REAL-TIME MONITORING of WELD POOL during GTAW using INFRA-RED THERMOGRAPHY and analysis of Infra-Red thermal images

摘要

Real-time monitoring of the weld pool using infra-red (IR) thermography during gas tungsten arc (GTA) welding is gaining importance due to the requirements for on-line monitoring and control of the welding process. To facilitate real-time monitoring of the weld pool, a computer-controlled GTA welding machine with sensing of the weld pool using IR camera has been developed. The IR camera, mounted on the torch assembly, monitors the molten pool and the surface temperature distribution surrounding the weld pool during GTA welding. Temperature profiles were measured on the plates using thermocouples in combination with IR thermography to determine the emissivity of the plate surface. GTA welding was carried out on 3 mm-thick 316LN stainless steel (SS) plates under different welding conditions. IR thermal images were acquired on-line and analysed. A linear relationship was obtained between the thermal bead width, determined by line-scan analysis technique, and the actual bead width, measured by cross-sectional optical microscopy. The computed macroscopic temperature gradient and the actual of weld bead depth of penetration showed an inverse relationship. Full-frame analysis was carried out to estimate the surface temperature distribution for square-butt weld joints. For 316LN SS weld joints, IR thermal signatures were acquired for various weld defects, such as lack of fusion, lack of penetration and tungsten inclusions, for use as reference signatures for on-line monitoring during GTA welding.