板料点阵热源加热充液温拉深及其基础理论

The application of aluminium and magnesium alloy sheets is taken increasingly into consideration. The formability of lightweight materials is one of the major barriers for their wide implementations. A new method, named warm hydroforming of lightweight sheet materials heated by matrix dot power was proposed after a validation that formability improvement can be achieved during sheet forming heating with matrix dot power compared with the normar power. Differential surface heating can be realized during sheet warm forming using the dot matrix heating technology, and the optimized temperature distributions can be obtained by controlling the paremeters of dot matrix power and its load path. The waved distributed temperature arises during this process among the plane and temperature gradient lies in the thickness direction. This research aims to detailed explain the basic theories about sheet warm hydroforming heating with dot matrix power, including analyzing the effect of dot matrix power on the deformation and the limited drawing ratio. Key technologies for warm hydroforming with dot matrix power heating will be explored in order to improve the formability of lightweight materials and the dimensional accuracy of the formed parts.

铝、镁等轻质合金板材应用日渐广泛，但其成形性能差是制约其获得更广泛应用的瓶颈之一。试验发现板料温成形中，采用离散热源相对于均匀热源可进一步提高板料成形性能的基础上，提出板料点阵热源加热充液温拉深新技术。采用点阵热源实现板料温成形过程中板料离散加热，通过控制点阵热源加载参数与加载历程形成一个和板料成形过程更为协调的动态温度场。点阵热源加热充液温拉深中板料平面内的温度呈层峦状分布，板料厚向存在温度梯度。项目旨在对点阵热源加热板料充液温拉深基础理论进行深入研究，阐明在点阵热源形成的非均匀温度场下，板料变形中的应力分布、能量起伏、单元滞剪和应变分布与成形性能之间的关系，获得铝、镁轻质合金板料在点阵热源加热充液温拉深中的变形规律，达到提高铝、镁合金板材成形性能的目的。通过研究适宜工业化生产的点阵热源板料充液温拉深中点阵热源实现方法，热源分布等关键问题，提高铝、镁合金成形性能和零件成形精度及质量。

为了开展该课题研究，设计开发了一套板料温充液拉深的试验装置，制定了点阵热源充液温拉深研究的详细实验方案。首先，测定了SUS304、铝合金7075-T6和5083-O等材料在不同温度和不同应变速率下的基本性能，掌握了其高温的基本性能，并对其得到的数据进行分析，找到了相应合金的合适温成形温度窗口；采用通用有限元软件MSC.marc建立了温成形模拟的有限元模型，通过试验获得了合适的边界条件；其次，对7075-T6和5083-O等材料进行了温成形、梯温拉深、梯温充液拉深等一系列的成形性能试验；采用1mm厚的不锈钢板SUS304，采用试验和模拟相结合，对点阵热源成形进行了研究。研究表明： 板料温热成形中，板料和模具传热接触面一定程度的不连续即离散，能提高板料成形性能；点阵热源加热板料成形技术是可行的；与均匀热流加热相比，在板料拉深过程中，采用一定规律的点阵热源对毛坯凸缘部位进行加热，能够进一步提高板料的极限拉深比。采用1.0mm厚的铝合金5083-O和7075-T6进行了等温成形、梯温成形和充液温拉深研究，研究表明：5083和7075铝合金适合成形温度都在150~200℃之间，能够方便进行充液温拉深，并且可以获得可以比较好的成形性能，能够满足工业成形的需要，并且其温成形制件性能和成形板料相比下降在可承受范围内；梯温成形时，凸、凹模间的温度梯度有上限和下限值，即凸模的温度不能低于一定值，当低于一定温度值时(85℃)，凸模圆角处会发生脆性断裂，此时并不能得到零件极限拉深比最大的零件。