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Thread: More arc-on, less arc-off
10-20-2011, 08:54 AM #1
More arc-on, less arc-off
Welding efficiency produces less waste and happier welders
By Tim Heston
A North Georgia fabricator analyzes welder productivity and revamps its operations so that welders spend more time actually welding, and less time moving material and fixtures, as well as typing in data.
The welding booths at Impulse Mfg. Co. are designed for optimal efficiency, with parts staged in stackable, space-saving metal carts. Photo courtesy of Impulse Mfg. Co.
Several years ago managers at Impulse Mfg. Co. noticed some productivity problems: Welders didn’t spend enough time actually welding during their shifts. Downtime, or arc-off time, amounted to a significant portion of the workday. So the Dawsonville, Ga., company launched an initiative to change matters. Personnel analyzed what exactly welders were doing when they weren’t welding. They talked with welders and installed welding arc monitors to not only monitor weld quality, but also track the time the arc was on versus off during a shift.
They found that downtime wasn’t at all intentional or malicious. Welders didn’t take excessive breaks. Instead, they looked for tools and fixtures; they entered information into job-tracking software; they retrieved new gas cylinders or welding wire spools—all necessary tasks, to be sure. But still, they weren’t welding.
As managers saw it, if a person is highly qualified in welding, that’s exactly what he should be doing most of the time. But if the weld shop isn’t well-organized, a welder may spend too much of his time without a welding gun in hand.
“We set out to make sure our welders have everything they need, so they don’t need to leave the welding cell so often,” said Jon Baysden, production manager. “The crazy thing is, that’s exactly what our welders wanted.”
Gas and Wire
Years ago Impulse managers tackled some basic efficiency initiatives, including shielding gas setup. Welders used cylinders, and when they ran out, they stopped welding and changed them out. That downtime added up, so it made good business sense to install a bulk tank system outside. The company also arranged a gas replenishment system with its supplier. A phone system automatically calls the supplier to send a delivery truck once gas in the bulk tank reaches a certain level.
For welding wire, they replaced spools with barrels that can be staged and switched out quickly. After that welders never ran out of wire in the middle of a job.
Fixtures at Impulse Mfg. are tagged and staged for the robotic welding cells. Photo courtesy of Impulse Mfg. Co.
Dissecting Arc-off Time
Basic efficiencies were just the beginning (see Figure 1). Using the Impact Engineering monitoring system, the welding team analyzed arc-off time and asked questions: What was going on that reduced downtime? What wasn’t adding value?
Admittedly, whether a welder’s task adds value can be subjective. For instance, keying in a job into an ERP (enterprise resource planning) or similar job-tracking system does add value. But should the welder be keying in all that data? Shop managers knew welders wanted to spend most of their time welding (big surprise), and as they soon found, that’s how a welder can provide the most value anyway.
As Production Supervisor Gordon Woody recalled, “We asked how we can make it so a [welder] has everything he needs in the welding booth. For instance, if a welder has to walk in and out of his cell and [using the ERP system] clock in and out of 10 jobs, that’s probably 15 to 20 minutes of his time just doing paperwork.”
Another problem was finding and replacing fixtures for the company’s repeat work. Before a job hits the floor, the part’s welding fixture is already made during what managers call the “e-job,” or evaluation, phase. Technicians fabricate and weld the part to ensure smooth manufacturing before it hits production. This reduces weld setup time, of course, but problems remained. Because of myriad parts flowing through the cell, arc-off time mounted as welders left their workbenches to hunt for fixtures to hold the various parts that flowed through the weld cell.
Today is different. One person, a bit like a department lead or coordinator, manages weld cell part flow. He clocks jobs in and out of the ERP system (in this case, JobBOSS) and ensures part components and fixtures are ready and organized for the welder. This person also places fixtures tagged for the job on staging racks near the welding cell. After the welder finishes, the part flow manager takes fixtures to a maintenance area, where each fixture is cleaned, inspected, and, if needed, repaired. When the repeat job comes up again, the fixture is ready for use.
Welding booths at Impulse are arranged so that tools are within easy grasp, and fixtures are staged on racks directly outside.Some booths (sometimes dubbed “welding lanes”) are now narrower, so that all the welder’s tools are close at hand.
The goal is to prevent unexpected delays before the welder strikes his arc, and the same efficient thinking is integral for implementing automation in a high-mix, low-volume environment. For instance, the shop has an area to stage the necessary fixtures—cleaned and tagged—for jobs queued up for robotic welding (see Figure 2).
At the manual welding cells, the part flow manager delivers components in standard metal carts that stack on top of one another to save floor space (see Figure 1) and transports larger parts on custom-fabricated metal pallets.
“Our goal is to be a wood-free shop. From a safety standpoint, wood obviously never goes well in a weld shop,” Baysden said.
Significant improvement ideas have come from welders themselves. One noticed that his arc-on time plummeted when he worked with numerous small parts at once. For one job, he would pick up and fixture five different parts, weld them, and then place all of them into a cart headed for the next operation.
But what if he placed all parts on a kind of channel? When he finished welding the parts on the workbench channel, he would lift the channel to slide all joined parts into the cart, eliminating tedious and time-consuming pick-and-place action. This idea significantly cut arc-off time.
A new weld booth design also helped increase efficiency (see Figure 3). Parts enter from one side and exit the other to avoid traffic jams at the booth entrance. Booth sizes also were changed to make the welder’s job easier. Some booths now are longer and narrower so that all the welder’s tools are within a few steps.
Welding and Manufacturability
Although parts are test-welded before they go into production, a welder may catch a small annoyance that makes his welding a little less efficient. This is where the company’s custom intranet comes into play. Say that before placing a component in a fixture a welder needs to file off a tab left over from a previous laser cutting operation. It’s certainly doable, but it’s not the most efficient way to join a part, so the welder may propose that tab be eliminated the next time around.
To do this, he simply talks to the part flow manager, who then types the suggestion into a shop floor computer terminal that’s connected to what the company calls its “all-request system.” It uses numbers to categorize problems from the most severe—the job can’t run as is—to the relatively minor—the job can run as is this time, but a few changes could make it faster next time, such as eliminating or moving a small tab left over from laser cutting.
Maximizing a Welder’s Value
Welders possess a specialized skill. It takes concentration and dexterity. An experienced welder develops a rhythm with a welding gun to weave or string a bead just right to ensure a solid joint, while not overwelding, which wastes wire and makes for inefficient grinding. It’s a delicate act, and an unexpected halt may interrupt a welder’s rhythm.
“I love welders,” Baysden said. “They have the best sense of humor in the entire world. But when you hire welders, they want to weld. If you prevent him from welding, you’ve frustrated him.”
Clean Weld Cells, Clean Welds
Removing cable clutter, as this boom design does at Seattle-based Shinn Mechanical, increases safety and reduces material handling time. Photo courtesy of Miller Electric Mfg. Co.
A welding cell cluttered with cables, tools, and equipment probably isn’t the most efficient working environment. Much of this can be remedied with straightforward organization techniques like 5S, but process standardization also plays a role.
“Let’s say you need to weld three different parts of three different materials and thicknesses,” said John Talkington, director of innovation at Thermadyne, St. Louis, Mo. “Now you go from mild steel 0.25-inch plate to 1-in. plate. You don’t want operators or shop supervisors to be changing procedures continually. When you group projects so that fixturing and welding procedures are similar, you reduce downtime.”
Another danger is that various parts may be made of different materials that react poorly with each other, which is why it’s standard industry practice to separate work flow by material—cells dedicated to stainless steel, for instance—to prevent cross-contamination.
Good communication between shifts is paramount, particularly in shops welding large components that may take several days to complete. “We visited a facility that is welding huge mining equipment buckets, with 1- to 5-in.-thick base metal. And the material is being welded over several days,” said Jeff Henderson, global product line manager, arc accessories, at Thermadyne. “So to stay consistent from shift to shift and day to day, welders mark on the base plates the parameters, including the required preheat.”
In these cases, welding procedure specifications (WPS) should spell out operational details, sources said, but actually writing selected procedures and job status data on the base plate itself improves communication between shifts.
The communication helps “reduce downtime that would be caused by weld defects from improper settings,” said Jim Barker, Thermadyne’s arc accessories engineering sustaining services manager.
Getting cables out of the way reduces the chance for cable damage and the resulting downtime. Photo courtesy of Thermadyne.
As for other basic efficiencies, sources preach process standardization and welder ergonomics. Ideally, settings should remain consistent from shift to shift. Changeout of contact tips, nozzles, and gas diffusers should be simple, as should the weld position. A highly skilled welder may be a master at welding overhead, but out-of-position welding is never ideal. Henderson referred to another heavy fabricator that improved efficiency by 25 percent by investing in positioners that could lift a 30-foot-long workpiece to the flat position.
Brent Williams, manager of TIG solutions at Miller Electric Mfg. Co., Appleton, Wis., added that not only does position matter, but large gaps in the weld joint can add to downtime as well.
“Designing a joint for optimal welding makes a big difference,” he said, adding that good fit-up not only gives the welder a better chance of producing a good weld, but also reduces setup. In these cases, self-fixturing components—such as laser-cut tab-and-slot designs—also help, speeding and simplifying setup and reducing the amount of weld required.
He added that a lot of welding downtime occurs from simple clutter. Some shops use booms to get power sources and cables up and out of the way. In gas tungsten arc welding booths, many have opted for wireless foot pedals. “If you’ve got to move something in and out of a weld cell, and you have cords in the way, you may damage them. That’s going to cause downtime, and downtime always leads to higher part costs. By eliminating that cord, you eliminate a failure point,” he said.
Modern welding machines help reduce the clutter, too. “Machines today are capable of running a larger-diameter wire, which gives you more range,” he said. “It used to be that to weld really thin parts you had to go with a very small wire. Pulsing allows you to take a larger-diameter wire and dial it down to thin material. So now you don’t have to switch wire. The machines can also count how many inches or pounds of wire in a spool, and it will alert you before you run out. This way, a welder can prevent running out of wire in the middle of the part.”
Related Company Showrooms:
Miller Electric Mfg. Co.
Thermadyne Industries Inc.
FMA Communications Inc.
833 Featherstone Road
Rockford, IL 61107