Before we can get into what is plasma cutting let’s take a closer look at plasma? Well, plasma is defined as the fourth stage of matter and appears after gas. As it is in all matter change an amount of energy is required to change from one state of matter to another. That being said to change into plasma you need to apply a high electric charge to a gas. Plasma is therefore defined as an electrically conductive gas which has roughly an equal number of positive and negative ions.
So how does Plasma Cutting work now that we know what plasma is?
Well put simply the plasma is used to cut electrically conductive materials but let’s dive a bit further into how that works. So let’s take a main look at the components needed first.
- A Power Supply
- Compressed gas (usually Oxygen, Nitrogen, Argon or could be a mixture depending on the material)
- The electrode
- Swirl Ring
These can be classified as the main components needed for the plasma cutter.
- The Power Supply
Let’s take a look at this. Now the power supply is usually needed for the Arc. Now to sustain the arc you don’t require large amounts of power anywhere between 40 to 50V can help keep the Plasma arc sustained. However, to initiate the arc a large of electricity is needed and this is where the power supply is really necessary. The initial arc can take up to 10 times the electricity and need 400V Direct Current.
- Compressed Gas
Now the gas used will mainly depend on the type of material being cut for example, oxygen is usually in mild steel cutting operations because oxygen helps speed up the process and give a better edge cut. This is mainly due to the reaction of oxygen with mild steel. Other than this instance oxygen is not used and cheaper alternatives such as Nitrogen are preferred.
This compressed gas gets ionized by the electrode and is then used as a pathway for the initial arc to travel from the electrode to the work piece. After the initial Arc the plasma cutter will increase its power to the cutting power which has much higher current. The gas mixture is changed accordingly. Now since the high current from the electrode to the work piece and the gas are flowing out of the same orifice the gas is changed into plasma due to the high amount of energy and this (plasma) is what helps cut the material.
The plasma flow and current level must be monitored at all times. If gas flow is too low for current or vice versa (current too high for gas flow) for the nozzle, this would lead in the nozzle melting.
- The Orifice/Nozzle
The orifice is generally made out of copper and the tip out of steel due to the Arc. If the tip was made of copper the arc would just cause it to melt. Tungsten is also a good material used for the orifice however due to its reaction with oxygen is not preferred. When Oxygen is used as the gas another material is implemented. This material is called Hafnium and is represented by Hf.
The orifice also helps in focusing the flow and creating more pressure of the plasma while cutting. The shape also helps increase the speed of the plasma in turn increasing the cutting speed
- The Swirl Ring
This is mainly used to shape the compressed gas. This usually causes the gas to swirl around the electrode this usually helps confine the gas and prevent it from going all over the place it also ensures proper arc attachment.