Method for fastening metal wire to connection element and connection arrangement

Abstract

The invention relates to a method for fastening a metal wire (10) to a connection element (12), in which the metal wire (10) is cold-formed (V1) in order to introduce cold hardening and then thermally compressed (V3) to the connection element (12).

Description

TECHNICAL FIELD

[0001] The invention relates to a method for fixing a metal wire on a terminal element and to a connection arrangement system of a metal wire on a terminal element. BACKGROUND

[0002] DE 10 2007 021 321 A1 discloses a stator of an electric machine having a plurality of coils which are connected to one another on one side of the stator. Furthermore, the stator comprises at least one busbar with which two coils from the plurality of coils are connected, in that an end of the busbar is crimped or welded to one end of one of the coils.

[0003] Furthermore, it is known from DE 10 2017 205 078 A1 a connection system for establishing an electrical and mechanical connection between at least one electrical conductor and a terminal element. The connection system comprises a spring clip and the terminal element, wherein the at least one conductor and the terminal element can be connected to one another form- locking and electrically. The at least one electrical conductor and the terminal element can be mechanically fixed to one another by means of the spring clip, wherein in the mechanically fixed state the at least one electrical conductor is clamped between the terminal element and the spring clip. SUMMARY

[0004] It is an object of the invention to create a solution which enables a particularly durable connection of a metal wire to a terminal element.

[0005] This object is achieved according to the invention by the technical solutions of the independent claims. Further possible design solutions of the invention are disclosed in the dependent claims, the description and the drawings. The features, advantages and possible design solutions set out in the scope of the description for one of the technical solutions of the independent claims can be considered at least analogously as features, advantages and possible design solutions of the respective technical solution of the other independent claims and of every possible combination of the technical solutions of the independent claims, if necessary in combination with one or more dependent claims.

[0006] The invention relates to a method for fixing a metal wire on a terminal element, in which method the metal wire is cold formed to introduce cold work hardening and then the metal wire is crimped with the terminal element. The metal wire refers in particular to a thin and long shaped bendable member made of metal. The metal wire has in particular a circular cross section. Alternative cross section shapes are also possible. The metal wire is in particular electrically conductive. Via the connection between the metal wire and the terminal element, an electrical connection of the metal wire to the terminal element is created. Thus, an electrical connection can be provided via the connection between the metal wire and the terminal element.

[0007] In order to achieve a particularly high fatigue strength of the connection, the metal wire is first cold-work hardened and then hot pressure-bonded to the terminal element. Thereby, a particularly fine structure is produced in the metal wire, thereby achieving a particularly high cyclic load capacity of the metal wire. The principle of cold work hardening is based on the introduction of additional dislocations into the material during plastic deformation. During each plastic deformation, new dislocations are also introduced into the material. The dislocations prevent each other from moving, which leads to a strength-increasing effect. Due to the cold work hardening, plastic deformation of the material only occurs at higher stress values. This means that cold-work-hardened materials have an increased yield strength. In order to cold-work-harden, the metal wire is cold-formed. At present, forming is understood to be plastic forming of the metal below the recrystallization temperature. By the cold work hardening produced thereby, the material strength is increased. The recrystallization temperature is approximately 40% to 50% of the absolute melting temperature and depends on the material and the degree of forming applied. By cold forming, it is possible to increase the strength and reduce the ductility and thus the elongation at break.

[0008] Pressure bonding is understood to be a joining method in which two components are connected to one another by plastic deformation, for example by flanging, extruding, crimping or folding. A pressure-bonded connection can only be loosened to a limited extent and can only be refurbished with suitable tools when repairing. Pressure bonding enables a uniform, difficult-to-loosen electrical connection to be established between a conductor, in particular a metal wire, and a connecting element, in particular a terminal element. The connection ensures high electrical and mechanical safety.

[0009] High-temperature pressure bonding or hot pressure bonding is a technique from the field of resistance welding. The combination of pressure and the introduction of thermal energy produces a durable connection. The thermal energy can be introduced by means of a current being introduced into the metal wire. Alternatively, it is possible to work without a current and with only a heat flow, for example by using induction or oven-heated pressure-bonding pliers. This means that pressure bonding has the side effect that the insulating lacquer layer, if present, of the metal wire is burned off by the heat generated. It is thus possible to dispense with chemically or mechanically removing the insulating lacquer from the metal wire before the connection is established. It is thus possible to achieve a particularly rapid connection of the metal wire to the terminal element, also because the metal wire is a metal wire coated with insulating lacquer. The most important parameters when establishing a connection via the hot pressure bonding technique are the pressure with which the pressure-bonded connection is extruded, the amount of heat used, or the high temperature, for example the heat generated by the electrical or thermal resistance of the material to be welded when a current is introduced, and the time for which the heat generated acts on the material. The connection produced is characterized by a very high electrical conductivity and a low contact resistance. By hot pressure bonding, the structure of the metal wire can be recrystallized, whereby a particularly fine-grained structure can be achieved as a result of the cold work hardening before the hot pressure bonding. This is advantageous in terms of cyclic load capacity. The method thus makes it possible to achieve a mechanically particularly stable electrical connection between the metal wire and the terminal element.

[0010] In a possible further development of the application it is provided that the wire element is fixed with a non-alloyed or low-alloyed copper wire as metal wire. Thus, a copper wire with a copper content of more than 95% according to IACS is used. In particular when using a copper wire, a particularly fine-grained structure can be achieved due to cold work hardening and subsequent thermal crimping. Thus, in particular when using a non-alloyed copper wire, a mechanically particularly stable connection between the metal wire and the wire element can be achieved.

[0011] In this respect it can be provided in particular that the metal wire is made of CuETP or CuOF or CuOFE or CuDHP or CuHCP. CuETP is a copper grade with a residual oxygen content produced by electrolytic refining. This material has a very high electrical conductivity and is particularly economical. CuOF is an oxygen-free copper with a high purity of at least 99.99% copper content. This material combines the advantages of CuETP with those of a phosphorus-deoxidized copper grade. The high purity and the absence of oxidic inclusions enable an electrical conductivity of 100% IACS. Furthermore, CuOF is not susceptible to hydrogen embrittlement. CuOF can be deformed very well and is suitable for soldering and brazing. In these respects, CuOF is superior to CuETP alloys. CuOFE is a high-purity, non-deoxidized and oxygen-free copper which does not contain elements which can be evaporated in a vacuum and which has a high electrical and thermal conductivity. In addition to very good hot formability and cold formability, this copper grade also has good corrosion resistance, in particular to the atmosphere (well-adhering oxide layer) and water, and is practically insensitive to stress corrosion cracking. It is resistant to heat treatment in reducing atmospheres and can be well soldered and brazed and soft-soldered. CuDHP is a deoxidized, oxygen-free copper which has a certain residual phosphorus content. This material combines good formability with suitability for soldering and brazing, with the electrical conductivity being reduced due to the residual phosphorus content. CUHCP is a high-purity and deoxidized copper which has a low residual phosphorus content, which has a high electrical and thermal conductivity. In addition to very good cold formability and hot formability, this copper grade also has good corrosion resistance, in particular to the atmosphere (including industrial atmospheres) and water. The copper has good solderability and brazability and is resistant to hydrogen. The described non-alloyed copper materials each form a particularly fine-grained structure after cold forming and subsequent thermal crimping, whereby a particularly high cyclic load capacity can be achieved.

[0012] In another possible design of the application it is provided that the winding wire of an active part of the electric machine, in particular of the rotor, is fixed as a wire on the connection element. Alternatively, the active part can be the stator of the electric machine. In particular, the winding wire is part of a coil member of the electric machine. In particular, the connection element can be held on a switching ring of the rotor. The method thus enables a particularly secure and electrically conductive connection of the winding wire to the switching ring of the rotor. The wire is thus an electrical conductor of the rotor, which is wound into a coil. The method thus enables a particularly durable connection of the winding wire on the connection element and via the connection element on the switching ring of the rotor. A particularly long service life of the rotor can thus be achieved.

[0013] In this regard it can in particular be provided that the winding wire is cold-work-hardened by means of the winding needle by means of forming when it is wound onto the lamination stack of the active part. This means that the winding wire is cold-work-hardened when it is wound onto the lamination stack. The cold-work-hardening is thus introduced into the winding wire by means of the winding needle in such a way that the winding wire is cold-formed by means of the winding needle when it is wound onto the lamination stack. By adapting the winding technology or the orientation of the winding needle, the degree of cold-forming and thus the cold-work-hardening of the winding wire can be precisely adjusted. Alternatively, the cold-work-hardening can be introduced by deflecting the winding wire in front of the winding needle, for example by guiding the winding wire via a deflection roller having a "small" radius and a corresponding arrangement. By cold-work-hardening the winding wire when it is wound onto the lamination stack, the active part can be produced particularly quickly by simultaneously cold-work-hardening and winding the winding wire onto the lamination stack.

[0014] In this regard it can in particular be provided that the deflection angle of the winding wire when it is wound onto the lamination stack by means of the winding needle is selected in accordance with the cold-work-hardening to be achieved for the winding wire. The stronger the winding wire is deflected when it is wound by means of the winding needle, the greater the adjusted cold-work-hardening of the winding wire. The deflection angle of the winding wire is here in particular selected in such a way that an excessively strong cold-forming of the winding wire does not occur, which can lead to local damage or tearing of the winding wire. This means that the deflection angle is selected in such a way that the winding wire is cold-formed sufficiently strongly to achieve the predetermined cold-work-hardening, but not to such an extent that the winding wire is damaged. In order to adjust the deflection angle, in particular the angle of attack and / or the movement profile of the winding needle can be adapted in order to achieve the forming of the winding wire in the predetermined deflection angle. It can thus be ensured that the winding wire is cold-formed sufficiently to achieve the predetermined cold-work-hardening and that the risk of damage to the winding wire is particularly low here.

[0015] In an alternative possible design of the application it is provided that the winding wire is cold-work hardened first by cold forming, is then wound onto the lamination stack of the coil member and is then hot pressure-bonded to the connection element. In other words, the winding wire is cold formed before being wound onto the lamination stack. The already cold-work hardened winding wire is then wound onto the lamination stack. By separating the cold-work hardening of the winding wire from the winding of the winding wire onto the lamination stack, it is possible to optimize the cold-work hardening and the winding of the winding wire onto the lamination stack, respectively. This means that the winding wire can be cold-work hardened independently of the respective deflection limit present during the winding of the winding wire onto the lamination stack. Furthermore, during the winding process of the winding wire onto the lamination stack, the winding of the winding wire onto the lamination stack can be optimized, wherein the deflection angle to be observed for the cold-work hardening of the winding wire is not taken into account, since the winding wire is already cold-work hardened when being wound onto the lamination stack. Thus, the winding wire can be cold formed in an optimized manner and then wound onto the lamination stack in an optimized manner.

[0016] In a further possible design of the application it is provided that the wire is heated at least locally to a temperature of 450 to 900 °C and / or for a duration of 100 to 1200 milliseconds during the hot pressure bonding. Here, the temperature and the duration of the heating during the hot pressure bonding are selected in accordance with the desired recrystallization of the wire structure. By heating the wire at least locally to a temperature of 450 to 900 °C and / or for a duration of 100 to 1200 milliseconds during the hot pressure bonding, a particularly fine structure of the wire and thus a particularly high cyclic load capacity of the wire, in particular of the connection of the wire to the connection element, can be achieved after the hot pressure bonding.

[0017] In a further possible design of the application it is provided that, for the pre-fixing, the wire is cold pressure-bonded to the connection element first and then hot pressure-bonded to the connection element at the same location. By cold pressure-bonding the wire to the connection element, the wire can be positioned relative to the connection element and held particularly securely in this position. The wire can then be connected to the connection element in this position by hot pressure-bonding securely and durably, in particular material-lockingly, relative to the connection element. A particularly precise positioning and orientation of the wire relative to the connection element can be achieved by the pre-fixing by cold pressure-bonding. Cold pressure-bonding is understood to mean that the wire is pressure-bonded to the connection element, wherein neither the wire nor the connection element is heated. By deforming the wire during the cold pressure-bonding, a local cold-work hardening can be introduced into the wire to be pressure-bonded.

[0018] In another possible design of the application it is provided that the metal wire is cold-pressed to the connection element at the same location after the hot-pressing. Thereby it is possible to further increase the strength of the press connection. Thus, a particularly stable connection between the metal wire and the connection element is obtained.

[0019] Furthermore, the application relates to a connection arrangement system for a metal wire on a connection element, in which a metal wire that is cold-formed for cold work hardening is fixed to the connection element via a hot-press connection. Thereby, the metal wire has a particularly fine structure caused by recrystallization upon hot-pressing. In particular, the connection arrangement system is part of an active component of an electric machine, in particular a coil member. The electric machine can in particular be a traction machine of an electrically drivable motor vehicle. In particular, the active component is a rotor of the electric machine. In this case, the metal wire can be a winding metal wire of the rotor, which is wound as a coil winding on a lamination stack of the rotor. The connection element can be fixed on a switching ring of the rotor, whereby the coil winding is electrically connected to the switching ring via the connection arrangement system. BRIEF DESCRIPTION OF DRAWINGS

[0020] Further features of the application can be gathered from the claims, the drawings and the drawings description. The features and feature combinations mentioned in the above description and in the claims and those singly- or in any combination shown in the drawings, can be used not only in the respectively indicated combinations, but also in other combinations or on their own, without leaving the scope of the present application.

[0021] In the drawings:

[0022] Figure 1 a method diagram showing a method for fixing a metal wire on a connection element; and

[0023] Figure 2 a schematic perspective view showing a rotor of an electric machine with a connection arrangement system for a metal wire on a connection element. DETAILED DESCRIPTION

[0024] In the drawings, identical and functionally identical elements are provided with the same reference signs.

[0025] Figure 1 a method diagram showing a method for fixing a metal wire 10 on a connection element 12. Due to the fixing of the metal wire 10 on the connection element 12, a connection arrangement system 14 of the metal wire 10 on the connection element 12 is manufactured. In Figure 2 an example is shown in which a connection arrangement system 14 can be used. In Figure 2The diagram shows a schematic perspective view of the rotor 16 of a traction motor in a current motor vehicle. The rotor 16 includes a lamination assembly 18 on which metal wire 10 is wound, thereby providing the rotor coil 20 of the rotor 16. The metal wire 10 is therefore the winding metal wire of the rotor 16. Currently, the metal wire 10 is unalloyed or low-alloyed copper wire, particularly copper wire made of CuETP, CuOF, or CuDHP.

[0026] exist Figure 2 The rotor 16 is shown in a partially enlarged view. Here it can be seen that the wiring element 12 is fixed to the switching ring 22 of the rotor 16. The metal wire 10 is thus electrically connected to the switching ring 22 via the wiring element 12 through the connection configuration system 14.

[0027] Currently, the wiring element 12 is configured as a fork, wherein the metal wire 10 is inserted between the two fork tips of the fork-shaped wiring element 12 for connection with the wiring element 12.

[0028] The following is combined with Figure 1 The method for securing the metal wire 10 to the wiring element 12 is described. The states Z of the metal wire 10 at different times in the method are shown in corresponding frame boxes. In the first frame, the metal wire 10 is shown in its first state Z1—its original state. Starting from this first state Z1, the metal wire 10 is cold-worked in the first method step V1 by cold forming. Here, the metal wire 10 can be cold-worked first by cold forming and then wound onto the lamination group 18 of the rotor 16, or cold-worked simultaneously with winding onto the lamination group 18. Here, the necessary cold work is primarily introduced by the geometry of the coiling needle, which places the metal wire 10 onto the lamination group 18. This means that the metal wire 10 is cold-worked by forming with the help of the coiling needle while being wound onto the lamination group 18. Here, the deflection angle of the metal wire 10 when being wound onto the lamination group 18 with the help of the coiling needle is selected according to the desired cold work of the metal wire 10.

[0029] Alternatively, the metal wire 10 that has been cold-work-hardened is used for the winding process. This means that the winding metal wire is first cold-work-hardened by cold forming, then wound onto the lamination stack 18 of the rotor 16 and subsequently thermally pressure-bonded with the connection element 12. The cold-work-hardened metal wire 10 is placed into the connection element 12, which is configured as a fork, thereby achieving the second state Z2 shown in the second frame. As can be seen particularly well in the second frame, the connection element 12 currently has a U-shaped cross section, wherein the metal wire 10 is placed into the recess of the connection element 12 via the open side of the U-shaped cross section. Here, the metal wire 10 can rest on the bottom of the recess of the U-shaped cross section of the connection element 12 or can be held only by the prongs of the fork. Alternatively, the connection element 12 can have a V-shaped cross section, wherein the metal wire 10 is placed into the recess of the connection element 12 via the open side of the V-shaped cross section. The metal wire 10 is then cold- pressure-bonded with the connection element 12 in a second method step V2. Here, a mechanical force F acts on the connection element 12 and the metal wire 10. This results in a cold- pressure-bonded third state Z3 of the metal wire 10 with the connection element 12, which is shown in the third frame. After the cold pressure-bonding, the metal wire 10 and the connection element 12 are thermally pressure-bonded in a third method step V3. Here, not only a mechanical force F acts on the connection element 12 and the metal wire 10, but also heat 24 is introduced at least into the metal wire 10. Currently, the thermal pressure-bonding is carried out in a temperature range of 450 to 900 °C, wherein the metal wire 10 and, if necessary, additionally the connection element 12 are thermally pressure-bonded for a duration of 100 to 3000 milliseconds, in particular for a duration of 100 to 1200 milliseconds. This is to be understood as meaning that the set temperature for the thermal pressure-bonding is maintained for 100 to 3000 milliseconds, in particular for 100 to 1200 milliseconds, and the mechanical force F is maintained for 100 to 3000 milliseconds, in particular for 100 to 1200 milliseconds. The fourth state Z4 of the thermal pressure-bonding of the metal wire 10 is shown in the fourth frame. This means that, in order to pre-fix, the metal wire 10 is first cold- pressure-bonded with the connection element 12 and then the metal wire 10 is thermally pressure-bonded with the connection element 12 at the same location.

[0030] In order to introduce further cold-work-hardening after the recrystallization of the metal wire and thus in order to further increase the strength, the thermally pressure-bonded connection can then be re-cold- pressure-bonded.

[0031] If a metal wire coated with insulating lacquer is used as metal wire 10, the lacquer is burned off via the temperature influence at the hot crimping. Thus, after the cold crimping, the metal wire 10 material is lockingly joined to the terminal element 12 via the hot crimping process. Via the associated heat treatment, a fine structure and thus a fine-grained microstructure is formed as a result of the recrystallization of the structure in the metal wire 10. This is advantageous in terms of the fatigue strength of the connection arrangement system 14. The cold-worked metal wire 10 with a hardness of 90 HV0.1 leads to a particularly fine-grained structure after the energy input at the hot crimping, by which the recrystallization of the structure of the metal wire 10 takes place. This has a particularly good cyclic load capacity. After the hot crimping, the hardness of this metal wire 10 is 55 to 60 HV0.1.

[0032] The described method enables a particularly high fatigue strength of the hot crimping connection of the metal wire 10 to the terminal element 12.

[0033] In summary, the invention shows how a fatigue-resistant, current-carrying copper connection can be created.

[0034] List of reference signs

[0035] 10 metal wire

[0036] 12 terminal element

[0037] 14 connection arrangement system

[0038] 16 rotor

[0039] 18 lamination stack

[0040] 20 rotor winding

[0041] 22 switching ring

[0042] 24 heat

[0043] Z1 to Z4 state of the metal wire

[0044] F force

[0045] V1 to V3 method steps

Claims

1. Method for fixing a metal wire (10) on a terminal element (12), in which method the metal wire (10) is cold formed (V1) to introduce cold work hardening and then the metal wire is hot pressure joined (V3) with the terminal element (12).

2. The method of claim 1, wherein, Fixing a non-alloyed or low-alloyed copper wire as the metal wire (10) on the terminal element (12).

3. The method of claim 2, wherein, The metal wire (10) is made of CuETP or CuOF or CuOFE or CuDHP or CuHCP.

4. The method according to one of the preceding claims, characterized in that, The winding metal wire of an active component of an electric machine, in particular of a rotor (16), is fixed as the metal wire (10) on a terminal element (12).

5. The method of claim 4, wherein, The winding metal wire is cold work hardened by means of the forming by means of a winding needle when being wound on a lamination stack (18) of the active component.

6. The method of claim 5, wherein, The deflection angle of the winding metal wire when being wound on a lamination stack (18) by means of a winding needle is selected depending on the cold work hardening to be achieved of the winding metal wire.

7. The method of claim 4, wherein, The winding metal wire is cold work hardened by cold forming first and then wound on a lamination stack (18) of the coil member and thereafter hot pressure joined with the terminal element (12).

8. The method according to one of the preceding claims, characterized in that, The metal wire (10) is heated at least locally to a temperature of 450-900°C and / or for a duration of 100-3000 milliseconds when hot pressure joining.

9. The method according to one of the preceding claims, characterized in that, For pre-fixing, the metal wire (10) is cold pressure joined (V2) with the terminal element (12) first and then the metal wire (10) is hot pressure joined (V3) with the terminal element (12) at the same location.

10. The method according to one of the preceding claims, characterized in that, The metal wire (10) is cold pressure joined with the terminal element (12) at the same location after hot pressure joining.

11. A connection arrangement system (14) of a metal wire (10) on a wiring element (12), wherein The metal wire (10) cold formed for cold work hardening is fixed on the terminal element (12) via the hot pressure joining connection, whereby the metal wire (10) has a particularly fine structure caused by recrystallization when hot pressure joining.

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