焊接缺陷磁光成像三维轮廓重构识别

Three-dimensional reconstruction and recognition of weld defects based on magneto-optical imaging

对焊件表面及亚表面缺陷进行无损检测是保证焊接产品质量的关键。提出了一种基于法拉第磁致旋光效应的磁光成像焊接缺陷三维重构方法,实现焊接缺陷形状和大小的识别。基于磁光成像原理分析漏磁场磁感应强度与磁光成像的对应关系,以脉冲激光焊接凹坑(3 mm×0.3 mm×0.25 mm)为研究对象,建立焊接凹坑缺陷三维有限元磁场仿真模型,探索漏磁场磁感应强度分布规律。通过图像数字化技术及磁光成像像素值的分布规律,提取缺陷的二维轮廓信息,并设计梯度-偏差算法构建深度信息,最终获得焊接缺陷的三维轮廓。实验结果表明:缺陷处距离中心点越远磁场应强度越大,场强变化梯度越大处越接近Y轴方向中心点。与共聚焦显微镜获取的缺陷轮廓信息对比,凹坑最大深度均在150~200μm之间,平均深度及深度中位数相差较小,分别为0.1,2μm。磁光成像检测技术具有较高的识别精度,可实现对焊接缺陷的三维轮廓重构。

Nondestructive testing of the surface and subsurface of welding defects is key for ensuring the quality of welding products.A three-dimensional(3D)reconstruction method of welding defects based on Faraday magneto-optical imaging(MOI)is investigated to realize the shape and size recognition of welding defects.First,based on the principle of MOI,the corresponding relationship between the magnetic induction intensities of the magnetic leakage field and MOI is analyzed.Subsequently,using a pulsed laser welding pit(3 mm×0.3 mm×0.25 mm)as the research object,a 3D finite element magnetic field sim ulation model of the pit is established to investigate the distribution of magnetic induction intensity of the leakage field.Moreover,a two-dimensional plane contour of welding pit defects is extracted via image digitization and the pixel value distribution of MOI.A gradient-deviation algorithm is designed to construct the depth information.Finally,the 3D profile of the welding defect is obtained.Results show that the magnetic field intensity should be greater the farther it is from the center point of the welding pit defects.Meanwhile,the closer it is to the center point of the Y-axis direction,the larger is the gradient of the field intensity change.The maximum depth of the pits is between 150 and 200μm,and the differences in the average and median depths are 0.1 and 2μm,respectively,which are different from those of a confocal microscope.MOI technology affords high identification accuracy and can realize the 3D contour reconstruction of welding defects.