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[Featured Article] Dynamic modeling of ultra-precision fly cutting machine tool and the effect of ambient vibration on its tool tip response

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Release Date: 2020-04-02 Visited: 

PAPER  OPEN ACCESS                                                                                                    Read More

Jianguo Ding, Yu Chang, Peng Chen, Hui Zhuang, Yuanyuan Ding, Hanjing Lu and Yiheng Chen

1. Introduction

The dynamic characteristic of ultra-precision fly cutting machine tool (UFCMT) exhibits inevitable impact on the quality of ultra-precision machining, which is the important indicator to measure the performance of the UFCMT. Prof. Jianguo Ding introduced the dynamic modeling method of the UFCMT based on the transfer matrix method for multibody systems (MSTMM), the key technologies of large-span scale flow field modeling for aerostatic bearings system based on computational fluid dynamics (CFD), and the realization strategies of simulating the ambient vibration excitation by measured data. This paper presents the latest research achievements of the machine tool dynamics, and reveals the influence mechanism of ambient vibration on the tool tip response. At present, MSTMM has been gradually applied to the dynamic modeling of complex equipment systems, which has laid a theoretical foundation for the dynamics research of ultra-precision equipment. Prof. Jianguo Ding, Yu Chang, Peng Chen, Hui Zhuang, Yuanyuan Ding, Hanjing Lu, Yiheng Chen, from the Nanjing University of Science and Technology, published a research paper of "Dynamic Modeling of Ultra-precision Fly Cutting Machine Tool and the Effect of Ambient Vibration on Its Tool Tip Response" in "International Journal of Extreme Manufacturing" (IJEM) , which systematically introduced the research background, the latest progress and the future outlook of dynamic modeling and analysis of the UFCMT. 

2. Research Background

Ultra-precision machine tool plays an irreplaceable role in national defense construction and national economic development, as well as an important supporting technology for modern high-end equipment manufacturing. In the machining process, the vibration caused by various factors will seriously reduce the processing quality of the machine tool. Hence, in order to reveal the vibration mechanism, it is necessary to study the dynamic performance of the machine tool, which leads to the essentiality of dynamic analysis. For machine tool dynamics analysis, ordinary methods need to establish the global dynamics equations of the system, which not only need to solve the difficulties of high computation workload of the high order matrix involved, but also may face ill-conditioned problems. Therefore, it is of great significance for the research of UFCMT dynamic performance to seek a highly efficient and reliable dynamics modeling and calculation method. For the UFCMT with high precision and high sensitivity, the effect of ambient vibration on the processing quality cannot be ignored. Ambient vibration is mainly excited by the surrounding environment and has the characteristic of random process, it is really important to study the effect of ambient vibration on the processing quality of the UFCMT. This paper introduced in detail the dynamic modeling of the UFCMT and the influence mechanism of ambient vibration on the tool tip response. 

3.  Recent Advances

Based on the MSTMM, the dynamic model of the UFCMT is established, and CFD analysis of the aerostatic bearings system is carried out using the large-span scale dynamic mesh modeling method, which provides important parameters for the dynamic model. The influence of ambient vibration on the tool tip response is studied by simulating the ambient vibration excitation with measured data. 

Dynamic modeling of the UFCMT system

MSTMM, with some competitive features such as: without global dynamics equations of the system, low order of the system matrix, high computational speed and avoiding the ill-conditioned problems in computing eigenvalue of the system, provides a new means with high precision and high efficiency for dynamic calculation of the UFCMT. By adopting MSTMM, the dynamic modeling of the UFCMT system is realized, and the dynamic characteristics of the system and the dynamic response of the tool tip are analyzed. The dynamic model is shown in Figure 1.

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(a) Topology figure of the dynamic model   (b) Topology figure of the tree multibody system

Figure 1. Dynamic model

Modeling of the aerostatic bearings system flow field

Aiming at the problem of grid distortion and negative grids during the process of establishing the large-span scale dynamic mesh technique calculation model of aerostatic bearings system, based on the ANSYS® ICEM CFD™ software, a multiblock method is applied to establish the mesh model for the flow field. The variations of flow field are revealed under different gas film thickness, which provides the important parameters for dynamic analysis of UFCMT. The flow field modeling of aerostatic bearings system is shown in Figure 2.

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(a) Configuration of aerostatic bearings system    (b) Mesh model and boundary conditions

Figure 2. Modeling of aerostatic bearings system flow field

Analysis on the influence mechanism of ambient vibration

Owing to the diversity of ambient vibration sources, and to reflect the ambient vibration excitation characteristics with complex randomness, the power spectrum density estimation method is used for statistical analysis of the long-time measured ambient vibration signal, so as to simulate the equivalent ambient vibration excitation. Through the dynamic analysis of the UFCMT system under the ambient vibration, the influence mechanism of ambient vibration on the tool tip response is revealed, and the necessity and effectiveness of the vibration isolation foundation are verified, as shown in Figure 3.

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(a) Whole machining process       (b) In one revolution       (c) In the cutting process

Figure 3. Displacement response of the tool tip relative to the workpiece 

4. Future Prospects

Under the background of Industry 4.0 and "Made in China 2025", it is urgent for the independent R&D of China's ultra-precision machining technology, with the processing quality improvement as its primary goal. The research team in Nanjing University of Science and Technology of the key laboratory of system dynamics of complex equipment of MIIT of China has been working on the MSTMM for many years. Combined with the CFD based large-span scale fluid dynamics modeling technology, the team has gradually carried out research in the field of ultra-precision machining in recent years. The research methods and results have positive guiding significance for the design and improvement of the UFCMT. In the near future, the team will make more remarkable progress in engineering vibration control for the enhancement of processing quality and operation stability of ultra-precision equipment.

5.  About the Authors

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Prof. Jianguo Ding has long been engaged in the research of complex equipment system dynamics, multi-rigid-flexible system dynamics and structural dynamics. He currently undertakes or participates in Key Basic Research Projects of the National Basic Strengthening Plan, Major Basic Research Projects on National Security and Science Challenging Program.

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