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Old October 6, 2007, 03:02 AM   #1
FS2K
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What does "MIM" Stand for?

I've seen it referred to twice this week. Something to do with parts?
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Old October 6, 2007, 03:55 AM   #2
oldbillthundercheif
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I think it stands for "Metal Injection Moulded".

As I understand it thay make fat sheets of moulds and squirt metal into them to make the parts.
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Old October 6, 2007, 04:43 AM   #3
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Metal Injection Mold is correct. Molten metal is injected into a mold to form complex shapes inexpensively. Before I switched to computers I spent 20 years as a tool maker (glorified machinist) and I know a lot about the subject. With the right metal formulations, and correct conditions and proper quality control MIM is fine for moderately stressed components. Blasphemy I know, but MIM is fine for most moderately stressed parts if it's done right. The problem is that if the wrong material is used, or if the process isn't done correctly, or if proper quality control isn't done then you can get a brittle product. Lot's of ifs.

Parts machined from solid bar stock, if properly heat treated, are usually much stronger. The problem is that the cost of machining for example a thumb safety out of sold bar stock - even with modern CNC equipment is impractically high. Many times the cost of injection molding.

The next step up is metal forging. This is similar to stamping but involves much, much heavier material and high tempertures. Out of the three methods, assuming that high quality steel is used, and proper quality control is maintained forging can produce the strongest components.

Is it worth the added cost? That's a big maybe. For slides and frames I'll always choose forged steel, but machined from solid stock is in reality plenty strong. Barrels can only be machined or forged and then machined. It's pretty hard to justify machining a thumb safety from solid bar stock. It would also be a complex part to forge but it could be done for a premium price. In reality a properly formed and heat treated injection molded part would probably last a lifetime. Then again a flaky process or flaky materials and flaky quality control may let a few excessively brittle pieces out into the wild. I like to keep MIM parts to a minimum but I'm realistic enough to know that I probably can't afford a 100% forged components handgun.
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Old October 6, 2007, 07:35 AM   #4
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Scholling that is actually casting. From what I have read metal powders are blended and mixed with a polymer and additives.
Then they are processed on conventional injection molding machines used for thermoplastic materials into so-called green parts. The polymers serve as a binder that allows the metal powders to be injection-molded. The binder is removed from the green parts in a continuous process under a highly defined and controlled temperature-time profile. Subsequently, the parts are sintered to their final density.

After they are finished, there is little machining to do.
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Old October 6, 2007, 07:47 AM   #5
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Thank you so much!

I would have never figured that out on my own!
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Old October 6, 2007, 09:54 AM   #6
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Or "made in Mexico" if you're talking about Stratocasters.
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Old October 6, 2007, 11:56 AM   #7
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Quote:
I would have never figured that out on my own!
I actually cut and pasted that from a website about MIM. I ain't dat smart eether.

If MIM is done right it is good. I have read of MIM part failures in Kimbers, but then I have been reading of forged and cast part failures in Colts, who make it a point that they only use 3 or 4 MIM parts. I have not come across anything on failed Springfield MIM parts though. Over on the 1911 board one of the know gunsmiths said that Springfield parts are done right. If Pat Rogers, the Marines MARSOC and countless others in the know don't sweat it, i don't either.
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Old October 6, 2007, 12:12 PM   #8
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I'd like to see a discussion of investment cast verses MIM for strength and material density. It's said that MIM parts are made slightly oversize as during the heating process they shrink a bit. Also it's said that they have a bit of porosity, probably not measurable by most of us. If it looks like a duck, quacks like a duck,,,,,
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Old October 6, 2007, 01:03 PM   #9
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Quote:
Or "made in Mexico" if you're talking about Stratocasters.
Or my MIM Tele! Seriously, that's what I thought it meant the whole time... (duh)
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Old October 6, 2007, 02:22 PM   #10
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Quote:
cholling that is actually casting. From what I have read metal powders are blended and mixed with a polymer and additives.
Then they are processed on conventional injection molding machines used for thermoplastic materials into so-called green parts. The polymers serve as a binder that allows the metal powders to be injection-molded. The binder is removed from the green parts in a continuous process under a highly defined and controlled temperature-time profile. Subsequently, the parts are sintered to their final density.
THAT process is sintering, hence the last line in your paragraph. As best as I can tell from my manufacturing textbook it is not the same thing as injection molding.
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Old October 6, 2007, 02:34 PM   #11
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THAT process is sintering, hence the last line in your paragraph. As best as I can tell from my manufacturing textbook it is not the same thing as injection molding.
Google metal injection molding, and you will see it is produced from powdered metal and polymer. There is no other MIM. Pouring molten metal into a mold is casting, which is what Ruger is very noted for.
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Old October 7, 2007, 11:22 AM   #12
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http://manufacturing-fabrication.glo...g_MIM_Services
http://www.kimberamerica.com/knowled...d=12&questId=8
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Old October 7, 2007, 02:28 PM   #13
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You have it right Rob.

What Scholling is talking about is 'die-casting'

MIM is indeed polymer and metal which is sintered after molding. They can also be forged, which basically means beat on hot parts with a hammer, to increase their density and toughness.
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Old October 7, 2007, 04:53 PM   #14
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We have to machine many sintered parts for industry, what's commonly called sintered is often very much like cast iron, very porous and weak. MIM parts on the other hand, though it is a sintering process, are much more like cast or forged parts as far as their homogeneous nature and strength. I have not done strength tests, but I can say without doubt, if these were made the way sintered hubs and gears are they would never stand up to the hammering parts take in a handgun. In my opinion they are practically the same as investment cast parts, closely approaching the strength of solid steel.
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Old October 8, 2007, 07:45 PM   #15
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MIM= Most in Malfunction! Or Minimum in Manufacturing! Or Master's in Mediocrity!
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Old October 8, 2007, 08:04 PM   #16
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Avenger11, have you seen many failures? I would like to know about it if so, I like milled steel, but haven't seen failures yet in MIM parts. In fact I haven't seen failures in handgun parts at all, which I guess says something about how much shooting I do. I usually shoot alone or with a friend, not at matches or ranges.
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