Welding
Heat input calculator
In short
Welding heat input is worked out from the arc voltage U, the current I, the travel speed v in mm/min and the thermal efficiency k of the process (EN 1011-1). Arc energy E = U × I × 60 / (1000 × v), then heat input Q = k × E, in kJ/mm.
Calculation
Example calculated with the tool’s default values.
Inputs
- Process (ISO 4063)
- 135: MAG (solid wire, active gas)
- Current
- 180 A
- Arc voltage
- 24 V
- Speed given as
- Travel speed
- Travel speed
- 300 mm/min
Results
- Heat input Q
- 0.69 kJ/mm
Worked example
Every value in this section belongs to the example, calculated with the tool’s default values.
Other results of the example
- Arc energy (no k)
- 0.86 kJ/mm
- Thermal efficiency k
- 0.8
- Travel speed
- 300 mm/min
- Heat input
- 6.9kJ/cm
- Indicative value: it does not replace a qualified welding procedure specification (WPS).
- Compare with the WPS limit: some codes (ASME IX, AWS D1.1) call the arc energy without the k factor "heat input".
Step-by-step calculation
Thermal efficiency
k (135)
k = 0.8
Arc energy
E = U × I × 60 / (1000 × v)
24.0 × 180 × 60 / (1000 × 300) = 0.864 kJ/mm
Heat input
Q = k × E
0.8 × 0.864 = 0.691 kJ/mm
How to use it
- Pick the process (ISO 4063 number): it sets the thermal efficiency k.
- Enter the current in A and the arc voltage in V.
- Give the travel speed in mm/min, or the bead length and the arc time.
- Read the heat input Q in kJ/mm.
Frequently asked questions
What is the welding heat input formula?
The arc energy is E = U × I × 60 / (1000 × v), with U the arc voltage in V, I the current in A and v the travel speed in mm/min. The heat input is Q = k × E, where k is the thermal efficiency of the process to EN 1011-1. The result is in kJ/mm; multiplied by 10, it is in kJ/cm.
How do I calculate the heat input of a MAG weld in kJ/mm?
For MAG (135), k = 0.8. At 24 V, 180 A and 300 mm/min, the arc energy is E = 24 × 180 × 60 / (1000 × 300) = 0.864 kJ/mm, so the heat input is Q = 0.8 × 0.864 = 0.691 kJ/mm.
Which thermal efficiency k applies to each process?
The calculation uses the values of EN 1011-1 and ISO/TR 17671-1: 1.0 for submerged arc (121); 0.8 for manual metal arc (111), MIG (131), MAG (135), flux-cored wire (136) and metal-cored wire (138); 0.6 for TIG (141) and plasma arc (15).
How do I get the heat input without the travel speed?
Enter the bead length L and the arc time t: the travel speed is v = L / t × 60, in mm/min. For example, 150 mm welded in 30 s gives 300 mm/min.
Heat input or arc energy: which value goes against the WPS?
Some codes (ASME IX, AWS D1.1) call the arc energy without the k factor "heat input". The calculation gives both values: compare the one that matches the limit written in your WPS.
Limits
Indicative results: the value does not replace a qualified welding procedure specification (WPS). The k values are those cited for EN 1011-1 and ISO/TR 17671-1, cross-checked on public sources. Above 4 kJ/mm, the heat input is outside the usual range of the EN 1011-2 preheat methods.
Sources
- EN 1011-1:2009 Soudage, recommandations pour le soudage des matériaux métalliques : Partie 1, art. 19 (apport de chaleur, facteur de rendement thermique k)
- ISO/TR 17671-1:2002 : art. 19, tableau 2 : valeurs de k (relais public : https://grahamfry.com.au/technical-resources/heat-input-calculator)
- EN 1011-1 : valeurs de k recoupées : https://therness.com/tools/heat-input-calculator