Draft - Where and When Required
This is a design aspect where MIM often differs from plastic injection molding requirements. Generally, MIM components do not require draft. There are a couple of factors that contribute to this ability. First, the MIM feedstock is highly loaded with metal powders that retain heat long after the molding cycle has been completed. Post molding shrinkage that occurs with plastic parts while they are still in the mold, occurs for MIM parts during the first several minutes after they have been removed from the mold. This allows the part to be ejected before it can cool and shrink around cores and/or other mold cavity features. Secondly, the polymer binder used in MIM feedstock acts as a lubricant to assist in the ejection of the part from the mold cavity. With these influences in mind, there are circumstances when draft should be provided in MIM component designs. Fig. 12 illustrates some of these circumstances.
