bonding and adhesive spraying are repeated until the complete 3D part is produced. From the experiments, it is verified that the proposed Bridge-LOM process not only saves laser-cutting time, the time on waste material removal is also reduced significantly by more than 80%. Furthermore, the hollow bottle can even be fabricated.
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    Adhesive Bonding of Sheet for Laminated Metal Tooling
    (2002) Zak, Gene; Wang, Wendy Xu
    There exists a significant body of work on metal laminate tooling built by the “cut-stack-bond” approach; however, automation with this method is difficult. Building laminations by "stack-bond-cut" sequence, on the other hand, is more amenable to automation. Two main challenges of "stack-bond-cut" sequence are blind contour cutting and bonding of the sheet. In this study, we investigate the hot-roller method of thermoplastic adhesive bonding for the metal laminations. Metal sheet, having thermal characteristics significantly different from paper, poses its own specific problems. During the bonding process, in order to achieve good bond strength, appropriate heat and pressure must be applied. As the stack builds up, thermal and mechanical properties change. This inconsistency of process conditions can potentially lead to part warpage, unless carefully controlled. Temperature measurements with a thermocouple embedded into lamination stack showed the effect of bonding process parameters on the laminate temperature.