Which is better: Forging versus power metallurgy of a large gear?

Question

Manufacturing. Which process would be more appropriate to making a Large gear?

Answer 1

Are you thinking in terms of cost or durability? Also do you mean powder metallurgy?

I would think a forged gear would be better from a durability standpoint.

As far as costs are concerned, I don't know the relation between forged versus powder metallugry. I would guess forged it more expensive.

Answer 2

“Powder” metallurgy makes sense in this context; “power” does not. Hence I assume you mean the former. If by a ‘large’ gear, you mean one that’s say 6 inches or 15 centimeters in diameter, then it is a no-brainer, slam dunk decision: forged gears will be better, by almost any measure, than P/M gears. Even the good folks at mpif.org will not tell you differently, and they are admittedly biased.

Generally what is done is you forge a blank- something close to the shape of your final gear. Then you machine in the teeth and the other close tolerances. Forging tolerances vs. final tolerances are a manufacturing decision- you can certainly pay more money for more dies, to give you higher precision forging- yet since you will likely end up machining for the final dimensions anyway, you stop forging when you have something close.

P/M is a different animal. For a large gear, you would need a very large press: larger than the equivalent press for forging, because you have to press the entire thickness of the gear. Remember also that P/M properties are DIRECTLY related to density, and you have to achieve that density primarily by the pressing (the sintering helps, but the press counts for most of the density).

So with a large forged blank that I make into a machined gear, I will have a stronger, less expensive part than I will with a P/M equivalent. There’s no contest.

Answer 3

I imagine there is more upfront cost associated with forging, but the power metallurgy process is more expensive. So if you are making a large number of these gears (over 1000) go with forging, but if you make less than 1000 then go with power metallurgy. If you need just 1 piece then expect to pay a lot of money with either method.

Answer 4

I may be wrong here, but I would never have "forged" a gear.
I would have machined it.
power metallurgy is i think a quite new process, which still has issues with stresses on the part, so I would say the larger gear can be made with machining.