Rethinking what plasma cutting can do for metal fabricators

Plasma cutting technology advancements allow fabricators to plasma-cut materials at higher amperages while at the same time minimizing the bevel angle of the resulting cut edge. Because the torch can tilt during cutting, it can compensate for the increased edge angle. This produces faster cuts while keeping a square edge and improved cylindricity on small holes.

Plasma cutting technology has advanced to the point that it has forced metal fabricators to rethink its usage. High-definition plasma cutting provides a squarer edge-cut than previous generations of the technology. On 0.25-in. mild steel, plasma torches can reach cutting speeds of more than 100 IPM. Plasma systems also can deliver bolt-ready holes that help to minimize secondary machining activities once the plate parts leave the table.

Even with those advancements, plasma cutting technology manufacturers continue to put money into research and development. Laser cutting systems are becoming more powerful and cost-effective, so more shops are using them to cut thicker materials more regularly. Waterjets remain a suitable way to cut very thick materials, and steps have been taken to improve productivity on the machines. That leaves plasma cutting technology companies trying to defend their turf as the cutting method of choice for heavy-duty fab shops and service centers.

These companies have used the time wisely. Thinking of a plasma cutting table as a tool to process only 0.25- to 2-in. mild steel does not reflect the current reality of the technology, especially as it relates to cutting thick nonferrous materials. Fabricators and service centers would be wise to ask themselves what plasma cutting systems of today can do—and maybe what they might be capable of tomorrow. Here are some questions that can help plate processors understand what plasma cutting technology has to offer.

Does a plate processor have to invest in a powerful plasma power source just to cut thick specialty material, such as nonferrous metal between 2 and 6 in.?

Fab shops and service centers are used to processing thick materials, and usually the tools of the trade are familiar. Two-hundred, 300-, and 400-amp plasma systems are used to cut ferrous and nonferrous material up to 2 in. Oxyfuel systems make the most sense for ferrous material thicker than 2 in. because the rapid oxidation process, in which the steel surface is heated up to approximately 1,800 degrees F and then hit with an oxygen stream to blow away the slag, produces a square cut, leaves a smooth cut surface, and creates little to no slag on the bottom edge. (On its own, oxyfuel would have a difficult time cutting nonferrous metal. For example, in stainless steel, the resulting oxide created during the cutting process has a higher melting point than stainless steel, which means no material is being removed. Technically, oxyfuel could be used to cut nonferrous, but it involves injecting an iron-rich powder into the cutting zone. The iron powder combusts, increasing the reaction temperature, creating a fluidization of the oxidized layer and making it possible to remove material in the cut zone. This powder cutting is used on a very limited basis.) Waterjets are popular because they can cut very thick metals, up to 1 ft., but they are relatively slow compared to other cutting methods.

What about cutting nonferrous materials between 2 and 6 in.? Dirk Ott, global vice president, mechanized plasma systems, Thermal Dynamics, said that plasma systems, some of which had power sources of 1,000 amps, were cutting those stainless steel thicknesses back in the 1960s. The issue today, of course, is that heavy-duty fab shops and service centers typically don’t cut nonferrous materials of that thickness often enough to warrant such a powerful plasma system. That’s a big investment for a company that won’t be running the table over a full shift.

In recent months, however, a new level of flexibility has been introduced to plasma power systems to give users the ability to attain the cutting output of 600 and 800 amps, even if they have only 300- and 400-amp power sources, respectively. Think of it like a fab shop using two welding power sources in parallel to accommodate larger-diameter electrodes in search of increased productivity, Ott said.

For example, a service center might have two 400-amp power sources powering two separate torches on a cutting table. Both torches are cutting 1.25-in. stainless steel every day, and company management is pleased with the quality and output. But one day an order for some parts to be cut out of 4-in. stainless steel comes in. By flipping a few switches and changing over a cable, the shop can convert its two 400-amp systems into one 800-amp system.

“You get flexibility with this arrangement. You have your two 400-amp systems most of the time, and without a lot of technical knowledge or having a service guy visit, you can make it into one big 800-amp system,” Ott said.

This type of system might be more attractive for those companies that process not only high volumes of plate parts in the 0.25- to 2-in. range, but also the occasional small order of nonferrous parts up to 6.25 in. Such manufacturers might be found in the power generation, pressure vessel, and chemical and petrochemical processing industries.

Ott added that any operator of one of these types of systems in which the power output can be doubled has to be mindful of consumables changeout. Achieving optimal cut quality and speed requires consumables designed for the application. Cutting at 800 amps with consumables designed for 400-amp output will result in poor-quality cuts and very short-lived consumable life.

Paralleling two 400-amp power sources to create an 800-amp output enabled cutting of this 5-in.-thick section of nonferrous material.

If a plate processor is looking to upgrade its plasma cutting capabilities, does it have to invest in future capacity now?

When it comes to investing in capital equipment, balancing today’s cutting needs with tomorrow’s possible requirements is tricky. Most fab shops and service centers have a budget, and they want to make the most of it without totally sacrificing future opportunities.

That’s why providers of plasma technology have moved to a modular approach in building their cutting systems. It’s very much like the fiber laser manufacturers that are able to boost the power of their machines by adding laser-producing modules. It’s one of the reasons that the metal fabricating industry has seen the recent rise in available wattages in laser cutting machines.

Steve Zlotnicki, global product manager, cutting systems, ESAB Welding & Cutting Products, said that a company can purchase a plasma cutting system with a 200-amp power source and have confidence that it can upgrade without changing out the torch, gas boxes, leads, and table. New power supply modules are simply added to the cabinet with the existing modules, and corresponding electronics are updated.

“It really eliminates the fear of underbuying because obviously these systems can be expensive,” Zlotnicki said. “Someone could be OK with the system designed to cut 0.5 in., but doesn’t have to worry if a really big project comes in to cut 1.5 in. The company doesn’t have to pay for another entire system. It can just upgrade with new modules.”

The price for that upgrade could be about half of what it would cost for a new, higher-amperage plasma cutting system.

What does advanced amperage mean for cutting thick nonferrous material?

More power translates into faster cutting speeds on thick nonferrous material, according to Zlotnicki. An 800-amp power source can cut through 6-in. stainless steel at about 8 IPM, while a 600-amp power source cuts the same material about half as fast.

Does this increase in plasma power cause a plate processor to rethink its plasma/shield gas combination?

Traditionally, a fab shop or service center cutting thick nonferrous will use H35—a gas mix of 35% hydrogen and 65% argon—as the plasma gas and nitrogen as the shielding gas when cutting aluminum and stainless steel thicker than 0.75 in. This combination helps to produce a good-quality edge and allows for fast cutting.

For some shops, however, it might be time for a new tradition. Ott said that a process that uses nitrogen as the plasma gas and ordinary tap water for shielding can result in a cutting process that is 300% faster than systems using H35 for the plasma gas and can reduce the cost per cut by 20%.

What does a plasma cutting system with beveling capability mean beyond the ability to make bevels?

For the most part, beveling is associated with weld preparation for heavy-duty fabrication projects. The beveled edges make more room for welding wire, creating sturdy joints to support massive weight and loads. That’s why you see a lot of beveling required in applications associated with the agricultural, construction, forestry, mining, oil and gas, and shipbuilding industries.

One of the most efficient ways to make those beveled edges is using a plasma cutting system with a plasma torch that can tilt while cutting the workpiece. But what if that beveling capability could be used outside of weld prep?

Zlotnicki said that beveling technology has advanced to the point where it can be used to minimize the bevel edge when plasma cutting flat stock. For example, if a fabricator cuts 0.5-in. steel with a 200-amp plasma power source, it is going to be cutting at just over 100 IPM. The fabricator also is going to see a slight bevel of 1 to 3 degrees because of the way that the plasma stream naturally trails the cutting torch.

Now, if that fabricator were to cut the same material with a 400-amp plasma power source, it will be able to go faster, but the bevel angle increases as well. Zlotnicki said that by being able to tilt the torch at 4 to 6 degrees while cutting with the 400-amp system, the fabricator can enjoy increased cutting speeds and something much closer to a square edge.

“You really get to ramp up your speed and therefore ramp up your productivity while correcting for the increased bevel angle that you would normally get when you overpower your material,” he said.

Beveling capability also can be used to improve the quality of small holes. When a correction value is applied to the cutting head as it plasma-cuts a small hole, the cylindricity of the hole is improved. Typically, using a torch without beveling capability on small holes might produce a 0.4- to 0.6-mm difference between the hole’s top and bottom. With adjustments made by a beveling torch, that difference can be shrunk to 0.1 mm, Zlotnicki said.

Taking on more plate cutting is a big step for a fabricator or service center. What should they consider as they plan to grow their plate processing business?

A plate processor running multiple plasma cutting tables and possibly some oxyfuel tables has plenty to keep an eye on. Digital connectivity is making it easier for them to do just that.

With machines capable of feeding real-time production information to shop management systems, company owners and managers know exactly what’s happening and who is involved. This transparency into the production process keeps everyone honest and, typically, keeps everyone focused on getting parts out the door by deadline dates.

Facility managers don’t have to interrupt evenings, weekends, or vacations because they can use their phones to check on the status of production or a specific job. The production manager looks forward to Fridays because reports can be pulled together easily with a few mouse clicks. The purchasing agent is pleased to know exactly how much material has been used and that cutting nests are optimized on each sheet of plate. The quality control technician is thankful that information is collected and stored in case a customer has a question about a part and requires knowledge about the production process and even the material’s original lot. Holger Hahn, global product manager application software, ESAB, said the promise of Industry 4.0 technology and the digital connectivity that comes with it can make life easier for all parts of a heavy-duty fab shop or service center.

“First, if you can monitor it, you can manage it,” Hahn said. “If you don’t know what’s going on, how can you improve?

“Second, these systems can help you to avoid downtime,” he added. “If you look at the future of digital technology, there will be more machine learning. It’s growing. There will be more data to analyze, and it’ll be easier to predict certain events that can lead to unplanned downtime.”

Is a discussion of digital connectivity more for larger operations with multiple cutting tables?

Hahn said that even smaller operations understand what can be accomplished with a clearer picture of what’s happening on the shop floor and connectivity to front office systems. In fact, some of the pressure to consider this type of digital overview of production might be coming from larger manufacturing companies that want their provider of fabricating services and parts to be as efficient as they can be. That comes only by measuring production operations and taking steps to eliminate waste.

In some instances, these large OEMs send out their own experts to get metal fabricators in the supply chain up to speed on best practices to become a digital enterprise. More efficient fabricating operations give companies a chance to make more money and reinvest in their businesses. The large OEMs, in turn, can rest assured that supply chain partners won’t succumb to operational hardships that can disrupt part deliveries.

Heavy-duty plate fabricating might not be the first thing that people think of when they speak of modern manufacturing, but it is getting more sophisticated. Plasma cutting technology is evolving at the same rapid pace.