You know, the discussion would be nothing without educated and helpful posters. I come from a world where posting in a forum takes somewhat of a leap of faith which only half the time results in an intelligent discussion. This is very gratifying for me. I am considering joining the AWS because of it, and really taking hold of this subject as a professional pursuit. If I can get this shop on one gas (instead of 3-4) it will through no small part of you guys' help.
Anyway, we are working upstream as well, mostly catalyst sections on that side. We also produce mufflers and cats themselves from base raw materials. But the focus is really on our exhaust systems. Visual quality is a priority. To that end, failure due to corrosion is not our concern. It is primarily on the overall aesthetics.
Our mufflers welding with 5% O2 do not have great "finish good" visual quality welds. They are nice beads, but have a sort of greyish/brownish scaly buildup on them. I was told it was "glass" as a result of silicon buildup, or something of that nature. That was one of those moments when I scratched my head, as someone I know has history in the company and with the product was giving me honest to goodness 3rd or 4th hand information. We could scrape the buildup off and reveal a lustrous weld, but the labor at that point is too intensive. As such, mufflers with welds having a brownish buildup are "acceptable."
This appearance is not acceptable on the cat back systems though. With the current configuration on the cat-back robots we have low spatter (meaning, some spatter on start arc here and there, but not a major issue), satin grey welds. There is minimal discoloration on the base material, and no buildup whatsoever. This looks better next to our polished tips and mufflers, and satin stainless pipes than the "grey/browninsh" color ones. But it is not silvery in my initial mental image. All in all, the welds look good from a structural standpoint, but not evoking a "wow, look at those welds!" reaction. When we internally say the weld look good, it might only be in comparison to our mufflers.
Anyway, I pulled some parameters from the teach pendant. Ed called me today and an naturally suggested an AR/CO2 mix. Bump the feed by about 20% and the travel about 10%, drop the volts 'til we're happy. We might get some black or dark coloring on the surface, but we might be able to live with it. I guess it is time to give it a shot!!!
Marcus