Plasma Cutting – Process, Applications, Safety, Variants and Selection
Plasma cutters are capable of cutting metals in simple and complex shapes including producing holes, bevel edges, gouging, and markings. Plasma is a cost effective and practical alternative to oxy-fuel, laser and water jet cutting processes and is used in industrial, trade and DIY applications. Plasma cutters are used in all types of industries including manufacturing, pharmaceutical, oil/gas and arms industries.
When gas is heated to extremely high temperatures, the electrons in the gas molecules break free from the nucleus, turning the gas into plasma. Plasma cutting is carried out by directing the plasma jet through the metal.
The advantages and disadvantages of plasma cutting as compared to the other cutting processes are as follows:
- Ability to cut all electrically conductive materials including stainless steels and non-ferrous alloys (aluminium, brass, copper etc.). Note: Stainless steel and non-ferrous alloys cannot be cut using oxy-acetylene cutting
- Good quality cuts
- Can be used on a work site for manual cutting as the equipment is portable and light weight.
- Automation is readily achievable as with other cutting processes. CNC plasma cutting machines are able to cut complex shapes at high speeds.
Effective in cutting metals up to 6” thick.
- Not good for cutting non-conductive materials. Note: Water jet and laser cutting processes are a better alternative for these types of materials.
The following content is for general information only and should not be understood to be a complete guide to plasma cutting safety. Be sure to follow the manufacturers’recommendations and all standard safety practices employed when working with electrical equipment.
Electrocution: The high power output and voltage (110 to 150VDC) required for the plasma cutting poses potentially fatal risks of electric shock. Some of the precautions to avoid electrocution include: Electrical grounding of the plasma cutter, appropriate personal protective equipment (PPE – e.g. rubber gloves in addition to welding gloves) needs to be worn, check all cables before starting work, ensure work area is dry etc.
Eye and Skin Protection:
The plasma cutting process emits severe infrared and ultraviolet rays which are harmful to the eyes and skin. A face shield or safety glasses fitted with the correct lens shade must be worn. To protect the skin against molten metal and fumes, PPE (protective clothing, safety shoes, welding gloves, welding apron when appropriate etc.) covering the whole body is required.
Toxic Fumes and Gases:
The plasma cutting process emits smoke and potentially harmful gases (as is the case with laser and oxy-acetylene cutting). Appropriate ventilation is required to direct the fumes away from the operator. This may be achieved by fume extraction systems. A welding helmet with fume protection may also be required in certain situations.
Ensure there are no flammable materials near the work place.
Noise: Noise levels of up to 120 decibels, the operator and personnel near the plasma cutter require hearing protection.
Risks due to Pressurised Gases: Secure cylinders, secure/check hoses and connections.
Variations of plasma cutting
Gases: Different gases are used to suit the metal being cut. Compressed air or oxygen are generally used for cutting carbon steels, whereas inert gases like argon or nitrogen are used for cutting stainless steels. Dual gas system (plasma and shielding gas) allows you to run on separate plasma and shielding gases to optimize the performance e.g. Air/Air, O2/Air, N2/Air, N2/CO2, Ar-H2/N2 or other combinations. Shielding gas also assist with torch cooling. Additionally, liquid cooled torches are available for high power applications which provide maximum cooling and long consumable life.
On board compressors:
Plasma cutters are available with integrated air compressor for portable units and are suitable for lighter cutting applications.
CNC machines with water bed:
As an alternative to fume extraction systems, plasma cutting on CNC machines is carried out with the water under or fully covering the work piece. This provides for a more cost effective fume removal option. The water bed also suppresses the noise caused by the plasma cutting process. Under water cutting, additionally minimizes distortion which is particularly useful when cutting thin materials.
There are two types of arc starts available –pilot arc or touch. In touch arc start, the nozzle has to contact the work piece to start the arc, whereas in a pilot arc, an arc is present in the plasma nozzle and there is no contact required between the nozzle and the work piece.
High frequency start relies on high frequency and voltage power to ionize the gas. If can be used with a pilot arc torch or touch start to initiate the plasma. The disadvantage of high frequency start is that it can interfere with the electronic circuitry in the vicinity.
In back blow plasma initiation, the flame is started in the inside of the torch by the movement of a piston, initiating an arc and ionising the gas. This arc forms the pilot arc and stays on whether the nozzle is in touch with the work piece or not.
How to select a plasma cutter?
The following needs consideration when selecting a plasma cutter:
Manual or mechanised ?
Are you looking to cut by hand or use a CNC machine? – consider the availability of CNC interface signals and voltage divider (to provide safe voltage levels from the torch to control the height of the torch automatically).
Required Cut thicknesses and quality
Material thickness needs to be matched with the capabilities of the plasma cutter. The cutting capabilities are specified as thickness limits by the manufacturers as follows:
Sever cut – just capable of cutting this thickness with dross and slag left behind
Rated cut – this is the rated cut thickness specified by the manufacturer of the plasma cutter
Quality cut – a quality cut is achieved for materials up to this thickness
Kerf (cut width) – higher quality plasma cutting systems can make narrower cuts
Consumables cost and life considerations – consumable life is specified as the number of cuts or starts
Red-d-Arc has a wide selection of plasma cutting equipment from the market leading manufacturer Hypertherm covering the following:
Amperage range: 15A to 200A
Cutting range: 5/16” to 2” thickness
Single and 3 phase
Single and dual gas systems
Packages of plasma cutter with generators are available.
Also, mobile compressors run on diesel up to 450 CFM are also available for rental.
Have a look at our complete range of plasma cutting products.