The Research On Ultrasonic Testing On The Quality Of Laser Welding Joint Stainless Steel

Laser welding as a precision connected method, have power density, high speed,narrow welding heat affected zone etc, It is more and more used in lapped sheet ofcars and railway vehicle. But thin lapped sheet laser welding is a complicated physicaland chemical process, the welding process is easily affected by many factors, such aswelding, the fast cooling speed and improper protection. Not complete fusion or gascavity will be produced in the weld. The existence of these defects will greatly reducethe strength and lifetime of weld. Serious accident may occur. In order to improve thestability and reliability of the stainless steel laser welding, it is necessary to inspect.Inthis way we can ensure the safety of the structure.There are two kinds of method to inspect laser welding joint quality, destructivetesting and nondestructive testing. In the actual production, destructive testing canonly provide reference information, because the practical work of the welding joint isstill without detection. As welding quality requirements is more and more needed, onehundred percent nondestructive testing of weldment to ensure the safety andreliability is more and more important. Ultrasonic testing technology is most widelyapplied in industry of nondestructive testing technology. It is also the most activetechnology of nondestructive testing field study. But the traditional ultrasonicnondestructive testing instrument operates complexly, it is not intuitive, no recordsand large influence defects of human factors. These can not satisfy the modernindustrial of ultrasonic nondestructive testing reliable portable requirements.In order to adapt laser welding quality detection requirements of modernindustrial fields such as auto and aerospace, the subject researches the stainless steellapped sheet laser welding, studies relationship between weld quality and ultrasonicnondestructive testing characteristic signal. Signal analysis and processing technologyis used to set up the stainless steel lapped sheet laser welding ultrasonicnondestructive testing system. The industrial computer is the core control, it apply the full function ultrasound card (ultrasonic pulse launch/receiving and A/D conversionare integrated on one PCI bus board).Speed controller and automatic scanning device(miniature linear motor platform and ultrasonic probe) accomplishes launch andreceiving of ultrasonic signal. The hardware system is simple, reliable, high accuracyand is suitable for application in industrial production environment. We develop thestainless steel lapped sheet laser welding ultrasonic nondestructive testing softwaresystem based on Visual C++platform. The software system can collect the echo data,store information and predict welding quality information. It realizes digitalization,intelligent, visualization and quantitative and qualitative analysis of defect in theultrasonic testing. At the same time the software also completes intelligentmanagement of weld quality information, it has the strong anti-interference, highspeed testing analysis and reliability etc.We ascertain parameters affecting the ultrasonic nondestructive inspection by alot of the stainless steel laser welding testing. The paper Introduces the ultrasonictesting system" ultrasonic settings" and "scanning settings", In order to improve thesensitivity and reliability of testing system, reasonable settings of C scan mainparameters will be made such as sampling frequency, gain, detection step length etc.In the time domain, we analyze the characteristics of A signal on the stainlesssteel laser welding in different areas. We sum up with principle about measuring laserweld width by A scanning signals. According to the information, we can writesoftware with measurement method of A scanning signal laser welding. Meanwhile, inthe frequency domain we analyze the ultrasonic echo signal amplitude spectrumcharacteristics on the stainless steel lapped sheet laser welding in different area. Wesum up with whether the main frequency amplitude change and the distance betweenprobe and weld have corresponding relation. The high frequency component spectrumattenuates faster than low frequency components when distance and grain size havechanged. The main amplitude frequency of the echo move to the low frequency.According to this information features, we can write software with ultrasonic FFT measurement method.Finally, we analyze the accuracy and stability of above two kinds of ultrasonicnondestructive testing method by metallographic experiment. Statistics suggest therange of error about this two kinds of ultrasonic nondestructive testing method. Thepaper analyzes the advantages and disadvantages of two methods. The experimentresults show that A scanning signal measurement method is not stable enough. Whenthe threshold value of40%, the relative error of measurement results is very small, butthe variance is a little higher compared with ultrasonic FFT signal measuring method.Ultrasonic FFT information measuring method is accurate and stable enough atexperimental condition.The measured value agrees with the actual measured valuewell, the average value of the relative error normal distribution curve is0.01417, thevariance is0.06986, both number are small.