I like to use a 90 degree Die grinder with 2” 36 grit disc to take the welds down. Keep it moving and always use new disc when working small areas as worn disc will just heat the metal instead of cutting the weld down. When the welds are mostly cut down you can hammer and dolly the panel flat and then finish off the leftover weld with a 60 grit disc.





Note before hammer and dolly the panel you will need to grind down the weld on the back side!







The last thing I do is use a 6” random orbital sander with a ¾” foam pad and 100 grit paper to clean the metal.
Thanks
Pat