Post on 28-Feb-2023
Effects of Coolants on Improving Machining Parameters while Mach-inability Titanium Alloy (Ti-6Al-4V): A Review
Moaz H. Ali1, a, R. Balasubramanian1, Bashir Mohamed1 and Basim A. Khidhir2, b
1COE, University Tenaga Nasional, Kuala Lumpur, Malaysia
2FK, University Industry Selangor, Bestari Jaya, Malaysia
amuezhm@hotmail.com, bBak-time@hotmail.com
Keywords: component; Coolants, Improving machining, Titanium alloy.
Abstract. In this review, present day, the best versatile material Titanium alloy (Ti-6Al-4V) plays
the most vital role in the manufacturing of aero engines as a base material. It has been observed that
machining this type of alloys is the complicated tasks with optimum machining results. This
research investigates the consequences of machining parameters by making use three types of
technique: firstly, nitrogen gas technique; secondly, high pressure coolant (HPC); thirdly, cryogenic
cooling technique as the coolant’s techniques compared to the normal coolant. Utilizing liquid
nitrogen and gas nitrogen as a coolant will decrease friction, heat at the cutting zone, surface
roughness, the amount of power consumed in a metal cutting process in addition significantly
increase the tool life, dimensional accuracy and so improve the productivity.
Introduction
Machining is the most widespread metal shaping process in mechanical manufacturing industry.
All over the world, machining operations such as turning, milling, drilling, grinding and shaping to
consume a huge amount of money and time while machining of titanium alloys (Ti–6Al–4V).
Because it is having a high strength to weight rate, high toughness, high rigidity, low elasticity
models and high chemical reactivity at elevated temperatures.
Sharma [1] studied researchers have focused their attention on improvements in conventional
turning, so that tool life can be enhanced or tool failure can be avoided. By tool failure is meant
damage so large that the tool has no ability to remove material from a work piece. This tool damage
cannot be avoided, but we can find out ways to minimize it by analyzing its causes [2]. Stress and
the temperature at the tool surface influence the damage at the cutting tool [3]. Tool damage is very
sensitive to changes in the cutting conditions (cutting speed, feed rate and depth of cut) and
presence of cutting fluid. While tool damage cannot be avoided, it can often be reduced if its failure
mechanism and the factors controlling it are properly understood [4]. Tool damage is classified as:
adhesion, thermal damage (plastic deformation, thermal diffusion and chemical reaction),
mechanical damage (abrasion, chipping, fracture and fatigue). Out of these damages, thermal
damage increases drastically with increasing temperature. Adhesion wear is also a temperature
dependent phenomenon. The temperatures at which thermal damage and adhesion damage occur to
vary with a tool and work material combination. Thus heat generation in turning leads to a
reduction in tool life and as a result reduced surface finish [2]. The diffusion type thermal damage
occurs at high cutting temperature if cutting tool and work material elements diffuse mutually into
each other’s structure. The plastic deformation type of thermal damage is observed when a cutting
tool at high cutting temperature cannot withstand the compressive stress on its cutting edge [5, 6].
In metal turning operation, material is subjected to extremely high strain, and the elastic
deformation forms a very small proportion of the total deformation; therefore, it may be assumed
that all the energy is converted into heat [7]. Ying-lin [8] found that for very high temperature in the
machining zone can damage the finished surface of titanium alloys easily. Another impairment
caused by the high temperature is the melting of titanium alloy chips and adhesion to the tool and
on the machined surface.
Applied Mechanics and Materials Vols. 110-116 (2012) pp 1657-1666Online available since 2011/Oct/24 at www.scientific.net© (2012) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMM.110-116.1657
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 115.133.110.80-29/11/11,05:25:37)
Where as Palanisamy [9] explain that the cutting fluids are used to remove heat generated at the
work-piece and tool interface during the machining process. These fluids act as both a coolant to
reduce tool temperature and also as a lubricant. Poor coolant delivery and low pressure can lead to a
number of adverse effects while machining titanium and its alloys. These effects include premature
tool failure due to abrasion and thermal shock resulting in severe chipping of the tool [10].
However, cutting fluids, which are supplied at high pressure (above 70 bars) and accurately directed
at the cutting zone can counter all these problems. The coolant pressure of machining centres has
progressively risen from initial pressures of around 4 bars too much higher pressures in the range of
70 bars and above [11]. A number of investigations [12–18] have shown that applying high-
pressure coolant (HPC) technology not only increases production efficiency, by increasing the
cutting speed but also improves chip removal, resulting in increased tool life while machining
titanium alloys [19]. It has also been shown that HPC results in better surface integrity and lower
compressive residual stress, which improves the properties of the machined work-piece [15].
Sharma [1] the coolant effect reduces the temperature in cutting zone and the lubrication action
decreases cutting forces. Thus the friction coefficient between the tool and chip becomes lower in
comparison to dry machining [20]. Minimizing the friction between the cutting edge of the tool and
work piece, corrosion control, chip ejection and washing are the functions of the cutting fluid in
machining [21].
Researchers have focused their attention on issues related to environmental problems, fluid
disposal, toxicity, filterability, misting, staining, surface cleanly-ness and indirect cost involved
while using coolant/lubricants and have tried to find out ways to improve the current techniques of
cooling during turning in order to reduce the temperature at the cutting zone and to
eliminate/minimize these problems. The lubricating action is more important to low cutting speed,
whereas the cooling effect is more important for higher cutting speed due to large increase in heat
generated by the chip removal process [5].
Then Yildiz [22] said the purpose of the application of the cutting fluids in metal cutting was
stated as reducing cutting temperature by cooling and friction between the tool, chip and work-piece
by lubrication [23]. Chip’s formation and curl, which affects the size of the crater wear and the
strength of the cutting tool edge, is also affected when coolant is carried out during machining.
Generally, a reduction in temperature results in a decrease in wear rate and an increase in tool life.
However, a reduction in the temperature of the work-piece can increase its shear stress, so that the
cutting force may be increased, and this can lead to a decrease in tool life [24].
Ali Khan [25] observed by [26] when machining Titanium alloys (Ti–6Al–4V) with high-
pressure coolant supplies and the recorded surface roughness values were found to be below the
tool rejection criteria.
[27] Introduced a new technique of application of cryogenic coolant during machining of Ti–
6Al–4V. They designed a special micro-nozzle for application of liquid nitrogen. Liquid nitrogen
was introduced through the gap between the chip breaker and the rake surface. The new technique
provides an effective way of cooling the tool using very low flow rate of nitrogen. Tool life was
reported to enhance five times to that using emulsion cooling. An innovative and economical
dispensing method of applying liquid nitrogen and nitrogen gas were introduced by [28] In this
study, liquid nitrogen and nitrogen gas cooling application methods and their effects on production
in machining operations have been reviewed in detail. Most of the liquid nitrogen and nitrogen gas
cooling applications in machining studies have been examined in turning operations even though
there were its applications in other machining operations such as drilling, milling and grinding.
1658 Mechanical and Aerospace Engineering
Fig.1- Techniques for reduction in heat generation during turning [1].
Nitrogen Gas Technique
For instance, Ying-lin [8] able to obtain that for when there was no nitrogen gas, the shape of
chips was continuous and undue. It was obvious that the chip was composed of several serrated
small chips. This characteristic was more obvious when observing the chip from its back side
“Fig.2”. The reason why this configuration was formed during high speed machining of Ti-6Al-4V
can be explained as follows. Chips that absorbed the majority of machining heat and could not be
removed away immediately from the machining zone would be softened and burnt by the high
temperature when the edge cut into the material. The temperature softening effect in the primary
shear zone was especially stronger than the other part and resulted in the plastic instability, leading
to catastrophic shear failure along the shear surface. So, after every constant length along the
cutting edge trajectory, a serrated chip would be formed. A longer chip composed of several
serrated parts was generated when an edge cut out the work-piece material. The fact that the chip
length was almost the same as the length of cutting layer showed that the chip did not break from an
edge cutting-into to cutting-out work-piece material. The dark blue color of the chip showed it was
burnt in the machining process. The continuous and burnt chips adhered to cutting edge and
machined surface would result in the poor integrity of machined surface, and increased cutting force
at the same time. This conclusion agreed well with the analysis of cutting force. “Fig.2 (b)” shows
the shape of chips obtained when nitrogen gas arrived at the machining zone. It was every obvious
that the color, length and shape of the chips were changed. The length was about 1/3−1/4 that with
nitrogen gas; the color was even gray; and the shape was not serrated.
Applied Mechanics and Materials Vols. 110-116 1659
Fig. 2- Configuration of chips under high speed machining of Ti-6Al-4V: (a) Without nitrogen gas;
(b) With nitrogen gas [8].
All these differences showed that, in an edge cutting process, the cutting layer was broke into
3−4 parts, and the chips did not burn but was removed away from machining zone because the
existence and high speed flowing of nitrogen gas. So, the chips did not adhere to the cutting tool,
and the abrasion of tool could be improved greatly. The surface integrity could be polished
correspondingly. The majority of machining heat was absorbed by chips. With nitrogen gas, not
only chip burning was prevented but also machining heat was removed by the flowing nitrogen gas.
So, when the surface was just finished, the temperature increment was very low (nearly the room
temperature), which could prevent the increase of hardness on the top layer of the finished surface.
In general, elements that affect chip shape include work-piece material properties, machining
parameters and tool geometry [29]. But based on above analysis, nitrogen gas is another factor that
affects chip shape of titanium alloys.
Prussure Technique
Besides that, Palanisamy [9] could get the different types of chips were generated during the
turning operation, and these chips have been classified according to ISO 3685 for tool life testing
[30]. When machining with standard coolant pressure (6 bar), short lustrous tubular chips (with an
average length of 30mm as shown in Fig. 3a) were generated when the insert was new and long
tubular chips (average length of 210mm) dull bluish in colour were produced towards the end of the
tool’s life. The application of HPC at 90 bars has resulted in very loose arc-shaped chips (with an
average length of 5mm as shown in Fig. 3b) at the beginning and then short washer-type helical
chips (average length of 40mm) after 10 minimums of cutting.
Serrated chip
Adhered burnt
chips
1660 Mechanical and Aerospace Engineering
Fig. 3- Chips obtained after1min cutting time (first cut) from the application of (a) standard
pressure coolant and (b) HPC [9].
Cryogenic Coolant Technique
However, Ali Khan [25] found the results show that nitrogen liquid and nitrogen gas cooling
enhances tool life. Tool life with a cutting speed of 100m/min (depth of cut and feed rate are 0.5mm
and 0.1mm/rev, respectively) using conventional coolant is 13.45 min, where for the same cutting
conditions the life is 57.45 min in nitrogen liquid and nitrogen gas cooling. It shows that the
application of nitrogen liquid and nitrogen gas coolant has increased the tool life by 4.27 times.
Again, at a higher cutting speed of 250m/min tool lives with conventional coolant and nitrogen
liquid and nitrogen gas cooling are 22.5 and 4.62 min, respectively with the same feed rate and
depth of cut. This shows an increase of tool life by 4.87 times. It can be observed that tool life at a
higher depth of cut is substantially low compared to that at a low depth of cut. For a cutting speed
of 200 m/min, tool lives for nitrogen liquid and nitrogen gas cooling and conventional cooling are
20.7 and 4.2 min at a depth of cut of 1mm, whereas the same are 25.92 and 5.4 min at a depth of cut
of 0.5mm.
That, he [25] found from his experimental as shown in “Fig.5” the SEM image of the flank wear
after a machining time of 2 min with conventional coolant at a cutting speed, feed and depth of cut
of 250 m/min, 0.5mm/rev and 1mm, respectively. The image shows extensive wear of the flank as
well as the face and this is due to heavy cutting conditions. The flank surface suffered from attrition
and abrasion wear. A crater wear is seen on the tool rake face that is caused by adhesion and
diffusion due to high temperature. But “Fig.6” shows that a little wear took place on the flank and
face of the tool while using cryogenic coolant after a machining time of 2min under the same
cutting conditions. The cutting edge suffers minor micro-chipping for high cutting speed. “Fig.7”
shows the flank wear of the tool after a machining time of 3min with conventional coolant while
“Fig.8” shows the same for cryogenic coolant under the same machining conditions (v = 200
m/min, f = 0.1mm/rev and t = 0.5 mm). “Fig.8” shows a little flank wear in cryogenic cooling. Less
abrasion and attrition wear is observed at the flank surface as compared to “Fig.6” (v = 250 m/min)
because of lower cutting speed (v = 200 m/min). “Fig.7” shows an extensive flank wear during
machining with conventional coolant. Flank wear is caused by abrasion. Micro-cracks are also
observed on the cutting edge. “Fig.9” illustrates the flank wear of the tool after 20 min of machining
Short washer-type
helical chips
Short
lustrous
tubular
chips
Applied Mechanics and Materials Vols. 110-116 1661
with conventional coolant while “Fig.10” shows the same for cryogenic cooling under the same
cutting conditions (v = 100 m/min, f = 0.05mm/rev and t = 0.5 mm). “Fig.10” shows a very little
flank wear after a machining time of 20min with cryogenic coolant.
Fig. 4(a)-Tool life at different cutting speeds (f = 0.1mm/rev) [25].
Fig. 4(b)-Percentage increase in tool life at different cutting speeds [25].
Fig. 5- Flank wear after 2min of machining with conventional coolant (v = 250 m/min, f =
0.1mm/rev and t = 1 mm) [25].
Fig. 6- Flank wear after 2min of machining with cryogenic coolant (v = 250 m/min, f =
0.1mm/rev and t = 1 mm) [25].
1662 Mechanical and Aerospace Engineering
Fig. 7- Flank wear after 3min of machining with conventional coolant (v = 200 m/min, f =
0.1mm/rev and t = 0.5 mm) [25].
Fig. 8- Flank wear after 3min of machining with cryogenic coolant (v = 200 m/min, f =
0.1mm/rev and t = 0.5 mm) [25]
.
Fig. 9- Flank wear after 20min of machining with conventional coolant (v= 100 m/min, f =
0.05mm/rev and t = 0.5 mm) [25].
Fig.10- Flank wear after 20min of machining with cryogenic coolant (v = 100 m/min, f =
0.05mm/rev and t = 0.5 mm) [25].
Discussion
This study shows us to confirm the presence of a basic and important role in more operations
machining of titanium and of various kinds of cooling, which coincide with the operations of the
mechanical operation of the work-piece and that effect on many factors, including the forces of
cutting, surface roughness, temperature distribution in a cutting process and deformation as well.
To prove the validity of verification of all, we have adopted in this research the different results
of the researchers, but those results in the same area and under the working conditions of different
methods of cooling are multiple. We found that Ali Khan could get the results show that cryogenic
cooling reinforced the age of the tool. Cryogenic cooling has increased the tool life by 4.27 times
more than normal cooling.
As it is well known that the temperature rise when tool and work-piece are interfaced, so could
do this case to lead the welding process, but also when the cooling could reduce the intense heat and
improve the specifications required of it and end the phenomenon of welding between the chip and
the work-piece.
Applied Mechanics and Materials Vols. 110-116 1663
However, Palanisamy adopted of pressure cooling, but the different pressure cooling between
lower pressure of 6 bars to the extreme pressure 90 bars. He found that the form of chip will be
spiral and is connected with a long distance according to the “fig.3” Furthermore, a significant rise
in temperature between the work-piece and the tool, however, found that the cooling pressure 90
bars may be produced by Reich intermittent short with a significant decrease in temperature and an
increase in the smoothness of the surface and improve the properties of the work-pieces.
It is also noticeable in the work of researcher Yildiz, who put himself to special conditions for
logging operations of the cutting forces, temperature, specific use of the work-pieces and the tool.
He found that there is a big difference and marked clearly on each of these properties before cooling
and after. The results were the best after cooling.
We can get a result in this a review paper after all this investigation depth of the working
conditions from different researchers. For instance, the cutting forces, and cooling are also different
than the cooling associated with operations that have taken advantage from the right way and using
the distinct under what conditions they will, we can get a smooth surface and a decrease in
temperature resulting in longer life of the tool for three times. These are cases save for us time and
cost and improve product quality as well.
Conclusion
The aim of this study is to analyze and point out the effect types of cooling on cutting performance
in material removal operations and its application methods. Other conventional coolants, heat
generation and temperature distribution in a cutting process have been also discussed. When
compared with dry cutting and conventional cooling, the most considerable characteristics of the
cryogenic cooling, nitrogen gas, and high pressure coolant (HPC) application in machining
operations could be determined as enabling substantial improvement in tool life and surface finish-
dimensional accuracy through reduction in tool wear through control of machining temperature
desirably at the cutting zone. This type of cooling has been executed in cutting operations in
different ways by using liquid nitrogen and nitrogen gas for pre-cooling the work piece, cooling the
chip, cooling the cutting tool and cutting zone. In these studies, comparisons and discussion have
been made between conventional cutting strategies and liquid nitrogen and nitrogen gas cooling
methods and found the importance of cooling during machining titanium alloys. Consequently, the
conclusions described above could change relating to tooling work piece pairs and cutting
conditions.
Acknowledgment
The authors would like to acknowledge the support our University Tenaga Nasional “UNITEN”.
References
[1] S.Sharma a, ManuDogra b, N.M.Suri c. Cooling techniques for improved productivity in
turning[J]. International Journal of Machine Tools & Manufacture, 49 (2009) 435–453.
[2] Geoffrey Boothroyd, Winston A. Knight, Fundamentals of Machining and Machine Tools,
third ed, CRC Taylor & Francis, 2005.
[3] H. Zhao, G.C. Barber, Q. Zou, A study of flank wear in orthogonal cutting with internal
cooling, Wear 253 (2002) 957–962.K. Elissa, “Title of paper if known,” unpublished.
[4] T.H.C. Childs, K. Maekawa, T. Obikawa, Y. Yamane, Metal Machining Theory and
Applications, Butterworth Heinemann, Oxford, 2001.
[5] E.M. Trent, P.K. Wright, Metal Cutting, fourth ed, Butterworth Heinemann, Oxford, 2000.
1664 Mechanical and Aerospace Engineering
A. Rahmath Zareena, M. Rahman, Y.S. Wong, Binderless CBN tools, a breakthrough for
machining titanium alloys, Journal of Manufacturing Science and Engineering 127 (2005) 277–
279.
[6] G. Barrow, A review of experimental and theoretical techniques for assessing cutting
temperatures, Annals of the CIRP 22 (2) (1973) 203–211.
[7] Ying-lin1, 2, Hui-yue1, LIU Gang1, ZHANG Ming1. Use of nitrogen gas in high-speed milling
of Ti-6Al-4V [J].Trans. Nonferrous Met. Soc. China 19(2009) 530-534.
[8] Palanisamy , D.McDonald, S.Dargusch. Effects of coolant pressure on chip formation while
turning Ti6Al4V alloy [J]. International Journal of Machine Tools & Manufacture 49 (2009)
739–743.
[9] E.O.Ezugwu,Z.M.Wang,Titaniumalloysandtheirmachinability—a review, Journal
ofMaterialProcessingTechnology68(1997)262–274.
[10]E.O. Ezugwu, Key improvements in the machining of difficult-to-cut aero- space superalloys,
International Journal of Machine Tools and Manufacture 45 (12–13) (2005) 1353–1367.
[11]E.O. Ezugwu, J. Bonney, R.B. Da Silva, O. Cakir, Surface integrity of finished turned Ti–6Al–
4V alloy with PCD tools using conventional and high pressure coolant supplies, International
Journal of Machine Tools and Manufacture 47 (6) (2007) 884–891.
[12]A.R. Machado, J. Wallbank, E.O. Ezugwu, I.R. Pashby, Tool performance and chip control
when machining Ti–6Al–4V and Inconel 901 using high pressure coolant supply, Machining
Science and Technology 2 (1998) 1–12.
[13]K. Sorby, K. Tonnessen, High-pressure cooling of face-grooving operations in Ti6Al4V,
Proceedings of Mechanical Engineering Part B: Journal of Engineer- ing Manufacturing 220
(2006) 1621–1627.
[14]M. Vosough, I. Svenningsson. Influence of high pressure water-jet assisted machining on
surface residual stresses on the work-piece of Ti–6Al–4V Alloy, in: Proceeding of SPIE, SPIE,
Singapore, Bellingham, 2004.
[15]A.R. Zareena, M. Rahman, Y.S.Wong, High speed machining of aerospace alloy TI–6Al–4V,
in: Proceedings of the 33rd International SAMPE Technical Conference, Seattle, United States,
2001.
[16]A.E. Diniz, R. Micaroni, Influence of the direction and flow rate of the cutting fluid on tool life
in turning process of AISI 1045 steel, International Journal of Machine Tools and Manufacture
47 (2) (2007) 247–254.
[17]E.O. Ezugwu, R.B. Da Silva, J. Bonney, A.R. Machado, Evaluation of the performance of CBN
tools when turning Ti–6Al–4V alloy with high pressure coolant supplies, International Journal
of Machine Tools and Manufacture 45 (9) (2005) 1009–1014.
[18]L.N.Lo’pez de Lacalle,etal.,Using high pressure coolant in the drilling and turning of low
machinability alloys, International Journal of Advanced Manufacturing
Technology16(2000)85–91.
[19]M.A.EI. Baradie, Cutting fluids, Part I. Characterisation, Journal of Materials Processing
Technology 56 (1996) 787–797.
[20]T.C. Jen, G. Gutierrez, S. Eapen, G. Barber, H. Zhao, P.S. Szuba, J. Lambataille, J.
Manjunathaiah, Investigation of heat pipe cooling in drilling application, Part 1: preliminary
numerical analysis and verification, International Journal of Machine Tools & Manufacture 43
(2002) 634–652.
Applied Mechanics and Materials Vols. 110-116 1665
[21]YILDIZ Y, NALBANT M. A review of cryogenic cooling in machining processes [J].
International Journal of Machine Tools andManufacture 2008, 48(9): 947−964.
[22]D.P. Adler, W.S. Hii, D.J. Michalek, J.W. Sutherland, Examining the role of cutting fluids in
machining and efforts to address associated environmental/health concerns, Machining Science
and Technology 10 (2006) 23–58.
[23]W.A. Carter, Metal Machining, Part VI, Cutting Fluids, Machinery Lloyd, Overseas Edition,
1956.
[24]Ali Khan, I. Ahmed. Improving tool life using cryogenic cooling [J]. Journal of materials
processing technology, 196 (2008) 149–154.
[25]Ezugwu, E.O., Bonney, J., Rosemar, B., Da Silva, B., C¸ akir, O., 2007.Surface integrity of
finished turned Ti–6Al–4V alloy with PCD tools using conventional and high pressure coolant
supplies.Int. J. Mach. Tool Manuf. 47 (6), 884–891.
[26]Hong, S.Y., Markus, I., Jeong, W.C., 2001. New cooling approach and tool life improvement in
cryogenic machining of titanium alloy Ti–6Al–4V. Int. J. Mach. Tool Manuf. 41 (15), 2245–
2260.
[27]Hong, S.Y., Ding, Y., 2001. Cooling approaches and cutting temperatures in cryogenic
machining of Ti–6Al–4V. Int. J.Mach. Tool Manuf. 41 (10), 1417–1437.
[28]LI Liang. Study on the mechanism and process of high speed milling of titanium alloys [D].
Nanjing: Nanjing University of Aeronautics and Astronautics, 2004. (in Chinese).
[29]ISO, Tool-Life Testing with Single-Point Turning Tools-ISO 3685, International Organization
for Standardization, 1993.
1666 Mechanical and Aerospace Engineering
Mechanical and Aerospace Engineering 10.4028/www.scientific.net/AMM.110-116
Effects of Coolants on Improving Machining Parameters while Mach-InabilityTitanium Alloy (Ti-6Al-4V): A Review
10.4028/www.scientific.net/AMM.110-116.1657