Research On Tool Holder Type Piezoelectric Cutting Dynamometer

As a primary way of processing in the machinery manufacturing field, its technology level directly affects the country’s industrialization process. The processing methods (such as milling, drilling, boring, etc.) which mainly rely to tool rotation as the main motion play an important role in the machinery manufacturing field. Improving these processing methods’ intelligent monitoring technology is an important way to promote the machinery industry. Cutting force is an important state parameter reflecting machinery process, so there is important significance to monitor the cutting force accurately and in real-time for improving the mechanical manufacturing level. Aiming at the cutting force monitoring in the cutting process based on the tool rotation as the main movement, conventional rotary piezoelectric dynamometer uses multiple groups of Y0°-cut quartz wafers uniformly spaced as a circle to measure the torque, which results in complicated structure of the dynamometer, the larger size, high technological requirements and high cost. Faced with these deficiencies, this paper develops a kind of tool holder type piezoelectric cutting dynamometer with only one group of X0°-cut and one group of YO°-cut quartz wafers to measure three-dimensional forces including axial force, radial force and torque. The new dynamometer achieves simple and compact structure, ease of processing and assembly and low cost.This paper designs reasonable force-measuring quartz wafer group through the analysis of piezoelectric quartz crystal force-electric conversion law. At first, this paper analyses the cutting force which can be mainly decomposed into the axial force, radial force and torque applied to the tool in the cutting process which based on the tool rotation as the main movement. In the premise of analyzing the stress distribution and the surface charge density distribution of the arbitrary cutting type quartz wafer with force applied to the surface, this paper analyzes the force-electric conversion relationship of X0°-cut and YO°-cut quartz wafers by the methods of theoretical calculations and ANSYS piezoelectric analysis. After that, the suitable combination of quartz cutting type and the electrode is gotten, which measures the three-dimensional cutting forces using only one group of X0°-cut and YO°-cut quartz wafers.This paper designs the dynamometer’s structure. About signal transmission when the dynamometer rotates with the spindle, this paper proposes two methods:one non-contact mode is electrostatic induction and one mechanical contact mode is bearings which are analyzed and experimentally verified. By comparison, the second one is chosen as the signal transmission method. On this basis, the overall structure of the dynamometer is designed which is easy to connect, can protect the force-measuring quartz group effectively and pass force accuracy and reliably. This paper carries out modal analysis by ANSYS Workbench and achieves the one-grade natural frequency. Then the measuring range of the dynamometer is calculated. The natural frequency and the measuring range meet the general requirements of cutting force measurements. After that, static structural analysis by ANSYS is carried out, and the result shows that the maximum stress of the dynamometer with the maximum load within the range is in the allowable range of the material. After the structure design is completed, the whole dynamometer is machined and assembled.In this paper, a comprehensive performance test of the tool holder type piezoelectric cutting dynamometer is conducted. Static calibration result is:all the linearity and repeatability are good, interferences between the directions meet the requirements after compensation. Dynamic calibration result is:one-grade natural frequency of each direction is high enough, and the exciting experiment shows the dynamometer has a good dynamic response. Finally, the dynamometer is been installed on the milling machine and the actual milling cutting force measurement experiment is conducted. The results show that the correctness of theoretical analysis, which provides a new way for rotary force-measuring.