A practical method to monitor tool wear in end milling using a changing cutting force model that requires no additional sensors

Abstract

In end milling, proper tool life management is crucially important for achieving highly accurate machining, avoiding tool failure, and optimizing production costs. In recent years, a number of tool condition monitoring (TCM) methods aimed at improving tool life management have been proposed. However, these methods have generally been impractical, and tool life still tends to be determined based on machining time or the quantity of the product produced. To address this shortcoming, a practical online TCM method is proposed. The proposed method is based on the idea that the frictional force acting on the flank face of a tool increases with increasing flank wear resulting from an increase in the contact surface area between the flank face and the machined surface. The implication is that tool wear can be indirectly monitored using the change in frictional force on the flank face, which can be determined by tracking the spindle motor torque obtained using a computerized numerical control (CNC) controller and a real time cutting force simulation. The influence of tool wear is not considered in the simulation model; rather, the frictional force is estimated from the difference between the average predicted cutting torque and the average monitored spindle motor torque. With the proposed method, no additional sensor is needed to monitor tool wear. Additionally, no parameter determination is necessary to perform the simulation because the parameters needed for the simulation are immediately determined at the beginning of the milling operation based on the monitored spindle motor torque. Thus, the TCM method proposed here offers a practical online alternative.

Keywords

• end milling
• tool condition monitoring
• sensor-less
• flank wear
• cutting torque simulation