Modern Mechan ical Engineering, 2014, 4, 1-7
Published Online February 2014 (
Understanding of Ultrasonic Assisted Machining with
Diamond Grinding Tool
Kyung-Hee Park1, Yun-Hyuck Hong2, Kyeong-Tae Kim3, Seok-Wo o Lee3,
Hon-Zong Choi2, Young-Jae Choi2
1Korea Institute on Industrial Technology, Future Manufacturing System R&D Group,
Manufacturing System R&D Department, Cheonan-si, South Korea
2Korea Institute on Industrial Technology, IT Converged Process R&D Group,
Convergent Technology R&D Department, Ansan-si, South Korea
3Korea Institute on Industrial Technology, Chungcheong Regional Division, Cheonan-si, South Korea
Email: kpa,,,,,
Received November 8, 2013; revised December 11, 2013; accepted December 23, 2013
Copyright © 2014 Kyung-Hee Park et al. This is an open access article distributed under the Creative Commons Attribution License,
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In this work, machining test was carried out in various machining conditions using ultrasonic vibration capable
CNC machine. For work material, alumina ceramic (Al2O3) was used while for tool material diamond electrop-
lated grinding wheel was used. To evaluate ultrasonic vibration effect, grinding test was performed with and
without ultrasonic vibration in same machining condition. In ultrasonic mode, ultrasonic vibration of 20 kHz
was generated by HSK 63 ultrasonic actuator. On the other hand, grinding forces were measured by KISTLER
dynamometer. And an optimal sampling rate for grinding force measurement was obtained by a signal proces-
sing and frequency analysis. The surface roughness of the ceramic was also measured by using stylus type sur-
face roughness instrument and atomic force microscop e (AF M). Besides , the scanning electron microscope (SEM)
was used for observation of surface integrality.
Ultrasonic Vibration; Grinding; Alumina Ceramic; Grinding Forces; Surface Roughness
1. Introduction
Ceramics have been considered as one of the important
materials in engineering application due to its outstand-
ing physical and mechanical prop erties such as high melt-
ing temperature, high wear resistant, etc . [1-3]. However,
there are some difficulties in machining of the ceramic
materials owing to its hard and brittle nature on top of
bad uniformity and low reliability, so the ceramics are
classified into ha rd-to-cut materials [4,5]. For this reason,
ultrasonic assisted machining, which is a hybrid process
that combines the material removal mechanism and ul-
trasonic vibration, has been considered. This process can
be useful for ceramic machining because an additional
axial ultrasonic vibration can lead to reduction in cutting
temperature and tool wear while maintaining high sur-
face quality, which cannot be obtained from conventional
machining [6-10]. Therefore, ultrasonic assisted machin-
ing has been applied for machining of the ceramics as an
alternative method to traditional machining [9]. Several
studies have been performed for machining of hard and
brittle materials using ultr asonic vibration, which applied
to either work mater ial or a cutting spindle [2,6,7]. From
the literature, it was found that better surface roughness
and fracture strength were obtained. In addition, the cut-
ting forces and tool wear were also reduced with apply-
ing ultrasonic vibration. On the other hand, in ultra-pre-
cision micromachining of brittle materials, elliptical vi-
bration was capable of ductile machining without a brit-
tle mode [11]. And Zhao et al. discussed theoretical crit-
ical grinding depth based on the ductile removal me-
chanisms of ultrasonic vibration grinding for the ceram-
ics [5,12,13].
This paper studied the ultrasonic vibration effect of
diamond grinding tool on the ceramic machining. To
evaluate the ultrasonic vibration effect, machining test
was performed with and without the ultrasonic vibration.
Finally, machining performance, such as grinding forces
and surface roughness, was compared. Before the ma-
chining experiment, an optimal sampling rate of grinding
force measurement was identified. The grinding forces
were measured by KISTLER dynamometer while the
surface roughness was measured by stylus type surface
roughness instrument and atomic force microscope
(AFM). In addition, the surface image of the ceramic was
obtained by using scanning electron microscope (SEM).
2. Experimental Method
The experiment was performed on a CNC machine,
which enables to generating ultrasonic vibration. Figure
1 shows a schematic of the machining experiment. The
machining started at one corner of ceramic block while
measuring grinding forces by KISTLER dynamometer
(Type 9256C). Af ter the machining , surface roughn ess of
the ceramic was measured using stylus type surface
roughness instrument (CS 3100S4 by Mitutoyo Co.) and
Diamond grinding tools with a diameter of 8 mm,
where the diamond grains were electroplated on the
stainless tool with nickel matrix, was used. For the work
material, alumina ceramic (Al2O3 ~ 96%) was used. To
evaluate the ultrasonic vibration effect, conventional
machining and ultrasonic assisted machining were per-
formed. For the ultrasonic vibration in a longitudinal
direction, a frequency of 20 kHz generated by the HSK
63 type of ultrasonic actuator was used. The machining
conditions are summarized in Table 1.
In addition, amplitude of ultrasonic grinding tool was
measured by laser vibrometer (Polytec OFV-3001) and
oscilloscope (Tektronix TDS1000B). The average am-
plitude was 4.5 μm as shown in Figure 2.
3. Measurement
The grinding forces were measured by the dynamometer
Figure 1. Schematic of experimental setup.
and then the raw force data obtained was processed
through a simple signal processing using commercially
available software such as MATLAB and Dasylab. First,
to identify an optimal sampling frequency in grinding
process, the signal processing and frequency analysis
were carrie d out by testing the sampling frequencies of 1
kHz, 10 kHz and 20 kHz. Fig u re 3 shows the grinding
force measurement at the sampling frequencies at each
time domain obtained by MATLAB software. Figure 3(a)
represents the grinding force in y-axis at the sampling
rate of 1 kH z. It was observed that the force signals a t th e
sampling rate of 1 kHz were severely drifted and dis-
torted compared to at those of 10 kHz and 20 kH as seen
in Figu res 3(b) and (c). There fore, it can be said that the
Table 1. The machining conditions.
Workpiece material Alumina
(96%, 20 × 10 × 10 mm)
Cutter Ø8
Machining speed (m/s) 1.67, 3.35
Coolant Dry
Feedrate (mm/min) 300, 500
Depth of cut (mm) 0.05 (radial), 2 (axial)
Diamond size (μm) D76 (FEPA standard)
Ultrasonic Vibration frequency (kHz) 20
Amplitude (μm) 4.5
Figure 2. Amplitude of ultrasonic vibration.
(a) (b) (c)
Figure 3. Grinding forces in y-axis at various sampling fre-
quencies. (a) 1 kHz; (b) 10 kHz; (c) 20 kHz.
sampling frequency beyond 10 kHz should be used for
reliable data in this work.
In addition, the force signals at sampling frequencies
of 1 kHz and 10 kHz were compared by 3-D waterfall
FFT analysis using MATLAB as in Figure 4. Figure 4(a)
shows the FFT analysis for 1 kHz and the frequency
peaks observed was not clearly identified due to noise
and signal distortion. However, for the case of 10 kHz
the peaks were distinguishable. For example, 133 Hz and
2.4 kHz were found to be the frequencies of machining
spindle and machine jig. On the other hand, a maximum
frequency band width was only up to 500 Hz for 1 kHz
while it was up to 5 kHz for 10 kHz. In these regards, the
sample frequency of 10 kHz was finally selected for the
grindi ng f orc e measure ment.
Figure 5 shows the grinding forces measured at each
direction. To obtain the grinding forces, there are several
steps as depicted in Figure 6. Using Dasylab, first, drift s
of the force signal in raw data was eliminated by a high-
pass filtering and then the maximum values were calcu-
lated from absolute values of the filtered signals, which
were considered as the grinding forces.
A stylus type surface roughness instrument (Model:
CS 3100S4-Mitutoyo Co.) was used for surface rough-
(a) (b)
Figure 4. 3-D waterfall FFT at the sampling rate of 1 kHz
and 10 kHz. (a) 1 k Hz (X-axis); (b) 10 kHz (X-axis).
ness measurement. For evaluating the surface integrity of
the work material, SEM equipment (Model: Hitachi S-
4300) and AFM were used.
4. Results and Discussions
Figure 7 exhibits comparison of the grinding forces at
various grinding conditions. Overall, the grinding forces
in ultrasonic assisted grinding were slightly reduced
compared to the conventional grinding. However, in
some cases, the grinding forces in ultrasonic case showed
higher forces, especially for y-axis components. This
could be mainly because cutting depth in the ultrasonic
grinding was deeper than that in the conventional grind-
ing. As shown in Figure 8, groove depths generated by
diamond grain in both the ultrasonic and conventional
grinding were about 2.5 µm and 3.2 µm respectively.
This difference might cause higher grinding forces in y
Figure 5. Grinding forces at each direction.
Figure 6. Grinding force signal proce s sing procedure s.
(a) (b)
(c) (d)
Figure 7. Analysis data of grinding forces. (a) f = 300 mm/min, v = 1.67 m/s; (b) f = 300 mm/min, v = 3.35 m/s; (c ) f = 500 mm/
min, v = 1.67 m/s; (d) f = 500 mm/min, v = 3.35 m/s.
Figure 8. AFM images with 2D cross-sectional profiles. (a) Conventional grinding; (b) Ultrasonic grinding.
direction. Another possible scenario could be that a
grinding length of the ultrasonic grinding for a single dia-
mond grain at one contact time, Δt, is much larger than
that of the conventional grinding as seen in Figure 9.
This might increase the grinding force slightly. In addi-
tion, it was also found that the grinding force increased
with grinding wheel speed and feed rate increased.
Surface roughness was measured by stylus type mea-
surment equipment in terms of the grinding speed and the
feed rate. As shown in Figure 10, the ultrasonic grinding
shows better surface roughness about 4% - 15% than the
conventional grinding. And also it was observed that
surface roughness improved as the feed rate decreased
and the grinding speed increased.
Figure 11 shows SEM images of machined surface of
the ceramic at various grinding conditions. Figure 11(a)
Figure 9. Kinematics of a diamond grain in conventional
and ultrasonic grinding at a contact time, Δt.
and (b) depicts the surface images at low grinding speed
(v = 1.67 m/s). In Figure 11(a), straight scoring marks of
diamond grains were clearly observed in the convention-
al grinding while, in Figure 11(b), the sinusoidal paths
of the grains were identified in the ultrasonic grinding.
Actually the scoring marks showed 85 μm period of a
sine wave (Figure 11(b)), which was about to be same as
kinematic calculation (83.7 μm) as seen in Figure 12. In
addition, width of the scoring marks was larger in ultra-
sonic grind ing (30 μm) than in conventional grinding (21
μm) (See Figure 8). This means that one diamond can
cover more surface area in the ultrasonic grinding, which
shows that the ultrasonic vibration can grind the surface
effectively. Figures 11(c) and (d) show the surface im-
ages at high grinding spe ed (v = 3.35 m/s). For both cas-
es, the scoring marks were not clearly formed as that at
low grinding speed. This might be because the more di-
amond grains were involved for grinding action at a unit
grinding distance, Δd, due to high wheel speed. This is
why the high wheel speed can enhance the surface inte-
5. Conclusions
In this study, the conventional and ultrasonic assisted
machining for the alumina ceramic was performed by
using the dia mond grinding wheel. The ultrasonic vibrat ion
effect was evaluated in terms of the grinding force and
Figure 10. Surface roughness, Ra.
(a) (b)
(c) (d)
Figure 11. Surface image by SEM at f = 500 mm/min. (a) v = 1.67 m/s (Conventional); (b) v = 1.67 m/s (Ultrasonic); (c) v =
3.35 m/s (Conventional); (d) v = 3.35 m/s (Ultrasonic).
Figure 12. Kinematic of a diamond grain in ultrasonic grin-
the surface roughness.
The following conclusions can be drawn from the
present wo rk:
The optimal sampling rate was selected based on the
signal processing and waterfall FFT analysis. Besides,
the signal processing method was considered as the grind-
ing force a na lysis .
In the comparison of conventional and ultrasonic as-
sisted grinding, the forces in ultrasonic assisted machin-
ing were lower about 20 % - 30%. However, the forces in
the ultrasonic grinding in y direction were higher than that
in the conventional grinding possibly due to deeper d ep th
of cut in the ultrasonic grindin g.
From the surface roughness measurement, it can be
concluded that ultrasonic assisted machining could re-
duce the surface roughness by 5% - 15%. And also it wa s
observed that the surface roughness was imp roved as the
feed rate decreased and the grinding speed increased.
From SEM and AFM measurements, the sinusoidal
scoring marks were clearly observed on the machined
surface in ultrasonic grinding while the straight marks
were observed in the conventional grinding. These sinu-
soidal waves generated by ultrasonic vibration in longi-
tudinal direction can improve the surface integrity effec-
This work was supp orted by the Industrial strategic tech-
nology development program, Development of Next-
generation Hybrid Grinding Systemfunded by the Min-
istry of Trade, Industry & Energy (MOTIE, Korea).
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