MIM Barrel?

[Dave85]

I was reading the Feb. 2010 issue of Combat Handguns (I know, Feb. 2010?!), and there was a write-up of the Cobra Shadow .38 Spl. Externally, it appears to be a Cobra knockoff of the S&W 642. What I found most interesting is the fact that the barrel is MIM.

The president of the company states in the article that the rifling is cut, and the threads are machined, after molding. He further states that pressures in the barrel stay low enough for this to be viable. I have always been under the impression that barrel pressures on a revolver are indeed relatively low compared to chamber pressures, so that sounds right to me. Especially since it is chambered for the low-pressured .38 Spl.+P. I just don't know that much about the details of the MIM process and the results it yields.

I do know that there are people here with a good understanding of metallurgy; certainly much greater than mine; and I have looked on as MIM parts have been both decried and defended in these forums. So, the question is: what are their chances of success in this endeavor? Can they really mold, machine, and rifle a barrel and expect it to hold up? And has this been done before?

 

[tekarra]

I read the article and then went to the Cobra website and must admit that I read it several times to understand the process. The cylinder is machined from bar stock to handle the pressure whilst the barrel is MIM which sees a lower pressure as you stated. I believe the statement regarding the machining operations on the barrel after moulding should be after sintering. The parts, after moulding, are somewhat fragile.

In powder metallurgy, which is the basis of MIM, the powder is compressed in a mould and the part is then placed in a furnace at a temperature that melts only the surface of the powder so it fuses to adjacent powder particles. Temperature control is precise as too low a temperature will result in little or no fusion and too high a temperature will result in puddle of metal. In MIM, a polymer is added as a lubricant to aid the movement of the powder particles relative to each other during the moulding operation to lessen moulding pressure. During sintering, the polymer volatilises leaving only the metal. Sintering is done in an oxygen free atmosphere so no oxides are formed on the fused particles which would lead to brittleness.

I have not been involved in powder metallurgy for some years now, so someone else may jump in here and shed some recent thoughts on the topic. The whole aspect of powder metallurgy is interesting and involved, and it is the only process by which the density of metals can be varied.

 

[Dave85]

Thanks for the description, tekarra. Based on what you know about it, is this a sound application for this process?

 

[Jart]

I couldn't locate the article (weak search-fu this day) but, if I'm reading the summary correctly, there's all kinds of wrong here, or at least a series of puzzles.

The part is on the large size for MIM, it's evidently not saving them much in the way of secondary operations since he's threading and rifling the blank. MIM is a dynamic field and has been changing rather quickly relative to other forming methods but I can't see any way he wouldn't be paying more for a MIM barrel blank than one produced by traditional means.

Which makes me wonder what the point of the enterprise is.

Wild speculation leads me to wonder if he's confused MIM with P&S or simply appropriated the initials. MIM is not a copyrighted term and could be applied to any process whereby metal is injected into a mold. I suppose investment cast stainless could be described as "MIM" (though not by me) and would make considerable more sense.

Speculation aside, I would wonder why Cobra is an early adopter of a process not generally applied to a similar part, at what I believe to be higher cost, which brings nothing to the table as he apparently is explaining that it can be used do to lower pressures.

Color me one gigantic question mark until somebody else comes along.

This was my "go to" sub and "barrel blank" still doesn't seem to fit the design guide or FAQ:
http://www.alberox.com/mim.htm

 

[Pestman]

I work at a steel processing plant and I know for a fact if done right Powder Metullurgy is far superior over conventional milling processes. It makes a much more durable metal but I think everyone has their own "secret" way to make it.

 

[Jart]

Powder metallurgy, to include CPM (which the knifeknuts here will be familiar with), P&S and MIM among others, can do some spiffy stuff.

However, my issue with the Cobra implementation is why?

He's not using it due to any sort of "superiority" apart from cost - at least I'm assuming that based on the references to the article where he seems to be allaying fears over pressure containment issues.

Why would anyone preemptively apologize over the use of something superior? It's not like the traditional method has been proven unsatisfactory.

Cobra does not have a long and storied history of spending more than their competition on similar parts. If whatever this mystery blank is happens to be "superior" and "cheaper", how does one reconcile the tone of the article which I take to be "don't worry, be happy"? If it is indeed MIM, it's a new kind of large part, secondary operation required, simple geometry, small lot cost-effective MIM. My personal wild guess based on advances since the mid-70s would be an eventual MIM barrel already threaded and rifled. Invoking the process for a barrel blank has me doing the scene from the Exorcist, minus the hurling part.

Did he mention who his supplier is?

While certainly not a requirement, MIM parts usually have a flat surface somewhere for the prosaic purpose of being able to lay them on a surface during the sintering process.

Alberox design guide excerpt:

Flat Sides: This is not an absolute necessity, however, if there is a flat surface upon which the part can be placed during sintering, it makes setting of the part that much easier. This also greatly reduces the amount of engineering, and therefore cost, that goes into manufacturing a quality MIM part.

Just another puzzle.

 

[w_houle]

Would this explain how the barrel and metal frame can appear as being made from one piece on an LCR, or is the barrel sleeved? Sorry about the question, but the closest I've been is my keyboard and from all the pictures I see, it looks the case.

 

[gyvel]

OMG!!! I can't wait until the first one blows up. LMAO!!: