Grinding operation

1. Abrasive Processes
(Grinding)

2. Grinding



Material cutting process which engages an abrasive tool
whose cutting elements are grains of abrasive material
known as grit.
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.

3. Grinding – Advantages &
Applications

Advantages




Dimensional accuracy
Good surface finish
Good form accuracy
Applications




Surface finishing
Descaling, deburring
Finishing of flat as well as cylindrical surface
Grinding of tools and cutters and resharpening of
the same.

4. Grinding Characteristics


Low material removal process capable of providing
both high accuracy and high finish
Advance Abrasive Machining – High Accuracy,
Surface Finish, Material removal rate

5. Grinding Wheel & Workpiece
interaction

6. Grinding Wheel & Workpiece
interaction

7. Grinding Wheels
Abrasive Particles
Bond

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.

8. Grinding Wheels
Alumina


Silicon Carbide

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.

9. Specifications of Grinding
Wheels

Geometrical specification



Wheel diameter,
Width and depth of rim
Bore diameter

10. Specifications of Grinding
Wheels

Compositional specification






Type of grit material
Grit size
Bond strength of the wheel, commonly known
as wheel hardness
Structure of the wheel denoting the porosity
i.e. the amount of inter grit spacing
Type of bond material
Other than these parameters, the wheel
manufacturer may add their own identification
code prefixing or suffixing (or both) the
standard code.

11. Specifications of Grinding
Wheels
Prefix
Grain
Type
Grain
Size
Aluminium Oxide (A)
Silicon Carbide (C)
10-24:
30-60:
80-180:
220-600:
Grade
Wheel
Structure
B: Dense
E: Normal
R: Open
S: Silicate
V: Vitrified
A-G: Soft
H-P: Medium
Q-Z: Hard
Coarse
Medium
Fine
Very Fine
Bond Type
1-4: Dense
H-P: Normal
Q-Z: Open
Suffix

12. Specifications of Grinding
Wheels

A 60 K 5 V




The letter ‘A’ denotes that the type of abrasive is
Aluminium oxide. In case of silicon carbide the letter ‘C’ is
used.
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.

13. Selection of Grinding Wheel

Selection of grinding wheel means
selection of composition of the grinding
wheel and this depends upon the following
factors:



Physical and chemical characteristics of the
work material
Grinding conditions
Type of grinding (stock removal grinding or
form finish grinding)

14. Selection of Grinding Wheel

Type of Abrasives



Aluminium oxide
 For high tensile strength materials e.g. steel,
malleable and wrought iron
Silicon Carbide
 For low tensile strength, brittle materials and
non-metallic materials
 Cast iron, soft non-ferrous metals, marble,
stone
Diamond
 For carbides and very hard materials

15. Selection of Grinding Wheel

Grit Size

Coarse grit
 Soft or ductile materials when fast grinding is
required

Fine grains
 Hard and brittle materials
 Good surface finish

16. Selection of Grinding Wheel

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.
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 can be avoided.
Rough grinding: Medium to Hard Grade
Precision grinding needs soft wheels
Higher the wheel speed, harder the grade required
Harder grades used when coolant applied

17. Selection of Grinding Wheel

Structure







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.
Open structure for soft and ductile materials
Surface grinding requires more open structure than
cylindrical grinding
Rough grinding requires open structure
Fine finish needs close structure

18. Selection of Grinding Wheel

Bond Material




Vitrified Bond (V)
 Wheel surface speed 2000 m/min
 Can not be used where mechanical impact or thermal
variations are like to occur.
Resin bond (B)
 For operations requiring very strong wheels
 Surface speed up to 3000 m/min
Shellac Bond (S)
 Grinding fine edges on cutters
 Making very large wheels
Rubber (R)
 High finish at 5000 m/min
 Thin wheels for wet cut-off operation.

19. Truing of Grinding Wheel




Truing is the act of regenerating the required
geometry on the grinding wheel, whether the
geometry is a special form or flat profile.
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.

20. Truing of Grinding Wheel
Truing of Grinding Wheel

21. 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
workpiece material.

Also, in dressing attempts are
made to splinter the abrasive
grains to make them sharp
and free cutting and also to
remove any residue left by
material being ground.

22. Dressing of Grinding Wheel

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.