Abstract:
A methodology for applying ultrasonic welding processes to insulation jacketed wires without firstly stripping them. A preferred acronym therefor is “UWTI” (Ultrasonic Welding Through Insulation). A wire with its insulation jacket thereon and intact is placed upon a top surface of a base of a terminal to which it is to be bonded and the staking wings of the terminal are staked down onto the wire. The operator places the insulation jacketed wire and terminal combination into a conventional ultrasonic welder, such that the a bottom surface of the base rests upon the anvil and the insulation jacketed wire is aligned with the tip. The operator then causes the sonic welder to automatically sequence so as to provide an ultrasonic weld of the wire to the terminal.

Description:
TECHNICAL FIELD 
     The present invention relates to ultrasonic welding of electrical wires to terminals. More particularly, the present invention relates to ultrasonic welding of wires to terminals through the insulation jacket of the wires. 
     BACKGROUND OF THE INVENTION 
     Ultrasonic welders are known in the art, as exemplified by U.S. Pat. No. 5,772,100, 4,867,370 and 3,053,124. This class of devices utilizes ultrasonic energy to join metals, particularly nonferrous metals used in the electrical arts, as for example the splicing of wires and the attachment of a wire to a terminal. Ultrasonic welding is not actually “welding” in the sense that there is no application of heat as is used in conventional welding, wherein metals are heated to the point of melting into each other. In the case of ultrasonic welding, a mechanical vibration is applied to the metals, typically in the preferred frequencies of 20 kHz or 40 kHz. 
     The frequency and the amplitude of the vibration cause the metals to mutually gall at their contact surfaces. This galling results in contaminants, such as for example surface oxidation, to be displaced. The galling further causes the contact surfaces to be polished. As galling continues, the contact surfaces become intimate, whereupon atomic and molecular bonding occurs therebetween, thereby bonding the metals together with a weld-like efficacy (ergo, the term “ultrasonic welding”). 
     A number of considerations determine the efficacy of the metal-to-metal surface bond, the major considerations being the amplitude of the vibration, the applied force and the time of application. These variables collectively define the efficacy of bonding between the contacting metal surfaces. The applied power (P) is defined by the amplitude (X) of vibration times the force (F) applied normal to the metal surfaces (P=FX), and the applied energy (E) is defined by the applied power (P) times the time (t) of application (E=Pt). These variables are predetermined to achieve the most efficacious bond based upon the metals and the particular application. 
     To provide reliable and predictable bonds by ultrasonic welding, ultrasonic welders include power supplies and actuators controlled by a microprocessor. An example thereof is the “ULTRAWELD®/40” ultrasonic welder of AMTECH® (American Technology, Inc.) of Milford, Conn. This class of commercially available ultrasonic welders include: a power supply, a transducer where electrical energy is converted into mechanical vibration, an amplitude booster where the mechanical vibrations are amplified, and an output tool in the form of a horn which tunes the vibrations to a tip. The tip is aligned with a stationary anvil, and the ultrasonic welder includes one or more actuators which allow for movement of the tip relative to the anvil. Preferably, the tip and the anvil are knurled so as to grip the metals placed therebetween. 
     In operation of a conventional ultrasonic welder, a wire is stripped of its insulation jacket at an end section, and the stripped end section is then placed adjacent a top surface of a base of a terminal to which it is to be bonded. The operator places the stripped section of wire and terminal into the ultrasonic welder, such that the a bottom surface of the base rests upon the anvil and the stripped section of the wire is aligned with the tip. The operator then causes the sonic welder to automatically sequence. 
     A typical sequence for bonding a wire to a terminal may go as follows: the tip descends onto the stripped section of wire and applies a compressive force between it and the anvil (compressing the stripped section of wire onto the base of the terminal), the location of the tip relative to the anvil is sensed, and if within tolerances, the transducer is actuated so as to apply ultrasonic vibration to the tip for a preset time. Finally, the tip is retracted away from the stripped section of wire. The result is a bond of the stripped section of wire relative to the top surface of the base of the terminal in an area defined generally by the tip area. 
     A typical sequence for splicing a first wire to a second wire may go as follows: the wires are stripped and then compressed along a horizontal axis, the tip descends onto the stripped section of the wires and applies a compressive force between it and the anvil (compressing the stripped section of the wires along a vertical axis), the location of the tip relative to the anvil is sensed, and if within tolerances, the transducer is actuated so as to apply ultrasonic vibration to the tip for a preset time. Finally, the tip is retracted away from the stripped section of the wires. The result is a bond of the stripped section of the wires relative to each other in an area defined generally by the tip area. 
     While ultrasonic welding methodologies have advanced considerably in recent years, there remains a universal perception that before ultrasonic welding can occur, the insulation jacket must first be stripped off from the wire. One believed reason for this perception is that while ultrasonic welding is capable of removing surface contaminants, a wire insulation jacket is obviously quite different from mere surface contamination in comparative terms of both the quantity and quality of the material, such that it cannot be regarded simply as a “contaminant” which is capable of being dissipated during application of ultrasonic vibration. 
     SUMMARY OF THE INVENTION 
     The present invention is a methodology for applying ultrasonic welding processes to insulation jacketed wires without firstly stripping them. A preferred acronym therefor is “UWTI” (Ultrasonic Welding Through Insulation). 
     The ultrasonic welding methodology according to the present invention is counter-intuitive, in that it has been discovered that a conventional ultrasonic welding apparatus is capable of providing an ultrasonic bond between a wire and another metal surface through the insulation jacket of the wire. 
     During the process according to the present invention, the insulation jacket is melted. Accordingly, the insulation jacket must be of a meltable material, as for example a thermoplastic, preferably for example a PVC or a polyester. 
     According to a method of the present invention, an insulation jacketed wire (multi-stand or single stand) with its insulation jacket thereon and intact is placed upon a top surface of a base of a terminal to which it is to be bonded and the staking wings of the terminal are stacked down onto the insulation jacketed wire. The operator places the insulation jacketed wire and terminal into a conventional ultrasonic welder, such that the a bottom surface of the base rests upon the anvil and the insulation jacketed wire is aligned with the tip. The operator then causes the sonic welder to automatically sequence. 
     A typical sequence for bonding the insulation jacketed wire to the terminal may go as follows: the tip descends onto the section of wire and applies a compressive force between it and the anvil (compressing both the wire and the insulation jacket onto the base of the terminal), the location of the tip relative to the anvil is sensed, and if within tolerances, the transducer is actuated so as to apply ultrasonic vibration to the tip for a preset time, and finally the tip is retracted away. During application of the ultrasonic vibration, the insulation jacket melts and is entirely displaced and dissipated between the wire and the base of the terminal as the tip presses forceably toward the anvil. The result is a bond of the wire relative to the top surface of the base of the terminal in an area defined generally by the tip area. 
     Accordingly, it is an object of the present invention to provide an ultrasonic weld of a wire to a secondary metal through the insulation jacket of the wire. 
     This and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an ultrasonic welder with an insulation jacketed wire and terminal combination. 
     FIG. 1A is a perspective view of an ultrasonic welder as in FIG. 1, wherein an insulation jacketed wire and terminal combination as in FIG. 1 is seated with respect to the ultrasonic welder, wherein the tip of the ultrasonic welder is at its retracted position. 
     FIG. 2 is a side view of the ultrasonic welder and insulation jacketed wire and terminal combination as in FIG.  1 A. 
     FIG. 2A is a top plan view of the insulation jacketed wire and terminal combination of FIG.  2 . 
     FIG. 3 is a side view of the ultrasonic welder and insulation jacketed wire and terminal combination of FIG. 2, wherein the tip of the ultrasonic welder is at a first operative position. 
     FIG. 3A is a top plan view of the insulation jacketed wire and terminal combination of FIG.  3 . 
     FIG. 4 is a side view of the ultrasonic welder and insulation jacketed wire and terminal combination of FIG. 2, wherein the tip of the ultrasonic welder is at its final operative position. 
     FIG. 4A is a top plan view of the insulation jacketed wire and terminal combination of FIG.  4 . 
     FIG. 4B is a side view of the insulation jacketed wire and terminal combination of FIG.  4 . 
     FIG. 5 is a partly sectional view of an ultrasonic welder being utilized to ultrasonically weld (splice) wires through the insulation jackets thereof. 
     FIG. 5A is a sectional view of the wires of FIG. 5 after being ultrasonically welded through their insulation jackets. 
     FIG. 6 is a top plan view of a jig for sequentially placing a plurality of jacketed wire and terminal combinations into an ultrasonic welder. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the Drawing, FIG. 1 depicts a conventional ultrasonic welder  10  and an insulation jacketed wire and terminal combination  12 . 
     The insulation jacketed wire  14  is composed of a wire  16 , which may be single strand or multiple strand (as for example copper), and an insulation jacket  18  which covers the surface of the wire (that is, the surface of the wire parallel to its length). The insulation jacket  18  is of a meltable material, as for example a thermoplastic, preferably for example a PVC or a polyester. The terminal  22  is metallic (as for example a soft metal) and may have any configuration, a male terminal being depicted merely for illustration purposes. The terminal  22  includes a base  24  having opposed; top and bottom surfaces  24 T,  24 B (see also FIG.  2 ), and the insulation jacketed wire is placed abutting the top surface. Preferably, but not necessarily, the insulation jacketed wire  14  is staked to the terminal  20  by staking wings  26  of the terminal which preferably do not penetrate the insulation jacket  18  so as not to risk damage or cutting of the multiple-stranded, small-gauged, wire or core  16  (ie., equal to or smaller than 26 gauge). 
     The ultrasonic welder  10  is generally conventional, as for example (for illustration purposes and not by way of requirement) an “Ultraweld® 40” ultrasonic welder of AMTECH® (American Technology, Inc.) of Milford, Conn. This class of commercially available ultrasonic welders include: a solid state power supply  28  which is user adjusted by controls of a microprocessor based controller  30 , a transducer where electrical energy of the power supply is converted into mechanical vibration and an amplitude booster where the mechanical vibrations of the transducer are amplified  32 , an output tool in the form of a horn  34  which tunes the vibrations to a tip  36 . The tip  36  is aligned with a stationary anvil  38 , and the ultrasonic welder further includes one or more actuators which allow for movement of the tip relative to the anvil  38 . Preferably, the tip  36  and the anvil  38  have mutually facing work surfaces  40 ,  42  which are knurled so as to grip objects placed therebetween as the tip is forced toward the anvil. The frequency may be fixed at 20 kHz, at 40 kHz or at another frequency, or the frequency may be other than fixed. 
     As comparatively depicted by FIGS. 1,  1 A and  2 , the base  24  of the terminal  22  is oriented so that the bottom surface  24 B rests upon the anvil  38  and the insulation jacketed wire  14  faces the tip  36 . This step is shown completed at FIG. 2, wherein FIG. 2A depicts a top plan view of the jacketed wire and terminal combination  12 , as seen from the work surface  40  of the tip  36 . 
     The operator now actuates operation of the ultrasonic welder  10 . In this regard, prior trial runs should be made to determine optimum parameters for efficacious bonding of the wire  16  to the terminal  22 , and these optimum parameters should have been entered via the microprocessor based controller  30  (as for example optimum amplitude, force and time (the frequency being a usually, but not necessarily, set feature of the ultrasonic welder). 
     An intermediate operational stage is depicted at FIG. 3, wherein the work surface  40  of the tip  36  has been moved into forceful abutment with the insulation jacketed wire  14 , wherein the insulation jacketed wire is sandwiched against the top surface  24 T of the base  24  of the terminal  22  in that the bottom surface  24 B of the base is now in forceful abutment with the work surface  42  of the anvil  38 . As shown at FIG. 3A, the insulation jacket  18  is dimpled  44  by the work surface  40  of the tip  36 , but not broken (although it could be). At this stage of operation, the microprocessor based controller  30  determines whether surfaces are located within in predetermined allowances. If not, an error is called out, otherwise the microprocessor programming advances to the next and final step. 
     As shown at FIG. 4, the solid state power supply  28  now activates the transducer/booster  32 , whereupon mechanical vibration arrives via the horn  34  to the tip  36 . The insulation jacket  18  is believed to now vibrate with the work surface  40  of the tip  36  relative to the wire  16 . And, while this view may present to a skilled artisan a reason to argue that ultrasonic welding of the wire to the terminal  22  will not happen, Applicant has discovered that ultrasonic welding does, in fact, happen. Visibly, the insulation jacket melts and flowably displaces both at the work surface  40  of the tip  36  and at the top surface  24 T of the base  24  as the tip vibrates and continues being forced toward the anvil  38 . It is believed that after this flowing displacement, any remaining insulation jacket material is then dissipated from between the contact surfaces of the wire  16  and the base  24  in the manner of conventional dissipation of contaminants by ultrasonic welding. 
     As shown at FIGS. 4A and 4B, upon conclusion of the application of ultrasonic vibration, the insulation jacket  18  has formed a displacement mass  18 ′ around on diametrically opposing sides where the tip  36  was located, so that now the wire  16  is exposed at one side and bonded by an ultrasonic weld  46  to the top side  24 T of the base  24 . 
     FIG. 5 depicts an alternative mode of carrying out the present invention, wherein two insulation jacketed wires  50 ,  52 , each having a single strand wire  54 ,  56 , are spliced together by ultrasonic welding through the insulation jackets  58 ,  60 . The wires are compressed horizontally by gathering members  62 ,  64 , compressed vertically by an opposed tip and anvil  36 ,  38  and then subjected to ultrasonic vibration by the tip, as described hereinabove. The result is shown at FIG. 5A, wherein the insulation jackets  58 ,  60  are now jumbled into a displacement mass  58 ′,  60 ′ and the wires  54 ,  56  are bonded at an ultrasonic weld  66 . 
     For purposes of automation, it is preferred to place a plurality of the insulation jacketed wires and terminal combinations  12  onto a jig  70 . The jig has a seat  72  respectively for each insulation jacketed wire and terminal combination  12 . A floor  74  of the jig has apertures  76  for sequentially receiving therethrough the aforesaid anvil  38 . Each seat  72  has a resilient boss  78  for holding seated thereat its respective insulation jacketed wire and terminal combination  12 . 
     Operatively, several considerations relative to the present invention discovery should be kept in mind. Firstly, there must be provided some place for the insulation jacket displacement mass to go. While this is not a concern for ultrasonically bonding an insulation jacketed wire to a terminal, this can be an impeding problem for splicing of multi-stranded wires. Secondly, the type of insulation jacket is critical: the insulation jacket must be of a composition which melts when heated so that it will flowably displace. Suitable insulation jacket materials include thermoplastics. Lastly, the thinner the insulation jacket the better, particularly in terms of accommodating insulation jacket dissipation mass. 
     Examples of the method according to the present invention will now be detailed. Three insulation jacketed wires were tested as indicated by Table 1. Insulation jacketed wires having I.D. numbers 1 and 2 are a seven strand copper wire with an ultra thin wall PVC insulation jacket 0.25 mm thick. Insulation jacketed wire having 1.D. number 3 is composed a solid core copper wire with an ultra thin wall PVC insulation jacket 0.25 mm thick. In each case the terminal was of a copper alloy. The ultrasonic welder was an “UItraweld® 40” ultrasonic welder of AMTECH® (American Technology, Inc.) of Milford, Conn. operating at 40 kHz, having anvil and tip cross-sections of 2.1 mm by 2.1 mm. In each example an excellent ultrasonic bond was achieved between the wire and the terminal, in terms both of strength and electrical conductivity. 
     
       
         
               
               
               
               
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                   
                   
                   
                   
                   
                   
                 Thickness 
                 Thickness 
               
               
                 I.D. 
                 Wire Size 
                 Energy 
                 1 st  Contact 
                 Weld Contact 
                 Amplitude 
                 Before Weld 
                 After Weld 
               
               
                 No. 
                 (mm 2 ) 
                 (Joules) 
                 Pressure (psi) 
                 Pressure (psi) 
                 (microns) 
                 (mm) 
                 (mm) 
               
               
                   
               
             
             
               
                 1 
                 0.35 (22 gauge) 
                 31 
                 23 
                 28 
                 25 
                 1.66 
                 0.73 
               
               
                 2 
                  0.5 (20 gauge) 
                 34 
                 30 
                 33 
                 27 
                 1.80 
                 1.00 
               
               
                 3 
                 0.14 (26 gauge) 
                 13 
                 18 
                 21 
                 20 
                 1.42 
                 0.81 
               
               
                   
               
             
          
         
       
     
     The methodology according to the present invention has great utility for the handling of small (ie., 26 gauge) wires. Small gauge wires are frequently very difficult to strip without injuring the wire or multi-stranded core  16 . For instance, small gauged insulated wires  14  of less than 26 gauge are known to have cores  16  containing less than seven strands of copper along with very thin insulation jackets (ie., less than 0.25 mm) which are particularly difficult to strip without cutting at least one of the strands. Because each strand of the core  16  may be necessary to carry required circuit currents, when stripping is conducted, wires  14  have typically been sized larger than required expecting some core damage. Consequently, ultrasonic welding of small gauge wires is costly and difficult. However, the method according to the present invention does not require pre-stripping of wires, so that now small wires can, for the first time, be economically attached to terminals. 
     It is to be understood that any number of insulation jacketed wires may be simultaneously sonicly welded through the insulation thereof. For example, a large number of small (ie., 26 gauge) wires may be simultaneously sonically welded to the base of a terminal using the herein methodology. 
     To those skilled in the art to which this invention appertains, the above described preferred embodiment may be subject to change or modification. Such change or modification can be carried out without departing from the scope of the invention, which is intended to be limited only by the scope of the appended claims.