CH-5-6 Merchant Theory &Temperature in Cutting.pdf

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1. MANUFACTURING ENGINEERING II
CHAPTER FIVE
MERCHANT THEORY

1
By: Teshome D. (M.Sc)

2. Note Outline
Introduction
Mechanics of Cutting
Cutting Forces and Power
Temperatures in Cutting
Tool Life: Wear and Failure
Cutting Fluid
2

3. Mechanics of Cutting
3

4. Mechanics of Cutting
Major independent variables in the cutting process:
•Tool material and coatings
•Tool shape, surface finish, and sharpness
•Workpiece material and condition
•Cutting speed, feed, and depth of cut
•Cutting fluids
•Characteristics of the machine tool
•Work holding and fixturing
4

5. Mechanics of Cutting
Dependent variables in cutting (influenced by changes in
independent variables):
•Type of chip produced
•Force and energy dissipated during cutting
•Temperature rise in the workpiece, the tool and the chip
•Tool wear and failure
•Surface finish and surface integrity of the workpiece
5

6. 6

7. Mechanics of Metal Cutting

Assumptions (Orthogonal Cutting Model)
•The cutting edge is a straight line extending perpendicular to the
direction of motion, and it generates a plane surface as the work
moves past it.
•The tool is perfectly sharp (no contact along the clearance face).
•The shearing surface is a plane extending upward from the cutting
edge.
•The chip does not flow to either side
•The depth of cut/chip thickness is constant uniform relative velocity
between work and tool
•Continuous chip, no built-up-edge (BUE)

7

8. TERMINOLOGY

8

9. Mechanics of Cutting
•Merchant model is known as orthogonal cutting
•It is two dimensional and the forces involved are perpendicular to
each other
•Cutting tool has a rake angle () and a relief or clearance angle
•Shearing takes place in a shear zone at shear angle ()
9

10. 10

11. Mechanics of Cutting
11 Basic mechanism of chip formation by shearing
Velocity diagram
showing angular
relationship among
3 speeds in cutting
zone:
V: cutting speed
V
s: shearing speed
V
c: chip velocity

12. Mechanics of Cutting
•Imagine shearing: “deck of cards” sliding along each other
•Below shear plane, workpiece: undeformed
•Above shear plane: chip moves up rake face (tool)
•Dimension d (distance between shear planes, OC)
–highly exaggerated to show mechanism
–It is only in order of 10
-2
to 10
-3
mm
•Some materials shear in a zone (not plane:)
–e.g. cast iron
–this leads to surface defects in workpiece
12

13. Mechanics of Cutting
Cutting Ratio (or chip-thickness ratio, r )
•The ratio is related to the two angles
–shear angle, 
–rake angle, 


•Chip thickness t
c is always > than the depth of cut, t
o
⇒ the value of r is always less than unity (i.e. <1)
•Reciprocal of r (i.e. 1/r ) is known as the chip-compression ratio or
chip-compression factor
–It‟s a measure of how thick the chip has become
–Always > 1 13 








cos
sin
sin1
cos
tan
0
ct
t
r
r
r

14. Mechanics of Cutting
Making use of cutting ratio in evaluating cutting conditions:
•depth of cut, t
o: machine setting (i.e. independent variable)
•Chip thickness, t
c can be measured using micrometer
•Cutting ratio, r can then easily be calculated
•Rake angle,  is also known for cutting operation
–It is function of tool and workpiece geometry
•Cutting ratio and rake angle can be used to find shear angle, 
14

15. 15

16. Mechanics of Cutting
Shear Strain
•The shear strain (i.e. deformation relative to original size) that the
material undergoes can be expressed as

•Large shear strains (≥5) are associated with low shear angles or
with low or negative rake angles
•Based on the assumption that the shear angle adjusts itself to
minimize the cutting force,
16   tancot
OC
OB
OC
AO
OC
AB 45
22
45





β = friction angle, related to μ :
μ = tanβ  coefficient of –dynamic – friction
μ usually: 0.5 – 2
Note, first form is more generally used

17. Mechanics of Cutting
•Chip encounters friction as it moves up the rake face
•Large variations in contact pressure and temperature are
encountered at the tool-chip interface (rake face)
•This causes big changes in μ and it is thus called “apparent mean
coefficient of friction”
•Equation thus indicates:
–As rake angle ↓ or friction at rake face ↑
⇒ shear angle ↓ and chip becomes thicker
–Thicker chip ⇒ more energy lost because shear strain is higher
–Because work done during cutting is converted into heat ⇒
temperature rise is higher
17

18. 18

19. Mechanics of Cutting
Velocities in the Cutting Zone
•Since t
c > t
o ⇒ V
c (velocity of chip) < V (cutting speed)
•Since mass continuity is maintained,


•From Velocity diagram, obtain equations from trigonometric
relationships (V
s velocity at shearing plane):


•Note also thatc
19 



cos
sin
or
0
V
VVrVtVVt
cccc   sincoscos
cs VVV

 V
V
t
t
r
c
c

0

20. Mechanics of Cutting: Oblique Cutting
•Orthogonal cutting: chip slides directly up face of tool
•Oblique cutting: chip is helical, at an inclination angle
–Chip movement is like snow from snowplow blade: sideways
–i.e. helical chip don‟t interfere with cutting zone, unlike
orthogonal cutting
•The effective rake angle is
–Note i, 
n can be measured directly to find 
e
–As i ↑ ⇒ 
e ↑ ⇒ chip becomes thinner and longer ⇒ cutting
force ↓ (very important finding!)
20  
ne
ii  sincossinsin
221

 )(i

21. Mechanics of Cutting: Oblique Cutting
Shaving and Skiving
•Thin layers of material can be removed from straight or curved
surfaces (similar to shaving wood with a plane)
•Shaving can improve the surface finish and dimensional accuracy
•Parts that are long or combination of shapes are shaved by skiving
–A specially shaped cutting tool is moved tangentially across the
length of the workpiece
21

22. 22
c
t

23. 23

24. Terminology

24

25. 25

26. Cutting Forces and Power
Knowledge of cutting forces and power involves:
1.Data on cutting forces
–important to minimize distortions, maintain required dimensional accuracy, help
select appropriate toolholders
2.Power requirements
–enables appropriate tool selection
26
Forces acting in the
cutting zone during
2-D (orthogonal)
cutting
Force circle to determine various
forces in cutting zone

27. Cutting Forces and Power
•Forces considered in orthogonal cutting include
–Cutting, friction (tool face), and shear forces
•Cutting force,F
c acts in the direction of the cutting speed V, and supplies the
energy required for cutting
–Ratio of F
c to cross-sectional area being cut (i.e. product of width and depth of
cut, t
0) is called: specific cutting force
•Thrust force,F
t acts in a direction normal to the cutting force
•These two forces produces the resultant force, R
–see force circle
–On tool face, resultant force can be resolved into:
–Friction force, F along the tool-chip interface
–Normal force, N to  to friction force
27

28. Power

28 Vwt
VF
u
ss
s
0


29. Cutting Forces and Power
Power
•The power dissipated in friction is


•The specific energy for friction, u
f is


•Total specific energy, u
t is


29 cFVfrictionfor Power 00wt
Fr
Vwt
FV
u
c
f  fst uuu 

30. Cutting Forces and Power
Power
30
•Prediction of forces is based
largely on experimental data
(right)
•Wide ranges of values is due
to differences in material
strengths
•Sharpness of the tool tip also
influences forces and power
•Duller tools require higher
forces and power

31. Cutting Forces and Power
Measuring Cutting Forces and Power
•Cutting forces can be measured using a force transducer, a
dynamometer or a load cell mounted on the cutting-tool holder
•It is also possible to calculate the cutting force from the power
consumption during cutting (provided mechanical efficiency of
the tool can be determined)
•The specific energy u, in cutting can be used to calculate cutting
forces
31

32. 32
CHPTER SIX
TEMPERATURE IN CUTTING
&
CUTTING FLUIDS

33. Temperatures in Cutting
Temperature rise (due to heat lost in cutting ⇒ raising temp. in
cutting zone) - its major adverse effects:
1.Lowers the strength, hardness, stiffness and wear resistance of the
cutting tool (i.e. alters tool shape)
2.Causes uneven dimensional changes (machined parts)
3.Induce thermal damage and metallurgical changes in the machined
surface (⇒ properties adversely affected)
33

34. Temperatures in Cutting
Sources of heat in machining:
a.Work done in shearing (primary shear zone)
b.Energy lost due to friction (tool-chip interface)
c.Heat generated due to tool rubbing on machined surface
(especially dull or worn tools)
34

35. 35

36. Temperatures in Cutting
Temperature Distribution
Sources of heat generation are concentrated in
–primary shear zone, and
–At tool–chip interface
–⇒ v. large temp. gradients
in the cutting zone (right)
•Note max. temp is about
halfway up tool-chip
interface (why?)


36

37. Temperatures in Cutting
Temperature Distribution
•Note:
–Highest temp.:
1100ºC
–High temp.
appear as dark-
color on chips
(by oxidation
at high V )
–Reason: as V ↑
⇒ time for heat
dissipation ↓
⇒ temp. ↑
37
a) flank temperature
distribution
Temperatures developed in turning 52100 steel
b) tool-chip interface temp.
distribution (note, abscissa:
0: tool tip; 1: end of tool-chip
contact)

38. Temperatures in Cutting
Temperature Distribution
•The temperature increases with cutting speed
•Chips can become red hot and create a safety hazard for the
operator
•The chip carries away most (90%) of the heat generated during
machining (see right)
–Rest carried by tool and workpiece
•Thus high machining speed (V ) ⇒
1.More energy lost in chips
2.Machining time decreases
(i.e. favorable machining economics)
38

39. Temperatures in Cutting
Techniques for Measuring Temperature
•Temperatures and their distribution can be determined using
–thermocouples (placed on tool or workpiece)
–Electromotive force (thermal emf) at the tool-chip interface
–Measuring infrared radiation (using a radiation pyrometer) from
the cutting zone (only measures surface temperatures)
39

40. Tool Life: Wear and Failure
•Tool Wear is a term that describes the gradual failure of a cutting tool due to its
operation.
• A cutting tool is ground with various angles to perform cutting operation
efficiently & effectively on different materials & in different situations of varying
speed, depth & feed of cut
• Under regular operation, the tool wears out gradually leading to changes in the
angles ground on the cutting tool, which in turn ceases to tool to function
satisfactorily
• A very short tool life is not economical, as tool grinding & tool replacement
increases the cot of machining and in-turn increases the cost of the product
• Tool wear cannot be avoided, but under suitable operating conditions it can be
minimized 40

41. Tool Life: Wear and Failure
Tool wear and the changes in tool geometry
are classified as:
a)Flank wear
b)Crater wear
c)Nose wear
d)Notching
e)Plastic deformation of the tool tip
f)Chipping and Gross fracture
41

42. Conditions of Cutting Tool
a.High localized stresses at the tip of the tool
b.High temperatures, especially along the rake face
c.Sliding of the chip along the rake face
d.Sliding of the tool along the newly cut workpiece surface
These condition leads to Tool Wear:
•These conditions induce tool wear, which is a major consideration in
all machining operations.
•Tool wear adversely affects tool life, the quality of the machined
surface and its dimensional accuracy, and, consequently, the
economics of cutting operations.
•Wear is a gradual process.
42

43. •The rate of tool wear depends on tool and workpiece materials, tool
geometry, process parameters such as speed, feed and depth of cut,
cutting fluids, and the characteristics of the machine tool.
There are 3 possible ways a cutting tool can fail in machining:
• Fracture Failure: This mode of failure occurs when the cutting
force at the tool point becomes excessive, causing it to fail suddenly
by brittle fracture (Mechanical Chipping)
•Temperature Failure: This failure occurs when the cutting
temperature is too high for the tool material, causing the material at
the tool point to soften, which leads to plastic deformation and loss
of the sharp edge
43
Conditions of Cutting Tool

44. • Gradual Wear: Gradual wearing of the cutting edge causes loss of
tool shape, reduction in cutting efficiency, an acceleration of wearing
as the tool becomes heavily worn, and finally tool failure in a manner
similar to a temperature failure
Gradual Wear/Tool Wear can be classified into:
• Crater Wear: It consists of a cavity in the rake face of the tool that
forms and grows from the action of the chip sliding against the
surface.
•High stresses and temperatures characterize the tool–chip contact
interface, contributing to the wearing action.
•The crater can be measured either by its depth or its area
44

45. Tool Life: Wear and Failure: Crater Wear
Factors influencing crater wear are:
1.Temperature at the tool–chip interface
2.Chemical affinity between tool and workpiece materials
•Crater wear occurs due to “diffusion mechanism”
–This is the movement of atoms across tool-chip interface
–Since diffusion rate increases with increasing temperature, ⇒
crater wear increases as temperature increases (see ↓)
45

46. Tool Life: Wear and Failure: Crater Wear
Crater wear occurs on the rake face of the tool (↓)
46
Types of wear associated
with various cutting tools
Catastrophic tool failures (many variables involved)

47. Tool Life: Wear and Failure: Crater Wear
•Note how quickly crater wear-rate increases in a small
temperature range
•Coatings to tools is an effective way to slow down diffusion
process (e.g. titanium nitride, alum. oxide)

47

48. Tool Life: Wear and Failure: Flank Wear
48
Flank Wear: Flank wear occurs on the relief (flank) face of the tool.
•It generally is attributed to rubbing of the tool along the machined
surface, thereby causing adhesive or abrasive wear and high
temperatures, which adversely affect tool-material properties
•Effect of workpiece hardness and microstructure on tool life in
turning ductile cast iron. Note the rapid decrease in tool life
(approaching zero as V increases).

49. 49
Tool Life: Wear and Failure: Flank Wear

50. Tool Life: Wear and Failure: Flank Wear
Tool-life Curves
•The exponent n can be determined
from tool-life curves (see right)
–Smaller n value ⇒ as V
increases ⇒ tool life decreases
faster
–n can be negative at low cutting
speeds
•Temperature also influences wear:
–as temperature increases, flank
wear rapidly increases 50
Tool-life curves for a variety of
cutting-tool materials. The negative
reciprocal of the slope of these
curves is the exponent n in the
Taylor tool-life Equation, and C is
the cutting speed at
T = 1 min, ranging from about 60 to
3,000 m/min in this figure.

51. Tool Wear Mechanism

•Abrasion. It is a mechanical wearing action caused by hard particles
in the work material gouging and removing small portions of the
tool.
•This abrasive action occurs in both flank wear and crater wear; it is
a significant cause of flank wear.
• Adhesion. When two metals are forced into contact under high
pressure and temperature, adhesion or welding occur between them.
51

52. Tool Wear Mechanism
•These conditions are present between the chip and the rake face of
the tool.
•Diffusion: This is a process in which an exchange of atoms takes
place across a close contact boundary between two materials.
• In the case of tool wear, diffusion occurs at the tool–chip boundary,
causing the tool surface to become depleted of the atoms responsible
for its hardness.
•Diffusion is believed to be a principal mechanism of crater wear.

52

53. Tool Wear Mechanism
•Oxidation/Corrosion: Oxidation is the result of a chemical reaction
b/w the tool surface & surrounding oxygen at high temperatures.
•During metal cutting, the high temperatures generated at the tool-
work interface causes oxidation of carbide in the cutting tool,
forming a layer on tool surface.
•This layer is removed during ,machining process by abrasion,
another layer is formed and it repeats

53

54. Tool Life: Wear and Failure
54
a) Features of tool wear in a turning operation. VB: indicates average flank wear
(b – e)
Examples of
wear in
cutting tools
b) Flank
wear
c) Crater
wear
d) Thermal
cracking
e) Flank
wear and
built-up
edge
(BUE)

55. Tool Life
•Tool life is the time duration a tool can be reliably used for cutting
before it must be discarded or re-ground.
•The life of the cutting tool is one of the most important economic
considerations in metal cutting.
•Hence the tool must be utilized efficiently to the maximum possible
extent before it can be ground or discarded, because tool grinding or
replacement costs are very high.
•The life of the tool is affected by various parameters. 55

56. Cutting speed:
•Cutting speed has the greatest influence on tool life. As the cutting
speed increases the temperature also rises.
•The heat is more concentrated on the tool than on the work and the
hardness of the cutting tool changes so the relative increase in the
hardness of the work accelerates the abrasive action.
•The criterion of the wear is dependent on the cutting speed because
the predominant wear may be wear for flank or crater if cutting
speed is increased.

56
Parameters Affecting Tool Wear

57. Parameters Affecting Tool Wear
•Feed and depth of cut: The tool life is influenced by the feed rate
also. With a fine feed the area of chip passing over the tool face is
greater than that of coarse feed for a given volume of metal removal.
• Tool Geometry: The tool life is also affected by tool geometry. A
tool with large rake angle becomes weak as a large rake reduces the
tool cross-section and the amount of metal to absorb the heat.
•Tool material: Physical and chemical properties of work material
influence tool life by affecting form stability and rate of wear of
tool.
57

58. Parameters Affecting Tool Wear
• Cutting fluid: It reduces the coefficient of friction at the chip tool
interface and increases tool life.
• Type of workpiece material: work pieces with greater hardness
require greater cutting forces leading to greater power consumption,
tool wear increases with greater forces thereby reducing the life of
cutting tool. Ductile materials deform easily, and low cutting forces
are needed, thus tool wear reduces

58

59. •Nature of cutting: Tool life is more in case of continuous cutting
when compared to intermitted type of cutting where the cutting edge
of the tool will not be in continuous contact with the work surface,
intermittent cutting causes regular impacts on the tool resulting in
failure of tool in short span. It must be ensured through all means to
have continuous type of cutting in order to enhance tool life

59
Parameters Affecting Tool Wear

60. Tool Wear v/s Cutting Time
•The general relationship of tool wear versus cutting time is shown in
Figure Although the relationship shown is for flank wear, a similar
relationship occurs for crater wear.
•Three regions can usually be identified in the typical wear growth
curve. The first is the breaking period, in which the sharp cutting
edge wears rapidly at the beginning of its use. This first region
occurs within the first few minutes of cutting. The break-in period is
followed by wear that occurs at a fairly uniform rate.
60

61. •This is called the steady-state wear region. In our figure, this region
is pictured as a linear function of time, although there are deviations
from the straight line in actual machining.
• Finally, wear reaches a level at which the wear rate begins to
accelerate. This marks the beginning of the failure region, in which
cutting temperatures are higher, and the general efficiency of the
machining process is reduced.
• If allowed to continue, the tool finally fails by temperature failure
61
Tool Wear v/s Cutting Time

62. 62 Tool Wear v/s Cutting Time
Tool Wear v/s Cutting Time

63. Tayler’s Tool Life Equation
•Cutting speed forms the most important parameter of all the
variables (feed, depth of cut, type of work material, coolant, etc.,),
that affects the tool life.
• F. W. Taylor, an American engineer developed a standard test to
determine the relationship b/w cutting speed & time the tool remains
useful.
•Test has been carried out for different combination of tool
workpiece material; and the flank wear of the tool under test has
been measured 63

64. • It has been found that a practical amount of wear to measure before
breakage was 0.75 mm (VB) for solid & brazed tips, and 1.25 mm
(VB) for ceramic tools
• Tests have been carried out to determine the time taken to reach this
amount of wear at different cutting speeds
•The results have been plotted on a graph showing that a logarithmic
relationship existed b/w the cutting speed & the tool life (cutting
time) an empirical relation for tool life with cutting speed has been
given by Taylor & is known as Taylor‟s tool life equation

64
Tayler’s Tool Life Equation

65. 65
Tayler’s Tool Life Equation

66. •Table shows the range of values of „n‟ for different combinations of
tool-workpieces materials
• The value of „n‟ increases with increase in the refractoriness of the
tool material
66
Tayler’s Tool Life Equation

67. Effect of Cutting Parameters on Tool Life
67

68. Effect of Cutting Parameters on Tool Life
68
Effect of Speed on Tool Life

69. Effect of Cutting Parameters on Tool Life
•Feed: Feed is the amount of material removed for each revolution,
or per-pass of the tool over the workpiece.
• Increasing feed rate increases cutting temperature and flank wear
thereby shortening the life of cutting tool. However, effect on the
tool life is minimal when compared to cutting speed. The rate of
feed given depends on the depth of cut.
•Depth of cut: Depth of cut relates to the depth of cutting edge of the
tool engages the work. Small depths of cuts result in friction when
cutting hardened layer of work metal.
69

70. Effect of Cutting Parameters on Tool Life
70

71. Effect of Cutting Parameters on Tool Life
71

72. Tool Life: Wear and Failure: Tool-condition Monitoring
1.Direct method for observing the condition of a cutting tool involves optical
measurements of wear
•e.g. periodic observation of changes in tool using microscope
•e.g. programming tool to touch a sensor after every machining cycle (to detect
broken tools)
2.Indirect methods of observing tool conditions involve the correlation of the tool
condition with certain parameters
•Parameters include forces, power, temp. rise, workpiece surface finish,
vibration, chatter
•e.g. transducers which correlate acoustic emissions (from stress waves in
cutting) to tool wear and chipping
•e.g. transducers which continually monitor torque and forces during cutting,
plus measure and compensate for tool wear
•e.g. sensors which measure temperature during machining
72

73. Cutting Fluids
•During metal cutting, as the cutting tool slides in the workpiece material, heat is
generated due to the friction b/w the tool & workpiece material
•Also, as chip slides up the tool face, heat is generated due to friction at the contact
points b/w the chip & tool-face
• The excessive heat thus generated can damage the microstructure of both the
cutting tool & the workpiece
•Also, the life of the cutting tool reduces at higher temperatures
• In order to reduce friction or heat generated, cutting fluids are used
• A cutting fluid or coolant is a liquid, added to the cutting zone, in order to reduce
the effects of friction between (b/w) the tool-work & tool-chip interface by way of
cooling & lubrication 73

74. Functions of Cutting Fluids
• Controls the temperature at the cutting zone through cooling &
lubrication, which in turn helps in decreasing tool wear & extending
tool life
•Cooling & lubricating action of cutting fluid helps in achieving the
desired size, shape & finish of the workpiece.
•The removal of heat by cutting fluid prevents the workpiece from
expanding during the machining operation, which would other wise
cause size variations as well as damage to the microstructure.
74

75. • Also, proper use of coolants can make higher metal removal
rates possible
•Cutting fluid helps to flush away chips & metal fines from the
cutting zone thereby preventing the tool & the finish of the work
surface from becoming marred & occurrence of built-up-edge
75
Functions of Cutting Fluids

76. Properties of Cutting Fluids
•High specific heat & High Thermal Conductivity, so that maximum
heat will be absorbed & removed per unit of fluid volume circulated
• Good lubricating property, so that a strong protective film b/w the
tool face & the workpiece metal can exist. Such a film assists the
chip in sliding easily over tool face.
•Besides reducing heat, a good lubricating fluid lower power
consumption & reduces the rate of tool wear, particularly in
machining tough & ductile metals 76

77. •Non-Corrosive, in order to avoid damage to the workpiece & the
m/c parts
•Non-Toxic & Odorless, in order to provide better working
conditions to human operators
• A cutting fluid should have high flash point to avoid problems
associated with heat damage, production of smoke, or fluid ignition
•Low Viscosity, far easy circulation. Low viscosity fluids also allow
grit & dirt to settle out of suspension & helps for easy re-circulation
through the machining system
• Highly stable, in order to resist its decomposition during its storage
& use
77
Properties of Cutting Fluids

78. Types of Cutting Fluids
Oil-based fluids:
Straight oils
Soluble oils
Chemical fluids:
Synthetic oils
Semi-Synthetic oils
78

79. Oil-Based Cutting Fluids
•Oil-based fluids include straight oil & soluble oils.
•Straight Oils: Straight Cutting Oils (or Neat Oils) are so called
because they do not contain water. The cutting fluid is composed of
100% petroleum oil or mineral oil along with some lubricants such
as fats, vegetable oil & esters, as well as extreme pressure (EP)
additives in order to improve specific properties.
•Generally, additives are not required for light duty machining
operations,
79

80. •However, for severe machining operation, where heavy cuts are to
be taken, and machining hard materials like titanium, stainless steel
etc., EP additives such as sulfur, chlorine or phosphorous
compounds are often used. These additives improve the lubricating
& wettability property; that is, the ability of the oil to coat the
cutting tool, workpiece & the chips.
80
Oil-Based Cutting Fluids

81. Straight Oils: Advantages and Disadvantages
Advantages:
• Provides excellent lubricating property b/w the workpiece & cutting tool
• Tool life can be increased
• Good rust protection
• Absence of water eliminates bacterial development & odour problems
Disadvantages:
• Costlier
•Poor heat dissipating properties
• Increased fire risk, and hence its use is limited to low-temperature & low-
pressure operations
81

82. Soluble Oils
•Soluble Oils, also referred as Emulsions, emulsifiable oils or water-
soluble oils, are generally comprised of 60%-90% petroleum or
mineral oil, emulsifiers and other extreme pressure (EP) additives.
•Use of soluble oils for a particular application depends on the
concentration of water & oil. Lean concentrations containing more
water & less oil provide better cooling, but less lubrication.
•On the other hand, rich concentrations containing less water & more
oil provide better lubrication qualities, but poor cooling.
82

83. Soluble Oils: Applications, Advantages, and Disadvantages
Applications: Soluble oil is suitable for general purpose cutting operations on low &
medium tensile steels, free machining of brass bronze & cast iron. It may also be used
as a grinding fluid in non-critical applications, however it is not suitable for high
tensile or stainless steel or nickel alloys.
Advantages: Good lubrication capability, Suitable for light & medium duty
operations involving both ferrous & non-ferrous metals, Concentration of oil can be
varied for heavy-duty applications, Least expensive among all the cutting fluids.
Disadvantages: Presence of water makes the oil more susceptible to corrosion,
bacterial growth & odourness, Maintenance cost to retain the desired properties of the
oil is relatively high, Not suitable for high tensile or stainless steel alloys
83

84. Chemical Cutting Fluids
•Chemical cutting fluids contain little or no oil with pre-concentrated
emulsions on low & medium tensile steels, free machining of brass
bronze & cast Iron. It may be used as a grinding fluid in non-critical
applications, however it is not suitable for high tensile or stainless
steel or nickel alloys.
Synthetic Oils
Synthetic oils generally consist of chemical lubricants & rust inhibitors
dissolved in water.
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85. Synthetic Oils

•Emulsifiers can be added to create lubrication properties similar to
soluble oils, allowing the fluid to act as a lubricant & coolant in
heavy duty machining operations.
The various synthetic chemicals found in this type of oil include:
a.Amines & nitrates for rust prevention
b.Phosphates & Borates for water softening
c.Soaps & wetting agents for lubrication
d.Glycols to act as blending agents e) Biocides to control bacterial
growth
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86. Synthetic Oils: Application, Advantages, and Disadvantages

Application:
•Used in grinding carbide tools with diamond wheels, ordinary
commercial grinding where finish is not very critical, in some CNC
machines where stock removal is low etc.
Advantages:
• Good corrosion control
• Superior cooling properties
• Greater stability when mixed with hard water
•Can be stored for long periods of time without any problems
• Easy maintenance
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87. Synthetic Oils: Application, Advantages, and Disadvantages
Disadvantages:
• Synthetic coolants have a tendency to foam. If the rate of coolant
flow from a particular application is high, excessive foaming can be
caused, resulting in poor surface finish & reduced tool life
• Lubricating property is not satisfactory
• Ingredients added to enhance the lubricating property can result in
component rusting & leave gummy residues on the m/c system
• Synthetic fluids are easily contaminated by other m/c fluids like
lubricating oils, & hence need to be monitored & maintained so that
it can be used effectively

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88. Selection of cutting fluids
•Cutting speed, feed & depth of cut selected
• Type, hardness & microstructure of the workpiece material being
machined
•Operating temperature range
• Cost & life expectancy of fluid
• Fluid compatibility with workpiece & machine components
• Ease of storage & handling while in use
•Ease of fluid recycling or disposal
•Shelf-life required
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89. Methods of Cutting Fluids
•Apart from selecting the right cutting fluid, it is also important to
choose a proper method of circulating the fluid to the cutting zone.
The principal methods of applying the cutting fluid include:
•Flood Application of Fluids: A flood of cutting fluid is delivered to
the cutting zone by means of a pipe, hose or nozzle system
•Jet Application of Fluid: A jet of cutting fluid is directed to the
cutting zone

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90. Mist (spray) Application of Fluid: The cutting fluid is atomized by a
jet of air, & the mist is directed to the cutting zone
•In certain machining operations like drilling deep holes, or
machining ultra tough materials, it is very difficult to circulate the
cutting fluid into the cutting zone. In such cases, the cutting fluid is
supplied through the tool by drilling small holes in the tool.
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Methods of Cutting Fluids