| Due to its low rigidity,high plasticity and high electrical conductivity,pure copper is widely used in modern electronic information industry and national defense industry,such as the preparation of diamond films,the development of shaped charge liners,and the manufacture of ultra-smooth surfaces with large dimensions and low rigidity.The processing of thin-walled workpieces is also an important issue in the field of mechanical manufacturing.Thin-walled workpieces are often used in aerospace,vehicle engineering,military and other fields.Thin-walled workpieces require high dimensional accuracy and positional accuracy,while their low rigidity and low controllability during the machining process may result in deformation and further lead to machining errors.These have increased their processing difficulty.This paper takes ultra-precision machining of low rigid pure copper disk-shaped thin-walled round parts as the research object,and single-point diamond fly-cutting is used as the processing method.Through the clamping experiment,cutting experiment,finite element simulation and analytical modeling,the deformation of the workpiece during clamping and cutting was analyzed,which provided theoretical and technical support for the precision machining of stress-distortion sensitive weak rigid components.The main work and conclusions are as follows:(1)The workpiece was fixed by vacuum clamping during the machining process,and the deformation of the workpiece with different thickness under different vacuum degree was studied.The experiment finds that the deformation of the workpiece during clamping increases as vacuum degree rises;The larger the thickness,the smaller the deformation caused by the vacuum adsorption force;the workpiece-fixture fitting condition has an influence on the clamping deformation.Based on the experimental results,the prediction model of workpiece clamping deformation was established through the finite element method.The influence of workpiece and vacuum surface appearance on the simulation results was considered in this model.The prediction of workpiece clamping deformation was implemented,and the clamping angle optimization method was proposed to reduce the deformation of the clamping.(2)The dynamic mechanical properties of fine-grained T2 pure copper were measured by Hopkinson pressure bar experiment,and the J-C constitutive model parameters of the material were fitted.When cutting thin-walled parts,residual stress is caused by cutting force,elastic deformation and thermomechanical coupling,which affects the surface quality and production efficiency of the workpiece.Based on the cutting edge radius,the tool nose radius and the machining path of the diamond tool,the classic orthogonal cutting model was improved in order to apply to the fly-cutting process.The formation mechanism of residual stress during the fly-cutting process was analyzed with the analytical model of the residual stress field.(3)The deformation of the workpiece surface due to the residual stress field redistribution was studied.The residual stress field calculated via the analytical model was taken as the initial state of the workpiece.The definition of the finite element model was completed via the SIGINI subprogram provided by the finite element simulation software ABAQUS,after which the surface appearance of the workpiece being machined with different cutting parameters was obtained by simulation.The experimental platform was built and test cuts were carried out to verify the correctness.The prediction results and the experimental results were compared,the mechanisms of how the depth of cut,feed speed and cutting speed would influence the surface flatness of the workpiece were analyzed,and the prediction method was verified. |
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