Penetration depth estimation for monitoring CO2 laser welding processes

Abstract

Penetration depth is one of the most important factors critical to the quality of a laser weld. However, no robust, on-line, nondestructive method exists for the direct measurement of this quantity. In this paper, a model-based method for estimating penetration depth through the measurement of the weld width at the top surface and the temperature on the bottom surface is proposed. The core of this method is a model relating the penetration depth to incident power, weld width and the Peclet number which is a function of the welding speed and the keyhole radius. This model is validated by a number of laser welds made to join a low-carbon steel hub and plate assembly using a 5 kW CO2 laser with different combinations of power and speed. The feasibility of using the temperature measurement on the bottom surface below the keyhole as a signal for penetration depth is investigated. The results indicate that the proposed model and estimation scheme can provide consistent and sensitive depth estimates and are suitable for process monitoring in production environment.Penetration depth is one of the most important factors critical to the quality of a laser weld. However, no robust, on-line, nondestructive method exists for the direct measurement of this quantity. In this paper, a model-based method for estimating penetration depth through the measurement of the weld width at the top surface and the temperature on the bottom surface is proposed. The core of this method is a model relating the penetration depth to incident power, weld width and the Peclet number which is a function of the welding speed and the keyhole radius. This model is validated by a number of laser welds made to join a low-carbon steel hub and plate assembly using a 5 kW CO2 laser with different combinations of power and speed. The feasibility of using the temperature measurement on the bottom surface below the keyhole as a signal for penetration depth is investigated. The results indicate that the proposed model and estimation scheme can provide consistent and sensitive depth estimates and are suit...