| With the rapid development of rail transit industry at home and abroad,stainless steel body has a wide range of applications due to its excellent corrosion resistance,high strength,high safety,low life cycle cost and light weight.In order to realize the lightweight manufacturing of the stainless steel rail vehicle body,the thin plate structure design is mainly adopted.The stainless steel body is usually in the form of a thin plate lap weld with a thickness of 0.5-4 mm.The side wall of stainless steel vehicle body adopts laser welding method with high energy density,which can obtain good appearance quality of vehicle body.Due to the small size of the lap laser welding seam,the welding quality control is difficult,and it is necessary to adopt certain technical means to detect the weld quality.Aiming at the problem of quality inspection of stainless steel thin plate lapped laser weld,this paper attempts to find a convenient and high precision laser weld quality evaluation method by analyzing the surface morphology of lapped laser weld.In this paper,a laser weld surface quality automatic scanning and detecting device is developed based on the structural characteristics of stainless steel rail vehicle body laser welding components.It is suitable for surface profile detection of laser welding seams in a certain size range,which can realize non-contact,high precision and intelligence detection.According to the change of surface profile and computer generated image,the stability of the technology and welding quality are evaluated,and the problems of low precision and harsh detection conditions of the existing non-destructive testing technology are solved.The detection device consists of industrial computer,laser displacement sensor,scanning driver,etc.The laser displacement sensor has a focal length of 30 mm,a range of ± 4 mm,a spot diameter of 0.1 mm,round spot,and a sampling period of 200 ?s,which is very suitable for fast measurement of small scale geometry.The appearance inspection method in this paper is based on the principle of laser triangulation.The slight convexity and concave on the surface of the seam changes the distance from the point source of the sensor to the surface of the seam,resulting in the change of the position of the imaging spot on the detector.The height difference on the surface of the actual object is obtained according to the relationship between the amount of change in the object surface displacement and the amount of change in the position of the imaging spot on the detector,thereby obtaining the surface profile.The single contour of the laser weld,that is,the cross section of the weld,is a direct representation of the weld morphology,and the profile includes information such as the weld reinforcement and width.The appearance quality of the weld can be evaluated by collecting the test data,using the data to generate a contour image of the weld appearance and identifying the features on the contour.Generally,the stainless steel thin plate lapped laser welding seam has a certain weld height,and in the case where the two steel plates are not clamped,the weld height is lower than that of the base material,that is,the seam has a certain amount of collapse,so that the performance of the weld is not guaranteed.In this paper,the single contour image of the weld surface is denoised,and the contours of different shapes are respectively denominated by various denoising methods to find the best denoising method applicable to the contours of different shapes.The denoised profile visually characterizes the actual shape of the seam.The tilt profile is corrected to level to ensure accuracy of subsequent analysis of the weld feature.Using various data fitting methods and geometric feature recognition methods to identify and extract the height,collapse amount and width of the seam profile.It is found that the 14-level polynomial fitting method is used to identify the weld features with high accuracy and stability.The detection error of weld height is less than 0.05 mm,and the average error is less than 10 ?m,which can meet the inspection requirements of the surface quality of stainless steel vehicle body laser weld.The influence of the welding technology on the quality of the weld is analyzed.The large gap in the lapped joint and the small thickness of the welded side plate will increase the amount of collapse of the weld.According to the analysis of the relationship between the appearance characteristics of the weld and the tensile shear performance of the weld.It can be seen that when the surface profile of the weld is collapsed,the mechanical properties deteriorate with the increase of the amount of collapse,and the weld reinforcement can only be maintained within a certain range to obtain better mechanical properties.The surface morphology of the stainless steel sheet lap laser welding joint can reflect the welding quality of the joint to some extent.In the industrial production,the inside connection condition of the joint and the quality of the laser welding can be evaluated by detecting the surface quality of the weld,thereby optimizing the welding process parameters and improving the joint quality. |
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