A Study on the Generation of Negative Tapered Holes in Laser Process of the Metal Material

This study investigates the effect of laser processing parameters on the generation of negative tapered holes and their potential application in improving adhesive joint strength for an overlap joint. A process variable experiment was conducted to analyze the relationship between the laser beam pulse energy, the number of laser scans for depth adjustment, and the laser focus position on the inner hole geometry. The results show that the peak pulse energy and laser focus depth are the primary factors affecting the formation of negative taper angle, with the largest negative angle recorded locally at − 29°. To evaluate the practical application of holes with negative tapered geometry, an overlap joint of titanium alloy specimens was performed using epoxy adhesive. Eight holes with taper angles of 10° and − 29° were fabricated on the surface of the titanium alloy specimen and used for joining. The tensile shear strength of the negative tapered holes was found to be 77.6 MPa, nearly double that of the positive tapered holes. Overall, this study highlights the potential benefits of negative taper holes for enhancing adhesive joint performance in overlap joints and provides insights into the impact of laser processing parameters on negative tapered hole formation.