1) Properties of the billet material and how it deforms under different conditions of strain, strain rate, and temperature 2) Geometry and properties of the forging tools and die interface 3) Conditions within the deformation zone such as metal flow, stresses, and temperatures during forming

1. ERC
NSM
Near Net Shape Cold, Warm
& Hot Forging
A Short Course Developed at
The Engineering Research Center
For Net Shape Manufacturing (ERC/NSM)
Presented By
Dr. Taylan Altan, Professor & Director
© Copyright
Engineering Research Center for
Net Shape Manufacturing.
All Rights Reserved.
http://www.ercnsm.org
1

2. ERC
References NSM
• T. Altan. S.Oh, H. Gegel, Metal Forming: Fundamentals and
Applications, American Society for Metals, Metal Park Ohio
1983.
• K. Lange, Hand Book of Metal Forming, McGraw-Hill Book
Company 1985.
• A.J. Schey, Tribology in Metal Working, American Society for
Metals, Metal park Ohio 1983.
• Forging Industry Association (FIA), Forging Handbook –
www.forging.org
• ASM International, ASM Hand Book: Forming and Forging,
Volume 14, 1988.
• T. Altan, F.W. Boulger, J.R. Becker, N.Akgerman, & H.J.
Henning, Forging Equipment, Materials, and Practices, Metals
and Ceramic Information Center, Ohio 1973.
• International Cold Forging Group – Various Documents
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3. Near Net Shape Cold, Warm ERC
& Hot Forging NSM
1.1 & 1.2
Forging Processes
3

4. Forging Processes ERC
NSM
Cold Forging - Starts at room temperature
(RT to 600-800 F)
Warm Forging - Below or near recrystallization
temperature (900 F - 1800 F
for steel)
**Tool designs for cold & warm forging are similar,
but temperatures and lubricants are different
Hot Forging - Above recrystallization
temperature (1800 F - 2200 F
for steel, 800 F for Al)
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5. Effects of Test Temperature and ERC
Test Speed NSM
Effects of test
temperature and test
speed (strain rate) on
tensile strength and
reduction of area of hot
rolled type 1045 steel
(Courtesy: Technical Report by
Bethlehem Steel Corporation,
Bethlehem, PA)
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6. Cold, Warm, & Hot Forging ERC
- Advantages & Disadvantages - NSM
Cold Warm Hot
Advantages Advantages Advantages
• Precision Process (Tight • Combines Advantages of • Can Forge Complex
Tolerances) Cold & Hot Forging Shapes
• Improved Part Strength • Better Formability • Good Formability
• Better Surface Finish
• Lower Forming Pressures • Low Forming Pressures
• Material Conservation
• Higher Deformation Ratio • Can Forge Parts of Higher
• No Annealing Required Weight and Volume
Disadvantages
• High Forming Pressures
Disadvantages Disadvantages
• Several Pre-Forming Steps
Needed • High Tooling Costs • Formation of Scale
• Annealing Steps May Be • Tooling Must Withstand • Decreased Accuracy
Required During Process Forming Pressures as well as (Larger Tolerances)
• Low Formability High Temperatures
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7. Cold Forging ERC
- Forming Sequence - NSM
Rear View Mirror Holder
(Cold Forged)
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8. Forging With Flash ERC
NSM
Standard terminology for various features of a typical forging die
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9. ERC
Hot Forging With Flash
NSM
9

10. ERC
Hot Forged Connecting Rods
NSM
Finish forging
Preforms prepared before and
in reducer rolls after trimming
10

11. ERC
Hot Forging - Track Links
NSM
11

12. Examples Of Hot Forgings ERC
NSM
12

13. Forging Without Flash ERC
(trapped die) NSM
A billet with carefully controlled volume is deformed (hot or
cold) by a punch to fill a die cavity without any loss of
material
13

14. Multiple-step Cold Forging ERC
NSM
(a) Sheared Billet (c) Forward extrusion (e) Upsetting of flange and
coining of shoulder
(a)
(b) (c)
(d) (e)
(b) Forward rod and (d) Backward cup
backward cup extrusion extrusion
Schematic illustration of forming sequences
in cold forging of a gear blank 14

15. Cold Forged Components ERC
NSM
Reference: Mitsubishi Heavy Industries 15

16. Cold Forged Parts ERC
NSM
Courtesy: Raufoss 16

17. Open Die Forging ERC
NSM
17

18. Orbital Forging ERC
NSM
Various Stages in Orbital Forging Processes
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19. Radial (Or Rotary) Forging ERC
NSM
Radial Forging of a Shaft
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20. Upset Forging ERC
NSM
Upsetting With Flat-heading Tool 20

21. ERC
Economics of Cold Forging
NSM
Number of forged parts in:
Part Weight Universal Special
machines machines
<20 g…………..………………..… 10,000 500,000
20 to 500 g……………………….. 5,000 50,000
500 g to 10 kg……………………. 1,000 20,000
10 to 50 kg…………….………….. 1,000 10,000
Minimum number of parts in a production lot for
economic production in cold forging of steel
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22. Forging Process as a System ERC
NSM
(2)
(4)
(4) (6)
(1)
(3)
(2)
(5) (7)
(1) Billet Material (5) Equipment
(2) Tooling (6) Product
(3) Tool/Material Interface (7) Plant Environment
(4) Deformation Zone/Workpiece
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23. Forging Process as a System ERC
- Significant Variables - NSM
• Billet Material
– Flow Stress (instantaneous yield stress) as a Function of
Strain, Strain Rate,Temperature, & Microstructure
– Workability (forgeability) as a Function of Strain, Strain
Rate,Temperature, & Microstructure
– Surface Conditions
– Thermal/Physical Properties
– Initial Conditions (composition, temperature, history)
– Effects of Changes in Microstructure & Composition
• Tooling
– Geometry of Tools
– Surface Conditions
– Material/Heat Treatment/Hardness
– Temperature
23

24. Forging Process as a System ERC
- Significant Variables - NSM
• Conditions at Tool/Material Interface
– Lubricant Type and Temperature
– Insulation & Cooling Characteristics of the Interface Layer
– Lubricity & Frictional Shear Stress
– Characteristics Related to Lubricant Application &
Removal
• Deformation Zone
– Deformation Mechanics, Model Used for Analysis
– Metal Flow, Velocities, Strain Rates, & Strains
– Stresses (variation during deformation)
– Temperatures (Heat Generation & Transfer)
24

25. Forging Process as a System ERC
- Significant Variables - NSM
• Equipment
– Speed/Production Rate
– Force/Energy Capabilities
– Rigidity & Accuracy
• Product
– Geometry
– Dimensional Accuracy, Tolerances, Surface Finish
– Microstructure, Mechanical & Metallurgical Properties
• Plant & Environment
– Manpower
– Air, Noise, & Wastewater Pollution
– Plant & Production Facilities and Control
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26. Process & Equipment ERC
Variables in Forging NSM
PROCESS VARIABLES MACHINE VARIABLES
STRAIN RATE SLIDE VELOCITY, Vp
MATERIAL DIE TEMPERATURE CONTACT TIME, tp
FLOW STRESS
TEMPERATURE, θ STIFFNESS, C
FRICTION,
CLEARANCES,
LUBRICATION
FLATNESS,
& PARALLELISM
PART GEOMETRY SURFACE TO
VOLUME RATIO MACHINE LOAD, LM
PART
TOLERANCES MACHINE ENERGY, EM
VARIATIONS IN STROKES/MIN, no
STOCK WEIGHT (IDLE)
& TEMPERATURE
REQ’D LOAD, Lp
ENERGY, EP STROKES/MIN, no
(UNDER LOAD)
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