For high-volume, high-precision needs of many automotive applications, metal injection molding (MIM) Is a growing, though largely overlooked, process that could result in significant cost savings. The window of economic advantage in metal injection molded parts lies in complexity and volume for small-size parts.For automotive, this includes brake components, rocker arms, injector nozzles, and numerous fittings and connectors.
The concept of using the injection molding process familiar to plastics processors to shape a metal excites many design engineers, especially when they learn the final part properties are the same, if not better, compared with most machining processes. MIM succeeds in part because there is little material loss; typically 98 percent of the purchased raw material ends up in final products.
Metal Injection Molding(MIM) is not traditional powder metallurgy.Some engineers confuse MIM with traditional press-sinter powder metallurgy (PM). Standard powder metallurgy forming relies on vertical axis compaction to press a coarse powder into a compact shape. Die compaction is best at forming squat shapes that are easily ejected from the tooling. The ejection step requires the sides be parallel, a restriction in geometry not required for MIM. Thus, in MIM undercuts and holes are possible perpendicular to the main axis.
Dimensional control is the critical difference. MIM components are formed with uniform density and the scatter in final component mass and dimensions is small. For PM, the standard protocol is to use larger powders versus MIM and to sinter at lower temperatures for shorter times to avoid distortion during sintering densification, resulting in lower properties. As a result, MIM strengths are about two-fold higher than PM;fatigue strength is more than three-fold that of PM, and impact toughness is eight-fold higher.
Automotive applications for MIM started to escalate with use in turbochargers, fuel injectors, control components (clock mounts, entry locks, knobs, and levers), and valve lifters. The process has found global acceptance. The metal injection molding process might be a green technology due to the significant reduction in wastage compared to "traditional" manufacturing methods such as 5 axis CNC machining. However, some of the older operations generate toxic emissions such as formaldehyde, dispose of chlorinated solvents, and must burn off wax or other polymers, leading to greenhouse gas emissions.