Uploaded by Norlaila Ahmad

A Critical Review on Minimum Quantity Lubrication

A Critical Review on Minimum Quantity Lubrication (MQL) with The
Addition of Nanoparticles towards Green Machining
Norlaila Binti Ahmad1 and Willey Yun Hsien Liew 1
Faculty of Engineering, Universiti Malaysia Sabah,Jalan UMS,Kota Kinabalu,Sabah
In this study, a review on the most possessing good technique which is minimum quantity
lubrication (MQL) has been focusing towards achieving green machining. A technique that is
working in reducing the consumption of lubricant which are almost 90% where it able to prevent
undesirable effect to human health and environment. This review will emphasize on the analysing
of MQL technique with different techniques such as dry machining, gaseous lubrication, solid
lubrication, and mist lubrication. The paper will also discuss in depth the effect of MQL on
stainless steel, the application of MQL technique without nanoparticles and the effect of all the
types of nanoparticles on MQL. According to many articles published, MQL has been sought the
most highly recommended technique because it has reduced the wear, improved the surface
roughness and enhanced the tool life. Hence, the performance of MQL has been increased and
upgraded when the addition of nanoparticles into lubricant which that can reduce the tool wear,
cutting zone temperature on cutting tools and produces surface finish of workpiece which much
better than other techniques machining.
1. Introduction
2. Towards Green Lubrication Machining
2.1 Dry Machining
2.2 Gaseous Lubrication
2.3 Solid Lubrication
2.4 Mist Lubrication
2.5 Minimum Quantity Lubrication
3. MQL technique on stainless steel
4. The Application of MQL technique without Nanoparticles
5. The Effect of All the types of Nanoparticles on MQL
6. XRD Analysis
7. Conclusion
In the manufacturing industries, metal cutting is basically the process to remove the metal
chip from the workpiece by several industries such as milling, turning and drilling while milling
machine is known as fundamental machining operation (Kuwahara et al., 1994).The most highly
used in manufacturing industries is end milling that applied in automotive and aerospace sectors
because the performance itself can reduce the corrosion resistance and improves fatigue
strength.(Joshua et al., 2015) has studied the cutter generally rotates on an axis vertical in end
milling while the quality of surface roughness depends on the accuracy of parameter that specified
by designer.
Recenctly ,the application of Stainlees steel as material used worldwide in machining
industries due to the excellent properties itself where it has high durability and sustainability
compared to other materials (Varghese et al., 2018).(Baddoo, 2008) has mentioned that the rate
growth of stainless steel used in consrtruction has been even faster.. Philip et al. (2014) has been
studied that stainless steel is highly requested due to the properties such as low thermal expansion,
excellent in corrosion resistance, good toughness, highly energy absorption and highly strength.
Based on the properties analysed, it can be found that the properties of stainless steel play
an important role in deciding the process of milling machine. In this milling process,artensitic steel
type of stainless steel will be employed due to an excellent of its properties achieved the
requirements of market. The structure of austenitic stainless steel is least corrosion-resistant where
able withstand to the normal corrosive attack and also boling state(Demeri, 2020).However,these
stainless steel is extremely hard to cut compared to others material due to work hardening and this
lead to formation of (BUE) high built up on the tool flank and low heat conductivity(Kaladhar et
al., 2012).
This is caused on high heat generated due to the plastic deformation occured on the shear
zone and also the friction existed in between the cutting tool and workpiece that will resulitng on
tool wear and poor suface finish.In order to reduce the detrimental effect by the heat and
friction,the coolant techniques are suggested.However, (Tosun & Huseyinoglu, 2010) have been
studied that the coolant-based are costly.Therefore,minimum quantity lubrication(MQL) is highly
recommended to be used as it can be a massive beneficial in stainless steel
machining.Then,(Joshua et al., 2015) has been mentioned the applicatio of MQL can reduce the
thermal distortion and improve the tool life and results in excellent surface finish.
According to (Hamdan et al., 2012) studied that cutting fluid is essential method that
provides lubrication and cooling in order to achieve the high product quality during
machining.Lubrication is defined as process using of lubricant where act as a smoothen catalyst
when added on the surface of the cutting tool that met up with the surface of stainless steel during
machining process.The basic role of lubrication is basically for reducing the friction and prevent
the formation of wear during the cutting process(Academy, 2012). Lubricant is basically can be
formed into three type of states such as solids, liquids and gases. It is expected to improve and
control the deficiency occurred in the tool wear as well as preventing the corrosion and overheating
when handling the machining.
(Uysal et al., 2015) have been found that MQL has been showed an excellent method as an
alternative to flood cooling in some milling process .However, there was a problem when cutting
the hard material lead to MQL needed to be upgraded to increase the performance by addition of
oxide(Al2O3),Molybdenum Disulphide) and others.Nanoparticles have been highly recommended
to be used due to their enormous technological important in modern material science. When
nanoparticles are added into the lubricant, both mixture formed would react more active in
preventing the friction and tool wear. However, there are many types of nanoparticles that
commonly used, which they had different level of effectiveness to enhance the wear and friction.
Therefore,this review paper will disccuss on the analysing of MQL technique with different
techniques such as dry machining, gaseous lubrication, solid lubrication, and mist lubrication and
in depth the effect of MQL on stainless steel, the application of MQL technique without
nanoparticles and the effect of all the types of nanoparticles on MQL.
Towards Green Lubrication Machining
Many of manufacturers have been used various green machining strategies in order to
increase the pressure for the sustainability (Helu et al., 2012). According to the report of the world
commission on environment and development, the sustainability is defined as the products produce
with green strategies and techniques in order to reduce the negative impact to the
environment.(Haapala et al., 2013) reported that the phrase of sustainable manufacturing are
related to reducing and characterizing and reducing the environmental impacts in manufacturing.
The demands for improved of materials or metals is increasing as well as requirement of
environmentally friendly in manufacturing industries (Bocanet, 2018).
Many green techniques have been developed in manufacturing industries that have shown
some of beneficial to the machining. There are, lubricants used in green techniques have reduced
the tool wear and produced the superior surface finish of workpiece. (Boubekri & Shaikh, 2014)
was study on AISI 1045 under MQL that has been supplied continuously which is beneficial to the
tool life where it can prolong the tool life. A similar study was conducted that the implementation
of MQL performance in machining has a significant to reduce the temperature cutting and resulted
lower the tool wear compared to dry machining.
Based on findings, there some reported on lubrication techniques used of chemical
substances in lubricants have been affected to the environment such as human health and also drive
into high cost of lubrication year by year. Based on (Sharma et al., 2016) study has shown the cost
cutting fluid is 16-20% of total manufacturing and a lot of lubricants used in machining can be
highly affected to the environment.
For the past few years, many researchers have been carried out on their research to figure
out the best alternative lubrication method, biodegradable lubricants, the addition of nanoparticles
and without the addition of nanoparticles which can be an alternative to improve lubricants
performance to be more convenient and efficiently in reducing the tool wear effectively. This
review will be discussed based on selected recently research on the several alternative lubrication
methods towards green machining such as dry machining, mist lubrication, gaseous lubrication,
minimum quantity lubrication (MQL), and solid lubrication.
Dry machining
Dry machining has been implemented in manufacturing industries which is well-known as
machining techniques without using cutting fluids. Research so far has been carried out that cutting
fluid has become a major contribution to the environmental problem and human health. This is
become quite challenging to the manufacturing industries where cutting fluids are also needed as
a cooling agent to a large amount of heat released during the cutting process, in order to improve
surface finish and prolong the tool life.(Elbah et al., 2019) has presented the research on the coated
mixed ceramic TiN (CC6050) in hard turning of low alloy steel under wet,dry and MQL where
the results observed tool life for both (MQL,wet) higher than dry machining. From the perspective
environmental view, dry machining is the best alternative to solve the environmental problems.
Furthermore,the dry machining so far has shown an excellent result in reducing the
environmental problems as it has non-pollution to the air and water due to free from disposal in
cutting fluid where the present of cutting fluids will be polluted the water and contaminated the
soil due to disassociation of cutting fluid (Dixit et.al 2012).Then, the cost of related to cutting fluid
such as the coolant ,disposal and maintenance can be reduced in dry machining. The similarity of
dry machining can be found in Minimum Quantity Lubrication (MQL) where there is no needed
of cleaning of disposal since the chip from the cutting can be recycled(Dureja & Bhatti, 2016).
Unfortunately, without lubricants or cutting fluids during machining may be produced
more heat at interface surface of cutting tool and workpiece due to existing of excessive friction.
Liew (2015) has been studied that high temperature, severe tool wear and poor surface finish have
been occurred caused by excessive metal flow to the interface of cutting tool when in high friction
state. Goindi et al. (2017) has been studied on dry machining process where it is possible to
eliminate the cutting fluid completely during machining, to overcome this challenge is by using
minimum quantity lubrications (MQL) or near dry machining. Dr Neil (2009) reports that
elimination of lubricants in machining has led to excessive tool wear and low quality of surface
finish may occur due to a tremendous heat and friction is generated during the interface cutting of
The technology of dry machining has been improved, but it unable to carry on for metal
such as stainless steel and titanium because of the hardness that are required of high of speeds and
high of feed rates which is needed to the benefit of lubricants to ensure meet the superior surface
finish.(Kasim et al., 2013) has been observed that during end milling of Inconel 718 under MQL
with increased cutting speeds (100-170m/min) and feed rates(0.15-0.25 mm/rev) showed the
results of high surface finish from 0.173µ to 0.3µm. (Kagnaya et al., 2014) The effect of wear on
the cutting tools during high-speed dry machining of AISI 1045 steel has been investigated. It was
observed that the increase of cutting speed has influenced the cutting force, friction coefficient,
and cutting pressure led to wear formed. As cutting speed is increased at 400-500m/min, crater
wear depth maximum is also linearly increased at 40-124 µm. Then, the adhesion, abrasion and
chipping are formed as the increasing of cutting speed. In addition, increasing of feed rate in dry
machining might affect on the tool wear, such as when cutting speed at 320m/min ,0.05 mm/ref of
feed rate, the maximum of flank wear has resulted at 232 µm. While, at 0.15 mm/rev of feed rate,
the flank wear reduced to 203 µm(Mia et al., 2018).
Dry and minimum quantity lubrications (MQL) are proven that both of them are
environmentally-friendly and the cost machining can be reduced as there is no disposal existing.
However, there are some of limitations found in many published works on the technology of dry
machining. As dry machining has been more improved but unfortunately still the problem exist
when machining cannot be done without the benefit of cutting fluid or lubricants even with the
help of new coating of cutting tools and not at all machining operation are suitable undergo through
dry machining(Dr. Neil Canter - MWF, 1999).In order to achieve the best performance in reducing
the tool wear, higher surface finish and cutting tool can be used in a long period of time were best
found in MQL technique as well-known as environmentally friendly.
Gaseous Lubrication
Air, helium, oxygen and nitrogen are examples of lubricants in gaseous state.(Liew &
Hsien, 2015) has published paper related that lubricants in gaseous state are environmentally
friendly and highly influence the performance of cutting tool.In addition,(Yi et al., 2021) has
studies that gaseous and liquids are generally categorized as fluids and it has ability to flow
viscously ,resist to pressure and forming a film of gas for lubrication purposes similar in liquid
film lubrication. Then, some of the properties of gaseous are having lower viscosity and heat
capacity which is enable to form laminar lubrication film as liquids.
On top of that, the parameter of cutting speed in gaseous lubricants are always take into
consideration when handling the machining. The reason is, most of gaseous lubricants are unable
to run efficiently when at high speeds due to the formation of sliding contact in between the chip
and the tool, whereas led to present of unlubricated friction and unable to dispel the heat formed.
(Liew & Hsien, 2015).
(Kaynak, 2014) has been emphasized on the cutting conditions and parameter in machining
of Inconel 718 at various condition such as cryogenic, dry and MQL in turning machining. Cooling
or lubrication are significantly important in improving the performance of Inconel 718.At low
speeds, MQL has shown the best performance in reducing the force component compared with
cryogenic and dry machining. While, cryogenic cooling produced least forces among three
As mentioned earlier, nitrogen gas is also categorized as inert gas that having less reactivity
to chemical reactions and resulting material damage was reduced. According to (Mia et al.,
2018),The combination of MQL and nitrogen gas as lubricants has extremely reduced the
maximum of flank wear compared with pure nitrogen gas and dry machining. There are not more
than 80% to 85% of the tool flank wear has reduced when it carried out at high or low of feed rates.
The properties of gaseous lubricant had limitation when the viscosity of gaseous is low. It
can be seen through lubricated bearing which is the very low viscosity of gaseous will be generated
small heat that results affected on the load-carrying capacity of self-acting where it is possible to
achieve better bearing performance(BARTZ, 1974).However, according to (Khanna et al.,
2020),the tool life in the cryogenic machining with LCO2 was observed to be 44% and 68%
compared to dry, flood and MQL during in turning test of 1505 PH SS.(Khan & Ahmed, 2008)
were studied that the tool life at cutting speed 100 m/min ,0.05mm feed rate is more efficient and
increased two times compared to the same cutting speed and 0.1mm of feed rate from 57.43
minutes to 114 minutes due to high feed rate, more high chip is produced that lead to more heat is
In metal cutting process, most of the researched work that had been carried out proved that
the limitation of gaseous lubricants is unable to be carried out in low speed during the machining
that make they not to be suggested to be used for experiments that are involving low speed
parameter. The surface finish is also observed during in cryogenic machining are low compared
through the flood machining.
Solid Lubrication
A solid lubricant is a formed of powder or thin film that is working as reducing friction and
wear. It is also used to protect and prevent wear from damage during the lubrication process take
places. It can be seen when there are two interfaces sliding, shear will be formed easily and
automatically reduce friction and wear. Another name of solid lubrication that is commonly used
is dry-film lubrication or solid-film lubrication. There are several classifications of solid lubricants
lamellar, Soft metals, mixed oxides, single oxides, Halides and sulphates of alkaline earth metals
carbon-based solids, organic materials /polymers, bulk or thick -film, and thin-film composites.
However commonly used in industry and has been studied by many researchers is lamellar solids
such as MoS2,WS2 HBN, Graphite ,Graphite fluoride,H3B03,GaSe,Gas, and SnSe. This is because,
most lamellar solids have shown good capability in terms of chemical affinity.
Basically, solid lubrication takes over under dry conditions and also in minimal fluid
conditions. Rahmat at al. (2013) stated during milling of AL6061-T6 Aluminium alloy with the
present of solid lubricants such as MoS2 (molybdenum disulphide) at concentration 0.5 % and the
undergo using MQL with flow rate of 30 ml/h during machining showed the best performance in
improving the quality surfaced finish of workpiece. From the previous researched paper, solid
lubricants can be dissolved in water or oil which improve their performances in enhancing wear
effectively when under high temperature or temperature condition. However ,(BARTZ, 1974)
pointed out in the researched work that many solid film lubrication consists of poor wear resistance
that affect to the efficiency of solid lubricants performance.
On the other hand, solid lubricants are well known as lubricant has unique layered
structure. The are several reasons such as when the atoms are in the same layer will be strongly
bonded each other with forces are called as van der walls. Strongly interatomic bonds formed is
enable to prevent wear from highly damage. From this mechanism can be prolonged wear life and
responsible in lowering friction when the interface meets each other. The present of MoS2 solid
lubricants into the LB 2000 oil under MQL technique can be prolonged the tool life which is about
12% compared to dry machining and 46% compared to pure LB oil by MQL technique(Marques
et al., 2019). A. Dudarev (2019) has been studied solid lubricant added may extend the time of
drilling and critical wear compared to dry machining Thus, these moisture conditions is
accelerating the performance of solid lubricants where there is addition of certain chemical into
The surface finish will be formed is smoother and better than others when using lamellar
solid characteristic as lubricant because its particle can be used to cover and enough fill into the
whole pores or asperities on top of the surface. According to (Marques et al., 2019) stated in finding
results, the lamellar structures can be a factor in lowering the friction .In industrial manufacturing,
the most preferred one to be used as solid lubricants is ws2 because made of synthetic lubricant
but are too expensive compared to Mos2.Nb, Mo and others . This showed that solid lubricants are
significantly highly recommended to be used as it can enhance the wear and the cutting tool
Unfortunately, many findings have been studied that solid lubricants performance better
when there is addition of other element and probably can be contributed into the high cost in
lubrication. Then, Solid lubricants also unable to work efficiently in reducing the wear by itself
without under several techniques and the most preferred technique and applicable by MQL.