Burr Formation in Drilling Intersecting Holes with Machinable Austempered Ductile Iron (MADI™)

This paper presents an investigation of the burr formation for a new material, machinable austempered ductile iron (MADI™), while drilling intersecting holes in the presence of tool wear. A factorial design is used to evaluate the effects of drill point angle and helix angle as well as feed rate and cutting speed on the burr width and height at both curved and flat hole exit conditions. The result indicates the presence of a complex interrelationship among these four variables, particularly the interaction between helix and point angle and its influence on drill corner wear and, hence, burr geometry. Burrs are considerably larger at the flat exit condition. Further experiments were conducted in a central composite design scheme to develop second-order polynomial models of the burr width and height. The result suggests that burr width and height can be reduced by using larger helix and smaller point angles. The result further demonstrates that the somewhat unique work-hardening characteristic of MADI™ during machining can lead to smaller burrs when smaller chiploads are used, regardless of the drill helix and point angles.