柔性零件车削振动系统建模与实验

Modeling and Experimental Research on Vibration System in Turning of Flexible Workpieces

由于刀具进给运动致使工件系统所受切削力的位置实时改变,根据实际车削加工过程,建立柔性工件颤振动力学模型,得到工件车削时系统的时变稳定性极限图。考虑在加工过程中主轴-卡盘、顶尖-尾座对工件的影响,建立实际切削系统的主轴-卡盘-工件-顶尖有限元模型,研究工件在不同位置的刚度分布和不同支承条件下固有频率的变化规律,并开展相应的车削实验。研究结果表明:工件刚度在不同切削位置具有时变性,在中间靠近顶尖位置刚度最低;增大主轴、顶尖支承刚度可在一定程度上提高系统固有频率,改善系统动态特性。切削实验表明,柔性工件在车削状态下通常经历稳定-颤振-再稳定的变化过程,在中间靠近顶尖位置容易发生颤振,轴心轨迹发生混乱。实验结果与理论有限元模型计算结果基本吻合,该模型可用于指导实际柔性工件的车削加工。

Considering the moving tool position in machining processes,the chatter model of a flexible workpiece is formulated to investigate the time-varying stability during a straight operation.The finite element model of the spindle-chuck-workpiece-tailstock system is established to analyze the effect of the supporting conditions on dynamics of the machined workpiece.Accordingly,the stiffness distribution and the natural frequency variation of the flexible workpiece under different boundary conditions is obtained.Finally,turning experiments are performed to verify the theoretical analysis.It has been shown that the stiffness of workpiece exhibits time-varying characteristics at different cutting positions and the minimum stiffness locates approximately at the midpoint close to the tailstock side.And increasing the spindle bearing or tailstock support stiffness can effectively im-proves the eigenfrequency and the dynamic characteristics of the system to a certain extent.The cutting observations demonstrated that the state of the turning operation of the clamped-simply supported flexible workpiece generally underwent shift from stable to chattering then back to stable states,showing the time-varying nature of the process.Furthermore,the workpiece is with chaotic trajectory of the shaft axis when chatter happened.The proposed model and analytical method could be useful to guide the turning operations of the flexible components in practice.