An important point to bring out:
Nearly every welder is a 100% duty cycle welder at some point. Duty cycles vary with amperage output. It is also a tool that has often been skewed by marketing, especially in MIGs.
A Mig's duty cycle rating, is almost always rated at an amperage LESS than the maximum output of the welder in order to improve the rating. People are buying what they think is a 200 amp unit and they are, but with a duty cycle rating of may 8-10% at maximum rating. The actual duty cycle may be rated for an amp level as much as 50 amps lower than the maximum output. The "effective" range of output, where welding is practical is really overlooked, and often it is hard to compare apples to apples across brands. The only way to get a true picture of performance is to look at the amps where the duty cycle is given, and try to compare other units in that range.
But companies count on the ignorance of a customer to promote their product. I am not picking on Miller here,but for example... I get a constant request for comparing their 211 model against our 200 model.
They advertise 210 amp output....That's quite good for a small box welder. Ours is only 200 max output...which is a LITTLE weaker. They also advertise 30% duty cycle...but it is only at 150 amps. Ours is 35% not much more, but it is at 160 amps. Our rating at 150 amps is actually 40%. Our 60% duty cycle rating is at 135 amps, and 100% duty cycle rating is right at 100 amps. Miller rates their 100 amp level at 60% and there 100% is around 50 amps or so.
What most people don't realize that the average weld is at a much lower than the 200 amps. In fact, if you were to put an amp meter on it, I would say the amp level would top out at about 130 -160 amps or so for most short circuit welds on average with .030 or .035. So having a high end is great advertisement, but having a respectable duty cycle in the main range of use is more important.
My point being, when you look at duty cycle compare closely the performance at different levels of out put, if you can and consider the type of welding you will be doing. Shield Arc has welded in heavy industrial applications, where it was not an option to take a break. But in reality most MIG welders never get above a 60% duty cycle, even at maximum amps. IF you think you need more duty cycle, then simply get a bigger welder...