Question

A punching press punches 30 holes per min in a plate requiring 12 kJ of energy per hole during each cycle. Actual punching takes 30% of the cycle time. A flywheel connected to the machine electric motor. The flywheel rotates at a mean speed of 240 rpm and the fluctuation of speed is not to exceed $\pm$ 2 percent of the mean speed.

The power of the electric motor required is

• A. 3 kW
• B. 6 k W
• C. 12 kW
• D. 15 kW

Answer 1

The correct option is B 6 k W

n = 30 hole/min = 2 sec/hole.

E = 12 kJ/hole, cycle time = 2 sec

P= 12 kJ/2 sec = 6 kW

$C_s=0.04;N=240rpm,\omega =\frac{240\times 2\pi }{60}=8\pi$

$\therefore$ Power of motor required = 6 kW