Molten Pool Of Metal Reflux Laser Welding Process Simulation Through The Holes

Keyhole formation is a typical characteristic of laser deep penetrationwelding. This study predicts accurate information of the temperature field ofweld pool and the morphology of the keyhole filled of the weld pool metal fluidwhen the laser beam is left. It has been a focus on the object of study in the fieldof welding process to grasp the flow of the pool fluid and the temperature fieldof the molten bath in order to improve the weld quality and the reliability of thewelded structure. Laser weld pool is small and frozen quickly and the moltenpool metal reflux flow is difficult to test,so the numerical simulation isbecoming an important mean to understand the physical mechanism of thewelding process.This study compares with changes of the shape and size of the backfilledkeyhole under the interaction of gravity and surface tension of melt pool, as wellas the two respectively by numerical simulation of Fluent software. It has a veryimportant guiding significance for reducing welding quality defects in actuallaser deep penetration welding to analysis how do the gravity and surfacetension of the molten metal influence the backflow of keyhole for the moltenpool solution.The heat transfer and fluid flow of molten pool in solidification stage oflaser deep penetration welding are simulated by building the two-dimensionalphysical model.We research the following aspects mainly:(1) solidificationcooling temperature field change of the molten bath;(2) instantaneousmorphology of keyholes backfilled by the pool fluid;(3) flow velocity field offluid of the laser weld pool;(4) the pressure field distribution of the molten poolbackfilling the keyhole.First, we establish two more realistic two-dimensional physical model ofthe molten pool of laser deep penetration welding through a large number ofreferences.Second, we get the temperature field distribution of the molten pool if wethink that the temperature of liquid-gas interface on the keyhole is considered to be the vaporization temperature of the metal, and the temperature of liquid-solid interface on the molten pool is the solidification temperature of the metal.Finally, the temperature of field molten pool and the transient morphologyof the keyhole filled by molten metal are simulated under different physicalfactors (surface tension, the thermal capillary force and static pressure) and thethermophysical parameters (kinematic viscosity, specific heat, thermalconductivity) in laser welding process after the establishment of temperaturefield model of molten pool.Liquid/gas interface changes on the keyhole are tracked by Volume OfFluid (VOF) technology when molten pool fluid backfill the keyhole. This studysimulates the instantaneous morphology of the backfilled keyhole and thetemperature field and velocity field of molten pool under the gravity and surfacetension of metal solution respectively. Then, the research analysis the physicalmechanism of metal solution backflow of keyhole in each case. That lays thefoundation for the study of the formation mechanism of the dynamic weld pool/keyhole stability and controlling measures for shrinkage.Results show that obvious melt pool vortices are discovered in the directionof keyhole, and the large melt pool vortices is the main factor to promoteconvection heat transfer of the weld pool; the vortex phenomenon also exists onthe rear of the surface of the molten pool and is the only factor that led to theuplift of the melt; these vortices are the result of the action of the surface tensiongradient of molten pool directly. Surface tension of metal solution has an greatereffect than gravity of its on the metal solution backflow of keyhole. So it has anvery important guiding significance for reducing welding quality defects inactual laser deep penetration welding to take effective measures to control thesize and orientation of the surface tension.