Modeling Laser Heating for Roller Hemming Applications
In order to improve fuel efficiency, the use of lightweight materials in the automotive industry is continuously increasing. The AA6XXX and AA7XXX aluminum alloys in particular are the subject of significant attention. The aim is to use them in the same way as other structural materials such as conventional steel. Unfortunately their formability presents major challenges. These alloys lack sufficient formability for bending/hemming operations in particular. To overcome this, forming can take place at elevated temperatures. In this study, a combined laser-assisted roller hemming process is set up. Therefore, a 4000 W Nd:YAG-laser with a wavelength of 1096 nm is used. The first step involves qualifying the process window for laser heating. Several parameters are defined and effects on temperature and surface quality for AA6014 are detected using the design of experiments. The second step involves setting up a finite element model of the heating process. Different modeling strategies for laser heating are compared and a new approach is presented. The laser heating source is modeled by a semi-circular Gaussian temperature distribution and is validated through comparison of the temperature with laser heating experiments, showing very good agreement in the range from 600-4000 W. Finally, the validated thermal model is coupled with the roller hemming simulation and investigations into the thermal process window are performed.
J.R. Duflou, R. Clarke, M. Merklein, F. Micari, B. Shirvani and K. Kellens
T. Kleeh et al., "Modeling Laser Heating for Roller Hemming Applications", Key Engineering Materials, Vol. 473, pp. 501-508, 2011