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Posted on Dec 21, 2020
Thermal cutting is a series of processes that the heat produced by an electric arc, radiation energy, or an exothermic reaction is applied to melt or oxidize a metal at an accelerated rate in order to achieve a cut. The plasma machine applies such a principle to cut the workpieces.
A plasma machine is a thermal cutting machine, which utilizes electricity to actuate the heat to be produced, then the torch of the machine would be able to cut the workpieces that are made of conductive metals.
Thermal cutting is a series of processes that the heat produced by an electric arc, radiation energy, or an exothermic reaction is applied to melt or oxidize a metal at an accelerated rate in order to achieve a cut. The plasma machine applies such a principle to cut the workpieces. The power source of the plasma machine is electricity. When the plasma machine is connected with the power source, the electric energy would be transferred into thermal energy. Once the temperature of the thermal energy achieves a certain point, then the cutter of the plasma machine can cut the desired shapes on the metal.
Unlike the other methods of making products by removing materials from the workpieces to achieve the preset design, plasma machines apply cutting tools that directly cut the workpieces, such as through drilling or milling. The cuts that are made by thermal cutting would be able to reach smoother finishes instead of sharp edges.
The invention of the plasma machines can be dated back to the 1960s when the handheld plasma cutters and the machine mounted plasma cutters started to become available. The scientists then found that when the device is charged with electrical current, and the gases are coming out of a small hole from the device at a high speed, the plasma can be produced.
The device that is used to produce plasma is the so-called torch. In 2005, the plasma was found to be made with a more progressive method, which applies finely tuned power sources and newer precise cutting torches to produce the “fine plasma”. This process is achieved by the controlling of the computer, which is called computer numerical control (CNC).
Nowadays, with the assistance of the computer, the cutting that is made by the plasma machine can be provided with even better surface finishes, part accuracies, and detail, which shows the progress of the plasma machine is continuously increasing.
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The system that comprises the plasma machine contains several parts, including the power source, the arc starting console (ASC), the media, the torch assembly, and the workpieces:
The cutting that applies the plasma machine is finished by the arc that flows with the plasma. There would be two categories of the arc that are produced when the power source is connected, including the pilot arc and the main arc. The pilot arc requires relatively high and non-load voltages from the power source, while the main arc only requires a certain degree of voltages that it can be maintained.
The arc starting console produces the initial spark that facilitates the pilot arc and the main arc to be made.
During the cutting that is achieved by the plasma machine, there would be two main procedures. One is igniting and the other is cutting. These two procedures are both actuated by the gases as a medium, which also makes the gases that are used during the procedures as ignition gases and cutting gases. When the thermal energy is made by the gases, there should be a coolant system to cool the device as well as the workpieces, in order to prolong the lifespan of the device and prevent damage to the workpieces. In the operating process of the plasma machine, the coolant system is formed by the secondary media, which can also be the gases or water, which make the gases indispensable components of the plasma machine.
The torch assembly is connected to the power supply and contains the electrode and the nozzle, which ionize the plasma gas by the high-frequency spark that is made by them and causes the plasma gas to become electrically conductive and produce a low-resistance current path between the electrode and the nozzle. The current path that is generated would be delivered through the tool, which is the torch, to the workpiece to conduct the plasma cutting operation.
The workpiece of the plasma machine should be electrically conductive, as it is supposed to be worked with the plasma gases that are produced by the electricity from the power source.
As mentioned above, the plasma gas is actuated by the arcs that are generated by the electrode from the power source. The first is the pilot arc and followed by the main arc.
When the power source is operated, it would apply the negative voltage to the electrode, which is the cathode of the pilot arc circuit. Then a temporary, positive voltage was placed on the nozzle, which is the anode of the pilot arc circuit, and the pilot arc would then be initiated. As the pilot arc flows through the nozzle opening to the workpiece, the main arc circuit would be generated and the actual cutting operation would be driven to increase to optimal cutting amperage.
When the nozzle is opened by the main arc, the plasma machine would produce plasma up to 20,000°C and move towards the workpiece. Once the heat is given to the workpiece, the localized workpiece starts to melt by the vaporized plasma gas. After the localized workpiece is completely weakened, the desired parts of the material on the workpiece would start to be removed. At that time, the current and the nozzle would control the flow of the plasma gas, in order to pursue the most precise cuts and reduce the deformation of the products.
When everything is ready, the torch of the plasma machine would follow the instructions of the CNC program, to move across the surface of the workpiece with appropriate speed and required movement. After that, the desired cuts would be made on the workpiece with the optimal precision and smooth finishes as necessary.
The automated operated plasma machine, which follows the CNC program and is widely used nowadays, is able to ensure the optimal precision of the products. In addition, even the thicker materials can be worked with the plasma machine simply by the adjustment of the power source. Therefore, the plasma machine can be used in a variety of applications. Furthermore, the plasma machine allows for lower equipment and operational costs, which makes it a cutting machine with high value and effectiveness. In short, among all of the thermal cutting machines or devices, the plasma machine in combination with the CNC technology can be regarded as the most practical choice in the industrial fields.
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