Lost Wax Casting
Lost wax casting is a production method best suited for small quantities, precious metals, or intricate designs. It is most commonly used to produce rings but it can often be utilized in the manufacture of pins and charms. Just as in rubber mold casting, a model or replica of the desired product must be created. This model is used to make a rubber mold into which hot wax is injected to produce the cavities for the casting process. An alternative is to make a metal mold by carving the replica into an aluminum block which forms the die into which hot wax is injected. A wax injection machine maintains the wax at a proper temperature and air pressure. When activated, it injects the wax smoothly into the cavity. Thus a wax model is made for each piece that is to be produced.
The individual wax pieces are then joined together in a tree-like fashion. This tree is placed inside a metal cylindrical pipe and the bottom is sealed with a rubber mount. A heat resistant compound called investment which resembles Plaster of Paris is poured into the cylinder completely encasing the tree. Care must be exercised in making the investment slurry including elimination of air bubbles which would result in voids or imperfections. Next the cylinder is allowed to sit for several hours until the investment hardens. The bottom rubber mount is removed and the flask (cylinder) is placed in a burnout oven. The process of burnout requires about 8 hours during which time the oven is programmed to gradually bring the flask to a temperature of about 1300 to 1400 degrees and then returned to room temperature. During this process the investment is completely hardened, the wax melts and flows out of the flask leaving a perfect cavity. This process is called “lost wax”.
Next the flask is placed into a special centrifugal casting machine. Molten metal is forced into the flask and centrifugal force sends the molten metal into all parts of the cavities. After proper cooling, the investment is removed from the tree by means of a strong stream of water leaving a tree of parts. The individual parts are removed from the tree and properly cleaned in preparation for final finishing.