surface roughness and cutting forces in …jestec.taylors.edu.my/vol 10 issue 7 july 2015/volume...

Journal of Engineering Science and Technology Vol. 10, No. 7 (2015) 911 - 920 © School of Engineering, Taylor’s University

911

SURFACE ROUGHNESS AND CUTTING FORCES IN CRYOGENIC TURNING OF CARBON STEEL

T. C. YAP1,*, SIVARAOS

2, C. S. LIM

1, J. W. LEAU

3

1Faculty of Engineering and Technology, Multimedia University,

Jalan Ayer Keroh Lama, 75450 Melaka, Malaysia 2Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka,

Hang Tuah Jaya, 76100, Durian Tunggal, Melaka, Malaysia 3Microtherm Sdn Bhd, HICOM Industrial Area, 40000 Shah Alam, Selangor, Malaysia

*Corresponding Author: [email protected]

Abstract

The effect of cryogenic liquid nitrogen on surface roughness, cutting forces, and

friction coefficient of the machined surface when machining of carbon steel

S45C in wet, dry and cryogenic condition was studied through experiments.

The experimental results show that machining with liquid nitrogen increases the cutting forces, reduces the friction coefficient, and improves the chips

produced. Beside this, conventional machining with cutting fluid is still the

most suitable method to produce good surface in high speed machining of

carbon steel S45C whereas dry machining produced best surface roughness in

low speed machining. Cryogenic machining is not able to replace conventional

cutting fluid in turning carbon steel.

Keywords: Cryogenic machining, Cutting forces, Friction coefficient, Surface

roughness.

1. Introduction

Manufacturing sector is the second major contributors to Malaysia’s gross

domestic product in the year 2013 [1]. Machining or other material removal

processes are normally applied in manufacturing plant as part of the

manufacturing processes. Conventionally, cutting fluids are used to reduce the

cutting temperature and prolong the life of the machining tools. However, most

cutting fluids are harmful to environment, especially when they were disposed

improperly [2, 3]. Kovoor et al. studied the impact of effluent waste from

machining process on the quality of drain water. They found that effluent waste

increased the chemical oxygen demand, ammoniacal nitrogen, and total suspended

912 T. C. Yap et al.

Journal of Engineering Science and Technology July 2015, Vol. 10(7)

solids in the drain water [3]. Beside this, conventional cutting fluids also

produces health problems [4-6]. Some of the additives added on cutting fluids

to provide the lubricating effects might cause a carcinogenic potential [4].

In addition, some additives such as barite is added as weighting agent in

drilling fluids can discharge heavy metal to the environment during drilling

process [7].

As such, new machining techniques/concepts such as dry machining and

cryogenic machining were proposed to replace conventional machining using

conventional cutting fluids [8]. Two types of cryogen are commonly used in

cryogenic machining. They are liquid carbon dioxide and liquid nitrogen. The

boiling points for both gases are –78.5oC and –196

oC. Both gases are abundant

and can be recycled; they can be compressed to liquid form, cool the cutting tools

and evaporate and become gas again.

Cryogenic machining was first explored by Bartle who used liquid carbon

dioxide as the coolant at 1953 [9]. Most of the recent study works on cryogenic

machining were focused on cutting forces, friction coefficient, tool wear, and

surface roughness. Improvements in cutting tool life or surface roughness under

cryogenic conditions have been reported by many researchers such as Biček et al.

[10], Hong et al. [11, 12], Wang et al. [8, 13], Dhar et al. [14] and Yap et al. [15].

In cryogenic machining, surface finish was improved due to reduction in tool

wear [8]. Beside this, Hong et al. [16] reported that cryogenic machining tends to

increase the cutting force because the titanium alloys become harder and stronger

at low temperature.

In this study, the cutting forces, friction coefficients and surface roughness

while machining carbon steel S45C were investigated under three conditions (dry

cutting, with cutting fluid and with cryogenic- liquid nitrogen cooling). Surface

roughness, cutting forces, and friction coefficient have been examined for

comparing the cryogenic machining to wet and dry turning.

2. Experimental Details

2.1. Work piece materials

The work materials used in this experiment was a medium carbon steel S45C. The

chemical composition and properties of carbon steel S45C are shown in Tables 1

and 2. The diameter and length of the carbon steel work piece are 36 mm and 500

mm respectively.

Nomenclatures

Ra Average roughness

Rmax Maximum roughness depth

Rq Root mean square roughness

Abbreviations

TiN Titanium nitride

CVD Chemical vapor deposition

Surface Roughness and Cutting Forces in Cryogenic Turning of . . . . 913


Table 1. Chemical Composition of Carbon Steel [17].

Grade C

(%)

Si

(%)

Mn

(%)

P(%)

max.

S(%)

max.

Cr(%)

max.

Ni(%)

max.

Cu(%)

max.

S45C 0.42-

0.50

0.17-

0.37

0.50-

0.80 0.035 0.035 0.25 0.25 0.25

Table 2. Selected Properties of Carbon Steel S45C [17].

Tensile

strength,

(MPa)

Yield

strength,

(MPa)

Elongation

ratio, (%)

Reduction of

area, (%)

Degree of

hardness

≥600 ≥355 ≥16 ≥40 ≤229HB

2.2. Cutting tool

The cutting tool used in this experiment was TiN CVD coated carbide Mitsubishi

TNMG 160408R -ES US735. Tool holder MTJNR-2020K-16 was used in this

experiment. A new cutting edge was used for each condition.

2.3. Cutting conditions

The experiments were conducted at constant depth of cut of 0.3 mm and feed rate

of 0.121 mm/rev. Three different cutting speeds were used; they are 175.93,

201.06, and 226.19 m/min. Three environments (Cryogenic liquid nitrogen, dry

and with cutting fluid) were studied. The cutting conditions are shown in Table 3.

Table 3. Cutting Conditions.

Cutting speed (m/min) Depth of cut (mm) Feed rate (mm/rev)

175.93, 201.06, 226.19 0.3 0.121

2.4. Experimental setup and procedure

All machining tests were carried out on a SunMax Machine LA-430 conventional

lathe. The cutting force components (feed force, radial force, cutting force) were

observed by a 3-component dynamometer (Kistler, Type 9265 B). The surface

roughness of the machined surfaces was measured using a surface roughness

tester (Mahr Perthometer S2). The standard cut-off length of 0.08 mm was used

for surface roughness measurement. The turning tests were conducted in three

environments. For cryogenic condition, liquid nitrogen jet was injected to the

interface between the carbon steel and cutting insert by internal pressure of the

liquid nitrogen tank. The internal pressure of the liquid nitrogen tank is 0.0345

MPa. The set-up of cryogenic machining is shown in Fig. 1. For machining with

cutting fluid, water-based emulsion (AEROIL Kool cut C-300, 5% oil and 95%

water) was selected.



Fig. 1. Set-up of Cryogenic Machining.

3. Results and Discussion

3.1. Surface roughness

The surface roughness was measured and presented in average roughness (Ra),

root mean square roughness (Rq), and maximum roughness depth (Rmax). Figure 2

shows the surface roughness of carbon steel work piece under different cutting

conditions. In general, dry machining is able to generate good surface finished at

lowest cutting speed (175.93 m/min). Turning at lowest cutting speed (175.93

m/min) generated good surface roughness, and the difference due to environment

(dry, cutting fluid, cryogenic) is not significant. However, at highest cutting speed

studied, 226.19 m/min, conventional cutting fluid outperformed dry machining

and cryogenic machining (in terms of Ra, Rq, and also Rmax).

Machining without cutting fluid or with liquid nitrogen produced higher

roughness depth, Fig. 2(c). Beside this, Figs. 2(a)-(c) indicates that cutting with

conventional cutting fluid provided a stable surface roughness within the range of

speed studied (175.93 – 226.19 m/min). Cryogenic machining with low pressure

is not able to replace conventional cutting fluid if good surface roughness is

required. Current results are different from results reported by previous studies

[18, 19]. This might due to different tool work materials selected.

(a)



(b)

(c)

Fig. 2. Surface Roughness of Carbon Steel

under Three Different Cutting Environments.

3.2. Cutting forces

In this study the first 10 s of machining were used for measurement of cutting

forces. In general, higher cutting forces (main cutting force, feed force and

radial force) were obtained under application of cryogenic liquid nitrogen. This

results is similar to Hong et al. [16] where this phenomenon can be attributed to

hardening of carbon steel by cryogenic liquid nitrogen. The details of feed

force, radial force and main cutting force at two different cutting speeds are

presented in Figs. 3 and 4. In cutting speed of 201.06 m/min, conventional

cutting oil showed the lowest cutting forces when compare to dry machining

and cryogenic machining. However, when the cutting speed increased to 226.19

m/min, dry machining produced the lowest cutting forces. The reduction of

cutting forces with cutting speed in dry machining can be due to the hot

softening at the tool work interface.



Fig. 3. Measured Cutting Forces at 201.06 m/min.

Fig. 4. Measured Cutting Forces at 226.19 m/min.

3.3. Friction coefficients

The feed force, radial force and main cutting force were converted into

component of force along the tool face (tangential force) and component of force

normal to the tool face (normal force) based on equations discussed in [15, 20].

The friction coefficients while machining carbon steel in dry, wet, and cryogenic

condition were then calculated by dividing the tangential force by the normal

force. Figure 5 shows the friction coefficient increases as the cutting speed

increases and friction coefficient in cryogenic machining is lower than friction

coefficient in dry and wet machining of carbon steel. In dry machining, dry

sliding motion of tool-work generates heat. High interface temperature soften the

surface asperity and this further causes asperity easier to deform [15]. When

asperities deform, it enlarges the actual contact area of the tribo pairs and then

increases the friction force. In addition, Fig. 5 also shows that cryogenic liquid

nitrogen reduces the friction coefficient between cutting tool and carbon steel for

about 32% for cutting speed of 201.06 m/min and 24% for cutting speed of



226.19 m/min. This is because cryogenic liquid nitrogen reduces the interface

temperature and then reduces the actual contact area and then the adhesive

friction force.

Fig. 5. Friction Coefficient while Machining Carbon Steel.

3.4. Macro morphology of chips produced

The macro morphology images of the cutting chips obtained by dry and cryogenic

machining are shown in Figs. 6-9. At cutting speed of 175.93 m/min, cutting

chips collected from dry machining were continuous (Fig. 6) while chips

collected from cryogenic machining were broken into smaller pieces, (Fig. 7).

When the cutting speed increased from 175.93 m/min to 201.06 m/min, the

cutting chips obtained from dry machining were still in continuous and snarled

shape (Fig. 8) while cryogenics turning produced more short cutting chips

(Fig. 9). Generally, long/snarled chips collected from dry machining are

unfavourable in machining [20]. In contrast, smaller and shorter chips are

favourable in machining; smaller chips allowed liquid nitrogen to penetrate into

the elastic zone of the tool-work interface, similar to finding of Nandy et al. [21].

In term of chips produced, cryogenic machining is better than dry machining.

Fig. 6. Cutting Chips Obtained from Dry Turning, at 175.93 m/min.



Fig. 7. Cutting Chips Obtained from Cryogenic Turning, at 175.93 m/min.

Fig. 8. Cutting Chips Obtained from Dry Turning, at 201.06 m/min.

Fig. 9. Cutting Chips Obtained from Cryogenic Turning, at 201.06 m/min.



4. Conclusions

An experiment was conducted to study dry, wet and cryogenic turning of carbon

steel S45C. The experimental result shows that cryogenic liquid nitrogen jet

reduces friction coefficient in turning the carbon steel and also improves the chips

produced. However, turning with liquid nitrogen deteriorates the surface

roughness of the machined surface. Dry machining is able to produce best surface

roughness in low speed machining but it also produces unfavourable long chip

and high friction coefficient. Therefore, the conventional wet machining is still

the best method to produce good machined surface of carbon steel at higher

machining speed.

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