Machining accuracy reliability evaluation of CNC machine tools based on the milling stability optimization

The machining accuracy reliability of machine tools has important practical significance for the quality of processed parts. In the milling process, the geometric errors and vibration errors are the two key error sources which severely decrease the machining accuracy reliability of machine tools. To ensure that machine tools can maintain high machining accuracy and reliability for a long time, the paper proposes a machining accuracy reliability evaluation method that considers both the geometric and vibration errors. Based on the milling dynamics theory and the full-discretization method (FDM), a four degrees of freedom (DOF) milling dynamics model of the tool-workpiece vibration system and a vibration error prediction model of the tool-workpiece system are established. The former is used for the milling stability prediction and the milling parameter optimization, while the latter is used for the vibration errors prediction. Utilizing the multi-body system (MBS) theory, a comprehensive error model considering both the geometric and vibration errors is established to explain the influence of errors on machining accuracy. Based on the Monte Carlo simulation of directional importance sampling (DIS-MCS), a machining accuracy reliability model is proposed to evaluate the machining ability of machine tools. The method is applied to a five-axis CNC machine tool, and the application results explain the correctness and competitiveness of the proposed method. It can realize the milling parameter optimization, the vibration error prediction of the tool-workpiece system, and the machining accuracy reliability evaluation of machine tools.