GB2129716A

GB2129716A - Electrical connectors

Info

Publication number: GB2129716A
Application number: GB08231682A
Authority: GB
Inventors: James Milner
Original assignee: H & T Components Ltd
Current assignee: H & T Components Ltd
Priority date: 1982-11-05
Filing date: 1982-11-05
Publication date: 1984-05-23
Also published as: GB2129716B

Abstract

A fork-like electrical contact element for an insulation displacement connector is made from a blank, by a coin pressing operation to locally reduce the thickness of the blank in a region (11) between the fork arm portions (12). Material is displaced outwardly from region (11) to stress the fork arm portions (12) in the plastic state. The blank is then severed by a punch having converging side walls shaped such that when the punch is removed the fork arms (12) so formed, relax to define the required conductor- receiving slot (14) with a favourable residual stress (SR) remaining in the root portions of the fork arms. The residual stress (SR) improves the creep resistance and resistance to thermally induced stress relaxation of the contact element. <IMAGE>

Description

SPECIFICATION Electrical connectors This invention relates to electrical connectors and more particularly to insulation displacement connectors and contact elements therefor.

Insulation displacement connectors, particularly for multi-conductor ribbon cable, are known which utilize separate fork-like insulation piercing contact elements for receiving and firmly gripping respective conductors of the cable when they are pressed into engagement therewith. Such contact elements have been made of various metallic materials, in particular of a beryllium-copper alloy or a phosphor-bronze alloy Such contact elements need to have a resistance to creep and to thermally induced stress relaxation in order to maintain a firm grip on conductors engaged therein during a period of use thereof. It has been felt by certain users that contact elements made of the beryllium-copper alloy have the better properties in these respects.The invention is concerned with providing a way of improving these properties of fork-like insulation piercing contact elements, particularly those to be made of phosphor-bronze.

In accordance with the invention, a fork-like electrical contact element is formed such that during its manufacture the fork arm portions are flexed outwardly in the plastic state and then allowed to relax so as to define the required conductor-receiving slot therebetween with a favourable residual stress remaining in the region of the root portions of the fork arms.

In this way the stress induced in the fork arms during use, which is greatly reduced compared to similar fork-like contact elements that are initially unstressed, is small compared to the material yield stress thereby improving creep resistance and resistance to stress relaxations as a result of thermal shocks.

According to the invention, there is provided a method of making a fork-like electrical contact element for insulation displacement connectors, which method comprises locally reducing the thickness of a blank from which the contact element is to be formed, so as to flex outwardly portions of the blank which are to form the fork arms to cause stressing thereof in the plastic state, and then severing the blank between the fork arm portions thereof with a tool which is shaped to allow the fork arms so formed to relax to positions defining the required conductor-receiving slot therebetween with a residual stress remaining in the fork arms at least in the region of the root portions thereof.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figures 1 to 4 illustrate diagrammatically the steps of a press forming operation in accordance with the invention to produce a fork-like electrical contact element from the blank shown in Figure 1; Figures 5 and 6 are respectively a detail of part of a fork-like contact and a conductor engaged therein, and the conductor alone; and Figure 7 is a graph showing the relationship between stress remaining in a typical phosphor-bronze contact element against time in use at room temperature and at 1050 C.

Referring to Figures 1 to 4, a fork-like contact element is made from a blank (10), which has an end portion, as shown in Figure 1, from which the fork arms of the contact element are formed. The first step is to form a depression (11) in the blank (10) by a coining operation, as illustrated in Figure 2. This operation locally reduces the thickness of the blank. The material thereat is displaced outwardly to such an extent that the fork-arm portions (12) are flexed outwardly and stressed in the plastic state.

As illustrated in Figure 3, the next step is to sever a region of the blank extending centrally of the depression with a punch (13), the side surfaces of which are shaped to converge towards the tip thereof in order to form a corresponding slot in the blank between the fork arms (12). When the punch (13) is removed the fork arms (12), which have been stressed in the plastic state by the coining operation (Figure 2), relax to define the required substantially parallel-sided conductor receiving slot (14) with a residual stress (SR) remaining in the fork arms (12) as a result of the plastic deformation thereof. This residual stress (SR) iS of the order of one half of the yield stress (Sy) of the material.On subsequent bending of the fork arms in the outward direction, this residual stress must initially be overcome in addition to the normal elastic stress region of the material of the fork arms before the plastic region is reached so that the resistance to creep and to thermally induced stress relaxations during use is increased.

Referring to Figures 5 and 6, the dimensions of a fork arm (20) of a typical contact element (21) and of a conductor (22) engaged therewith, are shown. The following calculations give the compressive and tensile forces acting at the root portion of the fork arm: Initial stress in conductor = 20,000 Ibf/in2 Contact area = 0.0097" x 0.009" x1.751bf.

Contact force (F) = stress x area Compressive and tensile forces induced in beam by this force are given by Induced stress

S = 65,500 Iblin2 The following three examples indicate the practical effects of such stress in a conventional phosphorbronze contact, a conventional beryllium-copper contact and a phosphor-bronze contact fabricated in accordance with the invention: 1. Conventional phosphor-bronze contact Material - PB102 Yield stress - 75,5001bf/in2 The induced stress of 65,500 Ibf/in2 is large compared with the material yield stress, therefore creep and thermally induced stress relaxations are inevitable.

2. Conventional beryllium-copper contact Material - Be Cu 25 Yield Stress - 160,000 ib$in2 The induced stress of 65,500 Iblin2 is small (less than half) compared to the material yield stress, therefore creep and thermally induced stress relaxations are insignificant.

3. Phosphor-bronze contact embodying the invention with favourable residual stresses Material - PB102 Yield stress - 75,5001bf/in2 Residual stresses (SR), which are equal to half the material yield stress (Sy) exist in this contact. The stress (S) induced in this design is therefore not 65,5000 lb/in2, but S = 65,500- 1/2. 75,500 S = 27,7501bf/in2 This stress is small (approximately one third) compared with the material yield stress, therefore creep and thermally induced stress relaxations are insignificant.

Figure 7 illustrates the progressive decline in the stress remaining in the fork arms of a conventional phosphor-bronze contact element over a time period at room temperature and at 105" C. It will be appreciated that the performance thereof is greatly improved by the residual stress provided in the fork arms of a contact element in accordance with the invention since a 50% greater deflection of the fork arms is then possible before overstressing occurs.

Claims

1. A method of making a fork-like contact element for an insulation displacement connector, wherein fork arms portions of a blank, from which the contact element is to be made, are caused to be flexed outwardly and stressed in the plastic state, and then allowed to relax so as to define the required conductor-receiving slot therebetween with a residual stress remaining at least in the root portions of the fork arms.

2. A method of making a fork-like contact element for an insulation displacement connector, which method comprises locally reducing the thickness of a blank from which the contact element is to be formed, so as to flex outwardly portions of the blank which are to form the fork arms to cause stressing thereof in the plastic state, and severing the blank between the fork arm portions with a tool which is shaped so as to allow the fork arms so formed to relax to positions defining the required conductor-receiving slot therebetween with a residual stress remaining in the fork arms at least in the region of the root portions thereof.

3. A method as claimed in Claim 2, wherein the blank is locally reduced in thickness as aforesaid by a coining operation.

4. A method as claimed in Claim 2 or Claim 3, wherein the blank is severed by a punch which has side walls which converge so as to form a slot between said fork arm portions which slot initially converges in the direction towards the bottom of the slot, prior to relaxation of the fork arms as aforesaid.

5. A method as claimed in any preceding Claim, wherein the blank has a fork arm end portion, the side edges of which converge towards the tip thereof, and the tip is formed with a V-shaped recess having a pair of oppositely inclined edges to form insulation-piercing surfaces of the fork arms of the contact element.

6. A method as claimed in any preceding Claim wherein the contact element is made of a phosphor-bronze alloy.

7. A method of making a fork-like electrical contact element for an insulation displacement connector, which method is substantially as herein before described with reference to Figures 1 to 4 of the accompanying drawings.

8. A fork-like electrical contact element when made by a method as claimed in any preceding Claim.

9. An insulation displacement connector having at least one fork-like electrical contact element as claimed in Claim 8.