Forging Notes

7/21/2019 Forging Notes

http://slidepdf.com/reader/full/forging-notes 1/16

lntroduction

and

Concepts

1.1 lntroduction

I'let

processinll

is

lhe

Dreflcr:l

of

ptastir:1ll),

rleformi

g

thc nlr:tol irLLi)

rcquired shape. XIost largescalc

delonnaiiolr

pr_ocesscs

ar c

pcrlbrrned

in h{n.

condition,

s.r

that

mininum

forcc

is ]leeded Lo rL-.1orm

thc rnctnl to r'equir-eri

shitpc

and

the

consequcrnt

rccrl'siallisation Ielines

thc

ntctellic

struclur'- .

ColcL

rlor'ki g

pr'ocess

is

cnplo1'ed

\\'her1 srD.roLh

stlr_frc.r iinish.1nd Liglr

dinrelrsiona]

accuracy

is

dcnranded.

'fhe processes

used

are clivclsc iD scele, rllryirll liun forqiDg

encl

r'ol1irrg oi

ingots weighing

sever-al

tonncs to dr'arrir,g ol ujr.es less

than

0.u05 rnn rl

dianletcr. Allhoullh a number

of a componelrts can Le manufactureci

cornpletelr',

nlctal

lbrming

is

prin

arily usccl to

produce

such

matcr'ial

es

bar

anrl

sheets

rvhich

erc

subsequenUv

machined

or

pr-essed

iDto

the

final

shape. A char.t showing

the

major

mctal

fornring

processcs

is

given

in lig

1.1

1.2

General Classilication

of metal lorming

process

Selectiorl ol a

par-ticular

anulhclurjng

process

depends

oD

\':uiolrs Iactors

lilie

size

ancl

shape

oi the

finishcd

conrponent.

rnrterial

used, cost

etc.

|ig.1.1 shorvs

thc

gener.al

classificaiion

ol

forning; processes

as the type

anC

size of the components

that

can bc

pr.oduced

using these

proccsse-r.

HoFcvcr

the

final

selection

clepends largely

on

the

cost. tDeLe

al

and

availabilitv

olthe laciljtv

in a

particular

industry.



lngot

(

Ca-sl)

Billet

(aasr)

Round,

Square

Special

seclions

Plates Strips

Large

Heary

Iightseclions

Seamless



1.3

Classification

ot

metal

forming

processes based

on the

nature

ol force

apPlied.

Baseal on

the

nature of

force applied,

the forming

processes can be

clessified

(i)

Ditect

compression

type:

llere

the

ibrcc

is

applied

to the

surface

of

the

work

piece

and

the

metal flo1vs

at

i {ht angles

to

the direction

ol

compressirn

(Fig

1.2).

The

best er<amples

ofthis

type

ofprocess

are

ro]ling

and

forging

(ii)

Indirect

compression

type:

In

ihese

types of

forces,

though

the

prinarj

applied

forces

are

lrequently

tensile,

clue

to the

reaction

of

work

piece

wilh

the

di".

indi."ct

"o-pressive

forces are

developed

(Fig

13)

Best exampies

of

this type

are

wire

drawing,

extrusion

and deep

drawing'

(iii)

Tension

tlpe:

Shetch

forming

is the

best

example

ofthis

tlTe

(fig

1

4) Here

a metal

sheet

is wrapped

to the

contour-

ol

the

die

under

the

application

of

tensiie

force-

(iv)

Bending

tnter

This

involves

application

of bending

moments

to the

sheet

(fig

1.5) as

in

sheet

bending

operation.

(v)

Shearing:

In this

process

shearing

forces

of

sulfrcient

magnitude

is

applied

to rupture

the

material

in

the

plane

of

shear

(fig

1

6)

Rolls

-

Dircction oi leed



(c)

Decp

Drd 0i19

Fig.

1.3 Indirect

Co,npressiorl

trpe

k

piece

Force

or

nessurc

appti.d

Strelch

lornring

Fig.

1.4

I'ension

trpe process

Fig.

1.5 Bending

Process

-*\vP

Fig,

1.6 Shcaring

1.4

Classification

ot

metal

lorming processes

based

on working



I

nt

rod.u.

tiot atd Conc e

p

t s

2. li does not shain

-

harden

thc

metals.

3. It refines the

grain

structure.

4.

Dclccts

in

mctals

such

as

blo\\' holes and

porosity tends

lo

get

fllled

up

due to

plastic

delorm.rtion.

J. R""idLcr 5trpjca- Jra nor nL" oLrvd

'r.hc

mc

al.

6.

lt

does

not iniluence

mechanical

properties-

7.

Due

to

oxidation

and scaling.

the

sudace

finish

is

poor.

The various hot working

processes

ar.el

a) Forging,

d)

Extrusion,

b)

Rolling,

e) Spinning,

c) Pipe

wekling,

0

Piercing,

g)

Draw

g.

(ii)

Cold working

\trhen a

melal is

rvorked

at

temperiitures belorv the recrystallisation

tcmperature it is called

cold

working.

Thc

tcmperature rnay vary

fi.onr

room

temperature lo temperatur-e

beiow recrystallisation tenperaturc.

It ]equires

greater lorce

to

achieve

plastic

deformation- The

amount

ol

delormatjon

is

consider.ably

jess.

The ellects

of

cold

working

are:

1.

Greater

stress

is required

to achievc deformation.



c) Cold

drawing

e)

Coining

g)

Shearing,

etc.

d)

Embossing

fl

Bending

1.5 Casl \rersus wrought

metals

or

alloys

Castings of various

metals and alloys

are

used

when the shape is very

large

or awkward

to

{brge,

rvhen

quality

and strength are noi

pdmary

considerations,

when

economy is desirable,

or

when

the metal or alloy is

difficult to shape bl

hot

or

cold working. In castings

local differences of

[retallurgical

structure and

chemical composition

as

well

as any

blow

holes

lormed

duling

solidification

oi the

metal are

permanent.

Thus in

general

castings have inferior rnechanical

propeliies.

Wrouglrt

metals, although

they

also

start from the liquid

state, are cast into

ingots

of simple

shape

and

size. The ingots are later

subjected

to hot

worhiDg

operation.

The

subsequent

rcheating

before

hot wortring

reduces

the

tendency

for

local segregation

and

subsequent mechanical

working eliminates

further.rny

existing de{ects

such

as blow holes.

llot working aiso imparts

directional

propedies

to the metals

caused

by the d€formation

of

g?ains

along

the

direction

of

working.

Castings do nol

show directional

propeities.

The

rvrought

metals

generally

exhibit

superior

rnechanical properties

lihc

strength,

ductilitv

and

toughness

compared to

castings.

1.6

Advantages

and limitations

ol

metal working processes

Ad antaEes

1.

Defects in

metals

such as

blow

holes

and

porositl

tend to

get

filled

up



Forging

3.1 lntroduction

-

In

forging the

metals

using

compressive

force,

presses.

A

pair

of dies is used: One die

is stationery and the other

is attached to the

hammer which has a

linear

nrotiorr.

Forging

process

can be

canicd out bol]r

in the

cold and

hot

state

of

the

mei,al.

Horvever

in

majority

ol

cases

forgug

is

done

rthen

the

metal is in

hot

statc.

3.2 ForgeableMaterials

A netal lvlich has to

be

forged should

possess good

ductility.

Ductility refcrs

to the

capacity ofa

rnatedal to undcrgo

plastic

deformation when subjectecl

ro a

Ioad or stress.

In

addition

to this, the

material

should have

good

resistancc to

shock and

fatigue,

good

machining characteistics

etc. some ol

the

comnlon

metals

and alloys which can be forged,

include aluminium alloys, copper alloys,

stainless

stcel, lorv carbon steel,

Nickel

alloys,

Magncsium

alloys,

Titanium alloys

ctc.

3.3

ForgingTemperatures

In forging, the

metal

is hcated

to

higher lemperature so that

it

bccomcs

plastic

befbre

delomation.

Excessive

tempcrature

may

result in

the burDing

of

the

metal.

Insufficient

temperature

$'iil

not

give

adequate

plasticity

to

the

n1ctal. In

addition the finishing

temperature should be such that at

rvhich no

grain grorvth

takes, so that

the lvorh

piece

possesses

a

{ine

grained

structure.

Table 3.1

giYes

the

lorging

tenperatures

lbr

diflerent

nelals

and

allols.

or

alloys

are

plastically

deformed

to

the

desired

shapes,

The compressive

force

is

appliecl

using

hammers

or



3,4 Advantages ol

forging

process

1)

Superior

nechanical

properties

are obtained especially along the

fibre

Ilolr

dirccLi.n.

2)

Elinination

of

porosity

prcsent

in

the

metal.

3)

Impu

ties

present

in the metal

in

the

fonn

off slag and other

inclusions

are broken up and distr:ibuted

throughout the

metal.

4) Refinement

of

€i'ain

structure.

5)

X{etal removai in subsequent machining

in

minimised.

6)

Forgings

can

be

readily

u'elded.

-

?)

Fairly

closc

dimensional tolerances

are achieved.

3.5

Disadvantages

1)

In

hot forging, due to high temperature,

rapid

oxidalion

and

scaling

of

the

surface

occurs

which results

in

poor sudace

hnish.

2)

Highly intricllte shapes

possible

by

casting

process

cannot be

forged.

3)

Tooling

and

handling

costs

are high.

4)

Normally forgings costs

more

than castings.



3.8 classification

of

forging

process

Forgrng

process

can

he

broadly classified

as

a) Open

die lolging.

b)

Closed

die forging.

3.8.1

Open

die forging

Fie.

3.13. Open

Die

foreing

This is also

knorvn

as

hand,

smiih,

hammer of

flat

die forging.

The simplest

open

die forging operation

is the upsetting

of a

cylindrical

billet between lrvo

flat

dies as

shown in hgure 3.13-

As

the

metal

llows laterally between

the

advanting

die surfaces,

there

is

less delornation

at the die

intedaces

because ol

the

frictional

lorces, than

at the

mid height

point.

Thus the

sides of the upset

cylinder

becomes

baralled.

As

a

general

rule

netal will

flow

more easily towards

thc

nearest

free

surfaces because this

represents the lowest

frictional

path.

Operl die

lorging is

employed under the

following

circumstanccs:

(i)

When the forging is

too

large

to be

produced

in

closed dies.

(ii)

To obtain super:ior

nechanical

properties which

cannot

be obtaincd

bl



3.8.2

Closed Die Forging

In this

ca,ce

the sheping

of

the hot.

nctal

is

achieved compleLely

rvithin

thc

$'alls

or cavities of trvo dies

that coDe

together to

errclose

the

rvorkpiece

on all

siclos.

The in]pression

for

rhe forging

can be entircly in

either

die

or divided

betweer the top

and

botton

dies.

The forging

slock rvhich is

generally

a lound

ol' squarc

bar is cut to

rhe

required lengih

to

get

the volune

of

metal

necdcd

to fill the die cavities,

plus

an

allowancc

for

flash-

The

stock after heating

to

the required

forging tcnlperature is

kcpt

in

bel*,een

the

two

halves ol the die.

Thc

for.ce is applied

by

means

c,ff

hanlmers

which

allorvs

the

melal to

undergo

plastic

deformetion and

fill

the

dic

cavity. Figure

3.1?

shou,s

a

schenatic

of closed die forging.

FiE.

3.17 Closed. die

forginq.

l)epending

on the

nanner

in

rvhich

lhe

pressure

is applicd,

closed

die lorgine

can

be

classified

as:

a) Drop forging.

b)

Press lbrging.

c)

Nlachirre lbrging.

a)

Drop

fbrging:

In drop

forging the various

types

of

hammers

are used

to



dies as

in figure. In this

operation

there is drastic

flow of metal

'I'o ensure

ploper

flow of

the metal dudng

the intermittent

bjows,

the operation

is directed

into

:1

number

of

si,eps.

cach step

changes the

form

gadually

contrclling

Lhe

flo$' oi

the

lnetal

until

the

flnal

shape

is

obtaiDed-

Number of

steps involved depends

upon

the

forged

qu:llities

of

the

etal,

size

and

shapc

ol

the parts

and

the

lolerances

required. Large

and cornplicated

shapes

may require use of

nlore

thcn one

set

ol

die.

Fig.

3.18

Steps

in

forging

of a urerrch

in

a

board

han ner,

Figure

3.1E

shows

the steps involved

in

forging

of a $'rench

usilrg closed idca

gradually

change shape ol

lhe



slender

ibrgin€is

and

forgings

lrorn

less

ductile

produced

by

press

fbrging

al'e:

large levers.

flanges.

railway $.heel

discs, ctc-,

al1oys. The

typical

products

toothed rvheels.

]rollorv

boclies,

Fig.

3.19 Hytlroulic

foryne

press

Cornparison

betu:ecn

Itammer

forging

antl

press

forgjng;

Flamner

blorv

produces

shock

and

vibrations

in

the

structure

and

founclation

au.l

th.l

surrounding_s.

This

implies

a

practjcal

lirnit

to the

sjze ol the

harnlr-rer.

The

hanmering proccss

is more

thorough

and

effcctive

than

pressing

but $.hcn

fhe

thickness

of

the

material

is

largJe

the eflects

olhammering

rna],

not

penetrate

right

through,

and the

oLrter

surface

of the

netal

will

be be er \aorked

than thosc

deeper

below.

In the

hamnering process

speed

of operation

can

be altered



plovides

a

unifomr

finished

shapes-

Shapes

dense and

hornogeneous

in

structure.

formed by

press

lorging

are

gcncrally

Il I

0l

(i)

FiE.

3.20

Steps inDolDed

in upset

forsinr,.

In

upset

forging,

one end of

the bar is

heated and the

other

end

is

gripped

in

a

fixed

die.

Pressure is

applied

lengthwise

on lhe

hot

end causing

it

to

be

upseL or

formed

to

shape.

The

length

of

the

stock to

be

upset should

not

be

more

than

2

to

3

times the diameter or else the material is

bent

rather

lhan

bulge out to

li1l

the dic

cavity.

For some

products

entire

operations

nay

be compJetcd in

one

position

although in

rnost

cases work is

progr'essively placed

in

differcnt

positions

in the

dics. Ihe impressions may

be

in

the

punch

in

the

g'ripping

die or in both. In mosl

cases tdmming is not

necessary.



is

grooved

according to

the

shape

lequired.

Heated

rod is

placed

bettveen

them and

thc rolls are

rotated

which

gives

shape of the

job.

By rolling

like lhis

through

required nun,ber

ol steps final shapc can be

achieved.

Ro1l lbrging is

primarily

used

lor

reducing

and tapcdng operations on

short

lengths

of

bar

stock. Finaliy

after

rolling

it

requires sizing

operations.

To manufacture

chisels,

tapered tubing,

ends of

leal

springs. axles, crow bars,

knife,

blades,

etc.,

roll

forging

is

ernployed.

Conpared to drop forging 2070 of matedal

is

saved

and

production

rate is 3000

times

grcater.

This

process

has

limitations

as

to the

shapes that can be

rolled and

the rolls are costly.

Fig.

3.21 Roll

foreirlg



achieved by

hamrnering

the heated bar

kept on

the

aivil.

As the metal

flows

laterally between

the advancing

die surlace.

'I'here is

less

deformation

at

the

die

interfaces.

because

of

frictional

lorces than at the

middle.

Thc sides of

the upset eylinder

gets

barreled

as the metal

flows easily towards

the nearest

fi'ee surthce.

ii' Fullering:

whpn

rhcrc

is

a

,FFU

ro

ln u..-l

"-

cp::_:lql-9ra4l

4teg li-@r

Lhc

sr

ock.

fqllggltliq-

ssea:

Here

as the

dies advance,

the

metal

flow takes

place

outwards and

away ftom

the centre

of

the

fullering die.

'lhis

operation

is

extensively

used

in lhe forging of

coonecting

Fie.

3.23

Fuuerine.

Edgtzg. This

is

used

rvhile

shaping

the

Fig : 3.22

Upsetting

ends of the bars

nhich

helps in

(.i)

Ilpsetting:

In simple

open

die

lolging

the

upsetting

of a

cyiindrieal

lillcts

is

:11



i\r) Drauting: This

process

is

used to reduce

the

cross section of

the work

with

a

corresponding increase in length. As

the

force is applied

through the

dies on

the

heated

metal the

cross

section

gradually

reduces.

(v)

Fig.

3.25

Drawing.

use of concave dies to reduce

the

diameters

of

small

waging:

This

makes

diameter

bars.

Fig. 3.27

piercing

Fig,

3,28 Punching.

(.vi)

Piercing: Piercing involves

making

a

blind hole in

a

heated

billet.

ivri)

Punching:

This is used to

produce

through holes

in thjnner materials-

Fig,

3.26

Swagine.

Forging Notes

Documents

Transcript of Forging Notes