Joining element made of shape memory steel and method for producing a releasable joining connection

Abstract

The present invention relates to a joining element (1) for producing a releasable joining connection, wherein the joining element (1) consists at least partially of a shape memory steel and in order to produce a joining connection with a joining partner (2, 2A, 2B) can be deformed, starting from a basic state, into a joining state through the application of force, and in order to undo the joining connection can be deformed at least partially from the joining state back into a disassembly state through the application of heat. Furthermore, the present invention relates to a system (5) for producing a releasable joining connection and to a method for producing and releasing a joining connection.

Description

[0001] Joining element made of shape memory steel and method for producing a detachable joining connection

[0002] Technical area

[0003] The present invention relates to a joining element made of shape memory steel for producing a detachable joint and to a method for producing and releasing a joint using such a joining element.

[0004] In many areas of technology, it is necessary to join two components together. Classic mechanical joining methods include riveting, crimping, or locking ring bolts to reliably join components together. Such methods are known for their irreversibility, as the joining partners are plastically deformed by pressing, thus resulting in an irreversible joining process. This prevents both the easy, non-destructive disassembly of such joints and the easy recycling of the components and joining partners.

[0005] Recently, the focus has shifted to the economic aspects of dismantling and the reusability of raw materials. In other words, recyclability and dismantling must be economically viable, not only for products made from highly valuable raw materials. Researchers have already explored this topic in various ways. Some ideas are based on integrating actuators made of shape memory materials into products. What shape memory materials have in common is that, when a certain switching signal is exceeded or undershot, they switch from a first solid phase to a second solid phase that differs from the first. A switching signal, such as when a switching temperature is exceeded, can return a previously plastically deformed shape memory material to its original shape.Thus, activation can occur, triggered from the outside, to return a component, for example by heating, to a state that allows easier disassembly.

[0006] Description of the state of the art

[0007] Joining methods with detachable joining elements that facilitate the disassembly of the components are known in the art. Patent document DE 101 09222 shows a joining element for connecting two objects. The joining element is partially made of a shape memory alloy and has a first shape in the initial state and a second shape in the final assembly position that mechanically connects the objects. By activating the shape memory alloy through sufficient cooling to the switching temperature, the joining element can be reshaped to its initial state. This facilitates disassembly after the joining element has been used.

[0008] However, the joining element described above also has some disadvantages: Classic shape memory alloys are thermoelastic. Thermoelasticity describes the property of a material being reversible between two solid phases, and being able to change the solid phase only by changing the temperature. The phase present in the cold state is called martensite, and the warm phase is called austenite. Classically, the shape memory alloy exhibits a twinned structure in the martensite (imagined two-dimensionally like a fan). If the shape memory alloy is deformed, this twinned structure is untwinned (smoothed out). Heating converts the shape memory alloy into austenite, reversing the stretching and macroscopic deformation. If the alloy is subsequently cooled, twinned martensite forms again, and the cycle is closed.There is only a small difference in the temperature transition range of classic shape memory alloys, the so-called hysteresis. This describes the temperature difference between the martensite-to-austenite and the austenite-to-martensite transformation. This is a few degrees Celsius (in the single- to low double-digit Kelvin range).

[0009] Classic shape memory alloys have several disadvantages for use in joining connections. The biggest disadvantage is the very high cost, which results from the high material costs and the high production costs due to the complex and labor-intensive processing. These costs alone make the use of large quantities of shape memory alloys uneconomical. Furthermore, the transformation temperatures are in ranges that are unsuitable for most joining elements. Adapting these temperatures to suitable ranges is sometimes possible but is associated with higher material and / or process costs. Another disadvantage for a joining element is that the mechanical properties such as strength and Young's modulus are significantly lower in martensite than in austenite. Since shape recovery occurs in the transition from detwinned martensite to austenite, the shape memory alloy must be present in martensite in the joined state.This means the material can only develop a fraction of its potential.

[0010] The present invention is based on the object of solving the problems known from the prior art and of providing a joining element which is economical in production and application and which is mechanically resilient, which is stable in the technically relevant temperature range and enables very easy disassembly.

[0011] To achieve the above-defined object, the present invention discloses a joining element according to claim 1. The joining element according to the invention serves to produce a detachable joining connection and consists at least partially of a shape memory steel and is deformable from a basic state into a joining state by deformation to produce a joining connection with a joining partner and is deformable at least partially from the joining state into a disassembly state by heat input to remove the joining connection.

[0012] Shape memory steels are iron-based shape memory alloys. Currently, two base alloy systems are known: Fe-Mn-Si and Fe-Ni-C. The inventive solution utilizes the very special properties of shape memory steel to create inexpensive, stable, and easily removable joints after use. The advantages of this alloy for fasteners, particularly for mechanically joining components, lie in the mechanically induced martensite formation and the wide temperature range of most applications in which the inventive fasteners are stable, since retransformation only begins at approximately 50-80°C and is completed at 200-300°C. Furthermore, the mechanical properties are phase-independent.

[0013] In addition, shape memory steels have significantly lower material and processing costs, as processes used in the conventional production of high-alloy stainless steels can be used, and the shape memory steels exhibit good processability, similar to other high-alloy steels. Good mechanical properties such as high elastic modulus, high strength, and very high elongation at break are further advantages of joining elements made of shape memory steel.

[0014] The properties of shape memory steels are due to a deformation-induced one-way effect. The one-way effect of shape memory steels is based on a stress-induced deformation, which forms Shockley partial dislocations. These lattice defects are split dislocations that do not shift atomic layers by a full atomic distance, thus enabling the formation of reversible e-martensite. These dislocations can be restored by applying heat (approximately 50–300 °C), resulting in macroscopic shape recovery. In contrast to classic shape memory alloys, the recovery is not 100% (80% or less, depending on the forming process). Thermal martensite only forms at very cold temperatures (below -20 °C) and is not relevant for most applications. The hysteresis is very high, exceeding 150 K.Another important property for fasteners is that shape memory steels, in contrast to thermoelastic shape memory alloys, are not subject to any change in mechanical properties due to phase changes.

[0015] Advantageous developments of the invention are the subject matter of the dependent claims. It can be advantageous if the shape memory steel is an iron-based shape memory alloy, preferably an Fe-Mn-Si alloy or an Fe-Ni-C alloy. Iron-based shape memory alloys exhibit a good non-thermoelastic shape memory effect combined with good machinability, corrosion resistance, and low material and production costs. Fe-Mn-Si alloys are cost-effective and exhibit good machinability and weldability.

[0016] It can prove useful if the joining element has at least one joining section, preferably made entirely of shape memory steel. This allows the joining connection to be designed according to the joining partners. Furthermore, a targeted change in the shape of the joining element can be enabled upon heating.

[0017] It can be helpful if the joining element is designed as a female joining element and has a receptacle into which a male joining partner can be inserted in the basic state and is fixed in a force-fitting and / or form-fitting manner in the joined state, in particular by reducing the size or tapering of the receptacle, wherein the receptacle is expanded in the disassembled state compared to the joined state in order to release the joining partner arranged therein. Thus, by enclosing the male joining partner with the female joining element, a firm connection between the female joining element and the male joining partner can be guaranteed. Furthermore, the detachability of the joining element is improved, since only heating is required and accessibility for mechanical release using high forces does not have to be ensured.

[0018] It may prove advantageous for the joining element to be ring-shaped and have an opening as a receptacle into which a male joining partner can be inserted in the initial state, secured in the joined state, and withdrawn during disassembly. This facilitates the assembly of the joining partner into the joining element. Additional joining components can be easily added via a through hole and plugged onto one of the male joining partners.

[0019] It can be advantageous if the joining element is designed as a male joining element, preferably as a cylindrical or cuboid-shaped one with a cross-section, and can be inserted into a female joining partner that has a receptacle in the basic state and is fixed in a force-fitting and / or form-fitting manner in the joined state, in particular by widening the cross-section, wherein the cross-section is reduced in the disassembled state compared to the joined state in order to release the joining partner arranged therein. Thus, by enclosing the female joining partner with the male joining element, a firm connection between the male joining element and the female joining partner can be guaranteed. Furthermore, the detachability of the joining element is improved, since only heating is required and accessibility for mechanical release using high forces does not have to be ensured.

[0020] It can be useful if the joining element is designed as a locking ring, hollow rivet, or crimp shoe. This makes the joining element versatile and can be applied to a variety of conventional joining methods.

[0021] It can be practical if the shape memory steel is austenite in its ground state and martensite in its joined state. Thus, the martensite of the shape memory steel of the joining element can be returned to the disassembled state by heating.

[0022] It can prove advantageous if the joining element can be converted from its initial state to the joined state by narrowing, widening, lengthening, compressing, squeezing, flanging, crimping, spreading, or pressing. Accordingly, the joining process for converting the joining element to the joined state is versatile, and the joining element can be used in a variety of conventional joining processes.

[0023] However, it can also be beneficial if the joining element transitions from the joined state to the disassembled state at a temperature in the range of 50°C - 300°C, preferably in the range above 100°C. Thus, the joining element continues to exhibit high stability and strength even at high temperatures. The joining element according to the invention thus enables a reliable connection in a wide range of temperature applications.

[0024] It can be practical if the joining element exerts bending and / or shear forces on a joining partner during the joining state. This further stiffens the frictional connection between the joining partner and the joining element. A reliable connection between the joining partner and the joining element can thus be ensured.

[0025] To achieve the above-defined object, the present invention discloses a system for producing a detachable joint, comprising a joining element, in particular according to one of the preceding claims, and a joining partner, wherein the joining element consists at least partially of a shape memory steel and, in order to produce a joint connection with the joining partner, is deformable from a basic state into a joined state by the application of force, and is deformable at least partially from the joined state into a disassembled state by the introduction of heat in order to release the joint connection. To achieve the above-defined object, the present invention discloses a method for producing and releasing a joint, comprising the steps: Step A: Providing a joining element that consists at least partially of a shape memory steel, in particular of an above-mentioned joining element.Step B: Creating a joining connection between the joining element and a joining partner, starting from a basic state of the joining element by applying force and deforming the joining element into a joined state. Step C: Releasing the joining connection by at least partially reshaping the joining element from the joined state to a disassembled state through heat input. The joining connection can be used between steps B and C. This can be chosen for any length of time. Any length of time can elapse between the individual steps. The method according to the invention can be used to carry out a joining process holistically, from its assembly to its disassembly. Such a method achieves the secure connection of components during the joined state and enables reusability of the resources after use. The disassembly state enables disassembly without additional tools or instructions.In addition, economical disassembly is possible without having to know or identify the structure of the components or the joining element (disassembly with an undetermined effective point is possible).

[0026] It can be practical if a large number of individual joints with a large number of joining elements are produced individually in step A. The process can thus be parallelized and thus carried out efficiently.

[0027] It may prove advantageous to remove a plurality of joints together in step C. Thus, a global heat input can simultaneously transfer a plurality of joints to the disassembly state. Heat input can be applied to the plurality of joining elements as a whole, without knowing the location where the connection is released. Such a process can eliminate individual disassembly steps and thus be highly cost-effective.

[0028] Further preferred developments of the invention result from combinations of the features disclosed in the description, the claims and the figures.

[0029] Short description of the characters

[0030] They show:

[0031] Fig. 1 is a side view of a first embodiment of a joining element. Fig. 2A is a sectional view in the direction of section AA from Fig. 1 of the first

[0032] Embodiment of a joining element in a basic state.

[0033] Fig. 2B is a sectional view in the direction of section AA in Fig. 1 of the first

[0034] Embodiment of the joining element in a joining state.

[0035] Fig. 2C is a sectional view in the direction of section AA in Fig. 1 of the first

[0036] Embodiment of the joining element in a disassembled state restored by heat input.

[0037] Fig. 3A is a sectional view of a second embodiment of a joining element in a basic state.

[0038] Fig. 3B is a sectional view of the second embodiment of the joining element in a joining state.

[0039] Fig. 3C is a sectional view of the second embodiment of the joining element in a disassembly state restored by heat input.

[0040] Fig. 4A is a plan view of a variety of systems in the disassembly process.

[0041] Fig. 4B is a side view of a plurality of systems in the dismantling process in a dismantling tank.

[0042] Detailed description of the preferred embodiments

[0043] [First embodiment]

[0044] Fig. 1 shows a side view of a first embodiment of a joining element 1. The joining element 1 has a flat base plate 1A. Two joining sections 1B extend vertically upwards from the base plate 1A. There is a gap between the joining sections 1B. The joining sections 1B can thus be formed independently of one another. Fig. 1 shows two joining partners 2A, in the form of round wires 2A, which are arranged on the base plate 1A of the joining element 1 with their ends inclined towards one another. The round wires 2A, 2B extend along the base plate 1A and are located in the longitudinal direction of the base plate 1A in the region of the two joining sections 1B, so that the end faces of the round wires 2A, 2B meet in the region of the gap between the joining sections 1B. The round wires 2A, 2B are shown shortened in the longitudinal direction. Joining element 1 is in its basic state, i.e., joining element 1 is not mechanically connected to the round wires 2A, 2B.The joining sections 1 B preferably consist entirely of shape memory steel.

[0045] Shape memory steel is an iron-based shape memory alloy, preferably an Fe-Mn-Si alloy or an Fe-Ni-C alloy. Unlike traditional shape memory alloys, shape memory steels lack thermoelasticity (under normal conditions) and exhibit very high hysteresis. Due to the lack of thermoelasticity, the mechanical properties of shape memory steels are identical in both austenite and martensite.

[0046] Fig. 2A shows a sectional view in the direction of section AA in Fig. 1 of the first embodiment of the joining element 1 in a basic state. Fig. 2A shows that the joining element 1 has a U-shaped cross-section, and the U-shaped cross-section forms two joining sections 1B. The U-shaped cross-section includes a receptacle for the round wire 2B and forms a female joining element 1, while the round wire 2B represents a male joining partner 2B.

[0047] Fig. 2B shows a sectional view in the direction of section AA in Fig. 1 of the first embodiment of the joining element 1 in a joined state. By applying a force F from the outside to the joining sections 1B, the joining element 1 is deformed into a joined state. Due to the deformation into the joined state, the austenite of the shape memory steel transforms into reversible martensite. In the joined state, the joining sections 1B enclose the round wire 2B in order to clamp the round wire 2B force-fittingly and, if necessary, to lock it positively in the holder. In the joined state, the joining element 1 exerts bending and / or shear forces on the joining partner 2, 2A, 2B, here the round wire 2B. By reducing the size or tapering the holder, the round wire 2B is fixed in the joining element 1. Analogously, the round wire 2A is fixed to the base plate 1A of the joining element 1 by the additional joining sections 1B (not shown). The connection process shown in Fig. 2B is referred to as crimping.Depending on the design, the joining element can alternatively be converted from the basic state to the joining state by tapering, squeezing, flanging, crimping or folding.

[0048] Fig. 2C shows a sectional view in the direction of section AA in Fig. 1 of the first embodiment of the joining element 1 in a disassembled state returned by heat input. Due to the heat input 7 into the joining sections 1B, the shape memory effect causes the martensite to reform into austenite. The joining sections 1B reform at least partially (the deformation compared to the basic state is at best between 2 and 8%). The receptacle of the joining element 1 in the disassembled state is thus expanded compared to the joined state, and the round wire 2B arranged therein is released. The joint is released. Analogously, the round wire 2A is released by the additional joining sections 1B of the joining element 1 subjected to heat input 7 (not shown). The joining element 1 transitions from the joining state (martensite) to the disassembled state (austenite) at a temperature in the range of 50°C - 300°C. [Second embodiment]

[0049] Fig. 3A shows a sectional view of a second embodiment of a joining element in a basic state. Fig. 3A shows a joining partner 2 in the form of a lockbolt 2, which is guided through a bore of two components 3, 4 to be joined (here sheets 3, 4). The joining element 1 in the form of a lockring 1 made of shape memory steel is placed onto the lockbolt 2. The joining element 1 is therefore annular and designed with an internal opening 1C as a receptacle. The inner diameter of the opening 1C of the lockring 1 is larger than an outer diameter of the lockbolt 2. Thus, the lockring 1 can be easily placed onto the lockbolt 2, or the male joining partner 2 in the form of the lockbolt 2 can be inserted into the female joining element 1. The two sheets 3, 4 to be joined are arranged between a head of the locking ring bolt 2 and the locking ring 1.

[0050] Fig. 3B shows a sectional view of the second embodiment of the joining element 1 in a joined state. The joining process is analogous to that with a conventional lockbolt. The element to be deformed, here the lockbolt 1 made of shape memory steel, is pushed onto the lockbolt 2. The assembly is then axially preloaded using a setting tool. This tool grips the lockbolt 2 to fix it and then forms the lockbolt 1 onto the lockbolt 2 by applying a force F. The resulting deformation leads to the formation of reversible martensite in the lockbolt 1. The lockbolt 2 can have a tensile part with a predetermined breaking point, which breaks in a defined manner when the maximum forming force is reached and the connection is set.

[0051] Fig. 3C shows a sectional view of the second embodiment of the joining element 1 in a disassembled state restored by heat input 7. By using the shape memory steel and its shape memory effect, the deformation of the locking ring 1 can be partially reversed by heating to 200-300 °C, so that the connection between the locking ring 1 and the locking bolt 2 is released. With suitable support, the locking ring 1 and the locking bolt 2 can separate from each other by gravity, without further intervention or tools being necessary.

[0052] The joining element 1 and the associated joining partner 2, 2A, 2B each form a system 5 for producing a detachable joining connection. It is within the scope of the invention that a joining element 1 can also form a detachable joining connection with different joining partners, such as the joining element 1 according to the first exemplary embodiment, which can clamp joining partners with different cross-sectional shapes and dimensions between the joining sections. The joining element 1 according to the second exemplary embodiment can also form a detachable joining connection with different joining partners, as long as the joining partners can be secured in the joined state and released again in the disassembled state. The joining partner is preferably made of a harder material than the joining element, so that the joining connection can be easily released when the joining element is disassembled.

[0053] In general, the method for producing and releasing a joint connection with the present joining elements 1 from the exemplary embodiments can be summarized in the following steps: Step A: Providing a joining element 1 that consists at least partially of a shape memory steel. Step B: Producing a joint connection of the joining element 1 with a joining partner 2, 2A, 2B starting from a basic state of the joining element 1 by applying force and deforming the joining element 1 into the joined state. Step C: Releasing the joint connection by at least partially reshaping the joining element 1 from the joined state into a disassembled state by applying heat.

[0054] Fig. 4A shows a top view of a plurality of systems 5 in the disassembly step. The plurality of systems 5 used in the joined state are collectively subjected to heat input 7 from a heat source 6 in order to reform the joining elements 1 of the systems 5 and to transfer the joining elements 1 from a joined state to a disassembled state.

[0055] Fig. 4B shows a side view of a plurality of systems 5 during the disassembly process in a disassembly container 8 or in a disassembly tank 8. The disassembly container 8 or the disassembly tank 8 are filled with a warm fluid, and thus all joining elements 1 are reached by the fluid and transferred into the disassembly state. A disassembly process, as shown by way of example in Figs. 4A and 4B, can thus parallelize disassembly and thus make it more economical.

[0056] Step C can therefore be carried out specifically by heating a single joining element 1 or globally by heating an entire system 5 comprising joining element 1 and joining partner 2 or an entire collection of systems 5. Disassembly is therefore possible without knowing or having to identify the structure of system 5 (disassembly with an undetermined effective point).

[0057] The present invention is not limited to the described embodiments. Further modifications and variations of the embodiments are conceivable within the scope of the claims. Analogous to the first or second embodiment, the inventive concept is transferable to all mechanical joining methods in which at least part of the joining element 1 consists of a shape memory steel. These include, in particular, riveted joints such as hollow rivets, etc., and other crimped joints.

[0058] List of reference symbols

[0059] 1 joining element

[0060] 1A base plate

[0061] 1 B joining section

[0062] 1C Opening

[0063] 2, 2A, 2B joining partners

[0064] 3 Component, round wire, sheet metal

[0065] 4 Component, round wire, sheet metal

[0066] 5 Systems

[0067] 6 Heat source

[0068] 7 Heat input

[0069] 8 dismantling basins, dismantling containers

Claims

PATENT CLAIMS Joining element (1) for producing a detachable joining connection, wherein the joining element (1) consists at least partially of a shape memory steel and, in order to produce a joining connection with a joining partner (2, 2A, 2B), is deformable from a basic state into a joined state by deformation and, in order to remove the joining connection, is at least partially re-deformable from the joined state into a disassembled state by heat input. Joining element (1) according to the preceding claim, characterized in that the shape memory steel is an iron-based shape memory alloy, preferably an Fe-Mn-Si alloy or an Fe-Ni-C alloy. Joining element (1) according to one of the preceding claims, characterized in that the joining element (1) has at least one joining section (1B) made entirely of shape memory steel, preferably consisting entirely of shape memory steel.Joining element (1) according to one of the preceding claims, characterized in that the joining element (1) is designed as a female joining element (1) and has a receptacle into which a male joining partner (2, 2A, 2B) can be inserted in the basic state and is fixed in a force-fitting and / or form-fitting manner in the joined state, in particular by reducing the size or tapering of the receptacle, wherein the receptacle is widened in the disassembled state compared to the joined state in order to release the joining partner (2, 2A, 2B) arranged therein. Joining element (1) according to the preceding claim, characterized in that the joining element (1) is annular and has an opening (1C) as a receptacle, into which a male joining partner (2) can be inserted in the basic state and is fixed in the joined state and can be pulled out in the disassembled state.Joining element (1) according to one of the two preceding claims, characterized in that the joining element (1) is designed as a locking ring, hollow rivet, or crimp shoe. Joining element (1) according to one of claims 1 to 3, characterized in that the joining element (1) is designed as a male joining element (1), preferably as a cylindrical or cuboid with a cross-section, and can be inserted into a female joining partner (2, 2A, 2B) which has a receptacle, in the basic state and is fixed in a force-fitting and / or form-fitting manner in the joined state, in particular. by widening the cross-section, wherein the cross-section is reduced in size in the disassembled state compared to the joined state in order to release the joining partner (2, 2A, 2B) arranged therein. Joining element (1) according to one of the preceding claims, characterized in that the shape memory steel is in the form of austenite in the basic state and in the joined state as martensite. Joining element (1) according to one of the preceding claims, characterized in that the joining element (1) can be converted from the basic state into the joined state by narrowing, widening, lengthening, upsetting, squeezing, flanging, crimping, spreading, pressing, or folding. Joining element (1) according to one of the preceding claims, characterized in that the joining element (1) transitions from the joined state to the disassembled state at a temperature in the range of 50°C - 300°C, preferably above 100°C.Joining element (1) according to one of the preceding claims, characterized in that the joining element (1) exerts bending and / or shear forces and / or normal forces on a joining partner (2, 2A, 2B) in the joined state. System (5) for producing a detachable joining connection, comprising a joining element (1), in particular according to one of the preceding claims, and a joining partner (2, 2A, 2B), wherein the joining element (1) consists at least partially of a shape memory steel and, in order to produce a joining connection with the joining partner (2, 2A, 2B), is deformable from a basic state into a joined state by the application of force and, in order to release the joining connection, is at least partially deformable from the joined state into a disassembled state by the introduction of heat. Method for producing and releasing a joining connection, comprising the steps: a.Step A: Providing a joining element (1) which consists at least partially of a shape memory steel, in particular a joining element (1) according to one of the preceding claims. b. Step B: Producing a joining connection of the joining element (1) with a joining partner (2, 2A, 2B) starting from a basic state of the. Joining element (1) by applying force and deforming the joining element (1) into a joined state. c. Step C: Releasing the joining connection by at least partially reshaping the joining element (1) from the joined state into a disassembled state by applying heat. Method according to the preceding claim, characterized in that in step A, a plurality of individual joining connections with a plurality of joining elements (1) are individually produced. Method according to claim 13 or 14, characterized in that in step C, a plurality of joining connections are removed together.

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