Stretch Forming of Aluminum Extruded Tubes for Automotive Applications

空间框架是全铝轻型汽车的首选设计理念。它是由挤压管拉伸形成所需的形状和节点连接。自动化组装对成形管的尺寸公差要求非常严格。为了实现这些，中空挤压件被预拉伸并在模具上弯曲成所需的形状。这个过程的一个不希望的副产品是它们的横截面变形。在心轴上弯曲期间施加的张力使这种横截面变形变小。为了减少这种不必要的变形，零件内部加压。目前，每个零件的设计参数（即模具形状、预拉伸载荷、内部压力水平）都是凭经验选择的，这既昂贵又缓慢。 这个为期两年的项目将使用实验和分析相结合的方法来研究拉伸成形过程，了解控制它的因素，并开发优化它的方法。该项目是工业（美铝）和大学（UT-奥斯汀）之间的合资企业。实验将在最近开发的定制弯曲拉伸压力成形设备中进行。三个装载轴具有闭环控制，允许通过计算机操作设备。自定义非线性分析已经开发，这是能够预测的横截面变化的矩形管弯曲的刚性表面，而被拉伸和内部加压。这项工作将涉及使用测试设施沿着的分析，以了解和优化这种制造过程中更一般的形状。

DMI-9734947 Kyriakides The space frame is the preferred design concept for all-aluminum light-weight cars. It is made of extruded tubes that are stretch formed to the required shape and joined by nodes. Automated assembly requires unusually tight dimensional tolerances on the formed tubes. To achieve these, the hollow extrusions are prestretched and bent to the required shapes over dies. An unwanted byproduct of this process is distortion of their cross section. Tension applied during bending over a mandrel aggravates such cross sectional distortions. To reduce this unwanted deformation, the parts are internally pressurized. At the present, the design parameters for each part (i.e. die shape, prestretch load, level of internal pressure) are selected empirically which is both costly and slow. This two-year project will use a combination of experiment and analysis to study the stretch forming process, understand the factors that govern it, and develop methods for optimizing it. The project is a joint venture between Industry (Alcoa) and University (UT-Austin). The experiments will be conducted in a custom bend-stretch-pressure forming facility recently developed. The three axes of loading have closed-loop control that allows operation of the facility via a computer. Custom nonlinear analyses have been developed which are capable of predicting the cross sectional changes of rectangular tubes bent over a rigid surface while being stretched and internally pressurized. This work will involve the use of the test facility along with the analyses to understand and optimize this manufacturing process on more general shapes.