Welding body panels (MIG, rookie) questions

More of an art than a science - discuss metalworking and welding here.



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PostPosted: Sat Nov 28, 2020 11:36 pm
Good evening! Very glad to be here. Newish to welding and very new to autobody work (the right way)

I have an 86 Grand National, and I have its donor, an 84 Regal. I will be essentially swapping my complete driveline and every body panel to the 84 Regal chassis, seeing as its complete and will be easier for me than doing a shell swap (no easy access to a lift)

My questions -
I will be replacing the floor pan, filling in some rust holes around the front and rear windshield area, and installing a patch panel on the passenger rear quarter. I have a LOTOS 175A MIG running 220V, and will run two setups - 100% argon with Silicone Bronze wire, or 75A/25C with some mild steel wire (70S6 is what it's running now). What would be the best way to prevent warpage when working on that quarter? I'm assuming the floorpan should be pretty straight forward, and some warpage will not hurt. It's going to be 90% butt welding. Im thinking the SiBronze wire will be ideal on the rear quarter seeing as its melts much sooner than the steel, but butt welding with this wire is very tedious.

Please remember I am here for advice, and want to do this myself. I'm mechanically inclined and have welded quite a bit of stick, but not alot of MIG.

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PostPosted: Sun Nov 29, 2020 4:22 pm
I prefer using 75/25 gas and .023" steel wire for sheet metal.

Replacing panels right now on a 1969 Chevy C-10 and you can see pictures of the process here: viewtopic.php?f=12&t=28438

I have a number of other projects with pictures of panel replacement in that forum.
1968 Coronet R/T


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PostPosted: Mon Nov 30, 2020 9:35 am
I haven't used silicone bronze yet, and I'm not sure it's recommended for butte joints. Best thing, if you MUST do butte welds on your panels (factory panels not available) do a bunch of practicing your welding on scrap pieces. Once you get it down pretty well, practice hammer and dolly on your welds. ANY sort of welding is going to put enough heat in a panel to warp it. You must learn to control the warpage. While MIG is not super receptible to H & D work, it can be done, if you are getting good penetration. Some welds will crack, but that's part of the game, just re-weld.
There are other ways to minimize panel damage due to welding, you can look them up. One is keeping weld seams close to a body line, where the strength of the line helps minimize warp damage. Another is weld on a curve, again, the strength of the curve minimizes damage.

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PostPosted: Mon Nov 30, 2020 10:33 am
:goodpost: :goodpost:

For an example of the above. You can see in these pictures how I stayed close to bends and in the curve when welding this used quarter panel in place (they didn't make reproduction panels for this car).
Quarter Install Welding.JPG

Quarter Install Welding 1.JPG


After grinding the welds flat:
Quarter Welds 2.JPG


Because it was a used quarter and had a number of surface imperfections I used polyester primer:
LH Quarter - Poly Primer.JPG
1968 Coronet R/T


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PostPosted: Mon Nov 30, 2020 1:44 pm
I have used Silicon bronze with Tig welding, But Not with my Mig though.
Silicon bronze is almost as strong as ER70S6, But I wouldn't recommend Butt welding sheet metal with it, Its more for Brazing in my opinion.

Keeping heat down in any panel is a Trick! While I do Mig weld panels I don't go in to the idea of Blowing on my welds with a Blow gun to control heat or using heat sinks or wiping with a water soaked rag.

The best way to control heat and minimize its effects is to select the proper type of welding process to use for the particular welding job at hand, IF you have a choice? MIG, TIG or GAS.

Heat warped panels are not an end all deal, Understanding whats going on and how to fix it is the key.
Any weld is going to cause Shrinking of the Panel on the Weld bead area thus the need to Hammer and dolly "ON DOLLEY" on the Weld bead to STRETCH the metal which when done correctly straitens the panel and the warpage caused by the heat.
https://www.youtube.com/watch?v=Rv5bKXJ3kEM&t=13s

If I was going to do a Floor or panels I would probably chose MIG for most of it, If I were to do a Quarter panel repair or any panel that needs to be relatively strait after welding I would chose GAS or TIG,

Both Tig and Gas weld Beads are relatively soft as compared to Mig weld bead.
This is a definite benefit when Hammer and dollying on the weld bead.
Gas weld Bead is softer than TIG! weld bead, but Tig puts less heat into the panel.
So straining the panel is MUCH easier when its Gas welded OR Tig welded.
Mig Weld bead is ROCK HARD! It does not like to be Hammered on, It can crack as Chopolds said when it does all you can do is re-weld and try again.

If all you Have is a Mig all this means nothing to you, But if you have the time and the extra coin investing in some Gas welding equipment and or a Tig welder is really the way to go with Body panel repair.
If I only had enough money to invest in one process Hands down it would be GAS!

https://www.youtube.com/watch?v=tnXDKuMtj_Q&t=68s
https://www.youtube.com/watch?v=fkNtUjxSf7Q&t=312s
https://www.youtube.com/watch?v=cmkx7CKhvxw

Aluminum Gas welded
https://www.youtube.com/watch?v=aF1Srs_e1Aw
Dennis Barnett
A&P Mechanic, FCC General radio Telephone Operator
Line Maintenance A&P Mechanic and MOC Tech specialist.



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PostPosted: Mon Nov 30, 2020 5:19 pm
My trick to hammering MIG welds is to carefully grind off about 80-90% of the weld bead. If there's a lot of bead on the inside of the weld seam, try to knock it down, as well. THEN do your hammer work.



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PostPosted: Mon Nov 30, 2020 8:23 pm
chopolds wrote:My trick to hammering MIG welds is to carefully grind off about 80-90% of the weld bead. If there's a lot of bead on the inside of the weld seam, try to knock it down, as well. THEN do your hammer work.


I agree 100%
Dennis Barnett
A&P Mechanic, FCC General radio Telephone Operator
Line Maintenance A&P Mechanic and MOC Tech specialist.

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