Study On Machined Surface Integrity In Whirlwind Milling Of Large-scale Screw

As the rapid development of large manufacturing equipment in such fields as NC machine and aerospace, power-transmitting parts with large-scale, over loading burden, accuracy exact and high speeds are greatly demanded. With greater than 6m in length,30 in slenderness ratio and P3-grade precision, processing of large-scale and high precision screw is one of the most important researches in extremely manufacturing. Together with the challenge of hardened materials, a study on processing such a large and hardened screw is of academic and practical importance.With advantage of high efficiency, high precise and environmental protection, whirlwind milling is gradually grown to the mainstream processing technology of large-scale screw. Nevertheless, due to the lack of high processing level in the country, the machining precision problem in whirlwind milling is most obvious. Additionally, specific cutting rules in whirlwind milling still need to be determined, and research on machined surface integrity is prone to be neglected.For achieving high precision and high efficiency of large-scale screw processing, geometric and physical characteristics of surface integrity in whirlwind milling would be studied theoretically and experimentally. Response analysis of surface roughness, surface residual stresses and full width at half maximum(FWHM) were studied. Combined with indicators’weight coefficients, the improvement plan of surface integrity was finally proposed. Studies were followed by:(1) On the base of Timoshenko beam theory, bending vibration model caused by cutting force was attained to study offset displacements in radial direction. Immediately after, surface topography considering cutting vibration was modeled considering radial offset displacements in whirlwind milling, which solves the problem of modeling surface topography without the consideration of cutting vibration. Effects of cutting parameters on surface topography and roughness were discussed in detail.(2) Aimed at describing the microstructure change of whirlwind milled surface, advanced surface testing methods, such as Electron Backscatter Diffraction and X-ray diffraction, were utilized to observe changes on microstructure, grain sizes and grain boundaries of uncutting surface and machined surface. Then, effects of cutting parameters on grain sizes and boundaries in microstructure were also investigated.(3) With the purpose of analyzing whirlmind-milling-caused physical properties changes, interconnections of those properties were intuitively studied. Then, effects of cutting parameters on residual stresses and nanohardness in whirlwind milling were discussed in experiments.(4) For the end of evaluating and improving surface integrity caused by whirlwind milling, indicators such as surface roughness, surface residue stress and full width at half maximum(FWHM) were separately analyzed based on response surface method. Combined with indicators’weight coefficients, the maximum improvement of surface integrity were together aimed at minimal surface roughness, surface residual stress -200MPa and maximal full width at half maximum. After improvement of surface integrity, surface roughness was reduced from Ra0.33μm to Ra0.17μm, no obvious change was shown in surface residual compressive stress, and full width at half maximum was improved from 4.78° to 5.16°. Thus surface integrity was comprehensively improved.By applying methods in this study, all results proved that better machining precision and surface quality can be obtained in whirlwind milling of large-scale screw, which provide theoretical basis and technological support for popularizing the application of whirlwind milling.