US3112150A - Electrical connections - Google Patents

Description

Nov. 26, 1963 K. M. HAMMELL 3,112,150

ELECTRICAL CONNECTIONS 5 Sheets-Sheet 1 Filed Aug. 16, 1956 IN VEN TOR.

Kemper Hqmmt Nov. 26, 1963 K. M. HAMMELL ELECTRICAL CONNECTIONS Filed Aug. 16, 1956 3 Sheets-Sheet 2 IN VEN TOR. Kemyer Mrflamme Nov. 26, 1963 K. M. HAMMELL ELECTRICAL CONNECTIONS 5 Sheets-Sheet 3 Filed Aug. 16, 1956 IN VEN TOR. Kemyer Humme" M W+W United States Patent 3,112,150 ELECTRICAL C0 CTIONS Kemper M. Hammell, Harrisburg, Pa, assignor to Aircraft-Marine Products, Inc, Harrisburg, Pa. Filed Aug. '16, 1956, Ser. No. 604,544 2 Claims. (Cl. 339-276) This invention relates to electrical connectors and connections between such electrical connectors and wires.

In the art of manufacturing crimpable electrical tenninals and connectors from strip metal stock by progres sive die forming operations, the thickness or gauge of the strip is of importance for several reasons. A high quality crimped connection between a wire and a connector or terminal must be mechanically strong, must possess a high degree of electrical conductivity, and must maintain its electrical and mechanical integrity under deleterious conditions such as vibration, temperature cycling and corrosive conditions. In the past it has been found that from the standpoint of most electrical and mechanical properties, the connector should be manufactured from metal stock of at least some minimum thickness which will be dependent upon the particular type and size of the connector and the manner in which it is crimped. If metal stock having a thickness less than this minimum thickness is employed, the electrical and mechanical properties of the crimped connection will be inferior.

However, other considerations encourage the use of relatively thin gauge strip metal in the manufacture of electrical connectors and terminals. In the first place, the thinner the gauge of the strip metal from which the connector is formed, the lower will be the cost of the connector since thinner strip material is cheaper than thicker material and can be more easily formed into a connector by progressive die forming operations. An additional consideration is that some types of connectors and terminals are adapted to receive a complementary mating connector and grip this complementary connector resiliently to form an electrical connection. With this type of connector it is desirable, if not essential, that the receptacle portion (which is adapted to receive the complementary element) possess a degree of resilience such that it will firmly grip the complementary mating connector to form a sound and electrically conductive connection. For connectors of this type the receptacle portion should be of relatively thin stock since the resilience of the connector decreases as the thickness of the stock is increased above an optimum level.

It is thus apparent that antagonistic factors enter into the determination of the thickness .or gauge of the metal stock from which electrical connectors are manufactured. In the past it has frequently been necessary to fix the thickness of the stock on .the basis of a compromise between those factors which would require a relatively thick strip stock for the crimped part or the connector and those other factors which indicate the use of a relatively thinner stock such as material costs, die-forming costs and the desirability of having a resilient receptacle.

A further problem which confronts the art of forming electrical connectors and terminals by progressive die forming operations is that of providing grooves or serrations on the interior of the wire barrel or wire ferrule of the terminal. Commonly, connectors and terminals include a wire barrel or wire ferrule portion which, when crimped onto the wire, is in close electrical and mechanical contact with the stripped end of the wire. It is desirable to provide serrations or grooves on the internal surface of this wire gripping fenrule in order to improve the electrical and mechanical properties of the crimp as dis closed, for example, in the copending application of Kemper M. Hammell, Serial No. 361,205, filed June 12,

. 3,1 12,159 Patented Nov. 26, 1963 -3, for Electric Connector. Where the connectors or terminals are formed by progressive die forming operations upon strip metal, it is difficult to form such grooves or serrations by a simple coining operation for the reason that coining causes longitudinal extrusion, or flow, of the metal. Such flow changes the pitch of the terminals being formed and this in turn necessitates changing the spacing of the forming dies which operate on the strip after the elongation takes place. It is difficult to make such changes in the spacing of the dies because of the very close tolerances involved in the dieaforming of terminals.

'It is an object of the present invention to provide an improved electrical connector or terminal which can be manufactured of relatively thinner gauge strip metal than has heretofore been practical.

A further object of the invention is to provide an improved connector or terminal of relatively thinner gauge stock metal which when crimped onto the end of a. wire exhibits improved electrical and mechwical properties.

A further object of the invention is to provide a connector providing a wire barrel forming portion having depressions thereon which can be formed by an operation which does not involve changing of the pitch of the strip during a progressive die forming operation.

It is a further object of the invention to provide a solderless connector which is simple, durable, rugged and economical to manufacture, and which will effectively withstand severe service, and meet the most rigid electrical requirements.

Other objects and attainments of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings in which there is shown and described an illustrative embodiment of the invention; it is to be understood, however, that this embodiment is not intended to be exhaustive nor limiting of the invention but is 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 it in various forms, each as may be best suited to the conditions of a particular use.

In the drawings:

FIGURE 1 is aview in elevation of a pair of integrally connected terminals embodying the invention;

FIGURE 2 is a perspective view of one of the terminals shown in FIGURE 1;

FIGURE 3 is a perspective view of a wire termination showing a terminal of a type of FIGURE 1 crimped onto the end of a wire;

FIGURE 4 is a greatly enlarged view taken .on a cross section parallel to the axis of the wire barrel forming portion of a terminal of the type shown in FIGURE 1, indicating the microstructure of this terminal prior to its being crimped onto the end of a wire;

FIGURE 5 is a fragmentary cross sectional view showing the die forming operation in which the corrugations of the terminals of FIGURE 1 are made;

FIGURE 6 is a cross sectional view of a preferred type of crimped connection in accordance with the present invention;

FIGURE 7 is a fragmentary view of a crimping die set of the type which will produce a crimped connection of the type shown in FIGURE 3 in crimping a connector of the type shown in FIGURE 1;

FIGURE 8 is a view similar to FIGURE 6 showing an alternative type of crimped connection in accordance with the invention;

FIGURE 9 is a view similar to FIGURE 6 showing another type of crimped connection in accordance with the principles of the invention;

FIGURES 10 and 11 are views of a modified die set similar to the die set of FIGURE 7 usable to crimp connectors of the type shown in FIGURE 1 in accordance with the invention, FIGURE 11 being taken along the lines I-I-II of FIGURE and FIGURE 12 is a perspective view of a progression showing the various stages in the progressive die forming from strip material of strip terminals of the type shown in FIGURE 1.

The reference numerals 2 generally indicate a commonly known type of wire termination which is advantageously manufactured from a strip material by progressive die forming operations and which is usually supplied in strip form, each connector being joined to the next adjacent connector by means of a slug 4. These connectors provide a receptacle portion having a base or floor 6 from which extend a pair of overhanging flanges 7 which are adapted to receive the tab 9 of a complementary terminal thereby to form an electrical connection between two terminated wires. Adjoining the receptacle portion 6 is a wire ferruledorming portion 8 of troughlike or U-shaped cross section having upstanding sidewalls 16 which are beveled at their tops as indicated at 20. When the terminal is crimped onto the end of a wire, the upstanding sidewalls 16 of this wire ferrule-forming portion are inwardly curled towards each other and bent downwardly to cause them to enter the wire strands as shown at 8 of FIGURE 3, it being preferable to provide bevel 20 in order to facilitate complete downward movement of the edges 26 after these edges meet during the curling operation. Adjoining the 'wire ferrule-forming portion 8 is an insulation ferrule-forming portion 10 which comprises upstanding sidewalls 18 which are curved and bent against each other over the end of the insulation 12 of the wire. The edges 22 of sidewalls 18 are also beveled in order to facilitate the crimping operation and to promote close contact of the edges when the sidewalls are crimped against each other and downwardly onto the wire as shown at 10'.

The invention herein disclosed and claimed is applicable to a great number of types of terminals, particularly those formed by progressive die forming operations. It should be realized at this point, however, that the invention is disclosed with particular reference to the type of terminals shown in the drawing for the reason that with this type of terminal the thickness of the stock from which the terminal is to be made presents a particularly vexatious problem. The stock should preferably be relatively thin insofar as the receptacle portion 6 is concerned in order that the overhanging flanges 7 will possess the requisite degree of resilience so that the tab 9 will make satisfactory electrical contact with the receptacle and may be connected and disconnected from receptacle 7 repeatedly. However, the crimped connection between the wire gripping ferrule 8 and the stripped end of the wire 12 should be sound and secure from both an electrical and mechanical standpoint and to this end, it is desirable to use a somewhat thicker gauge metal than that which would be the optimum thickness for the receptacle portion 6 from the standpoint of resilience. However, if the terminal is made in accordance with the principles of the present invention, the metal used may be of the optimum gauge (i.e. relatively thin) insofar as the receptacle portion 6 is concerned and notwithstanding this fact the crimped connection 8 will be electrically conductive, mechanically strong and resistant to the deleterious effects such as vibration, corrosion, etc.

. According to the principles of the invention as applied to the disclosed type of terminal, I provide a plurality of outwardly displaced sections or corrugations on the wire ferrule-forming portion 8 which result in the formation of ribs 24 on the external surface of this portion of the terminal and depressions 26 on the internal portion thereof, the preferred manner of imparting this configuration to the wire ferrule-forming portion being shown in FIG- URES 5 and 12. Referring to FIGURE 12 it can be seen that the terminals are produced from strip material 3 which is formed in a series of dies to carry out the various cutting, blanking and bending ope-rations involved. After the blank portion 5 of the strip is formed, which blank portion ultimately becomes the ferrule-forming portion 8, the strip is passed under a die set of the type shown in FIGURE 5 comprising an upper die 28 having projections 32 depending therefrom and a lower die 30 having depressions 34 therein beneath projections 32. The dies should be so arranged that when die 28 is bottomed, a slight clearance 36 remains between the strip material and the face of the upper die. As this die 28 bottoms the metal immediately beneath the projections is displaced downwardly and into the depressions 34.

It will be noted from FIGURE 5 that depressions 34 in die 36 are somewhat broader than projections 32 on die 28. As a result of this relationship, the depressions 26 in the uncrimped terminal extend into the ferrule forming portion a greater depth than projections 24 project beyond the ferrule-forming portion. However, projections 24 are broader than depressions 26 so that the thickness of the strip is not materially reduced, if it is reduced at all, by the action of die set 28, 39.

Preferably, and in common practice, the strip material 3 will have a direction of rolling indicated by the arrow in FIGURE 12 so that the microstructure of the strip will, as shown schematically in FIGURE 4, consist of elongated and flattened grains extending parallel to the direction of rolling or, in other words, parallel to the longitudinal axis of the strip. After downward displacement of the metal is effected by die set 28, 30, the grains at each end of the displaced section will exhibit an abrupt downward turn while the microstructure within the displaced section itself will exhibit elongated and flattened grains which are substantially undisturbed and which present substantially the same appearance as the metal on each side of the downwardly displaced section. In other words, the elements beneath projections 32 are shifted as units downwardly in FIGURE 5 into the depressions 34 and during such shifting or displacing of these elements, the grains in zones on each side of the shifted elements are deformed although the grain structure with in each element is not altered. Thus these discontinuities in the grain structure at each end of the displaced metal constitute zones of deformed or cold worked metal circumferentially coextensive with the displaced metal and bordering it on each side thereof. In FIGURE 4 zone 38 of cold worked metal, indicated by shading on each side of the rib 24, borders the rib and its corresponding depression 26.

Hardness tests show a higher average hardness in these zones than in adjacent areas as indicated by the hardness data in Table A (below. These data were obtained by measuring the hardness with a Vickers hardness tester (25 gram load) on a longitudinal cross section of a specimen of the type shown in FIGURES 1 through 3 which specimen was of fine grained 70-30 brass, 0 .016 in thickness. Hardness test indentations were made in the areas indicated at a, b, c, d, and e in FIGURE 4, the areas b and d constituting the cold worked zones, the area 0 being within the displaced section, and the areas a and 2 being on each side of the displaced section and remote from the cold worked zone. The values given are averages of hardness tests taken on two different specimens.

Thus hardness and microstructure are distinguishing characteristics of uncrimped terminals manufactured in accordance with principles of the invention as compared with tenninals provided with depressions or serrations produced ll" manner such as 'by a simple coining operahowever, that the hardness values given in Table A are not absolute values that will be encountered in every instance in which the invention is practiced since the hardness of the strip itself will vary depending upon such factors as its composition, the degree to which it has been cold worked during rolling and the heat treatment, if any, which it had previously received. Also the increase in hardness at the cold worked zones will depend upon similar factors. The data of Table A clearly show, however, that cold work has been performed in the localized zones on each side of the displaced section of metal.

An important feature of the invention insofar as the formation of the outwardly displaced section of metal is concerned, is the fact that the cold forming operation of FIGURE does not result in any change in the pitch of the strip as indicated on FIGURE 12 by the letter F. As briefly explained above, in a progressive die forming operation of the type illustrated in FIGURE 12, it is highly desirable that this pitch remain constant and that it not be changed by any of the various forming operations. This is particularly true where the terminals are formed head-to-tail as in FIGURE 1. If the pitch is increased by one of the early die forming operations, it is very difficult to maloe proper allowance (is. in the spacing of the forming dies) for this change in pitch in the later stages of a precison progressive die set and such allowance for a change in pitch must be made in order for positioning the strip properly. In the practice of the instant invention, the depressions 26 and ribs 24 are produced, by what I call, for want of a more exacting term, a combination of a coining operation and a drawing operation. The die forming operation of FIGURE 5 is a drawing operation insofar as the upper die 28 functions as a drawing punch and it is a coining operation in that the metal is forced into the depressions for relieved portions 3 4 of lower die 30 to permit a restricted or limited amount of metal displacement. In a normal drawing operation shrinkage always occurs and in a normal coining operation, extrustion occurs relative to the face of the dies. In the practice of the instant invention, the sizes of the punches 3-2 and the sizes of the depressions 34 are chosen such that the tendency toward shrinkage is offset by the tendency toward extrusion brought about by the coining aspect of the operation.

Terminals manufactured in accordance with the invention can be crimped in one of several ways as shown in FIGURES 6, 8, and 9 to produce crimped connections having somewhat differing appearances and characteristics, all of which types of crimps ofifer decided advantages over the prior FIGURE 6 shows a preferred type of crimped connection which is obtained if a terminal of the type shown in FIGURE 2 is crimped in a die set of the type shown in FIGURE 7. This die set comprises an upper die .40 having slanted sidewalls 41 which meet at a cusp 43. A lower die 42 is adapted to receive the terminals as shown in phantom in FIGURE 7 so that as upper die 40 approaches lower die 42 the upstanding sidewalls 16 of the terminal are curled inwardly towards each other and then bent downwardly and forced within and among the wire strands. As upper die 40 bottoms the crimping force is concentrated upon the outstanding ribs 24 on the external surface of the terminal as indicated by the arrow in FIGURE 4. This concentrated force pushes the displaced sections of metal at least partially, and usually almost entirely, hack into their original positions so that they are corplanar or nearly co-planar with the portions of the ferrules separating the displaced metal sections. As shown by FIGURE 6, after crimping, shallow notches remain at each side of the sections of metal which had, in the forming and crimping operations, been displaced outwardly and inwardly.

It can be additionally noted from FIGURE 6 that in the crimped connection the bottom or base of each dein some other tion. It is understood,

pression 26 assumes a somewhat arcuat'e, inwardly convex form while the bands of metal separating the displaced metal 24' are outwardly convex as indicated by the convex surfaces 44 and the surface 46. These arcuate surfaces are probably formed by the effect of the concentrated crimping force, as indicated by the arrow in FIG- URE 4. It should be mentioned, however, that arcuate surfaces 44, 46 mayor may not :be produced in the practice of the invention, depending upon the extent to which the terminal is crimped. FIGURE ,6 shows the ideal .case, the arcuate surfaces 44 and 46 being slightly exaggerated in the interest of clarity of disclosure. 1

It is also apparent from FIGURE 6 that as the crimp is made, the wire of the conductor 14 is forced to flow inwardly to the depressions thereby providing the desirable keying or locking effect which has been recognized as a beneficial feature in crimped connections.

FIGURES 8 and 9 show alternative types of crimped connections in cross section which can be produced with terminals of the types. shown in FIGURE 1, but with slightly modified dies as shown in FIGURES 10 and 11. In these figures, the reference numeral 40' indicates an upper die similar to die 40', and 42 indicates a lower die or anvil corresponding to anvil 42 of FIGURE 7. Die set 40', 42' differs from the die set of FIGURE 7 in that there are provided a plurality of depressions 48", 50 on the upper die and lower die respectively which receive the ribs 24 of the terminal project during the crimping operation. It is, of course, necessary to space the depressions 48, 50 by the same amount as the ribs 24 are spaced from each other in the terminal and in this respect the dies of FIGURES 10 and 11 require a high degree of exactitude in manufacture and operation. The depth of the depressions 48, 50 will to some extent determine the characteristics and physical structure -as explained below.

Where the indentations 48, 50 are of substantially the same depth as the height of the ridges or ribs 24 on the terminal barrel, a crimp of the general type shown in FIGURE 8 is produced. The ribs 24 project upwardly above the surface of the ferrule substantially the same distance as do the ribs 24 of the uncrimped terminal. Also, when the crimp is made with depressions 48, 50 of about the same depth as the height of the ribs 24, the bands of metal separating the displaced metal sections do not tend to assume an arcuate cross section. The crimp of FIGURE 8 of course provides keying or locking of the strands of the wire 14 as does the crimp of FIGURE 6.

Referring now to FIGURE 9, a crimp of this type will be produced if the depressions 48, 50 are made somewhat deeper than the height of the ribs 24 on the terminal barrel. Where this is the case, the crimping operation will result in some small amount of flow of metal in the vicinity of the ribs and the depressions, and as a result these ribs and depressions 24", 26, will be accentuated somewhat as a result of the crimping operation. This phenomenon enhances the keying effect between the conductor 14 and the terminal and in this respect it improves the quality of the connection. Again, as in FIGURE 8 the crimp of FIGURE 9 does not provide the arcuate bands as shown in FIGURE 6. It will be apparent that in order to obtain the arcuate effect of FIGURE 6 it is then necessary to concentrate the crimping force on the upstanding ribs 24 whereas in the modifications of FIG- URES 8 and 9 the actual crimping force is either evenly distributed over the entire surface of the ferrule-forming portion (FIGURE .8) or is concentrated on the areas separating the ribs 24 (FIGURE 9).

. The improved tensile or pull out strength afforded by the practice of the invention is shown by the results of a series of tests conducted with terminated wires of the type shown in FIGURE 3. The tests were conducted with three different wire sizes and one size connector in two different thicknesses. In the case of each wire size, pull out tests were conducted on connections between the wire and a connector of 0.018" stock which connector did not embody the invention, between the wire and a connector of 0.016" stock which did not embody the invention and between the wire and a connector 1 Readings exceeded scale of 110 lbs.

It is apparent from the data presented in Table B that for the conditions there reported, the invention permits a reduction in the metal stock thickness of 0.002" (i.e. from 0.018" to 0.016") without detracting from the pull out strength of the crimped connection; in fact, in the case of a #12 wire and a #14 wire, a marked improvement in pull out strength is obtained when a connector of 0.016 stock embodying the invention is substituted for a connector of 0018" stock which does not embody the invention. In the case of #16 wire, an improvement is obtained in that the minimum pull out strength is 64 pounds for a 0.016" connector embodying the invention as against a pull out strength of 58 pounds for a 0.018" connector which does not embody the invention. The data of Table B show clearly that if the thickness of the connector is decreased from 0.018" to 0.016" without incorporating the invention into the latter connector, the pull out strength is reduced materially.

From the foregoing description it will be apparent that crimped connections in accordance with the invention differ structurally in several respects from crimped connections of the prior art and it will be apparent from the test data presented above that markedly improved results are obtained in the practice of the invention. In the paragraphs which follow there is presented a discussion of some of the factors which, it is believed, contribute to the improved results obtained. It is to be understood, however, that applicant does not intend to be bound to the theories presented and that this discussion is not presented as limiting of the invention but only in the interest of completeness of disclosure.

Pull out or tensile failures of crimped connections of the type shown in FIGURE 3 frequently occur as a result of opening up of the ferrule 8' as the wire 12 and the terminal are pulled apart, particularly when the wire is relatively large as compared to the thickness of the connector. Also, under some circumstances the ferrules 8' have some tendency to spring back or to spring upwardly after the crimp is formed and if this occurs, the ferrule is partially opened and the connection is thereby weakened. It follows that for a mechanically and electrically sound crimp the tendency of the ferrules 8' to spring back after crimping and their tendency to open up when a tensile load is applied must be nullified. In the instant invention it is believed that these tendencies are nullified by the following factors.

It is likely that the zones of hardened metal 38 which border each set of depressions and ribs contribute to the strength of the crimped connection. The relatively severely cold worked metal in these zones has less tendency to spring back after the crimping operation and would tend to take the set of the crimp more permanently than would metal which has not been cold worked by displacement. These zones 38 thus constitute bands of hardened and stiffened metal which reenforce the crimp. Additionally, it is possible that the strength of the crimp is enhanced by virtue of the slightly arcuate configuration of the bands 44. Such bands of arcuate cross section would offer a greater resistance to being sprung apart or opened up than would a band having non-arcuate cross section. Other factors may contribute to the improved pull out strengths obtained, for example, the ribs 24" and 24 of the embodiments of FIGURES 8 and 9 would tend to reenforce the ferrules in the same manner that the corrugations commonly provided on metallic drums reenforce and strengthen such drums.

While I have here disclosed preferred embodiments of my invention it will be obvious to those skilled in the art that modifications thereof might be made within the scope of the appended claims and the spirit of the invention. It is contemplated that the ribs in the terminals as disclosed in my invention might be provided for instance on the insulation ferrule-forming portion 10 of the terminal as well as on the wire ferrule-forming portion 8. Such provision of the corrugations to the insulation-forming portion would have a beneficial effect of strengthening the union between this portion of the terminal and the insulataion 12 of the conductor. Under some circumstances it might prove feasible to provide the corrugations on ribs 24 as being discontinuous, for example to provide some outwardly displaced sections which extend only partially around the wire ferrule forming portion 8. Also, it will be apparent that the invention is not restricted to crimped connections of the type shown in the drawing but is applicable to a variety of crimped connections known to the art.

I claim:

1. An electrical connection comprising a sheet metal ferrule crimped about a conductor wire, the ferrule having at least one transversely displaced section to form a transversely extending groove and rib on the interior and exterior surfaces thereof respectively, said riband groove being of generally similar trapezoidal shape in cross-section, said section being displaced by cold-working to harden the ferrule metal between each side of the rib and the corresponding side of the groove, the ferrule being cold-forged into tight compression about the conductor wire with portions of the conductor Wire projecting into said groove and with the rib being pressed back into substantially flush relation with the adjacent outer surface of the ferrule.

2. An electrical connection in accordance with claim 1 wherein said section is displaced so as to form the rib wider and shallower than said groove.

References Cited in the file of this patent UNITED STATES PATENTS 1,262,155 Zimmerman Apr. 9, 1918 1,823,158 Mogford et a1. Sept. 15, 1931 2,130,424 Grant Sept. 20, 1938 2,327,650 Klein Aug. 24, 1943 2,433,358 Garberding Dec. 30, 1947 2,452,932 Johnson Nov. 2, 1948 2,552,109 Nahman May 8, 1951 2,596,528 Carlson May 13, 1952 2,639,754 Macy May 26, 1953 2,674,725 Buchanan Apr. 6,1954 2,685,127 Kaufmann Aug. 3, 1954 2,716,741 Ustin Aug. 30, 1955 2,716,744 Swanson et al Aug. 30, 1955 2,747,170 Batcheller May 22, 1956 2,748,452 Pierce June 5, 1956

Claims (1)

1. AN ELECTRICAL CONNECTION COMPRISING A SHEET METAL FERRULE CRIMPED ABOUT A CONDUCTOR WIRE, THE FERRULE HAVING AT LEAT ONE TRANSVERSELY DISPLACED SECTION TO FORM A TRANSVERSELY EXTENDING GROOVE AND RIB ON THE INTERIOR AND EXTERIOR SURFACES THEREOF RESPECTIVELY, SAID RIB AND GROOVE BEING OF GENERALLY SIMILAR TRAPEZOIDAL SHAPE IN

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