While the latest and greatest technology makes the headlines in the metal fabrication industry, some fab processes work just fine with current technology. Oxyfuel and plasma cutting are two such steadfast technology examples for cutting metal today in shops and on jobsites. A good, solid oxyfuel or plasma cutting system offers a range of benefits for various industries.
One process works better than the other depending on the specific needs of the application. For many operations, it makes sense to have both oxyfuel and plasma cutting at their disposal.
“It depends on what the shop is doing,” says Robert Rodriquez, product manager, Miller Electric Mfg. LLC. “Shops that have a wider range of jobs or that are experienced most likely will have both cutting solutions. It’s about having the right tool for the job. Both processes have pros and cons so having both is a plus in most any shop or jobsite. For anyone that thinks that having just one solution over the other is better, give it a shot. It will change their results dramatically and make their job a lot easier.”
“I agree,” says Emily Larsen, associate product manager, Smith Gas Equipment. “People think they can have a plasma cutter or an oxyfuel torch and it can provide them what they need. But it’s not like a Swiss Army knife as much as people want it to be. It takes educating people a bit.”
Years of use
The oxyfuel cutting process has been around for more than 100 years. It’s still widely used and is an important technology for many industries.
Before cutting, an oxygen and fuel gas flame preheats the metal to its ignition temperature. A high-power oxygen jet is then directed toward the preheated section, creating an exothermic reaction between the oxygen and the metal to form iron oxide, a.k.a., slag. The oxygen jet removes the molten slag and pierces through the metal to cut it. The exothermic reaction is a continuous process and creates a cut as the cutting torch moves. The torch keeps the metal heated to keep the exothermic reaction working during the cutting.
Oxyfuel cutting uses a combination of fuel gases and oxygen to cut metals. A variety of fuels may be used, with the most common being acetylene. Other gases utilized include natural gas, propane and propylene.
“Acetylene is still the most popular gas used,” Larsen says. “However, some operations are moving to propane and propylene based on their flame characteristics as well as their cost.”
The plasma cutting process was developed in the 1950s. Plasma provides quality cutting at high speeds, which makes it a good fit for many industries.
Plasma is an ionized gas that conducts electricity, created by adding energy to an electrically neutral gas. The energy is high voltage and the gas is typically nitrogen found in compressed air. Inside the torch, both elements combine in a chamber between an electrode and nozzle, creating the plasma gas. High air pressure forces the plasma gas through a small orifice in the nozzle, creating a concise constricted flow that is electrically conductive. The more power added via the plasma cutter, the hotter the plasma arc becomes. This provides more cutting capacity, faster travel speeds or a combination of both.
Best of both processes
As stated, both oxyfuel and plasma cutting processes offer a range of advantages for shops and jobsites.
Oxyfuel cutting is typically used to cut ferrous material, making it desirable for cutting carbon steel. Oxyfuel is not suitable for cutting cast iron, stainless steel or any type of non-ferrous metal, like aluminum. Plasma cutting, on the other hand, is used for cutting nonferrous material like stainless steel, mild steel and aluminum.
Oxyfuel cutting is ideal for cutting through metal thicker than 2 in. Plasma cutting is good for metals less than 2 in. thick. Oxyfuel loses some of its benefits on thinner metals. It creates a large heat-affected zone, which can cause distortion. Also, oxyfuel tends to affect a larger area than plasma, which leads to more cleanup.
Overall, plasma cutting provides more precise cuts than oxyfuel. It is also easier to use and cuts faster. Pre-heating the metal is not required, the width of the cut is smaller and there is a smaller heat-affected zone. Plasma typically cuts with minimal slag, which means minimal cleanup.
“Precision with oxyfuel is possible but it does take a little more talent,” Larsen notes. “The ability to get a clean result with an oxyfuel torch on thinner metal.”
Versatility and flexibility
A huge benefit of oxyfuel cutting is its versatility. It can be used to cut, weld, braze, solder, heat and gouge. Operations use plasma for cutting and gouging.
“Oxyfuel allows the operator to go from cutting to heating to welding or brazing with just the switch of a torch’s tip, saving time and money,” Larsen says. “Smith offers torches for just cutting and torches that can cut, heat, weld and braze and this also includes the tips needed for these processes.”
In the field, oxyfuel provides a high degree of portability because it doesn’t require electrical power or compressed air, which plasma cutters typically do require.
“Oxyfuel is a very portable process making it a solution not only found in metal fabrication, but also in a lot of outdoor applications such as farm and ranch, shipyards, pipelines, rail and scrapyards,” Larsen says. “In these same applications, oxyfuel is frequently used for pre- or post-heating applications to prepare metal to be worked on, whether it’s bending it, welding it or even loosening up bolts. On a smaller scale, oxyfuel is used for maintenance and repair, especially in the HVAC industry. Torches are designed specifically for those applications that provide quick, concentrated heat.”
Top-notch tips
Just like choosing the right process, choosing the right cutting tip size for the application is important. The thickness of the metal determines the size of the tip, with thicker metals typically requiring bigger tips.
“Each cutting tip is rated to cut through a certain thickness of metal,” Larsen says. “Sometimes, people think that if they just use the biggest tip, they can cut through everything. But then, their cut quality isn’t that great with some of the thinner metal because they have problems with slag or other issues. Again, shops should make sure they have the right tool for the job and that includes the cutting tips.”
Larsen adds that it’s important to pay attention to the features of the oxyfuel torch and cutting tips being chosen. Certain torch and tip designs offer features for improving efficiency as well as safety.
“When it comes to these designs,” she says, “from a torch standpoint, it’s a tube-mix, head-mix and tip-mix design. Smith offers the tip-mix design torch. With this design, sustained backfires that can put the operator at risk as well as cause torch damage can be isolated in the tip. This increases safety for the operator and saves the torch because only the tip has to be replaced.
“From a cutting tip standpoint,” she continues, “it’s either a metal-to-metal, or hard-seat, design or a soft-seat design. Smith offers the soft-seat design, which is more pliable and conforms to imperfect surfaces, allowing it to seal and still work properly. Even if the tip is nicked from say dropping the torch, it will still conform to the torch head, allowing the operator to keep using the tip, saving time and money.”
When it comes to affordability, plasma cutting is more expensive than oxyfuel cutting. Oxyfuel is a more economical solution because investment costs, consumables costs and operating costs are all lower than with plasma. However, processing speeds are typically faster with plasma and it requires less cleanup, which can lead to overall greater cost savings.
Oxyfuel and plasma are both well-established processes for cutting metal. Most metal fabrication operations will benefit from having both processes at their disposal. The type of metal influences whether to use oxyfuel or plasma. Each shop should answer its own set of questions. What exactly will they be using the cutting process for? What results do they expect to achieve? Is there another process that they should consider?
As far as oxyfuel cutting equipment is concerned, there is a lot of general user satisfaction around the product.
“There are ways to enhance user experience and there have been some innovations in this space to do that,” Larsen says. “These include achieving more precise cuts for different shapes, auto-ignition and producing a perfect flame. Other innovations would be on the gas regulation side to increase the safety and user friendliness of the regulator.”
The Spectrum plasma cutting system also receives a lot of user satisfaction.
“Reliability and durability in a plasma cutter is expected,” Rodriquez says, “especially in our market where it’s almost supporting the welders. Plasma cutting is secondary to some of them and so they really have high expectations for that plasma equipment. They may not be using it as frequently as their welders, so they need it to be really robust, last forever and not have problems.”
