The effects of laser wavelength and wire feed rate on dilution behavior and energy efficiency were systematically investigated by comparing a blue diode laser with a near-infrared (NIR) disk laser under identical processing conditions. Particular attention was paid to the role of laser–material interaction in governing energy coupling and melt pool behavior during deposition.　In the case of the blue diode laser, a pure copper layer with an extremely low dilution of 1% was successfully formed, achieving an energy efficiency of 16.0 × 10⁻³ mm³/J at a wire feed rate of 225 mg/s. In comparison with the NIR disk laser, the blue diode laser reduced dilution by 43% and improved energy efficiency by a factor of five. This improvement is attributed to the significantly higher absorptivity of pure copper at the blue wavelength (~60%), which enhances energy coupling and promotes stable melting of the feed wire and substrate.

　Furthermore, three distinct deposition modes were identified depending on the wire feed rate, and transitions between these modes were found to strongly influence dilution behavior. At lower wire feed rates, excessive substrate melting led to increased dilution, whereas optimized conditions enabled efficient deposition with minimal substrate interaction. At higher feed rates, insufficient melting resulted in unstable deposition behavior. These results demonstrate that optimization of wire feed rate, in combination with appropriate wavelength selection, enables the formation of low-dilution and high-efficiency pure copper layers in W-DED processes, providing a practical guideline for process design.