Electrochemical corrosion assisted laser drilling of micro-hole without recast layer

Abstract

High-power pulsed laser is an efficient tool for drilling micro-holes on metal, but due to the melt ejection dominated material removal mechanism, recast layer can hardly be avoided. This paper proposes to use electrochemical corrosion as a kind of postprocessing technique to remove the laser induced recast layer. A tungsten steel wire-electrode based electrochemical machining head was designed. During the research, it was discovered that the laser and electrochemical corrosion (ECC) processes may interact due to the assist gas used in the laser drilling process. Although ECC can theoretically dissolve all kinds of metal as ions, the laser induced recast layer showed special characteristics. By comparative study, it was found that oxidative assist gas would lead to oxidizing thermal reaction on the surface of the molten metal during laser drilling, resulting in an insulating layer of oxide, which disabled the ECC to fulfil its validity on recast layer dissolving. When non-oxidative assist gas was used, the recast layer on the hole wall could easily be removed, and ideal micro hole can be produced, with smooth side wall, rounded entrance and decreased taper. After optimization of the overall drilling efficiency, the efficiency of the presented method is over 4 times higher in contrast to the conventional electrochemical drilling.