| With the improvement of living standards,rail transport has become an important means of transport to meet people's growing demand for convenient travel.In the development of rail transport,stainless steel rail coaches have become one of the fastest growing rail transport carriers with their advantages of light weight and long maintenance intervals.In order to achieve the light weight of the stainless steel railbus body,the main use of thin plate assembly welding structure.Resistance spot welding is the main welding process of stainless steel body manufacturing,each car body has up to 40,000 to 50,000 spot welding joints,is the key process of stainless steel body welding manufacturing,its welding quality is also related to the manufacturing quality of the car body.Therefore,the efficient inspection and evaluation of spot welding quality is of great importance to ensure the safety of the vehicle body.For the non-destructive testing and assessment of stainless steel body spot weld quality,traditional testing methods include radiographic testing,ultrasonic flaw detection and other testing methods,which are limited by the testing conditions of the inspected parts and the limitations of the testing methods themselves,making it difficult to achieve high efficiency and high proportional testing.The infrared thermal wave inspection method has the advantages of high efficiency,large area,non-contact and long distance detection,and is of great academic and application value in the nondestructive inspection of the resistance spot weld quality of stainless steel car bodies.This paper establishes an infrared non-destructive testing model for stainless steel spot welding based on COMSOL software,simulates and analyses the heat transfer conduction process of stainless steel resistance spot welding under transient pulse thermal excitation conditions,and then investigates the characteristics of surface temperature distribution and the factors affecting thermal wave detection under different parameters such as molten core diameter and different defect types.The simulation analysis reveals the principle of infrared detection and provides an important theoretical basis for the quantitative analysis of molten core size and defect information..In infrared non-destructive testing,image processing techniques are at the heart of the detection technology.For the original image data obtained,methods such as data fitting,compression and reconstruction are used to achieve the reduction of timedomain noise and reduce the influence of uneven heat distribution,and to enhance the accuracy of image recognition through image sequence alignment and enhancement techniques,and to carry out image segmentation and edge detection to finally achieve defect feature extraction and quantitative recognition of thermal wave images.Therefore,how to enhance the signal-to-noise ratio and clarity of the image,improve the contrast ratio,make the edges of the image visible and extract the target area through image segmentation techniques will be the focus of quantitative analysis and defect recognition.By establishing a data processing program,the infrared thermogram is automatically enhanced,detected and segmented,and the quantitative calculation and quality assessment of the spot weld fusion core is completed,fulfilling the pre-defined quality assessment and defect identification objectives of the subject.The actual diameter dimensions are obtained through metallographic testing,and the error between the tested and measured values is calculated and analysed to determine the cause of the error.The test results show that the test platform established in this paper is highly reliable for the assessment of spot weld quality. |
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