7/30/2019 ertyer
1/3
.5 The Drawing ProcessIn
drawing,
t h e c r o s s - s e c t i o n o f a l o n g r o d o r w i r e
t y p i c a l l y
i s r e du c ed o r c h an g ed b y p u ll i ng (h e nc e t h e
t e rm d raw i ng )
i t th rough a d ieca l led a
draw d ie
(Fig. 8 .5) . Thus, the difference between drawing
andextrusion
is that in extrusion the material is pushed through a die,
whereasin
d r a w i n g i t i s p u l l e d t h r o u g h i t . R o d a n
d w i r e p r o d u c t s
c o v e r a
v e r y w i d e r a n g e o f a p p l i c a t i o n s , i n c l
u d i n g r o d s f o r
s h a f t s f o r p o w e r a n d motion transmissions, machine
and
structural components, and as
blanksf o r b o l t s a n d r i v e t s , e l e c t r i c a l w
i r i n g , c a b l e s , t e ns i o n - l o a d e d s t r u c t u
r a l m e m b e r s , w e l d i n g e l e c t r o d e s ,
s p r i ng s , p a p er c l i ps , s p o ke s f o r b i c yc l e
wheels, and
st r inged musica l ins t ruments .The major process ing var iab
les
i n d r a w i n g a r e s i m i l a r t o t h o s e i n e x t r
u s i o n -
t h a t i s , r e d u c t i o n i n c r o s s - s e c t i o n a
l a r e a , d i e a n g l e ,
f r i c t i o n a l o n g t h e d i e - w o r k p i e c e
i n t e r f a c e s , a n d d r a w i n g s p e e d . T h e d i
e a n g l e i nf lu en ce s
t h e d ra w in g fo rc e a n d t h e q u al i ty o f t h e d ra
w n p ro d uc t A s
can be seen f r om these equat ions , the dr awing for ceinc
reases a s reduc t ion inc reases . However , t he re has to be
a
l imi t to the magni tude of the force , because when the tens i
le
s t r es s re a ch e s t h e y i el d s t re s s o f th e me t a
l b e i n g d r a w n , t h e
w o r k - p i e c e w i l l s i m p l y y i e l d a n d , e v e
n t u a l l y , b reak. I t
can be shown tha t , idea l ly and without f r ic t ion ,
the
maximum r e du c t i o n i n c r o s s - s e c t i o na l a r e
a p e r p a s s i s
6 3 % . T h us , f o r e x a mp l e , a 1 0 - m m d i a me t e r
r o d c a n b e
r e d uc e d ( a t m o s t ) t o a d i a me t e r o f 6 . 1 m m
in one pass
wi thout fa i lu re . I t c a n b e s h o w n t h a t , f o r a
c e r t a i n
r e d u c t i o n i n d i a m e t e r a n d a c er ta in f r ic
t ion-a lcondi t ion , there i s an
opt imum die angle
a t which thedrawing force i s a min imum. This does no t
mean
t ha t t he p ro ces s s h oul d b e c a r r i e d o u t a t t h
i s o p t i m u m
a n g l e , b e c a u s e t h e r e a r e o t h e r p r o d u c
t qual i ty
considera t ions
