A process known to join a workpiece by heating or pressurizing, or a combination of both, and with or without a filler material, is referred to as welding. The workpiece can be made of various metal materials of the same kind or different types, such as metal, non-metal materials (plastic, graphite, ceramic, glass, etc.), or a metal and a non-metal material. Metal welding has a wide range of applications in modern industry, so in a narrow sense, welding generally refers to the welding of metallic materials.

According to the state of the metal materials in the welding process, the welding methods are currently classified into the following three categories:

  1. Fusion Welding,  In the welding process, the weldment joint is heated to a molten state, and the method of welding without pressure is called fusion welding. Commonly used welding methods are arc welding, gas welding, electroslag welding, and the like.
  2. Pressure welding, During the welding process, it is necessary to apply pressure (heated or not) to the weldment. The method of completing the welding is called pressure welding. Commonly used pressure welding methods include resistance welding (butt welding, spot welding, seam welding), friction welding, rotating arc welding, ultrasonic welding, and the like.
  3. brazing process, a metal material having a lower melting point than the base material is used as the brazing material, and the weldment and the brazing material are heated to a temperature higher than the melting point of the brazing material and lower than the melting point of the base material, and the mother is wetted by the liquid brazing material. The method of filling the joint gap and interdifing with the base material to achieve the welding of the weldment is called brazing. Common brazing methods include flame brazing, induction brazing, furnace brazing, salt bath brazing, and vacuum brazing.

So how do we choose the welding method that suits us? There are three aspects to consider:
Product Structure Types Welded products can be roughly divided into four categories according to their structural characteristics.

a) Structural types such as bridges, construction projects, petrochemical containers, etc.

b) Mechanism parts such as auto parts.

c) Semi-finished products such as I-beams, pipes, etc.

d) Microelectronic devices.

These different structures have different welding methods depending on the length, shape and welding position of the weld. Submerged arc welding is recommended for regular long welds and circumferential seams in structural products. Hand arc welding is used for bottom welding and short weld welding. Mechanical products are generally short, and according to their accuracy requirements, gas shielded welding (general thickness), electroslag welding, gas welding (heavy components are suitable for vertical welding), electric resistance welding (thin plate), friction welding (round) Profile) or electron beam welding (required for high precision). The welded joints of semi-finished products are often regular, and welding methods suitable for mechanization such as submerged arc welding, gas shielded arc welding, and high frequency welding are preferred. The connectors of microelectronic devices mainly require sealing, electrical conductivity, and low heat, so electron beam welding, ultrasonic welding, diffusion welding, brazing, and capacitor energy storage welding are preferred.

Workpiece thickness The thickness of the workpiece can determine the welding method to be used to some extent. Each welding method has a range of applicable material thicknesses due to the different heat sources used. It is easier to control the quality of the weld and maintain a reasonable productivity when welding within the recommended thickness range.

Connector type and welding position According to the use requirements of the product and the thickness and shape of the base material used, the designed products can be connected by several types of joints such as butt joints, lap joints and corner joints. The butt type is suitable for most welding methods. Brazing is generally only suitable for lap joints with a large welding area and a small material thickness. The position of each joint in the product is often determined by the structural requirements and force of the product. These joints may need to be welded at different weld locations, including flat, vertical, horizontal, overhead, and all-position welding. Flat welding is the easiest and most common welding position. Therefore, the joint of the product should be placed in the flat welding position as much as possible. This way, the welding method can be selected to ensure good welding quality and obtain high productivity. Such as submerged arc welding and gas metal arc welding. For the vertical welding head, it is preferable to use gas metal arc welding (thin plate) and gas electric welding (medium thickness). When the plate thickness exceeds about 30 mm, electroslag welding can be used.

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