Research On Milling Stability In Different Postures And Milling Parameters Optimization

The problem of milling stability caused by regenerative chatter has been an important issue in the study of machine tool accuracy.Only by guaranteeing a stable dynamic milling process can make the process parameters optimization and the increase of processing efficiency significant.This article first focuses on the use of the classical theory of machine tool chatter stability.Combine the dynamic change of cutting thickness and the force condition of the tool to establish the milling dynamics model.The full-discrete method is used to draw the milling stability lobe diagram.Then,a hybrid 5-axis machine tool which is jointly developed by Tsinghua University and Shenyang Machine Tool Plant is taken as a research subject.The milling stability of the parallel machine tool in different attitudes is taken as the target.And use two space angles to describe the different attitudes of the parallel mechanism.Take the advantage of the conversion theory of the spatial coordinate system and the positional relationship of the points to work out the kinematic relationship between the working end of parallel mechanism and drive rod.The Jacobian matrix of the parallel mechanism is obtained from the closed-loop velocity vector equation.Based on the Jacobian matrix,the static stiffness matrix related to the attitude change is obtained.From the aspect of static stiffness,it is proved that the stability of the milling system including the parallel mechanism,electric spindle,handle and tool changes with the attitude of the parallel mechanism's change.Do hammering experiment to obtain tool tip frequency response function of different poses.Identify the modal parameters of different poses through the experimental results.Combining the full-discrete method,MATLAB programming is used to draw the chatter stability lobe diagram in different postures.Analyze changes in chatter stability among different poses.Finally,the dynamic dynamometer is used to identify the cutting force coefficient based on the average cutting force model.Then,the modal parameters of tool tip are obtained by the hammering experiment's result.With the help of cutting force coefficient and modal parameters,the stability lobe diagram of hybrid 5-axis machine tool can be drawn.A milling experiment is performed on that machine tool to verify the correctness of the lobe diagram.Aiming at more stable cutting,the parameters of radial cutting depth,spindle speed and axial depth of cut are optimized.