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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
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