Dynamic Micro/Nano Cutting System Modeling For Prediction And Analysis Of Surface Topography

Nowadays, the requirement of the surface quality is higher and higher since the developmental technology and common life, such as the fields in electronic industry, information industry, national defense, aerospace related techniques. Since the ultra-precision machined surface contains lots of texture characteristic, researchers are paying more and more attentions to the formation of the surface micro structures and their impacts in the modern manufacturing. The purpose of this paper is to bridge the gap between the dynamic cutting process and the surface topography/texture generation. The proposed dynamic cutting system model leads to the surface topography prediction, and the spectral analysis of surface height data can identify the vibration situation during cutting. It help better understanding for the surface topography and texture formation and provides an approach to optimize the cutting process.In the nano/micro cutting process, the surface quality is heavily dependent on all the dynamic factors, including those from the material, tooling, process parameters, servo accuracy, mechanical structural deformation, and non-linear factors as well. Thus, the whole cutting system is modified by introducing the linear/non-linear dynamic factors based on the classical cutting mechanics.In the consideration of various intricate aspects of the cutting process resulting in the surface topography and texture formation, such as spindle runout, ground vibration, air pressure oscillation, motor servo vibration, material heterogeneity, built-up edge, regenerative chatter, (BUE), etc, the dynamic cutting system follows better to the practice. Moreover, the machine for experiment employed the linear motor and aerostatic slides as the feed system. The tool position accuracy is totally determined by the motor servo performance. Therefore, it is important to design and test the control system for the machine. The controller adopts the advanced PID algorithm, such as integral separation, differential forward, low-pass filter, and feed forward compensation. The tracking test is based on the correlation analysis to design the feed forward section. The control response shows the effectiveness of the control law. Finally, the integrated simulation-based approach is presented involving the dynamic cutting process, control/drive system, surface generation and analysis.The machined surface is generated based on the tool profile and the real tool path combining with the various external and internal disturbances as the footprint process. In the model to predicate the micro/nano cutting surface topography, the influence of tool interference on the surface formation is considered. The 3D surface generation algorithm is presented and typical surface topographies are illustrated. Alsop, the influence of tool-workpiece relative vibration on surface topography is analyzed. Both the frequency ratio method and sampling theorem are used to interpret the surface topography and texture formation. The effects of vibration amplitude, frequency and tool interference on the surface roughness are analyzed in detail. The micro/nano turned surface under the multi-dynamic factors is simulated as a complex 3D surface topography.In respect that traditional surface roughness parameters is unable to explain the complexity of the surface texture and the cause of formation, the area spectrum method and wavelet transformation are employed to analyze the surface spectrum signature. The power spectral density (PSD) analysis of tool path and surface profiles leads to the frequency relations between time domain and spatial domain.The areal PSD (APSD) of surface topography states the typical patterns in frequency domain. Furthermore, a systematic approach based on APSD is employed to identify the composition of the vibratory motions with the surface data analysis. To characterize the surface texture in specific scale, the surface is decomposed and reconstructed by wavelet multi-scale analysis. In the practice, the multi-scale analysis based on discrete dyadic wavelet transform will cause the resolution limitations in the frequency domain. So some surface with specific scale contains multi-frequencies and some frequency feature appears on many multi-scale decomposed surfaces. Comparatively speaking, the 2D continuous wavelet transform is more effective to decompose the surface topography with specific scale.The significance of dynamic factors on the surface roughness is analyzed by three methods: from APSD analysis, from wavelet multi-scale analysis and from system simulation. Through the significance, it is clearly to obtain the control measures to improve the cutting surface quality and direct the cutting practices.Finally, the proposed systematic modeling approach is verified by cutting trials. The dynamic signals are detected by on-line measurement of the micro/nano turning machine. And the corresponding 3D surface topography is predicted in well accordance with the experiment result. The experimental result shows that the proposed APSD vibration identification method is validated through face turning with the assist of` forced vibration.