G. UZUN et al.: EFFECT OF CUTTING PARAMETERS ON THE DRILLING OF AlSi7 METALLIC FOAMS
19–24
EFFECT OF CUTTING PARAMETERS ON THE DRILLING OF
AlSi7 METALLIC FOAMS
VPLIV PARAMETROV REZANJA PRI VRTANJU KOVINSKIH PEN
IZ AlSi7
Gultekin Uzun1, Ugur Gokmen2, Hanifi Cinici1, Mehmet Turker1
1Gazi University, Faculty of Technology, 06500 Ankara, Turkey
2Gazi University, Vocational School of Technical Sciences, 06500 Ankara, Turkey
uzun.gultekin@gazi.edu.tr
Prejem rokopisa – received: 2015-05-27; sprejem za objavo – accepted for publication: 2015-12-17
doi:10.17222/mit.2015.106
In this study, the behaviors of Al matrix metallic foams, produced by the powder-metallurgy method, against the hole-drilling
operation were examined. The stirred Al, 7 % Si and 1 % TiH2 powders were pressed in a mould under uniaxial pressure
(600 MPa) and then deformed, and in this way foamable block samples were obtained. The block samples were subjected to a
foaming process at 710 °C. The obtained samples were drilled at different cutting speeds (10, 30, 50, 70) mm/min and feed rates
(0.15, 0.225, 0.30) mm/r with drill tips of different diameters (4, 5 and 6) mm. It was observed that the foam affected the chip
breakings and chip adhesions increased in proportion to the cutting speed. In the deviation from circularity, the feed rate turned
out to be a more effective parameter than the cutting speed.
Keywords: foams, cutting, machining, tooling
V {tudiji je bilo preiskovano obna{anje kovinskih pen na osnovi Al, izdelanih po metodi metalurgije prahov, pri vrtanju luknje.
Me{anica Al, 7 % Si in 1 % TiH2 prahov je bila stisnjena v orodju z enoosnim tlakom (600 MPa) in potem deformirana, da so
bili dobljeni vzorci sposobni za penjenje. Vzorci so bili izpostavljeni procesu penjenja pri temperaturi 710 °C. Dobljeni vzorci
so bili vrtani pri razli~nih hitrostih rezanja (10, 30, 50, 70) mm/min in hitrostih podajanja (0,15, 0,225, 0,30) mm/r, s svedri z
razli~nimi premeri (4, 5, 6) mm. Ugotovljeno je, da pena vpliva na lomljenje ostru`kov, oprijemanje ostru`kov pa se pove~uje
proporcionalno s hitrostjo rezanja. Pokazalo se je, da na odstopanja od kroga bolj vpliva hitrost podajanja kot pa hitrost rezanja.
Klju~ne besede: pene, rezanje, strojna obdelava, orodja
1 INTRODUCTION
Foams of cellular structure and materials having high
porosity are materials on which intensive studies are
made due to their combination of mechanical and physi-
cal properties.1 Maintaining the high-temperature
strength and structure of metallic foams with respect to
porous polymer materials is one of their important cha-
racteristics.2 Al has a great importance among the
metallic foams.3 Nowadays, these materials are used in
engineering applications and attract a lot of attention.4 Al
foams are known with their thermal strength, acoustic
insulation, and sound- and energy-absorbency proper-
ties.5 They can be used as a filling material in profiles for
energy absorption.6 Among their areas of usage, auto-
motive and space industry lead, especially where a lower
density is needed.7 The machines that are being used in
industrial applications are subjected to vibration and
dynamic loads during running. These vibration and
dynamic loads cause high noise and wear in the moulds.
For the purpose of minimizing these problems aluminum
foams are preferred in the machine manufacturing be-
cause of their low- and high-energy damping abilities.8
In the industrial applications, metallic foams can be
joined with bolts and rivets because of their porous struc-
tures. During the drilling of foams, cutting and feed
speeds cause the breakdown or plastic deformation of
porosities. Besides the chip formation that occurred the
during drilling operation, it also affects the cutting speed
and cutting temperature. For this reason the surface
quality and gauge accuracy of the hole change.9-13
In this study, Al matrix metallic foams were pro-
duced by the powder-metallurgy (PM) method. For the
purpose of examining the effect of the foaming time
period on the porosity morphology, foaming was carried
out for different periods (8, 10, 12, 14 and 16) min. After
determining a suitable foaming period, depending on the
porosity structure, foam samples of 25×40×120 mm
were produced. Al foams of high porosity were sub-
jected to drilling at different cutting speeds (10, 30, 50,
70) m/min and feed rates (0.15, 0.225, 0.30) mm/r with
drill tips of different diameters (4, 5, and 6 mm). During
the drilling operation, effects of the cutting parameters
on the cutting force were examined by measuring the
cutting forces. After the drilling operation, measure-
ments of the deviation from circularity were made and
the samples were compared, depending on the process
parameters.
Materiali in tehnologije / Materials and technology 51 (2017) 1, 19–24 19
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS
UDK 621.762:621.9:532.6:661.862 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 51(1)19(2017)
2 MATERIALS AND METHOD
2.1 Material
In the experimental studies, Al powders and Si
powders with 99.9 % purity were used as the matrix
material and 98 % pure TiH2 powders as the foaming
agent. The physical properties of the used powders are
given in Table 1.
Table 1: Physical properties and production methods of the powders
used in the tests
Tabela 1: Fizikalne lastnosti in metode izdelave prahov, uporabljenih
pri preizkusih
Materials
Physical properties
Production
method
Melting
temperature
(°C)
Density
(g/cm3)
Powder size
(μm)
Aluminum Gasatomization 660 2.7 <160
Si Gasatomization 1410 2.34 <10
TiH2 – <400 3.91 <45
2.2 Method
2.2.1 Aluminum foam production
7 % Si and 1 % TiH2 (both by weight) were added to
99.9 % pure Al powder and stirred for 1 h. The powder
mixture was pressed one-way in a mould under 600 MPa
pressure and block samples were obtained. The obtained
samples were subjected to preheating at 550 °C for 1 h.
Then, the samples were 50 % deformed and cut for foam
production in (10 × 40 × 120) mm sizes (Figure 1).
Foamable block samples were subjected to the foaming
process at 710 °C and Al foams of (25 × 40 × 120) mm
were obtained.
2.2.2 Drilling operation
Drilling tests were made at the Johnford VMC 550
CNC vertical machining center. As the cutting tool,
uncoated HSS (DIN 338) drills (manufactured by the
WERKO cutting tool company) having (4, 5, and 6) mm
diameter were employed. The technical characteristics
and cutting parameters of the HSS drills used in the tests
are given in Table 2.
Table 2: Cutting-tool characteristics and cutting parameters
Tabela 2: Zna~ilnosti rezilnega orodja in parametri rezanja
Cutting tool materials HSS
Standard DIN 338
Cutter geometry Ø4, Ø5, Ø6, mm 118°
Cutting speed 10, 30, 50, 70 m/min
Feed rate 0.15, 0.225, 0.30 mm/r
Cutter type Cylindrical shank drill
Drilling tests were made under dry cutting conditions
and 15 mm deep longitudinal holes were drilled. Taking
into consideration the heat distribution around the drilled
hole, the distance between the hole axes was specified to
be 8 mm.
In the drilling operation, among the three force con-
stituents, since the radial and cutting forces are relatively
small, the third force constituent which is axial force
(feed force, Fz) and torque (Mz) values are taken into
consideration. In this study, three cutting-force con-
stituents were measured, but only the axial force (Fz) was
evaluated. Because of the porous structure of the
material, variations occurred in the axial force. For this
reason the maximum-cutting force values were taken as a
reference for the axial force. Cutting-force measure-
ments were made with a Kistler 9257A type dynamo-
meter attached to the vertical machining center worktop.
An attachment mould was designed and manufactured
for better attachment of the samples to the dynamometer.
In Figure 2 the test set-up is given. For the purpose of
eliminating the twisting effect on the drill, the dis-
location distance of drill tip from the tool holder was
kept to a minimum. This value remained constant in all
of the tests to determine the comparison accuracy in the
obtained data.
Deviation from circularity is defined as the difference
between the biggest and smallest radius measured from a
certain center point (Figure 3a). However, there are
several ways of determining a hole center. There are
widely used methods such as the minimum radial
deviation (MRD), in which the point of the smallest
radial deviation is assumed to be the center and the
least-squares circle (LSC). In the measurements of
deviation from circularity of the holes using CMM, the
G. UZUN et al.: EFFECT OF CUTTING PARAMETERS ON THE DRILLING OF AlSi7 METALLIC FOAMS
20 Materiali in tehnologije / Materials and technology 51 (2017) 1, 19–24
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS
Figure 2: Test set-up
Slika 2: Eksperimentalni sestav
Figure 1: Sample picture before and after foaming process
Slika 1: Posnetek vzorca pred in po postopku penjenja
LSC method was employed for the determination of the
center point. The LSC method center point expresses the
center of the circle, having the sum of least squares of
the radial coordinates (Figure 3b).
The measurements of DFC of the drilled holes were
carried out with a Mitutoyo CMM (Coordinate Measur-
ing Machine). The deviation from circularity and from
the hole diameter were determined by taking coordinates
from at least three separate points in each hole by using a
Ø4 mm prop.
3 EXPERIMENTAL RESULTS AND DISCUSSION
3.1 Pore morphology and density
In the foam production by pore morphology (PM)
method the parameters must be selected properly and the
process must be controlled.14 Banhart, in his study, exa-
mined the linear expansion of Al/TiH2 mixture that was
subjected to the foaming process at 750 °C and stated
that linear expansion varied with respect to the time and
in the case of exceeding the maximum expansion dura-
tion, the adhesion of pores and then breakdowns
started.15 In the case of suitable foaming duration it is
possible to produce a homogeneous structured foam with
high porosity. The pore morphologies of Al foams ob-
tained in the experimental studies are given in Figure 4.
In the produced foams, the highest density value (1.01
g/cm3) was obtained in the foaming processes lasting for
8 min, whereas the lowest value (0.58 g/cm3) was ob-
tained in the foaming processes for 16 min. When the
pore morphology (Figure 4a) obtained in the foaming
process for 8 min is examined, it is clearly seen that
certain areas remained without foaming. This is attri-
buted to the insufficient foaming duration. The porosity
structure of the 16 min foaming process is shown in
Figure 4c. With the increasing of the foaming duration
thinning on the pore walls and partially adhesions of
pores were observed. It is thought that adhesion of the
pores is leading to pore coarsening and causing a de-
crease in density. It can be said that parallel to the pore
structure and the obtained density (10 min – 0.88 g/cm3)
the ideal foaming duration is 10 and 12 min (Figure 4b).
When time saving is considered, it is thought that 10 min
foaming duration will be sufficient.
Mechanical characteristics of metallic foams may
vary depending on the shape size and surface area of the
pores in the structure. Mechanical characteristics of the
foam structure are mostly affected by the density and
metal matrix specification.16 The mechanical perfor-
mance of Al matrix foams is evaluated depending on the
microstructural properties and the pore geometry. Pore
wall thickness and side geometry involve microstructural
variables. Geometrical characteristics involve pore
shape, pore size and the distribution and defects in the
pore structure.17 During 10 min of foaming duration in
which the homogeneous distribution of pore structures
were observed, drilling (with different diameters) was
applied to the obtained foams (Figure 5). When the sec-
G. UZUN et al.: EFFECT OF CUTTING PARAMETERS ON THE DRILLING OF AlSi7 METALLIC FOAMS
Materiali in tehnologije / Materials and technology 51 (2017) 1, 19–24 21
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS
Figure 4: Effect of foaming duration on pore morphology: a) 8 min, b) 10 min, c) 16 min
Slika 4: Vpliv trajanja penjenja na morfologijo por: a) 8 min, b) 10 min, c) 16 min
Figure 3: Circularity measurements: a) DFC-deviation from circul-
arity, b) LSC-least squares circle12
Slika 3: Merjenja kro`nosti: a) DFC-odstopanja od kro`nosti,
b) LSC-krog najmanj{ih kvadratov12
tional pictures of drilled surfaces given in Figure 5 were
examined, closure and regional concentrations were lo-
cated on the pores, depending on the effect of the drilling
force. H. Bart-Smith et al.18, in a study on the energy-
damping capacity of Al foams, mentioned the distri-
bution of regional deformation bands and accumulation
depending on the compression deformation. In their
study, during drilling, it is thought that the pores around
the drill tip joined partially (depending on the applied
pressure) and regional concentrations were created.
3.2 Evaluation of cutting forces
The variation of feed force (Fz) values with respect to
the cutting force, feed and tool type of the holes obtained
after the drilling operations is given in Figure 6. From
this figure it is clear that for all three cutting types, the
obtained feed force values increased with the increasing
cutting speed and feed. The increased feed values caused
the chip volume removed per unit time to increase and
consequently growing of cutting forces.19,20 With the
increasing feed amount, the feed force increased in the
interval of 200–500 %. From the graphs it was observed
that feed force was 80–164 N at the 0.15 mm/r feed
amount, 120–254 N at 0.225 mm/r and 132–282 N at
0.30 mm/r. The feed force increased for all feed rates
with the increasing cutting speed. This was attributed to
the higher adhesion tendency of the Al material on the
cutting tool. The adhesion criteria on the cutting tool are
clearly seen in Figure 7.
In Figure 7 it is clearly seen that the chip adhesions
increase with increasing cutting speed. During machin-
ing of aluminum and some aluminum alloys, the chip is
continuous, quite thick, strong and is not broken easily.
An increase was observed in the cutting forces with the
increasing difficulty of the hard chip discharge. Diffi-
culties in the chip discharge depending on drilling
length, which is the most important problem in drilling
operations, cause the chips to squeeze in the hole, to in-
crease the cutting forces and even to break the tool.21–23 It
was seen that due to the porous structure in the foam
material, chip breakings failed with the increasing
cutting speed and more material adhered on the cutting
tool. Chips were broken at lower cutting speeds and
fewer adhesions were observed. With the increasing feed
amount, formation of more chip caused higher feed
G. UZUN et al.: EFFECT OF CUTTING PARAMETERS ON THE DRILLING OF AlSi7 METALLIC FOAMS
22 Materiali in tehnologije / Materials and technology 51 (2017) 1, 19–24
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS
Figure 5: Pictures of drilling surface and holes section of Al foam
sample
Slika 5: Posnetek vrtane povr{ine in presek lukenj na vzorcu Al pene
Figure 7: Built-up edge on the cutting tool with the increasing cutting
speed
Slika 7: Nastajanje roba na rezilnem orodju pri nara{~anju hitrosti
rezanja
Figure 6: Variation in feed force depending on the cutting speeds,
feed amount and drill diameter
Slika 6: Spreminjanje sile podajanja v odvisnosti od hitrosti rezanja,
podajanja in premera svedra
force, whereas at lower feed rates less feed force was
created. In all feed rates and cutting speeds the highest
cutting force was obtained with Ø4 mm drills. This can
be explained with the cutting tool of small diameter
causing extensive squeezing of the chips. The lowest
feed forces were obtained with Ø6 mm drill.
3.3 Evaluation of hole diameters
In the literature it is stated that the diameter in the
hole inlet and deviation from circularity (DFC) values
are higher with respect to the hole outlet because of the
dynamic instability of cutting tool in the first entry to the
hole. It is said that there are decreases in these values
along the hole inlet and outlet and this is due to guidance
of the hole to the drill till the hole outlet.12 For the pur-
pose of providing a comparison accuracy, deviation
values in the hole diameter were obtained by the measu-
rements made at the hole inlet. Variations in the diameter
values of the holes drilled under different cutting condi-
tions and cutting parameters are given in Figure 8.
From the Figure 8 it was observed that at 0.15 and
0.225 mm/r feed rate, the hole diameter values decreased
with the increase of cutting speed, whereas at 0.30 mm/r
feed rate, hole diameter values increased. At 0.15 and
0.225 mm/r feed rate, increasing of cutting speed caused
decreases of 11 % in hole diameters for all drills. The
increasing tendency in the hole diameters depending on
cutting speed at the highest feed rate (0.30 mm/r) was
measured to be 16 % in the Ø4 mm drill, 23 % in the Ø5
mm drill and 7 % in the Ø6 mm drill. It is thought that
the increasing cutting and feed speeds caused the hole
diameters to get bigger by increasing the vibrations.24 It
was decided that fewer deviations in the hole diameters
are due to less vibration at lower feed rate and slower
penetration into the pieces. During the cutting operation,
bending and shape variations occur in the material at the
feed direction due to its porous structure. This can be
more clearly seen at higher feed rates. For this reason,
higher deviations from the diameter were determined at
higher feed rates. It can be said that the feed rate is more
effective than the cutting speed for the increase in the
hole diameters.
When the DFC graph (Figure 9) was examined, a
maximum DFC value of 0.2 mm was recorded. De-
creases were observed in the DFC values with the in-
creases in cutting speed. Especially at 70 m/min cutting
speed and 0.3 mm/r feed rate, the lowest DFC values
were obtained. The effect of feed rate on the DFC value
at 50 m/min cutting speed is seen more clearly. De-
creases were observed in the DFC values with the
increase in the feed rate. This can be explained with the
more rapid penetration and less distortion on the surface.
At lower feed rates, overcontact of drill to the hole walls
caused the DFC value to increase. As far as the DFC is
concerned, the feed rate was more effective than the
cutting speed.
4 CONCLUSION
In this study, the effect of different foaming durations
on the pore structure of Al foam material was examined
and the foaming duration for homogenous pore distribu-
tion was determined. The obtained samples were drilled
with drills of different diameters at different feed rates
and cutting speeds. The behaviors of the Al foam struc-
ture were evaluated during the drilling operation,
depending on the drilling parameters. The obtained data
as a result of the experimental study is given below.
G. UZUN et al.: EFFECT OF CUTTING PARAMETERS ON THE DRILLING OF AlSi7 METALLIC FOAMS
Materiali in tehnologije / Materials and technology 51 (2017) 1, 19–24 23
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS
Figure 9: Variations of DFC depending on cutting parameters and
cutting conditions
Slika 9: Spreminjanje DFC od parametrov rezanja in pogojev pri
rezanju
Figure 8: Variations in the hole diameters depending on the cutting
parameters and cutting conditions
Slika 8: Spreminjanje premera luknje v odvisnosti od parametrov
rezanja in pogojev pri rezanju
Feed forces increased with the increase in cutting
speed. This can be explained by the increasingly harder
chip discharge.
Feed force exhibited increases in the interval
200–500 % with the increase in feed amount.
Foamed structure affected the chip breakings causing
an increase in chip adhesions proportionally with the
cutting speed.
The highest feed forces were measured with Ø4 mm
drills, whereas the lowest ones were determined with Ø6
mm drills.
The lowest DFC values were obtained with Ø6 mm
drills by using the tool on which the lowest feed forces
occurred.
Feed rate turned out to be a more effective parameter
than the cutting speed for DFC.
In all of the cutting tools, DFC was less at the higher
cutting speed and higher feed feed rate combinations.
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