Currently, some high-end BMW and Mercedes-Benz models utilize laser welding, such as the welding of automotive headlamp covers, which has already been adopted in some high-end models of BMW and Mercedes-Benz. Laser-welded headlamp covers feature a smooth surface without a granular texture, ensuring stability and sealing performance even when the car is driving at high speeds.
Generally, laser welding can be divided into metal welding and non-metal welding. This article explains “how does laser welding work”, mainly for metal laser welding.
1. What is Laser Welding？
Laser welding is a method that converts light energy into thermal energy, causing the bonding materials to melt rapidly in a localized area, and then instantly cool and solidify to form a permanent weld.
Since laser welding is a non-contact welding process, even narrow gaps can be welded as long as the laser heat energy is introduced. Compared with traditional welding, laser welding can greatly improve the quality of precision welding.
Tips:
When laser welding metals, it is recommended to weld the same type of metal, because similar metals have the same melting points.
Although different metals can sometimes be welded, it is necessary to conduct welding process tests based on their physical and chemical properties to achieve optimal laser welding results.
2. Why Choose Fiber Lasers to Weld Metals?
To understand how laser welding works, it is essential to introduce the common types of lasers. Common types of lasers are categorized by wavelength:
- Fiber lasers (1060–10800 nm)
- ultraviolet (UV) lasers (wavelength < 400 nm),
- visible lasers (wavelength 400–760 nm)
- near-infrared lasers (760–2500 nm).
When it comes to welding metals such as carbon steel and stainless steel, among these kinds of lasers, fiber lasers operating at 1060–1080 nm are often the preferred choice.
At room temperature, the absorption rate of these materials for fiber laser light is approximately 30–50%. Moreover, fiber lasers are significantly more cost-effective at equivalent power levels compared to lasers of other wavelengths.
Although UV lasers offer higher absorption rates in metals, they are considerably more expensive and challenging to scale to high power, making them a less practical option for standard welding applications. This combination of reasonable absorption and affordability is why fiber lasers are the first choice for welding carbon and stainless steels.
3. How Does Laser Welding Work?
3.1 How does laser Welding Work – Welding Thin Sheets
When the laser welds the metal material, such as stainless steel, the laser beam heats the metal instantly.
Energy is transferred via thermal conduction, melting the surface metal to form a shallow melt pool, with a depth of less than 0.9 mm.
As the laser moves manually or mechanically, the stainless steel cools rapidly, forming a weld seam that joins the two materials.
Shadow Melting Pool
3.2 How does laser Welding Work – Welding Medium and Thick Plates
In this case, a high-power laser (power density > 10⁶ W/cm²) is required.
The laser beam instantly heats the stainless steel to 2200–2500°C, causing it to vaporize and form a plasma plume.
As the beam moves, it pushes the molten metal aside, forming a keyhole
—a liquid cavity resembling a keyhole.
This keyhole effect is critical. As the laser advances, molten metal continuously fills the space behind the keyhole, forming a continuous weld.
The heating (millisecond-level) and cooling (10³–10⁴ °C/s) during laser welding are extremely fast. As a result, welded parts often require no additional cooling and can proceed directly to the next processing step, significantly reducing production time.
4. About Weld Width
The diameter of a typical laser beam ranges from 0.05 to 0.1 mm, which usually results in a weld spot of about 1–1.5 mm on the surface of stainless steel. However, in actual production, a weld seam width of 3–5 mm is often required to enhance joint strength or to adequately cover the gap between two metal pieces. To achieve this wider weld, oscillating laser welding is employed.
As illustrated in the figure below:
During this process, the laser beam is driven by a galvanometer to oscillate within a small area—following patterns such as circles or figure-eights. This motion allows the laser to remelt the metal multiple times over a broader area, improving keyhole stability and facilitating the escape of gases from the molten pool. As a result, porosity is reduced and weld quality is enhanced. By using oscillation, the weld width can be increased from less than 1 mm to over 3 mm. With the addition of wire feeding, it is even possible to achieve weld widths of 4–5 mm.
Conclusion
Laser welding, with its high precision, speed, and flexibility, has become an indispensable technology in modern industrial manufacturing. From delicate medical device components to robust automotive applications, laser welding delivers superior performance in joining a wide range of materials.
The above explains how laser welding works. We hope this information is helpful.
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