October 2008 Edition

ROBOTICS

Robots to the Rescue

Many fab shops in the U.S. are getting pounded by foreign competition, but LB Steel, LLC/Coburn Steel Products is successfully fighting back – thanks in part to robotic welding

LB Steel, LLC/Coburn Steel Products is an industry leader in certified chemistry plate, prime A-36, A572 GR 50 fabrication, machining, and counterweight solutions. Much of the facility of the Harvey, IL, company is dedicated to fabrication. Most of the welding it does involves large, heavy components for the construction, railroad, and mining industries, as well as various OEMs.

Products include heavy counterweights for forklifts, man-lifts, elevators, separators for mining, and oil pans for locomotive engines. Materials used include carbon steel, stainless steel, mild steel, A36 or high-strength alloy steel, and aluminum, and range from light 10- or 12-gage metal to steel up to 4" thick. Quality is an important company goal, and finding skilled welders is a challenge. In order to improve productivity and quality, it looked to robotic automation.

"Except for one older robot from a European manufacturer, all the welding in the plant was being done manually," Mike Powers, a manufacturing engineer who joined LB Steel/Coburn in 2002, said.

"The old robot had some reliability issues and was costly to run in terms of both consumables and replacement parts," he said. "Controller boards and other spare parts were expensive – $8,000 for this, and $6,000 for that – as well as hard to get. Programming had to be done by a representative from the manufacturer, which was also expensive."

In 2004, LB Steel/Coburn began manufacturing a large volume of parts, used in rail industry discharge gates, that had significant potential to be welded robotically with little setup or fixturing. Owner Michael Goich, and Michael Powers, engineer, both saw the need for a new robotic welding system.

Impressive ’bots

"When it was time to get new robots, we looked around, but one robot company in particular really impressed us," Powers said. "I had a Motoman ArcWorld 1000 robotic welding cell previously, so I was familiar with the robot programming language, and also knew the company’s support was good.

"Plus, the Motoman training facility is only a few hours away, so the decision was easy."

“Using the robots versus manual welding, we’re able to produce parts three to four times faster”

In early 2006, the company implemented the first of three state-of-the-art Motoman robotic welding cells from Motoman Inc., West Carrollton, OH. The first robotic welding cell at the Harvey facility was a modified FabWorld solution that consists of a Motoman HP50-20 robot with a 44.1 lb payload, 122.3" reach, and ±0.006" repeatability.

The extended-reach robot rode on a 6'-long, three-position pneumatic shuttle track located between two heavy-duty Motoman MHT3000 headstock/tailstock positioners.

These headstock/tailstocks have a maximum payload of 13,889 lb and a 39.4" maximum sweep radius. Motoman’s MotoMount HD fixture mounting system eliminated the need for precision headstock/tailstock alignment.

LB Steel/Coburn provided its own part fixtures for the positioners.

"The fixtures are modular and interchangeable, so changeover is easy," Powers said. "We use locating pins and bushings to mount fixtures onto large frames that span between the positioner head- and tailstocks, so they are easy to just drop in, as needed.

Flexible Coverage

"Having the robot mounted on the shuttle track provides additional flexibility and allows us even better coverage to access welds on large parts," Powers said.

Welding equipment includes Miller AutoAxcess 450 welding power source packages with water-cooled Tough Gun torches that use 0.045" or 0.052" ER70S6 solid wire from 1,200 lb bulk boxes. The robot uses an automatic nozzle cleaner – reamer/sprayer – and wire cutter. Shielding gas is a 90/10 Argon/CO₂ mix. High-speed – 200 V – seam-tracking and touch-sensing functions are also included.

The FabWorld cell has two load/unload stations. Two fence-mounted remote operator stations with thumbwheel switches for program selection and manual jog joysticks to facilitate part loading are included.

It also features a safety environment that meets the ANSI-RIA15.06-1999 standard and includes light curtains, wire safety fencing, and an interlocked 4' sliding gate.

Parts are run in batches that range from several hundred parts to thousands. The operator uses an overhead hoist or a forklift to load the parts onto the fixtures. The FabWorld cell’s primary use is for single-pass welding.

"Using the robots versus manual welding, we’re able to produce parts three to four times faster," Powers said. "We’re also saving a tremendous amount of handling with the automatic positioners."

In 2007, LB Steel/Coburn added a stand-alone HP50-20 robot at the Harvey facility with the primary purpose of multi-pass welding on parts that are located on stationary tables.

The cell produces a large volume of parts used in big man-way portals for a major mining equipment company.

"Manually welding these parts would take anywhere from 10 to 12 hours; using the robot, they can be welded in only 2-1/2 to three hours," Powers said.

Also in 2007, the company implemented a Motoman ArcWorld 4000 cell at its facility in Chicago Heights, IL. The system includes a Motoman EA1900N Expert Arc welding robot with a 6.6 lb payload and 75" reach with ±0.003" repeatability.

This robot features integrated cabling through the upper arm, which reduces interference and makes programming easier.

Parts are fixtured on a MSR2S-500-2.0 high-speed double-ended headstock/tailstock positioner with a 1,102.5 lb payload capacity per side. An operator loads/unloads parts from the headstock/tailstock on one side of the positioner while the robot welds on a second headstock/tailstock on the other side.

The positioner rotates the frame that holds both headstock/tailstocks to present the parts to the welding robot for processing. The ArcWorld and stand-alone robot cells use the same Miller AutoAxcess 450 welding equipment as the original FabWorld cell.

“Manually welding these parts would take anywhere from 10 to 12 hours; using the robot, they can be welded in only 2-1/2 to three hours”

All three of the Motoman robot welding cells run one shift, five or six days a week.

"We machine a lot of the weldments. We try to build parts with specific gage stops and use key data points for references," Powers said. "Using those points all the way through helps us get consistent parts and makes for better repeatability.

"With that in mind, the robots also have seam-tracking and touch-sensing. Using that combination, we can end up with some productive welding.

Non-warp Speed

"To get repeatability of parts using robotic welding, correct fixturing is important and so is the sequence of welding to avoid warpage.

"Weld appearance is key to many customers. For example, we need to be meticulous about the cosmetics when welding the locomotive oil pans," he said.

"On the oil pan job, we had almost 2-1/2 weeks tied up in programming and optimizing the weld sequence to minimize warpage from welding distortion. The results were worth it. The robot cell produces parts with the dimensional stability and cosmetics we need."

Powers creates most of the master robot jobs himself, and the cell operators make minor programming changes, as needed.

"I’ve taken classes in basic and advanced programming, seam-tracking and touch sensing, coordinated motion and multiple robot control, and ladder editor programming, as well as maintenance training at the Motoman Technical Education Center in Dayton," Powers said.

"After returning from an advanced programming class, I applied what I learned to do – a series of stitch welds. When I took the coordinated motion and multiple robot control programming class I immediately applied the training to do coordinated motion on the oil pan job the sales department brought in while I was away." he said.

Powers has embraced the robotic welding technology, and has also seen a change in worker’s attitudes toward robots at the company.

"At first, some of our welders were a little paranoid that the robots would take away their jobs. But, they’ve realized that wasn’t the case once they used them. Now our guys like the robots," Powers said.

Short Learning Curve

The operator who runs the robot cell at the Chicago Heights facility is not a welder, but had some exposure to computer programming, so he was quick to learn how to run the system and program the robot.

"He does really well," Powers said. "The Windows interface touch screen is familiar to people and it makes programming easier to learn."

According to Powers, the robots have been reliable. The company had a couple of minor issues the Motoman 24-hour hotline helped solve.

"Due to the low volume of part runs, payback for the robot cells is probably about two or three years," he said. "However, in addition to making parts three to four times faster using the robots, we have less scrap, and quality has improved.

"Quality improvement is one of the big keys in justifying these welding cells," he said. "It was the primary justification for a planned new cell that will use multiple robots to weld parts weighing 88,000 lb."

Every U.S. manufacturer has been affected by overseas competition, and LB Steel has been no exception.

"Robotic welding helped us slow job exodus," Powers said.

For his company, robotic welding machines leveled the playing field by decreasing cost of the products, improving the quality of work, and providing a consistent manufacturing process with fewer rejects. It also has helped fill the void caused by the lack of qualified welders.

"The next addition will probably be Motoman’s simulation and off-line programming software package – MotoSim EG," Powers said. "That will let us create jobs on the PC and download them to the robot controllers, instead of doing point-to-point programming with the teach pendant. This will let us keep the machines doing what they do best; saving everyone’s job." Motoman Inc.

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