Welding, also known as fusion welding or fusion welding, is a manufacturing process and technology that uses heating, high temperature, or high pressure to join metals or other thermoplastic materials such as plastics. Welding achieves the purpose of joining through the following three methods:

1. Fusion welding - heating the workpiece to be joined to locally melt and form a molten pool. After the molten pool cools and solidifies, it is joined. If necessary, filler materials can be added to assist. It is suitable for welding and processing various metals and alloys without pressure.

2. Pressure welding - The welding process must apply pressure to the welded part, which belongs to the processing of various metal materials and some metal materials.

3. Brazing - Using a metal material with a lower melting point than the base material as the brazing material, wetting the base material with liquid brazing material, filling the joint gap, and diffusing with the base material to achieve the connection of the welded part. Suitable for welding processing of various materials, as well as welding processing of different metals or dissimilar materials.

There are many sources of energy for modern welding, including gas flames, arcs, lasers, electron beams, friction, and ultrasound. In addition to being used in factories, welding can also be carried out in various environments, such as outdoors, underwater, and space. No matter where, welding can pose a danger to the operator, so appropriate protective measures must be taken when welding. Welding may cause harm to the human body, including burns, electric shock, visual impairment, inhalation of toxic gases, and excessive exposure to ultraviolet radiation.