Composite Stiffness Field Modeling And Analysis Of Multi-axis Machining System For Impellers

Recently,with the development of national defense industry,transportation industry and energy industry etc.,more and more requirements are brought forward for key parts of fundamental equipment such as ship propeller,turbine blade and air compressor impeller.Complex surface,weak stiffness are features of these kinds of impellers,which make them easy to have deformation in the process of machining.So,stiffness modeling and analysis for impeller machining system can improve the machining precision and efficiency.Firstly,focus on the impeller to get the sampling model based on adaptive sampling method of freeform surface.The normal vectors will be calculated for all of the samples.The flexibility matrix will be calculated and saved based on FEA(Finite Element Analysis).Moreover,based on the research of the kinematic chain and stiffness character of the impeller machining system,a stiffness model for the whole machining system will be built with the concern of the main parts which are the key factor of system stiffness.The coordinate transformation matrixes and the Jacobian matrixes will be calculated based on the kinematic chain of the machining system,and then the stiffness matrixes of the main parts will be transformed to workpiece coordinate system.The general stiffness matrix of the system will be solved by the addition of the transformed stiffness matrixes based on the principle of virtual displacement and the principle of deformation superposition of small elastic deformation theory.Recur to the concept of ellipsoid in classic analytical geometry and the character of the positive definite quadratic form,the general stiffness matrix is decoupled and a 3D force ellipsoid is achieved.Based on the characteristics of 3D ellipsoid,a series of stiffness index and general stiffness nephogram of the impeller are put forward to reflectthe machining ability.Based on general stiffness field theory and the kinematic chain of 4-axis machining tool,a general stiffness field model aimed at the 4-axis machining tool of open impeller will be put forward.Stiffness distribution of the machining system will be analyzed.Then,focus on the open impeller,stiffness distribution of the open impeller will be analyzed,week stiffness part will be optimized.Based on general stiffness field theory and the kinematic chain of 5-axis machining tool,a general stiffness field model aimed at the 5-axis machining tool will be put forward.Stiffness distribution of the machining system will be analyzed.Then,focus on the closed impeller and open impeller,stiffness distribution of the impellers will be analyzed respectively,week stiffness part will be optimized.Focus on the 5-axis machining tool for open impeller.A general stiffness field analysis and a vibration experiment will be put forward to optimize the posture of the stage with stiffness index as the objective function.In the meantime,the theory of this thesis will be verified by the comparison between the simulation analysis and the vibration experiment.