Calibration And Application Of PVDF Piezoelectric Film For Ultrasonic Vibration Assisted Cutting Force Measurement

Ultrasonic vibration assisted cutting system has broad application prospects in the field of hard and brittle materials processing.Accurate measurement of the cutting force can not only analyze the propagation of stress waves,but also monitor the wear of the tool.This can be beneficial to explore the vibration cutting mechanism,optimize the cutting method,improve the accuracy and efficiency of the machining.PVDF piezoelectric film sensor has the characteristics of high sensitivity,good dynamic response and good flexibility.It is a good method to measure cutting stress at ultrasonic frequency.However,how to obtain the accurate piezoelectric constants and make the PVDF film accurately measure the cutting force and improve the measurement accuracy is a difficult problem.Under this background,this paper proposed a piezoelectric constant calibration method based on the falling ball method,and carried out the experiments of piezoelectric constant calibration and ultrasonic cutting force measurement.The specific research is as follows:1.A piezoelectric constant calibration method that can be used in the tensile and compression directions was proposed by analyzing the stress of the falling ball system using the Ansys workbench software.A calibration system based on piezoelectric force measuring platform and the falling ball was set up.The piezoelectric constants in the tensile and compression directions of the PVDF film were calibrated and their uncertainties have been analyzed.The results showed that the relative uncertainties of the piezoelectric constants in the tensile and compression directions were 1.896% and 1.28%.2.The shape and size of the PVDF film suitable for stress measurement have been selected according to the characteristics of ultrasonic vibration assisted cutting system.In response to the characteristics of the ultrasonic vibration assisted cutting system,a suitable shape and size of the piezoelectric film was selected to make it more suitable for the measurement of the cutting force.The theoretical analysis of the machining principle of the ultrasonic vibration assisted cutting system was carried out.The strain of the end face of the horn was measured by PVDF film and the relationship between the strain and the input voltage of the transducer was explored.The results proved that the two have a good linear relationship.3.An ultrasonic horn strain measurement system was built based on the PVDF film and cutting experiments were performed.The results showed that ultrasonic vibration assisted cutting can effectively reduce the cutting force by about 10%.The change in cutting speed had a small effect on the strain and the strain increased with the increase of the cutting depth.Combined with finite element simulation and experimental measurement results,the validity and practicability of the PVDF film calibration and cutting force measurement described in this paper are verified.