"The wire feed speed is in direct relation to the amperage at a given wire stickout (length of wire from the contact tip to the arc). The voltage is in the case of a CV (wire welder) the constant and is the length of the arc from the end of the wire to the weld pool, as you change the wire stick out the amperage changes to maintain the weld voltage. A normal wire stick out for short circuit mig welding is 1/4".

The following example may help you understand this with .035 ER70S-6 wire and C25 shield gas set at 20 SCFH flow.
1/4" wire stickout, volts 17 and wire feed speed 150 IPM = 100 amps
3/8" wire stickout, volts 17 and wire feed speed 150 IPM = 50-60 amps due to the resistive heating of the wire between the tip and the arc the weld current drops to the level required to maintain the set voltage.
If you were to reduce the stickout to 1/8" the weld current would increase to approximatly 150 amps to maintain the set voltage.

Typical min and max ranges of each wire diameter for ER70S-6

.024 minimum 30A 15V 105 IPM WFS, maximum 150A 21V 710 IPM WFS
optimum vert. setting 80A 18V 310 IPM WFS
optimum horiz. setting 110A 21V 465 IPM WFS

.030 minimum 50A 17V 95 IPM WFS, maximum 200A 23V 600 IPM WFS
optimum vert. setting 100A 18V 235 IPM WFS
optimum horiz. setting 150A 20V 385 IPM WFS

.035 minimum 50A 18V 75 IPM WFS, maximum 225A 25V 500 IPM WFS
optimum vert. setting 150A 18V 185 IPM WFS
optimum horiz. setting 215A 22V 415 IPM WFS

I hope this helps more than confuses you.
DrIQ"

http://www.hobartwelders.com/weldtal...ire-Feed-Speed