In: Mechanical Engineering
. A punching machine makes 24 working strokes per minute and is capable of punching 30 mm diameter holes in 20 mm thick steel plates having an ultimate shear strength of 350 MPa. The punching operation takes place during 1 10 th of a revolution of the crankshaft. Find the power required for the driving motor, assuming a mechanical efficiency of 76%. Determine suitable dimensions for the rim cross-section of the flywheel, which revolves at 9 times the speed of crankshaft. The permissible coefficient of fluctuation of speed is 0.4. The flywheel is to be made of cast iron having a safe tensile stress of 6 MPa and density 7250 kg/m3. The diameter of the flywheel must not exceed 1.05 m owing to space restrictions. The hub and spokesmay be assumed to provide 5% of the rotational inertia of the wheel. Check for the centrifugal stress induced in the rim.