Hydroforming of Aluminum Tubes for Automotive Applications

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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.