Practical Welding Today - May/June 2009

When working

with aluminum,

Ekblaw said,

“The question is,

When you weld it,

can you keep

it straight?”

FIGURE 2

Some sections with this X configuration oil canned. To eliminate this, Ekblaw removed a small section of metal from the center section and filled the gap with a 100 percent-penetration weld.

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Minding the Heat

To start welding, Ekblaw tacked every joint, evenly distributing heat around Nereus. He then locked Nereus to the fixturing table and began welding, again evenly distributing the heat by shifting between the port and starboard sides and making shorter welds.

Unlike welders who leave a machine’s balance control set in one spot, Ekblaw uses the AC balance control to adjust the ratio of cleaning action (duration of the electrode-positive half-cycle) to penetration (duration of the electrode-negative half-cycle, when the heat flows from the tungsten into the workpiece).

“I really like Miller square-wave machines because of their balance control,” he said. “I make constant adjustments. As the heat builds up, I turn down the penetration. If I see the weld puddle is a little cold, I turn up the heat.”

Ekblaw welded Nereus only in the flat, horizontal, and vertical-up positions, moving Nereus’ frame as necessary.

“I think vertical-up helps ensure good fusion, and I can see the joint better. With vertical-down, I would be worried about the puddle rolling over the top of the joint and causing cold lap,” said Ekblaw.

Despite Ekblaw’s best efforts, distortion occurred. He explained, “The center pipe shrunk ³⁄ 4 inch. I could see from the centerline that my layout was perfect, but welding caused the pipe to shrink ¹⁄ 2 inch, and heat treating caused it to shrink another ¹⁄ 4 inch. Fortunately, the distance between the two pods doesn’t affect the design. Our primary goal was keeping the pods parallel, which we achieved.”

Welding heat also created an old-fashioned oil can problem (see Figure 2). The smaller sections on the bottom of the pods designed with an X configuration had insufficient mass to dissipate the heat of welding. They subsequently popped out of plane.

“On the sections that oil canned, I cut out a small piece of the center section and rewelded the halves. As the weld cooled, it shrunk the section and put the part back into true.”

Overall, Ekblaw said it took him 80 to 100 hours to weld the pipe main cross member, the two outside frames, and the manipulator arm sled, using about 35 lbs. of filler rod in the process. ■