Laser (Light Amplification by Stimulated Emission of Radiation) welding is one of the most technically advanced forms of welding. Its applications span across a diverse array of industries from aerospace to fine jewelry making.
However, there are several types of welding which were used long before laser welding, so it begs the question of why do we need laser technology when we have other alternatives?
We will delve into that after briefly going over the inception of the technology. It was Einstein who predicted stimulated emission, which is the basic principle of laser.
However, it was only in 1967 that we first used laser for its welding and cutting capabilities. The laser used in the 1967 experiments used oxygen assisted gas with a concentrated CO2 laser beam.
The project was spearheaded by Dr. Peter Houldcroft. The experiment and its details were explained in a paper titled Gas-jet laser cutting' by A B J Sullivan and P T Houldcroft.
Laser cutting led the foundation for Laser welding as it involves melting the metal without punching through it.
The process of laser welding
Laser welding uses a highly concentrated beam of light on a very tiny spot so that the area under the laser beam absorbs the light and becomes highly energetic. As powerful laser beams are used, the electrons in the area get excited to a point where the material melts as the result of the atoms breaking the bonds with each other.
Laser welding can also be used to join plastics.
This melting of the two materials at their seams fuse them into a joint. It is surprising how light can be powerful enough to metal metals within milliseconds. To achieve such powerful laser beams, the laser welding machine uses several parts that direct and amplify the laser.
Gas lasers, solid-state lasers, and fiber lasers are the three most common lasers used in a laser welding machine.
Normally, the laser beam is supplied to the laser welding machine by the use of optical fibers. There are single fiber welding machines and there are multiple fiber welding machines. The multiple fiber welding machines have a laser connected to each fiber, with each fiber, the strength of the laser increases.
To concentrate the beam to a point before it leaves the machine, a collimator lens in conjunction with a focusing lens is often used.
Four main weld joints are capable with laser welds:
- Butt Weld
- Filler Lap Weld
- Overlap Weld
- Edge Flange Weld
The use of processing gas in laser welding
If you have been looking into laser welding, you might have noticed the constant companion to the laser nozzle which is another nozzle that supplies a gas which is called Process Gas or Cutting Gas.
Basically, it is the flow of gas, which is most commonly CO2, that is also directed towards the weld location with an aim to prevent the contact of the weld surface with the atmosphere.
Without the use of cutting gas, there are only two options for weld atmosphere – Either normal atmosphere or vacuum. Laser welding in a vacuum is certainly possible, but not plausible because of its high cost and the requirement for a specialty setup.
In a normal atmosphere, laser welding without processing gas can yield unfavorable effects. Since nitrogen in the air is in very high concentration, it can mix with the molten metal and cause the formation of voids or holes within the weld. Such occurrences can lead to weld failures.
Factors like humidity in the air can cause the production of hydrogen when welding. The diffusion of hydrogen into the metal also leads to weak weld joints. Hence laser welding in a normal atmosphere without shielding is not entertained at all.
Weld machines come with a cutting gas attachment that shoots gas to the weld surface making sure that no impurities are mixed with the weld.
Types of laser welding
Laser welding can be done in two ways – Heat conduction welding and keyhole welding.
Heat conduction welding: In this process, the metal surface is heated above the melting point of the metal, but not to an extent that it vaporizes. This process is used for welds that do not need high weld strength.
The advantage of hot conduction welding is that the final weld will be highly smooth and aesthetical. Low power laser in the range of <500W is used for heat conduction welding.
Keyhole welding: In this process, the laser beam heats up the metal in such a way that the contact surface vaporizes, digging deep into the metal. This creates a keyhole where a plasma-like condition is created with temperatures rising well above 10,000K.
This process required high powered lasers with power above 105W/mm2.
laser welding with other weld processes
Laser welding is often used in conjunction with arc welding to create something called Hybrid Laser Arc Welding. In hybrid laser arc welding, any one of the arc welding processes like MIG, TIG or SAW is used with deep penetration laser welding.
The result is a weld that has the advantages of both laser welding and arc welding.
The resultant weld will have deep penetrating joints, thanks to the laser weld and will also have improved tolerance to joint fit-up. Other undesirable effects like cracking and internal porosity are also reduced.
The advantages of using a laser welding technique
Laser welding offers several advantages that are often not found in other welding methods. Some of the defining characteristics of laser welding are:
- The whole welding process can be easily automated using a CAD/CAM setup
- No electrode is used in the process
- No form of tool wear occurs
- Laser welding is highly specific in targeting
- High-quality welds are obtained
Laser Beam welding is used for high precision welds. Since it doesn’t employ any electrode, the final weld will be light but strong. The initial investment is certainly expensive, but the quality and characteristics of a laser weld cannot be easily replicated.
As lasers get more powerful and energy-efficient, the future of laser welding is certainly bright!