GB2216223A - Radially-resonant structures - Google Patents

Abstract

A resonator, for use especially in the ultrasonic vibratory forming of metals, comprises a block 2 of cylindrical or other generally axisymmetric shape, formed with a central cavity 3, Fig 2. Vibrators 19, 15, 16 are attached to the outer wall 8 of the block, at least one mandrel 33 or other vibratable member is also attached to the outer wall of the block, and the block is tuned so that the resonant radial vibration into which it is set, by way of items 15, 16, and 19 attached to its outer wall, is transmitted by way of that same outer surface to mandrel 33. The block may be attached to supporting structure by means of a tube 52 which passes through and engages with the central cavity 3. Arrangements are described and illustrated whereby more than one vibrator unit, and more than one vibrated unit, may be mounted on the outer wall of a single axisymmetric block. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO RADIALLY-RESONANT STRUCTURES This invention relates to radially-resonant structures, by which we mean structures presenting an axis and of generally symmetrical shape about that axis, and capable of being set into a standing wave of resonant radial vibration by means of vibration generators attached to them at their outer periphery.

It relates in particular to resonators for use in the ultrasonic vibratory forming of metals. Examples of such resonators are described in several published UK patent specifications, for example numbers 1389214, 1434533 and 1470053.

In all of those examples the resonator has the general shape of a hollow cylindrical block. Vibratory energy is supplied to it by way of vibration transducers fixed to its outer periphery, and useful vibratory energy is extracted from the inner periphery, which is formed as or supports a hollow die through which solid or hollow metal components are drawn.One limitation of such equipment is that because the vibrations are ultrasonic the wavelength of the energy tends to be quite short (of the order of 250mm at 20 KHz, say) and efficient transfer of vibratory energy from the resonating structure to the workpiece at the die-workpiece interface requires that that interface should be located at some distance from the centre of the resonator, that is to say at some radial distance from the displacement node of the standing wave of radial vibration which exists at the centre of the resonator. This sets a lower limit to the diameter of the die.

The present invention arises from appreciating the potential advantages of extracting useful vibratory energy from a quite different part of the resonator, and in particular from appreciating that if the central region of the resonator is used for mounting it, instead of for extracting energy from it, what was previously a limitation can be turned into an asset.

According tos the present invention a resonator comprises a structure of generally axisymmetric shape, adapted to be set into resonant radial vibration relative to the axis, in which there are means at the outer wall of the structure to attach at least one vibrator to set the structure into the said radial vibration, and in which there are also means at the outer wall of the structure to attach at least one vibratable member, whereby the radial vibrations of the structure may set such member or members into vibration. The resonator may include mounting means for the structure, these means engaging with the structure in the region of the axis.

The mounting means may be in the form of a bracket comprising two parallel and spaced-apart plates between which the structure lies with clearance, and a shaft which is attached to the plates and spans the gap between them, and also passes through and engages with a central cavity of the structure, and there may be means, at the end of the bracket remote from where it engages with the resonant structure, to attach it to a support. The attachment means may be in the form of a cylindrical spigot, threaded to receive a nut. The shaft may be hollow.

The outer wall of the structure may be formed so as to receive two vibrators at points diametrically-opposite each other relative to the axis, and to receive one vibratable member at a point substantially mid-way between the points where the two vibrators are attached. Alternatively the outer wall may be formed so as to receive four vibrators at points spaced from each other by 90" of arc relative to the axis, and to support one vibratable member at a location mid-way between two adjacent vibrators, or formed to support three vibrators at locations spaced from each other around the wall, and to support two vibratable members at locations spaced equally one to each side of one of the vibrators.

The outer wall of the structure will typically be cylindrical but could also be of other generally axisymmetric configuration, for instance spherical or part-spherical.

The vibratable member or members will typically be of elongated shape, and be adapted to be set into longitudinal vibration by the vibrating structure to whose outer wall they are attached. However, the invention also includes members of different shape, adapted to be set into vibration of a different type. For instance the vibratable member could include a second structure of generally axisymmetric shape, adapted to be set into resonant radial vibration by being connected to the first structure. The connection will typically be in the form of a short bar connected to the outer walls of the two structures and lying radially relative to each of them.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a radial section through a resonator and associated parts; Figure 2 is a section on the line II-II in Figure 1 through some of the parts shown in that Figure, and Figures 3 to 5 are diagrammatic plan views of two alternative arrangements.

In Figure 1 the resonator 1 comprises a cylindrical block 2 formed with a central cavity 3. Reference 4 (Figure 2) indicates the axis of the cylinder.

Three flats 5 to 7, spaced from each other by right angles of arc relative to the axis 4, are formed on the outer wall 8 of the block 2, and threaded bores 9, 10 and 11 are drilled radially inwards from these flats respectively. The end faces of vibrator concentrator horns 15 and 16 are held in firm contact with flats 5 and 7 respectively by threaded studs 13 and 14 which engage with the bores 9 and 11 and also with corresponding bores 17 and 18 formed in the two horns. Magnetostrictive vibration transducers 19 are mounted on the rearward faces 20 of horns 15 and 16, and are excited by an electrical power supply indicated schematically at 21.Transducers 19 are protected from damage by cylindrical housings 22, clamped by collars 23 to flanges 24 which are mounted on the bodies of horns 15, 16 at locations which will correspond in use with displacement nodes of the vibration set up by transducers 19, thereby minimising wasteful transfer of vibratory energy to the housings 22 from the horns 15, 16. The housings 22 are formed with vent holes 25 and inlet pipes 26, for connexion to air blowers 27, to promote the movement of air through the housings to cool the transducers 19.

It is well known in the art, as exemplified by the published UK patent specifications already recited, that transducer/horn combinations such as 19, 15, 16 can be tuned to ultrasonic frequencies so as to excite a resonator such as item 1 into resonant radial vibration, that is to say vibration in which all elements of the resonator 1 are in continuous and synchronised oscillation along a line normal to the axis 4 and passing through the element concerned. In each of the recited prior publications the useful vibratory output from the resonator was taken from a central cavity, such as item 3, within which a hollow metalforming die was mounted. According to the present invention the energy output is extracted from the outer wall 8 of the resonator 1. The opposite ends 30 and 31 of a stud 32 are threaded. End 30 engages with threaded bore 10 in flat 6, and end 31 engages with a threaded bore in the end of a long mandrel 33. A spacer collar 34, prevented from rotation relative to stud 32 by the engagement of a key 35 with a keyway 36, ensures an ascertained clearance between flat 6 and the end face 37 of mandrel 33, and flats 38 are formed on the body of the mandrel so that it may be turned by a spanner to achieve tight contact between body 2, stud 32, collar 34 and mandrel 33. It will be apparent that the resonant radial vibrations of resonator 1 will be transmitted to mandrel 33 as lengthwise vibrations of that body, aligned with its long axis 39.As is well known in the art, particularly from UK Specification No. 1380421, such vibrations of a metal drawing mandrel may substantially reduce the loads and otherwise improve the efficiency of a metalforming operation in which the mandrel is involved. At the foot of Figure 1 there is a diagrammatic respresentation of a tube 40 being reduced in section by being drawn by jaws 43 through a die 41 over a plug constituted by the shaped tip 42 of mandrel 33.

The mounting of resonator 1 and of its attached parts, as already described, is provided by a bracket-like structure comprising two rectangular plates 50, 51 spanned by a hollow tube 52 which passes through and makes an interference fit within the central cavity 3 of the block 2. There is clearance between the end faces 53 and 54 of the block 2 and the inner faces 55 and 56 of the plates 50 and 51. These clearances are ensured by spacer bushes 57, and bushes 58 locate and hold the ends of tube 52 within cavities formed in the plates. A bolt 59 holds plates 50 and 51 against opposite side faces 60 and 61 of a spacer block 62, and a clearance 63 is ensured between one end face 64 of that block and the outer wall 8 of block 2.A spigot 65 projects from the other end face 66 of block 62, and the cylindrical end of spigot 65 is threaded at 67 to engage with a nut 68 by which the resonator and its mounting structure, as so far described, may be attached to other structure indicated in outline at 69 in Figure 1. If mandrel 33 supports a vibratory but otherwise stationary plug, over which tube 40 is drawn through a die 41 by jaws 43 as already described, structure 69 will be stationary. If, however, a deep-drawing punch were substituted for the mandrel 33 then the structure 69 would of course by part of the moving punch mechanism, and capable of the reciprocating movement which it must impart to the punch.

Figure 3 shows in outline an alternative arrangement in which the cylindrical block 2 is again supported by plates 50 and 51 and supports a single output member 70 (the equivalent of mandrel 33), but is now driven not by a pair of horn/transducer assemblies but by four of them, arranged as indicated at 90-degree spacing at 71 - 74, with the output member 70 meeting the outer wall 8 of block 2 midway between units 71 and 74. In the further alternative arrangement shown in Figure 4 the resonator 1 carries three horn/ transducer assemblies 75 - 77 located as shown at 90" - 135 - 135 spacing from each other and two output members 78, the latter located 450 to each side of horn/transducer assembly 77.

Figure 5 shows a further embodiment of the invention even more diagrammatically. In the embodiments of Figures 1 to 4 the output members (33, 70, 78) have all been of elongated shape and have been set into resonant longitudinal vibration in response to the radial vibration of the cylindrical block 2. In Figure 5 a cylindrical block 80 is set into resonant radial vibration by the bl-ock 2, to which it is connected by a short bar-like member 81.

To achieve resonance the dimensions of both block 80 and bar 81 must of course be carefully chosen, and in particular the length of the bar will require to be substantially equal to an integral number of half-wavelengths of the resulting radial vibration of block 80.

While the invention as illustrated by Figures 1 to 4 has been described with relation to an output member (33, 70, 78) in the form of a mandrel or punch, other output members in the forms of waveguides, other tools or plain bars are of course within the scope of the invention. It should also be noted that although the horns and output members described by way of example in this specification have all projected from the resonator in a direction at right angles to the axis 4, it is also within the scope of the invention that they could also project at other angles, although still lying within radial planes relative to axis 4: such orientations could, for instance, release more space on the outer wall of resonator 1 for the support of further vibrators and/or output members Finally it should be noted particularly that because the output energy of the system is extracted essentially from the outer wall of resonator 1, the diameter of cavity 3 (and of tube 52 which fits within it) is not critical to the operation of the device. Indeed it is possible to contemplate doing away with the cavity 3 entirely by using a solid circular-section block and supporting it in some way quite different from the illustrated tube 52. In practice, however, efficient operation of the body 2 as a radial resonator is likely to be promoted by having a central cavity no greater in diameter than is necessary to receive a tube 52 of adequate strength to support the resonator.

This is to be contrasted with the requirements of the apparatus described in the prior specifications already recited in this specification, in which the useful output of the resonator was taken from the central cavity, so constraining the minimum value of the radius of that cavity as already described.

Claims (11)

1. A resonator comprising a structure of generally axisymmetric shape, adapted to be set into resonant radial vibration relative to the axis, in which there are means at the outer wall of the structure to attach at least one vibrator to set the structure into the said radial vibration, and in which there are also means at the outer wall of the structure to attach at least one vibratable member, whereby the radial vibrations of the structure may set such member or members into vibration.

2. A resonator according to Claim 1 including mounting means for the structure, these means engaging with the structure in the region of the axis.

3. A resonator according to Claim 2 in which the mounting means engage with a central axial cavity passing through the structure.

4. A resonator according to Claim 3 in which the mounting means is in the form of a bracket comprising two parallel and spaced-apart plates between which the structure lies with clearance, and a hollow shaft which is attached to the plates and spans the gap between them, and also passes throught and engages with the central cavity of the structure.

5. A resonator according to Claim 4 in which there are means, at the end of the bracket remote from where it engages with the resonant structure, to attach it to a support.

6. A resonator according to Claim 5 in which the attachment means are in the form of a cylindrical spigot, threaded to receive a nut.

7. A resonator according to Claim 1 in which the outer wall of the structure is formed so as to receive two vibrators at points diametrically-opposite each other relative to the axis, and to receive one elongated vibratable member at a point substantially mid-way between the points where the two vibrators are attached.

8. A resonator according to Claim 1 in which the outer wall of the structure is formed so as to receive four vibrators at points spaced from each other by 90" of arc relative to the axis, and to support one elongated vibratable member at a location mid-way between two adjacent vibrators.

9. A resonator according to Claim 1 in which the outer wall of the structure is formed to support three vibrators at locations spaced from each other around the wall, and to support two vibratable members at locations spaced equally one to each side of one of the vibrators.

10. A resonator according to Claim 1 in which the vibratable member and the structure are both of generally axisymmetric shape, are arranged with their axes parallel and are joined by a member attached at one end to the outer wall of the structure and at its opposite end to the outer wall of the vibratable member, whereby the radial vibrations of the structure may set the vibratable member into resonant radial vibration.

Amendments to the claims have been filed as follows 9. A resonator according to Claim 1 in which the outer wall of the structure is formed to support three vibrators at locations spaced from each other around the wall, and to support two vibratable members at locations spaced equally one to each side of one of the vibrators 10. A resonator according to Claim 1 in which the vibratable member and the structure are both of generally axisymmetric shape, and are joined by a member attached at one end to the outer wall of the structure and at its opposite end to the outer wall of the vibratable member, whereby the radial vibrations of the structure may set the vibratable member into resonant radial vibration.

11. A resonator according to Claim 1 substantially as described with reference to the accompanying drawings.