Modification of bent angle of mechanically formed stainless steel sheets by laser forming

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Laser forming, being a flexible non-contact forming technique, is an attractive tool for the correction of spring back, over-bending or distortion of sheets formed mechanically or by other means. However, literatures are scarce on this topic. This work investigates the modification of bent angle of mechanically formed stainless steel blanks by laser forming using experiments and finite element (FE) simulations. Changes in angle imparted by laser forming, in specimens bent with the help of different die-punch combinations, have been studied for different Fourier numbers and laser spot diameters. Laser parameters were decided with the help of an analytical model so as to keep the peak surface temperature due to laser scan nearly constant for all the laser scan parameter combinations. Laser forming was carried out by scanning laser beam on both concave and convex sides of the mechanically bent specimens. The change in bent angle was found to be significantly larger when laser was scanned on convex side than on concave side. Further, for laser scanning on convex side, the change in bent angle increased with initial bent angle. Opposite trend was observed for laser scan on the concave side of the bending edge. However, for the similar mechanically bent angle, change in bent angle increased for laser scan on the concave side with increasing punch radius. For laser scan on the convex side the trend was just the opposite. Laser scans corresponding to different Fourier numbers did not significantly affect the change in bent angle. However, increase in laser spot diameter increased the change in bent angle. These observations were explained with the help of FE simulations considering temperature dependent material properties and multimode intensity distribution of the laser beam. Simulation results matched fairly well with their experimental counterparts in most of the cases.