MIM Parts

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gyvel

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OK, guys, educate me. What, if anything, is wrong with MIM parts? Or is this another forged vs. investment cast prejudice?
 
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MIM has gotten a bad reputation mostly from all the problems they had in early life (poor quality and fatigue). Many companies including Wilson Combat and Kimber use MIM. Contrary to what some people will say it's not the same as cast. I have several 1911s which use many MIM parts (extractor, sear, hammer, slide release) and have never had an issue. While I'm sure it's happened I have yet to see an MIM part break during normal use. It's much less expensive to make MIM parts versus machined parts. To quote from Kimber:

"Metal injection molding is a technique for producing high density metal parts by processing powdered metal through conventional plastic injection molding machines. The powdered metal is first mixed with plastic binders, and vegetable oil. The three ingredients are heated and then cooled. Once the solidified material is granulated to a form suitable for feeding into an injection molding machine. A “green” part emerges from the mold in a soft pliable state. At this stage it is 18% oversize due to the presence of the binding materials."

If this thread makes it without Kimber bashing I'll be so amazed....
 
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OP:
OK, guys, educate me. What, if anything, is wrong with MIM parts? Or is this another forged vs. investment cast prejudices?
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For those not familiar with the process, here's something about the advantages:

Metal injection molding, also called "MIM," is a process which combines the way injection molded plastics are formed with powdered metal sintering to create metal or ceramic parts which are stronger, denser and more capable of complex geometric shapes than most forged or die cast metal parts. A relatively new invention in manufacturing, metal injection molding is a fast-growing manufacturing process which combines the flexibility of the injection molding process (which until very recently was used only with rubbers and plastics) with the strong structural integrity of sintered powdered metal. The strength, economy and capacity for complex shapes demonstrated in injection molded metal and ceramic parts are sought-after attributes becoming more widely utilized by telecommunications, automotive, medical and dental instrumentation, industrial parts, orthodontics, firearms, hardware and lock components, computer and electrical application industries, among many others.

Injection molded metal parts are formed from sintered powdered metal, just as are regular powdered metal parts. The powdered metal used in the injection molding process must, however, become "plasticized" in order to flow through the injection molding machine, which is the same machine used for plastic injection molding. Polymers and sometimes wax are added to the powdered metal base, creating what manufacturers call "feedstock." Sometimes feedstock is formed into pellets for easy feed; the pellets are fed through a hopper into a screw conveyor where they are sheared and friction heated until the material becomes malleable, or "plasticized," then it is extruded into a closed die at the screw conveyor's opposite end. The molded part is allowed to cool until it has solidified, then it is ejected and the mold is filled again. These molded but not yet sintered parts are called "green parts."

Green parts' polymers must be extracted through a process called "debinding." Debinding can be done chemically (as through a solvent bath) or thermally, and sometimes the sintering process is even sufficient to break down green parts' polymers, dissipating them during the sintering process. Green parts are sintered between 2200 and 2550 degrees Fahrenheit and shrink 15-20% in the process as the pores where polymers were close, creating densities between 95 and 98%, almost as high as that of wrought metals. Despite the shrinking, closer and more accurate tolerances can be achieved with injection molded metals than with die-casting or forging. This is because the plasticity of the feedstock and the nature of the closed injection mold allow greater design freedom than more restricted methods. Parts which must be cast or forged in multiple pieces can often be molded and sintered as a single part, cutting down on expensive secondary assembly processes.

Ferrous-based alloys are most commonly used in metal injection molding, as well as low alloys, stainless steels, copper, chrome, nickel alloys, semimetals, intermetallic compounds and magnetic ceramics. Injection molding is easier and faster than the process used to form green sand castings, and the sintered parts require very little or no machining to reach their finished state, greatly cutting down on secondary finishing costs such as drilling, etching or assembling. The densities injection molded metals achieve not only give parts much higher strength, but also higher corrosion resistance and, for magnetic compounds, improved magnetic qualities. Injection molded metal parts are usually limited to 100 grams due to feedstock costs and the difficulty of maintaining the structural integrity of the part during the sintering process. Although some short runs may still be more economical than die-casting or forging, injection molded metals are usually manufactured in long runs to balance high overhead mold tooling costs.
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http://www.iqsdirectory.com/metal-injection-molding/

Here's something from STI's web page:

Q. Does STI use any MIM parts?
A1 Yes. We, like most manufacturers, do but not in any of the "critical" stress or wear components. Our good friend Bob Serva of Fusion Firearms has graciously allowed us to quote his response to this question.

"Gentlemen, the hysteria over MIM has been going on for many years. The facts are that MIM and PM (powder metal) are modern manufacturing processes that do have their place. Many parts lend themselves to MIM processes due to there shape and function. I have been working as a manufacturing engineer and closely with the firearms industry for over 20 years. I can give you some of my experience and facts of MIM and PM.

Q. Are MIM parts of lesser quality than cast, forged or barstock?
A. NO. MIM and PM parts if designed and processed properly are as good as the other process for most small part applications. Design, material selection and heat-treatment processes play a big part in quality and serviceable life of the part. For example, most people don’t understand how many products they use everyday that are MIM and PM processed. Items such as the transmission gears in your car, valves, the jaws on the cordless drill you use and many types of carbide tooling for machining to name a few.
Q. Why do manufactures use them in there product?
A. Quality and cost. MIM and PM allow for consistent process that produces repeatability and good quality parts of complicated geometry. Tooling for MIM parts is very expensive and you need to produce a product with some volume in sales or it is very hard to justify the costs.
Q. Can you make substandard quality MIM parts?
A. Yes. Again, design and process control are critical to good quality MIM parts. But this is also true with cast, forged, or barstock parts. If good manufacturing processes are not followed you will get parts of sub-standard quality.
Q. Why do we seem to see more MIM parts fail?
A. This is pure Numbers. Most production firearms include MIM or PM parts- Yes, you might not want to believe it but most all pistols, revolvers, and rifles contain MIM or PM parts. Most people, without knowing the difference, have been using these for many years. Why we hear about it more is because the majority of pistols and revolvers have some MIM content in them. So, if we want to look at this logically you have to think in PPM. (PPM is Parts Per Million- it is a basis to how to figure a parts failure rate and its effect on the product.) For example if in 2005 there were 500,000 pistol produced with MIM slide stops and the failure rate worked out to be 1 failure per 1000, we would see 500 MIM slide stops fail. If in the same year we produced 50,000 with bar stock slide stops with the same failure rate we would hear of 50 failures. So Yes, we do hear of more MIM failures and we probably should due to the fact that they are, at a minimum, of 10 to 1 in annual sales.
So Yes, MIM does has its place and it can and does produce high quality and durable parts. Yes, some will fail, just as cast, forged, and barstock parts also fail. I have used 1000’s of STI parts in production 1911’s over the years and the failure rate was basically the same with MIM as with the other manufacturing processes. I have worked closely with the people at STI for many years and their designs and process controls are first class. They do not skimp or try to cheapen their product to save a nickel. They use the best processes and materials available and they always have the goal to offer their customers products of exceptional quality and attention to detail."
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The advent of MIM parts in commercial applications occurred some time after my engineering education, but it is now relatively mature. I will say that earlier powder metallurgy techniques were once used in critical spacecraft applications, and for low-rate production, even newer techniques are coming down the pike--I've seen amazing demonstrations.

The fact that forging was a traditional technique does not make it better. Heck, there was once a time in which buyers paid extra for "twist" barrels, thinking them to be superior to more modern "fluid steel" barrels!
 
Not all MIM, please

I don't know a lot about MIM, but it has been my experience that firing pins should not be made this way. I have a model 29-10 S&W, and the tip of the firing pin disintegrated after about 1000 or so rounds. S&W was very good about repairing the gun, and they even paid the shipping both ways. I cannot complain about the customer service there. Last time I took it out, however, the replaced pin began breaking up again! Unacceptable!!

Well, I griped on this site, and was directed to Apex Tactical, and I ended up buying a solid, heat-treated, competition firing pin, and I replaced it myself. My point is, I think some have gone too far with these MIM parts. They are sub-standard in some applications, it would appear.
 
OK, guys, educate me. What, if anything, is wrong with MIM parts? Or is this another forged vs. investment cast prejudices?
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MAC / Alberox, in addition some generic MIM info, offers a basic MIM design guide PDF that can be downloaded here: http://www.alberox.com/mim.htm

There's nothing wrong with properly designed and executed MIM. It may not the best choice to blindly duplicate parts designed in 1908 for the fabrication methods of the time but with a little thought and/or starting with the proverbial "clean sheet of paper" it'll perform as well as any of the alternatives.

If this thread makes it without Kimber bashing I'll be so amazed....
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I'm too old to enjoy bashing. However, Kimber was the poster child for "MIM done badly" in the early days. I have had (personally, zero degrees of separation, first person) Kimber MIM parts fail - in fact, twice. This doesn't sour me on MIM or even all of Kimber - just the first wobbly steps that they took.

It would probably be impossible to prove but my memory of the time is that S&W and others had adopted some MIM and most forumites didn't know or care. In the case of S&W, MIM predated the Lock Mess Monster (H/T Tamara) and, if discussed at all, went in the same bucket as crush-fit barrels and unrecessed chambers. After a couple high-profile Kimber-MIM issues, the MIM witchhunt commenced in earnest.

I'm usually circumspect regarding stereotypes but I make an exception for many firearm enthusiasts, most especially revolver aficionados, who can lean dramatically in the direction of hidebound reactionaries. [Seinfeld]Not that there's anything wrong with that.[/Seinfeld]

This subset of revolver folks, if they were fishermen or golfers, would still be using bamboo and persimmon respectively. Fooey on carbon fiber and they would probably boycott Ruger if they learned Ruger was casting titanium heads for Callaway.

These are the folks you remember that griped and moaned at family reunions about the bean counters taking over when transistor radios started showing up in the '50s - they sounded tinny and were made by furr in oars. Clearly, vacuum tubes were superior to transistors and would remain so for for millennia. Their great-great-grandparents stroked out when Eli Whitney started using black heart iron in firearms. Their grandfathers quit their jobs at Rolls-Royce when the automaker went from hand-cut to machine made bolts, stating that the auto was "no longer fit for a gentleman to drive". They state emphatically that every single, solitary, change, without exception, that S&W instituted since the Wright brothers flew at Kittyhawk was mandated by accountants in an effort to cheapen the product and intentionally reduce quality - partially to pad the bottom line but partially simply to irritate the speaker. Any new material or process introduced in the 20th century was an indication of shoddy workmanship, the decline of civilization and the harbinger of poor personal hygiene on the part of our youth.

Worst of all, we have lost contact with the extraterrestrials that taught us how to erect the pyramids, render navigational aids in the form of pictures of chickens discernible only in flight, (space aliens are restricted to VFR) and taught us the mysteries of metallurgy - not since the first half of the 20th century have we even possessed the ability to forge metal with nobility, keeping it both tougher than Tonya Harding and harder than a thrice-divorced diamond.

I'm taking my yew bow, my hand-tooled boots, my 1958 Winchester, a life expectancy of 53 years and susceptibility to polio and going to catch the train. If I hurry, I'll get there before they transition to diesel.
;)
 
I guess I will find out how a revolver holds up with MIM parts. I bought a new S&W 10-14 about six months ago. I have about 125 rounds put throught it and so far nothing has gone wrong. But I will tell you the trigger action is not as smooth as my older Smiths and Rugers. I am a old school guy who believes the best years of gunmaking have past by. Time will tell.
roaddog:rolleyes:
 
I'm too old to enjoy bashing. However, Kimber was the poster child for "MIM done badly" in the early days. I have had (personally, zero degrees of separation, first person) Kimber MIM parts fail - in fact, twice. This doesn't sour me on MIM or even all of Kimber - just the first wobbly steps that they took
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.

I'd have to agree MIM had some real growing pains in the earlier days. Sadly enough some people haven't moved their views on from those early failing parts.
 
MIM = Squeezable metal. Well, I've got my own MIM setup and it's called JB Weld.
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How does it behave after sintering?

MIM does not inject liquid metal, but powdered metal.

It has a very long history in the manufacture of carbide.

When correctly done it is fine.
With low quality control it is a problem.

Almost like machining parts.
Do it right it works.
Have poor QC and the parts may not fit or fail.
 
Like any other manufacturing process, the process has to be appropriate to the task. As many have noted above, the problem isn't necessarily MIM per se, but the improper application. Early Kimbers - and I'll not bash - had just about every part other than slide, frame and barrel, from MIM, and parts failures - such as barrel bushings - revealed that some parts that were designed and intended to be made from machined forgings could not be "replicated" properly via MIM. I'm all for $5 MIM grip safeties, but I still think the critical components should be machined from forgings or barstock if that's the original material and process for which the part was designed.
The first gun to make extensive use of MIM was the Bren Ten, but there never were enough of them to make any determinations about whether or not the design and execution of the parts was really correct for long-term use, and even then, that wouldn't necessarily translate into correct observations about MIM replicas of, for instance, 1911 parts.
 
What about finishing? I have read that MIM parts are difficult to blue or coat due to the (admittedly tiny) presence of "plastic" in them.
 
From the Alberox FAQ:

Q: What type of finish can I expect from a MIMed part?

A: We can get"" Ra 32 micro inches (Ra 0.8 microns) finish straight out of the mold and better with an optional secondary polishing operation.
...

Q: Can you plate a MIMed part?

A: Yes. Basically you can do anything to a MIMed part that you would do with a part of the same material made from a more traditional forming method.
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I am aware of a Grant Cunningham report of flash chrome flaking from MIM hammers in Miculek edition 625s which have a forged trigger / MIM hammer combination. However, I'm going to go out on a limb and speculate that the issue is QC related rather than intrinsic to the process.
 
Worst of all, we have lost contact with the extraterrestrials that taught us how to erect the pyramids, render navigational aids in the form of pictures of chickens discernible only in flight, (space aliens are restricted to VFR) and taught us the mysteries of metallurgy - not since the first half of the 20th century have we even possessed the ability to forge metal with nobility, keeping it both tougher than Tonya Harding and harder than a thrice-divorced diamond.
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FWIW I have evidence that they left circa 1960 after teaching us how to make 3-speed automatic transmissions and Spandex. ;)

Oh yeah, ROFLMAO. :D
 
FWIW I have evidence that they left circa 1960 after teaching us how to make 3-speed automatic transmissions and Spandex.
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.....and jb weld. I wonder if anyone has ever tried to make a gun out of JB Weld?
 
Stamped metal parts had a bad rep too, when the P.38 was a new pistol. Truth is that in some parts on that pistol, like the slide cover, the stamping is vastly superior to the same part milled from forged steel

It all depends on the part being made correctly, and having good engineering behind it. Nothing wrong with MIM. I like steel frames and slides and prefer them. My P.38, my M1911A1, and my Colt 1903 all steel frames and steel slides, love those pistols

I also love my P22 with the MIM slide and poly frame
 
sintering

Sintering is a method for making objects from powder, by heating the material in a sintering furnace below its melting point until its particles adhere to each other. Sintering is traditionally used for manufacturing ceramic objects, and has also found uses in such...
en.wikipedia.org/wiki/Sintering - Cached
 
The P22 has a Zamak (zinc) slide. I guess you could call it injection molded, but cast is closer to accurate. MIM in the context of this thread means steel.
 
MIM generalizations

1. Can we say yet, that the "bugs" have been worked out of the MIM manufacturing process regarding firearms? ......that "quality" MIM parts, in the appropriate application work as well cast or forged parts?

2. Anyone care to discuss what those "appropriate" applications are in a 1911?
 
The Quick, down-and-dirty, Real World answer is to check and see which top custom 1911 builders use MIM parts and for which parts do they choose MIM ??? :)
 
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