5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014,

IIT Guwahati, Assam, India

516-1

Behaviour of Cutting Forces in Hard Turning Considering Effect of Tool

Wear on Principal Flank, Auxiliary Flank and Rake Faces: Individually

and in Combination

Amarjit Prakashrao Kene1*, S.K. Choudhury2

1*Ph.D. Scholar, Indian Institute of Technology Kanpur, Kanpur, 208016, Email: amarjitk@iitk.ac.in

2Professor, Indian Institute of Technology Kanpur, Kanpur, 208016, Email: choudhry@iitk.ac.in

Abstract

In the present work behaviour of cutting forces was investigated considering the effect of tool wear on flank and

rake face individually and also in combination. The relationship between cutting forces and wear land was

studied by performing the turning operation on EN24 hardened steel of diameter 70 mm and length 400 mm

using commercially available single layer PVD coated TiSiN-TiAlN nanolayer insert at constant cutting

conditions. In the beginning the inserts were worn out artificially using electric discharge machining process.

From the plot of cutting forces with wear land and experimental results taken individually, it has been observed

that the tangential cutting force was more affected by crater wear. However axial and radial forces observed to

be predominantly affected by principle flank wear. On the other hand, wear on auxiliary flank face showed no

specific effect on any of the forces. Axial and radial forces were observed to be affected mostly when

combination of flank wear and crater wear was considered. The average axial force Fx, tangential force Fz, radial

force Fywere found to be 176.73 N, 225.56 N and 245.84 N respectively in case of no wear (zero wear) and

165.26 N, 219.27 N and 198.36 N respectively in case of combination of wear. Keywords: Hard turning, cutting forces, PVD coated insert, Artificial tool wear.

1 Introduction

Hard turning is a process which involves the

machining of steel of above 45 HRC. In the present

scenario, hard turning gained the popularity because

of its noticeable advantages over conventional

grinding process such as greater accuracy, higher

productivity, more flexibility and above all, the

economy (Hembrug Machine Tools Manual, Finish

Hard Turning). Hard turning is being widely used in

industries for the production of gears, hydraulic

pistons and injection pump components etc. In this

process, the forces generated are expected to be high,

so as per convention of machining a harder tool

material with low wearing capabilities is required for

continuous machining operations. Hard turning is of a

great interest to both the manufacturing industry and

research community.

Hard materials require harder tools to carry out

machining process and indulge more cutting forces in

the process. The cutting forces were in feed direction,

in the direction normal to the workpiece axis and in

vertical direction are named as axial force Fx, radial

force Fy and tangential force Fzrespectively. The value

of these forces is expected to be low and dependent on

practical cutting conditions. Hamdi et al (2012) have

claimed that the cutting force components are

influenced principally by the depth of cut and

workpiece hardness whereas feed is responsible for

surface roughness. Chinchanikar et al. (2013) have

used the optimization technique and found that cutting

forces were mostly affected by depth of cut (60-70 %)

and feed (25-30 %), while tool life is prominently

dependent on cutting speed and then depth of cut for

hard materials. Kaynak et al. (2013) proclaimed that

cryogenic cooling plays a significant role on reducing

notch wear which decreases the cutting force

requirement. Agustina et al. (2013) have proclaimed

that the magnitude of cutting forces are strongly

related to the amount of heat in the cutting area, tool

wear, quality of machined surface and accuracy of the

workpiece. Chinchanikar et al. (2013) have concluded

that coatings increases the limiting cutting speed for

machining of AISI 4340 steel of 35 HRC. Dimla et al.

(2000) have suggested that the vertical components

(z-direction) of both cutting forces and the vibration

signatures were the most sensitive to tool wear.

Behaviour of Cutting Forces in Hard Turning Considering Effect of Tool Wear on Principal

Individually and in Combination

For the machining of hard materials, different tool

materialslike CBN, Ceramics and carbides

tried by many researchers. Tugrul et al. (2007) have

used ceramic tool insert for machining 60 HRC steel.

The cutting forces were observed to be reduced but

roughness remained unaffected. Suresh et al. (2012)

have used multilayer coated carbide tool for

machining of hardened AISI 4340 steel

proclaimed that the reduction in cutting forces were

observed while turning at higher cutting speeds.

Coelho et al. (2007) have used PCBN coated and

uncoated edges for machining of AISI 4340 steel. The

surface finish was observed to be increase

PCBN compared to uncoated edge. The carbide

been chosen in present study to attain eco

process as CBN and ceramic tools are costlier

wear is also a big challenge in the field of machining

as it directly affects the machining performanc

particular operation. During a continuous turning

process, the online monitoring of tool condition plays

a vital role which can be used to protect the process

from unexpected hike in cutting forces as well as

workpiece roughness. Therefore in the p

the behaviour of the cutting forces was

respect to the tool wear. The data was collected from

the force measurement sensor (force dynamometer)

which was then analysed to minimize

The artificially worn-out insertswere used to carry out

the turning operation on EN24 hardened steel of 45

HRC hardness with single layer PVD coated TiSiN

TiAlN insert. The work was mainly concentrate

the artificial tool wear generation and then machining

using these worn out tools to identify performance of

cutting process at constant cutting conditions.

2 Experimental details

2.1 Cutting conditions

Turning operations were carried out on the HMT

center lathe with artificially worn out inserts. Wear

patterns on principle flank face, auxiliary flank face

and rake face, were considered as varying parameters

in present experimentation. Therefore experimen

were carried out at constant values of cutting

parameters viz. cutting speed(V), feed(f

cut(d). According to capability of machine,

recommendation from insert manufacturer, and

literature review, the values of cutting parameters

used in the present work are as given in Table 1.

Table 1 Cutting parameters

Parameters

Cutting Speed, V (m/min)

Feed, f (mm/rev)

Depth of Cut, d (mm)

2.2 Workpiece material and cutting insert

Behaviour of Cutting Forces in Hard Turning Considering Effect of Tool Wear on Principal Flank, Auxiliary Flank and Rake Faces:

For the machining of hard materials, different tool

like CBN, Ceramics and carbides have been

tried by many researchers. Tugrul et al. (2007) have

ert for machining 60 HRC steel.

The cutting forces were observed to be reduced but

Suresh et al. (2012)

have used multilayer coated carbide tool for

machining of hardened AISI 4340 steel and

proclaimed that the reduction in cutting forces were

observed while turning at higher cutting speeds.

Coelho et al. (2007) have used PCBN coated and

r machining of AISI 4340 steel. The

observed to be increased with

The carbide has

been chosen in present study to attain economy in the

are costlier. Tool

wear is also a big challenge in the field of machining

as it directly affects the machining performance for a

particular operation. During a continuous turning

process, the online monitoring of tool condition plays

a vital role which can be used to protect the process

from unexpected hike in cutting forces as well as

roughness. Therefore in the present work

was observed with

s collected from

the force measurement sensor (force dynamometer)

to minimize the tool wear.

e used to carry out

the turning operation on EN24 hardened steel of 45

HRC hardness with single layer PVD coated TiSiN-

mainly concentrated on

the artificial tool wear generation and then machining

entify performance of

at constant cutting conditions.

Turning operations were carried out on the HMT

center lathe with artificially worn out inserts. Wear

patterns on principle flank face, auxiliary flank face

varying parameters

ore experiments

were carried out at constant values of cutting

(f) and depth of

. According to capability of machine,

recommendation from insert manufacturer, and

literature review, the values of cutting parameters

in Table 1.

Table 1 Cutting parameters

Values

150

0.1

0.6

Workpiece material and cutting insert

In this study, 45 HRC EN24 hardened

diameter 70 mm was turned. The hardness was

assumed to be constant (± 1 HRC) throughout its

cross section because of uniform hardening and

tempering process. The workpiece material wa

400 mm in length. The chemical composition of

EN24 workpiece material is given in Table 2. The

turning operation has been carried out using

commercially available single layer PVD coated

TiSiN-TiAlN nanolayer, graded as SECO TH1000,

CNMG120408 (80o diamond shape with 0.8 mm nose

radius) insert with MF2 chip breaker geometry. The

fractograph of insert has been described in Figure 1. A

right handside tool holder designated by ISO as

PCBNR 2020 K12 was used for mounting the insert.

Table 2 Chemical composition of EN24 Steel by

weight percentage

C Mn Si S P Cr

0.4 0.65 0.21 0.012 0.015 1.05

Figure 1 Fractograph of PVD coated insert [2]

2.3 Experimental procedure

Experiments were carried out with varying flank

wear and crater wear. The wear lands

insert artificially using Micro-Electro

Machining (µ-EDM) process. The MIKROTOOLS

DT-110 system was used for creat

different faces of insert as shown in Figure 2. Digital

microscope having maximum amplification

was used to identify the amount of wear produced on

inserts. Average values of the cutting force

components were measured using a three

piezo-electric dynamometer (KISTLER

9257B).

3 Result and discussion

In this section, the experimental observations

summarized.Graphs showing relationship between

cutting force components with respect to

wear are presented keeping cutting parameters and

workpiece hardness constant. The behaviour of

cutting force components with change in tool wear on

principle flank, auxiliary flank and rake faces

considered individually and in combination.

Flank, Auxiliary Flank and Rake Faces:

516-2

In this study, 45 HRC EN24 hardened steel of

diameter 70 mm was turned. The hardness was

assumed to be constant (± 1 HRC) throughout its

cross section because of uniform hardening and

rocess. The workpiece material was of

400 mm in length. The chemical composition of

e material is given in Table 2. The

turning operation has been carried out using

commercially available single layer PVD coated

TiAlN nanolayer, graded as SECO TH1000,

diamond shape with 0.8 mm nose

r geometry. The

fractograph of insert has been described in Figure 1. A

right handside tool holder designated by ISO as

PCBNR 2020 K12 was used for mounting the insert.

Table 2 Chemical composition of EN24 Steel by

Cr Mo Ni

1.05 0.3 1.36

Figure 1 Fractograph of PVD coated insert [2]

Experiments were carried out with varying flank

lands were created on

Electro-Discharge

EDM) process. The MIKROTOOLS

creating wears on

different faces of insert as shown in Figure 2. Digital

amplification of 230X

identify the amount of wear produced on

inserts. Average values of the cutting force

components were measured using a three-component

electric dynamometer (KISTLER- Type

In this section, the experimental observations are

.Graphs showing relationship between

cutting force components with respect to varying tool

wear are presented keeping cutting parameters and

workpiece hardness constant. The behaviour of

cutting force components with change in tool wear on

inciple flank, auxiliary flank and rake faces was

considered individually and in combination.

5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014,

IIT Guwahati, Assam, India

516-3

3.1 Preparation of worn out inserts

The inserts were worn out artificially before

performing the actual turning operation on lathe. As

discussed earlier the µ-EDM process was used for

wearing the insert. Three wear patterns were

generated on auxiliary flank, principle flank and rake

faces separately by varying wear land, VB on flank

faces assuming the rectangular wear geometry as

shown in Figure 2. The crater wear has been

considered as circular in shape and is varied by

varying diameter of crater keeping depth of crater as

constant at 0.03 mm. Table 3 gives the actual

dimension of the wear generated on different faces

along with its designation. The titanium wire was

used as a cathodeand insert was used as anode in µ-

EDM process. The other parameters like voltage,

current, discharge gap, dielectric etc. were selected

accordingly as per the literature.

Table 3 Tool wear dimensions and their

designations

Insert Face Dimensions

VB (mm) Designation

Fresh Tool 0 T0

Auxiliary flank

face

0.2 T1

0.6 T2

1.0 T3

Principle flank

face

0.2 P4

0.6 P5

1.0 P6

Rake face

(Crater Wear)

Φ 0.2 × 0.03 C7

Φ 0.5 × 0.03 C8

Φ 0.8 × 0.03 C9

Combination of

wears 0.6 × 0.6 × Φ0.5 R10

3.2 Fresh tool inserts

The coating on inserts used is comparatively much

harder than work material. Therefore it provides more

abrasion resistance and high temperature resistance to

the insert so that most of the heat could get away

along with the chips (Chinchanikar et al., 2013).

In this section, the behaviour of cutting forces using

fresh insert (T0) has been presentedwhich was used as

reference data for further comparison of cutting forces

using inserts T1, T2, T3, P4, P5, P6, C7, C8, C9 and R10.

The dynamic force signal plot shown in Figure 3

illustrates that the feed force (Fx) is lower as

compared to tangential force (Fz) and radial force (Fy).

In machining, the behaviour of feed force and radial

force is mostly dependent on feed rate and depth of

cut respectively. Also, chip breaker geometry controls

the size of chips flowing out of the machining zone

and it will affect the tangential force.

Figure 2 Optical microscope images of the worn-

out inserts before machining

The machining was carried out at higher cutting

velocity with low feed rate. The average value of

Fxwas found to be 176.73 N whereas Fz and Fywere

found to be 225.56 N and 245.84 N respectively.

Figure 3 Dynamic cutting forces at insert T0

3.3 Worn out inserts

As discussed in the section 3.1, the inserts were

worn out on respective faces by removing the nano-

layer of TiSiN-TiAlN coating. Machining operation

has been carried out using these inserts individually at

constant cutting conditions as given in Table 1. The

average cutting force value has been found out from

the data obtained from force dynamometer as given in

Table 4. Machining was carried out at room

temperature without cutting fluid. The relationship

between wear on auxiliary flank, principle flank and

rake face and cutting forces have been plotted in

Figure 4.The variation of cutting forces with respect

to increasing wear has been plotted in Figure 4 (a). As

the Auxiliary flank wear (AFW) increases, the feed

force increases whereas radial force decreases initially

and then a rapid increase was observed. This is

because, at VB = 0.2 mm the temperature of the

workpiece increases rapidly beyond the temperature

of recrystallization causingthermalsoftening. This

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ttin

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Sample point

Zero Wear

Series 1 - Feed force

Series 2 - Tangential force

Series 3 - Radial force

T0

Behaviour of Cutting Forces in Hard Turning Considering Effect of Tool Wear on Principal Flank, Auxiliary Flank and Rake Faces:

Individually and in Combination

516-4

softening causes the work material to become softer

reducing the forces required for machining. But as

wear land increases further, the work tool contact

length increases which causes forces to increase. Later

as wear land increased beyond 0.6 mm radial force

did not vary and showed a constant trend line.

Auxiliary flank wear has very less effect on tangential

cutting force as there was no formation of crater on

the rake face.

Table 4 Average values of cutting force at different

wear patterns

Insert Cutting Forces (N)

Fx -Axial Fz - Tangential Fy -Radial

T0 176.7303 225.564 245.8464

T1 172.0002 219.6684 205.305

T2 176.7253 214.1122 248.6737

T3 191.619 228.2009 245.7835

P4 194.8359 240.3799 220.6959

P5 196.4953 250.9214 254.1375

P6 198.6157 250.8907 238.2105

C7 91.12476 117.1587 194.3619

C8 104.4299 116.52 208.2673

C9 108.2441 115.2553 211.9306

R10 179.2655 227.2789 198.3629

The behaviour of cutting forces with the increase in

principle flank wear are described in Figure 4(b).

Feed force was observed to be increased as wear land

increases from 0 to 1.0 mm whereas radial force

showed the same nature as in case of auxiliary flank

wear. Initially radial force decreases because of

thermal softening and then increases as VB increases.

Compared to feed and radial forces, tangential forces

have shown negligible change but overall range of

tangential force increases compared with the range in

case of auxiliary flank wear.

In Figure 4(c), the behaviour of cutting forces

with varying crater wear has been presented. The

attempthas been made to wear out the chip-breaker

geometry on the rake face. The crater wear was

assumed to be circular in shape.The plot shows that,

as the crater wear diameter increases, forces decrease

down rapidly. Tangential force was observed to be

reduced compared to the case of auxiliary flank wear

and principle flank wear. The crater wear alone,

specifically does not limit the tool life, instead the

crater increases the effective rake angle and thus

reduces the cuttingforces. In Figure 4 (c), the region

from wear 0.2mm to 1.0 mm, the forces were

observed to be constant. This happened because the

diameter of the crater was varied by keeping the depth

of the crater constant i.e. 0.03 mm. The optical images

of cutting inserts after machining have been shown in

Figure 5.

Figure 4 Behaviour of cutting forces (a) Auxiliary

flank wear Vs Cutting force (b) Principle flank

wear Vs Cutting force (c) CraterWear Vs Cutting

force.

3.4 Combination of wear

In the previous section, the inserts were worn out

individually on different faces and bahaviour of

cutting forces was observed. In this section, the

combinationof wear on the three facesi.e. auxiliary

0.0 0.2 0.4 0.6 0.8 1.0

100

120

140

160

180

200

220

240

260

Cutt

ing

Fo

rces (

N)

Auxiliary Flank Wear (mm)

Fx - Feed Force

Fz - Tangential Force

Fy - Radial Force

(a)

0.0 0.2 0.4 0.6 0.8 1.0

100

120

140

160

180

200

220

240

260

(b)

Principle Flank Wear (mm)

Cutt

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Fo

rces (

N)

Fx - Feed Force

Fz - Tangential Force

Fy - Radial Force

0.0 0.2 0.4 0.6 0.8 1.0

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160

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(c)

Crater Wear (mm)

Cu

ttin

g F

orc

es (

N)

Fx - Feed Force

Fz - Tangential Force

Fy - Radial Force

5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014,

IIT Guwahati, Assam, India

516-5

Figure 5 Optical microscope images of the worn-

out insertsafter machining

flank, principle flank and rake faces,simultaneously

has been presented.The flank and crater wear were

generated on the insert as described in section 3.1.

The middle values from the Table 3 were selected for

wears i.e. 0.6 mm on auxiliary flank and principle

flank wear, and Ф 0.5 mm for crater wear. The

turning experiment has been performed using

insertR10 on AISI 4340 work material. Figure 6 shows

the optical microscope images of fresh as well as

combined worn-out insert. In Figure 6 (b), it can be

observed that edge of the insert has become weak

because of the wearing and therefore the cutting

forces increase as compared to fresh tool insert. The

plot shown in Figure 7 explains that the cutting forces

are comparatively higher for the insert R10

(combination of wear) than the cutting forces in case

of fresh inserts. The average axial force Fx, radial

force Fy and tangential force Fz are found to be 179.26

N, 227.27 N and 198.36 N respectively.

Figure 6 Optical microscope images of (a) fresh

insert (b) combination of wear

Figure 7 Dynamic cutting forces at insert R10

4 Conclusion

The following conclusions were made on the basis

of experimentation performed.

• For the fresh PVD coated TiSiN-TiAlN

nanolayer Carbide insert, the feed force (Fx) is

lower as compared to tangential force (Fz) and

radial force (Fy) because for fresh insert the chip

breaker geometry increased the tangential force

and the high depth of cut increased the radial

force.

• For worn out tools, initially, higher values of

cutting forces were recorded as compared to the

subsequent valuessince thermal softening plays a

vital role. With increasein auxiliary flank wear

(AFW), the feed force increases whereas radial

force decreases initially and then a rapid increase

were observed.

• In case of principle flank wear (PFW), Feed force

was increased as wear land increases from 0 to

1.0 mm, whereas radial force showed the same

nature as in case of AFW because the

temperature of the workpiece increases rapidly

beyond the temperature of recrystallization

causing thermal softening. This softening causes

the work material to become softer reducing the

forces required for machining.

• As the crater wear diameter increases, forces

lowers down rapidly. Overall range of values of

cutting forces has also been reduced to a great

extend i.e. axial forces by 48.43%, radial forces

by 20.94% and tangential forces by 48.05%.

• In case of combination of wears, feed and

tangential forces are comparatively higher than

the cutting forces in case of fresh inserts as sharp

edge of the insert was used for machining. The

average axial force Fx,radial force Fy and

tangential force Fzwere found to be 179.26 N,

227.27 N and 198.36 N respectively.The

tangential cutting force was more affected by

crater wear as chip flows on the rake face and the

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Sample points

T10

PFWCW

AFW

Series 1 - Feed force

Series 2 - Tangential force

Series 3 - Radial force

Behaviour of Cutting Forces in Hard Turning Considering Effect of Tool Wear on Principal Flank, Auxiliary Flank and Rake Faces:

Individually and in Combination

516-6

tangential i.e. vertical force was reduced as

continuous chips were generated.

• However feed and radial forces observed to be

predominantly affected by principle flank wear.

On the other hand, wear on auxiliary flank face

showed no specific variation in any of the forces.

Feed and radial forces were observed to be

affected mostly when combination of flank wear

and crater wear was considered.

Nomenclature----------------------------------------------

EN : Euronorms (European standards)

PVD : Physical Vapour Deposition

ISO : International organization for standardization

TiAlN : Titanium Aluminum Nitride

TiSiN : Titanium Silicon Nitride

AFW : Artificial Flank Wear

PFW : Principle Flank Wear

CW : Crater Wear

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Access Date: 14-04-2014.