Apparatus For Shock-deformation Of Workpieces

Abstract

A die is located in a receptacle and has an exposed surface of predetermined contour which it is desired to impart to a workpiece. Support means is provided for supporting a workpiece proximal to the exposed surface in such position relative to the latter as to be deformable into conformance with the exposed surface. A shock energy transmitting medium is accommodated in the receptacle surrounding the die and the workpiece. Shock-energy producing means is provided for producing shock-energy in the medium. Shock-energy transfer means is interposed between the medium and the workpiece for receiving shock energy from the former and for transmitting on optimum amount of the shock energy to the latter.

Description

CROSS-REFERENCE TO RELATED APPLICATION

A related application was filed on Sept. 24, 1969 in the name of Heinrich Hertel et al. under the title of "Device for Shock-Deformation of Workpieces," it is copending under Ser. No. 860,752.

BACKGROUND OF THE INVENTION

The present invention relates generally to the deformation of workpieces by shock pressure energy, and more particularly to an apparatus for effecting the shock-deformation of such workpieces.

The concept of deforming workpieces into conformance with the surface contours of a die by subjecting them to shock originating from setting off of explosives, or other means, is already known. Processes for carrying out such deformation are known in the art under various names, for instance explosive forming and the so-called "Hydrospark" process. The workpiece, which may be a sheet material member or a semifinished blank, is superimposed with spacing on an exposed surface of a die, the exposed surface having been given the configuration which it is intended to reproduce on the workpiece itself. The die and the workpiece are accommodated in a suitable receptacle containing a pressure-transmitting medium, preferably a liquid medium. Now shock energy is produced in the medium, for instance by detonating an explosive or in one of the other ways already known from the art, and this shock energy is transmitted through the medium in form of kinetic energy to the workpiece to be deformed, effecting deformation of the workpiece into close conformance with the exposed surface of the die.

All of this requires only a brief period of time, but nevertheless the transmission and deformation process is not instantaneous and the period of time required for it is finite. It follows from this that in order to absorb the optimum amount of kinetic energy which carries out the deformation process, the workpiece requires a certain starting or acceleration distance which, depending upon the particular deformation problem and the particular deformation method used, may vary but is generally on the order between approximately 2 and approximately 10 cm. In other words, taking the lower limit, if the workpiece moves into contact with the exposed surface of the die before it has been deflected through a distance of approximately 2 cm. (or more as pointed out above) it has not yet absorbed the optimum quantity of kinetic energy from the energy transmitting medium.

This means that wherever the necessary distance range mentioned above is not present between the workpiece and the exposed surface of the die into conformance with which it is to be deformed, the energy available for the deformation is not fully utilized.

This is true, not exclusively but in particular, in deformation methods having a limited energy availability, for instance in the aforementioned "Hydrospark" method or where apparatus is used of the type disclosed in our aforementioned copending application. The problem exists in particular where a preformed semifinished blank is to be deformed, that is a blank which has been preformed to approximate roughly the contours of the exposed surface of the die so that is deformation into contact with this exposed surface is required only to provide sharper and more precise contours of the workpiece. Under these circumstances the juxtaposed surfaces of the die and of the workpiece must be closely adjacent prior to initiation of the deformation process because of the high-dimensional accuracy which is desired to be obtained in the finished product, that is in the deformed workpiece. For this reason there is under these circumstances almost never any possibility of providing the necessary acceleration distance mentioned above. This is evidently a disadvantage, which is further coupled with the fact that residual air remaining in the space between the juxtaposed surfaces of the die and the workpiece undergoes high compression when the deformation occurs and thus may lead to flaws in the finished workpiece.

SUMMARY OF THE INVENTION

It is, accordingly, an object of the present invention to provide an apparatus for shock-deformation of workpieces which is not possessed of the aforementioned disadvantages.

More particularly it is an object of the present invention to provide such an apparatus which is capable of supplying an optimum quantity of deformation energy to the workpiece even though an inadequate acceleration distance exists between the workpiece and the surface of the die.

In pursuance of the above objects, and others which will become apparent hereafter, one feature of our invention resides in an apparatus of the type mentioned above, which briefly stated comprises a receptacle and a die located in this receptacle and having an exposed surface of predetermined contour which it is desired to impart to a workpiece. Support means is provided for supporting a workpiece proximal to the exposed surface of the die in such position relative to the exposed surface as to be deformable to conformance with the same. A shock-energy transmitting medium is provided in the receptacle surrounding the die and the workpiece and shock-energy producing means is present for producing shock-energy in the medium. Finally, shock-energy transfer means is interposed between the medium and the workpiece for receiving shock-energy from the former and for transmitting an optimum amount of such shock-energy to the latter.

In accordance with one embodiment of the invention the shock-energy transfer means may be in form of a transfer element which is arranged in juxtaposition with the workpiece, being spaced from the same by the necessary acceleration distance so that it is the transfer element which undergoes acceleration by the shock energy transmitted through the transmitting medium before it in turn transmits its energy to the workpiece, so that the transmission of energy from the transfer element to the workpiece takes place under optimum conditions with a resulting optimum transmission of energy. The transmission may take place directly or by interposing a pressure transmitting medium, preferably of liquid type. It is particularly advantageous to evacuate the space between the transfer element and the workpiece or, if a pressure transmitting medium is utilized, the space between the pressure transmitting medium and the transfer element. This makes it possible for the transfer element to move without encountering any resistance while it traverses the aforementioned acceleration distance.

However, while this is an advantageous concept it is not necessary in every instance. Tests have shown that if the aforementioned space is not evacuated and air is allowed to remain in it, the energy exchange between the transfer element and the workpiece is not disadvantageously influenced by the included air which, it will be appreciated, is subjected to significant compression and consequent to rapid heating. It was observed that the degree of effectiveness was approximately on the same order whether or not the space between the transfer element and the workpiece was evacuated.

In fact, if air is allowed to remain in the space and thus undergoes compression and heating as the shock deformation takes place, this fact may be utilized for providing an additional energy input into the deformation process. Under the conditions which are encountered in the space between the transfer element and the workpiece when this space is not evacuated, that is under the pressure and temperature conditions which take place as the transfer element is caused to move towards the workpiece under the influence of explosively released shock energy, such ordinary fuel as petroleum may be instantaneously combusted with the oxygen contained in the air in accordance with the Diesel effect, and the same is true of fuel containing oxygen in chemically combined form and which under normal circumstances combust only slowly. Therefore, such fuels may be accommodated in the aforementioned space and their combustion and instantaneous energy release may be triggered when the air in the space reaches a predetermined temperature as a result of its compression by the transfer element which advances towards the workpiece under the influence of shock energy transmitted from the shock energy producing means through the shock energy transmitting means. In fact, the fuels themselves may constitute a secondary pressure transmitting medium. For instance, if the fuel selected is petroleum the quantity of fuel accommodated in this case may be so chosen as to larger than the quantity which can be combusted with the available oxygen in the space. Thus, after combustion a certain quantity of the petroleum will remain in liquid form and act as a secondary pressure transmitting medium.

It will be appreciated, of course, that it is also possible to fill the space between the transfer element and the workpiece, or the space between the transfer element and a secondary pressure transmitting medium which may be located intermediate the workpiece and the transfer element, with reactable gas mixtures--such as an acetylene-oxygen mixture--instead of with air and liquid fuels.

Whatever combustible fuels may be selected for inclusion in the aforementioned space to thereby provide an additional energy input into the deformation process, it will be appreciated that these fuels are not explosive in character and are therefore considerable safer than the use of actual explosives. In addition, whereas the use of some explosives is governed by laws and statutes in certain countries so that they cannot be freely utilized in shock deformation processes and apparatus, the fuels which can be used in the apparatus according to the present invention are not of explosive nature and therefore their use is in no way subject to governmental regulation.

The possibility of using the aforementioned fuels in the aforementioned manner in the apparatus according to the present invention makes possible embodiments of the apparatus which utilize cascade-type energy amplification, that is the summation of successively produced amounts of shock energy with the combined total acting upon the workpiece. In such embodiments the actual shock-energy producing means serves primary or even merely for triggering the initial energy release of the cascade, with this initially released energy then triggering another release of energy which will in turn serve to trigger still a further release of energy. The number of stages may in this case be quite freely selected depending upon requirements. Evidently, the initial shock-energy producing means need under these circumstances produce considerably less energy than if it alone is responsible for producing an adequate amount of energy capable of effecting deformation of the workpiece. Such embodiments are particularly advantageous because they make it possible to control the direction of energy flow movement and thus to reduce stresses on highly stressed parts of the apparatus. For instance, in the apparatus according to the aforementioned copending application the use of the energy cascade principle increases the deformation effectiveness while requiring less than half the working pressures heretofore necessary. One advantage of this in conjunction with the apparatus according to the aforementioned copending application is the fact that it permits a significant reduction in the amplitude of movement of the movable structural element of the apparatus.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagrammatic sectional elevation of an apparatus according to one embodiment of the invention;

FIG. 2 is a view analogous to FIG. 1 but illustrating an apparatus according to a further embodiment of the invention;

FIG. 3 is another view similar to FIG. 1 but illustrating still a further embodiment of the invention; and

FIG. 4 is a diagrammatic sectional elevation illustrating yet another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Discussing firstly the embodiment illustrated in FIG. 1 it will be seen that reference numeral 5 identifies a vessel or receptacle which accommodates in its inferior a die 1. In the illustrated embodiment the die 1 rests on the bottom wall of the receptacle 5 and has an upwardly directed exposed surface which is recessed to provide a contour desired to be obtained in the finished workpiece. In the illustrated embodiment a semifinished workpiece or blank 11 is supported on the exposed surface of the die 1 but defines with the exposed surface a free space or gap 9. The slight spacing between the exposed surface and the marginal portions of the workpiece 2 with which the latter rests on the exposed surface is illustrative only, because there will of course be contact between them. The spacing has been utilized in FIG. 1 to illustrate that there is no sealing contact between the marginal portions of the workpiece 2 and the exposed surface of the die 1, that is that the space 9 is not sealed.

According to the invention there is provided shock-energy transfer means which here comprises an annular element 13 peripherally surrounding the workpiece 2 and projecting upwardly above it, and an energy transfer element 10 which rests on the other edge of the annular element 13. Reference numeral 12 identifies suitable seals, for instance O-rings, which provide for a fluidtight seal between the annular element 13 and the die on the one hand, and between the annular element 13 and the transfer element 10 on the other hand.

Because of the spacing of the element 10 from the outer side of the workpiece 2, that is the side facing away from the die 1, there exists between the outer side of the workpiece 2 and the element 10 a space 14. A body of shock-energy transmitting medium, for instance a liquid such as oil, is identified with reference numeral 6 and accommodated in the receptacle 5 surrounding the die 1, the annular element 13 and the transfer element 10. Because of the seals 12 the medium 6 cannot enter into the spaces 9 and 14.

Reference numeral 8 identifies an evacuating conduit which may be connected to a source of vacuum, for instance a vacuum pump, and which communicates with the space 9. Because the space 9 is not sealed, as mentioned before, it in turn communicates with the space 14 so that when evacuation is carried out through the conduit 8, the spaces 9 and 14 are both evacuated together.

The outer side of the workpiece 2 will be seen to be concave, and it is filled entirely with a body 11 of secondary pressure transmitting medium, which may again be a liquid such as oil, but which need not be the same as the medium 6. The spacing between the element 10 and the outer side of the workpiece 2 is selected in accordance with the aforementioned requirement relative to the desirable acceleration distance, that is the spacing will generally be on the order of between approximately 2 and 10 cm; the precise distance can be readily determined empirically or by calculation in dependence upon the requirements and circumstances of a given case.

Reference numeral 7 identifies diagrammatically a shock-energy producing means which may be any of the various types known to those skilled in the art and thus is not believed to require detailed discussion. It is simply necessary that the means 7 be capable of producing a predetermined amount of shock energy. This is transmitted through the medium 6 to the element 10 which is thereby deflected towards the workpiece 2 in order to drive the same into precise conformance with the surface contour of the die 1.

The presence of the body 11 of secondary pressure transmitting medium not only provides for an even distribution of a pressure impulse from the element 10 over the entire surface area of the workpiece 2. In addition its presence protects the surface of the workpiece 2, that is the surface facing towards the transfer element 10, against mechanical damage on contact with the transfer element 10.

It should be emphasized that in the embodiment of FIG. 1, where both the spaces 9 and 14 are evacuated, the secondary pressure transmitting medium 11 must have a correspondingly low-vapor pressure, for instance it must be mineral oil or the like. In addition the presence of vacuum in the spaces 9 and 14 requires evidently that the elements 10 and 13 have sufficient mechanical strength to withstand collapse until and unless the element 10 is subjected to shock energy released by the means 7.

Coming to the embodiment of FIG. 2 it will be seen that this differs from that of FIG. 1 essentially in that the space 14 is fluid-tightly sealed with respect to the space 9. Like reference numerals identify like elements and it will be seen that here the marginal zone of the workpiece 2 is sealed with reference to the die 1 by means of suitable sealing means 15, for instance an elastomeric sealing element or any other means suitable for the purpose. Thus, only the space 9 is evacuated through the conduit 8, it being understood that this evacuation aids in the deformation of the workpiece 2 into conformance with the surface contour of the die 1. Because the spaces 9 and 14 are fluid-tightly sealed from one another it is now possible to increase the quantity of secondary pressure transmitting medium 11, which in FIG. 2 as in FIG. 1 is illustrated as a liquid, so that it not only fills the depression in the outer side of the workpiece 2 but actually has a level above the marginal portions of the workpiece 2. This facilitates the transmission of pressure also to these marginal portions and improves fold retention.

In the embodiment of FIG. 2 the transfer element 10 is of course not subjected to stresses resulting from the presence of vacuum in the space 14. It therefore requires less mechanical strength than in the embodiment of FIG. 1 and may for instance be constructed of lead or the like. Of course, in FIG. 2 as in FIG. 1 the element 10 must either be replaced with a new one after each deformation process, that is each time when a workpiece 2 has been deformed in conformance with the contour of the die 1, or it must be straightened.

It is advantageous that the elements 10 have relatively great mass but low-deformation resistance (hence lead) to require as little energy as possible for deforming them because evidently the energy necessary for deforming the element 10 is no longer available for deformation of the workpiece 2.

The vessel in FIG. 2 is the same as in FIG. 1, and while the shock energy producing means 7 has not been shown in FIG. 2 it will be appreciated that it will also be required, the same as in FIG. 1.

Coming, to the embodiment illustrated in FIG. 3 it will be seen that this differs primarily from FIGS. 1 and 2 in that the shock energy transfer means is reusable, and that moreover it is reusable without requiring straightening or any other actions. In FIG. 3 the same reference numerals identify the same elements in the preceding Figures. Here, however, the transfer element 10 and the annular element 13 of FIGS. 1 and 2 are replaced with a one-piece unit 16 of inverted substantially cup-shaped configuration. Advantageously the unit 16 may be composed in part or predominantly of elastomeric material, such as rubber or synthetic plastic, and can be sealingly placed over and into engagement with a portion 1a of the die 1. If necessary or desirable the die 1 may be provided with one or more circumferential grooves 1b in the portion 1a, and corresponding circumferential ridges 16a may be provided on the unit 16 and engage in the associated grooves 1b. Of course, the grooves may be continuous or discontinuous, and other possibilities for connection are also possible. If grooves and projections are utilized as in FIG. 3 they can of course provide an additional seal.

In the illustrated embodiment that portion of the unit 16 which corresponds to the transfer element 10 of FIGS. 1 and 2 has embedded therein plate-shaped members 17--which may also have other configurations, for instance be ball-shaped--which may consist of lead, Wolfram or another suitable material and which serves to increase the mass of the unit.

While this has not been specifically illustrated it is possible to protect the unit 16 against damage in response to contact with the secondary pressure transmitting medium 11, or against damage by the elevated temperatures which the air in the space 14 will assume upon compression, by covering the inner side of the element 16 with a protective foil of suitable material which may or may not be self-adhesive and can be replaced from time-to-time whenever necessary. Plastic or metal foils an be used for this purpose.

It should be understood that it is not necessary for the elements 10 and 13 to be replaced with element 16, but that instead the element 13 may be utilized as before and may carry an element corresponding to the element 10 of FIGS. 1 and 2 but consisting in its entirety of elastomeric material or composed predominantly of such material with inclusion corresponding to the members 17. In this case suitable clamping means of well-known construction would be utilized to clamp the element analogous the element 10 to the annular element 13. A protective foil may then be held in place against the inner side of the element which corresponds to but replaces the element 10 of FIGS. 1 and 2, by being clamped between the same and the annular element 13.

It will be appreciated that the apparatuses according to the present invention, for instance those of FIGS. 2 and 3, may be utilized not only with semifinished partly preformed workpieces, but also with sheet material workpieces which are as yet undeformed, and with other configurations.

If it is desired for the particular embodiment to use energy-cascade amplification, that is if an additional energy input within the respective space 14 is desired, then it is evidently necessary to provide additional energy-releasing agents, such as fuels, in the space 14. In FIGS. 2 and 3 this may be accomplished for instance by replacing the medium 11 with a combustible fluid, such as petroleum. The quantity of petroleum may be so selected that it is larger than the petroleum quantity which can be combusted with the oxygen available in the space 14 so that, when as much petroleum is combusted as is possible in view of the available oxygen, the residual liquid petroleum will continue to act as a secondary pressure transmitting medium.

FIG. 4 illustrates an embodiment using energy-cascade amplification. Like reference numerals identify like elements as in the preceding embodiments. Here, however, a plurality of the elements 10 of FIGS. 1 and 2 have been utilized and in each of the chambers defined between successive ones of the elements 10 provision has been made for supplying additional energy by utilizing chemical energy-liberating agents. The elements 10 may consist of elastomeric material and are protected at their exposed surfaces by self-adhesive protecting foils 18. Conical spacing rings 19, 19a maintain the elements 10 in their desired rest positions. Screws 26 serve to connect the spacing rings with one another, and also to connect the lowermost spacing ring 19 with the flange 1c of the member 1.

The uppermost chamber is filled with a combustible gas mixture 21, for instance a mixture of acetylene and oxyen, which is supplied through the conduit 24. The middle chamber contains a chemical energy carrier 22, for instance a solid fuel Oxydator. In the lowermost chamber energy is supplied by a cellulose foil 23 which is suspended as indicated by reference numeral 25 so as to be kept out of contact with the secondary pressure transmitting medium 11.

When energy is applied to the uppermost element 10 (for instance by a means analogous to the one identified with reference numeral 7 in FIG. 1), the movement of the uppermost element 10 towards the center element 10a compresses the gas mixture 21 in the upper chamber, an occurrence which is coupled with an adiabatic temperature increase of the mixture 21. This results in ignition and subsequent combustion of the mixture 21 whereby the element 10a is downwardly accelerated into the middle chamber in which the compression phenomenon is repeated. The temperature increase of the residual air content of this chamber causes combustion of the solid fuel 22 and this in turn results in downward acceleration of the element 10b. The operation in the lowermost chamber corresponds to what has already been explained with reference to FIGS. 2 and 3.

If desired it is also possible to use a solid fuel in form of a liquid fuel. Such solid fuel may for instance contain oxygen in chemically combined form and in known manner it may be on cellulose basis. In fact, to simplify the problem of providing the proper quantity of fuel, the solid fuel may be produced in form of a foil or sheet. In this case particularly it is advantageous to separate the solid fuel from the secondary pressure transmitting medium 11--which in this case of course has no combustible function--in order to prevent the medium 11 from inhibiting the combustion of the solid fuel. This can be accomplished in various different ways, for instance by interposing a foil of synthetic plastic material between the medium 11 and the solid fuel which, assuming that it is employed in the embodiment of FIG. 3, would then of course be located between the upper surface of the medium 11 and the upper wall of the unit 16.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of applications differing from the types described above.

While the invention has been illustrated and described as embodied in an apparatus for shock deformation of workpieces, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

Claims

We claim:

1. An apparatus for shock-deformation of workpieces, comprising a receptacle; a die located in said receptacle and having an exposed surface having predetermined contours which it is desired to impart to a workpiece; support means for supporting a workpiece proximal to said exposed surface in such position relative to the latter as to be deformable into conformance with said exposed surface, and at a spacing from said surface which is smaller than a given distance through which said workpiece must yield to absorb an optimum amount of deformation energy; a shock-energy transmitting medium in said receptacle surrounding said die and said workpiece; shock-energy producing means for producing shock-energy in said medium; and shock-energy transfer means interposed between said medium and said workpiece being spaced from the latter by at least substantially said given distance and operative for receiving shock-energy from said medium and for transmitting an optimum amount of such shock-energy to said workpiece.

2. An apparatus as defined in claim 1, said workpiece having an outer side and an inner side with the latter facing and being spaced from said exposed surface by said distance; and wherein said transfer means comprises a transfer element at least in part juxtaposed with but spaced from said outer side of said workpiece by a distance greater than said distance.

3. An apparatus as defined in claim 2, wherein said workpiece and said transfer element both are of self-supporting deformable sheet material.

4. An apparatus as defined in claim 3, wherein said sheet material is sheet metal.

5. An apparatus as defined in claim 2, wherein said transfer element defines with said outer side of said workpiece an evacuated space.

6. An apparatus as defined in claim 2, wherein said transfer element defines with said outer side of said workpiece a space; further comprising a body of gas confined in said space and subject to rapid heating in response to compression resulting from transmission of shock energy to said transfer element; and auxiliary energy producing means confined in said space and operative for producing auxiliary energy for transmission to said workpiece, in response to heating of said gas to a predetermined temperature.

7. An apparatus as defined in claim 6, wherein said auxiliary energy producing means is a combustible oil capable of flash combustion in response to rise of the temperature of said gas to a predetermined level.

8. An apparatus as defined in claim 7, wherein said combustible oil is a predetermined quantity of petroleum, and wherein said gas consists at least in part of oxygen in an amount smaller than that required for supporting combustion of the entire predetermined quantity of petroleum, so that some of said petroleum remains uncombusted and constitutes an auxiliary shock-energy transmitting medium.

9. An apparatus as defined in claim 6, wherein said auxiliary energy producing means is a nonexplosive chemical substance.

10. An apparatus as defined in claim 2, wherein said transfer element comprises an annular first portion peripherally surrounding said workpiece, and a transverse second portion extending transversely of said first portion juxtaposed with said outer side of said workpiece and spaced from the same axially of said first portion.

11. An apparatus as defined in claim 10, wherein said first and second portions are of one piece.

12. An apparatus as defined in claim 11, wherein said portions consist at least in part of elastomeric material.

13. An apparatus as defined in claim 12, wherein said transfer element is of inverted cup shape.

14. An apparatus as defined in claim 2, wherein said transfer element comprises an interior side; and further comprising a protective foil releasably secured to and covering said interior side.

15. An apparatus as defined in claim 14, wherein said foil is self-adhesive.

16. An apparatus as defined in claim 10, wherein said second portion consists at least predominantly of elastomeric material; and further comprising connecting means connecting said second portion with said first portion.

17. An apparatus as defined in claim 6, wherein said auxiliary energy producing means comprises a solid fuel capable of rapid combustion for thereby producing said auxiliary energy.

18. An apparatus as defined in claim 6, wherein said auxiliary energy producing means comprises a solid fuel containing oxygen in chemically combined form and capable of rapid combustion for thereby producing said auxiliary energy.

19. An apparatus as defined in claim 18, wherein said solid fuel is a cellulose-based compound in sheet-material form.

20. An apparatus as define in claim 6, said auxiliary energy producing means being combustible; further comprising a body of auxiliary shock-energy transmitting medium in space in contact with said workpiece; and wherein said auxiliary energy producing means is spaced from said body for preventing possible interference of the latter with combustion of said auxiliary energy producing means.

21. An apparatus as defined in claim 1, said workpiece having an outer side and an inner side with the latter facing and being spaced from said exposed surface; and wherein said transfer means comprises a plurality of transfer element means spaced from one another and from said outer side of said workpiece, and being arranged for serially transferring shock energy to the latter.

22. An apparatus as defined in claim 21, said transfer element means comprising a plurality of differently sized transfer elements arranged serially in pyramidal form and ascending in order of size in direction towards said outer side of said workpiece; and a plurality of spacing rings each arranged between two successive ones of said transfer elements.

23. An apparatus as defined in claim 1, wherein said transfer means comprises amplifying means for cascade-amplification of shock energy in direction towards said workpiece.

24. An apparatus as defined in claim 23, said amplifying means comprising an initial and a terminal auxiliary shock-energy producing means, and the first-mentioned shock-energy producing means being operative for triggering production of shock energy by said initial auxiliary shock energy producing means.