EP0552741A2

EP0552741A2 - Electrical contact as well as material and method for producing the same

Info

Publication number: EP0552741A2
Application number: EP93100807A
Authority: EP
Inventors: Friedrich Josef Alois Kourimsky
Original assignee: Whitaker LLC
Current assignee: Whitaker LLC
Priority date: 1992-01-22
Filing date: 1993-01-20
Publication date: 1993-07-28
Also published as: EP0552741A3; DE4201670A1; KR930017238A; JPH05347165A; BR9300243A

Abstract

In an electrical contact (11) made by stamping and bending from one single metal strip and comprising at least one spring portion (13), for instance a contact spring portion, and at least one deformation portion (15) which is plastically deformed or to be deformed, for instance a crimping portion, the spring portion (13) has a higher temper than said deformation portion (15).

Description

The invention relates to an electrical contact comprising at least one spring portion and at least one deformation portion, as well as material and method for producing the same.
Electrical contacts mostly have one or several portions that should have as good as possible spring properties, in particular contact spring portions and locking spring portions, as well as portions that should display as good as possible plastic deformation properties for permanently maintaining a deformation, in particular crimping portions, bending portions and folding portions. An example in this respect are crimping contacts having contact spring portions and locking spring portions as well as crimping portions.
Such electrical contacts are produced mainly from strip material by stamping, bending and deep drawing in multistage operation tools. The strip material used therefor is homogeneous, i.e. it has the same material properties everywhere. Conventional strip material for producing such contacts constitutes a compromise between good spring properties for the spring portion and good deformation properties in the deformation portion. Such a compromise means that the desired spring properties for the spring portion and the plastic deformability in the deformation portion are not achieved in the desired extent. This means, in the contacting portion comprising the contact springs one must put up with lesser spring properties than desired, and in the deformation portion comprising the crimping portion one is confronted with a plastic deformability that is poorer than desired.
On the basis of these facts, it was recognized already a longer time ago that an additional spring component is required in the contacting portion for high-quality contacts having a long lifetime. This additional spring component is obtained by means of a back-up spring of stainless steel disposed on the contact body. This back-up spring has a contact-force supporting effect and, furthermore, is provided with locking springs for locking the contact in a contact receiving housing.
Such contacts with back-up spring necessitate a high manufacturing and assembling expenditure with correspondingly high production and assembly costs.
It is the object of the invention to make available an electrical contact which, without using a back-up spring, has both good spring properties in the spring portion and good deformability in the deformation portion. In addition thereto, a material and a method suitable therefor are to be made available as well. This object is met by an electrical contact having a harder or higher temper in the spring portion than in the deformation portion. According to the invention, such a contact is produced from a single metal strip having at least two zones of different tempers extending parallel to each other in the longitudinal direction of the strip. For producing such strip material, one starts with a metal strip having the same temper across its entire length and width, this temper being the higher temper desired for the spring portion. That zone or zones from which the deformation portions with the softer or lower temper are to be formed during the subsequent production of the electrical contacts is/are thermally stress-relieved by selective heating of the metal strip. This can be effected by selective inductive high-frequency heating, gas flame heating, heating by contact with a heated object, or the like. In order to obtain as sharp as possible transitions between zones of higher temper and zones of lower temper, heating of the zones that are to receive a lower temper can be carried out simultaneously with cooling of those zones in which the higher temper is to be maintained and which thus are not to be subjected to thermal stress-relief.
A specific temper of a metal strip is usually and preferably obtained by cold rolling to a specific extent. A specific temper in metal strips is correlated with a specific tensile strength value and a specific hardness value. For instance, the hardness can be indicated in the form of Vickers hardness. Temper classes for strips and sheets of copper and copper alloys are indicated e.g. in DIN (German Industrial Standard) 17670, Part 1, December 1983. For tin bronze designated CuSn4, which is frequently used for electrical contacts, the temper classes and the related Vickers hardness are indicated on page 8 of said DIN standard.
Corresponding standards are contained in ASTM B103 (ASTM = American Society for Testing and Materials) and in ISO 427 (ISO = International Organization for Standardization) as well as in ISO 6507 and ISO 6892.
For CuSn4 as strip and contact material, the values preferred for the measures according to the invention are in the range from 80 to 90 Vickers hardness for the deformation portion with the lower temper and in the range from 180 to 190 Vickers hardness for the spring portion with the higher temper. According to the afore-mentioned DIN standard, this corresponds, when CuSn4 is used, to material classes F54 and F59 for the spring portion with the higher temper and to material classes F33 and F38 for the deformation portion with the lower temper.
The measures according to the invention result in electrical contacts having both improved spring properties and improved crimpability. The improved spring properties mean that in many cases which so far required a back-up spring such a back-up spring can be dispensed with. Improved crimpability means on the one hand that the crimp connection between the electrical contact and the electrical conductor to be connected thereto can be more intimate and stable than with conventional electrical contacts. Improved crimpability means on the other hand that the crimping tools used for the crimping operation are subject to less wear due to the enhanced softness of the material present in the crimping portion. The crimping tools may thus be used longer, thereby reducing the costs for attaching the contacts to electrical lines.
The measures according to the invention also yield electrical contacts which are sufficiently hard in the spring portion for affording a desirably high spring force for instance for contact springs, and which at the same time are sufficiently soft in the deformation portion for rendering possible softer resilience of the crimping edges of the contact and, thus, an improved electrical and mechanical crimping connection.
For metal strip according to the invention for producing the electrical contacts according to the invention, materials can be used that are commonly employed for electrical contacts, namely brass, phosphor bronze and in general all highly conductive copper alloys, i.e. low-alloy copper alloys having a high copper content, e.g. tin bronze such as CuSn4.
The zones of the metal strip according to the invention with a higher temper will be formed into such portions of electrical contacts in which good spring properties are important, such as contact springs, locking springs and the like. Of the zones of the metal strip having a lower temper, those portions of electrical contacts will be formed in which good permanent deformability is important, such as crimping portions, transition portions from the contact to the crimping portion, and folding portions.
The invention shall now be elucidated in more detail by way of embodiments shown in the drawings, wherein

Fig. 1: shows a developed view of an embodiment of an electrical flat spring contact;
Fig. 2: shows a developed view of an embodiment of a socket-like round contact;
Fig. 3: shows a plan view of a flat tab contact;
Fig. 4: shows a cross-sectional view along sectional line 4-4 in Fig. 3; and
Fig. 5: shows a portion of the flat tab contact depicted in Fig. 3.

Fig. 1 shows a developed view of a flat spring contact 11 designed to cooperate with a flat tab contact, e.g. of the type shown in Fig. 3. The flat spring contact 11 comprises a spring portion 13, a crimping portion 15 and a carrier strip 17. The crimping portion 13 includes a base portion 19 from which two locking springs 21 are cut out, and two flat contact springs 23 each projecting from said base portion 19.
The crimping portion 15 comprises a conductor crimping zone 25 and an insulation crimping zone 27.
In the flat spring contact 11 formed of the developed material shown in Fig. 1, the base portion 19 is formed in a box-shaped base by bending, substantially at right angles, along bend lines 29, with a dovetail projection 33 and a dovetail groove 33 retaining the base portion 19 in this box shape. In the base bent into the box shape, the two flat contact springs 23 are located opposite one another and are bent such that they extend from the base obliquely towards each other, contact each other in contact lines 35 and diverge from the contact lines 35 so as to form an insertion funnel for a flat tab contact.
In the finished flat spring contact 11, the locking springs 21 project outwardly from the box-shaped base so that they can lockingly cooperate with locking shoulders in the contact receiving cavity of a connector housing, not shown.
The conductor crimping zone 25 and the insulation crimping zone 27, in the finished flat spring contact 11, are bent in the manner of a V with rounded tip such that they can be crimped in known manner to a stripped conductor and to insulation surrounding the conductor, respectively.
The carrier strip 17 serves to hold together a large number of lined up flat spring contacts 11 in the form of a contact strip. This facilitates the manufacturing steps for the individual flat spring contacts 11 and the insertion thereof in the contact receiving cavities of connector housings. After having performed this function, the carrier strips 17 are separated from the flat spring contacts 11.
According to the invention, the spring portion 13 and the carrier strip 17 have a higher temper than crimping portion 15. The effect achieved thereby is that the spring portion 13 and the carrier strip 17 have sufficient hardness for displaying good spring properties, whereas the crimping portion 15 has a lower temper, so that it is sufficiently soft for enabling good permanent deformation.
For electrical contacts consisting of the tin bronze CuSn4, preferred Vickers hardnesses are in the range from 180 to 190 for the spring portion and in the range from 80 to 90 for the deformation portion.
For producing the developed configuration of a flat spring contact 11, a metal strip of the material usual for electrical contacts, for example tin bronze, is used which at the beginning evenly has across its entire length and width the higher temper desired for the spring portion 13 and the carrier strip 17. This metal strip is then selectively thermally stress-relieved by heating in a longitudinal zone corresponding to the crimping portion 15 so as to assume the lower temper desired for the crimping portion 15. To this end, one employs for instance (non-contacting) inductive heating, heating by gas flames or heating by passing the metal strip in contacting manner across a heated object having the width of the crimping portion 15. For obtaining as sharp as possible transitions between the zone of lower temper and the zones of higher temper, the zones of the metal strip corresponding to the spring portion 13 and the carrier strip 17 may be cooled, for instance by means of cooling water or cooling air whose effect is restricted to the zones of the metal strip corresponding to the crimping portion 15 and the carrier strip 17.
Fig. 2 shows the developed view of a round contact 37 designed to receive a pin contact of a complementary connector. Parts identical to those of the developed configuration in Fig. 1 are designated with the same reference numerals. Im comparison with the flat spring contact developed configuration of Fig. 1, the round contact developed configuration of Fig. 2 displays differences in the spring portion 13 only. This portion is rolled together to form a round socket, with round-contact springs 39, which are formed by cutting them free from the spring portion 13, being bent towards each other in convex manner.
The round contact developed configuration according to Fig. 2 can be made from the same metal strip as the flat contact spring developed configuration according to Fig. 1.
Fig. 3 shows a flat tab contact 41 after stamping and deformation bending from a metal strip, having four zones of different tempers located parallel beside each other in the longitudinal direction. An outer zone with lower temper has been formed into a flat tab 43 by stamping and folding. An adjacent zone with higher temper has been stamped and formed into locking spring portion 45 comprising a locking spring 21 cut free and stuck out from the locking portion 45. A crimping portion 15 adjacent the locking portion 45 has been stamped and formed from a metal strip zone having the lower temper. The other outer zone of the metal strip, which has the higher temper, constitutes the carrier strip 17.
Fig. 4 illustrates the manner in which the flat tab of the flat tab contact 41 has been formed. To this end, a flat tab strip 43 has been stamped out from the metal strip material that is about twice as broad as the finished flat tab 43. The two edge portions of the flat tab strip have been folded over until they contact the central portion of the flat tab strip, as shown in Fig. 4. In this manner, a flat tab 43 of double material thickness of the metal strip used for making the flat tab contact 41 has been achieved. During folding of the edge portions of the flat tab strip, considerable tensile stresses are exerted at the folding locations on the material constituting the flat tab 43. When this material has a relatively high temper and thus relatively high resilience, relatively high forces must be applied for the folding operation on the one hand, with corresponding stress on the folding tool, and on the other hand material cracks occur in the fold lines, as indicated e.g. in Fig. 5. Problems of this kind have been overcome in a flat tab contact 41 according to the invention. Due to the fact that the flat tab 43 is formed of a zone of lower temper, the material participating in the formation of the flat tab 43 can be made sufficiently soft so that it may be folded over without any problems and without the formation of cracks at the fold lines.
Due to the fact that the crimping portion 15 consists of equally soft material, the conductor crimping zone 25 can be brought into very intimate and lasting contact with the conductor wires of the line to be terminated.
In contrast thereto, it is advantageous for the carrier strip 17 to consist of material with good spring properties. For, on the one hand contact strips held together by the carrier strip 17 are passed through various working stations for the individual contact portions and, on the other hand, such contact strips, when finished, are wound on contact strip reels from which they can be unwound for further processing steps, such as for instance for insertion into the contact cavities of connector housings. If the carrier strip 17 consisted of relatively soft material, permanent deformations of the carrier strip 17 would occur while the contact strip is being passed through working stations and, after unwinding of the contact strip from the reel, there would be a curve or bend left in the carrier strip, which would aggravate subsequent working steps on the contact strip and the individual contacts.
By producing electrical contacts according to the invention from metal strip having several zones of different tempers, different functions and requirements of different sections of an electrical contact can be taken into account in optimum manner.
The applicability of the invention is not restricted to the three contact types according to Figs. 1 to 3. It may also be applied to other contact types in which several portions are present posing different requirements to the spring behavior and the deformability, respectively. An example in this respect are pin contacts having a locking spring and a crimping portion, in which the pin portion, which is insertable into a complementary contact, is produced by rolling flat material into a circular shape. With such a pin contact, the pin portion and the crimping portion will be made of soft strip material zones with lower temper, and the locking spring portion and the carrier strip will be formed of hard strip material zones with higher temper.

Claims

An electrical contact (11; 37; 41) made by stamping and bending from one single metal strip and comprising at least one spring portion (13; 45), in particular a contact spring portion (13) and/or locking spring portion (45), and at least one deformable portion which is plastically deformable, in particular a folding or bending portion (43), or which is to be plastically deformed, in particular a crimping portion (15), characterized in that said spring portion (13; 45) has a higher temper than said deformation portion (15; 43).
An electrical socket-type contact according to claim 1, comprising a socket-like contact spring portion (13) and a crimping portion (15), characterized in that said contact spring portion (13) has a higher temper than said crimping portion (15).
An electrical socket-type contact according to claim 2, comprising a locking spring portion (45), characterized in that said locking spring portion (45) has the higher temper.
An electrical plug-type contact according to claim 1, comprising a flat tab portion (43) formed by folding or a pin contact portion formed by rolling, a locking spring portion (45) and a crimping portion (15), characterized in that said locking spring portion (45) has a higher temper than said flat tab portion (43) or, respectively, said pin contact portion and said crimping portion (15).
A contact assembly comprising a multiplicity of electrical contacts according to any one of claims 1 to 4, which are lined up in the form of a strip by means of a carrier strip (17) connected thereto, characterized in that said carrier strip (17) has the higher temper.
An electrical contact or an electrical contact assembly according to any one of claims 1 to 5, characterized in that said electrical contact or contact assembly consists of a copper-tin alloy designated CuSn4 and in that the spring portion (13; 45) having the harder temper has a Vickers hardness in the range from 180 to 190, and the deformation portion having the softer temper has a Vickers hardness in the range from 80 to 90.
A metal strip for producing electrical contacts or contact assemblies according to any one of claims 1 to 6, characterized in that the metal strip has at least two zones of different tempers extending parallel to each other in the longitudinal direction of the strip.
A metal strip according to claim 7, characterized in that the metal strip has two zones of different tempers extending parallel to each other in the longitudinal direction of the strip.
A metal strip according to claim 7 or 8, characterized in that the metal strip has three zones of different tempers, with the two outer zones having a higher temper than the central zone.
A metal strip according to claim 7 or 8, characterized in that the metal strip has four zones of different tempers, with a first and third zone as seen in transverse direction of the metal strip having a lower temper than a second and a fourth zone.
A metal strip according to any one of claims 7 to 10, characterized in that the metal strip consists of a copper-tin alloy designated CuSn4, and in that the zones of higher temper have a Vickers hardness in the range from 180 to 190 and the zones of lower temper have a Vickers hardness in the range from 80 to 90.
A method of making a metal strip according to any one of claims 7 to 11, characterized in that a metal strip is made having across its entire width and length a uniform temper as desired for the spring portion of an electrical contact, and in that the metal strip is then thermally stress-relieved by selective zone heating in that zone or zones, respectively, which are to have a lower temper as desired for the deformation portion of an electrical contact.
A method of making a metal strip according to claim 12, characterized in that a metal strip is made from CuSn4 having across its entire length and width a uniform temper with a Vickers hardness in the range from 180 to 190, and in that the metal strip is then thermally stress-relieved to a Vickers hardness in the range from 80 to 90 by selective zone heating in that zone or zones, respectively, which is or are to obtain a lower temper.
A method according to claim 12 or 13, characterized in that said thermal stress-relief is effected by selective zone heating of the metal strip by inductive high-frequency heating, gas flame heating or heating by contact with a heated object.
A method according to any one of claims 12 to 14, characterized in that said selective zone heating is carried out simultaneously with selective zone cooling of the zones of the metal strip which are not to be heated.
An electrical contact (11; 37; 41) made by stamping and bending from one single metal strip and comprising at least two sections (13; 45), characterized in that at least one of said sections (13; 45) has a higher temper than said other section (15; 43).