CONTRIBUTION

Current Status and Issues of Eco-Machining

Professor Takashi NAKAMURA

Environmentally-friendly technologies have been developed for manufacturing processes to reduce burden to
the environment. Especially in machining, the measures called “Eco-Machining” were progressed; these werereduction of cutting fluid usage, use of energy-saving devices and improvement on tools. There was, however, a low
estimation left on the reduction of cutting fluid usage, where the existing production equipment was used for the
eco-machining, because many malfunctions occurred in these machines. Improvement must be made on handling of
cutting chips in order to realize the environmentally-friendly machining.
Key Words: eco-machining, cutting fluid, energy-saving, tool, cutting chips

1. Introduction
At the beginning of the year, I was asked to write apaper on the theme of “Eco-machining, Tribology, or
another topic of choice” and, with no small amountof hesitation, I accepted. I believe one of the reasons I
received this request was because I had been the chief
examiner of the workshop “Eco-machining & Tribology”,
proposed by members of the Japanese Society of
Tribologists. However, in reality, this workshop had
not been in session for sometime, and in March of thisyear, dissolved upon integration with another workshop,“Machine Tool Tribology.” The main reason why theworkshop was not held was due to the difficulty of finding
contributors.

2. Shift in CO2 Emissions
Figures 1 and 2 are sourced from reference material
1 (Transitional changes in emissions amount by CO 2
1)thsector) used in the 9 Carbon Planning Study Groupsession (Mar. 9 2018) hosted by Japan’s Ministry of theEnvironment. Carbon planning is an initiative to reduce
CO2 emissions through carbon tax, etc. and it is vexing
to think that professors in literature sit around in a wellair-conditioned room discussing such a topic at length.
Figure 1 shows the sectors where a power plant’s power(CO 2 emissions, etc.) is ultimately consumed, and it
is evident that there has been a remarkable increase inCO2 emissions by the “Business and Other Sector” over
* Visiting professor, Nagoya University (Professor Emeritus of
Nagoya Institute of Technology)

2

the past 25 years, with the majority of this comprisingof electric power. The “Household Sector” shows thesecond largest increase (personal cars are included in the“Transportation Sector”) and here as well, two-thirds ofthe total comprises of electric power. Ultimately, as seenin Fig. 2, which shows the sources of CO2 emissions,
it is apparent that in the Energy Conversion Sector,
represented by power plants, etc., CO2 emissions havebeen increasing at a constant rate. The reason for this isbecause it is now taken for granted that electric power
will be used to cover the air conditioning in our homes
and offices in order to create a comfortable environment.
Thinking back, I remember that twenty years ago, there
was no air conditioning in the university lecture halls orlabs, and students had to bear the heat during graduate
school entrance exams held in summer to continue
writing answers all day long -this was the borderline
between victory and defeat. Moreover, I personally canrecall on extremely hot days, when I simply couldn’t
stand the thought of working even in shorts, how mycolleague and I would go to eat ayu sweetfish at the “yana”(“fishing weir”). Meanwhile, CO 2 emissions by theTransportation Sector, which is often the target of ruthless
public scrutiny, show a downward trend over the past 20
years. The number of cars, however, has increased overthis period of time, therefore it is clear that fuel economy
improvements are contributing to this reduction. The
CO2 emissions of the Industrial Sector, which involves
eco-machining, have also decreased consistently since
1990, with the difference in the CO2 emissions shown by
Fig. 1 and Fig. 2 being primarily due to electric power
consumption, and it is clear that this electric power
consumption has also fallen consistently. It is the way

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−Current Status and Issues of Eco-Machining−of Japanese industry to wring out an already somewhat
dry cloth, and eco-machining is the manifestation of thisspirit. The reason why we were unable to find contributors
for the workshop I mentioned at the outset, is believed502

to be because the use of eco-machining is expanding in
production sites where application of such technology
is possible, and it is difficult to find an angle of ecomachining that serves as a new research theme.

Industrial Sector (factories, etc.)

500(Compared to FY2005)
457
432
411 mill tons (-10.0%)300

Business and Other Sector(commerce/service/business sites, etc.)
239

Transportation Sector(cars, ships, etc.)
206

278

180

Household Sector

265 mill tons (+11.1%)

225

240

200

213 mill tons (-11.0%)

201

179 mill tons (-0.2%)

137

80 mill tons (-23.3%)
46 mill tons (-17.1%)

2015

29 mill tons (-8.8%)
3.4 mill tons (-23.6%)
2014

2013

2012

2011

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

1999

1998

1997

1996

1995

1994

1991

48
29
3.5

32
Other (agriculture/indirect CO2, etc.) 4.5

24 Waste Sector
6 5
1990

99

Usage of industrial processes and products 56

65

0Energy Conversion Sector 104(power plants, etc.)

91 131

1993

100

1992

CO2 emissions, mill ton CO2

400

Fiscal year
The values in parentheses are the rate of change for the FY2015
emissions compared to FY2005 emissions by individual sector＊

Fig. 1 Trends of CO2 emissions by sector (after allocation of emissions from power and steam generation)(Compared to FY2005)

600
537
Energy Conversion Sector(power plants, etc.)

500

480 mill tons (14.7%)

Industrial Sector (factories, etc.)

400

356
390

344 mill tons (-11.6%)

300
Transportation Sector (cars, ships, etc.)

109

2015

2014

2012

2011

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

1999

1998

1997

1996

1995

1994

1993

Source: Greenhouse Gas Emissions/
Absorption Catalog

67 mill tons (-38.8%)

69
58
48
29
3

Household Sector 70
56
Usage of industrial processes and products
32 Waste Sector
Other (agriculture/indirect CO2, etc.) 4.5
1990

0

216
205 mill tons (-11.9%)

Business and Other Sector(commerce/service/business sites, etc.)

1992

100

232

2013

200

1991

CO2 emissions, mill ton CO2

418

53 mill tons (-23.6%)
46 mill tons (-17.1%)
2 mill tons (-8.8%)
3 mill tons (-23.6%)

Fiscal year
The values in parentheses are the rate of change for the FY2015
emissions compared to FY2005 emissions by individual sector＊

Fig. 2 Trends of CO2 emissions by sector (before allocation of emissions from power and steam generation)

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−Current Status and Issues of Eco-Machining−

3. Current Status of Eco-machining
3. 1 MQL Machining Technique
Conventionally, the cutting process has involved
supplying large volumes of cutting fluid to cutting points.
The roles of cutting fluid in the cutting process are (1)lubrication, (2) cooling, and (3) cutting chip removal, andthe reason why cutting fluid became a focal point of ecomachining is the large power consumption required for
its usage. Depending on the type of machining, there arecases where over half of a factory’s power consumption is2)
by cutting fluid-related equipment . In the case of steel,the material’s oxide film possesses lubricant properties,
therefore oil-free dry machining is achievable withwide machining conditions. However, in the case of
precision machining which affects heat generation, or themachining of aluminum alloy, etc., oil must be supplied
to ensure sufficient lubrication performance. This led tothe emergence of MQL (Minimal Quantity Lubrication),a form of eco-machining whereby an extremely small
amount of oil (primarily naturally-derived ester) is
supplied to the machining point in mist form.
MQL machining was first used by NASA in ultrahigh-speed machining as a technique to supply oil tomachining points. The technology was then advancedin Germany, a country with a high awareness ofenvironmental issues. I stayed at RWTH Aachen
University in 1995 and had the opportunity to be present
at a research site for MQL. Here, the application limitsof MQL had already been verified, with the conclusion
being that, even with MQL and cool air combined, it was
impossible to support the heavy cutting (ramping using
an end mill) of aluminum alloy. I suggested to Prof. F.
Klocke, director of the Laboratory for Machine Tools
and Production Engineering (WZL), that perhaps it wasnecessary to use even just a small amount of water forheavy cutting, but he rejected this immediately, sayingthat they simply could not use water. The reason for this,I was told, was that German people are extremely fearfulof leaking waste fluid into the Rhine, which flowed into
other countries also.
With an awareness of the need to develop a new
eco-machining technology, I returned to Japan and,considering that it would suffice as long as there were no
waste fluid leakages, not to mention the fact that Japan
had no rivers that flowed into other countries, I began
research into MQL that used a small volume of water.
Initially, I supplied water mist and MQL separately to themachining points but this did not work well at all, andin fact resulted in a larger cutting force than when MQL
was used in isolation. I trialed various oil types used in
MQL, and even developed an apparatus to supply water
mist and oil mist from one nozzle, but met with failure
upon failure. Meanwhile, in an experiment by a student

4

engaging in graduation research, suddenly promising
results were obtained. An investigation into how the goodresults came about revealed that the student had mistaken
the water and oil supply pipes. Initially, the student had
arranged it so that water mist was blown through thefront and oil mist was blown through the back of a single
nozzle. The order was probably made this way to ensure
the water reached the machining point with certainty
however, the student felt that it really didn’t matter which
was which. Nevertheless, water has a high surface tension
and the particle size of water mist is larger than that ofoil mist, therefore the water mist on its own reachedthe machining point first. The student had accidentally
reversed this order, creating a situation whereby the water
droplets first passed through the oil mist and became
coated in oil, before reaching the machining point.
Fortunately, the oil used on this occasion was rapeseedoil. Oil mist permeates the air in the surrounding vicinity,
therefore in order not to negatively impact student
health, and to prevent students from emitting an unusual
odor after returning home from the lab, I had them use
rapeseed oil, which is a familiar odor in the common
household kitchen. I did not know that rapeseed oil andwater had a low interfacial tension, therefore rapeseedoil spread swiftly across the surface of water. As a result,oil adhered to the water droplets that passed through theoil mist and spread swiftly, resulting in the configuration
shown in Fig. 3.
Work surface
Smearedoil

Oil film

0.1mm

Water
Tool surface

Fig. 3 Conceptual diagram of OoW (Oil on Water) cutting
fluid

Figure 3 shows the OoW cutting fluid (OoW: Oil on
3)
Water) technique proposed by myself and the authors ,which can be considered a form of MQL due to the fact
it only uses a minute amount of oil. The diameter ofthe water droplets are relatively larger, and the waterto-workpiece arrival rate is higher. The surface of thesewater droplets is coated in oil, and if the oil film thickness
is equal, the larger the water droplet diameter, the smaller
the volume fraction of oil relative to water will become.
For the experiment, the standard water:oil ratio was made100:1. For the oil mist, we used vegetable oil with the

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−Current Status and Issues of Eco-Machining−

JTEKT ENGINEERING JOURNAL English Edition No. 1016E (2019)

Refined rape oil only (10 mL/h)
Water only (1 000 mL/h)
Oil on Water

primary ingredient of tri fatty acid ester or synthetic esterwith an added surfactant. Since long ago, vegetable andanimal oils have been used as machining oils as theseare biodegradable and offer good breakdown of bacteria.
We experimented with a variety of oils, from olive oil
to castor oil, but eventually settled on rapeseed oil as
our standard in light of its machining performance foraluminum alloy, odor and price. Incidentally, soy sauceoil, which is treated as a fuel, has the highest performanceon stainless steel, but was deemed inappropriate due tothe students’ dislike for the soy sauce smell and the factthat it would cause rust on the machine tool table, etc.
Figure 4 shows the results of performing heavy
cutting using an end mill on aluminum alloy and testing
the performance of OoW under various cutting fluid
4)
conditions . The measuring result for cutting force ofemulsion flood coolant (shown on bottom row of graph)of 200 N was made the standard, and it is only in thecase of supplying refined rapeseed oil in mist form
that the cutting force increases (shown on top row ofgraph). This is the “MQL application limit” confirmed at
RWTH Aachen University, and it cannot be considered
a good cutting state. Incidentally, in dry cutting, cutting
chips weld with all tools and enter a state of friction stir
welding (FSW). The second row of the graph shows that,
if the water droplets alone are supplied, this also resultsin the cutting chips welding with the finished surface andcutting being unsuccessful. From the third row of thegraph onwards, we used a combination of oil and wateror OoW (water: 1 000 mL/h, oil: 10 mL/h) and changed
the oil type. The first was normal mineral-based oil and,while cutting was achieved, the cutting force was large.
The configuration shown in Fig. 3 was not achieved
because mineral-based oil does not spread across thesurface of water. Secondly, we used edible frying oil,and this resulted in a lower cutting force than emulsion
and a good finished surface. Thirdly, we used synthetic
ester with added surfactant and this demonstrated aneven lower cutting force. Fourthly, we used refinedrapeseed oil and this had the second lowest cutting force,
however there was no significant difference between the
cutting forces for the last three oil types mentioned. My
apologies to lubricant manufacturers, but this experimentshowed us that the frying oil available off-the-shelf at
supermarkets could sufficiently meet our requirements.
However, if vegetable oil is used, just as in the household
kitchen, oxidative degradation and polymerization leads
to stickiness after extended periods of time, therefore
regular cleaning is necessary.

Mineral base oil
Edible frying oil
Synthetic ester + 2%TCP
Refined rape oil
Emulsion flood coolant
0

50

100

150

200

250

300

Cutting force, FH (N)Measured cutting forces with some cutting fluids

Fig. 4 Change in cutting force when using different supply
methods and oil types

It is necessary to consider the water used in OoW also.
We observed cases whereby OoW that worked well in theuniversity laboratory in Nagoya city did not perform as
well as expected when trialed in other regions. The waterused in Nagoya city is soft water from the Kiso River,whereas the water sourced from underground used inother regions is hard, therefore performance was poor due
to the imbalance of the water/oil interfacial tension. This
problem was solved, however, by adding the right amountof surfactant to the oil.
OoW also uses air. From the perspective of power
consumption, we want to minimize the supply of aircompressed using a compressor. As such, we trialed
blowing OoW on the machining points using waterpressure and oil pressure alone. There was no great
difference in the amount of air used by OoW whenmachining steel material, however there was a majordifference in relation to aluminum alloy, for which
the effects of oil are notable. In the case of steel, themachining temperature is high and the machining
points are cooled by the water at boiling point. In
contrast, the machining temperature of aluminum alloy
is comparatively low and cooling is done with water at
the heat of vaporization, therefore if the vicinity enters asaturated vapor state, it is no longer possible to vaporize
and cooling performance falls. We realized that weneeded a new way of supplying dry air. There was aneed for different approaches to suit the material beingmachined.

3. 2 MQL Failed
MQL became known as an effective method for
reducing the burden on the environment, and around 10
to 15 years ago, there was a strong movement primarily
led by automakers and parts suppliers to introduce
MQL to dedicated machining lines. I know factories
that ordered custom-made tools for the introduction of
MQL, flipped workpieces upside-down to improve thedischarging of cutting chips created during drilling, and5

−Current Status and Issues of Eco-Machining−built cutting chip discharge systems to ultimately create
factories capable of producing aluminum alloy parts in an
eco-friendly environment. However, these were newlyconstructed factories, and according to an employee of
one particular equipment manufacturer who visits a lotof factories, there are many cases where factories leftthe existing production line as is and simply switchedfrom cutting fluid to MQL, only to meet with failure. The
reason why the switch to MQL was considered a failure
are as follows:
1) Reduced discharging performance of cutting chips
during drilling2) No cooling performance with oil mist alone, andsurface roughness worsened due to insufficient controlof the built-up cutting edge3) Due to the reduced cutting chip removal function, there
were frequent cases of cutting chips becoming stuck in
the jig seat, resulting in quality defects
4) When MQL is supplied from inside the spindle, oilmist undergoes centrifugation and the supply amountbecomes unstable
I will discuss the issue of the cutting chips later,
however in regards to the lack of cooling performanceraised in point 2 above, this can be solved by adopting3)
the OoW technique proposed by myself and the authors ,or by blowing emulsion onto the target in mist form.
Furthermore, in regards to point 4 above, a method
has been developed whereby oil and air are supplied
separately to the spindle then mixed in the vicinity of the5)tool (internal mixing method) .
As for the processing of cutting chips, this had been an
issue of concern since the outset of OoW development.
Cutting fluid such as emulsion does not only movecutting chips created at the machining point far fromthe machining point, it also adequately suppresses thescattering of cutting chips. In the case of MQL or dry
machining, however, the cutting chips scatter in the air,and for MQL specifically, cutting chips adhere to theceiling of the machine tool due to the stickiness of oil.
Cutting chips may even penetrate the most unlikely ofplaces in a machine tool and trigger various problems. In
light of these concerns, we developed the system shownin Fig. 5. A custom-made end mill, drill and tap form
6)
a tool that sucks in the cutting chips from its tip andcutting chips are sent to the collection/compression unit
through the hollows in the tool, holder and spindle. The
issue of point 4 above was solved by supplying OoWfrom the outside. Cutting fluid is sucked up together
with cutting chips, therefore even when supplied fromthe outside, cutting fluid could be effectively supplied tothe machining point. However, in order for this system
to work, the cutting chips must be small enough to passthrough the tool interior, therefore this method cannot beapplied to heavy cutting.

6

Cutting chips

Cutting chip collection/
compression unit

SpindleSucking tool

Oil on Water (OoW)

Table

Flow of cutting chips

Sucking tool holder

Compressed
cutting chips

Fig. 5 Developed chip sucking machining system

3. 3 A New MQL Era
Even after the attempts to switch to MQL ended in
failure, factories were still under pressure to reduce
power consumption, therefore the technique of supplying
emulsion cutting fluid in mist form (hereinafter referred
to as “emulsion MQL”) is growing in popularity as asolution to the issue mentioned in point 2 above forexisting equipment. For emulsion cutting fluid, surfactant
is added to the oil and micelles form in the water. Oil
disperses in water and the micelles are larger than the
wavelength of visible light, therefore appear as whiteemulsion. If a certain oil concentration is reached or
exceeded, an oil film also forms on the interface between
water and air, therefore if emulsion is sprayed in mist
form, it results in the same configuration as Fig. 3.
However, micelles also exist within water droplets,
therefore, in contrast to the water vs. oil volume of 100:1
for OoW, this ratio must be around 100:5 in the case ofemulsion MQL. For regular machining, around 100 mL/hof emulsion MQL is supplied, and compared to OoW,
both the amount of water and oil are reduced.
In either case, MQL lacks the ability to remove
and discharge cutting chips therefore trials have been
completed whereby washing agent is cascaded down
the interior wall of a machine tool or air pulses are used
to remove/discharge cutting chips while suppressing
air consumption. Furthermore, if the sucking method
shown in Fig. 5 and the sucking tools developed by tool
manufacturers (for example http://carbide.mmc.co.jp/
magazine/article/cut_vol06) continue to be utilized, theissues mentioned in points 1 and 3 above could be solved.
Also, in regards to passage through the spindle, if internal
mixing is used to solve the issue mentioned in point 4, it
is anticipated we would enter a new MQL era.

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−Current Status and Issues of Eco-Machining−

4. Conclusion
It is believed that the factories who introduced MQL
to existing equipment “as is” between 10 and 15 years
ago still consider this attempt to have been a failure. It is
my hope that these factories refresh their view of MQL,
which enables cutting with minimal oil. If the issue ofcooling performance arises, emulsion MQL would be
one potential solution, however I recommend OoW. In
regards to supplying MQL through the spindle, interior
mixing is an excellent method from the perspective of
responsiveness. For all of these technologies, the related
patents are due to expire in the near future, and I plan onrecommencing development of a technology for sucking
up cutting chips in a broad range of cutting. In closing, I
wish to express my strong hope that Japan becomes oneof the leading eco-machining countries in the world.

References
1)
2)

3)

4)

5)

6)

https://www.env.go.jp/earth/ondanka/cp/arikata/conf09/
cp09_ref01.pdf, 44-45.
S. IKAWA, M. IWATSUBO, K. MIYAZAKI: Measuresagainst Dry Machining for Environmental Response (inJapanese), Vol. 47, No. 5, (1999) 18.
T. NAKAMURA, T. MATSUBARA, F. ITOIGAWA,
K. NIWA: Study on Minimal Oil Film on Water Fog
Metalworking Fluid Emphasizing on Environment(in Japanese), Proc. of Japan Society for Precision
Engineering Annual Meeting 1999 Spring, (1999) 550.
T. NAKAMURA, T. MATSUBARA, F. ITOIGAWA,
K. KAWATA: Oil Film on Water Fog Metalworking
Fluid, Proc. of 10th International Conference on Precision
Engineering, (2001) 269.
T. MAKIYAMA: Near-dry Machining Technology
for High Capability Machining Center, Society of
Manufacturing Engineers IMTS 2000 Manufacturing
Conference, (2000), CD-ROM, Session #210.
T. NAKAMURA: Necessity for Newly Developed Tools
and These Far-reaching Effects (in Japanese), Vol. 54,
No. 3, (2010) 10.

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