Abstract—minor Problems Arising from Optimizations By
welding of fixed prostheses frameworks can be identified by macroscopic and microscopic visual inspection. The purpose of this study was to highlight the visible discontinuities present in the laser welds of dental Ni-Cr alloys. Ni-Cr base metal alloys designated for fixed prostheses manufacture were selected for the experiments. Using cast plates, preliminary tests were conducted by laser welding. Macroscopic visual inspection was done carefully to assess the defects of the welding rib. Electron microscopy images allowed visualization of small discontinuities, which escapes visual inspection. Making comparison to Ni-Cr alloys taken in the experiment and laser welded, after visual analysis, the best welds appear for Heraenium NA alloy.
Characterization of the keyhole formed during pulsed Nd–YAG laser interaction with a Ti–6Al–4V metallic target
We observed, with an x-ray apparatus, the keyhole formed during the interaction of a pulsed Nd–YAG laser beam with a metallic target of a Ti–6Al–4V titanium alloy. We noted that the keyhole formation is not instantaneous and that it grows linearly during the duration of the interaction. We highlighted that its depth, at the end of the laser pulse, is practically equal to the melting-zone depth in the material. Finally, we showed from the results of these tests that a quick estimation of the melting depth can be made simply from the ratio of the power densities used with a reference test.
Gas protection optimization during Nd:YAG laser welding
Many laser processes, such as welding or surface treatments are associated with an undesired phenomenon, which is oxidation. The solution commonly employed to solve this problem approaches the shielding gas and/or the shielding gas device. What we propose in this paper is a methodology with the goal to optimize the protection gas device design as well as the gas flow in the case of laser welding and surface treatments. The pressure created by the gas flow on the sample surface is recorded and analysed together with the operating parameters influence in order to reach the objectives. The nozzle system designed and presented below assures the protection against material oxidation using minimal gas flow rates and increases the welding penetration in the case of high-power Nd:YAG laser welding.