Evaluation of on-machine measuring method for dynamic stiffness of thin-walled workpieces

Abstract

Machining of thin-walled workpieces is a popular issue due to its static and dynamic displacements during machining. It is required to set machining conditions sufficiently considering the vibration characteristics of the workpiece. An automatic on-machine system to measure the dynamic stiffness of the workpiece enables a reliable and frequent measurement. In this study, an on-machine measurement device for workpiece dynamic stiffness is evaluated. The cause of the difference in natural frequency between the on-machine measurement method and impact test is investigated. The influence of the additional mass by a shaker and accelerometer on the natural frequency is investigated using the Rayleigh-Ritz method. A cutting test is conducted to verify whether appropriate cutting conditions can be set from the measurement results of the on-machine dynamic stiffness measurement. The natural frequency difference between the on-machine measurement method and impact test was caused by the additional mass by the contact of the piezoelectric actuator. When the additional mass is 5% or less of the workpiece equivalent mass, the difference in natural frequency was as small as 10 Hz or less. In the cutting test using the workpiece with the sufficiently large mass, the compliance between the on-machine measurement method and impact test was comparable. When the forced vibration was small, the stability limit was correctly estimated from the on-machine dynamic stiffness measurement.