Pure copper is widely used in industries, especially in automotive and electrical components, due to its excellent thermal and electrical conductivity. In the growing electric vehicle (EV) sector, pure copper is commonly used in busbars that connect battery electrodes. As battery capacities increase, busbars are becoming thicker, requiring more advanced joining methods.

Conventional techniques like arc and resistance welding face limitations, including slow processing speeds and the formation of a large heat-affected zone (HAZ). As a result, laser welding has gained attention for its ability to offer high-speed, low-heat-input, and precise joining through its high energy density.

However, standard infrared (IR) lasers used in laser welding have low absorption rates for pure copper (only 5–10%). Additionally, copper's optical absorption and thermal conductivity vary with temperature, making stable welding difficult with IR lasers alone.

To overcome these issues, this study introduces a Blue-IR hybrid laser welding system. The system incorporates a blue diode laser with a much higher absorption rate for copper (around 60%) and minimal temperature dependence. The blue laser preheats and melts the copper surface, reducing absorption variability and stabilizing the welding process.

The main objective of the research is to achieve stable enlargement of the keyhole opening width while minimizing spatter generation. By analyzing the spatial beam profile in the hybrid laser system, the study aims to better understand and control spatter formation, leading to improved weld quality in copper busbars for electric vehicles.