基于选区加热预制有益皱纹管坯的内高压成形方法及变形行为

Both of fracture and wrinkling defects are easily happened on thin-walled aluminum alloy tubes and magnesium alloy tubes when they are used to manufacture the hollow components with large cross-section difference in conventional hydroforming process due to their low plasticity at room temperature. Although tubular parts with large expansion can be obtained using the preforming method with useful wrinkles, it is hard to control the shape and size of wrinkles because of the numerous influence factors and their interaction effect. In order to solve these problems, a new method for preforming of useful wrinkles based on selective heating is proposed in this project. The fundamental is that the local heating is introduced to the wrinkling position of tube firstly, so the tube’s yield strength at this position will be decreased. Materials locate in the heating area firstly satisfy the yield and plastic instability conditions under the action of axial feeding, and then lead to the local axisymmetric wrinkles. Using this method, dependence of wrinkles on the die structure, as well as the interdependence between different wrinkles, could be avoided. Then, the preformed tube specimens with useful wrinkles are placed inside the hydroforming die for calibration under higher internal pressure. In this way, the tubular parts with large expansion and better thickness uniformity can be manufactured. In this project, through the in-depth and systematic investigation on the deformation behavior of tubes during the preforming process of useful wrinkles based on selective heating and subsequent hydroforming process, the wrinkling mechanism of tubes under non-uniform temperature field and its influence factors, the evolution rule of wrinkles shape and the thickness distribution of tubular parts will be revealed. Then the theory and method for the control of tube wrinkles will be obtained, and the challenge about fracture and non-uniform thickness distribution for low-ductility tubes could be resolved, so as to provide theoretical basis and technical support for their industrial application in key components for aerospace.

铝合金和镁合金薄壁管材室温塑性低，采用内高压成形技术制造大截面差空心管件时，出现破裂与起皱缺陷难于克服。利用有益皱纹作为预制坯可获得大膨胀率管件，但皱纹形状与尺寸难以精确控制。为了解决利用有益皱纹提高管材成形性能存在的难题，本项目提出了选区加热预制有益皱纹管坯的新方法。基本思路是在管材待起皱位置进行局部加热，使管材局部屈服强度降低，管材在轴向补料的作用下则会在加热位置首先发生屈服及塑性失稳，形成局部轴对称皱纹，避免了对模具结构的依赖性以及皱纹之间的相互影响；然后将有益皱纹管坯放入内高压成形模具进行整形，获得壁厚均匀性较好的大膨胀率管件。通过对选区加热预制有益皱纹管坯变形行为深入系统的研究，揭示非均匀温度场作用下管材起皱机制及影响因素，获得管材皱纹形状的控制理论与方法，揭示皱纹形状演变规律、管件壁厚分布规律，解决低塑性管材易破裂及壁厚均匀性差难题，为在航空航天关键构件上应用提供理论基础。

铝/镁合金薄壁构件是实现运载工具轻量化的关键结构，管材内高压成形是一种先进的轻量化薄壁构件整体制造技术。然而，铝/镁合金管坯室温塑性低，采用内高压成形技术制造空心薄壁管件时，极易产生破裂缺陷。本项目提出了一种利用选区加热预制铝/镁合金有益皱纹管坯从而提高内高压成形极限的新方法。研制出可实现管坯选区感应加热与内压和轴向压缩联合加载的实验装置，建立了热-力耦合有限元模型。研究了选区加热形成的非均匀温度场分布规律、非均匀温度场中铝/镁合金管材的失稳起皱行为、以及起皱管坯的自由胀形与内高压成形规律。分析了起皱管坯的壁厚分布规律、微观组织和显微硬度分布规律。研究结果表明：通过选区感应加热可在管坯局部快速形成非均匀温度场，最高温度点一般位于中心偏上10 mm位置，并向管坯两端逐渐递减；当加热区最高温度达到200℃及以上时，可在5052铝合金和AZ31B薄壁管材上获得轴对称皱纹；通过控制温度、支撑内压、轴向压缩量以及皱纹间距，可连续在管坯上预制出多个皱纹；利用起皱管坯成功制造出具有三处非连续凸起的变径管，最大膨胀率达43.4%（原始管坯极限膨胀率8.3%），成形极限提高4倍以上。本项目研究成果不仅可为构建非均质管壳失稳起皱理论提供数据，而且可为铝/镁合金薄壁构件在航空航天、汽车等关键结构中的应用提供理论基础与技术支撑。成果作为重要组成部分，获得2021年中国汽车工业技术发明一等奖。