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MF7203 THEORY OF METAL FORMING L T P C3 0 0 3

AIM: To impart knowledge on plasticity, surface treatment for forming of various types of metal forming process.

OBJECTIVES: To study the basic concepts of metal forming techniques and to develop force calculation in metal

forming process. To study the thermo mechanical regimes and its requirements of metal forming

UNIT I THEORY OF PLASTICITY 9

Theory of plastic deformation Yield criteria Tresca and Vonmises !istortion energy "tress strain

relation #ohr$s circle representation of a state of stress cylindrical and spherical coordinate system

upper and lower bound solution methods %verview of &'# applications in #etal &orming analysis.

UNIT II THEORY AND PRACTICE OF BULK FORMING PROCESSES 8

(nalysis of plastic deformation in &orging, )olling, '*trusion, rod+wire drawing and tube drawing

'ffect of friction calculation of forces, work done rocess parameters, equipment used !efects

applications )ecent advances in &orging, )olling, '*trusion and !rawing processes !esign

consideration in forming.

UNIT IIISHEET METAL FORMING 8

&ormability studies -onventional processes ' ) & techniques "uperplastic forming techniques

ydro forming "tretch forming /ater hammer forming rinciples and process parameters

(dvantage, 0imitations and application.

UNIT IV POWDER METALLURGY AND SPECIAL FORMING PROCESSES 9

%verview of +# technique (dvantages applications owder preform forging powder rolling

Tooling, process parameters and applications. %rbital forging 1sothermal forging ot and cold

isostatic pressing igh speed e*trusion )ubber pad forming &ine blanking 0("') beam forming

UNIT V SURFACE TREATMENT AND METAL FORMING APPLICATIONS 9

'*periment techniques of evaluation of friction in metal forming selection influence of temperature and

gliding velocity &riction heat generation &riction between metallic layers 0ubrication carrier layer

"urface treatment for drawing, sheet metal forming, '*trusion, hot and cold forging. rocessing of thin (l

tapes -ladding of (l alloys !uple* and triple* steel rolling Thermo mechanical regimes of Ti and

(l alloys during deformation &ormability of welded blank sheet 0aser structured steel sheet

&ormability of laminated sheet. T%T(0: 23 ')1%!"

REFERENCES:

4. elmi ( Youssef, assan (. 'lofy, #anufacturing Technology: #aterials, rocesses and 'quipment, -)-

publication press, 5645.

5. "(' Transactions, 7ournal of #aterials and #anufacturing "ection 3, 4889566

9. "urender kumar, Technology of #etal &orming rocesses, rentice all 1ndia ublishers,5646

2. #arciniak,;., !uncan 7.0., u ".7.,

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Lecture 1

FUNDAMENTALS OF METAL FORMING

There are four basic production processes for producing desired shape of a

product. These are casting, machining, joining (welding, mechanical fastners, epoxy,

etc.), and deformation processes. Casting process exploit the fluidity of a metal in

liquid state as it takes shape and solidifies in a mold. achining processes pro!ide

desired shape with good accuracy and precision but tend to waste material in the

generation of remo!ed portions. "oining processes permit complex shapes to be

constructed from simpler components and ha!e a wide domain of applications.

#eformation processes exploit a remarkable property of metals, which is their

ability to flow plastically in the solid state without deterioration of their properties.

$ith the application of suitable pressures, the material is mo!ed to obtain the

desired shape with almost no wastage. The required pressures are generally high

and the tools and equipment needed are quite expensi!e. %arge production

quantities are often necessary to justify the process.

Fig 1.1 &tate of the stresses metal undergo during deformation.

's a metal is deformed (or formed, as often called) into useful shape, it

experiences stresses such as tension, compression, shear, or !arious combinations

there of ig .illustrates these states of stresses. &ome common metal forming

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processes are schematically gi!en in ig .*along with the state of stress(es)

experienced by the metal during the process.

Numb

erProcess

State of Stress i

Mai Part Durig

Formig

+olling

i-axial compression

*

orging

Tri-axial compression

/xtrusion

Tri-axial compression

0 swaging i-axial compression

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1

#eep

drawing

2n flange of blank, bi-

axial tension and

compression. 2n wall ofcup, simple uni-axial

tension.

3

$ire and tube drawing

i-axial compression,

tension.

4

&traight bending

't bend, bi-axialcompression and bi-axial

tension

Fig 1.! Common metal forming processes. &tate of stress experienced by metal is

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also gi!en

To understand the forming of metal, it is important to know the structure of

metals. etals are crystalline in nature and consist of irregularly shaped grains of

!arious si5es. /ach grain is made up of atoms in an orderly arrangement, known as a

lattice. The orientation of the atoms in a grain is uniform but differs in adjacent

grains. $hen a force is applied to deform it or change its shape, a lot of changes

occur in the grain structure. These include grain fragmentation, mo!ement of atoms,

and lattice distortion. &lip planes de!elop through the lattice structure at points

where the atom bonds of attraction are the weakest and whole blocks of atoms are

displaced. The orientation of atoms, howe!er, does not change when slip occurs.

To deform the metal permanently, the stress must exceed the elastic limit. 't

room temperature, the metal is in a more rigid state than when at higher

temperature. Thus, to deform the metal greater pressures are needed when it is in

cold state than when in hot state.

$hen metal is formed in cold state, there is no recrystalli5ation of grains and

thus reco!ery from grain distortion or fragmentation does not take place. 's grain

deformation proceeds, greater resistance to this action results in increased hardness

and strength. The metal is said to be strain hardened. There are se!eral theories to

explain this occurrence. 2n general, these refer to resistance build up in the grains byatomic dislocation, fragmentation, or lattice distortion, or a combination of the three

phenomena.

The amount of deformation that a metal can undergo at room temperature

depends on its ductility. The higher the ductility of a metal, the more the

deformation it can undergo. 6ure metals can withstand greater amount of

deformation than metals ha!ing alloying elements, since alloying increases the

tendency and rapidity of strain hardening. etals ha!ing large grains are more

ductile than those ha!ing smaller grains.

$hen metal is deformed in cold state, se!ere stresses known as residualstresses are set up in the material. These stresses are often undesirable, and to

remo!e them the metal is heated to some temperature below the recrystalline range

temperature. 2n this temperature range, the stresses are rendered ineffecti!e

without appreciable change in physical properties or grain structure.

"OLD AND #OT $OR%ING OF METALS

"o&' $or(ig)

6lastic deformation of metals below the recrystalli5ation temperature is known as

cold working. 2t is generally performed at room temperature. 2n some cases, slightlyele!ated temperatures may be used to pro!ide increased ductility and reduced

strength. Cold working offers a number of distinct ad!antages, and for this reason

!arious cold-working processes ha!e become extremely important. &ignificant

ad!ances in recent years ha!e extended the use of cold forming, and the trend

appears likely to continue.

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2n comparison with hot working, the ad!antages of cold working are

. 7o heating is required

*. ettter surface finish is obtained

. etter dimensional control is achie!ed8 therefore no secondary machining is

generally needed.

0. 6roducts possess better reproducibility and interchangeablity.

1. etter strength, fatigue, and wear properties of material.

3. #irectional properties can be imparted.

4. Contamination problems are almost negligible.

&ome disad!antages associated with cold-working processes are9

. :igher forces are required for deformation.

*. :ea!ier and more powerful equipment is required.

. %ess ductility is a!ailable.

0. etal surfaces must be clean and scale-free.

1. &train hardening occurs ( may require intermediate annealing ).

3. ;ndesirable residual stresses may be produced

Cold forming processes, in general, are better suited to large-scale production of

parts because of the cost of the required equipment and tooling.

$arm $or(ig)

etal deformation carried out at temperatures intermediate to hot and coldforming is called Warm Forming . Compared to cold forming, warm forming offers

se!eral ad!antages. These include9

< %esser loads on tooling and equipment

< =reater metal ductility

< ewer number of annealing operation ( because of less strain hardening )

Compared to hot forming, warm forming offers the following ad!antages.

< %esser amount of heat energy requirement

< etter precision of components

< %esser scaling on parts

< %esser decarburi5ation of parts

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< etter dimensional control

< etter surface finish

< %esser thermal shock on tooling

< %esser thermal fatigue to tooling, and so greater life of tooling.

#ot $or(ig)

6lastic deformation of metal carried out at temperature abo!e the

recrystalli5ation temperature, is called hot working. ;nder the action of heat andforce, when the atoms of metal reach a certain higher energy le!el, the new crystals

start forming. This is called recrystalli5ation. $hen this happens, the old grain

structure deformed by pre!iously carried out mechanical working no longer exist,

instead new crystals which are strain-free are formed.

2n hot working, the temperature at which the working is completed is critical

since any extra heat left in the material after working will promote grain growth,

leading to poor mechanical properties of material.

2n comparison with cold working, the ad!antages of hot working are

. 7o strain hardening

*. %esser forces are required for deformation

. =reater ductility of material is a!ailable, and therefore more deformation is

possible.

0. a!orable grain si5e is obtained leading to better mechanical properties of

material

1. /quipment of lesser power is needed

3. 7o residual stresses in the material.

&ome disad!antages associated in the hot-working of metals are9

. :eat energy is needed

*. 6oor surface finish of material due to scaling of surface

. 6oor accuracy and dimensional control of parts

0. 6oor reproducibility and interchangeability of parts

1. :andling and maintaining of hot metal is difficult and troublesome

3. %ower life of tooling and equipment.

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