Three ways of laser marking

There are three main laser beam transmission systems used to produce marks on the surface of the object, and the current domestic laser marking can be divided into mask mode marking, array marking and scanning marking according to its working mode.

Mask mode marking

The mask marking method is also called the projection marking method. The system is composed of a laser, a mask and an imaging lens, and its principle is to carve out the numbers, characters, bar codes, images, etc. to be played on a template to make a mask. The laser is evenly shone on the mask plate that has been proudly carved in advance through the beam expansion of the telescope, and the light passes through the carved part of the mask plate, covering the part that is not carved out. The light through the mask is focused with a lens on the surface of the workpiece to be marked, and then the surface of the workpiece is marked.

Pros and cons:

Usually each pulse can be printed with a complete mark containing multiple symbols, the surface of the material subject to laser radiation is rapidly heated and vaporized or a chemical reaction is generated, and the color changes to form a clear mark that can be distinguished, and for high-volume products, laser marking can be carried out directly on the production line; The disadvantages are poor marking flexibility, low energy utilization, and the mask needs to be remade every time the pattern is changed, which is time-consuming and laborious to make the mask, and the efficiency is low.

Dot matrix notation

The array marking system uses several small lasers to emit pulses at the same time, and after passing through the mirror and the focusing lens, several laser pulses are ablated (melted) on the surface of the marked material to create small pits of uniform size and depth, and each character and pattern is composed of these small round black pits, generally 5 points are drawn horizontally and 7 points vertically, thus forming a 5×7 array. Array marking generally uses low-power RF-excited CO2 lasers, which can mark up to 6000 characters per second, making it ideal for high-speed in-line marking, but its disadvantage is that it can only mark dot matrix characters, and can only achieve a resolution of 5×7, which is powerless for Chinese characters.

Static marking

The main disadvantage of mask and lattice beam delivery systems is that the code they generate is static, in contrast to writing a laser beam like a pen on the surface of the product, which is a more general principle of beam delivery. As a result, scanning marking technology is now the most popular technology.

Galvanometer scanning marking

The galvanometer marking method is to incident a laser beam on two mirrors (galvanometers) and use a computer to control the scanning mirrors, which can be scanned along the X-Y axis respectively, and typed numbers, words, graphics, etc. on a determined plane. The marking area can be large or small, and several small parts can be marked at the same time, and a variety of words and patterns can also be marked on one part. In a nutshell, scanning is the use of a laser pen to engrave on the workpiece to be processed. In the scanning and marking system, the computer usually uses vectors to represent graphics and words, that is, various graphics and words are drawn with directed line segments.

This method adopts the processing mode of the computer advanced graphics system to the graphics, which has the characteristics of high drawing efficiency and good graphics accuracy, and can enlarge and reduce the graphics without distortion and deformation. However, in addition to the material factors in the actual processing of the scanning mark, the resolution of the marking area, the laser power, the marking speed and other parameters will have an impact on the quality, and the parameters simply interact with each other and restrict each other.

Laser classification

1. The galvanometer scanning marking system generally uses an Nd:YAG laser with a working wavelength of 1.06μm with a continuous optical pump, with an output power of 10~120W, and the laser output can be continuous.
2. RF-stimulated CO2 lasers, which have been developed in recent years, are also used in galvanometer scanning laser markers. The disadvantage of Nd:YAG lasers and CO2 lasers is that the thermal damage and heat diffusion of the material are severe, and the resulting hot edge effect often blurs the marking.
3. When the ultraviolet light produced by the excimer laser is marked, it does not heat the substance, but only evaporates the surface of the substance, which produces a photochemical effect on the surface structure and leaves a mark on the surface of the substance. Therefore, when marking with an excimer laser, the marking edge is very clear. Due to the large absorption of ultraviolet light by the material, the effect of the laser on the material only occurs in the most surface layer of the material, and there is almost no burning phenomenon on the material, so the excimer laser is more suitable for the labeling of the material.

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