Abstract: A method, which is called the hybrid femtosecond laser layered micro-hole drilling via applying external voltage based on ring feeding, is proposed for carrying out an experimental study using super-alloy GH4133 sheets and ceramic Al₂O₃ chips. The effect of the applied voltage field intensity on the micro-hole formation characteristics induced by femtosecond laser layered drilling via ring feeding is analyzed comparatively with mechanism discussion. Furthermore, after femtosecond laser layered drilling based on ring feeding, the effect of the external voltage applied on through-hole sidewall element contents and longitudinal section middle micro hardness performance is also studied on the basis of the mechanism analysis. It is indicated that the machining adaptability of the method proposed is good for different workpiece materials under different process conditions as a result of the good morphology for the micro-hole entrances and exits machined as well as the good stability and repeatability of the hole geometry. The surface roughness is reduced while the uniformity is improved for the through-hole sidewall by applying an external voltage. It is also found that the hole depth is effectively increased while the hole taper is reduced somewhat by using the external voltage, but the hole diameter and circularity are slightly influenced by the external voltage applied. In addition, both carbon and oxygen contents of the hole sidewall are reduced while the micro hardness performance for the micro region around the hole sidewall is effectively improved by applying an external voltage.

Key words: femtosecond laser, external voltage, micro-hole, ring feeding, layered drilling