Efficient stock cutting for laminated manufacturing
When an object is made using Laminated Manufacturing (LM), the output is a rectangular block with the required object trapped inside. In order to enable extraction of the object, the remaining sheet in each layer is cut into square grids that grow into tiny tiles. Thus, the remaining stock inside and surrounding the object is in the form of tiled fragments. The operator decubes or removes these tiles using sharp tools and extracts the object. Making use of the remaining stock as support structure and grid cutting to enable extraction of the object are very innovative ideas in the paste-and-cut LM approach. However, this method is very inefficient for two reasons: firstly, cutting efficiency is poor since laser spends most of its time in grid cutting; secondly, decubing takes several hours. In this paper, an efficient method of cutting the remaining stock to extract the object is presented. Extraction of the object from the stock block has analogy with the extraction of casting from its moldthe present and proposed methods respectively being analogous to sand casting and permanent mold casting processes. In the proposed method, rather than fragmenting the remaining stock into tiny tiles, it is segmented into two stock halves that open about a parting surface of minimum area. This optimal parting surface is obtained for the convex hull of the object, rather than for the object itself, due to its complete visibility along any pair opposite directions. The convex hull is further segmented into the object and plugs. The plugs are so shaped that they do not get entangled inside the concave portions of the object. The plugs whose drawing directions coincide with the opening direction of the stock halves are merged with the corresponding stock halves. The object, all the plugs and both the stock halves form the stock block. All these pieces are made together in the LM machine. For disassembly, first the convex hull will be extracted by opening the stock halves. Subsequently the plugs that fill the concave portions of the object will be extracted from the convex hull. Thus, grid cutting and decubing are eliminated in the proposed method resulting in drastic reduction in prototyping time and improved quality of the prototype.
parting surfaces convex hulls visibility rapid prototyping layered manufacturing parting directions