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Two metallic sheets, each of 2.0 mm thickness, are welded in a lap joint configuration by resistance spot welding at a welding current of 10 kA and welding time of 10 millisecond. A spherical fusion zone extending up to the full thickness of each sheet is formed and properties of the metallic sheets are given as: Ambient temperature = 293 K Melting temperature = 1793 K Density = 7000 kg/m³ Latent heat of fusion = 300 kJ/kg Specific heat = 800 J/kgK. Assume:
(i) contact resistance along sheet-interface is 500 micro-ohm and along electrode-sheet interface is zero;
(ii) no conductive heat loss through the bulk sheet materials; and
(iii) the complete weld fusion zone is at the melting temperature. The melting efficiency (in%) of the process is
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- 50.37
- 60.37
- 70.37
- 80.37
Correct Option: C
Heat generated due to current,
H1 = I²Rt= (10 × 10³)² × 500 × 10-6 × 10 × 10-3 = 500 J
Heat required for melting,
H2 = 300 × 10³ × 7000 × volume + 800 × (1793 – 293) × 7000 × volume
Since fusion zone is spherical is shape, therefore volume = 4/3πR³
where, r = t = thickness of sheet = 2 mm
Melting efficiency = 70.35%
