Lo# 3a(2033 common) manufacturing technology PART 1
1. Hot and Cold Metal
Working Process
LO#3a, EMC 2033
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2. Hot and cold Metal Working
1. Rolling
2. Forging
3. Extrusion
4. Drawing
5. Bending
6. Material removal
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3. Classification of Metal Forming
Metal forming includes a large group of manufacturing
processes in which plastic deformation is used to
change the shape of metal work piece.
Metal Forming classified into:
Bulk Deformation.
Sheet Metal working.
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4. Reasons for metal forming:
The cast ingots produced by the raw
material producers are of little use for
manufacturing processes until they have
been formed to a suitable shape, i.e.
sheet, plate, strip, bar sections.
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5. Basic Bulk Deformation
In these processes significant deformation and
massive shapes happened to the starting work piece,
and its surface area-to-volume ratio is small.
The starting work piece usually cylindrical billets or
rectangular bars, and the processes includes:
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6. Rolling
In each case, (hot and cold rolling), the metal is
worked while in a solid state and is shaped by plastic
deformation.
Working metals in its solid state will help to produce
shapes which would be difficult or expensive to
produce by any other method, example: Long length of
sheet, sections, rod, etc.,
and to improve mechanical properties.
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7. ROLLING PROCESS
1. Rolling: this is a compressive deformation process in which the
thickness of a slab or plate is reduced by two opposing
cylindrical tools called rolls. The rolls rotates so as to draw the
work into the gap between them and squeeze it.
http://www.doitpoms.ac.uk/tlplib/metal-forming-2/rolling.php
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8. Hot rolling advantages
Most ingots when cast contain many small holes- a
condition known as porosity. During hot rolling, these
holes are pressed together and eliminated.
Any impurities contained in the ingot are broken up
and dispersed throughout the metal.
The internal grain structure of the metal is refined,
resulting in an improvement of the mechanical
properties, e.g. ductility and strength.
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9. Hot Rolling Disadvantages
Due to high temperatures, the surface oxidizes,
producing a scale which result in poor surface finish,
making it difficult to maintain dimensional accuracy.
Where close dimensional accuracy and good surface
finish are not of great importance, e.g. structural
shapes for construction work, a descaling operation is
carried out and the product is used as-rolled.
Alternately further work can be carried out by cold
rolling.
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10. Cold Rolling
When metal is cold rolled, greater forces are required
,necessitating a large number of stages before
reaching the required shape. The strength of the
material is greatly improved, but this is accompanied
by decrease in ductility.
Depending upon number of stages required in
producing the shape, annealing may have to be carried
out between stages.
Beside improving mechanical properties, cold rolling
produces a good surface finish with high dimensional
accuracy.
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11. EXTRUSION PROCESS
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3. Extrusion: similar to plastics extrusion process, but
here a compression process used in which the work
metal is forced to flow though a die opening. Thereby
taking the shape of the opening as its own cross section.
12. Extrusion
The extrusion produced has a constant cross section
along its entire length.
The die may contain a number of openings,
simultaneously producing a number of extrusions.
There are number of variations of extrusion process,
the two most common methods are
Direct extrusion and indirect extrusion.
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14. Important Features of the extrusion process
The complexity of the shape possible is practically
unlimited, and finished products can be produced
directly.
A good surface finish can be maintained.
Good dimensional accuracy can be obtained.
Large reduction in cross sectional area can be
achieved.
Since the metal is in compression during the process,
so relatively brittle materials can be extruded.
The mechanical properties of the material are
improved.
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15. Extrusion Limitation
The extrusion process is however, limited to products
which have a constant cross section. Any slots, holes
etc. not parallel to the longitudinal axis have to be
machined.
Due to extrusion-press power capabilities, the size of
shape which can produced is limited.
The process is normally limited to long runs, due to die
costs, but short runs can be economical with simple
die shapes.
Typical materials used are copper and aluminum
alloys.
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16. DRAWING PROCESS
Drawing :The process of drawing is a cold working
process, i.e. carried out at room temperature. It is mainly
used in the production of wires, rods and bar.
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17. Drawing
In continuous wire drawing , the wire is pulled through
the series of progressively smaller dies until the final-
size section is reached.
The strength of the material will limit the force which
can be applied in pulling the wire through the die,
while the ductility of the material limits the amount of
reduction possible through each die.
Typical materials used are steel, copper, aluminum and
their alloys.
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18. FORGING RPOCESS
2. Forging: In forging a work piece is compressed
between two opposing dies, so that the die shapes are
imparted to the work. Forging is traditionally a hot
working process, but many types of forging are
performed cold.
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19. Forging
The oldest form of forging is Hand forging as carried
out by the black smith. Hand tools are used to
manipulate the hot metal to give changes in section
and changes in shape by bending, twisting, etc.
Due to hand operation, it is not possible to achieve
high degree of accuracy or extreme complexity of
shape.
This method is limited to one -off or small quantities
and requires a high degree of skill.
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20. Forging
When forging is large, some form of power is
employed. Steam or compressed air hammers or a
forging press is used , the process is know as Open-
sided forging.
This method is used to produce large forgings such
ads propeller shaft for ships.
When large quantities of accurately shaped product
are required, these are produces by a process known
as closed-die forging or Drop forging.
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21. Forging application
Forging is used in the production of parts which have
to withstand heavy or unpredictable loads, such as
levers, cams, gears, connecting rods and axel shafts
and spanners.
Mechanical properties are improved by forging due to
controlled grain flow.
For Example: A spanner cut from the rolled sheet
would be much weaker compared to one produced
from forging.
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22. Selection of manufacturing process
A number of factors have to be considered before a
choice of process for a given component can be
made.
For example: consideration would have to be given to
the type of material used, the mechanical properties
required, shape, accuracy, degree of surface finish
and the quantity to be produced.
Table on the next slide gives the idea.
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24. Sheet Metalworking:
sheet metalworking processes are forming and cutting
operations performed on metal sheets, strips, and
coils.
The surface area-to-volume ratio of the starting
metal is high, this is an important point to distinguish
these processes from the bulk deformation processes.
Pressworking is the term often used to sheet metal
operations because the machines used in these
operations are presses.
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25. Sheet Metalworking
Sheet metal operations are always performed as cold
working processes, using a set of tools called a punch
and die.
The punch: is the positive portion of the tool set.
The Die: is the negative portion of the tool set.
basic sheet metalworking operations includes:
1. Bending.
2. Drawing.
3. Shearing.
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27. Bending operation
Bending involves straining of a metal sheet or plate to
take an angle along a straight axis.
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28. Sheet metal drawing and Shearing
Drawing in sheet metalworking refers to the forming of
a flat metal sheet into a hollow or concave shape, such
as a cup, buy stretching the sheet metal.
A blank holder must be used to hold down the blank while
the punch pushes throw the sheet metal.
to distinguish sheet metalworking drawing from wire
drawing the term deep drawing is used here.
Shearing : in this process involves cutting rather
than forming.
A shearing operation cuts the work using a punch and
die.
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