板材磁流变液软模成形新方法及其机理研究

Magnetorheological fluid medium forming using magnetorheological fluid as flexible-die is a new method presented in this project for sheet metal forming. This new technology has unique properties. By reversible transition of rheological property and physical state（liquid?semi-solid?solid）of magnetorheological fluid under the effect of external magnetic field, the property of magnetorheological fluid is controlled by magnetic induction device and is matched with forming pressure under certain mode loading during sheet forming, which can reasonably utilize respective advantages of hydroforming, viscous pressure forming and solid medium flexible-die forming. This can make the sheet metal to be at its best deformation state, and so that formability of the sheet metal is increased, which develop a new way for precision forming of difficult-to-form sheet metals and complex shape parts with high efficiency and low cost. In this project, carrying out extrusion of magnetorheological fluid medium, magnetorheological fluid medium bulging and magnetorheological fluid medium drawing with automatic measurement for geometrical shape and strain distributions of specimens and magnetorheological fluid pressure and finite element analysis, following main contents are studied systematically: the relationships among the magnetorheological fluid flow stress, the magnetic field intensity and the loading velocity, the matching relationship between the rheological property of magnetorheological fluids and the forming pressure under certain mode loading, the effect of rheological property of magnetorheological fluids on formability of sheet metals, evaluation and selection for magnetorheological fluids suitable for sheet forming, and establishing the mathematical model and finite element analysis method to describe the interaction between magnetorheological fluids and sheet metals. It is aim of this project to explore the influence of rheological property of magnetorheological fluids on formability of sheet metals, and to resolve key foundation problems for application of magnetorheological fluid medium forming.

本项目提出的板材磁流变液软模成形新方法采用磁流变液作为软模材料，利用磁流变液在外部磁场作用下流变性质发生可逆变化的特性（液态?半固态?固态），成形过程通过磁场产生装置控制磁流变液流变性质，可以合理地利用液压、粘性介质和固态软模成形的优点，并与压力加载方式相匹配，使板材处于较好的变形状态而提高其成形性，为难变形板材和复杂形状零部件高效、低成本精密成形提供新方法。本项目采用挤压、胀形和拉深等实验方法，对试件几何形状与应变、磁流变液压力进行测量，并与数值模拟分析相结合，研究磁流变液流动应力与加载速度、磁场强度之间的关系，磁流变液流变性与压力加载方式之间匹配关系对板材成形性的影响。评价和选择适合板材成形用磁流变液类型和特性，建立磁流变液与板材之间相互作用的数学模型和数值分析方法。揭示磁流变液软模对板材成形性的影响机理，解决板材磁流变液软模成形新方法关键的应用基础性问题。

本项目创新性地提出并实现了一种新的板材成形方法—将智能材料磁流变液作为一种新的成形软模，目的在于探索应用智能材料软模提高难变形材料成形性的可能性及其机理。主要研究了磁流变液流动应力与加载速度和磁场强度之间的关系、磁流变液流变性对板材成形性的影响规律及其机理、磁流变液流变性与压力加载方式之间匹配关系对板材变形的影响规律，评价和选择适合板材成形软模用磁流变液类型和特性，建立磁流变液与板材之间相互作用的数值分析方法。获得如下具有科学意义和应用前景的重要成果：(1) 可实现成形过程中通过软模性能的调控，提高板材的成形极限，如对铝合金板材成形极限可提高8.43%，这对在航空、航天、汽车等领域有着广泛应用的铝合金等轻质难变形材料复杂形状零件的整体成形，具有重要的实用价值；(2) 通过将智能材料作为成形软模，实现了成形过程中对板材应力状态的实时调控，这是现有成形工艺无法达到的，开辟了板材成形的新方向；(3) 建立了三向应力状态下磁流变液流动应力的本构方程，对拓展这种智能材料在其它领域的应用具有重要的意义；(4) 揭示了磁流变软模成形中板材成形性提高的机理。