As we know, plasma cutting is essentially a thermal process of cutting, where an ionised gas jet, which is at a very high pressure is constricted and forced through a copper nozzle. This produces a dense plasma arc which heats the conductive metal to a very high temperature, more than its melting point and cuts the metal by melting and blowing it through the kerf. Both manual, as well as mechanised plasma cutting systems, follow the same principal.
Manual Plasma Cutting
These cutting systems usually use a plasma torch that is handheld to cut different types of metals and they are mostly small power supply cutters. Manual plasma cutters are versatile, and they can be controlled quite easily. These cutters can be used for several kinds of cutting applications. Manual systems can work on power supplies as low as 7-25 amps to as high as 30-100 amps. These systems usually use shop air as the shield or plasma gas and can be operated with varied incoming voltages.
Manual plasma cutters are commonly used by small fabricating units that cut thin metal, metal service outlets, welding repair units, farm maintenance, factory maintenance, commercial manufacturing, construction industries like bridges and buildings, auto repair, trailer manufacturing, artwork, hobby shops, etc. Typically, manual cutters are used for light metal applications that involve trimming extra material, etc.
A manual cutting system is usually selected on the basis of the required cutting speed and the thickness of the material that is to be cut. A high amperage cutter cuts faster; however, when the cutting amperage is very high, the cut quality is difficult to control.
Mechanised Plasma Cutting
These automated cutting systems are usually larger and more complex when compared to manual plasma cutting systems. Mechanised plasma cutters are usually used along with a cutting table, including a downdraft table equipped with a gantry system that operates with many motors and drives or a water table.
Mechanised plasma cutting systems usually have a CNC and a THC (torch height control) that may have voltage control and initial height sensing (IHS). Mechanised plasma cutting can also be used along with a punch press, robotic cutting or laser cutting system. The size of plasma cutting system depends on the gantry and cutting table that is being used and also on the layout of the facility.
Typically, the power supplies for a mechanised plasma cutting system is 100-600 amps for nitrogen cutting and 100-400 amps for oxygen cutting and commonly, the incoming voltage for automatic plasma cutters varies between 200 and 600.
Usually, compressed air, nitrogen, oxygen and a mixture of hydrogen and argon are used for cutting stainless steel, mild steel, aluminium and other exotic metals. A combination of these gases is used as the shield gas and the plasma gas. When installing a mechanised plasma cutting system, the choice of the plasma gas and the shield gas is an important decision to make. Proper wiring and plumbing for the coolant and the gas must also be done. Apart from the plasma cutting system, the other components that must be selected are the table, CNC, THC and the gantry.
Since setting up a mechanised plasma cutting system is a complex process, you must devote sufficient time and research the different configurations available and make your purchase decision on the basis of factors such as – the types of parts that will be cut, required speed, cut quality, number of pieces that will be cut per batch, consumable cost, overall operating cost, etc. The type of table, CNC and gantry required may depend on the quantity, size and shape of the parts to be produced. For instance, you will require a gantry with a specialised drive package for small and intricate parts. The cut quality and cutting speed also depend on the plasma cutting system, the choice of gases and the CNC. Further, a CNC that offers different programming options and fast processing speed will result in increased precision and cut speed while decreasing operational downtime.
Finally, your decision to install or upgrade a mechanised plasma cutting system or a manual process must be made after evaluating the various factors and as a fabricator, you must also take into consideration the shape, size and the thickness of the material you will be cutting before making your final purchasing decision.