03 January 2012

Metal Injection Molding

Metal injection molding, also known as MIM.

I think it's misunderstood.

It's a process of making parts with complicated shapes cheaply.  That's really it.

The problem with it is too many shops try to use it on forged and machined parts that are not suited to the process.

The part produced via MIM, while dimensionally identical, is not the same metallurgically.  What that means is, although it fits, it breaks.

Parts designed from the outset as MIM parts will be fine.

What it boils down to is your material selection is predicated by the form and function of your part.  Some materials and forming processes cannot be used for particular parts.  Some parts are process neutral.

Sometimes you can tell a smith did the design and not an engineer.  That sounds disparaging, but it's not.  They are related, but separate paths of learning about machines.  The differences stand out when you jump into the realm of theory and conjecture and begin applying new processes to old designs.

An example that sticks out is a cast receiver for an M1A.  Casting technology today and steels available mean you can make a receiver that's just as strong as a forged one made from the 1930's processes Springfield National Armory was using in 1950.  "Can make" is an important part of that phrase, some don't.

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