An Overview of Laser Welding

Laser welding is a state-of-the-art technology revolutionising the welding industry. This article will delve into the intricate details of this precision technology. Learn how a laser welding operation yields unique benefits compared to other, more conventional, methods. 

How to Weld with a Laser Beam

Exploring the intricacies of laser welding begins with understanding its core components and the distinct types of lasers used in the process.

What Is a Laser Welding Machine? The Advanced Equipment and Devices Used by Welders

A laser welding machine consists of several key components that work together to create precise welds. It's comprised of the following: 

• Laser source

• Cooling system

• Beam delivery system (mirrors, fibres, and lenses)

• Focusing optics (beam shaping)

• Optical cavity (2 reflective mirrors)

• Welding head

• Workpiece handling system 

• Control and monitoring system

Note that there are three different types of lasers: 

1. CO2 Laser

To function, the laser must travel through an amplifier. A CO2 laser consists of a three-gas mixture:

• Helium

• Nitrogen

• Carbon dioxide

The energy stems from the electric discharge produced through the gas mixture.

The beam’s wavelength, produced by the CO2 laser, measures 10.6 µm.

2. YAG Laser

This laser is named after its amplifier. Indeed, it’s made with a YAG electrode—yttrium aluminum garnet. Said electrode is typically reinforced with about 1% neodymium, meaning ion-doped crystals. 

The energy excitation needed to operate this system is provided by a high-speed light produced by a pulsed flash lamp. 

With this welding machine, the beam’s wavelength measures 1.064 µm.

Below are the upsides of YAG laser welding: 

• Effective

• Powerful

• Reliable

• Size (smaller than CO2 laser) 

3. Fibre Laser

Fibre laser is a type of welding technique that relies on ytterbium ion-doped crystals. The excitation light source is produced by diode lasers paired inside the fibre core.

The beam’s wavelength measures between 1.07 µm and 1.09 µm.

We’ll circle back on the matter in more detail in the section below.  

How Does Laser Welding Work?

Laser welding benefits from a high-power and high-density heat source to achieve a weld pool that enables materials to weld together using one of two welding processes:  

• Keyhole welding

• Heat conduction welding

With three welding techniques: 

• Lap joints (metal pieces overlap) 

• Corner and T joints (two metal pieces joined at a right angle)

• Butt joints (metal pieces joined end-to-end)

When it comes to keyhole (deep penetration) welding, the laser beam is denser compared to that of heat conduction welding, allowing for a straight weld, secured in a cavity balanced by plasma pressure.

Heat conduction welding isn’t as commonly employed, but more stable. Said technique heats metal to its melting point without merging into its boiling point. As we will come to know, this welding technique is used for special alloys, such as those made of aluminum. 

Let’s turn our attention to two particular welding techniques: fibre laser and hybrid welding.

Fibre Laser

Fibre laser welding is: 

• Compact 

• Effective

• Reliable 

• Stable

• Small in size

• Cheaper than a traditional laser 

Fibre laser machines are perfect for micro-cutting, micro-welding, and micro-drilling. Why? The fibre tip is smaller than 10 micrometres, thus ensuring the laser beam’s high precision.  

Said laser was built to produce 500 W of power with water-cooled diodes, lasting 100,000 hours. However, when the system employs forced air cooling, the laser power solely reaches 120 W when the ambient temperature is below 35°C (95°F).

It performs in a continuous wave mode. The laser is highly effective, courtesy of a beam parameter product (BPP) below 10 mm.mrad.

Therefore, it’s commonly used in the following fields: 

• Electronics

• Aerospace

• Automotive

• Railway

• Defence

• Construction

Hybrid Laser Welding 

Hybrid laser welding joins three other welding methods: 

• GTAW (Gas Tungsten Arc Welding)

• GMAW (Gas Metal Arc Welding)

• Plasma 

As such, it combines two welding processes: 

• Laser welding

• Arc welding (traditional)

Joining two welding methods results in a synergy that enables the following:

• Greater welding speed

• Deeper penetration

• Improved weld quality

The above-mentioned benefits are made possible by the highly complementary nature of said two techniques. Indeed, this method’s success is owed to the positioning of the arc and laser, ensuring one makes up for the other’s weaknesses.

As such, a shared interaction zone is created between the laser and the electric arc. The heat source can be secured in the first position along the same line or parallel to the line. 

With the former, the electric arc will serve to heat the welding zone, allowing the laser beam to carry out an effective weld. The laser won’t need as much energy to heat a material, which limits energy losses through conduction. 

With the latter, a predetermined distance must be upheld between the two heat sources. The goal here is to warm up the weld spot once completed to alter its microstructure. 

The aforementioned aren’t the sole advantages of using said welding technique. Using a laser also means greater arc stability, given that the arc is drawn to the laser beam, enabling the laser beam to penetrate the workpiece at greater depths. 

The laws of physics at work during this welding process are still not clearly defined. However, industry professionals still consider this type of welding underdeveloped, meaning it could be further optimised, most notably to ensure that welds have fewer: 

• Cracks

• Brittle bits

• Heat-caused distortions 

Where Is Laser Welding Used and What For?

Aluminum 

Laser welding is a technique that enables the welding process of aluminum. However, the quality of the weld won’t always be consistent, given that aluminum’s properties account for the following: 

• High thermal conductivity

• Very reflective surface (can reflect more than 80% of visible light) 

• Low molten viscosity

To weld aluminum, given its thermal conductivity, the laser beam used must be more powerful compared to the laser used to weld another material. However, said property does vary based on the alloys added to the aluminum. Zinc and magnesium will improve the aluminum's weldability. 

How does aluminum's reflectivity come into play when using a laser welding technique? Aluminum will solely absorb a small part of the radiation. To limit its reflectivity, aluminum can be:

• Etched

• Sandblasted

• Laser-textured 

As for its low viscosity, to this day, no solution has ever been found to offset this property.

Steel 

Laser welding steel is done depending on its alloy composition. Based on its composition, the thermal conductivity coefficient is modified. As such, molybdenum significantly increases said coefficient, while nickel and copper only do so moderately. On the flip side, an aluminum-silicone alloy reduces it, much like chromium, vanadium, tin, and antimony.  

Stainless Steel

Stainless steel, primarily used in the aerospace, automotive (airbag systems), defence, and medical industries, can be laser welded. However, to avoid creating flaws in the welds, or possibly material corrosion or oxidation, a distinction is made between the following: 

• Austenitic stainless steel, which has low thermal conductivity, is perfectly suited for laser welding 

• Ferritic or martensitic stainless steel is much more difficult to weld.

Titanium

Titanium can be laser welded. However, a distinction must be made between the three types of titanium: 

• Alpha phase (near-pure grade titanium) 

• Beta phase (metastable alloy) 

• Alpha-beta two-phase alloy 

The alpha phase has great weldability on account of its resistance and strength. The same applies to a two-phase alloy. However, metastable alloys have very poor weldability due to strength deterioration post-welding.  

What Other Materials Can Be Joined with Laser Welding?

Glass

Glass is still rarely assembled using a welding process. This is because the most commonly used lasers in the industry are CO2 lasers. And, the latter causes glass materials with a low thermal expansion coefficient to crack.

However, an ultrashort pulse laser (also known as an ultrafast laser) is a technology that allows glass workpieces to be welded together. It boasts the following:

• Doesn’t crack glass

• Weld spot doesn’t need to be heated pre- and post-welding

• Glass can be welded no matter its thermal expansion coefficient 

Plastics and Thermoplastics

Laser welding plastics and thermoplastics has several advantages over other techniques on account of the following: 

• The heat source is particularly controlled

• Accurate beam focus and spot size 

• Beam resolution can be lower than 100 micrometres

• This type of welding enables to creation of intricately shaped joints

Advantages and Benefits of Laser Welding

Laser welding has four key advantages:

• Laser welding works with numerous materials

• Precise weld spots

• Laser welding adapts to an array of material thicknesses

• It has exceptional characteristics

1. Laser Welding and Materials

As we already covered, laser technology can be used to weld a lot of different materials: 

• Steel

• Stainless steel

• Titanium

• Aluminum

• Glass

• Plastics and thermoplastics 

2. High-Precision Welding

As detailed in the plastics and thermoplastics section above, the beam resolution can be under 100 micrometres. The latter is why lasers are used for precision/fine mechanics, for example.  

3. Laser Welding and Thickness

Laser welding can be used to weld 0.01 to 50 mm thick plastic or metal pieces.

4. Laser Welding Characteristics

Laser power density is much greater than that produced through arc or plasma welding. Consequently, it makes for two exceptional welding spot characteristics: 

• Narrow welds

• Deep welds 

Moreover, here are other technique-specific characteristics:

• High-quality

• Great precision

• High performance

• Welding speed

• Significant flexibility

• Low distortion 

We could limit ourselves to simply detailing the four upsides to laser welding if said process couldn’t be robotised. Thanks to robot-assisted processes, laser welding lowers labour costs and makes for efficient production lines in manufacturing plants and factories. 

Disadvantage and Drawback of Laser Welding

Laser welding has one main disadvantage:

• Its cost is quite high

High Cost

The many advantages of laser welding come at a significant cost. While the precision, speed, and quality of laser welding are unmatched in many applications, the initial investment required can be substantial. Typically, the upfront cost of a laser welder can range from double to triple that of a traditional welding system. This higher cost reflects the advanced technology, precision optics, and complex control systems integrated into laser welding machines, contributing to their superior performance and efficiency.

FAQ

When Was Laser Welding Invented?

Laser welding emerged in the 1960s, soon after Theodore H. Maiman introduced the first operational laser in 1960.

Is Handheld Laser Welding as Strong as MIG Welding?

Laser welding is not only known for its typically greater strength compared to MIG welding, but it also operates three to ten times faster.

Want to learn more about welding? Check out these articles:

• Welder: Ins and Outs of the Job

• Everything to Know About MIG/MAG Welding

• Flux-Cored Arc Welding Techniques and Advantages