ch17

Solutions for Fundamentals of Modern Manufacturing , 5e (published by Wiley)  MPGroover 2012

FUNDA MENTALS ALS OF METAL METAL FORMING 17 FUNDAMENT Review Questions 17.1

Wht re the the differen!e differen!ess bet"een bet"een bul# bul# defor$tion defor$tion pro!esses pro!esses nd nd sheet sheet $etl $etl pro!esses pro!esses%% Answer. &n bul# defor$tion, the shpe !hn'es re si'nifi!nt, nd the "or# prts hve  lo" retovolu$e rtio. &n sheet $etl pro!esses, the retovolu$e rtio is hi'h.

17.2 17.2

*trus *trusion ion is is  fund$ fund$ent entl l shpi shpin' n' pro!e pro!ess. ss. +es! +es!rib ribee it. Answer. *trusion is  !o$pression pro!ess in "hi!h the "or# $teril is for!ed to flo" throu'h  die orifi!e, thereby for!in' its !ross se!tion to ssu$e the profile of the orifi!e.

17. 17.

Why is is the ter$ ter$ press" press"or# or#in' in' often often used used for for sheet sheet $etl $etl pro!esse pro!esses% s% Answer. -he ter$ press"or#in' is used be!use $ost sheet $etl opertions re perfor$ed on  presses.  presses.

17. 17.

Wht Wht is the the diffe differen! ren!ee bet"ee bet"een n deep deep dr"in dr"in' ' nd br br dr"i dr"in'% n'% Answer. +eep dr"in' is  sheet $etl for$in' pro!ess used to fbri!te !upshped prts/ br dr"in' is  bul# defor$tion pro!ess used to redu!e the di$eter of  !ylindri!l "or# prt.

17.5 17.5

&ndi! &ndi!te te the the $the$ $the$ti ti!l !l eu eutio tion n for for the flo" flo" !urve !urve..   K   Answer. -he flo" !urve is defined in ution (17.1) s Y  f   K  n  .

17.

3o" does does in!resi in!resin' n' te$pertu te$perture re ffe!t ffe!t the the pr$eters pr$eters in the the flo" flo" !urve !urve eution% eution% both  K  nd  nd n in the flo" !urve eution. Answer. &n!resin' te$perture de!reses both K 

17.7

&ndi!te &ndi!te so$e so$e of the dvnt dvnt'es 'es of of !old "or#in' "or#in' reltive reltive to "r$ "r$ nd hot "or#in' "or#in'.. Answer. 4dvnt'es of !old "or#in' re (1) better !!ur!y, (2) better surf!e finish, () in!resed stren'th due to "or# hrdenin', () possible dire!tionl properties due to 'rin flo", nd (5) no hetin' of "or# reuired.

17. 17.

Wht Wht is is iso isoth ther er$ $ll for$ for$in in'% '% Answer. 4n isother$l for$in' opertion is perfor$ed in su!h  "y s to eli$inte surf!e !oolin' nd ther$l 'rdients in the "or# prt. -his is !!o$plished by prehetin' the for$in' tools.

17.6 17.6

+es!rib +es!ribee the the effe! effe!tt of strin strin rte rte in $etl $etl for$ for$in' in'.. Answer. &n!resin' strin rte tends to in!rese the resistn!e to defor$tion. -he tenden!y is espe!illy pro$inent in hot for$in' opertions.

17.10 Why is fri!tio fri!tion n 'enerlly 'enerlly undesirb undesirble le in $etl $etl for$in' for$in' opertions% opertions% Answer. esons "hy fri!tion is undesirble in $etl for$in' in!lude the follo"in'8 (1) it inhibits $etl flo" durin' defor$tion, !usin' residul stresses nd produ!t defe!ts/ (2) it in!reses for!es nd po"er reuired/ nd () it in!reses "erin' of the tools.

17.11 17.11 Wht is sti!#in sti!#in' ' fri!tio fri!tion n in $etl"or#in' $etl"or#in'%% Answer. Sti!#in' fri!tion is "hen the "or# surf!e dheres to the surf!e of the tool rther thn slides 'inst it/ it o!!urs "hen the fri!tion stress is 'reter thn the sher flo" stress of the $etl.

Probles 4ns"ers to proble$s lbeled !A" re listed in n 4ppendi* 4ppendi* t the b!# of the boo#.

*!erpts fro$ this "or# $y be reprodu!ed by instru!tors for distribution on  notforprofit bsis for testin' or instru!tionl purposes only t o students enrolled in !ourses for "hi!h the te*tboo# hs been dopted.  Any other reproduction reproduction or translation of this work work beyond that  permitted by Sections 107 or 108 108 of the 1976 nited States States !opyri"ht Act without the permission permission of the copyri"ht owner is unlawful# unlawful#

171

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Solutions for Fundamentals of Modern Manufacturing , 5e (published by Wiley)  MPGroover 2012

Flow #urve in Forin$

17.1

!A" (S& units) &n the flo" !urve for pure lu$inu$, the stren'th !oeffi!ient  175 MP nd strin hrdenin' e*ponent  0.20. &n  for$in' opertion, the finl true strin  0.75. +eter$ine the flo" stress nd ver'e flo" stress tht the $etl e*perien!ed t this strin. Solution8 9lo" stress Y  f     175(0.75) 0.20  1%& MP' 4ver'e flo" f lo" stress Y   f    175(0.75) 0.20:1.20  1() MP'

17.2

(S& units) units) 4usteniti! 4usteniti! stinles stinlesss steel hs hs  flo" !urve "ith "ith stren'th stren'th !oeffi!i !oeffi!ient ent  1200 1200 MP nd strin strin hrdenin' e*ponent  0.0. 4 tensile test spe!i$en "ith ''e len'th  100 $$ is stret!hed to  len'th  15 $$. +eter$ine the flo" stress nd ver'e flo" stress tht the $etl e*perien!ed t this strin. Solution8      ln (15:100)  ln 1.5  0.72 9lo" stress Y  f     1200(0.72) 0.0  )*) MP' 4ver'e flo" f lo" stress Y   f    1200(0.72) 0.0:1.0  &77 MP'

17.

!A" (;S
  ln (.:2.0)  ln 1.5  0.501 Solution8    9lo" stress Y  f     75,000(0.501) 0.25  %(+*,, lb-in. 4ver'e flo" f lo" stress Y   f    75,000(0.501) 0.25:1.25  &*+/7, lb-in. 17.

(;S
17.5 17.5

+erive +erive the the eutio eution n for ver' ver'ee flo" stres stress, s, uti ution on (17.2) (17.2) in the the te*t. te*t.   K   Solution8 9lo" stress eution =ution (17.1)>8 Y  f   K   n Y   f   over the rn'e     n d      K    n d     K  n$1   : (n?1)  K  n-!n -!n01"   0 to        is  is 'iven by      K     K        K  

17.

(S& units) units) 9or pure !opper !opper (nnel (nneled), ed), the the stren'th stren'th !oeffi!i !oeffi!ient ent  00 00 MP nd strinh strinhrdeni rdenin' n' e*ponent  0.50 in the flo" !urve eution. +eter$ine the ver'e flo" stress tht the $etl e*perien!es if it is sub@e!ted to  stress tht is eul to its stren'th !oeffi!ient  K . Solution8 Y  f   K   n  00 #50   K     00  K   K    $ust be eul to 1.0   $ust Y   f    00(1.0) .50:1.50  00:1.50   .** MP'

17.7

+eter$ine +eter$ine the vlue of of the strin strinhrden hrdenin' in' e*ponent e*ponent for  $etl $etl tht tht "ill "ill !use the ver'e ver'e flo" flo" stress to be 0A of the finl flo" stress fter defor$tion.

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Solutions for Fundamentals of Modern Manufacturing , 5e (published by Wiley)  MPGroover 2012

0.20  0.0n 0.0n 17. 17.

n  *2.&

(;S
17.6

!A" (S& units) &n  tensile test, t"o pirs of vlues of stress nd strin "ere $esured for the spe!i$en $etl fter it hd yielded8 (1) true stress  217 MP, nd true strin  0.5/ nd (2) true stress  256 MP, nd true strin  0.. Bsed on these dt points, deter$ine the stren'th !oeffi!ient nd strinhrdenin' e*ponent. Solution8 Solve t"o eutions, t"o un#no"ns8 ln  K     ln      n ln & (1) ln K     ln 217 C n ln 0.5 (2) ln K     ln 256 C n ln 0. '1( ln K  ln K     5.766 C (1.06)n (1.06) n  5.766 ? 1.06 n ')( ln K  ln K     5.55 C (0.57)n (0.57) n * 5.55 ? 0.57 n 5.766 ? 1.06 n  5.55 ? 0.57 n 1.06 n C 0.57 n  5.55 C 5.766 0.1 n  0.176 n  *2.%%/  K     .)7 MP' ln K  ln K     5.766 ? 1.06 (0.2)  5.56

17.10 (;S
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Solutions for Fundamentals of Modern Manufacturing , 5e (published by Wiley)  MPGroover 2012

Solution8 () strin rte



 

  200:100   .2* s31

(b) strin rte

 



 200:75  .2%%7 s31

(!) strin rte

 



 200:51  (2,.. s31

17.12 (;S


 

  1.5:5.25   *2.)% se431



 1.5:5.0  *2( se431



 1.5:.0  *2.& se431

(b) strin rte

 

(!) strin rte

 

17.1 (;S
(b) Y  f     0,000(1.0) 0.15  (*+*** lb-in. (!) Y  f     0,000(100) 0.15  &,+)&) lb-in. 17.1 (S& units) units) 4 tensile tensile test is perfor$ed perfor$ed to deter$ine deter$ine the stren'th stren'th !onstnt !onstnt !  nd  nd strinrte sensitivity e*ponent m in ution (17.) for  !ertin $etl. -he te$perture t "hi!h the test is perfor$ed  500<. 4t  strin rte  12:s, the stress is $esured t 10 MP/ nd t  strin rte  250:s, the stress  00 MP. () +eter$ine !  nd  nd m in the strin rte sensitivity eution. (b) &f the te$perture "ere 00<, "ht !hn'es "ould you e*pe!t in the vlues of !  nd  nd m% Solution8 () -"o eutions8 (1) 10  ! (12) (12)m nd (2) 00  ! (250) (250)m (1) ln 10  ln ! ? m ln 12 or ln 10  m ln 12  ln !  (2) ln 00  ln !  ?  ? m ln 250 or ln 00  m ln 250  ln !  (1) nd (2)8 ln 10  m ln 12  ln 00  m ln 250 5.0752 C 2.6 m  5.70 C 5.5215 m (5.5215 C 2.6)m 2.6) m  5.70 C 5.0752 .0 $  0.2 m  *2.*7 0.207 (1) <  10:(12)   10.1.72  65.5 (2) <  00:(250) 0.207  00:.11  65.0 4ver'in' these vlues, C     ,&2%&, MP'3s

(b) &f te$perture "ere 00 <, the stren'th !onstnt !  "ould  "ould de!rese nd the strinrte sensitivity e*ponent m "ould in!rese. 17.15 !A" (;S
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Solutions for Fundamentals of Modern Manufacturing , 5e (published by Wiley)  MPGroover 2012

(b) &f te$perture "ere de!resed to 600 9, the stren'th !onstnt !  "ould  "ould in!rese nd the strin rte sensitivity e*ponent m "ould de!rese.