Sensing and control of GTAW welding process using a point infrared sensor

The thermal phenomena associated with the gas tungsten arc welding process was studied to monitor and control weld penetration. One analytical model developed by previous investigators was used to study the 3-D quasi-steady-state temperature distribution of the weldment. The focus of the theoretical analysis was to study the relationship of temperature at certain point inside the HAZ (Heat Affected Zone) and the penetration of the weld. The weld penetration conditions were investigated in three types of situation: (1) plate with constant thickness; (2) plate with step changes in thickness; (3) plate with different back-face convection coefficients.;One point infrared sensor was developed using self-powered thermopile detector. Two distinctive advantages of this self-developed device, compared with other infrared devices, are low cost and arc interference resistant. A feedback penetration control system was built around an IBM PC-compatible computer. The developed system was used to weld three types of plates which correspond to the plate configurations used in the theoretical analysis. The plates were then cut and penetration of the plates was measured. The results show that the theoretical predictions conform well to the experimental values. The PID (Proportional/Integral/Differential) feed back controller can greatly improve the penetration of the weldments under perturbation situations.