Honing is an abrasive machining process used to improve the geometric form and surface texture of metal workpieces, applicable in finishing cylinders and gears. It utilizes honing stones, which are made of irregularly shaped abrasive grains, and provides a precision surface that other methods cannot achieve. Similar processes include lapping and electroplating, the latter using electric current to deposit metal coatings for improved surface properties.

1. Honing
• Honing is an abrasive machining process that produces a
precision surface on a metal work piece by scrubbing an
abrasive stone against it along a controlled path.
• Honing is primarily used to improve the geometric form of a
surface, but may also improve the surface texture.
The surface of a honed
workpiece

2. • 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.
• In terms of sharpening knives, a honing steel does not actually
hone knives, but simply realigns the metal along the edge.
• Other similar processes are lapping and superfinishing.
Honing tools

3. Honing stones
• Honing uses a special tool, called a honing stone or a hone, to
achieve a precision surface.
• The hone is composed of abrasive grains that are bound
together with an adhesive.
• Generally, honing grains are irregularly shaped and about 10 to
50 micrometers in diameter (300 to 1,500 mesh grit).
• Smaller grain sizes produce a smoother surface on the
workpiece.
• A honing stone is similar to a grinding wheel in many ways, but
honing stones are usually more friable so that they conform to
the shape of the workpiece as they wear in.
• To counteract their friability, honing stones may be treated
with wax or sulfur to improve life; wax is usually preferred for
environmental reasons.

4. Process Mechanics
• In grinding, the wheel follows a simple path. For example, in
plunge grinding a shaft, the wheel moves in towards the axis of
the part, grinds it, and then moves back out.
• Since each slice of the wheel repeatedly contacts the same slice of
the workpiece, any inaccuracies in the geometric shape of the
grinding wheel will be transferred onto the part.
• Therefore, the accuracy of the finished workpiece geometry is
limited to the accuracy of the truing dresser.
• The accuracy becomes even worse as
the grind wheel wears, so truing must
occur periodically to reshape it.
A flat honing machine

5. Performance advantages of honed
Surface
• The flexible honing tool is a relatively inexpensive honing
process. This tool produces a controlled surface condition
unobtainable by any other method.
• It involves finish, geometry and metallurgical structure. A high
percentage plateau free of cut, torn and folded metal is
produced.
• The flexible hone is a resilient, flexible honing tool with a soft
cutting action.
• The abrasive globules each have independent suspension that
assures the tool to be self-centering, self-aligning to the bore,
and self-compensating for wear.

6. 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.
• This can take two forms. The first type of lapping involves
rubbing a brittle material such as glass against a surface such as
iron or glass itself with an abrasive such as aluminum oxide,
jeweller's rouge, optician's rouge, emery, silicon carbide,
diamond, etc., between them.
• This produces microscopic conchoidal fractures as the abrasive
rolls about between the two surfaces and removes material
from both.
• The other form of lapping involves a softer material such
as pitch or a ceramic for the lap, which is "charged" with
the abrasive.

7. • The lap is then used to cut a harder material the workpiece. The
abrasive embeds within the softer material, which holds it and
permits it to score across and cut the harder material.
• Taken to a finer limit, this will produce a polished surface such
as with a polishing cloth on an automobile, or a polishing cloth
or polishing pitch upon glass or steel.
Small lapping plate
made of cast iron
• Taken to the ultimate limit, with the aid of accurate
interferometry and specialized polishing machines or skilled
hand polishing, lensmakers can produce surfaces that are flat to
better than 30 nanometers.

8. • In operation, the rings stay in one location as the lapping plate
rotates beneath them. In this machine, a small slurry pump can
be seen at the side, this pump feeds abrasive slurry onto the
rotating lapping plate.
• When there is a requirement to lap very small specimens (from
3" down to a few millimetres), a lapping jig can be used to hold
the material while it is lapped (see Image 3, Lapping machine
and retention jig).
• A jig allows precise control of the orientation of the specimen to
the lapping plate and fine adjustment of the load applied to the
specimen during the material removal process.
• Due to the dimensions of such small samples, traditional loads
and weights are too heavy as they would destroy delicate
materials.
Operation

9. Accuracy & surface roughness
• Lapping can be used to obtain a specific surface roughness; it is
also used to obtain very accurate surfaces, usually very flat
surfaces. Surface roughness and surface flatness are two quite
different concepts.
• A typical range of surface roughness that can be obtained
without resorting to special equipment would fall in the range
of 1 to 30 units Ra (average roughness), usually microinches.
Lapping machine and retention jigSmall lapping machine

10. Electroplating
• Electroplating is a process that uses electric current to reduce
dissolved metal cations so that they form a thin coherent metal
coating on an electrode.
• The term is also used for electrical oxidation of anions onto a
solid substrate, as in the formation silver chloride on silver wire
to make silver/silver-chloride electrodes.
• Electroplating is primarily used to change the surface properties
of an object (e.g. abrasion and wear resistance, corrosion
protection, lubricity, aesthetic qualities, etc.), but may also be
used to build up thickness on undersized parts or to form
objects by electroforming.
• The process used in electroplating is called electrodeposition. It
is analogous to a galvanic cell acting in reverse. The part to be
plated is the cathode of the circuit. In one technique, the anode
is made of the metal to be plated on the part.

11. Process
• The cations associate with the anions in the solution. These
cations are reduced at the cathode to deposit in the metallic,
zero valence state.
• For example, for copper plating, in an acid solution, copper is
oxidized at the anode to Cu2+ by losing two electrons. The
Cu2+associates with the anion SO42− in the solution to form
copper sulfate.
• At the cathode, the Cu2+ is reduced to metallic copper by gaining
two electrons. The result is
the effective transfer of copper from
the anode source to a plate covering
the cathode.
• The plating is most commonly a
single metallic element, not an alloy.
Copper electroplating machine for layering PCBs

12. Electrochemical deposition is generally used for the growth of
metals and conducting metal oxides because of the following
advantages:
• The thickness and morphology of the nanostructure can be
precisely controlled by adjusting the electrochemical
parameters.
• Relatively uniform and compact deposits
can be synthesized in template-based
structures.
• Higher deposition rates are obtained, and
the equipment is inexpensive due to the
non-requirements of either a high vacuum
or a high reaction temperature.
Electrochemical deposition
Electroplating of a metal (Me) with copper
in a copper sulfate bath

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