Research On Key Technology Of Robotic Automatic Machining

As a part of the closed impeller,the semi-open impeller is usually combined with the cover plate by welding.Thus,the blade flange surface needs to be processed to form a welding groove after finishing milling.Semi-open integral impeller is a typical hard-tomachine part with complex structure,large change of blade curvature and small distance between blades.Because of the large number of blades,the use of CNC machining will increase the tool change time and affect the processing efficiency.In the process of machining,the chatter of the cutter is large,which affects the machining quality and the machining cost is high.At present,the welding groove is mainly formed by manual grinding machine,which has poor processing consistency,low efficiency and poor working environment,so it is difficult to guarantee the processing accuracy and quality.Therefore,this paper proposes to use robot instead of manual to process the welding groove of the whole impeller.However,the positioning accuracy of the robot itself is low,and the positioning error of the impeller is large.It is difficult to achieve the correct relative machining position of the cutter and the blade flange line simply depending on the trajectory generated by the robot motion accuracy along the impeller model.The width of blade flange surface is different after finishing milling,while the width of the process between the cover and disc lines of the welding groove is same.This needs to adopt the machining method of variable allowance,which cannot be realized by the existing robot machining method.Considering these processing difficulties,this paper proposes to improve the motion accuracy of the robot by using the repeated positioning accuracy of the robot itself,in order to realize the variable allowance machining.The main research contents are as follows:(1)Build the robot automatic machining system platform for automatic machining of impeller blade welding groove.Select different machining tools for machining.Analyze and compare the actual machining efficiency and quality,select the cylindrical rotary file as the machining tool.(2)The processing mechanism of the rotary file is analyzed,and the finite element simulation is carried out by using workbench software.A material removal model is established for the cylindrical rotary file,and the influence of each process parameter on the material removal rate is analyzed in detail by using MATLAB software.(3)Carry out single factor test and orthogonal test.The accuracy of theoretical analysis is verified by single factor test,and the best combination of process parameters for robot welding groove processing is found by orthogonal test.(4)According to the 3D model of the impeller,the flange lines of the discrete blades are extracted,and the off-line point pair and the central axis are generated.The width of the groove after machining is known,and the cover line are generated based on the central axis.Finally,generate the theoretical machining path.Set and adjust the local standard frame according to the actual processing situation.The coordinate system is established and unified.Considering the weight of the tool itself and other external factors,gravity compensation is carried out.Based on the force / position feedback control method,the tool and the flange line are closely fitted,and the actual machining path is obtained.Calculate the error between the actual and theoretical machining path,correct and smooth the theoretical path.Based on the revised theoretical trajectory,the movement positioning accuracy is improved by means of repeated positioning accuracy,and the accurate machining of welding groove is realized.