Luckily I ran out of flux-core!
 

I just blew a hole in a patch panel that I spent three hour on. Are there any certified welders out there that can give me some tips on welding butt joints? I set the MIG up to run a flat bead, should I back the tip off, lower the settings, weld on one side of the joint or what!

I have a new found appreciation for you guys that butt weld flares now.

You can not use flux-core to weld sheet metal. You need solid wire and CO2 gas.

???? Can anyone confirm that!

I concur that there is no way that you should be using flux core on sheet metal. Use a small wire (.045 in.) MIG set-up, CO2 gas and low voltage (MIG uses a drooping voltage power supply as opposed to stick/TIG which uses drooping current).

For what it is worth, .045" mig wire would not be "small" in fact that is huge! You would wat an .023" wire which unless memory fails me is about as small as is readily available. .030" & .035" are also common, but again for detail work I would stick with the .023" Yes, these are standard mig for use with C25 gas.

yes yes needs to be gas with your wire and if you tring to plug up a small hole use a block of brass behind it to suck up some heat and or use a small scap of metal to patch it. also just a little weld at a time ,,ya can not run a lot at once.bouce a round between a couple of spots a lot

Agreed on the flux core. I often back the other side of the weld with a chunk of wood or iron to keep all the CO2 from escaping the work, especially if I am outdoors. If you are doing sheetmetal joints, low voltage, rapid feed, and an EXCELLENT ground have been my keys to success.

I use .023 wire with a CO2/Argon mix (75/25). I feel that .045 is too big; I've even tried .030 and that was too big. I think flux core is .035

Give yourself about a hacksaw blade width or better gap. Start the weld with the tip at about a 45 degree angle to the surface, with the wire dead in the gap. Pull the trigger and only lay enough bead to bridge the gap. Let up, check your work and let the weld cool for a couple of seconds - until it's just stoppped glowing. Hit it again a couple of millimeters past where the previous 'bridge' was - and build ahead of that to make another bridge. Let it cool again. Get a really damp cloth and quench the area periodically to prevent heat buildup and warping.

That's how I do it, YMMV.

Excellent advice Thom, yes the CO2/Argon mix (75/25) you mention is commonly called C25 in the industry. And if setup properly you wont need any added heatsink or quenching, not that it's a bad idea, just not required. The base metal will cool sufficiently via atmosphere in mere moments, just weld a little, take a break, weld a little, etc...

Wow! Guess I need a new welder. Can it be done with flux core wire? Can I spot weld punched lapped panels with flux core?

One more question. This welder is a HF Easy MIG. It says you can weld with this units wire without gas. Is this really flux core or did I use the wrong term!

You'll probably make a bigger mess trying to fix up that blown weld with your current setup. (Current!!! Ha! No pun intended).

Please note that lap welding patch panels is not recommended - rustproofing such joints fully is not possible and will eventually result in fresh, penetrating rust in the joint.

Yes, that's flux core. There's a special compound in the core of the wire, which burns when you strike the arc, creating a sort of shielding gas.

I was actually talking about welding in the front gas tank support. How else can you do it. It came overlapped from the factory as do many of the welds on the car. The suspension pan is also lapped at the inner fenders as well as at the front support. If you don't punch them and spot weld them what do you do?

Thanks you all for the replies, they are much appreciated.

You can get a" zinc rich" weld through primer(spray bomb) .Then drill the flange on one side with about 5/16 holes to separate the old parts through the existing spot welds .You then fill the holes with weld to attach to the new part.I know it as plug welding.It looks like spot welds when done well. Body shops use the technique to replace individual members in a unitbody all the time. Apply undercoating and your pan can look as new.It looks much more correct than a full bead of weld if the parts were spot welded originally.

I've been doing just what you said, using zinc rich primer, punching 5/16 holes in the top panel and plug welding. Just for the record you actually can weld sheet metal with flux core wire. It seems that it is easier with solid wire and gas. I ran about 15 inches of butt welds before I burned thru it in one spot.

For the area that you burned through there is an easy fix....

get a piece of copper pipe. flatten with a hammer , then back up the burned through area (try to shape the copper to closely match the profile of the area your working on)

Then weld closed the area you burned through.. the weld wont stick to the copper...

dress the area with some scotch brite wheels and you should never know you burned through.

Much good advice. A piece of copper sheet works well. I use a fairly fast wire feed and low power setting. Check out my web page. http://users.rcn.com/kcope/index1.html it shows my struggle welding sheet metal (I've gotten better).

I agree with "widebody911", His answers are spot on, no pun intended.

No substitute for gas. Sure, you can do it, but if you go buy the gas kit, you'll never look back.

I take that back. I have used flux core on my trailer. You can weld a little thicker metal and get good penetration with flux core. But on the sheet metal, I only use MIG. (I want a TIG).