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Near Net Shape Cold, Warm & Hot Forging

A Short Course Developed at

The Engineering Research CenterFor Net Shape Manufacturing (ERC/NSM)

Presented ByDr. Taylan Altan, Professor & Director

© Copyright Engineering Research Center for

Net Shape Manufacturing. All Rights Reserved.

http://www.ercnsm.org

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References

• 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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1.1 & 1.2Forging Processes

Near Net Shape Cold, Warm & Hot Forging

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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)

Forging Processes

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Effects of Test Temperature and Test Speed

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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Cold, Warm, & Hot Forging-- Advantages & Disadvantages -

Cold Warm HotAdvantages

• Precision Process (Tight Tolerances)

• Improved Part Strength• Better Surface Finish• Material Conservation

Disadvantages• High Forming Pressures• Several Pre-Forming Steps

Needed• Annealing Steps May Be

Required During Process• Low Formability

Advantages• Combines Advantages of

Cold & Hot Forging• Better Formability• Lower Forming Pressures• Higher Deformation Ratio• No Annealing Required

Disadvantages• High Tooling Costs• Tooling Must Withstand

Forming Pressures as well as High Temperatures

Advantages• Can Forge Complex

Shapes• Good Formability• Low Forming Pressures• Can Forge Parts of Higher

Weight and Volume

Disadvantages• Formation of Scale• Decreased Accuracy

(Larger Tolerances)

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Cold Forging- Forming Sequence -

Rear View Mirror Holder(Cold Forged)

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Standard terminology for various features of a typical forging die

Forging With Flash

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Hot Forging With Flash

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Hot Forged Connecting Rods

Preforms prepared in reducer rolls

Finish forging before and after trimming

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Hot Forging - Track Links

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Examples Of Hot Forgings

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A billet with carefully controlled volume is deformed (hot or cold) by a punch to fill a die cavity without any loss of material

Forging Without Flash(trapped die)

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Multiple-step Cold Forging

(a) Sheared Billet

(b) Forward rod and backward cup extrusion

(c) Forward extrusion

(d) Backward cup extrusion

(e) Upsetting of flange and coining of shoulder

(a)

(b) (c)(d) (e)

Schematic illustration of forming sequences in cold forging of a gear blank

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Cold Forged Components

Reference: Mitsubishi Heavy Industries

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Cold Forged Parts

Courtesy: Raufoss

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Open Die Forging

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Various Stages in Orbital Forging Processes

Orbital Forging

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Radial Forging of a Shaft

Radial (Or Rotary) Forging

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Upset Forging

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Economics of Cold Forging

Minimum number of parts in a production lot for economic production in cold forging of steel

Number of forged parts in:Part Weight Universal Special

machines machines

<20 g…………..………………..… 10,000 500,00020 to 500 g……………………….. 5,000 50,000500 g to 10 kg……………………. 1,000 20,00010 to 50 kg…………….………….. 1,000 10,000

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Forging Process as a System

(1) Billet Material(2) Tooling(3) Tool/Material Interface(4) Deformation Zone/Workpiece

(5) Equipment(6) Product(7) Plant Environment

(1)

(3)

(5)

(6)

(7)

(2)

(4)

(2)

(4)

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Forging Process as a System- Significant Variables -

• 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

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• 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)

Forging Process as a System- Significant Variables -

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• 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

Forging Process as a System- Significant Variables -

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Process & EquipmentVariables in Forging

SLIDE VELOCITY, Vp

CONTACT TIME, tp

STIFFNESS, C

CLEARANCES, FLATNESS,

& PARALLELISM

MACHINE LOAD, LM

MACHINE ENERGY, EM

STROKES/MIN, no(IDLE)

STROKES/MIN, no(UNDER LOAD)

STRAIN RATE

DIE TEMPERATURE

TEMPERATURE, θ

MATERIAL FLOW STRESS

FRICTION,LUBRICATION

PART GEOMETRY

VARIATIONS INSTOCK WEIGHT

& TEMPERATURE

PARTTOLERANCES

REQ’D LOAD, LpENERGY, EP

MACHINE VARIABLESPROCESS VARIABLES

SURFACE TO VOLUME RATIO