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Welding heat input calculator
Type voltage, current and travel speed, pick the process, and read arc energy and heat input in kJ/mm, with an optional maximum to check against. The factors are the EN 1011-1 thermal efficiency values; the un-factored figure is the one ASME Section IX and AWS D1.1 call heat input. The theory, the worked examples and the standard limits by material are in the heat input formula guide.
One formula, two conventions
Arc energy [kJ/mm] = (U × I × 60) / (v × 1000), with U in V, I in A, v in mm/min
Heat input [kJ/mm] = k × arc energy
| Process | ISO 4063 | k |
|---|---|---|
| Submerged arc (SAW) | 12 | 1.0 |
| Manual metal arc (MMA / SMAW) | 111 | 0.8 |
| MIG / MAG (GMAW) | 131 / 135 | 0.8 |
| Flux-cored (FCAW) | 136 / 137 | 0.8 |
| TIG (GTAW) | 141 | 0.6 |
| Plasma | 15 | 0.6 |
- Travel speed carries the error. Volts and amps come off the power source; speed is the value welders estimate. Heat input goes with 1/v: a speed read 20 % too high hides 17 % of the real heat input, a speed 20 % too low overstates it by 25 %, and either error is most of a qualified band.
- Weave breaks the range invisibly. Wider weave means slower advance along the joint at the same meter readings, so heat input rises while every display looks normal.
- State the convention. An EN ISO 15614-1 WPQR may quote arc energy or k-factored heat input; an ASME IX PQR quotes the un-factored value and calls it heat input. Comparing the two numbers without the convention is a common audit finding.
For preheat, interpass and cooling-rate effects on the heat-affected zone, read interpass temperature: measurement, limits and control and heat input, cooling rate and t8/5.
Heat input questions engineers ask
What is the welding heat input formula?
Heat input in kJ/mm = k × (U × I × 60) / (v × 1000), with U in volts, I in amperes and v the travel speed in mm/min. The bracket is the arc energy; k is the thermal efficiency factor of the process (EN 1011-1 / ISO/TR 17671-1). ASME Section IX and AWS D1.1 work in J/in: (U × I × 60) / v with v in inches per minute and no division by 1000.
What is the difference between arc energy and heat input?
Arc energy is the electrical energy delivered per unit length of weld. Heat input in the EN/ISO sense is arc energy multiplied by the process factor k, the share that actually enters the joint. EN ISO 15614-1 accepts either quantity as long as qualification and production use the same one; ASME IX QW-409.1 and AWS D1.1 call the un-factored value heat input. Two documents can therefore quote “heat input” for the same weld and differ by 20 to 40 percent, so state the convention next to the number.
What are the EN 1011-1 thermal efficiency factors?
Submerged arc welding k = 1.0; manual metal arc (MMA/SMAW), MIG/MAG (GMAW) and flux-cored (FCAW) k = 0.8; TIG (GTAW) and plasma k = 0.6. The factor accounts for the arc energy lost to radiation, spatter and the shielding gas before it reaches the plate.
Why does heat input matter for a WPS?
Heat input sets the cooling rate, and cooling rate sets microstructure, hardness and toughness in the heat-affected zone. It is an essential variable in EN ISO 15614-1 and ASME IX QW-409.1. In EN ISO 15614-1 the bounds are conditional: where impact testing is required the qualified value may rise by at most 25 %, where hardness testing is required it may fall by at most 25 %, and both bounds apply when both tests apply (check the edition in force). A production weld outside those bounds is outside the qualification, even if every meter reading looked normal.
Stop estimating arc energy. Record it on every weld.
WeldTrace records voltage, current and wire feed speed at 25 kHz on every pass, so the arc energy of each weld is calculated from measured values rather than from the nominal figures on the sheet; synchronised with a validated travel speed it gives the heat input estimate per weld against the WPS limit.
