Investment casting products are parts produced through the metallic replication of wax models. The parts may be made of almost any castable metal including carbon, stainless steel, aluminum, copper, titanium and brass. Because the parts are made from a wax model made to the exact specifications of the intended design, there is a high degree of dimensional accuracy.
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Investment casting products have walls of even thicknesses and are made whole; that is, there are no flash or parting lines. The finish is smooth and very fine because of the impression left by the wax. After is it cast, little machining is required to finish it except to remove it from the sprue and grind down the stump. Comparatively this process is more expensive but it also has lower equipment costs and less material waste. Investment casting products can be miniature parts weighing only fractions of an ounce or they can be very large, weighing up to 1,000 pounds; the average part is 15 pounds or less. The range of products is expansive and includes parts from a dental brace to an aircraft engine component. Other examples include pipe fittings, medical instruments and turbocharger parts. Investment casting products have many applications and are used in the aerospace, automotive, defense, dental, mining, medical, food processing, transportation, power generation, marine, sports and telecommunication industries.
Investment casting begins with the production of a master die or wax pattern. This process is also known as lost wax casting because of the wax model that is melted and therefore lost. The original pattern can be either hand carved or carved by machine. It may also be made through injection molding. The pattern is then mounted on a wax sprue using a heated metal tool. Multiple patterns numbering in the hundreds may be attached on a single sprue; this cluster is called a tree. Any flaws or imperfections in the wax are removed so the patterns look like a finished piece. Next, ceramic slurry known as the investment is prepared; the tree is repeatedly dipped in investments of decreasing fineness. Another technique is to affix the sprue in a flask and pour the investment into the flask, vibrating it to remove air bubbles. The investment is allowed to dry and harden before it is placed in an oven or furnace. The tree is placed upside down so that the melting wax will run out the bottom. The hollow shell is exposed left in the oven even when the wax has melted during the burnout stage to ensure that any moisture or residual wax is gone. Molten metal is poured into the mold; vacuum casting, positive air pressure or centrifugal casting may also be used to fill it. When the metal is hardened the shell is removed by media blasting, vibrations, hammers or a dissolving agent and the casting is released.
