Wire Feeding Methods for Narrow Groove GMAW

Several different wire feeding methods can be used when narrow-groove-gas-metal-arc-welding heavy-section materials that have nearly square butt configurations and minimal groove widths of approximately 13 mm (½ in.).

AWS Publications | April 4, 2022 | Processes
Welding Digest ►  Wire Feeding Methods for Narrow Groove GMAW

Several different wire feeding methods can be used when narrow-groove-gas-metal-arc-welding heavy-section materials that have nearly square butt configurations and minimal groove widths of approximately 13 mm (½ in.).

Narrow groove gas metal arc welding (GMAW) is an efficient, multipass technique for joining heavy-section carbon and low-alloy steels with minimal distortion, but it requires special precautions to assure that the tip of the electrode is positioned accurately for proper fusion into the groove faces. Numerous wire feeding methods have been devised and successfully used in production environments.

 

Photo: Typical wire feeding techniques for narrow groove GMAW.

 

In one, two wires with controlled cast and two contact tips can be used in tandem. The arcs are directed toward each groove face, producing a series of overlapping fillet welds. The same effect can be achieved with one wire by means of a weaving technique, which involves oscillating the arc across the groove in the course of welding. This oscillation can be created mechanically by moving the contact tip across the groove. However, because of the small contact tip-to-groove face distance, this technique is impractical and seldom used.

The weaving electrode technique uses a contact tip bent to an angle of about 15 deg. Along with a forward motion during welding, the contact tip twists to the right and left, giving the arc a weaving motion.

The waved electrode technique is more sophisticated. During feeding, this electrode is formed into a waved shape by the bending action of a flapper plate and feed rollers as they rotate. The wire is continuously deformed plastically into this waved shape as the feed rollers press it against the bending plate. The electrode is almost straightened while passing through the contact tip, but it recovers its waviness after having passed through the tip. The continuous consumption of the waved electrode oscillates the arc from one side of the groove to the other. This technique produces an oscillating arc even in a very narrow groove, with the contact tip remaining centered in the joint.

The twisted electrode technique was developed to improve groove face penetration without moving the contact tip. The twist electrode consists of two intertwined wires that, when fed into the groove, generate arcs from the tips of the two wires. Due to the twist, the arcs describe a continuous rotational movement that increases penetration into the groove face without any special weaving device.

These arc oscillation techniques often require special feeding equipment. An alternate method has been developed in which a larger electrode (e.g., 2.4–3.2 mm [0.093–0.125 in.] in diameter) is fed directly into the center of the groove from a contact tip situated above the plate surface. With this technique, the wire placement is still critical, but there is less chance of arcing between the contact tip and the workpiece, and standard welding equipment can be used. However, it has a more limited thickness potential and is normally restricted to the flat position.

 

This article was excerpted from the Welding Handbook, Ninth Edition, Volume 2, “Welding Processes, Part 1.”