A criticism I have read of MIM parts is that they are not as strong as traditionaly manufactured parts. Does anyone know if there is empirical research on this issue ?

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I like Ike.

I think that is a difficult question to answer. I took part in a study group which resulted in converting some internal transmission parts from high tensile malleable iron castings to MIM.
It depends upon the part design and usage requirements, the gunsmiths here could probably tell us if broken triggers and hammers are common.
In theory MIM parts can be made to closer tolerances and with very good finishes. In practice? It all depends

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Ipsis Rebus Dictantitbus

Below is from a post I copied and saved a coupla years back. Don't recall which of our members posted it. (But wasn't me!):

By popular request, here's the post from Mr. Herb Belin of S&W -----------------------
"I have read with much interest the many comments in this forum pertaining to MIM, MIM Parts and the use of same in a S&W product. So far I have come away with several impressions and they are "people in general don't like/trust MIM parts" and "no one has said why" I will take a stab at this issue and see where it goes.

As background to our decision to use MIM in some areas of our Mfg Process we took a long hard look at our "Life Time Service
Policy". It was clear to us that any change in any of our products such as the use of MIM components had to show equivalent or better performance and durability to those components that were being replaced or the "Lifetime Service" would haunt us forever. The second consideration was to determine if the change was too radical a departure from S&W mainstream design.

For the performance and durability issues we decided that if MIM could be used for the fabrication of revolver hammers and triggers successfully this would truly be an "Acid Test". There is nothing more important to a revolvers feel than the all-important Single Action Sear that is established between the hammer and the trigger. Mechanically few places in a revolver work harder than at the point where the hammer and trigger bear against each other. If these surfaces wear or loose there "edge" the "feel" is lost. Initial testing was on these two critical parts. Over time we arrived at a point where our best shooters could not tell the difference between a revolver with the old style hammer and trigger and the new MIM components. Special attention was given to their endurance when used in our very light Magnum J frames such as the early prototype 340 & 360 Sc's. None of our revolvers work their components harder than these small magnum revolvers. Throughout this testing MIM held strong and finally we determined that this change judged on the basis of durability and feel was a good one.

The second area of concern to S&W was our customer’s reaction to this departure from the traditional. Many heated, intense discussions resulted but in the end the decision was made to move ahead with MIM.
The issue of cost was only one of the considerations in making this decision. Equally as important was the issue of part-to-part uniformity and the result of this of course is Revolver-to-Revolver consistency. We found that revolvers that used MIM hammers and triggers required almost no Fitter intervention in those areas during final assembly and final inspection and Trigger Pull Monitor rejection rates dropped markedly on finished guns. From an internal process point of view it appeared a "Winner".

Lets shift gears for a moment and talk about the MIM process. It is unclear to me as to the reason for many of the negative feelings on the forum concerning MIM. Typically when people complain and aren't specific in the reason why, the problem is often created by a departure from the "Traditional". Perhaps that is indeed what is bothering some people when they view MIM.

The term MIM stands for Metal Injection Molding. It holds some similarities to Plastic Injection Molding and many differences as well. To start we would take a finally divided metal powder. This could be stainless or carbon steel. Today even Titanium is being used in some MIM fabrications. We would mix the metal powder and a thermoplastic binder (generally a Wax) forming slurry of sorts when heated and inject this mix into a precision mold and finally form what is known as a “Green Part". This part is roughly 30% larger than the finished part it will become at the end of the process. Interestingly enough the Green Part at this stage can be snapped in two with simple finger pressure. The Green Parts are then placed in a Sintering furnace filled with dry Hydrogen gas and the temperature is brought almost to the melting point of the metal being used. Over time the "Wax" in the Green Part is evaporated, the metal fuses and the part shrinks 30% to it's final correct dimensions. At this stage of the process the MIM part has developed 98 to 99%of the density of the older wrought materials and a metallurgy that is almost identical. Dimensionally it is finished and no machining is required. However the job is not yet done and the MIM parts are brought to our Heat Treat facility for hardening and in the case of Hammers and Triggers, Case Hardening. Depending on the particular metal alloy that was used at the start of the process we apply a heat treat process that is the same as would be used if the material were the older wrought style. Final hardness, Case thickness and core hardness are for the most part identical to parts manufactured the older way.

Lets look for a moment at how we achieve dimensional precision when comparing these 2 processes. The old parts were each machined from either bar stock or a forging. Each cut and every resulting dimension was subject to machine variations, Cutter wear, operator variations etc. If every operation was done exactly right each and every time and the cutter didn't let you down you would have produced a good part but sometimes this didn’t happen resulting in a rejected gun and rework or in the worst case an unhappy customer. With MIM parts you must still machine to very high tolerances and your cutters have to be perfect and your machinist has to be highly qualified but all of this only has to come together one time. That time is when the injection mold is made. Typically a mold for this process costs S&W between 30,000 and 50,000 dollars. Once it is perfect every part it makes mirrors this perfection and you have in my view a wonderful manufacturing process.

Hopefully this description will help us all better understand the MIM process.
Please forgive the spelling errors and misplaced punctuation. I have no spell checker on this and the phone continues to ring!

Have a Great Weekend,
Herb

Additional Point.
Currently S&W is paying about $1.20/Lb for stainless steel bar stock. Raw MIM stainless steel inject able material costs $10.00/Lb."



Post on MIM from S&W Forum, requoted by a member as an old post, April 2007

In theory MIM parts can be very strong. Some manufacturers or their suppliers have had less than perfect quality control during the manufacturing process and caused the whole MIM issue to come to light. I think some people would be amazed to find out just how many MIM parts are out there working just fine.

Wilson Combat used MIM parts for a few years, forget exactly which, but early years of this century, I believe. Then they stopped because of the perception that they are not good. Here is a Wilson guy at the time explaining MIM. (I snatched this off another site some years ago.)


"...One other thing I forgot to address. MIM parts. A company that I will not name gave the MIM parts a bad name because they had a bad batch of MIM parts. This was many years ago. Since then remarkable things have happened.

MIM parts are extremely dense and very exact. They are much less prone to wear and breakage than a factory Colt, Spfg. etc. part. This is why we use them in our CQB's, etc.

Although not quite as hard as our tool steel parts, they will last a very long time. This is why we can still quarante our total gun, including the MIM parts, for life.

The tool steel parts are actually overkill. The MIM parts last for life (I know of one gun that has over 100,000 rounds thru it and the trigger pull feels the same as it did when new) therefore I guess you could say the tool steel parts lasts for a lifetime and ½.

We use the tool steel parts in our full custom guns. (These are the ones that cost from $2800.00 up) Our full custom guns, Stealth, Tactical Elite, Super Grade and Tactical Super Grade, are not for everyone because of price. They are intended for someone that can afford the very best we can do.

They actually won't last any longer, shoot any straighter or be more dependable than our CQB's, Protectors and Classics, but we spend many extra hours in fitting and prepping them for a perfect cosmetic handgun as well as a great shooter. And because of this, we use the tool steel parts that take longer to fit.

Again, all of us guys here, including Bill Wilson use the very same MIM parts in our guns. And we shoot a bunch! Once installed and fit, no one can tell the difference in the feel of the trigger pull with either type of parts.

Ok, I'm done with my book. Hope this helps too. Just didn't want you all to believe everything you read from self appointed experts.

Frank Robbins Wilson Combat"

It is also a misconception to think that a forging is necessarily stronger than a bar stock or MIM part. Nor is the bar stock part necessarily stronger. Again it all depends, all other things being equal, grain structure is a tricky thing.
Investment cast steel has had a bad reputation, yet the very highest strength turbine parts are usually investment castings.
I can remember when the first Stainless Steel production guns came on the market. Much moaning---won’t work, won’t last, blow up in your hand, etc, etc.
So we pick a company and depend upon them, beware of engineering advice coming from the gun writers, it is about as sound as financial advice from a community organizer.

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Ipsis Rebus Dictantitbus

Hmmm...let's see now...would I rather have FORGED STEEL PARTS that were finish-machined by human hands on real machine tools or replicas of those parts made from a powdered metal held together with a plactic binder injected into a mold and popped out by the thousands?

Decisions, decisions....

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'Merica!

Without wanting to be argumentative, any binder in a MIM part is long gone during the sintering stage of the process. Modern forging of small parts on a high production basis is much automated process (except maybe in China?). I suggest not a hell of a lot of hands on there. Same could be said of the machining from bar stock.
Some makers put plastic parts in their pistols, not for me I guess. I took a perfectly usable plastic guide rod out of my SIG 220, bleah, probably voided the warrantee.

I like the forged and case hardened parts too, but in my case it’s mostly tradition not science.

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Ipsis Rebus Dictantitbus

No argument from me, Roger. Yes, you're right, the binder is a temporary part of the process. I know that current MIM technology produces accurate, high-quality parts...but that's why I only buy older S&W's...because they don't make them like that anymore.

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'Merica!

I honestly don't know if MIM parts are better or worse than traditional forged/machined parts, but the PERCEPTION is strong that gun manufacturers went to MIM parts simply because they are cheaper to produce. To me it falls into the same category as S&W's decision to produce multi-piece barrels for certain guns. I don't believe they made that decision because it results in a superior handgun, but because it is cheaper and most buyers will not notice or care.

Custom gun makers generally don't use MIM parts...ya gets what ya pays for!

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'Merica!

True, but I would not expect someone who makes their living hand fitting mismatched parts to be a fan of parts that don't require that fitting. Why would they advocate something that is taking food off their table?

Bob

I am trying to keep an open mind when it comes to advances in materials and manufacturing techniques. I waited well over 25 years to buy a polymer handgun. I have an M&P and love it. It is apparently pretty reliable since I have read about 50,000+ round tortue test that it passed. I should have at least tried a polymer firearm years ago. I have only one S&W with an MIM trigger and hammer. It is the 638 that I use for concealed carry. It has been reliable and can tell no difference in the feel of the action or trigger pull. MIM parts are in use successfully in a lot more demanding applications than firearms parts. I don't have a problem with them.

XYZ entity produces a widget of some sort. XYZ tells the unknowing that the widget is produced to the highest quality standards and manufacturing technology. What XYZ isn’t telling the unknowing is that their producing the widget with the technology they have available to them. XYZ may not have the option of employing better technology because of economic constraints.

Like it or not Glock is a cost effective design. Its basically drop in assembly. SIG has a modular fire control system now that allows multiple configurations and calibers in a pistol series. The other day I received a Dillon pistol die set which is modular in concept.

There is vast array of manufacturing technology they maybe employed. The quantity/cost to be produced usually decided the method of production with all other considerations being equal.

Quote: ”Custom gun makers generally don't use MIM parts.”
If you were to put the cost in order from cheapest to most expensive of the first say 100 pcs similar to hammers, I think it would go; bar stock mostly material & labor; forged dies and set-up quite expensive; and MIM very expensive, the savings comes from volume. So for someone making only a few machined from bar stock is the way to go.
Add to that the perception that the part is better and we get: “We carefully machine and hand fit all of our parts” thus making virtue of necessity.
Quote; “True, but I would not expect someone who makes their living hand fitting mismatched parts to be a fan of parts that don't require that fitting. Why would they advocate something that is taking food off their table?”
Exactly, especially if they have no real choice except use a part made buy say Caspian.

In the 1911 world the great gunsmiths of the 60’s like Swenson (sp?) & Clark made their parts, welded-up, slides and barrels etc, and produced something very fine from what was a rough machine.
Now of course, all sorts of parts made by every method are available. The result is certainly a better 1911.

Would I like to find a triple lock that I could afford? You bet.

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Ipsis Rebus Dictantitbus

I was JUST about to repost it myself, as I had also saved it. Then, I thought I'd better search the board first. Kudos to you for saving it also.

MIM is so good, that the Performance Center says they don't use MIM parts in their guns. Nuff said. Regards 18DAI.

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7 +1 Rounds of hope & change

Many of my clients are PM and MIM manufacturers, and I design and custom program PLC controls for their presses and ovens.

PM and MIM parts are as strong as the application requires them to be. Strength is a function of design features of the part itself, as well as compacted (green) density, sintered density, and the alloy of the powder being pressed. A part without much loading can be pressed from straight iron powder. If strength or hardness is needed, then nickel-containing sinter-hardening powders or heat-treatable powders are used. I'm aware of some hardened PM and MIM parts that actually wear out softer parts which they mate aganst in their respective assemblies.

There are even forged PM and MIM parts. Yes, the sintered compacted part is later heated and forged. An example of this is engine connecting rods. Approximately 35% of all production engines use forged PM connecting rods made by two PM companies. The forging step serves to further densify the sintered con rod, increasing strength.

Transfer case drive chain sprockets, engine timing gear and sprockets, and automatic transmission sprockets and clutch rings have been PM for decades. The gearing in virtually every power tool manufactured is PM or MIM. The one-way drive clutches in the hubs of my 25-yr-old self-propelled Honda walk behind mower are PM, and have never been replaced.

As for firearms, I think that most people would agree that the industry shift to machining firearm components in CNC machining centers is an improvement. Repeatability and accuracy of machined receivers, frames, barrels, and cylinders is much improved over that of former methods requiring much hand fitting and assembly. Consider then, that these more "true to print" CNC-machined components require more accurate and equally "true to print" internal parts. MIM and PM offer the firearm manufacturer parts that meet those requirements.

IMO and experience, MIM doesn't deserve the bad rep that it has. I fully recognize that MIM parts have broken for some owners. Some parts may not have been properly processed or even designed correctly from the start. And I do NOT like 1911 extractors made from MIM. But the vast majority of MIM parts function and function well. Personally, I do not like the higher-pitched "tinny" sound that S&W MIM lockwork has, but I don't let it stop me from buying a non-lock MIM-containing S&W revolver.

JMO and experience,

Noah

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Nicht mehr als 30 Zeichen

Quote: "MSRP: $325The Offset's rugged and complex blade geometry is provided through state-of-the-art Metal Injection Molding (MIM) and hot isostatic pressing. The result is a precision blade with two bevel geometries, hollow and flat, for incredible cutting power. This process produces a premium 440C-PM stainless-steel blade with complex, true 3-D geometry. The Offset also features the latest SpeedSafe configuration. It's our "Double Pumper" design and it features two torsion bars to ensure easy assisted opening for folding knives with larger blades"

It's a Kershaw knife with a complex shaped blade.Note it is made with a modified MIM process.Anyone have one of these or familiar with it?

IIRC , Colt tried sintered metal lockwork parts in their early Mk.III revolvers. I believe they had a few recalls.

S&W makes a few transmission parts for Harley Davidson. They make forged shifter forks and MIM gears. The forks are fine. Gears have been known to fail.

"Hmmm...let's see now...would I rather have FORGED STEEL PARTS that were finish-machined by human hands on real machine tools "
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Human hands, that get tired, have an off day, have a fight with the wife, etc. - in short, they are human.

Like everyone else, I like pretty, hand-finished parts, but I can rarely afford to pay for them anymore. Would I rather have a precision part that works well, or a part rushed through production as fast as possible by humans? No contest.

I have another thread somewhere about a recent show that had a segment on making the .500 magnum. Computers check each frame after it's machined, and if there's a discrepancy of 1/1000 of an inch, they "tell" the milling machine to change bits - and it does so without human help. Really very impressive. If I could afford to have all my guns made by hand one at a time by one person or a small shop, I would, but I can't. I'm gald S&W makes it affordable to buy their products, which I love. This process also makes it possible for them to stay in business.