Real-time peak force control in CNC milling

This paper focuses on a peak force milling control system that is an integral component of a real-time process monitoring and control system for CNC milling. In process planning, reference peak forces are selected for each tool move for safe, accurate, and efficient machining. Peak forces are selected based on constraints such as dimensional tolerance and desired chip load. The peak force controller adjusts the feedrate during machining to maintain the reference peak force. This is very important as the tool wears or as unexpected workpiece geometry is encountered. The peak force controller is based on a nonlinear division algorithm that adjusts the feedrate based on a ratio of the desired force to the measured peak force. The stability and performance of this algorithm is investigated by analysis, simulation, and experiment. Describing function analysis of the linearized system shows stable controller behavior for excessive tool wear and unexpected cutting geometry. Simulations using the complete nonlinear equations, along with experiments, verify the good performance of the controller for a number of workpiece materials, including aluminum, steel and Inconel.