The use of rapid prototyping (RP) has reduced time to market, cut total costs and improved product quality by giving design and manufacturing teams the opportunity to verify and fine tune designs before committing them to expensive tooling and fabrication. Rapid prototyping processes are integrated manufacturing processes that include CAD/CAM, control of devices, materials and so on. Individual processes can introduce some errors that reduce RP product accuracy and hinder its further applications. Accuracy improvement is required as a result. A new rapid prototyping process, transfer-type variable lamination manufacturing process by using expandable polystyrene foam (VLM-ST), has been developed to reduce building time, apparatus cost and additional post-processing. At the same time, VLM Slicer, the CAD/CAM software for VLM-ST has been developed.
In this study, the accuracy of VLM-ST is improved by offset and overrun of a cutting path and generation of a reference shape. Algorithm for each case is proposed and applied to VLM-ST process for verification. The melting zone caused by the characteristics of hot wire cutting system for VLM-ST is a major source of error. Algorithm for generation of an offset path using Voronoi diagram, which is widely used for offset contour generation, is proposed and verified by applying it to real process. From the result of the preceding research, the offset value is determined. After an offset algorithm is employed, the percent error is reduced to under 40 % of error without offset. Concentrated heat at a sharp edge is also a source of an error. Algorithm for correction of a cutting path, so that a hot wire is overrun along the path to the outside of the shape, is proposed and verified by applying it to real processes. When the angle of sharp edge is smaller than the critical angle, this algorithm allows the overrun in the path of a hot wire by overrun value. From the result of the preceding research, the critical angle and overrun value are determined. As a measure of error, the lost area at sharp edge is used. Area is approximated by a triangle. After the algorithm for path correction is applied, the lost area is reduced to under 50 % of error (area) without path correction. In the VLM-ST process, semi-automatic lamination is performed in online. A pilot pin is employed for stacking and fixing the boards. In order to use a pilot pin, a reference shape with pilot hole must exist in each layer. A reference shape can be generated by adding six points to the cutting path. An algorithm for generation of a reference shape, which enables fmding needed points and adding them to the cutting path, is proposed and verified by applying it to real process. For removal after lamination, the reference shape has a neck at the connection with the original shape and width of the neck is important. For proper functioning range of the neck width is proposed by the result of finite element analysis. It has been shown that, through the verification experiments for given practical shapes, the proposed algorithms are effective for diverse categories of three-dimensional shapes.
