Research On Workpiece Thermal Deformation Modeling Method Of Thin-wall Milling

The heat generated by milling process will greatly affect the machining accuracy and performance of the parts.For thin-walled parts such as controllable pitch propellers,the deformation of the workpiece caused by heat during the machining process urgently needs to be systematically studied.According to the characteristics of thin-wall milling,this paper has studied the thermal deformation modeling method of thin-wall milled workpiece from three aspects: temperature field model,thermally induced residual stress model and residual stress deformation model.(1)An analytical prediction model for the temperature field of milling workpieces based on the moving surface heat source method is established.In view of the characteristics of intermittent cutting and continuous changes of the intensity and position of the heat source in milling,the milling cutter is discretized along the axial and time history.Each instantaneous micro-element cutting edge is regarded as a bevel cutting process,considering the influence of shear heat source and side friction heat source on the temperature rise of the workpiece.After coordinate transformation,all the temperature rise caused by micro element cutting heat source is converted to the workpiece coordinate system for superposition,and a more accurate temperature field model of the milling workpiece is obtained.(2)An analytical prediction model of thermally induced residual stress in milling processing based on characteristic strain theory was established.First,the transient thermal stress is calculated according to the temperature gradient predicted by the temperature field model,the processing time history is discrete,and the transient thermal stress is used as the load for cyclic loading.The stress is released according to the unique boundary conditions of the milling process,and the thermally induced residual stress distribution model on surface of the milled workpiece is obtained.(3)An analytical prediction model of thermal deformation in milling processing based on the equivalent bending moment method was established.Based on the theory of structural mechanics,considering the characteristics of residual stress changing with the depth of the layer,the workpiece after processing is discretized along the thickness direction to form a structure similar to the multilayer film substrate.The equivalent bending moment of residual stress in each layer of film is calculated and the thermal deformation model of milling parts is obtained.(4)The thin-walled plate milling processing experiment was designed to verify the proposed thermal deformation prediction model.The influence of different milling processing parameters and workpiece thickness on the final thermal deformation,and the reasons for the prediction error are explained.The experimental results prove the validity of the thermal deformation prediction model.