The Theory And Experiment Research Of Thermal Cycle On CO₂ Laser Welding Of High-strength Zinc Galvanized Steel

Deep penetration CO₂ laser welding with high-power has become a kind of standard processing craftwork in modern industry, due to the fast jointing, high-quality welding and good production efficiency. It plays a increasingly significant role in auto industry. High-strength zinc galvanized steel possesses excellent mechanical properties, upstanding corrosion resisting properties, and anti-crash properties. Nowadays, we are much accounted of security and light-weighting of motors. Therefore, High-strength zinc galvanized steel is broadly applied for auto body and the manufacture of safety member. Based on that laser welding temperature field thermal cycle analysis is the presupposition of the welding stress and deformation analysis, it is worthy of lucubrating the high-power CO₂ laser welding thermal cycle property and the growing discipline of heat effecting grain. It makes great senses to the simulation of laser welding process, the forecast of tie-in performance and optimization of welding process.At the very beginning, this thesis introduces the applied condition of laser welding in auto manufacturing, according to the reference summarization. Then, it presents the study evolvement of laser welding analysis models. Later, it proposes the background and the purpose of laser welding dead-hard steel thematic cycle. This paper presents two absolutely different kinds of laser welding that are heat exchange welding and deep penetration welding respectively.Also it explains the formation of heat effect in the process of welding, organization distribution and properties. Contra-posing the nail head shape of dead-hard steel deep penetration CO₂ laser welding, consulting the welding heat source model of Steen W M, I want to refer to model of point-line heat source model。According to the supposition principle ,we could get mathematical model of temperature change caused by heat effect of welding workpiece in a certain point. Then we may acquire the type curve of thermal cycle through calculation in theory.In the next place,this thesis makes great use of the idea of PHC-1500 collapsible CO₂ laser developed by Hunan university itself. According to the laser welding thermal cycle curve hydrogenation and fast cooling, I design a scenario of using thermoelectric couple to measure temperature. This paper introduces the detail information of thermoelectric couple measuring temperature system, experimental program and approaches. According to the results, we could prove the rationality of the theory model, and analyses the effect of thermal cycle parameters Tm and t8/5 to the properties of laser welding of dead-hard steel and the organization. The results shows that if we promise the work piece fusion penetrated and adopt the fast high-power welding manufacture, both the ablation width of zinc surface of work piece and heat effect field will reduce, and also the organization function of the welding tie-in will be improved.Finally, according to the point-line heat source model of laser welding sheet, it propose the characteristic grain in the calculation.According the calculation of three different craftwork parameters, it forecasts the grain growth disciplinarian.