NUMERICAL ANALYSIS OF FLUID FLOW IN LASER+GMAW HYBRID WELDING

Abstract

Laser + gas metal arc welding(GMAW) hybrid welding fully combines the merits of both laser welding and GMAW, which can achieve high quality, high efficiency and comparatively low-cost welding of thin and thick plate, thus having great application prospect in manufacturing industry. However, compared with single heat source welding, hybrid welding involves more welding parameters and more complicated physical process,leading to difficult process optimization. When mismatching the process parameters, welding defects can still appear in high-speed welding, which affects the reliability of hybrid welding. Therefore, it is necessary to study the physical mechanism in hybrid welding deeply for suppressing welding defects and improving welding stability. In hybrid welding, fluid flow in weld pool has a critical influence on the weld formation. So, modeling and simulating the fluid flow is helpful for understanding the process mechanism completely. To date, however, there is only little study on velocity field in hybrid welding due to its complexity. In this work, with considering the effects of droplet and keyhole on weld pool, a three dimensional transient model is developed to numerically analyze fluid flow in weld pool of laser+GMAW hybrid welding based on FLUENT software. Arc heat input is modeled using an doubleellipsoid heat source; laser heat input is regarded as a hyperbolic curve- rotated heat source with changing peak power density, its distribution parameters being determined based on the simplified model for keyhole geometry and size. Droplet transfer is described as the process of high temperature liquid metal flowing into weld pool from the certain domain above the weld pool. Using the built model, the keyhole behavior, fluid flow and temperature distribution in laser+GMAW hybrid welding under different welding conditions are calculated. The features of velocity field in hybrid welding are analyzed and the effect of laser power on the weld pool dynamic behavior is discussed. The results show that, in the case of 1 m/min, weld bead hump is generated in single GMAW(laser power0 W); when laser power is 500 W, bead hump disappears in welding, but there is no keyhole emerging in hybrid weld pool and fluid flow pattern is close to that in GMAW. When increasing laser power to 2000 W, keyhole is formed, which makes the fluid flow in weld pool more complicated. The predicted weld geometries and dimensions for varied laser powers are compared with the measured data, which are in good agreement, thereby indicating accuracy and applicability of the established model.