Vibration Propagation Characteristics of Micro-Milling Tools

Abstract

Micro-milling tools are usually used for the 3D precision processing of micro metal parts under ultra-high speed. However, due to the structural characteristics of small scale, variable cross-section, and weak stiffness, the vibration of micro-milling tools is weak and easily mutates, which can potential cause great harm to the stability and machining accuracy of machine tools. To reveal the transfer law of micro-milling tool vibration, guiding the method selection of tool vibration measurement and providing new means for mechanical model verification; firstly, the vibration mechanics model and vibration transfer matrix of the micro-milling tool were established. The vibration propagation characteristics of the micro-milling tool were analysed in contrast with the time domain and frequency domain, taking two representative micro-milling tools, Tool A and Tool B, as examples which with different cross-sections and structural parameters. Secondly, a micro-milling tool vibration measurement experimental system was set up and a sensor array with four optical fibre displacement sensors was used to obtain the vibration displacements at different positions of the tool under pulse and start-stop excitation. Finally, the results show the following: for Tool A, the max vibration displacement of the measurement of point 1 is about 3.5 times of measurement point 2 but near 18 times the measurement of point 3; meanwhile, compared with measurement point 1, the 16.8 kHz signal disappeared in measurement point 2, measurement point 3 and measurement point 4. However, for Tool B, the max vibration displacement of measurement point 1 is about 11.24 times the measurement of point 2; in contrast, the signal strength of the measurement of point 3 and point 4 is too weak to compare and analyse, although there are three resonant frequencies (10.2 kHz, 17.6 kHz, and 26.7 Hz) of Tool B based on the signal of measurement point 1, the 26.7 kHz signal disappeared in measurement point 2. The vibration amplitude of the tool tip decreases rapidly in the process of tool transfer, a bigger ratio cross-section with bigger attenuation of vibration amplitude and smaller size will aggravate this process. This study provides a reference for the selection of measuring points of micro-milling tool vibration displacement.