Question

Resistance spot welding of two steel sheets is carried out in lap joint configuration by using a welding current of $3kA$ and a weld time of $0.2s$. A molten weld nugget of volume $20m{m}^3$ is obtained. The effective contact resistance is $200\mu \Omega$.

The material properties of steel are given as

$\text{(i) latent heat of melting}1400kJ/kg\text{,}$
$\text{(ii) density}8000kg/m^3\text{,}$
$\text{(iii) melting temp}{1520}^{o}C$
$\text{(iv) specific heat}0.5kJ/k{g}^{o}C\text{.}$

$\text{The ambient Temperature is}{20}^{o}C$

Heat (Joules) dissipated to the base metal will be (neglecting all other heat losses)

• A. $16$
• B. $10$
• C. $22$
• D. $32$

Answer 1

The correct option is A $16$

$\text{Given data :}$

$I=3000A$

$t=0.2s$

$R=200\mu \Omega$

$V=20m{m}^3$

$\text{Latent heat of melting,}$

$L=1400kJ/kg$

$\text{Density:}\rho =8000kg/m^3$

$\text{Specific heat:}C=0.5kJ/k{g}^{o}C$

$\text{Heat generated}=I^{2}RT={3000}^2\times 200\times {10}^{-6}\times 0.2$

$=360J$

$\text{Heat utilised for production of weld nugget}$

$=m[L+c\Delta T]$

$=8000\times 20\times {10}^{-9}[1400+(1500\times 0.5\left)\right]\times 1000$

$=344J$

$\text{Heat dissipated}=360-344=16J$