EP1817819B1 - Method for production of an electrical connection between an aluminium conductor and a contact element - Google Patents

Abstract

A method for producing a reliable and permanent electrical connection between an aluminum conductor and a contact element includes melting a supply of a contact-making material and forming a cohesive material connection between the aluminum conductor and the contact element by subsequent solidification in order to form the electrical connection. In order to ensure that the functions of electrical contact-making and strain relief do not interact with one another in a disadvantageous manner, the contact element is shaped to form the mechanical strain relief, after the formation of the electrical contact.

Description

The invention relates to a method for producing an electrical connection between an aluminum conductor and a contact element, in which a stripped end of the aluminum conductor is inserted into the contact element and electrically contacted with this and in which to form a mechanical strain relief of the aluminum conductor by forming the contact element in this is clamped.

From the DE 199 02 405 A1 as well as the DE 33 16 563 A1 and the GB 1 329 634 Such a procedure can be found in each case. It is provided that an existing of several tinned stranded aluminum conductors is first mechanically clamped in a crimp barrel. After the mechanical clamping, which takes place by forming the crimp sleeve, the crimp barrel is soldered or welded to the tinned aluminum conductor.

Significant weight-saving efforts are being made, especially in the automotive sector. One means of doing so is to use aluminum conductors instead of the otherwise commonly provided copper conductors. As far as aluminum or copper conductors are concerned, it is understood here that the conductors consist to a large extent of aluminum / copper or an aluminum / copper alloy. Due to the significantly lower specific weight of aluminum, a weight saving can be achieved.

Since aluminum in conjunction with atmospheric oxygen forms an oxide layer that covers the aluminum conductor and that has only low conductivity, the contacting of an aluminum conductor is problematic. When contacting the aluminum conductor with a contact element must be ensured for the lowest possible contact resistance, that in the region of the contact surface between the aluminum conductor and the contact element, the oxide layer is at least largely removed.

The invention has for its object to provide an easy to manufacture and safe and long-term stable contact between an aluminum conductor and a contact element with low contact resistance.

The object is achieved according to the invention by the method according to claim 1. Thereafter, a stripped end of the aluminum conductor is inserted into the contact element and contacted with this electrically. To form the electrical contacting, a supply of a contacting agent is provided, wherein the contacting agent is heated at least to the region of its melting temperature, so that it is preferably present in molten form. With the subsequent cooling and curing of the contacting agent, in particular tin or a tin alloy, a material connection between the aluminum conductor and the contact element is produced. To form the electrical contact, therefore, the aluminum conductor is immersed in particular in a recorded in the contact element melt of the contacting agent. The heating of the contacting takes place here for example by irradiation of a high-frequency field, by irradiation of high-energy light (laser light) or directly by a flame or by another heating element.

Furthermore, the contact element is mechanically deformed during or after the formation of the electrical contact, so that the aluminum conductor is clamped in the contact element to form a mechanical strain relief.

By providing the supply of liquefied contacting agent and "dipping" the commonly tinned stranded wires of the aluminum conductor, good electrical contact is made between the aluminum conductor and the contact element with low contact resistance. The contact element is usually also tinned on its inner surface. By choosing the amount of contacting agent is thereby advantageously set the penetration depth of the contacting between the individual stranded wires and thus the contact surface to the stranded wires.

Another decisive advantage can be seen in the simultaneous or subsequent deformation of the contact element. For one thing, due to the heated contacting agent and the contact element is heated, so that a process-safe forming without material damage and in particular can be done without cracking. Also, a particular advantage is the fact that the contacting on the formation of the material compound, which requires the heating of the contacting agent, does not take place after the forming. Because the heat required for liquefaction of the contacting agent in this case would possibly lead to relaxations in the material structure of the reshaped region in the already formed contact element, so that the mechanical clamping force is weakened. As a result, in particular the long-term stability of the strain relief would be endangered. In the method described here, therefore, the functions of the formation of the mechanical strain relief on the one hand and the formation of the electrical contact on the other hand are separated from each other and do not adversely affect.

According to an expedient development, the contact element is formed in a forming zone, which is spaced from a contacting zone in which the electrical contacting takes place. This measure again serves to separate the mechanical from the electrical function. In particular, this has the advantage that the formed prior to forming contact, in particular via tin or a tin alloy, is not affected by the exercise of the pressure necessary for the forming. The contacting zone is not exposed to pressure, so that there is no risk of subsequent flow of the contacting agent, which could worsen the electrical contact.

Preferably, the contact element is additionally heated in the forming zone in order to allow material-saving forming with improved flow behavior without cracking compared to cold forming. Conveniently, the contacting agent is heated to a maximum of about 280 ° C. By this measure, damage to an insulation of the aluminum conductor is avoided.

In addition, the insulation can be protected by special terminals or other protective mechanisms. At a temperature of 280 °, smelting is assured with the use of tin or a tin alloy because the melting temperature of tin is about 232 ° C and the melting temperature of a tin alloy with 10% zinc is 198 ° C.

As an alternative to the use of a tin alloy, a solder paste which is in molten form at 280.degree. C. can in principle also be used as the contacting agent. However, there is a requirement that the solder paste halogen-free, non-corrosive flux to avoid subsequent corrosion of the solder joint.

According to an expedient development, at least a portion of the stripped end piece of the aluminum conductor is tinned in particular prior to the formation of the electrical contact. According to a first advantageous embodiment, the portion to be tinned is shock-heated for this purpose and then immersed in a tin bath. Preferably, the section is heated to about 400 ° C or more. The advantage here is that the section is shock-heated in a time <1 second. This rapid heating can be done inductively by irradiation of a high-frequency field or by the use of a high-energy laser light. The shock heating leads to a different elongation behavior of the aluminum and the oxide layer. As a result, at least microcracks form in the oxide layer, into which tin then penetrates during the subsequent immersion in the bath and infiltrates the oxide layer, so that it flakes off and the pure aluminum is largely coated over the whole area with the contacting agent. In order to prevent the formation of a renewed oxide layer after the shock heating and until immersion in the bath, a protective gas atmosphere is preferably provided.

According to a preferred second embodiment, the tinning of the section is carried out by ultrasonic tinning in a tin bath. This is understood to mean that the section is immersed in a tin bath and that suitable ultrasonic waves, which in particular have an amplitude of> 10 μm, are coupled in. For this are suitably trained ultrasonic generator used. This type of tinning takes advantage of the fact that the irradiation of ultrasound in the tin bath creates small cavities, so-called cavitations, which collapse explosively. This results in locally significant pressure forces, which lead to damage and spalling of the oxide layer, so that the pure aluminum is in turn largely wetted over the entire surface of the tin.

According to a third preferred embodiment for tinning, the aluminum conductor is immersed in a tin bath and a part of the aluminum conductor is separated or cut in the tin bath. Decisive here is that the separation in the tin bath, a "fresh" separation or cutting surface is formed, which is wetted directly and without contact with atmospheric oxygen with tin. This measure ensures that the cut surface is tinned over the entire surface. In the case of a separating direction perpendicular to the longitudinal propagation of the individual stranded wires, the separating surface corresponds to the cross-section, so that no reduction in the cross-sectional area takes place in the contacting region with regard to the electrical contact surface. Conveniently, it can be provided in this case that the individual strands are cut obliquely to their longitudinal orientation, so that the sectional area is greater than the cross-sectional area.

With regard to the forming of the contact element is provided in a preferred development that the forming process takes place within a very short forming time, which is in the μs range in particular in the range to about 10 microseconds. The decisive advantage of such a rapid forming process is the fact that the individual stranded wires of the aluminum conductor behave less like solid stranded wires than rather like a liquid, so that the individual stranded wires are caked or melted together. This effect is similar to a projectile piercing a metal plate at high speed. In the reference system of the projectile, the metal plate does not appear as a solid. Rather, the projectile penetrates the metal plate like a liquid.

With the sudden forming of the contact element is the particularly advantageous possibility, simultaneously with the formation of the mechanical Strain relief and bring about the electrical contact. In this case, advantageously even dispensed with the use of the contacting means as well as on the tinning of the aluminum conductor. Decisive for this in turn is the high speed of the forming process and the associated very high pressures, which cause the oxide layer bursts and both a positive connection and a direct electrical contact connection between the contact element and the aluminum conductor takes place. This sudden reshaping can be used in place of a slow, conventional one in combination with the contacting agent. Independently of this, however, this abrupt reshaping can also be used as an independent possibility for configuring the connection between the contact element and the aluminum conductor with the simultaneous formation of a mechanical and electrical connection.

To form a good electrical contact connection is expediently provided that the inner surface of the contact element is roughened or structured. As a result of this roughening or structuring, when the aluminum conductor is deformed and clamped, its oxidation layer is additionally injured and penetrated so that a contacting takes place in the deformation area between the contact element and the aluminum conductor. The inner surface of the contact element is in this case provided, for example, with grooves or with threads which are preferably sharp-edged. When forming, therefore, these grooves or threads virtually intersect in the individual stranded wires. By cutting an additional mechanical strain relief is formed at the same time. This contacting can be done in addition to the contact via the contacting or as an independent contact. In particular, in the independent design without the use of the contacting can be realized by the sudden reshaping and the simultaneous formation of electrical and mechanical connection easily an automated process, so an automated striking the contact element on the aluminum conductor with very high clock rates.

For the abrupt reshaping, it is provided according to a preferred first embodiment that the shaping takes place by magnetocompression rapid magnetic forming. In magnetocompression are to be reshaped Contact element generates very high magnetic fields, so that high currents are induced in the contact element, which in turn form a magnetic field, so that due to the Lorentine force the contact element is repelled and thereby reshaped. The contact element is preformed for this purpose, for example, in the manner of a sleeve or slotted sleeve, in which the aluminum conductor is inserted. The externally applied magnetic field in this case leads to a radially inwardly directed forming of the sleeve, so that the inserted aluminum conductor is clamped. By magnetocompression pressures can be achieved in the range of, for example, 2000 bar in the choice of suitable magnetic fields. Since no mechanical forming elements are necessary in this case, the contact element is not damaged despite these high pressures.

In an advantageous second embodiment, the abrupt reshaping takes place by means of a forming element by mechanical impact pressing. Conveniently, this applies to the forming element at a speed> 5m / sec, in particular> 10m / sec, on the contact element. Conventional hydraulic presses do not reach these speeds and are therefore not suitable for abrupt reshaping. The speeds for the forming element are in this case preferably generated solely by the weight, that is, for example, formed as a mandrel or claw forming element applies in the manner of a Fallbeils on the reshaped contact element.

Preferably, furthermore, the connection between the aluminum conductor and the contact element is isolated from moisture. In this case, in particular, a shrink tube is mounted or the compound is coated with an insulating varnish or insulation adhesive.

Fig. 1

eine Verbindung zwischen einem Kontaktelement und einem Aluminiumleiter,

Fig. 2

eine ausschnittsweise Darstellung des Kontaktelements mit dem Aluminiumleiter zur Illustration der Magnetokompression,

Fig. 3

eine ausschnittsweise Darstellung des Kontaktelements und des Aluminiumleiters zur Illustration des Umformens mittels Schlagpressens und

Fig. 4 bis 6

beispielhafte Flussdiagramme für unterschiedliche Verfahrensabläufe.

Embodiments of the invention will be explained in more detail below with reference to FIGS. In each case, in schematic and greatly simplified representations:

Fig. 1

a connection between a contact element and an aluminum conductor,

Fig. 2

a partial representation of the contact element with the aluminum conductor to illustrate the magnetocompression,

Fig. 3

a partial view of the contact element and the aluminum conductor to illustrate the forming by means of impact pressing and

4 to 6

exemplary flowcharts for different procedures.

In the figures, like-acting parts are provided with the same reference numerals.

In Fig. 1 is an already finished connection between a particular existing copper and designed as a cable lug contact element and an aluminum conductor 4 is shown. The contact element 2 is in this case designed in the manner of a sleeve and has a receiving space into which a stripped end piece 6 of the aluminum conductor 4 is inserted. In the tail 6 individual strand wires of the aluminum conductor 4 are exposed. The stranded wires are tinned at least at their frontal portion. Between the front end of the stranded wires and the rear wall or the bottom of the contact element 2, a supply or reservoir of a contacting means 8 is provided. In particular, this tin or a tin alloy is provided. The electrical contact between the aluminum conductor 4 and the contact element 2 takes place via the tin alloy. The inner surface of the contact element 2 is preferably also pre-tinned.

To form the contact, the tin alloy is introduced into the contact element 2 and melted. Subsequently, or even before the melting of the aluminum conductor 4 is inserted with the stripped end piece 6 in the contact element 2. In particular, the front ends of the stranded wires are immersed in the molten tin alloy 8. After cooling, therefore, there is a cohesive material connection between the contact element 2 and the individual stranded wires of the aluminum conductor 4. It is in the region of the contacting means 8 and the front ends of the stranded wires a contacting zone 10 is formed.

Spaced apart from the contacting zone 10, a forming zone 12 is provided, within which a deformation of the contact element 2 takes place. The Fig. 1 already shows the deformed state in which a reshaped portion 14 of Contact element 2 has penetrated into the stripped end piece 6. By this measure, the aluminum conductor 4 is clamped in the contact element 2, whereby an effective mechanical strain relief is formed. After the formation of the electrical and the mechanical connection between the contact element 2 and the aluminum conductor 4, the connecting region in the exemplary embodiment is still surrounded by a shrink tube 16 as insulation against moisture.

For the forming process, it is provided that the contact element 2 is heated at least in the forming zone 12. For this purpose, a heating element 18 is provided, which is constructed in two parts in the embodiment and at the same time also serves to heat the contacting agent 8 into the region of its melting temperature. The heating element 18 is divided in the exemplary embodiment into two functional zones, which are designed for the different requirements, namely the heating of the supply 8 and the heating of the contact element 2. Alternatively, only one heating element 18 may be provided for heating the contacting means 8. In this case, there is inevitably also a heating of the contact element 2. In the embodiment of the Fig. 1 Furthermore, an ultrasonic generator 20 is provided. This serves to form the electrical function by the tinning of unleaded stranded wires by means of the ultrasound irradiation when the stranded wires are immersed in the molten pool. The Kotaktelement is hereby suitably mechanically fixed to an ultrasound sono-red or acoustically coupled by a transmission medium for the transmission of the required ultrasound energies.

By taking place in particular in chronological order electrical contacting and reshaping of the contact element 2 and further by the spatial separation of the contacting zone 10 of the forming zone 12, the functions of electrical contacting on the one hand and the provision of mechanical strain relief on the other hand effectively separated from each other. As a result, these two functions do not affect adversely. Because by the occurring after the heating of the contacting means 8 forming the risk is excluded that the deformed region of the contact element 2 is relaxed and weakened by a heat input. Due to the spatial separation of Forming zone is further ensured that the cooled tin does not flow through the pressure occurring during the forming process, which can lead to an undesirable weakening of the electrical contact and an increase in the contact resistance.

The forming process can be carried out in a conventional manner by mechanical or hydraulic pressing of forming elements against the contact element 2. As an alternative to this conventional forming according to the embodiment Fig. 2 a shaping provided by means of magnetocompression. Namely, a very strong magnetic field is thereby generated by magnetic coils 22 in the immediate outer region of the contact element 2, so that currents are induced in the conductive contact element 2 and the Lorenz force is formed. This works in the direction of in the Fig. 2 Arrows shown on the contact element 2 and thereby causes the forming of the contact element 2 forth.

Alternatively, according to the embodiment according to Fig. 3 for forming a so-called mechanical impact molding provided. In this a forming element 24 is struck at very high speed against the contact element. In the embodiment, the forming element 24 is formed like a mandrel. On the opposite side of the contact element 2, a counter element 26 is arranged, which can in particular also give shape for the forming process. The high speed of the forming element 24 in the direction of in the Fig. 3 shown arrow direction is preferably achieved solely by acceleration due to gravity. Alternatively, it is possible to accelerate the forming element 24 by compressed air using a hammer blower or pyrotechnic.

In the in the FIGS. 2 and 3 shown forming processes is a very fast forming with a duration in the μs range. Due to the sudden deformation of the special effect is achieved that the individual stranded wires connect materially together.

The sudden forming processes according to FIGS. 2 and 3 Therefore, in addition to the mechanical connection, it is also possible to carry out electrical contacting additionally or alternatively to the electrical contacting via the contacting means 8. For this purpose, the inner surface of the contacting element 2 is roughened or structured at least in the forming zone 12. In the exemplary embodiment, a thread 28 is cut into the sleeve-like contact element 2. The FIGS. 2 and 3 show the situation before the forming process. After forming, the threads of the thread 28, which are in particular sharp-edged, cut into the stranded wires and in particular penetrate the oxide layer.

• I: Verzinnen der Litzendrähte des Aluminiumleiters 4,
• II: Elektrisches Kontaktieren zwischen dem Aluminiumleiter 4 und dem Kontaktelement 2,
• III: Ausbildung der mechanischen Verbindung / der Zugentlastung.

On the basis of in the 4 to 6 Flowcharts shown below are explained below different process variants for the formation of both electrical and mechanical connection between the contact element 2 and the aluminum conductor 4. The individual process steps are characterized as follows:

• I: tinning the stranded wires of the aluminum conductor 4,
• II: electrical contact between the aluminum conductor 4 and the contact element 2,
• III: Formation of the mechanical connection / strain relief.

• A: herkömmliches Verzinnen oder Verwenden eines Aluminiumleiters mit vorverzinnten Litzendrähten,
• B: Verzinnen durch Schockerwärmung und Eintauchen in ein Zinnbad,
• C: Verzinnen durch Ultraschallbehandlung in einem Zinnbad und
• D: Trennen oder Schneiden der Litzendrähte in einem Zinnbad.

The method step "I: tinning the aluminum conductor 4" can alternatively be carried out by one of the following partial methods:

• A: conventional tinning or using an aluminum conductor with pre-tinned stranded wires,
• B: tinning by shock heating and immersion in a tin bath,
• C: Tinning by sonication in a tin bath and
• D: cutting or cutting the stranded wires in a tin bath.

• i: herkömmliches Umformen,
• ii: Umformung durch Magnetokompression
• iii: Umformung durch Schlagpressen.

The process step "III: Forming the strain relief" is carried out by one of the following sub-processes:

• i: conventional forming,
• ii: transformation by magnetocompression
• iii: Forming by impact pressing.

According to the procedure according to Fig. 4 First, the aluminum conductor 4 in the stripped portion 6 by one of the partial process A, B, C or D pre-tinned.

In particular, the partial processes B, C and D are characterized by a very good tinning result, so that these partial process can be used independently of the electrical contact of the aluminum conductor 4 with the contact element 2 as an independent tinning process. Subsequent to tinning the electrical contact takes place, as they are Fig. 1 has been described. The individual stranded wires are in this case immersed in a molten reservoir of the tin or the tin alloy, so that via the tin after solidification a cohesive connection between the individual stranded wires and the contact element 2 is formed. Subsequently, in the process step III, the forming, in particular according to one of the Fig. 2 or 3 described method (ii, iii).

In a modification to the procedure according to Fig. 4 If necessary, the process steps II and III can also take place simultaneously, that is to say that the transformation does not necessarily have to take place after the melt has cooled down. All that matters is that the melting does not take place after the forming process.

According to the procedure according to Fig. 5 If the method steps I and II are combined with one another in a common operation, they take place simultaneously. Namely, it is provided that the tinning of the stranded wires by means of ultrasonic tinning after the sub-process C takes place, as this Fig. 1 has been described.

The procedure according to Fig. 6 Overall, it is characterized by a one-step process, in which process step I, namely the tinning of the stranded wires can be dispensed with. The electrical contact (II) and the mechanical connection (III) take place within a single process step in accordance with sub-procedures ii or iii. This on the basis of Fig. 6 illustrated one-step process for the production of electrical and mechanical connection is particularly suitable for high-speed automation.

LIST OF REFERENCE NUMBERS

2

contact element

4

aluminum ladder

6

tail

8th

contacting

10

contacting zone

12

forming zone

14

reshaped section

16

shrinkable tubing

18

heating element

20

ultrasonic generator

22

solenoids

24

deforming

26

counter-element

28

thread

Claims (19)

1. Method for production of an electrical connection between an aluminum conductor (4) and a contact element (2), in which a stripped end piece (6) of the aluminum conductor (4) is inserted into the contact element (2) and makes electrical contact with it, and in which, in order to form mechanical strain relief, the aluminum conductor (4) is clamped in the contact element (2) by shaping said contact element (2),
   wherein a supply of a contact-making means (8) is provided, and the contact-making means (8) is heated at least up to the region of its melting temperature, so that a cohesive connection is produced between the stripped end piece (6) and the contact element (2) via the contact-making means (8) in order to form the electrical contact, characterized in that the contact element (2) is shaped at the same time or subsequently.
2. Method according to Claim 1,
   characterized
   in that the contact element (2) is shaped in a shaping zone (12) which is at a distance from a contact-making zone (12) in which the electrical contact is made.
3. Method according to Claim 2,
   characterized
   in that the contact element (2) is heated in the shaping zone (12).
4. Method according to one of the preceding claims,
   characterized
   in that the contact-making means (8) is heated to a maximum of about 280°C.
5. Method according to one of the preceding claims,
   characterized
   in that tin or a tin alloy is used as the contact-making means (8).
6. Method according to one of the preceding claims,
   characterized
   in that at least one subarea of the stripped end piece (6) of the aluminum conductor (4) is tinned.
7. Method according to Claim 6,
   characterized
   in that the subarea to be tinned is shock-heated and is then immersed in a tin bath.
8. Method according to Claim 7,
   characterized
   in that the subarea is heated to about 400°C or more.
9. Method according to Claim 7 or 8,
   characterized
   in that the subarea is shock-heated in a time of less than 1 s.
10. Method according to one of Claims 7 to 9,
    characterized
    in that the shock heating and the subsequent immersion are carried out in an inert gas atmosphere.
11. Method according to Claim 6,
    characterized
    in that the tinning of the subarea is carried out by ultrasound tinning in a tin bath.
12. Method according to Claim 11,
    characterized
    in that the ultrasound tinning and the making of the contact between the aluminum conductor (4) and the contact element (2) are carried out in one process.
13. Method according to Claim 6,
    characterized
    in that a part of the aluminum conductor which is immersed in a tin bath is cut off for tinning.
14. Method according to one of the preceding claims,
    characterized
    in that the shaping of the contact element (2) is carried out within a shaping time in the µs range.
15. Method according to Claim 14,
    characterized
    in that the inner surface of the contact element (2) is roughened or structured.
16. Method according to Claim 14 or 15,
    characterized
    in that the shaping is carried out by magneto compression.
17. Method according to Claim 14 or 15,
    characterized
    in that the shaping is carried out with the aid of a shaping element (24) by mechanical impact molding.
18. Method according to Claim 17,
    characterized
    in that the shaping element (24) strikes the contact element (2) at a speed of more than 5 m/s, in particular of more than 10 m/s.
19. Method according to one of the preceding claims,
    characterized
    in that the connection between the aluminum conductor (4) and the contact element (2) is insulated against moisture.

Images