Problems Linked to Laser Welding of components having Large Thicknesses

摘要

There are a great many applications of laser sources in the field of welding, even in sectors where considerable difficulties of execution were previously verified. The specific characteristics of heating by means of laser, with a high concentration of energy in localised areas and the simultaneous presence of restricted areas that have been thermally altered, represent special conditions as a whole and the material's answer to them opens a field of study that is of considerable interest in the metallurgical field. The complex phenomena of a thermofluid mechanics nature, which are involved in the deep penetration welding technique, also involve a preliminary and accurate experimental set-up of the process in order to assure the high quality of welding that can be achieved with this technology. The problems linked to the welding of components having large thicknesses were examined in this work while referring to the operative parameters and analysis of the types of defects, both internal and external, that were encountered when setting up and in the laser CO_2 welding of these components. Welding on thicknesses varying from 6 to 34 mm., with and without weld material, were taken into consideration in order to evaluate the modifications of the operative parameters and, in particular, the evolutions of the defects. Head-bondings were analysed for transparency, individually and/or in several runs, even with unlike materials. The work carried out pertained to the examination of samples that were characterised by the types of microscopic and macroscopic defects that can intervene in the laser welding process, in the view of ascertaining the origin and relations with the welding process in order to optimise the parameters of the process itself for each of the applications examined.