machining and machine tools

ME 482 - Manufacturing SystemsME 482 - Manufacturing Systems
Machining
Cutting
by
Rohit

In an industry, metal components are made
into different shapes and dimensions by
using various metal working processes.
MATERIAL REMOVAL PROCESSES

Machining
Process of finishing by which work pieces are produced to the desired
dimensions and surface finish by gradually removing the excess material
from the preformed blank in the form of chips with the help of cutting
tool(s) moved past the work surface(s).

Principle of machining (Turning)
A metal rod of irregular shape, size and surface is converted
into a finished product of desired dimension and surface finish
by machining by proper relative motions of the tool-work pair.

Purpose of machining
Machining to high accuracy and finish essentially enables a product:
 Fulfill its functional requirements.
 Improve its performance.
 Prolong its service.

MACHINE TOOLS
A machine tool is a non-portable power operated device or system of
devices in which energy is expended to produce jobs of desired dimension
and surface finish by removing excess material from the preformed blanks
in the form of chips with the help of cutting tools moved past the work
surface(s).
Eg. Lathe Machine, Boring Machine, Drilling Machine,
Milling machine, Hobbing Machine Etc.

THEORY OF METAL CUTTING
cutting tools :
Cutting tool or cutter is any tool that is used to remove material
From w/p by means of shear deformation.
According to the number of major cutting edges (points)
involved:
 Single point: e.g., turning tools, shaping, planning and slotting
tools and boring tools.
 Double (two) point: e.g., drills.
 Multipoint (more than two): e.g., milling cutters, broaching tools,
hobs, gear shaping cutters etc.
Types of cutting tools

Geometry of single point cutting
(turning) tools:
• Both material and geometry of the cutting tools play very important
roles on their performances in achieving effectiveness, efficiency
and overall economy of machining.
• Referred to some specific angles or slope of the faces
and edges of the tools at their cutting point

Rake angle (γ): Angle of inclination of rake surface from reference
plane.
• Rake angle is provided for ease of chip flow and overall
machining.
• Rake angle may be positive, or negative or even zero

 Positive rake - helps reduce cutting force and thus cutting
power requirement.
 Zero rake - to simplify design and manufacture of the form
tools.
 Negative rake - to increase tool edge-strength and life of the
tool.

Clearance angle (α): Angle of inclination of clearance or flank surface
from the finished surface
• Clearance angle is essentially provided to avoid rubbing of the tool
(flank) with the machined surface which causes loss of energy and
damages of both the tool and the job surface.
• Clearance angle is a must be positive depending upon tool-work
materials and type of the machining operations

Cutting Velocity (VC): Speed with which cutting tool move through
the work material (mm/s)
depth of cut (d) - perpendicular penetration of the cutting tool tip in
work surface (mm).
feed (f) - axial travel of the tool per revolution of the job (mm/rev).

Systems of description of tool geometry
 Machine Reference System - ASA system.
 Tool Reference System - Orthogonal Rake System - ORS.
 Normal Rake System - NRS.
Tool geometry in Machine Reference System / ASA
System
• Geometry of a cutting tool refers mainly to its several angles or
slopes of its salient working surfaces and cutting edges.
• Those angles are expressed with respect to some planes of
reference.

In Machine Reference System (ASA),
The planes of reference and the coordinates used in ASA system
for tool geometry are:
ΠR - ΠX - ΠY and Xm - Ym - Zm; where,
Planes and axes of reference cutting (turning) tool in ASA system

ΠR = Reference plane; plane perpendicular to the velocity vector.
ΠX = Machine longitudinal plane; plane perpendicular to ΠR and
taken in the direction of assumed longitudinal feed.
ΠY = Machine transverse plane; plane perpendicular to both ΠR
and ΠX. [This plane is taken in the direction of assumed cross
feed]
The axes Xm, Ym and Zm are in the direction of longitudinal feed,
cross feed and cutting velocity (vector) respectively

Basic features of single point cutting (turning) tool

Definition of:
Face: The surface against which the chip slides upward.
Flank: The surface which face the work piece.
Heel: The lowest portion of the side cutting edges.
Nose radius: The conjunction of the side cutting edge and
end cutting edge. It provides strengthening of the tool nose and
better surface finish.

angles:
Side rake angle (γx = axial rake): angle of
inclination of the rake surface from the
reference plane (ΠR) and measured on
machine longitudinal plane, ΠX.
Side clearance angle (αx = Side relief
angle): angle of inclination of the principal
flank from the machined surface and
measured on ΠX plane.

Back rake angle (γy ): angle of
inclination of the rake surface from the
reference plane (ΠR) and measured on
machine transverse plane, ΠY.
Back clearance angle (αy) (End relief
angle): same as αx but measured on
ΠY plane.

Side cutting edge angle (φs = Approach
angle): angle between the principal
cutting edge (its projection on ΠR) and
ΠY and measured on ΠR.
End cutting edge angle (φe ): angle
between the end cutting edge (its
projection on ΠR) from Πx and
measured on ΠR.

CHIP FORMATION
• Machining is a process of gradual removal of excess material from
the preformed blanks in the form of chips.
• The form of the chips is an important index of machining

• During continuous machining the uncut
layer of the work material just ahead of
the cutting tool (edge) is subjected to
almost all sided compression
• Due to such compression, shear stress
develops, within that compressed
region, in different magnitude, in
different directions and rapidly increases
in magnitude.
• The actual separation of metal start from
the cutting tool tip as yielding (Ductile
w/p) or fracture (Brittle w/p) depends on
cutting conditions.

* The chip in actual manufacturing practice is variable in both size
and shape.
The pattern and extent of total deformation of the chips due to
the shear deformations of the chips ahead and along the tool
face depend upon:
 Work material.
 Material and geometry of the cutting tool.
 cutting velocity, feed and depth of cut.
 Machining environment or cutting fluid that affects temperature
and friction at the chip-tool and work-tool interfaces.

I. Continuous Chip
II. Continuous chip with BUE
III. Discontinuous Chip
The chip formation in metal cutting could be classified
into three types:

I. Continuous Chip
 Chip is produced when there is low friction between the chip and tool face.
 This chip has the shape of long string or curl into tight rolls.
 Chip is produce when machining ductile materials such as Al, Cu, MS and wrought
iron
 Formation of lengthy chip is hazardous to machining process and machine operators.
 It may be wrap up on the cutting tool, W/P and interrupt the cutting process.
 It may become necessary to break or deform long continuous chip into small pieces.

2. Continuous chip with BUE
When high friction existed between chip and tool, the chip material weld itself to
tool face.
Welded materials increase friction further which in turn lead to the building a
layer of chip material (BUE) upon w/p .
Build up edge grow and break down when become unstable.
Chip with build up edge result in higher power consumption, poor surface finish
and large tool wear.

3. Discontinuous Chip
Chip is produced in form of small pieces.
These type of chip is produced while machining brittle materials like cast iron,
brass and bronze at low cutting speed and high feed rate.
For brittle materials it is associate with batter surface finish, lower power
consumption and reasonable tool life.
For ductile materials it is associate with poor surface finish and excessive tool
wear.

Chip breakers:
Often in machining of ductile metals at high speed, the chips are
deliberately broken (using chip barkers) into small segments of
regular size and shape mainly for convenience and reduction of chip-
tool contact length.
Need and purpose of chip-breaking
 Safety of the working people.
 Prevention of damage of the product.
 Easy collection and disposal of chips.
Chip breaking is done in proper way for the additional purpose of improving
machinability by reducing the chip-tool contact area, cutting forces and wear
of the cutting tool.

MECHANICS OF ORTHOGONAL METAL
CUTTING
Cutting force components and their significances
Determination of the cutting forces are required for:
 Estimation of cutting power consumption, which also enables selection of
the power source(s) during design of the machine tools.
 Structural design of the machine - fixture - tool system.
 Evaluation of role of the various machining parameters on cutting forces.
 Study of behavior and machinability characterization of the work
materials.
 Condition monitoring of the cutting tools and machine tools.

The single point cutting tools being used for turning, shaping, planing,
slotting, boring etc. are characterized by having only one cutting force
(F) during machining.
Cutting force F resolved into Fx, Fy and Fz
• Single cutting force (F) in turning is resolved into three components
along the three orthogonal directions; X, Y and Z.

Significance of FZ, FX and FY
 Fz: Called the main or major component as it is the largest in magnitude.
It is also called power component as it being acting along Vc and being
multiplied by VC decides cutting power consumption (Fz.VC) .
 FY: May not be that large in magnitude but is responsible for causing
dimensional inaccuracy and vibration.
 Fx: It, even if larger than FY, is least harmful and hence least
significant.

Merchant’s Circle Diagram (minimum energy principal)
Where:
FH – Cutting force along primary
cutting motion
FV – Force perpendicular to primary
cutting motion (thrust force)
FS – Force along shear plane
NS – Force normal to shear plane
N - Force normal to rake face.
F - Friction force at chip tool interface.
The magnitude of FS provides the yield
shear strength of the work material under
the cutting action.

Calculation ?

Metal Removal Rate (MRR)
• volume of metal removed in unit time.
For turning operation, MRR = d.f.VC
Cutting power consumption (FC) :
FC = FZ.VC + FX.Vf
Specific energy requirement (Us):
• amount of energy required to remove unit volume of material.
Us, should be low as far as possible, depends not only on the work
material but also the process of the machining, such as turning, drilling,
grinding etc. and the machining condition, i.e., VC, f, tool material and
geometry and cutting fluid application.
where,
d - Depth of cut (mm),
f - Feed (mm / rev) and
VC - Cutting speed (mm /
sec).

Some limitations of use of MCD:
 Merchant’s circle diagram (MCD) is only valid for orthogonal cutting.
 By the ratio, F/N, the MCD gives apparent (not actual) coefficient of
friction.
 It is based on single shear plane theory.

CUTTING TOOL MATERIALS:
The cutting tools need to be capable to meet the growing demands for higher
productivity, economy as well as to machine the exotic materials.
The cutting tool material essentially require the following properties:
 High mechanical strength; compressive, tensile
 Fracture toughness - high or at least adequate.
 High hardness for abrasion resistance.
 High hot hardness to resist plastic deformation and reduce
wear rate at elevated temperature.

 Chemical stability or inertness against work material, atmospheric
gases and cutting fluids.
 Resistance to adhesion and diffusion.
 Thermal conductivity - low at the surface to resist incoming of
heat and high at the core to quickly dissipate the heat entered.
 Manufacturability, availability and low cost.

Needs and development of cutting tool materials
With the progress of the industrial world it has been needed to
continuously develop and improve the cutting tool materials and
geometry:
 To meet the growing demands for high productivity, quality and
economy of machining.
 To enable effective and efficient machining of the exotic materials.
 For precision and ultra-precision machining.
For micro and even nano machining.

Characteristics and applications of cutting tool
materials
a) High Speed Steel (HSS)
The basic composition of HSS is 18% tungustan W, 4% Cr, 1% V, 0.7% C
and rest Fe. Such HSS tool could machine (turn) mild steel jobs at speed
only up to 20 ~ 30 m/min.
However, HSS is still used as cutting tool material where:
 Cutting tool suitable under shock loading.
 The small scale industries (cannot afford costlier tools).
 The tool geometry and mechanics of chip formation are complex,
such as helical twist drills, reamers, gear shaping cutters, hobs etc.
 The tool is to be used number of times by resharpening.

The effectiveness and efficiency of HSS (tools) can be
enhanced by improving its properties and surface condition
through:
 Refinement of microstructure.
 Addition of large amount of cobalt and Vanadium to increase hot
hardness and wear resistance respectively.
 Manufacture by powder metallurgical process.
 Surface coating with heat and wear resistive materials like TiC, TiN, etc.
by Chemical Vapour Deposition (CVD) or Physical Vapour Deposition
(PVD).
•Addition of large amount of Co and V, refinement of microstructure and
coating increased strength and wear resistance and thus enhanced
productivity and life of the HSS tools remarkably.

b) Stellite
• This is a cast alloy of Co (40 to 50%), Cr (27 to 32%), W (14 to 19%)
and C (2%). Stellite is quite tough and more heat and wear resistive
than the basic HSS.
• But such stellite as cutting tool material became no longer in use
because of its poor grindability

c) carbides:
They have the following properties which make them very effective
cutting-tool materials:
•High hardness over a wide range of temperatures.
•High elastic modulus, 2 to 3 times that of steel.
•No plastic flow even at very high temperature.
•Low thermal expansion.
•High thermal conductivity.
*Carbides are used in the form of inserts or tips which are clamped or
brazed to a steel shank.

i) Straight or single carbide
 Single carbide tools are powder metallurgically produced by mixing,
compacting and sintering of 90 to 95% WC powder with cobalt.
 Such tools are suitable for machining grey cast iron, brass, bronze
etc. which produce short discontinuous chips and at cutting
velocities two to three times of that possible for HSS tools.

ii) Composite carbides
 The single carbide is not suitable for machining steels because of
rapid growth of wear, particularly crater wear (chips under the high
stress and temperature (plastic) when contact between the
continuous chip and the tool surfaces.)
 Composite carbide have been developed by adding (8 to 20%) a
gamma phase to WC (mix of TiC, TiN, etc.) and Co mix.

iii) Mixed carbides
• Large quantity (5 to 25%) of TiC is added with WC and Co to
produce another grade called mixed carbide.
• Titanium carbide (TiC) is not only more stable but also much
harder than WC.
 For finishing with light cut but high cutting speed (the harder
grades containing up to 25% TiC) .
 For heavy roughing work at lower cutting speed (lesser amount
(5 to 10%) of TiC) .

*Each group again is divided into some subgroups like P10, P20 etc.,
depending upon their properties and applications.
The standards developed by ISO for grouping of carbide tools
according to machining applications:
K-group : Suitable for machining short chip producing ferrous and
non-ferrous metals and also some non metals.
P-group : Suitably for machining long chip forming common materials
like plain carbon and low alloy steels.
M-group : Suitable for machining long or short chip forming ferrous
materials like Stainless steel.

d) Ceramic, or oxide:
• Consist primarily of fine aluminum oxide grains which have been
bonded together. Minor additions of other elements help to obtain
optimum properties.
• Other ceramics include silicon nitride, with various additives such
as aluminum oxide, yttrium oxide, and titanium carbide.
 Ceramic tools have very high abrasion resistance, are harder than
carbides, and have less tendency to weld to metals during cutting.
 However, they generally lack impact toughness, and premature tool
failure can result by chipping or general breakage.

The ceramic outperformed the existing tool materials in some application
areas like high speed machining mainly for obtain higher hot hardness
as indicated:
Hardness of tool materials as a function of temperature.

Development and applications of advanced tool materials
a) Coated carbides
• Thin but hard coating of single or multilayer of more stable and heat
and wear resistive materials like TiC, TiCN, TiN, Al2O3 etc on the
tough carbide (substrate) by processes like chemical Vapour
Deposition (CVD), Physical Vapour Deposition (PVD) etc at
controlled pressure and température

 Reduction of cutting forces and power consumption.
 Increase in tool life for same VC or increase in VC for same tool
life.
 Improvement in product quality.
 Effective and efficient machining of wide range of work materials.
 Pollution control by less or no use of cutting fluid
The properties and performances of coated inserts and tools are getting
further improved by:
 Refining the microstructure of the coating.
 Multilayering coating (already up to 13 layers within 12 ~ 16 μm).
 Direct coating by TiN instead of TiC, if feasible.
 Using better coating materials.
Enhanced MRR and overall machining economy remarkably by:

b) Cermets
These sintered hard inserts are made by combining ‘cer’ from ceramics
like TiC, TiN or TiCN and ‘met’ from metal (binder) like Ni, Ni-Co, Fe etc.
The characteristic features of such cermets, in contrast to sintered
tungsten carbides, are:
 The grains are made of TiCN (in place of WC)
 Harder, more chemically stable and hence more wear resistant.
 More brittle and less thermal shock resistant.
 Cutting edge sharpness is retained unlike in coated carbide inserts.
 Can machine steels at higher cutting velocity than that used for
tungsten carbide, even coated carbides in case of light cuts.

Diamond Tools
• Single stone, natural or synthetic, diamond crystals are used as
tips/edge of cutting tools.
• Owing to the extreme hardness and sharp edges, high hardness,
good thermal conductivity, low friction and good wear resistance
natural single crystal is used for many applications, particularly
where high accuracy and precision are required.
• Single point cutting tool tips for high speed machining of non-ferrous
metals, ceramics, plastics, composites, etc. and effective machining
of difficult-to-machine materials.
 Limitation of diamond cutting tool is very high cost, possibility of
oxidation in air, Very high brittleness and difficulties in shaping it.

Polycrystalline Diamond (PCD)
• The polycrystalline diamond (PCD) tools consist of a layer (0.5 to 1.5
mm) of fine grain size, randomly oriented diamond particles sintered
with a suitable binder (usually cobalt) and then metallurgically bonded
to a suitable substrate like cemented carbide.
 PCD exhibits excellent wear resistance, hold sharp edge,
generates little friction in the cut, provide high fracture strength,
and had good thermal conductivity.
 PCD is particularly well suited for abrasive materials.
The main advantage of such PCD tool is the greater toughness due to
finer microstructure with random orientation of the grains.
* Negative rake angle are used for machining hard materials and positive
rake angle can be used for soft materials such as copper.

Cubic Boron Nitride (CBN):
• Next to diamond, CBN is the hardest material presently available.
• It is made by bonding a 0.5 - 1 mm layer of polycrystalline cubic boron
nitride to cobalt based carbide substrate at very high temperature and
pressure.
The characteristic features of CBN are:
 Excellent performance in grinding any material due to high hardness
and strength.
 High material removal rate (MRR) as well as precision machining.
 Firmly stable at temperatures up to 1400 0C.
 Machining wide range of work materials.

TOOL WEAR
Failure of cutting tools
Smooth, safe and economic machining requires:
 Prevention of premature and terrible failure of the cutting tools.
 Reduction of rate of wear of tool to prolong its life.
Cutting tools generally fail by:
 Mechanical breakage due to excessive forces and shocks.
 Quick dulling by plastic deformation due to intensive stresses and
temperature..
 Gradual wear of the cutting tool at its flanks and rake surface.

Tool failure need to be prevented by using suitable tool materials and
geometry depending upon the work material and cutting condition.
The common mechanisms of cutting tool wear are:
• Thermally insensitive type; like abrasion, chipping and de-lamination.
• Thermally sensitive type; like adhesion, fracturing, flaking etc.
 It commonly takes place when machining brittle materials.
 It is caused by the pressure of the chip as it slides up the face of the
cutting tool when feed is high at low or moderate speeds.

The following effects are also caused of the growing tool-wear:
 Increase in cutting forces and power consumption mainly due to the
principal flank wear.
 Increase in dimensional deviation and surface roughness.
 Odd sound and vibration.
 Very high temperature gradients.
 Very high stress gradients.
 Worsening surface integrity.
 Mechanically weakening of the tool tip.
• Flank wear is a flat portion worn behind the cutting edge which
eliminates some clearance or relief. It takes place when machining
brittle materials.
• Wear at the tool-chip interface occurs in the form of a depression
or crater. It is caused by the pressure of the chip as it slides up the
rake face of the cutting tool.

TOOL LIFE
Tool life generally indicates the amount of satisfactory performance or
service rendered by a fresh tool or a cutting point till it is declared failed.
It can be defined in two ways:
• Actual machining time (period) by which a fresh cutting tool (or point)
satisfactorily works after which it needs replacement or
reconditioning.
• The length of time of satisfactory service or amount of acceptable
output provided by a fresh tool prior to it is required to replace or
recondition.

Assessment of tool life
Tool life is can be assessed or expressed in many ways:
 span of machining time in minutes
 Number of pieces of work machined.
 Total volume of material removed.
 Total length of cut
Taylor’s tool life equation
Wear and hence tool life of any tool for any work material decided mainly
by the level of the machining parameters i.e., cutting velocity (VC), feed
(f) and depth of cut (t).

Tool wear as function of machining time:

The tool life decreases with the increase in cutting velocity keeping
other conditions unaltered
Cutting velocity - tool life relationship:
Cutting velocity - tool life relationship
Where:
T= Tool life (min)
Vc=Cutting speed (m/min)
C , n = Const.
VcTn
= C
Taylor’s Equation

With the slope, n and intercept, c, Taylor derived the simple
equation as,
VcTn = C
where, n is called, Taylor’s tool life exponent. The values of
both ‘n’ and ‘C’ depend mainly upon the tool-work materials
and the cutting environment

Factors affecting tool life
The life of the cutting tool is affected by the following factors:
Cutting speed.
 Feed and depth of cut.
 Tool geometry.
 Tool material.
 Cutting fluid.
 Work piece material.
 Rigidity of work, tool and machine.

Machinability:
‘Machinability’ has been introduced for gradation of work materials with
respect to machining characteristics.
 It refers to material (work) response to machining.
 It is the ability of the work material to be machined.
 It indicates how easily and fast a material can be machined.
For Instance, saying ‘material A is more machinable than material B’
may mean
 ‘A’ causes lesser tool wear or longer tool life.
 ‘A’ requires lesser cutting forces and power.
 ‘A’ provides better surface finish.

Machinability can be defined as “ability of being machined” and more
reasonably as “ease of machining”.
machinability characteristics of any tool-work pair is to be judged by:
 Magnitude of the cutting forces.
 Tool wear or tool life.
 Surface finish.
 Magnitude of cutting temperature.
 Chip forms.
speed (fpm) of machining of work giving 60 min. tool life x100
Machinability rating (MR) = speed (fpm)of machining the standard metal giving 60 min. tool life

SURFACE FINISH :
Generally, surface finish of any product depends on the following
factors:
 Cutting speed (VC).
 Feed (f).
 Depth of cut (d).
Cutting speed
•Better surface finish can be obtained at higher cutting speeds and
Rough cutting takes place at lower cutting speeds.
Feed
•Surface finish will not be good when coarse feed is applied. But
better finish can be obtained in fine feeds.

Depth of cut
•Lighter cuts provide good surface finish to the work piece. If depth of
cut increases during machining, the quality of surface finish will
reduce.
Therefore, higher cutting speeds, fine feeds and low depth of cuts
ensure good surface finish. But, lower cutting speeds, coarse feeds
and heavier depth of cuts are applied in rough cutting operations.

CUTTING FLUIDS
Purposes and application of cutting fluid
 Cooling of the job and the tool to reduce the detrimental effects of
cutting temperature on the job and the tool.
 Lubrication at the chip-tool interface and the tool flanks to reduce
cutting forces and friction and thus the amount of heat generation.
 Cleaning the machining zone by washing away the chip - particles
and debris.
 Protection of the finished surface.
Cutting fluids, frequently referred to as lubricants or coolants,
comprise those liquids and gases which are applied to the cutting
zone in order to facilitate the cutting operation.

However, the main aim of application of cutting fluid is to improve
machinability through reduction of cutting forces and temperature,
improvement of surface integrity and enhancement of tool life.
Essential properties of cutting fluids
 High specific heat, thermal conductivity and film coefficient for
heat transfer.
 High lubricity without gumming and foaming.
 Wetting and spreading.
 High film boiling point.
 Friction reduction at extreme pressure (EP) and temperature.
 High resistance to bacterial growth.
 Non toxic in both liquid and gaseous stage.
 Easily available and low cost.

Types of cutting fluids and their application
Generally, cutting fluids are employed in liquid form but occasionally
also employed in gaseous form and for lubricating purpose, often solid
lubricants are employed in machining and grinding.
The cutting fluids, which are commonly used, are:
 Air blast or compressed air
 Solid or semi-solid lubricant
 Soluble oil
 Cutting oils
 Chemical fluids
 Cryogenic cutting fluid

Selection of cutting fluid
Application of cutting fluid largely depend upon proper selection of the
type of the cutting fluid depending upon the work material, tool material
and the machining condition.
Selection of cutting fluids for machining some common engineering
materials and operations are :
Grey cast iron:
 Air blast for cooling and flushing chips.
 Soluble oil for cooling and flushing chips in high speed machining
and grinding.

Steels Alloys:
 Sol. Oil for low carbon and alloy steels
 EP cutting oil for high alloy steel.
Aluminium and its alloys:
 Preferably machined dry.
 Light but oily soluble oil.
Copper and its alloys:
 Oil with or without inactive EPA for tougher grades of Cu-alloy.
Stainless steels and Heat resistant alloys:
 High performance soluble oil or neat oil with high concentration with
chlorinated EP additive.

Problem statement:
A series of tool life tests is conducted on two work materials under
identical cutting conditions, varying only speed in the test procedure.
The first material, defined as the base material, yields the Taylor tool
life equation
v T0.28
= 1050
and the other material (test material) yields the Taylor equation
v T0.27
= 1320
Determine the machinability rating of the test material using the
cutting speed that provides a 60 min. tool life as the basis of
comparison. This speed is denoted by v60.

Solution:
The base material has a machinability rating = 1.0. Its v60 value can
be determined from the Taylor tool life equation as follows:
v60 = 1050/600.28
= 334 fpm
The cutting speed at a 60 min. tool life for the test material is
determined similarly:
v60 = 1320/600.27
= 437 fpm
Accordingly, the machinability rating can be calculated as:
``MR (for the test material) = 437/374 = 1.31 (or 131%)
speed (fpm) of machining of work giving 60 min. tool life x100
Machinability rating (MR) = speed (fpm)of machining the standard metal giving 60 min. tool life

Machining
• A material removal process in which a sharp cutting tool is used to
mechanically cut away material so that the desired part geometry
remains.
• Machining is the most versatile and accurate of all manufacturing
processes in its capability to produce a diversity of part geometries
and geometric features.
 Casting can also produce a variety of shapes, but it lacks the
precision and accuracy of machining

Machine Tools:
• A machine tool is defined as tool which while holding the cutting tool
would be able to form a work piece, in order to generate the requisite
jobs of given size, configuration and surface finish.
• A machine tool is required to provide proper support to the workpiece
and cutting tool as well as provide motion to one or both of them to
generate the required shape and finish.
Eg. Lathe Machine, Boring Machine, Drilling Machine,
Milling machine, Hobbing Machine Etc.

Classification of Machine Tools:
Machine tools of different type and shape have been developed because
of variation in shape to be machined and quantity to be produced.
Classification based on desired purpose:-
General purpose machine tool
Production machine tool
Special purpose machine tool

General purpose machine tool (GPM):
•Designed to perform a variety of machining operations on a wide range
of components.
Convention or traditional machine tools: like Lathe, Milling machine
etc are used more widely for faster material removal by shearing or
Brittle fracture.
Non convention of Non tradition machine tools: like EDM, ECM, USM
etc. which remove materials from the exotic materials slowly by electro-physical
Electro-chemical processes.
Modern numerical and computer controlled machine tools: like CNC
lathe, CNC milling.

Special purpose machine tools are meant for specific operation or jobs
such as gear cutting machine, thread grinding machine, transfer machine or
machining center.
This type of machine tools are designed only for a limited number of
operation.
They are costlier and suited for large volume of production only.
Production machine tools
This types are used where a number of the function of the machine tools
are automated. This helps in reducing the idle time of the machine tool.
It is possible that GPM may be converted into a PMT by utilization of jigs
and fixtures.
Examples: capsan and turret lathe, multiple spindle drilling etc

Machining Operations and Part Geometry
Each machining operation produces a characteristic part
geometry due to two factors:
1.Relative motions between the tool and the workpart
• Generating –part geometry is determined by the feed
trajectory of the cutting tool
2. Shape of the cutting tool
• Forming –part geometry is created by the shape of the
cutting tool

VARIOUS CUTTING OPERATIONS:
Turning
•A single point cutting tool removes material from a rotating
workpiece to generate a cylindrical shape.
Performed on a machine tool called a lathe.
Workpiece is held in a chuck and rotates at N rev/min; a cutting tool
moves along the length of the piece at a feed f (in/rev or mm/rev) and
removes material at a radial depth d, reducing the diameter from D0
to Df .

Turning operation

VARIOUS OPERATIONS
The machining operations generally carried out in centre lathe are:

Facing
Tool is fed radially inward.
Machining the end of the
work piece to produce flat
surface.

Contour Turning
Instead of feeding the tool
parallel to the axis of
rotation, tool follows contour
that is other than straight,
thus creating a contoured
form.

Chamfering
Cutting edge cuts an angle on the
corner of the cylinder, forming a
"chamfer“.
The operation of producing conical
shape on both ends of the work piece.

Cutoff/Parting off
Tool is fed radially into rotating work
at some location to cut off the part

Threading
Pointed form tool is fed linearly
across surface of rotating workpart
parallel to axis of rotation at a large
feed rate, thus creating threads.

THREAD CUTTING METHODS (Thread cutting on a centre lathe)
 It is possible to cut both external and internal threads with the
help of threading tools.
 The principle of thread cutting is to produce a helical groove on a
cylindrical surface by feeding the tool longitudinally.
 The longitudinal feed should be equal to the pitch of the thread
to be cut per revolution of the workpiece.

principle of thread cutting
 The lead screw of the lathe has
a definite pitch.
 Relative speeds of rotation of
the work and the lead screw will
result in the cutting of a thread
of the desired pitch.
 This is done by change gears
arranged between the spindle
and the lead screw or by the
change gear mechanism.
*Thread cutting on a centre lathe is
a slow process.

Calculation for change gear ratio
Metric thread on Metric lead screw
Driver teeth = Lead screw turn = Pitch of thread to be cut
Driven teeth Spindle turn Pitch of lead screw
Depth of cut in thread cutting
• The depth of cut is applied by advancing the tool either radially
(called as plunge cutting) or at an angle equal to half angle of the
thread (called as compound cutting).

Plunge cutting
 Cutting takes place along a longer length of the tool.
 Rise to difficulties in machining in terms of higher cutting
forces and consequently chattering.
 Poor surface finish and lower tool life.
 Used for very light finishing cuts and for cutting square and
worm threads.
Compound cutting
 cutting take place on one edge of the tool only.
 Allows the chips to slide easily across the face of the tool.
 Reduces cutting strain that acts on the tool.
 Reduces the tendency to cause the tool to ‘dig-in’.
*So compound cutting is more preferred compared with plunge cutting.

method of applying plunge cut and compound cut

Other methods for cutting external threads
External thread cutting by milling cutters
• This process gives quite fast production by using suitable thread
milling cutters in centre lathes.
Thread milling is of two types:
Long thread milling :
Long and large diameter screws (like machine lead screws) are
reasonably accurately made by using a large disc type milling cutter.
Short thread milling:
Threads of shorter length and fine pitch are machined at high production
rate by using a HSS milling cutter, having a number of annular threads
with axial grooves cut on it.

Internal thread cutting
 It is similar to that of an external
thread, the only difference being in the
cutting tool used.
 The tool is similar to a boring tool with
cutting edges.
 The hole is first bored to the root
diameter of the thread.
 The tool is fixed on the tool post after
setting it at right angles to the lathe
axis, using a thread gauge.
 The depth of cut is given by the
compound slide and the thread is
finished.

Internal thread cutting by taps
 Internal screw threads of usually small
size are cut manually.
 Threads are often tapped by manually
rotating and feeding the taps through the
drilled hole in the blank held in centre
lathe spindle.
Internal thread cutting by milling cutters
 This cutter produces internal threads
very rapidly.
 The principle of operation is similar to
that of an external thread milling. Internal thread milling cutters
Hand operated tapping in centre lathe
Other methods for cutting internal threads

TAPER TURING:
A taper may be defined as a uniform change in the diameter of a work piece
measured along its length.
Generally, taper is specified by the term
conicity.
Conicity is defined as the ratio of the
difference in diameters of the taper to its
length. Conicity,
K = (D – d)/l
Where:
D - Large diameter of the taper.
d - Small diameter of the taper.
l - Length of tapered part.

MACHINING POWER and TIME ESTIMATION
• Power is the product of cutting force and velocity.
Force involved in orthogonal cutting is the force component in the
direction of cutting speed.
E.g. turning, facing, parting-off operations, etc. so;
Power required (WC) = FC x Vc
where, V – Cutting speed (m/min) and
FC – Force in the direction of cutting speed (N).

Due to shear and friction, this total power is divided into two
components. They are;
1. Power due to shear.
2. Power due to friction.
So, Total power = Power due to shear + Power due to friction
WC = Ws + Wf = [Fs x Vs] + [Ff x Vf]
where, Fs – Force due to shear.
Vs – Velocity of shear.
Ff – Force due to friction.
Vf – Velocity of friction / feed velocity.

Machining time
Cutting speed (V) = (pi*D*N)/1000 m / min
where, D – Mean diameter of the work piece (mm).
N – Rotational speed of the work piece (rpm).
The time (t) for a single pass is given by
t = (L+Lo) / f*N
where, L – Length of the work piece (mm).
Lo – Over travel of the tool (mm).
f – Feed rate (mm / rev).

Tool force dynamometers:
• To estimate power required for machining operations, the force has
to be measured by a suitable measuring instruments.
• Dynamometers are generally used for measuring cutting forces.
Especially, strain gauge dynamometers are used.
Design requirements for Tool force Dynamometers
 Sensitivity: The dynamometer should be reasonably sensitive for
precision measurement.
 Rigidity: The dynamometer need to be quite rigid to withstand the
forces without causing much deflection which may affect the
machining condition.
 Stability against humidity and temperature.
 Quick time response.
 Consistency: The dynamometer should work desirably over a long
period.

Milling
• It is one of the most versatile machining processes and is capable
of producing a variety of shapes involving flat surfaces, slots, and
contours.
• Work piece is fed into a rotating cutter which use single or multiple
cutters with multiple teeth in contrast with the single-point tools of
the lathe and planer.
Parts of milling machine

Milling Operation:
In general, all milling operations can be
grouped into two types.
peripheral milling and face milling.
Peripheral milling
 The finished surface is parallel to the
axis of rotation of the cutter and is
machined by cutter teeth on the
periphery of the cutter.
face milling
 The finished surface is perpendicular to
the axis of rotation of the cutter and is
machined by cutter teeth on the
periphery and the flat end of the cutter.

According to the relative movement between the tool and the work, the
Peripheral milling operation is classified into two types:
Up milling or conventional milling
Down milling or unconventional milling
Up Milling: The cutter rotates in the opposite direction to the work table
movement. In this, the chip starts as zero thickness and gradually increases
to the maximum.
Down Milling: The cutter rotates in the same direction as that of the work
table movement. In this, the chip starts as maximum thickness and gradually
decreases to zero thickness. suitable for obtaining fine finish on the work
surface.

TYPES OF MILLING MACHINE
Milling-machine classification is based on design, operation, or purpose.’
•Column and knee type:
Hand milling machine.
 Plain or horizontal milling machine.
 Universal milling machine.
 Omniversal milling machine.
 Vertical milling machine.
•Manufacturing or bed type
•Planer type
•Special type
Drum milling machine.
 Rotary table milling machine.
 Profile milling machine.
 Pantograph milling machine.
 Planetary milling machine

Column and knee type milling machines:
 This is the most commonly used milling
machine in view of its flexibility and
easier setup.
 The table is mounted on the knee which
in turn is mounded on the vertical slides
of the main column.
 The knee is vertically adjustable on the
column so that the table can be moved
up and down to accommodate work of
various height.
 They are mainly used for face or end
milling.

Chamfer
Taper Contou
r
FormFacing
Cutoff
Boring Drilling
Planer type milling machine:
 They are used only on the heaviest work.
 They are used to machining a number of flat surfaces on a particular
part or group of parts arranged in series such as lathe beds.
 Limited to production work only and ultimate material removal
capacity.
Manufacturing or bed type:
 The fixed bed type milling machines are comparatively large, heavy,
and rigid.
 The table movement is restricted to reciprocation (longitudinal
motion) at right angles to the spindle axis with no provision for cross
or vertical adjustment.
 They are simple and rigidly built and are used primarily for high-
production work.

Milling time analysis - example
Problem statement:
A face milling operation is performed to finish the top surface
of a steel rectangular workpiece 12 mm long by 2 mm wide
with cutting speed 60 mm/min. The milling cutter has 4 teeth
(cemented carbide inserts) and is 3 mm in diameter. Cutting
conditions are 500 fpm, f = 0.01 mm/tooth, and d = 0.150 mm.
Determine the time to make one pass across the surface, the
metal removal rate during the cut and milling power
estimation.

Time to mill workpiece, Tm:
Tm = (L + L0)/fr
Spindle rpm related to cutter diameter and
speed:
N (rpm) = v/(π D)
Feedrate in mm/min:
fr = N nt f
Material removal rate (mm3/min):
MRR =w d fr
where
L – Length of the work
piece (mm).
Lo – Over travel of the
tool (mm).
f = feed per tooth
nt = number of teeth

For Slab milling:
Approach distance, A :
A = (D/2)2 – (D/2 – d)2 = d (D-d)
Time to mill workpiece, Tm:
Tm = (L + L0)/fr
For Face milling:
Allow for over-travel O where A = O:
Full face A = O = D/2
Machining time:
Tm = (L + 2A)/fr
Slab milling movements
Face milling movements

Milling time analysis - example
Solution?
Full face A = O = D/2
Machining time (min.) Tm = (L + 2A)/fr
Metal removal rate(Q) MRR = fr*w*d
(mm3/min)
Feed per revolution (mm/min) fr = N*nt*f
Spindle speed N (rpm) = Vc/(π D)
Where:
Vc: Cutting
Speed
nt: Number of
tooth
f: feed rate
(mm/tooth)
D: Dia of cutter
d: Depth of cut
W: width of w/p

Peripheral Face
GEAR MANUFACTURING:
Gear Cutting
•Gears are important machine elements and widely used in various
mechanisms and devices to transmit power and motion.
•Gears can be manufactured by most of manufacturing processes.
(casting, forging, extrusion, powder metallurgy, blanking, etc.)
•Machining is applied to achieve the final dimensions, shape and
surface finish in the gear.

Peripheral Face
GEAR MANUFACTURING:
Gear Cutting
•Most gear-cutting processes can be classified as either forming or
generating.
Two principal methods of gear manufacturing include:
 Gear forming - where the profile of the teeth are obtained as the
replica of the form of the cutting tool (edge); e.g., milling, broaching etc.
 Gear generation -The shape produced on the workpiece depends
on both the shape of the tool and the relative motion between the tool
and the workpiece during the cutting operation e.g., gear hobbing, gear
shaping etc.
• In general, a generating process is more accurate than a forming
process.

GEAR FORMING
•Production of gears by gear forming method uses form-milling cutter,
which have shape identical of the gear teeth.
•Two machining operations, milling and broaching can be employed.
Gear Form Milling:
Gear teeth can be produced by both disc type and end mill type form
milling cutters.

The form milling cutter have the shape of
the teeth similar to the tooth space.
The cutting tool is fed radially into the
work piece till the full depth is reached. The
cutter travel axially (feed) along the length
of gear tooth at the appropriate depth to
produce the gear tooth.
After gear is cut, the cutter is withdrawn,
gear blank is rotated and cutter proceed to
cut another teeth. Process is continue untill
all teeth are cut.
 it is suitable for small volume production.

Characteristics of Production of gear teeth by form milling are:
Use of HSS form milling cutters.
 Use of ordinary milling cutters.
 Low production rate:
Low accuracy and surface finish.
 Inventory problem
End mill type cutters are used for teeth of large gears

GEAR GENERATION
 To obtain more accurate gears, the gear is generally generated using
a cutter, which is similar to the gear.
 The gears produced by generation are more accurate and the
manufacturing process is also fast.
• In gear generating, two machining processes are employed, shaping
and milling. There are several modifications of these processes used:
 Gear shaping with a pinion-shaped cutter.
 Gear shaping with a rack-shaped cutter.
 Milling with a hob (gear hobbing).
Gear generating is used for high production runs and for finishing cuts.

Shaping, planing and slotting:
 Both productivity and product quality are very low in this process. So
this process is used only for making one or few teeth when required
for repair and maintenance purpose.
 Planing machine is used for making teeth of large gears whereas
slotting, generally, for internal gears.

Gear shaping with a rack-shaped cutter
The rack type HSS cutter reciprocates to accomplish the machining
(cutting) while rolling type interaction with the gear blank like a pair of
rack and pinion.
Essential applications of this method
include:
 Moderate size straight and helical
external spur gears with high
accuracy and surface finish.
 Cutting the teeth of double helical
or herringbone gears with a
central recess (groove).
External gear teeth generation by rack type
cutter

Gear shaping with a pinion-shaped cutter
• It is similar to the rack type cutting process, except that, the linear
type rack cutter is replaced by a circular cutter.
• Both the cutter and the blank rotate as a pair in addition to the
reciprocation of the cutter.
 Gear shaping can cut external as
well as internal gears, splines and
continuous herringbone gears that
cannot be cut by other processes.
 Straight or helical teeth of both
external and internal spur gears
can be produced with high
accuracy and finish.

Gear hobbing
• Gear hobbing is a machining process in which
gear teeth are progressively generated by a
series of cuts with a helical cutting tool (hob).
• The gear hob is a formed tooth milling cutter
with helical teeth arranged like the thread on a
screw.
 All motions in hobbing are rotary, and the hob
and gear blank rotate continuously as in two
gears meshing each other until all teeth are cut.
 The work piece is mounted on a vertical axis
and rotates about its axis.
 Hobbing provides lesser accuracy and finish
and is used only for cutting straight or helical
teeth of external spur gears and worm wheels.

SURFACE FINISHING
PROCESSES:• To ensure reliable performance and prolonged service life.
• Influencing functional characteristics like wear resistance, fatigue
strength, corrosion resistance and power loss due to friction.
HONING
• Honing is a abrasive machining operation that produces a
precision surface on a metallic or nonmetallic surface by
scrubbing a number of abrasive stones against it along a
controlled path.
• Primarily used to improve the geometric form of a surface and
also improve dimensional accuracy.

 Performed by a honing tool called as hone which contains a set
of three to a dozen and more bonded abrasive sticks.
 The sticks are held against the work surface with controlled light
pressure.
 Examples include finishing bores of internal combustion engines,
bearings, hydraulic cylinders, and gun barrels.

LAPPING
• Lapping is a surface finishing process used on flat or cylindrical
surfaces.
• Lapping is the abrading of a surface by means of a lap.
The process is employed to get:
 Geometrically true surface.
 Extreme accuracy of dimension.
 Correction of minor imperfections in shape.
 Refinement of the surface finish, and
 Close fit between mating surfaces.

 The lapping tool is called a lap, which is
made of soft materials like copper, lead
or wood.
 the lap is pressed against the work and
moved back and forth over the surface.
 Accomplish the process with greater
consistency and efficiency.
 Lapping is performed either manually
or by machine.
Parallel lapping
Lapping is used to produce optical lenses,
bearing surfaces, gauges, and other parts
requiring very good finishes and extreme
accuracy.

SUPER FINISHING
 Super finishing is a micro finishing process
 produces a controlled surface condition on parts which is not
obtainable by any other method.
 Super finishing is a finishing operation similar to honing, but it
involves the use of a single abrasive stick.
 In super finishing, the finishing action terminates by itself when a
lubricant film is built up between the tool and work surface. Thus,
super finishing is capable only of improving the surface finish but
not dimensional accuracy.

Super finishing is generally used
for:
 Removing surface
fragmentation.
 Reducing surface stresses and
thus restoring surface integrity.
 Correcting inequalities in
geometry.
Produces a high wear resistant
surface on any objet which is
symmetrical.
In this The abrasive stone is slowly fed in radial direction while its
oscillation is imparted in the axial direction.

ABRASIVE PROCESSES: GRINDING
Abrasive processes consist of a variety of operations in which the
tool is made of an abrasive materials (small, nonmetallic hard particle
having sharp cutting edges and an irregular shape).
The most common examples are grinding (using wheels, known as
bonded abrasives), honing, and lapping.
Remove material in the form of tiny chips and produce very nice
surface finishes and dimensional accuracies.

TYPES OF GRINDING PROCESS
Grinding processes are generally classified based on the type of
surface produced.
1. Cylindrical grinding process.
2. Surface grinding process.
3. Centreless grinding process.
Grinding is most common form of abrasive process. It is material
removal process which engage the abrasive tool whose cutting
elements are grain of abrasive materials known as grit. These grits are
characterized by sharp cutting points, high hot hardness, chemical
stability and wear resistance .

CYLINDRICAL GRINDING PROCESS:
In this operation internal and external cylindrical surface of workpiece
are groung.
In External cylindrical grinding ( Center-type grinding) the work piece
and grinding wheel rotate and the workpiece reciprocate along its axis,
although for large work part the grinding wheel also reciprocates.
In Internal cylindrical grinding, a small wheel grind the inside diameter
of the workpart. The workpiece is held in a rotating chuck in the
headstock and the wheel rotate at high speed. In this operation, the
workpiece rotate and grinding wheel reciprocates.

Surface Grinding Process:
In Suface grinding, spindle position may be either horizontal or
vertical, and the relative motion of the workpiece is achieved either by
reciprocating the workpiece past the wheel or by rotating it.
The possible combination of spindle orientations and workpiece
motions yields four type of surface grinding process illustrated in figure.

Centre less grinding process :
 In this process the workpece is placed on
workrest blade between two wheels namely
grinding and regulating wheel, which are rotaing
in clockwise and workpiece rotate in counter
clockwise. Grinding wheel remove the material
from the w/p surface and regulating wheel
regulate the w/p.
 Center less : means workpiece is not held
between centres.
 Curved or cylindrical surfaces of long slender rod
which cannot be ground on cylindrical grinding.

Applications of grinding
 To remove small amount of metal from work pieces and then finish
to close tolerances.
 To obtain a better surface finish.
 To machine hard surfaces that cannot be machined by high-speed
steels.
 Grinding of tools and cutters and resharpening.
 Grinding of threads.
 Finishing of flat as well as cylindrical surface after stock removal.
 Slitting and parting.
 Descaling and deburring.

Types of abrasives:
Abrasives may be classified into two types:
1. Natural abrasives - Emery, Sandstone or Solid Quartz,
Corundum and Diamond.
2. Artificial abrasives - Aluminium Oxide (Al2O3), Silicon Carbide
(SiC), Artificial diamond, Boron Carbide(BC) and Cubic Boron Nitride
(CBN).
The abrasives that are generally used are:
•Aluminium Oxide. (Al2O3)
•Silicon Carbide. (SiC)
•Diamond.
•Cubic Boron Nitride. (CBN)

GRINDING WHEELS
• Grinding wheel consists of hard abrasive grains called grits, which
perform the cutting or material removal action.
 Diamond and cubic boron nitride grains are used to grind very
hard materials and are known as superabrasives wheels.
 The most commonly used abrasives in grinding wheels are
aluminum oxide and silicon carbide.
Interaction of grit with the work piece:
Grits do not have definite geometry unlike a cutting tool and the grit
rake angle may vary from +45 deg to -60 deg or more

 Grit with favorable geometry can produce chips in shear mode.
 Grits having large negative rake angle or rounded cutting edge
do not form chips but may rub or make a groove by ploughing
leading to lateral flow of the work piece material.

Reconditioning of grinding wheel:
Truing of grinding wheel
 Truing is the act of regenerating the required geometry on the
grinding wheel.
 Truing is also required on a new conventional wheel to ensure
concentricity.
Dressing of grinding wheel
 Dressing is the conditioning of the wheel surface which ensures
that grit cutting edges are exposed from the bond and thus able to
penetrate into the work piece material.
 Dressing produces micro-geometry which make grits sharp and
free cutting edge and also to remove any residue left.

* Truing and dressing are commonly combined into one operation for
conventional abrasive grinding wheels.
Dressing of super abrasive wheel
 Dressing of the super abrasive wheel is commonly done with soft
conventional abrasive stick, which relieves the bond without
affecting the super abrasive grits.
 Dressing depth is precisely controlled in micron level to obtain better
uniformity of grit height resulting in improvement of work piece
surface finish.

SELECTION OF GRINDING WHEEL
Selection of a proper grinding wheel is very important for getting the
best possible results in grinding process. The selection will depend
upon the following factors:
Constant factors
Physical and chemical properties of material to be ground.
Area of contact.
Amount and rate of stock to be removed.
Types of grinding machine.
Variable factors
Work speed.
Wheel speed.
Condition of the grinding machine.
Type of grinding (stock removal grinding or form finish grinding).

Grit size or grain size
It refers to the actual size of the abrasive particles.
The grain size is denoted by the number.
The grain size affects material removal rate and the surface quality of
work piece in grinding.
Large grit : Big grinding capacity, rough work piece surface.
Fine grit : Small grinding capacity, smooth work piece surface.

Grade:
 Grade or hardness indicates the strength with which the bonding
material holds the abrasive grains in the grinding wheel.
 The amount of force required to pull out a single bonded abrasive
grit.
*It does not refer to the hardness of the abrasive grain.
 Soft grade should be chosen for grinding hard material.
 During grinding of low strength soft material grit does not wear out
so quickly.
Different grades of grinding wheels

Structure / Concentration of wheels:
 This term denotes the spacing between the abrasive grains or in
other words the density of the wheel.
 Structure of the grinding wheel is designated by a number.
 The space between the grits also serves as pocket for holding
grinding fluid.
 Dense structured wheels are used for longer wheel life.
Two types of structure with their numbers

Bond:
It is an adhesive substance which holds the abrasive grains
together to form the grinding wheel.
Types of bonds - Bonds are classified into two types:
Organic - Resinoid, Rubber, Shellac & Oxychloride
Non - Organic - Metallic, Vitrified & Silicate
• Vitrified bond (V)
• Rubber bond (R)
• Silicate bond (S)
• Metal bond (M)
• Shellac bond (E)
• Oxychloride bond (O)
• Resinoid bond (B)
• Eloctroplated Bond

Designation of Grinding Wheel:

Polishing and Buffing Processes
• Polishing is a surface finishing process to a smooth and shining
surface.
• To improve surface finish by means of polishing wheel made of
fabrics or leather and rotating at high speed.
• The abrasive particles are glued to outer periphery of the polishing
wheel.
• Often accoplished manually.
• The grit size of the abrasive is: 20 – 80 for roughing, 90 -
120 for dry fining and 130 - 150 for fine finishing.
**The parts with irregular shapes, sharp corners, deep recesses and
sharp projections are difficult to polish.

BUFFING
 Buffing is a finishing operation similar to polishing, in which the
abrasive grains are not glued to the wheel but are contained in a
buffing compound that is pressed into the outer surface of the
buffing wheel while it rotates.
 Negligible amount of material is removed during buffing.
 It can be perform either by manually or automatically.
**Polishing is used to remove scratches and burrs and to smooth
rough surfaces while buffing is used to provide attractive surfaces
with high luster.
**The dimensional accuracy of the parts is not affected by polishing
and buffing operations.

BUFFING
Polishing

Broaching operation
Basic principles of broaching
• Broaching is a machining process for removal of a layer of material of
desired width and depth.
• Usually complete in single stroke by a slender rod or bar type cutter
having a series of cutting edges with gradually increased protrusion.
• Broaching enables remove the whole material in one stroke only by
the gradually rising teeth of the cutter called broach.
Basic principle of broaching

BROACHING MACHINES
 The basic function of a broaching machine is to provide a precise
linear motion of the tool past a stationary work position.
 Broaching machines are relatively simple as they have to move the
broach in a linear motion at a predefined speed and provide a means
for handling the broach automatically.

Classification of broaching machines
There are different types of broaching machines which are broadly
classified as:
According to purpose of use
 General purpose.
 Single purpose.
 Special purpose.
According to nature of work
 Internal broaching.
 External (surface) broaching.
According to configuration
 Horizontal.
 Vertical.
According to the type of drive
 Mechanical drive.
 Hydraulic drive.

Specification of broaching machines
Broaching machines are generally specified by:
 Type; horizontal, vertical etc.
 Maximum stroke length.
 Maximum working forces (pull or push).
 Maximum cutting velocity possible.
 Type of drive - Electro-Mechanical, Hydraulic etc.
 Power rating of electrical motor.
 Floor space required.

Problem statement:
A part is measuring 250 mm x 100 mm x 40 mm is to be
machined using a hydraulic shaper along its wide face (250
mm x 100 mm). Calculate the machining time taking
approach as well as over travel as 20 mm each. The cutting
speed as 5m/min, a machining allowance on either side of the
plate width is 3 mm and feed is 1 mm/stroke.

Machining operations
Solution
Given:
Approach and over-travel distance (l1 = l2) = 20 mm
Length of stroke = l+l1+l2 Where :
Length of stroke (L) = 250 + 20 +20 = 290 mm L = Length of stroke
Width of plate to be machined (W) = w + 2 * w0 l = Length of workpart
l1=Approach distance
W = 100 + 2 * 3 = 106 mm l2 = Overtravel distance
Feed (f) = 1 mm/stroke
Number of stroke required (Ns) = W/f = 106/1 = 106
Cutting speed (Vs) = 5 m/min. = 83.333 mm/sec

Machining operations
Machining time ( t ) to complete one stroke
* Cutting time for one stroke, total distance travel is twise the stroke length
(including the return distance)
t = (2 * L) / Vs
(2 X 290) / 83.33 = 6.96 sec.
Total machining time (T) = 6.96 X 106 = 737.76 sec. = 12.296 min.

machining and machine tools

More Related Content

What's hot

Similar to machining and machine tools

Recently uploaded

machining and machine tools