An RP part is used to create a master pattern.

• The RP part is then putty finished to achieve the desirable finish on the PU parts.
• The master pattern is fitted with a sprue and gate and then surrounded by a parting surface, which establishes the parting line for the mold. Alternatively, the cured mold can be cut carefully to form the parting line.
• The assembly is fixtured in a wooden box, the size of which is determined by the size of the master.
• The liquid RTV is degassed in a Vacuum casting machine, which eliminates air bubbles trapped in it. The degassed liquid RTV is then poured over the pattern and parting surface combination.

• Once cured, the RTV is removed from the box and separated from the pattern and parting line surface to yield the two halves of the molding tool.
• Thermoset resin such as urethane is first degassed in the Vacuum chamber and then poured or injected into the mold.
• Finally, the finished part is removed from the mold. Undercuts are overcome by distorting the mold, which springs back to its original shape as long as distortion is not too severe.
• The part must then be post-processed by trimming any flash.