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MMM LECTURE NOTES FINAL.pdf

Applications of rp technologies rp technology has

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APPLICATIONS OF RP TECHNOLOGIES RP technology has potential to reduce time required from conception to market up to 10-50 percent (Chua and Leong, 2000) as shown in figure 10. It has abilities of enhancing and improving product development while at the same time reducing costs due to major breakthrough in manufacturing (Chua and Leong, 2000). Although poor surface finish,limited strength and accuracy are the limitations of RP models, it can deposit a part of any degree of complexity theoretically. Therefore, RP technologies are successfully used by
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Modern Manufacturing Methods various industries like aerospace, automotive, jewelry, coin making, tableware, saddletrees,biomedical etc. It is used to fabricate concept models, functional models, patterns for investment and vacuum casting, medical models and models for engineering analysis (Pham and Demov, 2001). Various typical applications of RP are summarized in figure . PART DEPOSITION PLANNING A defect less STL file is used as an input to RP software like QuickSilce or RPTools for further processing. At this stage, designer has to take an important decision about the part deposition orientation. The part deposition orientation is important because part accuracy,surface quality, building time, amount of support structures and hence cost of the part is highly influenced (Pandey et al., 2004b). In this section various factors influencing accuracy of RP parts and part deposition orientation are discussed.
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Modern Manufacturing Methods 1. Factors influencing accuracy Accuracy of a model is influenced by the errors caused during tessellation and slicing at data preparation stage. Decision of the designer about part deposition orientation also affects accuracy of the model. 2.Errors due to tessellation: In tessellation surfaces of a CAD model are approximated piecewise by using triangles. It is true that by reducing the size of the triangles, the deviation between the actual surfaces and approximated triangles can be reduced. In practice, resolution of the STL file is controlled by a parameter namely chordal error or facet deviation as shown in figure 2. It has also been suggested that a curve with small radius (r) should be tessellated if its radius is below a threshold radius (ro) which can be considered as one tenth of the part size, to achieve a maximum chordal error of (r/ro) .Value of can be set equal to 0 for no improvement and 1 for maximum improvement.Here part size is defined as the diagonal of an imaginary box drawn around the part and is angle control value (Williams et al., 1996). 3.Errors due to slicing: Real error on slice plane is much more than that is felt, as shown in figure 12(a). For a spherical model Pham and Demov (2001) proposed that error due to the replacement of a circular arc with stair-steps can be defined as radius of the arc minus length up to the corresponding corner of the staircase, i.e., cusp height (figure 12 (b)). Thus maximum error (cusp height) results along z direction and is equal to slice thickness.Therefore,
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  • Fall '12
  • JeraldBrevick
  • EDM, conventional machining processes, Jet Machining

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