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REVIEW OF MODERN EQUIPMENT FOR PLASMA-ARC CUTTING OF METALS
Korzhyk V.,
Corresponding Member of the National Academy of Sciences of Ukraine, Doctor of Technical Sciences,
Head of Department of electrothermal processes of materials processing Shandong (Yantai) Sino-Japan Industrial Technology Research Institute (Yantai Industrial Technology Research Institute), West Tower of the Chuangye Building, No. 69, Keji Avenue, High-tech Zone, Yantai, Shandong, China,
The Paton Electric Welding Institute of the NAS of Ukraine, Kyiv
Wang Haichao,
Researcher of Department of Welding Production Shandong (Yantai) Sino-Japan Industrial Technology Research Institute (Yantai Industrial Technology Research Institute), West Tower of the Chuangye Building, No. 69, Keji Avenue, High-tech Zone, Yantai, Shandong, China Khaskin V.,
Doctor of Technical Sciences, Leading Researcher of Department of electrothermal processes of materials
processing
The Paton Electric Welding Institute of the NAS of Ukraine, Kyiv
Illiashenko Ye.,
Postgraduate Student of Department of electrothermal processes of materials processing The Paton Electric Welding Institute of the NAS of Ukraine, Kyiv
Peleshenko S.,
Postgraduate Student of Department of Welding Production The Paton Electric Welding Institute of the NAS of Ukraine, Kyiv
Aloshyn A.
Postgraduate Student of Department of electrothermal processes of materials processing The Paton Electric Welding Institute of the NAS of Ukraine, Kyiv
DOI: 10.5281/zenodo.7275989
Abstract
The paper analyzes the plasma cutting equipment market, proposes its classification, formulates the main trends and sets the main goals for further research and development for the development and progress of plasma cutting technology. It has been established that an increase in the thickness of a high-quality and cut-off burn at the existing power level of power sources will allow: to expand the scope of plasma cutting; increase the efficiency of the process; create more versatile and flexible cutting systems. Increasing the accuracy of cutting out parts, especially in the range of large thicknesses, will make it possible to abandon the machining of edges in many areas of technology, which will positively affect the speed of manufacturing processes and their cost. Increasing the cutting speed will reduce the payback period of equipment, reduce the cost per linear meter of cut, and reduce the number of installations in large industries. Increasing the service life of consumables, even with a proportional increase in their prices, will reduce losses from equipment downtime.
Keywords: plasma cutting, power sources, cutting torches, ignition of the cutting arc.
Introduction
The purpose of this article is to analyze the plasma cutting equipment market, classify the offered equipment, formulate the main trends and set the main goals
for further research and development for the development and progress in plasma cutting technology. For market analysis, data obtained from open sources of the
following companies were used: Hypertherm, Kjell-berg Finsterwalde, Esab, Miller, Lincoln Electric and Victor Thermal Dynamic [1-6]. The choice of these companies was due to their fame and the presence of a sufficient amount of information on the official websites.
The market overview is divided into three parts: manual cutting, mechanized cutting and dual-use systems. The division into systems for manual and mechanized cutting is, in some cases, very conditional; the authors were guided by the following criteria when classifying:
- the weight of the system and its mobility;
- cutting accuracy;
- plasma-forming medium;
- the duration of the working cycle;
- technological flexibility.
Manual plasma cutting
Based on the above criteria, the system for manual cutting is oversized, fairly light (up to 50 kg), unified (1 block), a system that uses air as a plasma gas, has low technological flexibility (both in terms of the range of materials and in terms of operations performed). ), with time limits when working at maximum parameters and low cut accuracy.
Modern manual cutting systems (Fig. 1) are complex solutions with a compressor and a source in one housing. The availability of cutting tables with numerical control systems has led to the fact that most of these systems are optionally or in the base equipped with plasma torches for mechanized cutting, and also have the appropriate interfaces for integration with entry-level CNC, but in this review they belong only to the manual category - according to main purpose.
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a) b) c)
Fig. 1. Manual cutting systems: a) - Hypertherm; b) - Linkoln Electric; c) - Kjelberg.
thickness/weight/price" ratio. The relationship between All systems are similar to each other, have similar recommended cutting thickness and system weight is parameters and principles of operation. The main com- illustrated in Figure 2. petition in this niche market is based on the "cutting
Fig. 2. Composite weight and thickness data for various handheld plasma cutting systems.
An important integral characteristic of the cutting process is the ratio of the maximum power of the power source and the pierce thickness (Fig. 3). When constructing this dependence, a polynomial approximation was used.
Fig.3.
Dependence of the maximum recommended pierce thickness on the power supply for manual cutting systems.
The cutting thickness for manual systems varies from 2 to 44 mm for systems of different capacities. Along with the recommended cutting thickness, manufacturers declare the cutting cutting thickness, this parameter can be 20-50% more than the recommended cutting thickness, but has the following limitations:
- duty cycle less than 100%;
- the need to connect an external compressor (in some cases);
MM
- deterioration of cutting accuracy and surface quality;
- increased wear of plasma torch parts.
Cutting accuracy is regulated by the international standard DIN EN ISO 9013 and for manual cutting systems it meets class 5 (Fig. 4).
Толщина изделия
Fig. 4. Cutting angle accuracy range for various thermal cutting methods [7].
Without exception, all hand cutting systems operate on compressed air, sometimes nitrogen or oxygen serves as the second working gas. Plasma torches are cooled by air.
An important fundamental difference between equipment from different manufacturers is the method of ignition of the plasma arc. The first and most com-
monly used method is the non-contact oscillatory ignition. Its disadvantage is the creation of interference for the operation of electronic equipment and the possibility of its failure, this problem is solved with the help of oscillators that generate a single low-frequency pulse. The second method, contact ignition (Fig. 5), disadvantages - increased erosion of the plasma torch parts and the complexity of its design.
Fig. 5. Contact arc ignitionb in Lincoln Electric plasma torches.
A very important parameter is the resource of the plasma torch parts, the ease of their replacement and the price. Depending on the design of the plasma torch, the number of wear parts may vary, but in any of them the cathode and nozzle are consumable parts.
The general trend in the market is to increase the thickness of the pierce while reducing the weight of the system, its price and the price of consumables, increasing the service life of these parts.
It is the desire to reduce weight that explains the massive transition of manufacturers to inverter power supplies.
The power of the sources is limited both by technical and weight and size characteristics, and by the focus on the output power of portable diesel generators, to which plasma systems of this class are very often connected. Thus, an increase in the thickness of the burn is possible either with an increase in the efficiency of sources and identical or smaller weight and size characteristics, or with an increase in the thickness of the burn at the same power (raising the curve in Figure 2). This, in turn, is possible by changing the designs of plasma torches, and using technological and technical
solutions to increase the input energy of the plasma arc, increase its penetrating power and stabilization accuracy, which requires understanding and studying the processes in the plasma arc itself, electrode spots and cut cavity.
Increasing the cut accuracy for manual plasma torches is not significant, and for most applications the current level is sufficient. The same applies to the chemical composition of the cut surface, which determines the use of compressed air as the cheapest and easiest gas to use.
Consumable parts resource problems are common to all plasma torches and will be discussed at the end of the article.
Mechanized plasma cutting
Mechanized cutting systems (Fig. 6) are systems designed for stationary use (have large weight and size characteristics), consist of several separate blocks, have a 100% duty cycle in all technological modes, high cutting accuracy (comparable to laser cutting [8]) and high level of technological flexibility. All of the considered systems allow for plasma cutting, gouging and part marking.
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а) b)
Fig. 6. Complexes for mechanized plasma cutting: a) - Hypertherm; b) - Victor Thermal Dynamic.
In the case of mechanized plasma cutting, the ratio of the power of the power source to the maximum recommended pierce thickness is important. For industries that use cutting sheets of different thicknesses, a correctly selected system allows cutting in the entire range of required production. These relationships are shown
in Figure 7. The general dependence of the burn thickness on the power of the source (Figure 8) makes it possible to determine the efficiency of converting electrical energy into thermal energy over the entire range of thicknesses. Pierce thickness refers to the maximum thickness of a high-quality cut in low-alloy steel.
Fig. 7. Converging data on the ratio ofpower supply power to maximum pierce thickness for various mechanized
plasma cutting systems
Мощность источника питания
Fig. 8. Maximum Recommended Pierce Thickness versus Power Supply Power for Mechanized Cutting Systems.
The maximum cutting thickness is limited by the long plasma arc, which in turn is determined by both the maximum voltage that the power source can generate and the physical features of the arc shunting process in the cut cavity [9]. For materials with a low melting point (aluminum) or low thermal conductivity (stainless steel), it is possible to achieve an almost twofold
increase in the pierce thickness by increasing the operating current, that is, increasing the heat input at the same arc length [10]. To achieve this goal, most manufacturers use complexes with two power supplies, which are connected in parallel (Fig. 9). Characteristically, the penetration thickness of unalloyed steels for these systems is the same as for their single versions.
а) b)
Fig.9. Plasma cutting systems with dual power supplies: a) - Hypertherm; b) - Kjelberg.
All complexes for mechanized plasma cutting have two circuits for supplying gas to the plasma torch. The 1st circuit is used to supply the plasma gas, the 2nd circuit is used to supply the shielding gas. For all complexes, air, oxygen, nitrogen, argon, hydrogen (and their mixtures) can be used as a plasma gas. The list of protective (forming) gases is the same, but sometimes methane, CO2 and coaxial water supply are also used.
Depending on the mode, the plasma and shield gases may be the same, and in some systems the protective circuit may be disabled.
Some companies aim to sell ready-made solutions that include not only plasma equipment and plasma torches, but also:
- various manipulators for plasma cutting of sheets, complex profiles and pipes;
- movement and process control systems;
- NEST/CAM software (for optimal placement of parts on a sheet and creation of control programs);
- exhaust tables and ventilation systems, submersible tables (in case of cutting under a ball of water).
The most noticeable trend is the use of multicom-ponent plasma media and automatic consoles to control the supply and dosing of gases (Fig. 10). All manufacturers have an automatic gas console - a paid option; in
the basic equipment, the equipment is equipped with a manual gas console, which does not allow working on gas mixtures and making a quick change of modes (for example, cutting / marking).
a)
b)
Fig.10. Automatic gas consoles: a) - Kjelberg; b) - Victor Thermal Dynamic.
An equally important trend is an increase in the accuracy of cut parts. Depending on the configuration of the equipment and the mode of operation, most of the complexes allow cutting parts with 1-2 accuracy classes (Fig. 4). This trend is not only affecting straight-line classic nesting, manufacturers are actively patenting and promoting technologies (implemented on their standard equipment) for precise hole cutting, chamfering, angle and cone cutting.
Increasing the maximum thickness of a high-quality cut is an urgent task for the industry, allowing it to find new applications in the industry. At the moment, the largest thickness of high-quality cutting through of non-alloyed steel is 80 mm, stainless steel is 160 mm.
From the point of view of economic efficiency, an important parameter of the process is the cutting speed.
It is due to the high cutting speed that this method has become widespread.
Dual purpose systems
In the line, each manufacturer has one or more complexes that use air or oxygen as a plasma gas and allow cutting large thicknesses (up to 75 mm) but with poor surface quality and cut geometry. These systems (Fig. 11) are positioned as an alternative to oxy-fuel cutting and can be used both for manual (cutting off rolled products, cutting for scrap metal) and mechanized cutting (with low quality requirements).
It can be assumed that further development of manual cutting systems will allow them to occupy this market niche.
Fig.ll. Dual purpose systems: a) - Hypertherm; b) - Kjelberg; c)
c)
Esab.
Service life of plasma torches
The most urgent problem for all types of systems is the service life of plasma torch consumables. Manufacturers actively advertise their patented technologies that increase the resource of their work. The essence of these technologies is reduced to the following points:
- precise centering of the plasma arc along the axis of the plasma torch;
- improvement of heat removal from the active insert];
- alloying of the insert metal;
- current rise control.
In addition to the cost of the consumables themselves, an important economic parameter is the downtime of the equipment when replacing them. Therefore, manufacturers strive to make plasma torches easily collapsible and simple, use quick-release fittings to connect communications, and sometimes even automatic replacement of the plasma torch (Fig. 12).
Conclusions
1. Increasing the thickness of high-quality and cutoff pierce at the existing power level of power sources will allow:
- expand the scope of plasma cutting;
- increase the efficiency of the process;
- create more versatile and flexible cutting systems.
2. Increasing the accuracy of cutting out parts, especially in the range of large thicknesses, will make it possible to abandon the machining of edges in many areas of technology, which will positively affect the speed of manufacturing processes and their cost.
3. Increasing the cutting speed will reduce the payback period of equipment, reduce the cost per linear meter of cut, and reduce the number of installations in large industries.
4. Increasing the service life of consumables, even with a proportional increase in their prices, will reduce losses from equipment downtime.
5. The search for optimal plasma-forming and protective media for plasma cutting continues. Different manufacturers use different solutions. The key criteria for this search is the cost of the gas used and its effect on the chemical composition of the cut edges.
The work was supported by the project: "Development and application of technology for plasma cutting c with the addition of water of steel sheets for shipbuilding", No. WSG2021012, China.
References
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2. Kjellberg Finsterwalde. Plasma Cutting from 0.3 to 160 mm. - Электронный ресурс: https://www.kjellberg.de/cutting.html
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