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.
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.
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.
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.
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.
Types of Laser Welding
There are two primary types of laser welding based on the produced energy density:
Conduction welding
Keyhole welding
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.
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).
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.
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.
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.
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.
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.