How to *properly* straighten out TVP's (or metal..)

[rawfuls]

Been wondering this for ages..

I usually just toss them in the bench vice grips and tighten it until it straightens out..

But I've been doing that, but not completely sure if it's the "proper" way... maybe it damages it in the long run.

But my TVP's are way bent out of the shape, so I'd like to straighten them out without damaging them in the long run?

Thanks...