Abstract
Uniform melting of fine wires in the bundle without cutting has been studied using YAG laser. Melting and cutting behavior for the twisted bundle in 3.5 mm pitch is observed, and the applied forces to the melting portion were discussed. Furthermore, laser absorption and heat transfer in the bundle are considered as compared with these in the single wire in the terms of melting length. The following results are obtained:
(1)Process from melting to cutting of the bundle is almost the same as that of the single wire. After the molten pool reaches from the laser irradiation side to the opposite side, it extends to the longitudinal direction by heat conduction. Next, it is spherodized by surface tension. Then necking occurs by the growth of spherodizing, and it comes into cutting.
(2)Surface tension is the most influenced factor of the force acting to the melting portion. Gravity appears to shift the spherodized molten metal downward, but does not cause cutting directly. Recoil force of evaporation and solid-liquid interfacial tension seem to be little for cutting.
(3)Laser energy is easier to be absorbed in the bundle as compared with the single wire, but the absorbed heat is more difficult to transfer in the bundle than in the single wire.
(4)In order to prevent the bundle from cutting, it must be straightened without elastic strain, and the pulse energy should be selected to optimize the melting length without necking.
