FOCUS ON PLASMA CUTTING
SAY IT WITH PLASMA
We highlight best practice tips , guidelines and processes for plasma cutting .
“ After learning the basics of plasma cutting , there is still more to learn such as improving cut quality , prolonging consumable life and improving efficiency …”
Plasma cutting is a melting process of cutting through electrically conductive materials by using an accelerated jet of hot plasma . It is widely used in many industries . A jet of ionised gas at temperatures of above 20,000 ° C is used to melt and expel material from the cut . During the process , an electric arc is struck between an electrode ( cathode ) and the workpiece ( anode ). The electrode is recessed in a water- or air-cooled gas nozzle which constricts the arc , causing the narrow , high-temperature , high-velocity plasma jet to form .
“ When the plasma jet hits the workpiece , recombination takes place and the gas reverts to its normal state , emitting intense heat as it does so . This heat melts the metal and the gas flow ejects it from the cut ,” explained TWI Ltd .
“ Plasma arc can cut a very wide range of electrically conductive alloys including plain carbon and stainless steels , aluminium and its alloys , nickel alloys and titanium . Normally , the component or sheet to be cut remains stationary and the plasma torch is moved . Additionally , because the cost of the plasma torch is low compared with the price of the manipulation equipment , it is common to fit several torches to a cutting table . Plasma arc cutting can also be carried out under water using specialised equipment . High-tolerance plasma arc cutting ( HTPAC ) gives better precision on material under 12mm thick and can be a low-cost alternative to laser cutting ,” it added .
The plasma process
Plasma cutting is often used in fabrication shops , automotive repair and restoration , industrial construction , and salvage and scrapping operations . Due to the high-speed and precision cuts combined with low cost , plasma cutting is in widespread use by largescale industrial CNC applications down to small hobbyist shops . It is an effective way of cutting both thin and thick materials .
Since plasma cutters produce a very hot and very localised ‘ cone ’ for the cutting operation , they are extremely useful for cutting sheet metal in curved or angled shapes .
There are three main configurations of CNC plasma cutting , and they are largely differentiated by the forms of materials before processing and the flexibility of the cutting head .
1 . Two-dimensional / Three-axis plasma cutting This is the most common and conventional form of CNC plasma cutting . It produces flat profiles , where the cut edges are at 90 degrees to the material surface . High-powered CNC plasma cutting beds are configured in this way , able to cut profiles from metal plate up to 150mm thick .
2 . Three-dimensional / Three + axis plasma cutting A process for producing flat profiles from sheet or plate metal . However , with the introduction of an additional axis of rotation , the cutting head of a CNC plasma cutting machine can tilt whilst being taken through a conventional twodimensional cutting path . This means cut edges at an angle other than 90 degrees to the material surface , for example 30 to 45-degree angles . This angle is continuous throughout the thickness of the material . This is typically applied in situations where the profile being cut is to be used as part of a welded fabrication as the angled edge forms part of the weld preparation . When the weld preparation is applied during the CNC plasma cutting process , secondary operations such as grinding or machining can be avoided , reducing cost . The angular cutting capability of three-dimensional plasma cutting can also be used to create countersunk holes and chamfer edges of profiled holes .
32 | sheetmetalplus . com | ISMR December 2021 / January 2022