Laser cutting machine is widely used in teaching, military and industrial fields because of its high cutting quality and high cutting efficiency. Laser cutting machine can cut metal and nonmetal, and Han’s super energy laser cutting machine is mainly used for cutting metal materials, so what is the principle of laser cutting machine?
Principle of laser cutting machine – introduction
Laser cutting machine technology uses the energy released when the laser beam hits the metal plate surface. The metal plate melts and the slag is blown away by gas. Because the laser power is so concentrated, only a small amount of heat is transferred to other parts of the metal plate, resulting in little or no deformation. Complex shaped blanks can be cut very accurately by laser, and the cut blanks do not need further processing.
The laser source generally uses a carbon dioxide laser beam with a working power of 500-5000 watts. This power level is lower than the requirements of many domestic electric heaters. The laser beam is focused in a small area through a lens and a reflector. The high concentration of energy causes rapid local heating to melt the metal plate.
Stainless steel below 16 mm can be cut by laser cutting equipment, and stainless steel with 8-10 mm thickness can be cut by adding oxygen to the laser beam, but a thin oxide film will be formed on the cutting surface after oxygen cutting. The maximum thickness of cutting can be increased to 16mm, but the dimension error of cutting parts is large.
As a high-tech laser technology, since its inception, it has been developing laser products suitable for various industries according to different social needs, such as laser printers, laser beauty machines, laser marking CNC laser cutting machines, laser cutting machines and other products. Due to the late start of the domestic laser industry, it has lagged behind some developed countries in technology research and development. At present, domestic laser products manufacturers produce laser products, Some key spare parts, such as laser tubes, drive motors, galvanometers, and focus lenses, are still imported. This has resulted in an increase in costs and increased the burden on consumers.
In recent years, with the progress of domestic laser technology, the R&D and production of the complete machine and some parts have gradually moved closer to foreign advanced products. In some aspects, it is even better than foreign products. In addition to the advantages of Jaeger, it still dominates the domestic market. However, in terms of precision processing and equipment, stability and endurance, foreign advanced products still have absolute advantages.
Principle of laser cutting machine – principle.
In the laser cutting machine, the main work is the laser tube, so it is necessary for us to understand the laser tube.
We all know the importance of laser tubes in laser equipment. Let’s use the most common laser tubes to judge. CO2 laser tube.
The composition of the laser tube is made of hard glass, so it is a fragile and brittle material. To understand the CO2 laser tube, we must first understand the structure of the laser tube. Carbon dioxide lasers like this use a layered sleeve structure, and the innermost layer is a discharge tube. However, the diameter of the CO2 laser discharge tube is thicker than the laser tube itself. The thickness of the discharge tube is proportional to the diffraction reaction caused by the size of the light spot, and the length of the discharge tube is also related to the output power of the discharge tube. The scale of the sample.
During the operation of the laser cutting machine, the laser tube will generate a large amount of heat, affecting the normal operation of the cutting machine. Therefore, a water cooler in a special area is needed to cool the laser tube to ensure that the laser cutting machine can work normally at a constant temperature. The 200W laser can use CW-6200, and the cooling capacity is 5.5 KW. The 650W laser uses CW-7800, and the cooling capacity can reach 23KW.
Principle of laser cutting machine – cutting characteristics.
Advantages of laser cutting:.
Advantage 1 – high efficiency.
Due to the transmission characteristics of the laser, the laser cutting machine is generally equipped with multiple numerical control worktables, and the whole cutting process can be fully digital controlled. In the process of operation, only by changing the NC program, it can be applied to the cutting of parts with different shapes, which can realize both two-dimensional cutting and three-dimensional cutting.
Advantage 2 – fast.
1200W laser cutting 2mm thick low carbon steel plate, cutting speed up to 600cm/min. The cutting speed of 5mm thick polypropylene resin board can reach 1200cm/min. There is no need to clamp and fix the material during laser cutting.
Advantage 3 – good cutting quality.
1: Laser cutting slit is thin and narrow, both sides of the slit are parallel and perpendicular to the cut surface, and the dimensional accuracy of the cut part can reach ± 0.05 mm.
2： The cutting surface is smooth and beautiful, and the surface roughness is only tens of microns. Even laser cutting can be used as the last process, and parts can be directly used without processing.
3： After the material is cut by laser, the width of the heat affected zone is very small, and the performance of the material near the slit is almost unaffected, and the workpiece deformation is small, the cutting accuracy is high, the geometry shape of the slit is good, and the cross-section shape of the slit is relatively smooth. Regular rectangle. Comparison of laser cutting, oxyacetylene cutting and plasma cutting methods is shown in Table 1. The cutting material is 6.2mm thick low-carbon steel plate.
Advantage IV – non-contact cutting.
During laser cutting, there is no direct contact between the welding torch and the workpiece, and there is no tool wear. To process parts with different shapes, it is not necessary to change the “tool”, but only the output parameters of the laser. The laser cutting process has low noise, small vibration and small pollution.
Advantage 5 – many materials can be cut.
Compared with oxyacetylene cutting and plasma cutting, laser cutting has many kinds of materials, including metal, non-metal, metal matrix and non-metallic matrix composite materials, leather, wood and fiber, etc.
Principle of laser cutting machine – cutting method.
This means that the removal of the treated material is mainly carried out by evaporating the material.
During the vaporization cutting process, the temperature of the workpiece surface rises rapidly to the vaporization temperature under the action of the focused laser beam, and a large number of materials vaporize, and the high-pressure steam formed is sprayed outward at supersonic speed. At the same time, a “hole” is formed in the laser action area, and the laser beam is reflected in the hole for many times, so that the absorption of the material to the laser increases rapidly.
In the process of high-pressure steam injection at high speed, the melt in the slit is blown away from the slit at the same time until the workpiece is cut off. The intrinsic vaporization cutting is mainly carried out by vaporizing the material, so the requirement for power density is very high, which should generally reach more than 108 watts per square centimeter.
Vaporization cutting is a common method for laser cutting some low ignition point materials (such as wood, carbon and some plastics) and refractory materials (such as ceramics). Vaporization cutting is also often used when cutting materials with pulsed laser.
II Reaction melting cutting
In melt cutting, if the auxiliary air flow not only blows away the molten material in the cutting seam, but also can react with the workpiece to change the heat, so as to add another heat source to the cutting process, such cutting is called reactive melt cutting. Generally, the gas that can react with the workpiece is oxygen or mixture containing oxygen.
When the surface temperature of the workpiece reaches the ignition point temperature, a strong combustion exothermic reaction will occur, which can greatly improve the ability of laser cutting. For low carbon steel and stainless steel, the energy provided by combustion exothermic reaction is 60%. For active metals such as titanium, the energy provided by combustion is about 90%.
Therefore, compared with laser vaporization cutting and general melting cutting, reactive melting cutting requires less laser power density, which is only 1/20 of that of vaporization cutting and 1/2 of that of melting cutting. However, in reactive melting and cutting, the internal combustion reaction will cause some chemical changes on the surface of the material, which will affect the performance of the workpiece.
Ⅲ Melting cutting
In the process of laser cutting, if an auxiliary blowing system which is coaxial with the laser beam is added, the removal of molten substances in the cutting process is not only dependent on the material vaporization itself, but mainly depends on the blowing effect of high-speed auxiliary air flow to continuously blow molten substances away from the cutting seam, such a cutting process is called melting cutting.
In the process of melting and cutting, the workpiece temperature no longer needs to be heated above the vaporization temperature, so the required laser power density can be greatly reduced. According to the latent heat ratio of material melting and vaporization, the laser power required for melting and cutting is only 1/10 of that of vaporization cutting method.
Ⅳ Laser scribing
This method is mainly used for: semiconductor materials; A laser beam with high power density is used to draw a shallow groove on the surface of the semiconductor material workpiece. Because this groove weakens the binding force of the semiconductor material, it can be broken by mechanical or vibration methods. The quality of laser scribing is measured by the size of surface debris and heat affected zone.
Ⅴ Cold cutting
This is a new processing method, which is proposed with the emergence of high-power excimer lasers in the ultraviolet band in recent years. Its basic principle: the energy of ultraviolet photons is similar to the binding energy of many organic materials. Use such high-energy photons to hit the binding bond of organic materials and break it. So as to achieve the purpose of cutting. This new technology has broad application prospects, especially in the electronic industry.
Ⅵ Thermal stress cutting
Under the heating of laser beam, brittle materials are prone to generate large stress on their surface, which can cause fracture through the stress points heated by laser in a neat and rapid manner. Such cutting process is called laser thermal stress cutting. The mechanism of thermal stress cutting is that the laser beam heats a certain area of brittle material to produce obvious temperature gradient.
The expansion will occur when the surface temperature of the workpiece is high, while the lower temperature of the inner layer of the workpiece will hinder the expansion, resulting in tensile stress on the surface of the workpiece and radial extrusion stress on the inner layer. When these two stresses exceed the fracture limit strength of the workpiece itself. Cracks will appear on the workpiece. Make the workpiece break along the crack. The speed of thermal stress cutting is m/s. This cutting method is suitable for cutting glass, ceramics and other materials.
Summary: Laser cutting machine is a cutting technology that uses laser characteristics and lens focusing to concentrate energy to melt or vaporize the material surface. It can achieve the advantages of good cutting quality, fast speed, multiple cutting materials, high efficiency and so on.