Analytic weld pool model calibrated by measurements - Part 1: Principles

Weld penetration is a major parameter determining weld integrity. However, the depth of the penetration underneath the workpiece is not directly nor conventionally measurable during the welding process. To address this challenge, the authors used an analytic model to compute the temperature distribution and then calibrate it using measurements. In this paper, Nguyen's single-ellipsoidal, stationary heat-source-based analytic solution was used to provide temperature distribution in a finite-thick plate. The computed weld pool radius for stationary welding was compared with that from the measurement. The temperature distribution was shrunk/expanded through an adjustment ratio in the radius direction (x-y directions) such that the error of the computed radius with the measurement became zero. Such calibrated temperature distribution was used to compute the increase in the volume due to thermal expansion. The resultant volume was then compared with that from the measurement on the weld pool surface. The temperature distribution was shrunk/expanded again but in the depth direction so that the volume error became zero. The temperature distribution was thus fully calibrated in all directions and capable of providing the depth of the weld penetration. An experiment has been conducted to illustrate the calibration process. The cross section of the resultant weld verified the accuracy of the calibrated model.