US2818632A

US2818632A - Electrical connection and method

Info

Publication number: US2818632A
Application number: US311265A
Authority: US
Inventors: Kemper M Hammell
Original assignee: AMP Inc
Current assignee: TE Connectivity Corp
Priority date: 1952-09-24
Filing date: 1952-09-24
Publication date: 1958-01-07
Anticipated expiration: 1975-01-07
Also published as: NL180928B; FR1088004A; CH332285A; DE1763066U; DE1062782B; NL84266C; GB737150A; BE522982A

Description

Jan. 7, 1958 K. M. HAMMELL 2,818,632

ELECTRICAL CONNECTION AND METHOD Filed Sept. 24, 1952 1 E /Z INVENTOR t T q- 0 finals? M Alma/15.4.4 1'7 4 fiWJ/W ATTORNEYS:

United States Patent 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

7 Claims. (Cl. 29-15555) 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 open.- sided 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 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 maximum 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 Patented Jan. 7, 1958 ice 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 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 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 connector from which the wire extends and toward which mechanical pull will be exerted. Moreover, as indicated above, it should be sufiiciently spaced from both ends to make sure that it is well within the tightly forged connection and thus protected against corrosion. A plurality 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 preferred 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 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 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 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 forming 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 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 it 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 12%, 19, already curled, are thus forced down against the wire, pressing it solidly against the bottom of the ferrule portion 12. The final movement of the dies thus occurs with the connection confined on all sides by the die and its only avenue of escape by longitudinal extrusion. The movement is continued until the cross sectional area remaining in the recess of they die between the anvil 14 and the 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 sect on, 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 approxinately

semi-cylindrical surfaces

20, 21 in the top meeting 111 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 semi-- cylinders. 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 sufiicient 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 14in 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 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 elfect of this, of course, is to increase the height by changing the wire from circular to elliptical form and by squeezing apart 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 shouldbe 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 said diameter plus twice the thickness of the metal, and the height of the final forged connection should be about two-thirds to three-quartersor, 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 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 form ing portion is readily cammed into centered position on the anvil by the closing together of the dies, and in which the 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 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 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 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 otherwise 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,

' 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 satisfactory 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 inth art.

I claim:

1.The method of making electrical connection to a conductor which comprises forming a connector of malleable sheet metal with a ferrule-forming portion U-shaped in cross-section with the sides of the U flared to an inside diameter greater than that of the conductor and the diameter of the conductor being at least as great as the inside diameter at a point half the thickness of the conductor above the bottom of the U, inserting the conductor, and curling together the ends of the projecting sides of the U and driving them against the conductor, and forging at least a portion of the resulting ferrule and conductor to generally rectangular configuration of a width between and 100 percent of the diameter of the conductor plus twice the thickness of the metal of said ferrule-forming portion before said forging and to a height between 60 and percent of said width, said height being measured from the top of said curled ends to the mean depth below the maximum diameter, the forging including conforming the conductor by radial deformation and longitudinal extrusion to the inside surface of the ferrule.

2. The method of making electrical connection to a conductor which comprises forming a connector of malleable sheet metal with a ferrule-forming portion U-shaped in cross-section with the sidesof the U. flared. to an in.-

side diameter greater than that of the conductor and the diameter of the conductor being at least as great as the inside diameter at a point half the thickness of the conductor above the bottom of the U, inserting the conductor, and curling together the ends of the projecting sides of the U and driving them against the conductor, and forging at least a portion of the resulting ferrule and conductor to generally rectangular configuration of a width about 90 percent of the diameter of the conductor plus twice the thickness of the metal of said ferrule-forming portion before said forging and to a height about 75 percent of said width, said height being measured from the top of said curled ends to the mean depth below the maximum diameter, the forging including conforming the conductor by radial deformation and longitudinal extrusion to the inside surface of the ferrule.

3. The method as defined in claim 1 in which the conductor is forced down to the bottom of the ferrule-forming portion by the ends of said portion when curled back against the conductor, and the ferrule portion and conductor are compressed together laterally by being driven between slightly converging planar sides of a female die.

4. The method of making electrical connection to a conductor including the steps of forming a connector of malleable sheet metal with a ferrule-forming portion U- shaped in cross section; disposing the conductor in the ferrule-forming portion; curling together the ends of the projecting sides of the U and driving them against the conductor; and forging the resulting ferrule to generally rectangular configuration including applying pressure downwardly at the curled ends of the U and upwardly at the bottom of the U, simultaneously therewith applying downward and inward pressure to the sides of the U to decrease continuously the maximum lateral diameter of the ferrule during formation and to form therefrom planar ferrule sidewalls abruptly extending from the ferrule bottom at an angle of convergence of approximately 6 toward the curled ends, and conforming the conductor by radial deformation and longitudinal extrusion to the inside surface of the ferrule.

5. The method of making electrical connection to a conductor which comprises forming a connector of malleable sheet metal with a ferrule-forming portion U-shaped in cross section with the sides of the U flared to an inside diameter greater than that of the conductor and the diameter of the conductor being approximately as great as the inside diameter at a point half the thickness of the conductor above the bottom of the U, inserting the conductor, curling together the ends of the projecting sides of the U and driving them against the conductor, and forging at least a portion of the resulting ferrule and conductor to generally rectangular configuration to conform the conductor by radial deformation and longitudinal extrusion to the inside surface of the ferrule, the forging including applying pressure downwardly at the curled ends of the U and upwardly at the bottom of the U simultaneously with continuously decreasing the maximum lateral dimension of the ferrule being formed by applying downward and inward pressure to the sides of the U to form a ferrule having a width between and percent of the diameter of the conductor plus twice the thickness of the metal of the ferrule-forming portion before said forgmg.

References Cited in the file of this patent UNITED STATES PATENTS 1,706,005 Thompson Mar. 19, 1929 1,836,497 Phelps et al. Dec. 15, 1931 2,302,767 Hackbarth Nov. 24, 1942 2,327,650 Klein Aug. 24, 1943 2,535,013 Freedom Dec. 19, 1950 2,557,126 Macy June 19, 1951 2,600,012 Macy June 10, 1952 2,659,871 Berg Nov. 17, 2,692,422 Pierce Oct. 26, 1954 FOREIGN PATENTS 656,029 Great Britain Aug. 8, 1951