Research On Stiffness Characteristic And Milling Stability Of Industrial Robot Machining System

At present,industrial robots have been applied in the processing of large-scale workpieces such as space cabins,aircraft skins and ship blades by virtue of their large movement space and flexible operation.However,problems such as low dimensional accuracy and poor surface quality of machining parts often occur due to the weak rigidity and low absolute positioning accuracy of industrial robots.In order to ensure the stable and reliable processing of industrial robots,and to ensure the quality of processing,this thesis mainly carries out the following research.Firstly,micro-element method is used to model the milling force in the process of robot milling,and quadratic regression model is used to identify the milling force coefficient through the orthogonal cutting experiment of robot.Moreover,the milling force coefficient calculated under the specific cutting parameters is substituted into the milling force program prepared by MATLAB for calculation so as to verify the correctness of the milling force coefficient identification model.In addition,milling simulation model of 6061 aluminum alloy is established in ABAQUS to obtain the milling force and surface roughness of parts.The simulation results are compared with the data collected in the experiment to verify the validity of the simulation model.It shows that the process of robot milling can be predicted by finite element simulation.Then,the comprehensive stiffness field model of the robot machining system is established by taking the joint stiffness of the robot and the stiffness of spindle-tool system into comprehensive consideration.The stiffness performance in the milling plane is taken as the index to draw the stiffness performance cloud map of the end of the robot machining system in the machined part surface.By comparing the measured deformation values in the machining experiment and calculated deformation values,it is verified that the comprehensive stiffness field established after considering the rigidity of the spindle-tool system is closer to the actual situation.Finally,taking the robot milling of thick workpieces as the application background,only considering the dynamic characteristics of the robot machining system,the robot machining system is equivalent to a two-dimensional mass-spring-damping system.A dynamic milling force model is established for the robot milling process based on the principle of regenerative flutter.The zero-order frequency domain method is introduced to draw the chatter stability lobe diagram.For two different milling cutters,the corresponding modal parameters are obtained by conducting the modal test at the same seven redundant angles,and the influence of suspended stretch of the cutter on the modal parameters is analyzed.At last,the differences of the stable regions at different redundant angles are analyzed.The effects of natural frequency,damping ratio,modal stiffness and radial depth of cut on the chatter stability of robot milling are discussed respectively based on the modal test results,thus providing theoretical guidance for the suppression of chatter in robot milling in the future.