内环筋直筒件旋转挤压成形折叠缺陷机制研究

发布时间：2019-03-18 10:07

【摘要】：镁合金内筋壳体作为典型轻质轻体结构件广泛应用于航天、航空领域,传统加工方法存在废品率高、性能差、成本较大等缺点,无法满足构件轻量化与高性能的要求。基于内筋壳体结构特点和镁合金变形特性,提出旋转挤压成形方法以实现该类构件整体塑性成形。旋转挤压成形具有降低载荷、改善成形性、细化晶粒、弱化各向异性和保证筋部流线完整等优点,但由于加载方式的特殊性导致容易产生折叠缺陷。通过限元数值模拟与实验相结合,研究了模具结构参数及成形工艺参数对缺陷形成的影响,揭示了镁合金内环筋直筒件旋转挤压成形过程中折叠缺陷形成机理,为新工艺应用奠定基础。内环筋直筒件旋转挤压分为旋转轴向挤压和旋转径向挤压两种模式,对成形过程中各区域应力、应变分布与金属流动情况进行了分析。旋转挤压过程中,变形区金属处于强压剪应力状态能够充分发挥镁合金塑性;渐开式组合模具加载下产生微区累积剧塑性变形,有利于性能的提升;建立旋转挤压成形金属速度场,为折叠缺陷研究提供了理论基础。为深入了解内环筋直筒件旋转挤压成形以进一步分析折叠缺陷的产生,利用数值模拟对某一内环筋直筒件旋转挤压成形过程进行研究,该零件成形轴向载荷极值为57.1kN、径向载荷极值为57.6kN以及成形扭矩极值为2867.1kN·mm;获得等效应力、应变分布特点,其中壁部与内环筋部分金属等效应变量大,有利于细化晶粒、提高构件整体性能。对折叠缺陷进行研究,折叠缺陷分布于内筋直筒件薄壁内侧。旋转轴向挤压过程中折叠缺陷产生是由于渐开式组合模间隙处凸起金属径向流动变形抗力过大,使凸起金属内侧流动速度低于边缘处金属流动速度,最终使凸起金属与薄壁内侧金属汇流形成折叠缺陷。旋转径向挤压过程中,由于瞬时挤压量过大导致金属向坯料空心处流动在凸模工作带侧面形成金属堆积,在凸模作用下与未成形区金属汇流产生折叠缺陷。确定模具结构与工艺参数对折叠缺陷产生的影响,并绘制折叠极限图,为实际生产与实验避免折叠缺陷提供模拟依据。根据内环筋直筒件旋转挤压成形过程中金属流动特点以及折叠缺陷产生原因,设计实验进行验证。通过利用Gleeble-3500热压缩模拟实验机进行热模拟实验,结果表明内环筋直筒件旋转挤压成形中产生折叠缺陷,验证了数值模拟结果可靠性。
[Abstract]:Magnesium alloy inner reinforcement shell is widely used in aerospace and aviation field as a typical lightweight structural component. The traditional machining method has the disadvantages of high waste rate, poor performance and high cost, and can not meet the requirements of lightweight and high performance of components. Based on the structural characteristics of the inner reinforcement shell and the deformation characteristics of magnesium alloy, the rotary extrusion forming method is proposed to realize the integral plastic forming of this kind of components. Rotary extrusion has the advantages of reducing load, improving formability, refining grain, weakening anisotropy and ensuring the integrity of rib streamline, but it is easy to produce folding defects due to the particularity of loading mode. Through the combination of finite element numerical simulation and experiment, the influence of die structure parameters and forming process parameters on the formation of defects was studied, and the forming mechanism of folding defects in the forming process of magnesium alloy inner ring stiffened straight tube parts was revealed. It lays a foundation for the application of the new process. The rotary extrusion of inner ring stiffened straight tube is divided into two modes: rotating axial extrusion and rotating radial extrusion. The stress, strain distribution and metal flow in each region during the forming process are analyzed. In the process of rotating extrusion, the metal in the deformation zone in the state of strong compressive shear stress can give full play to the plasticity of magnesium alloy, and the accumulative severe plastic deformation in the micro-region under the loading of the progressive composite die is beneficial to the improvement of the performance. The velocity field of rotating extrusion forming metal is established, which provides a theoretical basis for the study of folding defects. In order to understand the forming of inner ring stiffened straight tube by rotary extrusion to further analyze the forming of folding defects, the forming process of a inner ring stiffened straight cylinder was studied by numerical simulation. The extreme value of axial load of the part is 57.1kN, the maximum value of axial load of the part is 57.1kN, The extreme value of radial load is 57.6kN and the extreme value of forming torque is 2867.1kN mm;. The equivalent stress and strain distribution characteristics are obtained, in which the metal equivalent variables of the wall and inner ring bars are large, which is beneficial to refine the grain and improve the overall performance of the component. The folding defects were studied, and the folding defects were distributed on the inside wall of the inner stiffened straight tube. In the process of rotating axial extrusion, the folding defect is due to the excessive radial flow deformation resistance of convex metal at the gap of the involute composite die, which makes the flow velocity of the inner side of the raised metal lower than the metal flow velocity at the edge of the convex metal. Finally, a folding defect is formed between the bulge metal and the thin-walled inner metal confluence. In the process of rotating radial extrusion, due to the excessive amount of instantaneous extrusion, metal accumulation is formed on the side of the punch working belt, and folding defects are formed with the metal confluence in the unformed region under the action of the punch due to the excessive amount of instantaneous extrusion. The influence of die structure and process parameters on folding defects is determined, and the folding limit diagram is drawn, which provides a simulation basis for avoiding folding defects in practical production and experiment. According to the characteristics of metal flow and the reasons of folding defects during the rotary extrusion process of inner ring stiffened straight cylinder, the design experiment is verified. The thermal simulation experiment is carried out by using Gleeble-3500 hot compression simulator. The results show that folding defects occur in the rotary extrusion forming of inner ring stiffened straight tube, and the reliability of numerical simulation results is verified.
【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】：TG379

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