| where: | V is the voltage used, in volts
I is the current used, in amperes
v is the travel speed of the welding torch, in distance per minute (the units of v dictate whether the arc energy is measured in kJ/mm or kJ/in) |
A number of Amercian codes also use the term Heat Input when referencing arc energy.
Heat input
Heat input (the present best practice term, as it provides a more relevant way of comparing arc welding processes) considers the effect process efficiency has on the energy that actually reaches the workpiece to form the weld. HI is given by the following relationship to AE:
HI = ηAE
where: η is the process efficiency
Each arc welding process has a different efficiency rating. To simplify the rating system, all efficiency factors relate to the efficiency of submerged arc welding.
| Process | Efficiency
factor |
| Submerged arc welding (SAW) | 1.0 |
| Manual metal arc (MMA)/Shielded metal arc welding (SMAW) | 0.8 |
| Cored wire welding/Flux cored arc welding (FCAW) | 0.8 |
| Metal active gas/Metal inert gas (MAG/MIG)/Gas metal arc welding(GMAW) | 0.8 |
| Tungsten inert gas (TIG)/Gas tungsten arc welding (GTAW) | 0.6 |
| Plasma arc welding | 0.6 |
Power beam processes
For power beam processes, such as laser or electron beam welding, an arc is not set up between the heat source and the workpiece. The energy transfer (efficiency) factor of the process may vary with the power intensity of the beam, and joint configuration.
In laser welding, the efficiency factor is not included in any terming of 'heat input'. In electron beam welding, an adjusted current value is entered into the expression for heat input, as an 'over-current' is used for full penetration welds to ensure the weld depth. The excess current can be reported by detectors behind the workpiece, so the energy absorbed by the workpiece is calculated when using this adjusted value, rather than the energy supplied by the machine. The effect of heat input on cooling rates for power beam processes is not the same as for arc welding processes, due to the differences in weld shape.
The expression for heat input is similar to that for arc welding processes, and has the same units (kJ/mm or kJ/in):
Heat Input =
