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Unread 12-09-2011, 07:00 AM   #1
Matt1981CJ7
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Help with MIG welding body panels?

Hey guys,

I'm brand new to welding. Using a Lincoln 140 with .024 solid wire and 75/25 argon/CO2 shield. Power and wire-speed is set per the chart on the welder for 16 ga. mild steel and gas.

I can run nice clean beads, with good penetration, all day long on a flat sheet with no seam. But, when I butt two pieces and try to weld them together, I get blow-thru, especially at any gaps in the butt larger than say 1/32"

I'm aware you should only weld short segments at a time (about 3/4-1"). I've also tried the start/stop spot weld technique, which is better, but I still have trouble at the gaps. I'm going to try using a copper "heat sink" behind the weld, today, to see it that helps.

Any other suggestions?

Thanks,

Matt

weld1.jpg   weld2.jpg   weld3.jpg   weld4.jpg   weldbolwthru.jpg  

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Unread 12-09-2011, 07:10 AM   #2
BioTex
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When I get that blow through, I turn up the wire speed a tad. It cools the puddle a bit. The copper heat sink should help also.
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Unread 12-09-2011, 07:18 AM   #3
Matt1981CJ7
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BioTex,

Well, that's one thing I was doing wrong. In my small mind, reducing the wire speed would cool things down. I'll try going the other way with it.

Matt
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Unread 12-09-2011, 07:19 AM   #4
82JeepCJ7
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You need to add a backing strip in behind the patch panel to make it a lap joint on metal that thin with that big of a gap. You can tack the strip in before putting the patch panel in. Doing that will save you a ton of time and frustration when working with thin metal. Since you can get to the back side, you can put a 1/2" wide strip behind the joint and tack it in. Take your time and allow the metal to cool between spot welds. Also, hard wire does not like any rust or deteriorated metal. If you have to go bigger on the patch panel to get into some good meat, then that's what it takes. I sand blasted my replacement tub and any rusty metal that blew away, I did not want in there anyway. I ended up with some larger patch panels, but I knew in the end that those would be solid and the material around the welds would not crack a few years down the road. And as always with welding..... Practice, practice, practice.
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Unread 12-09-2011, 07:28 AM   #5
Matt1981CJ7
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82JeepC17,

I was into good metal all the way around my patch. It sounds like the heat sink and a backer strip do about the same thing.

I may try the backer strip, since I can't find a scrap piece of copper, and the wife won't let me cut up one of her serving trays.

Thanks,

Matt
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Unread 12-09-2011, 07:35 AM   #6
BioTex
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The draw back to a backing strip welded in is that you now have a seam on the back side that will hold dirt and moisture. It will rot out very fast. The idea is to leave a smooth finish on the back side so it will dry out fast after getting wet. You don't want any ledges for anything to grip to.
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1971 800B with 345/T-19
06' TJ Rubicon, 4" R.C. springs, BFG/AT 35s M.C. 6" fenders, rockers and surrounds, Currie front & rear adj. tracbars, tattons DC rear shaft, adj. upper - lower CA's. Bilstein 5100's
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Unread 12-09-2011, 07:43 AM   #7
Area.3.Fiftyone
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Take a piece of copper pipe and flatten it out for a backer.

You should be able to fill those gaps, they aren't that big. I would start at the bottom and lay a tack then slowly move your way up (after tacking the entire piece in place to prevent movement).

Gravity will help here and the bottom tack will hold the puddle as you progress upwards. If your heat is set right, you should be able to start the arc on one side and then pull the puddle across to the other good piece to bridge the gap.

Good luck!
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Unread 12-09-2011, 07:53 AM   #8
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*Great thread*

Great pics Matt, keep the pics coming on your progress, i'm fixing to tackle the same thing.
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Unread 12-09-2011, 07:54 AM   #9
Matt1981CJ7
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Stan,

You sure know your way around body work...smashing a chunk of copper pipe is a great idea, and it sounds like fun, too.

I still may use a backer in the area shown on my last picture, because I got a little aggressive with the grinder and I think I thinned the metal a little too much.

Thanks, I'll keep working at it until I get it right. I've got one more side to practice on. Thankfully, the areas around the Jeep logos are the only 2 spots on the entire tub that have serious cancer. The rest is all just surface rust that should sand off easily.

Matt
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Unread 12-09-2011, 08:19 AM   #10
Area.3.Fiftyone
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No problem Matt.

I have been doing this for over 35 years and you learn quite a bit from trial and error.
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Unread 12-09-2011, 09:06 AM   #11
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You might also try the Tac,tac,tac method. Keep jumping around. The sheet metal is just too thin to do MIG welding on. If you had TIG you could do a bead. But for Sheet Metal the Multiple tac method works pretty well.

Start out spacing Tac's about 1" apart and then go back and weld 1/2 way in between. Continue to do this untill you are starting to get too much heat in one area. Maybe 3-4 passes. Then just jump around to other parts of the patch.

You will have to wait some times between rounds. You really do not want to put too much heat into the metal at a time. A lite breeze will help to cool but do not take heat out too quick with something like water. You can cause shrinkage issues too. Best if you can jump to another patch on a different area of the body, or take a quick break for a Soda.

Just remember to go slow with the heat. Much easier to do the patch once than to have to try and fix a Shrink/Stretch issue from heat.



Carl
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Unread 12-09-2011, 09:16 AM   #12
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Matt,
One of the best threads I've ever seen for patch panel installations. It's a long read, but worth it.

http://www.garagejournal.com/forum/s...ad.php?t=53534
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Unread 12-09-2011, 09:18 AM   #13
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I've been doing the same thing on my 72 CJ5. I'm using a piece of brass from a truck radiator as a backer. Hold brass on back side with left hand and weld with the right. I'm using the exact same welder and gas combo. I'm new to welding so this has been a learning experience for me. Small spot welds skipping around to prevent too much heat build up is the key. Grind joints smooth when finished. With practice it's hard to tell old metal from new. Take your time and enjoy your results. Good luck and keep us posted.
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Unread 12-09-2011, 09:33 AM   #14
LargeAl
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Magnetic copper backer plate

You might want to try one of these from Eastwood...


I believe Harbor Freight also has something similar if there's one close by.

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Unread 12-09-2011, 09:46 AM   #15
Matt1981CJ7
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Carl,

I used the tac method on the panel shown. It was working beautifully to begin with, but I think I got impatient and rushed it towards the end. The small panel got too hot and wouldn't hold the edge on the last several tacs. Lessen learned.

CSP, if I read another how-to, or watch another youtube, I think I'll go blind. Sometimes there's no substitute for just jumping in and getting your hands dirty.

Overall, I'm fairly pleased with my first body patch attempt. The straight-edge indicates that everything stayed flat and flush. I shouldn't have to use much putty at all. If I can get these last few holes closed up and ground flat, I should be able to move to the other side.

Matt
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