Abstract:
An ultrasonic welding apparatus and method for detaching or effecting release of an ultrasonic welding tool stuck or attached to a weldment. The method includes the step of utilizing a mechanism mounted adjacent to the ultrasonic welding tool to hold the weldment in position during welding and/or while the ultrasonic welding tool is withdrawn and, if necessary, using the mechanism to detach the weldment from the ultrasonic welding tool. The method contemplates providing a twist, rotary or axial motion to one of the ultrasonic welding tool or weldment to effect release of the ultrasonic welding tool. The apparatus may include a clamp member having a distinct clamping area or pad located adjacent to the sonotrode or anvil of the ultrasonic welding tool. The clamp mechanism provides vibration control, noise mitigation, and a more uniform boundary condition during welding and facilitates part release upon the completion of the welding process.

Description:
FEDERAL SPONSORSHIP 
       [0001]    The U.S. Government has a paid-up license in this invention and the right, in limited circumstances, to require the patent owner to license others on reasonable terms as provided for by the terms of Contract No. 70NANB3H3015 awarded by the National Institute of Standards and Technology. 
     
    
     CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention relates generally to an ultrasonic welding apparatus and more specifically to an ultrasonic welding apparatus having weld tooling designed for vibration control and part release. 
         [0005]    2. Description of Related Art 
         [0006]    Ultrasonic welding of various materials is known. The process involves vibrating overlapping workpieces clamped between a sonotrode and an anvil. Frictional forces occurring between the vibrating workpieces create a bond or weld that occurs at the interface between the workpieces, effectively joining them to one another. Various sonotrode and anvil surface configurations; i.e., the surface that contacts the workpieces, are known and used to transfer energy from the sonotrode to the interface between the workpieces. 
         [0007]    Ultrasonic welding of thin metal sections is well known. It is also known that during ultrasonic metal welding, a circular collar clamp may be applied around the weld area in order to prevent workpiece rotation, effect weld quality consistency, and mitigate the energy emanating from the weld area, thereby allowing welding in close proximity to prior welds. Collar clamps, about the anvil and welding tip, however, can restrict access to numerous joint locations, such as sheet metal flanges, whose size is typically minimized in order to reduce component weight and material cost. 
         [0008]    Another common issue during ultrasonic welding of metals is sticking/welding of the sonotrode tip and/or anvil to the workpiece. The magnitude of sticking is a function of weldment materials, weld tooling design, and welding parameters employed. When sticking forces are low, removing the tools, both the sonotrode and anvil, from the workpiece or weldment typically does not cause any damage. However, when the sticking force is high, pulling the tool off the weld can damage the weld or deform the workpiece or weldment. The deformation problem worsens with thinner gauge workpieces. Further, even if no workpiece deformation results, stresses induced into the joint or weld when pulling the tool off may have a negative influence on the weld properties. Accordingly, it is desirable to have some mechanism or device for detaching a stuck ultrasonic welding tool. 
       SUMMARY OF THE INVENTION 
       [0009]    Accordingly, the present invention is an apparatus and method for vibration control during ultrasonic metal welding and part release upon the completion of the welding process. The method includes the steps of utilizing a mechanism mounted adjacent to the sonotrode to hold the weldment in position during welding and potentially while the sonotrode is withdrawn and, if necessary, using the mechanism to detach the weldment from the sonotrode. 
         [0010]    In one embodiment, rotating the weldment, the sonotrode and/or the anvil provides a twist, rotary or angular motion relative to the sonotrode axis to effect a release of the ultrasonic welding device from the weldment. The rotation may be about the axis of the sonotrode and in the plane of the weldment or the axis of rotation may be transverse to the weldment and in the same plane as the sonotrode axis. In some instances, it may be a combination of both. 
         [0011]    In an additional embodiment, the ultrasonic welding apparatus includes a mechanism located adjacent to or near the sonotrode to hold the weldment when retracting the sonotrode. In an alternative embodiment, mechanisms located on each side of the weldment operate to remove either the anvil and/or the sonotrode from the weldment. 
         [0012]    In a further embodiment of the invention, a mechanism located adjacent to or near the sonotrode holds the workpiece or weldment stationary while the sonotrode and/or anvil rotate to detach the workpiece from the sonotrode or anvil. 
         [0013]    A further embodiment of the invention includes a clamp mechanism having a clamping area or pad located adjacent to the sonotrode or anvil. The clamp mechanism provides vibration control, noise mitigation, and a more uniform boundary condition during welding and facilitates part release upon the completion of the welding process. Clamp material can be selected to achieve optimal damping, surface marking, durability, and welding characteristics. 
         [0014]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0016]      FIG. 1  is a schematic view of an ultrasonic welding apparatus according to one embodiment of the present invention. 
           [0017]      FIGS. 2A-2C  are schematic views of various embodiments of a device for use in detaching a sonotrode and/or anvil according to the present invention. 
           [0018]      FIG. 3  is an alternative embodiment of an ultrasonic welding apparatus according to the present invention. 
           [0019]      FIG. 4  is a schematic view of an alternative embodiment of an ultrasonic welding apparatus according to the present invention. 
           [0020]      FIG. 5  is a perspective view of the respective upper and lower portions of the ultrasonic welding apparatus illustrated in  FIG. 4 . 
           [0021]      FIG. 6  is a schematic view of a further embodiment of a sonotrode for use with an ultrasonic welding apparatus according to the present invention. 
           [0022]      FIG. 7  is a schematic view of another embodiment of an ultrasonic welding apparatus according to the present invention. 
           [0023]      FIG. 8  is a top view of the ultrasonic welding apparatus illustrated in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]      FIG. 1  shows an ultrasonic welding apparatus, seen generally at  10 , according to one embodiment of the present invention. The ultrasonic welding apparatus  10  includes a reed  12  having a sonotrode  14  mounted at one end thereof. The reed  12  is mounted for movement in a side-to-side or horizontal direction of vibration, shown by the arrow  16 . The reed  12  also moves in a vertical manner, shown by the arrow  18 , and in cooperation with an anvil  20  holds first  22  and second  24  workpieces in position under moderate clamping forces. Once the workpieces  22 ,  24  are held in position, a transducer  26 , connected to the reed  12  by a wedge  28 , vibrates the reed  12  at a high frequency (typically 15 to 40 kHz) to impart energy through the sonotrode  14  to the first  22  and second  24  workpieces at a location between the sonotrode  14  and the anvil  20  to create a bond or weld at the interface or adjacent surfaces  31  of the workpieces  22 ,  24  thereby creating a weldment. As used herein, the term sonotrode generally refers to a tool attached to the reed of an ultrasonic welding apparatus and it may be referred to as the sonotrode tip. Accordingly, the sonotrode or sonotrode tip refers to a gripping tool attached to the end of the reed. 
         [0025]      FIG. 1  also illustrates a clamp mechanism or engagement member, seen generally at  30 , including a clamp member  32  and a support member  34 . The clamp mechanism  30  is mounted for movement in a vertical manner as indicated by the arrow  36 . The clamp mechanism  30  is mounted such that it moves or travels independently of the ultrasonic welding apparatus  10 . Accordingly, the clamp mechanism  30  provides a clamping force to secure and hold the first  22  and second  24  workpieces in position. It should be understood that this clamp force may be in addition to a separate force provided by the reed  12  and anvil  20 . As set forth more fully herein, the clamp mechanism  30  also assists in removing a weldment from the ultrasonic welding apparatus  10  if the weldment becomes stuck to the ultrasonic welding apparatus  10 . In addition, it also operates as an isolator to isolate other areas of the weldment from the ultrasonic vibrations occurring during the welding process. 
         [0026]    Various embodiments of a clamping mechanism  30  for use with an ultrasonic welding apparatus  10  are schematically illustrated in  FIGS. 2A-2C .  FIG. 2A  illustrates the clamping mechanism  30  moving downward in the direction of the arrow  38  to engage the first workpiece  22 . The anvil  20  has a size such that the clamping mechanism  30  holds the first  22  and second  24  workpieces in position against the anvil  20 . The sonotrode  14 , moving independently of the clamping mechanism  30 , engages the first workpiece  22  and performs the welding operation. Accordingly,  FIG. 2A  illustrates the use of a single clamping mechanism  30  operating on one side of the weldment only. 
         [0027]    In the preferred embodiment, the clamp  32  of the clamp mechanism  30  is located as close as possible to the sonotrode  14 . Once the weld is completed, the sonotrode  14  is retracted with the clamp  32  still engaging the weldment. Thus, the clamp  32  stabilizes the weldment and minimizes the likelihood of deformation. In some instances, the clamp  32  applies additional force to push the weldment off the sonotrode  14 . As set forth more fully herein, the clamp mechanism  30  also functions as a weld isolation device. 
         [0028]    Turning to  FIG. 2B  there is illustrated an ultrasonic welding tool utilizing upper and lower clamping mechanisms  30 . Again, the sonotrode  14  moves independently of the upper and lower clamping mechanisms  30 , with the clamping mechanisms  30  moving independent of one another; i.e., the upper clamping mechanism  30  moves downward as illustrated by the arrow  38  and the lower clamping mechanism  30  moves upward as illustrated by the arrow  42 . The upper and lower clamping mechanisms  30  oppose one another and may or may not engage the first and second workpieces  22 ,  24  during the ultrasonic welding operation. As required, the upper and lower clamping mechanisms  30  engage the weldment; i.e., the unit formed by welding the first and second  22 ,  24  workpieces together, to hold the weldment stationary while the respective anvil  20  and sonotrode  14  are removed or withdrawn. Accordingly, the upper and lower clamping mechanisms  30  function to hold the weldment stationary while the sonotrode tip  14  or anvil  20  are rotated, twisted or otherwise moved to release a stuck sonotrode  14  or anvil  20 . The clamping mechanism  30  also pushes the weldment off the anvil  20  or sonotrode  14  should the weldment become stuck to either the sonotrode  14  or the anvil  20 . In addition, the clamping mechanism  30  acts to isolate vibration during the welding process. 
         [0029]      FIG. 2C  illustrates a further embodiment wherein the second workpiece  24  is of a size and mass where it functions as an anvil. The clamping mechanism  30  helps with removal of the sonotrode  14  should the sonotrode  14  become stuck to the first workpiece  22  during the welding operation. Again, the upper clamping mechanism  30  either pushes the weldment off the sonotrode  14  or holds the weldment stationary while the sonotrode  14  is withdrawn or released from the first workpiece  22 . In addition to the axial motion set forth above, a rotating, twisting or other type of angular motion can also be used to withdraw or release the sonotrode  14  from the first workpiece  22 . 
         [0030]    Turning now to  FIG. 3 , shown is an alternative embodiment illustrating a clamping mechanism, seen generally at  50 , including a clamp member  52  mounted for reciprocal motion in the direction shown by the arrow  54 . Power cylinders  56  or other drive members are used to move the clamp member  52 . As illustrated, the anvil  20  is rotatably mounted in a support  66  located on the frame member  68 . Upon receiving a signal from a controller  62  a rotatable shaft  60  connected to the anvil operates to rotate the anvil  20  in the direction shown by the arrow  64 . The clamping mechanism  50  holds the weldment stationary whereby rotation of the anvil  20  in the direction of the arrow  64  releases the stuck anvil  20 . In addition, the clamping mechanism  50  may also function to apply an axial force to the second workpiece  24  to separate the anvil  20  from the second workpiece  24 . As such, part release from the anvil  20  can be effected independently of release from the tip. 
         [0031]    Turning now to  FIGS. 4-5  there is shown a further embodiment of the present invention illustrating an isolation and welding clamp, seen generally at  70 , used in conjunction with an ultrasonic welding device, including a sonotrode  14 , to weld sheet metal flanges  72 ,  74  of the first  22  and second  24  workpieces, respectively. As illustrated, the first and second  22 ,  24  workpieces are located or inserted into the opening or space forming the work area located between the anvil  20  and sonotrode  14 . The clamp  70  includes distinct clamping areas or pads  76  located close to the sonotrode  14 . As with the previous embodiments, the sonotrode  14  and reed  12  move independently of the clamp  70 . Support bars  78  attached to the clamp  70  operate to raise and lower the clamp  70  into engagement with the workpiece  22 . 
         [0032]    A similar lower clamp design, seen generally at  80 , includes clamp pads  82  located close to the anvil  20 . The lower clamp  80  also moves independent of the anvil  20 . The clamp pads  82  on the lower clamp member  80  are located opposite the clamp pads  76  located on the upper clamp  70 . Together with the clamp pads  76  on the upper clamp  70  the lower clamp pads  82  operate to secure the flanges  72 ,  74 , isolate the effect of vibrations occurring during the ultrasonic welding operation on adjacent welds or structures and facilitate, if necessary, the removal of a stuck sonotrode or anvil. 
         [0033]    As illustrated, the clamp geometry, specifically the location and placement of the clamp pads  76 ,  82  is such that the clamp and correspondingly the clamp surface is not completely concentric about and does not surround the sonotrode  14  or the anvil  20 . Instead, the upper and lower clamps  70 ,  80  are designed to engage a flange portion  72 ,  74  of the respective workpieces  22 ,  24 . As illustrated, the rectangular shape of the clamp pads  76 ,  82  enables placement of the clamps  70 ,  80  close to the inboard edge or surface  75  of the respective flanges  72 ,  74 . While shown as two rectangular shaped clamp pads  76  located on opposite sides of the sonotrode tip  14 , the shape or configuration and position or location of the clamp pads  76 ,  82  are all variable. For example, angle or corner welds may require that the clamp pads be placed at angles relative to one another. Further, the configuration of the clamp pads  76 ,  82  may change to change the isolation and vibration control aspects of the clamp  70  in order to reduce or mitigate vibration in certain areas or locations of the workpiece during the welding operation. In this manner, welds can be placed adjacent or close to one another without a subsequent welding process disturbing previous welds. Accordingly, depending upon the particular welding process the use of separate and distinct clamps or clamp pads provides an easily modified and changed multifunctional ultrasonic welding tool. 
         [0034]    In addition, the clamp pads  76 ,  82  can be made of various materials to mitigate and dampen vibration and thereby isolate the flange area beyond the clamp pads  76 ,  82  from the effect of vibrations in the weld region. For example, the clamp pads  76 ,  82  can be made of various materials including plastics, polymers and copolymers such as polytetrafluoroethylene, ceramics, steels, and other metals. The particular clamp pad  76 ,  82  material chosen for use may depend on material wear life; vibration, noise isolation and absorption qualities; and material and manufacturing costs. In addition, the clamps  70 ,  80  and the material forming the clamp pads  76 ,  82  also function and cooperate with the particular clamp configuration to mitigate component or part vibration and reduce noise occurring during the welding process. 
         [0035]    Accordingly, the clamp  70 ,  80  or clamp pad  76 ,  82  shapes or surfaces can undertake or be formed of different geometries and be formed of different materials. In addition, the clamps  70 ,  80  or clamp pads  76 ,  82  may have a contact or pad surface  83  that utilizes different patterns or textures to enhance gripping of the first and second workpieces  22 ,  24  and ultimately the weldment formed once the individual workpieces are welded together. For example, as shown in  FIG. 4 , the contact or pad surface  83  of the clamp pad  82  is knurled. It may also have a diamond shape or include a particular design. Thus, the pad surface  83  patterns and textures, including pad surface  83  shapes or designs can vary as necessary to improve part gripping, impart a mark on the weldment, or add a functional characteristic, such as a recess, to the workpiece in the area of the weld. 
         [0036]    In addition, while the clamp pads  76 ,  82  are shown inline or collinear in the disclosed embodiment, it is not necessary for the clamp locations to be aligned in such a manner. The position of the clamp pads  76 ,  82  depends, in part, upon the workpieces being welded. For instance, the clamp pads are placed at various positions, such as 90° angles, when the ultrasonic welding tool is used to weld in corners, and more than two clamp pads could be used to isolate vibrations and facilitate part release when welding complicated geometries such as a T-junction. In addition, a single clamp pad on only one side of the tip may be used to facilitate improved access when welding in restrictive locations. Further, the clamp pads  76 ,  82  may be positioned such that they are located off or distanced from a sonotrode center line, such as when used with an offset sonotrode contact surface which can facilitate equipment application on reduced size flanges, as shown in  FIG. 6 . 
         [0037]    In the alternative embodiment illustrated in  FIG. 6 , the sonotrode  14  has a contact surface  88  that is positioned on one side of the sonotrode  14 . Forming the contact surface  88  of the sonotrode  14  in this manner increases the amount of surface area of the contact surface  88  placed on the flange  72 , which correspondingly, transfers a greater amount of ultrasonic vibration to the respective first  22  and second  24  workpieces. In this embodiment, the width of the contact surface  88  depends on the width of the flange portion  72 ,  74 . The upper clamp pads  76 , and when used lower clamp pads  82 , may also either be offset or have a reduced size or profile whereby they fully contact and engage the respective flange portions  72 ,  74 . 
         [0038]    As with the previous embodiments, if the second workpiece  24  is an adequately heavy or thick substructure, the second workpiece  24  can function as an anvil and only the upper clamp  70  and sonotrode  14  are used. Such one-sided clamping reduces the need to place an anvil on the backside of the structure. In addition, the upper and lower clamp members  70 ,  80  may also include a cooling assembly, such as cooling passageways located in the clamp members  70 ,  80 . A cooling fluid circulated through the passageways cools the clamp members  70 ,  80  and clamp pads  76 ,  82  and correspondingly reduces or dissipates heat occurring during the ultrasonic welding process. 
         [0039]    Turning now to  FIGS. 7-8  there is shown a further embodiment of an ultrasonic welding apparatus including a release mechanism for releasing a weldment stuck or attached to a sonotrode tip or anvil. As illustrated in the disclosed embodiment, the ultrasonic welding apparatus, seen generally at  90 , is mounted on the head portion  108  of a robot arm, seen generally at  92 , that moves the ultrasonic welding apparatus  90  into position to perform an ultrasonic welding operation. The present embodiment discloses an apparatus for releasing or freeing a weldment from the ultrasonic welding apparatus  90  if it sticks to the ultrasonic welding apparatus  90  upon conclusion of the welding operation. As shown, the robot arm  92  includes a wrist joint, seen generally at  94 , that operates to rotate the ultrasonic welding apparatus  90  slightly about its longitudinal axis  95 , as shown by the arrow  96 , to effect a release of the ultrasonic welding apparatus  90 . Typically, only a slight rotation is required. For example, 1-5° of rotation is sufficient to disengage the ultrasonic welding apparatus  90  from the weldment. 
         [0040]    As illustrated in  FIGS. 7-8  the wrist joint  94  includes a wrist pin  98  and a dampening/power cylinder  100  pivotally attached, via pivot pins  112  and struts  110  to respective arm portions  102 ,  104  on opposite sides of the wrist pin  98 . A slide joint  106  located in the robot arm  92  operates to allow the arm portions  102 ,  104  to move slightly when the wrist action or movement of the wrist joint  94  imparts rotation to the ultrasonic welding apparatus  90  about its longitudinal axis  95 . This is one method of imparting rotation to the ultrasonic welding apparatus  90 ; other mechanisms such as rotatably mounting the ultrasonic welding apparatus  90  on the head portion  108  of the robot arm  92  are also suitable. In addition, while the embodiment illustrated in  FIGS. 7-8  illustrates a stationary anvil  20 , a rotatable anvil  20  of the type or design illustrated in  FIG. 3  may also be mounted on the head portion  108  of the robot arm  92 . 
         [0041]    In a further embodiment, the fixture used to hold the workpiece or weldment may be configured such that part clamping can be implemented at remote locations to mitigate component or part vibration during the ultrasonic welding process. The fixture may also be rotated, typically about the longitudinal axis  95  of the ultrasonic welding apparatus  90  to release the ultrasonic welding apparatus  90  from the weldment. Accordingly, the invention contemplates rotating either the ultrasonic welding apparatus, including either the sonotrode or the anvil, or the weldment to effect release of a stuck ultrasonic welding tool. 
         [0042]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.