Aluminium strips of 2 mm thickness are joined together

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Aluminium strips of 2 mm thickness are joined together by resistance spot welding process by applying an electric current 6000 A and 0.15 second. The heat required for melting aluminium is 2.9 J/mm³. The diameter and thickness of the weld nugget are found to be 5 mm and 2.5 mm respectively. Assuming the electrical resistance to be 75 micro ohms, the percentage of total energy utilized in forming the weld nugget is

1. 28
2. 35
3. 65
4. 72

Correct Option: B

h_n = 2.5 mm, I = 6000 A
R = 75 µΩ, t = 0.15sec
d_n = 5 mm Energy/Volume = 2.6 J/mm³
Energy generated = I² R t
= 6000² × 75 × 10^-6 × 0.15 = 405 J
Energy Required = 2.9 × volume of Nugget

= 2.9 ×	π	d²_nh_n
	4

= 2.9 ×	π	5²2.5 = 142.35 joules
	4

Efficiency =	142.35	× 100 ≃ 35%
	405