Plasma cutting

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Plasma cutting is a manufacturing method to process conductive materials that is usually applied to cut parts out of metal sheets.

What is Plasma Cutting?

Plasma cutting is a manufacturing process where a high-velocity jet of ionised gas melts and cuts through electrically conductive materials. Gases commonly used in this cutting process include compressed air, oxygen, argon, hydrogen, nitrogen, and some combinations.

Plasma gun cuts through a pipe

Plasma cutting, also known as Plasma arc cutting is widely used in several industries, such as metal manufacturing, construction, Maritime (shipbuilding), automotive and Oil and gas, to produce structural beams, Ship hulls, bulkheads, gunwales, Platforms and storage tanks, and Vehicle bodywork.

How does plasma cutting work?

When machines are automated, the CNC program must be loaded into the machine to provide the instructions that will dictate the movement of the cutter. However, there are some manual plasma cutters where the operator dictates the movement.

The critical components of a plasma cutting machine are:

Plasma cutting overview (Source :Open university)
  • DC power supply
  • An electrode
  • A swirl ring
  • Cutting tip or nozzle
  • Nozzle holder or shield cup
  • Shield gas
  • Plasma gas

In general, the process of plasma cutting involves the following steps:

  • Electric arc generation – The DC power supply energises the electrode to generate an electric arc.
  • Gas supply – An ignition or plasma gas supply helps complete the arc generation, also known as the pilot arc.
  • Ionization – The copper nozzle and a secondary gas, the shield gas, constrict the electric arc, thus increasing the temperature and ionising the air gap between the electrode and the workpiece.
  • Plasma generation and arc transfer – The constricted electric arc ionises and heats the gas to temperatures as high as 20,000 °C. This extreme temperature converts the gas into what is known as the fourth state of matter, plasma. Then, the arc transfers to the workpiece thanks to the conductivity of the plasma.
  • Cutting – The plasma gas is pushed at high pressure and speed onto the workpiece, thus cutting the material by melting it. Here, the secondary gas also plays a critical role since it cools down the torch and protects the cutting area from external contamination.

What are the advantages of plasma arc cutting?

  • Increased sheet thickness – Hand-operated plasma cutting can cut sheets with a thickness of up to 38 mm, which is more than the laser cutting capabilities. Moreover, manufacturers can use automated cutters to cut sheets up to 150 mm. However, this requires a much higher energy input.
  • Lower cost – Plasma arc cutting usually requires a lower initial investment than laser cutting.
  • Low maintenance – Plasma arc cutting machines require less maintenance than laser cutting, and replacement parts are cheaper.
  • Speed – Plasma arc cutting can cut thick sheet metal faster than laser cutting.
  • No warping – Plasma arc cutting speed prevents heat transfer and accumulation. So, no warping is generated.

What are the disadvantages of plasma arc cutting?

  • Material limitation – Plasma arc cutting is limited to conductive materials. Manufacturers needing to cut other types of material may need to look for an alternative.
  • Low-quality finish – Plasma arc cutting leaves a lot of molten residue and rough edges.
  • Post-processing requirements – Plasma arc cutting requires post-processing due to its low-quality finish. Deburring and polishing are common after plasma cutting.
  • Larger kerf – Plasma cutting cannot achieve as highly accurate and delicate contours as laser cutting.

Common plasma arc cutting materials

Plasma cutting works only with conductive materials since the workpiece must be able to receive the electric arc and complete the circuit. Therefore, the most common plasma-cutting materials are:

What is the difference between plasma and laser cutting?

FeatureLaser cuttingPlasma cutting
Heat sourceConcentrated beam of lightJet of plasma
Materials cutMetals, plastics, wood, glassMetals, plastics, ceramics
Cut thicknessThin to thickThick to thin
Cut accuracyVery highHigh
Cut qualityExcellentGood
SpeedFastFast to medium
CostHighLow to medium
Plasma cutting vs Laser Cutting

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