Diecasting is a similar process to that of injection molding. A die or mold is used to inject molten metal into the tool which then cools until the part can be removed and handled without distortion. This is typically used for high-volume applications due to the tooling investment being typically between $10K to $100K for the mold die. The mold die is commonly made from high performance tool steels, and its lifespan consists of millions of shots until the steel tool begins to deteriorate. Deterioration of a mold die is due to the high temperatures of the molten metals, and the constant heating/cooling of the steel die which causes the steel to progressively crack on its outer surfaces until the cast part is no longer acceptable. Amfas has often refurbished sections of the tool to save our customers the expense of a new tool. Parts produced from diecasting are very consistent, and offer the lowest cost to cast a part.
In the case of sandcasting, sand as the mold die. A pattern of the actual part is made typically from wood or metal with two halves representing the part needed. These patterns are then used to make a temporary die made of sand. A binder is added to the sand which causes the sand to stick together when compressed. The two halves of the sand mold are joined together, and the molten metal is poured into the sand mold. Within a few minutes the metal cools and the sand mold is removed using vibration and mechanical means (hammer, chisel, etc.), being careful not to damage the casting. The sand is then pulverized, sifted, and reused.
Investment casting offers high precision and repeatability, but tends to be labor intensive. Wax or Styrene patterns are molded which represent the actual part desired. These patterns are then bonded to a tree using the same wax or molten styrene in order to simultaneously cast as many parts as possible. This tree comprising of parts is dipped into a thin mud slurry to provide a coating on all the surfaces. The mud coating will reveal the smallest details of the part when casting. Once dry, the coated tree is packed into a cylinder and packed with sand to support the coated parts. The container is then placed into a very hot furnace to melt and burn out the wax, or styrene, patterns. Immediately after removal from the furnace, the molten metal is poured into the hollow tree. Vacuum at the base of the sand/coating container removes air that may cause imperfections. The parts are allowed to cool and are then removed from the sand/investment using mechanical means. The sand is easily vibrated loose and reused. The tree must often be cut with saws and the coating chipped away carefully with impact tools. The process can be very labor intensive and involve high skill levels, however, this process can produce a part in almost any metal with features that cannot be easily machined or diecast.
Amfas will advise the best casting option given the material, part geometry, volumes, and other considerations. With extensive experience in all types of casting, we will provide the best value option for your needs.