S. P. Edwardson, K. G. Watkins, G. Dearden, J. Magee*
Laser Group, Department of Engineering, The University of Liverpool, UK
(*Currently at: National Centre for Laser Applications, NUI Galway, Ireland)
Abstract: There has been a considerable amount of work carried out on two-dimensional laser forming, using multi-pass straight line scan strategies to produce a reasonably controlled bend angle in a number of materials, including aerospace alloys. However in order to advance the process further for realistic forming applications and for straightening and aligning operations in a manufacturing industry it is necessary to consider larger scale 3D laser forming. The objective of this investigation is to establish rules for the positioning and sequencing of the irradiation lines required for the controlled 3D-laser forming of a symmetrical saddle shape from rectangular sheet material. The saddle shape was chosen due to its more complex 3D geometry, the double curvature providing a useful case study with which to build up the design rules for such 3D shapes. The investigation consisted of the laser forming of 400mm x 200mm 1.5mm gauge Mild Steel CR4 sheet using a CO2 laser source. The scan strategies tested consist of straight and radial lines and concentric circular patterns. The active laser forming mechanism used varied from the temperature gradient to the upsetting mechanism depending on beam parameters and traverse speed used. The final geometries of the parts formed were verified using a co-ordinate measuring machine and are presented. It was possible to produce a controlled repeatable saddle shape using a concentric race-track strategy, employing the upsetting mechanism at the centre of the sheet, thus shortening the material at the centre and the plate naturally saddles. However the results of the investigation show that the problem of 3D laser forming is extremely complex. It was found that once a successful scan strategy was discovered symmetry was difficult to achieve due to the asymmetrical nature of the forming process itself, in that it was not possible to form the whole sheet at the same time.