Permanent mould casting is a metal casting process that shares similarities to both sand casting and die casting. As in sand casting, molten metal is poured into a mould which is clamped shut until the material cools and solidifies into the desired part shape. However, sand casting uses an expendable mould which is destroyed after each cycle. Permanent mould casting, like die casting, uses a metal mould (die) that is typically made from steel or cast iron and can be reused for several thousand cycles. Because the molten metal is poured into the die and not forcibly injected, permanent mould casting is often referred to as gravity die casting. Permanent mould casting is typically used for high-volume production of small, simple metal parts with uniform wall thickness. Non-ferrous metals are typically used in this process, such as aluminum alloys, magnesium alloys, and copper alloys. However, irons and steels can also be cast using graphite moulds. Common permanent mould parts include gears and gear housings, pipe fittings, and other automotive and aircraft components such as pistons, impellers, and wheels.