Heat input converter
Convert welding heat input between kJ/mm and kJ/in, and see the travel speed that produces it.
That's 2× as hot as sheet metal welding, while structural welding is 1.25× higher. A 200 A, 25 V arc would have to travel about 200 mm a minute.
What it means
How much heat goes in?
Heat input is arc energy times a process efficiency: about 0.8 for stick and MIG, 0.6 for TIG, and 1.0 for submerged arc.
Every unit
Your heat input in every unit
Learn
Three things worth knowing
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kJ/mm = V × A × efficiency ÷ (mm/s × 1000)
A 200 A, 25 V MIG arc at 80% efficiency travelling 4 mm a second gives 1.0 kJ/mm. Slow down and the heat input climbs.
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What happens beside the weld
The heat-affected zone never melts, but it is cooked. High heat input coarsens its grain and costs toughness; low heat input can leave it hard and cracking-prone.
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Arc energy is not heat input
They differ by the process efficiency. Quoting arc energy where the code asks for heat input overstates it by 25% for MIG and about 67% for TIG.
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Popular heat input conversions
Background
About heat input
Heat input is the energy the arc puts into each millimeter of weld: volts × amps × efficiency ÷ travel speed. Too little and the weld does not fuse; too much and the metal beside it is left coarse and brittle.
Welding procedures are qualified at a stated heat input for exactly this reason, and inspectors check it by timing the run.