Using Ultrasonic Machining process, a cylindrical impression of 10 mm diameter and 1 mm deep is to be made on a WC specimen. Feed force is constant, and is 5 N. Average diameter of grains in the slurry is 10 m. Tool oscillates with the amplitude of 30 m at 20 kHz. Abrasive and water ratio in the slurry is 1. Fracture hardness of WC workpiece may be taken as 7000 N/mm and that of copper tool as 1500 N/mm. Calculate the time required to complete the job, if only 20% of pulses are effective. Assume K -0.3, K=1.8 mm and K3 = 0.6. Make the assumptions if necessary.