某杯形件热挤压凸模结构优化及疲劳寿命研究

发布时间：2018-04-28 21:24

本文选题：热挤压 + 凸模　；参考：《中北大学》2017年硕士论文

【摘要】：热挤压技术作为金属塑性加工技术的重要手段之一,越来越被广泛应用于航空航天、军工、民用、电器等行业。在热挤压工艺得到广泛应用的同时,对模具的强度、疲劳寿命提出了较高的要求。当热挤压模具在高温、高压、局部应力集中的环境中长时间工作,极易使模具内部应力分布不均匀、断裂失效。热挤压模具的失效严重阻碍工厂的批量化生产,使得经济效益大大降低。因此,为使挤压工艺在实际生产中广泛使用,有必要对这种类型的杯形件挤压模具进行优化,提高其使用寿命。此类杯形件以前提高其模具寿命的方法有:选取优质高温合金钢作为模具材料、研究模具材料淬火和回火的热处理最合理温度区间以及模具使用工作过程的模具预热温度、润滑等进行了大量的研究,这些方法可提升挤压模具的寿命。但是当前模具的使用周期仍不能满足工厂实际需求,迫切需要寻求新思路来提高模具的使用寿命。随着有限元数值模拟技术、优化设计、传热学、热疲劳、热弹塑性等理论的不断发展,为建立热挤压实际工况的有限元数值仿真模拟提供了有力的理论指导。基于高精度有限元软件的应用,可通过数值模拟的方法得出:热挤压模具应力的分布以及估算出模具的使用寿命,为设计者优化模具提供新思路。本文以实际生产中杯形件热挤压凸模的断裂失效问题为切入点,对模具材料为H13钢的使用寿命进行了研究。通过有限元数值模拟,分析了凸模不同紧固方式和内部水冷却结构对使用寿命的影响,最后对模具疲劳寿命进行了实际验证。具体做了以下几方面的工作:(1)采用ANSYS(APDL)分别对单螺纹紧固实心凸模、组合紧固式凸模进行了静力学分析,得到等效应力最大的危险点,从而为下一步的疲劳寿命分析,提供科学依据。(2)基于软件ANSYS里的Fatigue模块对不同结构参数的凸模进行了疲劳计算。用电液伺服疲劳试验机Instron8032测试H13钢模具材料的S-N曲线数据。采用模拟和实验相结合,进行疲劳分析,增加了模具疲劳寿命估算的精确度。通过比较疲劳结果发现:采用组合式结构紧固方式的凸模比单螺纹紧固的凸模疲劳寿命长。(3)在结构优化理论、传热学等理论的支持下,通过ANSYS对凸模内部水循环冷却结构进行优化。首先通过对不同内径D、底厚H凸模的热应力强度校核,得到空心凸模的参数取值范围:实验参数是底厚H为25mm,内径D为18mm、20 mm、22 mm、24 mm、26 mm、28 mm。(4)利用CFX软件对上一步得到的不同结构参数的空心凸模进行了流体分析。模拟计算完成后,得到不同内径(D)结构凸模的温度场云图。分析发现:在空心凸模同一切面上,D(内径)分别为24mm、26mm、28mm的凸模冷却效果较好。(5)综合上述紧固结构的改进以及内部内径、底厚尺寸的优化参数范围,分别制作凸模进行生产验证其优化前后的疲劳使用寿命情况。
[Abstract]:As one of the important means of metal plastic processing, hot extrusion technology has been widely used in aerospace, military, civil, electrical and other industries. While the hot extrusion process is widely used, the strength and fatigue life of die are required. When the hot extrusion die works for a long time in the environment of high temperature, high pressure and local stress concentration, it is easy to make the internal stress distribution uneven and fracture failure. The failure of hot extrusion die seriously hinders the mass production of the factory and greatly reduces the economic benefit. Therefore, in order to make the extrusion process widely used in practical production, it is necessary to optimize this type of cup extrusion die and increase its service life. The methods used to improve the life of this kind of cup are as follows: select high quality high temperature alloy steel as mould material, study the most reasonable temperature range of quenching and tempering of die material and the preheating temperature of die during the working process of die. A lot of researches have been done on lubrication. These methods can improve the life of extrusion die. However, the current life cycle of the die still can not meet the actual needs of the factory, so it is urgent to find new ways to improve the service life of the mould. With the development of finite element numerical simulation technology, optimization design, heat transfer, thermal fatigue, thermoelastic-plastic theory and so on, it provides a powerful theoretical guidance for the establishment of finite element numerical simulation under the actual conditions of hot extrusion. Based on the application of high precision finite element software, it can be obtained by numerical simulation that the stress distribution of hot extrusion die and the service life of die can be estimated, which provides a new idea for designers to optimize dies. In this paper, the service life of H13 steel is studied by taking the fracture failure of hot extrusion punch of cup in production as the breakthrough point. Through finite element numerical simulation, the influence of different fastening modes and internal water cooling structure on service life is analyzed. Finally, the fatigue life of die is verified. In this paper, the following work is done: 1) the single thread solid punch and the combined fastening punch are analyzed by ANSYS APDL, respectively, and the maximum equivalent stress danger point is obtained, which is the next step in the fatigue life analysis. Based on the Fatigue module in the software ANSYS, the fatigue calculation of the punch with different structural parameters is carried out. The S-N curve data of H 13 steel die materials were measured by Instron8032. Fatigue analysis is carried out by combining simulation and experiment, and the precision of die fatigue life estimation is increased. By comparing the fatigue results, it is found that the fatigue life of the punch with combined structure fastening is longer than that with single thread fastening, with the support of structural optimization theory and heat transfer theory. The water circulation cooling structure inside the punch was optimized by ANSYS. First of all, the thermal stress intensity of H punch with different inner diameters and bottom thickness is checked. The parameters of the hollow punch are obtained: the experimental parameters are: the bottom thickness H is 25mm, and the inner diameter D is 18mm 20 mm 20 mm 22 mm 24 mm 26 mm 28 mm. 4) the flow analysis of the hollow punch with different structure parameters obtained from the previous step is carried out by using CFX software. After the simulation, the temperature field of the punch with different inner diameters is obtained. It is found that the cooling effect of the die with D (internal diameter) of 24mm / 26mm / 28mm on the hollow punch and all surfaces is better. (5) the improvement of the above fastening structure and the optimum parameter range of the internal diameter and the bottom thickness size are synthesized. The punch was made to verify the fatigue life before and after optimization.
【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG375.41

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