板材超声振动颗粒介质成形工艺及理论研究

With an attempt to solve the difficulty for stamping complex shape parts with difficult-to-deform materials, the Ultrasonic-Vibration Granules Medium Forming (UGMF) technology of sheet metal was proposed, wherein, combined with the ultrasonic vibration, the solid granules were selected as pressure-transfer medium to conduct the flexible-die forming on sheet metal. Focusing on the step surface shell and biconical shell parts forming of magnesium alloy, the research on the sheet metal forming theory and the surface effect generation mechanism of UGMF technology was put emphasison. The reaearch issues included: 1) study the effect laws of the vabriation amplitude and frequency on the pressure-transfer characteristics so as to establish the mechanical model of the granules medium with vibration excitation under high-pressure. 2) analysis the forming mechanism, distribution and characteristic of friction under ultrasonic vibration, reveal the varying law of friction force and build up the corresponding mathematical method. 3) conduct simulation analysis and experiment research on the ultrasonic-vibration granules medium forming of the magnesium alloy objective parts in order to explore the deformation law, the defect formation mechanism, the friction mechanism as well as the technology control strategies of improvement on the sheet formability，and establish the plastic forming theory and process specifications of UGMF technology. Therefore, the development of this project provides new approaches and means for the stamping of difficult-to-deform materials, which exhibits certain significant theoretical value and extensive practical prospect.

针对目前难成形材料在复杂形状零件冲压成形中存在的困难，提出板材超声振动颗粒介质成形工艺，该工艺将固体颗粒作为传力介质，并融合超声振动对板材实施软模成形。以镁合金阶梯曲面壳体和双锥壳体零件成形为目标，着重研究基于此工艺的板材成形理论及其成形过程中的表面效应形成机理等基本问题。研究内容包括：1)研究振动频率和振幅对颗粒物质传力性能的影响规律，以期建立振动激励下高压状态颗粒物质力学模型。2)分析超声振动下摩擦力的成形机理、分布和特点，揭示摩擦力在表面效应作用下的变化规律，建立摩擦力的数学模型。3)针对镁合金目标工件超声振动颗粒介质成形进行仿真分析和试验研究，探索板材变形规律、缺陷形成机理、摩擦机理以及提高板材成形性能的工艺控制策略，建立板材超声振动颗粒介质塑性成形理论及其相应工艺规范。本项目的开展为难成形材料冲压加工提供了新的方法和手段，具有一定理论价值和广阔工程应用前景。

轻量化是目前汽车、航空航天、军工等领域设计和开发的重要研究方向，镁合金、铝合金、（超）高强度钢等轻量化材料的应用是实现产品轻量化的有效途径，但由于轻量化金属板材在常温下难成形或变形塑性低的特点，对轻量化金属板材的研究和开发提出新的挑战。为了提高轻量化板材成形极限从而达到成形复杂零件的目的，本项目提出了板材超声振动颗粒介质成形工艺，该工艺将固体颗粒作为传力介质，并融合超声振动对板材实施软模成形。本项目将镁合金板材作为研究对象，以创建板材振动颗粒介质塑性成形理论及其工艺规范为目标，基于非局部摩擦理论，建立了颗粒介质传力模型，得到超声振动下颗粒介质传力规律，并针对承受高压下颗粒介质剪切过程演化规律从力链细观角度进行了分析，获得了该条件下颗粒内摩擦系数随剪切速率、颗粒粒径、颗粒表面摩擦系数的幂率函数关系式；采用超声激励下金属板材剪切摩擦试验，结合接触力学理论和粗糙表面弹-塑性接触模型，建立了考虑金属板材表面形貌的超声振动激励下金属板材摩擦力表达式，揭示了超声激励下金属板材表面效应的致成机理；基于金属失稳理论，运用离散元-有限元分体耦合仿真的方法，分别建立颗粒散体和金属板材连续体的模型，并以力与位移边界交互迭代的方式，对成形过程进行分析，探索超声振动颗粒介质成形工艺条件下金属板材变形规律，并结合振动激励下颗粒介质传压特点及板材表面效应，得到板材拉深成形过程的力学解析模型；在理论及模拟仿真综合分析的基础上，针对镁合金目标零件的结构特点，自行设计并制造了镁合金超声振动颗粒介质成形系统，成功试制出合格零件，并比较了不同施振条件(包括无振动激励)下成形试样断口形貌及其微观组织，从微观角度阐明超声振动提高材料成形性能的原因，验证了理论及仿真模型的有效性。本项目的开展为轻合金板材冲压加工提供了新的方法和手段，具有一定理论价值和广阔工程应用前景。