First, an expendable pattern, of the same shape as the intended end part, is made by injecting wax into a metal die. Multiple patterns are assembled on a central wax stick, called a ‘sprue,’ to form a branched gating system.
Next, the entire cluster is repeatedly dipped (or ‘invested’) into a refractory ceramic slurry until the desired strength and thickness is reached. The shell is then allowed to dry out and harden, after which it is fired in an autoclave to melt out and remove the wax. Molten metal is then poured into the assembly to fill all the negative space left by the melted wax, and left to cool down and solidify.
Once cool, the ceramic shell is removed by vibrating and/or breaking it to reveal the metal tree. Lastly, the multiple parts are cut off from the central sprue and minor finishing and/or cleaning operations are performed as necessary, and packed for delivery to the OEM customer.