Wire feed speed (WFS)

Wire feed speed is the throttle on a continuously fed welding process: it is the one setting an operator or a robot controller dials directly, and current, deposition rate and bead size all follow from it rather than the other way round. In gas metal arc and flux-cored welding, current is largely a consequence of feed speed at a given wire diameter and stick-out, which is why WFS — not current — is the parameter actually programmed.

The mechanical relationship is straightforward: the mass of wire entering the arc per unit time is feed speed multiplied by the wire’s cross-sectional area and density, and deposition rate is that melting rate reduced by whatever share is lost to spatter, fume and stub ends rather than staying in the joint. A larger wire diameter delivers more mass at the same feed speed, which is why a process change that swaps wire diameter without re-checking feed speed changes deposition rate and arc energy together, often without anyone deciding that on purpose.

Cold wire feeding — filler introduced at room temperature rather than pre-heated as in hot-wire TIG — is the clearest case where WFS optimisation has two opposing limits. Too low, and the wire does not remove enough energy from the pool, risking overheating and burn-through in thin material. Too high, and the wire cools the pool faster than the arc can compensate, producing lack of fusion or an irregular bead surface. Both limits are process- and joint-specific, which is why feed speed is verified against the specific procedure rather than assumed transferable between jobs. Automated systems typically read WFS directly from the wire feeder over a digital interface and correlate it with thermal and electrical data in one timeline, distinguishing an intentional parameter change from a drifting drive roll or an emptying spool — the latter shows up as feed speed and current drifting together while the programmed setpoint stays fixed.