Six Robotic Welders Help Utility Produce Aluminum Platforms

July 1, 2000
Robotic MIG welding of 48-foot aluminum trailers has upgraded product quality and improved productivity at the Utility Trailer plant in Enterprise, Alabama.To

Robotic MIG welding of 48-foot aluminum trailers has upgraded product quality and improved productivity at the Utility Trailer plant in Enterprise, Alabama.

To prepare for the introduction of its new aluminum and steel hybrid flatbed trailer, Utility made substantial changes to the plant, including new tooling and the introduction of robotic welding. The side rail, a welding-intensive subassembly, was a key reason Utility decided to use robotic welding, according to Grant Barton, director of manufacturing at the Enterprise plant.

Implementing a sophisticated robotic welding system, however, was not easy-even with the help of a systems integrator to design and implement the initial robotic system. Barton soon realized that the integrator's plan was not yielding the levels of quality and productivity needed.

"It was a difficult decision to turn to another integrator, but we knew that there had to be an answer," Barton recalls. "We recognized that successful robotic welding of aluminum requires a special knowledge of both robotics and welding, skills the first company did not have."

Utility chose another company, Progressive Systems Inc of Richmond, Kentucky, a systems integrator with a close relationship with Panasonic Factory Automation of Franklin Park, Illinois. Barton selected the vendor after visiting two aluminum welding operations-one designed and executed by Progressive Systems, plus a second Panasonic installation in Kansas City. The visits convinced Barton that a robotic aluminum welding system could effectively produce the aluminum welds required to manufacture the new platform.

The initial installation used two robots mounted on a belt-driven servo-controlled track to travel the length of the rail. The new system uses six stationary robots to produce the welds for the trailers. In implementing the revised system, Utility kept the two Panasonic AW-005AL robots from the original system and added four new Panasonic VR-006AL robots.

The robots are teamed with a Panasonic RA-350 welding power source. Utility bought the RA-350 power source in part because it addressed one of the keys to a successful robotic welding operation-consistent, repeatable arc starts. The RA-350 welding power source is a microprocessor-controlled machine designed specifically for MIG welding aluminum.

Working Together Another consideration was how well the individual components work together. The system that Utility implemented consists of components that were designed and integrated by Panasonic right from the start. The alternative would have been to integrate elements produced by different manufacturers to work together at maximum efficiency, often a difficult task, according to John Foust, president of Progressive Systems.

Foust made his purchasing recommendations following an analysis of the original robotic system.

"We evaluated the processes during a two-week on-site study to determine if significant improvements in productivity were feasible," he says. "As configured, cycle times were two hours, plus some manual welding was also required. We observed, as did the supervisors at Utility Trailer, that the original system was operational, but not sufficiently efficient. Therefore, operating efficiencies were our primary target. For example, a critical production planning factor, estimated cycle time, was grossly incorrect. Another of the needs we identified was to provide adequate training for the operators. It is critical in a robotic installation that several people be fully qualified to program, operate, and maintain the work cells, plus fully understand the details in welding aluminum."

Two Utility Trailer maintenance people and one operator trained at Progressive Systems' facilities. This step alone doubled uptime for the robot, according to Barton.

Installing the System Following Barton's authorization, Progressive Systems spent the next 14 weeks planning and implementing the revisions, beginning with the removal of the servotrack device and the installation of the six new robots. In one set of rails, there are 814 arc starts, all of which are on aluminum and must be exact.

Beyond knowledge of robotics, however, the installers also must have expertise in welding, Barton says. For example, Foust had the robot operators use an alcohol-based, spray-and-wipe cleaning just prior to robotic MIG welding to assure porosity-free welding.

Because of the size of the rails (48-ft-long by six-inch-wide by quarter-inch-thick aluminum extrusions), distortion wasan issue. The Progressive Systems team planned on thermal expansion of 3/8 to 1/2 in by including a touch sensing system on each of the six robots. This technique uses the aluminum welding wire itself as the sensing mechanism. Therefore, the touch sensing allows the arc to consistently start in the weld joint, regardless of the thermal distortion.

Barton noted the final results were dramatic. "This new robotic cell increased productivity dramatically. Previously, we were able to produce 11 sets of rails on the robot (with significant additional manual welding) in a two-shift workday. We had to supplement that output with manual welding of five sets of rails to achieve the required 16 rails per day. We now produce all 16 rails in only one shift each day, with no added manual welding.

Manual welders were reassigned within the plant to provide other services."

Barton says he also gained the ability to make a full 1/2-in fillet weld in a single pass. Alan Traylor, Panasonic product manager, says this is the result of the RA-350 machine's ability to control the welding arc's waveform and the resulting welding parameters.

Securing Cargo Tie-Downs Quality was another major factor. The robot can produce a stronger weld, as shown by Utility Trailer tests. Like its predecessor, the new Utility trailer uses aluminum pipe spools as anchor points for chains or other devices to secure loads. The side rails of the previous design, when subjected to tensile testing, typically were able to withstand approximately 32,000 pounds of force applied to the chain.

"Today when we test the robotic welded rails, the rails can withstand 39,000 to 40,000 pounds," Barton says. "We have gained as much as a 23% increase in strength. We also observed a more aesthetic weld, which is important since these welds are visible to the customer. Anything that makes the trailer look good to our customer is significant."

Future Plans Progressive Systems and Utility Trailer both have plans involving robotics for the future. The systems integrator has retained the services of Dr Joe Li, a PhD welding engineer from the University of Kentucky's Center for Robotics & Automation. Li is conducting research on the impact of key variables in robotic welding such as torch angles, crater fill techniques, and quality issues such as undercut and weld tie-ins in multi-pass applications.

As a result of the robotic installation at the Enterprise plant, Barton says Utility Trailer management is committed to robotic welding at its dry freight plant in Arkansas with the combined assistance of Progressive Systems and Panasonic. Panasonic Factory Automation Company is a Division of Matsushita Electric Corporation of America.