When plasma cutting cobots meet complex geometries

Automated plasma cutting with cobots has become a viable option to address any significant issues stemming from manual plasma cutting, including rework.

Tank Technology Inc. (TTI) has been in business since 1991, but its water heater plant has produced water heaters since the early 1960s. The Princeton, Wis.-based TTI is a 100% employee-owned company with around 50 employees. The fact that all its employees are trained welders, with metalworking experience and a vested interest in producing quality products, gives the company an edge in the market.

TTI produces custom, porcelain-lined water heaters and storage tanks, both ASME (H, HLW, and U) and non-ASME certified. It fabricates tanks used in geothermal, hydronic, domestic water heating, solar, marine, and other applications.

However, TTI relied on manual plasma cutting in production, an inconsistent and error-prone process. The fabricator knew automation could solve the significant rework issues it had, but choosing the right cutting automation system required some thought as cutting curved geometries posed a higher challenge than plate cutting.

TTI grappled with inconsistency and rework with manual plasma cutting on tank heads. Much of its work is customized, so the company modifies the base for couplers, fittings, and other engineering details.

“Twenty-five percent of our products are customizable, so we were getting a lot of volatility and inconsistency when cutting our heads and bases by hand,” said Dan Church, senior manufacturing engineer at TTI. “We had some fixtures to trace the parts but still inconsistencies on producing circles or other shapes that are needed to help with welding.”

TTI typically would need to perform recuts and then grind the cut to prepare it for subsequent welding, wasting time and resources and making production less efficient.

The manual plasma cutting process also required frequent consumable changes—the company burned through about a set of consumables per day. Considering the number of recuts and inconsistency in manual plasma cutting with a variable torch-to-work distance and torch manipulation, the consumable wasn’t used efficiently.

The curved geometry of the tank head posed a challenge for TTI as it considered implementing automated plasma cutting. It’s more challenging to automate the cutting of a dome shape with varying elevation than it is a flat surface, like a plate.

TTI tried CNC cutting, but ultimately the available methods couldn’t handle the tank dome's curved geometry. The company also investigated other systems, but the complex geometry of the tank head remained the primary issue.

“We did look at laser cutting, different gantry system plasma cutters, but nothing would work with the contour of the head,” Church said. “We needed the additional axis that the robot offers.”

Tank Technology Inc. produces custom, porcelain-lined water heaters and storage tanks used in geothermal, hydronic, domestic water heating, solar, marine, and other applications.

After deciding on a robot for its automated cutting work, the company needed to decide which system could be readily adopted by the team. TTI had previously integrated a welding cobot from Hirebotics, Nashville, Tenn., so choosing a Hirebotics Cobot Cutter plasma cutting cobot made the most sense.

Other robots TTI tried couldn't adapt to its needs and ended up being a frustration for the team. The company liked that the plasma cutting cobot could be operated using a tablet, didn’t require an engineer to program it, was flexible, and allowed employees to be trained and producing parts all in the same day.

For TTI, the simplified software was the primary deciding factor.

“I can hand any of the guys the iPad, and they can handle it. They know what’s going on. It’s point and click and done. I don’t need to teach them the coordinate system or anything like that,” Church said.

“The advantage of the app versus the teach pendant is that I can use my phone, I can use an iPad, and when we drop the iPad and break it, you can just grab another one and you are good to go. You don’t have to buy a pendant that’s proprietary and costs way more,” he added.

The cobot’s installation and training was fairly straightforward, allowing it to quickly integrate into TTI’s routine. The box showed up, team members took the cobot out of the box, plugged it in, downloaded the app, followed instructions, turned it on, and were cutting within hours.

One of the first things TTI noticed was the sheer speed difference between manual and cobot plasma cutting.

“A human, on average, will go from 11 to 13 in. per minute—whether you are welding or cutting—and we are traveling anywhere from 70 up to 140 in. per minute on our thinner-gauge stuff,” said Eric Parmenter, ASME production lead at TTI.

The company first used the cobot to modify a tank head, which often are customized to user specifications. The cutting cobot customized a base tank head, which allowed TTI to prove how valuable cobots can be for variable production.

The shop floor quickly became acclimated to the cobot. Parmenter said within a week, operators were programming and cutting parts.

The plasma cutting cobot TTI chose can be operated with a tablet, requires no programming, and is flexible and easy for operators to learn and use.

The integration helped TTI nearly eliminate cutting-related rework and significantly improve the repeatability and accuracy of the plasma cuts. What used to be a manual process with frequent errors and postcutting work now required almost no postcut grinding. Furthermore, the dome cuts became much more precise and rework dropped from 25% to almost zero.

Parmenter and Church said the rework they saw was due to inconsistent cuts—those that were too large or too small. But now, the precision of the cobot had helped reduce or eliminate these issues entirely.

Cutting times improved drastically after TTI switched to a plasma cutting cobot. The system also eliminated cutting-related bottlenecks in production. Since the parts are cut accurately without the need for rework, production doesn’t get bogged down by recuts or excessive grinding.

“We saw a reduction in cycle time from three minutes to 11 seconds on the majority of our heads,” Church said about the productivity gain. This difference in production speed, coupled with almost no postcutting work, meant a higher production capacity and reduced load on the operators.

The benefits TTI experienced after it switched to a plasma cutting cobot include:

“Some of the stuff that we do in our ASME department, where we are working with reasonably thick material anywhere from ¼ in. up to ½ in., and when we are beveling some of the ½ in. and extending that to ¾ in. or 7/8 in., after the run is done, you could place your hand on the part and you could say that the part was never cut,” Parmenter said.

When it was previously cut by hand, “it would be so scorching hot that even wearing thick gauntlet welding gloves, you wouldn’t be able to touch that part comfortably for at least 15 minutes,” Parmenter added.

“The life of the consumables is unbelievable with this thing too, because of the control and consistency of the speed,” he added. “I think we changed out two or three [cartridges] in the three or four months that we’ve had it. If you are doing it by hand, you can burn through one set of consumables in a day.”

Manual plasma cutting can be physically straining and puts the operator at risk of burns and arc exposure. The plasma cutting cobot integration helped improve worker safety around cutting applications and reduced fatigue and strain.

Shorter cutting times and increased cutting accuracy can improve production by reducing or eliminating recuts or excessive grinding.