Wire feed speed and deposition rate
On a MIG/MAG machine the wire feed speed is the current: set one and the other follows. This converts between them, and tells you how much metal per hour that means.
Why they are linked
A constant-voltage power source holds the arc length by adjusting its output until the wire burns off exactly as fast as it is fed. Push more wire in and the machine answers with more current. That is why a MIG set has a wire speed knob and not an ampere knob, and why two machines set to the same amps can behave quite differently if the stick-out is not the same.
Stick-out changes everything
The free length of wire between the contact tip and the arc is a resistor. Longer stick-out preheats the wire more, so it melts at a lower current and the penetration drops even though nothing on the panel has changed. Keep it at about 10–15 mm for short arc and 15–25 mm for spray, and keep it constant — a stick-out that wanders is a common cause of a bead that varies along its own length.
Deposition rate is what turns this into money: multiply it by the price per kilogram and the hours, and you have the input for the cost per metre.
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