We also notice the Design of Part Improvement as following:
Cored holes are normally used to reduce MIM parts cross section, uniform wall thickness, reduce metal material consumption, reduce or eliminate secondary machining operation. Its preferred direction is parallel to mold opening and perpendicular to parting plane. When length/diameter ratio is great than 4:1, through hole is preferred because both ends support core pin, otherwise, blind holes will be used with cantilevered pin.
Holes and Slots
Hole and Slots can provide functional features in MIM parts without additional cost, besides reduce part mass and uniform wall thickness. Holes are perpendicular to parting line is easy to mold with least cost, these are parallel require mechanical sliders or hydraulic cylinders. For internal connected holes, we need to consider carefully of potential sealing-off problems and flashing issues.
External undercuts can be formed on a parting line by split mold. Internal undercuts can be produced by slides, or collapsible cores. In MIM design, avoid internal undercuts because of additional cost and potential flashing problems.
Both internal and external threads can be formed in MIM process, internal thread is more precise and cost effective than unscrewing cores. External threads optimum location is on a parting line. To hold thread tolerance on thread diameter, narrow flat is typically 0.005”.
MIM can easily mold features as logo, knurl, part number and identification marks in place without added cost, all these feature can be raised or sub-surface. We also can pride high level feature detail like diamond knurling in MIM process.
Although MIM part wall thickness is uniformed desirably, coring for thickness uniformity is not a perfect option, and it is difficult to avoid variations. We need to design a gradual transition between different thickness.