Abstract:
Dielectric welding apparatus has opposed electrodes that can be engaged on either side of a product to be welded and a dielectric welding power supply that supplies welding potentials to the electrodes. The apparatus includes electrically insulating buffer material adjacent to at least one of the electrodes. A recess formed in a surface of the buffer material receives an end of an electrically-conductive member in the product. The buffer material prevents arcing between the electrodes and the electrically-conductive member.

Description:
TECHNICAL FIELD  
       [0001]     This application is a divisional of U.S. patent application Ser. No. 11/128,277 filed on 13 May 2005 and entitled DIELECTRIC WELDING METHODS AND APPARATUS which claims the benefit under 35 U.S.C. §119 of U.S. provisional patent application No. 60/570,817 filed on 14 May 2004 and entitled DIELECTRIC WELDING METHODS AND APPARATUS which is hereby incorporated by reference herein. 
     
    
     TECHNICAL FIELD  
       [0002]     The invention relates to methods and apparatus for welding dielectric materials such as plastics. Some embodiments of the invention relate to welding using electromagnetic signals (e.g. radiofrequency signals). The invention may be applied to welding plastic membranes together in the presence of metals or other exposed electrically conductive materials (hereinafter referred to as ECM). The invention has broad application for manufacturing products which include welded plastic membranes that have ECM near to the weld locations.  
       BACKGROUND  
       [0003]     Dielectric welding, also known as capacitance, radio-frequency, or high frequency welding, provides a way to fuse materials together. The resulting weld can be as strong as the original workpiece materials. Dielectric welding is commonly used for joining various plastic materials together.  
         [0004]     In dielectric welding, an alternating electrical field (typically alternating at a high frequency) is applied across an area to be welded. This is typically done by applying a signal between electrodes. The signal creates a varying, high-frequency electromagnetic field. When a material which is a poor electrical conductor is exposed to such a field, heat is generated in the material. The heat results from electrical losses that occur in the material. The heat deposited in the material causes the temperature of the material to rise. The heated materials become fused together.  
         [0005]     Dielectric welding relies on certain properties of the material in the parts being welded, for example, the geometry and dipole moments of molecules of the material, to cause the generation of heat in a rapidly alternating electromagnetic field. Not all materials can be dielectric welded. Polyvinyl chloride (PVC) is commonly welded by dielectric welding. Other thermoplastics that can be dielectric welded are EVA and polyurethanes.  
         [0006]     A typical dielectric welding apparatus places materials to be joined between two electrodes, which are typically metal plates or bars. The electrodes are connected to an oscillator. The oscillator is turned on to heat the materials, which fuse together when they have been heated sufficiently. The electrodes may hold the materials together during heating and cooling.  
         [0007]     There are situations where it is desirable to make products which have ECM, e.g. metal components, embedded in or attached to one or more membranes or other parts of a dielectric material which are to be welded together. A problem is that ECM in the vicinity of the electrodes of a dielectric welder can cause electrical discharges in the form of arcs or sparks. Such electrical discharges can damage the product being made, the welding apparatus and/or the dielectric welder itself. Electrical arcing can be dangerous to machines and humans.  
         [0008]     It is not always possible or convenient to add ECM after welding has been completed. There is a need for methods and apparatus which may be used to perform dielectric welding in the vicinity of ECM.  
       SUMMARY OF THE INVENTION  
       [0009]     The invention relates to methods and apparatus for welding plastic materials membranes together in the vicinity of electrically conductive materials.  
         [0010]     Various aspects of the invention and features of specific embodiments of the invention are described below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     In drawings which illustrate non-limiting embodiments of the invention,  
         [0012]      FIG. 1  is a schematic view of a dielectric welding apparatus;  
         [0013]      FIG. 2  is an isometric view showing first and second electrode assemblies;  
         [0014]      FIG. 3  is a perspective view of one of the electrode assemblies of  FIG. 2 ;  
         [0015]      FIG. 4  is a plan view of one of the electrode assemblies of  FIG. 2 ;  
         [0016]      FIG. 4A  is a cross sectional view (in the plane A-A of  FIG. 4 ) of the electrode assembly of  FIG. 4 ;  
         [0017]      FIG. 4B  is an exploded view of the electrode assembly of  FIG. 4 ;  
         [0018]      FIG. 5  is a plan view of the other one of the electrode assemblies of  FIG. 2 ;  
         [0019]      FIG. 6  is an isometric view of a buffer member;  FIG. 6A  is a top plan view thereof;  FIG. 6B  is a section in the plane A-A thereof; and  FIG. 6C  is a section in the plane B-B thereof;  
         [0020]      FIG. 7  is an isometric view of a part of an electrode assembly;  
         [0021]      FIG. 7A  is a top plan view thereof;  FIG. 7B  is a section in the plane C-C thereof; and  FIG. 7C  is a section in the plane D-D thereof;  
         [0022]      FIG. 8  is an isometric view the electrode assembly of  FIG. 7  holding a product to be welded with a top membrane removed for clarity;  FIG. 8A  is a top plan view thereof;  FIG. 8B  is a section in the plane E-E thereof; and  FIG. 8C  is a section in the plane F-F thereof;  
         [0023]      FIG. 9  is an isometric view the electrode assembly of  FIG. 8  with the top membrane of the product in place to be welded;  FIG. 9A  is a top plan view thereof;  FIG. 9B  is a section in the plane G-G thereof; and  FIG. 9C  is a section in the plane H-H thereof;  
         [0024]      FIG. 10  is an isometric view the electrode assembly of  FIG. 9  showing electrodes, but not a buffer portion, of a top electrode assembly;  FIG. 10A  is a top plan view thereof;  FIG. 10B  is a section in the plane I-I thereof; and  FIG. 10C  is a section in the plane J-J thereof;  
         [0025]      FIG. 11  is an isometric view the electrode assembly of  FIG. 10  showing the buffer portion of the top electrode assembly;  FIG. 11A  is a top plan view thereof;  FIG. 11B  is a section in the plane K-K thereof; and  FIG. 11C  is a section in the plane L-L thereof;  
         [0026]      FIG. 12  is an isometric view of the top electrode assembly portion shown in  FIG. 11 ;  FIG. 12A  is a top plan view thereof;  FIG. 12B  is a section in the plane M-M thereof; and  FIG. 12C  is a section in the plane N-N thereof; and,  
         [0027]      FIG. 13  is an isometric view of the top electrode assembly portion shown in  FIG. 11  supporting a top membrane of a product;  FIG. 13A  is a top plan view thereof;  FIG. 13B  is a section in the plane O-O thereof; and  FIG. 13C  is a section in the plane P-P thereof. 
     
    
     DESCRIPTION  
       [0028]     Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense.  
         [0029]     Consider the case where one wishes to create a pattern of welds joining a pair of membranes. The membranes are made of a plastic material which is suitable for dielectric welding. However, one or both of the membranes has attached to it, or embedded in it, one or more electrically conductive elements (ECM). The ECM may, for example, be metal parts. The ECM may be exposed. If the one or more ECM is near to a location in which it is desired to weld the membranes together then the presence of the one or more ECM may interfere with dielectric welding of the membranes together using conventional methods.  
         [0030]     Welding methods and apparatus can interpose an electrically insulating barrier between ECM in a product being fabricated and the electrodes of a dielectric welder. Provision of an electrically insulating barrier supports welding non-conductive membranes in close proximity to ECMs.  
         [0031]     Electrode structures for dielectric welding may have integrated insulating barriers located so that the insulating barriers will be interposed between electrodes of the electrode structures and the ECMs when the electrodes are in position to make a weld. In some embodiments, the electrode structures include one or more electrodes arranged in a pattern corresponding to a desired weld pattern.  
         [0032]     The electrodes may be made of any suitable electrically conducting materials. Aluminum, brass, and copper are examples of materials from which electrodes may be fabricated. The electrodes may be fabricated using any suitable process. For example, the electrodes may be machined, assembled from component parts, cast, etc.  
         [0033]     Buffers are located between the electrodes. The buffers are made of electrically insulating materials. The buffers are hollowed out to receive projecting portions of one or more ECMs. In some embodiments the buffers fill the spaces between the electrodes.  
         [0034]     The buffers may be made from any of a wide variety of suitable materials. Examples of materials suitable for use as buffers include: electrically non-conductive ceramic materials, polytetrafluoroethylene, polyurethane, polypropylene, polyethylene, silicone, and combinations of these materials. The buffers may be made using any suitable manufacturing processes. For example, the buffers may be machined or otherwise formed from solid materials or cast. A castable polyurethane or silicone may be used to cast all or part of the buffers. The buffers may be partially cast and partially made from solid materials. In preferred embodiments, the buffers have dielectric strengths at least 2 times greater than a dielectric strength of air in a range of frequencies of a high frequency welding current to be used.  
         [0035]      FIG. 1  shows schematically a dielectric welding apparatus  10  according to one embodiment of the invention. Apparatus  10  includes first and second electrode assemblies  12 A and  12 B. Electrode assemblies  12 A and  12 B are disposed on either side of a product  14  comprising plastic materials, typically membranes  16 , to be welded together and one or more ECMs  18 . First and second electrode assemblies  12 A and  12 B each have a face  13  facing toward the other electrode assembly.  
         [0036]     Apparatus  10  comprises a frame  11 . First electrode assembly  12 A is supported by frame  11  and is movable toward and away from second electrode assembly  12 B to permit product  14  to be compressed between electrode assemblies  12 A and  12 B. In some embodiments, electrode assemblies  12 A and  12 B can be pressed together with a desired force by a mechanical linkage mechanism, a pneumatic or hydraulic mechanism, an electrically controlled actuator or some other suitable pressing means. Electrode assemblies  12 A and  12 B may be supported by any suitable mechanisms which maintain registration between electrode assemblies  12 A and  12 B.  
         [0037]     In the illustrated embodiment, frame  11  may be the frame of a conventional dielectric welding machine, for example. First electrode assembly  12 A is mounted to a first platen  19 A. Second electrode assembly  12 B is mounted to a second platen  19 B. Either or both of the platens are movable to achieve placement of products to be welded and removal of welded products. Apparatus  10  supports the compression, welding, and cool down phases of dielectric welding. As the basic operation and constructions of dielectric welding machines are understood by those skilled in the art, features known from conventional dielectric welding apparatus are not described in detail herein.  
         [0038]     First and second electrode assemblies are each connected to a dielectric welding power supply  20 . In the illustrated embodiment, the first and second electrode assemblies are in electrical contact with power supply  20  by way of electrical contact between their bases (or non-welding sides) and the corresponding platens  19 A,  19 B. Except as indicated herein, apparatus  10  may be constructed and operated in substantially the same manner as an existing dielectric welding machine. In operation: 
        product  14  is compressed between first and second electrode assemblies  12 A and  12 B;     power supply  20  is operated to supply high frequency dielectric welding current to first and second electrode assemblies  12 A and  12 B; and,     after sheets  16  have had an opportunity to fuse together at the weld locations, the high frequency current is discontinued and, optionally after a cooling interval, first and second electrode assemblies are separated to allow the welded product  14  to be removed.        
 
         [0042]      FIG. 2  is an isometric view showing first and second electrode assemblies  12 A and  12 B according to an example embodiment of the invention. Each electrode assembly  12 A and  12 B has one or more electrodes  30 . Electrodes  30  of first electrode assembly  12 A are arranged as a mirror image of electrodes  30  of second electrode assembly  12 B. When first and second electrode assemblies  12 A and  12 B are brought together face-to-face the electrodes  30  of electrode assemblies  12 A and  12 B follow one another. Electrodes  30  of first and second electrode assemblies  12 A and  12 B are directly opposed to one another on either side of product  14 . The pattern of electrodes  30  defines the pattern of locations at which membranes  16  will be welded together.  
         [0043]     In the illustrated embodiment, electrodes  30  include a peripheral electrode  30 A which welds a peripheral seam on product  14 , internal electrodes  30 B which define a pattern of welds in the interiors of products  14 , and electrodes  30 C which make spot welds on product  14 . In the illustrated embodiment, electrodes  30 A and  30 B are linear electrodes and electrodes  30 C are isolated spots. All of the electrodes are electrically connected to an electrically conducting base  33 . When first and second electrode assemblies  12 A or  12 B are mounted to corresponding platens  19 A and  19 B, bases  33  are in electrical contact with the platens and thereby establish electrical contact between the welding power source  20 , which is connected to the platens, and electrodes  30 .  
         [0044]     The spaces between electrodes  30  are filled with buffer areas  32 . In the illustrated embodiment, buffer areas  32  are composed of a cast material  32  cast between electrodes  30 .  
         [0045]     Buffer areas  32  have recesses  34  to receive the projecting parts of ECMs  18 . Recesses  34  may be shaped to substantially conform with the shapes of the projecting parts of ECMs  18 . Different ones of recesses  34  may have different shapes and configurations.  
         [0046]     As shown best in  FIG. 4A , buffers  32  fill the space between electrodes  30 . Buffers  32  are flush with the tops of electrodes  30 . Buffers  32  provide barriers  33  of electrically insulating material between recesses  34  and electrodes  30 .  
         [0047]     When first and second electrode assemblies are brought together on either side of product  14 , the embedded and projecting ECMs  18  are seated in features  34 . This insulates ECMs  18  from electrodes  30 . Features  34  can also support, locate, and align ECMs  18  in relation to one another and the membranes  16  to be welded.  
         [0048]     Buffer areas  32  may optionally contain features to pre-form, locate and pre-align membranes  16  to be welded. Such features may include electrical-mechanical devices and or intermittent differential air pressures or vacuums.  
         [0049]     Buffer areas  32  may contain features to assist the ejection and removal of welded membranes with embedded ECM from the major components of the device. Such features could be implemented, for example, by providing electrical-mechanical devices and or intermittent differential air pressures or vacuums.  
         [0050]      FIGS. 6 through 13 C are more detailed views of portions of example first and second electrode assemblies which cooperate to make a weld.  
         [0051]      FIG. 6  shows a section of buffer material  32  which extends between a pair of electrodes  30  in an electrode assembly  12 B as shown in  FIG. 7 .  FIG. 7  shows only a part of electrode assembly  12 B. Electrode assembly  12 B cooperates with another electrode assembly  12 A as shown in  FIG. 11 . When electrode assemblies  12 A and  12 B are brought together on either side of a product  14 , electrodes  30  of electrode assembly  12 A overlie and are aligned with electrodes  30  of electrode assembly  12 B.  
         [0052]     As shown in  FIGS. 8 through 11 C, an ECM  18  is received in recess  34  of electrode assembly  12 B. ECM  18  is attached to a first membrane  16 B of a weldable plastic material. Recess  34  is shaped to generally correspond to the shape of the end of ECM  18  which projects from membrane  16 B on the side toward electrode assembly  12 B.  
         [0053]     As shown in  FIGS. 9 through 11 C, a second membrane  16 A of product  14  is curved away from membrane  16 B to provide a tubular passage  37  in product  14 . The buffer  32  of first electrode assembly  12 A is cut away to form a groove  38  which accommodates and shapes second membrane  16 A. Vacuum ports (not shown) may be provided in buffer  32  of second electrode assembly  12 A to pull second membrane  16 A into and against the contours of groove  38  prior to welding. After welding, the end of ECM  18  which is closest to first electrode assembly  12 A is located within passage  37 .  
         [0054]     Applying a high frequency alternating welding current between electrodes  30  of first electrode assembly  12 A and second electrode assembly  12 B causes membranes  16 B and  16 A to become fused together at locations  17  ( FIG. 11B ).  
         [0055]     Where a component (e.g. a member, part, assembly, device, circuit, etc.) is referred to above, unless otherwise indicated, reference to that component (including a reference to a “means”) should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention.  
         [0056]     As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. For example: 
        Buffers  32  are not necessarily present in areas away from ECMs.     Buffers  32  are present in only one of first and second electrode assemblies in some embodiments of the invention.     The widths of electrodes  30  may be varied.     Electrodes  30  may be arranged to form any suitable pattern.     A welding power supply may be connected directly to electrodes  30  or bases  33  instead of indirectly by way of platens  19 A and  19 B, as illustrated.        
 
         [0062]     While a number of example aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true scope.