Laser Welding: the Complete Guide for Beginners - xTool

How Does Laser Welding Work?

The core principle behind any welding process is generating enough heat to melt and fuse the materials.

In traditional welding, this heat is produced through methods like an electric arc or a flame.

For laser welding, a highly concentrated laser beam generates the necessary heat, but with much greater precision and efficiency.

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When the laser beam is directed at the material, it rapidly heats a small, concentrated area, causing the temperature to rise above the melting point.

As the material melts, a molten pool forms, where the materials fuse together. Once the molten pool cools, it solidifies, creating a strong, metallurgical bond between the pieces.

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What sets laser welding apart is its ability to focus a high-energy beam onto a tiny area, resulting in exceptionally high energy density.

This rapid energy concentration allows the materials to fuse quickly, reducing the overall welding time compared to other methods.

The precision of the laser also minimizes heat distortion and reduces the risk of damage to surrounding areas.

Power Adjustment and Laser Types

The laser's power can be precisely controlled, which is crucial because different materials require different levels of heat.

The laser power is adjusted according to the material being welded, ensuring optimal results.

Each laser type, such as fiber lasers or CO2 lasers, has a maximum power limit depending on the source and intended application.

Shielding Gas and Its Role

During the laser welding process, a shielding gas is used to protect the molten weld pool from contaminants in the air, such as oxygen and nitrogen.

Common shielding gases include inert gases like argon, helium, nitrogen, and sometimes CO2. These gases create a protective atmosphere around the weld, ensuring that the weld pool maintains its integrity and the final joint is of high quality.

Filler Materials in Laser Welding

Unlike traditional welding, laser welding typically doesn’t require filler materials. The process can weld materials directly without the need for additional substances. However, in some cases where there are gaps to be filled or to improve strength, filler materials may be added to complete the weld.

Types of Laser Welding

Laser welding can be classified into two main types based on the welding process: Conduction Welding and Keyhole Welding. Each method has its unique advantages and is suited to different applications depending on the material and desired result.

Conduction Welding

As the name suggests, Conduction Welding relies on heat conduction to melt the material. When the laser beam hits the surface, it evenly distributes heat across the material, causing it to melt without penetrating deeply into the workpiece. This makes it ideal for materials with low melting points.

In this process, the laser heat affects only the surface, causing minimal penetration and no vaporization.

The result is a clean, aesthetically pleasing weld with a minimal Heat-Affected Zone (HAZ). The reduced HAZ ensures that the material surrounding the weld remains unaffected, preserving its strength and properties.

Because the process uses low power and is carried out slowly with precise control, Conduction Welding is ideal for high-precision applications.

It is commonly used in industries like jewelry, electronics, and medical devices, where fine details and a smooth finish are required.

Additionally, because of the lower power requirements, the equipment for conduction welding is often compact and cost-effective.

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However, this method is not suitable for thick materials or those with high melting points, as it results in a shallow penetration and a less durable weld compared to Keyhole Welding.

Keyhole Welding

In Keyhole Welding, a high-energy laser is used to create deep penetration in the material. As the laser heats the material, the temperature exceeds the fusion point, causing not only melting but also vaporization. This vaporization leaves behind a narrow cavity known as the Keyhole.

The molten pool forms between the keyhole's walls, flowing as the laser moves forward and filling the gaps. If the gaps are too deep, filler material may be introduced to ensure a solid bond and eliminate imperfections. This deep penetration process requires a powerful laser source capable of generating intense energy.

Keyhole Welding is typically used for thicker materials and those with higher melting points, making it suitable for heavy-duty applications such as aerospace and automotive manufacturing.

The result is a strong, durable weld, making it the preferred choice for applications where strength and longevity are critical.

However, Keyhole Welding also has a larger Heat-Affected Zone (HAZ), which can put stress on the material and cause damage to lighter or more delicate materials.

Fields of Application

Aerospace

The aerospace industry requires quality welds. It needs high precision and accuracy to weld some expensive materials. The weld should be smooth and clean, and at the same time, it should be strong enough to withstand the conditions in space. That’s why laser welding is an ideal option.

The materials used in the industry are pretty expensive, so there should be minimal chances of errors and damage. And post-processing of materials like in traditional welding could affect the material. 

Laser welding can meticulously weld materials used for aerospace projects. It’s able to focus even on tiny parts without disturbing the surrounding area. The surrounding area is not under heat stress or damage. Therefore, it is suitable for welding lightweight and thin materials and creates reliable and strong welds.

Automotive

In the automotive industry, a strong and clean weld is needed. High strength is required to bear extreme road conditions, while exceptional smoothness is necessary to keep the aesthetics of the vehicle. 

Laser welding is a great option because it’s flawless and fast, and almost no post-processing is needed. And most importantly, during the welding process, it does not deform the material and affect other areas. It’s extremely precise and under control.

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Another great feature of laser welding is incredible speed. The automotive industry requires fast processing due to massive demands. Laser welding can save time and increase productivity.

On the macro level, laser welding is used in the automotive industry to create joints in the chassis, body panels, and other parts. The joints are smooth and seamless and require minimal post-processing. They are neither visible nor feelable after paint, so they do not affect the aesthetics in any way.

On the micro level, they can also be used to create some small joints, such as electronic components. They are capable of targeting small areas that are not possible with other types of welding.

Medical

Extreme precision and accuracy are needed in the medical industry. For instance, surgical instruments are very complex and have tiny components. They require meticulous welding without affecting the neighboring area of the instrument. That’s why laser welding is a feasible option. It can do the job without damaging delicate components and affect the quality of the instrument.

Similarly, medical implants, such as pacemakers and orthopedic devices, require clean and precise welds. There is no option for post-processing. Therefore, laser welding is used in the fabrication of such implants to make them flawless.

Laser welding is also a great option for the medical industry because it’s a no-contact process. It does not contaminate the working piece. It ensures sterility and hygiene.

Electronics

The electronics industry deals with tiny components that cannot be handled with bare hands. Welding them on the PCB or chips is not an easy task. It requires incredible precision and control.

The heat should not affect the delicate components around. Therefore, the perfect option is laser welding. It helps in connecting tiny components with extreme accuracy.

Similarly, the connections of sensors, actuators, and other delicate devices are also done through laser machines. It creates a meticulous weld that is not only clean but also reliable.

You might have seen laser welds on lithium-ion battery terminals. These welds are just like dots and do not harm the battery itself or occupy any space.

Jewelry

Laser welding is the best option for jewelry making because of its focused beam, incredible precision, high control, and no effect on the surrounding area. It is compatible with precious metals, such as Gold and Silver.

With laser welding, it’s quite easy to weld intricate and delicate jewelry pieces and items. Within a blink of an eye, it welds with exceptional quality. 

Laser welding is to make custom designs for customers in minimal time. It’s also capable of joining dissimilar metals. Apart from that, it is used for repairing jewelry pieces and resizing.

Over the years of evolution in the lithium battery industry, spot welding equipment has undergone continuous advancements, progressing from the initial AC pulse spot welder to the energy storage spot welder, intermediate frequency spot welder, transistor spot welder, and eventually to the laser spot welder. This ongoing development has led to a consistent enhancement in the quality of spot welding equipment.

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AC Pulse Spot Welder

The AC pulse spot welder operates by having the thyristor controlled by a single-chip microcomputer intercept the AC pulse voltage to the primary coil of the welding transformer. The transformer then converts the high-voltage pulse into a low-voltage large current, which is outputted to the spot welding needle for discharge spot welding.

The advantages of the AC pulse spot welding machine include its low cost and low failure rate. However, a notable disadvantage is that once the thyristor is triggered and turned on, it must wait until the AC zero-crossing point before turning off. This results in prolonged welding time, which is detrimental to the welding effect. Prolonged welding time increases the temperature of the solder joints, leading to reduced power, virtual welding, frying welding, tin melting, and other issues. This phenomenon is commonly observed in the spot welding of nickel sheets on protective plates, particularly due to the high spot welding temperature of the AC pulse. When spot welding the negative electrode of the aluminum shell or the positive electrode of the steel shell, the small area of the rivets makes heat dissipation challenging, often resulting in the melting of the sealing ring.

Energy Storage Spot Welding Machine

The energy storage spot welding machine delivers concentrated discharge energy, resulting in a short welding time and relatively low costs, making it highly suitable for battery spot welding applications. However, it is associated with large welding sparks and a higher failure rate. The performance of the welding machine can decline due to the capacity attenuation of the energy storage capacitor. In recent years, with the increasing trend of welding automation, the charging time of the energy storage capacitor has posed limitations, preventing the quick and stable output of welding energy. Consequently, it is best suited for manual spot welding applications.

Intermediate Frequency Welding Power Source

The frequency and control method of an inverter welding machine serve as crucial indicators for assessing its performance. Generally, an inverter frequency ranging from 1-10KHz is collectively referred to as intermediate frequency, while frequencies above 10KHz are termed high frequency. In terms of control mode, the primary side constant current is considered an ideal control method. The primary side constant current involves closed-loop control, allowing for the adjustment of high-frequency pulse width based on the actual output current. In less optimal cases, fixed pulse width modulation is adopted, falling under open-loop control.

During spot welding, the spot welding needle and the weldment itself significantly influence the welding process, resulting in relatively poor stability. The preferred frequency for an intermediate frequency welding power supply typically falls within the range of 4-5KHz. This frequency range ensures the attainment of a stable welding waveform at the output end and facilitates effective feedback and control of a large discharge current. It's noteworthy that transformers have a specific response time, and excessively high frequencies may not contribute significantly to the current.

Transistor Welding Power Source

The most optimal resistance welding power source eliminates the need for a welding transformer, enabling rapid current rise and direct high-frequency output of the current waveform. It offers flexibility in selecting control modes, including constant current, constant voltage, or a combination of constant current and constant voltage. However, it comes with the drawback of being relatively expensive.

Laser Spot Welding Machine

The laser spot welding machine comprises components such as a crystal, xenon lamp, condensing cavity, optical resonant cavity, cooling filter, and laser power supply. Widely utilized in the battery industry, it finds application in the welding of steel shells and aluminum shell cover plates, with recent advancements extending to the spot welding of polymer PACK protective plates. In comparison to resistance welding, the laser welding machine offers several advantages, including the elimination of the need for spot welding needle grinding, firm and uniform welding, and a reduced likelihood of false welding.

From the production of lithium-ion battery cells to battery pack assembly, welding stands as a critical manufacturing process. The conductivity, strength, airtightness, metal fatigue, and corrosion resistance of lithium-ion batteries serve as crucial quality evaluation standards for battery welding. The choice of welding methods and processes directly impacts the cost, quality, safety, and consistency of lithium-ion batteries.

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