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EXTRUSION PROCESS•In extrusion, the material is
compressed in a chamber and
the deformed material is
forced to flow through the die.
•The die opening corresponds
to the cross section of
required product.
• Cylindrical bars, hollow
tubes as also shapes of
irregular c.s are made.
Extrusion of a round blank through a die
• Extrusion process equipment consists of a cylinder/ container
into which the heated metal billet is loaded.
• On one end of container, die plate with necessary opening is fixed.
• From other end, plunger/ ram compress the metal billet against
the container walls & die plate, thus forcing it to flow through die
opening, acquiring shape of opening.
• Dummy block which is steel disc about 40 mm thick, is kept btn
billet & ram to protect it from heat & pressure.
• Pressures applied may range from 35-1000
Mpa.
• Pressures for given metal depends on
extrusion temperature, reduction in area &
extrusion speed.
• Materials that can be extrudes are aluminum,
copper, steel, magnesium, and plastics,
polymers, ceramics, concrete.
Typical products of Extrusion
• Typical products made by extrusion are railings for
sliding doors, tubing's having various cross sections.
• Extruded parts are cut into desired lengths which then
become discrete parts such as brackets, gears, coat
hangers.
• its ability to create very complex cross-sections and
work materials that are brittle, because the material
only encounters compressive and shear stresses.
Typical Extruded Products
The extrusion process is often likened to the squeezing of tooth paste from a tube, as is illustrated :
Hot extrusion:
• Keeping the processing temperature to above the materials
re-crystalline temperature to keep material from work
hardening.
•Most are done on horizontal hydraulic presses that range
from 230 to 11,000 metric tons.
• Pressures range from 30 to 700 MPa (4,400 to 100,000 psi)
therefore lubrication is required, which can be oil or
graphite for lower temperature extrusions, or glass powder
for higher temperature extrusions.
Extrusion Processes
Hot extrusion temperature for various metals
Material Temperature [°C (°F)]
Magnesium 350-450 (650-850)
Aluminium 350-500 (650-900)
Copper 600-1100 (1200-2000)
Steel 1200-1300 (2200–2400)
Titanium 700-1200 (1300-2100)
Nickel 1000-1200 (1900–2200)
Refractory alloys up to 2000 (4000)
Cold extrusion:
• Done at room temperature or near room temperature.
• Ductile metals like lead, tin, aluminum, copper, zirconium,
titanium, molybdenum, beryllium, vanadium, niobium, and
steel.
• The advantages of this over hot extrusion are improved
mechanical properties, high production rate, closer
tolerances, good surface finish.
• Tools & automobile parts, motor cycles, collapsible
tubes, fire extinguisher cases, shock absorber cylinders
and gear blanks.
TYPES OF EXTRUSION PROCESSES
• Direct extrusion (or forward extrusion),
• Indirect extrusion (or backward extrusion),
• Impact extrusion, and
• Side extrusion.
Direct (or) Forward Extrusion
Direct Extrusion
• It is most widely used method, in which starting
ram material used is a heated billet.
• It is heated to its heated temperature and fed
into its forging temperature and fed into
machine chamber/ container & pressed with
hydraulically operated ram through die.
• Flow of metal in forward extrusion is same as
that of ram direction.
• There is a reusable dummy block between the ram
and the billet to keep them separated.
• major disadvantage is force required to extrude the
billet is greater than that needed in the indirect
extrusion process because of the frictional forces
introduced by the need for the billet to travel the
entire length of the container.
• To reduce this friction lubricants are used.
• Ex: Oils with graphite powder at low temp.
Advantages:• Complex Integral Shapes• Cost-Effective• Design Flexibility• Simple fastening and assembly• Easy fabrication• Low Tooling Costs• Good Machinability • Precision Tolerances • Shorter Lead Times• Versatility in Joining
• Virtually Seamless
INDIRECT EXTRUSION OR BACKWARD EXTRUSION
• In order to completely overcome the friction,
backward extrusion process is used.
• Ram/ plunger used is hollow, as it presses the
billet against back wall of die chamber/
container the metal flows through die.
• As the billet does not move inside the
chamber there is no friction between them.
• Less force is required in this process .
ADVANTAGES:
• A 25 to 30% reduction of friction, which allows for
extruding larger billets, increasing speed, and an
increased ability to extrude smaller cross-sections
• There is less of a tendency for extrusions to crack
because there is no heat formed from friction
• The container liner will last longer due to less wear
• The billet is used more uniformly so extrusion defects
and coarse grained peripherals zones are less likely.
DEFECTS IN EXTRUSION• Depending on material condition & on process
variables, extruded parts can develop several types of
defects that can significantly affect their strength, quality.
• Principal extrusion defects are;
1.Surface cracking (c)
2.Pipe (b)
3.Internal cracking (a)
DEFECTS
1. Surface Cracking:
• If extrusion temp, friction/ speed is too high,
surface temperatures rise significantly, and
this condition may cause surface cracking &
tearing.(fir-tree cracking, speed cracking)
• These occur specially in Al, Mg, Zinc alloys.
• These defects can be avoided by lowering the
billet temperature & extrusion speed.
2. Pipe:
• This type of metal flow pattern tends to draw
surface oxides, impurities towards centre of
billet which is called as pipe defect/ tail pipe/
fishtailing.
• These are obtained because of high friction,
maximum temperatures at outside of billet.
• Defects as much as one third of length of
extruded product, to be cut off as scrap.
3. Internal / Centre/ Chevron cracking:
• The centre of the extruded product can develop
cracks called center-burst, arrow head fracture.
• These are attributed to a state of hydrostatic
tensile stress at the centre line in the
deformation zone in the die.
Hydrostatic Extrusion
• It is another way to extrude aluminum profiles.
• In this process, the chamber is first filled with a
fluid which transmits the pressure to the billet.
• This billet is then extruded using the die. There
is no question of friction along the container -
walls.
• the main difference is that in case of
Hydrostatic extrusion there is no direct contact
between the container and the billet.
• It is usually carried at room temperature, using
vegetable oils as the fluid.
• For elevated temperatures waxes, polymers,
glass are used.
• Brittle materials like gray c.i are extruded
successfully by this method, because
hydrostatic pressure increases the ductility of
material.
Advantages
• Owing to the pressurized fluid, the lubrication is very
effective
• Extruded product has good surface finish along with
dimensional accuracy
• As friction is almost absent, it is quite possible to use
dies that has very low semi-cone angle.
• Minimal friction
• Some typical shapes produced are angles,
rods, T-profiles or dumbbells.
• Other shapes to be produced can single-hollow
sections like tubes.
IMPACT EXTRUSION
• In backward cold extrusion called Impact
extrusion, the set up consists of die, punch as
shown in fig.
• The slug for making the component is kept on
die & punch strikes the slug against the die.
• Metal is then extruded through the gap between
punch & die opposite to movement of punch.
• The height of side walls is controlled by amount
of metal in slug.
• This process is mainly used for making short
lengths of hollow shapes like collapsible tubes
for housing plates, liquids, spray cans.
• Diameter of parts made can approach 150 mm.
• For making discrete parts.
• performed at higher speeds and shorter strokes
than conventional extrusion.
Manufacturing of toothpaste tube
Applications: Tooth paste tubes, soft drink cans & shell cases.
SIDE EXTRUSION
•In side extrusion the movement of the material is
in a direction perpendicular to that of ram motion.
• Since the metal flows in sideward direction the
force required is very high& hence mostly used in
the case of non ferrous metals and highly plastic
materials like lead.
•Presence of cable produces a seamless tube.
TUBE EXTRUSION
• It is actually a forward extrusion method using a
mandrel to form the bore of the tube as shown in fig.
• First mandrel is pushed through centre of billet & die,
followed by applying pressure on billet by advancing the
plunger.
• Metal is forced to flow through the opening between the
die & mandrel.
• Most of the metals are hot extruded, although some of
these are cold extruded, for production of seamless
tubes.
• the clearance between the mandrel and the die wall
determines the wall thickness of the extruded tube.
Metals that are commonly extruded include:
Aluminium is the most commonly extruded material. Aluminium can be
hot or cold extruded. If it is hot extruded it is heated to 575 to 1100 °F
(300 to 600 °C). Examples of products include profiles for tracks,
frames, rails, mullions, and heat sinks.
Brass is used to extrude corrosion free rods, automobile parts, pipe
fittings, engineering parts.
Copper (1100 to 1825 °F (600 to 1000 °C)) pipe, wire, rods, bars, tubes,
and welding electrodes. Often more than 100 ksi (690 MPa) is required
to extrude copper.
Lead and tin (maximum 575 °F (300 °C)) pipes, wire, tubes, and cable
sheathing. Molten lead may also be used in place of billets on vertical
extrusion presses.
DRAWING• It is a metalworking process
used to reduce the
cross-section of a wire/ rod by
pulling the wire through a
single, or series of, drawing
die(s).
• Although similar in process,
drawing is different from
extrusion, because in drawing
the wire is pulled, rather than
pushed, through the die.
• Major variables in drawing are similar to those
in extrusion: reduction in c.s area, die angle,
friction along die work interfaces, drawing
speed.
• In this process, rods made of steel or non
ferrous metals and alloys are pulled through
conical dies having a hole in the centre.
DRAWING PROCESS• The wire is prepared by shrinking the beginning of
it, by hammering, filing, rolling or swaging, it will fit
through the die.
• The wire is then pulled through the die. As the wire
is pulled through the die, its volume remains the
same, diameter decreases, the length increases.
• Usually the wire will require more than one draw,
through successively smaller dies, to reach the
desired size.
• An example of product produced in a
continuous wire drawing machine is telephone
wire.
• It is drawn 20 to 30 times from hot rolled rod
stock.
• The diameter and wall thickness of tubes that
have been produced by extrusion or other
processes can be reduced by tube drawing
process.
• The process of tube drawing is similar to wire
or rod drawing except that it usually requires a
mandrel of the requisite diameter to form the
internal hole.
Tube Drawing
• Equipment designs can be classified into two basic types;
Draw bench, Bull block.
• A draw bench uses a single die and the pulling force is
supplied by a chain drive or by hydraulic means.
• Used for single length drawing of rod or tube with diameter
greater than 20mm.
• Length can be as much as 30 m.
• Drawing speed attainable on a draw bench ranges from 5
m/min to 50 m/min.
Bull block or rotating drum used for drawing rods or wires of very long length.
Lubrication
• Lubrication in the drawing process is essential for
maintaining good surface finish and long die life.
1.Wet drawing: the dies and wire/rod are completely
immersed in lubricant.
2.Dry drawing: the wire or rod passes through a
container of lubricant which coats surface of the
wire or rod
3.Metal coating: the wire or rod is coated with a soft
metal which acts as a solid lubricant
4. Ultrasonic vibration: the dies and mandrels are vibrated,
which helps to reduce forces and allow larger
reductions per pass
• Various lubricants, such as oil, are employed.
• Lubricants normally used are soap solution, for very
thin wires electrolytic coating of copper is used to
reduce friction.
DIES• Various die materials used are chilled cast iron,
tungsten carbide diamond, tool steel.
• For small runs cast iron dies are used.
• For medium sized, large production wires
tungsten made dies are used.
• For very large sizes alloy steels are used.
Wire Drawing
• Drawing machines can be arranged in tandem
so that the wire coming from one die is coiled to
sufficient length before it is reentered in to
subsequent die.
• This coiling of sufficient wire helps for any
discrepancy in speed of wire drawing in any
die.
• Such that successive drawings are to be done
ah high speeds.
TUBE MAKING
• Tubes are basically of two types. They are either seamless (i.e.,
without any joint) or with joint all along the length of the tube.
• Seamless tubes are made by processes such as casting, extrusion
or rolling.
• Tubes with joint are made by welding.
• Usually, the weld joint is made by electric resistance welding
process, such tubes are referred to as ERW tubes.
• The size of a tube or pipe is indicated by the size of its bore in
mm.
• Since the requirement of tubes is so large, a special rolling
process called Mannesmann rotary piercing process has
been developed.
• In this process, a heated round billet with its leading end, in
the centre of which a short guide hole has been punched or
drilled, is pushed longitudinally between two large tapered
rolls as shown in Fig.
• The rolls revolve in the same direction and their axes are
inclined at opposite angles of approx 6° from the axis of the
billet
• As the billet is caught by the rolls and is rotated, their
inclination causes the material to be drawn forward.
• The guide hole drilled/punched at centre of billet tears open.
• This action is assisted by a suitably placed mandrel.
• As the billet mores forward and keeps rotating the tearing
action is propagated throughout the length of the billet.
• End result is a roughly formed seamless tube of ellipitical
cross-section.
DEEP DRAWING
• It is a cold metal forming process, in which a flat sheet
metal blank is forced into a die cavity by hydraulically
driven punch.
• A cup-like cylindrical part, having the depth greater than its
diameter, is formed as a result of deep drawing, process
requires a blank, blank holder, punch, and die.
• The blank is a piece of sheet metal, typically a disc or
rectangle, which is pre-cut from stock material and will be
formed into the part.
• The blank is clamped down by the blank holder over the
die, which has a cavity in the external shape of the part
• A tool called a punch moves downward into the blank and
draws, or stretches, the material into the die cavity.
• Movement of the punch is usually hydraulically powered to
apply enough force to the blank.
• Both the die and punch experience wear from the forces
applied to the sheet metal and are therefore made from tool
steel or carbon steel.
DEEP DRAWN PARTS
• In each step, a punch forces the part into a different die,
stretching the part to a greater depth each time.
• After a part is completely drawn, the punch and blank
holder can be raised and the part removed from the die.
• The portion of the sheet metal that was clamped under the
blank holder may form a flange around the part that can be
trimmed off.
• Deep drawing is most effective with ductile metals, such as
aluminum, brass, bronze, iron, copper, and mild steel.
• The following alloys are used in deep drawing process: pure copper,
some aluminum alloys and pure aluminum, 70-30 brass, cupro-
nickel, mild steels
• Car bodies, pans, cartridge cases, kitchen sinks, beverage cans, bullet
envelopes and other cup-like parts.
• These parts can have a variety of cross sections with straight, tapered,
or even curved walls, but cylindrical or rectangular parts are most
common.