Welding tool having a curved and structured working surface, method for welding and welded workpiece

Abstract

The invention relates to a tool (10) for welding a workpiece (21) by means of friction welding, in particular by means of ultrasound, the tool (10) having a working surface (5) which contains at least one, preferably a plurality of grooves (6). The working surface (5) has a curvature. The invention also relates to a method for welding a workpiece and a welded workpiece.

Description

[0001] Tool, welding process and welded workpiece

[0002] The present invention relates to tools, in particular sonotrodes, for welding workpieces by means of friction welding, to methods for welding a workpiece using such a workpiece and to welded workpieces.

[0003] A typical application for such sonotrodes is the welding of battery cell components. The familiar sonotrodes have welding surfaces that are usually knurled. This often leads to the formation of unwanted metal particles (so-called whiskers), which can, for example, lead to short circuits. Another application is the welding of contact points on IGBT modules (IGBT: Insulated-Gate Bipolar Transistors). Metal particles can also cause damage there.

[0004] It is an object of the present invention to eliminate the aforementioned disadvantages. In particular, the formation of disruptive metal particles should be prevented as much as possible during friction welding, and especially during ultrasonic welding of metals. The same problem should also be eliminated during friction welding of plastics, particularly metallized or carbon fiber-reinforced plastics.

[0005] In a first aspect of the invention, this object is achieved by a tool for welding a workpiece by means of friction welding, in particular by means of ultrasound. The tool can be a sonotrode or an anvil. The tool has a working surface, in particular a welding surface. The working surface contains at least one groove. According to the invention, the working surface has a curvature. As has been shown in series of tests, such a geometry of the working surface ensures a considerable reduction in unbound metal particles or carbon particles. Without the invention being restricted thereto, it is currently assumed that the material flow of the workpiece resulting from welding is specifically guided in the direction of the grooves.The curvature of the work surface ensures that initially only part of the work surface comes into contact with the workpiece, so that the pressure on the workpiece is increased locally. This leads to plastic deformation and material flow. The grooves specifically direct the softened material of the workpiece away from the weld point and form material strands that cannot be easily removed during or after welding. Metal particles or carbon particles are bound into these material strands and can no longer be removed. Nevertheless, the inventive method can be used to produce welded joints that can withstand high tear-out forces.

[0006] The sonotrode can have a longitudinal axis, with respect to which the sonotrode can be excited to torsional ultrasonic vibrations. The working surface can be aligned substantially perpendicular to the longitudinal axis. Furthermore, the at least one groove can extend substantially in a radial direction with respect to the longitudinal axis. Alternatively, it can also be a sonotrode that can be excited to linear vibrations, wherein the welding surface vibrates along a surface of the workpiece when used as intended. In this case, the grooves can run parallel or transverse to the direction of vibration.

[0007] In a currently preferred embodiment, the working surface has a convex curvature, at least in sections. In particular, the entire working surface can have a convex curvature. This results in a central section of the working surface initially coming into contact with the workpiece during welding, and the workpiece material is guided radially outward along the grooves. It is preferred if the at least one groove extends to the center of the working surface.

[0008] Alternatively, it is also possible for the working surface to have a concave curvature, at least in sections. In particular, the entire working surface can have a concave curvature. In this variant, an outer region of the working surface initially comes into contact with the workpiece, and the grooves ensure a radially inward flow of material. For this purpose, it is preferred if the at least one groove extends to the outer circumference of the working surface, especially in the radial direction.

[0009] The working surface can have a curvature height in the range of 0.1 mm to 0.3 mm. This refers to the height of the curvature in a projection along the longitudinal axis.

[0010] Alternatively or additionally, the working surface can have a radius of curvature in the range of 0.5 mm to 20 mm. In particular, the radius of curvature can be in the range of 6 mm to 12 mm in the case of a convex curvature, and in the range of 12 mm to 20 mm in the case of a concave curvature. The radius of curvature can also be equal to half the diameter of the working surface; the working surface is then hemispherical.

[0011] The at least one groove can have a depth in the range of 0.2 mm to 0.5 mm, at least in sections. In particular, the depth of the groove can be in the range of 0.3 mm to 0.4 mm in the case of a convex curvature of the working surface, and in the range of 0.4 mm to 0.5 mm in the case of a concave curvature of the working surface.

[0012] The at least one groove can have a width in the range of 0.4 mm to 0.6 mm, at least in sections. In particular, the width of the groove can be in the range of 0.4 mm to 0.5 mm in the case of a convex curvature of the working surface, and in the range of 0.45 mm to 0.55 mm in the case of a concave curvature of the working surface.

[0013] The at least one groove may have a flank angle which may be in the range of 15° to 75°, preferably in the range of 30° to 60°.

[0014] In the region of at least one of its ends, in particular in a center point and / or on an outer circumference of the welding surface, the depth and / or width of the groove may be smaller than in its central region.

[0015] The groove can be cut into the work surface using a milling cutter, for example, and taper off towards the end.

[0016] The working surface can, for example, have 8 to 12, particularly 10 to 12 grooves. The grooves are preferably evenly distributed circumferentially over the entire circumference. Tests have shown that the effect of material flow is less in the case of a convex curvature than in the case of a concave curvature. Therefore, a larger number of grooves is recommended in the case of a convex curvature.

[0017] The working surface can have a diameter measured perpendicular to the longitudinal axis in the range from 1 mm to 8 mm, preferably from 1.5 mm to 6 mm.

[0018] However, it is also conceivable to design an anvil with a curvature and grooves in order to bind particles present on the side of an anvil.

[0019] The tool, especially the sonotrode, can be made of steel, titanium or a hard metal, for example.

[0020] A further aspect of the invention relates to a method for welding a workpiece by means of ultrasound using a tool with a curved working surface provided with grooves, but also with workpieces that have a 3-dimensional surface with structural features that allow the softened material to flow. The method is carried out in particular using a tool as described above, in particular a sonotrode as described above. The method includes a step in which the working surface of the tool is brought into contact with the workpiece and the tool, in particular the sonotrode, is excited to vibrate so that the workpiece is welded, in particular welded to a further, second workpiece. According to the method, the material of the workpiece is softened during welding and displaced along the grooves or along the structural features on the surface of the workpiece.Through this material flow, any particles are bound into a material accumulation, in particular in a strand, which is formed by the passage of the molten material along the groove or by a movement along the structural features.

[0021] When this procedure is carried out, the advantages explained above result.

[0022] The workpiece can be made of a metal such as aluminum. In particular, it can be type H14 aluminum. It has been shown that, due to the material properties and in particular the flow properties, even better results can be achieved with this type of aluminum than with other types of aluminum. Alternatively, the metal can also be copper, for example. To increase the flow effect, softer copper with a relatively low yield strength can be used. In yet another variant, the workpiece can also be made of a plastic, in particular a plastic containing metal or carbon particles.

[0023] In some applications, one workpiece is a terminal, and the second workpiece is a battery receptacle to which the terminal is to be welded. Alternatively, the second workpiece can be a capacitor or a semiconductor device, such as an IGBT (insulated-gate bipolar transistor).

[0024] In a third aspect, the invention also relates to a workpiece assembled from several parts by welding, which is obtained or obtainable by a method as described above. The welded workpiece thus has a weld point whose geometry corresponds to that of the working surface of the tool. In particular, the assembled workpiece and in particular the weld point contains accumulations of material in which metal particles (in particular whiskers) or other particles are embedded. The accumulations of material are in particular ribs which preferably extend in a radial direction. As already explained, such a workpiece welded according to the invention contains significantly fewer unbound particles, in particular metal particles, on the surface.

[0025] The workpiece may be made of a metal such as aluminium, in particular aluminium of type H14, or of copper.

[0026] The invention is explained in more detail below with reference to two exemplary embodiments and drawings. These show:

[0027] Figure 1: a first sonotrode according to the invention in a perspective view;

[0028] Figure 2a: a welding surface of the first sonotrode according to the invention in a perspective detailed view;

[0029] Figure 2b: the welding surface of the first sonotrode according to the invention in a detailed side view;

[0030] Figure 2c: a top view of the welding surface of the first sonotrode according to the invention; Figure 3a: a perspective detailed view of a welding surface of a second sonotrode according to the invention;

[0031] Figure 3b: the welding surface of the second sonotrode according to the invention in a detailed side view;

[0032] Figure 3c: the welding surface of the second sonotrode according to the invention in a plan view;

[0033] Figure 4: a representation of a weld joint produced with a sonotrode not according to the invention;

[0034] Figure 5a: a representation of a weld joint produced with the first sonotrode according to the invention;

[0035] Figure 5b: a representation of a weld joint produced with the second sonotrode according to the invention;

[0036] Figure 6: a welding surface of a third sonotrode according to the invention in a perspective detailed view;

[0037] Figure 7: a welding surface of a fourth sonotrode according to the invention in a perspective detailed view;

[0038] Figure 8: a welding surface of a fifth sonotrode according to the invention in a perspective detailed view;

[0039] Figure 9: a welding surface of a sixth sonotrode according to the invention in a perspective detailed view.

[0040] Figure 1 shows a first sonotrode 10 according to the invention. It has a base body 1 with a coupling surface 3 for coupling in ultrasonic vibrations and a machining pin 2 extending along a longitudinal axis L with a welding surface 5 for transmitting the ultrasonic vibrations to a workpiece (not shown here). The welding surface 5 is arranged on an end face of the machining pin 2 opposite the base body 1. The machining pin 2 is connected to the base body 1 by being pressed into a press-in opening 4 formed in the base body 1. Alternatively, the connection could be created, for example, by laser welding.

[0041] The machining pin 2 is generally circular-cylindrical in shape. It can have a diameter d in the range of, for example, 1.5 mm to 6 mm. If the machining pin 2 is made of steel, it can have a length 1 of, for example, 80 mm or 160 mm, which corresponds to half or a whole wavelength at a resonant frequency of 20 kHz. If, however, the machining pin 2 is made of, for example, a hard metal such as tungsten carbide, half the wavelength at the aforementioned frequency is approximately 130 mm. In the exemplary embodiment shown here, the base body 1 is made of titanium and has a length which, in this example, corresponds to half the wavelength in this material.

[0042] Figures 2a to 2c show the welding surface 5 in detail. The entire welding surface 5 has a convex curvature with a curvature radius of 9 mm and a curvature height h of 0.2 mm. Twelve grooves 6 are formed in the welding surface 5, evenly distributed over the entire circumference and extending radially from a center point 7 to the outer circumference 8 of the welding surface 5. The grooves 6 have a depth t of 0.36 mm at the center point 7 and a width of 0.45 mm, and taper towards the outer circumference 8. They have a flank angle α, which in this example is 45°.

[0043] Figures 3a to 3c show a second embodiment, in which, however, the welding surface 5 is concavely curved and contains only 10 grooves 6. The grooves 6 have a depth of 0.42 mm and a width of 0.49 mm at the outer circumference 8 and taper towards the center point 7.

[0044] Deviating from the embodiments described above, the sonotrode can, of course, also be formed in one piece. Figures 4 to 5a show sections of welded workpieces 21 that were welded with sonotrodes not according to the invention or with sonotrodes according to the invention.

[0045] Figure 4 shows a weld made with a conventional sonotrode, which has a substantially flat weld surface with knurling. Several unwanted metal particles 23 ("whiskers") can be seen at the edge of the weld, which can lead to quality problems.

[0046] The weld shown in Figure 5a was created with the first sonotrode according to the invention, as shown in Figures 2a to 2c. The image clearly shows that, due to its convex curvature, the sonotrode was only in contact with the workpiece 21 in a central region. The grooves of the sonotrode formed a material flow created during welding radially outward into thicker material strands. These strands cannot be easily removed even after welding and are embedded with metal particles.

[0047] The weld shown in Figure 5b was produced with the second sonotrode according to the invention as shown in Figures 3a to 3c. As can be seen from the photo, the sonotrode was only in contact with the workpiece 21 in its outer region due to the concave curvature of the welding surface.

[0048] Welds were performed using a sonotrode with a convex welding surface and the input parameters listed below: amplitude, energy, and pressure. At least 10 tests resulted in welding times ranging from 220 ms to 240 ms and peak powers ranging from 240 W to 280 W, with only one "whisker" forming. The welds withstood pull-off forces ranging from 10 N to over 140 N.

[0049] When the workpieces were cleaned before welding, no or only a few whiskers were found in 10 tests, but the welds consistently withstood even pull-off forces of more than about 60 N.

[0050] Welds were performed using a sonotrode with a concavely curved welding surface with the input parameters amplitude, energy, and pressure listed below. Welding times ranged from 90 ms to 100 ms and peak powers ranged from 450 W to 550 W, with a maximum of three whiskers being formed in 10 tests. The welds withstood pull-off forces ranging from approximately 50 N to approximately 190 N.

[0051] When the workpieces were cleaned before welding, the welds consistently withstood pull-off forces of more than 140 N.

[0052] The following parameter combination has proven particularly advantageous for welding with a convex welding surface:

[0053] - Amplitude: 90% of the maximum amplitude achievable with the sonotrode, for example 15 pm to 50 pm;

[0054] - Diameter: 1.5 mm to 6 mm (corresponding to an area of ​​1.77 mm 2 up to 28.3 mm 2) ;

[0055] - Force: 100 N to 600 N;

[0056] - Energy: 5 Ws to 500 Ws, in particular 20 Ws to 60 Ws, in particular 30 Ws to 50 Ws, for example 40 Ws;

[0057] - average time: 100 ms to 400 ms, in particular 200 ms to 300 ms, for example 230 ms.

[0058] The following parameter combination has proven to be advantageous for welding with a concave welding surface:

[0059] - Amplitude: 75% of the maximum amplitude achievable with the sonotrode, for example 15 pm to 50 pm;

[0060] - Diameter: 1.5 mm to 6 mm (corresponding to an area of ​​1.77 mm 2 up to 28.3 mm 2 ) ; - Force: 100 N to 600 N;

[0061] - Energy: 5 Ws to 500 Ws, in particular 20 Ws to 60 Ws, in particular 30 Ws to 50 Ws, for example 40 Ws;

[0062] - average time: 100 ms to 400 ms, in particular 200 ms to 300 ms, for example 230 ms.

[0063] Figures 6 to 9 show working surfaces of further sonotrodes according to the invention, each having a diameter d = 2.5 mm and working surfaces 5 with the following geometric parameters:

Claims

Patent claims 1. Tool (10) for welding a workpiece (21) by means of friction welding, in particular by means of ultrasound, wherein the tool (10) has a working surface (5) which contains at least one, preferably several grooves (6), characterized in that the working surface (5) has a curvature.

2. Tool (10) according to claim 1, wherein the tool (10) is a sonotrode (10) for welding a workpiece (21) and the working surface (5) forms a welding surface (5).

3. Sonotrode (10) according to claim 2, wherein the sonotrode (10) has a longitudinal axis (L) with respect to which it can be excited to torsional ultrasonic vibrations.

4. Sonotrode (10) according to claim 3, wherein the at least one groove (6) extends substantially in a radial direction with respect to the longitudinal axis (L).

5. Tool (10), in particular sonotrode (10), according to one of claims 1 to 4, wherein the working surface (5) has a convex curvature at least partially, in particular the entire working surface (5).

6. Tool (10), in particular sonotrode (10), according to one of claims 1 to 4, wherein the working surface (5) has a concave curvature at least in sections, in particular the entire working surface (5).

7. Tool (10), in particular sonotrode (10), according to one of the preceding claims, wherein the at least one groove (6) extends to the center point (7) of the working surface (9).

8. Tool (10), in particular sonotrode (10), according to one of the preceding claims, wherein the at least one groove (6) extends to the outer circumference (8) of the working surface (5).

9. Tool (10), in particular sonotrode (10), according to one of the preceding claims, wherein the working surface (5) has 8 to 16, in particular 10 to 12 grooves (6) which are preferably evenly distributed in the circumferential direction.

10. Tool (10), in particular sonotrode (10), according to one of the preceding claims, wherein the working surface (5) has a diameter measured perpendicular to the longitudinal axis (L) in the range of 1 mm to 8 mm, preferably from 1.5 mm to 6 mm.

11. Tool (10) , in particular sonotrode (10) , according to one of the preceding claims, wherein the working surface (5) has a curvature height (h) in the range of 0.1 mm to 0.3 mm.

12. Tool (10), in particular sonotrode (10), according to one of the preceding claims, wherein the working surface (5) has a radius of curvature in the range of 0.5 mm to 20 mm.

13. Tool (10) , in particular sonotrode (10) , according to one of the preceding claims, wherein the at least one groove (6) has at least sectionally a depth (t) in the range of 0.2 mm to 0.5 mm.

14. Tool (10), in particular sonotrode (10), according to one of the preceding claims, wherein the at least one groove (6) has at least sectionally a width in the range of 0.4 mm to 0.6 mm.

15. Tool (10), in particular sonotrode (10), according to one of the preceding claims, wherein the at least one groove (6) has a flank angle (a) in the range of 15° to 75°, preferably in the range of 30° to 60°.

16. Sonotrode (10) according to one of the preceding claims, wherein the sonotrode (10) has a base body (1) with a coupling surface (3) for coupling ultrasonic vibrations and a processing pin (2) extending along a longitudinal axis (L) with a welding surface (5).

17. Sonotrode (10) according to claim 16, wherein the processing pin (2) has a diameter (d) in the range of 1.5 mm to 6 mm.

18. Method for welding a workpiece (21), in particular by means of ultrasound, - using a tool (10), in particular a sonotrode (10) according to one of the preceding claims, having a curved working surface (5) provided with grooves (6), and / or - using a workpiece which has a particularly 3-dimensional surface with structural features, comprising a step in which a working surface (5) of the tool (10) is brought into contact with the workpiece (21) The tool (10) is excited to vibrate, causing the workpiece (21) to be welded, in particular to another workpiece, whereby the material of the workpiece is at least partially softened and displaced along the grooves (6) or along the structural features on the surface of the workpiece (21), so that particles are incorporated into an accumulation of material by the material flow, which is formed by the passage of the molten material along the groove (6) or by movement along the structural features. A method according to claim 18, wherein the workpiece (21) consists of a metal such as, for example, aluminum, in particular aluminum type H14, or copper. A method according to one of claims 18 and 19, wherein the workpiece (21) is a terminal contact of a battery and the other workpiece is a receiving container for a battery.Welded workpiece (21) obtained or obtainable by a method according to any one of claims 18 to 20. Welded workpiece (21) according to claim 21, wherein the workpiece (21) consists of a metal such as, for example, aluminum, in particular aluminum type H14, or copper. Welded workpiece (21) with a weld joint, in particular workpiece (21) according to claim 21 or 22, wherein the workpiece (21) and in particular the weld joint has material accumulations in which metal particles are embedded, wherein the material accumulations are ribs that preferably extend in a radial direction.

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