Before we get into the nitty-gritty of the inner workings of a plasma cutter, we first need to understand what exactly plasma is. You must have a read that it is also known as the fourth state of matter. The traditional understanding that we have of states is that there are 3 matter states including liquid, solid and gas.
A matter keeps changing from one state to another when energy such as heat is introduced. For instance, water in solid form which is known as ice will change to liquid state on application of certain amount of heat. It will change from liquid to gaseous state (steam) when more heat is applied. The steam is made up of gases and when more heat is applied to steam, it becomes ionized which makes it electrically conductive. This electrically conductive and ionized form of steam is known as plasma. Now that you’re clear about plasma, it will be easier for you to understand the inner workings of a plasma cutter.
A plasma cutter is nothing but a device that uses plasma (an electrically conductive gas) to transfer immense amount of heat energy to a conductive material. This process results in a faster and cleaner cutting process as compared to oxyfuel.
In a plasma torch, the plasma starts forming when shop air or a gas such as argon, nitrogen or oxygen is pushed through a small nozzle in the torch. This high-pressure gas flow is then brought in contact with an electric arc (generated from an external power supply) and it results in formation of a plasma jet. This plasma jet is extremely hot and can reach temperatures of up to 40,000 degrees F. This temperature is high enough to cut through the work piece and to blow away the molten material.
Components of a Plasma System
Power supply – The role of power supply is to convert three phase or single phase AC line voltage into a constant and smooth DC voltage which ranges from 200 to 400 V. Constant DC voltage is essential for plasma arc to remain live throughout the cutting process. Power supply also helps in regulating the current output which is decided on the basis of thickness and type of material being processed.
ASC Circuit – Creation of plasma arc inside the plasma torch requires extremely high voltage and this is where ASC (arc starting console) circuit comes in. It is responsible for generating around 5000 AC volts at 2 MHz which is required to generate the spark needed for generation of plasma arc.
Plasma torch – Plasma torch is required for proper cooling and alignment of the consumables. A nozzle, swirl ring and an electrode are the consumable parts needed for generation of plasma arc. Cut quality can be further improved with the help of a shielding cap. All these parts are kept together with the help of retaining caps on the inside as well as outside.
Many different types of plasma systems to make plasma cut metal signs are available for sale today but most of these systems can be grouped into precision or conventional categories.
In a conventional plasma system, the shop air is used for generating plasma gas and the nozzle orifice decides the shape of the plasma arc. As far as the amperage of plasma arc is concerned, it ranges from 12,000 to 20,000 amps per square inch. All the handheld plasma cutters utilize conventional plasma. Some mechanized applications also make use of conventional plasma system in situations where part tolerances are not that strict.
The precision plasma systems are used in applications where the highest quality and sharpest cuts are needed. It is a high current density system where consumable and torch design is much more complex. In this system, additional pieces are used for further shaping and constricting the plasma arc. The approximate amperage in case of a precision plasma system ranges from 40,000 to 50,000 amps per square inch. A variety of gases including nitrogen, high-purity air or oxygen as well as a mix of nitrogen/argon/hydrogen is used for generating plasma gas. This combination of gases gives optimum results when used on a variety of conductive materials.
The nozzle consumable parts and the electrode remain in contact in a handheld plasma system. These remain in contact inside the torch even when it’s in the OFF state. When you push the trigger, DC current is generated by the power supply and this DC current flows through the connection which begins the production of plasma gas. The plasma gas starts building up pressure and once the pressure reaches a certain point, the nozzle and electrode are separated which leads to generation of electrical spark and it is responsible for turning air into a plasma jet. When this happens, the DC current switches to a path between the work piece and the electrode. This airflow and current flow remains active until the release of the trigger.