heat input in welding



What is Heat Input?
In arc welding, energy is transferred from the welding electrode to the base metal by an electric arc. When the welder starts the arc, both the base metal and the filler metal are melted to create the weld. This melting is possible because a sufficient amount of
power (energy transferred per unit time) and energy density is supplied to the electrode.

Heat input is a relative measure of the energy transferred per unit length of weld. It is an important characteristic because, like preheat and interpass temperature, it influences the cooling rate, which may affect the mechanical properties and metallurgical structure
of the weld and the HAZ.

Calculation:

Heat input is typically calculated as the ratio of the power (i.e., voltage x current) to the velocity of the heat source (i.e., the arc) as follows:

H = 60 E I / 1000 S

where,
H = heat input (kJ/in or kJ/mm)
E = arc voltage (volts)
I = current (amps)
S = travel speed (in/min or mm/min)