Laser Welding Copper: Challenges and Their Solutions

Laser welding is favored for its precision, speed, and minimal post-processing, making it a desirable technique across industries. Copper, in particular, would benefit from laser welding's ability to deliver high-quality welds with minimal distortion.

However, copper's inherent properties—high heat conductivity and reflectivity—present significant hurdles for laser welding.

Welders face notable challenges in achieving quality copper welds with lasers. Success relies on understanding and implementing modern solutions to overcome these material-specific obstacles. Let's examine the challenges of laser welding copper and explore strategies for a streamlined, efficient process.

Why Laser Welding Copper is Challenging?

As we've established, laser welding copper presents a unique set of difficulties. These challenges stem from copper's inherent physical properties, which react unfavorably to the concentrated energy of a laser beam. Several key factors contribute to this complexity, hindering the ability to achieve consistently high-quality welds.

High Thermal Conductivity

Copper is a very good conductor of heat. Its thermal conductivity is 401 W/m·K at 0⁰C and 384 W/m·K at 300⁰C. That said, it can conduct heat extremely faster, even faster than aluminum, which has a thermal conductivity of 237 W/m·K.

Due to high thermal conductivity, the heat generated by the laser spreads to other areas of the metal quickly. It’s difficult to localize the heat and focus only on the welding point.

As the heat spreads in other areas, the weld pool is not properly created. The fusion is incomplete, which results in weaker welds and cracks.

If you increase the power to generate excessive heat at the welding point, the heat-affected zone (HAZ) will be large, and it will deform the metal or other areas. You might end up damaging the material itself.

The cherry on the top is the high coefficient of thermal expansion, which means the materials expand more compared to other metals when heat is absorbed. That said, there are chances of deformity and warping of the material.

Laser Reflection

Another great challenge is the reflection of the laser beam from the copper surface. Copper is highly reflective, which means only a small part of the laser energy is absorbed by the metal, and the rest of the energy is wasted.

Therefore, you need a high-power laser to weld copper. It is necessary to generate enough heat, melt copper, and create a weld pool. But again, high-power lasers are expensive, and applying higher power could lead to weld defects.

The reflection of the laser on copper isn’t straightforward. At normal temperature, it reflects most of the laser. But as the temperature increases, the absorption also increases.

So, if you are using a high-power laser at normal temperatures to generate enough heat, the material will reflect most of the energy. However, as the temperature increases, the material will be able to absorb more energy. It will suddenly increase the heat, which broadens the heat-affected zone and could deform or damage the material.

Low Viscosity Weld Pool

In most metals, when the weld pool is created, the metal pieces are welded properly after solidification. There is no complication. But in the case of copper, achieving quality weld is difficult.

The weld pool created has a low viscosity. The melted metal flows forward and backward. The laser also creates ripples in the weld pool. Therefore, it’s quite difficult to control the molten material.

Copper solidifies quickly, which is an additional challenge. There is no time for the ripples or waves to settle. Thus, the final weld is uneven, having excessive or lack of material at different places. The weld gap is not properly or evenly filled at all places because of the turbulence.

The worst part is that it’s difficult to find a suitable filler material to bridge the gaps and create a strong weld.

Oxidation

The worst part is that it’s difficult to find a suitable filler material to bridge the gaps and create a strong weld.

The worst part is that it’s difficult to find a suitable filler material to bridge the gaps and create a strong weld.

The worst part is that it’s difficult to find a suitable filler material to bridge the gaps and create a strong weld.

Solutions to Those Challenges

Successfully laser welding copper demands a strategic approach to overcome its inherent difficulties. Fortunately, advancements in laser technology and welding techniques provide effective solutions. By carefully considering laser selection, operational modes, and process parameters, welders can mitigate the challenges of thermal conductivity, reflection, weld pool control, and oxidation. Let's explore these key strategies:

1. Optimize Laser Wavelength for Absorption

Combatting copper's high reflectivity begins with laser selection. Reflection rates are heavily influenced by wavelength. While conventional lasers struggle with copper's high reflectivity (absorbing as little as 5%), shorter wavelengths dramatically improve absorption rates.

Green lasers (532nm) offer significantly enhanced absorption (up to 35%), and blue lasers (around 445nm) provide the most substantial improvement, reaching absorptions of 60% or higher.

Utilizing these wavelengths allows for efficient melting of copper even at lower power settings. This minimizes sudden temperature spikes, enhances control over the heat-affected zone, and ultimately facilitates higher quality, more precise welds. Conversely, infrared lasers, due to their poor absorption by copper, are generally unsuitable for this application.

2. Select the Appropriate Laser Operation Mode

The choice between continuous wave (CW) and pulsed lasers is crucial for copper welding and depends on the specific application requirements.

Continuous Wave (CW) lasers are generally favored for copper welding. Their consistent heat input promotes deeper keyhole welding, which is vital for creating robust, crack- and porosity-resistant welds. However, achieving optimal results with CW lasers necessitates precise control over travel speed and power settings.

Pulsed lasers have a more niche application in copper welding, primarily for spatter-sensitive scenarios like electronics assembly and battery tab welding. While they minimize spatter, their use is more limited compared to the broader applicability of CW lasers.

3. Implement Preheating Strategies

Preheating copper is a highly effective method for reducing laser reflection and boosting initial energy absorption. As copper's absorption rate increases with temperature, preheating ensures a greater percentage of the laser energy is utilized from the outset.

This technique not only accelerates the welding process but also contributes to improved weld quality and consistency by promoting more efficient energy coupling.

4. Employ Shielding Gas for Oxidation Prevention

Oxidation is a significant concern during copper laser welding at elevated temperatures. To safeguard the weld integrity, the use of a suitable shielding gas is essential.

The shielding gas creates a protective atmosphere around the weld zone and molten pool, preventing atmospheric oxygen from reacting with the copper. This effectively minimizes oxidation, reducing the formation of detrimental oxides that can lead to porosity, inclusions, and weakened welds.

5. Utilize Wobble Welding Techniques

To address the challenges of copper's low viscosity molten pool and its tendency for turbulent flow, employing a wobble welding pattern is highly advantageous.

By oscillating the laser beam in a wobble motion, the technique promotes more controlled fusion and even material distribution. This results in smoother, more uniform weld beads, minimizing ripples and spatters, and ensuring consistent weld gap filling despite the molten pool's fluidity.

6. Engage Highly Skilled Operators

Laser welding copper is not a process for novices. The nuances of achieving high-quality welds demand significant skill, knowledge, and practical experience.

A proficient laser welder possesses a deep understanding of optimal parameter selection, precise laser control, and the critical factors that contribute to impeccable weld quality. Extreme precision and meticulous attention to detail are paramount for success in this demanding application.

Recommended Lasers to Weld Copper

Blue Laser

Blue laser is an ideal option for welding copper. The reason behind this is its high absorption. Around 60-65% of the laser energy is absorbed by the material.

The wavelength of a blue laser is around 445nm, and it is a type of diode laser. It is an inexpensive and suitable option for delicate tasks like battery terminals and electronics.

Using a Blue laser, it is possible to focus on the welding point. It heats only the required area, so the heat-affected zone (HAZ) is smaller. It reduces the chances of material deformation.

Users can precisely control the laser parameters. It is quite precise when it comes to speed, power, and other variables. Therefore, achieving good welds becomes easier.

But keep in mind that the power of the Blue laser is limited. And when going with a higher power, the beam quality is compromised. Thus, it becomes less efficient and less precise.

Green Laser

The second suitable option for laser welding copper is the Green laser. It’s also a diode laser like the Blue Laser, but its wavelength is 500-530nm.

It is better in absorption compared to infrared lasers, but inferior to the Blue Laser. It offers up to 30-35% absorption during copper welding.

It is preferred for high precision and quality welds. Not only pure copper but it can also be used for copper alloys. Green lasers have similar advantages to Blue lasers. They affect a minimal area and offer incredible control. However, the power is limited.

Fiber Laser

Fiber lasers can also be used to weld copper. Even though their absorption is only 5%, they are still used for this purpose because of their immense power.

They can weld copper very well and offer better control and precision compared to diode lasers (Blue and Green lasers). The weld is exceptionally clean and strong because of the deep penetration.

For those who prefer welding different materials (other than copper), fiber laser is a versatile option. It can work on thin and thick materials and offer excellent results. However, it is a bit expensive compared to other lasers.

When Laser Welding is Preferred to Weld Copper

Laser welding of copper is preferred over other welding methods in the following scenarios：

High Precision and Intricate Details are Required

When the design necessitates very fine weld beads, narrow heat-affected zones (HAZ), and the ability to join delicate components with complex geometries, laser welding truly excels. Traditional welding methods, with their broader heat input, might be too aggressive and imprecise, leading to distortion or damage, especially with copper's high thermal conductivity.

Practical Examples: Imagine joining tiny copper wires in microelectronics, creating intricate patterns on copper jewelry, or sealing sensors with minute, leak-proof welds. In these scenarios, the pinpoint accuracy of a laser beam allows for welds that are virtually impossible to achieve with other techniques.

Think of heat exchangers with very closely spaced copper fins; laser welding can join these with minimal impact on the fin spacing and heat transfer efficiency. The ability to create very narrow welds also minimizes the visible weld seam, which is crucial for aesthetic applications or components where surface finish is critical.

Low Heat Input and Minimal Distortion are Crucial, Especially for Thin Materials and Delicate Components

Copper's exceptional thermal conductivity means heat spreads rapidly. This can be a significant disadvantage in welding, as it can lead to excessive heat buildup, distortion, and burn-through, particularly when working with thin sheets, foils, or delicate copper parts.

Laser welding's concentrated and precisely controlled energy input minimizes the total heat introduced into the workpiece. This results in a very narrow HAZ and significantly reduces the risk of distortion, warping, or damage to heat-sensitive components in the vicinity of the weld.

Practical Examples: Welding thin copper foils for battery current collectors in electric vehicles requires extreme control over heat input to prevent melting or damaging the delicate foil structure. Joining thin copper tubes in heat exchangers, where distortion can affect flow characteristics and efficiency, also benefits immensely from laser welding's low heat input. Think of delicate copper components in scientific instruments or medical devices – laser welding can join them without altering their precise dimensions or sensitive functionalities.

High Welding Speed and Productivity are Desired:

In manufacturing environments where high throughput and efficiency are paramount, laser welding can offer significantly faster welding speeds compared to traditional methods like TIG welding or MIG welding, especially for thinner copper sections. The focused energy of the laser allows for rapid melting and joining, leading to shorter cycle times and increased production volume.

Practical Examples: In high-volume production lines for electronics, automotive components (like busbars), or heat exchangers, the faster welding speeds of laser welding translate directly into increased output and reduced manufacturing costs.

For instance, continuously welding seams on copper tubing for HVAC systems or joining large quantities of copper connectors can be significantly accelerated using laser welding, boosting overall productivity.

Clean, Contamination-Free Welds are Necessary:

Copper is susceptible to oxidation at high temperatures, and any contamination in the weld can compromise its mechanical and electrical properties. Laser welding, often performed with inert gas shielding (like Argon or Helium), creates a protective atmosphere around the weld pool, preventing oxidation and atmospheric contamination.

Furthermore, being a non-contact process, laser welding eliminates the risk of electrode or filler material contamination, resulting in cleaner, higher-purity welds.

Practical Examples: In medical devices and semiconductor manufacturing, weld purity is critical to avoid contamination and ensure reliable performance. Laser welding of copper components in these applications ensures a clean, oxide-free weld joint, which is essential for biocompatibility, electrical conductivity, and long-term reliability. For electrical connectors and busbars, a clean weld ensures good electrical contact and minimizes resistance, crucial for efficient power transmission.

Automation and Consistent Weld Quality are Priorities:

Laser welding is highly amenable to automation and robotic integration. This allows for precise control over welding parameters, consistent weld quality, and repeatability in high-volume production. Automated laser welding systems can be programmed to execute complex weld patterns with high accuracy, reducing variability and minimizing human error.

Advanced systems often incorporate real-time process monitoring and feedback control, further ensuring consistent and reliable weld quality across production runs.

Practical Examples: In industries producing large quantities of identical copper components, such as automotive wiring harnesses, electrical connectors, or heat exchanger components, automated laser welding lines can ensure every weld meets stringent quality standards.

This reduces scrap rates, improves overall product quality, and enables cost-effective high-volume manufacturing with predictable output.

Electronics, Medical Devices, and Certain Automotive Components

These sectors have demanding requirements that often align perfectly with the strengths of laser welding for copper. In electronics, miniaturization and precision are key. In medical devices, biocompatibility and sterilization are paramount.

In the automotive industry, especially with the rise of electric vehicles, high conductivity and reliable connections in power electronics (like battery busbars and connectors) are crucial. Laser welding provides the necessary precision, low heat input, clean welds, and automation capabilities to meet these specific industry needs for copper joining.

Practical Examples:

Electronics: Joining copper heat sinks to electronic components, welding fine copper conductors on circuit boards, connecting copper terminals in sensors.

Medical Devices: Sealing copper enclosures for implantable devices, welding copper components in surgical instruments requiring sterilization, joining copper tubing in medical gas delivery systems.

Automotive: Welding copper busbars and battery connectors in electric vehicles, joining copper wiring harnesses, fabricating copper heat exchangers for vehicle cooling systems.

Clean, Contamination-Free Welds are Necessary:

On the other hand, UV DTF requires UV inks, a UV printer, and AB transfer film. But the costs alone of a UV printer can get higher than the whole standard setup. Typically, UV printers are available between $5,000 to $13,000.

Conclusion

In summary, while copper's properties present laser welding challenges, modern solutions like optimized wavelengths, strategic techniques, and skilled operators enable high-quality welds. Blue, green, and fiber lasers offer versatile options. Laser welding's precision, low heat input, and speed make it ideal for applications demanding intricate details and consistent quality, solidifying its importance in diverse industries.