The production of sheet metal blanks, as well as its cutting, are carried out strictly according to special technologies that require certain operations to be performed. This takes into account the chemical and physical properties of metal alloys (their chemical composition, strength, brittleness, electrical conductivity and heat resistance). As a result, parts and workpieces of the required dimensions should be obtained while maintaining the connection properties. For high-quality execution of technological operations, various types of metal cutting are used. They differ in the scope and complexity of the operations.
Today, technologies that are characterized by a high speed of manufacturing parts and the highest accuracy of work are most often used. Large metal-working enterprises use the following types of cutting:
Gas cutting of metal – is the effect on the material by a jet of an oxygen-propane mixture, the temperature of which far exceeds the melting point of the metal. This type of cutting is similar to electrode cutting and is characterized by low precision cutting. The operation can be performed in various conditions without the use of sophisticated equipment, unlike welding, which requires the presence of an electrical network.
Plasma cutting – is carried out by applying a plasma jet to a metal sheet with a temperature from +5000 to +30 000 ° С. The jet is accelerated by an electric field to a speed of the order of 1500 m / s, which is enough to cut a metal sheet up to 20 cm thick. As a result of exposure to a hot plasma, a fairly even and smooth cut is obtained that does not need further processing.
Today this type of metal cutting is one of the fastest and most accurate. The material around the cut zone does not overheat, its structure does not change. In this way, dielectrics and sheets of electrically conductive metals of various degrees of hardness are mainly processed.
Laser cutting – is comparable in accuracy to plasma cutting. Instead of plasma, a laser beam is used here, melting a metal sheet in the cutting zone. Due to the high-precision focusing and high power of the laser beam, the metal not only melts, but also instantly evaporates, leaving the cut line clean and smooth. When processing a sheet with a thickness of more than 15 mm, additional blowing of the cut line with inert gas or cooling with water is required. Laser cutting is usually used to produce parts of complex shape from sheets of relatively small thickness (up to 20 mm). As billets use steel and its alloys, various non-ferrous metals. The main advantage of laser processing is the ability to process very thin and brittle types of materials.
Waterjet cutting differs from other methods in that it acts on the material mechanically and not thermally. The working body here is a mixture of water with an abrasive substance, which is supplied under ultrahigh pressure. The width of the cut with this method is from 0.5 to 1.5 mm.
For this method, metal sheets with a thickness of up to 30 cm can be used. It is typical that the temperature in the cut zone does not exceed +90 ° C. Therefore, structural changes in the metal in this zone associated with exposure to high temperatures are completely excluded. Also, there are no harmful fumes and emissions to humans.
This type of processing using CNC machines allows you to cut packs of several sheets and thereby greatly increase productivity. A serious disadvantage of this method is the susceptibility of the metal preform to corrosion.
How various types of gas cutting are performed
The principle of gas cutting is based on the property of metals to burn in pure oxygen at a temperature of + 1200 … + 1300 ° C. Today, this method not only cuts metal parts at different angles, but also processes the edges of workpieces for subsequent welding.
Cutting the workpiece begins with its edge. Previously, the surface of the sheet is cleaned of traces of rust, scale and dirt. To cut the sheet, gas is used, which is in cylinders under high pressure.
Compressed oxygen is usually used as a gas, the jet of which burns through a metal billet with the formation of iron oxides. Oxides are melted and blown out of the cut area. To supply oxygen, a special device located on the welding torch is used. Technologically, the welding torch acts as a torch.
In addition to oxygen, coke, petroleum and natural hydrogen, acetylene, kerosene and gasoline in the vapor state are also used, when ignited, they give a temperature of +3200 ° С. Accordingly, depending on the gas used, cutting can be of hydrogen-oxygen, acetylene-oxygen and gasoline-oxygen types. To a lesser extent, machine and manual methods are used.
There is also an oxygen-flux treatment, allocated in a separate form. It can be used to cut refractory and difficult to cut metals such as cast iron, aluminum alloys, high-chromium and nickel-chromium steels. To facilitate the procedure, flux is added to oxygen, and the resulting mixture is then blown out.
Directly cutting the material is carried out by a jet perpendicular to the surface. In addition, oxygen treatment can be performed with compressed gas by directing the cutting jet at an acute angle to the surface of the workpiece.
In this way, medium-alloyed and low-alloyed carbon steel sheets up to 300 mm thick are treated. Oxygen cutting is used both in the metallurgical industry and in individual construction. Using gas, you can cut fairly thick metal sheets. This is the main advantage of this method. The width of the cut is from 2 to 2.5 mm. Hardening of the metal during processing does not occur. The edge of the cut is perpendicular to the surface.
Types of plasma cutting of metal
The use of oxygen has some disadvantages that are completely eliminated when using plasma. Having appeared in the middle of the last century, the first equipment for plasma processing of metal billets was very expensive. Only large engineering corporations could afford it. By the end of the XX century, the cost of equipment has significantly decreased, and this method of cutting material has become more affordable. Now it is used in almost any industry.
Plasma processing of metal products is either surface or separation, the latter is today the most common type of plasma treatment. Directly cutting is carried out either by a plasma arc or by a jet.
The use of a plasma arc is to create an electrical circuit in which the workpiece itself is included. An electric arc arises between the tungsten electrode and the metal workpiece being machined. In the case of a plasma jet, an arc arises between two electrodes, the metal workpiece is not included in the circuit, but is only cut by the formed jet.
The principle of the technology is to quickly melt a portion of the workpiece along the line of action of a compressed electric arc and to subsequently blow molten metal through a plasma stream. Since plasma is an ionized gas with a temperature of +15 000 to +20 000 ° С, it cuts metal much more efficiently than compressed oxygen, which has a temperature of only +1800 ° С.
Although the productivity of the plasma method is higher, oxygen treatment is better than plasma to cope with solid types of metals (for example, titanium). For cutting non-ferrous metals, and especially aluminum, preference should be given to plasma.
In the metal industry, plasma cutting today is a leader among other ways of cutting sheet metal. An important advantage of the use of plasma is the low demands on equipment and, as a consequence, the efficiency of the method. Only an electric network, air and consumables (electrodes, nozzles) are needed. As with oxygen, there is no need to use and move hazardous gas cylinders.
The use of plasma is economically beneficial for the treatment of the following metals:
- aluminum and its alloys up to 120 mm thick;
- copper up to 80 mm thick;
- alloy and carbon steel up to 50 mm thick;
- cast iron up to 90 mm thick.
Plasma can be cut with a thicker metal (up to 200 mm), however, for cutting workpieces with a thickness of more than 120 mm, it is more expedient to use the gas-oxygen method.
The thickness of the metal sheet and its thermal conductivity are the defining characteristics for choosing a cutting method. The permissible thickness for a particular type of processing depends on the thermal conductivity of the metal. With an increase in thermal conductivity (respectively, with an increase in heat removal), the maximum possible thickness of a metal billet decreases. For example, a copper sheet for cutting should have a smaller thickness than a sheet of stainless steel.
The indisputable advantage of the plasma cutting method over the gas one is the cutting speed, which in this case is 6–10 times higher. This is especially true when processing metal sheets with a thickness of 40-60 mm.
Among other advantages of plasma cutting stand out:
- high precision cutting without sagging;
- the ability to perform curly cutting;
- limited heating area, which eliminates overheating of the entire workpiece;
- universality of use without the need for a change of equipment;
- lack of explosive and fire hazardous elements;
- relatively low cost of equipment.
Modern CNC machines provide high speed plasma processing. In addition, the automated system allows the operator of any skill to control the process.
Plasma processing of metal eliminates the need to further clean the part. Even traces of rust, paint and various types of contaminants do not affect the quality of the cut.
Among the disadvantages of the method, we note, first of all, the thermal nature of the processing. This means that the hardness of the edge of the cut increases with respect to the rest of the workpiece, which complicates the possible further processing of the part. In addition, during thermal cutting, part of the material inevitably burns or melts. Nevertheless, the plasma method outperforms the gas-oxygen one in terms of cut quality, width of the zone with tint colors (it is 5 times smaller) and in the presence of scale, which is absent when using plasma.
The main types of lasers for metal cutting
The laser is one of the most spectacular inventions of the 20th century. Moreover, for a long time after the discovery did not understand its true importance and applicability in industry. For many scientists, a laser was a device capable of independently seeking a solution to various problems. Currently, laser technology is used everywhere – from medicine to the space industry.
In mechanical engineering, laser cutting has been used for a long time. The first to use this technology were enterprises in the shipbuilding, aviation and automotive industries who were interested in introducing advanced technologies in order to increase productivity. Increasing competition has motivated manufacturers to implement innovative workflow management systems.
The following types of laser cutting machines are currently used at enterprises:
solid-state installations using compounds of rare-earth elements and crystalline precious minerals based on the principle of pumping photons by flash lamps or laser diodes;
gas plants using activators of an inert gas mixture as activators, excited by electric discharges or directed by a chemical reaction;
fiber installations where the active medium with a resonator is made of fiber completely or in combination with other elements.
Corrosion-resistant steels and non-ferrous metals are highly reflective. Therefore, specifically for their processing, laser systems with a resonator made of fiber optic tubes were created in which the laser beam focuses more strongly and does not scatter on the surface of the metal blanks.
Widespread are gas types of laser systems operating on a mixture of carbon dioxide, helium and nitrogen. For greater reflectivity, silver or gold spraying is applied to the resonator mirrors in this setup.
Laser cutting technology is constantly being improved. To increase the productivity of equipment, accuracy and quality of cuts, new types of plants are being tested, computerized process control is being introduced and complicated with the control of all processing modes.
Features of laser metal cutting
In the process of laser processing, a metal billet passes through several stages of exposure to a laser beam until the finished part is received:
- at the first stage, the laser beam, acting on the workpiece, heats it at the cut start point to the melting point of the metal and forms a shrink shell on the surface;
- at the second stage, under the influence of laser energy, the metal boils and evaporates at a given point;
- at the third stage, the workpiece is melted to the entire thickness, and then the working body of the installation begins to move along a given contour of the part.
Evaporation occurs only on thin metal sheets. Billets of medium and large thickness require blowing of the particles of the molten metal with auxiliary compressed gas, which is used as oxygen, nitrogen, inert gases or air mixtures.
Compressed oxygen supplied to the cut area performs several functions at once: it blows particles of molten metal, cools the surface being treated, maintains the temperature of the workpiece and accelerates its processing. During the operation of the machine, the workpiece is not deformed. Therefore, additional fitting of parts is not required, respectively, there are no material costs for these operations.
Prospects for the application of this technology today are obvious to specialists in the engineering industry. Laser processing can be used for conventional cutting of metal workpieces, and for high-precision production of complex parts for various units. Among the advantages of laser metal cutting, we single out the most obvious:
- high quality of products;
- low material consumption;
- the possibility of delicate processing of brittle and thin workpieces;
- the possibility of manufacturing products of complex shape.
The most significant drawback of the laser processing method is the high cost of equipment and materials.
Laser processing technology is currently in great demand by manufacturers of metal products due to the ability to quickly and accurately manufacture all kinds of parts and at different scales – from single orders to industrial production. Laser technology is also in demand in the decorative products industry and in design, allowing you to create original souvenirs.
Hydroabrasive types of metal cutting. Advantages and disadvantages
Waterjet cutting is the most advanced and innovative technology for cutting materials. Water supplied under ultra-high pressure can cut even thick sheets of steel (up to 300 mm).
The water-jet installation includes a pump, which in experimental versions can produce a pressure of up to 6000 bar. Water, under tremendous pressure, passes through a diamond, sapphire or ruby nozzle with a diameter of only 0.1 mm and accelerates to a speed three times the speed of sound. The forming jet has sufficient focus and strength to cut through virtually any material.
The speeds of operations reach impressive values. For example, a 100 mm stainless steel sheet runs at speeds up to 22 mm / min. When processing a steel sheet with a thickness of 1 mm, the cutting speed can reach up to 2700 mm / min, and when processing glass – up to 11 000 mm / min!
For cutting soft materials, pure water is used. Cutting of solid materials is possible due to the addition of abrasive substances to the liquid (usually it is granite sand).
In the framework of foreign experiments, waterjet technology was compared with more traditional cutting methods. In particular, a comparison was made with laser technology.
Laser and waterjet installations were used to cut packs of metal sheets 0.3 mm thick. The result showed that packs with a total thickness of up to 6 mm are more efficiently cut with a laser, and waterjet installation was more efficient in handling packets of thickness more than 6 mm.
The most significant advantage of waterjet technology in comparison with other types of processing is the absence of strong heating of the workpiece. Since there is no thermal effect on the workpiece, the deformation and stress associated with this are also excluded. The result is the highest quality cut, which does not require additional processing.
Some materials cannot be laser cut because of their reflective abilities. Plasma is not able to process non-conductive materials. In both cases, hydroabrasive treatment will serve as a universal and effective method, however, it should be used with caution in materials subject to corrosion, as it gets wet during cutting of the workpiece.
The water jet is very thin, due to which a fairly narrow cut is created and much less material loss occurs in comparison with thermal methods. This is another advantage of the hydroabrasive method. At the same time, the method also has a rather significant drawback – its high cost. For example, an hour of installation will cost about 1,500 rubles. Due to high loads, the working elements of the equipment are subject to rapid wear and require periodic maintenance and repair. This is expressed in additional financial costs.
The temperature of the workpiece during such processing is in the range from +55 to +90 ° C. This allows you to work with various types of materials, the structure of which changes when heated. In addition to this obvious advantage, we list the remaining significant advantages of the method:
- the possibility of using safe abrasives with water;
- the permissibility of processing a huge number of types of materials, with the exception of diamonds and tempered glass;
- the possibility of cutting sheets up to 300 mm thick;
- lack of harmful gas and steam emissions during operation;
- the ability of the working head to change the cutting angle;
- fire safety of equipment and the permissibility of its use in rooms dangerous for gas;
- obtaining a high-quality surface of the edge of the product with a decrease in its roughness and with the absence of fusion.
Types of mechanized methods of cutting and chopping metals
For mechanical cutting of workpieces, various cutters, saws, abrasive wheels, and presses are used. Mechanical methods cut, for example, gas and oil pipelines, as well as any pipelines for pumping flammable materials. The technology of fireless cutting of metal is popular both in industry and in domestic conditions.
Abrasive cutting wheels can be used in both hand tools and stationary. In the process of cutting a metal part with a rotating abrasive wheel due to strong friction, rapid heating and burnout of the metal in the impact zone occurs. Moreover, the width of the cut is small and does not exceed 2 mm. Cutting is carried out with high speed and accuracy. It is convenient to use this equipment in household construction, in the repair and during the installation of water pipes.
For mechanical cutting of metal sheets, in addition to cutting, cutting is also widely used, in which a knife is pressed against a horizontally located sheet, and the workpiece is cut at the point of contact by hydraulic or pneumatic force. The work of such a press is based on the principle of ordinary scissors, when two blades slide past each other. In addition to pneumatics and hydraulics, eccentric mechanisms are also used to create force.
Pneumatic or hydraulic shears are called guillotines, with sufficient power, they are able to cut durable and thick sheets of metal alloys. However, this method is not applicable to brittle and non-ductile materials, for their cutting it is better to use laser, plasma and other types of processing. Guillotines can also be equipped with software that can increase the speed and accuracy of operations. This is the advantage of using this equipment.
Cutting of the profiled sheet can be done by mobile saber guillotines, which do not require an electric network and work exclusively due to the muscular strength of a person. The profiled sheet, as a rule, is coated with galvanized or polymeric material, so it should not be thermally treated and cut using a grinder. The local destruction of the coating, which occurs at the same time, creates pockets of corrosion that are difficult to eliminate.
The metal tile can only be machined. In the longitudinal direction, the profile is cut with a roller cutter or metal scissors. For cutting in the transverse or diagonal directions, special electric scissors with appropriate nozzles should be used.
Types of metal cutting shears
In everyday life, metal hacksaw and roofing scissors are most often used for working with metal. It should be borne in mind that manual cutting with a hacksaw takes a lot of time and spends a lot of effort.
Scissors for metal provide a much faster cutting. Consider the main types of scissors.
1. Manual scissors.
This type is used only for cutting thin sheets of metal. In this case, it is possible to provide a fairly quick and accurate cut along the intended line. In turn, manual scissors are divided into the following subspecies:
- for cutting curved contours.
2. Slotted scissors.
This type of scissors can be used for both direct and curved cutting. They provide high-quality cutting of local sections of metal sheets. The tool is driven by an electric motor.
3. Guillotine shears.
Advantages of using this type of scissors:
- elimination of cutting defects;
- preservation of coverage of the processed material;
- high precision cutting.
Scissors perform longitudinal and transverse cutting of sheet material using an oblique guillotine knife. The oblique shape of the blade cuts the sheet at an angle, which reduces the required force. The larger the angle between the blade and the workpiece plane, the less force is required, but the cut quality is worse.
4. Manual guillotine shears.
This type of scissors has a significant drawback – they will not be able to cope with a sheet of very durable metal.
5. Mechanical guillotine shears.
This mechanism uses an electric motor, so its performance is higher compared to the manual version of the guillotine.
6. Hydraulic guillotine shears.
An improved type of guillotine shears is often equipped with a CNC system, which allows to achieve high productivity and cutting accuracy. In addition, all standard parameters of operations are stored in the firmware, which also positively affects performance.
Summary tables comparing various types and methods of cutting metals