Fusion welding technology sharing, gas welding, gas pressure welding, electroslag welding, laser welding and other technical points.

【Summary Description】 Gas welding: A fusion welding method that uses the heat generated by the combustion of combustible gas in oxygen to melt the welding place of the base metal to realize the connection. Gas welding is a welding method using gas flame as heat source. The oxygen-acetylene flame with acetylene gas as fuel is the most widely used. Because the equipment is simple and easy to operate, but the heating speed and productivity of gas welding are low, the heat affected zone is large, and it is easy to cause large deformation. Gas welding can be used for the welding of many ferrous metals, non-ferrous metals and alloys. Combustible gas: acetylene, liquefied petroleum gas, etc. Taking acetylene as an example, its flame temperature can reach 3200 ℃ when burning in oxygen. there are three kinds of oxygen acetylene flame: ① Neutral flame: the volume mixing ratio of oxygen and acetylene is 1~1.2, acetylene is fully burned, suitable for welding carbon steel and non-ferrous alloys. ② carbon flame: oxygen and acetylene volume mixing ratio is less than 1, acetylene excess, suitable for welding high carbon steel, cast iron and high speed steel. ③ oxidation flame: oxygen and acetylene volume mixing ratio is greater than 1.2, excess oxygen, suitable for brass and bronze brazing. The gas welding flame temperature is low, the heating speed is slow, the heating area is wide, the welding heat affected zone is wide, the welding deformation is large, and the molten metal is poorly protected during the welding process, and the welding quality is not easy to guarantee, so its application has been rare. However, gas welding has the characteristics of no power supply, simple equipment, low cost, convenient movement and strong versatility, so it has practical value in the field work without power supply. At present, it is mainly used for welding of thin steel plate (thickness 0.5~3mm), copper and copper alloy and repair welding of cast iron. 2 Air pressure welding Gas pressure welding and gas welding, gas pressure welding is also a gas flame as a heat source. During welding, the ends of the two abutting workpieces are heated to a certain temperature, and then sufficient pressure is applied to obtain a firm joint. Is a solid phase welding. Gas pressure welding without filler metal, commonly used in rail welding and steel welding. 3 electroslag welding Electroslag welding is a welding method using the resistance heat of slag as energy source. The welding process is carried out in the vertical welding position in the assembly gap formed by the end faces of the two workpieces and the water-cooled copper sliders on both sides. During welding, the end of the workpiece is melted by the resistance heat generated by the current through the slag. According to the shape of the electrode used in welding, electroslag welding is divided into wire electroslag welding, plate electroslag welding and melting tip electroslag welding. The characteristics of electroslag welding: in the welding process of electroslag welding, except for an arc process at the beginning, the rest are stable electroslag process, which is essentially different from submerged arc welding. The advantages of electroslag welding are: large thickness of weldable workpieces (from 30mm to more than 1000mm) and high productivity. It is mainly used for welding of butt joints and T-joints in section. Electroslag welding can be used for the welding of various steel structures, and can also be used for the welding of castings. Due to the slow heating and cooling of electroslag welding joints, the heat affected zone is wide, the microstructure is coarse and tough, so it is generally necessary to normalize after welding. the limitations of electroslag welding: (1) Due to the large welding pool, slow heating and cooling, it is easy to overheat in the weld and heat affected zone to form coarse tissue, so electroslag welding usually uses normalizing treatment to eliminate coarse grains in the joint after welding. (2) electroslag welding is always carried out by vertical welding, not flat welding, electroslag welding is not suitable for workpieces with a thickness of less than 30mm, and the weld should not be too long. Classification and application of electroslag welding Classification of electroslag welding: wire electrode electroslag welding, plate electrode electroslag welding, melting tip electroslag welding and tube electrode electroslag welding, etc. Wire electrode electroslag welding is the most commonly used electroslag welding method. It uses welding wire as electrode. According to the different thickness of weldments, one or more welding wires can be used. The thickness of weldments that can be welded by single wire welding is 40~60mm. When the thickness of weldments is greater than 60mm, the welding wire should swing laterally. Three wires can weld 450mm thick weldments. Wire electrode electroslag welding is mainly used for welding thickness of 40~450mm weldments and longer weld weldments, can also be used for large weldments of the ring weld. Application: mainly used in heavy machinery manufacturing industry, manufacturing forging-welding structure and casting-welding structure, such as heavy machine tool base, high pressure boiler, weldment thickness is generally 40~450mm, the material is carbon steel, low alloy steel, stainless steel and so on. 4 Electron beam welding Electron beam welding is a method of welding with the heat energy generated when the concentrated high-speed electron beam bombards the surface of the workpiece. In electron beam welding, an electron beam is generated by an electron gun and accelerated. Commonly used electron beam welding are: high vacuum electron beam welding, low vacuum electron beam welding and non-vacuum electron beam welding. The first two methods are carried out in a vacuum chamber. The welding preparation time (mainly the vacuum time) is longer, and the workpiece size is limited by the size of the vacuum chamber. Compared with arc welding, the main characteristics of electron beam welding are large weld penetration, small weld width and high weld metal purity. It can be used for precision welding of very thin materials and for welding of very thick (up to 300mm thick) components. All metals and alloys that can be fusion welded by other welding methods can be welded by electron beam welding. It is mainly used for welding of products requiring high quality. It can also solve the welding of dissimilar metals, easily oxidized metals and refractory metals. But not suitable for high-volume products. Electron beam welding machine: The core is the electron gun, which is a device that completes the generation of electrons, the formation and convergence of electron beams, and is mainly composed of filaments, cathodes, anodes, and focusing coils. The filament is energized to heat up and heat the cathode. When the cathode reaches 2400K, electrons are emitted. Under the action of the high voltage electric field between the cathode and the anode, the electrons are accelerated (about 1/2 of the speed of light), emitted through the anode hole, then converge into an electron beam with a diameter of 0.8~3.2mm through the focusing coil, and the kinetic energy is converted into heat energy on the surface of the weldment, so that the weldment joint is rapidly melted, the weld is formed after cooling crystallization. According to the vacuum degree of welding workshop (weldment placement place), the classification of electron beam welding: (1) High vacuum electron beam welding. The studio and the electron gun are in the same room, the vacuum degree is 10-2~10-1Pa, which is suitable for precision welding of refractory, active, high-purity metals and small parts. (2) Low vacuum electron beam welding. The studio and the electron gun are divided into two vacuum chambers. The vacuum degree of the studio is 10-1~15Pa, which is suitable for larger structural parts and refractory metals that are less sensitive to oxygen and nitrogen. (3) Non-vacuum electron beam welding. An inert gas protective cover or nozzle is required, and the distance between the weldment and the electron beam outlet should be controlled at about 10mm to reduce the scattering caused by the collision of the electron beam and the gas molecules. Non-vacuum electron beam welding is suitable for welding carbon steel, low alloy steel, stainless steel, refractory metal and copper, aluminum alloy, etc., and the size of the weldment is not limited. The advantages of vacuum electron beam welding: (1) The energy density of the electron beam is large, up to 5 × 108W/cm2, which is about 5000 to 10000 times that of the ordinary arc. The heat is concentrated, the thermal efficiency is high, the heat affected zone is small, the weld is narrow and deep, and the welding deformation is extremely small. (2) Welding in a vacuum environment, the metal does not interact with the gas phase, and the joint has high strength. (3) The electron beam focus radius can be adjusted in a large range, flexible control, and strong adaptability. It can weld thin parts of 0.05mm and thick plates of 200~700mm. Application: Especially suitable for welding some refractory metals, active or high purity metals and heat sensitive metals. However, the equipment is complex, the cost is high, the size of the weldment is limited by the vacuum chamber, the assembly accuracy is high, and it is easy to excite X-rays, the welding auxiliary time is long, and the productivity is low. These weaknesses limit the wide application of electron beam welding. 5 Laser welding Laser welding is the use of high-power coherent monochromatic photon flow focused by the laser beam as a heat source for welding. This welding method usually has continuous power laser welding and pulsed power laser welding. The advantage of laser welding is that it does not need to be carried out in a vacuum, but the disadvantage is that the penetration is not as strong as the electron beam welding. Laser welding can be precise energy control, which can achieve precision micro-device welding. It can be applied to many metals, especially to solve some difficult to weld metal and dissimilar metal welding. Laser generation: after the material is excited, the wavelength, frequency, direction is exactly the same beam. The characteristics of laser: with good monochromaticness, good direction, high energy density characteristics, laser by transmission or mirror focus, can be less than 0.01mm in diameter, power density up to 1013W/cm2 energy beam, can be used as welding, cutting, drilling and surface treatment of the heat source. The material of laser is solid, semiconductor, liquid, gas, etc., which is mainly used for welding, cutting and other industrial processing is yttrium aluminum garnet (YAG) solid laser and CO2 gas laser. The main advantages of laser welding are: (1) The laser can be bent and transmitted through optical fibers, prisms and other optical methods. It is suitable for welding parts that are difficult to reach by miniature parts and other welding methods, and can also be welded through transparent materials. (2) High energy density, high-speed welding can be realized, the heat-affected zone and welding deformation are very small, especially suitable for welding heat-sensitive materials. (3) The laser is not affected by electromagnetic fields, does not produce X-rays, does not require vacuum protection, and can be used for welding large structures. (4) can be directly welded insulated conductors, without the need to strip off the insulating layer in advance; can also be welded to different materials with different physical properties. The main disadvantages of laser welding are: expensive equipment, low energy conversion rate (5% ~ 20%), high requirements for processing, assembly and positioning of weldment interfaces. At present, it is mainly used for the welding of micro devices in the electronics industry and instrument industry, as well as the welding of silicon steel sheet and galvanized steel sheet.

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