Study On Influence Of Groove On Plasma Plume Induced During High Power CO₂Laser Welding

During CO₂high power laser welding process, the presence oflight-induced plasma causes a significant impact on welding processmonitoring and weld quality, and therefore plasma has been a researchfocus at home and abroad. With the development of economic andindustrial, the quality of thick plate weld that manufacturing demands isincreasing. However, during laser welding with groove, the plasma isobvious different with plasma induced during plate welding. Therefore,this paper researches the influence of groove on plasma by means ofexperiment and numerical simulation, in order to further understand theimpact mechanism and improve welding productivity.A system is established to acquire and analyze the characteristics ofplasma induced during laser welding inside groove with high speedphotography and spectrograph. It could real-time acquire the plasmaimages, remove the noise from images and equalize the gray level throughthe pretreatment of images. And then it could extract the contour of plasmaplume. In order to eliminate the interference caused by side walls ofgroove and molten pool, an improved active contour models Snakealgorithm was proposed and it could improve the accuracy and reliabilityof the plasma edge extraction. Moreover, the spectral information could beused to calculate the temperature of plasma.Extracting the shape characteristic, gray degree feature, and anglecharacteristic parameters of plasma, this paper investigated the influence ofgroove, gas flow and size of groove on the plasma shape and dynamiccharacteristics. The experimental results showed that the groove restricting plasma that width of plasma inside groove slightly reduced, the heightslightly increased, the root width kept same. The angle of core layerplasma indicated the angle of iron vapor ejected from keyhole. However,the angle of inner layer plasma reflected the influence of assisting gas.With the gas flow increased, the plasma inside groove shown a narrow,darkened trend, but it was more stable. When the groove size changed, theplasma changed too. Under the experimental conditions in this paper, withthe increasing of groove width, the size characteristic parameters of plasmaincreased. With the increasing of groove depth, the restricting of plasmaincreased.Based on computational fluid dynamics, this paper established athree-dimensional numerical model for the plasma plume induced duringlaser welding with groove. Simulation results showed that the trends ofplasma width, height and temperature were consistent with theexperimental results. The temperature field, concentration field andvelocity distribution of plasma all showed the constraint of groove to thediffusion of plasma. With the increase in gas flow, plasma was part beingblown away, the size parameters had different levels of decreases and thetemperature decreased, which showed the inhibition of assisting gas onplasma..