Development of Scanning Acoustic Microscopy System for Evaluating the Resistance Spot Welding Quality

Scanning acoustic microscopy (SAM) system (TSAM-400) was designed and developed for evaluating the quality of resistance spot welding (RSW) joints of 1.5 mm-thick SUS 316 stainless steel sheets under different welding parameters. Indentation and nugget information (diameter and shape) were used for evaluating the RSW quality. SAM A-scan signals were used to calculate the indentation. The nugget diameter was determined in the C-scan image. Internal information (nugget shape, splashes, and defects) was visualized in the B- and C-scan images. In addition, the spot weld area was treated to examine the surface topography effect. The nugget diameters of treated and untreated areas were measured and compared to conclude that the surface topography effect can be neglected in the quality evaluation by SAM system. By implementing TSAM-400, some specimens were successfully tested with a scanning area of 55 × 15 mm², and a scanning time of 33.5 s corresponding to a B-scan frame rate of 4.5 Hz, and a resolution of 0.1 × 0.1 mm². Finally, the good input parameters for welding two 1.5 mm-thick SUS 316 were determined by analyzing the results from TSAM-400.

本研究设计并研发了一款扫描声学显微镜（Scanning Acoustic Microscopy，SAM）系统TSAM-400，用于评估不同焊接参数下1.5mm厚SUS 316不锈钢薄板的电阻点焊（Resistance Spot Welding，RSW）接头质量。以压痕与熔核的相关信息（直径及形貌）作为电阻点焊接头质量的评估指标，其中通过SAM的A扫描信号计算压痕尺寸，在C扫描图像中确定熔核直径；熔核形貌、飞溅与内部缺陷等信息则可通过B扫描与C扫描图像实现可视化呈现。此外，本研究对焊点区域进行预处理以探究表面形貌对检测结果的影响，通过测量并对比预处理与未预处理区域的熔核直径，最终得出结论：采用该SAM系统开展质量评估时，可忽略表面形貌带来的干扰。借助TSAM-400系统，本研究成功完成多组试样的检测，其扫描区域为55×15 mm²，扫描时长33.5秒，对应B扫描帧率为4.5Hz，空间分辨率达0.1×0.1 mm²。最终通过分析TSAM-400的检测结果，确定了适用于两块1.5mm厚SUS 316不锈钢板材的最优焊接工艺参数。