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i
SURFACE CHARACTERISTICS OF EN24 BY
ROLLER BURNISHING
A PROJECT REPORT
Submitted by
RAJIV.K 211611114077
SASIRAM KUMAR.S.P 211611114090
in partial fulfilment for the award of the degree
of
BACHELOR OF ENGINEERING
IN
MECHANICAL ENGINEERING
RAJALAKSHMI COLLEGE OF ENGINEERING, THANDALAM
ANNA UNIVERSITY: CHENNAI 600025
APRIL 2015
ii
ANNA UNIVERSITY: CHENNAI 600 025
BONAFIDE CERTIFICATE
Certified that this project report “SURFACE CHARACTERISTICS OF
EN24 BY ROLLER BURNISHING” is the bonafide work of “RAJIV.K
(211611114077) AND SASIRAM KUMAR.S.P (211611114090)”who carried
out the project work under my supervision.
SIGNATURE SIGNATURE
Dr.S.P.SRINIVASAN Mr.E.SHANKAR
HEAD OF THE DEPARTMENT, SUPERVISOR
ASSISTANT PROFESSOR,
Department of Mechanical Engineering, Department of Mechanical Engineering,
Rajalakshmi Engineering College, Rajalakshmi Engineering College,
Thandalam, Chennai-602105 Thandalam, Chennai-602105.
Submitted for the Anna University examination held on…………….
INTERNAL EXAMINER EXTERNAL EXAMINER
iii
ACKNOWLEDGEMENT
We would like to thank our Chairman Mr.S.Meganathan and our
Chairperson Dr. Mrs.Thangam Meganathan for providing us an institution,
which is an exemplary center for learning.
We express our sincere thanks to our Principal Dr.G.Thanigaiarasu and
Dr.S.N.Murugesan (Vice Principal) for providing adequate infrastructure and
congenical environment.
We would like to thank Dr.S.P.Srinivasan, HOD and for his timely
guidance and invaluable support.
We would like to thank our project guide Mr.E.Shankar, Assistant
Professor, Mechanical Department for his continuous support and the knowledge
shared and the practical exposure in completing our project.
We also extend our sincere thanks to all the staff members of mechanical
department who gave us valuable suggestions for doing this project.
Last but not the least, we would like to thank the Almighty for giving us
all the strength and courage in doing this project. We are grateful to our beloved
Parents, without whom we would not have been, as we are today. We also thank
all our friends and well wisher who have always been with us.
iv
TABLE OF CONTENTS
CHAPTER
NO.
TITLE PAGE
NO.
ABSTRACT vi
LIST OF TABLES vii
LIST OF FIGURES viii
1 INTRODUCTION 1
1.1 BURNISHING 1
1.2 BALL BURNISHING 2
1.2.1 In manufacturing 2
1.3 ROLLER BURNISHING 3
1.3.1 Advantages 5
1.3.2 Applications 5
2 LITERATURE SURVEY 7
3 MATERIAL SELECTION 9
3.1 TUNGSTEN CARBIDE 9
3.1.1 Properties of tungsten carbide 9
3.2 WORKPIECE 10
3.2.1 EN 24 10
4 MACHINING 13
4.1 INPUT PARAMETERS 14
4.2 KEROSENE 14
4.3 OUTPUT PARAMETERS 15
4.4 HARDNESS 16
4.4.1 Rockwell hardness 16
4.5 ROUGHNESS 17
v
4.6 TABULATION 19
5 COATING 22
5.1 INTRODUCTION 22
5.2 TITANIUM ALUMINIUM NITRIDE (TiAlN)
COATING
24
5.2.1 Applications 25
5.3 PHYSICAL VAPOUR DEPOSITION(PVD) 25
5.3.1 Process of PVD 26
5.4 CATHODIC ARC DEPOSITION 27
5.4.1 Process 27
5.4.2 Applications 28
5.5 TABULATION 30
6 RESULTS AND DISCUSSIONS 33
7 COST ESTIMATION 38
REFERENCE 39
vi
ABSTRACT
This project describes burnishing process as an alternate finishing process
for EN24 grade steel. Burnishing is a chipless machining process in which a
rotating roller or ball is pressed against metal piece. It is a cold working process
and involves plastic deformation under cold working conditions by pressing hard
against the workpiece. The burnishing process help to improve surface roughness
and hardness. The advantage of the burnishing process is non-chip removal to
attain surface finish. The effect of various input parameters such as spindle speed,
lubricants and number of passes on the output parameters such as surface
roughness and surface hardness is studied. The tool is coated with Titanium
Aluminium Nitride (TiAlN) and the machining is carried out with the coated
roller with the same input parameters. The effect of coating on the output
parameters are then calculated. From the results, it is noted that the coated
burnishing tool results in a better surface finish.
vii
LIST OF TABLES
TABLE NO. TITLE PAGE NO.
3.1
International Steel Specification Comparison
(EN24)
11
3.2 EN24 Steel Mechanical Properties 12
4.1 Hardness and surface roughness of EN24 after
machining without coating the tool
19
5.1 Hardness and surface roughness of EN24 after
machining with TiAlN coated roller
30
7.1 Cost Estimation 38
viii
LIST OF FIGURES
FIG. NO. TITLE PAGE NO.
1.1 Surface profile - Before Burnishing 1
1.2 Surface profile - After Burnishing 1
1.3 Roller Burnishing 4
1.4 Burnishing Tool 5
4.1 Experimental Setup 13
4.2 Rockwell Hardness C Test 17
4.3 Rockwell Hardness Tester 17
4.4 Surface Roughness Tester 18
4.5 Effect of speed on roughness – before coating 20
4.6 Effect of speed on hardness – before coating 21
5.1 Coated Roller 29
5.2 Effect of speed on hardness – after coating 31
5.3 Effect of speed on roughness – after coating 32
6.1 Comparing hardness values before and after
coating the tool – without lubricant
33
6.2 Comparing hardness values before and after
coating the tool – with lubricant
34
6.3 Comparing surface roughness values before and
after coating the tool – without lubricant
35
6.4 Comparing surface roughness values before and
after coating the tool – with lubricant
36
1
CHAPTER 1
INTRODUCTION
1.1 BURNISHING
Burnishing is the plastic deformation of a surface due to sliding contact
with another object. Visually, burnishing smears the texture of a rough surface
and makes it shinier. Burnishing may occur on any sliding surface if the contact
stress locally exceeds the yield strength of the material. As the pressure exceeds
the yield point of the work piece material, the surface is plastically deformed by
cold-flowing of subsurface material. Roller burnishing is a metal displacement
process. Microscopic “peaks” on the machined surface are caused to cold follow
into the “valleys”, creating a plateau- like profile in which sharpness is reduced
or eliminated in the contact plane. The main advantage of burnishing process over
other processes is the chip less removal to attain the required surface finish
thereby saving material and increasing hardness.
FIG 1.1 SURFACE PROFLIE FIG 1.2 SURFACE PROFILE
(BEFORE BURNISHING) (AFTER BURNISHING)
2
The most common forms of burnishing process are:
1. Ball burnishing
2. Roller burnishing
1.2 BALL BURNISHING
It is a metal-displacement process, in which, an oversize ball is pushed
through an undersized hole. The ball expands the hole by displacing an amount
of material equal to the interference fit.
The ball burnishing devices recommended for die and moulds are based on
a hydrostatic spring, whose main advantage is that ball load is constant during the
process and related to the maximum pressure survey by an external pump. This is
a high-pressure pump with low flow, taking coolant up from the machine-tool
reservoir. A movement of the ball head up to 10 mm is possible without changes
in the force value. The key element is a ceramic ball diameter 6 mm; this material
exhibits low adhesion to steels and cast irons, the constitutive materials of moulds
and dies.
Ball burnishing creates a shiny, highly reflective surface. This process is
typically done using steel media or a media with a high bulk density that yields a
cost effective, attractive finish. Ball burnishing finishes are very popular.
Typically they will have a shiny, high lustre appearance. In addition to polishing
the surface of the processed parts ball burnishing also creates a peening effect,
increasing the surface density which can improve the corrosion resistance of the
finished components.
3
1.2.1 BALL BURNISHING IN MANUFACTURING
A burnishing tool rubs against the work piece and plastically deforms its
surface. The work piece may be at ambient temperature, or heated to reduce the
forces and wear on the tool. The tool is usually hardened and coated with special
materials to increase its life.
Ball burnishing, Burnishing Balls, or ballizing, is a replacement for other
bore finishing operations such as grinding, honing, or polishing. A ballizing tool
consists of one or more over-sized balls that are pushed through a hole. The tool
is similar to a broach, but instead of cutting away material, it plows it out of the
way.
Burnishing Balls also occurs to some extent in machining processes. In
turning, burnishing occurs if the cutting tool is not sharp, if a large negative rake
angle is used, if a very small depth of cut is used, or if the work piece material is
gummy. As a cutting tool wears, it becomes blunter and the burnishing effect
becomes more pronounced. In grinding, since the abrasive grains are randomly
oriented and some are not sharp, there is always some amount of burnishing. This
is one reason the grinding is less efficient and generates more heat than turning.
1.3 ROLLER BURNISHING
In roller burnishing process, the tool is in the form of a cylinder which is
moved on the work piece at a constant feed rate. The single roller carbide
burnishing tool is used for burnishing varying outer diameters with a single tool.
With one tool different diameters can be burnished to achieve low surface finish.
Also there is no limitation on the burnishing length for this design tool. Highly
finished superior grade carbide rollers are used with precision assembly
arrangement. This tool is highly suitable in batch production where the diameter
of the job varies from one work order to another work order. Job Order quantity
4
as low as one number can also be processed with this tool so this tool is highly
useful in job shop production.
FIG 1.3 ROLLER BURNSIHING
Roller burnishing does not requires a skilled operators. This process can be
effectively used in many field such as aerospace industries, automobile
manufacturing sector, production of machine tool, hydraulic cylinders, etc.
Even though polishing occurs as a result of burnishing, polishing in itself not
burnishing. The distinction is that polishing will produce a smooth finish, but not
a hard one. Polishing is more about removing material to obtain the desired finish
where as one. Polishing is more about removing material to obtain the desired
finish whereas burnishing will generally result in a deeper polish than is possible
with polishing alone. A hardness or roughness test would be necessary to
distinguish between them.
5
FIG 1.4 BURNISHING TOOL
1.3.1 ADVANTAGES
1. Mirror like surface finish
2. Dimensional Consistency / Repeatability
3. Increase in Surface Hardness
4. Reduces the Reworks and Rejections.
1.3.2 APPLICATIONS
Roller burnishing was first applied in American industry in the 1930s to
improve the fatigue life or railroad car axles and rotating machinery shafts. By
the 1960s, roller burnishing was more widely applied, particularly in
the automotive industry, as other process advantages were recognized. The
primary benefits, related to part quality, are as follows: Accurate size control
(tolerances within 0.0005 inch or better, depending on
material types and other variables). ¸ Surface finished (typically between 1 to 10
micro inches Ra). ¸ Surface hardness (by as much as 5 to 10 % or more). Roller
6
burnishing has long been used on a wide variety of automotive and heavy
equipment components (construction, agricultural, mining and son on), including
piston and connecting rod bores, brake system components, transmission parts
and torque converter bubs. Burnishing tools are also now widely applied in non-
automotive applications for a variety of benefits; to produce better and longer
lasting seal surfaces; to improve wear life; to reduce friction and noise levels in
running parts; and to enhance cosmetic appearance.
Examples include valves, pistons of hydraulic or pneumatic cylinders, lawn
and garden equipment components, shafts for pumps, shafts running in
bushings, bearing bores, and plumbing fixtures.
7
CHAPTER 2
LITERATURE SURVEY
R. L. Murthy et al (1981) discussed the types and working methods of
burnishing process. Burnishing is considered as a cold working process which can
be used to improve surface characteristics. Surface roughness and hardness plays
an important role in many areas and is factor of great importance for the
functioning of machined parts.
Shankar et al (2008) discusses the effect of various input parameters on the
surface roughness and surface hardness of Al-(SiC)p metal matrix composites by
roller burnishing process and found out that when kerosene with graphite power
comparing with other lubricants such as soluble oil, mineral oil and kerosene
yields better results on surface roughness and surface hardness
A.M. Hassan et al (2000) explained the effects of ball and roller burnishing
on the surface roughness and hardness of some non- ferrous metals. It was
suggested by many investigators that an improvement in wear resistance can be
achieved by burnishing process.
U M Shirsat and B B Ahuja (2004) performed burnishing operation on
aluminium and found out that about 60-70% improvement in surface finish is
obtained and at different values of force ,speed and feed ,Kerosene gave best
surface finish.
A.A. Ibrahim et.al.(2009) performed burnishing on mild steel.
Experimental and fuzzy results showed that an increase in burnishing speed up to
1.5 m/s leads to a decrease in the burnished out-of-roundness whereas the increase
in burnishing speed more than 1.5m/sec results in an increase in out-of-roundness
8
L.N. Lo´pez de Lacalle et.al (2005) performed burnishing on heat treated
and tempered steel and found out that maximum pressure of 30 MPa leads to
highest quality improvement for the materials of 35-55 HRC.
Dabeer P.S. and Purohit G.K.(2010) used aluminium workpiece. Optimum
surface finish was obtained at 425rpm speed,7 mm ball diameter,70 N force and
2 tool passes.
S. Thamizhmnaii (2008) et al presented the surface roughness and hardness
investigations on titanium alloy using a roller burnishing tool.
M. H. El- Axir (2008) presented his experimental investigations in to roller
burnishing and the parameters which will affect the surface roughness values on
the specimens.
9
CHAPTER 3
MATERIALS
3.1 TUNGSTEN CARBIDE
The roller used is of tungsten carbide material. Tungsten carbide (WC) is a
chemical compound (specifically, a carbide) containing equal parts
of tungsten and carbon atoms. In its most basic form, tungsten carbide is a fine
grey powder, but it can be pressed and formed into shapes for use in industrial
machinery, cutting tools, abrasives, armour-piercing rounds, other tools and
instruments, and jewellery. Tungsten carbide is characterised by its high strength,
toughness and hardness. Its name derives from the Swedish for tung (heavy) and
sten (stone) and it is mainly used in the form of cemented tungsten carbides.
Cemented carbides (also known as hard metals) are made by 'cementing' grains
of tungsten carbide into a binder matrix of cobalt or/and nickel.
Tungsten carbide as a material can vary in carbide grain size (0.2 – 50
microns) and by binder contents (up to 30%), as well as by the addition of other
carbides. By varying the grain size of the tungsten carbide and the binder content
in the matrix, engineers have access to a class of materials whose properties can
be tailored to a variety of engineering applications. This includes high-tech tools,
wear parts and tools for the construction, mining and oil and gas sector.
Tungsten carbide products typically have a high resistance to wear and can
be used at high temperatures, allowing tungsten carbide's combined hardness and
toughness to significantly outperform its steel product equivalents.
3.1.1 PROPERTIES OF TUNGSTEN CARBIDE
1. Strength - Tungsten carbide has very high strength for a material so hard
and rigid. Compressive strength is higher than virtually all melted and cast or
forged metals and alloys.
10
2. Rigidity - Tungsten carbide compositions range from two to three times
as rigid as steel and four to six times as rigid as cast iron and brass. High resistance
to deformation and deflection is very valuable in those many applications where
a combination of minimum deflection and good ultimate strength merits first
consideration. These include spindles for precision grinding and rolls for strip or
sheet metal.
3. Impact Resistant - For such a hard material with very high rigidity, the
impact resistance is high. It is in the range of hardened tool steels of lower
hardness and compressive strength.
4. Heat and oxidation resistance - Tungsten-base carbides perform well up
to about 1000°F in oxidizing atmospheres and to 1500°F in non-oxidizing
atmospheres.
5. Wear-Resistance - Tungsten carbide wears up to 100 times longer than
steel in conditions including abrasion, erosion and galling. Wear resistance of
tungsten carbide is better than that of wear-resistance tool steels.
6. Melting and boiling points - Tungsten carbide has a high melting point
at 2,870 °C (5,200 °F), a boiling point of 6,000 °C (10,830 °F) when under a
pressure equivalent to 1 standard atmosphere (100 kPa).
3.2 WORKPIECE
3.2.1 EN24
EN24 is usually supplied in the T condition with a tensile strength of
850/1000 N/mm2.
EN24 steel is a popular grade of through-hardening alloy steel due to its
excellent machinability in the "T" condition. EN24 is used in components such as
11
gears, shafts, studs and bolts, its hardness is in the range 248/302 HB. EN24 can
be further surface-hardened to create components with enhanced wear resistance
by induction or nitriding processing.
Table 3.1 : International Steel Specification Comparison (EN24)
BS 970:1955 EN24
BS 970:1991 817M40T
German / DIN 34CrNiMo6
French AFNOR 35NCD6
American AISI /
SAE
4340
German
Werkstoff No.
1.6582
European
Standard
EN10277-5
817M40T - EN24T steel is a high tensile alloy steel renowned for its wear
resistance properties and also where high strength properties are required. EN24
is used in components subject to high stress and with a large cross section. This
can include aircraft, automotive and general engineering applications for example
propeller or gear shafts, connecting rods, aircraft landing gear components.
817M40 (EN24) Specification:
Chemical composition of EN24:
Carbon - 0.36-0.44%
Silicon - 0.10-0.35%
Manganese - 0.45-0.70%
12
Sulphur - 0.040 Max
Phosphorus - 0.035 Max
Chromium - 1.00-1.40%
Molybdenum - 0.20-0.35%
Nickel - 1.30-1.70%
Table 3.2 : 817M40T / EN24T Steel Mechanical Properties
Size
mm
Tensile
Strength
N/mm²
Yield
Stress
N/mm²
Elongation Impact
Izod J
Impact
KCV J
Hardness
HRC
63 to 150 850-1000 680 Min 13% 54 50 24-32
150 to 250 850-1000 654 Min 13% 40 35 24-32
Hardening EN24: Heat uniformly to 823/850°C until heated through. Quench in
oil.
Tempering: Heat uniformly and thoroughly at the selected tempering
temperature, up to 660°C and hold at heat for two hours per inch of total thickness.
Stress Relieving: Heat slowly to 650-670°C, soak well. Cool the EN24 tool in a
furnace or in air.
13
CHAPTER 4
MACHINING
The machining process is done on an automatic centre lathe. The input
parameters chosen to be studied are:
1. Speed
2. Number of passes
3. Lubricant
FIG 4.1 EXPERIMENTAL SETUP
14
The work piece is rotated at varying speeds of 200rpm, 300rpm, and 500rpm.
This is because the recommended value of speed is 530rpm. The machining is
done at 1, 2 and 3 number of passes for each speed. In addition, kerosene is used
as a lubricant and the effect of lubricant on the machinihg process is studied.
4.1 INPUT PARAMETERS
SPEED: N1 = 200rpm
N2 = 300rpm
N3 = 500rpm
NO. OF PASSES = 1, 2, 3
LUBRICANT USED: Kerosene
4.2 KEROSENE
Kerosene is a combustible hydrocarbon liquid widely used as a fuel, in
industry, and in households. Its name is derived from Greek keros meaning wax,
and was registered as a trademark by Abraham Gesner in 1854 before evolving
into a genericized trademark. It is sometimes spelled kerosene in scientific and
industrial usage. The term "kerosene" is common in much of India, Canada, the
United States, Australia and New Zealand. Kerosene is usually called paraffin in
the UK, Ireland, Southeast Asia and South Africa. A more viscous paraffin oil is
used as a laxative. A waxy solid extracted from petroleum is called paraffin wax.
15
In industry:
As a petroleum product miscible with many industrial liquids, kerosene can
be used as both a solvent, able to remove other petroleum products, such as chain
grease, and as a lubricant, with less risk of combustion when compared to using
gasoline. It can also be used as a cooling agent in metal production and treatment
(oxygen-free conditions).
In the petroleum industry, kerosene is often used as a synthetic hydrocarbon for
corrosion experiments to simulate crude oil in field conditions.
Kerosene has been found to be an effective pesticide.
4.3 OUTPUT PARAMETERS
The output parameters measured are:
1. Surface hardness – HRC scale
2. Surface roughness – Ra scale
The feed rate and depth of cut were kept constant at 180mm/m and 0.5mm
respectively.
4.4 HARDNESS
Hardness is defined as the ability of a material to resist plastic deformation,
usually by indentation. The term may also refer to resistance to:
1. Scratching
2. Abrasion
3. Cutting
4. Penetration
It is the property of a metal which gives it the ability to resist being
permanently deformed when a load is applied. Therefore, hardness is important
from an engineering standpoint because resistance to wear by either friction or
16
erosion by various elements generally increases with hardness. The greater the
hardness of the metal, the greater resistance it has to deformation.
The common indentation hardness tests are:
1. Rockwell hardness
2. Brinell hardness
3. Vickers hardness
4.4.1 ROCKWELL HARDNESS
The Rockwell scale is a hardness scale based on indentation hardness of a
material. The Rockwell test determines the hardness by measuring the depth of
penetration of an indenter under a large load compared to the penetration made
by a preload. There are different scales, denoted by a single letter, that use
different loads or indenters.
HRC scale is taken. Load - 150 kgf. Indenter - 120° diamond cone
FIG 4.2 ROCKWELL HARDNESS C TEST
17
FIG 4.3 ROCKWELL HARDNESS TESTER
4.5 ROUGHNESS
Surface roughness, often shortened to roughness, is a component of surface
texture. It is quantified by the deviations in the direction of the normal vector of
a real surface from its ideal form. If these deviations are large, the surface is
rough; if they are small, the surface is smooth. Roughness plays an important role
in determining how a real object will interact with its environment. Rough
surfaces usually wear more quickly and have higher friction coefficients than
smooth surfaces. Roughness is often a good predictor of the performance of a
mechanical component, since irregularities in the surface may form nucleation
sites for cracks or corrosion.
The roughness is taken in the Ra scale. Ra is the arithmetic mean of all
values in a particular area.
18
FIG 4.4 SURFACE ROUGHNESS TESTER
A portable surface roughness tester able to operate independently of mains
power and make measurements on almost any part of a workpiece of practically
any size. The 2.4-inch colour graphic back-lit LCD provides excellent readability
and an intuitive display that is easy to use. Operation is by keys on the front of
the unit and under the sliding cover. Up to 10 measurement conditions and one
measured profile can be stored in the internal memory. An optional memory card
can be used as an extended memory to store large quantities of measured surface
profiles and setup conditions. Access to each feature can be protected to prevent
unintended operation. An alarm warns when the stylus should be checked for
wear. Complies with the applicable international standards concerning definition
and calculation of the values of surface roughness parameters. In addition to
calculation results, sectional calculation results and assessed profiles, bearing
curves, and amplitude distribution curves can be displayed.
19
4.6 TABULATION
BEFORE COATING:
Table 4.1: Hardness and surface roughness of EN24 after
machining with uncoated tool
PASS SPEED
(rpm)
WITHOUT LUBRICANT WITH LUBRICANT
HARDNESS
(HRC)
ROUGHNESS
(Ra)
HARDNESS
(HRC)
ROUGHNESS
(Ra)
1
200 33 1.55 32 1.68
300 32 0.73 33 1.38
500 32 0.91 33 1.2
2
200 32 1.54 31 0.85
300 32 0.72 34 1.2
500 33 0.83 32 1
3
200 30 1.51 32 1.1
300 33 0.71 33 0.85
500 31 1.10 32 1.12
The results are drawn as a graph.
20
FIG 4.5 Effect of speed on roughness
LEGEND:
Straight lines – without lubricant
Dotted lines – with lubricant
From the graph, it can be inferred that the surface roughness of the
workpiece decreases as the number of passes and the speed increases. The surface
roughness increases when kerosene is used as lubricant. For the lowest surface
roughness, it is recommended to machine at 300rpm since the lowest roughness
is obtained at this speed – 0.71µm for 3 passes, 0.72 µm for 2 passes and 0.73 µm
for 1 pass.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 100 200 300 400 500 600
No. of pass - 1
No. of pass - 2
No. of pass - 3
No. of pass -1
No. of pass - 2
No. of pass - 3
SPEED(rpm)
RO
UG
HN
ESS(
Ra)
21
FIG 4.6 Effect of speed on hardness
LEGEND:
Dotted lines – with lubricant
Straight lines – without lubricant
The hardness increases slightly but the burnishing process has no
significant effect on the hardness of the workpiece. The best hardness is obtained
at 2 number of passes and 300rpm (34 HRC).
29.5
30
30.5
31
31.5
32
32.5
33
33.5
34
34.5
0 100 200 300 400 500 600
No. of pass - 1
No. of pass - 2
No. of pass - 3
No. of pass - 1
No. of pass - 2
No. of pass - 3
SPEED(rpm)
HA
RD
NES
S(H
RC
)
22
CHAPTER 5
COATING
5.1 INTRODUCTION TO COATING
Friction and wear are major factors limiting the performance and service
life of tools and precision components. Coating them is the most effective and
frequently the only possibility of making a decisive difference to their operational
performance.
Tools coated improve the productivity and quality of metalworking and
plastics processing, while coated components in vehicles, machines and
appliances fulfil their functions more reliably and for a longer time.
It was vacuum coating that first made forward-looking developments
possible, for instance with tools for high-speed and dry working or highly loaded
components for the latest diesel injection systems.
Coating offers the following practical advantages:
1. Improved performance with smaller dimensions
2. Increased operational reliability and service life
3. Protection against deficient lubrication / emergency running conditions and
the possibility of running dry
4. Reduction in energy, fuel and lubricant consumption
5. Avoidance of the use of expensive materials
6. Reduction in liability to corrosion
7. Bio-compatibility and approval for food processing applications
23
Coating processes may be classified as follows:
Vapour deposition:
Chemical vapour deposition
1. Metalorganic vapour phase epitaxy
2. Electrostatic spray assisted vapour deposition (ESAVD)
3. Sherardizing
4. Some forms of Epitaxy
5. Molecular beam epitaxy
Physical vapour deposition
1. Cathodic arc deposition
2. Electron beam physical vapour deposition (EBPVD)
3. Ion plating
4. Ion beam assisted deposition (IBAD)
5. Magnetron sputtering
6. Pulsed laser deposition
7. Sputter deposition
8. Vacuum deposition
9. Vacuum evaporation, evaporation (deposition)
Chemical and electrochemical techniques
1. Conversion coating
2. Anodising
3. Chromate conversion coating
4. Plasma electrolytic oxidation
5. Phosphate (coating)
6. Ion beam mixing
7. Pickled and oiled, a type of plate steel coating
8. Plating
9. Electroless plating
10. Electroplating
24
Some of the common materials used for coating tools are:
1. TiN
2. TiCN
3. AlCrN
4. TiAlN
5. TiCrN
The material that has been chosen to coat the burnishing tool is TiAlN because of
its wear resistance properties.
5.2 TITANIUM ALUMINIUM NITRIDE (TiAlN) COATING
One commercial coating type used to improve the wear resistance of
tungsten carbide tools is the TiAlN coating. The coating are sometimes doped
with at least one of the elements like silicon, boron, oxygen in order to improve
selected properties for specific applications These coatings are also used to create
multilayer systems. The coating types mentioned above are applied to protect
tools including special tools for medical applications. They are also used as
decorative finishes. Aluminium Titanium Nitride (TiAlN) is a hard coating that
solves many tribological problems with components that can be coated at
temperatures of 450°C - 475°C. Calico-TiAlN is normally applied to steels,
hardened steels, aluminium and materials where high wear resistance and
lubricity are needed. TiAlN coating provides exceptional oxidation resistance and
extreme hardness. That's why this coating works well in very demanding cutting
tool applications, especially when tools are being pushed to the max.
Titanium aluminium nitride (TiAlN) or aluminium titanium nitride (AlTiN; for
aluminium contents higher 50 at. %) stands for a group of metastable hard
coatings consisting of the metallic elements aluminium and titanium, and
nitrogen. Four important compositions (metal content 100 at. %) are deposited in
industrial scale by physical vapour deposition methods.
25
The coatings are mostly deposited by cathodic arc deposition or magnetron.
Even though most TiAlN and AlTiN coatings are industrially synthesized using
alloy targets with specific percentages of aluminium and titanium it is possible to
produce TiAlN coatings with pure Al and Ti targets using a cathodic arc
deposition technique. TiAlN and AlTiN coatings from pure Al and pure Ti targets
by Cathodic arc deposition have been produced industrially by Nano Shield PVD
Thailand since 1999. By using separate target technology it is possible to offer
more flexibility regarding the structure and composition of the coating.
5.2.1 APPLICATIONS
1. High performance coating in ferrous materials.
2. Excellent high temperature resistance and hardness.
3. Maintains high surface hardness at elevated temperatures improving
tool life and allowing faster feed rates.
4. Produces aluminium oxide layer at high temperature which reduces
thermal conductivity transferring heat into the chip.
5. Excellent in dry machining, machining titanium alloys, stainless
alloys, and cast iron.
5.3 PHYSICAL VAPOUR DEPOSITION
Physical vapour deposition (PVD) describes a variety of vacuum
deposition methods used to deposit thin films by the condensation of a vaporized
form of the desired film material onto various workpiece surfaces (e.g., onto
semiconductor wafers).
The coating method involves purely physical processes such as high-
temperature vacuum evaporation with subsequent condensation, or plasma sputter
bombardment rather than involving a chemical reaction at the surface to be coated
as in chemical vapour deposition.
26
5.3.1 PROCESS OF PHYSICAL VAPOUR DEPOSITION
The high-purity, solid coating material (metals such as titanium, chromium
and aluminium) is either evaporated by heat or by bombardment with ions
(sputtering). At the same time, a reactive gas (e.g. nitrogen or a gas containing
carbon) is introduced; it forms a compound with the metal vapour and is deposited
on the tools or components as a thin, highly adherent coating. In order to obtain a
uniform coating thickness, the parts are rotated at uniform speed about several
axes. The properties of the coating (such as hardness, structure, chemical and
temperature resistance, adhesion) can be accurately controlled.
In the automotive world, it is the newest alternative to the chrome plating that has
been used for trucks and cars for years. This is because it has been proven to
increase durability and weigh less than chrome coating, which is an advantage
because a vehicle's acceleration and fuel efficiency will increase. Physical vapour
deposition coating is gaining in popularity for many reasons, including that it
enhances a product’s durability. In fact, studies have shown that it can enhance
the lifespan of an unprotected product tenfold.
Variants of PVD include, in alphabetical order:
1. Cathodic Arc Deposition: In which a high-power electric arc discharged at
the target (source) material blasts away some into highly ionized vapor to
be deposited onto the work piece.
2. Electron beam physical vapour deposition: In which the material to be
deposited is heated to a high vapour pressure by electron bombardment in
"high" vacuum and is transported by diffusion to be deposited by
condensation on the (cooler) work piece.
3. Evaporative deposition: In which the material to be deposited is heated to
a high vapour pressure by electrically resistive heating in "low" vacuum.
4. Pulsed laser deposition: In which a high-power laser ablates material from
the target into a vapour.
27
5. Sputter deposition: In which a glow plasma discharge (usually localized
around the "target" by a magnet) bombards the material sputtering some
away as a vapour for subsequent deposition.
PVD is used in the manufacture of items, including semiconductor devices,
aluminized PET film for balloons and snack bags, and coated cutting tools for
metalworking. Besides PVD tools for fabrication, special smaller tools (mainly
for scientific purposes) have been developed. They mainly serve the purpose of
extreme thin films like atomic layers and are used mostly for small substrates. A
good example are mini e-beam evaporators which can deposit monolayers of
virtually all materials with melting points up to 3500 °C.
Common coatings applied by PVD are Titanium nitride, Zirconium nitride,
Chromium nitride, Titanium aluminium nitride.
The source material is unavoidably also deposited on most other surfaces
interior to the vacuum chamber, including the fixtures to hold the parts.
5.4 CATHODIC ARC DEPOSITION
Cathodic arc deposition or Arc-PVD is a physical vapour deposition
technique in which an electric arc is used to vaporize material from a cathode
target. The vaporized material then condenses on a substrate, forming a thin film.
The technique can be used to deposit metallic, ceramic, and composite films.
5.4.1 PROCESS OF CATHODIC ARC DEPOSITION
The arc evaporation process begins with the striking of a high current, low
voltage arc on the surface of a cathode (known as the target) that gives rise to a
small (usually a few micrometres wide), highly energetic emitting area known as
a cathode spot. The localised temperature at the cathode spot is extremely high
(around 15000 °C), which results in a high velocity(10 km/s) jet of vaporised
28
cathode material, leaving a crater behind on the cathode surface. The cathode spot
is only active for a short period of time, then it self-extinguishes and re-ignites in
a new area close to the previous crater. This behaviour causes the apparent motion
of the arc.
As the arc is basically a current carrying conductor it can be influenced by
the application of an electromagnetic field, which in practice is used to rapidly
move the arc over the entire surface of the target, so that the total surface is eroded
over time.
The arc has an extremely high power density resulting in a high level of
ionization (30-100%), multiple charged ions, neutral particles, clusters and
macro-particles (droplets). If a reactive gas is introduced during the evaporation
process, dissociation, ionization and excitation can occur during interaction with
the ion flux and a compound film will be deposited.
One downside of the arc evaporation process is that if the cathode spot stays
at an evaporative point for too long it can eject a large amount of macro-particles
or droplets. These droplets are detrimental to the performance of the coating as
they are poorly adhered and can extend through the coating. Worse still if the
cathode target material has a low melting point such as aluminium the cathode
spot can evaporate through the target resulting in either the target backing plate
material being evaporated or cooling water entering the chamber. Therefore
magnetic fields as mentioned previously are used to control the motion of the arc.
If cylindrical cathodes are used the cathodes can also be rotated during deposition.
By not allowing the cathode spot to remain in one position too long aluminium
targets can be used and the number of droplets is reduced. Some companies also
use filtered arcs that use magnetic fields to separate the droplets from the coating
flux.
29
5.4.2 APPLICATION OF CATHODIC ARC DEPOSITION
Cathodic arc deposition is actively used to synthesize extremely hard film
to protect the surface of cutting tools and extend their life significantly. A wide
variety of thin hard-film, Super hard coatings and Nano composite coatings can
be this technology including TiN, TiAlN, CrN, ZrN, AlCrTiN and TiAlSiN.
This is also used quite extensively particularly for carbon ion deposition to create
diamond-like carbon films. Because the ions are blasted from the surface
ballistically, it is common for not only single atoms, but larger clusters of atoms
to be ejected. Thus, this kind of system requires a filter to remove atom clusters
from the beam before deposition. The DLC film from filtered-arc contains
extremely high percentage of sp3 diamond which is known as tetrahedral
amorphous carbon, or ta-C.
The coating was done at Oerlikon Balzers Coating India Ltd. by cathodic
arc deposition method.
Machining was done again after the tool was coated with TiAlN.
The input parameters were kept the same and the output parameters were
measured to know the effect of TiAlN coating on the burnishing tool.
FIG 5.1 COATED ROLLER
30
5.5 TABULATION
AFTER COATING:
Table 5.1: Hardness and surface roughness of EN24 after
machining with TiAlN coated roller.
PASS SPEED
(rpm)
WITHOUT LUBRICANT WITH LUBRICANT
HARDNESS
(HRC)
ROUGHNESS
(Ra)
HARDNESS
(HRC)
ROUGHNESS
(Ra)
1
200 32 1.24 32 1.08
300 33 0.88 33 0.86
500 33 0.88 32 1.65
2
200 33 1.18 33 0.60
300 34 0.79 33 0.83
500 34 0.46 34 0.37
3
200 32 1.12 34 0.98
300 33 0.86 34 0.77
500 34 0.72 35 1.12
The results are drawn as a graph.
31
LEGEND:
Dotted lines – with lubricant
Straight lines – without lubricant
FIG 5.2 Effect of speed on hardness
From the graph it can be inferred that after coating, there is a general
trend of increasing hardness as the number of pass and speed increases. Highest
hardness is obtained at 300rpm and 3 passes when using kerosene as lubricant
(35HRC). Higher hardness are obtained when using lubricant.
31.5
32
32.5
33
33.5
34
34.5
35
35.5
0 100 200 300 400 500 600
No. of pass - 1
No. of pass - 2
No. of pass - 3
No. of pass - 1
No. of pass - 2
No. of pass - 3
SPEED(rpm)
HA
RD
NES
S(H
RC
)
32
LEGEND:
Dotted lines – with lubricant
Straight lines – without lubricant
FIG 5.3 Effect of speed on roughness
From the graph, it is inferred that there is a general trend of decreasing
roughness with speed. However, the best surface finish is obtained at 300rpm and
2 passes on an average. Lubricant has no effect on the roughness of the workpiece.
Best surface finish is obtained at 200rpm and 2 passes without lubricant.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 100 200 300 400 500 600
No. of pass - 1
No. of pass - 2
No. of pass - 3
No. of pass - 1
No. of pass - 2
No. of pass - 3
SPEED(rpm)
RO
UG
HN
ESS(
Ra)
33
CHAPTER 6
RESULTS AND DISCUSSIONS
FIG 6.1 HARDNESS – WITHOUT LUBRICANT
LEGEND:
Straight lines – before coating
Dotted lines – after coating
29.5
30
30.5
31
31.5
32
32.5
33
33.5
34
34.5
1 Pass, 200rpm 1 Pass, 300rpm1 Pass, 500rpm2 Pass, 200rpm 2 Pass, 300rpm2 Pass, 500rpm3 Pass, 200rpm 3 Pass, 300rpm3 Pass, 500rpm
34
FIG 6.2 HARDNESS – WITH LUBRICANT
LEGEND:
Straight lines – before coating
Dotted lines – after coating
28
29
30
31
32
33
34
35
1 Pass,200rpm
1 Pass,300rpm
1 Pass,500rpm
2 Pass,200rpm
2 Pass,300rpm
2 Pass,500rpm
3 Pass,200rpm
3 Pass,300rpm
3 Pass,500rpm
35
FIG 6.3 SURFACE ROUGHNESS – WITHOUT LUBRICANT
LEGEND:
Straight lines – before coating
Dotted lines – after coating
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
1 Pass,200rpm
1 Pass,300rpm
1 Pass,500rpm
2 Pass,200rpm
2 Pass,300rpm
2 Pass,500rpm
3 Pass,200rpm
3 Pass,300rpm
3 Pass,500rpm
36
FIG 6.4 SURFACE ROUGHNESS – WITH LUBRICANT
LEGEND:
Straight lines – before coating
Dotted lines – after coating
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
1 Pass,200rpm
1 Pass,300rpm
1 Pass,500rpm
2 Pass,200rpm
2 Pass,300rpm
2 Pass,500rpm
3 Pass,200rpm
3 Pass,300rpm
3 Pass,500rpm
37
1. Effect of speed on hardness and roughness of EN24
There is an increase in hardness as the speed increases and decrease in
roughness as the speed increases and then increases as the speed increases. This
is due to better stabilization of the tool and workpiece at increasing speeds. The
highest values of hardness and the lowest values of surface roughness are obtained
at the speed of 300rpm – 35HRC and 0.71µm on an average. The best surface
finish is at 0.37µm at 500rpm.
2. Effect of number of pass on hardness and roughness of EN24
As the number of passes increases, the roughness goes on decreasing
generally. The best surface finishes are obtained at 2 passes on an average. The
best surface finish is 0.37 µm at 2 passes. This may be because of repeatedly
passing the burnishing tool on the workpiece.
3. Effect of lubricant on hardness and roughness of EN24
The use of kerosene as lubricant has little to no effect on the roughness
of the workpiece. Usage of kerosene increases hardness generally but the increase
in hardness is very little. This may be because the heat generated while burnishing
is not so great so as to warrant the use of lubricant.
4. Effect of coating of roller on hardness and roughness of EN24
From the comparative graphs, it can be inferred that the coating the
tool with TiAlN increase the hardness and decreases the roughness significantly.
This may be due to increase in hardness of the tool after coating the tool. There
is a maximum reduction of 40.48% in surface roughness value after coating the
tool.
38
CHAPTER 7
COST ESTIMATION
NO. PROJECT DETAILS COST(Rs.)
1 TOOL 15000
2 WORKPIECE 600
3 MACHINING 1100
4 HARDNESS TEST 1600
5 ROUGHNESS TEST 1600
6 COATING 220
TOTAL 20120
39
REFERENCE
1. Malleswara Rao J. N., Chenna Kesava Reddy A. & Rama Rao P. V.,“The
effect of roller burnishing on surface hardness and surface roughness on mild
steel specimens”, International Journal Of Applied Engineering Research,
Dindigul Volume 1, No 4, (2011).
2. Deepak Mahajan, Ravindra Tajane - A Review on Ball Burnishing Process.
International Journal of Scientific and Research Publications, Volume 3, Issue
4, April 2013 ISSN 2250-3153
3. Hudayim Basak and H. Haldun Goktas,”Burnishing process on al-alloy and
optimization of surface roughness and surface hardness by fuzzy logic”,
Materials and Design ,Vol. 30 (2009),pp.1275–1281.
4. C.H. Che-Haron, Tool life and surface integrity in turning titanium alloy,
Journal of Materials Processing Technology 118 (2001) 231-237.
5. A.M. Hassan, The effects of ball and roller burnishing on the surface
roughness and hardness of some non-ferrous metals, Journal of Materials
Processing Technology 72 (1997).