Abstract:
An ultrasonic welding assembly is disclosed. The assembly includes an ultrasonic welder having nodal horn support for improving transmission of transducer energy to the weld comprising an acoustical tool having a horn; a weld tip on the end of said horn; and at least two nodal mounts which are in contact with and axially and radially support said horn. The horn self-aligns in housing by sitting a housing-key within a keyway in the horn. The weld tip self aligns by sitting the keyed tip in a keyway of the horn.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Applicant claims priority benefits under 35 U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 61/078,826 filed Jul. 8, 2008. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an ultrasonic welding apparatus and more particularly to an improved method of mounting an ultrasonic stack and weld tip. 
       BACKGROUND OF THE INVENTION 
       [0003]    Ultrasonic welding uses high frequency ultrasonic acoustic vibrations to hold materials together. Such systems contain an ultrasonic horn assembly having a number of distinct components, which are connected in a stack. Common configurations include a converter to convert electrical signal into a mechanical vibration, a booster to modify the amplitude of the vibration, and a horn to apply mechanical vibrations to the parts to be welded. In standard systems the booster is also used to clamp the stack into a press. 
         [0004]    The most typical mounting method for an ultrasonic stack is supporting the horn, preferably at its nodal point, in order to prevent loading of the tip by the anvil from deflecting the horn off the transducer axis. Several nodal mounting means have been devised such as set screws, clamps, and spring mounting. With such mounting systems, the horn deflects when weld force is applied causing the interface between the horn and anvil to hinge open. This results in loss of energy transmission and a loss of positional accuracy. Additionally, the horn has no radial orientation feature because it is screwed onto the booster. A skilled technician with special set up tools is therefore required to accurately orient the horn. 
         [0005]    Another disadvantage of the prior art lies in the lack of accuracy and rigidity of the weld position. In many applications such as wire splicing and wire termination, the position of the weld tip must be maintained within 3 microns (0.001 inches). This is not possible to achieve under full load of prior mounting systems. For example, U.S. Pat. No. 4,610,750 to Branson Ultrasonics Corp. shows a replaceable tip mounted onto the tapered end of a round horn. A problem with this design is limited access to weld larger components due to interferences with the body of the horn. 
         [0006]    What is desired, therefore, is an ultrasonic welder where the body is nodally and radially mounted, and also is self-aligning with respect to the housing. A self-positioning horn with a replaceable, self-aligning weld tip is also desired. 
       SUMMARY OF THE INVENTION 
       [0007]    Accordingly, it is an object of the invention to disclose nodal support for an ultrasonic welder that exerts radial forces and, in addition, exerts equal and opposite axial forces upon the welder through forces applied to the nodal support to decrease deflection of the horn and increase energy transmission to the weld. 
         [0008]    Another embodiment of the invention is to disclose a housing for an ultrasonic welder having axial and radial nodal support wherein the housing provides axial support and converts axial force to radial force in order to decrease deflection of the horn and increase energy transmission to the weld. 
         [0009]    A further object of the invention is to disclose a self-aligning ultrasonic welder having axial and radial nodal support and axial and radial support from a housing that will diminish longitudinal displacement, improve transmission of energy to the weld, and eliminate timely set up. 
         [0010]    Yet another object of the invention is to provide a self-aligning weld-tip for an ultrasonic welder having axial and radial support to maintain rigidity of the weld position within 3 microns. 
         [0011]    In one embodiment of the invention at least two nodal mounts having slanted faces are coupled to the welder and exert radial forces as well as equal and opposite axial forces upon the welder through forces applied to the slanted faces of nodal mounts. A full wave acoustical tool and semi-rigid nodal mounts are utilized. A keyway that is useful to secure the tool within housing is provided in the ultrasonic welder having at least two nodal mounts having slanted faces which exert radial and axial support. 
         [0012]    In another embodiment of the invention, a bushing exerts axial forces on an ultrasonic welder having a keyway for securing the tool and having at least two nodal mounts which provide radial forces and, in addition, exert equal and opposite axial forces upon the welder. The bushing abuts a face of the nodal mounts converting at least some of the bushing&#39;s axial force into radial force. 
         [0013]    In yet another embodiment of the invention, a key in the weld tip fits into a keyway in the horn of an ultrasonic welder having at least two nodal mounts having slanted faces which are coupled to the welder and which exert radial forces and also equal and opposite axial forces upon the welder through forces applied to the slanted faces. 
         [0014]    In a further embodiment of the invention, an ultrasonic welder having a cantilevered weld zone and dynamic nodal horn support is set inside a housing. The housing provides equal and opposite axial support for the welder by exerting force on the slanted faces of nodal mounts positioned at λ/4 and 3λ/4 of a full wave acoustical tool. 
         [0015]    In still another embodiment of the invention, a key is set in a housing of an ultrasonic welder having a cantilevered weld zone and dynamic nodal horn support which provides axial support for the welder, to self-align the welder within a keyway in the horn. 
         [0016]    In a further embodiment, a bushing abuts the slanted faces of nodal mounts on an ultrasonic welder having a cantilevered weld zone and dynamic nodal horn support for improving transmission of transducer energy to the weld. The bushing converts some of the axial forces applied to the stack into radial forces, thus exerting more axial force to secure the stack. 
         [0017]    Still another embodiment of the invention provides a self-aligning ultrasonic welder having axial and radial support with a self-aligning weld tip. Keys in a housing and the weld tip fit into keyways in the stack. The welder is a full wave tool. A bushing exerts axial forces on the horn. The bushing provides radial support by exerting force on the slanted faces of nodal mounts thereby converting some of the axial forces into radial forces. 
         [0018]    Thus, the present invention discloses mounting means for the acoustical tool of an ultrasonic welder. The tool is provided at its nodal region with a radially extending mounts that are coupled to the tool. At least two such nodal mounts are present so they provide opposite and equal forces. The surface of a housing or bushing exerts force on the nodal mounts. The tool contains a keyway for entry of a keyed member provided in the housing. Additionally, the horn of the tool contains a channel having one or more keyways. A weld tip having coordinating key(s) fits into the channel and keyway of the horn. 
         [0019]    Further and still other objects of this invention will become more clearly apparent from the following description when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  shows basic representation of an ultrasonic welder employing typical mounting means described in the prior art; 
           [0021]      FIG. 2  shows a side view of a representative apparatus that may incorporate the present invention; 
           [0022]      FIG. 3  shows a front view of the ultrasonic welder that may embody the present invention; 
           [0023]      FIG. 4  shows frontal view of a representative weld tip; 
           [0024]      FIG. 5  shows a front perspective view of the booster horn that may incorporate the present invention; 
           [0025]      FIG. 6  shows an exploded view of a housing that may embody the present invention, and within the housing a side view of a stack of the present invention; 
           [0026]      FIG. 7  is a cross section of  FIG. 2  having mounting means that may incorporate the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    The mounting means described hereafter is particularly suited for mounting a full wave acoustical tool with rigid nodal mounts and a cantilevered weld zone. In a typical industrial apparatus the frequency is in the ultrasonic range, and the apparatus includes a stack of three members, namely a converter, booster, and horn. The booster and horn may be connected at an interface by various means, or a “booster horn” in which the booster and horn are fused together may be employed to transfer vibrations to a weld tip. See e.g. U.S. Pat. No. 7,786,383 to Stegelmann, incorporated herein by reference. Often, in addition to functioning as a mechanical impedance transformer, the booster horn serves as a means for mounting the stack in a stationary housing. The following description describes the mounting means in connection with a booster horn, although the invention is applicable to other vibration members. 
         [0028]    Referring now to the drawing figures and in particular  FIG. 1 , there is shown an ultrasonic welder  32  with mounting means common in the prior art. Welder  32  is an acoustical tool that comprises a horn  10 , a weld tip  11 , a booster  12  for amplifying and subsequently inducing vibrations into the acoustical tool, and a converter  13  for converting electrical impulses to mechanical oscillations via a piezo electric assembly. The combination of horn  10 , booster  12 , and converter  13  is also referred to as the “stack.” 
         [0029]    The mounting of welder system  32  is along the plane of maximum amplitude where the stack is fastened to a mounting shell  15  via a frontal diaphragm spring  16  and a rear diaphragm spring  14 . The springs  14  and  16  isolate the vibrations. However, horn  10  may deflect when weld force is applied to tip  11 , causing the interface between the horn  10  and an anvil (not pictured) to hinge open, resulting is a loss of energy transmission from the stack to the object to be welder. Positional accuracy of the tip  11  is also compromised. 
         [0030]    Referring to  FIGS. 2 ,  6  and  7 , an ultrasonic welder  33  in accordance with the invention is depicted. Welder  33  comprises a booster horn  17 , nodal mounts  18  for mounting the booster horn  17  and dampening vibrations, a weld tip  21 , and nut  22  which helps secure the weld tip  21  to the booster horn  17 . The booster horn  17  contains an upper keyway  19  and lower keyway  20  that assist in positioning the booster horn  17  in a stationary housing. The use of a booster horn  17  is preferred since there is greater efficiency of transmitting ultrasonic energy along the axis of the acoustical tool from a converter (not pictured) to the weld tip due to the elimination of the interface between the horn and booster. Thus, no hinge separation of the interface is observed when radial weld force is applied reducing the efficiency energy transmission and eventually damaging the interface. 
         [0031]    The welder may have multiple nodal mounts  18 . A node is a point or region on an ultrasonic horn where the displacement is negligible or zero. Preferably, the nodal mounts are positioned at λ/4 and 3λ/4 of a full wave acoustical tool. The mounts  18   a  and  18   b  radially resist deflection. Moreover, the mounts  18   a  and  18   b  force the stack components to oppose each other axially and help prevent the housing from moving. 
         [0032]    Mounts  18   a  and  18   b  are depicted as frusto-conical, but may be of any shape so that they may be coupled to the surface of the booster horn  17 . Coupled means that the respective elements are linked or connected together, but not necessarily in direct physical contact. The mounts  18  contain a slanted face or tapered bearing. They may be constructed of various materials such as flexible metal, elastomeric polymers, or rigid metal, all discussed in U.S. Pat. No. 5,590,866 to Cunningham, incorporated herein by reference. Mounts constructed of a semi-rigid material are preferred. For example, glass filled nylon is used because it may achieve intimate contact with the tool  17  and a tapered bearing is easily cut into it. 
         [0033]    In  FIG. 1 , the stack is mounted at 0 and λ/2, the points of maximum amplitude by diaphragm springs  14  and  16 . These springs require an axially flexible seating. However, the welder of the present invention provides mounts  18  at λ4 and 3λ/4, the points of zero amplitude. Thus, maximum amplitude can be applied to the weld in the present invention. Moreover, the occurring radial and axial forces, as well as bending moments, and possibly torsion moments, caused by welding can be absorbed. 
         [0034]    Further, mounts  18  of  FIG. 2  are of much different shape and construction than those of  FIG. 1 .  FIG. 1  depicts springs  14  and  16  that are typically statically stiff, contain multiple components, and resonate at the frequency of the horn. The mounts  18  of  FIG. 2  are one piece and are coupled to and often intimately contact the welder. The mounts  18  force components opposite each other and help resist deflection. The mounts  18  also help prevent housing from moving, as opposed to allowing the tool to move, as in welder  32  of  FIG. 1 . In welder  33 , an embodiment of the present invention, there is a slanted face of the mount (better depicted in  FIG. 6 ) that helps to achieve intimate contact with a housing member and helps secure the tool  17  in multiple directions at multiple points. 
         [0035]    Referring to  FIG. 6 , booster horn  17  is surrounded by housing  28 , which accommodates and secures the acoustical tool. The housing may be constructed of any durable material suitable to secure the acoustical tool. The housing  28  contains one or more housing keys  36 . The key  36  is meant to fit into the keyway  19  to align the tool in the housing. It is preferable to have at least a second keyway  20  in the acoustical tool. The housing may also have a surface  29  that matches the taper of the nodal mounts. The housing applies axial force to the acoustical tool through this surface  29  in order to secure the tool  17  within the housing  28 . Because the taper in the housing surface  29  matches that of the mount  18 , in can intimately contact the nodal mount  18  converting some of the axial force to radial forces. 
         [0036]    Bushing  27  is used to secure the housing assembly  28 .  FIG. 3  depicts a threaded insert that fixes the bushing to the housing  28 ; however the type of bushing  27  may be of any type and material commonly used in the art. The bushing  27  is preferably screwed into the housing  28  creating high clamping forces in the axial direction. Further, the bushing  27  has a surface  35  that abuts and exerts force on the slanted face of the nodal mount  18 . The longitudinal force created by screwing the bushing  27  to the housing  28  is exerted onto booster horn  17  by abutting the bushing to a surface of the tool. Preferably, the bushing abuts the nodal mount  18 . Thus, some of the axial force is converted into radial force by contact of the bushing with the tapered face of the mount, further securing the tool. The longitudinal or axial forces created by the bushing  27  on the rear nodal mount  18   b  are opposite to the forces applied by the housing surface  29  to the nodal mount  18   a . The opposing application of axial force ensures minimal longitudinal displacement of the booster horn  17 . 
         [0037]    Referring now to  FIGS. 3 ,  4  and  5 , the weld tip  21  is secured to the booster horn  17  by a nut  22 . The weld tip  21  has a tip center  30  that is adaptable to the booster horn  17 . The tip  21  may contain multiple weld surfaces such as a medium knurl  26  and a course knurl  25 . The weld surface utilized is positioned by way of one or more tip key(s)  24 . The tip keys  24  fit into corresponding keyways  34  of the key channel  31  located in the booster horn  17 . The tool depicted has two tip keys and tip keyways, however less or more may be utilized. By fitting snuggly in the keyways  34 , the keys  24  help to align the tool and prevent tip displacement. This is especially important in applications such as wire splicing and wire termination, where the position of the weld tip must be maintained within three microns. The tool of the present invention was able to maintain this accuracy under full load. 
         [0038]    In addition to the tip key  24  and keyway  34 , the tip  21  is secured by a nut  22 . The booster horn may contain a threading in the tip center  30 . Securing means are not limited to nut  22  and other means of securing the weld tip  21 , such as an external screw or bolt that may fit into tip center  30 , are contemplated by the invention. 
         [0039]    Although the invention has been described with reference to a particular arrangement of parts, features and the like, these are not intended to exhaust all possible arrangements or features, and indeed many other modifications and variations will be ascertainable to those of skill in the art.