EP0156090A2

EP0156090A2 - Liners for shaped-charge warhead and method of making same

Info

Publication number: EP0156090A2
Application number: EP84630146A
Authority: EP
Inventors: Meir Mayseless; Eliezer Faibish
Original assignee: State of Israel Ministry of Defence Raphael Armament Development Authority; State of Israel
Current assignee: State of Israel Ministry of Defence Raphael Armament Development Authority; State of Israel
Priority date: 1983-09-28
Filing date: 1984-09-28
Publication date: 1985-10-02
Also published as: IL69868A0

Abstract

A method for making a tinerfor a shaped-charge warhead comprises explosively-welding a sheet of a high-density metal to a sheet of a dissimilar, lower-density metal to produce a laminated sheet in which the bond between the two metals includes a plurality of interlocking wavelets; compacting the laminated sheet by compressing it to reduce its thickness and also to flatten the interlocking wavelets; and forming the laminated sheet into the required shape of the liner. Also described is a shaped liner for a shaped-charge warhead comprising an inner layer of a high-density metal to be located extemally of the warhead, and an outer layer of a dissimilar, lower-density metal, to be located intemally of the warhead, the two layers being bonded together by a plurality of interlocking wavelets of the two metals.

Description

The present invention relates to shaped-charge warheads, and is particularly directed to the liners (e.g., conically-shaped liners) for such warheads, and to a method of making such liners.
It is known that the penetration capability of a shaped-charge warhead is proportional to the square root of the density of the liner material. Therefore, heavy metals are more effective for penetration purposes. However, their high cost, the weight added to the warhead in the use of such heavy metals, and sometimes their poor mechanical properties, limit their use as liner materials. The most commonly used materials for such liners are copper, aluminium and steel because of their mechanical properties during dynamical loading and also because of their relatively low cost.
It is also known that, during the detonation process, the liner in a shaped-charge warhead generates a high velocity penetration jet only from the inner portion of the liner, i.e., the portion on the external side of the charge; the remainder of the liner forms a slug which contributes very little, if anything, to the penetration process. It has therefore been proposed that the shaped liner be made of two distinct metals, namely: an outer layer of low-density material such as copper, serving as the base liner metal; and an inner layer of a high-density material, such as gold, electroplated over the inner surface of the copper base liner metal. Insofar as we are aware, however, such an electroplating technique for producing a bimetallic liner has been used only for experimental purposes, in studying the penetration capabilities of high-density materials, and has not found commercial application because of a number of drawbacks, including the high cost and the special equipment required in producing the liner according to that technique.
An object of the present invention is to provide a method of making a liner for a shaped-charge warhead having advantages in the above respects. Further objects of the invention are to provide a novel liner, and also a shaped-charge warhead including the novel liner.
According to one broad aspect of the present invention, there is provided a method of making a liner for a shaped-charge warhead-, comprising: explosively-welding a sheet of a high-density metal to a sheet of a dissimilar metal to produce a laminated sheet in which the bond between the two metals includes a plurality of interlocking wavelets; compacting the laminated sheet by compressing it to reduce its thickness and also to flatten the interlocking wavelets; and forming the laminated sheet into the required shape of the liner.
Particularly good results have been obtained when the compacting and forming steps are effected simultaneously by shear-spinning the laminated sheet.
The successful use of the above-described explosive welding technique for producing the shaped liner was found particularly surprising since it was expected that the wavelets produced at the interface between explosively-welded metals would create such instabilities because of the high dynamic pressure produced at detonation, as to prevent the proper formation of the high-speed jet which effects the penetration. Thus, in the electroplating technique, which was the only bimetallic liner technique previously known to properly produce the penetration jet, the interface between the two bonded metals is substantially flat and without the wavelets produced in explosive welding. It was surprisingly found, however, that the production of such wavelets in the explosive-welding step, and the flattening of these wavelets in the subsequent shear-spinning step, not only enhanced the bond between the two'metals, but also during the detonation process produced a well-defined, highly-penetrating, high-speed jet of the high-density metal.
The invention thus provides an important advantage over the conventional shaped liner used in shaped-charge warheads, in that the invention permits the penetration of shaped-charge jets to be greatly increased without an increase, or with only a slight increase, in the warhead weight. The invention also provides advantages over the previously-proposed electroplating technique for producing such liners particularly in that the new technique is not restricted to the use of materials which can be electroplated and moreover, it does not require the special equipment needed for electroplating. Thus, whereas the previously proposed electroplating technique was used, insofar as we are aware, only for experimental purposes in studying the pentration capabilities of high-density materials, the technique of the present invention has been found to be a practical way of producing such shaped liners at low cost.
The invention also provides a shaped liner made in accordance with the above-described technique, and a shaped-charge warhead constructed with such liners.
Further features and advantages of the invention will be apparent from the description below.
The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:

Fig. 1 is a side elevational view, partly in section, illustrating one form of shaped-charge warhead including a liner, in this case a conical liner, constructed in accordance with the present invention;
Fig. 2 illustrates the formation of the penetration jet and the slug as a result of the detonation of the warhead of Fig. 1;
Fig. 3 illustrates a laminated double-layer sheet for use in making the conical liner in the shaped-charge warhead of Fig. 1;
Fig. 4 illustrates the manner of making the laminated sheet of Fig. 3 by explosive-welding;
Fig. 5 illustrates the shear-spinning step applied to the laminated sheet of Fig. 2, for compacting the sheet and forming it into the conical liner illustrated in Fig. 1;
Fig. 6 is a macrograph (multiplication of 60x) of the interface between the two bonded metal layers in the laminated sheet of Fig. 3 before compaction and forming by the shear-spinning step; and
Fig. 7 is a macrograph corresponding to that of Fig. 6, but showing the interface after the laminated sheet has been compacted and formed by the shear-spinning step.

With reference first to Fig. 1, there is illustrated a shaped-charge warhead, generally designated 2, including a charge 4 within a cylindrical shell 6 (which may be omitted), a detonator 8 at one end, and a shaped (conical) liner, generally designated 10, at the opposite end. Conical liner 10 is constituted of two metal layers, namely: (a) layer 12, which is the outer layer of the cone but is internally of the warhead 2, this layer 12 being preferably of a low-density metal; and (b) layer 14, which is the inner layer of the cone but the external layer of the warhead, this layer 14 being of a dissimilar, high-density metal.
Fig. 2 illustrates what happens to the conical liner 10 upon detonation of the warhead charge 4. Thus, the inner high-density layer 14 of the cone forms a high-velocity penetration jet 14' which contributes most to the penetration of the charge, whereas the outer layer 12 of the cone forms the slug 12' which contributes very little to the penetration. It will thus be seen that by making the inner layer of the cone of high-density metal, and the outer layer 12 of low-density metal, the penetration of the shaped charge warhead 2 is significantly increased without an increase for with only a very little increase in the total weight of the warhead.
Fig. 3 illustrates the laminated sheet in its initial flat condition, and therefore designated 10i, which is used for making the conical liner 10 of Fig. 1, which flat laminated sheet includes the two layers, namely the lower-density metal layer 12i and the high-density metaly layer 14i. Fig. 4 illustrates the method of making the laminated sheet 10i of Fig. 3.
Thus, as shown in Fig. 4, the sheet 14i of high-density metal (which sheet in this example is the "base plate") is placed against a heavy anvil 20; and the sheet 12i of low-density metal (which sheet in this example is the "flier plate") is placed to overlie the high-density metal sheet 14i, but is spaced therefrom by a plurality of stand-off spacer elements 22. These elements are spaced around the periphery between sheets 14i and 12i, and may be made of a plastic foam or the like, such as polystyrene foam, which is disintegrated during the explosive-welding process.
Over the upper, low-density sheet 12i is placed an explosive charge 24 within a container 26. The detonation of charge 24 produces an exceptionally high pressure which forces the low-density metal sheet 12i into intimate engagement with the high-density metal sheet 14i, resulting in the disintegration of the standoff spacer elements 22 initially placed peripherally between the two sheets. The interface between the two explosively- welded sheets 12i and 14i is formed, by the high pressures produced by the explosion, with a plurality of interlocking wavelets of the two metals, as will be described more particularly below with respect to the macrographs of Figs. 6 and 7, which wavelets produce a very intimate bonding of the two layers in the laminated sheet 10'.
The laminated sheet 10c is then subjected to a shear-spinning process, as illustrated in Fig. 5, which compacts the laminated sheet by compressing it to reduce its thickness, and also to flatten the interlocking wavelets; at the same time, the laminated sheet is formed into the right-circular conical shape of the liner 10 in Fig. 1.
Thus, the laminated sheet 10i, in its flat condition, is placed against the apex of a conical mandrel 30 in a spinning lathe, and is held against the apex of the mandrel by one or more rollers 32 engaging the laminated sheet around the apex of the mandrel. Back-up ring 34 engages the opposite face of the laminated sheet, which back-up ring is movable in the axial direction along the outer face of the mandrel as guided by back-up pins 36. During the shear-spinning process, mandrel 30 is rotated about its axis; rollers 32 are likewise rotated about their axes, and at the same time are moved in the radial direction of the mandrel as relative movement in the axial direction is effected between the mandrel and the rollers. Thus, the rollers 32 simultaneously compress the laminated sheet 10i, reducing the thickness of its two layers 12i and 14i, and at the same time form the sheet into the conical configuration of the mandrel 30. Such shear-spinning techniques and apparatus are known, and therefore further details of the construction and operation of this apparatus are not considered essential here.
In Fig. 5, the upper roller, designated 32, its back-up ring 34, and back-up pin 36, and the thickness of the laminated sheet 10 between that roller and back-up ring 34, illustrate the positions of the parts and the form and thickness of the laminated sheet at the beginning of the shear-spinning process; whereas the lower roller designated 32', its back-up plate 34', back-up pin 36', and the lower part of the laminated sheet 10 illustrate the position of the parts and the thickness and form of the laminated sheet at the end of the shear-spinning process. Upon the completion of this process, the outer marginal rim 10' of the laminated sheet is trimmed away to provide the conical liner 10 illustrated in Fig. 1.
Examples of metals which may be used as the high-density layer 14 include tantalum, silver, depleted uranium, gold, and tungsten and their alloys; and examples of metals which may be used as the low-density layer 12 include copper, aluminum, and steel.
As one example, the low-density metal layer 12 may be copper having an initial thickness of 4 mm.; the high-density metal layer 14 may be of tantalum having an initial thickness of 1.25 mm.; and the shear-spinning process may reduce the thickness of both about one-half when the liner is formed with a cone angle of 60°.
The results of this example are illustrated in Figs. 6 and 7, both at a magnification of 60X. Fig. 6 illustrates the condition of the interface before the shear-spinning step; and Fig. 7 illustrates the condition of the interface after the shear-spinning step. Thus, as shown in Fig. 6, the initial thickness of the high-density metal layer 14i is indicated at t ; and the height of the wavelets 40, interlocking the two metal layers 12i and 14i, is indicated at h. As a result of the shear-spinning step, the height of the high-density metal layer 14 is reduced to "t" and the height of the wavelets 40 is reduced to "h," wherein t=t_o sinα, and h=h_o sinα. In this example, wherein a=30° (the total cone angle being 60°), t=1/2 t_o, and h=1/2 h_o.
The so-produced liner was used as the conical liner 10 in the shaped-charge warhead 2 illustrated in Fig. 1, and upon detonation of the charge, it was found that the liner produced a well-defined high-velocity penetration jet as illustrated at 14' in Fig. 2, whereas the low-density metal layer produced the slug 12' illustrated in Fig. 2.
While the invention has been described with respect to one preferred embodiment, it will be appreciated that many other variations, modifications, and applications of the invention may be made.

Claims

1. A method of.making a liner for a shaped-charge warhead, comprising: explosively-welding a sheet of a high-density metal to a sheet of a dissimilar metal to produce a laminated sheet in which the bond between the two metals includes a plurality of interlocking wavelets; compacting the laminated sheet by compressing it to reduce its thickness and also to flatten said interlocking wavelets; and forming said laminated sheet into the required shape of the liner.

2. The method according to Claim 1, wherein said compacting and forming steps are effected simultaneously.

3. The method according to Claim 2, wherein said compacting and forming steps are effected simultaneously by shear-spinning.

4. The method according to any one of Claims 1-3, wherein said laminated sheet is formed into a right-circular cone.

5. The method according to any one of Claims 1-4, wherein said dissimilar metal is a low-density metal.

6. The method according to Claim 1, wherein said bonded sheet is compacted by shear-spinning to reduce its thickness by at least one-half.

7. A shaped liner for a shaped-charge warhead comprising: an inner layer, to be located externally of the warhead, which inner layer is of a high-density metal; and an outer layer, to be located internally of the warhead, which outer layer is of a dissimilar metal bonded to the inner layer by a bond which includes a plurality of interlocking wavelets of the two metals.

8. The shaped liner according to Claim 7, wherein said high-density metal is silver, tantalum, depleted uranium, gold, tungsten, or their alloys.

9. The shaped liner according to Claim 7, wherein said outer layer is of copper, steel, or aluminum.

10. A shaped-charge warhead including a shaped liner according to Claim 7, said dissimilar metal layer being located internally within the warhead and outwardly of the high-density metal layer, which latter layer is located externally of the warhead and inwardly of the dissimilar metal layer.