Complementarity between the hottest electron beam

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Complementarity of electron beam processing and laser processing

ten years after the advent of electron beam welding, Osaka University in Japan developed the world's first 1kW CO 2 laser processing machine in 1967, which was used for welding and cutting thin plates. In the past 30 years, laser processing has moved from the laboratory to the practical stage, and has entered various fields originally processed by electron beam, which has a great momentum to replace electron beam processing. However, practice has proved that laser and electron beam, as high-energy density heat sources, in addition to having many same technical characteristics, still have different characteristics in terms of technical and economic performance for different applications. Therefore, in practical application, reasonably selecting one of the processing means has become a very necessary process selection process

this paper will illustrate the complementarity of electron beam processing and laser processing through some application examples, so as to provide reference for rational application

I. The rapid development of low-power laser processing

after laser enters the processing field, it has made continuous efforts to improve the output power. Axial flow above 1kW, CO2 above 2kW and YAG laser above 300W have been widely used in industrial production lines such as cutting, welding and heat treatment. However, in recent years, small power lasers have developed faster. In terms of quantity, sealed off CO2 lasers and lamp pumped YAG lasers used for processing have increased by 20 ~ 25% every year. The applications of excimer lasers, diode lasers and diode pumped solid-state lasers in the field of material processing have also been developed. From 1994 to 1996, they doubled every year

previously, low-power lasers were mainly used for marking, drilling, exposure, annealing and resistance adjustment in semiconductor and microelectronic manufacturing industries. In other industrial sectors and the processing of daily necessities, although it is also used for various processing such as marking, non-metallic cutting, thin piece welding and punching, the overall quantity is not large. Sealed off CO2 laser has the advantages of small size, convenient use and low price, but it is not widely used in material processing. First, because of the lack of understanding of its potential application value; Second, it is limited by its small output power. In recent years, sealed off RF excited CO2 lasers have developed rapidly, creating conditions for exploring new application fields. American coherent company has developed a slow flow RF excited CO2 laser with a continuous output power of 500W (pulse power of 1.5KW), and its overall size is only 280 × two hundred and forty × 1200mm, weight 61kg. The service life after one-time inflation is up to 20000 ~ 25000 hours, and has been used for cutting die-cutting plates and ceramic substrates

The emergence of three-dimensional rapid prototyping technology has opened up an extremely important application field for low-power CO2 lasers. In addition to UV laser exposure, it is also used as a heat source for laser sintering and laser paper cutting and re hot pressing. This mold manufacturing technology has the characteristics of low cost, short cycle and high precision, and is widely used

the output of glass (or quartz) tube sealed off lasers in China is large and the cost is lower. In the past, there was almost no market for lasers above 40 ~ 50W, except for low-power (below 25W) lasers used for medical devices, scientific research and export. In view of the advantages of this device in our country, we have successively developed a low-power CO 2 laser cutting machine, scoring machine and marking machine. The cutting machine and the engraving machine adopt a 1.6m long laser tube with an output power of 70W, and use the flight optical external light path system, special cutting and engraving software, 486 computer control, special text programming software and general AutoCAD drawing software. Dozens of simplified and traditional Chinese characters and English letters are installed in the character programming software, which can be called directly. Complex graphics and special words can be scanned and input by scanner. The cutting and engraving files adopt DXF file format, which can be easily input and output in AutoCAD, and can also be easily converted and compatible with CorelDRAW and popular lettering software on the market. The cutting machine is mainly used to cut non-metallic materials such as plexiglass, plastic, plywood, paper, cloth, mica board, etc. the thickness of cutting plexiglass can reach 10mm. The engraving machine is mainly used for trademark and character engraving of mechanical parts such as steel and cast iron. Its engraving depth is deeper than that of general YAG marking, and the equipment investment and operation cost are much lower than the latter. Galvanometer CO2 marking machine is used for non-metallic marking, especially for wood, plastic, ceramics and other materials, such as marking on the surface of plastic or ceramic encapsulated integrated circuits

compared with traditional processing methods, laser processing usually has higher production efficiency, better processing quality and more economical processing cost. Compared with electron beam processing, the equipment cost is low. A typical example is the welding of automotive engine spark plugs. The United States, Japan and other countries used electron beam welding to replace traditional spot welding, but now YAG laser spot welding is used, which has higher welding efficiency and lower cost. The monthly output of a single equipment can reach 40000 pieces. The low processing cost also makes some low value products produced by laser processing. For example, in the production of window bolts in the construction industry, 1kW CO 2 laser welding is used, and the welding speed can reach 100m/min. By 1986, 22 such production lines had been put into use in the United States. The packaging of AA battery is usually resistance spot welding, but the electrode should be polished and cleaned with sandpaper every 15 ~ 30 minutes in the production process, and it also takes 30 minutes to replace the electrode every day. Using YAG laser spot welding saves these time, and the production efficiency is 30% higher than that of resistance welding. Cardiac pacemakers, pressure sensors and other products have been sealed and welded by electron beam, and the rollers for concave printing and textile printing and dyeing have also been engraved by electron beam. Now they are all processed by laser. Laser processing is also more used in high-precision hole drilling, micro hole drilling and VLSI exposure and resistance adjustment in microelectronics, but it cannot replace electron beam for a long time. In high-speed drilling, the pulse frequency of the electron beam is high, and the electron beam can be deflected at the moment of drilling, so that the electron beam can deflect synchronously with the high-speed moving workpiece, and holes with good roundness can be punched (laser can also realize this process, but the speed is much lower), and 20000 holes can be punched per second

micromachining such as VLSI, integrated optical path, surface acoustic wave devices and extremely high-precision grating engraving increasingly rely on electron beam processing and laser processing. At present, electron beam processing is still used in nano scale processing and direct plate making. However, the deep UV exposure of excimer laser has been able to produce 256mbits DRAM chips. Excimer lasers are also used to directly manufacture various micro shaped components, such as comb shaped components, sensing components and control components used in microsurgery. The shape of surgical "comb" element made of polyester sheet is only 0.75 × one point one × 0.075 cubic mm. Excimer lasers can also cut, punch holes or mark materials similar to hair, including shape processing. With excimer laser or solid laser, 25 can be made on copper clad plate μ The production rate of M small holes is 10000 per minute. From the close comparison between the drilling cost and the industry, it can also be seen that for holes smaller than 0.2mm, the cost of mechanical drilling increases rapidly. When the aperture is as small as 25 μ M, the cost of mechanical drilling is as high as $17.9 per hole. While YAG laser drilling, the hole diameter is from 0.2mm to smaller, and the cost gradually decreases, drilling a 25 μ M hole is only $0.43

it can be seen that low-power laser processing has obvious advantages over electron beam processing in terms of application scope and economic performance. In addition to electron beam exposure, laser has the trend to replace electron beam

second, high-power electron beam processing is unique

due to the low energy conversion efficiency of laser (the conversion efficiency of industrial laser is usually only about 10%, while the electron beam can reach 80 ~ 90%) and other technical limitations, the power of laser can not be very high, usually not more than 10kw. At present, the most powerful industrial CO2 laser is developed by the French Welding Research Institute, with a power of 45KW. The operation stability and reliability of high-power lasers and the flexibility of parameter control are also inferior to electron beams. In addition, economy is an important factor that restricts the development and application of high-power laser equipment. Compared with the same level of electron beam generator, the price of small and medium power laser is lower. However, with the increase of power, the price of lasers increases rapidly. In terms of 5kW level, the prices of foreign laser and electron beam equipment were roughly the same in 1988. However, in recent years, with the improvement of laser manufacturing level, the cost is relatively reduced, and the application of high-power lasers is increasing. This is clearly reflected in the welding of automotive transmission gears. Except Japan, the United States, Germany, France, Italy and other countries have largely used lasers to replace electron beam welding. In previous years, gear laser welding mostly used 1.7 ~ 2kW axial flow or 6kW transverse flow CO 2 laser. Now, 2 ~ 3KW axial flow or 9kw transverse flow CO 2 laser is mostly used. The increase in equipment investment was offset by the increase in productivity. For example, Chrysler now has 24 lasers for production, and the power of the lasers used for transmission welding has also been increased to 14kw, and the worktables have been changed to double worktables, with an average welding cycle of only about 13 seconds per piece. Despite the rapid development of laser technology, high-power laser is still far from being compared with electron beam. Generally, the electron beam welding gun with a power of more than 30kW is used as a high-power welding gun, and its welding depth is usually 50 ~ 80mm, while the 45KW laser with the world's largest power mentioned above can only weld 40mm. At present, the power of industrial high-power electron beam welding gun has reached 200kW, and the penetration can reach hundreds of millimeters. High power electron beam welding has been widely used in power generation equipment, petrochemical equipment, mining machinery, heavy vehicles, aerospace vehicles, atomic energy equipment and shipbuilding industry. The typical application is to weld load-bearing parts such as reactor matrix and steam turbine rotor shaft, with a penetration of more than 300mm. Compared with laser welding, another important feature of electron beam is that it is not affected by the reflection of repair materials, so it can easily weld gold, silver, copper, aluminum and other materials that are difficult to laser weld. For example, oxygen free copper parts in electronic devices, high current copper bars, copper tungsten contacts and aluminum pistons of high-power diesel engines can all get welded joints with high strength and deep penetration

in order to make high-power electron beam welding better used for large workpieces, technologies such as large vacuum chamber, local vacuum and non vacuum are developed synchronously with high-power electron beam. The volume of large vacuum chamber reaches tens to hundreds of cubic meters, and the largest reaches 800 cubic meters. Such a vacuum chamber can weld giant components with a diameter of 10 meters. Although the cost of large vacuum chamber is expensive, the excellent welding performance and extremely high welding speed of high-power electron beam welding can make the comprehensive cost (including equipment investment and operation cost) lower than the traditional welding method. It is estimated that when the welding depth exceeds 50mm, the cost of electron beam welding can be lower than that of narrow gap welding and submerged arc welding. The deeper the welding depth, the greater the price difference. When the welding depth exceeds 150mm, the comprehensive cost of electron beam welding is only 1/2 ~ 1/3 of narrow gap welding and submerged arc welding. Most of the large vacuum chambers are used to weld the casing, turbine disk, wing girder and steam turbine diaphragm in power generation equipment in aerospace and spacecraft. These products are often very demanding for welding. For example, the single welding depth of steam turbine diaphragm can reach more than 150mm, and the shroud where the weld is located is very narrow, which is very easy to deform

for products with flat shape, such as the splicing of hull steel plates, oil storage tanks, gas storage tanks and raw materials

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