Heat input
Arc energy and heat input from travel speed (BS EN 1011-1)
- where
- arc energy (kJ/mm)
- arc voltage (V)
- welding current (A)
- travel speed (mm/min)
- heat input (kJ/mm)
- thermal efficiency factor
Explain this equation
Works out the arc energy and heat input of a weld run from the volts, amps and travel speed. Use it to check a run against a welding procedure specification, or as an input to preheat and cooling-time checks.
Volts times amps is the arc power in watts (joules per second). Travel speed is per minute, so the 60 turns it into seconds; dividing power by speed gives joules per millimetre of weld, and the 1000 converts to kJ. Not all the arc energy reaches the joint: the factor k is the share that does, depending on the process.
Energy per unit length equals power divided by speed.
Sense check: 24 V, 200 A at 300 mm/min is 0.96 kJ/mm arc energy, about 0.77 kJ/mm heat input for MIG/MAG. Halve the travel speed and the heat input doubles.
Watch out: some codes quote arc energy and others heat input. Check which one your WPS uses before comparing.
Works out the arc energy and heat input of a weld run from the volts, amps and travel speed. Use it to check a run is inside the heat input range on the WPS.
Enter your values to see the result.
Good to know
Read volts and amps at the arc (or close to it) during welding, and time the run over a measured length to get travel speed. BS EN 1011-1 gives k = 1.0 for submerged arc, 0.8 for MMA, MIG/MAG and flux-cored, and 0.6 for TIG and plasma. Typical manual MIG fillet runs come out around 0.5–1.5 kJ/mm.
Common mistake
Quoting arc energy as heat input (or the other way round). A WPS written to BS EN ISO 15614-1 may state either, so check which one the procedure uses and use the matching k.
Limits
Average values for steady welding. Pulsed and waveform-controlled power sources need instantaneous power or energy readings (from the power source) rather than U × I. For weaving, use the actual forward travel speed, not the torch path length.
Sources
- BS EN 1011-1:2009 Welding – Recommendations for welding of metallic materials – Part 1: General guidance for arc welding (arc energy, heat input and thermal efficiency factors k)
- TWI FAQ: What is the difference between heat input and arc energy? (HI = η × arc energy; η = 1.0 SAW, 0.8 MMA, FCAW and MIG/MAG, 0.6 TIG and plasma)
- SSAB: How to weld – welding heat input (arc energy and heat input in kJ/mm)
- BS EN ISO 15614-1:2017 Specification and qualification of welding procedures for metallic materials – Welding procedure test – Part 1: Arc and gas welding of steels (heat input recorded and controlled within the qualified range)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow the welding procedure specification (WPS), BS EN ISO 15614/9606, BS EN 1090, BS EN 1993 and manufacturers’ data. Structural welds need qualified welders and engineered designs.