Surface Topography Analysis Of Variable Cross-section Scroll Based On Wavelet

Scroll is the core part of the scroll compressor.The milling of the variable cross-section scroll plate composed of multiple combined profiles is difficult,and the surface quality is easily affected.Therefore,the reasonable design of variable cross-section scroll processing scheme and the selection of appropriate analysis methods play an important role in the study of surface morphology characteristics and the influence mechanism of processing factors.In this paper,the simulation and experiment are combined,and the variable cross-section scrolls of hard aluminum7075 and 45#steel are taken as the research objects.The machining surface characteristics are divided by wavelet,improved threshold noise reduction,and frequency band division.The frequency band range of surface morphology corresponding to milling parameters,milling force and milling cutter vibration is qualitatively analyzed.The main contents are as follows:(1)Manufacturing and profiling measurement of variable cross-section scroll based on simulation results.In order to obtain the research samples accurately,the secondary development of ABAQUS was carried out by Python language,and the two-dimensional milling plug-in was established.Taking the milling force as the evaluation standard,the optimal milling parameters for the workpieces of two materials were determined.Secondly,according to the design principle of variable cross-section scroll profile,two-dimensional and three-dimensional reference models are established by CAD and Solid Works,and the milling scheme is designed under the condition of optimizing milling parameters.Finally,Talysurf CLI1000 contour morphology measuring instrument was used to collect surface images and data signals,which laid the foundation for the development of surface images and data analysis.(2)Wavelet transform based on improved threshold and fractal dimension analysis of surface image.The preliminary analysis of the surface profile morphology of the sample was realized by combining wavelet with fractal dimension.Firstly,the gray surface image of surface morphology is drawn,and the relationship between surface fractal characteristics and contour texture roughness is obtained.The image is processed by improved wavelet threshold function.Secondly,the fractal dimension values of each sample solved by traditional fractal method,projection coverage method and wavelet fractal method are compared.The results show that the value of wavelet fractal method is 2?2.2,which is slightly smaller than the range of traditional difference box dimension method and projection covering method(2?3 and2.5?2.8),and indicate that the surface texture roughness is small and the interference factors are less.The values of hard aluminum 7075 samples(2.1819 and 2.1712)are slightly larger than those of 45#steel samples(2.0880 and 2.0682),indicating that the surface characteristics of hard aluminum 7075 samples are more complex than those of 45#steel samples.This study provides a basis for analyzing the actual measurement data and delimiting the interval of each influencing factor.(3)The biorthogonal wavelet de-noising reconstruction and frequency band division of the surface topography of the variable-section scroll.Firstly,based on the research of surface morphology image,the problem of noise interference in sample preparation and data signal acquisition is solved by using bior6.8 wavelet.Secondly,the quantitative evaluation criteria(smoothness,energy ratio,correlation and three-dimensional root mean square roughness)and qualitative criteria(macroscopic smoothness)were compared and analyzed.The results show that the three-dimensional root mean square roughness of each surface sample after reconstruction increases by 25.11%and 24.09%,28.78%and 27.68%respectively.Finally,in order to further determine the processing frequency band corresponding to the surface morphology,the wavelet spectrum algorithm is used to realize the frequency band division of the reconstructed signal.The results show that the frequency band corresponding to the surface morphology of the two materials is less than 0.173?m^-1,and the frequency band corresponding to the milling parameters is in0?0.035?m^-1,the frequency band where the milling force changes is 0.008?0.07?m^-1,milling cutter vibration corresponding is 0.04?0.105?m^-1,the frequency band corresponding to high frequency vibration of CNC milling machine occurs in 0.1?0.173?m^-1.