A scientific approach is presented and the related logic developed for design of parting surfaces of patterns, moulds and dies used in the manufacture ot cast, forged, injection-moulded and die-cast components. This has enabled computer-aided generation of parting surfaces and the determination of projected area, flatness and draw for a parting surface, identification of surfaces to which draft is provided, recognition of component segments causing undercuts, testing for dimensional stability, and location of flash, machined surfaces and feeders. Influencing criteria for parting-surface design have been formulated and developed into algorithms implemented on a personal computer. This approach greatly aids the engineer in rational decision making, paving the way for a systematized code for parting-surfac e design.
computer-aided design, boundary representation, die castings, forging
Castings are manufactured by pouring molten alloys into various shaped mould assemblies. Moulds are in turn prepared by compacting sand around patterns in segments or halves, one each for the bottom and the top mould. A forged component is manufactured by compressing a heated blank between two shaped dies. In die-casting and plastic injection-moulding the material is forced under high pressure into a cavity formed by bringing together two die-halves. In all these manufacturing processes, the design of patterns, moulds and dies, the crucial tooling, directly affects productivity and component quality. The most significant design aspect is the choice of the surface separating the two halves of the mould or die, referred to as the parting surface (Figure 1). A combination of several mechanical, metallurgical and process parameters influences parting-surface location, rendering the design exercise complex.
Parting surfaces for typical components are suggested through illustrations in technical literature 1' 2. A few broad recommendations for locating the parting surface are available. Matousek 3 discusses the effect of locating the parting plane at different positions on a lever handle