Modeling and torque control of a form tool drilling process

Torque control through feed manipulation can provide significant machining economic benefit for drilling processes by preventing tool breakage and reducing cycle time. This paper presents the dynamic modeling and real-time torque control for a form tool drilling process. The form tool produces a desired shape in a workpiece through a drilling process. In this study, the form tool drilling process resembles the combination of drilling, reaming, counter-boring, and chamfering operations. The machining process is modeled as a linear time-varying system with variable gain due to the form tool geometry. The process is also subject to unknown disturbances such as unpredictable chip jamming and tool-workpiece friction. Spindle motor power and speed measurements were used to estimate drilling torque for cost effective practical implementation. An input-output pole placement controller with adaptive feedforward gain scheduling was designed and implemented. Through experimental studies, this controller provided superior performance and robustness compared to a conventional proportional-integral control approach