IMPROVEMENTS RELATING TO CUTTING DEVICES

Abstract: A cutting device comprises an annular cutting member (6) provided with a flat drive face (8) on one side of a diametral plane, by which the cutting member (6) is attached to an ultrasonic horn (10) providing a source of ultrasonic vibrations. The face (8) is arranged to constitute an anti-node of the device (a portion of maximum displacement), and the centre of the aperture 12 of the member (6) provides a theoretical node (portion of no displacement). The relative values of R1, the radius of the hole of the cutting member (6), and R2, the outer diameter thereof, are selected, in dependency on the physical characteristics of the cutting member itself, such that the member (6) vibrates radially inwardly and outwardly, in a pulsating manner. The member (6) is provided with a circumferential cutting edge (14) subtending an angle of about 180 DEG on the opposite side of the drive face (8) by which a cutting action may be obtained.

Description: Title: Improvements relating to cutting devices Description of Invention This invention is concerned with improvements relating to cutting devices, particularly cutting devices which are operative at high (ultrasonic) frequency. According to this invention there is provided a cutting device comprising: [a] a cutting member having on one side of a diametral plane a driving face to be attached to a source of ultrasonic vibrations, said vibrations acting in a direction radially of the member; and [b] a cutting edge on the other side of said diametral plane. Preferably the cutting member is generally annular, but may be provided in its outer surface with "flats", or surfaces curved on different centres. By attachment of a circumferential portion of the cutting member to (e.g.) an ultrasonic horn at an anti- node, the centre of the annulus constitutes a theoretical anti-node, and vibration will occur alternately radially outwardly and inwardly from the centre of the annulus, so that the cutting member effects a "pulsation". Thus, the cutting edge may subtend at an angle of between 45° and 270°, although in practise a cutting edge above 180° is unlikely to be of wide value, and preferably the range of the cutting edge is between 60° and 160°, with a cutting edge vibrating radially of the annular cutting member. The cutting edge may be V-shape in cross-section, or two parallel cutting edges may be provided by machining a V-shape or U-shape groove into circumference of the cutting member at least over the circumferential distance thereof required to perform a cutting operation. Such a cutting device may be used for cutting brittle and hard materials, such a ceramics or concrete, or soft materials, such as fabric, or foodstuffs. A theoretical analysis of radial vibrations in thin annular discs can be found in Young, Winsper and Sansomes papers in Applied Acoustics vol 3 1990 P212-216. The wave equation for pure radial simple harmonic motion can be written as:- d 2 Ur 1 ( dUr ) ( 1 ) + - ( ) + (K- ) Ur=0 (1) dr r ( dr ) ( r 2 ) Ur is the particle displacement in a radial direction at radius r and k is the wave number. Where W is angular velocity Cr is wave velocity in a radial direction E is Young's Modulus ) For the material p is density ) in question v is Poisions ration ) Equation (1) is a well known Bessel equation and a discrete solution is obtained for radial motion (after Watson 1962 Theory of Bessel Functions; London, Cambridge University Press) for an annular ring with inner and outer radii RI and R2 or at RI and R2 with zero stress. In the region 1 >KR1> 0.3 a simple approximate solution can be written K (RI + R2) = 2n (2) Where n is an integer, which means that radial motion occurs when the mean circumference of the annular ring (RI + R2) is equal to an integral number of wavelengths. The analysis shows that radial motion is independent of disc thickness. Finite Element modelling (eg PAFEC'S FEA Computer Programmes, Nottingham, UK) now enables the disc dimensions to be calculated to show that the radial mode vibration of a disc 150 mm outer and 50 mm inner diameter, and of aluminium with 4% copper alloy giving vibrational frequency of 18.2 kHz. Thus, preferably the ratio of the inner radius RI to the outer radius R2 of the annular disc is determined by the equation K (RI + R2) = 2N, to within an accuracy of plus/minum 5%. The device may comprise a plurality of cutting members secured (e.g. by welding or bolting) in parallel array to a single drive member, to enable a plurality of parallel cuts to be produced simultaneously. The invention will become more clear from the following description, to be read with reference to the accompanying drawings, of cutting devices which have been selected for the purposes of illustrating the invention by way of example. In the accompanying drawings: FIGURES la. and lb. are respectively side and front elevations of a cutting • device which is the first embodiment of the invention; FIGURES 2a, and 2b are respectively side and front elevations of the cutting device which is the second embodiment of the invention; and FIGURE 3 is a schematic view showing a multi-bladed cutting device. The device which is the first embodiment of the invention comprises an annular cutting member 6 having an inner radius of 50mm and an outer radius of 150mm, the cutting member being of aluminium with 4% copper alloy. The member 6 is provided with a flat drive face 8 on one side of diametral plane, by which the cutting member is attached to an ultrasonic horn 10 providing a source of ultrasonic vibrations at a frequency of 18.2 kHz. The face 8 will constitute an anti-node (portion of maximum displacement) and the centre of the aperture 12 of the member 6 providing a theoretical node. With such a construction, the member 6 vibrates radially inwardly and outwardly, as shown by the arrows, in a pulsating manner. The member 6 is provided with a circumferential cutting edge 14 subtending an angle of about 180° at the centre of the member which in the operation of the drive vibrates at a substantially uniform amplitude, allowing when the device is moved in the direction of the arrow A through a substrate 18, a cutting action to be effected. In the second embodiment, parallel cutting edges 20a, 20b . are afforded by the provision of a generally U-shape groove or channel into the circumferential edge of the cutting member, to enable twin cutting tracks to be provided. In the embodiment illustrated in Figure 3, a plurality, specifically three cutting member 6a, 6b. 6c, each similar to the cutting member illustrated in Figure 1, are connected in parallel to a multi-stage ultrasonic horn 28, whereby the cutting edges 14 are all caused to vibrate together, enabling a multiple cut to be obtained in the substrate. It will of course be appreciated that by the utilisation of a cutting member of the kind illustrated in Figure 2, a multiple increase of the number of cuts may be obtained. By the use of the invention a significantly deeper cut than may conventionally be obtained may be made, and the device may be used to cut a wide variety of materials, including those with which difficulty may otherwise be experienced. Whilst in the preferred embodiment the cutting member is annular, if desired "flats" or alternatively curved faces may be provided on the other drcumference. The features disclosed in the foregoing description, or the accompanying drawings, expressed in their specific forms or in the terms or means for performing the desired function, or a method or process for attaining the disclosed result, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims: CLAIMS 1. A cutting device comprising (a) a Cutting member (6, 6a, 6b, 6c) having on one side of a diametral plane a driving face (8) to be attached to a source (10) of ultrasonic vibrations, said vibrations acting in a direction radially of the member; and (b) a cutting edge (14, 20a, 20b) on the other side of said diametral plane. 2. A cutting device according to Claim 1 wherein the cutting member is generally annular, being provided on its outer surface with a flat, or a surface curved on a different centre, constituting said driving face 8. 3. A cutting device according to one of Claims 1 and 2 wherein the cutting edge subtends an angle of between 45° and 270°, preferably between 60° and 160°. 4. A cutting device according to any one of the preceding claims wherein he cutting edge is V-shape in cross section. 5. A cutting device according to any one of Claims 1, 2 and 3 wherein to parallel cutting edges (20a, 20b) are provided by machining a V-shape or U- shape groove into the circumference of the cutting member at least over part of the circumferential distance thereof. 6. A cutting device according to any one of the preceding claims comprising a plurality of cutting members (6a, 6b, 6c) secured in parallel array to a single drive member 28. 7. A cutting mechanism comprising an ultrasonic device (10) and an annular cutting member (6), the cutting member comprising a flat drive surface (8) on the circumference thereof attached to the ultrasonic device (10), and a circumferentially extending cutting edge (14, 20) located generally opposite to the drive face. 8. The invention according to any one of the preceding claims wherein the values of the inner radius RI and the outer radius R2 are in approximate accordance with the equation K (RI + R2) = 2N. 9. The invention according to Claim 8 wherein said approximation is to within plus/minus 5%.

Inventors: RAWSON FRANCIS FREDERICK HAMIL, RAWSON, FRANCIS, FREDERICK, HAMILTON
Applicants: RAWSON FRANCIS F H, RAWSON, FRANCIS, FREDERICK, HAMILTON
Application year: 1993
Main classification: B26D7
IPC codes: B26D7