Visualization and simulation of 1700MS sheet laser welding based on three-dimensional geometries of weld pool and keyhole

Laser butt welding experiments assisted with high speed imaging were conducted to isochronously observe the keyhole and weld pool in this study. The time-averaged characteristics of the keyhole and weld pool geometries were extracted by image processing. The characteristics contained the upper width, bottom width and upper length of the weld pool, and the diameter and inclining angle of the keyhole. The effect of welding speed on the characteristics was investigated and the results showed the increased welding speed gave rise to a decrease in the keyhole diameter and the weld pool widths, while the weld pool upper length firstly decreased from 5.795 mm to 4.308 mm until the speed was 4.2 m/min, and then increased to 4.941 mm when the speed was 6.9 m/min. Based on the measured time-averaged characteristics, a double cylindrical heat source model considering the keyhole angle and diameter was derived to predict the weld size. Thermal analysis based on the heat source model was performed and the prediction results were validated using the time-averaged characteristics and the single weld cross section sizes respectively. The results showed the model had good simulation accuracy (7.20%-12.48%) for sub-millimeter weld cross section and had good adaptability of multi-process parameters. The max difference in the errors of the two validations was 3.92%, indicating the thermal analysis validating with the time-averaged results had higher accuracy.