The concept of net shape for castings

A quantitative study of the factors influencing the variability of casting dimensions has been attempted. The variability of casting size limits the achievement of a finished (i.e. net) shape in one operation. The casting processes include lost wax, lost foam, sand casting, gravity die (permanent mould) casting, and high-pressure die casting. Lost wax (the so-called precision casting process) is found to be highly repeatable in dimensions only for small castings, and rapidly loses repeatability as casting size increases, becoming as poor as a low technology sand casting process at sizes of approximately 1 m. The other casting processes are less influenced by casting size. Pressure die casting and high technology sand casting are found to have similar excellent performance with regard to control over casting dimensions over the whole spectrum.