The “Lost Wax” Process of Precision Casting

The paper describes a casting process which differs from standard foundry practice in that it uses a wax pattern in a high refractory one-piece mould to produce metal castings with a good surface finish to an accuracy of ±0·002 inch. The process involves making a master pattern in either hard wood or metal, relating it to a soft metal die by precision casting technique, and then the production of wax patterns from the die on an injection machine. Finally, the wax patterns are invested in refractory moulds, the wax is melted out, the mould baked, and the metal component is cast. The “lost wax” process is advantageous in cases where ( a) the metal is unmachinable, or ( b) where the component is of an unmachinable shape, or ( c) where production by other methods takes too long. One of the most common applications is in the manufacture of gas-turbine blades. The tool costs are relatively low compared to the costs involved in alternative methods of manufacture, the die cost being a function of the number of castings required. The production of cheap castings is necessarily dependent on the scrap percentage being kept to a minimum; at present the scrap from the manufacture of gas-turbine blades is less than 30 per cent, and the author surmises that it would not be unreasonable to expect it to be less than 10 per cent in two years' time.