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INSIGHT Woodinville, WA, USA Welding Fitness Equipment Is no Sweat for Robots Robots offer Precor, a fitness equipment manufacturer, the flexibility to ramp up production to meet rapidly changing order variations while producing quality, cosmetically appealing welds. The robots eliminate human errors resulting from inattention, boredom, and fatigue when manually welding assemblies that require from 80 to 175 individual welds. Robots make thousands of welds per shift on frames and subassemblies used in exercise equipment - and never even break a sweat. Robots help Precor, Woodinville, WA, make a range of premium equipment for homes and clubs, including treadmills, stationary bikes, EFX Elliptical Fitness Crosstrainers, and Stretch Trainers. "We're all about delivering an unmatched workout experience on equipment that looks as good as it feels," says Steve Larson, Precor operations manager. "Robotic welding has definitely helped us achieve these goals and gain a competitive advantage in the marketplace." In 1989, the company acquired
the first of five six-axis K6SB welding robots with ERC controllers from
Precor has used local systems integrators to help them implement the robotic welding cells, including FAM, Integrated Systems, and currently Willamette Valley Co. "If we run into any service issues, we use Motoman's RobotPro software for troubleshooting," Larson says. "If it is something our own maintenance staff can't handle and we still need help, we first call our local systems integrator. If we need further help, we call the Motoman 24-hour customer support hotline for assistance." "Through the years, we've upgraded our welding robots to stay competitive by using state-of-the-- art equipment," Larson said. "Each time we upgraded, we benchmarked the competition using Motoman robots as the standard. They really keep up with the latest advances in robotics and welding technology. We also think their robot programming language is the easiest to use," he continues. Suppliers Also Benefit from Robotics "More than a decade later, the five original K6SB robots with ERC controllers are still in production - only now the robots make parts for some of our suppliers under lease agreements," Larson says. "These robots help our suppliers keep their manufacturing costs low while also providing us with the consistent, high quality and cosmetically appealing welds that we need." One such supplier has two K6SB robots simultaneously welding high- - volume parts on a single positioner. However, the nine Motoman robots in the Precor shop are configured as single-robot workcells. "These single robot work cells provide the flexibility to match our production needs of JIT (Just In Time) MRD (Market Rate of Demand)," states Troy Brown, operations supervisor, who has seen the peaks and valleys in volume firsthand. "We produce weldments at a rate to replenish what our assembly operations used that day. The robots give us the flexibility to ramp up production to meet orders as they come in - allowing us to quickly respond to these MRD variations. Most cells usually run two shifts, depending on production needs," he says. Each system features a headstock/tailstock positioner located on either side of the welding robot. Many of these positioners include a manual jog feature, that the operator controls by a joystick on the control station. While the robot is welding on the opposite side of the cell, the operator can jog the headstock/tailstock into the optimal position for loading and unloading the large, 80 lb. frames. The operator loads and unloads parts with the help of a jib crane. The operator then uses the joystick to signal the positioner to return to it's home position. Fully integrated safety workcell protection features, including safety fencing, mats, light curtains, and arc curtains help safeguard operators. In some cells, pneumatically controlled arc flash curtains provide additional protection for the operator who is loading or unloading parts and performing quality control inspections. "Our goal is to maximize arc-on time - when the robots are actually welding on parts - so we load and unload parts while the robot is welding on the other side," Brown says. "Cycle time on large frames is approximately eight minutes per side. Some cells use coordinated motion between the robot and the headstock/tailstock during welding. The robot controller coordinates all movement. The robot welds while the positioner turns the parts. This optimizes torch access and weld angle, which results in better welds. Coordinated motion is particularly advantageous when the robots are welding joints on bent tubing," he continues. Weld Procedures Precor uses water-cooled Kobelco Sensarc welding packages with 350 A power sources on all of the robots. Sensarc technology uses feedback from a voltage sensing torch to ensure arc stability. Robotically welded parts all consist of mild steel approximately 1/ 16 to 3/16 in. thick. The number of welds on each part varies from 12 on small subassemblies to more than 170 on large treadmill frames. Weld lengths average anywhere from 2 to 6 inches. Precor uses 0.035 in. ER70S-7 wire from ESAB and a gas-assist mixture of 90 Ar-10 CO^sub 2^ for the gas metal arc welding process. Use of an assist gas improves the quality of the welds, reduces spatter, and allows the robots to weld at higher speeds, which helps reduce cycle time. At Precor, each welding workcell features a headstock/tailstock positioner with pneumatically actuated multi-stage fixturing. Precor also uses other Motoman options, such as Toolsight to calibrate the welding torches; MotoCal calibration hardware and software to improve the accuracy of their programming; and PC-based RobotPro software for troubleshooting. When Looks Are Important "At Precor, the design and appearance of our equipment is an inherent part of our competitive advantage," Larson says. "We show off the precision forming and bending of our steel, and the powder coating. Robotic welding helps us achieve this distinctive look. Plus, the weld strength and integrity are excellent," he continues. "Robots reliably produce quality, cosmetically appealing welds every time. That's a tough act for a manual welder to follow day in and day out. "The need for anywhere from 80-- 175 individual welds on some of our larger assemblies increases the opportunity for human errors resulting from inattention, boredom, fatigue, or other factors," Larson explains. "A robot never forgets to perform a weld," he continues. "The larger the weldment, the longer the welds and the greater quantity of welds you have, the more benefit you get from a robot," Larson says. "On average, a welding robot in our operation can do the work of 1.5 to 2 people - or even 3 people in some cases." "Robotic welding offers many advantages, particularly in a tight labor market. Four years ago it was difficult to get skilled welders," Larson says. "And I have yet to have a robot call in sick," he adds. Continuous Training "At Precor, we invest in our employees as well as our equipment," Larson says. "We send employees for robotic arc welding and maintenance training annually so that we can take advantage of what the robots have to offer and be able to fully support the equipment. Most of our robot operators are welders, so they have a good understanding of what a quality weld is and how to keep up on the robot maintenance and troubleshoot problems. "We send our people to Motoman's headquarters for robot programming and maintenance training," Larson adds. "The courses they offer are excellent. The lab and classroom facilities are top- notch, and so are their instructors." Proper Fixturing Is Key Precor uses pneumatically actuated multi-staged fixturing on their welding robots. The firm sees its ability to design and build all its own welding fixtures in-house as an advantage. "We have a great tooling group," Larson says. "They are a key element to our success in robotic welding. When we develop a product, our people know the capabilities and reach requirements of our robots, and they understand the importance of sequencing. Over the years they have been integrating pneumatics and PLC controls into our fixturing, helping to take us to the next level with regard to part positioning," he continues. "Sequence of loading a fixture is important with robotic welders. Load sequence and clamping sequence can be critical to provide proper fit-up for the robots," explains Joe Whittum, a robotic programmer. "We equipped some of the cells used to run high-volume parts with identical dedicated fixtures on both headstock/tailstock positioners," says Whittum. "In cells where we run more than one type of weldment with low volumes, we use flexible tooling fixtures mounted on "picture frames" located on the headstock/ta i1 stock positioners to facilitate quick changeover," he says. Precor also has applied the manufacturing concept of SMED (Single Minute Exchange of Dies) to their welding process. "Our goal is to perform any changeover in under 10 minutes," Whittum says. One Way to Make Parts the Right Way Precor uses Motoman ComArc touch-\sensing and seam-tracking options in an innovative way during the welding process. Larson explained how Precor uses a Japanese manufacturing concept developed by Shigeo Shingo, creator of the Toyota production system, called "pokayoke." Literally translated it means "to avoid (yokeru) inadvertent errors (poka)." This requires a "mistake proofing" system to design parts and processes so the worker cannot create an error. Whenever possible, Precor designs parts to only fit the right way in staged welding fixtures. For example, a pin in the part fits only one way in a hole in the fixture. "Precor also uses the robots as a poka-yoke tool - for example, the robot might use touch-sensing to check to see if the part has a hole in the right location process," Larson says. "If the robot detects the presence of the hole, the welding process continues. If not, the robot stops and will not continue welding until the proper corrective action has been taken. Using the robots this way is a good option when we are unable to achieve the poka-yoke resuit in the part design or fixturing." Competitive Advantage "Robotic welding is an integral part of our manufacturing operation," Larson says. "By partnering with Motoman we can support our welding processes with cutting-edge technology. Robotic welding has helped us achieve a competitive advantage, which has helped Precor become the industry leader in the exercise equipment market." Mary Kay Morel, Motoman Inc. Mary Kay Morel is a staff writer and editor for Motoman Inc., West Carrollton, Ohio. (937) 847-6200 www.motoman.com
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Source: Welding Design & Fabrication, Including Welding Engineer
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