| The aluminum alloy laser weldment has good comprehensive performance and is widely used in national defense,railway,military,aerospace and other fields.However,due to the rapid solidification characteristics of laser welding,gas holes and other defects are easy to occur in the weld.The existence of these defects will seriously reduce the performance of laser weldments,and even cause catastrophic accidents.Therefore,it is of great theoretical and practical significance to carry out nondestructive testing and defect location of important laser weldments of high-speed trains.According to the nondestructive testing requirements of aluminum alloy laser weldment of T-joint,the scheme demonstration of the nondestructive testing of the weldment was carried out.The 225 k V micro-focus X-ray inspection system was used to carry out the X-ray inspection of the T-joint weldment with left and right rotation 45 degrees,and the X-ray inspection image of the T-joint weldment was obtained.Based on the analysis of the gray distribution characteristics of the X-ray inspection image of weldment,the noise of the X-ray inspection image was denoised using the LMFPM model.LMFPM model was used to improve the clarity of X-ray detection image,increase the contrast between the background and defects of the detection image,improve the details of the detection image,and further improve the overall quality of the detection image.According to the characteristics of the gray level change of the X-ray inspection image of weldment,the method based on morphological background simulation has been proposed.The defect segmentation has been studied by using global threshold and iterative threshold.The results show that the iterative threshold segmentation method can realize the fidelity segmentation of welding defects in the X-ray inspection image of T-joint weldment,and the algorithm has strong adaptability.The thickest part of X-ray penetration weldment was selected as the location feature point,and the mathematical model of the defect depth and offset of the weldment has been established according to the geometric relationship of parts of the X-ray detection image.On the basis of defect fidelity segmentation of weldments,the automatic corresponding criteria of defects and the automatic extraction algorithm of defect projection distance has been proposed,and the spatial location data of internal defects of weldments has been extracted automatically.Then,X-ray inspection has been carried out on several T-joint weldments,and the statistical analysis has been carried out on the extracted defect spatial location data.The experimental results show that the defect offset is within the range of [-1.5 1.5] mm,and 64.8 percent of the defects are within the range of [0 1.5] mm,that is to say,most of the defects are located on the left side of the sternum centerline.The defect depth is mostly within the range of [1.4 2.8] mm,that is to say,most of the defects are concentrated at the joint surface of the sternum and wing plate of the weldment.Defects distribute randomly along the longitudinal direction of the weld.The defect radius is within the range of [0 0.7] mm.In order to more intuitively display the spatial distribution of welding defects in the T-joint weldment,the user interface with good interaction has been established,which can freely switch and select the processing images at each stage for inspection personnel.At the same time,the three-dimensional model of T-joint weldment has been established in the same interface,and the visualization of the spatial location data of the internal defects of T-joint weldment has been realized,which can provide valuable reference for the rapid nondestructive testing and structural integrity evaluation of weldments of this type. |
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