CONNECTION OF PLUG PIN TO WIRE CONDUCTOR

Abstract: A wire conductor is connected to a plug pin by laying the conductor (5) in a groove (4) formed in the pin (1), heating the material at the sides of the groove with an electric current and displacing the softened material to embed the con­ ductor.

Description: Connection of plug pin to wire conductor This invention relates generally to the manufacture of electric plugs, especially plugs intended for use with sockets of mains supply circuits, and in particular the invention concerns a method of attaching a wire conductor to a plug pin. It is known in the manufacture of electrical plugs to attach the conductor wires of a cable permanently to respective plug pins and then to mould a plug body over the pin ends to encapsulate the pin-to-wire connections. Plugs made in this way can be of advantage since when supplied with an appliance there is no danger of the applicable cable being wired to a plug incorrectly. Various methods of attaching the conductor wires to the pins have been proposed. According to one proposal a pin made by slicing from an extrusion is provided with a groove into which the conductor wire is placed and a side of the groove is then deformed by a percussive tool to clamp the conductor wire. For economy it is an advantage if a pin can be made by cutting from an extrusion without requiring any subsequent machining operations to enable a conductor wire to be attached to it. The previously proposed method has a drawback however since the act of cold deforming the pin to grip the conductor can disturb the surfaces of the pin which serve to locate the pin during the moulding of the body. According to the present invention there is provided a method of connecting a wire conductor to a plug pin having a groove in a surface thereof, comprising the steps of laying the conductor in the groove, and deforming the material of the pin to fix the conductor to the pin, characterised in that over at least a portion of the groove the material of the pin at the side of the groove is softened by heating with an electric current, and the softened material is displaced to embed the conductor in the material of the pin. With this method a good low resistance connection is possible without any risk of disturbing the pin location surfaces. In one preferred method the groove extends laterally across a surface at the upper end of the pin, which is suitable for pins of rectangular or square cross-section. In an alternative method the groove extends longitudinally the full length of the pin. The invention also resides in an electric plug having at least one pin with a conductor attached thereto by the method. A better understanding of the invention will be had from the following detailed description given with reference to the accompanying drawing, in which: Figure 1 is a front view of a plug pin ready for attachment to a conductor wire; Figure 2 is a top plan view of the completed connection; Figure 3 is a section taken along the line III-III in Figure 2; Figure 4 is a side view of another plug pin ready for connection to a conductor wire; Figure 5 is an end view of the pin shown in Figure 4; Figure 6 is a top view of the pin after attachment of the wire; and Figure 7 is a view similar to Figure 5 showing an alternative shape for the pin. The pin 1 of Figures 1-3 is made by cutting from an extruded rod, the profile of the extrusion being as seen in Figure 1. The pin has lateral chamfers at its forward end and an enlarged head 2 of generally rectangular configuration at the other end. Extending across the top surface of the head 2 is a shallow recess with parallel side walls and a flat bottom wall 3. A U-shaped groove 4 extends along the bottom wall 3 and is of sufficient depth to receive the stranded wire conductor 5 of a cable lead 6. To connect the lead to the pin, the conductor, stripped of insulation, is laid into the groove 4. An electrode 7 having a diameter greater than the width of groove 4 but less than the width of the recess, is lowered into contact with the bottom wall 3 either side of groove 4 at a central portion A of the pin head. The electrode is connected to a resistance welding machine. The material at the sides of the groove 4 in region A is heated by the electric current flowing between the pin and electrode and is deformed under heat to embed and effectively stake the conductor 5 to the pin 1. A secure and low resistance joint is obtained without any risk of disturbing the location surfaces of the pin. In a subsequent body moulding step the top surface 8 of the pin head may be acted upon by protruberances on a cover to hold the pin in position, which means that the pin dimensions including the head height X must be maintained to close tolerances. By providing the recess into which the electrode 7 fits it is ensured that the disruption to the top of the pin is confined within this recess so that the upper surface 8 remains undisturbed and undamaged. In Figures 4 to 6 there is illustrated a plug pin 10 of substantially circular cross-section formed by cutting a length from an extruded rod. Extending along the pin over its full length are a recess 11 and a groove 12, the latter being located at the centre of the flat bottom wall of the recess. Both the recess 11 and the groove 12 are produced during extrusion of the rod from which the pin is cut so the profile of the extruded rod is as seen in Figure 5. The connection of a conductor 13 to the pin is essentially as described above in connection with Figures 1-3. An end portion of the wire, stripped of insulation, is laid into the groove 12 at one end of the pin, which end will be the upper end in the finished plug. An electrode of diameter greater than the width of the groove 12 but less than the width of the recess 11 is moved into contact with the bottom wall of the recess above the conductor wire. The material of the pin heated by the electric current flowing between the pin and electrode is displaced locally under heat in the region A where the electrode is applied, and the wire becomes embedded in the material of the pin and effectively staked to it. The deformation to the pin is confined within the recess 11 and the outer surfaces of the pin are not disturbed. Although Figures 4 to 6 refer to pins of circular cross-section the same principles are applicable to pins which are square or rectangular in cross-section. For example, Figure 7 shows the end profile of a rectangular pin 14 formed by extrusion with a recess 11 and groove 12 running continuously along one side face. A conductor may be secured to the pin in exactly the same way as described above. The above described methods of attaching a conductor to a pin according to the invention enables a good electrical connection to be obtained at low cost, the pins can be made economically by extrusion without requiring any machining, and dimensional tolerances are easily maintained,

Claims: Claims: 1. A method of connecting a wire conductor to a plug pin having a groove in a surface thereof, comprising the steps of laying the conductor in the groove, and deforming the material of the pin to fix the conductor to the pin, characterised in that over at least a portion of the groove the material of the pin at the side of the groove is softened by heating with an electric current, and the softened material is displaced to embed the conductor in the material of the pin. 2. A method according to claim 1, wherein the electric heating current is passed between the pin and an electrode, and the electrode is applied against the pin for displacing the softened material. 3. A method according to claim 1 or 2, wherein the pin has a recess extending over a surface thereof and the groove is formed along the bottom wall of the recess, and the conductor is attached to the pin without disturbing the material of the pin at either side of the recess. 4. A method according to claim 2 and claim 3, wherein the recess is of greater width than the tip of the electrode which is applied against the bottom wall of the recess either side of the groove. 5. A method according to any one of claims 1 to 4, wherein the groove is of sufficient depth to receive the conductor. 6. A method according to any one of claims 1 to 5, wherein the groove extends across an end surface of the pin. 7. A method according to any one of claims 1 to 5, wherein the groove extends longitudinally of the pin. 8. An electric plug comprising at least one pin having a wire conductor attached thereto by the method of any one of the preceding claims.

Inventors: BEALE, MICHAEL DAND
Applicants: DURAPLUG ELECTRICALS LIMITED
Application year: 1983
Main classification: H01R4
IPC codes: B23K33, H01R4