激光焊接技术

激光焊接技术 Stimulating electrons or molecules to produce concentrated and identical beams in the process of converting to energy, and Laser comes from the first letter of the Light Amplification by Stimulated Emission Radiation. Consists of the optical oscillator and oscillator medium is placed in the hole between both ends of the mirror. When the medium is excited by the highest energy state, it begins to produce the same phase light wave and reflects back and forth between the mirrors, forming a photoelectric cascade effect, amplifying the light wave and obtaining enough energy to start emitting the laser. Lasers can also be interpreted as a device that converts electrical energy, chemical, thermal, light, or nuclear energy into specific electromagnetic beams (ultraviolet, visible, or infrared). The transition form is easy to do in some solid, liquid, or gaseous medium. When these media are excited by atoms or molecules, they produce almost identical and almost single wavelength beams - lasers. Because of the same phase and single wavelength, the angle of difference is very small, and the distance can be quite long before the function of welding, cutting and heat treatment is highly concentrated. The world's first laser beam, produced in 1960 using flash bulbs to excite Ruby crystals, was limited to the heat capacity of the crystals, producing very short pulsed beams with very low frequencies. Although the peak energy of the instantaneous pulse can be as high as 10^6 watts, it still belongs to the low energy output. Using yttrium (ND) as the excitation element of yttrium aluminum garnet Shi Jing rods (Nd:YAG) can produce 1---8KW continuous single wavelength beams. YAG laser, 1.06uM wavelength, can be connected to the laser processing head by flexible optical fiber. The equipment is flexible in layout and suitable for welding thickness 0.5-6mm. The CO2 laser (wavelength 10.6uM) with excitation energy of CO2 and output energy of up to 25KW can be used to make 2mm sheet thickness single penetration welding. The industrial field has been widely used in metal processing. The utility model belongs to melt welding, and uses laser beam as energy source to impact on the welding piece joint. The laser beam can be guided by a planar optical element (such as a mirror), and then the beam is projected on the weld by means of a reflective focusing element or lens. Laser welding is non-contact welding, the operation process without pressure, but need to use inert gas, in order to prevent oxidation of molten pool, filler metal occasionally used. Laser welding can be combined with MIG welding to achieve large penetration welding with laser MIG composite welding. Meanwhile, the heat input is much smaller than that of MIG welding. (1) the amount of heat can be reduced to the minimum requirement. The range of the heat affected zone is small, and the deformation due to heat transfer is also the lowest. (2) the welding process parameters of 32mm thick plate and single channel welding have been certified, which can reduce the time required for heavy plate welding and even avoid the use of filler metal. (3) there is no need to use electrodes, no electrode pollution or damage concerns. And because it does not belong to the contact type welding process, the loss and deformation of the machines and tools can be minimized. (4) laser beam focusing, easy alignment and by optical instrument guide, can be placed in the appropriate distance from the workpiece, and can guide in the equipment or the obstacles around the work piece, and other welding rules can not play due to the limited space. (5) the workpiece can be placed in enclosed space (controlled by vacuum or internal gas environment). (6) the laser beam can be focused in a small area and can be welded with small and close spaced parts. (7) weldable materials can be made of a wide range of materials and can also be bonded to various heterogeneous materials. (8) it is easy to perform high-speed welding with automation, or digital or computer control. (9) when welding thin or thin wire, it is difficult to melt back like arc welding. (10) it is not affected by magnetic field (arc welding and electron beam welding is easy), and can precisely align welding parts. (11) two kinds of metal (12) which can be welded with different physical properties (such as different resistance), do not need vacuum, and do not need X ray protection. (13) in case of piercing welding, the width of the weld is as wide as 10:1 (14), and the switching device transmits the laser beam to a plurality of workstations. (1) the position of the weldment must be very accurate, be sure to be within the focus range of the laser beam. (2) when welding clamps need to be used, the final position of the weldment must be aligned with the spot welded by the laser beam. (3) the maximum welding thickness is limited, the penetration thickness is far more than 19mm of the workpiece, the production line is not suitable for the use of laser welding. (4) materials with high reflectivity and high thermal conductivity, such as aluminum, copper and their alloys, can be changed by laser. (5) when the laser beam welding of the energy high energy is carried out, it is necessary to use a plasma controller to expel ionized gas around the molten pool to ensure the re emergence of the bead. (6) energy conversion efficiency is too low, usually less than 10%. (7) the rapid solidification of the bead may have concerns about porosity and embrittlement. (8) equipment is expensive. In order to eliminate or reduce the defects of laser welding, the better application of this excellent welding method, put forward some other heat source and the laser welding process of composite, the main laser and arc, laser and plasma arc, laser and induction heat source composite welding, laser beam welding, dual beam laser welding etc.. In addition, put forward various auxiliary technical measures, such as laser welding with filler wire (can be divided into cold and hot wire welding wire welding), magnetic field enhanced laser welding, protective gas control of weld pool depth of laser welding, laser assisted friction stir welding etc.. (1) power density. Power density is one of the most important parameters in laser processing. With higher power density, the surface layer can be heated to boiling point and produce a large amount of vaporization in the microsecond time range. Therefore, high power density is advantageous for material removal processing such as punching, cutting and engraving. For a lower power density, the surface temperature reaches a boiling point, which takes several milliseconds. Before the surface evaporation, the lower layer reaches the melting point and is easy to form a good fusion welding. Therefore, in conduction type laser welding, the power density is in the range of 10^4~10^6W/CM^2. (2) laser pulse waveform. Laser pulse waveform is an important problem in laser welding, especially for thin plate welding. When the high intensity laser beam is drawn to the material surface, the metal surface will be reflected by the laser energy of the 60~98% and will be lost, and the reflectivity will change with the surface temperature. The reflectivity of metals varies greatly during the action of a laser pulse. (3) laser pulse duration. Pulse width is one of the important parameters of pulsed laser welding. It is an important parameter that is different from material removal and material melting, It is also a key parameter to determine the cost and volume of processing equipment. (4) the influence of defocusing quantity on welding quality. Laser welding usually requires a certain number of articles, because the power density at the laser spot is too high, which makes it easy to evaporate into holes. The power density distribution is relatively uniform on each plane leaving the laser focal plane. There are two kinds of defocusing modes: positive defocusing and negative defocusing. The focal plane is located at the top of the workpiece for positive defocusing, and vice versa. According to the theory of geometrical optics, when the positive and negative defocusing planes are equal to the welding plane, the power density of the corresponding plane is approximately the same, but in fact the shape of the weld pool is different. Larger melting depth can be obtained when negative defocusing occurs, which is related to the formation process of molten pool. Experiments show that laser heating 50~200us materials begin to melt, form liquid metal, and appear "partial vaporization", forming the city pressure steam, and at a very high speed jet, a dazzling white light. At the same time, the high concentration vapor moves the liquid metal to the edge of the molten pool and forms a depression in the center of the molten pool. When negative defocusing occurs, the internal power density of the material is higher than that of the surface, so it is easier to form a stronger fusion and vaporization, and to transfer the light energy to the material more deeply. Therefore, in practical application, when the melting depth is large, negative defocusing is used to weld the thin material, and the positive defocusing is used. 1, the use of manufacturing laser welding (TailoredBlandLaserWelding) technology has been widely used in foreign car manufacturing, according to statistics, in 2000 the global range of tailored plate laser welding production line more than 100, with an annual output of car component welding blank plate 70 million, and continues to grow at high speed. Domestic production of imported models Passat, Buick, Audi and so on, also adopted a number of cutting slab structure. Connecting Japan to CO2 laser welding instead of flash butt welding of steel coil steel industry, research in welding thin plate, such as the thickness of the foil, 100 microns to welding, but by YAG laser welding with special power output waveform is successful, shows the broad prospects of laser welding. Japan is also the world's first successful development of the YAG laser welding used in nuclear reactors, steam generator, tube maintenance, etc., in the country, Su Baorong also carried out the gear laser welding technology. 2, powder metallurgy field with the development of science and technology, many industrial technology of special material requirements, manufacturing method of materials metallurgy application has been unable to meet the needs. The powder metallurgy material with special performance and manufacturing advantages, in some areas such as the traditional metallurgy materials are being replaced by cars and planes and cutting tools in manufacturing industry, with the increasing development of powder metallurgy materials, and other parts of the connection problem has become increasingly prominent, so that the application of powder metallurgy materials limited. In early 80s, the laser welding processing into the field of powder metallurgy materials with its unique advantages, open up new prospects for the application of powder metallurgy materials, such as the connection method commonly used in powder metallurgy materials welding brazing diamond, because of low bonding strength, heat affected zone width especially can not adapt to high temperature and high strength caused by melting off by laser welding can improve the weld strength and high temperature performance. 3, the automotive industry in the late 1980s, kW laser successfully applied in industrial production, Now, the laser welding line has appeared in the automobile industry extensively, and has become one of the outstanding achievements of the automobile manufacturing industry. Germany's Audi, Mercedes Benz, Volkswagen, Volvo and other Swedish European car factory in early 1980s took the lead by laser welding roof, side frame body, such as sheet metal welding, GM, Ford and the United States in 90s Chrysler company has introduced the laser welding of automobile manufacturing, despite a late start, but the development is very fast. Italy Fiat in most components of the steel plate welding assembly used in laser welding, Japan's Nissan, Honda and Toyota Auto Body Co in the manufacture of auto body panels are used in laser welding and cutting process of high strength steel, laser welding fittings because of its excellent performance in the automobile body manufacturing have become increasingly used, according to the American metal market statistics, to by the end of 2002, the laser welded steel consumption will reach 70000t 3 times higher than in 1998. According to the characteristics of large batch and high automation in the automotive industry, laser welding equipment has been developed to high power and multi way. In the process of U.S. Sandia National Laboratory and PrattWitney joint research add metal powders and metal wire in the laser welding process, has done a lot of research on Application of beam technology Bremen where the use of laser welding Aluminum Alloy body frame, as in the weld filler metal added to help eliminate heat crack, improve welding to solve the problem of development speed, tolerance, the production line has been put into production in the factory of Benz Corp. 4 、 laser welding in the electronics industry has been widely used in the electronics industry, especially in the micro electronics industry. As the laser welding heat affected zone small heating quickly, low thermal stress, which is integrated circuit and semiconductor device shell package, show the unique superiority, in a vacuum device, laser welding has also been applied, such as Mo focusing electrode and stainless steel support ring, fast hot cathode filament assembly etc.. Elastic thin wall corrugated sheet sensor or thermostat in its thickness in 0.05-0.1mm, using the traditional welding methods are difficult to solve, TIG welding to welding, plasma stability, influence factors and the laser welding effect is good, widely used. In 1970s 5, biomedical laser tissue welding, the superiority of the fallopian tubes and vessels for laser welding Klink and the success of jain[13] welding and display, so that more researchers tried various biological tissue welding, and extended to other welding organization. The laser welding of neurological research at home and abroad mainly focus on the laser wavelength, and dose on functional recovery and the selection of laser solder and so on, Liu Tongjun made a basic research foundation of small blood vessels and skin of laser welding and the rat bile duct by welding research. Comparison of suture method and the traditional method of laser welding, laser welding has fast anastomosis, no foreign body reaction in the healing process, to maintain the mechanical properties of welding parts, repair organization advantages according to its original biomechanical properties and growth in the future will be more widely applied in biomedicine. 6. Laser welding has also increased gradually in other fields, especially in the welding of special materials in china, As of BT20 titanium alloy, HEl30 alloy, Li-ion battery laser welding, German glass machinery manufacturer GlamacoCoswig and IFW bonding technology and material experiment research institute has developed a laser welding technology for flat glass. Edit the advantages of this laser hybrid welding technology Laser hybrid welding technology has remarkable advantages. For the advantages of laser mixing, mainly reflected in: greater penetration / large gap welding; weld toughness better, by adding auxiliary materials influence on weld lattice organization; no burning phenomenon of back weld sag wear; wide application range; with the help of laser technology to replace less investment. For laser MIG welding, the advantages are as follows: higher welding speed, higher welding depth, less welding heat, higher weld strength, smaller weld width and smaller weld seam. The production process so that the stability of the whole system, equipment availability; weld preparation workload and welding processing workload; welding production time is short, low cost, high production efficiency; optical equipment with good performance. However, the cost of laser hybrid welding in power equipment is relatively high. With the further expansion of the market, the price of power equipment will be reduced, and laser hybrid welding technology will be applied in more fields. At least laser hybrid welding technology is a suitable welding process for aluminum alloy material, and it will become the main welding tool in a long time.