Kumar

Advance Manufacturing
Process
Submitted by :-
Mr. Shambhu Kumar
Roll No. :- 14M332
Branch :- CAD-CAM
Date :- 12-11-2014

Chapter1.
ENGINEERING MATERIALS
AND MANUFACTURABILITY:
Classification, Mechanical, Physical and
Thermal properties, common FERROUS
METALS AND ALLOYS( Alloys steels, Tool
steels and Cast irons) and NON-FERROUS
METALS AND ALLOYS ( Copper,
aluminum, nickel and zinc)

Presented by :-
Shambhu Kumar
CAD-CAM
14M332
Ferrous Metals

Engineering
Materials
Metals
Ferrous
Iron
Steel
Pig iron
Cast iron
Wrought
iron
Non-Ferrous
Copper &
Alloys
Aluminium
Zinc
Tin
Lead
Non-Metals
Rubber
Plastics
Resin
Classification of Materials

Metals
 Metal is an element, having vacant d-shell
 good conductor of both electricity and heat
 Metal crystal structure and specific metal properties are
determined by metallic bonding – force, holding together
the atoms of a metal
 Ability of the valence free electrons to travel throughout
the solid explains both the high electrical conductivity and
thermal conductivity of metals.

Metals
Other specific metal features are:
• luster or shine of their surface (when polished)
• Malleability (ability to be hammered) and
• Ductility (ability to be drawn).
 These properties are also associated with the metallic
bonding and presence of free electrons in the crystal lattice.

Ferrous metals
 Iron
 Pig iron
 Cast iron
 white cast iron
 grey cast iron
 Malleable iron
 Wrought iron

Iron
 Iron (Fe) – atomic number 26 , lustrous metallic with a grayish tinge
 Electron configuration :- [Ar] 3d6 4s2
 Most widely used of all metals as base metal in steel and cast iron
 Iron is extracted from iron ores such as Hematite (Fe2O3) and Magnetite
(Fe3O4)
 The iron ores contain 25% to 70% metallic iron. Sulfur, phosphorous,
silica and clay are the principal impurities.
Physical properties
 Phase :- solid
 Melting point :- 1811 K (1538 °C, 2800 °F)
 Boiling point :- 3134 K (2862 °C, 5182 °F)
 Density :- 7.874 g/cc( liquid) at m.p.6.98 g/cc
 Heat of fusion :- 13.81 kJ/mol
 Heat of vaporization :- 340 kJ/mol
 Molar heat capacity :- 25.10 J/(mol·K)

Ferrous metals
Pig iron –
 The intermediate product of smelting iron ore with a
high-carbon fuel such as coke, usually with
limestone as a flux
• Materials used to produce pig iron are coke, limestone
and iron ore.
 Iron ore, coke and limestone are heated together at
high temperatures in blast furnaces for the extraction
process of iron

Pig iron
 Pure iron is a soft metal having a structure of iron crystals. In
metallurgy, pure iron is called “Ferrite”
 Coke → provides the heat & supplies carbon (C) to extract iron
C + O2 → CO2
CO2 + C → 2CO
3CO + Fe2O3 → 2Fe + 3CO2
 Limestone is used to reduce the impurities.
 Ordinary pig iron as produced by blast furnaces contains iron,
about 92 percent; carbon :- 3 or 4 %; silicon :-0.5 to 3 %;
manganese(Mn) :-0.25 to 2.5 % ; phosphorus :- 0.04 to 2% and
a trace of sulfur.

Blast furnace
 A blast furnace is a type of metallurgical furnace used
for smelting industrial metals, generally iron.
 In a blast furnace, fuel, ore and limestone as flux are
continuously supplied through the top of the furnace,
while air (sometimes with oxygen enrichment) is blown
into the bottom of the chamber
 Chemical reactions take place throughout the furnace as
the material moves downward.
 The end products are usually molten metal and slag
phases tapped from the bottom, and flue gases exiting
from the top of the furnace.

Wrought iron
 Iron alloy with a very low carbon (less than 0.08%), in
comparison to steel, and has fibrous inclusions (slag)
 Tough, malleable, ductile and easily welded
Fig :- Iron pillar at Delhi, India, containing 98%
wrought iron
Fig :- The Eiffel tower is constructed
from puddled iron, a form of wrought iron

Cast Iron
• When pig iron is further processed by remelting to eliminate
some of the carbon, cast iron (having a carbon content of about
1.5 to 4%) is produced.
• The remelting process is usually performed in a cupola (a
smaller version of blast furnace).
• During the remelting operation in the cupola, no particular
chemical change in the iron is ecpected. Some of the impurities
may be eliminated and a more uniform product is obtained.

Cast Iron
 White cast iron is named after its white surface when
fractured, due to its carbide impurities which allow cracks to
pass straight through.
 Grey cast iron is named after its grey fractured surface, which
occurs because the graphitic flakes deflect a passing crack and
initiate countless new cracks as the material breaks.
White Grey Ductile Malleable

Steel Steels
Low alloy
Low
Carbon
Medium
Carbon
High
Carbon
High
alloy
Stainless
Tool
Low Alloy
Low Carbon (<0.25 wt%)
Medium Carbon (0.25 to 0.60 wt%)
High Carbon (0.60 to 1.5wt%)
High Alloy
Stainless Steel (> 11 wt% Cr)
Tool Steel

Steel
 Steel is an alloy that consists mostly of iron and has a
carbon content between 0.2% and 2% by mass
 Carbon is the most common alloying material for iron, but
various other alloying elements are used, such as
manganese, chromium, vanadium, molybdenum,
tungsten, etc.

Stainless steel
 Stainless steel is a steel alloy with a minimum of 10.5 or
11% chromium content by mass.
 It does not corrode, rust with water as ordinary steel does.

High –speed steel(Tool Steel)
 High speed steel is commonly used in tool bits and cutting
tools.
 It can withstand higher temperatures without losing its
hardness. This property allows HSS to cut faster than high
carbon steel, hence the name high speed steel.
 Tool steel is a term used for a variety of high-hardness,
abrasion resistant steels.
 Specific tool applications are
Dies (stamping or extrusion), cutting, moldmaking, or
impact applications like hammers (personal or industrial).

Non-ferrous metals
 Copper
 Aluminium
 Zinc
 Tin
 Lead

Copper & Alloys
 Copper – Latin cuprum (Cu) – ranks next to
iron in importance and wide range of
application
 Good heat and electrical conductivity
 Resistance to corrosion
 Pure copper is soft and malleable; a freshly
exposed surface has a reddish-orange color
 Alloys : Brass, Bronze, cupro- nickel (copper
nickel) alloys
 Symbol :- Cu , Atomic number : 29
 Molar mass :- 63.546 g/mol
 Melting point :- 1,085 °C
 Electron configuration : - [Ar] 3d104s1
 Atomic mass :- 63.546 ± 0.003 u

Aluminium
 Aluminium :- – Al, atomic number 13
 whitish with bluish cast
 The third most abundant element (after oxygen and silicon).
 It is a silvery-white, soft, nonmagnetic, ductile metal
 The most abundant metal in the Earth’s crust
 Symbol :- Al
 Melting point : -660.3 °C
 Atomic number :- 13
 Electron configuration :- [Ne] 3s23p1
 Boiling point : - 2,519 °C
 Atomic mass :- 26.981539 u
 Discoverer :- Hans Christian Ørsted

Aluminium
 low density and ability to resist corrosion; good
conductivity
 structural components made from aluminium and its
alloys are vital to the aerospace industry and are important
in other areas of transportation and structural materials

Zinc
 Zinc (Zn), Atomic number 30
 Bluish white
 corrosion resistant in air due to a thin oxide film forming on its
surface
 Used as a coating for protecting steel - galvanisation is the
process of applying a protective zinc coating to steel or iron, in
order to prevent rusting
 Electron configuration : -[Ar] 3d104s2
 Melting point :- 419.5 °C
 Boiling point :- 907 °C
 Atomic mass :- 65.38 ± 0.002 u

Nickel
 Nickel is a chemical element with symbol Ni
and atomic number 28.
 It is a silvery-white lustrous metal with a
slight golden tinge.
 Nickel belongs to the transition metals and is
hard and ductile.
 Symbol: Ni
 Electron configuration: [Ar] 4s23d8
 Melting point: 1,455 °C
 Atomic number: 28
 Atomic mass: 58.6934 ± 0.0002 u
 Discoverer: Axel Fredrik Cronstedt

Tin
 Tin – Latin stannum (Sn), atomic number 50
 white, lustrous, soft, malleable, ductile, resistant to
corrosion
 used as coating for steel and sheet iron
 white metal – tin based alloy with amounts of lead,
copper and antimony – lining material

Lead
 Lead – Latin plumbum (Pb), atomic number 82
 Metallic lead has a bluish-white colour after being
freshly cut, but it soon tarnishes to a dull grayish color
when exposed to air
 has a shiny chrome-silver luster when it is melted into a
liquid
 Soft, malleable, has little ductility
 usage: plates for storage batteries, covering for electrical
cables

Non-Metals
 Non-Metals are poor conductors of heat and electricity when
compared to metals as they gain or share valence electrons
easily (as opposed to metals which lose their valence
electrons easily)
 Usually have lower densities than metals;
 They have significantly lower melting points and boiling
points than metals
 Brittle, non-ductile, dull (do not posses metallic luster)

Introduction, Cold and hot chamber die
casting, Shell, Investment and
Centrifugal casting, Casting defects and
their remedy and Stir casting technology

Gravity Die Casting
(Higher strength obtain in this process
as compare to the sand casting
process)

Gravity die casting process
 Mazak, an alloy of Zinc and aluminium, is first melted
in a crucible furnace
 Molten metal is then poured by ladle in to an open
steel mould where it is allowed to cool and solidify.

 The mould is then turned upside down and tapped
with a hammer to release the finished casting.
 Gravity die casting requires minimal finishing and
waste as minimal because excess metal can be melted
down and used again.

 Uses the force of gravity, instead of high pressure means, to fill a permanent
mould, or die, with molten material.
There are four major steps in the die casting process.
1) First, the mould is heated and then sprayed with lubricant and closed. The
lubricant both helps control the temperature of the die during manufacture and
it also assists in the removal of the casting.
2) Molten metal is then manually poured into the die, (although in some cases a
machine can be used) and allowed to solidify.
3) The die is then opened and the cast parts either removed by hand or in some
cases ejector pins are used on the mechanized machines.
4) Finally, the scrap, which includes the gate, runners, sprues and flash, must be
separated from the casting(s). This can be done using a special trim die in a
power press or hydraulic press. This scrap is recycled by remelting it.
Approximately 15% of the metal used is wasted or lost due to a variety of
factors.

Things that you may recognise
 Things that are made from gravity die casting are:
 Toaster -
 Lawnmowers -
 Car wheel rims -

Identifying the process
 When something has been created by gravity pressure die
casting there would be:
 Section hair lines
 ejector pin marks
 sprue and runner marks
The materials used in gravity
die casting is a mixture of Zinc
and aluminium.

Advantages
 Good dimensional accuracy
 Smooth cast surfaces
 Thinner walls can be cast as compared to sand
 Inserts can be cast-in (such as threaded inserts, heating
elements, and high strength bearing surfaces).
 Reduces or eliminates secondary machining operations.
 Rapid production rates.
 Casting tensile strength is higher than sand casting.
Disadvantages
High initial cost.
A large production volume is needed to make this an economical
alternative to other processes

Pressure die casting
1.Low pressure die casting
 Pressure range used here is 20
to 100 KPa
2.High pressure die casting
 Pressure range used here is 30
to 200 MPa

High pressure die
casting
1. cold chamber(70-200MPa)
2. Hot chamber( 3 - 5MPa )

High Pressure Die Casting
 Forcing metal under high pressure to form a mould.
 These moulds are called dies and are made from steel.
 This produces non-ferrous metals.
 Metals that are commonly used are also:
Aluminium - Zinc -

What is made from the process
 In this process you can make:
 Golf club heads –
 Car engine blocks -
 Radiators -

High pressure die casting process
 First the mould is sprayed with lubricant and closed.
 Molten metal is then injected into the mould under high
pressure.
 Once the cavity is filled, the pressure is kept at a steady level
until the casting has become solid.
 Finally, the die is opened and the casting

High pressure die casting process
Steps to be followed
1. Application of lubricant on mould cavity.
2. Closing the mould by moving the ejector die towards the cover
die
3. Holding the two die securely together
4. Forcing the molten metal into the die cavity through the inlet
passage
5. Keeping the metal for solidification under pressure
6. Opening the mould by moving the ejector die backward
7. Ejection of the casting using ejector pins
8. Removal oh hot casting from the mould using manipulator
9. Trimming the fin and gating system to get finished casting.

Cold Chamber die casting process
 Cold chamber die casting is a permanent mold metal casting process.
 A reusable mold, gating system and all, is employed.
 It is most likely machined precisely from two steel blocks.
 Large robust machines are used to exert the great clamping force
necessary to hold the two halves of the mold together against the
tremendous pressures exerted during the manufacturing process.

 A metal shot chamber, (cold-chamber), is located at the entrance of the
mold.
 A piston is connected to this chamber, which in turn is connected to a
power cylinder.
 The correct amount of molten material is poured into the shot chamber
from an external source holding the material for the metal casting.

 The power cylinder moving the piston forward forces the molten
material into the casting mold with great pressure.
 Pressure causes the liquid metal to fill in even thin sections of the metal
casting and press the mold walls for great surface detail. maintained the
pressure some time after the injection phase of die casting manufacture.
 Once the metal casting begins to solidify, Then the mold is opened and
the casting is removed by way of ejector pins.
 The mold is sprayed with lubricant before closing again, and the piston
is withdrawn in the shot chamber for the next cycle of production.

Advantages
 Excellent dimensional accuracy
 Smooth cast surfaces.
 Thinner walls can be cast as compared to sand and permanent
mold casting .
 Rapid production rates.
 Casting tensile strength as high
 Complex part designs can be cast.
 Weight reduction through adequate shape and materials is
possible.
 Shape part rigidity is given.
 Temperature resistance of the material.
 Good mechanical properties.
 Good EMI shielding effect of a casted housing.
 Noise and vibration damping properties of the metals.
 High-quality coating of castings is possible.
 Castings can be recycled completely.

Disadvantages
 Casting weight must be between 30 grams (1 oz) and 10 kg (20
lb).
 Casting must be smaller than 600 mm (24 in)
 Limited to high-fluidity metals.
 A certain amount of porosity common.
 Thickest section should be less than 13 mm (0.5 in).
 A large production volume is needed to make this an economical
alternative to other processes.
 Very High Pressure required (50 -200MPa)
 Can’t Cast the metal having high Melting Point (it suitable of
Aluminium alloys, Mg, & Zinc)

Hot Chamber die casting process
 Attributed to the use of pressure to ensure the flow of metal
through the die.
 In hot chamber die casting manufacture, the supply of molten
metal is attached to the die casting machine and is an integral part
of the casting apparatus for this manufacturing operation.

 The shot cylinder provides the power for the injection
stroke(located above the supply of molten metal).
 The plunger rod goes from the shot cylinder down to the plunger,
which is in contact with the molten material. At the start of a
casting cycle, the plunger is at the top of a chamber (the hot-
chamber).
 Intake ports allow this chamber to fill with liquid metal.
 The pressure exerted on the liquid metal to fill the die in hot
chamber die casting manufacture usually varies from about
700psi to 5000psi (5MPa to 35 MPa).
 The pressure is held long enough for the casting to solidify.

 The plunger travels back upward in the hot chamber exposing
the intake ports again and allowing the chamber to refill with
molten material.(For the next cycle)

Advantages
 Low Hydraulic Pressure required (5-35 Mpa)
 Excellent dimensional accuracy
 Smooth cast surfaces.
 Thinner walls can be cast as compared to sand and permanent
mold casting .
 Rapid production rates(very high rate of productivity).
 Complex part designs can be cast.
 Weight reduction through adequate shape and materials is
possible.
 Good mechanical properties.
 Good EMI shielding effect of a casted housing.
 Noise and vibration damping properties of the metals.
 High-quality coating of castings is possible.
 Castings can be recycled completely.

Disadvantages
 Suitable for low Melting point alloys( Aluminium alloys, lead,
tin, and zinc)
 The setup requires that critical parts of the mechanical apparatus,
(such as the plunger),
 Must be continuously submersed in molten material.
 Continuous submersion in a high enough temperature material
will cause thermal related damage to these components rendering
them inoperative.

Application
Fig - Belt roll (Zinc) Fig. - Mobile phone (Mg)
Fig - Zylinder crank housing (Al)

Shell Moulding Casting
 Shell mold casting or shell molding is a metal casting process in
manufacturing industry in which the mold is a thin hardened
shell of sand and thermosetting resin binder, backed up by some
other material.

The Process
Step 1
The sand we use for the shell molding process is of a much smaller
grain size than the typical green sand mold. This fine grained sand is
mixed with a thermosetting resin binder. A special metal pattern is
coated with a parting agent, (typically silicone), which will latter
facilitate in the removal of the shell. The metal pattern is then heated
to a temperature of 350F-700F degrees, (175C-370C).

The Process
Step 2
The sand mixture is then poured or blown over the hot casting
pattern. Due to the reaction of the thermosetting resin with the hot
metal pattern, a thin shell forms on the surface of the pattern. The
desired thickness(.3in (7.5mm) thick) of the shell is dependent upon
the strength requirements of the mold for the particular metal casting
application.

The Process
Step 3
The excess "loose" sand is then removed, leaving the shell and
pattern

The Process
Step 4
The shell and pattern are then placed in an oven for a short period of
time, (minutes), which causes the shell to harden onto the casting
pattern.

Step 5
Once the baking phase of the manufacturing process is complete, the
hardened shell is separated from the casting pattern by way of
ejector pins built into the pattern

Step 6
Two of these hardened shells, each representing half the mold for
the casting, are assembled together either by gluing or clamping.

Step 7
The manufacture of the shell mold is now complete and ready for
the pouring of the metal casting. In many shell molding processes,
the shell mold is supported by sand or metal shot during the casting
process

Properties and Considerations of Manufacturing
by Shell Mold Casting
 The internal surface of the shell mold is very smooth and rigid.
This allows for an easy flow of the liquid metal through the mold
cavity during the pouring of the casting, giving castings a very
good surface finish.
 Shell mold casting enables the manufacture of complex parts with
thin sections and smaller projections than green sand mold casting.
 Tolerances of .010 inches (.25mm) are possible. Further machining
is usually unnecessary when casting by this process.
 Shell sand molds are less permeable than green sand molds and
binder may produce a large volume of gas as it contacts the molten
metal being poured for the casting.
 Shell mold casting processes are easily automated.
 The special metal patterns needed for shell mold casting are
expensive, making it a less desirable process for short runs.
 economical for large batch production

Shell Mold Casting
 Can form complex shapes and
fine details,
 Very good surface finish,
 High production rate,
 Low labor cost,
 Low tooling cost,
 Little scrap generated.
 Can produce very large parts,
 Can form complex shapes,
 Many material options,
 Low tooling and equipment
cost,
 Scrap can be recycled,
 Short lead time possible
 High equipment cost
 Poor material strength,
 High porosity possible,
 Poor surface finish and tolerance,
 Secondary machining often required,
 Low production rate,
 High labor cost.
Disadvantages:Advantages:
Applications:
 Cylinder heads,
 Connecting rods
 Engine blocks and manifolds,
 Machine bases,
 Gears,
 Pulleys

Investment Casting
Prepared By :- Shambhu Kumar
Investment casting is a metal-forming process and also
called lost-wax casting.

Investment Casting
The Process
Step 1
 Manufacture the wax pattern for the process. The size of master die must be
carefully calculated. It must take into consideration shrinkage of wax, shrinkage
of the ceramic material invested over the wax pattern and shrinkage of the metal
casting. It may take some trial and error to get just the right size, therefore these
molds can be expensive.
 Several wax patterns may be combined for a single casting

Investment Casting
Step 2A
The metal casting pattern is then dipped in a refractory slurry whose composition
includes extremely fine grained silica, water and binders. A ceramic layer is
obtained over the surface of the pattern. The pattern is then repeatedly dipped
into the slurry to increase the thickness of the ceramic coat. In some cases the
pattern may be placed in a flask and the ceramic slurry poured over it.

Investment Casting
Step 2B
 Once the refractory coat over the pattern is thick enough, it is allowed to dry in
air in order to harden

Investment Casting
Step 3
 The hardened ceramic mold is turned upside down and heated to a temperature
of around 200F-375F (90C-1750C). This causes the wax to flow out of the mold,
leaving the cavity for the metal casting.
 The ceramic mold is then heated to around 1000F-2000F (550C-1100C). This
will further strengthen the mold, eliminate any leftover wax or contaminants and
drive out water from the mold material. The metal casting is then poured while
the mold is still hot. Pouring the casting while the mold is hot allows the liquid
metal to flow easily through the mold cavity, filling detailed and thin sections.

Investment Casting
Step 4
 Pouring the metal casting in a hot mold also gives better dimensional accuracy,
since the mold and casting will shrink together as they cool.
 After pouring of the molten metal into the mold, the casting is allowed to set as
the solidification process takes place.

Investment Casting
Step 5
 Breaking the ceramic mold from the investment casting and cutting the parts
from the tree.

Investment Casting
Properties And Considerations Of Manufacturing By Investment
Casting
 Investment casting is a manufacturing process that allows the casting of
extremely complex parts, with good surface finish.
 Very thin sections can be produced by this process. Metal castings with
sections as narrow as .015in (.4mm) have been manufactured using
investment casting.
 Investment casting also allows for high dimensional accuracy.
Tolerances as low as .003in (.076mm) have been claimed.
 Practically any metal can be investment cast. Parts manufactured by this
process are generally small, but parts weighing up to 75lbs have been
found suitable for this technique.
 Parts of the investment process may be automated.
 Investment casting is a complicated process and is relatively expensive.

Centrifugal Casting
 The manufacturing process of centrifugal casting is a metal
casting technique, that uses the forces generated by centripetal
acceleration to distribute the molten material in the mold.
 Cast parts :- various pipes and tubes, ( sewage pipes, gas pipes,
and water supply lines)bushings, rings, the liner for engine
cylinders, brake drums, and street lamp posts.
The Process
 In centrifugal casting, a permanent mold is rotated continuously
about its axis at high speeds (300 to 3000 rpm) as the molten
metal is poured.
 The molten metal is centrifugally thrown towards the inside mold
wall, where it solidifies after cooling.
 Impurities and inclusions are thrown to the surface of the inside
diameter, which can be machined away.

Type of Centrifugal Casting
1. True centrifugal casting.
2. Semicentrifugal casting.
3. Centrifuge casting.

Centrifugal Casting
Features of centrifugal casting
 Castings can be made in almost any length, thickness and diameter.
 Different wall thicknesses can be produced from the same size
mold.
 Eliminates the need for cores.
 Resistant to atmospheric corrosion, a typical situation with pipes.
 Mechanical properties of centrifugal castings are excellent.
 Only cylindrical shapes can be produced with this process.
 Size limits are up to 6 m (20 feet) diameter and 15 m (50 feet)
length.
 Wall thickness range from 2.5 mm to 125 mm (0.1 - 5.0 in).
 Tolerance limit: on the OD can be 2.5 mm (0.1 in) on the ID can be
3.8 mm (0.15 in).
 Surface finish ranges from 2.5 mm to 12.5 mm (0.1 - 0.5 in) rms.

Centrifugal Casting
Materials
Typical materials that can be cast with
this process are iron, steel, stainless
steels, glass, and alloys
of aluminum, copper and nickel.
Applications
 Pipes, flywheels, cylinder liners and
 other parts that are axi-symmetric.
 Cylinder liners & sleeve valves for
piston engines,

Stir Casting

 Bulk and Surface Treatments
 Annealing, Normalizing, Hardening, Tempering
 Hardenability
Chapter 3.HEAT TREATMENT
With focus on Steels

HEAT
TREATMENT
BULK SURFACE
ANNEALING
Full Annealing
Recrystallization Annealing
Stress Relief Annealing
Spheroidization Annealing
AUSTEMPERING
THERMAL THERMO-
CHEMICAL
Flame
Induction
LASER
Electron Beam
Carburizing
Nitriding
Carbo-nitriding
NORMALIZING HARDENING
&
TEMPERING
MARTEMPERING
An overview of important heat treatments

Heat Treatment of Steel
 Heat Treatment is the controlled heating and cooling of metals to alter their
physical and mechanical properties without changing the product shape.
 Heat treatment is sometimes done inadvertently due to manufacturing
processes that either heat or cool the metal such as welding or forming.
 Heat Treatment is often associated with increasing the strength of material,
but it can also be used to alter certain manufacturability.
 Heat treatment is an operation or combination of operations involving heating
at specific rate, soaking at a temperature for a period of time and cooling at
some specified rate. The aim is to obtain a desired microstructure to achieve
certain pre determined properties (physical ,mechanical ,magnetic or
electrical).
objectives
1. improve machining,
2. improve formability,
3. restore ductility after a cold working operation.
4. improve product performance by increasing strength or other desirable
characteristics

Heat Treatment of Steel
Steels are heat treated for one of the following reasons:
1. Softening
2. Hardening
3. Material Modification
1. Softening
 Softening is done to reduce strength or hardness, remove residual
stresses, improve toughness, restore ductility, refine grain size or change the
electromagnetic properties of the steel.
 Restoring ductility or removing residual stresses is a necessary operation
when a large amount of cold working is to be performed, such as in a cold-
rolling operation or wiredrawing.
 Annealing — full Process, spheroidizing, normalizing and tempering —
austempering, martempering are the principal ways by which steel is
softened.

Steels are heat treated for one of the following reasons
2. Hardening
 Hardening of steels is done to increase the strength and wear properties.
 One of the pre-requisites for hardening is sufficient carbon and alloy content.
 If there is sufficient Carbon content then the steel can be directly hardened.
Otherwise the surface of the part has to be Carbon enriched using some diffusion
treatment hardening techniques.
 Heat treatment is used to modify properties of materials in addition to
hardening and softening.
 These processes modify the behavior of the steels in a beneficial manner to
maximize service life, e.g., stress relieving, or strength properties,
e.g., cryogenic treatment, or some other desirable properties, e.g., spring
aging.
3. Material Modification

Objectives of heat treatment (heat treatment processes)
The major objectives are
 To increase strength, harness and wear resistance (bulk
hardening, surface hardening)
 To increase ductility and softness (tempering, recrystallization
annealing)
 To increase toughness (tempering, recrystallization annealing)
 To obtain fine grain size (recrystallization annealing, full
annealing, normalizing)
 To remove internal stresses induced by differential deformation
by cold working, non-uniform cooling from high temperature
during casting and welding (stress relief annealing)
 To improve electrical properties ( recrystallization, tempering,
age hardening)
 To improve magnetic properties (hardening, phase
transformation)

it contains the following solid phases :
α ferrite : interstitial solid solution , BCC , maximum
solubility of 0.02% C at 723oC
austenite (γ) : interstitial solid solution , FCC , maximum
solubility of 2.08% C at 1148oC
δ ferrite : interstitial solid solution , BCC , maximum solubility of
0.09% C at 1495oC
cementite (Fe3C) : negligible solubility , 6.67% C & 93.33% Fe
at eutectic point : L (4.3%C) ---> γ (2.08%C) + Fe3C (6.67%C)
at eutectoid point : γ (0.8%C) ---> α (0.02%C) + Fe3C(6.67%C)
at peritectic point : δ (0.09%C) + L (0.53%C) ---> γ(0.17%C)
eutectoid steel = plain carbon steel with 0.8%C
hypoeutectoid steel = plain carbon steel with less than 0.8%C
hypereutectoid steel = plain carbon steel with more than 0.8%C

Type of Heat Treatment

Annealing
 It is a heat treatment wherein a material is altered,
causing changes in its properties such as strength
and hardness
 It the process of heating solid metal to high
temperatures and cooling it slowly so that its
particles arrange into a defined lattice
The annealing consists of
 Heating the steel to a certain temperature
 Soaking at this temperature
 Cooling at a predetermined rate

Annealing

Types of Annealing
1. Full Annealing
2. Stress-Relief Annealing (or Stress-relieving)
3. Process Annealing
4. Spheroidizing Annealing (or Spheroidizing )

A1
A3
Acm

T
Wt% C
0.8 %
723C
910C
Spheroidization
Full Annealing
Ranges of temperature where Annealing, Normalizing and Spheroidization treatment are
carried out for hypo- and hyper-eutectoid steels.

Cold worked grains → New stress free grains
Used in between processing steps (e.g. sheet rolling)
Heat below A1 → Sufficient time → Recrystallization
A1
A3
Acm
T
Wt% C
0.8 %
723oC
910oC
Spheroidization
Full Annealing
Full Annealing NormalizationNormalization
A1
A3
Acm
T
Wt% C
0.8 %
723oC
910oC
Spheroidization
Full Annealing

1.A Full Annealing
 Hypoeutectoid steel and eutectoid steel are heated into the austenitic region (ca.
40oC above the austenite-ferrite boundary) and hypereutectoid steel are heated
into the austenitic-cementite region (ca. 40oC above the 723oC),
 it is then held at these respective temperatures for a sufficient time in order for
the carbon atoms to diffuse in the materials,
 finally it is cooled slowly (usually in the furnace where it is treated). The
word full implies complete transformation.

Full Annealing
 The steel is heated above A3 (for hypo-eutectoid steels) | A1 (for hyper-eutectoid steels) → (hold) → then the
steel is furnace cooled to obtain Coarse Pearlite
 Coarse Pearlite has ↓ Hardness, ↑ Ductility
 Not above Acm → to avoid a continuous network of proeutectoid cementite along grain
boundaries (→ path for crack propagation)
A1
A3
Acm

T
Wt% C
0.8 %
723C
910C
Spheroidization
Full Annealing
Full Annealing
Normalization
Normalization

1.B. Stress-Relief Annealing
 It is an annealing process below
the transformation temperature
Ac1, with subsequent slow
cooling, the aim of which is to
reduce the internal residual
stresses in a workpiece without
intentionally changing its
structure and mechanical
properties

Annihilation of dislocations,
polygonization
Welding
Differential cooling Machining and cold working Martensite formation
Residual stresses → Heat below A1 → Recovery
A1
A3
Acm
T
Wt% C
0.8 %
723oC
910oC
Spheroidization
Full Annealing
A1
A3
Acm
T
Wt% C
0.8 %
723oC
910oC
Spheroidization
Full Annealing

Causes of Residual Stresses
1. Thermal factors (e.g., thermal stresses caused
by temperature gradients within the workpiece
during heating or cooling)
2. Mechanical factors (e.g., cold-working)
3. Metallurgical factors (e.g., transformation of
the microstructure)

How to Remove Residual Stresses?
 R.S. can be reduced only by a plastic deformation in the
microstructure.
 This requires that the yield strength of the material be
lowered below the value of the residual stresses.
 The more the yield strength is lowered, the greater the
plastic deformation and correspondingly the greater the
possibility or reducing the residual stresses
 The yield strength and the ultimate tensile strength of
the steel both decrease with increasing temperature

Stress-Relief Annealing Process
 For plain carbon and low-alloy steels the
temperature to which the specimen is heated is
usually between 450 and 650˚C, whereas for hot-
working tool steels and high-speed steels it is
between 600 and 750˚C
 This treatment will not cause any phase changes, but
recrystallization may take place.
 Machining allowance sufficient to compensate for
any warping resulting from stress relieving should
be provided

Stress-Relief Annealing – R.S.
 In the heat treatment of metals, quenching or rapid
cooling is the cause of the greatest residual stresses
 To activate plastic deformations, the local residual
stresses must be above the yield strength of the material.
 Because of this fact, steels that have a high yield
strength at elevated temperatures can withstand higher
levels of residual stress than those that have a low yield
strength at elevated temperatures
 Soaking time also has an influence on the effect of
stress-relief annealing

Stress Relief Annealing - Cooling
 The residual stress level after stress-relief annealing will be
maintained only if the cool down from the annealing
temperature is controlled and slow enough that no new
internal stresses arise.
 New stresses that may be induced during cooling depend on
the (1) cooling rate, (2) on the cross-sectional size of the
workpiece, and (3)on the composition of the steel

 Spheroidise annealing is one of the variant of the annealing
process that produces typical microstructure consisting of the
globules (spheroid) of cementite or carbides in the matrix of
ferrite.
The following methods are used for spheroidise annealing
1. Holding at just below AC1
Holding the steel component at just below the lower critical
temperature (A1) transforms the pearlite to globular cementite
particles. But this process is very slow and requires more time
for obtaining spheroidised structure.
2. Thermal cycling around AC1
Spheroidize annealing is applicable to steels which have more
than 0.8% carbon. Parts are heated to between 1150°F and
1200°F and holding it at this temperature for a period of time to
convert the microstructure.
Spheroidise annealing

Spheroidise annealing
 Essentially, cementite changes from a lamella formation to an alpha ferrite matrix
with particles of spheroidal cementite (Fe3C).
 Spherodize annealing is generally done on parts which have been work hardened,
to allow them to be further worked, either rolled in the case of coils, or drawn for
wire. This resulting product has improved ductility and toughness with reduced
hardness and strength.
 Spherodize annealing is normally carried out under a protective (endothermic)
atmosphere to prevent oxidation and decarburization.

Spheroidization Annealing
Heat below/above A1 (long time)
Cementite plates → Cementite spheroids → ↑ Ductility
• Used in high carbon steel requiring extensive machining prior to final hardening & tempering
• Driving force is the reduction in interfacial energy
A1
A3
Acm
T
Wt% C
0.8 %
723oC
910oC
Spheroidization
Full Annealing
A1
A3
Acm
T
Wt% C
0.8 %
723oC
910oC
Spheroidization
Full Annealing

2. Normalizing
 A heat treatment process consisting of austenitizing at temperatures of 30–
80˚C above the AC3 transformation temperature followed by slow cooling
(usually in air)
 The aim of which is to obtain a fine-grained, uniformly distributed, ferrite–
pearlite structure
 Normalizing is applied mainly to unalloyed and low-alloy hypoeutectoid steels
 For hypereutectoid steels the austenitizing temperature is 30–80˚C above the
AC1 or ACm transformation temperature

Normalizing – Heating and Cooling

Normalizing – Austenitizing Temperature Range

NORMALIZING
Refine grain structure prior to hardening
To harden the steel slightly
To reduce segregation in casting or forgings
Heat above A3 | Acm → Austenization → Air cooling → Fine Pearlite (Higher hardness)
• In hypo-eutectoid steels normalizing is done 50oC above the annealing temperature
• In hyper-eutectoid steels normalizing done above Acm → due to faster cooling
cementite does not form a continuous film along GB
Purposes
A1
A3
Acm
T
Wt% C
0.8 %
723oC
910oC
Spheroidization
Full Annealing
A1
A3
Acm
T
Wt% C
0.8 %
723oC
910oC
Spheroidization
Full Annealing

Effect of Normalizing on Grain Size
 Normalizing refines the grain of a steel that has
become coarse-grained as a result of heating to a
high temperature, e.g., for forging or welding
Carbon steel of 0.5% C. (a) As-rolled or forged; (b)
normalized. Magnification 500

The variation in the properties of the
annealed and normalized components
Annealed Normalized
Less hardness, tensile strength and
toughness
Slightly more hardness, tensile strength
and toughness
Pearlite is coarse and usually gets
resolved by the optical microscope.
Pearlite is fine and usually appears
unresolved with optical microscope.
Grain size distribution is more uniform. Grain size distribution is slightly less
uniform.
Internal stresses are least Internal stresses are slightly more.

 Hardening is process in which steel is heated to a temperature
above the critical point, held at this temperature and quenched
(rapidly cooled) in water, oil or molten salt baths
 following factors:
1.Adecuate carbon content to produce hardening.
2.Austenite decomposition to produce pearlite , bainite and
martensite structures.
3.Heating rate and time.
4.Quenching medium.
5.Quenching rate.
6.Size of the part.
7.Surface conditions.
Hardening (Quenching)

Hardening (Quenching)
Quenching media
The quenching media in general use are
:Water : it is probably the most widely used as it simple and effective, it cools at
the rate of 982°C per second. It tends, however, to form bubbles on the surface of
the metal being quenched an causes soft spots
Brine : it is very rapid cooling agent and may tend to cause distortion of the parts ,
as will water.
Oil : it is used when there is any risk of distortion although it is more suitable for
alloy steels than plain carbon steels.
Air blast : when the risk of distortion is great, quenching must be carried out air
blast. Since the rate of cooling is then lower, more hardening elements must be
added to the steel , forming an air-hardening alloy
Molten salts : high speed steels are often quenched in molten salt to hardened
them.

Tempering
 Heat below Eutectoid temperature → wait→ slow cooling
 The microstructural changes which take place during tempering are very complex
 Time temperature cycle chosen to optimize strength and toughness
 Tool steel: As quenched (Rc 65) → Tempered (Rc 45-55)
Cementite
ORF
Ferrite
BCC
Martensite
BCT Temper )(Ce)()(' 3
 

steel must be tempered to:
1.reduce a brittleness,
2.reliev e the internal stresses, and
3.obtain pre-determined mechanical
properties

 Tempering is a process of heat treating, which is used to increase
the toughness of iron-based alloys.
 Tempering is usually performed after hardening, to reduce some of the
excess hardness, and is done by heating the metal to some temperature below
the critical point for a certain period of time,
 then allowing it to cool in still air

Austenite
Pearlite
Pearlite + Bainite
Bainite
Martensite
100
200
300
400
600
500
800
723
0.1 1 10 102 103 104
105
Eutectoid temperature
Ms
Mf
t (s) →
T→
 + Fe3C
MARTEMPERING
AUSTEMPERING
 To avoid residual stresses generated during quenching
 Austenized steel is quenched above Ms for homogenization of temperature across the
sample
 The steel is then quenched and the entire sample transforms simultaneously
 Tempering follows
 To avoid residual stresses generated during quenching
 Austenized steel is quenched above Ms
 Held long enough for transformation to Bainite
Martempering
Austempering

Chapter 4
MECHANICS OF METAL
MACHINING
 Overview of Machining Technology
 Theory of Chip Formation in Metal Machining
 Force Relationships and the Merchant Equation
 Power and Energy Relationships in Machining
 Cutting Temperature
 The Mechanism of Chip formation. Chip Morphology.
 Sources of heat, Heat in Primary and Secondary shear
zone.
 Evaluation of surface roughness , Surface quality &
measurement of surface texture.

Material Removal Processes
A family of shaping operations, the common feature of
which is removal of material from a starting workpart
so the remaining part has the desired shape
 Categories:
 Machining – material removal by a sharp cutting tool,
e.g., turning, milling, drilling
 Abrasive processes – material removal by hard, abrasive
particles, e.g., grinding
 Nontraditional processes - various energy forms other
than sharp cutting tool to remove material

Machining
Cutting action involves shear deformation of work
material to form a chip
 As chip is removed, a new surface is exposed
Figure 21.2 - (a) A cross-sectional view of the machining process, (b) tool
with negative rake angle; compare with positive rake angle in (a)

Why Machining is Important
 Variety of work materials can be machined
 Most frequently applied to metals
 Variety of part shapes and special geometry features
possible, such as:
 Screw threads
 Accurate round holes
 Very straight edges and surfaces
 Good dimensional accuracy and surface finish

Disadvantages with Machining
 Wasteful of material
 Chips generated in machining are wasted material, at least in
the unit operation
 Time consuming
 A machining operation generally takes more time to shape a
given part than alternative shaping processes, such as
casting, powder metallurgy, or forming
 Generally performed after other manufacturing processes, such
as casting, forging, and bar drawing
 Other processes create the general shape of the starting workpart
 Machining provides the final shape, dimensions, finish, and special
geometric details that other processes cannot create
Machining in the Manufacturing Sequence

Machining Operations
 Most important machining operations:
 Turning
 Drilling
 Milling
 Other machining operations:
 Shaping and planing
 Broaching
 Sawing

Turning
Single point cutting tool removes material from a
rotating workpiece to form a cylindrical shape
Figure 21.3 (a) turning

Drilling
Used to create a round hole, usually by means of a
rotating tool (drill bit) that has two cutting edges
Figure 21.3 - The three most
common types of machining
process: (b) drilling

Milling
Rotating multiple-cutting-edge tool is moved slowly
relative to work to generate plane or straight surface
 Two forms: peripheral milling and face milling
Figure 21.3 - (c) peripheral milling, and (d) face milling

Cutting Tool Classification
1. Single-Point Tools
 One cutting edge
 Turning uses single point tools
 Point is usually rounded to form a nose radius
2. Multiple Cutting Edge Tools
 More than one cutting edge
 Motion relative to work usually achieved by rotating
 Drilling and milling use rotating multiple cutting edge
tools.

Figure 21.4 - (a) A single-point tool showing rake face, flank, and tool
point; and (b) a helical milling cutter, representative of tools with
multiple cutting edges

Cutting Conditions in Machining
 The three dimensions of a machining process:
 Cutting speed v – primary motion
 Feed f – secondary motion
 Depth of cut d – penetration of tool below original work
surface
 For certain operations, material removal rate can be
found as
MRR = v f d
where v = cutting speed; f = feed; d = depth of cut

Cutting Conditions for Turning
Figure 21.5 - Cutting speed, feed, and depth of cut for a turning operation

Roughing vs. Finishing in
Machining
In production, several roughing cuts are usually taken on the
part, followed by one or two finishing cuts
 Roughing - removes large amounts of material from the
starting workpart
 Creates shape close to desired geometry, but leaves some
material for finish cutting
 High feeds and depths, low speeds
 Finishing - completes part geometry
 Achieves final dimensions, tolerances, and finish
 Low feeds and depths, high cutting speeds

Machine Tools
A power-driven machine that performs a machining
operation, including grinding
 Functions in machining:
 Holds workpart
 Positions tool relative to work
 Provides power at speed, feed, and depth that have been set
 The term is also applied to machines that perform metal
forming operations

Four Basic Types of Chip in
Machining
1. Discontinuous chip(or Segmented chip)
2. Continuous chip
3. Continuous chip with Built-up Edge (BUE)
4. Serrated chip

Continuous Chip
 Ductile work materials
(e.g., low carbon steel)
 High cutting speeds
 Small feeds and depths
 Sharp cutting edge on
the tool
 Low tool-chip friction
Figure 21.9 - Four types of chip
formation in metal cutting:
(b) continuous

Continuous with BUE
 Ductile materials
 Low-to-medium cutting
speeds
 Tool-chip friction causes
portions of chip to adhere to
rake face
 BUE formation is cyclical; it
forms, then breaks off
formation in metal cutting: (c)
continuous with built-up edge

Serrated Chip
 Semicontinuous - saw-
tooth appearance
 Cyclical chip formation
of alternating high
shear strain then low
shear strain
 Most closely associated
with difficult-to-
machine metals at high
cutting speeds
formation in metal cutting: (d)
serrated

Chip Thickness Ratio
where r = chip thickness ratio; to = thickness of the chip prior to
chip formation(t1); and tc = chip thickness after separation(t2)
c
o
t
t
r 

Determining Shear Plane Angle
where r = chip ratio, and  = rake angle

Shear StrainShear strain in machining can be computed from the following
equation, based on the preceding parallel plate model:
 = tan( - ) + cot 
where  = shear strain,  = shear plane angle, and  = rake angle
of cutting tool
Figure 21.7 - Shear strain during chip formation: (a) chip formation depicted as a
series of parallel plates sliding relative to each other, (b) one of the plates
isolated to show shear strain, and (c) shear strain triangle used to derive strain
equation

Figure 21.8 - More realistic view of chip formation, showing
shear zone rather than shear plane. Also shown is the
secondary shear zone resulting from tool-chip friction

Forces Acting on Chip
 Friction force F and Normal force to friction N
 Shear force Fs and Normal force to shear Fn
Figure 21.10 -
Forces in metal
cutting: (a) forces
acting on the chip in
orthogonal cutting

Cutting Force and Thrust Force
 Forces F, N, Fs, and Fn cannot be directly measured
 Forces acting on the tool that can be measured:
 Cutting force Fc and Thrust force Ft
Figure 21.10 - Forces in
metal cutting: (b) forces
acting on the tool that
can be measured

Forces in Metal Cutting
 Equations can be derived to
relate the forces that cannot be
measured to the forces that can
be measured:
F = Fc sin + Ft cos
N = Fc cos - Ft sin
Fs = Fc cos - Ft sin
Fn = Fc sin + Ft cos
 Based on these calculated force,
shear stress and coefficient of
friction can be determined

What the Merchant Equation Tells
Us
 To increase shear plane angle
 Increase the rake angle
 Reduce the friction angle (or coefficient of friction)
22
45

 

Coefficient of Friction
Coefficient of friction between tool and chip:
Friction angle related to coefficient of friction as follows:
N
F

 tan
= (Fc sin + Ft cos)/ (Fc cos - Ft sin )
Or (Ft +Fc tan )/ (Fc - Ft tan )

Shear Stress
Shear stress acting along the shear plane:
sin
wt
A o
s 
where As = area of the shear plane
Shear stress = shear strength of work material during cutting
s
s
A
F
S 

 Higher shear plane angle means smaller shear plane
which means lower shear force
 Result: lower cutting forces, power, temperature, all of
which mean easier machining
Figure 21.12 - Effect of shear plane angle : (a) higher  with a resulting
lower shear plane area; (b) smaller  with a corresponding larger shear plane
area. Note that the rake angle is larger in (a), which tends to increase shear
angle according to the Merchant equation

Power and Energy Relationships
 A machining operation requires power
The power to perform machining can be computed from:
Pc = Fc v
where Pc = cutting power; Fc = cutting force; and v = cutting
speed
In U.S. customary units, power is traditional expressed as
horsepower (dividing ft-lb/min by 33,000)
where HPc = cutting horsepower, hp
00033,
vF
HP c
c 

Power and Energy Relationships
Gross power to operate the machine tool Pg or HPg is
given by
or
where E = mechanical efficiency of machine tool
• Typical E for machine tools =  90%
E
P
P c
g  E
HP
HP c
g 
Unit Power in Machining
 Useful to convert power into power per unit volume
rate of metal cut
 Called the unit power, Pu or unit horsepower, HPu
or
where MRR = material removal rate
MRR
P
P c
u 
MRR
HP
HP c
u 

Specific Energy in Machining
Unit power is also known as the specific energy U
Units for specific energy are typically N-m/mm3 or J/mm3 (in-lb/in3)
wt
F
wvt
vF
MRR
P
PU
o
c
o
cc
u 

Cutting Temperature
 Approximately 98% of the energy in machining is converted into
heat
 This can cause temperatures to be very high at the tool-chip
 The remaining energy (about 2%) is retained as elastic energy in the
chip
 Several analytical methods to calculate cutting temperature
 Method by N. Cook derived from dimensional analysis
using experimental data for various work materials
where T = temperature rise at tool-chip interface; U = specific energy; v =
cutting speed; to = chip thickness before cut; C = volumetric specific heat of
work material; K = thermal diffusivity of the work material
3330
40
.
.







K
vt
C
U
T o


Cutting Temperature
 Experimental methods can be used to measure
temperatures in machining
 Most frequently used technique is the tool-chip
thermocouple
 Using this method, K. Trigger determined the
speed-temperature relationship to be of the form:
T = K vm
where T = measured tool-chip interface temperature

Metal Cutting theory
 Plastically deform a material using a hard tool in order
to obtain desired physical shape and properties
 Very complex phenomena
 Essential for high precision; high performance
products

Evaluation of surface roughness

Question 1 & Answer
Ques.1 What is surface finish?
Ans :- Surface finish or surface texture:-The local deviations of a
surface from a perfectly flat plane . It has three
components: lay, surface roughness, and waviness
 Lay :-Lay is the direction of the predominant surface pattern .
Surface roughness (roughness):- It is a measure of the finely spaced surface
irregularities. In engineering, this is what is usually meant by "surface finish.
Waviness :- it is the measure of surface irregularities with a spacing greater
than that of surface roughness. These usually occur due to Vibrations, or
deflection during machining.
Surface finish grades
specified

Calculation of surface Roughness
The surface roughness is evaluated by the
height, Rt and mean roughness index Ra of
the micro-irregularities
 Surface roughness number (Ra) is
expressed in microns.
Ra = (h1+h2+-----+hn)/n
• Actual profile, Af
– It is the profile of the actual surface obtained by
finishing operation.
• Reference profile, Rf
– It is the profile to which the irregularities of the
surface is referred to. it passes through the highest
point of the actual profile.
• Datum profile, Df
– It is the profile, parallel to the reference profile .it
passes through the lowest point B of the actual
profile
• Mean Profile, Mf
– It is that profile, within the sampling length
chosen (L) such that the sum of the material-
filled areas enclosed above it by the actual
profile is equal to the sum of the material void
area enclosed below it by the profile.
• Peak to valley height, Rt
– It is the distance from the datum profile to the
reference profile.
• Mean roughness index, Ra
– It is the arithmetic mean of the absolute value of
the highest hi between the actual and mean
profile.
Ra
 Ra = 1/L ∫x=0 |hi| dx , where L is
sampling length
Question 2 & Answer
or

Surface Texture Symbol
Here ,
a = surface roughness value(in
micron)
or
=Roughness grade no. N1 to N12
b= Production method
c = Sampling length
d = direction of lay
e = Machining allowance
d Lay Interpretation
= Parallel
Perpendicular
X Cross-hatch
M Multi-
directional
C Circular
R Radial

INDICATION OF SURFACE TEXTURE
 If the removal of material by machining is required, bar is
added to the basic symbol,
 If the removal of material is not permitted a circle is added to
the basic symbol.
 When special surface characteristics have to be indicated, a
line is added to the longer arm of any of the above symbols.
Indication of Surface Roughness
The value or values defining the principal criterion of roughness are added to
the symbols
a- surface
roughness
value(in micron)
 If it is necessary to impose maximum
and minimum limits of the principal
criterion of surface roughness, both
values shall be shown
maximum limit (a1)
;minimum limit (a2).
Roughness a obtained
by any production
process
Roughness a obtained
by removal of material
by machining
Roughness a shall be
obtained without removal
of any material

CUTTING TOOL MATERIALS
& CUTTING FLUIDS
DEVLOPMENT OF TOOL MATERIALS
Chapter 5

TOPICS :
 Introduction
 Carbon and medium alloy
steels
 High speed steels
 Cast-cobalt alloys
 Carbides
 Coated tools
 Alumna-based ceramics
 Cubic Boron Nitride
 Silicon Nitride based
ceramics
 Diamond
 Whisker-reinforced tool
materials
 Cutting-Tool
Reconditioning
 Cutting fluids

Introduction
 Cutting tool is subjected to:
1. High temperatures,
2. High contact stresses
3. Rubbing along the tool–chip interface and along the machined
surface
 Cutting-tool material must possess:
1. Hot hardness (see right)
2. Toughness and impact strength
3. Thermal shock resistance
4. Wear resistance
5. Chemical stability and inertness

REASONS FOR DEVELOPMENT OF
CUTTING TOOL
GLOBLE COMPETATION
 PRODUCTIVITY :
 Cutting Speed
 Reduce Machining Time
 Improve Tool Life
 QUALITY AND RELIABILITY:
 High accuracy & tolerances
 Better surface finish
 Cost:
 Reduce Unnecessary Cost
 Reduce non-productive cost

BASIC REQUIREMENT OF A TOOL MATERIALS
 Hot hardness
 Wear resistance
 Toughness and strength
 Thermal conductivity
 Co-efficient of friction
 Co-efficient of thermal expansion
 Machinability and grindability

Introduction:
Characteristics of cutting tool :
 Hardness (Elevated temperatures)
 Toughness (Impact forces on tool in interrupted
operations)
 Wear resistance (tool life to be considered)
 Chemical stability or inertness (to avoid adverse
reactions)

Cutting tool materials
 Carbon & medium alloy steels
 High speed steels
 Cast-cobalt alloys
 Carbides
 Coated tools
 Alumina-based ceramics
 Cubic boron nitride
 Silicon-nitride-base ceramics
 Diamond
 Whisker-reinforced materials

Carbon and Medium alloy steels :
 Oldest of tool materials
 Used for drills taps, broaches ,reamers
 Inexpensive ,easily shaped ,sharpened
 No sufficient hardness and wear resistance
 Limited to low cutting speed operation
High speed steels (HSS)
 Hardened to various depths
 Good wear resistance
 Relatively
 Suitable for high positive rake angle tools

Two basic types of HSS
 Molybdenum ( M-series)
 Tungsten ( T-series)
M-series - Contains 10% molybdenum, chromium,
vanadium, tungsten, cobalt
 Higher, abrasion resistance
 H.S.S. are majorly made of M-series
T-series - 12 % - 18 % tungsten, chromium,
vanadium & cobalt
 undergoes less distortion during heat treating

High-speed Steels
 High-speed steel (HSS) tools were developed to machine at
higher speeds than was previously possible
 They can be hardened to various depths, have good wear
resistance and are inexpensive
 There are two basic types of high-speed steels: molybdenum
(M-series) and tungsten (T-series)
 High-speed steel tools are available in wrought, cast and
powder-metallurgy (sintered) forms
 They can be coated for improved performance
 H.S.S. available in wrought ,cast & sintered (Powder
metallurgy)
 Coated for better performance
 Subjected to surface treatments such as case-hardening for
improved hardness and wear resistance or steam treatment at
elevated temperatures
 High speed steels account for largest tonnage

High-speed Steels
EXAMPLE 22.1
Alloying Elements in High-speed Steel Cutting Tools
List the major alloying elements in high-speed steels and
describe their effects in cutting tools.
Solution
The major alloying elements in HSS are chromium, vanadium,
tungsten, cobalt, and molybdenum

Cast-Cobalt alloys
 Commonly known as stellite tools
 Composition ranges – 38% - 53 % cobalt ,30%- 33% chromium
10%-20%tungsten
 Less tough than high-speed steels and sensitive to impact forces
 Less suitable than high-speed steels for interrupted cutting
operations
 Continuous roughing cuts – relatively high feeds & speeds
 Finishing cuts are at lower feed and depth of cut
 Cast-cobalt alloys have high hardness, good wear resistance and
can maintain their hardness at elevated temperatures

Carbides :
3-groups of materials
 Alloy steels
 High speed steels
 Cast alloys
 These carbides are also known as cemented or sintered
carbides
 High elastic modulus,thermal conductivity
 Low thermal expansion
2-groups of carbides used for machining operations
 tungsten carbide
 titanium carbide

Tungsten Carbide
 Composite material consisting of tungsten-carbide particles
bonded together
 Alternate name is cemented carbides
 Manufactured with powder metallurgy techniques
 Particles 1-5 Mum in size are pressed & sintered to desired
shape
 Amount of cobalt present affects properties of carbide tools
 As cobalt content increases – strength hardness & wear
resistance increases
 Titanium carbide has higher wear resistance than tungsten
carbide
 Nickel-Molybdenum alloy as matrix – Tic suitable for
machining hard materials
 Steels & cast irons
 Speeds higher than those for tungsten carbide

Inserts
 Individual cutting tool with severed cutting points
 Clamped on tool shanks with locking mechanisms
 Inserts also brazed to the tools
 Clamping is preferred method for securing an insert
 Carbide Inserts available in various shapes-Square, Triangle,
Diamond and round
 Strength depends on the shape
 Inserts honed, chamfered or produced with negative land to improve
edge strength
 The smaller the included angle, the lower the strength of the edge

Insert Attachment
Fig : Methods of
attaching
inserts to
toolholders :
(a) Clamping
and (b) Wing
lockpins. (c)
Examples of
inserts attached
to toolholders
with threadless
lockpins, which
are secured
with side
screws.
Carbides: Inserts

Edge Strength
Fig : Relative edge
strength and
tendency for
chipping and
breaking of inserts
with various shapes.
Strength refers to the
cutting edge shown
by the included
angles.
Fig : edge preparation of
inserts to improve
edge strength.
Carbides: Inserts

Chip breakers:
Purpose :
 Eliminating long chips
 Controlling chip flow during machining
 Reducing vibration & heat generated
 Selection depends on feed and depth of cut
 Work piece material, type of chip produced during cutting
Carbides: Inserts

Coated tools :
- High strength and toughness but generally abrasive and
chemically reactive with tool materials
Unique Properties :
Lower Friction
High resistance to cracks and wear
High Cutting speeds and low time & costs
Longer tool life
Higher adhesion
Acting as a diffusion barrier
Higher hot hardness and impact resistance

Coating materials
 Titanium nitride (TiN)
 Titanium carbide (Tic)
 Titanium Carbonitride (TicN)
 Aluminum oxide (Al2O3)thickness range – 2-15 µm (80-
600Mu.in)
Techniques used :
 Chemical –vapor deposition (CVD)
Plasma assisted CVD
 Physical-vapor deposition(PVD)
 Medium –temperature chemical- vapor deposition(MTCVD)

Properties for Group of Materials
Fig : Ranges of properties for various groups of tool materials.

Cutting tool Characteristics for coating :
 High hardness
 Chemical stability
 Low thermal conductivity
 Good bonding
 Little or no Porosity
Titanium nitride (TiN) coating :
 Low friction coefficients
 High hardness
 Resistance to high temperatures
 Good adhesion to substrate
 High life of high speed-steel tools
 Improve the life of high-speed steel tools and improve the lives of carbide
tools, drill bits, and cutters
 Perform well at higher cutting speeds and feeds
Titanium carbide (TiC) coating:
 Titanium carbide coatings on tungsten-carbide inserts have high flank wear
resistance.

Ceramics Coatings :
 Low thermal conductivity ,resistance ,high temperature
 Resistance to flank wear and crater wear
 Ceramics are suitable materials for tools
 Al2O3 (most commonly used)
Multi Phase Coatings :
 First layer –Should bond well with substrate
 Outer layer – Resist wear and have low thermal conductivity
 Intermediate layer – Bond well & compatible with both layers
 Coatings of alternating multipurpose layers are also formed.

Multiphase Coatings
Fig : Multiphase coatings on a tungsten-carbide substrate. Three alternating layers of aluminum
oxide are separated by very thin layers of titanium nitride. Inserts with as many as thirteen
layers of coatings have been made. Coating thick nesses are typically in the range of 2 to 10
µm.

Diamond Coated tools :
 Use of Polycrystalline diamond as a coating
 Difficult to adhere diamond film to substrate
 Thin-film diamond coated inserts now commercially available
 Thin films deposited on substrate with PVD & CVD techniques
 Thick films obtained by growing large sheet of pure diamond
 Diamond coated tools particularly effective in machining non-
ferrous and abrasive materials
Coated Tools

New Coating materials : Titanium carbon nitride (TiCN)
 Titanium Aluminum Nitride(TiAlN)
 Chromium Based coatings
 Chromium carbide
 Zirconium Nitride (ZrN)
 Hafnium nitride (HfN)
Recent developments gives nano coating & composite coating
Ion Implementation :
 Ions placed into the surface of cutting tool
 No change in the dimensions of tool
 Nitrogen-ion Implanted carbide tools used for alloy steels &
stainless steels
 Xeon – ion implantation of tools as under development
Coated Tools

Alumina-Based ceramics:
 Cold-Pressed Into insert shapes under high pressure and
sintered at high temperature
 High Abrasion resistance and hot hardness
 Chemically stable than high speed steels & carbides
 So less tendency to adhere to metals
 Good surface finish obtained in cutting cast iron and steels
 Negative rake-angle preferred to avoid chipping due to poor
tensile strength
Cermets, Black or Hot- Pressed :
 70% aluminum oxide & 30 % titanium carbide
 cermets(ceramics & metal)
 Cermets contain molybdenum carbide, niobium carbide and
tantalum carbide.
CeramicsTool

Cubic boron Nitride ( CBN ) :
 Made by bonding ( 0.5-1.0 mm ( 0.02-0.04-in)
 Layer of poly crystalline cubic boron nitride to a carbide substrate by
sintering under pressure
 While carbide provides shock resistance CBN layer provides high resistance
and cutting edge strength
 Cubic boron nitride tools are made in small sizes without substrate
Fig : (a) Construction of a polycrystalline cubic
boron nitride or a diamond layer on a tungsten-
carbide insert.
b) Inserts with polycrystalline cubic boron
nitride tips (top row) and solid
polycrystalline CBN inserts (bottom row).

Silicon-Nitride based ceramics (SiN)
 They consists various addition of Aluminum Oxide ythrium
oxide, titanium carbide
 SiN have toughness, hot hardened & good thermal – shock
resistance
 SiN base material is Silicon
 High thermal & shock resistance
 Recommended for machining cast iron and nickel based super
alloys at intermediate cutting speeds

Diamond Tool :
 Hardest known substance
 Low friction, high wear resistance
 Ability to maintain sharp cutting edge
 Single crystal diamond of various carats used for special
applications
 Machining copper—front precision optical mirrors for ( SDI)
 Diamond is brittle , tool shape & sharpened is important
 Low rake angle used for string cutting edge

Polycrystalline-Diamond ( PCD ) Tools:
 Used for wire drawing of fine wires
 Small synthesis crystal fused by high pressure and temperature
 Bonded to a carbide substrate
 Diamond tools can be used fir any speed
 Suitable for light un-interrupted finishing cuts
 To avoid tool fracture single crystal diamond is to be re-
sharpened as it becomes dull
 Also used as an abrasive in grinding and polishing operations

Polycrystalline-Diamond ( PCD ) Tools:
PCD:
 Synthetic having diamond matrix structure.
 Sintered under extremely high temperature and pressure.
 High in uniform hardness and abrasive resistance in all
direction.
 Very high tool life compare to carbide tool (50 times).
 Shock resistance is more than natural diamond.
 Consistency in wear resistance.
 Available in large verity of shapes and sizes.
 Discs as large as 58 mm in diameter.
 Better thermal conductivity then natural diamond.
 Lower cost then natural diamond.
 Used for machining milling, turning, grooving, facing and
boring.

Whisker –reinforced & Nano
crystalline tool materials
New tool materials with enhanced properties :
1. High fracture toughness
2. Resistance to thermal shock
3. Cutting –edge strength
4. Hot hardness
5. Creep resistance
 Examples: Silicon-nitride base tools reinforced with silicon-
carbide( Sic)
 Aluminum oxide based tools reinforced with silicon-carbide with
ferrous metals makes Sic-reinforced tools
 Progress in nano material has lead to the development of cutting
tools
 Made of fine grained structures as (micro grain) carbides

Cutting-Tool Reconditioning
 When tools get wormed, they are reconditioned for further
use
 Reconditioning also involves recoating used tools with
titanium nitride
 Tool costs depend on the tool material, size, shape, chip-
breaker features and quality
 The cost of an individual insert is relatively insignificant
 Cutting tools can be reconditioned by resharpening them
 Reconditioning of coated tools also is done by recoating
them

Cutting Fluids: (Lubricants + Coolants)
Used in machining as well as abrasive machining processes
 Reduces friction wear
 Reduce forces and energy consumption
 Cools the cutting zone
 Wash away the chips
 Protect Machined surfaces from environmental corrosion
o Depending on the type of machining operation, a coolant, a
lubricant, or both are used
o Effectiveness of cutting fluids depends on type of machining
operation, tool and workpiece materials
and cutting speed
Cutting Fluids

Cutting Fluids
Cutting-fluid Action
 Cutting fluid seep from the sides of the chip through the
capillary action of the interlocking network of surface asperities
in the interface
 Discontinuous cutting operations have more straightforward
mechanisms for lubricant application, but the tools are more
susceptible to thermal shock
EXAMPLE
Effects of Cutting Fluids on Machining
A machining operation is being carried out with a cutting fluid that
is an effective lubricant. What will be the changes in the mechanics
of the cutting operation if the fluid is shut off?

Cutting FluidsSolution
Effects of Cutting Fluids on Machining
Chain of events taking place after the fluid is shut off:
1. Friction at the tool–chip interface will increase
2. The shear angle will decrease in accordance
3. The shear strain will increase
4. The chip will become thicker
5. A built-up edge is likely to form
As a result:
1. The shear energy in the primary zone will increase
2. The frictional energy in the secondary zone will increase
3. The total energy will increase
4. The temperature in the cutting zone will rise
5. Surface finish will to deteriorate and dimensional tolerances
may be difficult to maintain

Cutting Fluids
Types of Cutting Fluids
 4 general types:
1. Oils - mineral, animal, vegetable, compounded, and synthetic
oils,
2. Emulsions - a mixture of oil and water and additives
3. Semisynthetics - chemical emulsions containing little
mineral oil
4. Synthetics - chemicals with additives

Application of Cutting Fluids
Fig : Schematic illustration of proper methods of applying
cutting fluids in various machining operations: (a)turning,
(b)milling, (c)thread grinding, and (d)drilling
 4 basic methods:
1. Flooding
2. Mist
3. High-pressure systems
4. Through the cutting
tool system

Cutting Fluids
Effects of Cutting Fluids
 Selection of a cutting fluid based on:
1. Workpiece material and machine tools
2. Biological considerations
3. Environment
 Machine-tool operator is in close proximity to cutting fluids,
thus health effects is a primary concern
 Progress has been made in ensuring the safe use of cutting
fluids
 Recycling involves treatment of the fluids with various
additives, agents, biocides, deodorizers and water treatment

Cutting Fluids:
Near-dry and Dry Machining
 Near-dry cutting is the application of a fine mist of an air–
fluid mixture containing a very small amount of cutting fluid
 Dry machining is effective on steels, steel alloys, and cast
irons, but not for aluminium alloys
 One of the functions of a metal-cutting fluid is to flush chips
from the cutting zone
Cryogenic Machining
 Using nitrogen or carbon dioxide as a coolant
 The chips are more brittle and machinability is increased

Computer Numerical Control
 Numerical control is a method of automatically
operating a manufacturing machine based on a
code of letters, numbers, and special characters.
 The numerical data required to produce a part is
provided to a machine in the form of a program,
called part program or CNC program.
 The program is translated into the appropriate
electrical signals for input to motors that run the
machine.

 Increase production throughput
 Improve the quality and accuracy
of manufactured parts
 Stabilize manufacturing costs
 Manufacture complex or otherwise
impossible jobs -2D and 3D
contours
Why Use CNC Machines?

Numerical Control
“a form of programmable automation in which the
mechanical actions of machine tool or other equipment
are controlled by a program containing coded
alphanumeric data”
Figure 1.1:- Numerical Control (NC) Machine

NC System
FIGURE :-1.2 Three basic component of a NC system :
(a) program of instruction (b) Control unit ; ( c) machine tool

NC Machine system
1. Software :-
 The programmes or set of instructions, languages, punched
cards, magnetic tape, punched paper tape and other such
information processing items.
Step :-
i. The programmer plans the operations and their sequence from
seeing the drawing
ii. Part programme
iii. Punch on control tape ,
iv. Tape reader reads the codes and sends it to Machine Control
Unit.
Basic Component of NC Machines

NC System
2. Machine Control Unit (MCU) :-
 Main unit
Consist of following unit :-
a) Input or Reader Unit :- Electro-mechanical devices used to
collect the input from punched tape, cards, magnetic tape and
disk.
b) Memory
c) Processor
d) Input Channels
e) Control Panel
f) Feedback Channel

NC System
3. Machine Tool
It may consist of :-
 Worktable,
 Cutting tools,
 Jigs and fixtures,
 Motors for driving spindle
 Coolant and lubricating system
Figure 1.3:- Numerical Control
(NC) Machine Tool

Types NC System
Type of NC system:-
1. Point to point System(Eg. Drilling)
 Move the tool or the workpiece from one point to
another and then the tool performs the required task
Figure 1.4. Cutter path between holes in
a point-to-point system

NC System
2.Continuous & Linear (eg. Milling)
(b)
(a)
Figure 1.5. (a) Continuous path cutting and (b) Position
error caused by the velocity error

NC System
3. Interpolator
Figure 1.6. Types of interpolation (a) linear, (b)
continuous path approximated by incremental straight
lines, and (c) circular

NC System
4 Absolute and incremental System
(a) Absolute system (b) Incremental system

NC System
5. Loop System
(b) Closed loop control system
a) Open loop control system

Advantages of NC
 Runs automatically
 Greater flexibility
 Less machine idle time
 Complex geometries
 Reduced fixturing
 Higher accuracy ±.0001"
 Reduced scrap
 Enhances engineering
change
 Reduced inventory
 Reduced tooling cost
 Increases productivity
 Less inspection time

Disadvantages of NC
The main disadvantages of NC systems are
 Machine cost :- Relatively higher cost compared to manual
versions
 More complicated maintenance due to the complex nature of
the technologies
 Programming training.
 Need for skilled part programmers
 Manual reload the NC tapes for each new part and the lack of
program editing abilities.

NC Application Characteristics
 Batch and High Volume production
 Repeat orders (Mass production)
 Complex part geometries
 Many separate operations on one part

CNC System
“Computer Convert the design into number which computer
usage to control the cutting & Shaping of material.”
Figure 2.1 : Computer Numerical Control (CNC) Machine

CNC System
A CNC system basically consists of the following :
(a) Central processing unit (CPU)
(b) Servo control unit
(c) Operator control panel
(d) Machine control panel
(e) Programmable logic controller
(f) Other peripheral devices.
Figure 2.2 : CNC Lathe Machine

CNC System
Figure 2.3 : Computer Numerical Control (CNC) System
Major Elements of CNC system :-
1. Part program (Computer)
2 . Machine Control Unit (MCU)
3 . Machine tool (lathe, drill press, milling machine etc)

CNC System
Figure 2.3. A typical numerical control
system for a milling machine

Advantages of CNC Machine
 High Repeatability and Precision, e.g. Aircraft parts.
 Volume of production is very high.
 Complex contours/surfaces need to be machined, e.g. Turbines.
 Flexibility in job change, automatic tool settings, less scrap.
 Safer, higher productivity, better quality.
 Less paper work, reduction in lead times.
 Easier to program.
 Easy storage of existing programs.
 Avoids human errors.
 Usually generates closer tolerances than manual machines.
 Program editing at the machine tool.
 Control systems upgrades possible.
 Option -resident CAM system at machine tool.
 Tool path verification.

Disadvantages of CNC Machine
1. High investment cost
2. Maintenance is difficult.
3. Computers, programming knowledge required.
4. Specialized & skilled operator required for handling.
5. Less workers are required to operate CNC machines
compared to manually operated machines. Investment in
CNC machines can lead to unemployment.

Applications of CNC Machines
 Aerospace equipments.
 Automobile Parts
 Fabrication
 Sewing Machine
 Industries for removing metal
 Involved in unconventional
machine(ECM,EDM,laser,USM)
 Used in food industry,
packaging, Electronic industries. Figure 2.4. CNC Laser Cutting Machine

Differences between NC & CNC Machine
Numerical control Machine CNC Machine
1. The program is fed to the
machine through magnetic
tapes or other such media
The machines are
interfaced with computers.
2. The part program is entered on
the program tape in the form of
punched holes.
The part program is entered into
computer using input devices like
keyboard, mouse, cd etc
3. In NC machines the tape reader
forms the machine control unit.
In CNC the computer and the
controller forms the machine control
unit
4. Has No memory storage and is
run off of the tape each time
the machining cycles.
Has memory storage and program can
be stored in its control unit.

Direct numerical control
 Direct numerical control (DNC), also known as distributed
numerical control (also DNC),
 A common manufacturing term for networking CNC machine
tools from Hoist/Main computer.
Industries with significant sheet metal fabrication, such as the
automotive and aerospace industries.
Advantages of DNC
(a) The computer can be remotely located.
(b) The computer can program simultaneously many NC
machines.

DNC System
Figure :- Systematic diagram of DNC System

Motivation and uses
 To manufacture complex curved geometries in 2D or
3D was extremely expensive by mechanical means
(which usually would require complex jigs to control
the cutter motions)
 Machining components with repeatable accuracy
 Unmanned machining operations

Advantages of CNC
- Easier to program;
- Easy storage of existing programs;
- Easy to change a program
- Avoids human errors
- safer to operate
- Complex geometry is produced as cheaply as simple
ones
- Usually generates closer tolerances than manual
machines

Vertical Milling machine architecture
Conventional milling machines

Types of CNC machines
Based on Motion Type:
Point-to-Point or Continuous path
Based on Control Loops:
Open loop or Closed loop
Based on Power Supply:
Electric or Hydraulic or Pneumatic
Based on Positioning System
Incremental or Absolute

Basic CNC Principles
 Using a vertical mill
machining center as an
example, there are typically
three linear axes of motion.
Each is given an alphabetic
designation or address. The
machine table motion side to
side is called the “X” axis.
Table movement in and out
is the “Y” axis, while head
movement up and down the
column is the “Z” axis.

Basic CNC Principles Coordinates System
Absolute Coordinate System
Incremental Coordinate System

All computer controlled machines are able to accurately and repeatedly
control motion in various directions. Each of these directions of motion is
called an axis. Depending on the machine type there are commonly two to
five axes.
Additionally, a CNC axis may be either a linear axis in which movement is
in a straight line, or a rotary axis with motion following a circular path.

If a rotary table is added to the machine table, then the
fourth axis is designated the “b” axis.

How CNC Works
 Controlled by G and M codes.
 These are number values and co-ordinates.
 Each number or code is assigned to a particular operation.
 Typed in manually to CAD by machine operators.
 G&M codes are automatically generated by the computer
software.

Features of CNC Machinery
 The tool or material moves.
 Tools can operate in 1-5 axes.
 Larger machines have a machine control unit (MCU)
which manages operations.
 Movement is controlled by a motors (actuators).
 Feedback is provided by sensors (transducers)
 Tool magazines are used to change tools automatically.

Tools
 Most are made from
high speed steel (HSS),
tungsten carbide or ceramics.
 Tools are designed to direct waste away from the material.
 Some tools need coolant such as oil to protect the tool and
work.

Tool Paths, Cutting and Plotting Motions
 Tool paths describes the route the cutting tool takes.
 Motion can be described as point to point, straight cutting or
contouring.
 Speeds are the rate at which the tool operates e.g. rpm.
 Feeds are the rate at which the cutting tool and work piece
move in relation to each other.
 Feeds and speeds are determined by cutting depth, material and
quality of finish needed. e.g. harder materials need slower
feeds and speeds.
 Rouging cuts remove larger amounts of material than finishing
cuts.
 Rapid traversing allows the tool or work piece to move rapidly
when no machining is taking place.

Manual NC programming
Part program: A computer program to specify
- Which tool should be loaded on the machine spindle;
- What are the cutting conditions (speed, feed, coolant ON/OFF etc)
- The start point and end point of a motion segment
- how to move the tool with respect to the machine.
Standard Part programming language: RS 274-D (Gerber, GN-code)

History of CNC
The RS274-D is a word address format
Each line of program == 1 block
Each block is composed of several instructions, or (words)
Sequence and format of words:
N3 G2 X+1.4 Y+1.4 Z+1.4 I1.4 J1.4 K1.4 F3.2 S4 T4 M2
sequence no
preparatory function
destination coordinates dist to center of circle
feed rate spindle speed
tool
Other function

Manual Part Programming Example
Tool size = 0.25 inch,
Feed rate = 6 inch per minute,
Cutting speed = 300 rpm,
Tool start position: 2.0, 2.0
Programming in inches
(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3
p4
p5
Motion of tool:
p0  p1  p2  p3  p4  p5  p1  p0

Spindle CCW
(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3
p4
p5
1. Set up the programming parameters
N010 G70 G90 G94 G97 M04
Programming in inches
Use absolute coordinates
Spindle speed in rpm
Feed in ipm

Flood coolant ON
(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3
p4
p5
2. Set up the machining conditions
N020 G17 G75 F6.0 S300 T1001 M08
Machine moves in XY-plane
Feed rate
Tool no.
Spindle speed
Use full-circle interpolation

(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3
p4
p5
3. Move tool from p0 to p1 in straight line
N030 G01 X3.875 Y3.698
Linear interpolation
target coordinates

(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3
p4
p5
4. Cut profile from p1 to p2
N040 G01 X3.875 Y9.125
target coordinates
N040 G01 Y9.125
X-coordinate does not change  no need to program it
or

(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3
p4
p5
5. Cut profile from p2 to p3
N050 G01 X5.634 Y9.125
target coordinates
1”
p3
.125
(x, y)
(6.5, 9)
y = 9 + 0.125 = 9.125
(6.5 - x)2 + 0.1252 = (1 - 0.125)2
x = 5.634

coordinates of center of circle(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3
p4
p5
6. Cut along circle from p3 to p4
N060 G03 X7.366 Y9.125 I6.5 J9.0
circular interpolation, CCW motion
target coordinates

(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3
p4
p5
7. Cut from p4 to p5
N070 G01 X9.302
target coordinates (Y is unchanged)

(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3
p4
p5
8. Cut from p5 to p1
N080 G01 X3.875 Y3.698
target coordinates (see step 3)

(4, 4)
(2, 2)
5”
p0
p1
p2
5”
2.5”
1”
45°
p3
p4
p5
9. Return to home position, stop program
N090 G01 X2.0 Y2.0 M30
end of data
target coordinates (see step 3)
N100 M00
program stop

CNC Programming Basics
 CNC instructions are called part program commands.
 When running, a part program is interpreted one
command line at a time until all lines are completed.
 Commands, which are also referred to as blocks, are made
up of words which each begin with a letter address and end
with a numerical value.

CNC Programming Basics
 Each letter address relates to a specific machine function.
“G” and “M” letter addresses are two of the most common.
A “G” letter specifies certain machine preparations such as
inch or metric modes, or absolutes versus incremental
modes.
 A “M” letter specifies miscellaneous machine functions and
work like on/off switches for coolant flow, tool changing, or
spindle rotation. Other letter addresses are used to direct a
wide variety of other machine commands.

CNC programming
Important things to know:
• Coordinate System
• Units, incremental or absolute positioning
• Coordinates: X,Y,Z, RX,RY,RZ
• Feed rate and spindle speed
• Coolant Control: On/Off, Flood, Mist
• Tool Control: Tool and tool parameters

 Programming consists of a series of instructions in form of letter codes
 Preparatory Codes:
 G codes- Initial machining setup and establishing operating conditions
 N codes- specify program line number to executed by the MCU
 Axis Codes: X,Y,Z - Used to specify motion of the slide along X, Y, Z
direction
 Feed and Speed Codes: F and S- Specify feed and spindle speed
 Tool codes: T – specify tool number
 Miscellaneous codes – M codes For coolant control and other activities
CNC programming

Programming Key Letters
 O - Program number (Used for program identification)
 N - Sequence number (Used for line identification)
 G - Preparatory function
 X - X axis designation
 Y - Y axis designation
 Z - Z axis designation
 R - Radius designation
 F – Feed rate designation
 S - Spindle speed designation
 H - Tool length offset designation
 D - Tool radius offset designation
 T - Tool Designation
 M - Miscellaneous function

Explanation of commonly
used G codes
• G00 – Preparatory code to control final position of the tool and
not concerned with the path that is followed in arriving at the
final destination.
• G01 – Tool is required to move in a straight line connecting
current position and final position. Used for tool movement
without any machining- point to point control. (linear
interpolation)
• G02 – Tool path followed is along an arc specified by I, J and
K codes.( circular interpolation)

Table of Important G codes
G00 Rapid Transverse
G01 Linear Interpolation
G02 Circular Interpolation, CW
G03 Circular Interpolation, CCW
G17 XY Plane,G18 XZ Plane,G19 YZ Plane
G20/G70 Inch units
G21/G71 Metric Units
G40 Cutter compensation cancel
G41 Cutter compensation left
G42 Cutter compensation right
G43 Tool length compensation (plus)
G43 Tool length compensation (plus)
G44 Tool length compensation (minus)
G49 Tool length compensation cancel
G80 Cancel canned cycles
G81 Drilling cycle
G82 Counter boring cycle
G83 Deep hole drilling cycle
G90 Absolute positioning
G91 Incremental positioning

Table of Important M codes
 M00 Program stop
 M01 Optional program stop
 M02 Program end
 M03 Spindle on clockwise
 M04 Spindle on counterclockwise
 M05 Spindle stop
 M06 Tool change
 M08 Coolant on
 M09 Coolant off
 M10 Clamps on
 M11 Clamps off
 M30 Program stop, reset to start

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