Study On Key Techniques Of Rotary Ultrasonic Machining Of Ceramic Matrix Composite Based On Industrial Robot

The ceramic matrix composite connection holes of skin and skeleton structure are key parts in spacecraft compartments assembly.Their accuracy and quality directly affect the assembly reliability of spacecraft compartments.Conventional manual drilling is time consuming and difficult to guarantee the quality.The large-scale special machine tools have good processing quality,but their installation space is big,the flexibility is poor,are difficult to meet the space structure parts processing demand which the shape is complex.Therefore,in this dissertation,a rotary ultrasonic machining of ceramic matrix composites method based on industrial robot is proposed.Aiming at the problems of low mechanical rigidity and easy deformation of robot,poor drilling quality of ceramic matrix composites,some key techniques such as stiffnessoriented robot position error compensation and drilling quality optimization of ceramic matrix composites are studied in depth.Based on the design of a robot end-effector with integrated automatic drilling,hole diameter measurement,nail feeding and nail inserting functions,a rotary ultrasonic machining of ceramic matrix composites system based on industrial robot is constructed and the structure of the system are introduced in detail.Combined with the practical application scenario,the technical route of robot rotating ultrasonic machining is formulated,and its specific technological process is analyzed.In order to realize accurate positioning of the robot,a complete coordinate system of the system is constructed,in the meanwhile the tool and workpiece coordinate system are calibrated.In robotic drilling,the robot deforms under the pressure force of the pressure foot,resulting that the robot end slides on the workpiece surface.In order to solve the problem and improve robot positioning accuracy,a robot stiffness model under the constraint of pressure foot is proposed,and with the model the robot deformation is predicted and compensated.The kinematics model of robot is established based on the D-H method and the relationship between the translational deformation of the robot end and the pressure force of the pressure foot is studied deeply,and the robot stiffness model under the constraint of pressure foot is established.On these basis,a method of joint stiffness identification based on L-M algorithm is proposed,and the joint stiffness of robot is obtained through joint stiffness identification experiment.Based on the robot stiffness model under the constraint of pressure foot,a method for predicting and compensating the deformation of the robot is proposed and the experiment shows the effectiveness of the method.Combined with the robot rotating ultrasonic machining system,the off-line compensation method of drilling program based on DELMIA software is proposed,which is used for off-line compensation of position error caused by robot slide deformation.In view of the quality problem of rotating ultrasonic machining of ceramic matrix composites,the optimization of drilling quality of ceramic matrix composites is studied.The formation mechanism of drilling defects in ceramic matrix composites is elaborated,and a quantitative evaluation method of tear defects is proposed.The orthogonal test of the influence of processing parameters on hole quality is carried out and the processing parameters are optimized.Based on the optimal processing parameters,the tool wear test is carried out further,and the results show that the drilling defects and hole accuracy meet the tolerance requirements after the optimized parameters are adopted in the tool life.Combined with the actual production demand,a realization strategy of maximum drilling efficiency to meet the requirement of defect tolerance is proposed.