Laser radiation heats the surface to be machined, the surface heat is guided to internal diffusion by heat transfer, and the workpiece is melted by controlling the laser pulse width, energy, peak power and repetition frequency to form a specific molten pool.
Spot weld the weldment
Continuous laser welding
Laser welding can be realized by the continuous or pulsed laser beam.
The principle of laser welding can be divided into heat conduction welding and laser deep penetration welding.
When the power density is less than 10 ~ 10W/cm, it is heat conduction welding;
When the power density is greater than 10 ~ 10W/cm, the metal surface is concave into “holes” under the action of heating, forming deep fusion welding, which has the characteristics of fast welding speed and large depth width ratio.
Laser welding technology is widely applied in high-precision manufacturing fields such as automobiles, ships, airplanes and high-speed railways, which has greatly improved people’s quality of life and led the home appliance industry into the era of precision manufacturing.
Especially after the 42 meter seamless welding technology created by Volkswagen has greatly improved the body integrity and stability.
Haier Group, the leading enterprise of home appliances, solemnly launched the first washing machine produced by laser seamless welding technology. Advanced laser technology can bring great changes to people’s lives.
2. Laser hybrid welding
Laser hybrid welding is the combination of laser beam welding and MIG welding technology, which can obtain the best welding effect, fast welding speed and weld bridging ability. It is the most advanced welding method at present.
The advantages of laser hybrid welding are: high speed, small thermal deformation, small heat affected area, and ensure the metal structure and mechanical properties of the weld.
Laser hybrid welding is not only suitable for the welding of automobile sheet structure, but also suitable for many other applications.
For example, when this technology is applied to the production of concrete pump and mobile crane boom, these processes need to process high-strength steel, and the traditional technology often needs other auxiliary processes (such as preheating) to increase the cost.
Moreover, the technology can also be applied to the manufacture of rail vehicles and conventional steel structures (such as bridges, fuel tanks, etc.).
3. Friction stir welding
Friction stir welding uses friction heat and plastic deformation heat as welding heat source. Friction stir welding (FSW) is a process in which a cylinder or other shape (such as a threaded cylinder) pin is inserted into the joint of the workpiece. Through the high-speed rotation of the welding head, it rubs against the material of the workpiece, so that the temperature of the material at the joint increases and softens.
In the process of friction stir welding, the workpiece should be rigidly fixed on the back pad, the welding head side rotates at high speed, and the seam of the edge workpiece moves relative to the workpiece.
The protruding section of the welding head extends into the material for friction and stirring, and the shoulder of the welding head rubs against the surface of the workpiece to generate heat, which is used to prevent the overflow of the plastic material and to remove the surface oxide film.
A keyhole is left at the end of the FSW. Usually, the keyhole can be removed or sealed with other welding methods.
Friction stir welding can be used to weld dissimilar materials, such as metals, ceramics, plastics, etc. Friction stir welding has the advantages of high welding quality, less defects, easy mechanization, automation, stable quality and high cost efficiency.
4. Electron beam welding
Electron beam welding (EBW) is a kind of welding method which uses the heat energy produced by accelerating and focusing electron beam bombarding the weldment in vacuum or non vacuum.
Electron beam welding (EBW) is widely used in aerospace, atomic energy, national defense and military industry, automobile, electrical instrument and many other industries due to its advantages of no electrode, no oxidation, good process repeatability and small thermal deformation.
Working principle of electron beam welding
The electron escapes from the emitter (cathode) of the electron gun. Under the action of accelerating voltage, the electron is accelerated to 0.3-0.7 times of the speed of light and has a certain kinetic energy.
Then the electron beam with high density can be converged by the electrostatic lens and electromagnetic lens in the electron gun.
The electron beam impinges on the surface of the workpiece, and the kinetic energy of the electron is transformed into heat energy, which makes the metal melt and evaporate rapidly.
Under the action of high pressure metal vapor, a small hole, also known as keyhole, is quickly drilled out on the surface of the workpiece.
With the relative movement of the electron beam and the workpiece, the liquid metal flows to the back of the weld pool around the keyhole and solidifies to form the weld.
Main characteristics of electron beam welding
The results show that the penetration of electron beam is strong, the power density is very high, and the depth width ratio of weld is large, which can reach 50:1. The large thickness material can be formed at one time, and the maximum welding thickness can reach 300 mm.
Welding accessibility is good, welding speed is fast, generally more than 1m / min, heat affected zone is small, welding deformation is small, welding structure precision is high.
The energy of electron beam can be adjusted, and the thickness of the metal to be welded can be from 0.05mm to 300 mm without groove, which can not be achieved by other welding methods.
Electron beam welding can be used in a wide range of materials, especially for active metal, refractory metal and high quality workpiece welding.
5. Ultrasonic metal welding
Ultrasonic metal welding is a special method to connect the same metal or different metal by using the mechanical vibration energy of ultrasonic frequency.
When the metal is welded by ultrasonic wave, neither current nor high temperature heat source is applied to the workpiece, but under static pressure, the vibration energy of the frame is transformed into friction work, deformation energy and limited temperature rise.
Metallurgical bonding between joints is a kind of solid state welding without melting of base metal.
It effectively overcomes the spatter and oxidation during resistance welding.
Ultrasonic metal welding machine can be used for single spot welding, multi spot welding and short strip welding of copper, silver, aluminum, nickel and other non-ferrous wire or sheet materials.
It can be widely used in the welding of SCR lead, fuse, electrical lead, lithium battery pole piece and pole lug.
Ultrasonic metal welding uses high frequency vibration wave to transmit to the metal surface to be welded
Under pressure, two metal surfaces rub against each other to form a fusion between molecular layers.
The advantages of ultrasonic metal welding are fast, energy saving, high fusion strength, good conductivity, no spark, close to cold processing;
The disadvantages are that the welded metal parts should not be too thick (generally less than or equal to 5mm), the welding spot should not be too large, and the pressure should be applied.
6. Flash butt welding
The principle of flash butt welding is to use butt welding machine to make the two ends of metal contact, through the low voltage and strong current, when the metal is heated to a certain temperature and becomes soft, the axial pressure forging is carried out to form the butt welding joint.
The two weldments are clamped by two clamp electrodes and connected to the power supply before contacting.
When the movable clamp is moved, the two end faces of the weldment are slightly contacted, that is, they are electrified and heated.
The contact point explodes due to liquid metal formed by heating, and the jet spark forms flash.
When the movable fixture is moved continuously, flash occurs continuously and both ends of the weldment are heated.
After reaching a certain temperature, extrude the end faces of the two workpieces, cut off the welding power, and firmly weld them together.
The resistance is used to heat the joint of the weldment to make the contact point flash, melt the metal on the end face of the weldment, and quickly apply the top force to complete the welding.
Steel flash butt welding is to install two steel bars into butt joint.
The resistance heat produced by welding current passing through the contact point of two steel bars makes the metal at the contact point melt, produce strong splash, form flash, accompanied by pungent smell, release trace molecules, and quickly apply forging force to complete the pressure welding method.