Feedrate optimization on complex workpieces for CNC milling machines

The purpose of this research is to establish a new methodology for the optimization of feedrate in CNC milling process. In this optimization, the objective was to maximize the metal removal rate in the machining of complex workpieces under the constraint of a maximum resultant force for the prevention of tool breakage or tool deflection. In other words, the goal was to establish the maximum achievable feedrate while maintaining a constant maximum resultant force in the milling of the complex workpieces, The basic concept involved is the mathematical formulation of maximum feedrate in the machining of complex workpieces based on the prediction of cutting force harmonic components. The optimization used a closed form cutting force model developed in the frequency domain for the machining of complex parts with multi-flute cutters. High harmonics of the cutting forces in two orthogonal directions were predicted from the model as functions of cutting condition and part geometry. These harmonics were utilized to determine the instantaneous maximum resultant cutting force. Feedrate was maximized by maintaining a constant value of the maximum resultant cutting force at various location on the workpiece of complex geometry. A series of experiments have been conducted on a vertical milling machine at constant feedrates to compare the theoretical force model predictions with the experimental cutting force spectrums for a complex workpiece with a circular hole. The discrete amplitude spectrums agreed well with the results of the analytical model in the frequency domain. These predictions were used in determining the optimum feedrates during the machining. Results show that a 55% decrease in the manufacturing time of the particular complex part can be accomplished by using the optimum feedrates.