Hong Shik Shin

Analysis of the side gap resulting from micro electrochemical machining with a tungsten wire and ultrashort voltage pulses

Micro wire electrochemical machining (ECM) using a O 10 µm tungsten wire as the tool electrode is presented. Since electrochemical machining does not wear out the tool, it can be easily applied to the fabrication of micro grooves by moving the tool electrode along a programmed toolpath. To minimize the side gap, ultrashort voltage pulses were applied between the tool electrode and the workpiece. Changes in the side gap according to the applied pulse voltage, pulse on-time and pulse period were investigated, and the optimal pulse condition for stable machining was obtained. By using this method, micro features such as micro grooves and gears were fabricated into stainless steel plates.

Surface finishing of micro-EDM holes using deionized water

In this paper, with the use of deionized water, a finishing process of micro hole surfaces processed by micro electrical discharge machining (micro-EDM) is investigated. A micro hole is machined by micro-EDM using deionized water as a dielectric fluid. The inner surface of the hole is finished successfully via electrochemical dissolution in deionized water. The effects of finishing conditions such as the resistivity of deionized water, the voltage, the tool rotation and the finishing time on the surface quality and accuracy of the shape were investigated. After a finishing process using deionized water with a resistivity of 2 MΩ cm, a voltage of 80 V, a tool rotation of 1200 rpm and a finishing time of 6 min, the surface roughness was reduced considerably from 0.225 µm Ra after micro-EDM to 0.066 µm Ra.

Hybrid micromachining using a nanosecond pulsed laser and micro EDM

Micro electrical discharge machining (micro EDM) is a well-known precise machining process that achieves micro structures of excellent quality for any conductive material. However, the slow machining speed and high tool wear are main drawbacks of this process. Though the use of deionized water instead of kerosene as a dielectric fluid can reduce the tool wear and increase the machine speed, the material removal rate (MRR) is still low. In contrast, laser ablation using a nanosecond pulsed laser is a fast and non-wear machining process but achieves micro figures of rather low quality. Therefore, the integration of these two processes can overcome the respective disadvantages. This paper reports a hybrid process of a nanosecond pulsed laser and micro EDM for micromachining. A novel hybrid micromachining system that combines the two discrete machining processes is introduced. Then, the feasibility and characteristics of the hybrid machining process are investigated compared to conventional EDM and laser ablation. It is verified experimentally that the machining time can be effectively reduced in both EDM drilling and milling by rapid laser pre-machining prior to micro EDM. Finally, some examples of complicated 3D micro structures fabricated by the hybrid process are shown.

Electrochemical etching of stainless steel through laser masking

A new micro patterning process without the need for a mask is proposed in this paper. It is a combination of laser masking and electrochemical etching. In electrochemical etching through laser masking (EELM), selective electrochemical dissolution of stainless steel is achieved in a 2 M sodium nitrite electrolyte. The micro-patterned surface layer of stainless steel is formed by laser marking using an ytterbium pulsed fiber laser. After the laser masking process, the patterned surface of stainless steel is selectively dissolved under an appropriate electrochemical etching condition because the laser-marked area can temporarily act as a barrier during electrochemical etching. The characteristics of the laser-marked surfaces have been investigated by scanning electron microscopy (SEM), x-ray diffractometry (XRD) and x-ray photoelectron spectroscopy (XPS). The polarization curve has been used to evaluate electrochemical dissolution behaviors. The EELM process enables the electrochemical micro-machining of stainless steel without photolithography technology; thus, it can be applied in micro fabrication, micro patterning and surface texturing.

Micro Electrochemical Machining for Complex Internal Micro Features

Micromachining of internal features by electrochemical machining (ECM) is investigated. By controlling pulse conditions and using a customized tool electrode, micro features were machined on the side wall of a micro hole. In micro ECM, longer pulse on-time enlarges the side gap. A reverse tapered hole and a barrel-shape hole were fabricated through pulse duration control. Micro cavity was machined by controlling the pulse duration and machining time in similar manner. A micro disk-shape electrode was used to machine microgroove inside the hole, which is similar to turning lathe process.