H13钢硬态铣削切屑相变及加工表面完整性研究

发布时间：2018-12-13 00:56

【摘要】：H13钢硬态切削具有大塑性变形、高应变、高切削热等特点,切削区材料的晶体会发生剧烈的变形和材料相变,形成变质层。且切屑通常呈现锯齿状,锯齿形切屑变质层的存在对刀具与切屑之间的摩擦产生影响,影响切削温度、切削力与刀具磨损等,因此研究切屑变质层的形成机理具有重要的意义。本文依托国家自然科学基金的资助,研究了切削过程应力、应变、温度场等物理量的形成机理,并探究了切屑变质层的相变机制,分析了加工表面完整性,为优化铣削工艺,获得性能符合要求的工件提供技术支持。主要研究工作如下:(1)建立了 H13钢硬态铣削二维有限元仿真模型,对铣削过程进行了仿真模拟,并对有限元模型仿真结果的有效性进行了验证。模型结果表明,铣削过程(顺铣)中,切屑的厚度由厚变薄,在铣削初始阶段切屑成锯齿状,进而随着刀具的运动,切屑厚度减小,切屑慢慢变成连续形态。与实验结果对比,仿真切削力的误差不超过10%,验证了有限元模型的准确性。研究分析了铣削过程中切削温度随切削速度与刀具钝圆半径的变化规律(2)基于有限元仿真的结果,分析了 H13钢切屑形成过程及变质层相变。研究了切屑背面与绝热剪切带内的应力、应变、温度分布与实验变质层分布规律。结果表明,切屑背面与绝热剪切带内变质层分布与应力、应变、温度高度吻合。绝热剪切带内变质层与晶粒变形、再结晶有关,切屑背面变质层的形成与相变有关。通过理论分析研究了硬态铣削过程中合金元素、应力、应变能对奥氏体化相变温度的影响规律。结合有限元仿真结果,对硬态铣削变质层尺寸进行了预测,预测结果与实验结果误差不超过15%,对变质层的相变机制研究有着重要的意义。(3)结合不同切削参数,研究了考虑刀具钝圆半径影响的H13钢硬态铣削表面完整性各评价指标变化规律。对加工表面形貌进行了分析,铣削表面形貌具有明显的周期性。分析了不同参数对表面粗糙度的影响规律,建立了考虑刀具钝圆半径影响的表面粗糙度的经验模型并进行了显著性检验。分析了不同参数对残余应力的影响规律,并建立了基于二次多项式的残余应力经验模型。以加工硬化作为评价指标分析不同参数条件下的工件表面质量,研究了表层显微硬度、表面层硬化程度随参数的变化规律。研究发现,加工硬化程度随钝圆半径的增大而显著增大。对工件亚表层的显微硬度分析发现,显微维氏硬度随层深的增大而逐渐减小,即随着层深的增大,塑性强化作用逐渐减小,热软化作用逐渐加强,在一定深度内热软化作用大于强化作用,硬度小于基体硬度。本研究分析了切屑变质层的形成机制,研究了 H13钢铣削加工表面完整性,可以为揭示H]3钢铣削机理、指导铣削加工工艺并获得良好的加工表面完整性提供技术支持。
[Abstract]:The hard cutting of H13 steel is characterized by large plastic deformation, high strain and high cutting heat. The crystal in the cutting zone will undergo severe deformation and material transformation, forming a metamorphic layer. The chip is usually serrated, and the existence of sawtooth chip metamorphic layer affects the friction between cutting tool and chip, affects cutting temperature, cutting force and tool wear, etc. Therefore, it is of great significance to study the formation mechanism of chip metamorphic layer. In this paper, the formation mechanism of stress, strain and temperature field in cutting process is studied with the aid of the National Natural Science Foundation. The mechanism of phase transition of chip metamorphic layer is discussed, and the machining surface integrity is analyzed in order to optimize milling process. Provide technical support for obtaining performance-compliant artifacts. The main research work is as follows: (1) the two-dimensional finite element simulation model for hard milling of H13 steel is established. The milling process is simulated and the validity of the simulation results of the finite element model is verified. The model results show that the chip thickness changes from thick to thin in the milling process, and the chip becomes sawtooth in the initial stage of milling. Then, with the movement of the cutter, the chip thickness decreases and the chip becomes a continuous shape. Compared with the experimental results, the error of the simulation cutting force is less than 10, which verifies the accuracy of the finite element model. The variation of cutting temperature with cutting speed and cutting tool radius during milling is studied. (2) based on the results of finite element simulation, the formation process of H13 steel chip and the phase transformation of the modified layer are analyzed. The stress, strain, temperature distribution and experimental metamorphic layer distribution in the chip backside and adiabatic shear band are studied. The results show that the distribution of metamorphic layer on the back side of chip and adiabatic shear zone is highly consistent with stress strain and temperature. The metamorphic layer in adiabatic shear zone is related to grain deformation and recrystallization, and the formation of metamorphic layer on the back of chip is related to phase transformation. The influence of alloying elements, stress and strain energy on austenitic transformation temperature during hard milling was studied theoretically. Combined with the finite element simulation results, the size of the hard milling metamorphic layer is predicted. The error between the prediction result and the experimental result is not more than 15. It is of great significance to study the phase transition mechanism of the metamorphic layer. (3) combined with different cutting parameters, The changes of evaluation indexes of surface integrity of H13 steel hard milling considering the influence of blunt radius of cutting tools are studied. The machined surface morphology is analyzed, and the milling surface morphology has obvious periodicity. The influence of different parameters on surface roughness is analyzed. The empirical model of surface roughness considering the influence of blunt radius of cutting tool is established and the significance test is carried out. The influence of different parameters on residual stress is analyzed, and an empirical model of residual stress based on quadratic polynomial is established. The surface quality of workpiece under different parameters was analyzed by using work hardening as evaluation index. The variation of surface microhardness and hardening degree of surface layer with parameters was studied. It is found that the degree of work hardening increases with the increase of the radius of blunt circle. The microhardness analysis of the subsurface layer of the workpiece shows that the microhardness decreases with the increase of the layer depth, that is, with the increase of the layer depth, the plastic strengthening effect decreases gradually, and the thermal softening effect is gradually strengthened. The effect of thermal softening is greater than that of strengthening in a certain depth, and the hardness is smaller than that of matrix. In this paper, the formation mechanism of chip metamorphic layer is analyzed, and the surface integrity of H13 steel milling is studied, which can provide technical support for revealing milling mechanism of H] 3 steel, guiding milling process and obtaining good surface integrity.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG54

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