Electrical connection and method

Jan. 7, 1958 κ. m. hammell 2,818,632

ELECTRICAL CONNECTION AND METHOD

Filed Sept. 24, 1952

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2,818,632

Patented Jan. 7, 1958

United States Patent Office provides a further mechanical key against pull-out and also provides an area of very severe extrusion wherein the longitudinal flow of the metal assures the exposure of fresh metal at the contact surfaces, and this being 5 well within the area of the crimp already described, it is, for reasons set forth, protected against entry of moisture or corrosive atmosphere which would allow the surfaces to be re-oxidized or otherwise corroded before they are fully united or forged together. This maintains a 10 low resistance conducting area of high current carrying capacity and an entirely permanent connection. Because there is some weakening of the wire due to the reduced cross section in the indented area, it is advantageous to have the indented area well beyond the end of the con15 nector from which the wire extends and toward which mechanical pull will be exerted. Moreover, as indicated above, it should be sufficiently spaced from both ends to make sure that it is well within the tightly forged connection and thus protected against corrosion. A plu20 rality of such indents may be used if desired, and in such case it is advantageous to have them progressively deeper in a direction away from the end of the connection from which the wire extends on which the pull will be exerted.

In the accompanying drawings I have shown a pre25 ferred embodiment of the invention and a die set in which the crimping or forging is effected. In these drawings

Figure 1 is an isometric phantom view of the die set at the beginning of its operation for applying a terminal connector to an ordinary insulated wire conductor with 30 the end of the wire stripped to make contact with the central conductor;

Figure 2 is a similar view of the same die set at the end of its operation, showing a connection forged thereby on the end of a wire;

Figure 3 is an enlarged cross section of a connection made as illustrated in Figures 1 and 2; and

Figure 4 is a fragmentary view in longitudinal vertical section of a modified die set and electrical connection crimped therein.

Referring to these figures and an illustrative example, a #14 wire AWG has a diameter of 64 mils (.064). The terminal connector used for this is made of sheet metal of twenty mils thickness (.020), and the ferrule forming portion thereof is formed to a U shape cross section with a rounded bottom and substantially straight ⁴⁵ sides flaring a little toward the top to facilitate gathering in of the wire. The diameter of the U, measured at a height of thirty-two mils above the bottom inside surface of the U (at a height equal to the radius of the wire), is approximately equal to, but advantageously a little ⁵⁰ less than, the diameter of the wire, in the present example about sixty mils, and the inside of the U flares to a width a little greater than the wire, e. g., to about ninety mils i. d.

With the terminal connector 10 having its ferrule form⁵⁵ ing portion 12 positioned on the anvil 14 of the die set as shown, the dies 14 and 16 are brought together to a position shown in Figure 1. The wire 17 may be inserted into the upper part of the U of the connector portion 12 or into the female die 16 above the connector. In any ⁶θ case, as the dies are closed together, the upper ends of the portion 12 are forced along the converging surfaces of the recess in the female die 16 and eventually meet over the ridge in the top of the female die recess, thus gathering in the wire if it was not already positioned within the ferrule portion 12. Further movement of the dies toward one another drives the ferrule portion 12 up into the top of the recess in the die 16 and the ends 18, 19, already curled, are thus forced down against the wire, pressing it solidly against the bottom of the ferrule portion 7° 12. The final movement of the dies thus occurs with the connection confined on all sides by the die and its

2,818,632

ELECTRICAL CONNECTION AND METHOD

Kemper M. Hammell, Harrisburg, Pa., assignor to AMP Incorporated, a corporation of New Jersey

Application September 24,1952, Serial No. 311,265

Claims. (CI. 29—155.55)

This invention relates to connecting electrical conductors to other electrical elements and to electrical connections. More particularly, the invention relates to pressure-forming (which will be referred to herein as “forging”) of ferrules of electrical connectors onto conductors and to forged connections.

Prior to my invention one of the epoch-making advances in the art of terminating wires and making other electrical connections to conductors was the use of opensided ferrule connectors (i. e., sheet metal portions formed to a U-shaped cross-section applied in a die with sloping sides and bottoms smoothly curved from each side to a central ridge, the wire being gathered in by the legs of the U which scrape the sides of the die and are curled back toward the bottom of the U and the whole being ultimately compressed in the die with the entire periphery being confined so that the ferrule and conductor are forged into a solid mass and the metal flowed in a lengthwise extrusion as well as transversely to fill voids in the cross-section. In order to facilitate entry of wire into the ferrule it has ordinarily been made about 25 percent wider in internal diameter than the end of the wire and, since the forging is done between dies moved toward one another the final compression has resulted in flattening the connection. This has left the free edges extended across the top relatively long compared with their thickness and thus has limited the rigidity with which they can maintain pressure on the central seam area of the connection. In many cases the dies have been designed to come together in the final compression so that their concave surfaces are substantially contiguous and the resulting connection is smoothly elliptical in cross-section.

I have now found that a substantially better and especially a stronger connection, which will retain its low electrical resistance better over very long and severe usage, results when the connection is forged to a more nearly square cross-section. The curled ends at the top of the forged portion are retained as before and the bottom may be convex if desired, although a flat bottom is better (for purposes of this application a convex bottom is treated as though it were flat with the same cross-sectional area; i. e., at the same mean depth below the maximinn diameter). The sides however are flat and substantially perpendicular to the bottom. Thus the curled ends at the top are keyed to the forged metal of the conductor against outward movement which could relax the tight pressure engagement at the sides of the connection, while the curled ends themselves are curled on such short radius compared to their thickness that they are essentially rigid and do not relax resiliently. With the pressure engagement thus maintained over the length of the forged connection a secure mechanical engagement is assured and corrosion does not work up between the contact surfaces.

For special cases, and especially with aluminum wire or like conductors, a still more secure connection is made if projections are provided in the bottom die, especially with transverse ridges of sufficient height and width to indent the ferrule wall inward into the conductor. This

2.818.632 only avenue of escape by longitudinal extrusion. The movement is continued until the cross sectional area remaining in the recess of the. die between the anvil 14 and die bottom of the recess in the die 16 is substantially less than the solid, cross-section of the wire and the ferrule portion of the connector before the crimping began, thus assuring flow of metal in the die to produce a solid cross section, and additoinal longitudinal flow resulting in extrusion as stated above, and altering the stress relations in the metal of the ferrule portion which would otherwise tend to cause the metal to spring back away from the wire.

The overall dimension of the ferrule forming portion at a height above the inside of the bottom equal to the radius of the wire is sixty mils plus forty mils (twice the thickness of the ferrule metal), and this tends to be expanded somewhat when the wire is driven down into the bottom because of the four mils greater diameter of the wire than the interior diameter of the ferrule portion.

The recess in the female die is formed with two approximately semi-cylindrical surfaces 20, 21 in the top meeting in the central ridge. Actually, these are somewhat less than semi-cylindrical since the radius of their curvature is slightly more than one-quarter of the width of the die recess at the level of their axes of curvature. This radius may be, for example, between twenty-three and twentyfour mils instead of twenty-two and. a half mils as would be necessary to give two complete and tangent semicylinders. The sides 22 and 23 of the die recess are tangent to the sides of the cylindrical surfaces 20, 21 respectively, and may be parallel for a short distance, as described above, or for ease in manufacturing may be slightly flared from the surfaces 20, 21,. e. g., may be tangent to the cylindrical surfaces at 3 ° to the axis of symmetry of the die recess (6° included angle between the sides). In any case, from approximately the level of the die surface of the anvil 14 at the fully closed position, the sides 22, 23 are flared at said 3 ° angle for a substantial distance until the inside diameter between the sides is at least equal to the o. d. of the ferrule forming portion at radial height above the bottom. After sufficient diameter has thus been reached, the sides of the recess are more sharply flared, e. g., at an angle of 45 °, this portion of the die recess serving to automatically position the ferrule forming portion of the connector, and may also give the initial inward bending of the flared sides of the ferrule portion.

The bottom of the die at a height equal to the radius of the wire plus the thickness of the ferrule has a width of ninety mils, and this width is maintained substantially to the level reached by the anvil 14 in the completion of the final forging operation. The anvil 14 has a width to give a close fit in this portion of-the female die 16. Thus, the ferrule forming portion is compressed laterally by the converging sides of the female die as it is driven up. into the die during the crimping operation, the compression being from 100 mils diameter (60 i. d. plus 20 metal thickness at each side) to 90 mils diameter, and at the same time, as indicated above, the wire within has been compressed from sixty-four mils diameter to the smaller i. d. of the ferrule after compression, presumably of the order of fifty-five mils. The first effect of this, of course, is to increase the height by changing the wire from circular to elliptical form and by squeezing a part of the metal from the bottom of the U into the sides, but in the final compression step the dies come together until the height is about seventy-five percent of the width and, as pointed out above, this requires substantial flow of the metal under the forging pressure of the dies.

Although I have given in this example preferred dimensions, it is of course possible to vary these dimensions appreciably without departing from the scope of the present invention. In general the width of the die in the portion into which the ferrule is finally compressed should be no greater than the diameter of the wire plus twice the thickness of the metal of the ferrule, but should be between eighty and one hundred percent of- said¹ diameter plus twice the thickness of the- metal, and’ the height of the final forged connection should be about two-thirds to three-quarters or, at the outside, from sixty percent to eighty-five percent of the width of the forged connection. Obviously, the lower heights would have to be used with 5 the greater widths in these ranges, and vice versa. The 3° angle and 45° angle in the female die are not critical, but are respectively angles at which the open ferrule forming portion is readily cammed into centered position on the anvil by the closing together of the dies, and in which the 10 ferrule portion and the wire can be laterally compressed by being cammed along the converging sides when driven to the bottom of the recess.

In Figure 4 is shown a modified anvil and the connection crimped thereon. In this case transverse blunt ridges 15 are provided which indent the ferrule wall into the wire at a position or positions spaced from the ends for the purpose and results indicated above.

My invention is applicable to either solid wire or stranded wire. Since solid wire does not have the voids 20 between the strands to be filled, it does not require the same degree of lateral flow in the metal in the wire, and therefore can be satisfactorily crimped, with less lateral compression with respect to the initial diameter of the wire than in the case of stranded wire, 'but it is important in 25 either case that the metal be flowed so as to give a substantially solid cross-section which substantially fills the inside of the curled ends 18 and 19, and thus keys them against lateral movement which might open the seam. This keyed-in form, moreover, combined with the other30 wise nearly square cross-section, gives a security toward torsional stress and alternating torsional stresses, which is most important with solid wire.

One of the important advantages of this type of connection is its ability to handle very small wires. Thus, 35 wires as small as #36 have been successfully connected in terminals crimped in accordance with the present invention, and wires as small as #48 have been crimped together with larger wires by the present invention, both under commercial conditions of operation, and. giving sat40 isfactory performance requirements. This advantage of the crimp appears particularly when wires of eighteen gauge and smaller, are used in the comparison with other available types of crimped connection.

As will be clear to those skilled in the art, this invention is well applicable either to machine application, as, for example, with machines illustrated in the copending application of Harold E. Cootes, Serial No. 65,645, filed December 16, 1948, or to hand tools of the pivoted jaw or parallel action type, such as are now in common use in the art.