The document discusses abrasive processes for material removal. Grinding is the most important abrasive process where abrasive particles in a rotating wheel remove material from a workpiece. Other abrasive processes include honing, lapping, and superfinishing which use bonded abrasive sticks or abrasive particles in a fluid to create very fine surface finishes on complex geometries. Grinding can be done on surfaces or cylinders and is often used as a finishing process to achieve close tolerances and surface finishes not possible with other machining operations.

1. GRINDING AND
OTHER ABRASIVE PROCESSES
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2. Material Removal Processes
A family of shaping operations, the common feature of which
is removal of material from a starting workpart so the
remaining part has the desired geometry.
Machining – material
removal by a sharp
cutting tool, e.g., turning,
milling, drilling.
Material Removal
Nontraditional processes various energy forms other than
sharp cutting tool to remove
material, e.g. electrochemical and
thermal energy processes.
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Abrasive
processes –
material removal by
hard, abrasive
particles, e.g.,
grinding.

3. Machining Processes
Traditional Chip Removal
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Turning
Milling
Drilling
Boring
Reaming
Shaping
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Sawing
Broaching
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Planing
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Grinding
Honing
Lapping
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Nontraditional Machining
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Ultrasonic
Electrical Discharge
Electro-arc
Optical Lasers
Electrochemical
Chem-milling
Abrasive Jet Cutting
Electron Beam Machining
Plasma Arc Machining

4. Abrasive Machining
 Material removal by action of hard, abrasive particles
usually in the form of a bonded wheel
 Generally used as finishing operations after part
geometry has been established by conventional
machining
 Grinding is most important abrasive process
 Other abrasive processes: honing, lapping,
superfinishing, polishing, and buffing
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5. Why Abrasive Processes are Important
 Can be used on all types of materials
 Some can produce extremely fine surface finishes,
to 0.025 m (1 -in)
 Some can hold dimensions to extremely close
tolerances
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6. Grinding
Material removal process in which abrasive
particles are contained in a wheel that
operates at very high surface speeds.
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7. Wheel Structure
The grinding wheel:
is usually disk-shaped and precisely balanced for high
rotational speeds.
Consists of abrasive particles and bonding material.
• Abrasive particles accomplish cutting.
• Bonding material holds particles in place and
establishes shape and structure of wheel.
Figure 25.1 Typical structure of a grinding wheel.
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8. Abrasive Material Properties
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High hardness
Wear resistance
Toughness
Friability - capacity to fracture when cutting edge dulls,
so a new sharp edge is exposed
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9. Traditional Abrasive Materials
Aluminum oxide
(Al2O3) - most common
abrasive
Silicon carbide
(SiC) - harder than
Al2O3 but not as tough
Used to grind steel
and other ferrous
high-strength alloys
Used on aluminum,
brass, stainless steel,
some cast irons and
certain ceramics
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10. Hardness of Abrasive Materials
Abrasive material
Aluminum oxide
Silicon carbide
Cubic boron nitride
Diamond (synthetic)
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Knoop hardness
2100
2500
5000
7000

11. Surface Finish
Most grinding is performed to achieve good surface
finish
Best surface finish is achieved by:
 Small grain sizes
 Higher wheel speeds
 Denser wheel structure = more grits per wheel
area
Two main categories of grinding:
 Surface grinding
 Cylindrical grinding
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12. Four Types of Surface Grinding
Figure 25.7 (a) Horizontal spindle with reciprocating worktable,
(b) horizontal spindle with rotating worktable, (c) vertical spindle
with reciprocating worktable, (d) vertical spindle with rotating
worktable.
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13. Surface Grinder
Figure 25.8 Surface grinder with horizontal spindle and
reciprocating worktable (most common grinder type).
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14. Cylindrical Grinding
Figure 25.9 Two types of cylindrical grinding: (a)
external, and (b) internal.
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15. Other Abrasive Processes
 Honing
 Lapping
 Superfinishing
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16. Honing
Abrasive process performed
by a set of bonded
abrasive sticks using a
combination of rotational
and oscillatory motions.
Creates a characteristic
cross-hatched surface that
retains lubrication.
Grit sizes range between 30 and
600.
Figure 25.16 The honing
process: (a) the honing tool
used for internal bore surface.
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Surface finishes of 0.12 m (5 -in)
or better.

17. Honing
Common application is to finish the bores
of internal combustion engines.
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18. Lapping
Uses fluid suspension of very small abrasive particles
between workpiece and lap (tool).
Lapping compound - fluid with abrasives, general
appearance of a chalky paste.
Applications: optical lenses, metallic bearing surfaces,
gages.
Figure 25.17 The lapping process in lens-making.
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19. Superfinishing
Similar to honing - uses bonded abrasive stick
pressed against surface and reciprocating
motion
Differences with honing:
* Shorter strokes
* Higher frequencies
* Lower pressures
between tool and
surface
* Smaller grit sizes
Figure 25.18 Superfinishing on
an external cylindrical surface.
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