QUALITATIVE CONSEQUENCES IN FINISHING PROCESS OF HOLES GRINDING INTO CERAMICS WITH THE HIGH POWER ULTRASOUND APPLICATION

QUALITATIVE ments between tool and machined component. In spite of lower
toughness of grinding machine headstock, contrarotating grinding
CONSEQUENCES is more advantageous to obtain higher accuracy to size. It was ex-
perimentally proved.
IN FINISHING PROCESS 3. Finishing high power ultrasound grinding
OF HOLES GRINDING Ultrasonic machining technology requires using ultrasound tool re-
sonator, which is one part of ultrasound resonant system. This ultra-
INTO CERAMICS WITH sound resonant system consists of tools resonator and machining
tool, which are fixed together and have one element behaviour. All
THE HIGH POWER part of this system has to the same resonant frequency. Ultrasound
resonant system task is providing for mechanical oscillations in ul-
ULTRASOUND trasound resonator range up 20 kHz. This system caused oscillations
APPLICATION end of all system. Tool resonator consists of ultrasound transducer,
concentrator and wavequide.
Cutting edges are positioned in loop of longitudinal oscillation re-
Fr. Pechá?ek, M. Charbulová, A. Javorová
sonant ultrasound systems. Acoustic ultrasound energy is transpor-
Slovak Univerzity of Technology in Bratislava,
ted on grinding place with cooling liquid. This energy has influence
Faculty of Material science and Technology in Trnava, Slovak Republic
on oscillating movement grinding grains kinematics and dynamics
effects. Result of this influence is periodical change of orientation
e-mail: frantisek.pechacek@stuba.sk
and instantaneous value of cutting speed and force.
The paper deals with qualitative changes of machining of holes
The using ultrasound major effect in grinding place is dynami-
in ceramic materials applying by finishing conventional grinding
cal change of grinding process cutting conditions and technological
and high power grinding. Measured and determined values
characteristics. Conventional grinding instantaneous value cutting
of surface roughness of machining material definitely indicated
speed vector is constant with stable direction. Ultrasound grinding
the advantages of high power ultrasound application. Ultrasound
instantaneous value cutting speed vector and grinding grain directi-
grinding is the technological method of grinding useful
on are periodically varying. This change are described by relation:
for hard machinable materials.
v = v + v + v , v = A . ? . cos ?t
Keywords
K
f
A
A
high power ultrasound, ultrasound system, ultrasonic spindle,
High power ultrasound grinding makes use of longitudinal ultra-
roughness, technical ceramics, hard machined materials
sound oscillation as the additional movement of grinding tool in the
cutting rotation process. High power ultrasound grinding of holes
1. Introduction
makes a use of a join of sinusoidal ultrasound oscillations of grinding
The roughness of grinding surface characterised by its microrough-
tool with classic cinematic scheme of longitudinal grinding. It leads
ness and the quality of surface layer characterised by its state (struc-
to modified movement of cutting edges of grinding tool what can be
ture, residual stress) has dominant influence for reliable function of
seen in Fig. 2. Ultrasound grinding generates less heat than conven-
components. Starting faze of wearing depends mainly on surface tional grinding. It leads to the lower probability of microcracks ori-
roughness of machined components. The process of microgeom-
gin, the improvement of the quality of machined surface and almost
etry creating is a complex physical process of relative mechanical
no wearing of grinding tool was experimentally proved.
and chemical interaction among involved materials. The common
phenomenon of grinding process is characterised by an intersec-
tion of trajectories of abrasive grains movement and trajectories of
grinding surface.
The mechanism of chip removal process during ceramic materi-
als grinding and steels grinding is different. The chip reduction of
ceramic materials is characterised without an extensive plastic de-
formation because of high hardness, brittleness and low plastic de-
formation ability of ceramics. The machinability of technical ceram-
ics applying by conventional methods is very low. The problem is the
achievement of required quality of machining surface, productivity Figure 1. Kinematics model of grinding grains sinusoid trajectory
and economical effectiveness of machining.
by using ultrasound grinding process
2. Finishing conventional grinding of technical ceramics
Applying fine?grained diamond wheels, accuracy and correctness
of wheel spindle settings or low feed are the factors that influence ce-
ramics machining and allow chip removal process by plastic defor-
mation. Final cutting force at grinding is the addition of cutting forc-
es that affect grains of a grinding wheel. Radial forces at ceramics
machining are bigger than tangential forces. Radial forces at metal
machining are lower than tangential forces.
Applying cooling liquid with high cooling and lubricant effect dur-
ing grinding with low feed application is very important because of
decreasing the friction wearing of grains. Contact area of grains and
material of grinding component is large. The size of cutting force
Figure 2. Kinematic variants of grinding A –longitudinal conventional grinding,
is significantly influenced by low feed and by the relation of move-
B –longitudinal ultrasound grinding, C –transversal ultrasound grinding

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Figure 4. Dependence graph
Figure 3. Workstation of SiSiC rings grinding with integrate ultrasound system.
4. Ceramics – characteristic of silicium carbide
infiltrated by silicium (SiSiC)
SiSiC is widely applicable material with special technical properties,
mostly with wide temperature range. Technical parameters are the
result of the molten silicium implant process. During the process car-
bides of silicium are infiltrated by molten liquid silicium. The reaction
of carbon contained in a component with molten silicium produces
new silicium carbides. The reaction is exothermic. Existing grains of
Figure 5. Dependence graph
silicium carbide make the threedimensional bone structure after the
silicium infiltration process and the grains are strengthened.
All specimens were firstly centred and then fixed in special jigs. The
Better mechanical properties and corrosion protection after the size of diamond wheels was ? 30 x 15. Cooling liquid was applied
method application was proved. The structure configuration of SiS-
for both methods of grinding.
iC is very tight. The application possibilities of SiSiC are limited by si-
licium properties. The advantage of infiltrated structure is very low Technological conditions:
value of thermal expansion coefficient. Large and not easily shaped
– frequency of component speed
120 – 180 min?1
components with very low measure tolerance can be produced by – frequency of spindle speed
16.000 – 20.000 min?1
the method. Silicium carbide is convenient material solution to pro-
– longitudinal feed

0.2 – 1.5 m.min?1
duce the sealings made of two sealing rings.
– cutting depth


0.02 – 0.04 mm
Mechanical properties of SiSiC (for example abrasion resistance)
– amplitude of ultrasound oscillations 6 – 12 µm
are very high because of high hardness, good thermal conductivity
– resonance frequency
and next properties. The special abrasion ability of SiSiC is the com-
of ultrasound system

22.8 kHz
mon result of complex of the mechanical properties. The strength
and the stability of grains is stabile enough to protect the material in
6. Conclusions
conditions of friction load, during grinding with no cooling liquid or
Achieved results of grinding process used ultrasound and compar-
no lubricant (time limited self friction ability).
es with conventional grinding process at SiSiC rings grinding lea-
ding towards conclusion, that grinding process with ultrasound sup-
5. Comparing the results of conventional
port is new progressive method of hard machining materials ma-
and ultrasound grinding
chining. Roughness, grinding process-monitoring parameter, was
Values of surface roughness Ra and the hight of undulations Rz of achieved in IT 1-2.
grinding holes were compared for conventional and ultrasound
grinding. Equal technological conditions were kept for both grind-
The best achieved improvement Ra parameter was 82,86 %.
ing methods. The size of machined component was ? 55 x ? 40 x 5. This improvement was achieved with technological conditions:
Table 1. Measured values for conventional grinding and ultrasound grinding, longitudinal feed f = 0.6 m.min?1, cutting depth a = 0.04 mm
p
No.
frequency of component speed min?1
Cutting speed m.min?1
frequency of tool speed min?1
Ra
Rz
Ultrasound Ra
Ultrasound Rz
1
120
1500
16 000
0.68
5.3
0.28
2.0
2
120
1880
20 000
0.5
4.5
0.12
1.3
3
180
1500
16 000
0.72
6.0
0.3
2.2
4
180
1880
20 000
0.68
5.5
0.15
1.6
Table 2. Measured values for conventional grinding and ultrasound grinding, longitudinal feed f = 0.3 m.min?1, cutting depth a = 0.02 mm
p
No.
frequency of component speed min?1
frequency of tool speed min?1
Ra
Rz
Ultrasound Ra
Ultrasound Rz
1
120
16 000
0.45
3.2
0.18
2.0
2
120
20 000
0.35
3.0
0.06
0.7
3
180
16 000
0.5
3.0
0.2
2.1
4
180
20 000
0.35
3.8
0.08
1.7
Qualitative consequences in ?nishing process | December | 2008 | 56/57

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• longitudinal feed – 0,3m.min –1;
• Ultrasound grinding is more progressive and productive method
• cutting depth – 0,02 mm;
of ceramics machining than conventional grinding.
• frequency of component speed – 120 min –1;
• frequency of spindle speed – 20 000 min –1.
Acknowledgements
This paper was supported by VEGA 1/009/ 08 – Optimised systems
The least significant improvement Ra parameter was 58,34 %
and processes of high power ultrasound.
with technological conditions:
• longitudinal feed – 0,6m.min –1;
References
• cutting depth – 0,04 mm;
[Holesovský 2004] Holesovský, F., Hrala, M.: Grinding of Silicon
• frequency of component speed – 120 min –1;
and Nitride Ceramics. In: Production engineering 2004, Vol. 3,
• frequency of spindle speed – 16 000 min –1.
No. 2, pp. 21 – 23, 2004
[Batora 2000] Batora, B.,Vasilko, K.: Machined surfaces, techno-
The best achieved improvement Rz parameter was 76,7 %.
logical heredity, function. TU in Trencin 2000, pp. 183, 2000.
This improvement was achieved with technological conditions:
[Ciutrila 2001] Ciutrila, G.: Stand and results of the researches on
• longitudinal feed – 0,3m.min –1;
the processing technology of internal grinding using ultrasonic vib-
• cutting depth – 0,02 mm;
rations. In: International Symposium MteM Cluj – Napoca, Romania,
• frequency of component speed – 120 min –1;
2001
• frequency of spindle speed – 20 000 min –1.
[Svehla 1986] Svehla, S., Abramov, O., Chorbenko, I.: The appli-
cation of ultrasound in engineering. Alfa Bratislava, 1986, pp. 314,
The least significant improvement Rz parameter was 60,00 %
1986
with technological conditions:
[Vogt 2002] Vogt, B.: Ultrasonic technology revolutionises the machining
• longitudinal feed – 0,6m.min –1;
of brittle – hard materials. Industrial Diamond Review, 2002, Vol. 62,
• cutting depth – 0,02 mm;
No. 4, pp. 242 – 245, 2002.
• frequency of component speed – 120 min –1;
• frequency of spindle speed – 16 000 min –1.
Contacts:

Dipl. Ing. Frantisek Pechacek, PhD.
In conclusion:
Slovak Univerzity of Technology in Bratislava
• Positive influence of high power ultrasound on the grinding pro-
Faculty of Material science and Technology in Trnava
cess of hard and brittle materials (SiSiC);
Institute of manufacturing systems and applied mechanics
• Better quality (from two till three times) of machined surface ap-
Rázusova 2, 917 24 Trnava, Slovak Republic
plying by ultrasound grinding at right choice of technological pro-
tel.: +421 918 646 035
perties of grinding and diamond tools application;
e-mail: frantisek.pechacek@stuba.sk

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