abrasive machining

2. Medisetty Harish
¾-A ;Roll-47
Mechanical Engineering
Gitam Institute of Technology

3. Basics
Types of Abrasive Machining Processes
• Grinding
• Honing
• Lapping
• Superfinishing
• Polishing
• Buffing
• Abrasive water jet machining
• Ultrasonic machining
content
Grinding Wheel
Parameters
• Properties Abrasive
material
• Grain size
• Wheel grade
• Wheel structure
• Bonding material
• Grinding chip
• Chip formation
• Testing of grinding wheel

5. An abrasive is a material, often a mineral, that is used to
shape or finish a workpiece through rubbing which leads to
part of the workpiece being worn away by friction. While
finishing a material often means polishing it to gain a
smooth, reflective surface, the process can also involve
roughening as in satin, matte or beaded finishes. In short,
the ceramics which are used to cut, grind and polish other
softer materials are known as abrasives.
Lets go the basics
What is an abrasive?
???

6. • Grinding
• Honing
• Lapping
• Superfinishing
• Polishing
• Buffing
• Abrasive water jet machining
• Ultrasonic machining
Types of Abrasive Machining
Processes

7. Grinding is an abrasive machining process that uses a
grinding wheel as the cutting tool.
A wide variety of machines are used for grinding:
• Hand-cranked knife-sharpening stones (grindstones)
• Handheld power tools such as angle grinders and die
grinders
• Various kinds of expensive industrial machine tools
called grinding machines
• Bench grinders
Grinding

8. HONING
• Honing is an abrasive machining process that produces
a precision surface on a metal workpiece by scrubbing
an abrasive grinding stone or grinding wheel against it
along a controlled path. Honing is primarily used to
improve the geometric form of a surface, but can also
improve the surface finish.
• Typical applications are the finishing of cylinders for
internal combustion engines, air bearing spindles and
gears. There are many types of hones, but all consist of
one or more abrasive stones that are held under
pressure against the surface they are working on.

9. LAPPING
• Lapping is a machining process in which two surfaces
are rubbed together with an abrasive between them, by
hand movement or using a machine.

10. SUPERFINISHIN
G
• Superfinishing, also known as micromachining,
microfinishing, and short-stroke honing, is a metalworking
process that improves surface finish and workpiece
geometry. This is achieved by removing just the thin
amorphous surface layer left by the last process with an
abrasive stone or tape; this layer is usually about 1 μm in
magnitude. Superfinishing, unlike polishing which
produces a mirror finish, creates a cross-hatch pattern on
the workpiece.

11. • Polishing is the process of creating a smooth and shiny surface
by rubbing it or by applying a chemical treatment, leaving a
clean surface with a significant specular reflection (still
limited by the index of refraction of the material according to
the Fresnel equations).In some materials (such as metals,
glasses, black or transparent stones), polishing is also able to
reduce diffuse reflection to minimal values.
Polishing

12. A water jet cutter, also known as a water jet , is
an industrial tool capable of cutting a wide
variety of materials using an extremely high-
pressure jet of water, or a mixture of water and
an abrasive substance. The term abrasive jet
refers specifically to the use of a mixture of water
and abrasive to cut hard materials such as metal,
stone or glass, while the terms pure waterjet and
water-only cutting refer to waterjet cutting
without the use of added abrasives, often used
for softer materials such as wood or rubber
Abrasive Water
jet

13. • Ultrasonic machining is a subtractive manufacturing process
that removes material from the surface of a part through
high frequency, low amplitude vibrations of a tool against the
material surface in the presence of fine abrasive particles.
The tool travels vertically or orthogonal to the surface of the
part at amplitudes of 0.05 to 0.125 mm (0.002 to 0.005
in.).The fine abrasive grains are mixed with water to form a
slurry that is distributed across the part and the tip of the
tool. Typical grain sizes of the abrasive material range from
100 to 1000, where smaller grains (higher grain number)
produce smoother surface finishes.
Ultrasonic
machining

14. • Properties of Abrasive material
• Grain size
• Wheel grade
• Wheel structure
• Bonding material
• Grinding chip
• Chip formation
• Testing of grinding wheel
Grinding Wheel
Parameters

15. General Properties
Hardness, wear resistance, toughness, friability
Properties of Abrasive
material

16. Grain size is expressed in terms of a SIEVE NUMBER, Sn which corresponds to the number of openings per linear inch.
The diameter of an abrasive grain is given by Dg =
0.6
𝑆𝑛
The larger the size of grains, more will be material removal, but surface finish will be worse.
Sieve No. Type of Grain
• 10-24 Coarse
• 30-60 Medium
• 70-180 Fine
• 220-600 Very Fine
Grain size

17. “Open” and “dense”
In what conditions
these structures be
provided?
Grinding Wheel
Structure

18. Indicates the strength of the binding material.
When the work material is hard, the grains wear out easily and the sharpness of the
cutting edges is quickly lost. This is known as WHEEL GLAZING.
To avoid this problem, a soft wheel should be used.
A-H – Soft Wheel
J-P – Medium Wheel
Q-Z – Hard Wheel
Wheel grade

19. • Vitrified Bond (V) – Strong and Rigid, commonly used.
• Resinoid (B) – Provides shock absorption and elasticity. They are
strong enough.
• Silicate (S) – Provides softness (grains dislodge quickly)
• Shellac (E) – Used for making thin but strong wheels possessing
some elasticity.
• Rubber Bonds (R) – For making flexible wheels.
• Metallic Bond (M) – For diamond wheels only.
Bonding
material

20. Grinding Chips
Fig: (a) Grinding chip being produced by a single abrasive grain. (A) chip, (B)
workpiece, (C) abrasive grain. Note the large negative rake angle of the grain. The
inscribed circle is 0.065mm in diameter. (b) Chip formation by an abrasive grain with a
wear flat. Note the negative rake angle of the grain and the small shear angle

21. • Chips in this process are formed by the same mechanism of compression and shear
as other machining processes.
• As the grains or abrasives become dull, the cutting forces increase. The increase in
the cutting force causes the grains to plow and rub rather than cut. As the plowing
and rubbing increases, the grains fracture at the cutting edge to revile a new cutting
edge.
Chip Formation

22. • The importance of the grit shape can be easily realized because it determines the grit
geometry e.g. rake and clearance angle.
• The grits do not have definite geometry and the grit rake angle may vary from +45 to -60
or more.
• Grit with favorable geometry can produce chip in shear mode. However, grits having large
negative rake angle or rounded cutting edge do not form chips but may rub or make a
groove by plowing leading to lateral flow of the workpiece material.

23. • Strength of a bond: pass a sintered metal carbide or diamond chisel over the wheel surface in such
a way that it tears a layer of grains from the bond.
• The forces required to separate a layer of grains from the bond are taken as a measure of the
strength of the bond.
Hardness
• a) Drill the wheel with a hard spade-type drill with a constant force. The depth of penetration in a
given time is a measure of wheel hardness.
• b) Use an air/abrasive jet to break the bond. The depth of penetration of the jet erosion in a
standard period of time is used to determine equivalent wheel hardness.
• c) Measure the resonant frequency of an isolated wheel after a sharp blow with a rubber hammer
and relate it to hardness
Testing of Grinding
Wheels

25. THANKYOU