Real-time estimation of weld penetration using weld pool surface based calibration

Appropriate depth of weld penetration is required in many precision joining application but the weld penetration underneath the work-piece is not directly/conventionally measurable during the welding process. This work aims at establishing an analytic model to correlate the measurable weld pool surface to the development of the weld pool. To this end, the analytical solution of single-ellipsoidal static heat source in finite thick plate is used to calculate the temperature filed that provides the penetration of the developing weld pool. However, the analytical solution may not be as accurate as expected because the convection, radiation etc. have been omitted in order to obtain the analytic solution. A 3D measurement of the weld pool surface is thus used to calibrate the size and shape of the calculated weld pool such that the analytical model after the calibration will provide weld pool boundary and penetration to control the welding parameters. It is found that such calibration that combines analytic model and on-line weld pool surface can provide an estimation for the weld pool underneath the work-piece with an accuracy better than 90% in all three dimensions. As a result, the weld pool development will be able to be dynamically controlled to assure the desired weld penetration for the desired weld integrity as well as for future optimal control of the welding process.