Stelios Kyriakides, Research
Aluminum auto parts are commonly cold formed by stretch forming thin aluminum sections. The forming must be designed so that the part has accurate shape, is free of wrinkles and has minimal distortion of the cross section. These items are very sensitive to small changes in the forming loads. Currently, selection of these loads is an expensive trial and error process. The problem has been studied through a combination of experiment and analysis. Rectangular tubes have been formed under controlled conditions in a custom bend-stretch-pressure forming facility. Dedicated nonlinear models of the process have been developed.
Shown below is an image of the forming machine developed. The machine is unlike the commercial machines in that it operates in a vertical plane which simplified the design. It also incorporates the necessary transducers and servo controllers to operate each mode in a computer controlled feedback loop (tension, pressure and motion of die).
During this test the tube is first tensioned to the desired value. Internal pressure is then applied and both the tension and pressure are held constant while the die is moved upwards. When the entire tube has been formed, the motion of the die is stopped and the loads are removed. The animation incorporates formed shapes calculated from custom nonlinear analyses developed.
Results from the experiments and analyses which clarify how bending, tension and pressure interact and a simple methodology for selecting these to produce optimally shaped parts can be found in the publications listed below.
To download a simulation of a typical forming experiment, click here.
Acknowledgements:
The financial support of the National Science Foundation through grant DMI 9734947 and of Alcoa is acknowledged with thanks.
Publications:
Miller, J.E., Kyriakides, S. and Bastard, A.H. “On Bend-Stretch Forming of Aluminum Extruded Tubes: Part I Experiments.” Int’l J. Mechanical Sciences 43, 1283-1317, 2001.
Miller, J.E., Kyriakides, S. and Corona, E. “On Bend-Stretch Forming of Aluminum Extruded Tubes: Part II Analysis.” Int’l J. Mechanical Sciences 43, 1319-1338, 2001.
Miller, J.E. and Kyriakides, S., “Stretch Forming of Rectangular Aluminum Tubes for Automotive Applications.” In Proceedings of the International Body and Engineering Conference, Detroit, MI October 2-5, 2000.
