Impact of Laser Wavelength Variations on Copper Welding Process Performance and Joint Properties in EV Manufacturing

01 Introduction

Researchers from Friedrich–Alexander‑University Erlangen‑Nuremberg in Germany published the article Effects of different laser wavelengths on process performance and weld seam properties in copper processing for electric vehicle applications in the journal Optics and Lasers Technology. Modern production of battery and electric drive systems requires copper-to-copper connections to achieve maximum power-density transmission and enhanced functional integration. In recent years, laser welding has matured into a manufacturing technology in this field due to its flexibility and reproducibility. Near‑infrared lasers are commonly used for copper welding; they are well‑validated equipment in automotive body manufacturing. However, when processing highly reflective copper surfaces, the low absorption in the near‑infrared band causes unstable energy coupling or reflection issues, limiting process effectiveness. Using visible‑band lasers—especially green lasers at 515 nm with excellent beam quality and kilowatt‑class output power—is a viable strategy to address these challenges. This paper systematically analyzes the effects of wavelength on deep‑penetration threshold, weld seam morphology, defect control, and energy efficiency by comparing 515 nm green lasers and 1030 nm infrared lasers when welding Cu‑ETP and CuSn6, using high‑speed imaging and analytic models.

02 Full‑text Overview
This study used two disk lasers with wavelengths of 515 nm and 1030 nm to systematically compare the welding performance of two copper‑based materials, Cu‑ETP and CuSn6, under identical spot conditions. The experiments covered both conduction‑mode and deep‑penetration welding modes. Using high‑speed imaging and modeling analysis, process performance was evaluated in terms of energy coupling, weld morphology, penetration depth, weld width, defect formation, and process stability. Results show that green laser exhibits higher welding efficiency in conduction‑mode welding, achieving deeper seams and greater depth-to-width ratios. In deep‑penetration mode, the green laser also demonstrates a lower penetration threshold and more uniform energy distribution, producing steeper weld profiles concentrated at the leading edge of the molten pool. Although infrared lasers can achieve greater penetration depths at higher power, they suffer from significant molten‑pool oscillations, increased spatter, and lower stability. Ray‑tracing and physical modeling revealed significant differences in energy distribution within the vapor capillary between wavelengths: green laser energy is primarily absorbed at the front wall, while infrared relies on multiple reflections.

03 Figures & Analysis
Figure 1 shows the focused spot intensity distributions for the 515 nm and 1030 nm lasers, which are nearly identical in shape—verifying the comparability of the experimental setup.

Figure 1. Measured intensity distribution of 515 nm (left) and 1030 nm (right) beam profiles at 1000 W laser power.

Figure 2 analyzes the transition from conduction welding to deep‑penetration welding, showing a sharp increase in penetration depth at the critical energy density. The threshold for green laser is noticeably lower than for infrared.

Figure 2. Process states (a)-(d) and their corresponding model representations during copper laser welding observed by high-speed imaging; weld depth variation with P/dF and the corresponding relationship with the corresponding states (right).

Figures 3 and 4 plot the deep‑penetration thresholds for Cu‑ETP and CuSn6 as laser parameters vary, indicating that the green laser enters deep penetration at lower power densities.

Figure 3. Effect of process parameters on the deep melting threshold of Cu-ETP.

Figure 4. Effect of process parameters on the deep melting threshold of CuSn6.

Figure 5 uses ray‑tracing to simulate absorbed energy distributions, revealing that green laser energy is concentrated at the front wall—beneficial for process stability.

Figure 5. Absorption intensity versus irradiation intensity and capillary depth.

Figure 6 uses high‑speed photography to compare molten‑pool dynamics during copper welding: at low feed speed (4 m/min), the infrared laser exhibits a prominent front‑edge bulge due to poor energy coupling, which eventually ruptures and causes widespread melt expulsion—resulting in significant material loss. In contrast, the green laser, with its high absorption rate, triggers intense evaporation and frequent ejection of fine spatter, but the molten‑pool structure remains intact.

Figure 6. Processing zone and instability formation during infrared and green laser welding of copper observed by high-speed photography.

04 Conclusion
This study, based on high‑speed imaging of laser–material interaction zones and analysis of process parameters and beam characteristics, focuses on key factors such as deep‑penetration threshold and thermal efficiency. The main conclusions are as follows:

1. The 515 nm green laser outperforms in conduction‑mode welding and shallow‑penetration control, producing narrow and stable welds suited for high‑precision battery electrodes and DCB applications; the 1030 nm infrared laser forms deeper and wider welds suitable for applications requiring large penetration and tolerance compensation, such as motor yokes.

2. Increasing feed speed and using lower‑thermal‑conductivity alloys (like CuSn6) help reduce conduction losses and improve thermal efficiency; under conduction‑mode or shallow‑penetration conditions, the green laser shows higher melting efficiency due to higher absorption; in deep‑penetration welding, the infrared laser—relying on multi‑reflection mechanisms—performs well at high P/dF ratios.

3. At low feed speeds, the infrared laser often causes molten‑pool bulging and material loss; the green laser exhibits slightly more spatter but in a more controlled distribution and overall greater stability. Increasing feed speed effectively reduces defect generation.

**--Cite the article published by 高能束加工技术 on June 19, 2025, in the WeChat public account "High-Energy Beam Processing Technology and Applications."