An Exit Burr Model for Drilling of Metals

The mechanics of the formation of exit burrs for drilling metals are analyzed. A burr formation model is developed where the material in front of the drill is modeled as an axi-symmetric, circular plate of varying thickness. The drilling thrust forces are distributed as a pressure along the top surface of this plate. The stress state is then calculated. Material removal continues until a failure condition is reached. At the point of failure of the plate the remaining material is bent out to form the burr. The model also includes temperature effects. Experimental verification was conducted on 2024-T351 aluminum and on 7075-T561 aluminum. Two types of drill geometry were considered. The experiments were conducted with feeds from 0.05 to 0.35 mm/rev. The model accurately predicts the experimental data.