Abstract
The formation of burr in micro drilling has a tendency to reduce in the case of drilling with minute drill feed in the workpiece containing with crystal grains of larger size. In this study, three postulations were set up to clarify this tendency, and following results were obtained by the method to verify the postulation experimentally. (1) When the cutting depth per one revolution is minute, minute protrusions on lip edge of drill act as lip edges individually, and micro drilling with small burr is possible to be realized. (2) Cutting resistance of drilling in the workpieces containing with small crystal grains becomes high comparing with the case of workpieces with large size grains on account of crystal anisotropy. (3) Area having easy formation of burr becomes broad in crystal grain of large size. But burr formation in micro drilling becomes small in the case of drilling in the workpiece with crystal grains of larger size, because crystal grain boundary which disturb the propagation of plastic deformation exist in close vicinity to drilled part in the relation of micro drill diameter and crystal grain size.
