Laser processing of metallic surfaces for controlled micro-texturing and metallic bonding

This study investigated the development of a novel method for designing high-end interference fit fasteners. In this work, a new surface laser treatment process was developed and implemented to enable enhanced usability and bond strength control of interference-fit connections. Stainless steel 316L cylindrical samples of 10 mm diameter were textured over a 10 mm length using a pulsed a 1.5 kW CO2 laser. The laser beam was focused one millimetre below the metal surface, with the thermal energy adjusted to bring the surface to just above the melting point to avoid the loss of the metal. Due to the localized surface melting, rotational movement of the pin and the gas jet impingement, the re-solidified metal creates raises in the sample diameter. The pin surface morphology and dimensions were precisely controlled by controlling the laser processing parameters specifically the laser beam power, the pulse repetition frequency, the rotational speed, the gas pressure, 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 measured and 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 0.1 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 complete separation providing a more secure joint and increased safety. This joining method allows for the possibility of joining different materials. The modified surface layer did not reveal any distinct variation in the elastic modulus or hardness across the cross section of the insertion