| Aero-engine and gas turbine precision-cast blades are key components involved in energy conversion in the engine,with large bending and twisting,the maximum torsion angle is about 25°,fast curvature change,the curvature radius varies from 15 to 1000 mm,material difficult to process,widely used nickel-based high-temperature alloys,etc.The blade surface machining allowance is uneven,usually located between+0.2-+0.4mm,the surface roughness Ra≥1.0μm.This paper uses robot-assisted abrasive cloth wheel polishing cast blades,robot large work space,good flexibility,low cost,abrasive cloth wheel as derivative of the abrasive belt,which not only has the advantages of good surface quality and high efficiency of abrasive belt polishing,but also has the advantages of adjustable abrasive cloth shape,simple installation structure,good accessibility,flexibility with shape and cold polishing.In the polishing process,by selecting reasonable process parameters(normal polishing force,feed speed,linear velocity),abrasive cloth wheel parameters(shape and size,compression,mesh)and trajectory parameters(polishing mode,step length,line distance,speed),the surface roughness of the precision-cast blade after polishing meets Ra≤0.4μm,the overall profile accuracy of the blade surface is basically within ±0.05mm.The main research contents of this paper include:(1)Reverse reconstruction of precision cast blades model and machining allowance extraction.The coordinate measuring instrument and three-dimensional laser scanner was used to collect point cloud data,and after repair,filtering,simplification and other operations,complete blade surface data point cloud was obtained.The inverse reconstruction was carried out by Geomagic software,the NURBS surface method is proposed to reconstruct the surface model,combined with MATLAB and SOLIDWORKS to complete the surface reconstruction of the precision cast blade.The reconstruction accuracy of the three methods is compared and analyzed,the reconstructed accuracy meets ±0.05mm,and the machining allowance data of the surface of the precision-cast blade is obtained.(2)Polishing force modeling and experimental study of abrasive cloth wheel polishing process.Based on the elastic Hertz contact theory,the contact profile and contact pressure distribution law when the abrasive cloth wheel is in contact with the blade surface,as well as the compression interval of the abrasive cloth wheel under the certain normal polishing force are analyzed,and the relationship model between the normal polishing force and the compression is established.ABAQUS simulation software is used to simulate the contact process between the abrasive cloth wheel and the blade,and the pressure distribution law is studied when the diameter of the abrasive cloth wheel,the workpiece curvature and the normal polishing force change,the normal polishing force was controlled by controlling the compression amount,the positionbased impedance control strategy is proposed,and the contact profile of the titanium alloy plate surface is experimentally verified.(3)The material removal mechanism study on the surface of precision cast blades.Analyzed the abrasive grain distribution model on the abrasive cloth surface,and study of the elasto-plastic deformation process when the abrasive grains are in contact with the precision cast blades surface.The material removal depth and material removal amount were modeled according to the statistical normal distribution of multiple abrasive grains,and the material removal depth patterns were analyzed by ABAQUS simulation software for different press-in depths,top cone angles and spherical radius of abrasive grains.The material removal profile of the polished area before and after polishing was measured by laser displacement sensor,and compared with the theoretical calculation,to obtain the microscopic material removal mechanism on the surface of the precision cast blade and to prove the reliability of the model.(4)Flexible adaptive trajectory planning study.For the flexible contact deformation of the abrasive cloth wheel and the "overthrow" caused by the large curvature change of the blade surface,the path planning of surface sub-area polishing was studied,proposed used the improved constant chord height error to calculate the polishing step length,and the equal residual height method based on the material removal profile to calculate the polishing line distance..The number of polishing path points and polishing time required by the algorithm are reduced,which verifies the accuracy of the method.The kinematics during rotational polishing was analyzed in Cartesian space and joint space,respectively,and the distribution laws of T-and Sshaped velocity planning were compared,and the simulation analysis was carried out using MATLAB and SprutCAM software.(5)Experimental study on polishing of robot-controlled precision cast blades with abrasive cloth wheel.We have built an integrated "measuring-machining-inspection"polishing system,and the calibration method of abrasive cloth wheel flexible polishing tools and workpieces was studied.The process factors affecting the surface roughness were analyzed,and the single factor and orthogonal experiment were carried out to obtain the optimal process interval under specific conditions.The polishing experiments for gas turbine and turbine blades were conducted,and the surface roughness after polishing was analyzed to verify the feasibility of the proposed processing method.Through the application study of flexible contact behavior and process technology for robot-controlled the precision cast blades abrasive cloth wheel polishing,it realizes the full type surface of the precision cast blades with high efficiency automatic polishing,improves the surface profile consistency of the precision cast blades,and reduces the surface roughness,to provide theoretical basis for the subsequent mass polishing of precision cast blades. |
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