Device For The Explosive Forming Of Workpieces

Abstract

A device for explosive forming of workpieces through a fluid comprising a vessel containing liquid (water), a bottom plate, and an anvil spaced from the bottom plate by biasing means (springs). The workpiece is positioned on top of the anvil. Guide means are provided which are operable with the anvil so that when the explosive-forming force strikes the anvil it moves linearly downwardly, and the liquid between the anvil and the bottom plate progressively damps the downward movement as it laterally escapes. The guide means may be a series of pistons and cylinders, and preferably the explosive forming is done completely under water and a wall of bubbles is produced adjacent the anvil. It is possible that the level of water is only equal to the level of the upwardly biased position of the anvil, in which case the explosive forming takes place in air, but the damping is still accomplished by water.

Description

In the case of the process known as "explosive forming," the working of workpieces, preferably metal as is well known takes place through the pressure and shock waves which are produced by the detonation of explosive charges. As a rule water is used in these cases as the medium for the transfer of energy. A problem that occurs when utilizing this process is that of mitigating the destructive effect of the explosive shock waves on the floor of the vessel in which the detonation occurs. Solutions have been suggested in which air-filled rubber hoses are used to damp the shock waves. Thus, for example, a proposal has been made to place the bottom plate, designated as the "anvil," and on which the object that is to be formed rests, onto a number of rubber hoses lying one beside the other. However, this proposal turned out to be unsatisfactory, primarily because the rubber walls of the hoses themselves are subject to great strains as a result of the shock wave explosive pressure.

The present invention teaches a way to damp the shock waves occurring in the case of explosive forming without the aid of substances subject to wear and tear.

Water is used as a damping medium, whereby use is made of the physical phenomenon of the so-called progressive damping. The latter phenomenon rests on the inertia of a layer of water, compressed between two parallel surfaces, with a possibility for lateral escape of the compressed medium. In this case it turned out that the resistance against a further relative approach of two parallel plates will become greater, the greater their approach is which has already taken place, i.e. progressive resistance. In the case of explosive forming, this phenomenon expresses itself in the fact that, for example, a resiliently supported anvil, between which anvil and a bottom plate there is a water cushion with a possibility for lateral escape, will first be quickly pressed downwards through the explosive pressure. The resistance against further downward movement increases progressively, whereby the portion of spent kinetic energy grows progressively so that the anvil will either not strike against the bottom plate at all, or strike with only a small force. The damping effect will be greater, the greater the surface area of the pressure-producing surfaces. The damping effect will decrease the more the opposing surfaces of the anvil and bottom plate deviate from parallelism, therefore, it is required that they be substantially parallel. In order to keep the lateral pressure components as small as possible, the sidewalls of the water vessel should have a small angle of inclination with relation to the bottom plate. Generally speaking, however, the problem of the protection of the sidewalls can be considered as having been solved by the fact that a curtain of air bubbles is produced between the place of detonation and the sidewalls of the vessel. On the other hand, protection for the bottom of the water vessel has been solved only insufficiently heretofore, but will be largely guaranteed if a device according to the present invention is used for carrying out the explosive forming.

The accompanying drawing shows an exemplary embodiment of the invention as used, for example, for the expansion of a metallic hollow cylinder.

The hollow cylinder 1 that is to be expanded rests on the anvil 2, which is supported in such a way that it can move only in the direction perpendicular to the bottom plate 4. The linear guidance of the anvil is essential, since if it tilts and goes out of parallel with the bottom plate the damping effect will be strongly reduced. Reference numeral 3 designates the cylindrical bores in the bottom plate 4, and reference numeral 5 designates the pistons attached at the lower side of the anvil, which slide in the cylinders 3 in order to guarantee a linear guidance of the anvil. The anvil rests on the springs 6 which, however, do not necessarily have to encompass the pistons, as happens to be the case in the preferred embodiment. In order to hold the anvil at a distance from the base plate prior to the blast, it is also possible to support it by means of a central spring in the middle, or through a series of springs along the periphery.

To guarantee the linear movement of the anvil, for example, it is possible to attach guide rods to the bottom plate which reach through corresponding bores in the anvil, so that the latter can glide along them in a direction perpendicular to the bottom plate.

The entire arrangement is in a vessel 8 filled with water 7, which has been equipped with an overflow device 9. An air tube 10 with holes is the device for the production of a curtain of air bubbles, already mentioned. The explosive charge, in this instance, is detonated inside the hollow cylinder 1. The layer of water located between the anvil 2 and the bottom plate 4 exercises such an effective progressive damping that even after a many times of repeating the explosive process, no damage whatever of the apparatus could be observed.

It is also possible to alternatively provide a lateral, closed limiting surface on the surface of the bottom plate facing the anvil, assuring at the same time the ability to lower the anvil and provide for the lateral escape of the water. The axis of symmetry of the limiting surface would preferably coincide with the axis of symmetry of the casing of the anvil. In case the anvil is circular, it will thus submerge into a water-filled hollow cylinder connected with the bottom plate, the inside diameter of which is larger than the diameter of the anvil. As a result of this, the laterally escaping water is forced into a change of direction upwards along the wall of the limiting surface, which leads to an intensification of the damping effect. Of course, polygonal shapes can be used.

Furthermore, it is possible to surround the anvil together with the workpiece that is to be formed either with water on all sides, or to fill the blast vessel only up to the height of the anvil, so that the workpiece that is to be formed is not under water.

In order to avoid catapulting the workpiece upwards, it will be advantageous in certain cases to provide a holding mechanism for the workpiece, such as a clamp, which will hold it firmly without preventing the shaping of it, whereby the arrangement for the damping, consisting of anvil, bottom plate and water filling located between the two, can constitute a component of this holding mechanism.

Naturally, other liquids can be used instead of water for force transmitting and damping mediums, but, generally speaking, water will be given preference if for no other than economic reasons.

Claims

I claim:

1. A device for the explosive forming of workpieces through a fluid medium comprising a vessel containing liquid and having a bottom plate; an anvil spaced from said bottom plate by biasing means and adapted to hold a workpiece, said space being completely filled with liquid; and guide means operable with said anvil so that when the explosive-forming force strikes said anvil it moves linearly downwardly, which movement is substantially solely progressively damped by said liquid laterally escaping from between said anvil and said bottom plate.

2. A device as claimed in claim 1 wherein said anvil is planar, is substantially parallel to the plane of said bottom plate, and said linear movement of said anvil is perpendicular to said bottom plate.

3. A device as claimed in claim 1 wherein said biasing means are springs; said guide means include a series of pistons and cylinders attached to said bottom plate and anvil and permitting linear movement only in a direction perpendicular to said bottom plate; and said liquid is water.

4. A device as claimed in claim 1 wherein the explosion occurs completely under water; means are provided to form a wall of bubbles in said water adjacent said anvil; and the lateral walls of said vessel form an obtuse angle with said bottom plate.

5. A device as claimed in claim 1 wherein said bottom plate has an upstanding ridge circumscribing a shape the axis of symmetry of which coincides with the axis of symmetry of the peripheral shape of said anvil, and the dimensions of which allow said anvil to fit within said circumscribed shape and further allows the liquid between said anvil and plate to laterally escape.

6. A device as claimed in claim 1 wherein the level of said liquid is the same as the level of said anvil in biased position.

7. A device as claimed in claim 6 wherein holding means are provided on said anvil to prevent the workpiece from catapulting upwards while allowing the explosive forming thereof.