Research On Weld Image And Penetration State Of Thick Stainless Steel By Laser Welding

Compared with traditional welding,laser welding has the advantages of high energy density,fast heating and cooling,narrow welding heat affected zone,small welding deformation and easy automation.Therefore,it has been widely used in military,automotive and marine fields.With the increasing level of automation and intelligence in welding,control of welding quality is becoming more and more important.In order to achieve real-time control of the welding quality,it is necessary to obtain the information generated during the welding.At present,direct monitoring of weld pools through visual image information has become an important research and application direction.Laser welding produces strong interference signals such as arc,metal vapor and plasma.To capture a clear image of the welding area,this paper builds a passive robot laser welding stainless steel coaxial monitoring system.By analyzing the spectrum generated by laser welding of austenitic stainless steel by spectrometer,the appropriate filter and attenuator and camera acquisition parameters are selected to suppress the influence of the interference signal on the image of the welding area,and a clear image of the welding area can be collected.In this paper,the image of the welding area under different process parameters is collected.The image of the welding area when the keyhole penetrates the workpiece contains the molten pool,keyhole and penetration hole.The penetration image can accurately acquire the information of the molten pool,keyhole and penetration hole by setting a series of processes such as setting the image processing area,median filtering,threshold segmentation and morphological image processing.The surface morphology of the weld and the cross-section of the weld under different welding process parameters were analyzed to determine the welding process parameters in different penetration modes.Then,by analyzing the area characteristic information of the keyhole and the penetration hole in different penetration modes,the relationship between the keyhole and the penetration hole and the penetration state of the workpiece is established.The main conclusions of the experiment are as follows:(1)When other process parameters remain unchanged,laser power is too low or welding speed is too fast,due to insufficient heat input,the liquid metal under the keyhole and the bottom of the keyhole has not penetrated the workpiece.The keyhole image has been displayed as a complete white circular bright spot.There is no penetration in the welding process.The penetration area is 0,and the front of the weld is shown as discontinuous surfacing height.The weld width on the back of the weld is 0,the cross section shape of the weld is "Y" shape,and the workpiece is obviously not penetrated.(2)With the increase of laser power or the decrease of welding speed and the increase of heat input,the liquid molten pool under the bottom of the keyhole melts through the heat conduction,but at this time the keyhole has not penetrated the workpiece,and the image of the keyhole has been displayed as a complete white circular bright spot.There is no penetration during the welding process,and the penetration area is 0.The weld width on the back of the weld is narrower and smaller than that on the back of the weld.The cross section of the weld is "I" shape.At this time,the workpiece belongs to non-penetration(only the pool penetration).(3)With the increase of laser power or the further decrease of welding speed,the heat input is further increased,so that the keyhole penetrates the workpiece,and the keyhole image shows low-gray penetration holes.When the maximum area ratio of penetrating hole to keyhole is greater than 0 and less than 0.54,the cross-section of the weld is "X" shape,the weld surface is well formed,the weld width on the back is uniform,and the weld width on the back is less than the weld width,and the workpiece is moderately penetrated.When the maximum area ratio of penetrating hole to keyhole is greater than or equal to 0.54,the weld width on the back of the weld is uniform,but the surface of the weld is poorly formed.Although the cross section shape of the weld is "X",the weld width on the back of the weld is larger than the weld width,and the workpiece is overmelting.(4)The change trend of the weld width detection value is consistent with the actual measurement value,and the weld width detection value is also less than the corresponding actual measurement value,because the weld width detection value is the molten state molten pool width during welding,and the actual measurement value is a measure of the solidification state of the molten pool after welding.The average relative error between weld width detection value and actual value is 3.31%.The validity of passive robot coaxial laser welding monitoring system for weld width detection is verified.