Some demands on rapid prototypes used as master patterns in rapid tooling for injection moulding

Injection moulded components are finding vigorously increasing applications in numerous sectors. The flexibility of the process allows complex components to be manufactured in high volumes in fully automated environments. Associated with such components are equally complex tools whose manufacture is both expensive and time consuming. It is therefore vital that the component design be evaluated thoroughly with regard to both performance and manufacturability before commitment is made to expensive production tooling. The use of a physical prototype often provides the best method of design evaluation. The major routes to prototype manufacture are; material removal, rapid prototyping and rapid tooling. Rapid tooling techniques provide the most representative route, with the ability to produce polymeric prototypes (often in final material) by an injection moulding process. Research has been undertaken into two rapid tooling processes; enhanced silicone moulding and sand moulding. Both processes involve casting material against a rapid prototype (master pattern) to form a mould which is then used in the manufacture of product prototypes by injection moulding. The focus of this paper is on the demands of these tooling techniques placed on rapid prototypes when used as master patterns. The demands are discussed in terms of surface finish, surface porosity, dimensional accuracy, thermal resistance and thermal expansion.