The calculation-experimental determination of penetration of a spot welded by a fixed arc
The modern software systems simulating the welding process do not cover all its specific features. For example, they are too cumbersome to be applied in the penetration automatic regulation according to the mathematical model. For this purpose, the authors proposed using a mathematical model of heat distribution within the parts from a normal circular heat source acting on the flat layer surface. The coefficients of such a model should be determined by the experiments close to the data of a problem to be solved (the reduction method). The paper presents the results of hanging surfacing of spots on the 12H18N10T high-alloy steel plate of 4 mm thick. To record in time the welding arc current in argon medium with the non-consumable electrodes, the authors used the recorder. The relative deviations of the spots' diameters from the average value were checked for the compliance with the normal distribution law. It is determined that the deviations of the spots' shape from the circle do not meet this law. The average diameters of the obtained spots were used to predict the penetration depth, which was determined by macrosections with the 20 amplification. In this case, the authors used several values of axial heat flux of the heat source: 2800, 3500 and 4200 W/cm<sup>2</sup>. The values of thermal diffusivity were taken from literature data averaged a =0.04 cm<sup>2</sup>/s. Using the diameters of spots, the effective power of the welding arc and the specific effective power per 1A of welding current were calculated. The penetration of the spots was calculated using the average power density. The best convergence of calculated and experimental data was obtained at the axial heat flux of 2800 W/cm<sup>2</sup>; it averages about 5 % in absolute value. Similar results were obtained when predicting the diameters of spots using penetration depth. Thus, the authors developed the technique for determining three coefficients of the model to apply them for the welding process automatic control.