A model for estimating penetration depth of laser welding processes

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Abstract
Penetration depth is one of the most important factors critical to the quality of a laser weld. However, no on-line, non-destructive method exists by which to inspect this quantity. Indirect, model-based estimation schemes are feasible solutions for monitoring laser welding processes. In this paper, a model for estimating penetration depth based on a 2D heat conduction model and a conical keyhole assumption is developed. This model relates the penetration depth to the incident power and the Péclet number, which is a function of the welding speed, the keyhole radius and thermal diffusivity. The Péclet number is determined by measuring the weld width on the top surface. The model is validated by a number of laser welds made to join a low-carbon steel hub and plate assembly using a 5 kW laser with different combinations of power and speed. The results show that the proposed model is consistent with the experimental data and is computationally efficient. Therefore, this model is suitable as a basis for model-based, on-line depth estimation schemes.