High Density, Complex Shaped P/M Assemblies Via MIM for Chassis Applications

A metal injection molded (MIM) assembly consisting of three parts used in an electric door locking mechanism is presented as an example of what is achievable by the MIM process when Design for Manufacturability (DFM) principles are applied to MIM. The net-shape assembly greatly reduced the labor content over a machined design. The assembly presented considerable challenges for MIM due to the need for high dimensional accuracy (mating parts, sliding fits), geometric tolerances (squareness, flatness, and parallelism), surface finish (for cosmetics and anti-friction), and the complex shape of the components. This paper will show how design optimization, preproduction testing, processing methods, and quality control methods were used to achieve the high process capability requirement. Material selection justification for optimized strength and cost will also be shown. The high density (>96% of theoretical) produced by the MIM process coupled with the ability to heat treat parts to a desirable toughness and strength level allowed for a simple, compact design capable of passing UL requirements. This cost saving approach can offer the same benefits and design possibilities to numerous applications in automotive design.