The boundary of key-hole generation in micro-welding of aluminum alloy by pulsed Nd: YAG laser with superposition of continuous diode laser

In micro-welding of aluminum alloy, its low melting point and high thermal conductivity make it difficult to obtain the large penetration depth with the good surface integrity. In order to perform the stable key-hole welding with little defects, it is important to understand the processing phenomenon near the boundary between heat conduction and key-hole type welding. Therefore, the boundary condition of key-hole generation in micro-welding of aluminum alloy was experimentally and numerically investigated with hybrid Nd:YAG laser system, in which a continuous diode laser (LD) of 808nm in wavelength was superposed in a pulsed Nd:YAG laser of l064nm in wavelength. It became clear that the keyhole generation became stable when the continuous LD was superposed with pulsed Nd:YAG laser, and the shorter pulse interval time and higher continuous LD power led to the generation of the key-hole. The results of numerical analysis made it clear that the superposition of continuous diode laser is effective to stabilize the key-hole generation in micro-welding of aluminum alloy by pulsed Nd:YAG laser, since the continuous diode laser could keep the temperature near the boundary condition of key-hole generation appeared at the time when the temperature of welded bead was around the boiling point.