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Plasma Cutting: Explaining The Working Principle, Materials, Advantages, and Limitations

The concept of plasma cutting is rather simple. You use a super hot stream of ionized gas to melt down the selected conductive metal and separate the section.

Compared to other cutting processes, plasma cutting seems economical and convenient for conductive metals. Read this article to learn everything about this plasma-cutting technology.

Plasma Cutting: A Quick Introduction

Are you familiar with the fourth fundamental state of matter? Yes, plasma.

You can not bind plasma using simple gas, solid, or liquid definitions. Instead, plasma is a special matter made of electrically conductive ionized gas.

It is definitely possible to transform gas into superheated plasma. You would need a high heating source and electrical energy for this purpose.

In a heated electrical state, the gas molecules vibrate violently, losing their electron neutrality. Hence, an ionized gas, aka. plasma is formed.

The plasma cutting technology utilizes this superheated ionized gas to create an electric arc. This arc can cut through materials by melting them instantly.

Are you wondering how an ionized gas can melt and separate materials?

Well, plasma torches can reach up to 40,000˚ F temperature while the sun’s surface is only 10,000˚ F. Now, you can do the math!

Figure: Plasma Cutting Technology

Types of Plasma Cutting

You can divide the plasma cutting technology into two main categories. Such as,

1. Conventional Plasma Cutting System

In this system, the surrounding air is used as the plasma arc. You receive a less precise cut with the conventional plasma cutting. This system only suits materials with lower tolerance.

2. Precision Plasma Cutting System

Compressed oxygen, nitrogen, hydrogen, and argon, or a mixture of a few gases, are used in this plasma-cutting system. With this technique, you can cut a wide range of materials with superior precision.

Figure: Precision Plasma Cutting

The plasma cutting technology can be further classified into two types. Such as,

1. High Frequency Contact

In this system, the plasma arc is initiated by direct contact between the nozzle and the workpiece. Typically, a high-frequency contact plasma cutter can cut materials around 38 mm thick. This fast process is used in industries to produce clean cuts.

2. Pilot Arc

There is no direct contact between the nozzle and the workpiece here. Instead, a high-voltage current is applied to create an arc from the electrode to the workpiece. The arc ionizes the gas, transforming it into a plasma stream. This plasma stream then melts and cuts the materials.

How Does The Plasma Cutting Work?

In simple terms, the superheated plasma melts the materials at the targeted zone. Then, this high-velocity stream blows away the molten materials, leaving a clean cut behind.

But how exactly do you get this precise cut?

If you break down the plasma cutting system, you will find 3 main components. Such as,

Power supply
Plasma torch
Workpiece

Once you turn on the power supply, it produces a high-voltage electrical arc from the electrode torch to the workpiece. At the same time, compressed air is passed through a nozzle surrounding the electrode.

As mentioned above, electrical power can rip away the electrons of gaseous molecules, turning the stream into high-temperature plasma. The plasma generates enough temperature to cut steel, brass, copper, and aluminum-like materials.

Figure: Working Principle of Plasma Cutting

Main Parts of A Plasma Cutting Machine

You would need multiple elements to complete a plasma cutting system.

1. Power Supply

A ground-stationed power supply is the source of electricity in a plasma cutter. It provides a constant DC voltage between 200 and 400 volts.

2. Arc Starting Console

ASC is responsible for creating the spark that starts the plasma arc.

3. Gas Console

This console controls the flow rate and pressure of supplied gases required for plasma generation and cutting. It also ensures the proper functioning of the plasma and shields gases inside the torch nozzle. If necessary, you can add an air compressor to your plasma cutting system.

4. Plasma Torch

The metal plasma cutter torch is handheld or mounted, similar to a welding torch. It consists of a torch head, an electrode, a nozzle, and a swirl plate. The needle and nozzle are often replaced due to natural wear and tear.

5. Cooling System

You might want to install a cooling system to avoid overheating the torch components. The cooling system can use either water or air to cool the cutter torch body and consumable parts.

Figure: Plasma Cutter System

Process Parameters of Plasma Cutting Process

You can control the plasma cut quality and finish with the following parameters,

1. Gas Flow Rate

The plasma gas flow affects the arc stability and efficiency. By adjusting the gas flow rate, you can choose the shape and quality of the cut.

2. Arc Current

Plasma intensity, cutting speed, and capacity are directly linked to the arc current. A higher arc current causes more heat and leads to faster cutting speeds. Lower arc currents give slow cutting speeds but are good for precision cuts.

3. Cutting Speed

The cutting speed is the rate at which the metal plasma cutter torch moves across the workpiece. An excessively high cutting speed causes uneven cuts with rough edges. Again, slow cutting speed might lead to heat input deformation.

4. Arc Voltage

It is the electrical potential difference across the plasma arc. This voltage value influences stability and the length of the arc, which, in turn, determines the quality of cuts.

5. Gas Type and Pressure

The choice of a gas and its pressure can be defining factors of cutting quality and dross production. The higher gas pressures may be advantageous only to improve the cutting efficiency.

6. Nozzle Size and Shape

You can use different nozzles, for instance, fine detail cut, bevel cut, and gouging, according to your task. Nozzle size and shape decide the arc length and gas flow rate.

7. Material Thickness and Type

The materials with the higher thickness mostly go hand in hand with higher arc currents, lower cutting speeds, and larger nozzle orifice sizes. Furthermore, some materials require particular gas types or kerf-cutting approaches to obtain clean cuts and reduce waste.

Materials Compatible with Plasma Cutting

Plasma cutting is mainly dedicated to cutting conductive metals. Common metals and their usages are highlighted below,

Metals	Served Industries
Steel, mild steel, and stainless steel	Automotive, food, and medical
Cast iron	Automotive and construction
Aluminum	Aerospace and automotive
Copper	Electrical
Brass	Architectural and decorative
Titanium	Aerospace and medical

Figure: Conductive Materials for Plasma Cutting

Gases Used in Plasma Cutting System

You can use only some selective gases to conduct the plasma-cutting operation.

Gases	Compatible with Metals	Comments
Compressed air	Mild steel, stainless steel, aluminum	Quality cut and economical
Oxygen	Mild steel	Can cut metals greater than 1’’
Nitrogen	Stainless steel and aluminum	Quality cut
Argon/hydrogen	Stainless steel and aluminum	Can cut metals greater than 1/2’’

Benefits of Plasma Cutting

The major advantage of plasma cutting is that you can cut conductive metals with this technique. You can achieve precise and quality cuts with a metal thickness of up to 50 mm. You can push the thickness limit to 150 mm with a few adjustments.

Plasma cutting creates a minor heat-affected zone in the workpiece. However, you can control the severity using coolants.

Plasma cutting is cheaper and faster than other cutting technologies. With a CNC plasma cutting setup, you can upgrade the cut and finishing quality.

Figure: Benefits of Plasma Cutting

Limitations of Plasma Cutting

No matter how lucrative the plasma-cutting advantages seem, there are a few downsides as well. You must consider both sides before selecting this cutting technology. The main downsides are,

You can not achieve precise cuts for thin sheets and plates.
Plasma cutters are only compatible with conductive metals. This means you can not process non-conductive materials like polymer, glass, ceramics, etc., using plasma cutting technology.
Plasma cutting can’t always fulfill the standards for precision machining. It might leave slag, residual scrap or rough edges on complex geometries.

Comparison Between Plasma Cutting, Laser Cutting, and Waterjet Cutting

Plasma cutting is mostly compared to laser cutting and waterjet cutting. You can find a plasma cutting vs. laser cutting vs. waterjet cutting comparison chart below,

Features	Plasma Cutting	Laser Cutting	Waterjet Cutting
Installation Cost	Cheap	Expensive	Expensive
Cutting Depth	<3.15’’	< 0.98’’	Up to 12’’
Cutting Non-Metallic Materials	No	Yes	Yes
Cutting Quality	Good	Excellent	Excellent
Cutting Speed	Very Fast	Fast	Slow
Tolerance	±0.02 to ±0.1 inches	±0.002 to ±0.01 inches	±0.001 to ±0.005 inches

Conclusion

Plasma cutting technology is comparatively simple and cheaper than other cutting operations. It ensures a quick turnover and quality mass production.

Plasma cutting is well-suited and guarantees a precise cut for metals with moderate thickness. If you want the utmost accuracy for your products, explore other cutting options, e.g., waterjet cutting.