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laser cutting

laser cutting 
Using a high power density laser beam to irradiate the material to be cut, the material is quickly heated to the vaporization temperature, and holes are formed by evaporation. As the beam moves towards the material, the holes continuously form narrow (such as about 0.1 mm) slits to complete the cutting of the material.
brief introduction
The price of laser cutting equipment is quite expensive, about 1.5 million yuan or more. With the continuous development of the current storage tank industry, more and more industries and enterprises have applied storage tanks, and more and more enterprises have entered the storage tank industry. However, due to the reduced cost of subsequent processing, it is still feasible to use this equipment in large-scale production.
Because there is no tool processing cost, laser cutting equipment is also suitable for producing small batches of components of various sizes that previously could not be processed. Laser cutting equipment usually uses computerized digital control (CNC) devices. With this device, cutting data can be received from a computer aided design (CAD) workstation using a telephone line.
Laser cutting can be divided into four categories: laser vaporization cutting, laser melting cutting, laser oxygen cutting, and laser scribing and controlled fracture.
1. Laser vaporization cutting
Using a high energy density laser beam to heat the workpiece, the temperature rises rapidly, reaching the boiling point of the material in a very short time, and the material begins to vaporize, forming vapor. These vapors are emitted at a high speed, forming a cut in the material as they are emitted. The heat of vaporization of materials is generally large, so laser vaporization cutting requires significant power and power density.
Laser vaporization cutting is mostly used for cutting extremely thin metal materials and non-metallic materials (such as paper, cloth, wood, plastic, rubber, etc.).
2. Laser melting and cutting
During laser melting and cutting, the metal material is melted by laser heating, and then non oxidizing gases (Ar, He, N, etc.) are injected through a nozzle coaxial with the beam of light. The strong pressure of the gas allows the liquid metal to be discharged, forming a cut. Laser melt cutting does not require complete vaporization of metal, and requires only 1/10 of the energy required for vaporization cutting.
Laser melt cutting is mainly used for cutting materials or active metals that are not easily oxidized, such as stainless steel, titanium, aluminum, and their alloys.
3. Laser oxygen cutting
The principle of laser oxygen cutting is similar to oxyacetylene cutting. It uses laser as a preheating heat source and active gases such as oxygen as cutting gases. On the one hand, the injected gas reacts with the cutting metal to produce an oxidation reaction that emits a large amount of oxidation heat; On the other hand, molten oxides and molten substances are blown out of the reaction zone, forming a cut in the metal. Due to the large amount of heat generated by the oxidation reaction during the cutting process, the energy required for laser oxygen cutting is only 1/2 of that for melt cutting, and the cutting speed is far greater than that of laser vaporization cutting and melt cutting. Laser oxygen cutting is mainly used for oxidizing metal materials such as carbon steel, titanium steel, and heat treated steel.
4. Laser scribing and controlled fracture
Laser scribing uses a high energy density laser to scan the surface of a brittle material, causing the material to evaporate into a small groove, and then applying a certain pressure, the brittle material will crack along the small groove. The lasers used for laser scribing are generally Q-switched lasers and CO2 lasers.
Controlled fracture is the use of the steep temperature distribution generated during laser grooving to generate local thermal stress in brittle materials, causing the material to break along small grooves.
Compared with other thermal cutting methods, laser cutting has the overall characteristics of fast cutting speed and high quality. Specifically summarized as follows.
(1) Good cutting quality
Due to the small laser spot, high energy density, and fast cutting speed, laser cutting can achieve better cutting quality.
① The laser cutting cut is narrow, with both sides of the cut parallel and perpendicular to the surface, and the dimensional accuracy of the cut part can reach ± 0.05mm.
② The cutting surface is smooth and beautiful, with a surface roughness of only tens of micrometers. Even laser cutting can be used as the final process, without mechanical processing, and components can be directly used.
③ After laser cutting, the width of the heat affected zone of the material is very small, and the performance of the material near the cutting seam is almost unaffected. Moreover, the workpiece deformation is small, the cutting accuracy is high, the geometric shape of the cutting seam is good, and the cross-sectional shape of the cutting seam presents a relatively regular rectangular shape. The 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.
⑵ High cutting efficiency Due to the transmission characteristics of laser light, laser cutting machines are generally equipped with multiple CNC worktables, and the entire cutting process can be fully CNC controlled. During operation, it is only necessary to change the numerical control program to adapt to the cutting of parts with different shapes. It can perform both two-dimensional cutting and three-dimensional cutting.
High cutting speed
Using a laser with a power of 1200W to cut 2mm thick low-carbon steel plates, the cutting speed can reach 600cm/min; Cutting 5mm thick polypropylene resin board with a cutting speed of 1200 cm/min. During laser cutting, materials do not need to be clamped and fixed, which not only saves tooling fixtures, but also saves auxiliary time for loading and unloading.
(4) Non contact cutting
During laser cutting, the cutting torch does not contact the workpiece and there is no tool wear. When machining parts with different shapes, it is not necessary to replace the "cutter", but only to change the output parameters of the laser. The laser cutting process has low noise, small vibration, and no pollution.
(5) Multiple types of cutting materials
Compared to oxyacetylene cutting and plasma cutting, there are many types of laser cutting materials, including metal, non-metal, metal based and non-metal based composite materials, leather, wood, and fiber. However, different materials exhibit different laser cutting adaptability due to their different thermophysical properties and laser absorption. Using a CO2 laser, the laser cutting performance of various materials is shown in Table 2.
(6) Disadvantages Due to the limitations of laser power and equipment volume, laser cutting can only cut medium and small thickness plates and pipes, and with the increase of workpiece thickness, the cutting speed significantly decreases.
Laser cutting equipment costs high and one-time investment is large.
Key Features
Narrow slit, small workpiece deformation
The laser beam is focused into very small light spots, achieving a high power density at the focal point. At this point, the heat input by the beam far exceeds the portion reflected, conducted, or diffused by the material, and the material quickly heats up to a degree of vaporization, vaporizing to form holes. As the light beam moves relatively linearly with the material, the hole continuously forms a slit with a very narrow width. Trimming is slightly affected by heat, and there is basically no workpiece deformation.
An auxiliary vapor suitable for the material to be cut is also added during the cutting process. During steel cutting, oxygen is used as an auxiliary vapor to produce exothermic chemical reactions with molten metal to oxidize the material, while helping to blow away the molten slag in the slit. Compressed air is used for cutting plastics such as polypropylene, and inert vapors are used for cutting flammable materials such as cotton and paper. The auxiliary vapor entering the nozzle can also cool the focus lens, preventing smoke and dust from entering the lens holder to contaminate the lens and cause the lens to overheat.
Most organic and inorganic materials can be cut by laser. In the metal processing industry, which plays a significant role in industrial manufacturing systems, many metal materials, regardless of their hardness, can be cut without deformation. Of course, for high reflectivity materials, such as gold, silver, copper, and aluminum alloys, they are also good heat transfer conductors, so laser cutting is difficult, or even impossible. Laser cutting has no burrs, wrinkles, and high accuracy, which is superior to plasma cutting. For many electromechanical manufacturing industries, modern laser cutting systems controlled by microcomputer programs can easily cut workpieces of different shapes and sizes, and they are often preferred over punching and molding processes; Although its processing speed is still slower than that of die stamping, it does not require mold consumption, does not require mold repair, and also saves time for mold replacement, thereby saving processing costs and reducing production costs. Therefore, it is generally more cost-effective.
Non-contact machining
After focusing a laser beam, it forms a very small point of action with extremely strong energy, which has many characteristics when applied to cutting. First of all, laser light energy is converted into amazing heat energy and kept in a very small area, providing ⑴ narrow straight edge slits; ⑵ Minimum heat affected zone adjacent to the cut edge; ⑶ Minimal local deformation. Secondly, the laser beam does not exert any force on the workpiece, and it is a non-contact cutting tool, which means that ⑴ the workpiece has no mechanical deformation; ⑵ There is no tool wear or tool conversion; ⑶ Cutting materials does not require consideration of their hardness, which means that the laser cutting ability is not affected by the hardness of the material being cut, and materials with any hardness can be cut. Thirdly, the laser beam has strong controllability, high adaptability, and flexibility. Therefore, ⑴ it is convenient to combine with automation equipment, and it is easy to automate the cutting process; ⑵ Due to the absence of restrictions on cutting the workpiece, the laser beam has unlimited profiling cutting capabilities; ⑶ Combined with a computer, it can layout the entire sheet and save materials.
Adaptability and flexibility
Compared with other conventional machining methods, laser cutting has greater adaptability. Firstly, compared to other thermal cutting methods, as a thermal cutting process, other methods cannot act on a very small area like laser beams, resulting in wide cuts, large heat affected areas, and significant workpiece deformation. Laser can cut non-metals, while other thermal cutting methods cannot.
Generally speaking, the quality of laser cutting can be measured by the following six standards.
Cutting surface roughness Rz
2. Cutting slag size
3. Trimming perpendicularity and slope u
4. Cutting edge fillet size r
5. Stripe drag amount n
6. Flatness F
Scope of application
Most laser cutting machines are controlled by CNC programs or made into cutting robots. As a precision machining method, laser cutting can cut almost all materials, including two-dimensional or three-dimensional cutting of thin metal plates.
In the field of automobile manufacturing, the cutting technology of spatial curves such as car roof windows has been widely used. The German Volkswagen Company uses a laser with a power of 500 W to cut complex shaped vehicle body sheets and various curved parts. In the field of aerospace, laser cutting technology is mainly used for the cutting of special aviation materials, such as titanium alloy, aluminum alloy, nickel alloy, chromium alloy, stainless steel, beryllium oxide, composite materials, plastics, ceramics, and quartz. Aerospace components processed by laser cutting include engine flame barrels, titanium alloy thin-walled casings, aircraft frames, titanium alloy skins, wing stringers, tail wall panels, helicopter main rotors, and ceramic thermal insulation tiles for space shuttles.
Laser cutting and forming technology is also widely used in the field of non-metallic materials. Not only can it cut materials with high hardness and brittleness, such as silicon nitride, ceramics, quartz, etc; It can also cut and process flexible materials, such as cloth, paper, plastic sheets, rubber, etc. If you use laser to cut clothing, it can save 10% to 12% of the clothing material and increase the efficiency by more than three times.

Copyright: NIIC (suzhou) Su ICP Bei No. 2020061042-1

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