GATE 2022 ME (ME1) – Question 57
Two mild steel plates of similar thickness, in butt-joint configuration, are welded by gas tungsten arc welding process using the following welding parameters.
Welding voltage: 20 V; Welding current: 150 A; Welding speed: 5 mm/s
A filler wire of the same mild steel material having 3 mm diameter is used in this welding process. The filler wire feed rate is selected such that the final weld bead is composed of 60% volume of filler and 40% volume of plate material. The heat required to melt the mild steel material is 10 J/mm$^3$. The heat transfer factor is 0.7 and melting factor is 0.6. The feed rate of the filler wire is __________ mm/s (round off to one decimal place).
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Show answer and explanation
Correct answer: 10.65 to 10.75
Explanation
The heat delivered to the work is $0.7 \times 20 \times 150 = 2100$ W, and only the melting factor 0.6 of it goes into melting: $1260$ W. The volume melted per second is $\frac{1260}{10} = 126$ mm³/s. The filler is 60% of it: $75.6$ mm³/s. The wire cross-section is $\frac{\pi}{4} \times 3^2 = 7.069$ mm², so the wire feed rate is $\frac{75.6}{7.069} = 10.7$ mm/s.