Guide written by:
Michael, Professional and passionate welder, Sheffield
Plasma, the saviour of metalworkers, coachbuilders and boilermakers! Unlike oxygen cutting (acetylene oxygen), plasma is reserved for high thicknesses, allowing rapid and versatile cutting and dismantling. Torch, nozzle, action!
- Cutting thickness
What is plasma?
First off, we're not talking about blood plasma! Excuse the brief physics lesson - plasma is defined as an ionized conductive gas, or a gas in which free electrons move about without being attached to atoms. In the case of a plasma cutter, the gas is air that has entered a plasma state to cut through metal (definitionally conductive, high melting point).
A plasmacutter allows you to cut metal sheet from 2 to 40mm in thickness thanks to the high temperatures it produces. Like MMA or TIG welding equipment, the cutter requires an inverter (a device that transforms alternating into direct current) to produce the electric arc that causes ionization, generating a temperature of about 18,000°C. To supply the air, a separate or integrated compressor is also required. A sophisticated torch and an earthing clamp to attach to the metal sheet are the final components of a plasma cutting kit.
Plasma cutting kit.
Anatomy of a plasma cutter
A plasma cutter combines several key components to allow you to cut metal with a precision of the order of 1mm. This impressive feat of metalworking requires know-how, but above all the right gear! The following are essential components:
- A DCinverter at 230V or 400V, with or without integrated compressor;
- A torch with cables and pipes 3–4m in length, for practicality's sake;
- A stock of spare parts and consumables for the torch, since maintenance is frequent when working at such high temperatures;
- An earthing cable for - guess what - earthing the earthing clamp;
- Cutting guides for improved precision;
- Electronic Inverter technology, for enhanced intelligent control of your cutter.
How does a plasma cutter work?
Be aware that plasma cutting produces a lot of smoke. Always use your cutter in a well-ventilatedspace, open to the outside and with adequate respiratory protection.
After powering up the machine and fixing the ground clamp to your cutting sheet, you apply the torch and press the trigger to initiate high-frequency remote priming and start melting the metal. The trick is to keep the torch at a comfortable distance for a clean and regular cut. A range of accessories are available to make your job easier, such as:
- Remote grip for users who tend to rock back and forth;
- Compass for cutting out discs;
- Guide rule, etc.
A plasma cut often ends up with one sharp side and a rougher, less precise side. This must be taken into account when assembling your plasma-cut metal parts.
What are the key cutting components?
You already know that a plasma cutter will have an inverter, a compressor (integrated or not), cables and pipes, an earthing clamp and guide accessories. But the cutting head has a few gems of its own!
- Torch: an impressive handheld gadget which combines at least four chemical elements to produce the plasma - even more on the most sophisticated models.
- Emissive electrode: pointed, made of tungsten or zirconium. Due to the wear it receives, this is the most frequently changed piece of the cutting head.
- Supply nozzle: channels the plasma produced to the diffuser; made of pure copper so malleable and sensitive to shocks. So take care!
- Diffuser: regulates the air and standardizes flow. Should be replaced when its holes become blocked.
- Cooling nozzle: regulates flow of cooling air to the torch; exposed to flying shrapnel during cutting. Must be replaced if it becomes deformed.
- Buffer: mounted on the nozzle and made of steel wire. Maintains the gap between cutting sheet and nozzle. Experienced pros can do without this accessory due to their great manual dexterity.
Compressor: integrated or separate?
Since the torch doesn't require an extreme airflow rate (150 l/min at 5 bar on average), the role of the compressor is to supply the air used to produce plasma to drive off droplets of molten metal.
Portable plasma cutters with integrated compressors are becoming more widespread. This all-in-one solution is both practical and effective. If you're using a separate compressor, you'll also need an oil separator. This is a type of cartridge filter placed at the compressor outlet to collect oil and impurities carried in the air supply.
What thickness of metal can you cut?
Typical 220V+, 60–100A machines can get through metal sheet of thickness 0.2–8mm.
For greater thicknesses, you'll need a 400V model (up to 40mm) - some professional machines can even cut up to 70mm. Warning - HOT!!
Are there variants for mechanical applications?
A few yes! And they're all adapted to specific precision-cutting tasks:
- Double-plasma cutters use a second gas to cool the cut for greater precision.
- Water-cooled plasma cutters use water in place of a second coolant gas, giving high cutting precision with less fumes.
- Water-injection cutters are for dedicated pros only! Water is injected into the cutting arc to increase compression... Requiring a high-current power supply (250A+) and a water recovery system. In short, a professional workshop setup!
- Automatic plasma cutting benches are usually computer-operated. You'll be amazed by the speed, precision and sharpness of their cut! For increased throughput, several torches can be arranged in parallel to cut simultaneously. Huge investment - factory production only!
Plasma cutting: essential user advice
Working with a plasma cutter requires good visibility of the cutting area. Since the process generates ultraviolet light, a welding mask is essential. Choose the opacity of the glass according to your visual acuity - check out our welding mask guide if in doubt!
Also bear in mind that nitrogen can be used in place of air, but you must always ensure adequate ventilation of your workspace!
Various additional kit can be obtained to ensure user safety and ease of operation:
- Thermostatic protection cuts off electrical power in the event of a current surge or voltage error, to prevent overheating and electrical accidents;
- Voltage signalling acts as a failsafe, allowing the torch to operate only when conditions are right;
- High-frequency (HF) priming of the pilot arc lets you begin cutting at a safe distance, without the nozzle coming into contact with the metal.
Any final advice?
Your choice of machine will ultimately depend on the type of cutting work you need to do. Narrow down your choice by considering your requirements and the constraints imposed by your working environment.
Your budget is also an important factor, but remember that you can achieve lots even with the most affordable model of portable cutter.
A portable plasma cutter with integrated compressor may be the most effective solution for a first-time user. Their limited size, weight and bulkiness, as well as their technical characteristics, recommend them for most sheet-metal cutting applications. With Inverter technology making them all the more versatile, compact plasma cutters are the best in show for first-time buyers!
Learn more about metalworking tools...
To find out more about welding equipment, follow our editors' advice and check out their other guides:
- How to choose your torch, cutter, pressure regulator and flame welding fittings?
- How to choose your electrode holder and earthing clamp for arc welding?
- How to choose your welding mask?
Guide written by:
Michael, Professional and passionate welder, Sheffield, 71 guides
I was trained as a pipe worker and a pipe-welder and after having traveled for 35 years working around the UK, I became the head a metal shop and then a designer and in the end the head engineer. I have designed and built a workshop where I make metal sculptures: I managed to find a piece of paradise where I can to let my imagination run wild. Auctions and garage sales are no secret to me. I find unusual objects and old tools there that I collect or transform into works of art. I also like decoration, painting on canvas, and gardening. I am developing new technologies concerning tools. To share my passion and humbly advise you in your choice of materials is a real pleasure.