航空发动机机匣类复杂薄壁件等温精锻成形的回弹预测和控制机理

Due to high material utilization efficiency, the isothermal precision forging is one of the processes that are well suited to making the billets of aero-engine casings. The aero-engine casings are a kind of thin wall part with complex shape. Thus, springback will greatly affect the shape accuracy of aero-engine casings during isothermal precision forging. So, the prediction and control of springback are very important for the designs of mould and isothermal precision forging process. However, due to the unknown of its mechanisms, it is a great challenge for the prediction and control of the springback of aero-engine casings during the isothermal precision forging. In order to reveal the mechanisms for the springback of aero-engine casings, this project will do the following works. Firstly, based on the tension tests, compression tests and cyclic loading tests, the hot deformation behaviors of materials of forging and mould will be investigated, and the new constitutive equations will be established by considering the effects of microstructure and deformation conditions. Secondly, based on the established new constitutive equations, the finite element models for analysing the springback of aero-engine casings will be established; the isothermal precision forging experiments of aero-engine turbine casing will be done to validate the established finite element models. Thirdly, the effects of the temperature of forging and velocity of mould on stress field, temperature field and microstructure of forgings before unloading, and the effects of stress field, temperature field and microstructure of forgings before unloading as well as the variations of temperature field during unload on the springback and shape of aero-engine casings will be investigated by finite element simulation. The research findings of this project can provide the theoretic guidances for making the isothermal precision forging process of aero-engine casings and other thin wall parts with complex shape.

在制定航空发动机机匣类复杂薄壁件的等温精锻工艺时，预测和控制回弹是确保锻件形状精度的重要手段。然而，在复杂薄壁件的等温精锻过程中，影响锻件回弹的因素众多且机理复杂，精确预测和控制回弹十分困难，成为开发等温精锻工艺亟待解决的技术瓶颈。本项目拟通过实验和理论分析，研究锻件和模具材料的高温变形行为，建立考虑微结构和变形条件影响的材料本构模型；采用建立的高精度材料模型，建立分析复杂薄壁件等温精锻成形的有限元模型，并采用航空发动机涡轮机匣缩比件的等温精锻实验，验证有限元模型的正确性；通过有限元模拟，获得温度和锻压速度对卸载前锻件应力场、温度场和微结构的影响规律；揭示卸载前应力场和温度场、以及卸载过程温度场演变影响锻件回弹的规律及机理，为在机匣类复杂薄壁件等温精锻过程中，通过控制全过程锻件温度和压机加/卸载速度实现锻件回弹最小化提供理论基础。本项目研究成果可为制定复杂薄壁件的等温精锻工艺提供理论指导。

在制定航空发动机机匣类复杂薄壁件的等温精锻工艺时，预测和控制回弹是确保锻件形状精度的重要手段。然而，在复杂薄壁件的等温精锻过程中，影响锻件回弹的因素众多且机理复杂，精确预测和控制回弹十分困难，成为开发等温精锻工艺亟待解决的技术瓶颈。为了解决上述难题，本项目研究了典型航空发动机机匣材料高温变形过程中的流变行为，建立了精确的高温流变应力本构方程；揭示了材料高温变形过程中的微观组织演变规律和机制，并发现采用先快后慢阶梯应变速率可促进材料发生动态再结晶，且建立了可描述材料在变工况条件下动态再结晶动力学行为的数学模型；研究了变形参数对高温卸载行为的影响，并建立了一个新的统一弹粘塑性本构模型用于精确描述材料高温卸载行为。提出了新的有限元仿真策略用于计算锻件卸载过程中的回弹行为，即：首先将锻件材料模型设置成粘塑性模型，直到模锻结束之前的一小段行程，再将材料改成弹粘塑性模型计算弹性变形，极大地提升了仿真效率。利用有限元仿真，深入揭示了卸载前应力场演变影响锻件回弹的规律及机理，提出了减小机匣类复杂薄壁锻件回弹的方法。研究成果在国际期刊上发表SCI收录论文17篇、国际会议论文1篇，申请/获批发明专利4项，全部论文已被引用87次。