Abstract:
The invention relates to a device for connecting metallic materials, in particular electrical conductors such as flexible cables, by means of a transducer ( 10 ) which generates ultrasonic oscillations and contains a sonotrode ( 16 ) with a sonotrode head ( 14 ) as well as a converter ( 12 ). In order to be able to embody the transducer compactly, it is provided that the transducer alone is seated in the first oscillation node remote from the sonotrode head.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a device for connecting metallic materials, in particular electrical conductors such as flexible cables, by means of ultrasound with a transducer which generates ultrasonic oscillations of a wavelength lambda and containing a sonotrode with a sonotrode head, as well as a converter, wherein the transducer is seated at a distance of at least lambda/4 in respect to the sonotrode head. 
     Conventional transducers for generating ultrasonic oscillations comprise a converter for converting electric oscillations into ultrasonic oscillations of a desired frequency and amplitude, a booster, as well as a sonotrode with a sonotrode head having an electrode, or respectively a work surface, wherein the contact with the materials to be welded takes place for welding metal elements, such as flexible cables. Since the welding surface, or respectively the welding point, extends parallel in respect to the sonotrode oscillation axis, the seating must not only absorb axial and radial forces, but also bending moments. 
     In this connection it is known to seat a transducer, comprising a converter, a booster and a sonotrode, in oscillation nodes extending in the booster as well as in the sonotrode. This in turn means a long structure of the transducer. 
     With a booster-less embodiment of a transducer, which therefore only contains a converter and a sonotrode, a partition can be formed between the converter and the sonotrode, in which a diaphragm spring is clamped, by means of which the transducer is seated. Moreover, a support in the oscillation node (FIG. 9) extending in the sonotrode is provided. In this case the diaphragm spring extends in the oscillation maximum. Not only is a radially large structure necessary because of the use of the diaphragm spring, but also an axially flexible seating. In connection with a further booster-less oscillation embodiment, seating is provided in the oscillation neutral point in the converter, as well as support in the oscillation zero point of the sonotrode (FIG.  10 ). It has been found here that the zero point seating in the converter leads to considerable problems. 
     In connection with a further known transducer, which includes a converter, booster and sonotrode, the booster and the sonotrode are respectively seated, or respectively supported, in the oscillation zero point (FIG.  7 ). The use of the booster results in a long structure. Moreover, transducers are known having partitions between the converter and the booster on the one hand, and the booster and the sonotrode on the other hand, from which diaphragm spring extend (FIG.  8 ). Since seating takes place in the oscillation maximum, the transducer is very flexibly supported. In addition, a large radial structure results because of the diaphragm spring used. 
     A device of the type known at the outset is known from DE 35 08 122 C2. Here, the sonotrode is supported by a plurality of locking screws, which are aligned perpendicularly in relation to the longitudinal axis of the sonotrode, which themselves do not absorb the occurring axial and radial forces, as well as bending moments, to the required degree. It is therefore necessary to additionally support the converter or booster. In actual use this takes place in the booster. 
     SUMMARY OF THE INVENTION 
     The present invention is based on the problem of further developing a device of the type mentioned at the outset in such a way that, along with a short construction, the appearing axial and radial forces, as well as the bending moments, are absorbed to the extent necessary. However, sufficient rigidity should also be provided in order to compensate static forces. 
     In accordance with the invention, the problem is essentially solved in that the transducer is exclusively supported at a distance of lambda/4 in respect to the sonotrode head by means of a seating for absorbing radial and axial as well as bending moments and torsion moments. 
     By means of the teaching of the invention there is the possibility of making available a booster-less and therefore compact transducer having a single seating which extends in the area of the sonotrode, namely in the first oscillation node from the direction of the sonotrode head. 
     By means of the teaching of the invention, a transducer is made available for the first time for welding metal elements together, which has a single seating, which is a possibility which up to now was only available in connection with plastic welding, namely in the oscillation zero point of a booster which, however, causes a long structure of the transducer, since the seating point is 3·lambda/4 away from the sonotrode head. Furthermore, the seating need not absorb any bending moments, since in plastic welding the oscillation axis of the sonotrode extends perpendicularly in relation to the surfaces to be welded. For this reason, transducers intended for metal welding were always seated in two areas. 
     In accordance with a preferred embodiment of the invention it is provided that the seating has a first section which radially projects from the sonotrode and which makes a transition into a second section, which extends in the longitudinal direction of the transducer and is spaced apart from the latter. The transducer itself is then fixed in place by means of the second section and at a distance from the first section, because of which an elastic uncoupling takes place from the occurring transverse forces, or respectively transverse stretching, which occur in the oscillation node because of stretching, or respectively compression, of the sonotrode. In particular, the first section is a circumferential ring, or respectively a circumferential disk, and the second section is a hollow cylinder, which can be designed as one piece or as separate elements, which are then connected with each other, for example screwed together. 
     The first section can be embodied integrally with the sonotrode. But alternatively there is also the possibility of designing the sonotrode in several pieces, and to clamp the first section into a partition extending at a distance lambda/4 from the sonotrode head, from which section the second section for elastic coupling starts, which extends along the transducer. Because of the embodiment of the sonotrode in several pieces there is the advantage, that worn elements can be exchanged without problems, without the entire sonotrode needing to be replaced. The individual sonotrode elements can be screwed together. 
     In accordance with an alternative solution suggestion it is provided that the sonotrode has a partition, which divides it into two axial sections and from which a radially extending disk-shaped element starts, which itself is fixed in place in areas extending diametrically in relation to the sonotrode. In this case the areas themselves are clamped between cheeks which preferably are made of plastic, so that the transverse forces, or respectively transverse stretching, occurring because of the stretching and compression of the sonotrode, can be absorbed. In particular, each area extends in an oscillation node of the disk-shaped element. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further details, advantages and characteristics ensue not only from the claims, the features to be taken therefrom—by themselves and/or in combination—but also from the following description of exemplary embodiments to be found in the drawings: 
     FIG. 1, a basic representation of a transducer intended for an ultrasonic welding device for connecting metallic materials, 
     FIG. 2, a first embodiment of a sonotrode, 
     FIG. 3, a second embodiment of a sonotrode, 
     FIG. 4, a third embodiment of a sonotrode, 
     FIG. 5, the sonotrode in FIG. 4 in a front view, and 
     FIGS. 6 to  10 , basic representations of transducers in accordance with the prior art, as well as a transducer in accordance with the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A transducer  10 , which is intended for a device for welding together metallic materials, in particular electrical conductors such as flexible cables, by means of ultrasound, is represented purely basically in FIG.  1 . The transducer  10  consists of a converter  12  and a sonotrode  14 , which is connected with it, preferably by means of a screw connection. Electrical oscillations are converted into ultrasonic oscillations of the desired frequency and amplitude by means of this converter  12 . 
     However, in this respect reference is made to the applicable prior art, without further explanations being required. 
     The sonotrode  14  has a sonotrode head  16  with a surface, which can be called an electrode, acting on the metallic workpieces to be welded together, wherein the weld surface of the materials extends parallel in relation to the sonotrode oscillation axis. 
     In accordance with the invention, the transducer  10  is seated in only one area, namely in the first oscillation node, i.e. at a distance of lambda/4 from the sonotrode head  16 , viewed from the direction of the sonotrode head  16 . Here, the seating is designed in such a way that the occurring radial and axial forces, as well as bending moments caused by welding and possibly torsion moments, can be absorbed to the required extent. 
     A preferred embodiment of a sonotrode  18  with seating  20  is represented in FIG. 2, which consists of a ring-shaped section  22 , projecting radially from the oscillation zero point, as well as of a cylinder section  24  extending in the longitudinal direction of the sonotrode, which form a unit. Here, the cylinder section  24  extends at a distance from the exterior surface  26  of the sonotrode  18 . 
     If in the exemplary embodiment the hollow-cylindrical section  24  extends in the direction toward the converter, it is of course possible that an extension in the direction toward the sonotrode head  16  can also take place. 
     Now the sonotrode  18  is seated via the holder  20  in the area of the section  24  spaced apart from the radially extending ring  22 . By means of this an elastic uncoupling, or respectively buffering, of the transverse forces, or respectively stretching, occurring in the oscillation zero point because of the stretching, or respectively compression of the sonotrode, takes place. It is simultaneously possible to absorb the bending moments, or respectively torsion moments, to the required extent. In the exemplary embodiment, the support area of the sonotrode  18  has been provided with the reference numeral  26  and extends in the free end area of the hollow-cylindrical section  24 , which is separated from the area on the ring side by a step  28 . 
     A sonotrode  30  is represented in FIG. 3 which is made of two pieces, i.e. consists of two axial sections  32 ,  34 , the front section  34  of which has the sonotrode head  16 . Thus, a partition is formed between the sections  32 ,  34 , in which a disk  36  is clamped, whose circumference projects past the sonotrode  30  and in this way can correspond to a geometry which is equal to the radially projecting ring  22  in the embodiment of FIG. 2. A hollow-cylindrical section also starts at the disk section  36  and extends along the sonotrode  30 , so that the reference numerals which can be found in FIG. 2 are used. If the radial section  22 , or respectively the disk  36 , are embodied integrally with the hollow-cylindrical section  24  in the exemplary embodiments in FIGS. 2 and 3, a multi-piece version can also be used, wherein the radially and axially extending elements are screwed together, for example. 
     Even if the seating preferably has a hollow-cylindrical section  24  extending along the longitudinal axis of the sonotrode  14 ,  18 ,  30 , on which the sonotrode  14  is clamped, in accordance with the exemplary embodiment in FIGS. 4 and 5 there is the option of seating and clamping the sonotrode  30  in the oscillation zero point by means of a disk-shaped element  38 , which is preferably rectangular in a view from above, which itself is clamped in areas  40 ,  42  extending diametrically in respect to the sonotrode  30 . In this case the disk-shaped element  38  is preferably fixed in place between cheeks made of plastic, so that the possibility of compensating occurring transverse forces to a sufficient extent exists. The areas  40 ,  42  should moreover extend in oscillation nodes of the disk-shaped element  38 . 
     In the exemplary embodiment of FIGS. 4 and 5, the sonotrode  30  is also preferably made of two pieces, wherein the partition extends in the oscillation node in which the disk-shaped element  38  is connected with the sonotrode elements. 
     A compact structure results from the teaching in accordance with the invention, which is achieved in a particularly preferred manner by means of the exemplary embodiments of FIGS. 2 and 3; because a small construction results both in the length of the respective sonotrode  18 ,  30  as well as in the radial dimensions. 
     Typical sizes of sonotrodes of the invention, which correspond to the exemplary embodiments in FIGS. 2 and 3 are: 
     Output: 1000 to 3000 Watt 
     Frequency: 20 to 40 KHz 
     Wavelength: 125 to 145 mm 
     Length of the transducer consisting of the sonotrode and the converter: 250 to 290 mm 
     Diameter of the sonotrode in the area of seating (exterior surface of the hollow-cylindrical section) in the area of support: 
     
       
         30 to 60 mm. 
       
     
     In FIGS. 6 to  10  the transducer seating known from the prior art (FIGS. 7 to  10 ) is again shown juxtaposed to the seating in accordance with the invention (FIG.  6 ).