Cutting sheet metal ways. How to cut thick metal

How to cut metals

Metals (and especially. rolled steel). an indispensable part of modern life. Rolled steel is used everywhere, it is strong and durable, it can be used in industry and in the home The only problem. it is not so easy to get out of a continuous sheet of steel is required by size and shape. In general. the metal should be cut and cut, for which there are many ways that may be optimal in different conditions.

Let’s start with the fact that the methods of metal cutting in the very first approximation are divided into mechanical and thermal. Mechanical includes cutting steel with cutters and circular saws, band saws, and guillotines; thermal includes all others.

The main advantage of mechanical methods is that they are “cold. and the metal is not red-hot when machining with these methods. hence its physical properties cannot change either. In addition, this technology of metal cutting may not require particularly complex mechanisms, which makes it especially attractive for use in domestic conditions.The best example of this is cutting steel with a cutter or circular saw by a device commonly referred to as an “angle grinder”.

For these machines there are not only cutters made of high-strength alloys, but also relatively light blades with special coating of abrasive mixtures. Such disks can cut only relatively soft metals, such as copper and aluminum, while steel cutters can cut almost any ferrous metal (except for high-strength alloyed steels), as long as the sheet thickness does not exceed 10-12 mm.

Convenience on a domestic level is obvious, but the main disadvantage is not noticeable at this level. high labor intensity, low accuracy and very low speed of such method.

Band saw machine with its saw, stretched on pulleys, is able to cut metals with a very high quality and minimal cutting waste. It can also be noted that this method in principle allows cutting metal at an angle that can reach up to sixty degrees.

However, the speed of metal processing on such machines is still not very high. and if you need to cut a large number of pieces of metal, it would be better to use other equipment. an industrial guillotine.

The principle of its work is clear from the name. beveled at 80-85 degrees knife made of high-strength steel under the action of a heavy torch falls on a steel sheet and its with the formation of an almost perfect edge.

The coating on the metal (if any) is not even damaged and the resulting cuts are very easy to work with afterwards. cutting precision is very high and produces no waste products in the form of chips.

This method of metal cutting is virtually ideal if only for cutting sheets and cutting in a straight line. But alas. in a straight line to cut the metal is not always necessary, and have to cut not only sheets, but also angles, pipes, channels and other rolling.

Laser cutting methods

This method involves heating the metal with a laser beam to boiling temperature, which causes evaporation of material in the cutting zone. The laser source generates very short pulses and emits a much more powerful beam of light than a continuous laser beam. This process requires considerably more energy and power than fusion cutting, since the metal must be heated to a higher temperature. For example, aluminum melts at 660 °C and boils at 2518.82 °C. Because of its high cost, vapor cutting is seldom used, e.g., for cutting thin sheets and thin parts.

This method allows to significantly reduce energy consumption, use less powerful equipment and cut thicker metal sheets.

While cutting, the laser beam heats the material to the melting temperature, and the flow of auxiliary gas (oxygen, nitrogen, argon, air) blows the molten metal out of the zone of cutting, cools the cut edges, preventing their deformation, and performs other important functions which depend on the type of gas used.

Laser cutting metal with oxygen

When oxygen interacts with heated material, an oxidation reaction occurs, during which a lot of heat is released, and the temperature in the treatment area rises significantly. This makes it possible to increase the processing speed and thickness of the cut sheet. Another advantage. low cost of production operation compared to other types of laser cutting. Cutting with oxygen requires less energy than cutting with inert gas and evaporation cutting.

The disadvantage of the method consists in oxidation of edges of some materials which are cut. In this regard, the scope of the method includes cutting of ferrous metals, unalloyed steels, ferrous steel. Non-ferrous metals, stainless steels, and other alloy steels are oxidized by contact with oxygen and are therefore not suitable for oxygen-assisted cutting.

Laser cutting of metal in inert gases (nitrogen, argon)

This technique is used when it is necessary to prevent oxidation of the cut material edges. The inert gases separate oxygen-containing atmospheric air from the cutting zone. This eliminates contact between the edges and the oxygen and keeps the edges clean, smooth and in no need of subsequent machining. Cutting speed in inert gases is lower compared to cutting in oxygen, and the cost is higher, because there is no oxidation, which is an additional source of heat. Argon is used to cut titanium, nitrogen is used to cut alloy steels, stainless steel, non-ferrous metals, and alloys.

Two types of laser equipment are widespread in Russia: fiber laser machines and gas (CO2) laser machines. The most important difference between them is the wavelength of light emitted from the laser. Fiber laser machines have a wavelength of 1064 μm and a very small focus diameter, which provides high beam intensity (100 times higher than a CO2 laser with the same radiated power) and high intensity of material heating. over, metals, especially non-ferrous ones, are very absorbing to short-wave laser radiation. Because of this, it is most effective to use fiber laser machines for cutting metals.

The wavelength of CO2 lasers is 10.6 µm. This equipment is intended primarily for working with non-metallic materials (wood, plastics, glass, rubber, plastics, ceramics, etc.).д.). Base metals (copper, aluminum, aluminum alloys, etc.).д.) have a high reflectance for 10.6 µm wavelength radiation. Therefore, CO2 lasers are not suitable for these materials. over, gas lasers are more power consuming, more complicated to maintain and have a more complex optical system that requires periodic alignment and diagnostics.

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Modern laser machines are equipped with computer numerical control (CNC) which greatly simplifies the manufacturing process. The cutting program is loaded into the machine controller with special codes that create the cutting beam path and other cutting parameters. Automation of the process makes it possible to quickly obtain large batches of completely identical parts of any complexity.

Oxyfuel cutting

Cutting metal using oxyfuel metal cutting is acceptable under a number of conditions:

  • The metal element contains a small amount of alloyed components;
  • the product is characterized by low thermal conductivity;
  • the processed material has a melting point higher than the combustion temperature.

Oxyfuel cutting is not recommended as a general metalcutting technique. After gas cutting, oxides remain on the material, which affect its entire quality.

Gas-oxygen metal cutting

Today, oxy-fuel cutting is probably the most popular form of metal cutting due to its high productivity. It is provided, thanks to a completely different principle of action, which is the combustion of metal. Before this, it is mandatory to preheat the place of cutting to the ignition temperature, which is made by the heating flame of the torch without the supply of cutting oxygen. Depending on the thickness of the metal and its surface condition, the initial heating time varies from 5 to 40 seconds. When sufficient heating is achieved, oxygen is supplied, and when its jet cuts through the entire thickness of the metal, the torch begins to move evenly along the cutting line. The oxygen cuts the heated metal, and simultaneously removes the resulting oxides, and the radiated heat of combustion heats the neighboring layers of the metal. The cutting nozzle must always be at the same distance from the workpiece surface, which is determined experimentally. The maximum thickness of gas-oxygen metal cutting is 200 mm.

However, not all metals are amenable to gas-oxygen cutting. For example, you will never be able to cut aluminum. First, its combustion temperature is 900° C and its melting temperature is 660° C, so it will burn only in the liquid state, and a stable shape of the cut is simply impossible. Aluminium in combustion produces oxides with a melting point of 2,050°C. This oxide will be hard when you cut it, and it is difficult to remove. Finally, aluminum is a very heat conductor, so you need a high power density and high gas consumption. Similarly, high-alloyed, high-carbon and chromium-nickel steels are not susceptible to oxy-fuel cutting.

When working with gas-oxygen cutting devices, it is important to choose the right speed of the nozzle and the flow of air and gas. For example, too high cutting speed, in addition to the significant lag of the cutting jet, gives uneven grooved surface of the cut; too low cutting speed causes melting of the edges on the input side and increases the width of the cut, which leads to significant loss of metal. The easiest way to determine the cutting speed is by the nature of ejection of sparks and slag: they must be ejected from the back side of the workpiece at a slight angle from the vertical axis.

The disadvantages of this type of cutting include the large width of the cut (along which, in addition, there are overlaps, burrs and oxides), its poor quality, the inability to pass through the curved contours of small radii, a significant thermal impact on the metal. Uneven heating creates stresses in the metal and deforms it, distorting its geometric shape. The stresses can be completely removed only by heat treatment, and this is a high additional cost. This method is not suitable for every type of metal.

Gas-oxygen metal cutting

The gas method of metal processing is considered one of the earliest thermal cutting methods: the time of the appearance of gas-oxygen cutting is the end of XIX century.

This technology involves the impact of a jet of flaming gas, which is directed at the trimmer line to cut the material, and is designed to blow out the resulting oxides. The metal is heated by the gas flame to a temperature of approx. 1000° С.

The main advantages of gas-oxygen cutting are the ability to process:

The disadvantages of this method of cutting include:

  • The inability to cut all types of metal;
  • low quality of the cutting line;
  • the possibility of deformation of the material;
  • fire risk due to the gases used and the large open flame torch
  • High demands on the conditions under which cutting is performed.

Therefore, gas and oxygen cutting is not used when high quality and precision cutting of parts is needed.

Professional and industrial metal cutting tools

Professional metal cutting tools are used to process workpieces in industrial environments.

Tools and machines for mechanical cutting

Mechanical cutting has the following advantages:

The main disadvantage is that only straight cuts can be made with the mechanical method.

  • Angle grinders are most often used for cutting small and medium-diameter bars. Guillotines are used for producing rebar, angles and square and round tubes. The method is notable for its low productivity, but the amount of waste tends to be minimal.

Consumable material for metal processing angle grinder. abrasive and diamond wheels.

  • Circular saws. With their help, it is possible to make cuts at an angle. The advantages of the method. high precision and quality. Disadvantages. limited by the depth of cut, a large amount of waste.

Photo : metal cutting with a circular saw

  • Guillotines. Billets are cut into parts using the chopping method. This method of processing is considered the most productive and cheapest, but is not intended for the manufacture of parts of complex configuration.

Photo : guillotine metal cutting

  • Band saws are designed for cutting all metals and alloys. The method has a low amount of waste. Cut edges are as straight as possible. There are restrictions in terms of the size of blanks.

Photo : metal cutting on a band saw machine

Waterjet cutting

Metal is cut with a special equipment using a solution (water, abrasive sand), which is pumped at high pressure through a narrow nozzle. The innovative technology is designed for cutting metal with a thickness of up to 30 cm. The parts do not require any further processing. The metal is not deformed because. к. No thermal influence.

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Photo : water-jet cutting of metal

This processing method is very expensive and not suitable for metals that are vulnerable to corrosion.

Hot Cutting Technologies

  • Laser. Workpieces are processed on special machines. The laser beam causes some of the metal to vaporize. Remaining molten material is blown out with a gas mixture.

Laser cutting produces high-precision parts of any configuration that do not require additional processing. However, the method has disadvantages:

  • limitation on the thickness of the metal. laser machines can process workpieces up to 20 mm thick;
  • Expensive. the of machines and their operation are kept high;
  • Restriction on the type of metal. laser cutting is not suitable for stainless steel, aluminum, and other alloys with high reflectivity.
  • Gas. Workpieces are machined on special machines. Cutting technology is based on intense melting of the metal. It is subjected to a directional flow of the gas-oxygen mixture.

Suitable for rough cutting of metals and alloys with low thermal conductivity. High temperatures cause pitting and scale formation at the work area. The resulting parts require additional processing.

  • Plasma. the metal is cut with a high-pressure gas mixture. As a result, the material melts and burns out, and the residue and scale are completely blown away.

Photo : plasma cutting metal

Plasma cutting has the following advantages:

  • Cost-effectiveness. the amount of waste tends to be minimal, and the resulting parts do not require additional processing;
  • productivity. plasma cutting is 4, 8 and 10 times faster than laser, waterjet and mechanical cutting respectively
  • versatility. the technology is suitable for any electrically conductive metal from 1 mm up to 15 cm thick.

Plasma cutting is used for both batch and single-piece production.

Cutting steel of small, medium, and large thicknesses

Cutting steel of small thicknesses (especially less than 5 mm) is usually accompanied by considerable overheating of the metal by the heating flame, which leads to increased melting of the upper edges and to an increase in the proportion of unoxidized (melted) iron in the slag. This slag is welded to the bottom edges of the cut and requires a lot of labor to remove it.

Furthermore, when cutting thin sheets of steel, warpage out of the plane of the sheet material increases and leads to increased distortion of the shape of the cut parts and workpieces.

A normal cutting process with normal equipment is possible with sheet thicknesses of at least 4 mm. Cutting with a preheating flame and cutting oxygen in a sequence produces better results for thinner sheets (Fig. 5). Fig. 78, a), but even in this case sheets under 3 mm thickness are difficult to cut and do not give good results. High cutting quality in thin sheets can be achieved with batch cutting, which is especially efficient for batch production of identical cut parts. Sheets from 1 mm thick can be cut with batch cutting.

The essence of the steel batch cutting process is as follows. Sheets are stacked and cut with an oxygen beam in a single cutter pass Up to 50 or more sheets can be stacked, depending on their thickness, the number of identical parts required, and the means for assembling the stacks. In some cases it is appropriate to pack sheets with such a thickness that they can be cut separately (8-10 mm and more).

Batch cutting has some special features. When cutting with conventional cutters it is very important to assemble sheets tightly with minimal gaps between them. If there are gaps, the heating of the underlying sheet is impaired, and the oxygen jet, without cutting it through, begins to spread to the sides, taking the hot slag with it, heating and burning the already cut parts and underlying sheets. To prevent this, the sheets are straightened and stiffened beforehand either by clamps or by welding rolls applied at the ends. Presses are sometimes used when squeezing thin sheet packages.

Due to the fact that the power of the heating flame is taken in accordance with the total thickness of the package, the upper sheet is greatly overheated and at low thickness is warped, departing from the underlying and creating a gap. As a consequence, cutting may stop. That is why a thicker sheet (usually 6-8 mm, even if the parts are cut from thinner metal) is often placed on top of the package.

To some extent, the part of the lower sheet (for thicknesses up to 3 mm) is also damaged, and a large amount of flowing slag collects on it, which leads to melting of the edges. When cutting from the edge, it is useful to assemble the package with an offset of the edges. It is also possible to assemble a bundle without an offset, but then the cutting should be started on a roll that has been previously welded on the edge. Start cutting in the center of the package by pre-drilling a through hole. After cutting is complete, rapid cooling (sometimes with water) of the cut pieces is recommended to make it easier to separate them.

Cutting with low pressure oxygen with large machine cross-sections requires less accuracy of plate alignment in the package by planes, allowing for cutting with local gaps. In this case the slow down flow of slag facilitates heating of the underlying plate as the slag filling the gap prevents the oxygen jet from spreading sideways and helps to keep its direction. The pack cutting with low pressure oxygen is especially appropriate when cutting sheets with a thickness of 8-20 mm with a gap between the sheets of 2-4 mm. When cutting with low pressure oxygen the number of clamps that compress the pack can be reduced.

Medium-thickness steel cutting modes

The best cutting quality results are achieved with oxygen for medium thicknesses (approx. 12-100 mm). Oxygen cutting of such metal does not cause technological difficulties and can be easily performed with conventional gas cutting equipment, both manually and mechanically.

Cutting of middle thickness steel with standard equipment should be done with oxygen pressure in the reducer working chamber of 2,5-6 kgf/cm2 depending on thickness of metal being cut.

Approximate technical speeds of machine severing cutting of steel of various thicknesses with oxygen purity not less than 98,5-99% are given in table. 20.

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Using the best thermal preparation of the upper edge to reduce the probability of non-cutting, VNIIavtogenmash has developed a method of high-speed straight-line cutting “with the angle forward”. f up to 50-70° Cutting speeds with the torch at right angles (conventional cutting) and with the torch “angle forward” (high-speed cutting) are shown in Fig. 106. From the given data it follows that this method gives the increase of cutting productivity at thicknesses of steel being cut up to 30 mm.

It is economically very expedient to carry out gravity-free cutting. Currently, regimes of gravity-free cutting have been developed based on the use of oxygen of high purity (99.5%), selection of optimal mode, direction and pressure of the cutting oxygen jet, in which there is no slag flowing along the cut in the opposite direction to the cutting (t. е. with small lag A), maximal decrease of heating flame power and substitution of acetylene with other fuels (kerosene, propane, etc.), with small lag B), maximal decrease of heating flame power and substitution of acetylene with other fuels (kerosene, propane, etc.).).

Regimes of gravity-free cutting for achievement of II quality class of cutting according to recommendations of All-Russian Scientific and Research Institute of Automobile industry are given in table 1. 21.

For thicknesses up to 12-15 mm a machine cutting without grit is also possible with less pure oxygen and with the torch facing forward (cf. Fig. 105).

Cutting of medium thickness steel with low pressure oxygen with a torch with a larger cutting oxygen channel is not reasonable.

Cutting of steel of big thicknesses

Conventional gas cutting equipment is usually designed for steel thicknesses up to 300 mm but already at thicknesses above 200 mm some cutting problems appear. Even more complicated the cutting of the metal with thickness more than 300 mm. Cutting of steel of such thicknesses is applied mainly in metallurgical industry and at some heavy engineering enterprises.

Topic 5: Metal cutting

Cutting is a locksmith’s operation in which metal is cut into pieces.

Hand scissors are used to cut sheets of steel with a thickness of 0.5-1.0 mm and of non-ferrous metals with a thickness of up to 1.5 mm.

Depending on the structure of the cutting blades, the shears are classified in the following way: straight. with straight cutting blades, designed primarily for cutting metal in a straight line or on a large radius circle; curved. with curved knives; finger knives. with narrow cutting blades for cutting out holes and surfaces with small radius in sheet metal.

According to the arrangement of the cutting blades, the scissors are divided into right-hand and left-hand. Bevel of lower blade on right-hand shears is on the right, on left-hand shears. on the left.

Chair shears differ from conventional manual shears in their larger size and are used for cutting sheet metal up to 2 mm thick.

Lever scissors are used for cutting steel sheets up to 4 mm thick (non-ferrous metals. up to 6 mm).

When working with thick sheets of flat or profiled metal, and if you do not need to saw the metal, and to cut a slot or slots, the scissors can replace the hacksaw. But before you start working with this tool, it should first be properly adjusted. First, you need to choose a blade for the hacksaw. It is selected depending on the type of metal. Secondly, the blade must be tensioned correctly in the frame of the hacksaw; the degree of tension can be easily checked by lightly pressing the side of the blade: if it does not sag, it means that the tension is sufficient. The most comfortable hand position when working with a hacksaw is as follows: the end of the handle rests in the middle of the right hand palm, and the fingers of the left hand grasp the tensioning screw of the moving head.

Movements of the hacksaw should make smooth, without jerks; frequency of movement. 30-60 double strokes (from yourself. on itself) per minute; it should work for at least 2/3 of the length of the blade. The saw blade must be perfectly perpendicular to the axis of the workpiece.

Special note when cutting metal pipes. When cutting them with a hacksaw there is always a fear (especially if the mechanic is not experienced enough) that the blade of the hacksaw “goes” to the side and the cut will turn out in the form of an oval rather than a circle. To avoid this it is preferable not to cut pipes with a hacksaw but with a special tool. pipe cutter

Safety precautions when cutting metal with scissors:

When cutting thin sheets with scissors, the cut portion is severely bent; the edges of the sheet are made very sharp at the point of cut. Care must be taken not to injure your hands. Students should wear gloves.

When cutting, make sure the fingers of the left hand do not get caught in the cutting part of the scissors, and the fingers of the right hand do not get caught in the handles or levers of the scissors. Never keep your left hand in the cutting line when supporting the material you are cutting.

Chair shears must be rigidly and securely fastened to their bases. If hand scissors are used that are fixed in a vice, their fixation must also be done very firmly and quite securely. It is easy to injure not only yourself but also a comrade in case of a tear in the scissors.

When the shears approach the end of the cut, the workpiece should be moved closer to the middle of the cutting part of the shears to avoid cutting by the edges of the blades. Besides, when finishing the cut it’s necessary to decrease the cutting force, making it as smooth and quiet as it’s possible, so that the scissors won’t tear off.

As mentioned above, electric scissors, guillotine scissors, drive scissors are used for mechanization of the heavy and labor-intensive process of cutting sheet metal.

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