The Optimization Method Of Fixture Layout For The Low-rigidity Thin-walled Annular Structure And Vibration Control

As a common structure,thin-walled annular workpiece has the advantage of light weight,simple structure and heavy strength,and it is widely applied to the aerospace field,such as engine casing,aircraft and satellite shell.Above components play an important role in the complete machine design and security operating,therefore the requirements of the machining surface quality and machining accuracy is extremely severe.However,due to its thin wall and poor rigidity,vibration is more easier to occur in the machining process and chatter marks are formed on the surface of the workpiece,resulting in a decrease in the surface quality of the casing and making it difficult to meet the machining requirements.Therefore,it is particularly important to control the vibration of the workpiece in the process of machining.In this paper,the thin-walled annular workpiece is taken as the research object,and the vibration control and clamping layout optimization of the thin-walled annular workpiece are studied by combining analytical modeling,finite element simulation and experimental verification.The vibration characteristic of the workpiece is the basis of study on vibration control of thin-walled annular workpiece.In order to obtain accurately modal parameters,this paper establishes an analytical model for modal analysis of the thin-walled annular workpiece under elastic boundary conditions based on the LOVE shell theory,and obtains the vibration characteristics of thin-walled annular workpiece with the boundary conditions of clamped-free supported.The model of the finite element analysis is established in the ABAQUS,and the vibration characteristic is obtained through the modal analysis.the correctness of the model is verified by modal test.Based on workpiece-fixture system stiffness distribution characteristics,this paper established the finite element model adopting the semi-elastic contact model and using the spring to replace the contact stiffness between the workpiece and fixture.By studying on the effect of different ways of supports layout on the workpiece-fixture system stiffness distribution and vibration characteristic,and comparing it with the thin-walled annular workpiece without supports,the stiffness enhancements and vibration control with different ways of supports were obtained.In order to obtain the optimal supports layout satisfied the machining accuracy,this paper establishing the workpiece-fixture system support recursive optimization model,adopting the genetic algorithm and the finite element simulation method.The objective function of the model is the maximum deformation of workpiece in machining process is less than the given machining precision,and then,the support optimal layout is obtained.At the same time,the workpiece-fixture system stiffness distribution and the vibration characteristic under the optimal supports layout is also obtained.Comparing it with the distribution of stiffness and vibration characteristics of the workpiece without supports,it can verify the effect of vibration control.The modal test can verify the accuracy of the contact model between the workpiece and the auxiliary support and the influence of vibration characteristics of the work-fixture system with different layout of the supports.In order to control the vibration of the engine casing in the process of the milling,this paper designs a synchronous telescoping multi-point auxiliary support fixture to enhance the rigidity of the casing.Using the control variable method,the vibration characteristics of the engine casing under different workpiece-fixture parameters are studied by the finite element simulation analysis,so as to provide guidance for the selection of the workpiece-fixture parameters of the casing fixture in the actual machining process.