Chassis Welding - warping

[hotrod56]

Before I get started - wanted opinions. Have a full length chassis to weld up with a center stiffener between the rails. How do you you weld in the center section without causing the rails to pull in towards the center? There is nothing welded to the outside to counter balance the heat. If I keep the rail clamped down, will it stop the pull or will it just spring once its released from being clamped? See the example picture - not my chassis. 174965 Thanks in advance.

[raustinss]

Brace the rails so they cant move inwards , depending on the actual situation I would hydraulically push the frame out maximum of 1/8 " then weld and remove the bracing depending on how "hot " you have your welder will determine how much the frame rails come back . Ideally you would want to weld at most 6" welds ... hop around the frame , left side right side top of frame bottom of frame, front, back etc.. this will help with stress reduction causing shrink

[Canadianwraith]

Spot on advice. Like Ryan said, brace between the rails with something bigger than your final dimension. It will pull in.
The less time you are introducing heat to a spot the better.

[WOLF1732]

Back in the day we use to start at the front and weld all the left hand welds to the back and then go backwards and weld all the right hand welds to the front.

[raustinss]

Back in the day we use to start at the front and weld all the left hand welds to the back and then go backwards and weld all the right hand welds to the front.

Not to be rude but what in the hell does that mean .. left hand or right hand doesnt matter its thermal input into steel ..once cooled it will pull 100 percent true .. unless braced or welded correctly...ie small short welds at a time

[WOLF1732]

Well , weld one direction to the end of the chassis and weld backwards the other side and direction taking the stress out of what you welded going the other way. Any way you do it your going to need to straighten it after welding. all you can do is minimize the warping while welding. I have probably welded 100 chassis in my life and tried every technique possible. warping is going to happen more with mild steel and a lot less with 4130.