Development And Application of Laser Welding Technology

Development and application of laser welding technology

What is laser welding? What is the current development of laser welding technology? In what fields can laser welding technology be applied?

1. What is laser welding?

In short, laser welding is to heat the surface of the workpiece with laser radiation, and the surface heat diffuses to the inside through heat conduction. Then, by controlling the width, energy, peak power and repetition frequency of the laser pulse, the workpiece is melted to form a specific molten pool, thereby achieving welding.

Laser welding can reduce the input heat to the minimum required amount, the metallographic change range of the heat-affected zone is small, and the deformation caused by heat conduction is also minimal.

Non-contact welding can reduce the wear and deformation of the machine to a minimum. The laser beam is easy to focus, align and guide by optical instruments. It can be placed at an appropriate distance from the workpiece and can be guided between the machines or obstacles around the workpiece.

The laser beam can be focused on a very small area, can weld small and closely spaced parts, can weld a wide range of materials, and can also join various heterogeneous materials.

It is easy to perform high-speed welding with automation, and can also be controlled digitally or by computer. When welding thin materials or thin-diameter wires, there is no trouble such as remelting.

2. What is the current status of laser welding technology?

Laser welding technology has developed along with the development of laser technology. In recent years, new light sources such as blue laser, green laser, femtosecond laser, swing welding, ARM (adjustable ringmode) ring adjustable spot welding and other new processes have been introduced, which have innovatively solved some welding problems in industrial production, which has enabled laser welding to be rapidly promoted and developed in various fields of industrial production.

(1) Metal laser welding technology

The high energy density of laser makes it possible to weld some difficult-to-weld metal materials, but there are still some problems with the welding of highly reflective materials and dissimilar metal materials such as gold, silver, copper, and aluminum. The main reasons include:

①High reflectivity and high thermal conductivity, laser welding requires a higher starting power;

②During high-power laser welding, it is sensitive to changes in the surface state of the material, resulting in poor solder joint/weld formation;

③The laser welding speed is fast, resulting in welding defects such as pores inside the weld, especially aluminum and aluminum alloys.

(1.1) Efficient laser welding of copper and copper alloys

Copper has excellent electrical and thermal conductivity and is widely used in the manufacturing fields of electronic products and electric vehicles. Among them, motors, batteries, sensors, wiring harnesses, and terminals are the most widely used.

In the past, laser welding of metal materials mainly relied on infrared lasers. However, the thermal conductivity of copper is too high, almost 5 times that of pure iron and 1.7 times that of pure aluminum. Copper has a low absorption rate for infrared lasers. The use of infrared lasers for linear welding alone has an unstable process window and the largest fluctuation in melting depth, which is prone to problems such as welding spatter, molten metal splashing, pores, and large fluctuations in penetration depth.

Therefore, after the emergence of high-power short-wavelength lasers, visible light laser welding and hybrid welding have become ideal processing methods for highly reflective materials such as copper and copper alloys.

①Green light laser welding

Green laser is a kind of visible light with a wavelength of 500-560nm. The absorption rate of copper for green light with a wavelength of λ = 515nm is as high as 40%, which is about 8 times the infrared light absorption rate of about 1μm, and the energy coupling efficiency is higher. Sensitivity to the degree of oxidation is also reduced.

The use of green laser can significantly reduce the threshold power of copper deep penetration welding, the amount of melt spray and spatter on the weld surface is small, and it is almost unaffected by the welding speed. If the beam scanning, beam defocus and correct laser power modulation are increased, the welding quality can be significantly improved. While the number of weld defects is greatly reduced, the weld surface will be more regular and uniform.

②Blue light laser welding

The shorter the wavelength, the higher the photon energy, which helps to increase the material’s absorption rate of laser light. The wavelength of blue laser is 400nm~500n. The semiconductor laser based on gallium nitride material can directly generate laser with a wavelength of 450 nm without further frequency doubling. It has the advantages of simple structure, easy use, electro-optical conversion efficiency, and high absorption rate.

Compared with fiber lasers commonly used in industrial processing, blue light lasers have a 10-60% increase in the absorption rate of metal materials at 450nm, especially the increase in the absorption rate of highly reflective metal materials such as copper and gold. It has been verified that the energy consumption required for copper welding is 84% lower than that of infrared lasers. This means that when an infrared laser requires 10 W of laser power to weld copper materials, using a blue laser only requires about 1 kW or 0.5 kW of power.

③Double beam hybrid welding

Using the infrared-visible light double-beam composite welding process, using a smaller power visible light laser, the infrared laser can achieve forced deep-penetration welding of copper when the power is lower than the deep-penetration welding threshold power, and significantly reduce welding spatter, and the equipment cost is low. The welding quality is high and is considered to have very outstanding advantages and good application prospects.

(1.2) Laser swing welding of aluminum alloys

When conventional single-focus laser beams are used to weld aluminum alloys, pores are common defects. The main reasons for the formation of pores in aluminum alloys are:

① The welding molten pool and keyhole are prone to collapse and instability due to severe vibration, forming pores;

② The solubility of hydrogen in aluminum alloys will drop sharply with the decrease of temperature, resulting in the precipitation of supersaturated hydrogen during solidification and the formation of hydrogen pores. The presence of pores will cause stress concentration in the weld, which will cause the weld to crack during solidification.

Laser swing welding. During the welding process, the beam moves along the direction of the weld and swings in various forms such as circular, 8-shaped, and spiral lines at the same time.

At present, the realization of beam swing is mainly achieved by a galvanometer that can withstand high-power lasers. The beam action area of laser swing welding is increased, which increases the area of the keyhole and the molten pool and the size of the root of the molten pool, improves the stability of the keyhole and the molten pool, and has a significant improvement effect on defects such as poor fusion and undercut. At the same time, the stirring of the molten pool by the swinging light beam accelerates the convection of the molten pool, which increases the escape speed of bubbles in the molten pool and reduces the porosity.

3. Current Application of Laser Welding Technology in Various Fields

Laser welding is no later than cutting. At present, there are enterprises in my country that specialize in laser welding. In the early days, lamp-pumped laser and YAG laser welding were the main methods. They are all very traditional low-power laser welding, which has been applied in molds, advertising characters, glasses, jewelry and other fields, but the scale is very limited. In recent years, with the continuous improvement of laser power, more importantly, semiconductor lasers and fiber lasers have gradually developed laser welding application scenarios, breaking the technical bottleneck of laser welding and opening up new market space.

(1) Application of laser welding technology in automobile manufacturing

With the development of science and technology and the improvement of people's consumption level and quality of life, the requirements for lightweight and artistic aesthetics of automobile bodies in the automobile production field are getting higher and higher. Laser welding technology stands out due to its excellent processing effect, good product quality and high work efficiency, and quickly becomes the darling of welding process technology application in the automobile production field.

In vehicle production, laser welding technology is mainly used in processes such as laser welding of thick steel plates, laser welding of automobile assemblies and subsystem assemblies, and laser welding of vehicle parts. Automakers in some European and American countries started to apply laser welding technology relatively early, starting in the 1980s. Audi, Mercedes-Benz, GM and other well-known automobile brands began to introduce laser welding technology into vehicle production and manufacturing at that time, which promoted the in-depth application and development of laser welding technology in the field of vehicle production and manufacturing.

Laser welding of power batteries should be the most eye-catching welding application demand in recent years, which has a great impetus for laser equipment manufacturers. The second should be the welding of automobile bodies and parts. China is the world's largest automobile market, with many old car companies and new car companies emerging continuously, with nearly 100 automobile brands. Most manufacturers use kilowatt-level welding technology or automated laser welding production lines; especially in the field of power batteries, the leading new energy battery companies have used a large number of laser welding equipment.

4. What is the development trend of laser welding technology?

With the further development and breakthrough of welding technology, its uniqueness is more evident in the research and development process of laser welding technology. Laser welding technology can weld metal materials quickly and efficiently. When the laser beam is generated, due to its own high focusing characteristics, it can cause extremely high power density in the laser beam, which enables the laser beam to release a large amount of heat energy in a very short time, thereby greatly improving the welding efficiency and ensuring the welding quality.

In addition, due to the instantaneous welding advantage of laser welding technology, it has a very broad application prospect. In the actual application of laser welding technology, when the laser beam directly irradiates the surface of the metal material, it will not affect the metal material outside the irradiation area, so it does not cause significant damage to the surface of the metal material during the welding process, and after the welding process is completed, there is no need to perform related surface processing. This makes laser welding technology particularly suitable for processing the surfaces of various precision parts, so that more difficult welding operations can also be quickly achieved.

Moreover, in the previous welding technical specifications, it is usually stipulated that the material requirements for all welding materials must be consistent. With the use of laser welding technology, there is no need to have great restrictions on the material of the welding materials, so even welding materials of different materials can be easily welded using laser welding technology. It can be said that the formation and widespread application of laser welding technology has effectively overcome the problems in traditional welding technology and reduced the difficulty of traditional welding operations.

After more than half a century of development, the technical level of laser welding technology has also become increasingly perfect, and it has gradually been widely used in more and more industrial fields.

In the application fields of aerospace, electronic instruments, machinery manufacturing, steel metallurgy, automobile manufacturing, medical equipment and other industries, laser welding technology plays an increasingly huge role. For example, in the production of automotive parts, laser welding technology can be used to process and produce the covering parts of the vehicle, and advanced countries such as the United States and Japan have also applied laser welding technology to the production of aviation parts in a pure nitrogen environment.