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Welding Sheet Metal


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I am in the process of doing a restoration myself and need to weld some new metal in some cancer areas.  Welding sheet metal is something new for me.  I have purchased a small MIG welder and am using .023” .60 mm wire with 75/25 argon/CO2.  I have practiced stitch butt welding 22 gauge and am improving but still need more practice to keep from burning holes.  The metal I need to weld appears to be 18 gauge.  I have located a supplier of 18 gauge metal but have yet to get it.  Bending the replacement metal to the proper shape without specialty tools could be problematic also.  A couple videos I have watched have said to use 90/10 Argon/CO2 for welding sheet metal.  Will having a higher argon content help that much?

Rust.jpg

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To form the metal, you can make a "buck" using a piece of oak or MDF particle board.  You can also use a steel bar if you are good at grinding.  Shape it to fit the back side of the metal and maybe 1/4"-1/2" thicker than the depth of that rib.  Make a paper pattern for the replacement piece and add 1/4" all around to permit trimming after forming.  Cut out the metal using 20 gauge (easier to form) cold rolled steel, clamp it on top of the wood, and use a body hammer (buy a set with dollies) or slapper to gently tap the metal over the edge of the form and gradually bring it tight to the form.  Grind it smooth with 150-220 grit.  Pick a line on the old part and on the new part and trim both pieces not quite to the line.  Don't make the joint on an inside corner because you won't be able to grind it smooth.  Use a small angle die grinder (Harbor Freight or Tractor Supply) with a 2" diameter pad with 80 grit abrasive to bring the pieces exactly to the lines.  The joint should be very tight before welding, no big gaps.  Tack the repair piece in place, clamping near where you want to weld, then weld an inch at a time and let it cool to prevent warping.  Grind the weld smooth starting with 80 grit, work to 220 grit.  Grind along the length of the weld, not across it.  You will probably have to use a dolly and metal slapper to level the welded area after grinding because the weld metal shrinks as it cools.

 

To fill some of the rust holes, grind away the paint and rust on both sides.  Clamp a piece of copper sheet, perhaps 1/32" to 1/8" thick behind the hole and weld in some metal, grind to level it.  This works for small holes, not 1/2" long openings.

 

The 75/25 Ar/CO2 mix will be fine.   

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18 minutes ago, Gary_Ash said:

To fill some of the rust holes, grind away the paint and rust on both sides.  Clamp a piece of copper sheet, perhaps 1/32" to 1/8" thick behind the hole and weld in some metal, grind to level it.  This works for small holes, not 1/2" long openings.

 

The reality is that the area in the photo is all swiss cheese and any remaining metal between the rust holes is a mere fraction of it's original thickness. Try to weld those rust holes and you'll only end up burning out larger holes when the gossamer sections that remain are melted down into smoking globs. This is just a section and replace job.

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Thanks for the advice.  I have most of the tools Gary shows.  The previous picture did not show the full area.  I hope to avoid cutting all the way to the door because of the complexity of forming the metal in a double curve.  Hoping that I can weld the holes at the far right to avoid that.  There is wood about 3/4 inch behind the rust holes and nails underneath.  Not much room inside either.   Any comments about the shielding gas would be helpful also. 

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75/25 is what I always used in the collision repair shop.  Never heard of 90/10. Gas supplier never offered it back then. Ask your gas supplier for their recommendation.

 

Can you get the wood away from the weld? Even placing  sheet of copper or aluminum in there could help catching that very dry wood on FIRE.

 

So, get a CO2 or other non-destructive fire extinguisher. Water can work, just gets the wood wet. But it will dry. Dry chemical is quite a mess to clean up, but it is easier to clean up dry chemical than to buy another car with another garage.

 

Practice with your 22 awg metal. That will simulate the Swiss cheese door bottom you show. When you can weld that with a minimum of burn through, you are ready to start on the door. 

 

3 hours ago, joe_padavano said:

This is just a section and replace job.

 

Joe is right. Cut the bad area is out and form a replacement part. Butt weld in place where possible. Flange welding leaves an unprotected area to rust again. However, if the car stays inside away from rain and salt, hidden areas from flange welding are not as problematic as cars that are driven in weather.

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Can't get the wood out but I think I can slip a piece of 1/4" copper between the metal and wood.  Do not plan on letting it get wet as it will be garage kept.  This is the only repair left that is keeping me from painting the body.  Lots of fender repairs still to go but I hope to do those through the winter and they will be a different color.  

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On 10/1/2019 at 2:38 PM, ArticiferTom said:

Old piece house siding , that asbestos . Neighbors would miss it ;).

I have three or four bundles of that stuff in my garage attic that was left by the previous owner over 46 years ago.

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This is going to sound sacrilegious, but from what I see in your first picture, and what you know is behind that beer can thick sheet metal, would it not be smarter to lay in some fiberglass on the back side and just bondo the front face ?

You cannot turn the amps (wire feed) down low enough to not constantly blow holes in what I see.

Even with a torch or a TIG this would be tough, and brazing or leading is not the answer either.

So, it is either cut it out and do a patch panel or fiberglass the back side and build up from that.

 

Mike in Colorado 

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23 hours ago, FLYER15015 said:

This is going to sound sacrilegious, but from what I see in your first picture, and what you know is behind that beer can thick sheet metal, would it not be smarter to lay in some fiberglass on the back side and just bondo the front face ?

You cannot turn the amps (wire feed) down low enough to not constantly blow holes in what I see.

Even with a torch or a TIG this would be tough, and brazing or leading is not the answer either.

So, it is either cut it out and do a patch panel or fiberglass the back side and build up from that.

That was what I was going to do at first but became fearful that it would soon reappear after looking at many YouTube videos.    The car has not been outside in 53+ years since I bought it (long story) and I am now on year two of it's restoration.   Not planning on selling it, just want to get it on the road.  

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Hupp,

If you lay the glass cloth on a CLEAN surface in the back, it will bind to the sheet metal just fine and enough of the resin will ooze out to give you something to start with.

You may need just a bit of Bondo as a surface coat to get the finish you want.

Lord only knows how many old cars have had the whole body "floated" with Bondo to get the panels to look right.

I have personally seen the crew at Dave Kindig's place in Salt lake City float a whole car (55 Chevy) to make the panels "better than new".

Then LOTS of sanding primer, prior to any color.

 

Mike in Colorado

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I mention this only because you mention limited welding experience. Should you decide to stitch any of the holes, think of the way a bee seals a honeycomb. If you are welding the left side of a hole your wire should be directed at a shallow angle from the right hitting the edge not the face of the metal. A steep angle can just push the weld to the inside and striking the face builds a protruding weld nugget. 

As far as gas, I have always used c25.

I also agree with fabricating a part and cutting out all but the last half inch so you do not need to shape the end.

Although the others are correct that lap welds will promote corrosion, you may consider leaving an inch above the top bead line on your patch and use structural adhesive along with some plug welds.

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I’ve done both MiG and Tig welding on my cars. While tig welders were very expensive, they are no longer and for the work you are doing, much better than MiG. There can be virtually no grinding necessary nor much or any warping of the metal. I purchased my tig for $730 including a foot pedal control and have never looked back. The guy who did my fine body work told me my welding was better than any he had seen and that most use MiG. The piece you show looks very much like the bottom edge of GM cowls and there are patch panels with the correct shaped molding available. Not sure if they would be exact for your car and might require some massaging like they did on my Olds but still a huge time saver. I believe the company is called American Muscle that makes the patch panels. The pictures show my patch panels that I mig welded in. The running board I tacked with MiG then welded the whole 46” seam with my tig when I got it. Needed almost no filler after some hammer and dolly work. In the bottom picture the running board has been welded about one inch up on the splash apron with the yellow welder in the background. It’s one of the best investments I’ve made for my shop and it has paid for itself already.

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Edited by chistech (see edit history)
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