Method for attaching a wire to a connecting element and connection arrangement

Abstract

The invention relates to a method for attaching a wire (10) to a connecting element (12), in which the wire (10) is cold-formed (V1) to introduce cold working and is then hot-crimped with the connecting element (12) (V3).

Description

[0001] The invention relates to a method for fastening a wire to a connecting element and a connecting arrangement of a wire to a connecting element.

[0002] DE 10 2007 021 321 A1 discloses a stator of an electrical machine with a plurality of coils interconnected on one side of the stator. Furthermore, the stator comprises at least one busbar to which two of the plurality of coils are interconnected by hot-crimping or welding the ends of the busbar to one end of each of the coils.

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

[0004] The object of the present invention is to provide a solution which enables a particularly durable connection of a wire to a connecting element.

[0005] This object is achieved according to the invention by the subject matter of the independent claims. Further possible embodiments of the invention are disclosed in the subclaims, the description, and the figures. Features, advantages, and possible embodiments presented in the description for one of the subject matter of the independent claims are to be regarded at least analogously as features, advantages, and possible embodiments of the respective subject matter of the other independent claims, as well as any possible combination of the subject matter of the independent claims, optionally in conjunction with one or more of the subclaims.

[0006] The invention relates to a method for fastening a wire to a connecting element, in which the wire is cold-formed to introduce work hardening and is then hot-crimped to the connecting element. The wire is, in particular, a thin and long, flexible component made of a metal. The wire has, in particular, a circular cross-section. Alternative cross-sectional shapes are also possible. The wire is, in particular, electrically conductive. An electrical connection between the wire and the connecting element is established via the connection between the wire and the connecting element. An electrical connection can thus be provided via the connection between the wire and the connecting element.

[0007] To achieve a particularly high fatigue strength for this connection, the wire is first work hardened and then hot-crimped to the connecting element. This creates a particularly fine microstructure in the wire, which results in the wire's particularly high cyclic load-bearing capacity. The principle of work hardening is based on the introduction of additional dislocations into a material during plastic deformation. With every plastic deformation process, new dislocations are always introduced into the material. The dislocations prevent each other from moving, which increases the strength. Due to work hardening, plastic deformation of the material only occurs at higher stress values. This means that the work-hardened material has a higher yield strength. For work hardening, the wire is cold-formed.In this context, forming refers to the plastic deformation of metals below the recrystallization temperature. The resulting hardening increases the material's strength. The recrystallization temperature is approximately 40 to 50 percent of the absolute melting temperature and depends on the material and the degree of deformation applied. Cold forming can increase strength and reduce ductility, and thus elongation at break.

[0008] Crimping is a joining process in which two components are joined by plastic deformation, for example, by flanging, squeezing, crimping, or folding. A crimped connection is only partially removable and can only be repaired with suitable tools. Crimping enables the creation of a homogeneous, difficult-to-remove electrical connection between a conductor, especially a wire, and a connecting element, especially a terminal element. This connection ensures high electrical and mechanical reliability.

[0009] Hot or thermal crimping is a technique from the field of resistance welding. A combination of pressure and the introduction of heat energy creates a permanent connection. The heat energy can be introduced by introducing an electric current into the wire. Alternatively, it can be done without a current flow and only with a heat flow, for example by heating the crimping pliers using induction or a furnace. This means that crimping has the side effect that the generated heat burns off any insulating varnish layer that may be present on the wire. This eliminates the need for chemical or mechanical removal of the insulating varnish from the wire before making the connection. This enables a particularly quick connection of the wire to the connecting element, also because the wire is coated with an insulating varnish.The most important parameters when creating a connection using a hot crimping technique are the pressure with which the crimp connection is pressed, the amount of heat used (for example, the heat generated when the electrical current is introduced due to the electrical or thermal resistance of the material to be welded), and the time for which the generated heat acts on the material. The resulting connection is characterized by very high electrical conductivity and low electrical contact resistance. Hot crimping can cause recrystallization of the wire structure, which, due to work hardening prior to hot crimping, allows a particularly fine-grained structure to be achieved. This is advantageous in terms of cyclic load capacity.The process thus makes it possible to achieve a mechanically particularly stable electrical connection between the wire and the connecting element.

[0010] In a possible further development of the invention, an unalloyed or low-alloyed copper wire is used as the wire to be attached to the connecting element. Thus, a copper wire with a copper content of more than 95% according to IACS is used. In particular, when using copper wire, a particularly fine-grained structure can be achieved as a result of work hardening and subsequent hot crimping. Consequently, a particularly mechanically stable connection between the wire and the connecting element can be achieved, particularly when using unalloyed copper wire.

[0011] In this context, the wire may, in particular, be made of CuETP, CuOF, CuOFE, CuDHP, or CuHCP. CuETP is a copper grade produced by electrolytic refining with a residual oxygen content. The material exhibits very high electrical conductivity and is particularly cost-effective. CuOF is a high-purity, oxygen-free copper with at least 99.99 percent Cu. This material combines the advantages of CuETP with those of phosphorus-deoxidized copper grades. The high purity and the absence of oxide inclusions enable 100 percent IACS electrical conductivity. Furthermore, CuOF is not susceptible to hydrogen embrittlement. CuOF is highly formable and suitable for welding and brazing. In these aspects, CuOF is superior to the CuETP alloy.CuOFE is a high-purity, non-deoxidized, and oxygen-free copper that contains no elements that vaporize in a vacuum and exhibits high electrical and thermal conductivity. This copper grade not only exhibits excellent hot and cold formability but also good corrosion resistance, particularly against atmospheric agents (a well-adhering oxide layer) and water, and is virtually immune to stress corrosion cracking. It is resistant to heat treatment in a reducing atmosphere and is easy to weld and braze. CuDHP is a deoxidized, oxygen-free copper with a certain residual phosphorus content. The material combines good formability with suitability for welding and brazing, although its conductivity is reduced due to the residual phosphorus content. CUHCP is a high-purity, deoxidized copper with a low residual phosphorus content that exhibits high electrical and thermal conductivity.In addition to excellent hot and cold formability, this copper grade also exhibits good corrosion resistance, particularly against atmospheric conditions (including industrial atmospheres) and water. It exhibits good weldability and brazing properties, as well as hydrogen resistance. The unalloyed copper materials described form a particularly fine microstructure after cold forming and subsequent hot crimping, enabling the particularly high cyclic load capacity to be achieved.

[0012] In a further possible embodiment of the invention, it is provided that a winding wire of an active part of an electrical machine, in particular a rotor, is fastened to the connection element as the wire. Alternatively, the active part can be a stator of the electrical machine. In particular, the winding wire is part of a coil component of the electrical machine. In particular, the connection element can be held on a switching ring of the rotor. The method thus enables the winding wire to be connected to the switching ring of the rotor in a particularly secure and electrically conductive manner. The wire is therefore the electrical conductor of the rotor, which is wound into a coil. The method thus enables a particularly durable connection of the winding wire to the connection element and, via the connection element, to the switching ring of the rotor. This makes it possible to achieve a particularly long service life for the rotor.

[0013] In this context, it can be provided in particular that the winding wire is work hardened by forming using a winding needle when it is wound onto a laminated core of the active part. This means that the work hardening of the wire occurs while the winding wire is being wound onto the laminated core. The work hardening is thus introduced into the wire by means of the winding needle, in that the wire is cold-formed by means of the winding needle as it is wound onto the laminated core. By adjusting a winding technique or adjusting the orientation of the winding needle, the degree of cold forming and consequently the work hardening of the wire can be precisely adjusted. Alternatively, work hardening can be introduced by deflecting the wire in front of the winding needle, for example by guiding the wire over deflection rollers with "small" radii and a corresponding arrangement.By work hardening the wire during winding onto the laminated core, the active part can be manufactured particularly quickly, as the work hardening and winding of the winding wire onto the laminated core take place simultaneously.

[0014] In this context, it can be provided, in particular, that a deflection angle of the winding wire during winding onto the laminated core by means of the winding needle is selected depending on the desired strain hardening of the winding wire. The more the winding wire is deflected during winding by means of the winding needle, the greater the set strain hardening of the winding wire. In this case, the deflection angle of the winding wire is selected, in particular, such that excessive cold forming of the winding wire, which could lead to local destruction or tearing of the winding wire, is avoided. This means that the deflection angle is selected such that the winding wire is cold formed sufficiently to achieve the specified strain hardening, but not so far that the winding wire is damaged.To adjust the deflection angle, the angle of attack and / or the movement path of the winding needle can be adjusted to achieve the forming of the winding wire at the specified deflection angle. This ensures that the wire is sufficiently cold-formed to achieve the specified work hardening, while keeping the risk of damage to the wire to a minimum.

[0015] In an alternative possible embodiment of the invention, the winding wire is first cold-formed, then wound onto the laminated core of the coil component, and then hot-crimped to the connecting element. In other words, the winding wire is cold-formed before being wound onto the laminated core. This already cold-hardened winding wire is then wound onto the laminated core. By carrying out the winding of the winding wire onto the laminated core and the cold-hardening of the winding wire separately, the cold-hardening and the winding of the winding wire onto the laminated core can be optimized. This means that the winding wire can be cold-hardened independently of the respective deflection limits that exist during the winding of the winding wire onto the laminated core.Furthermore, during the winding process of the winding wire onto the laminated core, it is possible to optimize the winding of the winding wire onto the laminated core. The required deflection angles for work hardening the winding wire are not taken into account, as the wire is already work hardened when wound onto the laminated core. The winding wire can thus be cold-formed in an optimized manner and then wound onto the laminated core in an optimized manner.

[0016] In a further possible embodiment of the invention, it is provided that the wire is heated during hot crimping, at least in some regions, to a temperature of 450 to 900 degrees Celsius and / or for a duration of 100 to 1,200 milliseconds. The temperature and heating duration during hot crimping are selected depending on the desired recrystallization of the wire structure. By heating the wire during hot crimping, at least in some regions, to a temperature of 450 to 900 degrees Celsius and / or for a duration of 100 to 1,200 milliseconds, a particularly fine wire structure can be achieved after hot crimping, and consequently, a particularly high cyclic load capacity of the wire, in particular of the wire connection to the connecting element, can be achieved.

[0017] In a further possible embodiment of the invention, it is provided that for pre-fixing the wire is first cold-crimped to the connecting element and then the wire is hot-crimped to the connecting element at the same point. By cold-crimping the wire to the connecting element, the wire can be positioned relative to the connecting element and held particularly securely in this position. The wire can then be securely and permanently connected to the connecting element in this position relative to the connecting element by hot-crimping, in particular with a material bond. Pre-fixing by cold crimping enables particularly precise positioning and alignment of the wire to the connecting element. Cold crimping means that the wire is crimped to the connecting element without heating either the wire or the connecting element.By deforming the wire during cold crimping, local work hardening can be introduced into the wire to be crimped.

[0018] In a further possible embodiment of the invention, the wire is cold-crimped at the same location as the connecting element after hot crimping. This further increases the strength of the crimped connection. Thus, a particularly stable connection between the wire and the connecting element is achieved.

[0019] The invention further relates to a connection arrangement of a wire to a connection element, in which the wire, which has been cold-formed for work hardening, is fastened to the connection element via a hot-crimp connection. As a result, the wire has a particularly fine microstructure caused by recrystallization during hot-crimping. In particular, the connection arrangement is part of an active part, in particular a coil component, of an electrical machine. The electrical machine can in particular be a traction motor of an electrically driven motor vehicle. In particular, the active part is a rotor of the electrical machine. In this case, the wire can be a winding wire of the rotor, which is wound as a coil winding onto a laminated core of the rotor.The connecting element can be attached to a switching ring of the rotor, whereby the coil winding is electrically connected to the switching ring via the connecting arrangement.

[0020] Further features of the invention may emerge from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features shown below in the description of the figures and / or in the figures alone, can be used not only in the respective combinations specified, but also in other combinations or on their own, without departing from the scope of the invention.

[0021] The drawing shows: Fig. 1 is a process diagram for a method for attaching a wire to a connecting element; and Fig. 2 a schematic perspective view of a rotor of an electrical machine with a connection arrangement of the wire to the connection element.

[0022] In the figures, identical and functionally identical elements are provided with the same reference numerals.

[0023] In Fig. 1 shows a process diagram for a method for attaching a wire 10 to a terminal element 12. As a result of attaching the wire 10 to the terminal element 12, a connection arrangement 14 of the wire 10 to the terminal element 12 is produced. In Fig. 2 shows an example where this connection arrangement 14 can be used. In Fig. Figure 2 shows a schematic perspective view of a rotor 16 of an electrical machine, in this case a traction machine of a motor vehicle. This rotor 16 comprises a laminated core 18 onto which the wire 10 is wound, thereby providing a rotor coil 20 of the rotor 16. The wire 10 is thus a winding wire of the rotor 16. In this case, the wire 10 is an unalloyed or low-alloyed copper wire, in particular made of CuETP, CuOF, or CuDHP.

[0024] In Fig. In Figure 2, the rotor 16 is also shown in an enlarged detail. It can be seen that the connecting element 12 is attached to a switching ring 22 of the rotor 16. The wire 10 is thus electrically connected to the switching ring 22 via the connecting element 12 via the connecting arrangement 14.

[0025] In the present case, the connecting element 12 is fork-shaped, wherein the wire 10 for connecting to the connecting element 12 is inserted between the two prongs of the fork-shaped connecting element 12.

[0026] In connection with Fig.1, the method for attaching the wire 10 to the connecting element 12 is explained below. The respective framed boxes show the state Z of the wire 10 at different times in the process. The first box shows the wire 10 in its first state Z1 - its original state. Starting from this first state Z1, the wire 10 is work hardened by cold forming in a first process step V1. Here, the wire 10 can either first be work hardened by cold forming and then wound onto the laminated core 18 of the rotor 16, or it can be work hardened by cold forming at the same time as it is wound onto the laminated core 18. The necessary work hardening is introduced primarily via the geometry of a winding needle, which deposits the wire 10 onto the laminated core 18. This means that the wire 10 is work hardened by forming using the winding needle when it is wound onto the laminated core 18.In this case, a deflection angle of the wire 10 when winding onto the laminated core 18 by means of the winding needle is selected depending on the work hardening of the wire 10 to be achieved.

[0027] Alternatively, the already work-hardened wire 10 is used for the winding process. This means that the winding wire is first work-hardened by cold forming, then wound onto the laminated core 18 of the rotor 16, and later hot-crimped to the connecting element 12. The work-hardened wire 10 is inserted into the connecting element 12, which is designed as a fork, whereby the second state Z2 shown in the second box is achieved. As can be seen particularly clearly in the second box, the connecting element 12 in this case has a U-shaped cross-section, with the wire 10 being inserted into the recess of the connecting element 12 via the open side of the U-shaped cross-section. The wire 10 can come to rest on the bottom of the recess of the U-shaped cross-section of the connecting element 12 or can simply be held by the tines of the fork.Alternatively, the connecting element 12 can have a V-shaped cross-section, wherein the wire 10 is inserted into the recess of the connecting element 12 via the open side of the V-shaped cross-section. In a second method step V2, the wire 10 is then cold-crimped to the connecting element 12. A mechanical force F is applied to the connecting element 12 and the wire 10. This results in the cold-crimped third state Z3 of the wire 10 with the connecting element 12, shown in the third box. Following cold crimping, the wire 10 and the connecting element 12 are hot-crimped in a third method step V3. This involves a mechanical force F being applied to the connecting element 12 and the wire 10, and heat 24 being introduced at least into the wire 10.In this case, hot crimping takes place in a temperature range of 450 to 900 degrees Celsius, with the wire 10 and, if applicable, the connecting element 12 being hot crimped for a period of 100 to 3000 milliseconds, in particular a period of 100 to 1200 milliseconds. This means that the set temperature for hot crimping 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 box shows the hot-crimped fourth state Z4 of the wire 10. This means that for pre-fixing, the wire 10 is first cold-crimped to the connecting element 12 and then the wire 10 is hot-crimped to the connecting element 12 at the same point.

[0028] To achieve further work hardening after recrystallization of the wire and thus to further increase strength, the hot-crimped connection can then be cold-crimped.

[0029] If a wire coated with insulating varnish is used as wire 10, the varnish is burned away due to the temperature influence during hot crimping. Following cold crimping, the wire 10 is then firmly joined to the connecting element 12 via the hot crimping process. The associated heat treatment results in the recrystallization of the microstructure in the wire 10, creating a fine microstructure and thus a fine-grained microstructure. This is advantageous with regard to the fatigue strength of the connecting arrangement 14. A cold-hardened wire 10 with a hardness of 90 HV0.1 results in a particularly fine-grained microstructure after the energy input during hot crimping, which causes the microstructure of the wire 10 to recrystallize. This microstructure exhibits particularly good cyclic load-bearing capacity. After hot crimping, the hardness of this wire 10 is 55 to 60 HV0.1.

[0030] The described method makes it possible to achieve a particularly high fatigue strength of the hot crimp connection of the wire 10 with the connecting element 12.

[0031] Overall, the invention shows how a durable, current-carrying copper connection can be created. List of reference symbols 10 wire 12 connecting element 14 Connection arrangement 16 Rotor 18 sheet package 20 rotor winding 22 Switching ring 24 Heat Z1 to Z4 states of the wire F force application V1 to V3 process steps QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2007 021 321 A1

[0002] DE 10 2017 205 078 A1

[0003]

Claims

[1] Method for fastening a wire (10) to a connecting element (12), in which the wire (10) is cold-formed (V1) to introduce work hardening and is then hot-crimped (V3) with the connecting element (12). [2] Method according to claim 1, characterized by that an unalloyed or low-alloyed copper wire is attached to the connecting element (12) as the wire (10). [3] Method according to claim 2, characterized by that the wire (10) consists of CuETP or CuOF or CuOFE or CuDHP or CuHCP. [4] Method according to one of the preceding claims, characterized by that a winding wire of an active part of an electrical machine, in particular a rotor (16), is fastened to the connection element (12) as the wire (10). [5] Method according to claim 4, characterized by that the winding wire is cold-hardened by forming using a winding needle when winding onto a laminated core (18) of the active part. [6] Method according to claim 5, characterized by that a deflection angle of the winding wire when winding onto the laminated core (18) by means of the winding needle is selected depending on the work hardening of the winding wire to be achieved. [7] Method according to claim 4, characterized by that the winding wire is first cold-hardened by cold forming, then wound onto a laminated core (18) of the coil component and then hot-crimped to the connecting element (12). [8] Method according to one of the preceding claims, characterized by that the wire (10) is heated at least in some areas to a temperature of 450-900 °C and / or for a duration of 100 - 3000 milliseconds during hot crimping. [9] Method according to one of the preceding claims, characterized bythat for pre-fixing the wire (10) is first cold-crimped (V2) with the connecting element (12) and then the wire (10) is hot-crimped (V3) with the connecting element (12) at the same point. [10] Method according to one of the preceding claims, characterized by that the wire (10) is cold-crimped at the same point with the connecting element (12) after hot-crimping. [11] Connection arrangement (14) of a wire (10) to a connecting element (12), in which the wire (10) cold-formed for work hardening is fastened to the connecting element (12) via a hot crimp connection, whereby the wire (10) has a particularly fine structure caused by recrystallization during hot crimping.

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