Laser welding is a welding technique that utilizes a focused laser beam to join different materials. This is primarily used to weld metals and thermoplastics. By heating the workpiece to its melting point, the materials merge upon cooling.

In the 1960s, laser welding emerged concurrently with the development of laser technology. Early experiments in laser welding were carried out by scientists at the Bell Telephone Laboratories in the United States. They utilized a ruby laser, delivering brief, intense pulses of coherent energy. Focusing these pulses onto a tiny spot where metal parts met caused the metals to melt and merge. Remarkably, these initial tests produced exceptionally narrow and accurate welds, minimizing heat-affected zones (HAZ) and distortion. Moreover, these experiments showcased the capability to join dissimilar materials.

The HAZ refers to the area surrounding the weld where the material experiences changes in its microstructure and mechanical properties due to the heat from the welding process. In laser welding, the HAZ is typically smaller compared to traditional welding methods like electron beam welding, owing to the precise control of the laser beam. This minimized heat-affected zone is advantageous as it reduces the risk of material distortion, ensuring the welded joint retains desired material properties.

The intense heat generated by the laser beam permits rapid welding in thin materials at speeds of meters per minute. For thicker materials, it facilitates accurate, deep welds between square-edged components. This focused light energy concentrated on tiny spots or specific areas, enables precise control of thermal energy and the welding process. The laser welding beam is typically generated by a solid-state, fiber, or CO₂ laser, each of which has its advantages.

Laser Welding: Setup and Working

The laser welding setup consists of a range of equipment that includes a laser source, beam delivers system, and CNC System. The laser source can be a fiber laser or be based on CO₂, / Nd:YAG technology. The beam delivery system comprises of mirrors and lenses, that are used to guide and focus the welding laser beam onto the material. The laser welding setup often has a CNC system or is attached to a robotic arm to ensure precise control.

The laser welding machine directs an intensely concentrated laser beam onto the space between two or more materials that need to be welded. This high-power focused laser beam delivers substantial energy levels that cause the materials at their joints or edges to melt, forming a unified joint. This concentration of light occurs within a small area, ranging from a fraction of a millimeter to a few millimeters in diameter. As the workpiece absorbs the energy from the laser beam, its temperature rises to the melting point. The molten areas of the materials then blend together, creating a strong weld between the objects being joined.

To maintain a stable temperature within the laser machine, a cooling system is used to prevent damage to the laser source and other components due to the intense heat generated during operation.

Selecting a Laser for Welding Applications

When selecting a laser source, it is crucial to consider numerous application-specific factors such as material type, joint design, penetration depth, welding speed, alignment precision, integration needs, and budget constraints. Every laser source has unique characteristics that cater to specific welding demands, although there might be some similarities in certain scenarios.

The size of the laser used for welding purposes can vary widely based on the specific application and requirements. There are both compact, handheld laser welding devices and larger, industrial-grade lasers used in manufacturing settings. The choice of laser size depends on factors such as the material being welded, the thickness of the material, the desired welding speed, and the precision needed for the task.

Types of Lasers for Welding

• Continuous Wave (CW) Lasers: CW lasers are used in applications requiring high precision and accuracy, such as microelectronics and medical device manufacturing. The stable and controlled energy output ensures precise and clean welds. CW laser welding can achieve high welding speeds, making it efficient for mass production and industrial applications. The consistent heat input minimizes the heat-affected zone, reducing the risk of material distortion (changes in the shape, dimensions, or alignment of the welded material) and ensures good structural integrity. 
• Pulsed Lasers: Pulsed lasers are suitable for applications where fine and detailed welding is required, such as in jewelry manufacturing and microelectronics. These lasers are used for welding materials that are sensitive to heat. By controlling the energy input, pulsed lasers minimize heat-affected zones, reducing the risk of thermal distortion.

The classification of materials as thin or thick in the context of laser welding can indeed vary based on the specific application and the perspective of the industry or field. While a general guideline often considers materials with a thickness below 3 millimeters (or 0.12 inches) as thin, and materials with a thickness above 3 millimeters as thick.

Varieties of Laser Welding Equipment

Although CO₂ models with powers up to 20 kilowatts exist, their beam quality diminishes compared to lower power options. The optimum irradiance can be achieved on a workpiece at around 5000 watts, where the beam quality and focusing are superior.

Nd:YAG lasers have gained prominence in industrial welding and are the second most commonly used lasers for welding after CO₂ lasers. Initially, CO₂ lasers dominated applications requiring multi-kilowatt power due to their earlier development in this range. However, Nd:YAG lasers are increasingly replacing CO₂ lasers in certain industrial applications due to their shorter wavelength, enabling better focusing capabilities.

Traditional Welding vs Laser Welding

Traditional welding techniques like tungsten inert gas (TIG), metal inert gas (MIG), and spot welding have been used in manufacturing due to their long-standing use and deep understanding within the industry.

• Tungsten inert gas (TIG) welding involves the utilization of a non-consumable tungsten electrode to heat the workpiece and, if necessary, melt the filler material, producing the weld through an arc welding process.
• Metal inert gas (MIG) welding, on the other hand, utilizes a consumable wire component that serves both as the electrode and filler material, creating the weld through an arc welding method.
• Spot-welding, another technique, utilizes a pair of electrodes to clamp workpieces together and applies an electric current between them, resulting in the creation of the weld.

Advantages of Traditional Welding

• They can accommodate less precise and accurate workpiece fit-up
• Traditional welding processes are generally easier to automate
• Lower initial investment costs
• Manual implementation

Conversely, emerging welding methods like laser welding leverage recent technological advancements. Laser welding provides advantages such as a reduced heat affected zone (HAZ), minimized risks of deformations, faster processing speeds, and enhanced suitability for welding thin metals.

Advantages and Disadvantages of Laser Welding

Advantages of Laser Welding

Laser welding is a highly adaptable technique with numerous merits across various applications. Here are some of the key advantages of laser beam welding:

• Reduced Thermal Impact: Laser welding significantly minimizes the risk of thermal distortion in workpieces by applying less thermal stress at the weld seam. This process curtails the heat dispersed to the surrounding material, preventing issues such as bending or stress.
• Versatility: The welding process demonstrates remarkable versatility, accommodating thick plates, precious metals, copper contacts, and dissimilar metals. Its compatibility with diverse applications has made it a prevalent method in sheet metal fabrication.
• High Speed: The technique can achieve speeds up to five times faster or more than traditional processes. This rapid welding pace translates into shorter processing times and heightened productivity within a limited timeframe.
• Reliability: It ensure high reliability due to their force-free, non-contact, and wear-free attributes. Additionally, the process offers exceptional strength owing to its significant welding depths.

Disadvantages of Laser Welding

• High Initial Cost: Laser beam welding equipment is generally costly, rendering the process more expensive compared to other welding techniques. Laser setups can be twice or more the cost of traditional welding systems, making it financially prohibitive for low-volume applications and smaller productions.
• Incompatibility with Irregular Workpieces: It necessitates a direct line of contact between the laser beam and the joint being welded, making it challenging to weld joints in irregularly shaped workpieces.

Applications of Laser Welding

Laser welding technology is widely utilized across various industries due to its precision, efficiency, and versatility. Some of the key industries that extensively use laser welding include automotive, aerospace, electronics, medical, jewelry, plastics, construction, energy, etc.: 

• Scientific: In the field of nuclear fusion, laser welding is used to fabricate components for experimental fusion reactors, such as containment vessels and diagnostic equipment. It is utilized in various scientific research facilities for fabricating specialized equipment, sample holders, and experimental setups requiring precise and non-contaminating joining methods.
• Automotive: Laser welding plays a pivotal role in the automotive sector due to its cost-effectiveness, quality, and efficiency. Operating in a tool-free mode and often eliminating the need for head replacements, it finds extensive use in various automotive components. Engine parts, solenoids, fuel injectors, and air conditioning units are examples of components produced using laser welding.
• Aerospace: In the aerospace industry, laser welding offers the precision necessary for applications like airframes and security metal detectors. This method is instrumental in joining lightweight and intricate structures crafted from materials such as aluminum, titanium, and other alloys. Welding in aerospace applications not only ensures precision but also aids in reducing aircraft weight by minimizing the use of rivets.
• Electronics Industry: The electronics sector heavily relies on laser welding and sheet metal cutting techniques to fabricate advanced electronic equipment. Laser welding methods, including continuous wave, Nd:YAG, fiber, and pulse laser welders, are adopted by product designers. These machines produce meticulous welds for tiny, sophisticated electrical components like sensors, microelectronic parts, circuit boards, specific transistors, and control units.
• Jewelry and Watchmaking: Laser welding finds widespread usage in the jewelry industry for both production and repair tasks involving intricate and delicate designs. It effectively joins precious metals like gold and platinum while minimizing discoloration and distortion. The industry employs a "free moving" welding concept, allowing operators to rotate jewelry pieces, rings, or bracelets safely while the laser beam maintains a fixed position, ensuring ease of operation and safety.
• Marine: This is also employed for underwater welding applications, such as the manufacture and maintenance of subsea equipment, including underwater pipelines, remotely operated vehicles (ROVs), and underwater sensors, due to its precision and durability in underwater conditions.

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