Towards Sustainability Using Minimum Quantity Lubrication Technique and Nano-Cutting Fluids in Metal-Machining Processes. Author: Marta García Tierno Publication type: Master thesis Supervisor: Amir Rashid University: KTH Royal Institute of Technology, Stockholm, Sweden Department: Department of Production Engineering
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Towards Sustainability Using
Minimum Quantity Lubrication
Technique and Nano-Cutting Fluids
in Metal-Machining Processes.
Author: Marta García Tierno
Publication type: Master thesis
Supervisor: Amir Rashid
University: KTH Royal Institute of Technology, Stockholm, Sweden
Department: Department of Production Engineering
Marta García I
ACKNOWLEDGEMENTS
First, I would like to thank professor Amir Rashid, for giving me this opportunity and for his
support. Also, I would like to thank Javier Echavarri, for supervising my thesis from Spain, thanks
for all your comments and corrections given.
Secondly, I want to express my gratitude to LetsNano AB team. Professor Muhammet Toprak,
Bernhard Hirschauer, Tafazzul Mahmood and Nader Nikkam. This project and my work at KTH
couldn’t be possible without their effort and support. I would also like to thank to the people
working at the laboratory at IIP-KTH, specially Anton Kviberg, Jan Stamer and Mats Bejhem for
sharing with me his endless knowledge and wisdom.
Finally, I would like to mention my family, always supporting me in all the aspects of my life,
specially my father and my aunt, Pascual and Rosa. And to my friends, both the ones living in Spain
and the ones in Stockholm, for helping me every day and making me happy.
For those of you who helped me directly or indirectly and I may have forgotten, many thanks.
Marta García II
ABSTRACT
Sustainable manufacturing is making products from processes which have minimal environmental
impact, energy and resource efficient, economically viable and safe for consumers and society as
whole. Achieving sustainability in manufacturing would mean infusing sustainability methods on
product process and system level. On the process level, machining technology is one of the most
widely extended processes in the industry. One way to attain sustainability in this technology is by
adopting efficient management of Metal Working Fluids (MWF). In this purpose to reduce the
amount of MWF starts Minimum Quantity Lubrication (MQL), where very small quantity of fluid
is applied to the cutting zone with maximum precision. Moreover, addition of nanoparticles to
these ´minimum quantity lubricants´ further enhances its tribological properties leading to higher
reduction in friction and temperature in the machining process.
The main objective of this thesis is to study the performance of cooling-lubricating fluids and these
fluids modified with nanoparticles, how the use of this new lubricants improves the results obtained
in material process technologies, particularly in turning. This project is being supported by the
company LetsNano AB, providing the lubricants enhanced with nanoparticles and the funding,
and Accu-Svenska AB, providing base oil and MQL technology.
The experiments are carried out at Kungliga Tekniska Högskolan (KTH), at Institutionen för
Industriell Produktion (IIP) laboratory. The turning process was tested with two different
workipiece materials: hardened steel (Toolox® 44) provided by SSAB, and grey cast iron (Scania
case study material). Two different tooling systems, due to the different materials. One provided
by Mircona AB, and the other given directly by Scania, provided by Sandvik AB and Cermatec AB.
The MQL system is a high-performance booster provided by Acuu-Svenska AB. The lubricant is
a vegetable oil that will also be the base for the Nanofluids (NF). This Nanofluids and produced
and developed by LetsNanoAB.
The study revealed an encouraging potential of moving from conventional (dry) cooling techniques
to the vegetable oil based MQL. Machining performance of MQL was encouraging as in most of
the cases the systematic reduction in tool wear reveals a better machinability. The contribution of
this work for Scania could help them to take the decision and move to more sustainable machining
processes. To prove the potential of the nanotechnology in this kind of processes further study is
needed, and it is going to be tested at IIP facilities in near future. The implementation of this
technology brings more challenges that should considered a study of the hazards of the technology
(emissions, fire and explosion, noise, skin…) necessary safety measures (cleaning, operator
instruction, skin protection…) and modifications in the machine tools system beyond the process
only. This could also be a next step in the further study of this research.
operatörsinstruktion, skydd mot huden ...) och modifikationer i verktygsmaskinerna system utöver
processen bara. Detta kan också vara nästa steg i den fortsatta studien av denna forskning.
Marta García IV
TABLE OF CONTENTS
LIST OF FIGURES .................................................................................................................................................. VI
LIST OF TABLES ..................................................................................................................................................... IX
LIST OF ABBREVIATIONS ................................................................................................................................. XI
LIST OF NOMENCLATURE ............................................................................................................................. XII
1.4.1 LetsNano AB ........................................................................................................................................4
1.4.2 Accu-Svenska AB .................................................................................................................................4
1.4.3 Scania: Case study .................................................................................................................................5
1.5 Time planning ............................................................................................................................................6
2 STATE OF THE ART ......................................................................................................................................8
2.1 Sustainable manufacturing in machining ...............................................................................................8
2.2 Tribology of metal cutting .......................................................................................................................9
3.2.2 Workpiece material ............................................................................................................................ 31
3.2.3 Tooling system ................................................................................................................................... 34
3.3 Description of the MQL system .......................................................................................................... 38
3.4 Collection of the machining variables ................................................................................................. 40
3.4.1 Measurement of tool wear mechanisms and tool life .................................................................. 40
3.4.2 Measurement of Temperature in the cutting zone ....................................................................... 44
3.4.3 Measurement of the Surface Roughness ....................................................................................... 45
4 RESULTS AND DISCUSSION: TOOLOX® 44 ...................................................................................... 49
5.1.3 Temperature ....................................................................................................................................... 67
6 CONCLUSIONS AND FUTURE WORK ................................................................................................ 69
6.1 Recommendations for future work ..................................................................................................... 70
APPENDIX A. CODES .......................................................................................................................................... 76
APPENDIX B. FLANK WEAR EVOLUTION ................................................................................................ 82
APPENDIX C. SURFACE ROUGHNESS MEASUREMENTS ................................................................... 85
APPENDIX D. POSTER PVC ANNUAL CONFERENCE .......................................................................... 86
Marta García VI
LIST OF FIGURES
Figure 1. Structure of the master thesis. .................................................................................................. 3
Figure 2. LetsNano AB [3]. ........................................................................................................................ 4
Figure 3. Accu-Svenska AB [4].................................................................................................................. 4
Figure 4. Scania AB [6]. .............................................................................................................................. 5
Figure 5. Gantt diagram of the master thesis. ......................................................................................... 7
Figure 6. Basic elements of sustainable machining [8]. .......................................................................... 8
Figure 7. Cutting process as a tribological system [10]. ....................................................................... 10
Figure 8. Flood cooling with Emulsion [15]. ........................................................................................ 12
Figure 9. Minimum Quantity Lubrication System (MQL) [17]. ......................................................... 13
Figure 10. Metal working fluid costs in metal machining [20]. ........................................................... 15
Figure 11. Percentage of energy consumption in wet machining [18]. ............................................. 16
Figure 12. Comparison of emission during machining between wet and MQL turning [22]. ....... 16
Figure 13. Heat generation in metal cutting [19]. ................................................................................. 17
Figure 14. Possible lubrication mechanisms by the application of Nano-oil between the frictional
Figure 43. Crater images x10, 0,5 mm of depth of cut. ....................................................................... 52
Figure 44. Flank wear vs. machining time for dry and MQL, 1 mm of depth of cut, Toolox 44. 52
Figure 45. Comparison of tool life, dry and MQL, 1 mm of depth of cut, Toolox 44. ................. 53
Marta García VIII
Figure 46. Flank wear measurement, 1 mm of depth of cut, dry,MQL with vegetable oil and
compressed air. ........................................................................................................................................... 53
Figure 47. Flank and Crater images x10, 13,3 mins of machining, 1 mm, Toolox 44 (a)Dry
machining (b)Compressed air (c)MQL. .................................................................................................. 54
Figure 48. Temperature graphs 1 mm, dry, air and MQL, Toolox 44(a)Average temperature vs.
machining time (b)Evolution of T during 90 s of machining (c) Evolution of T last 15 s of one
Table 21. Tool life, dry and MQL, 1 mm, Toolox 44. .......................................................................... 53
Table 22. Average temperature values, 0,5 and 1 mm, Toolox 44. ..................................................... 59
Table 23. Cutting parameters, Scania Case Study. ................................................................................. 60
Marta García X
Table 24. Flank wear, Scania used inserts, 120 test specimens. ........................................................... 62
Table 25. Tool life for different techniques, Scania case study. .......................................................... 64
Marta García XI
LIST OF ABBREVIATIONS
Al2O3 Aluminium oxide
BUE Built up edge
CFD Computational Fluid Dynamics
CLF Cooling Lubricating Fluids
CNC Computer Numerical Control
CVD Chemical Vapour Deposition
ECEA Cutting edge angle
ENP Engineered NanoParticles
FE Finite Element.
FOV Field of View
GDP Gross Domestic Product
ICP -MS Inductively coupled plasma mass spectrometry
IR Infrared
MoS2 Molibdenum Disulfide
MWF Metal Working Fluid
MQL Minimum Quantity Lubrication
MWF Molibdenum Disulfide
nCLF Nano-Cooling Lubricating Fluids
NF NanoFluid
PVD Physical Vapour Deposition
TiC Titanium Carbide
TiN Titanium Nitrate
TiO2 Titanium dioxide
Marta García XII
LIST OF NOMENCLATURE
Symbol Parameter Units
µ Vicosity cP
Ap Cutting depth mm
d Insert size/Cutting edge length mm
Fc Cutting force N
fc Feed mm/rev
fr Feed rate mm/min
lc Length of cut mm
n Spindle speed rpm
NR Nose radius/ Corner radius mm
Pc Flank wear µm
Ra Arithmetical mean surface roughness µm
Rai Theoretical mean surface roughness µm
Rq Root mean square surface roughness µm
Rz Ten points mean surface roughness µm
tc Machining time s
Tc Cutting temperature ºC
VB Flank wear µm
Vc Cutting speed m/min
ρ Density g/cm3
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1 INTRODUCTION
1.1 Background
The concept of sustainability directly affects to all the stages in the production chain. Nowadays
the corporative strategy of a company should be developed integrating sustainability as a major
concept. Sustainable manufacturing is defined as making products and pieces from processes,
which have minimal environmental impact, safe for consumers, energy and resource efficient and
economically feasible. Sustainable manufacturing should involve both the process and the system
level. The material processing technologies are included in the process level and a fundamental part
of them is the need of cooling and lubricating.
Cutting fluids have several functions in material processing technologies, such as lubrication,
cooling and chip removal. Usually the cutting fluids, also known as cooling-lubricating fluids (CLF)
are toxic and dangerous for the nature and the human health. The disposal of these fluids also
needs a special attention and there is strict environmental legislation in this regard. In order to
reduce the quantity of CLF used in machining processes it is desirable to machine in dry or near
dry environments. Minimum Quantity Lubrication (MQL) is a lubrication technique in which a
very small quantity of lubricant is applied on the cutting zone with high precision. It goes from
flow rates of litres per minute with conventional flood cooling methods to 2-100 millilitres per
hour flow rates with MQL systems. The benefits of the method could be synthetizing in [1]:
• Reduction of friction.
• Improvement of surface finish.
• Better removal of heat and its consequent reduction of temperature.
• Tool wear reduction and increase of tool life.
Of course, a reduction of flow of lubricant is also considered a positive impact of MQL.
In recent years nanoparticle-based cooling-lubricating fluid (nCLF) have been designed and
produced by suspending engineered nanoparticles (ENP) in conventional lubricants, for example
vegetable-based oils. These vegetable oils are biodegradable and not hazardous for the nature and
the human health, but the influence of the nanoparticles suspended on should be considered.
The usage of ENP increases both the heat transfer capabilities and the tribological properties of
the lubricants. Previous research in using nanotechnology to improve the lubricants’ properties has
been developed in KTH in the department of Production Engineering (IIP). The results of this
experiments and research have been published in the form of papers in prestigious publications
[2].
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1.2 Objectives
The main objective of this project is to study the performance of the MQL technology using
vegetable base oil and using cooling-lubricating fluids modified with nanoparticles for two different
set-ups and case studies. How the use of this new coolants improves the results obtained in material
processing level.
For this aim, a scientific analysis between three different lubrication techniques will be employed:
• MQL using vegetable-based oil.
• MQL using nCLF, also called in this project NanoFluids, NF.
• Dry machining.
Some of these techniques are widely known and developed but will be used due to the need to
compare the results obtained with the new nanofluids.
The nanoparticle-based cooling-lubricating fluid selected for the experiments must be
economically and environmentally sustainable, which means that it should not be harmful to health
and the environment and must be economically feasible and produced.
The MQL technique can efficiently reduce the associated environmental impact produced by the
disposal of the lubricants. Due to the development of nanoparticles suspended in the CLF the
results can be greatly improved.
The literature review presented in the next chapter shows that the benefits of introducing this kind
of fluids in machining processes, especially in turning, are significant. In most of these articles three
different cooling-lubricating techniques are compared, sometimes including also flood cooling.
Mostly, empirical models have been developed to predict the tool wear evolution and tool life,
usually utilizing home-made MQL systems. The potential of this research resides also in the fact
that the utilized booster is a high-performance booster available in the market. This makes the
project more interesting from the side of the companies involved.
The second part of the project is focused on experimental work for a well-known automotive
Swedish company. This fact gives the opportunity to test the potential of this technology in an
industrial process that it is being used for production, and how this process can be improved and
make it more sustainable.
The scope of this master thesis has a time limitation. It is restricted to the experimental work of
turning two different materials for two case studies that will be explained in detail in the following
sections.
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1.3 Thesis structure
The master thesis consists in 6 chapters. The project is structured separating two big groups of
results: Pre-hardened steel experiments and Scania case study. Common material and information
is presented in previous chapter: State of art and Experimental methodology. Four Appendix, A
to D, are added at the end of the document to extend and complete the information about some
relevant topics.
• Background of the problem
• Thesis scope and objectives
• Calendar of the project (Gantt)
Chapter 1. Introduction
• Explain the following, based on published literature:
• Minimum Quantity Lubrication Technique, its main characteristics, advantages and restrictions.
• Nano-cutting fluids development and advantages.
Chapter 2.State of art
• Planning of the experimental work.
• Explain the process followed to conduct the research, facilities and set-up.
• Collection of relevant variables and MQL system description.
Chapter 3. Experimental methodology
• The results from the experimental study to evaluate the potental of MQL technology for machining pre-hardened steel Toolox 44.
• Tool wear and tool life, temperature and chips.
Chapter 4. Results and discussion.
Toolox® 44
• The results from experimental study to evaluate the potential of MQL technology and Nano-cutting fluids for machining grey cast iron, Scania case study.
• Tool wear and too life, temperature and surface roughness.
Chapter 5. Results and discussion.
Scania case study
• Conclusions and future work in the topic. Chapter 6.
Conclusion and future work
Figure 1. Structure of the master thesis.
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1.4 Collaborators
This project is being supported by the company LetsNano AB and it is done in collaboration with
Accu-Svenska AB. Scania AB is in close contact with KTH, and they understood the potential of
this technology, thus a case study to test the system in one of their processes was proposed.
1.4.1 LetsNano AB
LetsNano AB is a start-up grown at KTH. Their occupation is focused on the developing and
production of Nanofluids for lubrication, heat transfer and energy storage. This Nanofluids that
they produce provide several benefits, such as reduced down time from change events, reduced
thermal deformation of workpiece, better surface finish, reduced consumption of CLF, improve
tool life by reducing tool wear rate or absence of toxic additives giving a healthier working
environment [3].
1.4.2 Accu-Svenska AB
Accu-Svenska AB is a supplier of products and services for MQL systems to industrial applications
of all kinds. Their entire offerings include an ecological profile; and lubricants are brought to
customers directly from the nature with no additives. MQL System is completely designed and
produced in Sweden. The system meets the entire EU standards through the reach directive in
order to be an exempt from the restrictions. The system is completely sustainable; and it does not
expose any environmental or personal health risks [4].
Accu-Svenska AB has been active in industrial lubrication and cooling technology since 1996.
During the first ten years, the company was an agent of the Accu-Lube GmbH, one of the world’s
leading company in production of MQL systems. To meet today’ demands and needs of Swedish
industry for quality health and environment, Accu-Svenska AB developed its unique MQL system
n that is a competent Programmable Logic Controlled, PLC, application system. The system is
exclusively used in conjunction with Accu-Svenska’s self-produced vegetable-based oil. The system
launched to the market in 2006; and it is offered with performance guarantee. It is the only MQL
system that employs Accu-Svenska’s special-processed vegetable-based oil that contains no
additives of any kind [5].
Figure 3. Accu-Svenska AB [4].
Figure 2. LetsNano AB [3].
KTH Royal Institute of Technology Introduction
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1.4.3 Scania: Case study
Scania AB is a major Swedish automotive industry manufacturer of commercial vehicles –
specifically heavy trucks and buses. It also manufactures diesel engines for heavy vehicles as well
as marine and general industrial applications. Scania AB was formed in 1911 through the merger
of Södertälje-based Vabis and Malmö-based Maskinfabriks-aktiebolaget Scania. The company's
head office has been in Södertälje since 1912. Today, Scania has production facilities in Sweden,
France, Netherlands, India, Argentina, Brazil, Poland, and Russia. In addition, there are assembly
plants in ten countries in Africa, Asia and Europe. Scania's sales and service organization and
finance companies are worldwide [6].
Figure 4. Scania AB [6].
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1.5 Time planning
In this section, the temporary planning of the thesis is presented. Firstly, Table 1 shows the
decomposition of the work packages, including start and end days of the tasks. Once the
decomposition in work packages is done, the Gantt diagram is made with the help of Microsoft
Project software. The diagram is shown in Figure 5. During the development of the project the
progress was presented in various presentations. These presentations have been set in the time
planning as milestones.
Table 1. Work packages decomposition.
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Fig
ure
5. G
antt
dia
gram
of th
e m
aste
r th
esis
.
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2 STATE OF THE ART
2.1 Sustainable manufacturing in machining
Machining is the most widely extended industrial process, especially machining of metal products.
In the last years, sustainability in manufacturing is becoming a key issue due to strict environmental
legislation and the necessity of reuse and recycle materials. But for the companies adopting
sustainable strategies would suppose a big effort and investment for the first years. Achieving
sustainability in manufacturing should consider aspects in all levels: system, process and product
levels, trying to find a general view of all them. Concretely the main objective of the sustainable
manufacturing is to change from the classical ideology of manufacturing based on increase the
productivity to a new vision focus on the concept of global value. There is not an official definition,
but the recent work describes it as a process that leads to [7, 8]:
• Environmental friendliness.
• Reduced cost.
• Reduced power consumption.
• Reduced wastes.
• Enhanced operational safety.
• Improved personnel health.
Sustainable manufacturing
Enviromental Friendliness
Machining cost
Power Consumption
Waste Management
Operational Safety
Personnel Health
Figure 6. Basic elements of sustainable machining [8].
KTH Royal Institute of Technology State of the Art
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By changing usual practices in metal cutting sector to sustainable activities would benefit the
company economically, ecologically and socially. In the metal machining sector, a fundamental part
are the cutting fluids. These fluids have several functions, such as lubrication, cooling or chip
removal.
The usual cutting fluids,CLF, the ones that are used for flood cooling are an emulsion, made with
water and oil, usually up to 90% of water. This water must be recycled because it is hazardous for
both the environment and the human health. They can cause problems to human skin and pollute
the soil. These cutting fluids affect directly to some all the basic elements to achieve sustainable
manufacturing, shown in Figure 6.
Klocke and Eisenblätter [9] studied the influence of CLF emulsions in the total cost of the
machining process. The conclusion was that the 15% of the total cost of machining is due to the
CLF emulsions, while the cost fraction of tools is only 4%.
These are also important reasons, not only environmental but also economic reasons, for
developing new cooling and lubrication techniques such as dry or near dry machining or MQL.
The main drawback that the mentioned techniques must deal with is the quality of the results. This
problem is even harder machining difficult-to-cut materials, such as titanium and nickel base alloys
or hardened steels.
2.2 Tribology of metal cutting
The complexity of the machining processes makes very difficult to define systematic friction and
wear mechanisms. The detailed information of what happens in the interface between the tool and
the workpiece is particularly important to understand control and design the machining processes.
The optimization of the processes can be achieved by understanding the tribology of the contact
between tool and workpiece.
Tribological contacts are usually defined by pairs of bodies in contact. This contact is characterized
by a basic body, as an element subjected to the wear, and a counter body [10]. In any machining
process the basic body Is the tool and the counter body the machined workpiece. But apart from
the contact and interfacial element itself the cutting process needs to be understood as a whole and
keep all the parameters of the cutting process under control. All these variables have a direct
influence and impact in one of the main studies of the tribology: the wear (Figure 7). The main
wear mechanisms present in the cutting inserts are abrasion, adhesion, tribochemical reactions and
surface damage. This wear mechanisms of cutting tools often detrimentally limit the performance
of cutting processes. The complexity of a machining process makes it difficult to systematically
analyse the friction and wear mechanisms at the active areas of the tool [11].
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Focusing on the interfacial element in the cutting process, three cooling-lubricating strategies can
be defined: flood-wet cooling (emulsion), MQL (vegetable oil) and Compressed air. The last two
strategies could be considered as a dry or near dry machining, with the benefits that this involves.
As it is said before, the primary functions of the cutting fluids are cooling, lubricating and chip
removing. In Table 2 shows a summary of the functions and how each lubrication strategy is fixing
them.
The conventional coolant, also known as emulsion has other functions such as transporting chips
or cleaning tools, fixtures and workpieces. If the coolant is removed from the process, these
secondary functions must be taken by other components.
Table 2. Lubrication strategies and its functions [10].
Thermal conductivity increased, and specific heat decreased with the concentration of NP. Best performance in surface roughness and temperatures at 0,5 wt.% of NP.
2 Rao et al., (2011) [27]
Dry, MQL and MQL+NF CNT (Carbon nanotube) nanoparticles 0.5-5 wt.%
AISI 1040 steel Cemented carbide tools
Vc=102m/min f=0,44mm/rev d=0,5mm
The decrease of tool wear and nodal temperature is limited to 2 wt.% of nanoparticles in the oil
3 Khandekar et al., (2012) [28]
Dry, MQL and MQL+NF 1 wt.% Al2O3
AISI 4340 steel Uncoated carbide tools
Vc=350m/min f=0,1mm/rev d=1mm
Great reduction in crater and flank wear. Reduction of 50% and 30% in cutting force and 54,5% and 28,5% in Ra compared to dry and machining with conventional cutting fluid.
4 Amrita et al., (2014) [29]
Dry, Wet, MQL and MQL+NF NanoGraphite, Nanoboric acid and MoS2 NP 0.3 wt%
AISI 1040 steel Uncoated cemented carbide tools
Vc=65m/min f=0,14mm/rev d=0,75mm
Oil with MoS2 shows better performance in cutting forces. NanoFluids, starting with MoS2 showed better results in terms of tool wear, even better than wet machining.
5 Sharma et al., (2016) [30]
Dry, Wet, MQL and MQL+NF 1 wt.% Al2O3
AISI 1040 steel Uncoated cemented carbide tools
Vc=96,7m/min f=0,1mm/rev d=1mm
NF reduced cutting force up to 59.1%, 29.2% and 28.6% compared to dry, conventional mist and wet machining, respectively. Tool wear up to 63.9%, 44.9% and 5.27%. The machining performance is comparable to wet machining.
KTH Royal Institute of Technology State of the Art
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6 Sharma et al., (2016) [31]
Dry, Wet, MQL and MQL+NF 1 wt.% TiO2
AISI 1040 steel Uncoated cemented carbide tools
Vc=96,7m/min f=0,1mm/rev d=1mm
NF reduced cutting force up to 62.67%, 34.88% and 35.85% compared to dry, conventional mist and wet machining, respectively. Tool wear up to 58.1% and 35.85%, compared to dry and conventional oil. The machining performance is comparable to wet machining.
7 Su et al., (2015) [32]
Dry, MQL and MQL+NF 0.1-0.5 wt% NanoGraphite
AISI 1045 steel Uncoated carbide tools
Vc=55/96mm/min f=0,1mm/rev d=1mm
The main cutting force with respect to dry cutting was 11 and 26 %, for the two selected cutting speeds. The maximum reduction of cutting temperature relative to dry cutting was 11.9 and 21% respectively for the different speeds.
8 Chetan et al., (2016) [33]
Dry, MQL and MQL+NF 0,1-10 wt.%Al2O3 and Ag
Nimonic 90 Nickel based alloy Multilayered carbide inserts
Vc=60 mm/min f=0,12mm/rev d=0,5mm
The smallest flank wear obtained was with the lowest flow and Al2O3 NF. Best surface quality also with Al2O3 in sunflower base oil.
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Table 4. Summary of MQL with NF with different nanoparticles literature for milling process.
Two flows were tested (20-40mL/h), not seeing a big difference. The reductions of the surface roughness were determined as 36,3% and 39,2% at 20 ml/h and 40 ml/ flow rates in nano MQL. The nano MQL method could reduce the tool wear by 16,8% and 19,9% at 20 ml/h and 40 ml/h flow
2 Sarhan et al., (2012) [35]
MQL and MQL+NF 0.2 wt% SiO2
Al 6061-T6 Aluminium alloy HSS with 2 flutes and 10 mm diameter
n=5000 1/min f=100mm/min d=5mm
The range of cutting force reduction is 40.22–42.13% compared to conventional oil. Power consumption analysis was also done obtaining a range of reduction of 40.22-42.13%.
3 Sayuti et al., (2014) [36]
MQL and MQL+NF 0.2-1 wt% SiO2
Al 6061-T6 Aluminium alloy HSS with 2 flutes and 10 mm diameter
n=5000 1/min f=100mm/min d=5mm
Protective thin films were developed on the feed marks of the machined surface providing much less friction and thermal deformation. Drastic reduction of cutting oil consumption using MQL+NF was recorded.
4 Sayuti et al., (2013) [37]
MQL and MQL+NF 0.5-1.5 wt% Carbon onions
Duralumin AL2017-T4 Aluminium alloy SEC-ALHEM2S8 end mill, 8 mm diameter
n=5000 1/min f=75,408-100mm/min d=5mm
The highest carbon onion concentration (1.5 %wt) produces the lowest cutting force and best surface quality. The cutting force and surface roughness reduction percentage are found to be 21.99 and 46.32 %.
5 Rahmati et al., (2014) [38]
MQL and MQL+NF 0.2-1 wt% MoS2
Al 6061-T6 Aluminium alloy Tungsten
n=5000 1/min f=100mm/min d=5mm
Machined surface quality was superior when NP of 0.5 wt% concentration. NP in the tool-workpiece
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carbide, 2 flutes and 10 mm diameter
interface enhanced the machined surface due tothe rolling, filling and polishing actions.
6 Rahmati et al., (2014) [39]
MQL and MQL+NF 0.2-1 wt% MoS2
Al 6061-T6 Aluminium alloy Tungsten carbide, 2 flutes and 10 mm diameter
n=8000 1/min f=2100mm/min d=5mm
Minimum cutting force with 1 wt.% and 30º nozzle angle. Minimum temperature with 0.5 wt.% and 30º nozzle angle. Best surface roughness with 0.5 wt.% and 60º nozzle angle. The best performance is found with air pressure of 4 bars.
7 Mao et al., (2013) [40]
MQL and MQL+NF (Grinding) 0.2-1 wt% MoS2
AISI 52100 Vc=31,4m/s f=0,05m/s d=0,01mm
The lubricating and cooling performance in the grinding zone are improved with the increase of the NP concentration. Not significant influence on the diameter of the NP.
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2.5 Previous work at KTH-IIP
Krajnik et al. [2] performed in 2016 experimental work at KTH-IIP laboratory, machining
experiments of MoS2 based nCLF in turning of hardened steel. Three cooling-lubricating
techniques were compared: flood cooling, MQL using vegetable-based soya bean oil and this base
oil enhanced with NP, 1% wt. MoS2, 10 nm co-axial nanotubes. The workpiece material is Toolox®
44, pre-hardened steel. The properties of this material will be explained in detail in experimental
methodology chapter, since it is the material selected for the current work
The machining experiments were carried out on a Swedturn 300 (SMT) CNC lathe machine.
Characteristics of metal-working process kept into consideration were tool wear evolution, tool
life, chip formation and temperature evolution (only for MQL and nCLF). Figure 19 shows the
evolution of tool wear vs. number of cuts for one measurement and three cooling techniques. It
can be observed that there is systematic reduction in evolution of flank wear each step of all three
measurements, for three lubrication methods. Also, there is apparent increase in tool life in nCLF
based lubrication method when compared with flood and MQL lubrication.
Figure 19. Tool wear vs. number of cuts [2].
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3 EXPERIMENTAL METHODOLOGY
3.1 Planning of the experiments
The experiments were focused in turning under dry, vegetable base oil for MQL and new
developed Nano-cutting fluids in CNC turning machine. The steps for running these experiments
are the following:
1. Problem statement. to investigate the potential of MQL technique and specially MQL
technique using Nano-cutting fluids in turning of two different materials, pre-hardened
steel (Toolox® 44) and grey cast iron (Scania case study).
2. Objectives. The main aim of this project is to measure different variables in the machining
process to prove the potential of this technology in different conditions. The secondary
aim could be study if this technology could be used as an alternative cooling technology in
industrial machining process.
3. Selection of the measurable variables. Considering which facilities were available in
KTH-IIP laboratory the influencing measurement variables were selected. Tool wear
mechanisms and tool life, surface roughness and cutting temperature will be measured.
4. Selection of the cutting parameters. This step of the planning was particularly important
since it affects directly to the succeed of the experimental work.
5. Experimental work. Execution of the experimental work, following the planned steps
and decisions.
6. Results and analysis. Analyse the collected variables and interpret the results. The
experiments were repeated to validate them and find repeatability.
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3.2 Experimental set-up
3.2.1 CNC turning-lathe machine
Turning experiments were conducted in CNC lathe turning machine SMT Swedturn 300 [41]. Each
experiment was repeated at least two times to avoid possible errors.
Table 5. General technical data SMT Swedturn 300 [41].
Some general definitions and formulas should be defined in order to understand the turning
process properly. Turning generates cylindrical and rounded forms with a singlepoint tool. The
tool is stationary with the workpiece rotating. Turning is the most common process for metal
cutting and is a highly optimized process, requiring thorough consideration of the various factors
in the turning application [42].
Some equations should be presented to comprehend turning process and to calculate subsequently
the cutting parameters [43]:
Max distance
spindlenose - ref.plane
Machine weight
(approx)
Spindle
drive
Number of
spindle speeds
1295 mm 8000 kg 40 kW Stepless
Figure 20. Schemetic and picture SMT Swedturn 300 [41].
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Cutting speed vc (m/min) 𝑣𝑐 =𝐷2×𝜋×𝑛
1000
Spindle speed n (rpm) 𝑛 =𝑣𝑐×1000
𝜋×𝐷2
Metal removal rate Q (cm3/min) 𝑄 = 𝑣𝑐 × 𝑎𝑝 × 𝑓𝑛
Machining time Tc (min) 𝑇𝑐 =𝑙𝑚
𝑓𝑛×𝑛
Cutting depth ap (mm) 𝑎𝑝 =𝐷1−𝐷2
2
Net power Pc (kW) 𝑃𝑐 =𝑣𝑐×𝑎𝑝×𝑓𝑛×𝑘𝑐
60×103
Table 6. Turning parameters.
Symbol Designation Unit
D1 Initial diameter mm
D2 Machining diameter mm
fn Feed per revolution mm/rev
ap Cutting depth mm
n Spindle speed rpm
Pc Net power kW
Q, MRR Metal removal rate cm3/min
Tc Machining time min
lm Machining length mm
ap
n
fn
Vc
Figure 21. Schematic diagram of turning operation and cutting parameters [43].
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3.2.2 Workpiece material
The metal cutting industry produces an extremely wide variety of components machined from
different materials. Each material has its own characteristics that are influenced by heat treatments,
alloying elements…
Therefore, workpiece materials have been divided into six groups according to ISO-standard.
Toolox® 44 is pre-hardened steel and its hardness value is 45 HRC. Regarding to the ISO-standard
this material should be part of two groups: ISO H and ISO P. Its hardness is 45 HRC, which is the
limit between hardened steel and usual steel.
• ISO H. Hardened steel is the smallest group of steels from a machining point of view.
This group contains hardened and tempered steels with hardness between 45 and 65 HRC.
The hardness makes them all difficult to machine. The material generates heat during
cutting and it is very abrasive for the cutting tool.
• ISO P. It is the largest of all the workpiece material groups. This group includes unalloyed
to high-alloyed materials, martensitic and ferritic stainless steel… The machinability of
these steels differs a lot depending of the properties of the material: hardness, carbon
content etc. [44].
• ISO K. Machining cast is completely different from machining steel, and there many
difference as well between the types of cast irons. All cast irons contain SiC which is very
abrasive for the tool.
Figure 22. Workpiece material groups [44].
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Toolox® 44
The first workpiece material used in this research is Toolox® 44 provided by the company SSAB.
Toolox® 44 is low-alloyed steel because its alloying elements are less than 5% in concentration,
around 3% indeed. (Table 7).
Toolox® is based on low-carbon concept, which provides low carbide concentration. The
inclusions (carbides in this case) make the steel difficult to machine. This is the reason why Toolox®
44 is easy to machine despite its hardness, and it has good stability during machining [45].
This material is delivered quenched and tempered at a minimum temperature of 590ºC. Toolox®
is not supposed to have more heat treatments, which could avoid expensive and risky heat
treatments. Toolox® is produced to rigorous quality standards, its potent mechanical properties are
measured and guaranteed [46]. The mechanical properties of this steel are summarized in Table 8.
Element C (%) Si (%) Mn (%) P (%) S (%) Cr (%) Mo (%) V (%) Ni (%)
% Wt. 0,32 0,6-1,1 0,8 max 0,001 max 0,003 1,35 0,8 0,14 max 1
Table 8. Mechanical and phyical properties of Toolox® 44 [46].
Mechanical properties at 20 ºC Physical properties at 20 ºC
Regarding to these properties, Toolox® has high toughness compared to other steels of similar
hardness (two or three times tougher). This high toughness ensures longer tool life and better
machinability [45]. Toolox® 44 is suitable for plastic moulding, rubber moulding and machine
components.
Department of Production Engineering at KTH have valuable experience in machining this pre-
hardened steel. Daghini and Nicolescu [47] have investigated the influence of inserts coating and
substrate on Toolox® 44 turning process. Tool life, tool wear, chips morphology and temperature
were measured using seven types of cutting inserts and different combinations of two coatings and
four substrates.
Table 7. Chemical composition Toolox 44 [46].
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Grey cast iron (Scania Case study)
The second material that is being tested is a Grey Cast Iron. This material is widely used in
automotive industry because it has very good antivibration properties. The chemical composition
of the material is shown in Table 9.
Table 9. Chemical composition of grey cast iron.
A typical chemical composition to obtain a graphitic microstructure is 2.5 to 4.0% carbon and 1 to
3% silicon by weight. Graphite may occupy 6 to 10% of the volume of grey iron. The presence of
graphite flakes makes the Grey Iron easily machinable as they tend to crack easily across the
graphite flakes. Grey iron also has very good damping capacity and hence it is often used as the
base for machine tool mountings.
The machinability of the grey cast iron is affected by variation in the surface composition, such as
free ferrite residues, which affects directly to the cutting process. The ferrite generates harder zones
in the metal, located randomly, and the graphite instead generates softer areas. This variations in
hardness could influence in the machinability of grey cast iron. In the tested material, to ensure its
machinability, the concentration of ferrite must be below 5%. The microstructure of it and the
hardness, which also affects highly to the machining behaviour are shown in Table 10.
Table 10. Hardness and microstructure of grey cast iron.
Element C (%) Si (%) Mn (%) P (%) S (%) Cr (%)
% Wt. 3-3,5 2 0,6-1 0,4-0,8 0,12 0,4-0,7
Hardness (HB) Microstructure
240-290
Ferrite<5%
Cementite <1%
Graphite (flakes) >90%
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3.2.3 Tooling system
Since in this project two different materials are being tested, also two tooling systems are necessary.
Toolox® 44
The tooling system chosen for this project is provided by the company Mircona AB, cutting inserts
and tool holder. Table 11 shows the ISO designation of these inserts. These cutting inserts are
designed for medium roughing to finishing of all types of steel and cast iron.
Table 11. Geometrical properties of the carbide inserts.
Regarding to the material, chosen inserts are cemented carbide inserts, with three coatings, coated
by the method of CVD (Chemical Vapour Deposition). Coated cemented carbides represent 80 to
90 % of the total of the cutting inserts [48]. These inserts are widely used because they give a good
combination of toughness and tool wear resistant.
The coatings are TIN, Al2O3 and TiCN. CVD coating process is more recommended for inserts
for turning, milling or drilling steels or grey-cast irons. The typical thickness of this type of coatings
is between 9 to 20 µm. The layers are generated by chemical reactions at temperatures between
700ºC to 1050ºC. PVD (Physical Vapour Deposition) process allows obtaining layers of 2-3 µm.
These coatings are used mainly in cutting difficult to machine materials, such as superalloys or
titanium alloys [49]. The benefits of the CVD-coatings types are summarized in Table 12. These
coatings are continuously being improved, trying to optimize the toughness, adhesion and wear
resistance.
Code DCMT 11 T3 08-PM7
D 55 º (Rhombic)
C Clearance angle 7º
M Tolerances
T Type of clamping
11 Insert size, d=9.52 mm
T3 Insert thickness, 3.18 mm
0.8 Corner radius 0,8mm
PM Medium pass
Figure 23. Cemented carbide inserts, DCMT 11 T3 08-PM7.
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Table 12. Benefits of insert coatings [54].
On the other hand, for the present study a specially designed tool holder is used. This MQL holder,
also designed by Mircona AB, allows to apply the lubricant with precision in the cutting zone. This
tool holder applies the oil internally [50]. Figure 24 shows the design of the tool holder utilized.
TiN coatings TiC Coatings Al203 Coatings
• Excellent build-up edge resistance
• Excellent wear resistance
• Excellent crater resistance
• Excellent on gummy materials • Effective at medium speeds
• Effective at high speeds and high heat conditions
• Excellent for threading and cut off operations
• Excellent on abrasive materials
• Makes it easy to identify what insert corners have been used
• Effective at lower speeds
Figure 25. Tool holder for MQL, Mircona AB..
Figure 24. Tool holder design for MQL, Mircona AB [8].
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Selected holder has two outlets to supply the oil. On top, 1 mm diameter hole, to supply oil to the
crater, and on the front relief, 1.5 mm one, to apply the oil in the cutting edge. The connection
between in hose and the tool holder in made with a tread of 1/8”, and a cylindrical hole of 5 mm
of diameter. To ensure that the system works properly in particularly important to seal all the
connections, to avoid oil and air leakage. It is also important to ensure that the oil is reaching the
cutting zone. For this purpose, the amount of oil supplied can be controlled.
Grey cast iron (Scania case study)
For the second part of the project, Scania case study, it was necessary to use a new tooling system.
This tooling system was provided directly by Scania, to reproduce the same process as it is being
carried out at their plant.
Cutting inserts used are oxide ceramics, a standard cutting material for turning cast iron and alloyed
cast iron with high standards for wear resistance [51]. These inserts were provided by Ceramtec
AB. Oxide ceramics are aluminium oxide based (Al2O3) with added zirconia (ZrO2) for crack
inhibition. The composition makes cutting inserts very resistance to tool wear but lacks of thermal
shock resistance [48].
Table 13. Geometrical properties of the ceramic inserts.
The tool holder suitable for these inserts is provided by Sandvik Coromant. This tool holder is
designed for machining under flood cooling conditions, or dry cutting, but it is not suitable for
MQL technology. Sandvik Coromant is already working with this technology, so they can
customize tool holders for MQL. But for running this second experimental part, instead of using
a fixed tool holder designed by Sandvik Coromant, a system designed at KTH-IIP was chosen.
Code DNMX 15 T07 12
D 55 º (Rhombic)
N Clearance angle 0º
M Tolerances
X Type of clamping
15 Insert size, d=12.7 mm
T07 Insert thickness, 7.94 mm
12 Corner radius 1.2mm
Figure 26. Oxide ceramic inserts, DNMX 15 T07 12.
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This new design allows to control the direction of the oil flow. The design has two nozzles. These
nozzles are made of 2 mm of internal diameter copper hoses. The decision of choosing the copper
is because it is flexible enough to be adjusted, but on the other hand it is stiff and resistant. The
tool holder with the design attached is shown in Figure 27.
One of the nozzles supplies the oil to the flank and the cutting edge, and the other directly to the
nose. In results and analysis section, the influence of the control of the direction of the oil flow
will be explained in detail.
The second challenge that appears while designing the experimental set-up for Scania case study
was the clamping. The workpiece material provided by Scania comes in the form of cylinders,
which poses a difficulty when clamping. The pressure that the clampers of the turning machine.
The pressure that the clampers of the chuck exert in the cylinders can break them. For this purpose,
two solid cylinders or bars were machined. The first one is made of aluminium alloy, and it is
introduced inside the cylinder, in the side of the chunk, to clamp it without damaging it. The
reason for choosing this material is that it is tough enough to withstand the pressure of the
clampers. The second one, machined in steel, is designed to fix the tailstock. Figure 28 shows the
clamping system used for the experimental work.
Workpiece rotation
Cylinder 1
Cylinder 2
Clampers
Figure 28. Clamping system for Scania Set-up.
Figure 27. MQL external supplier designed at KTH-IIP.
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3.3 Description of the MQL system
MQL is known a lubrication technique in which a small amount of oil is applied in form of mist
directly into the cutting zone. Actually, as it is explained in the state of art, this technique is
worldwide used in the metal working industry and it effectiveness is already proved.
There are many alternatives of MQL boosters available in the market, but the Swedish company
Accu-Svenska AB is a leader in this type of technology, offering in their catalogue high
performance MQL boosters, such as ECOLUBRIC® booster, that is the one chosen for this
project. The booster system provided by Accu-Svenska AB transports the lubricant-air mixture
through the machine tool, in order to reach the cutting edge of the tool [52].
The oil chosen for performing the first experiments is ECOLUBRIC® E200L, also provided by
Accu-Svenska AB. This lubricant is an economic and environment-friendly alternative for friction
reduction in industry. The lubricant is directly extracted from plants; this oil is pure vegetable-based
lubricant without any chemical modification. The properties of ECOLUBRIC® E200L are shown
in Table 14 [53].
Table 14. General properties of Ecolubric E200L [11].
Properties Description
Chemical description
Cold-pressed rapeseed oil without additives.
Health hazard The product is not harmful to health and involves no special hazards for humans or the environment
Appearance Liquid
Colour Yellowish
Smell Neutral
Melting point -18°C
Flash point 325°C
Density (20°C) 0,92g/cm3
Viscosity (20°C) 70 cP
Figure 29. Ecolubric MQL booster and Ecolubric E200L vegetable oil.
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Figure 30. MQL booster drawing and components list.
Figure 30 shows the schematic of the MQL Ecolubric booster system used for this research project. All the components are presented in the table in the right of the image.
1 oil and air (mist) outlet
2 oil refill
3 oil gauge
4 oil deposit
5 electric switch
6 air cleaner
7 handle
8 pressure gauge
9 electric plug
10 air connection
11 electric switch
12 electric plug
13 solenoid
14 mounting plate
15 oil pump
16 terminal
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3.4 Collection of the machining variables
The equipment available in the KTH-IIP laboratory used for this project will be described in the
following section.
3.4.1 Measurement of tool wear mechanisms and tool life
The wear in the cutting insert appears due to the friction between the tool and the workpiece. To
measure the evolution of the wear, optical microscope NIKON Optiphot 150 is used. The flank
wear and the crater wear are being measured.
DeltaPix Insight software has the option to calibrate the different magnifications and to create a
ruler and a scale to quantify the wear. Also, surfaces can be measured. The capture of the images
of the flank and the crater is done with a Delta Pix Invenio II microscope camera and analysed
with the DeltaPix InsIght proed by DeltaPix.
Figure 32. DeltaPix Insigtht software.
Figure 31. Microscope NIKON Optiphot 150.
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Wear on cutting edges
To understand the cutting process properly it is particularly important to study the different wear
mechanisms that occur in the cutting inserts and its causes.
a. Flank wear
Flank wear is the most common type and most desirable and predictive. It could cause bad surface
finish and bad tolerances in the workpiece. The variable that affects more to the presence of this
wear is the high cutting speed. This type of wear can be measured and quantified. The maximum
flank wear can be used as a limit for the end of the tool life. Flank wear occurs due to abrasion,
caused by hard constituents in the workpiece material [54].
b. Crater wear
This type of wear is located in the rake side of the cutting insert. It is usually caused by chemical
reactions between the workpiece material and the insert. Extreme crater wear could cause insert
breakage. It can be reduced decreasing the relation between cutting speed and feed (vc/fn). It is due
to chemical reaction between the workpiece material and the cutting tool and is amplified by cutting
speed [54].
c. Built-up edge
Material from the workpiece is welded into the cutting insert due to the high pressure. It is very
common in machining sticky and soft materials such as low carbon steel or aluminium. Low
machining speed increases the possibility to appear build-up edge. It occurs due to adhesion
processes.
d. Notch wear
Notch wear it is characterized by excessive damage localized in both the rake and the flank. The
damage appears at the depth of cut line. It usually appears in machining stainless steels and HRSA.
Cermets or Al2O3 coated inserts help to reduce this type of wear. It is caused by adhesion, pressure
welding of chips, and a deformation hardened surface [54].
e. Plastic deformation
Plastic deformation appears when the tool material is softened. High cutting temperatures are the
main cause. Harder grades or thicker coatings might be a solution. It could lead to premature chip
breakage.
f. Thermal cracks
Thermal cracks appear when there is fast variation in temperature. These cracks are perpendicular
to the cutting edge. This type of wear is related to interrupted cuts, and commonly appears in
milling operation. It can be avoided by using a tougher grade or controlling the cooling, using
abundant coolant or none at all.
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g. Insert breakage
It is usually the result of an overload mechanical tensile stresses. But it can also be due to many
other reasons such as wrong cutting parameters, inclusions in the workpiece material, vibrations,
built-up edge or excessive wear.
a b
c d
e f
g
Figure 33. Types of tool wear (a. Flank wear, b. Crater wear, c. Built-up edge, d. Notch wear, e. Plastic deformation, f. Thermal cracks, g.
Edge breakage) [55].
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Machining processes
The flank tool wear was measured in the machining experiments fixing the cutting time steps. Two
different procedures were follow for the two experimental set-ups. The maximum values of the
flank tool wear were measured after these defined cutting steps.
It was estimated a tool life of 15 minutes for the experiments with Toolox® 44 hardened steel. The
time of each cutting step was 90 seconds, so the flank wear was observed and measured under the
microscope every 90 seconds of continuous machining. In order to achieve this 90 seconds, the
cutting length has been adjusted for the different diameters of the round steel bar that was available.
On the other hand, the machining process for the grey cast iron was partially different. In this case,
since the objective was to compare the obtained results with real machining parts an equivalent test
specimen was defined.
Table 15. Test specimen equivalent cutting parameters.
Cutting paramenters 1 test specimen
Feed (mm/r) 0,3
Depth of cut (mm) 0,5
Cutting speed (m/min) 520
Spindle speed (rpm) 1210-1260
MRR (cm3/min) 78
Length of cut (mm) 50
Time (s) 7,9
Material removed (cm3) 10,3
0,5mm x 50mm
Equivalent to 1 test specimen
Figure 34. Cutting profile for grey cast iron machining experiments.
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3.4.2 Measurement of Temperature in the cutting zone
FLIR SC 640 supplies a combination of infrared and visible spectrum images of superior quality
and temperature measurement accuracy [55]. The purpose of the Infrared Camera in the Project is
to measure the evolution of the temperature in the cutting zone. The specification of the camera
FLIR SC 640 is shown in the Table 16.
Table 16. General specification on thermal infrared camera FLIR SC 640 [12].
The thermal camera FLIR SC 640 needs a software to analyse and collect the data. The software is
called ThermaCAM Researcher Professional. This software allows to extract temperature data in
and IR images and videos. Afterwards, to analyse and extract conclusions from the temperature
values, Matlab software is being utilized to filter and plot the results.
Specifications Thermal camera FLIR SC 640
Field of View (FOV) / minimum focus distance
24° x 18° / 0.3 m – 12° x 9° / 1.2 m – 45° x 34° / 0.2 m as an option
Spatial resolution 0.65 mrad for 24°lens – 0.33 mrad for 12° lens – 1.3 mrad for 45° lens
Thermal sensitivity 30 mK at 30°C
Electronic zoom 1-8x continuous including pan function
Electric and manual focus Auto and manual
Accuracy ± 2°C or ± 2% of reading
Temperature range -40°C to +1500°C (optional up to +2000°C)
Figure 35. Thermal infrared camera FLIR SC 640 [55].
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3.4.3 Measurement of the Surface Roughness
The surface roughness tester chosen for conducting the study is the Mitutoyo SJ-210 [56]. The
most significant value measured and analysed is Ra, arithmetical mean of the surface profile. The
surface roughness was measured three times in each workpiece after machining, and only the mean
values are presented in this report. The roughness standard selected was JIS’01.
Table 17. Specifications of Surface Roughness Tester Mitutoyo SJ-210 [56].
The surface roughness was measured for the Scania study case. In this case the workpieces were
removed every 21-equivalent test specimen, so the surface roughness was measured for different
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Following JIS 2001 standard Rz value is ten points mean roughness. This value is obtained from
the total of the mean value of each distance between the mean line and 5 peaks, Yp, from the
highest one, and the mean value of each distance between the mean line and the 5 valleys, Yv, from
the lowest one, of the roughness curve in a sample reference length “l”.
𝑅𝑧 =∑ 𝑌𝑝𝑖 + ∑ 𝑌𝑣𝑖5
𝑖=15𝑖=1
5
Root mean square surface roughness, Rq, is referred to as the sum of the squares of the individual
heights and depths from the mean line in a sample reference length “l”.
𝑅𝑞 = √1
𝑙∫ 𝑓2(𝑥)𝑑𝑥𝑙
0
Machining is usually the manufacturing process that determines the final geometry and dimension
and surface finish. The surface roughness of a machined piece is determined by geometric factors,
work material factors and vibration and machine tool factors. Within geometric factors there are
different parameters that determined the surface finish of a machined part [57]. They include:
• Type of machining operations.
• Cutting tool geometry, most importantly nose radius.
• Feed
Ra
Rz
Rq
Figure 38. Surface roughness profile and values, Ra, Rz and Rq for JIS 2001 standard [57]
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Type of machining operation refers to the process that generates the surface, turning in this case.
Tool geometry combined with feed from the surface geometry. The effects of the feed and
geometry of the cutting insert in surface finish can be seen in Figure 39.
The effect of the nose radius can be seen in Figure 39. (a). Keeping the feed constant, a larger nose
radius causes less pronounced feed marks, thus leading to a better surface roughness. If two feeds
are compared with the same nose radius, larger feed rate increase the separation between feed
marks, leading to an increase in the surface roughness Figure 39 (b). Higher end cutting edge angle
(ECEA) will also result in a higher surface roughness value Figure 39 (c).
The effects of nose radius and feed can be combined in an equation to predict the ideal average
roughness of a surface machined by a single point tool. This equation will be use in this project to
compare the theoretical value with the experimental one.
𝑅𝑎𝑖 =𝑓𝑛
2
32𝑁𝑅
Where Rai=theoretical arithmetic average surface roughness, (mm), fn=feed (mm/rev) and NR= nose radius
on the tool point (mm) [57].
Figure 39. Effect of geometric factors in determining the theoretical finish on a work surface for single-point tools: (a) effect of nose radius, (b) effect of
feed, and (c) effect of end cutting-edge angle [57].
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4 RESULTS AND DISCUSSION: TOOLOX® 44
The results and discussion section show the experimental values obtained after machining under
different cooling-lubrication techniques at KTH-IIP laboratory. As it was explained in the
experimental methodology section, while Toolox® 44 pre-hardened steel was machined, internal
MQL is being tested. The comparison was made under different conditions that will be explained
in detail in this chapter. At the beginning of the experimental work some troubles were found with
the experimental set-up that did not allow to extract any conclusion from the collected values.
After solving these problems, valuable results were obtained, and the performance revealed
encouraging potential of MQL technology for turning Toolox® 44. In order to show the potential
of MQL three machining variables are going to be measured: tool wear, temperature and tool life.
Chips shapes and colour is also analysed.
To analyse the tool wear properly the subsequent procedure was followed:
• Flank and crater picture were captured. The flank wear was measured using the software
mentioned in the experimental methodology section.
• Chips were collected for each cooling lubricating technique. The chips were analysed
visually, paying attention to the colour and the shape.
• Every insert was utilized twice, following the recommendations of the producer.
• The experiments under each cooling-lubrication strategy were repeated three times.
The most significant wear type that appears in coated carbide inserts is the flank wear. The criteria
selected to declare the end of the tool life is 0.3 mm of wear in the flank. During the experimental
work, other types of wear also appear and will be explained in this section.
4.1 Preliminary results
First experiments were carried out using various cooling strategies at a cutting speed of 110 m/min,
feed of 0.2 mm/rev and depth of cut of 0.5 mm, following the recommendations suggested for
the cutting inserts. The cutting parameters are shown in Table 19. The flow rate used for these
experiments was between 2 and 5 mL/h and 4 bars of air pressure. As it is explained in the previous
section, the machining time is fixed for these experiments, in this case 48 seconds of continuous
machining for each step.
Table 19. Cutting parameters, first experiments Toolox® 44.
Cutting parameters Value
Cutting speed 110 m/min
Feed 0.2 mm/rev
Depth of cut 0.5 mm
Machining time (1 step) 48 s
Flow rate 2-5 mL/h
Air pressure 4 bars
KTH Royal Institute of Technology Results and Discussion: Toolox® 44
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Figure 40 shows the evolution of the flank wear observed for dry machining in the steel that was
available in the laboratory. This material came from an old batch with an uncertain origin. The
repeatability in the dry machining results was quite high, after three experiments three tool lives
were recorded, 11.2, 10.4 and 12.8 mins. After these dry experiments, different lubrication
techniques started to be tested in the same Toolox® 44 round bar.
As soon as the second experimental work started the drawbacks begin to appear. The experiments
were repeated at least three times for each lubrication technique, but the dispersion that appeared
in the results was too high. Figure 41 shows some examples of tool wear evolution for the different
tested techniques. Some experimental work with a Nanofluid with wt. 1% of MoS2 nanoparticles
was also tried (MQL+NF in the graph). But as it is presented in Figure 41, the results were
unconcluded, because repeatability could not be extracted from the experimental outcomes.
After these troubling outcomes, the reasons to explain them began to be an objective. The first
idea was that the problem resided in the tooling system, that it was not appropriated for the material
and the selected cutting parameters. Mircona engineers were contacted and they came to IIP-KTH
laboratory to analyse the cutting parameters. They concluded that the cutting variables were
adequate for the experimental work. Secondly, the material was studied, looking for an explanation.
The hardness was measured, extracting the conclusion that there was a significant difference from
the outside of the piece to the core. This was the reason why new Toolox 44 round bar was bought,
4 m length and 160 mm of diameter. Once the new bar arrived, the second round of experiments
started. These results are presented in the following section.
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0 2 4 6 8 10 12
Fla
nk
wear
(mm
)
Machining time (min)
Dry 1
Dry 2
Dry 3
End of tool life
0
0,05
0,1
0,15
0,2
0,25
0,3
0,35
0 5 10 15 20
To
ol
wear
(mm
)
Machining time (mm)
End of tool life
MQL+Veg oil
Dry
MQL + NF
Figure 40. Flank wear vs. Machining time, first experiments Toolox® 44, dry machining.
Figure 41. Flank wear vs. Machining time, first unsuccessful experiments Toolox® 44, three lubrication techniques.
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4.2 Comparison between different lubrication techniques
Once new hardened steel bar arrived, the second round of experiments started. In this case, the
cutting parameters were selected to cut under extreme conditions, increasing the cutting speed up
to 120 m/min and extending the continuous machining time up to 100 seconds. Two depths of
cut were tested: 0.5 and 1 mm, finding significant differences between them that will be explicated.
The experiments for each cooling-lubricating technique were repeated three times to understand
the process completely and rely in the results. In Table 20 the cutting parameters are presented.
[57] M. P. Groover, Fundamentals of moder Manufacturing: Materials, Processes and Systems 4ed. 2010.
KTH Royal Institute of Technology Appendix A. Codes
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APPENDIX A. CODES
1. CNC Codes for turning operations
Toolox® 44
Channel 1: File name: MQLTEST
;Testing Toolox 44
;Cutting parameter
;v120 f0,2 d0,5-1
;Starting the experiment at D=150 L1=500
DEF REAL L1=139 ;Final diameter: external-cutting depth
DEF REAL L2=500 ;Length of the workpiece
N10 G54 G18 DIAMON
N11 TRANS X0 Z=L2 ;Change the origin of the workpiece
N12 T9D1
N20 G0 X=L1+10 Z10
N21 G0 Z5 ;Moving to the starting point
N22 G0 X=L1+5
N23 G96 F0.2 S120 M4 LIMS=3000
N24 G1 X=L1
N25 G1 Z-50 ;Finishing Z
N26 G1=L4+5
N27 GO X=L4+50
N28 M5
N29 G0 Z50
N40 M2
Channel 2: File name: MQLTEST
;Machining the chamfer before testing
DEF REAL L1=150 ;External diameter
DEF REAL L2=500 ;Length of the workpiece
N101 G54 G18 DIAMON
N102 TRANS X0 Z=L2 ;Change the origin of the workpiece
N103 T22 D1
N104 G0 X=L1+20 Z10
N105 G96 F0.15 S100 M4 LIMS=1000
N110 G0 Z5
N120 G0 X=L1+5
N130 G0 X=L1-4 Z1
N131 G1 X=L1+4 Z-3 ;Linear movement
N140 G0 X200 Z20
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N150 M5
N152 M2
Scania Case Study
Channel 2: File name: SCANIA2017
;Testing Scania cylinder liners
;Cutting parameter
;v550 f0,3 d0,5
;Definition of geometrical parameters
DEF REAL L1=306; Total length (longer than the cylinder itself)
DEF REAL L2=138; Machining diameter
;Moving to the starting position N100
N101 G54 G18 DIAMON
N102 TRANS X0 Z=L1
N103 T22 D1 ;Selection of tool number
N105 G0 Z-205
N106 G0 X=L2+5
;Start machining N110
N111 G6 F0.3 S550 M4 LIMS=1500
N112 G1 X=L2
N113 G1 Z-30
;Returning to initial position N200
N201 G1 X=L2+5
N202 G0 X=L2+80
N203 G0 Z20
N211 M5
M2
Channel 2: File name: SCANIA2017GROOVES
;Definition of geometrical parameters
DEF REAL L1=306 ;Total length (longer than the cylinder itself)
DEF REAL L2=138 ;Diameter of the cylinder
DEF REAL L3=138 ;Diameter of the groove
;Machining grooves
N101 G54 G18 DIAMON
N102 TRANS X0 Z=L1
N103 T23 D1 ;Selection of tool number
N104 G0 X=L2+20 Z10
N105 G0 Z-22 ;Starting Z
N106 GO X=L2+5
;First groove
N111 G96 F0.2 S300 M4 LIMS=1500
N112 G1 X=L2
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N113 G1 X=L3 Z-24
N114 G1 Z-27
N115 G1 X=L2 Z-29
N116 G1 X=L2+7
;Second groove
N121 G0 Z-79
N122 G1 X=L2
N123 G1 X=L3 Z-81
N124 G1 Z-84
N125 G1 X=L2 Z-86
N126 G1 X=L2+7
;Third groove
N131 G0 Z-136
N132 G1 X=L2
N133 G1 X=L3 Z-138
N134 G1 Z-141
N135 G1 X=L2 Z-143
N136 G1 X=L2+7
;Fourth groove
N141 G0 Z-193
N142 G1 X=L2
N143 G1 X=L3 Z-195
N144 G1 Z-198
N145 G1 X=L2 Z-200
N146 G1 X=L2+7
;Returning to initial position
N201 GO X=L2+60
N212 G0 Z20
N213 M5
M2
Channel 2: File name: SCANIA2017FIRSTFACING
;First facing
;Definition of geometrical parameters
DEF REAL L1=306 ;Total length (longer than the cylinder)
DEF REAL L2=139 ;Cutting diameter
N101 G54 G18 DIAMON
N102 TRANS X0 ZZ=L1
N103 T23 D1 ;Selection of tool number
N104 G0 x=l2+20 z10
N105 G0 Z-18 ;Starting Z
;Machining
N111 G96 F0.2 S300 M4 LIMS=1500
N112 G1 X=L2
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N113 G1 Z-205
N114 G1 X=L2
;Returning to initial position
N211 GO X=L2+20 Z20
N212 M5
2. Matlab Codes for Temperature Analysis
Extraction of one temperature measurement
clc clear all
%Extracting temperature data data=load('ImageMax10.irp'); a=size(data);
%Parameters x1=5;%Diference in temperature at the beginning of the machining x2=10; seg=8.5; %Number of seconds machining %Temperature vector T(:,1)=data(:,1)+0.001*data(:,2)-273.15;
%Time vector t=zeros(a(1),1); t(1)=0;
for i=2:(a(1)-1) aux=0.001*[data(i+1,4)-data(i,4)]; aux2=data(i+1,3)-data(i,3); t(i)=t(i-1)+aux+aux2; end
%Plotting all temperature values plot(t,T) grid on hold on xlabel('Time (s)') ylabel ('Temperature (ºC)')
%Extracting values for cutting time j=1; while([T(j+1)-T(j)]<x1) j=j+1; end aux3=j;
%Time from the raise of T lim=seg+t(aux3); aux4=lim/(t(2)-t(1));
aux4=round(aux4);
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t2=t(aux3:aux4); T2=T(aux3:aux4); mean1=mean(T2);
%Smoothing the curve 1 b=size(T2); if rem(b(1),2)==0 T3=sgolayfilt(T2,2,(b(1)-1)); else T3=sgolayfilt(T2,2,b(1)); end
%Deleting strange values u=1; for p=1:(b(1)-1) if(T2(p)<(T3(p)+5)&&(T2(p)>(T3(p)-5))) T4(u)=T2(p); t4(u)=t2(p); u=u+1; end end
Tm(1:a(1))=mean1;
%Cutting time calculation tcut=t(b(1))-t(1)
xmax=t(a(1)-1); ymin=min(T)-20; ymax=max(T)+20;
%Smoothing T4 c=size(T4); if rem(c(2),2)==0 T5=sgolayfilt(T4,2,(c(2)-1)); else T5=sgolayfilt(T4,2,c(2)); end
%Plotting xlabel('Time (s)') ylabel ('Temperature (ºC)') scatter(t,T,3); grid on hold on plot(t4,T4); hold on plot(t4,T5,'linewidth',3); xlim([0 xmax])
mean2=mean(T4) hold on
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Plotting multiple temperature curves %Plotting tool wear clc clear all
scatter(nc, DRY1,18,[1,0.6,0.2],'filled'); hold on plot(nc,DRY1,'LineWidth',0.5,'Color', [1,0.6,0.2],'LineStyle', '- -'); hold on grid on scatter(nc, DRY2,18,[0,1,1],'filled'); hold on plot(nc,DRY2,'LineWidth',0.5,'Color', [0,1,1],'LineStyle', '- -'); hold on scatter (nc, MQL2,18,[0,1,0],'filled'); hold on plot(nc,MQL2,'LineWidth',0.5,'Color', [0,1,0],'LineStyle', '- -'); hold on scatter (nc, NF1,18,[0,0,1],'filled'); hold on plot(nc,NF1,'LineWidth',0.5,'Color', [0,0,1], 'LineStyle', '- -'); hold on scatter (nc, MQL3,18,[1,1,0],'filled'); hold on plot(nc,MQL3,'LineWidth',0.5,'Color', [1,1,0],'LineStyle', '- -'); hold on
max=zeros(aux(1),1); max(:,1)=300; plot(nc,max,'Color',[1,0,0]); hold on
xlabel('N of test specimen'); ylabel('Tool wear (um)'); legend('DRY1','DRY1','DRY2','DRY2','MQL','MQL','NF','NF'); ylim([0 300]);
KTH Royal Institute of Technology Appendix B. Flank Wear Evolution