To estimate the weld pool shape in gas tungsten arc(GTA) welding in which a filler wire in fed, it is essential to derive an analytical solution to predict the transient temperature distribution of the plate. An analytical solution is derived from the transient three-dimensional heat conduction equation by applying a convection boundary condition to the top and bottom surface of an infinite plate which has a finite thickness. The electric arc is assumed to be a moving heat source with a Gaussian distribution. The point heat sink is located in the spot where the filler wire is fed to the weld pool. However, the feed position of the filler wire is ever with time because the size of the weld pool changes in accordance to the welding conditions. Nevertheless, the algorithm capable of determining the presented certain point. Also, the influence of the filler wire on the temperature distribution of the plate is unveiled by removing the filler wire from the analytical solution and comparing these two different situations. In order to verify the validity of this solution, a GTA welding experiment is conducted for various welding conditions. And after this stage is through, the resulting isotherms of the cross sections of the plate and the analytical results are compared. Proved analytical solution which is in good agreement with experimented results, it is the very first to put the filler wire deliverance into consideration.
But, to estimate the weld pool shape using the analytical solution, it needs much time to calculate the isotherms for melting temperature. Therefor, this paper propose a very simple monitoring device which is adapted the principle of the welding process. The filler wire of GTA welding is fed from the front side of the welding torch in progress, and must be fed to the liquid and solid boundary of the weld pool. If this is accomplished correctly, it can be fed actively to the weld pool from every welding position. To do like this, the filler wire is fed by pressing down the plate. At this moment, the filler wire is bended and can be measured the bending force on it. Monitoring device is set up with one load cell and some link system, in order to measure the bending force on a certain point of the filler wire. By experiments, the relation between the weld pool size and measured filler wire bending force is revealed and this can be put to use as a useful device to estimate the weld pool size. Finally, the design method of the optimal weld parameters is proposed by using standard genetic algorithm. Results of the simulation are presented and verify them with searching the fitness surface.
