Electron beam welding residual height measurement by line laser illumination and telecentric imaging

Residual height significantly affects the fatigue life of electron beam welding (EBW) joints. Therefore, accurate measurement of the EBW residual height is necessary for grinding and removing it, to improve the fatigue resistance of the joint. However, there is no specific method for the EBW residual height measurement, and existing methods for other regular welds are often unsuitable due to their limitations. This paper proposes a novel EBW residual height measurement method, to the best of our knowledge, based on line laser illumination and telecentric imaging [line laser telecentric imaging (LLTI)]. Unlike regular line-structured light methods based on near-centered imaging, telecentric imaging has advantages on the simple imaging model, minimal aberration, and can avoid a complex calibration process and improve the detection accuracy. In this paper, residual height calculation algorithms for both flat and cylindrical bases of LLTI are discussed, and, for cylindrical base welds, an error analysis is conducted and a corresponding solution is proposed. A series of experiments is conducted, and the accuracy is under 0.02 mm, which proves the effectiveness of the LLTI method.