What Is Plasma, Exactly?
Most people are familiar with three states of matter: solid, liquid, and gas. Plasma is the fourth. When you heat a gas to extreme temperatures -- above 20,000 degrees Celsius -- the atoms lose their electrons entirely, producing a superheated soup of ions and free electrons that conducts electricity. That is plasma, and it is the heart of how plasma cutting works.
Stars are made of it. Lightning bolts are made of it. And your parts are cut with it.
How the Arc Is Struck
A plasma cutter works by establishing an electrical arc between an electrode inside the torch and the workpiece itself. Here is the sequence:
- High-frequency current ionizes the plasma gas inside the torch body, creating a pilot arc between the electrode and the nozzle.
- When the torch approaches the workpiece, the arc transfers from the nozzle to the metal, completing a circuit through the workpiece and back to the machine.
- The plasma gas -- pressurized and channeled through a small orifice in the copper nozzle -- is superheated by the arc and exits as a focused, high-velocity jet.
- That jet melts the base metal almost instantly. The velocity of the gas blows the molten material downward and out of the cut path.
The workpiece must be electrically grounded (clamped to the machine's work lead) for the transferred arc to function. This is why plasma cutting is limited to electrically conductive materials.
Plasma Gas and Shield Gas
The composition of gases used matters. Most shop plasma systems use compressed air as the plasma gas because it is cheap and effective on mild steel and aluminum. More specialized systems use:
- Nitrogen for a cleaner cut on aluminum and stainless, reducing oxidation on the cut edge
- Oxygen for faster cutting speeds on mild steel, producing a brighter cut face
- Argon-hydrogen blends for premium stainless steel cutting, minimizing heat tint
A secondary gas -- the shield gas -- surrounds the plasma jet and protects the cut zone from atmospheric contamination. On fine-cut machines, the shield gas shape is optimized to keep the plasma column tight and stable.
Why It Only Works on Conductive Materials
Plasma cutting requires the arc to complete a circuit through the material. Non-conductors -- wood, plastic, glass, composites -- cannot do this. Among metals, it works well on mild steel, stainless steel, aluminum, copper, brass, and titanium. The specific cutting parameters differ by material and thickness, but the physics is identical.
Fine/HD Plasma vs. Conventional Plasma
Not all plasma cutting is equal. Conventional plasma -- the kind in a repair shop or farm shed -- produces a wide kerf, significant edge bevel, and heavy dross on the bottom of the cut.
Fine-cut and high-definition (HD) plasma use a more tightly constrained nozzle geometry, precise gas flow control, and optimized voltage and amperage ramps to produce dramatically better results:
- Kerf width: fine cut is typically 0.060" to 0.090" vs. 0.150"+ on conventional
- Edge bevel: 1-3 degrees on fine cut vs. 5-10 degrees on conventional
- Dross: significantly reduced, often minimal on thin gauge
- Dimensional accuracy: fine cut machines hold +/- 0.030" routinely
For part quality that approaches laser on thin and mid-thickness material, fine cut plasma is the standard.
Cutting Speed vs. Thickness
Plasma cutting speed is inversely proportional to material thickness. On 18-gauge steel (0.048"), a fine-cut machine can move at several hundred inches per minute. On 3/4" plate, the speed drops to tens of inches per minute and the amperage rises substantially.
This has practical implications for quoting: thin sheet is fast and inexpensive per square inch; thick plate takes more time and machine power per part, reflected in higher prices.
Can-Cut's CNC Table
Can-Cut runs a CNC plasma table with a 48" x 96" working area. Every order is cut at fine-cut standard -- no conventional plasma, no shortcuts. The CNC controller drives the torch along the programmed path generated from your DXF file, holding consistent arc voltage through automatic height control. Parts are nested automatically to maximize sheet utilization before cutting.
How Plasma Compares to Laser and Waterjet
Each process has a home:
Laser cutting produces the tightest kerf and best edge quality on thin gauge (under 1/4"). It is slower and more expensive on mid-thickness plate and generally cannot compete with plasma on anything above 3/8".
Waterjet cutting uses abrasive water at extreme pressure. It produces no heat-affected zone and can cut nearly any material. However, it is slow, expensive, leaves a wet part, and requires additional drying and cleanup. It excels on composites, stone, and glass where plasma cannot reach.
Plasma cutting sits in the practical middle: fast on thin and mid-thickness metal, cost-effective, no water cleanup, and capable through 3/4" plate without a dramatic speed penalty. For structural and fabricated metal parts, plasma is almost always the most economical choice at mid-thickness.
Real-World Applications
Plasma cut parts show up everywhere in fabrication:
- Structural brackets, gussets, flanges, and frame components
- Agricultural equipment parts: hitch plates, toolbar brackets, wear components
- Automotive: subframe gussets, skid plates, trailing arm brackets, exhaust hangers
- Architectural and decorative panels, signage, gates, and railings
- Industrial: machine guards, mounting plates, conveyor components
- Shop tooling: jigs, fixtures, templates
If it needs to be cut out of flat metal stock and it doesn't require machined tolerances, plasma is usually the fastest and most cost-effective path.
Ready to Cut Your Parts?
Upload a DXF file and get an instant quote at can-cut.ca. No account required -- just drop your file, pick your material and thickness, and see your price.