【作者】 李亮亮；

【导师】 孙玉文；

【作者基本信息】 大连理工大学 ， 机械制造及其自动化， 2012， 硕士

【摘要】 钛合金由于其比强度大、高低温性能好、耐腐蚀强等众多优点,在航空、航天等行业部门得到广泛应用。许多钛合金零件需要在极其恶劣的环境工作,其不仅需要零件表面粗糙度达到要求,还需要表面完整性达到要求,这无疑给实际加工带来巨大难度。而国内外对钛合金磨削表面完整性研究尚少,对于复杂曲面、微小型腔或由于加工空间所限,大砂轮、砂带不易磨削,而工人手工磨削,效率极低,磨削表面质量难以保证。基于此,本文以TC11为实验对象,研究小磨头在数控加工中心磨削钛合金的表面完整性。首先,选择了具有一定弹性的绿色SiC小磨头和超强硬度的陶瓷CBN小磨头来磨削钛合金TC11。SiC小磨头在低速情况下磨削,CBN小磨头在高速情况下磨削,并分别制定了多因素多水平的正交磨削实验参数。其次,对钛合金TC11进行了表面完整性的分析。在表面粗糙度方面,对其进行性噪比S/N分析,得出了最优磨削参数组合,并以此加工获得了良好的表面粗糙度值,对磨削因素做了ANVOA分析,获得了各因素对磨削表面质量的影响因子；在显微硬度方面,绘制出了显微硬度分布图,分析了引起硬度变化的原因；在金相组织方面,获得了磨削后表面的金相组织,观察发现没有出现重铸层和白层及金相组织的变化,分析了晶粒的变形原因；在残余应力方面,分析了形成残余应力的原因,给出了残余应力测量方法与计算公式,经测量分析后获得残余压应力,达到了表面完整性要求。再次,建立了砂轮与工件的接触模型,针对磨削过程中磨削力对工件变形与所引起的残余应力进行了有限元模拟。获得磨削力对各方向位移变化的规律,在法向磨削力方向产生最大位移变形量。随着磨削力的增大,位移变形量和应力值也将变大。最后,建立了热流密度模型,对磨削温度场及应力场进行了有限元模拟。随着热源的移动,温度场也随之变化,热影响区从磨削接触区逐渐向外扩大,温度从磨削中心区向外逐渐降低,之后达到稳定状态。模拟结果表明,磨削温度随磨削力的增大而增大,在几何磨削接触长度情况下磨削温度要大于实际接触长度时的温度。在随之进行的应力场模拟中,获得了应力值为-49.0--64.2MPa表面应力状况,和实际应力测量结果相比,应力性质相同,数量级一致,为磨削加工预测,制定合理的磨削参数提供了很好依据。更多还原

【Abstract】 The titanium alloys, duo to their high specific strength, good performance at high or low temperature and good corrosion resistance, were widely used in the aviation, aerospace, and so on. Lots of titanium alloy parts had to be applied in the hostile environment, therefore, not only the surface roughness needed to be fulfill the requirements, but also the surface integrity needed, which gave to the considerable difficulty in the machining. However, the surface integrity in grinding titanium alloy was not widely researched at home and abroad. The large grinding wheel and belt were not easily used for the complex curved surface, small cavity or small grinding space. What’s more, it is not efficient to grind parts by hand, and the surface quality is not easily guaranteed. Thus, the titanium alloy TC11is chosen, and it is necessary to investigate the surface integrity in grinding titanium alloy with small grinding wheel on the computerized numerical control machine.Firstly, the small green SiC wheel with elasticity and vitrified CBN wheel with super hardness were chosen to grind the titanium alloy TC11. The small SiC wheel was used to grind titanium at low velocity, and the vitrified CBN wheel was used at high speed. The many factors and levels orthogonal grinding parameters were estabilished for the two kinds of grinding tools, respectively.Secondly, the investigation on surface integrity in grinding titanium alloy TC11was done. For the surface roughness, the surface rouness values were measured, and the sign-noise ratio S/N were done subsequently. The optimal combination of grinding parameters was gotten, which was used to grind titanium, and the good surface topography was gotten. The ANVOA was also done, and the factors that have the most important influence on the surface roughness will be confirmed. For the microhardness, the microhardness profiles were drawn, and the reason of the microhardness variation was analysed. The metallotraphic structure of ground surface was measured. Phase transformation, white layer and recrystallized amorphous layer were not observed, and the reason that caused deformation of the crystalline grain was gotten. For the residual stress, the reason causing the residual stress was analysed, and the measurement method and stress formual were given. The residual compressive stress was obtained, which satisfied the requirement. Thirdly, the contact model of grinding wheel and workpiece was established, and the finite element simulation that grinding force caused the deformation of workpiece and residual stress in the grinding process was done. The law of grinding force casusing displacement variation was obtained, the maximal displacement deformation in the normal grinding force direction was observed. The larger grinding force was, the larger the displacement deformation and residual stress were.Finally, the heat flux model was set. The grinding temperature field and stress field were simulated by finite element method. The temperature field was changed with the heat source moving. The temperature reduced gradually from the grinding center to outer, and then reached to the stable state as time went. The simulated results indicated that the grinding temperature rised when the grinding force was larger and larger. The temperature was larger at the geometric contact length rather than at the actual contact length.The residual compressive stresses-49.0-62.2MPa were obtained in the ground surface. Compare to the actual measurement value, they were all residual compressive stresses and the same order of magnutide, which was a good base to establish grinding parameters and to forecast the grinding result.更多还原