The Tie-In Procedure
The process of joining a bead, in this case the root bead, is called a tie-in. The previous weld may be a tack weld or it may be the first half of the root bead. In either case, the two welds must be brought together smoothly and without discontinuities.
Making a tie-in requires extra care in welding. It is easier to make a good tie-in if the edges of the existing weld are ground to a feather edge, as shown in Fig. 5-11. This is done with a hand grinder, using a thin grinding wheel. When the ends of the existing bead are ground to a thin edge, the metal in the bead will heat up more rapidly than
GRIND SIDES TO SMOOTH ROUND EDGE GRIND ENDS TO SHARP FEATHERED EDGE
Courtesy of the Hobart Brothers Co.
Fig. 5*11. Edges of a tack weld ground to a feather edge in preparation for
making a tie-in.
in the case of an unground edge, where there is a. relatively large bulk of metal.
Sometimes facilities are not available for grinding the edges of the existing bead, and the tie-in must be made to an underground edge, which is a more difficult job. Since this situation does occur, the beginner should first practice making the tie-in to an unground edge. Having mastered this technique, he will have no difficulty in making a tie-in to a feathered edge.
Sometimes the tie-in must be made on approaching the keyhole, while at other times it must be made by approaching the opposite, heavy end, of the bead. These conditions are shown in Fig. 5-12. Two different welding techniques must be used in these cases.
TACK WELD OF TACK WELD
Fig. 5-12. A. Tie-in being made to heavy end of bead; B. Tie-in being made to
keyhole end of bead.
When the root bead approaches the keyhole, maintain the same speed of welding used to deposit the bead. Weld toward the previous weld at this speed and then gradually close the keyhole. As the keyhole is beginning to close up, watch the liquid puddle. When the liquid puddle appears to have joined the previous weld in a smooth pattern, withdraw the electrode by simultaneously reversing the electrode beyond the point of the tie-in and lengthening the arc somewhat; then break the arc with a sudden movement.
Sometimes the keyhole will become enlarged as the arc approaches the point of the tie-in. In this event, the whipping technique is used to cool the metal and to avoid excessive penetration at the tie-in. If necessary, there should be no hesitancy in using the whipping technique; however, the welder must be sure that there is penetration to the bottom of the root face at the tie-in. A perfect tie-in is shown in Fig. 5-13.