| As a welding method with many advantages such as high energy density,large welding depth and small welding distortion,the application of laser welding is increasing in the rail cars manufacturing and other industrial fields.The welding structure of the stainless steel side wall on the latest edition railway vehicle,in order to ensure the flat and beautiful appearance of the side wall,mainly use semi-permeable lap laser welding method,which means the plate under the laser is fully penetrated,and another underlying plate is half penetrated.In the process of thin plate lap laser welding,the influence factors such as fluctuations in welding parameters and poor accuracy of workpiece mounting may cause defects such as incomplete penetration or porosity in the weld seam,and will seriously reduce the strength and service life of the weld seam.It is essential for ensuring the safety of the welded structure by controling the quality of laser welding of stainless steel sheet effectively.The quality detection methods of welded joints can be divided into destructive testing and non-destructive testing.Destructive testing is widely used in actual production with the disadvantages of wasting material,reducing production efficiency and having a large detection error.With the increasing requirements for welding quality,mass nondestructive testing of the weld seam becomes more and more important.Nowadays,ultrasonic testing is one of the most widely used during all of the industrial nondestructive testing technology,and it is also one of the most active technologies in the field of nondestructive testing.However,the conventional conventional ultrasonic detection with disadvantages as complicated operation,non-intuitive,non-recording,and severely influenced by human factors,which can not meet the reliable and portable requirements in modern industry.Therefore,phase array ultrasonic testing as a high efficient technology is close in this paper research the quantitative and graphical ultrasonic testing technology for laser welding seam of stainless steel lamellar lap.In this paper,an automated and intelligent ultrasonic testing system for laser welding seams is established,which is based on a portable industrial computer,including a phased array ultrasonic inspection module,a motion control module,and a probe mechanical movement module.Phased array ultrasonic focusing electronic scanning technology and stepper motor mechanical drive technology are combined together to achieve a rapid and high-precision ultrasonic C-scan detection on laser welding seam.The unique method of water-immersed coupling in the phased array ultrasonic probe was studied,which greatly improved the stability of the acoustic signal in the ultrasonic testing process.The relationship between the ultrasonic A-scan signal and the connection status of the laser welding seam has been systematically studied and the ultrasonic detection model for laser welding seam width calculation is established,which lay foundations for wide-ranging quantitative ultrasonic testing and ultrasound C-scan imaging.The actually width of the weld seam has been measured on the metallographic specimen and compared with the phased array ultrasonic testing result to analysis the accuracy.Experimental analysis shows that for the A-scan signal measurement method,when the threshold value is 40%,the relative error is small,but the variance is higher than the ultrasonic FFT signal measurement method,indicating that the stability of the A-scan signal measurement method needs to be improved.The FFT result matches the actual measurement value well.The average error of the relative error normal distribution curve is 0.02871,and the variance is 0.07149,Those small gap indicate that the ultrasonic FFT signal measurement method has a high accuracy and stability under the test conditions. |
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