MIM vs. Forged Parts.

bountyhunter · Jan 19, 2009

Originally posted by 5Wire:
The crappy reputation you claim for MIM is from people who don't know what they're talking about, not from metallurgists, or, in this case, reputable firearms manufacturers who actually employ metallurgists, listen to them, and perform tests-to-failure on new parts/materials before incorporating them in the products that keep them in business.

Uh- HUH. That's why the gun makers making 1911's started putting out crappy quality MIM extractors and safety levers that sheared or cracked. That's why somebody (I think it was Colt) later exploited the problem and marketed what they called "real steel" extractors machined from..... say it with me now... forged bar stock and charged higher prices for it.

Like I said, there is nothing inherently wrong with MIM, but when the process is poorly controlled it is subject to these catastrophic defects:

1) Air voids in the mold causing weak spots in the part.

2) Inconsistent slurry desnity if powder particle grain size is not uniform.

When MIM is poorly controlled, the probability of failure increases greatly in long thin pieces subject to shear force like extractors and safety levers.

Some people have an irrational fear of MIM based on ignorance and some people just don't get it in general.

I haven't seen any plague of fialures in SW parts made using MIM so I don't think they are a problem. Some people do.

5Wire · Jan 20, 2009

Originally posted by bountyhunter:
[...]
Uh- HUH. That's why the gun makers making 1911's started putting out crappy quality MIM extractors and safety levers that sheared or cracked. That's why somebody (I think it was Colt) later exploited the problem and marketed what they called "real steel" extractors machined from..... say it with me now... forged bar stock and charged higher prices for it.

Like I said, there is nothing inherently wrong with MIM, but when the process is poorly controlled it is subject to these catastrophic defects:

1) Air voids in the mold causing weak spots in the part.

2) Inconsistent slurry desnity if powder particle grain size is not uniform.

When MIM is poorly controlled, the probability of failure increases greatly in long thin pieces subject to shear force like extractors and safety levers.

Some people have an irrational fear of MIM based on ignorance and some people just don't get it in general.

I haven't seen any plague of fialures in SW parts made using MIM so I don't think they are a problem. Some people do.

Well, thanks for answering my questions, bountyhunter. You're a prince.

"Cut from forged bar stock": that would be cut by (milling) EDM, Laser, Bridgeport, or even die cut under pressure, as I posted. Is that right? The feed stock was forged in the sense of the definitions posted, correct? Hammered/hydraulically formed. I get it. But the part itself is not forged as you seemed to imply in earlier posts. Thanks for clearing up.

And as for low bidder, I referred to "reputable" manufacturers. 1911s have some of those among the hundreds who have taken on that design. The good ones changed their ways if things didn't work out. Most outsource placements I'm familiar with are based on quality, delivery, and competitive price (not necessarily low bid).

A long way around to more or less the same page.

44wheelman · Jan 20, 2009

They don't cut a part and then heat it and beat it like blacksmiths did to swords 500 years ago.

That's funny. And yea, I got one of Stevie's guns too, in fact I think I'll go hammer me up a new hand for it now....how do they get all those little dents out of them?

bountyhunter · Jan 20, 2009

Originally posted by 44wheelman:

They don't cut a part and then heat it and beat it like blacksmiths did to swords 500 years ago.

Click to expand...

That's funny. And yea, I got one of Stevie's guns too, in fact I think I'll go hammer me up a new hand for it now....how do they get all those little dents out of them?

That's easy, the hard part is finding a place to buy the tiny anvil and hammer.....

bountyhunter · Jan 20, 2009

Originally posted by 5Wire:

Well, thanks for answering my questions, bountyhunter. You're a prince.

You're entirely welcome.

HOUSTON RICK · Jan 20, 2009

Assuming proper procedures are followed, whether forged or MIM, metal parts can be defective for a number of reasons and that is the more likely source of failure rather than wear - so say my metalurgical friends.

MX-5 · Jan 20, 2009

Hi, folks. Some folks prefer MIM, some forged, but I personally don't believe that "they're both the same" or that its just a matter of taste or preference. There are differences in the two.

After single action firing my "classic" M36, I noticed scratch marks on the backstrap. When I posted a question, a few members suggested that I check the seam on the underside of the MIM hammer. I did. Sure enough, the MIM seam was nicking the backstrap. I sent the gun back to the factory; they "repaired" free of charge. Unfortunately, when I next single action fired the M36, similar nicks reappeared. While this sometimes can happen with forged hammers, you can file the offending portion of the hammer and not lose any structural integrity of the hammer. From what I understand, I don't think it's a good idea to file the seams on an MIM hammer, as it might compromise its integrity.

Deputy · Jan 20, 2009

Funny thing....but Ruger has been making cast firearms for a VERY long time and I don't see them experiencing any problems related to casting.

bountyhunter · Jan 20, 2009

Originally posted by Deputy:
Funny thing....but Ruger has been making cast firearms for a VERY long time and I don't see them experiencing any problems related to casting.

Some of the best frames made were cast, even some high-end 1911's had cast frames. But, for the record, cast and MIM are not at all similar except for the fact they both use a mold.

cast material has less density than either MIM or forged material, but it still can make a good piece depending on what the requirements are. I don't think it's a good choice for small thin parts like extractors or safeties, but Para Ordnance did use cast extractors for a while. They were not great, but most worked OK if you didn't mind retensioning them frequently.

bountyhunter · Jan 20, 2009

Originally posted by MX-5:
While this sometimes can happen with forged hammers, you can file the offending portion of the hammer and not lose any structural integrity of the hammer. From what I understand, I don't think it's a good idea to file the seams on an MIM hammer, as it might compromise its integrity.

Not at all. An MIM part does not have seams. The mold it was in may have had seams which could put surface lines on the MIM part, but the interior of the piece is homogenous mmetal that is fused during the sintering process. Any surface lines are cosmetic. Filing an MIM part is no different than filing a cast or forged part. However, many hammers and triggers are surface hardened and filing through that can cause accelerated wear.

bountyhunter · Jan 20, 2009

Originally posted by HOUSTON RICK:
Assuming proper procedures are followed, whether forged or MIM, metal parts can be defective for a number of reasons and that is the more likely source of failure rather than wear - so say my metalurgical friends.

That is completely true. Even forged bar stock can have defects. The key difference is that both a cast part and a MIM part are molded and then put into service basically without much stress applied to it. If there is an internal defect it usually is not detected until it fails in service.

If a part is cut and machined from bar stock or tool steel, there is more of a chance it will fail during the cutting and grinding and not get into service. Of course, some bad parts get out regardless.

Wyatt Earp · Jan 20, 2009

The misinformation and misunderstanding of sintered metal technology is staggering.

moosedog · Jan 20, 2009

Looks aside, I can feel the difference in double action trigger pulls between my older S&Ws and the MIM actions.
Hard to describe, but I noticed the different feel years ago when they first came out with the newer MIM actions. They may break at the same poundage, but there is a difference how the two surfaces mate and interact.

bountyhunter · Jan 21, 2009

Originally posted by moosedog:
Looks aside, I can feel the difference in double action trigger pulls between my older S&Ws and the MIM actions.
Hard to describe, but I noticed the different feel years ago when they first came out with the newer MIM actions. They may break at the same poundage, but there is a difference how the two surfaces mate and interact.

Maybe it's the rebound slide. The new MIM ones are softer than the old hardened ones and dig into the frame a little more. I have to be honest, after I get done slicking mine up, I can't tell the difference in trigger pulls with MIM if both are equally tweaked up.

However, the new guns with frame mounted firing pins require about 1/2 pound more on the DA trigger because the FMFP takes a bit more pop to get the same level of strike energy.

MX-5 · Jan 21, 2009

Bountyhuner: I'm not an expert on such things. But some folks here mentioned "sintered" metal. I've worked with sintered metal. If it's the same thing as "MIM," in my opinion, I don't think that it is comparable to forged metal. In my experience, sintered metal didn't react the same as forged metal under certain stresses (e.g., sintered metal products tended to crack rather than bend) and when the surface is abraded, sintered metal products lost their structural integrity. I understand what you are saying about the seam in the mold; but I'm not sure that the seam on the MIM hammer is just a cosmetic result of the mold's seam. Whenever I've filed sintered metal products, the integrity of the product was compromised. Granted, these were not gun parts, but from what I've seen, I personally favor forged rather than sintered.

dsf · Jan 21, 2009

Originally posted by moosedog:
Looks aside, I can feel the difference in double action trigger pulls between my older S&Ws and the MIM actions.
Hard to describe, but I noticed the different feel years ago when they first came out with the newer MIM actions. They may break at the same poundage, but there is a difference how the two surfaces mate and interact.

Perhaps someone who knows metallurgy quite well can help, but I always polish (wet'n dry paper) all my bearing surfaces to a high shine & remove all tool marks. Nothing fancy, but smooth as heck. And I've always felt the carbon steel parts have a bit less drag interacting and are just a bit more slick.

Having bought Smiths in the '70's I've felt some pretty gritty factory actions, something I've never encountered on the few MIM guns I've used. So I've tended to think off the shelf MIM beats the machined, but that with a bit of handwork the older internals interact smoother. Perhaps the MIM composition or that it is cast as a liquid presents a slightly less smooth surface?

bountyhunter · Jan 21, 2009

Originally posted by MX-5:
Bountyhuner: I'm not an expert on such things. But some folks here mentioned "sintered" metal.

The MIM part is metal powder that is heated hot enough to fuse solid. That step of the process is comparable to sintering.

Originally posted by MX-5:
Bountyhuner: I've worked with sintered metal. If it's the same thing as "MIM," in my opinion, I don't think that it is comparable to forged metal.

Kind of depends on the definition of "comparable": MIM is about 95% - 98% as dense as forged stock or tool steel. It can be annealed or surface hardened exactly the same after fabrication. If properly made, an MIM piece is so close to a milled part in strength and hardness it is indistinguishable in service life. It clearly has a different appearance, and it holds tolerances so well it requires no fitting or machining after fabrication (the big cost saver).

Originally posted by MX-5:
In my experience, sintered metal didn't react the same as forged metal under certain stresses (e.g., sintered metal products tended to crack rather than bend)

All the data shows that a finished MIM piece is solid steel and behaves as one. It's ductility, tensile strength, etc will depend on what heat treatment and hardening it gets AFTER fusing solid.

Originally posted by MX-5:
I understand what you are saying about the seam in the mold; but I'm not sure that the seam on the MIM hammer is just a cosmetic result of the mold's seam.

If it is made right, it is a solid homogenous piece. If there is an internal defect it's an air void or grain size irregularity or dirt particle or something else.

Originally posted by MX-5:
Granted, these were not gun parts, but from what I've seen, I personally favor forged rather than sintered.

Don't misunderstand: nobody is claiming an MIM part is SUPERIOR to a part milled from forged stock, rather it is NEARLY as good with respect to strength and servicability.... if and only if it is properly made.

If you don't mind paying even more for guns, they can use only machined parts. I think guns already cost way too much.

I read tons of posts from comp shooters who beat the crap out of guns. The routinely dump all the internals out of a new 1911 and spend $300 for new trigger, hammer, sear, disconnector etc without blinking.

For the SW guns, there has been no stampede of MIM failures. In fact, basically NONE of any volume. There were MANY 1911 extractor failures on new guns when they went to MIM but that was pobably a quality problem. My point is, if SW's MIM parts were crap, the comp shooters would be screaming it. They had no bones blowing the whistle on the C+S firing pins that failed frequently and often.

IMHO, when it comes to the hysteria about SW parts that are MIM it's all smoke.

bountyhunter · Jan 21, 2009

Originally posted by sailing1801:

Perhaps the MIM composition or that it is cast as a liquid presents a slightly less smooth surface?

Click to expand...

MIM is never a liquid. The metal powder is mixed with glue to make a slurry paste which is forced into the mold under pressure. That piece is removed from the mold and heated up to burn out the glue and fuse the metal powder (the part also shrinks to it's final size during this step). It's never liquid so it can't be poured into the mold like a cast part is, it has to be injected in.

bountyhunter · Jan 21, 2009

For general info:

http://www.gknsintermetals.com/technology/mimprocess.htm

As shown in this MIM schematic, 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.

http://www.globalspec.com/reference/3198/Metal-Injection-Molding-MIM

Metal injection molding (MIM) is a powder metallurgy process used for manufacturing metal parts. Although MIM uses powder metal, it is nothing like conventional powder metal process. The metal powders used in MIM are 10-100 times smaller than in powder metal processes. Also, the end product of MIM is much higher in density (greater than 95% theoretical density). Unlike powder metal, products manufactured by MIM can be case or through hardened, painted, and drilled and tapped. Metal injection molding can provide a substantial cost savings over conventional metal machining options.

http://www.remingtonpmpd.com/

Remington’s process for metal injection molding (MIM), is a marriage of thermoplastic injection molding and conventional powder metallurgy technologies.

Metal Injection Molding

When we custom-mix quality ingredients, we're starting them on a complex and precisely defined path. The result will be alloys that meet the most exacting specified performance requirements and the highest quality standards.

Design

It's our exclusive, custom-built sintering furnaces that really set us apart. Sintering is the most crucial element in both powder metal and MIM production. Our furnaces feature up to 11 precisely controlled temperature zones.

skeete · Jan 24, 2009

MIM is not as durable as a forging. It will have a very slightly higher failure rate than forgings but not enough to cause cocern to the factory considering how much money they save.
However, even a very slightly higher failure rate means a lot to me in a product used to defend my life.
Colt stopped using MIM extractors several years ago because it was a poor application for MIM parts. Concrete is very strong for a post in compression but I would not want a concrete diving board. Colts MIM extractors were like concrete diving boards-not a good idea.
MIM is absolutely great for manufacturers in saving them time/money in fitting as the MIM parts are usually the correct size out of the mold.
I think one of the reason Glock has such a great reliability record is that it uses no MIM parts and the plastic used is a good application use. I have seen Kimber breakages with MIM parts and some will say that forgings can break too but I think no one has kept an accurate record or comparison though I am sure the firearms service departments have a good idea of this. The cost to failure ratio is acceptable to them.
You will never see MIM parts in critical aircraft components yet you see it in firearms.

MIM vs. Forged Parts.

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