Question
The resistance spot welding of two 1.55 mm thick metal sheets is performed using welding current of 10000 A for 0.25 s. The contact resistance at the interface of the metal sheets is 0.0001 Ω. The volume of weld nugget formed after welding is 70 mm³ . Considering the heat required to melt unit volume of metal is 12 J/mm³ , the thermal efficiency of the welding process is ________ % (round off to one decimal place).
Answer :
Correct answer is : 33.6
I = 10000 A, R = 0.0001 Λ, t = 0.25 sec.
Heat supplied (Hs) = I2Rt
Hs = (10000)2 × 0.0001 × 0.25
∴ Hs = 2500 Joule
Now,
Heat required to melt
Hm = 12 J/mm3, Volume = 70 mm3
Hm = 12 × 70 = 840 Joule
Now,
η = 0.336
∴ η = 33.6 %
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