Method for connecting two elements by means of a self-piercing rivet and joining tool

Abstract

The invention relates to a joining tool (10) for connecting at least two elements (36, 38) by driving in a connecting element in the form of a self-piercing rivet (34), comprising a drive (14) which is designed to generate an axial force in order to drive the self-piercing rivet (34) into the elements (36, 38) to be connected; and an actuator (22) which is designed to apply the force generated by the drive (14) to the self-piercing rivet (34); wherein the joining tool (10) comprises a linear induction motor (14) as a drive (14). The invention also relates to a method for connecting at least two elements (36, 38) by driving in a self-piercing rivet (34), wherein the self-piercing rivet (34) is driven into the elements (36, 38) to be connected by applying an axial force to the self-piercing rivet (34), wherein the axial force is generated by a linear induction motor (14).

Description

[0001] Atlas Copco IAS GmbH, Case: 12N2024PA1065DE September 24, 2024

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

[0003] The present invention relates to a joining tool for connecting at least two elements by driving in a punch rivet, wherein the joining tool comprises a linear induction motor as a drive, and a method for connecting at least two elements by driving in a punch rivet comprising a linear induction motor 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 method. 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. It is a further object of the present invention to provide a method in which the joining tool is... Atlas Copco IAS GmbH, Case: 12N2024PA1065DE 24.09.2024

[0011] The tool can drive the punch rivet into the elements to be joined using a precise, fast and robust process.

[0012] 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.

[0013] According to one aspect of the invention, a joining tool for connecting at least two elements by driving in a connecting element in the form of a self-piercing rivet comprises a drive configured to generate an axial force to drive the self-piercing rivet into the elements to be joined, and an actuator configured to apply the force generated by the drive to the self-piercing rivet. The joining tool includes a linear induction motor as the drive. According to another aspect of the invention, the linear induction motor comprises a stator and a rotor; the rotor forming the actuator of the joining tool.

[0014] A linear induction motor (abbreviated LIM) is a special type of induction motor that generates linear motion instead of rotary motion. Conventional induction motors produce rotary motion, while a linear induction motor uses the same technique to generate straight motion.

[0015] The stator in a linear induction motor is the stationary part (primary part) containing coils. A magnetic field is generated here by a multiphase alternating current. This magnetic field constantly changes its polarity and generates a moving electromagnetic field along the length of the stator. This moving magnetic field induces eddy currents in the rotor through electromagnetic induction. According to Lenz's law, these induced currents generate their own magnetic field, which opposes the original magnetic field. The two opposing fields repel each other. The interaction between the stator's magnetic field and the induced magnetic field in the rotor produces a force that pulls or pushes the rotor in the direction of the moving magnetic field, resulting in linear motion.

[0016] The magnetic field of the stator always moves slightly faster than the rotor, a phenomenon known as slip. This slip generates the movement. The speed of the movement depends on the frequency of the multiphase alternating current. A higher frequency produces a magnetic field that moves faster along the stator, which in turn leads to faster rotor movement. The linear induction motor can be, for example, three-phase or four-phase.

[0017] According to one aspect of the invention, the linear induction motor comprises a housing in which the stator is received and a rotor that is displaceable along its longitudinal axis. For example, the rotor extends at least partially out of the housing. Atlas Copco IAS GmbH, Case: 12N2024PA1065DE 24.09.2024

[0018] The housing includes at least one opening and corresponding bearings to mount the rotor so that it can move linearly. For example, the rotor is a cylinder made of stainless steel.

[0019] The linear induction motor according to the invention as a drive is designed in such a way that it generates the required axial force through the generated linear movement, which drives the punch rivet into the elements to be joined.

[0020] In one respect, the rotor at least partially forms the actuator of the inventive joining tool by directly or indirectly applying its movement and the force generated to the rivet being driven. For example, it has a threaded end protruding from the housing to accommodate a rivet punch. The force of the linear induction motor can be generated, for instance, by accelerating the rotor to a high speed, such as up to 3.4 m / s², and the application of this force, and consequently the driving of the rivet, is accomplished by the kinetic energy of the rotor.

[0021] This allows the linear induction motor to replace the drive and actuator of conventional joining tools. This offers significant advantages over the state of the art. Since no mechanical connection is required between the rotor and other components, there is less friction and wear, which reduces maintenance costs and noise. This also leads to higher reliability and a longer service life. Direct control of the magnetic field allows for very precise and flexible control of the movement, making linear induction motors ideal for driving self-piercing rivets. The speed and applied force can be flexibly varied during movement, ensuring ideal conditions for creating a stable and durable joint at all times.

[0022] According to one aspect of the invention, the linear induction motor further comprises a control unit. This unit is, for example, arranged in the housing of the linear induction motor and enables direct control of the motor and the magnetic field. The control unit can include any combination of sensors for detecting position, force, speed, energy consumption, and temperature. This data is then transmitted to the control unit to enable precise control of the movement. This makes the linear induction motor a smart linear induction motor.

[0023] The control unit can adjust the frequency and amplitude of the supplied current to precisely control the movement. For this purpose, the linear induction motor preferably includes an inverter that controls the alternating current supplied to the stator. This enables real-time adjustments to minimize energy consumption and maximize efficiency. Atlas Copco IAS GmbH, Case: 12N2024PA1065DE 24.09.2024

[0024] A linear induction motor, including a control unit, can adapt to different loads or environmental conditions. For example, the motor can automatically reduce its power output when full power is not required, or it can use machine learning to predict when maintenance is needed to minimize wear. Furthermore, such a linear induction motor can react very quickly to changes in the load or operating conditions. This significantly improves the functionality of a joining tool designed with it. The linear induction motor, acting as both a drive and actuator, can easily and quickly determine and adjust the parameters required for different application situations. For this purpose, the joining tool according to the invention can have an interface and / or sensors through which the necessary data about the workpiece and the rivet are provided or detected.

[0025] According to a further aspect of the invention, the joining tool is designed such that the axial force is generated intermittently in several steps and applied to the self-piercing rivet. The joining tool and / or the drive within the joining tool can be guided along the self-piercing rivet as it is driven section by section into the elements to be joined. The linear induction motor exerts several successive impacts on the self-piercing rivet, with each linear movement generating and applying a portion of the force required to fully drive in the rivet.

[0026] According to a further aspect of the invention, the linear induction motor is designed to generate vibrations during the application of the generated force, which are then transmitted to the punch rivet. The vibration can represent an intermittent application of the axial force in several steps.

[0027] 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.

[0028] The invention further relates to a method for joining at least two elements by driving in a punch rivet; wherein the punch rivet is driven into the elements to be joined by applying an axial force to the punch rivet; wherein the axial force is generated by a linear induction motor.

[0029] Such a method can, for example, be carried out with one of the embodiments of the joining tool according to the invention.

[0030] According to one aspect of the invention, the axial force is applied to the punch rivet by the linear induction motor. Atlas Copco IAS GmbH, Case: 12N2024PA1065DE 24.09.2024

[0031] According to one aspect of the invention, the axial force is generated intermittently in several steps and applied to the punch rivet.

[0032] Description of the characters

[0033] Fig. 1 shows a schematic representation of an embodiment of a joining tool according to the invention. The method according to the invention can be carried out with this tool and is therefore also described schematically with reference to Fig. 1.

[0034] The inventive joining tool 10 comprises a housing 12 and a drive 14. The drive is a linear induction motor; these terms can therefore be understood interchangeably below. It comprises a stator 16 with a plurality of coils 18. These are, for example, arranged in a 4-phase overlapping configuration. A control unit 20 generates a traveling magnetic field by applying a multiphase alternating current to the coils 18. In the illustrated embodiment, this field moves along the stator 16 from the upper end of the stator 16 in the zl direction. This generates eddy currents in the rotor 22. The rotor 22 extends completely through the stator 16 and also through the housing 12, but is not limited to this embodiment. In the illustrated embodiment, the housing 12 includes openings 24 and 26, which contain replaceable bearings 28 that support the rotor 22 for linear movement in the z-direction.The housing 12 of the joining tool 10 can be the housing of the linear induction motor 14. An interface 30 enables control and power supply of the tool 10.

[0035] According to Lenz's law, the induced eddy currents in the rotor 22 generate their own magnetic field, which opposes the moving magnetic field of the stator 16. This creates a force that moves the movable rotor 22 in the direction of the moving magnetic field of the stator 16, i.e., in the zl direction.

[0036] The axial force generated in this way can be transmitted from the runner 22 via a punch surface 32 on the runner 22 to an exemplary self-piercing rivet 34. The self-piercing rivet 34 is intended for connecting the elements 36, 38.

[0037] The action of the punch surface 32 on the self-piercing rivet 34 drives the rivet into the elements 36, 38. The runner 22 thus also acts as the actuator of the joining tool 10. The runner 22 can be accelerated by the induced movement, for example, such that it drives the self-piercing rivet in using its kinetic energy. Furthermore, the joining tool 10 can be designed to perform the driving in several steps, whereby the force is generated intermittently and several movements of the runner 22 result in the complete driving of the self-piercing rivet 24 into the elements 36, 38. A return movement of the runner 22 between the individual movements can also be generated by a magnetic field of the stator 16. Atlas Copco IAS GmbH, Case: 12N2024PA1065DE 24.09.2024

[0038] The control unit 20 can include sensors to detect, for example, position, force, speed, energy consumption, and temperature. This allows the linear induction motor 14 to be controlled, for instance, so that during intermittent driving, it generates the required force for further driving, depending on the position of the punch rivet 34. This force can be metered so precisely that damage to the elements 36, 38 during driving is reduced or prevented.

[0039] The invention is of course not limited to the embodiment shown, but includes any embodiment falling under the claims.

Claims

1. Atlas Copco IAS GmbH, Case: 12N2024PA1065DE September 24, 2024 Claims 1. Joining tool (10) for joining at least two elements (36, 38) by driving in a connecting element in the form of a self-piercing rivet (34), comprising: a drive (14) configured to generate an axial force to drive the self-piercing rivet (34) to be driven into the elements (36, 38) to be joined; and an actuator (22) configured to apply the force generated by the drive (14) to the self-piercing rivet (34); wherein the joining tool (10) comprises a linear induction motor (14) as the drive (14). Joining tool (10) according to claim 1, wherein the linear induction motor (14) comprises a stator (16) and a rotor (22); and wherein the rotor (22) forms the actuator of the joining tool (10). Joining tool (10) according to claim 1 or 2, wherein the linear induction motor (14) further comprises a control unit (20). Method for joining at least two elements (36, 38) by driving in a self-piercing rivet (34); wherein the punch rivet (34) is driven into the elements (36, 38) to be joined by applying an axial force to the punch rivet (34); wherein the axial force is generated by a linear induction motor (14).

5. Method according to claim 4, wherein the axial force is applied to the punch rivet (34) by the linear induction motor (14).

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