Laser peen forming induced two way bending of thin sheet metals and its mechanisms

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Laser peen forming, is a purely mechanical forming method achieved through the use of laser energy to form complex shapes or modify curvatures. It is flexible and independent of tool inaccuracies that result from wear and deflection. Its nonthermal process makes it possible to form sheet metal without material degradation or even improve them by inducing compressive stress over the target surface. Experimental investigation has been carried out to understand the effect of process parameters such as laser intensity, scanning velocity on the bending deformation of thin sheet metal with different thicknesses. It is found that the sheet metal can be made to bend not only toward but also away from the laser beam depending on the process condition. The bending deformation is found to be varied continuously and smoothly from the concave form to the convex by increasing the sheet thickness or decreasing the laser intensity. There is also a specific thickness for sheet metal to remain flat after laser peen forming. Two mechanisms are proposed to understand all experimental results, which are shock bending mechanism and stress gradient mechanism for bending toward and away from the laser beam, respectively. Due to the coupling effect of two mechanisms, the smoothly switching from one mechanism to the other depending on process conditions makes the laser peen forming to be an easily controlled process for forming complex shapes and high precision curvature modification.