Analytical reconstruction of three-dimensional weld pool surface in GTAW

The reflective characteristic of mirror surfaces such as a liquid pool surface in arc welding makes many traditional 3D measurement/reconstruction methods fail. The authors proposed to intercept, image, and measure two points in each laser ray reflected from a mirror surface with two diffusive planes and cameras to analytically calculate the equation of the ray. The samples of the points on the mirror surface where the incident laser rays are reflected can thus be analytically calculated as the intersections of the reflection rays with the corresponding incident rays. In this paper, the proposed method is applied to reconstruct the samples on the specular three-dimensional weld pool surface in GTAW (gas tungsten arc welding). Since two diffusive planes are used and must be placed with considerable distance to assure the accuracy of the calculated equations of the reflected rays, focusing reflected laser rays on these two planes becomes an issue. A trade-off among the size of the projected laser pattern, the distances of the arc light with the two diffusive planes, the focus range of the laser rays and the quality of the reflected laser dot images on the diffusive planes has been made to resolve this issue successfully. Further, calibration errors in the locations of the diffusive planes directly affect the accuracy of the calculated equations of reflected rays and an accurate calibration appears to impractical. To resolve this issue, the authors found the least deformation principle and successfully applied it to minimize the calculation errors through calibration rectification. Several weld pool surfaces have been sampled and reconstructed and experimental results verified the effectiveness of the proposed analytical method.