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 |  موضوع: محاضرة بعنوان Introduction of Machining, Geometry of Tool and Nomenclatu السبت 03 سبتمبر 2022, 2:08 am | |
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محاضرة بعنوان
Introduction of Machining, Geometry of Tool and Nomenclature
Subject: Manufacturing Science & Technology-II
Department of Mechanical Engineering
(RME-503)
Faculty: Mr. Brijesh Kumar
Unit-1 /Lecture No: 1
Manufacturing
و المحتوى كما يلي :
Manufacturing is the application of physical and chemical processes to change the geometry, properties and appearance of a given raw material to make parts or products based on customer's specifications and expectations. Manufacturing commonly employs a man-machine setup with division of labor in a large scale production.
Classification of Manufacturing Processes
Classification of “material removal” processesMachining
• Machining is the process of removing excess material from a work surface in the
form of chips. The removal of the material occurs by the shearing action of the
cutting tool. The shear stress is developed due to relative motion between tool
and work piece. This shear stress causes the plastic deformation of the material in
the form of chips.
• Objective of Machining: Parts are manufactured either by casting, forming or
powder metallurgy process. These parts require further operations before the
product is ready for use. So machining of materials is basically adopted to get –
1: Excellent dimensional accuracy
2: Excellent geometrical accuracy
3: Excellent surface finish
4: Complex geometrical features like Sharp corners, grooves, fillets etc.
Machining System
• A machining system consists of following components:
1: Machine tool 2: Cutting tool
3: Workpiece 4. Work holding devices• Machine Tool: A machine tool is one which is used for machining purpose and
operated by external energy. Machine tool holds the cutting tool as well as
workpiece and provides necessary relative motion between the cutting tool and
work piece. Ex: Lathe machine, drilling machine, milling machine etc.
• Cutting Tool: The body which removes the excess material through a direct
mechanical contact is called cutting tool. Ex: Single point cutting tool, drill bit,
milling cutter etc.
• Workpiece: It is the metallic or non-metallic parts needs to be machine.
• Work holding devices: Work holding devices are used to hold the workpiece
and guide it against the cutting tool.
Manufacturing Process Selection
Two stage decision process
1. Feasibility Criteria:
Can the shape be produced by the process?
Can the material be shaped by the process?
2. Process performance criteria:
Cycle time
Material utilization,
Process flexibility,
Operating costs
Surface finishMachining Conditions
1. Cutting parameters
Cutting velocity
Depth of cut
Feed rate
2. Cutting environment
Cutting Fluid
Cutting temperature
Presence of air (oxygen )
3. Work and tool holding devices
Jigs
Fixtures
Cutting tool
• Both material and geometry of the cutting tools play very important roles on
their performances in achieving effectiveness, efficiency and overall economy of
machining.
• The word tool geometry is basically referred to some specific angles or slope of
the salient faces and edges of the tools at their cutting point.
• Rake angle and clearance angle are the most significant for all the cutting tools.Rake Angle:
It is the angle between rake face of the tool and a plane perpendicular to the
machining direction. Rake angle is provided for ease of chip flow and overall
machining.
Higher the rake angle, less are the cutting forces
Increasing the rake angle reduces the strength of the tool tip.
There is maximum limit to the rake angle and this is generally 20º for HSS
tools cutting mild steel.
• It is possible to have rake angles “positive, zero or negative”. Relative
advantages of such rake angles are:
Positive rake – helps to reduce cutting force and thus cutting power
requirement.
Negative rake – helps to increase edge-strength and life of the tool.
Zero rake – to simplify design and manufacture of the form tools.
• Zero or negative rake angles are generally used in the case of highly brittle tool
materials such as carbides or diamonds for giving extra strength to the tool tip.
Example:
HSS: +5° < rake angle< +20°
Carbides: -5° < rake angle < +10°
Ceramics: -5° < rake angle < -15°Clearance Angle:
• It is the angle between the machined surface and the flank face of the tool. The
clearance angle is provided such that tool will not rub the machined surface thus
spoiling the surface and increasing the cutting force.
• A very large clearance angle reduces the strength of the tool tip, and hence
normally an angle of the order of 5 - 6º is used. It is always positive.
Geometry of single point turning tool• The single point cutting tool have 6 different angles. These are:
1. Back rake angle: The back rake angle is the angle between the face of the
tool and a line parallel with base of the tool measured in a perpendicular
plane through the side cutting edge. Back rake angle helps in removing the
chips away from the workpiece.
2. Side rake angle: Side rake angle is the angle by which the face of tool is
inclined side ways. It is the angle between the surface of the flank
immediately below the point and the line down from the point to the base. It
is provided on tool to provide clearance between workpiece and tool so as to
prevent the rubbing of workpiece with end flank of the tool.
3. End relief angle: It is defined as the angle between the portion of the end
flank immediately below the cutting edge and a line perpendicular to the base
of the tool measured at right angles to the flank. End relief angle allows the
tool to cut without rubbing on the workpiece.
4. Side relief angle: It is the angle between the portion of the side flank
immediately below the side edge and a line perpendicular to the base of the tool
measured at right angles to the side. It provides relief between flank face and the
work surface.
5. End cutting edge angle: It is the angle between the end cutting edge and a
line perpendicular to the shank of the tool. It provides clearance between tool
cutting edge and workpiece.
6. Side cutting edge angle: It is the angle between straight cutting edge on the
side of tool and the side of the shank. It is responsible for turning the chip away
from the machined surface.Thank
You
Department of Mechanical Engineering
Subject: Manufacturing Science & Technology-II
(RME-503)
Faculty: Mr. Brijesh Kumar
Unit-1 /Lecture No: 2
(Orthogonal vs. Oblique cutting)Mode of Machining
• Based on the orientation of cutting edge with respect to the direction of cutting
velocity, there are two methods of metal cutting.
1. Orthogonal Cutting 2. Oblique Cutting
Orthogonal Cutting: When the cutting edge of the tool is perpendicular to
the direction of cutting velocity, the process is called orthogonal cutting.
The chip generated flows on the rake face of the tool and the chip velocity
is perpendicular to the cutting edge.
The cutting forces act along X and Z directions only.Oblique Cutting: When the cutting edge of the tool is inclined at an Angle “i”
with the normal to the direction of cutting velocity, the process is called oblique
cutting.
• The chip generated flows on the rake face at an angle approximately equal to “i”
with normal to the cutting edge. The cutting forces acts along all the three X, Y
and Z directions.
• In actual machining, Turning, Milling, Drilling etc/ cutting operations are
oblique cutting
Difference between orthogonal and oblique cutting
Orthogonal cutting
• The cutting angle of tool make right
angle to the direction of motion.
• The chip flow in the direction
normal to the cutting edge.
• In orthogonal cutting only two
components of force considered
cutting force and thrust force which
can be represent by 2D coordinate
system, so it is known as 2D cutting.
Oblique cutting
• The cutting angle of tool not make
right angle to the direction of
motion.
• The chips make an angle with the
normal to the cutting edge.
• In oblique cutting three component
of force are considered, cutting
force, thrust force and radial force
which is represented by 3D
coordinate system, so it is known as
3D cutting.Difference between orthogonal and oblique cutting
Orthogonal cutting
• The chips flow over the tool.
• The shear force act per unit area is
high which increase the heat
developed per unit area.
• This tool has lesser cutting life
compare to oblique cutting.
Oblique cutting
• The chips flow along the sideways.
• The shear force per unit area is low,
which decreases heat develop per
unit area hence increases tool life.
• This tool has higher cutting life.
THANK
YOUDepartment of Mechanical Engineering
Subject: Manufacturing Science & Technology-II
(RME-503)
Faculty: Mr. Brijesh Kumar
Unit-I /Lecture No: 3
(Mechanics of chip formation, types of chips)
Mechanics of chip formation
• Machining is a process of gradual removal of excess material from the work
surface in the form of chips. Knowledge of basic mechanism of chip
formation helps to understand the characteristics of chips and to attain
favorable chip forms.
• Two mechanics of chip formation are:
1. Mechanics of chip formation in ductile materials
2. Mechanics of chip formation in brittle materials1. Mechanics of chip formation in ductile materials
• During continuous machining the uncut layer of the work material just ahead of
the cutting edge is subjected to compression. Due to such compression, shear
stress develops, within that compressed region, and rapidly increases in
magnitude. Whenever the value of the shear stress exceeds the shear strength of
that work material in the deformation region, yielding takes place resulting
shear deformation in that region along the plane of maximum shear stress. Then
the deformed metal (called chip) flows along the tool rake face.
• The region of maximum shear stress is called primary shear zone. If the friction
between the tool rake face and the underside of the chip is considerable, the
chip gets further deformed, which is termed as secondary shear zone.
In ductile material, the chips are initially compressed ahead of the tool tip, the final
deformation is accomplished mostly by shear in machining ductile materials.Primary and secondary deformation zone: The pattern and extent of total
deformation of the chips due to the primary and the secondary shear deformations of
the chips ahead and along the tool face is shown in fig.
Machining of ductile materials generally produces flat, curved or coiled continuous
chips.
2. Mechanics of chip formation in brittle materials
• During machining, first a small crack develops at the tool tip as shown
in fig. due to wedging action of the cutting edge. At the sharp crack-tip
stress concentration takes place. In case of ductile materials
immediately yielding takes place at the crack-tip and reduces the effect
of stress concentration and prevents its propagation as crack. But in
case of brittle materials the initiated crack quickly propagates, under
stressing action, and total separation takes place from the parent
workpiece through the minimum resistance path as indicated in fig.
• Machining of brittle material produces discontinuous chips and mostly
of irregular size and shape.Mechanics of chip formation in brittle materials……..
• During machining of brittle materials, chip formation occurs due to brittle
fracture of the work material.
Types of Chip
• Depending on the properties of work material and cutting conditions, three
basics types of chips are produced by the machining process. These are:
1. Continuous chips
2. Continuous chips with Built-Up Edge
3. Discontinuous chipsContinuous Chip:
• Continuous chips are normally produced when machining ductile metals at high
cutting speeds. Continuous chip which is like a ribbon flows along the rake face
of the tool. Production of continuous chips is possible because of the ductility of
the metal. Thus on a continuous chip you do not see any notches.
• Some ideal conditions which promote the formation of continuous chips are:
1. Ductile work material
2. Small uncut thickness
3. High cutting speed
4. Large rake angle
5. Sharpe cutting edge
6. Less friction
Continuous Chip with BUE:
• In the cutting zone, when friction is high while machining ductile materials,
some particles of the chip get welded to the tool rake face near the tool tip.
• Such sizeable particles piles upon the rake face and forms the built-up edge.
• The BUE grows up to a certain size but finally breaks due to the increased
forced exerted on it by the adjacent flowing material. After it breaks, the broken
fragments adhere to the finished surface and the chip surface, results in a rough
finish.• Some ideal conditions which promote the formation of continuous chip with
BUE chips are:
1. Ductile work material
2. Large uncut thickness
3. Low cutting speed
4. Small rake angle
5. High friction between chip-tool interface
Discontinuous chips
• When brittle materials like cast iron are cut, the deformed material gets fractured
very easily and thus the chip produced in the form of discontinuous segments. In
this type the deformed material instead of flowing continuously gets ruptured
periodically.
• Conditions which promote the formation of discontinuous chips are:
1. Brittle work material
2. Low cutting speed
3. Small rake angle
4. Large uncut thicknessTHANK
YOU
Department of Mechanical Engineering
Subject: Manufacturing Science & Technology-II (RME-503)
Faculty: Mr. Brijesh Kumar
Unit-I / Lecture No: 4
(Shear angle relationship)Shear Angle (φ)
• It is the angle made by the shear plane with the direction of cutting
speed. Higher the shear angle better is the cutting performance.
Importance of shear angle:
• If all other factors remain the same, a higher shear angle results in
a smaller shear plane area. Since the shear strength is applied across this area,
the shear force required to form the chip will decrease when the shear plane
area is decreased. This tends to make machining easier to perform, and
also lower cutting energy and cutting temperature.
Determination of Shear angle• Chip thickness ratio (r ) also known as cutting ratio.
• Chip thickness ratio is always less than 1. this is because, chip
thickens and due to volume constancy shortens.
• 1/r is known as chip compression ratio.THANK
YOU
Department of Mechanical Engineering
Subject: Manufacturing Science & Technology-II
(RME-503)
Faculty: Mr. Brijesh Kumar
Unit-I / Lecture No: 5
(Merchant’s force circle diagram)Orthogonal machining
Forces in orthogonal metal cutting
• Forces in the secondary deformation zone:
1- Friction force along the rake face, Fr
2- Force perpendicular to rake face, Nr
• Forces in the Primary deformation zone:
1- Force along the shear plane, Fs (shear force)
2- Force normal to the shear plane, Ns
• Forces on the cutting tool:
1- Cutting force, Fc
2- Thrust force, Ft1. Forces on the cutting tool
2-Forces in the secondary deformation zone:3-Forces in the Primary deformation zone:
The resulting diagram Merchant,s force circle diagramForce analysis
1- Friction force along the rake face
F = F
c sin α + Ft cosα
2- Force perpendicular to rake face
F
c cosα - Ft sinα
3-Force along the shear plane (shear force)
F
c cosφ - Ft sin φ
4- Force perpendicular to the shear plane
F
c sin φ + Ft cosφ
Shear strain in chip formationShear strain rate
Shear strain rate (γ ) is given by:
• where Δt is the time required for the metal to travel the distance Δs along the
shear plane.
• Δy is the distance between two successive shear planes.
• A reasonable value of spacing between successive planes (Δy) would be
around 25×10-4 mm.Velocity analysis in orthogonal machining
THANK
YOUDepartment of Mechanical Engineering
Subject: Manufacturing Science & Technology-II
(RME-503)
Faculty: Mr. Brijesh Kumar
Unit-I / Lecture No: 7
(Cutting forces, power required in metal cutting)
Force analysis
From Merchant,s force circle diagramCoefficient of friction between chip-tool interface
• The coefficient of friction between two sliding surfaces is defined as
• Here, it is implied that the forces F and N are uniformly distributed over the
entire chip-tool contact area.
Shear angle relationship based on Merchant’s theoryWhat the Merchant’s relation tells us?
To increase shear plane angle
Increase the rake angle
Reduce the friction angle (or coefficient of friction)Cutting energy or power requirement
• The cutting energy required for machining depends on the cutting force and
cutting velocity. It can be express as:
Cutting energy = Cutting force × Cutting velocity
Parameters which affects the cutting force & power requirement
The variables that have significant effect on tool life are:
1- Cutting conditions
> Speed
> Feed
> Depth of cut
2- Tool geometry
> Rake angle
> Clearance angle
> Nose radius
3- Work material
4- Cutting fluid
5- Built-Up-EdgeTHANK
YOU
Department of Mechanical Engineering
Subject: Manufacturing Science & Technology-II
(RME-503)
Faculty: Mr. Brijesh Kumar
Unit-I / Lecture No: 7
(Thermal aspects of machining)Thermal Aspect of Machining Process
The machining operation is basically a deformation process of the work material
through the application of force by the cutting tool. In all the machining
processes where plastic deformation is involved, the mechanical energy
dissipated in cutting is converted into heat which in turn, raises the temperature
in the cutting zone. During machining almost 99% of the energy is converted in
to heat.
Sources of Heat Generation in Machining: The heat generation
occurs in three distinct regions:
1- Primary shear zone
2- Secondary shear zone (at chip-tool interface)
3- Tool-work interface
• Primary shear zone: In primary shear zone heat is generated due to plastic
deformation of the work material. About 80 – 85% heat is generated in this
zone.
• Secondary shear zone: In this zone, heat is generated due to frictional rubbing
between the rake face of the tool and chip. Some plastic deformation also
occurs in this zone. About 15 – 20% heat is generated in this zone.
• Tool – Work Interface: At the tool-work interface, heat is generated due to
frictional rubbing between flank face of the tool and machined work piece
surface.
• In this region only 1 – 3% heat is generated.Heat Flow in Metal Cutting
The heat generated is shared by the chip, cutting tool and the workpiece. The
percentage of sharing that heat depends upon the configuration, size and
thermal conductivity of the tool – work material and the cutting condition.
About 80 – 85 % of the total heat generated during machining is carried
away by the chip.
About 15 – 20% of the total heat is flows in to the tool.
Less than 5% heat is conducted in to the work piece.Temperature distribution in metal cutting process
• Figure shows temperature distribution during orthogonal cutting. The workpiece
material is free cutting mild steel where the cutting speed is 0.38 m/s, the depth
of cut is 6.35 mm.Temperature distribution in metal cutting process
• From figure it is clear that the maximum temperature in the cutting process
occurs not at the tool tip but at some distance away from the cutting edge.
• Point X. The material at point x gets heated as it passes through the shear zone
and finally leaves as chip.
• Point Y. Material at point y first heated in shear zone but heating is continued
until they cross the frictional heat zone. This point losses some shear zone heat
while moving up but gains more frictional heat.
• Point Z. Point such as z remains in the workpiece and are heated due to
conduction of heat into the workpiece as they pass below the cutting edge.
• The above factors cause maximum tool temperature to occur at some
distance away from the cutting edge.
Effect of the High Cutting Temperature on Tool and Job
The high temperature in machining zone is harmful for both the tool and the
job. The major portion of the heat is taken away by the chips. But it does not
matter because chips are thrown out. So attempts should be made such that the
chips take away more and more amount of heat leaving small amount of heat to
harm the tool and the job.
Effect of cutting temperature on the tool:
1- Rapid tool wear, which reduces tool life.
2- Plastic deformation of the cutting edges if the tool material is not enough
hot-hard .
3- Chipping of the cutting edges due to thermal stresses.
4- Built-up edge formation.Effect of cutting temperature on the machined job:
1. Dimensional inaccuracy of the job due to thermal distortion and
expansion-contraction during and after machining.
2. Surface damage by oxidation, rapid corrosion, burning etc.
3. Excessive temperature rise can induce metallurgical changes in the
machined surface, adversely affecting its properties
4. Induction of tensile residual stresses and micro-cracks at the surface /
subsurface.
Factors Affecting the heat generation in Cutting Zone
The following factors influence the cutting temperature:
1- Machining parameters
> Speed
> Feed rate
> Depth of cut
2- Properties of workpiece material
> Hardness
> Strength
3- Tool geometry
> Rake angle
> Clearance angle
> Nose radius
4- Cutting fluids
5- Built-up-edgeTHANK
YOU
Department of Mechanical Engineering
Subject: Manufacturing Science & Technology-II
(RME-503)
Faculty: Mr. Brijesh Kumar
Unit-I / Lecture No: 8
(Cutting fluid)Cutting Fluids
• Need: During machining process, friction between work-tool and chip-tool
interfaces causes high heat generation which results high temperature in
machining zone. The effect of this generated heat decreases tool life,
increases surface roughness and decreases the dimensional accuracy of work
material. This case is more important when machining of difficult-to-cut
materials, when more heat would be observed. Due to this reason, most
machining operation is carried out in the presence of a cutting fluid.
Functions of a cutting fluid
1- Lubrication: Lubrication at the chip–tool and tool-work interface to reduce
friction force and thus the amount of heat generation.
Lubrication of cutting zone is very important at low cutting speeds.
2- Cooling: Cooling of the job and the tool to reduce the detrimental effects of
cutting temperature on the job and the tool.
The cooling of the workpiece is very important at high cutting speeds.
3- Cleaning: Cleaning the machining zone by washing away the chip – particles and
debris which, if present, spoils the finished surface and accelerates damage of the
cutting edges.
4- Corrosion Protection. A thin layer of the cutting fluid sticks to the machined
surface and thus prevents it from harmful atmospheric gases like SO2, O2, NxOy
present in the atmosphere.Principles of cutting fluid action
The chip-tool contact zone is usually comprised of two parts; plastic or bulk
contact zone and elastic contact zone as indicated in Fig.
Principles of cutting fluid action.....................
• The cutting fluid cannot penetrate or reach the plastic contact zone but
enters in the elastic contact zone by capillary effect. With the increase in
cutting velocity, the fraction of plastic contact zone gradually increases and
covers almost the entire chip-tool contact zone. Therefore, at high speed
machining, the cutting fluid becomes unable to lubricate and cools the tool
and the job only by bulk external cooling.
• The chemicals like chloride, phosphate or sulphide present in the cutting
fluid chemically reacts with the work material at the chip under surface
under high pressure and temperature and forms a thin layer of the reaction
product. The low shear strength of that reaction layer helps in reducing
friction.Essential properties of cutting fluids:
• It should have high thermal conductivity and specific heat.
• Have low viscosity and molecular size (to help rapid penetration into the chiptool interface).
• Should have good spreading and wetting ability.
• Friction reduction at extreme pressure and temperature.
• Chemical stability, non-corrosive to the tool and work materials.
• Odourless and also colourless.
• Non toxic in both liquid and gaseous stage.
• Easily available and low cost.
Types of Cutting Fluid:
Generally, cutting fluids are employed in liquid form but occasionally also
employed in gaseous form. Only for lubricating purpose, often solid lubricants
are also employed in machining and grinding. The cutting fluids, which are
commonly used, are:
1. Compressed air
2. Water
3. Straight oils (or neat oils)
4. Water Soluble oils ( or soluble oils)
5. Synthetic oils (chemical fluid)
6. Solid or semi-solid lubricant• Compressed Air: Machining of some materials like grey cast iron become
inconvenient or difficult if any cutting fluid is employed in liquid form. In such
case only compressed air is recommended for cooling and cleaning purpose.
• Water: For its good wetting and spreading properties and very high specific
heat, water is considered as the best coolant and hence employed where cooling
is most urgent.
• Straight Oils: These fluid composed of a base petroleum oil or vegetable oils
with extreme pressure additives of chlorine, sulphur and phosphorus. Straight
oils provide the best lubrication and the poorest cooling characteristics among
all the cutting fluids.
These fluids are used where cutting speed is very low, feed and depth of cut
is high.
• Water Soluble Oils: (water + mineral oil + emulsifier agent + rust inhibitor
agent and EPA). These oils are used in diluted form and provide good
lubrication as well as cooling performance. Soluble oils are widely used in
industry.
Water....................Provides cooling
Mineral oils...........Provides lubricity
Emulsifier..............Breaks oil into small globules
Rust inhibitor....... Since water can cause rusting
• Synthetic Oils: Synthetic Fluids contain no petroleum or mineral oils. These
oils are formulated from alkaline inorganic and organic compounds along with
EPA additives for corrosion inhibition. Synthetic fluids provide the best cooling
performance among all cutting fluids but limited lubricity.
• Solid or semi-solid lubricant: Paste, waxes, soaps, graphite, Moly-disulphide
(MoS2) may also often be used as cutting fluids.Cutting Fluid Application Methods
The effectiveness and expense of cutting fluid application significantly depend
also on how it is applied in respect of flow rate and direction of application. In
machining, depending upon the requirement and facilities available, cutting
fluids are generally employed in the following ways.
• Flood Application: In this method tool and workpiece are supplied with high
volume of the cutting fluids which are generally in liquid condition.
• Jet Application: In this method the cutting fluids which may be either gas or
liquid are applied with high pressure on the tool and workpiece.
• Mist (atomised) Application: In this method cutting fluid is atomised by a jet of
air and the mist is directed at the cutting zone. This method gives maximum
cooling effect.THANK
YOU
Department of Mechanical Engineering
Subject: Manufacturing Science & Technology-II (RME-503)
Faculty: Mr. Brijesh Kumar
Unit-I / Lecture No: 9
(Cutting tool materials)Cutting Tool Materials
• Since machining is accomplished by the deformation of work material and so
cutting tool is subjected to :
High temperatures
High contact stresses
Rubbing along the chip-tool and tool-work interface.
• Under these condition, the stability of geometric form (or shape) of the tool is
key factor. Thus, the cutting tool must provide the maximum resistance to any
tendency of alteration of its geometric form. To achieve this, the cutting tool
material must be properly selected.
Desirable properties of cutting tool material
The cutting tool materials must possess a number of important properties to
avoid excessive wear, fracture failure and high temperatures in cutting. The
following characteristics are essential for cutting materials to withstand the
heavy conditions of the cutting process and to produce high quality and
economical parts:
1- High Hardness
2- Hot hardness (or Red hardness )
3- Toughness
4- Wear resistance
5- Low friction
6- High thermal conductivity and specific heat
7- Chemical stabilityHigh Hardness: A cutting tool material must have higher hardness than that of
the workpiece material being machined, so that it can penetrate into the work
material.
Hot hardness: It is defined as ability to retain hardness at elevated (high)
temperatures in view of the high temperatures existing in the cutting zone. Thus,
the tool retains its shape and sharpness. This requirement becomes more and more
important when machining under high cutting speeds to increase the production
rate.
Diamond is having the highest hot hardness. Ceramics also maintain their
hardness at high temperatures. While carbon tool steels rapidly begin to lose their
hardness at moderate temperatures (cannot be used at high speeds Æ high
temperatures).
Toughness: Toughness is a resistance to shock or impact forces. Higher the
toughness, more shock load material can withstand. It is desired so that impact
forces on the tool encountered repeatedly in interrupted cutting operations (such
milling) do not chip or fracture the tool.
Wear resistance: It is the ability of material to resist wear. Wear resistance
depends on hardness as well as undissolved carbides. It is desired so that an
acceptable tool life is obtained before the tool has to be replaced.
Low friction: The coefficient of friction between the tool and work should be
low. This will lead to improve the surface finish, reduction in frictional heat
generation and absorbs less cutting energy.
High thermal conductivity and specific heat: These properties ensure
rapid dissipation of heat generated during cutting process, thus avoid softening
of the cutting tool material and improves its life.Chemical stability: A cutting tool material should be chemically stable with
respect to the work material and cutting fluid, so that any adverse reaction
contributing tool wear are avoided.
Types of Cutting Tool Material
• The demand for higher productivity has led to the development of a variety of
cutting tool materials with vastly improved properties. Each stage of
development has facilitated the use of higher cutting speeds. No one cutting
material is best for all purposes. No tool material has been able to fully replace
the older one since each one of them has a unique combination of properties.
The following cutting tools materials are still in use are:
1- High carbon steel
2- High speed steel
3- Cemented Carbides
4- Ceramics
5- Cubic boron nitride (CBN)
6- DiamondHigh Carbon Steel
• This is the oldest material used for making cutting tools is much less used
today. It contains 0.8 – 1.2% carbon and some very small alloy additions such
as manganese, tungsten, molybdenum, chromium and vanadium.
• These steel have very good hardenability and wear resistance at low
temperature. The major disadvantage of these cutting tool materials is their
inability to withstand high temperature.
• Beyond 200ºC they lose their hardness and become soft. Therefore, they are
useful only for very low cutting speeds (about 0.15 m/s). Due to this, high
carbon steel mainly used with low temperature generating operations or
machining of the soft materials such as wood, magnesium, brass and
aluminium etc.
High Speed Steel
• These steel are called high speed steel because they can cut metal at three to
five times higher speeds than that can be done by the high carbon steel. They
can retain their hardness up to about 650ºC.
• These are carbon steel with major alloying elements such as tungsten,
molybdenum, chromium, vanadium and cobalt.
• Toughness of HSS is highest among all the cutting tool materials. Thus they are
extensively used in interrupted cutting such as milling. HSS also used for
making drill, reamer, milling cutter, single point cutting tool etc.Cemented Carbides
• Three group of cutting tool materials just described (high carbon steel, HSS and
cast-cobalt alloys) possess the necessary toughness, impact strength and thermal
shock resistance. But, still these materials are limited in their hot hardness, wear
resistance and strength. Consequently, they cannot be used very effectively
where high cutting speeds (and therefore high temperature) are required. To meet
the challenge of higher speeds for higher production rates, cemented carbides
were developed around 1930 in Germany.
• Cemented carbide tool consists of carbide particles (carbides of tungsten and
titanium) bound together in a cobalt matrix by powder metallurgy process.
• The two groups used for machining are :
1- Tungsten carbide
2- Titanium carbide
Ceramics
• Ceramics are inorganic compounds, and usually made either of oxides, carbides, or
nitrides. The following ceramic materials used as cutting tool material:
1- Aluminium Oxides (Al2O3) or alumina
2- Silicon Carbides (SiC)
3- Silicon Nitrides (Si3N4)
4- Titanium Carbide
5-Titanium Oxides
Properties:
• Ceramic cutting tools are harder and more heat-resistant than carbides tools, but more
brittle.
• They can withstand very high temperatures, due to which the cutting edge retains its
hardness almost up to 1200ºC.
• They have higher wear resistance than other cutting tool materials.
• They are chemically more stable than carbides.• Cubic boron nitride (CBN): Cubic boron nitride is the second hardest material
available for machining purpose. It is not a natural material, it is produced in
laboratory.
• CBN mainly used as coating material. But cubic boron nitride tools are also
made in small sizes without a carbide insert.
• Diamond: Diamond is the hardest known material that can be used as cutting
tool material. Diamond tools are available as insert. Diamonds are suitable for
cutting very hard materials like glass, ceramics and other abrasive materials.
Use is limited because it gets converted into graphite at high temperature (700
°C). Graphite diffuses into iron and makes it unsuitable for machining steels.
• The curve shows that:
> High speed steel is much better than carbon tool steel (high carbon
steel).
> Cemented carbides and ceramics are significantly harder at elevated
temperatures.THANK
YOU
Department of Mechanical Engineering
Subject: Manufacturing Science & Technology-II
(RME-503)
Faculty: Mr. Brijesh Kumar
Unit-I / Lecture No: 10
(Tool life)Tool Life
• During machining, the cutting edge of the tool gradually wears out and it does not perform
satisfactorily. When the wear reaches a certain stage, it is said that the tool has lost its
utility and its life is over. It must be reground or replace by a new tool if machining is to
be continued.
> The time interval during which a cutting tool performs given function
satisfactorily is called tool life.
> Flank wear generally considered as the decisive factor to measure the tool life.
> However, at higher cutting speed, crater wear also used as tool failure criterion.
• Measuring tool life: There are various ways in which tool life can be specified.
> Actual cutting time to failure.
> Length of work cut to failure.
> Volume of metal removed to failure.
> Number of components produced to failure.
Taylor's equation of tool life
• Wear and hence tool life of any tool for any work material is governed mainly
by the level of the machining parameters i.e., cutting velocity, feed, and depth
of cut . Cutting velocity affects maximum and depth of cut minimum.
• Taylor gave the relation between cutting speed and tool life. That is:
Where
V= cutting speed(m/min)
T=tool life(in minutes)
C=machining constant
n= Tool life exponent(it depends on tool material)Parameters Affecting Tool Life
1-Cutting conditions
> Speed
> Feed
> Depth of cut
2- Tool geometry
> Rake angle
> Clearance angle
> Nose radius
3- Tool material
Hardness
Wear resistance
Thermal conductivity
4- Work material
5- Cutting fluid
6- Built-Up-Edge
Effect of cutting conditions on tool life
1- Speed: The tool life decreases with the increase in cutting speed. This is
because; temperature in the cutting zone increases with increase in cutting
speed, which makes the tool soft. Higher cutting temperature also increases the
rate of abrasive, adhesive, and diffusion wear.
2- Feed: Tool life decreases with increase in feed rate. This is because cutting
force increases with the increase in feed rate. Due to increase in cutting force,
temperature in cutting zone increases and finally tool life decreases.
3- Depth of Cut: Tool life decreases with increases in depth of cut. This is
because, as the depth of cut increases, the chip-tool contact area and cutting
force increases which rises the temperature due to increasing frictional heat.Tool Life Criteria
The following are some of the possible tool life criteria that could be used for
limiting tool life.
Direct Criteria (based on tool wear).
• Wear land size
• Crater depth and width.
• Total destruction of the tool
Indirect Criteria (based on effects of a worn tool).
• Limiting value of surface finish.
• Limiting value of change in component dimensions.
• Limiting value of increase in cutting force.
Wear land size: Wear land size on the flank face of the tool is widely used
criteria to assess tool life. When the wear land reaches a critical value, cutting
becomes difficult and tool leaves rough marks on the machined surface. Under
this condition it is said that life of the tool is over.
The length of wear land is not of uniform. It is larger near the two ends of the
active portion of the side cutting edge. The maximum width of the wear land is
at the rear end of the flank face. The tool life values as suggested by ISO are:
VB = 0.3 mm, if the flank is regularly worn in zone B
VB
max = 0.6mm, if the flank is irregularly worn in zone BCrater depth and width: At high speeds and feeds crater wear is
more, therefore, it is also used as tool life criteria. Since, larger the depth of
crater, weaker is the tool. According to ISO recommendation, the maximum
allowable crater depth can be given as:
KT = 0.06 + 0.3f (f = feed in mm/rev)
Total destruction of the tool: Tool destruction occurs when the tool is unable
to support the cutting force over the tool-chip contact area and results in fracture
of small part of cutting edge. It is Common in interrupted cuts and in non rigid
setups.
Limiting value of surface finish: According to this criterion, the surface is
continuously monitored and RMS values of surface roughness are compared with
the limiting value. Whenever, the measured value of the surface roughness
exceeds the limiting value, the tool is said to have failed and must be reground.
Limiting value of change in component dimensions: In this method, the
dimensions of the each component are measured. When the dimensional accuracy
falls below a limiting value, the tool is said to have failed.
Limiting value of increase in cutting force: The change in cutting force is
measured with the help of a tool dynamometer or power meter. If the cutting force
increases beyond a limiting value, the tool is said to have failed.THANK
YOU
Department of Mechanical Engineering
Subject: Manufacturing Science & Technology-II
(RME-503)
Faculty: Mr. Brijesh Kumar
Unit-I / Lecture No: 11
(Tool wear)Failure of Cutting Tools
• The success of machining process depends on the sharpness of the tool. The use of a
blunt tool results in a large power consumption and poor surface finish.
• When a cutting tool unable to cut, consuming large power, and cannot produce an
acceptable surface finish, it is considered to have failed. The failure of a cutting tool
may be due to one or a combination of the following modes:
1- Plastic deformation of the tool.
> Plastic deformation of the tool occurs due to high temperature and
stresses.
2- Mechanical breakage of the tool.
> Mechanical breakage of the tool occurs due to large forces and shocks.
The other factors are insufficient strength and toughness of the tool material.
3- Progressive or gradual wear failure.
>The progressive wear makes the tool blunt. It occurs due to relative sliding
between two surfaces.
• The plastic deformation and mechanical failure can be prevented by
proper selection of cutting tool material, tool geometry and cutting
conditions.
• But failure by gradual wear cannot be prevented but can be slowed
down only to enhance the service life of the tool.Progressive Tool Wear
• The wear is generally defined as loss of material from surfaces. The wearing
action takes place on those surfaces along which there is a relative sliding with
other surfaces. Thus, the wear takes place on the rake face where the chip flows
over the tool. The wear also takes place on the flank face where rubbing between
the work and tool occurs.
Types of progressive tool wear: The progressive wear of a cutting tool takes
place into distinct ways:
1- Crater wear (measured in terms of the “depth of crater”)
2- Flank wear (measured in terms of the “length of the wear land”)
Crater Wear: Crater wear occurs on the rake face of the tool due to relative
sliding between rake face and chip. In orthogonal cutting this typically occurs
where the tool temperature is highest
> Diffusion process is mainly responsible in the development of crater
wear.
• Flank Wear: Flank wear occurs on the flank face of the tool, due to rubbing
between flank face and machined surface. It modified the tool geometry and
changes the cutting parameters (depth of cut).
> The abrasion and adhesion are primarily responsible for the flank wear.
> Flank wear directly affects the surface finish produced. Thus there is
always a close limit kept on the value of the wear land.Progressive tool wear
workpiece
tool
crater wear
flank wear
chip
Tool Wear Mechanisms:
• Under high temperature, high pressure, high sliding velocity and mechanical or
thermal shock in cutting area, cutting tool has normally complex wear
mechanism. A number of wear mechanisms have been proposed to explain the
tool wear phenomenon. These mechanisms are:
1- Abrasion wear
2- Adhesion wear
3- Diffusion wear
4- Oxidation wear
5- Chemical decomposition
6- Chipping (or Thermal fatigue wear)• Abrasion wear: Abrasion wear occurs when hard particle of the chip material
abrading (rubbing) the tool surface. The rate of wear depends on the relative
hardness of the contacting surfaces, as well as mating geometries.
• This is a mechanical wear, and it is the main cause of the tool wear at low
cutting speeds.
• Adhesion wear: Under high pressure and temperature when two surfaces come
in close contact, strong metallic bonds are formed due to welding of the surface
asperities. The spot weld results in an irregular flow of chips over the tool face.
Sliding of chip causes the fracture of these small weld joints and some tool
material carried along with them. Adhesive wear can be reduced by using a
suitable cutting fluid which can provide a protective film on the contacting
surfaces.• Diffusion wear: Diffusion wear means the material loss due to diffusion of
atoms of the tool material into the workpiece moving over it. Requirements
for diffusion wear are metallurgical bonding of the two surfaces so that
atoms can move freely across the interface and high temperature.
• Oxidation wear: Oxidation is the result of a chemical reaction between the
tool surface and oxygen at high temperature. It forms a layer of oxides on the
surface. When this layer is destroyed during the cutting process by abrasion,
another layer begins to form. Tool wear takes as this removal and formation of
the corrosive layer is repeated.
• Chemical decomposition: This type of wear occurs due to interaction
between the tool and work material in the presence of chemicals (cutting fluid).
• Chipping: Chipping means breaking away of a small metal piece from the
cutting edge of the tool. The chipped piece may be very small or may be
relatively large. Unlike gradual wear, chipping results in a sudden loss of tool
material and a corresponding change in shape, and has a major detrimental
effect on surface finish and dimensional accuracy of the workpiece.• The two main cause of chipping are
Mechanical Shock (impact due to interrupted cutting, as in milling)
Thermal Fatigue (cyclic variations in temperature of the tool in interrupted
cutting).
Variables Affecting Tool Wear
The important parameters which affect the tool wear are:
1-Cutting conditions
> Speed
> Feed
> Depth of cut
2- Tool geometry
> Rake angle
> Clearance angle
> Nose radius
3- Tool material
> Hardness
> Wear resistance
> Thermal conductivity
4- Work material
5- Cutting fluid
6- Built-Up-EdgeTHANK
YOU
Department of Mechanical Engineering
Subject: Manufacturing Science & Technology-II
(RME-503)
Faculty: Mr. Brijesh Kumar
Unit-I / Lecture No: 12
(Machinineability)Machineability
• It is already known that pre-formed components are essentially machined to
impart dimensional accuracy and surface finish for desired performance and
longer service life of the product.
• It is attempted to accomplish machining effectively, efficiently and
economically as far as possible by removing the excess material smoothly and
speedily with lower power consumption, tool wear and surface deterioration.
But this may not be always and equally possible for all the work materials and
under all the conditions.
• The machining characteristics of the work materials widely vary and also
largely depend on the conditions of machining. A term; ‘Machinability’ has
been introduced for gradation of work materials w.r.t. machining
characteristics.
Machineability…..
• A term; ‘Machineability’ has been introduced for gradation of work materials
w.r.t. machining characteristics or machining properties .
• It is defined as “ easy to machine”.
• A material is said to have good machineability if;
> The tool wear is low
> The metal removal rate is high (or high cutting speed)
> The surface finish produced is good
> Power consumption is low
> Good dimensional accuracy
> Formation of small chipsCriteria’s for judging Machineability
• For judging the machineability, the criteria to be chosen depends on the type
of operation and production requirements. The following criteria may be
considered for judging the machineability of a metal.
1- Tool life criteria (or tool wear criteria)
2- Surface finish criteria
3- Power consumption criteria
4- Production rate criteria
5- Chip forms
• But practically it is not possible to use all those criteria together for
expressing machineability.
Tool Life Criterion:
• When tool life criterion is used, machinability is expressed in terms of ‘cutting
speed’for given tool life.
• A material with higher cutting speed for a given tool life will have better
machinability.
• In this method, the effect of surface finish is not accounted. This is most widely
used criterion for assessing machinability of a material.
Assessing machinability: For assessing machinability, a common material (free
steel) is chosen as a standard and the machineability of the other materials is
compared and expressed as a machinability index or machinability rating.
Let , Vs = Cutting speed of standard material for a given tool life (T).
V
m = Cutting speed of the test material for same given tool life (T).• Than the machinability Index (MI) can be calculated as:
• Thus, a material with higher cutting speed for a given tool life will have greater
machinability.
• Surface Finish Criterion: This criterion is used in a situation where poor surface
finish is the cause of rejection on machined parts.
A material that produces better surface finish under a given set of conditions
may be considered to have better machinability.
Some materials may permit use of higher cutting speed or lower cutting forces but
give poor surface finish. In such situations, the surface finish criterion is important.
• Power Consumption Criterion: The power consumption during machining is
related to the cutting force. Higher the cutting force, the greater is the power
consumption. The material requiring higher cutting forces will have lower
machinability.
• Production Rate Criterion: The metal removal rate is directly related to the
cutting speed, and hence, production rate. For given surface finish and tool life, if a
material permits high cutting speeds or higher metal removal rate will have higher
machinability.Parameters Affecting Machineability
The important parameters which affect the machineability are:
1-Cutting conditions
> Speed
> Feed
> Depth of cut
2- Tool geometry
> Rake angle
> Clearance angle
> Nose radius
3- Tool material
Hardness
4- Work material (Hardness, Toughness)
5- Cutting fluid
THANK
YOUDepartment of Mechanical Engineering
Subject: Manufacturing Science & Technology-II
(RME-503)
Faculty: Mr. Brijesh Kumar
Unit-I / Lecture No: 13
(Machine tool vibration and surface finish)
Machining tool vibration
• Introduction: Machine tool structures are multi-degree-of-freedom systems
and always subjected to vibration during machining. Vibrations during a
cutting operation affect the accuracy of the machining, which in turn affects
the surface finish and dimensional accuracy. Severe noise is also an
important factor which is induced by tool holder vibrations.
• The cutting process with variable feed is one of the principles cause of
arising of vibrations. That results in the variable dynamic cutting force.
• These vibrations affects the machine tool, quality of work-piece, cutting tool
and the cutting conditions (feed rate, depth of cut, and cutting velocity.Effect of Vibration
The vibration of machine tools during cutting, affects
• Life of machine tool , particularly transmission elements
• Life of the cutting tool
• Quality of the workpiece
• Cutting conditions
Effect of vibrations on life of machine tool: The machine tool is made of
various parts and when vibrations are produced, they also start vibrating at
same frequency. If this frequency approaches the natural frequency of
vibration of that part then amplitude of vibrations will be very excessive
and the part may break even.
• Effect of vibrations on life of the cutting tool: As the tool-life is a function of
the cutting variables only, the tool-life is greatly affected by presence of
vibrations in machine tools. It is found out that the tool life is decreased by
about 70—80% of the normal value if vibrations are present.
• Effects of vibrations on work-piece: Due to presence of vibrations the surface
finish obtained will be very poor and thus this aspect is very important for fine
finishing operations of grinding and boring etc.
• Due to vibrations, the dimensional accuracy and geometrical accuracy of the
job is also affected.• Effect of vibrations on cutting conditions:
> Due to presence of vibrations in machine tools, the chip thickness as
removed by the cutting tool does not remain constant and so the cutting forces
also vary.
> Also due to vibrations, vibratory displacement of tool takes place in the
direction of motion of the job which results in the chatter of tool.
> The penetration rate also varies and therefore penetration force does not
remain constant. Further due to vibration of the tool, cutting velocity does not
remain constant and it varies about the correct value.
Sources of Vibrations
Machine tools operate in different configurations (positions of heavy parts,
weights, dimensions, and positions of work pieces) and at different regimes
(spindle rpm, number of cutting edges, cutting angles, etc.). Due to this machine
tool and cutting tool are always subjected to vibration. These vibrations are due to
one or more of the following causes:
1. In-homogeneities in the workpiece material.
2. Variation of chip cross section area
3. Disturbances in the workpiece or tool drives.
4. Dynamic loads generated by acceleration/deceleration of moving
components.
5. Intermittent cutting.
6. Self-excited vibration .• Vibration Due to in homogeneities in the Work piece: Hard spots or a crust
in the material being machined impart small shocks to the tool and work piece,
as a result of which free vibrations are set up. When machining is done under
conditions resulting in discontinuous chip removals, the segmentation of chip
elements results in a fluctuation of the cutting thrust. If the frequency of these
fluctuations coincides with one of the natural frequencies of the structure,
forced vibration of appreciable amplitude may be excited.
• Vibration Variation of chip cross section area: Variation in the crosssectional area of the removed material may be due to the shape of the machined
surface or to the configuration of the tool. In both cases, pulses of appreciable
magnitude may be imparted to the tool and to the work piece, which may lead
to undesirable vibration.
Disturbances in the workpiece or tool drives: Unbalance and disturbances in
the drives caused due to rotating unbalanced masses, faulty arrangement of
drive and fault in the supporting bearings.
Dynamic loads generated by acceleration/deceleration of moving
components: In dynamically stable system, the amplitude of vibration keeps
on decaying with time whereas in dynamically unstable system, it
exponentially increases with time
Intermittent cutting: Intermittent cutting as in milling. Due to it, forced
vibrations may be generated due to elastic nature of system.
Self-excited vibration: Self-excited vibration or chatter due to the interaction
of cutting process and machine tool dynamicsVibration Control in Machine Tools
• The tolerable level of vibration between tool and workpiece, i.e., the maximum
amplitude and to some extent the frequency, is determined by the required
surface finish and machining accuracy as well as by detrimental effects of the
vibration on tool life and by the noise which is frequently generated.
The vibration behavior of a machine tool can be improved by:
> Rigidify the workpiece, the tool and the machine as much as possible
> Choose the tool that will excite vibrations as little as possible (modifying
angles, dimensions, surface treatment, etc.)
> Choose exciting frequencies that best limit the vibrations of the machining
system (spindle speed, number of teeth and relative positions, etc.)
> Choose tools that incorporate vibration-damping technology.
Surface finish & its importance
• Functioning of machine parts, load carrying capacity, tool life, fatigue life,
bearing corrosion, and wear qualities of any component of a machine have
direct relation with its surface texture. Therefore, these effects made the
control of surface texture very important.
• The root of any surface irregularity acts as sharp corner and such part fails
easily.
• Thus in order to increase the life of any part which is subjected to fatigue
loading, the working and non-working surfaces of that part must be given
very good finish.Importance of surface finish
• It improves the service life of the components
• Better surface finish improves the fatigue strength of the component.
• It reduces initial wear of parts due to increased surface to surface contact.
• It gives close dimensional tolerance on the parts
• It reduce corrosion by minimizing depth of irregularities
• It give good surface texture.
THANK
YOUDepartment of Mechanical Engineering
Subject: Manufacturing Science & Technology-II
(RME-503)
Faculty: Mr. Brijesh Kumar
Unit-II / Lecture No: 14
(Lathe Operations)
Introduction to the Lathe
• The lathe is a very useful and versatile machine tool and is capable of
performing a wide range of machining operations.
• The workpiece is held by a chuck in one end and when possible also by a
tailstock at the opposite end. The chuck is mounted on a headstock, which
incorporates the engine and gear mechanism. The chuck is holding the
workpiece with three or four jaws and a spindle engine causes the chuck and
workpiece to rotate.
• A tool-post is found between the headstock and tailstock, which holds the
cutting tool. The tool-post stands on a cross-slide that enables it to move along
the workpiece. An ordinary lathe can accommodate only one cutting tool at the
time, but a turret lathe is capable of holding several cutting tools on a revolving
turret.Types of Lathe
1-Engine Lathe
2- Bench Lathe
3- Automatic Lathe
4- Turret Lathe
5- Computer Controlled Lathe
• Engine Lathe : The most common form of lathe, motor driven and comes in
large variety of sizes and shapes.
• Bench Lathe: A bench top model usually of low power used to make
precision machine small work pieces.• Automatic Lathe: A lathe in which the work piece is automatically fed and
removed without use of an operator.
• Turret Lathe: Lathe which have multiple tools mounted on turret either
attached to the tailstock or the cross-slide, which allows for quick changes in
tooling and cutting operations.
• Computer Controlled Lathe: A highly automated lathe, where both cutting,
loading, tool changing, and part unloading are automatically controlled by
computer coding.Lathe Operations
• Turning: To produce straight, conical, curved, or grooved work pieces .
• Facing: To produce a flat surface at the end of the part or for making face grooves.
• Drilling: To produce a hole by fixing a drill in the tailstock
• Boring: To enlarge a hole or cylindrical cavity made by a previous process or to
produce circular internal holes.
• Reaming : It is used for finishing internal diameter of holes.
• Threading: To produce external or internal threads
• Knurling: To produce a regularly shaped roughness on cylindrical surfaces
• Parting: To cut a piece in to two or more pieces.
• Forming : To generate specific geometry on work surface.
• Chamfering: Chamfering is the operation of beveling the extreme end of a
workpiece. Chamfering is an essential operation before thread cutting so that the
nut may pass freely on the threaded workpiece.
Turning OperationFacing Operation
Drilling OperationBoring Operation
Reaming OperationThreading Operation
Knurling OperationParting operation
Forming OperationChamfering Operation
THANK
YOUDepartment of Mechanical Engineering
Subject: Manufacturing Science & Technology-II
(RME-503)
Faculty: Mr. Brijesh Kumar
Unit-II / Lecture No: 15
(Shaper, planner, slotter)
Shaper Machine
• Introduction: Shaper is a machine tool that uses reciprocating straight line
motion of the tool and a perpendicular feed of the job or the tool to produce flat
work surfaces. The shaper is used primarily for:
1. Producing a flat or plane surface which may be in a horizontal, a vertical
or an angular plane.
2. Making slots, grooves and keyways
3. Producing contour of concave/convex or a combination of these.
• Features:
1- Single point cutting tool is used for machining. The tool is clamped on
the tool post mounted on the ram of the machine.
2- The ram reciprocates to and fro, tool cuts the material in forward stroke
only, no cutting during return stroke.
3- It uses linear relative motion between the tool and workpiece.
4- The cross-feed is provided by the machine table on which workpiece is
fixed.Working Principle:
The job is rigidly fixed on the machine table. The single point cutting tool held
properly in the tool post is mounted on a reciprocating ram. The reciprocating
motion of the ram is obtained by a quick return motion mechanism. As the ram
reciprocates, the tool cuts the material during its forward stroke. During return,
there is no cutting action and this stroke is called the idle stroke. The forward and
return strokes constituteone operating cycle of the shaper.
Construction of shaper
The main parts of the shaper are:
1- Base 2- Column 3- Ram
4- Table 5- Cross rail 6- Tool head• Base: The base is a heavy cast iron casting which is fixed to the shop floor. It
supports the body frame and the entire load of the machine. The base absorbs
and withstands vibrations and other forces which are likely to be induced
during the shaping operations.
• Column: It is mounted on the base and houses the drive mechanism
compressing the main drives, the gear box and the quick return mechanism for
the ram movement.
• Ram: It is the reciprocating member with tool head mounted on its front face.
The ram is connected to with the quick-return mechanism housed inside the
hollow of the column. The back and forth movement of ram is called stroke
and it can be adjusted according to the length of the workpiece to bemachined.
• Table: The worktable of a shaper is fastened to the front of the column. The
table moves across the column on crossrails to give the feed motion to the job.
• Cross rail: The cross rail is mounted on the front of the body frame and can
be moved up and down. The vertical movement of the cross rail permits jobs
of different heights to be accommodated below the tool.
• Tool Head- It holds the cutting tool and is fastened to the front of the ram.
Crank and slotted link mechanism
• Slotted link mechanism is very common in mechanical shapers.
• It converts the rotary motion of the electric motor into the reciprocating
motion of the ram. The return stroke allow the ram to move at a faster rate
to reduce the idle time which is known as “quick return mechanism”,
reduces the time waste during return stroke.
• Bull gear is driven by a pinion which connects to the motor shaft through
gear box.
• The bull wheel has a slot. The crank pin A secured in to this slot, at the
same time it can slide in the slotted crank B.Crank and slotted link mechanism
• As the bull gear rotates causes the crank pin A also to turn and side by side
slides through the slot in the slotted crank B.
• This makes the slotted crank to oscillate about its one end C.
• This oscillating motion of slotted crank (through the link D) makes the ram
to reciprocate.
• The intermediate link D is necessary to accommodate the rise and fall of
the crank.Principle of Quick Return Mechanism
• When the link is in position AP1, the ram will at extreme backward
position of stroke.
• When the link position is at AP2, the extreme forward position ram will
have been reached.
• AP1 and AP2…….Tangent to the crank pin circle.
• Forward cutting stroke takes place when the crank rotates through an angle
C1KC2.
• Return stroke ……the crank rotates through angle C1LC2
• It is seen that C1KC2 > C1LC2
• The angular velocity of crank pin remains constant.Planer Machine
• Like shaping machines, planning machines are also basically used for
producing flat surfaces in different planes. A planer is generally used for
machining large workpieces which cannot be held in a shaper.
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