Heat Input Formula (original) (raw)

Last Updated : 23 Jul, 2025

The heat input formula is given as follows:

**Heat input = Voltage × Current × Time/distance travelled × 1000

Heat input and arc energy are the two most essential energy metrics in the arc welding process. This energy is applied to the item component in order to create a weld. Both are measured in kilowatts per meter of length. Weld length, a bead, and the diameter of a weld spot or cross-section are examples of characteristics. The amount of heat injected into a weld varies with time. Let's look at the heat input formula.

**What is Heat Input?

For arc welding procedures, heat input is a key parameter. The heat input will guarantee that the sound weld quality is maintained. It can be defined as the amount of electrical energy delivered to a weld during the welding process.

The amount of heat used to weld is calculated as a function of time. Faster cooling rates are often measured in weldment because they produce embrittlement in the heat-affected zone. When working with materials that are prone to hydrogen-induced cracking, for example, appropriate heat input is necessary.

**Significance of Heat Input

• The amount of heat used in welding has an effect on the cross-sectional area of the weld. The related sluggish cooling leads to austenite grain development in the HAZ, resulting in poor toughness.
• High heat input welds feature a broad weld bead and are often used for submerged arc welding. A deep narrow form in a high heat input arc weld might add to the likelihood of solidification cracking.
• Weld beads are smaller in low-heat-input welds, such as multi-pass welds. Fast cooling can cause hard brittle zones in the HAZ and danger of hydrogen cracking, necessitating the use of preheating or limiting the heat input.

**Also Read,

• Applications of Heat
• Heat, Internal Energy, and Work

Solved Examples of Heat Input Formula

**Question 1: Compute the heat input of the engine which operates at 2000 V with a current of 5500 calories. The distance is 10 meters with a time of 40-sec duration.

**Solution:

Voltage = 2000 V
Current = 5500 A
Distance travelled = 10 m
Time = 40 sec

Heat-input = Voltage × current × time/distance travelled×1000

Substitute all the values in the given formula.
Heat-input = 2000 × 5500 × 4010 × 1000

**Therefore, Heat input is 44000 Joules per meter.

**Question 2: A heat engine operates at a voltage of 1500 V. Flowing current is 3400 A. Find out the heat input if the distance is 24 meters with time 80 sec.

**Solution:

Voltage = 1500 V
Current = 3400 A
Distance = 24 m
Time = 80 sec

Heat-input = Voltage × current × time/distance travelled ×1000

Substitute all the values in the given formula we get,
=1500 × 3400 × 8024 ×1000
= 17000

**Therefore, Heat input will be 17000 joules per meter.

**Question 3: Calculate the heat input for a procedure qualification test coupon welded with a current range of 140A to 190 Amp, 16-18 Volts, and travel speed of 80 mm/min to 110 mm/min.

**Solution:

Considering the practical situation here in this example, the heat input shall be having two values as:

1. Minimum heat input
2. Maximum heat input

For minimum heat input we will take the current and voltage on the lower side as it’s a multiplication factor, and travel speed on higher side as travel speed is dividend factor. So,

Minimum Heat input (J/min) = (140 × 16 × 60)/110 = 1221.8 J/min or 1.22 kJ/mm

Whereas, the maximum heat input (J/min) = (190 × 18 × 60)/80 = 2565 J/min or 2.57 kJ/mm

Here, the unit of travel speed if is inches, the heat input will be in Joules/inch or kJ/inch.

**Question 4: You weld at 400 inches and 39 volts per minute. The weld is 35 inches long, and welding takes 4 minutes. While welding you find that the system shows an amperage of 425. What is your input heat?

**Solution:

Travel speed = Length of the weld / Time to weld
Travel speed = 35/4
Travel speed = 8.75 inches per min

Heat Input=60 × Current x Voltage/distance travelled ×1000
**Heat input = 113.65 KJ/in