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Robot deposits welds in high gear with Tip TIG

Wire-fed process approaches GMAW deposition rates, sources say

During a presentation at ABB’s Customer Day event in Atlanta in June, Mark Oxlade showed a video of a manual welder performing a vertical-up weld on a highly complex weld geometry, all with one hand. That’s no easy feat.

The welder used a process involving a tungsten electrode with a wire being fed into the arc underneath. Yet this wasn’t conventional gas tungsten arc welding (GTAW, or TIG). Instead, he was using TIP TIG, a process that ABB has now incorporated into a robot welding cell.

Siegfried Plasch, an Austrian welding engineer, invented and patented the process, which uses a constant-feed hot wire superimposed by a high-speed wire oscillation. As Oxlade explained, “This oscillation absolutely changes the characteristics of what takes place in that welding pool. When you oscillate the wire, you basically agitate the weld pool, which is key. It increases the fluidity of the pool, and that wets the sides of the joints more easily and reduces sensitivity to fit-up tolerance.”

This allows the welding torch to travel at a high speed—several times faster than conventional GTAW, according to sources. The high speeds reduce heat. “We’re approaching MIG [GMAW] speeds here,” Oxlade said.

The high speeds, low heat, and small heat-affected zone, and the fact that the process occurs in the electrode-negative polarity, also reduce the chance for weld oxidation.

The mechanical agitation to the weld pool also gives energy to the gaseous and particulate inclusions, allowing them to better evacuate the weld pool. Oxlade illustrated this with a video during his presentation. “This is slow motion; look at the pool and see how the particulate gas is coming out, giving you a very clean weld.

“A pool that’s agitated like this can accommodate more wire, reduces cycle time, and reduces heat input,” Oxlade continued. “There’s a direct correlation to speed. So we can put more wire in, we can go faster, and so have reduced heat input and distortion.”

As Oxlade explained, ABB worked for two years to interface with the TIP TIG process. This includes an integrated Ethernet interface that enables control of all attributes from within the robot controller, directly on the teach pendant. “Because it was a manual power source, we couldn’t talk to anything. So we created an interface,” Oxlade said. “We’ve worked with Tip TIG for more than two years, and now we have a launched product.”

During his presentation, Oxlade showed a setup illustrating how the process tolerates fit-up variation. “We did this setup for the oil and gas industry, and we got it so we could hold two pieces of pipe together and not require any special fixturing to go in between.”

For pipe welds and similar situations, the process has the potential to eliminate process changeovers between welding passes. “In the oil and gas world, you use one process for the root, another for the fill, and another for the cap pass. With this process, you can go from start to finish in one go.”

He added that the process characteristics give welding engineers some flexibility when developing weld procedures. “It can put as much metal down as the joint can withstand.”

If the joint can withstand a large amount of metal, the process may be able to lay down a lot of weld at once, essentially creating a massive weld in one pass. This is possible in part because the process has lower heat input overall. If the torch needs to travel a little slower to deposit more metal, the joint may be able to withstand it, since the additional heat still may not amount to much. Regardless, if the joint can’t withstand more heat, the process can weld at high speed and lay the weld down in multiple passes.

In its robot cell, called RoboTiP-TiG™, ABB has incorporated several power sources—including those from Miller, Lincoln, and Fronius—to be used with a Tip TIG system that oscillates and heats the wire as it feeds into the weld.

During his presentation, Oxlade pointed to an aerospace application involving a lap weld connecting a 3⁄16-in.-thick stainless steel sheet to a 0.5-in.-thick stainless bar. “You look at this joint, and it looks like conventional TIG,” he said. “But again, because we’re agitating the weld pool, we can go so much faster, and we can get the quality of a TIG welding process. The deposition rate for this weld was about 6.4 pounds per hour. In this world, that’s quite a bit.”

About the Author
The Fabricator

Tim Heston

Senior Editor

2135 Point Blvd

Elgin, IL 60123

815-381-1314

Tim Heston, The Fabricator's senior editor, has covered the metal fabrication industry since 1998, starting his career at the American Welding Society's Welding Journal. Since then he has covered the full range of metal fabrication processes, from stamping, bending, and cutting to grinding and polishing. He joined The Fabricator's staff in October 2007.