Dielectric welding methods and apparatus

This application claims the benefit under 35 U.S.C. §119 of U.S. patent application No. 60/570,817 filed on 14 May 2004 and entitled DIELECTRIC WELDING METHODS AND APPARATUS.

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.

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.

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.

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.

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.

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.

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.

The invention relates to methods and apparatus for welding plastic materials membranes together in the vicinity of electrically conductive materials.

Various aspects of the invention and features of specific embodiments of the invention are described below.

In drawings which illustrate non-limiting embodiments of the invention,

FIG. 1 is a schematic view of a dielectric welding apparatus;

FIG. 2 is an isometric view showing first and second electrode assemblies;

FIG. 3 is a perspective view of one of the electrode assemblies of FIG. 2 ;

FIG. 4 is a plan view of one of the electrode assemblies of FIG. 2 ;

FIG. 4A is a cross sectional view (in the plane A—A of FIG. 4 ) of the electrode assembly of FIG. 4 ;

FIG. 4B is an exploded view of the electrode assembly of FIG. 4 ;

FIG. 5 is a plan view of the other one of the electrode assemblies of FIG. 2 ;

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;

FIG. 7 is an isometric view of a part of an electrode assembly; 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;

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;

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;

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;

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;

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,

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 .

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 .

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.

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 .

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.

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.

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.

FIGS. 6 through 13C are more detailed views of portions of example first and second electrode assemblies which cooperate to make a weld.

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.

As shown in FIGS. 8 through 11C , 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.

As shown in FIGS. 9 through 11C , 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 .

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 ).

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.

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.

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.