Method for securing a wire on a terminal element

Abstract

The invention relates to a method for fixing a wire (10) on a terminal element (12), wherein a cold-work-hardened wire (10) made of a copper alloy containing at least 70% copper, in particular at least 75% copper, is joined (V2) with the terminal element (12) in a material-locking manner with heat input, wherein the breaking elongation of the wire (10) is adjusted to a value greater than or equal to a predetermined minimum breaking elongation after cold work hardening and before joining (V1).

Description

Technical Field

[0001] The present invention relates to a method for securing wires to a wiring element. Background Technology

[0002] A stator for an electric motor is known from DE 10 2007 021 321 A1. The stator has a plurality of coils connected to each other on one side of the stator. The stator includes at least one busbar by which two of the plurality of coils are connected to each other by means of the busbar, wherein the ends of the busbar are respectively heat-pressed or welded to one end of one of the coils.

[0003] Furthermore, a spring clip for securing at least one electrical conductor to a wiring element is known from DE 10 2017 205 078 A1. The at least one electrical conductor and the wiring element can be interconnected by form-fitting and electrical means. Summary of the Invention

[0004] The objective of this invention is to provide a solution that enables particularly fatigue-resistant connections of wires in wiring elements.

[0005] According to the present invention, this task is solved by the technical solution of the independent claim. Other possible embodiments of the present invention are disclosed in the dependent claims, the specification, and the drawings.

[0006] This invention relates to a method for securing a wire to a wiring element. The wire, in particular, refers to an elongated, shaped, and flexible component made of metal. The wire, in particular, has a circular cross-section. Other cross-sectional shapes are also possible. The wire is particularly configured to be conductive. An electrical connection is established between the wire and the wiring element through a connection between the wire and the wiring element. Therefore, an electrical connection can be provided through the connection between the wire and the wiring element. For example, the wire can be a conductor of a motor, particularly a traction motor for a motor vehicle, which is connected to a voltage source or electrical equipment by connection to the wiring element.

[0007] This method specifies that a cold-worked wire made of a copper alloy containing at least 70% copper, particularly at least 75% copper, is material-locked to a wiring element under heat input. The wire, in particular, has a copper content of up to 99.9%. Therefore, the material used to manufacture the wire is a low-alloy copper compound and is not pure copper. It has been shown that if the elongation at break of the wire is adjusted to a value greater than or equal to a predetermined minimum elongation at break after cold work and before joining, particularly high strength of the connection between the wire and the wiring element can be achieved through material-locking joining. This minimum elongation at break can be predetermined, for example, based on the material of the wire. If the elongation at break of the wire is lower than the predetermined minimum elongation at break for the wire material after cold work and before joining, it may result in the joined wire having only particularly low strength, and thus the connection between the wire and the wiring element having particularly low strength.

[0008] The principle of cold work hardening is based on the introduction of additional dislocations into a material during plastic deformation. New dislocations are introduced into the material with each plastic deformation process. These dislocations hinder each other's movement, resulting in an increase in strength. Through cold work hardening, the material only undergoes plastic deformation at higher stress values. This means that cold-worked materials have higher yield strength.

[0009] By adjusting the elongation at break of the wire to a value greater than or equal to the minimum elongation at break before joining, exceptionally high strength of the wire can be achieved by joining the wire, and thus exceptionally high fatigue strength of the connection between the wire and the connecting element.

[0010] The winding wires of the motor's active components, particularly the rotor, can be fixed to the connecting element as wires. Alternatively, the active component can also be the motor's stator. In particular, the winding wires are part of the motor's coil structure. In particular, the connecting element can be held on the rotor's commutator rings. Therefore, the described method allows the winding wires to be connected to the rotor's commutator rings in a particularly safe and conductive manner. The wires are thus the rotor's electrical conductors, wound into coils. A particularly long rotor service life can be achieved through the particularly fatigue-resistant connection of the winding wires on the connecting element and via the connecting element on the rotor's commutator rings.

[0011] In one possible extension of the invention, it is specified that the elongation at break of the wire is adjusted to at least 5% before joining. Elongation at break is a material science property representing the ratio of the remaining elongation after a tensile specimen breaks to its initial measured length. Elongation at break characterizes the deformability or ductility of a workpiece. Therefore, for wire of any material, a value of 5% can be predetermined as the minimum elongation at break. It has been found that if the remaining elongation at break of the wire is at least 5% after cold work hardening and before joining, particularly high strength of the wire can be achieved after joining. If the cold work hardening of the wire is too high before joining and therefore the elongation at break of the wire before joining is less than 5%, the heat input during joining will cause a disproportionately large decrease in the strength of the wire after joining. Therefore, it is specified that the cold work hardening of the wire ends no later than when the elongation at break reaches the value of 5% to avoid the elongation at break falling below the value of 5%. Alternatively, the cold work hardening can be at least partially eliminated by heat treatment of the cold work hardened wire, thereby increasing the elongation at break of the wire to at least 5%.

[0012] In another possible embodiment of the invention, copper-zirconium wire, such as CuZr0.1, or copper-chromium wire, such as CuCr, or copper-chromium-zirconium wire, CuCrZr, are used as the wire. These corresponding wires have a conductivity of 75% to 98% according to IACS (International Standard for Annealed Copper). In particular, the CuZr0.1 wire is alloyed with only 0.1% zirconium. Based on their properties, especially their conductivity, these wires are particularly suitable as conductors in the active components of traction motors. With the aid of copper-zirconium wire, copper-chromium wire, or copper-chromium-zirconium wire, a connection with particularly good conductivity and high strength can be achieved between the wire and the connecting element.

[0013] In another possible embodiment of the invention, the wire is cold-formed for work hardening and heat-treated during this process to adjust the elongation at break; or alternatively, the already cold-worked wire is heat-treated to adjust the elongation at break. In other words, work hardening can be part of the method of the invention and the wire is cold-formed for work hardening. To ensure that the elongation at break of the wire after work hardening and before joining is not less than a predetermined minimum elongation at break, the wire can be heat-treated during the work hardening process to adjust the elongation at break. For example, the wire can be alternately cold-formed and subsequently heat-treated for work hardening until a predetermined shape of the wire is achieved. For example, the wire can be lengthened for work hardening, thereby reducing the diameter of the wire by cold forming. Subsequently, the wire can be heat-treated. Afterward, the wire can be lengthened again within the cold-forming range to further reduce the diameter of the wire. Then, the wire can be further heat-treated again. In particular, the wire can be continuously or repeatedly lengthened until the diameter of the wire reaches the predetermined diameter of the wire. By applying appropriate heat treatment, wire hardening caused by cold forming can be partially eliminated, thus increasing the elongation at break of the wire. If the wire is cold-formed for work hardening, it undergoes plastic deformation below its recrystallization temperature. The resulting hardening increases the material's strength. The recrystallization temperature is approximately 40% to 50% of the absolute melting temperature and depends on the material and the degree of deformation applied. Cold forming achieves increased strength, as well as ductility and, consequently, reduced elongation at break.

[0014] Alternatively, cold work hardening may not be part of the method of the present invention, but rather the cold-worked wire may be heat-treated to adjust the elongation at break. In other words, the cold-worked wire is used and heat-treated to increase the elongation at break of the wire to at least a predetermined minimum elongation at break, particularly to at least 5%. For example, the cold-worked wire can be supplied by a supplier to a manufacturer that manufactures the connection between the wire and the wiring element. The manufacturer can then heat-treat the cold-worked wire to increase the elongation at break of the wire to at least the predetermined minimum elongation at break. In particular, the heat treatment for adjusting the elongation at break and the heat input for joining are two separate process steps, so that each process step is precisely adapted to the corresponding function of the process. In other words, the heat input for heat treatment can be optimized such that the elongation at break of the wire is adjusted to a predetermined value, particularly to a value higher than the predetermined minimum elongation at break, before joining. The heat input for joining can be selected in particular to enable a material-locking connection between the wire and the wiring element with particularly high reliability.

[0015] In another possible embodiment of the invention, the wire is cold-worked within the scope of the method, and cold-working is stopped once the wire reaches a predetermined value for elongation at break. This predetermined value for elongation at break is particularly higher than a predetermined minimum elongation at break, particularly higher than 5%. Heat treatment for adjusting the elongation at break can be omitted here. For example, if the wire is cold-worked by cold forming, cold forming is stopped once the wire reaches the predetermined value for elongation at break. This allows for a particularly simple and cost-effective way to ensure that the elongation at break of the wire before joining is greater than or equal to the predetermined minimum elongation at break. Furthermore, this allows for particularly rapid adjustment of the elongation at break and cold-working, since cold-working can be simply stopped when the predetermined value for elongation at break is reached.

[0016] In another possible embodiment of the invention, the wire and the connecting element are thermally pressed and / or brazed and / or fused. Brazing is a thermal process for joining materials in a locking manner, wherein a liquid phase is generated by melting a filler metal or by diffusion at the interface. In particular, the wire and the connecting element can be soft-brazed or hard-brazed. Fusion welding is understood as joining or fusing workpieces by using heat and / or pressure, so that the workpieces form a unit. In particular, the wire can be laser-welded or electron-beam-welded to the connecting element. Pressing is understood as a joining process in which two components are connected to each other by plastic deformation, such as by flanging, extrusion, curling, or folding. Pressed connections can only be conditionally separated and can only be re-pressed during maintenance using suitable tools. Pressing can establish a uniform, difficult-to-separate electrical connection between conductors, especially wires, and connecting elements, especially connecting elements. This connection ensures high electrical and mechanical safety.

[0017] Hot crimping, or heat bonding, is a technique in the field of resistance welding. The combination of pressure and heat generation creates a permanent connection. Heat energy can be introduced by introducing an electric current into the wire. Alternatively, it can operate solely by heat flow without an electric current, for example, by heating the crimping clamps through induction or a furnace. That is, hot crimping has the added benefit of burning away any insulating varnish that may be present on the wire. Therefore, it is not necessary to remove the insulating varnish from the wire by chemical or mechanical means before establishing a connection. Thus, hot crimping enables particularly rapid connections between wires and connecting components, especially when the wire is coated with an insulating varnish.

[0018] When establishing a connection using thermoforming, the most important parameters are the pressure applied during the pressing process, the heat used (e.g., the heat generated when current is introduced through the resistance or thermal resistance of the material to be welded), and the duration of this heat application to the material. The resulting connection is characterized by extremely high conductivity and low contact resistance.

[0019] In this case, it is specifically stipulated that during heat compression, the wire is heated to a temperature of 500°C to 1000°C, particularly 650°C to 900°C, for 300 to 1500 milliseconds, particularly 500 to 1000 milliseconds. By using the above-mentioned heat compression parameters for heat-compressing the wire to the wiring element, exceptionally high strength can be achieved after bonding of the wire and the connection between the wire and the wiring element.

[0020] In another possible embodiment of the invention, a wire with a yield strength of at least 420 MPa is specified as the wire. This wire has a yield strength of at least 420 MPa, particularly before and / or after cold work hardening and before joining. The yield strength of the wire used is at least 420 MPa, especially independent of elongation at break. This allows for particularly high fatigue strength in the connection between the wire and the connecting element.

[0021] Other features of the invention can be derived from the claims, drawings, and description of the drawings. The features and combinations thereof mentioned above in the specification, as well as the features and combinations thereof shown separately in the description of the drawings and / or in the drawings, may be used not only in the given combinations, but also in other combinations or individually, without departing from the scope of the invention. Attached Figure Description

[0022] The attached image is as follows:

[0023] Figure 1 A process flow diagram showing a method for securing wires to a wiring element is shown; and

[0024] Figure 2 A schematic side view of a wire being inserted into a notch in a connector during the connection of the wire to the connector element. Detailed Implementation

[0025] In the accompanying drawings, identical and functionally identical elements are given the same reference numerals.

[0026] The attached image is in Figure 1 The image shows a method for... Figure 2 The diagram illustrates the process flow of the method for fixing the wire 10 to the wiring element 12. The wire 10 can be, in particular, a conductor of a coil component of a motor vehicle drive motor. The wiring element 12 can be disposed on the commutation ring of the drive motor. Therefore, in order to electrically connect the conductor to the commutation ring, it is necessary to connect, in particular, to the wiring element 12. Figure 2The diagram illustrates how the wire 10 is inserted into the recess 14 of the connector element 12. The corresponding crimping electrode 18 of the crimping pliers rests against the outer side arm 16 of the corresponding defining recess 14 of the connector element 12. By moving the crimping electrodes 18 toward each other, the wire 10 and connector element 12 are thermally crimped using the crimping pliers to achieve a material-locking connection and thus a mating.

[0027] Wire 10 is made of a copper alloy containing at least 70% copper, particularly at least 75% copper. Currently, wire 10 is copper-zirconium wire, copper-chromium wire, or copper-chromium-zirconium wire. It is specified that the yield strength of wire 10 is at least 420 MPa. To ensure particularly high strength of wire 10 and its connection to connector 12 after joining, this method specifies that, in the first method step V1, after cold work hardening of wire 10, the elongation at break of wire 10 is adjusted to a predetermined value greater than or equal to a predetermined minimum elongation at break. Currently, the predetermined minimum elongation at break is 5%. Subsequently, in the second method step V2, wire 10 is joined to connector 12, currently by heat pressing. Alternatively, wire 10 may also be brazed and / or fusion welded to connector 12. During hot pressing, the wire 10 is heated to a temperature of 500°C to 1000°C, especially 650°C to 900°C, for 300 to 1500 milliseconds, especially 500 to 1000 milliseconds.

[0028] Therefore, this method specifies that the cold-worked wire 10 (whose elongation at break has been adjusted to be greater than or equal to a predetermined minimum elongation at break) is material-locked to the connecting element 12. It is possible that the wire 10 is cold-worked before joining and cold-worked is stopped once the wire 10 reaches the predetermined elongation at break (which is greater than or equal to the predetermined minimum elongation at break). Alternatively, it can be specified that the wire 10 is cold-formed for cold-working and heat-treated during this period to adjust the elongation at break. Further alternatively, the cold-worked wire 10 may also be heat-treated to adjust the elongation at break. In other words, either the cold-working of the wire 10 can be stopped once it reaches the predetermined elongation at break, or the wire 10 can be subjected to the aforementioned at least one heat treatment during or after cold-working to adjust the elongation at break of the wire 10 before joining to a predetermined value greater than or equal to the predetermined minimum elongation at break.

[0029] When joining (e.g., brazing, crimping, or fusion welding) high-strength alloy copper wires, the energy input, depending on the degree of work hardening of the corresponding wire 10, may result in an excessive reduction in strength and thus a shortened product lifespan. Within the scope of this method, an optimal balance between the degree of work hardening of the alloy wire 10 and the energy input during joining is utilized to achieve maximum strength in the joint connection between the wire 10 and the connecting element 12.

[0030] Here, a specific level of cold work hardening can be adjusted in the alloy wire 10 through pre-treatment. This level of cold work hardening can be coordinated with the parameters of the joining process, especially the parameters concerning temperature and time, as well as the content of alloying elements in the copper wire. For hot bonding, the elongation at break of the wire 10 may need to reach at least 5% in order to obtain the maximum strength of the joint after the joining process. If the cold work hardening in the wire 10 is too high before the joining process and the elongation at break of the wire 10 is therefore lower than the predetermined minimum elongation at break (e.g., because the elongation at break is less than 5%), the heat input during joining will cause a disproportionately large decrease in the strength of the wire 10 after joining.

[0031] In the cold work hardening range, the wire 10 can be drawn at room temperature, thereby reducing its diameter from 5 mm to 2 mm. Afterward, the wire 10 can be heat-treated to adjust its elongation at break, in which case the wire 10 is heated to a temperature of 400°C to 450°C.

[0032] In summary, this invention demonstrates how to manufacture a copper connection that can withstand cyclic loads, is high-strength, and is electrically conductive.

[0033] List of reference numerals

[0034] 10 wires

[0035] 12 wiring components

[0036] 14 notches

[0037] 16-arm

[0038] 18 crimp electrodes

[0039] The corresponding method steps for V1 to V2

Claims

1. A method for securing a wire (10) to a wiring element (12), wherein, A cold-worked wire (10) made of a copper alloy containing at least 70% copper, especially at least 75% copper, is joined to a wiring element (12) in a material-locking manner under heat input (V2), wherein, after cold work and before joining, the elongation at break of the wire (10) is adjusted to a value greater than or equal to a predetermined minimum elongation at break (V1).

2. The method according to claim 1, characterized in that, The elongation at break of the wire (10) is adjusted to a predetermined minimum elongation at break of 5% or greater.

3. The method according to claim 1 or 2, characterized in that, Use copper-zirconium wire, copper-chromium wire, or copper-chromium-zirconium wire as wire (10).

4. The method according to any one of the preceding claims, characterized in that, The wire (10) is cold-formed for work hardening and heat-treated during this period to adjust the elongation at break; or the cold-worked wire (10) is heat-treated to adjust the elongation at break.

5. The method according to any one of claims 1 to 3, characterized in that, The wire (10) is cold-worked and the cold-work is stopped once the wire (10) reaches the predetermined value of elongation at break.

6. The method according to any one of the preceding claims, characterized in that, The wire (10) is heat-pressed and / or brazed and / or fused to the wiring element (12).

7. The method according to claim 6, characterized in that, During hot pressing, the wire (10) is heated to a temperature of 500°C to 1000°C, especially 650°C to 900°C, for 300 to 1500 milliseconds, especially 500 to 1000 milliseconds.

8. The method according to any one of the preceding claims, characterized in that, Use wire with a yield strength of at least 420 MPa as wire (10).

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