Welding Heat Input

Arc energy and heat input

Arc energy is electrical power divided by travel speed. Multiplying it by thermal efficiency gives net heat input. At 25 V, 200 A and 300 mm/min, arc energy is 1 kJ/mm. With 80 percent efficiency the net value is 0.8 kJ/mm.

Limits

The model describes one pass under steady conditions. Pulsed welding requires instantaneous power measurements. Preheat, interpass temperature, material transformations and procedure acceptance limits are outside its scope. Verify efficiency and permitted limits against the applicable welding procedure.

Making the speed conversion explicit

Voltage times current gives electrical power in watts. Power is energy per second, so the time basis of travel speed matters. With mm/min, omitting the minute to second conversion changes the answer. When comparing arc energy and net heat input, also check whether efficiency has been applied.

For example, 24 V and 150 A give 3600 W. Travel at 360 mm/min equals 6 mm/s, so arc energy is 3600/6 = 600 J/mm = 0.6 kJ/mm. Choosing an illustrative efficiency of 75 percent gives net heat input of 0.75 × 0.6 = 0.45 kJ/mm. This efficiency is an arithmetic example, not a recommended factor for a welding process.

At unchanged power, higher travel speed reduces energy per length in this model. This alone does not establish weld acceptability. Assess different passes separately in a multipass joint. Adding heat inputs is not the same as calculating the component's temperature history. This preliminary estimate does not solve temperature for material, thickness, preheat or interpass waiting. Interpret it with the applicable welding procedure.

Frequently asked questions

How do you calculate welding heat input in kJ/mm?

For example voltage 25 V, current 200 A, travel speed 300 mm/min and thermal efficiency 80 percent, net welding heat input is 0.8 kJ/mm. This preliminary calculation divides electrical power by travel speed and applies efficiency, excluding preheat, interpass temperature and procedure acceptance limits.

Calculate with these values