Powder metallury

So we learned about powder metallurgy in one of my classes but I don't understand why you would use it over casting. Can some one inform me?

Not just castings but forgings as well as some other applications. The real driving force is cost. Powdered metal is cheeper.

faster, cheaper, less machinging required.

IIRC its the metallic version of styrofoam. Without much real education on the matter, it would appear though as this form of manufacturing produces a part thats significantly weaker than cast/forged/CNC etc, am I correct?

Its been a while, but I seem to recall its not as strong, so the part might need to be made beefier, but yes, its a lot cheaper in a lot of cases.

A decent number of smaller firearms parts are made with this way now, and there are naysayers. I think they don't really have a high failure rate or anything, its just the're more likely to fail catastrophically than something thats been forged.

Yes it is stronger to machine a part. But I was under the impression that casting was cheaper.

Edited

Different applications also. You make bronze bearings and filters with powdered metals. It is interesting stuff.

Powder also comes in handy for rapid prototyping machines that use lasers to sinter selected areas of powder in each layer. Neat-O.

I dunno if it's cost. Can't you have all sorts of fancy impregnated things if you make a more porous material? And can't you mix stuff that wouldn't otherwise mix? Oh, and aren't 3D printers able to do sintering now?

It's been 10 years since I had an engineering class. I may be misremembering.

Pumpkin Escobar wrote: IIRC its the metallic version of styrofoam. Without much real education on the matter, it would appear though as this form of manufacturing produces a part thats significantly weaker than cast/forged/CNC etc, am I correct?

No.

It is also far easier to make very complicated parts that would otherwise have to be forged, then rough, and finish machined. A lot of transmission parts are now powdered metal. Drive and driven (chain drive) sprockets for most of the GM auto trans are powdered metal. Clutch hubs, synchro hubs, auto trans clutch plates, pump bodies, gerotors, and VVT gears for ecotec motors are all manufactured in the powdered metal plant I work in.

One of our plants is trying to close, and another manufacturer took over a fairly complicated transmission part for the new GM/Ford 6 spd auto. They're casting, and machining, and having a very difficult time making a part that matches the quality, and strength of our PM parts.

http://www.stackpole.com/main.html

If you click on our products, then put the cursor over clutch components, that's the part they're trying to cast.

WOAH...I stand corrected. thats a pretty awesome process then. I am trying now to remember what it was that I was referring to...this may take a while.

As mentioned on another post. Engine connecting rods made of powdered metal are use in a lot of engines. Work vey well.

We had one at work for small components. I don't get the "over cast" statement but I miss a lot sometimes.

Ours used something like very fine baby powder poured into a mold and then subjected to intense heat and pressure. It comes out as a finished part. That's how you make money, but the problem is you need to make a bunch of them to profit.

Castings are omni-directional but brittle. Forgings are uni-directional but subject to porosity, inclusions and cracking. Powders have no grain flow or direction; thus lowering the failure potentilal.

I don't understand it, but my buddy bought big $$$ connecting rods made by this method and pressed as one piece. They break the part at the point where there is normally a machined rod-/-bottom half. The ides is that when you bolt it back together, it goes together along metollographic fissures making it as strong as a one piece unit.

A bit OT, but if you're doing metallurgy in school just for your own information; look into Samurai Swords. When you bang hot metal like a horseshoe and fold it onto itself, that's a fold. These swords are folded over 400 times! Uniderectional folding had a name, omnidirectional has a name, hard, high carbon streels are folded over softer metals to produce a hard edge but with flexibility allowed by the softer stuff. The science of these swords was done at a time when we were throwing rocks at each other!

Ask your teacher about salt quenching, Japanese were doing that 1300 years ago. This forging was done by priests and a maker's apprenticeship was over 25 years. You started with making the wooden scabbards.

Sorry to rant, but this stuff gives me a chubby.

Dan

Lost wax process?

The poster formally known as 96DXCivic wrote: So we learned about powder metallurgy in one of my classes but I don't understand why you would use it over casting. Can some one inform me?

Mostly it allows for injection molding of small and complex parts more cheaply/easily then casting or machining.

I would guess that since less heat is required it is not only cheaper to sinter then to melt, and with less heat the dies likely take less punishment.

It would also allow you to change the alloy through out the part, so wear/contact points can be made of a harder or more expensive alloy while the body is made of a more ductile or cheaper material.

There is another reason to use PM. You get VERY uniform carbide size and grain size. If you are using it in an environment where it will wear, this can be important.

We make and use PM for a variety of applications. One of the biggest that I use is for hot rolling mill rolls. When the material wears, it leaves the same "form" or shape in the rolls. There is no jagged edge or change is shape. The PM does not get "chunks" or "pits" because there are no large grains or carbides to pull out of the material.

914Driver wrote: I don't understand it, but my buddy bought big $$$ connecting rods made by this method and pressed as one piece. They break the part at the point where there is normally a machined rod-/-bottom half. The ides is that when you bolt it back together, it goes together along metollographic fissures making it as strong as a one piece unit.

If I recall correctly, the connecting rods in the first BMW V12 were done this way. I thought the process they used was called "sintering" or something along that line. I don't know that they were powdered metal, but I do remember them being fractued and "re-assembled".

Rob

^They've been using "cracked" rods in sportbike engines for years.

The Ford Zetec as used in the ZX2 has these rods, for one.

I wouldn't be surprised if all of the new Ford engines use them. They are most likely not the only one.

almost every production engine that GM has put in cars for about the last 20 years has had PM connecting rods. the only exceptions i can think of are the high end ultra high performance engines like the LS7 Vette engine that has Titanium rods and maybe some of the supercharged and turbocharged engines.

GM also has a block listed in the '10 Performance Parts catalog for a "compacted graphite" engine block in the DRCE series- for the engines used the the NHRA Pro Stockers.. the part number is 25534406 if anyone wants to look into it..