Shi Hyoung Ryu

Micro electrochemical milling

In this paper, electrochemical machining (ECM) for fabricating micro structures is presented. By applying ultra short pulses, dissolution of a workpiece can be restricted to the region very close to an electrode. Using this method, 3D micro structures were machined on stainless steel. Good surface quality of the structures was obtained in the low concentration electrolyte, 0.1 M H2SO4. In ECM, when the machining depth increases, structures taper. To reduce the taper, a disc-type electrode is introduced. By electrochemical milling, various 3D micro structures including a hemisphere with 60 µm diameter were fabricated.

The form error prediction in side wall machining considering tool deflection

In this research, an effective method for the form error prediction in side wall machining with a flat end mill is suggested. The form error is predicted directly from the tool deflection without surface generation by cutting edge locus with time simulation. The developed model can predict the surface form error accurately about 300 times faster than the previous method. Cutting forces and tool deflection are calculated considering tool geometry, tool setting error and machine tool stiffness. The characteristics and the difference of generated surface shape in up milling and down milling are discussed. The usefulness of the presented method is verified from a set of experiments under various cutting conditions generally used in die and mold manufacturing. This study contributes to real time surface shape estimation and cutting process planning for the improvement of form accuracy.

Cutting Characteristics of Ball-end Mill with Different Helix Angle

볼 엔드 밀링은 자유곡면 금형의 정삭가공에 널리 사용되며 형상정밀도, 표면거칠기 등 금형의 결정하는최종가공공정이다. 볼엔드밀은 복잡한 3차원 형상의 절삭날이 반구면 상에 형성되어 있어 절삭날의 위치에 따라 절삭조건이 달라지기 때문에, 가공면 형상에 따른 가공조건의 선정이 용이하지 않아 이를 주로 현장 전문가의 경험에 의존하고 있는 실정이다. 절입 깊이가 상대적으로 작은 볼 엔드밀 정삭가공에서 절삭은 주로 반구부의 절삭날에 의해 이뤄지며 이 때 공작물과 절삭날의 접촉위치에 따라서 칩 생성 기구가 달라진다. 볼 엔드밀 가공에 관한 연구로는 절삭력 및 공구변형의 예측과 가공오차 최소화,

Nano-dot and nano-pit fabrication on a GaAs substrate by a pulse applied AFM

The nano-patterning characteristics of GaAs is investigated using a pulse applied atomic force microscope (AFM). Very short range voltage pulses of micro to nano-seconds’ duration are applied to a conductive diamond-coated silicon (Si) tip in contact mode, to regulate the created feature size. The effects of pulse conditions such as pulse voltage, duration, frequency, offset voltage, anodization time, and applied tip pressure on nano-dot generation are characterized, based on the experiments. An interesting phenomenon, nano-pit creation instead of nano-dot creation, is observed when the applied pulse duration is less than 100 μs. Pulse frequency and offset voltage are also involved in nano-pit generation. The electrical spark discharge between the tip and the GaAss surface is the most probable cause of the nano-pit creation and its generation mechanism is explained by considering the relevant pulse parameters. Nano-pits over 15 nm in depth are acquired on the GaAs substrate by adjusting the pulse conditions. This research facilitates the fabrication of more complex nano-structures on semiconductor materials since nano-dots and nano-pits could be easily made without any additional post-processes.