Plasma cutting might look like a welding process from a distance. A casual observer stands a safe distance away, watches the metal fabrication shop start the machinery, and it’s assumed that some form of welding is beginning. That’s not quite true. Welding is the joining of two metal parts. They fuse together to form a near seamless finish. Plasma cutters, on the other hand, slice through already complete metal parts, leaving intricate holes or entirely separated pieces. One metal sheet arrived, and two or more cut pieces leave after the cutting completes.
Technically, it’s a subtractive process, whereas welding, TIG, MIG, Stick Welding, etc., refers to an additive process. As for how the machinery operates, there’s less talk of electrical arcs and more talk about a mysterious fourth state of matter called plasma. More than an electrical arc, there’s a focused gas stream involved too. That gaseous element might be argon, nitrogen, even CO2, but air is the default stream, as supplied by a compressor.
A Lesson in Fourth State Cutting Basics: What is Plasma?
Back to the classroom, fabrication shop workers don’t need to know the inner workings of a plasma cutting machine, but they are encouraged to know the finer principles behind their operation. It begins with a substance that isn’t a liquid, isn’t a gas or a solid. Plasma is formed when a gas is super-heated. Essentially, the excitation of gaseous particles causes ionization, to the point where the gas breaks down into a focused stream of charged particles. Given momentum by compressed air and electrically charged by the equipment, this is the cutting plasma, a narrowed, energized beam capable of slicing through hardened metal like a hot knife through butter.
The plasma conducts an electrical current now, and this high-velocity jet melts metal with incredible accuracy. This is what metal workers look for when selecting their gear. Note: A Tooliom TL-50C plasma cutter will be used in examples throughout this post to illustrate the process.
Learn The Basics: How Plasma Cutting Equipment Works
Just as with any other high-current, super-heated cutting or welding gear, preparation and safety are key. All flammable materials should be kept well away from the cutting area. Warning signs are placed where they can be seen and personal protective equipment (PPE) is worn. That includes a welding helmet with adequate eye shading, flame retardant gloves and coveralls, and ear defenders. Plasma cutting ejects hot splash back and is noisy, too.
The ignition system triggers a high-frequency (HF) burst of ionized energy. Now, users should refer to their specific manufacturer’s guidelines when operating the ignition circuit. The Tooliom TL-50C comes standard with a non-touch pilot arc, which is impressive, to say the least. There’s also a non-HF variant available. This latter machine eliminates high-frequency interference, which is a beneficial feature to have on hand when working near interference sensitive electrical devices. There’s even some debate over whether such signals are hazardous to human health. The HF field causes fatigue, headaches, and other potential health risks, too. We suggest reading literature on this feature if electrical interference and/or health matters are a concern.
Back with the plasma cutting machine, the arc has been triggered and the focused, charged plasma jet is active. A steady hand is needed to control the arc. It will vaporize metal in a split-second, so even the smallest jerk will introduce cut irregularities. The plasma cutting head never touches the metal, it just remains a consistent distance from the cut. Compressed air is providing the source of the plasma stream. Inside the handheld torch, a consumable electrode and nozzle converts this high-pressure air flow into cutting plasma. At the core of the handheld torch, the aforementioned high-frequency spark has finished its job, having worked in tandem with the pilot arc to facilitate a non-touch path between the electrode and the workpiece.
While the cutting operation is simple, the plasma generation phase is not. There’s compressed air to manage, which is generally done on an in-built pressure gauge. The business end of the gear is loaded with preflow gas funneling innards and a pilot arc circuit, plus a potentially electrically disruptive HF ignition system. Still, at least to the individual overseeing the process, there’s not a great deal to control. The equipment and air compressor settings must be configured to allow a desired travel speed, of course. Then there’s the issue of arc stability. Consistent control of the arc won’t mean much if the air isn’t dry or the equipment isn’t grounded properly.
Even with the equipment current dial set to its sweet spot, as decided by the thickness of the metal and the desired travel rate, it’ll take practice to create clean cuts. It’s suggested that the torch be positioned at a 90° angle to the cutting line. It’s also a good idea to try out different travel speeds and cutting distances on scrap metal pieces. The tip of the torch head maintains this angle throughout, and the resulting intricate cut cools rapidly. Oftentimes, a heavy-duty fan is also integrated into equipment builds. It’s utilized to dissipate excessive quantities of thermal energy before they can deform the base metal.
The torch be positioned at a 90° angle to the cutting line.
A list of cuttable ferrous and non-ferrous alloys follows:
Note: Titanium isn’t the easiest metal to plasma cut. As for the above alloys, Tooliom plasma cutters are entirely capable of slicing through ½” metal sheeting. That’s assuming the dual voltage power supply is accessing 220V. For 110V power, expect thinner sheet metal cutting, possibly in the range of 25/64” of effortless slicing.
Setting Up for Success: Plasma Cutter Site Prep
Done correctly, a clean cut is guaranteed every time. The charged plasma cuts and vaporizes, then the high momentum stream takes on a second role, that of ejecting any cut debris. There won’t be a great deal of waste, not when the tool literally destroys metal, but it’s still good to know that the force of the superheated jet will take care of any remaining detritus. Ideally, paint and dirt have been cleaned away, scraped abrasively through use of a powered grinding tool or a wire brush. If not, plasma cutters are non-contact machines, so they’ll still slice through an interfering coating of filth without too much effort.
A checklist compiling all steps is as handy as any tool. It’s used to tick off all of the preparation work and serves a similar function as an equipment setup aid. The area the cutting is being done in is well ventilated, safety equipment is on, and workpiece metallurgical characteristics have been assessed. The equipment is portable, weighing less than 14 lbs. Its return lead is securely grounded against the base metal. On the plasma cutting cable, the connection plugs into the third terminal from the left on the Tooliom TL-50C plasma cutting machine. A red ignition cable comes next. It plugs into the pilot arc ignition terminal (second from the left). All that’s left, after checking to see that the ground connector is hooked up correctly, is to attach the air supply line to the first terminal (first connector on the left). All of these steps are taken before the equipment is turned ON position. By the way, the power supply for this machine allows for dual voltage input. The plug will hook up to a 110V or 220V (50/60Hz) power outlet, thereby giving users the flexibility to plug into domestic power or commercial/industrial outlets as well.
The last couple of pre-check steps have arrived. The cutting area is safe and so is the user. The same can be said for the equipment. The cutting head now requires attention. It’s assembled according to instructions in the operator’s manual. Again, the gear covered here features a non-touch pilot arc. The plasma cutting head must be assembled, complete with electrode and nozzle, as instructed so that the cutter will slice through the base metal as designed. If there are any irregularities in torch operation, the consumable components in the head will age prematurely. As a worst-case scenario, the torch won’t work at all.
As readers can probably guess, there’s one last operational component missing. That would be the pressurized air. The checklist has ensured proper hose connectivity. Now we have to provide pressurized air. An independent air compressor can easily take on this role, but it must deliver a consistent steam of high-momentum air to maintain arc stability. Likewise, that gaseous stream cannot contain any amount of humidity, which is something of a problem when air compressors are known to trap moisture within their inner workings. To address this issue, one that’ll cause a rough, uneven arc to form, a moisture trap is incorporated within the compressor line. Regular maintenance to the air compressor is advised if the moisture trap is to work effectively.
Post Plasma Cutting Care and Maintenance
This section of the post acts as a bookend for the pre-cutting portion. All of the prep work can be taken care of easily enough. The actual cutting workflow requires a conservative approach to what is a comparatively mild learning curve. The secret to mastering the technique lies in developing a precision-based approach to plasma cutting. Consistent torch head distance and angle are maintained from start to finish. The metal thickness, and this tool slices through most ferrous and non-ferrous alloys with equal alacrity, clues experienced journeymen into entering the correct amperage settings on the control panel, then there are data tables to aid those who don’t have that level of experience.
After the work area cools, though, a new set of operational criteria is set in motion. The cut cools. A heavy-duty fan, either built into the plasma cutter or placed independently within reach of a user, aids cooling. The equipment is turned off and made safe. If the machine user has practiced their sharp cutting skills on scrap metal pieces, there’s a good chance of a clean cut. Debris is gone, the base metal is cool, the job is complete. If the cut isn’t clean, there’s a few ragged edges to take care of, then the post-cut work adds some powered grinding to the job. This isn’t ideal, but it’s acceptable. Those post-clean-up jobs can accumulate, though, until work productivity numbers take a nasty tumble. Although this article deals mostly in basics, in principles dealing with how to plasma cut, the tech using the machine should work hard on eliminating such productivity losses.
A fan is built into the plasma cutter.
Maintenance is the final piece of the puzzle. Incidentally, there are 2 versions of the Tooliom TL-50C Plasma cutter available. The first model features the ever-desirable no contact pilot arc, but it employs a high-frequency (HF) ignition circuit. The second model incorporates NHF (Non-High-Frequency) starting. You’ll see this label added to the TL-50C designation on the front panel. That same front panel also includes a pressure gauge and the built-in Post Flow control. Use this latter setting to continue the gas stream after the arc has deactivated. The cooling effect initiated by this gaseous jet helps preserve the lifespan of the consumable components inside the torch head.
Besides consumable maintenance, there are a few other actions users can take to extend the life of their gear. For one thing, there’s no guaranteeing those consumables will remain free of metal debris. The torch head will need to be dismantled and cleaned to ensure optimal functionality next time a plasma cutting operation is called upon. As for the air compressor, its moisture trap and desiccant system could probably use some care. Then, inside the Tooliom machine at least, there’s a final-line water trap. It’ll require cleaning and drying every time a cutting project is completed.
Knowing how plasma cutters work, whether portable or sized to operate in large fabrication shops, is only the beginning. There are techniques to learn, equipment settings to master, and there’s always so much more to learn.
A Table-Condensed View of a Plasma Cutting Job
|Site preparation and safety
|Clear site of flammables. Ground clamp
|User safety and base metal prep
|Equipment setup. Torch head assembly
|Amperage settings and cable hookups
|Configure cutter for base metal thickness
|Compressed gas configuring
|Controls the quality of the plasma arc
|Optimizes cut quality
|Torch ignition and cutting
|Initiates the non-touch arc
|Delivers accurate and clean cutting power
|Post-cutting cooling and care
|Ensures quality cuts
|Assures quality end results
|Preserves equipment and torch head
|Extends equipment life
Welding Primer Series 3: How Does Plasma cutting Work - FAQ
Q: What is the difference between plasma cutting and welding?
A: Plasma cutting and welding are two completely different metalworking processes. Welding is the joining of two or more metal parts so that they fuse into a whole. Plasma cutting, on the other hand, cuts already formed metal parts by using a high-temperature plasma beam to separate them into different shapes or parts. Welding is an additive process whereas plasma cutting is a subtractive one.
Q: What is plasma?
A: Plasma is a state of matter that is not liquid, gas or solid. Plasmas are formed by superheating a gas, which causes electrons in the gas molecules to become excited, breaking the gas down into focused streams of charged particles. These charged particles form a high-energy plasma beam that can be used to cut through metals.
Q: How does plasma cutting work?
A: Plasma cutting is a process that uses a high-temperature plasma beam to cut metal. Here's how plasma cutting basically works:
- Plasma Formation: Plasma is a state of matter that is formed by superheating a gas. Excitation of the gas particles results in ionization of the gas, causing the gas to break down into a focused stream of charged particles.
- Airflow and Charge: Compressed air and equipment charges form these charged particles into a focused plasma beam. This plasma beam has high speed and can precisely melt the metal surface.
- Cutting operation: The operator uses a hand-held spray gun to control the cutting, maintaining a consistent distance and angle to ensure the accuracy of the cut. The cutting head never touches the metal but stays a consistent distance from the cut.
- Material Suitability: Plasma cutting is suitable for a wide variety of metal alloys, including copper, stainless steel, carbon steel, aluminum, and brass, among others.
- Safety and Maintenance: Plasma cutting requires following safety regulations, including wearing personal protective equipment, securing the cutting area, and maintaining equipment and air systems.