Plasma Cutting: Definition, Process And Advantages
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Plasma Cutting: Definition, Process And Advantages
Plasma cutting has been a game-changing technology in the manufacturing space. Also known as plasma arc cutting, this fabrication process uses a jet of high-temperature ionized gas to melt and remove molten material from the cut surface. This accelerated jet of hot plasma is only effective for electrically conductive materials.
The plasma cutting process offers a variety of benefits in the manufacturing industry — these range from high precision and speed to repeatability and cost-effectiveness. Thanks to these advantages, plasma arc cutting has plenty of applications including metal fabrication, construction work, car repairs and restoration, military manufacturing, and artistic endeavors.
In this guide, I’ll comprehensively cover the basics and fundamental principles of plasma cutting. I’ll answer all your pressing questions starting with What is plasma cutting? How does it work? What are the different types of plasma cutting processes? And what are the pros and cons of this machining process? Join me as I share fascinating insights into the plasma cutting process and provide you with all the details you need to know.
History of plasma cutting
Today, plasma cutting is recognized as a fast, effective, and affordable cutting method with a wide range of applications. However, this has not always been the case. To appreciate the capabilities of modern plasma cutting machines, we need to recognize their fascinating evolution over the decades.
Plasma cutting has been around since 1957. It was created by Dr. Robert Gage of Union Carbide as part of the GTAW (Gas tungsten arc welding) process.
In the early stages, plasma cutters were massive, slow, and quite costly. Therefore, this technology was mainly used by large corporations in mass-producing products.
Today, plasma torches have become dramatically compact. Equipment that would once occupy an entire room can now be slung over an operator’s shoulder as they climb up a ladder. Further, this technology has become more affordable. Even hobbyists can now purchase plasma cutters and this has expanded the uses of these equipment.
Here are some of the most significant moments in the plasma cutting evolution timeline.
1957 — Union Carbide introduces the plasma arc cutting process. The conventional plasma process is slow and the cut quality is quite low. It typically uses a costly gas mixture argon and hydrogen.
1962 — Dual flow plasma torches are developed. This improves the cutting speed, cut quality, and longevity of the electrode and nozzle in plasma cutters.
1963 — Air plasma cutting is adopted for mild steel. This process had significantly higher cutting speeds.
1968 — Water injection plasma cutting is introduced. This process requires only one gas (nitrogen), making it more cost-efficient and simpler to use.
1977 — Underwater cutting is developed as a solution to excessive noise and smoke generation.
1985 — The first handheld plasma cutting system is introduced.
As computer technology was adopted across most industries, CNC (computer numerically controlled) plasma cutters emerged in the 1980’s and 90’s.
Now that we’re familiar with the backstory of plasma cutting, I’ll take you through the basics of this fabrication method.
What is plasma cutting?
Plasma cutting is a sheet metal fabrication process that uses an accelerated jet of hot plasma to cut through electrically conductive metals. But what is plasma? Plasma is considered to be the fourth state of matter — after solid, liquid, and gas. Plasma is generated when a gas is subjected to very high temperatures such that its electrons are separated from the atoms. This creates a mix of free electrons and ions(atoms with an electric charge due to gaining or losing one or more electrons.)
With this cutting method, the hot plasma is responsible for melting the material and removing the molten material from the cut. This creates the desired parts.
Plasma arc cutting is specific to electrically conductive materials such as aluminum, stainless steel, and copper. Unfortunately, this means that this process is not viable for non-conductive materials such as glass, stone, and wood.
This fabrication method has proven very affordable when cutting thick metals. Further, it offers high precision and is, therefore, capable of machining intricate details and complex geometries.
How does plasma cutting work?
The next question that you may be asking is “How exactly does plasma cutting work?” In this section, I’ll cover the step-by-step workings of a plasma cutter.
Instead of mechanical cutting processes, plasma cutters utilize heat to melt a metal. These systems require compressed air or gases such as oxygen, nitrogen, argon, and hydrogen. The gas or gas mixture is super-heated to create plasma. The choice of gas will depend on the specific cutting method, cutting material, and its thickness.
Different plasma cutting systems will operate in different ways. However, the underlying principle is essentially the same for all processes.
Here is a step-by-step breakdown of the primary plasma arc cutting process.
A pilot arc is initiated
The pilot arc originates from a 400VDC open-circuit voltage charge that triggers the flow of the plasma gas into the plasma torch assembly. The plasma torch is equipped with an electrode and a nozzle.
The power source will also supply a negative voltage to the electrode and close the plasma nozzle. Therefore, the electrode will become a cathode(negatively charged) while the nozzle becomes the anode(positively charged.)
The ASC or arc starting console generates a high-voltage potential between the cathode and the anode. This results in a high-frequency spark. The spark will then ionize the plasma gas making it electrically conductive. This generates an electric arc known as the pilot arc.
The Main arc is created
The main arc is formed when the pilot arc and plasma gas pass through the nozzle, flowing towards the workpiece. This main electrical arc occurs when the pilot arc connects with and transfers to the workpiece. The main arc, also known as the plasma arc, performs the actual cutting processes.
Heating and melting is localized
Ionized gas and the main arc pass through the constricted nozzle opening. The restricted opening means that the gas squeezes through at a high speed resulting in high velocity plasma. Plasma can reach temperatures of up to 20,000°C and it approaches the workpiece at very high speeds.
As the plasma arc comes into contact with a localized region of the workpiece, it melts and vaporizes the material. Owing to the electrical conductivity of plasma, the workpiece should be grounded through the cutting table.
Molten metal is removed
Next, the loosened material is removed from the workpiece thanks to the energy generated by the moving plasma gases. The ideal flow of the plasma gas is contingent on the current and nozzle. If the flow deviates from the optimal range, it can affect the precision of the system.
Arc is moved
To complete the cut, the plasma arc is repositioned across the workpiece surface as required. This can either be a manual or automatic process. If you’re working with handheld units, the operator will need to manually move the plasma torch to perform machining operations. Conversely, in the case of an automated plasma cutter, the machine is designed to do the heavy lifting for you.
As we’ve already established, different plasma arc cutting systems will operate in different ways. Here are the three types of cutting processes that you can expect to come across.
Types of Cutting Process
High-Frequency Contact
High-frequency contact is a cheaper cutting process. Note that this method is not used with CNC plasma cutters since it isn’t compatible with modern equipment.
As the name suggests, this cutting technique utilizes a high-frequency spark and high voltage. Once the plasma torch head touches the cut metal, this contact creates the spark, generating the plasma required for cutting operations.
Pilot Arc
With this process, the spark comes from a mix of low current circuit and high voltage. The spark is necessary for the generation of a pilot arc as well as some plasma. Contact between the plasma cutter and workpiece generates the main arc used to cut metals.
Spring Loaded Plasma Torch Head
In this technique, the plasma torch head is pressed against the surface of the workpiece. This generates a short circuit, and current will flow as a result. To form the pilot arc, the pressure will need to be released.
Materials for Plasma Cutting
Plasma cutting can be used for many materials since this fabrication process works for any conductive materials. However, this cutting method is commonly used with metals and metal alloys. I’ll share some of the most common materials for this cutting method.
Stainless Steel
Steel is, without a doubt, the most commonly used metal globally. Stainless steel is an iron-based alloy that is resistant to rusting and corrosion. Further, this material is electrically and thermally conductive which means that plasma cutting equipment can be used in the fabrication process. Plasma is one of the best ways to cut stainless steel over a range of thicknesses.
Mild Steel
Mild steel, also known as low-carbon steel, is an iron and carbon alloy. Due to its lower carbon content, it’s malleable and ductile. Mild steel is also popular for its machinability, weldability, affordability, as well as its conductive properties. Plasma cutting has proven extremely effective for varying thicknesses of mild steel.
Aluminum
Aluminum is a widely popular metal with a range of uses including roofing, interior design, foil insulation, automotive, aerospace, and aircraft applications. Similar to other materials on this list, aluminum is a conductive material making plasma cutters a viable machining tool.
Plasma cutting aluminum offers notable advantages over laser cutting. For starters, plasma cutting machines can cut through aluminum of up to 160 mm thick compared to 25 mm for laser cutting. Also, this fabrication process is more cost-efficient.
Cast Iron
Cast iron is best known for its high strength, good malleability, ductility, and low melting point. It’s also quite conductive and this allows for the plasma arc cutting process.
Brass
Brass is a metal alloy of copper and zinc. Some of its most notable properties include corrosion resistance, malleability, and conductivity. Brass’s conductivity makes it possible to machine this material using plasma cutters.
However, if you choose to cut brass using this fabrication method, you must do so in a well-ventilated area. This is because exposure to burning zinc fumes has toxic effects.
Copper
Copper is the third most widely used metal in the world — after aluminum and steel. It is corrosion-resistant, extremely ductile, and a highly conductive material.
When using CNC plasma cutters to fabricate copper parts, ensure that you’re working in a well-ventilated space.
Advantages and Disadvantages for of Plasma Cutting
As with any other manufacturing process, plasma cutting is not a perfect fabrication method — it comes with its advantages and disadvantages. In this section, I’ll take you through the standout features as well as the challenges associated with the plasma arc cutting process.
Pros
CNC plasma cutting can accommodate a wide thickness range (0.5mm – 180mm) depending on the specifications of the plasma cutter.
It is suitable for all conductive materials, and this makes it highly versatile.
Plasma arc cutting is a high-speed process — this technology significantly outperforms oxy-fuel torches.
It is relatively affordable, especially when cutting through medium-thickness stainless steel and aluminum.
With just a few tweaks, a plasma cutter can be used for plasma welding.
Compared to laser cutting, this is a simpler process with lower energy requirements.
Plasma cutters can operate underwater. This reduces the heat and noise levels.
CNC plasma cutters offer a high degree of precision and repeatability.
Plasma cutters are capable of generating high-quality cuts — they typically outperform flame cutting and waterjet cutting by achieving a more refined kerf.
Cons
Plasma cutting processes can only be used for conductive materials. Plasma cutters will not cut through materials such as glass, plastic, wood, coated metals, and concrete.
It is noisy and can generate irritating fumes. Operations need to be conducted in a well-ventilated workshop.
Plasma arc can negatively affect your eyes. The operator needs to wear eye protection.
Laser produces a smaller heat-affected zone (HAZ) compared to plasma cutting method.
Author
Gavin Leo is a technical writer at Aria with 8 years of experience in Engineering, He proficient in machining characteristics and surface finish process of various materials. and participated in the development of more than 100complex injection molding and CNC machining projects. He is passionate about sharing his knowledge and experience.