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The history of the laser began in 1917 with the presentation by Albert Einstein of his concept of forced radiation of the world of scientists. Since then, several decades have been conducted various experiments to confirm this theory and its application in practice. And finally, in 1960, researchers at Bell Laboratories introduced the world's first gas laser to a mixture of helium and neon, which is applied to our days in optics and laboratories during experiments. After the appearance of the first working laser and the precise understanding of the principles of its work, the experimenters began to work hard on the appearance of various sources of laser radiation.
Laser technologies are used in practically all branches of industry, engineering and science. In industry, a laser is often used for cutting a variety of materials. For the convenience and quality of the cutting of different types of materials were created different types of lasers, which differ in the intensity of radiation in the working zone, the composition of the gas for cutting and its pressure.
The principle of cutting by laser is technologically very simple - the laser beam destroys (melt) the surface of the material, and the stream of compressed gas blows, obtained during melting, evaporation from the working zone. As a result, a cutting line is obtained and the finished pieces of workpieces are separated.
There are several types of laser cutting:
As is clear from the name, the cutting gas is oxygen. Oxygen is a strong oxidant and when it interacts with the metal, there is intense oxidation with a high heat release (exothermic reaction). For example, when reacting with iron, heat is allocated in 3-5 times more than the power of the summed up laser. The oxides formed during the reaction, are blown out of the working zone by the same stream of oxygen.
Features of laser-oxygen cutting:
- The diameter of the focused beam and the cutting speed are determined by the width of the cut. As the processing speed increases and when the thickness of the sheet is reduced, the cutting width is reduced (the minimum cutting width is even less than 100 microns). But with this the diameter of the oxygen jet is more (usually 1-2 mm) than the diameter of the focused beam;
- The larger the thickness of the material being cut, the lower the pressure in the stream of oxygen, and vice versa. Thus, when cutting thin metal pressure in a jet 3-4 atm, and sheet thickness of about 30 mm - about 0.3 atm;
- The laser cutting is performed by an expanding beam. The focal point is above the surface of the material;
- The thickness of the sheet also depends on the gap between the cut of the nozzle, which forms a stream of oxygen. For a thin sheet - from 0.5 mm, and about 3 mm - for a sheet of thickness up to 30 mm (precisely this thickness of the sheet is maximal for laser-oxygen cutting);
- The greater the thickness of the sheet of metal, the slower the cutting speed will occur. The minimum cutting speed is 0.5 - 0.6 m / min and occurs when cutting metal sheet thickness of 30 mm. With further reduction of the cutting speed - the quality of the cutting is slowly deteriorating and various defects begin to appear on the surface of the cutting. At the moment, for cutting 30mm sheets a laser with a power of 6kW is required.
Oxygen cutting with laser beam support (LASOX)
The technology of oxygen cutting with the support of a laser beam (LASOX) is used for cutting thick sheets - this method has recently been widely used, especially in shipbuilding. This method consists in the fact that at first the laser beam heats the surface of the material (approximately 1000 degrees), after which a "superheated" oxygen stream is added to the "warmed up" metal, which allows to increase the depth of the cut, in comparison with the laser-oxygen cutting. In this case, despite the direct dependence of the rate of oxidation on temperature, the oxidation process remains stable, which allows the surface of the cutting to remain smooth and without defects..
Features of oxygen cutting with laser beam support:
- The supersonic oxygen jet is created by high pressure gas, about 6-10 atm;
- The cutting width is equal to the diameter of the oxygen jet and usually exceeds 3 mm;
- On the surface of the material, the diameter of the stain is greater than the diameter of the jet;
- The distance between the metal and the cut of the nozzle must be at least 7 mm;
- Cutting speed is much lower than with laser-oxygen cutting and is about 1.2 m / min.;
- With a power of 6 kw laser beam, it is possible to cut metal in a thickness up to 100 mm.
Laser cutting in inert gas
This technology is used in cases where the metal edges must be oxidized, and a group of inert gases, under normal conditions, has a very low chemical reactivity. Used when cutting aluminum alloys, stainless steel, titanium. This cutting assumes no additional heating source, which greatly reduces the cutting efficiency.
Features of laser cutting in inert gas:
- The most popular inert gas for this cutting is nitrogen, while titanium cutting uses argon;
- This technology requires high pressure cutting gas, usually from 10 atm or more. Therefore, in this case, focusing lenses of increased thickness are used;
- The formed supersonic jet of inert gas blows drops of metal from the cutting zone;
- Focusing radiation is carried out on the bottom of the sheet;
- The minimum permissible distance between the cut of the nozzle and the material surface is from 0.5 mm to 1 mm;
- When cutting thick metal sheets, the diameter of the nozzle is quite large (reaching up to 3 mm), which increases the flow of inert gas. This fact often increases the cost of cutting;
- In an inert gas, the cutting speed is relatively low.
Laser thermal breakdown of glass
Used to evenly divide brittle materials, such as glass or ceramic materials. The laser beam unevenly heats the material, which is then cooled by a jet of inert gas, which leads to a crack. By moving the heating source on the surface of the material it is possible to control the direction of propagation of the crack, which, in the end, allows you to get a fairly smooth edge of the separation. The principle of laser thermal breakdown of glass is that the voltage across the surface of the material is distributed evenly and leads to the formation of a crack in the desired pattern and with smooth smooth edges.
Laser sublimation cutting
This cutting technology is most often used in microscopic technology, when a minimum thermal effect on the substrate material, which is placed under the influence of the laser, is required. This effect is possible to obtain only at a very high intensity of laser radiation, which is achieved at pulse mode of laser operation. Short laser pulses (from nanoseconds to picoseconds) make a continuous incision in the material, through the implementation of openings that go one after the other. Such lasers, as a rule, have a wavelength of less than 1 μm - they are solid, excimer and metal pairs. The process of laser sublimation cutting is characterized by a small utility coefficient.
The most common at present is a laser-oxygen cutting method. Other types of laser cutting have specific characteristics and are used to solve non-standard production tasks.