Appreciation of over a dozen welding methods~~~~~~~~~~~~

bg7.png II. Tungsten Inert Gas Shielded Arc Welding: This is a type of non-fusing electrode gas shielded arc welding, in which the arc between the tungsten electrode and the workpiece is used to melt the metal and thus form a weld seam. During welding, the tungsten electrode does not melt; it merely serves as an electrode. At the same time, argon or helium is supplied through the nozzle of the welding torch for protection. Additional metals can also be added as needed. (Internationally known as TIG welding.) Tungsten inert gas arc welding is an excellent method for joining thin metal sheets and for performing root welding, as it allows for good control of heat input. This method can be used for joining almost all metals, especially suitable for welding metals such as aluminum and magnesium that form refractory oxides, as well as reactive metals like titanium and zirconium. This welding method produces welds of high quality, but its welding speed is slower compared to other arc welding methods.

bg7.png III. Gas metal arc welding With this welding method, an electric arc formed between a continuously fed welding wire and the workpiece serves as the heat source; the welding is carried out under the protection of gas ejected from the torch nozzle. The shielding gases commonly used in gas metal arc welding include argon, helium, CO2, or mixtures of these gases. When argon or helium is used as the shielding gas, it is called metal inert gas shielded arc welding (internationally abbreviated as MIG welding). When an inert gas mixed with oxidizing gases (O2, CO2) is used as the shielding gas, or when CO2 gas or a mixture of CO2 and O2 is used as the shielding gas, this process is collectively referred to as metal active gas shielded arc welding (internationally abbreviated as MAG welding). The main advantage of gas metal arc welding is the ability to weld in various positions easily, along with advantages such as a fast welding speed and high deposition rate. GMAW can be applied to most major metals, including carbon steel and alloy steel. GMAW is suitable for stainless steel, aluminum, magnesium, copper, titanium, zirconium, and nickel alloys. Arc spot welding can also be performed using this welding method.

bg7.png IV. Plasma arc welding Plasma arc welding is also a type of non-consumable electrode arc welding. It achieves welding by utilizing a compressed arc between the electrode and the workpiece (called a forward transfer arc). The electrodes used are usually tungsten electrodes. The plasma gas used to generate the plasma arc can be argon, nitrogen, helium, or a mixture of two of these gases. It is also protected by an inert gas through a nozzle. During welding, filler metal can be used or it can be omitted. During plasma arc welding, the arc is straight and has a high energy density, which gives it strong penetration capability. The hole effect that occurs during plasma arc welding allows for butt welding of most metals within a certain thickness range without the need for beveling, while ensuring full penetration and a uniform weld seam. Therefore, plasma arc welding has high productivity and good weld quality. However, plasma arc welding equipment (including nozzles) is relatively complex, and it requires high precision in controlling the welding process parameters. Plasma arc welding can be used for virtually all metals that can be welded by tungsten inert gas arc welding. In contrast, welding extremely thin metals of 1 mm or less can be carried out more easily using plasma arc welding.

bg7.png V. Tubular Wire Arc Welding: Tubular wire arc welding also uses the arc that is generated between the continuously fed wire and the workpiece as a heat source for welding; it can be considered a type of gas shielded metal arc welding. The welding wire used is a tubular wire, which contains fluxes of various components inside it. During welding, a shielding gas is applied; mainly CO2. The flux decomposes or melts when heated, serving functions such as forming slag to protect the molten pool, alloying, and stabilizing the arc. In addition to the advantages of gas shielded arc welding with a solid wire, tubular wire arc welding possesses further metallurgical advantages due to the effect of the flux inside the tube. Tubular wire arc welding can be used for welding various joints of most ferrous metals. Flux-cored arc welding has been widely used in some industrially advanced **. “\"Tubular welding wire\" is what is now referred to as \"flux-cored welding wire\".

bg7.png VI. Resistance welding This is a category of welding methods that utilize resistive heat as the energy source. It includes electroslag welding, which uses the resistive heat of molten slag as its energy source, and resistance welding, which utilizes the resistive heat of solids as its energy source. Since electroslag welding has more unique characteristics, it is covered later. Here, several types of resistance welding that use solid resistive heat as an energy source are introduced, mainly including spot welding, seam welding, butt welding, and lap welding. Resistance welding is a welding method that typically involves subjecting the workpieces to a certain electrode pressure, and using the resistive heat generated when electricity passes through the workpieces to melt the contact surfaces between them, thereby achieving connection. A larger current is usually used. To prevent arcing at the contact surface and to forge the weld metal, pressure must be applied throughout the welding process. When performing this type of resistance welding, the surface condition of the workpieces to be welded is of paramount importance for achieving stable welding quality. Therefore, the contact surfaces between the electrode and the workpiece, as well as between the workpieces themselves, must be cleaned prior to welding. The differences between spot welding, seam welding, and butt welding lie in the fact that the welding current (single-phase) is high (several thousand to several tens of thousands of amperes), the electrical conduction time is short (several cycles to a few seconds), the equipment is expensive and complex, yet the productivity is high; therefore, these methods are suitable for mass production. It is mainly used for welding thin sheet components with a thickness of less than 3 mm. All types of steel, non-ferrous metals such as aluminum and magnesium and their alloys, stainless steel, etc., can all be welded.

bg7.png VII. Electron beam welding: Electron beam welding is a method of welding that utilizes the heat energy generated when a concentrated, high-speed electron beam strikes the surface of a workpiece. In electron beam welding, an electron beam is generated and accelerated by an electron gun. Common types of electron beam welding include: high-vacuum electron beam welding, low-vacuum electron beam welding, and non-vacuum electron beam welding. The first two methods are both carried out in a vacuum chamber. The welding preparation time (mainly the vacuum pumping time) is long, and the size of the workpiece is limited by the size of the vacuum chamber. Compared with arc welding, the main advantages of electron beam welding are a large weld depth, a small weld width, and high purity of the weld metal. It can be used for the precise welding of very thin materials as well as for welding thick components (up to 300 mm thick). All metals and alloys that can be welded by fusion welding using other methods can also be welded by electron beam welding. It is mainly used for welding applications that require high-quality products. It can also handle the welding of dissimilar metals, oxidizable metals, and refractory metals. But it is not suitable for mass-produced products.

bg7.png VIII. Laser Welding Laser welding is a welding process that uses a laser beam, generated by focusing a high-power coherent monochromatic photon stream, as the heat source. This type of welding method generally includes continuous-power laser welding and pulsed-power laser welding. The advantage of laser welding is that it does not require a vacuum environment, while its disadvantage is that its penetration power is lower than that of electron beam welding. During laser welding, precise energy control is possible, thus enabling the welding of precision microdevices. It can be applied to many metals, especially for solving the welding of some difficult-to-weld metals and dissimilar metals.

bg7.png 9. Brazing: The energy source for brazing can be the heat generated by chemical reactions, or it can be indirect heat energy. It uses a metal with a melting point lower than that of the materials to be welded as a filler metal; upon heating, the filler metal melts, and *capillary action drives it into the gaps at the contact surfaces of the joints, wetting the surfaces of the metals to be welded. This allows for interdiffusion between the liquid and solid phases, thereby forming a welded joint. Therefore, brazing is a welding method that involves both solid and liquid phases. The brazing heating temperature is low; the base material does not melt, and no pressure needs to be applied. However, certain measures must be taken before welding to remove oil, dust, oxide films, and other contaminants from the surface of the workpieces to be welded. This is an important guarantee for achieving good wettability of the workpiece and ensuring joint quality. When the liquidus temperature of the filler metal is higher than 450°C and lower than the melting point of the base metal, it is referred to as hard brazing ； Below 450°C, it is called soft soldering. Depending on the heat source or heating method, brazing can be classified into flame brazing, induction brazing, furnace brazing, dip brazing, resistance brazing, etc. During brazing, the heating temperature is relatively low, so it has little impact on the properties of the workpiece material, and the stress deformation of the welded joint is also minimal. However, the strength of brazed joints is generally low, and their heat resistance is poor. Brazing can be used to weld metal materials such as carbon steel, stainless steel, superalloys, aluminum, and copper, as well as to join different types of metals or metals with non-metals. It is suitable for joints that are subjected to low loads or operate at room temperature, and is particularly appropriate for precise, miniature, and complex multi-brazed components.

bg7.png X. Electroslag welding: Electroslag welding is a welding method that uses the resistive heat of slag as its energy source. The welding process is carried out in the vertical welding position, within the assembly gap formed by the end faces of the two workpieces and the water-cooled copper sliders on both sides. During welding, the resistance heat generated by the current passing through the slag is used to melt the ends of the workpiece. Based on the shape of the electrode used during welding, electroslag welding is divided into wire-electrode electroslag welding, plate-electrode electroslag welding, and nozzle-electrode electroslag welding. The advantages of electroslag welding are: it can weld workpieces with large thicknesses (from 30 mm to over 1000 mm), and it offers high productivity. It is mainly used for welding butt joints and T-joints on cross-sections. Electroslag welding can be used for welding various steel structures, as well as for assembling castings. Due to the slow heating and cooling processes, electroslag welded joints have a wide heat-affected zone, a coarse microstructure, and low toughness; therefore, normalizing treatment is generally required after welding.

bg7.png XI. High-frequency welding: High-frequency welding uses solid resistive heat as its energy source. During welding, the resistive heat generated within the workpiece by high-frequency current is used to heat the surface layer of the welding area to a molten state or a plastic state close to it; subsequently, a upsetting force is applied (or not) to achieve the bonding of the metals. Therefore, it is a solid-state resistance welding method. High-frequency welding can be divided into contact high-frequency welding and induction high-frequency welding, based on the way in which high-frequency current generates heat in the workpiece. When in contact with high-frequency welding, the high-frequency current is transmitted into the workpiece through mechanical contact with it. During induction high-frequency welding, the high-frequency current generates an induced current within the workpiece through the coupling effect of the external induction coil surrounding it. High-frequency welding is a highly specialized welding method that requires specialized equipment tailored to the product. It features high productivity, with a welding speed of up to 30 m/min. It is mainly used for welding the longitudinal or spiral seams when manufacturing pipes.