În timp ce fiber laser is a primary laser source for welding, its near-infrared (IR) wavelength output is highly reflected by certain metals, particularly copper, which limits its effectiveness for processing these materials. As a result, high-power solid-state green lasers have emerged as a potential alternative for copper welding, since these wavelengths are more easily absorbed by copper. However, these green lasers have several practical limitations, ultimately leading to higher operational costs.

This article introduces recent tests on copper welding using a new type of fiber laser with a high-brightness central beam and adjustable ring mode (ARM). Compared to commercially available kilowatt-class green lasers, the high-brightness ARM fiber laser achieved superior welding quality, better penetration at various welding speeds, and cost-effective advantages for copper welding tasks. These results demonstrate how lasere cu fibră offer low-cost, reliability, and practicality for demanding copper welding applications.

Electric Vehicle Manufacturing

The booming electric vehicle (EV) manufacturing industry has significantly driven the demand for copper welding solutions. Compared to other metals, copper has ideal electrical, thermal, mechanical, and cost properties, which make it widely used in electric vehicles for components such as stators, batteries, and power distribution systems. Many of these components and systems involve copper welding.

However, while copper’s high conductivity and thermal properties make it an ideal material for these applications, they also present challenges when using traditional lasere cu fibră for welding. Specifically, its electronic properties result in high reflectivity at the near-infrared wavelength of lasere cu fibră. Moreover, copper’s excellent thermal conductivity requires a substantial amount of laser energy to melt the material and initiate the welding process.

Thus, using traditional lasere cu fibră often necessitates extremely high power to reach the required power density for melting the material. However, this “brute force” method can make the welding process unstable and extremely sensitive to minor surface changes. Specifically, localized surface oxidation or small-scale surface irregularities can cause process instability, leading to inconsistent welds, poor surface quality, and porosity. Additionally, splattering is a common issue, requiring time-consuming post-processing or leading to a reduced yield.

Solid-State Green Lasers

Copper absorbs green light much more efficiently than near-infrared light, but only at room temperature. The energy from green lasers couples more effectively with the workpiece, enabling a more stable and less sensitive process than traditional lasere cu fibră. Therefore, some manufacturers are using high-power solid-state green lasers, while others are evaluating their potential.

However, there are significant practical issues in deploying high-power green lasers for electric vehicle manufacturing. Some challenges arise from the inherent properties and structure of these green lasers.

Green lasers can be generated by frequency-doubling near-infrared laser light, which results in solid-state green lasere cu fibră or disc lasers. While this technology is widely used in low-power (sub-kilowatt) applications, it encounters difficulties in most industrial copper welding tasks that require kilowatt-level power. Specifically, the frequency-doubling process has an efficiency of around 50%. Thus, a 4 kW single-mode infrared laser is required to produce a 2 kW green light output. The unused energy becomes heat, which must be dissipated by water-cooling systems. This makes these lasers energy-inefficient, leading to higher operating costs and requiring large amounts of cooling water. Additionally, because of the high power, the frequency-doubling crystals degrade over time, potentially causing reliability and downtime issues without constant monitoring.

HighLight™ ARM Fiber Laser

Lasere cu fibră are far more energy-efficient than solid-state green lasers. In other words, they require less power to deliver the same rated output, producing less waste heat. This reduces operational costs and simplifies cooling. Moreover, lasere cu fibră are highly reliable and transmit infrared light efficiently through optical fibers. However, despite these ideal characteristics, lasere cu fibră have not been widely used for copper welding due to the previously mentioned challenges.

High-power lasere cu fibră have been used successfully in automotive production for some time. However, the most challenging welding tasks in EV production, especially for lightweight materials, require more than just basic energy and high power. In practice, many applications include:

Very thin or heat-sensitive materials

“Difficult” materials to weld such as aluminum, copper, and high-strength steels

Joints involving different materials

To address these more challenging tasks, the laser must provide two primary functions. First, it must offer sufficient energy to support the required output. For thicker parts, high power is also needed to achieve adequate material penetration. Second, the laser must precisely control how the power is distributed across the working surface—both in terms of energy density per unit area and energy density per unit time.

Coherent introduced the HighLight series of adjustable ring mode (ARM) lasere cu fibră, which bring the cost and practical benefits of these light sources to applications that traditional technologies cannot fully address. In these tasks, it is crucial to carefully control the power distribution and power density on the work surface to produce high-quality welds (reducing spatter, minimizing cracks, and reducing porosity). Typical examples include zero-gap welding of galvanized steel, low-spatter welding of powertrain components, and crack-free aluminum suspension parts welding without filler wire.

This precise control of spatial power distribution is achieved through the unique beam output of the ARM laser, which consists of a central spot and an additional concentric annular beam. The power of the central and annular beams can be independently adjusted and customized to achieve fine control over the molten pool dynamics.

Copper Welding Results with ARM Fiber Laser

Coherent’s application engineers conducted a series of copper welding tests using the ARM fiber laser with a high-brightness central beam of 22 µm and an annular beam with a 100 µm/170 µm inner/outer diameter. The welding material was pure copper. All tests used a 4 kW laser power, with 1.5 kW for the central beam and 2.5 kW for the annular beam. The experiments showed that when adjusting the focal position to 1.5 mm above the material surface, the best welding quality was achieved. This position strikes a good balance between weld penetration depth and quality.

Welding Efficiency

The welding efficiency of the ARM fiber laser was measured and compared with results published for a 2 kW green laser. Both welding tests used nitrogen as the shielding gas. The green laser was reported to have a constant weld cross-section of 0.5 mm² and a penetration depth of about 1 mm. To achieve similar results with the ARM laser, it required a 3.5 kW output power and a welding speed of 300 mm/s, compared to the green laser’s 200 mm/s welding speed.

Surface Quality

Another key consideration is surface quality. Traditional lasere cu fibră can weld copper but are highly sensitive to changes in surface quality. The high-brightness ARM fiber laser maintained stable welding quality on both sanded and polished copper surfaces.

Concluzie

These tests demonstrate that Coherent’s unique high-brightness ARM fiber laser is a practical solution for the demanding copper welding applications in electric vehicles. The weld penetration depth and processing speed meet or exceed current production requirements. Historically, surface quality sensitivity and process instability have limited the use of lasere cu fibră for copper welding, but ARM lasers overcome these issues. This new ARM laser, with its cost-effectiveness, reliability, and practical advantages, positions fiber laser technology as the preferred choice for many industrial applications, ultimately bringing all of these advantages to demanding copper welding tasks.