With accelerating growth and competition in today's global marketplace, manufacturers
face the daunting tasks of meeting changing market needs, maintaining market share, and
reasserting a technological edge. Now, more than ever, adopting new technologies is a key
component in ensuring the successful outcome of new projects--and in producing longterm
market success.Mechanical Engineerin

Kent, Nutt

English

With accelerating growth and competition in today&apos;s global marketplace, manufacturers
face the daunting tasks of meeting changing market needs, maintaining market share, and
reasserting a technological edge. Now, more than ever, adopting new technologies is a key
component in ensuring the successful outcome of new projects--and in producing longterm
market success.Mechanical Engineerin

Texas ScholarWorks

SELECTIVE LASER SINTERING AS ARAPID PROTOTYPING AND MANUFACTURING TECHNIQUEBy Kent NuttIntroductionWith accelerating growth and competition in today's global marketplace, manufacturersface the daunting tasks of meeting changing market needs, maintaining market share, andreasserting a technological edge. Now, more than ever, adopting new technologies is a keycomponent in ensuring the successful outcome of new projects--and in producing long-term market success.Over the last decade, great strides have been made in the advancement of conceptualdesign technologies, including the development and maturity of three-dimensional (3-D)CAD and CAE software tools. Additionally, the development and implementation of CAMand CIM technologies have streamlined mass production processes.Design for manufacturing (DFM), design for assembly (DFA), and concurrentengineering are additional techniques developed to enhance communications and interactionamong design, marketing, and manufacturing personnel. The collaborative effortscultivated by these techniques provide ongoing reality checks as products evolve fromconceptual design to final form.Amidst all this technology and innovation, remaining bottlenecks between conceptualdesign and mass production occur:1.) in the rapid creation of three-dimensional models and prototypes; and2.) in the cost-effective production of patterns, molds, and tools.These bottlenecks are especially prevalent where complex shapes or geometries areinvolved and occur primarily because traditional techniques, including manual methods,often require weeks--or even months.Although product designers and manufacturing engineers must be able to visualize andassess designs for form, function, fit, and other factors before designs can be finalized forproduction, there is only so much time that companies can afford to spend on the creationof models, prototypes, patterns, and tools. This is especially true in industries wheredeclining volumes and increasing varieties of parts and products must be produced.What's more, lengthy delays can prevent designers and engineers from going throughthe reiterations and fine-tuning necessary to create a design with superior qualities,functionality, manufacturability, and market potential.During recent years, several new technologies for quickly creating three-dimensionalrepresentations have emerged to address these needs and challenges. They are knownunder a variety of names, including rapid three-dimensional prototyping, desktopmanufacturing, solid free-form fabrication, and conceptual modeling, among others.131These technologies offer the capability to rapidly produce three-dimensional solidobjects directly from designs created by CAD, CAE, or CAM systems. Instead of waitingseveral weeks for a model, prototype, or pattern to be completed, these technologies canfinish the job in a few days--or even a few hours.Testing for Form, Fit, and FunctionalityAs evidenced throughout the manufacturing industry, one of today's most criticalrequirements is the ability to quickly fabricate prototypes that allow both a review of theproduct's proposed form and the testing and verification of fit, function, and otherspecifications. To provide accurate results, however, these prototypes must employmaterials with characteristics similar to those used in the final product.Unfortunately, early rapid prototyping technologies like stereolithography, which useonly photo-sensitive liquid polymers, have limited applications here.Another technology, however, the Selective Laser SinteringTM (SLS) processdeveloped by DTM Corporation provides greater potential and a wide range of applications.In contrast to stereolithography, the SLS process offers a multiple-materials approach torapid prototyping technology, addressing the need for functional, comprehensive designevaluations, while at the same time offering the ability to generate patterns and tools--andthe future potential for direct fabrication of parts using metals and other materials.How tbe Selective Laser Sintering (SLS) Process WorksAs the SLS process begins, a very thin later of heat-fusible powder is deposited into awork space container and heated to just below its melting point. An initial cross-section ofthe object under fabrication is traced on the layer of powder by a laser. The temperature ofthe powder impacted by the laser beam is raised to the point of "sintering," forming a solidmass. As the process is repeated, each layer fuses to the underlying layer, and successivelayers of powder are deposited and sintered until the object is complete.The laser beam intensity is modulated to sinter the powder only in areas defined by theobject's design geometry. In areas not sintered, powder remains loose and serves as anatural support for the next layer of powder and the object under fabrication.CAD and CAE: Conceptual Design Requirements for tbe SLS ProcessThe SLS process requires the use of CAD and CAE software, with designs createdpreferably in three-dimensional surface or solid form. Designs created in 2-D CAD or CAErequire modification prior to SLS acceptance and processing.132Design models created in CAD, CAE, or CAM software are entered into the rapidprototyping syste,n through a compatible interface known as the ".STL file. II This fileformat is currently the industry de facto standard and is a method used to convert CADdatabases into a form usable by rapid prototyping systems.The .STL file is transferred to the SLS machine for computer-based processing. Themodulated laser beam selectively describes the object's geometry based on the coordinatepoints. The design information is thus transferred from a computer representation toa real world, physical object through a unified, completely digital process.The SLS process: A. tangible realityThe SLS process has several inherent advantages that address the basic requirements forfast modeling, prototyping, and pattern-maldng within industry. These include:1.) Speed;2.) The additive-layer nature of the part building process; and3.) The ability to employ a variety of heat-fusible powdered materials.Speed: Using the SLS process a model or prototype can be produced at the rate of one-half to one-inch per hour, depending on the complexity of its geometry. A four-inch partcan conceivably be fmished in four to eight hours.The SLS process software also allows concurrent slicing of the part geometry fileswhile processing of the object is taking place. Non-SLS technologies currently requiretime-consuming, crossha~ching scans of various types of lasers intersPersed withre-application of photopolymer resins. This must take place before the part can be removedfor fmal curing.Moreover, no post-production curing is necessary with the SLS process, except whenceramic materials are used. In contrast, current implementations of non-SLS processesrequire some degree of post-production curing to completely harden the liquidphotopolymer resins.An additive process: Based on an additive-layer process, SLS technology does notrequire traditional dies or part-specific tooling and is particularly applicable where fewer,more complex designs are to be prototyped or modeled.The additive-layer nature of the SLS process also allows for the creation of verycomplex parts without the need for external support structures, clamping, or repositioningof specific portions of the design geometry. Designs with internal cavities, overhangs,notches within notches, and other intricate geometries, which are difficult to achievethrough other processes, are easily produced using the SLS process.Moreover, the unsintered powder that surrounds the fabricated part during the SLSprocess provides a customized support structure that is easily removed upon partcompletion.133Multiple materials: The SLS process can use a variety of materials. In fact, virtually anymaterial that softens and has decreased viscosity upon heating can potentially be used.Materials currently available include: polycarbonate, investment casting wax, and PVC.Materials commercially available by the end of 1991 include ABS plastic and nylon.Additionally, low-temperature ceramic parts can be fabricated with the SLS processusing polymer-coated ceramic powder, with curing as a secondary process. While not yetreleased for commercial use, ceramic materials will be available in the near future.The natural evolution of the SLS technology is also heading toward the use of powderedmetals and alloys. Current market research indicates that this capability will havewidespread application throughout manufacturing industries, primarily because more thanpercent of all design prototypes are currently made from various metals using conventionalprocesses.DTM is currently conducting tests using metal powdered with the SLS process. In fact,early laboratory research efforts in sintering brass, copper, aluminum, and cobalt at theUniversity of Texas at Austin have proven very successful. These efforts are continuingwith additional metal alloys and metal powder blends. Commercial use of metals isexpected to be a reality in the near future.Primary applications of SLS technologyPrimary applications of the SLS process are occurring in three major areas:1.) Visual representations (models);2.) Functional, durable prototypes; and3.) Production capabilities, including the creation of the molds, patterns, and toolsrequired for limited production runs and on-demand batch manufacturing.The advantages of the SLS process are significantly impacting product designcapabilities in manufacturing organizations across many industries, resulting in shorterdesign cycles and superior design. In effect, the use of the SLS process serves as a time-saving, communications-enhancing bridge between design and manufacturing.Specific industrial segments where the SLS process is in use include the automotive,aerospace, computer, consumer goods, electronics, foundry, and medical industries. SLStechnology also serves as a front-end process to conventional machining,mold-making, and investment casting processes.SLS Technology Applied to Investment CastingIn addition to its ability to rapidly transform CAD drawings into three-dimensionalmodels and prototypes, the SLS process provides the ability to quickly create wax patternsdirectly from CAD drawings--without tooling. These patterns are then used with thelost wax method.134Eliminating the tooling stage translates into numerous benefits for investment casters,including:1.) Minimized upfront tooling costs;2.) Significant time savings; and3.) The ability to prOduce complex shapes that were previously too difficult toprOduce via tooling.The SLS process and wax pattern-making are extremely well-matched for a number ofreasons:1.) The SLS process is the only process that can utilize investment casting wax.2.) With average tolerances ranging from +/- .002 to +/- .010 inches, the SLSprocess offers the accuracy required by investment casting applications.3.) The SLS process can easily create complex shapes and geometries that aredifficult to produce via other methods.4.) The problems, delays (as long as 100 hours for resin-based patterns), andcomplications sometimes associated with burnouts are virtually eliminated withthe SLS process.5.) Wax patterns created with the SLS process feature a surface finish that issuitable for most investment casting applications, typically 100 to 120 averagemicro inches RMS.Specific applications where the SLS process can be useful to investment casters include:1.) The creation of prototypes, short run parts, and marketing samples;2.) Process development and refinement of gating and metal shrink requirements;3.) Prototyping and creation of production tooling.Additional Applications for the SLS Process....Present and FutureBecause the SLS process utilizes an expanding and diverse variety of powderedmaterials and allows for the formation of complex geometries, a number of additionaltooling and production applications become possible, including the following:Short Run Tooling and Soft Tooling - Here, the SLS process can be used to create amaster pattern from which various types of soft tools, including those made of siliconrubber and epoxy, can be made. These tools can then be used to generate short runs ofparts for use in testing, marketing, and verification of fit and form. These short run partsalso can be used, in some cases, to meet custom manufacturing requirements.Spray Metal Tooling An SLS-created pattern made of polycarbonate, is coated withthin a layer of protective material, followed by sprayed-on layers of liquid metal to furthercoat all surfaces. The metal-coated pattern is then put in a container filled with moltenmetal. The metal cools, and a tool for casting additional parts is created. Because the toolis made of metal, usually zinc with epoxy or aluminum backing, it is more durable than softtools and can produce runs of up to several thousand parts, depending on the application.Plaster Cast Tooling - As with other tooling methods, an SLS-generated pattern can beused to create a plaster cast tool, which is then used to make steel and other metal parts.135Vacuum Form Tooling - The SLS process can be used to create the master form, fromwhich the vacuum-formed object will achieve its final shape. During the creation of theform in the SLS process, the form's porosity can be adjusted. This is an inherentadvantage because a master form created with a suitable level of porosity eliminates theextra step of drilling the dozens of tiny holes needed to allow air to pass through during thevacuum process. With the SLS-generated form, air from the vacuum passesdirectly through the porous material.Numerically-controlled (NC) tooling and path verification - An SLS-generated part canbe used to trace and program the tooling paths that run numerically-controlled machines.Electro Discharge Machining (EDM) - Upon availability of carbon materials for use withthe SLS process, it will be possible to quickly and affordably generate the carbon orgraphite electrodes used in electrode EDM. Currently, these electrodes are difficultand time-consuming to produce.Forging Dies - Drop-forge dies are made of steel or steel castings at a grade of 0.60percent carbon open hearth. Dies of this steel will forge mild steel, copper, and tool steel.SLS-generated wax patterns can be used to produce forging dies of steel castings. Apair of these dies can then be used to produce up to 20,000 pieces.Service Bureaus: Bringing SLS Technology to the MarketplaceTo fully understand customer requirements and how SLS technology and applicationscan meet these requirements, DTM has opened two SLS sales and service centers. Thesefacilities provide a low-cost, low-risk way for customers to utilize the SLS technologyand receive customized technical support as needed.The DTM service bureaus offer a staff of technical support personnel, advanced CADequipment, and multiple SLS 125 Systems. Customer designs are accepted as physicaldrawings and/or 2-D or 3-D CAD files in STL/IGES formats.DTM's Sales and Service Centers are located in Austin, Texas at the company'sheadquarters and in Brecksville, Ohio. Direct sales of SLS Systems to end users will beginin late 1991.For additional information on the SLS process and its applications, please contact DTMCorporation at 512/339-2922.####136SLSPATTERN...CASTING...IWaxPatternIInvestment CastingSLS & Metal ManufacturingSelective LaserSinteringIIPlasticPatternSandCastingConcurrent Tooling Intermediate ToolingTOOLING....MOLDEDPATTERN...IExpendablePatternToolingIExpendablePatternsIIWaxPatternToolingWaxPatternIIForgingToolingIDie CastingToolingISoftToolingWaxPatternISpray MetalToolingWaxPatternICASTING...Expendable InvestmentPattern CastingCastingForging DieCastingInvestmentCastingInvestmentCastingPARTS One-----.......... PartProduction Production ProductionParts Parts PartsProduction Hundreds of Thousands ofParts Parts PartsProductionParts

Selective Laser Sintering as a Rapid Prototyping and Manufacturing Technique

https://repositories.lib.utexas.edu/bitstream/2152/64328/2/1991-17-Nutt.pdf

Selective Laser Sintering as a Rapid Prototyping and Manufacturing Technique

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