Wire Burn Back Time

In MIG welding the wire does not start melting the instant the arc is struck. A short distance of the wire, called the burn‑back length, is consumed before a stable metal transfer begins. This burn‑back length is directly related to the time the wire tip is exposed to the arc without the shielding effect of the molten pool.

The burn‑back time can be predicted by balancing the electrical energy delivered to the wire tip with the energy required to raise the wire material to its melting point and to vaporize a thin layer. Key variables include the welding voltage (V), current (I), wire feed speed (v_f), and the thermal efficiency of the process (η).

By rearranging the energy balance, the burn‑back time (t) can be expressed as a simple ratio of the burn‑back length (L) to the effective wire feed speed. This relationship allows weld engineers to set the wire feed speed to achieve a desired burn‑back time, improving arc stability and reducing spatter.