What is Laser Marking?

Laser marking technology is one of the largest application areas of laser processing. Laser marking is a method that uses a high-energy-density laser to locally irradiate a workpiece to vaporize the surface material or change the color of the chemical reaction, leaving a permanent mark. Laser marking can produce a variety of characters, symbols and patterns, and the character size can be on the order of millimeters to micrometers, which has special significance for product anti-counterfeiting.

Chinese name: Laser Marking
Foreign name: laser marking

Application area: laser processing
Principle: High energy density laser
which performed: Surface material vaporizes or changes color

Basic principles of laser marking

The basic principle of laser marking is that a high-energy continuous laser beam is generated by a laser generator. The focused laser acts on the printing material to instantly melt or even vaporize the surface material. By controlling the path of the laser on the surface of the material, it forms Graphical markers required.

Laser marking is characterized by non-contact processing, which can be marked on any special-shaped surface, and the workpiece will not deform and generate internal stress. It is suitable for marking metal, plastic, glass, ceramics, wood, leather and other materials.

The laser can mark almost all parts (such as pistons, piston rings, valves, valve seats, hardware tools, sanitary ware, electronic components, etc.), and the marks are wear-resistant. The production process is easy to automate and the marked parts have little deformation.

The laser marking machine uses scanning method to mark, that is, the laser beam is incident on the two mirrors, and the computer controls the scanning motor to drive the mirrors to rotate along the X and Y axes, respectively. The laser beam is focused and falls on the marked workpiece, thereby forming Laser Marked Traces

In the Pearl River Delta, Hong Kong and Taiwan regions, laser marking is called laser laser processing according to the laser transliteration in English.

Laser marking advantages

Laser marking (2 photos)

The focused ultra-fine laser beam is like a tool, which can remove the material on the surface of the object point by point. Its advancement lies in the non-contact processing of the marking process, which does not cause mechanical compression or mechanical stress, so it will not damage the processed object. The laser focused size is small, the heat affected area is small, and the processing is fine. Therefore, some processes that cannot be achieved by conventional methods can be completed.

The "tool" used in laser processing is the focused light spot. No additional equipment and materials are needed. As long as the laser can work normally, it can be continuously processed for a long time. Laser processing is fast and low cost. Laser processing is controlled automatically by a computer, and no human intervention is required during production.

What kind of information the laser can mark is only related to the content designed in the computer. As long as the artwork marking system designed in the computer can identify it, the marking machine can accurately restore the design information on a suitable carrier. So the function of the software actually determines the function of the system to a large extent.

Comparison of laser marking methods

Laser marking technology, as a modern precision machining method, has unparalleled advantages compared to traditional machining methods such as corrosion, electric discharge machining, mechanical scoring, printing:

1. The laser is used as the processing means, and there is no processing force between the workpiece and it has the advantages of no contact, no cutting force, and small thermal influence, which ensures the original accuracy of the workpiece. At the same time, it has a wide adaptability to materials, can make very fine marks on the surface of a variety of materials, and has very good durability;

laser marking machine

2. The laser has good space controllability and time controllability. It has great freedom in the material, shape, size and processing environment of the processing object, and is especially suitable for automatic processing and special surface processing. And the processing method is flexible, which can not only meet the needs of laboratory-style single design, but also meet the requirements of industrialized mass production;

3 Laser engraving is fine, lines can reach millimeters to micrometers. Marking and modification using laser marking technology are very difficult, which is very important for product anti-counterfeiting;

4 The combination of laser processing system and computer numerical control technology can constitute efficient automatic processing equipment, which can print a variety of words, symbols and patterns, easy to design marking patterns with software, change the content of the mark, and meet the requirements of modern production with high efficiency and fast pace

5. Compared with traditional screen printing, laser processing has no pollution source and is a clean and pollution-free high environmental protection processing technology;

Laser marking technology has been widely used in all walks of life, opening up broad prospects for high-quality, efficient, pollution-free and low-cost modern processing and production. With the continuous expansion of the field of modern laser marking applications, the requirements for laser manufacturing equipment systems are miniaturized, and the requirements for high efficiency and integration are becoming higher and higher.The successful development of new high-power fiber laser technology will surely produce extremely Big push.

Development of 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 the marking control system. In a short period of 8 years from 1995 to 2003, the control system has experienced the large format era, the mirror era and the galvanometer era in the field of laser marking. The control method has also been completed from direct software control to upper and lower computer control to A series of evolutions of real-time processing and time-division multiplexing. Today, the emergence and development of semiconductor lasers, fiber lasers, and even ultraviolet lasers have brought new challenges to optical process control.

Laser marking large format era

The so-called large format is to initially use the control part of the plotter directly on the laser device, remove the drawing pen, and install 45 on the (0,0) point X-axis base point, Y-axis base point, and the original drawing pen position. ° Folding mirror, a small focusing lens is installed at the lower end of the original drawing pen to guide the optical path and focus the light beam. Directly using the printing software to output the print command can drive the operation of the optical path. The most obvious advantage of this method is that the format is large, and basically it can meet the marking requirements with low accuracy, and no special marking software is needed; however, this kind of The method has the disadvantages of slow marking speed, low control accuracy, large mechanical wear of the pen arm, poor reliability, and large volume. Therefore, after the initial attempt, the large-format laser marking system for the drawing ceremony gradually withdrew from the marking market. The large-format equipment of the same type used basically imitated the previous control process and was driven by servo motors. High-speed large-format systems, and with the gradual improvement of 3D dynamic focusing galvanometer scanning systems, large-format systems will gradually disappear from the field of laser marking.

Laser marking and turning mirror era

Seeing a series of shortcomings of large-format systems, under the situation that high-speed galvanometer technology has not been widely popularized in China, some control engineers have developed a rotary mirror scanning system driven by a stepper motor. The working principle is The laser light exiting from the resonant cavity is expanded by the reflection of the gold mirror driven by two stepping motors installed at 90 °. After being focused by the F-theta field lens, the output is applied to the processing object. The rotation of the gold mirror makes the working plane The laser application points on the X and Y axes respectively move, and the two mirrors cooperate to enable the laser to complete straight and various curve movements on the work plane. This control process far exceeds the large format in terms of speed and positioning accuracy, so it can largely meet the requirements of the tool industry for laser control, although it is still more obvious than the galvanometer scanning system that was popular internationally at the time. However, strictly speaking, the emergence and gradual improvement of this design idea represent a milestone in China's laser application, and it is a typical sign that China can fully design and produce laser application equipment on its own. Until the rise of the large-scale application of galvanometer in China, this control method gradually withdrew from the stage of laser application in China.

Laser marking galvanometer era

In 1998, the large-scale application of galvanometer scanning system in China began to arrive. [The so-called galvanometer can also be called an ammeter. Its design idea completely follows the design method of the ammeter. The lens replaces the meter needle, and the signal of the probe is replaced by a DC signal of -5V-5V controlled by the computer to complete the predetermined action. Same as the rotating mirror scanning system, this typical control system uses a pair of folding mirrors. The difference is that the stepper motor that drives the lens is replaced by a servo motor. In this control system, the use of position sensors The design ideas of the negative feedback loop further ensure the accuracy of the system, and the scanning speed and repeat positioning accuracy of the entire system reach a new level.

Laser marking domestic status

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

Laser marking mask mode marking

Mask mode marking is also called projection marking. The mask mode marking system consists of a laser, a mask plate, and an imaging lens. Its working principle is that the laser beam expanded by the telescope is evenly projected on the mask plate prepared in advance, and the light is transmitted from the hollow part. The pattern on the mask is imaged onto the workpiece (focal plane) through the lens. Usually one mark is formed per pulse. The surface of the material irradiated by the laser is rapidly heated and vaporized or a chemical reaction occurs, and a color change occurs to form a clearly distinguishable mark. Mask mode marking generally uses CO2 lasers and YAG lasers. The main advantage of mask mode marking is that a laser pulse can mark a complete mark including several symbols at a time, so the marking speed is fast. For high-volume products, marking can be done directly on the production line. Disadvantages are poor marking flexibility and low energy utilization.

Laser marking array marking

It uses several small lasers to emit pulses at the same time. After passing the mirror and focusing lens, several laser pulses are ablated (melted) on the surface of the material to be marked to form small pits of uniform size and depth. Each character, The pattern is composed of these small round black pits. Generally, 5 dots are horizontally stroked and 7 dots are vertically drawn to form a 5 × 7 array. Array marking generally uses a low-power RF-excited CO2 laser. Its marking speed can reach up to 6000 characters per minute, making it an ideal choice for high-speed online marking. Its disadvantage is that it can only mark dot matrix characters, and it can only reach 5 × 7 resolution, can not do anything for Chinese characters.

Laser Marking Scanning Marking

The scanning marking system is composed of a computer, a laser and an XY scanning mechanism. Its working principle is to input the information that needs to be marked into the computer. The computer controls the laser and the XY scanning mechanism according to a pre-designed program so that it is transformed by a special optical system. The high-energy laser spot scans on the processed surface to form a mark.

Usually XY scanning mechanism has two structural forms: one is a mechanical scanning type, and the other is a galvanometer scanning type.

(1) mechanical scanning

The mechanical scanning marking system does not move the beam by changing the rotation angle of the mirror, but uses a mechanical method to translate the mirror's XY coordinates to change the position of the laser beam to the workpiece. The XY of this marking system The scanning mechanism is usually modified with a plotter. The working process: After passing through the reflecting mirrors and , the laser beam turns the optical path, and then passes through the light pen (focusing lens) to hit the workpiece to be processed. Among them, the pen arm of the plotter can only move back and forth along the X-axis direction with the mirrors and ; the light pen together with the mirror on the upper end (the two are fixed together) can only move in the Y-axis direction. Under the control of the computer (usually through the parallel port output control signal), the movement of the light pen in the Y direction and the movement of the pen arm in the X direction are synthesized, so that the output laser can reach any point in the plane, so as to mark any graphics and text .

(2) Galvanometer scanning type

Galvanometer scanning marking system is mainly composed of laser, XY deflection mirror, focusing lens, computer and so on. The working principle is that the laser beam is incident on two mirrors (galvanometers), and the reflection angle of the mirrors is controlled by a 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 focusing point of a certain power density moves on the marking material according to the required requirements, thereby leaving a permanent mark on the surface of the material. The focused spot can be circular or rectangular.

In the galvanometer marking system, vector graphics and text can be used. This method uses graphics software in the computer to process graphics. It has the characteristics of high mapping efficiency, good graphics accuracy, and no distortion, which greatly improves The quality and speed of laser marking. At the same time, galvanometer type marking can also use dot matrix marking method. This method is very suitable for online marking. Depending on the production line with different speeds, one scanning galvanometer or two scanning galvanometers can be used. Compared with the array-type marking, it can mark more dot matrix information, which has a greater advantage for marking Chinese characters.

Galvanometer scanning marking systems generally use a continuous optical pump Nd: YAG laser with a working wavelength of 1.06m, and the output power is 10 ~ 120W. The laser output can be continuous or Q-switched. The developed RF-excited CO2 laser is also used in galvanometer scanning laser marking machines.

Due to its wide application range, galvanometer scanning marking can perform vector marking and dot matrix marking, the marking range is adjustable, and it has fast response speed and high marking speed (hundreds of characters can be marked per second) The advantages of high marking quality, good optical path sealing performance and strong environmental adaptability have become mainstream products, and are considered to represent the development direction of future laser marking machines, and have broad application prospects.

The lasers used for marking are mainly Nd: YAG lasers and CO2 lasers. The laser generated by Nd: YAG laser can be well absorbed by metal and most plastics, and its short wavelength (1.06m) and small focused spot make it most suitable for high-definition marking on metals and other materials. The wavelength of the laser generated by the CO2 laser is 10.6 m. Wood products, glass, polymers, and most transparent materials have a good absorption effect, so it is particularly suitable for marking on non-metallic surfaces.

The disadvantages of Nd: YAG lasers and CO2 lasers are that the thermal damage to the material and the thermal diffusion are relatively serious, and the hot-edge effect often makes the mark fuzzy. In contrast, when marking by ultraviolet light generated by an excimer laser, the substance is not heated, only the surface of the substance is evaporated, a photochemical effect is generated on the surface tissue, and a mark is left on the surface of the substance. Therefore, when marking with an excimer laser, the edge of the mark is very clear. Due to the material's large absorption of ultraviolet light, the effect of the laser on the material only occurs at the outermost layer of the material, and there is almost no burning of the material. Therefore, excimer lasers are more suitable for marking materials. ^[1]