Micro Feature Enhanced Sinter Bonding of Metal Injection Molded (MIM) Parts to Solid Substrate

In MIM, fine metal powders are mixed with a binder and injected into molds, similar to plastic injection molding. After molding, the binder is removed from the part, and the compact is sintered to almost full density. The obstacle to sinter bonding a MIM part to a conventional (solid) substrate lies in the sinter shrinkage of the MIM part, which can be up to 20%, meaning that the MIM part shrinks during sintering, while the conventional substrate maintains its dimensions. This behavior would typically inhibit bonding and/or cause cracking and deformation of the MIM part. A structure of micro features molded onto the surface of the MIM part allows for shrinkage while bonding to the substrate. The micro features tolerate certain plastic deformation to permit the shrinkage without causing cracks after the initial bonds are established. In a first series of tests, bond strengths of up to 80% of that of resistance welds have been achieved. This paper describes how the authors developed their proposed method of sinter bonding and how they accomplished effective sinter bonds between MIM parts and solid substrates.