Back in the dark ages when I ran a high school paint and body shop, we used a tool like this with an air hammer to put a flange on patch panels. It reinforced the joint better than a butt weld, and also helped to minimize warp when the panel was installed. The flea-bay seller is in UK and the shipping is outrageous, but there's probably one on this side of the pond that's less expensive.
www.ebay.com/itm/364539187666?Jerry
