Club Car's ABB robotic arc welding system helps the company produce 25,000-30,000 aluminum-frame gasoline-powered golf car frames per year. Four ABB IRB 1400 robots weld about 130 welds per Club Car frame. Club Car Carryall 1 carts in their completed state.

According to Project Manager Rusty Johnson, company officials decided in the early stages of automation planning to concentrate on applying the new welding technology first to gasoline-powered car frame manufacturing. A cross-functional team spent two years designing and testing a new frame design to make it robotically compatible before the system was installed about two years ago. The team focused on designing stronger joints that would also be easier for the robot to access, and achieved both of these goals by using interlocking parts with lapped and fillet joints.

"The whole focus was to try to get as many welds as possible completed with the robot," said Johnson. "On the final product we designed, there's about 130 welds that could be done by the robot, and of the 130 we can get to about 128." The remaining two are welded manually by an operator while the robot is welding.

Floor space was a primary concern in designing the system. Assembly-plant personnel needed the ability to increase production without a corresponding increase in floor space. Much of the equipment—including welding machines, robotic controls, and water chillers—was placed overhead on a mezzanine, saving 46 m2 (500 ft2) of floor space. The rest of the cell configuration is also unusual. "Our fixture was too large—about 2.4 m (8 ft) long and about 1220 mm (48 in) wide—to go with a standard rotating table, so ABB had to come up with a different scheme to get the part and fixturing in front of the robot," said Johnson. The solution involved two ABB IRBP Orbit 750L positioners. Mounted on a 15-m (50-ft) servo track, they move to place the various parts in the correct position for welding by four IRB 1400 robots located along the track. The setup enables large parts to be turned and welded on all sides.

The positioners can hold up to 1650 lb (750 kg) each. The capacity is necessary—even though the car frame has a mass of only about 27-32 kg (60-70 lb)—because each positioner must hold and support the mass of a number of steel locators and pneumatic clamps required to hold the 30 different parts of the frame. The unusually large number of parts, along with all of the locators and clamps, required a system of "checks and balances" to ensure that all parts, particularly those that are small, are in the right location and loaded correctly before being clamped into place. Therefore, Club Car's system uses a Flex I/O programmable logic controller (PLC) on each fixture that communicates with the robot system's Allen-Bradley Remote I/O PLC. An important advantage of the ABB system's S4 controller is its ability to interface directly with the Allen-Bradley system without special wiring, though some additional software programming is necessary.

Along with flexibility, two other features of the ABB system were important to Johnson and his team. He explained: "With these robots, we have 25 to 42 welds apiece, and with that many welds you're going to be bumping and rubbing and banging around a little bit with the torch, so it's necessary to have an automatic torch alignment system." The ABB system can make 3-D and angular calculation via its BullsEye automatic TCP calibration system, he added. The BullsEye system adjusts the program to the torch, eliminating the need for touchups. "We needed to run the system for as many hours per day as possible, and not be standing with the teach pendant in our hands touching up weld programs. That's one of the main reasons we chose ABB."

Another reason Club Car chose the ABB system is its automatic error-handling capability—a necessary feature when the robots complete almost 130 welds on each frame. "Special error handlers were developed by ABB for us," Johnson said. "We have four robots in the cell, all welding on the same part at the same time, so there has to be some communication between the robots." To accomplish this, ABB used robot I/O between all four robots. If one robot has an error, it communicates it to the other three. The other robots finish the weld they are doing, but will not move to the next weld until they receive a "clear to go" signal. In the meantime, the robot with the error automatically goes to a service position where an operator checks the problem.

Programming four robots to weld simultaneously was a challenge. Adding to the complexity was the need to program error handling as well as welding. Each group of welds had to have its own error handler program, so developers had to keep in mind the path of each robot and make sure that it wouldn't cross the path of another robot. Johnson and other members of the team went to ABB in Fort Collins, CO, and spent about six weeks writing these programs.

The system was delivered in October 1997 and began production in early 1998 in time for Club Car's peak season. Since that time, the company has produced 25,000-30,000 gasoline car frames per year—operating 24 h per day, six days a week, during peak season from January through June. Two people operate the system during peak season; one loads each fixture while the robot is welding in the other. During the off-peak season, the company usually runs with one fixture and one person for half the peak output. All of the operators are welders trained to run the robots. Cycle time for a complete frame is 12 minutes, including 6 minutes for the operator to load the fixture, and 6 minutes for the robots to weld the part. The cycle time compares with 27 minutes to manually weld the frame—a savings of more than 50%.

For more information, visit www.abb.com, call 800-242-3722, or circle 57.

SAE Off-Highway Engineering June 2000