Welding burn thru

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



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PostPosted: Wed Dec 22, 2021 8:40 am
A quick hint: sometimes porosity is not a shortage of shielding gas. On the older stuff we work on, it could be contamination on the backside of the metal being welded. As the metal melts, it also brings forward rust, undercoat, and such, from the inside surface. Try cleaning the backside of the seam before welding, if possible.



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PostPosted: Thu Dec 23, 2021 12:39 am
Doright wrote:Jim
Most of us started with Mig Most are still using a Mig for their own reasons.
I only use the Mig process when it fits the repair I am doing I use Mig, Tig and Gas just depends on the repair, Where its at how easy it is to get access too how strong repair needs to be and what I want after welding.

I learned how to weld with Gas Originally then played with Stick and then bought a Mig and loved it! A Mig is great for welding so many things BUT Thin sheet metal is not one of them in my opinion.
You would be better off Gas welding Body panels in my opinion yes your gonna have a Bigger heat effected zone BUT gas welding weld Bead is softer and easier to Hammer and Dolly than Tig weld bead yes this means whole panels being affected by heat requiring More Dolly work to straiten.
It really is possible to Gas weld with the precision of a Tig IF your really good I have seen it done. Gas really is the best for Auto sheet metal and its cheap to get into!
https://www.youtube.com/watch?v=Rv5bKXJ3kEM

That said Yes Mig weld bead SUCKS! Yes its rock hard, Yes it cracks when Hammer and dolly-ed, Yes its very Porous and Yes you got pin holes! these are the things the promoters of Mig welding thin sheet metal never talk about!!! Or Show in their pics!

After your happy with cleaning up your bead this means grinding front and back doing ALL your hammer and Dolly work, Paint BOTH sides with EPOXY Let it fully cure this can take DAYS depending on Temps! SCUFF it THEN Yes cover both sides with Fiberglass filler Sand as required before paint.

There are many opinions and thoughts on what to do with Weld bead:

Some say to metal treat both sides of weld with a Phosphoric acid treatments before Epoxy, As a rule Epoxy does not like acid of any type! so cleaning surgically clean after treatment is a Must and easier said than done! Advanced stuff not for the lazy Stay away from Acids Till your really willing and able to completely neutralize and surgically clean the metal after treatment this point can not be overstated!
Super clean Lots of soap and water, YES water! and SCRUB! red Scotchbrite and YA! YOUR GONNA GET WET! I like this process for rust protection with a Cold Galvanizing system I use I do whole cars this way But I get help I get a few people involved with the process.
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I have played with just cleaning with Alcohol first As Alcohol is water based, then cleaning with Acetone or MEK then painting with Zinc rich Epoxy followed by Fiberglass and have had good results so far.

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Another Idea is to Tin it and then use Lead which would be the ultimate in my opinion as The Tinning coat will not stick to metal unless its super clean and rust free. Chevman is the guy to talk to about lead hes got it down really good I encourage you to check out his Nomad Build.

viewtopic.php?f=12&t=17047

https://www.youtube.com/watch?v=87fuTnBS2bE

Another idea which would be really cool is Brush Plating which is really out their and over kill BUT would be really Cool. BOTH require surgical Cleaning before and after repair!
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Some just Grind there bead and cover with filler and Paint the car and swear by it!!!!
Point being its your car their is no rite or wrong, really! its up to you decide which is best.


The area is in behind the rear tail light. There is factory bracing back there that doesn't allow me good access. I was able to treat my weld beads from the front but the back is a different story. Because I'm not perfect and rewelded some spots the finished surface in the rear is not smooth. It would be difficult to sand or scuff although I will try. I can however reach with a brush so coating it will have to do. I think I will coat with epoxy then resin and then paint at least a couple layers of our version of Rustoleum, called Tremclad. The face side of course epoxy then fillar.



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PostPosted: Thu Dec 23, 2021 12:47 am
chopolds wrote:A quick hint: sometimes porosity is not a shortage of shielding gas. On the older stuff we work on, it could be contamination on the backside of the metal being welded. As the metal melts, it also brings forward rust, undercoat, and such, from the inside surface. Try cleaning the backside of the seam before welding, if possible.


After I cut the metal out I was able to reach in and prep the back side pretty good. After patching I can only reach in thru the tail light opening. Tricky getting tools and hands all at once back there.



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PostPosted: Thu Dec 23, 2021 1:02 am
So I was just wondering about welding wire. So I've read a few times that mig welding makes the dots or beads hard? Meaning harder to planish, cracks when dollied. Is there not a different makeup of welding wire you can get that would make the result beads softer? More copper or something softer in make up perhaps? Maybe a stupid question...but what the hey!



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PostPosted: Fri Dec 24, 2021 1:51 am
Jimmy

Yes their are other filler wires to use. If you have been doing your research on this web sight you would have read about my choice for Auto metal..... READ.

IF you can get to the back side clean it to bare metal Treat with EPOXY only! front and back Then cover with a Fiberglass filler front and back and leave it alone Then move on. Brush or spray it doesn't matter. DO not try wonder gimmicks or treatments stick to what works clean bare metal epoxy and fiberglass filler. your patch will work fine as long as you use that.

Practice your welding try different wires Try different techniques try Gas welding its cheap to get into, read a lot and Practice! A LOT! go to junk yard get some old hoods or fenders cut them up weld em back together.
You will get their NO it will not happen in one project or over nite!
I been doing this **** for a very long time It takes time, it takes practice, it takes money!
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 Dec 27, 2021 11:41 am
Doright wrote:Jimmy

Yes their are other filler wires to use. If you have been doing your research on this web sight you would have read about my choice for Auto metal..... READ.

IF you can get to the back side clean it to bare metal Treat with EPOXY only! front and back Then cover with a Fiberglass filler front and back and leave it alone Then move on. Brush or spray it doesn't matter. DO not try wonder gimmicks or treatments stick to what works clean bare metal epoxy and fiberglass filler. your patch will work fine as long as you use that.

Practice your welding try different wires Try different techniques try Gas welding its cheap to get into, read a lot and Practice! A LOT! go to junk yard get some old hoods or fenders cut them up weld em back together.
You will get their NO it will not happen in one project or over nite!
I been doing this **** for a very long time It takes time, it takes practice, it takes money!

Got it. Epoxy first then fiberglass. I'm on the right track. Thx Dennis. I'll probably stay with the mig for now. I am practicing a lot...I think. I have what I call my donor cab that I rob sheet metal from. It's all stripped and walnut shelled. Been welding on it, cutting holes in it and then welding them up. It's a learning experience that I'm enjoying. I'm going to look into different wires in the next few days. I appreciate all your guy's experience and knowledge. I'm in the construction biz. People ask me how to 'build' things. I roll my eyes lol. So I know your thoughts when I throw out those newb questions! :rolleyes:



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PostPosted: Sat Jan 08, 2022 12:00 pm
I was on the Eastwood site, checking out new tools and what not, and came across this Magnetic Welding Copper Backer. Comes in different sizes depending on what your doing. https://www.eastwood.com/welders/clamps-tools.html?p=2
Thought this could be good idea for guys like me that tend to burn thru too often. Any thoughts?



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PostPosted: Wed Feb 09, 2022 5:07 pm
jimmystoys wrote:I was on the Eastwood site, checking out new tools and what not, and came across this Magnetic Welding Copper Backer. Any thoughts?


It does work to a point, BUT if you look at back side afterwards you'll see why I don't care for using the Technique (Its a Bandaid for poor welding technique in my opinion.)
Have I done it ? YUP! Do I do it any more? No not if I can help it their are just better ways.

One being :
Use a Step drill bit to clean up the Hole nice a round, then using a Punch tool Punch out a similar size of steel Plug fit it to hole then weld the Plug in as a Patch.

Punch tool :
https://www.amazon.com/Capri-Tools-CP21 ... s9dHJ1ZQ==

Step drill:
https://www.amazon.com/Drill-Titanium-C ... s9dHJ1ZQ==

The Punch tool I show above is just a elcheapo their are Many many mfg of these types of Punches in all kinds of sizes. I have and use Two different Roper Whitney Punches.
I have had good luck with them they stay sharp and punch clean holes.

I credit and thank Chevman for this Technique!
Dennis Barnett
A&P Mechanic, FCC General radio Telephone Operator
Line Maintenance A&P Mechanic and MOC Tech specialist.



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PostPosted: Wed Feb 09, 2022 9:54 pm
Got it Dennis, thx again. It's great hearing from you guys that give awesome suggestions based on your years of experience! :goodjob:



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PostPosted: Sat Apr 23, 2022 11:11 am
So a little update. I've done a small patch repair. Went relatively well. Had a small burn thru but managed to fill it without a lot of drama lol. Unfortunately now I must of had a little too much heat going because I have some distortion going on. The worst is at the body line. I can't really get back there to dolly it because of the inside box curves down there. Any thoughts? I'm curious about my welding. Obviously applied too much heat? I used air to cool the area but maybe too much or should have let it cool naturally? Did a light check from behind and found some pinholes that I've welded up already, so I'm happy with that. Although I will remove all the original paint eventually and spray with epoxy, could I at least treat the patch with epoxy so I could apply some filler? I understand it's better to seal the metal then apply the filler after. The backside I will clean up and treat right away with epoxy. :pcorn:
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