Design And Optimization Of Grinding Mechanism Of Steam Turbine Blade And Its Process Performance Test Verification

As a key part of steam turbine device,steam turbine blade affects the working efficiency to a large extent.The grinding of abrasive belt is the last process of steam turbine blade in the finish machining,which determines the final performance of the blade.Due to the foreign technology blockade in the field of finish machining,the domestic technology of steam turbine blade development in the finish machining is slow.At present,the manual grinding of abrasive belt is generally used in the finish machining of blade at home,which seriously restricts the development of domestic power equipment.This paper studies the design of the grinding mechanisms,which are included in the device that is the grinding of robot system abrasive belt of steam turbine blade,in order to achieve the high stiffness and light weight of this device,meanwhile ensure the roughness of blade is not greater 1.6μm.First,these mechanisms were designed and the key parts were optimized.Then,the grinding mechanism of blade material was studied by experiment of grinding wheel.Finally,the experiment of the grinding of robot system abrasive belt was conducted,in order to verify the process performance of device in grinding,the mechanism of this process,and the roughness of blade.The main research contents are as follows:（1）The frame was preliminarily designed according to the requirements of installation of each part in the grinding mechanism.Assuming that the package angle of the drive wheel was 135°,this paper calculated that the minimum force of tension of abrasive belt was 39.03 N,based on the Euler’s formula.Considering the error of calculation,the force of tension of abrasive belt was selected as 50 N.Then,the tensioning device was designed,based on the force of tension.Final,the active compliant device was designed according to the geometric characteristics of the blade.The frame and the stent of active compliant device were considered as key parts affecting the rigidity and stability of the grinding mechanism,based on its working conditions and performance requirements.（2）The mathematical model of the topological optimization of the frame was found based on the variable density method and the solid isotropic material penalty model.The boundary conditions and distributions of loads were set according to the actual bearing situation of the frame.The topology optimization design of frame was conducted,for the aim of high stiffness and light weight.Then,the maximum deformation,the maximum stress and the first order natural frequency of the assembly of the frame and the stent of active compliant device were taken as the optimization targets,for the multi-objective optimization of assembly.Relevant contact relationship,boundary conditions and loads were set according to the actual work and assembly situation.After that,the relevant simulations were conducted by the software of Abaqus.Combining the sensitivity analysis,the second-order response surface model and the algorithm of NSGA-Ⅱ,the structure of assembly was multi-objective optimized.Finally,the excellent structure of the frame and the stent of active compliant device was obtained.（3）According to the actual working states of active compliant device,the mechanical model of controlling grinding force was established.Simulations calculated that the minimum control range of normal grinding force is0～36.8N.（4）The grinding wheel’s experiment of material of 20Cr13 was conducted,in order to find the influence exerted by grinding wheel’s line speed,grinding wheel’s moving speed and grinding depth on the grinding force,workpiece roughness and surface morphology.In this experiment,the grinding wheel line speed has a significant effect on the workpiece roughness.The range of grinding force ratio is 0.44 to 0.63,and its average value is 0.54.The mechanical control model of the grinding force is perfected by using the average value of the grinding force ratio of 0.54,in order to control the grinding force in the grinding experiment of abrasive belt.The experiment of the grinding of robot system abrasive belt was conducted,where the workpiece was the steam turbine blade and its material is 20Cr13.And this experiment verifies that the abrasive belt line speed has a significant influence on the blade roughness.Under the process parameters of abrasive belt line speed of16m/s and normal grinding force of 10 N,the blade roughness was 1.477μm,and the performance of the grinding device meets the requirements.