US2806328A - Vibratory tools - Google Patents

Description

Sept 17,-1957 G. BRADFIELD 2,806,328

VIBRATORY TooLs Filed Jan. 29, 1955 2 sheets-smet 1 /N VE N TOP l Geoffrey Brad/'e/o' A TTOPNEY SePt- 17, 1957 G. BRADFIELD 2,806,328

VIBRATORY TOOLS Filed Jan. 29, 1953 2 Sheets-Sheei 2 Fig. 4.

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Patented Sept. 17, 1957 lice vIRAToRYrooLs Geolrey Bradield, Teddington, England, assignor to Council for Scientific and` Industriali Research, London,` England, a corporationof Great Britain Application January 29, 1953, Serial No. 333,989

Claims priority, applicatiorfL Great Britain JanuarySI, 11952 9 Claims. (CII. 51-59) This invention relates`- to supersonic oscillators or transducers and to vibratory tools such as dent-al drills and engraving tools incorporating such oscillators.

A transducer according to the invention .comprises a bar member of magnetostrictive material, the length of which is an integr-al odd multiple,rincluding a unit multipl'e, of one half Wavelength `at the frequency atwhi'ch the transducer is to be operated, helical windings around said bar member, an magnetic yoke, spacedV pole pieces around said yoke co-Operating with said'bar member, and means yanchoring said bar member Alongitudinally in relation to said unit at the' nodes of vibration without substantially hinderingthe transverseexpansion and contraction of said bar member while it is in vibration. The bar member may be a solid block of magnetostrictive material such as a ferrite, if it is substantially non-conductive so that substantially no eddy currents dow, or it may'beof Ilaminated structure if the material is conductive. To' constitute a vibratory tool the transducer may be provided with a tapering shank of a material of low internal damping, e. g. steel, secured at its-larger end to one end of the transducer bar member and: carrying or' constituting an abrading tip at its smaller end, andthe overall length ofthe tool-and. frequency being" such that having regard to the material of the shank if any and of the oscillator, the tool as a whole vibrates in. substantially free-free mode, in which case the abrasive tipend" is a vibration anti-node. This last condition' may be ensured by making the length of the shank effectively equal to one half wave length of the operating frequency (or an odd integral` multiple thereof). If, however, the material of the shank and of the oscillator are matched as to characteristic impedance and Poissons ratio, rigid adherence to the foregoing length requirement is not essential; it being then merely `necessary to 'adjust the overall length of the toolto provide vibration-anti-nodes at the extremities of the assembly. To enable the `abrading tip to` be exchanged, a face-to-face joint with seating surfaces having a surface finish such that irregularities are of the order of =a few microns or less may be provided at ya suitable point between the transducer bar member and the abrading tip convenientlyat the large end of the tapering shank, thus giving a large area for the transmission of energy. An oil or a` material such as a wax, resin or low temperature solder is used at the joint to ensure satisfactory transmission of energy.

The abrasive tip itself may seat on carefully prepared surfaces as described above, and may then be secured in or' clamped by a metal sleeve which screws `on to the shank or oscillator. The tip may be of abrasive material, e. g., diamond, or the action of the abrading tip enhanced by the use of powdered abrasive suspended in oil or other liquid between the tip and the work. In general such av practice permits the use of points which arey made'of some relatively soft material (i. e., readily fabricated) such as mild steel. The tip can take the form of the desired peripheral shape `of the hole, i. e., square tube to trepan a square-hole, an oval tube to cut an oval hole and the like. This is of especialV value when soft tips are usedrsince these can readily be` fabricated in the desired form".

It isi preferable to= set the transducer in excitation uslng feed back from a separate or built-in electrode mechanical transducer actuated by the mechanical' Inotion. Such feed-back transducer may be attached to the transducer bar memberattheopposite end to the tapering section leading tothe abrasive tip.

The invention will. be further described with reference to the accompanying drawings, in which:

Fig. l is' `a longitudinal section of an example of the invention` embodying. a magnetostrictive transducer;

. Fig. 2` isa longitudinal section taken at right angles Ito Fig. l`;`

. Fig. 3 isvaldetail crosssection; Figure 4 is` ai detail of Figure 2 on an enlarged scale g with. thef bar member in section.

Fig. 5 isa diagrammatic cro'ss section of a modifica tion ofmagnetostrictive transducer;

Fig. 6 is a detail longitudinal section corresponding to Fig. 5;A

i Fig. 7 `is a diagram: illustrating `a preferred mode of excitation. of `the magnetostrictive type of transducer.

Fig. 8` isfavdet'ailf s'ho'wing one way of securing the abrasive tip;

Figs.` 9" and `l() .are'details`.sl1owin`g` a quick action clamp;

Figure l1 isa diagrammatic view of another modiiica- .tion for applying greater mechanic/al forces at one point.

. In -the example shown in Figs. ll to 4, a `separate tapering `section. 1 is used,- for' example of steel tapering .from a transverses'eatingl-Z- at the larger `end,\v/hicl`1` may -seating 4 'at the other end. The base of the section 1 is held toftheexci'ting means the aid of'a clamping ring 5"or`the like,l which bears against" the flange 3 and carriesY a` split' clamp 6 or, the likepwhich engagesaA ange ouv the exciter. The ring `5 conveniently carries the clamp 6 by screws, enabling the clamping pressure to be applied: and varied. It will be` understood thatthe seating. surfaces are highlyV finished and-:make good contact over a large are'a so that satisfactory transmission of the Vibrations through thesurfaces `takes place.

ln' the alternative' attac ent shown in Figs. 9 and 1l), al `split clamp or the like 7 engaging: a ange or groove ofthe e'xcitercarries screws 8 under the heads of which can" engage hoek arms 9 on a ring 110 which tits over the tapering section 1". This is a quickly releasable clamp -which enables the" tapering section and its abrasive tip' to` be' changed rapidly.

Whereithe abrasive tipi's of hard material, such asV a diamond, i-t may be mounted as shown in Fig. 8 1`n= which the' tipiv 11 isheld: downby al sleeve 12 which screws on `tothe endl of thetaperingsshank 1 and holds the tip 1'1 `against the seating 4. The seating 4 and the base' of the -tip 1.1 must behighlyr finished and `contact over a largearea. TheA exciter `operates by magnetostriction; and inFigs. l to 4 Vits magnetic circuit -is made up of a. bar 14 and two external yokes 315 having three polar projections .16. The polar projections are spaced half a wave length apart, so that` inthe illustrated example the bar 14 consists'of twohalfwaveV length sections, but the invention is not limited to this andany' desired Vnumber of half wave length secti'onscan be used. Excitation is elfected by the aid of windings 17 whichsurround the'bar 147helically, these windings carrying a direct polarising current as well as driving alternating current. The form` of the magnetic circuit is such that very high eld strength can be used'.` Both thebar l14 `and the yokes 15 are laminatedintheplane of Fig. 1,-i. e., the-.plane wherein the laminations of ofV nickel or Permendur (an alloy'of very high magnetic saturation,-cornposition 49% Y cobalt, 49% iron, 2%

vanadium) the curvedsection of Fig. 3 is to be preferred. Alternatively solid ferrite may be used, ferrite belng a double oxide of the .aAO bBO.Fe type wherein A and B are certain divalent metals and a and b are proportions, a typical example being (90% NiO, 10% ZnO). FezOa-see Philips Res. Rep. 8 91-132, 1953.

The yokes are mounted in an outer housing 18 of insulating material, e. g., moulded synthetic resin and the l housing is made'in parts to 'allow for assembly and to clamp the windings 17 and the yokes 15 in place. Spacers 19 assist in locating and lclamping Vthe windings.` Spiders 20, 21, at opposite ends ofy the bar.14,maintain the air gaps 1n the magnetic circuit constant without imposing longitudinal Vconstraint suicient to interfere with the longitudinal vibrations. Y

The bar 14 is anchored longitudinally in relation to the yokes 15 and the outer housing 1$,at the vibration nodes in such a way as not to constrain the transverse exlongitudinally, arising from the Poisson effect. This anchoring is effected by the aid of forks 22 anchored through the yokes 15 to the main housing 18 and carrying at their 'ends Vtlat springs 23 parallel to the length of the bar. bar. These lugs may in fact as shown in Fig. 4 be cross bars passing right through the bar 14, being a tight fit in a short part ofthe bore at the centre of the bar r14, the bar elsewhere being counterbored as at 24a to clear the cross bars. i

The construction shown in Figs. l to 4 is completed by an end cover 25 incorporating air , ducts 26, 27, by which cooling air blast is led in and away. The yokes 15 restrict movement of the air from the inlet tothe outlet and Central lugs 24 on these springs engage the Vpansion and contraction of the bar'while it is vibrating i this restriction is desirably graded to keep the cooling constant Valong the whole length of the transducer.

,Figs. 5 and 6 show how greater powercan be obtained within substantially no greater compass by the use of multiple elements. Here there are four bar members 14a and four yoke members 15a. The yoke members are arranged radially and the bar members so that each extends between two adjacent yoke members.;l Corresponding with the disposition of the bar membersA a v,tapering shank 1a is usedvwhich has a central conicalrcavity 1b so that its end corresponds as nearly -as may be with the ends of the bar members. Manifestly the construction shown in Figs. 5 v and V6 is only one example of an arrangement inwhich there is a plurality of pairs of yoke bars distributed round the circle and a corresponding number of bar members arranged between Iadjacent yoke members. Y

Fig. 7 shows schematically .how the device of Figs'. 1 to `4 ispreferably excited. A power valve 31- is used as the source of alternating current its anode Vcircuit is transformer coupled to the windings 17 on'the bar member 14. Polarising current is supplied to the same circuit by a battery 32, a condenser 33 being provided to carry vthe alternating current and a choke 34 to prevent the designed to keep the damping low.

4 Y is preferably of piezo-electric type using a barium titanate crystal.

Figs. 5 and 6 described above show one'way in which increase-d activity of the abrading tip` can be achieved for a given bulk of tool. Another possibility is to couple together mechanically several tapered sections 1 conveying the mechanical Waves at or near the abrading tip. An example is illustrated in Figure 11, which shows three transducers each of which is of the structure shown in Figures l to 4 or it might be as in `Figures 5 and 6. The outer casings 18 are united by webs 18a while the outer ends of their tapered Shanks 1 are united by a Y member 1c which carries the abrading tool 11a. The re sulting structure is fan-shaped in two dimensions if the axes of the Shanks 1 all lie in the same plane and in three dimensions if the axes of the shanks 1 do not lie in the same plane. Lateral mutual coupling orconstraint between elements must be light.

It should be mentioned that if the load at kthe point of a tool according to the invention is reactive so that in effect there is compliance at the working point, the resonant frequency of Athe tool will be modified. As the length of the tool cannot be alteredgto restore its resonantY frequency to the desired value, the condition is met by adjusting thefrequency of the exciting current.

Another point of importance which should be mentioned is that in any very high frequency device used on the cutting It is therefore the device. One way of achieving this is to employ a magnetostrictive device with low damping. The devices above-described with reference to Figs. l to 6 have been The damping arises from several sources. For instance, a laminated structure isinecessary to eliminate eddy currents, but this gives rise to distortional damping due to the motion of some of the laminations being non-parallel to their own planes. This is reduced by cementing the laminations firmly together with no air bubbles, e. g., with shellac or by cementing them together at the edges in the case of the coustruction of Fig. 3, leaving the central parts adjacent but not in actual contact. Or the vdamping may be reduced by curving the laminations in a plane normal to their longitudinal motion. A further component of damping Varises from the magnetostrictively developed eddy currents in the interior of the laminations themselves which occurs during mechanical vibration. This component can `be reduced by operating the material near to magnetic saturation when the Q will be high and the damping low. The excitation is then somewhat pulse-like sothat the lamination stays 'in the high damping condition for a relatively short part of the vibratory period.

An alternative construction of exciter to those abovedescribed isV one of the Ferroxcube (a. commercial ferrite of VBritish origin), Ferrospinel (a commercial ferrite lof U. S. A. origin), Magnetite V(magneticV iron or ferrosoferric oxide FeO.Fe2O3) type i. e., using the magnetostrictive material in solid block form. The principle of high stored energy can also be extended by making the material of the tapering section 1 a heavy but very strong material such as tungsten carbide or tungsten. Y

In the'latter case, as the -material is more dense than that of the transducer itself, the junction is desirably matched as follows. The taper section will taper uniformly for Y radius 'Reza/@ i m.

where R is the radius of the transducer end or its equivalent radius, which in the case of a rectangular transducer of sides ab, such that 1rR2=nb. This diameter part of the tapering section will be where Cz is the longitudinal velocity in the transducer material and Ch is the longitudinal velocity in the dense material.

I claim:

1. An electromechanical transducer comprising a bar member of magnetostrictive material, the length of which is an integral odd multiple, including a unit multiple of one half wavelength at the frequency at which the transducer is to be operated, helical windings around said bar member, a magnetic yoke, spaced pole pieces on said yoke co-operating with said bar member, and means anchoring said bar member longitudinally in relation to said yoke at the nodes of vibration without substantially hindering the transverse expansion and contraction of said bar member While it is in vibration.

2. An electromechanical transducer as set forth in claim l wherein said anchoring means includes flat springs set parallel with the length of said bar member, secured by their ends axially in relation to said yoke and by their centres axially in relation to the bar at the nodes of vibration.

3. An electromechanical transducer as set forth in claim 1 also comprising spiders mounted at the ends of the yokes and bar member whereby the bar member is centred in the air gaps of the yoke without substantially hindering the longitudinal vibrations of the bar member.

4. An electromechanical transducer as set forth in claim 1 also comprising an outer shell fitting closely over the outer edges of said yokes so that the yokes extend inwardly therefrom, a cover closing an end of said shell and entry and outlet connections for a supply of cooling fluid in said cover, said connections being respectively on opposite sides of said yokes so that the yokes are in the path of the flow of iluid.

5. An electromechanical transducer comprising a Iaminated bar member of magnetostrictive material, the length of which is an integral odd multiple including a unit multiple of one half wave length at the frequency at which the transducer is to be operated, helical windings around said bar member, a magnetic yoke, spaced pole pieces on said yoke co-operating with said bar member and means anchoring said bar member longitudinally in relation to said yoke at the nodes of vibration without substantially hindering the transverse expansion and contraction of said bar member while it is in vibration.

6. An electromechanical transducer as set forth in claim 5 wherein the laminations of which said bar member is composed are of curved cross section arranged adjacent but out of contact with one another, the structure also including cement securing the laminations togeth'er along their edges.

7. An electromechanical transducer comprising a plurality of bar members of magnetostrictive material, the length of which is an integral odd multiple of one half wave-length at the frequency at which the transducer is to be operated, helical windings located to set up longitudinal` fields in said bar members, a plurality of .magnetic yokes, spaced pole pieces on said yokes each co-operating with two adjacent bar members and means anchoring said bar members longitudinally in relation to said yokes at the nodes of vibration without substantially constraining said bar members transversely.

8. An electromechanical transducer as set forth in claim 7 wherein said bar members are of laminated construction.

9, A vibratory tool comprising a combination of a plurality of transducers each as set forth in claim l, means securing the yokes of said transducers together with the axes of their bar members directed substantially towards a common point, a tapering shank of vibration-transmitting material of low damping, secured at its larger end to the end of the bar member of each'transducer nearer said point, and` a member uniting the smaller ends of said shanks and serving to carry an abrading tool tip, the overall length of each transducer and shank being such as to provide a vibration anti-node at the location of said uniting member at the frequency at which the transducers are to be operated.

References Cited in the file of this patent UNITED STATES PATENTS

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