Die-Casting

This process uses a permanent metal mould, which results in more accurate and better finished castings than those produced in sand. Die-casting can be subdivided into ‘gravity’ or ‘pressure’ processes, depending on how the metal is fed into the mould.

• Gravity Die-Casting: Sometimes known as Permanent-Mould Casting. This casting process is virtually identical to sand-casting except that the mould is metal. A wide range of metals can be cast and hollow castings are possible if a sand core is used. Fine grain structures are produced due to the more rapid rate of cooling, compared to that achieved in sand-casting.
• Pressure Die-Casting: As implied, molten metal is fed under high pressure (thousands of psi) and held during solidification. Most die-castings are in non-ferrous materials (aluminium, magnesium, zinc, copper and their alloys), because steels have too-high a melting temperature for the metal dies to accommodate. Usually, the dies are made from hard, tool-steels and are water cooled. This process can achieve excellent detailed, super finish, low porosity and thin sections. Expensive equipment is necessary, but very high production rates are possible. Automatic ejection occurs and on small components, 100 units per minute is not uncommon. Hollow castings cannot be made by die-casting.