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.
Diameter, current and feed
| Ø, mm | Working current, A | Feed, m/min | Metal thickness, mm |
|---|---|---|---|
| 0.8 | 60–180 | 3–12 | 0.8–4 |
| 1.0 | 100–250 | 4–11.5 | 1.5–8 |
| 1.2 | 140–330 | 3.5–10.5 | 3–15 |
| 1.6 | 240–450 | 4–8 | from 8 |
The feed column is worked out with the same formula the calculator above uses, so the table and the result cannot drift apart.
Frequently asked questions
Why does the machine set feed speed rather than current?
Because in MIG/MAG the current follows the feed. The power source holds the voltage and supplies exactly the current needed to melt the wire arriving at the arc, so more feed means more current automatically. On cheaper machines the knob marked in amps is in fact the feed control with an amp scale printed on it.
The arc crackles and spatters — what do I change?
Check the pairing of feed and voltage first. A harsh crack with big spatter means the voltage is too low for the feed. A long arc with a wide, flat bead means it is too high. The right sound is a steady sizzle, like frying. The calculator gives an indicative voltage for the current you entered — start there.
What is stickout and why does it matter?
It is the distance from the contact tip to the work. Over that length the wire is preheated by its own resistance, so a longer stickout needs less current to melt the same wire. The rule of thumb is 10 to 15 wire diameters. Doubling it drops the current and the penetration with nothing changed on the machine.
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