Ultrasonic Testing And Phased Array Imaging Of Laser Weld Seam For Automotive Moderate Thick Plate Structural Parts

Laser welding is an advanced manufacturing process and an important connection technology in the lightweight manufacturing process of automobiles.With the continuous development and advancement of laser welding technology,laser welding has been widely used in the manufacture of automotive parts such as shifting forks of automobile gearbox,transmission gears,clutches,transmission shafts,body frame and chassis.The internal quality of laser welds has an important impact on the safety of automotive moderate thick plate structural parts.Therefore,it is necessary to detect the internal quality of laser welded joints in automotive moderate thick plate structural parts.At present,the detection method for the internal defects of laser welded joints of automobile moderate thick plate structural parts is mainly destructive slicing,but this method has the defects of destructiveness,hysteresis,small sample and high detection cost,which can not meet the high reliability and low cost inspection requirements required for modern industrial production.In this thesis,the laser welding seam of shifting fork of automobile gearbox is taken as the specific research object,and the ultrasonic nondestructive testing of welding quality is carried out.The specific contents are as follows:(1)The parts of the shifting fork of the automobile gearbox are introduced.The types and causes of the internal defects of the laser welded joint are analyzed.According to the characteristics of the welded joints of the plate,three conventional ultrasonic testing methods are discussed and formulated.Developed a suitable ultrasonic testing process.The location and quantitative analysis of internal defects in the weld are discussed.(2)Based on the discussion of three conventional ultrasonic testing methods,the ultrasonic water immersion focusing probe was selected and designed.Then,the sound field simulation and analysis of the water immersion focusing probe were carried out,and the rationality of the selected probe was verified.(3)Based on COMSOL software,the finite element simulation model of plate weld structure is established.The acoustic simulation of the welded structure of the plate is carried out and the corresponding experiments are carried out.Then the simulation and experimental signals are processed,and the time domain and frequency domain eigenvalues of the extracted signals are analyzed.It is proved that the ultrasonic immersion focus detection method can detect the tiny defects in the laser weld seam,and the ultrasonic signal spectrum analysis can effectively identify different defect types,and the weld quality is also evaluated.(4)Introduced the theory of ultrasonic phased array imaging and ultrasonic phased array imaging equipment,and developed the ultrasonic phased array detection technology.Based on this,the ultrasonic phased array imaging experiment was carried out on the laser weld seam structure of the shifting fork of the automobile gearbox.And verified with ultrasonic water immersion focus test results.This thesis proposes a conventional ultrasonic water immersion focusing and ultrasonic phased array imaging detection process for the laser gear shifting fork of the automobile gearbox,and realizes the detection of the internal diameter Φ0.2mm equivalent defect of the 3-5mm wide laser weld.The research results are of great significance and practical value for ensuring the high quality welding manufacturing of key structural parts of automobiles.