Grinding is a chip-removal process that uses individual abrasive grains as cutting tools to precisely remove small amounts of material from a workpiece. It can produce very smooth finishes and accurate dimensions. Various grinding wheel types are used on different grinding machines to grind flat, cylindrical, internal, or complex surfaces. Process parameters like depth of cut, speed, and grinding fluid usage must be optimized to control grinding forces, temperature, and residual stresses without excessive wheel wear.

1. Lecture 7 - Grinding
R Ramful
Mechanical Processing of Materials
I. Grinding
II. Grinding Wheels
III. Grinding Parameter
IV. Grinding Operations & Machines
V. Grinding Fluids
VI. Grinding Chatter

2. The process of removing metal by the use of
grinding wheels. The work for grinding is
pressed against the grinding wheel which
rotates at a comparatively high speed and the
surplus metal is removed by abrasion.
R Ramful
Mechanical Processing of Materials
Grinding

3. The grinding process is mainly used for the following purposes;
(a) To remove a very small amount of metal from the workpiece
after rough finishing and heat treatment operations.
(b) To obtain better finish on the surface.
(c) For sharpening the cutting tools.
(d) For grinding threads to have better finish.
(e) For machining hard surfaces which are otherwise difficult to
be machined by high speed steel and carbide cutters.
R Ramful
Mechanical Processing of Materials
Grinding

4. Grinding
Grinding is a chip-removal process that uses an
individual abrasive grain as the cutting tool.
R Ramful
Mechanical Processing of Materials

5. Grinding
The major differences between the action of an abrasive grain and that
of a single-point cutting tool can be summarized as follows;
• The individual abrasive grains have irregular shapes and are spaced
randomly along the periphery of the wheel.
• The average rake angle of the grains is highly negative, typically -600.
Consequently, grinding chips undergo much larger plastic
deformation than they do in other machining processes.
• Surface speeds (i.e., cutting speeds) in grinding are very high,
typically 20 to 30 m/s, and may be as high as 150 m/s in high-speed
grinding using specially designed and manufactured wheels.
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Mechanical Processing of Materials

6. Grinding Wheels
A very wide variety of
types and sizes of abrasive
wheels is made today.
Some of the more
commonly used types of
grinding wheels for
conventional abrasives are
shown below.
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Mechanical Processing of Materials

7. Grinding Forces
A knowledge of grinding forces is essential for;
• Estimating power requirements.
• Designing grinding machines and work-holding fixtures and
devices.
• Determining the deflections that the workpiece, as well as the
grinding machine itself, may undergo. (Note that, unless
accounted for, deflections adversely affect dimensional
accuracy).
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Mechanical Processing of Materials

8. Specific Energy
The energy dissipated in producing a grinding chip
consists of the energy required for the following
actions:
• Chip formation
• Friction, caused by rubbing of the grain along the
workpiece surface.
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Mechanical Processing of Materials

9. Specific Energy
Approximate Specific-energy Requirements for Surface
Grinding.
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Mechanical Processing of Materials

10. Grinding Parameter
The grinding process and its parameters can be observed best in
the surface-grinding operation.
A straight grinding wheel with diameter D removes a layer of
metal at a depth d (wheel depth of cut).
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Mechanical Processing of Materials

11. Grinding Parameter
Material-removal rate (MRR).
MRR = dwv
Where d is the depth of cut, w is the width of cut
and v is the feed rate of the workpiece.
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Mechanical Processing of Materials

12. Grinding Parameter
Power
Power = (u)(MRR)
Where u is the specific energy, and MRR is the
material-removal rate in mm3/min.
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13. Grinding Parameter
Power
Power = Tw
Where T is the Torque and w is the rotational
speed of the wheel in radians per minute (w =
2πN).
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Mechanical Processing of Materials

14. Grinding Parameter
Torque
T = Fc D/2
Where Fc is the cutting force (the force
tangential to the wheel), D is the wheel
diameter.
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Mechanical Processing of Materials

15. Temperature
Temperature rise in grinding is an important consideration
because;
• It can adversely affect the surface properties of the
workpiece, including metallurgical changes.
• Can cause residual stresses on the workpiece.
• Temperature gradients in the workpiece cause distortions due
to thermal expansion and contraction of the workipece
surface, thus making it difficult to control dimensional
accuracy.
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Mechanical Processing of Materials

16. Temperature
Peak temperatures during grinding can reach 16000C. However,
the time involved in producing a chip is extremely short
(microseconds), so the chip produced may or may not melt.
Because the chips carry away much of the heat generated, only a
fraction of the heat produced in grinding is conducted to the
workpiece.
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Mechanical Processing of Materials

17. Sparks
The sparks produced when grinding metals are actually
chips that glow, due to the exothermic (heat-producing)
reaction of the hot chips with oxygen in the
atmosphere.
Sparks do not occur during grinding in an oxygen-free
environment or when the workpiece material does not
readily oxidize at elevated temperatures.
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Mechanical Processing of Materials

18. Tempering & Buring
An excessive temperature rise in grinding can cause tempering and
softening of the workpiece surface. Process variables must be
selected carefully in order to avoid excessive temperature rise.
The use of grinding fluids is an effective means of controlling
temperature.
Excessive temperature during grinding may burn the workpiece
surface. A burn is characterized by a bluish colour on ground steel
surfaces – an indication that high temperature caused oxidation.
It can be detected by etching and metallurgical techniques.
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Mechanical Processing of Materials

19. Heat Checking
High temperatures in grinding may cause the
workpiece surface to develop cracks; this
condition is known as heat checking. The cracks
usually are perpendicular to the grinding
direction.
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Mechanical Processing of Materials

20. Residual Stresses
 Temperature gradients within the workpiece
during grinding are primarily responsible for
residual stresses.
 Residual stresses usually can be reduced by
lowering wheel speed and increasing
workpiece speed (called low-stress grinding).
Softer grade wheels also may be used.
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Mechanical Processing of Materials

21. Grinding-wheel Wear
Similar to wear on cutting tools, grinding-wheel wear is an
important consideration because it adversely affects the shape and
dimensional accuracy of ground surfaces. Grinding wheel wear is
caused by;
1. Attritious grain wear – the cutting edge of an originally sharp grain
become dull and develop a wear flat.
2. Grain fracture – because abrasive grains are brittle, their fracture
characteristics in grinding are important.
3. Bond fracture – the strength of the bond (grade) is a significant
parameter in grinding.
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Mechanical Processing of Materials

22. Dressing, Truing, and Shaping of Grinding Wheels
Dressing is the process of;
• Conditioning worn grains on the surface of a grinding wheel
by producing sharp new edges on grains so that they cut more
effectively.
• Truing, which is producing a true circle on a wheel that has
become out of round.
Dressing is necessary when excessive attritious wear dulls the
wheel.
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Mechanical Processing of Materials

23. Grindability of Materials
Grindability is a general indicator of how easy it is to grind
a material and includes considerations such as;
 the quality of the surface produced
 surface finish
 surface integrity
 wheel wear
 cycle time
 and overall economics of the operation
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Mechanical Processing of Materials

24. Grinding Operations and Machines
The selection of a grinding process and machine
for a particular application depends on;
 the workpiece shape and features
 size
 ease of fixturing
 production rate required
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Mechanical Processing of Materials

25. Surface Grinding
 One of the most common operations, generally
involving the grinding of flat surfaces.
 Do the same operation as the planers, shapers or
milling machines but with more precision.
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26. Surface Grinding
Reciprocating table, horizontal spindle type surface grinder.
The work reciprocates under the wheel and the wheel down feed
determines the depth of cut.
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27. Surface Grinding
Rotary table, horizontal spindle type surface grinder.
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28. Cylindrical Grinders
 The centre type cylindrical grinders are intended primarily for
grinding plain cylindrical parts.
 Can also be used for grinding contoured cylinders, tapers,
faces, fillets and even cams and crank shafts.
 The workpiece in cylindrical grinding is held between centers
or in a chuck, or it is mounted on a faceplate in the headstock
of the grinder. For straight cylindrical surfaces, the axes of
rotation of the wheel and workpiece are parallel.
 The wheel and workpiece are each driven by separate motors
and at different speeds.
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Mechanical Processing of Materials

29. Cylindrical Grinders
Cylindrical (centre type) grinder
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30. Cylindrical Grinders
Thread grinding is done on cylindrical grinders using specially
dressed wheels matching the shape of the threads.
Diagram
Thread grinding by (a) traverse and (b) plunge grinding.
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Mechanical Processing of Materials

31. Internal Grinding
A small wheel is used to
grind the inside diameter
of the part. The
workpiece is held in a
rotating chuck and the
wheel rotates at 30 000
rpm or higher.
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Mechanical Processing of Materials

32. Centreless Grinding
A high-production process for continuously grinding cylindrical
surfaces in which the workpiece is supported not by centers
(hence the term ‘centerless’) or chucks, but by a blade.
Typical parts made by centreless grinding are:
 Roller bearings
 Piston pins
 Engine valves
 camshafts
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Mechanical Processing of Materials

33. Centreless Grinding
The 3 different methods by which centreless grinding can be done on
different types of work are:
i. Through feed grinding
ii. Infeed or plunge-cut grinding
iii. End-feed grinding
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Mechanical Processing of Materials

34. Other Grinding Operations
• Universal tool and cutter grinders - used for grinding single-
point or multipoint tools and cutters, including drills.
• Tool-post grinders - self-contained units and usually attached
to the tool post of a lathe.
• Portable grinders – driven pneumatically, electrically, or with a
flexible shaft connected to an electric motor or a gasoline
engine.
They are used for operations such as grinding off weld beads
and cutting-off operations using thin abrasive disks.
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Mechanical Processing of Materials

35. Grinding Fluids
The use of a fluid is important because it:
1. Reduces temperature rise in the workpiece
2. Improves part surface finish and dimensional accuracy
3. Improves the efficiency of the operation by reducing
wheel wear and loading and by lowering power
consumption.
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Mechanical Processing of Materials

36. Grinding Chatter
Chatter is particularly important in grinding operations because
it adversely affects surface finish and wheel performance.
The important factors in controlling chatter are the stiffness of
the grinding machine, the stiffness or work-holding devices, and
damping.
General guidelines have been established to reduce the
tendency for chatter in grinding, especially;
a) Using soft-grade wheels
b) Dressing the wheel frequently
c) Changing dressing techniques
d) Reducing the material-removal rate
e) Supporting the workpiece rigidly.
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Mechanical Processing of Materials

37. 1. Produces extremely smooth finish due to small
cutting edges on the grinding wheel.
2. Can finish work to very accurate dimensions in a
short time.
3. The only method for cutting hardened steel.
4. A very small pressure is required in this process,
thus permitting its use on very light work.
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Mechanical Processing of Materials
Advantages of Grinding over other Cutting Processes

38. Lecture 7 Summary
I. Grinding
II. Grinding Wheels
III. Grinding Parameter
IV. Grinding Operations & Machines
V. Grinding Fluids
VI. Grinding Chatter
BIBLIOGRAPHY:
1. Kalpakjian S, Schmid SR. Manufacturing Engineering and Technology, Sixth ed. Singapore:
Prentice Hall; 2010.
Copyright © 2014 by Pearson Education South Asia Pte Ltd. All rights reserved. PEARSON
2. Gupta JK, Khurmi RS. Manufacturing Processes (Workshop Technology), Seventh ed. India:
S.Chand; 1981.
R Ramful
Mechanical Processing of Materials