by Noelle Stapinsky
While many may debate which of the two cutting technologies reigns supreme, at the end of the day both hold their rightful place in a job shop’s toolbox
When looking at plasma and oxy fuel cutting technologies, both have their benefits in terms of cut quality and processing different materials, whether handheld or mechanized. They also have limitations. Plasma relies on electricity and shop air—oxygen, nitrogen, or argon—which circulates through the swirl ring above the electrode, causing the plasma to turn rapidly as it passes. The oxy fuel typically uses an acetylene gas mix and is a process that rapidly oxidizes mild steels, which can be done inhouse or out in the field. What really matters when comparing these two technologies though is the material type, the thickness, considerations about operating and consumable costs, and their additional capabilities.
The first big question is around material type. Plasma systems can cut any material that is conductive with high precision and speed. “With a handheld plasma torch, you’re looking at ¾-inch thick material maybe. With an automated or mechanized plasma system you can get up in the 3-inch range,” says Bradley Nicoll, a weld engineer at Miller Electric Mfg.
Some argue that plasma maxes out above one to two-inch material thicknesses, but if you consider that 90 per cent of manual plasma cutting applications are with stainless and aluminum-based materials, those gauges and thicknesses, for the most part, are easily processed.
“The number one reason that someone would choose a plasma cutter over oxy fuel for mild steel would be the cut quality. Plasma cuts have less dross, so fewer secondary operations in terms of clean-up of each part,” says Vince Tucker, distribution sales manager for Hypertherm. “If you look at cutting thinner metals, you’ll get less warping with plasma, and the deformity of the material due to heat is less. If you’re going to have a secondary operation, such as cutting a hole or tapping it, the heat affected zone is smaller with plasma.”
Comparing the two cutting processes, Nicoll adds, “oxy fuel cuts do have some slag or dross that will need to be cleaned off before welding. But plasma cutting leaves an oxide layer. And if you’re working with aluminum or stainless steel, those have a thick oxide layer that tends to make it more difficult to weld, whether it’s cut or not.”
With a plasma hand torch versus an oxy fuel hand torch, Tucker says that you can still see a speed advantage on materials 1.5-inches thick. But to process thicker mild steel, from two inches to three inches, you will need a larger, mechanized plasma system to gain these speed advantages. “Everything depends on the power supply and the plate thickness that’s being cut. For example, if you were to compare cutting time on half-inch mild steel with a 125-amp air plasma, you’re probably cutting four parts for every one cut with oxy. With a larger, mechanized plasma system at 200 or even 300 amps, that speed advantage jumps from five to seven parts for every one part cut with oxy. It’s considerably faster, which makes it less expensive because you can produce more.”
Once you get into thicker materials such as mild steels, that is where oxy fuel really shines—it can cut up to 15-inch steel. “The magic of oxy fuel is that it rapidly oxidizes the material, and it really does feel magical, especially when you’re cutting something ridiculously thick,” says Kris Scherm, global manual plasma business and product director, ESAB.
Holding up a piece of one-inch-thick steel cut with oxy fuel, Scherm says, “This is actually not that thick for oxy fuel. The cut looks amazing and is clean on the top and bottom, but that’s a handheld cut, and you can see it’s not quite straight. That’s where a mechanized system comes in.”
And while many job shops might get creative with rigging up a system that will hold the torch in place, there are mechanized options that will hold the torch and guide it in a straight line, or at an angle for an even bevel.
ESAB’s MechPak is a mechanized package that allows operators to connect their torch, oxy or plasma, to a cutting table with a power connector that integrates the start/stop trigger. And you can swap out torches in as little as 30 seconds. “With this, we are demonstrating what the MechPak can do and how easy it is to switch from a handheld cutting system to a mechanized torch attached to an apparatus, whether it is made up with some rubber bands or you’ve spent money on a pipe beveler or MiggyTrac,” says Scherm.
A simple, yet grossly underutilized tool is ESAB’s VCM Victor tractor. “It’s still around and still popular,” says Scherm. “But people don’t realize that same system, they see the oxy fuel torch on, we’ve designed the plasma torches to the exact same diameter for the VCM track, so they’re interchangeable. With it, you can pre-set your speed and set the position to a fixed point to cut and bevel. You can do a zig-zag motion and there are a lot of little things you can optimize with your cutting, welding, or gouging.”
With such a mechanized system not only do you get a cleaner line, but it has speed advantages for both cutting processes. “Speed is the name of the game when it comes to cost. The cost of the cut is not in the oxy fuel or the plasma, but in how long the operator stands there and holds the button,” says Scherm. “With thin, 10 gauge, 1/8-inch material, the cutting can be as much as 10 times faster with plasma. At that thickness you can travel 100-inches per minute. With oxy fuel, the fastest speed you can travel is at the 20 to 24-inch per minute range. Any faster than that and you risk losing the cut because you’re trusting that oxy fuel magic is happening. That chemical reaction that causes the cut to happen—oxidation—must have time. Although it seems to happen quickly, it’s still slower compared to plasma.”
Another advantage of plasma cutting technology, according to Tucker, is that it’s safer. “There’s no flammable or explosive gas present. It’s also incredibly simple to use compared to oxy fuel. To be a good oxy fuel operator, it’s kind of an art form. I’ve seen fantastic oxy fuel cuts, but it takes a lot of training and practice to get that good. I can literally make anybody a good plasma operator in five minutes, it’s that easy to use,” he says.
“And with plasma advancements, we now have a single-piece cartridge consumable that automatically sets up the machine and the process — the amperage, cut mode, air pressure, etc., ” says Tucker. “The cartridges replaced a five-piece stack up, previously needed for handheld or mechanized plasma cutting applications. For the Powermax SYNC series (65- to 105-amp process), you can change the cartridge in 1/6th of the time it took with previous models. That means more cutting time, and once the cartridge is placed on the torch, it uses RFID technology to send messages to the torch and power supply to choose the correct settings automatically. That means no chance for errors like choosing the wrong setting or mixing up the consumables.”
These cartridge consumables also track usage, like arc starts, transfers and cutting time, making it easier for operators to know when to replace the cartridge as well as optimize their own performance. “You can still base consumable change-out on the cut quality, but with a standard five pieces, those parts don’t wear at the same rates so you need to do routine visual checks. It is hard to know when to change the swirl ring and if you do not change it in time, your cut quality suffers,” says Tucker. “With a cartridge, you don’t need to think about wear rates or consumable schedules.
Nicoll says you also need to consider the consumables required for oxy fuel. “The simplicity of the technology is that you have the cutting torch and the typical thing that would need to be replaced would be the nozzle, which often lasts a couple of years. If you look at plasma, the cutting tip, swirl ring, electrode, drag shield, etc. are all consumables that you replace on a regular basis if you use the technology frequently,” he says.
Another cost consideration regarding oxy fuel is the burning fuel used. Typically oxy acetylene is the most common combination. But it’s not the cheapest option and supply can be an issue. “You can use propane, which is the cheapest option you’ll find. Some use natural gas or MAPP. But acetylene will give you a more refined flame allowing you to cut thinner materials without getting much distortion, whereas with natural gas or propane, the flame is going to be spread out more, causing more distortion. But if you’re cutting a three-inch piece of metal, the propane will help you distribute that heat more evenly through the thickness of the metal,” says Nicoll.
Tucker adds that when people say they are going to dump their oxy fuel once they get a plasma, he always mentions there is a place for oxyfuel. “If a shop does any heating, they’ll need it. “What if you have a bolt stuck and want to heat it up to break it free? Plasma will cut and gouge, but it can’t heat. And you can do other things with oxy such as braising and welding. There really is a place for both technologies, but make sure you are taking advantage of their strengths,” he emphasizes.
“Oxy fuel is more versatile in that way. But with plasma, on the other hand, you can also do etching and gouging, it just depends on your amperage settings. There are a lot of things between the two technologies that can use one or the other, but not both. So instead of having a ‘one size fits all’, there’s definitely a need for both on the shop floor.” SMT