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Rapid Prototyping & Manufacturing TechnologiesRapid Prototyping &ManufacturingTechnologiesObjectives:To understand the importance and applications of rapid prototyping andmanufacturing (RP&M) technologies in the product design anddevelopment processes.To understand the general function of prototype in the product design anddevelopment process.To appreciate the common types of rapid prototyping systems.To understand the basic steps in RP process.To learn the basic of Rapid Tooling process.1. IntroductionIn recent years, opening up local markets for worldwide competition has led to afundamental change in new product development (NPD). In order to staycompetitive, manufacturers should be able to attain and sustain themselves as"World Class Manufacturers". The manufacturers should be capable in deliveringproducts in fulfilling the total satisfaction of customers, products in higher quality,short delivery time, at reasonable costs, environmental concern and fulfill all thesafety requirements.In many fields, there is great uncertainty as to whether a new design will actuallydo what is desired. New designs often have unexpected problems. A prototype isoften used as part of the product design process to allow engineers and designersthe ability to explore design alternatives, test theories and confirm performanceprior to starting production of a new product. Engineers use their experience totailor the prototype according to the specific unknowns still present in theintended design.Rapid Prototyping technology employ various engineering, computer control andsoftware techniques including laser, optical scanning, photosensitive polymers,material extrusion and deposition, powder metallurgy, computer control, etc. todirectly produce a physical model layer by layer (Layer Manufacturing) inaccordance with the geometrical data derived from a 3D CAD model. RP candeliver working prototype at the early design stage of the new product cycle. Somanufacturers can use the working prototypes in bridging a multi-disciplinedPage 1IC Professional Training

Rapid Prototyping & Manufacturing Technologiesteam composed of the marketing, design, engineering and manufacturing peopleto design right at the first instance in catering for the customers.Rapid prototyping (RP) is rapid creation of a physical model. However, rapidprototyping is slowly growing to include other areas. So, Rapid Prototyping,Tooling and Manufacturing (RP&M) should be used to include the utilization ofthe prototype as a master pattern for tooling and manufacturing.1.1 Types of prototype for NPDBefore getting involves to the topic of RP&M, the fundamental concepts andapplications of prototypes should be obtained. Prototypes that will be required inthe product design and development process are commonly divided into thefollowing types.• 3D sketches• Cosmetic prototypes• Engineering / Functional prototypes• Samples for safety approval• Marketing Samples1.1.1 3D sketchesTraditionally product designer use foam, cardboard, clay or wood to make quickmodels. The designers may generate a lot of simple model a day to visualizedifferent ideas. They also interchange portions of different models by cut andpaste, or reshape the model to explore different possibility. Since it is the earlystage of the project, usually the models are not presented to outside clients,therefore colors and textures and surface finishing are not an issue.Among various RP technologies, Multi-jet Modeling (MJM) and 3D-printing (3DP)technologies is most suitable for 3D sketches not only because they are faster, butalso because they are less expensive and the models are easier to reshape.1.1.2 Cosmetic prototypesAs the name implied, the prototypes are used to evaluate the appearance andfeeling of the design, and get early comments from potential clients. Apart fromsolid and non-functional, cosmetic prototypes are the same as finished product inaspect, such as shape, color, texture and hardness.Most RP technologies can be used for cosmetic prototypes. However, those withbetter post-processing properties will have a competitive edge because a lot ofpolishing and painting will be applied on the model. In this perspective, SLA &MJM are easier to polish because of its smooth surface. FDM is more difficultbecause the part have to be cover with a layer of putty. SLS and LOM are amongthe most difficult, due to the tough nylon material and fiber strands of paper.'Concept modelers' is the choice where time is the most critical concern. Theseinclude droplet deposition systems such as InVision, Objet and ZCorp's machine.Page 2IC Professional Training

1.1.3 Engineering / Functional prototypesRapid Prototyping & Manufacturing TechnologiesIn engineering development, Engineers will evaluate the form, fit and function ofthe parts. The prototype will use the same material of the final product iftechnology permitted. If exact material is not available, the materials with similarmechanical, thermal and electrical properties are used. The SLS and FDM allow theuse of production grade plastic material, although the mechanical properties arenot exactly the same.1.1.4 Samples for safety approvalFor those products that are regulated by safety standards of importing country, atlease 5-10 product samples have to be submitted to the laboratory for eachapplication. If pilot run of the product is ready, the finish products will besubmitted. However, in most case the project is still in tooling stage, and samplesby PU duplication may be used if the laboratory accepts. 5 to 10 duplicates can beproduced in a day. PU duplicate cannot be used as substitution if the part underconsideration is subjected to high temperature, voltage and mechanical abuse. Inthis Rapid Tooling techniques can be used. Manufacturers have a choice to quicklybuild a mould and produce a small batch of sample parts in actual productionmaterial.1.1.5 Marketing SamplesAt a later stage when all design details are finalized and the project is in toolingstage, the marketing department will start the promotion campaign. A lot ofsamples may be distributed to clients. In this case, up to a hundred products maybe needed. Normally the samples will be made by RTV mould and PU duplicationtechnique. In many cases, these models are also used to take the picture thatappears in the package box or user manual.1.2 Differences between conventional machining and rapid prototypingConventional machining can produce prototypes using metal removal methodwith almost any type of engineering materials however there are only a limitedtype of materials for any particular type of RP&M systems. RP&M systems areusually used for making one or a few sample of prototype, while the number ofprototype produced in conventional machining can be adjusted as required. Thebasic working principle of RP technologies is totally different from conventionalmachining processes which build up a solid by mean of addition approach likeconstruction of the building. Hence the RP also started from foundation thengradually increase in height until it reached the top layer.Page 3IC Professional Training

Rapid Prototyping & Manufacturing TechnologiesFig. 1.1 Differences between conventional machining and rapid prototyping1.3 Why RP&MThe application of the RP&M in the NPD can resolves the Fuzzy Front End – themessy getting started period of NPD process - would be relatively costly andtimely. However using RP&M enable manufacturers to schedule the right productbeing developed in a timely manner is the most important winning strategy. Thecombination of the RP&M and CAD technologies in blending with traditionaltechnologies and gradually formation of cross-functional team are the strategiesfor survival or strategies for empowering organization, people and facilities.1.4 Limitations of RP&MHigh precision RP machines are still expensive at around US$ 100 thousands to 1million and not easy to justify economically and many service bureaus in providingthe physical prototypes output services. However, as the RP technologies aregetting more mature while RP manufacturers are facing more head-to-headcompetition, the price will go down significantly in the near future such as thelaunch of V Flash priced at US$ 10 thousands. Most of the budget RP systems aredifficult to build parts with accuracy under +/-0.02mm and wall thickness under0.5mm. This is sufficient for prototypes built for concept evaluation and functionaltest.However, prototypes that will be used as master pattern for downstreamprocesses always require a much higher and consistent accuracy. Although thereare quite a large variety of materials that can be used in most RP processes, thephysical properties of the RP parts are normally inferior to those samples thatmade in proper materials and by the traditional tooling. The RP parts are notcomparable to traditional Computer Numerical Control machined (CNC) prototypeparts in the surface finishing, strength, elasticity, reflective index and othermaterial physical properties.Page 4IC Professional Training

1.5 The future market profile of RP&M systemsRapid Prototyping & Manufacturing TechnologiesThe future market profile of the rapid prototyping/manufacturing industry willhave two specific niches. The first one will be focused on Digital DirectManufacturing (DDM) of engineering parts for not only testing form fit, functionalevaluation, but also can be directly used in products. The second niche will belooking at the market requirement in another point of view. It will focus onconcept modeling or 3-Dimensional printing for design verification, preliminarymarketing tool and manufacturability studies. In this case, the most importantconsiderations are speed and low cost. The accuracy and resolution requirement isminimal so far it can provide the designer a reasonable representation of thedesign.2. Common Types of Rapid Prototyping TechnologiesWhile there are many ways in which one can classify the numerous RP systems inthe market, one of the better ways is to classify RP systems broadly by the initialform of its material, i.e. the material that the prototype or part is built with. In thismanner, all RP systems can be easily categorized into (1) liquid-based (2) solidbasedand (3) powder-based.Liquid-based RP systems have the initial form of its material in liquid state.Through a process commonly known as curing, the liquid is converted into thesolid state. The Stereolithography Apparatus (SLA) falls into this category.Solid-based RP systems encompass all forms of material in the solid state. In thiscontext, the solid form can include the shape in the form of wire, roll, laminates,pellets and powders. The Selective Laser Sintering (SLS), Three-DimensionalPrinting (3DP) Fused Deposition modeling (FDM) fall into this definition.2.1 Stereolithography Apparatus (SLA) – Liquid based RPStereolithography Apparatus (SLA) technology fabricates three-dimensional, solidobjects resin using a computer-directed, ultraviolet (UV) laser beam to curesuccessive layers of photo-sensitive polymer resin in a vat.SLA part is fabricated by laser spot instead of continues scanning on the resinwhich forms a thin solid layer on the surface of the liquid resin through thephotopolymerization. Figure 2.1 shows the schematic diagram of this spotscanning mechanism.Polymerization is the process of linking monomers and oligomers into largermolecules (polymers). When photoinitiators in the SLA resin are energized by thelaser spot energy exposure (Ec value in mJ/cm2) will undergoes thephotopolymerization process. It creates a thin layer of solid resin with thicknessabout 2-3 times thicker than the layer thickness (overcure). The total thickness ofPage 5IC Professional Training

Rapid Prototyping & Manufacturing Technologiescontrol in ensuring the reaction conditions. For example, the chamber of SLA ismaintained at 28°C ± 1°C.Resins used in SLA process are mixture of photo-initiator, linkers, oligomers andmonomer mixture in liquid state, photonic energy source will trigger the chainreaction of polymerization. Two parameters penetration depth (Dp) and criticalexposure (Ec), which are vary from different resins, are as the primary input to theSLA machine for controlling the power and time of laser emission. The followingillustrate the underlying principle of the two important parameters;Penetration Depth (Dp) and Critical Exposure(Ec)When a beam of light hit the resin surface, it will cure a region of resin in theshape of a bullet. The intensity of the beam determined the extent of reaction andthe size of the bullet.The threshold exposure, Ec, is the energy required for the photopolymer changesfrom the liquid to the gel phase. In the process, D p and E c is primary characters ofthe resin provided by manufacturer. The SLA machine determine P L and V s on thefry by the relation that the draw speed of the laser V s proportional to (P L /E C )exp(-C d /D p ).C pD pE maxE cCritical depth, given by the functionC d =D p ln(E max /E c )The depth of penetration which thepower of laser decay to approx. E max /3The power of laser at resin surfaceCritical Exposure, a primary resincharacter, unit in mJ/cm 2Page 8IC Professional Training

Rapid Prototyping & Manufacturing Technologies2.1.3 Support StructureSupport usually need for liquid-based and solid-based RP systems in order to anchorthe part to the platform hence the part can be separated from the platform thuspreventing floating layers and make removal of the part became simple.Also support is needed for overhanging and tilted surfaces hence minimize part curland stabilize the part while being built. Self support angle is a predetermined anglefor the particular SLA RP system such that tilted surfaces with this angle from thehorizon needs no support.The supported surfaces are the overhanging down face of the part. Since supportsneed to anchor the surface at the contact point. Hence the surfaces in contact withthe support are rough and coated with resin gel after the part build completed. So donot place supports on surfaces where finish is important.PartPartProjectionStandFig. 2.4 SLA support structure, Left: curtain support. Right: fine-point supportSupport can be classified according to the support structure and the type of surfacesbeing supported. Support types include solid, box, web and fine point supports.Besides supports classified according to the geometry of the down face include point,line and surface supports.SLA uses Fine-point support style as the default support style, however when longand slender support is need then Curtain support style can be used to ensure thestrength of the support while the prototypes are build in the vat. Figure 2.4 showsboth SLA support styles.2.1.4 Building StylesThe rapid prototyping systems usually bundled with software which can control the buildstyles, generate supports, slicing of the STL files and creating control file for buildingthe prototype in the RP machine. There are Part build style, Support build style, PartRecoat style and the Support Recoat style in the SLA software called 3DLightyear.Part build style controls the laser when drawing the part. Different part build stylecan produce part in different patterns which include the solid part – the exact buildstyle, the hollow part for investment casting – Quickcast build style. The fast buildstyle which shortens the build time of the part by filling the part in alternate layers.Page 10IC Professional Training

Rapid Prototyping & Manufacturing TechnologiesSupport build styles control the laser when drawing the support. Curtain support orFine point support can be created by choosing different support build styles in SLAbuilding platform.Part recoat styles controls the recoating process including the dipping depth andspeed of the build platform and the speed and the number of recoats of the recoatblade.Support recoat styles controls the recoating process while building the support.2.2 Fused Deposition Modeling (FDM)2.2.1 Processes descriptionFused Deposition Modeling (FDM) was developed by Scott Crump, the founder ofStratasys. It was commercialized by Stratasys in 1991. FDM process create componentby extruding material (normally a thermoplastic material) through a nozzle thattraverses in X and Y to create each two-dimensional layer.Heaters which surround two separated nozzles keep the plastic at a temperature justabove its melting point so that it flows through the nozzle and forms the layeraccording to the tool path. In each layer separate nozzles extrude and depositmaterial that forms the parts and the support structure. The plastic hardensimmediately after flowing from the nozzle and bonds to the layer below. Once a layeris built, the platform lowers, and the extrusion nozzle deposits another layer and theprocess is repeated until the object is completed. Figure 2.5 show a schematicdiagram of FDM process.Fig. 2.5 Schematic diagram of FDM processesPage 11IC Professional Training

Rapid Prototyping & Manufacturing TechnologiesSupport structure can be removed manually or, when water soluble supports areemployed, they can be simply dissolved by put into particular chemical solution.However, soluble support is only available for building ABS model, other high meltingpoint plastic material such as polycarbonate (PC) and polysulphone (PPSF) are notapplicable.2.2.2 FDM materialThe build material is usually supplied in filament form with 1.8mm diameter, but thelayer thickness and vertical dimensional accuracy is determined by the extrusionnozzle diameter and the rate of feeding of the building material, which ranges from0.018 to 0.008 inches. In the X-Y plane, 0.001 inch resolution is achievable.Thermoplastic material is most often used which including Acrylonitrate ButadieneStyrene (ABS), Polycarbonate (PC), polysulphone (PPSF), and investment casting wax isdesigned for investment cast.ABSi ABS-M30* PC-ABS PC* ULTEM9085PPSF*Appearance Ivory White TanTensile Strength(MPa)Tensile Modulus(MPa)FlexuralStrength (MPa)FlexuralModulus (MPa)Notched IzodImpact (J/m)Heat deflection( o C)38 36 34.8 52 72 551993 2413 1827 2000 2220 206859 61 50 97 115 1101797 2317 1863 2137 2507 2206139 123 53.39 106 5995 96 326 127 153 189Density g/cm 2 ) 1.09 1.04 110 1.2 1.34 1.28Elongation atBreak (%)SupportStructure>10 4 1.2 3 4 3Soluble Soluble Soluble Bass Bass Bass*Material Available in ICPage 12IC Professional Training

Rapid Prototyping & Manufacturing Technologies2.2.3 Support StructureSupports in the form of solid type or box type are usually required for the Solid-basedRP system. Box type support is used in FDM. The support material used for FDMdepending on the type of model mater used for making the prototype and can beclassified into two main type – soluble support and break away support. The solublesupport uses a "water-soluble" material which turns into liquid in an ultrasonicheating tank filled with hot (70 degree F) amino based water solution for 4 hours, thesupport is then dissolved in the tank. However the soluble support is only suitable forABS grade model material as shown in the table above. Break away support is usedfor model material which melts at a higher temperature than ABS. Break away supportneed to be removed by hand tools upon the completion of the building of theprototype.The self support angle of FDM is 45 degree and 4 types of support styles are availablefor the creation of support namely Basic support, Sparse support, Surround supportand Break away support. The support curves can be created after the appropriatesupports style is determined.Basic supports will create supports under all part features that are exposed to air onthe underside. The top layer of each support column will have a solid fill and thelayers underneath will have a small air gap between toolpath passes. These passes arecalled the support raster curves. This type support is particular suitable for modelwith fine details in the down face however the build time is long and the moresupport material is used compared with the Sparse support.Sparse supports will create supports that use less material than basic supports. This isaccomplished by creating a new raster fill pattern that has a much larger air gapbetween raster. Like basic supports, the top layer of a support column is built with asolid pattern of raster. The next several layers have the basic raster pattern that has asmall air gap. Progressing downward, a new sparse support region is used below theseveral layers of basic support raster fill. The sparse support regions use a much largerair gap when building the tool path raster. In addition, the region is surrounded by asingle closed tool path-perimeter curve.Surround supports are used to surround small features or parts that require fewactual supports, but cannot stand upright on the platform during the part build.Surround supports will create the support tops just like basic supports but will alsosurround every layer of the model with a minimum thickness of supports.Break-away supports are similar to sparse supports but consist of boxes instead of acontinuous raster. There is no closed toolpath-perimeter curve around the breakawaysupports. They are easier to remove than other support styles for somematerials but build slower than sparse supports. Break-away supports are notrecommended for use with WaterWorks.Page 13IC Professional Training

Rapid Prototyping & Manufacturing Technologies2.2.4 ToolpathThe software which bundled with FDM is Insight which transforms the STL file into aCMB file. The CMB file contains information about the hardware setup, the tooth path(Road) for building the part and the details which control the movement of thebuilding platform and the FDM head. Curves in Insight are group into different setnamely part set and support set. The set contain information about the fill up patternof the empty space inside the slice curve.Fig. 2.6 Example of FDM ToolpathThe fill up pattern usually contain a perimeter and a raster fill as shown in figure 2.7.Different fill pattern for support and model can be achieved by configuring theparameters of the fill so 4 types of support styles is available to suit differentconditions.Fig 2.7 Illustrations of Raster and PerimeterPage 14IC Professional Training

Rapid Prototyping & Manufacturing TechnologiesThe fill up pattern of the part need to be investigated layer by layer to ensure there isno overfill. Overfill occurs when too much material is squeezed into a geometry ofless volume. Underfill occurs when the software doesn't detect enough room in whichto squeeze the raster road. Overfill will hinder the parts surface finish or even causepart to topple over. Hence overfill usually need to be fixed before the CMB file isloaded to the machine for building. Figure 2.8 shows the overfill and underfill ofdeposition.PerimeterOvefill RasterUnderfill rasterFig. 2.8 Descriptions of overfill and underfill2.3 Selective Laser Sintering (SLS)Selective Laser Sintering (SLS) was developed and patented by Ross House-holder in1979, but it was commercialized by Carl Deckard at the University of Texas in Austin inmid-1980s. DTM Corporation was first the company taking this technology intocommercial market and it was acquired by 3D Systems in 2001. The major competitorof 3D systems; EOS, a Germany based company existed in the market in 1994, whichstill enjoys a significant market share. The major difference of the machine among 3Dsystems and EOS is that 3D’s SLS machine can be processed multi material includingplastic, metal and resin sand but EOS’s machine is targeted for single application, i.e.EOS-S machine is solely for sand material processing.2.3.1 Processes DescriptionThe basic concept of SLS is similar to sterolothography, but the powdered polymerand/or metal composite material is sintered or melted by a laser that selectively scansthe surface of a powder bed to create a two-dimensional solid shape. Threedimensional object is then created by attaching together of the two-dimensionallayers.As in all rapid prototyping processes, the parts are built upon a platform that adjustsin height equal to the thickness of the layer being built and the commonly used layerthickness is 0.15mm. After every layer of scanning, building platform lower one layerthickness distant and a roller convey a new layer of material on top of the part surfacefor the next scanning and the process is repeated until the object is formed. Figure2.9 show a schematic of the selective laser sintering process.Page 15IC Professional Training

Rapid Prototyping & Manufacturing TechnologiesFig. 2.9 Schematic of selective laser sintering process(Source: CustomPartNet)Since the sintering operation is performed by high power laser, the building platformand the powder bed need to be pre-heated by infrared heaters and kept in a certaintemperature during processing to avoid part deformation. Nitrogen gas, as protectivegas, is launched into the working chamber throughout the sintering process toprevent oxidization reaction. Unlike SLA, special support structures are not requiredbecause the excess powder in each layer acts as self-support function while the partbeing built except processing of metal powder.Direct Metal Laser Sintering (DMLS) is the parented term used to describe the processof metal powder sintering developed by EOS Company. The major competitiveadvantage among DMLS and SLS provided by 3D systems is no further infiltrationprocess required in which SLS metal “green” part is required to be placed into afurnace, temperature in excess 900 °C, for removal of polymer binder and infiltratingwith bronze.Page 16IC Professional Training

Rapid Prototyping & Manufacturing Technologies2.3.2 SLS Material (Polymer)Physical Properties Units PA PA-GF AlumideTensile Modulus N/mm² 1700+/- 150 3200 +/- 200 3800+/- 150Tensile Strength N/mm² 45 +/- 3 48 +/- 3 46 +/- 3Elongation at Break % 20 +/- 5 6 +/- 3 3.5 +/- 1Flexural Modulus N/mm² 1240 +/- 130 2100 +/- 150 3000 +/- 150Charpy – Impact strength kJ/m² 53 +/- 3.8 35 +/- 6 29 +/- 2Charpy – Notched ImpactStrengthkJ/m² 4.8 +/- 0.3 5.4 +/- 0.6 4.6 +/- 0.3Izod – Impact Strength kJ/m² 32.8 +/- 3.4 21.3 +/- 1.7 NAIzod - Notched ImpactStrengthkJ/m² 4.4 +/- 0.4 4.2 +/- 0.3 NABall Identation Hardness kJ/m² 77.6 +/- 2 98 NAShore D-hardness kJ/m² 75 +/- 2 80 +/- 2 76 +/- 2Heat Deflexion t° °C 86 110 130Vicat SofteningTemperature B/50Vicat SofteningTemperature A/50°C 163 163 169°C 181 179 NARemark: PA is Polyamine (Nylon), GF is glass fiber reinforcement, Alumide is PA powder mixwith aluminum powder; the materials are used in EOS INT P system.Page 17IC Professional Training

2.4 Three Dimensional Printing (3DP)Rapid Prototyping & Manufacturing TechnologiesThe three Dimensional Printing (3DP) technology was invented at theMassachusetts Institute of Technology and licensed to several corporations. 3DPindeed is the innovation and further evolution of two-dimensional printingtechnology. The process is similar to the Selective Laser Sintering (SLS) process,but instead of using a laser to sinter the material, an ink-jet printing headdeposits a liquid adhesive that binds the material. The following mainly describes3DP technology which is employed in Z-corp 3D printing.2.4.1 Process descriptionThe 3D printing process begins with the powder supply being raised by a pistonand a leveling roller distributing a thin layer of powder to the top of the buildchamber. A multi-channel ink-jet print head then deposits a liquid adhesive totargeted regions of the powder bed. These regions of powder are bondedtogether by the adhesive and form one layer of the part. The remaining freestanding powder supports the part during the build. The processes repeated andsolid model is competed and underneath inside the powder bed. Figure 2.10show a schematic illustration of the 3DP processInput Binder MaterialPrint HeadFig. 2.10 Schematic of 3D printing technologyFeedingpistonAfter the part is finished, the loose supporting powder can be brushed away andthe removed by vacuum cleaner. Since the “green part” is very fragile, infiltrationof glue/ epoxy is needed to be applied on the part surface to improve thestrength of part. It should be noticed that any loose supporting powder shouldbe removed completely before performing infiltration to avoid generation ofugly surface.Page 18IC Professional Training

Rapid Prototyping & Manufacturing Technologies2.4.2 3DP MaterialMaterial used in Z-corp 3DP include plaster, starch and ceramic powders, plasterpowder is commonly used for making concept design model, it is most suitablefor concept proofing as the build speed is very fast, typically 2-4 layers perminute. Starch powder is particular used to produce master patterns forinvestment cast since it can be vaporized in high temperature. Ceramic powdercoated with resin is specially designed for making sand casting mould, i.e. Z-castis a special mixture of sand particle and resin for casting purpose.Although the build speed of 3DP is relatively fast compared with other RPprocesses, post-process is time-consuming and laborious. Infiltration is usuallyperformed by manual dipping of glue or epoxy resin. Wax-dipping has beingdeveloped and utilized to speed up the post-process but the part strength ismuch weaker than glue infiltration. A new powder system zp140 has been justdeveloped in which the parts can be cured by dipping into water or spaying onthe part surface.3. Workflow of RP processesThere are basically three stages of building physical RP models based on theCAD data, namely the pre-processing, building and the post processing.Whatever the CAD model is generated by solid modeling or surface modelingapproaches, most of RP machine accept only STL file as digital data input inwhich most commercial Engineering CAD system is capable to convert 3D CADmodel into STL format. The STL model is then slice into layers data set andtransfer to machine for building model. Completed RP model is then performedcorresponding post-processed operations such as cleaning, post-curing andinfiltration. Figure 3.1 shows the typical workflows of RP processesFig. 3.1 RP processes workflowPage 19IC Professional Training

Rapid Prototyping & Manufacturing Technologies3.1 Pre-processingThe first step in the RP&M process is virtually identical for all of the varioussystems, and involves the generation of a three-dimensional computer-aideddesign model of the object. A good, preferably solid CAD modeling or a totalenclosed surface – water tight – CAD model is a key component of success RPprocessing. The CAD file is then translated into a triangulation tessellated STLformat, which is the standard of the RP&M field. Figure 3.2 shows a typicalexample of STL model which is composed of triangles and each triangle isdescribed by a unit normal vector direction and three points representing thevertices of the triangle.Fig. 3.2 Example of STL model3.1.1 Verification and fixing of STL fileWhen one create 3D surface model using common surface modeler, there is verylittle concern on the orientation of the surface normal, as most of the tool pathgeneration algorithms can detect the material side correctly.However, when one generate STL data using these surface models, manyconverters just use the normal data straight from the NURBS surfaces – free formsurfaces, thus the STL files generated are not useable without repair.Triangles in an STL file must all mate with other triangle at the vertex and mustbe properly oriented to indicate which side of the triangle contains mass. ManySTL viewers like Magics RP from Materialise read a STL file to analysis and tocorrect, the connectivity and gap in the three-dimensional triangle matrix. Thisprocess is totally automatic and simple to operate. Figure 3.3 shows a “bad” and“good” STL file.Page 20IC Professional Training

Rapid Prototyping & Manufacturing TechnologiesHole exists in STL fileHole is filled by“Automatic Fixing”Fig. 3.3 “Bad” STL file is fixed “Good” STL file3.1.2 Part OrientationPart orientation has a significant effect on the final part quality and prototypingcost. The switching between individual layers takes a significant part of theoverall building time and hence must be properly optimized hence to reduce tobuilding time and the building cost. The part should be orientated with minimumheight in order to reduce the number of layers.For processes that need supports structures, part orientation should also beoptimized such that it would require minimal support hence reduce to buildingtime and the building material. The ultimate strength of the part will be affectedby its orientation within the print box. The part will be strongest along the Y-Axisand the X-Axis and less strong along the Z-Axis which is illustrated in figure 3.4Fig. 3.4 Effect of orientation to part strengthPage 21IC Professional Training

Rapid Prototyping & Manufacturing TechnologiesFurthermore, staircase effect will be appeared on the near flat curve surface.Hence proper orientation can produce a smooth external curve surface of theprototype. In addition the minimum wall thickness of the part can only be built insome particular orientation.3.1.3 Support Generation & EditingThe rapid prototyping systems usually bundled with software which allows theautomatic creation and editing of the supports. The software will initiallygenerate the supports for all overhang regions based on the default supportparameters; figure 3.5 shows the problem of missing support for overhanggeometry. After the creation, the support structure can be individually modify,edit, delete or add based on the part geometry. The region by region editing orcustomization for supports generation has strengthened the essential supportand also minimizing the building of unnecessary supports.Desired part or modelgeometryWithout supports, overhanging areas ofpart may peel away and damage thewhole modelFig. 3.5 Result of missing supports for overhanging areasProjectionDown-facing RegionStandUp-facing RegionFig. 3.6 SLA Fine-point supportSupport can reinforce delicate part while building and in the post processingstage. However over support for delicate part will increase the difficulties ofsupport removal and even destroy the fine details on the down face. Figure 3.7shows an example of over support.Page 22IC Professional Training

Rapid Prototyping & Manufacturing TechnologiesFig. 3.7 Over support of SLA part3.1.4 Slicing (Layer thickness)A STL model used for RP contains a collection of planar triangular surfaces. Thesefaces define an approximate boundary for the object. Horizontal layers of equalthickness are produced while slicing to produce the outer boundary of the part –slice curve. Then void and solid region of the slice curve can be identified andproper fill pattern can be created for part filling. Typical layer thickness ofcommonly RP system is ranged from 0.05mm to 0.15mm.3.1.5 Part BuildingThe prototype can be built in the RP machine according to the toolpath andcontrol codes generated by the software of the RP system. By laser scanning,disposition, sintering, etc and under limited working envelope with closedcontrol of the processing environment the machine will start the build at thebottom layer. Subsequent layer is added after the completion of the previouslayer until the final layer was build. Hence, RP process also refers to layermanufacturing.3.1.6 Post processingOnce the last layer on the part has been built, the prototype need to haveundergo some post processing processes such as removal of support, cleaning,depowder, drain excessive resin, post curing in SLA, infiltration of resin/wax, etc.The post processing is aimed to clean and reinforce the green part.Additional surface finish procedures such as sanding, sand blasting, painting oreven electroplating are normally employed for cosmetic prototypes.Page 23IC Professional Training

4. Rapid Tool ProductionRapid Prototyping & Manufacturing TechnologiesOnly when the production quantity is massive that the expensive tooling cost canbe justified. As a result, the way of how to produce tooling quicker and moreeconomically especially for small batch manufacturing becomes a big concern.Furthermore, in the product design and development process, there is always inneed of some intermediate tooling to produce samples for marketing, functionaltest, or production process planning and evaluation purposes. In this respect, RTis the ideal mean to fit the needs.Rapid Tooling (RT) is the result of combining Rapid Prototyping techniques withconventional tooling practices to produce small quantity of plastic or metalcomponents from electronic CAD data directly or indirectly. Direct RT technologysuch as Direct Metal Laser Sintering (DMLS) which fabricate production toolingfrom CAD data whereas Room Temperature Vulcanization (RTV) silicone rubbermould is the most commonly used indirect approach for plastic componentsduplication.4.1 Type of RT ProcessesLow volume (from 10 to 100)• RTV Soft ToolingIntermediate volume (from 100 to 1000)• Metal filled Epoxy Tooling• Direct Metal Laser Sintering4.2 RTV Soft ToolingRTV silicone rubber mould is one of the important kinds of soft tooling which isan effective, high fidelity and inexpensive way to create multiple copies of amaster prototype part. Indeed, this technology has been used by the industry formany years. The only thing new is that the master pattern is produced by the RPtechnology. The other common kind of soft tooling material is tooling gradePolyurethane.This technology is not specially designed for a particular RP process. In fact,master patterns produced from most RP processes are suitable to apply for thistechnology.RTV molds can faithfully duplicate details and textures present on the masterpattern. Apart from detail, geometry can also be fully duplicated from the masterpart when prototypes are removed from the mould. Great care should be takento ensure that the pattern is in perfect condition. After RTV mould is completed,it can be used to further produce limited quantity of prototypes with a widevariety of material properties.Page 24IC Professional Training

Rapid Prototyping & Manufacturing TechnologiesIts application is mainly to produce plastics or metal prototypes in small batch byvacuum assisted casting or gravity casting method. The casting materialsnormally used are PU, polyester, epoxy, tin-lead alloy (200 °C), pewter (230 °C)and zinc alloy (400 °C).The batch size is from several pieces to hundreds. Multiple moulds, sometimes,are required depend on the complexity of the parts. In fact, the ease ofproducing multiple moulds is one of the advantages of this technology.However, the process is tedious and required high skill workers attendance.4.2.1 Process DescriptionOne-piece mould approachThis process begins with a master pattern which normally output from RP systemdirectly. It requires to sand and polish the part surface well since the RTV mouldwill reproduce any and all surface defects on the master pattern, and in turn willtransfer them onto the final model. Then, the pattern attached with gatingsystem is mounted in a mould box. Silicone rubber is mixed with specific amountof hardener and poured into the mould box. Degassing in vacuum chamber ispreferred to avoid trapped air caused by mixing and pouring. After solidification,the mould is then spitted into mould halves according to the predeterminedparting lines. Figure 4.1 shows the RTV mould making process of one piecemould approach.Fig. 4.1 Processes of making RTV mould (one-piece mould approach)Page 25IC Professional Training

Rapid Prototyping & Manufacturing TechnologiesTwo-pieces mould approachFirstly, master pattern is prepared and laid horizontally inside a mould box withthe parting line built up by hand with model clay. Prepared silicone rubber ispoured inside the mould box to form one half of the mould. After solidification,clay is removed, the other half of the mould is produced by repeating the abovesteps with the master pattern turned upside down. Figure 4.2 shows the differentparting line surface of one-piece mould and two-pieces mould.Fig. 4.2 Left; one-piece mould Right; two-pieces mouldTwo-pieces mould is typically required when the parting line is difficult to bedetermined. Two-pieces mould approach requires less skill compared with onepiecemould. However, it requires double time to make the mould and thedimension accuracy of part is poor than one piece mould.Page 26IC Professional Training

4.2.2 Type of RTV Silicone RubberRapid Prototyping & Manufacturing TechnologiesRTV silicone rubber can be divided into two types; condensation and additiontypes, the following table shows the differences among them.FeaturesCondensation Type• Lower costs• Broader product range• Less sensitive to exact mixratio• Accelerator catalystsavailable to speed up cure• Mixing of grades possible toachieve desired hardnessAddition Type• Low shrinkage, below 0.1%• Marginally higher tensilestrength• Slightly tougher rubber• Need for careful and accuratemixing• Good abrasion resistance• Can be accelerated using heatShrinkageWhenTemperatureIncreaseWhenHumidityIncreaseWhenQuantity ofCuring AgentIncreaseSlightly higher than the additiontypeCuring Time decreases(5 o C----7hrs;25 o C-----5hrs;50 o C-----4hrs(max temp))Curing Time decreasesCuring Time decreases but thereare limits• Tolerant to the addition ofsilicone fluid as a softenerLowCuring Time decreases(50 o C-----2hrs;100 o C-----30min;150 o C-----10min;)Curing Time decreasesCuring speed will not be alteredbut will adversely affect thephysical properties.*Quantity of curing agent must becarried out as accurately aspossible.CuringImpedimentsRemarksNoBy product will come out.Dimensions of mould will beslightly affected. (about 0.5%)YesWarm the rubber mold to thecuring temperature before pouringresin into a thermally cured therubber mold to raise dimensionalaccuracy.Page 27IC Professional Training

Rapid Prototyping & Manufacturing TechnologiesMixing Ratio is a term used to state the amount of each material to be mixed ina multi-component material. The mixing ratios for two-part RTV products aredescribed on the individual product data sheets and are given as a ratio byweight of each material.Pot life is the length of time that a catalyzed resin system retains a viscosity lowenough to be used in processing. This is also known as WORKING LIFE orUSABLE LIFE.Curing condition is the condition which can provide the optimum properties fora silicone rubber. This typically depends on time and temperature.4.2.3 Considerations of making RTV mouldTo duplicate a good product by soft tooling, planning is very important as thepart may be blocked inside the mould if the parting surface is not well defined.All holes should be filled by tapes to separate individual mould half beforepouring of silicone rubber.For master pattern with flat surface, the parting surface should be located on theflat surface and use plastic type as a marking. For master pattern with free-formgeometry, parting line should be located on the position which gives lowesteffect to the appearance.It is important to evaluate the pattern if there are any undercuts that would lockthe casting in the mold. Small undercuts can be ignored since the silicone rubberis flexible material. To deal with some deep holes feature such as boss, metalinserts can be used to replace the silicon material by attaching the inserts to thepart before pouring of moulding material.4.3 PU CastingEven RTV mould can be used for different material, PU is the most popularmaterial accompany with RTV mould for producing plastic components. Thereare two different approaches for PU casting, Top-down approach (direct gate)and Bottom-up approach (by gravity).For Top-down approach, PU is poured into the mould directly through a gateconnected on top of the part. Firstly, weighted material and RTV mould are putinto a vacuum chamber for degassing. PU resins are mixed together inside avacuum chamber, it is then poured into the mould via a funnel and air isreintroduced simultaneously to force the PU material into the mould. Thismethod is suitable for casting small components such as jewelry that has finedetail. Figure 4.3 shows the processes of PU casing by this top-down approach.Page 28IC Professional Training

Rapid Prototyping & Manufacturing TechnologiesFig. 4.3 Steps of PU castingFor Bottom-up approach, PU material is poured into the RTV mould and filledinto the moulding cavity by gravity. Vent channels are need to be added at thetop areas of part to allow air out. This method is most suitable for large castingpart in which the mould is unable to put inside a vacuum chamber. Figure 4.4shows the different set up of top-down and bottom-up approachesMaterial inputRTV MouldMaterial inputVent channelsCavityFig. 4.4 Left; top-down approach Right; bottom-up approachPage 29IC Professional Training

Rapid Prototyping & Manufacturing Technologies4.4 Epoxy ToolingEpoxy tools are used to manufacture parts or limited runs of production parts.Expoxy tools are used for:• Plastics injection prototype Mould• Mould patterns for casting• Vacuum forming moulds• Sheet metal forming moulds• Reaction injection mouldsMould that is made of plastics is built from casting some special grade epoxyresins directly onto the RP master model. This mould making method does notrequire high precision machine tools as with conventional metal mouldproduction. This technology of direct transversal from the master model allowslarge reduction in mould production costs and time.In the past, plastics materials are not suitable for injection mould due to the lackof strength and the high shrinkage during curing. Many problems arise such asdamage during mould making and moulding process. However, a special gradeepoxy resin is developed for better strength and stiffness. Epoxy resin is athermoset plastic reinforced with composite materials that can be cast to shapebefore cured. This special grade epoxy resin is aluminum powder filled forstrength, stiffness and thermal conductivity improvement.The mould made by this process is only suitable for injection moulding ofplastics parts. Common plastics materials like ABS, POM, etc. can be producedfrom this mould in small batch size up to 3,000 pieces.4.4.1 Process DescriptionThe process of producing epoxy tooling is somehow similar as making RTV twopiecemould but usually double duplication techniques is used. A RP masterpattern is sanded and polished and the parting line is formulated by clay. A thinlayer of mould release agent is applied on the surface of the master pattern, RTVis then poured into the mould box. The RTV is used as the negative mouldmaster patterns for casting of metal epoxy in forming the mould cavity andmould core. As the density and viscosity of epoxy resin is relativity high,degassing is carried out by several times in order to extract out all of the trappedgases. After pre-curing, the master pattern is removed and the mould halves areput into oven step by step increasing the temperature to 280℃ for post thermalcuring.The mould halves are then turned to CNC machine for producing the sprue,runner, gate and ejecting system. The mould is completed and ready for plasticinjection.Page 30IC Professional Training

4.5 Direct Metal Laser Sintering (DMLS)Rapid Prototyping & Manufacturing TechnologiesDirect Metal laser Sintering (DMLS) builds solid metal parts directly frompowdered metals. It always used to build simple rapid tooling because of shortlead times, eliminate the cavity machining required. For advanced, coolingchannels and inserts can also be built in the rapid tools. Rapid tools using harder,tougher materials can be used to inject hundreds to thousands of plastic parts.Fig. 4.5 Example of DMLS insert for injection mouldingPage 31IC Professional Training

Rapid Prototyping & Manufacturing TechnologiesReferences• Wohlers, Terry T. (1999), Rapid prototyping & tooling, state of theindustry : 1998 worldwide progress report, Fort Collins, Colo. :Wohlers Associates, Inc.• Friedrich B. Prinz (1997), JTEC/WTEC panel on rapid prototyping inEurope and Japan : final report, Baltimore, Md.: Rapid PrototypingAssociation of the Society of Manufacturing Engineers• Lamnont Wood (1993), Rapid Automated Systems: An Introduction,New York: Industrial Press• Dearborn, Mich. (1994), Rapid prototyping systems : fast track toproduct realization : a compilation of papers from Rapid Prototypingand Manufacturing '93, Society of Manufacturing Engineers incooperation with Rapid Prototyping Association of SME• Chua Chee Kai, Leong Kah Fai. (1997), Rapid prototyping : principles& applictions in manufacturing, New York : John Wiley & Sons• Marshall Burns (1993), Automated fabrication : improving productivityin manufacturing, Englewood Cliffs, N.J. : PTR Prenrice Hall• Jerome L. Johnson (1994), Principles of Computer AutomatedFabrication, Irvine, Calif. : Palatino Press, c1994• D. Kochan (1993), Solid Freeform Manufacturing - Advanced RapidManufacturing, Amsterdam ; New York : Elsevier (Request)• Joseph J. Beaman (1997), Solid freeform fabrication : a new directionin manufacturing : with research and applications in thermal laserprocessing, Dordrecht ; Boston : Kluwer Academic Publishers(Request)• øyvind Bjørke (1996), Layer manufacturing : a tool for reduction ofproduct lead time, Trondheim, Norway : Tapir Publishers• Graham Bennett (1996), Second National Conference onDevelopments in Rapid Prototyping and Tooling, Bury St. Edmunds :Mechanical Engineering Publications• Preston G. Smith, Donald G. Reinertsen (1991), Developing productsin half the time, New York : Van Nostrand ReinholdBibliographyhttp://www.custompartnet.com/Rapid Prototyping Journal, Bradford, West Yorkshire, England Birmingham, AL: MCBUniversity Press Ltd.Prototyping Technology International, Surrey : UK & International PressTime-compression technologies. Europe, Tattenhall [England] : Rapid News PubThe rapid prototyping directory, San Diego, Calif. : CAD/CAM PubPage 32IC Professional Training