What is Plasma Cutting? Definition, CNC Machine, How it Work


In this article, we will learn what is Plasma cutting, definition, process, types, CNC plasma cutting machine, applications, advantages, disadvantages, etc.

Let’s explore!

What is Plasma Cutting? Definition 

Plasma Cutting Definition

Plasma cutting is a method of cutting electrically conductive materials through an accelerated jet of hot plasma. It is also known as plasma arc cutting because an external power supply energizes the gases to such an extent that they ionize and create a plasma arc.

Firstly, the plasma arc melts the workpiece, cuts the targeted area, and finally blows away the molten metal.

Plasma Cutting Meaning

Plasma is the fourth state of matter. Ice melts if we provide energy in the form of heat. This melted ice is now water. If we give more heat, it will convert into steam. If we provide heat up to 11,700 °C, the steam gets ionized.

This ionized gas having high energy is plasma, the fourth state of matter.

what plasma cutting definition CNC machine how work
What plasma cutting definition CNC machine how work

Plasma cutting is also known as plasma arc cutting or plasma fusion cutting. It uses highly heated, ionized gas from a plasma torch to heat, melt, and then cut electrically conductive materials into desired designs and shapes.

  • This technique is often referred to as an alternative to laser cutting, oxy-fuel cutting, or water jet cutting.
  • It can be used for many metals like aluminium, steel, alloy steel, copper, etc.
  • It is applicable for materials with a thickness between 0.5 mm and 180 mm.
  • The process is very effective and budget-friendly; however, it has limitations.
  • The blog is focused on the process, working, the merits, demerits, and applications of plasma cutting. 

Brief Historical background 

Plasma cutting emerged from plasma welding in the 1960s. It became a very productive process in the 1980s while it was used for cutting sheet metal. The early plasma cutters were slow, ineffective, and costly.

In the 1980s and 1990s, CNC technology was introduced. It gave plasma cutting greater flexibility by allowing the metal to be cut in many different shapes. 

Since the last decade, manufacturers have introduced more features that have enhanced the process dramatically. New models have small nozzles and thinner plasma arcs which produce laser-like precision.

So. The new technology is advanced and efficient as well as budget-friendly. 

How Does Plasma Cutting Work?

Plasma Cutting Working Principle

The cutting of different types of metals occurs through two processes: mechanical cutting and the other is thermal cutting. The working principle of the Plasma cutting process is thermal cutting. Thermal cutting is based on melting the metal using heat instead of mechanical cutting.

The overall working of the system is such that the plasma cutters use compressed air or gases such as nitrogen. These gases then ionize, which produces plasma. The compressed gases come in contact with an electrode, and then ionization happens. This way, more pressure builds up. This building of pressure pushes a stream of plasma towards the cutting head. 

what plasma cutting cnc machine how work process
What plasma cutting CNC machine how work process Image: Machinemfg.com

The cutting tip narrows the flow, which aids in creating a stream of plasma. This stream is then subjected to the target area. There is a cutting table that connects the target area to the ground because plasma is electrically conductive. The plasma arc contacts the metal, and the high temperature melts it.

In the same instance, molten gases are blown away by high-speed gases. So, this is the basic working principle behind plasma cutting. 

Plasma cutting process

There is a variation available for the plasma cutting process, but the basic principles and components remain the same. The process completes in phases which are:

  • Pilot arc initiation 
  • Main arc generation 
  • Localized heating and melting 
  • Material ejection 
  • Arc movement 

Pilot arc initiation 

The process begins with the generation of 400V DC open-circuit voltage. The flow of compressed plasma gas is introduced into plasma torch assembly, which comprises an electrode and plasma nozzle. The power source provides negative voltage to the electrode, which acts as the cathode for the pilot arc circuit.

It closes the open nozzle circuit contacts, which generates a positive voltage on the nozzle temporarily. Hence, it serves as an anode for the pilot arc circuit.

Plasma cutting pilot arc initiation Image: WeldingPros.net

Then the ACS (Arc starting console) produces high frequency, the high voltage potential between electrode and nozzle, resulting in a high-frequency spark. The spark ionizes the plasma gas, and it becomes electrically conductive, creating a low-resistance current path between electrode and nozzle.

Then The pilot arc (low energy arc) forms on this path due to the flow and discharge of energy between the two components. 

Generation of Main Arc 

After the initiation, the pilot arc flows with plasma gas out from the nozzle onto the workpiece, which partially ionizes the in-between area. It forms a new current path which is low resistance.  The gas flow forces the pilot arc forwards, due to which it comes in contact with the workpiece.

The transfer produces the main plasma arc. The main arc carries out the cutting process. This way, the workpiece becomes part of the newly formed main arc circuit with an electrode.

The arc transfer also results in reopening or normally opening nozzle contacts. Now, the nozzle is no longer part of the pilot arc circuit, which allows the main arc to increase the cutting amperage.

Localized heating and melting of Workpiece

Consider a plasma-cutting torch head. The parts of this torch head include a shield, shield gas, nozzle, electrode, and cutting gas. The cutting gas may be argon or nitrogen. The shield gas may be CO2, compressed gas, or water jet, which keeps the workpiece and nozzle cooled.

  • The electrode part is negatively charged, while the nozzle is positively charged.
  • The workpiece is the area under consideration or we are working on; it also stays positively charged.
  • Since the electrode is negatively charged and cutting gas flows through an electrode, it ionizes.
  • When the ionized gas comes out of the nozzle, a spark ignites, converting it into superheated plasma.
  • The workpiece attracts it, and the temperature increase heats the workpiece due to which it melts.
  • Localized melting and heating are such that the nozzle compresses the flow through the opening, resulting in increased velocity and energy density of the plasma.
  • A high temperature plasma (20 thousand degree Celsius) is used.

The workpiece absorbs thermal energy from the plasma gas, increasing the internal energy of the material. Hence, the heating, melting, and then vaporization of the workpiece happens during the process. This way, the accurate and precise desired cut is achievable.

Material ejection 

The kinetic energy of plasma gas removes the width of the material and the cut product. In material ejection, the weakened material expels out of the kerf.

The current and the nozzle are responsible for the proper plasma gas flow so that the cuts are accurate. 

Arc movement 

The last step is arc movement, in which The initiation of localized heating and melting results in arc movement. The plasma arc either manually or automatically moves across the workpiece surface and creates the entire cut.

In the handheld system, the operator is performing the moving procedure with the help of a torch. The machine has programmed software that produces the torch head movement across the surface and creates perfect cuts in an automated system. 

Variants of Plasma Arc Cutting Process 

As mentioned earlier, the basic principle and components remain the same, but there are variants in the plasma cutting process. The variations differ based on the cooling system, type of plasma gas, kind of plasma, and electrode design.

Each variation gives advantages related to manufacturing application in terms of the material used and its properties. Some variations that are available include:

  • Standard plasma arc cutting 
  • Plasma arc cutting using a secondary medium 
  • Plasma arc cutting with water injection 

Processes accompanying Plasma Cutting 

Some processes accompany plasma cutting. They include; 

  • Fabrication
  • Bending
  • Rolling
  • Welding
  • Machining
  • Plough/Lumsden grinding
  • Edge preparation
  • Cleaning and preserving

Types of Plasma Cutting & Machine

There are many types of plasma cutting. They include:

  • Inverter plasma cutting 
  • Computer Numerical Control (CNC) plasma cutting. 

CNC Plasma cutting has three types: 

  • two-dimensional
  • three-dimensional cutting
  • Tube and section plasma cutting.

Let’s see the basics of these types of plasma cuttings in brief.

CNC Plasma Cutting Machine

It is an automated method. CNC techniques constitute CNC tables. These tables have torch heads controlled by a computer to achieve neat and sharp cuts. The computer software processes the information on ductwork so that flat patterns are formed to be cut with a plasma torch on the cutting table.

plasma cutting cnc machine
Plasma cutting CNC machine Image: CNC Laser Engraving

This technology was first launched in the early 1980s, and since then, it has gained popularity. 

Many workshops use CNC plasma cutters to manufacture decorative metalwork. The plasma tables used in CNC cutting were horizontal. But due to advancement, vertical tables are also introduced, resulting in more safety, high speed, and greater flexibility.

Configuration of CNC plasma cutting 

There are three main configurations;

  • 2-dimensional,
  • 3-dimensional,  and
  • tube and section plasma cutting. 

They differ based on the flexibility of the cutting head and forms of material used before processing. 

2-Dimensional/ two-axis plasma cutting 

It is also known as flatbed plasma cutting. It produces a flat profile from a sheet or plate and cuts the edges straight at 90 degrees to the profile surface. High-powered plasma cutting beds are configured through two-axis plasma cutting, which gives a large depth to cuts. ( between 100-150 mm)

3-Dimensional/ three-axis plasma cutting

It is similar to 2-Dimensional. But three-axis plasma cutting adds a third dimension by introducing an angular cut or beveled edge through the material. High-definition plasma cutting beds are operated this way; hence they give more flexibility, speed, and accuracy.

The three-axis plasma cutting process is performed when the cutting profile is used for welded fabrication. Due to the angular cutting ability, this technique can also create chamfer edges and countersunk holes on profiled holes.  

Tube and section plasma cutting

Compared to flatbed plasma cutting, the stock material and cutting axes are different in tube and section plasma cutting. The pipe is maneuvered under the beam while the cutting head stays still. It creates slots, tags, and holes within the pipe or section in addition to the end profiles. 

Inverter Plasma Cutting Machine

Inverter technology uses inverter plasma cutters. They need two kilowatts, and they are analogue plasma cutters. These cutters rectify mains supply over to DC.

It is then fed into a high-frequency transistor inverter between 10-200 kHz. A few years back, MOSFET transistors were used, which are now drastically replaced by IGBTs. 

Types of Plasma used in Plasma cutting

Depending upon the products to be manufactured and work volume, your CNC table uses different plasma sources. Based on these factors, different types of plasma are:

  • Air plasma 
  • Oxygen plasma 
  • High-definition plasma 
  • Conventional plasma 

All these types of plasma are common to manual plasma cutters, which are preferred for low volume work.

Air plasma 

Air plasma is the best go-to option for low-volume manufacturing. Steel fabrication machines of entry-level mostly use air plasma.

Oxygen plasma 

Oxygen plasma has better quality as compared to air plasma. Most mid-range fabrication shops use it.

High-definition plasma 

Precision plasma units are used to produce high-quality cuts. It is best for industrial use—the system utilizes multiple gases like hydrogen, argon, oxygen, nitrogen mixture, or compressed air.

The precision arc used in this process is 40-50 kilo amps per square inch. High definition plasma is the best choice for Steel services centers and other shops that perform high volume works.

This type of plasma provides high-quality fabrication. A manual plasma cutter uses high definition plasma 

Conventional plasma 

The handheld units are based on conventional plasmas. Manual plasma cutters use conventional plasma. Instead of plasma gas, it uses shop air. The nozzle shape determines the shape of the arc.

It produces amperage ranging between 12-20 kilo amps per square inch.

Applications of Plasma Cutting

The applications of plasma cutting are listed below:

  • Both mechanized and handheld systems use plasma cutting to cut a variety of conductive materials. 
  • Workshops use manual plasma cutters for factory maintenance, processing thin metal, agricultural maintenance, welding repair centres, and metal service centres. It is also used in construction, commercial shipbuilding, trailer production, cars repair, manufacturing, and welding. 
  • Mechanized plasma cutters are larger than manual ones fixed into punching, laser, or robot cutting systems. They are used in conjunction with Cutting tables.
  • General fabrication and job shops, HVAC and mechanical fabrication, and steel service centres use plasma arc cutting.
  • Farming and ranching, construction equipment, automotive restoration, ornamentation, pipes and pipelines, general construction, civil service construction, and many others use plasma cutting techniques. 
  • Manual plasma cutters are appropriate for light work. They are primarily seen in auto repair shops, garages, hobby shops and homes.

Advantages of Plasma Cutting

The advantages of plasma cutting are as follows:

  • Plasma cutting has versatility and compatibility. It can cut all electrically conductive materials; For example, mild steel, carbon steel, aluminium, stainless steel, brass, copper, and other metals. 
  • It produces different cuttings like bevel cutting, straight cutting, gouging, hole cutting, extended reach cutting, marking, fine feature cutting, etc. 
  • Plasma cutting can create Both large and medium thickness cuts on High alloy steel and aluminium materials.
  • It requires lower heat input, even for high-strength structural steel.
  • Compared to oxy-fuel, the cutting speed in plasma arc cutting is ten times higher.
  • It guarantees automation.
  • Plasma cutting software has many features. They are collision avoidance, bridge cutting, chain cutting, common-line cutting, multi-head cutting, and skeleton cut-up. 
  • The software ensures easier bevel set-up, improved hole quality, and faster cycle time. 
  • CNC machines possess high precision and repeatability.
  • It has a smaller cutting kerf compared to flame cutting. 
  • It can also cut in water which results in smaller HAZ.
  • It is a cost-effective method for medium thickness cuts. 
  • The reflective properties of material don’t affect plasma cutting. 
  • Whether automated or manual, the plasma torches can generate exact lines such as drawn with pencils. It results in higher accuracy and a cleaner cut edge.
  • Plasma cutters are quick and efficient. The fast process lessens the risk of metal abrasion, errors, and distortion. 
  • Plasma cutting is safer as compared to oxy-fuel. 

Disadvantages of Plasma Cutting

The disadvantages of plasma cutting are as follows:

  • It can be noisy in the case of dry cutting.
  • It results in increased power consumption.
  • It is more expensive than an oxyacetylene cutting system. 
  • Plasma cutting can be done up to 180 mm and 120 mm for dry cutting and underwater cutting, respectively. 
  • It has a more extensive Heat Affected Zone as compared to laser cutting.
  • The kerf is wider than laser cutting.
  • Most plasma cutters are not suitable for thick and dense metals.
  • Plasma cutting is noisy, and it produces excessive fumes. 
  • The process is cheaper, but it may become costly. Replacing The electrodes can be expensive if the machine breaks down. 
  • Specialist equipment is required to carry out the process. Similarly, a large amount needs to be paid to the specialist gas supplier. 

Conclusion 

Plasma cutting is a high-tech method that uses ionized gas to cut electrically conductive materials. The working principle is thermal cutting. It’s an efficient and cost-effective technique with many applications in different fields. Plasma cutting has many benefits like ease of use, cost-effectiveness, cutting speed, applicability to a wide range of materials, multi-tasking, and safer use.

The process of plasma cutting is either manual or automated. CNC plasma cutting is based on computer software to produce precise and neat cuts. CNC plasma cutting is then divided into three types of configurations that are 2D, 3D, and tube and section cutting. Another type is inverted plasma cutting which rectifies mains supply over to DC. 

Plasma cutting has numerous commercial and industrial uses mentioned above. Due to the versatility of the process, it can be used on several electrically conductive materials. It is an efficient and inexpensive technique that is much safer. It is safer, quicker, compatible, versatile, and results in greater accuracy.

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