Method for connecting two elements by means of a stamped rivet, and joining tool

Abstract

The invention relates to a method for connecting at least two elements by driving in a stamped rivet; wherein the stamped rivet is driven into the elements to be connected by applying an axial force to the stamped rivet; wherein the axial force is generated by a linear resonant actuator. The invention further relates to a joining tool (10) for connecting at least two elements by driving in a connecting element in the form of a stamped rivet, comprising a drive (12) which is designed to generate an axial force in order to drive the stamped rivet into the elements to be connected, wherein the drive (12) is a linear resonant actuator.

Description

[0001] Atlas Copco IAS GmbH, Case: 12N2024PA1067DE

[0002] Method for joining two elements using a punch rivet and joining tool

[0003] The present invention relates to a method for joining at least two elements by driving in a punch rivet using a linear resonant actuator and a joining tool for such a method comprising a linear resonant actuator as a drive.

[0004] background

[0005] Joining tools are, among other things, mechanical tools for connecting at least two elements made of different materials such as high-strength steel, aluminum, cast iron, magnesium, carbon fiber, or plastics with varying strength properties. One method used with a joining tool to join, for example, two metal sheets, involves the use of self-piercing rivets.

[0006] In this process, a fastener, particularly a self-piercing rivet, acts as a cutting die and is deformed during the joining process. The elements to be joined are placed on a die, the rivet element is positioned at the joint, and fixed in place by the advance of the blank holder. In the subsequent joining process, the self-piercing rivet penetrates the upper element and plastically deforms the lower element into a locking head. Such self-piercing rivets are also known as "seif piercing rivets (SPR)." This eliminates the need for pre-drilling the materials to be joined and ensures a tight joint.

[0007] In particular, this type of self-piercing riveting process allows for the joining of various material combinations, especially carbon fiber workpieces. Even high-strength or ultra-high-strength steels can be joined without pre-drilling.

[0008] Appropriate tools and processes are used particularly in the automotive industry. The joining process is carried out by advancing the rivet punch or joining tool and driving the rivet into the elements to be joined. Due to the materials being processed and the requirements for joint quality and reliability, high demands are placed on the rivet punch or joining tool and the precise advancing process. Accordingly designed joining tools, and thus efficient and robust joining processes, result in expensive, large, and heavy tools with high maintenance costs and wear.

[0009] Disclosure of the invention

[0010] It is therefore an object of the present invention to provide an improved joining tool that is robust, suitable for continuous use, and cost-effective. A further object of the present invention is to provide a method in which the joining tool can drive the punch rivet into the elements to be joined by means of a precise, fast, and robust process. Atlas Copco IAS GmbH, Case: 12N2024PA1067DE

[0011] These and other problems arising for the person skilled in the art from the present disclosure are solved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims and the description.

[0012] According to one aspect of the invention, a method for joining at least two elements comprises driving the punch rivet into the elements to be joined by applying an axial force to the punch rivet; wherein the axial force is generated by a linear resonant actuator.

[0013] A known method for inserting self-piercing rivets into a material comprises the following steps: a) providing an element made of a material that is to receive the self-piercing rivet, or several elements that are to be joined by means of the self-piercing rivet; the elements may be made of different materials; b) positioning the self-piercing rivet at the desired insertion point; c) applying an axial force to the self-piercing rivet to insert it into the element, the force being generated by a drive; d) generating a plastic deformation of the element around the self-piercing rivet to create a firm connection between the rivet and the element; e) checking the quality of the connection.

[0014] A linear resonant actuator (LRA) is an electromechanical component that generates oscillations to produce linear movements or vibrations. Linear resonant actuators achieve high efficiency and strong oscillations with low energy consumption. A linear resonant actuator according to the invention comprises a voice coil made of insulated wire wound around a cylindrical support, a permanent magnet, a movable mass connected to the magnet or the voice coil, a voice coil yoke, and a wave spring that provides a restoring force. These components are housed in a casing and, depending on the component, are mounted either rigidly or movably.

[0015] When an electric current flows through the wire windings of the voice coil, this current generates a magnetic field around the coil. The voice coil is located within the magnetic field of the permanent magnet. Due to the interaction between the magnetic field of the permanent magnet and the current flowing through the coil, the Lorentz force is generated. This Lorentz force acts on the voice coil or the permanent magnet and causes a linear movement of the coil relative to the permanent magnet, or vice versa, depending on which components are mounted for movement. Depending on the direction of the current, the coil or magnet is deflected either inwards or outwards. This linear movement can be precisely controlled. In particular, the moving mass can amplify this linear movement of the coil or the permanent magnet and set the linear resonant actuator in motion in such a way that mechanical work can be performed.The wave spring exerts a restoring force after the oscillation in the opposite direction of the displacement. In the following, a linear resonance actuator refers to other known embodiments that correspond to the basic structure and the described function. Atlas Copco IAS GmbH, Case: 12N2024PA1067DE.

[0016] By applying a defined current, the linear motion, and thus the oscillation, can be precisely controlled. This is particularly advantageous when oscillations are generated by applying the current at defined frequencies. The linear resonant actuator can therefore generate force in the form of a single oscillation or a multitude of oscillations and perform corresponding mechanical work. The force is exerted in the direction of the linear motion or the return motion.

[0017] Through linear motion and the resulting applicable force, the axial force applied to the self-piercing rivet can be generated by a linear resonant actuator in the inventive method. The required force can be generated by a single oscillation. According to one aspect of the invention, the axial force required to drive in a self-piercing rivet is generated as oscillations in the form of a vibration and applied to the rivet intermittently. In this context, "intermittent" means that with each oscillation, a portion of the force required to drive in the rivet is generated and applied, driving the rivet in a further distance. The totality of the intermittently applied force enables the complete drive-in of the rivet. This allows for precise control of the force application and the use of smaller and less robust tools.

[0018] Another aspect of the invention relates to a joining tool for connecting at least two elements by driving in a connecting element in the form of a self-piercing rivet, comprising a drive configured to generate an axial force to drive the self-piercing rivet into the elements to be joined, wherein the drive is a linear resonant actuator. The point at which the at least two elements are joined is also referred to as the joining point. Driving in the self-piercing rivet is also referred to as setting the self-piercing rivet (rivet setting).

[0019] A force applied in this way can drive a self-piercing rivet into the elements to be joined (hereinafter also referred to as the workpiece). With sufficient displacement or linear movement of the linear resonant actuator, the self-piercing rivet can be driven into the workpiece with a vibration. However, with smaller resonant actuators, the displacement and generated force are insufficient to drive the self-piercing rivet in with a single movement.

[0020] Therefore, according to another aspect of the inventive process, the linear resonance actuator generates the force intermittently as oscillations in the form of a vibration. This means that with each oscillation and corresponding deflection in a working direction of the linear resonance actuator, an axial force is applied to the self-piercing rivet, driving it a short distance into the workpiece. The multitude of intermittent force applications, or rather the total applied force, enables the self-piercing rivet to be driven in completely. Atlas Copco IAS GmbH, Case: 12N2024PA1067DE

[0021] Advantageously, the vibration can soften the workpiece, similar to metal, and reduce friction at the joint surface. This improves ductility and formability. Particular advantages also arise when riveting carbon fiber materials, as damage to the carbon fibers during the driving process is reduced, resulting in a longer service life for the joint.

[0022] The joining tool according to the invention can include a rivet punch. The linear resonance actuator, acting as the drive, drives the rivet punch, which in turn applies the axial force to a punch rivet via a punch surface. Alternatively, the linear resonance actuator can act directly on a punch rivet, allowing the joining tool according to the invention to be designed without a dedicated rivet punch, or for the rivet punch to be represented by the linear resonance actuator. The linear resonance actuator can be a Z-axis linear resonance actuator.

[0023] One aspect of the joining tool is its design: it ensures a uniform force is applied to the rivet during the intermittent force application and the resulting progressive driving of the rivet. This can be achieved, for example, by adjusting the joining tool according to the driving path, or alternatively, by adjusting the drive mechanism within the joining tool accordingly.

[0024] Brief description of the characters

[0025] Embodiments of the present disclosure are described in more detail below with reference to the figures.

[0026] Fig. 1 shows the steps of a method according to the invention;

[0027] Fig. 2 shows a schematic representation of a tool according to the invention for carrying out the method according to Fig. 1.

[0028] Detailed description of the drawings

[0029] Fig. 1 shows the steps of a method according to the invention in one embodiment of the method. In step S1, an axial force is applied to a self-piercing rivet, which in step S2 is driven into, for example, at least two elements to be joined as the workpiece. The axial force of the method according to the invention is generated by a linear resonant actuator. The axial force represents at least a linear displacement of the linear resonant actuator, which is generated by a vibration of the linear resonant actuator.

[0030] The linear force drives a self-piercing rivet into the workpiece. A vibration can only partially drive the rivet in. Therefore, step S1 can be repeated, and another axial force applied to the rivet, driving it further into the workpiece in step S2. The axial force is thus applied intermittently to the rivet, driving it in accordingly.

[0031] The sequence of steps S1 and S2 is repeated until the self-piercing rivet is completely driven into the workpiece. Preferably, the vibrations that generate the axial force are produced at a frequency such that the linear resonant actuator generates the axial force as a vibration and applies it to the self-piercing rivet.

[0032] This method allows a self-piercing rivet to be driven into the workpiece in a simple and precisely controlled manner. Furthermore, the workpiece material can be softened and / or damage to the workpiece can be reduced or prevented. A joining tool as shown in Fig. 2 can preferably be used. The following steps of the method are therefore described using the joining tool in Fig. 2, but are not limited to its use with this tool.

[0033] Fig. 2 shows a joining tool 10 comprising a drive 12 and a riveting punch 14, which are arranged in a housing 16. The riveting punch 16 comprises a punching surface 18 which engages a self-piercing rivet (not shown). The drive 12 can be movably or rigidly mounted in the housing 16. The drive 12 can be adjustable in the z-direction within the housing 16.

[0034] The drive 12 can be connected to the riveting die 14 and moves the riveting die 14 in the z-direction, whereby the riveting die 16, with its punching surface 18, acts on a self-piercing rivet and applies an axial force to it in the zl-direction. When the riveting die 14 is moved in the zl-direction by the drive 12, the drive exerts the axial force on a self-piercing rivet via the punching surface 18.

[0035] The actuator 14 is a linear resonant actuator. It comprises a circuit board 20 and a voice coil 22. The actuator 14 also includes a permanent magnet 24, which is connected to a movable mass 26. The movable mass 26 comprises a voice coil yoke 28, in which the voice coil 22 is at least partially enclosed and which surrounds the permanent magnet 24 (shown separately here for clarity). A wave spring 30 provides a restoring force.

[0036] The drive 12 can also include a movably mounted voice coil connected to the movable mass 26, with the permanent magnet 24 being fixedly mounted in the drive. Alternatively, the drive can also be a Z-axis linear resonant actuator, with the voice coil's axis perpendicular to the direction of movement of the voice coil or the permanent magnet. The joining tool 10 further includes a control unit (not shown here). Atlas Copco IAS GmbH, Case: 12N2024PA1067DE

[0037] When the drive 12 is activated, an electric current flows through the wire windings of the voice coil 22, generating a magnetic field around the coil 22. This coil is located within the magnetic field of the permanent magnet 24. The interaction between the magnetic field of the permanent magnet 24 and the current in the coil 22 creates the Lorentz force. This force acts on the permanent magnet 24, causing a linear movement of the magnet 24 relative to the coil in the z-direction (step 11). Depending on the current direction, the magnet 24 moves in either the z1 or z2 direction. This movement can be precisely controlled. The movable mass 26 amplifies the linear movement, causing the drive 12 to be deflected and perform mechanical work.The wave spring 30 provides the restoring force that counteracts the deflection of the movable mass 26 after the oscillation and deflects the movable mass 26 and the permanent magnet 24 in the opposite direction to their starting position.

[0038] By deflecting the drive in the working direction, here in the zl direction, the drive 12 can axially drive the rivet punch 14 in the zl direction, allowing the punch surface 18 to drive the rivet into the workpiece. In other words, the drive 12 causes the rivet punch 14 to advance in the zl direction.

[0039] Depending on the embodiment of the drive 12, a single movement may be sufficient to fully drive in the punch rivet. In a preferred embodiment, each oscillation only effects part of the driving process. The total force required for complete driving is applied intermittently in portions.

[0040] The joining tool 10 can be designed such that the drive 12 and the riveting die 14 are movable within the housing 16 to follow the change in the arrangement of the self-piercing rivet during the driving process and to ensure consistently uniform driving by means of force transmission. Alternatively, the entire joining tool 10 can be moved, in which case the drive 12 can be fixed in the housing 16 and the riveting die 14 is only movable within the housing 16 to the extent of the deflections mediated by the drive 12. The drive 12 can also encompass the die surface 18 on its housing 16 and directly engage the self-piercing rivet, thus enabling an embodiment of the joining tool 10 without a riveting die 14.

[0041] The invention is of course not limited to the embodiment shown, but includes any embodiment falling under the claims.

Claims

Atlas Copco IAS GmbH, Case: 12N2024PA1067DE Claims 1. Method for joining at least two elements by driving in a self-piercing rivet; wherein the self-piercing rivet is driven into the elements to be joined by applying an axial force to the self-piercing rivet; wherein the axial force is generated by a linear resonant actuator.

2. Method according to claim 1, wherein the axial force is generated as oscillations in the form of a vibration and is applied intermittently to the punch rivet.

3. Joining tool (10) for joining at least two elements by driving in a connecting element in the form of a punch rivet, comprising a drive (12) configured to generate an axial force to drive the punch rivet into the elements to be joined; wherein the drive (12) is a linear resonant actuator.

4. Joining tool according to claim 3, wherein the linear resonance actuator intermittently generates the force as oscillations in the form of a vibration.

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