Fundamental research of laser micro welding for practical use of titanium eyeglass frames

Micro welding of titanium eyeglass frames requires sound strength, good exterior appearance and stable production, which suit micro laser welding. The objective of this work is to fundamentally investigate butt welding conditions with a pulsed yttrium aluminium garnet laser beam for exterior appearance and joint strength. Eleven factors of welding conditions which influence joint strength were evaluated from the viewpoint of quality engineering. It was found that two factors of defocused distance and processing of welding surface of the welding parts led to fluctuation of the joint strength. Therefore, sub-millimetre scale control of the laser irradiated point along the optical axis and the removal of impurities lead to brittle metallic compounds on the surface and produce sound strength of the joints. Furthermore, the optimized laser condition is applied to fabrication of components with the shape of titanium eyeglass frames. The qualities of the obtained joints were confirmed by a stripping test, cyclic bending test, metallographic observation and hardness determination. It was revealed that the laser welding method is more reasonable than conventional resistance brazing methods.