2. INTRODUCTION TO GRINDING PROCESS
• It is the only economical method of cutting hard
material like hardened steel.
• It produces very smooth surface , suitable for bearing
surface.
• Surface pressure is minimum in grinding. It is suitable
for light work,which will spring away from the cutting
tool in the other machining processes.
3. Grinding principle
Grinding is a material removal
process by abrasive particles
contained in a bonded grinding wheel
rotating at very high surface speeds.
The rotating grinding wheel consists
of many cutting teeth ( abrasive
particles ) and the work is fed relative
to the rotating grinding wheel to
accomplish material removal.
Due to action of rubbing or friction
between the abrasive particles and work
piece, material is removed.
6. 1. Rough / Non precision Grinders
1. Bench / Pedestal / Floor grinders
2. Swing frame grinders
3. Portable
4. Belt grinders
2. Precision Grinders
(i) Cylindrical grinders:
a. Plain cylindrical grinders
b. Universal cylindrical grinders
c. Centre less grinders
6
Classification of grinding machine
7. (ii) Surface grinders :
a. Reciprocating table
I. Horizontal spindle
II. Vertical spindle
b. Rotary table
I. Horizontal spindle
I. Vertical spindle
(iii) Internal grinders:
a. Plain internal grinders
b. Universal internal grinders
c. Planetary internal grinders
d. Centre less internal grinders
(iv) Special grinding machines
7
8. These types of grinders are mostly used for Snagging and Off-hand grinding of
different materials and cutting tools in tool room, foundries, general workshops, etc
can be easily bolted on a bench at convenient height..
9. The floor or pedestal grinders are nothing but a bench grinder which can be
mounted on a steel stand or pedestal of suitable height.
10. The motor revolves the wheel and the frame is swung by the operator about its
suspension point.
This is used for snagging, particularly for casting that are too large for the
operator to hold up to the wheel.
11.
12.
13. Cylindrical grinding involves holding of the workpiece rigidly on centres, in a
chuck or in a suitable holding fixture, rotating it about its axis and feeding a
revolving grinding wheel against the same.
14. Plain cylindrical grinder
• Various motion required to
grinding
• The machine is similar to center
lathe.
• The work piece held between
head stock & tail stock.
• Disc type grinding wheel
perform grinding operation.
17. Center-less grinder
• Work piece rests on a work-rest blade and is
backed by a second wheel called as regulating
wheel.
• Grinding wheel pushes the work piece down
the work-rest blade against the regulating
wheel.
• Center less grinding is the method when the work-piece is supported by a blade instead
of by center or chuck.
• Two wheel used : larger wheel for grinding smaller wheel for regulate the axial
movement of the work-piece.
• It is used to grind curved surface work piece which are long and slender.
18.
19.
20.
21.
22. How Centerless Grinders Work
• Work supported on work rest blade equipped with suitable guides
• Rotation of grinding wheel forces work onto rest blade against regulating
wheel
• Regulating wheel controls speed of work and longitudinal feed movement
– Set at slight angle (angle controls rate of feed)
• Centers fixed – diameter of work controlled by distance between wheels and
height of work rest blade
83-22
24. 1) Thru-Feed Centerless Grinding
• Consists of feeding work
between grinding and
regulating wheels
• Work fed by regulating wheel
past grinding wheel
• Speed of feeding work
controlled by speed and angle
of regulating wheel
83-24
25. 2) Infeed Centerless Grinding
• Form of plunge grinding
• Used when work being ground has shoulder or head
• Several diameters of workpiece may be finished
simultaneously
• Work rest blade and regulating wheel clamped in fixed
relation to each other
83-25
26. 3 ) Endfeed Centerless Grinding
• Used for grinding
tapered work
• Grinding wheel,
regulating wheel,
and work rest
remain in fixed
position
• Work fed in from
front up to fixed stop
• Grinding wheel and
regulating wheel
often dressed to
required taper
83-26
27. Advantages of Centerless Grinding
• No limit to length of work being ground
• No axial thrust on workpiece
– Permits grinding of long w/P that would be distorted by other methods
• Less stock required on workpiece for truing purposes
• Less wheel wear and less grinding time required because there is less stock
to be removed
83-27
Disadvantages of Centreless Grinding :
Workpiece having multiple diameters is difficult to handle.
In hollow workpiece, there is no certainty that the outside diameter will be
concentric with the inside diameter.
28. Surface grinders :
• The operation of surface grinders is similar to shaper, planer or
milling machines but with more precision.
• Basically, surface grinders are used to machine flat surfaces and
irregular, regular or tapered surfaces.
a. Reciprocating table
I. Horizontal spindle II. Vertical spindle
b. Rotary table
I. Horizontal spindle II. Vertical spindle
(iii) Internal grinders:
a. Plain internal grinders
b. Universal internal grinders
c. Planetary internal grinders
d. Centre less internal grinders
(iv) Special grinding machines
28
29. Reciprocating table
The horizontal spindle machine
carries a straight wheel
whereas; vertical spindle
machine carries a cup type wheel.
The cutting action is carried
by the periphery of the straight
wheel in case of horizontal spindle
machine,
whereas on the revolving edge
of the cup wheel in case of
vertical spindle machine.
30. • On these machines, the workpiece is generally held on a magnetic chuck.
• These machines are mostly used for grinding flat surfaces.
• In case of vertical spindle grinder, the table along with the workpiece
reciprocates under the wheel and wheel covers all or major portion of the width
of the job.
31. Rotary table
ln these machines the w/p are held on a magnetic chuck and arranged in a circle.
In both of the machines, the direction of rotation of wheel and table is opposite.
In horizontal spindle grinder, the cross feed is given by the horizontal movement
of the wheel spindle whereas in vertical spindle grinder it is by sliding a table on a
slide.
32. Internal grinding
Used for grinding internal surfaces of cylindrical, tapered, formed holes , etc.
Blind or through holes can be ground by internal grinders.
1) Plain Internal Grinders :
It carries an individually driven wheel head mounted on a cross-slide.
To hold the w/p, the work head carries either a chuck or face plate, or sometimes
fixture attached to the work head spindle.
For grinding the tapered holes, the warhead can be swiveled.
33. 2)Universal internal grinders
Universal internal grinder carries all the similar features of plain internal grinder.
In addition its work head is mounted on a cross-slide which provides a cross-feed to
the work head.
Another important feature of universal grinders is that, its work head can be
swivelled through 90.
Universal grinders are used to grind cylindrical and tapered holes, flat surfaces,
convex and concave surfaces etc.
34. 3)Planetary internal grinders
In planetary grinding, workpiece is mounted on a slide and remains stationary.
The wheel head carries a mechanism, because of which the axis of the rotating
grinding wheel travels along a circular path around the hole axis.
The longitudinal traversing movement can be obtained By reciprocating
movement of the grinding wheel & By moving the slide (forward and backward), on
which the workpiece is mounted.
Planetary grinders are used to grind holes in large, irregular shaped and
heard workpiece.
35. 4)Centreless internal grinders
The principle is almost similar to external cylindrical grinding. Only the method
of supporting the workpiece is different.
In an internal centreless grinding the workpiece is supported between three rolls
i.e.pressure roll, supporting ro11 and a regulating wheel
36. All the three rolls, rotate in the same direction whereas, workpiece and the
grinding wheel rotate in the opposite direction
The grinding wheel remains in contact with the internal surface of the workpiece at
the horizontal centre line of the regulating wheel.
It ensures a uniform wall thickness of the workpiece and hence, concentncitv of
the grounded internal hole with the external surface of the workpiece.
For loading and unloading of the workpiece, the pressure roll can be swung to a side.
63. CONSTRUCTION OF A GRINDING WHEEL
• In order make the grinding wheel suitable for
different work situations, the features such as
abrasive, grain size, grade, structure and bonding
materials can be varied.
• A grinding wheel consists of an abrasive that does the
cutting, and a bond that holds the abrasive particles
together
72. GRAIN SIZE
• The number indicating the size of the grit represents
the number of openings in the sieve used to size the
grain. The larger the grit size number , the finer the
grit.
73. GRADE
• Grade indicates the strength of the bond and,
therefore, the `hardness` of the wheel.
• In a hard wheel the bond is strong and it securely
anchor the grit in place, and therefore, reduces the
rate of wear.
• In a soft wheel, the bond is weak and the grit is easily
detached resulting in a high rate of wear.
74. STRUCTURE
• This indicates the amount of bond present between the
individual abrasive grains, and the closeness of the
individual grain to each other. An open structured
wheel will cut more freely. That is, it will remove more
metal. In a given time and produce less heat.
75. BOND
• Vitrified bond (V)
• Silicate bond (S)
• Shellac bond (E)
• Rubber bond (R)
• Resinoid bond (B)
76. Vitrified
• Essentially a Glass ,a vitrified bond is also
called a ceramic bond. It is the most common
and widely used bond. The raw materials used
consist of feldspar ( crystalline mineral) and
clay. They are mixed with the abrasives
,moistened and molded under pressure into the
shape of grinding wheels.
77. • They are fired slowly, up to a temperature of
aboutb1250Deg C to fuse the glass and
develop structural strength.
• They are then cooled and finished.
• Vitrified bonded wheels are strong, stiff,porus
and resistant to oils, acids and water.
78. Resinoid
• They are made of thermosetting resins .They
are also called organic wheels. They are cured
after mixing with phenolic resins at 175 deg,c.
• They are more flexible than vitrified wheels,
79. Rubber
• They are more flexible and manufactured by
mixing with crude rubber ,sulphur and the
abrasive grains together rolling into sheets and
then heated and vulcanized.
• They are mainly used for cutting.
80. Grinding ratio
• G = Volume of material removed / Volume of
wheel wear
• G = 2 to 200
81.
82. • Grinding MRR = dwv
• d = depth of cut
• W= width of cut
• v = feed rate of the workpiece
• Power = u x MRR
• u = specific cutting energy
83. • Torque = Fc x D/2 x 2∏x wheel speed.
• POWER= Torque x rotational speed
• Rotational speed = 2 ∏N
84. STANDARD SHAPES OF GRINDING WHEELS
• Straight wheel
• Cylinder
• Tapered
• Recessed one side
• Straight cup
• Recessed both sides
• Flaring cup
• Dish
• Saucer
• Mounted wheels
85. SPECIFICATION OF GRINDING WHEELS
• Standard wheel markings
• Diameter of the wheel
• Bore diameter of the wheel
• Thickness of the wheel
• Type of the wheel
86. SELECTION OF GRINDING WHEEL
For grinding a job the right grinding wheel is to be
selected. The selection of a grinding wheel will depend
on the following factors.
• Material to be ground
• Amount of stock to be removed
• Finish required
• Area of contact
• Wheel speed
• Work speed
• Personal factor
• Method of cooling
87. GRINDING WHEEL DRESSING &TRUING
• Dressing refers to the removing of clogs and blunt
abrasive grains from the surface of the grinding wheel.
Dressing exposes the cutting edges which restore the
correct cutting action of the wheel. Dressing is done on
a glazed or loaded wheel to recondition it.
• Truing refers to the shaping of the wheel to make it
run concentric with the axis. When a new grinding
wheel is mounted, it must be trued before use to
remove the run out.
88. GLAZING & LOADING
• When the surface of a grinding wheel develops a
smooth and shining appearance, it is said to be glazed.
This indicate the abrasive particles on the wheel face
are not sharp. These are worked down to bond level.
• When soft materials like aluminium, copper, lead, etc.
are ground the metal particles get clogged between
the abrasive particles. This condition is called loading.
90. TYPE OF GRINDING
WHEEL
SPEED
m/sec.
Rough grinding wheel with vitrified bond 25
Rough grinding wheels with resinoid bond 45
Surface grinding wheels with vitrified bond 20-25
Internal grinding wheels with vitrified bond 20-35
Centreless grinding wheels with vitrified bond 30-80
Cylindrical grinding wheels with vitrified bond 30-35
Cutting off wheels with resinoid bond 45-80
Hand grinding of tools 20-25
Automatic grinding of tools 25-35
Hand grinding of carbide tools 18-25
91. WORK SPEED
CLASS OF WORK ROUGH
GRIND m/min.
FINISH GRIND
m/min.
Soft steel 10-20 20-25
Hardened steel 25-30 30-40
Cast iron 35-55 45-65
Aluminium and fine
brass
50-65 50-65
92. DEPTH OF CUT
• It is the thickness of the material removed in
surface grinding for one cut.
• Depth of cut in grinding depend on the:
• Cutting load
• Power of the machine
• Finish required
93. SURFACE GRINDING MACHINE
• It is precision grinding machine to produce flat
surface on a workpiece. It is a more economical
and more practical method of accurately finishing
flat surface than filling and scraping.
95. SPECIFICATION OF A SURFACE GRINDER
• Maximum dia. of the wheel that can be held on
the spindle.
• Maximum size of the job that can be
ground.(length*width*height)(150*150*400).
• The type of drive of the work
table:hydraulic/electrical.
98. WORK HOLDING DEVICES
The work holding devices used in grinding are:
• Magnetic chuck
• Vice
• Angle plates
• `V`blocks
• clamps
99. MAGNETIC CHUCK
Magnetic chucks are of two types
• Electromagnetic chuck
• Permanent magnetic chuck
The magnetic power of the electro magnetic chuck
can be varied according to the size of the work.
But not so in the case of a permanent magnetic
chuck.
100. TILTING TYPE VICE
• A tilting vice is used to hold the workpiece while
grinding angular surfaces. If required the tilting
base can be removed and it can be mounted on the
magnetic chuck as a plain vice.
102. CYLINDRICAL GRINDERS
• Cylindrical grinders are used to grind the external
of internal surface of a cylindrical workpiece. By
cylindrical grinding the diameter of a workpiece
can be maintained to a close tolerance (up to
0.0025 mm), and a high quality surface finish can
be obtained (up to N4).
104. GRINDING ALLOWANCE
• Machine parts are processed in different machine
such as lathes, shaping machines, etc. in such a
way that their final dimension have some stock
left, which is finished during the grinding
operation. The amount of this stock left is called
the `grinding` allowance.
105. IMPORTANT FACTORE OF GRINDING
ALLOWANCE
• Hardness of material to be ground
• Whether the part has to be heat – treated
• Case depth of case hardened workpiece
• Grint and grade of grinding wheel
• Whether grinding is done wet or dry grinding
109. Diamond wheel on steels and CBN on carbides?
• A diamond wheel is specifically used for carbides,
plastics and other synthetic materials. It will not grind
steel well at all.
• CBN wheels should only be used on steels.
• There is a hybrid grit available that will grind both;
However, it is a compromise in wheel life and grind-
ability. But in cases where you must grind both materials
at the same time, it can be a real time saver.
114. Grinding wheel selection
• Abrasive : Generally, Aluminium Oxide
abrasives are well suited for steels and ferrous
metals, while Silicon Carbide abrasives are
ideal for grinding cast iron, non-ferrous metals
and non-metallic materials.
115. Grinding wheel selection
• Grit Size : A relatively fine grit-size works best
on hard and brittle material. A coarser grit
capable of taking heavier cuts can be used
advantageously on soft and ductile materials
that are readily penetratable.
116. • On hard materials the increased number of
cutting points, on the face of a moderately fine
grit wheel (Fig. 1) will remove stock faster
than the fewer cutting points
presented by a coarser wheel (Fig. 2).
The larger abrasive grains in a coarser grit
wheel can not penetrate as deeply into the hard
work-piece without burning it.
117.
118.
119. The second factor in selecting the
correct wheel is the amount of stock to
be removed and the finish required. These affect the
choice of grit size and bond.
120. Grit-size : As a rule, coarser grit is selected for
fast-cutting action and fine grit where a high
finish is required.
121. Bond : Vitrified bonded wheels are generally
used for fast-cutting action and commercial
finish. Resinoid, Rubber and Shellac bonded
wheels produce the highest finish.
122.
123. Grade : The severity of the grinding operation also
influences the .grade.. Hard grades provide durable
wheels for rough grinding such as snagging, while
medium and soft grade wheels are generally used for
less severe precision grinding operations
124. • STRUCTURE : Wheel structure refers to the relative spacing
of the abrasives in the wheel. In addition to the abrasives and
bond the grinding wheel contain air gaps or pores.
• Pg + Pb +Pp = 1
• Pg = Proportion of grains.
• Pb = Proportion of bond
• Pp = Proportion of pores
130. • P =Ft ( Vs ± Vw)+FVfn.+ FaVfa
• Ft= Tangential force
• Fn= Normal Force
• Fa = Axial Force
• Vs = Wheel Speed
• Vw= Work Speed
• Vfn= Normal feed
• Vfa = Axial feed
136. Advantages of Centerless Grinding
• Due to shorter loading times, actual grinding time is decreased
compared with other methods of grinding. Once the centerless
grinder has been properly set-up for a particular run, no further
adjustment or additional set-ups are needed as opposed to
centertype (cylindrical) grinding.
• This alone offers substantial savings. The workpiece is under
constant, rigid support while in the grinding mode, making it
feasible to take heavier cuts and grind fine pins, rods and
wires.
137. • When grinding easily distorted workpieces, the
centerless grinder is most advantageous because of
its lack of axial thrust. Automatic feeding offers
continuous production of large quantities of smaller
size workpieces.
• Centerless machines are designed for simplicity
which in itself cuts down on machine maintenance
138. Methods of Centerless Grinding
• Depending on the shape and condition of the
work piece to be ground, the machine setup of
the grinding wheel, the regulating wheel, work
support blade and feeding mechanism will
vary. The four basic methods of centerless
grinding in use are through feed, infeed, end
feed and infeed through feed combination.
139. Through feed grinding
• Throughfeed grinding is used to grind straight, cylindrical
workpieces which have no interfering projections. This
method is a continuous production operation. To provide
continuous, automatic throughfeed, the axis of the
regulating wheel is tilted relative to the axis of the
grinding wheel.
• The feed rate is controlled by the speed, angle and
diameter of the regulating wheel. The parts are guided
into and out of the machine in a straight line. If this line is
not perfectly straight, taper and/or concavity conditions
can result on the workpiece.
140. Infeed Grinding
• Infeed (Plunge) Grinding is used to grind workpieces
which have projections or shoulders, multiple diameters
or other irregular shapes which preclude the use of
throughfeed grinding. The wheels are opened to allow for
the part to be loaded (from above if multi-diameters).
Most often the part is fed along with the blade and
regulating wheel to a set finish position against a
stationary grinding wheel.
141. • The grinding wheel must have sufficient width
to cover the entire surface being ground. In
many cases, the desired shape is cut into the
face of the wheel either by single point
diamond trueing or by diamond roll crush
trueing. Diamond roll trueing is used on
intricate shapes which are difficult to form
with a single point diamond
142. Endfeed Grinding
• Endfeed Grinding is used principally on
tapered work. The grinding wheel, regulating
wheel and work support blade are set at a fixed
relationship to each other. All three are shaped
to meet the desired taper of the part to be
ground. The work is fed from the front of the
machine and is ground until it reaches an end
stop.
143. Infeed-Throughfeed Combination Grinding
• Infeed-throughfeed combination is for parts which are
more conveniently ground in one pass, but have too large
an amount of stock for the conventional throughfeed
method. It is also for grinding the smaller diameter of
two diameter parts, where the portion to be ground
exceeds the width of the grinding wheel.
144. Work Support Blades
• The blade is an essential and important
component in centerless grinding. The
workpiece is held in contact with the grinding
and regulating wheels by an adjustable blade
made of various materials.
• The selection of the proper blade will affect
the roundness and quality of the surface finish
obtainable.
145. • Four types of support blades in general use are:
aluminum bronze, chilled iron, high speed
steel and tungsten carbide. For the majority of
centerless grinding operations, the 30° angular
top support blade is used.
146. • It should be noted however, that as the
diameter of the workpiece to be ground
increases, the angle of the blade decreases. The
length of the blade is determined by the width
of the wheels and thickness should be slightly
less than the diameter of the workpiece.
147. • Work ground below the centerline may come
out of round as well as work ground too high
above the centerline. Long lengths generally
have to run lower than short pieces due to the
possibility of warpage or whip in the rods.
Shims are used to adjust the height of the
blade.
