GB2140345A

GB2140345A - Horn assembly for ultrasonic welding machine

Info

Publication number: GB2140345A
Application number: GB08314433A
Authority: GB
Inventors: Francis Frederick Hamil Rawson; Anthony Roy Stuart; L Simpson
Original assignee: British United Shoe Machinery Ltd
Current assignee: Noxet UK Ltd
Priority date: 1983-05-25
Filing date: 1983-05-25
Publication date: 1984-11-28
Also published as: GB2140345B; GB8314433D0

Abstract

A horn assembly for use in an ultrasonic welding machine, when operating with a frequency of the order of 20 KHz, with a tip amplitude of 40 to 80 microns, and under an applied load of the order of 200 Kg force, for an operating cycle of 0.6 to 1 second, comprises a horn member (32) having a profiled work-engaging surface and a further member (30) connecting the horn to a transducer. The horn member (32) is secured to the further member (30) by a stud (34) having two threaded portions (36, 38) with an intermediate smooth-surfaced portion (40) of reduced diameter. The length of each threaded portion (36, 38) of the stud is proportional to its diameter, according to the strength of the member into which it is screwed. Also, the thread of each threaded bore (42, 44) is spaced from the open end by a distance equal to not less than two turns of the thread. Further, the threaded bores are not subjected to any surface treatment. These various features serve to mitigate the tendency of the stud and/or the members to fracture. <IMAGE>

Description

SPECIFICATION Horn assembly for use in an ultrasonic welding machine This invention is concerned with a horn assembly for use in an ultrasonic welding machine comprising a horn member having a profiled work-engaging surface, a further member which is adapted to be secured to a transducer forming part of an ultrasonic welding machine, and a stud for securing said horn member and said further member together, whereby ultrasonic vibrations can be transmitted from the transducer through said further member to the work-engaging surface of the horn member, wherein, for securing said members together, the stud is received in threaded bores which open into abutting end surfaces of said members.

It will be appreciated that the aforementioned abutting end surfaces need to be substantially flat so that they can be secured together in intimate contact with one another, thereby avoiding any significant energy loss therebetween and also avoiding the risk of heat generation at their interface. To this end, the stud by which the two members are secured together serves to enable the end surfaces to be brought into a close abutting relationship by screwing them together.

In known horn assemblies the stud has a continuous thread extending along the whole of its length. For positioning the stud, furthermore, either it is sufficiently long to contact the bottom of the threaded bore in one of the members, while projecting beyond the end surface of such member, or alternatively it is of relatively short length and may be secured in a desired position in the threaded bore of one of the members by a suitable fixing agent, e.g. "Loctite", so that it projects sufficiently beyond the end surface of said member to enable the other member to be screwed on to it.

The above arrangement has proved generally satisfactory in most applications, but in the case of an application involving a high frequency (in the order of 20 KHz), high amplitude (40 to 80 microns), a high applied load (in the order of 200 Kg force) and a relatively long operating time (in the order of 0.6 to 1 sec.), e.g. an ultrasonic heel attaching machine as described in our UK Patent Specification No.1591402, a tendency has been observed for the stud to fracture in the vicinity of the abutting end surfaces of the two members, after a relatively low number of operating cycles has been performed.

It is the object of the present invention to provide an improved horn assembly for use in an ultrasonic welding machine, especially but not exclusively for use in an ultrasonic heel attaching machine, in which the tendency of the stud to fracture is mitigated.

This object is resolved in accordance with the invention, in a horn assembly as set out in the first paragraph above, in that the stud has two threaded portions, at opposite ends thereof, and an intermediate portion which is smooth-surfaced and the diameter of which does not exceed the core diameter of either of the threaded portions, the arrangement being such that, when the threaded portions of the stud are received in the bores of said members, the abutting end surfaces of said members lie in a plane intersecting the intermediate portion at a point along its length.

By using a stud having a smooth-surfaced intermediate portion, the two members may be screwed together without there being any threaded engagement between the stud on the one hand and the two members on the other in the plane of contact between the two members, so that any dimensional variations in the stud in the region of said plane, which variations take place under the action of the ultrasonic energy applied to the horn assembly, can take place without being impeded by any threaded engagement with the members.

It has been found that, by this arrangement, any tendency of the stud to fracture in said region is mitigated.

Conveniently, in a horn assembly in accordance with the invention, the threaded portion of the stud received in said further member is so dimensioned that, when said portion is in contact with the bottom of said bore, it is wholly accommodated within the bore and the end surface of said member lies in said plane intersecting the intermediate portion. Locating the stud by its being in contact with the bottom of the bore in said further member dispenses with the need for use of a fixing agent, and this too has been found to contribute to the mitigation of the tendency to fracture.

In the horn assembly in accordance with the invention, furthermore, in order better to distribute the load applied to the threaded portions of the stud, the length of the threaded portion of the stud received in its associated bore preferably has a proportional relationship with the diameter of said portion.

Thus, where the further member is made of an aluminium alloy, preferably the length of the threaded portion of the stud received in its bore is at least twice the diameter thereof; on the other hand, where said member is of a titanium alloy, then the length of the threaded portion of the stud is preferably at least one and a half times the diameter thereof. A similar relationship should also preferably apply with respect to the threaded portion of the stud received in the bore of the horn member.

In the machine in accordance with the invention, furthermore, preferably the further member is of an aluminium alloy or of a titanium alloy while the horn member is preferably of a titanium alloy.

As already stated, in the event of a fracture of the stud, the fracture usually takes place in the vicinity of the interface between the two members. Furthermore, it has been known for one of the members also to fracture, such fracture of a member taking place closely adjacent to the end surface thereof. Further to mitigate the tendency of the stud to fracture, and also to mitigate the tendency of a member to fracture, preferably in accordance with the invention the thread of the threaded bore of each member is spaced from the end surface by a distance equal to not less than two turns of the thread; that is to say, preferably the thread start is located, in the body of the material, spaced from the open end of the bore by such distance.

Further to enhance the fatigue strength of the stud, preferably the thread thereof is sinusoidal, e.g. a Whitworth thread; in such a case, the thread of the bores is similarly sinusoidal The horn member may be secured directly to a so-called booster member, that is a member which is secured directly to the trans- ducer. On the other hand, preferably in the assembly in accordance with the invention said further member is constituted by an extension member which is secured as aforesaid at one end to the horn member and at the other is adapted to be secured to a booster member. (If desired the booster member may be secured to such extension member by a stud of the same type used as aforesaid for securing the horn and extension members together).In this way, not only can a stepped amplitude magnification be achieved satisfactorily, but also an elongated horn assembly can be provided, which is advantageous in certain applications. For example, in the case of an ultrasonic heel attaching machine, an elongated horn assembly is useful for accommodating boots.

It has further been found that in surface treatment, e.g. anodising, may in certain circumstances have contributed to the tendency of the member thus treated to fracture. Consequently, in the machine in accordance with the invention preferably at least the threaded bores formed in the members are not subjected to any surface treatment.

The horn assembly in accordance with the invention has been developed especially, but not exclusively, for use in an ultrasonic heel attaching machine. Whereas the advantages arising out of such a horn assembly are particularly useful in such a machine, nevertheless they are also to be regarded as advantageous in other forms of ultrasonic welding machines.

With this in mind, the invention also provides, in another of its several aspects, an ultrasonic heel attaching machine comprising a support for the heel end of a shoe, said support being accommodated within the shoe, a clamp arrangement for holding a heel which is to be attached to a shoe supported by the shoe support, a horn assembly as set out above, the horn member of which is accommodated within the shoe support, and vibrating means, including an ultrasonic transducer operatively connected with the horn assembly, wherein the shoe support has guide means for guiding fasteners by which heels are to be attached to shoes, the arrangement being such that a fastener is inserted through the insole of a shoe supported by the shoe support and into a heel clamped against such shoe by the application to the fastener of pressure and ultrasonic vibrations via the horn assembly.

There now follows a detailed description, to be read with reference to the accompanying drawings, of one ultrasonic heel attaching machine in accordance with the invention, incorporating a horn assembly in accordance with the invention. It will be appreciated that this machine and this assembly have been selected for description merely by way of exemplification of the invention and not by way of limitation thereof.

In the accompanying drawings: Figure 1 is a side elevation of an ultrasonic heel attaching machine in accordance with the invention; Figure 2 is a fragmentary view showing the construction of a horn assembly in accordance with the invention, incorporated in the machine of Figure 1; and Figure 3 is a fragmentary view, on an enlarged scale, indicating the manner in which a horn member and a further member of said horn assembly are secured together.

The machine now to be described is an ultrasonic heel attaching machine comprising a frame 10 on which is supported a shoe support 12 on which a shoe S can be supported, bottom uppermost, with the upper end of the support 12 accommodated within the shoe. The machine also comprises a clamp arrangement, comprising two clamping members 14, 16 supported on an arm 18 which is movable heightwise relative to the shoe support 12 by means of a piston-andcylinder arrangement (not shown). The clamp arrangement 14, 16 is arranged to clamp a heel H against the heel end of the bottom of a shoe S supported by the shoe support 12, when the heel is being attached to said shoe.

The clamp arrangement is supported on an overhanging portion of the frame 10. The heel H, which is of thermo-plastic material, is attached to the shoe S using a fastener F in the form of a broad-legged staple made from strip steel, the fastener being inserted through an insole I of the shoe S and into the heel H by the application to the fastener of pressure and ultrasonic vibrations, as will now be described.

The shoe support 12 is hollow and accommodates therewithin a horn assembly in accordance with the invention, generally desig nated 20. The assembly 20 is movable heightwise within the shoe support 12 by means of a piston-and-cylinder arrangement 22 supported on a base of the frame 10. The shoe support 12 has, at its upper end, a recess 18 which constitutes guide means for guiding a fastener F placed therein as it is inserted through the insole I and into the heel H as aforesaid.

The horn assembly 20 is connected to an ultrasonic transducer 24 which is supported within the shoe support 12 and is operatively connected to a power source (not shown), the transducer being effective, when power is supplied thereto from said source, to cause vibrations in the ultrasonic range to be applied through the horn assembly 20 to the fastener F to cause the latter to cut through the insole I and then to cause the thermo-plastic material of the heel H to be melted or softened thus to allow the fastener F to penetrate thereinto and become embedded therein.

Viewing Figure 2, the transducer 24, which is of any conventional type, and which has an output amplitude, when operating at a frequency of some 20 KHz, of some 20 microns, has rigidly secured thereto a first stage of the horn assembly 20, referred to as a booster member 26, which is stepped, in a conven tional manner, so as to produce an output amplitude in the ratio 1:1.4 in relation to the output of the transducer itself. The booster member 26, furthermore, has, intermediate its length, an integral flange 28, arranged at a node of the booster member, by which flange the horn assembly 20, together with the transducer 24, is mounted on the shoe support 12. (By arranging the flange at a node, the vibrations in the mounting are reduced to a a minimum).

The booster member 26 is secured at its lower end to the transducer 24 by means of a stud 46, opposite ends of which are received in threaded bores in abutting end faces of the booster member and transducer. Similarly, at the upper end of the booster member 26, a further, "extension", member 30 is similarly connected to the booster member. The extension member 30 is also stepped at a node, so as to produce an output amplitude in a ratio of 1:1.25 in relation to the output amplitude of the booster member 26. The member 30 has secured to its upper end a horn member 32 having a work-engaging surface which is profiled according to the shape of the fastener F which is to be inserted in the operation of the machine.Thus, in the particular instance, the horn member 32 has a bifurcated upper end portion by which pressure and ultrasonic vibrations are applied to a fastener F in the vicinity of the legs, in which vicinity the pressure requires to be concentrated for inserting the fastener. The horn member 32 is again stepped at a node and provides an output amplitude in the ratio 1:1.6 in relation to the output amplitude of the "extension" member 30. The horn member 32 has an integral flange 32a by which it is guided within the shoe support 20; this flange is located at a node of the horn member, thus to minimise vibrations in the shoe support caused by engagement thereof with the flange.

It will thus be appreciated that, by stepping each of the three stages of the horn assembly 20, a magnification of output amplitude as between the transducer 24 and the horn member 32 is in a ratio of some 1:2.8. Thus, with this arrangement the amplitude at the tip of the horn assembly 20 is of the order of 56 microns. (Desirably the tip amplitude is in the range 40 to 80 microns).

In the operation of the machine, the staple F is thus subjected to ultrasonic vibrations at a frequency of approximately 20 KHz, with an amplitude of 40 to 80 microns, and under a pressure applied by the piston-and-cylinder arrangement 22 of the order of 200 Kg force, for a period of 0.6 to 1 second. Using such parameters, it has been found that a staple can be driven through the insole I of a shoe supported by the shoe support 12 and into a heel H clamped against the shoe by the clamp arrangement 14, 16.

Figure 3 shows details of the manner in which the horn member 32 is secured to the extension member 30. Thus, a stud 34 is provided which has two threaded portions 36, 38 and an intermediate, un-threaded, portion 40. The intermediate portion has to be smooth-surfaced; that is to say, its surface must be free from cracks or scratches. In addition, the diameter of the intermediate portion 40 should not exceed the core diameter of either of the threaded portions 36, 38. Preferably the diameter of the intermediate portion 40 is some 90% of the core diameter of the threaded portions.

The lower threaded portion 36, which is received in a threaded bore 42 formed in the upper end of the extension member 30 and opening into the end surface thereof which will abut the corresponding end surface of the horn member 32, is so dimensioned that, when it is in contact with the bottom of the bore 42, it is wholly accommodated within said bore, while the end surface of the member 30 lies adjacent the intermediate portion at a point along its length, preferably in the vicinity of the centre of said intermediate portion. The extension member 30 may be made of an aluminium alloy or of a titanium alloy (as will be discussed below). If aluminium is used, then the length of the threaded portion 36 is preferably at least twice the diameter thereof, while if titanium is used, then the length is preferably at least one and a half times the diameter thereof.The same criteria apply also to the relationship between length and diameter of the upper threaded portion 38, received in a threaded bore 44 formed in the horn member 32 and opening into its abutting end surface.

Each of the threaded portions 36, 38 of the stud 34 has a thread formation which is sinusoidal in cross-section, e.g. a Whitworth thread; the thread of each of the threaded bores 42, 44 of course corresponds to that of the stud.

Whereas in the horn assembly herein described the stud 34 is used only to secure together the horn and extension members 32, 30, similar studs may be used, if desired, for securing the extension and booster members 30, 26 together and also the booster member and transducer 26, 24, instead of the studs 46.

The choice of materials for the two members 30, 32 is determined by the requirements of the application, bearing in mind that, apart from considerations of cost, the material must be capable of transmitting ultrasonic vibrations without significant loss of energy and also it must have a high fatigue strength. In the case of the horn member 32, furthermore, the problems of wear by contact with the fastener F as it is being inserted must be taken into account. In the machine in accordance with the invention now being described, therefore, the extension member 30 is preferably made of an aluminium alloy; a suitable alloy for the purpose is identified by the code "201 4A(TB)", which is manufactured to British Standard 1474.The horn member 32, on the other hand, is preferably of a titanium alloy, identified as a titanium 6/4 alloy, manufactured under the code "IM1318".

Further to mitigare any tendency to fracture in the stud 34 or in the member 30, the thread of each of the threaded bores 42, 44 is spaced from the end surface of its member by a distance equal to not less than two turns of the thread. This has the effect of avoiding subjecting the members in the vicinity of their abutting surfaces to any distortion-creating forces, so that the faces can lie flat and in intimate contact with one another.

The stud 34 is of a high strength low alloy steel, of the type conventionally used for bolts. One suitable material is identified as "EN 1 9T". For securing the stud in the threaded bore 42 of the extension member 30 an Allen key recess is formed at the upper end of the stud. For securing the horn member to the stud, on the other hand, flats 46 are provided on the outer surface of the horn member and extension member, so that a conventional spanner may be used.

The effect of using the stud 34 for securing together the members 30, 32 is to ensure that a compressive force is applied between the abutting end faces of the members while the intermediate portion 40 of the stud is held in tension, but without any stress concentration therein in the vicinity of the abutting faces of the members (which previously arose because of the continuous thread along the length of the stud).

Claims

1. A horn assembly for use in an ultrasonic welding machine comprising a horn member having a profiled workengaging surface, a further member which is adapted to be secured to a transducer forming part of an ultrasonic welding machine, and a stud for securing said horn member and said further member together, whereby ultrasonic vibrations can be transmitted from the transducer through said further member to the work-engaging surface of the horn member, wherein, for securing said members together, the stud is received in threaded bores which open into abutting end surfaces of said members, and further wherein the stud has two threaded portions, at opposite ends thereof, and an intermediate portion which is smoothsurfaced and the diameter of which does not exceed the core diameter of either of the threaded portions, the arrangement being such that, when the threaded portions of the stud are received in the bores of said members, the abutting end surfaces of said members lie in a plane intersecting the intermediate portion at a point along its length.

2. A horn assembly according to Claim 1 wherein the threaded portion of the stud received in the bore of said further member is so dimensioned that, when said portion is in contact with the bottom of said bore, the end surface of said member lies in said plane intersecting the intermediate portion.

3. A horn assembly according to either one of Claims 1 and 2 wherein the further member is made of an aluminium alloy, and wherein the length of the threaded portion of the stud received in the bore of said further member is at least twice the diameter thereof.

4. A horn assembly according to either one of Claims 1 and 2 wherein the further member is made of a titanium alloy, and wherein the length of the threaded portion of the stud received in the bore of the horn member is at least one and a half times the diameter thereof.

5. A horn assembly according to any one of the preceding Claims wherein the horn member is made of a titanium alloy, and wherein the length of the threaded portion of the stud received in the bore of the horn member is at least one and a half times the diameter thereof.

6. A horn assembly according to any one of the preceding Claims wherein the thread of the stud and of each of the threaded bores is sinusoidal.

7. A horn assembly according to any one of the preceding Claims wherein the thread of the threaded bore of each member is spaced from the end surface by a distance equal to not less than two turns of the thread.

8. A horn assembly according to any one of the preceding Claims wherein said further member is constituted by an extension member which is secured as aforesaid at one end to the horn member and at the other is adapted to be secured to a booster member.

9. A horn assembly according to any one of the preceding Claims wherein the threaded bores formed in the members are not subjected to any surface treatment.

10. A horn assembly constructed and arranged as hereinbefore described with reference to the accompanying drawings.

11. An ultrasonic heel attaching machine comprising a a support for the heel end of a shoe, said support being accommodated within the shoe, a clamp arrangement for holding a heel which is to be attached to a shoe supported by the shoe support, a a horn assembly according to any one of the preceding Claims, the horn member of which is accommodated within the shoe support, and vibrating means, including an ultrasonic transducer operatively connected with the horn assembly, wherein the shoe support has guide means for guiding fasteners by which heels are to be attached to shoes, the arrangement being such that a fastener is inserted through the insole of a shoe supported by the shoe support and into a heel clamped against such shoe by the application to the fastener of pressure and ultrasonic vibrations via the horn assembly.

12. A machine according to Claim 11 wherein the horn member has a support flange arranged at a nodal point along its length, by which flange the member is guided within the shoe support.