This process is similar to permanent mold casting except that the metal is injected into the mold under high pressure of 10-210Mpa (1,450-30,500) psi . This results in a more uniform part, generally good surface finish and good dimensional accuracy, as good as 0.2 % of casting dimension. For many parts, post-machining can be totally eliminated, or very light machining may be required to bring dimensions to size.
Permanent mold castings:
This is a precision process produced by pouring molten aluminum into CNC machined steel molds under gravity, centrifugal force, or low pressure. Due to the rapid heat transfer from the molten aluminum to the mold itself, the castings have finer grain structures and better strength properties than casts made by Sand Casting method. Permanent Mold aluminum casting permits casting designs with thinner walls and less weight. Permanent mold castings are less subject to shrinkage and gas porosity than Sand Castings and do not contain the entrapped gas often found in Die Castings.
This process reduces turbulence as molten metal enters the die cavity, provides shorter cycle times, and requires less metal for feeding systems. Aluminum castings produced in metal molds have a tighter dendrite structure than castings produced in other processes. In addition, aluminum castings are harder and have a better pressure characteristics. Value added options, such as sand cores or cast-in ferrous inserts are quite simple.
This process is used to make large parts (typically Iron, but also Bronze, Brass, Aluminum). Molten metal is poured into a mold cavity formed out of sand (natural or synthetic). The processes of sand casting are discussed in this section, include patterns, sprues and runners, design considerations, and casting allowance.