[Kevin Sevcik]

We've taken to riveting our frames specifically because of this. We're just too easily annoyed by everything going completely wonky after welding. So what I'm about to say is from theory and not actual practice welding robot frames.

Theoretically, the best answer to things warping during welding is more heat, not less. Allow me to explain for the uninitiated. Things warp during welding because you're dumping a lot of heat into a small area. That small area heats up and expands. Or tries to. There's all this cold, unexpanded metal around it that resists it expanding, you see. So it expands as much as it can, pushing against the metal around it, and if the force and stress exerted from this expansion exceeds the yield stress, then it yields. It yields and takes a set in its currently not quite as expanded as temperature requires state. And then it cools and shrinks down to smaller than its original size, on account of it's starting to shrink from a smaller size than it really should have been. There's also the fact that the filler metal itself is going to shrink an awful lot just because it froze at the solidification temperature, and it's going to cool down all the way to room temperature.

You can't completely prevent all this from happening, but you can reduce the effects by preheating your part. The closer the surrounding material is to the temperature of the welded area, the less warping you'll see, thanks to there being less difference in expansion between the hot metal and the cold metal. 6061 anneals at 775F, so you don't want to get that hot or your whole piece will get soft. 300F-400F seems to be the recommended range for a preheat temperature.