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Effect of Crystal Grain Size in Stainless Steel on Cutting Process in Micromilling

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The crystal grain size of the work material is relatively large compared to the removal depth in micro-scale cutting. Therefore, the micromilling requires the small crystal grains in the material to machine accurate products in a stable manner. The study investigates the effect of crystal grain size on the cutting process in micromilling. The crystal grains of stainless steel in this study are downsized to an average size of 1.5 μm by repetition of material forming and phase transformation. The milling processes of ultra fine-grained steels were compared with those of normal grain steels. The milling tests were performed to measure the cutting force and the surface quality. The force component ratio of the ultra fine-grained steel is higher than that of the normal grain steel. The shearing force decreases in cutting of the ultra fine-grained steel; meanwhile, the friction and/or the indentation forces increase. Burr formation can be reduced with the crystal grain size. In cutting of the normal grain steel, thrust component in the cutting force suddenly drops near the end of the grooves and a large burr is left on the edge of the groove.
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Procedia CIRP 1 ( 2012 ) 150 155
Available online at www.sciencedirect.com
2212-8271 © 2012 The Authors. Published by Elsevier B.V. Selection and/or peer-review under responsibility of Professor Konrad Wegener
http://dx.doi.org/ 10.1016/j.procir.2012.04.026
5
th
CIRP Conference on High Performance Cutting 2012
Effect of Crystal Grain Size in Stainless Steel
on Cutting Process in Micromilling
Takafumi Komatsu
a
*, Tomoaki Yoshino
b
, Takashi Matsumura
b
, and Shiro Torizuka
c
a
Komatsuseiki Kosakusho Co., Ltd., Production Department, Japan
b
Mechanical Engineering, Tokyo Denki University, Japan,
c
National Institute for Material Science, Materials Reliability Centre, Japan
* Corresponding author. Tel.: +81-266-52-6100; fax: +81-266-58-0107.E-mail address: takafumi@komatsuseiki.co.jp.
Abstract
The crystal grain size of the work material is relatively large compared to the removal depth in micro-scale cutting. Therefore, the
micromilling requires the small crystal grains in the material to machine accurate products in a stable manner. The stud
y
investigates the effect of crystal grain size on the cutting process in micromilling. The crystal grains of stainless steel in this stud
y
are downsized to an average size of 1.5ȝm by repetition of material forming and phase transformation. The milling processes o
f
ultra fine-grained steels were compared with those of normal grain steels. The milling tests were performed to measure the cutting
force and the surface quality. The force component ratio of the ultra fine-grained steel is higher than that of the normal grain steel.
The shearing force decreases in cutting of the ultra fine-grained steel; meanwhile, the friction and/or the indentation forces increase.
Burr formation can be reduced with the crystal grain size. In cutting of the normal grain steel, thrust component in the cutting force
suddenly drops near the end of the grooves and a large burr is left on the edge of the groove.
© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Prof. Konrad Wegener
K
eywords: Milling; Micromachining; Burr,
1. Introduction
Micromilling has been applied to manufacturing of
micro devices in automobile, medical and bio industries
with downsizing of the products. Such milling
operations require fine surfaces with high machining
accuracy. Crystal grain size of material has an influence
on the cutting process in micromilling. Fig. 1(a) shows
an example of the crystal grains of 0.15% carbon steel.
When materials are removed in volumes comparable to
the grain size, the surface finishes depends on
microstructures of the materials. In the micro cutting,
burr formation is another factor to be considered for
finishing a fine surface. Then, such the burrs cannot be
removed easily.
Ultra fine-grained metals have recently been
developed to improve the mechanical strengths and their
uniformity of the materials. Murty et al. reduced the
crystal grain size of 0.15% carbon steel with
deformation at a large strain [1]. Saito et al. developed
bulk materials with roll-bonding process [2]. Belyajov e
t
al. applied multiple deformations to forming a fine-
grained structure in austenitic stainless steel [3]. Kimur
a
et al. studied the changes in microstructure and the
mechanical properties with reduction of the crystal grai
n
size [4]. Umemoto formed nanocrystaline structure in
a
large plastic deformation [5]. Ohmari et al. also forme
d
ultra fine-grained structure with repeating the war
m
caliber-rolling [6]. Fig. 1(b) shows an example of the
nanocrystaline structure in the ultra fine-grained carbo
n
steel. The materials have been made by with repeating
plastic deformation and phase transformation [7].
From the point of machining process, many studies
have also discussed the effect of the crystal grain size o
n
the process. Liu et al. studied vibrations in machining o
f
homogeneous materials and they associated the
crystallography and the grain orientation effects [8].
Chae et al. suggested that micro cutting of normal grai
n
steels were regarded as non-homogeneous materials in
micro cutting, and they predicted the cutting force easil
y
© 2012 The Authors. Published by Elsevier B.V. Selection and/or peer-review under responsibility of Professor Konrad Wegener
Takafumi Komatsu et al. / Procedia CIRP 1 ( 2012 ) 150 – 155
151
if ultra fine-grained materials were machined [9]. In
piercing of micro holes on the ultra fine-grained steel,
quality at the edge of the hole was dramatically
improved with reducing vibration and burr formation
[10]. Authors studied the effect of the crystal grain size
on the micro cutting in planning manner [11]. They
reported the dynamic component in the cutting force was
reduced with the crystal grain size and the surface finish
was improved with controlling burr formation. As
another manner, milling is commonly applied to the
practical cutting operations for profiling of the products.
Fig. 1. Micro structures of 0.15% carbon steel. (a) normal grain steel;
(b) ultra fine-grained steel
The paper studies micromilling of an ultra fine-
grained stainless steel for machining micro-scale
grooves. First, the cutting force of the ultra fine-grained
stainless steels is compared with those of the
conventional stainless steel. The difference of cutting
force is distinguished by the cutting force ratio. Then,
the surface finishes and burr formation are observed.
The cutting force in removing at the end of groove is
associated with the burr formation.
2. Material properties
Nickel-Chromium stainless steels (
JIS SUS304, ISO
X5CrNi18-10
) were employed in this study. The materials
were manufactured in a heat batch processing. Table 1
shows the chemical composition of the materials.
Table.1 Chemical composition
Composition %
Carbon (C) 0.06
Silicone (Si) 0.4
Manganese (Mn) 1.09
Phosphorus (P) 0.03
Sulphur (S) 0.004
Nickel (Ni) 8.03
Chromium (Cr) 18.02
Table 2. Mechanical properties
Normal grain
steel
Ultra fine-
grained steel
Vickers Hardness [HV] 260 260
Tensile Strength
[MPa]
RD 870 919
ND 858 880
Elongation [%]
RD 51.1 42.5
ND 57.5 46.4
Ave. Grain Size [ȝm] 9.10 1.52
Fig. 2. Micro structures of stainless steels. (a) normal grain steel; (b)
ultra fine-grained steel
Takafumi Komatsu et al. / Procedia CIRP 1 ( 2012 ) 150 – 155
152
The normal grain stainless steel was formed to reduce
the plate thickness from 3 mm to 0.2 mm in rolling with
heat treatment. Fig. 2(a) shows the microstructure, which
is observed by Electron Back Scatter-diffraction Patterns
(EBSP).
θ
is crystal orientation angle; and α' and γ are
crystal phase. The marten-sites structures are observed
and the grain sizes are ranged from 2 μm to 20 μm,
where the average grain size is 9.10 μm.
Fig. 3. Cutting test
Fig. 4. Workpiece fixture
The ultra fine-grained steel was formed with repeating
plastic deformation and reverse phase transformation.
Fig. 2(b) shows the microstructure, where the average
grain size is 1.52 μm.
Although the grain sizes of the tested materials were
different, the tensile stresses of the materials were
adjusted to be around 900 MPa. Table 2 shows the
mechanical properties of the normal grain steel and the
ultra fine-grained steel.
3. Cutting experiment
The cutting experiments were conducted to machine
grooves with measuring the cutting forces and the
surface profiles, as shown in Fig. 3. A piezoelectric
dynamometer (Kistler Type 9256C2) was mounted on
the machine table of a vertical machining center to
measure the cutting forces. Because the thickness of
samples was 0.2 mm, the samples were clamped on a
fixturing device to perform the stable cutting, as shown
in Fig. 4. The samples were mounted on a glass plate
with adhesive bond.
Fig. 5. Ball end-mill
Fig. 5 shows 0.8 mm diameter ball end mill used in
the cutting experiments. The tool material was tungsten
carbide coated by TiAlN thin layer. Because the cutting
speed is low at the bottom of the ball end mill, the end
mill is inclined in the feed direction. Considering the
stable cutting at certain cutting speeds, a brushless motor
spindle was mounted on the head stock of the machining
center at an inclination angle of 45 degrees. The
maximum spindle speed was 60,000 rpm. The cutter
runout was guaranteed to be less than 1 μm according to
the specification of the spindle.
Table 3. Specifications of end mill
Items Specifications
Ball radius [mm] 0.4
Tool diameter [mm] 0.8
Helical angle [deg] 30
Number of edge 2
Material Tungsten carbide
Coating TiAlN
Table 4. Cutting conditions
Items Specifications
Spindle speed [rpm] 500
Feed per edge [mm/edge] 0.05
Feed rate [mm/min] 50
Depth of cut [μm] 40̚50
Cutting travel [mm] 3
Takafumi Komatsu et al. / Procedia CIRP 1 ( 2012 ) 150 – 155
153
Table 4 shows the cutting conditions in the tests.
Because the detection at contact of the tool and the
workpiece could not be controlled with an accuracy of
less than 1 μm, the depth of cut was ranged from 40 to
50 μm. The end mill was fed to the rolling direction of
the plate sample. As decreasing the cutting speed, the
cutting force data during a milling process become 2400
and the data of materials are comparable.
4. Cutting force
Cutting forces were measured in millings at a
sampling rate of 0.05 ms. Fig. 6(a) shows the measured
cutting forces of the normal grain steel when a groove 43
μm deep is machined. The components in the cutting
force are designated in Fig. 3. The cutting force changes
with the cutting thickness. Fig. 6(b) shows the measured
milling forces of the ultra fine-grained steel, where the
depth of cut is 42 μm. Because the end mill was fed to
the rolling direction of the material plate, the cutting
direction on the rotating edge is perpendicular to the
rolling direction at the maximum cutting thickness.
According to Table 2, the tensile strengths of both of
materials in the normal direction to rolling (ND) are not
different so much. Therefore, little difference is
observed in the maximum cutting forces.
Fig. 6. Cutting forces. (a) normal grain steel; (b) ultra fine-grained steel
Figure 7 shows the cutting forces and the ratios of Z
component to X component in cutting of an edge. The
force ratios are compared in cutting of the ultra fine-
grained steel with that of the normal grain steel, where
the ratio is set to be 0 in non-cutting. Because the dept
h
of cut is no more than 50 μm, X and Z components are
regarded as the tangential and radial forces, respectively.
The ratio of the force component of the ultra fine-
grained steel is higher than that of the normal grain size.
The radial component is associated with friction on the
rake face and the indentation force induced by ploughing
Then, the tangential component is related to the principa
l
force, which is largely associated with the shearing forc
e
Based on the results, the shearing force in cutting of the
ultra fine-grained steel is smaller than that of the normal
grain steel. On the other hand, the friction and/or the
indentation forces increase with reducing the crystal
grain size.
Fig. 7. Cutting forces and force ratios in cutting of an edge. (a) normal
grain steel; (b) ultra fine-grained steel
5. Surface finish
Figure 8 compares the surface finishes in milling,
where the surfaces are oberved with a laser confocal
micro scope. Because the end mills are fed to the botto
m
to the top in the pictures, the cutting edges penetrate the
workpiece at the left of the groove and exit at the righ
t
hand. The cutter marks are left on the surfaces in both o
f
Takafumi Komatsu et al. / Procedia CIRP 1 ( 2012 ) 150 – 155
154
grooves. Remarable difference of the surface finishes is
observed at the right edges of the grooves. Large burrs
are formed along the edge of the groove of the normal
grain steel.
Fig. 8. Surface finishes. (a) normal grain steel; (b) ultra fine-grained
steel
Fig. 9 shows the surface profiles in cross sections
around the right hands of the grooves. Table 4 shows the
m
esured heights and widths of the burrs. Burr formation
of the normal grain steel is much larger than that of the
u
ltra fine-grained steel.
Fig. 10 shows the cutting forces and the force
component ratios when cutting edges finish the right
edges of the grooves. It should be notified that X
component suddenly drops at 0.0233 sec in cutting of the
n
ormal grain steel. Then, the ratio of Z component to X
component increases after 0.0233 sec. Meanwhile, when
cutting of the ultra fine-grained steel, X component
gradually decreases in the end of cut. Furthermore, the
force component ratio does not change.
Fig. 9. Surface profiles. (a) normal grain steel; (b) ultra fine-grained
steel
Fig. 10. Cutting forces and force ratios in finishing the right edges of
grooves. (a) normal grain steel; (b) ultra fine-grained steel
Takafumi Komatsu et al. / Procedia CIRP 1 ( 2012 ) 150 – 155
155
The drop of X component is associated with burr
formation. Normally cutting is performed with shearing
at the positive shear angle. According to Pekelharing, the
shear angle changes to negative at the end of cut and
then a “foot-like” chip is formed and the shear
deformation does not occurs any more [12].
Consequently the deformed material is left on the end
face of the workpiece. When the negative shear occurs,
X component reduces. Then the chip rotates around the
ends of the groove and Z component does not decrease
due to contact of the workiece with the flank face on the
edge. The force component ratio proves the “foot-like”
chip formation. Meanwhile, the force component ratio
does not change in cutting of the ultra fine-grained steel.
As Morris and Ovid’Ko reported on deformation in the
small crystal grained materials, lattice dislocation is
associated with the grain boundaries [13, 14]. Because
the plastic deformation area reduces with the grain size,
the stable shearing continues even if the edge approaches
the end of the groove. Therefore, X component gradually
decreases around the end of cut.
6. Conclusions
The paper compared the cutting force, surface finish
and burr formation of the ultra fine-grained steel with
those of the normal grain steel in micromilling. The
effects of the reduction in the crystal grain size are
summarized as follows:
1. The cutting force can be associated with the tensile
stress of the material under the same chemical
composition of the stainless. For the tested
material, the cutting force does not change because
the tensile strength in the normal direction of the
rolling is nearly same.
2. The ratio of Z component to X component of the
ultra fine-grained steel is higher than that of the
normal grain steel. The shearing force decreases in
cutting of the ultra fine-grained steel. Meanwhile,
the friction and/or the indentation force increases.
3. Burr formation can be controlled by reduction of
the crystal grain size. The size of burr formation is
associated with the change in the cutting force at
the end of cut. In cutting of the normal grain steel,
X component in the cutting force suddenly drops
near the end of cut with changing the shear angle.
Then, large burrs are left on the ends of the groove.
Meanwhile, X component gradually decreases
around the end of cut in milling of the ultra fine-
grained steel. Therefore, the size of burrs becomes
small.
References
[1] Murty SVSN, Torizuka S, Nagai K. Microstructural and micro-
textural evolution during single pass high Z-large strain
deformation of a 0.15C steel. ISIJ Int 2005; 45:1651-1657.
[2] Saito Y, Utsunomiya H, Tsuji N, Sakai T. Novel ultra-high
straining process for bulk materials—development of the
accumulative roll-bonding (ARB) process. Acta Mater 1999; 47:
579-583.
[3] Belyakov A, Sakai T, Miura H. Fine-grained structure formation in
austenitic stainless steel under multiple deformation at 0.5Tm.
Material Trans JIM 2000; 41: 476.
[4] Kimura Y, Suejima S, Goto H, Takaki S. Microstructures and
mechanical properties in ultra fine-grained oxide-dispersion
ferritic stainless steels. ISIJ Int. 2000; 40; 174.
[5] Umemoto M. Formation of nanosrystaline structure by severe
plastic deformation. Feram 2000: 781.
[6] Ohmori A, Torizuka S, Nagai K, Koseki N, Kogo Y. Evolution of
ultrafine-grained ferrite structure through multi-pass warm
caliber-rolling. Tetsu-to-Hagane 2003; 89:781-788.
[7] Nagayama S, Torizuka S, Komatsu T. Test production for ultra fine
gain SUS 304 stainless steel with cold rolling and clad rolling.
The Proceedings of the 2008 Japanese spring conference for the
technology of plasticity 2008: 341.
[8] Liu X, Devor RE, Kappor SG, Ehman KF. The mechanics of
machining at the microscale: assessment of the current state of the
science. Transactions of the ASME, Journal of Manufacturing
Science and Engineering 2004; 126: 666- 678.
[9] Chae J, Park SS, Freiheit T. Investigation of micro-cutting
operations. International Journal of Machine Tools &
Manufacture 2005; 46: 313- 332.
[10] Komatsau T, Kobayashi H, Torizuka S, Nagayama S. Micro hole
piercing for ultra fine grain stainless steel. The Proceedings of 4
th
Asian Workshop on Nano /Micro Forming Technology 2011: 25-
26.
[11] Komatsu T, Matsumura T, Torizuka S. Effect of grain size in
stainless steel on cutting performance in micro-scale cutting.
International Journal of Automation Technology 2011; 5: 334-
341.
[12] Pekelharing AJ. The exit failure of cemented carbide face milling
cutters Part 1 – Fundamentals and phenomena. Annals of the
CIRP 1984; 33: 47-50.
[13] Morris DS. Nanostructured metals and alloys. In: Whang SH,
editors. Strengthening mechanisms in
nanocrystalline
metals,UK: Woodhead Publishing; 2011, p.299-374.
[14] Ovis’Ko IA. Nanostructured metals and alloys. In: Whang SH,
editors. Strengthening mechanisms in
nanocrystalline
metals,UK: Woodhead Publishing; 2011, p.430-458.
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