Forging document for mechanical engineering students

Forging

1. FORGING
MODULE 3

4. UPSET FORGING

6. Open Die forging
Impression/Closed Die forging

7. Flashless/ Precision forging

13. STANDARD TERMINOLOGY

21. Forgingisametalworkingprocessinwhichuseful
shapeisobtainedinsolidstatebyhammeringor
pressingmetal.
FORGING –OPERATIONS AND
CLASSIFICATIONS
1. Upsetting

22. 2. Edging
Endsofthebarareshapedtorequirement
usingedgingdies.

23. 3. Fullering
Crosssectionalareaoftheworkreduces
asmetalflowsoutward,awayfromcentre

24. 4. Drawing
Crosssectionalareaoftheworkisreduced
withcorrespondingincreaseinlengthusing
convexdies.

25. 5. Swaging
Crosssectionalareaofthebarisreduced
usingconcavedies.

26. 6. Piercing
Metal flows around the die cavity as a moving
die pierces the metal.

27. 7. Punching
Itisacuttingoperationinwhicharequired
holeisproducedusingapunchingdie.
8. Bending: The metal is bent around a die/anvil.

28. Roll forging
Inthisprocess,thebarstockisreducedincross-sectionor
undergoeschangeincross-sectionwhenitispassedthrough
apairofgroovedrollsmadeofdiesteel.
Thisprocessservesastheinitialprocessingstepforforging
ofpartssuchasconnectingrod,crankshaftetc.

29. Aparticulartypeofrollforgingcalledskewrollingis
usedformakingsphericalballsforballbearings
SKEW ROLLING

30. Cogging
Successivelyreducingthethicknessofabarwith
opendieforging
•Alsocalleddrawingout
•Reducingthethicknessofalongsectionofabar
withoutexcessiveforcesormachining

31. Forgingbetweentwoshapeddies
•FulleringandEdgingdistributematerialinto
specificregionsoftheblank
•Blockingcreatesaroughshape

32. Precision Forging
•Truecloseddieor
flashlessforginguses
precisevolumesof
material to
completelyfillthe
diecavity

33. •Undersizeblankswillnotfillthecavity,oversize
blankswillcausehighpressuresandmaydamage
thedies
••Reducesthenumberofadditionaloperations
andwastedmaterial
••Near-net-shapeforging(ornet-shape)

34. DIE INSERTS

38. SWAGING

39. Rotaryswagingorradialforgingand
Tubeswaging
•Asolidrodortubeissubjectedto
radialimpactforcesbyreciprocating
dies(workpieceisstationary)
•Screwdriverbladesmadethisway

41. •Coiningisforminting
coinsandjewelry
•Completelycloseddies
andhighpressures(5-6
timesthestrengthofthe
material)toobtainfine
details
•Lubricantscannotbe
usedsincetheyare
incompressible
COINING

42. Anexampleofacoiningoperationtoproducean
impressionoftheletterE

43. Die Design
Mustknowworkpiecematerialstrengthandductility,
deformationrate,temperaturesensitivity,frictional
characteristics
Forgeabilityofmaterialsiscapabilitytoundergo
deformationwithoutcracking
Mustevaluateshape,size,andcomplexityofdesign
Materialflowsinthedirectionofleastresistance,which
iswhyintermediateshapesmayneedtobeformed

44. Preshapingshouldpreventmaterialfromeasily
flowingintoflash,producefavorablegrainflow
patterns,andminimizefrictionandwearatthedie-
workpieceinterface
Computerscanmodelandpredictmaterialflow

45. •Parting lines are usually at the largest cross section
•Flash specifications:
•Flash clearance should be 3% of maximum forging
thickness
•Land that is 2-5 times flash thickness, then a larger
gutter that does not restrict flash flow

46. • Draft angles are needed (7-10 deginternal, 3-5
external)
• Avoid small radii
• Avoid sharp corners
• Inserts can be used

47. Diematerialsmusthavestrengthandtoughnessat
elevatedtemperatures,hardenability,resistanceto
mechanicalandthermalshock,wearresistance
Dieselectionbasedonsize,requiredproperties,
forgingtemperature,operationtype,cost,and
productionquantities
Commondiematerialsaretoolanddiesteelswith
chromium,nickel,molybdenum,andvanadium

48. Diesareforgedfromcastings,andthenmachined
andfinishedasneeded,oftenwithheattreatment
toincreasehardnessandwearresistance
Lubricantsactasthermalbarriersforhot
workpieceandcoolerdies,improvemetalflow,
andarepartingagents

49. Die Failure Causes
Improperdesign
Defectivematerial
Improperheattreatmentandfinishing
operations
Overheatingandcrackscausedbytemperature
cycling–usuallypreheatdiesto1500-2500
degreesCelsius
Excessivewear–chippingorcrackingfrom
impactforces(canberepairedbyweldingor
lasermetaldeposition)

50. Overloading
Misuseorimproperhandling–failureto
removeaforgedpartbeforeinsertinga
newblank

51. Types of Forging Machine
Work Restricted Machines (Energy or Load
Limited) –Hammers
• Gravity drop hammers
• Power hammers
• Counterblow hammers –Friction Screw
Presses –Hydraulic Presses
• Stroke Limited (Restricted) Machines –
Mechanical presses

52. DIFFERENT TYPES OF DROP HAMMERS

53. Mechanical board hammer
Itisastrokerestrictedmachine.
•Repeatedlytheboard(weight)israisedbyrolls
andisdroppedonthedie.
•Ratingisintermsofweightoftheramandenergy
delivered.

56. Steam Hammer (Power Hammer)
Range: 5 kNto 200 kN
• It uses steam in a piston and cylinder
arrangement.
• It has greater forging capacity.
• It can produce forgings ranging from a
few kgsto several tonnes.
• Preferred in closed die forging

57. FORGING MACHINES
Hydraulic press

58. It is a load restricted machine.
• It has more of squeezing action than hammering
action.
• Hence dies can be smaller and have longer life
than with a hammer.
Hydraulic press

60. Features of Hydraulic Press
• Full press load is available during the full
stroke of the ram.
• Ram velocity can be controlled and varied
during the stroke.
• It is a slow speed machine and hence has
longer contact time and hence higher die
temperatures.
• The slow squeezing action gives close
tolerance on forgings.
• Initial cost is higher compared to hammers.

61. Mechanicalpresswithan
eccentricdrive;the
eccentricshaftcanbe
replacedbyacrankshaftto
givetheup-and-down
motiontotheram.

62. Knuckle -joint pressScrew press

63. RACK AND PINION PRESS CRANK PRESS

64. Gravity drop hammer

65. ForgingHammers
•GravityDropHammers–dropforgingwith
afreefallingram;energybasedonproductof
ram’sweightanddropheight
Ramweightsof180-4500kg(400-10000lbs)
•PowerDropHammers–downstrokeis
acceleratedbysteam,air,orhydraulic
pressure
Ramweightsof225-22500kg

66. CounterblowHammers–tworamsthat
approacheachotherhorizontallyor
vertically(partmayberotatedbetween
successiveblows);operateathighspeeds
withlessvibrationstransmitted–verylarge
capacitypossible
HighEnergyRateMachines–ram
acceleratedbyaninertgasathighpressure;
veryhighspeedsbutproblemswith
maintenance,diebreakage,andsafety

67. FORGING HAMMERS

68. Mechanical Presses
MechanicalPresses–crankor
eccentricshaftdriven,orknuckle-joint
forveryhighforces;strokelimited
2.7-107MN(300-14000tons)
Higherproductionratesthan
hammers
lessblowsMoreprecisethan
hammers
movingdieplateguidedbyslide
waysorcolumns

69. Hydraulic Presses
HydraulicPresses–constant
speeds,loadlimited,longer
processingtimes,higherinitial
costthanmechanicalpresses
butrequirelessmaintenance
125MN(14000tons)
opendie,450MN(50000
tons)closeddie

70. Friction Screw Presses
ScrewPresses–
flywheeldriven,energy
limited(ifdiesdonot
completelyclose,cycle
repeats)
•Smallproduction
runs,highprecision
•1.4-280MN(160-
31500tons)

72. FORGING DEFECTS
The different types of defects, occurring in the
forging operations are as follows:
1.Incomplete die filling.
2.Die misalignment.
3.Forging laps.
4.Incomplete forging penetration-should forge on
the press.
5.Microstructural differences resulting in
pronounced property variation.
6.Hot shortness, due to high sulphurconcentration
in steel and nickel.

73. 7.Pittedsurface,duetooxidescalesoccurring
athightemperaturestickonthedies.
8.Buckling,inupsettingforging,duetohigh
compressivestress.
9.Surfacecracking,duetotemperature
differentialbetweensurfaceandcenter,or
excessiveworkingofthesurfaceattoolow
temperature.
10.Microcracking,duetoresidualstress.

76. EXTRUSION

77. EXTRUSION
HOT EXTRUSION COLD EXTRUSION
Forward or direct extrusion
Backward or indirect extrusion
Hooker Extrusion
Hydrostatic extrusion
Impact extrusion

78. Extrusionisaplasticdeformationprocess
inwhichablockofmetal(billet)isforced
toflowbycompressionthroughthedie
openingofasmallercross-sectionalarea
thanthatoftheoriginalbillet

79. Extrusion is an indirect-compression process
Definition and principle of DIRECT extrusion

80. 1. DIRECT EXTRUSION

81. 2. INDIRECT EXTRUSION

82. INDIRECT EXTRUSION

83. Inindirectextrusion,thedieatthefrontendof
thehollowstemmovesrelativetothecontainer,
butthereisnorelativedisplacementbetween
thebilletandthecontainer.
Therefore,thisprocessischaracterizedbythe
absenceoffrictionbetweenthebilletsurface
andthecontainer,andthereisnodisplacement
ofthebilletcenterrelativetotheperipheral
regions.

86. HYDROSTATIC EXTRUSION_Cold
Extrusion Forward

87. LATERAL EXTRUSION

88. HOOKER EXTRUSION

89. Cold Extrusion_ Backward

90. Processvariablesindirectextrusion.Thedie
angle,reductionincrosssection,extrusion
speed,billettemperature,lubricationallaffect
theextrusionpressure.

91. Typicalextrusion–dieconfigurations:(a)diefor
nonferrousmetals;(b)dieforferrousmetals;(c)die
foraTdieforaT-shapedextrusionmadeofhot-work
diesteelandusedwithmoltenglassasalubricant

92. Extrusions and examples of products made by
sectioning off extrusions

93. Extrusion ratio,f
o
x
A
A
r

95. Extrusion
Defects
a)Centre-burst:internalcrackduetoexcessivetensile
stressatthecentrepossiblybecauseofhighdieangle,
lowextrusionratio.
b)Piping:sinkholeattheendofbilletunderdirect
extrusion.
c)Surfacecracking:Highparttemperatureduetolow
extrusionspeedandhighstrainrates.

96. Extrusion Force
Force,F,dependson:
Strengthofbilletmaterial
ExtrusionRatio,R,A
o/A
f
Frictionbetweenbilletandchamber&die
surfaces
Processvariables:temperature,velocity
F = A
0k ln(A
0/A
f)
TheExtrusionconstant,k,isdetermined
experimentally.

97. Extrusionconstantkforvariousmetalsat
differenttemperatures

98. Metal Flow in Extrusion
Influences quality & mechanical
properties of extruded product
Material flows longitudinally
Elongated grain structure

99. Typesofmetalflowinextrudingwithsquaredies.
(a)Flowpatternobtainedatlowfrictionorinindirectextrusion.
(b)Patternobtainedwithhighfrictionatthebillet–chamberinterfaces.
(c)Patternobtainedathighfrictionorwithcoolingoftheouterregionsofthebilletinthe
chamber.Thistypeofpattern,observedinmetalswhosestrengthincreasesrapidlywith
decreasingtemperature,leadstoadefectknownaspipe(orextrusion)defect.

100. Usehighertemperaturestoimproveductility&
metalflow
Cancauseexcessivediewear,resultofabrasion
fromsurfaceoxides
Canhavenonuniformdeformationcausedby
coolingsurfacesofbilletanddie
Improvebypreheatingdie
Surfaceoxidesonproductmaybeundesirable
whengoodsurfacefinishisimportant
Canpreventextrusionofsurfaceoxidesbymaking
thediameterofthedummyblockalittlesmaller
thanthecontainer;thiskeepsathinshell(“skull”)
ofoxidesinthecontainer
HOT EXTRUSION

102. Extrusionofaseamlesstube
(a)usinganinternalmandrelthatmovesindependently
oftheram.(Analternativearrangementhasthe
mandrelintegralwiththeram.)
(b)usingaspiderdietoproduceseamlesstubing.

103. Poorandgoodexamplesofcrosssectionstobeextruded
Poorandgoodexamplesexamplesofcrosssectionssections
tobeextrudedextruded.
Notetheimportanceofeliminatingsharpcornersandof
keepingsectionthicknessesuniform.

104. Lubrication
Usefulinhotextrusion:
Materialflowduringextrusion
Surfacefinish&integrity
Productquality
Extrusionforces
Glassisexcellentlubricantfor:
Steels
Stainlesssteels
High-temperaturemetals&alloys
Glassappliedaspowdertobilletsurfaceor
Insertglasspadatdieentrance;whenheated,meltedglass
lubricatesdiesurface

106. ColdExtrusion
Usesslugscutfromcoldfinishedorhotrolledbars,
wire,orplates
Smallerslugs(≤40mmor1.5”40mmor1.5”)are
sheared;endssquaredifnecessary
Largerslugsaremachinedtospecificlengths
Stressesontooldiesareveryhigh
Lubricationiscritical,especiallywithsteels
Applyphosphate-conversioncoatingonworkpiece,
conversioncoatingonworkpiece,followedbysoap
orwax

107. Cold Extrusion
Force = F = 1.7A
oY
avgέ
A
oiscrosssectionalareaofblank
Y
avgisaverageflowstressofmetal
έistruestrainthatpieceundergoes
=ln(A
o/A
f)

108. DRAWING

109. Drawing
•Changingthecross-sectionalareaorshapeof
asolidrod,wire,ortubingbypullingitthrough
adie
•Rodisthetermforlargercrosssections,wire
forsmaller
•Typicalproducts:Electricalwiring,Cable,Tension-
loadedstructuralmembers,Weldingelectrodes,Springs,
Paperclips,Bicyclewheelspokes,Musicalinstrumentstrings.
Dieandmandrelmaterialstypicallytoolsteels(chromium
plated)andcarbides(titaniumnitridecoated),diamondfor
finewire

110. DrawingParameters
•Parametersincludedieangle(a),reductionincross
sectionalarea,drawingspeed,temperature,andlubrication
•Foracertainreductionindiameterandfrictionconditions,
thereisanoptimumdieangle
•Y
avgisaveragetruestressofthematerialinthediegap
•Dieangleistypically6-15degrees
•Maximumreductionperpassis63%,butmorethan45%
cancauselubricantbreakdownandsurface-finish
deterioration
•Thesmallertheinitialarea,thesmallerthereductionper
passpercentagethatistypicallyused
•Intermediateannealingmaybeneededbetweenpasses

112. Indrawing,thecrosssectionofalongrodor
wireisreducedorchangedbypulling(hence
thetermdrawing)itthroughadiecalledadraw
die

113. DrawingVariousShapes•Drawingflatstrips
(ironing)isusedinmakingbeveragecans•
Bundledrawingisusedtosimultaneouslydraw
thousandsofwireswithfinalpolygonalcross
sectionalshapes

114. TubeDrawing:
Drawingcanbeusedtoreducethediameteror
wallthicknessofseamlesstubesandpipes,after
theinitialtubinghasbeenproducedbysome
otherprocesssuchasextrusion.
Tubedrawingcanbecarriedouteitherwithor
withoutamandrel.
Thesimplestmethodusesnomandrelandis
usedfordiameterreduction.
Thetermtubesinkingissometimesappliedto
thisoperation.

115. Examplesoftubedrawingoperations,withandwithoutaninternal
mandrel.Notethatavarietyofdiametersandwallthicknessescan
beproducedfromthesameinitialtubestock(whichhasbeen
madebyotherprocesses).

116. Wiresizesdownto0.03mm(0.001in)are
possibleinwiredrawing
Continuous drawing of wire

117. Wiredrawingisdoneoncontinuousdrawing
machinesthatconsistofmultipledrawdies,
separatedbyaccumulatingdrumsbetween
thedies.
Eachdrum,calledacapstan,ismotordriven
toprovidetheproperpullforcetodrawthe
wirestockthroughtheupstreamdie.
Italsomaintainsamodesttensiononthe
wireasitproceedstothenextdrawdiein
theseries.

118. Eachdieprovidesacertainamountof
reductioninthewire,sothatthedesired
totalreductionisachievedbytheseries.
Dependingonthemetaltobeprocessed
andthetotalreduction,annealingofthewire
issometimesrequiredbetweengroupsof
diesintheseries.