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TURNING MACHINABILITY
ASSESSMENT OF HARDENED
STEEL USING UNCOATED
CARBIDE
Md. Abdul Jalil
DEPARTMENT OF MECHANICAL ENGINEERING
DHAKA UNIVERSITY OF ENGINEERING & TECHNOLOGY, GAZIPUR
GAZIPUR-1700
ii
TURNING MACHINABILITY
ASSESSMENT OF HARDENED
STEEL USING UNCOATED
CARBIDE
A Project
By
Md. Abdul Jalil
Department of Mechanical Engineering
Dhaka University of Engineering & Technology, Gazipur
Gazipur-1700
March 2016
iii
TURNING MACHINABILITY
ASSESSMENT OF HARDENED
STEEL USING UNCOATED
CARBIDE
A Project
By
Md. Abdul Jalil
Submitted to the Department of Mechanical Engineering, Dhaka University of
Engineering & Technology, Gazipur, in partial fulfillment of the requirements for the
degree of MASTER OF ENGINEERING IN MECHANICAL ENGINEERING
Department of Mechanical Engineering
Dhaka University of Engineering & Technology, Gazipur
Gazipur-1700
March 2016
iv
The project titled “Turning Machinability Assessment of Hardened Steel Using
Uncoated Carbide”, submitted by Md. Abdul Jalil, Student No. 122301 (F) session
2012-2013, has been accepted as satisfactory in partial fulfillment of the requirements
for the degree of Master of Engineering in Mechanical Engineering on March 2, 2016.
BOARD OF EXAMINERS
1. Professor Dr. Md. Kamruzzaman
Professor
Chairman and
Supervisor
Department of Mechanical Engineering
DUET, Gazipur.
2. Professor Dr. Mohammad Asaduzzaman Chowdhury
Head
Member
(Ex-officio)
Department of Mechanical Engineering
DUET, Gazipur.
3. Professor Dr. Mohammed Alauddin Member
Professor
Department of Mechanical Engineering
DUET, Gazipur.
4. Prof. Dr. Md. Arefin Kowser Member
Professor
Department of Mechanical Engineering
DUET, Gazipur.
5. Prof. Dr. Mohammad Muhshin Aziz Khan Member
Professor
Department of Industrial & Production Engineering
Shahajalal University of Science & Technology (SUST)
Sylhet
(External)
v
Declaration
I do hereby declare that this work has been done by me and neither this project nor
any part of it has been submitted elsewhere for the award of any degree or diploma
except for publication.
Countersigned
Prof. Dr. Md. Kamruzzaman
Supervisor
&
Professor
Department of Mechanical Engineering
DUET, Gazipur.
Md. Abdul Jalil
vi
This Project work is dedicated to
My beloved
Parents
vii
TABLE OF CONTENTS
Table of Contents vii
List of Figures ix
List of Tables x
Notations xi
Acknowledgement xii
Abstract xiii
CHAPTER 1 INTRODUCTION 1
1.1 Introduction 1
1.2 Literature Review 9
1.2.1 Hard Turning 9
1.2.2 Dry Machining 11
1.2.3 Machining with conventional cutting fluids 12
1.2.4 Liquid Nitrogen Technology/Cryogenic Cooling 15
1.2.5 High Pressure Coolant 16
1.2.6 Minimum Quantity Lubrication 18
1.3 Summary of review 34
1.4 Scope of the Present Work 40
1.5 Objectives of the Present Work 41
CHAPTER 2 EXPERIMENTAL INVESTIGATIONS AND RESULTS 43
2.1 Introduction 43
2.2 Experimental Setup 45
2.2.1 Near Dry Lubrication System 45
2.2.2 Experimental Procedure and conditions 49
2.3 Experimental Methodology 52
2.4 Experimental Results 53
2.4.1 Cutting temperature 53
2.4.2 Machining Chips 57
2.4.3 Surface roughness 61
2.4.4 Dimensional Deviation 63
CHAPTER 3 EXPERIMENTAL RESULTS AND DISCUSSION 66
3.1 Machining Chips 66
viii
3.2 Cutting Temperature 70
3.3 Product Quality 74
CHAPTER 4 CONCLUSIONS AND RECOMMENDATIONS 78
4.1 Conclusions 78
4.2 Recommendations 79
REFERENCES 81
ix
LIST OF FIGURES
No. Description Page no.
Fig. 1.1 Classification of Near Dry machining. 19
Fig. 1.2 Fishbone diagram showing cause and effect in MQL assisted
machining.
20
Fig. 1.3 Distribution of Fabrication costs in engineering. 37
Fig. 2.1 Photographic view of the Near Dry Lubrication applicator 47
Fig. 2.2 Schematic view of the Near Dry Lubrication applicator 47
Fig. 2.3 Photographic view of air nozzle for near dry lubrication for
Supplying high velocity air
48
Fig. 2.4 Schematic view of the near dry jet issuing and impinging system. 48
Fig. 2.5 Photographic view of surface roughness measuring technique 51
Fig. 2.6 Variation of Chip-tool interface temperature with different cutting
speed and feed rates at 1 mm depth of cut by using uncoated
carbide under dry, wet and near dry condition during machining
hardened AISI 1060 steel.
54
Fig. 2.7 Variation of Chip-tool interface temperature with different cutting
speed and feed rates at 0.50 mm depth of cut by using uncoated
carbide under dry, wet and near dry condition during machining
hardened AISI 1060 steel.
55
Fig. 2.8 Variation of Chip-tool interface temperature with different cutting
speed and feed rates at 1 mm depth of cut under dry, wet and near
dry condition during machining of hardened AISI 1060 steel by
using uncoated carbide insert.
56
Fig. 2.9 Variation of Chip-tool interface temperature with different cutting
speed and feed rates at 0.50 mm depth of cut under dry, wet and
near dry condition during machining of hardened AISI 1060 steel
by using uncoated carbide insert.
56
Fig. 2.10 Variation of Chip Thickness ratio (rc) with different cutting speed
and different feed rate under different conditions at 1 mm depth
of cut by using uncoated carbide during machining of hardened
AISI 1060 steel.
60
Fig. 2.11 Variation of Chip Thickness ratio (rc) with different cutting speed
and different feed rate under different conditions at 0.50 mm
depth of cut by using uncoated carbide during machining of
hardened AISI 1060 steel.
60
Fig. 2.12 Variation of Roughness (Ra) with different cutting speed and
different feed rate under different conditions at 1 mm depth of cut
by using uncoated carbide during machining of hardened AISI
1060 steel.
62
Fig. 2.13 Variation of Roughness (Ra) with different cutting speed and
different feed rate under different conditions at 0.50 mm depth of
cut by using uncoated carbide during machining of hardened AISI
1060 steel.
63
Fig. 2.14 Dimensional deviation observed after one full pass turning of
hardened steel by SNMG insert with different depth of cut under
dry wet and near dry conditions.
65
x
LIST OF TABLES
No. Description Page no.
Table 2.1 Experimental conditions 50
Table 2.2 Comparison of chip shape and color at different speed and feed
at depth of cut 1 mm under dry, wet and near dry conditions
during machining of hardened AISI 1060 steel by SNMG
uncoated carbide insert.
57
Table 2.3 Comparison of chip shape and color at different speed and feed
at depth of cut 0.50 mm under dry, wet and near dry conditions
during machining of hardened AISI 1060 steel by SNMG
uncoated carbide insert.
58
Table 3.1 Percentage increment in chip thickness ratio (rc) 69
Table 3.2 Average percentage increment in chip thickness ratio (rc) 70
Table 3.3 Percentage reduction in chip-tool interface temperature (θ) 72
Table 3.4 Average percentage reduction in θ 73
xi
NOTATIONS
AISI American Iron and Steel Institute
BUE Built-up edge
CBN Cubic boron nitride
HPC High Pressure Coolant
HSM High speed machining
MQL Minimum quantity lubrication
MRR Material removal rate
NDL Near Dry Lubrication
NIOSH National Institute of Occupational, Safety and Health
V Cutting Speed
d Depth of cut
f Feed rate
θ Temperature
rc Chip Thickness ratio
Ra Surface Roughness
xii
ACKNOWLEDGEMENT
At first the author expresses his heartiest thanks to the Almighty for giving his the
patience and capability to bring this project in light. The author is deeply indebted to
Prof. Dr. Md. Kamruzzaman, Professor of the Department of Mechanical
Engineering, and Director (Student Welfare), DUET for his continuous guidance,
perpetual help, endless support, valuable suggestions and encouragement throughout
the progress of the project work.
He also wants to thank especially to the Head of the Department of Mechanical
Engineering for the help rendered for allowing and providing Machine Shop facilities
to carry out the experiment whenever required. The help extended by the Director
(Research and Extension) for providing research fund is highly acknowledged.
The author is highly thankful to Engr. Hasan Mohammad Quamruzzaman, Principal
of Patuakhali Polytechnic Institute, he is also thankful to Engr. Md. Kamruzzaman
Khan, Instructor & Head of Civil Technology of the same Institute for their support
in various stages of this project research work. Also expresses his heartiest thanks to
Engr. Goutam Panday who helped the author to make this project work a successful
one. The author is deeply indebted to his elder brother for providing mental strength
to continue the study smoothly. A special word of thanks is due to all the staff
members of Machine Shop for their helps in conducting the experimental work.
Finally, the author offer his sincere thanks to all those who either directly or
indirectly helped him in various ways to complete this project.
March, 2016 Author
xiii
ABSTRACT
High cutting velocity and feed in metal machining generates large amount of heat as
well as high cutting temperature which shortens the tool life by increasing tool wear,
and deteriorates the product quality. Use of cutting fluid reduce this high cutting
temperature is a common belief. The conventional cutting fluids are ineffective in
such high production machining even is mixed with extreme pressure additives.
Further, the conventional cutting fluids are not environmentally friendly because it
contaminates air, water and soil. Performance of machining operations can be
changed by the lubrication, cooling and chip flushing functions of cutting fluid.
Recycling and reuse of conventional cutting fluids are also problematic. In this
decade, with increased environmental awareness, the researchers are striving to
develop environmentally friendly machining technology; one such technology is to
use minimum quantity lubrication with cutting oil. Minimum quantity lubrication
(MQL) or Minimum volume of oil (MVO) or Near Dry Lubrication (NDL) machining
presents itself as a possible alternative for machining with respect to tool wear, heat
dissertation and machined surface quality. This research compares the mechanical
performance of dry cutting without coolant, soluble cutting fluid as conventional
application and soluble cutting fluid as NDL for the turning of hardened AISI 1060
steel using uncoated carbide based on experimental measurement of cutting
temperature, Chips form (chip shape, chip color and chip thickness ratio, rc), Surface
finish (Ra) and Dimensional deviation.
Compared to the dry and conventional turning, the use of cutting fluid as NDL leads
to reduce surface roughness, decrease dimensional deviation and lower cutting
temperature, while also having favorable chip tool interaction.
1
CHAPTER 1
INTRODUCTION
1.1 Introduction
The present and future manufacturing industries are required essentially to
address different challenges and needs, such as high production rate along with high
quality product and development of advanced materials, cost competitiveness and
environmentally friendly. The requirement of manufactured parts in terms of
complication, shape, material, size, etc. predictably enforces the manufacturing firms to
adapt new optimization strategies for the manufacturing processes, allowing the use of
latest manufacturing techniques. The part sequences in the manufacturing process are
generally diverse, and are directly linked to the part shaping process. Optimization
strategies can avoid or delete certain sequences, according to the initial shapes and the
necessary requirement of the final part. The actual optimization strategies aim at
increasing the productivity, quality, or the cost reduction by searching of optimal material
removal, improving machining accuracy, reduction of the number of operations and the
machining allowances and introducing of efficient and flexible sequences.
Producers of machined components and manufactured goods are continually
challenged to reduce cost, improve quality and minimize setup times in order to remain
competitive. Frequently the answer is found with new technology solutions. Such is the
case with grinding where the traditional operations involve expensive machinery and
generally have long manufacturing cycles, costly support equipment, and lengthy setup
2
times. The newer solution is a hard turning process, which is best performed with
appropriately configured turning centers or lathes [Noordin et al., 2007].
Machining is the broad term which describes the removal of material from a work
piece that typically involves the cutting of metals using different types of cutting speed,
feed and tools in which a tool removes material from the surface of a less resistant body.
The relative movement of the cutting speed, feed, tool and application of force and is
particularly useful due to its high dimensional accuracy, flexibility of process, and cost-
effectiveness in producing limited quantities of parts along with quality. The new
surfaces are break off from the work piece accompanied by a large consumption of
mechanical energy which in turn transformed into heat, leading to high temperature and
severe thermal conditions at the tool-chip interface due to removal of material in the form
of chips. The higher the tool-chip interface temperature, the faster the flank wears. The
cutting zone temperature reduces by its cooling effect, using of cutting fluids in the
machining processes and reduces the frictional heat generation due to its lubrication
effect. Also the cutting fluid serves is chip flushing or transportation of chips from the
cutting zone by the used / waste coolant stream.
Possibilities of controlling high cutting temperature in high production machining
by some alternative methods have been reported. Cutting forces and temperature were
found to reduce while machining steel with tribologically modified carbide inserts. High
pressure coolant injection technique was not only provided reduction in cutting forces
and temperature but also reduced the consumption of cutting fluid by 50%. Application
of CO2 in the form of liquid jet at high pressure also enabled some reduction in cutting
forces. Some works have recently been done on cryogenic cooling by liquid nitrogen jet
3
in machining and grinding some steel of common use. For the companies, the costs
related to cutting fluids represent a large amount of the total machining costs. Several
research workers state that the costs related to cutting fluids are frequently higher than
those related to cutting tools. Consequently, elimination on the use of cutting fluids, if
possible, can be a significant economic incentive. Considering the high cost associated
with the use of cutting fluids and projected escalating costs when the stricter
environmental laws are enforced, the choice seems obvious. Because of them some
alternatives has been sought to minimize or even avoid the use of cutting fluid in
machining operations. Some of these alternatives are dry machining and machining with
minimum quantity lubrication (MQL) and near dry lubrication (NDL) machining.
Manufacturers generally attempt to produce a product within the shortest possible
time keeping the cost of the product at a minimum level without affecting the quality of
the product as well. As, environmental regulations are being emerged and imposed, the
manufacturers are put to re-fabricate their manufacturing processes and reduce or
eliminate harmful chemicals, dusts and effluents associated with machining that can
deteriorate the environment. The harmful waste present in machining includes cutting
fluid, chip and worn out cutting tool.
The performance and service life of engineering component depends on their
material, dimensional or form accuracy and surface quality. The growing demand for
higher productivity, product quality and overall economy in manufacturing by machining
and grinding, particularly to meet the challenges of global cost competitiveness, insists
high material removal rate and high stability and long life of the cutting tools. But high
production machining with high cutting speed, feed, and depth of cut is inherently
4
associated with generation of large amount of heat and high cutting temperature. Such
high cutting temperature not only reduces dimensional accuracy but also impairs the
surface integrity of the product by inducing tensile residual stresses and surface and
subsurface micro cracks in addition to rapid oxidation and corrosion. In high speed
machining, conventional cutting fluid application fails to penetrate into the chip-tool
interface and thus cannot remove heat effectively [Paul et al., 2000]. Addition of extreme
pressure additives in the cutting fluids does not ensure penetration of coolant at the chip-
tool interface to provide lubrication and cooling [Cassin and Boothroyed, 1965].
Moreover, reaching to the boiling point conventional coolant vaporizes and makes a non-
conductive vapor barrier to enter the coolant effectively into the interface. With the
increase in cutting speed, feed and depth of cut this problem becomes acute and cooling
process become ineffective gradually.
The challenge of modern machining industries is mainly focused on the
achievement of high quality, in terms of work part dimensional accuracy and surface
finish, high production rate and cost saving, with a reduced environmental impact. High
temperature generated during machining at high cutting speed and feed results in high
tool wear, reduced tool life, poor surface finish and dimensional accuracy and larger
force is required for machining. The temperature generation during machining is an
important factor since it affects the thermally activated mass transport phenomena in the
cutting tool-work-piece contact zone. While primarily dependent on the cutting speed and
the work-piece material properties, the cutting temperature is also affected by the cutting
tool properties. Almost all of the mechanical energy in metal cutting is transformed into
heat. The major portion of the produced heat is conducted into and removed with the
5
chips from the cutting region with nearly the entire remaining portion conducted into the
workpiece and cutting tool. At such elevated temperature the cutting tool if not enough
hard may lose their form stability quickly or wear out rapidly resulting in increased
cutting force, dimensional inaccuracy of the product and shorter tool life [Kitagawa et
al., 1997]. On the other hand, high cutting temperature accelerates the growth of tool
wear and also enhances the chance of premature failure of the tool by plastic deformation
and thermal fracturing.
The temperature at the cutting tool interface is one of the important factors
influencing the machining process. The primary function of cutting fluid is cooling and
lubrication to avoid the high temperature effect on a machined surface. A secondary
function of cutting fluid is to flash away chips and metal fines from the tool/work piece
interface to prevent a finish surface from becoming marred and also to reduce the
occurrence of built-up-edge (BUE). The surface quality of the machined parts also
deteriorate with the increase in cutting temperature due to built-up-edge formation,
oxidation, rapid corrosion and induction of tensile residual stress and surface micro
cracks. Such problems become more acute and serious if the work materials are very
hard, strong and heat resistive and when the machined or ground part is subjected to
dynamic or shock loading during their functional operations. Therefore, it is essential to
reduce cutting temperature as far as possible.
When carbide tools were introduced with other new methods of machining, the
efficiency of the metal cutting operations improved to a certain extent under normal
cutting conditions. Presently the high temperature problems are tried to be eliminated by
reducing heat generation and removing the generated heat from the cutting zone by using
6
the combination of optimum machining parameters along with the work and tool material
and application of effective cutting fluid. The foremost process parameters in this case
are the cutting speed, feed rate and depth of cut. Some recent techniques have enabled
partial control of the machining temperature by using heat resistant tools like coated
carbides, PCD, CBN, PCBN etc. However, diamond and CBN tools are very expensive
and the practices in the industry are still not wide spread. Machining productivity can be
significantly improved by employing the right combination of cutting tools, cutting
conditions and machine tool that prop up high speed machining without compromising
the integrity and tolerance of the machined components.
Over a long period the manufacturers have been trying to reduce cutting
temperature by applying water soluble cutting fluid from overhead position. This type of
cutting fluid not only cools the tool and job but also provides lubrication and handles the
chip to clean the cutting zone and protects the nascent finished surface from
contamination by the gases(such as; oxygen) present in the atmosphere. But these
conventional types of coolants and the methods of their application surely have some
limitations.
In turning process, single-point cutting tool that is nothing but insert can
complete the entire machining process in a single fixture, thereby reduced setup times
as well as lower costs. Also there is many optional thing to improve the turning
process rather than grinding process. In recent there is big problem for all industrialist for
achieving high quality products with more productivity within less machining time which
affects on surface roughness during turning of hardened steel. Even rough surfaces
wear more quickly & have high friction coefficient than smooth surfaces. As the surface
7
roughness increases then customer demand & quality of product goes on decreasing. So
that there should be bridge between quality and productivity. In short there should be
such optimum condition on which tool wear rate is minimum & maximum productivity
with maximum quality within less time. Generally hard turning requires large quantities
of coolants and lubricants. The cost associated with storage and disposal of coolants and
lubricants increases the total cost of production considerably.
Conventional cutting fluid application fails to penetrate the chip-tool interface and
thus cannot remove heat effectively due to which there is loss of surface finish and also
loss of tool life. This cooling system, the cutting zone is often flooded with coolant
without considering the requirements of the specific process. Scientific investigations and
industrial applications have indeed shown that the type of coolant and its supply
influence the quality of product and tool life to a great extent. But in some cases,
application of cutting fluids is considered undesirable, especially in machining some
alloys and heat treated materials.
To overcome this problem there are some solutions. Some of these alternatives
are dry machining and machining with minimal fluid application. Dry machining is now
of great interest and actually, they meet with success in the field of environmentally
friendly manufacturing. However, they are sometimes less effective when higher
machining efficiently, better surface finish quality and serve cutting conditions are
required. Minimal fluid application refers to the use of cutting fluids of only a minute
amount typically of flow rate of 50 to 500 ml/hour. The concept of minimal fluid
application sometimes referred to as near dry lubrication or micro lubrication.
8
In the recent years a lot of work has been done to avoid the cutting fluids from the
production system. Dry cutting and semi-dry cutting such as Minimum Quantity
Lubrication (MQL) have been favored by the industry. Dry and near-dry machining
operations are the key technology of environmentally friendly manufacturing process.
The conventional flood supply system demands more resources for operation,
maintenance, and disposal, and results in higher environmental and health problems.
MQL machining has many advantages in this regard. [Weinert et al., 2004]. By
abandoning conventional cooling lubricants and using the technologies of dry machining
or Minimum Quantity Lubrication (MQL), this cost can be reduced significantly. In fact,
the cooling lubricant performs several important functions, which, in its absence, must be
taken over by other components in the machining process. For instance cooling lubricants
reduce the friction, and thus the generation of heat, and dissipate the generated heat. In
addition, cooling lubricants are responsible for a variety of secondary functions, like the
transport of chips as well as the cleaning of tools, work pieces and fixtures.
Most investigations of using MQL have been focused mainly on turning and
drilling operations. Most research has concluded positive effects to its lubrication ability.
Thus, the aim to evaluate the use of soluble cutting fluid and insoluble cutting oil through
the application of MQL technique when turning AISI 1040 steel using solid uncoated
SNMG tool.
9
1.2 Literature Review
It appears that the high temperature in cutting zone is the main problem and hence
methods were tried out over the years to tackle this problem. Application of proper
cutting fluids at times, reduced the above problems to some extent through cooling and
lubrication of the cutting zone. The commonly used fluids are neat oil, semi synthetic and
synthetic fluids with or without additives and inorganic salts. The application procedures
of these fluids are generally by flood cooling, or in the form of jet or even mist. Ample
research has been done in various directions and is still going on aiming improvement in
overall machining efficiency through controlling the aforesaid problems.
1.2.1 Hard Turning
Hard machining makes a major contribution to search flexibility during the
machining of hard alloys or high mechanical strength materials. In fact, intermediate
operations such, as grinding operations can be eliminated. This, in most cases, leads to
substantial cost reduction in manufacturing, and therefore hard turning operations are
developing wide applications in industry. In order to change from grinding to hard
turning, three levels of substitution can be recognized: the first level substitutes rough
grinding; the second level substitutes fine grinding; and the last level includes
substitution of the honing operation. The more grinding and honing can be substituted,
the greater are the benefits of hard turning. In order to accomplish this, it is necessary to
have good knowledge of the surface integrity created by hard turning [Michael
Jacobson, 2002].
10
Hard turning is an emerging technology that can potentially replace many
grinding operations due to improved productivity, increased flexibility, decreased capital
expenses, and reduced environmental waste. The ultimate aim of hard turning is to
remove work piece material in a single cut rather than a lengthy grinding operation in
order to reduce processing time, production cost, surface roughness, and setup time, and
to remain competitive. So hard turning is a developing technology that offers many
potential benefits compared to grinding, which remains the standard finishing process for
critical hardened steel surfaces. High material removal rate and relatively low tool cost
are some of the economical benefits. To increase the implementation of this technology,
questions about the ability of this process to produce surfaces that meet required surface
finish and integrity requirements must be answered. Additionally, the economics of the
process must be justified, which requires a better understanding of tool wear patterns and
life predictions. The potential economic benefits of hard turning can be offset by rapid
tool wear or premature tool failure if the brittle cutting tools required for hard turning are
not used properly. Even steady, progressive tool wear can result in significant changes in
cutting forces, residual stresses, and micro-structural changes in the form of a rehardened
surface layer (often referred to as white layer) [Kevin Chou et al., 2003].
Precision hard turning applications have increased drastically in manufacturing
industry because it potentially provides an alternative to conventional grinding in
machining hardened components. This new technology significantly reduces the
production time, tooling costs and the capital investment, especially for low volume
production. Koning et al. [1993] also presented that turning of hardened steels have been
an attractive alternative to costly, yet environmentally harmful, grinding processes.
11
Benefits of hard turning over grinding have been reported including short cycle time,
process flexibility, part longevity, and less environmental impact. Scientific and
engineering issues of hard- turning, been frequently investigated, range from cutting
mechanics, tool wear surface integrity, to part accuracy [Davies, M.A., Chou et al.,
1996].
1.2.2 Dry Machining
Dry machining has been around for as long as traditional machining and
ecologically desirable. It will be considered as a necessity for manufacturing enterprises
in the near future and dry machining to enforce environmental protection laws for
occupational safety and health regulations. The advantages of dry machining include:
non-pollution of the atmosphere (or water); no residue on the swarf which will be
reflected in reduced disposal and cleaning costs; no danger to health; and it is non-
injurious to skin and is allergy free.
Dry machining is great interest and actually, they meet with success in the field of
environmentally friendly manufacturing. In reality, however, they are sometimes less
effective when higher machining efficiency, better surface finish quality and severe
cutting conditions are required. For these situations, semi-dry operations utilizing very
small amount of cutting lubricants are expected to become a powerful tool. Moreover, it
offers cost reduction in machining. Due to dry machining more heat is generated during
the machining process and without the coolant effect, it cannot be as efficiently removed
from the interface of the tool and the work piece. The dimensional accuracy is not as
good during dry machining because of the high temperature produced. Surface finish can
12
also be negatively affected. The increase in temperature increases the ductility of the
metal, changing the formation of chips [Klocke et al., 2006].
1.2.3 Machining with conventional cutting fluids
The primary function of cutting fluids is to reduce this cutting temperature and
increase tool life. In addition the cutting fluid has a practical function as a chip-handling
medium. Cutting fluids also help in machining of ductile materials by reducing or
preventing formation of a build-up-edge (BUE), which degrades the surface finish.
Conventional machining prevails [Ekinovic et al., 2005] plastically deformation in
generating chips whereas in high speed machining chip generation is followed by
segmentation process. Usually the high cutting temperature is controlled by profuse
cooling [Alaxender et al., 1998]. But such profuse cooling with conventional cutting
fluids is not able to solve these problems fully even when employed in the form of jet or
mist. With the advent of some modern machining process and harder materials and for
demand for precision machining, the control of machining temperature by more effective
and efficient has become extremely essential. Generally, suitable cutting fluid is
employed to reduce this problem through cooling and lubrication at the cutting zone. But
it has been experienced [Cassin ans Boothroyed, 1965] that lubrication is effective at
low speeds when it is accomplished by diffusion through the work piece and by forming
solid boundary layers from the extreme pressure additives, but at high speeds no
sufficient lubrication effect is evident. The ineffectiveness of lubrication of the cutting
fluid at high speed machining is attributed [Shaw et al., 2005] to the inability of the
13
cutting fluid to reach the actual cutting zone and particularly at the chip-tool interface due
to bulk or plastic contact at high cutting speed.
Most of the energy generated in the plastic deformation converts into heat, which
causes the temperature rise in the primary deformation zone. However a small amount of
heat transfer occurs between the work piece and tools due to very short time of the
deformation. Thus the temperature can be localized in some areas of chips. This
deformation and temperature localization will increase with increasing cutting speed.
Since vast amount of heat is generated during high speed machining, low pressure
conventional cutting fluid is vaporized due to high temperature when it comes in contact
with the work-tool-chip interface, makes a barrier (film).That’s why no cutting fluid
reach in the tool-chip interface or cutting zone [Ezugwu, 2004]. The film boiling
temperature of conventional cutting fluid is about 3500 [Ezugwu and Bonney, 2003].
The use of cutting fluids on machining operations has been questioned, due to problems
they may cause to the environment, due to damage to human health and also more due to
the severe laws regarding industrial waste that have been passed.
High machining of metal inherently generates high cutting zone temperature
causes dimensional deviation and premature failure of cutting tools. The application of
cutting fluid during machining operation reduces cutting zone temperature to prevent
overheating and increases tool life acts as lubricant as well. It reduces cutting zone
temperature either by removing heats as coolant or by heat generation as lubricant. It is
believed that heat is carried away from the tool and the work by means of cutting fluid
which at the same time reduce the friction between the tool and the chip and work and
also facilitates the chip formation.
14
The use of cutting fluids on machining operations has been questioned, due to
problems they may cause to the environment, due to damage to human health and also
more due to the severe laws regarding industrial waste that have been passed. Therefore,
industries are being forced to review the production processes aiming either, at
elimination or when it is not possible a sharp reduction in the use of these fluids. The
conventionally applied cutting fluid can do this job properly at normal cutting conditions
where the feed and depth of cut are very low. But the main problem with conventional
coolant is that it does not reach the real cutting area. In case of ductile material and under
high speed-feed condition conventionally applied coolant is completely ineffective to do
so as the bulk and progressive contact between tool face and the flowing chips cannot
allow the coolant to enter into the interface where maximum temperature attains.
Moreover water soluble coolant is a major source of environmental pollution, soil
contamination and carrier of bacteria borne diseases like lunch cancer, dermatitis and
others. Cutting fluids are important causes of occupational contact dermatitis which may
involve either irritant or allergic mechanisms. Water mixed fluids generally determine
irritant contact dermatitis, allergic contact dermatitis when they are in touch with workers
skin. Cutting fluids are widely used to reduce the cutting temperature. But the major
problems associated with the use of conventional methods and types of cutting fluids,
which are mostly oil based, are;
i. Ineffectiveness in desired cooling and lubrications.
ii. Health hazards due to generation of obnoxious gases and bacterial growth.
iii. Inconvenience due to un-cleanliness of the working zone.
15
iv. Need of storage, additional floor space, pumping system, recycling and
disposal.
v. Corrosion and contamination of the lubricating system of the machine
tools.
vi. Environmental pollution and contamination of soil and water.
The disposal of used chemical coolants involves incineration and partially
contributes to global warming. Also use of flood coolants does not inhibit the air
boundary layer and a protocol was made for further investigation of coolant flow
mechanism. The presence of chemical substances like sulfur, phosphorous, chlorine or
any other extreme pressure additives in the coolant introduces health hazard to the
operator. Skin exposure is the dominant route of exposure and it is believed that about 80
percent of all occupational diseases are caused by skin contact fluids.
1.2.4 Liquid Nitrogen Technology/Cryogenic Cooling
One solution to the problem of cutting fluid management currently under
development is the use of liquid nitrogen as a coolant and lubricant. The small flow rate
of liquid nitrogen makes this technique a very attractive alternative. There is no cutting
fluid to dispose as the nitrogen evaporates harmlessly into air. Reportedly, tool life and
finish quality are also improved by this technique due to high reduction of the tool-chip
interface temperature [Dhar et al., 2002]. But liquid nitrogen is hazardous to workers due
to its extremely low temperature. Exposure can result in mild to extreme frostbite.
Nitrogen that is stored in a sealed vessel will increase in pressure dramatically as it
warms, potentially resulting in a non-combustion explosion. Large spills can displace all
16
of the oxygen in a room in a short time. However, when proper equipment and handling
technique are used nitrogen is a very safe and environmental friendly alternative.
1.2.5 High Pressure Coolant
Coolants are used to reduce the amount of heat and friction at the point where a
tool cut into a metal work piece. This heat reduction allows the cutting tool to operate at
higher speeds and reduces tool wear. However, at the lower pressures typically used to
deliver cutting fluid, the coolant cannot effectively remove the majority of heat at the
cutting point because it does not reach the real cutting interface. Instead the coolant
washes over the tool holder and work piece, cooling the surfaces somewhat, but not
removing the intense heat within the cutting area, itself. In fact most of this heat is
conducted to the material around the shear zone and to the tooling. Thus the temperature
at the cutting point keeps higher than desired. By directing the coolant stream more
precisely and with the optimum amount of pressure and flow rate, more heat can be
removed dramatically. High pressure assisted cooling is one of the preferred
technologies, currently under exploitation especially in the aerospace and power plant
industries for machining exotic materials. The creditability of high-pressure coolant
assisted machining had been thoroughly investigated over the years [Ezugwu and
Bonney, 2004; Dhar et al., 2006 and Kamruzzaman, 2008]. This system not only
provides adequate cooling at the tool-work-piece interface but also provides an effective
removal (flushing) of chips from the cutting area. The coolant jet under such high-
pressure is capable of creating a hydraulic wedge between the tool and the work-piece,
penetrating the interface deeply with a speed exceeding that necessary even for very high
17
speed machining. The high-pressure coolant stream helps to break up chips and remove
them from the cutting zone area more effectively. The combination of reduced heat and
more efficient evacuation of chips prolong tool life and makes replacement more
predictable because the cutting tool wears out naturally, rather than failing prematurely
because of excessive heat or chip damage. Properly applied high-pressure coolant allows
users to achieve maximum performance. The coolant jet under such high-pressure is
capable of creating a hydraulic wedge between the tool and the work piece, penetrating
the interface deeply with a speed exceeding that necessary even for very high speed
machining. This phenomenon also changes the chip flow conditions [Kovacevic et al.,
1994]. The penetration of high- energy jet at the tool-chip interface reduces the
temperature gradient and minimizes the seizure effect, offering an adequate lubrication at
the tool-chip interface with a significant reduction in friction. It was found about the
performance of high-pressure coolant jet on grind ability of steel [Dhar et al., 2006]
based on the experimental results that high-pressure coolant jet reduces grinding zone
temperature significantly due to effective cooling and lubrication at the grinding zone
area. HPC grinding yields to less significant lamellar chips can be found due to change in
feed rate.
18
1.2.6 Minimum Quantity Lubrication
In MQL process, oil is mixed with high-pressure air and the resulting aerosol is
supplied near to the cutting edge. This aerosol impinges at high speed on the cutting zone
through the nozzle. Air in the aerosol provides the cooling function and chip removal,
whereas oil provides lubrication and cooling by droplet evaporation. The flow of
lubricant in MQL process varies from 10 to 100 ml/h and air pressure varies from 4 to 6.5
Kg/cm2 [Silva et al., 2005]. Different ranges for flow rate were also reported in literature
such as 50 to 500 ml/h [Dhar et al., 2006a] and 2 to 300 ml/h [Zhong et al., 2010].
However, in industrial applications consumption of oil is approximately in the range of
10-100 ml/h [Kamata and Obikawa, 2007]. When the flow rate of cutting fluid in MQL
is less than or equal to 1 ml/h it is termed as Micro-Liter Lubrication (μLL) [Obikawa et
al., 2008; Liu et al., 2011]. As the quantity of cutting fluid in MQL is very less (in ml/h
instead of l/min) in comparison to flood cooling, the process is also known as Near Dry
Machining. If oil is used as fluid medium in NDM, better lubrication is obtained with
slight cooling effect whereas, when emulsion, water or air (cold or liquid) were used,
better cooling is achieved with slight/no lubrication so, the processes were termed as
Minimum Quantity Lubrication and Minimum Quantity Cooling respectively [Weinert
et al., 2004; Tawakoli et al., 2010]. NDM can be classified on the basis of method of
aerosol spray and aerosol composition as shown in Fig. 1.1. Detailed description is
available with Astakhov, 2008.
In MQL, cooling occurs due to convective and evaporative mode of heat transfer
and thus is more effective than conventional wet cooling in which cooling occurs due to
convective heat transfer only. In addition, cutting fluid droplets by virtue of their high
19
velocity penetrates the blanket of vapor formed and provides more effective heat transfer
than wet cooling [Varadarajan et al., 2002]. However, according to Astakhov [2008]
aerosols do not acts as lubricants or boundary lubricants as they do not have access to the
tool-chip and tool-work-piece interfaces due to too low penetration ability. In addition,
the cooling action due to droplet evaporation is also small due to very small flow rate of
oil. MQL action on forming chip is also negligibly small as compared to high pressure
water soluble metal working fluids due to low mass of aerosol. Astakhov [2008]
suggested that the application of MQL enhances the rebinder effect and thus reduces the
work due to plastic deformation.
Fig. 1.1 Classification of Near Dry machining [Astakhov, 2008; Weinert et al., 2004]
20
Possible parameters and machining conditions affecting the performance of MQL
assisted machining are illustrated in fishbone diagram as shown in Fig. 1.2. As little
quantity of cutting fluid was utilized in MQL process, the cutting fluid should possess
significantly higher lubrication qualities than mineral oil. Vegetable oil and synthetic
ester oil are two viable alternatives. Vegetable oils are nontoxic as they are based on
extract from plants. Molecules of these oils are long, heavy and dipolar in nature and
provides greater capacity to absorb pressure.
Fig. 1.2 Fishbone diagram showing cause and effect in MQL assisted machining
Higher viscosity index provides stable lubrication in operating temperature range
and higher flash point provides opportunity to increase metal removal rate due to reduced
smoke formation and fire hazard [Krahenbuhl, 2002]. Wakabayashi et al. [2006]
introduced some synthetic esters, synthesized from a specific polyhydric alcohol. These
synthetic esters have high biodegradability, excellent oxidation stability, good storage
21
stability, and satisfactory cutting performance. Investigated synthetic esters were
suggested as satisfactory MQL cutting fluid on the basis of cutting performance and
optimal fluid for MQL machining on the basis of biodegradability, oxidation and storage
stability.
Some studies reported that application of MQL results in zero airborne mist levels
as the oil mist either vaporizes or clings to the work-piece or chips [Dasch and Kurgin,
2010]. However, Dasch and Kurgin [2010] found MQL mist level comparable to wet
application and proportional to the volume of oil entering the system. So, mass
concentration and particle size as well as composition and physical state of mist requires
serious attention. Advantages of MQL assisted machining are: fluid supplied to the
cutting tool is consumed at once so there is no need of fluid monitoring, maintenance or
disposal, reduction in solid waste by 60%, water use by 90%, and aquatic toxicity by 80%
due to delivery of lubricants in air instead of water [Clarens et al., 2008]; decreased
coolant costs due to low consumption of cutting fluid; reduced toxicity and hazardous
effects as mostly vegetable oils are used which are nontoxic and biologically inert [Khan
et al., 2009]; reduced cleaning cost and time due to low residue of lubricant on chip, tool
and work-piece, better visibility of cutting operation [Attansio et al., 2006].
Turning of AISI 52100 hardened steel was studied Diniz et al. [2003] using TiN
coated CBN inserts under dry cutting, wet cutting and minimum volume of oil (MVO).
Mostly similar values of flank wear and surface roughness were obtained with dry and
MVO cutting. Values of flank wear and surface roughness were always found better than
wet cutting. Based on study, dry cutting was concluded as the best technique for turning
22
of this material. The better performance of dry cutting was attributed to increased cutting
zone temperature that caused easier deformation and shearing of chip, reduced cutting
forces and vibration, and reduced tool wear. Attansio et al. [2006] studied tool wear in
finish turning of 100Cr6 normalized steel pieces under MQL and dry cutting conditions
using triple coated carbide tip (TiN outer layer, Al2O3 intermediate layer and TiCN inner
layer). MQL was applied on rake and flank face of the tool at constant cutting speed of
300 m/min and depth of cut of 1 mm, and at feed rate of 0.2 and 0.26 mm/rev with
cutting length of 50 mm and 200 mm. Equal or greater mean removed material was
reported with flank MQL as compared to dry and rake MQL. Tool life decreased with
feed rate in all cutting conditions however the tool life obtained in flank MQL was
highest. Tool life increases in flank MQL with increase in cutting length whereas it does
not influence tool life in dry and rake MQL. In rake MQL, lubricant was not able to reach
the cutting area as no elements indicating compounds from lubricant were seen on worn
surface of tool tip. Tool wear and surface roughness of AISI-4340 alloy was studied by
Dhar et al. [2006b] with uncoated carbide insert under MQL conditions. Principal flank
wear and auxiliary flank wear were selected to study the tool wear as former affects the
cutting force, and latter affects the surface finish and dimensional deviation. Reduced tool
wear and improved surface finish was achieved with MQL as compared to dry and wet
machining mainly due to effective reduction in cutting temperature.
In another study on same alloy, chip tool interface temperature and dimensional
deviation were also monitored along with surface roughness and tool wear. At low
cutting speeds the chip makes partially elastic contact with the tool but with increase in
cutting speed chip makes fully plastic or bulk contact with the rake face of the tool. So, at
23
low cutting speeds more effective cooling was observed as MQL was dragged due to
capillary effect in the elastic contact zone. While, at high cutting speed less reduction in
cutting temperature was observed due to reduction in time to remove accumulated heat
and due to fully plastic or bulk contact preventing the MQL to reach the hot chip-tool
interface. Decrease in feed improves the cooling effect to some extent particularly at low
cutting speed possibly due to slight lifting of the thinner chip. About 5 to 10% decrease in
average cutting temperature was recorded depending upon the level of cutting speed and
feed rate. Reduced dimensional deviation with machining time was observed with MQL
as compared to that in dry and wet turning [Dhar et al., 2007]. Rahman et al. [2009]
reported about 5 to 10% reduction in average cutting temperature in MQL turning of
AISI 9310 alloy depending upon the levels of cutting speed and feed.
In MQL turning of AISI-1040 with uncoated carbide, MQL jet was targeted on
the rake and flank face of the auxiliary cutting edge to achieve better dimensional
accuracy. With MQL application the cutting temperature is effectively reduced and blue
colored spiral shaped chips produced under dry and wet conditions became metallic
colored and half turn. Also the back surface of chip under MQL is much brighter and
smoother indicating the favorable chip tool interaction and elimination of built–up edge
formation. Reduced value of chip compression ratio and improved dimensional accuracy
was also achieved with MQL [Dhar et al., 2006a]. Similar improved results were also
reported in MQL turning of AISI-9310 and AISI-1060 alloy by using vegetable oil-based
cutting fluid [Khan and Dhar., 2006; Khan et al., 2009]. Physics based models for
MQL was developed by Li and Liang [2007] to predict the cutting temperature, cutting
force, tool wear and aerosol generation rate.
24
The models were validated with the experimental results obtained in turning of
AISI 1045 material. MQL was supplied on the flank face of the tool by a 0.762 mm
diameter opening in the tool holder. Cutting forces for MQL are found smaller than dry
cutting but higher than wet cutting. At lower cutting speeds lubrication was effective but
at high cutting speed (228.75 m/min) ineffective lubrication was observed. MQL was
most effective in reducing the tangential cutting force among the cutting force
components. MQL also reduced the cutting temperature for the entire range of speed and
provided a lower wear rate in comparison to dry cutting. However, it was expected that
MQL will generate more cutting fluid aerosol than flood cooling due to splash
mechanism. Tasdelen et al. [2008] investigated the affect of different cooling techniques
such as MQL, compressed air and emulsion on tool chip contact length in turning of
100Cr6 steel with different engagement times of inserts. Lower contact lengths were
observed with MQL and compressed air as compared to dry cutting. However, emulsion
assisted cutting provided the shortest contact length. For long engagement times, MQL
and compressed air have same contacts lengths, as the cooling effect was mainly from air
constituent in aerosol. For short engagement times, lubrication effect of oil drops
decrease the friction in the sliding region and overcomes the cooling effect resulting in
shorter contact lengths than compressed air. Also at short engagement times, increase in
quantity of oil decreases the contact length. More up curled chips were obtained with
emulsion than MQL and air assisted cutting. Chips obtained from MQL and compressed
air have almost same radius of curvature. Whereas, chips obtained from dry cutting have
largest radius of curvature. Chips obtained in dry cutting were wider than the chips
obtained with other methods due to side flow in the shear plane and have side curl due to
25
difference in speed at outer and inner diameter of work-piece. Shorter contact lengths
were observed with TiN coated tool due to different friction and temperature distribution
in the cutting zone. Effect of oil drops were found even at reduced engagement time for
TiN coating than uncoated carbides. On the basis of study it was concluded that for short
engagement time machining MQL is very suitable.
A study was conducted by Hwang and Lee [2010] to predict the cutting force and
surface roughness and to determine the optimal combination of cutting parameters in
turning of AISI 1045. To determine the significant parameters among supplied air
pressure, nozzle diameter, cutting speed, feed rate and depth of cut a two level fractional
factorial design is employed. It was reported that except supplied air pressure all the
parameters significantly affected the surface roughness. Models are then developed for
prediction of cutting speed and surface roughness in MQL and wet turning using Central
Composite Design. From the validation experiment cutting force equations are found
valid whereas surface roughness equations were not appropriate for accurate prediction.
The mismatch in experimental and predicted values was attributed to uncontrolled
parameters such as work material defect, lathe vibration and measuring errors. Nozzle
diameter of 6 mm, cutting speed of 361 m/min, feed rate of 0.01 mm/rev and depth of cut
of 0.1 mm were found optimal for MQL turning whereas nozzle diameter of 6 mm,
cutting velocity of 394 m/min, feed rate of 0.02 mm/rev and depth of cut of 0.1 mm were
found optimal for wet turning considering surface roughness and cutting forces
simultaneously. MQL turning was found to be more advantageous than wet turning when
only surface roughness and cutting forces were considered.
26
The cutting fluids are used in machining processes to improve the characteristics
of tribological processes, which are always present on the contact surfaces between tool
and work pieces. Due to several negative effects, a lot of works have been done in the
recent past years to minimize or even completely avoid the use of cutting fluids [Sokovic
and Mijanovic, 2001]. A number of attempts were made in the past to improve
cooling/lubrication in high speed machining and in the case of machining of difficult -to-
machine materials by the use of a minimum quantity lubricant jet to overcome these
problems. The results achieved by these investigators were very encouraging
[Wakabayashi et al., 1998; Suda et al., 2004; McCabe and Ostaraff, 2001]. Cutting
forces were reduced, chip shape, surface quality and tool life improved, thereby
increasing the metal removal rate and improving the overall performance of the
machining operation. In particular, Minimum Quantity Lubrication (MQL) machining
has already played a significant role as successful near-dry machining in a number of
practical applications [Sutherland et al. 2000; Rahman et al., 2002]. Minimum
Quantity Lubrication (MQL) in machining is an alternative to completely dry or flood
lubricating system, which has been considered as one of the solutions for reducing the
amount of lubricant to address the environmental, economical and mechanical process
performance concerns [Heinemann et al., 2006]. The concept of MQL sometimes
referred to as near dry machining that is based on the principle of total use, without
residues, applying lubricant between 10 to 100 ml/h at a pressure from 4 to 6.5 Kg/cm2
[Silva et al., 2005]. The minimum quantity lubricants have the advantages of advanced
thermal stability and lubricating capability over conventional cutting fluids. In this
technology, the lubricating function is ensured by the oil and the cooling function is
27
provided mainly by the compressed air. From the viewpoints of environment, safety,
health, performance and cost, the vegetable based oils are considered as alternatives to
petroleum-based metalworking cutting fluids because of its high biodegradability, high
viscosity indexes and good thermal stability. The vegetable-based oils could produce
better results than the mineral reference oil in view of increased machining performance
as well as renewable sources. Many researchers [Rahman et al., 2002; Khan and Dhar,
2006; Heinemann et al., 2006] have conducted various machining investigations using
MQL with both synthetic oils and vegetable oils. Many researchers have suggested the
MQL techniques in machining processes [Rahman et al., 2001; Davim et al., 2006].
They applied this technique in reaming process of grey cast iron and aluminum alloy with
coated carbide tools. The significant reduction in tool wear and improvement in surface
quality of the holes have been observed using MQL technique when compared to dry
cutting. Dhar et al. [2006] employed MQL technique in turning of AISI 1040 steel and
the results clearly indicated that a mixture of air and soluble oil machining is better than
conventional flood coolant system.
Braga et al. [2002] reported that the holes obtained during drilling of aluminium–
silicon alloys with uncoated and diamond coated K10 carbide tools using MQL technique
presented either similar or better quality than those obtained with flood lubricant system.
The investigations carried out by Kelly and Cotterell [2002] on aluminium alloy revealed
that the MQL technique is preferable for higher cutting speeds and feed rates. Davim et
al. [2007] carried out experimental investigations on machining of brass under different
conditions of lubricant environments. The primary function of cutting fluid is cooling and
lubrication. The cooling and lubricating properties of cutting fluids are critical in
28
decreasing tool wear and extending tool life. Cooling and lubrication are also important
in achieving the desired size, finish and shape of the workpiece. In respect of profit,
safety and convenience a number of alternatives to traditional machining are currently
under development. Minimum quantity lubrication (MQL) is an obvious and very
intricate balance between dry machining and traditional methods. MQL (Minimum
Quantity Lubricant) technique, a very small quantity of oil is applied to the cutting point
and it improves the cutting performance as compared to dry cutting. Some investigations
have been performed to examine the effect of MQL technique on the reduction of tool
wear and the improvement of surface roughness of work materials, but there are few
studies which have investigated the influence of MQL technique on the tool temperature
[Byrne et al., 2003].
The reduced utilization of cooling lubricants, in order to improve environmental
protection, safety of machining processes and to decrease time and costs related to the
number of machining operations, can be pursued performing machining processes with
the MQL (minimum quantity of lubricant) technique or without any cutting fluid (dry
cutting) [Diniz et al., 2003]. Such approaches can allow the obtaining of the product
specifications, in terms of surface roughness and dimensional accuracy, by the shortening
conventional process cycles (i.e. avoiding grinding). The effect of the lubrication-cooling
condition on the surface quality of the machined part strongly depends on the type of
machining operation to be performed (e.g. turning, milling, etc.), as well as on the
process parameters to be used. In particular, in face milling operations cutting takes place
with high frequency tooth impacts, depending on the cutting speed, and discontinuously
due to the presence of several teeth; for such reasons dry and MQL face milling can be
29
performed over a wide field of workpiece materials [Weinert et al. 2004, Vieira et al.
2001]. In line with growing environmental concerns involved in the use of cutting fluids
in machining processes, as reported by several researchers and manufacturers of machine
tools, strong emphasis is being placed on the development of environmentally friendly
technology, i.e., on environmental preservation and the search for conformity with the
ISO 14000 standard. On the other hand, despite persistent attempts to completely
eliminate cutting fluids, in many cases cooling is still essential to the economically
feasible service life of tools and the required surface qualities. This is particularly true
when tight tolerances and high dimensional and shape exactness are required, or when the
machining of critical, difficult to cut materials is involved. This makes the minimum
quantity of lubrication an interesting alternative, because it combines the functionality of
cooling with an extremely low consumption of fluids (usually < 80ml/h). These minimal
quantities of oil suffice, in many cases, to reduce the tool’s friction and to prevent the
adherence of materials. The minimization of cutting fluids has gained increasing
relevance in the past decade [Dorr & Sahm, 2000]. This small amount of fluid suffices
to reduce friction in cutting, diminishing the tendency of adhesion in materials with such
characteristics. A comparison with conventional cooling revealed numerous advantages
[Dorr and sahm 2000 and Diniz and Micarony 2002]. However, compared with the
conventional technique, MQL involves additional costs to pressurize the air and
technological supports needed in the process in order to overcome the technological
restrictions of the MQL technique. For instance, special techniques for transporting chips
may be necessary, and productivity may decrease due to the thermal impact on the
machined components. Oil vapor, mist and smoke generated during the use of MQL in
30
machining can be considered undesirable byproducts, since they contribute to increase
the index of airborne pollutants. This has become a factor for concern, requiring a
adequate exhaustion system in the machine tool. A compressed air line that works
intermittently during the process is used for atomization. These compressed air lines
generate noise levels that usually exceed the legally established limits [Machado &
Diniz, 2001]. Based on the known costs of wet machining and MQL machining, a
comparison was made of the costs of investments and annual fixed and proportional costs
at the BMW company. The comparison of the total investment costs in the transfer line,
results of the process still merit further in-depth studies. Minimum quantity lubrication
systems employ mainly cutting fluids that are no soluble in water, especially mineral oils.
Due to the very small amounts of cutting fluids used, one must consider that the costs
should not prevent the use of high technology compositions in the field of basic and
additive oils. Vegetal-based materials are being increasingly used. These oils, inhaled in
the form of aerosol, reduce the health hazard factor [Novaski & Dorr, 1999].
Kamata and Obikawa [2007] investigated finish turning of Inconel 718 under
MQL with three types of coated carbide tool (TiCN/Al2O3/TiN (CVD), TiN/AlN
superlattice (PVD) and TiAlN (PVD)). Biodegradable synthetic ester was supplied with
compressed air on both the rake and flank face of the tool. On the basis of tool life and
surface finish, TiCN/Al2O3/TiN (CVD) and TiN/AlN superlattice (PVD) were found
suitable for finish turning of Inconel 718 with MQL. They reported that optimization of
air pressure is required for appropriate application of MQL in finish turning of Inconel
718. They also reported that carrier gas plays a vital role in cooling of cutting point as
short tool life were obtained with argon gas as compared to air. Increase in cutting speed
31
from 1m/s to 1.5 m/s resulted in drastic decrease of tool life and worse surface finish for
both the coatings under MQL condition. Also, increase in lubricant quantity, increased
the tool life and surface roughness for TiCN/Al2O3/TiN coating, whereas it decreased the
tool life and surface roughness slightly for TiN/AlN coated tool.
Su et al. [2007] used cooled air (at a temperature of -200C) with MQL at a
pressure of 6 bar in finish turning of Inconel 718 alloy. Application of cooled air and
cooled air with MQL resulted in 78% and 124% improvement respectively in tool life
over dry cutting. Improvement in tool life was attributed to reduction in cutting
temperature resulting in reduced abrasion, adhesion and diffusion wear. Surface
roughness was also reduced drastically in both conditions due to reduction in tool wear.
Significant improvement in chip shape was also reported as short continuous tubular
chips were obtained under both conditions.
Obikawa et al., [2008] observed that control of oil mist flow and decrease in
distance between nozzle and tool tip enhances the cutting performance of MQL
particularly in Micro-liter lubrication range (oil consumption less than 1 ml/h). Finish
turning of Inconel 718 was investigated in micro-liter lubrication (μLL) range with
biodegradable ester using three different types of nozzles: ordinary type, cover type for
normal spraying and cover type for oblique spraying.
Effectiveness of MQL (eMQL) was computed by the relation (1)
eMQL=
TMQL - Tdry
Twet- TWet - Tdry
......... (1)
32
where TMQL, Tdry and Twet are tool life for MQL, dry and wet turning.
Ordinary nozzle and cover type nozzle for normal spraying are not found suitable
for μLL. Values of eMQL decreased to 0.50, 0.47 and 0.36 as oil consumption (Q)
decreased to 1.1 , 0.5 and 0.2 ml/h for ordinary nozzle whereas with cover type nozzle
for normal spraying increase in eMQL is 0.22 and 0.18 for Q =0.50 and 0.20 ml/h over
ordinary nozzle. The cover type nozzle for oblique spraying provided significant
improvement as value of eMQL was 0.80,0.94 and 0.97 for Q =0.2, 0.5 and 1.1 ml/h
respectively. Good surface finish and tool life of 47 min was obtained at an oil
consumption of 0.5 ml/h and cutting speed of 1.3 m/s.
A study on effects and mechanisms in MQL intermittent turning of Aluminum
alloy (AlSi5) was conducted by Itoigawa et al. [2006]. MQL was studied with oil and oil
film on water droplet using rapeseed oil and synthetic ester as lubricant. MQL with
rapeseed oil showed only a small lubrication effect in light loaded machining conditions.
MQL with synthetic ester shows a lubrication effect but there was significant tool
damage and aluminum pick-up on the tool surface. MQL with water droplets using
synthetic ester provided good lubrication. They reported that influence of water for good
frictional performance depends not on the film chemi-sorption process but on water’s
chilling effect to sustain boundary film strength. In MQL machining of 6061 aluminum
alloy the quantity of adhered material to the tool was more as compared to flooded
coolant and less as compared to dry cutting. No considerable reduction in material
adhesion and flank wear was observed by increasing the lubricant quantity to two times.
33
Significant increase in flank wear was reported with increase in cutting speed. Cutting
forces were found highest under dry cutting and lowest under flooded condition. The
variation of cutting forces with different machining strategies is attributed to the amount
of adhesion. Surface roughness obtained by MQL is found to lie between dry cutting and
flooded condition [Sreejith, 2008].
Davim et al. [2007] conducted a study on turning of brass with MQL to study the
effect of the quantity of cutting fluid. They compared the cutting power, specific cutting
force, surface roughness and chip form with MQL at Q =50, 100, 200 ml/h and with
flood cooling at Q =2000 ml/h. Cutting parameters in the experimental test are cutting
speed (v) =100, 200 and 400 m/min, feed rate (s) =0.05, 0.10, 0.15 and 0.2 mm/rev, depth
of cut (t) =2 mm. Slightly higher cutting power was observed with MQL lubrication at 50
ml/h and flood lubrication at 2000 ml/h whereas almost same power is noticed with MQL
at flow rate of 100 and 200 ml/h. This suggests that similar/better cutting conditions can
be achieved with MQL as compared to flood lubrication. The specific cutting force is
found lower at a cutting velocity of 200 m/min except for fluid lubrication and reported it
to be a critical speed for brass machining. At Q =200 ml/h specific cutting force is found
to be lowest. Surface roughness decreased with increase in flow rate. Similar surface
roughness is observed with MQL at Q =200 ml/h and flood lubrication. Also for all the
machining conditions the relation between Rt and Ra was found maintained. Similar chip
forms were observed MQL and flood lubrication. In further work by Gaitonde et al.
[2008] quantity of lubricant, cutting speed and feed rate were determined for
simultaneously minimizing surface roughness and specific cutting force by using Taguchi
method and utility concept. They reported that Q =200 ml/h, v =200 m/min and s =0.05
34
mm/rev are optimal process parameters. Feed rate is found to be most significant factor
followed by quantity of MQL lubricant and cutting speed in optimizing the machinability
characteristics.
Effect of dry cutting, flood coolant, and minimum quantity lubrication were
studied in continuous and interrupted turning of Ti-6Al-4V alloy with uncoated carbide
inserts. It was reported that in continuous cutting, MQL seems to be more effective than
flood cooling at high cutting speed and feed rate due to its better lubrication ability. In
interrupted cutting MQL was also found more effective than dry and flood coolant
particularly in two slots cutting [Wang et al., 2009]. The main problem with machining
of titanium alloys is related to high heat generation at tool-chip interface due to which
machining of these alloys is recommended only with copious amount of cutting fluid. As
the main concern in titanium alloy machining is to remove the heat generated during the
process, Minimum quantity cooling (MQC) seems to be more appropriate than MQL. A
sequential procedure for determining operating parameters in MQC assisted turning of
Ti-6Al-4V alloy is presented in following section.
1.3 Summary of Review
During machining temperature is the apprehensive element and it is essential to
control this cutting temperature for better surface finish. Cutting fluid reduces cutting
temperature and also provides lubrication effect between the tool and work-piece
interface. There are different types of lubrication as well as cooling system available to
minimize the cutting temperature. Many researchers also made their investigations using
these different types of cooling and lubrications systems like flood cooling, near dry
35
cooling, or micro lubrication, high pressure jet cooling, cryogenic cooling and MQL
cooling. Flood cooling reduces temperature to some extent by bulk cooling but is not
very much effective because it cools only the top surface of the job and this is due to its
overhead application. It has some bad effects too, when cutting/cooling fluid comes in
contact with the human body it creates skin irritation, lung cancer etc. Near dry cooling is
based on air coolant, a little amount of temperature is reduced. Cryogenic cooling
effectively reduces temperature from the cutting zone but it is very costly and in nitrogen
rich atmosphere notch wear of the tool takes place. High pressure coolant has been
reported to provide quickly reduction in cutting temperature [Aronson, 2004]. It reduces
temperature very quickly due to high pressure jet coolant reaches very easily in the chip-
tool interface. It has been experienced that lubrication is effective at low speeds when it is
accomplished by diffusion through the work piece and by forming solid boundary layers
from the extreme pressure additives, but at high speeds no significant lubrication effect in
evident. The ineffectiveness of lubrication of the cutting fluid at high speed machining is
attributed to the inability of the cutting fluid to reach the actual cutting zone and
particularly at the chip-tool interface due to bulk or plastic contact at high cutting speed.
On the other hand the cooling and lubricating affects of cutting fluid influence each other
and diminish with increase in cutting velocity. The machining temperature could be
reduced to some extent by improving the machinability characteristics of the work
material metallurgical, optimizing the tool geometry and by proper selection of process
parameters. Some recent techniques have enabled partial control of machining
temperature by using heat resistance tools like coated carbides, CBN etc. the thermal
deterioration of the cutting tools can be reduced by using CBN tools. But CBN tools are
36
very expensive. Although the modified inserts offer reduced cutting force, their beneficial
effect on surface finish is marginal. Some recent techniques have enabled partial control
of machining temperature by using heat resistance tools like coated carbides, CBN etc
while dry cutting. The thermal deterioration of the cutting tools can be reduced by using
CBN tools. But CBN tools are very expensive. It was reported that [Alaxender et al.,
1998] that coolant injection offers better cutting performance in terms of surface finish,
tool force and tool wear when compared to flood cooling.
Coolants are frequently used in machining processes. They reduce tool wear,
dissipate heat from the work piece and machine, assist in the removal of swarf and
release cutting residues attached to the work piece, tool and equipment. The increased use
of coolants in recent years has caused a considerable increase in costs for procurement,
maintenance and disposal. The compatibility of coolants with the environment and the
potential health risks to the machine operator generated by the latter have increasingly
become the subject of criticism. The disposal of used coolants is not entirely sound
ecologically and is also causing rising costs. These costs are often underestimated
because they are mainly included in general overheads. Thus in fabrication operations
with centralized systems, they reach a level of 7 to17 % of the total fabrication costs. In
comparison with the latter, the tool costs in general amount to just 2 to 4 % of overall
costs (Figure 1). Minimizing lubricant consumption therefore has to be the ecological and
economic objective of a fabrication operation which looks towards the future. Against the
background of modern cutting materials and advanced coatings, the question arises as to
whether machining without lubricant i.e. “dry” is possible on an industrial scale.
37
Fig. 1.3 Distribution of Fabrication costs in engineering
The influence of cutting speed and feed rate on machinability aspects were
studied and concluded that flood lubrication can be successfully replaced by MQL type
of lubrication. However, in manufacturing machining industries, the temperature and its
detrimental effects are generally reduced by:
i. Proper selection of process parameters and geometry of the cutting tools.
ii. Proper selection and application of cutting fluid.
iii. Using heat and wear resistant cutting tool materials like carbides, coated
carbides and high performance ceramics (CBN and diamond are extremely
heat and wear resistive but those are too expensive and justified for very
special work materials and requirements where other tools are not
effective.
38
Coolant plays a significant role in improving lubrication as well as minimizing
temperature at the tool-chip and tool-work interfaces, consequently seizure during
machining. Flood cooling is not effective in terms lowering cutting temperature when
machining exotic materials. The coolant does not readily access the tool-work and tool-
chip interfaces that are under seizure condition as it is vaporized by the high cutting
temperature generated close to the tool edge. Machining of medium carbon based alloys
at high-speed conditions can therefore be achieved by combination of the appropriate tool
material, machining technique and the choice of a suitable cooling technology. Minimum
quantity lubrication is one of the preferred technologies currently under exploitation.
In general, when machining steel with coated carbide tools different tool wear
mechanisms occur, such as: abrasion, adhesion, oxidation and even some diffusion,
which act simultaneously and in proportions depending mainly on the temperature. The
task of defining which of those mechanisms is the predominant one has become a very
complex task. However, some researches relating wear mechanisms to the cutting speed
have been made and some important results have been published. For example, the raise
in temperature at the cutting zone occurs basically due to the cutting speed increase. The
abrasion phenomenon occurs predominantly at low cutting speeds, adhesion at medium
ones, and oxidation/diffusion at high ones. The limit of growing for cutting speed
depends on several other factors, such as tool-work combination, contact time between
them and the presence of cutting fluids. However, those findings are only indications and
may not offer more than recommendations for practical applications. By superimposing
wear mechanisms and their relations with cutting speed, it is possible to explain most of
the tool wear observed in practice; although in some cases the causes may depend on
39
some other factors occurring at the cutting zone and tool/work piece contact area,
[Arsecularatne et al., 2006]. In machining of steels the use of proper coating structure
can contribute to substantial reduction of the friction action between the rake and chip
and result in a decrease in heat generation and lower the tool-chip interface temperature.
The selection of work piece material with low thermal conductivity and low heat capacity
and a coating material with low thermal conductivity leads to a reduction in the contact
length, resulting in the effect of a thermal barrier. As a consequence, heat is concentrated
within the thin top layer of the coating to protect the tool against diffusion.
The application of MQL or dry cutting techniques requires that the functions of
the cooling lubricant are carried out by the other components of the machining system.
To this purpose, the cutting material and tool coating play a key role. In the last decades,
research has led to the development of cutting materials with improved performances,
such as ultra-fine grain cemented carbides, cermets, ceramics, cubic boron nitrides and
diamond, in order to withstand the higher temperatures occurring under MQL and dry
machining conditions, and provide a longer tool life. A further contribution has been
given by the development of tool coatings that can compensate for the lack of the cooling
lubricant; in particular, they can improve the tool wear behavior, reduce the thermal load
of the cutting tool by acting as thermal barrier and improve the sliding behavior on the
flank and rake faces by acting as a solid lubricant. Improvements in coating technology
have led to the development of multilayer coatings, nanolayer coatings, supernitrides,
self-lubricating coatings, CBN coatings and diamond coatings [Zhang et al. 2007;
Belmonte 2003].
40
At present, industry and researchers are looking for ways to reduce the use of
lubricants because of ecological and economical reasons. Therefore, metal cutting is to
move toward dry cutting or semi-dry cutting. This project presents an investigation into
MQL (Minimum Quantity Lubrication) machining with the objective of deriving the
optimum cutting conditions for the turning process of 42CrMo4. To reach these goals
several finish turning experiments were carried out, varying cutting speed, feed rate and
Cutting fluid with MQL. The surface roughness and tool wear results of tests were
measured and the effects of cutting conditions were analyzed by the graphical
presentation. From the experimental results, it is found that a better surface roughness can
be obtained by decreasing oil quantity and feed rate.
1.4 Scope of the Present Work
There are lot of scope and necessary to carry out extensive research and
development work for more effective and efficient machining of such increasingly used
steels. Such research and development work through understanding of mechanism and
mechanics of machining of this critical steel will essentially enable enhanced
productivity, product quality, tool life and overall economy in machining though
optimum selection of process parameter, tool material and geometry and environment.
Chapter 1 comprises with Introduction and Literature Review of the previous works. The
objective of the present work is included at the end of the chapter.
Chapter 2 comprises with Experimental set-ups, Experimental procedures, data collected
and Investigations on experiment.
41
Chapter 3 comprises with the detail Discussion on Experimental Results. The
experimental results are plotted or tabulated where necessary and presented in this
chapter.
In Chapter 4 pin pointed conclusions are drawn from the research outcomes.
Finally a list of reference is provided in separate Chapter.
1.5 Objectives of the present work
The main objectives of the present work is to make an experimental investigation
on the role of soluble cutting fluid as conventional application and as NDL and applied
the conventional coolant and Near Dry Lubrication (NDL) in continuous turning of
hardened steel (likely hardened AISI-1060 steel) using uncoated carbide insert on the
major mach inability characteristics in respect of
i. Cutting Temperature such as average chip-tool and work-tool interface
temperature. Monitoring of cutting zone temperature by tool-work thermocouple
technique. A tool-work thermocouple technique is developed and used to measure
the average chip-tool interface temperature. It is obvious that chip-tool interface
temperature is reduces drastically by the application of cutting fluid as NDL
because of its effective cooling and lubrication.
ii. Chip morphology such as chip shape, color and chip thickness ratio. The
machining chips is collected during all the treatments for studying their shape,
colour and nature of interaction with the cutting insert at its rake surface. It is
42
expected that application of cutting fluid as NDL is changed the chip colour and is
changed the mode of chip formation.
iii. Surface finish (Ra). The surface roughness and variation in finished diameter
along the job-axis is monitored by a Roughness checker (usually Talysurf,
surtronic 25) and precision dial gauge respectively. As application of cutting fluid
as NDL is protect the cutting edges during gradual wear regime surface roughness is
reduced and as a result deviation in diameter is also reduced.
iv. To check the dimensional accuracy.
in machining hardened steel by the industry used uncoated carbide tool (SNMG
120408) at different speeds and feeds combination. In this study, the Near Dry
Lubrication (NDL) was provided with a spray of air and soluble cutting fluids in which
air at a pressure of 15 bar and lubrication at atmospheric pressure through an externally
fitted metering unit at lubricant flow rate of 35 ml/hr. The results indicated that the use of
the very small amount Lubrication by soluble cutting fluid leads to reduced surface
roughness and lowered cutting temperature significantly in compare to other
environments.
These results are being expected to improve machinability due to reduction in cutting
zone temperature enabling favorable chip formation and chip-tool interaction. It is also
provide reduction in tool wear which is enhance the tool life, surface finish and
dimensional deviation. It is expected that the use of cutting fluids leads to reduce surface
roughness, increase dimensional accuracy, and lower cutting temperature, while also
having favorable chip tool interaction.
43
CHAPTER 2
EXPERIMENTAL INVESTIGATION
2.1 Introduction
The high cutting temperature generated during machining of hardened steel is
not only reduces tool life but also impairs the product quality. The temperature becomes
more intensive when cutting speed and feed are increased for higher MRR and the work
materials are relatively difficult to machine for their high strength, harden-ability and
lesser thermal conductivity. Cutting fluids are widely used to reduce the cutting
temperature. But the major problems associated with the use of conventional methods. It
has already been observed through previous research that proper application of reduced
amount of lubricant may play vital role in providing not only environment friendliness
but also some techno-economical benefits.
The machining responses have been studied and evaluated for assessing the
machinability characteristics of the steel specimen under dry, wet and NDL with soluble
cutting fluid conditions by using uncoated carbide insert. The economy of machining
steel is strongly related to effective chip control, for higher utilization of machines and
temperature reduction in the tool, for raising the rates of metal removal. Cutting with the
excess amount of cutting fluids is still very common in conventional machining to control
high cutting temperature which adversely affects, directly and indirectly, chip formation,
cutting forces, tool life and dimensional accuracy and surface integrity of the products.
The effectiveness, efficiency and overall economy of machining any work material by
44
given tool depend largely on the machinability characteristics of the tool-work material
under the recommended conditions. The conditions are
i. Cutting temperature; which affects product quality and cutting tool
performance
ii. Chip formation
iii. Magnitude of cutting forces; which affects power requirements, vibration
and dimensional accuracy
iv. Surface finish
v. Tool wear and tool life
For achieving substantial technological and economical benefits in addition to
environmental friendliness, Near Dry Lubrication system needs to be properly designed
considering the following important factors:
i. Effecting cooling by enabling cutting liquid along with air jet reach as close
as to the actual hot zones as possible.
ii. Avoidance of bulk cooling of the tool and the job, which may cause
unfavorable metallurgical changes.
iii. Minimum consumption of cutting fluid by pin-pointed impingement and
only during chip formation.
The machining responses have been studied and evaluated for assessing the
machinability characteristics of the hardened steel specimen under dry, wet and near dry
conditions by using uncoated carbide insert.
45
2.2 Experimental Setup
2.2.1 Near Dry Lubrication System
The aim of the present work is primarily to explore and evaluate the beneficial
role of Near Dry Lubrication system on machinability characteristics of commonly used
tool-work combinations mainly in terms of cutting temperature, surface finish and chip-
forms, which governs productivity along with quality and overall economy.
Typically a very small amount coolant and/or lubricant supply system consists of
a compressor, small container for cutting fluid, fluid supply system, nozzle, separate
device and pipes for supply of cooling lubricant and air for their independent adjustment.
However, the components of the near dry lubrication system may vary depending upon
the type of fluid delivery system and atomization. The photographic view of the
experimental set-up fabricated at Machine Tool Laboratory, Dhaka university of
Engineering & Technology, Gazipur is presented in Fig. 2.1. In order to deliver metered
supply of air at desired pressure, pressure regulator is fitted in air supply line. The
pressurized air from nozzle can be directed on rake face depending upon experimental
requirement. The very important factor is design of near dry mixing system for supplying
lubricant on tool-work interface. First of all it is necessary to mix air and lubricant to
obtain the mixture to be spread on the cutting surface. There are two different types of
mixing methods can be used: mixing inside nozzle and mixing outside nozzle. Using the
mixing outside nozzle equipment, pressurized air and lubricant are mixed outside the
nozzle by create vacuum pressure due to dropping nozzle high pressure to atmospheric
pressure and increasing its velocity. The fluid pressure line was blocked by turning the
46
knobs of the set-up developed by Mr. Makinuzzaman Shahadat at Machine tool lab of
DUET under the supervision of same supervisor for MQL delivery. A separate fluid
chamber fitted with controller was used to store and deliver the coolant to outlet orifice of
the nozzle. A very precise wheel type metering system usually used in intravenous fluid
application apparatus traditionally known as saline pushing device is used to measure a
small amount of fluid that in turn was applied externally to the flowing stream of high
velocity air jet delivered from the specially designed nozzle at 15 bar. The high velocity
stream atomized the lubricant delivered as a feebler stream from the dispenser towards
the cutting interface as a pin pointed impingement. Figure 2.1 and figure 2.2 show the
photographic view of high velocity air supply system and schematic views of mixing
system for near dry lubrication supply system. A commercially available flexible tube
and wheel type flow controller was used to control the supply of cutting fluid to outlet
orifice of the nozzle. A special designed nozzle was used to impinge aerosol at high
velocity in the cutting zone. The lubrication is obtained by the lubricant, while a minimal
cooling action is achieved by the pressurized air that reaches the cutting surface. Several
advantages derive applying this method. Mist and dangerous vapors are reduced and the
mixture setting is very easy to control.
47
Fig. 2.1 Photographic view of the Near Dry Lubrication applicator
Fig. 2.2 Schematic view of the Near Dry Lubrication applicator
48
Fig. 2.3 Photographic view of air nozzle for near dry lubrication for Supplying high
velocity air
Fig. 2.4 Schematic view of the near dry jet issuing and impinging system
Figure 2.1 to Figure 2.4 show the photographic and schematic views of near dry
lubrication applicator, Photographic view of air nozzle for supplying high velocity air
and Schematic view of near dry jet issuing and impinging system respectively.
49
2.2.2 Experimental Procedure and conditions
In this experiment, Near Dry Lubrication conditions are used during machining to
compare the results with the same by dry and wet condition. For Near Dry Lubrication
supply the positioning of nozzle tip is very important and that has been settled after a
number of trials. During machining the Near Dry Lubrication jet is directed along the
auxiliary cutting edge over the tool rake face and partially under the flowing chips to the
cutting edges.
The photographic view of the experimental setup is shown in Figure 2.1. In the
figure it is shown that a jet of air along with a very amount of lubricant was injected
through the tool rake face, consists of a compressor, Near Dry Lubrication applicator,
USSR made engine lathe of Model 16K20, tool-work thermocouple and experimental
hardened steel. In this study, the Near Dry Lubrication was provided with a spray of air
and cutting fluids at a pressure 15 bars and coolant flow rate of 35 ml/hr.
The experiment was carried out on lathe, which has a 7.5 kW motor and
maximum spindle speed of 1600 rpm. The work material was hardened AISI 1060 steel
having diameter of 105 mm and length of 840 mm. The uncoated SNMG 120408 WIDIA
made inserts were clamped in a PSBNR-2525 M12 (Drillco) type tool holder. The tool
holder provided negative 6° side and back rake angles and 6° side cutting-edge and end
cutting-edge angles. The ranges of the cutting velocity (V), feed (f) and depth of cut (d)
were selected based on the tool manufacturer’s recommendation and industrial practices.
The following cutting conditions were employed in this investigation, shown in Table
2.1.
50
Table 2.1 Experimental conditions
• Machine tool : Engine Lathe, 7.5 kW, 1600 rpm, model 16K20, made in
Rusia (USSR)
• Work material : Hardened AISI 1060 steel
• Chemical Composition : Chemical Composition by weight percent
AISI 1060 steel (C-0.55-0.66 , Fe- 98.35-98.85, Mn-
0.60-0.90, P- ≤ 0.040 and S ≤ 0.050)
• Cutting insert : Uncoated Carbide, SNMG 120408 , WIDIA
Geometry : -6°,-6°,6°,15°,75°,0.8 mm
Process parameters
• Cutting speed, V : 41, 53, 66 and 82 m/min
• Feed, f : 0.09, 0.10 and 0.125 mm/rev
• Depth of cut, d : 0.50 mm and 1mm
• Coolant type : Soluble Cutting Fluid
• Coolant delivery methods : Near Dry Lubrication with a spray of air and cutting fluids
(in which air at a pressure of 15 bars and lubricant flow
rate of 35 ml/hr under atmospheric pressure)
• Environment : i. Dry
ii. Wet
iii. Near Dry
A number of cutting velocity V and feed rate f have been taken over relatively wider
ranges keeping in view the industrial recommendations for the tool-work materials
51
undertaken and evaluation of role of variation in V and f on the effectiveness of Near Dry
Lubrication.
Figure 2.5 Photographic view of surface roughness measuring technique
A tool-work thermocouple technique is developed and used to measure the
average chip-tool interface temperature. Calibration of tool-work thermocouple is taken
from the previously done research work of Kamruzzaman and Dhar, 2007. A polynomial
regression analysis is done for the set of temperature and milivolt data obtained by him
using a small crucible and a tiny junction of carbide rod and sample steel rod. Regression
equation is derived and the obtained result of mV under different process parameters and
conditions are put into that equation. Results of temperature readings are plotted against
cutting speed to visualize the trend of graph and effectiveness of different conditions.
The thickness of the chips directly and indirectly indicates the nature of chip-tool
interaction influenced by the machining environment. The chip samples were collected
during short run machining for the V-f combinations under dry, wet with soluble fluid
and Near Dry Lubrication with soluble fluid conditions. Cutting temperature as mV was
measured by a reliable tool-work thermocouple technique. The thickness of the chips was
repeatedly measured by a slide caliper to determine the value of chip thickness ratio. The
52
surface roughness of the machined surface after each cut was measured by a Talysurf
(Surtronic 25), rank Hobson, UK using a sampling length 4 mm and cut-off 0.8 mm,
shown in Figure 2.5. The results are documented and plotted against various
environments having different combinations of velocities and feeds.
2.3 Experimental Methodology
The research work is mainly experimental in nature. The methodology would be as
follows:
i. A 60 grade traditional used steel specimen of solid bar stock (840 mm X φ
107 mm) is hardened above critical hardness for carbide insert i.e. 33 HRC
keeping in mind that avoidance of case hardening also while cooling brine
solution mixed with ice may cause surface hardening. The hardening process
is carried out from Bangladesh Industrial and Technical Assistance center
(BITAC) because of absence of gas furnace in DUET.
ii. Monitoring of cutting zone temperature by tool-work thermocouple technique.
A tool-work thermocouple technique is developed and used to measure the
average chip-tool interface temperature.
iii. The machining chips is collected during all the treatments for studying their
shape, colour and nature of interaction with the cutting insert at its rake surface.
The surface roughness and variation in finished diameter along the job-axis is
monitored by a Roughness checker (usually Talysurf, Surtronic 25, Rank Hobson, UK)
and precision dial gauge having 0.1 μm accuracy respectively.
53
2.4 Experimental Results
2.4.1 Cutting Temperature
High production machining associated with high velocity (V), feed rate (f) and
depth of cut (d) inherently generates high heat as well as high cutting zone temperature.
The cutting temperature if not controlled properly, cutting tools undergo severe flank
wear and notch wear, lose sharpness of the cutting edge by either wearing or become
blunt by welded built-up edge and weaken the product quality. In normal cutting condition
all such heat sources produce maximum temperature at the chip-tool interface, which
substantially influence the chip formation mode; cutting forces, tool life and product quality.
High production machining needs to increase the process parameters further for meeting up
the growing demand and cost competitiveness. Cutting temperature is increased with the
increase in process parameter as well as with the increase in hardness and strength of the
work material. Therefore, attempts are made to reduce this detrimental cutting temperature.
In the Present work, the average cutting temperature was measured by tool-work
thermocouple technique with proper calibration under all the machining conditions. The
evaluated role of NDL on average chip-tool interface temperature in turning hardened AISI
1060 steel by uncoated carbide inserts at different V, f and d combinations in compare to
dry, wet and near dry condition have been shown in Fig.2.6, Fig.2.7, Fig.2.8 and Fig.2.9
respectively.
54
38 63 8825 50 75 100
450
550
650
750
400
500
600
700
800
Feed rate 0.09 mm/revAvera
ge c
hip
-tool in
terf
ace tem
pera
ture
, oC
Cutting speed, m/min
Dry
Wet
Near Dry
38 63 8825 50 75 100
450
550
650
750
400
500
600
700
800
Feed rate 0.10 mm/revAvera
ge c
hip
-tool in
terf
ace t
em
pera
ture
, oC
Cutting speed, m/min
Dry
Wet
Near Dry
38 63 8825 50 75 100
450
550
650
750
400
500
600
700
800
Feed rate 0.125 mm/revAvera
ge c
hip
-tool in
terf
ace tem
pera
ture
, oC
Cutting speed, m/min
Dry
Wet
Near Dry
Fig. 2.6 Variation of Chip-tool interface temperature with different cutting speed at feed
rates and 1 mm depth of cut by using uncoated carbide under dry, wet and near
dry condition during machining hardened AISI 1060 steel.
55
38 63 8825 50 75 100
450
550
650
750
400
500
600
700
800
Feed rate 0.09 mm/revAve
rag
e c
hip
-too
l in
terf
ace t
em
pe
ratu
re,
oC
Cutting speed, m/min
Dry
Wet
Near Dry
38 63 8825 50 75 100
450
550
650
750
400
500
600
700
800
Feed rate 0.10 mm/revAve
rag
e c
hip
-too
l in
terf
ace t
em
pe
ratu
re,
oC
Cutting speed, m/min
Dry
Wet
Near Dry
38 63 8825 50 75 100
450
550
650
750
400
500
600
700
800
Feed rate 0.125 mm/revAve
rag
e c
hip
-too
l in
terf
ace t
em
pe
ratu
re,
oC
Cutting speed, m/min
Dry
Wet
Near Dry
Fig. 2.7 Variation of Chip-tool interface temperature with different cutting speed at feed
rates and 0.50 mm depth of cut by using uncoated carbide under dry, wet and
near dry condition during machining hardened AISI 1060 steel.
56
Fig. 2.8 Variation of Chip-tool interface temperature with different cutting speed at feed
rates at 1 mm depth of cut under dry, wet and near dry condition during
machining of hardened AISI 1060 steel by using uncoated carbide insert.
Fig. 2.9 Variation of Chip-tool interface temperature with different cutting speed at feed
rates at 0.50 mm depth of cut under dry, wet and near dry condition during
machining of hardened AISI 1060 steel by using uncoated carbide insert.
57
2.4.2 Machining Chips
Machining is a process of shaping by the removal of material which results in chips
and the geometrical and metallurgical characteristics of these chips are very
representative of the performance of the process because the form (Shape, color) and
thickness of the chips directly and indirectly indicate the nature of chip-tool interaction
influenced by the machining environment. In general chip formation in machining can be
categorized as forming continuous, discontinuous or serrated chips.
In the present work, the chip samples are collected while turning of the hardened
AISI 1060 steel by uncoated carbide insert at different speed-feed and depth of cut
combinations under dry, conventional coolant and Near Dry Lubrication conditions by
the soluble cutting oil, have been visually examined and categorized with respect to their
shape and color. The form and color of all these chips were noted down based on ISO
3658-1977 (E) standard chip forms. The results of such categorization of the chips
produced at different environments have been shown in Table 2.2 and Table 2.3.
Table 2.2
Comparison of chip shape and color at different speed and feed at depth of cut 1 mm
under dry, wet and near dry conditions during machining of hardened AISI 1060 steel by
SNMG uncoated carbide insert.
Feed (f)
Cutting
Velocity
(V)
Dry Wet Near Dry
Chip
Shape Color
Chip
Shape Color
Chip
Shape Color
0.09
41 Long
Tubular Metallic
Small
Tubular Metallic
Small
Helical Metallic
53 Helical Burn Blue Small
Tubular Metallic
Small
Helical Metallic
66 Long
Helical Burn Blue
Small
Tubular Metallic
Small
Tubular Metallic
82 Long
Helical Burn Blue
Long
Helical Goldish
Small
Helical Metallic
0.10
41 Long
Tubular Metallic
Small
Tubular Metallic
Small
Helical Metallic
53 Tubular Metallic Small
Tubular Metallic Loose Arc Metallic
66 Long Burn Blue Small Metallic Small Metallic
58
Helical Helical Tubular
82 Long
Helical Burn Blue
Long
Helical Goldish
Small
Helical Metallic
0.125
41 Long
Helical Metallic
Small
Tubular Metallic
Long
Helical Metallic
53 Tubular Goldish Small
Tubular Metallic Loose Arc Metallic
66 Helical Burn Blue Small
Helical Metallic Loose Arc Metallic
82 Long
Helical Burn Blue
Long
Helical Goldish
Small
Helical Metallic
Chip Shape
Group Loose Arc Chips Long Tubular Snarled Tubular
Chips Snarled Ribbon
Table 2.3
Comparison of chip shape and color at different speed and feed at depth of
cut 0.50 mm under dry, wet and near dry conditions during machining of
hardened AISI 1060 steel by SNMG uncoated carbide insert.
Feed (f)
Cutting
Velocity
(V)
Dry Wet Near Dry
Chip
Shape Color
Chip
Shape Color
Chip
Shape Color
0.09
41 Small
Helical Goldish
Small
Tubular Metallic
Small
Helical Metallic
53 Small
Helical Bluish
Small
Tubular Metallic
Small
Helical Metallic
66 Small
Helical Bluish
Long
Tubular Metallic
Long
Helical Metallic
82 Snarled Blue Long
Tubular Metallic
Long
Helical Metallic
0.10
41 Small
Helical Bluish
Small
Tubular Metallic
Long
Helical Metallic
53 Small
Helical Bluish
Small
Tubular Metallic
Long
Helical Metallic
66 Long
Helical Blue
Long
Tubular Metallic
Long
Helical Metallic
82 Snarled Blue Long
Tubular Metallic
Long
Helical Metallic
0.125
41 Small
Helical Bluish
Small
Tubular Metallic
Long
Helical Metallic
53 Small
Helical Blue
Long
Tubular Metallic
Long
Helical Metallic
59
66 Long
Helical Blue
Long
Tubular Metallic
Long
Helical Metallic
82 Snarled Blue Long
Tubular Metallic
Small
Helical Metallic
In machining another important machinability index is chip thickness ratio, rc
(ratio of chip thickness before and after cut). For a given tool geometry and cutting
conditions, the value of rc depends upon the nature of chip-tool interaction, chip contact
length and chip form all of which are expected to be influenced by Near Dry Lubrication
conditions to the level of speed and feed. The thickness of the chips was repeatedly
measured by a digital slide caliper to determine the value of chip thickness ratio, rc (ratio
of chip thickness before and after cut). The variation in value of chip thickness ratio (rc)
with speed and feed at dry, wet and Near Dry Lubrication condition has been plotted
which are shown from Fig. 2.10 and Fig. 2.11 respectively.
40 45 50 55 60 65 70 75 80 85
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
Environment: Dry
Ave
rag
e C
hip
Th
ickn
ess R
atio
(rc
)
Cutting speed, m/min
0.09 mm/rev
0.10 mm/rev
0.125 mm/rev
40 45 50 55 60 65 70 75 80 85
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.09 mm/rev
0.10 mm/rev
0.125 mm/rev
Environment: Wet
Ave
rag
e C
hip
Th
ickn
ess R
atio
(r c
)
Cutting speed, m/min
60
40 45 50 55 60 65 70 75 80 85
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.09 mm/rev
0.10 mm/rev
0.125 mm/rev
Environment: Near Dry
Ave
rag
e C
hip
Th
ickn
ess R
atio
(r c
)
Cutting speed, m/min
Fig. 2.10 Variation of Chip Thickness ratio (rc) with different cutting speed and different
feed rate under different conditions at 1 mm depth of cut by using uncoated
carbide during machining of hardened AISI 1060 steel.
40 45 50 55 60 65 70 75 80 85
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.09 mm/rev
0.10 mm/rev
0.125 mm/rev
Environment: Dry
Ave
rag
e C
hip
Th
ickn
ess R
atio
(r c
)
Cutting speed, m/min
40 45 50 55 60 65 70 75 80 85
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.09 mm/rev
0.10 mm/rev
0.125 mm/rev
Environment: Wet
Ave
rag
e C
hip
Th
ickn
ess R
atio
(r c
)
Cutting speed, m/min
40 45 50 55 60 65 70 75 80 85
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.09 mm/rev
0.10 mm/rev
0.125 mm/rev
Environment: Near Dry
Ave
rag
e C
hip
Th
ickn
ess R
atio
(r c
)
Cutting speed, m/min
Fig. 2.11 Variation of Chip Thickness ratio (rc) with different cutting speed and different
feed rate under different conditions at 0.50 mm depth of cut by using uncoated
carbide during machining of hardened AISI 1060 steel.
61
2.4.3 Surface Roughness
Quality of the product is very crucial issue. The performance and service life of
any machined parts mainly vary by the quality of that product. For a given material
quality is generally assessed by dimensional and form accuracy and surface integrity of
the product in respect of surface roughness, oxidation, corrosion, residual stresses and
surface and subsurface micro-cracks.
To evaluate the quality of the product only the surface roughness and the
dimensional deviations on diameter have been investigated in this present work. This
investigation is carried out under different cutting environment at various V-f
combinations. But depth of cuts are 1.0 mm and 0.50 mm.
Finished Surface is a very vital consideration for product quality. This important
index of machinability is substantially influenced by the machining environment for
given tool-work pair and speed-feed conditions. So the development of surface roughness
in continuous machining processes like turning, is caused by
i. vibration in the machining system
ii. improper machine set-up
iii. gradual wear of the cutting tool
Surface roughness has been measured after a few seconds of machining with the
sharp tool while recording the cutting temperature. Here the surface finish has been
measured by a Talysurf (Surtronic 25, Rank Taylor Hobson) by the machining of the
hardened steel bar by the coated carbide insert at different V-f combination under dry,
62
wet and Near Dry Lubrication with soluble oil conditions using a sampling length of 4
mm along with cut-off 0.80 mm.
The surface roughness, Ra attained of machining of hardened AISI 1060 steel by
the sharp uncoated carbide (SNMG 120408, Widia) insert at various V-f combinations
under dry, Near Dry Lubrication with soluble oil, conditions are shown in Fig.2.12 and
Fig.2.13 respectively.
40 45 50 55 60 65 70 75 80 85
2.5
3.0
3.5
4.0
4.5
5.0
0.09 mm/rev
0.10 mm/rev
0.125 mm/rev
Environment: Dry
Ave
rag
e S
urf
ace
Ro
ug
hn
ess R
a(µ
m)
Cutting speed, m/min
40 45 50 55 60 65 70 75 80 85
2.5
3.0
3.5
4.0
4.5
5.0
0.09 mm/rev
0.10 mm/rev
0.125 mm/rev
Environment: Wet
Ave
rag
e S
urf
ace
Ro
ug
hn
ess R
a(µ
m)
Cutting speed, m/min
40 45 50 55 60 65 70 75 80 85
2.5
3.0
3.5
4.0
4.5
5.0
0.09 mm/rev
0.10 mm/rev
0.125 mm/rev
Environment: Near Dry
Ave
rag
e S
urf
ace
Ro
ug
hn
ess R
a(µ
m)
Cutting speed, m/min
Fig. 2.12 Variation of Roughness (Ra) with different cutting speed and different feed rate
under different conditions at 1 mm depth of cut by using uncoated carbide
during machining of hardened AISI 1060 steel.
63
40 45 50 55 60 65 70 75 80 85
2.5
3.0
3.5
4.0
4.5
5.0
0.09 mm/rev
0.10 mm/rev
0.125 mm/rev
Environment: Dry
Ave
rag
e S
urf
ace
Ro
ug
hn
ess R
a(µ
m)
Cutting speed, m/min
40 45 50 55 60 65 70 75 80 85
2.5
3.0
3.5
4.0
4.5
5.0
0.09 mm/rev
0.10 mm/rev
0.125 mm/rev
Environment: Wet
Ave
rag
e S
urf
ace
Ro
ug
hn
ess R
a(µ
m)
Cutting speed, m/min
40 45 50 55 60 65 70 75 80 85
2.5
3.0
3.5
4.0
4.5
5.0
0.09 mm/rev
0.10 mm/rev
0.125 mm/rev
Environment: Near Dry
Ave
rag
e S
urf
ace
Ro
ug
hn
ess R
a(µ
m)
Cutting speed, m/min
Fig. 2.13 Variation of Roughness (Ra) with different cutting speed and different feed rate
under different conditions at 0.50 mm depth of cut by using uncoated carbide
during machining of hardened AISI 1060 steel.
2.4.4 Dimensional Deviation
Dimensional accuracy often affects the performance and service life of the
machined component. The diameter of the machined part during the straight turning in an
engine lathe is generally found to increase along length of cut due to gradual wear of the
tool tip; decrease due to thermal expansion and subsequent cooling of the job if the job
temperature rises significantly during machining and increase due to system compliance
of the machine-fixture-tool-work (M-F-T-W) system under the action of the cutting
64
forces. So the development of dimensional deviation in continuous machining processes
like turning, is caused by
iv. vibration in the machining system
v. improper machine set-up, tool
vi. excessive heat development
vii. gradual wear of the cutting tool
The order of dimensional deviations possible due to thermal expansion of the
job even under dry machining and due to compliance of the M-F-T-W system were
calculated for the steel specimens being machined under the present conditions and the
values appear to be extremely small (less than 1 µm) compared to that possible due to
wear of the tool tips. Therefore, in the present study, the dimensional deviations are
considered to be mainly due to wear of the tool tips.
The gradual increase in dimensional deviations on diameter observed along the
length of cut on the hardened AISI 1060 steel after one full pass of machining at cutting
velocity of 82 m/min, 0.15 mm/rev feed and 1.0 mm depth of cut under dry, wet and Near
Dry Lubrication conditions have been considered. For Near Dry Lubrication
environment only the water soluble oil has been applied. Dimensional deviation of the
machined work piece has been measured by fitting a dial gauge of least count 10 µm on
the carriage of the machine tool under a complete pass of machining. During machining
gauge reading has been taken in 10 mm interval and plotted in Fig.2.14.
65
50 150 2500 100 200 300
50
150
250
350
0
100
200
300
400
Depth of cut: 1 mm
Devia
tion in D
imensio
n,
m
Length of cut, mm
Dry
Wet
Near Dry
50 150 2500 100 200 300
50
150
250
350
0
100
200
300
400
Depth of cut: 1 mm
De
via
tion
in D
ime
nsio
n,
m
Length of cut, mm
Dry
Wet
Near Dry
Fig. 2.14 Dimensional deviation observed after one full pass turning of hardened steel by
SNMG insert with different depth of cut under dry wet and near dry conditions.
66
CHAPTER 3
EXPERIMENTAL RESULTS AND DISCUSSION
3.1 Machining Chip
Chip morphology and thickness of the chips directly and indirectly indicate the nature
of chip-tool interaction influence by the machining environment. The pattern of chips in
machining ductile metals are found to depend upon the mechanical properties of the work
material, tool geometry particularly rake angle, levels of V and f, nature of chip-tool interaction
and cutting environment. In absence of chip breaker, length and uniformity of chips increase with
the increase in ductility and softness of the work material, tool rake angle and cutting velocity
unless the chip-tool interaction is adverse causing intensive friction and built-up edge formation.
From Table 2.2 and Table 2.3 it is stated that under dry condition most of the chips
produced are long tubular in nature and the colour of the chips are bluish, blue or burn blue.
Under lower speed –feed conditions where temperature is not more severe the chips produced are
lighter in colour but with the changing incremental interfacial temperature due to increase in
speed-feed as the metal becomes ductile, chips produced got incremental shapes like helical as
well as chip morphological changes takes place, more darker coloured chips are produced with
the incremental change in speed-feed. Wet condition changes the mode of chip formation due to
its cooling effect. Bulk cooling changes the shape the shape of the chips from long tubular to
small helical or small tubular or loose arc also colour changes to goldish or metallic that also an
indication of decrease in cutting temperature due to application of cutting fluid though in bulk
amount. Under Near Dry condition the shape of all most all the chips are small helical that is near
to loose are and morphologically metallic in colour. But when V=82 m/min ie. the highest speed
employed for this experiment at all the feed range, the shape of the chips are small helical under
67
the application of near dry lubrication. Again from Table 2.2 and Table 2.3 it is clear that when V
and f increase, the chip-tool interface temperature increases. Thus chip become much deeper, i.e.
from metallic to golden to blue or even burn blue. Again the colour of the chips have also become
much lighter depending upon V and f due to reduction in cutting temperature by wet and Near
Dry condition. At dry condition the colour of the chips are very deeper, i.e. blue due to high
temperature. Wet condition changes the colour to golden by reducing temperature and Near Dry
condition changes the colour to metallic by reducing the cutting temperature by effective and
efficient cooling and lubrication as well as pin pointed impingement of the cooling jet to the
actual cutting interface.
The chip-thickness ratio (rc) is an important index of chip formation and specific energy
consumption for a given tool-work combination. It is evaluated from the ratio,
22
1c
a
φsin f
a
ar == (3.1)
Where,
rc = Chip thickness ratio
a1 = Chip thickness before cut = f sinφ
a2 = Chip thickness
f = Feed rate
φ = Principal cutting edge angle
68
During the machining of the metals and alloys, continuous chips are produced and the
value of rc is generally less than 1.0 because chip thickness after cut (a2) becomes greater than
chip thickness before cut (a1) due to almost all sided compression and friction at the chip-tool
interface. Smaller value of rc means larger cutting forces and friction and hence is undesirable.
Chip thickness depends on almost all the parameters involved in machining. The degree
of chip thickness which is measured by chip thickness ratio, plays an important role on cutting
forces and hence on cutting energy requirements and cutting temperature. The effect of increase
in V and f and the change in environment on the value of chip-thickness ratio (rc) obtained during
turning hardened AISI 1060 steel are shown in figure from Fig. 2.10 and Fig. 2.11 which depict
some significant facts;
i. values of rc has all along been less than 1.0
ii. the value of rc has increased by the application of minimum quantity of lubricant
iii. the value of rc increases with increase in V and f
Figure 2.10 and Figure 2.11 show that Near Dry condition has increased the value of
chip thickness ratio for all V-f combinations due to reduction in friction at the chip-tool interface,
reduction in built-up-edge formation and wear at the cutting edges. In all V-f combinations Near
Dry condition by cutting fluid shows more effectiveness than that of conventional application of
cutting fluid and completely absence of cutting fluid ie, dry cutting. The figures from Fig. 2.10
and Fig. 2.11 clearly show that throughout the present experimental domain the value of rc
gradually increased with the increase in V and f in different degree under dry, wet and Near Dry
conditions. Among these three conditions, NDL has shown the best performance, because the
value of rc has increased more than the other conditions, i.e. dry and wet. The value of rc usually
increases with the increase in V particularly at its lower range due to plasticization and shrinkage
of the shear zone for reduction in friction and built-up edge formation at the chip-tool interface
69
due to increase in temperature and sliding velocity. In machining steels by tools like carbide,
usually the possibility of built-up edge formation and size and strength of the built-up edge, if
formed gradually increase with the increase in temperature due to increase in V and also f and
then decrease with the further increase in V due to too much softening of the chip material and its
removal by high sliding speed.
The percentage increment in chip-thickness ratio, rc attained by Near Dry for different
cutting velocity and feed have been calculated from the previous figures and shown in Table 3.1
for hardened AISI 1060 steel. For ease of comparison, the ranges and averages of percentage
increment in rc has been separately shown in Table 3.2 which visualizes how the beneficial role of
Near Dry varied with different cutting conditions.
Table 3.1 Percentage increment in chip thickness ratio (rc)
Feed rate, f,
mm/rev
Cutting velocity,
V,
m/min
Percentage increment in rc
for depth of cut 1.0 mm
Percentage increment in rc
for depth of cut 1.0 mm
Wet Near Dry Wet Near Dry
0.09
41 0.95 20.24 12.05 4.79
53 4.99 22.51 12.86 4.74
66 5.77 20.41 11.54 5.97
82 9.92 16.67 11.11 6.62
0.10
41 7.35 15.58 11.57 5.70
53 8.70 17.59 12.11 4.53
66 11.82 16.71 11.02 9.41
82 13.93 13.34 10.80 10.88
0.125
41 11.81 15.11 12.52 7.99
53 11.57 17.14 11.55 5.95
66 14.03 16.73 14.24 7.75
82 12.05 14.90 11.13 10.94
70
Table 3.2 Average percentage increment in chip thickness ratio (rc)
Savings Average Percentage increment in rc
for depth of cut 1.0 mm
Average Percentage increment in rc
for depth of cut 0.50 mm
Wet Near Dry Wet Near Dry
Range 0.95-14.03 13.34-22.51 10.80-12.86 4.53-10.94
Average 9.41 17.24 11.88 7.11
From Table 3.1 the percentage of increment in chip thickness ratio for the stated V-f
combinations for wet and Near Dry by traditional cutting fluid over dry condition are 1~14%, and
13~23% respectively for depth of cut 1 mm and 10~13%, and 4~11% respectively for depth of
cut 0.50 mm. It can also show that at low feed and low cutting speed increase in chip thickness
ratio is more. But if feed increases better result is shown at 82 m/min cutting speed.
3.2 Cutting Temperature
During hard turning the maximum heat generated at the chip-tool interface, as a result
temperature of chip-tool interface is increased quickly. This machining temperature at the cutting
zone needs to be controlled as far as possible. Cutting temperature increases with the increase in
specific energy consumption and material removal rate (MRR). Such high cutting temperature
adversely affects, directly and indirectly, chip formation, cutting forces, tool life and dimensional
accuracy and surface integrity of the products. That is why, attempts are made to reduce this
detrimental cutting temperature. In some cases dry cutting is preferable in machine to hard
materials at low speed. But in case of high speed machining cutting fluids may apply.
Conventional cutting fluid application may, to some extent, cool the tool and the work piece in
bulk but cannot cool and lubricate expectedly and effectively at the chip-tool interface where the
71
temperature is maximum. This is mainly because the flowing chips make mainly bulk contact
with the tool rake surface and may be followed by elastic contact just before leaving the contact
with the tool. Bulk contact does not allow the cutting fluid to penetrate in the interface. Elastic
contact allows slight penetration of the cutting fluid only over a small region by capillary action.
The cutting fluid action becomes more and more ineffective at the interface with the increase in V
when the chip-tool contact becomes almost fully plastic.
Therefore, application of Near Dry Lubrication at chip-tool interface is expected to
improve machinability characteristics that play vital role on productivity, product quality and
overall economy in addition to environment-friendliness in machining particularly when the
cutting temperature is very high. The average chip-tool interface temperature has been
determined by using the tool work thermocouple technique and plotted against different cutting
velocity, V under dry, wet and Near Dry environment in turning hardened steel by uncoated
SNMG 120408 insert.
The variation in average chip-tool interface temperature at different cutting velocity,
feed and environment combinations are shown Fig. 2.6 and Fig. 2.7. The cutting temperature
generally increases with the increase in V and f though in different degree due to increased
energy input. So, for high-speed machining it is very important to control the cutting temperature.
It could be expected that Near Dry Lubrication would be more effective at higher values of V and
f. Fig. 2.6 and Fig. 2.7 show that Near Dry Lubrication is better than dry and wet machining for
all the V-f combinations.
It is evident from Fig. 2.6 and Fig. 2.7 that as the cutting velocity and feed rate
increases, the percentage reduction in average cutting temperature decreases. It may be for the
reasons that, the bulk contact of the chips with the tool with the increase in V and f do not allow
significant entry of air-coolant jet. Only possible reduction in the chip-tool contact length by the
72
Near Dry coolant jet particularly that which comes along the auxiliary cutting edge can reduce the
temperature to some extent particularly when the chip velocity is high due to higher V. So, at
industrial speed-feed conditions, this amount of reduction in average cutting temperature is quite
significant in pertaining tool life and surface finish.
The percentage saving in average chip-tool interface temperature θ attained by Near
Dry Lubrication for different V-f combinations have been extracted from the previous figures and
shown in Table 3.3 for hardened AISI 1060 steel. For convenience of comparison, the ranges and
averages of percentage savings in θ have been separately shown in Table 3.3 which visualizes
how the beneficial role of Near Dry Lubrication varied with different cutting conditions.
Table 3.3 Percentage reduction in chip-tool interface temperature (θ)
Feed rate, f,
mm/rev
Cutting velocity,
V,
m/min
Percentage reduction in (θ)
doc 1 mm
Percentage reduction in (θ)
doc 0.50 mm
Wet Near Dry Wet Near Dry
0.09
41 15.13 4.75 4.93 4.32
53 14.58 4.08 6.65 8.51
66 7.13 7.36 10.33 15.36
82 5.78 9.93 9.80 15.75
0.10
41 9.75 7.51 5.74 3.78
53 6.77 2.60 5.25 9.18
66 7.23 3.02 12.21 6.69
82 4.18 5.32 6.12 14.22
0.125
41 6.89 3.53 6.46 10.17
53 4.36 2.99 6.17 12.79
66 2.86 5.15 10.20 9.49
82 2.20 3.71 8.39 7.63
73
Table 3.4 Average percentage reduction in θ
Savings
Average percentage reduction in θ for
depth of cut 1.0 mm
Average percentage reduction in θ
for depth of cut 0.50 mm
Wet Near Dry Wet Near Dry
Range 2 16 3 10 5 11 4 16
Average 7.24 5.00 7.69 9.82
From the Table 3.3 and Table 3.4 it is found that, in case of Near Dry Lubrication by
cutting fluid among all V-f combinations the reduction in cutting temperature for V=82m/min and
f=0.09 mm/rev is more. In this V-f combination temperature reduction under wet and Near Dry
Lubrication by cutting fluid varies from 2~16% and 3~10% respectively for depth of cut 1 mm
and 5~11%, and 4~16% respectively for depth of cut 0.50 mm. It can be noticed that with the
increase in feed rate Near Dry Lubrication becomes less effective at higher cutting velocity but it
shows better performance at lower cutting velocities. This may be due to the increase in chip load
and increase in plastic contact length during cutting prevents the Near Dry Lubrication jet to enter
into the chip-tool interface. More over, it shows best reduction at higher velocity for lower feed
rate. Again Table 3.4 presents that the average percentage reduction in chip-tool interaction
temperature under wet and Near Dry Lubrication by cutting fluid and soluble oil are 7.24% and
5% respectively for depth of cut 1 mm and 7.69%, and 9.82% respectively for depth of cut 0.50
mm. Therefore, in all the tests through out the entire experiment, Near Dry Lubrication with
cutting fluid shows the best performance due to its better cooling and lubrication irrespective of
speed feed and depth of cut.
74
3.3 Product Quality
The value of any machined product of given material is generally assessed by surface
integrity and dimensional accuracy, which govern the performance and service life of that
product. For the present study, only dimensional accuracy and surface finish have been
considered for assessment of quality of product under dry, wet and Near Dry machining
conditions.
Surface finish is an important index of mach inability or grind ability because the
quality of any machined product of given material is generally assessed by dimensional accuracy
and surface integrity, which govern the performance and service life of that product. Generally,
good surface finish, if essential, is achieved by finishing processes like grinding but sometimes it
is left to machining. The major causes behind development of surface roughness in continuous
machining processes are:
i. regular feed marks left by the tool tip on the finished surface
ii. irregular deformation of the auxiliary cutting edge at the tool-tip due to chipping,
fracturing and wear
iii. vibration in the machining system
iv. built-up edge formation, if any
Even in absence of all other sources, the turned surface inherently attains some amount
of roughness of systematic and uniform configurations due to feed marks. The peak value of such
roughness depends upon the value of feed, f and the geometry of the turning inserts. Nose radius
essentially imparts edge strength and better heat dissipation at the tool tip but its main
contribution is drastic reduction in the aforesaid surface roughness as indicated by the simple
relationship,
75
r8
fh
2
m = (3.2)
Where,
hm = Peak value of roughness caused due to feed marks
r = Nose radius of the turning inserts
f = Feed rate
In actual machining, particularly at high feed and cutting velocity, the peak value, hm
may decrease, due to rubbing over the feed mark ridges by the inner sharp edge of the flowing
chips. Further deterioration of the cutting edge profile takes place due to chipping, wear etc.
Formation of built-up edge may also worsen the surface by further chipping and flaking of the
tool materials and by overflowing to the auxiliary flank at the tool-tip.
For the present study, only surface finish has been considered for assessment of quality
of product under dry, wet and Near Dry machining conditions. Surface roughness is an important
measuring criterion of machinability because performance and service life of the machined
component are often affected by its surface finish, nature and extent of residual stresses and
presence of surface or subsurface micro-cracks, if any, particularly when that component is to be
used under dynamic loading or in conjugation with some other mating part. However, it is evident
that Near Dry improves surface finish depending upon the work-tool materials and mainly
through controlling the deterioration of the auxiliary cutting edge by abrasion, chipping and built-
up edge formation.
76
Feed force as well as chip thickness ratio is responsible for surface roughness along the
longitudinal direction of the turned job. Usually surface roughness decreases with the increase in
cutting velocity as cutting force decreases and chip thickness ratio increases with the increase in
cutting speed. Fig 2.12 and Fig. 2.13 show the variation of the values of surface roughness, Ra
attained of machining of hardened AISI 1060 steel by the sharp SNMG 120408 Widia inserts at
various V-f combinations under dry, wet and Near Dry conditions. The surface roughness
increases with the increase in feed, f and decreases with the increase in V. Increase in f raises Ra
mainly. Reduction in Ra with the increase in V may be attributed to smoother chip-tool interface
with lesser chance of built-up edge formation in addition to possible truncation of the feed marks
and slight flattening of the tool-tip. Increase in V may also cause slight smoothing of the abraded
auxiliary cutting edge by adhesion and diffusion type wear and thus reduces surface roughness.
So, cutting velocity, V influences on surface roughness under dry, wet and Near Dry machining
conditions. It is clear that the surface roughness quite decreases with increasing cutting velocity
under dry machining. In case of Near Dry machining, surface roughness faster decreases with
increases cutting velocity. This is mainly because of formation of built-up edge frequently and
behaviour of materials to be machined in dry machining compared that of Near Dry machining.
It appears from Fig 2.12 and Fig. 2.13 that surface roughness grows quite fast under dry
machining due to more intensive temperature and stresses at the tool-tips. Near Dry condition
appeared to be effective in reducing surface roughness. However, it is evident that Near Dry
improves surface finish depending upon the work-tool materials and mainly through controlling
the deterioration of the auxiliary cutting edge by abrasion, chipping and built-up edge formation.
It has been also observed that the roughness of the machined surfaces is high at high feed rates
and vice versa, under dry, wet and Near Dry Lubrication conditions. The factors influence in that
phenomenon is the irregular deformation of the auxiliary cutting edge at the tool-tip due chipping,
fracturing and wear.
77
Figure 2.14 shows the effect of Near Dry Lubrication by cutting fluid on the
dimensional accuracy of the turned job. The finished job diameter generally deviates from its
desired value with the progress of machining, i.e. along the job-length mainly due to change in
the effective depth of cut for several reasons which include wear of the tool nose, over all
compliance of the machine-fixture-tool-work system and thermal expansion of the job during
machining followed by cooling. Therefore, if the machine-fixture-tool-work system is rigid,
variation in diameter would be governed mainly by the heat and cutting temperature. With the
increase in temperature the rate of growth of auxiliary flank wear and thermal expansion of the
job will increase. Near Dry Lubrication takes away the major portion of heat and reduces the
temperature resulting from decrease in dimensional deviation.
78
CHAPTER 4
CONCLUSIONS AND RECOMMENDATIONS
4.1 CONCLUSIONS
The following conclusions can be deduced from the experiments performed:
i. The present NDL systems enabled reduction in average chip-tool interface
temperature upto 16% by using water soluble cutting fluids and even such
apparently small reduction, unlike common belief, enabled significant
improvement in the major machinability indices.
ii. The form and color of the hardened steel chips became favorable for more
effective cooling due to NDL application.
iii. Reduction of cutting temperature has not been more effective for those tool-work
combinations and cutting conditions, which provided lower value of chip
thickness ratio, rc for adverse chip-tool interaction causing large friction and
build-up-edge formation at the chip-tool interface.
iv. Surface finishes also improved mainly due to reduction of wear and damage at the
tool tip by the application of NDL.
The dimensional deviation is less in near dry lubrication (NDL) condition
compared to dry machining by using uncoated SNMG insert due to fewer breaks
in wear or initial wear and absence of notching at the auxiliary flank of the insert.
79
4.2 RECOMMENDATIONS
As the research work is experimental in nature, the measurements should be taken
with not only a great care but also should use more precision tools and instruments.
i. Temperature is measured by using tool-work thermocouple technique.
Though this technique is reliable, infrared technique or XRD can be used
to compare the measured data. Data acquisition system for temperature
reading may be incorporated along with tool-work thermocouple.
ii. Measuring the chip thickness is a very difficult task. Riz produced on the
top surface can create some obstacle to take proper measurement by slide
caliper. More precision technique can be used.
iii. Under NDL only one jet is used along auxiliary cutting edge over the rake
face at an angle of 15 to 20 degree. Another one jet may be used along
principal cutting edge. Bore better performance third jet may be used from
the bottom side targeting the nose if the cutting insert. In this situation
summation of the lubricant amount for all these jets will be less than 50
ml/hr as prescribed for NDL.
iv. Various types of lubricant may be used for checking the performance and
comparative study among the lubricants. Synthetic, semi-synthetic,
insoluble oil, vegetable oil and olive oils may be tested for this purpose.
v. A high pressure pump either normal or common rail type may be used to
inject a very small amount oil into the flowing stream for proper
atomization and mixing.
80
vi. Formation of aerosol can be measured in parts per million and concluded
whether it is harmful for operators health or environment.
81
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