Casting is the original and most widely used method of forming aluminum into products. Technical advances have been made, but the principle remains the same: Molten aluminum is poured into a mold to duplicate a desired pattern. The three most important methods are die casting, permanent mold casting and sand casting.
The die casting process forces molten aluminum into a steel die (mold) under pressure. This manufacturing technique is normally used for high-volume production. Precisely formed aluminum parts requiring a minimum of machining and finishing can be produced through this casting method.
Permanent mold casting
Permanent mold casting involves molds and cores of steel or other metal. Molten aluminum is usually poured into the mold, although a vacuum is sometimes applied. Permanent mold castings can be made stronger than either die or sand castings. Semi-permanent mold casting techniques are used when permanent cores would be impossible to remove from the finished part.
The most versatile method for producing aluminum products is sand casting. The process starts with a pattern that is a replica of the finished casting. Virtually any pattern can be pressed into a fine sand mixture to form the mold into which the aluminum is poured. The pattern is slightly larger than the part to be made, to allow for aluminum shrinkage during solidification and cooling. As compared to die and permanent mold casting, sand casting is slow process but usually more economical for small quantities, intricate designs or when a very large casting is required.