Another example is the welding of molybdenum and molybdenum. The electron beam bombardment is closely related to the strength of the weld. If the bombardment is in the middle of the weld, its strength is 66.6 N/mm2, which belongs to the intergranular fracture (Fig. 5(a)); When the beam bombardment is about 0.2 mm on the Nb side, the weld strength is greater than 279.5 N/mm2, which is a transgranular fracture (Fig. 5(b)). This is because Nb has good plasticity and a certain gas absorption capacity, which will reduce the gas composition at the grain boundary and the weld quality is high. The crystal grain of the molybdenum crystal recrystallizes, and the grain boundary impurities are affected. After the molybdenum fusion welding It is brittle [5].
(3) Electron beam defocus welding. For the welding of some workpieces, the electron beam is slightly defocused, such as the welding of the mesh workpiece. If the electron beam is too finely focused, the workpiece is easily cut during welding.
6. Preheating and annealing
For the welding of certain materials or structural parts, in order to prevent the occurrence of cracks, the workpiece to be welded needs to be preheated or post-weld annealed.
(1) Electron beam preheating and annealing. The workpiece is bombarded with a smaller power and defocused electron beam to provide a certain temperature for the purpose of preheating or annealing. The specific process (temperature difference) depends on the material and the structure of the workpiece, as it also relates to the phase change of the material structure.
(2) Auxiliary preheating and annealing. The workpiece is preheated and annealed using an electric resistance furnace or a graphite furnace. When we conducted the welding process test of ceramics and metals, we put a lot of effort into the trial production of the resistance furnace (Fig. 6) and the operation of the preheating annealing process (Fig. 7). In the end, good results were achieved and the success of ceramic and metal welding was achieved [6].
7. Add material (filled wire)
Usually, electron beam welding does not use any solder, but for some special structure workpieces and some dissimilar materials, in order to achieve the success of welding, in addition to the method of using electron beam bombardment on the side of the weld, a third type can be added. Material, that is, the method of filling the wire.
(1) Brazing. The third material used here acts as a solder, that is, the material is bonded and the two parts are bonded.
Together, or have some diffusion on the surface of the weld, the workpiece substrate has not melted. As shown in the pinion welding shown in Figure 8, in order to prevent excessive deformation of the teeth and the shaft, the electron beam bombardment only melts the brazing material (silver-copper brazing material), bonds the pinion gear to the shaft, and the joint strength meets the design requirements ( The torque strength is greater than 118 N.cm), and the amount of deformation is small (the amount of runout of the shaft is less than 0.05 mm).
(2) Wire filling welding. For dissimilar materials with poor weldability, in order to avoid cracks, a good metallographic structure can be obtained, and a filler material can be added to the weld to play a transitional role. When welding, the material and the local substrate are simultaneously melt. The hardness of the weld, the composition and microstructure of the alloy elements, depends on the welding parameters and the filler material used. The filling material has a shape of a wire or a sheet; the automatic wire bonding machine uses a wire feeding mechanism for wire fusion welding. The composition of the filler material depends on the material of the workpiece to be welded, and must be considered to form a suitable composition (such as a solid solution, etc.) with the substrate, such as a nickel-based material, a silver-based material, a silicon-aluminum material, or the like.
8. Other factors
In the actual welding process, in order to solve the problems encountered and obtain good welding performance, there are still many factors to be aware of, although for each workpiece, it does not have to be all-inclusive, but it still has a role in some cases.
8.1 Influence of vacuum
According to the vacuum degree of the welding chamber where the workpiece is located, it can be divided into high vacuum, low vacuum (including partial low vacuum) and non-vacuum (local protective atmosphere) welding. The weld depth of the workpiece and the quality of the weld are very different. Which state of welding is used depends on the material and structure of the workpiece being welded.
8.2 Electron beam tracking welding
For curved or skewed welds, it is appropriate to use an electron beam to automatically track the weld. It uses an electron beam to scan the front of the weld at an extremely fast speed, and collects secondary electrons on both sides of the weld as a signal to control the tracking weld (electron beam shift or table movement). During the test, we used a memory oscilloscope to take a picture of the voltage waveform of the secondary electronic signal during normal operation, and at the same time obtained the success of the welded curve weld (Fig. 9).
8.3 Electron beam yaw welding
Sometimes the workpiece to be welded is fixed on the workbench, and the programmed yaw electron beam is used to weld around the weld of the weldment. It is suitable for the symmetrical weld of the smaller and thinner workpiece, as shown in Fig. 10. The square waveguide is welded to the flange. This working process is relatively simple, and is suitable for multi-station welding of multi-station devices, which is helpful for improving production efficiency.
8.4 Electron beam scanning welding
For thicker workpieces, in order to make welds
The gas in the molten pool can be fully discharged to reduce welding
It is meaningful to use a scanning electron beam for the pores or cracks in the slit. It is essentially an electron beam that agitates the weld pool to allow gas to escape. Scanning welding is also possible in order to achieve successful welding of dissimilar materials. The waveform, frequency and amplitude of the electron beam scan are determined on a case-by-case basis.
8.5 pulse welding
In order to prevent overheating of the workpiece to be welded and other special purposes (such as increasing the aspect ratio of the thin weld), pulsed electron beam welding is suitable. Parameters such as beam peak value, pulse width, repetition frequency, average input power, and welding speed are determined by experiments.
8.6 modified welding
Some workpiece welds require a high finish or for other reasons, and a modified welding process can be used. In general, the electron beam power density of the modified solder is lower than the power density of the actual solder.
9. Conclusion
Electron beam welding is a high-tech processing method. It belongs to advanced manufacturing technology and welding equipment (welding machine) is more and more advanced. However, as a process technology, factors affecting welding quality need to be explored in practice and given comprehensive analysis.
Through long-term experiments and applied research, we have found some general rules and special experiences. Although it is impossible to cover all of them, there may be some help for the workers engaged in electron beam welding.
references
1. Lin Shichang, Qiu Ningmao. Some application prospects of electron beam welding technology and comprehensive comparison with laser welding. Proceedings of the 6th Academic Conference of China Electrotechnical Society, 1999, Beijing, p467-472
2.Schultz H. Electron beam welding. Abington Publising, Cambridge England, 1993
3.Setsuji Minehisal, et al. Proceedings of the International Conference of the International Institute of Welding, 1986, Tokyo Japan
4.Lin Shichang, Fan Binglin, Hu Zongyao, Wang Xiumel, Zhang Yansheng, Packaging technology of ultrathin film sensors by electron beam welding. Sensors and Actuators, 1993 (35 ), p283-285
5. Lin Shichang (Fan Shichang), Fan Binglin (Fan Binglin), Guan Zuoyoa (Guan Wei). Proceedings of the International Conference of the IIW, 1896, Tokyo Japan. Electron and Laser Beam Welding. Pergamon Press, 1986, p227-235
6. Lin Shichang (Xiao Shichang), Xiao Naiyuan (Xiao Naiyuan). Proceedings of 4th International Colloquium on Welding and Melting by Electron and Laser Beam. Cannes France, 1988, p251-258
About the Author:
Lin Shichang, Researcher, Institute of Electronics, Chinese Academy of Sciences, Director of China Electrotechnical Society and Chairman of Electron Beam Ion Beam Committee, Member of Senior Committee of China Electronics Society and Vice Chairman of Welding Special Committee, High Energy Beam and Special Welding Committee of China Welding Society Member of the committee.
Previous page
stainless steel commercial flat washers are used under bolt heads or nuts to increase the bearing surface area, or to offer protection so that the nut or bolt can be rotated without distortion of the bearing surface. Flat washers are also used to give tightness to a joint, to prevent leakage, and especially to distribute pressure under the head of a bolt or nut. Dimensional specifications are governed by ASME B18.21.1. Commercial flat washers generally have a larger outer diameter than SAE (Society of Automotive Engineers) flat washers, and can be utilized in nearly any application. stainless steel fasteners are commonly used in applications that require general atmospheric corrosion resist ance, such as chemical and food processing equipment. Stainless steel has a higher corrosion resistance than carbon steel.
Stainless Steel Washer,Ss Washer,Stainless Steel Square Washers,Black Metal Washers
Taizhou Hongchuang Hardware Co., Ltd. , https://www.taizhouhongchuang.com