Abstract
In this study, transient responses of thermal cycle and bead geometry to step change in welding conditions are investigated. The experiments are made on automatic TIG arc welding of mild steel and aluminum alloy plates, and the thermal cycles and bead size are examined. These experimental results are compared with theoretical values calculated by FEM of three-dimensional heat conduction, from which the transient behaviors and factors controlling them are discussed. The main results are summarized as follows.
The transient response of maximum temperature is corresponding to that of penetration, and their transient behaviors from one quasi-state to another one depend upon the difference of heat input between two welding conditions and upon the thermal properties of materials. These results are confirmed by theoretical calculation by FEM. There are two fundamental phenomena referring to the transient response of bead geometry and maximum temperature. One is abrupt change in the molten pool due to the step change in welding condition, which results in the abrupt change of penetration and maximum temperature. Another is the delayed phenomenon due to the heat conduction which depends upon the thermal properties of material and the variation of heat input.
