8
Y. Wang and Y. Zeng
By using the MEMS module of the COMSOL Multiphysics, the electric field
density value on each point of the anode surface has been calculated. Figure 1.3b
shows the variation of electric field density with applied voltage. Both the machined
depth and side gap increased with increasing voltage. Thus, a higher voltage enhanced
the materials removal rate but deteriorated the machining localization. Figure 1.3c
shows the variation of electric field density with spherical stylus diameter. It could be
noted that the EMM localization could be enhanced by using the spherical tip with
a smaller diameter. Microstructures with smaller sizes could be processed utilizing
smaller rounded tip as the tool electrode. Figure 1.3d shows the variation of electric
field density with the initial inter-electrode gap. Micro contours with higher depth and
narrower width could be obtained by EMM with the smaller initial inter-electrode
gap. Therefore, the electric current density distribution and the machined contour on
the workpiece surface could be controlled by regulating the various parameters. As
the analysis above, microfeatures with higher precision and smaller sizes could be
fabricated by EMM utilizing moving spherical tip, with the smaller voltage, smaller
spherical tip diameter, and narrower inter-electrode gap. The following experiments
were conducted to verify the proposed method and the simulation results.
1.3 Results and Discussions
1.3.1 Influences of the Applied Voltage
Based on the principle of EMM with a moving spherical tip as the tool electrode,
microchannels were fabricated with the workpiece feeding rate of 0.1 μm/s in the
lateral directions (XY plane). Voltage ranging from 4 to 6 V was applied between the
workpiece and the tool electrode. A tool electrode with a spherical tip of 650 nm in
diameter was employed. The initial inter-electrode has been set to 1 μm. Afterward,
the contour of the fabricated microchannels was measured by AFM. The width of
the microchannel has been defined as the with at the half depth.
Figure 1.4a shows the variation of depth and side gap of the machined microchannels, and the three-dimensional profiles of the microchannels at each corresponding
applied voltage. Figure 1.4b shows the cross-sectional contours of the microgrooves
under different pulse voltage. It was demonstrated that both the width and the depth
of the microchannels increased with increasing applied voltage. The experimental
results were in accordance with the simulation results. The workpiece materials
removal rate increases with increasing voltage. As illustrated in Eq. (1.1), the electric
current density increases with a bigger voltage amplitude, which makes the dissolution rate increase. During the electrochemical reaction, the dissolution current (i diss )
could be expressed as Eq. (1.9) [2]:
i diss = i 0 · exp
ααϕ
K T
(1.9)
Y. Wang and Y. Zeng
By using the MEMS module of the COMSOL Multiphysics, the electric field
density value on each point of the anode surface has been calculated. Figure 1.3b
shows the variation of electric field density with applied voltage. Both the machined
depth and side gap increased with increasing voltage. Thus, a higher voltage enhanced
the materials removal rate but deteriorated the machining localization. Figure 1.3c
shows the variation of electric field density with spherical stylus diameter. It could be
noted that the EMM localization could be enhanced by using the spherical tip with
a smaller diameter. Microstructures with smaller sizes could be processed utilizing
smaller rounded tip as the tool electrode. Figure 1.3d shows the variation of electric
field density with the initial inter-electrode gap. Micro contours with higher depth and
narrower width could be obtained by EMM with the smaller initial inter-electrode
gap. Therefore, the electric current density distribution and the machined contour on
the workpiece surface could be controlled by regulating the various parameters. As
the analysis above, microfeatures with higher precision and smaller sizes could be
fabricated by EMM utilizing moving spherical tip, with the smaller voltage, smaller
spherical tip diameter, and narrower inter-electrode gap. The following experiments
were conducted to verify the proposed method and the simulation results.
1.3 Results and Discussions
1.3.1 Influences of the Applied Voltage
Based on the principle of EMM with a moving spherical tip as the tool electrode,
microchannels were fabricated with the workpiece feeding rate of 0.1 μm/s in the
lateral directions (XY plane). Voltage ranging from 4 to 6 V was applied between the
workpiece and the tool electrode. A tool electrode with a spherical tip of 650 nm in
diameter was employed. The initial inter-electrode has been set to 1 μm. Afterward,
the contour of the fabricated microchannels was measured by AFM. The width of
the microchannel has been defined as the with at the half depth.
Figure 1.4a shows the variation of depth and side gap of the machined microchannels, and the three-dimensional profiles of the microchannels at each corresponding
applied voltage. Figure 1.4b shows the cross-sectional contours of the microgrooves
under different pulse voltage. It was demonstrated that both the width and the depth
of the microchannels increased with increasing applied voltage. The experimental
results were in accordance with the simulation results. The workpiece materials
removal rate increases with increasing voltage. As illustrated in Eq. (1.1), the electric
current density increases with a bigger voltage amplitude, which makes the dissolution rate increase. During the electrochemical reaction, the dissolution current (i diss )
could be expressed as Eq. (1.9) [2]:
i diss = i 0 · exp
ααϕ
K T
(1.9)