基于多场耦合仿真的弧齿锥齿轮渗碳淬火热处理优化

发布时间：2019-01-19 08:50

【摘要】：弧齿锥齿轮齿面几何形状与啮合理论非常复杂。在生产中,一方面对其齿面质量要求很高,另一方面需要在拥有优良耐磨性的同时具备较高抗接触疲劳和抗弯曲疲劳性能。现今汽车工业通常采用渗碳淬火表面强化技术提高零件机械性能,工件淬火后可以获得外硬内韧的组织分布。但是淬火过程冷却介质流动不均、组织转变、热应力作用将使零件不可避免地产生扭曲和变形,降低几何精度。过去弧齿锥齿轮相关热处理研究集中于热应变及组织应变对工件几何精度的影响,忽略淬火过程冷却介质流动对热边界条件变化的影响。这种简化方式适于淬火槽内流场分布均匀、工件几何形状简单的情况,但对于预测结构复杂零件的冷却历史有一定局限性。相关研究结果显示,淬火冷却阶段换热系数的取值对仿真计算结果影响很大。为减小弧齿锥齿轮热处理畸变,了解热处理过程组织演变、应力应变分布规律,对考虑冷却介质流动影响的弧齿锥齿轮渗碳淬火热处理进行了如下研究:(1)使用三维软件UG建立弧齿锥齿轮及现有淬火槽模型,使用流体动力学软件CFX对现有淬火槽内冷却介质流场分布进行了研究,得到槽内流场分布及相关因素影响规律。(2)在上述研究基础上提出均化流场分布的方案,得到单向、均匀、可控的淬火槽流场分布;将考虑介质流动的换热系数作为淬火槽内冷却背景下多场耦合计算动态热边界条件,使考虑介质流动的多场耦合渗碳淬火仿真计算成为可能,并提高了仿真预测准确度。(3)使用材料预报软件Jmatpro预测了20CrMoH低碳合金钢的材料性能,使用热处理仿真软件Deform-HT对考虑冷却介质流动的渗碳淬火热处理进行了仿真研究,分析了弧齿锥齿轮在渗碳淬火热处理中温度变化、组织演变规律,得到了碳元素分布、微观组织分布、硬度分布、残余应力及热畸变等信息,为热处理工艺参数的调整提供参考。仿真计算结果显示,淬火后齿顶产生鼓形凸起,可能使齿轮副出现顶缘接触。(4)为了在保证齿面硬度的同时缩短鼓形长度,使用正交试验对考虑介质流动影响的渗碳淬火热处理工艺进行了优化,以介质温度、入口速度、保温温度及扩散碳势为试验因素,鼓形长度及齿面硬度为试验指标,对热处理工艺参数进行优化,得到了最优工艺参数组合,从流场分布和热处理工艺优化两个方面提高现有热处理水平。本文从流场分布和热处理工艺参数两个方面对淬火槽冷却背景下的渗碳淬火热处理进行了优化设计,效果良好,能够为实际生产提供参考。
[Abstract]:The tooth surface geometry and meshing theory of arc bevel gear are very complicated. In production, on the one hand, the quality of tooth surface is very high, on the other hand, it is necessary to have high contact fatigue and bending fatigue properties while having excellent wear resistance. Nowadays, Carburizing and quenching surface strengthening technology is usually used to improve mechanical properties of parts in automobile industry. After quenching, the hard and tough microstructure distribution of workpiece can be obtained. However, the uneven flow of cooling medium, the transformation of microstructure and thermal stress during quenching will inevitably cause distortion and deformation of the parts and reduce the geometric accuracy. In the past, the related heat treatment of arc bevel gears focused on the effect of thermal strain and microstructure strain on the geometric accuracy of workpiece, and the influence of cooling medium flow on the change of thermal boundary conditions during quenching was ignored. This simplified method is suitable for the cases where the flow field in the quenching tank is uniform and the geometric shape of the workpiece is simple, but it is limited to predict the cooling history of the complicated parts. The results show that the heat transfer coefficient of quenching cooling stage has a great influence on the simulation results. In order to reduce the distortion of arc bevel gear during heat treatment, to understand the microstructure evolution and the distribution of stress and strain during heat treatment, The Carburizing quenching heat treatment of spiral bevel gear considering the influence of cooling medium was studied as follows: (1) the model of arc bevel gear and existing quenching slot was established by using 3D software UG. The flow field distribution of cooling medium in the existing quenching tank was studied by using the fluid dynamics software CFX. The distribution of the flow field in the tank and the influence of related factors were obtained. (2) based on the above research, the scheme of homogenizing the flow field distribution was put forward, and the unidirectional flow field distribution was obtained. Uniform and controllable flow field distribution in quenching tank; Taking the heat transfer coefficient of medium flow into account as the dynamic thermal boundary condition of multi-field coupling calculation under the background of cooling in the quenching tank, it is possible to simulate the multi-field coupled Carburizing quenching with the consideration of the medium flow. (3) material prediction software Jmatpro is used to predict the material properties of 20CrMoH low carbon alloy steel, and the heat treatment simulation software Deform-HT is used to simulate the Carburizing quenching heat treatment considering the flow of cooling medium. The temperature change and microstructure evolution of arc bevel gear during Carburizing quenching heat treatment are analyzed. The information of carbon element distribution, microstructure distribution, hardness distribution, residual stress and thermal distortion are obtained. It provides reference for the adjustment of heat treatment process parameters. The simulation results show that after quenching the top of the tooth produces a bulge which may make the gear pair contact with the top edge. (4) in order to ensure the hardness of the tooth surface at the same time to shorten the length of the drum shape. The orthogonal test was used to optimize the Carburizing and quenching heat treatment process considering the influence of medium flow. The factors such as medium temperature, inlet velocity, holding temperature and diffusion carbon potential were taken as the test factors, and the drum length and tooth surface hardness were taken as the test indexes. The optimal combination of process parameters was obtained by optimizing the process parameters of heat treatment, and the existing heat treatment level was improved from two aspects: flow field distribution and heat treatment process optimization. In this paper, the optimum design of Carburizing and quenching heat treatment under the cooling background of quenching tank is carried out from two aspects of flow field distribution and heat treatment process parameters. The results are good and can provide reference for practical production.
【学位授予单位】：江西理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG162.73

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