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The workpiece made of conductive material is cut by using an accelerated thermal plasma jet.It is an effective method for cutting thick metal plates.
Whether you are creating artwork or manufacturing finished products, plasma cutting provides unlimited possibilities for cutting aluminum and stainless steel.But what is behind this relatively new technology?We clarified the most important issues in a brief overview, which contains the most important facts about plasma cutting machines and plasma cutting.
Plasma cutting is a process of cutting conductive materials with accelerated jets of thermal plasma.Typical materials that can be cut with a plasma torch are steel, stainless steel, aluminum, brass, copper, and other conductive metals.Plasma cutting is widely used in manufacturing, automobile maintenance and repair, industrial construction, salvage and scrapping.Due to the high cutting speed, high precision and low cost, plasma cutting is widely used, from large industrial CNC applications to small amateur companies, and the materials are subsequently used for welding.Plasma cutting-Conductive gas with a temperature of up to 30,000°C makes plasma cutting so special.
The basic process of plasma cutting and welding is to create an electrical channel for overheated ionized gas (ie plasma), from the plasma cutting machine itself through the workpiece to be cut, thereby forming a complete circuit that returns to the plasma cutting machine through the ground terminal. This is achieved by blowing compressed gas (oxygen, air, inert gas and other gases, depending on the material to be cut) through a focused nozzle at high speed to the workpiece.In the gas, an arc is formed between the electrode near the gas nozzle and the workpiece itself.This arc ionizes part of the gas and creates a conductive plasma channel.When the current from the plasma cutting torch flows through the plasma, it will release enough heat to melt the workpiece.At the same time, most of the high-speed plasma and compressed gas blow away the hot molten metal, separating the workpiece.
Plasma cutting is an effective method for cutting thin and thick materials.Hand-held torches can usually cut 38 mm thick steel plates, and more powerful computer-controlled torches can cut 150 mm thick steel plates.Since plasma cutting machines produce very hot and very localized “cones” for cutting, they are very useful for cutting and welding curved or angled sheets.
Manual plasma cutting machines are generally used for thin metal processing, factory maintenance, agricultural maintenance, welding repair centers, metal service centers (scrap, welding and dismantling), construction projects (such as buildings and bridges), commercial shipbuilding, trailer production, car repairs And artwork (manufacturing and welding).
Mechanized plasma cutting machines are usually much larger than manual plasma cutting machines and are used in conjunction with cutting tables.The mechanized plasma cutting machine can be integrated into stamping, laser or robotic cutting systems.The size of the mechanized plasma cutting machine depends on the table and portal used.These systems are not easy to operate, so all their components and system layout should be considered before installation.
At the same time, the manufacturer also provides a combined unit suitable for plasma cutting and welding.In the industrial field, the rule of thumb is: the more complex the requirements of plasma cutting, the higher the cost.
Plasma cutting emerged from plasma welding in the 1960s and developed into a very efficient process for cutting sheet metal and plates in the 1980s.Compared with traditional “metal-to-metal” cutting, plasma cutting does not produce metal shavings and provides precise cutting.Early plasma cutting machines were large, slow and expensive.Therefore, they are mainly used for the repetition of cutting patterns in mass production mode.Like other machine tools, CNC (computer numerical control) technology was used in plasma cutting machines from the late 1980s to the 1990s.Thanks to CNC technology, the plasma cutting machine has gained greater flexibility in cutting different shapes according to a series of various instructions programmed into the machine’s CNC system.However, CNC plasma cutting machines are usually limited to cutting patterns and parts from flat steel plates with only two motion axes.
In the past ten years, manufacturers of various plasma cutting machines have developed new models with smaller nozzles and thinner plasma arcs.This allows the plasma cutting edge to have laser-like precision.Several manufacturers have combined CNC precision control with these welding guns to produce parts that require little or no rework, simplifying other processes such as welding.
The term “thermal separation” is used as a general term for the process of cutting or forming materials by the action of heat. In the case of cutting or not cutting the oxygen flow, there is no need for further processing in further processing.The three main processes are oxy-fuel, plasma and laser cutting.
When hydrocarbons are oxidized, they generate heat.Like other combustion processes, oxy-fuel cutting does not require expensive equipment, energy is easy to transport, and most processes require neither electricity nor cooling water.One burner and one gas cylinder are usually sufficient.Oxygen fuel cutting is the main process for cutting heavy steel, non-alloy steel and low-alloy steel, and is also used to prepare materials for subsequent welding.After the autogenous flame brings the material to the ignition temperature, the oxygen jet is turned on and the material burns.The speed at which the ignition temperature is reached depends on the gas.The speed of correct cutting depends on the purity of oxygen and the speed of oxygen injection.High purity oxygen, optimized nozzle design and correct fuel gas ensure high productivity and minimize the overall process cost.
Plasma cutting was developed in the 1950s for cutting metals that cannot be fired (such as stainless steel, aluminum, and copper).In plasma cutting, the gas in the nozzle is ionized and focused by the special design of the nozzle.Only with this hot plasma stream can materials such as plastics be cut (no transfer arc).For metal materials, plasma cutting also ignites an arc between the electrode and the workpiece to increase energy transfer.A very narrow nozzle opening focuses the arc and plasma current.An additional connection of the discharge path can be achieved by auxiliary gas (shielding gas).Choosing the right plasma/shielding gas combination can significantly reduce the overall process cost.
ESAB’s Autorex system is the first step to automate plasma cutting.It can be easily integrated into existing production lines.(Source: ESAB Cutting System)
Laser cutting is the latest thermal cutting technology, developed after plasma cutting.The laser beam is generated in the resonant cavity of the laser cutting system.Although the consumption of resonator gas is very low, its purity and correct composition are decisive.The special resonator gas protection device enters the resonant cavity from the cylinder and optimizes the cutting performance.For cutting and welding, the laser beam is guided from the resonator to the cutting head through a beam path system.It must be ensured that the system is free of solvents, particles and vapors.Especially for high performance systems (> 4kW), liquid nitrogen is recommended.In laser cutting, oxygen or nitrogen can be used as cutting gas.Oxygen is used for unalloyed steel and low-alloy steel, although the process is similar to oxy-fuel cutting.Here, the purity of oxygen also plays an important role.Nitrogen is used in stainless steel, aluminum, and nickel alloys to achieve clean edges and maintain the key properties of the substrate.
Water is used as a coolant in many industrial processes that bring high temperatures to the process.The same applies to water injection in plasma cutting.Water is injected into the plasma arc of the plasma cutting machine through a jet.When using nitrogen as the plasma gas, a plasma arc is usually generated, which is the case with most plasma cutting machines.Once water is injected into the plasma arc, it will cause height shrinkage.In this particular process, the temperature rose significantly to 30,000°C and above.If the advantages of the above process are compared with traditional plasma, it can be seen that the cutting quality and the rectangularity of the cutting have been significantly improved, and the welding materials are ideally prepared.In addition to the improvement in cutting quality during plasma cutting, an increase in cutting speed, a decrease in double curvature, and a decrease in nozzle erosion can also be observed.
Vortex gas is often used in the plasma cutting industry to achieve better containment of the plasma column and a more stable necking arc.As the number of inlet gas vortices increases, centrifugal force moves the maximum pressure point to the edge of the pressurizing chamber and moves the minimum pressure point closer to the shaft.The difference between the maximum and minimum pressure increases with the number of vortices.The large pressure difference in the radial direction narrows the arc and causes high current density and ohmic heating near the shaft.
This leads to a much higher temperature near the cathode.It should be noted that there are two reasons why the twisting gas accelerates the corrosion of the cathode: increasing the pressure in the pressurized chamber and changing the flow pattern near the cathode.It should also be considered that, according to the conservation of angular momentum, a gas with a high vortex number will increase the vortex velocity component at the cutting point.It is assumed that this will cause the angle of the left and right edges of the cut to be different.
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Post time: Jan-05-2022