大锻件控性锻造过程的计算机模拟技术

Computer Modeling of Property-controlled Forging Process for Heavy Forgings

提出能够模拟大锻件空洞型缺陷演化和微观组织演变等控性指标的数值模拟方法。基于典型体元模型建立空洞体积变化与宏观应力应变场关系的数学模型,以图从多尺度角度揭示宏观的塑性变形及其应力状态对随机分布的微小空洞的体积变化影响规律。将该模型与有限元法集成,当锻件内任意一点有空洞型缺陷(给定缺陷体积百分比)时,能够模拟得到成形过程中空洞型缺陷的体积变化,从而可被用来评估含缩孔缩松缺陷材料的压实状态。采用元胞自动机方法建立一种转子钢的微观组织演变模拟方法,根据'应变—位错密度—动态再结晶—流动应力'之间的宏微观相互影响规律,模拟出动态再结晶晶粒尺寸和完成分数。将这些模型与热力耦合有限元法相结合,构造大锻件控性锻造过程的数值模拟技术。根据大锻件增量成形的变形特点开发基于刚性区自由度凝聚技术的快速有限元法,从而为大锻件成形的工艺优化提供有效的计算工具。

A numerical simulation method is presented to evaluate the controlling issues of property for heavy forgings such as the evolvement of void defect and the evolution of microstructure. In order to reveal the multi-scale effect of macroscopic plastic deformation as well as the stress state on the volumetric evolvement of tiny voids stochastically distributed in the forgings,a model calculating the void volumetric change through macroscopic stress and strain field is investigated by using a representative volume element model. By integrating the model with finite element method,with the void fraction is assumed,the void volume evolvement at each element can be evaluated simultaneously with the simulation of forging process. So it can be used to assess the degree of void closure for the forging materials with shrinkage cavity and porosity. For the simulation of microstructure evolution,a cellular automata modeling is investigated and applied to a rotor steel. According to the micro-and macroscopic relationship among ＂strain,dislocation density,dynamic recrystallization and flow stress＂,the dynamic recrystallization process is simulated and the R-grain size and kinetics percentage are obtained. By combining these property-related models with thermo-mechanical finite element method,the numerical technique is established to simulate the forging process and predict the deformed shape and evolution of void defect and grain size. Besides that,according to the features of incremental forming typically used for heavy forgings,a fast finite element method is developed by using rigid degree of freedom condensation technique. This method is an effective tool for simulating and optimizing the forming process.