Nothing wrong with MIM, if the engineering team and process team do their jobs properly
Interesting. I assume you're qualified to make that claim? I happen to be a mechanical engineer who works with metal specifications daily. You?
MIM parts are GREAT if you want a low-cost part that requires only very minimal machining to very tight dimensional tolerances. The problem is, the process inherently increases the chance of steel inclusions.
Most people don't really understand MIM. Basically (in layman's terms), you melt powdered steel into a polymer (plastic) media. You then inject this metal/plastic slurry into a regular injection mold, just like as if the parts were plastic.
Next, you use a series of solvents to dissolve out as much of the plastic as possible. This leaves metal loosely bonded with minimal grain adherence.
Finally, you sinter the part until the steel grains fully adhere and then you finish machine and use whatever heat treatment the specification calls for.
The problem step is the polymer removal. It's easy to not get it all out. when you sinter the part, any remaining polymer is vaporized and can create inclusions. At the best of times, you only get 98% density as compared to a billet-machined part. That extra 2% is accounted for by micro-inclusions. Sometimes the micro-inclusions aren't so "micro" and given the cost-reduction reason you probably went the MIM route, you aren't going to non-destrctive test (NDT) every single part.
MIM can be a good, cost effective alternative, but nobody in their right mind would use MIM instead of machined steel except as a cost reduction strategy, or to create a part that would otherwise not be possible to make due to complex shape, etc.
If/when a MIM part fails, it usually happens at an inclusion site.
MIM parts aren't overly likely to fail, but they are
more likely to fail than a part machined from billet. Period. It's an undisputed FACT amongst design engineers.
