Effect of Water Injection Systems on Sheet Metal Bending by Nanosecond Green Laser Peen Forming

Laser peening is a surface treatment designed to improve fatigue life by introducing compressive residual stress via laser-induced shock waves. However, there is currently no simple method of evaluating the depth of a compressive residual stress layer in a production factory. The author attempted to propose a simple evaluation method using a sheet-forming process called laser peen forming, which is based on the same principle as laser peening. In this study, pure titanium sheets were bent by nanosecond green laser peen forming performed in a water pool. The bending angle decreased with the increase in the amount of floating debris generated by laser ablation. Various water injection systems were employed to wash away the debris. The bending angles and their reproducibility were improved by injecting water coaxially with the laser beam. These results demonstrated that the improvement of residual stress distribution could be visualized through bending deformations, and suggested a potential evaluation method. However, further clarification of the process is required.