Electric discharge apparatus for electrohydraulic explosive formin

Schwinghamer, R. J.

English

NASA Technical Reports Server

June 15, 1965 R. J. SCHWINGHAMER 3,188,844 
ELECTRICAL DISCHARGE APPARATUS FOR FORMING 
Filed Jan. 17, 1962 
TRIGGERING 
 SWITCH 
POWER 
SUPPLY 
INVENTOR. 
-.I 
, " (NASA CR OR TMX OR AD NUMBER) i 
ROBERT J. SCHWINGHAMER 
ATTORNEYS 
https://ntrs.nasa.gov/search.jsp?R=19700024933 2020-03-17T01:58:17+00:00Z
3,188,844 United States Patent Ofice , :,, ,,, ,, ,, 
3,188,844 between which has a V-shaped portion converging away 
ELECTRICAL DISCHARGE APPARATUS from the apex of the blast chamber. Also, within the 
FOR FOWdNG blast chanlber is a pressure trnnsrnitting liquid. 
Robert I. Schwinghramzr, Hwdsville, Ah., assignor to the The two e!ectrodes are electrically connccted to a con- 
United States of America as represented by the Adminin- 5 denser bmk through a suitable triggering switch. When 
istratos of the N a B i o n a U e r o n a ~ ~ c s  and Space the condenser bank is discharged throueh the electrodes 
Admirnistrafion 
- 
and wire, t h s v i r e  explodes and generates a shock wave 
Filed Jm. 17,1962, Scr. NO. 3166,969 which is transmitted by the liquid toward ihe blank. The 2 Claims. (@1. 72-56) 
(Gra~ted  under Titile 35, U.S. Code (B952), see. 266) electrical circuit and wire parameters are selected where- 1 0  bv a current pause or "dunkel~ause" does not occur. 
-- - 
The invention dcscribed herein may be manufactured This will b; more readily understood by the following 
and used by or for the Government of the United States detailed description when taken together with the accom- 
of America for governmental purposes without the pay- panying drawings, in which : 
ment of any royalties thercon or therefor. FIGURE 4 is a perspective view of an apparatus for 
This invention relates to high energy rate forming and I j elcctrical discharge forming. 
more particularly to an electrical disch~rge apparatus for FIGURE 2 is an elevation cross-sectional view taken 
high energy rate forming. along line 2-2 of FIGURE 1, showing some parts in full, 
Recent trends in manufacturing for formed metal parts and including an e1ec:rical schematic wiring diagram. 
in large sizes and formed metal parts having cornplcx FIGURE 3 is a partial elevation cross-sectional view 
configurations have led to the development of high energy 20 showing the electrode and wire relationship for the ap- 
rate forming techniques which provide an instantaneous paratus of FIGURE 1. 
force for forming which would be impractical by conven- Rcierring now to the drawings, there is shown in ]FIG- 
tional machinery such as the hydraulic forging press and URES 1 and 2 an apparatus B B  for electrical discharge 
drop hammer. These high cnergy rate forming techniques forming having a die block 13 with a forming cavity 115 
(generally involve the use of chemical compoucds which 25 and a bore 17 communioating with the cavity 15. A 
are exploded undcr water whercby shock waves are gen- metal blank 19 rests upon the upper surface 21 of the 
erated and transmitted by the water against a metal blank. die block 13 and covers the forrning cavity 15. The 
Chemical explosives do not, however, provide for rapid blank 119 has a hold-down ring 23 upon its upper sur- 
and uniform repeatability and are often hazardous to face 25 to frictionally hold it in position. A blast head 
handle and store. 30 27 with an inner cone-shaped chamber 29 converging 
The explosivelike energy reiease of a rapid discharge from an opening in its base surface 31 is situated upon 
of electrostatically stored energy between two electrodes the upper annular surface of the hold-down ring 23. The 
has also been satisfactorily utilized to a limited exient forn~ing cavity 15 of the die bloclc 13, the aperture 33 
for high energy rate forming. The placing of a high elec- of the hold-down ring 23, and the conical chamber 29 of 
trical potential of several kilovolts between two electrodes 35 the blast head 27 are in an aligned relationship. As shown 
located under water results in a current flow which first best in FIGURE 2, cap screws 35 extend through lugs 37 
vaporizes the water in the vicinity of the electrodes and integral with the blast hcad 2'7 and on throvgh the hold- 
then causes the vapor to become highly dissociated and down ring 23 near its outer periphery, and into threaded 
ionized. This ionized vapor is a highly conductive pat1 bores 39 within the die block 13. 
and permits a tremendous electrical current discharge be- 40 The blast head 27 has a dielectric material portion 41 
tween the two electrodes with a cor~esponding intense which forms the region adjacent the apex of Ithe chamber 
pressure or shock wave that radiates radially from the 29 and extends to the upper surface 43 of the blast head 
 conductive path and is transmitted by the water. HOW- 27. The dielectric malerial portion 41 has a peripheral 
ever, a considerable anrount of current is necessary before flange 45 resting upon an a n n ~ l a r  shoulder 47 of the blast 
the ionized vapor is formed which means less useful work 45 head 27 to prevent it from slipping down into the cham 
and somewhat unpredictabl-, results from one e!ectrical ber 29. A pressure plate 49 is secured by a series of cap 
discharge to another. Also, the explosive path of the elec- sorews 51 to the upper surface 43 of the head 27 to pre- 
trical discharge could not be shaped to obtaln the versatil- vent the dielzctric material portion 41 from being blown 
ity of chemical explosive charges which by having a cyl- out by an electrical discharge within the chambcr 29 as 
inder, cord, or sheet shape could obtain an energy release 50 described hereinafter. 
pattern which would tend to apply a forming force exactiy Extending through the dielectric material portion 41 
where needed. are two spaced electrodes 55 and 55 having inner bent 
Accordingly, it is an object of this invention to provide portions 57 and 53, respectively, directed in an opposed 
a highly efficient electrical discharge apparatus which manner into tha chamber 29 adjacent its apex. A metal 
rapidly and repeatedly obtains energy releases in a par- 56 wire 61 having a centrally located V-shaped portion is 
ticular direction. fixed by its opposite ends to the o2posed bent portions 
A further object is to provide an elcctrical discharge 57 and 59 of the electrodes 53 and 55, respectively. 
apparatus which will release and control sufficient energy This is accomptished as shown in FIGURE 3 by  lacing 
to eiiiciently form materials. each end of the wire 61 into a bore 63 provided within 
Other and further objects, uses, and advantagas of the each of bent portions 5'9 an6 59 ai:d securing it by 
present invention will become apparent as the description a S" Screw 65. The wire 61 is positioned whereby its 
proceeds. V-sheped portion converges in the diverging direction of 
In accordance with this invention an e!ectrical discharge the chamber 29 and points toward the metal blank 319. The pressure plate 49 has a centrally located boss 67 
apparatus is constructed having a blast head with a cone- 65 upon its upper surlace and an opening 69 whicll extends 
shaped chamber and a die b!ock in cooperative relation- tllrough the boss 67 and plate A coaxial 
ship thereto which has a forming cavity aligned with the line 71 exte~ds through the 69 and is held therein 
chamber. A me:al blank which is adapted to be formed by , cdfet chucic 73 fis lightly about * L E ~ ~  line 
separates the cl~amber I ro~n  the forming cavity. and is in threaded contact with the boss 69. 
Within the chamber and adjacent the apex thereof are 70 The coaxial transmission line 71 is con- 
two spaced electrodes having a metal wire bridged there- nected to the electrodes 53 alld s§ by aitachillg its core 
3,188,844 
3 4 
conductor 73 to electrode 55 and its shield condnctor 77 ful would be encon~passeil within the conical volun~e 
to the other electrode 53. The electrical conductors 75 defined by the metal blank 19 and the wire 61. The 
and 77 are also attached to a high energy electrical stor- rest of the energy distribution outside of this conical 
age bank 78, which is illustrated in FIGURE 2 as a volume would have been lost from performing u s e f ~ ~ l  
series of parallel related capacitors $@ having a power r, work. 
supply 82 to charge them to their high electrical potential. For efficient operation, the parameters of the metal 
A suitable triggering switch 84 is provided in the elec- wire 61 and it$ electerical circuit should be selected by 
trical conductor 77 for discharging at the proper moment known criteria whereby a current pause or "dunkelpause" 
the capacitors 80 through the electrodes 53 and 55 and will not occur and whereby the capacitors 80 are corn- 
wire 61 whereby the wire 61  will be vaporized with ex- 10 pletely discharged approximately instantaneously with 
plosive violence. the exploding of the wire 61. It  is also preferred if the 
The chamber 29 is fil!cd with liquid 85, water for ex- included angle of the V-shaped portion of the wire 63 
ample, for transmitting the shock wave generated by has an angle between 50 and 70 degrees and the included 
the exploding wire 61 against the metal blank $9 so that cane angle of the chamber 29 has an angle of appro:ii- 
it will be formcd against the die cavity 15. 15 mately 55 degrees. 
The metal blank 19, although tightly held between It is apparent that an electrical discharge system utiliz- 
the die block 13  and the hold-down ring 23, is able to ing a bent bridge wire has been disclosed which is in- 
slip slightly when being iorced into the forming cavity strumental in concentrating the explosive force of an 
15. This slight slippage prevents the blank 10 from electrical dischgrge and this system has been incorporated 
rupturing when undergoing the forming operation. 00 into an apparatus which takes full advantage of the di- 
As the exploding wire 61 within the chamber 29 will rectional sense of the electrical discharge by bringing 
form the blank 19 against the cavity I5 faster than the the explosive force generated thereby against a metal 
air therein has time to leave through the bore 14, it is blank with high efficiency. 
necessary to exhaust the air within the cavity 15 before Obviously, many modifications and variations of the 
the wire 61 explodes by attaching a vacuum line 86 to 25 present invention are possible in the light of the above 
the bore 17. Otherwise, the air, after being compressed teachings. It  is, therefore, to  be understood that within 
by the blank 49, would deform the blank. the scope of the appended claims the invention may be 
A directional shock wave is generated by the explod- practiced other than as specifically described. 
ing wire 61  because it is bent into a V-shape. This is What is claimed is: 
believed to be due to the magnetic flux which normally 33 1. In combination with a die having a forming cavity 
surrounds an electrical current path and which tends to adapted to be covered by a restrained blank: 
bring itself into a state of equilibrium. When the cur- (a)  means for directing a shock wave having a sub- 
rent path is bent, as would result in using the V-shaped stantially V-shaped front toward the center of said 
wire 61, the magnetic flux in the acute angle region of forming cavity whereby the point of said shock wave 
the bent path, region A in FIGURE 3, would have a :.j will strike the middle portion of said blank to form 
high density due to its concentration in a region of said blank from its center outwardly; 
smaller dimensions, and, correspondingly, the magnetic (b) said means including: 
flux in the obtuse angle region, region B in FIGURE 3, (1) a blast head having an inner cone-shaped 
would have a low density due to its spreading out in a chamber converging from an opening in the 
region of greater dimensions. Accordingly, a situation 40 peripheral surface thereof; 
occurs in the region of the bent current path which re- (2) said blast head joining said die with said 
sults in a preferential motion of particles of matter away opening being aligned with said cavity; 
from the high density magnetic flux toward the low ( 3 )  two spaced electrodes supported by said blast 
density magnetic flux in an effort, to bring a b w t  a state head and extending into said chamber adjacent 
of equilibrium. It  is this preferential motion which is 4j the apex thereof; 
believed to result in the shaped shock wave generated (4) a wire having a V-shaped portion substan- 
by an electrical discharge through a V-shaped path be- tially aligned with the center of said cavity and 
ing directed in the converging direction of that path. fixed to and extending between said electrodes, 
The shock wave generated by exploding the wire 61 and 
has substantially the same V-shape as the wire so that (5) said V-shaped portion converging away from 
when the shock wave moves outwardly from the vapor- said apex of said chamber. 
ized wire 61  its apex strikes against the middle region 2. In an apparatus for forming metal blanks: 
of the metal blank 19. This is advantageous because (a)  a blast head having a base surface adapted to rest 
the forming of the middle portion of the metal blank 19 upon the surface of a die block having a forming 
first will result in a more uniform wall tlnicltness to the 55 cavity; 
finished blank 19 and more efficient forming. Other- (b) said blast head having an inner cone-shaped cham- 
wise, if the apex of the shock wave front first came ber converging from an opening in said base surface, 
against the metal blank 19 adjacent its outer periphery said opening adapted to be aligned with the forming 
and formed that portion against the cavity 1 5  and then cavity of said die block; 
started forming the middle  ort ti om, the blank 29 would 60 (c) two spaced electrodes supported by said blast head 
have been prevented from slipping properly. Improper and extending into said chamber adjacent the apex 
slipping of the metal blank 19 may cause a rupture, non- thereof; 
uniform wall thickness, and decrease in efficiency of the (d) a wire having a V-shaped portion; 
forming operation. (e) said wire being fixed to and extending between 
In addition, the cone-shaped configuration of the cham- 65 said electrodes and having its ~ - ~ h ~ ~ ~ ~  portion con- 
ber 29 further shapes the explosive pressure or shock verging in the diverging direction of said chamber 
wave generated by a e  exploding of the wire 61. The and pointing toward the center of the opening in said 
conical shape of the chamber 29 represents the minimum blast head; 
volume condition for deforming a metal blank 29, and ( f )  said wire being adapted to vaporize with explosive 
with the explosion occurring adjacent the apex of the 70 violence upon the placing of a high electrical poten- 
chamber 29, the shock wave is driven toward the diverg- tial between said electrodes so as to cause a shock 
ing direction of the chamber 29 without appreciable wave having a V-shaped front diverging toward the 
loss of energy. If, for example, the wire 61 exploded opening in said blast head and pointing toward the 
in an unconfined medium, only that portion of the re- center of the opening in said blast head whereby 
sulting spherical energy distribution which would be use- 7 j a metal blank adapted to be placed over the forming 
5 
cavit-y of the die block will be formed from its center 
6 
References Cited by the Examiner 
outwardly; FOREIGN PATENTS 
(g) said cone-shaped chamber of said blast head being 
adapted to drive the shock wave toward the opening 119,435 3/58 Russia. 
of said blast head withoat appreciable loss of energy; 5 OTHER REFERENCES 
and 
"Shape Fasten Engrave Test Materials With Explo- (h) means including a switch for supplying a hi& sives," Materials in Design Engineering, February 1959, trical potential to said electrodes so as to cause said pages 82-87. 
wire to explode at a desired instant; 
(i) said means and said wire having parameters 10 WIUIAM J. STEPHENSON, Primary Examiner. 
. . 
selected whereby a current pause or "du~kelpause" NEDWIN BERGER, ~ ~ ~ ~ j ~ ~ ~ .  
does not occur. 


Electrical discharge apparatus for forming Patent

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