Calculate welding heat input in kJ/mm or kJ/in from arc voltage, current and travel speed, with optional process efficiency, or solve for travel speed.

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Heat Input Formula

The following formulas are commonly used to calculate welding heat input (energy per unit length). They are equivalent because travel speed v equals weld length L divided by time t.

HI = eta(VIt) / (L); = eta(VI × 60) / (v)
  • Where HI is the heat input (energy per unit length, e.g., J/in or kJ/mm)
  • V is the arc voltage (V)
  • I is the welding current (A)
  • η is the arc efficiency (unitless, typically 0 to 1)
  • t is the welding time (s)
  • L is the weld length (in)
  • v is the travel speed (in/min); the factor 60 converts minutes to seconds so the result is in J/in

To calculate heat input using time and length, multiply current by voltage (to get power), multiply by time and arc efficiency, then divide by the weld length. To calculate using travel speed, divide by travel speed with the appropriate unit conversion (as shown above).

What is welding heat input?

Definition:

Arc energy is electrical arc energy per weld length before a process factor. Effective heat input applies the selected efficiency factor. Some codes use different terminology; follow the governing procedure. This steady-parameter calculator does not replace instantaneous-power measurement for pulsed or waveform-controlled welding.

How to calculate heat input?

Example problem:

The following example problem outlines the steps and information required to calculate a welding heat input.

First, determine the welding current. For this example, the welding current is 60 amps.

Next, determine the welding (arc) voltage. This example uses an arc voltage of 20 volts.

Next, determine the total time of welding. In this example, the time is measured to be 100 seconds.

Next, determine the length of the weld. For this example, the length of the weld is 10 inches.

For this arc-energy example, select Arc energy, enter 20 V, 60 A and travel speed 6 in/min (10 inches in 100 seconds). With no process factor, calculate:

HI = V * I * t / L

HI = 20 * 60 * 100/10

Arc energy = 12,000 J/in = 12 kJ/in ≈ 0.4724 kJ/mm