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I'm convinced I must have been in a weld "bubble" these past few years... been doing the same old thing for years, only welding MIG with 75/25 gas, .030 wire, using steel and some stainless (welded to steel) from 16 ga to 3/8 inch. Recently I started to experiment with other metals with MIG, TIG and even a spoolgun (aluminum)... so naturally I've got questions... Using a Miller 251 MIG machine. Trying to weld 304 SS tube and 304 SS 3/8 plate. I have 308L solid .030 wire. Material has been on the shelf for awhile because I was under the impression I needed trimix. While at the LWS the other day, the guy tells me trimix is special order because everyone has a different preference. Then he asks, why not use 100% argon? Says most people use it fine. I didnt know it was an option, but I had a tank... so I tried it. Result: Not what I expected. For starters, this seemed to put me into spray mode? I've only been used to short circuit. (correct me if I am wrong). I experimented with machine settings around 18-20V and 300-400 wire speed. Material was 304 SS 16 ga tube. It seems like the biggest issue I had was gas flow? When I had it up to 20-25 cfm, the weld barely stuck... I experimented in increments down to 8 cfm, which seemed to work the best (but still not good). Is this right? Or is 100% argon, just NOT the way to go? I noticed big droplets in the weld... and it seemed like the eectrode was being "thrown" at the puddle. I must not be used to this mode? I've been reading as I experiment... Is there a way to get a short circuit mode with 304 SS? Similar to what I have been doing? I tired the 75/25 afew months back and it seemed to work better, but I didnt like the final weld apperance. It "looked" brittle to me, which is why I have been holding out for tri mix. (but didnt want to sink the cash or special order, unless needed).Thanks for any insights... Also... when welding SS with MIG, I assume the torch nozzle and gas diffuser are the same for steel? Or should I have different parts for SS?
Reply:100% argon is not a standard gas for use with GMAW SS solid wire. The arc stability sucks, and penetration will be crappy as well. I'm not surprised that you had difficulties. Perhaps the guy behind the counter assumed you were TIG welding? Or just didn't know any better.If you want to run in short circuit, the tri-mix is the best option. 90/7.5/2.5 He/Ar/CO2 is the best mix for this. You can also run 80/18/2 Ar/He/CO2, but the low helium content reduces the heat transfered to the puddle. Arc stability is better with the Ar rich mix, but wetting and penetration are better with the He-rich mix. You can run in spray transfer very nicely with these gases also. but they give the best bang for your buck if you're running in short circuit; because you don't have enough power supply to run spray or you're welding thin material that won't take the heat of spray transfer.If you can run in spray transfer then 98/2 Ar/CO2 is a great choice. Just enough CO2 to stabilize the arc, with senstitizing the stainless and causing corrosion issues. 98/2 Ar/Oxygen will also work, but the puddle is really fluid and harder to control. Surface appearance of the beads is really gray and crappy looking with the Oxygen blend also. It's functional, but not pretty. You'll see the 98/2 Ar/O2 gas listed on most datasheets because the AWS requires the manufacturer's to test with this gas mix when they qualify a product; not because it's their first choice for welding...(EDIT: I have seen 100% argon used with GMAW and SS solid wire for overlay applications. But this is work where they want very little dilution with the base metal usually, and the 100% argon reduces penetration and the resulting dilution; so they put up with the poor arc quality)Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector |
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发表于 2021-8-31 22:24:09