Laser surface texturing of stainless steel 316L cylindrical pins for interference fit applications

This study is focused on the development of a novel method for designing high-end interference fit fasteners. In this work, a new surface laser treatment process was utilized to enable enhanced usability and bond strength control of press-fit connections. Cylindrical 10 mm diameter pins of 316L were textured over a 10 mm length using a pulsed CO2 laser beam focused one millimeter below the surface, with the thermal energy adjusted to bring the surface to just above the melting point of the metal. The pin surface morphology and dimensions were precisely controlled by controlling the laser processing parameters specifically the laser beam power, the pulse repetition frequency, and the overlap between scan tracks. The pin was inserted into a hub hole diameter of 10.05 ± 0.003 mm and pull out joint bond strengths were examined. The results of this study showed that surface thus altered provided improved control of the bond strength which is a particular novelty of this new interference fit joining method. Surface roughness, Ra, from 40 to 160 μm, melt pool depths from 0.4 to 1.7 mm, increases in the pin outer diameter from 0.5 to 1.1 mm, and pull out forces of up to 7.51 kN were achieved. The bond joint was found to re-grip before final failure providing a more secure joint and increased safety. This joining method allows for the possibility of joining different materials. The pulse repetition frequency was measured to be the most significant processing parameter for control of the resulting mechanical properties and the bond strength with a clear inverse relationship.