Metal casting lectures notes
Transcript of Metal casting lectures notes
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Metal Casting
Weeks 1 - 2
EMU - Manufacturing Technology
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METAL CASTING
1 !"er"ie# of Casting Technology
$ San% Casting
& In"est'ent Casting
( )ie Casting
* Centrifugal Casting
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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
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Classification of soli%ification rocesses
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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
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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
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)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
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+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
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!"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
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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
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!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
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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
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San% Casting Mol%
San% casting 'ol%
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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
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=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 ?
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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 ?
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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
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>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
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?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
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+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
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+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
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N O T I N C L U D
E D
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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
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N O T I N C L U D
E D
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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
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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
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=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
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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
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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
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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
-
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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
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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
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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
-
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"ure
metal
#e$%iAlloy
#e
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Soli%ification0 Eutectic Alloys
5 Eutectic alloys soli%ify si'ilar to ure 'etals5 Eutectic oint on hase %iagra' is a oint at #hich the li,ui%.
on cooling. co'letely con"erts into soli% at one te' No
inter'e%iate hase 2LS3 eists
5 Al-Si 211FD Si3 an% Cast Iron 2(&D C3 are rele"ant castingeutectic alloys
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N O T I N C L U D
E DSoli%ification Ti'e Chorino"Hs >ule
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Chorinov! "#$e
Sh i k i S li%ifi i % C li
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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
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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(
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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??
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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
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)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
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)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
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>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%
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Self +ractice
Design a riser according to conditions given in"#ample $%.&.
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'"()* C)+(I, P/C"++"+
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T#o Categories of Casting +rocesses
1. Expendable mold processes - 'ol% issacrifice% to re'o"e art
,dvantage0 'ore co'le shaes ossi/le
isadvantage0 ro%uction rates often li'ite%
/y ti'e to 'ake 'ol% rather than castingitself
2. Permanent mold processes - 'ol% is 'a%e of
'etal an% can /e use% to 'ake 'any castings
,dvantage0 higher ro%uction rates isadvantage0 geo'etries li'ite% /y nee% to
oen 'ol%
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!"er"ie# of San% Casting
"and casting is a cast art ro%uce% /y for'inga 'ol% fro' a san% 'iture an% then ouring
'olten li,ui% 'etal into the ca"ity in the 'ol% The
'ol% is then coole% until the 'etal has soli%ifie%
Most #i%ely use% casting rocess. accounting for
a significant 'a:ority of total tonnage cast
Nearly all alloys can /e san% caste%. inclu%ing
'etals #ith high 'elting te'eratures. such as
steel. nickel. an% titaniu'
Castings range in si4e fro' s'all to "ery large
+ro%uction ,uantities fro' one to 'illions
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A large san% casting #eighing o"er F6 kg 21*66 l/3 for an air
co'ressor fra'e
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Stes in San% Casting
1 +our the 'olten 'etal into san% 'ol% CAITJ$ 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
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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‑ ‑
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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%
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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
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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
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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.
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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
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)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
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=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
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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
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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
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!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
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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
&ther '(pendable )old "rocesses
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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
&ther '(pendable )old "rocesses
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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
&ther '(pendable )old "rocesses
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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%
&ther '(pendable )old "rocesses
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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
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acuu' Mol%ing
acuu' Mol%ing&ther '(pendable )old "rocesses
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acuu' Mol%ing
Ean%e% +olystyrene +rocess or&ther '(pendable )old "rocesses
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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
&ther '(pendable )old "rocesses
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Ean%e% +olystyrene +rocess
Ean%e% olystyrene casting rocess0 213 attern ofpolystyrene is coate% #ith refractory co'oun%8
&ther '(pendable )old "rocesses
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Ean%e% +olystyrene +rocess
Ean%e% olystyrene casting rocess0 2$3 foa' attern islace% in 'ol% /o. an% san% is co'acte% aroun% the
attern8
&ther '(pendable )old "rocesses
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Ean%e% +olystyrene +rocess
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%
&ther '(pendable )old "rocesses
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A%"antages an% )isa%"antages
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
&ther '(pendable )old "rocesses
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Ean%e% +olystyrene +rocess
,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
&ther '(pendable )old "rocesses
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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
&ther '(pendable )old "rocesses
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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
&ther '(pendable )old "rocesses
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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%
&ther '(pendable )old "rocesses
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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
&ther '(pendable )old "rocesses
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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
&ther '(pendable )old "rocesses
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In"est'ent Casting
A one iece co'ressor stator #ith 16 searate airfoils‑
'a%e /y in"est'ent casting
&ther '(pendable )old "rocesses
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A%"antages an% )isa%"antages
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
&ther '(pendable )old "rocesses
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+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
&ther '(pendable )old "rocesses
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A%"antages an% )isa%"antages
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%
&ther '(pendable )old "rocesses
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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
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+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
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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
"ermanent )old "rocesses
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+er'anent Mol% Casting
Stes in er'anent 'ol% casting0 213 'ol% is reheate% an%
coate%
"ermanent )old "rocesses
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+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
"ermanent )old "rocesses
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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
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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
ariations of +er'anent Mol% Casting0"ermanent )old "rocesses
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/ 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
ariations of +er'anent Mol% Casting0"ermanent )old "rocesses
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/ 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
"ermanent )old "rocesses
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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
"ermanent )old "rocesses
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)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
"ermanent )old "rocesses
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)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
"ermanent )old "rocesses
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?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
"ermanent )old "rocesses
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?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
"ermanent )old "rocesses
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?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
"ermanent )old "rocesses
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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
"ermanent )old "rocesses
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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
"ermanent )old "rocesses
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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
"ermanent )old "rocesses
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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 an% Li'itations
"ermanent )old "rocesses
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A%"antages an% Li'itations
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
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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
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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%
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N O T I N C L U
D E D
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>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
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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
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N O T I N C L U
D E D
2/3 Se'icentrifugal Casting
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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
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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
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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
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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
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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
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)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
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?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#
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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
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=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
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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
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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
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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
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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
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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
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!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
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Metals for Casting
Casting alloys can /e classifie% as0 =errous
Nonferrous
=errous Casting Alloys0 Cast 4ron
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=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
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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
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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
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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
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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 .
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Term Project
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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"