Laser principles and classification
Lasers are laser generating devices and are widely used in medical, aerospace, machining, automotive electronics, shipbuilding and cutting-edge scientific research fields. The laser is mainly composed of three parts: pump source, gain medium and optical resonant cavity. The pump source provides energy to the laser. The gain medium absorbs the energy provided by the pump source, inverts the particle number, and provides a medium system for the light amplified by stimulated emission of radiation. The optical resonant cavity provides a space for energy excitation, which can repeatedly reflect light, enhance the excited light, and finally release the laser.
According to the time domain characteristics of optical fiber, lasers are divided into continuous fiber lasers and pulsed fiber lasers. According to the structural differences of the resonant cavity, lasers are divided into linear cavity fiber lasers, ring cavity fiber lasers and distributed feedback fiber lasers. According to the different gain fibers and pumping methods, lasers are divided into single-clad fiber lasers and double-clad fiber lasers. With the development of high-end equipment manufacturing industry, laser technology has been widely used around the world due to its advantages such as high precision, high efficiency, and low cost. As a representative of the third generation of laser application technology, fiber laser has the advantages of high efficiency, low threshold, low loss, etc., which provides the possibility for more compact and smaller structural design, and has gradually become an important part of industrial processing, medical, military and national defense, etc. Mainstream lasers in aerospace, automobile manufacturing, shipbuilding, and scientific research.
Laser cutting type
Vaporization cutting
When strong laser radiation hits the workpiece, it will quickly heat the material to a boiling state, causing part of the material to become liquid, while the other part will be discharged from the cutting base with the flow of high-temperature gas. The laser produced at this time The energy is 10 times greater than the effect of fusion cutting. Laser cutting is a special cutting method that can fuse objects that cannot be fused, such as wood, rubber or other metals. The laser emits laser light towards the surface of the object, part of which will be refracted by the object, and the other part will be absorbed by the object. As the temperature of an object increases, its refractive index gradually decreases. When the energy of the laser beam is released, it heats the sheet until the surface temperature reaches the boiling point. Steam is ejected from the workpiece at the speed of sound.
Melting cutting
In laser melting cutting technology, high-energy laser is first used to irradiate metal materials to reach the melting point of the metal and melt it, and then high-energy Ar, N2, He and other non-flammable gases and high-energy compressed air are used as a driving force. The agent is pushed towards the metal surface for efficient cutting. Laser melting technology can be used to cut metals that are difficult to oxidize into hard metals. For example, the precise cutting of stainless steel, titanium, aluminum and their complex components consumes only 1/10 of the original laser energy.
Oxidation cutting
Laser oxidation cutting technology can achieve rapid processing of objects. The processing tools used include high-energy laser beams and oxidants that accelerate oxygen to the surface of the object and convert it into small particles that can be separated. Laser technology can be used to efficiently oxidize the surface of steel (such as carbon steel and titanium steel), thereby improving its surface quality. This technology is more efficient than traditional vaporization or welding techniques without consuming too much energy.
Laser cutting application advantages
Improve parts processing accuracy
The application of laser cutting technology in the mechanical processing process can further improve the processing accuracy of parts and ensure that the dimensions of the parts meet the corresponding requirements. Compared with traditional processing modes such as plasma processing or manual processing, laser cutting technology can control the shape and size deviation of processed parts within an appropriate range, improve processing accuracy, ensure the uniformity of part cross-sections, improve the surface smoothness of parts, and provide better conditions for subsequent splicing. It provides convenience for assembly, etc., optimizes the processing process, eliminates grinding and processing links, ensures that welding operations are carried out in an orderly manner, and improves product quality.
Reduce machining costs
Compared with traditional mechanical processing modes, the application of laser cutting technology can effectively reduce processing costs, improve processing levels, and meet the development needs of enterprises. In the laser introduction process, as my country’s technological level improves, laser power continues to increase from kilowatts to 10,000 watts, and prices gradually decrease, reducing enterprise investment costs. The use of lasers can effectively improve processing efficiency and processing accuracy, reduce energy consumption levels, ensure parts qualification rates, reduce production costs, and improve corporate benefits. At the same time, the laser has a relatively long service life, which can reduce equipment maintenance costs.
Improve the level of mechanical processing
The application of laser cutting technology in the mechanical processing link can facilitate the forming and processing of parts and improve the level of product finishing. For example, the laser cutting process heat-treats the metal surface, which can realize metal laser welding, improve production efficiency, ensure production quality, and provide assistance for enterprise development. Laser cutting technology also helps meet processing accuracy requirements and improves the application level of mechanical parts. With the advent of 60 000 W laser cutting machines, medium and thick plates have been redefined. In the past, 20 mm and 30 mm carbon steel were thick plates that were difficult to process, but now the 30 mm plate is redefined as a thin plate. Because 60 000 W can cut a 30 mm carbon steel plate at a speed of 5 m·min-1, which is much faster than plasma, flame and other cutting methods. At present, the limit thickness of 60 000 W cutting has exceeded 300 mm, and the cutting range has also exceeded that of flame cutting, so it can fully replace plasma and flame cutting. The increase in laser power has greatly improved the level of machining and brought historic changes to machining/sheet metal processing.
Laser cutting process The effect of laser cutting is affected by many factors, including but not limited to the input energy, conversion frequency, adjustment distance, auxiliary materials used and gas pressure. The main requirements for laser cutting quality include narrow cutting slits, small thermal influence on the cutting edges, good parallelism of the cutting edges, no cutting residue, and smooth cutting surfaces. There are many factors that affect laser cutting quality, so how to quickly and easily determine the processing process parameters in actual processing is an important task.
Laser power
Laser power is not only affected by the equipment, but also by external conditions, such as the properties of the cutting material. If the surface of the cutting material is relatively smooth, the reflectivity of the laser on the surface of the material is relatively high. The laser is reflected into the interior of the laser and can easily damage the laser. Therefore, the anti-reflection performance of the laser is particularly important. If the cutting material has relatively good thermal conductivity, as laser cutting proceeds, heat will be transferred from the cutting surface to the interior of the material, causing thermal deformation of the material and adversely affecting the application of mechanical parts. In practical applications, the properties of the material to be processed should be analyzed, and an appropriate laser should be selected according to the cutting accuracy requirements to improve the cutting level and promote the realization of mechanical processing goals.
Cutting speed
For a given laser power density and material, the cutting speed follows an empirical formula. As long as the cutting speed is above the pass threshold, the cutting speed of the material will be proportional to the laser power density, that is, increasing the power density can increase the cutting speed. Cutting speed is inversely proportional to the density (specific gravity) and thickness of the material being cut. When the cutting speed is too low, the laser transfers more heat to make the incision wider. The molten material on both sides of the incision gathers and solidifies at the bottom edge of the incision, forming slag that is difficult to clean. The upper edge of the incision forms a round shape due to excessive heating and melting. horn. Appropriately increasing the cutting speed can improve the quality of the cut, that is, the cut slit becomes narrower, the cut surface is flatter, and deformation can be reduced. When the cutting speed is too fast, the cutting linear energy is lower than the required value, and the jet in the cutting seam cannot quickly blow away the molten cutting melt, resulting in a large drag amount. As slag hangs on the incision, the surface quality of the incision decreases.
Gas pressure
When selecting auxiliary gas, its pressure is crucial to obtain high-quality laser cutting results, which directly affects the cutting speed and slag amount. In addition, different types of materials and materials of the same type with different thicknesses will require different types and pressures of auxiliary gases. Therefore, when selecting auxiliary gas, comprehensive considerations should be made based on the actual situation. During the cutting process, the function of the auxiliary gas is to blow away the slag in the cutting seam, thereby ensuring good cutting quality while improving the processing capacity. The auxiliary gas can also cool the slit area, reduce the heat affected zone, and reduce the thermal deformation of the plate. When using oxygen for laser cutting, the auxiliary gas oxygen can both help melt the metal material and disperse the liquid metal by applying gas pressure, thereby improving cutting efficiency. The use of oxygen can also cause an oxidation reaction between the metal and the air, thereby generating a large amount of heat to help complete the cutting process.
Focus position
In laser cutting work, changes in the focus position, that is, the amount of defocus, have a direct impact on the quality of laser cutting. Under certain plate thickness and cutting power conditions, select the best focus position. Within this range, the slit width is small and stable, and the cutting quality is high. The characteristics of laser cutting at different focus positions are different. First, zero-defocus cutting. The smoothness of the upper and lower surfaces of the workpiece is different. The cutting surface close to the focus is relatively smooth, while the lower surface far away from the cutting focus appears rough. Second, positive defocus cutting. The irradiation range of the laser beam on the surface of the processed material becomes wider, and the beam within the slit has a divergence angle, which expands the width of the slit.
Conclusion
In recent years, the types of technologies that can be used in the mechanical processing industry have gradually increased. How to improve processing accuracy and ensure the implementation of production and processing plans deserves in-depth study. Laser cutting has significant advantages in processing efficiency, processing quality and production and maintenance costs, and has been widely used. In actual laser cutting, there are many factors that affect cutting quality. With the rapid development of the laser industry, it is necessary to continuously improve the application level of lasers, give full play to the application value of laser cutting technology, master the key points of process application, and further improve the quality of mechanical processing.
