2. IntroductionIntroduction
Practically all metals, which are not used in cast form arePractically all metals, which are not used in cast form are
reduced to some standard shapes for subsequent processing.reduced to some standard shapes for subsequent processing.
Manufacturing companies producing metals supply metalsManufacturing companies producing metals supply metals
in form of ingots which are obtained by casting liquid metalin form of ingots which are obtained by casting liquid metal
into a square cross section.into a square cross section.
Slab (500Slab (500--1800 mm wide and 501800 mm wide and 50--300 mm thick)300 mm thick)
Billets (40 to 150 sq mm)Billets (40 to 150 sq mm)
Blooms (150 to 400 sq mm)Blooms (150 to 400 sq mm)
Sometimes continuous casting methods are also used to castSometimes continuous casting methods are also used to cast
the liquid metal into slabs, billets or blooms.the liquid metal into slabs, billets or blooms.
These shapes are further processed through hot rolling,These shapes are further processed through hot rolling,
forging or extrusion, to produce materials in standard formforging or extrusion, to produce materials in standard form
such as plates, sheets, rods, tubes and structural sections.such as plates, sheets, rods, tubes and structural sections.
3. Sequence of operations for obtainingSequence of operations for obtaining
different shapesdifferent shapes
4.
5. Primary Metal Forming ProcessesPrimary Metal Forming Processes
RollingRolling
ForgingForging
ExtrusionExtrusion
Tube and wire drawingTube and wire drawing
and Deep drawingand Deep drawing
Although Punching and Blanking operations areAlthough Punching and Blanking operations are
not metal forming processes however these will benot metal forming processes however these will be
covered due to similarity with deep drawingcovered due to similarity with deep drawing
process.process.
7. Change in grains structure in rollingChange in grains structure in rolling
8. Salient points about rollingSalient points about rolling
Rolling is the most extensively used metal formingRolling is the most extensively used metal forming
process and its share is roughly 90%process and its share is roughly 90%
The material to be rolled is drawn by means of frictionThe material to be rolled is drawn by means of friction
into the two revolving roll gapinto the two revolving roll gap
The compressive forces applied by the rolls reduce theThe compressive forces applied by the rolls reduce the
thickness of the material or changes its cross sectionalthickness of the material or changes its cross sectional
areaarea
The geometry of the product depend on the contour ofThe geometry of the product depend on the contour of
the roll gapthe roll gap
Roll materials are cast iron, cast steel and forged steelRoll materials are cast iron, cast steel and forged steel
because of high strength and wear resistancebecause of high strength and wear resistance
requirementsrequirements
Hot rolls are generally rough so that they can bite theHot rolls are generally rough so that they can bite the
work, and cold rolls are ground and polished for goodwork, and cold rolls are ground and polished for good
finishfinish
9. In rolling the crystals get elongated in the rolling direction.In rolling the crystals get elongated in the rolling direction. In coldIn cold
rolling crystal more or less retain the elongated shape but in hrolling crystal more or less retain the elongated shape but in hotot
rolling they start reforming after coming out from the deformatirolling they start reforming after coming out from the deformationon
zonezone
The peripheral velocity of rolls at entry exceeds that of theThe peripheral velocity of rolls at entry exceeds that of the
strip, which is dragged in if the interface friction is highstrip, which is dragged in if the interface friction is high
enough.enough.
In the deformation zone the thickness of the strip gets reducedIn the deformation zone the thickness of the strip gets reduced
and it elongates. This increases the linear speed of the at theand it elongates. This increases the linear speed of the at the
exit.exit.
Thus there exist a neutral point where roll speed and stripThus there exist a neutral point where roll speed and strip
speeds are equal. At this point the direction of the frictionspeeds are equal. At this point the direction of the friction
reverses.reverses.
When the angle of contactWhen the angle of contact ฮฑฮฑ exceeds the friction angleexceeds the friction angle ฮปฮป thethe
rolls cannot draw fresh striprolls cannot draw fresh strip
Roll torque, power etc. increase with increase in roll workRoll torque, power etc. increase with increase in roll work
contact length or roll radiuscontact length or roll radius
10. Pressure during rollingPressure during rolling
Typical pressure variation along
the contact length in flat rolling.
The peak pressure is located at
the neutral point. The area
beneath the curve, represents
roll force.
Friction in rolling: It depends on lubrication,
work material and also on the temperature. In
cold rolling the value of coefficient of friction
is around 0.1 and in warm working it is
around 0.2. In hot rolling it is around 0.4. In
hot rolling sticking friction condition is also
seen and then friction coefficient is observed
up to 0.7. In sticking the hot wok surface
adheres to roll and thus the central part of the
strip undergoes with a severe deformation.
11. Roll passes to get a 12 mm rodRoll passes to get a 12 mm rod
from 100 x 100 mm billetfrom 100 x 100 mm billet
12. RollRoll configurationsconfigurations in rolling millsin rolling mills
TwoTwo--high and threehigh and three--high mills are generallyhigh mills are generally
used for initial and intermediate passes duringused for initial and intermediate passes during
hot rolling, while fourhot rolling, while four--high and cluster millshigh and cluster mills
are used for final passes.are used for final passes.
Last two arrangements are preferred for coldLast two arrangements are preferred for cold
rolling because roll in these configurations arerolling because roll in these configurations are
supported by backsupported by back--up rolls which minimizeup rolls which minimize
the deflections and produce better tolerances.the deflections and produce better tolerances.
13. Various Roll Configurations (a) TwoVarious Roll Configurations (a) Two--high (b) Threehigh (b) Three--highhigh
(c) Four(c) Four--high (d) Cluster mill (e) Tandem millhigh (d) Cluster mill (e) Tandem mill
back
15. ForgingForging
Forging is perhaps oldest metal working process and wasForging is perhaps oldest metal working process and was
known even during prehistoric days when metallic toolsknown even during prehistoric days when metallic tools
were made by heating and hammering.were made by heating and hammering.
Forging is basically involves plastic deformation ofForging is basically involves plastic deformation of
material between two dies to achieve desiredmaterial between two dies to achieve desired
configuration. Depending upon complexity of the partconfiguration. Depending upon complexity of the part
forging is carried out asforging is carried out as open die forging and closed dieopen die forging and closed die
forging.forging.
In open die forging, the metal is compressed by repeatedIn open die forging, the metal is compressed by repeated
blows by a mechanical hammer and shape is manipulatedblows by a mechanical hammer and shape is manipulated
manually.manually.
In closed die forging, the desired configuration isIn closed die forging, the desired configuration is
obtained by squeezing theobtained by squeezing the workpieceworkpiece between two shapedbetween two shaped
and closed dies.and closed dies.
16. On squeezing the die cavity gets completely filled andOn squeezing the die cavity gets completely filled and
excess material comes out around the periphery of theexcess material comes out around the periphery of the
die asdie as flashflash which is later trimmed.which is later trimmed.
Press forging and drop forging are two popularPress forging and drop forging are two popular
methods in closed die forging.methods in closed die forging.
In press forging the metal is squeezed slowly by aIn press forging the metal is squeezed slowly by a
hydraulic or mechanical press and component ishydraulic or mechanical press and component is
produced in a single closing of die, hence theproduced in a single closing of die, hence the
dimensional accuracy is much better than dropdimensional accuracy is much better than drop
forging.forging.
Both open and closed die forging processes are carriedBoth open and closed die forging processes are carried
out in hot as well as in cold state.out in hot as well as in cold state.
In forgingIn forging favorable grain orientationfavorable grain orientation of metal isof metal is
obtainedobtained
20. Self reading in forgingSelf reading in forging
FulleringFullering
EdgingEdging
CoggingCogging
UpsettingUpsetting
HeadingHeading
SwagingSwaging
Radial forging etc.Radial forging etc.
Go through any book on
Manufacturing processes
by Kalpakjian, Groover
or Degarmo
21. ExtrusionExtrusion
It is a relatively new process and its commercialIt is a relatively new process and its commercial
exploitation started early in the nineteenth century with theexploitation started early in the nineteenth century with the
extrusion of lead pipes. Extrusion of steels becameextrusion of lead pipes. Extrusion of steels became
possible only after 1930 when extrusion chambers couldpossible only after 1930 when extrusion chambers could
be designed to withstand high temperature and pressure.be designed to withstand high temperature and pressure.
In extrusion, the material is compressed in a chamber andIn extrusion, the material is compressed in a chamber and
the deformed material is forced to flow through the die.the deformed material is forced to flow through the die.
The die opening corresponds to the cross section of theThe die opening corresponds to the cross section of the
required product.required product.
It is basically a hot working process, however, for softerIt is basically a hot working process, however, for softer
materials cold extrusion is also performed.materials cold extrusion is also performed.
22. Direct and Indirect ExtrusionDirect and Indirect Extrusion
In direct extrusion metal flows in theIn direct extrusion metal flows in the
same direction as that of the ram.same direction as that of the ram.
Because of the relative motion betweenBecause of the relative motion between
the heated billet and the chamber walls,the heated billet and the chamber walls,
friction is severe and is reduced by usingfriction is severe and is reduced by using
molten glass as a lubricant in case ofmolten glass as a lubricant in case of
steels at higher temperatures. At lowersteels at higher temperatures. At lower
temperatures, oils with graphite powdertemperatures, oils with graphite powder
is used for lubrication.is used for lubrication.
In indirect extrusion process metalIn indirect extrusion process metal
flows in the opposite direction of theflows in the opposite direction of the
ram. It is more efficient since it reducesram. It is more efficient since it reduces
friction losses considerably. The process,friction losses considerably. The process,
however, is not used extensively becausehowever, is not used extensively because
it restricts the length of the extrudedit restricts the length of the extruded
component.component.
23. Impact ExtrusionImpact Extrusion
It is similar to indirectIt is similar to indirect
extrusion. Here the punchextrusion. Here the punch
descends rapidly on to thedescends rapidly on to the
blank which gets indirectlyblank which gets indirectly
extruded on to the punch andextruded on to the punch and
to give a tubular section. Theto give a tubular section. The
length of the tube formed islength of the tube formed is
controlled by the amount ofcontrolled by the amount of
metal in the slug or by themetal in the slug or by the
blank thickness. Collapsibleblank thickness. Collapsible
tubes for pastes are extrudedtubes for pastes are extruded
by this method.by this method.
24. Hydrostatic ExtrusionHydrostatic Extrusion
In this process theIn this process the
friction betweenfriction between
container wall and billetcontainer wall and billet
is eliminated, however,is eliminated, however,
this process has gotthis process has got
limited applications inlimited applications in
industry due toindustry due to
specialized equipment &specialized equipment &
tooling and lowtooling and low
production rate due toproduction rate due to
high set up time.high set up time.
25. DrawingDrawing
Large quantities of wires, rods,Large quantities of wires, rods,
tubes and other sections aretubes and other sections are
produced by drawing processproduced by drawing process
which is basically a coldwhich is basically a cold
working process. In thisworking process. In this
process the material is pulledprocess the material is pulled
through a die in order tothrough a die in order to
reduce it to the desired shapereduce it to the desired shape
and size.and size.
In a typical wire drawingIn a typical wire drawing
operation, once end of the wireoperation, once end of the wire
is reduced and passed throughis reduced and passed through
the opening of the die, grippedthe opening of the die, gripped
and pulled to reduce itsand pulled to reduce its
diameter.diameter.
26. By successive drawing operation through dies ofBy successive drawing operation through dies of
reducing diameter the wire can be reduced to a veryreducing diameter the wire can be reduced to a very
small diameter.small diameter.
Annealing before each drawing operation permitsAnnealing before each drawing operation permits
large area reduction.large area reduction.
Tungsten Carbide dies are used to for drawing hardTungsten Carbide dies are used to for drawing hard
wires, and diamond dies is the choice for fine wires.wires, and diamond dies is the choice for fine wires.
27. Tube drawingTube drawing
โขโขTube drawing is also similar to wire drawing, except that a mandTube drawing is also similar to wire drawing, except that a mandrelrel
of appropriate diameter is required to form the internal hole.of appropriate diameter is required to form the internal hole.
โขโขHere two arrangements are shown in figure (a) with a floating plHere two arrangements are shown in figure (a) with a floating plugug
and (b) with a moving mandreland (b) with a moving mandrel
โขโขThe process reduces the diameter and thickness of the tube.The process reduces the diameter and thickness of the tube.
28. Deep DrawingDeep Drawing
This operation isThis operation is
extensively used to forextensively used to for
making cylindricalmaking cylindrical
shaped parts such as cups,shaped parts such as cups,
shells, etc from sheetshells, etc from sheet
metal.metal.
As the blank is drawn intoAs the blank is drawn into
the die cavitythe die cavity
compressive stresscompressive stress is setis set
up around the flange andup around the flange and
it tends toit tends to wrinkle orwrinkle or
bucklebuckle the flange.the flange.
30. Defects in drawingDefects in drawing
(a)Wrinkling in the flange or (b) in the wall (c) tearing,(a)Wrinkling in the flange or (b) in the wall (c) tearing,
(d)(d) earingearing, (e) surface scratches, (e) surface scratches
31. The effect of wrinkling and buckling can be seen fromThe effect of wrinkling and buckling can be seen from
the way a trapezoid on the outer surface of the blank isthe way a trapezoid on the outer surface of the blank is
stretched in one direction and compressed in anotherstretched in one direction and compressed in another
direction to become a rectangle on the cup drawn.direction to become a rectangle on the cup drawn.
32. Wrinkling and buckling is avoided by applying aWrinkling and buckling is avoided by applying a
blank holder force through a blank holder.blank holder force through a blank holder.
Blank holder force increases friction and hence theBlank holder force increases friction and hence the
required punch load. Therefore, blank holder forcerequired punch load. Therefore, blank holder force
should be just enough to prevent wrinkling of theshould be just enough to prevent wrinkling of the
flange.flange.
The edges of the punch and die are rounded for theThe edges of the punch and die are rounded for the
easy and smooth flow of metal.easy and smooth flow of metal.
Sufficient clearance is also provided so that sheetSufficient clearance is also provided so that sheet
metal could be easily accommodated. In sufficientmetal could be easily accommodated. In sufficient
or large clearance may result into shearing andor large clearance may result into shearing and
tearing of sheet.tearing of sheet.
A drawn cup can be redrawn into a smaller cupA drawn cup can be redrawn into a smaller cup
but it must be annealed to prevent failure.but it must be annealed to prevent failure.
33. Punching and BlankingPunching and BlankingPunching and blankingPunching and blanking
operations are not metaloperations are not metal
forming operations but areforming operations but are
discussed together with metaldiscussed together with metal
forming because of theirforming because of their
similarity with deep drawingsimilarity with deep drawing
operation.operation.
Objective of punching andObjective of punching and
blanking is to removeblanking is to remove
material from the sheet metalmaterial from the sheet metal
by causing rupture, the punchby causing rupture, the punch
and die corners are notand die corners are not
provided with the any radius.provided with the any radius.
Tool steel is the mostTool steel is the most
common material for tool andcommon material for tool and
die. Carbides are also useddie. Carbides are also used
when high production iswhen high production is
needed.needed.
37. Self reading for your interestSelf reading for your interest
Defects in metal forming processesDefects in metal forming processes
and their remedies. (useand their remedies. (use KalpakjianKalpakjianโโss
book)book)
