Laser (Light Amplification by Stimulated Emission of Radiation) was first used in welding and cutting in 1967. In the first experiments, the laser used oxygen-assisted gas with a concentrated CO2 laser beam.
Today, laser welding might be one of the most technologically advanced welding processes. Therefore, we will explain how laser beam welding works, the laser welding system, and where it is widely used.
Of course, laser welding has its advantages and drawbacks, but let us start by explaining the basics.
What is Laser Welding [LW/LWB], and How Does it Work?
The laser welding (LW) or laser beam welding (LWB) process uses a highly concentrated beam of light energy to form weld and join metals or thermoplastics. As a powerful and focused laser beam is used, the electrons in the area get excited to a point where the material melts due to the atoms breaking the bonds with each other.
By using a concentrated heat source, laser welding can join thin materials at a very high welding speed. Meanwhile, focused heat can produce narrow, deep welds between square-edged parts in thicker materials. It is surprising how light yet powerful enough laser welding can join metals or plastics within milliseconds.
To understand how standard laser welding works, you should know there are two fundamentally different methods: heat conduction welding and keyhole welding.
Heat Conduction Laser Beam Welding
The heat conduction welding process occurs when the power density is typically less than 105W/cm2. In this type, the metal surface is heated above the melting point of the metal. But not to the extent that it vaporizes. That is why a low-power laser in the range of <500W is most often used.
Therefore the laser beam does not penetrate the metal surface, and it is only absorbed. As a result, the heat conduction laser weld exhibit a high width to depth ratio, and the final weld is highly smooth and aesthetical.
Whit all being said, this type of laser welding is used for welds that do not need high weld strength.
Keyhole laser welding is used when the projects require high power density, typically over 106-107 W/cm2. To achieve higher quality welds, a keyhole mechanism is used.
Whit higher power densities, the laser beam simultaneously melts and evaporates the metal surface while conductors absorb excess heat. Next, the laser beam penetrates the workpiece, forming a keyhole cavity.
This cavity is now filled with evaporated metal, which can even form plasma-like conditions if ionized. The temperatures of the evaporated metal can rise well above 10,000K.
Finally, as the laser beam travels across the joint, the keyhole moves, achieving deep welds, significant penetration, and an excellent depth to width ratio. As a result, small amounts of molten metal can flow around the keyhole cavity, resulting in the weld cap with a chevron pattern.
Processing Gas in Laser Welding
Laser welding can be done in a standard atmosphere or vacuum. However, like other welding methods such as TIG welding or MIG welding, a laser weld pool can be contaminated if it interacts with hydrogen in the atmosphere. High concentrations of hydrogen can mix with the molten metal and cause the formation of voids or holes within the weld.
That is why laser welding utilizes process gas or cut gas when working in a normal atmosphere. Processing gas, most often CO2 shields the weld and prevents the contact of the weld surface with the atmosphere. However, since different factors in the atmosphere can cause defects and poor weld results, laser welding in a familiar atmosphere without process gas is not recommended.
One alternative to prevent interaction and weld contamination is working in a vacuum atmosphere. However, the costs of setting up and specific requests make it highly unprofitable.
Laser Welding Machine or Laser Welder
The laser welding machine includes motored guide, laser optics, and a worktable if needed. In addition, there are motionless and mobile laser beam welding systems.
With the portable machines, the appliance is moved near merchandise. Meanwhile, immobile laser welding appliances come with a worktable and fixating mechanism.
Regardless of the machine, there are three standard laser types: gas lasers, solid-state lasers, and fiber lasers. Each laser is connected and powered by optical fiber. Therefore, there is a difference between single fiber and multiple fiber laser welding machines. Within multi-fiber laser welding machines, more optical fibers increase the laser power.
A collimator lens in conjunction with a focusing lens is often used to concentrate the beam to a point before it leaves the machine. In addition, the cutting system is a perfect addition to a welding system. The cutting system produces perfect shapes cuts to the precise geometry.
Laser Beam Welding Applications
Due to high productivity, efficiency, and precision, laser welding is used in various industries such as automotive, steel construction, shipbuilding, and construction tools. Furthermore, with hybrid laser technology, this method is also used in the railway industry with a fast-growing trend within agricultural equipment, tipper bodies, and containers.
In the automotive industry, laser welding provides a tool-free operation style. As a result, the overall performance when working with thin materials used in automotive is outstanding. In addition, all welding parameters increase the aesthetics of the welds.
The same advantages apply to shipbuilding. Low output heat allows working with thin materials, which reduce the overall weight of the ships, therefore reducing the fuel consumption. In addition, high-quality welds are defect-free, and there is no hot cracking.
Laser Welding And Other Welding Processes
The process we explained so far is also known as pure laser welding where consumable filler material is not used. The key feature of pure laser welding in steel joining applications is the weld seam has close to the same material properties as the base material.
However, keep in mind that in certain situations, you can add a filler wire to the laser weld. It is suitable to add cold feed wire, or induction heated wire to reduce thermal effects in the melt pool.
In addition to adding the filler material, manufacturers started combining the good properties of laser welding and traditional methods.
Combining laser and other welding methods are referred to as hybrid welding. For example, when combining laser and MAG welding, heat energy is on a higher level than in pure laser welding but still much lower than in traditional MIG/MAG – welding. Therefore, by combining high-powered lasers and MAG welding you get a higher working speed and ability to weld thicker materials.
Besides MAG, laser welding can be combined with any other arc welding process. The hybrid process has the individual advantages of both welding processes.
The temperature of Laser Welding
While traditional welding methods have fixed output temperature and heat, laser welding allows you to control heat during welding.
Most lasers can output temperature between 200 and 5400 F, therefore, you can use the process to join different materials, such as plastics, aluminum, copper, and steel.
Knowing the melting point of different materials is crucial, but adjusting the proper heat can be energy efficient. Therefore, to avoid high heating, you should know the material properties, and here are some examples:
- Steel: 2550 F
- Copper: 1985 F and higher
- Glass: ranges from 1110-1470 F
- Aluminum: 1110 F
- Plastics: Between 300-660 F
Advantages and drawbacks of Laser welding
In the end, let’s discuss the advantages and drawbacks of laser beam welding. Of course, as with any other process out there, laser welding is not perfect, but let’s look at the main characteristics.
- Excellent mechanical properties: Lasers provide high-quality weld seams that are well-welded, durable, strong, and consistent.
- Narrow HAZ: Laser pulses with continuous-wave that creates a very narrow heat-affected zone to the contact surface, meaning the risks of distortion are minimal
- Less heat: Laser welding provides lower heat compared to traditional welding, and the temperature can even be controlled
- Efficiency: The whole process can be easily automated, resulting in high travel speed and less time to train experienced welders
- Accuracy: You can use it to weld even the most minor parts together due to its high accuracy and level of control
- Versatility: Laser welding can be used to join various materials and different material thicknesses
- No form of tool wear occurs: Lasers are easy to maintain, and you don’t have to buy consumables such as TIG welding fillers or MIG wire electrodes
- High initial investment: Laser welding equipment and machines are very expensive, so the initial investment is significantly higher compared to traditional welding
- Limited material thickness: Today’s lasers used in hybrid welding are capable of joining a maximum of 25 mm thick materials
- Low energy conversion efficiency: Lasers usually utilize less than 10% of energy
With everything begin said, manufacturers state laser welding is best recommended method for thinner gauges, high strength and wear resistant steels.