Also known as lost wax casting, investment casting is an industrial process used to create metal parts with great detail that would be difficult or impossible to achieve with other casting methods. Investment casting uses a pattern that is destroyed as part of the process, thus making an investment in the finished product. This process is the oldest known casting process used by man, and the original investment casting patterns were made using beeswax.
Investment casting is one of the most basic metal-forming techniques. It is a multi-step process that delivers fine details at a reasonable cost. The equipment cost for investment casting is considered to be minimal, compared with other forms of full-mold casting or die casting.
In investment casting, a master pattern is created using wax, wood, foam or other materials. The master pattern is essentially a prototype of the part that is to be made. This master pattern is then converted into a mold, or master die, that might be made of metal steel wood or rubber.
After the mold has been made, wax is poured into it to make the wax patterns and allowed to cool. After cooling, the wax patterns are assembled in preparation for casting. During this stage, the wax patterns might also be chased and dressed, removing the flashing and any other imperfections in the surface of the pattern using a heated tool.
The investment, a ceramic mold that will be destroyed after casting, is created by dipping the wax pattern into the investment media or placing the wax pattern in a flask and pouring the investment media around it. The investment is then allowed to dry and harden before being dewaxed, subjected to a burnout process and preheated for the pouring process. The burnout process subjects the investment to extreme heat that will remove any trace moisture or wax residue that could interfere with the pouring process. Preheating warms the investment mold in preparation for the pouring process so that the molten metal will stay in its liquid form longer and fill in any small detailed areas.
The next step in investment casting is pouring the molten metal into the investment mold. The mold is placed, cup side up, in a tub of sand and then filled with molten metal. The flow of this metal typically is gravity-fed, but it might be pressurized in cases where thin sections of the mold make gravity-fed pouring ineffective.
After the metal and the investment mold are allowed to cool, the finished product is retrieved. This is done by destroying the investment mold using a one of several means. Common methods of destroying the investment mold are hammering, media blasting, high pressure washing, vibration and chemical baths that dissolve the investment mold.