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module assembly for a popular model. To meet the required just-in-time next- day delivery requirements, Wellington installed a robotic-welding cell within an e-coating facility.
“This reduced the number of con- tainers required from 300 to 100,” says Richards, “allowing us to be extremely
The first two robots (far right, top photo) in the bumper-assembly cell make resistance spot welds to hold the bumper components in place, functioning as tack welds for further welding operations.
Then, three material-han- dling robots (bottom photo) take over, moving the assembly through a series of operations in stationary resistance- welding machines. The cell pumps out more than 100 bumper assemblies per hour.
competitive on the project while expe- diting shipments and streamlining the production/delivery process.”
Next, late in 2011, came another bur- geoning program for another Tier One supplier, a takeover job that proved a perfect fit for Wellington’s goal to become a prime source for front-end modules.
“When we gained that second front- end-module program,” says Richards, “we partnered with ABB Robotics to help us develop new robotic-welding cells rather than rely on the existing equipment used by the original sup- plier. We’d had previous experience with ABB on a robotic laser-trimming line working with hot-stamped roof side rails, and that gave us the confi- dence to use them for our first big inhouse robotic-welding project. And the rest, as they say, is history.”
A Stampede of Robotic-Welding Work
With an impressive pair of robotic- welding projects under its belt, Welling- ton had made its mark. In short order, it added a third ABB robotic-welding cell, to fabricate upper cross members. Next came a pair of robotic arc-welding cells used to assemble both steel and aluminum parts. This work required Richards and Wellington to tackle unique challenges.
“We work to modify tolerances to best navigate process variances,” he says. “This means that in the press- room, we have to learn to design the stamped parts to accommodate the distortion, or drift, we experience dur- ing arc welding.”
In addition to predicting (using simulation software) and adapting its metalforming processes to accom- modate the heat input from arc weld- ing, Wellington also has adopted the MIG-brazing process on certain assemblies. This process promises to deliver significantly less heat input than does traditional gas-metal-arc welding. MIG brazing, using power supplies from Fronius, employs a cop- per-based filler wire with a relatively low fusion temperature—typically 1600 to 2000 F—and weld current typ- ically in the 40- to 130-A range. The rel- atively low process temperature—no fusion of the base material takes place—generates several benefits, including minimum distortion, less zinc vaporization and fume genera- tion, and reduced or, in some cases, eliminated weld spatter.
Tips for Spot Welding Boron Steels
Source: Wieländer and Schill UK Ltd
To spot-weld boron steels, metalformers must pay close attention to three parameters:
• Electrode force
• Weld power
• Tip size and shape
Electrode force must be greater than 300 kg, to ensure the workpiece materials
are kept firmly in place and will fuse correctly at the spot. With weaker electrode force, the sheetmetal may explode (spark fiercely) and leave porous, weak welds.
Welding power needed to correctly fuse the steel must be at least 8000 A for the entire welding process, not just for a momentary spike of power at some time during the weld. Each spot weld must have a very small burn mark around it so that the strength of the steel remains constant.
With lower power or longer burn times, the welds will have a bigger burn mark and the integrity of the welds will be compromised.
Weld tips should be flat, not domed or pointed. The essence of the profile is to give a flat weld that does not push into the surface of the steel, which would in turn weaken the steel at the spot.
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