EXPERIMENTAL INVESTIGATIONS ON MINIMIZATION OF BURR SIZE IN DRILLING USING STEP DRILLS

Abstract

Burrs formed during machining operations are the cause of many industrial problems. Buns are sharp projections on the workpiece left uncut while machining. The presence of these burrs requires additional manufacturing steps for disassembly and deburring. These additional steps are typically difficult to automate and are usually performed manually. For precision parts, deburring and edge finishing can amount to as much as 30% of the cost of the part. Therefore it is necessary to know how to reduce the burr size. Burr formation is a phenomenon involving plastic deformation with multi degrees of freedom. Formation of burr is affected by many parameters like tool geometry, cutting conditions, workpiece material and its geometry. Many studies have been conducted to understand the burr formation mechanism. Concept of step drills is the latest addition to these studies, which is supposed to reduce burr size. Present thesis work was focused on step drills. In the first stage, experiments were conducted to optimize the step parameters so as to produce minimum burr height. Regression models were developed for burr height, thrust force and torque in terms of step parameters. In the second stage, experiments were conducted with the optimized step drills and regression models were developed for burr height, thrust force and torque in terms of feed and diameter of drill bit. All the models were developed by using Design-Expert software. Finally comparative study was performed to prove the superiority of the step drills over conventional drills in reducing burr size.