Welding method with vibration detection, and welding tool therefor

Abstract

The present invention relates to a welding method for connecting a joining surface of a first joining partner to a joining surface of a second joining partner, said method comprising the steps of: A) arranging the two joining partners between a first coupling surface of a sonotrode and a second coupling surface of a counter-tool such that the first joining partner is in contact with the first coupling surface, the second joining partner is in contact with the second coupling surface, and the two joining surfaces are in contact with each other, B) applying a force to the two joining partners via at least one of the coupling surfaces in the direction of the other coupling surface, C) exciting the sonotrode with a mechanical vibration so that the first coupling surface moves at a vibration frequency, D) reducing or stopping the force applied in step B) and / or reducing or stopping the excitation in step C), characterised by the step of E) detecting a connection between the first and second joining partners during step B) and / or step C) by detecting a mechanical vibration of at least one side surface of a joining partner that is in contact with a coupling surface and, if a value detected in step E) meets a predefined criterion, determining that there is a connection between the first and second joining partners.

Description

[0001] Welding process with vibration detection and welding tool for this

[0002] The present invention relates to a welding method for connecting a joining surface of a first joining partner with a joining surface of a second joining partner, comprising the steps

[0003] A) Arranging the two joining partners between a first coupling surface of a sonotrode and a second coupling surface of a counter-tool, so that the first joining partner is in contact with the first coupling surface, the second joining partner is in contact with the second coupling surface and the two joining surfaces are in contact with each other,

[0004] B) Exerting a force on the two joining partners via at least one of the coupling surfaces in the direction of the other coupling surface,

[0005] C) Excitation of the sonotrode with a mechanical vibration so that the first coupling surface moves with a vibration frequency,

[0006] D) Reducing or stopping the application of force from step B) and / or reducing or stopping the stimulation from step C).

[0007] Such a welding process is essentially known as an ultrasonic welding process. The two joining partners are positioned between the sonotrode and the counter-tool, also known as the anvil, and then the sonotrode and counter-tool are moved towards each other so that the two joining partners are clamped between the sonotrode and the counter-tool. At the latest in this state, the sonotrode is set into vibration at an ultrasonic frequency, which creates a relative movement at the coupling surfaces between the first and second joining partners, thus generating frictional heat. Steps B) and C) are carried out simultaneously during the welding process. The start of steps B) and C) do not have to be simultaneous. It is possible to start with either step B) or step C). Once the welding is complete, the force on the joining partners and / or the ultrasonic excitation is reduced or even stopped.If the two joining partners are made of a thermoplastic material, they are melted and bonded together. Recently, metallic joining partners have also been increasingly joined using ultrasound. However, this does not result in the metal melting at the interfaces. Instead, the application of ultrasonic vibrations creates a cold-pressure welding process, which joins the adjacent metal surfaces in a solid state.

[0008] Especially in metal welding, it is difficult to determine the necessary welding time, the optimal welding force and / or the optimal oscillation amplitude of the ultrasonic vibration, as these depend on a variety of factors, such as the surface condition of the joining partners. This means that the welding time required to join the joining partners varies from case to case, so that in practice the welding time is selected so that reliable welding is achieved even if a longer welding time is required due to unforeseeable circumstances. This generally leads to the welding time being selected too long, which not only consumes unnecessary energy but also leads to increased wear on the coupling surface of the sonotrode. Furthermore, if the welding time is too long, the joint quality can deteriorate again.In addition, it is not uncommon for material to stick, particularly metal stick during metal welding, primarily on the sonotrode and counter tool, but also on any clamping and holding devices that may be present.

[0009] In addition to the described method of initiating step D) when a predetermined welding time is reached, it is also known to perform step D) when the sonotrode has traveled a predetermined distance or when a predetermined amount of energy has been applied to the joining partners. However, all of these methods cannot directly determine whether a connection has actually been made between the joining partners. Therefore, the welding time, the distance traveled by the sonotrode, or the amount of energy applied are usually set too long or too high to ensure that a connection has been made in every case.

[0010] Based on the described prior art, it is therefore the object of the present invention to provide a welding method of the type mentioned above, with which at least one welding parameter, in particular the welding time, can be individually adjusted, ie from the two actual joining partners of the connection to be produced, to the joining partners to be joined. According to the invention, this object is achieved by the step

[0011] E) Detecting a connection between the first and the second joining partner during step B) and / or C) by detecting a mechanical vibration of at least one side surface of a joining partner which is in contact with a coupling surface, and then, if a value detected in step E) meets a predetermined criterion, detecting that a connection exists between the first and second joining partners and by starting a time interval after step D) is carried out as soon as a connection is detected in E).

[0012] The invention is therefore based on the idea that a mechanical vibration applied by the sonotrode to the joining partners leads to the surfaces in contact with the coupling surfaces of the sonotrode or the counter tool also experiencing a vibration movement, the vibration path or speed amplitude and / or vibration frequency of which changes when a connection has been made between the two joining partners.

[0013] In the described ultrasonic welding process, the ultrasonic vibration introduced by the sonotrode is used both to generate the (frictional) heat that is helpful for the formation of the connection and to detect the connection time between the two joining partners.

[0014] While the first use is known, the second use is the use according to the invention. Therefore, the method according to the invention can also be used in welding processes that do not require ultrasonic vibration to generate heat. Rather, it simply requires that a mechanical vibration is transmitted to the two joining partners using the sonotrode and that the mechanical vibration, in particular the speed of movement and the displacement amplitude transmitted to the joining partners, is detected.

[0015] Since the method according to the invention was developed in connection with an ultrasonic welding process, the invention will be described below with reference to the excitation of the sonotrode with an ultrasonic vibration as a particularly preferred embodiment. It is understood, however, that in principle the method according to the invention can also be used with vibration excitations of other frequencies. In a preferred embodiment, the sonotrode is part of an ultrasonic vibration unit (also called an ultrasonic resonance unit) consisting of at least one converter and the sonotrode, wherein the converter and sonotrode are arranged next to one another in an ultrasound propagation direction, optionally with an amplitude transformer (amplitude transformer) interposed.Booster), wherein the coupling surface of the sonotrode is not oriented perpendicular to the propagation direction, wherein preferably the coupling surface is oriented at an angle of less than 45° to the propagation direction, wherein particularly preferably the coupling surface is oriented parallel to the propagation direction.

[0016] In other words, the ultrasonic vibration unit generates a so-called "in-plane vibration" on the coupling surface of the sonotrode. The sonotrode thus does not move toward the joining partner and back again, but rather oscillates at an ultrasonic frequency on the corresponding surface of the associated joining partner. This ultrasonic vibration is therefore initially transmitted to the first joining partner, from there at least partially to the second joining partner, and finally from the second joining partner at least partially to the counter tool.

[0017] In a preferred embodiment, a longitudinal vibration of the sonotrode is transmitted to the first joining partner as an in-plane vibration via the coupling surface of the sonotrode. This increases the relative movement and thus the frictional heat at the contact surfaces between the first and second joining partners. In principle, the method according to the invention also functions with a transverse vibration.

[0018] Because it is detected for the first time that the two joining partners have already formed a connection, the welding process can in most cases be carried out much more quickly. Often, the two joining partners are not yet very firmly connected to one another once a connection has been formed, so it can be advantageous if, after a connection between the two joining partners has been detected, the welding process is continued for a predetermined time, namely a predetermined time interval. However, the time interval can also be 0 seconds, so that the application of force and / or excitation is stopped immediately as soon as a connection between the two joining partners is detected. In a preferred embodiment, however, the time interval is longer than 0 seconds.

[0019] In a further preferred embodiment, it is provided that in step E) a vibration amplitude, a vibration frequency or a movement speed of the side surface is detected, and then, if the value detected in step E) fulfills a predetermined criterion, it is determined that a connection exists between the first and second joining partners.

[0020] In a preferred embodiment, in step E), a mechanical vibration is detected from a side surface of the second joining partner that is in contact with the second coupling surface. Since the vibration excitation is carried out by the sonotrode, the second joining partner is only set into vibration via the first joining partner, which is in contact with the first coupling surface of the sonotrode. Therefore, the observed effect on the mechanical vibration of the second joining partner is significantly greater during a forming connection between the first and second joining partners than during the mechanical vibration of the first joining partner.

[0021] As long as the two joining partners are not connected, a relative movement occurs at the contact surface between the two joining partners. This means that the two joining partners differ in magnitude and phase, and possibly also in frequency, of the vibration. Only a portion of the vibration is transferred from the first joining partner to the second joining partner via the acting friction force. This changes abruptly as soon as the joining partners form the first material connection. This moment can be determined using the described detection method through a quantitative direct comparison of the vibration characteristics of the sonotrode and the second joining partner.

[0022] In a further preferred embodiment, a generator is used to excite the sonotrode, which is designed to regulate the oscillation amplitude. The generator's power can be detected. If the generator power changes and the change meets a predetermined criterion, this can be interpreted as an indication that a connection exists between the first and second joining partners. Typically, the required generator power changes significantly as soon as the two joining partners are connected.

[0023] Since the fluctuation in generator power and the change in the mechanical vibration of the second joining partner can theoretically have causes other than the formation of a connection between the first and second joining partners, a preferred embodiment provides that a connection between the first and second joining partners is only detected if both a value detected in step E) meets a predetermined criterion and a change in generator power is detected that also meets a predetermined criterion. Likewise, in addition to generator power, other available generator parameters (such as amplitude, frequency, etc.) can be used in combination with the measured speed signal of the second joining partner to guarantee an exact determination of the weld quality.

[0024] Instead of the generator power or in addition to it, other parameters, such as the position of the sonotrode or the oscillation amplitude of the sonotrode, could also be recorded, and a connection between the first and second joining partners could only be detected if both a value detected in step E) fulfills a predetermined criterion and a change in the other parameter is detected that also fulfills a predetermined criterion.

[0025] The present invention also relates to a welding tool for use in the described welding method according to the invention. The welding tool has a coupling surface intended to come into contact with a joining partner. According to the invention, the coupling surface has a recess designed such that a mechanical vibration of a side surface of the joining partner covering the recess of the sealing surface can be detected through the recess. The recess can, for example, be a cutout at the edge of the sealing surface. In a preferred embodiment, however, the recess is completely surrounded by the sealing surface. The recess can be arranged approximately in the center of the sealing surface. The recess should not be too large so as not to negatively influence the welding process.Because the side surface of the joining partner in contact with the sealing surface is not in contact with the sealing surface in the area of ​​the recess, this area of ​​the side surface can be accessed in order to record the mechanical vibration.

[0026] In a preferred embodiment, the boundary walls of the recess are surface-treated, e.g., covered with black paint, to suppress reflections of the laser beam on the recess walls.

[0027] In a preferred embodiment, a measuring device for quantifying mechanical vibrations is provided, with which a mechanical vibration of a side surface of the joining partner covering the recess of the sealing surface can be detected.

[0028] It is intended that the measuring device can detect a mechanical vibration of the side surface of the material to be processed that is in contact with the sealing surface in a direction perpendicular to the sealing surface and / or in a direction parallel to the sealing surface.

[0029] For example, the measuring device can be a laser Doppler vibrometer that directs a laser beam onto the side surface of the joining partners. To detect mechanical vibrations both perpendicular to the sealing surface and parallel to the sealing surface, the laser beam impinging on the side surface is positioned such that it forms an angle a with a perpendicular to the side surface that is < 90°, with the angle preferably being between 5° and 30°.

[0030] For reasons of space, it may be advantageous if the laser generating the laser beam is arranged in such a way that the laser beam first hits a mirror and the laser beam reflected by the mirror hits the side surface covering the recess.

[0031] In a further preferred embodiment, the surfaces of the recesses are blackened or otherwise surface-treated to minimize the reflection of the laser beam.

[0032] To obtain a sufficiently strong laser signal from the lower joining partner, it may be advantageous to prepare it with a reflective foil or to process it in another way, such as polishing. This improves the reflection from the lower joining partner.

[0033] Further advantages, features and possible applications of the present invention will become clear from the following description of a preferred embodiment and the associated figures.

[0034] Figure 1 A partial sectional view of an ultrasonic processing device for carrying out the method according to the invention,

[0035] Figure 2 is a detailed enlargement of the section marked Z in Figure 1, Figure 3 is a perspective view of an alternative embodiment of a welding tool according to the invention and

[0036] Figure 4 is a sectional view of the welding tool of Figure 3.

[0037] Figure 1 shows a welding machine 1. The welding machine 1 has a holder 5 that can be moved vertically by means of an actuator 6. The holder 5 holds an ultrasonic vibration unit consisting of a sonotrode 2, an amplitude transformer 3, and a converter 4. As can be better seen in the partial enlargement in Figure 2, the sonotrode has a coupling surface that is arranged opposite an anvil 8, 11. The anvil 8, 11 consists of an anvil base 8 and an anvil cover 11 that supports the coupling surface of the anvil 8, 11. In order to weld a product, e.g., metallic elements, these are arranged between the downward-facing coupling surface of the sonotrode 2 and the coupling surface arranged on the top side of the anvil cover 11.The anvil cover 11 has a bore 10 in the area where the welding is to take place, which continues into a groove-like recess 12 in the anvil base 8 and into recesses 13 of a table 9 on which the anvil 8, 11 is mounted. Furthermore, a laser vibrometer 7 is provided, which directs a laser beam through the recess 13, the groove-like recess 12, and the bore 10 onto the joining partner positioned between the coupling surfaces. By analyzing the reflected beam, conclusions can be drawn about the movement of the joining partner 18 resting on the anvil 8, 11 and thus about a connection between the two joining partners 18, 19.

[0038] Figures 3 and 4 show a perspective view and a sectional view through an alternative embodiment of a welding tool designed as an anvil 14. The anvil 14 has a coupling surface 15 on its upper side, which is pyramid-shaped here, with the sides of the pyramid provided with a waffle structure. In the apex of the pyramid is a bore 17 that extends to a slot in the side surface of the anvil 14. This anvil 14 also allows a laser beam to be directed from below via the groove 16 and the bore 17 onto a joining partner 18 resting on the coupling surface 15 of the anvil 14, using a laser vibrometer.

[0039] Since the ultrasonic vibration is applied via a sonotrode arranged on the opposite side of the joining partners to the first joining partner 19, which rests against the sonotrode or its coupling surface, the ultrasonic vibration is first transmitted to the first joining partner and then from the first joining partner to the second joining partner. Initially, the second joining partner will not, or not completely, follow the movement of the first joining partner. However, as soon as a material-to-material connection is formed between the two joining partners, the joining partner resting on the coupling surface of the anvil will also follow the vibrational movement of the first joining partner, which can be recorded using the laser vibrometer 7, so that this measure can reliably detect when a material-to-material connection exists between the two joining partners. List of reference symbols

[0040] 1 welding device

[0041] 2 sonotrode

[0042] 3 Amplitude transformer

[0043] 4 converters

[0044] 5 Bracket

[0045] 6 Actuator

[0046] 7 laser vibrometers

[0047] 8 anvil

[0048] 9 Table

[0049] 10 Hole

[0050] 11 Anvil cover

[0051] 12 groove-like recess

[0052] 13 Recess

[0053] 14 Welding tools

[0054] 15 coupling area

[0055] 16 grooves

[0056] 17 Hole

[0057] 18 lower joining partner

[0058] 19 upper joining partner

Claims

Patent claims 1. Welding method for joining a joining surface of a first joining partner with a joining surface of a second joining partner with the steps A) Arranging the two joining partners between a first coupling surface of a sonotrode and a second coupling surface of a counter tool, so that the first joining partner is in contact with the first coupling surface, the second joining partner is in contact with the second coupling surface and the two joining surfaces are in contact with each other, B) exerting a force on the two joining partners via at least one of the coupling surfaces in the direction of the other coupling surface, C) Excitation of the sonotrode with a mechanical vibration so that the first coupling surface moves with a vibration frequency, D) reducing or stopping the application of force in step B) and / or reducing or stopping the excitation in step C), characterized by the step, E) Detecting a connection between the first and the second joining partner during step B) and / or step C) by detecting a mechanical vibration of at least one side surface of a joining partner which is in contact with a coupling surface and, if a value detected in step E) meets a predetermined criterion, detecting that a connection exists between the first and second joining partners.

2. Welding method according to claim 1, characterized in that as soon as a connection is detected in step E), a time interval is started after step D) is carried out.

3. Welding method according to claim 1 or 2, characterized in that in step C) the sonotrode is excited with an ultrasonic vibration.

4. Welding method according to claim 1, 2 or 3, characterized in that in step E) the vibration amplitude or the movement speed of a transverse vibration and / or a longitudinal vibration is detected.

5. Welding method according to one of the preceding claims, characterized in that the two joining partners consist of metal.

6. Welding method according to one of the preceding claims, characterized in that in step E) a mechanical vibration of a side surface of the second joining partner which is in contact with the second coupling surface is detected.

7. Welding tool for use in a welding method according to one of the preceding claims with a coupling surface which is intended to come into contact with a joining partner, characterized in that the coupling surface has a recess which is designed such that a mechanical vibration of a side surface of the joining partner covering the recess of the sealing surface can be detected through the recess.

8. Welding tool according to claim 7, characterized in that the recess is completely surrounded by the sealing surface.

9. Welding tool according to claim 7 or 8, characterized in that a measuring device for quantifying mechanical vibrations is provided, with which a mechanical vibration of a side surface of the joining partner in contact with the sealing surface can be detected.

10. Welding tool according to one of the preceding claims, characterized in that the measuring device can detect a mechanical vibration of the side surface of the material to be processed that is in contact with the sealing surface in a direction perpendicular to the sealing surface and / or in a direction parallel to the sealing surface.

11. Welding tool according to one of the preceding claims, characterized in that the measuring device is a laser vibrometer which directs a laser beam onto the side surface.

12. Welding tool according to claim 11, characterized in that the laser beam incident on the side surface encloses an angle a with a perpendicular on the side surface which is less than 90°, wherein preferably 5° < a < 30° applies.

13. Welding tool according to claim 10 or 11, characterized in that a mirror is provided which is arranged in such a way that the laser beam is initially hits the mirror and the laser beam reflected by the mirror hits the side surface.

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