| Screw rotors are core parts in screw compressors as well as screw pumps.Their profile accuracy and surface roughness affect the performance of screw compressors as well as screw pumps directly.The complex profile of the screw rotor is usually composed of asymmetric complex curves,and as screw rotor has characteristics of large helix angle and few teeth,the machining accuracy of form grinding screw rotor with complex profile can not be ensured easily.With the development of screw compressors and screw pumps,requirements on the accuracy and surface roughness of screw rotor are getting higher and higher.Thus,researches on high precision forming technology of screw rotor with complex profile are very necessary.In this context,researches on profile error control of high precision form grinding for screw rotor,as well as optimization of grinding process parameters for reducing surface roughness of screw rotor,have been thoroughly carried out with domestic CNC screw rotor grinder.The work covers:(1)The mapping model bewteen geometric errors of the screw rotor grinder and installation parameter errors of grinding wheel was established on the basis of the theory of multi-body system.To obtain this model,the structure of CNC screw rotor grinder was introduced,and its movement mechanism was also analyzed.The ground point on rotor profile was regarded as the actual grinding point on grinding wheel profile.Accordingly,the conversion between the geometric error of the grinder and the installation parameter errors of grinding wheel was achieved.And the correction process of the grinder geometric error was simplified.In addition,upon the geometry theory of form grinding screw rotor,the mathematical model of conjugated rotor profile,as well as the geometric relationship between rotor and grinding wheel were established,and the verification software of rotor profile and grinding wheel profile was developed.(2)The design method of grinding wheel profile was proposed based on interference checking method for dressing path of grinding wheel during its dressing process and dynamic calibration method for interference between grinding wheel rotor during grinding process.According to the existing design approach of grinding wheel profile,the adjustment ranges of installation parameters of grinding wheel were obtained by reference to the adjustment conditions of installation parameters of gear grinding.The grinding wheel interference phenomenon can be avoided by the above interference checking methods with adjusting installation parameters of grinding wheel within its adjustment range.Thus the accuracy of grinding wheel profile was ensured.(3)A numerical method to evaluate the effects on rotor profile caused by the single factor of installation angle error,center distance error and axis position error as well as their coupled factors was presented.The decoupling relationship between effects of single factor and coupled factors on rotor profile error was investigated.And these conclusions were verified by experiments.(4)A comprehensive error correction method of screw rotor profile with NC form grinding was proposed.Based on the profile error measurement of screw rotor and its form grinding process,adjusting strategies of the grinding wheel dresser parameters and grinding wheel installation parameters were proposed respectively to correct profile error of screw rotor for the wheel dressing stage and grinding wheel processing stage.To further improve the rotor profile accuracy,based on the existing profile error correction method of screw rotor,pre-correction profile of screw rotor was constructed by introducing error correction factor,and a pre-correction strategy of screw rotor profile error was presented by updating grinding wheel profile.Grinding experiments were performed to verity this method,and the results show that this method can effectively reduce the profile error of screw rotor.Compareing with the existing profile error correction method of screw rotor,the proposed pre-correction strategy of screw rotor profile error can make the percentage of bad points on female rotor profile decrease from 34.8%to 7.05%and 20%to 1.33%for the male rotor with once correction.The efficiency of existing profile error correction method of screw rotor was improved significantly.(5)Orthogonal experiment of the effect of grinding parameters on the surface roughness of screw rotor and the vibration of the grinding system was carried out by using the orthogonal design theory.After analyzing the orthogonal data,the optimizations of grinding process parameters to reduce the single-target such as surface roughness of screw rotor and the vibration of the grinding system was obtained,and the the power function prediction model of the surface roughness of screw rotor on grinding process parameters was eatabished.The model was validated by numerical analyzing.Considering the effect of the vibration of the grinding system on rotor surface roughness,the attention degree for surface roughness of screw rotor was introduced,and the multi-objective function of the surface roughness of screw rotor and the vibration of the grinding system was established by using the normalization theory,then the multi-objective optimizations of grinding parameters for different requirements were obtained.The verification results show that the surface roughness of male rotor was reduced by 2.4%and the female one was reduced by 1.6%with the proposed single objective optimization.Considering the effects of the system grinding vibration on the surface roughness of the screw rotor,the surface roughness of the male rotor was reduced from 0.291?n to 0.282?m and the female one was reduced from 0.315?m to 0.313?m with the multi-objective optimizations.By applying methods in this study,all results proved that better profile accuracy and surface roughness can be obtained in form grinding of screw rotor with complex profile,which provide theoretical support for the development of processing equipment of high precision grinding screw rotor. |
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