AN ELECTRODE EXTENSION MODEL FOR GAS METAL ARC-WELDING - SHORT-CIRCUITING TRANSFER CAN BE PREDICTED WITHIN 9-PERCENT FOR A GIVEN ELECTRODE FEED SPEED

The electrode extension during gas metal arc welding is predicted usin g a one-dimensional model of the melting electrode. Joule heating in t he electrode, heat directly applied to the end of the electrode from t he condensing electrons, and heat transferred from the droplet, togeth er with conduction along the electrode are considered. The thermal con ductivity, the thermal diffusivity, and the electrical resistivity of the electrode material are allowed to vary with temperature. The stead y-state electrode extension is predicted to an accuracy of 1.9 mm (0.0 74 in.). The onset of short-circuiting as the current is decreased for a given electrode feed speed is predicted within 9%. Dynamic analysis shows that the gas metal arc welding process acts as a low-pass filte r for electrode extension with respect to the square of the current (p roportional to power) and with respect to electrode feed speed. As the mean welding current is increased, the electrode extension (or arc le ngth if the contact-tube-to-work distance is constant) has a smaller r esponse to perturbations in the current or electrode feed speed. The q uasi-linear transfer functions between electrode extension and current squared and between electrode extension and electrode feed speed can be described by one zero, two pole parametric fits. The transfer funct ions are linear in the amplitude of the excitation up to 10% of the me an excitation. The model transfer functions were verified with experim ents.