On the Improvement of Tool Life in Self-Piloting Drilling with External Chip Removal

Abstract

This paper presents both the design and the method of grinding of self-piloting drills (SPDs) with external chip removal. The main advantage of the proposed SPDs over the standard SPDs is brought out using a comprehensive analysis of the SPD auxiliary flank design. The concept of increasing the cutting fluid pressure in the limited space between the tool flanks and the bottom of the hole being drilled by increasing the hydraulic resistance of the channel connecting this space and the chip removal passage is proposed. For the realization of the concept, the mathematical model for the auxiliary flank has been derived on the basis of the obtained condition for a free tool penetration into the workpiece. Using this model, the detailed grinding procedure for the proposed SPDs is explained. The two-stage experimental comparison of the standard and proposed SPDs shows that a significant improvement of tool life is achieved by using the proposed SPDs.