Sand, die or investment casting: how to choose

The three common methods

Most cast parts in Indian workshops are made by one of three methods. The right one depends on how many parts you need, how large they are, the metal, and how good the surface must be.

• Sand casting: the mould is made of sand around a pattern. It suits iron, steel, aluminium and brass, works for almost any size, and has the lowest tooling cost. The surface is rougher and usually needs machining.
• Die casting (gravity and pressure): the mould is a metal die. It suits aluminium and other non-ferrous parts in repeat quantities. The die is expensive, but the part price is low at volume and the finish is good.
• Investment casting: a wax pattern is coated in ceramic. It gives fine detail and a good finish on small and complex parts, in many alloys, at a higher cost per part.

How to decide

Start with the quantity. For a handful of parts or a large casting, sand casting is normally the practical choice. For thousands of aluminium parts, die casting usually brings the part cost down enough to justify the die. For small, detailed parts in steel or stainless steel, look at investment casting.

Do not forget machining

Almost every casting needs some machining. Tell the foundry which surfaces will be machined, so they leave extra material. If you also need machining, say so in your requirement, and ask whether the foundry does it or works with a partner.

Questions to ask a foundry

Ask who makes the pattern or die and who owns it, what inspection and testing is included, how they handle rejected pieces, and what a typical lead time is for the first batch.

Kinds of work

• Die making
• Mold making
• CNC machining
• Casting
• Fabrication