Analysis of Milling Stability Based on Cutting Force Signal Processing

• Main Author: TRAN MINH QUANG
• Other Authors: Chun-Hui Chung
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/12182103234702486998

碩士 === 國立臺灣科技大學 === 機械工程系 === 105 === The milling operation is the most common form of machining. Because the action of each cutting edge and workpiece is intermittent and periodical, the chip thickness varies periodically. This could lead to self-excited vibrations and unstable cutting which is called chatter vibration. Chatter causes machining instability and reduces productivity in the metal cutting process. It has negative effects on the surface finish, dimensional accuracy, tool life and machine life. Chatter identification is therefore necessary to control, prevent, or eliminate chatter and to identify the stable machining condition. A dynamic cutting force model of the end-milling process with tool runout error was established in this research to understand the underlying mechanism of chatter. The accuracy of the cutting force model in both time and frequency domains was evaluated by comparing to experimental force signals. Time-frequency analysis approaches, specifically short time Fourier transform, continuous wavelet transform and Hilbert-Huang transform, were utilized to give an utterly different perspective of chatter from the conventional Fourier spectrum which is insufficient in analyzing the signals of rich nonlinear characteristics. By comparing the simulation with experimental result, chatter frequency was found to consist of two major components, frequency modulation alongside tooth passing frequency caused by the increased tool runout error and the non-stationary high frequency from the regenerative vibration. Moreover, dimensionless chatter indicators, defined by the standard deviation and energy ratio of the specific intrinsic mode function, could identify the occurrence of chatter effectively. The analysis result was then validated by the workpiece surface topography, surface roughness and the stability lobe diagram