Patent Publication Number: US-6658725-B1

Title: Apparatus for forming a crimped electrical joint

Description:
FIELD OF THE INVENTION 
     This invention generally relates to a method and to an apparatus for forming a crimped joint and more particularly, to a method and to an apparatus for forming a crimped joint in an electrical wire terminal and which provides reduced electrical contact resistance within the formed joint. 
     BACKGROUND OF THE INVENTION 
     Crimped joints are commonly used in electrical systems, such as automotive electrical systems, in order to selectively and electrically interconnect electrical components. For example and without limitation, crimped joints are used in electrical wire harnesses which electrically interconnect various components or portions of an automobile. Particularly, crimped joints are used to couple electrical connectors or terminals to the ends of the wires in the harness in order to facilitate the connection of the wires to various components, devices or other terminals. 
     These types of crimped joints are typically formed by use of a die set (e.g., a punch and an anvil) which are selectively used to compress and/or deform a “barrel” portion of the terminal in which the electrical wire resides. Particularly, the electrical wire is placed in the “barrel” portion of the terminal which is subsequently compressed by the die set. As the die set is compressed, two “wings” or flanges which typically form the barrel portion of the terminal are bent downward into the wire bundle. Further compression of the die set further deforms the barrel and tightly packs the strands of the wire bundle together, thereby forming a crimped joint. 
     While these types of crimped joints are effective to relatively quickly connect terminals to the ends of electrical wires, they suffer from some drawbacks and are generally considered a “weak link” in the wiring harness. For example and without limitation, when compared with other permanent electrical connection methods (e.g., soldering), crimped joints typically show higher initial contact resistance and have a greater tendency to introduce electrical failure within a wiring harness over their respective service lives. One cause of the relatively high contact resistance in these types of crimped joints arises from resistive material (e.g., “oxides”) which resides on the outer surfaces of the various strands of the electrical wire and on the inner surfaces of the terminal barrel. The crimping process and die set generate primarily only “normal” type forces between the wire strands which are not effective to remove a significant amount of the resistive material from the wire strands and from the terminal barrel. Furthermore, attempts at removing these resistive materials or oxides prior to forming the crimped joint are excessively costly and/or time consuming. 
     There is therefore a need for a method and an apparatus for forming a crimped joint which overcomes the previously delineated drawbacks of prior methods and apparatuses and which provides a crimped joint having a reduced amount of contact resistance. 
     SUMMARY OF THE INVENTION 
     It is a first object of the present invention to provide a method and an apparatus for selectively forming a crimped joint in an electrical wire terminal or connector which overcomes the previously delineated disadvantages of prior automotive electrical interconnection schemes and systems. 
     It is a second object of the present invention to provide a method and apparatus for forming a crimped joint in an electrical wire terminal or connector which provides a joint having reduced contact resistance. 
     It is a third object of the present invention to provide a method and an apparatus for forming a crimped joint between an electrical wire and a terminal barrel which automatically causes oxides to be removed from the surfaces of the electrical wire and the terminal barrel, thereby forming a joint with reduced contact resistance. 
     According to one aspect of the present invention, an apparatus for forming a crimped joint is provided. The apparatus forms a crimped joint between an electrical wire terminal having a first longitudinal axis and a barrel portion having an interior surface, and a wire having an exterior surface which is disposed within the barrel portion and a second longitudinal axis. The apparatus includes a first die member having a first surface which is concave relative to the first and second longitudinal axes; and a second die member having a second surface which is convex relative to the first and second longitudinal axes and which is adapted to selectively engage the barrel portion and to cooperate with the first die member to deform the barrel portion effective to form a crimped joint between the wire and the terminal and to bend the barrel portion and the wire respectively along the first and second longitudinal axes, the longitudinal bending being effective to cause the interior surface of the barrel portion to slide longitudinally relative to the exterior surface of the wire, thereby reducing contact resistance between the barrel portion and the wire. 
     According to a second aspect of the present invention, a method is provided for forming a crimped joint having reduced contact resistance. The crimped joint is formed between a terminal having a hollow barrel portion with an inner surface and an electrical wire having an outer surface. The method includes the steps of disposing the electrical wire within the hollow barrel portion; deforming the hollow barrel portion effective to compact the barrel portion and the wire, thereby forming the crimped joint; and twisting the barrel portion and the electrical wire about their respective longitudinal axes, effective to cause the inner surface of the barrel portion to slide relative to the outer surface of the electrical wire, thereby reducing the contact resistance within the crimped joint. 
    
    
     Further objects, features, and advantages of the present invention will become apparent from a consideration of the following description and claims when taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an apparatus for forming a crimped joint between an electrical wire and a wire terminal and which is made in accordance with the teachings of the present invention. 
     FIG. 2 is a side view of a crimped joint which is formed by use of the apparatus shown in FIG.  1 . 
     FIG. 3 is a sectional view of the crimped joint shown in FIG.  2  and taken along view line  3 — 3 . 
     FIG. 4 a  is a sectional view of the crimping apparatus shown in FIG.  1  and taken along view line  4   a — 4   a.    
     FIG. 4 b  is a sectional view of the crimping apparatus shown in FIG. 4 a  and taken along view line  4   b — 4   b.    
     FIG. 5 is an apparatus for forming a crimped joint between an electrical wire and a wire terminal which is made in accordance with the teachings of an alternate embodiment of the present invention. 
     FIG. 6 is a side view of a crimped joint which is formed by use of the apparatus shown in FIG.  5 . 
     FIG. 7 is a sectional view of the crimped joint shown in FIG.  6  and taken along view line  7 — 7 . 
     FIG. 8 a  is a sectional view of the crimping apparatus shown in FIG.  5  and taken along view line  8   a — 8   a.    
     FIG. 8 b  is a sectional view of the crimping apparatus shown in FIG.  5  and taken along view line  8   b — 8   b.    
     FIG. 9 is a perspective view of a the crimped joint shown in FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
     Referring now to FIG. 1, there is shown an apparatus  10  which is made in accordance with the teachings of the preferred embodiment of the invention and which is effective to form a crimped joint in an electrical connector assembly or wire terminal  12 . As shown, apparatus  10  includes a pair of die pieces or members  14 ,  16 . It should be appreciated that members  14 ,  16  may be operatively coupled and/or attached in a conventional manner to a conventional manual and/or mechanical crimping tool (not shown) , such as a hand-held crimping tool or a mechanical press, which is effective to move and/or force the members  14 ,  16  together in the directions of arrows  18 ,  20 . 
     In the preferred embodiment of the invention, member  14  comprises a conventional “anvil” type member and member  16  comprises a conventional “punch” type member which cooperates with anvil member  14  to form a crimped joint in terminal  12 , such as joint  22  illustrated in FIGS. 2 and 3. As shown best in FIG. 4 b , die member  14  includes a pair of substantially identical curved or “arched” surfaces  24  which meet at a ridge  26  which is substantially aligned with (e.g., is parallel to) the horizontal axis  30  that resides between members  14 ,  16  and which intersects the vertical axis of symmetry  28  of apparatus  10 . As shown best in FIG. 4 a , surfaces  24  are also curved inward with respect to the horizontal axis  30  (i.e., surfaces  24  are concave relative to axis  30 ). 
     Die member  16  includes an outer surface  32  which is curved outward with respect to axis  30  of apparatus  10  (i.e., surface  32  is convex relative to axis  30 ), as illustrated in FIG. 4 a . Surface  32  is also curved slightly inward with respect to the transverse axis  31  which is perpendicular to axis  28  and axis  30  (i.e., surface  32  is slightly concave relative to axis  31 ). This slight “inward” curvature of surface  32  is adapted to conform to and/or engage the bottom surface  35  of terminal  12 . 
     Electrical wire  50  includes a generally cylindrical insulating shell or casing  52  which holds a plurality of bundled electrically conductive wire strands or fibers  54 . Terminal  22  is made from a conductive and relatively deformable metal material. Terminal  22  includes a generally “U”-shaped crimping or “barrel” portion  34  having a pair of substantially identical vertically extending “wings” or flanges  36  which are selectively deformed or crimped by apparatus  10 , as described more fully and completely below. Terminal  22  further includes an electrical connecting portion or end  38  and a generally cylindrical hollow portion  40  which selectively and conventionally engages insulating cover  52 . 
     In operation, wire  50  is inserted into terminal  22 , as shown in FIG. 1, such that the bundle of wire strands  54  is disposed substantially within barrel portion  34  and the longitudinal axis  60  of wire  50  and the longitudinal axis  62  of terminal  22  are substantially aligned with axis  30  (e.g., such that surfaces  24  are concave relative to axes  60 ,  62  and surface  32  is convex relative to axes  60 ,  62 ). Die members  14  and  16  are then forced together (e.g., in the directions of arrows  18  and  20 ) in a conventional manner (e.g., die members  14 ,  16  are attached to a crimping tool). As die members  14  and  16  are forced together, flanges  36  engage surfaces  24  and are deformed or bent downward in the direction of arrows  56 . Flanges  36  move downward and engage wire strands  54  and compress and/or pack the wire strands  54 , thereby tightly compacting the wire strands together, as shown best in FIG.  3 . As flanges  36  compress wires  54 , the generally convex surface  32  of die  16  and the concave surface  34  of die  14  cooperate to deform or bend barrel  34  and wire strands  54  along and/or relative to the longitudinal axis  60  of wire  50  and the longitudinal axis  62  of terminal  22 , as shown best in FIG.  2 . 
     The deformation or bending of barrel portion  34  and wire strands  54  along and/or relative to their respective longitudinal axes  62 ,  60  reduces the electrical contact resistance of the resulting crimped joint  22  and improves the quality of the electrical connection provided by the crimped joint  22  relative to prior crimped joints. Particularly, as barrel portion  34  is deformed and/or bent along axis  62 , the upper inner surfaces  42  and the lower inner surface  44  of the barrel  34  experience sliding against all wire strands  54  which are in contact with the respective surfaces  42 ,  44  due to the angular deformation of the barrel relative to wire strands  54 . This “sliding” action is caused by a shear force which is generated along the wire bundle and which cause the surfaces in contact (e.g., surfaces  42 ,  44 , and  46 ) to slide against each other in the longitudinal direction (e.g., the bending of wire strands  54  “lags” behind the bending of barrel  34 , thereby causing relative longitudinal movement between the strands  54  and barrel  34 ). This relative sliding motion causes the oxides and other resistive materials on the exterior or outer surfaces  46  of wire stands  54  and on the interior or inner surfaces  42 ,  44  of barrel  34  to be “wiped” away. This oxide removal results in a significant reduction in contact resistance between barrel  34  and wire  50 . It should further be appreciated that apparatus  10  allows oxides to be removed from barrel  34  and wire strands  54  substantially simultaneously with the formation of joint  22  and without performing any additional steps in the crimping process. In alternate embodiments, the length  64  of barrel  34  and the thickness  66  of die members  14 ,  16  may be increased, or the radius of curvature  48  of member  16  may be altered, to provide for a greater amount of sliding motion between wire strands  54  and surfaces  42 ,  44 . In other alternate embodiments, additional curves may be formed within die members  14 ,  16  to provide for additional bends (e.g., double bending) in crimped joint  22 . 
     Referring now to FIG. 5, there is shown an apparatus  100  which is made in accordance with the teachings of an alternate embodiment of the Invention and which is effective to form a crimped joint in an electrical connector assembly or wire terminal  12 . As shown, apparatus  100  includes a pair of die pieces or members  114 ,  116 . It should be appreciated that members  114 ,  116  may be operatively coupled and/or attached in a conventional manner to a conventional manual and/or mechanical crimping tool (not shown), such as a hand-held tool or a mechanical press  117 , which is effective to move and/or force the members  114 ,  116  together in the directions of arrows  118 ,  120 . 
     In the preferred embodiment of the invention, member  114  comprises a conventional “anvil” type member and member  116  comprises a conventional “punch” type member which cooperates with anvil member  114  to form a crimped joint in terminal  12 , such as joint  122  illustrated in FIGS. 6,  7  and  9 . As shown best in FIG. 8 b , die member  114  includes a pair of substantially identical curved or “arched” surfaces  124 ,  125  which meet at a ridge  126  which passes through the vertical axis of symmetry  128  of apparatus  10 . As shown best in FIG. 8 a , surfaces  124 ,  125  are each angled or sloped in opposite directions with respect to the horizontal (e.g., relative to the horizontal axis  130  disposed between die members  114 ,  116 ). Particularly, surface  124  is sloped upward from the back surface  113  of die  114  to the front surface  115  of die  114  at an angle  127 . Furthermore, surface  125  is sloped upward from the front surface  115  of die  114  to the back surface  113  at an angle  129 . In the preferred embodiment of the invention, angles  127  and  129  are substantially identical and in one non-limiting embodiment are each equal to approximately 20 degrees. 
     As shown best in FIG. 8 b , die member  116  includes an “upper” or barrel-engaging surface  132  which includes a pair of opposing raised corners  133 ,  135  and a pair of opposing recessed corners  137 ,  139 . Surface  132  is sloped downward from each raised corner  133 ,  135  to each recessed corner  137 ,  139  at an angle  141  of approximately 20 degrees. As described more fully and completely below, the sloped surface  132  of die member  116  is adapted to cooperate with surfaces  124 ,  125  of die member  114  to engage barrel portion  34  and to cause barrel portion  34  to “twist”, as shown best in FIGS. 7 and 9, when the barrel  34  is crimped. 
     In operation, wire  50  is inserted into terminal  122 , as shown in FIG. 5, such that the bundle of wire strands  54  is disposed substantially within barrel portion  34  and the longitudinal axis  60  of wire  50  and the longitudinal  62  of terminal  22  are each substantially aligned with axis  130 . Die members  114  and  116  are then forced together (e.g., in the directions of arrows  118  and  120 ) in a conventional manner (e.g., die members  114 ,  116  are attached to a crimping tool or press). As die members  114  and  116  are forced together, flanges  36  engage surfaces  124 ,  125  and are deformed or bent downward in the direction of arrows  156 . Flanges  36  move downward and engage wire strands  54  and compress and/or pack the wire strands  54 , thereby tightly compacting the wire strands  54  together, as best shown in FIG.  7 . As flanges  36  compress wires  54 , the surface  132  of die  116  and the surfaces  125 ,  125  of die  114  cooperate to deform and/or “twist” barrel  34  and wire strands  54  respectively about (e.g., relative to) the longitudinal axis  60  of wire  50  and the longitudinal axis  62  of terminal  22 , as shown best in FIGS. 7 and 9. 
     The deformation or twisting of barrel portion  34  and wire strands  54  about their respective longitudinal axes reduces the electrical contact resistance of the resulting crimped joint  122  and improves the electrical connection provided by the crimped joint  122  relative to prior crimped joints. Particularly, as barrel portion  34  is deformed and/or twisted about longitudinal axis  62 , the upper inner surfaces  42  and the lower inner surface  44  of the barrel  34  experience sliding against all wire strands  54  which are in contact with the respective surfaces  42 ,  44  due to the angular deformation of the barrel  34  relative to wire strands  54 . This “sliding” action is caused by a torsional or shear force which is generated along the twisting wire bundle and barrel  34  and which causes the surfaces in contact to slide against each other (e.g., the twisting of the wire strands  54  lags behind the twisting of the barrel  34 , thereby causing relative movement between the strands  54  and barrel  34 ). This relative sliding motion causes the oxides and other resistive materials on the outer or exterior surfaces  46  of wire  50  or wire stands  54  and on the inner or interior surfaces  42 ,  44  of barrel  34  to be “wiped” away. This oxide removal results in a significant reduction in contact resistance between barrel  34  and wire  50 . It should further be appreciated that apparatus  100  allows oxides to be removed from barrel  34  and wire strands  54  without performing any additional steps in the crimping process. In alternate embodiments, the length  64  of barrel  34  and the length  166  of die members  114 ,  116  may be increased, or the twisting angle (e.g., 20 degrees) which is determined by angles  127 ,  129  and  141  may be altered, to provide for a greater amount of twisting of barrel  34  and wires  54  and a corresponding greater amount of relative motion between the outer surfaces of wire  50  or wire strands  54  and surfaces  42 ,  44 . 
     It should be understood that this invention is not limited to the exact construction or embodiments listed and described, but that various changes may be made without departing from the spirit and scope of the invention.