Sonotrodes, devices and methods for the ultrasonic machining of workpieces

Abstract

The application relates to a sonotrode (11) for the ultrasonic machining of workpieces, in particular for welding electrical conductors. The sonotrode (11) has, on a circumferential surface (13), at least one protrusion (14) with a working surface (15). The sonotrode (11) is able to be excited to vibrate relative to a longitudinal axis (L). The working surface (15) is at an angle (a) relative to the longitudinal axis of the sonotrode (11). The application also relates to a device, in particular having such a sonotrode, and to a method for the ultrasonic machining of workpieces, in particular using such a device.

Description

[0001]Sonotrode, Device and Method for Ultrasonic Machining of Workpieces The invention relates to a sonotrode, a device and a method for ultrasonic machining of workpieces according to the preamble of the independent claims. It is known to machine workpieces by introducing ultrasonic vibrations. Typical applications include joining workpieces by ultrasonic welding. In particular, electrical conductors such as stranded wires or terminals are also welded together. From WO 2011 / 138404 A1, for example, a so-called torsion sonotrode is known, by means of which a welded joint can be produced. In this case, a working surface is provided on a circumferential surface surrounding a torsion axis at a distance from a torsion axis. The working surface is arranged in a central region of the sonotrode.20 From WO 2012 / 069413 A1, a device for torsional welding of metal parts using ultrasound is also known. A welding surface is arranged at one end of a torsionally oscillating sonotrode, which can be set into torsional oscillations by means of one or more converters. 25 While these solutions allow satisfactory welding results in many applications, challenges arise, especially in connection with larger workpieces to be welded, regarding the accessibility of the workpieces and regarding the uniformity of the introduced vibrations. 30 Due to the torsional oscillations, the vibration amplitude is not constant along the length of the sonotrode. Especially with long weld joints extending in the direction of the sonotrode, variations in amplitude therefore occur.Furthermore, the solution according to WO 2011 / 138404 A1 is difficult to use for components with a relatively large height, such as terminals, because increasing the distance of the weld surface from the torsional axis leads to large, oscillating masses. The object of the invention is therefore to avoid the disadvantages of the known method and, in particular, to provide a sonotrode, a device, and a method for ultrasonic machining of workpieces that allow for uniform application of the ultrasonic energy and, in particular, also enable the machining of large workpieces. According to the invention, these objects are solved with sonotrodes, devices, and methods having the features of the independent patent claims. According to a first aspect of the invention, a sonotrode for ultrasonic machining of workpieces is proposed. In particular, it is a sonotrode for welding electrical conductors.25 The sonotrode has a circumferential surface and is provided with at least one projection on the circumferential surface. The projection has a working surface. 30 The sonotrode can be excited to oscillations with respect to a longitudinal axis. These are preferably torsional oscillations. According to the invention, the working surface is arranged at an angle with respect to the longitudinal axis of the sonotrode. The angle is selected such that the distance of the working surface to the longitudinal axis changes along the longitudinal axis. Due to this 5 inclination of the working surface, the amplitude variation resulting from the torsional oscillation can be compensated. The amplitudes of the torsional oscillation on the circumferential surface are almost 0 in the circumferential direction at a torsional oscillation node. At an antinode, they are a maximum of 10 times greater. The torsional amplitudes on the working surface depend on the distance of the working surface to the longitudinal axis of the sonotrode.The greater the distance to the longitudinal axis, the greater the torsional amplitude in the area of ​​the working surface. The sonotrode according to the invention is therefore preferably designed 15 such that it can be excited to torsional vibrations about its longitudinal axis with a coupling point, as described, for example, in WO 2012 / 069413. Such compensation of an amplitude could also be advantageous for longitudinal sonotrodes. 20 The angle between the working surface and the longitudinal axis of the sonotrode is selected, depending on the length, the radius of the working surface and / or the distance between torsional vibration minima and vibration maxima, such that 25 the best possible compensation of the amplitude changes is achieved. Preferably, the angle is between 5° and 35°, more preferably between 10° and 20°, and particularly preferably about 14°.In this specific application, the angle is determined by a simulation for a particular geometry such that the amplitude changes along the working surface are minimized. Preferably, the sonotrode has a plurality of projections, each with a working surface. The projections are arranged particularly evenly around the circumference of the sonotrode. Preferably, there are two projections. This makes it possible to reinstall the sonotrode when it reaches the end of its service life, rotated 180 degrees around its axis, so that a second, unused working surface can be used. The working surface preferably extends over a relatively large length of the sonotrode, typically over 30 to 60 percent and particularly preferably over 45 to 55 percent of the length of the sonotrode, measured in the longitudinal direction of the sonotrode.Preferably, the working surface has a structure, in particular in the form of grooves extending in the direction of the longitudinal axis. This increases the energy input into the workpieces. Preferably, the sonotrode has a mounting contour for its attachment. The mounting contour is typically located in the region of a vibration minimum and is adjacent to a rear side of the projection. Preferably, the working surface adjacent to the rear side of the projection has the greatest distance from the longitudinal axis. This results in the amplitude being most greatly increased adjacent to the vibration minimum due to the greater distance, so that a relatively constant amplitude is achieved over the length of the working surface. The projection preferably has an undercut on its rear side extending from the circumferential surface.Preferably, an annular surface extending in a plane perpendicular to the longitudinal axis adjoins the undercut and transitions into the working surface. The undercut also assists in compensating for amplitude changes. Irregularities in the amplitude can be homogenized by means of the undercut. 5 The working surface preferably has the smallest distance to the longitudinal axis adjacent to an end face of the projection. This also serves to better homogenize the amplitude along the working surface. 10 Preferably, the end face has an end section adjoining the working surface that extends perpendicular to the working surface. 15 According to a further aspect of the invention, a device for the ultrasonic machining of workpieces is proposed. The device comprises a sonotrode and an anvil. Typically, a sonotrode designed as described above is used.The sonotrode is set into vibration, in particular torsional vibrations, by means of a converter 20 in a manner known per se. A working space for receiving the workpieces to be machined is formed between the sonotrode and the anvil. The anvil can be a passive component. However, it is also conceivable to excite the anvil itself to ultrasonic vibrations 25 in order to increase the energy input. It is also conceivable to use a second sonotrode as described above. The sonotrode has a circumferential surface on which at least one projection with a working surface is provided. The working surface is arranged at an angle 30 to the longitudinal axis of the sonotrode. This also means that the longitudinal axis of the sonotrode lies at an angle to a contact surface of the anvil and that the sonotrode is installed obliquely in the device according to the invention.Preferably, the device can have side limits for laterally defining the working space 5 in a manner known per se. A further aspect of the invention relates to a method for the ultrasonic processing of workpieces, in particular for welding electrical conductors. Preferably, a device 10 as described above is used. In a first step, workpieces are placed in a working space formed between a sonotrode and an anvil. These can be, for example, several strands that are to be connected (spliced) together or joined together to form a 15 node. Likewise, they can be a terminal onto which one or more strands are welded. The anvil can serve as a support surface for the terminal.However, it can also form a contour that can be moved in a known manner, by means of which the working space can be closed and workpieces placed therein, such as stranded wires, can be compressed. The sonotrode is preferably excited to torsional vibrations. According to yet another aspect of the invention, a device for ultrasonic processing of workpieces, and in particular for welding electrical conductors, is proposed. The device comprises a sonotrode and an anvil. A working space for receiving the workpieces to be processed is formed between the sonotrode and the anvil. The sonotrode has a circumferential surface on which at least one projection with a working surface is formed. The sonotrode can be excited to vibrations with respect to a longitudinal axis. According to the invention, the projection is arranged adjacent to the end of the sonotrode with respect to its longitudinal direction.Because the projection is located adjacent to the end of the sonotrode, the device can also be used for welding components with a relatively high overall height, such as terminals. The parts of the workpiece to be welded with a greater height can therefore be arranged laterally to the sonotrode, in a sense extending its axis. Preferably, the sonotrode is provided with at least one projection at both ends. This allows for a symmetrical design of the sonotrode, which leads to an optimized vibration pattern. It is particularly preferred that the sonotrode has a plurality of projections, each with a working surface, at one end, preferably at both ends. This allows unused working surfaces to be used when the working surfaces wear down due to rotation of the sonotrode, as is shown, for example, for a centrally arranged working surface in EP 1 566 233.In a preferred embodiment, the sonotrode has a counterweight 25 on its circumferential surface in a central section. Such an additional mass allows the distances between the vibration minima to be reduced. This enables the sonotrode according to the invention to be mounted in the same manner as the sonotrode shown in WO 2011 / 138404. The distances between structures used for mounting at a vibration minimum 30 can thus be adapted to existing devices. Preferably, the counterweight is also rotationally symmetrical with respect to the longitudinal axis. Furthermore, the counterweight preferably has an outermost surface that is located at a distance from the longitudinal axis that is smaller than the distance 5 of the working surface from the longitudinal axis. This makes it particularly easy to integrate the sonotrode according to the invention into the device.Preferably, the sonotrode has at least one, and preferably two, mounting contours in a vibration minimum for attaching the sonotrode. Preferably, a mounting contour is provided between the at least one projection and the counterweight. Preferably, if projections are at both ends of the sonotrode, mounting contours are provided on both sides of the counterweight. If projections are on only one side, preferably two mounting contours are provided on both sides of a counterweight. Another aspect of the invention relates to a sonotrode for a device as described above. The sonotrode has at least one projection with a working surface on a circumferential surface. The sonotrode can be excited to vibrations about its longitudinal axis, in particular torsional vibrations. According to the invention, the projection is arranged adjacent to the end of the sonotrode.Preferably, the sonotrode is configured as described above in connection with the device, in particular with a projection at both its ends and preferably with several projections at each end, as well as with a counterweight. 30 Another aspect of the invention relates to a method for the ultrasonic processing of workpieces, in particular for welding electrical conductors. In particular, a sonotrode as described above is used. First, workpieces are placed in a working chamber formed between a sonotrode and an anvil. Preferably, the workpieces are a terminal and at least 5 a stranded wire. The sonotrode is then excited to torsional vibrations about its longitudinal axis. A working surface on a projection 10 extending from a circumferential surface of the sonotrode is excited to vibrations.The work surface is located adjacent to the end of the sonotrode with respect to its longitudinal axis. The workpieces are placed in the work space such that a portion of at least one of the workpieces extends laterally to the sonotrode along an extension of its axis. 15 The invention is explained in more detail below with reference to exemplary embodiments and the drawings. Figure 1 shows a schematic representation of a first embodiment of a device according to the invention. Figure 2 shows a perspective view of a sonotrode according to the device in Figure 1. Figure 3 shows an enlarged view of a projection of the sonotrode according to Figure 2. Figure 4 shows a perspective view of the sonotrode according to Figures 2 and 3 in its assembled form. Figure 5: A cross-section through the sonotrode according to Figures 2 to 4. Figure 6: A top view of the sonotrode according to Figures 2 to 5. Figure 7: A representation of the state of the art.Figure 8: A schematic representation of part of a sonotrode according to a second embodiment of the invention. Figure 9: A representation of a complete sonotrode according to the second embodiment of the invention. Figure 10: The sonotrode according to Figure 9 in an assembled arrangement within a device. Figure 11: A representation of an alternative sonotrode according to the second embodiment. Figure 1 shows a device 10 for welding strands. The device 10 has a sonotrode 11. A projection 14, which has a working surface 15, is arranged on a circumferential surface 13 of the sonotrode 11. The working surface 15, together with an anvil 12 and two side limiters 16a, 16b, forms a working chamber A for the strands.The working chamber A can be opened and closed in a manner known per se, so that the strands inserted therein can be closed and compressed by moving the anvil 12 in a vertical direction and by moving the side limiters 16a, 16b in a horizontal direction. This compacts the inserted strands. The sonotrode 11 can be excited to torsional vibrations about a longitudinal axis L in a manner known per se. The working surface 15 is arranged at an angle α with respect to the longitudinal axis L. Therefore, the sonotrode 11 is installed obliquely in the device 10, so that its longitudinal axis L also runs at an angle α with respect to a horizontal. Figure 2 shows a perspective view of the sonotrode 11 5 from Figure 1. The sonotrode 11 has two projections 14, which are evenly spaced on the circumferential surface 13, offset by 180° in the circumferential direction. The working surface 15 is provided with grooves 17.10 The projection 14 has a back side 19 that faces a mounting contour 18 for attaching the sonotrode. The mounting contour 18 is located in a region of a torsional vibration minimum of the sonotrode 11. An undercut 20 is located on the back side 19 of the projection 14. 15 The projection 14 transitions from the undercut 20 via an annular surface 21 into the working surface 15. The annular surface 21 lies in a plane that is perpendicular to the longitudinal axis L. Positioning grooves 29 are also located parallel to the longitudinal axis L. On the side of the back side 19 opposite the longitudinal axis L, the projection 14 has an end face 22. Figure 3 shows an enlarged section of one of the projections 14 of the sonotrode from Figure 2. Identical reference numerals denote identical parts. A circumferential groove 25 is located between the undercut 20 and the mounting contour 18.The undercut 20 serves to achieve the most uniform amplitude possible over the entire length 30. The undercut 20 transitions into the groove 25, which forms a radius that is chosen to be as large as possible to reduce mechanical stress. Figure 4 shows a perspective view of a mounted sonotrode 11. The sonotrode 11 is vibrationally decoupled in a mounting 30 of the device 10 via the mounting contour 18 (see Figures 2 and 3). The sonotrode 11 is also connected to a coupling piece 32, which has a mechanical connection interface 31 for connection with converters 34 in a manner known per se. The converters 34 allow ultrasonic vibrations to be introduced into the sonotrode 10 in a direction perpendicular to the longitudinal axis L in a manner known per se, so that the sonotrode 11 is excited to torsional vibrations around the longitudinal axis L.Figure 5 shows a side view of the sonotrode 11 described in Figures 2 to 4. The sonotrode 11 has a threaded bore 15 33 for connection with the coupling piece 32 (see Fig. 4). On the end face 22, the projection 14 adjoins the working surface 15 and has an end section 23 that runs perpendicular to the working surface 15. The sonotrode also has a recess 24 on the side 20 facing away from the threaded bore 33, viewed in the axial direction L. The recess 24 forms a space for receiving one of the side limiters 16a, 16b of the welding chamber when the sonotrode 11 and the anvil 12 approach each other. The working surface 15 has a length l1 in a projection onto the longitudinal axis L, which is typically about 40 mm. The length l2 of the sonotrode is typically about 80 mm.The distance of the working surface 15 from the circumferential surface 13 increases continuously from a minimum distance b to a maximum distance a, such that the working surface 15 runs at an angle α of 14° to the longitudinal axis L. This means that the working surface lies on a radius relative to the longitudinal axis L that increases from approximately 34.4 mm to 44 mm. Figure 6 shows a top view of the sonotrode according to Figures 25 to 5. The threaded bore 33 is arranged on a connecting surface 28, which can be brought into contact with the coupling piece 32. The projections 14 have grooves 17. Longitudinally extending positioning grooves 29 serve to align and secure the sonotrode 11. Figure 7 shows, for the purpose of illustrating the prior art, a device 5 with a known sonotrode 1, such as that known from WO 2011 / 128404. The sonotrode 1 has a projection 3 with a working surface 2.The sonotrode 1 15 serves to weld workpieces W, exemplified in the form of a terminal, onto which strands (not shown) are to be welded. Due to the relatively large height of the terminal W, the welding point 4 cannot be contacted by the working surface 2. Increasing the radius of the working surface 20 is not an option because this would result in an excessively long sonotrode 1 at a certain frequency and vibration mode. Furthermore, with an excessively large working surface radius, vibration under full load would cause the projection 3 to bend circumferentially. Figure 8 shows a first embodiment of a sonotrode 51 modified compared to Figure 7. The sonotrode 51 has a circumferential surface 53. From the circumferential surface 53, two projections 54 extend at both ends, which are provided with a working surface 55 30.The working surface 55 runs parallel to a longitudinal axis LL, about which the sonotrode can be excited to torsional vibrations. The projection 54 is arranged directly adjacent to the end E of the sonotrode 51. Due to this arrangement, unlike in the prior art, the sonotrode 51 can readily be used for welding components W with a large height without having to increase the radius r1 of the working surface 55. The sonotrode 5 has an undercut 56 between the working surface 55 and the circumferential surface 53. Thanks to this undercut 56, the amplitude can be corrected, so that a chamfer according to the embodiments described above can be dispensed with. Figure 9 shows a perspective view of the sonotrode from Figure 8. The sonotrode 51 has two projections 54 at each of its two ends, each with a working surface 55. A compensating mass 59 is also provided in the middle.The counterweight 59 extends from a central section 60. The counterweight 59 has a radius r2 that is smaller than the radius r1 of the working surface 55 from the longitudinal axis LL. Between the counterweight 59 and the projection 54, there are mounting contours 58 on both sides for mounting the sonotrode 51. The mounting contours 58 are arranged in the region of a torsional vibration minimum. The sonotrode 51 is rotationally symmetrical overall with respect to the longitudinal direction LL and mirror-symmetrical with respect to a median plane passing through the counterweight 59. Figure 10 shows a device 50 in which the sonotrode 51 is installed and fastened with a mounting 61. The sonotrode 51 forms a working space AA with a support surface 52 of the workpiece W. The support surface 52 serves as an anvil for the 30 support of a strand not shown.The workpiece W is mounted laterally next to the sonotrode 51 in the longitudinal direction LL. Figure 11 shows an alternative embodiment of a sonotrode 51. In comparison to the embodiment according to Figure 9, a projection 54 with a working surface 55 is arranged only on one side. Mounting contours 58 are arranged on both sides of a compensating mass 59. In the embodiments of Figures 8–11, the sound is transmitted in a manner known per se through an end face 63 of the sonotrode 10 opposite the active working surface 55'.

Claims

Claims 1. Sonotrode (11) for ultrasonic processing of workpieces, in particular for welding electrical conductors, 5 wherein the sonotrode (11) is provided on a circumferential surface (13) with at least one projection (14) and a working surface (15), and 10 wherein the sonotrode (11) can be excited to vibrations with respect to a longitudinal axis (L), characterized in that the working surface (15) is arranged at an angle 15 (α) with respect to the longitudinal axis of the sonotrode (11).

2. Sonotrode (11) according to claim 1, wherein the sonotrode (11) can be excited to torsional vibrations about the longitudinal axis (L). 20 3. Sonotrode (11) according to one of claims 1 or 2, wherein the angle (α) is between 5° and 30°, preferably between 10° and 20°, and particularly preferably about 14°. 4.A sonotrode (11) according to any one of the preceding claims, wherein the sonotrode (11) has a plurality of projections (14) each having a working surface (15), the projections (14) being arranged uniformly around the circumference of the sonotrode (11), in particular two projections (14). A sonotrode (11) according to any one of the preceding claims, wherein the working surface (15) extends over a length (l1) of 30% - 60% of the length (l2) of the sonotrode (11), preferably 45% - 55%.

6. Sonotrode (11) according to any one of the preceding claims, wherein the working surface (15) has a structure, in particular in the form of grooves (17) extending in a plane through the longitudinal axis.

7. Sonotrode (11) according to any one of the preceding claims, wherein the sonotrode (11) has a fastening contour (18) for fastening the sonotrode (11), which is arranged adjacent to a rear side of the projection (14) in a region of a vibration minimum.

8. Sonotrode (11) according to claim 7, wherein the working surface (15) has the greatest distance (a) to the longitudinal axis adjacent to the rear side (19) of the projection (14). 9.A sonotrode (11) according to claim 7 or 8, wherein the projection (14) on the rear side (19) has an undercut (20) extending from the circumferential surface (13) of the sonotrode (11), to which a ring surface (21) preferably extends in a plane perpendicular to the longitudinal axis (L) of the projection (15) is connected, which transitions into the working surface (15).

10. A sonotrode (11) according to any one of claims 7 to 9, wherein the working surface (15) adjacent to an end face (22) of the projection (14) has the smallest distance (b) to the longitudinal axis (L).

11. A sonotrode (11) according to claim 10, wherein the end face (22) has an end section (23) adjoining the working surface (15), which extends perpendicular to the working surface (15).

12. Device (10) for ultrasonic processing of workpieces, in particular for welding electrical conductors, 5 wherein the device (10) comprises a sonotrode (11), in particular a sonotrode (11) according to one of claims 1 – 11, and an anvil (12), wherein a working space (A) for receiving the workpieces to be processed is formed between the sonotrode (11) and the anvil (12), wherein the sonotrode (11) is provided with a working surface 15 (15) on a circumferential surface (13) with at least one projection (14) and wherein the sonotrode (11) can be excited to vibrations with respect to a longitudinal axis (L), 20 characterized in that the working surface (15) is arranged at an angle (α) with respect to the longitudinal axis of the sonotrode (11).

13. Device (10) according to claim 12, wherein the device 25 (10) comprises side limiters (16a, 16b) for laterally limiting the working space (A). 14.Method for ultrasonic processing of workpieces, in particular for welding electrical conductors, especially with a device (10) according to claim 12 or 13, comprising the steps:. - Placing the workpieces in a working space (A) formed between a sonotrode (11) and an anvil (12). 5 - Exciting the sonotrode (11) with respect to a longitudinal axis, wherein a working surface (15) on a circumferential surface (13) is excited to vibrate, the working surface (15) being arranged at an angle (α) with respect to the longitudinal axis (L) of the sonotrode (11). 10 15. Method according to claim 14, wherein the workpieces are strands.

16. Method according to one of claims 14 or 15, wherein the sonotrode (11) is excited to torsional vibrations.

17. Method according to one of claims 14 to 16, wherein the working space is laterally bounded by side limiters (16a, 16b). 20 18.Device (50) for ultrasonic processing of workpieces (W), in particular for welding electrical conductors, 25 wherein the device has a sonotrode (51) and an anvil (52), wherein a working space (AA) for receiving the workpieces (W) to be processed is formed between the sonotrode (51) and the anvil (52), wherein the sonotrode is on a circumferential surface (53) with at least one projection (54) with a working surface (55).

19. Device (50) according to claim 18, wherein the sonotrode (51) is provided with at least one projection (54) at both its ends (E).

20. Device (50) according to claim 18 or 19, wherein the sonotrode (51) has at one end (E), preferably at both ends, a plurality of projections (54) each with a working surface (55), which projections (54) are arranged uniformly around the circumference of the sonotrode (51), in particular two projections (54). 20 21. Device (50) according to one of claims 18 – 20, wherein the sonotrode (51) has a compensating mass (59) on its circumferential surface (53) in a central section (60). 25 22.Device (50) according to claim 21, wherein the compensating mass (59) is rotationally symmetrical with respect to the longitudinal axis (LL).

23. Device (50) according to claim 21 or 22, wherein the compensating mass (59) has an outermost surface which has a distance (r2) from the longitudinal axis (LL) that is smaller than the distance (r1) of the working surface (55) from the longitudinal axis (LL).

24. Device (50) according to one of claims 18 to 23, wherein the sonotrode (51) has at least one and preferably two fastening contours (58) for fastening the sonotrode (51), wherein preferably a fastening contour (58) is arranged on both sides of the counterweight 5 (59).

25. Sonotrode (51), in particular for a device according to one of claims 18 to 24, wherein the sonotrode is provided on a circumferential surface (53) with at least one projection (54) having a working surface (55), and wherein the sonotrode (51) can be excited to vibrations with respect to a longitudinal axis (LL) 15, characterized in that the projection (54) is arranged adjacent to the end (E) of the sonotrode. 26.Method for ultrasonic processing of workpieces, in particular for welding electrical conductors, in particular with a sonotrode (51) according to one of claims 18 - 24, comprising the steps: 25 - Inserting the workpieces (W) into a working space (AA) formed between a sonotrode (51) and an anvil (52), wherein the workpieces (W) are preferably inserted into the working space (AA) such that a part of at least one of the workpieces (W) extends laterally to the sonotrode (51) in an extension of its axis. - Excitation of the sonotrode (51) to torsional vibrations with respect to a longitudinal axis (LL), wherein a working surface (55) on a projection (54) extending from a circumferential surface (53) of the sonotrode (51) is excited to vibrations, wherein the working surface (55) is arranged adjacent to the end (E) of the sonotrode (51) with respect to the longitudinal axis (LL) of the sonotrode (51).

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