Pulse is just the switching of 2 values (peak and background) currents, so it will effect the weld pool (heating and cooling Effect) in the same way as on DC. However it is generally used more on DC, more so on Stainless Steel than any other material. Perhaps because it is not easy to weld Aluminium succesfully without filler wire, where as with Stainless Steel especially on thinner material, it is quite common to put Pulse on and run down a seam (Autogenously) particulary thin section outside corners and butt welds
Helps narrow the arc cone on machines that lack frequency adjustment... not that there are many inverters with fixed frequency - Hitachi owners I'm looking at you...
Personally, I can't stand pulse on AC. Its just completely backwards from how I learnt to weld aluminum 'properly' which was on a synchrowave 250 dx.
Pulse is great for stainless steel or other ferrous/nickel/exotic alloys where you want to reduce heat input and narrow your arc.
On aluminum, you want your puddle to form and then you want to get moving (although not too fast sometimes). The bigger your HAZ on aluminum the larger the area you are softening is.
On the other hand you want your aluminium to gas off as you're welding it.
True or false I heard a lot of aerospace shops had real issues when they started getting the first inverters in. Where the square wave pools the aluminium so quick and good welders can speed down the joint at a rate of knots, they started getting big porosity problems. Basically what was happening is where these guys were super fast, the heat input was reduced by the square wave at increased frequencies. This was particularly prevalent in humid times of the year or humid climates.
They went back to the transformers and the issue went away or decreased. They were welding too fast and the moisture on the surface was dissociating leading to hydrogen embrittlement and gross porosity.
I dislike it on ac and there are no real benefits using pulse on materials that are so conducting of heat.
Aluminium soaks up heat so quickly then hangs on to it for a long time. The whole part becomes evenly heat soaked and problems like distortion ain’t usually a big deal. Most of the time it’s very effortless to pull back with manual method.
Stainless is the opposite. It doesn’t dissipate heat it keeps it very locally and shrinkage is very local to the weld.
Heat input reduction is key to avoid distortion. One good method is pulse. So. It’s useful on some dc applications I don’t think it’s very useful on ac at all. Or at least I’ve never seen a benefit