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.
