Numerical Simulation And Analysis Of The Molten Pool Flow Characteristics Of Laser Deep Penetration Welding

Currently, with the diversified development of laser welding, in the aerospace, shipbuilding and automobile manufacturing high speed laser welding and high power laser welding are used more and more widely, the applications of active laser welding, laser material manufacturing and preheating laser welding methods have a certain application. For some new physical phenomena during the welding process, the classical theory of molten pool flow may not be applicable, and it is not able to fully explain them.At the beginning of the test, in the combining research institute at the university of Osaka, Japan, based on X-ray on-line monitoring system, we took the "particle tracer method" test, made a collection of the flow of the molten pool at different welding speed, testing found that tracer particle trajectory with the welding speed and obvious changes in the different laser powerTo explore the influence factors of fluid flow behavior of deep penetration laser welding, this article established the deep penetration laser heat-flow coupling mathematical model based on the three-dimensional fluid dynamics software-Fluent, researched the influence law of fluid flow of molten pool of the welding speed and preheating condition, using physical simulation experiment to validate the results of numerical calculation, analyzed the essential reason of the influence of the molten flow.The calculation results show that:Welding speed significantly influence on molten pool flow and the molten pool size. Increases with the welding speed, the molten pool shape changes obviously, convection weakened, fluid flow rate is reduced, surface of molten pool temperature gradient and temperature are lower, there is a connection with fluid flow velocity and temperature gradient. So, by applying preheat condition, this article simulated the temperature gradient effect of flow field, found that with the increase of the temperature gradient, the molten pool fluid flow rate increases, but the flow changes, think that in addition to the temperature gradient, fluid drive and thermal physical property parameters is also the important factors that affect the flow.Based on the finite element simulation and physical simulation, this paper illustrates the fluid flow mechanism of deep penetration laser welding:among the main driving force, surface tension is predominant, is influenced by the temperature gradient and the active elements. buoyancy, a driving force for the secondary contribution to fluid flow, is small, is affected by temperature. Material thermal physical property parameters of molten pool flow have certain effect, mainly influenced by temperature.