Simulation Analysis And Experimental Study On Micromilling Characteristics Of Dispersed Oxygen-Free Copper Slow-Wave Structure

As the core part of the traveling-wave tube amplifier(TWTA),slow wave structure(SWS)is composed of periodic microstructures,with features of small size and large depth-width ratio.Its dimensional accuracy,shape accuracy and surface roughness are closely related to the working performance of electric vacuum amplifier.The stability and reliability of manufacturing technology of slow wave structure has become a bottleneck restricting the development of terahertz vacuum devices due to its complex geometry,strict requirement of machining accuracy and surface quality.In this thesis,micro-milling was used to explore the technology of the folded waveguide SWS with the working frequency of 0.34THz,and particle-reinforced dispersed oxygen-free copper(DOFC)was used as the matrix material.Combined with cutting simulation and process experiment,the processing characteristics of DOFC were studied,on this basis,the processing scheme formulation,process strategy optimization,sample manufacturing and testing were completed.Based on the composition of DOFC,the material was divided into Al₂O₃reinforcement phase and oxygen-free copper(OFC)matrix phase,ABAQUS was used to establish a two-dimensional material model.By executing the Python scripts,Al₂O₃particles were randomly distributed inside the oxygen-free copper.A series of finite element models of DOFC with enhanced phase's volume fraction of 0.3%?1.1%and particle size of 50nm?200nm were established by this method.In order to make the finite element model can reflect the size effect of microscale deformation and suitable for micro cutting,based on the strain gradient theory,the constitutive model of the anaerobic copper matrix was modified,and VUMAT subroutine was written to define the modified model,providing model basis for subsequent cutting simulation analysis.Using the modified material model,the influence of cutting condition,material component and tool parameters on the cutting characteristics of DOFC is studied by means of cutting simulation.The analysis results show that the size effect of the modified material model comes from the plow effect of blunt circle and the strain gradient effect of microscale deformation.Under the condition of different volume fraction and particle size,the chip morphology and cutting specific energy of DOFC are different,the simulation results obtained under different parameters agree well with the experimental results.The influence of tool geometric parameters on burr size and cutting specific energy is investigated.The simulation results show that the main influencing factor of burr size and cutting specific energy is cutting edge radius,while the main influencing factor of chip fracture probability is rake angle.It provides theoretical reference for the selection of cutting parameters and cutting tools in subsequent process experiments.Based on the previous theoretical research,the processing technology was explored and optimized for the folded waveguide SWS with a working frequency of 0.34THz.The depth consistency of the full-period SWS is improved by surface pre-milling,the recommended feeding speed parameters suitable for different characteristic parts of SWS are optimized,so as to reduce the influence of machine position error on the shape accuracy of the microstructure.According to the results of the influence of different tool replacement methods on the size accuracy and shape accuracy of the microstructure,the tool changing scheme of segmented processing is determined,and the dislocation at the junction of segments are suppressed by using the tool-rematching process based on the bidirectional tool groove,on this basis,the tool path optimization at different depths is realized.Finally,on the basis of the above process research,the processing and detection of the full-period SWS sample are completed.The dimensional accuracy(<5?m)and surface quality(<Ra28.7nm)of the sample are all meet the requirements of indicators.