El culto a las imágenes

2 . THE BULGE FORMING MACHINE DESIGN 2 . 1 ) The Bulge Forming Machine S p e c i f i c a t i o n s

The s p e c i f i c a t i o n s t h a t f o l l o w are of the bul ge formi ng machine ( P l a t e 2) p r i o r to the

a l t e r a t i o n s necessary f o r the t e s t i n g c a r r i e d out in t h i s work. The desi gn and commissi oni ng of t he machine was conducted by B a r l o w ( 2 9 ) .

2 . 1 . 1 ) The H y d r a u l i c Components 2 . 1 . 1 . 1 ) H y d r a u l i c Supply Pressur e

A maximum i n t e r n a l pr essur e o f 69 N/mm*- is a v a i l a b l e f o r the f ormi ng pr oc e ss, being ob t a i ne d by using a main c i r c u i t pr essur e of 17. 5 N/mm^ which is i ncr eased to the necessary f or mi ng pr e s sur e through a 6 . 5 : 1 pr e s sur e i n t e n s i f i e r .

2 . 1 . 1 . 2 ) The H y d r a u l i c C y l i n d e r s Appl yi ng A x i a l Load In or de r to pr ovi de a x i a l d e f o r ma t i o n of the tube dur i ng f o r mi n g , two h y d r a u l i c c y l i n d e r s , each wi t h a d i a me t e r of 125 mm and a s t r o k e o f 100 mm are used. The s t r o k e i s s u i t a b l e f o r the i n s e r t i o n o f a 150 mm ---tube bl ank i n t o the d i e - b l o c k s wi t h t he pl unger s

wi thdrawn and to pr ov i d e s u f f i c i e n t a x i a l d e f o r m a t i o n of i t dur i ng f o r mi n g . I t al so al l ows the use o f l o n g e r tube bl anks which may be r e q u i r e d f o r more c ompl i c a t e d component shapes.

2 . 1 . 1 . 3 ) The H y d r a u l i c Pump and E l e c t r i c Motor

The power source f o r the h y d r a u l i c system is a v a r i a b l e d i s p l a c e me nt p i s t o n pump d r i v e n by a 7 . 5 kW e l e c t r i c mot or . Thi s pump i s capabl e of o p e r a t i n g at

pressures o f up to 21 N/mm , but i s set a t an o p e r a t i n g

p

pr essur e o f 17. 5 N/mm .

The maximum t h e o r e t i c a l f o r c e s t h a t can be a ppl i e d by t he h y d r a u l i c c y l i n d e r s are 215 kN f o r the c y l i n d e r s a p p l y i n g the compressi ve a x i a l l o a d , and 352 kN f o r the cl ampi ng c y l i n d e r s .

The maximum f l o w r a t e o f t he h y d r a u l i c pump i s 32 l i t r e s / m i n u t e accordi ng to the ma n u f a c t u r e r s

s p e c i f i c a t i o n s , but l ess than t h i s i s ob t a i ne d when p

o p e r a t i n g at 17. 5 N/mnr and using onl y a 7 . 5 kW mot or . Thus t he maximum t h e o r e t i c a l f l o w r a t e is

2 5 . 7 l i t r e s / m i n u t e .

The a c t ua l d e l i v e r y f l o w r a t e is in f a c t a l i t t l e l e ss than t h i s due to the v o l u m e t r i c e f f i c i e n c y o f t he pump being l ess than 100%, and due to l osses in the c i r c u i t between the pump and the- c y l i n d e r s . The maximum v e l o c i t y dur i ng the outward s t r o k e ( c l o s i n g the

two d i e hal ves) is t h e r e f o r e , 21 mm/s, hence a f u l l s t r o k e o f 150 mm is compl eted i n . j u s t over 7 seconds. For the r e t u r n st r o k e (openi ng the d i e ) , t he v e l o c i t y i s f a s t e r , 31 mm/s due to the s ma l l e r p i s t o n area

around the p i s t o n r od. Thi s g i v e s a r e t u r n s t r o k e t i me o f under 5 seconds. For the c y l i n d e r s a p p l y i n g the compressi ve a x i a l l o a d , t he outward v e l o c i t y i s

17 mm/s, and f o r the r e t u r n s t r o k e , 25 mm/s. Thi s g i v e s an outward s t r oke t i me o f under 6 seconds and a r e t u r n s t r o k e t i me o f 4 seconds to compl ete the 100 mm s t r o k e o f both c y l i n d e r s .

2 . 1 . 2 ) The H y d r a u l i c C i r c u i t

The h y d r a u l i c c i r c u i t performs t h r e e f u n c t i o n s i . e . to connect the power u n i t and c o n t r o l the supply to :

1) the h y d r a u l i c c y l i n d e r clamping the two di e hal ves t o g e t h e r ,

2) the two h y d r a u l i c c y l i n d e r s p r o v i d i n g the compressi ve a x i a l l o a d ,

3) the i n t e r n a l p r e s s u r i s e d r e gi on o f t he tube

blank.

These are c o n t r o l l e d i n d e p e n d e n t l y and each has d i f f e r e n t c o n t r o l r e q u i r e me n t s .

2 . 1 . 2 . 1 ) The Clamping H y d r a u l i c C y l i n d e r

The f u n c t i o n o f t he h y d r a u l i c c i r c u i t

p r o v i d i n g the cl ampi ng f o r c e is si mpl y one o f e x t e n d i n g and r e t r a c t i n g the c y l i n d e r r od. The basi c component of t h i s p a r t o f t he h y d r a u l i c c i r c u i t i s thus si mpl y a d i r e c t i o n a l c o n t r o l v a l v e wi t h t h r e e p o s i t i o n s - one p o s i t i o n to extend the ram ( t o cl ose the two d i e hal ves and when t o g e t h e r to p r o v i d e the cl ampi ng f o r c e ) , one to stop i t , and one to wi t hdr a w i t ( t o open the d i e ) . 2 . 1 . 2 . 2 )The H y d r a u l i c C y l i n d e r s Applying A x i a l Load

The two c y l i n d e r s p r o v i d i n g the compr essi ve a x i a l load move r e l a t i v e to one a n o t h e r , in o r d e r to produce equal d e f o r ma t i o n o f each end of t he tube and so form the bul ge c e n t r a l l y on the t ube . Thi s i s

achi eved by the use o f a f l o w d i v i d e r in the c i r c u i t between the pump and the h y d r a u l i c c y l i n d e r s . Thi s d i v i d e s the f l o w from the pump i n t o equal p a r t s

r e g a r d l e s s o f t he load on each c y l i n d e r , and so s ynchr oni ses the movement o f t he two c y l i n d e r s . A pr e s s u r e r educi ng v a l v e i s - a l s o used to c o n t r o l the f o r c e being a ppl i e d to the ends of t he t u b e . A

d i r e c t i o n a l c o n t r o l v a l v e c o n t r o l s t he e x t en di ng and