## 5 Conclusions  
In this paper, a new chatter identification method based on signal processing was proposed to identify chatter phenomenon during the 3D-EVC process. The 3D vibration signals of the tool-tip are obtained by the displacement sensor, which is installed in the 3D-EVC apparatus, and the vibration signals were chosen as the object of decomposition, based on the visualized time and frequency domain data in the \(Z\) direction. The method of chatter identification developed is divided into two parts: initial identification and feature extraction identification. The amplitude spectrum obtained by FFT was used as a preliminary criterion for chatter identification. Then, the EMD method was employed to decompose the vibration signal including the rich undesired vibration information, the mean square frequency, and the one-step self-correlation coefficient, which were calculated as the identification criteria for identifying the chatter in the 3D-EVC process. The experimental results show:  
1. The vibration signals obtained by the displacement transducer and the amplitude spectrum obtained by FFT have reflected the trend of vibration state in the 3D-EVC process from the time and the frequency domain, respectively. The frequency shift phenomenon appeared with the vibration energy increasing gradually in the machining processes. 2. Both the mean square frequency and the one step self-correlation coefficient have been changed suddenly in the cutting process. The value of the mean square frequency increases from 210 to 6800, in contrast, the value of the one step self-correlation coefficient reduces from 0.95 to 0.29. Therefore, these two parameters can be used as the index of the chatter phenomenon. In future work, the effects of model parameters will be theoretically analyzed with stability lobe theory. Moreover, a chatter suppression method should be developed by combining sensorless chatter detection with an optimization algorithm. [PERSON], [PERSON] and [PERSON] conceived and designed the experiments; [PERSON], [PERSON], and [PERSON] performed the experiments; [PERSON], [PERSON] and [PERSON] analyzed the data; [PERSON] and [PERSON] contributed reagents/materials/analysis tools; [PERSON] wrote the paper; [PERSON], [PERSON], [PERSON] and [PERSON] reviewed and revised the paper. **Funding:** This research was funded by [Ministry of Science and Technology State Key Support Program] grant number [2016 YFE0105100], [Micro-Nano and Ultra-Precision Key Laboratory of Jilin Province] grant number [2014622008]C, [Science and Technology Development Projects of Jilin Province] grant number [20180101034 JC, 20180201052 GX], [Education Department Scientific Research Planning Project of Jilin Provincial] grant number [JJKH20181038 KJ] And the APC was funded by [20180101034 JC]. **Acknowledgments:** Special thanks to the experimental installation provided by the Key Laboratory of Micro-Nano and Ultra-precision Manufacturing of Jilin Province. **Conflicts of Interest:** The authors declare no conflict of interest. +++ ==WARNING: Truncated because of repetitions==
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