| Ultrasonic-assisted ball burnishing technology is a new type of surface finishing and strengthening technology that can significantly improve the surface integrity and fatigue performance of materials.In present work,based on the Hertz contact theory,the ultrasonic-assisted ball burnishing process is theoretically analyzed,a theoretical model for surface roughness of shaft component after ultrasonic-assisted ball burnishing was established,and an ultrasonic-assisted ball burnishing experiment was performed to verify the theoretical calculation results.Secondly,a single-factor experiment and an orthogonal experiment of ultrasonic-assisted ball burnishing were carried out using an ultrasonic-assisted ball burnishing equipment,and the influence rules and degree of influence of various process parameters on surface integrity were obtained.Finally,18CrNiMo7-6 fatigue components processed by ultrasonic-assisted ball burnishing were subjected to high-frequency fatigue experiments to study the effect of ultrasonic-assisted ball burnishing on the fatigue life of 18CrNiMo7-6.The main research work is shown below:1.In this thesis,the effects of static force,dynamic force,feed rate,amplitude,and elastic rebound on the surface roughness of 18CrNiMo7-6 components after ultrasonic-assisted ball burnishing were studied in theory.A theoretical model for surface roughness of shaft component after ultrasonic-assisted ball burnishing was established.The ultrasonic-assisted ball burnishing dynamic force test device was used to detect the dynamic force under different amplitudes and static forces.Finally,an ultrasonic-assisted ball burnishing experiment was performed to verify the theoretical calculation results.The results of surface roughness from ultrasonic-assisted ball burnishing experiment were in good agreement with the theoretical calculation results,which verified the validity of the surface roughness theoretical model eastablished in the paper,and provided a new method for the surface roughness prediction of shaft targets after ultrasonic-assisted ball burnishing.2.The single-factor experiment was carried out on the CAK4085 CNC lathe us-ing an ultrasonic-assisted ball burnishing equipment with process parameters such as spindle speed,feed rate,static force,number of passes and amplitude,etc.The surface roughness,microhardness and residual stress of the components before and after ultrasonic-assisted ball burnishing were compared and analyzed.The results show that after ultrasonic-assisted ball burnishing,the surface roughness of the components was improved significantly,the surface roughness Ra was decreased from 0.632?m to 0.235?m,which decreased by 62.82%;the surface hardness was increased from 228.7HV to 339.0HV,and surface hardness increased by 48.23%,and the surface maximum tangential compressive residual stress increased to-525.78 MPa,the surface maximum axial compressive residual stress increased to-869.61 MPa.3.In order to study the effect of different ultrasonic-assisted ball burnishing process parameters on the surface integrity of 18CrNiMo7-6 shaft components,a 5-factor and 4-level orthogonal experiment was designed and conducted based on the single-factor experiment.After the range analysis and variance analysis of the orthogonal experiments,the order of significant influence on surface roughness is: feed rate> static force> number of passes> amplitude> spindle speed;The order of significant influence on surface hardness is: static force> feed rate> number of passes> spindle speed> amplitude;The order of significant influence on residual stress is: static force> number of passes> spindle speed> amplitude> feed rate.4.In order to study the effect of ultrasonic-assisted ball burnishing on the fatigue performance of 18CrNiMo7-6 gear steel,three sets of process parameters of the optimal surface roughness,optimal surface hardness,and optimal residual stress obtained by the above orthogonal experiment were used to analyze the 18CrNiMo7-6 gear steel,respectively.Fatigue components were processed by ultrasonic-assisted ball burnishing,and fatigue experiments were performed on a QBG100 high-frequency fatigue machine.Results show that the fatigue life of the components after ultrasonic-assisted ball burnishing was improved significantly compared with the fatigue components without ultrasonic-assisted ball burnishing.And the fatigue life of the component after ultrasonic-assisted ball burnishing with the optimal surface residual stress process parameters is the largest,from the original fatigue life 1394.8k cycles of the workpiece to 20075.85 k cycles,14.39 times the fatigue life of the original component,the fatigue life after ultrasonic-assisted ball burnishing with the optimal hardness and the optimal roughness process parameters are 7356.05 k cycles and 11932.65 k cycles,respectively.It can be seen from the results that ultrasonic assited ball burnishing has a significant effect on the improving of fagigue life of 18CrNiMo7-6 gear steel. |
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