We are welding an aluminum joint of 2219 to 2219. The plates are 7/8" thick and the joint has a u-groove configuration with a 1/8" root land. We are currently welding this joint with the following parameters.
Root pass
DC
100% helium
15 volts
10.5 ipm travel speed
35 ipm wire speed
200-210 amps (the part is quite large, so we typically have to dump more heat into it to counteract the heatsink action going on)
Fill passes
DC
100% helium
15 volts
10.5 ipm travel speed
45 ipm wire
240 amps
With the root pass and all the fill passes, it totals roughly 16-17 passes on this joint. Each pass takes about 40 minutes because the part is about 10 feet in diameter.
We etch the mating surfaces prior to any welding, however I'd rather be using an AC balance control to add some cleaning action. I'd like to find a way to juggle a couple things... I'd like to run at a faster travel speed, possibly switch to argon due to the high cost of helium and the wider arc helium creates, maintain control of porosity formation, and also try to maintain a low heat input.
Any suggestions on accomplishing this with a combination of AC vs DC, shielding gases, etc?
Thanks.
Why not GMAW?
1. Way faster
2. Cleaning Action
3. Much smaller HAZ
I'm just throwing this out there cause I've heard of a guy in AL that was doing Nasa stuff DC TIG and preferred it on heavier aluminum, x-ray quality. Anyhow, from what I understand he was using a 60/40 helium/argon mix from what the guy at the WSH was telling me.
That's about all the information I have, unfortunately I have very little on the benefits of using it but thought I'd throw that mix out there for you to ponder.
Shawn
It does sound like a job for GMAW.
Maybe too costly to change the joint but with the penetrating power of GTAW DC helium, couldn't the weld joint be much smaller, requiring fewer passes?
As for GTAW AC, it seems with a good inverter power supply you could run balance 80% or more to the electrode negative side, and run the frequency up 150 Hz or so to constrict the arc.
And then there is variable polarity GTAW as with the old Miller Aerowave.
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