【作者】 李永志；

【导师】 余世浩； 毛华杰；

【作者基本信息】 武汉理工大学 ， 材料加工工程， 2004， 硕士

【摘要】 粉末锻造是将传统的粉末冶金工艺和精密模锻相结合发展起来的一种新型高性能精密塑性成形技术。论文运用理论研究、物理模型实验、有限元数值模拟等相结合的方法，系统地研究了粉末锻造(冷锻)成形规律、致密化机制。 在粉末多孔材料塑性成形理论研究方面，论文分析了各种粉末烧结材料的屈服准则，重点研究和比较了基于粉末冷锻的多孔体屈服准则，并运用其推导了粉末锻造成形的变形力和密度计算表达式，进行了定量分析和讨论。 基于粉末锻造成形致密理论的研究，论文采用物理实验方法，通过对还原铁粉预成形坯的镦粗、复压、闭式模锻等实验研究，确定了粉末冷锻镦粗成形断裂极限准则，绘制了成形极限应变曲线。分析了不同初始相对密度、不同高径比、不同摩擦因子等对粉末锻造镦粗断裂极限应变的影响，确定了锻造镦粗成形极限工艺参数，据此可以进行粉末锻造预成形坯和模具尺寸的优化设计。根据物理实验结果的微观金相分析，进一步研究了粉末锻造塑性成形的密度分布规律。 论文导出了粉末多孔体刚塑性有限元屈服准则及其本构方程，建立了可压缩系数和相对密度的关系式。运用MARC有限元软件，对粉末锻造镦粗、闭式模锻的成形过程进行了数值模拟，分析了不同初始相对密度、高径比、摩擦因子等对粉末锻造成形规律和致密机制的影响，并将其结果与实验结果进行了比较。 论文所得到的研究结论对于拓展和深化粉末冶金材料精密塑性成形理论，促进粉末锻造精密塑性成形技术的应用和计算机模拟优化技术的发展具有重要意义。更多还原

【Abstract】 Powder forging (P/F) is a new-style and high-performance plastic forming technology which combines conventional powder metallurgy (P/M) with precision forging techniques. The paper has systemically studied the deformation law and the densification mechanism during powder forging process (especially cold forging) based on the combined methods of theoretical study, experimental testing and numerical simulation.In theoretical study field of plastic forming for porous metal materials, the yield cfiterions for compressible P/M materials are systemically studied and those for compressible P/M materials based on cold-forging are analyzed and compared especially. Then the calculation formulae of deforming force, the density of workpiece and sizes for upsetting, repressing, and closed die forging are deduced. They are analyzed and discussed quantificationally at the same time.Based on the study of the deformation law and densification mechanism of powder forging, the experimental research method is adopted in this paper. According to experimental results of upsetting and closed die forging of deoxidize Fe porous materials, the local strain limit criterion for the cracking on surface has been achieved. The effect of different initial relative density( 0), the relative height(H/D) and the factional factor(m) on cracking strain limit of upsetting deformation is farther discussed. Meanwhile, based on the experimental results, the limit process parameters have been confirmed for the cracking limitation. After that, the sizes design of mould and that of sintered porous materials green can be optimized. And according to microcosmic analysis of experimental workpieces, the law of density distribution of powder forging is researched, too.At the same time, the yield criterion and constitutive equations for the compressible rigid plastic finite element method have been deduced and the formula representing relationship between g, the coefficient of materialvolume compressibility method of rigid plastic finite method, and , the relative density of powder materials, has been established and researched. The MARC finite element method is used to simulate the deformation process of a cylindrical upsetting and closed die forging of porous metal materials, and influence on its deformation law and densification mechanism brought by different initial relative density, the relative height and the frictional factor is analyzed then. The numerical results are compared with those of experiments at last.Therefore, the results obtained in this paper may enrich the precision plastic forming theory, promote the applications of P/F technology and improve the development of numerical simulation for powder metallurgy. This is of significant.更多还原