Plasma cutting is used in the processing of conductive metals. The processed material receives energy from the current source through ionized gas. The standard system includes a current source, an ignition circuit and a torch, which provide power supply, ionization and control necessary for high-quality high-performance cutting of various metals.
The output of the DC source sets the thickness and processing speed of the material and maintains the arc.
The ignition circuit is made in the form of a high-frequency alternating voltage generator of 5-10 thousand. At a frequency of 2 MHz, which creates a high-intensity arc, ionizing the gas to a plasma state.
The torch is a holder for consumables - nozzle and electrode - and provides cooling of these parts with gas or water. The nozzle and electrode are compressed and support the ionized stream.
Manual and mechanized systems serve different purposes and require different equipment. Only the user can determine which one is best suited to his needs.
Plasma metal cutting is a thermal process in which a beam of ionized gas heats an electrically conductive metal to a temperature above its melting point and removes the molten metal through a hole made. An electric arc arises between the electrode in the burner to which the negative potential is connected and the workpiece with the positive potential, and the material is cut by an ionized gas stream under pressure at a temperature of from 770 to 1400 ° C. A plasma jet (ionized gas) is concentrated and directed through a nozzle, where it is compacted and becomes able to melt and cut a wide variety of metals. This is the main process for both manual and mechanized plasma cutting.
Hand cutting
Manual plasma metal cutting is performed using fairly small plasma torch devices. They are maneuverable, versatile and can be used to perform various tasks. Their capabilities depend on the current strength of the cutting system. The parameters of manual cutting units vary from 7–25 A to 30–100 A. Some devices, however, allow you to get up to 200 amperes, but they are not widely used. In manual systems, technical air is usually used as a plasma and shielding gas. They are designed so that they can be used with different input voltages, which can vary from 120 to 600 V, and can also be used in single or three-phase networks.
Manual plasma for metal cutting is usually used in workshops dealing with the processing of thin materials, factory technical services, repair shops, scrap metal collection points, during construction and installation works, in shipbuilding, auto repair shops and art workshops. As a rule, it is used to trim the excess. A conventional 12-amp plasma apparatus cuts a maximum of 5 mm metal layer at a speed of about 40 mm per minute. A 100-amp device cuts a 70 mm layer at speeds up to 500 mm / min.
Typically, a manual system is selected depending on the thickness of the material and the desired processing speed. A device that provides high amperage is faster. However, when cutting with high current strength, it becomes more difficult to control the quality of work.
Machine processing
Mechanized plasma metal cutting is carried out at plants, which, as a rule, are much larger than manual ones, and is used in combination with cutting tables, including a water bath or a platform equipped with various drives and motors. In addition, mechanized systems are equipped with CNC and control of the height of the jet cutting head, which may include a preset torch height and voltage control. Mechanized plasma cutting systems can be installed on other metalworking equipment, such as stamping presses, laser cutters or robotic systems. The size of the mechanized configuration depends on the size of the table and the platform used. The cutting machine can be smaller than 1200x2400 mm and larger than 1400x3600 mm. Such systems are not very mobile, therefore, prior to installation, all their components should be provided, as well as their location.
Nutrition requirements
Standard power supplies have a maximum current range from 100 to 400 A for oxygen cutting and from 100 to 600 A for nitrogen. Many systems operate in a lower range, for example, from 15 to 50 A. There are nitrogen cutting systems with a current strength of 1000 A and above, but they are rare. The input voltage for mechanized plasma systems is 200–600 V in a three-phase network.
Gas requirements
For cutting mild and stainless steel, aluminum, and various exotic materials, compressed air, oxygen, nitrogen, and a mixture of argon and hydrogen are usually used. Their combinations serve as a plasma-forming and auxiliary gas. For example, when cutting mild steel, the starting gas is often nitrogen, plasma is oxygen, and compressed air is used as auxiliary.
Oxygen is used for mild carbon steel because it produces high-quality cuts in material up to 70 mm thick. Oxygen can also play the role of a plasma-forming gas for stainless steel and aluminum, but the result is not entirely accurate. Nitrogen serves as a plasma and auxiliary gas, because it provides excellent cutting of almost any type of metal. It is used at high currents and allows processing sheet metal up to 75 mm thick and in the role of auxiliary gas for nitrogen and argon-hydrogen plasma.
Compressed air is the most common gas, both plasma and auxiliary. When a low-current cutting of sheet metal up to 25 mm thick is performed, it leaves an oxidized surface. When cutting with air, nitrogen or oxygen is an auxiliary gas.
A mixture of argon and hydrogen is typically used to process stainless steel and aluminum. It provides a high-quality cut, and is necessary for mechanized cutting of sheets with a thickness of more than 75 mm. Carbon dioxide can also be used as an auxiliary gas when cutting metal with a plasma of nitrogen, as this allows you to work with most materials and guarantees good quality.
A mixture of nitrogen with hydrogen and methane is also sometimes used in plasma cutting.
What more is needed?
The choice of plasma and auxiliary gases are only two of the most important decisions that must be taken into account when installing or using a mechanized plasma system. Gas tanks can be purchased or rented, they are available in various sizes, and appropriate conditions must be created for their storage. Installation of the system requires a significant amount of electrical wiring and pipes for gas and coolant. In addition to the mechanized plasma system itself, you need to choose a table, a cutting machine, CNC and THC. OEMs usually offer a variety of equipment options that will suit any device configuration.
Do you need mechanization?
Due to the difficulty of choosing a mechanized plasma cutting process, it is necessary to devote a lot of time to the study of various configurations and system criteria. Please note:
- types of parts to be cut;
- the number of industrial products in the party;
- desired cutting speed and quality;
- cost of consumables.
- the total cost of operating the configuration, including electricity, gas and labor.
The size, shape and number of parts produced can determine the necessary industrial production equipment - type of CNC, table and platform. For example, the production of small parts may require a platform with a specialized drive. Rack and pinion drives, servo drives, drive amplifiers and sensors used on the platforms determine the cutting quality and maximum system speed.
Quality and speed also depends on which metalworking equipment, CNC and gases are used. A mechanized system with adjustable current and gas flow at the beginning and at the end of cutting will reduce material consumption. In addition, CNC with a large amount of memory and the choice of possible settings (for example, the torch height at the end of the section) and fast data processing (input / output communication) will reduce downtime and increase speed and accuracy.
Ultimately, the decision to purchase or upgrade a mechanized plasma cutting system or use a manual one should be justified.
Plasma cutting of metal: equipment
Hypertherm Powermax45 is a portable device with a large number of standard components based on an inverter, i.e. an insulated gate bipolar transistor. It is very easy to work with it, regardless of whether thin steel or sheet metal is cut with a thickness of 12 mm at a speed of 500 mm / min or 25 mm at a speed of 125 mm / min. The device is capable of generating high power for cutting various types of conductive materials, such as steel, stainless steel and aluminum.
The power system has an advantage over analogues. Input voltage - 200-240 V single-phase current with a power of 34/28 A at a power of 5.95 kW. Changes in the input voltage of the network are compensated by Boost Conditioner technology, due to which the torch demonstrates increased performance at low voltages, with fluctuations in the input power, as well as when powered by a generator. Internal components are efficiently cooled with PowerCool, which provides enhanced performance, uptime, and device reliability. Another important feature of this product is the FastConnect burner connection, which facilitates mechanized use and increases versatility.
The Powermax45 has a double-angle design that extends nozzle life and reduces operating costs. It is equipped with the Conical Flow function, which increases the energy density of the arc, which greatly reduces throttle and produces high-quality plasma cutting. Price Powermax45 - $ 1800.
Hobart AirForce 700i
Hobart AirForce 700i has the highest cutting ability in this line: the nominal cutting thickness is 16 mm at a speed of 224 mm / min, and the maximum is 22 mm. Compared with analogs, the device’s operating current is 30% less. Plasma cutter is suitable for service stations, repair shops and for the construction of small buildings.
The device features a lightweight but powerful inverter, an ergonomic starting fuse, efficient air consumption and low-cost burner consumables, which makes safe, high-quality and inexpensive plasma cutting. The price of AirForce 700i is $ 1500.
The kit includes an ergonomic hand torch, cable, 2 replaceable tips and 2 electrodes. Gas consumption is 136 l / min at a pressure of 621–827 kPa. The weight of the device is 14.2 kg.
The 40-amp output delivers exceptional sheet metal cutting performance — faster than mechanical, gas, and plasma devices from other manufacturers.
Miller Spectrum 625 X-treme
The Miller Spectrum 625 X-treme is a small machine powerful enough for cutting various types of steel, aluminum and other current-conducting metals.
It is powered by an AC voltage of 120-240 V, automatically adjusting to the applied voltage. Lightweight and compact design makes the device highly portable.
Thanks to Auto-Refire technology, the arc is controlled automatically, eliminating the need to constantly press a button. The nominal cutting thickness at a current of 40 A is 16 mm at a speed of 330 mm / min, and the maximum is 22.2 mm at 130 mm / min. Power consumption - 6.3 kW. The weight of the device in manual execution is 10.5 kg, and with a machine cutter - 10.7 kg. As a plasma gas, air or nitrogen is used.
The reliability of the Miller 625 is provided by Wind Tunnel technology. Thanks to the integrated high-speed fan, dust and debris do not enter the device. LED indicators inform about pressure, temperature and power. The price of the device is $ 1800.
Lotos LTP5000D
Lotos LTP5000D is a portable and compact plasma apparatus. With a weight of 10.2 kg, problems with its movement will not arise. The 50-amp current produced by the digital converter as well as the powerful MOSFET transistor provide efficient cutting of mild steel with a thickness of 16 mm and 12 mm of stainless steel or aluminum.
The device automatically adjusts to the voltage and frequency of the network. The length of the hose is 2.9 m. The auxiliary arc does not contact the metal, which allows the use of the apparatus for cutting rusty, unprocessed and painted materials. The device is safe to use. Compressed air used for cutting is not harmful to humans. A sturdy shockproof housing reliably protects the device from dust and debris. The price of Lotos LTP5000D is $ 350.
When buying a plasma torch, you should always give preference to quality. You should beware of the temptation to purchase a cheap low-quality device, since its quick wear in the long run will lead to much greater costs. Of course, it is also not worth overpaying, there are quite decent budget options without accessories and high capacities that may never be needed.