Deposition rate

Deposition rate is what a shop actually cares about when it asks how fast a joint fills: not how fast the wire feeds, but how much of that fed wire ends up as sound weld metal in the joint per hour. It is calculated from wire feed speed, wire diameter and density — which together give the melting rate — reduced by a deposition efficiency factor that accounts for material that never makes it into the joint: spatter, fume, and, for flux-cored and stick processes, slag-forming ingredients and the unused stub end left in the holder or feeder.

Process choice is largely a deposition-rate decision once code compliance and access are settled. Flux-cored arc welding is favoured for heavy structural and shipbuilding fabrication specifically because its deposition rate at a given current is higher than solid-wire GMAW, and submerged arc reaches higher rates still on long, straight, flat-position seams, because the granular flux has to be retained on the joint by gravity — and the buried arc means the process is monitored from parameters and post-weld NDT rather than by watching the pool. None of these processes deliver their rated deposition efficiency automatically — it depends on technique, consumable condition and joint access, and is worth verifying on the actual job rather than assumed from a datasheet figure.

The productivity gain from raising deposition rate has a hard limit: heat input. Deposition rate rises with wire feed speed and current, but heat input rises with current too unless travel speed rises to compensate — and a procedure qualified within a given heat input window cannot simply run hotter to weld faster. This is why deposition rate improvements in qualified production work come from process substitution, multiple simultaneous arcs, or reduced non-arc time — duty cycle — rather than from pushing a single arc’s current past its qualified range. A deposition-rate figure quoted without reference to the heat input it was achieved at describes a process capability, not a number that can be adopted into an existing procedure.