Several commonly used fusion welding methods

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Welding by fusion refers to the process in which, during welding, the joint is brought to a molten state under the action of high temperature and other factors. Since the workpieces to be welded are in close contact, under the influence of factors such as the temperature field and gravity, the molten materials from the two workpieces mix with each other without the need for any external pressure. Once the temperature drops, the melted portion solidifies, and the two workpieces are firmly welded together, completing the welding process. Several common fusion welding methods include shielded metal arc welding, submerged arc welding, carbon dioxide gas shielded welding, MIG/MAG welding, TIG welding, and plasma arc welding. Principle of shielded metal arc welding: An arc welding method that uses a manually operated electrode for welding; it is the most basic type of fusion welding. It utilizes a stable burning arc established between the welding electrode and the workpiece to melt both, thereby creating a strong welded joint; this is a form of gas-slag combined protection. Advantages: Flexible process, strong adaptability, easy to operate ； The assembly requirements for the joint to be welded are low ； Weldable metal materials are diverse. Disadvantage: Low welding productivity ； Weld quality is highly dependent (on the welder’s skill and performance on site). Applications: Widely used in manufacturing and maintenance industries such as shipbuilding, boilers and pressure vessels, machinery manufacturing, building structures, and chemical equipment. Suitable for welding various metal materials, of different thicknesses and with various structural shapes, in (the aforementioned industries). Principle of submerged arc welding (automatic welding): The arc burns beneath the flux layer. It uses the heat generated by the arc that burns between the welding wire and the workpiece to melt the welding wire, flux, and base material (workpiece), thereby forming a weld; this is a type of slag protection. Advantages: High welding productivity ； Good weld quality ； Low welding cost ； Good working conditions ； Disadvantage: Difficult to weld in terms of spatial position ； High requirements are placed on the assembly quality of welded joints ； It is not suitable for welding thin sheets (arc stability is poor when the welding current is less than 100A) and short welds. Applications: Widely used in the shipbuilding, boiler, bridge, lifting machinery, and metallurgical machinery manufacturing industries. S submerged arc welding can be used for all weldments whose welds can be kept in a horizontal position or with a small inclination angle. The plate thickness must be greater than 5 mm (to prevent burn-through). Welding of carbon structural steel, low-alloy structural steel, stainless steel, heat-resistant steel, composite steel, etc. Principle of carbon dioxide gas shielded welding (automatic or semi-automatic welding): A fusion electrode arc welding method that uses carbon dioxide as a shielding gas, and it falls under the category of gas-shielded welding. Advantages: High welding productivity ； Low welding cost ； Minimal welding deformation (arc heating is concentrated) ； High welding quality ； Simple to operate ； Disadvantage: High splashing rate ； It’s difficult to weld using AC power ； Poor wind resistance and strong arc light ； Metals that are prone to oxidation cannot be welded. Applications: Primarily used for welding low-carbon steel and low-alloy steel, suitable for various thicknesses. It is widely used in industries such as automobile manufacturing, locomotive and vehicle production, chemical machinery, agricultural machinery, and mining machinery. MIG/MAG welding: Principle of MIG welding – An arc welding process that uses an inert gas as a shielding gas and a welding wire as the melting electrode. The shielding gas is usually argon or helium, or a mixture of them. MIG uses an inert gas, while MAG uses an inert gas with a small amount of active gases added, such as oxygen or carbon dioxide. Advantages: Good welding quality ； High welding productivity ； Disadvantages: No dehydrogenation reaction (prone to welding defects; very strict requirements for surface preparation of welding materials) ； Poor wind resistance ； Welding equipment is complex. Applications: It can weld almost all metal materials, and is mainly used for welding non-ferrous metals and their alloys, as well as stainless steel and certain alloy steels (which are too expensive). The thinnest thickness is about 1 mm, while the maximum thickness is essentially unrestricted. Principle of TIG welding (Tungsten Inert Gas welding): A welding method in which, under the protection of an inert gas, the heat generated by the arc between the tungsten electrode and the workpiece is used to melt the base material and the filler wire (filler wire may also be omitted) in order to form a weld. The electrode does not melt during welding. Advantages: Strong adaptability (stable arc, no spatter) ； Disadvantages: Low welding productivity (the tungsten electrode has a poor capacity to carry current; this leads to melting and evaporation of the electrode as well as tungsten inclusion in the weld) ； The production cost is high. Applications: It can be used to weld almost all metal materials, and is commonly employed in the welding of stainless steel, superalloys, aluminum, magnesium, titanium and their alloys, refractory reactive metals (zirconium, tantalum, molybdenum, niobium, etc.), as well as dissimilar metals. It is used for weldments with a welding thickness generally below 6 mm, or as a root pass for thicker parts. Using a small-angle groove (narrow-groove technique), automatic TIG welding with a narrow gap can be achieved for thicknesses of over 90 mm. Principle of plasma arc welding: A welding method that utilizes the constraining effect of a water-cooled nozzle on the arc to generate a plasma arc with high energy density. Advantages (compared to TIG welding): concentrated energy and high temperature, enabling a keyhole effect in most metals over a certain thickness range; this results in thorough penetration and welds with uniform formation on the reverse side. The arc has good stiffness; the plasma arc is essentially cylindrical, and changes in arc length have a relatively small impact on the heating area and current density on the weldment. Therefore, the effect of arc length variation in plasma arc welding on weld shape is not significant. The welding speed is faster than that of TIG welding. It is capable of welding finer and thinner workpieces. Disadvantages (compared to TIG welding): complex equipment and higher costs ； It is difficult to operate and has limited application scenarios. Applications: ① Penetrating (hole-forming) plasma arc welding: This welding method takes advantage of the small diameter, high temperature, high energy density, and strong penetration capability of the plasma arc. Under appropriate process parameters (a higher welding current of 100A–500A), it enables complete melting of the workpiece. The plasma flow creates a hole that penetrates the workpiece, and part of the plasma arc is ejected from the back side of the workpiece. It allows single-sided welding with double-sided formation, and is most suitable for butt welding of 3–8 mm thick stainless steel, titanium alloys up to 12 mm thick, 2–6 mm thick low-carbon or low-alloy structural steel, as well as copper, brass, nickel, and nickel alloys. (The plate is too thick; due to the limitations imposed by the energy density of the plasma arc, it is difficult to create holes.) ； The plate is too thin, so the small holes cannot be completely sealed by the liquid metal; therefore, the hole welding method cannot be applied. ) ② Penetrating (penetration-type) plasma arc welding: This method uses a lower welding current (30A–100A) and a lower flow rate of plasma gas, and employs a mixed-type plasma arc welding approach. No pore formation effect. It is mainly used for welding thin plates (0.5–2.5 mm or less), welding the layers subsequent to the root pass in multi-layer welding, and welding fillet joints. ③Micro-beam plasma arc: Plasma arc welding with a welding current of 30A or less. The nozzle diameter is very small (Φ0.5～Φ1.5mm), resulting in a needle-shaped, fine plasma arc. It is mainly used for welding ultra-thin, ultra-small, and precision weldments of 1 millimeter or less. Note: The above are several commonly used fusion welding methods, each with its own advantages and disadvantages. When choosing a welding method, various factors need to be taken into consideration, such as the type of material being welded, the thickness of the plate, and the position of the weld in space. The principle for selecting a welding method is to use the one with the lowest total cost, while ensuring the quality of the welded joint.