What is the heat input formula for GMAW, and how would you use it to compare two welding setups?

• A. Heat input per unit length ≈ (Volts × Amps) / travel speed
• B. Heat input per unit length ≈ (Volts × Amps × 60) ÷ travel speed
• C. Heat input per unit length ≈ (Volts × Amps × 60) ÷ travel speed
• D. Heat input per unit length ≈ (Volts × Amps) ÷ travel speed × 60

Answer: (C)

Heat input per unit length tells you how much energy from the arc is delivered for each inch (or mm) of weld. Since welding power is volts times amperes (V × I) giving watts (joules per second), you need to account for how long the arc stays on each length of weld. Travel speed tells you how fast you’re laying down bead, so the time per inch is 60 divided by the speed (inches per minute). Multiplying power by that time per inch gives energy per inch: (V × I × 60) ÷ travel speed. That’s why the formula uses the 60 factor.

To compare two welding setups, calculate heat input per unit length for each using the same unit conventions (same speed units, typically inches per minute). The setup with the higher heat input delivers more energy per inch, typically increasing penetration and distortion, while the lower heat input reduces penetration and distortion. This direct comparison helps you predict bead shape, penetration, and warping for your material and thickness.