Use the power of light to melt metal!
Laser (optical amplified by stimulated emission) welding is one of the most technologically advanced forms of welding. Its applications span various industries from aerospace to fine jewelry manufacturing.
However, several types of welding have been used long before laser welding, so when we have other options, why do we need laser technology?
We will discuss this in depth after a brief review of the birth of the technology. It was Einstein who predicted stimulated emission, which is the basic principle of lasers.
Related article: Ultrasonic welding: a promising technology for welding plastics and metals
However, it was not until 1967 that we first used the welding and cutting capabilities of lasers. The laser used in the 1967 experiment used oxygen assist gas and a concentrated CO2 laser beam.
The project is led by Dr. Peter Houldcroft. ABJ Sullivan and PT Houldcroft explained the experiment and its details in a paper entitled "Gas Jet Laser Cutting".
Laser cutting lays the foundation for laser welding because it involves melting metal without perforating.
Laser welding uses a highly concentrated beam on a very small spot, so the area under the laser beam absorbs light and becomes high-energy. Due to the use of a powerful laser beam, the electrons in this area will be excited to the extent that the material melts, which is the result of atoms breaking bonds with each other.
Laser welding can also be used to join plastics.
The two materials melt at the seam, fusing them into a joint. Surprisingly, light is strong enough to be metallic within a few milliseconds. In order to obtain such a powerful laser beam, the laser welding machine uses several components to guide and amplify the laser.
Gas lasers, solid-state lasers and fiber lasers are the three most commonly used lasers in laser welding machines.
Generally, the laser beam is supplied to the laser welding machine by using an optical fiber. There are single-fiber fusion splicers and multi-fiber fusion splicers. A multi-fiber welding machine connects a laser to each optical fiber, and the intensity of the laser increases with each optical fiber.
In order to concentrate the beam to a point before it leaves the machine, collimating lenses and focusing lenses are usually used.
Four main welding joints can be laser welded:
If you have been studying laser welding, you may have noticed the constant companion of the laser nozzle, which is another nozzle that provides a gas called process gas or cutting gas.
Basically, it is an airflow, most commonly CO2, which is also directed to the welding position in order to prevent the welding surface from contacting the atmosphere.
Without using cutting gas, there are only two options for welding atmosphere-normal atmosphere or vacuum. It is certainly possible to perform laser welding in a vacuum, but it is not feasible due to the high cost and the need for special settings.
Under normal atmosphere, laser welding without processing gas will produce adverse effects. Due to the very high concentration of nitrogen in the air, it will mix with molten metal and cause voids or holes to form in the weld. This situation will cause welding failure.
Factors such as humidity in the air can cause hydrogen to be generated during welding. Diffusion of hydrogen into the metal can also cause the welded joint to weaken. Therefore, laser welding in a normal atmosphere without shielding is not welcome at all.
The welding machine is equipped with cutting gas accessories, which can spray gas to the welding surface to ensure that there are no impurities in the welding seam.
There are two methods of laser welding-thermal conduction welding and keyhole welding.
Heat conduction welding: In this process, the metal surface is heated above the melting point of the metal, but it will not reach the level of evaporation. This process is used for welds that do not require high welding strength.
The advantage of heat conduction welding is that the final weld will be very smooth and beautiful. Low-power lasers in the range of <500W are used for thermal conduction welding.
Keyhole welding: In this process, the laser beam heats the metal, causing the contact surface to evaporate and penetrate deep into the metal. This creates a keyhole where plasma-like conditions will occur when the temperature rises above 10,000K.
This process requires a high-power laser with a power higher than 105W/mm2.
Laser welding is often used in combination with arc welding to create something called hybrid laser arc welding. In hybrid laser arc welding, any kind of arc welding process (such as MIG, TIG or SAW) is used together with deep penetration laser welding.
The result is welding with the advantages of laser welding and arc welding.
Due to laser welding, the resulting weld will have a deep penetration joint and will also improve the resistance to joint assembly. Other adverse effects such as cracking and internal porosity are also reduced.
Laser welding has many advantages that other welding methods do not have. Some defining characteristics of laser welding are:
Related: A guide to making money from welding: career choices and advice
Laser beam welding is used for high-precision welding. Since it does not use any electrodes, the final weld will be very light but very strong. The initial investment is of course expensive, but the quality and characteristics of laser welding cannot be easily replicated.
As lasers become more powerful and energy-saving, the future of laser welding is undoubtedly bright!