Minimization of Ovality of Circular Holes in Drilling Process

Abstract

In drilling and boring process, the relief in clamping stress causes deformations that cause variations in the geometry of the drilled hole. In automobile industry, when such holes are used to hold gear systems or rods in place, this variation in geometry leads to poor fitting and subsequent failure. To avoid this, high level accuracy is required which is both expensive and time-consuming. Therefore, a high percentage of such drilled parts are rejected in industry. The present paper addresses this problem by characterizing the variations in hole geometry as a function of clamping force, hole diameter, hole eccentricity (distance of hole-center from center of drilled face) and angular position of hole with respect to clamp location. The analysis result quantifies the comparative effect of each aforementioned factor on hole geometry variation. Taguchi Method based Design of Experiments using L25 orthogonal array has been used for performing the parametric design to arrive at the best settings of the 4 parameters. The optimal settings minimize ovality and displacement of the hole-center, and thus increase hole-fitting and its reliability against manufacturing variability.