Papers by Author: Li Bin Guo

Abstract: Innovative algorithms and software evaluating the three-dimension topography in laser micro-machining are developed in this paper. First according to the features of the three-dimension surface consisted of micro peaks and pits, Gaussian curve parameters are presented and used to form a evaluation system with 22 parameters for three-dimension topography. Based on this, to completely and precisely evaluate the three-dimension topography,an assessment module for power spectral density is designed and implemented. Through integrating this module with the 22 parameters, a complete and precise evaluation system is built, which can evaluate the performance not only in vertical direction but also in horizontal is obtained. In software, through using MATLAB/GUI latest interface to implement integration, the following functions are implemented: surface three-dimension topography rebuilding, signal noise reducing, assessment data extracting, roughness calculating, and two-dimensional frequency domain analyzing. Furthermore, with this software, through comparing the parameters and spectrum, it is easy to determine the frequency affecting the roughness,thus providing some clues on how to further reduce the surface roughness. Test results show that this software system can provide more accurate assessment for the surfac three-dimension topography, and can be used to ultra-precision machining surface assessment.

Abstract: Laser micro machining is one of modern precision machining methods, which has significance on the modern manufacturing. The solid-state pulse laser (YAG) is processed by overlapped laser spots to remove material from a surface. Through studying the single pit with single pulse laser, the paper proposes two parts-melted part and molten pool and three parameters to describe single pit topography. Meanwhile it puts forwards the relation of the coincidence degree and the feed rate of the worktable, because the single pit model is the basic unit of convex and concave topography, affected by pulsed spot coincidence degree, and the coincidence degree is directly determined by the worktable feed rate, therefore it derives the relationship between the spot coincidence degree and the worktable feed rate. Using the scanning electron microscope (SEM) to photograph the machined surface, it verifies the correctness of the model of the coincidence degree and the worktable feed rate.

Abstract: Micro wire electrical discharge machining (MWEDM) and flat grinding were used to manufacture test specimens of W18Cr4V. Electrochemical impedance spectroscopy and potentiodynamic polarization curves were made to test the corrosion resistance of specimens’ surface with micro cell and electrochemical workstation. Besides, the surface micro-topography after corrosion had been observed with inverted metallographic microscope. The results show that MWEDM surface is better than flat grinding surface in the corrosion resistance. The best Anticorrosive discharge energy of W18Cr4V is 1.25J.

Abstract: Micro wire electrical discharge machining (Micro-WEDM) is one key micro-processing technology for intricate micro parts. The surface texture is different with a single mechanical cutting surface and conventional spark-erosion formation machined surface. Assessment of the existing surface texture roughness parameters in terms of accuracy, or in the characterization of fine sense, can not meet the Micro-WEDM surface texture characterization needs. Through the analyses of surface autocorrelation function, structural shape ration, steepest attenuation autocorrelation function and surface texture direction, explicit the precise meaning of surface texture parameter characterization, make it really reflect the actual condition of Micro wire electrical discharge machining surface, modify Characterization Parameter algorithm, simplify the calculation process, make the results more accurate and more intuitive. Keywords: Micro wire electrical discharge machining; autocorrelation function; surface texture

Abstract: The surface topography errors of Micro-EDM are mainly composed of surface roughness, surface waveness and so on, which have influence on the workpiece’s functions and performances in various degrees. Thus, how to pick up these errors without distortion is quite important for evaluating the surface topography. It is well known that Wavelet Transform has good time-frequency localization properties, which is especially suitable for image processing. Therefore, in this paper, a wavelet method for surface roughness of Micro-EDM is presented, in which, the time of wavelet decomposition is determined by Pearson Chi-square goodness of fit test. Furthermore, the results of simulation and experiments show that the proposed methods can separate Micro-EDM’s surface roughness well, meanwhile, using the mean and variance of ideal surface as accuracy requirements of the reference surface could help the separation have a certain certainty and precision.

Abstract: The surface micro-topography of micro-WEDM is random, disordered and multi-scale and has been proved that it is fractal with the characteristic of self-affinity within a certain scale on the basic of the fractal geometry theory. According to the characterization of W-M fractal function, the principles of three evaluation methods about power spectrum method, structure function method and wavelet criterion have been described. The advantages and disadvantages of them evaluating the fractal property of the surface micro-topography of micro-WEDM have been compared in this paper. The experimental results indicate that the wavelet criterion is more stable and dependable than the other two methods, so the fractal dimension D of the surface micro-topography of micro-WEDM has been calculated using it. The result shows that the fractal dimension has the tendency of decrease with the increase of root mean square deviation (Sq) value while it is not absolutely monotonic, which can be used as a beneficial supplement to traditional evaluation parameters of surface roughness.

Abstract: The topography errors of micro electrical discharge machining (micro-EDM) surface are mainly composed of surface roughness, surface waveness and profile error. These three errors influence the workpieces functions and performances in varying degrees. Thus, how to pick up these compositions without distortion is very important for surface comprehensive topography evaluation. In this paper, the roughness of micro-EDM surface contour lines is separated by wavelet method. Firstly, it is certified that any curve line could be indicated by different frequency parts with multi-resolution analysis, which is the feasibility study for roughness separation with wavelet method. Then, the mathematical model of roughness separation of contour lines is set up. Finally, the formula of roughness separation times with wavelet theory is given.

Abstract: The surface micro-topography characteristics of micro-WEDM, which can have a directly significant impact on the parts usability properties, have been attached more and more importance by people. In this study, the method of statistical analysis is applied to work out the two-dimensional autocorrelation function figure and the power spectrum density function figure of the surface micro-topography of micro-WEDM. It can be seen that there are more sharp and narrow peaks and high frequency components, meanwhile, there are some low frequency wave components on the surface. A conclusion is arrived at that the three-dimensional (3D) surface micro-topography of micro-WEDM shows isotropy through analyzing its texture characteristics. The results can provide the theoretical basis for further establishing the appropriate evaluation parameters for the surface roughness of micro-WEDM.