Experimental Research On The Influence Of Powder Beam On Characteristics Of Keyhole And Molten Pool In Laser Welding

Morphology,temperature and velocity are three important characteristics of the keyhole and molten pool in powder filling laser welding,and dynamic behaviors of morphology,temperature and velocity can reflect the stability of welding process from one aspect.The influence rules of powder filling rate and welding speed on surface characteristics and internal characteristics are studied.Surface characteristics are mainly concerned about the surface morphology,the surface temperature of keyhole,the surface temperature of pool and the surface velocity of pool,while internal characteristics focuses on the longitudinal keyhole profile and the internal temperature of keyhole.High-speed camera and two-color pyrometer are used to establish the experimental platforms for surface characteristics and internal characteristics.Dynamic morphology of keyhole and molten pool is captured by high-speed camera during powder filling laser welding of 304 stainless steel.As for surface morphology,when powder filling fails to reach the powder saturation,the mean keyhole diameter,the mean pool width and the pool length at the same time increase with the increase of powder filling rate,however,when powder reaches the saturation,as powder filling rate continues to increase,the mean keyhole diameter and the mean pool width first decrease slightly,then go into a quasi-steady state,and there is no significant changes in the pool length at the same time.As welding speed increases,in the stable stage of laser welding,the mean pool width and the time that pool width reaches a quasi-steady state decrease,while pool length at the same time increases with welding speed increasing.As for the longitudinal keyhole profile,when powder filling rate is less than 14.15 g/min,the keyhole depth increases with powder filling rate increasing.When powder filling rate is more than 14.15 g/min,the keyhole depth decreases obviously with powder filling rate increasing.As welding speed increases,the mean keyhole depth and its maximum change rate at initial time decrease,while the slope of the front keyhole wall increases slightly in the welding direction.The temperatures of keyhole and molten pool are measured by two-color pyrometer during powder filling laser welding of 304 stainless steel.As for the surface temperature of keyhole,the larger powder filling rate is,the higher the surface temperature of keyhole is.With welding speed increasing,there is no significant changes in surface temperature of keyhole.As for the internal temperature of keyhole,when powder filling rate is less than critical rate of the powder saturation,the internal temperature in the detection region of keyhole increases with powder filling rate increasing.The internal temperature of keyhole decreases with welding speed increasing.As for the surface temperature of pool,it increases with increasing powder filling rate and welding speed.Based on the experimental platform for surface characteristics,the movements of powders on the weld pool surface are captured by high-speed camera,thereby measuring the surface velocity of pool.Movements of powders are divided into two categories,mainly along the edge and across the pool width.The effect of powder filling rate on the surface velocity of pool is little.The surface velocity of pool is greatly affected by the metallic vapor plume or plasma.The surface velocity of pool decreases with increasing welding speed.