Metal Molds

Other molds are made from metal. Here a die of the desired shape is machined from cast iron or steel. If the metal flows into the mold by gravity, the process is called permanent mold casting. If the molten metal is forced in under pressure, the process is called die casting. Die-casting dies are water-cooled; consequently, they can produce parts with thinner walls at a higher rate than permanent mold machines. The rapid cooling creates a stronger part than sand-casting, but ductility may be poorer owing to entrapped gas and porosity.

Since the initial cost of a die is substantial, metal molds are cost-effective only when many identical parts are to be made. Indeed, a die may be made to produce several parts at once.