Turning of Hardened H13 Steel with Interrupted and Continuous … · 2014-12-14 · 5th...

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

Guwahati, Assam, India

25-1

Turning of Hardened H13 Steel with Interrupted and Continuous

Surfaces using Multilayer Coated Carbide Tool

R. Suresh1* and S. Basavarajappa2 1* Department of Mechanical Engg., Alliance College of Engineering and Design,

Alliance University, Bangalore-562106, Karnataka, India *Email: [email protected]

2Department of Mechanical Engineering, U.B.D.T. College of Engineering, Davangere-577004, Karnataka, India,

Email: [email protected]

Abstract

Turning of hardened steels has been used increasingly to replace grinding/finishing operations due to the

development of advanced tool materials and rigid machine tools, which can ensure the same accurate geometrical

and dimensional tolerances. However, when turning of interrupted surfaces, the tool requires not only these

properties but also sufficient toughness to resist impacts against work piece interruptions. In the present study,

performance of multilayer hard coatings (TiC/MT-TiCN/Al2O3) on cemented carbide substrate using chemical vapor

deposition (CVD) for turning of hardened AISI H13 steel (50 HRC) was evaluated. Performance evaluation of the

multilayer coated carbide tool was done on the basis of tool flank wear and was supplemented by cutting force and

surface roughness analyses. The results show that the thrust force and cutting force increases with increased depth of

cut and feed rate, while reduces with increase in cutting speed in both continuous and interrupt cutting. The tool

flank wear was influenced mainly by the cutting speed followed by feed rate. Within the investigated range, abrasion

and plastic deformation were deliberated to be the active wear mechanisms for the multilayer coated carbide tool.

The feed rate was the dominant factor affecting work piece surface quality. The main conclusions of this work were

that in both continuous and interrupted cutting, the multilayer coated tools exhibited a better performance with

respect to both tool life and workpiece surface roughness. Keywords: Hard turning, Coated Carbide tool, Cutting forces, Tool Wear, Surface Roughness.

1. Introduction

Hard turning has been used increasingly in industry.

Numerous studies have been reported on the successful

implementation of hard turning. Most of these studies

involve work materials with hardness values in the range

of 45–65HRc and also they involve the use of coated

carbide, ceramic and CBN cutting tools. Hard turning

offers a number of potential benefits over traditional

grinding like reducing manufacturing lead time, process

flexibility, compitable surface finish, higher material

removal rate and the possibility of dry machining (Ozel et

al. 2008 and Bartarya and Choudhury (2012)).

In industrial applications, many components that are

heat treated before the finish turning operation have

surfaces interrupted by keyway slots, holes, lubrication

flow channels and fins. Interrupted turning of hardened

surfaces imposes extra difficulties on machining

operations (Diniz and Oliveira (2008), Oliveira et al. 2009

and Vitor et al. 2009). In such cases, advanced tools are

preferable, due to its high hardness allied to moderate

toughness. PCBN and ceramic tools have good

properties for use in hardened steel turning, such as

hot hardness, wear resistance and excellent chemical

stability.

Diniz and Oliveira [3] studied the effect of cutting

parameters on tool wear during hard turning with

continunous and interrupted surfaces using CBN

tools. Their results shown that high CBN content

(90% of CBN) is sufficiently resistant to the impacts

inherent in the cutting of interrupted surfaces and

provided the longest life. Oliveira et al. (2009)

performed experiments with a PCBN and whisker

reinforced ceramic tool for hardened AISI 4340 steel

turning of continuous and interrupted surfaces. The

results indicated that, in continuous turning, the

longest tool life was achieved using PCBN, but

similar tool longevity was attained in interrupted

turning using both PCBN and ceramic tools. In terms

Turning of Hardened H13 Steel with Interrupted and Continuous Surfaces using Multilayer Coated Carbide Tool

25-2

of surface roughness, the PCBN tools showed better

results for continuous and interrupted surfaces.

Dogra et al. (2012) investigated the effect of cutting

parameters on tool wear and surface roughness in finish

hard turning of continuous and iterrupted surfaces with

CBN and coated carbide tools. They concluded that the

surface integrity achieved with carbide tools was

comparable with that of CBN tools. The surface

roughness value observed with both tools was below

1.6 µm. No white layer was observed while turning the

interrupted and fully interrupted surfaces with both tools.

As can be seen from the above literatures, cutting

performance of PCBN and ceramic tool materials has

been widely measured in hard machining field and

observed to be acceptable. However, these tools are very

costly. Undoubtedly, a relatively low cost cutting tool

material needs to be searched to perform in an acceptable

range of hard machining. Coated carbide insert is the

proposed alternative in this regard, which is

comparatively when cheaper compared to CBN and

ceramic tools. However the usage of coated carbide insert

in machining of hardened steel is still lacking during

turning of interrupt surfaces. Hence, it is necessary to

investigate the machinability assessments in turning

hardened steels under dry environment to verify the

cutting performance and economical viability.

In the present work, attention is paid towards the

study on the influence of cutting speed (Vc), feed rate (f)

and depth of cut (d), which affect the machinability

characteristics such as cutting forces, tool wear and

surface roughness during turning of hardened H13 steel

with continuous and interrupt surfaces using multilayer

CVD(TiN/MT-TiCN/Al2O3) coated carbide inserts.

Moreover, analysis of the workpiece surface roughness

and of the tool wear lands using scanning electron

microscopy (SEM) were carried out.

2. Experimental Procedure

The dry turning experiments were carried out on a

‘MAZAK CNC’ lathe with 22kW of spindle power and

5000rpm of spindle speed. The work piece material was

AISI H13 steel with 50 HRC of hardness. Round bars of

100 mm diameter and 400 mm length were selected. The

chemical composition of the work piece material is given

in Table 1. These work pieces were produced in order to

obtain continuous and interrupted surfaces (slot width of

12mm x 4 interruptions) as shown in Figure 1. Axial

interruptions were cut in the round bar before hardening.

The multilayer CVD coated (TiC/TiCN/Al2O3) carbide

insert grade KCP05 with ISO geometry CNMG 120408

was used. The experimental setup is as shown in Figure 2.

The average width of flank wear and nose wear was

measured using a tool maker’s microscope connected to a

digital camera and computer. The average surface

roughness average (Ra) on turning surface was

measured by ‘Surftest-201’ roughness tester. Cutting

conditions were specified in accordance with

recommendations from the insert suppliers. In each

experiment a fresh cutting tool was used for fixed

cutting time of 6.0min and the experiments were

repeated twice at each condition in order to keep

experimental error at a minimum.

Table 1 The chemical composition of AISI H13 steel

in percentage by weight.

C Si Mn Cr Ni Mo V

0.4 1.0 0.35 5.3 0.3 1.4 1.0

Figure 1 Types of work piece surfaces (a) continuous

surface (b) Interrupt surface.

Figure 2: Experimental setup

(a)

(b)

Tool Turret

Axial slots

Tool

Dynamomete

r



25-3

3. Results and Discussions 3.1 Effect of cutting parameters on cutting forces

The cutting forces acting on tool is an important facet

in hard machining. The cutting forces directly influence

on heat generation, tool wear, quality of machined surface

and accuracy. Hence, in the present work, influence of

cutting parameters on cutting forces during turning of

AISI H13 steel during continuous and interrupted cutting

with multilayer coated carbide tool has been studied. Fig. 3(a) shows the effect of cutting speed on cutting

forces at constant feed rate of 0.14 mm/rev and depth of

cut of 0.45mm. It is observed that the increase in cutting

speed resulted in decrease of cutting forces. It reveals that

the increase in temperature at shear zone resulting in the

thermal softening of the workpiece material and hence

reduced shear strength of the material. The trend on

cutting forces shows that thrust force (Ft) was the

dominant force while compared to cutting force (Fc) and

feed force (Ff) during both continuous and interrupted

cutting operations. Fig. 3(b) depicts the effect of feed rate

on cutting forces at constant cutting speed of 140 m/min

and depth of cut of 0.45 mm. It perhaps due to the

increase of feed rate induces a larger volume of the cut

material in a same unit of time, besides establishing a

dynamic effect on the cutting forces. Fig. 3(c) shows the

effect of depth of cut on machining forces at constant feed

rate of 0.14mm/rev and cutting speed of 140 m/min. It

indicates that increased depth of cut increases the

machining forces. This is because, an increased depth of

cut results in increased tool work contact length.

Subsequently, chip thickness becomes significant that

causes the growth of volume of deformed metal, which

requires greater cutting forces to cut the chip. The

experimental results indicate that the thrust force and

cutting force affected by the depth of cut, followed by the

feed force in interrupt turning.

3.2 Effect of cutting parameters on tool wear

The tool wear purely depend on the type of tool

grade, geometry, work material composition and hardness

and cutting conditions. It can be concluded that generally,

adhesion, abrasion and diffusion are considered to be the

main tool wear mechanisms in hard turning: however the

individual effect of each mechanism depends on the work

material, cutting conditions and tool geometry (Yallese et

al. 2009). Fig. 4(a) shows the results of tool wear in

continuous and interrupt cutting experiments at different

cutting speed. As can be seen, the cutting speed increases

with increase in tool wear. It indicates that the cutting

speed increases, the tool’s temperature rises, causing it to

lose hardness and accelerate tool wear in both continuous

and interrupt cutting. The main wear mechanism on the

coated carbide tool at both cutting conditions was

abrasion, indicated by the thin scratches parallel to

the cutting direction depicted in SEM image (Fig. 5).

Abrasion may be caused either directly by

friction with hard particles from the workpiece or by

removal of binder caused by workpiece friction with

the tool, and consequently, pullout of hard particles

from the tool. These particles rub against the tool,

causing wear. However, at high speeds the tool

reached higher temperatures, and the diffusion

resistance was insufficient to prevent flank wear in

interrupt cutting conditions. Furthermore, this was

the tool with the most severe rake face wear, which is

often caused by diffusion. These findings can be

observed in SEM images Fig. 6(a) & (b). One more

important point is in interrupted cutting, besides

abrasion, chipping of the edge also occurred at higher

cutting conditions.

Constant f=0.14 mm/rev and d=0.45mm

0

100

200

300

400

500

600

80 110 140 170 200

Cutting Speed (Vc) in m/min

Fo

rce

s (

N)

Ft (Int.) Ft (Cont.)

Fc (Int.) Fc (Cont.)

Fa (Int.) Fa (Cont.)

(a)

Constant Vc=140m/min anf d=0.45mm

0

100

200

300

400

500

600

0.06 0.1 0.14 0.18 0.26

Feed Rate (f) in mm/rev

Fo

rce

s (

N)


Fc (Int.) Fc (Cont.)

Fa (Int.) Fa (Cont.)

(b)


25-4

Figure 3: Effect of cutting forces with different cutting

conditions at constant (a) f= 0.14mm/rev & d= 0.45mm,

(b) Vc= 140m/min & d=0.45mm and (c) f=0.14mm/rev,

Vc=140m/min & cutting time (t) =6 min.

Figure 4: Effect of tool wear with different cutting

conditions at constant (a) f= 0.14mm/rev & d=

0.45mm, (b) Vc= 140m/min & d=0.45mm and (c)

f=0.14mm/rev, Vc=140m/min and cutting time (t) =6

min.

Fig. 4(b) and (c) indicates the characteristic wear

of tool is caused by the fact that, the speed is no

longer the influential factor on wear, but it is more

likely that wear is the consequence of the feed and

depth of cut. From the above discussions, it is clear

that a combination of lower values of cutting speed,

feed rate and depth of cut is favorable in reducing

tool wear. It should be noted that edge chipping was

visible on the cutting edge at higher depth of cut

(0.75mm) in interrupted turning. It indicating that

these tools are not sufficiently tough to withstand

impacts caused by interrupted cutting and that the

machine setup was not suitable for this type of

operation.

Figure 5: SEM images of the cutting edges used in

continuous cutting at Vc=140m/min, f=0.14mm/rev

and d=0.45mm and cutting time (t)=6min.

3.3 Effect of cutting parameters on work piece

surface roughness

Constant Vc=140 m/min and f=0.14mm

0

100

200

300

400

500

600

0.15 0.3 0.45 0.6 0.75

Depth of cut (d) in mm

Fo

rce

s (

N)


Fc (Int.) Fc (Cont.)Fa (Int.) Fa (Cont.)

(c)

0

0.05

0.1

0.15

0.2

0.25

0.15 0.3 0.45 0.6 0.75

Depth of cut (mm)

To

ol

We

ar

(mm

)

Continuous

Interrupt

(c)

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.06 0.1 0.14 0.18 0.26

Feed Rate (mm/rev)

To

ol W

ea

r (m

m)

Continuous

Interrupt

(b)

0

0.05

0.1

0.15

0.2

0.25

80 110 140 170 200

Cutting Speed (m/min)

Tool W

ear (m

m)

Continuous

Interrupt

(a)

Abrasive

marks



25-5

Surface roughness is one of the most indicators of the

surface integrity of the machined parts and besides serves

as the control criterion for tool failure. A proper

combination of cutting parameters is very important

because this determines the surface quality of hardened

machined parts. The effect of cutting conditions on

surface roughness in turning of hardened H13 steel with

continuous and interrupt cutting using multilayer-coated

carbide tool is exhibited in Fig. 7. The surface roughness

value observed with both continuous and interrupt

cuttings was below 1.6 µm.

Figure 7(a) presents the effect of cutting speed on

surface roughness at constant feed rate of 0.14 mm/rev

and depth of 0.45 mm. It is observed from this figure that

lower surface roughness values are obtained at higher

cutting speeds, mainly because of the generation of lower

forces during machining of hardened steel. Higher cutting

speed reduces the surface roughness due to less heat

dissipated to the work material, as it was swept away in

the chip.

Fig 7(b) demonstrates the effect of feed rate on

surface roughness at constant cutting speed of 140 m/min

and depth of cut of 0.45 mm. The surface roughness

increases with increased feed rates, however it remains

almost unaffected at lower feed rate. It shows that the

amount of heat generation increases with increase in feed

rate, because the cutting tool has to remove more volume

of material from the workpiece. The plastic deformation

of the workpiece is proportional to the amount of heat

generation in the workpiece and promotes roughness on

the workpiece surface. Another reason is that the

alterations in roughness values are related mainly to

changes in tool topography as a function of tool wear rate,

which tend to be transferred to the workpiece surface,

especially changes in secondary cutting edge shape. Thus,

the behavior of workpiece roughness and the worn tool

surface may be directly correlated. It indicates that the

continuous machining leads to increased tool nose wear

resulting in ploughing of larger part of the uncut chip

hence; severe material side flow exists on the machined

surface (Fig. 8).

Figure 6: SEM images of the cutting edges used in

interrupted cutting conditions at (a) Vc=140m/min,

f=0.14mm/rev and d=0.45mm and cutting time (t)=6min (b)

Vc=200m/min, f=0.26mm/rev and d=0.75mm and cutting

time (t)=6min.

Fig. 7(c) displays the effect of depth of cut on

surface roughness at constant cutting speed of 200

m/min and feed rate of 0.14 mm and it is observed

that the depth of cut has less significant as compared

to feed rate. Depth of cut parameter has a very less

effect compared to that of the feed rate. This is due to

the increased length of contact between the tool and

the work piece. This improves the conditions of heat

flow from the cutting zone and consequently slows

down the process wear. In interrupt cutting, surface

roughness values can be related to the shape of the

worn tool nose (Fig. 4 (a)). The increase in abrasive

scratches caused a significant change in the coated

carbide tool nose shape (Fig. 4(b)), thus contributing

to the increase in roughness values along the tool’s

life. However, the chipping that occurred at the

coated carbide (TiN/TiCN/Al2O3) tool’s cutting

edges did not contribute to the increase in roughness.

(a) Crack developed

before edge chipping

(b) Edge chipping


25-6

Figure 7: Effect of surface roughness (Ra) with different

cutting conditions at constant (a) f= 0.14mm/rev and d=

0.45mm, (b) Vc= 140m/min and d=0.45mm and (c)

f=0.14mm/rev and Vc=140m/min.

Figure 8 Effect of tool wear on material side flow

during turning of hardened AISI H13 steel with

ceramic tool at Vc= 200 m/min, f= 0.26 mm/rev, d=

0.45.mm and t =6min.

4. Conclusions

The following conclusions can be drawn from

this investigation on turning of continuous and

interrupted surfaces in hardened AISI H13steel using

multilayer coated carbide at different cutting

parameters:

• The thrust force is the dominant force followed

by cutting force and feed force. The cutting force

increases with increased feed rate and depth of

cut, while it decreases with increased cutting

speed. The combination of low feed rate and

low depth of cut with high cutting speed is

desirable for minimizing the cutting forces in

both continuous and interrupt turning.

• The main wear mechanism of the multilayer

coated carbide tool was abrasion at low and

medium cutting speeds. Chipping and breakage

of the cutting edge, which led to a sharp increase

in flank wear, was observed at the higher cutting

speeds.

• In continuous cutting using coated carbide tool

coated with TiN/MT-TiCN/Al2O3, abrasion and

diffusion contributed to the end of tool life.

When this tool machined the work piece with

interruptions, sudden chipping of the cutting

edge occurred in response to mechanical shocks.

• The feed rate was the dominant factor affecting

work piece surface roughness in both continuous

and interrupt cutting.

• The work piece roughness values obtained with

the carbide tool during their lives were

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0.15 0.3 0.45 0.6 0.75

Depth of cut (mm)

Ro

ug

hn

es

s (

Ra

) in

mic

ron

s Continuous

Interrupt

(c)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

80 110 140 170 200

Cutting Speed (m/min)

Ro

ug

hn

es

(R

a)

in (

mic

on

s) Continuous

Interrupt

(a)

0

0.4

0.8

1.2

1.6

2

0.06 0.1 0.14 0.18 0.26

Feed Rate (mm/rev)

Ro

ug

hn

es

s (

Ra

) in

mic

ron

s

Continuous

Interrupt

(b)



25-7

considered high for an operation intended to replace

grinding, because the type of wear these tools

underwent caused considerable variations in the tool

nose shape.

• Based on the results of this work, it can be

concluded, in terms of tool life and surface

roughness, multilayer coated carbide performs better

at lower cutting conditions in both interrupted and

continuous surface.

5. Acknowledgements

The authors are grateful to Kennametal India Ltd.,

Bangalore for providing facilities to conduct experiments

and support throughout this work.

6. References

[1] Ozel T, Karpat, Y and Srivastava, A. (2008) Hard

turning with variable micro geometry PCBN tool.

CIRP Ann: Manuf Techn., Vol. 57, pp. 73–76.

[2] Bartarya, G and Choudhury, S.K. (2012) State of the

art in hard turning, Int J Mach Tool Manu., Vol. 53, pp.

1–14.

[3] Diniz, A.E and Oliveira, A.J., (2008) Hard turning of

interrupted surfaces using CBN tools. J. Mater.

Process. Technol., Vol. 195, pp. 275–281.

[4] Oliveira, A. J., Diniz, A. E., Ursolino, D. J. (2009)

Hard turning in continuous and interrupted cut with

PCBN and whisker-reinforced cutting tools, J. Mater.

Process. Technol., Vol. 209(12–13), pp. 5262–5270.

[5] Vitor Augusto A. de Godoy, Anselmo Eduardo

Diniz.(2009)Turning of interrupted and continuous

hardened steel surfaces using ceramic and CBN

cutting tools, J. Mater. Process. Technol., Vol. 211, pp.

1014–1025.

[6] Dogra, M., Sharma, V., Sachdeva, A and Suri, N.M.

(2012) Tool life and surface integrity issues in

continuous and interrupted finish hard turning with

coated carbide and CBN tools, Proc. IMechE Part B:

J. Engineering Manufacture, Vol. 226, pp. 431-443.

[7] Yallese, M.A., Chaoui, K., Zeghib, N., Boulanouar, L.

(2009) Hard machining of hardened bearing steel

using cubic boron nitride tool, J. Mater. Process.

Technol., Vol. 209, pp. 1092–1104.

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