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<p>CH2 STEREOLITHOGRAPHY</p> <p>StereoLithography (SL) is the first process ever developed in rapid prototyping field with the meaning of 3-dimensional printing. Charles Hull developed and 3patented the completed system in 1986. Then he founded 3D Systems, inc. to develop commercial applications of the process. Stereolithography builds plastic parts or objects a layer at a time by tracing a laser beam on the surface of a vat of liquid photopolymer. This class of materials originally developed for the printing and packaging industries, quickly solidifies wherever the laser beam strikes the surface of the liquid</p> <p>PROCESS</p> <p>Stereolithography uses additive fabrication method where a UV-sensitive photopolymer resin is cured by a UVlaser to build parts a layer at a time. Parts are traced by the laser beam on the surface of the photopolymer, causing it to cure and solidify the prototype layer. After each layer has been traced, the build platform lowers the part by a single layer thickness, typically 0.002" to 0.006", and sweeps a blade filled with photopolymer ("resin") across the part to deposit fresh SLA Resin.</p> <p>PROCESS</p> <p>This creates a new surface for the part and a subsequent layer is traced, fusing it to the previous layer. After each layer is built the Prototype is ready for post-processing and excess resin is removed postusing a solvent such as alcohol and cured using a uv light source.</p> <p>PROCESS PARAMETERSSLA 250/50HR SLA 3500 SLA5000 SLA7000 Laser type, wavelength, power Layer thickness mm Beam diameter mm Drawing speed HeCd,325nm, 6mW Solid state Solid state frequency tripled Nd:YVO4 354.7nm 160mW Nd:YVO4 354.7nm 216mW 0.05-0.1 0.050.05-0.1 0.05Solid state frequency tripled Nd:YVO4 354.7nm 800mW 0.0254-0.127 0.0254-</p> <p>0.06250.0625-0.1</p> <p>0.060.06-00.08</p> <p>0.20-0.30 0.20-</p> <p>0.20-0.30 0.20-</p> <p>0.23-0.28 to 0.230.6850.685-0.838 2.54-9.52 m/s 2.54-</p> <p>635 mm/s</p> <p>3.45 m/s</p> <p>Up to 5.0 m/s</p> <p>Max part weight, Kg</p> <p>9.1</p> <p>56.8</p> <p>68.04</p> <p>68.04</p> <p>PROCESS PARAMETERSElevator resolution and repeatability mm Vat capacity,L 0.0025 0.00177,+/0.00177,+/0.005 0.00177,+/0.00177,+/0.013 0.001,+/0.001,+/- 0.001</p> <p>32.2</p> <p>99.3</p> <p>253.6</p> <p>253.6</p> <p>Max build envelop ,mm Operating system Weight kg</p> <p>250 x 250 x 250</p> <p>350 x 350 x 400</p> <p>508 x 508 x 584</p> <p>508 x 508 x 600</p> <p>MSMS-DOS</p> <p>WINDOWS NT 1100</p> <p>WINDOWS NT 1363</p> <p>WINDOWS NT</p> <p>461</p> <p>1455</p> <p>BUILD STYLES</p> <p>ACES STARWEAVE QUICKCAST</p> <p>Z</p> <p>ACESX</p> <p>Y</p> <p>Line Width</p> <p>Hatch Spacing</p> <p>STARWEAVEX X</p> <p>Y</p> <p>Y</p> <p>Hatch Spacing</p> <p>Part Border</p> <p>Offset distance is half the hatch spacing</p> <p>QUICKCAST</p> <p>First Section Second Section</p> <p>Part Border</p> <p>Vertex of one section is the centroid of the above previous section</p> <p>ADVANTAGES</p> <p>Unattended building process - The system is very stable. Once started the process is fully automatic and can be unattended until the process is completed. Good dimensional accuracy - The process is able to maintain the dimensional accuracy of the built parts to within +/-0.1mm. +/Good surface finish - Glass-like finishing can be obtained on the Glasstop surfaces of the part although stairs can be found on the side walls and curve surfaces between build layers. The process is of high resolution and capable to build parts with rather complex details 3D Systems Inc. have developed a software called "Quick cast" for building parts with hollow interior which can be used directly as wax pattern for investment casting It is the most widely used process in the RP field</p> <p>DISADVANTAGES</p> <p>Curling and warping - The resin absorb water as time goes by resulting curling and warping especially in the relatively thin areas. Relatively high cost (US$200-500K) - However, it is anticipated (US$200that the cost will be coming down shortly. Narrow range of materials - The material available is only photo sensitive resin of which the physical property, in most of the cases, cannot be used for durability and thermal testing. Post curing - The parts in most cases have not been fully cured by the laser inside the vat. A post curing process is normally required. High running and maintenance cost - The cost of the resin and the laser gun are very expensive. Furthermore, the optical sensor requires periodical fine tuning in order to maintain its optimal operating condition which will be considerable expensive.</p> <p>APPLICATIONS </p> <p>Prototypes for concept models FormForm-fit for assembly tests and process planning Models for investment casting, replacement of the wax pattern Patterns for metal spraying, epoxy moulding and other soft tooling</p> <p>Stereolithography Models Aid Surgeons with Ear ImplantsFor the prosthetic ear implant, prosthesis's began with a three-dimensional computed tomography scan. Data was used to create virtual models of the soft head tissue, the healthy ear and the bone structure at the implant site</p> <p>Three-dimensional software was used to create a mirror image of the patient's existing ear. The ear was then virtually positioned in the correct place. Cylinders, representing the implants, were positioned on the virtual ear, and soft tissue was virtually removed to reveal the points at which the implants would intersect with bone. After checking bone quality, a virtual block was created to overlap the head and implants. The skull and implant cylinders were subtracted from the block to create the template design, which was produced. After sterilisation, the template was placed on the patient's head to indicate to the surgeon where to drill.</p>