PRESS I NG TECHNOLOGY

DEVELOPMENT DIVISION

e OCTOBER - DECEMBER 19’91

ENT IS UNUMITa - N ~ r m a l Process Development

Endeavor No. 207

f

NOTICE

This report was prepared as an account o f work sponsored by the United States Government. Neither the United States nor the United States Atomic Energy Commission, nor their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal l iabi l i ty or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that i ts use would not infringe privately-owned rights.

PRESS I NG TECMIOLOGY -

3. P. ffmeee

DEVELOPMENT D I V I S I O N

Advancing the s ta te-of-ar t and developing processes r e l a t ed t o pressing explosives.

October - December 1971 Endeavor No. 207

Acct. NO. 22-2-44-01-207

Section H

I .

PRESS I NG TECHNOLOGY

ABSTRACT

A new process has become ava i lab le t h a t might be useful f o r compacting materials. The process is t r i a x i a l : it u t i l i z e s the f a m i l i a r i sostat vectors to form a b i l l e t and f o r l a t e r a l reinforcement while a shear higher pressure is included over t h e b i l l e t ends with a mechanical pu

The 20-inch press has been inspected a t the si te of manufacture and is .:;- sit t o Pantex Plant .

DISCUSSION

A laboratory test t o measure the physical p roper t ies of s o i l has used ax ia l concept f o r several years. The work has been concentrated i n t of c i v i l engineering with bibliographies referencing repor t s i n 1 compacting pressures have customarily been 150 psi t o 1,000 ps i .

R. M. Koerner, of Drexel University, has recent ly investigated t h e t it may be r e l a t ed t o processing powdered m e t a l . The f i r s t known puh of t h i s work appeared i n the I n t e r n a t i o n a l Journa l of Powder M e t a l , R. M, Koerner's work has continued the bas ic tes t but a t pressures up tc kpsi.

The tr iaxial system of compaction o f f e r s a new pressing technique bees:'*>, r e s u l t s i n a d i f fe rence i n t h e movement of c r y s t a l s of explosives.

Previous methods of HE compaction ( i s o s t a t i c , hydrostat ic o r mechanica1- 8

i n a c rys t a l movement t h a t i s primarily toward the p a r t center with xu.8 tendencies t o bridge aga ins t each other and c rea t e high pressure spoks of ten break the c rys t a l s . The r e su l t i ng cracks within t h e c r y s t a l s bke L

t h a t t h e binder cannot be extruded in to them and a densi ty l imi ta t ion i s en countered t h a t is r e l a t ed t o the problem of not completely f i l l i n g the i c rys t a l l i ne voids with the p las t ic ized binder.

The tr iaxial system seems t o compact mater ia l i n such a fashion t h a t t a l wants t o move c loser to a l l of i t s neighboring c r y s t a l s , ra ther k. j u s t pushed toward the center by i ts adjacent outboard neighbor. Whew is dislocated and moved c loser t o i t s neighbors, it alters the envizti? nearby c rys t a l s , and a s they a l s o begin t o move a condition of f lux L throughout t h e b i l le t .

The t r iaxial compression process uses a combination of isostatic and forces t o impose uneven loadings. This can a l s o be accomplished in-& t iona l i s o s t a t i c press by at taching an intensifying pisten/cylinder of a housing t h a t contains the HE charge. See Fig. 1 f o r t he concepz,,

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+ &. . - Isostatic Vectors * I.

Mechanical Vectors .. Mechanical Piston/Ram

A i r Chamber - HE Charge

- Rubber Sac

Cyl indr ica l Housing

B a s e

Fig. 1. Triaxial Tooling Concept

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Accurate l i s t i n g s of desired s tudies with a t r i a x i a l system cannot be P

a t t h i s time; there i s not enough known about the process. The studisc- are obvious ones t h a t w i l l be needed. invest igat ion progresses.

Others w i l l surely be present

1. S u i t a b l e r a t i o of i s o s t a t i c p r e s s u r e t o s h e a r p r e s s u r e . T h i ~ . e o . c ” ?

n e c e s s i t a t e a t l eas t t w o s u b s t u d i e s :

a . Optimum p r e s s u r e b. Optimum d w e l l period

2. D e n s i t y i n c r e a s e , i f a n y , b y r e p r e s s i n g i n a water-bag.

3, R e s u l t s of p h y s i c a l p r o p e r t i e s once a r a n g e of s u i t a b l e deubsi,g t a i n e d .

Y _ > -

4. Minimum p r e h e a t t e m p e r a t u r e s r e q u i r e d for s u i t a b l e p r e s s i n g f : .

MECHANICAL PRESSING EVALUATION

The objec t ive of this discussion i s t o reconsider the merits of mech pressing, taking i n t o consideration the various problems and advanta pressing, while conducted i n similar equipment, is spec i f ica l ly not con a p a r t of t h i s discussion. Pe l l e t s may be defined as s m a l l cyl inders , 1 inch i n diameter and weighing less than 20 grams.

The problems of mechanical pressing are concerned bas ica l ly with safe:ri omics and design l imi ta t ions enter the consideration, but t o a l e s s e r i L ^

The primary problems are:

1. Alignmtent o f Press P a r t s

The punches and the matching d i e mus t be m a i n t a i n e d i n a c a d p x e c i s e a l i g n m e n t when p r e s s i n g h i g h e x p l o s i v e s . T h i s a l i s u b j e c t t o a l t e r a t i o n f o r a v a r i e t y o f r e a s o n s . These reas be a s subtle as b e a r i n g l u b r i c a t i o n and i n c l u d e b u s h i n g f i e h or b e a r i n g f a i l u r e , o b j e c t s l e f t on p r e s s p l a t e n s t h a t w i l l i n g d u r i n g o p e r a t i o n , s t r a i n - r o d f a i l u r e , t e m p e r a t u r e v a r i a k and uneven l o a d i n g of the e x p l o s i v e w i t h i n the d i e prior t o t ion . A l ignmen t may be s a t i s f a c t o r y d u r i n g a c h e c k o u t b u t noi so a t a1 1 punch psi tions d u r i n g compact ing o p e r a t i o n s .

2. L a t e r a l F l o w

Extreme conditions of uneven l o a d i n g can combine w i t h the POS of HE t o f l o w so t h a t some a r e a s of a p r e s s e d p a r t may not be p a c t e d . This i n t u r n c a u s e s a c o n c e n t r a t i o n of force a g a i n s t punch f a c e s w h i c h c a n r e s u l t i n b r e a k a g e , distortion or des* of a l i g n m e n t .

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::.

3 .

4 .

5.

6.

7,

8 .

Heated P u n c h and D i e Sets

The h i g h thermal c o n d u c t i v l t y o f steel and the i n t i m a t e p o s i t i o n to the e x p l o s i v e s make p r e h e a t i n g a n o b v i o u s choice f o r h i g h q u a l i t y p r e s s i n g s . The r e s u l t o f a h e a t i n g control f a i l u r e here i s more critical t h a n would be the case i n a p r e h e a t i n g oven where the r a w m a t e r i a l i s not be ing s u b j e c t e d to intensive work.

Design

P u n c h and d i e p a r t s mus t be considerably stronger t h a n would be re- q u i r e d f o r p r e s s i n g p l a s t i c s or other inert parts. be t o l e r a t e d and c h i p p i n g or s p a l l i n g h a v e the p o t e n t i a l o f c a u s i n g a detonation. responsible for d e s i g n needs a s o l i d background of m e t a l l u r g y and HE c h a r a c t e r i s t i c s .

C r a c k s c a n n o t

T h i s i s a complex f i e l d i n i t s own r i g h t . a n d the p e r s o n

P a r t E j e c t i o n

E j e c t i n g s t r a i g h t c y l i n d r i c a l parts mre t h a n 1 d i a m e t e r t a l l is a b r u i s i n g o p e r a t i o n at best and it becomes d e s i r a b l e to i n d u c e a s l i g h t t a p e r i n the d i e to r e d u c e the fr ic t ion. l i m i t a t i o n s on what s h a p e s may be p r e s s e d and c a u s e s prob lems w i t h the gap be tween the punch and d i e ,

However, a t a p e r p r e s e n t s

F r i &ion

Compaction forces n o r m a l l y t r a n s f e r f r o m the punch into the HE and a p o r t i o n is expended a s fr ic t ion a g a i n s t the d i e w a l l . tion of the compact ing force i s born b y the d i e i t s e l f . of d i e l o a d i n g t o working lozd i s d i r e c k l y p r o p o r t i o n a l to the s u r f a c e a r e a o f the d i e t h a t i s i n c o n t a c t w i t h the HE and n o r m a l l y amounts co abou t 20% of the total . force, b u t may become a s h i g h as 80% i n s i t u a t i o n s o f poor s u r f a c e f i n i sh or p a r t i c u l a r 1 y a b r a s i v e m a t e r i a l s . T h i s r e s u l t s i n p r e s s u r e and d e n s i t y g r a d i e n t s w i t h i n the b i l l e t , p r e s e n t i n g l imi ta t ions on the r a t i o o f height to d i a m e t e r t h a t c a n be s u c c e s s f u l l y p r e s s e d .

T h u s , a por- The r a t i o

PBX E x t r u s i o n

P l a s t i c bonded e x p l o s i v e s tend to be e x t r u d e d in to the narrow j o i n t s b e t w e e n the punch and d i e . These thin f i l m s . o f e x p l o s i v e s , confined between m e t a l parts, present a p a r t i c u l a r hazard i n k h a t t h e y may be s u b j e c t to v e r y h e a v y f r i c t i o n a l l o a d i n g i f there i s s u b s e q u e n t mt ion .

D r i f t i n g i n Double A c t i n g Presses

Double a c t i n g p r e s s e s a r e s u b j e c t to a hazard not f o u n d i n single a c t i n g p r e s s e s , either u p or down, of the punches w h i l e t h e y a r e m a i n t a i n i n g the ap- p r o x i m a t e l o a d of compac t ion . enough one punch may become withdrawn f r o m the d i e and c a u s e the PBX

An imba lance i n the h y d r a u l i c s y s t e m s c a n a l l o w d r i f t i n g ,

P f this condition of imba lance i s severe

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t o shear a s i t i s e x t r u d e d t h r o u g h the o p e n i n g jo in t b e t w e e n p and d i e . The e x t r u d i n g m a t e r i a l c a u s e s a reduction of the r i n g f o r c e a g a i n s t the o p p o s i t e punch and the a c t i o n w i l l con an a c c e l e r a t e d r a t e .

9. F o r e i g n Material

F o r e i g n m a t e r i a l that i s included i n the PBX a t the t i m e of may be f o r c e d into i n t i m a t e c o n t a c t w i t h the d i e s u r f a c e and ,pme a point of h i g h s h e a r c o n c e n t r a t i o n a s the HE i s compacted. a c t i o n p r o b a b i l i t y i s i n c r e a s e d if the m e l t i n g point of the m a t e r i a l i s h i g h ( i n f l u e n c e d b y hardness).

10. C a p i t a l I n v e s t m e n t

Punches and d i e s su i tab le f o r p x e s s i n g e x p l o s i v e s compr i se a s s e m b l y of t o o l i n g . A basic c y l i n d r i c a l c o n f i g u r a t i o n t o 6 inches i n d i a m e t e r , i n c l u d i n g a h e a t - j a c k e t and the capa vacuum s e a l i n g , w i l l cost on the order o f $3,000.00. T h i s e s c a l a t e s r a p i d l y as s h a p e s become more complex . Punch an used for p r e s s i n g a complex s h a p e have cost $30,000.00 and v e r y e a s y to envision $50,000.00 i n s i m i l a r s h a p e s a t t o d a y - % ’

Shape pressing t o f i n a l dimensions becomes more d i f f i c u l t when press i parts, because of the above described problem of lateral flow. I n sm-- it would be advisable t o press the shape across one surface and aroun phery; then machine the simpler surface, probably the inner radius , control and the densi ty problems described above would then be improver

some machining w i l l probably be required f o r high-quality p a r t s most adi;iedlk, I t o shape pressing.

ADVANTAGES

Advantages of shape pressing a r e primarily economic. improvement i n safe ty and usually l i t t l e i n qual i ty . Advantages are c i

There is no s iga j ’

1. P r o d u c t i o n c a p a b i l i t y

Mechanical p r e s s i n g p r e s e n t 1 y h a s a b o u t 1 /2 the turn-around

equ ipmen t . T h u s , i f complex s h a p e s a r e b e i n g considered and t s e q u e n t mach in ing o p e r a t i o n s c a n be reduced or e l i m i n a t e d , inee p r e s s i n g cou ld r e s u l t i n a c o n s i d e r a b l e economic advan tage . t a g e p a r t i c u l a r l y i n c r e a s e s when NC m a c h i n i n g t i m e i s consf W e a r e a l r e a d y i n p o s s e s s i o n of the NC mach ines so investme t h a t c a p i t a l equipment need not be considered, a 1 though i nm, maintenance e x p e n s e f o r the NC machines i s a def ini te fac tor

i s o s t a t i c p r e s s i n g and this a u l d be reduced f u r t h e r b y use &.. <-

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2 . High D e n s i t y PBX

T h e o v e r a l l d e n s i t y of a m e c h a n i c a l l y p r e s s e d p a r t i s u s u a l l y h igher t h a n t h a t of a s i m i l a r p a r t p r e s s e d i s o s t a t i c a l l y . p r e s s e d p a r t s w i l l h a v e a higher d e n s i t y o n l y a f t e r a r e p r e s s i n g o p e r a t i o n . D e n s i t y spread w i t h i n p res sed - to - shape parts c a n be re- duced b y machining away t h a t portion o€ a piece t h a t had been added t o a l l o w l a t e r a l f l o w o f the HE.

I s o s t a t i c a l l y

HYDRAULIC PUMP

The hydraulic pump t h a t dr ives the i n t e n s i f i e r s of the Elmes press has broken down. Inspection without complete disassembly indicates t h a t a t l e a s t one pis ton has broken and generated m e t a l scraps i n t h e pump and hydraulic c i r c u i t . The pump has been shipped t o t h e manufacturer f o r rebuilding. The E h e s press is not expected t o be operational u n t i l la te January.

20-INCH PRFSS

The 20-inch i s o s t a t i c .press and pumping s t a t i o n is i n t r a n s i t from the manufacturer. The vesse l w a s tested hydrostat ical ly t o 20 ,kps i and cycled f o r systemroperation several t k m e s before leaving the manufacturer. The operational tests proved the f i t of t h e modified breech and t h e f l u i d i c inter locks t o de t ec t improper assembly. Press i n s t a l l a t i o n should be s t a r t ed by mid-January.

CONCLUSIONS

A few pressings of 90010 Mock have been made by the t r i a x i a l technique. c i l i t i e s a t Drexel University, under the d i rec t ion of Koerner, were used to' press seven s m a l l b i l l e t s i n t h e i r tr iaxial equipnent. Density w a s higher than obtained i n i s o s t a t i c pressings a t 20 kpsi . The chamber containing the HE w i l l have t o be evacuated p r i o r t o compaction. N o change from present pract ice . Final development of t h i s concept w i l l probably allow i s o s t a t i c pressures lower than those presently used t o compact HE'S, or it w i l l generate a higher densi ty if t h e present norm of 20 kpsi is continued.

The fa-

MECHANICAL PRESSING

The enormous expense incurred as a direct r e s u l t of a s igni f icant detonation incident would seem t o make mechanical pressing undesirable a t this time i f there is another way t o make the pa r t . The qua l i f ica t ion "at t h i s t i m e " fer added because the balance could tilt i n favor of mechanical pressing i f it becomes urgent t h a t we produce a t maximum capacity. Mechanical pressing is f a s t e r than i s o s t a t i c and may be j u s t i f i e d f o r s izable production runs of several thousands of pieces i n t h a t s i t ua t ion .

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