Welding is a manufacturing process and technology that uses heat, high temperature or high pressure to join metal or other thermoplastic materials such as plastics. According to the state of the metal in the welding process and the characteristics of the process, the welding methods can be divided into three categories: welding, pressure welding and braze welding.
The workpieces to be joined are heated to partially melt to form a molten pool, and then joined after the molten pool is cooled and solidified. If necessary, fillers can be added to assist.
- Laser welding
Laser welding uses the heat generated by the focused laser beam as the energy source to bombard the workpiece for welding. It can weld various metal materials and non-metal materials such as carbon steel, silicon steel, aluminum and titanium and their alloys, tungsten, molybdenum and other refractory metals and dissimilar metals, as well as ceramics, glass and plastics. At present, it is mainly used in electronic instruments, aviation, aerospace, nuclear reactors and other fields. Laser welding has the following characteristics:
- The energy density of the laser beam is high, the heating process is extremely short, the solder joints are small, the heat-affected zone is narrow, the welding deformation is small, and the dimensional accuracy of the weldment is high.
- It can weld materials that are difficult to weld by conventional welding methods, such as welding refractory metals such as tungsten, molybdenum, tantalum, and zirconium.
- Non-ferrous metals can be welded in air without additional shielding gas.
- The equipment is complicated and the cost is high.
Gas welding is mainly used in the welding of thin steel plates, low melting point materials (non-ferrous metals and their alloys), cast iron parts and hard alloy tools, as well as repair welding of worn and scrapped parts, flame correction of component deformation, etc.
Arc welding can be divided into manual arc welding and submerged arc welding.
Gas electric welding
- Manual arc welding can perform multi-position welding such as flat welding, vertical welding, horizontal welding and overhead welding. In addition, because the arc welding equipment is portable and flexible in handling, welding operations can be performed in any place with power supply. It is suitable for welding of various metal materials, various thicknesses and various structural shapes.
- Submerged arc welding is generally only suitable for flat welding positions, and is not suitable for welding thin plates with a thickness less than 1mm. Due to the deep penetration of submerged arc welding, high productivity and high degree of mechanized operation, it is suitable for welding long welds of medium and thick plate structures. The materials that can be welded by submerged arc welding have developed from carbon structural steel to low alloy structural steel, stainless steel, heat-resistant steel, etc., as well as certain non-ferrous metals, such as nickel-based alloys, titanium alloys, and copper alloys.
Arc welding that uses external gas as the arc medium and protects the arc and welding area is called gas shielded arc welding, or gas electric welding for short. Gas electric welding is usually divided into non-melting electrode (tungsten electrode) inert gas shielded welding and melting electrode gas shielded welding, oxidizing mixed gas shielded welding, CO2 gas shielded welding and tubular wire gas shielded welding according to whether the electrode is molten or not and the shielding gas is different.
Among them, non-melting extremely inert gas shielded welding can be used for welding almost all metals and alloys, but due to its high cost, it is usually used for welding non-ferrous metals such as aluminum, magnesium, titanium and copper, as well as stainless steel and heat-resistant steel. In addition to the main advantages of non-melting electrode gas shielded welding (welding in various positions; suitable for welding of most metals such as non-ferrous metals, stainless steel, heat-resistant steel, carbon steel, and alloy steel), it also has faster welding speed and higher deposition efficiency.
Plasma arc welding
Plasma arc is widely used in welding, spraying and surfacing. It can weld thinner and thinner workpieces (such as welding of extremely thin metals below 1mm).
Electroslag welding can weld various carbon structural steels, low-alloy high-strength steels, heat-resistant steels and medium-alloy steels, and has been widely used in the manufacture of boilers, pressure vessels, heavy machinery, metallurgical equipment and ships, etc. middle. In addition, electroslag welding can be used for large-area surfacing and repair welding.
Electron beam welding
Electron beam welding equipment is complex, expensive, and requires high maintenance; the assembly requirements of weldments are high, and the size is limited by the size of the vacuum chamber; X-ray protection is required. Electron beam welding can be used to weld most metals and alloys and workpieces requiring small deformation and high quality. At present, electron beam welding has been widely used in precision instruments, meters and electronic industries.
The welding process must exert pressure on the weldment, which is divided into resistance welding and ultrasonic welding.
- Resistance welding
There are four main resistance welding methods, namely spot welding, seam welding, projection welding and butt welding. Spot welding is suitable for stamped and rolled thin plate members that can be overlapped, the joints do not require airtightness, and the thickness is less than 3mm. Seam welding is widely used in sheet welding of oil drums, cans, radiators, aircraft and automobile fuel tanks. Projection welding is mainly used for welding stamping parts of low carbon steel and low alloy steel. The most suitable thickness for plate projection welding is 0.5-4mm.
- Ultrasonic welding
Ultrasonic welding is in principle suitable for welding most thermoplastics.
Use a metal material with a lower melting point than the base material as the base material, use the liquid base material to wet the base material, fill the gap, and diffuse with the base material to realize the connection of the weldment.
- Flame annealing welding
Flame annealing welding is suitable for annealing welding of materials such as carbon steel, cast iron, copper and its alloys. An oxyacetylene flame is a commonly used flame.
- Resistance welding
There are two methods of resistance welding: direct heating and indirect heating. Indirect heating resistance welding is suitable for welding of weldments with large differences in thermophysical properties and thickness.
- Induction welding
Induction welding is characterized by fast heating, high efficiency, local heating, and easy automation. According to the protection method, it can be divided into induction welding in air, induction welding in shielding gas and induction welding in vacuum.