Study of undeformed chip and cap geometries at three machining stages in the orbital drilling process

The characteristics of undeformed chip geometries generated by a dedicated cutting tool are complex in orbital drilling of Ti6Al4V and they have an important influence on the quality of hole-making. This study investigates the orbital drilling kinematics and the undeformed chip geometry based on the definition of three machining stages. A model of undeformed chip geometry is developed through simulation. The thickness of the undeformed chips and their resultant cutting volume at different stages are further analyzed and calculated. Experiments are conducted by orbital drilling of TC4 titanium alloy to verify the characteristics of the undeformed chip and cap geometries, and to ascertain their relevance to the cutting forces as well as the hole quality. It is found that the main type of chip with “a tadpole shape,” considerable chipping, and two types of caps geometries appears at three machining stages of orbital drilling process. The corresponding cutting forces reflect an approximately linear increase, stable fluctuation, and a gradual decrease, which are nearly consistent with the characteristics of the simulated unformed chip geometries. Two types of cap geometries can be used to monitor tool wear and improve the burr situation at the hole exit.