Welding Tips and Tricks

So I took on a job building a custom fuel cell / gas tank. It’s 1/8” aluminum 31” x 14” x 7”. I put two baffles in the middle of it and everything was going fine until I put the end caps on. I could get a puddle on either piece of the metal but when I added filler it just went all to pieces. The filler rolls up and turns blackish and will not hardly bond. Is this a sign of a needed back purge or do you guys have another suggestion? Putting the top, bottom and two sides and baffles went fine but the caps killed it.
100% argon
4043 filler 1/32”
Cleaned both sides with acetone
I also cut a hole for the sending unit and spout. This didn’t seem to help. Any ideas, as always, are appreciated.

try welding a piece no a piece same material scrap and make sure its not torch, gas related.
craig

....on open ended queries like yours--pics really help

For whatever reason, you're not getting adequate shielding, probably due to the unknown
joint design, with torch attitude pulling in air to the arc zone--which can relate to lack of technique.

1st rule out the usual suspects for inadequate gas coverage.

are the joint edges sanded/filed/brightened to remove normal AL oxidation and the cut edges,
really brushed, clean of oil, etc. Acetone doesn't remove oxidation.

what is the end cap joint?

why 1/32" filler?

why 4043 on either 5000 or 6000 series parent?

Blocking the inside of the joint with angle or strip helps for top side contamination, as does
back purge, but it's not a cure-all if one can't even get clean puddle on the topside.

Machine setup?

torch used?

This aluminum had the sticky plastic shrink wrap stuff on it so I think the only dirty stuff on the top side could’ve been the filmy stuff. I also could weld a piece of scrap right on top of the tank and it welded fine so I don’t think it’s a gas or torch issue. It’s a CK worldwide torch. 3/32” filler. Haha. My bad.
I didn’t file or grind the top, bottom or long sides and they tacked fine.
Same joint as the other tacks. Just seems like a issue with coverage or something like air trapped inside the tank coming out while I’m trying to tack?

dave is probably right, your not getting coverage on the corner.
what does the corner (end cap). look like pic would help
craig

I’m gonna give it another shot tonight. I’ll try to get a pic but it’s just a simple rectangular box with outside corner joints to weld. Just like the ones in Jody’s latest video.

It sounds like it's blowing out from being sealed. They aren't solid baffles are they? Haha it's probably a mixture of bad torch angle and filler angle or not enough gas flow.

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