Master the Art of Welding Copper Within 1mm with Ease and Efficiency

What is the best method for soldering copper?

Can fiber lasers be used to weld copper?

What precautions should be taken during the welding process?

We conducted tests on four sets of plans to find a suitable solution for welding copper within 1mm.

Copper possesses excellent ductility, electrical conductivity, thermal conductivity, and a certain degree of corrosion resistance. It also has good elasticity, friction resistance, abrasion resistance, and other physical characteristics.

Copper is widely used in the construction industry, electrical equipment production such as generators, bus bars, cables, switchgear, transformers, as well as heat exchangers, pipes, solar heating devices such as plate collectors, and other thermal equipment. Therefore, it finds extensive applications in the electrical, machinery manufacturing, defense, and other industries.

According to the research findings in the thesis “Copper Laser Welding Process and Application Research,” the current industrial use of copper and copper alloys is shown in Figure 1.

Fig. 1 Current share of copper and copper alloys

The CPU, which we are familiar with in our daily lives, generates a lot of heat when it operates. If the heat is not dissipated quickly, it can impact the CPU’s performance or even cause damage to it.

The typical method for dissipating heat, as illustrated in Figure 2, involves using a fan on one side and a copper heat sink on the other. The copper heat sink needs to be soldered in place for effective heat dissipation.

Fig.2 CPU Cooling structure

As the widespread use of copper applications increases, the quality of copper connections is required to be higher, and welding connections are the commonly used methods.

Currently, copper welding mainly employs traditional friction stir welding, argon arc welding, ultrasonic seam welding, brazing, laser welding, and other methods.

Due to copper’s high thermal conductivity, large expansion coefficient, and high reflectivity to infrared laser, the absorption rate of copper to the infrared laser is about 5% at room temperature, increasing sharply to about 20% after heating to near the melting point.

Therefore, in fiber laser welding of copper, the energy at the bottom of the hole may be too large, leading to over-expansion and destabilization of the hole, resulting in welding defects.

In summary, several issues may arise when fiber laser welding copper:

（1）High laser energy density is required.

（2）Prone to porosity and splashing during the welding process.

（3）Poor stability and molding of the welding process can occur.

（4）Weld joints may exhibit poor performance.

The following controls or welding methods are currently used to address these issues:

Laser fillet welding

In comparison to conventional laser welding, laser fillet welding is better suited for adapting to workpiece processing assembly gaps. Additionally, the weld area can be regulated by adjusting the composition of the filler wire. Figure 3 displays the welding pattern.

Fig.3 Schematic diagram of laser fillet welding

Laser-arc hybrid welding

Laser-arc hybrid welding combines the advantages of two independent heat sources: laser and arc.

For instance, the laser heat source has a high energy density, excellent directivity, and transparent medium conduction characteristics, while the arc plasma has a high thermal-electrical conversion efficiency, low operating costs, and technology development advantages.

By combining the two, the shortcomings of both are avoided. This includes the high reflectivity of metal materials on the laser, which can cause energy loss, high equipment costs, and low electrical-optical conversion efficiency. The arc heat source also has its shortcomings such as low energy density and poor discharge stability when moving at high speed.

Moreover, the combination of the two heat sources results in new features such as high energy density, high energy utilization, high arc stability, and low tooling preparation accuracy and surface quality of the workpiece to be welded. As a result, laser-arc hybrid welding has great prospects for application and has become a new welding heat source.

The welding form is shown in Figure 4.

Fig.4 Schematic diagram of laser-arc hybrid welding

Surface treatment

Following the surface treatment, the copper’s absorption rate of fiber laser will significantly increase, which in turn improves its weldability.

At present, the primary methods of treatment comprise surface blackening and the addition of light-absorbing material coatings.

Special Processes

At room temperature, copper has an absorptivity of 30%-40% for lasers with a wavelength of 532nm.

Previous research conducted by scholars on the use of lasers in copper welding has shown the following:

(1) Focusing both the 532nm and 1030nm lasers on the same spot on the workpiece’s surface for welding copper results in a significant reduction in spatter, an improvement in the weld surface’s shape, and a notable enhancement in the process’s repeatability.

(2) Modulating the laser output power with a sine wave of 400Hz to 600Hz and welding copper has been found to significantly improve the welding process’s stability, regularity of the weld shape, and reduction in the number of pores in the weld.

Although the above-mentioned methods have different positive effects, they have varying degrees of complexity in terms of equipment and procedures, and may not be cost-effective for welding some relatively simple workpieces.

Is there a simpler welding process for tailor welding and fillet joint welding of copper plates with a thickness of less than 1mm?

As they say, one test is better than a hundred questions.

Let’s start the welding test now:

6kW

Welding plan

Equipment:

Raycus laser RFL-C6000 with 100μm core diameter fiber and KUKA robot

Welding head:

Precitec YW52 laser welding head, collimator lens 125mm, focusing lens 250mm

Material and joint form:

copper, corner joint, as shown in Figure 5.

Fig. 5 Joint type and welding method

The following four types were used to test specific welding parameters.

Based on the welding equipment mentioned above and the four sets of welding parameters used for welding, we obtained four parameters for assessing the welding effects:

NO.1 weld

NO.2 weld

NO.3 weld

NO.4 weld

As can be seen in the diagram, the appearance of the weld formed by different welding parameters varies:

• Weld No. 1 has a very severe blowout and is poorly formed.
• Weld No. 2 has a small number of blow holes and is poorly formed.
• Weld No. 3 was not found to be popped and was well-formed, but there was some unevenness.
• Weld No. 4 seam has a better formation effect, uniformity and stability.

It can be concluded that the weld formation is greatly influenced by the welding speed, the faster the welding speed, the better and more stable the weld formation.

Reasons Analysis

When welding copper using a fiber laser, weld defects can occur when the energy at the bottom of a small hole is too high, leading to excessive expansion and instability. This also explains why faster welding speeds produce more stable weld seams.

Higher welding speeds reduce heat input, and the time that small holes exist in a fixed position during the welding process is shorter, preventing excessive expansion at the bottom of the hole due to accumulated heat input, which can cause instability and weld defects.

Parts processed using these welding techniques typically require no post-welding treatment. To achieve this type of welding effect, Raycus laser technical engineers recommend controlling the joint clamping gap within 0.05mm during the welding process to achieve optimal results.