Metal casting lectures notes

7/25/2019 Metal casting lectures notes

http://slidepdf.com/reader/full/metal-casting-lectures-notes 1/125

Metal Casting

Weeks 1 - 2

EMU - Manufacturing Technology




METAL CASTING

1 !"er"ie# of Casting Technology

$ San% Casting

& In"est'ent Casting

( )ie Casting

* Centrifugal Casting




Soli%ification +rocesses

We consi%er starting #ork 'aterial is either ali,ui% or is in a highly lastic con%ition. an% a

art is create% through soli%ification of the

'aterial

Soli%ification rocesses can /e classifie%accor%ing to engineering 'aterial rocesse%0

Metals

Cera'ics. secifically glasses

+oly'ers an% oly'er 'atri co'osites

2+MCs3




Classification of soli%ification rocesses




Casting

+rocess in #hich 'olten 'etal flo#s /ygra"ity or other force into a 'ol%

#here it soli%ifies in the shae of the

'ol% ca"ity

The ter' casting also alies to theart 'a%e in the rocess

Stes in casting see' si'le0

1 Melt the 'etal

$ +our it into a 'ol%

& Let it free4e




Caa/ilities an% A%"antages of Casting

5 Can create co'le art geo'etries that can not /e'a%e /y any other rocess

5 Can create /oth eternal an% internal shaes

5 So'e casting rocesses are net shape; others are

near net shape

5 Can ro%uce "ery large arts 2#ith #eight 'ore than

166 tons3. like '7c /e%

5 Casting can /e alie% to shae any 'etal that can

'elt

5 So'e casting 'etho%s are suite% to 'ass ro%uction

5 Can also /e alie% on oly'ers an% cera'ics




)isa%"antages of Casting

)ifferent %isa%"antages for %ifferent castingrocesses0

Li'itations on 'echanical roerties

+oor %i'ensional accuracy an% surface

finish for so'e rocesses8 eg. san%casting

Safety ha4ar%s to #orkers %ue to hot 'olten

'etals

En"iron'ental ro/le's




+arts Ma%e /y Casting

9ig arts

Engine /locks an% hea%s for auto'oti"e

"ehicles. #oo% /urning sto"es. 'achine

fra'es. rail#ay #heels. ies. /ells. u'

housings S'all arts

)ental cro#ns. :e#elry. s'all statues. frying

ans

All "arieties of 'etals can /e cast - ferrous an%

nonferrous




!"er"ie# of Casting Technology

Casting is usually erfor'e% in a foun%ry

Foundry ; factory e,uie% for

5 'aking 'ol%s

5 'elting an% han%ling 'olten 'etal

5 erfor'ing the casting rocess

5 cleaning the finishe% casting

Workers #ho erfor' casting are calle%foundrymen


http://slidepdf.com/reader/full/metal-casting-lectures-notes 10/125EMU - Manufacturing Technology

The Mol% in Casting

Mol% is a container #ith ca"ity #hose geo'etry%eter'ines art shae

Actual si4e an% shae of ca"ity 'ust /e

slightly o"ersi4e% to allo# for shrinkage of

'etal %uring soli%ification an% cooling Mol%s are 'a%e of a "ariety of 'aterials.

inclu%ing san%. laster. cera'ic. an% 'etal




!en Mol%s an% Close% Mol%s

T#o for's of 'ol%0 2a3 open mold. si'ly a container in the

shae of the %esire% art8 an% 2/3 closed mold. in #hich the

'ol% geo'etry is 'ore co'le an% re,uires a gating syste'

2assage#ay3 lea%ing into the ca"ity

Cavity is open toatmosphere

Cavity is closed




T#o Categories of Casting +rocesses

1. Expendable mold processes < uses aneen%a/le 'ol% #hich 'ust /e %estroye% to

re'o"e casting

Mold materials0 san%. laster. an% si'ilar

'aterials. lus /in%ers2. Permanent mold processes < uses a

er'anent 'ol% #hich can /e use% o"er an%

o"er to ro%uce 'any castings

Ma%e of 'etal 2or. less co''only. acera'ic refractory 'aterial3




San% Casting Mol%

San% casting 'ol%




San% Casting Mol% Ter's

Mol% consists of t#o hal"es0

Cope ; uer half of 'ol%

Drag ; /otto' half

Mol% hal"es are containe% in a /o. calle% a

flask

The t#o hal"es searate at the parting line




=or'ing the Mol% Ca"ity Cavity is inverse of final shape with shrinkage allowance

Pattern is model of final shape with shrinkage allowance

Wet sand is made by adding binder in the sand

Mol% ca"ity is for'e% /y acking san% aroun% a pattern

When the pattern is re'o"e%. the re'aining ca"ity of the acke%

san% has %esire% shae of cast art

The attern is usually o"ersi4e% to allo# for shrinkage of 'etal

%uring soli%ification an% cooling

Difference among pattern, cavit y &

part ?




Use of a Core in the Mol% Ca"ity

Cavity ro"i%es the external features of thecast art

Core provides internal features of the part.

It is lace% insi%e the 'ol% ca"ity #ith

so'e suort

In san% casting. cores are generally made of

sand

Difference b/w, cavity & core ?




Gating Syste'

It is channel through which molten metal flows intocavity from outside of mold

Consists of a down-sprue. through #hich 'etal

enters a runner lea%ing to the 'ain ca"ity

At the to of %o#n-srue. a pouring cup is oftenuse% to 'ini'i4e slash an% tur/ulence as the 'etal

flo#s into %o#n-srue




>iser

It is a reservoir in the mold which is a source of liquid metal tocompensate for shrinkage of the part during solidification

Most 'etals are less %ense as a li,ui% than as a soli% so

castings shrink uon cooling. #hich can lea"e a "oi% at the

last oint to soli%ify >isers re"ent this /y ro"i%ing 'olten'etal to the casting as it soli%ifies. so that the ca"ity for's

in the riser an% not in the casting




?eating the Metal

?eating furnaces are use% to heat the 'etal to'olten te'erature sufficient for casting

The heat re,uire% is the su' of0

1 ?eat to raise te'erature to 'elting oint

$ ?eat to raise 'olten 'etal to %esire%

te'erature for ouring




+ouring the Molten Metal

=or this ste to /e successful. 'etal 'ust flo# into all

regions of the 'ol%. 'ost i'ortantly the 'ain ca"ity.

/efore soli%ifying

=actors that %eter'ine success

+ouring te'erature

+ouring rate

Tur/ulence

Pouring temperature shoul% /e sufficiently high in or%er

to re"ent the 'olten 'etal to start soli%ifying on its #ayto the ca"ity




+ouring the Molten Metal

Pouring rate shoul% neither /e high 2'ay stuck therunner < shoul% 'atch "iscosity of the 'etal3 nor "ery

lo# that 'ay start soli%ifying on its #ay to the ca"ity

Turbulence shoul% /e ket to a 'ini'u' in or%er toensure s'ooth flo# an% to a"oi% 'ol% %a'age an%

entra'ent of foreign 'aterials Also. tur/ulence

causes oi%ation at the inner surface of ca"ity This

results in ca"ity %a'age an% oor surface ,uality of

casting



N O T I N C L U D

E D


Engineering Analysis of +ouring

1. v: velocity of liquid

metal at base of spruein cm/sec; g:

981cm/sec.sec; h:

height of sprue in cm

2. v1: velocity at section

of area A1; v2: velocity

at section of area A2

. !: volume of mold

cavity



N O T I N C L U D

E D


Calculation of +ouring +ara'eters0 Ea'le

1. If sprue area at its entrance is 5cm2, compute metal velocityat sprue entrance.

2. Calculate velocity & ow rate of metal when metal is in the

midway of sprue




Why Srue @-section is ket taer

In or%er to kee "olu'e flo# rate 2B;A3constant In case. -section is fie%. increase%

flui% "elocity %ue to gra"ity #ill increase flo# rate

This can cause air entra'ent into li,ui% 'etal



=lui%ity

A 'easure of the caa/ility of the 'etal to flo#into an% fill the 'ol% /efore free4ing

5=lui%ity is the in"erse of "iscosity 2resistance to

flo#3

actors affecting fluidity are!

-+ouring te'erature relati"e to 'elting oint

-Metal co'osition

-iscosity of the li,ui% 'etal

-?eat transfer to surroun%ing





Soli%ification of Metals

It is the transfor'ation of 'olten 'etal /ack intosoli% state

Soli%ification %iffers %een%ing on #hether the

'etal is

A ure ele'ent or An alloy

A Eutectic alloy



Soli%ification0 +ure Metals >ef cooling cur"e0

- +ure 'etal soli%ifies at a

constant te'erature e,ual to

its free4ing oint 2sa'e as

'elting oint3

- Local free4ing ti'e; Ti'e

fro' free4ing /egins an%co'lete%

- Total free4ing ti'e; Ti'e

fro' ouring to free4ing

co'lete%

- After free4ing is co'lete%.

the soli% continues to cool at

a rate in%icate% /y %o#n#ar%

sloe of cur"e




Soli%ification0 +ure Metals

- 9ecause of the chilling action of the'ol% #all. a thin skin of soli% 'etal is

initially for'e% at interface

i''e%iately after ouring

- The skin for'e% initially has e,ui-ae%. fine graine% an% ran%o'ly

oriente% structure This is /ecause of

rai% cooling

- As free4ing rocee%s. the grains

gro# in#ar%ly. a#ay fro' heat flo#%irection. as nee%les or sine of soli%

'etal

-




Soli%ification0 +ure Metals

- !n further gro#th of sine.lateral /ranches are for'e%.

an% as these /ranches gro#

further /ranches are for'e% at

right angle to the first/ranches This tye of gro#th

is calle% dendritic growth

- The %en%ritic grains are

coarse. colu'nar an% aligne%to#ar%s the center of casting




Soli%ification0 Most Alloys

- Most alloys free4e at range of te'erature rather than at a single

te'erature

- =ree4ing /egins fro' li,ui%us te'erature an% co'letes at

soli%us te'erature

- The cooling /egins in the sa'e 'anner as that in ure 'etals8 a

thin skin is for'e% at the interface of 'ol% an% 'akes shell asfree4ing rocee%s




Soli%ification0 Most Alloys

- The %en%rites /egin to for'#ith free4ing ?o#e"er. %ue to

large te'erature srea%

/et#een soli%us an% li,ui%us.

the earlier ortion of %en%riticgrains etract higher D of

ele'ents fro' li,ui% solution

than the ortion of grain for'e%

later

- As a result. the 'olten 'etal in

the center of 'ol% ca"ity

%eletes fro' the ele'ents

an% hence for's a %ifferent

structure 2see =ig3

-


"ure

metal

#e$%iAlloy

#e



Soli%ification0 Eutectic Alloys

5 Eutectic alloys soli%ify si'ilar to ure 'etals5 Eutectic oint on hase %iagra' is a oint at #hich the li,ui%.

on cooling. co'letely con"erts into soli% at one te' No

inter'e%iate hase 2LS3 eists

5 Al-Si 211FD Si3 an% Cast Iron 2(&D C3 are rele"ant castingeutectic alloys




N O T I N C L U D

E DSoli%ification Ti'e Chorino"Hs >ule


Chorinov! "#$e

Sh i k i S li%ifi i % C li




Shrinkage in Soli%ification an% Cooling

"hrin#age occurs in $ steps! a.

#hile cooling of 'etal in li,ui%

for' 2li,ui% contraction38 b. %uring

hase transfor'ation fro' li,ui%to soli% 2soli%ification shrinkage38

c. #hile soli%ifie% 'etal is coole%

%o#n to roo' te'erature 2soli%

ther'al contraction3




Shrinkage in Soli%ification an% Cooling

2$3 re%uction in height an% for'ation of shrinkage ca"ity cause% /y

soli%ification shrinkage8 2&3 further re%uction in height an%%ia'eter %ue to ther'al contraction %uring cooling of soli% 'etal

2%i'ensional re%uctions are eaggerate% for clarity3

%hy cavity forms at top & 'hy not at bottom(




Soli%ification Shrinkage 2Li,ui% <Soli% transfor'ation3

!ccurs in nearly all 'etals /ecause the soli%hase has a higher %ensity than the li,ui%

hase

Thus. soli%ification causes a re%uction in

"olu'e er unit 'ass of 'etal Exception0 cast iron #ith high C content

Grahiti4ation %uring final stages of free4ing

causes eansion that counteracts

"olu'etric %ecrease associate% #ith hasechange

Why solidification shrinkage is negligible in Cast

Irons??




Shrinkage Allo#ance

+attern'akers account for soli%ificationshrinkage an% ther'al contraction /y 'aking

'ol% ca"ity o"ersi4e%

A'ount /y #hich 'ol% is 'a%e larger relati"e

to final casting si4e is calle% pattern shrinkageallowance

Casting %i'ensions are eresse% linearly. so

allo#ances are alie% accor%ingly



)irectional Soli%ification- )esign !ti'i4ation

In or%er to 'ini'i4e the %a'aging effects of shrinkage. it is

%esira/le that the regions far fro' the riser 2'etal suly3shoul% soli%ify earlier than those near the riser in or%er to

ensure 'etal flo# to %istant regions to co'ensate

shrinkage This is achie"e% /y using Ch"orino"Hs rule

So. casting an% 'ol% %esign shoul% /e oti'al0 riser shoul%/e ket far fro' the regions of casting ha"ing lo# 7A ratio




)irectional Soli%ification- Use of Chills

The chills increase the heat etraction Internal an% eternal chills can also /e use% for

%irectional cooling

=or thick sections. s'all 'etal arts. #ith sa'e

'aterial as that of casting. are ut insi%e the ca"ityThe 'etal soli%ifies aroun% these ieces as it is

oure% into ca"ity

=or thin long sections. eternal chills are use% ent

holes are 'a%e in the ca"ity #alls or 'etal ieces areut in ca"ity #all

If Chorinov’s rule can not e employed! use chills





>iser )esign

>iser is use% to co'ensate for shrinkage of art %uring

soli%ification an% later it is searate% fro' the casting an%re-'elte% to 'ake 'ore castings

The Chvorinov)s rule shoul% /e use% to satisfy the %esign

re,uire'ents

There coul% /e %ifferent %esigns of riser0

- "ide riser 0 Attache% to the si%e of casting through a channel

- Top riser! Connecte% to the to surface of the casting

- *pen riser! Eose% to the outsi%e at the to surface of

coe- )isa%"antage of allo#ing of 'ore heat to escaero'oting faster soli%ification

- +lind riser! Entirely enclose% #ithin the 'ol%




Self +ractice

Design a riser according to conditions given in"#ample $%.&.




'"()* C)+(I, P/C"++"+




T#o Categories of Casting +rocesses

1. Expendable mold processes - 'ol% issacrifice% to re'o"e art

,dvantage0 'ore co'le shaes ossi/le

isadvantage0 ro%uction rates often li'ite%

/y ti'e to 'ake 'ol% rather than castingitself

2. Permanent mold processes - 'ol% is 'a%e of

'etal an% can /e use% to 'ake 'any castings

,dvantage0 higher ro%uction rates isadvantage0 geo'etries li'ite% /y nee% to

oen 'ol%




!"er"ie# of San% Casting

"and casting is a cast art ro%uce% /y for'inga 'ol% fro' a san% 'iture an% then ouring

'olten li,ui% 'etal into the ca"ity in the 'ol% The

'ol% is then coole% until the 'etal has soli%ifie%

Most #i%ely use% casting rocess. accounting for

a significant 'a:ority of total tonnage cast

Nearly all alloys can /e san% caste%. inclu%ing

'etals #ith high 'elting te'eratures. such as

steel. nickel. an% titaniu'

Castings range in si4e fro' s'all to "ery large

+ro%uction ,uantities fro' one to 'illions




A large san% casting #eighing o"er F6 kg 21*66 l/3 for an air

co'ressor fra'e




Stes in San% Casting

1 +our the 'olten 'etal into san% 'ol% CAITJ$ Allo# ti'e for 'etal to soli%ify

& 9reak u the 'ol% to re'o"e casting

( Clean an% insect casting

Searate gating an% riser syste'

* ?eat treat'ent of casting is so'eti'es

re,uire% to i'ro"e 'etallurgical roerties




San% Casting +ro%uction Se,uence

igure0 Stes in the ro%uction se,uence in san% castingThe stes inclu%e not only the casting oeration /ut also

attern 'aking an% 'ol% 'aking‑ ‑




Making the San% Mol%

The cavity in the san% 'ol% is for'e% /y acking san%aroun% a attern. then searating the 'ol% into t#o

hal"es an% re'o"ing the attern

The 'ol% 'ust also contain gating an% riser syste'

If casting is to ha"e internal surfaces. a core 'ust /einclu%e% in 'ol%

A ne# san% 'ol% 'ust /e 'a%e for each art ro%uce%




The +attern

A full si4e% 'o%el of the art. slightly enlarge% to‑

account for shrinkage an% 'achining

allo#ances in the casting

+attern 'aterials0

%ood - co''on 'aterial /ecause it is easyto #ork. /ut it #ars

Metal - 'ore eensi"e to 'ake. /ut lasts

'uch longer

Plastic - co'ro'ise /et#een #oo% an%'etal

T f + tt




Tyes of +atternsigure0 Tyes of atterns use% in san% casting0

2a3 soli% attern

2/3 slit attern2c3 'atch late attern‑

2%3 coe an% %rag attern




9uoyancy =orce %uring +ouring

!ne of the ha4ar%s %uring ouring is that /uoyancyof 'olten #ill %islace the core #ith the force0

=/; W'-Wc 2Archi'e%es rincile3

W'0 Weight of 'olten 'etal %islace%8

Wc0 Weight of core

00 In order to avoid the effect of F ! chaplets are

used to hold the core in cavity of mold.




Core in Mol%

, core is a full-scale 'o%el of interior surfaces of the art

2a3 Core hel% in lace in the 'ol% ca"ity /y chalets. 2/3 ossi/le chalet

%esign. 2c3 casting #ith internal ca"ity

1. Like pattern, shrinkage allowances

are also provided in core. (-ve or +)?

2. It is usually made of compacted sand,

metal




)esira/le Mol% +roerties

"trength A/ility of 'ol% to 'aintain shae an% resist

‑erosion cause% /y the flo# of 'olten 'etal )een%s

on grain shae. a%hesi"e ,uality of /in%ers

Permeability to allo# hot air an% gases to ass‑

through "oi%s in san%

Thermal stability a/ility of san% at the 'ol% surface‑

ca"ity to resist cracking an% /uckling on contact #ith

'olten 'etal

Collapsibility a/ility to gi"e #ay an% allo# casting to‑

shrink #ithout cracking the casting eusability can san% fro' /roken 'ol% /e reuse% to‑

'ake other 'ol%s




=oun%ry San%s

"ilica /"i*20 or silica 'ie% #ith other 'inerals

Goo% refractory roerties caacity to‑

en%ure high te'eratures

S'all grain si4e yiel%s /etter surface finish

on the cast art

Large grain si4e is 'ore er'ea/le. allo#ing

gases to escae %uring ouring

Irregular grain shaes strengthen 'ol%s %ue

to interlocking. co'are% to roun% grains

isadvantage0 interlocking ten%s to

re%uce er'ea/ility




9in%ers Use% #ith =oun%ry San%s

San% is hel% together /y a 'iture of #ater an%/on%ing clay

Typical mix0 K6D san%. D clay an% &D

#ater

!ther /on%ing agents also use% in san% 'ol%s0 !rganic resins 2eg . henolic resins3

Inorganic /in%ers 2eg . so%iu' silicate an%

hoshate3

A%%iti"es are so'eti'es co'/ine% #ith the'iture to increase strength an%7or er'ea/ility




Tyes of San% Mol%

reen sand molds

‑- 'iture of san%. clay. an%

#ater8

Green 'eans 'ol% contains 'oisture at

ti'e of ouring

ry sand mold‑

- organic /in%ers rather thanclay

An% 'ol% is /ake% to i'ro"e strength

"#in dried mold‑ - %rying 'ol% ca"ity surface

of a green san% 'ol% to a %eth of 16 to $*‑

''. using torches or heating la's




!ther Een%a/le Mol% +rocesses

Shell Mol%ing

acuu' Mol%ing

Ean%e% +olystyrene +rocess

In"est'ent Casting

+laster Mol% an% Cera'ic Mol% Casting

&ther '(pendable )old "rocesses




Shell Mol%ing

Casting rocess in #hich the ca"ity 2 gating syste'3

is a thin shell of san% hel% together /yther'osetting resin /in%er

Stes in shell 'ol%ing0 213 a 'atch late or coe an% %rag 'etal‑ ‑ ‑ ‑

attern is heate% an% lace% o"er a /o containing san%

'ie% #ith ther'osetting resin

part





Shell Mol%ing

Stes in shell 'ol%ing0 2$3 /o is in"erte% so that san% an%‑resin fall onto the hot attern. causing a layer of the

'iture to artially cure on the surface to for' a har%

shell8 2&3 /o is reositione% so that loose uncure%

articles %ro a#ay8





Shell Mol%ing

Stes in shell 'ol%ing0 2(3 san% shell is heate% in o"en for‑se"eral 'inutes to co'lete curing8 2*3 shell 'ol% is

strie% fro' the attern8





Shell Mol%ing

Stes in shell 'ol%ing0 2F3 t#o hal"es of the shell 'ol% are‑

asse'/le%. suorte% /y san% or 'etal shot in a /o. an% ouringis acco'lishe%8 23 the finishe% casting #ith srue re'o"e%





A%"antages an% )isa%"antages

A%"antages of shell 'ol%ing0 S'oother ca"ity surface er'its easier flo#

of 'olten 'etal an% /etter surface finish

Goo% %i'ensional accuracy - 'achining often

not re,uire% Mol% collasi/ility 'ini'i4es cracks in casting

Can /e 'echani4e% for 'ass ro%uction

)isa%"antages0

More eensi"e 'etal attern

)ifficult to :ustify for s'all ,uantities

acuu' Mol%ing&ther '(pendable )old "rocesses




acuu' Mol%ing

acuu' Mol%ing&ther '(pendable )old "rocesses




acuu' Mol%ing

Ean%e% +olystyrene +rocess or&ther '(pendable )old "rocesses




Ean%e% +olystyrene +rocess or

lost foa' rocess‑

Uses a 'ol% of san% acke% aroun% apolystyrene foam pattern #hich "aori4es

#hen 'olten 'etal is oure% into 'ol%

Other names0 lost foa' rocess. lost attern‑

rocess. e"aorati"e foa' rocess. an%‑full 'ol% rocess‑

+olystyrene foa' attern inclu%es srue.

risers. gating syste'. an% internal cores 2if

nee%e%3 Mol% %oes not ha"e to /e oene% into coe

an% %rag sections






Ean%e% olystyrene casting rocess0 213 attern ofpolystyrene is coate% #ith refractory co'oun%8






Ean%e% olystyrene casting rocess0 2$3 foa' attern islace% in 'ol% /o. an% san% is co'acte% aroun% the

attern8






Ean%e% olystyrene casting rocess0 2&3 'olten 'etal isoure% into the ortion of the attern that for's the

ouring cu an% srue As the 'etal enters the 'ol%. the

olystyrene foa' is "aori4e% ahea% of the a%"ancing

li,ui%. thus the resulting 'ol% ca"ity is fille%






A%"antages of ean%e% olystyrene rocess0 +attern nee% not /e re'o"e% fro' the 'ol%

Si'lifies an% see%s 'ol% 'aking.‑

/ecause t#o 'ol% hal"es are not re,uire%

as in a con"entional green san% 'ol%‑

)isa%"antages0

A ne# attern is nee%e% for e"ery casting

Econo'ic :ustification of the rocess is

highly %een%ent on cost of ro%ucingatterns






,pplications0 Mass ro%uction of castings for auto'o/ile

engines

Auto'ate% an% integrate% 'anufacturing

syste's are use% to1 Mol% the olystyrene foa' atterns an%

then

$ =ee% the' to the %o#nstrea' casting

oeration





In"est'ent Casting 2Lost Wa +rocess3

A attern 'a%e of #a is coate% #ith a refractory'aterial to 'ake 'ol%. after #hich #a is

'elte% a#ay rior to ouring 'olten 'etal

In"est'ent co'es fro' a less fa'iliar

%efinition of invest - to co"er co'letely.#hich refers to coating of refractory 'aterial

aroun% #a attern

It is a precision casting process - caa/le of

ro%ucing castings of high accuracy an%intricate %etail





In"est'ent Casting

Stes in in"est'ent casting0 213 #a atterns are ro%uce%. 2$3se"eral atterns are attache% to a srue to for' a attern tree





In"est'ent Casting

Stes in in"est'ent casting0 2&3 the attern tree is coate% #ith a thinlayer of refractory 'aterial. 2(3 the full 'ol% is for'e% /y co"ering

the coate% tree #ith sufficient refractory 'aterial to 'ake it rigi%





In"est'ent Casting

Stes in in"est'ent casting0 2*3 the 'ol% is hel% in an in"erte% ositionan% heate% to 'elt the #a an% er'it it to %ri out of the ca"ity. 2F3

the 'ol% is reheate% to a high te'erature. the 'olten 'etal is

oure%. an% it soli%ifies





In"est'ent Casting

Stes in in"est'ent casting0 23 the 'ol% is /roken a#ay

fro' the finishe% casting an% the arts are searate%

fro' the srue





In"est'ent Casting

A one iece co'ressor stator #ith 16 searate airfoils‑

'a%e /y in"est'ent casting






A%"antages of in"est'ent casting0 +arts of great co'leity an% intricacy can

/e cast

Close %i'ensional control an% goo% surfacefinish

Wa can usually /e reco"ere% for reuse

A%%itional 'achining is not nor'allyre,uire% this is a net shae rocess‑

)isa%"antages

Many rocessing stes are re,uire%

>elati"ely eensi"e rocess





+laster Mol% Casting

Si'ilar to san% casting ecet 'ol% is 'a%e oflaster of +aris 2gysu' ‑ CaS!( $?‑ $!3

In 'ol%-'aking. laster an% #ater 'iture is

oure% o"er lastic or 'etal attern an%

allo#e% to set Woo% atterns not generally use% %ue to

eten%e% contact #ith #ater

+laster 'iture rea%ily flo#s aroun% attern.

caturing its fine %etails an% goo% surfacefinish






A%"antages of laster 'ol% casting0 Goo% accuracy an% surface finish

Caa/ility to 'ake thin cross sections‑

)isa%"antages0

Mol% 'ust /e /ake% to re'o"e 'oisture.#hich can cause ro/le's in casting

Mol% strength is lost if o"er-/ake%

+laster 'ol%s cannot stan% high

te'eratures. so li'ite% to lo#er 'eltingoint alloys can /e caste%





Cera'ic Mol% Casting

Si'ilar to +laster Mol% Casting ecet the'aterial of 'ol% is refractory cera'ic 'aterial

instea% of laster

The cera'ic 'ol% can #ithstan% te'erature of

'etals ha"ing high 'elting ointsSurface ,uality is sa'e as that in laster 'ol%

casting




+er'anent Mol% Casting +rocesses

Econo'ic %isa%"antage of een%a/le 'ol%casting0 a ne# 'ol% is re,uire% for e"ery

casting

In er'anent 'ol% casting. the 'ol% is reuse%

'any ti'es The rocesses inclu%e0

9asic er'anent 'ol% casting

)ie casting

Centrifugal casting

"ermanent )old "rocesses




The 9asic +er'anent Mol% +rocess

Uses a 'etal 'ol% constructe% of t#o sections%esigne% for easy. recise oening an% closing

Mol%s use% for casting lo#er 'elting-oint alloys

2Al. Cu. 9rass3 are co''only 'a%e of steel or

cast iron Mol%s use% for casting steel 'ust /e 'a%e of

refractory material. %ue to the "ery high ouring

te'eratures





+er'anent Mol% Casting

Stes in er'anent 'ol% casting0 213 'ol% is reheate% an%

coate%





+er'anent Mol% Casting

Stes in er'anent 'ol% casting0 2$3 cores 2if use%3 are inserte% an%'ol% is close%. 2&3 'olten 'etal is oure% into the 'ol%. #here itsoli%ifies





A%"antages an% Li'itations

A%"antages of er'anent 'ol% casting0

Goo% %i'ensional control an% surface finish

ery econo'ical for 'ass ro%uction

More rai% soli%ification cause% /y the col% 'etal

'ol% results in a finer grain structure. so castings

are stronger Li'itations0

Generally li'ite% to 'etals of lo#er 'elting oint

Co'le art geo'etries can not /e 'a%e

/ecause of nee% to oen the 'ol%

?igh cost of 'ol%

Not suita/le for lo#-"olu'e ro%uction

ariations of +er'anent Mol% Casting0"ermanent )old "rocesses




ariations of +er'anent Mol% Casting0

a Slush Casting The /asic roce%ure the sa'e as use% in

9asic +er'anent Mol% Casting

After artial soli%ification of 'etal. the 'olten

'etal insi%e the 'ol% is %raine% out. lea"ing

the art hollo# fro' insi%e

Statues. La' /ases. +e%estals an% toys are

usually 'a%e through this rocess

Metal #ith lo# 'elting oint are use%0 Oinc.

Lea% an% Tin





/ Lo#-ressure Casting The /asic rocess is sho#n in ig.

- In /asic er'anent an% slush casting rocesses. 'etal in ca"ity isoure% un%er gra"ity ?o#e"er. in lo#-ressure casting. the 'etal is

force% into ca"ity un%er lo# ressure 261 M+a3 of air





/ Lo#-ressure Casting

5 ,dvantages!

- Clean 'olten 'etal fro' the center of la%le 2cu3 is

intro%uce% into the ca"ity

- >e%uce%- gas orosity. oi%ation %efects. i'ro"e'ent in

'echanical roerties

ariations of +er'anent Mol% Casting0

+ t M l% C ti





c acuu' +er'anent-Mol% Casting

This is a "ariation of lo#-ressure er'anent

casting

Instea% of rising 'olten into the ca"ity through air

ressure. "acuu' in ca"ity is create% #hich

cause% the 'olten 'etal to rise in the ca"ity fro'

'etal ool

)i C ti





)ie Casting

A er'anent 'ol% casting rocess in #hich'olten 'etal is in:ecte% into 'ol% ca"ity un%er

high ressure

+ressure is 'aintaine% %uring soli%ification.

then 'ol% is oene% an% art is re'o"e% Molds in this casting oeration are called

dies8 hence the na'e %ie casting

Use of high ressure 2-$3MPa3 to force 'etal

into %ie ca"ity is #hat %istinguishes this fro'other er'anent 'ol% rocesses

)i C ti M hi





)ie Casting Machines

)esigne% to hol% an% accurately close t#o'ol% hal"es an% kee the' close% #hile li,ui%

'etal is force% into ca"ity

T#o 'ain tyes0

1 ?ot cha'/er 'achine‑

$ Col% cha'/er 'achine‑

? t Ch / )i C ti





?ot-Cha'/er )ie CastingMetal is 'elte% in a container. an% a iston in:ects li,ui% 'etal

un%er high ressure into the %ie ?igh ro%uction rates - *66 arts er hour not unco''on In:ection ressure0 -&*M+a Alications li'ite% to lo# 'elting oint 'etals that %o not‑

che'ically attack lunger an% other 'echanical co'onents Casting 'etals0 4inc. tin. lea%. an% 'agnesiu'

? t Ch / )i C ti





?ot-Cha'/er )ie Casting

Cycle in hot cha'/er casting0 213 #ith %ie close% an% lunger‑

#ith%ra#n. 'olten 'etal flo#s into the cha'/er

? t Ch / )i C ti





?ot-Cha'/er )ie Casting

Cycle in hot cha'/er casting0 2$3 lunger forces 'etal in‑

cha'/er to flo# into %ie. 'aintaining ressure %uring

cooling an% soli%ification

Because the die material does

not have natural permeability

(like sand has), vent holes at

die cavity needs to be made

C l% Ch / )i C ti





Col% Cha'/er )ie Casting‑

Molten 'etal is oure% into unheate% cha'/er fro'eternal 'elting container. an% a iston in:ects

'etal un%er high ressure 21(-1(6M+a3 into %ie

ca"ity

?igh ro%uction /ut not usually as fast ashot cha'/er 'achines /ecause of ouring ste‑

Casting 'etals0 alu'inu'. /rass. an% 'agnesiu'

alloys

,dvantage of cold chamber is that high meltingpoint metals can be casted! %hy(((

Col% Cha'/er )ie Casting






Cycle in col% cha'/er casting0 213 #ith %ie close% an% ra'‑

#ith%ra#n. 'olten 'etal is oure% into the cha'/er

Col% Cha'/er )ie Casting






Cycle in col% cha'/er casting0 2$3 ra' forces 'etal to flo#‑

into %ie. 'aintaining ressure %uring cooling an%

soli%ification

Mol%s for )ie Casting





Mol%s for )ie Casting

Usually 'a%e of tool steel. 'ol% steel. or'araging steel

Tungsten an% 'oly/%enu' 2goo% refractory

,ualities3 are use% to 'ake %ie for casting steel

an% cast iron E:ector ins are re,uire% to re'o"e art fro'

%ie #hen it oens

Lu/ricants 'ust /e sraye% into ca"ities to

re"ent sticking







A%"antages of %ie casting0

Econo'ical for large ro%uction ,uantities

Goo% accuracy 2P66F''3an% surface finish

Thin sections are ossi/le

>ai% cooling ro"i%es s'all grain si4e an% goo%strength to casting

)isa%"antages0

Generally li'ite% to 'etals #ith lo# 'etal oints

+art geo'etry 'ust allo# re'o"al fro' %ie. so "eryco'le arts can not /e caste%

=lash an% 'etal in "ent holes nee% to /e cleane%

after e:ection of art

Centrifugal Casting




Centrifugal Casting

A fa'ily of casting rocesses in #hich the 'ol% isrotate% at high see% so centrifugal force

%istri/utes 'olten 'etal to outer regions of %ie

ca"ity

The grou inclu%es0 True centrifugal casting

Se'icentrifugal casting

Centrifuge casting

2a3 True Centrifugal Casting




2a3 True Centrifugal Casting

Molten 'etal is oure% into a rotating 'ol% to ro%uce a tu/ular art

In so'e oerations. 'ol% rotation co''ences after ouring

rather than /efore

>otational aes can /e either hori4ontal or "ertical

+arts0 ies. tu/es. /ushings. an% rings

!utsi%e shae of casting can /e roun%. octagonal. heagonal. etc

. /ut insi%e shae is 2theoretically3 erfectly roun%. %ue to ra%ially

sy''etric forces

Shrinkage alloance is

not considerable factor

>otational See% of Mol%



N O T I N C L U

D E D


>otational See% of Mol%

! *f +# is very lo,, the moltenmetal ill not remain forced

against the mold, rather it ill

rain inside cavity

! "herefore, #$ must be kept

beteen %&!'& (based on

eperiments)

Ea'le



Ea'le

Problem! A true centrifugal casting is to /e erfor'e%hori4ontally to 'ake coer tu/e sections0 !) ;$*c'8

I); $$*c'8 G=; F* =in% rotational see%

Solution0

!) ;); $*c'; 6$*'8 g; K1'7s$8 G=;F*

!n sol"ing #e get0 F1 >+M 2re"7'in3


N O T I N C L U

D E D

2/3 Se'icentrifugal Casting




2/3 Se'icentrifugal Casting

Centrifugal force is use% to ro%uce soli% castings rather than

tu/ular arts Mol%s are %esigne% #ith risers at center to suly fee% 'etal

)ensity of 'etal in final casting is greater in outer sections than

at center of rotationes of parts and rotational

ais does not match eactly

*ften used on parts in hich

center of casting is machined

aay, thus eliminating the

portion here +uality is loestamples- heels and pulleys

# factor keeps from .&!./

2c3 Centrifuge Casting




2c3 Centrifuge Casting

Mol% is %esigne% #ith artca"ities locate% a#ay fro'

ais of rotation. so that

'olten 'etal oure% into

'ol% is %istri/ute% to these

ca"ities /y centrifugal force

Use% for s'aller arts

>a%ial sy''etry of art is

not re,uire% as in other

centrifugal casting 'etho%s

General )efects0 Misrun




A casting that has soli%ifie% /efore co'letely

filling 'ol% ca"ity

So'e co''on %efects in castings0 2a3 misrun

General )efects0 Misrun

-easons:a0$luidity of molten metal is insufficient

b01ouring temperature is too lo

c01ouring is done too sloly

d0Cross section of mold cavity is too thin

e02old design is not in accordance ith Chvorinov3s

rule- 45 at the section closer to the gating system

should be higher than that far from gating system

General )efects0 Col% Shut




T#o ortions of 'etal flo# together /ut there is a

lack of fusion %ue to re'ature 2early3 free4ing

So'e co''on %efects in castings0 2/3 cold shut

General )efects0 Col% Shut

6easons-

Same as for misrun

General )efects0 Col% Shot




Metal slashes %uring ouring an% soli% glo/ules

for' an% /eco'e entrae% in casting

So'e co''on %efects in castings0 2c3 cold shot

General )efects0 Col% Shot

#ating system should be

improved to avoid splashing

General )efects0 Shrinkage Ca"ity




)eression in surface or internal "oi% cause% /y

soli%ification shrinkage

So'e co''on %efects in castings0 2%3 shrin#age cavity

g y

1roper riser design can solve this issue

General Casting )efects0 ?ot Tearing




?ot tearing7cracking in casting occurs #hen the

'olten 'etal is not allo#e% to contract /y an

un%erlying 'ol% %uring cooling7 soli%ification

Co''on %efects in san% castings0 2e3 hot tearing

g g

"he collapsibility (ability to give ay

and allo molten metal to shrink duringsolidification) of mold should be

improved

San% Casting )efects0 San% 9lo#




9alloon shae% gas ca"ity cause% /y release of‑

'ol% gases %uring ouring

Co''on %efects in san% castings0 2a3 sand blo'

g

7o permeability of mold, poor

venting, high moisture content insand are ma8or reasons

San% Casting )efects0 +in ?oles




=or'ation of 'any s'all gas ca"ities at or slightly

/elo# surface of casting

Co''on %efects in san% castings0 2/3 pin holes

g

Caused by release of gas duringpouring of molten metal0

"o avoid, improve permeability 9

venting in mold

San% Casting )efects0 +enetration




When flui%ity of li,ui% 'etal is high. it 'ay enetrate

into san% 'ol% or core. causing casting surface to

consist of a 'iture of san% grains an% 'etal

Co''on %efects in san% castings0 2e3 penetration

San% Casting )efects0 +enetration

:arder packing of sand helps to

alleviate this problem

6educe pouring temp if possible

;se better sand binders

San% Casting )efects0 Mol% Shift




A ste in cast ro%uct at arting line cause% /y

si%e#ise relati"e %islace'ent of coe an% %rag

Co''on %efects in san% castings0 2f3 mold shift

g

It is caused by buoyancy force of

molten metal0

Cope an drag must be alignedaccurately and fastened0

;se match plate patterns

San% Casting )efects0 Core Shift




Si'ilar to core 'ol% /ut it is core that is %islace%

an% the %islace'ent is usually "ertical

Co''on %efects in san% castings0 2g3 core shift

g

It is caused by buoyancy force of

molten metal0

Core must be fastened ith chaplet

San% Casting )efects0 San% Wash




An irregularity in the casting surface cause% /y

erosion of san% 'ol% %uring ouring

Co''on %efects in san% castings0 2h0 sand 'ash

g

"urbulence in metal flo during pouring

should be controlled0 lso, very high

pouring temperature cause erosion of

mold0

San% Casting )efects0 Sca/s




Sca/s are rough areas on the surface of casting

%ue to un-necessary %eosit of san% an% 'etal

Co''on %efects in san% castings0 2i3 scab

g

It is caused by portions of the mold

surface flaking off during solidificationand becoming embedded in the casting

surface

Improve mold strength by reducing

grain si<e and changing binders

San% Casting )efects0 Mol% Crack




!ccurs #hen the strength of 'ol% is not sufficient

to #ithstan% high te'eratures

Co''on %efects in san% castings0 2:3 mold crac#

Improve mold strength by reducing

grain si<e and changing binders

Metals for Casting




Metals for Casting

Casting alloys can /e classifie% as0 =errous

Nonferrous

=errous Casting Alloys0 Cast 4ron




=errous Casting Alloys0 Cast 4ron

Most i'ortant of all casting alloys Tonnage of cast iron castings is se"eral ti'es

that of all other 'etals co'/ine%

Se"eral tyes0 213 #hite cast iron iron. 2$3 grey

cast 2&3 no%ular7%uctile cast iron 2(3 'allea/leiron. an% 2*3 alloy cast irons

The %uctility of Cast Iron increases fro' 1-(

Tyical ouring te'eratures ∼ 1(66°C

2$*66°=3. %een%ing on co'osition

=errous Casting Alloys0 "teel




g y

The 'echanical roerties of steel 'ake it anattracti"e engineering 'aterial

The caa/ility to create co'le geo'etries

'akes casting an attracti"e shaing rocess

)ifficulties #hen casting steel0 +ouring te'erature of steel is higher than

for 'ost other casting 'etals ∼ 1F*6°C

2&666°=3

At such te'eratures. steel rea%ily oi%i4es.so 'olten 'etal 'ust /e isolate% fro' air

Molten steel has relati"ely oor flui%ity

Nonferrous Casting Alloys0 ,luminum




g y

Generally consi%ere% to /e "ery casta/le +ouring te'eratures lo# %ue to lo# 'elting

te'erature of alu'inu'

T m ; FF6°C 21$$6°=3

+roerties0 Light #eight

>ange of strength roerties /y heat

treat'ent

Easy to 'achine

Nonferrous Casting Alloys0 Copper,lloys




y

Inclu%es /ron4e. /rass. an% alu'inu' /ron4e +roerties0

Corrosion resistance

Attracti"e aearance

Goo% /earing ,ualities Li'itation0 high cost of coer

Alications0 ie fittings. 'arine roeller

/la%es. u' co'onents. orna'ental :e#elry

Assignment No. 1



g

+roose the /est suita/le casting rocess to 'ake an alu'inu'cu )uring selecting a rocess. kee the follo#ing oints in "ie#0

1.o of cups! "

#.$roduct cost! as low as possible

%.&urface quality! good. 'uality is not as important as cost

".(efects! some defects are acceptable

).$rocessing time! not important

(raw an analysis for each ma*or type of casting process with

reference to above conditions. Then choose one casting processand write a report in its support .


Term Project



j

Processing of--

5 Polymer /choose a oly'er tye use% in in%ustry0 55 Ceramic /choose a cera'ic tye use% in in%ustry0

Stu%ents can 'ake grous to #ork A grou shoul% not co'ose of

'ore than $ stu%ents

,ll pro6ects should include!- +rocess intro%uction. +rocessing %ata for at least one ro%uct 2either

'a%e of oly'er or cera'ics3 Also 'ention 'anufacturing 'etho% for

that articular ro%uct

-To o/tain rocessing %ata. the stu%ents can consult Metals ?an%/ooks

!> any other han%/ook !> Internet- The tye of 'aterial chosen shoul% /e %ifferent in each grou

Toic Su/'ission )ea% Line0 on or before +,- pril-#+1"

Documents

Metal casting lectures notes