Reduced stress sonotrode, ultrasonic machining apparatus comprising sonotrode and use of sonotrode

Abstract

The invention relates to a sonotrode for the ultrasonic machining of metals, having a resonance frequency in the ultrasonic range, having a welding surface (5) for contact with the metal to be machined, characterized in that when the sonotrode vibrates at the resonance frequency and the welding surface (5) is in contact with the metal to be machined, the welding surface (5) is heated, a temperature gradient is formed between the welding surface (5) and a section (6) of the sonotrode adjoining the welding surface, as a result of which the welding surface (5) is subjected to stress, and means for reducing the stress of the welding surface during processing are also provided.

Description

[0001] The present invention relates to a sonotrode for ultrasonic machining of metals, the sonotrode having a resonant frequency in the ultrasonic range and a welding surface for contacting the metal to be machined. During the machining operation, the sonotrode is excited by acoustic ultrasonic vibrations at a frequency close to the resonant frequency. Consequently, a standing wave having at least two vibration maxima and at least one vibration node is formed in the sonotrode.

[0002] When ultrasonically machining metals, such as wires, very high energies must be applied to melt the metal elements to be joined. This is the case, for example, when welding wires. As is known, corresponding ultrasonic electrodes are made of hardenable steel and heat-treated to achieve a hardness of 54 to 62 HRC.

[0003] Because welding requires extremely high energy, not only does a sudden temperature rise occur between the metal components being welded, but also at the interface between the sonotrode and the metal components. The weld surface temperature can briefly reach over 300°C.

[0004] When welding metals, defects in sonotrodes develop relatively quickly and are largely confined to the weld surface. This results in a shortened service life, which in turn increases processing costs. Therefore, some have proposed designing sonotrodes as reversible sonotrodes with two welding surfaces. This allows the sonotrode to be rotated and used on the other welding surface if a defect develops on the welding surface. This can significantly reduce costs. However, compared to the service life achieved when welding plastics, the service life of each welding surface is shortened in metal processing. Furthermore, defects caused by sudden temperature rise can sometimes be so severe that they affect the vibration behavior, rendering the entire sonotrode unusable, including the unused welding surface of the reversible sonotrode. In the worst case, material fractures occur on the welding surface when it is first used, and the sonotrode wears out, rendering it unusable.

[0005] Based on the prior art, the object of the present invention is to provide a sonotrode with increased durability, in particular when welding metals.

[0006] According to the present invention, this object is achieved by providing a device for reducing weld surface stress during processing.

[0007] As expected, when the sonotrode vibrates at or near its resonant frequency and the weld surface contacts the metal being machined, the weld surface heats up. Consequently, a temperature gradient forms between the weld surface and the adjacent sonotrode section. Temperature differences within the sonotrode material inevitably lead to thermal stresses within the material. Typically, these stresses are compressive, tensile, and shear. These stresses initially cause elastic deformations, which dissipate when the sonotrode is not in use. However, if the deformations are excessive, the resulting sonotrode material can change or even fracture. While this risk is negligible when welding plastics, it can be significant when welding metals.

[0008] Extensive investigations surprisingly revealed that it wasn't the high temperatures of the sonotrode during the welding process that caused the premature wear, but rather the extreme temperature gradient that developed between the weld surface and the section of the sonotrode adjacent to it. The welding process occurs so quickly that only the weld surface and the thin, immediately adjacent material layer are heated to such high temperatures. Material layers deeper within the sonotrode can't keep up with the extreme temperature rise so quickly.

[0009] Therefore, according to the present invention, the device for reducing weld surface stress during welding can extend the service life of a sonotrode for ultrasonic machining of metals.

[0010] In a preferred embodiment, when the sonotrode is excited at its resonant frequency, a standing wave forms along the sonotrode axis, and the weld surface is not arranged perpendicular to the sonotrode axis. This arrangement of the weld surface has proven advantageous when machining metal components. The weld surface is preferably parallel or substantially parallel to the sonotrode axis.

[0011] When welding plastic films, it is often advantageous if the weld surface has some structure. For example, one known method is to introduce narrow grooves into the weld surface that are arranged very closely together. This concentrates the energy introduced into the film in certain areas.

[0012] The depressions can also be designed as grooves, which are preferably arranged parallel to one another.

[0013] Research has shown that this surface structure is also beneficial for sonotrodes used for welding metals, enabling the vibration amplitude of the sonotrode to be optimally transferred to the component.

[0014] However, these surface structures can lead to additional stress increases on the weld surface due to the presence of the aforementioned temperature gradients.

[0015] To reduce stress on the weld surface, for example, several depressions with a depth of t and a width of a can be introduced, where α should be greater than 3 × t. Therefore, the depressions should be wide enough, at least three times their depth. If the depressions are narrow, the maximum stress will occur at the bottom of the depression, which may cause defects. For example, the depression can be circular. In this case, the width a corresponds to the diameter of the circle.

[0016] Furthermore, it is advantageous if the groove is curved in cross-section, preferably with a radius of curvature r greater than 1.5 mm, in particular greater than 3 mm.

[0017] In a preferred embodiment, it is further provided that each groove is arranged on a plane perpendicular to the sonotrode axis, and the welding surface is preferably arranged parallel to the sonotrode axis.

[0018] In another particularly preferred embodiment, the sonotrode comprises a sonotrode body and a welding section having a welding surface. A connecting web connecting the sonotrode body and the welding section is provided as a means for reducing stress on the weld surface. The connecting web has a cross-sectional area parallel to the welding surface that is at least 5%, preferably at least 10%, and particularly preferably at least 15% smaller than that of the welding surface. By reducing the cross-sectional area of ​​the connecting web, the heat introduced during the welding process is dissipated more slowly into the sonotrode body, resulting in a faster heating of the portion of the connecting web facing the welding surface, thereby reducing the temperature gradient across the weld surface area.

[0019] For example, the connecting web may have a first recess in its first side surface. Experiments have shown that the introduction of the recess reduces the cross-sectional area of ​​the connecting web, thereby reducing weld surface stress. It is particularly preferred to provide a second recess in its second side surface. The two side surfaces of the connecting web may be arranged parallel to each other.

[0020] In a preferred embodiment, the width of the connecting web in the region of the at least one recess is at least 5% smaller, preferably at least 10% smaller, particularly preferably at least 15% smaller than the length of the welding surface.

[0021] Furthermore, in a sectional view perpendicular to the sonotrode axis, the first and / or second recess can have a curved recess bottom.

[0022] It is advantageous if the first and / or second recess is parallel to the sonotrode axis.

[0023] In addition, at least one groove may be provided in the welding surface as a device for reducing the stress of the welding surface. The groove divides the welding surface into multiple welding surface segments, and the at least one groove preferably extends parallel to the axis of the ultrasonic electrode. Dividing the welding surface into individual welding surface segments can significantly reduce the maximum welding surface stress. To ensure that the groove has no negative impact on the welding result, the groove width b should be less than 0.3 mm, and preferably less than 0.15 mm. To prevent the individual welding surface segments from colliding with each other due to heat generation during processing, the groove width b should preferably be greater than 0.025 mm, and particularly preferably greater than 0.05 mm.

[0024] The groove width b is understood to be the width of the groove in the welding surface area. In principle, the groove can narrow or widen inside the material.

[0025] In addition, it is more advantageous if the depth t of the groove is at least ten times, preferably at least twenty times, the width b.

[0026] Alternatively, the groove can also have a depth t of at least 2 mm, and preferably at least 5 mm.

[0027] In another preferred embodiment, the groove has a curved groove bottom. The groove has a base portion including the groove bottom, and in this base portion, the width b of the groove G is greater than the width b, and preferably at least five times the width b.

[0028] The present invention also relates to an ultrasonic processing device having the ultrasonic electrode of the present invention.

[0029] Preferably, a converter that converts an alternating voltage into mechanical vibration is coupled to the ultrasonic electrode, and a generator for generating an alternating voltage with an amplitude of A0 is provided. At the same time, a control unit is provided as a device for reducing the stress of the welding surface. Before generating the alternating voltage with an amplitude of A0, the control unit first generates an alternating voltage with an amplitude of A V and a duration of t, where A V < A0. Here, t is preferably greater than 0.2 seconds, and particularly preferably greater than 0.4 seconds.

[0030] Since the welding surface and the area adjacent to the welding surface have been heated during the time interval before the actual welding process, more energy is indeed required, but the very steep temperature gradient in the welding surface area can be alleviated because the area adjacent to the welding surface has been heated before the actual welding process really starts. During the time interval t, the amplitude A V can increase from a minimum value A min , which can be zero, but is preferably greater than zero, to A V . Tests have shown that a linear increase in the amplitude is particularly advantageous.

[0031] During the welding process, considerable heat energy is transferred to the sonotrode. Since the sonotrode is typically connected directly or via a horn to a transducer containing temperature-sensitive piezoelectric elements, some known embodiments provide cooling of the welding surface, for example, between individual welding steps. However, studies have shown that this is detrimental to the sonotrode's service life, as the temperature gradients at the welding surface can again become extremely high during the subsequent welding steps.

[0032] In an alternative embodiment of the sonotrode according to the present invention, a cooling device is provided as a means for reducing stress on the weld surface. This cooling device cools the sonotrode in the region of the vibration node, but preferably does not cool the weld surface. Therefore, the goal is not to cool the weld surface and the section of the sonotrode immediately adjacent to the weld surface, but rather to maintain these at a higher temperature while ensuring that the transducer, located at the end of the sonotrode facing away from the weld surface, does not overheat. Typically, it is necessary to ensure that the transducer does not heat up to more than 50°C. Cooling devices are known to those skilled in the art. For example, the region of the vibration node can be ventilated, or compressed air or water cooling devices can be used at the vibration node. It is crucial not to cool the sonotrode at the weld surface, as this is precisely where the temperature increase is required to reduce the temperature gradient.

[0033] In a preferred embodiment, at least one ventilation device is provided that directs airflow toward the sonotrode, not toward the weld surface, but toward a segment spaced apart from the weld surface. For example, this segment can be located at a vibration node of a standing wave formed when the sonotrode is excited at an appropriate ultrasonic frequency. Furthermore, a barrier can be provided, positioned between the weld surface and the segment, such that the barrier largely prevents the airflow generated by the ventilation device from reaching the weld surface. The barrier preferably does not contact the sonotrode. For example, the barrier can be implemented as a partition or a separating curtain.

[0034] In an alternative embodiment, a heating device is provided as a device for reducing stress on the weld surface, the heating device being arranged and configured so that the weld surface can be heated. Heating devices are well known to those skilled in the art. For example, the heating device may include a heating die that contacts the weld surface or the connecting web before or during processing to heat the weld surface or the area immediately adjacent to the weld surface. Alternatively, a hot air flow may be provided that is blown directly onto the weld surface or the area immediately adjacent to the weld surface. Induction heating or the use of infrared radiation are also feasible.

[0035] In a preferred embodiment, an infrared emitter is provided which is either aimed directly at the welding surface or at a mirror arranged in such a way that the infrared radiation emitted by the infrared emitter is reflected onto the welding surface.

[0036] Induction heating has proven particularly advantageous because very high temperatures can be reached in the immediate vicinity of the weld surface within extremely short cycle times. To achieve this, the induction coil is positioned so that its turns encircle a portion of the sonotrode. For example, the induction coil can encircle the weld section. The induction coil can have multiple turns. The turns can be helical and arranged in a single plane. Alternatively, the turns can be arranged as a spiral.

[0037] The cooling device and / or heating device may be coupled to the sonotrode such that the cooling device and / or heating device can be moved together with the sonotrode relative to the counter-tool. Alternatively, the cooling device and / or heating device may be movable relative to the sonotrode so as to be positioned relative to the sonotrode during a phase when the sonotrode is not in contact with the metal being machined, thereby enabling efficient performance of the cooling and / or heating functions.

[0038] For example, the heating device can be a heating plate that comes into contact with the welding surface whenever the welding surface is not in contact with the metal to be processed, so as to preheat the surface and the area adjacent to the welding surface. If the welding surface has a structure according to the groove structure of the present invention, the heating plate should also have a corresponding structure.

[0039] Further advantages, options and possible applications will become clear from the following description of the preferred embodiment and the related drawings, in which:

[0040] Figure 1 is a side view of a first embodiment of a sonotrode according to the present invention,

[0041] Figure 1a yes Figure 1 A magnified detail of area A in the middle.

[0042] Figure 2 is a perspective view of a second embodiment of a sonotrode according to the present invention,

[0043] Figure 2a yes Figure 2 Front view of the ultrasonic welding electrode,

[0044] Figure 2b yes Figure 2a A magnified detail of the X area in the middle.

[0045] Figure 3 is a perspective view of a third embodiment of an ultrasonic welding electrode according to the present invention,

[0046] Figure 3a yes Figure 3 Front view of the ultrasonic welding electrode,

[0047] Figure 3b yes Figure 3a A magnified detail of the middle X area, and

[0048] Figure 4 It is a schematic diagram showing the separation of cooling equipment and heating equipment.

[0049] Figure 1 and Figure 1a A first embodiment of a sonotrode 1 according to the present invention is shown. The sonotrode 1 has a rear end face 2 and a front end face 3. The rear end face 2 is used to contact a converter, via which ultrasonic vibrations can be coupled into the sonotrode, so that the sonotrode forms a standing wave, with vibration maxima at the rear end face 2 and the front end face 3, and at the rear end face 3. Figure 1 The sonotrode 1 has a circumferential projection 4 in the region of the vibration node, on which the sonotrode can be held, for example supported, without the vibration behavior of the sonotrode being significantly influenced by the holder.

[0050] The sonotrode is essentially cylindrical, except for the section arranged at the front face 3. It has an approximately cylindrical sonotrode body 8. The section of the sonotrode body 8 facing the front face 3 is provided with two diametrically opposed connecting webs 6, which connect the sonotrode body to two welding sections, each of which includes a welding surface 5.

[0051] For the metal welding process, the welding surface 5 is pressed against the metal elements to be welded while the sonotrode 1 is simultaneously set into ultrasonic vibration.

[0052] When one welding surface 5 is worn, the sonotrode can be rotated by 180° about its sonotrode axis s connecting the rear end face 2 and the front end face 3 in order to subsequently use the second welding surface 5 .

[0053] During the welding process, the welding surface 5 is heated to a very high temperature in a short time, which may result in a very large temperature gradient between the welding surface 5 and the section of the connecting web 6 facing the welding surface 5 .

[0054] This large temperature gradient causes stress (also called mechanical stress) within the material. Specifically, the stress state at any specific point in the sonotrode material can be described by a stress tensor. This stress tensor typically contains at least six different stress values. To more conveniently describe the stress state, a scalar equivalent stress is often calculated. For example, the von Mises equivalent stress, named after Richard von Mises, can be used for this calculation. The present invention is also based on this von Mises equivalent stress. The objective of the present invention is to reduce the maximum von Mises equivalent stress occurring at any point on the weld surface 5.

[0055] exist Figure 1 and Figure 1aIn the illustrated embodiment, grooves 7 are formed in the welding surface 5. Each groove has a depth t and a width a. Width a is significantly greater than depth t, i.e., at least three times greater than depth t. The grooves 7 are arranged parallel to one another. Each groove is oblique to the sonotrode axis s, and each groove 7 lies in a plane perpendicular to the sonotrode axis s.

[0056] Figure 2 、 Figure 2a and Figure 2b A second embodiment of a sonotrode 101 is shown. Figure 2 A perspective view is shown. The sonotrode also has a rear end face 102 and a front end face 103, between which a standing wave is formed along the sonotrode axis s during operation. In the region where the vibration nodes are located, a projection 104 is provided, on which the sonotrode 101 can be held.

[0057] Likewise, the sonotrode 101 is substantially cylindrical, with two diametrically opposed connecting webs 106 extending radially outward from the sonotrode axis at the front end where the front face 103 is arranged, through the lateral surface of the cylindrical section of the sonotrode 101, and extending to two welding sections, each of which has a welding surface 105. In the embodiment shown, the welding surface 105 is constructed in the same manner as in the embodiment shown. Figure 1 and Figure 1a The welding surface 5 in the embodiment shown is identical. Its length is l S (like Figure 2a shown), and the width is b S (like Figure 1 (as shown). Furthermore, the connecting web 106 has two opposing notches 109. Calculations and experiments have shown that these notches significantly reduce material stresses in the area of ​​the weld surface 105. Preferably, the notches 109 are aligned parallel to the sonotrode axis s. In the illustrated embodiment, the notches have a notch depth of approximately 2.5 mm and a notch height of 2.4 mm from the weld surface 105. The resonant frequency of the illustrated sonotrode is approximately 20 kHz. If a sonotrode with a higher resonant frequency is manufactured, the same effect can be achieved with a smaller notch depth. A larger notch depth can also be selected. The notches significantly reduce the cross-sectional area of ​​the connecting web, thereby significantly reducing heat dissipation from the weld surface 105 to the sonotrode body and reducing temperature gradients in the immediate vicinity of the weld surface 105. Furthermore, because the material in the notch area provides lower resistance, mechanical stresses near the weld surface are generally reduced.

[0058] Figure 2b This is a view perpendicular to the sonotrode axis, from which it can be seen that the recess 109 has a curved recess bottom.

[0059] Figure 3 、 Figure 3a and Figure 3b A third embodiment of the invention is shown. The sonotrode 201 has a rear end face 202 and a front end face 203, between which the sonotrode axis s extends. During operation, a longitudinal standing wave is formed, the vibration nodes of which are occupied by the protrusions 204, where the sonotrode can be held. Here too, a connecting web 206 is provided, connecting the welding section 210 with the welding surface 205 to the sonotrode body 208. Figure 2 、 Figure 2a and Figure 2b As in the illustrated embodiment, a recess 209 is also provided here.

[0060] Unlike the previous embodiment, welding surface 205 has a groove 211 that divides welding surface 205 into welding surface section 212 and welding surface section 213. The width b of this groove is very small to avoid adversely affecting the welding result caused by the contact between welding surface 205 and the material to be welded. While the groove width b should be as small as possible, it must also ensure that the individual welding surface sections do not collide with each other when the welding surface is heated as expected.

[0061] The groove has a groove depth S t In addition, the groove gradually widens towards the bottom, with a maximum width of S b .

[0062] Figure 4 is a schematic diagram of one embodiment of a sonotrode 11 according to the present invention. The sonotrode 11 consists of a welding section 15 having a welding surface 18, a main section 13, and a connecting section 14 connecting the main section 13 and the welding section 15. The sonotrode is held by a holder 16, which engages at the sonotrode's vibration node. The entire sonotrode 11 can be moved upward or downward in the direction of the arrow to increase or decrease the distance between the welding surface 18 and the mating tool 12. The materials to be processed, in this case two metal parts, are inserted between the welding surface 18 and the mating tool 12 and joined together by ultrasonic welding using the sonotrode 11.

[0063] exist Figure 4 As shown, the weld surface 18 may be heated to preheat the entire weld section 15, thereby ensuring that temperature gradients in the immediate vicinity of the weld surface 18 are not excessive during welding.

[0064] Heating can be achieved, for example, with the aid of hot air or infrared emitters. It is important that only the welding surface 18, and at most the welding section 15, is heated. The main section 13, which is typically connected at its end facing away from the welding section 18 to a transducer (not shown) containing a temperature-sensitive piezoelectric element, should not be heated under any circumstances. While the area of ​​the welding section 15 may require elevated temperatures before the actual welding operation, the temperature of the main section 13 should be kept as low as possible to avoid damaging the transducer's piezoelectric elements.

[0065] Therefore, in a preferred embodiment, cooling of the main section 13 may be necessary. For example, the retainer 16 can be water-cooled, or a cooling air flow can be provided in this area. To keep the main section 13 relatively cool while simultaneously heating the welding surface 18 as much as possible, it is important to prevent hot or cold air from reaching the wrong section, particularly when using hot or cold air. Therefore, a spacer element 17 is provided. This element, while not contacting the connecting section 14, substantially surrounds the connecting section and largely prevents air flow from the welding section 15 to the main section 13, and vice versa.

[0066] According to the invention, the service life of the sonotrode is significantly extended by reducing the stresses. Although each measure alone can increase the service life of the sonotrode, it is advantageous to combine as many of the measures as possible.

[0067] Reference Signs List

[0068] 1, 11, 101, 201 ultrasonic welding electrodes

[0069] 2, 102, 202 rear end

[0070] 3, 103, 203 front end

[0071] 4, 104, 204 vibration nodes

[0072] 5, 18, 105, 205 welding surface

[0073] 6, 14, 106, 206 connecting webs

[0074] 7 grooves

[0075] 8, 108, 208 ultrasonic welding electrode body

[0076] 12 Pairing Tools

[0077] 13 main section

[0078] 15 welding sections

[0079] 16 retainer

[0080] 17 Separation Components

[0081] 109, 209 notches

[0082] 110, 210 welding sections

[0083] 211 slots

[0084] 212 Welding surface section

[0085] 213 Welding surface section

[0086] aThe width of the groove

[0087] b slot width

[0088] B v Width of the connecting web in the area of ​​the notch

[0089] b S Width of sealing surface

[0090] l S Length of sealing surface

[0091] k t Notch depth

[0092] k h Notch height

[0093] S Ultrasonic welding pole axis

[0094] S b Widened slot width

[0095] S t Groove depth

[0096] t groove depth

Claims

1. A sonotrode for ultrasonic machining of metals, the sonotrode having a resonance frequency in the ultrasonic range, the sonotrode having a welding surface (5) for contacting the metal to be machined, characterized in that When the ultrasonic welding electrode vibrates at a resonant frequency and the welding surface (5) contacts the metal to be processed, the welding surface (5) is heated and a temperature gradient is formed between the welding surface (5) and a section (6) of the ultrasonic welding electrode adjacent to the welding surface. Due to the effect of the temperature gradient, the welding surface (5) is subjected to stress, and a device is provided for reducing the stress of the welding surface during processing.

2. The ultrasonic welding electrode according to claim 1, characterized in that When the ultrasonic welding electrode is excited at a resonant frequency, a standing wave is formed along the ultrasonic welding electrode axis (s), and the welding surface (5) is not arranged perpendicular to the ultrasonic welding electrode axis (s). The welding surface (5) preferably extends parallel or substantially parallel to the ultrasonic welding electrode axis (s).

3. The sonotrode according to claim 1 , wherein: As a means for reducing the stress on the welding surface, a plurality of depressions with a depth of t and a width of a are introduced into the welding surface, where α>3×t.

4. The ultrasonic welding electrode according to claim 3, characterized in that The depressions are configured as grooves (7), which are preferably arranged parallel to one another.

5. The ultrasonic welding electrode according to claim 4, characterized in that The groove (7) is curved in a cross-sectional view, and the curvature radius r is preferably greater than 1.5 mm, particularly preferably greater than 3 mm.

6. The ultrasonic welding electrode according to claim 4 or 5, characterized in that Each of the grooves (7) is arranged in a plane extending perpendicular to the sonotrode axis (s), and the welding surface is preferably arranged parallel to the sonotrode axis (s).

7. The sonotrode according to any of the preceding claims, characterized in that The ultrasonic welding electrode comprises an ultrasonic welding electrode body (8) and a welding section having the welding surface (5), and is provided with a connecting web (6) connecting the ultrasonic welding electrode body (8) and the welding section. The connecting web (6) serves as a device for reducing the stress of the welding surface, and its cross-sectional area parallel to the welding surface (5) is at least 5%, preferably at least 10%, and particularly preferably at least 15% smaller than that of the welding surface (5).

8. The ultrasonic welding electrode according to claim 7, characterized in that A first recess (109) is arranged in a first side surface of the connecting section, and the connecting web (6) preferably has a second recess (109) in a second side surface.

9. The ultrasonic welding electrode according to claim 7, characterized in that The first and / or the second recess (109) has a curved recess bottom in a cross-sectional view perpendicular to the sonotrode axis (s).

10. The ultrasonic welding electrode according to claim 7 or 8, characterized in that The first and / or the second recess (109) extends parallel to the sonotrode axis (s).

11. The sonotrode according to any of the preceding claims, characterized in that At least one groove (211) is provided on the welding surface (5) as a device for reducing the stress of the welding surface, and the groove divides the welding surface (5) into a plurality of welding surface sections (212, 213). The at least one groove (211) preferably extends parallel to the ultrasonic welding electrode axis (s).

12. The ultrasonic welding electrode according to claim 11, characterized in that The width b of the at least one groove (211) is less than 0.3 mm, preferably less than 0.15 mm, and the width b is greater than 0.025 mm, and preferably greater than 0.05 mm.

13. The ultrasonic welding electrode according to claim 11 or 12, characterized in that The depth S of the groove (211) t It is at least ten times, preferably at least twenty times, the width b.

14. The ultrasonic welding electrode according to claim 11, 12 or 13, characterized in that The groove has a curved groove bottom, the groove has a base portion including the groove bottom, and in the base portion, the groove width b G Greater than said width b, and preferably at least five times said width b.

15. The sonotrode according to any one of the preceding claims, characterized in that When the sonotrode is excited at a resonant frequency, a standing wave having at least one vibration node is formed along the sonotrode axis, and a cooling device is provided as a means for reducing stresses on the weld surface, the cooling device cooling the sonotrode in the region of the vibration node, but preferably not cooling the weld surface.

16. The sonotrode according to any of the preceding claims, characterized in that A heating device is provided as a means for reducing stress on the welding surface, the heating device being arranged and configured such that the welding surface can be heated.

17. An ultrasonic processing device, which has an ultrasonic electrode according to any one of the preceding claims, a converter that converts an alternating voltage into mechanical vibration, the converter being coupled to the ultrasonic electrode, and a generator for generating an alternating voltage with an amplitude of A0, and further provided with a control unit as a means for reducing the stress on the welding surface. Before generating an alternating voltage with an amplitude of A0, the control unit generates an alternating voltage with an amplitude of A within a time interval t V where A V < A0, and t is preferably greater than 0.2 seconds, and particularly preferably greater than 0.4 seconds.

18. The ultrasonic processing equipment according to claim 17, characterized in that The control unit is configured to adjust the amplitude A within a time interval t. V From the minimum value A min , preferably increases from 0 to A0, and the amplitude preferably increases linearly.

19. Use of a sonotrode according to any of the preceding claims for joining two metallic materials by ultrasound, the two metallic materials preferably being arranged between the sonotrode and a counter tool, and for joining the two metallic materials the counter tool and the sonotrode are moved relative to one another, during which the sonotrode does not rotate about the sonotrode axis.

Images