Awesome work Donovan.
The last time I welded in a square patch on a broad flat expanse of sheet metal like that I had a lot of trouble with distortion, particularly with the corners wanting to suck in. I attributed it to shrinkage from each tack cooling. Have you encountered this, and how do you prevent/combat it?
Thanks Jared, and sorry for the late reply. It's been a long day.
What you're describing is pretty much just the nature of the beast unfortunately. Anytime you weld on sheetmetal, you can guarantee to get some sort of warpage or distortion. It's how and what you do to manage and minimize it as you go that can provide the difference.
This patch with the hole in the center of it is the absolute worst type to try to do. Having the hole in the center provides a path for the distortion to propagate, it can be a nightmare to try and bring back straight as evidenced by my 3 hours of hammer and dolly work between last night and tonight. (I did finally get it tho!)
As for just a straight patch, if the panel is particularly straight, that's gonna make it tougher as well. Curved panels are always easier to weld patches in than flat ones.
When I weld in a piece like above, I always start from the centers and work my way outwards. This keeps the distortion from showing up and bunching up in the middle of your patch.
I can't say that I've ever had a particularly bad problem with corners pulling in on me, it may have just been the particular spot or patch shape that you were working with. If you suspect that you may have an issue with a corner or corners pulling in on you, you could always make the corners a large curved radius instead of 90 degree. I've done this in the past, and it seems to help a bit.
After you place a tack how do you let it cool? Do you let it cool and equalize naturally, or do you cool it with other means? I always cool each and every tack for 5-10 seconds with compressed air through a blow gun. If the panel or patch is not cool/cold to the touch on a bare arm from the air, I don't move on to the next until it is.
No matter what you do, the metal is going to move around on you. Stopping frequently and checking what the metal is doing is pretty much a necessity. Hammer and dolly things back to where they need to be before resuming, and you should end up with a quality repair that needs very little finessing by the end. Also be mindful of the heat generated by grinding the welds down afterwards as well. That can cause as many problems as heat from welding.
Hope this helps you out some, any other questions don't hesitate to ask. Always happy to try and help out.
🙂
