Since my project is at a standstill until my wife gets licensed and starts work, I decided to fill in the swiss cheese called our engine bay and also fill in where the a/c lines were in the firewall. The small holes are going very smoothly, but i ran into a snag with the firewall. I made some plugs from the firewall of my parts car and when i went to weld them to my car the metal did nothing but burn and melt. I have my welder on the lowest voltage and my wire feed speed about half way. Has anyone else done this before that could give me some tips? I acquired some thicker plates to make plugs with, and if i have to i will just use alot of tack welds to hold them in place and cover the rest with body filler after grinding. Any help is appreciated!

i have done it on a honda. What kind of welder are you using?

Mig . I'm not sure if this has anything to do with it or not, but our firewalls seem to be made of 2 thin sheets pressed together.

you just need to do small welds on oposite sides so that it doesn't get to much heat in it

This
http://www.we-todd-did-racing.com/wetoddimage.wtdr/wMTEyODA2OTZzNDEzZGZkMzF5NTQx.jpg
To this
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To this
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Via this
http://www.we-todd-did-racing.com/wetoddimage.wtdr/wMTEyODI0ODZzNDEzZGZkMzF5NTQx.jpg

very nice. i will try that later tonight.

you could try turning down your wire speed a little more if you keep having problems

Yes you need to make multiple tack welds, the metal is to thin to run a straight bead. More than likely going to have to make alot of tacks and then grind and maybe some bondo.

For smaller holes,( under 1/2") I just angle the welder toward the edge and start filling slowly. Tack, hold, tack, hold, etc., until its filled. Don't turn the welder too hot, but dont be to cold either. This takes a fair bit of practice as every welder is different. Then grind it down smooth. You can also warp the metal pretty good when grinding, so be careful. Good luck.

Practice on simlar thickness of scrap man. Get the heat and speed down good and go for it. Small tacks are the way to go with thin stuff. Make sure all metal is bare and very clean.

Yep. With something that thin, you're going to need to only weld in 1/2" increments, tops. What you do is weld a bead for a couple of seconds (how much you weld in this time depends on your skill) and then stop. Wait for the metal to stop glowing, then start again. As long as your feed is set right so it doesn't sputter (I like to weld a little "hot" this way and turn the feed down relative to the power) your welds shouldn't look much different than if you had run a continuous bead.

Another thing to do is weld the two pieces on top of each other and weld through the cover plate. This effectively increases the thickness and you can weld more at a time than if you were welding adjacent pieces together. Also keep in mind that while it's thin one way, it's REALLY thick another way, so try to hold the welder parallel to the firewall. This way, you're trying to push your bead through the many feet of metal there instead of through the couple of millimeters' worth of thickness of the plate/firewall.

Lastly, make sure the welder is always moving. If you hold it still, it'll punch through.

if tacking tacking takes to long for you, get a thick piece of aluminum(at least an inch or more), and clamp that somehow behind what you are welding. the aluminum will get rid of the heat very quickly so that you do not burn through. but this also takes some skill too.

Have a friend ready with compressed air works good too.

thanks for the tips everyone! i will put them into use this weekend and let you know how it turned out. keep em coming if anyone has anymore insight.

Are you using gas? You have to on thin metal and make sure you grind/sand the paint off. Copper works alot better as a heat sink compared to aluminum. Weld in small 1/4" or so sections and go to the other side to keep warpage to a min.

Are you using gas?

I didn't even think of that. I don't see a tank near your welder. Are you just using flux? If so, you're going to need gas if you want to weld something that thin...

that is not my welder pictured, but i am not using gas. i'm using a flux core wire for mild steel. i did not think of needing gas either. so you guys strongly suggest i wait until i buy a tank to proceed?

You can flux it, it just greatly limits the amount of welding you can do at a time...

so i should drag the tv out to the garage if i plan to do this without gas. ;)

Nah, don't have to wait that long for it to cool. You won't be waiting half an hour between welds. Just weld a 1/4" or so, then wait until it stops glowing, then start again. Should only be a couple of seconds...

Repeat.