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Heat Input Formula

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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.

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.

Formula of Heat Input

The heat input formula is given as follows:

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

Sample Questions

Question 1. Compute the heat input of the engine which operates in 2000 V with a current of 5500 calories. The distance is 10 meters with 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. Which 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


Last Updated : 03 Feb, 2024
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