Fabrication of Micro Flat Drills by Precision Grinding and Drilling into Duralumin and Stainless Steel with Ultrasonic Vibration

The present paper deals with the fabrication of micro flat drills by precision grinding and their application to the drilling into duralumin and stainless steel without/with ultrasonic vibration on a vertical grinding/drilling machine. It is found from drill fabrication test that, by choosing grinding procedure of workpieces so that the stiffness may be kept as high as possible, the diameters range from 18 to 21µm for a nominal diameter of 20µm, and that precision measurement of the diameter after grinding of drill periphery and the precision positioning enabled us to fabricate a flat drill of minimum diameter 10.8µm. But, web eccentricity must be improved hereafter. From drill life test it is found that, irrespective of the existence of web taper, the drills without back taper showed longer tool life, and that irrespective of back taper, longer drill life was obtained in case of drills with web taper. This fact suggests that the stiffness at the root of a drill is very important for drill life. In duralumin longer drill life are gained without ultrasonic vibration than with ultrasonic vibration, and in stainless steel vice versa. Burr grows significantly with the increase in number of holes, but roundness of drilled holes is roughly good.