MIM parts

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MIM parts

Post by Jon Eulette on 1/24/2015, 1:47 pm

I saw a new Philippine made 1911 break 1st time it was shot. The disconnecter broke through the sear pin enlarged hole. It was MIM! This is why I replace all the MIM pets on pistols I build. My Marine Corps armorers buddy on the base I work on has seen MIM sears break. Just thought I'd share. 
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Re: MIM parts

Post by TexasShooter on 1/24/2015, 5:21 pm

Jon - for us under-educated folks, can you go into a little more detail? I understand MIM is metal injection molding, and can see why it might not be as strong. How can you tell if a part is MIM? Can you tell just by looking, does the manufacturer advertise or disclose how it's made? What to look for instead of MIM? What else do I need to know?

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Re: MIM parts

Post by Jon Eulette on 1/24/2015, 5:48 pm

Over the years I have used many GI cast parts with 100% success so far; knock on wood Razz)
Casting line on GI parts are nicely done. MIM parts typically have a large injection mark on the cast part. Mold lines are typically larger than GI cast part as well. I've never weighed a MIM part, but they seem less dense than quality cast parts.
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Re: MIM parts

Post by GrumpyOldMan on 1/25/2015, 12:33 am

There is often a mold artifact that will remind you of the old plastic parts of a model airplane kit. Typically a circle about 1/8-inch in some non-machined/non-contact area.

I would gladly use and not bother replacing MIM grip safeties, mag catches (the button thingy), 1911 style triggers, and just maybe slide catches and hammers.

NON-MIM parts I have seen fail: 1950s Colt Gold Cup slide catch, thumb engagement lever on two-piece takedown lever (think SIG class P series pistols' style, it was not a SIG), WunderNine slide stop just behind the "working" part (the part your thumb wold operate broke off), .22 rifle hammers (twice for one; another was the spur on a 1960s S&W revolver), transfer bars (twice for a different one), slides and frames (one was aluminum, the other steel, neither was a 1911), and I'm sure another three or more.

So, I'm not convinced that MIM is really worse than the "old" ways for most applications. But the nature of those beasts means I do NOT trust them for sears and most hammer designs.

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Re: MIM parts

Post by Bullshooter on 1/25/2015, 8:42 am

For identification of MIM parts, look for a slightly indented circle on a non-contact surface of the parts. IMHO, MIM parts have their place for non fire control parts like mainspring housings and grip safeties. If someone is going to pay me for a Bullseye quality trigger job, I'll give them a brief education on MIM parts with the disclaimer that the trigger job may not last as long unless the MIM parts are replaced.

I'm not a metallurgist, but I suspect that like many things, the process and quality control can have a bearing on the quality of the finished product. It's hard to find a stock gun today that doesn't have at least some MIM parts in it's bill of materials. I've done some trigger jobs on Springfield Armory 1911s that use a MIM hammer & sear, and so far have no complaints. That said, if it's my gun, I replace those parts with quality Cylinder & Slide and EGW parts that are a known quality and Rockwell tested.

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Re: MIM parts

Post by kwixdraw on 1/25/2015, 9:47 am

There is still more to the question than just MIM vs other base materials. Heat treating and other finishing processes have an effect too. I suppose MIM could be subject to inclusions in the casting or some other fault in the grain structure of the metal. Still you could have a nick that forms a stress riser or a condition of over hardening and improper tempering and still have the part fail. It's probably safest to go with parts you trust and have a history of performance.
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Re: MIM parts

Post by Jerry Keefer on 1/25/2015, 11:08 am

This debate rages from time to time on other forums.. Pros and cons... I personally don't care for MIM.. The only reason companies have gone to it, is cost...bottom line, it's cheaper..
In my younger days, late 50s, 60s, 70s up to the beginnings of the gas crunches, I was heavily involved in drag racing.. The first thing to go during an engine build, was the "cast" crankshaft...it could not with stand the forces... There's a reason the best parts are not castings...
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Re: MIM parts

Post by kwixdraw on 1/25/2015, 3:08 pm

Jerry, that was sort of my point. Best might be determined in a number of ways. MIM, correctly done, might be perfectly satisfactory for some applications. Gets a reasonably priced gun into a shooters hand and serves the use he needs it for. Ideally speaking. We put our guns through much heavier duty so we want to use more durable and more finely tunable parts. Sometimes its all just marketing. I had an (un named manufacturers) A2 tool steel hammer fail in my commander that I carried on duty. Sheared the half cock notch off during a demonstration of how the various safeties worked to a bunch of 1911 detractors. The damage was only found a few days later when I cleaned the gun due to getting it wet.  Just my opinion; the hammer was hard and gave a nice trigger pull but was not tempered to give the needed overall performance. No more super duper alloy, hard hammers in the duty gun. Its all a trade off. And of course good material can even have problems . Aircraft engines can fail over a scratch in the wrong place or a load applied incorrectly. Too tight on a nut or bolt is just as bad as too loose.
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Re: MIM parts

Post by Jerry Keefer on 1/28/2015, 5:09 pm

I received an e-mail from a friend who is very knowledgeable in this area. It is quite informative, and when I figure out how to post it from the e-mail, I will.. It  shines a very positive light on MIM  and will change some opinions.. It has mine..
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Re: MIM parts

Post by GrumpyOldMan on 1/28/2015, 5:40 pm

Well, as I understand it, most engine connector rods are MIM nowdays.

Not exactly a low-stress application.

But like a LOT of under-engineered junk I've looked at over the years both before and after failure, the fundamental design must not push the limits of the materials or the heat treat/tempering (as applicable) too close to the edge.

The closer the shape is to a sphere or cube, the more I trust both MIM *and* poor quality control materials (soft steel, excessive surface hardening, wrong alloy for the stresses) regardless of manufacturing method. Forged, cast, machined from bar stock--it's all meaningless if it's either too small or the wrong alloy/hardness/whatever.

So, thin cross-sections of less than 3/16-inch, more than 3x as long as it is wide until you're thicker than 3/8-inch at the thinnest dimension, and impact usage like the hammer spur on a revolver hammer--I don't think I trust MIM for that.

BUT within their limits and despite the small porosity caused by the plastic binder before sintering (as I understand the process), MIM can be a terrific way to inexpensively make good alloy steel parts in complex shapes without burning up a lot of money replacing the tools used for machining.

As one example, a Kimber mag catch in a 1911 model was really really good--except for leaving way too much material on the inside radius where it *should* clear the front of the magazine when the button is depressed.  Push it too far and it would contact the magazine and prevent drop at all, not to mention drop-free.  Someone wasn't paying attention to the mold shape there, and someone else failed to gage the part and machine out the 1/16-inch of extra material inside that curve. That was not a MIM problem, it was a tolerances/QC problem on an otherwise perfectly servicable item suitable for MIM manufacture.

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Re: MIM parts

Post by Jerry Keefer on 1/29/2015, 12:11 pm

OK... found a link to the same letter from  S&W official..
http://www.ar15.com/forums/t_5_49/125420_Herb__Belin_project_manager_for_SandW_on_the_efficacy_of_utilizing_MIM_in_the_manufacture_of_handguns.html
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Re: MIM parts

Post by beeser on 1/29/2015, 7:53 pm

Maybe MIM is just a step toward modular construction.

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Re: MIM parts

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