US3181328A

US3181328A - Shock aided extrusion

Info

Publication number: US3181328A
Application number: US236602A
Authority: US
Inventors: Zeitlin Alexander
Original assignee: Barogenics Inc
Current assignee: Barogenics Inc
Priority date: 1962-11-09
Filing date: 1962-11-09
Publication date: 1965-05-04
Anticipated expiration: 1982-05-04
Also published as: DE1452210A1; GB993100A

Description

y 1965 A. ZElTLIN 3,181,328

SHOCK AIDED EXTRUSION Filed Nov. 9, 1962 3 Sheets-Sheet 1 FIG! INVENTOR. ALEXANDER ZEITLIN his ATTORNEYS 3 Sheets-Sheet 3 his ATTORNEYS May 4, 1965 A. ZEITLIN SHOCK AIDED EXTRUSION Filed Nov. 9, 1962 United States Patent York Filed Nov. 9, 1962, Ser. No. 236,602 10 Claims. (Cl. 72-56) This invention relates generally to methods and apparatus for extruding objects such as billets through dies. More particularly, this invention relates to methods and apparatus for aiding such extrusion by the employment of a transient shock pressure to supplement the pressure normally used to effect the extrusion.

For a better understanding of the invention, reference is made to the following description and to the accompanying drawings wherein:

FIGURE 1 are graphs of the variation in pressure on a billet during an extrusion operation;

FIG. 2 are graphs of the variation in the total energy stored in a billet-extruding system during an extrusion operation;

FIG. 3 is a schematic view in cross section of one form of apparatus embodying the present invention;

FIG. 3a is a fragmentary view of a modification of the apparatus of FIG. 3;

FIG. 4 is a schematic view (partly in cross section) of another form of apparatus embodying the invention.

Referring now to the graphs shown in FIG. 1, the horizontal ordinate represents the length of a billet being extruded. The initial unextruded length of the billet is represented in FIG. 1 by the horizontal distance AP. The vertical ordinate of F IG. 1 represents the pressure to which the billet is subjected over the course of its extrusion.

The solid graph line 5 of FIG. 1 represents the total pressure on the billet when it is extruded by apparatus which lacks a pressure shock generator but which otherwise is the same as, say, the apparatus shown in FIG. 3 or in FIG. 4 hereof. In such apparatus without a shock pressure generator, the only applied pressure employed to effect the extrusion is that unidirectionally-acting pressure which is generated in a conventional manner by a hydraulic ram or the like, and which is termed herein, the primary drive pressure. Such primary drive pressure is to be distinguished from the pressure on the billet in that the pressure response of the billet extrusion system intervenes between the former and the latter pressure.

As shown by the graph line 5 of FIG. 1, when primary drive pressure alone is applied to the billet extrusion system to extrude the billet, the value of the pressure on the billet initially increases linearly from zero to level I to elastically compress the billet so that the length thereof shortens from AF to BF. The pressure at level I is, however, insufficient to force the billet through the die. Accordingly, the pressure on the billet must be further increased from level I to level II to deform the billet beyond its elastic limit and to thereby break down its internal structure so as to tend to render the billet plastic and capable of flowing through the die. In the course of such plastic deformation, the billet length shortens from HP to CF.

Upon reaching level II, the pressure on the billet attains a value sufficient to overcome the static friction force which has hitherto prevented the billet from flowing through the die. Accordingly, the billet starts to extrude. Since the dynamic coefficient of the friction force which opposes the flow of billet material is lower than the static coeflicient for that force, once the billet has started to extrude, less pressure on the billet is needed to keep the lbillet material flowing. Hence, the pressure on the billet suddenly drops from level II to level III.

dhlfild Patented May 4, 1965 "ice Following the sudden drop, the billet continues to extrude to shorten its length from CF to DF. While the billet is so extruding, the pressure on the billet required to maintain the extrusion drops slowly from level III to level IV. When the billet has reached length DP, the pressure on the billet necessary to continue the extrusion builds up again until it reaches level V. At the time level V is reached, so much of the billet has been extruded that there remains of it only a butt of length EF. While such butt may be extruded by application of pressure from the ram sufficient to develop pressure of level V on the billet, in practice the extrusion of the butt is often omitted. In fact, the extrusion can conveniently be terminated at the stage at which the pressure on the billet has dropped to level IV or thereabouts.

When a billet is extruded in the manner just described, potential energy is stored in the billet extrusion system (billet, container etc.) by virtue of the primary drive pressure applied thereto and the consequent energy-storing deformation of various of the elements constituting that system. FIG. 2 shows this phenomenon by a diagram wherein the horizontal coordinate is, as before, the unextruded length of the billet, and wherein the vertical coordinate is the total amount of potential energy stored by the system. In FIG. 2 the solid graph line 6 represents the total energy when primary drive pressure alone is used to effect extrusion of the billet.

During the build up of the pressure on the billet from zero to level II, the applied primary drive pressure is slowacting in the sense that the inertia to deformation of the elements of the lbillet extrusion system by which the energy is stored is a factor which does not delay the manifestation in the stored energy of a change in the applied pressure for a length of time which is of any significance on the scale of time over which that change takes place. Hence, during the mentioned build-up of pressure on the billet by the application of primary drive pressure alone, the amount of energy stored is commensurate in magnitude with the amplitude of the pressure applied.

Comparing graph line 5 in FIG. 1 to graph line 6 in FIG. 2, it will be seen that at the beginning of extrusion the sudden pressure drop from level II to level III is accompanied by a corresponding sudden drop from level II to level III in the total potential energy stored by the billetextrusion system. What this loss in stored potential energy means in physical terms is as follows.

When breakthrough is achieved at level H such that the billet starts to extrude, and such that, simultaneously, the friction force resisting billet extrusion changes suddenly from its relatively high static value to its relatively low dynamic value, the pressure on the billet needed merely to overcome the friction force drops in value to a fraction of a previously built-up level II of pressure. Hence, there is present in the billet-extrusion system an excess of pressure sustained by the energy stored in the system. That excess pressure acts against the billet to accelerate it as fast as its inertial reaction will allow and to effect a conversion of the stored potential energy into kinetic energy of the billet. As the stored potential energy is so converted into kinetic energy, the pressure which the stored energy can sustain decreases, and so, as shown by FIGS. 1 and 2, the pressure and the stored energy drop rapidly together until they reach level III at which the acceleration of the billet by the stored energy ceases, and at which a condition of equilibrium is reached between the pressure in the system and the pressure on the billet needed to overcome the dynamic friction force on the billet.

The practical consequence of this sudden conversion of the stored energy of the system into kinetic energy of the extrusion from the billet is that the acceleration of the a front portion of the extrusion is so violent that not only is the extrusion propelled like a bullet but actually the front of the extrusion may separate itself from the tail. Such separation may occur because once the energy released during the drop from level II to III is used up, the remainder of the extrusion does not take place at anywhere near the speed reached by the billet during its initial acceleration. Evidently, both such a violent initial acceleration of the billet and the resulting tendency of the billet to separate are disadvantageous.

It is accordingly an object of this invention to provide methods and apparatus for extrusion of billets and like object whereby the extruded object will not be subjected to violent acceleration immediately after extrusion has begun.

Another object of the invention is to provide methods and apparatus for extrusion of billets and like objects wherein the maximum pressure demanded of the source of primary drive pressure is lessened.

These and other objects are realized according to the invention as follows. Instead of using the primary drive pressure to build up the pressure on the billet all the way to the breakthrough value at level II, the primary drive pressure is used to raise the pressure on the billet before extrusion from zero only to about a level III substantially the same as the level III necessary to keep the billet extruding once the extrusion has begun. To further increase the pressure on the billet from level III to the level II which is needed for breakthrough, the primary drive pressure is supplemented by a momentary shock pressure of suflicient amplitude that the drive pressure and shock pressure together overcome the static friction resisting billet extrusion and, thereby, initiate, the extrusion. The shock pressure is, however, of short enough duration that the amount of energy stored in response thereto by the billet-extrusion system is smaller than the amount of energy which would have been so stored if the build-up to breakthrough of the pressure on the billet had been developed solely by the applied primary drive pressure. Because the amount of stored energy has so been diminished, less of such energy is available for conversion into kinetic energy of the billet, and, accordingly, the billet is not as violently accelerated immediately after breakthrough has occurred.

The mentioned shock pressure may be provided in various ways as, say, by an explosive charge or by a transient electric discharge in a body of pressurized hydraulic fluid which directly or indirectly develops the pressure on the billet. If desired, a shock effect similar to that from an electric discharge can be produced in the hydraulic fluid by a thin wire which is exploded by the passage therethrough of a high energy burst of electric current. Any of the ways just mentioned are suitable for producing a pressure shock-wave of extremely short duration (cg. a few microseconds). If found desirable or necessary, the duration of the shock wave can be increased in ways known to the art to last several milliseconds instead of microseconds. The figures mentioned of microseconds or milli-seconds for the order of magnitude of the duration of the shock wave are by way of example rather than by way of limitation since the duration of the shock wave may be made even longer if required. The amplitude of the shock wave can be varied in ways known to the art to fit the requirements of each case.

FIG. 3 shows a mode for carrying out the invention in connection with a hydrostatic extrusion apparatus disclosed in co-pending application Serial No. 107,836 filed May 4, 1961, in the name of Gerard et al. and owned by the assignee of this application. Except for the pressure shock generator, the components of that apparatus are disclosed in full in thementioned application and, therefore, will be described herein more briefly.

Referring now to FIG. 3, a pressure containing vessel has at its lower front end a flange 11 encircling a bore 12 formed in the vessel to be open at the lower end of the vessel, and to extend upwardly from that open end. The word bore is used herein as descriptive of the structure of the central hollow space of vessel 10 rather than as descriptive of its origin. Thus, the bore 12 need not be a hole formed by boring, but, instead, may be formed, say, by machining out the interior of a cast hollow vessel 10.

As shown in FIG. 3, the bore 12 extends upwardly only partway through vessel 10 so that the top 13 of the bore is closed off by an end portion 14 of vessel 10 which is integral with the rest of the vessel. If desired, however, the pressure containing vessel may be of a type in which the interior bore extends through the vessel from end to end thereof and in which the top of the bore is closed off by a removable end closure. Thus, for example, the bore 12 may be closed at its top by a closure means similar to one of those disclosed in United States Patent 3,063,594 issued November 13, 1962, in the name of Gerard et al.

The flange 11 of vessel 10 registers with a flange 15 disposed at the upper end of and forming an integral part of a piston housing 16. Such housing contains hydraulic cylinder 17 co-axial with and of greater diameter than the bore 12. As shown, the cylinder 17 extends upwardly in housing 15 towards bore 12 from a cylinder bottom 16 formed by an end portion 19 of the housing 16 integral with the rest of the housing. An adapter tube 20 with a hollow axial core 21 extends upwardly through the end portion 19 to project into cylinder 17 beyond the bottom 18 thereof.

Received with a sliding fit in cylinder 17 is an annular 7 piston 25 having a central cylindrical hollow space 26 in which the adapter tube 20 is in turn received with a sliding fit. The piston 25 has formed in the exterior circumference thereof an annular groove 27 in which there is an 0 ring 28 providing a pressure seal between the piston and the wall of cylinder 17. In like manner, the piston 25 has formed in the interior circumference thereof an annular groove 29 in which there is an 0 ring 30 providing a pressure seal between the piston and the wall of tube 20. A conduit 31 passing through the bottom portion 19 of housing 16 permits injection of pressurized hydraulic fluid into cylinder 17 behind piston 25.

Mounted coaxially on piston 25 is a lesser diameter ram 35 comprised of a head 36 and a stem 37. The ram extends upwardly from the piston to have the front end of the ram received with a sliding fit in the open end of the bore 12 of vessel 10. The ram plugs such open end so that the ram forms together with the part of the bore inwards thereof a billet container 38. Communicating with that chamber is a coaxial passageway 39 extending through the length of ram 35 from a lower junction with space 26 inside piston 25 to an upper orifice 40 by which the passageway opens into the lower end of chamber 38. The chamber 38 is otherwise rendered pressure tight at its front end by an O ring 41 seated in an annular groove 42 formed in the head 36 of the ram, the ring 41 bearing against the circumferential wall of bore 12 to form a pressure seal.

The chamber 38 is shown in FIG. 1 as containing (1) a lesser sized billet 45 having its lower end seated over orifice 40 in the head 36 of ram 35, and (2) a volume of hydrostatic pressure transmitting medium 46 filling the interspace in chamber 38 between the billet and the wall surface of bore 12 which bounds chamber 38. Thus, the medium 46 entirely surrounds the billet except at its front end where the billet is seated on the ram.

During an extrusion operation, the vessel 10 and the piston housing 16 are clamped together by a split ring clamp formed of two identical semi-circular halves of which one appears in FIG. 1. To assure that the two halves of the clamp do not become separated, a safety ring 61 is placed around the clamp. The clamp and safety ring may be constructed in accordance with the teachings in the aforementioned US Patent 3,063,594.

The head 36 of ram 35 is comprised of an upper annular primary die 70, a lower annular secondary die 71, and an annular die holder 72 disposed below die 70 and around die 71. The elements 79-72 of the die assembly are fastened together and to the stem 37 of the ram 35 by conventional securing means (not shown) as, say, bolts. The secondary die 71 needs no particular securing means since such die is entirely constrained by the primary die 70, the die holder 72 and the ram stem 37. If desired, the die assembly need include only a single die instead of the two dies 70 and 71.

The bottom face 80 of the billet 45 and the top face 81 of the primary die 70 are matched in contour to make flat contact with each other over an annular area disposed radially outward of the orifice 40. This annular area of contact forms a seal which prevents hydraulic fluid 46 in the interspace around the billet from leaking underneath the billet into orifice 40 and thence out passageway 39.

As shown, the billet 45 has formed at the front end thereof a cylindrical stub 85 which projects into the orifice 40. This stub serves both to center the billet in relation to the die assembly in the course of setting up the apparatus and to provide a leader into the die during the extrusion process.

As so far described, the apparatus is the same as that disclosed in the aforementioned application Serial No. 107,836. As an additional feature, however, the apparatus includes a pressure shock generator of the following construction. Within the vessel 10, a pair of ball electrodes 90, 91 are disposed in the space at the top of bore 12 to be immersed in the fluid 46 filling the bore. Those electrodes 90 and 91 are each mounted on a respective one of a pair of

conductor rods

92, 93 which pass upwardly through and project from the top of vessel by virtue of passing through respective ones of a pair of insulating liners or

bushings

94, 95 tightly received in separate auxiliary bores extending through the top of the vessel to the main bore 12. Exteriorly of vessel 10 the

rods

92 and 93 are connected through

respective leads

96, 97 and a switch 98 in lead 96 to the

terminals

99, 100 of a high voltage pulse generator 101. The generator 101 is shown schematically as being comprised of (a) large size capacitors 102 serially connected across the mentioned terminals, (b) a voltage step up transformer 103, (c) a rectifier 104 connecting the secondary winding 105 of transformer 103 in circuit with the serially connected capacitors 102, and (d) an A.C. power supply 1106 connected to excite the primary winding 107 of the trans former. As earlier pointed out, a shock wave similar to that from an electric discharge can be produced in the hydraulic fluid by a thin wire which is exploded by the passage therethrough of a high energy burst of electric current. As shown in FIG. 3a, a suitable exploding wire device may be provided by replacing the ball electrodes 90, 91 by clamping electrodes 90a, 91a and by stretching and clamping an explodablc wire 89 between those last named electrodes.

The FIG. 3 apparatus is set up for cold extrusion in the following manner. With the safety ring 61, the split ring clamp 56 and the vessel 10 being removed from the housing 16, with the piston 25 being at the bottom of the hydraulic cylinder 17, and with the ram 35 upstanding from the piston as shown, a billet 45 of material to be extruded is seated in centered relation on the ram 35. The vessel 10 is then placed over the housing so that the flange 11 of the vessel and the flange 15 of the housing are in registration, and so that the ram and the billet thereon slip into the bore 12 of the vessel. Next, the ring clamp is assembled to lock together the flanges 11, 15 and the safety ring 61 is placed around the assembled ring clamp. Finally, the chamber 33 within bore 12 is filled with hydraulic fluid in some suitable manner as,

6 say, in the manner described in the mentioned application Serial No. 107,836 or by injecting hydraulic fluid into bore 12 through passages 21 and 39. The apparatus is now ready to operate.

The extrusion operation is initiated by injecting hydraulic fluid through conduit 51 into cylinder 17 behind piston 25 so as to drive the piston upwardly. The pressure of the fluid injected behind the piston may be of the same order as that commonly used in the present day hydraulic art, i.e., between 10,000 psi. and 50,000 psi. In the view, however, that the face area of piston 25 is greater by, say, tenfold than the face area of ram 35, the driving pressure behind the piston is converted by a pressure multiplying action into a much higher pressure exerted by the front of the ram 35 on the fluid 46 in the chamber 38.

As the ram 35 is driven by piston 25 into the bore 12, the ram automatically compacts the fluid as to build up the hydrostatic pressure therein to the level III shown in FIG. 1. During this build up of hydrostatic pressure, the forward movement of the ram lifts the billet so that the top thereof moves towards the vessel top 14. Suthcient clearance is, however, provided between the top of the billet and the vessel top so that the hydrostatic pressure value of level III is reached Well before the top of the billet strikes the vessel top. Thus, it will be seen that the ram does not at any time exert any direct pressure on the billet.

Prior to the operative movement of ram 35 into the bore 12, the capacitors 102 have been charged so as to develop a high voltage across the

terminals

99, 100 of the voltage pulse generator 101. Simultaneously with the building up of the pressure in fluid 45 to level III by the advancement of the ram into the bore, the switch 98 is closed in a timed manner to produce a high energy spark discharge of capacitors 102 through the gap between ball electrodes and 91. That discharge acts upon the fluid 46 in which the ball electrodes are immersed to produce therein a pressure shock wave supplementing the ram-developed pressure and of an amplitude at least suflicient to bring the total pressure on the billet momentarily to the critical level II (FIG. 1) and to thereby initiate the extrusion of the billet. The total pressure so developed on the billet by the combined action of the ram pressure and the shock pressure is represented in FIG. 1 by the dotted graph line 115.

Once billet extrusion has begun, the friction force opposing the extrusion drops radically, and the pressure necessary to keep the billet extruding drops commensurately to level III. That level is substantially the same as the level III initially generated by the ram. Hence, even though the shock wave quickly dies away, the extruding of the billet can be and is continued to an unextruded length less than DF (FIG. 1) by continuing the advance of the ram 35 into the bore 12 without making any greater demand on the ram than to maintain the pressure on the billet the same as or less than the pressure intially built up on the billet by the ram.

Because the employment of the described pressure shock technique permits billet extrusion to be carried out by a primary drive pressure of lesser value than the level II needed for breakthrough, the technique permits the use of a source of primary drive pressure (e.g., ram 35 and its hydraulic cylinder and piston drive unit) which is of lighter construction than what would be required by safety considerations if the source alone had to supply the breakthrough level of pressure on the billet. Of course, if it is desired to extrude the butt end of the billet, the primary pressure source must be capable of developing a pressure of level V (FIG. 1). Even so, the demand for pressure from that source is less than what it would be if it were necessary for that source alone to develop the breakthrough pressure level.

While the amplitude of the shock wave is, as described, sufiicient (along with the ram developed pressure of level III) to initiate extrusion of the billet, the duration of the shock wave is short as, say, on the order of from microseconds to milli-seconds. During the short time interval over which the wave acts, the gross mass of the components of the billet extruding system in which energy is stored by deformation cannot be accelerated by the shock wave at a rate suflicient to produce an energystoring deformation of those components commensurate in magnitude with the amplitude of the shock pressure. Hence, as indicated by dotted graph line 116 in FIG. 2, the total energy stored in the billet-extrusion system by a shock wave used to raise the pressure level from III to II is much less than the total energy stored in the system when the primary drive pressure is used for this purpose. It follows that after breakthrough occurs at level II there is much less stored potential energy available to accelerate the billet. Therefore, the extruding billet is not subject to an initial violent acceleration and to the likelihood of separation of the front part of the billet from its tail.

In connection with the described shock-aided extrusion of a billet, the following additional matters are of interest. First, the pressure shock wave acts on the components of the billet extrusion system and particularly upon the fluid 46 in a manner different from the primary drive pressure from the ram 35. That is, the shock pressure is propagated as a true wave of pressure through the body of fluid 46 and the rest of the system rather than being eifective (as is the primary drive pressure) to produce a dimensional change in such body. While the amplitude of the shock pressure wave rises and falls like any other wave, the shock wave is preferably damped out within its first half period so that the wave is unidirectionally acting rather than alternating in character.

Second, it will be noted from FIG. 1 that an effect of the use of shock pressure to increase the total pressure level from III to II is to bypass most of the plastic de formation of the billet which occurs when the primary drive pressure is used to produce such increase. The plastic deformation spoken of is that which takes place when the billet is shortened in length from AF to CF in accompaniment with the shown rise of primary drive pressure from level I to level II.

Third, the pressure shock generator (discharge electrodes 1 9 and 91) is illustrated in FIG. 3 as being disposed in the top of the bore 12. In the event, however, that difhculty is encountered in obtaining pressure tightness of the insulating

bushings

94, 95 which pass at that location through vessel It), the pressure shock generator may be located in the hydraulic cylinder 17 behind the piston to be immersed in the hydraulic fluid which drives that piston forwardly. Ordinarily, however, it is preferable to have the pressure shock generator in the bore rather than in the hydraulic chamber of the hydraulic cylinder and piston drive unit. This is so because the first named location better assures that the pressure shock wave will not be transmitted back to the hydraulic pump for the cylinder-piston drive at an amplitude which might damage the pump.

The described technique of shock-aided extrusion is applicable not only to hydrostatic extrusion apparatus but also to, say, the extrusion apparatus which is shown by FIG. 4, and which (apart from its pressure shock generator) is conventional so that it need not be described herein in detail.

In the FIG. 4 apparatus, a pair of spaced parallel tie rods 129, 1251 run between a ram 122 and a platen 123. As shown, platen 123 is connected on opposite sides thereof to the tie rods 12%, 121 through respective shock absorber assemblies 124, 125. On its face towards the ram, the platen supports a die 126. A central passageway 127 is formed in the platen to the end of permitting passage therethrough of billet material extruded through the die.

The billet 13% which is extruded is contained within the hollow cylindrical liner 131 of a billet container 132 mounted on the tie rods between the platen and the ram. The billet-containing space within container 132 is open at both ends, and, as shown, the billet container and the billet are so disposed that the front end of the billet bears on the die 126 and is centered in relation to the opening through that die.

The back face of the billet is contacted by the front face of a stem 135 advanced a short Way into the open rear end of the billet-containing space within container 132. The stem 135 forms one of the components of the ram 122 of which other components are (a) a piston 136 for driving the stem 135 forwardly, (b) a main hydraulic cylinder 137 containing the piston, (c) a main cross head 138 connecting opposite sides of the cylinder 137 to respective ones of the tie rods 120, 121, (d) a body 139 of hydraulic fluid disposed behind piston 136 in a chamber defined by a cylinder 137 for the purpose of providing motivating power for the piston, and (e) a conduit 140 which passes from the mentioned chamber to exterior of cylinder 137, the said conduit permitting pressurization of the fluid 139 by a remote hydraulic pump (not shown).

Besides the conventional parts so far described, the FIG. 4 apparatus has a pressure shock generator comprised of an explosive charge disposed in cylinder 137 to be immersed in the hydraulic fluid 139. The charge 145 is supported in place by a pair of conducting wires 14-6, 147 connected to opposite ends of the charge and passing from the inside to the outside of the cylinder 137 through insulating liners 148, 1 .9 received in respective holes drilled through the cylinder. Exteriorly of cylinder 137, the wires 146 and 147 are adapted to be connected through a switch 150 to opposite terminals of a voltage and current source represented schematically by the battery 151.

In the operation of FIG. 4 apparatus, the ram 122 is used as before to raise the pressure on billet 130 from zero to level III (FIG. 1). As this pressure level is reached, the switch 150 is thrown in a timed manner to explode the charge 145 and to thereby generate a pressure shock wave which increases the total perssure on the billet from level III to the level II at which breakthrough occurs and the billet starts to extrude. The remainder of the operation of the FIG. 4 apparatus is obvious from the description already given of the operation of the FIG. 3 apparatus. As in the case of the FIG. 3 apparatus, the use in the FIG. 4 apparatus of a pressure shock wave permits the billet to be extruded without being subjected to initial violent acceleration and to the likelihood of separation of the front of the billet from the tail thereof.

It is to be understood in connection with the foregoing description that the graphs shown in FIGS. 1 and 2 are not necessarily accurate in a quantitative sense, but that, instead, their purpose is to depict in a qualitative manner the phenomena to which they relate.

The above described embodiments being exemplary only, it will be understood that additions thereto, omissions therefrom and modifications thereof can be made without departing from the spirit of the invention, and that the invention comprehends embodiments differing in form and/or detail from those specifically described. Thus, the invention may be practiced in conjunction with hydrostatic extrusion apparatus of the sort disclosed on pages 177-179 of the text Large Plastic Flow and Fracture by P. W. Bridgman (McGraw-Hill, 1952). Eurther, in certain applications of the invention the pressure shock wave may be alternating instead of unidirectionally acting. Accordingly, the invention is not to be construed as limited save as is consonant with the recitals of the following claims.

I claim:

1. Apparatus for extruding an object comprising container means for said object, die means at one end of said container means, means to subject said object to a pressure sufficient to produce extrusion thereof from said container means through said die means once said extrusion has been initiated, and a shock pressure generator responsive to actuation thereof to subject said object to a shock wave of pressure supplementing said first named pressure and adapted in conjunction therewith to initiate said extrusion of said object.

2. Apparatus as in claim 1 in which said first named pressure is developed by pressurized hydraulic fluid confined in a chamber, and in which said shock pressure generator comprises a pair of gap-spaced electrodes disposed within said chamber in said fluid, and means to produce an electric discharge between said fluid-immersed electrodes.

3. Apparatus for hydrostatically extruding a billet comprising container means providing a chamber for containing both a billet and a volume of hydraulic fluid disposed between said billet and the chamber-bounding wall of said container means, die means at one end of said chamber, means adapted by pressurizing said hydraulic fluid to subject said billet to a pressure suflicient to produce extrusion thereof from said chamber through said die means once said extrusion has been initiated, and a shock pressure generator responsive to actuation thereof to subject said billet to a shock wave of pressure supplementing said first named pressure and adapted in conjunction therewith to initiate said extrusion of said billet.

4. Apparatus as in claim 3 in which said pressure generator comprises a pair of gap-spaced electrodes disposed within said chamber in said fluid, and means to produce an electric discharge between said electrodes.

5. Apparatus as in claim 3 in which said container means has a hollow bore providing said chamber, said bore being open at said one end and being operably closed at its other end by stationary closure means, and in Which said fluid-pressurizing means comprises a single inwardlymovable ram projecting into said open end of said bore to have a sliding fit therewith and to be adapted to be driven thereinto, said ram having a lengthwise passageway therethrough, said die means forming part of said ram and being mounted on the front end of said ram to be disposed around said passageway, and said billet being extruded through said die means and thence through said passageway formed in said ram.

6. Apparatus for extruding a billet comprising container means having a bore extending axially from end to end thereof, said bore being adapted to contain a billet, die means disposed at one end of said bore in fixed relation with said container means, ram means inserted in said bore, means for driving said ram means into said bore to thereby subject a billet therein to a pressure suflicient to produce extrusion thereof from said bore through said die means once said extrusion has been initiated, and a shock pressure generator responsive to actuation thereof to subject said billet to a shock wave of pressure supplementing said first named pressure and adapted in conjunction therewith to initiate said extrusion of said billet.

7. Apparatus as in claim 6 in which said means for driving said ram means comprises a hydraulic cylinder and piston, and in which said shock pressure generator is disposed in said cylinder behind said piston to be immersed in the hydraulic fluid which actuates said piston and to produce a shock wave in said fluid.

8. The method of effecting extrusion of an object from a container and through die means at one end of said container comprising applying to said object a pressure suflicient to maintain such extrusion but insufiicient to initiate such extrusion, and further applying to said object a shock wave of pressure supplementing said first named pressure and adapted conjointly therewith to initiate such extrusion.

9. Apparatus comprising die means, means for positioning a formable object to be in registration with said die means, a container means for a volume of hydraulic fluid in pressure-coupled relation with a surface portion of said object which is away from said die means, mechanical fluid compressor means coupled with the space provided in said container means for said fluid to impart to said fluid a component of hydrostatic gauge pressure having an equal value at all points in said fluid, and means to then produce in said fluid a pressure Wave which is propagated to said surface portion and which supplements said component of hydrostatic pressure to initiate the forming of said object by said die means, said component of hydrostatic pressure being of a value to thereafter complete the forming of said object.

10. Apparatus comprising die means, means for positioning a formable object to be in registration with said die means, container means for a volume of hydraulic fluid in direct areal contact with a surface portion of said object which is away from said die means, wire means immersed in said fluid, mechanical fluid compressor means coupled with the space provided in said container means for said fluid to impart to said fluid a component of hydrostatic gauge pressure having an equal value at all points in said fluid, and means to pass through said wire means a burst of electric current which explodes said wire means to produce in said fluid a pressure wave, said wave being propagated to said surface portion to urge said object towards said die means, and said wave supplementing said component of hydrostatic pressure to initiate the forming of said object by said die means, said component of pressure being of a value to thereafter complete such forming of said object.

References Cited by the Examiner UNITED STATES PATENTS 2,962,164 11/60 Scribner 2076.2

FOREIGN PATENTS 476,793 9/51 Canada. 119,073 4/58 Russia. 119,435 3/58 Russia.

OTHER REFERENCES Carson: High-Energy-Rate Forming, Product Engineering, October 15, 1962, pp. 86-100.

Parr: Hydrospark Forming, The Tool Engineer, March 1960, pp. 81-86.

WILLIAM J. STEPHENSON, Primary Examiner.

CHARLES W. LANHAM, MICHAEL V. BRINDISI,

Examiners.

Claims

1. APPARATUS FOR EXTRUDING AN OBJECT COMPRISING CONTAINER MEANS FOR SAID OBJECT, DIE MEANS AT ONE END OF SAID CONTAINER MEANS, MEANS TO SUBJECT SAID OBJECT TO A PRESSURE SUFFICIENT TO PRODUCE EXTRUSION THEREOF FROM SAID CONTAINER MEANS THROUGH SAID DIE MEANS ONCE SAID EXTRUSION HAS BEEN INITIATED, AND A SHOCK PRESSURE GENERATOR RESPONSIVE TO ACTUATION THEREOF TO SUBJECT SAID OBJECT TO A SHOCK WAVE A PRESSURE SUPPLEMENTING SAID FIRST NAMED PRESSURE AND ADAPTED IN CONJUNCTION THEREWITH TO INITIATE SAID EXTRUSION OF SAID OBJECT.