Battle of the gases

For years, plasma cutting was seen as the upstart younger sibling of oxyfuel, a considerably older, more established cutting process. Sure plasma was faster, but it came burdened with a host of operational issues that made end users wary. Recent technological advances, however, have made plasma consideringly more appealing. Still, even its most ardent supporters don’t think plasma will completely displace oxyfuel any time soon.

Plasma is an ionized gas that conducts electricity. Developed in the 1950s, plasma cutting can be used on any electrically conductive metal with a minimum of pre-heating. It can, however, only cut about two inches deep on average. The plasma process is used in many industries, including metal fabrication, construction, agriculture, and automotive repair.

“The biggest benefit [of plasma] is the speed in which it cuts,” says Timothy Joslin, cutting machine product manager, Koike-Aronson, Arcade, NY.

Indeed, plasma can cut up to six times faster than its oxyfuel counterpart.

Oxyfuel typically uses one of five fuel gases—acetylene, propane, methylacetylene-propadiene (MAPP), propylene and natural gas—in combination with oxygen. An old-school cutting method, oxyfuel can pierce mild steel up to 24 in. (609 mm)thick. It won’t, however, cut aluminum or stainless steel and requires pre-heating. The oxyfuel process is popular in agriculture, fabrication, construction, maintenance repair, mining, automotive and among hobbyists.

“The main advantages of the oxyfuel cutting process are its simplicity, low cost and ability to cut thicker materials. However, its disadvantages are its slow cutting speed and the higher heat input into the plate,” says Steve Zlotnicki, regional product line manager, cutting, North America for ESAB Welding and Cutting Products.

Experts urge shop owners to ask themselves what materials they cut most often and the thickness of their cuts before purchasing one process or the other.

“The thing to remember about these two popular processes is that they each have their place. It makes no sense to favour one over the other because each has unique capabilities that lend themselves better towards some applications,” says Zlotnicki.

Nonetheless, a few hard-fast rules do exist: if you’re cutting aluminum or stainless steel, then obviously plasma is the way to go. Plasma is a wise choice for thin materials in general.

“For anything half-inch or less, plasma cutting really does shine,” says Steve Hidden, product manager, plasma group for Miller Electric, an arc welding and cutting equipment manufacturer from Appleton, Wisconsin.

On the other hand, if you’re cutting nothing but thick metal and aren’t using aluminum or stainless steel, then oxyfuel is your best bet.

Besides cutting thicker material, old-fashioned oxyfuel has two big advantages over plasma: cost and portability.

Plasma needs a primary power source, and is thus not hugely portable. By contrast, an oxyfuel cutting setup consists of a fuel tank, an oxygen tank and a torch. An oxyfuel system doesn’t require a primary power source (that is, electricity) to run, which means it can be easily toted around. This feature makes oxyfuel a good choice for repairing farm equipment in the field, for example.

Plasma’s power requirement limits how deep it can cut. Theoretically, plasma could cut well beyond two to three inches (50.8 to 76.2 mm), but this would require an enormous, power generation source—not something shop owners interested in maximizing floor space would welcome.

“The limitation [with plasma] is how much power you have to bring,” says Hidden.

If they’re more portable, oxyfuel systems are also cheaper than their plasma counterparts—up front, at least.

“Capital equipment costs for oxyfuel are dramatically lower,” states Jim Colt, strategic account manager of Hypertherm, Hanover, NH.

Colt points to his company’s HPR400 plasma system, released four years ago, for a cost analysis.

“The HPR400 has the ability to cut up to two inches thick on carbon steel, but it’s $60,000 for one plasma system, which would be bolted onto a CNC cutting machine … a one-torch oxyfuel system would probably be about $6 – 7,000,” says Colt.

The big difference is that “that HPR400 will cut six times faster … if you’re looking at long term operator costs, plasma is a far better deal over time,” he adds.

The HPR800 is a more recent Hypertherm offering. It promises dross-free cutting to 38 mm, and is capable of piercing 75 mm (three in.) of stainless steel and aluminum.

While plasma is faster than oxyfuel, it used to have a reputation for being complicated, finicky and tough to use. Fabricating equipment suppliers have made enormous strides, however, in improving the technology behind the plasma process.

“We’re not done developing greater capability with plasma. Plasma’s not going to get any cheaper, but it is getting more productive, with higher accuracy over time … oxyfuel has been pretty stagnant for about 30 to 40 years,” says Colt.

“Modern plasma equipment is far easier to set up than it used to be. Almost all plasma systems these days are available with an “automatic gas control” which simplifies setting up many of the plasma parameters. ESAB’s plasma systems are fully integrated with the CNC, so that they can be completely automated. In a fully automated system, the part program calls the plasma parameter file so that the operator doesn’t have to adjust anything. His only responsibility is to load the table with the correct plate and make sure the right consumables are in the torch,” adds Zlotnicki.

As Zlotnicki notes, a windows-based CNC control has enormously simplified the plasma cutting process.

In a recent magazine article, Colt stated that “virtually anyone can operate even the most complex, large, multi-torch CNC plasma machine manufactured today … the CNC controls every function that an expert operator was required to do in the past, thus eliminating errors and dramatically improving process consistency.”

“Other features of modern plasma systems also make operation easier and more reliable, such as pre-assembled consumable sets and on-screen process information. For example, ESAB’s PT36 plasma torch features a SpeedLoader system that allows the operator to pre-assemble a nozzle, diffuser, shield and retainer. Then when it comes time to switch from one nozzle size to another, switch out is a breeze,” adds Zlotnicki.

ESAB has also created a Vision T5 CNC that includes a database of plasma torch parts, depicting pictures and part numbers on a screen. The operator can use the system to look up detailed information or get close-up views.

The latest technological breakthrough for plasma centres around “bolt-ready” holes.

“Our goal was to make plasma cut holes more round. Plasma cut holes typically have a ding or a divet where the object entered into the cut-path of the hole,” says Colt.

Hypertherm’s patent-pending “True Hole Technology” eliminates the hole taper that usually comes with plasma cut holes, reduces ding and makes it easier to remove dross. The end-result is a “bolt-ready” hole.

True Hole is the “way to get extremely good holes… in some cases, better than laser cut holes,” says Colt.

Other companies have similar systems: ESAB’s process, for example, is called “Precision Hole Technology.”

This technology “allows users to dramatically improve their plasma hole cutting results on mild steel up to one inch thick,” says Zlotnicki.

Koike-Aronson, meanwhile, distributes a plasma cutter called the Kaliburn Spirit 400A which offers a 400 amp output and an automatic gas console. The latter automatically sets process parameters for maximum ease-of-use. The system also apparently makes a pretty decent hole.

For all of plasma’s advances, experts doubt it will become the dominant process in the future.

“It would be improper to say one process is superior overall. Rather, either could be superior for a specific application. And since so many fabrication shops and manufacturers deal with a wide array of cutting applications, the majority of cutting machines sold today are still equipped with both plasma and oxyfuel cutting tools. This allows the end user to choose the tool that is superior for the application. The important thing for the user to know is where that distinction lies for the equipment they have,” says Zlotnicki.

“Anybody that’s working with metal, especially in any type of repair situation, you’re always going to find a place to use that oxyfuel and you’re always going to find a place to use the plasma. It’s a matter of understanding which tool works the best in the application you’re working on,” agrees Hidden.  CM

Nate Hendley is a regular contributor and freelance writer based in Toronto.

www.esab.com

www.hypertherm.com

www.koike.com/index

www.millerwelds.com