Design consideration for investment casting.pptx

7/25/2019 Design consideration for investment casting.pptx

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DESIGN

CONSIDERATION FORINVESTMENT CASTING


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Introduction

Investment casting uses a piece of

ceramic moud!

T"e moud is prepared #$ surrounding

t"e ceramic materia over t"e %a& or

pastic pattern! Once t"e ceramic materia soidi'es( t"e

%a& repica is meted and drained out

from t"e moud and t"e meta is oured


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Steps in investment casting

Figure )* Steps in investment casting


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T$pes of investment castingprocess Soid moud

In t"e soid moud process t"e pattern is paced into a container and

moud materia poured around t"e pattern and ao%ed to soidif$ to ma+e

t"e soid #oc+!

Ceramic s"e moud

T"e pattern is dipped into ceramic surr$! ,attern is ta+en out from t"e

surr$ and rotated to produce a uniform coating! Furt"er( t"e coating is

ao%ed to dr$ and t"e dipping process repeated over severa times! As a

resut( mutipe coat forms a "ard ceramic s"e moud! T"e moud is again

paced in an oven to drain out t"e %a& so as to create t"e moud cavit$!


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,attern materias

,atterns used for investment casting are

in-ection mouded of eit"er %a& or

pastic!

,ara.n and microcr$staine %a&es are

t"e most common #ase materia forpatterns!


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T$pica c"aracteristics and appications

C"aracteristics features of investment

casting are*

Intricate s"ape

Cose toerances

Sma si/e

0ig" strengt" ao$s


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Appications of investment casting are*

Contoured surfaces( undercuts( ot"er

intricate s"apes( paces %"ere mac"ining is

di.cut or unfeasi#e!

T$pica e&ampes of suc" mec"anica

components are* se%ing mac"ines( 'rearms(

surgica and denta devices( tur#ine #ades(

gear impeer( "and toos( cran+s and evers!


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Genera designconsiderations Since patterns are in-ection mouded( a

good practice must #e foo%ed for

in-ection mouded parts!

Investment casting incude t"e use of a

%e ocated pattern( straig"t parting

ine( ade1uate draft and avoidance of

undercuts( generous radii and 'ets!


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Suita#e materia for investment casting

A %ide variet$ of materias suc" as #ot" ferrous

and non2ferrous can #e used in investment

casting!

An$ meta t"at can #e meted in standard

induction furnace or vacuum furnace can #e

considered for t"is case! Di.cut to mac"ine materias are aso good

candidate for investment casting!


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Ta#e)* Suita#e materia forinvestment casting!

Material Fluidity Shrinkage Resistanceto hottearing

Castabilityrating

Car#on stees

)343 5G)34336 7 7 7 78

)393 5G)39336 7 7 7 78

Ao$ stees

:;495G:;4936 7 7 7 A2

4);35G4);336 7 7 7 A2

Nic+e ao$sMone 5>965N3>>336

A 7 7 78

A 2E&ceent? 7 2 good? C2 poor


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Ta#e)* Suita#e materia for investmentcasting!

Material Fluidity Shrinkage Resistanceto hottearing

Castabilityrating

Co#at ao$s

Co#at :)5R;33:)6

A A 7 A2

Co#at ;)5R;33;)6

A A 7 A2

Auminum Ao$s

A ;9> 5A);9>36 A A A A8

C ;99 5A;;9936 A A A AToo stees

A2: 5T;3)3:6 7 7 7 78

02); 5T:3=);6 7 7 7 78

Copper ao$s

GunmetaC@3933

A C A 78


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Detai designrecommendations

T"e foo%ing important design guideines are

recommended for investment casting!

Minimum wall thickness: T"e minimum t"ic+ness of casting %a is

primari$ dependent upon t"e uidit$ of t"e meta

to cast and t"e engt" of t"e section invoved! If

t"e section is ong( "eavier %a ma$ #e re1uired!


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Ta#e :* Suggested Minimum Ba T"ic+ness for

Various Investment2CastingMetas!

Metal Minimum wall thickness(mm)

Ferrous metas

o%2car#on stee )!=

0ig"2car#on stee )!9

o%2ao$ stee )!9

Stainess stee( ;33 Series )!3

Stainess stee( 433 Series )!9

Co#at2#ase ao$s 3!9

Nonferrous metasAuminum )!3

7er$ium copper 3!9

7rass )!3

7ron/e )!9


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Detai designrecommendations Flatness and straightness:

Deviations from atness and straig"tness can #e minimi/ed #$

incorporating ri#s and gussets in t"e parts! Aso( due to

occurrence of s"rin+age t"ere is a tendenc$ to deveop a dis"

5concave6 s"ape instead of at surface! T"is can #e minimi/ed #$

designing parts %it" uniform %a t"ic+ness!

Figure :* eep %as uniform$ t"in to avoid dis"ing!


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Radii:

Even t"oug" use of s"arp corners is possi#e #$ t"is met"od(

generous radii are preferred! 7etter 1uait$ and more accurate

parts can #e produced #$ providing ampe 'ets and radii! A

minimum of 3!9mm 'et radius need to #e furnis"ed! 0o%ever( a

radius of )!9 to ; mm is prefera#e!

Figure ;*Hse generous 'ets and radii!


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Curved surfaces:

7ot" concave and conve& surfaces are possi#e to

cast in t"is categor$! Genera$ concave surfaces

can #e cast %it" greater accurac$!

Parallel sections:

,arae sections can #e cassi'ed into t%ogeometric categories name$* for+s or $o+es and

camp or pinc" coars!


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In case of for+( as t"e t"ic+ness t

increases( t"e %idt" of t"e opening w

also must increase.

Figure 4* For+s and $o+es "ave minimum practica sot %idt"s!


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T"e recommended minimum sot %idt" w

for clamps with ferrous and nonferrous

metas are )!9( and ) mm respective$!

Figure 9* Recommended minimum sot %idt"s W for clamps and pinch collars

are )!9 mm for ferrous metas and )!3 mm for non2ferrous metas!


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Keys and key ways:

T"e ratio of %idt" 5B6 to dept" 5D6 for ease

of casting of +e$s and +e$%a$s are +ept ) or

more! Recommended minimum +e$ %idt"

%"ic" can #e cast is :!;mm and )!9mm for

ferrous and non2ferrous metas respective$!

Figure >* e$s and +e$%a$s s"oud "ave a %idt" to2dept" ratio of )*) or


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oles:

Whenever holes are to !e incorporated a

minimum si"e #diameter$ must !e greater t"an or

e1ua to )!9mm and :!: mm for nonferrous and

ferrous ao$s respective$ are to #e used!

%lindholes:

&n general' !lind holes are not recommended for

casting. &f it is inevita!le' t"e dept" of t"e "oe

s"oud not e&ceed t"e diameter!


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(hrough holes:

(olerances for !lind holes and through holes are same.

)*+ ratio s"oud not e&ceed 4*) and 9*) for ferrous

and copper auminum respective$!

Ceramic cores:

&n the design of pattern mould' if any intricate internal

con,guration 5e&ampe interna t"read6 "as to #e

made %it" a ceramic core t"en provision must #e

provided in t"e moud to support t"e ceramic core t"e


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+raft:

(o remove wa- pattern from the mould a small amount

of draft is provided to t"e pattern! T"e recommended

vaues ie in t"e range #et%een )J4K to )J=K !

Figure * A sma amount of draft is necessar$ for t"e remova of patternsfrom t"e mouding die!


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crew threads:

%oth internal and e-ternal threads can !e

investment casted. %ut it is not a usua

recommended practice!

/ndercuts:

0ven though undercuts doesn1t create any pro!lem

to the casting operation #ut "as signi'cant eLect in

pattern mouding operation and "ence t"is "as to #e

avoided!


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+imensional factors:

(he most signi,cant factor in2uencing the dimensional

accuracy of investment casting is t"e s"rin+age of t"e

materias used! Some degrees of s"rin+age are t"ere

in a eves* %a& pattern( investment materia and cast

materia! T"e norma s"rin+age ao%ance provided for

s"e moud and as+ moud met"od are )!> to )!

and )!) respective$!


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Ot"er factors adverse$ aLectingdimensiona contro are*

Temperature variations in pouring

Fuidit$ of t"e meta used

,attern and pattern2moud dimensiona

variations

,attern distortion during "anding

Investment2moud crac+s and ot"er variations

Ba& s"rin+age and sag over a period of time


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Recommended toerances for various anges( generadimensions( roundness and atness are provided*

Figure =* Recommended toerances for anges* 5a$ angular openings as 3#45.67$8 #!$ anguar s"apes as % #49.67$8 #c$ parallelism #4.97$


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Ta#e ;* Recommended toerances foranges

Dimension(mm) Recommended tolerances(mm)

Norma Tig"t

Hp to > 3!4 3!3=

>); 3!4 3!)3

);:9 3!4 3!);

:993 3!4 3!)=

93)33 3!= 3!43

)33)93 )!) 3!>3

Over )93 )!9 3!=3

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Design consideration for investment casting.pptx