7 - Casting design

Abstract

The purpose of design is to achieve a functional performance of structures at minimum cost in materials and manufacture. Both these factors are involved in the initial choice of casting as the means of production; the individual design is itself usually a compromise between a purely engineering concept based on service requirements and a shape lending itself to a high quality and low cost production. The relative importance accorded to the two factors of function and cost, naturally depends on the class of product and the inspection standards to be applied, but both are always present to some degree. The concept of value analysis relates to the systematic weighting of all the factors in deciding between alternative processes and materials. Particular difficulties arise when a design originally intended for production by machining or weld fabrication is translated to the foundry without major modification. Shape, dimensional tolerances, and material specification may then be wholly unsuitable. This chapter focuses on the process by which a casting comes to be used; five separate stages can be distinguished: the decision to use a casting, detailed design, commercial contact, manufacture of tooling, and founding and finishing.