Fiber Laser Welding Explained: What It Is and How It Works

Table of Contents > 1. What Is a Fiber Laser?     1.1 How Do Fiber Lasers Work?         Step 1: The Pump source creates light         Step 2: Pump light travels through the optical cable         Step 3: Light amplification         Step 4: Creating different wavelengths         Step 5: Focusing and shaping the laser beam 2. Fiber Laser Welding     2.1 Main Parameters of Fiber Laser Welding         2.1.1 Laser Power         2.1.2 Laser Wavelength         2.1.3 Mode of Operation         2.1.4 Core Size (Mode)         2.1.5 Beam Size         2.1.6 Laser Beam Quality 3. Types of Fiber Laser Machines     3.1 Essential Parts of Laser Welding Systems     3.2 Optional Parts of the Laser Welding System 4. Advantages, Drawbacks, and Applications of Fiber Laser Welding     4.1 Drawbacks of Fiber Laser Welding     4.2 Fiber Laser Welding Applications     4.3 Fiber Lasers vs Other Lasers Used in Welding 5. Final Thoughts 6. 🧐Fiber Laser Welding Explained: What It Is and How It Works FAQ

Lasers have become an essential part of industries worldwide due to their diverse applications in engraving, cleaning, cutting, and welding. First, CO2 lasers have been around for some time, but the technology continues to evolve, allowing new solutions to emerge.

One of the significant advancements is the fiber laser, which provides much higher efficiency, a compact size, and lower maintenance requirements compared to traditional CO2 lasers. Its benefits made it a vital part of global applications, including welding.

In this article, we will explain the basics and working principle of fiber laser welding, including its equipment and applications. Let's learn more.

Fibre Laser Welding In Action
Source: https://www.youtube.com/watch?v=o_mogeXz-1Q

What Is a Fiber Laser?

Fiber lasers are a type of solid-state laser that generates and amplifies light within the core of an optical fiber. Optical fiber cable, which is made of silica glass, is doped with a rare-earth element and serves as a gain medium.

Compared to legacy lasers, such as CO2 lasers or disk lasers, fiber lasers are free of complex optics, frequent service requirements, and consumables. This working principle makes them much easier to use and maintain, prolonging their lifespan. Additionally, fiber lasers are much more efficient and produce shorter wavelengths, allowing them to address the issues with metal reflectivity.

Interestingly, fiber lasers are not a new discovery. Elias Snitzer invented the fiber laser in 1961 and showed its use in 1963. However, they didn't find a serious industrial use until the 1990s. The main reason was the lack of power.

Early laser pumps could only emit a few tens of milliwatts, whereas most applications require at least 20 watts of power. The technological advancement of the early 90s broke the 4W barrier, but the state-of-the-art, military-grade fiber lasers today can output 10-100 kW.

 

How Do Fiber Lasers Work?

All lasers have a basic working principle. The source generates the light, which then travels through a medium that transforms it into a laser beam. A series of lenses and mirrors directs and focuses the beam down to a tiny spot, creating an extremely high energy density.

However, with the fiber lasers, things are a bit different. Here is a step-by-step explanation of how fiber lasers work.

Fiber Laser Diagram
Source: https://www.laserlabsource.com/Solid-State-Lasers/fiber-laser-basics-and-design-principles

Step 1: The Pump source creates light

The process begins with high-power semiconductor laser diodes that use electricity to generate light. Once the electricity enters the diodes, an extra electron transforms into a photon. As electricity runs through the diodes, the number of photons increases, resulting in the creation of light.

The light is pumped into the fiber-optical cable, which transports it. Due to the action, these diodes are also known as a pump source. The generated light is further used to create a laser beam used for welding or cutting.

Source: https://www.rp-photonics.com/diode_pumped_lasers.html

Step 2: Pump light travels through the optical cable

In nature, light travels in all directions, so to obtain a laser beam, it must be directed. To avoid light distortion and refraction, diodes pump light into an optical cable that transports and directs it.

Two components transport and control the direction of the light:

• Cable core: The core of the optical cable is responsible for transporting the light. It is made of silica glass and includes a rare-earth element. But, due to refraction, light can escape the core, and that's why there is a second element.

• Cable cladding: The cladding surrounds the core, providing total internal reflection. Due to the cladding's refraction index, all light that strays off the path is reflected into the core.

Source: https://www.meetoptics.com/academy/optical-fibers-fundamentals

Step 3: Light amplification

The light created by diodes carries an initial energy, but it still isn’t a laser beam. As noted, the core of the optical fiber is doped with rare-earth elements such as ytterbium or erbium.

During its path through the optical fiber, pumped light encounters doped regions, or a laser cavity filled with rare-earth elements that radiate specific particles. These regions, also known as fiber Bragg gratings, amplify the light, creating a particular wavelength.

What is Fiber Bragg Grating
Source: https://www.fiberoptics4sale.com/

The first type of grating acts as a mirror, reflecting light into the cavity. The second type allows some light to exit the cavity, but reflects the rest back.

So here is what happens inside it. Photons from light hit excited particles of rare-earth elements, which also release photons. Since the Bragg gratings reflect photons into the cavity, and more pump light reaches the cavity, an exponential number of photons are released. 

If you remember, LASER stands for Light Amplification by Stimulated Emission of Radiation. Therefore, pumped light transforms into laser light.

Laser: Light Amplification by Stimulated Emission of Radiation
Source: https://www.youtube.com/watch?v=iAn2IivQHIM

Step 4: Creating different wavelengths

When sufficient laser light intensity accumulates within the resonator, it releases a high-intensity, coherent laser light. The wavelength of the laser beam depends on the rare-earth element inside the doped region.

For example, ytterbium generates a wavelength of 1064 nm, while other elements produce other wavelengths. This occurs because specific particles release specific photons.

Understanding the wavelength is crucial in determining the applications of lasers. Some are better suited for laser cutting and cleaning, while others are more suitable for welding and cutting, as they fight reflectivity by providing more power.

Step 5: Focusing and shaping the laser beam

As it undergoes the process of transformation and amplification, the fiber laser beam becomes collimated, which is undesirable in all applications. Before it exits the machine, the beam undergoes the final process of focusing and shaping.

Machines use different components to shape and focus the beam. Most commonly, these are lenses and beam expanders. For example, a short focal length is excellent for cleaning and engraving due to its better laser digging capabilities.

Laser Beam Expanders: Keplerian Telescope vs. Galilean Telescope
Source: https://www.edmundoptics.com/knowledge-center/application-notes/lasers/beam-expanders/

Fiber Laser Welding

Lasers are beneficial in various applications, including engraving, cleaning, cutting, and welding. Fiber laser welding is a process that uses the heat of a focused and directed laser beam to melt and fuse the pieces.

The fiber laser beam is highly precise, efficient, and low-heat, providing excellent value in delicate metal welding. The technology is compact, meaning it won't occupy the entire floor space for setup.

Let's examine the main parameters.

Fiber Laser Welding
Photo by @bestsign666 (TikTok)

Main Parameters of Fiber Laser Welding

Like any other process, Fiber laser welding also has parameters that directly affect its welding ability. Depending on the parameters, you can weld different types or thicknesses of metals or achieve better results.

The primary parameters of fiber laser welding are:

• Laser power

• Wavelength

• Mode of operation

• Core size

• Beam size and quality

Let's further explain each.

Laser Power

The power of the laser is expressed in watts, and it directly affects how thick pieces it can weld or cut. The more power the laser has, the deeper it can penetrate.

Initial fiber lasers were relatively weak, but strong diodes enabled them to reach very high power levels. Fiber laser power can vary from 10-20W, often used in marking and engraving, up to 1-2 kW, used for welding thicker pieces. Military-grade applications utilize fiber lasers that power up to 100 kW.

1500W Fiber Laser Welding
Source: https://www.youtube.com/shorts/pgRnqx1y_WY

Laser Wavelength

Fiber laser wavelengths typically range from around 780 nm to 2200 nm. But the power and wavelength of the fiber laser are primarily dependent on the rare-earth metal used for doping.

For example, ytterbium-doped lasers operate in the ~1 µm range (e.g., 1064 nm) and erbium-doped lasers operate in the ~1.5 µm range (e.g., 1550 nm). The wavelength of the laser directly affects the absorption rate.

Reflective metals tend to absorb only a fraction of power. Changing the wavelengths of the laser reduces the reflectivity. Reducing the reflectivity increases absorption, allowing the laser to melt and fuse the pieces without requiring excessive power or energy.

Laser Type and Wavelength
Source: https://www.gweikecloud.com/

Mode of Operation

Fiber lasers can operate as either:

• Continuous-wave (CW): lasers emit a constant amount of energy continuously. They produce a steady stream of average power, making them the most common on the market. CW fiber lasers are ideal for welding medium- to thick-walled pieces.

• Pulsed lasers: At the same time, pulsed lasers release energy at a set repetition rate. By adjusting several parameters, such as pulse energy, repetition rate, or pulse duration, you can control the heat to reduce heat exposure. As a result, a pulsed fiber laser is ideal for working with thin, delicate metals, as it reduces heat input and prevents overheating.

Continuous-Wave (CW) and Pulsed Lasers
Source: https://www.stylecnc.com/blog/pulsed-laser-vs-cw-laser.html

Core Size (Mode)

Depending on the core size, fiber lasers can be single-mode or multi-mode.

Single-mode lasers utilize a smaller core diameter, typically ranging from 8 to 9 micrometers. Due to a small core, they produce tiny spots that provide improved precision, a narrow heat-affected zone, and higher energy density. As a result, single-mode fiber lasers are often used in micro-welding applications, such as battery welding.

Multi-mode fiber lasers utilize a larger core, commonly ranging between 50 and 100 micrometers. As a result, they produce a wider laser beam, which is less accurate, efficient, and provides lower energy density. However, these fiber lasers can process larger surfaces faster.

Single Mode Fiber vs. Multimode Fiber
Source: https://www.bonelinks.com/single-mode-fiber-and-multimode-fiber/

Beam Size

As the laser beam hits the surface, it forms an area of laser light referred to as a spot. The size of the spot directly affects the energy density of the laser. Operators adjust the spot size by focusing lenses, altering the distance between the beam delivery and the target, or employing longer or shorter wavelengths.

As the beam size decreases, the energy density increases. It also improves the accuracy, narrows the HAZ, and allows the beam to penetrate the metal quickly. Using a small beam size is ideal for microprocessing applications.

Fiber laser welding often uses a larger beam size in structural welding applications. A wider beam can cover a larger area, melting and fusing thicker pieces, although it provides less energy density and precision.

Laser beam profiles: Spot diameter vs. power density comparisons.
Source: https://www.researchgate.net/figure/Fiber-laser-beam-spot-diameters-power-density-and-profiles-measured-with-respective_fig2_43169632

Laser Beam Quality

Beam quality for single-mode lasers is measured in terms of M2, and the Beam Parameter Product (BPP) for multi-mode lasers. This is a complex parameter that represents the degree to which a laser beam can be focused.

For example, M2 = 1 means perfect laser beam quality. This beam experiences no divergence, but it is hardly achievable with today's equipment. Nonetheless, industrial-grade fiber laser welders can achieve a quality of up to M2 = 1.1.

Generally, higher beam quality improves speed in applications that require focused beams, such as cutting and welding. In applications that require wider beams, such as laser cleaning or heating, beam quality is not a primary concern.

A visual comparison of an ideal Gaussian beam (M² = 1) and a distorted beam (M² > 1) to illustrate the impact of M² on beam quality.
Image courtesy of Dataray, Inc.

Types of Fiber Laser Machines

Fiber laser welding machines vary depending on the manufacturers, solutions, and needs. Technological advancements brought several commercial types, with the most popular being:

• Handheld fiber laser welders: User-friendly machines similar to traditional MIG or TIG welders. Compact and ideal for less experienced users.

• Fiber laser welding workstations: Small, semi-automated stations ideal for small production batches. Operators load the parts, while the machine automatically welds the pieces.

• Robot welding machines: Fully automated robotic arms equipped with fiber laser heads. They follow the pre-programmed paths, providing excellent precision and repeatability.

• Robot-assisted welding machines: Robot arms can move and position clamping tools during laser welding, helping manufacturers scale up production and improve quality.

Essential Parts of Laser Welding Systems

Regardless of the machine type, each fiber laser welding system comprises the following essential components:

• Power supply: The power supply converts outlet electricity into direct current (DC) to provide the pump power required for the diodes to produce light.

• Laser source: The laser source comprises the pump source, the gain medium, and the laser cavity. The source converts light produced by a diode into a laser beam, which is then used for welding.

• Fiber optic cable: The optic cable guides and transports the beam to the surface, without allowing it to stray or refract off its path.

• Fiber collimator: The lens that converges the beam that comes out of the optic cable to better focus its energy.

• Beam expander: Used to expand the beam for applications that favor a broader beam coverage over high energy density.

• Focusing lens: Contrary to the previous part, this lens focuses the beam into a tiny spot.

• Scanning head: Rotating galvo mirrors that control the direction of the laser beam.

Optional Parts of the Laser Welding System

Technological advancements have enabled engineers to enhance the efficiency, safety, and power of fiber laser systems by incorporating additional features. As a result, state-of-the-art systems use optional parts such as the following:

• Wire feeder: Hybrid-laser welding systems combine a fiber laser heat source with a MIG wire feeder to enhance quality in cases of poor fit-up or larger gaps. Although adding a wire feeder slows down the process, it improves its versatility.

• Shielding gas: In critical applications and on metals prone to oxidation, such as stainless steel or titanium, fiber lasers utilize shielding gas. An external source provides shielding gas coverage to protect the molten puddle from contamination and oxidation.

• Fume extractor: Heating, burning, and evaporizing metals with a laser creates toxic fumes. A fume extractor can significantly improve the working environment and help workers avoid long-term exposure.

• Weld monitors and data analytics: Modern fiber laser welding systems are part of an Industry 4.0 environment that includes detailed monitoring and analytics. Sensors monitor welding parameters, enabling real-time adjustments or providing suggestions that enhance weld quality and efficiency.

• Laser cooling systems: High-powered industrial-grade fiber lasers can produce extreme heat. Cooling systems are crucial for ensuring safe operation.

Laser Cooling Systems
Source: https://www.meetoptics.com/

Advantages, Drawbacks, and Applications of Fiber Laser Welding

Pros of fiber laser welding include:

• Fast and powerful: Fiber lasers are extremely fast, enabling operators to achieve exceptional productivity. Variable power, beam size, and wavelength will allow them to weld metals of varying thicknesses.

• Versatile: Fiber lasers can weld a wide range of metals, including copper, aluminum, stainless steel, as well as dissimilar metals.

• Precise and easy to control: Narrowing the laser beam provides extreme accuracy, especially in intricate designs. Adjustable parameters make heat and process control very convenient.

• Compact: Laser systems with fiber lasers are more compact than those with other types of lasers. They won't occupy the entire floor, but they are still more complex and larger than traditional arc welding.

• Lower maintenance requirements: The non-contact laser welding method, with significantly fewer lenses and mirrors than legacy lasers, makes maintenance much easier and less expensive.

• They last very long: Fiber lasers have a "mean time between failures" (MTBF) of roughly 100,000 hours. In reality, MTBF will vary with the laser source, but it is higher than that of CO2 lasers, typically ranging from approximately 30,000 to 40,000 hours.

• Easy to automate: Remote controls, data monitoring, and programming make fiber laser welding easy to automate.

• Very efficient: Fiber lasers have an efficiency of over 50%, meaning they waste minimal power while still providing excellent heat control.

Fiber Laser Welding Process
Source: https://www.xometry.com/resources/sheet/laser-welding/

Drawbacks of Fiber Laser Welding

Cons of laser welding include:

• Weld quality is dependent on external factors. Poor fit-up, contamination, uneven gaps, and other external factors can significantly affect the quality of the welds.

• Dust or fumes can obstruct the laser beam: Contaminants or gases on the laser path can distort the laser beam.

• More complex than traditional arc welding: Although compact and straightforward, fiber laser systems are still more complicated than conventional welding units.

• Optical components require protection: Consumable protection is needed to protect the components from dust or contamination.

• Reflectivity is always an issue: Welding metals with reflective surfaces requires adjusting the wavelength of the laser in order to maximize absorption.

• Higher initial investment: Fiber lasers typically have a higher upfront purchase cost per watt of power compared to CO2 lasers.

Source: https://www.stylecnc.com/blog/laser-welding.html

Fiber Laser Welding Applications

The speed, precision, and efficiency of fiber lasers made them valuable to industries worldwide. Here are some examples and typical applications of fiber laser welding:

• Automotive industry: Joining car body panels, powertrain components, sensors, and battery parts in electric vehicles (EVs).

• Electronics industry: Precision welding of connectors, circuit components, and micro parts.

• Medical device manufacturing: Manufacturing surgical instruments, pacemaker housings, and implants.

• Aerospace and airplane: Welding thin-walled structures, turbine components, and lightweight alloys.

• Jewelry and Watchmaking: Fine welding of precious metals with minimal heat distortion.

• Energy Sector: Producing batteries, fuel cells, and sensor housings.

• Defense and military: Welding frames and armor plates.

Fiber Lasers vs Other Lasers Used in Welding

Final Thoughts

Fiber lasers are a remarkable technology that offers exceptional accuracy, speed, and efficiency. Their advantages make them highly valuable in various applications, including welding.

Fiber laser welding is a joining process that uses the heat produced by a focused laser beam. The beam is focused down to a small spot with high energy density, which melts and fuses the two pieces.

Compared to legacy lasers, such as CO2, fiber laser systems are more compact and have a longer lifespan. Although the initial investment is higher, lower maintenance and higher efficiency make them a better long-term choice.

Source: https://www.youtube.com/shorts/t9-H2tmE-zw