CNC Plasma Cutting: Process, Key Components, and Advantages
A Computer Numerical Controlled (CNC) plasma cutter is a fabrication tool that can be utilized to cut through any electrically conductive material. A CNC plasma cutting machine utilizes plasma flow in a thermal process to cut through material following a tool path preprogrammed in the CNC software.
Plasma cutting is a process that delivers high-velocity gas flow through a nozzle that gets ignited through a spark and creates plasma flow that cuts through the material with a narrow, superheated plasma flow. Plasma cutting is typically used in: aerospace, automotive, and manufacturing industries.
This article will look at CNC plasma cutting, its process, key components, advantages, and how a plasma cutter works.
What Is CNC Plasma Cutting?
CNC plasma cutting is the automated process of using accelerated hot plasma flow to cut through electrically conductive materials. Plasma cutting is a thermal cutting process that forces high-velocity electrically charged gas through a miniscule orifice to cut a thin path through the material.
What Is the Process of CNC Plasma Cutting?
Within the CNC plasma cutting torch, gas is forced at high velocity through a nozzle. An electric spark is produced that ignites this high-velocity gas flow, producing a high-temperature plasma flow. Plasma is a state of matter that is a gaseous matter that flows like a liquid. The plasma flow can reach temperatures exceeding 20,000 °C and is hot enough to melt away slag from the cutting edge.
What Is the Use of CNC Plasma Cutting?
With the rapid expansion of manufacturing capabilities and the rapid technological advances in plasma cutting machines, the cost of cut parts is reduced. Plasma cutting is not just accurate and precise but is much quicker than other thermal cutting processes. Plasma cutters are also able to cut through any conductive material, making them very versatile. This versatility means that a shop can have one machine to cut through thin-gauge materials all the way to and exceeding 30 mm of material with ease, accuracy, and consistency. Intricate shapes can also be cut through CNC capabilities.
What Is the Key Component of CNC Plasma Cutting?
The key components of CNC plasma cutting are listed and discussed below:
1. Plasma Torch
There are two main types of torches in use today: high-frequency spark systems and moving-contact start-pilot arc systems. A high-frequency spark system creates a spark using a high-voltage transformer, capacitors, and spark-gap assembly. It interferes with sensitive electronics. A moving-contact start-pilot arc system creates a spark from either a moving electrode or a moving nozzle, producing a spark by lighting a pilot arc. It does not interfere with sensitive electronics.
2. CNC System
Equipping plasma cutters with CNC systems enables faster cutting times, creates better-utilized duty cycles, and leads to fewer mistakes being made. The digital environment enables operators to efficiently utilize metal workpieces for minimized off-cuts.
3. CAD File
In creating CAD (computer-aided design) files for CNC cutting, the CAM (computer-aided manufacturing) file format should be in a format that can be used by the CNC system. These formats include DXF (drawing exchange format) files that plot the outline of the parts to be cut and essentially plot the path of the plasma torch to follow.
To learn more, see our full guide on CAD Files.
4. CNC Program
Once the CAD file which is in the DXF format is finalized and imported into the CNC program, it is necessary to translate the outline into tool-path code which is known as G-code. G programming language is the language used by CNC machines to exactly control tool paths. This path consists of X, Y, and Z coordinates. It not only controls the tool path, it controls how the tool moves, and how fast the tool moves.
5. Metal Workpiece
Plasma cutting is only possible through electrically conductive materials such as metal. Being better at conducting electricity does not make it easier to cut with plasma. Melting point, material hardness, and material thickness play a crucial role in how metal is plasma cut. Common metals being cut with plasma include: steel, aluminum, brass, and copper.
6. High-Velocity Plasma Jet
Gas is forced through the torch nozzle’s minuscule opening at high velocity. The plasma-torch ignition system ignites this high-velocity stream transforming it into a plasma jet that can cut through steel. This plasma jet can reach 30,000 °C which is hot enough to cut through metal and burn away slag, creating a clean cut.
7. Torch Movement Control
The G-code parameters define the torch movement control. The speed and coordinates are subjected to the defined shape to be cut, plate thickness, and the duty cycle of the plasma cutter. The duty cycle dictates the amount of time the plasma cutter can cut a workpiece before it needs to cool down. The duty cycle is affected by the nozzle system in use and the cooling system function. The maximum cutting speed is usually defined in inches per minute and is a function of the whole system’s capabilities.
8. CNC Machine
The CNC machine is the structure that holds everything together. CNC machines provide accuracy, efficiency, and consistency that is not possible through manual processes. CNC machines operate according to pre-programmed coordinates and tool speed to produce parts in less time, reduce material wastage, and reduce errors. The CNC machine houses: the cutting table, the plasma cutting torch, the computer, the workpiece, the cooling system, and the power supply.
9. Power Supply
The power supply to the CNC plasma cutter will determine the thickness of the material that can be cut. A 3 mm steel can be cut with 12 A and 120 V supply, and a 20 mm steel can be cut with 60 A and 240 V supply. More than 30 mm of steel can be cut when using three-phase plasma cutters. For light-duty home applications, there are always inverter-based plasma cutters that consume less energy than the equivalent traditional plasma cutters.
10. Cooling System
CNC plasma cutting cooling systems are designed to remove heat from the source, increasing efficiency and extending the service life of the torch. The cooling system on the CNC plasma cutter is similar to those found in automobiles. The heat is conducted away from the plasma torch chamber through a combination of: conduction, radiation, and convection. Typical components include: the torch, cooling lines, pump, radiator, coolant, and reservoir.
11. Cutting Table
The cutting table is the backbone of the CNC plasma cutting system. The cutting table not only holds the metal workpiece, but the power supply, cooling system, and computer control are bolted to the table frame. The cutting table is a substantial parameter in the CNC plasma cutting equation. It enables the workpiece to be efficiently cut by the cutting torch through the pre-programmed coordinates held by the computer.
What Is the Advantage of CNC Plasma Cutting?
The key advantages of CNC plasma cutting include:
- Comparatively cheap
- Faster cutting than oxyfuel cutting
- Offers accuracy and repeatability
- Can cut in water to mitigate heat-affected zone
Is CNC Plasma Cutting Considered a Cost-Effective Method for Metal Cutting and Shaping?
Yes, CNC plasma cutting is a cost-effective method for cutting metal. Plasma cutting is the most effective method to cut stainless steel and aluminum. CNC plasma cutting has robust capabilities but might not be the most accurate method of cutting and shaping thin-gauge conductive materials. When accounting for the cutting speed advantage, consumables become more cost-effective when total cutting length is considered before replacement is due. Minimal post-processing mitigates extra costs by reducing the need for cutting and shaping tools.
What Are the Different Applications of CNC Plasma Cutting?
Plasma cutters are common metalworking tools. Where the handheld plasma tool lacks accuracy and edge finish, this is where the CNC plasma cutter comes into its own. Apart from industrial use such as shipyards, general metalworking, and automobile repairs, applications include: decorative artwork, signage, and recycling plants.
Is CNC Plasma Cutting Commonly Used in Industries Such As Automotive, Aerospace, and Manufacturing?
Yes, CNC plasma cutting is commonly used in industries such as: automotive, aerospace, and manufacturing. Although laser cutting is more accurate, plasma cutting can cut metal billets for machining purposes faster than laser cutters can. Plasma cutters can also cut thicker-gauge conductive materials than laser cutters.
What Is the Difference Between CNC Plasma Cutting and Laser Cutting?
Both plasma cutting and laser cutting are well suited for CNC control methods. Both of these methods are thermal processes for metal fabrication. Laser cutting delivers better precision and accuracy, and can be used on conductive and non-conductive materials. Plasma cutters offer lower initial capital outlay and increased cutting speed, and can only be used for conductive materials. The main difference comes in how the thermal cutting is conducted: high-velocity plasma flow for plasma cutting and high-concentration light energy for laser cutting. Figure 1 below shows a laser cutting wood:
Laser cutting on wood.
Image Credit: Shutterstock.com/vallefrias
What Is the Difference Between CNC Plasma Cutting and Flame Cutting?
Plasma cutting and flame cutting are similar only in that they are both thermal cutting processes. The differences are quite extensive. Flame cutting is rudimentary and crude yet cheaper than plasma cutters. Flame cutters are not conducive to CNC control but they can be controlled through CNC methods. Flame cutters are more conducive to portable fabrication. Flame cutters can only cut ferrous metals whereas plasma cutters can cut any conductive material. Table 1 below highlights these differences:
| Plasma Cutter | Flame Cutter |
|---|---|
Plasma Cutter High-velocity plasma flow | Flame Cutter Oxyfuel flame with a burst of oxygen |
Plasma Cutter Cleaner cutting | Flame Cutter Crude cutting |
Plasma Cutter Maximum cutting thickness is less than 25–50 mm (depending on the machine) | Flame Cutter Ideal cutting thickness starts from 25 mm+ |
Figure 2 below shows a flame cutter cutting thick-gauge steel:
Flame cutting thick-gauge steel.
Image Credit: Shutterstock.com/fotomarc
Summary
This article presented CNC plasma cutting, explained it, and discussed its key components and advantages. To learn more about CNC plasma cutting, contact a Xometry representative.
Xometry provides a wide range of manufacturing capabilities, including machining and other value-added services for all of your prototyping and production needs. Visit our website to learn more or to request a free, no-obligation quote.
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