All About Plasma Cutting
Cutting is usually the first step in most fabrication processes. It typically comes before forming, joining, and other metalworking operations. This step can be carried out through many methods. One of these is plasma cutting, which is often selected for its functionality, cut quality, and versatility.
Plasma cutting is a metal cutting process in which an accelerated stream of hot plasma is used to cut through electrically conductive materials. It is carried out using specialized equipment known as plasma cutters.
The History of Plasma Cutting
Plasma cutting began as plasma welding. Plasma welding was born in the early 1940s, following the US defense industry's efforts to find effective methods of manufacturing metallic structures and vehicles during the Second World War. This led to the creation of the tungsten inert gas (TIG) process, which is also known as gas tungsten arc welding (GTAW). It is a welding process that uses an electrical arc to melt metals.
The primary consumables in TIG welding were helium and argon. Therefore, it was no surprise that Union Carbide, a leading industrial gas manufacturer, took a significant interest in the technology. This company developed the technology into GTAW.
Further studies in the 1950s revealed that the arc temperature and the voltage rose exponentially when the torch nozzle opening was constricted. The ensuing jet was able to cut through metals.
In the years following, several developments and improvements were made to the technology to create plasma cutters as we know them today.
How Plasma Cutters Work
To fully understand how plasma cutters work, it is vital to first understand what plasma is. Solid, liquid, and gas are widely known as the three states of matter. However, there is a fourth, lesser-known state called plasma. The major difference between these four states of matter is their intermolecular energy. When energy is added to a solid, it turns into a liquid.
Further addition of energy transforms a liquid into a gas. Plasma is obtained when enormous amounts of energy, in the form of heat or electricity, are added to a gas. Plasma is extremely hot. It is also conductive. Some examples of naturally occurring plasma are lightning and the sun.
In plasma cutting, plasma is generated from a gas and used to cut through conductive materials. Various gases may be used in plasma cutting; however, air is the most ubiquitous of these as it is abundant and readily available. In plasma cutting, compressed air is fed to the cutting torch. The torch is also connected to the positive terminal of an electrical power supply system built for plasma cutting. The negative terminal is connected to the workpiece via a work clamp. In the nozzle of the torch, to which the air flows, is a chamber that contains an electrode. The pilot arc is started by placing the nozzle in contact with the workpiece, or by briefly causing contact between two internal components (nozzle tip - cathode | electrode - anode) of the nozzle. The arc completes the circuit, allowing electricity to flow through the electrode, effectively charging the air in the chamber and transforming it into superheated, ionized plasma. The plasma can reach temperatures well over 40,000°F.
The plasma flows through a small opening in the torch tip, which further increases its velocity to upwards of 20,000 ft/s. It is then brought into contact with the workpiece and controlled in the desired direction by the operator using the torch. The heat of the plasma melts the workpiece while its kinetic energy blows away the melted pieces. Plasma flows continuously from the torch to the workpiece, thereby creating a complete circuit from the power source to the torch, to the workpiece (through the plasma), and back to the power source via the workpiece clamp. This continues until the air supply is cut off, turning off the plasma and breaking the circuit. In some plasma cutting setups, another gas, known as the shielding gas, is simultaneously blown onto the workpiece from the torch to protect it and carry away the cut pieces. Such setups are carried out using special torches that have provision for the shielding gas to flow.
Plasma cutters can cut through materials of various thicknesses. The thicker the material, the hotter the plasma will need to be. The temperature of most plasma cutters is sufficient for most applications; however, certain industrial applications involve very thick materials that require even hotter plasma. The temperature of plasma is directly proportional to its energy and can be increased by increasing the amount of electricity supplied to the gas. For such applications, heavy-duty electrical power systems are used.
Plasma Cutting Equipment
Plasma cutting uses the following equipment:
An air compressor is required to provide a steady stream of high-pressure, high-velocity air for plasma cutting. It is the air supplied that is transformed to plasma.
The compressor must have the capacity to provide a stream of clean, dry air. In most plasma cutting setups, the compressed air is channeled through the electrical system to the torch. A filter/regulator for air filtration/pressure regulation is either connected to the compressor or integrated into the power system.
Also known as the power source, the electrical power supply system provides the electrical energy required to transform the air to plasma. The positive terminal is connected to the torch and the negative terminal to the workpiece.The power source is rated in amperage and voltage. The higher the ratings of the power source, the hotter the plasma it will produce. Also, depending on the power source's rating, it may require a simple AC outlet or a 3-phase power outlet.
The plasma torch plays several essentials roles in plasma cutting. It contains the electrode to which the electricity that charges the air is supplied. The compressed air also flows to the torch, where it is charged. As the compressed air flows directly into the chamber containing the electrode, it gets spun by a whirl ring wrapped around the electrode and is transformed to plasma in the process. The torch also features a trigger that serves as a switch for the entire process. When the trigger is pulled, air immediately flows to the torch, the arc is simultaneously started, and hot plasma ejects from the nozzle. This entire process happens in a fraction of a second. When the operator releases the trigger, the air supply is shut off, ceasing the flow of plasma and disconnecting the circuit.
Other components employed in plasma cutting are the workpiece clamp, the air-carrying hose, and the electric wires.
Plasma Cutting Applications
Plasma cutting is an electrical cutting process, so plasma cutters can only cut conductive materials such as stainless steel, steel, brass, aluminum, copper, and even tungsten of various thicknesses. It cannot be used to cut wood, glass, stone, or any other non-conductive materials. Plasma cutters are used in various applications including pipe cutting, metal fabrication, decorative art, salvage and scrapping applications, industrial construction, shipbuilding, manufacturing, and more.
Plasma cutters are versatile and can be used to carry out operations like straight cutting, template cutting, bevel cutting, piercing, circle cutting, and gouging. Plasma cutters may be manual, in which an operator manually controls the plasma torch to make the desired cut, or mechanized, in which a CNC-controlled cutting torch is used to make cuts on a special cutting table. Manual cutters are more ubiquitous for their versatility and functionality.
Benefits of Plasma Cutting
The following are some of the benefits of plasma cutting.
Plasma cutting is a precise process that can produce high-quality cut edges. With little or no heat-affected zone, this process can cut with a tolerance of 0.2 mm. This is much more accurate than oxyfuel and mechanical cutting.
Plasma cutting can cut a variety of electrically conductive materials, including tungsten. Hand-held cutters can cut thicknesses up to 1.5 inches, while heavy-duty CNC cutters can cut thicker profiles. In addition to being compatible with several materials, plasma cutting can cut in various shapes and orientations.
Plasma cutting is a fast process. In many cutting projects, speed is crucial, and plasma cutting delivers. Note that the speed of a project also depends on the operator's skill and the thickness of the material being cut.
The major consumable after electricity in most plasma cutting processes is air. Air is abundant and readily available.
Unlike many other cutting processes, plasma cutting can work under water. This makes it useful in marine applications.
Plasma cutters are portable and can easily fit inside a carrier for transportation.
Limitations of plasma cutting
The following are some of the limitations of plasma cutting:
Plasma cutting is restricted to metals. It cannot cut glass, wood, plastic, and other non-conductive materials.
Plasma cutting can be noisy when cutting thick materials.
While this cutting process's running cost may be low, it is usually expensive to set up, requiring an air compressor in addition to a power source and a cutting torch. A CNC setup would also require a specialized cutting table.
Plasma cutting produces smoke and toxic fumes.
Not as precise as laser cutting.
There's a limit to the thickness that plasma cutting can cut.
Red-D-Arc offers a range of plasma cutters for rent and lease. We also offer air compressors of various capacities. Our experienced and professional welding experts are ready to answer any questions you may have and can help you choose the right plasma cutter for your cutting application.