Plasma cutting uses a jet of superheated, electrically charged gas to melt through metal at temperatures approaching 28,000 °C (50,000 °F). It’s one of the fastest and most versatile ways to cut steel, aluminum, copper, and other conductive metals, and it’s widely used in fabrication shops, construction, automotive repair, and manufacturing. If you’ve seen someone slice through a steel plate like it’s butter, they were probably using a plasma cutter.
How Plasma Cutting Works
The process starts with an electric arc struck between an electrode inside the torch and the metal workpiece. A stream of gas, forced through a narrow copper nozzle, passes through this arc and becomes ionized, meaning its atoms lose electrons and the gas transforms into plasma. That constricted nozzle is critical: it squeezes the plasma into a tight, high-velocity jet that approaches the speed of sound.
When this plasma jet hits the metal, something interesting happens. The ionized gas recombines back into its normal state, and that transition releases intense heat concentrated in a very small area. The metal melts almost instantly, and the force of the gas stream blows the molten material out of the cut. The result is a narrow channel called a kerf, with the surrounding metal staying relatively cool compared to other thermal cutting methods.
What It Can and Can’t Cut
Plasma cutting works on any electrically conductive metal. That includes mild steel, stainless steel, carbon steel, aluminum, copper, brass, and hardened steel alloys. The electrical conductivity requirement is non-negotiable because the arc needs to complete a circuit through the material.
This means plasma cutting cannot handle wood, glass, plastics, rubber, or ceramics. Even some metals with poor conductivity, like lead, tin, and tungsten, are off the table. If your material doesn’t conduct electricity well, you’ll need a different cutting method entirely.
Gases Used in Plasma Cutting
The choice of gas affects cut quality, speed, and cost, and different metals pair best with different gases.
- Shop air is the most versatile and economical option. It produces good cut quality on mild steel, stainless, and aluminum without the cost of purchasing bottled gas. For shops that cut a variety of metals, compressed air handles most jobs well.
- Oxygen is the industry standard for mild steel specifically. It reacts with carbon steel to produce a finer spray of molten metal with lower surface tension, which ejects from the cut more cleanly. The result is the fastest cutting speed and best edge quality on mild steel, often eliminating the need for secondary cleanup.
- Nitrogen is the top choice for stainless steel and aluminum under half an inch thick. Consumable life is excellent with nitrogen, with electrodes and nozzles lasting more than 1,000 starts.
For cutting thick stainless steel and aluminum plate, some operators use a mixture of 65% argon and 35% hydrogen, which produces the hottest possible plasma arc.
Cutting Speed and Thickness
Plasma cutters are fast, especially on thinner material. A mid-range system can cut quarter-inch mild steel at around 145 inches per minute. More powerful units push that to 200 or even 220 inches per minute on the same thickness. As material gets thicker, speed drops significantly: one-inch steel typically cuts at 20 to 30 inches per minute, and heavy-duty systems can handle two-inch steel at about 6 inches per minute.
The power output of your system determines your maximum thickness. Smaller handheld units suited for light fabrication and repair work max out around half an inch. Industrial systems with higher amperage push well beyond an inch. Matching the right power level to your typical material thickness is the most important equipment decision you’ll make.
Precision and Cut Quality
Standard CNC plasma cutting systems hold tolerances between ±0.5 mm and ±1 mm, which is more than adequate for structural work, general fabrication, and most manufacturing applications. High-definition plasma systems tighten that to ±0.25 mm by using advanced nozzle designs, multiple gas types, and automated height controls.
Thicker materials naturally produce slightly looser tolerances because the increased heat input widens the kerf and can cause minor deviations. High-definition systems partly solve this problem with concentrated arcs and faster cutting speeds that limit the heat-affected zone around the cut. The practical benefit is cleaner edges with minimal taper, less dross (the hardened metal that clings to the bottom of a cut), and significantly less post-cut grinding or finishing work. Precision cutting also allows parts to be nested more tightly on a sheet, reducing scrap.
Safety Hazards to Know
Plasma cutting produces intense ultraviolet and infrared radiation that will burn exposed skin and damage unprotected eyes. “Arc eye,” the plasma cutting equivalent of sunburn on the surface of the eyeball, is caused by UV exposure and is painful enough to sideline you for days. A proper welding helmet or face shield with the correct shade lens is essential, not optional, along with long sleeves and gloves.
The other major hazard is fume exposure. The arc vaporizes metal in the kerf, producing smoke that can contain zinc, copper, magnesium, chromium, manganese, nickel, and cadmium depending on the material being cut. Short-term overexposure to zinc or copper fumes causes metal fume fever, which feels like a bad case of the flu. Cadmium fumes are far more dangerous: inhaling them can cause acute lung inflammation that is potentially fatal. Stainless steel is particularly concerning because it contains chromium.
Good ventilation is the first line of defense. A fume extraction system, either built into the cutting table or positioned near the work, pulls contaminated air away from the operator. When cutting stainless steel or coated metals, a respirator rated for metal fumes adds a necessary layer of protection. Keeping your head out of the plume sounds obvious, but it’s the single most common mistake operators make.
How Plasma Compares to Other Methods
Oxy-fuel cutting (using an oxygen and fuel gas flame) is the traditional alternative. It works well on thick carbon steel and costs less upfront, but it only cuts ferrous metals and is significantly slower on thinner material. Plasma handles any conductive metal and cuts thin to mid-range thicknesses much faster.
Laser cutting offers the tightest tolerances and finest edge quality, particularly on thin sheet metal. But laser systems cost substantially more to purchase and operate, and they struggle with very thick material where plasma excels. For most fabrication shops, plasma occupies the practical middle ground: faster than oxy-fuel, more affordable than laser, and versatile enough to handle the widest range of everyday cutting jobs.