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What Is Welding?

Welding is a technique that is generally used for binding materials together through the use of heat, pressure, or both to fuse two parts. Welding is generally used on metals and thermoplastics, but can also be used on wood.

The welding process is related to the welding method used and other factors engaged, and the operation needs to be determined according to the material, brand, chemical composition, structure type of the weldment, and welding performance requirements of the welded workpiece. First of all, it is necessary to determine the welding method, such as manual arc welding, submerged arc welding, argon tungsten arc welding, MIG welding, etc. There are many types of welding methods, which can only be selected according to specific conditions. After the welding method is determined, the welding process parameters are formulated. The types of welding process parameters are different. For example, manual arc welding mainly includes electrode type, diameter, current, voltage, welding power source, polarity connection method, number of welding layers, number of passes, Inspection methods, etc.

• Heat the workpiece to be joined to partially melt it to form a molten pool. The molten pool will be joined after cooling and solidification. If necessary, a molten filler can be added to assist.
• With soft soldering and brazing, the solder has a lower melting point than the workpiece. You do not need to melt the workpiece itself, but by heating and melting the solder, capillary action of the solder will connect the workpieces.
• At a temperature equal to or lower than the melting point of the workpiece, the process is supplemented with high pressure, superimposed extrusion, or vibration. The two workpieces are mutually infiltrated and joined, (such as in forge welding or solid welding).

Welding can be subdivided into other special welding methods, such as gas welding, resistance welding, arc welding, induction welding, and laser welding. There are many energy sources for welding, including a gas flame, electric arc, laser, electron beam, friction, and ultrasonic. In addition to being used in factories, welding can also be carried out in a variety of environments, such as the field, underwater, and space. No matter where it is, welding may bring danger to the operator, so appropriate protective measures must be taken when welding. The possible harm to the human body caused by welding includes burns, electric shock, visual impairment, inhalation of toxic gases, excessive ultraviolet radiation, etc.

Fusion welding is a method in which the joint of the workpiece is heated to a molten state during the welding process, and the welding is completed without pressure. During fusion welding, the heat source rapidly heats and melts the joint of the two workpieces to be welded to form a molten pool. The molten pool moves forward with the heat source and forms a continuous weld after cooling to connect the two workpieces into one. In the fusion welding process, if the atmosphere is in direct contact with the high-temperature molten pool, the oxygen in the atmosphere will oxidize metals and various alloying elements. Atmospheric nitrogen, water vapor, etc. enter the molten pool, and will also form pores, slag inclusions, cracks, and other defects in the weld during the subsequent cooling process, deteriorating the quality and performance of the weld.

In order to improve the welding quality, various protection methods have been developed. For example, gas-shielded arc welding is to isolate the atmosphere with argon, carbon dioxide, and other gases to protect the arc and molten pool rate during welding; another example is to add iron titanium powder with a high affinity for oxygen to the electrode coating to deoxidize when welding steel. It can protect the beneficial elements such as manganese and silicon in the electrode from oxidation and enter the molten pool, and obtain high-quality welds after cooling.

Pressure welding is to make two workpieces realize interatomic bonding in a solid state under pressure. This is also called solid-state welding. The commonly used pressure welding process is resistance butt welding. When the current passes through the connecting end of the two workpieces, the temperature rises due to the large resistance. When heated to a plastic state, the connection becomes a whole under the action of axial pressure. The common feature of various pressure welding methods is to apply pressure without adding filler material during the welding process. Most pressure welding methods such as diffusion welding, high-frequency welding, cold pressure welding, etc. have no melting process, so there is no problem of beneficial alloy elements burning like fusion welding and harmful elements intruding into the weld, thus simplifying the welding process, and improving welding safety and sanitation conditions. At the same time, because the heating temperature is lower than that of fusion welding and the heating time is shorter, the heat-affected zone is small. Many materials that are difficult to weld by fusion welding can often be welded by pressure welding to form a high-quality joint with the same strength as the base material.

Welding Quality

The main indicator to measure the quality of welding is the strength of the solder joint and its surrounding materials. There are many factors affecting strength, including the welding process, energy injection form, base material, filler material, flux, joint design form, and the interaction between the above factors. Usually, destructive, or non-destructive testing is used to check the quality of welding. The main objects of testing are the defects of the solder joints, the degree of residual stress and deformation, and the nature of the heat-affected zone. Welding inspection has a set of specifications and standards to guide operators to adopt appropriate welding processes and judge welding quality.

The Trends of Welding Processing

The economic cost of welding is an important factor in its industrial application. There are many factors that affect the cost of welding, such as the cost of equipment, manpower, raw materials, and energy. The cost of welding equipment varies greatly for different processes. Manual arc welding and combustible gas welding are relatively inexpensive, while laser welding and electron beam welding are relatively expensive. Due to the high cost of certain welding processes, they are generally only used to manufacture important parts. The cost of automatic welding equipment and welding robots is also very high, so their use is also restricted accordingly. The labor cost depends on the welding speed, hourly wages, and working hours for welding and subsequent processing. The cost of raw materials includes the cost of purchasing base materials, weld filler materials, and shielding gas. The energy cost depends on the arc working time and the energy demand of the welding.

For manual welding, labor costs often account for a large part of the total cost. Therefore, the reduction of manual welding costs often focuses on reducing the welding operation time. Effective methods include increasing the welding speed and optimizing welding parameters. DE slagging after welding is also time-consuming and laborious work. Therefore, reducing welding slag can improve safety, environmental protection, reduce costs, and improve welding quality. Mechanization and automation can also effectively reduce labor costs, but on the other hand, it increases equipment costs and requires additional equipment installation and commissioning time. When products have special needs, the cost of raw materials often rises accordingly. The energy cost is usually not important, because it generally only accounts for a few percentage points of the total cost.

In recent years, in order to reduce the labor cost of welding in high-end products, resistance spot welding and arc welding in industrial production have adopted many new forms of automatic welding equipment, (especially in the automotive industry). Welding robots can effectively complete welding, especially spot welding. With the advancement of technology, welding robots have also begun to be used for arc welding. The cutting-edge development areas of welding technology include welding between special-shaped materials, new welding processes, such as friction stir welding, magnetic pulse welding, heat conduction seam welding, and laser hybrid welding. Other research focuses on expanding the application range of existing welding processes, such as the application of laser welding to the aerospace and automotive industries. Researchers also hope to further improve the welding quality, especially to control the microstructure and residual stress of the weld, to reduce the deformation and fracture of the weld.