US2758491A - Crimping dies for electrical connectors - Google Patents

Description

Aug. 14, 1956 s BUCHANAN 2,758,491

CRIMPING DIES FOR ELECTRICAL CONNECTORS Original Filed Jan. 4, 1947 2 Sheets-Sheet l INVENTOR Szephenllzliuchanaa 14, 1956 s. N. BUCHANAN 2,758,491

CRIMPING DIES FOR ELECTRICAL CONNECTORS Original Filed Jan. 4, 1947 2 Sheets-Sheet 2 INVENTOR Sfep/ze'n MBuc/zanan 2,758,491 CR IMPING DIES FOR ELECTRICAL CONNECTORS Stephen N. Buchanan, Westmoreland Hills, Md., assignor to Aircraft-Marine Products Inc., Harrisburg, Pa.

Continuation of application Serial No. 720,296, January 4, 1947, which is a division of application Serial No. 559,604, October 20, 1944. This application December -6, 1951, Serial No. 260,125

3 Claims. (CI. 81-15) No. 720,296, filed January 4, 1947, now abandoned, which application was a division @of my priorapplication Serial No. 559,604, filed October 20, 1944, now Patent No. 2,554,813; which earlier application is a continuationin-part of my application Serial No. 421,408, filed December 3, 1941, now Patent No; 2,379,567, and application Serial No. 474,935, filed February 6, 1943, and later abandoned.

Connectors of the type which make mechanical and electrical connection by crimping onto'a conductor had been known before these inventions, but such earlier connectors Were not without inherent defects or disadvantages. In many of them the bond between the connector and the electrical conductor had not been sufficiently tight nor permanent to provide forall of the stresses which are imposed subsequently in use, with the result that the end of the electrical conductor sometimes pulled loose from the electrical connector. In other terminals the crimped portion which forms the bond between the connector and the conductor has been so deep that the ferrule of the connector and some of the wires of the conductor were seriously weakened, with the result that the tensile strength of the connection was unsatisfactory. Another defect found in many connections of this type lay in the fact that moisture or other foreign matter could creep into the compressed portion of the connector to promote corrosion of the contact surfaces and thus to lower the electrical conductivity through the connection.

It is an object ofthe presentinvention to provide .an improved connection wherein the connector is preman'ently attached to a wire or like member by a crimping operation. Another object is the provision of a crimped connection in which neither the ferrule nor the wire is damaged by the crimping. A further object is to previde a permanent electrical connection of high conductivity. Yet a further object is the provision of an improved method of connecting a ferrule to a wire. Still another object is the provision of crimped connectors having shapes and dimensions adapted to concentrate expansive forces in the strongest portions thereof. A further object of the invention is to provide a new and improved solderless connector in which a crimped ferrule is effectively held against bending and in firm gripping contact with the wires. Other objects will be in part pointed out as the description proceeds and will in part become apparent therefrom.

I .have by my present invention 'dem'onstarte'd that an electrical connector of the type provided with a ferrule for connection to a wire, etc., can be permanently attached to an electrical conductor by compression dies with a permanent low-resistance connection of highest quality, if the die surfaces which do the compressing are of size and form such that their dimensions bear a cerradius of curvature, the available force of compression may be utilized efficiently to compress the ferrule-and the conductor therewithin into a substantially solid and integral mass, and the residual stresses are balanced so that the contact surfaces do not spring back when the connection is released from the dies, but actually are held together under pressure .such that a truly conductive connection is established. p

The edge portions of the ferrule foldand undulate during the closing of the dies, and coining surfaces are pressed into the folds so re-distributing and work-hardening the metal as to destroy any tendency towardreopening,

'In this specification and the accompanying drawings Ihave shown and described a preferred embodiment of my invention and various modifications thereof; but it is to'be.understoodihat these arenot intended to be exhaustive nor limiting of the invention but, on the contrary, are given for, purposes of illustration .in order that others skilled .in the art may fully understand the invention and the principles thereof and the manner of applying it in practical use so that they may modify andadapt it .inlvarious forms, each as inay be best suited to the conditions of a particularuse. v In the accompanying drawings, in which .the invention is specifically illustrated:

Figure 1 :is .a perspective view of an electrical conhector attached to an elect ical conductor in a manner embodying the invention;

Figure 2 is an elevational view, partly in section, of a rolled ferrule typeelectrical connector;

Figure 3 is an end view of the electrical connector illustrated in Figure 2; I

Figure 4 is an elevational view, partly in section, of a modified form of rolled ferrule type electrical connector; I

Figure-S is an end view of the electrical connector illustrated in Figure 4;

Figure 6 is an elevational view, partly in section, of the electrical connector illustrated in Figures 2 and 3 positioned over the :end of an electrical conductor and between the jaws formed by a'pair of crimpng dies;

Figure 7 is a plan view of the 'die surfaces of the lower die of .Figure 6;

Figure .8 is a side elevation of the die of Figure 7;

Figure'9 is an elevational view similar to that of Figure 6 but showing the dies closed upon the electrical connector andc'rimping it onto the electrical conductor;

Figure 10 is aplan view of a crimped connector embodying the invention;

Figure .11:=is a sectional view taken-along the line 11-1'1'of Figure 10;

Figure 12 is a sectional view taken along the irregular line 12-12 of Figure 10; v

Figure 13 .is aplan view of a connector bearing, for purposes of illustration, n crimp not embodying the present invention;

Figure 14 is *a sectional view taken along the line 1414 of Figure .13; and

Figure v15 "is a view similar to that of Figure '14 but showing, by way of further example,ano'ther crimp not embodying thepresent invention.

Figures 2 and-3 illustrate an electrical connector, generally indicated by 20, having a ferrule portion 21 and a terminal contact portion 22. Preferably the electrical connector is made of relatively soft, tinned copper, that is, of copper sufficiently soft to be readily coined between crimping dies but at the same time such that it will retain a permanent set impressed by the dies tomaintain the high quality of the electrical connection. Fully annealed, pure, high-conductivity copper is advantageous in that it is readily formed as described and is workhardened by the bending and coining so that it cannot be as readily deformed from its crimped condition.

Figures 4 and 5 illustrate a modified type of electrical connector which may be used in practicing the invention. In this instance the electrical connector, gen erally indicated by 20a, includes a ferrule portion 21a, a terminal contact. portion 22a, and a seamless sleeve 23a positioned around the ferrule portion. Annular serra tions or ridges 24a are provided, in some instances, on the interior of ferrule portion 21a to afford an anchor between the electrical connector and an electrical conductor.

It has been found advantageous in an electrical connector of this type to form the ferrule portion 21a of dead soft, pure, ductile copper and to form the sleeve 23a of a relatively harder copper, so that the soft copper on the interior of the ferrule may be compressed with plastic flow into the fullest contact with every strand of the electrical connector and so thatthe metal will take a permanent set without spring back from the crimped condition, while the harder integumentary member will tend to restrain the deformation and thus hold the seam of the inner ferrule tightly closed and to some extent also may direct inwardly extrusion of metal from between the coining dies, whereby metal which otherwise might merely escape outwardly is accumulated in thickened borders around the coined areas such that the trapped stresses tend to maintain high pressure of the coined areas against the wire.

Figure 6 illustrates the electrical connector of Figures 2 and 3 positioned over the end 50 of an electrical conductor and caught between an upper die member 31 and a lower die member 32. Member 31 is provided with a concave die surface 33 while member 32 is provided with a concave die surface 34. These concave die surfaces lie, respectively, between upper fiat die surfaces 35 and lower flat die surfaces 36 and each of said surfaces 33 and 34 has a chord or width approximately equal to the diameter of the electrical connector ferrule. As shown for example in the drawing, the chordal dimension may be equal to the inside diameter of the ferrule; and it may vary from the over-all diameter of the ferrule portion of the connector to about three fourths of that diameter. (Note.-In' speaking of width of the crimp or'die, reference is being made to the horizontal dimension as shown in Figures 6 and 7, that is, the dimension crosswise of the ferrule; in speaking of length of the crimp or die, reference is being made to the vertical dimension in Figure 7 and horizontal dimension in Figure 8, that is, longitudinally of the ferrule.) Beyond the flat die surfaces there is provided on the upper die a pair of die stop portions 37 and on the lower die a pair of die stop portions 38, to be described in greater detail hereinafter.

Figure 9 illustrates the manner in which the concave die surfaces compress the electrical connector and conductor as die members 31 and 32 are brought toward one another during a crimping operation. The cross section and perimeter at the portion receiving the crimp are actually reduced and compressed; but the side portions of the ferrule, which lie between flat die surfaces 35 and into substantially perfect conformity with the contacted surfaces of the electrical conductor and to some extent in extruding metal of the ferrule from under the dies to the borders of the crimps.

With older types of crimping by dimple indentations (see Figure 15) or necking of the ferrule to smaller circumference, the closely packed wires around the exterior of the stranded conductor tend to form an arch or tube in which each wire is supported on the next, with the result that the strands of wire within such arch or tube are not satisfactorily compacted and corrosion easily enters the crimped area along the interstices between these wires. This tendency is minimized by the application of the crimping forces according to the present invention, as will be described, so as to displace some of the outer wires and cause collapse of the arch. At the same time, the concave surfaces tend to limit the extent of collapse and confine the strands of the electrical conductor so that the wire is not merely flattened, as would be the case if it were hit with a hammer or clamped in a vise (see Figures 13 and 14).

Although the shape of the crimp as shown in Figure 1 may appear difiicult to form in a die, I have found that it can be simply achieved as described and claimed in my application, Serial No. 474,935, filed February 6, 1943. Briefly, the die is made by forming a cylindrically-shaped transverse groove, thatis, a groove conforming to a portion of a cylindrical surface, in a simple dihedral angular die.

As best shown in Figures 7 and 8, each die member 31, 32 tapers toward the die surfaces; hence, the concave die surfaces 33, 34 become longer as they become deeper due merely to the taper of the die stock. The radius of curvature of the concave surfaces 33, 34 is somewhat greater than the outside radius of the ferrules upon which the dies are to operate so that, as the dies close upon a ferrule, the longer portions first come into contact with the surface of the ferrule. Figures 6 and 9 show how these longer portions of the die surfaces may be made to engage the ferrule along the seam where the butt edges of the ears of the rolled-up ferrule are brought together, so as to support these edges and to aid in keeping them from separating. Due to this greater area, the initial pressure exerted for collapsing the arching of the stranded wire produces first a flattening of the ferrule to elliptical form and a collapse of any tube or arch of wire strand, and then coining of the die into the top and bottom portions of the ferrule, as seen in Figure 6, with consequent flow of metal to the borders of the crimp area without excessive reduction in thickness at the center of the crimp area. In the final stage of the crimping (see Figure 9), the compression of the sides of the ferrule results in extrusion of metal from between the die surfaces at and beyond shoulders 40, 41, 42, 43 and back into the ellipitical space between the die surfaces 33 and 34, and at the same time in a readjustment of the metal in these side portions, which destroys any tendency to spring back from the flattened form.

The relationships between the radius of curvature of the concave die surfaces 33 and 34 and the outside radius of the ferrule, as Well as the angle subtended by the concave dies, are important; and a change in such relationships may result in one crimp which differs from another in no apparently material regard but having actually double the pull-out strength of the other crimp.

For maximum strength in the resulting crimp, the ratio of the radius of curvature of the concave die surface to the outside radius of the ferrule should be greater than 1, but small enough so that, when the distance between the flat die surfaces 35-36 is equal to the doubled thickness of the ferrule wall, there is still sufficient space within the collapsed ferrule to contain the solid cross-sectional area of wire 50. Obviously this limit depends upon the relation of the total solid cross section of the wire and the radius of the ferrule chosen to be crimped onto it. This choice, however, is-n otunlimited. If the ratio of radii becomes too great, that is, if the curvature of the die surfaces 33 and 34 becomes too flat, the holding power of the crimp will suffer. For best results I have used ratios on the range 1 /3 to 1% with best results at a ratio of 1.4 to 1.5. Good results are obtained when the subtended arc of each concave die surface 33 and 34 is in the range from about 60 to about 90. The best results have been obtained with an arc of about 85 -90. Correspondingly, the chordal distance across the concave die surface (that is, the chord of its arc) should be about 1% to 2 times the length of the outside radius of a ferrule to be crimped.

These relationships mean that the chordal distance will be on the order of four-fifths to one and one-half times the radius of curvature of the concave die surface for any given die. 7

Finally, the best results have been attained when the cross-sectional area of the crimped section (shown in Figure 9 between the dot and dash construction lines), neglecting the area of the copper extruded beyond the sides of the concave die segments 33 and 34, is, when the final coining step is completed and stops 3738 are brought together, about six tenths of the initial area included within the outer periphery of the ferrule before it was crimped. This relation is predetermined in the tool shown by the dimensions of the stop portions 37, 3 8, but it may obviously be determined in other ways.

It is to be noted that'the inventionpermits some latitude of sizes and shapes; that is, absolutely precise configurations are not essential. It seems to sutfice if the dimensions are kept within the general ranges specified. And correspondingly, the crimp surface need not follow a literally perfect arc. The arcuate shape appears to be best, but deviations therefrom are permissible.

In the ordinary construction prior to my present invention, if a ferrule were collapsed or bent onto a wire, after the bending or collapsing pressure had been released the two ferrule cars would have a tendency, to spring back or reopen outwardly along their fold lines, so that the gripping action on the wires would be somewhat relaxed. Also, if the two ferrule ears were not connected together along their line of juncture, they would tend to open farther, by bending outwardly along their fold lines under stresses encountered during use.

As a feature of the present invention, the ferrule is crimped in such a way as to give a secure grip and maintain a pressure contact. For that purpose it is important that, except for the folded edges, the ferrule walls are spread to a larger radius of curvature so that the tendency to spring back imposes pressure on the engaged wires. The special treatment according to this invention obliterates the tendency to spring back at the folded edges.

The ferrule is, in effect, corrugated on each lfaceb'y a series of narrow flattened areas formed at spaced positions to give alternate fold sections 25 and 26 .(see Figures 10-12) of different fold angles and thicknesses, as shown. This corrugation in itself gives rigidity; and beyond that it is my belief that the more acutely folded edges 27 have their tendency to spring back substantially obliterated by the coining, which causes plastic fiow of the metal in .the fold and thereby largely Wipes out stress conditions in the metal which may have been left from the bending of the Wall. The same pressure whichcoins the exterior of the ferrule under the die also produces coining on the interior so that the interior surface 'of the ferrule conforms more accurately to the surfac'esof the wires. The coining at the exterior, moreover, by extruding metal from under the die, causes a thickening of the borders around the crimp, so that these areas as well as the metal on the interior of the ferrule and in the wires, are stressed in compression; thus any tendency to recovery results in increase instead of diminution of the contact pressure. The strength of the crimp may also result, at least impart, from the fact that both the .bend- .ing and the plastic flow effect a work-hardening in these zones. r

Two of :the .depressedareae 25 on each .side -of .the ferrule are shown in .thedrawings spaced from the sides and ends of said ferrule to leavethe raised fold sections 26 at each end oftheferrule as well as between the two depressed areas '25, and to leave the bulges 27 at the sides of said ferrule. -As aresult :of this construction there is formed along each folded side .of the ferrule a continuous and .undulated border rib which adds to the rigidityof the ferrule, and which thereby aids .in resisting'the spreading apart ore'xpanding of the=opposed, de-

pressed wire-gripping sections 25.

By way of comparison contrast the crimp of Figures l()--12 with that of Figures 13 and 14, where the ferrule is simply flattened. 'The axis of the fold down eachside of the ferrule in Figure 1'3 forms substantially a straight line offering no great resistance to reopening. But the axis of the fold down each side of "the ferrule of Figure 1 0.has a distinct sinuoueness which offers inherent resistance to reopening. It cannot be reopened without further flow of metal to allow the fold axis to straighten. 7 Furthermore, the area adjacent crimp 25a is not reinforced toward the sides by longitudinal.swagingof metal, as is the case with 'the crimp @of- Figure 10. The metal is caused to l'flow "in my crimp into a bead surrounding .the

portions and wedge-like tool surfaces.

Figure 15 shows another type -:of crimped connection.

. Here, side walls 60 are drawn .around'crimp surface 2ft!) by the dimple-type crimp Iiiiipressed. During'the crimpin'g operation tensional stresses of considerable magnitude are set up in side walls '60. Any :elasticreturn of metal following the drawing operation would loosen the grip of the crimp. My crimp 'is not dependent upon any suchfdrawnconstruction. It is secure because of a combined cold flow and workeharden'in'g under compression. The reinforcinglpor'tio'ns 26 and the bead around thecrimp tend to maintain the compression. And in addition it is effective through the entire cross section of the crimp so as tocompact the whole and thus preclude longitudinal seepage of moisture and corrosion. But .a crimp such as shown in Figure 15 leaves a multiplicity of capillarylike interstices inviting deterioration, loss 'of holding power, and loss of electrical conductivity.

In the crimping operatiomitis desirable to form first one ,pairof opposed depressed area's'25, and then form the second adjoiningpair. 'In this way the crimped area first "formed is subjected to further compressive stress, as the result of the inherent resiliency of the ferrule metal, during the second crimping operation. This second crimping operation, therefore, imparts to said areas a more effective and corrosion resisting contact.

Tests of sample terminals made by sectioning through the crimped area have shown that themetaI of the ferrule and the metal of the wires within the ferrule are actually so pressed and fitted together thatno substantial voids are left between them; such perfection, however,

: is not necessary for many ,uses of the invention, and good electrical connections may bemadewith a lesser cornp'res'sion of the wires. Such sectioningis illustrated in theleft-hand .portion of Figure12. The right-hand half of this figure represents a section taken beyond the crimp.

.Accelerated corrosion tests have shown that with ter- 7 of cold welding between the wiresand ferrule, particularly in the case where tinned wire is used, or whether other coating of metal is present which exhibits a relatively high plastic flow or difiusion under the crimping pressure.

Another surprising advantage of the connection just described is in its extraordinarily high breaking strength. With an ordinary crimped-on terminal, the wire tends to be weakened so that it willbreak at the edge of the terminal with a pull very much below the normal tensile strength of the wire. With a single crimp, spaced at least one-sixteenth of an inch from the end of the ferrule and the crimp made substantially as shown, a pull test under vibration of approximately 90 per cent or more of the normal tensile strength of the wire is attained, but this falls off rapidly, as the edge of the crimp approaches closer than one-sixteenth of an inch to the edge of the ferrule, dropping to 50 per cent or less if the crimp actually overlaps the edge with a sharp-edged ferrule.

As a further protection against the reduction in tensile strength by crimping, the edge of the ferrule toward the wire is rounded or sloped gently in order to protect to a substantial extent against the effect described above; so that even if, the crimp is carelessly placed so as to overlap the edge, excessive reduction in the pull test strength would be avoided.

Advantageously, the-line of juncture 17 where the two ears of the ferrule are brought together extends centrally across the crimped areas so that on neither side of this line will the stock of the ferrulehave to act with an effective cantilever arm greater than one-half the width of the crimped ferrule.

The depressions 25 are preferably substantially ellipitical or segmental in plan (that is, simulating the area between a chord and its arc) except that the points may be cut off by short parallel sides 28, and are preferably arranged as shown. This results in an actual coining of the metal with production of lateral bulges 27 in which the side areas of the metal are compressed solidly into said bulges 27,'while the metal at the sections 26 between the two pairs of opposed depressions 25 and toward the ends of the ferrule retains a smooth elliptical cross section which, as described above, is reinforced by longitudinal extrusion of copper from the crimp areas. This construction also serves to afford optimum depressed areas 25 so as to grip effectively the wires 50, and to give maximum amounts of raised headlike areas along the folded sidesof the ferrule where it is needed most for rigidity.

The corrugations in the opposed facing surfaces of the ferrule formed by the alternate depressed and raised ferrule sections 25 and 26 serve not only to hold the ferrule as described against relaxing outwardly, butalso serve to wrinkle the wires in the ferrule. This wrinkling of the wires assists in preventing said wires from being pulled out of the ferrule.

Figure 1 shows generally crimps 25, such. as result from crimping operations as illustrated in Figures 6 and 9. The crimps there shown are only illustrative of my invention, however, and one, two or more crimps may be used, depending upon-the purposes for which the ferrule is intended. Likewise, the showing of Figures 6-9 is illustrative. The dies show n in Figures 6+9 may be closed together by anysuitable mechanism, power operated, or hand, or pedal operated. f

As many modifications of the invention are possible and as many variations in the forms illustrated and described will be necessitated in adapting the invention to the many instances in which it may be used, the accom panying specification and drawings should not be construed in any way to limit 'the scope of the invention. The scope of the invention, on the contrary, is intended to be limited solely by the boundaries defined by the accompanying claims. I

I claim:

1. In apparatus of the class described and adapted to crimp a ferrule onto an electricalconductor, a pair of dies having opposed die surfaces adapted to engage the ferrule between them and to compress it onto, and compact it with, the conductor, the central area of at least one of said dies being recessed to receive the central portion of the ferrule when thus compacted and portions of the die being extended laterally from opposite sides of said recessed area and adapted to compress portions of the sides of the ferrule, each die having two opposite sides Which taper dihedrally toward one another in thedirection of the working surface, the axes of the concave die surfaces extending substantially perpendicularly with respect to the plane of at least one of said opposite sides, whereby the more recessed portions of the concave die surface are of relatively greater length, and abutment means associated with said dies and operative to prevent further closing thereof after the area between the recessed die surfaces has been reduced to at least two thirds of the area of a circle of diameter equal to the width of said recessed die surfaces.

2. In apparatus of the character described, a pair of opposed jaws provided with crimping dies including: a central cylindrically concave die surface extending arcuately between a pair of fiat die surfaces disposed in the same plane, the length of the maximum chord across the arcuately concave central die surface being to the radius of curvaturev of said central die surface as the range of from one-and-one-third to two is to the range of from one-and-one-third to one-and-two-thirds, and said central die surface being longer at its more deeply recessed portions than where it meets said flat die surfaces; said apparatus including abutment means having portions defining surfaces which come into opposing contact to pre vent further approach of said jaws after the distance from the deepest part of one concave die surface to the deepest part of the other concave die surface is less than the length of said chord.

3. In apparatus of the class described and adapted to crimp a ferrule onto an electrical conductor, a pair of dies having opposed die surfaces adapted to engage the ferrule between them and to compress it onto, and compact it with, the conductor, the central area of at least one of said dies being recessed to receive the central portion of the ferrule when thus compacted and portions of the die being extended laterally from opposite sides of said recessed area and adapted to compress portions of the sides of the ferrule, each die having two opposite sides which taper dihedrally toward one another in the direction of the working surface, whereby the more recessed portions of the concave die surface are of rela tively greater length, and abutment means associated with said dies and operative to prevent further closing thereof after the area between the recessed die surfaces has been reduced to at least two thirds of the area of a circle of diameter equal to the width of said recessed die surfaces.

References Cited in the file of this patent UNITED STATES PATENTS 167,572 Seaver Sept. 7, 1875 507,892 Dyson Oct. 31, 1893 527,132 Teel Oct. 9, 1894 663,581 Rice Dec. 11, 1900 856,074 Lockhart June 4, 1907 1,336,610 Borchers Apr. 13, 1920 1,388,398 Adams Aug. 23, 1921 1,564,960 Horsman Dec. 8, 1925 1,727,895 Mraz Sept. 10, 1929 1,891,785 Siebert et al Dec. 20, 1932 ,2 ,89 Unger June 25, 1940 2,253,906- Lehman Aug. 26, 1941

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