LMS Week 2 Metal Casting

8/17/2019 LMS Week 2 Metal Casting

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MANUFACTURING PROCESS

EAT 227

WEEK 2

METAL CASTING


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Fundamental of metal casting


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Typi#a Cast $a%ts

Figure (a) Typical gray-iron castings used in automobiles, including thetransmission valve body (left) and the hub rotor with disk-brake cylinder(front). Source: ourtesy of entral Foundry !ivision of "eneral #otorsorporation. (b) $ cast transmission housing. (c) The %olaroid %!-

&''' digital camera with a $*! die-cast high-purity magnesiumcase. (d) $ two-piece %olaroid camera case made by the hot-chamber

(a)

(b

)

(c)

(d

)


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Casting of an Aluminum Piston

Figure '.+ $luminum piston for an internal combustionengine: (a) as-cast and (b) after machining.


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Intoduction


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Solidification of Pue Metals

Figure '. (a) Temperature as a function of time for the solidication of puremetals. ote that the freeing takes place at a constant temperature. (b)!ensity as a function of time


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Solidification !olume s"in#age

Fig. &.* hanges in volume as a metal alloysolidies.


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s"in#age


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C"ill$ columna and e%uai&ial gains

Fig. &./ 0ketch of solidied grain structure of an alloy: (a) chill crystals1(b) columnar grains1 and (c) region of coarse e2uia3ed grains in centre.


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Sand casting

SAN' CASTING (ENEFITS

1*Least E+pesi-e Casti! $%o#ess

2*Casti!s #a .e /p to Se-e%a Tos

"*Less E+pesi-e ta Ma#ii! Sapes %o 3a%

Sto#4&*Ca Cast It%i#ate Sapes

'*Ca .e Used 5it Most $o/%a.e Metas ad Aoys


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T"e sand casting )ocesses


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TE SAN7

Te sad /sed o% !%ee sad odi! is #%iti#a ad dete%ies te a-o%a.e o%

/a-o%a.e o/t#oe o te #asti!* It #ot%os te toe%a#es, s/%a#e iis adte %epeata.iity 5ie i p%od/#tio* ee.e%i! tat te toe%a#es o sad

#asti!s a%e /s/ay 5ide% ta te ote% #asti! etods*

Te sad /st e+i.it te oo5i! #a%a#te%isti#s:

*+F,O-A(I,IT./ Te a.iity to pa#4 ti!ty a%o/d te patte%+2+P,ASTIC 'EFORMATION/ a-e te a.iity to deo% si!ty 5ito/t #%a#4i! so

tat te patte% #a .e 5itd%a5*

0+GREEN STRENGT1/ a-e te a.iity to s/ppo%t its o5 5ei!t 5e st%ipped

%o te patte%, ad aso 5itstad p%ess/%e o ote eta 5e te od is

#ast*

+PERMEA(I,IT./ Tis ao5s te !ases ad stea to es#ape %o te odd/%i! #asti!*

A o tese %e9/i%eets a%e depedet o te ao/t o a#ti-e #ay p%eset ad

o te 5ate% #otet o te i+t/%e*


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!4F55T560. %6785" 7%: This is where the metal is poured into the mold.&. 0%874: The vertical channel from the top of the mold to the gating and risersystem. $lso, a generic term used to cover all gates, runners and risers.9. 8748: The portion of the gate assembly that connects the sprue to the castingin gate or riser.

. "$T4: The end of the runner in a mold where molten metal enters the mold cavity.;. 85048: $ reservoir of molten metal provided to compensate for the contraction ofthe metal as it solidies.+. #6: The impression in a mold produced by the removal of the pattern.?hen lled with molten metal it forms a casting./. 6%4: 7pper or top most section of a @ask, mold or pattern.A. %$8T5"


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$%od/#tio Steps i SadCasti!

Figure 6utline of production steps in a typical sand-casting operation.


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META, CASTINGPemanent Mould Casting


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Gravity die casting in a permanent mold.


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S"ell molding

The molding aggregate in shell-molding is a mi3ture of a ne base sand and athermosetting binder. $ metal match plate is used as a pattern and forms the coverof a dump bo3 that is lled with the molding aggregate. The match plate is heated toabout ;'-&9' B and the dump bo3 is inverted to allow the resin-bonded sand tophysically contact the hot pattern. The thermosetting plastic begins to cure andharden, forming a solid sand shell around the pattern. The dump bo3 is then broughtback to its normal uptight position, and e3cess (uncured) sand mi3ture is removed.

The partially cured shell is stripped from the match plate with the help of eCectorpins, and the curing is completed in an oven. The steps are repeated to make thematching half of the shell mold. $fter curing, the two mold halves are assembled,clamped, and readied for the pour (metal shot or sand is used as a physical supportfor the mold halves). 0ome of the resin evaporates during the pour and representsan unreclaimable material loss. =ery tight dimensional control (tolerances of '.''&-

'.''; inch) and e3cellent surface nish are achieved using shell-molds. This reducesthe need for machining, but very precise patterns are needed to start with. The

F5"784 &-& Shell-molding process that uses a fne basesand mixed with athermosetting binder. Themixture

partially cures and orms ahard shell upon contact with ahot match plate (which ormsthe cover o the dumpbox containing the sand mixture).(E. . !e"armo# $. T. %lac '.

. ohser# and %. E. lanec&i#*aterials and%rocesses in #anufacturing,

*th ed., ?iley, ew >ork,&''9, p. 9'A).


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I-estet Casti! $%o#ess

Figure 0chematic illustration of investment casting (lost-wa3)process. astings by this method can be made with very nedetail and from a variety of metals.

+ ld


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;IGUE 216 Low-pressure permanent mold casting in which an inert gas is used to pressurize the molten metal counter togravity through a feed tube and into the permanent mold that is placed on top of the pressure vessel. The solidification path is designed to enable the shrinkage to be fed by the pressurized molten metal. (Courtesy of Amsted Industries).

+ow-pressure permanent mold

casting


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F5"784 &-/ ,acuum permanent mold casting in which a vacuum is appfedthrough vents in the mold to raise the molten metal via a eed tube into themold. (E. . !e"armo# $. T. %lac 8. $. Dohser, and E. 4. Dlanecki, #aterialsand %rocesses in #anufacturing, *th ed., ?iley, &''9, p. 9&A).

,acuum permanent moldcasting


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'ie Casting

$%o#ess:< ote eta is i=e#ted ito a #osed eta die /de% i!

p%ess/%e*< p%ess/%e is aitaied d/%i! soidii#atio*< 7ie is sepa%ated ad #asti! e=e#ted

T5o types o die #asti!< ot #a.e% < Cod #a.e%


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otCa.e% 7ieCasti!

Figure 0chematic illustration of the hot-chamber die-castingprocess.


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< A i=e#tio syste o%#es ote eta o/t o te!oosee#4 ito te die #a-ity 5e%e te eta %apidysoidiies

< To ip%o-e die ie ad aid i te %apid #ooi!, dies a%e/s/ay #ooed .y #i%#/ati! 5ate%>oi t%o/!passa!e5ays i te die .o#4

< Appi#atio: p%ia%y /sed 5it ?i#, ti ad ead .asedaoys


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< Ad-ata!es

< No t%ase% p%o#ess o te ote eta, as it is eted i te

#a.e% %o 5i# it is i=e#ted ito te die #a-ity

< @e% ast #y#i! ties< Good st%e!t p%od/#t

< E+#eet diesioa p%e#isio ad s/%a#e iis

< 7isad-ata!es:

< E+pesi-e as te dies a%e ade %o a%deed ot5o%4ed too

stees

< e9/i%es i! p%od/#tio %ates to =/stiy te /sa!e

< Caot .e /sed o% i! eti! poit etas


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CodCa.e% 7ieCasti!

Figure 0chematic illustration of the cold-chamber die-castingprocess. These machines are large compared to the sie of the

casting, because high forces are re2uired to keep the two halves


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< Epoyed o% die #asti! o ate%ias tat a%e ot s/ita.e o% ot#a.e% desi!*

< E*!* A, M!, C/

< $%o#ess:

< Meta is eted i a sepa%ate /%a#e ad is t%aspo%ted to te die

#asti! a#ie*< Mote eta is ed ito a /eated #a.e%*

< A e#ai#a p/!e% o%#es te ote eta ito die #a-ity5e%e te eta soidiies*


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< Ad-ata!es:

< Good st%e!t p%od/#t

< E+#eet diesioa a##/%a#y< E+#eet s/%a#e iis

< 7isad-ata!es:

< E+pesi-e dies

< e9/i%es i! p%od/#tio %ate to =/stiy te /sa!e< Te eed to t%aspo%t ote etas


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Types o Ca-ities i 7ieCasti! 7ie

Figure =arious types of cavities in a die-casting die.


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Centifugal casting

< Utii?e ie%tia o%#e #a/sed .y %otatio to dist%i./te ote eta itood #a-ities

< $%o#ess:

< $o/% ote eta ito %otati! o/d

< Meta is ed a!aist te o/d 5a .y #et%i/!a o%#e /ti it is

soidiied< " types o #et%i/!a #asti!

< T%/e #et%i/!a #asti!

< Sei#et%i/!a #asti!

< #et%i/!i!


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Tue centifugal casting

< Mo/d o%ay ade o stee, i%o, o% !%apite ad ay .e #oated 5it a

%e%a#to%y ii! to i#%ease o/d ie

< Mo/d s/%a#es #a .e saped so tat pipes 5it -a%io/s o/te% sapes

i#/di! s9/a%e o% poy!oa #a .e #ast

< Ie% s/%a#e o #asti! %eais #yid%i#a .e#a/se te ote eta is/io%y dist%i./ted .y #et%i/!a o%#es

< $%od/#es oo5s #yid%i#a pa%ts:

< $ipes, !/ .a%%es, st%eetap posts, et#*


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characteristics: "ood 2uality !imensional accuracy

S i t if l ti


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Semi centifugal casting

5n this method, centrifugalforce is used to produce solid

castings rather than tubularparts. !ensity of the metal inthe nal casting is greater inthe outer sections than at thecenter of rotation. Theprocess is used on parts in

which the center of thecasting is machined away,such as wheels and pulleys.

used to cast parts with rotational symmetry

?heels


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Centifuging

< Mo/d #a-ities o ay sape a%e pa#ed at a #e%tai dista#e %o

te a+is o %otatio*< Mote eta is po/%ed %o te #et%e ad is o%#ed ito te o/d

.y #et%i/!a o%#es*


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< Ad-ata!es

< A.e to p%od/#e a 5ide %a!e o #yid%i#a pa%ts

< Good diesioa a##/%a#y

< 7isad-ata!es

< Sape is iited

< E+pesi-e spii! e9/ipet %e9/i%ed


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ontinuous casting (right, red arrows) is a method of working steel thatconveys steel from its molten state to blooms, ingots, or slabs. The white-

hot metal is poured into open-ended molds and continues on throughrollers cooled by water. $ series of guide rollers further shapes the steelinto the desired form. owever, hot rolling (left, blue arrows) is still theprimary means of milling steel. This process begins with pre-shaped steelslabs, which are reheated in a soaking pit. The steel passes through aseries of mills: the blooming mill, the roughing mill, and the nishing mill,

which make it progressively thinner. Finally, the steel is wound into coils


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Continuous casting

< Coti/o/s #asti! a##o/ts o% a.o/t )' o te 5o%d #ast stee< Tese #asti!s ta4e te o% o .oos, sa.s, ad .iets

< epa#ed i!ot #asti! 5i# is sti /sed i soe stee pats o% o% #e%tai

!%ades o stee

< Co#ept is o-e% 1'0 yea%s od ./t #oti/o/s #asti! .e#ae 5idesp%ead i

E/%ope espe#iay i te 1)(0s< $e%e#ty s/ited to te ii i #o#ept 5it ee#t%i# stee a4i! a#iities

ad a #oti/o/s #aste%*


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1* E+pai 5y a #asti! ay a-e to .e s/.=e#ted to -a%io/s eat t%eatets

2* 7es#%i.e te d%a5.a#4s to a-i! a %ise% tat is Ba too a%!e ad B. too

sa*

"* Wy a%e %ise%s ot as /se/ i die #asti! as tey a%e i sad #asti!D

&* Wy #a .id %ise%s .e sae% ta opetop %ise%sD

'* 7es#%i.e te p%o#ed/%es tat 5o/d .e i-o-ed i a4i! a a%!e o/tdoo%

.%o?e stat/e* Wi# #asti! p%o#essBes 5o/d .e s/ita.eD WyD

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LMS Week 2 Metal Casting