It is known to provide an assembly, such as for example an earthing strap arrangement for use in an electrical socket, in which at least one clip of a resilient metal is provided. Any such clip may be formed of a material such as phosphor bronze in order to provide the necessary resilience for engaging with a component such as an earth pin of an electrical plug.

Materials such as phosphor bronze are relatively expensive and it is therefore desirable to minimise their use. For this reason it is found advantageous to provide only the clip of an earthing strap arrangement from phosphor bronze and to secure the clip to a strap of a less expensive material, such as mild steel, which may be coated with a layer of another metal such as zinc. It is known to join such a clip to a strap by means of a rivet, but this is disadvantageous in that it involves significant manual labour and also the provision of a rivet as an additional component.

It is an object of the present invention to overcome or minimise this problem.

According to the present invention there is provided a process for joining together at least two components, at

least one of which is metallic, to form an assembly, the process comprising : providing a first component having first and second opposite faces and provided with a hole therethrough; providing a second component of a metallic material, having a hollow tubular projection; assembling the second component with the first component with the hollow tubular projection inserted through the hole in the first component from the first face thereof and such that a portion of the hollow tubular projection extends at the second face thereof ; and effecting deformation of the hollow tubular projection to cause it to expand laterally to engage tightly with the first component in the hole and to cause the extended portion of the hollow tubular projection to effect clenching engagement with the second face of the first component.

The hole provided through the first component may be arranged with a countersunk region at the second face of the first component and such that the extended portion of the hollow tubular projection of the second component is caused to effect clenching engagement with the countersunk region of the second face of the first component.

The first component may comprise a metallic or non- metallic material.

The first component may comprise a material of different mechanical properties, such as greater hardness and/or ductility and/or plasticity, compared with a material of the second component.

The first component may comprise an overlying arrangement of two or more layers of material provided with the hole therethrough.

The first and/or second components may be formed from one or more substantially planar materials, such as sheet- form or strip-form materials.

The first component may be provided by punching a hole through one or more first substantially planar material using a punch and die combination. The punch may be of substantially circular cross-section and may be optionally provided with a shoulder portion, such as of tapered form, to form the countersunk region of the hole at the second face of the first component, where required.

The second component may be provided by punching a hole through a second substantially planar material, such as sheet-form or strip-form material, using a first punch and die combination, and then deforming a region of the second substantially planar material surrounding the hole to form the hollow tubular projection, using a second punch and die combination. The punch of the first punch and die combination may be of substantially circular cross-section. The punch of the second punch and die combination may be of substantially circular cross- section, may have a leading end of stepped form and may have a tapered portion between steps.

Deformation of the hollow tubular projection after assembling the second component with the first component may be effected by clamping the assembled components between first and second support tools provided with aligned boreholes therein, such that the first support tool is in contact with the second face of the first component, and urging a punch tool through the borehole in the first support tool and into the hollow tubular projection of the second component to deform the hollow tubular projection and enter the borehole in the second support tool. The punch tool may have a substantially circular cross-section, may have a tapered leading end to effect lateral expansion of the hollow tubular projection, and may be formed with a shoulder region to effect the clenching engagement of the extended portion of the hollow tubular projection with the second face of the first component.

The second component may comprise steel, which may be coated with another metal, such as zinc. The first component may comprise phosphor bronze, or other alloy of copper and tin, or brass.

The assembly may be adapted to form part of an electrical socket, such as an earth strap in an electrical socket, in which the first component is electrically connected and joined to the second component and may be adapted to receive an earthing pin of an electrical plug arranged to be inserted in the socket.

The process of the present invention is advantageous in that it provides a simple arrangement for directly joining together components, particularly of different materials, and particularly requiring electrical

connection therebetween, without the need for additional securing devices such as rivets.

For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made by way of example to the accompanying drawings in which: Figure 1 is a cross-sectional view of an embodiment of a first component employed in the process of the present invention; Figure 2 is a cross-sectional view of an embodiment of a second component employed in the process of the present invention; Figure 3 is a cross-sectional view of the first and second components of Figures 1 and 2, joined together to form an assembly by the process of the present invention; Figure 4 is a perspective view of an earthing strap for an electrical socket embodying the assembly of Figure 3; Figure 5 is a cross-sectional view showing the formation of the first component of Figure 1; Figures 6A and 6B are cross-sectional views showing steps in the formation of the second component of Figure 2; and Figures 7A, 7B and 7C are cross-sectional views showing processing of the first and second components of Figures 1 and 2 according to the present invention to produce the assembly of Figure 3.

Referring to Figures 1,2 and 3, a first component 2 is assembled and joined to a second component 4 by a process according to the present invention, to form an assembly 6.

The first component 2 is formed from a sheet or strip 8 of a material having different mechanical properties, such as greater hardness and/or ductility and/or plasticity, compared with the properties of a corresponding sheet or strip 10 of material used to form the second component 4. The first component 2 may comprise a metallic or non-metallic material and the second component 4 comprises a metallic material. By way of example, the first component 2 may comprise phosphor bronze, which may for example comprise at least 58 percent of copper, and the second component 4 may comprise mild steel, such as a steel of low carbon content, and may be coated with another metal, such as zinc, such as by a galvanising process.

The first and second components 2,4 may be produced from bands, spools or reels of sheet-form or strip-form materials.

The first component 2, produced by a process to be described in detail hereinafter, has first and second opposite faces 12 and 14 respectively and is provided with a through-hole 16. The hole 16 is preferably arranged with a countersunk region 18 at the second face 14 of the first component 2.

The second component 4, produced by a process to be described in detail hereinafter, is formed with a hollow tubular projection 20 extending at a face 22 thereof.

As shown in Figure 3, the second component 4 is assembled with the first component 2 with the hollow tubular projection 20 inserted through the hole 16 in the first component 2, from the first face 12 of the first component 2. A leading end portion 24 of the hollow tubular projection 20 is arranged to extend beyond the second face 14 of the first component 2. As will be described in detail hereinafter, deformation of the hollow tubular projection 20 is effected to cause it to expand laterally to engage tightly with the first component 2 in the hole 16 at a peripheral region 26.

The extended leading end portion 24 of the hollow tubular projection 20 of the second component 4 is also deformed to effect clenching engagement with the countersunk region 18 of the second face 14 of the first component 2.

As a result, the first component 2 is securely joined to the second component 4 without any requirement for an additional fastening device, such as a rivet, and with the face 22 of the second component 4 in tight intimate contact with the first face 12 of the first component 2.

When the first and second components 2,4 are both metallic, reliable electrical connection also results between the components.

An assembly 6 results in which the use of a relatively expensive material, such as phosphor bronze, can be minimised by simply and efficiently joining it to a less expensive material such as steel.

As a result of the assembly process, the wall thickness of the hollow tubular projection 20 in the resulting assembly 6 varies along the length of the deformed hollow tubular projection 20. However, a dimension 28 will

generally not be less than about 30 percent of the component thickness at the base of the hollow tubular projection 20. When the leading end portion 24 of the hollow tubular projection 20 on the second component 4 is clenched into the countersunk region 18 of the first component 2, a small reduction in the inside diameter of the hollow tubular projection 20 occurs. Such reduction may be typically by about 10 to 15 percent.

The top of the clenched end portion 24 of the hollow tubular projection 20 on the second component 4 may stand above the level of the second surface 14 of the first component 2 by an amount 30 typically corresponding to about 5 percent of the length of the hollow tubular projection 20.

The first component 2 may comprise an overlying arrangement of two or more layers of material 8, provided with the hole 16 therethrough. The two or more layers may be of the same or different thickness and may comprise the same or different materials.

Figure 4 illustrates a particular application of the assembly of Figure 3. In Figure 4, an earthing strap 32 for use in an electrical socket comprises two of the assemblies 6 of Figure 3. Each of the assemblies 6 comprises the first component 2, of phosphor bronze material, shaped to form a resilient clip for receiving an earth pin of a standard 13 amp electrical plug when applied to the socket. The first component 2 is joined to the second component 4, of galvanised steel material, by the process of the present invention. The second components 4 are formed as an integral part of a shaped,

bent strip 34 which may be suitably fabricated from a metal sheet.

The first component 2 of Figure 1 is suitably formed as shown in Figure 5. The hole 16 is punched through the sheet or strip 8, using a punch 36 and an apertured die 38 combination. The punch 36 is suitably of substantially circular cross-section and is provided with a shoulder portion 40, such as of tapered form, to form the countersunk region 18 of the hole 16 at the second face 14 of the first component 2.

The second component 4 of Figure 2 is suitably formed as shown in Figures 6A and 6B. As shown in Figure 6A, a hole 42 is punched through the sheet or strip 10 of the second component 4, using a first combination of a punch 44 with an appropriately dimensioned leading end portion 46, and an apertured die 48. The punch 44 may be of substantially circular cross-section. The punched sheet or strip 10 is then transferred to a second combination of a punch 50 and apertured die 52, as shown in Figure 6B and a region of the material of the sheet or strip 10 surrounding the hole 42 is deformed to form the hollow tubular projection 20. The punch 50 of this second punch and apertured die combination may be of substantially circular cross-section and is of stepped form 54,56 at its leading end, and having an intermediate tapered portion 58.

Formation of the assembly 6 of Figure 3 from the first and second components 2 and 4 of Figures 1 and 2 is suitably effected by process steps illustrated in Figures 7A, 7B and 7C. As shown in Figure 7A, the first component 2 is assembled with the second component 4

between first and second support tools 60 and 62 respectively, provided with aligned boreholes 64 and 66 respectively therein. The first support tool 60, sometimes referred to as a stripper plate, is arranged in contact with the second face 14 of the first component 2, as shown in Figure 7B. A punch tool 68 is urged through the borehole 64 in the first support tool 60 and into the extended end portion 24 of the hollow tubular projection 20 of the second component 4, to deform the hollow tubular projection 20 and enter the borehole 66 in the second support tool 62. The punch tool 68 suitably has a circular cross-section and has a tapered leading end 70 to effect the necessary lateral expansion of the hollow tubular projection 20. The punch tool 68 is also formed with a shoulder region 72 to effect the clenching engagement of the extended portion 24 of the hollow tubular projection 20 with the countersunk region 18 of the second face 14 of the first component 2, as detailed in Figure 3.

The process of the present invention may be used to produce assemblies formed by joining together a range of materials for a wide variety of applications. It is important to ensure that the materials to be joined together are selected such that disadvantageous mechanical stresses do not occur in the resulting assemblies. Such stresses may be tensile, compressive or shear in nature, and may be temperature-induced, for example as a result of thermal cycling. A possibility of galvanic corrosion occurring between the materials employed for the components of the assembly should also be avoided.

The material of the first component 2 of the assembly should in general have a typical hardness, or 0.2 percent Proof Stress Range, at least equal to that of the material of the second component 4.

The material of the second component 4 should in general have a minimum ductility of about 15 percent, as measured by elongation in a tensile test.