Thermal Stress Coupling Research On Hybrid Grinding And Polishing Machine Tool For Blade Finishing

In recent years,with the rapid development of aerospace,construction machinery and traditional industries,the requirements of science and technology for the overall performance and processing accuracy of NC machine tools are constantly improving,which makes parallel NC machine tools develop rapidly.Thermal error is one of the most important factors to improve the accuracy of machine tools,and it is also a research difficulty in the field of machine tool accuracy.In the processing of the hybrid blade grinding and polishing machine tool,the whole machine system and its key substructures,such as the base feeding platform,parallel mechanism,gantry crossbeam and polishing tool head,will be affected by the combined action of processing chatter and thermal stress,which will produce coupling effect,i.e.thermo-mechanical coupling effect,which greatly affects the mechanical and thermal performance of the hybrid blade grinding and polishing system,and is very unfavorable to the processing accuracy.The traditional method for studying the thermal errors of machine tools is the finite element thermodynamic analysis or experimental measurement of machine tools and their key substructures.The limitation of the traditional method is that if only the thermodynamic finite element calculation of machine tool and its substructure is carried out,there are some defects such as the simplification of machine tool model is difficult to simulate the real working state,and the error and result of finite element software calculation are not unique.If only the machine tool is tested by measuring method,it is difficult to systematically inspect the performance of the machine tool and the contingency or non-repeatability of the test.In view of the above problems,this paper takes the hybrid blade grinding and polishing machine tool built independently in the laboratory as an example,and based on the research of thermo-mechanical coupling principle,carries out heat source identification,calorific calculation,finite element analysis of temperature field and modal test analysis respectively for the three key substructures of the machine tool,and puts forward a method of establishing a mathematical model of thermal error based on thermo-mechanical coupling effect,solving method and modal test analysis.Verification method.Fully combining the advantages of finite element method and experimental method,the validity and correctness of thermal error mathematical model are verified by comparison.The main research work and achievements of this paper are as follows:(1)The thermal deformation mechanism of the hybrid blade grinding and polishing machine tool is studied.The grinding and polishing machine tool is divided into three key sub-structures: parallel mechanism,base feed platform and beam system.The identification of internal and external heat sources,the calculation of calorific value and the calculation of thermal generation rate of three key substructures are carried out.Internal heat source and heat generation rate are important preconditions for thermodynamic finite element analysis.(2)Thermodynamic finite element analysis of the key substructures of the hybrid blade grinding and polishing machine tool is carried out.Firstly,the convective heat transfer coefficient trial-and-error method is applied to the temperature sensitive parts of the key substructures,and then the steady-state temperature field analysis and transient temperature field analysis of the three key substructures are carried out according to the constraints.Transient temperature field analysis and heat flux analysis can be used as boundary conditions for thermal deformation analysis.Thermal deformation nephogram and numerical value of key substructures are obtained.The node temperature table and curve are obtained by simulation calculation.Thermodynamic part of thermo-mechanical coupling mathematical model is completed.(3)Modal experiment analysis of hybrid grinding and polishing machine tool was carried out.According to the theory of modal analysis,the whole machine and sub-structure of the hybrid grinding and polishing machine tool are used as experimental objects to carry out modal experiments.The excitation of the machine tool is driven by hammering method,and the sampling method is based on Time-Varying Sampling method.The least squares complex exponential method and eigensystem realization method are used to identify the modal parameters,and the results are compared and optimized.The natural frequencies,damping ratios and mode shapes of the whole machine and its key substructures are obtained,which lays the foundation for the establishment of the mathematical model of thermal error of the grinding and polishing machine tool.(4)A mathematical model modeling method based on the coupling of temperature field and mechanical properties is proposed.The maximum thermal deformation,maximum thermal stress,first-order natural frequency and quality of the key sub-structures of grinding and polishing machine tools are selected for multi-objective optimization modeling of thermal errors.The response surface orthogonal test is used to solve the problem and the orthogonal test is used to verify the thermal error model.The final thermal error model includes the positive and negative deviations of the key substructures due to the force and heat under the thermal balance condition of the grinding machine tool.The compensation of the mechanical and thermal processing errors of the grinding machine tool is realized by using the algorithm in matlab,which verifies the correctness of the proposed modeling method.