Welding Tips and Tricks

I'm looking for advice on plug welds. I have searched the other posts and found some information, but I'm hoping someone can provide some additional suggestions.

I'm building a dry sump oil tank (all new construction) out of .050" 3003 Aluminum and using 1100 filler rod. I have a Miller Dynasty 200DX and do an OK job welding steel but don't have a lot of experience welding aluminum. I need to add internal baffles to the tank and was planning to use plug welds to anchor them to the cover once it is welded in place. I have tried practicing this type of weld and it didn't work very well. I drilled a 1/4" diameter hole in one piece of alum. and then tried to weld it to another piece underneath. All pieces were cleaned with an alum. only stainless steel brush and wiped down with Lacquer thinner. I was able to start melting the bottom piece, but as soon as I tried to add filler material the upper piece started melting and the hole just got bigger; if there was any gap between the two parts it just didn't work - no surprise there. I'm using 3/32" Lanthanated electrode, gas lens w/#7 cup and about 15 psi Argon.

The suggestions I did find were changing the pulse profile (triangular was suggested), using a larger hole and using a slot instead of a hole; I haven't tried these yet. So I'm looking for any suggestions on how to hold the inner pieces against the outer walls since I won't be able to clamp them together since the tank will be closed at this point - I have thought of using sheet metal screws to pull the pieces together for the plug weld and then removing the screws and welding those (smaller holes) closed, but am open to other ideas. Any ideas or suggestions? BTW: I do know I should use thicker material but the .050" is what I have on hand, and the design may change after some initial use so if it doesn't last, at least I will have the knowledge of how to do it.

Thank you in advance.

-Jim

Try 3/8 holes and sharpen your tungsten to a point so you can focus the heat better.

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If push comes to shove, you could make your baffles have tabs that come through the side of the tank and weld them from the outside.

Mick

First, I would try slots versus holes if that is at all possible with your tooling.

Is it not possible to tack the baffle to the sides before your "close up the tank"? Even reaching way down inside to put several tacks will hold that baffle.

I differ from Warren, in that I'd go smaller not larger on the holes. The trick I have found with this type of weld is that your heat needs to be on the baffle edge, not the tank. That requires a very tight arc and I use a high frequency (200+) to focus the beam. If you are getting blow-out, then you may be too long with the arc. You need to get a dab of filler onto the edge, then stop. Then add another dab and stop. (You are building up a "borrow pile" of filler that you will rely upon to take the heat). Then add filler to the tank side, and wick into the filler, fusing the two. Heat control is critical on this. That's why you can't keep chasing it when it opens up. Stop and let the part cool, or quench it.

Your other option is to weld this in reverse to the above. Add filler outside the hole in a ring. This helps close the hole. Before you get to the center, hit the edge with the arc and some filler to get it to fuse. Then once you're certain you have solid fusion, wick over with a few dabs of filler and close the hole. Let cool fully before grinding flush.

I'd be running balance at 65%, freq at 200, maybe 80 amps using a pedal. I'd also probably use a pyrex cup in a #5; below a #6 you don't need a gas lens, the standard collet body works perfectly well. I have found these types of "dainty and precise welds" in ally favor smaller cups for my best results.

I assume you are bending a 90 degree leg on the top of your baffle and you are not trying to weld to a cut end. If this is correct then you can stick your tungsten in a larger hole and melt into the flat on top of your baffle. Once you get filler to melt into that, the edges of the hole will be no problem to melt in. The tighter the hole the quicker the edges melt and the less time you have to get filler onto the baffle. Higher frequency will help focus the arc as will a sharp tungsten. The main thing is to get the baffle to fuse before the hole edges melt away.

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No mater what size you make the plug holes your welded finish will be a larger diameter. Just the nature of plug welds. There usually engineered based on how big the weld needs to be for the given situation.

Thank you for your comments and suggestions. I will have to give them a try and see what happens. One of the features of the tank is a cylindrical air/oil separator that will need to withstand the force of the air/oil combination from the pump and I'm skeptical that welding to one side of the tank will be adequate, which is one of the reasons I want to use the plug style welds (tank has a rectangular cross section with 3" being the small dimension). The baffles (with flanges) could indeed be welded to one side only as suggested, and I will consider that, though welding those to both faces will cut down on oil-canning of the tank and prolong it's life (or not....). Using the higher frequency was something I hadn't heard of and will certainly try.

All the suggestions are broadening my view of how to build a tank like this, and trying the ideas is giving me more experience welding aluminum.

Thank you.

-Jim