What Is Involved in Laser Cutting Steel?

The high-density laser beam is used to irradiate the material to be cut, so that the material is quickly heated to the vaporization temperature, and the holes are formed by evaporation. As the beam moves to the material, the holes continuously form a narrow slit (such as about 0.1mm). Finish cutting the material.

The high-density laser beam is used to irradiate the material to be cut, so that the material is quickly heated to the vaporization temperature, and the holes are formed by evaporation. As the beam moves to the material, the holes continuously form a narrow slit (such as about 0.1mm). Finish cutting the material.

Chinese name

laser cutting

Foreign name

laser cutting

Introduction to laser cutting

The price of laser cutting equipment is quite expensive, about 1.5 million yuan or more. With the continuous development of the current tank industry, more and more industries and enterprises are applying

Laser cutting (3 photos)

After the storage tank, more and more enterprises entered the storage tank industry. However, because the cost of subsequent processing is reduced, it is still feasible to use this equipment in large-scale production.

Since there is no tool processing cost, laser cutting equipment is also suitable for producing small-sized parts of various sizes that could not be processed previously. Laser cutting equipment usually uses computerized digital control technology (CNC) devices. With the device, cutting data can be received from a computer-aided design (CAD) workstation using a telephone line.

Laser cutting principle

Laser cutting is to use a focused high power density laser beam to irradiate the workpiece, so that the irradiated material quickly melts, vaporizes, ablates or reaches the ignition point, and at the same time blows out the molten material by means of a high-speed airflow coaxial with the beam, so as to cut the workpiece open. Laser cutting is one of the thermal cutting methods.

The principle of laser cutting is shown in the figure below.

Laser cutting classification

Laser cutting can be divided into four categories: laser vaporization cutting, laser melting cutting, laser oxygen cutting, and laser scribing and controlling fracture.

1) Laser vaporization cutting

High-energy-density laser beams are used to heat the workpiece, causing the temperature to rise rapidly, reaching the boiling point of the material in a very short period of time, and the material beginning to vaporize to form vapor. These vapors are ejected at a high speed, and when the vapors are ejected, a cut is formed in the material. The heat of vaporization of materials is generally large, so laser vaporization cutting requires a large power and power density.

Laser vapor cutting is mostly used for cutting very thin metal materials and non-metal 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 a non-oxidizing gas (Ar, He, N, etc.) is sprayed through a nozzle coaxial with the beam, and the liquid metal is discharged by the strong pressure of the gas to form a cut. Laser melting and cutting do not need to completely vaporize the metal, and the energy required is only 1/10 of that of vaporizing and cutting.

Laser melting cutting is mainly used for cutting of non-oxidizable materials or active metals, such as stainless steel, titanium, aluminum and its alloys.

3) Laser oxygen cutting

The principle of laser oxygen cutting is similar to oxyacetylene cutting. It uses laser as preheating heat source and active gas such as oxygen as cutting gas. The blown gas reacts with the cutting metal on the one hand, and an oxidation reaction occurs, releasing a large amount of oxidizing heat; on the other hand, the molten oxide and the melt are blown out from the reaction zone to form a cut in the metal. Because the oxidation reaction in the cutting process generates a lot of heat, the energy required for laser oxygen cutting is only 1/2 of the melting cutting, and the cutting speed is much faster than laser vaporizing cutting and melting cutting. Laser oxygen cutting is mainly used for carbon steel, titanium steel and heat-treated steel and other easily oxidizable metal materials.

4) Laser scribing and controlling fracture

Laser scribing uses a high-energy-density laser to scan the surface of a brittle material, heat the material to evaporate a small groove, and then apply a certain pressure, the brittle material will crack along the small groove. Laser dicing lasers are generally Q-switched lasers and CO2 lasers.

Controlled fracture is the use of the steep temperature distribution produced by laser engraving grooves, which generates local thermal stresses in brittle materials and breaks the material along small grooves.

Laser cutting features

Compared with other thermal cutting methods, laser cutting is characterized by fast cutting speed and high quality. It is summarized as follows.

Good cutting quality

Due to the small laser spot, high energy density, and fast cutting speed, laser cutting can achieve better cutting quality.

The laser cutting incision is narrow, the two sides of the slit are parallel and perpendicular to the surface, and the dimensional accuracy of the cutting part can reach ± 0.05mm.

The cutting surface is smooth and beautiful, and the surface roughness is only a few tens of micrometers. Even laser cutting can be used as the last process, without mechanical processing, and parts can be used directly.

After the material is laser cut, the width of the heat-affected zone is 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 of the slit is good, and the cross-sectional shape of the slit is more regular Rectangle. The comparison of laser cutting, oxyacetylene cutting and plasma cutting methods is shown in Table 1. The cutting material is a 6.2mm thick low carbon steel plate.

High cutting efficiency Due to the transmission characteristics of lasers, laser cutting machines are generally equipped with multiple numerically controlled worktables, and the entire cutting process can be fully numerically controlled. During operation, just changing the NC program can be used to cut different shapes of parts, both 2D and 3D.

Fast cutting speed

With a power of 1200W, a 2mm thick low carbon steel plate can be cut at a speed of 600cm / min. A 5mm thick polypropylene resin plate can be cut at a speed of 1200cm / min. The material does not need to be clamped and fixed during laser cutting, which can save tooling fixtures and save the auxiliary time of loading and unloading.

Non-contact cutting

The cutting torch has no contact with the workpiece during laser cutting, and there is no tool wear. When processing different shapes of parts, there is no need to change the "tool", only the laser output parameters need to be changed. The laser cutting process has low noise, low vibration and no pollution.

Many types of cutting materials

Compared with 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 fibers. But for different materials, due to their own thermophysical properties and different laser absorption rates, they show different laser cutting adaptability. CO2 laser is used. Table 2 shows the laser cutting performance of various materials.

Disadvantages Due to the limitation of laser power and equipment volume, laser cutting can only cut medium and small thickness plates and pipes, and the cutting speed decreases significantly as the thickness of the workpiece increases.

Laser cutting equipment has high cost and large one-time investment.

Laser cutting main features

Narrow slits, small deformation of the workpiece

The laser beam is focused into a small spot, resulting in a very high power density at the focal point. At this time, the heat input by the light beam far exceeds the part that is reflected, conducted or diffused by the material, and the material is quickly heated to the degree of vaporization, and the holes are formed by evaporation. As the light beam and the material move relatively linearly, the hole continuously forms a narrow slit. The cutting edge is little affected by heat and there is almost no deformation of the workpiece.

An auxiliary vapor suitable for the material to be cut is added during the cutting process. When steel is used for cutting, oxygen is used as an auxiliary vapor to generate an exothermic chemical reaction with molten metal. It also helps to blow away the slag in the cutting slot. Compressed air is used to cut plastics such as polypropylene, and inert vapor is used to cut flammable materials such as cotton and paper. The auxiliary vapor entering the nozzle can also cool the focusing 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 with a laser. In the metal processing industry where industrial manufacturing systems take a large part, many metal materials, regardless of their hardness, can be cut without deformation. Of course, for highly reflective 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 precision, which is superior to plasma cutting. For many electromechanical manufacturing industries, because modern computer-controlled laser cutting systems controlled by microcomputer programs can easily cut workpieces of different shapes and sizes, it is often preferred over punching and stamping processes; although its processing speed is slower than die punching, But it has no mold consumption, no need to repair the mold, and saves the time to replace the mold, which saves processing costs and reduces production costs, so it is more cost-effective in general.

Non-contact processing

After the laser beam is focused, it forms a small action point with extremely strong energy. There are many characteristics for applying it to cutting. First, the laser light energy is converted into amazing thermal energy and kept in a very small area, which can provide narrow straight edge slits; the smallest heat-affected zone adjacent to the cut edge; minimal local deformation. Secondly, the laser beam does not exert any force on the workpiece. It is a non-contact cutting tool, which means that there is no mechanical deformation of the workpiece; there is no tool wear, and it is not possible to talk about the conversion of the tool; the cutting material does not need to consider its hardness That is, the laser cutting ability is not affected by the hardness of the material being cut, and any hardness material can be cut. Thirdly, the laser beam is highly controllable, and has high adaptability and flexibility. Therefore, it is convenient to combine with automatic equipment, and it is easy to automate the cutting process. Because there is no restriction on the cutting workpiece, the laser beam has unlimited imitation. Shape cutting ability; (3) Combined with a computer, the whole board can be discharged, saving material.

Adaptability and flexibility

Compared with other conventional processing methods, laser cutting has greater adaptability. First, compared with other thermal cutting methods, the same as the thermal cutting process, other methods can not act on a very small area like a laser beam, resulting in wide cuts, large heat-affected areas, and obvious workpiece deformation. Lasers can cut non-metals, while other thermal cutting methods cannot.

Generally speaking, the laser cutting quality can be measured by the following 6 standards.

Cutting surface roughness Rz

Slit size

Cutting edge perpendicularity and slope u

Cutting edge fillet size r

Stroke after stripe n

Flatness F

Laser cutting applications

Most laser cutting machines are controlled by CNC programs or made into cutting robots. Laser cutting as a precision machining method can cut almost all materials, including 2D or 3D cutting of thin metal plates.

In the field of automobile manufacturing, cutting techniques for spatial curves such as car roof windows have been widely used. Volkswagen AG uses a 500W laser to cut complex shaped body sheets and various curved parts. In the field of aerospace, laser cutting technology is mainly used for cutting special aviation materials, such as titanium alloys, aluminum alloys, nickel alloys, chromium alloys, stainless steel, beryllium oxide, composite materials, plastics, ceramics and quartz. Aerospace parts processed by laser cutting include engine flame tubes, titanium alloy thin-walled cases, aircraft frames, titanium alloy skins, wing stringers, tail wall panels, helicopter main rotors, and space shuttle ceramic insulation tiles.

Laser cutting technology has also been 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 plates, rubber, etc. If clothing is cut by laser, it can save clothing 10 % 12%, it can improve the efficiency by more than 3 times.

Laser cutting material analysis

Laser cut structural steel

Good results are obtained when the material is cut with oxygen. When oxygen is used as the processing gas, the cutting edges are slightly oxidized. For plates up to 4mm thick, nitrogen can be used for high-pressure cutting. In this case, the cutting edges are not oxidized. For plates with a thickness of more than 10mm, using a special plate for the laser and applying oil to the surface of the workpiece during processing can achieve better results.

Laser cut stainless steel

Oxygen can be used when the cutting end face can be oxidized; nitrogen is used to obtain the edge without oxidation and burr, and no further treatment is required. Coating the oil film on the surface of the board will get better perforation effect without reducing the processing quality.

Laser cut aluminum

Despite its high reflectivity and thermal conductivity, aluminum up to 6mm can be cut, depending on the alloy type and laser capabilities. When cutting with oxygen, the cutting surface is rough and hard. When using nitrogen, the cut surface is smooth. Pure aluminum is very difficult to cut because of its high purity. It can be cut only when a "reflective absorption" device is installed on the system. Otherwise reflections can damage optical components.

Laser cut titanium

Titanium plates are cut with argon and nitrogen as process gases. Other parameters can refer to nickel chromium steel.

Laser cut copper and brass

Both materials have high reflectivity and very good thermal conductivity. Brass less than 1mm thick can be cut with nitrogen; copper less than 2mm thick can be cut, and the processing gas must be oxygen. Copper and brass can only be cut when a "reflective absorption" device is installed on the system. Otherwise reflections can damage optical components.

CO2 CO2 laser cutting

Laser cutting advantages

The advantages of CO2 laser cutting technology over other methods are:

Good cutting quality

Laser cutting engineering drawing

Narrow incision width (generally 0.1--0.5mm), high precision (general hole center distance error 0.1--0.4mm, contour dimension error 0.1--0.5mm), good incision surface roughness (generally Ra is 12.5--25m ), The slit is generally welded without further processing.

Fast cutting speed

For example, with 2KW laser power, the cutting speed of 8mm thick carbon steel is 1.6m / min; the cutting speed of 2mm thick stainless steel is 3.5m / min, the heat affected zone is small, and the deformation is extremely small.

Clean, safe and pollution-free

Laser cutting engineering drawings (2 photos)

Greatly improved the working environment of the operator. Of course, in terms of accuracy and surface roughness of the cut, CO2 laser cutting cannot exceed electric machining; in terms of cutting thickness, it is difficult to reach the level of flame and plasma cutting. But the above significant advantages are enough to prove that: CO2 laser cutting has replaced a part of the traditional cutting process, especially the cutting of various non-metal materials. It is an advanced processing method that develops rapidly and is increasingly widely used.

Since the 1990s, due to the development of China's socialist market economy, competition among enterprises has been fierce. Each enterprise must correctly select certain advanced manufacturing technologies according to its own conditions to improve product quality and production efficiency. Therefore, CO2 laser cutting technology has achieved rapid development in China.

Features of laser cutting laser

(A) directional light ordinary light source emits light in all directions. To make the emitted light propagate in one direction, a certain light-condensing device needs to be installed on the light source. For example, the headlights and searchlights of a car are both equipped with a light-concentrating reflector, so that the radiated light is collected and emitted in one direction. The laser light emitted by the laser is naturally emitted in one direction. The divergence of the beam is extremely small, only about 0.001 radians, which is close to parallel. In 1962, humans used a laser to illuminate the moon for the first time. The distance between the earth and the moon was about 380,000 kilometers, but the laser spot on the surface of the moon was less than two kilometers. If the focusing effect is very good, the seemingly parallel searchlight beams will hit the moon and cover the entire moon according to its spot diameter.

(2) Extremely high brightness Before the invention of the laser, the brightness of the high-voltage pulsed xenon lamp in the artificial light source was the highest, which was comparable to the brightness of the sun, and the laser brightness of the ruby laser could exceed the xenon lamp by several billions. Because the laser is extremely bright, it can illuminate distant objects. The light emitted by the ruby laser on the moon produces an illumination of about 0.02 lux (a unit of illumination), the color is bright red, and the laser spot is clearly visible. If the most powerful searchlight is used to illuminate the moon, the resulting illuminance is only about one trillionth of a lux, which is impossible for human eyes to detect. The main reason for the extremely high laser brightness is directional light emission. A large number of photons are concentrated and emitted in a very small spatial range, and the energy density is naturally extremely high. The ratio of the laser's brightness to sunlight is in the millions, and it is created by humans. Color of the laser The color of the laser depends on the wavelength of the laser, and the wavelength depends on the active material that emits the laser, that is, the material that can generate the laser when stimulated. Stimulating a ruby produces a deep rose-colored laser beam, which is used in medical fields, such as in the treatment of skin diseases and surgery. Argon, which is considered to be one of the most expensive gases, can generate a blue-green laser beam. It has many uses, such as laser printing, and is also indispensable in micro-ophthalmic surgery. The laser generated by semiconductors emits infrared light, so our eyes can't see it, but its energy can just "interpret" a laser record and it can be used for optical fiber communication. Laser separation technology Laser separation technology mainly refers to laser cutting technology and laser drilling technology. Laser separation technology focuses energy into a tiny space, and can obtain extremely high irradiation power density of 105 ~ 1015W / cm2. This high-density energy is used for non-contact, high-speed, high-precision processing methods. With such a high optical power density, laser cutting and drilling can be performed on almost any material. Laser cutting technology is a brand-new cutting method that breaks away from traditional mechanical cutting and heat treatment cutting. It has higher cutting accuracy, lower roughness, more flexible cutting methods and higher production efficiency. Laser drilling method, as one of the methods for processing holes in solid materials, has become a processing technology with specific applications, mainly used in the aviation, aerospace and microelectronics industries.
(3) Color The color of extremely pure light is determined by the wavelength (or frequency) of the light. A certain wavelength corresponds to a certain color. The wavelength distribution of sunlight is between 0.76 micrometers and 0.4 micrometers, and the corresponding color ranges from red to purple. There are 7 colors, so it is not monochromatic. A light source emitting a single color of light is called a monochromatic light source, and the wavelength of the light wave it emits is single. For example, krypton lamps, helium lamps, neon lamps, hydrogen lamps, etc. are all monochromatic light sources and emit only a certain color of light. Although the light wavelength of a monochromatic light source is single, it still has a certain distribution range. For example, the neon lamp emits only red light, which has good monochromaticity, and is known as the crown of monochromaticity. The wavelength distribution range is still 0.00001 nanometers. Therefore, the red light emitted by the neon lamp still contains dozens of red colors . It can be seen that the narrower the wavelength distribution interval of light radiation, the better the monochromaticity. The light output from the laser has a very narrow wavelength distribution, so the color is extremely pure. Taking a helium-neon laser that outputs red light as an example, the wavelength distribution range of its light can be as narrow as 2 × 10 ^ -9 nanometers, which is two ten thousandths of the wavelength distribution range of red light emitted by krypton lamps. It can be seen that the monochromaticity of the laser far exceeds that of any monochromatic light source.
(4) The energy of the photon with the maximum energy density is calculated using E = hv, where h is the Planck constant and v is the frequency. It can be seen that the higher the frequency, the higher the energy. The laser frequency range is 3.846 * 10 ^ (14) Hz to 7.89510 (14) Hz. The electromagnetic spectrum can be roughly divided into: (1) radio waves-wavelengths from several kilometers to about 0.3 meters, the general television and radio broadcast band This wave is used; (2) Microwavewavelength from 0.3m to 10 ^ -3m, these waves are mostly used in radar or other communication systems; (3) Infraredwavelength from 10 ^ -3m to 7.8 × 10 ^ -7 meters; (4) visible light-this is a very narrow wave band that people can photosensitive. The wavelength is from 780-380nm. Light is an electromagnetic wave that is emitted when the movement of electrons within an atom or molecule changes. Because it is the part of the electromagnetic wave that we can directly feel and feel very little; (5) Ultraviolet rays-the wavelength ranges from 3 × 10 ^ -7 meters to 6 × 10 ^ -10 meters. These waves have similar causes to light waves and are often emitted during discharge. Because its energy is comparable to the energy involved in general chemical reactions, the chemical effect of ultraviolet light is the strongest; (6) Roentgen rays-This part of the electromagnetic spectrum has a wavelength from 2 × 10 ^ -9 meters to 6 × 10 ^ -12 meters. Roentgen rays (X-rays) are emitted when the inner electrons of an electric atom jump from one energy state to another or when the electrons decelerate in the nuclear electric field; (7) Gamma rayswavelengths from 10 ^- 10 to 10 ^ -14 meters of electromagnetic waves. This invisible electromagnetic wave is emitted from the atomic nucleus, which is often accompanied by such radiation in radioactive materials or nuclear reactions. Gamma rays have a strong penetrating power and are very destructive to living things. From this point of view, the laser energy is not very large, but its energy density is very large (because its range of action is very small, usually only one point), a large amount of energy is gathered in a short time, and it can be used as a weapon I understand.
Edit the other characteristics of this laser. Laser has many characteristics: first, the laser is monochromatic, or single frequency. There are some lasers that can produce lasers of different frequencies at the same time, but these lasers are isolated from each other and are also separated when used. Second, the laser is coherent light. The characteristic of coherent light is that all its light waves are synchronized, and the entire light is like a "wave train". Thirdly, the laser is highly concentrated, which means that it will take a long distance to spread or converge. Laser (LASER) is a light source invented in the 1960s. LASER is an acronym for Stimulated Radiation Amplification in English. There are many types of lasers, ranging in size from a few football fields to a grain of rice or salt. Gas lasers have helium-neon lasers and argon lasers; solid-state lasers have ruby lasers; semiconductor lasers have laser diodes, like those in CD players, DVD players, and CD-ROMs. Each laser has its own unique method of generating laser light.

Applicable products for laser cutting

Products suitable for CO2 laser cutting can be roughly classified into three categories:

Laser cutting engineering drawing

The first category : metal sheet metal parts that are not suitable for making molds from a technical and economic perspective, especially with complex contour shapes, small batch sizes, and general thickness; 12mm low carbon steel; 6mm thick stainless steel to save the cost and cycle of mold making . Typical products that have been used are: automatic elevator structural parts, elevator panels, machine tool and food machinery covers, various electrical cabinets, switch cabinets, textile machinery parts, construction machinery structural parts, large motor silicon steel sheets, etc.

The second category : patterns, marks, fonts, etc. of stainless steel (usually 3mm thick) or non-metallic materials (usually 20mm thick) used in decoration, advertising and service industries . Such as the patterns of art photo albums, signs of companies, units, hotels, shopping malls, Chinese and English fonts of stations, terminals, public places.

The third category : special parts that require uniform slitting. The most widely used typical part is the die-cut plate for the packaging and printing industry. It requires a slot with a width of 0.7 ~ 0.8mm to be cut on a 20mm thick wooden template, and then a blade is inserted in the slot. Use fashion to cut various printed boxes on the die-cutting machine. A new field of application in China in recent years is the petroleum sieve slotted pipe. In order to prevent the sediment from entering the pump, a uniform cut slit with a width of 0.3 mm is cut on an alloy steel pipe with a wall thickness of 6 to 9 mm. The diameter of the small hole at the cut-off perforation can not be greater than 0.3 mm. The cutting technology is difficult. The unit is put into production.

Laser cutting applications

In addition to the above-mentioned applications abroad, their application fields are constantly expanding.

Use 3D laser cutting system or configure industrial robots to cut space curves and develop various 3D cutting software to speed up the process from drawing to cutting parts.

In order to improve production efficiency, we have researched and developed various special cutting systems, material conveying systems, linear motor drive systems, etc. Today, the cutting speed of cutting systems has exceeded 100m / min.

(3) In order to expand the application of construction machinery, shipbuilding industry, etc., the thickness of cutting low carbon steel has exceeded 30mm, and special attention is paid to researching the technology of cutting low carbon steel with nitrogen to improve the cutting quality of cutting thick plates. Therefore, in China, expanding the industrial application field of CO2 laser cutting and solving some technical problems in new applications are still important topics for engineering technicians.

The key technology of laser cutting

Several key technologies for CO2 laser cutting are integrated technologies of light, machinery and electricity.

The parameters of the laser beam, the performance and accuracy of the machine and the CNC system directly affect the efficiency and quality of laser cutting. Especially for the parts with high cutting accuracy or thickness, the following key technologies must be mastered and resolved:

Focus position control technology

Focus position control technology: One of the advantages of laser cutting is the high energy density of the beam, which is generally 10W / cm2. Because the energy density is proportional to 4 / d2, the focal spot diameter is as small as possible to produce a narrow slit; at the same time, the focal spot diameter is also proportional to the focal depth of the lens. The smaller the focal depth of the focusing lens, the smaller the focal spot diameter. However, the cutting has splashes, and the lens is too close to the workpiece, which easily damages the lens. Therefore, in general high-power CO2 laser cutting industrial applications, a focal length of 5 ~ 7.5 (127 ~ 190mm) is widely used. The actual focal spot diameter is 0.1 ~ 0.4mm For high-quality cutting, the effective focal depth is also related to the diameter of the lens and the material being cut. For example, using a 5mm lens to cut carbon steel, the focal depth is within + 2% of the focal length, that is, about 5mm. Therefore, the focus is controlled The position relative to the surface of the material being cut is very important. In consideration of cutting quality, cutting speed and other factors, in principle 6mm carbon steel, the focus is above the surface; 6mm stainless steel, the focus is below the surface. The specific size is determined experimentally.

There are three simple methods for determining the focus position in industrial production: Printing method: The cutting head is moved from top to bottom, and laser beam printing is performed on a plastic plate, and the smallest print diameter is the focus. Inclined plate method: Use a plastic plate that is placed at an angle to the vertical axis to pull it horizontally, and look for the smallest part of the laser beam as the focus. (3) Blue spark method: Remove the nozzle, blow air, hit the pulsed laser on the stainless steel plate, and move the cutting head from top to bottom until the blue spark is the focus. For the cutting machine of the flying light path, due to the divergence angle of the beam, the length of the optical path is different when cutting the near end and the far end, and the beam size before focusing is different. The larger the diameter of the incident beam, the smaller the diameter of the focal spot. In order to reduce the change in the size of the focal spot caused by the change in the beam size before focusing, manufacturers of laser cutting systems at home and abroad have provided some dedicated devices for users to choose from:

Parallel light tube. This is a commonly used method, that is, adding a parallel light pipe to the output end of the CO2 laser to expand the beam. The diameter of the expanded beam becomes larger and the divergence angle becomes smaller, so that the near and far ends are within the cutting working range. The beam size is nearly uniform before focusing.

Add an independent lower axis of the moving lens to the cutting head, which is two independent parts from the Z axis that controls the distance from the nozzle to the surface of the material (stand off). When the machine tool table moves or the optical axis moves, the light beam also moves from the near end to the far F axis at the same time, so that the beam spot diameter remains the same throughout the processing area after focusing.

(3) Control the water pressure of the focusing lens (generally a metal reflection focusing system). If the size of the beam before focusing becomes smaller and the focal spot diameter becomes larger, the water pressure is automatically controlled to change the focusing curvature to make the focal spot diameter smaller.

The compensation optical path system in the x and y directions is added to the flying optical path cutter. That is, when the optical path length of the cutting end is increased, the compensation optical path is shortened; when the optical path length of the cutting end is decreased, the compensation optical path is increased to maintain the same optical path length.

Cutting perforation

Any kind of thermal cutting technology, except in a few cases, can start from the edge of the board, generally must pass a small hole in the board. Earlier on the laser punching compound machine, a hole was first punched out with a punch, and then the laser was used to cut from the small hole. There are two basic methods for perforating a laser cutting machine without a punching device:

Blast drilling: (Blast drilling), the material forms a pit in the center after continuous laser irradiation, and then the molten material is quickly removed by the oxygen flow coaxial with the laser beam to form a hole. Generally, the size of the hole is related to the thickness of the plate. The average diameter of the blasting perforation is half the thickness of the plate. Therefore, the blasting perforation of the thicker plate is larger and not round. ), Can only be used on waste. In addition, because the oxygen pressure used for perforation is the same as that during cutting, the splash is large.

Pulse drilling: (Pulse drilling) uses a high peak power pulse laser to melt or vaporize a small amount of material. Air or nitrogen is often used as an auxiliary gas to reduce the expansion of holes due to exothermic oxidation. The gas pressure is lower than the oxygen pressure during cutting. Each pulsed laser produces only small jets of particles, stepping deeper, so thick plate perforations take a few seconds. Once the perforation is complete, the auxiliary gas is replaced with oxygen for cutting. In this way, the diameter of the perforation is small, and the quality of the perforation is better than that of blasting. The laser used for this purpose should not only have a high output power; more importantly, the time and space characteristics of the beam, so the general cross-flow CO2 laser cannot meet the requirements of laser cutting. In addition, pulse perforation also requires a more reliable gas path control system to achieve the switching of gas type, gas pressure, and perforation time. In the case of pulse perforation, in order to obtain high-quality incisions, the transition technology from pulse perforation when the workpiece is stationary to continuous constant-speed cutting of the workpiece should be taken seriously. In theory, the cutting conditions of the acceleration section can usually be changed: focal length, nozzle position, gas pressure, etc., but it is unlikely that the above conditions will be changed due to the short time. In industrial production, the method of changing the average laser power is more realistic. There are three specific methods: change the pulse width; change the pulse frequency; change the pulse width and frequency at the same time. The actual results show that the third kind of effect is the best.

Laser cutting key technology two

Nozzle design and control technology

When laser cutting steel, oxygen and a focused laser beam are emitted through the nozzle to the material being cut, thereby forming an airflow beam. The basic requirements for the air flow are that the air flow into the incision should be large and the speed should be high, so that sufficient oxidation allows the incision material to fully perform an exothermic reaction; at the same time, there is sufficient momentum to eject the molten material. Therefore, in addition to the quality of the beam and its control directly affecting the cutting quality, the design of the nozzle and the control of the air flow (such as the nozzle pressure and the position of the workpiece in the air flow) are also very important factors. Today's laser cutting nozzles have a simple structure, that is, a tapered hole with a small round hole at the end. Design is usually done experimentally and error-wise. Because the nozzle is generally made of copper, it has a small volume and is a fragile part that needs to be replaced frequently. Therefore, no hydrodynamic calculation and analysis is performed. When in use, a certain pressure of Pn (gauge pressure is Pg) is introduced from the side of the nozzle, which is called the nozzle pressure. It is ejected from the nozzle outlet and reaches the workpiece surface after a certain distance. Pa. Research work shows that with the increase of Pn, the air flow velocity increases, and Pc also increases.

It can be calculated by the following formula: V = 8.2d2 (Pg + 1)

V-gas flow rate L / min

d- nozzle diameter mm

Pg-nozzle pressure (gauge pressure) bar

There are different pressure thresholds for different gases. When the nozzle pressure exceeds this value, the airflow is a normal oblique shock wave, and the flow velocity of the gas transitions from subsonic to supersonic. This threshold is related to the two factors of Pn, Pa ratio and the degree of freedom of gas molecules (n): for example, n = 5 for oxygen and air, so its threshold is Pn = 1bar × (1.2) 3.5 = 1.89bar. When the nozzle pressure is higher Pn / Pa = (1 + 1 / n) 1 + n / 2 (Pn; 4bar), the normal airflow oblique shock wave seal becomes a positive shock wave, the cutting pressure Pc decreases, the airflow speed decreases, and The formation of vortices on the surface of the workpiece weakens the role of the airflow in removing molten material and affects the cutting speed. Therefore, a nozzle with a tapered hole and a small round hole at the end is used, and the oxygen nozzle pressure is often below 3 bar.

In order to further increase the laser cutting speed, according to the aerodynamic principle, under the premise of increasing the nozzle pressure, a positive shock wave is not generated, and a zoom nozzle is designed and manufactured, that is, a Laval nozzle. In order to facilitate manufacturing, the structure shown in FIG. 4 may be adopted. The Laser Center of the University of Hannover, Germany, uses a 500WCO2 laser with a lens focal length of 2.5 , and uses a small-hole nozzle and a Laval nozzle to perform experiments, as shown in Figure 4. The test results are shown in Fig. 5: the function of the cutting surface roughness Rz and the cutting speed Vc of the NO2, NO4, and NO5 nozzles under different oxygen pressures, respectively. It can be seen from the figure that the cutting speed of the NO2 small hole nozzle can only reach 2.75m / min (the thickness of the carbon steel plate is 2mm) when the Pn is 400Kpa (or 4bar). The cutting speeds of NO4 and NO5 Laval nozzles can reach 3.5m / min and 5.5m / min when the Pn is 500Kpa to 600Kpa. It should be noted that the cutting pressure Pc is also a function of the distance from the workpiece to the nozzle. Because the oblique shock waves are repeatedly reflected at the boundary of the airflow, the cutting pressure changes periodically.

Laser cutting key technology three

The first high cutting pressure zone is close to the nozzle outlet. The distance from the workpiece surface to the nozzle outlet is about 0.5 ~ 1.5mm. The cutting pressure Pc is large and stable. It is a common process parameter for cutting handles in industrial production today. The second highest cutting pressure zone is about 3 ~ 3.5mm of the nozzle outlet, and the cutting pressure Pc is also large. It can also achieve good results and help protect the lens and increase its service life. The other high cutting pressure areas on the curve are too far away from the nozzle exit to match the focused beam and cannot be used.

In summary, CO2 laser cutting technology is increasingly used in China's industrial production, and foreign countries are researching and developing cutting technologies and devices for higher cutting speeds and thicker steel plates. In order to meet the increasing requirements of industrial production for quality and production efficiency, it is necessary to pay attention to solving various key technologies and implementing quality standards so that this new technology can be more widely used in China.

Laser cutting cutting process

Laser cutting vaporization cutting

Under the heating of a high power density laser beam, the surface temperature of the material rises to the boiling point temperature so fast that it is sufficient to avoid melting caused by heat conduction, so part of the material vaporizes into steam and disappears, and part of the material is ejected from the bottom of the slit as an ejection. The auxiliary gas flow is blown away. Some materials that cannot be melted, such as wood, carbon materials and some plastics are cut by this vapor cutting method.

During the vaporization cutting process, the steam takes away the molten particles and scours debris to form holes. During the vaporization process, approximately 40% of the material disappears as steam, and 60% of the material is driven off by airflow in the form of droplets.

Laser cutting

When the power density of the incident laser beam exceeds a certain value, the inside of the material at the point of irradiation of the beam begins to evaporate, forming a hole. Once such a small hole is formed, it will act as a black body to absorb all the incident beam energy. The small hole is surrounded by a molten metal wall, and then a secondary air stream coaxial with the light beam removes the molten material around the hole. As the workpiece moves, the small hole moves horizontally in the cutting direction to form a slit. The laser beam continues to radiate along the leading edge of the slit, and the molten material is continuously or pulsed blown away from the slit.

Laser cutting

Melt cutting generally uses an inert gas. If it is replaced by oxygen or other active gases, the material is ignited under the irradiation of a laser beam, and a fierce chemical reaction with oxygen generates another heat source, called oxidative melting cutting . The specific description is as follows:

The surface of the plutonium material is quickly heated to the ignition temperature under the irradiation of the laser beam, followed by a fierce combustion reaction with oxygen, which emits a lot of heat. Under the action of heat, small holes filled with steam are formed inside the material, and the periphery of the small holes is surrounded by a molten metal wall.

The combustion material is transferred to slag to control the combustion speed of oxygen and metal. At the same time, the speed at which oxygen diffuses through the slag to reach the ignition front has a great influence on the combustion speed. The higher the oxygen flow rate, the faster the combustion reaction and slag removal. Of course, the higher the oxygen flow rate is, the better, because too fast a flow rate will cause rapid cooling of the reaction products, ie metal oxides, at the exit of the slit, which is also detrimental to the cutting quality.

(3) Obviously, there are two heat sources in the process of oxidative melting and cutting, namely the laser irradiation energy and the thermal energy generated by the chemical reaction between oxygen and metal. It is estimated that when cutting steel, the heat released by the oxidation reaction accounts for about 60% of the total energy required for cutting.

Obviously, compared with inert gas, higher cutting speed can be obtained by using oxygen as auxiliary gas.

In the process of oxidative melting and cutting with two heat sources, if the burning speed of oxygen is higher than the moving speed of the laser beam, the slit is wide and rough. If the laser beam moves faster than the combustion speed of oxygen, the resulting slit is narrow and smooth.

Laser cutting to control fracture

For brittle materials that are easily damaged by heat, high-speed, controlled cutting by laser beam heating is called controlled fracture cutting . The main content of this cutting process is: the laser beam heats a small area of the brittle material, causing a large thermal gradient and severe mechanical deformation in the area, which causes the material to crack. As long as a balanced heating gradient is maintained, the laser beam can guide cracks in any desired direction.

It should be noted that this kind of controlled break cutting is not suitable for cutting acute and corner cuts. Cutting oversized closed shapes is not easy to succeed. Controlling the cutting speed is fast and does not require too much power, otherwise it will cause the surface of the workpiece to melt and damage the edge of the slit. Its main control parameters are laser power and spot size.

Laser cutting cutting program

1. Detection of the intersection position. Before laser cutting, the position of the beam focus on the workpiece must be adjusted according to the material. Because the laser beam, especially the CO2 gas laser, is generally invisible to the naked eye, we can use a wedge-shaped acrylic block to detect the focus position, and then adjust the height of the cutting torch so that The focus is at the set position.

2, the main points of the piercing operation. In the century cutting process, some parts are cut from the inside of the board, which requires punching holes in the board first. One method is to use a continuous laser to perforate the thin plate. With normal auxiliary gas pressure, the beam can penetrate through the workpiece for 0.2 ~ 1s, and then it can be switched to cutting. When the thickness of the workpiece is large (for example, the thickness of the plate is 2 ~ 4mm), a normal gas pressure perforation will be used to form a large-scale melting pit on the surface of the workpiece. Not only does it affect the quality of the cut, but splashing molten material can damage the lens or nozzle. At this time, the pressure of the auxiliary gas should be appropriately increased. The colleague slightly increased the distance between the hole diameter of the nozzle and the workpiece. The disadvantage of this method is increased gas flow and reduced cutting speed.

3. Prevent melting of sharp corners of the workpiece. When using a continuous laser to cut parts with sharp angles, if the cutting parameters match or the operation is not proper, self-firing is likely to occur at the sharp corners, and sharp corners cannot be formed. This not only deteriorates the quality of the area, but also affects subsequent cutting. The method to solve this problem is to choose appropriate cutting parameters, and there is no burning problem at sharp corners when using pulsed laser cutting.

Laser cutting competitive advantage

Laser cutting machine is a technological revolution in sheet metal processing, and it is the "processing center" in sheet metal processing. Laser cutting machine has high flexibility, fast cutting speed, high production efficiency, short product production cycle, and has won a wide range of customers. In the market, the technology has a long effective life. Most foreign boards with a thickness of more than 2 mm use laser cutting machines. Many foreign experts agree that the next 30-40 years will be the golden period for the development of laser processing technology.
Generally speaking, it is recommended to cut metal materials such as carbon steel plates within 12mm and stainless steel plates within 10mm. Laser cutting machines are recommended. Laser cutting machine has no cutting force, no deformation during processing: no tool wear, good material adaptability: whether it is simple or complex parts, you can use laser for rapid and rapid prototyping and cutting: its narrow slit, good cutting quality and high degree of automation. Easy to operate, low labor intensity and no pollution: automatic cutting layout, nesting, improved material utilization, low production cost and good economic benefits.

There are many factors to consider when choosing a laser cutting machine. In addition to considering the maximum size, material, maximum thickness of the workpiece to be cut and the size of the raw material format, more needs to consider the future development direction, such as the product The size of the largest workpiece to be processed after the technology modification, the format of the material provided by the steel market, which is the most economical for your product, the loading and unloading time, etc.

Laser cutting market status

Although the development of China's laser industry is a preliminary development, it has completed a leap development under the leadership of international science and technology, and has a higher stage of outstanding than the same quality. In terms of laser cutting machines, the market demand is as high as tens of millions, adding new vitality to the broad market. Since the birth and application of the first laser equipment in the 1960s, many experts in China have made efforts in the laser industry and reached a small international difference. At the same time as the development of the laser industry, the complete set of laser industrial equipment has also entered the production market, freeing itself from long-term dependence on foreign countries and solving the embarrassing situation of the domestic laser industry.

The rapid development of the domestic economy has become the high industry pillar of the laser market and can reach a growth rate of more than 20% per year. It has become a new starting point for the global laser market. According to expert forecasts, the domestic laser market is still in a high-speed growth stage. In the future, it can be doubled to expand the market of laser cutting equipment to the largest, fill domestic gaps, lift domestic high-end laser equipment from the trapped state, and become an international pillar. At present, the domestic laser industry mainly gathers in Shenzhen and Wuhan. Among them, Shenzhen is an important domestic sales market, and with years of development experience, it has led other regions.

Laser cutting purchase

Laser cutting unit

The first category is large and medium-sized manufacturing enterprises. Many of the products produced by these companies need to be cut and cut, and they have strong economic and technical strength.

Laser cutting processing station

The other type of unit is the processing station (known abroad as the Job Shop) . The processing station is specialized in undertaking laser processing business. It has no leading products. Its existence can meet the needs of some small and medium-sized enterprises on the one hand; on the other hand, it can play a role of publicity and demonstration in the early stage to promote the application of laser cutting technology. In 1999, there were 2,700 laser processing stations in the United States, of which 51% were engaged in laser cutting. In the 1980s, China's laser processing stations were mainly engaged in laser heat treatment. After the 1990s, laser cutting and attack stations gradually increased. On this basis, with the deepening of the reform of China's large and medium-sized enterprises and the strengthening of their economic strength, more and more enterprises will use CO2 laser cutting technology.

From the analysis of current domestic applications, CO2 laser cutting is widely used in 12mm thick low carbon steel plates; 6mm thick stainless steel plates; and 20mm thick non-metallic materials. The cutting of three-dimensional space curves has also begun to find applications in the automotive and aviation industries.

Laser cutting development trend

Laser cutting refers to the use of laser emitting beams to punch holes in the product, and the corresponding gap according to the horizontal movement is called laser cutting. The laser can cut on multiple product materials, such as acrylic, knife template, cloth, leather and other industries. Laser cutting, so laser cutting is a new solution for cutting in multiple industries. What kind of advantages does such a new cutting method have over traditional cutting? Dr. Guang will take you to analyze it.

Laser light is generated by the excitation of matter. This light has a strong temperature. When it touches the material, it can quickly melt on the surface of the material to form a hole. It forms a cut according to the movement of the alignment point. Compared with the traditional cutting method, the cutting method has a smaller gap and can save most materials. However, the analysis is defined according to the cutting effect. The material that is cut according to the laser can have satisfactory cutting results and high accuracy. This is inherited. Because of the advantages of the laser, ordinary cutting methods cannot match.

Compared with traditional cutting methods, laser cutting is easier to understand, learn, and has absolute advantages in terms of processing effects and speed required by businesses. Therefore, it is believed that laser cutting machines will be the needs of the general public in the choice of cutting methods in the future.

Laser cutting market model change

Laser cutting processing refers to the use of laser equipment to process products. This model is targeted at those who are new to the laser industry and small processing households. However, this model is not advocated in today's society because the price of laser equipment It is no longer the high-level equipment. The perfect technical development and fine processing make today's laser equipment no longer so expensive, because their equipment is targeted at the industry. This can save the previous kind of equipment. Noble high-power equipment can be processed, and today's low-power equipment can also be processed. This makes these processes that want to buy laser cutting machines no longer need to borrow other people's equipment for processing. The laser cutting processing mode is gradually being replaced. This is inevitable. .

The following analyzes the laser cutting market and processing effects. In the laser cutting market, everything is clear. Laser cutting can process multiple industries. However, it needs to buy equipment for processing multiple industries. The price is expensive. However, if the purchase is a single Industries, such as knife die laser cutting machines , leather laser cutting machines, etc., these industry-specific equipment are not so expensive. This is the future market. In terms of processing effects, the processing effect of a single industry must be targeted at a single industry. Its function is the best and can meet the requirements of this industry. In the introduction of equipment in these industries, Dr. Guang mentioned that, so if you want to use laser cutting processing, you may try to use laser cutting equipment directly. Buy for processing, this can help you achieve and solve many problems! ^[1]