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There are several different types of plasma cutting and I will go through each here.
Brian actually cut his teeth with plasma cutting whilst spending his second and third years of on the job experience in scrapyards and salvage shops. So suffice to say, he knows his stuff about it!
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Different Types Of Plasma Cutting
Several different types of plasma cutting are used for starting the arc.
The arc is some units are created by the torch being put into contact with the piece of work.
A high frequency, high voltage circuit is used by some cutters to get the arc started.
There are several disadvantages to this method, including high amounts of radiofrequency emissions, spark gap maintenance, hard to repair and risk of electrocution.
Plasma cutters that work close to sensitive electronics, like computers or CNC hardware, use other means to get the pilot arc started. The electrode and nozzle are in contact.
The anode is the electrode and the cathode is the nozzle. The nozzle gets blown forward whenever the plasma gas starts to flow.
A method that is less common is capacitive discharge via a silicon controlled rectifier into the main circuit.
Inverter Plasma Cutters
This is a type of plasma cutting that heavy mains-frequency transformer that is used by analog plasma cutters, which tend to require over 2 kilowatts.
The mains supply over to DC is rectified by inverter plasma cutters. They are fed into a high-frequency transistor inverter at a range of 10kHz to around 200 kHz.
These higher frequencies make it possible to use a small transformer which results in an overall reduction in weight and size.
Initially, the transistors that were used were MOSFETs. However, increasingly they are using IGBTs these days.
When paralleled MOSFETs are used, if one transistor prematurely activates it can result in one-quarter of this inverter to experience cascading failure.
IGBTs were a later invention, and there are not subject as much to that failure mode.
Generally, IGBTs are used in high current machines since it is not possible to sufficiently parallel MOSFET transistors.
An off-line forward dual transistor convert describes the switch-mode topology.
Although more powerful and lighter, certain inverter plasma cutters, particularly those that do not have power factor correction, may not be run on a generator (meaning that it is forbidden by the inverter unit manufacturer, it is valid only for light, small portable generators).
However, there are newer models that come with internal circuitry that enable units that do not have power factor correction to use light power generators to run on.
CNC cutting methods
CNC cutting tables are built by certain plasma cutter manufacturers, and others build the cutter into the table, for types of plasma cutting that involve computer-aided cutting.
A CNC table allows the torch head to be controlled by a computer to produce sharp, clean cuts.
Today’s CNC plasma equipment can employ multi-axis cutting of very thick material, which provides opportunities for using complex welding seams which would otherwise not be possible.
Laser cutting is progressively replacing plasma cutting for thinner material, mainly due to the superior hole-cutting abilities of the laser cutter.
CNC Plasma Cutters have had specialized use within the HVAC industry. Information on ductwork is processed by software and flat patterns are created to be cut with a plasma torch on a cutting table.
The technology has increased productivity significantly within the HVAC industry since it was introduced during the early 1980s.
Many workshops also use CNC Plasma Cutters for creating decorative metalwork. For example, residential and commercial signage, outdoor garden art, address signs, and wall art.
Even greater development has occurred in recent years. The machines’ cutting tables traditionally were horizontal.
However, these days, there vertical types of CNC plasma cutting machines that are available, which provides faster operations, optimum safety, increased flexibility, and a smaller footprint.
Configurations of CNC Types of Plasma Cutting
CNC Plasma Cutting comes in 3 main configurations. They are mainly differentiated by the cutting head’s flexibility and forms of material prior to processing.
2-dimensional / 2-axis plasma cutting
It is the most conventional and common types of Plasma Cutting in the CNC form. It produces flat profiles, with cut edges at 90 degrees to the surface of the material.
This is how high- powered CNC Plasma Cutting beds get configured, and they cut profiles from up to 150 mm thick metal plate.
3-dimensional / 3+ Axis plasma cutting
This process also produces flat profiles from either plate or sheet metal. However, with an extra axis of rotation being introduced, the CNC plasma cutting machine’s cutting head can tilt while it is taken through a traditional 2-dimensional cutting path.
This results in cut edges that are at other than a 90-degree angle to the surface of the material. For example, 30 to 45-degree angles. The angle is continuous throughout the material’s thickness.
Typically, it is applied in circumstances where the profile that is being cut will be used as part of the welded fabrication with the angled edge forming part of the weld’s preparation.
When weld preparation is applied as part of the CNC plasma cutting process, you can avoid secondary operations like machining and grinding, which reduces costs.
The 3-dimensional plasma cutting has an angular cutting capability which also may be used for creating chamfer edges and countersunk holes on profiled holes.
Section and Tube Plasma Cutting
This method is used in the processing of pipe, tube, or any long section type.
Usually, the plasma cutting head remains stationary while the workpiece is being fed through, and then it rotates on its longitudinal axis.
With some configurations, the cutting head is able to rotate and tilt, as with 3-dimensional plasma cutting, that makes it possible to make angled cuts through a section or a tube’s thickness.
This is taken advantage of quite often in the pipework fabrication process where a cut pipe may be given weld preparation instead of a straight edge.
Manufacturers of plasma torches, over the past decade, have designed new models with a thinner plasma arc and smaller nozzles.
That allows for near-laser precision on the cut edges of the plasma.
A number of manufacturers have combined these torches with precision CNC control to allow parts that require no or little finishing to be produced by fabricators.
Initially, the transistors that were used were mainly MOSFETS. However, increasingly IGBTs are being used.
With paralleled MOSFETs, when one transistor is prematurely activated it can result in one-quarter of an inverter having a cascading failure. IGBTs are a later invention and not as prone to the failure mode.
In general, IGBTS are used in high current machines that do not allow for sufficient parallel MOSFET transistors to be used.
In the past, plasma torches were very expensive. That is why usually they were only found in either professional welding shops or very-well stocked private shops and garages.
But modern plasma torches continue to become less expensive and within many hobbyists price range, including for less than $300.
While older units can be quite heavy, yet still portable, newer ones that have inverter technology are lightweight, and exceed or equal the older ones’ capacities.
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