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5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT
Guwahati, Assam, India
25-1
Turning of Hardened H13 Steel with Interrupted and Continuous
Surfaces using Multilayer Coated Carbide Tool
R. Suresh1* and S. Basavarajappa2 1* Department of Mechanical Engg., Alliance College of Engineering and Design,
Alliance University, Bangalore-562106, Karnataka, India *Email: [email protected]
2Department of Mechanical Engineering, U.B.D.T. College of Engineering, Davangere-577004, Karnataka, India,
Email: [email protected]
Abstract
Turning of hardened steels has been used increasingly to replace grinding/finishing operations due to the
development of advanced tool materials and rigid machine tools, which can ensure the same accurate geometrical
and dimensional tolerances. However, when turning of interrupted surfaces, the tool requires not only these
properties but also sufficient toughness to resist impacts against work piece interruptions. In the present study,
performance of multilayer hard coatings (TiC/MT-TiCN/Al2O3) on cemented carbide substrate using chemical vapor
deposition (CVD) for turning of hardened AISI H13 steel (50 HRC) was evaluated. Performance evaluation of the
multilayer coated carbide tool was done on the basis of tool flank wear and was supplemented by cutting force and
surface roughness analyses. The results show that the thrust force and cutting force increases with increased depth of
cut and feed rate, while reduces with increase in cutting speed in both continuous and interrupt cutting. The tool
flank wear was influenced mainly by the cutting speed followed by feed rate. Within the investigated range, abrasion
and plastic deformation were deliberated to be the active wear mechanisms for the multilayer coated carbide tool.
The feed rate was the dominant factor affecting work piece surface quality. The main conclusions of this work were
that in both continuous and interrupted cutting, the multilayer coated tools exhibited a better performance with
respect to both tool life and workpiece surface roughness. Keywords: Hard turning, Coated Carbide tool, Cutting forces, Tool Wear, Surface Roughness.
1. Introduction
Hard turning has been used increasingly in industry.
Numerous studies have been reported on the successful
implementation of hard turning. Most of these studies
involve work materials with hardness values in the range
of 45–65HRc and also they involve the use of coated
carbide, ceramic and CBN cutting tools. Hard turning
offers a number of potential benefits over traditional
grinding like reducing manufacturing lead time, process
flexibility, compitable surface finish, higher material
removal rate and the possibility of dry machining (Ozel et
al. 2008 and Bartarya and Choudhury (2012)).
In industrial applications, many components that are
heat treated before the finish turning operation have
surfaces interrupted by keyway slots, holes, lubrication
flow channels and fins. Interrupted turning of hardened
surfaces imposes extra difficulties on machining
operations (Diniz and Oliveira (2008), Oliveira et al. 2009
and Vitor et al. 2009). In such cases, advanced tools are
preferable, due to its high hardness allied to moderate
toughness. PCBN and ceramic tools have good
properties for use in hardened steel turning, such as
hot hardness, wear resistance and excellent chemical
stability.
Diniz and Oliveira [3] studied the effect of cutting
parameters on tool wear during hard turning with
continunous and interrupted surfaces using CBN
tools. Their results shown that high CBN content
(90% of CBN) is sufficiently resistant to the impacts
inherent in the cutting of interrupted surfaces and
provided the longest life. Oliveira et al. (2009)
performed experiments with a PCBN and whisker
reinforced ceramic tool for hardened AISI 4340 steel
turning of continuous and interrupted surfaces. The
results indicated that, in continuous turning, the
longest tool life was achieved using PCBN, but
similar tool longevity was attained in interrupted
turning using both PCBN and ceramic tools. In terms
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Turning of Hardened H13 Steel with Interrupted and Continuous Surfaces using Multilayer Coated Carbide Tool
25-2
of surface roughness, the PCBN tools showed better
results for continuous and interrupted surfaces.
Dogra et al. (2012) investigated the effect of cutting
parameters on tool wear and surface roughness in finish
hard turning of continuous and iterrupted surfaces with
CBN and coated carbide tools. They concluded that the
surface integrity achieved with carbide tools was
comparable with that of CBN tools. The surface
roughness value observed with both tools was below
1.6 µm. No white layer was observed while turning the
interrupted and fully interrupted surfaces with both tools.
As can be seen from the above literatures, cutting
performance of PCBN and ceramic tool materials has
been widely measured in hard machining field and
observed to be acceptable. However, these tools are very
costly. Undoubtedly, a relatively low cost cutting tool
material needs to be searched to perform in an acceptable
range of hard machining. Coated carbide insert is the
proposed alternative in this regard, which is
comparatively when cheaper compared to CBN and
ceramic tools. However the usage of coated carbide insert
in machining of hardened steel is still lacking during
turning of interrupt surfaces. Hence, it is necessary to
investigate the machinability assessments in turning
hardened steels under dry environment to verify the
cutting performance and economical viability.
In the present work, attention is paid towards the
study on the influence of cutting speed (Vc), feed rate (f)
and depth of cut (d), which affect the machinability
characteristics such as cutting forces, tool wear and
surface roughness during turning of hardened H13 steel
with continuous and interrupt surfaces using multilayer
CVD(TiN/MT-TiCN/Al2O3) coated carbide inserts.
Moreover, analysis of the workpiece surface roughness
and of the tool wear lands using scanning electron
microscopy (SEM) were carried out.
2. Experimental Procedure
The dry turning experiments were carried out on a
‘MAZAK CNC’ lathe with 22kW of spindle power and
5000rpm of spindle speed. The work piece material was
AISI H13 steel with 50 HRC of hardness. Round bars of
100 mm diameter and 400 mm length were selected. The
chemical composition of the work piece material is given
in Table 1. These work pieces were produced in order to
obtain continuous and interrupted surfaces (slot width of
12mm x 4 interruptions) as shown in Figure 1. Axial
interruptions were cut in the round bar before hardening.
The multilayer CVD coated (TiC/TiCN/Al2O3) carbide
insert grade KCP05 with ISO geometry CNMG 120408
was used. The experimental setup is as shown in Figure 2.
The average width of flank wear and nose wear was
measured using a tool maker’s microscope connected to a
digital camera and computer. The average surface
roughness average (Ra) on turning surface was
measured by ‘Surftest-201’ roughness tester. Cutting
conditions were specified in accordance with
recommendations from the insert suppliers. In each
experiment a fresh cutting tool was used for fixed
cutting time of 6.0min and the experiments were
repeated twice at each condition in order to keep
experimental error at a minimum.
Table 1 The chemical composition of AISI H13 steel
in percentage by weight.
C Si Mn Cr Ni Mo V
0.4 1.0 0.35 5.3 0.3 1.4 1.0
Figure 1 Types of work piece surfaces (a) continuous
surface (b) Interrupt surface.
Figure 2: Experimental setup
(a)
(b)
Tool Turret
Axial slots
Tool
Dynamomete
r
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5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT
Guwahati, Assam, India
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3. Results and Discussions 3.1 Effect of cutting parameters on cutting forces
The cutting forces acting on tool is an important facet
in hard machining. The cutting forces directly influence
on heat generation, tool wear, quality of machined surface
and accuracy. Hence, in the present work, influence of
cutting parameters on cutting forces during turning of
AISI H13 steel during continuous and interrupted cutting
with multilayer coated carbide tool has been studied. Fig. 3(a) shows the effect of cutting speed on cutting
forces at constant feed rate of 0.14 mm/rev and depth of
cut of 0.45mm. It is observed that the increase in cutting
speed resulted in decrease of cutting forces. It reveals that
the increase in temperature at shear zone resulting in the
thermal softening of the workpiece material and hence
reduced shear strength of the material. The trend on
cutting forces shows that thrust force (Ft) was the
dominant force while compared to cutting force (Fc) and
feed force (Ff) during both continuous and interrupted
cutting operations. Fig. 3(b) depicts the effect of feed rate
on cutting forces at constant cutting speed of 140 m/min
and depth of cut of 0.45 mm. It perhaps due to the
increase of feed rate induces a larger volume of the cut
material in a same unit of time, besides establishing a
dynamic effect on the cutting forces. Fig. 3(c) shows the
effect of depth of cut on machining forces at constant feed
rate of 0.14mm/rev and cutting speed of 140 m/min. It
indicates that increased depth of cut increases the
machining forces. This is because, an increased depth of
cut results in increased tool work contact length.
Subsequently, chip thickness becomes significant that
causes the growth of volume of deformed metal, which
requires greater cutting forces to cut the chip. The
experimental results indicate that the thrust force and
cutting force affected by the depth of cut, followed by the
feed force in interrupt turning.
3.2 Effect of cutting parameters on tool wear
The tool wear purely depend on the type of tool
grade, geometry, work material composition and hardness
and cutting conditions. It can be concluded that generally,
adhesion, abrasion and diffusion are considered to be the
main tool wear mechanisms in hard turning: however the
individual effect of each mechanism depends on the work
material, cutting conditions and tool geometry (Yallese et
al. 2009). Fig. 4(a) shows the results of tool wear in
continuous and interrupt cutting experiments at different
cutting speed. As can be seen, the cutting speed increases
with increase in tool wear. It indicates that the cutting
speed increases, the tool’s temperature rises, causing it to
lose hardness and accelerate tool wear in both continuous
and interrupt cutting. The main wear mechanism on the
coated carbide tool at both cutting conditions was
abrasion, indicated by the thin scratches parallel to
the cutting direction depicted in SEM image (Fig. 5).
Abrasion may be caused either directly by
friction with hard particles from the workpiece or by
removal of binder caused by workpiece friction with
the tool, and consequently, pullout of hard particles
from the tool. These particles rub against the tool,
causing wear. However, at high speeds the tool
reached higher temperatures, and the diffusion
resistance was insufficient to prevent flank wear in
interrupt cutting conditions. Furthermore, this was
the tool with the most severe rake face wear, which is
often caused by diffusion. These findings can be
observed in SEM images Fig. 6(a) & (b). One more
important point is in interrupted cutting, besides
abrasion, chipping of the edge also occurred at higher
cutting conditions.
Constant f=0.14 mm/rev and d=0.45mm
0
100
200
300
400
500
600
80 110 140 170 200
Cutting Speed (Vc) in m/min
Fo
rce
s (
N)
Ft (Int.) Ft (Cont.)
Fc (Int.) Fc (Cont.)
Fa (Int.) Fa (Cont.)
(a)
Constant Vc=140m/min anf d=0.45mm
0
100
200
300
400
500
600
0.06 0.1 0.14 0.18 0.26
Feed Rate (f) in mm/rev
Fo
rce
s (
N)
Ft (Int.) Ft (Cont.)
Fc (Int.) Fc (Cont.)
Fa (Int.) Fa (Cont.)
(b)
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Turning of Hardened H13 Steel with Interrupted and Continuous Surfaces using Multilayer Coated Carbide Tool
25-4
Figure 3: Effect of cutting forces with different cutting
conditions at constant (a) f= 0.14mm/rev & d= 0.45mm,
(b) Vc= 140m/min & d=0.45mm and (c) f=0.14mm/rev,
Vc=140m/min & cutting time (t) =6 min.
Figure 4: Effect of tool wear with different cutting
conditions at constant (a) f= 0.14mm/rev & d=
0.45mm, (b) Vc= 140m/min & d=0.45mm and (c)
f=0.14mm/rev, Vc=140m/min and cutting time (t) =6
min.
Fig. 4(b) and (c) indicates the characteristic wear
of tool is caused by the fact that, the speed is no
longer the influential factor on wear, but it is more
likely that wear is the consequence of the feed and
depth of cut. From the above discussions, it is clear
that a combination of lower values of cutting speed,
feed rate and depth of cut is favorable in reducing
tool wear. It should be noted that edge chipping was
visible on the cutting edge at higher depth of cut
(0.75mm) in interrupted turning. It indicating that
these tools are not sufficiently tough to withstand
impacts caused by interrupted cutting and that the
machine setup was not suitable for this type of
operation.
Figure 5: SEM images of the cutting edges used in
continuous cutting at Vc=140m/min, f=0.14mm/rev
and d=0.45mm and cutting time (t)=6min.
3.3 Effect of cutting parameters on work piece
surface roughness
Constant Vc=140 m/min and f=0.14mm
0
100
200
300
400
500
600
0.15 0.3 0.45 0.6 0.75
Depth of cut (d) in mm
Fo
rce
s (
N)
Ft (Int.) Ft (Cont.)
Fc (Int.) Fc (Cont.)Fa (Int.) Fa (Cont.)
(c)
0
0.05
0.1
0.15
0.2
0.25
0.15 0.3 0.45 0.6 0.75
Depth of cut (mm)
To
ol
We
ar
(mm
)
Continuous
Interrupt
(c)
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.06 0.1 0.14 0.18 0.26
Feed Rate (mm/rev)
To
ol W
ea
r (m
m)
Continuous
Interrupt
(b)
0
0.05
0.1
0.15
0.2
0.25
80 110 140 170 200
Cutting Speed (m/min)
Tool W
ear (m
m)
Continuous
Interrupt
(a)
Abrasive
marks
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5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT
Guwahati, Assam, India
25-5
Surface roughness is one of the most indicators of the
surface integrity of the machined parts and besides serves
as the control criterion for tool failure. A proper
combination of cutting parameters is very important
because this determines the surface quality of hardened
machined parts. The effect of cutting conditions on
surface roughness in turning of hardened H13 steel with
continuous and interrupt cutting using multilayer-coated
carbide tool is exhibited in Fig. 7. The surface roughness
value observed with both continuous and interrupt
cuttings was below 1.6 µm.
Figure 7(a) presents the effect of cutting speed on
surface roughness at constant feed rate of 0.14 mm/rev
and depth of 0.45 mm. It is observed from this figure that
lower surface roughness values are obtained at higher
cutting speeds, mainly because of the generation of lower
forces during machining of hardened steel. Higher cutting
speed reduces the surface roughness due to less heat
dissipated to the work material, as it was swept away in
the chip.
Fig 7(b) demonstrates the effect of feed rate on
surface roughness at constant cutting speed of 140 m/min
and depth of cut of 0.45 mm. The surface roughness
increases with increased feed rates, however it remains
almost unaffected at lower feed rate. It shows that the
amount of heat generation increases with increase in feed
rate, because the cutting tool has to remove more volume
of material from the workpiece. The plastic deformation
of the workpiece is proportional to the amount of heat
generation in the workpiece and promotes roughness on
the workpiece surface. Another reason is that the
alterations in roughness values are related mainly to
changes in tool topography as a function of tool wear rate,
which tend to be transferred to the workpiece surface,
especially changes in secondary cutting edge shape. Thus,
the behavior of workpiece roughness and the worn tool
surface may be directly correlated. It indicates that the
continuous machining leads to increased tool nose wear
resulting in ploughing of larger part of the uncut chip
hence; severe material side flow exists on the machined
surface (Fig. 8).
Figure 6: SEM images of the cutting edges used in
interrupted cutting conditions at (a) Vc=140m/min,
f=0.14mm/rev and d=0.45mm and cutting time (t)=6min (b)
Vc=200m/min, f=0.26mm/rev and d=0.75mm and cutting
time (t)=6min.
Fig. 7(c) displays the effect of depth of cut on
surface roughness at constant cutting speed of 200
m/min and feed rate of 0.14 mm and it is observed
that the depth of cut has less significant as compared
to feed rate. Depth of cut parameter has a very less
effect compared to that of the feed rate. This is due to
the increased length of contact between the tool and
the work piece. This improves the conditions of heat
flow from the cutting zone and consequently slows
down the process wear. In interrupt cutting, surface
roughness values can be related to the shape of the
worn tool nose (Fig. 4 (a)). The increase in abrasive
scratches caused a significant change in the coated
carbide tool nose shape (Fig. 4(b)), thus contributing
to the increase in roughness values along the tool’s
life. However, the chipping that occurred at the
coated carbide (TiN/TiCN/Al2O3) tool’s cutting
edges did not contribute to the increase in roughness.
(a) Crack developed
before edge chipping
(b) Edge chipping
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Turning of Hardened H13 Steel with Interrupted and Continuous Surfaces using Multilayer Coated Carbide Tool
25-6
Figure 7: Effect of surface roughness (Ra) with different
cutting conditions at constant (a) f= 0.14mm/rev and d=
0.45mm, (b) Vc= 140m/min and d=0.45mm and (c)
f=0.14mm/rev and Vc=140m/min.
Figure 8 Effect of tool wear on material side flow
during turning of hardened AISI H13 steel with
ceramic tool at Vc= 200 m/min, f= 0.26 mm/rev, d=
0.45.mm and t =6min.
4. Conclusions
The following conclusions can be drawn from
this investigation on turning of continuous and
interrupted surfaces in hardened AISI H13steel using
multilayer coated carbide at different cutting
parameters:
• The thrust force is the dominant force followed
by cutting force and feed force. The cutting force
increases with increased feed rate and depth of
cut, while it decreases with increased cutting
speed. The combination of low feed rate and
low depth of cut with high cutting speed is
desirable for minimizing the cutting forces in
both continuous and interrupt turning.
• The main wear mechanism of the multilayer
coated carbide tool was abrasion at low and
medium cutting speeds. Chipping and breakage
of the cutting edge, which led to a sharp increase
in flank wear, was observed at the higher cutting
speeds.
• In continuous cutting using coated carbide tool
coated with TiN/MT-TiCN/Al2O3, abrasion and
diffusion contributed to the end of tool life.
When this tool machined the work piece with
interruptions, sudden chipping of the cutting
edge occurred in response to mechanical shocks.
• The feed rate was the dominant factor affecting
work piece surface roughness in both continuous
and interrupt cutting.
• The work piece roughness values obtained with
the carbide tool during their lives were
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0.15 0.3 0.45 0.6 0.75
Depth of cut (mm)
Ro
ug
hn
es
s (
Ra
) in
mic
ron
s Continuous
Interrupt
(c)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
80 110 140 170 200
Cutting Speed (m/min)
Ro
ug
hn
es
(R
a)
in (
mic
on
s) Continuous
Interrupt
(a)
0
0.4
0.8
1.2
1.6
2
0.06 0.1 0.14 0.18 0.26
Feed Rate (mm/rev)
Ro
ug
hn
es
s (
Ra
) in
mic
ron
s
Continuous
Interrupt
(b)
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5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT
Guwahati, Assam, India
25-7
considered high for an operation intended to replace
grinding, because the type of wear these tools
underwent caused considerable variations in the tool
nose shape.
• Based on the results of this work, it can be
concluded, in terms of tool life and surface
roughness, multilayer coated carbide performs better
at lower cutting conditions in both interrupted and
continuous surface.
5. Acknowledgements
The authors are grateful to Kennametal India Ltd.,
Bangalore for providing facilities to conduct experiments
and support throughout this work.
6. References
[1] Ozel T, Karpat, Y and Srivastava, A. (2008) Hard
turning with variable micro geometry PCBN tool.
CIRP Ann: Manuf Techn., Vol. 57, pp. 73–76.
[2] Bartarya, G and Choudhury, S.K. (2012) State of the
art in hard turning, Int J Mach Tool Manu., Vol. 53, pp.
1–14.
[3] Diniz, A.E and Oliveira, A.J., (2008) Hard turning of
interrupted surfaces using CBN tools. J. Mater.
Process. Technol., Vol. 195, pp. 275–281.
[4] Oliveira, A. J., Diniz, A. E., Ursolino, D. J. (2009)
Hard turning in continuous and interrupted cut with
PCBN and whisker-reinforced cutting tools, J. Mater.
Process. Technol., Vol. 209(12–13), pp. 5262–5270.
[5] Vitor Augusto A. de Godoy, Anselmo Eduardo
Diniz.(2009)Turning of interrupted and continuous
hardened steel surfaces using ceramic and CBN
cutting tools, J. Mater. Process. Technol., Vol. 211, pp.
1014–1025.
[6] Dogra, M., Sharma, V., Sachdeva, A and Suri, N.M.
(2012) Tool life and surface integrity issues in
continuous and interrupted finish hard turning with
coated carbide and CBN tools, Proc. IMechE Part B:
J. Engineering Manufacture, Vol. 226, pp. 431-443.
[7] Yallese, M.A., Chaoui, K., Zeghib, N., Boulanouar, L.
(2009) Hard machining of hardened bearing steel
using cubic boron nitride tool, J. Mater. Process.
Technol., Vol. 209, pp. 1092–1104.