Laser Welding Explained: What It Is and How It Works

Although Arc welding is undoubtedly the most popular welding method in the industry, as well as among home users, we are seeing improvements and technological advances every day.

Shortly after scientists discovered the laser in the 1960s, they began experimenting with its potential applications. This discovery led to the development of laser welding, also known as laser beam welding (LBW), a method highly regarded for its precision, speed, and quality.

In this article, we will delve into what laser welding is and how it works, emphasizing the high standards of quality that laser welding maintains.

Laser Welding Process
Source: https://www.bodor.com/us/blogs/handheld-laser-welding-vs-MIG-welding.html

What is Laser Welding?

Laser welding, also known as laser beam welding (LBW), is a joining method that utilizes the concentrated and focused heat of a laser beam to melt and fuse metals or thermoplastics. Laser welders produce a precise and focused beam that heats the joint. High-density energy melts or even evaporates the metals in the joint, and they fuse as they cool down.

What is Laser Welding?
Source: https://www.researchgate.net/figure/The-schematic-view-of-LBW-process_fig2_235996056

Compared to traditional Arc welding, laser welding differs in terms of its heat source. Arc welding methods utilize the heat generated by an electric arc that forms between an electrode and a workpiece. Laser welding uses the heat of a focused laser beam to reach the melting temperatures of metals, melt them, and fuse them, most often without the need for additional filler metal.

Today, laser welding is one of the most advanced welding techniques. Welders use it to join some of the most challenging metals, including aluminum, titanium, high-strength steel alloys, copper alloys, and nickel and its alloys. Additionally, lasers can fuse thermoplastics that can melt and solidify repeatedly, such as acrylic, PVC, PC plastics, or composites.

Laser Welding Aluminum Process
Source: https://www.youtube.com/watch?v=Vs9GCMRCg3M

How Does Laser Welding Work?

Laser welding works by tightly focusing the light of the laser into the joint. You can imagine it as focusing the sunlight through a magnifying glass to burn a piece of paper. But the science behind laser welding is a bit more complex than that.

The core of laser welding is the laser source that generates the laser beam. The raw laser beam carries an initial energy, but it is not high enough to melt the pieces.

The beam is transported through an optical fiber and then focused using mirrors and lenses. Optics focus the raw beam diameter to create a depth of focus. A curved mirror or a curved surface lens focuses light down to a spot size, which ranges from tens to a few hundred microns in diameter.

How Does Laser Welding Work
Source: https://www.stylecnc.com/blog/laser-welding-vs-plasma-arc-welding.html

Focusing the raw light into tiny spot sizes creates extremely high power density. Depending on the spot size, the density can reach the melting point of metal pieces, which will fuse as they solidify. However, the power can be extremely high, capable of melting and vaporizing the surfaces.

Welders often use laser welding for thin sheet pieces, so no additional filler metal is needed. However, adjustments are made in some applications. Laser welding can be carried out in atmospheric conditions. Nevertheless, reactive metals that are prone to oxidation and contamination require the use of an external inert shielding gas.

Manual Laser Welding without Filler Wire
Source: https://www.ipk.fraunhofer.de/en.html

Types of Laser Welding

There are two primary types of laser welding based on the produced energy density:

• Conduction welding

• Keyhole welding

Conduction Welding vs. Keyhole Welding
Source: https://www.researchgate.net/figure/Schematic-of-conduction-and-keyhole-welding-modes-45_fig2_369749519

Conduction laser welding uses low-power lasers, typically rated less than 500W, to melt and fuse pieces. The laser beam produces a power density of less than 105W/cm2, which is sufficient to melt and fuse the surfaces of the metal. Although the heat reaches the melting point of the metal, it doesn't penetrate it. Due to lower heat, this is a slower technique, best for thin pieces, but it yields high-quality results and aesthetically pleasing welds.

Keyhole laser welding is a rapid and highly efficient process that utilizes high-power lasers. The lasers produce a power density exceeding 105W/cm2, melting and vaporizing the metals, resulting in deeper penetration. As the laser melts, evaporates, and penetrates the metal, it forms a cavity known as the keyhole. This plasma-like state reaches extreme temperatures (over 17.000 F), which makes it ideal for high-volume production.

Keyhole Laser Welding of Dissimilar Materials
Source: https://www.youtube.com/watch?v=sdothbNw2GY

Based on the type of laser beam welding process, we also see types such as laser spot welding, laser seam welding, or hybrid laser welding.

• Laser spot welding is used to create precise, small, and strong spot welds on complex joints.

• Laser seam welding is best for long, continuous seams.

• Hybrid laser welding combines the basics of laser beam welding and arc welding methods, such as MIG welding, TIG welding, or Plasma Arc Welding (PAW).

Principles of Hybrid Laser Welding
Source: https://ahssinsights.org/joining/adhesive-joining/hybrid-welding-processes/

Parts of the Laser Welding System

A laser welding system, or laser welding machine, is more complex and expensive than traditional arc welders. These welders come in various types, each designed for specific applications. The most common types are:

• Portable laser welding machines: Offer lightweight and portable solutions, providing flexibility for various jobs.

• Handheld machines: Smallest and easiest to use, but deliver limited power.

• Fixed laser welding machines: Large, often robotic, and automated laser welding systems for mass production.

Regardless of the type, each machine consists of several key components. Each laser welder has the following parts of the system:

• Laser source

• Beam delivery system

• Cooling system

• Control system

• Gas supply system

• Protection system

Let us further explain how each part affects laser welding.

Source: https://www.accteklaser.com/cooling-system-and-maintenance-of-laser-welding-machine/

The laser is the central piece of LBW, so the laser source is the heart of this entire process. This source generates the laser beam needed for welding. The quality and type of the laser influence the precision, depth, and speed of the weld.

Machines can extract Laser energy from several different sources, including gas, solid, optical fiber, or UV light. As a result, lasers used in laser welding are divided into two categories: gas lasers and solid-state lasers.

Solid-state Lasers vs. Gas Lasers 
Source: https://www.keyence.com/ss/products/measure/welding/laser/difference.jsp

Types of Lasers Based on the Extraction Medium

Depending on the type of medium, the most common types of lasers in laser welding are:

CO2 lasers: The first type of lasers in laser beam welding. Source extracts laser from a gas mixture of carbon dioxide, helium, nitrogen, xenon, and hydrogen, which are electrically excited. While inexpensive, a CO2 laser is less energy-efficient than newer types; however, it is still widely used on thermoplastics and organic materials, such as wood and leather.

Solid-state lasers: These lasers utilize solid crystal lattices as the active medium, rather than gas mixtures. The most common type is the Nd: YAG laser, which uses neodymium-doped yttrium-aluminum garnet crystals. The crystals are excited by lamps or diodes and emit laser radiation with a wavelength of 1.064 μm. These performances make YAG lasers suitable for most metals, including reflective ones, and some plastics; however, they are expensive to maintain and operate.

Fiber lasers: utilize optical fiber as the gain medium, making them ideal for precision welding tasks. Optical lasers can fire particularly small spot sizes, making them suitable for applications that require high powers and excellent precision.

Fiber Laser Welding
Source: https://www.optica-opn.org/home/articles/volume_29/october_2018/features/high-power_fiber_lasers/

UV lasers: Newer types of lasers are emerging, and one of them is UV/IR lasers. These lasers generate laser beams by using high-energy photons in the ultraviolet or infrared spectrum, making them highly efficient and energy-dense.

Semiconductor laser (LD: laser diode): This type of excitation features a narrow emission spectrum, and it can be triggered by selecting the specific absorption transition of the laser medium. It provides high absorption efficiency and excellent beam convergence for high-density excitation.

Applications of Laser Diodes
Source: https://www.semiconductor-today.com/news_items/2019/apr/idtechex-090419.shtml

Types of Lasers Based on Oscillation Form

Regardless of the source, lasers can produce a continuous wave or a pulsed beam. Each type has its ups and downs in specific applications.

Continuous wave (CW) lasers emit a constant, uninterrupted beam. They are typically fiber-type lasers capable of producing small spots and deep penetration welds.

CW lasers have vast operating power, ranging from 200W to over 100,000+ watts. This wide power range and high energy density are ideal when fusing metals with different thermal and reflectivity characteristics, such as stainless steel or copper.

Pulsed lasers emit a series of short pulses at a specific width and frequency. They can produce very high peak powers for a few milliseconds, creating a series of overlapping spot welds. Pulsing limits the heat input, making lasers ideal for heat-sensitive and delicate metals. Additionally, they work great with reflective metals, as a high burst of power breaks reflection while keeping the average power low.

Pulsed Laser Welding vs. CW Laser Welding
Source: https://www.stylecnc.com/blog/pulsed-laser-vs-cw-laser.html

Beam Delivery System

Producing the laser beam is just the first step. The beam is further directed through the beam delivery system from the source to the welded pieces. This system ensures that the laser beam is accurately focused and directed to the weld area. It comprises several components, such as:

• Optical fiber: it transforms beams in fiber laser systems. Fiber provides flexibility and simplifies integration into automated systems.

• Mirrors and Lenses: Optical elements that focus and direct the laser beam onto the welded area.

• Collimators and Beam Expanders: These are devices that adjust the beam size and focus.

Beam Delivery Systems in Laser Applications
Source: https://laserscientist.com/beam-delivery-systems-in-laser-applications/

Cooling System

Laser sources and other components generate heat during the welding. A lack of energy efficiency and a laser-generating process causes pieces to heat up, and that's where the cooling system kicks in. The cooling system prevents overheating and damage to the components.

Based on the cooling methods, there are two common types:

Air cooling: This method utilizes ambient air circulation to cool the components and dissipate heat. Air cooling is a fairly cost-efficient and straightforward system, but it comes short with high-powered lasers. They produce so much more heat that regular air-cooling is often inefficient.

Water-cooling: Water-cooling systems use circulating water to dissipate the heat from the main components. Water is more efficient at cooling components, making it suitable for high-powered lasers and their components that require precise heat control. However, it is more complex and expensive.

Air Cooling vs. Water Cooling

Control System

The control system is the brain of Laser welding machines. It helps set up the parameters and optimize the welding process.

The central control enables you to adjust key parameters, including laser power, pulse frequency, welding speed, and focal length. Modern machines utilize a series of sensors that monitor and provide real-time feedback on the current laser welding process, enabling potential adjustments.

Automated laser welding systems support software integration. You can add CAD/CAM software to program welding paths precisely, achieving perfect results and repeatability in welds. Programming reduces the possibility of human error and improves efficiency.

Automated Laser Welding
Source: https://www.machinemfg.com/applications-of-laser-welding-robots/

Safety System

Although laser welding is less hazardous than Arc welding, welding safety is paramount. Laser welding systems use safety features to protect operators, components, and the environment from possible damage.

The first step in safety involves shields that protect a laser beam from escaping the designated welding area. The shield absorbs and reflects the laser light, protecting the operators from potential danger.

Designated Laser Welding Controlled Area
Source: https://cobot.systems/laser-welding-safety/

Emergency shut-off switches completely shut down the operation in case of an emergency. These are critical in stopping the operation to prevent accidents and damage to the equipment.

Interlock systems are sub-parts of safety systems that include specific criteria that must be met before the process can start. For example, laser welding won't start unless the laser shield is in place.

Laser Safety System
Source: https://www.lasersafetysystems.com/laser_interlock_education.html

Shielding Gas System

The gas supply system provides an external shielding gas, which is necessary when welding reactive metals. When heated, reactive metals are prone to contamination, and they can absorb atmospheric gases, leading to porosity. Therefore, laser systems often use high-purity, inert gases such as argon, helium, or sometimes nitrogen.

The shielding gas supply system provides the gas that shields the weld from oxidation. The shielding gas also stabilizes the weld pool, creating a controllable environment.

In high-power laser welding, vaporized metal creates a plasma-like state. This state can interfere with a laser beam, reducing its efficiency and power. Inert gases suppress plasma, allowing the beam to penetrate deeper into the metal.

How Plasma Affects Laser Welding
Source: https://algolaser.com/blogs/how-to/laser-and-material-interaction-plasma-effect

Pros, Cons, and Applications of Laser Beam Welding

Due to its advantages, manufacturers widely use laser welding across industries, often in complex joints and on advanced metals. Here's a quick breakdown of its pros and cons and applications.

Laser Welding Advantages

• High Precision and Control: Laser welding is exceptionally accurate and ideal for small, intricate welds.

Source: https://cobot.systems/laser-welder-cost/

• Deep, Narrow Welds: High-power lasers can produce an excellent depth-to-width ratio, making laser welding an ideal choice for welding thick materials.

• Fast Welding Speeds: Laser welding is significantly faster than arc welding, particularly in automated production lines.

• Non-Contact Process: No physical contact between the tool and the material yields less wear and tear.

• Easy to automate: Laser welding is compatible with CNC systems and robotics and is often part of large-scale, fully automated production lines.

Robotics Laser Welding Process
Source: https://www.youtube.com/watch?v=lhTvtFM6TE0&t=41s

• Limited Heat Input: Low-power lasers reduce the risk of thermal damage to surrounding areas. A narrow heat-affected zone (HAZ) reduces the heat impact and, thus, the distortion and warping on sheet metal and heat-sensitive pieces.

• Great for Difficult-to-Reach Areas: The laser can be directed via mirrors or fiber optics to work on complex designs and hard-to-reach areas.

• Produces high-quality results: Excellent heat control and precision of laser welding can yield the highest-quality results. Welds are contamination-free and visually appealing.

High-Quality Results with Laser Welding
Source: https://www.lasertherm.cz/eng/technologies/laser-technologies/laser-robotic-welding

Drawbacks of Laser Welding

• High Initial Investment: Laser welding equipment is more complex and expensive to buy and maintain. Although long-term assets yield higher returns due to their increased speed and better results, they require a substantial initial investment.

• Strict Joint Fit-Up Requirements: Gaps between parts must be minimal. Otherwise, weld quality may suffer.

• Issues with Reflectivity: Shiny materials, such as copper and aluminum, can reflect the laser. Reflecting the beam reduces the efficiency and power of the laser.

• Limited Thickness for Single Pass: Even though a high-power laser can achieve deep penetration, a single pass may not be sufficient for very thick sections. Arc welding thrives on thick metals.

• Sensitive to Surface Conditions: To produce the highest-quality results, laser welding requires clean, well-prepped surfaces.

Source: https://www.mechdaily.com/what-is-laser-welding/

Laser Welding Applications

Operators favor Laser Beam Welding (LBW) where precision, speed, and strength are critical. Here are the most common applications and real-world uses across industries:

Source: https://amadaweldtech.com/applications/methods/laser-welding/

• Automotive Industry: Manufacturers use lasers to weld body panels, gear components, transmission parts, exhaust systems, door panels, and engine components on production lines.

• Aerospace Industry: Lasers are often used to join parts of turbine blades, fuel nozzles, and structural components of jet engines.

• Electronics and Microelectronics: Microwelding sensors, circuit boards, battery tabs, and fine wires. Welding of lithium-ion battery connections in smartphones and laptops.

• Medical Device Manufacturing: Lasers are used to precisely weld surgical tools, pacemakers, stents, and implants made of titanium or stainless steel.

• Tool and Die Industry: Lasers are well-suited for repairing and joining precision tools, as well as worn-out mold edges.

• Jewelry and Watchmaking: Laser welding produces fine, non-invasive welds in precious metals and delicate components of luxury watches, resulting in minimal visible deformation.

• Energy Sector: Laser beam welding parts for fuel cells, batteries, and nuclear components. Welding thin stainless steel in heat exchangers or battery terminals.

Laser Beam Welding for Battery Parts
Source: https://www.youtube.com/watch?v=S_j89Cs1dcA

Final Thoughts

Laser beam welding is an exact and efficient welding method. The ability to produce deep, narrow welds with minimal heat distortion makes it ideal for intricate and high-strength applications. Some common examples are industries such as automotive, aerospace, electronics, and medical device manufacturing.

Despite the high initial cost and the need for precise joint alignment, its speed, automation potential, and quality make it a valuable choice for modern manufacturing. As technology advances, LBW continues to expand its role in producing reliable, high-performance components, especially in sectors where accuracy, cleanliness, and material integrity are critical to product success.