1. Hot Air Welding
Also known as hot gas welding.
Compressed air or inert gas (usually nitrogen) is heated to the desired temperature via a heater in the welding gun, sprayed onto the plastic surface and welding rod, allowing them to melt and bond together under minimal pressure.
Oxygen-sensitive plastics (such as polyamide) must use inert gas as a heating medium, while other plastics can generally use filtered air. This method is commonly used for welding plastics such as polyvinyl chloride, polyethylene, polypropylene, polyoxymethylene, polystyrene and acetate carbonate.
2. Hot pressing welding
Hot press welding employs heat and pressure to fuse a metal wire with the metal in the welding zone. The principle involves inducing plastic deformation in the metal in the welding area through heat and pressure, which disrupts the oxide layer at the welding interface. This allows the wire to enter the range of atomic attraction with the contact surface of the weld metal, leading to interatomic attraction and fulfilling the purpose of bonding.
3. Hot plate welding
Hot plate welding adopts a drawer-like structure where the heat from the hot plate machine is transferred to the melting surface of the upper and lower plastic heating components through electrical heating. This melts their surfaces, after which the hot plate machine is quickly withdrawn, allowing the molten surfaces of the two heated components to fuse, solidify and become unified.
The whole machine is in frame shape, composed of an upper jig, a lower jig and a hot jig, and is equipped with hot molds and upper and lower plastic cooling molds, operating by pneumatic control.
4. Ultrasonic metal welding
Ultrasonic metal welding uses high-frequency vibration waves transmitted to the surfaces of two metals that need to be welded. Under pressure, the two metal surfaces rub against each other, resulting in a fusion between the molecular layers. Its advantages include speed, energy efficiency, high melt resistance, good conductivity, lack of sparks and its near-cold processing nature.
However, it has its disadvantages: the metal parts to be welded cannot be too thick (generally less than or equal to 5 mm), the welding points cannot be too large and pressure is required.
5. Laser welding
Laser welding is an efficient and precise welding method that uses a high-energy density laser beam as a heat source. It represents a significant aspect of laser material processing technology. Typically, the connection of materials is achieved using a continuous laser beam. The physical metallurgical process is extremely similar to electron beam welding, where the energy conversion mechanism is completed through a “keyhole” structure.
The balanced temperature inside the cavity reaches about 2,500°C, and heat is transferred from the high-temperature cavity wall, melting the metal surrounding the cavity. The keyhole is filled with high-temperature vapor produced by continuous evaporation of wall material under beam irradiation.
As the beam continuously enters the keyhole and the external material flows out, the keyhole remains in a stable state with the movement of the beam. The molten metal fills the void left after the movement of the keyhole and subsequently solidifies, thus forming a weld seam.
6. Brazing
Brazing is a welding technique that heats a filler material, which has a lower melting point than the parts to be joined, until it becomes sufficiently fluid. This fluid then fills the gap between the two pieces through capillary action (known as wetting) and, after solidifying, bonds them together.
Traditionally in the United States, this method is referred to as brazing if the temperature exceeds 800°F (427°C), otherwise it is called soft welding.
7. Manual welding
Hand welding is a welding method that involves operating a portable welding torch, welding gun, or welding tong.
8. Resistance welding
Resistance welding is a manufacturing process and technique that joins metals or other thermoplastic materials, such as plastics, through heating. This method welds assembled parts by applying pressure through electrodes and using the resistive heat generated when an electrical current passes through the contact surface and adjacent areas of the joint.
9. Friction welding
Friction welding is a solid-state welding process that uses mechanical energy as an energy source. It works by generating heat through the friction of the ends of the part, bringing them to a plastic state, after which it completes the welding process through forge welding.
10. Electroslag welding
Electroslag welding is a process that uses the resistive heat generated by the electric current that passes through the molten slag as a heat source, fusing the filler metal and the base material. This results in a solid connection between the metal atoms after solidification. At the beginning of the welding process, the welding wire short-circuits with the groove to create an arc. A minute amount of solid flux is continually added and the heat from the electric arc melts it, forming liquid slag.
As the slag reaches a certain depth, the welding wire feed rate increases and the voltage is reduced, allowing the wire to be inserted into the slag pool. The arc is extinguished, passing to the electroslag welding process. The main types of electroslag welding include consumable guide electroslag welding, non-consumable guide electroslag welding, wire electrode electroslag welding and plate electrode electroslag welding.
Disadvantages of this method include high heat input, prolonged exposure of the joint to high temperatures, overheating near the weld seam, and coarse crystalline molten structures in the weld metal, which results in low impact toughness. Typically, post-welding heat treatment such as normalizing and tempering is required for the welded parts.
11. High frequency welding
High-frequency welding is a process that uses solid-state resistance heat as an energy source. During welding, high-frequency electrical currents generate resistive heat within the part, heating the surface area of the welding zone to a molten or nearly plastic state. Subsequently, forging pressure is applied (or not), facilitating the union of metals.
12. Riveting
Riveting refers to the method of connecting two relatively thin plates. This is achieved by drilling holes in the appropriate locations, inserting rivets, and then using a rivet gun to set the rivets, thus connecting the two plates or objects.
13. Hot Fusion
Hot fusion is a connection method after heating to the melting point, turning into a liquid state.
