GB2147832A - Twisted wire pin contact and method of fabricating - Google Patents

Abstract

A twisted wire pin contact is disclosed which has a straight centre core. The contact is fabricated by fusing one end 34 of a bundle of wires 36 comprising a centre core 14 surrounded by a plurality of helically wound wires 12. The opposite end of the bundle 36 is mounted in a contact sleeve 49 containing a tool (46, Figures 4-7, not shown) having a centre recess surrounded by an annular supporting surface. The bundle 36 is axially impacted causing the wires to bow outwardly while the centre core extends into the recess in the tool without the core deforming. The sleeve is then crimped around the inner ends of the wires and core to fix them together and to maintain the wires in a bowed condition. <IMAGE>

Description

SPECIFICATION Twisted wire pin contact and method of fabricating The present invention relates generally to a male or pin contact for an electrical connector and, more particularly, to such a contact formed of twisted wires and a method of manufacturing the same.

United States Patent No.3,277,560 to Franke et al discloses a method of manufacturing a twisted wire pin contact in which there is first produced an elongated strand or cable comprising a centre core around which there is helically wound a plurality of wires. The outer wires and centre core are fastened together at spaced points along the strand by welding. The strand is then untwisted to bow the wires outwardly from the centre core. Then the elongated strand is severed in the regions of the welds to produce a plurality of pin elements each comprising a centre core surrounded by wires which are bowed outwardly from the core, with the ends of the outer wires fused to the ends of the core. It will be appreciated that before the strand is untwisted to bow the outer wires outwardly, the centre core has the same length as the wires.

Thus, when the strand is untwisted causing the outer wires to bow outwardly, the pin element will shorten with the result that the centre core will deform, resulting in the core becoming bent or kinked.

United States Patent No.3,402,466 to Phillips discloses a different method for manufacturing a twisted wire pin contact similar to that disclosed in the Frank et al patent, which method is presently in use in the connector industry. In the Phillips method, the elongated strand or cable is initially cut into short lengths to form individual bundles each comprising a centre core surrounded by a plurality of helically wound wires. Then both ends of the bundle are welded to secure the outer wires to the ends of the core, and to form rounded noses on the ends of the bundle. Then one end of the thus formed pin element is mounted into a contact sleeve. The sleeve is crimped around the end of the pin element. Thereafter, an axial compressive load is applied to the opposite end of the pin element which results in the wires bowing outwardly from the centre core.Preferably this bowing operation takes place with the pin element mounted within a die to control the shape and location of the bowed wires. Coincident with the wires bowing outwardly, the centre core is over stressed because of the axial compression causing a kink to be formed in the now shorter length of the centre core. The kinked centre core is desirable in order to prevent the bowed outer wires from elongating and relaxing the bulged diameter of the pin element.

Due to the deforming or kinking of the centre core utilising the methods disclosed in the Frank et al and Phillips patents discussed above, the twisted wire pin element is forced off the axial centre line of the contact which makes alignment of the pin contact with a mating socket contact more critical.

Also, due to the overstressed centre core, the columnar strength of the contact is reduced making the contact more susceptible to excessive bending or crushing if it is engaged too hard by a probe or engages a mating socket contact off centre. The present invention seeks to overcome or at least improve some of the aforementioned shortcomings of the prior art.

According to the invention there is provided a method of fabricating a pin contact, comprising the steps of providing a wire bundle comprising a centre core surrounded by a plurality of wires, fixedly connecting one end of the wires to the corresponding end of the core, bowing the wires outwardly from the core by causing the other ends of the wires to shift toward said one end relative to the core, and firmly securing said other ends of the wires relative to the core in a contact sleeve to maintain the wires in a bowed condition.

A wire pin contact in accordance with the invention may be fabricated, rather than by welding both ends of the wire bundle cut from a wire strand as in the prior methods, by fixedly connecting only one end of the bundle, the unfixed end being then mounted within a hollow contact sleeve. This is possible by means of a tool inserted through the opposite end of the contact sleeve.

The tool has a centre recess surrounded by an annular supporting surface. The centre recess is aligned with the centre core of the bundle while the supporting surface engages the inner ends of the outer wires of the bundle. An axial compressive force is then applied to the welded end of the bundle, causing the exposed portions of the outer wires to bow outwardly while the centre core simply slides into the recess in the tool. By this technique, the centre core remains undeformed, and thus straight, rather than kinked as in the prior art method. Thereafter, the contact sleeve is crimped around the inner ends of the wires and the core to secure the elements together, and the tool is withdrawn from the opposite end of the contact sleeve.

Thus, by this a wire pin contact is formed which has a straight centre core that will provide greater columnar strength to the contact, making it more durable. Also the contact is more consistently straight for correct alignment with a mating socket contact.

Figure 1 illustrates a segment of a twisted wire strand which may be severed to form a bundle; Figure 2 illustrates a wire bundle connected in a welding circuit; Figure 3 illustrates a twisted wire pin element having one end welded to form a rounded nose; Figure 4 is a partial sectional view showing a contact sleeve mounted in a metal block containing a tool extending upwardly into the sleeve with crimp dies located around the upper portion of the sleeve; Figure 5 is a partial sectional view similar to Figure 4 showing the pin element of Figure 3 mounted in the upper portion of the contact sleeve, with the crimp dies moved inwardly to partially crimp the sleeve to the inner end of the pin element; Figure 6 is a partial sectional view similar to Figure 5 showing a pair of dies mounted around the exposed portion of the pin element providing a forming cavity around the pin element;; Figure 7 is a partial sectional view similar to Figure 6 showing an impact member for applying an axial compressive force to the outer end of the pin element causing the outer wires to bow outwardly in the forming cavity, while the centre core protrudes downwardly into a centre bore formed in the tool in the contact sleeve; Figure 8 is a partial longitudinal sectional view through the finished pin contact constructed in accordance with the present invention, wherein the pin element contains a single wire core; and Figure 9 is a partial longitudinal sectional view through a modified form of contact constructed in accordance with the present invention wherein the core consists of a plurality of twisted wires.

Referring now to the drawings in detail, Figure 1 illustrates a multiple wire strand 10 which may be wound on a reel, not shown. The strand comprises a plurality of outer wires 12 which are helically wound around a centre core 14. There may be, for example, five outer wires wound around a single wire which forms the core. Alternatively, the core could be formed of a plurality of twisted wires, for example, three twisted wires. When utilising the multiple wire twisted core, seven outer wires, for example, may be wound around the core in the direction opposite to the twist of the wires forming the core. The strand 10 may be fed from its supply reel to the first station of an automatic machine where a short length 16 of the strand is measured and then severed by a pair of blades 18.

The short length of strand or bundle 16 may then be connected to ground or one side of a welding circuit 20, as indicated at 22, at a welding station as shown in Figure 2. At this second station an electric arc 24 is applied by an electrode 26 to one end of the bundle 16. Any suitable welding circuit may be connected to the electrode to perform this function For example, the circuit may include a normally open switch 28 which may be closed to charge a capacitor 30 and a second normally open switch 32 which may be closed to discharge the capacitor for the purpose of creating the arc 24.

The result of the application of the arc to the end of the bundle 16 is to fuse the ends of the outer wires 12 to the corresponding end of the core 14 to form a rounded nose 34 on the end of the bundle, thus providing a unitary pin element 36, as seen in Figure 3. The rounded nose forms the forward mating end of the pin contact which is produced by the method of the present invention. In contrast to the methods disclosed in the aforementioned Frank et al and Phillip patents, both ends of the bundle 16 are not welded in practicing the present invention.

The next station utilised in the fabricating method of the present invention, as depicted in Figure 4, comprises a metal block 38 having a vertical bore 40 therein that opens at the upper surface 42 of the block. A smaller diameter bore 44 coaxial with the bore 40 opens to the bottom of the block. A cylindrical tool 46 extends upwardly through the bore 44 into the larger diameter bore 40. At this station a cylindrical contact sleeve 48 is positioned in the annular space defined between the outer surface of the tool 46 and the wall of the bore 40. The upper portion 49 of the sleeve extends upwardly beyond the upper surface 42 of the metal block 38. Crimp jaws 50 resting on top of the block 38 surround the upper exposed portion of the contact sleeve 48. Preferably four such jaws are used, although only two are visible in Figure 4.A centre bore 52 opens at the upper end of the tool 46 providing an annular supporting surface 54 around the bore. The centre bore 52 is dimensioned to slidably receive therein the core 14 of the pin element 36.

Referring now to Figure 5, at another station the unwelded end of the pin element 36 is inserted into the upper end of the contact sleeve of 48. The annular supporting surface 54 on the upper end of the tool 46 is dimensioned to engage and thus rigidly support the ends of the outer wires 12 of the pin element 36. The centre bore 52 in the tool 46 is aligned with the core 14 of the pin element. At this time, the crimp jaws 50 are moved inwardly to lightly compress or partially crimp the upper portion 49 of the contact sleeve 48 around the outer wires 12 of the pin element to hold the sleeve and pin element coaxially, but not so tightly as to significantly restrict free movement of the core 14 relative to the wires.

As seen in Figure 6, at a further station a split forming die 58 is mounted around the exposed portion of the pin element above the crimp jaws 50. The die embodies a forming cavity 60 which is open at both ends.

As seen in Figure 7, preferably the outer wires of the pin element 36 are bowed outwardly by exerting an axial compressive force against the rounded nose 34 of the pin element. The form of the bulge of the pin element is determined by the shape of the forming cavity 60. The axial compressive force may be an impact force applied, for example, by electromagnetically driving an impact member 62 by energising a coil 64. As the outer wires 12 of the pin element are compressed and bulged outwardly, the inner core 14 slides back, or downwardly as viewed in Figure 7, into the centre bore 52 in the tool 46. While the impact member 62 is applying the compressive force to the end of the pin element, the crimp jaws 50 are shifted further inwardly to their closed position completing the crimp of the upper portion 49 of the contact sleeve around the outer wires and core of the pin element, thereby firmly securing the elements together and retaining the core in its rearward position providing axial restraint to the bulged portion of the pin element. Since the centre core is not deformed, but slides back relative to the outer wires 12 of the pin element, the core retains its columnar strength and straightness while preventing elongation of the bulged pin element. The forming dies and crimp jaws may then be opened, allowing the resulting contact to be ejected from the block 38.

The finished contact, generally designated 66, may have a configuration as shown in Figure 8 wherein the pin element portion 36 thereof is depicted as having a single wire core 14. In Figure 9, the pin element 66' is illustrated as having a twisted multiple wire core 14'. Alternatively, the core could have a slight helical configuration (not shown) to reduce tension and radial compression forces on the bundle when the contact is inserted into a mating socket contact. In each case, the core protrudes behind, or below as viewed in the Figures, the outer wires 12, and is substantially straight, rather than bent or kinked as are the centre cores in the prior art twisted pin contacts.

By virtue of the straight centre core, the twisted wire pin element portion of the contact is more consistently straight to assure correct alignment with a mating socket contact, and is less susceptible to crushing if the pin contact engages the mating socket contact off centre, or is engaged too hard by a test probe or the like.

Claims (14)

1. A method of fabricating a pin contact, comprising the steps of providing a wire bundle comprising a centre core surrounded by a plurality of wires, fixedly connecting one end of the wires to the corresponding end of the core, bowing the wires outwardly from the core by causing the other ends of the wires to shift toward said one end relative to the core, and firmly securing said other ends of the wires relative to the core in a contact sleeve to maintain the wires in a bowed condition.

2. A method as claimed in claim 1, wherein the wires are bowed outwardly from the core by applying an axial compressive force against the bundle end.

3. A method as claimed in claim 1 or 2, wherein the wires are fixedly connected to said one end of the core by fusing.

4. A method as claimed in any one of the preceding claims, wherein,prior to bowing the wires outwardly, the free ends of the wires are positioned against a support positioned inside the sleeve, the support having a recess therein aligned with the core, and the core is allowed to move into the recess when the wires are bowed outwardly.

5. A method as claimed in claim 4, including the steps of providing a tool having a recess therein surrounded by a supporting surface, inserting the tool into one end of a hollow contact sleeve, placing the end of the pin element opposite to the mating end into the other end of the sleeve so that the core is aligned with the recess and the wires engage the supporting surface, urging the pin element and tool toward each other to bow the wires outwardly from the core while allowing the free end of the core to shift into the recess; and firmly securing the wires and core within the sleeve.

6. A method as claimed in claim 5, wherein the tool has a surface which engages the inner ends of the wires but not the core.

7. A method as claimed in any one of the preceding claims, including the steps of winding a plurality of wires around a centre core to make a multiple wire strand, severing a short length from the strand to provide the wire bundle.

8. A method as claimed in any one of the preceding claims, wherein said other ends of the wires are secured in the contact sleeve by crimping the sleeve around the wires and core to maintain the wires in a bowed condition.

9. A method as claimed in any one of the preceding claims, wherein the wire bundle comprises a centre core surrounded by a plurality of wires helically wound around the core.

10. A method as claimed in any one of the preceding claims, including the additional steps of prior to the bowing step compressing the sleeve, without significantly restricting axial movement of the core, to hold the pin element coaxially in the sleeve, and during the bowing step allowing the inner end of the core to slide relative to the wires into the sleeve.

11. A method of fabricating a pin contact as claimed in claim 10, wherein the compressing step is effected by partially crimping the sleeve around the pin element.

12. A method of fabricating a pin contact substantially as described herein with reference to the drawings.

13. An electrical contact, comprising a pin element comprising a flexible centre core surrounded by a plurality of wires helically wound around the core, one end of the pin element being solid, the other end of the pin element being fixedly mounted in a hollow contact sleeve, the inner end of the core inside the sleeve extending beyond the inner ends of the wires, and the core being substantially straight and the wires outside of the sleeve being bowed outwardly from the core.

14. An electrical contact substantially as described herein with reference to the drawings.