Hydroforming of Aluminum Tubes for Automotive Applications

液压成形是一种相对较新的成形金属管状部件的工艺。一个简单的管可以被液压成形成一个相当复杂的形状，适合用作一个结构部件的框架。在两个半模具之间放置一根管子，然后在内部加压。它膨胀，与模具接触，并被迫符合模具的形状。管的简单径向膨胀会导致许多缺陷，主要问题是膨胀壁变薄。这可能导致管道破裂。为了减少薄化，可以通过使用执行器从两端向模具内轴向喂入未变形的材料来增加破裂应变。然而，轴向压缩的发展程度受屈曲、起皱和摩擦的限制。因此，对于每个零件，必须在轴向进料压力平面上建立一个没有这些失效模式的工作包线。虽然管状铝是液压成形的理想材料，但它的延展性不如钢，并且具有更复杂的本构行为，这使得液压成形的工作包络更加紧密。由于需要更好地理解加工控制，再加上模具和工艺设计的经验方式，因此不允许在铝部件上广泛使用液压成形。这个为期三年的项目的目标是为建立工艺参数的工作范围建立科学基础。该问题将从三个方面着手解决，即液压成形实验，开发合适的铝合金挤压管的本构模型，以及开发用于分析液压成形和确定其极限的几个级别的数值模型。该项目的一个重要组成部分是定制的液压成形设备，该设备将被制造并用于参数化研究过程。美国铝业公司和通用汽车公司将作为该项目的工业合作伙伴，并将定期与研究生和本科生进行互动。

Hydroforming is a relatively new process for shaping tubular components out of metals. A simple tube can be hydroformed into a fairly complex shape suitable for use as a frame for a structural component. A tube is placed between two half dies and then pressurized internally. It expands, comes into contact with the dies and is forced to conform to their shape. The simple radial expansion of the tube can lead to a number of defects, with a major concern being thinning of the expanded wall. This can lead to tube burst. In order to reduce thinning, the burst strain can be increased by axially feeding undeformed material into the dies from the two ends using actuators. However, the extent of the developed axial compression in limited by buckling and wrinkling and by friction. Thus, for every part, a working envelope in the axial feed-pressure plane must be established which is free of these modes of failure. While aluminum in tube form is ideal for hydroforming, it is less ductile than steel and has more complex constitutive behavior, which make the hydroforming working envelope tighter. This need for a better understanding of processing control coupled with the empirical manner in which the dies and the process have been designed, have not allowed wide use of hydroforming for aluminum components. The objective of this three-year project is to develop a scientific basis for establishing the working envelopes of the process parameters. The problem will be tackled in a three prong manner consisting of hydroforming experiments, development of constitutive models for appropriate aluminum alloy extruded tubes, and development of several levels of numerical models for analyzing hydroforming and establishing its limits. An important component of the project is a custom hydroforming facility, which will be fabricated and used to study the process parametrically. Alcoa and GM will be act as industrial partners to the project and will interact with graduate and undergraduate students on a regular basis.