Thread: 2nd shop gathering, metal shaping

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SBC, if you started with a machine set up with flux core and then converted to gas and solid wire, you'll need to open up your machine and swap the leads (the + and -). The machine should be set at the factory where the Flux core burns before the base metal, essentially to create your shielding cloud first. Due to this polarity setup, weld penetration suffers. When swapping to argon mix, there is no longer a need to burn the wire first, and reversing the leads will thus also improve the weld penetration.

Next, sheet metal is a totally different animal than welding up the thicker steels. Probably the most effective method is either TIG or Gas weldiing, using no gap, and no filler, for a strictly fusion welding process. Speed is your friend here, and since my TIG machine is not very effective/responsive on the lower amperage settings, I have relegated myself to using the MIG until such time as I can get a better replacement. Although most people have a mig in their home shop, the disadvantage over the previous two mentioned methods would be the extra consumables needed for dressing the welds, the particulate introduced into the air (breathing protection needed), and what some refer to as a harder weld that is especially prone to cracking. I'd be curious to see the quality of weld that they are having these cracking issues with, and I will say that I have never had any issue with cracking, and I am using a full penetration weld.

I think you'll quickly find that the tighter your butt joint is, the less chance you have of blowing holes. For 18-19 ga sheetmetal, I use a "dot welding" method, of only welding one dot at a time. Next, your heat setting used should be determined by the obtaining of a full penetration weld when welding the dots. If you don't get a full penetration weld, and it just looks like the bead is sitting on top of the metal, your heat is not sufficient. By the time you grind the welds down there will be little holding your patch in and a year or so of road vibration will undo all of your hard work. Now, if you do find you are still blowing holes, before turning down the heat, increase the wire feed. It's like this, if you have enough heat to perform the weld but not enough filler going in, somethings gotta give, hence a blowout. The less the gap, the less the chance of a blowout. Wider gap = more weld filler = more heat = more shrinking = your panel just moved from where you wanted it. Any welding operation you do will cause shrinking, holding a gap isn't going to change that. As far as the TIG welder, they seem to be even more prone to blowing out holes, where a very tight gap is almost a neccessity.

Now, using a hammer and dolly, planish out the weld dots as you go, this should help to counter the shrinking effects from the heat from welding, and then grind the proud of the weld dots off from both sides. I like to use a 1/16 cutoff wheel perpendicular to the weld. It has less contact patch than any other grinding method, so less heat buildup. (Stop just above the metal surface, and it can be dressed flush later with a 3" roloc) This will get the dots out of your way for welding and then planishing the next set of dots. If you were to strike some of the previous dots while trying to planish subsequent ones, you'll be moving the panel causing waves and distortion. Planish and grind as you go, and it helps keep the panel straight and in check. And just like Prell, lather, rinse, repeat. Here's a link to a pretty good thread on welding sheet metal patches, I think with your welding background this stuff will be old hat for you in no time...

http://www.garagejournal.com/forum/s...ad.php?t=53534

I did change the polarity for solid wire.
Looks like I only got partial penetration.
Guess I could weld the back side where penetration is lacking?
Or do you think what is shown is adequate.

For the most part it does have good weld penetration. If I were to guess, I would say not grinding down some of the welds between tacks may be acting as a heat sink for the next one. You'd now need more heat to get the same weld penetration, especially if the panel had cooled any substantial amount. The more mass you have there, in essence you're now welding thicker metal. To check it, I'd do any final sanding/grinding across (perpendicular) the joint, so if a spot is needing to be re-welded the crack (butt joint) will more readily appear and not be hidden in sanding scratches. Also, shine a spot light from the outside and view from inside the panel. It should show you really quick if something needs a touchup.

Here's one I did on a trunk weatherstrip channel replacement. (This is one I planished after the fact) It does show a couple misses there about an inch in from the left end of the weld, but the with consistency of the remaining welds, and not showing any light with the spotlight test, I felt comfortable leaving as is.

NICE - I think you're right about grinding the welds. Its the last tack between 2 previous welds that is not penetrating properly.

AND - rather than continueing next to the previous tack, I was welding midway between two existing welds. Its the last gap that didn't tie in like it should have.

Thanks for the feedback!