Question

B1) 20 pts. The thickness of each of the two sheets to be resistance spot welded is 3.5 mm. It is desired to form a weld nugget that is 5.5 mm in diameter and 5.0 mm thick after 0.3 sec welding time. The unit melting energy for a certain sheet metal is 9.5 J/mm3 . The electrical resistance between the surfaces is 140 micro ohms, and only one third of the electrical energy generated will be used to form the weld nugget (the rest being dissipated), determine the minimum current level required.

Answer 1

Answer:

I = 8975.95 A            

Explanation:

Given :

Diameter of the nugget, D = 5.5 mm

Length of the nugget, l = 5.0 mm

Therefore, volume of the nugget,

$V = \frac{\pi}{4}D^2l$

  = $\frac{\pi}{4}(5.5)^25 = 118.73\ mm^3$

Now, required melting energy, (M.E.) = 9.5 x V

                                                              = 9.5 x 118.73

                                                              = 1127.95 J

Given efficiency of the heat used from electric energy, η = 1/3

Then actual required energy = ME/η

                                               = 1127.95 / (1/3) = 3383.84 J

We know that, electric energy (EE) = $I^2Rt$

where, I is current,  R is resistance and t is time in seconds.

                                           3383.75 = $I^2 \times 140 \times 10^{-6} \times 0.3$

                                                   I = 8975.95 A