Comparative evaluation on the performance of ...nopr.niscair.res.in/bitstream/123456789/34776/1/IJEMS 23(1) 45-59.… · SAMPATH KUMAR et al.: CARBIDE CUTTING TOOL ON TURNING EN24

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


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


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


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


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


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


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


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


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


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


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


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.

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Comparative evaluation on the performance of ...nopr.niscair.res.in/bitstream/123456789/34776/1/IJEMS 23(1) 45-59.… · SAMPATH KUMAR et al.: CARBIDE CUTTING TOOL ON TURNING EN24