MFGE303 Chp IX Forging

MFGE303 Theory of Manuf. Techn.IDept. of Manufacturing Engineering

ATILIM UniversityChapter IX: Bulk Forming (Forging)

Content:Forging

• Introduction• Examples of Application• Overview to Basic Forging

Processes• Open-Die Forging• Forging Machine Tools• Closed-Die Forging• Forging Temperature• Forging Defects• Forging Dies• Current Trends

01.21020.11.2001



Description of Forging

Advantages of Forging Process:• High material utilization• High production rates• High process stability• High recyclability of products

01.21120.11.2001

Forging consists of a group of manufacturing processes which aremainly deformation processes. The two other types of processes are separating (parting) and joining processes.

In order to reduce stresses and forces and to increase formability, forging is usually carried out after heating to a temperature range at which recovery and recrystallization occurs. Hence the workpieces after forging do not show a permanent work hardening.

Advantages of Forged Products:• Improved grain structure• Higher fatigue strength & ductility• Better surface quality than in casting• Beneficial grain flow (fibers)



Material Fibers (Grain Flow)

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Casting ForgingMachining

Forging Industry Association

The beneficial grain flow in forged parts leads to a longer fatigue life & higher ductility than machined or casted parts.

ASM Handbook



Forging Production

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2.368.000

35.000

1.360.000

9.600.000

0

3.000.000

6.000.000

9.000.000

12.000.000

Turkey(1989)

Germany(1999)

Europe(1998)

World(1998)

Clo

sed

Die

For

ged

Part

s in

t

Tekkaya/Hirschvogel



Examples of Application:

VariousParts

01.21420.11.2001

IDS



Examples of Application:Front Axle of a Truck

01.21520.11.2001

Daimler Benz AG




Automobile FrontWheel

Suspension

01.21620.11.2001

BMW AG



Examples of Application: Truck Gear Box

01.21720.11.2001

Daimler Benz AG



Examples of Application: Vehicle Power Shaft

01.21820.11.2001

Gelenkwellenbau Gmbh




Aircraft LandingGear Structure

01.21920.11.2001

Airbus Industrie



Basic Forging Processes

Open-Die Forging

Closed-Die Forging

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Hot Forging

Warm Forging

Cold Forging

Precision Forging Near-Net-Shape-Forging Net-Shape Forging

Isothermal Forging



Hot versus Cold ForgingHot Forging

• Production of discrete parts• Greater technical and

economical importance• Low stresses, no/low work-

hardening, homogenizedgrain structure

• High formability• Medium to low accuracy• Scale formation• Forging temperatures:

– Steel: > 1000oC (up to 1150 oC)– Al-Alloys: 360oC-520oC– Cu-Alloys: 700oC-800oC

Cold Forging• Production of discrete parts• Processes covered: extrusion

forging, upsetting, coining• High stresses, strain

hardening, high die loads• Limited formability• Near-net shape or net shape• High surface quality

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Open-Die versus Closed-Die Forging

Open-Die Forging• Aim: To achieve a convenient

mass distribution or shape forthe successive operations(machining or closed-die forging)

• Simple tools, whose geometry do not depend on the productgeometry

Closed-Die Forging• Aim: Achieve best possible

dimensional and shape accuracyof the product.

• Tools whose geometry is productdependent

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Open Die Forging

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Cogging

Video

Upsetting Heading (with no given form)

Spreading

Radial Forging (with no given form)

Kalpakjian

Geiger

Lange



Basic Processes of Open-Die Forging andAchievable Cross-Section Changes

A1/A0 < 4-5Upsetting, headingA0/A1 4-5Cogging, spreading

Cross-Section ChangeOpen-Die Forging Processes

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• Cogging (material displacement)• Spreading (material displacement)• Upsetting, heading (material concentration)



CompletePlastification

DuringCogging

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Lange



Closed Die Forging (1)

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Impression Die Forging

Video

Closed Die Forging (no flash)

Coining

Heading

Video

Kalpakjian



Closed Die Forging (2)

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Roll-Forging

Skew-Roll-Forging Upsetting in a Die

Kalpakjian



ClosedDie

Forging(3)

01.22820.11.2001

Radial Forging(Swaging)

Kalpakjian



Terminology for Impression DieForging

01.22924.11.2001

Kalpakjian



Material Flow in Closed-Die Forging

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Upsetting Spreading Rising

Geiger/Lange


ATILIM UniversityChapter IX: Bulk Forming (Forging) 01.231

24.11.2001

Lange

Work WWork W

StrokeF

orc

eF

s

b1

b2

plastic region

rigid region

low

er

die

workpiece

upper

die

AF1

AF2A

dc

r

z

str

esses

�r�r

�r�r

�z�z

�z�z

r

�f�f�f�f

�z,

fla

sh,

ma

x,2

�z,

flash

,m

ax,

2

�z,

fla

sh,m

ax,

1�

z,fl

ash

,ma

x,1

b1

< b2

Mechanics of Closed-Die Forging



Effect of Flash Dimesions

0 2 4 6 8 10

Die Land- Ratio b/s

1200

1000

800

600

400

200

0

Ax

ial

Str

es

sin

Fla

sh

inM

Pa

�zm

ax

30

25

20

15

10

5

0

Ex

ce

ss

Ma

teri

al

�m

in%

5500

5000

4500

4000

3500

3000

2500

Fo

rgin

gF

orc

ein

kN

F

55

50

45

40

35

30

25

Fo

rgin

gW

ork

kN

min

W

�zmax

�zmax

�m�m

W

F

80 mm

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Vieregge



Stress and Force Computation in Impression Die Forging: Slab Method

In the flash land the axial stress is given according to the slab method by Siebel as:

max 1 2z fbs

σ σ µ⎛ ⎞= − ⋅ + ⋅ ⋅⎜ ⎟⎝ ⎠

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Simple method to estimate the forging load:max max

P zF A σ= ⋅

where, the total projection area Ap is given by:

P dc FA A A= +

Adc: Projection area of die cavity, AF: Projection area of flash



s plastic region

rigid region

rigid region

d

D

Stress and Force Computation in ImpressionDie Forging: Upper Bound Method

• The material within the die cavity does not plastify anymore as the maximum force is recorded, since all free places are filled already.

• The material flow happens only in the materialslab of thickness s, i.e. the flash thickness. Theshape of the die cavity is therefore immaterial.

01.23425.11.2001

Assumptions for die with steep and deep cavities:

2 3 3 3max 2

4 3 812 3fD d D dF

ssσ π µ

⎡ ⎤⎛ ⎞−= ⋅ ⋅ + + ⋅ ⋅⎢ ⎥⎜ ⎟⋅⋅ ⎝ ⎠⎣ ⎦

2 3 3 3max

4 24 12fD d D dF

s sσ π µ

⎡ ⎤⎛ ⎞−= ⋅ ⋅ + + ⋅⎢ ⎥⎜ ⎟⋅ ⋅⎝ ⎠⎣ ⎦

(v. Mises)

(Tresca)

0.3 0.5 (0.577)µ< <

Lange



Typical Hot Flow Curves for Ck45

0

100

200

300

400

0 0.2 0.4 0.6 0.8 1 1.2Equivalent plastic strain

Flow

str

ess

in M

Pa

01.23525.11.2001

T = 800oC

140 sε −=18 s−

11.6 s−140 s−

18 s−11.6 s−

T = 1000oC

T = 1200oC 140 s− 18 s− 11.6 s−

MSC/AutoForge



Forging Press Characteristics

250 – 500 ms0.1 m/sHydraulic Press

50 – 150 ms0.5 m/sFriction Screw Press

20 – 100 ms( 1 m/s)Crank Press

1 – 10 ms6 m/sDrop-Forging Hammer

0.5 – 5 ms16 m/sHigh-Speed Hammers

Pressure TimeImpact Speed of ToolForging Press

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Lange



Forging Presses (1)

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Hydraulic Press Eccentric Press Kalpakjian



Forging Presses (2)

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Knuckle JointPress

Friction ScrewPress

Gravity Drop HammerKalpakjian


ATILIM UniversityChapter IX: Bulk Forming (Forging) 01.239

25.11.2001

Kalpakjian

Example for Forging Sequences



Examples of Forged Parts

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Courtesy Kanca



Closed-DieForgingwithoutFlash:

Example

01.24125.11.2001



Closed-Die Forging without Flash: Force-Displacement Diagram

01.24225.11.2001

Forg

ing

Forc

e in

tons

Punch Stroke in mm

Upsetting

Corner Filling

Johne



Closed-Die Forging without Flash: Material Flow

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Punch

Die

unfilled cornerplastic zone

stickingzone

Workpiece

Lange



Forging Temperature

• Lower Temperature: Significantly larger than therecyrstallization temperature

• Upper Temperature: As large as possible, but if toolarge:– Oxidation or melting of impurities at the grain boundaries– Excessive grain grow (overheating)– Increased scale formation and decarburization– Tendency of fracture on the blank surface

• Workpiece temperature is neither in time nor in space constant:– Heat losses due to radiation and conduction– Heat gain by friction and forming work

01.24425.11.2001



Forging Defects

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Kalpakjian



Forging Dies: Failure

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Kannappan

Wear (abrasion)

Thermal fatigue

Mechanical fatigue

Plastic deformation



Forging Dies: Design

• Positioning the forging stages• Design of die land and flash gutter• Design of the die cavity

– Design for material flow and die layout– Design for dimensional accuracy– Design for ease of machining

01.24725.11.2001



Current Trends• Thixo-Forging:

– Combination of casting and forming– Thixotropic state: both liquid and solid

states co-exist– Materials: basically aluminum and

magnesium alloys– Advantages:

• Low forging loads• Complicated shapes can be forged in

one stage• Near-net forming (as compared to

casting)• Large wall thickness differences

possible– Disadvantages:

• Very tight temperature window• Advance tool technology necessary• Not all materials can be thixoforged

01.24825.11.2001

• Precision Forging of Gears– Precision forging: Forging

with higher precision than described in the standards

– Higher tool costs are compensated by saving post-machining costs



Computer Aided Forging

01.27903.12.2001

unkown owner

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MFGE303 Chp IX Forging

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