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Old 05-04-2009, 10:03 PM
Britt Gardner Britt Gardner is offline
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Metal Injection Molding Demistified




There have been so many threads on this subject on so many forums that we're all sick of hearing about it, but I'm here to present a slightly different take on the matter. Realize that I am no expert on the process, but I have done more research than the majority of the droves who decry it or the few who defend it. It is my hope to put what I have learned and deduced into a form that will be useful and easily understood. Hopefully, if I do a good enough job explaining this, the mods will make this post sticky, so that it can become an easy point of reference for those with questions about MIM.

For those who don't know what it is, Metal Injection Molding (MIM) is a process of creating a metal part -- usually a small, complex one. It is done by injecting metal powder carried in a molten medium, usually a combination of wax and plastic, into a mold of the part. The plastic is then removed through the use of heat and chemicals. After that, the part is heated, again, to just below its melting point, in a process called "sintering." I was never really able to find a thorough explanation of why, but the part shrinks during these heating processes. It is my belief that this is caused by a reduction in its volume due to the removal of the plastic/wax medium that had formerly composed part of its makeup, but I could be wrong. At any rate, this final heating causes the powder to bond together into a solid unit that is the finished part.

The advantages to this process are that it's inexpensive, (Don't knock it; it means your gun is less expensive at the counter, too.) and that it can hold extremely precise tolerances.

Its disadvantages are that if the removal of the plastic and the final heating are not done properly, it can leave microscopic fissures in the part, which constitute weak points where breakage is likely to occur.

So, does that mean that your (Insert 1911 model here) is a piece of junk, because it has metal injection molded parts?

Not necessarily.

You see, a poorly made MIM part will tend to reveal itself very quickly. In almost every case that I've ever heard of where a MIM part broke, it did so very early in the firearm's life -- usually in the first few hundred rounds. I believe that this is because the fissures mentioned above are so weak that the part is simply doomed to a very early failure by their presence. MIM parts that break later than the first few hundred or so rounds, we can't really say much about, because even bar-stock parts occasionally suffer freak breakages at various points during their expected lifespans.

What all this means is that if you've got a firearm with MIM parts in it, you either need to replace the MIM parts with bar-stock parts, or you need to wring it out before you use it for serious purposes. This is particularly true of a 1911, as there is a strong tendency to have parts that were already known to break frequently back in the days when only bar-stock was in use, such as slide stops and ejectors, made with metal-injection-molding.

If you run 500 rounds through a pistol with MIM parts in it, and none of them break, then in all likelihood, you'll never have a problem, because none of the parts in your pistol probably have any of the delinquent fissures that cause breakage. It's my opinion that a well-made MIM part is a good part. In fact, the one time I tried to file on a MIM part, it actually yielded less easily to my file than did an equivalent bar-stock part I'd just been working on!

That said, any manufacturer can flub up once in a while, so you need to wring out even a high-quality pistol, if it has MIM parts in it. With ammunition being so expensive, nowadays, it may be cheaper for you to just replace the parts, anyway.

I will repeat, here, one last time, that I am NOT an expert on this process, so take what I have just said here with a grain of salt, and do your own research before you come to any conclusions.

I was just tired of people going back and forth about this subject with essentially no idea of what they were talking about.
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Old 05-04-2009, 10:31 PM
11,43mm 11,43mm is offline
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Quote:
Originally Posted by Britt Gardner View Post
I will repeat, here, one last time, that I am NOT an expert on this process, so take what I have just said here with a grain of salt, and do your own research before you come to any conclusions.

I was just tired of people going back and forth about this subject with essentially no idea of what they were talking about.
So...why should anyone listen, again?
Just busting your chops, sir - FWIW I think it's a good summary and I agree (not a metallurgist either).
But since I'm vocal in my MIM aversion, I'll give you a perspective.

Pretty much anything in the gun or gear (had the same talk about clip-on holsters recently) debates can boil down to this: it all depends on the execution. I'd rather have a good MIM part than a crappy forged one, that's a given.
The other side of that coin is that we're in a free market and I'm willing to pay a little more for a process I feel to be oriented more toward quality than cost-cutting. And if I'm looking at two 1911s in the same price range and one is cast and full of MIM, while the other is forged and with tool steel parts...you know where I'm going.

In a way, I'm sure that some manufacturers use the non-MIM or forged "badge of honor" as a selling point: what they're telling the customer is, "we know you're discriminating, and fear not, we're committed to quality". Whether they live up to that is another story, but the argument gets noticed by me. I don't think I'm a snob about it because I'll admit honestly that it's about personal preference and peace of mind rather than obvious superiority.

You're probably right that this issue, like a lot of others, can get overstated.
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Old 05-04-2009, 10:45 PM
Britt Gardner Britt Gardner is offline
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I agree with everything you said.

And I felt that I had to be honest about my credentials, here. I'd hate to mislead anyone into thinking I had some vast body of knowledge about the subject. I just know more than most, and I felt like other people on this board would be interested in knowing what I know.

Last edited by Britt Gardner; 05-04-2009 at 11:13 PM.
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Old 05-04-2009, 10:58 PM
11,43mm 11,43mm is offline
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I know what you mean: some absolute pronouncements are downright silly and it gets tiresome.
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Old 05-05-2009, 12:02 AM
Ordnance Ordnance is offline
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I've worked with various types of injection molding: plastic, metal, and various resins, in numerous configurations and types.

I wil tell you that the process you have described here in the OP does exist, but it is not used nearly as often as some make it out to be. It is a tedious process, and many companies won't touch the idea of it if they don't have any background or experience with it. That being said, it CAN be a reliable process when done right. But rest assured, most of the companies in the U.S. that do MIM are very skilled, and have numerous controls and standards that regulate the process. I cannot vouch for overseas standards, but I will tell you that this process is done on a limited basis when compared to traditional metalworking, and even then the parts that are formed on this are usually parts that are used within their means of limitation.

So personally, I wouldn't worry too much about the issue. Most of the companies that perform MIM are well aware of the reprocussions they could face in the event of a failure, which is why lesser-quality companies won't touch it in the first place unless they know they have the brains behind it in the first place.
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Old 05-05-2009, 11:00 AM
45tex 45tex is offline
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I'm glad the good Lord allowed me to see another day. And now that I have read this thread, I have not wasted my day, as I learned something.
Thanks to you all.

I have one 1911 and it only for about 6 months. Yes its a Taurus. Strangely enough I like it more now then at first. I had no idea what MIM was or why so many considered it important.
The 1911 is unlike any of the many auto-loaders I've owned before. Owning a 1911 is more like a hobby than just owning a handgun. I like it and I want more.
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Old 05-05-2009, 03:12 PM
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dsk dsk is offline
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Quote:
Originally Posted by Britt Gardner View Post
You see, a poorly made MIM part will tend to reveal itself very quickly. In almost every case that I've ever heard of where a MIM part broke, it did so very early in the firearm's life -- usually in the first few hundred rounds.
A MIM part may break in the first few hundred rounds, or it may break after a few thousand rounds. I had about 1500 through a Kimber when the ejector broke one of its studs. Roughly 500 rounds later the extractor wouldn't keep its tension. A few months after that, goodbye slide stop. I don't see why I should have to fire at least 2000 rounds through my pistol to see if it's going to hold together or not.
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Old 05-05-2009, 03:17 PM
rglock35 rglock35 is offline
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Originally Posted by dsk View Post
I don't see why I should have to fire at least 2000 rounds through my pistol to see if it's going to hold together or not.
You shouldn't have to.

MIM demistified: it shouldn't be used. If you have it, replace it.
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Old 05-05-2009, 03:38 PM
11,43mm 11,43mm is offline
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Originally Posted by dsk View Post
Roughly 500 rounds later the extractor wouldn't keep its tension.
Same thing happened to the one in my Mil-Spec. The gun was malf-free with any ammo for a little over 1K, then I started having pbs. After replacing springs and mags, I traced it back to the extractor. It looked fine and tension appeared correct, but replacing it solved the issues. It must have lost its springiness (?).

I think that manufacturers make a cold calculation here: most people who buy entry-level guns will shoot a box of ammo a year and be happy with that. Plastic and MIM parts can easily pull that off if they don't break right away.
Since the serious users (competition, LE, or else) either spring for higher-end models or replace the guts anyway, to be competitive and save money the companies cut corners.
It is annoying when guns over $1K and sold as "custom shop specials" are full of MIM, however...

OTOH, it's notable that MIM is widely used throughout the gun industry and only becomes a debate on 1911 and revolver forums, where users tend to be older and can be purists, let's face it. This is one reason why I think the OP is right in that we may exaggerate a bit sometimes.

But the thing is, it's also possible that designs dating back to the late 18th-early 19th century were never meant to be used in conjunction with parts manufactured at today's standards. A 1911 relies on critical parts to do their job and be stressed a certain way (like the extractor or the slide stop).

Whatever floats your boat, the fix is so easy that it shouldn't prevent anyone from sleeping at night.
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Old 05-05-2009, 03:39 PM
Nipperdog Nipperdog is offline
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Given the high retail prices of some of these MIM laden pistols it wouldn't hurt the manufacturer to install barstock or forged parts. After all a manufacturer will pay a fraction of what a consumer would pay for the same part. I would gladly pay another $100 for a gun that I would not have to question if and when something will break. I have had numerous mim parts fail over the years in various 1911s so I know it is not a rare occurance.
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Old 05-05-2009, 03:49 PM
DevilDave1911 DevilDave1911 is offline
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I think it speaks volumes that a competent smith will refuse to do a trigger job on mim components.
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Old 05-05-2009, 03:49 PM
11,43mm 11,43mm is offline
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I would gladly pay another $100 for a gun that I would not have to question if and when something will break.
Same here. And when I see a high-end piece full of MIM, I ask myself what other corners have been cut.
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Old 05-05-2009, 04:00 PM
AzDave AzDave is offline
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Quote:
Originally Posted by Britt Gardner View Post
It is my hope to put what I have learned and deduced into a form that will be useful and easily understood.
A good layman's description of the process. Well written and easily understood. Your suggestion of a stress test is a good one. Shame we have to resort to it though.

Other posts have also raised good points.

In another life I was involved in designing MIM parts. As stated, control of the process is very important to it's ultimate strength and longevity.

However, just as critical is the application and part design. I.E. dsk's ejector. Could be there was no radius at the bottom of the post creating a stress raiser. The extractor is a spring. Granted it's not stressed a lot, but IMHO this is a bad application for MIM.

I have a Kimber that is a 1996 with the original hammer and sear in it. It's been shot a lot in competition and still has a nice 2lb trigger on it. The APG pistolsmith who did the work on the gun said he has had good experiences with MIM on hammers and sears. When the gun was built I ask about new parts and I took his advice on those. Slide stop, safety, and other parts changed. Seems, so far he's right. Could be a fluke.

Having said all that, competition is one thing, but for serious work, I think bar stock is the most reliable material for critical parts.
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Old 05-05-2009, 05:45 PM
jackslimpson jackslimpson is offline
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I'll add my two cents, just to pile on: I don't like the look of MIM. The parts stand out like curb feelers on a Ferrari. I didn't really know that much or care about MIM parts until I began shopping seriously again for a 1911 and bought my SS Milspec. Springfield uses many MIM parts -- and they're easy to spot: Slidestop, Bushing, Thumb Safety, Grip Safety, Disconnector, Trigger, etc. I'm sure even other small parts. Basically, I bought a SS pistol, and noticed that it had about 4 different finishes, due to the prevalence of these parts. They just look bad.
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Old 05-05-2009, 06:39 PM
1saxman 1saxman is offline
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'It is my belief that this is caused by a reduction in its volume due to the removal of the plastic/wax medium that had formerly composed part of its makeup'

Exactly.
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Old 05-05-2009, 07:32 PM
KyJim KyJim is offline
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Quote:
In fact, the one time I tried to file on a MIM part, it actually yielded less easily to my file than did an equivalent bar-stock part I'd just been working on!
A MIM part may be harder but also more brittle. That's why pre-MIM triggers on SW revolvers are better and easier to smooth.

I also don't think you can simply fire a certain number of shots and expect that to reveal every weak MIM part. Even if we could shoot 1,000 rounds and weed out the bad MIM, then how much have you saved on buying a gun with lots of MIM parts and buying a non-MIM gun. At today's prices, say $20 for 50 rounds of .45, that 1,000 rounds just inflated the cost of your gun by another $400.

I'm not saying a gun has to be 100% MIM-free but they should never be used in stressed areas like slide stops and safeties. And that's exactly where some manufacturers put them.
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Old 05-05-2009, 07:54 PM
pendennis pendennis is online now
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Britt Gardner wrote:
Quote:
After that, the part is heated, again, to just below its melting point, in a process called "sintering."
Sintering is a process which heats the powdered metal to below its melting point, but causes it to become a solid. Sintered metals have been used in the auto industry for years, and it's also part of making ceramics.
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Old 05-05-2009, 08:08 PM
rglock35 rglock35 is offline
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I thought sintering something was putting it in the middle?

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Old 05-05-2009, 10:19 PM
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Quote:
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Britt Gardner wrote:

Sintering is a process which heats the powdered metal to below its melting point, but causes it to become a solid. Sintered metals have been used in the auto industry for years, and it's also part of making ceramics.
You mean like the piston rods GM uses in some of their high performance engines?
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Old 05-05-2009, 10:53 PM
Greyson Greyson is offline
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This topic has been debated incessantly for at least 8-10 years. It only really seems to be a hot topic in the Kimber section. If there is still an interest, I vote this thread be moved there.

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Old 05-06-2009, 07:52 AM
WalterGC WalterGC is offline
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Does "demistified" mean that MIM is no longer a mist?
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Old 05-06-2009, 08:50 AM
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Hilton states that MIM is fine as long as it is done right.

Pat Rogers stated that the MiM parts on the Kimber ICQBs that were issued for a while held up just fine. Many extractors were swapped out, then after that, parts were swapped at their normal maintenance interval.

I never gave it much though, until my Kimber bushing disassembled it's self. I still don't give it much thought. I had the chance to up grade and took it. I don't have any big issues with MIM, however, I think you may have better "luck" with better parts. For me it is moot.

If you want better parts in your gun, pay more money. If you don't care, don't worry about it.
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Old 05-06-2009, 09:54 AM
40dcoe 40dcoe is offline
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Quote:
Originally Posted by Britt Gardner View Post
The advantages to this process are that it's inexpensive, (Don't knock it; it means your gun is less expensive at the counter, too.) and that it can hold extremely precise tolerances.
Product pricing is not a function of cost.

Joe
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Old 05-06-2009, 10:20 AM
brickeyee brickeyee is offline
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Originally Posted by 40dcoe View Post
Product pricing is not a function of cost.

Joe
You have to price above cost, so a floor has been set.

If you can make the item for less money you can pocket the difference if you can support the same price.
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Old 05-06-2009, 10:33 AM
45caldan 45caldan is offline
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I won't worry about MIM in a range gun but I'll have none of it in my carry/SD gun.
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