Richard.
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- Cambridgeshire
I’m probably stepping outside of the general mig for general hobby home user here and entering more into my own personal line of things where we are looking into the specs on a wps.But you don't have direct control over it, and unless you're a machine it will fluctuate in use (more or less).
Also, unless your plant has a current display (or you attach a meter) you don't really know what you're pulling - you can roughly calculate, but it'll never be like setting 47 amps on a CC source.
If you had a mig plant with a current dial that automagically adjusts voltage and wire speed to maintain that current, then it'd be perfectly valid - but that's not a real CV source.
It can be stated (and I've said it myself) that you need about 40A per mm, but I can't set that, I have to fiddle with voltage, speed and stickout until it works, at which point I'm going to be in that ballpark.
Current is absolutely necessary in this case and although it’s a variable deemed by lots of things it can be controlled to with in practical tolerance. 250amps +-10amps is very achievable by manual processing proving everything else in the wps is followed. You then use the current to calculate the most important thing ever when welding heat input.
You could say exactly the same about travel speed PDG. Can’t be controlled but yes it can within practical tolerance and again without it documented and followed to you cannot calculate heat input. Wire speed is actually less relevant in this case. Yes it must be set to generate your current requirements but you don’t need it to calculate heat input. Man in a shed just needs to know number 6 and number 8 works. I need to know a little more and current is very applicable to mig in my line of things.