【作者】 黄荣学；

【导师】 范洪远；

【作者基本信息】 四川大学 ， 材料加工工程， 2005， 硕士

【摘要】 应力水平是造成冷挤压模具疲劳开裂的最主要原因,由于挤压成形过程中凹模内的应力变化十分复杂,对于挤压模具失效机理和原因缺乏较深入细致的研究。本文在分析了国内外材料成形有限元模拟的发展动态和FEM法在模具分析中的应用研究的基础上,采用有限元软件DEFROM^TM-3D对冷温下的AISI1010钢材毛坯进行挤压成形模拟,在成形条件相同的条件下,分别分析挤压过程中整体式凹模和有预应力的组合式凹模的应力应变分布和变化情况,结果表明: （1） 采用弹塑性有限元模型分析挤压过程模具的应力应变变化情况,模拟结果可靠,说明FEM法分析模具的力学行为是可行、有效的。从模拟结果来看,切向应力和径向应力峰值均出现在凹模内壁拐角处附近,应力集中较严重,容易导致模具的疲劳开裂。 （2） 传统的冷挤压组合模具优化设计是基于Lame公式,而Lame公式引入了许多假设并简化了作用条件,难以准确描述模具的真实应力应变情况,因而很难达到真正优化模具设计的目的。利用有限元模拟可以较全面、准确的掌握模具的力学信息。如:模具的应力、应变、应力集中、切向应力（变）、径向应力（变）、等效应力应变等的预测分析,为模具的优化设计和疲劳寿命估算研究提供了有效的理论依据,节省大量的试验费用。 （3） 通过对冷挤压整体式凹模和有预应力的组合式凹模两个方案的模拟结果进行比较,得出有预应力的组合凹模的应力应变分布情况较整体式的更为理想,能较大幅度地减小凹模内的切向拉应力,降低了模具材料受拉应力时的危险性,等效应力峰值也有所下降,从而可以提高模具的强度。 通过剖析挤压过程中凹模的应力应变分布规律,本文采用局部应力—应变更多还原

【Abstract】 Die stress is one of the main factors causing damage of cold-extrusion dies. The mechanics of fatigue has not been studied deeply due to the complex processes in die stress alternation. Base on the detail reviews of the development of materials forming and dies stresses analysis used finite element method （FEM）, in this work, the cold forming process of AISI 1010 billet is simulated by using the commercial finite element analysis package, DEFROM^TM-3D. For a comparison with the distribution of stress/strain in die, two FEM modeling approaches are simulated, which are integral die and composed die with pre-stress. The main results can be list as followed:（1） From consideration of the die as an elasto-plastic body, the FEM results are credible. It is showed that the finite element method used in die stresses analysis is feasible and effective. According to the results, both the peak of circumferential stress and radial stress are all appeared in the corners area of the cavity die. Serious stress concentration and continuous cyclic high stress contribute to cracks initiation and growth and then lead to die failure.（2） Because the Lame equation can’t describe die stress accurately, it is impossible to get the optimization of the cold extrusion composed die design as base on this formula. By FEM, it is easy to obtain all the accurate mechanical information, such as die stress, strain, stress concentration, circumferential stress, radial stress and effective stress etc. Obviously, the FEM analysis is paramount and effective for the prediction of fatigue life and reduction of high stress within the tools. And it can save a lot of cost in experimentation.（3） According to the results of numerical simulation, stress distribution within theshrink-fitted die is more perfect than the integral one. Circumferential tensile stress is decreased greatly and the effective stress is lower. Then, strength of die will be improved extremely.In this thesis, a fatigue failure model for die life estimation was set up by using local stress-strain approach. Pre-estimate the fatigue life of die will find a new way for cold extrusion die design optimization. According to this estimation equation, life of integral die is not more than 3000 cycles when the composed die with pre-stress is about 10000 cycles. Consideration of dimensional effect and stress gradient effect, index number of fatigue strength was amended. So the model could be appropriated for the estimation of low-cycle fatigue and high-cycle fatigue.Die stresses analysis using FEM and fatigue life model set up can help to determine die quality and can give a good reference for dies development and manufacture.更多还原