This paper summarizes the design and implementation of a model-based torque control strategy for drilling. During drilling, the torque often increases due to difficulties with chip evacuation from the drill flutes. Excessive torque can accelerate tool wear or cause torsional failure of the drill.
To avoid problems associated with excessive torque, closed loop torque control by manipulation of feedrate was pursued. This strategy simultaneously avoids tool breakage and decreases the cycle time compared to conventional practice. There can be significant cost benefits of torque control due to eliminating tool breakage. For example, reductions in scrap, rework, and machine maintenance costs may be realized.
Dynamic models were developed for the drive system, sensing system, and drilling process. These models were subsequently used to design a model-based torque control strategy. Experimental results are presented for conventional twist drilling and form tool drilling applications. Implementation using a PC-based open architecture control platform integrated with a production drive system is described.