Abstract:
A method of connecting a terminal fitting and an electric wire, includes the steps of: providing a terminal fitting; providing an electric wire in which a core wire is covered with an insulating sheath; providing a conductive connecting member formed with an insertion hole; inserting the electric wire into the insertion hole of the connecting member; compressing the connecting member radially inwardly so as to caulk an inserted portion of the electric wire uniformly over a whole periphery thereof; and welding the connecting member and the terminal fitting by applying ultrasonic wave.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a wire-terminal connecting method in which a wire for feeding a power source current or a signal current to an on-vehicle part is connected to a terminal by ultrasonic welding. 
     One known related wire-terminal connecting method is disclosed in JP-A-54-43588. 
     As shown in  FIG. 7 , this related wire-terminal connecting method is directed to the method of an invention in which a distal end portion  51   a  of a wire  51  is beforehand fixed into a semi-circular shape, and thereafter this fixed distal end portion  51   a , together with a flat-type aluminum wire  55  (serving as a connecting wire), is held between a tip  59  and an anvil  60  of an ultrasonic welding machine  56 , and an interface  65  ( FIG. 8 ) of joining between the wire  51  and the flat-type aluminum wire  55  is heated and melted by vibrational energy, thereby effecting the welding. 
     The distal end portion  51   a  of the wire  51  is fixed into the predetermined shape by the use of a resistance welding machine (not shown) including an upper electrode with a semi-circular fitting groove and a lower electrode disposed in opposed relation to this upper electrode. 
     In  FIG. 7 , reference numeral  55  denotes the flat-type aluminum wire to be connected to the wire  51 , reference numeral  56  denotes the ultrasonic welding machine, reference numeral  57  denotes an ultrasonic wave-generating source, reference numeral  58  denotes a horn for transmitting ultrasonic waves from the ultrasonic wave-generating source  57 , and reference numeral  59  denotes the tip provided at a distal end of the horn  58 . 
     The tip  59  has a semicircular groove  59   a  extending in a direction perpendicular to a direction a of vibration of ultrasonic waves. Reference numeral  60  denotes the anvil provided in opposed relation to the tip  59 . An upper surface of the anvil  60  is formed into a flat surface. 
     The flat-type aluminum wire  55  and the wire  51  are placed on the anvil  60  of the ultrasonic welding machine  56  in such a manner that the wire  51  is superposed on the aluminum wire  55 , and then the tip  59  is moved toward the anvil  60 , so that the distal end portion  51   a  of the wire  51  fits into the groove  59   a  in the tip  59 . As a result, the wire  51  is pressed from the upper side, and is held in place since the depth of the groove  59   a  in the tip  59  is slightly smaller than the height of the semi-circular distal end portion  51   a  of the wire  51 . 
     Then, when ultrasonic waves are applied from the ultrasonic wave-generating source  57  via the horn  58  and the tip  59 , the vibrational energy propagates to the interface  65  of joining between the wire  51  and the flat-type aluminum wire  55  while the wire  51  is kept in a restrained condition since the direction of extending of the groove  59   a  in the tip  59  is substantially perpendicular to the vibrating direction a. As a result, this joining interface portion  65  is heated and melted by frictional heat, thereby connecting the wire  51  and the flat-type aluminum wire  55  together. 
     However, the above related wire-terminal connecting method has the following problems to be solved. 
     Firstly, when the wire (workpiece)  51  is pressed by the tip  59  as shown in  FIG. 8 , stresses concentration a boundary portion  51   b  between each edge portion  59   b  of the tip  59  and the wire  51 , and besides when the tip  59  is ultrasonically vibrated, the edge portion  59   b  of the tip  59  and the wire  51  rub against each other at each boundary portion  51   b , thus inviting a problem that wire elements  51   c  undergo damage such as cutting. 
     Secondly, the larger the pressing force, applied by the tip  59 , is, and the higher the ultrasonic vibration frequency is, the shorter the time of heating and melting of the joining interface portion  65  is, and on the other hand there is encountered a problem that the plurality of wire elements  51   c  are more liable to become loose, and also are more liable to undergo damage such as cutting. Therefore, it has been desired to provide an ultrasonic connecting method in which even when the ultrasonic vibration frequency is high, the wire elements  51   c  will not undergo damage such as cutting, and the operation for connecting the wire  51  and the flat-type aluminum wire  55  together can be effected easily. 
     And besides, when a conductor portion of a thick wire (connected to a battery so as to supply a source current) or a conductor portion of a thin wire (connected to an on-vehicle part so as to feed a signal current) is kept in an exposed condition, waterdrops, dust and so on deposit on the conductor portion (conducting portion), which invites a problem that the performance of contact between the conductor portion and the terminal is lowered. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a method of connecting a wire and a terminal fitting, in which wire elements are prevented from being cut and from becoming loose during ultrasonic welding, and at the same time a water stop treatment of a wire is effected. 
     In order to achieve the above object, according to the present invention, there is provided a method of connecting a terminal fitting and an electric wire, comprising the steps of:
         providing a terminal fitting;   providing an electric wire;   providing a conductive connecting member formed with an insertion hole;   inserting at least a part of the core wire of the electric wire into the insertion hole of the connecting member;   compressing the connecting member radially inwardly so as to caulk an inserted portion of the electric wire uniformly over a whole periphery thereof; and   welding the connecting member and the terminal fitting by applying ultrasonic wave.       

     In the above method, the conductor portion is inserted into the insertion hole in the connecting member, and the outer periphery of the connecting member is compressed and shaped over the entire periphery thereof, so that the connecting member is reduced in diameter, and the connecting member is held in intimate contact with the conductor portion. Then, the connecting member and the terminal fitting are located between a tip and an anvil of an ultrasonic welding machine in such a manner that the connecting member and the terminal fitting are superposed together, and the tip is moved toward the anvil to press the connecting member and the terminal fitting, and in this condition vibrational energy is applied to the tip via a vibrator and a horn, so that slip at the interface of joining between the connecting member and the terminal fitting and the heating due to internal friction are effected at the same time, and the diffusion of atoms is effected while the interface portion melts to a certain degree, and as a result the wire and the terminal are welded together through the connecting member. Thus, the conductor portion, consisting of the plurality of wire elements, is not pressed directly by the tip, and therefore the plurality of the wire elements will not become loose, and stresses will not concentrate on the conductor portion, so that the wire elements are prevented from undergoing damage such as cutting. 
     Preferably, the connecting member is compressed and shaped by rotary swaging. 
     In the above method, a plurality of radially-arranged dies of a rotary swaging apparatus cooperate respectively with buckers (hammers) to move radially, thereby periodically applying blows to the outer peripheral surface of the connecting member, so that the outer periphery of the connecting member is compressed and shaped with uniform stresses uniformly over the entire periphery thereof, and therefore the conductor portion of the wire is held in intimate contact with the inner peripheral surface of the insertion hole in the connecting member. Also, the area of contact between the conductor portion and the connecting member increases, so that the fixing force increases, and besides the reliability of the electrical contact is enhanced. 
     Preferably, the connecting member includes a first hole portion and a second hole portion which is larger than the first hole in diameter. The core wire is inserted in the first hole portion and the insulating sheath is inserted in the second hole portion, and the first hole portion and the second hole portion are disposed coaxially with each other. The electric wire has a core wire covered with an insulating sheath. The connecting member is compressed so that the insulating sheath is held in intimate contact with the second hole portion. 
     In the above method, the insulating sheath portion of the wire is held in intimate contact with the inner peripheral surface of the second hole portion of the connecting member, so that a gap between the wire and the connecting member is closed, thereby preventing waterdrops, dust and so on from intruding into the interior of the connecting member. Also, the reliability of the electrical connection is maintained. 
     Preferably, the terminal fitting is provided with a clamping portion. The connecting method further comprises the step of press-clamping the terminal by the clamping portion. 
     In the above method, the connecting member and the terminal fitting are connected together by press-fastening the press-clamping piece portion provided at the terminal fitting, and therefore the terminal fitting and the connecting member are connected together by both of the fixing force obtained by the welding and the press-clamping force obtained by the press-fastening operation. Also, the terminal fitting is positively prevented from being disengaged from the connecting member, so that the reliability of the electrical connection is enhanced. 
     In the above method, the connecting member includes the first diameter portion and the second portion which are disposed coaxially with each other, and the first diameter portion and the second diameter portion are simultaneously compressed and shaped by the rotary swaging apparatus. 
     In the above method, the first portion and the second portion of the connecting member are simultaneously compressed and shaped by the rotary swaging apparatus, and therefore the smaller-diameter portion and larger-diameter portion do not need to be compressed and shaped separately from each other, so that the efficiency of the shaping operation is enhanced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above objects and advantages of the present invention will become more apparent by describing in detail preferred exemplary embodiments thereof with reference to the accompanying drawings, wherein: 
         FIG. 1  is an exploded, perspective view showing one preferred embodiment of a wire-terminal connecting method of the present invention; 
         FIG. 2  is a perspective view showing a condition in which a connecting cap is fitted on an end portion of a wire in the wire-terminal connecting method of  FIG. 1 ; 
         FIG. 3  is a front-elevational view of a rotary swaging apparatus for compressing and shaping the outer periphery of the connecting cap; 
         FIG. 4  is a cross-sectional view of a larger-diameter portion of the connecting cap compressed and shaped by rotary swaging; 
         FIG. 5  is a cross-sectional view of a smaller-diameter portion of the connecting cap compressed and shaped by rotary swaging; 
         FIG. 6  is a view showing a basic construction of an ultrasonic welding machine used for connecting the connecting cap and a terminal together; 
         FIG. 7  is a perspective view showing a related method of connecting a wire and a terminal together; and 
         FIG. 8  is a fragmentary cross-sectional view showing a condition in which the wire and the terminal, shown in  FIG. 7 , are ultrasonically welded together. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the present invention will now be described in detail with reference to the drawings. 
       FIGS. 1 to 6  show one preferred embodiment of a wire-terminal connecting method of the invention. 
     In  FIG. 1 , there are shown a connecting cap (connecting member)  10  made of an electrically-conductive material such as a copper alloy and an aluminum alloy, and an end portion of a wire  17  for insertion into an insertion hole  12  in the connecting cap  10 . 
     The electrically-conductive connecting cap  10  is fitted on the end portion of the wire  17  ( FIG. 2 ), and the outer periphery of the connecting cap  10  radially compressed by rotary swaging (described later), and the connecting cap  10  and an electrically-conductive terminal  40  are held between an anvil  31  and a tip  32  of an ultrasonic welding machine  30  ( FIG. 6 ), and the connecting cap and the terminal are ultrasonically welded together. 
     The wire  17  includes a conductor portion  18  consisting of a plurality of wire elements  18   a , and an insulating sheath portion  19  covering an outer periphery of the conductor portion  18 . Although a material for forming the conductor portion  18  is not particularly limited, the conductor portion  18  is made, for example, of copper, a copper alloy or an aluminum alloy. 
     In the case where the conductor portion  18  is made of copper or a copper alloy, oxygen-free copper or tough pitch copper is used. In the case where the conductor portion  18  is made of an aluminum alloy, an aluminum alloy, containing substances such as Mg—Si, Mg and Zr is used. When it is desired to enhance electrical conductivity while decreasing contact resistance, there is used, in some cases, an aluminum alloy containing zinc. 
     The insulating sheath portion  19  is made of a soft synthetic resin such as a polyethylene resin, a polyvinyl chloride resin and a polypropylene resin. Depending on the kind of resin material, a resin (polyvinyl chloride) containing a plasticizer or a crosslinked resin (polyvinyl chloride, polyethylene) is used. For exposing the conductor portion  18 , a slit is formed into the insulating sheath portion  19  by a cutter or the like, and the relevant portion of the insulating sheath portion  19  is removed by pulling it. 
     The terminal  40  shown in  FIG. 6  is a female terminal of an integral construction which is formed by blanking a piece from an electrically-conductive base sheet of metal (such as copper, a copper alloy or an aluminum alloy) and by bending this piece. The female terminal has a box-like electrical contact portion  43  formed at one end portion thereof, and is adapted to be electrically connected to a tab-like electrical contact portion of a male terminal provided as a mating terminal (not shown). The terminal  40  is not limited to such female terminal, but may be a male terminal, an LA terminal or others, and terminals having various electrical contact portions can be used. 
     A wire connection portion  41 , having a pair of press-clamping piece portions  42  (only one of which is shown), is formed at the other end of the terminal  40 , and this wire connection portion  41  is adapted to be connected to the connecting cap  10 . The pair of press-clamping piece portions  42  are pressed inwardly to be press-fastened and connected to a larger-diameter portion  11  of the connecting cap  10 , and a body portion  41   a  of the wire connection portion  41  is connected to a smaller-diameter portion  15  of the connecting cap  10  by ultrasonic welding as shown in  FIG. 6 . Therefore, the terminal  40  and the connecting cap  10  are positively connected together by both of a fixing force obtained by the welding and a press-clamping force obtained by the press-fastening operation. 
     Referring again to  FIG. 1 , the connecting cap  10  has a stepped cylindrical shape, and includes the smaller-diameter portion  15  and the larger-diameter portion  11  which are coaxial with each other. The insertion hole  12 , having a smaller hole portion  14  and a larger hole portion  13 , is formed in the connecting cap  10 . The smaller hole portion  14  of a circular cross-section for the insertion of the conductor portion  18  of the wire  17  thereinto is formed in the smaller-diameter portion  15 , and the larger hole portion  13  of a circular cross-section for the insertion of the insulating sheath portion  19  of the wire  17  thereinto is formed in the larger-diameter portion  11 . The smaller hole portion  14  is in the form of a blind hole so that the distal end of the conductor portion  18 , inserted in the smaller hole portion  14 , will not be exposed to the exterior. 
     The insertion hole  12  is formed by a boring process using a solid drill made of cemented carbide. Since the smaller hole portion  14  and the larger hole portion  13  are different in diameter from each other, the boring operation is effected using two drills (that is, a drill of a smaller diameter and a drill of a larger diameter). A distal end of the solid drill has a point angle of about 120 degrees, and therefore an inner end surface of the smaller hole portion  14  is formed into a conical tapering shape. 
     The shape of the distal end of the solid drill is reflected to a step portion  16  interconnecting the smaller hole portion  14  and the larger hole portion  13 , and therefore this step portion  16  is formed into an annular tapering shape. The step portion  16  can be formed into a surface disposed perpendicular to the axis of the connecting cap, in which case the front end of the insulating sheath portion  19  abuts against this step portion  16 , thereby limiting the length of insertion of the wire  17  in the longitudinal direction. In this case, the step portion  16  is cut into a surface disposed perpendicular to the axis of the connecting cap, using a boring tool having a tool angle of 90 degrees. 
     The inner diameter of the smaller hole portion  14  is generally equal to or slightly larger than the outer diameter of the conductor portion  18 . If the inner diameter of the smaller hole portion  14  is smaller than the outer diameter of the conductor portion  18 , the conductor portion  18  can not be smoothly inserted into the connecting cap  10 . 
     The inner diameter of the larger hole portion  13  is generally equal to or slightly larger than the outer diameter of the insulating sheath portion  19 . If the inner diameter of the large hole portion  13  is smaller than the outer diameter of the insulating sheath portion  19 , the insulating sheath portion  19  can not be smoothly inserted into the connecting cap  10 , and besides the air can not escape during the rotary swaging operation, so that the connecting cap  10  can not be compressed. 
     Even if a gap exists between the larger hole portion  13  and the insulating sheath portion  19 , this gap is closed by the rotary swaging operation, and therefore waterdrops, dust and so on are prevented from intruding into the interior. The insulating sheath portion  19  is made of the soft synthetic resin, and therefore when the insulating sheath portion  19  is deformed, the gap is positively closed by an elastic restoring force of the insulating sheath portion  19 . 
     The hole length (hole depth) of the smaller hole portion  14  is larger than the length of the exposed end portion of the conductor portion  18 . If the hole length of the smaller hole portion  14  is generally equal to or slightly smaller than the exposed end portion of the conductor portion  18 , the area of contact between the conductor portion  18  and the smaller hole portion  14  is small, so that the electrical connection performance is lowered. And besides, when the outer periphery of the smaller-diameter portion  15  is compressed by the rotary swaging operation (described later), the extension (elongation) of the conductor portion  18  is limited by the inner end surface of the smaller hole portion  14 . 
     The hole length of the larger hole portion  13  is so determined that this larger hole portion  13  can intimately hold the insulating sheath portion  19  in closely-contacted relation thereto so as to prevent the rearward withdrawal of the wire  17 . In this embodiment, the hole length of the larger hole portion  13  is generally equal to the hole length of the smaller hole portion  14 . 
     The larger-diameter portion  11  and the smaller-diameter portion  15  are generally equal in wall thickness, and therefore the connecting cap  10  has a stepped cylindrical shape. Although the larger-diameter portion  11  is larger in outer diameter than the smaller-diameter portion  15 , the larger-diameter portion  11  and the smaller-diameter portion  15  can be compressed at the same time by stepped inner surfaces  21   a  of dies  21  of a rotary swaging apparatus  20 . 
     When the connecting cap  10  can be radially compressed into a uniform diameter over the entire length thereof and over the entire circumference, the connecting cap  10  can have a uniform diameter over the entire length to have a cylindrical shape even if the peripheral wall of the connecting cap  10  is not uniform over the entire length, and therefore is uneven. In this embodiment, the connecting cap  10  is formed into the stepped cylindrical shape, and by doing so, the smaller-diameter portion  15  and the larger-diameter portion  11  are generally equal in wall thickness to each other, and the compressive shaping can be effected easily, so that the conductor portion  18  and the insulating sheath portion  19  can be held in intimate contact respectively with the inner peripheral surfaces of the smaller hole portion  14  and larger hole portion  13 , with no gap formed therebetween. 
       FIG. 2  shows a condition in which the connecting cap  10  is fitted on the end portion of the wire  17 . The conductor portion  18  of the wire  17  is inserted in the smaller hole portion  14 , while the insulating sheath portion  19  of the wire  17  is inserted in the larger hole portion  13 . In this condition, the wire  17  is set in the rotary swaging apparatus  20  as shown in  FIG. 3 , and the outer periphery of the connecting cap  10  is compressed and shaped uniformly over the entire circumference thereof. Any other suitable processing method than the rotary swaging method can be used in so far as it can compress the outer periphery of the connecting cap  10  uniformly over the entire circumference thereof. 
     Next, the rotary swaging (rotary forging) will be described in detail with reference to  FIG. 3 . The rotary swaging is a kind of forging in which while rotating one of dies and rollers, hammer-like blows are repeatedly applied to a round bar or a pipe, thereby compressing this workpiece into a predetermined shape. 
     The rotary swaging apparatus  20 , shown in  FIG. 3 , is a spindle drive-type apparatus in which dies  21  and buckers  22  are revolved by rotating a spindle  24 . There is known another drive method in which rollers are rolled while dies and buckers are not rotated by keeping a spindle stationary. 
     The spindle drive-type has advantages that the whole of the apparatus can be formed into a compact design since the number of component parts is small (a flywheel and pulleys are not needed), and that a workpiece of a small diameter can be processed with high precision. The roller-rolling type is used when a workpiece is formed into other shape (such as a square cross-sectional shape) than a circular shape. In this embodiment, the spindle drive-type is adopted. 
     Within the spindle  24  of the spindle drive-type rotary swaging apparatus  20 , the dies  21  and the buckers  22  are movably supported in such a manner that each die abuts against the corresponding bucker. In this embodiment, the two pairs of opposed dies  21  are arranged radially. The connecting cap (workpiece)  10  is located at the center of the spindle  24  in such a manner that this connecting cap  10  is gripped by inner surfaces  21   a  of the dies  21 . By thus locating the connecting cap  10  at the axis of rotation of the spindle  24 , blows can be applied to the outer peripheral surface of the connecting cap  10  uniformly over the entire circumference thereof. 
     The four dies  21  are arranged circumferentially at equal intervals. The number of the dies  21  is not limited to 4, but may be 2 or 8. By thus arranging the dies  21  at equal intervals, the outer periphery of the connecting cap  10  can be compressed uniformly. 
     The inner surface  21   a  of each die  21  is formed into a stepped shape, and the radially-arranged dies  21  press the smaller-diameter portion.  15  and larger-diameter portion  11  of the connecting cap  10  at the same time. With this stepped shape of the dies, the smaller-diameter portion  15  and larger-diameter portion  11  of the connecting cap  10  can be compressed at the same time in one step of the process, and the shaping operation can be effected easily and efficiently. 
     In the case where the connecting cap  10  has a cylindrical shape, the inner surface  21   a  of each die  21  does not need to be stepped, and also in the case where the smaller-diameter portion  15  and larger-diameter portion  11  of the connecting cap  10  of a stepped cylindrical shape are subjected to rotary swaging independently of each other, the inner surface  21   a  of each die  21  does not need to be stepped. 
     The bucker  22 , provided at the rear side of (that is, radially outwardly of) the die  21 , is separate from the die  21 , but the bucker  22  revolves together with the die  21 , and also can move in a radial direction (toward the center). This revolution is effected by rotating the spindle  24  by a motor (not shown). The movement in the radial direction is effected by the rotational contact between the bucker  22  and the roller  23 . 
     An outer surface of the bucker  22  defines a cam surface  22   a . This cam surface  22   a  is not formed into a constant radius of curvature, but a widthwise-central portion of the cam surface projects radially outwardly. Therefore, when the bucker  22  is brought into rotational contact with the roller  23 , the bucker  22  is pushed radially inwardly by the roller  23  by an amount corresponding to the amount of projecting of the central portion of the bucker, so that the die  21  moves radially inwardly. 
     The spherical rollers  23  are provided between the outer peripheral surface of the spindle  24  and an outer ring  25 , and are arranged at equal intervals, and are supported for rotation about their respective axes. The number of the rollers  23  is 4 (which is equal to the number of the dies  21 ), but may be 8. The larger the number of the rollers  23  is, the larger the number of the blows per rotation of the spindle is, and the processing rate of the connecting cap  10  is enhanced. High-carbon/low chromium bearing steel, having excellent wear resistance and impact resistance, is suitably used as a material for forming the rollers  23 . 
     The pressing condition and the non-pressing condition which are determined by the positions of the dies  21  and buckers  22  relative to the rollers  23  will be described. When the spindle  24  is rotated, the dies  21  and the buckers  22  revolve, and also the rollers  23  rotate about their respective axes. Each bucker  22  is located radially outwardly of the associated die  21 , and therefore the revolving bucker  22  is brought into contact with the roller  23 , and the cam surface  22   a  of the bucker  22  slides on the roller  23 , so that the inner surface of the bucker  22  pushes the die  21  radially inwardly, and as a result the inner surface  21   a  of each die  21  strikes against the outer peripheral surface of the connecting cap  10 , thereby effecting the forging operation When each bucker  22  is brought out of contact with the roller  23 , the bucker  22  slightly projects radially outwardly under the influence of a centrifugal force, so that the die  21  moves apart from the connecting cap  10 , and therefore the application of a blow by the die  21  is once stopped. Then, each bucker  22  is brought into contact with the roller  23 , and the above operation is repeated. 
       FIG. 4  shows a condition in which the larger-diameter portion  11  of the connecting cap  10  is compressed by rotary swaging, and  FIG. 5  shows a condition in which the smaller-diameter portion  15  is compressed by rotary swaging. As shown in  FIG. 4 , the conductor portion  18  and the insulating sheath portion  19 , disposed inside the larger-diameter portion  11 , are radially compressed hard, and the wire elements  18   a  of the conductor portion  18  are deformed in a honeycomb-like manner, and are held in intimate contact with one another, and an elastic restoring force of the insulating sheath portion  19  acts on the inner peripheral surface of the larger hole portion  13 . Like the larger-diameter portion  11 , the smaller-diameter portion  15  is compressed radially, and the conductor portion  18  is held in intimate contact with the inner peripheral surface of the smaller hole portion  14  as shown in  FIG. 15 . 
     Next, an ultrasonic welding method will be described. 
     Ultrasonic welding is a welding method in which vibrational energy is applied to an interface of joining between two workpieces while the two workpieces are pressed against each other. When the vibrational energy is applied, slip at the joining interface and the heating due to internal friction are effected, and the diffusion of atoms is effected while the workpieces melt to a certain degree, so that the two workpieces are welded together at the joining interface. In the ultrasonic welding, heat-affected layers in the vicinity of the welded portion are narrow, and therefore the ultrasonic welding is used, for example, for welding thin parts such as an electronic part and for welding low-melting non-metal materials. 
     As shown in  FIG. 6 , the ultrasonic welding machine  30  includes an ultrasonic generator  33 , a vibrator  34 , a horn  35 , the tip  32 , the anvil  31  and a weight  36 . These component parts will be described below. 
     The ordinary ultrasonic generator  33  can produce electric energy of about 100 W to about 10 kW. The vibrator  34  is a magnetostrictive vibrator of a ferromagnetic material placed in a magnetic field, and when the vibrator  34  receives the electric energy from the ultrasonic generator  33 , it produces vibration energy. The horn  35  serves to transmit ultrasonic vibrations from the vibrator  34  to the tip. Although the horn  35  is disposed horizontally, its direction can be suitably changed, and for example, this horn can be disposed vertically. 
     The tip  32  and the anvil  31  are upper and lower tools, respectively, and hold the connecting cap  10  and the terminal  40  (which are the workpieces) therebetween in a manner to press the two workpieces. The weight  36  serves to press the tip  32 . Instead of the weight  36 , a hydraulic apparatus may be used as pressing means. 
     Referring to one example of processing conditions for the ultrasonic welding machine  30  of this construction, the ultrasonic output is about several Kw, and the ultrasonic frequency is 15 to 30 kHz, and the ultrasonic amplitude (the amplitude of the horn) is 40 to 50 μm, and the pressing force of the tip  32  is 300 N to 500 N. 
     In this embodiment, the connecting cap  10  is attached to the end portion of the wire  17  in such a manner that the conductor portion  18  and the insulating sheath portion  19  are inserted into the insertion hole  12  in the connecting cap  10 , and the connecting cap  10  is compressed and shaped by rotary swaging, so that the connecting cap  10  and the terminal  40  are ultrasonically welded together in such a manner that the conductor portion  18  and the insulating sheath portion  19  are held in intimate contact with the inner peripheral surface of the insertion hole  12  in the connecting cap  10 , with no gap formed therebetween. Therefore, the plurality of wire elements  18   a , forming the conductor portion  18  of the wire  17 , will not become loose, and stresses will not concentrate on the conductor portion  18 , and the conductor portion  18  will not be rubbed, so that the wire elements  18  are prevented from undergoing damage such as cutting, and besides water, dust and so on are prevented from intruding into the interior of the connecting cap  10 . 
     Although the present invention has been shown and described with reference to specific preferred embodiments, various changes and modifications will be apparent to those skilled in the art from the teachings herein. Such changes and modifications as are obvious are deemed to come within the spirit, scope and contemplation of the invention as defined in the appended claims.