Powdered metallurgy vs forging

C

cordovan

Joined
May 30, 2007
Messages
47
Hello,

This question came up in another forum. I was hoping to get some weigh in from the amateur (and in Kevin's case not so amateur) metallurgists here on the forum.

The question wasn't asked specifically pertaining to knives but more with regards to machine parts. Sorry to invade the forum with an off topic post. If any consolation, the question could be put to knives as well.

So how do the two stack up. I guess maximum durability to repetitive like loads, shear strength, yield strength might all be good places to start. Is it an apples and oranges comparison or can like materials be used in both forging and metal injection moldings?

Thanks.....
 
Your question is difficult to answer for many reasons. For one it isn't usually an apples to apples comparison, very rarely are you choosing between either powder metallurgy or forged materials. Some machine parts are made by making the part to shape using powder metallurgy, but with powder metallurgy knife steels the powder metallurgy is used to form the initial casting which is then forged down to barstock. In this case the question isn't powder metallurgy vs. forged but conventionally cast vs. PM. If your question is about using powder metallurgy steels with stock removal vs. conventional steel with forging, then it's really just a stock removal vs. forging debate, with a steel comparison thrown in to make the argument more difficult. Of course forging or stock removal could be used with either conventionally cast or powder metallurgy steels, as well.

So the bottom line is I/we need more information for exactly what you're asking for.
 
Well.... You could say I'm researching. Hopeing you guys can help me reason my way through this.

The blanket statement I'm seeing is that pertaining to small parts in revolvers (linkages, sears, etc.) forged parts are the shin dig and MIM parts suck. That's not my blanket statement, just various web rants.

My thoughts are, depends on the manufacture, depends on metallurgical selection for either application, depends on process, depends on the manner / type of stess delivered to the part, depends on heat treat, depends on etc.......

Like I said, this is not necessarily a "knife" topic, but since many on this forum are interested in materials, I thought what the heck.
 
The problem with MIM and sintering is that the steel will not be fully dense, there will be some porosity. If the parts used a PM ingot which was then forged down and then machined or forged to the shape of the part this problem would not occur (at least not nearly to the same extent). How good the densities can be with MIM or how much this effects the final properties I couldn't say, since I don't know much about these things.
 
There' some confusion here as two different things are referred to a "powdered metal".
First is making a part by compressing and sintering [bonding the particles by heating] and a newer method MIM [metal injection molding] .MIM uses metal powder but it's mixed with a wax like polymer and injection molded then sintered. While MIM got a bad reputation especially in firearms it was due to a new technology and applications that were not appropriate. The MIM gun part problems have now been corrected but the MIM bashing seems to go on forever. Both of these methods have a number of variables. For example powder metal parts can be double compressed and sintered getting very close [99 % density] to wrought material properties. Remington Arms has done that for years .
Don't confuse these methods with PM steels such as the Crucible CPM steels or the various European equivalents which start out with powder but are then hot rolled .
In all metal working it's a matter of picking the most appropriate alloy, HT and forming system.
 
We can discuss knives too. I started this thread yesterday to discuss some of the more exotic stuff offered by Bud-K. The point being what sort of unusual process could their manufacturers be using in order to deliver knives, like the example shown, at such extrodinarily low costs. Is this what can be done through the use of powdered metal technology?

link:
http://www.bladeforums.com/forums/showthread.php?t=717411

n2s
 
Hmmmmmmmm..... you guys have my wheels turning which is exactly what I was looking for. Thanks for the input and the link.

True.... the density will never be the same between MIM parts and forged because of the binder initally used in MIM. Which in my way of thinking, MIM parts will always have voids and thus stress risers present. But then again, how much stess do the internals parts of revolvers actually see? Not much I would wager. I would think wear resistance was a bigger issue which can be addressed via case hardening of some sort. As a side note, anyone who thinks that forgings can't have voids is misguided. In work I ran across a 5" steel pin which had fractured right in half. We sent it to a metallurgist for examination. The base material for these forged pins had voids in it created by impurities in the steel. We had to pull the whole lot and replace them.

It seems that the technology of MIM is at a state of sophistication these days that it is competing with forgings. Of course many in the firearms community are resistant to change and will not accept MIM.

The use of MIM is as a cost savings technology. MIM has a very very low shrinkage rate, therefore tight tolerance parts can be produced without additional machining operations.
 
MIM "very low shrinkage rate" NO not at all ! It's actually very high. However that is taken into account when designing the part as is the warping.

Here's one source www.remingtonpmpd.com
 
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