machining and machine tool Unit 3&4

11
Machining and Machine toolsPresented By,
Alakshendra Pratap Singh
Asst. Prof.,
Mechanical Engineering Department,
Jodhpur Institute of Engineering and Technology,
jodhpur, Rajasthan

22
Cutting Fluid and Lubricants:
• Before discovery of HSS, cutting was carried out at low speed and water served
as coolant.
Function of the Cutting Fluid:
• Cools the tool and w/p.
• Provides lubrication.
• Flush away the chips.
Advantages of using cutting fluid:
• Improves tool life.
• Permits use of higher cutting speeds and larger metal removal rates.
• Lubrication helps reduce coefficient of friction and thus reduces cutting force.
• Improves surface finish by protecting newly generated surface from oxidation
and corrosion.
• Reduces formation of built up edge.

33
Requirements of cutting fluid:
• Should have good wetting characteristics.
• Should not gum moving parts .
• Should have good anti wear properties.
• Should not foam easily.
• Should not deteriorate in storage.
• Should have high specific heat, high thermal conductivity and high heat
vaporization.
• Should be odorless and transparent.
• Should have high flash point.
• Should prevent rusting.
•Should have low viscosity.
• Should be non poisonous.
• Should have low cost, and easily available.

44
Types of cutting fluid:
Gaseous Fluids:
• Applied through nozzle.
• Have poor cooling, poor lubrication poor anti seizure properties.
• Simple air or sub zero cooled air may be used.
• Other gases which can be used are CO2, Argon and oil mist.
Liquid Type:
Water:
• Plain water and NaOH.
• Water containing alkali or antiseptic.
• Free availability and cheapness are its advantages.
• Has high conductivity and specific heat.
Disadvantages:
• Can cause rusting.
• Has high surface tension thus does not spread over.

55
Oil based cutting fluids:
• Also referred as straight oil.
• May be mineral oil or fatty oils.
• Straight mineral oils possess lower viscosity and have good wetting and
penetrating power. They are fit for light duty operations on non ferrous metals.
• Fatty oils are used for heavy duty machining work. Because of their tendency to
decay and breed bacteria they are not preferred.
• Blended Fatty – Mineral oil: are obtained by mixing 10 to 30 % of fatty oil with
mineral oil of different viscosity. Its advantages are
1. Cost of fatty oil reduced.
2. Improved surface finish obtained with non ferrous alloys and steel.
3. Penetrating and wetting characteristics improved.
4. Little amount of fat is sufficient to act as lubricant.
5. Blended oil do not have any undesirable effects.
• Sulphurised Blend of Fatty Mineral Oils: Sulfur increases cooling and lubricating
characteristics by combining with fatty oils. These are used majorly on multi
spindle automats, where they act as hydraulic fluid also along with their action of
cooling an lubricating.

66
Water miscible cutting fluids:
Emulsions of soluble oils:
• Soluble oil may be mineral or fatty oil containing emulsifier like soap.
• Emulsions are product which when mixed with water forms milky colloidal solution.
• Emulsions possess good cooling characteristics due to abundance of water in them.
• For higher MRR this type of cutting fluid should be used.
Chemical Coolants:
• Pure coolants: contain no lubricant and are made of water softeners and rust
inhibitors.
• Coolants: have mild lubricity, contain water softeners, rust inhibitors and wetting
agents
• Lubricating Coolants: contain water softeners, rust inhibitors, wetting agents and
chemical lubricants and Cl, S, or P additives.
• They give high MRR, last longer, do not clog pipes
• They have inhibitors like Triethanol amine and NaNO3 for rust prevention and
Sodium Molybdate for corrosion prevention.
• Phosphates and Borates for water softening.
• Soap and wetting agents for lubrication and reducing surface tension.

7
Economics of Metal Cutting:
• Objective is to produce a component of required dimensions
and surface finish at the minimum possible cost.
• Parameters governing cost are speed, feed, depth of cut,
tool and work material, tool geometry and cutting edge.
•These constraints are pulling each other in opposite direction.
•Thus an optimized condition b/w these constraints is to be
attained.
Machining Cost:
1. Non Productive Cost (Cn)
2. Cutting Cost (Cc)
3. Tool Cost (Ct)

88Variation of cost and time per piece with cutting speed

99
Non Productive Time (Tn) Components:
1. Initial set up time (Ts min) (Occurring once per batch)
2. Loading and unloading time (Tl min) (Occurring once per piece)
3. Tool advance & withdrawal time (Ta min) (Occurring once per piece)
4. Tool removing and replacing time (Tr min) (Occurring once per tool regrind)
5. Idle time (Ti min)
Let ‘Nb’ be the number of components in a batch.
‘Ng’ be the number of components produced b/w each tool regrind; then Tn will be:
Tn = Ts + (Tl +Ta)*Nb + Tr(Nb/Ng) + Ti
Now let Cr be the cost including :
1. Labor cost (cl)
2. Overhead cost rate (co)
3. Depreciation cost (cd); Thus Cr becomes:
Cr = cl + co + cd
And non productive cost Cn will be:
Cn = Cr*Tn

1010
Cutting Cost (Cc):
It can be determined by multiplying total cutting time with cost rate Cr.
Thus;
Cc = Cr*Tc*Nb
Where Tc is cutting cost per component.
Tool Cost (Ct):
Includes initial tool cost Ci and tool regrinding cost Cg. Thus;
Ct = (Ci/Rg +Cg)*Nb/Ng
Here Rg is number of regrinds possible.
Concluding, machine cost per batch (Cb) will be;
Cb = Cn + Cc + Ct
And machining cost per piece (Cp) will be;
Cp = Cb/Nb

11
Machine Tools
A machine tool
is a power
driven device
where energy is
utilized to
deform
material to
attain required
shape size or to
process a
product to
desired
accuracy by
removing
excess
material.

12
Lathe
• Oldest known machine tool.
• Henry Mauldsley developed sliding carriage and screw cutting lathe in 1800 AD
• It is a general purpose machine tool used in production an repair work since it
permits large variety of operations on it.
Working Principle of Lathe:
• Lathe removes undesired material from a rotating w/p in from of chips with the
help of a tool of harder material than the w/p, traversed either across or deep in
the w/p.
• W/p should be held securely & rigidly on the machine tool.
• It is principally used to produce cylindrical surfaces and plan surfaces, at right
angle to axis of rotation.
Specification of a Lathe: Lathe is generally designated by:
• Swing: Largest work dia that can be swung over the bed.
• Distance b/w head and tail stock centre.
• Sometimes by the swing and length of the bed. Sometimes by the maximum dia of
bar which can be accommodated for Bar automatic Lathe..

14
Types of Lathe:
1.Speed Lathe:
• Referred so owing to its high speed of headstock spindle.
• Has headstock, tailstock and a tool post, no gear box or lead screw arrangement
and carriage.
• Cone pulley used for speed variation.
• Used in wood turning, metal spinning and polishing operations.
2.Engine or Centre Lathe:
• Referred so because earlier they were driven by separate engine or from
central engine with overhead belts and shafts.
• Stepped cone pulley or geared head are used for varying speed of lathe spindle.
• Tailstock is available for holding work b/w centers and accommodates tools
drills, taps etc.
• Cutting tools can be controlled either by hand or power.
• A carriage and tool post for supporting tool and feeding tool in cross and
longitudinal directions with reference to lathe axis is used.

15
3.Turret Lathe:
• Production M/c used to perform large number of operations simultaneously.
• Usually accommodates 6 tools for different operations, which are used by
indexing the turret.
4.Capstan Lathe:
• Similar to Turret Lathe & incorporate side moving on auxiliary slide & can be
clamped in any position.
• Used for fast production of small parts owing to its light weight & short stroke.
5.Tool Room Lathe:
• Modern engine lathe equipped with necessary accessories for accurate tool room
work.
• It is geared head driven m/c with good range in spindle speeds and feeds.
• Used for production of small tools, dies, gauges, etc.
6.Gap Bed Lathe:
• A gap on bed near headstock to accommodate jobs with flanges exist.
• A removable part is provided in bed, which can be removed or inserted.
7. Bench Lathe 8. Hollow spindle Lathe. 9. Vertical Turret Lathe.

16
Construction of Lathe Parts:
1.The Bed:
• Its upper surface is either scraped or ground & guiding & sliding surfaces are provided.
• It has two heavy metal slides running lengthwise, with ways or V’s formed on them
• It is supported on two broad box section columns and is made of cast iron.
• The inner guide ways support the tailstock and external ones support saddle.
• Headstock is permanently fixed to the bed
• Carriage can be traversed to & b/w headstock & tailstock either manually or by the
power.
• Lathe bed is made of high grade special cast iron having high vibration damping qualities.
• Top surface of bed is machined accurately.
• While designing lathe bed due consideration to factors like rigidity, alignment and
accuracy should be given.

17
2.Headstock:
• Supports main spindle in the bearings and aligns it property.
• It incorporates necessary transmission mechanism with speed changing levers.
• Live centre is rigidly held by taper in main hollow spindle.
• Centerline of headstock is parallel to guide ways in horizontal and vertical plane.
• Headstock also have self contained clutch and brake mechanism.
3.Main Spindle:
• It is a hollow cylindrical shaft such that long slender jobs can pass through it.
• Spindle end facing tailstock is called spindle nose.
• Spindle nose has a Morse taper hole for self locking and threads on outside.
• Morse taper accommodates collet chuck and threaded portion holds faceplate.
• While designing Morse taper due consideration to cutting tool thrust should be given.
• Anti friction bearing is used in headstock & spindle.
• Spindle is made up of high tensile steel, suitably hardened and tempered and is supported
in roller bearing.

18
4.Tailstock:
5.Carriage:
• It is located b/w headstock and tailstock and fitted on the bed.
• Can be locked on any position on the bed.
• Can be moved manually or by power.
• Consists of saddle (lower part of compound rest) & apron and slides over guide
ways.
• It has form of letter ‘H’ and carries cross slide, compound rest and tool post.
• Provides three movements to the tool
1. Longitudinal Feed: Through carriage movement.
2. Cross Feed: Through cross slide movement.
3. Angular Speed: Through top slide movement.
6.Saddle:
• Made of ‘H’ Shaped casting having “V’ and flat guide on one side for mounting on
lathe bed guide ways.

19
7.Compound Rest:
• Supports tool post and cutting tool.
• Can be swiveled on cross slide to any right angle in horizontal plane.
9.Tool Post:
• Holds various cutting tools
• Holder body rests on wedge which fits into a
concave shaped ring having rocker.
• This permits height of cutting edge to be adjusted.. Tool Post
8.Cross slide:
• Has a female dovetail on one side and assembled on
top of saddle.
• Top surface of cross slide is provided with ‘T’ slots
to enable fixing of rear tool post or coolant
attachment.

21
Operations on Lathe:
• Cylindrical and Conical Jobs.
• Flat Surfaces.
• Grooving
• Drilling and Reaming.
• Counter sinking and counter boring.
• Knurling, parting, chamfering.
• Thread cutting.
• Milling, slotting, grinding Etc.

22
Turret and Capstan Lathe:
•The turret lathe is a form of metalworking lathe that is used for repetitive
production of duplicate parts,.
• These parts by the nature of their cutting process are usually interchangeable.
• It evolved from earlier lathes with the addition of the turret.
• Turret is an index able tool holder that allows multiple cutting operations to be
performed, each with a different cutting tool, in easy, rapid succession.
• With no need for the operator to perform setup tasks in between, such as
installing or uninstalling tools, nor to control the tool path.
•The latter is due to the tool path being controlled by the machine, either in jig-
like fashion, via the mechanical limits placed on it by the turret's slide and stops,
or via electronically-directed servomechanisms for computer numerical control
(CNC) lathes.

23
Schematic configuration of capstan lathe.

24
Differences between capstan and turret lathes:
• Turret lathes are relatively more robust and heavy duty machines
• Capstan lathes generally deal with short or long rod type blanks held in collet,
whereas turret lathes mostly work on chucking type jobs held in the quick
acting chucks
• In capstan lathe, the turret travels with limited stroke length within a saddle
type guide block, called auxiliary bed, which is clamped on the main bed as
indicated in Figure, whereas in turret lathe, the heavy turret being mounted on
the saddle which directly slides with larger stroke length on the main bed as
indicated in Figure.
• One additional guide rod or pilot bar is provided on the headstock of the
turret lathes as shown in Figure, to ensure rigid axial travel of the turret head
• External screw threads are cut in capstan lathe, if required, using a self
opening die being mounted in one face of the turret, whereas in turret lathes
external threads are generally cut, if required, by a single point or multipoint
chasing tool being mounted on the front slide and moved by a short leadscrew
and a swing type half nut.

25
Schematic configuration of turret lathe.

26
Tool layout:
• Schematically showing the type and configuration of cutting tools and their
location and mounting.
• To draw tool layout for hexagonal headed mild steel bolt (below drawing).
• Hot rolled hexagonal mild steel bar of standard size is selected.

27
Elementary machining operations identified as follows:
Facing Centering Front Chamfering (1)
Chamfering bolt head (3) Drilling Grooving (forming)
Rough turning (1) – to make the bar circular from hexagon
Rough turning (2) – to reduce diameter to 12 mm
Finish turning – to φ10 mm
Thread cutting Initial parting Parting
Listed elementary operations can be combined and
sequenced as follows:
1. Rough turning (1), Initial parting, Chamfering (3).
2. Rough turning (2), drilling and centering for the next job.
3. Finish turning.
4. Spot facing and front chamfering.
5. Grooving and centre chamfering.
6. Thread cutting.
7. Parting.

28
S.S.
NoNo
OperationOperation ToolTool ToolTool
PositionPosition
NN SS LL CFCF
1. Stop stock & bar feed Stop HT (1) - - - - N
2. Rough Turning (1)
Initial parting
Chamfering
Turning Tool
Formed
Parting tool
HT (2) 640 0.10
0.05
30
6
Y
Y
3. Rough parting (2)
Drilling (φ6),
centering
Turning Tool
Drill bit
HT (3) 640 0.10 50 Y
4. Finish turning Turning tool HT (4) 640 0.05 25 Y
5. Spot facing
Chamfering (1)
Compound
tool
HT(5) 640 0.05 5 Y
6. Grooving
Chamfering (2)
Forming tool FS 640 0.05 10 Y

29
7. Threading Threading Die HT (6) 56 2 20 Y
8. Parting Parting Tool VS 640 0.05 12 Y
N – spindle speed; S – Feed; L – Tool Travel; CF – Cutting Fluid; HT – Hexagonal
Turret; RS – Rear Slide; FS - Front Slide; VS – Vertical Slide;

30
Shaper:
• A shaper is a type of machine tool that uses linear relative motion between the
work piece and a single-point cutting tool to machine a linear tool path
•Uses SPCT to machine flat or plane surfaces in hz, vertical and angular plane.
• Ram imparts reciprocating motion to the tool with the help of the ram on the
shaper head, while w/p is fixed on the table vice.

31
Principal Parts of Shaper:
1.Power Transmission:
• An electric motor with V belt drive is used to transmit power to the machine.
• A gear train is used to provide different speed.
• Speed change lever is used to shift he gears.
2. Ram:
• This is the reciprocating member which carries shaper head in front.
• Cutting tool is mounted on this shaper head, which provides it vertical as well as
angular movement.
• Ram slides on accurately machined guide ways on the top of the column.
• Gets drive from QRM.
3. Shaper Head:
• It is clamped in front of the ram.
• Consists of tool slide, tool post and clapper box.
• Can be swiveled to any angle for getting angular cuts on the job.

32
4. Column:
• Is rigid hollow structure made up of CI.
• Gives support to ram and gets supported by the base.
• A cross rail is mounted on column which gives drive to the table.
• On of the walls is made hollow to enable viewing and maintaining the driving QRM.
5. Base:
• Supports the complete machine.
• Bolted to the floor with the help of foundation bolts.
6. Cross Rail:
• Is box type structure over which saddle slides horizontally.
7. Saddle and Table:
• Table is bolted on table & is capable of moving in horizontal & vertical directions.
• Table is provided with T slots for clamping fixtures.

34
The Quick Return Mechanism:
A
B
B1
O
CC1
β
α

35
• Cutting operation is only in the forward stroke.
• While the return stroke is idle.
• Power is consumed in both the strokes.
•Thus it becomes necessary to reduce the non cutting or return stroke to save
power and time.
• QRM enables this.
• A crank slotter mechanism is used to achieve this.
• AB is the crank rotating at the center A.
• The slotter B has both rotating (about centre A) and sliding motion (along O-C).
• Link CO, is fixed at O and can rotate about it.
• Link Co has slot in which slotter B can slide freely.
• On rotation of crank AB about A, link CO oscillates about O b/w extreme OC1 and
OC2.
• Oscillation motion of CO makes ram to reciprocate through link CD.
• Ram stroke length is proportional to crank length AB.
• Forward motion is from AB to AB1 and return stroke from AB1 to AB during its
anti clockwise motion.

38
BASIC PRINCIPLES OF
BROACHINING…….
Broaching is a machining process for removal of a
layer of material of desired width and depth usually in
one stroke by a slender rod or bar type cutter having a
series of cutting edges with gradually increased
protrusion as indicated in Fig.
In shaping, attaining full depth requires a number of
strokes to remove the material in thin layers step – by
– step by gradually in feeding the single point tool
Whereas, broaching enables remove the whole
material in one stroke only by the gradually rising teeth
of the cutter called broach. The amount of tooth rise
between the successive teeth of the broach is
equivalent to the in feed given in shaping.

Construction And Operation Of
Broaching
Construction of broaching tools….
•Configuration
•Material and
•Cutting edge geometry
41

Configuration of broaching
tool
Both pull and push type broaches are made in the
form of slender rods or bars of varying section having
along its length one or more rows of cutting teeth
with increasing height (and width occasionally). Push
type broaches are subjected to compressive load
and hence are made shorter in length to avoid
buckling.
•The general configuration of pull type broaches,
which are widely used for enlarging and finishing
preformed holes, is schematically shown in Fig.
42

• The essential elements of the broach (Fig.)
are :
 Pull end for engaging the broach in the machine.
 Neck of shorter diameter and length, where the broach is
allowed to fail, if at all, under overloading
 Front pilot for initial locating the broach in the hole
 Roughing and finishing teeth for metal removal
 Finishing and burnishing teeth
 Rear pilot and follower rest or retriever
44

Material of broach
•Being a cutting tool, broaches are also made of materials
having the usual cutting tool material properties, i.e., high
strength, hardness, toughness and good heat and wear
resistance.
•For ease of manufacture and re-sharpening the complex
shape and cutting edges, broaches are mostly made of
HSS (high speed steel). To enhance cutting speed,
productivity and product quality, now-a-days cemented
carbide segments (assembled) or replaceable inserts are
also used specially.
45

Broaching Machines
• Horizontal broaching machine
• Horizontal broaching machines, typically shown in Fig.,
are the most versatile in application and performance
and hence are most widely employed for various types of
production. These are used for internal broaching but
external broaching work are also possible. The
horizontal broaching machines are usually hydraulically
driven and occupies large floor space.
47

• Vertical broaching machine
49

High production broaching
machines
50

Unit-4
GRINDING
Grinding is the most common form of abrasive machining.
It is a material cutting process which engages an abrasive
tool whose cutting elements are grains of abrasive material
known as grit. These grits are characterized by sharp
cutting points, high hot hardness, chemical stability and
wear resistance. The grits are held together by a suitable
bonding material to give shape of an abrasive tool.
51

Cutting action of abrasive grains
52

Major advantages and
applications of grinding
 dimensional accuracy
 good surface finish
 good form and locational accuracy
 applicable to both hardened and unhardened material
53

Applications
• surface finishing
• slitting and parting
• stock removal (abrasive milling) finishing of
flat as well as cylindrical surface
• grinding of tools and cutters and
resharpening of the same.
54

Grinding wheel and work piece
intraction
55

Grinding Machines
• Conventional grinding machines can be
broadly classified as:
(a) Surface grinding machine
(b) Cylindrical grinding machine
(c) Internal grinding machine
(d) Tool and cutter grinding machine
56

Surface grinding machine:
• Horizontal spindle and reciprocating table
• Vertical spindle and reciprocating table
• Horizontal spindle and rotary table
• Vertical spindle and rotary table
57

Horizontal spindle reciprocating
table grinder
• A: rotation of grinding wheel
• B: reciprocation of worktable
• C: transverse feed
• D: down feed
58
A
C
B
D

Vertical spindle reciprocating
table grinder
59

Horizontal spindle rotary table
grinder
60

Vertical spindle rotary table
grinder
61

2.Cylindrical grinding machine
62

External centreless grinder
• This grinding machine is a production machine in which
out side diameter of the workpiece is ground. The
workpiece is not held between centres but by a work
support blade. It is rotated by means of a regulating
wheel and ground by the grinding wheel.
• In through-feed centreless grinding, the regulating wheel
revolving at a much lower surface speed than grinding
wheel controls the rotation and longitudinal motion of the
workpiece. The regulating wheel is kept slightly inclined
to the axis of the grinding wheel and the workpiece is fed
longitudinally as shown in Fig
63

Grinding wheels
• Grinding wheel consists of hard abrasive grains called
grits, which perform the cutting or material removal, held
in the weak bonding matrix. A grinding wheel commonly
identified by the type of the abrasive material used. The
conventional wheels include aluminium oxide and silicon
carbide wheels while diamond and cBN (cubic boron
nitride) wheels fall in the category of superabrasive
wheel.
66

Specification of grinding wheel
• A grinding wheel requires two types of
specification
• (a) Geometrical specification
• (b) Compositional specification
68

1.Geometrical specification
• This is decided by the type of grinding machine and the
grinding operation to be performed in the workpiece.
This specification mainly includes wheel diameter, width
and depth of rim and the bore diameter. The wheel
diameter, for example can be as high as 400mm in high
efficiency grinding or as small as less than 1mm in
internal grinding.
69

Standard wheel configuration for conventional grinding
wheels
70

2.Compositional specifications
1) the type of grit material
2) the grit size
3) the bond strength of the wheel, commonly known as
wheel hardness
4) the structure of the wheel denoting the porosity i.e. the
amount of inter grit spacing
5) the type of bond material
6) other than these parameters, the wheel manufacturer
may add their own identification code prefixing or
suffixing (or both) the standard code.
71

2.1 Marking system for
conventional grinding wheel
• The standard marking system for conventional abrasive
wheel can be as follows:
• 51 A 60 K 5 V 05, where
• The number ‘51’ is manufacturer’s identification number
indicating exact kind of abrasive used.
• • The letter ‘A’ denotes that the type of abrasive is
aluminium oxide. In case of silicon carbide the letter ‘C’
is used.
73

51 A 60 K 5 V 05
•The number ‘60’ specifies the average grit size in inch mesh. For a very large
size grit this number may be as small as 6 where as for a very fine grit the
designated number may be as high as 600.
•The letter ‘K’ denotes the hardness of the wheel, which means the amount of
force required to pull out a single bonded abrasive grit by bond fracture. The
letter symbol can range between ‘A’ and ‘Z’, ‘A’ denoting the softest grade and
‘Z’ denoting the hardest one.
•The number ‘5’ denotes the structure or porosity of the wheel. This number
can assume any value between 1 to 20, ‘1’ indicating high porosity and ‘20’
indicating low porosity.
•The letter code ‘V’ means that the bond material used is vitrified. The codes for
other bond materials used in conventional abrasive wheels are B (resinoid), BF
(resinoid reinforced), E(shellac), O(oxychloride), R(rubber), RF (rubber
reinforced), S(silicate)
•The number ‘05’ is a wheel manufacturer’s identifier. 74

Selection of grinding wheels
1. Type of abrasives
•Aluminium oxide
•Silicon carbide
•Diamond
Natural diamond
Mono crystalline diamond
Polycrystalline diamond
•cBN (cubic boron nitride)
75

2.Grit size
•The grain size affects material removal rate and the
surface quality of workpiece in grinding.
•Large grit- big grinding capacity, rough workpiece surface
•Fine grit- small grinding capacity, smooth workpiece
surface
76

3.Grade
•The worn out grit must pull out from the bond and make
room for fresh sharp grit in order to avoid excessive rise of
grinding force and temperature. Therefore, a soft grade
should be chosen for grinding hard material. On the other
hand, during grinding of low strength soft material grit does
not wear out so quickly. Therefore, the grit can be held with
strong bond so that premature grit dislodgement (forced
removal) can be avoided
77

4.Structure / concentration
•The structure should be open for grinding wheels engaged
in high material removal to provide chip accommodation
space. The space between the grits also serves as pocket
for holding grinding fluid. On the other hand dense
structured wheels are used for longer wheel life, for holding
precision forms and profiles.
78

5.Bond
•vitrified bond - high stock removal
•Resin bond - heavy duty grinding
•Shellac bond - fine finish of rolls
•Oxy chloride bond - disc grinding operation
•Rubber bond - wet cut-off operation
•Metal bond - large stock removal & form accuracy
•Electroplated bond - making small diameter wheel ,
abrasive milling
•Brazed bond - very high material removal either with
diamond or cBN wheel
79

80
vitrified bond
Vitrified bond is suitable for high stock removal even
at dry condition. It can also be safely used in wet
grinding. It can not be used where mechanical impact
or thermal variations are like to occur.
Resin bond
Conventional abrasive resin bonded wheels are
widely used for heavy duty grinding because of their
ability to withstand shock load. This bond is also
known for its vibration absorbing characteristics and
finds its use with diamond and cBN in grinding of
cemented carbide and steel respectively.

• Shellac bond
• At one time this bond was used for flexible cut off
wheels. At present use of shellac bond is limited to
grinding wheels engaged in fine finish of rolls.
• Oxychloride bond
• It is less common type bond, but still can be used in disc
grinding operation. It is used under dry condition.
81

• Rubber bond
• Its principal use is in thin wheels for wet cut-off
operation. Rubber bond was once popular for finish
grinding on bearings and cutting tools.
• Metal bond
• Metal bond is extensively used with superabrasive
wheels. Extremely high toughness of metal bonded
wheels makes these very effective in those applications
where form accuracy as well as large stock removal is
desired.
82

• Electroplated bond
• This bond allows large (30-40%) crystal exposure above
the bond without need of any truing or dressing. This
bond is specially used for making small diameter wheel,
form wheel and thin superabrasive wheels. Presently it is
the only bond for making wheels for abrasive milling and
ultra high speed grinding.
• Brazed bond
• This is relatively a recent development, allows crystal
exposure as high 60-80%. In addition grit spacing can be
precisely controlled. This bond is particularly suitable for
very high material removal either with diamond or cBN
wheel. The bond strength is much greater than provided
by electroplated bond. This bond is expected to replace
electroplated bond in many applications.
83

Truing and dressing of grinding
wheel
• Truing
• Truing is the act of regenerating the required geometry
on the grinding wheel, whether the geometry is a special
form or flat profile. Therefore, truing produces the macro-
geometry of the grinding wheel.
• Truing is also required on a new conventional wheel to
ensure concentricity with specific mounting system. In
practice the effective macro-geometry of a grinding
wheel is of vital importance and accuracy of the finished
workpiece is directly related to effective wheel geometry.
84

Dressing
• When the sharpness of grinding wheel becomes dull
because of glazing and loading, dulled grains and chips
are removed (crushed or fallen) with a proper dressing
tool to make sharp cutting edges and simultaneously,
make recesses for chips by properly extruding to grain
cutting edges. Thus, these operations are for the
dressing
• 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.
86

• Dressing therefore produces micro-geometry. The
structure of micro-geometry of grinding wheel determine
its cutting ability with a wheel of given composition.
Dressing can substantially influence the condition of the
grinding tool.
• Truing and dressing are commonly combined into one
operation for conventional abrasive grinding wheels, but
are usually two distinctly separate operation for super
abrasive wheel.
• Dressing of superabrasive wheel
• Dressing of the super abrasive wheel is commonly done
with soft conventional abrasive vitrified stick, which
relieves the bond without affecting the super abrasive
grits.
87

• Honing
• Honing is a finishing operation used to improve the form
tolerance of an internal cylindrical surface – in particular, it
is used to improve the cylindricity. The honing tool is a
metal bar holding a set of grinding stones arranged in a
circular pattern. The tool brushes along the cylindrical
part surface by rotating, and moving up-and-down along
its axis. You can identify a honed surface by looking for
the helical cross-hatched scratch marks on the part
surface
• A honing stone is similar to a grinding wheel.
• Any abrasive material may be used to create a honing
stone, but the most commonly used are corundum,
silicon carbide, cubic boron nitride, or diamond.
89

Lapping
• Lapping is a finishing operation. The lapping tool is made
of metal, leather, or cloth, impregnated with very fine
abrasive particles. For preparing the surface of silicon
wafers, lapping operations use a flat metal disc that
rotates a small distance above the part. The gap is filled
with a slurry containing fine abrasive grains. The rotation
of the disc causes the slurry to flow relative to the part
surface, resulting in very fine surface finish. This process
gives dimensional tolerances of ≥ 0.5μm, and surface
finish of up to 0.1 μm.
93

(a) Schematic illustration of the lapping process.
(b) Production lapping on flat surfaces.
(c) Production lapping on cylindrical surfaces.
95

Polishing and buffing
• Polishing
• Polishing is a finishing operation to improve the surface
finish by means of a polishing wheel made of fabrics or
leather and rotating at high speed. The abrasive grains
are glued to the outside periphery of the polishing wheel.
Polishing operations are often accomplished manually
96

• Buffing
• It is a finishing operation similar to polishing, in which
abrasive grains are not glued to the wheel but are
contained in a buffing compound that is pressed into the
outside surface of the buffing wheel while it rotates. As in
polishing, the abrasive particles must be periodically
replenished. As in polishing, buffing is usually done
manually, although machines have been designed to
perform the process automatically.
• Polishing is used to remove scratches and burrs and to
smooth rough surfaces while butting is used to provide
attractive surfaces with high luster.
97

machining and machine tool Unit 3&4

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machining and machine tool Unit 3&4