Question

Resistance spot welding of two steel sheets of 3 mm thickness is done in lap joint configuration. Welding current of 10000A passed for 5 cycles in 50 Hz main supply The heat required for melting 1 ${\text{mm}}^3$' volume of steel is 30 J and interfacial contact resistance between sheets is 300 micro ohms. If the melting efficiency is 80%, then the volume $\left({\text{in mm}}^3\right)$ of weld nugget is

• A. 60
• B. 40
• C. 100
• D. 80

Answer 1

The correct option is D 80

Given data
$I=10000A$

$\text{Times},\tau =\frac{5}{50}=0.1\sec$

$\text{Heat required, u=}30J/m{m}^3$

$\text{Total heat required,}{H}_m=30V$

[Where, V=volume of weld nugget]

$\text{Contact resistance,}R=300\times {10}^{-6}\Omega$

Heat supplied,
$H_s=i^{2}R\tau$

$={10000}^2\times 300\times {10}^{-6}\times 0.1=3000J$

Now, ${\eta }_m=\frac{H_m}{H_s}$

$\Rightarrow 0.8=\frac{30V}{3000}$

$\therefore V=80{\text{mm}}^3$