【作者】 李峰；

【导师】 苑世剑；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2007， 博士

【摘要】 从塑性加工力学角度,将复杂构件模锻成形过程的不同阶段和区域抽象分解为圆柱压缩、圆环压缩和类挤压三个基本变形模式,使复杂模锻问题的分析模块化。通过深入分析不同变形模式及互相耦合流动行为,揭示了复杂构件模锻成形过程中金属的变形流动规律,为复杂锻件精确塑性成形的变形流动控制提供理论依据。对模锻成形过程的变形特征进行了深入分析,得到了模锻过程变形模式提出的理论依据。提出了罗德系数等应力场特征量对模锻过程进行变形类型分区的研究方法,给出了应力场与应变增量数值间的定量变化关系,并对金属的宏观变形流动行为进行了可视化表征。通过有限元模拟,分别对圆柱和圆环压缩变形模式的成形过程进行分析,得到了不同条件下压缩过程中金属塑性变形及流动的规律,并研究了不同变形过程中金属流动行为的力学机理,结果表明:圆环压缩变形时,随着高径比的增加,难变形区的范围逐渐扩大并显著左移;而随着摩擦因子的增大,塑性区内应变类型由均一的压缩类变为三种共存的形式。进行了不同类挤压变形过程的数值模拟和实验研究,研究了不同成形过程中金属的变形流动规律,并对其成形过程进行了变形分区及应力应变分析,结果表明:随着型腔模角和挤压比的增大,塑性区的范围明显缩小,该区内应变类型由均一的伸长类变为三种共存;带内锥凸模可消除平模成形过程中模底部金属分流流动的情形;与无润滑情况相比,采用积极摩擦时轴心处点的相对位移量数值降低了69.7%,由此可知,积极摩擦可显著地降低坯料横断面金属流速的不均性,有利于制品质量的提高。分别抽象构造出了不同变形模式耦合的轴对称和三维复杂构件模型。针对模锻成形过程的不同阶段和区域,利用前面研究所得基本变形模式的成形规律来对其进行深入分析,进而给出了耦合成形过程中金属变形及流动的规律,及不同模腔内金属流动分界面的形状和塑性区的分布特征,并揭示了成形过程中金属变形流动行为的力学机理。针对模锻成形过程中金属塑性应变和流线分布难于测定的问题,提出了一种用套环螺纹进行测量的方法。该方法不用替代材料即可实现对模锻成形过程中三维塑性变形的测量,并可作为其定量分析的依据。利用此方法对耦合成形过程中典型截面上四条流线及应变进行了测量分析,并定量给出了复杂锻件成形过程中变形及应变分布规律,该方法是测试模锻成形过程中金属塑性变形流动较为有效的实验手段。更多还原

【Abstract】 From the view of plastic mechanics, the deformation of closed-die forging can be divided into three basic deformation modes: cylindrical billet compression, ring compression and pseudo-extrusion. It makes the analysis modularizetion. Analyzing different deformation mode and coupled flowing behaviors, the rule of metal flowing was disclosed for complex components, which supplied with theoretical references for the investigation on the plastic forming of complicated forgings.The deformation characteristics of closed-die forging were analyzed deeply, which were the theoretical basis of three deformation modes for closed-die forging. Based on the Lode parameter, a new research method is proposed to study the different deformation zones for closed-die forging. The quantitative relation between stress field and strain increment has been determined, and the metal macroscopic flowing behavior has been attributed to visualize.Based on the FEM, the deformation modes of the column and the ring compression were analyzed, and the rule of metal flowing was obtained under the different compression conditions. The mechanics mechanism of metal flowing was investigated during the different deformation process. The results show that the stagnant zones expand and shift towards the left with height-diameter ratio increasing, and the strain in the plastic area changes into three coexistent modes from the single compression mode.For the different types of extrusion deformation, the rule of metal flowing was investigated by simulation and experiment. Deformation zones were divided, and stress-strain was analyzed during the forming process. The results show that the plastic zones decreases significantly with modular angle and deformation increasing, and the strain in the plastic zones changes into three coexistent modes from the single elongation mode; the male die with inner cone may eliminate the metal split-flow in the flat bottom of the male die during the forming process; compared with the non-lubrication case, the relative displacement reduced 69.7% by use of the active friction, thus it can be concluded that the active friction may significantly reduce the non-uniform of metal flowing, and be helpful to improve the product quality.An axisymmetric model and a 3D complex model were built, in which different deformation mode were coupled. With the above forming rule of three basic deformation mode, the closed-die forging process was analyzed during the different stage and at the different zones, and the rule of metal flowing was obtained in the coupled forming process. The distribution character of plastic zones and the interface configuration of metal flowing in the different die cavity were also given. The mechanics mechanism of metal flowing was disclosed during the forming process.A new measuring method, in which a few rings of screw threads was used, was put forward in order to solve the difficulties of measuring the strain and the streamlines distribution during the closed-die forging process. In the method, it does not need substitute material to measure the magnitude of three-dimensional plastic deformation during the closed-die forging process, which can be the references to quantitative analysis. Using the method, the strain and the four streamlines of typical sections were measured and analysed during the deformation of a coupled model. The distribution rule of stress-strain was given quantitatively. It is an effective method to measure and analyse the metal flowing of closed-die forging.更多还原