Development status and trend of laser processing

In principle, the laser can adapt to the processing and manufacturing of any material, especially in some special precision and requirements, special occasions and the processing and manufacturing of special materials play an irreplaceable role. This paper comprehensively reviews the development of laser manufacturing systems and the position of laser manufacturing technology in the modern industry. On the basis of analyzing the research trends of foreign countries, it is pointed out that the development trend of laser manufacturing technology will focus on the research and development of micro-structure, micro-etching, micro-tools, multi-functional micro-technology and micro-engineering. It can be predicted that the laser micro-manufacturing technology of three-dimensional micro-nano scale will become the mainstream manufacturing technology in the new century.

Foreword

Since the first laser was introduced in 1960, laser research and its application in various fields have developed rapidly. Its high coherence has been widely used in high precision measurement, material structure analysis, information storage and communication. The high monochromaticity of the laser can selectively excite some closely spaced energy levels in the field of photochemistry, and perform isotopic separation of heavy metals. The high directivity and high brightness of the laser can be widely used in the manufacturing industry (large to spacecraft, Aircraft, automotive industry, micro-electronics, information, biological cell separation and other micro-technologies). With the continuous innovation and optimization of laser devices, new stimulated radiation sources, and related processes, especially in the past 20 years, laser manufacturing technology has penetrated into many high-tech fields and industries, and has begun to replace or transform some traditional processing industries. .

Laser manufacturing technology includes two aspects, one is the technology of manufacturing laser light source, and the other is the manufacturing technology using laser as a tool. The former provides high-performance, stable and reliable lasers and processing systems for the manufacturing industry. The latter uses the former for various processing and manufacturing, providing a broad application space for the continuous development of laser systems. Both are indispensable links in laser manufacturing technology and cannot be neglected. Laser manufacturing technology has many advantages not found in traditional manufacturing technologies and is a green manufacturing technology that is consistent with sustainable development strategies. For example, less material waste, low manufacturing costs in large-scale production; programmed control (automation) according to the production process, high production efficiency in large-scale manufacturing; close to or reaching "cold" processing state, enabling conventional technology to be performed High-precision manufacturing; adaptable to processing objects, and free from electromagnetic interference, low requirements for manufacturing tools and production environment; low noise, no harmful rays and residuals, little pollution to the environment during production, etc. . Therefore, in order to adapt to the industrialization of high-tech in the 21st century and meet the needs of macro and micro manufacturing, it is imperative to research and develop high-performance light sources. At present, lasers with characteristics such as ultra-ultraviolet, ultra-short pulse, ultra-high power and high beam quality are being actively developed. Especially the laser light source that can meet the requirements of micro-manufacturing technology has attracted much attention and has formed an international competition. It can be predicted that laser manufacturing technology will become a high-tech that is rapidly popularized in the 21st century with its irreplaceable advantages.

1. Development of laser manufacturing systems

The laser system used in the manufacturing industry, that is, the laser manufacturing system, generally consists of a laser, a laser transmission system, a laser focusing system, a control system, a motion system, a sensing and detecting system, and the core thereof is a laser.

Laser as a heat source or light source (energy) is a "tool" or "tool" in laser manufacturing. The quality of the “tool” or “tool” directly affects the results of the manufacturing process. The quality of the laser beam can be expressed by the beam far-field divergence angle, the beam focusing characteristic parameter value Kf, and the diffraction limit multiplier M2 (M) or the beam transmission factor K value. For small power lasers, the working material is uniform and stable, and the basic mode output can be realized. The beam cross-section energy distribution is Gaussian, and it remains unchanged during transmission, and the beam quality is good. For high-power lasers, it is generally difficult to obtain a base. The mode output is often a multimode laser beam, and the laser beam quality is deteriorated. At present, high-power lasers commonly used in the industry include CO 2 lasers and YAG lasers. High-power lasers have a wide range of industrial applications. Laser cutting and laser welding require excellent beam quality, and high-power lasers that pursue high beam quality are the goal of industrial lasers.

From the emergence of the first CO 2 laser in 1964 to the present, after nearly 40 years of development, from sealed CO 2 lasers, slow axial CO 2 lasers, cross-flow CO 2 lasers, to high-frequency Rhodes pump-type fast axes. Flow, RF turbo-type fast axial current and the development of the current diffusion type Slab CO 2 laser can be seen. On the one hand, the laser output power is continuously increased, the volume is continuously reduced, and on the other hand, the efficiency of the laser is continuously improved, and the beam quality is increasingly The better. The intensity distribution of the diffused Slab CO 2 laser beam is close to the Gaussian distribution, and it has excellent beam quality. The drift of the focus in the enlarged laser processing working area is very small, which is very beneficial for large-scale laser transmission and aggregation. Cutting applications for large workpieces are very important.

Industrial solid YAG lasers have also been subjected to pumping from small power lamps (rods), lamp pumping (slats), dual lamp pumping (multiple bars) to fiber pumping (rods), semiconductor pumping (rods) and flakes The process of a solid laser. Due to the thermophysical properties of the working substance, the YAG laser beam quality mode is relatively poor. How to improve beam quality and laser power is still the main problem faced by YAG lasers.

Of note is the semiconductor laser that has been developed in recent years. Semiconductor lasers have broad application prospects such as miniaturization, high frequency, good coupling with optical fibers, and easy modulation.

The widespread use of laser manufacturing technology in different industries depends to a large extent on the performance and process of laser processing systems. The research and development of new light sources, processing systems and processes in some countries in Europe, America and Japan have never cooled down. With the research and development of laser working substances, the improvement and innovation of device and unit technology, lasers characterized by high performance, wide band and high power have made vigorous development, such as KrF and ArF excimer lasers with ultraviolet light output. Frequency doubled laser, etc. In particular, the emergence of high-power fiber lasers has made mobile positioning processing more convenient for laser manufacturing.

2. Laser manufacturing technology application

Compared with traditional manufacturing technology, laser manufacturing technology has outstanding advantages mainly in the following aspects:

(1) Processing of special requirements for special materials

Laser welding has outstanding advantages over most conventional welding methods. The high concentration of laser energy and the extremely rapid heating and cooling process can destroy the stress threshold of some refractory metal surfaces, or rapidly melt the high thermal conductivity and high melting point metals to complete the welding of certain special metal or alloy materials. There is no mechanical contact during the laser welding process, it is easy to ensure that the welded part is not deformed by thermal compression, and the possibility of unrelated substances falling into the welding part is eliminated; if a laser system with a large depth of focus is used, welding in special occasions can also be realized, for example The software controls the long-distance online welding to be isolated, the high-precision anti-pollution vacuum environment welding, etc.; the maximum amount of material can be melted without evaporation of the material surface to achieve high-quality welding. The above characteristics are difficult or impossible to achieve with traditional welding tools and methods. At present, laser welding technology has been widely used in some special industries such as automobile, national defense, and aerospace. For example, in some European countries, the welding of some special materials such as high-end automobile shells and bases, aircraft wings, spacecraft fuselage, etc., the application of laser has basically replaced the traditional welding tools and methods.

(2) Special precision processing and manufacturing

The high precision referred to here is mainly reflected in the control of the amount of heat conduction effect inside the material, in addition to the precise positioning in the usual sense. One of the distinguishing features of lasers is the ability to take continuous and pulsed outputs. Taking solid drilling and cutting as an example, the high concentration of laser energy and the fast heating and cooling characteristics can achieve the universal requirements of traditional technology, and the processing is a thermochemical process. It is important to note here that photochemical dynamic processes close to "cold" processing can be achieved by pulsed laser irradiation. On the one hand, the time width of the pulse is selected, so that the heat conduction process and the thermochemical reaction in the material are not too late; on the other hand, by controlling the power density and pulse counting of the laser, the determined removal depth is achieved as required, thereby realizing a high-precision "line". Cutting and "dot" drilling. Some countries in Europe and the United States have generally adopted this pulsed light manufacturing technology in many special requirements fields and industries.

(3) Microfabrication manufacturing

The most successful application of laser micromachining technology was in the field of microelectronics developed in the second half of the 20th century. As one of the unit micromachining technologies in the microelectronics integration process, laser micromachining has now formed a fixed mode and put into mass production. In addition, areas where advantages can be highlighted include the manufacture of precision optical instruments, the writing and storage of high-density information, and the medical treatment of biological cells. The laser of the appropriate wavelength is selected to obtain high-quality beam, high stability, and small-size focal spot output through various optimization processes and focusing systems that approximate the diffraction limit. Using its sharp and sharp "light knife" feature, it can be used for high-density micro-marking and high-density information. It can also use the "force" effect of its optical trap to carry out the clamping operation of tiny transparent balls. For example, high-precision grating engraving (precision lithography); simulation pattern (or text) and control through CAD/CAM software for high-fidelity marking; use of the "binding force" of the optical trap to perform moving operations on biological cells (Biolight). It is worth mentioning that laser recording of high-density information and light manufacturing of micro-mechanical components.

Whether it is digital recording or scanning recording, or analog recording of images and text, laser recording method (lithography) has special advantages and has made important breakthroughs, taking digital recording as an example: 1 high information recording density (107 ~ 108bit) /cm2 or more), the recording slot width is 0.7μm and depth is 0.1μm, which is more than two orders of magnitude higher than the magnetic recording density; 2 recording, retrieval and reading speed are fast, single channel reaches 50Mbit/s, multi-channel can reach 320Mbit/ s; the retrieval and reading speed of information is much less than 1 second; 3 low cost and long service life. In terms of light manufacturing of micro-mechanical components, it has been listed as a research project in foreign countries in recent years, and has become a hot spot in the future research of high-tech. Japan has used laser technology to create microscopic three-dimensional "nano-bovines", which shows that Japan has made great progress in the micro-nano-scale three-dimensional laser micro-forming mechanism. The Institute of Laser Engineering of Beijing University of Technology has applied excimer lasers and has processed micro-gears of 10 teeth / 50 μm and 108 teeth / 500 μm through the mask method.

(4) Efficient automatic process manufacturing

Thanks to the controllability of the laser output, the laser manufacturing process enables intelligent control of automated processes through software. According to the needs of the production nature, it is possible to carry out the positioning control of the processing table or the robot hand positioning control of the processing head through the optical fiber transmission of the laser, thereby realizing efficient automated and intelligent laser manufacturing. For example, three-dimensional positioning and cutting of automobile body panels, welding of body framing, welding of gear plates and other components, etc., have formed a one-stop production line for laser processing and assembly.

3. Laser micro-manufacturing will become the mainstream technology of high-tech industry in the new century

Richard Feynman, a Nobel laureate in physics, predicted in the late 1950s that manufacturing technology would evolve from large to small, using small machines to make small machines that could make more Small machines, and thus in the small-scale field to create a batch of processing tools from generation to generation. The revolution in science and technology confirms Feynman's prophecy. The emergence of microelectronics technology is the most convincing example. From the integration to large-scale integration to the rapid development of ultra-large-scale integration technology, it has been shown that the future manufacturing technology will surely march in the direction of “smaller and smaller”. In the 20th century, the main functions of electronic technology were highly integrated, forming the high-tech industry marked by the century and infiltrating into various fields of human activities. The 21st century is an integrated technology of multiple disciplines, namely micro-nano manufacturing and micro-system technology that integrates microelectronics, micro-optics, micro-mechanics, and signal processing units of sensors and actuators. Micro-nano manufacturing technology and functional micro-system will become a milestone in the 21st century high-tech and industry. Its development will enable human beings to reach a new height in their ability to recognize and transform nature, leading to huge human life and social material civilization and science and technology. change.

In the late 1980s, the United States realized the urgency of micro-nano manufacturing technology and micro-system research, emphasizing that the United States "should be ahead of competition with other countries in such a new important technology field" and launched the first study. plan. After entering the 1990s, Japan has also begun a large-scale research and development program for “micro-mechanical technology” with a total investment of 25 billion yen for 10 years. In order to find a technical way to adapt to the micro-machining of micro-system manufacturing, the European Union organized the Hanover Laser Center in Germany and related research institutions in France, Switzerland, Italy and other countries to conduct cooperative research and development. At present, international competition has formed in the micro-nano manufacturing technology, and the battle for the global market of high-tech industries in the new century has begun.

The current research progress has also shown that laser micro-technology is a three-dimensional micro-manufacturing technology with potential for development and will become one of the mainstream technologies for micro-system manufacturing. Since 2002, the German Ministry of Education and Research has launched a five-year optical funding program, an important part of which is the research of laser micro-manufacturing technology. The plan's capital investment in 2002 was only 0.478 billion euros, and the investment in the following years increased by a certain percentage. Germany adopts decomposed unit technology research. In the micro-manufacturing of light and the hardware of micro-nano technology, the goal of five-year research planning is to locate the new laser source and ultra-fine focusing system to achieve a spectral range of 150-0.1 nm. Ultraviolet output and a highly reproducible near-field lens that can cross the diffraction limit with a resolution of less than 100 nm.

Micro-nano light manufacturing and related technologies are the main areas of current international competition. The scale and technical level of the microelectronics industry has become one of the important indicators to measure the comprehensive strength of a country. Laser micro-technology will play a greater role in this field. In the development of modern light manufacturing, opportunities and challenges coexist in China. We must seize the opportunity to meet the arrival of the era of light manufacturing in the new century.

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