局部重载精冲模具崩刃机理研究

发布时间：2018-03-27 19:14

本文选题：精冲模具　切入点：崩刃　出处：《华中科技大学》2015年硕士论文

【摘要】：精冲是一种精密的近净成型工艺,被广泛应用于各个工业领域。国内精冲企业在对于含多齿等特征的复杂零件的精冲生产中频繁受模具崩刃的困扰。这类局部重载精冲模具的频繁及无规律的崩刃已经成为精冲技术向复杂零件冲压和高强钢冲压方向发展的瓶颈。所以研究局部重载精冲模具崩刃机理,进而针对崩刃问题提出预防解决方案,具有重大的理论研究和现实意义。本文首先通过对冲压过程中凸模底面形貌演变的间接跟踪实验,基本否认了局部重载精冲模具崩刃产生的裂纹源处在直接承受冲压力的模具底面的假说。然后,通过对模具刃口附近侧表面、剖切面及底表面上凹坑、裂纹等形貌的系统的显微观察分析,确定了引起崩刃产生的疲劳裂纹源处在模具侧面距刃口一定高度的位置。随后,本文提出了一种符合局部重载精冲模具实际使用工况及崩刃特征的崩刃机理假说,并通过模具应力应变CAE分析和实际精冲模具侧表面残余应力跟踪实验对其进行验证。该假说的核心是:现有国内精冲模具侧面手工研磨工艺未能将线切割引起的表面缺陷完全去除,这些残留缺陷很有可能成为崩刃裂纹源;模具上多齿等特征导致模具刃口在冲压过程中应力集中,产生微区塑性变形;在模具侧面该塑性变形微区靠近弹性变形区的边界区域内,不但在冲压中承受最大的应力,而且在卸载后产生最大的残余压应力退化,致使其内的裂纹源在冲压循环中优先扩展成主裂纹,直至崩刃。最后,分别提出了提高模具侧表面加工质量、优化模具刃口倒角设计及改善重载模具受力状况三种精冲工艺改善方案。
[Abstract]:Precision punching is a kind of precision near net forming process, It is widely used in various industrial fields. Domestic precision stamping enterprises frequently suffer from die breakage in the production of complex parts with multi-teeth and other characteristics. This kind of local heavy duty precision die breaks frequently and irregularly. It has become a bottleneck in the development of precision stamping technology towards the direction of complex parts stamping and high strength steel stamping. Furthermore, it is of great theoretical and practical significance to put forward a preventive solution to the breakage problem. Firstly, an indirect tracking experiment on the evolution of the bottom surface of the punch is carried out in this paper. This paper basically denies the hypothesis that the crack source produced by local heavy-duty precision punching die is located on the bottom surface of die directly subjected to impact pressure. Then, by the side surface near the cutting edge of the die, the cut surface and the pit on the bottom surface, The microscopical observation and analysis of the crack and other morphology indicate that the fatigue crack source caused by the breakage edge is located at a certain height from the edge of the die, and then the crack source is located at a certain height from the edge of the die. In this paper, a hypothesis of breakage mechanism is presented, which accords with the actual working conditions and the characteristics of breakage of the local heavy-duty precision blanking die. It is verified by CAE analysis of die stress and strain and residual stress tracking experiment on the side surface of precision stamping die. The core of this hypothesis is that the existing domestic precision stamping die side surface grinding technology can not lead to wire cutting. The surface defects are completely removed, These residual defects are likely to be the source of crack at the edge of the die, and the characteristics of multi-teeth on the die lead to the stress concentration of the cutting edge of the die during the stamping process, resulting in plastic deformation of the micro-region. In the boundary region of the plastic deformation microzone near the elastic deformation zone on the side of the die, not only the maximum stress is subjected to during stamping, but also the maximum residual compressive stress degenerates after unloading. As a result, the internal crack source is preferentially propagated into the main crack in the stamping cycle until the edge is broken. Finally, the improvement of the machining quality of the side surface of the die is proposed, respectively. Optimization of die cutting edge chamfering design and improvement of heavy-duty die stress condition three kinds of fine-blanking process improvement scheme.
【学位授予单位】：华中科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG385

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