[0001] This invention relates to a method of, and a die for use in crimping a metal ferrule
about the insulation of an insulated cable and also relates to the ferrule when it
has been so crimped.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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 guages, for example four different guages. This difficulty arises,
because even in the case of the larger guages 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.
[0006] 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.
[0007] The cable is accordingly securely supported by the crimped ferrule, no edges of which
bite into the cable insulation.
[0008] 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 guages. Thus
for example the same crimping tooling can be used in respect of four different cable
guages.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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 guage cable with which the ferrule
is to be used.
[0013] 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.
[0014] 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 guage cable
with which the die is to be used plus twice the thickness of the metal stock from
which the ferrule was formed.
[0015] 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.
[0016] Although dies for crimping ferrules to the insulation of insulated cables, are usually
finished only to a sixteen microinch finish, the crimping dye according to the invention,
is preferably finished to an eight microinch 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.
[0017] According to a further aspect of the invention, a metal ferrule which has been crimped
about an insulated cable, comprises a base engaging one side of the cable, a pair
of opposed ears up standing from opposite edges of the base and each terminating,
at a position remote from the base, in a scroll of the ferrule material, having a
smoothly arcuate surface which is convex in the direction of the cable and which engages
the opposite side of the cable insulation and urges the cable towards the base, the
scrolls being spaced from one another transverely of the longitudinal axis of the
cable so that the cable is gripped between said arcuate surfaces and the base, at
three discrete positions which are spaced from one another circumferentially of the
cable.
[0018] 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 an 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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/.
[0023] 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 guage 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 guages. 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.
[0024] 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.
[0025] 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 guage 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 guages, 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 relaxing slightly as described above, resiliently to apply substantial pressure
to the insulation 24/ of the cable.
[0026] 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.
1. 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, the method comprising 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 each 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.
2. A method as claimed in claim 1, wherein the arcuate surfaces of the scrolls engage
the insulation of the cable at positions which are spaced from one another about the
circumference thereof, by about 90°, the insulation engaging the base of the ferrule
at a position spaced from each of the positions at which the said arcuate surfaces
engage the insulation, by about 135°.
3. A method as claimed in claim 1 or 2, wherein those points on the scrolls 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.
4. A method as claimed in claim 1, 2 or 3, comprising the step of applying pressure
to the cable insulation whilst curling over the ears of the ferrule to form the scrolls,
so that free edges of the ears slide over the cable insulation without entering it.
5. A method as claimed in any one of the preceding claims, wherein the wall thickness
of the insulation of the cable is between 13% and 22% of the overall diameter of the
cable.
6. A method as claimed in any one of the preceding claims, wherein the ears are progressively
curled over to form the scrolls, first by a larger radius and then by a smaller radius
which is approximately half the larger radius.
7. A method as claimed in any one of the preceding claims, wherein the scrolls are
so formed that they act as energy storage means so that the smooth arcuate surfaces
of the scrolls are resiliently urged against the insulation of the cable.
8. A method as claimed in any one of the preceding claims, wherein the scrolling of
the ears is effected on either side of the cable so that the scrolls naturally centralize
the cable within the ferrule, whereby the cable is symmetrical with the crimped ferrule.
9. A crimping die for use in 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, said die comprising 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 the recess in parallel relationship with the axes of curvature
of said concave surfaces.
10. A die as claimed in claim 9, wherein each scroll forming surface 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.
11. A die as claimed in claim 10, wherein said bridge has lateral surfaces extending
at right angles to said flat surface and also being flat, each of said lateral surfaces
adjoining a respective one said scroll forming surfaces.
12. A die as claimed in claim 10 or 11, wherein said flat outwardly facing surface
of the bridge lies in a plane which is midway between the axes of the curvature of
the two parts of the scroll forming surfaces.
13. A die as claimed in any one of claims 9 to 12, wherein the width of said flat
outwardly facing surface of the bridge, in the plane of the die, is 28% of the overall
diameter of the largest guage cable with which the dye is to be used, plus twice the
stock thickness of the ferrule.
14. A metal ferrule which has been crimped about an insulated cable, the ferrule comprising
a base engaging one side of the cable insulation and a pair of opposed ears upstanding
from opposite edges of the base, and each terminating at a position remote from the
base, in a scroll of the ferrule material having a smooth arcuate surface which is
convex in the direction of the cable and which engages the opposite side of the cable
insulation and urges the cable towards the base,the scrolls being spaced from each
other transversely of the longitudinal axis of the cable so that the cable is gripped
between said arcuate surfaces and the base, at three discrete positions, spaced from
one another circumferentially of the cable.
15. A crimped ferrule as claimed in claim 14, wherein the smooth arcuate surfaces
of the scrolls, engage the insulation of the cable at the positions which are spaced
from one another by about 90° about the circumference thereof, the base of the ferrule
engaging the insulation of the cable at a position spaced by about 135° from each
of the positions at which said arcuate surfaces engage the cable.
16. A crimping ferrule as claimed in Claim 14 or 15, wherein those points on the scrolls
which are nearest to each other are spaced from one another by 28% of the overall
diameter of the cable plus twice the stock thickness of the ferrule.
17. A crimped ferrule according to Claim 14, 15 or 16, wherein the wall thickness
of the insulation of the cable is between 13% and 22% of the overall diameter of the
cable.