-
T l W T l Lif &T l W T l Lif & M hi biliM hi
biliToolWear,ToolLife&ToolWear,ToolLife&MachinabilityMachinability
BySKMondalBySKMondal
ToolFailureTool failure is two types1. Slowdeath: The gradual or
progressive wearingg p g gaway of rake face (crater wear) or flank
(flank wear) ofthe cutting tool or
both.g2.Suddendeath:FailuresleadingtoprematureendofthetoolThe
suddendeath type of tool failure is difficult topredict. Tool
failure mechanisms include plasticpredict. Tool failure mechanisms
include plasticdeformation, brittle fracture, fatigue fracture or
edgechipping. However it is difficult to predict which ofpp g
pthese processes will dominate and when tool failurewill occur.
ToolWear( ) Fl kW(a) FlankWear(b) CraterWear( )(c) Chipping off
of the cutting edge
lToolWear FlankWear:(Wearland)ReasonAb i b h d i l d i l i i h
kAbrasion by hard particles and inclusions in the
workpiece.Shearing off the micro welds between tool and
workmaterialmaterial.Abrasion by fragments of builtupedge
ploughing
i h l f f h lagainst the clearance face of the tool.At low speed
flank wear predominates.p pIf MRR increased flank wear
increased.
FlankWear:(Wearland)EffectFl k di l ff h di iFlank wear directly
affect the component dimensionsproduced.Flank wear is usually the
most common determinant oftool lifetool life.
FlankWear:(Wearland)StagesFl k W i h f iFlankWear occurs in
three stages of varying wear rates
FlankWear:(Wearland)PrimarywearTh i h h h i d i i klThe region
where the sharp cutting edge is quicklybroken down and a finite
wear land is established.
Secondary wearyThe region where the wear progresses at a uniform
rate.
FlankWear:(Wearland)Tertiary wearTh i h d llThe region where
wear progresses at a graduallyincreasing rate.In the tertiary
region the wear of the cutting tool hasbecome sensitive to
increased tool temperature due tobecome sensitive to increased tool
temperature due tohigh wear land.R i di i d d b f h hiRegrinding is
recommended before they enter thisregion.
For IES, GATE, PSUs Page 2 of 49 Bhopal -2014
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ToollifecriteriaISO(A i id h ffl k (VB)i h
(Acertainwidthofflankwear(VB)isthemostcommoncriterion)Uniformwear:0.3mmaveragedoverallpastLocalizedwear:0
5mmonanyindividualpastLocalizedwear:0.5mmonanyindividualpast
CraterwearMore common in ductile materials which produce
hcontinuous chip.
C h k fCrater wear occurs on the rake face.
At hi h d t d i tAt very high speed crater wear predominates
For crater wear temperature is main culprit and toolFor crater
wear temperature is main culprit and tool
defuse into the chip material & tool temperature isdefuse
into the chip material & tool temperature is
maximum at some distance from the tool tip.
CraterwearContd..Crater depth exhibits linear increase with
time.It increases with MRRIt increases with MRR.
Crater wear has little or no influence on cutting forcesCrater
wear has little or no influence on cutting forces,work piece
tolerance or surface finish.
WearMechanism1. Abrasionwear
2. Adhesionwear
3 Diffusionwear3. Diffusionwear
4. Chemicaloroxidationwear
Whychippingofforfinecracksd l d h ddevelopedatthecuttingedge
Tool material is too brittle
Weak design of tool, such as high positive rake angle
As a result of crack that is already in the toolAs a result of
crack that is already in the tool
E i i h k l di f h lExcessive static or shock loading of the
tool.
NotchWearNotch wear on the trailing edge is to a great extent
an
id ti h i i h th ttioxidation wear mechanism occurring where the
cutting
edge leaves the machined workpiece material in the feededge
leaves the machined workpiece material in the feed
direction.
But abrasion and adhesion wear in a combined effect can
contribute to the formation of one or several notches.
Listtheimportantpropertiesofcuttingtoolt i l d l i h h i i t
tmaterialsandexplainwhyeachisimportant.
Hardness at high temperatures this provides longerHardness at
high temperatures this provides longerlife of the cutting tool and
allows higher cutting speeds.Toughness to provide the structural
strength neededto resist impacts and cutting forcesto resist
impacts and cutting forcesWear resistance to prolong usage before
replacementdoesnt chemically react another wear
factorFormable/manufacturable can be manufactured in
aFormable/manufacturable can be manufactured in auseful
geometry
ToolLifeCriteriaTool life criteria can be defined as a
predeterminednumerical value of any type of tool deterioration
whichnumerical value of any type of tool deterioration whichcan be
measured.
Some of
thewaysActualcuttingtimetofailure.VolumeofmetalremovedVolumeofmetalremoved.Numberofpartsproduced.p
pCuttingspeedforagiventimeLengthofworkmachined.
TaylorsToolLifeEquationbasedonFlankWearCausesCausesSlidingofthetoolalongthemachinedsurfaceTemperaturerise
nVT CnVT C=Where,V=cuttingspeed(m/min)T
Time(min)T=Time(min)n=exponentdependsontoolmaterialC=constantbasedontoolandworkmaterialandcuttingcondition.For
IES, GATE, PSUs Page 3 of 49 Bhopal -2014
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ValuesofExponentnn = 0.08 to 0.2 for HSS tool= 0.1 to 0.15 for
Cast Alloys
f bid l= 0.2 to 0.4 for carbide tool[IAS1999; IES2006][IAS 1999;
IES 2006]
= 0.5 to 0.7 for ceramic tool5 7[NTPC2003]
ExtendedorModifiedTaylorsequation
i.e Cuttingspeedhasthegreatereffectfollowedbyfeedg p g
yanddepthofcutrespectively.
l fToolLifeCurve
1.HSS 2.Carbide 3.Ceramic
Cuttingspeedusedfordifferenttoolmaterials
HSS(min)30m/min
-
lFormula=no oV T C
Optimum tool life for minimumcost
1T T if T , & givento c c t mm
C n C CC n
= +
1 if & given
m
tt m
C n C CC
=
g
Optimum tool life for Maximum Productivity
t mmC n
p y(minimum production time)
1 1T To cn
n =
Units:Tc min(Toolchangingtime)c g gCt
Rs./servicingorreplacement(Toolingcost)cost)Cm
Rs/min(Machiningcost)V m/min(Cuttingspeed)
Toolingcost(Ct)=toolregrindcost+tooldepreciationperservice/replacement
Machiningcost(C ) labour
cost+overheadcostperMachiningcost(Cm)=labour
cost+overheadcostpermin
MinimumCostVsProductionRate
V V Vmax.production max.profit min. costV >V >V
MachinabilityDefinitionM hi bili b i l d fi d bili
fMachinability can be tentatively defined as ability ofbeing
machined and more reasonably as ease ofmachining.
h f h h hSuch ease of machining or machining charactersof any
toolwork pair is to be judged by:y p j g y
Tool wear or tool lifeMagnitude of the cutting forcesSurface
finishSurface finishMagnitude of cutting temperatureg g pChip
forms.
MachinabilityContd.M hi bilit ill b hi h h tti fMachinability
will be high when cutting forces,temperature, surfaces roughness
and tool wear are less,t l lif i l d hi id ll if d h ttool life is
long and chips are ideally uniform and short.
The addition of sulphur lead and tellurium to nonThe addition of
sulphur, lead and tellurium to nonferrous and steel improves
machinability.S l h i dd d t t l l if th i ffi i tSulphur is added
to steel only if there is sufficientmanganese in it. Sulphur forms
manganese sulphidehi h i t i l t d h d t i t lwhich exists as an
isolated phase and act as internal
lubrication and chip breaker.If insufficient manganese is there
a low melting ironsulphide will formed around the austenite
grainboundary. Such steel is very weak and brittle.
FreeCuttingsteelsAddition of lead in low carbon resulphurised
steels andalso in aluminium copper and their alloys help reducealso
in aluminium, copper and their alloys help reducetheir s. The
dispersed lead particles act as discontinuityand solid lubricants
and thus improve machinability byand solid lubricants and thus
improve machinability byreducing friction, cutting forces and
temperature, tool
d BUE f iwear and BUE formation.It contains less than 0.35% lead
by weight .35 y gA free cutting steel containsC % Si % M % P % S %
Pb %C0.07%, Si0.03%, Mn0.9%, P0.04%, S0.22%, Pb0.15%
MachinabilityIndexOrMachinabilityRating
The machinability index KM is defined byKM = V6 /V6 RKM =
V60/V60R
Where V60 is the cutting speed for the target materialh l lif f
6 i V i h f hthat ensures tool life of 60 min, V60R is the same for
thereference material.If KM > 1, the machinability of the target
material isbetter that this of the reference material and vice
versabetter that this of the reference material, and vice versa
For IES, GATE, PSUs Page 5 of 49 Bhopal -2014
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RoleofmicrostructureonMachinabilityC i l d l l
fCoarsemicrostructureleadstolesservalueofs.
Therefore,s canbedesirablyreducedbyP h lik li f
lProperheattreatmentlikeannealingofsteelsControlledadditionofmaterialslikesulphur
(S),leadp ( ),(Pb),Tellerium
etcleadingtofreecuttingofsoftductilemetalsandalloysmetalsandalloys.
Brittlematerialsarerelativelymoremachinable.
ff f l k l ( )Effects of tool rake angle(s)
onmachinabilitymachinability
AsRakeangleincreasesmachinabilityincreases.
Buttoomuchincreaseinrakeweakensthecuttingedge.
EffectsofCuttingEdgeangle(s)onmachinabilitymachinability
Th i ti i th tti d l d t ff tThe variation in the cutting edge
angles does not affect
cutting force or specific energy requirement for cuttingcutting
force or specific energy requirement for cutting.
Increase in SCEA and reduction in ECEA improvesIncrease in SCEA
and reduction in ECEA improves
surface finish sizeably in continuous chip formation
hence Machinability.
Effectsofclearanceangleonmachinability
Inadequate clearance angle reduces tool life and surfacefinish
by tool work rubbing, and again too largeclearance reduces the tool
strength and tool life hencegmachinability.
EffectsofNoseRadiusonmachinabilityProper tool nose radiusing
improves machinability tosome extent throughsome extent
throughincrease in tool life by increasing mechanical strength
d d i h l iand reducing temperature at the tool tipreduction of
surface roughness, hmaxg , max
2fmax 8
fhR
=max 8R
SurfaceRoughnessIdeal Surface ( Zero nose radius)
fPeak to valley roughness (h) =tan cot
fSCEA ECEA+
and (Ra) = ( )4 4h f
SCEA ECEA=a
Practical Surface ( with nose radius = R)( )4 4 tan cotSCEA
ECEA+
2 2
ah and R8 18 3f fR R
= =a8 18 3R RChange in feed (f) is more important than a change
in nose radiusg ( ) p g(R) and depth of cut has no effect on
surface roughness.
Cutting fluidCuttingfluidThe cutting fluid acts primarily as a
coolant and
dl l b i t d i th f i ti ff t tsecondly as a lubricant, reducing
the friction effects atthe toolchip interface and the workblank
regions.Cast Iron: Machined dry or compressed air, Soluble oilfor
high speed machining and grindingfor high speed machining and
grindingBrass: Machined dry or straight mineral oil with ori h
EPAwithout EPA.
Aluminium: Machined dry or kerosene oil mixed withymineral oil
or soluble oilStainless steel and Heat resistant alloy:
HighStainless steel and Heat resistant alloy: Highperformance
soluble oil or neat oil with high
i i h hl i d EP ddi iconcentration with chlorinated EP
additive.
IAS 2009
MainIAS2009MainWhatareextremepressurelubricants?Whatareextreme
pressurelubricants?
[3 marks]Wh hi h d bbi iWhere high pressures and rubbing action
areencountered, hydrodynamic lubrication cannot be
i i d E P (EP) ddi i bmaintained; so Extreme Pressure (EP)
additives must beadded to the lubricant. EP lubrication is provided
by a
b f h i l h bnumber of chemical components such as
boron,phosphorus, sulfur, chlorine, or combination of these.Th d i
d b h hi hThe compounds are activated by the higher
temperatureresulting from extreme pressure. As the temperaturei EP
l l b i d lrises, EP molecules become reactive and
releasederivatives such as iron chloride or iron sulfide andf lid i
iforms a solid protective coating.
For IES, GATE, PSUs Page 6 of 49 Bhopal -2014
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MetalFormingMetalFormingSh tM t lO tiSheetMetalOperationP d M
llPowderMetallurgy
BySKMondalBySKMondal
FourImportantformingtechniquesare:Rolling
Forgingg g
ExtrusionExtrusion
D iDrawing
TerminologyTerminologySemifinished productI i h fi lid f f
lIngot: is the first solid form of steel.Bloom: is the product of
first breakdown of ingot has squarep g qcross section 6 x 6 in. or
largerBillet: is hot rolled from a bloom and is square 1 5 in on
aBillet: is hot rolled from a bloom and is square, 1.5 in. on aside
or larger.Sl b i th h t ll d i t bl t lSlab: is the hot rolled
ingot or bloom rectangular crosssection 10 in. or more wide and 1.5
in. or more thick.
slabIngot Bloom Billet
TerminologyMill product
Plate is the product with thickness > 5 mm
Sheet is the product with thickness < 5 mm and width >
600
mmmm
Strip is the product with a thickness < 5 mm and width
-
St i H d
iStrainHardeningStrainhardening(coldWorking)Strainhardening(coldWorking)
no K =
Strainrateeffect(hotWorking)
o
( g)
mo C =o
VelocityPlaten1 vdhWhere heightousInstantane
VelocityPlaten1===
hv
dtdh
h
ll b lMalleabilityMalleability is the property of a material
whereby it can
b h d h ld b h llbe shaped when cold by hammering or
rolling.
A ll bl i l i bl f d i l iA malleable material is capable of
undergoing plastic
deformation without fracturedeformation without fracture.
A malleable material should be plastic but it is notA malleable
material should be plastic but it is not
essential to be so strong.g
Lead, soft steel, wrought iron, copper and aluminium are
some materials in order of diminishing malleability.
ColdWorkingColdWorkinggW ki b l li i
Workingbelowrecrystalizationtemp.
d f ld kAdvantagesofColdWorking1. Better accuracy, closer
tolerances
2. Better surface finish
3. Strain hardening increases strength and hardness
4. Grain flow during deformation can cause desirable
directional properties in productdirectional properties in
product
5 No heating of work required (less total energy)5. No heating
of work required (less total energy)
d f ld kDisadvantagesofColdWorking1.
Equipmentofhigherforcesandpowerrequired
S f f t ti k i tb f f l d2.
Surfacesofstartingworkpiecemustbefreeofscaleand
dirt
3. Ductilityandstrainhardeninglimittheamountofforming
thatcanbedone
4. Insomeoperations,metalmustbeannealedtoallow
furtherdeformationfurtherdeformation
5. Somemetalsaresimplynotductileenoughtobecold5 p y g
worked.
HotWorkingHotWorking
WorkingaboverecrystalizationtempWorkingaboverecrystalizationtemp.
AdvantagesofHotWorking1. The porosity of the metal is largely
eliminated.2 The grain structure of the metal is refined2. The
grain structure of the metal is refined.3. The impurities like slag
are squeezed into fibers anddi ib d h h h ldistributed throughout
the metal.4. The mechanical properties such as toughness,4 p p g
,percentage elongation, percentage reduction in area, andresistance
to shock and vibration are improved due toresistance to shock and
vibration are improved due tothe refinement of grains.
DisadvantagesofHotWorking1. It requires expensive tools.2 It
produces poor surface finish due to the rapid2. It produces poor
surface finish, due to the rapidoxidation and scale formation on
the metal surface.
D h f fi i h l l3. Due to the poor surface finish, close
tolerancecannot be maintained.
Mi St t l Ch i H tMicroStructuralChangesinaHotWorking Process
(Rolling)WorkingProcess(Rolling)
For IES, GATE, PSUs Page 8 of 49 Bhopal -2014
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AnnealingAnnealing relieves the stresses from cold working
threestages: recovery recrystallization and grain growth
g
stages: recovery, recrystallization and grain growth.During
recovery, physical properties of the coldworked
i l d i h b bl h imaterial are restored without any observable
change inmicrostructure.
WarmFormingDeformation produced at temperatures intermediate
to
h d ld f k fhot and cold forming is known as warm forming.
C d ld f i i d l d iCompared to cold forming, it reduces loads,
increase
material ductilitymaterial ductility.
Compared to hot forming it produce less scaling andCompared to
hot forming, it produce less scaling and
decarburization, better dimensional precision andp
smoother surfaces.
h lIsothermalFormingDuring hot forming, cooler surfaces surround
a hotter
interior and the variations in strength can result in
noninterior, and the variations in strength can result in non
uniform deformation and cracking of the surface.
For temp.sensitive materials deformation is performed
under isothermal conditions.
Th di li b h d h k iThe dies or tooling must be heated to the
workpiece
temperature, sacrificing die life for product quality.p , g p q
y
Close tolerances, low residual stresses and uniform metal
flow.
RollingRollingg
BySKMondalBySKMondal
RollingDefinition: The process of plastically deforming
metal
b b llby passing it between rolls.
M id l d hi h d i d l lMost widely used, high production and
close tolerance.
F i ti b t th ll d th t l fFriction between the rolls and the
metal surface
produces high compressive stressproduces high compressive
stress.
Hotworking (unless mentioned cold rolling.Hot working (unless
mentioned cold rolling.
Metal will undergo biaxial compression.g p
HotRollingDone above the recrystallization temp.
Results fine grained structure.
S f lit d fi l di i l tSurface quality and final dimensions are
less accurate.
Breakdown of ingots into blooms and billets is done byBreakdown
of ingots into blooms and billets is done by
hotrolling. This is followed by further hotrolling intog y g
plate, sheet, rod, bar, pipe, rail.
Hot rolling is terminated when the temp. falls to about
(50 to 100C) above the recrystallization temp.For IES, GATE,
PSUs Page 9 of 49 Bhopal -2014
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ColdRollingDone below the recrystallization temp..
Products are sheet, strip, foil etc. with good surface
fi i h d i d h i l h i h lfinish and increased mechanical
strength with close
product dimensionsproduct dimensions.
Performed on fourhigh or clustertype rolling millsPerformed on
four high or cluster type rolling mills.
(Due to high force and power)( g p )
RingRollingRing rolls are used for tube rolling, ring
rolling.
As the rolls squeeze and rotate, the wall thickness is
d d d h di f h i ireduced and the diameter of the ring
increases.
Sh d ll b d t d id i t fShaped rolls can be used to produce a
wide variety of
crosssection profilescross section profiles.
Ring rolls are made of spheroidized graphite bainitic andRing
rolls are made of spheroidized graphite bainitic and
pearlitic matrix or alloy cast steel base.
SheetrollingIn sheet rolling we are only attempting to reduce
the
h k f lcross section thickness of a material.
RollForming RollBendingA continuous form of threepoint bending
is roll
bending, where plates, sheets, and rolled shapes can
be bent to a desired curvature on forming rolls.
Upper roll being adjustable to control the degree of
tcurvature.
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Shaperolling PackrollingPack rolling involves hot rolling
multiple sheets of
l h l f lmaterial at once, such as aluminium foil.
A hi f id fil h i ldiA thin surface oxide film prevents their
welding.
ThreadrollingUsed to produce threads in substantial
quantities.
This is a coldforming process in which the threads are
f d b lli h d bl k b h d d diformed by rolling a thread blank
between hardened dies
that cause the metal to flow radially into the desiredthat cause
the metal to flow radially into the desired
shape.p
No metal is removed, greater strength, smoother, harder,g g
and more wearresistant surface than cut threads.
Threadrollingcontd.Major diameter is always greater than the
diameter of the
bl k (blank (
Bl k di i li l l h h i h di fBlank diameter is little larger
than the pitch diameter of
the threadthe thread.
Restricted to ductile materialsRestricted to ductile
materials.
ManufactureofgearsbyrollingThe straight and helical teeth of
disc or rod type external
l f ll d d d d lsteel gears of small to medium diameter and
module are
generated by cold rollinggenerated by cold rolling.
High accuracy and surface integrityHigh accuracy and surface
integrity.
Employed for high productivity and high quality (costlyEmployed
for high productivity and high quality. (costly
machine))
Larger size gears are formed by hot rolling and then
finished by machining.
Fig.Productionofteethofspurgearsbyrolling
llRollpiercing It is a variation of rolling called roll
piercing.The billet or round stock is rolled between two
rolls,,both of them rotating in the same direction with theiraxes
at an angle of 4.5 to 6.5 degree.axes at an angle of 4.5 to 6.5
degree.These rolls have a central cylindrical portion with thesides
tapering slightly There are two small side rollssides tapering
slightly. There are two small side rolls,which help in guiding the
metal.Because of the angle at which the roll meets the metal,it
gets in addition to a rotary motion, an additionalaxial advance,
which brings the metal into the rolls.This crossrolling action
makes the metal friable at thegcentre which is then easily pierced
and given acylindrical shape by the centralpiercing
mandrel.cylindrical shape by the central piercing mandrel.
For IES, GATE, PSUs Page 11 of 49 Bhopal -2014
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PlanetarymillConsist of a pair of heavy backing rolls surrounded
by a largeConsist of a pair of heavy backing rolls surrounded by a
largenumber of planetary rolls.Each planetary roll gives an almost
constant reduction to theEach planetary roll gives an almost
constant reduction to theslab as it sweeps out a circular path
between the backing rollsand the slab.As each pair of planetary
rolls ceases to have contact with thework piece, another pair of
rolls makes contact and repeath d ithat reduction.The overall
reduction is the summation of a series of smalld ti b h i f ll Th f
th l t illreductions by each pair of rolls. Therefore, the
planetary mill
can reduce a slab directly to strip in one pass through
themillmill.The operation requires feed rolls to introduce the slab
intothe mill, and a pair of planishing rolls on the exit to
improvethe mill, and a pair of planishing rolls on the exit to
improvethe surface finish.
Camber
Camber can be used to correct the roll deflection (at onlyone
value of the roll force).
LubricationforRollingHot rolling of ferrous metals is done
without a lubricant.
Hot rolling of nonferrous metals a wide variety of
d d il l i d f id dcompounded oils, emulsions and fatty acids
are used.
C ld lli l b i t t l bl il lCold rolling lubricants are
watersoluble oils, low
viscosity lubricants such as mineral oils emulsionsviscosity
lubricants, such as mineral oils, emulsions,
paraffin and fatty acids.p y
DefectsinRollingf hDefects Whatis Cause
Surface Scale, rust, Inclusions andSurfaceDefects
Scale, rust,scratches, pits,cracks
Inclusions andimpurities in thematerialscracks materials
Wavy edges Strip is thinner Due to roll bendingalong its
edgesthan at its centre.
edges elongates moreand buckle.
Alligatoring Edge breaks Nonuniformdeformationdeformation
GeometryofRollingProcess DraftT l d i d f k i
lliTotalreductionordrafttakeninrolling.
h h h 2 (R R ) D (1 ) 0 fh = h - h = 2 (R - R cos ) = D (1 - cos
) Usually,thereductioninbloomingmillsisabout100y, gmmandinslabbing
mills,about50to60mm.
MaximumDraftPossibleMaximumDraftPossible
( ) 2h R( ) 2maxh = R
TorqueandPowerTh i i i ll i fThe power is spent principally in
four ways1) The energy needed to deform the metal.) gy2) The energy
needed to overcome the frictional force.) Th l i h i i d i i3) The
power lost in the pinions and powertransmissionsystem.4) Electrical
losses in the various motors and generators.
Remarks: Losses in the windup reel and uncoiler mustpalso be
considered.
For IES, GATE, PSUs Page 12 of 49 Bhopal -2014
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TorqueandPower
Will bWill bediscusseddiscussedin class
[ForIESConventionalOnly][ForIESConventionalOnly]
AssumptionsinRollingR ll i h i id li d1. Rolls are straight,
rigid cylinders.
2. Strip is wide compared with its thickness, so that nop p
,widening of strip occurs (plane strain conditions).
3 The arc of contact is circular with a radius greater than3.
The arc of contact is circular with a radius greater thanthe radius
of the roll.
4. The material is rigid perfectly plastic (constant
yieldstrength).st e gt ).
5. The coefficient of friction is constant over the toolk i t
fwork interface.
StressEquilibriumofanElementinRolling
Considering the thickness of the element perpendicular tothe
plane of paper to be unity We get equilibriumthe plane of paper to
be unity, We get equilibriumequation in xdirection as,- h + ( +d )
(h + dh) - 2pR d sin x x x
x+ 2 R d cos = 0
xFor sliding friction, = p Simplifying and neglecting d d t i d
1 t
( )second order terms, sin and cos 1, we get
xd h
=
( ) 2 ( )x pRd
=
'0 0
23x
p = =
( ) ( )'03
2d h p pR = ( ) ( )0 2h p pRdd p
( )'0 '0
1 2d ph pRd
=
0
' d p ph
+ ( ) ( )'1 2d h pR = 0 ' '0 0
hd
+
( ) ( )01 2h pRd =
'0
'
Due to cold rolling, increases as h decreases,'0thus nearly a
constant and itsderivative zero. h
d
( )( )
'0/ 2
d p Rd
= ( )
( )
'0
2
/p h
=
( )( )
2
'
2 1 cos
/f fh h R h R
d
= + +
( )( ) ( )
02'
/ 2/
d p R dh Rp
=
+
( )0/Integrating both side
fh Rp +
( )'Integrating both side
2ln / R dp 2 ( )R d I II say ( )0ln /f
ph
=+ 2 2
( )f
d I II sayR h R
=+
22Rd 2Rd 2d hI ln
h h / R Rh R = = = = + f
2f
h h / R Rh RhNow h / R
+
= +Now h / R R
d h
= +
d hor 2d R
R
=
2f
2RII dh R
=+ f
22 d
h / R = 2
f
1
h / R R R
+
1
f f
R R2 .tan .h h
=
( ) = + ' 10
h R Rln p / ln 2 .tan . lnCR h h
( )
f f
' H
R h hhC =
H0p C eR
=
1
f f
R Rwhere H 2 .tan .h h =
f fh hNow at entry ,
=
=0Hence H H with replaced by in above equation
At exit 0== '0
At exit 0Therefor p
=
oH' o0
hIn theentryzone, p C. eR 0
y , pR
R= oH
o
Rand C .eh
( )= 0
o
H H'0
hp . e00
p . eh
I th it
In the exit zoneh
=
' H0
f
hp .eh f
At theneutral po int aboveequationswill givesameresults
For IES, GATE, PSUs Page 13 of 49 Bhopal -2014