GB2251570A - Improvements in or relating to vibratable ring-like structures - Google Patents

Abstract

A vibratable drawing die presenting a central, circular die orifice of mean radius A and a circular and coaxial outer surface of radius B, and having at least two radial projections 8 disposed symmetrically around the outer surface to which vibrators can be attached. Efficient transmission of energy from the vibrators to the wall of the die orifice is promoted by designing the die so that its imaginary circumference at its mid-radius - that is to say, a radius equal to the mean of the sum of A and B - equals n times the wavelength of the applied vibrations where n is a positive integer, and by dimensioning the arcuate width of each projection to half a wavelength. Examples of dies according to the invention having two, four and six projections are illustrated. The specification also teaches enhancing performance further, by equating certain other dimensions of the die to functions of the wavelength of the applied vibration. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO VIBRATABLE RING-LIKE STRUCTURES This invention relates to vibratable ring-like structures, and in particular to drawing dies capable of being set into standing waves of vibration at ultrasonic frequency, such that the walls of the orifice vibrate in what is substantially a radial mode. That is to say the orifice, as seen in a section taken at right angles to its axis, generally changes continuously in size but without substantial change of geometrical shape. In the typical case where the sectional shape is circular, the length of any radius of that ring therefore oscillates continuously, at the resonant frequency, between a maximum and a minimum value.In this specification, when talking of drawing dies, we include not only single ring-like structures to which vibrators can be directly attached, but also interfitted combinations of a central die or other ring member, and a surrounding resonator structure to which the vibrators are attached.

Dies capable of vibrating radially, and the means to set them into such vibration in a resonant state, have been proposed in several prior patent specifications and technical articles, for instance specification GB-A-1389214 and an article entitled "Radial Mode Vibrators for Oscillatory Metal Forming" in "Applied Acoustics" (3) (1970), pages 299-308. In both that specification and that article, one simple if approximate condition for achieving resonant vibration in such a die is stated by the following formula : the mean circumference of the die - that is to say, its circumference at the mean between its effective inner and outer radii - should equal an integral number of wavelengths.

Since 1970 the correctness of that approximate rule has frequently been demonstrated, for dies suitable for drawing small diameter wire, rod, cans and other products of both solid and hollow section. However a practical limitation has also become apparent. While it has proved relatively simple to achieve a substantial degree of radial vibration by applying the formula stated above to dies in which the diameter or other transverse dimension of the orifice is relatively small, it has proved impossible to achieve substantial radial oscillation, at the fundamental frequency of vibration, when that dimension exceeds say 50 millimetres.Attempts to generate similar vibration by simply applying the formula to dies of larger orifice diameter have resulted in setting the walls of the orifice into a variety of regimes of vibration, at a variety of frequencies in which the desirable radial mode is converted into elliptical and many other less desirable modes.

The present invention results from appreciating that in order to set a larger-orifice die into useful radial vibration, and to diminish to an acceptable level the proportion of other less desirable modes of vibration that will inevitably be present also, it is necessary to modify the outer radial surface of the die. The invention is defined by the claims, the contents of which are to be read as included within the disclosure of this specification, and the invention will now be described by way of example with reference to the accompanying drawings in which : Figures 1 to 3 are simplified plan views of three different rings; Figure 4 is an enlarged section through part of the ring of Figure 2, on which some dimensions and other constructional details are indicated, and Figure 5 is an elevation taken in the direction of the arrow V in Figure 4, but on a smaller scale.

Figures 1 to 3 each show a generally circular ring-shaped die 1 presenting a conventional, slightly frusto-conical drawing orifice 2. References 3 and 4 indicate the upper and lower rims of that cavity respectively, and reference 5 indicates the circumference at the mid-height of the die at which the cavity 2 will present its mean internal diameter, to be referred to as DMI. Reference 6 indicates the geometrical centre of the die, and the drawing axis which it defines in use. Reference 7 indicates a circular outer surface of the die, of diameter DV.

This surface corresponds, for vibrational considerations, with the outer surfaces of known vibratable die assemblies as shown for example in Figures 1 and 3 of specification GB-A-1389214, already mentioned. According to the present invention, however, that surface is interrupted by a number of projections 8, distributed axisymmetrically around centre 6 and presenting end faces 9. In Figure 1 there are two such projections, in Figure 2 there are four and in Figure 3 there are six. As Figure 5 shows best, each projection 8 is substantially rectangular in cross-section. The upper and lower faces of the projection are aligned with the upper and lower faces 10 and 11 of the rest of the die, and the length of the parallel side walls 12 is thus equal to the axial thickness 13 of the die.

In Figure 4 DMI and DV of the die of Figure 2 are clearly indicated, and also DM, which equals (DMI + DV)/2. According both to the present invention and to the teaching of the prior publications that have already been referred to, the length of diameter DM should be chosen so that the imaginary circumference 15, drawn at that diameter, is substantially equal in length to a whole number of wavelengths X of the resonant vibration that is to be set up within the die.Where the die orifice 2 is of small diameter, as is contemplated in the prior publications already quoted, such a matching of DM with the frequency of the applied vibration may in practice be enough to set the surface of the orifice 2 into substantially radial vibration at the same frequency, in a simple ring-shaped die in which the outer surface 7 has a simple circular outline, as indicated by the broken line 14 in Figure 4. As has already been stated, however, it has been found that this is more difficult to achieve, the larger the diameter of the die orifice becomes relative to outer diameter DV.According to this invention the radial oscillation of the orifice surface, in a large-orifice die or other ring-like structure, is improved by interrupting the outer surface with the projections 8, and preferably by generating the oscillation by vibrators, indicated in outline at 16 and attached directly to the outer end faces 9 of the projections. In the example shown in Figure 4 the threaded end 17 of a suitable transducer, of a kind well known in this art, is received by a threaded bore 18 opening onto a small flat 19 formed on the part-circular outer end face 9.

I have found that for a die with a large central orifice but with a typical axial thickness (13, Figure 5) of say one quarter of the wavelength of the resonant vibration, the radial and circumferential and radial dimensions of the projections 8 are significant. As indicated in Figure 4 the arcuate dimension 20 of a projection, taken at a radius substantially half-way between its outer end 9 and its inner end, which corresponds to circumference 4 (diameter DV) should be substantially equal in length to X/2. Secondly, the diameter D2 of the imaginary circle 22 which forms the locus of the outer end faces 9 of the projections 8 should exceed diameter DM by about pyx/2, where p is a positive and uneven integer and preferably, as shown, is equal to unity.That is to say, distance 24 (Figure 4) is equal to pyx/4, with p, as shown, again being equal to unity. Preferably the ends 9 of the projections, apart from the small parts of them that are flattened at 19, have a circular outline 23 that conforms to circle 22.

A simplified explanation of the significance of giving the dimensions 20 and 24 the respective values X/2 and pyx/4, as just described, runs as follows. Firstly, the natural effect of making each projection 8 with an arcuate width 20 of length W/2, and attaching to the outward end of that projection a vibrator 16 which generates vibration of wavelength X within the struct-ure, is to set up a standing half-wave of vibration within that projection, beginning with a displacement anti node (and therefore a stress node) on one side wall 12; rising to a stress antinode and displacement node on the centre radius (26, Figure 4) of the projection, and falling to a displacement antinode at the other side wall 12. Because the projection is parallel-sided, this pattern of transverse vibration will tend to exist to a substantial degree over the entire radial length of the projection, including its inner end, where as already stated the arc (14) shares the same diameter DV as the cylindrical outer surface 7 of the main body of the die 1. A degree of circumferential vibration of wavelength X is thus promoted within the main body of the die, and provided the imaginary circumference 15 at diameter DM is equal in length to an integral number of wavelengths as already explained, a degree of resonant radial vibration at the surface of the inner orifice 2 should follow. Maximum amplitude of the resonant radial-mode vibration at that surface is promoted, as one would expect, by maximising the amplitude of the resonant vibration around circumference 15.

The key to maximising that vibration lies in the pattern of the standing transverse vibration existing within the projections 8, and in particular in the stress anti node - already referred to of such vibration existing along the mid-radius 26. It is therefore to be expected that corresponding stress anti nods of circumferential vibration around circumference 15 will occur at those points (25) where that diameter intersects the centre-radii 26 of the projections 8. However, it is also obvious that anti nods of vibratory displacement, and therefore stress nodes, must be set up at the outer end faces 9 of the projections 8, that is to say where the transducer 16 are attached to them at diameter D2.Therefore, because stress nodes and anti nods are separated by a distance of pyx/4 in any resonant system, for maximum efficiency the radial distance from the mid-radius of the die (at diameter DM) to the outer end face of each projection (at diameter D2) should equal pX/4, where p is any odd and positive integer and particularly when p is unity.

It should be noted that by giving the projections 8 a slightly tapering shape, as indicated by broken lines 12a in Figure 4, instead of truly parallel sides, performance may be improved by causing the arcuate width to be more equal to W/2 over the entire radial length of the radius, rather than at only one value of that radius.

It will be apparent that if a die as shown in Figures 2 and 4 is modified by changing DMI, without a corresponding change in the frequency of the applied vibration, then DM and so D2 must also stay unchanged. This requires a change in DV. Thus if DMI is diminished DV must increase, so that the difference between DV and D2 diminishes and the radial dimension of projections 8 falls also. Conversely if DMI increases then DV must fall, and the radial dimension of the projections increases.

In the ring of Figure 1, which has two projections 8 each carrying a vibrator 16, circumference 15 at DM has a length of X and two stress anti nods (indicated at 25a) are set up along it.

In Figure 2, where a vibrator is mounted on the end of each of the four projections, circumference 15 will be 2X in length and four stress antinodes (25b) will be set up along it. In Figure 3, where a vibrator is mounted on the end of each of the six projections, circumference 15 will be 3X long and six stress anti nods (25c) will be set up.Although it is preferred to mount the vibrators on the end faces of the projections, as shown in all the illustrative figures, it is within the scope of the invention that the vibrators could be attached to the total structure elsewhere, provided the arcuate width of the projections is still W/2 and thus promotes a potential pattern of circumferential vibration within the ring, and provided the distances between the points of attachment of the vibrators, and the stress anti nods of the circumferential vibration at DM, are sympathetically related. It will be clear that the invention also applies to dies with more projections, and in which the length of the corresponding circumference 15 is equal to a higher multiple of x, and generally that the invention can apply to any die where an even number of stress anti nodes, equally-spaced apart, are set up along the imaginary circumference corresponding to diameter DM, and each such antinode lies radially-inboard of a corresponding projection. While maximum amplitude is promoted by attaching a vibrator to each projection, the invention still applies if some of the projections carry no vibrator, and ultimately if only one vibrator is present.

Claims (9)

1. For use in attachment to vibrators capable of generating vibrations of wavelength X within it, a drawing die or other ring-like structure presenting a central, circular orifice with a surface of mean radius A and a circular and coaxial outer surface of radius B, and including at least two radial projections disposed axisymmetrically around the outer surface, in which the imaginary circumference of the structure at its mid-radius, that is to say a radius equal to the mean of the sum of A and B, is subtantially equal in length to nX, where n is a positive integer, and in which the arcuate width of each projection, that is to say the transverse width between the side faces of the projection measured as a length of arc about the axis of the strucutre and at a radius coinciding substantially with the mid-length of the projection, is substantially equal to X/2.

2. A ring-like structure, for use according to Claim 1 in which the side faces of each projection lie parallel to the radial direction with which that projection is aligned.

3. A ring-like structure, for use according to claim 1, in which the outer end faces of the projections are adapted for the vibrators to be attached to them.

4. A ring-like structure, for use according to Claim 3, in which the radial distance from the mid-radius of the structure to the outer end face of each projection is equal to pyx/4, where p is a positive uneven integer.

5. A ring-like structure, for use according to Claim 1 having an axial dimension of about A/4.

6. A method of using a ring-like structure according to Claim 3, in combination with vibrators to set it into a standing wave of ultrasonic vibration, in which a stress antinode is established substantially at the mid-radius of the structure, along the radius of alignment of each projection to which a vibrator is attached.

7. A method of using a ring-like structure according to Claim 1, in combination with vibrators to set it into a standing wave of ultrasonic vibration, in which a displacement anti node is established upon the side faces of the projections.

8. A ring-like structure, for use according to Claim 1, in which the projections have a substantially rectangular shape when viewed in transverse section relative to the radius with which they are aligned.

AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS 7. A method of using a ring-like structure according to Claim 1, in combination with vibrators to set it into a standing wave of ultrasonic vibration, in which a displacement antinode is established upon the side faces of the projections.

8. A ring-like structure, for use according to Claim 1, in which the projections have a substantially rectangular shape when viewed in transverse section relative to the radius with which they are aligned.

9. A ring-like structure, for use according to Claim 1, substantially as described with reference to the accompanying drawings.

10 A method of using a ring-like structure in combination with vibrators to set it into a standing wave of ultrasonic vibration, according to Claim 6 and substantially as described with reference to the accompanying drawings.