comparative evaluation on the performance of...
TRANSCRIPT
Indian Journal of Engineering & Materials Sciences Vol. 23, February 2016, pp. 45-59
Comparative evaluation on the performance of nanostructured TiAlN, AlCrN,
TiAlN/AlCrN coated and uncoated carbide cutting tool on turning En24 alloy steel
T Sampath Kumara,b*, S Balasivanandha Prabuc & T Sorna Kumard
aDepartment of Mechanical Engineering, C Abdul Hakeem College of Engineering and Technology, Hakeem Nagar, Melvisharam 632 509, India
bSchool of Mechanical and Building Sciences, Vellore Institute of Technology, Vellore 632 014, India cDepartment of Mechanical Engineering, College of Engineering Guindy, Anna University, Chennai 600 025, India
dDepartment of Mechanical Engineering, Thiagarajar College of Engineering, Madurai 625 015, India
Received 10 November 2014; accepted 17 September 2015
In the present work, the performances of the nanostructured TiAlN, AlCrN, TiAlN/AlCrN coated are evaluated by comparing the machining performance with uncoated carbide cutting tool by conducting the machining studies on En24 alloy steel. Taguchi’s experimental design is used to design the turning experiments and fix the turning parameters, such as the cutting speed (V), feed rate (f) and depth of cut (d). The signal-to-noise ratio and anova were used to investigate the effects of the machining parameters and their contribution to the tool wear and surface roughness. The results show that the nanostructured TiAlN/AlCrN coated insert has developed minimum flank wear and shown minimum surface roughness on
the machined surface, compared to the TiAlN, AlCrN coated and uncoated tools. The cutting parameters in which the TiAlN, TiAlN/AlCrN coated and uncoated inserts have shown lesser tool flank wear and better surface finish of the work-piece are identified. For the TiAlN tool, the better machining parameters are, cutting speed = 160 m/min, feed rate = 0.119 mm/rev, and the depth of cut = 1.0 mm. For TiAlN/AlCrN, the better machining parameters are, cutting speed = 160 m/min, feed rate = 0.318 mm/rev, and the depth of cut = 0.3 mm, and for the uncoated tool, the cutting speed = 100 m/min, feed rate = 0.318 mm/rev, and the depth of cut = 1.0 mm is the best machining condition. But for the AlCrN tool the minimum tool wear was obtained, when the cutting speed = 40 m/min, feed rate = 0.477 mm/rev, and the depth of cut = 1.0mm and better surface finish of the work-piece was obtained, when the cutting speed = 160 m/min, feed rate = 0.119 mm/rev, and the depth of cut = 1.0 mm.
Keywords: Coated tools, Machinability, Cutting forces, Wear, Taguchi’s design
In recent days, cutting tools manufacturing industries are very keen in developing new cutting tool materials and hard coatings, in order to increase the productivity, dimensional accuracy and the surface finish of the machined components. In modern world, many such new hard coatings have been developed for cutting tool applications and reported. For example, TiAlN
1, TiAlSiN
1, TiSiN
1, and
TiAlN/TiSiN1 coatings have been developed, which
have shown higher wear resistance and lower heat generation, even under extreme machining conditions. Hari Singh and Pradeep Kumar
2 have used TiC coated
carbide tool to machine En24 alloy steel work-piece and studied the optimal value of cutting forces using Taguchi’s design approach. The interaction between cutting speed and depth of cut has significantly affected the cutting force. Rabinovich et al.
3 used
the AlTiN/Cu coated tool for machining Inconel 718. They have reported that the AlTiN based
coatings form a protective layer of alumina during the machining operation, which prevents adhesion between the work-piece and the tool surface during machining. The AlTiN/Cu has increased the tool life by 2.3 times higher than that of the AlTiN coating. This is attributed due to the lower thermal conductivity of AlTiN/Cu coating, as a result of the nanostructured morphology. Gill et al.
4 compared the
machinability of different coated tools such as TiC, CrC, WC/C, TiAlN and Al2O3. Among these coatings, the TiAlN coating has shown excellent hardness, good corrosion and oxidation resistance.
Ning et al.5 compared the performance of TiAlCrN,
TiAlCrN/CrN, TiAlCrN/WN, TiAlCrN/TaN and TiAlCrN/NbN coated tools using dry machining on AISI H13 steel. They have reported that the TiAlCrN/NbN coated tool has shown better cutting performance than the other coated tools. The oxide forming tendency of Al, Cr and Nb develops an oxide layer on the coated surface. Faga et al.
6 have reported
that a protective oxide layer is formed in ——————— *Corresponding author (E-mail: [email protected])
INDIAN J. ENG. MATER. SCI., FEBRUARY 2016
46
AlTiN/Si3N4, AlSiTiN, TiAlN, AlCrN coated tools while turning AISI M2 die steel. The oxide forming tendency is also observed in other coatings such as TiC/Ti(C, N)/Al2O3/TiN and TiC/Al2O3/TiN, which can withstand high cutting temperatures up to 1025°C, and gave better machining performance due to the protective Al2O3 layer
7. Prengel et al.
8 have
evaluated the machinability of TiAlNCB, TiN, TiAlN, TiN/TiCN/TiAlN and TiB2 coated tools using gray cast iron, Inconel 718, A390-Al alloy and Al-Si alloy as work-piece materials, in high speed machining conditions. The results proved that, the TiB2 coated tool has shown better machining performance while turning A390-Al alloy work-piece under high speed dry machining. Singh and Kumar
9 designed
turning experiments based on Taguchi’s design of experiments and machining was performed on En24 alloy steel work-piece using TiC coated cutting tool to predict the tool life. The cutting speed has high percentage contribution in tool wear, when compared to depth of cut and feed rate
9. Sarmah and Khare
10
have reported the flank wear and crater wear on TiC, Ti (C, N), TiN and AlON coated cutting tools while machining En24 steel. The AlON coated cutting tool has better crater wear resistance under high speed cutting conditions followed by TiN and TiC. The TiC coated cutting tool has better flank wear resistance followed by AlON and TiN coated cutting tools. Singh and Kumar
11 have developed a mathematical
model for turning En24 steel with TiC coated carbide cutting tool to predict the tool life and the surface roughness. The response surface methodology (RSM) model is suitable to predict the effect of parameter’s response and this act as a better tool for optimization. The predicted values of the tool life and surface roughness are 24.8688 min and 79.8236 ru, respectively. Chandrasekaran et al.
12 have reported that the
machining of AISI 410 stainless steel work-piece with three different coated tools such as TiCN+Al2O3,
Ti(C, N, B) and (Ti, Al)N. The feed rate and cutting speed has significantly affected the surface roughness with Ti(C, N, B) and (Ti, Al)N coated tools, but the feed rate and depth of cut has significantly affected the surface roughness with TiCN+Al2O3 coated tool. Among the three different coated tools the Ti(C, N, B) coated tool has shown best performance.
There have been numerous coatings developed in the recent years. However, each of the coatings has shown its merits and demerits. The present work
focuses mainly on the comparative evaluation of the
TiAlN, AlCrN, TiAlN/AlCrN coated and the
uncoated carbide tools on machining En24 alloy steel
work-piece, at different cutting speeds, feed rates, and
depth of cuts. The experimental work is carried out to
study the machining performance of the coated carbide tools and the uncoated carbide tools by
comparing the major machinability parameters such
as tool wear, cutting forces, chip formation and
surface roughness.
Experimental Procedure
In the present investigation the TiAlN, AlCrN, TiAlN/AlCrN coatings were deposited on the K10
tungsten carbide cutting tool inserts, using physical
vapour deposition (cathodic arc vapour deposition)
process (Balzer’s oerlikon coating machine, Make - Oerlikon Balzers Ltd., India). During the deposition
process, coating current: 80A; substrate temperature:
450°C; voltage: 200 V and deposition pressure: 4.5 E-4 mbar were used. The details of the process and
its characteristics are reported in ref.13,14
.
The coating thicknesses of TiAlN, AlCrN and TiAlN/AlCrN coatings were measured as 4±1 µm.
The developed TiAlN/AlCrN coating shows better
hardness value and adhesive strength, when compared
to the conventional monolayer coatings such as TiAlN and AlCrN
13. Table 1 presents the hardness and
adhesive strength of the different coatings. The higher
hardness value of the coating is due to the smaller crystallite size, which ranges from 30 nm to 50 nm,
and a dense structure of the TiAlN/AlCrN coating.
The surface roughness value of the TiAlN/AlCrN bilayer coated insert was measured using AFM. The
value of surface roughness was close to 120 nm,
which is due to less surface irregularities and pits14
.
The developed TiAlN/AlCrN coating shows lesser surface roughness (120 nm), when compared to the
conventional monolayer coatings such as TiAlN and
AlCrN which have shown surface roughness values 258 nm and 255 nm, respectively. The surface
roughness is higher for monolayer coatings due to
macro droplets and pits. The hardness, adhesive
strength and surface roughness of the mono layer coatings were measured for comparison.
The experiments were conducted using coated and
uncoated inserts. The En24 alloy steel was used as a work-piece material. A precision lathe machine in a
Table 1 – Hardness and adhesive strength of different coatings13
AlCrN TiAlN TiAlN /AlCrN
Hardness (GPa) 31 26 36
Adhesive strength (N)
45.0 41.5 45.5
SAMPATH KUMAR et al.: CARBIDE CUTTING TOOL ON TURNING EN24 ALLOY STEEL
47
dry environment was used to conduct the turning
experiments. The experimental trials were planned
according to the Taguchi’s design of experiments (L9). A solid bar of En24 alloy steel of 90 mm
diameter and 400 mm length was used as the work-
piece material. The triangular insert (60°) with a
clearance angle of 7°, Insert grade (K10) and corner radius (0.8 mm) was used as a cutting tool insert.
The ISO specification of cutting tool insert and
cutting tool holder are TNMA 160408 and MTGNR2525M16, respectively. The total machining
length was taken as 100 mm. The main factors and
levels for design of experiments are shown in
Table 2. The L9 orthogonal array of experimental parameters is shown in Table 3. The experiment trials
were conducted to evaluate the coatings based on the
tool wear, cutting forces, surface roughness and chips.
The tool maker’s microscope was used to measure the
flank tool wear, and the Mahr surface roughness tester (marsurf GD 120) was used to measure the surface
roughness of the work-piece. The machining forces
such as feed force (Fx), thrust force (Fy) and cutting
force (Fz) were measured by using the kistler® dynamometer, with the help of dynoware software.
The cutting parameters were analysed using minitab
15 software, for both the tool wear and surface roughness of the workpiece.
Results and Discussion
Cutting force analysis
Tables 4 and 5 show the cutting forces recorded
during the experimental trials conducted using TiAlN,
AlCrN, TiAlN/AlCrN coated and uncoated tools. The minimum cutting forces Fx = 6.19 N, Fy = 13.65
N and Fz = 35.60 N were obtained for the TiAlN
coating, when V = 40 m/min, f = 0.119 mm/rev and d = 0.3 mm. The minimum cutting forces Fx = 16.75
N, Fy = 41.14 N and Fz = 73.06 N were obtained
for the AlCrN coating, when V = 40 m/min, f = 0.119
mm/rev and d = 0.3 mm. The minimum cutting forces Fx = 11.70 N, Fy = 35.04 N and Fz = 37.82 N were
obtained for the TiAlN/AlCrN bilayer coating, when
V = 160 m/min, f = 0.318 mm/rev and d = 0.3 mm. The uncoated tool recorded the minimum cutting
forces Fx = 20.84 N, Fy = 47.23 N and Fz = 77.81 N,
when V = 40 m/min, f = 0.119 mm/rev and d = 0.3
mm. The highest machining forces were obtained, at L3 trial conditions for both TiAlN and AlCrN
coated tools. The highest machining forces were
obtained, at L5 and L3 trial conditions for TiAlN/AlCrN coated tool and uncoated tool, respectively.
Table 2 – Design of experiment for the main factors and levels
Levels Main factors
1 2 3
Cutting speed (m/min) V1 = 40 V2 = 100 V3 = 160
Feed rate (mm/rev) f1 = 0.119 f2 = 0.318 f3 = 0.477
Depth of cut (mm) d1 = 0.3 d2 = 0.7 d3 = 1.0
Table 3 – L9 orthogonal array of experimental parameters
Experiment trials
Cutting speed (m/min)
Feed rate (mm/rev)
Depth of cut (mm)
L1 V1 f1 d1
L2 V1 f2 d2
L3 V1 f3 d3
L4 V2 f1 d2
L5 V2 f2 d3
L6 V2 f3 d1
L7 V3 f1 d3
L8 V3 f2 d1
L9 V3 f3 d2
Table 4 – Various machining forces obtained for the TiAlN and AlCrN coated tools
Various machining forces for TiAlN coated tools (N)
Various machining forces for AlCrN coated tools (N)
Exper
imen
t
tria
ls
Cutt
ing s
pee
d
(m/m
in)
Fee
d r
ate
(mm
/rev
)
Dep
th o
f cu
t
(mm
)
Fee
d
forc
e
(Fx)
Thru
st
forc
e
(Fy)
Cutt
ing
forc
e
(Fz)
Fee
d
forc
e
(Fx)
Thru
st
forc
e
(Fy)
Cutt
ing
forc
e
(Fz)
L1 40 0.119 0.3 6.19 13.65 35.60 16.75 41.41 73.06
L2 40 0.318 0.7 163.60 401.10 403.90 106.10 242.40 319.00
L3 40 0.477 1.0 235.80 532.50 704.80 202.70 446.50 691.90
L4 100 0.119 0.7 70.89 103.20 145.90 76.22 108.60 161.00
L5 100 0.318 1.0 207.10 312.20 452.50 108.80 267.90 422.50
L6 100 0.477 0.3 31.02 157.60 178.10 33.99 151.70 184.50
L7 160 0.119 1.0 116.30 141.10 208.80 151.00 187.00 192.90
L8 160 0.318 0.3 39.21 129.40 142.40 42.24 158.60 156.60
L9 160 0.477 0.7 109.90 269.20 387.10 111.40 339.00 399.10
INDIAN J. ENG. MATER. SCI., FEBRUARY 2016
48
From the tool wear data, it is found that the flank tool
wear depends on the cutting forces. The L8 trial (i.e.,
V3, f2, d1) shows the minimum cutting forces, minimum tool wear and minimum surface roughness
value for the TiAlN/AlCrN bilayer coated tool (V =
160 m/min, f = 0.318 mm/rev and d = 0.3 mm)15,16
.
Cutting force is an important parameter that decides the power requirement of a machine tool. It also
influences the tool wear17
.
Tool wear analysis
The surface quality of the work-piece largely
depends upon the stability of the cutting nose and the dimensional accuracy is controlled by the flank wear
developed in the tools18
. The flank wear is primarily
attributed, due to the contact between the tool and the
chip causing abrasive, diffusive and adhesive wear mechanisms at high temperature
19. The tool flank
wear versus length of cut is shown in Fig. 1(a)-(d) for
Table 5 – Various machining forces obtained for the TiAlN/AlCrN coated tools and uncoated tools
Various machining forces for TiAlN/AlCrN coated tools (N)
Various machining forces for Uncoated tools (N)
Exper
imen
t tr
ials
Cutt
ing s
pee
d
(m/m
in)
Fee
d r
ate
(mm
/rev
)
Dep
th o
f cu
t
(mm
)
Fee
d
forc
e (F
x)
Thru
st
forc
e (F
y)
Cutt
ing
forc
e
(Fz)
Fee
d
forc
e (F
x)
Thru
st
forc
e (F
y)
Cutt
ing
forc
e
(Fz)
L1 40 0.119 0.3 26.64 41.59 97.29 20.84 47.23 77.81
L2 40 0.318 0.7 92.89 264.28 413.06 120.70 28.00 357.20
L3 40 0.477 1.0 114.36 147.20 249.59 233.10 552.90 690.70
L4 100 0.119 0.7 37.96 64.26 128.85 137.00 160.10 208.60
L5 100 0.318 1.0 195.64 369.67 575.80 206.60 332.40 449.90
L6 100 0.477 0.3 16.34 62.26 87.36 55.49 248.80 255.70
L7 160 0.119 1.0 91.13 180.97 279.06 142.90 189.80 224.10
L8 160 0.318 0.3 11.70 35.04 37.82 42.53 168.60 156.50
L9 160 0.477 0.7 90.17 239.83 345.08 122.70 373.50 407.50
Fig. 1 – Progression of the flank wear (a) TiAlN coated tools, (b) AlCrN coated tools, TiAlN/AlCrN coated tools and (d) Uncoated tools
SAMPATH KUMAR et al.: CARBIDE CUTTING TOOL ON TURNING EN24 ALLOY STEEL
49
the TiAlN, AlCrN, TiAlN/AlCrN and uncoated tools respectively. Fig. 2 (a)-(d) shows the optical images
of tool flank wear observed on the TiAlN, AlCrN, TiAlN/AlCrN coated and uncoated tools, respectively.
The minimum flank wear measured on the TiAlN,
AlCrN, TiAlN/AlCrN coated tool and the uncoated
tool were 0.05 mm, 0.04 mm, 0.03 mm and 0.09 mm,
respectively. The minimum tool wear was noticed on the TiAlN coated tool, when V = 160 m/min, f = 0.119
mm/rev and d = 1.0 mm. The minimum tool wear
Fig. 2 – Optical images of tool flank wear obtained from experimental trials (a)TiAlN coated tools, (b) AlCrN coated tools, (c) TiAlN/AlCrN coated tools and (d) uncoated tools
INDIAN J. ENG. MATER. SCI., FEBRUARY 2016
50
was noticed on the AlCrN coated tool, when V = 40
m/min, f = 0.477 mm/rev and d = 1.0 mm.
TiAlN/AlCrN coated tool shows minimum tool wear, when V = 160 m/min, f = 0.318 mm/rev and d = 0.3
mm. For uncoated tool, the minimum tool wear was
noticed, when V = 100 m/min, f = 0.318 mm/rev and
d = 1.0 mm. The tool wear increases when the cutting speed increases with low feed rate and high depth of
cut in the uncoated carbide tool. Meanwhile the tool
wear in the TiAlN/AlCrN coated tool increases when the cutting speed decreases with higher feed rate and
moderate depth of cut. The tool develops wear due to
the high stress and temperature during the cutting,
which causes the cutting edges to thermally soften and deform. This causes the cutting edge to blunt and
the Build-Up-Edge (BUE) to develop. The BUE is
observed in L2 (i.e., V1 f2 d2), L3 (i.e., V1 f3 d3), L4 (i.e., V2 f1 d2) and L5 (i.e., V2 f2 d3) experimental trials
for the TiAlN coated cutting tool inserts. However,
the same is observed in the L2, L5 and L8 experimental trials for the AlCrN coated cutting tool inserts. The
BUE is observed in L2, L3 and L5 experimental trials
in the TiAlN/AlCrN coated tools. But, the BUE is
evident in all the experimental trials in the uncoated
tools. The coated tool reduces the friction at the
cutting zone; therefore, the machining forces are reduced considerably. As a result, the coated tool
improves the surface quality and reduces the BUE
formation20
. The development of the BUE increases
the cutting forces, and significantly affects the surface finish of the machined work-piece
21.
The ANOVA for the tool wear of the TiAlN,
AlCrN, TiAlN/AlCrN coated tools and uncoated tools are shown in Table 6. The ANOVA results
revealed that the independent effect of cutting speed,
feed rate and depth of cut have significant effect on
tool wear. The various percentage contributions of the cutting parameters are shown in the ANOVA
table for tool wear. The cutting speed has high
percentage contribution, followed by feed rate and depth of cut for TiAlN and AlCrN coated cutting
tools. The cutting speed has high percentage
contribution, followed by depth of cut and feed rate for TiAlN/AlCrN coated cutting tool. But, the depth
of cut has high percentage contribution, followed by
cutting speed and feed rate for the uncoated cutting
Table 6 – Results of the ANOVA for the tool wear of TiAlN, AlCrN, TiAlN/AlCrN coated and uncoated tools
Cutting parameter Degree of freedom
Sum of square Mean square F ratio Contribution (%)
(a) TiAlN
Cutting speed 2 62.08877 31.04439 24.95503 76.506
Feed rate 2 15.27426 7.637128 6.139107 18.82099
Depth of cut 2 1.304373 0.652187 0.52426 1.607253
Error 2 2.488026 1.244013 3.065754
Total 8 81.15543 100
(b) AlCrN
Cutting Speed 2 77.24522 38.62261 10.78585 46.76563
Feed rate 2 46.45282 23.22641 6.486267 28.12336
Depth of cut 2 34.31543 17.15771 4.791508 20.77517
Error 2 7.161719 3.580859 4.335832
Total 8 165.1752 100
(c) TiAlN/AlCrN
Cutting speed 2 306.2884 153.1442 23.73841 85.42296
Feed rate 2 3.929934 1.964967 0.304584 1.096047
Depth of cut 2 35.43414 17.71707 2.746268 9.88248
Error 2 12.90265 6.451325 3.598512
Total 8 358.5552 100
(d) Uncoated
Cutting speed 2 35.59655 17.79827 6.55464 20.67275
Feed rate 2 31.56749 15.78375 5.812742 18.33287
Depth of cut 2 99.59588 49.79794 18.33928 57.84047
Error 2 5.43074 2.71537 3.153911
Total 8 172.1907 100
SAMPATH KUMAR et al.: CARBIDE CUTTING TOOL ON TURNING EN24 ALLOY STEEL
51
tool. The SEM images of the rake and flank faces of
maximum worn-out TiAlN, AlCrN, TiAlN/AlCrN
coated and uncoated inserts are shown in Fig. 3 (a-h). From the SEM image, it is evident that the TiAlN
coated tool has high wear in the rake face and the
formation of BUE, when compared to the AlCrN and
TiAlN/AlCrN coated tools. The tool wear is higher in uncoated tool, when compared with the TiAlN,
AlCrN and TiAlN/AlCrN coated tools. The tool wear
gradually decreases in TiAlN and TiAlN/AlCrN
coated tools when the cutting speed increases. But the AlCrN coated tool shows that the tool wear increases
gradually, when the cutting speed increases. The
uncoated tool shows that the tool wear decreases and
then increases, when the cutting speed increases gradually. The tool wear data indicate that the wear
Fig. 3 – SEM images of worn-out coated and uncoated cutting tool insert of rake and flank face (a) rake face of TiAlN coated insert, (b) flank face of TiAlN coated insert, (c) rake face of AlCrN coated insert, (d) flank face of AlCrN coated insert, (e) rake face of TiAlN/AlCrN coated insert, (f) flank face of TiAlN/AlCrN coated insert, (g) rake face of uncoated insert and (h) flank face of uncoated insert
INDIAN J. ENG. MATER. SCI., FEBRUARY 2016
52
increases with increase in feed rate for TiAlN coated
tools. But the AlCrN and TiAlN/AlCrN coated tools
shows that the tool wears increases and then decreases, when the feed rate increases gradually.
The uncoated tool shows that the tool wear decreases
gradually, when the feed rate increases. The tool wear
increases and then decreases, when the depth of cut increases gradually for TiAlN and TiAlN/AlCrN
coated tools. But the AlCrN coated and uncoated tools
show that the tool wear increases gradually, when the depth of cut increases.
Surface roughness analysis
Table 7 shows the surface roughness values
recorded in the work-piece, after performing the
machining trials, using nanostructured TiAlN, AlCrN, TiAlN/AlCrN coated and the uncoated tools. The
minimum surface roughness values measured on the
work-piece were 1.715 µm, 1.674 µm, 1.463 µm and 2.308 µm at L7, L7, L8 and L5 experimental conditions
for the TiAlN, AlCrN, TiAlN/AlCrN coated and the
uncoated tools, respectively. The minimum surface
roughness was obtained, when V = 160 m/min, f = 0.119 mm/rev and d = 1.0 mm in the case of the
TiAlN coated tool. The minimum surface roughness
in the case of AlCrN coated tool was obtained, when V = 160 m/min, f = 0.119 mm/rev and d = 1.0 mm.
The minimum surface roughness was obtained, when
V = 160 m/min, f = 0.318 mm/rev and d = 0.3 mm in the case of the TiAlN/AlCrN coated tool. For
uncoated tool, the minimum surface roughness was
noticed, when V = 100 m/min, f = 0.318 mm/rev and d
= 1.0 mm. The surface roughness value increases on increasing the feed rate at low cutting speed. But, at
moderate cutting speed the surface roughness is
directly proportional to the feed rate. The low surface roughness is measured when the feed rate is moderate,
depth of cut is low and at higher cutting speed. This
happens due to lesser machining forces obtained
during the L8 trial, which indicates the smooth machining of En24 alloy steel workpiece, using
TiAlN/AlCrN coated tool22,23
. Surface finish is also an
important index of machinability, because the
performance and service life of the machined components are often affected by its surface
finish24,25
. The ANOVA for the surface roughness of
the work-piece for TiAlN, AlCrN, TiAlN/AlCrN coated and the uncoated tools are shown in Table 8.
The ANOVA results revealed that the independent
effect of cutting speed, feed rate and depth of cut
have significant effect on surface roughness. The percentage contributions of each of the cutting
parameters are shown in the ANOVA table for the
surface roughness. The cutting speed has shown high percentage contribution, followed by the feed rate and
the depth of cut for TiAlN, AlCrN and TiAlN/AlCrN
coated cutting tools. But the feed rate has high percentage contribution, followed by the cutting speed
and the depth of cut for the uncoated cutting tool.
TiAlN, AlCrN, TiAlN/AlCrN coated and uncoated tools have gradually decreased the surface roughness,
when the cutting speed increases. Similarly, increases in surface roughness value was observed, when the
feed rate increases. However, the uncoated tool shows
that the surface roughness decreases and then increases, with increase in feed rate. Depth of cut on
surface roughness indicates that the TiAlN and
TiAlN/AlCrN coated tools have increase and then
decrease in surface roughness, when the depth of cut increases gradually. But the AlCrN coated tool shows
that the surface roughness value decreases and then
increases, when the depth of cut increases gradually. The uncoated tool shows that the surface roughness
Table 7 – Surface roughness values for the TiAlN, AlCrN, TiAlN/AlCrN coated and the uncoated tools
Surface roughness values (Ra) in µm Experiment trials
Cutting speed
(m/min)
Feed rate (mm/rev)
Depth of cut (mm)
TiAlN AlCrN TiAlN /AlCrN coated tool
Uncoated tool
L1 40 0.119 0.3 2.964 2.648 2.462 3.466
L2 40 0.318 0.7 3.657 3.532 3.407 3.747
L3 40 0.477 1.0 4.185 4.215 4.185 5.874
L4 100 0.119 0.7 3.010 2.762 2.364 3.122
L5 100 0.318 1.0 2.462 2.542 2.135 2.308
L6 100 0.477 0.3 3.349 3.618 3.213 4.108
L7 160 0.119 1.0 1.715 1.674 1.692 2.440
L8 160 0.318 0.3 2.124 2.371 1.463 2.811
L9 160 0.477 0.7 3.018 2.765 2.574 3.828
SAMPATH KUMAR et al.: CARBIDE CUTTING TOOL ON TURNING EN24 ALLOY STEEL
53
value increases gradually, when the depth of cut
increases.
Chip formation analysis
The macro views of chips collected during the experimental trials are shown in Fig. 4. (a)-(d) while machining the work-piece using the TiAlN, AlCrN, TiAlN/AlCrN coated and the uncoated tools respectively. The continuous helical chips are formed due to plastic deformation followed by thermal softening effects. The helical chip thickness and chip radius varies depending on the depth of cut and feed rate. As a result of the reduced friction between the chip and the tool surface, the continuous chip flows over the tool surface. The curved chips are formed when the depth of cut is low and feed rate is high, at
different cutting speeds. The curved chips with sharp segmented edges (serrated chips or wavy chips) with breakup chips; they are also known as saw-tooth chips, which have continuous cyclic segments, with uniformly spaced sharp points along the outer surface formed due to the gradually worn out tool. The segmented chips are formed due to the alternate changes in the shear strain from higher to lower.
It is observed that, when the cutting speed is low,
higher cutting forces and the tool wears are recorded, which results in the formation of the segmented chips. The continuous spring type chip with a smaller radius was produced in the L8 trial (V = 160 m/min, f = 0.318 mm/rev and d = 0.3 mm). This chip is formed due to the increase in the ductility of the work-piece material, because of high cutting temperature due to high machining speed. Therefore, it develops thermal softening and instability. The serrated chips are formed, when the temperature increases in the primary shear zone. The shear deformation weakens the material by thermal softening; therefore, the
deformation is concentrated in the shear bands26,27
. Usually the type of chip and the under surface morphology is a direct indicator of the frictional conditions at the tool/chip interface
28. Less friction
and wear have resulted in TiAlN/AlCrN bilayered coated tool, due to curlier chips and smoother under surface morphology, when compared with the mono-layered TiAlN, AlCrN coated and uncoated tools. Table 9 shows the comparison of chip shape and colour during hard turning of the TiAlN, AlCrN, TiAlN/AlCrN coated and the uncoated tools.
Table 8 – Results of the ANOVA for the surface roughness of the work-piece of TiAlN, AlCrN, TiAlN/AlCrN coated and uncoated tools
Cutting parameter Degree of freedom Sum of square Mean square F ratio Contribution (%)
(a) TiAlN
Cutting Speed 2 25.44788 12.72394 4.769892 55.34786
Feed rate 2 14.36764 7.183818 2.693037 31.24889
Depth of cut 2 0.827451 0.413726 0.155096 1.799665
Error 2 5.335106 2.667553 11.60359
Total 8 45.97807 100
(b) AlCrN
Cutting speed 2 21.23106 10.61553 10.05752 47.54818
Feed rate 2 19.30039 9.650196 9.142931 43.22434
Depth of cut 2 2.009261 1.004631 0.951822 4.499857
Error 2 2.110963 1.055482 4.727624
Total 8 44.65167 100
(c) TiAlN/AlCrN
Cutting speed 2 36.72535 18.36268 8.5739 54.53924
Feed rate 2 24.9541 12.47705 5.825783 37.05826
Depth of cut 2 1.374645 0.687322 0.320924 2.041425
Error 2 4.28339 2.141695 6.361077
Total 8 67.33749 100
(d) Uncoated
Cutting speed 2 17.17022 8.58511 14.56337 34.37071
Feed rate 2 28.14287 14.07144 23.87011 56.33535
Depth of cut 2 3.463879 1.73194 2.937979 6.933864
Error 2 1.179 0.5895 2.360079
Total 8 49.95597 100
INDIAN J. ENG. MATER. SCI., FEBRUARY 2016
54
Taguchi design analysis
Main effect and S/N analysis for the tool wear in the TiAlN,
AlCrN, TiAlN/AlCrN coated and the uncoated tools The process parameters with the highest signal-to-
noise (S/N) ratio gives the best possible quality with
least amount of variance29,30
. The variation of the individual response outputs, for the tool wear and the
surface roughness were analysed with the machining
parameters, i.e., cutting speed, feed rate and depth of
cut separately. The horizontal axis indicates the value
of each machining parameter at three levels, and the
vertical axis indicates the output response values. The main effect plots are used to determine the best
possible design conditions to obtain the minimum tool
wear. Figure 5 (a)-(h) shows the main effect plots of S/N ratios and mean for the tool wear in TiAlN,
AlCrN, TiAlN/AlCrN coated and uncoated tools
respectively. The cutting speed has more significant
Fig. 4 – Various chip shapes of the En24 steel for L9 orthogonal array trials (a) TiAlN coated tools, (b) AlCrN coated tools, (c) TiAlN/AlCrN coated tools and (d) uncoated tools
SAMPATH KUMAR et al.: CARBIDE CUTTING TOOL ON TURNING EN24 ALLOY STEEL
55
influence on tool wear, when compared to the feed
rate and depth of cut. The feed rate has moderate
effect on tool wear. The depth of cut has less significant effect on the tool wear for the TiAlN,
AlCrN, TiAlN/AlCrN coated tool and uncoated tools.
The responsible factors for the cutting parameters
based on the S/N ratios, and the confirmation experimental results for the tool wear are shown in
Table 10.
Main effect and S/N analysis for the surface roughness of the
workpiece in TiAlN, AlCrN, TiAlN/AlCrN coated and the
Uncoated tools
The main effect plots of S/N ratios and mean for the surface roughness of the work-piece machined using TiAlN, AlCrN, TiAlN/AlCrN coated and
uncoated tools are shown in Fig. 6(a)-(h) respectively. The cutting speed is the most dominating factor for the surface roughness, when compared to the feed rate and depth of cut. The depth of cut has less significant effect, and the feed rate has moderate significant effect for the surface roughness in TiAlN, AlCrN, TiAlN/AlCrN coated tools. For uncoated tool, the feed rate is the most dominating factor affecting the surface roughness, when compared to the cutting speed and the depth of cut. The depth of cut has less significant effect, and the cutting speed has moderate significant effect on the surface roughness
31,32.
The responsible factors for the cutting parameters based on the S/N ratios, and the confirmation experimental results for the surface roughness are shown in Table 11.
Table 9 – Comparison of chip shape and color during hard turning of the TiAlN, AlCrN, TiAlN/AlCrN coated and the uncoated tools
TiAlN AlCrN TiAlN/AlCrN Uncoated Experiment
trials Shape Color Shape Color Shape Color Shape Color
L1 Spiral with cone
(small radius) Metallic
Spiral
(small radius
with continuous)
Brown Ribbon Brown Spiral
(small radius) Metallic
L2
Spiral
(medium radius
with continuous)
Dark blue Long Spiral Dark blue Serrated
or wavy Burnt blue
Spiral curved
(discontinuous) Dark blue
L3
Spiral
(medium radius
with continuous)
Burnt blue Long Spiral Dark blue Breakup Burnt blue Helical
continuous Dark blue
L4
Spiral
(medium radius
with continuous)
Dark blue Spiral curved
(discontinuous) Dark blue Helical Dark blue
Helical
continuous Burnt blue
L5
Helical (larger radius
with continuous)
Metallic and
blue
Ribbon curved (with
one end
Saw tooth)
Dark blue Helical Burnt blue
Ribbon Curved
(with one end
Saw tooth)
Metallic and
blue
L6
Helical
(larger radius
with continuous)
Dark blue Long Spiral Dark blue Ribbon Burnt blue Helical
Long Curved
Metallic and
blue
L7
Helical
(larger radius
with continuous)
Brown and
metallic
Long Spiral
(with one end
Saw tooth)
Burnt blue Helical Dark blue Helical
Long Curved Burnt blue
L8
Spiral
(medium radius
with continuous)
Dark blue
Spiral
(small radius
with continuous)
Dark blue Helical Metallic and
blue
Spiral
(small radius)
Metallic and
blue
L9
Helical
(larger radii
with continuous)
Burnt blue Ribbon (Curved) Burnt Blue Ribbon Metallic and
blue
Helical
continuous Dark blue
Table 10 – Various responsible factors based on the S/N ratio and the confirmation experimental results for the tool wear
Tool wear
Coatings/
uncoated
Highly
responsible factor
Moderate
responsible factor
Least
responsible factor
Predicated
optimal levels
Predicted
value (mm)
Confirmation
experiment value (mm)
% of
variation
TiAlN Cutting Speed Feed rate Depth of cut V3 f1 d3 0.051 0.040 -21.56
AlCrN Cutting Speed Feed rate Depth of cut V1 f3 d1 0.042 0.060 30.00
TiAlN/AlCrN Cutting Speed Feed rate Depth of cut V3 f1 d1 0.030 0.038 21.05
Uncoated Cutting Speed Feed rate Depth of cut V3 f1 d1 0.280 0.285 1.754
INDIAN J. ENG. MATER. SCI., FEBRUARY 2016
56
Fig. 5 – Main effect plot for coated and uncoated cutting tool wears of S/N ratio and mean, (a) S/N ratio for TiAlN coated tool, (b) mean for TiAlN coated tool, (c) S/N ratio for AlCrN coated tool, (d) Mean for AlCrN coated tool, (e) S/N ratio for TiAlN/AlCrN coated tool, (f) Mean for TiAlN/AlCrN coated tool, (g) S/N ratio for uncoated tool and (h) Mean for uncoated tool
SAMPATH KUMAR et al.: CARBIDE CUTTING TOOL ON TURNING EN24 ALLOY STEEL
57
Fig. 6 – Main effect plot for the surface roughness of the work-piece in coated and uncoated cutting tools of S/N ratio and mean, (a) S/N ratio for TiAlN coated tool, (b) Mean for TiAlN coated tool, (c) S/N ratio for AlCrN coated tool, (d) Mean for AlCrN coated tool, (e)
S/N ratio for TiAlN/AlCrN coated tool, (f) Mean for TiAlN/AlCrN coated tool, (g) S/N ratio for uncoated tool and (h) Mean for uncoated tool
INDIAN J. ENG. MATER. SCI., FEBRUARY 2016
58
Table 11 – Various responsible factors based on the S/N ratio and the confirmation experimental results for the surface roughness
Surface Roughness
Coatings/
uncoated
Highly
responsible factor
Moderate
responsible factor
Least
responsible factor
Predicated
optimal l evels
Prediction
values (µm)
Confirmation
experiment values (µm)
% of
Variation
TiAlN Cutting Speed Feed rate Depth of cut V3 f1 d3 1.771 2.324 31.22
AlCrN Cutting Speed Feed rate Depth of cut V3 f1 d3 1.695 2.251 32.80
TiAlN/AlCrN Cutting Speed Feed rate Depth of cut V3 f1 d1 1.454 1.702 17.05
Uncoated Feed rate Cutting Speed Depth of cut V3 f2 d3 2.403 2.953 22.88
Conclusions
The following conclusions can be drawn from this
study:
(i) TiAlN/AlCrN bilayer coated tool has shown
minimum flank wear of 0.03 mm, at V3 = 160 m/min, f2 = 0.318 mm/rev and d1 = 0.3 mm
machining condition. From the main effect
analysis using the S/N ratio, the tool wear in the TiAlN/AlCrN bilayer coated tool was highly
influenced by the cutting speed. The minimum
flank wear is attributed due to the high hardness of the coating.
(ii) TiAlN/AlCrN bilayer coated tool provided better surface roughness (minimum surface roughness
of 1.463 µm) on the work-piece material. The
minimum surface roughness was observed, when V3 = 160 m/min, f2 = 0.318 mm/rev and
d1 = 0.3 mm machining condition. The better
surface finish obtained in this condition is mainly due to minimum cutting forces generated
at this condition (Fx = 11.70 N, Fy = 35.04 N
and Fz = 37.82 N). From the main effect analysis
using the S/N ratio, the surface roughness of the workpiece machined using TiAlN/AlCrN bilayer
coated tool was highly dominated by the cutting
speed. The coating minimised the friction at the cutting zone, which results in the minimum
surface roughness.
(iii) The minimum cutting condition has shown a continuous spring type of chip with a smaller radius at a higher cutting speed, moderate feed
rate and lower depth of cut. This chip is formed
due to the increase in the ductility of the work-
piece material, because of high heat produced due to high machining speed. This happens due
to the high shear energy and shear stress
developed during the cutting process.
(iv) Taguchi design was used to find the best cutting parameters for the tool wear and surface
roughness of the work-piece. The confirmation
experiments were conducted using predicted
optimal levels (V3, f1, d1) to obtain the tool wear
value (0.038 mm) for the TiAlN/AlCrN bilayer coating. The confirmation experiments were
conducted using predicted optimal levels
(V3, f1, d1) to obtain the surface roughness value
(1.702 µm) for the TiAlN/AlCrN bilayer coating.
References 1 Bouzakis K D, Bouzakis E, Kombogiannis S, Paraskevopoulou
R, Skordaris G, Makrimallakis S, Karirtzoglou G, Pappa M, Gerardis S, Saoubi R M & Andersson J M, Surf Coat Technol, 237 (2013) 379-389 .
2 Hari Singh & Pradeep Kumar, Indian J Eng Mater Sci, 12 (2005) 97-103.
3 Fox-Rabinovich G S, Yamamoto K, Aguirre M H, Cahill D G, Veldhuis S C & Biksa A, Surf Coat Technol,
204 (2010) 2465-2471.
4 Simranpreet Singh Gill, Jagdev Singh, Harpreet Singh & Rupinder Singh, Int J Mach Tools Manuf, 51 (2011) 25-33.
5 Ning L, Veldhuis S C & Yamamoto K, Int J Mach Tools
Manuf, 48 (2008) 656-665.
6 Faga M G, Gautier G, Calzavarini R, Perucca M, Aimo Boot E, Cartasegna F & Settineri L, Wear, 263 (2007) 1306-1314.
7 Grzesik W & Nieslony P, Int J Mach Tools Manuf, 44 (2004) 889-901.
8 Prengel H G, Jindal P C, Wendt K H, Santhanam A T, Hegde P L & Penich R M, Surf Coat Technol, 139 (2001) 25-34.
9 Singh H & Kumar P, Indian J Eng Mater Sci, 11 (2004) 19-24.
10 Sarmah B P & Khare M K, Wear, 127 (1988) 229-240.
11 Singh H & Kumar P, J Sci Ind Res, 66 (2007) 220-226.
12 Chandrasekaran K, Marimuthu P, Raja K & Manimaran A, Indian J Eng Mater Sci, 20 (2013) 398-404.
13 Sampath Kumar T, Balasivanandha Prabu S, Geetha Manivasagam & Padmanabhan K A, Int J Min Metall Mater, 21(8) (2014) 796-805 .
14 Sampath Kumar T, Balasivanandha Prabu S & Geetha Manivasagam, J Mater Eng Perform, 23(8) (2014) 2877-2884.
15 Elio Chiappini, Stefano Tirelli, Paolo Albertelli, Matteo Strano & Michele Monno, Int J Mach Tools Manuf, 77 (2014) 16-26.
16 Cantero J L, Diaz-Aluarez J, Miguelez M H & Marin N C,
Wear, 279 (2013) 885-894.
SAMPATH KUMAR et al.: CARBIDE CUTTING TOOL ON TURNING EN24 ALLOY STEEL
59
17 Sornakumar T & Senthilkumar A, J Mater Process Technol, 202 (2008) 402-405.
18 Sornakumar T, Krishnamurthy R & Gokularathnam C V, J Eur Ceram Soc, 12 (1993) 455- 460.
19 Shalaby M A, El Hakim M A, Magdy M, Abdelhameed Krzanowski J E, Veldhuis S C & Dosbaeva G K, Tribo Int,
70 (2014) 148-154.
20 Dahu Zhu, Xiaoming & Han Ding, Int J Machine Tools &
Manuf, 64 (2013) 60-77.
21 Outeiro J C, Pina J C, Saoubi R M, Pusavec F & Jawahir I S,
CIRP Ann Manuf Technol, 57 (2008) 77-80.
22 Zareena Veldhuis S C, J Mater Process Technol, 212 (2012)
560-570.
23 Paul S, Dhar N R & Chattopadhyay A B, J Mater Process
Technol, 116 (2001) 44-48.
24 Trent E M, Metal cutting, 3rd ed (Butterworths, London), 1991
25 Aslantas K, Ucun I & Cicek A, Wear, 274-275 (2012) 442-451.
26 Devillez A, Le Coz G, Dominiak S & Dudzinski D, J Mater Process Technol, 211 (2011) 1590-1598.
27 Zhaopeng Hao, Dong Gao, Yihang Fan & Rongdi Han, Int J Mach Tools Manuf, 51 (2011) 973-979.
28 Trent E M & Wright P K, Metal cutting, 4th ed (Butterworth-Heinemann, Boston), 2000
29 Mustafa Gunay & Emre Yucel, Measurements, 46 (2013) 913-919.
30 Suresh R, Basavarajappa S, Gaitonde V N & Samuel G L, Int J Refract Met Hard Mater, 33 (2012) 75-86.
31 Philip Selvaraj D, Chandramohan P & Mohanraj M, Measurememts, 49 (2014) 205-215.
32 Ashok Kumar Sahoo & Bidyadhar Sahoo, Measurement, 46 (2013) 2854-2867.