Robots Automate Pipe Welding

Manufacturing Engineering, Sep 2005

Reinke Mfg. Co. Inc. employs nearly 400 people-about half the population of Deshler, NE, where the company manufactures center-pivot and lateral-move irrigation systems. Demand for skilled workers far outstrips the available supply: at one point, the company had more than 50 job openings. With production demands increasing and no end to the labor shortage in sight, Reinke recently implemented robotic automation.

The fully automated, 60' (18.3-m) long system includes 10 robots that weld flanges, brackets, and couplers onto irrigation pipes, and also perform plasma cutting of holes and material handling. Six of the 10 robots automatically change end-ofarm tooling to perform multiple processes-either material handling and arc welding or material handling and plasma arc cutting.

Supplied by Motoman (W. Carrollton, OH), the robot system processes multiple configurations of irrigation pipe with 6, 6 5/8, and 8 5/8'' (152, 168, and 219-mm) diameters in 19, 24 and 38' (5.8, 7.3, and 11.6-m) lengths. Wall thickness of the carbon steel pipes is 0.100'' (2.54 mm), and they weigh up to 380 lb (172 kg) each. Component tolerances allow a nominal fit-up clearance of 0.050'' (1.3 mm) to accommodate automated assembly and welding processes. Because steel pipes grow and shrink with temperature variation, pipes are singulated and plasma-cut to length shortly before coming to the robot cell in order to maintain ±1/16'' (1.6 mm) length tolerance.

For each pipe, two UP350-200 robots each pick up a pre-oriented pipe flange from one of two 180° indexing positioners located at opposite ends of the workcell. The robots place their respective flanges in the Station 1 flange welding station headstock/tailstock. A tube dispenser loads . a pipe into the infeed conveyor, trims it to length, and moves it longitudinally into the weld system, positioning it up against a solid stop.

Moving with coordinated motion, the two robots grasp a pipe by both ends and transfer it from the staging area to roller steadyrests in Station 1. The robots are equipped with a parallel gripper for pipe handling and a three-jaw chuck that grabs flanges and also picks up a welding torch for flange-to-pipe welding.

"This is one area where we initially had some difficulty both in design and application," recalls Manufacturing Engineer Brian Schardt. "Reinke's flange-to-flange seal is unique in the irrigation industry. The pipe is inserted through a tapered flange to create a pocket for our V-Ring seal, which provides a positive seal with no water restriction. "

Because the pipe had to insert through the flange on either end of a 38' pipe with a gap smaller than 0.050", Reinke made changes to the flange design based on a recommendation from Motoman engineers to aid in part fit-up and create a stronger weld joint. The design of the tapered knives in the headstock and tailstock of Station 1 made it possible to guide the pipe through the flange ID.

One of the robots is mounted on a 19' servo track, along with a bulk weld wire feeder, tailstock with fixture, and Station 1 steadyrest. This robot moves along the track to push the pipe into the flanges. Tapered knives center the pipe during pipe and flange assembly. Pins on the headstock positioners locate the flanges, and pneumatically actuated paddles clamp the flanges during welding.

Next, the same robots pick up two welding torches for simultaneous welding of the two flanges while the headstock/tailstock rotates the pipe. Automatic nozzle cleaning/torch reaming occurs at preset intervals.

The robots return the welding torches to their nests, then grip the welded pipe/flange assembly and transfer it from the flange welding station to the bracket/coupler welding station (Station 2). Pneumatic steadyrests automatically adjust 4" (100 mm) longitudinally, as necessary, to accommodate bracket and coupler placement on the different pipe configurations.

During flange welding, four Motoman UP20 robots equipped with two-jaw parallel grippers pick up plasma cutting torches and cut holes for anywhere from two to 15 couplers in a pipe/flange assembly. After cutting the requisite number of holes, the four robots set down their plasma cutting torches, pick up one bracket each from one of two vibratory feeders, and position the brackets on the pipe for welding. Four UP20-6 robots, equipped with welding torches, tack and then finish-weld the brackets.

While the latter four robots weld the brackets, the first four robots each pick up a coupler from one of two vibratory feeders and place the couplers in position for tack welding. The UP20-6 robots then tack and finishweld the couplers.

All eight robots then move to a home position while the pipe ejects automatically onto an idle station. The two UP350-200 robots that started the process place a pipe/flange assembly into Station 2, then remove the finished assembly from the idle station and place it on gravity rails. Pipes transfer laterally to the next operation.

Multiple robot control technology facilitates the complex, coordinated motion required for production and automatically prevents collisions. One controller provides a single point of programming control for two UP350200 (material handling and welding) robots and two of the four external axes (servo track and headstock) at Station 1. Two controllers control four robots each and the headstock at Station 2. An Alien-Bradley SLC/505 PLC provides overall cell control.