Laser weld penetration estimation using temperature measurements

Penetration depth is an important factor critical to the quality of a laser weld. This paper presents a 3D heat conduction model with a moving line so urce to correlate the temperature measured on the bottom surface of the wor kpiece to the weld penetration, weld bend width and welding speed. Temperat ures on the bottom surface of the workpiece are measured using infrared the rmocouples located behind the laser beam. The averaging effect due to the t emperature measurement spot size is analyzed. This paper provides a model-b ased approach for laser weld penetration monitoring instead of a pure empir ical correlation between a measured signal (e.g., acoustic, infrared) and t he penetration depth. Experiments were conducted to compare the depth estim ation based on the model to bead-on-plate welds on low carbon steel plates of varying thickness at different laser power levels and speeds. It is show n that the temperature on the bottom surface is a consistent indicator of p enetration depth and that the correlation is also sensitive to the sensor l ocation as well as other process conditions such as weld shape, width, and the plate thickness. The proposed model is computationally efficient and is suitable for on-line process monitoring application.