Research On Machining Process Of Additive And Subtractive Hybrid Manufacturing For 316L Stainless Steel Thin-walled Parts

The hybrid process is the effective integration of two or more different processes.This process exploits the benefits of individual processes while overcoming their limitations.Taking the additive-subtractive hybrid manufacturing technology as an example.By introducing the traditional subtractive processing such as milling,drilling,grinding and polishing into the additive manufacturing process,additive-subtractive hybrid manufacturing technology can not only keep the advantages of additive manufacturing,such as high efficiency,high material utilization rate and near net forming,but also control the dimensional accuracy and surface quality of forming parts to meet the design requirements.In this thesis,the additive and subtractive hybrid machining experiments of 316 L stainless steel thin-walled parts were carried out.At the same time,a finite element model corresponding to the experiment of the hybrid manufacturing of thin-walled parts of 316 L stainless steel was established.The temperature field and distortion of thin-walled parts in the laser additive manufacturing process and the secondary distortion caused by the stress changes of the thin-walled parts in the subsequent milling process were studied.Firstly,the optimized process parameters of laser metal deposition forming were selected through systematic process experiments to be used in additive manufacturing of thin-walled parts.The temperature distribution on the surface of the thin-walled parts during the process of laser additive manufacturing was recorded by infrared thermal imager.The surface of the thin-walled part after the addition is scanned by the laser distance sensor,and the distortion data of the surface of the thin-walled part is obtained.Secondly,used ANSYS/Workbench finite element software to simulate the temperature field and thermal stress distortion of thin-walled parts during the additive manufacturing,the temperature distribution recorded by the infrared thermal imager and the distortion data of the laser distance sensor were verified.Then,the relationship between the milling force and milling parameters of the additive-manufactured parts was studied through the orthogonal test of the side milling of the additivemanufactured block specimen.And the mapping relationship model between the surface roughness of the additive-manufactured parts and the feed per tooth was established by using the method of neural network fitting analysis.Based on the data of milling force and the simulation results of the temperature field and stress distortion of the thin-walled parts in the AM process,the numerical simulation of implicit dynamics was carried out to predict the secondary distortion of the thin-walled parts after milling.Thirdly,the process parameters optimized in the milling orthogonal test were used to carry out the side milling test of the additive-manufactured thin-walled parts.The distortion data of the surface of the thin-walled parts after the composite processing was recorded,and the data was compared with that before the processing of subtractive processing.It can be seen that after the milling of the additive-manufactured thinwalled parts,the stress distribution,the type and value of the stress inside the thinwalled parts are obviously changed.Under the condition of selecting appropriate milling parameters,milling processing can release the residual tensile stress caused by laser additive manufacturing to a certain extent,and effectively reduce the thermal stress distortion of thin-walled parts,thus improving the machining accuracy and surface quality of thin-walled parts.Finally,the validity of the finite element model was verified by comparing the experimental data and the finite element numerical simulation results in the process of additive-subtractive hybrid manufacturing.The influence law of residual stress change on the distortion of 316 L stainless steel thin-walled parts in the process of additivesubtractive hybrid manufacturing was obtained.The research process and results of the thesis laied a foundation for further research on the influence mechanism of the material reduction process parameters on the surface quality of the additivemanufactured 316 L stainless steel parts,and the dynamic compensation of the cutting force in the milling process for the irregular shape of the additive-manufactured parts.