Cutting Fluids
Prof. Dr. S. Engin KILIÇ
Atılım University
Department of Manufacturing Engineering
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Cutting fluids-definition

Liquids and gases which are used in metal
cutting to improve the cutting performance
in comparison to dry cutting are called
Cutting Fluids
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Advantages of using cutting fluids
a. Increase in tool life
b. Improvement of surface finish
c. Reduction in cutting forces and power
consumption
d. Washing chips free from cutting region
e. Reduction in thermal distortion of workpiece
f. Protection of finished surface from corrosion
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The Action of cutting fluids
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The Action of cutting fluids
Cutting fluids affect cutting process through their two
basic actions:
1. Lubrication (reduction in tool friction)
. forms boundary lubrication and a layer of soft chemical
compound with chip and workpiece at very low cutting speeds
a) built-up edge formation is reduced.
b) Reduction in coefficient of friction, hence
increase in shear angle and reduction in cutting forces.
c) Improved surface finish.
d) Increase in tool life.
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The Action of cutting fluids
2. Cooling
. reduces temperature in cutting area by removing heat
a) Tool wear is reduced and tool life is increased; tool material
retains its hardness at reduced temperature, hence
. it gains more resistance to abrasion.
. diffusion wear rate is reduced
. due to reduced temperature, however, shear flow
stress may increase, resulting reduced tool life.
b) Reduced thermal expansion and distortion of workpiece
(especially in grinding)
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The Action of cutting fluids
3. Swarf removal
An important subsidiary function of a cutting fluid is to wash
away swarf.
. Third-body abrasion is avoided, or at least reduced.
. Surface finish is improved.
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Basic types of cutting fluids
a)
Straight or neat oils: blended from two types of oils:
•
Usually undiluted mineral oils: paraffin and other petroleum oils
•
Often include fats (fattyoils), vegetable oils, esters together with
high-pressure compounds based on chlorine, sulphur, phoshorus
(high pressure oils)
•
fatty oils: organic oils of animal or vegetable origin
- Mineral oils
. cheaper
. more stable
- Fatty oils
. have good lubricating properties
. promote good finishes
. less stable than mineral oils and may decompose if used for long
periods
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Basic types of cutting fluids
- Sulphurised oil-oils with chemically combined sulphur
. prevents pressure welding of chip to tool (B.U.E.)
b) Soluble oils: Cutting fluids which are mainly required to carry away heat
and swarf are generally based on water
•
Oil with emulsifiers to allow oil to disperse in water, to inhibit
rusting, to a certain extent for lubricating effect
•
2-15% in water (e.g. 2-2.5% for grinding, 5% for turning and
milling)
•
Least expensive and widely used
c) Synthetic fluids:
•
Oil-free solutions formulated from alkaline inorganic and organic
compounds with corrosion inhibitors
•
3-10% in water
•
Provide best cooling performance
d) Semi-synthetic fluids:
•
Combination of synthetic and soluble oil fluids
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Basic types of cutting fluids
Straight cutting oils have wide application for two major reasons:
a) Employed in automatic machines because water-base coolants may
find their way into headstock, contaminate lubricating oil and cause
serious deterioration of mechanism.
b) Promote a superior surface finish in gear cutting, honing,
threading and broaching. Paraffin is sometimes used on aluminum
alloys instead of soluble oils because of its wetting property.
-Greases are more convenient than oils in tapping and reaming operations
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Cost of using cutting fluids
Cost of applying cutting fluids:
Reported to constitute 20% of
total manufacturing cost whereas
cutting tool cost is around 7.5%
in European automotive industry
Quantities of different types of cutting
fluids
(U.S. Manufacturing industry)
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Potential benefits:
• in reducing quantities:
dry cutting, near dry
cutting
• in extending useful life of
cutting fluids:
use of synthetic oils
central recycling systems
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Cost of using cutting fluids
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General characteristics of water-miscible cutting fluids
After Holmes
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General characteristics of water-miscible cutting fluids
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ME 303 - Lecture 07
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Effects of Cutting fluids
Material cut: alloy steel
shear strength = 690 MPa , effective rake 15o
Tool
Life(min)
Power (kW)
Dry
12
1.36
Sulphurised oil
27
1.3
Sulphurised and chlorinated oil
33
1.35
Type of Cutting Fluid
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Effects of Cutting fluids
Coefficient
Condition of Friction
Heat from friction
(kj/kg of metal
removed)
Heat from
deformation (kj/kg
of metal removed)
Dry
1.0
102.3
222.7
Cutting
fluid
0.9
93.9
210.4
%
decrease
10
19.1
12.8
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Guide to the Selection of Cutting Fluids
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Cutting Fluids: Pre-conditions
for Applicability
• It must not be toxic or offensive to the operator;
• it should not be a fire hazard;
• it must not be harmful to the lubricating system of the
machine tool;
• it should not corrode or discolor the work material;
• it should give some corrosion protection to the
freshly cut metal surface;
• it should be as cheap as possible.
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Application of Cutting Fluids
 Cutting fluid should be effectively delivered to the cutting zone to
perform its function
• Lubricating fluids must be applied in such a way to form a film on the
sliding surfaces
• Coolants must gain access to the cutting edge:
− flooding cutting area with fluid
− continuous application of cutting fluids for intermittent cutting
to avoid micro crack formation in tool material
Fluid application methods:
a. Manual
b. Flood
c. Jet
d. Mist
e. Through the tool
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Cutting Fluid Applications
Different methods of cooling in milling: (a) compressed air (jet), (b) oil mist,
(c) internal cooling (jet), (d) external cooling (flood)
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Flood Application
•
•
Continuous flow to cutting zone,
helps remove chips from cuting
zone
•
Its effectiveness depends on the
geometry of the cutting process
performed
•
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Fluid delivered from a lowpressure
nozzle directed appropriately to
flood tool, workpiece and
cutting
zone
Fluid recollected, filtered and
pumped back to the delivery
nozzle
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Flood Application
Flood Lubrication in Gear Hobbing
Jet Application
•
•
•
•
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High-pressure fluid is directed
through
a nozzle as high speed jet at cutting
zone
Very effective in removing chips from
cutting zone, efficient for high speed
applications including grinding
Fluid recollected, filtered and
pumped back to the delivery nozzle
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Jet Application
•
Coolant supply at a high pressure up
to 1000 bars (i.e., 200 bars is the
maximum requirement for titanium
machining) shortens the tool/chip
contact length and provides
improved chip control.
The Jetbreak system, giving a
specifically directed nozzle, can be
coupled with the appropriate tooling
system; hence, coolant supplied
through the cone of the coupling into
the nozzle jet is directed towards the
cutting edge to form a hydraulic
wedge between the chip and the
rake face of the tool insert.
•
•
High pressure coolant (HPC) supply system called
Jetbreak
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Most applications are on single
spindle turning machines such as
vertical turning centres and turnmilling centres.
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Jet Application
It provides a high velocity of
122 m/s and a high pressure
flow of coolant at 110 bar to the
interface between the tool and
chip.
• System consists of a pumping
unit, the piping necessary to
transport the fluid, and a toolholder through which the
coolant can pass and which can
focus the high pressure flow of
coolant on the interface.
•
High pressure coolant (HPC) supply system called
Hyperson
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Mist Application
Cutting fluid as an air-carried
mist; a mixing system for oil-air
pulvarization needed
•
Usually applicable when cutting
speeds are high and uncut chip
thickness is relatively small (i.e.
end milling)
•
Good ventillation required due to
health hazard
•
Used in minimum quantity
lubrication applications
•
Minimized lubrication system (mist application)
Small lubrication particles suplied by micro-dosage pump
through the capillary tube are mixed with air and directed
to the cutting tool through the machine spindle
Mist Application
Various methods of inducing oil/air mix
(a) from the outside into the
bore
(c) oil and air flow entry and exit
simultaneously
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(b) through the cutting tool
(d) from a reservoir built into the
tool
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Cutting Fluids
Cutting fluid requirements for different machining operations
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