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Contd... |
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Set-up : |
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A LASER curable photopolyner liquid is kept in a tank.There is a Lens used to focus LASER on photopolymer.There is elevator which can be moved in vertical direction. This motion is used to expose new layer after exposing one layer to light.There is mirror used by rotating which we can achieve movement of LASER beam in one direction. Typically two mirrors are used so that scanning in two directions (perpendicular to each other) can be done. For sake of simplicity we have shown only one mirror. |
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Procedure: |
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LASER curable photopolymer is taken into a tank. Elevator which is initially above liquid level in tank is dipped into tank to certain depth & agin brought up so that liquid of suitable thikness is on the top of it. Then it is exposed to LASER. Here we are scanning the section line by line (Vector scan).For detain understanding of scanning see animation. One thing to mention is that as scanning is line by line, the actual section will be slightly different from desired one. There is slight error as the scanning is done line by line.(generally accuracy is 5-10% which can be tolerated in case of large sections but in case of submicron components it can not be tolerated.This is the limitation of this type of process. This is used to build components having dimensions above 30 micron size.we can use this process for compnents having dimensions less that 30 micron, but it will be costly & also it may persist accuracy problem. Once the section is built, the elevator is dipped again so that surface tension effects will gone & once again it is brought up so that suitable thickness of liquid is on top.Then same procedure is repeated for next section which will be built on previous section. |
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Factors affecting resolution of components: |
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Laser intensity. |
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Motion of the beam. |
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Photopolymer/ monomer used. |
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Focusing. |
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Exposure
time. |
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In case of ceramic materials we use ceramic powder & also use process of laser sintering. |
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Some Variations:
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In the set-up discussed above we have fixed tank & moving optics(i.e. Rotating mirrors) The problem with the set-up discussed above is that focal point of LASER beam is not fixed which changes as mirrors are rotated. So the focal point may not be exactly on the liquid surface. It may be slightly above or below the liquid surface. To avoid it we can used Fixed optics, & movement will be given to liquid tank for xy scanning.Also we can have variation in scanning method. In the set-up above described the mirrors used are Rotating galvano scanning mirrors but we can also have linearly moving mirrors. Advantage of using this is we can have focal point at fixed level. Another variation is use of Raster scan instead of vector scan. In case of Raster scan beam is moved in rectangular fashion irrespective of desired section. The only thing done is that it is kept off beyond section limits.it will be on only within section limits.Unnecessarily idle movements are there with this type of scan. Hence it will take more time. So it is not used in practice. |
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