Forging and Forging and Sheet Metal Forming Sheet Metal Forming Automotive Production Engineer by hol Suranaree University of Technology September 2007 Dr. Tapany Udomphol School of Metallurgical Engineering Suranaree University of Technology T. Udomph
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Forging andForging andSheet Metal FormingSheet Metal Forming
Dr. Tapany Udomphol
Automotive Production Engineer
by
T. U
dom
phol
Suranaree University of Technology September 2007
Dr. Tapany Udomphol
School of Metallurgical Engineering
Suranaree University of Technology
T. U
dom
phol
Forging andForging andSheet Metal FormingSheet Metal Forming
T. U
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phol
• Introduction to metal forming• Hot and cold working• Deformation geometry• Classification of forging processes• Die design and die materials• Metal flow in forging• Force in metal forging• Forging defects
Outline Part I: Forging of Metals ( )
Suranaree University of Technology September 2007
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• Introduction to metal forming• Hot and cold working• Deformation geometry• Classification of forging processes• Die design and die materials• Metal flow in forging• Force in metal forging• Forging defects
Forging andForging andSheet Metal FormingSheet Metal Forming
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Outline Part II: Sheet metal forming ( )
• Introduction to sheet metal forming• Sheet metal parts• Classification of sheet metal forming• Forming limit criteria• Defects in formed parts
Suranaree University of Technology September 2007
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• Introduction to sheet metal forming• Sheet metal parts• Classification of sheet metal forming• Forming limit criteria• Defects in formed parts
Introduction to metal formingIntroduction to metal formingT.
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Introduction to metal formingIntroduction to metal formingT.
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There are a wide range of different metal parts involved in anautomobile production.
www.designchain.com
Suranaree University of Technology September 2007
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encarta.msn.com
Introduction to metal formingIntroduction to metal formingT.
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Casting
• Gravity die casting• Pressure die casting• Centrifugal casting• Injection moulding• Rotational moulding
i.e.
• Electrochemical machining• Electrical discharge machining• Single/multiple point cutting• Grinding
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Metalprocessing
Cutting
Forming
Joining
• Electrochemical machining• Electrical discharge machining• Single/multiple point cutting• Grinding
i.e.
• Sheet metal forming• Forging• Rolling• Extrusion• Wire drawing
i.e.
i.e.• Fusion welding (arc, laser,electron beam)
• Solid state welding (friction)•Mechanical joining
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Metal forming
Compressiveforming
Combined tensileand compressive
forming
Tensileforming
Forming bybending
Forming byshearing
Classification of metal formingby subgroups
Suranaree University of Technology September 2007
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Compressiveforming
Combined tensileand compressive
forming
Tensileforming
Forming bybending
Forming byshearing
•Rolling
•Open die forming
•Closed die forming
•Indenting
•Pushing through a die
•Pulling through a die
•Deep drawing
•Flange forming
•Spinning
•Upset bulging
•Stretching
•Expanding
•Recessing
•Bending withlinear toolmotion
•Bending withrotary toolmotion
•Joggling
•Twisting
•Blanking
•Coining
Introduction to metal formingIntroduction to metal formingT.
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Forgings
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Forged wheelsHot forming
productForged aluminium
pistons andconnecting rods
Introduction to metal formingIntroduction to metal formingT.
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Net shape and metal powder forming products
Powder metalforming parts
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Net shapemetal power
parts
Sinteredmetal parts
Metal injectionmoulding parts
Powder metalforming parts
Introduction to metal formingIntroduction to metal formingT.
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Metal Sheet forming productswww.numerica-srl.it
Electromagneticforming of
automotive parts
Suranaree University of Technology September 2007
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Stamped plateswww.mse.eng.ohio-state.edu
Introduction to metal formingIntroduction to metal formingT.
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www.ducommunaero.com
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Forging machine
www.macri.it
Hot and cold workingHot and cold workingT.
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• The methods used to mechanically shape metalsinto other product forms.
Workingprocesses
Hot working (0.6-0.8Tm)
Suranaree University of Technology September 2007
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Cold working (< 0.3Tm)
• Primary process• Recrystallisation
• Secondary process• No recrystallisation
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Annealing mechanismsAnnealing mechanismsin cold worked metalsin cold worked metals
• Mechanical properties change dueto temperature after cold working
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Suranaree University of Technology September 2007
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Annealing mechanismsAnnealing mechanismsin cold worked metalsin cold worked metals
Ductility
Hardness
Strength
Pro
perti
es
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Annealing mechanisms in cold worked metals
Recovery Recrystallisation Grain growth
Temperature
Pro
perti
es
Cold worked andrecovered
New grains
~0.3Tm ~0.5Tm
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Effects of grain size and strainEffects of grain size and strainon recrystallisation temperatureon recrystallisation temperature
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Schematic of recrystallisation diagram
Smaller grains Better strength/properties
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Effects of grain size and strainEffects of grain size and strainon recrystallisation temperatureon recrystallisation temperature
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Flow stress of aluminium as a function ofstrain at different temperature
Flow curves of Cu Zn28
Flow stress Flow stressTemp Strain rate
Advantages and disadvantagesAdvantages and disadvantagesof hot and cold workingof hot and cold working
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Hot working Cold working
Advantages Advantages
• Stronger• Good surface finish• Good dimensional control• Easy handling
• Workpiece is formed under highpressure in a closed cavity.• Small components• Precision forging• Expensive die
Suranaree University of Technology September 2007
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• Workpiece is formed under highpressure in a closed cavity.• Small components• Precision forging• Expensive die
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Forg
ing
load
Forg
ing
com
plet
e
Die cavitycompletelyfilled
Flash beginsto form
Forging loadForging load
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Forg
ing
load
Forg
ing
com
plet
e
Forging stroke
Flash beginsto form
Dies contactworkpiece
Typical curve of forging load vs. stroke forclosed-die forging.
Flash is the excess metal, whichsquirts out of the cavity as a thickribbon of metal.
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The flash serves two purposes:• Acts as a ‘safety value’ for excess metal.• Builds up high pressure to ensure thatthe metal fills all recesses of the die cavity.
Functions of flashFunctions of flash
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The flash serves two purposes:• Acts as a ‘safety value’ for excess metal.• Builds up high pressure to ensure thatthe metal fills all recesses of the die cavity.
Remark: It is necessary to achieve complete filling of the forging cavitywithout generating excessive pressures against the die that maycause it to fracture.
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ClosedClosed--die designdie design
Considerations• workpiece volume and weight• number of preforming steps and their configuration• flash dimensions in preforming and finishing diesthe load and energy requirement for each forging operation, forexample; the flow stress of the materials, the fictional condition,the flow of the material in order to develop the optimum geometry forthe dies.
Suranaree University of Technology September 2007
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Considerations• workpiece volume and weight• number of preforming steps and their configuration• flash dimensions in preforming and finishing diesthe load and energy requirement for each forging operation, forexample; the flow stress of the materials, the fictional condition,the flow of the material in order to develop the optimum geometry forthe dies.
Shape classificationShape classificationT.
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Shape classificationShape classificationT.
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Die set and forging steps forDie set and forging steps forautomobile engine connecting rodautomobile engine connecting rod
• Preforming of a round piece in an open die arrangement.• Rough shape is formed using a block die.• Finishing die gives final tolerances and surface finish.• Removal of flash (excess metal).
General considerationsGeneral considerationsfor preform designfor preform design
• Metal used = Metal preform + Flash.
• Concave radii of the preform > radii on the final forging part.
• Cross section of the preform should be higher and narrower than the
final cross section.
draft angle
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• Shapes with thin and long sections orprojections (ribs and webs) are moredifficult to process due to
• higher surface area per unit volume• increasing friction• temperature effects.
draft angleweb
rib
Some typical nomenclature
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• Smooth metal flow – symmetry dies• Avoid shape change
• Minimum flash to do the job.
• Tapered or drafted to facilitate removal of the finished piece.
• Draft allowance is approximately 3-5o outside and 7-10o inside.
• Counterlock to prevent side thrust.
General considerationsfor preform design
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• Smooth metal flow – symmetry dies• Avoid shape change
• Minimum flash to do the job.
• Tapered or drafted to facilitate removal of the finished piece.
• Draft allowance is approximately 3-5o outside and 7-10o inside.
• Counterlock to prevent side thrust.
CounterlockSide thrust
draft angleweb
rib
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Die materials
• Thermal shock resistance• Thermal fatigue resistance• High temperature strength• High wear resistance• High toughness and ductility• High hardenability• High dimensional stabilityduring hardening• High machinability
Required properties
Die materials: alloyed steels (with Cr,Mo, W, V), tool steels, cast steels or castiron. (Heat treatments such as nitriding orchromium plating)
Forging die
www.nitrex.com
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• Thermal shock resistance• Thermal fatigue resistance• High temperature strength• High wear resistance• High toughness and ductility• High hardenability• High dimensional stabilityduring hardening• High machinability
Die materials: alloyed steels (with Cr,Mo, W, V), tool steels, cast steels or castiron. (Heat treatments such as nitriding orchromium plating)
1) Carbon steels with 0.7-0.85% C areappropriate for small tools and flatimpressions.
2) Medium-alloyed tool steels forhammer dies.
3) Highly alloyed steels for hightemperature resistant dies used inpresses and horizontal forgingmachines.
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Forgingmaterials
Steels Copper and copper alloys Light alloysDIN AISI DIN AISI DIN AISI
Forging dies C70 W2 -
C85 W2 -
60MnSi4 - X30WCrV53 H21 X30WCrV53 -
Die materials
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40CrMnMo7 - X38CrMoV51 H11 X38CrMoV51 H11
X32CrMoV33 H10
Die inserts 55NiCrMoV6 6F2 55NiCrMoV6
56NiCrMoV7 6F3 56NiCrMoV7 6F2
57NiCrMoV77 - 57NiCrMoV77 - 57NiCrMoV77 6F3
35NiCrMo16 -
X38CrMoV51 H11 X30WCrV93 H21 X38CrMoV51 H11
X32CrMoV33 H10 X32CrMoV33 H10 X32CrMoV33 H10
X30WCrV53 - X30WCrV52 - X30WCrV53 -
X37CrMoW51 H12
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To increase die life1) Improving die materials such
as using composite die or2) Using surface coating or self-
• Identify the neutral surface• Metal flows away from theneutral surface in a directionperpendicular to the die motion.
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• Identify the neutral surface• Metal flows away from theneutral surface in a directionperpendicular to the die motion.
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Metal flow in forgingMetal flow in forging
Cold forging • Forging of nut and bolt
Step I Step II Step III Step IV
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www.qform3d.com
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Metal flow in forgingMetal flow in forging
Cold forging • Forging of nut and bolt
Step I Step II Step III
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www.qform3d.com
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Metal flow in forgingMetal flow in forging
http://www.qform3d.com/en/59.html
Hot forging Titanium alloy being forged at 930oC toproduce preliminary turbine blade pre-form.
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Suck in flaw
www.qform3d.com
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Metal flow in forgingMetal flow in forging
Hot forging •AISI 1040 being forged from a squarebar at 1200oC to produce a shaft.
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• Extensive metal flow into flash• Incomplete fill up at the upper part
www.qform3d.com
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Metal flow in forgingMetal flow in forging
Hot forging • DIN/C43 being forged from a roundbar at 1250oC to produce a shaft fork.
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• Possible die filling with minimumflash used.
www.qform3d.com
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Metal flow in forgingMetal flow in forging
Forging from compact bar
• Powder compact bar of 0.78density being forged.
• The density increases firstin the intermediate area thenspread throughout the crosssection.
www.qform3d.com
Suranaree University of Technology September 2007
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density being forged.
• The density increases firstin the intermediate area thenspread throughout the crosssection.
Forces in metal forgingForces in metal forgingT.
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ol …Eq.1ppAA
PF i
r
ri
Friction between two surfaces
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Where= frictional coefficient= the shearing stress at the interface
P = the load normal to the interfaceF = the shearing forceAr= summation of asperity areas in contactp = the stress normal to the interface
ppAA
PF i
r
ri
Forces in metal forgingForces in metal forgingT.
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1. No friction2. Small friction3. Sticky friction
The calculation of forging load can beconsidered in three cases
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1. No friction2. Small friction3. Sticky friction
No frictionNo frictionT.
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Do
hoD
h hDhD oo22
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Where P is the compressive forceo is the yield stress of the metal
A is the cross sectional area of the metal.
oo
o
oo hDAh
hDPh
DPp 222
444
….Eq. 3
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p
• Assumption:- no barrelling- small thickness,
Then
- frictional conditions on the topand bottom faces of the diskare a constant coefficient ofCoulomb friction;
• Small friction (homogeneous forging)
Small frictionSmall friction
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p
Where= frictional coefficient= the shearing stress at the interface
p = the stress normal to the interface
…Eq.4
• Assumption:- no barrelling- small thickness,
Then
- frictional conditions on the topand bottom faces of the diskare a constant coefficient ofCoulomb friction;
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X=0 X=a
P
Pmax
Friction hill
o
Small frictionSmall friction
• Small friction(non-homogeneous forging)
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h
P
PXa-a
o
Functions of a metal working lubricant- Reduces deformation load- Increases limit of deformation before fracture- Controls surface finish- Minimises metal pickup on tools- Minimises tool wear- Thermally insulates the workpiece and the tools- Cools the workpiece and/or tools
Small frictionSmall frictionT.
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xahoy 2exp'
….Eq. 5 ‘o
y
ha
o 2exp'
xaho 2exp'
Friction hill
Forging stress
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….Eq. 5
x = ax = 0x = -a
Xa-a
‘o
hap o 1'
_
….Eq. 6
Average forging pressure
a/h Forging pressure
High friction (Sticky friction)High friction (Sticky friction)T.
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….Eq. 7
‘o
y
1'
ha
o
1'
hxa
oFriction hill
Forging stress
1'
hxa
oy
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x = ax = 0x = -a
Xa-a
‘o
….Eq. 8
Average forging pressure
a/h Forging pressure
123
2_
hap o
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Example:
A block of lead 25x25x150 mm3 is pressed between flat dies to a size6.25x100x150 mm3. If the uniaxial flow stress o = 6.9 MPa and = 0.25,determine the pressure distribution over the 100 mm dimension (at x = 0, 25and 50 mm) and the total forging load in the sticky friction condition.
xahoy 2exp
32 oo
32'
Dieter, page 574-575
Suranaree University of Technology September 2007
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xahoy 2exp
32
At the centreline of the slab (x = 0)
MPa43505025.6)25.0(2exp
3)9.6(2
max
Likewise, at 25 and 50 mm, the stress distribution will be 58.9 and 8.0 MParespectively.
oo 32' where
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Example: Dieter, page 574-575
The mean forging load (in the sticky friction condition) is
123
2_
hap o
MPap 8.3915.1250
3)9.6(2_
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MPap 8.3915.1250
3)9.6(2_
We calculate the forging load on the assumption that the stress distributionis based on 100 percent sticky friction. Then
The forging load is P = stress x area= (39.8x106)(100x10-3)(150x10-3)= 597 kN= 61 tonnes.
Defects in forgingDefects in forgingT.
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Fluorescence penetrantreveals Forging laps
files.bnpmedia.com
• Incomplete die filling.
• Die misalignment.
• Forging laps.
• Incomplete forging penetration- shouldforge on the press.