Referring now to FIGS. 6 and 7 the broad aspect of the present invention is illustrated. When torch T is transversely moving across backing plate A, wire W is melted by arc C as is the consumable back plate A. This creates a molten metal puddle P. As shown in FIG. 6, when welding wire W is moved by torch T at a rate greater than the formation of puddle P, the arc moves forward of the end 120 of puddle P to have a high tendency to cause a blow through indicated as hole BT. If correction action is not taken, hole BT becomes a kerf and cuts along plate A causing the plate to have a rough and uneven undersurface with metal protrusions. In accordance with the invention, the blow through that creates hole BT is sensed. When a blow through is detected, torch T is reversed in its movement along the selected welding path. When this occurs, wire W and arc C are at a position over the puddle as shown in FIG. 7. This causes the molten puddle to have a cavity 130; however, the molten metal in puddle P fills hole BT. Thereafter, torch T moves in the direction indicated in FIG. 6 over the filled blow through hole. Consequently, in this aspect of the invention, a blow through is detected. Torch T is reversed to fill the blow through hole and create a molten metal puddle below torch T. The puddle prevents arc blow through. As shown in FIG. 8, torch T has been pivoted toward end 14 of rail 10. At the intersection between plate A and edge 140, there is an illustrated blow through causing hole BT. When this occurs, torch T is reversed in direction as shown in FIG. 9 allowing puddle P to move forward and form a fillet between edge 140 and plate A now shown as molten metal mass 150. In this illustration, an unforced blow through occurs as the wire reaches edge 140. The reversal of torch T is in the transverse direction. If a blow through occurs as the torch is moving along edge 140, no reversal will take place. The blow through forms an ideal fillet joint at the lower edge 140 of rail 10. As will be explained later, it is desirable to periodically cause a blow through at the fillet joint along edge 140 of the rails 10, 12. If there is no unforced blow through, a blow through is forced by another aspect of the present invention as schematically illustrated in FIGS. 10-13. At the fillet, the wire will experience various conditions as shown in FIG. 22. With a gap as shown in the top view, a blow through is highly probable. With an overlap as shown in the bottom view, a forced blow through will most likely be needed.

2023 April-10