OK boys and girls; now that you have the patch panel built let's prep it for the welding process, first you need to grind a 45 degree angle, or as close as you can get on the outside edge of the patch that you built all the way around it.
You'll do the same around the hole in your corvette frame; this is to help the weld penetrate all the way through the frame on both sides; both sides being the patch side, and the frame side of the rust repair, once this is done we need just a little more prep work.
You'll need to clean the top side of the patch panel that you made with your grinder, and the frame side of the area that your repairing; you can't get the weld area to clean, if you have contaminants on the metal it will make it a lot harder to weld.
Now we need to get the mig welder set-up to do the welding; as I have said earlier you'll need at least 60 amps to weld the frame properly and at least .035 mig wire, now that you have this part finished we'll set the argon regulator, I usually use about 30 LBS.
Although you can play with the regulator to get it where you desire it to be, I'd recommend that you have a piece of the frame steel to test weld on, if you have the amps on the welder set to 60 you'll probably want the wire speed close to 6.
This is why you need a test piece of frame steel, run a few weld beads on it until you get a good looking bead; make sure that it penetrates through the metal by looking at the other side of the weld to see if it did; if it penetrated your ready to go.
You need a magnet to hold the patch in place as you weld it in the frame; use the magnet until you do your first two tack welds, then it's safe to remove it; I'd suggest that you don't just run a straight weld all the way around at once.
Run a one inch bead on the top of the patch, and then move to the bottom of it; after that move from side to side to keep the heat as even as possible, you'll have less of a chance to damage the frame steel this way, remember it's just mild steel.
After your done welding the patch in; it's time to smooth out the weld around the patch area, but first I'd let it cool down a bit, after it cools for about fifteen minutes you should be able to start grinding the welds that you made around the patch area.
Don't get in a hurry; if you think that your in a hurry it will be your first mistake, take your time and don't over grind the weld it will just make more work for you; at this point you should be able to grind the weld smooth, it should almost disappear if you done it right.
If you need to you can use a little body filler on the weld, but it would be much better if you don't have to; if you just take your time and pay attention you should not need body filler in the weld area, just use a smoother grit stone, or disc and the grind marks should go away.
At this point your done; you have successfully repaired the rust in the frame of your corvette and your ready to move to the next step, but that is for another article; I hope that this will help your with your corvette frame rust repair.