Tool cost for MIM is based on principles encountered in plastic injection molding. Although many models exist, the most accurate approach assumes purchase of a standard mold base. It then calculates the time needed to machine the component features into a cavity. For multiple cavities, the machining time for the first cavity is used to estimate the time and cost for each additional cavity, recognizing some cost reductions with increased experience. Mold cost is calculated from the total construction time multiplied by a shop hourly rate, with additions for profit and administrative costs.
Detailed quantitative cost analysis of tool cost builds from the assumption that a standard mold base is purchased and converted into the customized design required for the component molding. It needs to be modified to include the specific cavity and related sprue, runner, and cooling channel. Major cost additions are associated with hot runner material delivery systems.
Tooling tolerances are more stringent than part tolerances, and in many estimates the tool tolerance is held to less than 20% of the component allowance. Accordingly, considerable time is used to fabricate a precise tool for a tightly toleranced component, especially when the number of features is large.
The specified tool surface finish incurs a cost, especially if a polished tool is required. In a similar manner, texturing, lettering, or insignias on the tooling add to the tool fabrication time and cost. The tooling cost depends on several factors. MIM tool costs ranged from a low of $5,000 to $125,000 or more (not including process development costs).