DESIGN CONSIDERATIONS OF CASTINGS

DESIGN CONSIDERATIONS OF CASTINGS: Complex parts, which are otherwise difficlt to machi!e, are made "# casti!$ processes si!$ sa!d mold% The cast compo!e!ts are sta"le, ri$id a!d stro!$ compared with respect to some other part or strctre with machi!ed or for$ed parts% E$:& machi!e tool "ed a!d strctre, c#li!der "loc' of i!ter!al com"stio! e!$i!e, pmp a!d $ear "ox hosi!$% The $e!eral pri!ciples for the desi$! of casti!$ are as follows: (% Alwa# Alwa#ss 'eep the stresse stressed d areas areas of the part part i! i! compressi compressio!% o!% Cast iro! has more compressi)e stre!$th tha! its te!sile stre!$th% *% Ro Ro!d !d all ext exter! er!al al cor cor!er !ers% s% It has two ad)a!ta$es:& •

It i!creases the e!dra!ce limit of the compo!e!t%

•

It redces the formatio! of "rittle chilled ed$es%

+% her here) e)er er po possi ssi"l "le, e, th thee se sect ctio io! ! th thic ic'! '!es esss th thro ro$ $ho hot t sh sho old ld "e he held ld as ! !if ifor orm m as compati"le with o)erall desi$! co!sideratio!s%  A"rpt cha!$es i! the cross - sectio! reslt i! hi$h stress co!ce!tratio!% If the thic'!ess is to "e )aried at all, the cha!$e shold "e $radal% .% A)oid thic' thic'!ess !ess of of the the metals metals at the /!ct /!ctio!s% io!s% E)e! after the metal solidifies, the ce!tral portio! still remai!s i! the molte! sta$e, with thee re th res slt lt th that at a sh shri ri!' !'a$ a$ee ca ca)i )it# t# or "l "low owho hole le ma ma# # ap appe pear ar at th thee ce ce!t !tre re Th Thee co!ce!tratio! of metal ca! "e a)oided i! two wa#s:& •

O!e is to pro)ide cored ope!i!$ i! we"s a!d ri"s%

•

Sta$$er the ri"s a!d we"s%

0% A) A)oi oid d )er# )er# thi! thi! sec secti tio! o!s% s% The mi!imm sectio! thic'!ess depe!ds po! the process of casti!$, sch as sa!d casti!$, perma!e!t mold casti!$ or die casti!$% The mi!imm thic'!ess for $re# cast iro! compo!e!t is a"ot 1 mm for parts pto 022 mm lo!$, which $radall# i!creases to *2 mm for lar$e a!d hea)# casti!$s% 3% Sho Shott "last "last the part partss where)e where)err possi"l possi"le% e% The shot "lasti!$ impro)es the e!dra!ce limit of the compo!e!t, particlarl# i! case of  thi! sectio!s%

DESIGN CONSIDERATIONS OF FORGINGS: For$ed compo!e!ts are widel# sed i! atomoti)e a!d aircraft i!dstries% The# are sall#  made of steels a!d !o! - ferros metals% The# ca! "e as small as the $d$eo! pi! a!d as lar$e as cra!'shaft% For$ed compo!e!ts are sed !der followi!$ circmsta!ces:& •

•

•

•

•

4o)i!$ compo!e!ts re5iri!$ li$ht wei$ht to redce i!ertia forces% E$:& co!!ecti!$ rod of I%C% e!$i!e% Compo!e!ts s"/ected to excessi)e stresses% E$:& aircraft strctre% Small compo!e!ts that mst "e spported "# other strctre or part% E$:& ha!d tools a!d ha!dle% Compo!e!ts re5iri!$ pressre ti$ht!ess where the part mst "e free from i!ter!al crac's% E$:& )al)e "odies% Compo!e!ts whose failre wold case i!/r# a!d exte!si)e dama$e are for$ed for safet#%

I! order to o"tai! maximm "e!efit from for$ed compo!e!ts, followi!$ pri!ciple shold "e adopted:& (% hile desi$!i!$ a for$i!$, ad)a!ta$e shold "e ta'e! of the directio! of fi"re li!es% I! case of for$ed parts, the fi"re li!es are arra!$ed i! a fa)ora"le wa# to withsta!d stresses de to exter!al load% *% The for$ed compo!e!t shold "e pro)ided with a! ade5ate draft% +% A parti!$ li!e di)ides the for$i!$ i!to two hal)es which e!sres the mi!imm depth to  which the steel mst flow to fill the die impressio!s% .% The for$i!$ shold "e pro)ided with ade5ate fillet a!d cor!er radii% Small radis reslts i! folds o! the i!!er srface a!d crac's o! the oter srface% 6ar$e radis is !desira"le% Sharp cor!ers reslt i! i!creasi!$ difficlties ! filli!$ the material, excessi)e for$i!$ forces a!d poor die life% 0% Thi! sectio!s a!d ri"s shold "e a)oided i! for$ed compo!e!ts% A thi! sectio! cools at a faster rate i! the die ca)it# a!d re5ires excessi)e force for plastic deformatio!% It redces the die life a!d the remo)al of the compo!e!t from the die ca)ities "ecomes difficlt%  A properl# desi$!ed for$i!$ is !ot o!l# so!d with re$ard to stre!$th "t it also helps redce the for$i!$ forces, impro)es die life a!d simplifies die - desi$!%

DESIGN CONSIDERATIONS OF 4AC7INED 8ARTS: 4achi!ed compo!e!ts are widel# sed i! i!dstrial prodcts% The# are sall# made from ferros a!d !o! - ferros metals% The $e!eral pri!ciples for the desi$! of machi!e parts are as follows:& (% A)oid machi!i!$% 4achi!i!$ operatio!s i!crease the cost of the prodct% *% Specif# li"eral tolera!ces% Depe!di!$ o! the f!ctio!al re5ireme!t of the compo!e!t, the desi$!er shold specif#  most li"eral dime!sio!al a!d $eometric dime!sio!s% +% A)oid sharp cor!ers% The sharp cor!ers reslt i! stress co!ce!tratio!% .% 9se stoc' dime!sio!s% 9si!$ stoc' dime!sio!s elimi!ates machi!i!$ operatio!s% 0% Desi$! ri$id parts%  A!# machi!i!$ operatio!s sch as tr!i!$ or shapi!$ i!dce ctti!$ forces o! the compo!e!ts% The compo!e!t shold "e ri$id e!o$h to withsta!d sch forces% 3% A)oid sholders a!d !dercts% The# sall# i!)ol)e separate operatio!s a!d separate tools, which i!crease the cost of  machi!i!$% 1% A)oid hard materials% The# shold "e a)oided !less sch properties are esse!tial for the f!ctio!al re5ireme!t of the prodct%

DESIGN CONSIDERATIONS OF E6DED ASSE46IES:  eldi!$ is the most importa!t method of /oi!i!$ the parts i!to a complex assem"l#% The $e!eral pri!ciples i! desi$! of welded parts are as follows:& •

Select the material with hi$h welda"ilit#%  A low car"o! co!te!t steel is more easil# welded tha! a hi$h car"o! steel%

•

9se mi!imm !m"er of welds%

•

Do !ot shape the parts "ased o! casti!$ or for$i!

%$ •

•

9se sta!dard compo!e!ts%  A)oid straps, laps a!d stiffe!ers%

•

Select proper locatio! for weld%

•

8rescri"e correct se5e!ce of weldi!

%$TO6ERANCES: Tolera!ce is defi!ed as permissi"le )ariatio! i! the dime!sio!s of the compo!e!t% The "asic dime!sio! is called the !ormal or "asic si;e, while the differe!ce "etwee! the two limits is called permissi"le tolera!ce% The two limits are sometimes called the pper a!d lower de)iatio!s% There are two s#stems of specificatio!s for tolera!ces, !amel# !ilateral a!d "ilateral% •

•

I! !ilateral s#stem, o!e tolera!ce is ;ero while the other ta'es care of all permissi"le  )ariatio! i! "asic si;e% The# are sed for shafts a!d holes% I! case of "ilateral tolera!ces, the )ariatio! are $i)e! i! "oth directio!s from !ormal si;e%

Th? The differe!t cleara!ces or i!terfere!ces are o"tai!ed "# associati!$ )arios holes  with a si!$le shaft, whose pper de)iatio! is ;ero% The si;e of the shaft is the "asic si;e, while the cleara!ce or i!terfere!ce is applied to the dime!sio!s of the hole%

%I%S S