cj737 wrote:Seems counter intuitive. Dual shield is used mostly in structural applications where voltage and penetration is very high. Spray mode is never a problem in flat and horizontal positions. You won’t run spray overhead or vertical because either dual shield or hard wire will be the selected and approved process. So why pulse? Pulse is generally used to control heat input, not a concern in structural.
Hell, if you want pulse spray, just use hard wire. Already dozens of approved processes for it.
I don't disagree with where and when dual shield is primarily used, but I do disagree with the view of pulse being solely used to control heat input with a
wire-feed process. Yes it does do that (control heat input), but it is not the
only useful artifact that can be produced using the process.
Pulse in TIG, which is what I feel most people are familiar with, does indeed reduce heat via dropping the current down to a back-ground, lower current that reduces the heat input via lesser amperage for a portion of the pulse period. I know you know this, so I'm only stating it for the purpose of emphasizing the difference in how my pulse MIGs utilize pulse. In my pulse MIGs, there is of course a lower, background current/voltage happening for a specific time length, but the high-side is where it differs from TIG; in TIG the main welding amperage, the high portion is set at the machine by the user; in other words the welding machine will not increase this for you under any circumstance without user-intervention. Foot-pedal control aside, that is how much current is delivered. In my pulse MIGs, from the talks I've had with techs at HTP and from the research I've done, the high side is
higher than what the user-set WFS would
normally deliver via a traditional short-circuit or axial spray-transfer method. In those methods, WFS determines the amperage (with other variables held constant) because they are "tied together". That is the key difference between traditional GMAW and GTAW. Thus, metal transfer in conventional GMAW cannot be regulated as independent of heat input.
(1)
Example:
- Using 045 solid wire, in short circuit, you typically see about 1A per 1 IPM of wire feed speed
- So for the sake of simplicity, say 250 IPM gets you roughly 250A
In my pulse MIGs, the amperage is manipulated (increased to be specific) by exploiting the "on-portion", meaning the actual pulse that detaches the droplet from the wire. It is during that time-period that the machine can dump much larger serving of amperage,
without it being in proportion to the WFS (the way we are normally accustomed to thinking/viewing current delivery via a wire-feed process, similar to the solid wire example listed above). This is why even with a low WFS when pulse welding thinner steel, the penetration profile can be deeper (using pulse) than what that
same WFS would deliver in a short-circuit filler metal transfer, while still only delivering the
same actual amount of filler metal. WFS stays the same, filler metal delivered stays the same, yet the penetration profile can be made
deeper. Why?
The machine is invisibly (but audibly) "sneaking" in very large bursts of current specifically during the droplet-detachment event. The use of pulsing enables control of ...... and modify penetration without changing average or mean current
(2). Again I want to emphasize that the large burst of current can be much more than what the steady-state current transfer would normally be for that given WFS. IE:
The machine can now control the welding current independently of the metal transfer.
Example:
- At 250 IPM, for the same 045 solid wire in the previous example, the machine using pulse can now be dumping in (just as an example) 400A+ during the droplet detachment event
- .
- The large burst of current can produce two benefits
- a deeper penetration
- while keeping the mean steady-state amperage near the 250A mark.
So now, the key is that the amperage is not tied to the WFS, and can be manipulated "at will" by the machine, based on it's programming. So because the pulse frequency is fast enough that the puddle produced from the peak pulse has not fully solidified, you get the full benefits of the high-amperage peak pulse (deeper penetration) while still maintaining some resemblance of control due to the mean amperage being within reason for the given application.
(1)(2) Source:
Pulse Current Gas Metal Arc Welding: Characteristics, Control and Applications
THAT is why Pro Pulse MIG.
), the arc "on-time" is effectively "on" all the time, which allows the machine to manipulate the current output similar to TIG, but using the wire as the electrode, even if it is being consumed constantly as the droplets are being pinched off. The PP200/220MTS can exploit this scenario to dump up to 300A on the peak pulses in some programs, and the PP300 can dump up to 600A on the peak pulses in some programs. This is why they are sooo effortless in their execution of pulse. They doesn't play around. 
As far as I know, I'm the only person in the world even experimenting with this stuff. 