Downhand welds on Edges

by Rob
(Moose Jaw, Canada)

Where I work, we run a lot of downhand welds... more so than vertical up welds. Never on anything thicker tank gauge, unless it has a wicked gap or requires more than 3 fill passes (3/8'' wall plates gapped about 3/8''). On gauge it works well because you can catch the edges and watch it burn in real nice, without warping the material. On the heavier stuff though, don't even bother... I've actually gotten a scraper behind a downhand pass and peeled it out of there. Like you said, the weld puddle gets out of hand and kind of 'floats' away from the penetration point.

Porosity and lack of fusion in Copper welds

We have a customer that wants us to TIG weld two dissimilar alloys. The first alloy is Bronze 4640 (Nickel, Aluminum, Bronze)and the second alloy is UNS C10100 (Copper). We will also be using the UNS C10100 as filler material. We have done trials with a Miller Maxstar 200SD welder, AC voltage, 100% argon, and 2% thoriated electrodes. We have experienced a large amount of porosity and lack of fusion between the two alloys. Can you offer any suggestions to help? I have heard that DC voltage may work better. How about throwing in some Helium?
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Are you sure you used AC current? a miller maxstar is a DC machine. maybe you meant miller dynasty 200sd.

in any case, dc current will penetrate more. and yes helium would help tremendously. Either uhp pure helium, or a mix of about 80 percent helium, and 20 argon.

also a preheat of around 200-300f would help with better fusion as well as less porosity

Cracking in stainless welds

A friend of mine recently had a set of stainless turbo headers built for his car by a local fab shop. After only a few hours of use we noticed that almost all of the welds had a crack right down the center. After closer inspection it looks like they pulsed over the original welds to make them look cleaner. The welds look pretty good and I am just puzzled on why they cracked in the first place. Was it the pass on top that did it? improper back purging? to much heat? wrong filler? wrong type of stainless for the heating and cooling of an exhaust manifold? I'm fairly new to tig and am trying to educate myself as much as possible. Your site has been by far the best one i have come across so far and i greatly appreciate you taking the time to share your all of your knowledge on here. You kick ass!

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the cracking could be caused by all kinds of different things.

using 303 free machining stainless.

excessive stress

inadequate filler and cross sectional thickness of welds.

if the cracks appeared that quickly, it is possible they already existed and that is why they were welded over.

that seems most likely. cracks welded over by washing leaves a cosmetic weld pass that is very thin.

the crack underneath propagates quickly.