Crimping a ferrule to the insulation of an insulated cable

Abstract: Where the U-shaped insulation support ferrule (12) of an electrical terminal is to be crimped to a cable (20/) having thin walled insulation (24/), for example irradiated insulation, the wall thickness of which is as small as between 13% to 22% of the total diameter (D/) of the cable (20/), the crimping die (58) has surfaces which form end portions of ears (16) of the ferrule (12) into scrolls (50) having smoothly arcuate surfaces (52) which resiliently engage the cable insulation (24/) at spaced positions (54), so that the cable (20/) is supported between the scrolls (50) and the base (14) of the ferrule (12) in symmetrical relationship therewith, and the ears (16) do not penetrate the cable insulation (24/).

Description: This invention relates to a method of, and a die for use in crimping a metal ferrule about the insulation of an insulated cable Electrical terminals to be crimped to stripped end portions of electrical cables having a central metal core surrounded by a layer of insulation, comprise a first ferrule which is usually of U-shaped cross section and which is known as a wire barrel for crimping to the cable core and a second ferrule which is also of U-shaped cross section and which is known as the insulation barrel which is for crimping about the insulation of said stripped end portion. The purpose of the insulation barrel, is to minimise strain and vibration, that could affect the integrity of the crimped connection between the wire barrel and the cable core. Especially where the terminal, when crimped to the cable, is to be used in an environment, for example in an automotive vehicle, where considerable vibration may obtain, it is important that the connection between the insulation barrel and the insulation of the cable should remain intact throughout the working life of the terminal. Hitherto, in the automotive industry, it has been customary to use cable having relatively thick insulation, the wall thickness of the insulation amounting to up to about 33% of the total diameter of the cable, that is to say the diameter of the cable including that of the core and that of the insulation. Where such thick insulation is used, there is little difficulty in crimping the insulation barrel about the insulation so that it is tightly confined by the insulation barrel, and without the free edges thereof penetrating and thus damaging, the insulation, to any significant extent, the crimped connection being of substantially square cross section. Such thick insulation may be for example made of polyethelene or rubber. Cable insulation of improved resistivity, for example irradiated insulation, has now, however, been developed so that without impairing the insulating properties of insulated cables, the insulation about the core may be made much thinner than heretofore, being for example of a wall thickness equal to between 13% - 22% of the total diameter of the cable. In view of its ability to reduce the bulk of cabling, such improved insulation is increasingly being used, especially in the automotive industry. With insulation of such reduced thickness, it is difficult to provide a satisfactory crimped connection between the insulation barrel of a terminal and the cable insulation, bearing in mind that each terminal will usually be required to accommodate cables of several different gauges for example four different gauges. This difficulty arises, because even in the case of the larger gauges of the range, the cable cannot be made to fill the crimped insulation barrel. Although the crimping tooling can be arranged to curl over the side walls of the insulation barrel so that the insulated cable is engaged between the curled over free edges of the insulation barrel and its base, these free edges tend to bite into, and thus disrupt, the insulation and the cable is supported only between what are, in effect, two diametrically opposed points. The crimped connection between the insulation barrel and the cable, is therefore susceptible to being loosened under the action of cable strain, or vibration. Document US-A-3 239 924 discloses a crimping tool comprising a crimping die of the kind shown in fig. 5A of the accompanying drawings. According to one aspect of the invention, a method of crimping a metal ferrule about an insulated cable, the ferrule comprising a base and a pair of opposed ears upstanding from opposite edges of the base so that the ferrule is substantially U-shaped, comprises the steps of laying the cable upon the base of the ferrule and between said ears, and curling over each ear inwardly of the ferrule so that the ear forms a scroll having a smooth arcuate surface which is convex in the direction of the cable and engages the insulation thereof, whereby the cable is gripped between said arcuate surfaces and the base of the ferrule at three discrete positions spaced from one another circumferentially of the cable. The cable is accordingly securely supported by the crimped ferrule, no edges of which bite into the cable insulation. By suitable adjustment of the tooling used for crimping the ferrule, the ears can be curled over to a different extent to accommodate respective cable gauges. Thus for example the same crimping tooling can be used in respect of four different cable gauges. Preferably, the ears are curled over so as to engage the insulation at positions spaced circumferentially thereof by about 90°, the position at which the cable insulation engages the base of the ferrule being spaced from each ear by about 135°, so that a cable is incapable of escaping from the crimped ferrule. The scolls act as energy storing means, relaxing slightly following the crimping operation and thereby exerting pressure against the cable insulation securely to support the cable and to prevent the insulation from creeping back. The method can be used effectively with all types of insulation even where the wall thickness of the insulation of the cable is as small as between 13% and 22% of the total cable diameter. The minimum developed length of the ferrule required, that is to say the length of the ferrule when in a flat state, to provide satisfactory scrolling thereof should be 1.6 x the total circumference of the largest gauge cable with which the ferrule is to be used. According to another aspect of the invention, a crimping die for crimping a metal ferrule about an insulated cable, the ferrule comprising a base and a pair of opposed ears upstanding from opposite edges of the base so that the ferrule is substantially U-shaped, comprises a flat metal plate having extending inwardly from an edge thereof, a crimping recess for receiving a crimping anvil for externally supporting the base of the ferrule, the recess being defined by a pair of opposed, spaced side edges spanned by an ear -forming base edge defined by a pair of concave scroll forming surfaces arranged in mirror image symmetry on either side of a scroll separating bridge having a flat surface facing outwardly of said recess in parrallel relationship with the axes of curvature of said concave surfaces. The anvil with the base of the ferrule supported thereon can be advanced into said recess and towards said ear forming base edge, with the cable resting on the base of the ferrule and between the ears thereof, to cause, the scroll forming surfaces, in cooperation with the scroll separating bridge, to curl over each ear of the ferrule inwardly thereof, so that the ear forms a scroll having a smooth arcuate surface which is convex in the direction of the cable, and engages the insulation thereof so that the cable is gripped between the arcuate surfaces of the ears and the base of the ferrule at three discrete positions spaced from one another circumferentially of the cable. The width of the scroll separating bridge, in the plane of the crimping die is preferably 28% of the crimp width, that is to say the overall diameter of the largest gauge cable with which the die is to be used plus twice the thickness of the metal stock from which the ferrule was formed. Peferably also, each of the scroll forming surfaces has a first portion remote from the bridge, the radius of which portion is 24% of the crimp width and a portion of smaller radius, which is adjacent to the bridge, and the radius of which is 12% of the crimp width. The smaller radius portion of each of the scroll forming surfaces, preferably adjoins a flat lateral surface of the bridge which extends at right angles to the flat surface thereof and the flat surface of the bridge prefereably lies in a plane midway between the axes of curvature of the scroll forming surfaces. Although dies for crimping ferrules to the insulation of insulated cables, are usually finished only to a sixteen microinch (0.4 µm) finish, the crimping dye according to the invention, is preferably finished to an eight microinch (0.2 µm) finish. This smooth finish ensures that as the ears are curled over, they slide readily along the scroll forming surfaces and said lateral surfaces of the bridge, which ensure that the end surfaces of the ears do not bite into the insulation of the cable. For a better understanding of the invention and to show 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 side view of an electrical terminal; Figure 2 is a top plan view of the terminal; Figure 3 is a cross sectional view taken on the lines 3-3 of Figure 2; Figure 4 is an end view illustrating an insulation barrel of the terminal crimped to a cable having thick insulation, by a prior art method; Figure 5 is an enlarged end view showing the insulation barrel crimped to a cable having thin insulation, by a prior art method; Figure 5A is a fragmentary view of a crimping die and a crimping anvil for carrying out the prior art method; Figures 6 and 7 are enlarged views drawn from section photographs illustrating actual results achieved by the prior art method; Figure 8 is a fragmentary view of a crimping die and crimping anvil for carrying out the method of the present invention; Figure 9 is an enlarged fragmetary view illustrating details of Figure 8; Figure 9A is a reduced view taken on the lines 9A-9A of Figure 8; Figure 10 is an enlarged, diagramatic cross sectional view illustrating the insulation barrel when crimped to on insulated cable having thin insulation, by means of the die and anvil illustrated in Figure 8; and Figures 11 to 13 are enlarged views drawn from section photographs each illustrating the insulation barrel when crimped to an insulated cable having thin insulation, the cable being of a different gauge in each of these Figures. As shown in Figures 1 and 2 an electrical terminal 2 comprises a plug portion 4, a transition portion 6 a wire barrel 8, a stabilising portion 10 and an insulation barrel 12. The wire barrel 8 which is substantially U-shaped, is intended to be crimped about the bared end of the electrically conductive core of an insulated electrical cable. The insulation barrel 12 is also U-shaped comprising an arcuate base 14 and a pair of ears 16 upstanding from opposite edges of the base 14, the ears 16 having chamfered free edges 18 remote from the base 14. Figure 4 shows the insulation barrel 12 crimped to a cable 20 having an electrically conductive core 22 surrounded by a cover of insulation 24, made for example, of rubber or polyethelene which layer is relatively thick, the wall thickness W of the layer of insulation 24, at least prior to the crimping operation, amounting to as much as 33% of the total cable diameter D. As will be apparent from Figure 4, the insulation barrel 12 was crimped to substantially square shape, the thick insulation 24 filling the interior of the barrel 12 substantially voidlessly and the edges 18 of the barrel 12 being in contiguous relationship and thus not biting to any significant extent into the insulation 24. The cable 20 is accordingly tightly confined between the base 14 and the deformed ears 16 of the barrel 12 so as to provide satisfactory strain relief support for the core 22 to which the wire barrel 8 was crimped during the same crimping operation. The integrity of the electrical connection between the barrel 8 and the core 22 cannot, therefore, be impared by vibration to which the crimped terminal may be subjected. Figure 5 shows insulation barrel 12 when crimped to a cable 20 / having an electrically conductive core 22 / surrounded by a covering of insulation 24 / , for example irradiated insulation which is much thinner than the insulation 24, the wall thickness W of the insulation 24 / being only 13% to 22% of the total diameter D / of the cable 20 / . According to this prior art method of crimping the barrel 12 to the cable 20 / having thin insulation, the base 14 of the barrel 12 is supported upon a correspondingly configured working surface 26 of a crimping anvil 28, the cable 20 being layed on the base 14 of the barrel 12 and between the ears 16 thereof. A crimping die 30 is advanced towards the anvil 28 in the direction of the arrow A in Figure 5A so that the anvil and thus the barrel 12 are received in a crimping recess 32 of the die 30, which is in the form of a flat metal plate into an edge 34 of which the recess 32 opens. The recess 32 has opposed side walls 36 which diverge from one another towards the edge 34 to provide a mouth for receiving the anvil 28. The side edges 36 are spanned by a base edge 38 having a pair of concave, ear forming surfaces 40 arranged in mirror image symmetry on either side of a sharp cusp 42 which is defined by the surfaces 40, each of which is of constant radius. As the die 30 is advanced towards the anvil 28, the ears 16 of the barrel 12 are, at least in theory, curled over smoothly by the surfaces 40 so that the cable 20 / is gripped between the chamfered edges 18 of the barrel 12 and the base 14 thereof. That is to say the cable 20 / is, in effect, supported in the barrel 12 only at two opposite positions. Even so, the edges 18 bite to a substantial extent into the insulation 24 / and, since there are substantial voids between the cable 20 / and the remainder of the barrel 12 the cable 20 / could be dislodged from the position in which it is shown in Figure 5, under the action of vibration causing whipping of the cable and tension upon the cable cover would cause the edges 18 / to tear the insulation 24 / lengthwise, so that the insulation support provided by the crimped barrel 12 must clearly be defective even as envisaged in Figure 5, which as is only a theoretical diagram. Figures 6 and 7 show the practical results of employing the tooling shown in Figure 5 to crimp the barrel 12 to the cable 20 / . In practice, the shape of the crimped barrel 12 is, as shown in Figures 6 and 7 somewhat arbitary, at least one of the edges 18 deeply penetrating into the insulation 24 / with the cable 20 / being asymmetrical with respect to the crimped barrel 12 and therebeing substantial voids between the cable 20 / and the barrel 12. According to the present invention the disadvantages mentioned above are avoided by crimping the barrel 12 to the configuration that is diagramatically illustrated in Figure 10. As shown in that Figure, the ears 16 are so curled over that each ear forms a scroll 50 having a smooth arcuate surface 52 which is convex toward the cable 20 / and engages the insulation 24 / thereof at a position substantially opposite to the base 14 of the barrel 12. The cable 12 is thus gripped between the arcuate surfaces 52 at two positions 54 spaced circumferentially of the cable 20 / on one side thereof, and the base 14 on the opposite side thereof at a position 56. The cable 20 / cannot, therefore, move under the action of vibration and even if the cable is pulled there are no sharp surfaces engaging in the insulation 24 / , that would cause it to tear under the pulling force. As shown in Figure 10 the positions 54 are spaced from one another by about 90° circumferentially of the cable 20 / , the position 56 at which the cable is engaged by the base 14, being spaced from each position 54 by approximately 135°. Following the crimping operation, which is described below, the scrolling forces which produce the scrolls 50 cause the free end portions of the ears 16, each to roll up in the manner of a spring, so that following the crimping operation the scrolls 50 relax slightly, that is to say they uncoil slightly, so as to exert pressure against the insulation 24 / thereby pressing against the insulation 24 / to provide extra insulation support and prevent creep back of the insulation 24 / . The tooling for crimping the barrel 12 to the cable 20 / in the manner just described with reference to Figure 10, will now be described with reference to Figures 8, 9 and 9A. The tooling comprises an anvil 56 similar to the anvil 28 described above and having a concave working surface 57 for supporting the exterior of the base 14 of the barrel 12, and a crimping die 58 only the lower part of which is shown. The die 58 which is in the form of a flat metal plate has its upper end secured in the tool holder of a conventional crimping press (not shown), the anvil 56 being arranged upon the press base (not shown) with respect to which the die 58 is moveable by means of the press ram, vertically towards and away from the anvil 56. For crimping wire barrel 8 of the terminal 2 to the bared end of the electrically conductive core 22 / of the cable 20 / , a further crimping die 59 (Figure 9A) is mounted to the tool holder in juxtaposed relationship with the die 58, the die 59 being, for example, of similar shape to the die 30 described above, but being thicker, as shown in Figure 9A There extends inwardly, from an edge 60 of the dye 58, a crimping recess 62 for receiving the anvil 56, the recess 62 being defined by a pair of opposed, spaced, side edges 64 spanned by an ear forming base edge 66 defined by a pair of concave, scroll forming surfaces 68 which are of identical form and dimensions but are arranged in mirror image symmetry on either side of a scroll separating bridge 70 having a flat surface 72 facing outwardly of the recess 62, and having flat lateral edges 74 extending at right angles to the surface 72, as best seen in Figure 9, and which adjoin the surfaces 68. Each surface 68 is curved to two different radii, the part of each recess 68 remote from the bridge 70 having a radius R1 of 24% of the crimp width CW, CW being equal to the total diameter D / of the largest gauge cable 24 / to which a barrel 12 is to be crimped by means of the tooling, plus twice the stock thickness of the barrel 12, it being recalled that the barrel 12 will be of the same size in respect of a range of cable gauges. Between that part of each surface 68 having the radius R1 and the adjacent edge 74 of the bridge 70, each surface 68 has a radius R2 which is smaller than the radius R1 being approximately 12% of the crimp width CW. The width of the flat surface 72, in the plane of the die 78 is 28% of the crimp width CW, the depth of the bridge 70, that is to say the height of its edges 74 in the plane of the die 58 being 18% of the crimp width CW, so that the surface 72 extends in a plane P midway between the two axes of curvature of each of the surfaces 68. The edges 64 diverge from one another to provide a mouth opening into the edge 60, for guiding the anvil 56 into the recess 62, but towards the base edge 66, the edges 64 are parrallel to one another and are spaced apart by the crimp width CW. In the use of the tooling shown in Figures 8 to 9A, the terminal 2 is positioned with its barrels 8 and 12 supported on the surface 57 of the anvil 56 which is common to a die 58 and the die 59, so that the barrel 12 lies beneath the die 58, the barrel 8 lying beneath the wire crimping die 59. The crimp height, that is to say the shut height of both dies having been adjusted in accordance with the gauge of the cable 20 / , for example by means disclosed in US-A -3,184,950, the cable 20 / is laid in the barrels 8 and 12, with a stripped end portion of the core 22 / in the barrel 8 and the cable insulation 24 / , just back from the said stripped end, resting on the base 14 of the barrel 12 between the ears 16. The dies are then advanced towards the anvil 56, by means of the press ram, in the direction of the arrow B in Figure 8. As the die 58 advances towards the anvil 56, the chamfered edges 18 engage the outer radiused parts of the respective surfaces 68, so that the ears 26 are gradually curled over to the radius R1 being then more tightly curled over as the edges 18 follow the smaller radiused parts of the surfaces 68, as the surface 72 of the bridge 70 engages the insulation 24 / of the cable 20 / at a position opposite to the base 14, compressing the insulation slightly to allow the edges 18 to pass over the insulation 24 / without piercing it and to move towards the undeformed portions of the ears 26 as shown in Figure 10, whereby the smooth arcuate surfaces 52 of the scrolls 50 engage the insulation 24 / at the spaced positions 54 so that the cable 20 / is supported by the crimped barrel 12 at three spaced positions as described above with reference to Figure 10. As will be apparent from Figures 11 to 13, which show the barrel 12 crimped to cables 20 / A, 20 / B and 20/C, which are of substantially different gauges, the scrolls 50 are, in each case so formed that the insulation of the cable is not damaged during the crimping operation and in each case the cable insulation is engaged by the smooth arcuate surfaces of the scrolls 50 at positions spaced circumferentially of the cable. During the operations described above, the wire crimping die 59 crimps the barrel 8 to the bared end portion of the core 22 / according to well known practice. Following the crimping operations, the crimping dies 58 and 59 are withdrawn by the press ram from the anvil 56, the scrolls 50 relaxing slightly as described above, resiliently to apply substantial pressure to the insulation 24 / of the cable. Because the scrolling operations take place on either side of the cable, the scrolls naturally centralize the cable within the ferrule so that the cable is symmetrical with the crimped barrel 12.

Claims: A method of crimping a metal ferrule about an insulated cable (20), the ferrule comprising a base (14) and a pair of opposed ears (16) upstanding from opposite edges of the base (14) so that the ferrule is substantially U-shaped, the method comprising the steps of laying the cable (20) upon the base (14) of the ferrule and between said ears (16), and curling over each ear (16) inwardly of the ferrule so that each ear (16) forms a scroll (50) having a smooth arcuate surface (52) which is convex in the direction of the cable and engages the insulation (24) thereof, whereby the cable (20) is gripped between said arcuate surfaces (52) and the base (14) of the ferrule at three discrete positions spaced from one another circumferentially of the cable. A method as claimed in claim 1, wherein the arcuate surfaces (52) of the scrolls (50) engage the insulation (24) of the cable (20) at positions which are spaced from one another about the circumference thereof, by about 90°, the insulation (24) engaging the base of the ferrule at a position spaced from each of the positions at which the said arcuate surfaces (52) engage the insulation, by about 135°. A method as claimed in claim 1 or 2, wherein those points on the scrolls (50) which are nearest to one another are spaced from one another by 28% of the crimp width, that is to say the overall diameter of the largest gauge cable to be used in the method plus twice the stock thickness of the ferrule. A method as claimed in claim 1, 2 or 3, comprising the step of applying pressure to the cable insulation (24) whilst curling over the ears (16) of the ferrule to form the scrolls (50), so that free edges of the ears (16) slide over the cable insulation (24) without entering it. A method as claimed in any one of the preceding claims, wherein the wall thickness of the insulation (24) of the cable (20) is between 13% and 22% of the overall diameter of the cable. A method as claimed in any one of the preceding claims, wherein the ears (14) are progressively curled over to form the scrolls (50), first by a larger radius and then by a smaller radius which is approximately half the larger radius. A method as claimed in any one of the preceding claims, wherein the scrolls (50) are so formed that they act as energy storage means so that the smooth arcuate surfaces of the scrolls (50) are resiliently urged against the insulation (24) of the cable. A method as claimed in any one of the preceding claims, wherein the scrolling of the ears (16) is effected on either side of the cable (20) so that the scrolls (50) naturally centralize the cable (20) within the ferrule, whereby the cable (20) is symmetrical with the crimped ferrule. A crimping die for use in crimping a metal ferrule about an insulated cable (20), the ferrule comprising a base (14) and a pair of opposed ears (16) upstanding from opposite edges of the base (14) so that the ferrule is substantially U-shaped, said die comprising a flat metal plate, having extending inwardly from an edge (60) thereof, a crimping recess (62) for receiving a crimping anvil (56) for externally supporting the base (14) of the ferrule, the recess (62) being defined by a pair of opposed, spaced side edges (64) spanned by an ear forming base edge (66) defined by a pair of concave scroll forming surfaces (18) arranged in mirror image symmetry on either side of a scroll separating bridge (70) having a flat surface (72) facing outwardly of the recess (62) in parallel relationship with the axes of curvature of said concave surfaces. A die as claimed in claim 9, wherein each scroll forming surface (68) has a first part remote from the bridge and which is curved about a first radius and a second part adjoining said first part and said bridge and which is curved about a second radius which is substantially half said first radius. A die as claimed in claim 10, wherein said bridge (70) has lateral edges extending at right angles to said flat surface (72) and also being flat, each of said lateral edges adjoining a respective one said scroll forming surfaces (68). A die as claimed in claim 10 or 11, wherein said flat outwardly facing surface (72) of the bridge (70) lies in a plane which is midway between the axes of the curvature of the two parts of the scroll forming surfaces (68). A die as claimed in any one of claims 9 to 12, wherein the width of said flat outwardly facing surface (72) of the bridge (70), in the plane of the die, is 28% of the overall diameter of the largest gauge cable with which the dye is to be used, plus twice the stock thickness of the ferrule.

Inventors: RUNAGALL ROBERT TERENCE, RUNAGALL, ROBERT TERENCE
Applicants: WHITAKER CORP, THE WHITAKER CORPORATION
Application year: 1989
Main classification: H01R4
IPC codes: H01R4, H01R11, H01R43