The laser processing technology is a new technology developed in the 1960s. It uses light energy to focus to a high energy density through the lens and processes various materials by photothermal effect.
In recent years, laser processing technology is more and more used in drilling, cutting, welding and surface treatment.
1. Basic principle of laser processing technology
Laser is a kind of coherent light with high energy density, strong directivity and good monochromaticity produced by laser radiation.
Its power density can reach 108 ~ 1080W / cm2. It can process almost any metal and non-metal.
Laser processing refers to irradiating the laser beam on the surface of the material to be processed, using the energy of the laser beam to fuse or remove the material and change the surface properties of the material, so as to achieve the purpose of processing.
Laser processing belongs to non-contact processing, which has some advantages that other processing technologies do not have, such as small light spot, concentrated energy and small heat-affected zone;
It does not touch the processed workpiece and has no pollution to the workpiece;
It is free from electromagnetic interference and is more convenient to use than electron beam processing;
The laser beam is easy to focus, guide and automatic control.
According to the interaction mechanism between laser beam and material, laser processing can be divided into laser thermal processing and photochemical reaction processing.
Laser thermal processing refers to the thermal effect produced by the laser beam projected onto the material surface to complete the processing process;
Photochemical reaction processing refers to the processing process in which the laser beam irradiates the object and initiates or controls the photochemical reaction with the help of high-density and high-energy photons.
Laser thermal processing includes laser welding, laser cutting, surface modification and laser marking;
Photochemical reactions include photochemical deposition, stereolithography and laser etching.
The light source of photochemical reaction processing is mainly ultraviolet laser, such as excimer laser and hydrogen ion laser. It is mainly used in semiconductor processing and rapid prototyping stereo lithography.
2. Characteristics of laser processing technology
1) Laser processing is non-contact processing, with fast processing speed, small heat affected zone and no obvious mechanical force. It can process easily deformed thin plates and elastic parts.
2) Due to the high power density of laser, it can process almost all materials, such as various metal materials, ceramics, quartz, glass, diamond and semiconductors.
If it is a transparent material, some colorization and roughening measures shall be taken before processing.
3) Because the diameter of the laser spot can reach micron level, it can carry out very fine processing, such as processing deep and small micropores and narrow slots.
4) There is no need for processing tools, so there is no problem of tool loss, which is suitable for the automatic production system.
5) Good versatility. The same laser processing device can be used for various processing purposes, such as drilling, cutting, welding, etc. can be carried out on the same machine tool.
6) Laser processing is a thermal processing method of instantaneous local melting and vaporization, which is affected by many factors.
Therefore, when precision micromachining is carried out, its accuracy and surface roughness need to be tested repeatedly, and reasonable processing parameters can meet the required requirements.
3. Application of laser processing technology
(1) Laser welding
Laser welding has been widely used in the mechanical industry. It is a deep penetration welding based on the keyhole effect produced by high-power laser.
It is not only an efficient welding method with large penetration, fast speed and large fusion area per unit time, but also an accurate welding method with large weld depth width ratio, small specific energy, small heat-affected zone and small deformation.
Laser welding has many advantages, such as high depth width ratio and weld depth width ratio up to 10 ∶ 1;
After laser focusing, the power density is high, the linear energy is small, the thermal deformation of weldment is small, the weld is narrow, and the weld heat-affected zone is also very small;
It can realize precise and controllable micro zone welding, with small focus spot and precise positioning, as well as extremely fast heating and cooling speed, which makes it easy for the laser to realize precise micro zone welding and has little thermal damage to the area around the weld;
The welding speed is fast.
The laser welding speed is more than one order of magnitude faster than the arc welding speed. The laser welding speed of thin plate can be as high as 20 ~ 30m / min, which is an extremely efficient welding method;
The material has good adaptability.
The laser can realize the welding which is difficult to be realized by conventional methods, and can weld different materials with good effect;
Good process adaptability, through flexible beam conduction and combined with modern numerical control technology, it is easy to realize the welding of multi station, inaccessible parts and different parts of the same equipment.
However, laser welding also has the following limitations, such as high requirements for the assembly accuracy of weldments, small spot size after laser focusing, and generally no filling materials, so there are strict requirements for the assembly accuracy of workpieces and beam positioning accuracy;
The cost of laser and related systems is high and the one-time investment is large.
(2) Laser cutting
Laser cutting uses the focused high-power density laser beam to irradiate the workpiece.
On the premise of exceeding a certain power density, the beam energy and the additional chemical reaction heat energy in the active gas-assisted cutting process are all absorbed by the material, resulting in a sharp rise in the material temperature at the irradiation place.
After reaching the boiling point, the material begins to vaporize and form holes.
With the relative movement of the beam and the material, the material finally forms a slit.
The slag at the cutting seam is blown off by auxiliary gas with certain pressure to complete the cutting, as shown in Fig. 1.
Laser cutting can obtain faster cutting speed and higher machining quality due to its high energy density;
The edge cutting seam is narrow, the perpendicularity of the edge is good, and there is no mechanical stress;
It is suitable for a wide range of materials and no cutting noise.
It is an effective way of high-quality and fast cutting.
Its main shortcomings are limited cutting depth and large one-time investment, and the specific value is related to power.
Where conventional methods are inconvenient to cut, laser cutting has great advantages.
With the continuous improvement of the quality of the laser system and the gradual reduction of the price of the laser processing system, it will have stronger competitiveness.
Figure 1 laser cutting principle
(3) Laser drilling
The device of laser drilling is roughly similar to laser welding.
Compared with welding, drilling requires a higher power density of the focused laser beam, which can heat the material to the vaporization temperature and remove the material by vaporization.
The lasers used for laser drilling mainly include ruby, neodymium glass and CO2 laser.
Generally, the optical system is used to gather the spot size to several microns to tens of microns.
Because the light spot can gather very fine, it can process very fine and particularly deep holes.
From the aspect ratio of depth to diameter, the ratio of depth to aperture can be as high as more than 50, which is difficult to achieve by other methods.
For example, the depth diameter ratio obtained by machining small holes on extremely hard alumina ceramics by the general method is 2, the ultrasonic method is only 4, and the laser drilling can reach 25.
Laser drilling has many applications. It can drill holes in almost any material, such as the rubber nozzle on the baby bottle cover;
Hard is the hardest natural diamond ever found on earth.
Laser drilling can save many processes than ordinary technology, especially when drilling micro holes.
Due to the superior performance of micro drilling, laser drilling has also been widely used in the manufacture of printed circuit board.
With the rapid development of computer technology, the printed circuit board in computer is developing towards multi-layer and high-density.
The interconnection between layers requires thousands of wiring holes on the chip.
The diameter and depth of these holes are in the order of microns, which is very difficult to process by traditional methods, and the yield is very low.
Laser drilling technology has successfully solved this problem.
In addition, laser drilling is widely used in diamond molds, watches, gem bearings, ceramics, rubber and other non-metallic materials. Special shaped holes can also be made by using light spots of different shapes.
The disadvantage of laser drilling is that the accuracy and surface roughness of the processed hole is not ideal.
(4) Laser marking
Marking is an indispensable processing technology in industrial production. Its purpose is to mark various identifying words, patterns or numbers on the surface or outer package of products.
The laser can mark products of various textures and shapes, and its most distinctive feature is still marking small objects.
Many integrated circuit chips are printed with company trademarks and relevant data. The marking area of these chips is generally only a few millimeters to more than ten millimeters.
In the past, the marking system with ink has some problems, such as low quality or unable to maintain permanently.
After laser marking, the marking is clear and not easy to fall off.
Another application similar to laser marking is laser engraving.
Sculpture is an ancient art, and traditional crafts are carved from the outside;
However, the laser can go deep into the interior of the workpiece without damaging the outer surface of the workpiece.
In August 1996, at the annual meeting of the international society of engineering optics held in Denver, the United States, Russian scholars showed a high-tech handicraft.
It is a glass brick slightly thicker than the ordinary brick, which is carved with several church buildings in the Kremlin, and the brick surface is intact.
Since the birth of laser technology, great progress has been made in the basic research of theory and experiment.
In recent years, laser research pays more attention to the development of lasers with better performance and more practical value and applies laser technology to various fields.
Laser processing technology has many unique advantages due to the superior performance of lasers.
With the rapid development of laser technology, the application of laser processing technology will be more and more extensive, and it will bring more and more changes to people’s life.