Browsing by Subject "Selective Laser Sintering"
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Item Advances in SLS Powder Characterization(University of Texas at Austin, 2011-08-17) Amado, A.; Schmid, M.; Levy, G.; Wegener, K.This paper introduces a new Selective Laser Sintering (SLS) powder characterization methodology. A better understanding regarding powder flow processing range is targeted. Intrinsic properties of polymers are given from the basic chemical structure and non-intrinsic ones describe characteristics caused from pre-processing and production. The non-intrinsic ones are dedicated to the powder. Understanding the particle size distribution and shape coupled with its ability to flow under the particular SLS processing conditions is desired. In this direction, a system called Revolution Powder Analyzer is employed and the dynamic powder behavior is characterized in nearly roll spreading conditions. This allows a sensitive differentiation of powders regarding their flow-ability and predicts, to a certain extent, the behavior under SLS conditions.Item Advances in the Production of Infiltrated Aluminium Parts Using Selective Laser Sintering(2004-08-20) Sercombe, T.B.; Schaffer, G.B.Recent advances in a rapid freeform fabrication process for the production of aluminium parts are considered. The methodology involves the formation of an unconstrained, resin bonded aluminium powder part by Selective Laser Sintering, the burnout of the resin, the partial transformation of the aluminium into a rigid aluminium nitride skeleton by reaction with the atmosphere under a magnesium/alumina blanket and the subsequent infiltration with a second aluminium alloy. Here we describe the process and consider potential applications. Strategies for controlling the growth of the aluminium nitride are also to be discussed.Item Assessing Energy Requirements and Material Flows of Selective Laser Sintering of Nylon Parts(University of Texas at Austin, 2010) Telenko, Cassandra; Seepersad, Carolyn ConnerSelective laser sintering (SLS) is a prominent technology for rapid manufacturing (RM) of functional parts. SLS and competitive RM technologies are generally assumed to be more environmentally sustainable than conventional manufacturing methods because the additive process minimizes tooling, material waste, and chemical fluids. A thorough life cycle analysis (LCA) of the environmental impacts of SLS has yet to be published. This study focuses on a section of the SLS part life-cycle. It tracks the nylon powder material flows from the extraction and synthesis of the material to SLS part production. Basic material properties and environmental effects are reported. Estimates of material waste and energy use are also reported and compared with those of injection molding.Item Ceramic Structures by Selective Laser Sintering of Microencapsulated, Finely Divided Ceramic Materials(1992) Vail, N.K.; Barlow, J.W.The feasibility of producing ceramic green parts by Selective Laser Sintering from microencapsulated, finely divide ceramic powders has been reported in an earlier paper. Post-processing of a silica/zirconium orthosilicate system and an alumina system, both utilizing a polymer binder in the form of a coating, are discussed in this paper. Ceramic green parts require postprocessing to remove the intermediate polymer binder and to impart strength properties to the ceramic bodies. In this paper, the use of ceramic cements and high temperature firing to realize strengths will be discussed. The effects of cement concentration and controlled drying rates on the strengths and dimensional accuracy of the ceramic bodies are also discussed.Item Comparison of Compression Molding and Selective Laser Sintering Processes in the Development of Composite Bipolar Plates for Proton Exchange Membrane Fuel Cells(University of Texas at Austin, 2012-08-18) Taghipour, Ehsan; Leu, Ming C.; Guo, NannanBipolar plates are key components of Proton Exchange Membrane (PEM) fuel cells. They carry current away from the cell and withstand the clamping force of the stack assembly. Therefore, PEM fuel cell bipolar plates must have high electrical conductivity and adequate mechanical strength, in addition to being light weight and low cost in terms of both applicable materials and production methods. In order to attain these goals, we have manufactured graphite-carbon-polymer composite plates using Compression Molding (CM), which is suitable for mass production, and Selective Laser Sintering (SLS), which is suitable for making prototypes. In this paper, the electrical conductivity and flexural strength of the bipolar plates fabricated using the CM process versus constitutive materials are experimentally studied. The properties of bipolar plates fabricated using the CM process are compared with those of plates fabricated using the SLS process. Natural graphite (NG), synthetic graphite (SG), carbon black (CB), and carbon fiber (CF) are used as the constitutive materials for both processes, with epoxy resin employed as the binder matrix. By varying the volume fraction of each constituent, the distribution of the electrical conductivity and flexural strength of parts made using the CM and SLS processes are obtained, and the similarities and differences of the effects of the various constituents between these two processes are compared.Item Comparison of Material Properties and Microstructure of Specimens Built Using the 3D Systems Vanguard HS and Vanguard HiQ+HSSLS Systems(2007) Silverman, T. J.; Hall, A.; South, B.; Yong, W.; Koo, J. H.The HiQ upgrade to the 3D Systems Vanguard selective laser sintering (SLS) machine incorporates a revised thermal calibration system and new control software. The paper compares the tensile modulus, tensile strength, elongation at break, flexural modulus, Izod impact resistance and microstructure of two batteries of standard specimens built from recycled Duraform PA (Nylon 12). The first set is built on a Vanguard HS system and the second on the same system with the HiQ upgrade installed. The upgrade reduces user intervention, decreases total build time and improves surface finish. However, using the default processing parameters, tensile, flexure and impact properties are all found to decline after the upgrade is installed.Item Controlled Local Properties in the Same Part with Sintaflex A New Elastomer Powder Material for the SLS Process(2005) Levy, Gideon N.; Boehler, Paul; Martinoni, Raffaele; Schindel, Ralf; Schleiss, PeterA new powder material for the SLS (Selective Laser Sintering) process was recently released. The material is a result of fruitful research programs involving industry and university. The well known and widely used DuraFom™ (PA12) and theCastForm™ (PS) SLS-materials were developed by the same team. In the search for new powder materials many properties of the candidate polymer, e.g. the pulverization, the laser absorption and sintering parameters have to be tuned carefully. Previous Elastomer options materials were poor in strength, detailing, and long-term use. The new product overcomes most of the known deficits. It open completely new practices in many branches like: automotive, house appliances, office equipment, foot ware, medical, and many more. The Sintaflex has a Shore hardness variability 45-75 A and Elongation up to around 300%. The attainable yield strength range is 1.3 - 4.2 MPa. The resolution on the SLS part is up to 0.6 mm. It is positioned in good agreement compared with other commonly used injection plastics. Furthermore, the appeal of all SFF process beside geometry and complexity is thought in varying locally the mechanical properties. Some published patents make suggestions in this direction. The new material, due to the particular properties range in function of the sintering parameter, allows first time to realize this wish. The generated part has controlled variable local properties; a new and unique opportunity opens for the SLS process. The paper describes the basic material properties. Further the main sintering parameters are describes and indications on machine settings are given. RP (Rapid Prototyping) applications and the recent practical experience are illustrated. Distinctive examples of local variable properties in the same part and given limits are shown. Some conclusions are stated.Item Cryogenic Mechanical Alloying of Poly (ether ether ketone) - Polycarbonate Composite Powders for Selective Laser Sintering(1999) Schultz, J.; Kander, R.; Suchicital, C.Mechanical alloying is a solid state processing technique traditionally used in the metallurgical industry to extend solubility limits in alloy systems. Mechanical alloying can also be used to blend polymer systems at ambient or cryogenic temperatures. In this work, cryogenic mechanical alloying was employed to create composite powders of Poly (ether ether ketone) (PEEK) - Polycarbonate (PC) for use in selective laser sintering applications. The microstructural development of the PEEK-PC system that occurs during laser sintering and the effects of this microstructure on mechanical properties of the laser sintered parts was investigated.Item Design and analysis of a volume adjustable transtibial prosthetic socket for pediatric amputees in developing countries(2009-12) Vaughan, Meagan Renee; Crawford, Richard H.; Seepersad, Carolyn C.For pediatric amputees in developing countries, where characteristically rapid growth of children is compounded by a lack of medical services, maintaining proper socket fit is a challenging but necessary endeavor. A socket design that adjusts for radial and longitudinal growth will allow patients to wear the same socket for a longer period of time saving them the expense of subsequent fittings and hardware. Manufacture of such a socket poses a challenge for contemporary manufacturing processes. Due to its ability to rapidly manufacture complex part geometries, Selective Laser Sintering (SLS) is particularly suited to this application. Several preliminary design concepts for a volume adjustable transtibial SLS prosthetic socket for pediatric amputees in developing countries have been generated. These current design concepts utilize fasteners such as ratchet hooks and threads. Results from design and validation of theoretical models of these fastener concepts are the focus of this thesis.Item Design and Manufacture of an Attachment Fitting for Transtibial Prosthetic Sockets Using Selective Laser Sintering(2004) Burhan, Danny; Crawford, RichardThe focus of this work is using selective laser sintering to manufacture transtibial prosthetics sockets with compliant features to relieve contact pressure in sensitive areas. Each of these sockets requires an integrated attachment fitting to connect to the pylon and foot using standard hardware. Several design concepts of an attachment fitting are presented and compared. The design concepts were tested using a tensile test machine and analyzed using ground reaction force data to ensure a structurally sound connection. The resulting design employs standard hardware while maintaining the integrity of the connection for a normal gait cycle.Item Development of a feedforward laser control system for improving component consistency in Selective Laser Sintering(2019-06-18) Phillips, Timothy Bryce; Beaman, Joseph J.; Milner, Thomas; Crawford, Richard; Seepersad, Carolyn; Fish, ScottSelective Laser Sintering makes up a significant portion of the polymer additive manufacturing market and is often the process of choice for structurally significant polymer components. With its expanding market, especially among end-use components, comes a growing need for improving reproducibility. Components built using Selective Laser Sintering display a large range among their mechanical properties and it has been shown that the thermal history of the building process has a strong influence over these variations. Temperature fluctuations of just a few degrees can mean the difference between scrapped parts or those with excellent mechanical and dimensional properties. This dissertation will introduce a novel method of reducing temperature and mechanical variations among parts. Physical simulations and empirical measurements of laser-polymer interaction are evaluated and used to guide development of an advanced laser power controller. The feedforward control system developed uses thermal imagery and dynamic surrogate modeling to systematically modulate laser energy impinging on the polymer surface to homogenize post-sintering temperatures. Results from thermal and mechanical tests will be presented, showing the laser control system is capable of reducing standard deviations by up to 57% for post-sintering temperature and 45% for ultimate flexural strength.Item Development of Nanocomposites for Solid Freeform Fabrication(1993) Manthiram, A.; Chi, F.; Johnson, F.; Birmingham, B.R.; Marcus, H.L.Nanocomposites in which the constituents are mixed on a nanorneter scale can provide important advantages in the Selective Laser Sintering (SLS) and Selective Laser Reactive Sintering (SLRS) processes. The larger surface area and grain boundaries in the nanocolnposites compared to that in the conventional microcomposites are expected to enhance the solid state diffusion during laser irradiation as well as during any other subsequent processes. Our strategy is to design and develop nanocomposites in which one nanosize cOlnponent has a lower melting point than the other nanosize component, either of which can serve as the matrix phase. The nanoscale dispersion of the low melting component can aid the sintering process during SLS or SLRS. Nanocomposite powders of AI203-COOx, Ab03-NiO, A1203-CO and A1203-Ni have been synthesized by sol-gel processing and are evaluated by SLS.Item Direct Laser Sintering of Borosilicate Glass(2004-08-04) Klocke, F.; McClung, A.; Ader, C.Despite the advantages that selective laser sintering (SLS) offers in terms of material availability, many materials have yet to be explored for feasibility and even fewer are available on a commercial basis. This paper presents initial investigations for one such material, borosilicate glass, which could be of particular interest to filter manufacturers because it presents an attractive alternative to the conventional, time-consuming way of producing filters of various porosity classes. Process results are presented including a determination of the optimal parameter window and the effect of processing parameters on the density and surface quality. The effects of thermal post-processing and the inclusion of an additive are also discussed.Item Effect of Different Graphite Materials on Electrical Conductivity and Flexural Strength of Bipolar Plates Fabricated by Selective Laser Sintering(University of Texas at Austin, 2010-09-23) Guo, Nannan; Leu, Ming C.Graphite is an excellent material for bipolar plates used in Proton Exchange Membrane (PEM) fuel cell due to its great chemical resistance, but the brittle nature makes it difficult to manufacture. Selective Laser Sintering (SLS) based on layer-by-layer manufacturing technology can fabricate graphite bipolar plates with complex gas flow channels. To improve the performance of bipolar plates including electrical conductivity and flexural strength, different graphite materials (natural graphite, synthetic graphite, carbon black, and carbon fiber) were investigated to fabricate test samples. These samples then went through post processing including carbonization and infiltration. The results show that bipolar plates with electrical conductivity of 380 S/cm and flexural strength of 40 MPa are obtained from proper combinations of natural graphite and carbon fiber, which are higher than the target values set by the Department of Energy.Item Effect of In-Plane Voiding on the Fracture Behavior of Laser Sintered Polyamide(University of Texas at Austin, 2011-08-17) Leigh, David K.; Bourell, David L.; Beaman, Joseph J. JrThe primary contributors to poor mechanical properties in polyamide materials used during Selective Laser Sintering® are qualified. Methods to quantify the decreased mechanical properties, including Scanning Electron Microscopy (SEM) of fracture surfaces, are compared against each other and against mechanical properties of components fabricated using multiple process parameters. Of primary interest are Ultimate Tensile Strength (UTS) and Elongation at Break (EOB) of tensile specimens fabricated under conditions that produce varying degrees of ductile and brittle fracture.Item The Effects of Dry Heat Sterilization on Parts Using Selective Laser Sintering(University of Texas at Austin, 2010) George, Mitchell J.; Crawford, Richard H.Selective Laser Sintering (SLS) is a manufacturing process that can build arbitrarily shaped parts without part specific tooling. Its advantages have been employed in many different fields, one of these being medical surgery. Currently, SLS is limited in medical applications as a pre-operative modeling tool. For SLS manufacturing to progress in areas like compliant surgical tooling and patient specific bone matrices, concurrent work is needed to investigate the effects of medical sterilization on SLS materials. This paper presents the results of sterilization experiments on SLS parts built from nylon 11. To simulate the process of introducing tools into a sterile environment, these specimens were subjected to multiple rounds of dry heat sterilization. Changes to the dimensions, tensile strength and flexibility were recorded and analyzed. It was found that the specimens’ dimensions remained relatively constant. Both the tensile modulus and the flexural modulus decreased as the sterilization cycles progressed. The tensile modulus decreased by 25% and the flexure modulus decreased by 19% after ten rounds of sterilization.Item The Effects of Pre-Alloyed Steels Powder Compositions on Build Quality in Direct Metal Laser Re-Melting(2004) Akhtar, SP; Wright, CS; Youseffi, MItem Experimental feasibility of Electrochemical Infiltration of Laser Sintered Preforms(University of Texas at Austin, 2010-09-23) Goel, Abhishek; Bourell, DavidThis research deals with the experimental feasibility of room temperature infiltration of Selective Laser Sintered preforms with metals. The existing principles of electrochemical deposition techniques were adapted and modified for carrying out the infiltration at low temperatures. Electroless and electrolytic deposition processes were adapted and modified to carry out metal ion infiltration and deposition within interconnected pores. The electrolytic infiltration process was modified by inserting a conductive graphite cathode in the center to draw the positive nickel ions through the interconnected porous network and to deposit them on the pore walls. Forced diffusion method was also attempted by forcing the electrolyte through the preform at high pressures. One of the major benefits of electrochemical infiltration is low processing temperature. Low temperature reduces both energy consumption and associated carbon-footprint and also minimizes undesirable structural changes. Both conductive and non-conductive preforms may be electrochemically infiltrated, and MMCs produced by this method have potential for use in structural applications. This research is sponsored by the National Science Foundation, Grant CMMI-0926316.Item Experimental Study of Polymer Electrolyte Membrane Fuel Cells using a Graphite Composite Bipolar Plate Fabricated by Selective Laser Sintering(University of Texas at Austin, 2012-08-16) Guo, Nannan; Leu, Ming C.Selective Laser Sintering (SLS) can be used to fabricate graphite composite bipolar plates with complex flow fields for Polymer Electrolyte Membrane (PEM) fuel cells. The additive manufacturing process can significantly reduce the time and cost associated with the research and development of bipolar plates as compared to other fabrication methods such as compression molding. In this study, bipolar plates with three different designs, i.e., parallel in series, interdigitated, and bio-inspired, were fabricated using the SLS process. The performance of these SLS-fabricated bipolar plates was studied experimentally within a fuel cell assembly under various operating conditions. The effect of temperature, relative humidity, and pressure on fuel cell performance was investigated. In the tests conducted for this study, the best fuel cell performance was achieved with a temperature of 75℃, relative humidity of 100%, and back pressure of 2 atm.Item Fabrication of Electrically Conductive, Fluid Impermeable Direct Methanol Fuel Cell (DMFC) Graphite Bipolar Plates by Indirect Selective Laser Sintering (SLS)(2008-09-10) Alayavalli, Kaushik; Bourell, David L.Graphite bipolar plates are highly desirable due to their properties of high electrical conductivity and low weight but are associated with prohibitive machining costs arising from poor mechanical properties. Bipolar plates made by indirect Selective Laser Sintering (SLS) offer the advantages of complex part production in shorter times at lower cost. Due to the nature of the SLS process, the as-produced (green part) plates are porous and possess low electrical conductivity which can be improved by carbonizing the phenolic resin binder at high temperatures (brown part). It has been found that the electrical conductivity increases significantly (> 200 S/cm) with a corresponding increase in pyrolyzing temperature which correlates well with literature on the carbonization of phenol formaldehyde resins. The brown parts are subsequently infiltrated with low viscosity (~5 - 10 cps) cyanoacrylate to seal up the open pores, rendering the plates fluid impermeable.
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