Plasma Cutting
Also: CNC plasma cutting, plasma cutting service, high-definition plasma, HD plasma, plasma table, plasma profiling, plasma burning, plasma arc cutting
Plasma cutting profiles conductive plate with a constricted arc: the cheapest cut through 6-50 mm carbon steel, at ±0.5 mm with a small bevel and a hardened edge.
262 plasma cutting companies in the Noramark directory
An electric arc between an electrode in the torch and the workpiece is squeezed through a small nozzle with a gas (air, oxygen, nitrogen or an argon-hydrogen mix), heating the gas to a plasma at 20,000 °C and more. The plasma melts the metal and its velocity blows the melt out of the kerf as a CNC gantry moves the torch. High-definition (HD) systems use a tighter nozzle, a shield gas and a controlled arc to give a narrower kerf, a squarer edge and less dross than conventional air plasma. Bevel heads cut weld preparations in the same pass, and pipe and beam machines cut structural sections.
For carbon steel plate from 6 to 50 mm (1/4-2") plasma is the fastest and cheapest cut per meter, on tables up to 3 x 12 m: structural parts, base plates, gussets, brackets, weldment blanks and wear parts. HD plasma holds ±0.4-0.8 mm (±0.015-0.030") with a 1-3° bevel; conventional plasma holds about ±1.5 mm (±1/16") with 3-10° of bevel. Stainless and aluminum cut too, with nitrogen or argon-hydrogen, at a rougher edge with more dross. A fiber laser is faster on thin plate, plasma pulls level around 12-16 mm, and above 20 mm plasma wins on cost.
The edge is the compromise. A heat-affected zone of 0.5-3 mm hardens the edge on medium-carbon and alloy steels (drilling a plasma-cut edge in 4140 is unpleasant, and welding it without preheat cracks), air and nitrogen cutting leave a nitrided skin that causes weld porosity unless ground back, the top edge rounds, and a line of dross sticks to the bottom. Holes come out tapered with a divot at the lead-in unless the diameter is at least the plate thickness. Sheet under 3 mm warps, and non-conductive materials cannot be cut at all.
At a glance
| Typical tolerances | High-definition plasma: ±0.4-0.8 mm (±0.015-0.030") standard on plate 6-25 mm (1/4-1") thick, ±0.25 mm (±0.010") with care on a calibrated table with fresh consumables and torch height control; conventional air plasma ±1.5 mm (±1/16"). Edge bevel of 1-3° on HD, about 0.2-0.5 mm across a 12 mm edge and worse on one side of the kerf than the other, and 3-10° on conventional. Holes hold about ±0.25-0.5 mm when the diameter is at least the plate thickness; smaller holes taper and are usually drilled instead. Kerf 1.5-2.5 mm (0.060-0.100") on HD and 3-6 mm (1/8-1/4") on conventional. Long parts grow 0.5-1 mm per meter during the cut. |
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| Size limits | Tables from 1,500 x 3,000 mm (5 x 10 ft) to 3,000 x 12,000 mm (10 x 40 ft), with rail systems for longer plate. Thickness: HD systems at 130-300 A pierce carbon steel to 25-45 mm (1-1-3/4") and edge-start to 50-80 mm (2-3"); 400-800 A conventional systems cut mild steel to 100-160 mm (4-6") from an edge. Stainless and aluminum typically to 25-50 mm (1-2"). The practical minimum is about 1-1.5 mm (16-18 gauge) on HD, with warping below 3 mm (1/8"). Minimum hole about one plate thickness on HD with hole-cutting technology, 1.5-2 thicknesses otherwise. |
| Surface finish | Cut edge 6-12 µm Ra (250-500 µin) on HD plasma, rougher and more oxidized on conventional, with a rounded top edge and a line of dross on the bottom that a grinder or scraper removes in seconds on a good cut. Heat-affected zone of 0.5-3 mm (0.020-0.120"), hardened on medium-carbon and alloy steels (edge hardness on 4140 and 1045 can pass 50 HRC) and nitrogen-enriched when cut with air or nitrogen, which causes weld porosity unless the edge is ground back 1-2 mm. Oxygen plasma on carbon steel leaves a cleaner, more weldable edge. The finish suits structural and painted parts and nothing that seals or bears. |
| Lead time | Parts in 1-3 business days from stocked plate; production in 1-2 weeks. Plate availability (thickness, grade, mill certs) drives lead time more than cut time, and heavy plate beyond 50 mm (2") may be a mill order. |
Typical of U.S. job shops; confirm with the shop for your part.
Materials
Carbon steel plate is the home turf: A36 and A572 Grade 50 structural plate, 1018 and 1045, and abrasion-resistant plate. Alloy steels 4140, 4130 and 8620 cut fine but harden at the edge and need preheat or grinding before welding. Stainless 304, 316 and 2205 duplex cut with nitrogen or argon-hydrogen, leaving an oxidized, rougher edge that is dressed before welding. Aluminum 5052, 6061 and 5083 cut with argon-hydrogen or air, with more dross and a wider kerf. Gray cast iron cuts roughly. Copper and brass are poor because they conduct the heat away, and plastics, composites, wood, stone and glass cannot be cut.
What drives the cost
- Cut length and pierces at the speed the thickness allows: a plasma hour is cheap, about $60-120 in the U.S., and covers many meters of cut in 12 mm steel
- Plate cost and nest yield: material is the largest share of the price on thick plate
- Thickness: above 25 mm (1") pierce time grows and consumable life falls
- Consumables: nozzles and electrodes wear with every pierce and every meter, faster on stainless and aluminum
- Edge requirements: grinding off dross, hardened or nitrided edges before welding or machining is labor
- Holes and tolerances: small precise holes drilled or machined after cutting, and ±0.25 mm work that slows the table
- Secondaries: beveling for weld preps, forming, welding, blasting and painting
When to use it
- Carbon steel plate from 6 to 50 mm (1/4-2") thick: structural parts, base plates, gussets, brackets, weldment blanks and wear parts
- Large or long parts that fill a 3 x 6 m or 3 x 12 m table
- Parts that will be welded, ground and painted, where ±0.5 mm and a plasma edge are fine
- Beveled weld preparations cut in the same pass with a bevel head
- Quantities of one to hundreds in heavy plate, where the cutting cost must stay below the material cost
When not to
- Sheet under 3-6 mm (1/8-1/4"): a fiber laser is faster, squarer and does not warp it
- Tolerances below ±0.25 mm (±0.010"), square edges, small holes or bearing surfaces: laser, waterjet or machining
- Heat-sensitive or hardenable material where the edge must stay soft or the part must not distort: waterjet
- Non-conductive materials: plastics, composites, stone, glass and wood
Design tips
- Make holes larger than the plate thickness and call out drilled or machined for anything that needs a fit or a thread; plasma holes are tapered and keep a lead-in divot.
- Keep features 1.5-2 thicknesses from the edge and from each other so the web between them does not overheat and sag.
- Allow for the bevel and a 1-3 mm hardened, nitrided edge; if the edge will be welded, machined or fatigue-loaded, specify grinding back or an oxygen cut on carbon steel.
- Add 1-2 mm (0.040-0.080") of machining stock on datum edges and bores that will be finished later.
- Use a bevel head for weld preps: a 30-45° bevel with a 1-2 mm land cut in the same pass beats grinding it in.
- Send a 1:1 DXF with thickness, grade (A36, A572 Gr 50, 4140) and quantity, and say whether mill certs are needed.
- For 4140, 1045 and other hardenable steels, plan a preheat before welding the plasma-cut edge or ask for a stress relief.
Frequently asked questions
- How thick can plasma cut steel?
- A high-definition system at 130-300 A pierces carbon steel to 25-45 mm (1-1-3/4") and cuts to 50-80 mm (2-3") from an edge start. Heavy conventional systems at 400-800 A cut mild steel to 100-160 mm (4-6") from an edge. Stainless and aluminum usually stop at 25-50 mm (1-2").
- Plasma or laser cutting?
- Laser for sheet and plate to about 12-16 mm: faster, ±0.1 mm, square edge, small holes. Plasma for carbon steel from about 12 mm up to 50 mm and beyond: much cheaper per meter, ±0.5 mm, a small bevel and a hardened edge. Above 25 mm the laser has left the race; for stainless and aluminum over 20 mm consider waterjet.
- What tolerance can CNC plasma cutting hold?
- High-definition plasma holds ±0.4-0.8 mm (±0.015-0.030") on 6-25 mm plate and ±0.25 mm (±0.010") with care; conventional air plasma holds about ±1.5 mm (±1/16"). Edges carry a 1-3° bevel on HD. Anything that needs better is drilled, machined or cut on a laser or waterjet.
- Does plasma cutting harden the edge?
- On medium-carbon and alloy steels, yes: the 0.5-3 mm heat-affected zone quenches against the cold plate and can pass 50 HRC on 4140 or 1045. Mild steel (A36, 1018) stays soft enough to drill. Air and nitrogen cutting also leave a nitrided skin that causes weld porosity, so grind the edge back or specify an oxygen cut.
- Can plasma cut aluminum and stainless steel?
- Yes, with the right gas: nitrogen or argon-hydrogen for stainless and argon-hydrogen or air for aluminum, typically to 25-50 mm (1-2"). Expect a rougher, oxidized edge and more dross than on carbon steel, and dress the edge before welding. For thin material or a clean edge, a fiber laser or waterjet does better.
