Investment Castings

The investment casting process begins with the production of a wax pattern with the exact geometry of the finished casting. This pattern is usually made by injecting liquid wax or plastic into a metal die cavity. During construction, the die cavity is made oversize, as required, in order to compensate first for volumetric shrinkage of the hot wax as it cools and later for contraction of the molten metal as it solidifies in the mold. An investment casting wax pattern die may be a simple hand-filled split mold or may be a fully-automated tool with one or more cavities.

The ceramic-shell mold-making process starts by dipping the entire wax cluster into a fine ceramic slurry and then coating it with a fine ceramic sand. After the initial coating dries sufficiently, the cluster is dipped into progressively coarser grades of ceramic material. When the shell is between 3/16" and 5/8" thick, it is placed in a heated environment that melts the wax pattern gates, runners, and sprue. The remaining ceramic shell contains dimensionally precise cavities of the casting shape desired. KEYWORDS for this process: ceramic shell casting, lost wax

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