Current situation and development prospect of dome

The current situation and development prospects of domestic laser marking

I. overview

laser marking is a new processing technology developed after the application technologies of laser welding, laser heat treatment, laser cutting, laser drilling and so on. It is a new marking process without contact, pollution and wear. In recent years, with the improvement of the reliability and practicality of lasers, coupled with the rapid development of computer technology and the improvement of optical devices, the development of laser marking technology has been promoted

laser marking is a marking method that uses high-energy density laser beam to act on the target, causing physical or chemical changes on the target surface, so as to obtain visible patterns. The high-energy laser beam is focused on the material surface, which makes the material with high efficiency, energy-saving advantages and high cost performance rapidly vaporize and form pits. With the laser beam moving regularly on the surface of the material and controlling the disconnection of the laser, the laser beam is processed into a specified pattern on the surface of the material. Compared with the traditional marking process, laser marking has obvious advantages:

(1) the marking speed is fast, and the handwriting is clear and permanent

(2) non contact processing, less pollution and no wear

(3) convenient operation and strong anti-counterfeiting function

(4) high speed automatic operation and low production cost can be achieved

II. The development process of domestic laser marking

the core of laser marking equipment is the laser marking control system. Therefore, the development process of laser marking is the development process of marking control system. In just eight years from 1995 to 2003, the control system has experienced the era of large format, the era of rotating mirror and the era of galvanometer in the field of laser marking. The control mode has also completed a series of evolution from software direct control to upper and lower computer control to real-time processing and time-sharing multiplexing. Today, the emergence and development of semiconductor lasers, fiber lasers, and even UV lasers pose new challenges to optical process control

1. In the era of large format

the so-called large format, at the beginning, the control part of the plotter was directly used on the laser equipment, the drawing pen was removed, 45 ° turn back mirrors were installed on the x-axis base point at point (0, 0), the y-axis base point and the position of the original drawing pen respectively, and a small focusing lens was installed at the lower end of the original drawing pen position to guide the optical path and focus the beam. Directly using the drawing software to output the printing command can drive the operation of the optical path. The most obvious advantage of this method is that it has a large format, and can basically meet the marking requirements with relatively low accuracy, without the need for special marking software; However, this method has some disadvantages, such as slow marking speed, low control accuracy, large mechanical wear of the pen arm, poor reliability, large volume and so on. Therefore, after the initial attempt, the large format laser marking system of the drawing ceremony gradually withdrew from the marking market. The large format equipment of the same type now used is basically a high-speed large format system driven by servo motor, which imitates the previous control process. With the gradual improvement of the three-dimensional dynamic focusing galvanometer scanning system, the large format system will gradually disappear from the field of laser marking

2. The era of rotating mirror

seeing a series of shortcomings of large-scale systems, some control engineers have developed a rotating mirror scanning system driven by stepping motors under the condition that the high-speed galvanometer technology has not been widely popularized in China. Its working principle is to expand the beam of the laser derived from the resonant cavity and pass through the reflection of two gold mirrors driven by stepping motors installed at 90 °, After focusing by the f-theta field mirror, the output acts on the processing object. The rotation of the gold mirror makes the laser action point on the working plane move on the X and Y axes respectively. The cooperative action of the two mirrors enables the laser to complete the movement of straight lines and various curves on the working plane. This control process is far more than large-scale in terms of speed and positioning accuracy, so it can meet the requirements of the tool industry for laser control to a large extent. Although there is a clear gap with the internationally popular galvanometer scanning system at that time, strictly speaking, the emergence and gradual improvement of this design idea represents a milestone in the application of laser in China, It is a typical symbol that China can design and produce laser application equipment by itself. Until the large-scale application of galvanometer in China, this control method gradually withdrew from the stage of laser application in China

3. Galvanometer era

1998, the large-scale application of galvanometer scanning system in China began to come. The so-called galvanometer can also be called ammeter. Its design idea completely follows the design method of ammeter. The lens replaces the needle, and the probe signal is replaced by the computer-controlled -5v-5v DC signal to complete the predetermined action. Like the rotating mirror scanning system, this typical control system uses a pair of turn back mirrors. The difference is that the stepping motor driving this set of lenses is replaced by the servo motor. In this control system, the use of position sensors and the design idea of negative feedback loop further ensure the accuracy of the system, and the scanning speed and repeated positioning accuracy of the whole system reach a new level

III. technical status of domestic laser marking

at present, domestic laser marking can be divided into mask mode marking, array marking and scanning marking according to its working mode

1. mask mode marking

mask mode marking is also called projection marking. The mask mode marking system is composed of a laser, a mask and an imaging lens. Its working principle (as shown in Figure 1) is to carve the numbers, characters, bar codes, images, etc. to be marked on a template into a mask. The laser beam expanded by the telescope is evenly projected on the prepared mask, and the light is transmitted from the carved part. The pattern on the mask is imaged on the workpiece (focal plane) through the lens. Usually, each pulse can form a mark. The surface of the material irradiated by the laser is rapidly heated and vaporized or a chemical reaction occurs, and the color changes to form a clear and distinguishable mark. Generally, CO2 laser and YAG laser are used for mask mode marking. The main advantage of mask mode marking is that one laser pulse can make a complete mark including several symbols at one time, so the marking speed is fast. For large quantities of products, they can be marked directly on the production line. The disadvantages are poor marking flexibility and low energy utilization

2. array marking

the array marking system is shown in Figure 2. It uses several small lasers to emit pulses at the same time, and after passing through the reflector and focusing lens, several laser pulses will ablate (melt) small pits with uniform size and depth on the surface of the marked material. Each character and pattern is composed of these small round black pits, which are generally 5 points in the horizontal stroke and 7 points in the vertical stroke, thus forming 5 × 7 array. Array marking generally adopts low-power RF excited CO2 laser, and its marking speed can reach up to 6000 characters/minute, which makes it an ideal choice for high-speed marking. Its disadvantage is that it can only mark dot matrix characters, and it can only reach 5 × With a resolution of 7, there is nothing we can do about Chinese characters

3. scanning marking

the scanning marking system is composed of three parts: computer, laser and X-Y scanning mechanism. Its working principle is to input the information that needs to be marked into the computer. The computer controls the laser and X-Y scanning mechanism according to the pre-designed program, so that the high-energy laser points transformed by the special optical system scan and move on the machined surface to form a mark

generally, X-Y scanning mechanism has two structural forms: one is mechanical scanning type, and the other is galvanometer scanning type

(1) mechanical scanning

mechanical scanning marking system does not move the beam by changing the rotation angle of the mirror, but translates the X-Y coordinate of the mirror by mechanical method, so as to change the position of the laser beam reaching the workpiece. The X-Y scanning mechanism of this marking system is usually refitted with a plotter (as shown in Figure 3). Its working process: the laser beam passes through the reflector ① and ② to turn the optical path, and then passes through the light pen (focusing lens) ③ to shoot on the processed workpiece. Among them, the pen arm ④ of the plotter can only move back and forth along the x-axis direction with reflectors ① and ②; The light pen ③ and its upper reflector ② (both fixed together) can only move along the y-axis direction. Under the control of the computer (generally, the control signal is output through the parallel port), the motion of the light pen in the Y direction is combined with the motion of the pen arm in the X direction, so that the output laser can reach any point in the plane, so as to mark any graphics and words

(2) galvanometer scanning

galvanometer scanning marking system is mainly composed of laser, XY deflection mirror, focusing lens, computer, etc. Its working principle is that the laser beam is incident on two mirrors (galvanometer), and the reflection angle of the mirrors is controlled by the computer. These two mirrors can be scanned along the X and Y axes respectively, so as to achieve the deflection of the laser beam, so that the laser focus with a certain power density moves on the marking material according to the required requirements, so as to leave a permanent mark on the surface of the material. The focused spot can be circular or rectangular. In galvanometer marking system, vector graphics and text can be used. This method adopts the processing method of graphics by graphics software in computer, which has the characteristics of high drawing efficiency, good graphics accuracy and no distortion, and greatly improves the quality and speed of laser marking. At the same time, the galvanometer marking can also adopt the dot matrix marking method, which is very suitable for marking. According to the production lines with different speeds, one scanning galvanometer or two scanning galvanometers can be used. Compared with the array marking mentioned above, it can mark more dot matrix information and has greater advantages for marking Chinese characters

galvanometer scanning marking system generally uses continuous optical pump, and the working wavelength is 1.06 μ M nd:yag laser, the output power is 10 ~ 120W, and the laser output can be continuous or Q-switched modulation. RF excited CO2 lasers developed in recent years are also used in galvanometer scanning laser marking machines

galvanometer scanning marking has become a mainstream product because of its wide application range, vector marking and dot matrix marking, adjustable marking range, fast response speed, high marking speed (hundreds of characters per second), high marking quality, good optical path sealing performance, strong adaptability to the environment and other advantages. It is considered to represent the development direction of laser marking machines in the future, and has broad application prospects

at present, the lasers used for marking mainly include nd:yag laser and CO2 laser. The laser produced by nd:yag laser can be well absorbed by metals and most plastics, and its wave length (1) will also damage the equipment 06 μ m) , the focused light spot is small, so it is most suitable for high-definition marking on metal and other materials. The laser wavelength produced by CO2 laser is 10.6 μ m. Wood products, glass, polymers and most transparent materials have good absorption effect, so they are especially suitable for marking on non-metallic surfaces

the disadvantage of nd:yag laser and CO2 laser is that the thermal damage and thermal diffusion of materials are relatively serious, and the hot edge effect often blurs the mark. In contrast, when marking with ultraviolet light generated by excimer lasers, the material is not heated, only the surface of the material is evaporated, resulting in photochemical effects on the surface tissue and leaving marks on the surface of the material. Therefore, when marking with excimer laser, mark the edge ten