Posted by NCWayne on January 29, 2010 at 07:27:08 from (173.188.168.35):
In Reply to: Welding question posted by NCWayne on January 28, 2010 at 23:41:57:
Having read all of the replies so far let me add a few things from my experience. One is that I agree spray transfer is superior to short circuit transfer any day of the week. However saying it's not available to the typical homeowner is wrong. We have an old Miller MIG machine with 250 amp max output (not sure on the max voltage) and run .045 wire. We used to run a 75/25 gas mix but changed over to 98/2 (98 argon/ 2 oxygen) and it made a huge change. Changing the gas gave us a hotter arc at the same settings and allowed us to get into spray mode without any problems with a typical 'homeowner machine'. I've welded 1/2 plate with it single pass with plenty of penetration and have done multi pass welds on things like the hitch pin on a scraper neck and never had a problem with any of the welds letting go.
We also have one of the larger Millers with 100% duty cycle at 350 amp and the programable feeder. We run a 500lb spool of .054 on it and it's set up with a water cooled torch hooked to the carriage on an old Cincinatti lathe. We modified the lathe with hydraulic drives on head and the feed and use it for buildup work. Over the years we've built up many parts on this machine and have never had a problem doing it using straight. That said when using the 98/2 gas on it we can also get the .052 wire into spray mode with no problem and do it at just over 1/2 range of the machines capabilities.
I see the idea put out that welding poor fitup parts is easier with stick. That may be true for some but myself I can weld up a poor fit alot easier with MIG than stick. I guess that comes from spending some years in a fab shop where we had to do alot of gap filling on light guage materials. In that case there is no way you could weld it all at once so you had to use individual spots built upon each other to fill the gaps. Once you master the 'one spot at the time' technique it's not that hard to do regardless of the material thickness. The main thing is watch the puddle and stop the arc just before it drips. By doing this you achieve maximum heat input and therefore penetration with each individual spot weld. When done properly the resulting weld has the same look as a weld done with TIG (ie-it looks like a stack of dimes laid out).
As far as mfg specifying different methods I can see that happening but most of the mfgs I've seen use MIG more so than anything else. Just watch the Discovery Channel, History Channel, etc and see the shows on shipbuilding and bridge building. I've seen them with a robotic machine attached around the main support column on a bridge runnig MULTIPLE passes of wire on a joint, I've seen robots running sub arc on beams and panels for a ship. Even the repair/mfg shop for Norfolk Southern RR uses MIG for nearly everything. In their case they use flux cored wire with a shielding gas also. I've seen them building a machine that welds long ribbon rails togeher. It uses steel plates two inches thick as part of the frame. They typically V the materials as required and start welding. These machines run cylinders right at 12 inches in diameter in a hinged configuration, with a huge mechanical advantage to the side that grabs the track, since it takes alot to hold a mile long piece of track without slipping. I've seen the two side of one get out of synch where the two 12 inch cylinders acted against each other and bent parts of the frame. Even with all that stress/force applied to the welds, the welds weren't what bent.
I guess in the end my main thing is that I've seen MIG welding viewed as an inferrior process to stick when in fact both will produce a quality weld when done properly. I was just curious as to why people felt that way when history and industry has proven otherwise.
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