Abstract:
Vibratory welded connections are formed between first and second members of thermoplastic material by interposing a junction piece of similar material and vibrating the junction piece at high speed while pressing the first and second members in a controlled manner against opposite sides of the junction piece. Friction created by the vibration generates heat which melts a small amount of material at the engaging surfaces which upon cooling provides a strong welded joint having minimal flash. Entire frame systems such as window frames can be fabricated by an apparatus system which forms a friction welded joint between adjacent ends of the frame members. Furthermore the frame can be fabricated around a panel such as a glazing panel. The welded connections formed by the system do not mar the finish of the frame members and produce no unsightly flash bead requiring subsequent machining steps for its removal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. patent application Ser. No. 10/473,677, and is a divisional thereof. U.S. patent application Ser. No. 10/473,677 was filed on Sep. 30, 2003 as a National Phase application of PCT/CA02/00842, which was filed on Jun. 7, 2002 claiming priority from Canadian Patent Application Serial Number 2,349,795, filed on Jun. 7, 2001. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates generally to assembly methods for thermoplastic components and more particularly to methods and apparatus for manufacturing window and door frames using vibration welding techniques.  
       BACKGROUND OF THE INVENTION  
       [0003]     At present, plastic window and door frames are typically assembled from polyvinyl chloride (PVC) extruded profiles using hot plate welding technology. Typically, the corner welding process involves pressing the mitered cut ends of two profiles against a Teflon-coated heated metal plate. After the thermoplastic PVC material has melted, the heated metal plate is removed and the two ends are then pressured against each other forming a hermetically sealed welded bond. Typically, in manufacturing a four sided frame assembly either one-head, two-head or four-head welding equipment is used. For four-head welding equipment, the complete frame is assembled in one operation and, taking into account the time required for frame set-up, profile loading, corner welding, cool down and frame unloading, the total cycle time is about two minutes.  
         [0004]     As well as being a comparatively slow process, a further drawback of hot plate welding is that a large quantity of plastic flash is created at the weld line and this plastic flash has to be mechanically removed through a process that can involve cutting, shaving and routing operations. Generally, the equipment required for flash removal is complex and expensive and the process can also damage any surface coatings applied to the extruded profiles. In addition because the plastic flash material is contaminated during the welding process, the removed waste material cannot be recycled and the contaminated material can also effect the final weld strength. Finally to order consistently achieve a square right angled square corner, the equipment incorporates elaborate and complex mechanical support systems.  
         [0005]     Vibration welding is one commonly used method for welding together the flat surfaced end walls of two thermoplastic components. As described in U.S. Pat. No. 4,352,711, the typical vibration welding process involves one component being held firmly in place in a stationary bottom fixture while a second component is firmly held in place in a moveable top fixture. By applying pressure and moving the top fixture very rapidly, heat is generated through surface friction, in a very short period of time, that melts the two contact surfaces of components that are to be welded together and thus in addition to a short cycle time, a further key advantage of vibration welding is that minimum flash is generated so that the need for mechanical flash removal can be substantially reduced. Generally, the two plastic component parts are injection molded and this allows for flash dams and other features to be incorporated into the components. As a result, even with the limited flash that is generated, its movement and location is controlled so that it is not visually obtrusive or unsightly.  
         [0006]     Various efforts have been made in the past to use vibration welding techniques for plastic frame assembly but without commercial success. In U.S. Pat. No. 5,902,657, issued to Hanson et al, two alternative processes are described that are specifically developed for manufacturing window and door frames. One technique uses an apparatus similar to a conventional hot plate welder where a vibratory metal plate rapidly moves back forth between the ends of two profiles. To create a welded joint, the metal plate is then removed and the two profiles are pressed against each other. As described, there are some technical issues with this process because unlike conventional hot plate welding, only a thin surface layer is heated and as a result, when the vibratory metal plate is moved away, the small amount of surface plastic material that has been melted is either removed and/or rapidly cools down so that when the two profiles are finally pressed together the welded bond formed between the two profiles is poor.  
         [0007]     There are also some technical concerns with the second alternative process described in U.S. Pat. No. 5,902,657. With this method for a four-sided frame, two opposite sides are held fixed in position while the other two sides are moveable. The moveable sides are held in fixtures that are connected to four vibratory heads that are located at profile corner ends when directly welding together two hollow thin wall profiles. Because the vibratory head moves back and forth very rapidly, it is very difficult to accurately control the final position of the vibratory head and so consequently the thin profile walls are not correctly aligned and this results in reduced corner weld strength as well as an uneven joint line which is visually noticeable.  
         [0008]     With vibration welding, there is typically a minimum zone of disturbance at the weld line. However, for glass fiber re-enforced plastics as described in U.S. Pat. No. 5,874,146 by Kagan et al, higher structural strengths can be achieved with a wide weld zone that allows for some of the glass fibers to orient away from the flow direction and to cross the weld interface.  
       SUMMARY OF THE INVENTION  
       [0009]     The invention provides a method for forming a vibratory welded connection between first and second members and a junction piece where said members and said junction piece are composed at least in part of thermoplastic resin material,  
         [0010]     said method comprising providing a vibratory head; engaging said junction piece in a fixture connected to said vibratory head; mounting said first and second members in fixtures that are independent of said vibratory head; creating an engagement force between each of said first and second members with a respective opposite side of said junction piece; maintaining said engagement forces while vibrating said junction piece by means of said vibratory head at a frequency of from 50 to 500 Hz to create friction generated heat to melt material on the ends of said members and on each respective opposite side of said junction piece, such melted material upon cooling forming a weld between said junction piece and said members; and where said engagement forces between said first and second framing members and said junction piece are applied separately from the operation of the vibratory head.  
         [0011]     Preferably the engagement forces provide even pressure on each side of the junction piece. The engagement forces desirably are varied in the duration of the welding step such that after the desired degree of melting of the materials of the engaging faces has been achieved, each engagement force is reduced to a level wherein the melted material remains molten in position between the ends of the members and the junction piece.  
         [0012]     Preferably the junction piece has a planar flange that extends at an angle with respect to each of the members, the junction piece incorporating a removable tab that is an extension of the planar flange. The tab is held in the fixture connected to the vibratory head, and after the welding step has been completed it is removed. The tab preferably has a geometric shape that is held in the fixture in an insert hole with a similar geometric shape, e.g. T-shaped, the junction piece being held firmly in position by means of metal spring attachments or the like. Alternatively, the junction piece can incorporate insert holes for engagement by insert pins on the fixture to secure the junction piece in position.  
         [0013]     For a particular application, the vibratory corner welding process is controlled by adjusting the duration of the operation of the vibratory head for a specified amplitude, frequency, and engagement force.  
         [0014]     From another aspect the invention provides Apparatus for forming a vibratory welded connection between end faces of first and second frame members and a junction piece, and where said frame members and said junction piece are composed at least in part of a thermoplastic material, said apparatus comprising:  
         [0000]     a) a vibratory head including a drive for vibrating said head in a predetermined plane at an amplitude or at least 0.4 mm and at a frequency of from 50 to 500 Hz;  
         [0015]     b) opposed first and second fixtures each having clamping structure for securing thereon a respective one of said first and second frame members and where said first and second fixtures support said first and second frame members for movement independently of said vibratory head;  
         [0000]     c) a third fixture for holding the junction piece in a balanced way and typically in a central location on said vibratory head, said junction piece having a planar part that is aligned perpendicularly to said predetermined plane;  
         [0016]     d) guide structure for guiding relative movement between said frame members and said junction piece in directions parallel to said predetermined plane and perpendicular to said planar part and to said end faces to facilitate engagement between opposite sides of said junction piece and said first and second frame members respectively;  
         [0000]     e) pressure actuators coupled to first and second fixtures to provide an engagement force between opposite sides of said junction piece and said first and second members; and  
         [0000]     f) a control system to regulate the operation of the vibration corner welding apparatus.  
         [0017]     Preferably there are adjustment mechanisms associated with each pressure actuator whereby the engagement force provided by each pressure actuator is independently adjustable. In this way, a variable force of engagement can be provided through the duration of the welding step.  
         [0018]     The third fixture which holds the junction piece is preferably located so that the planar flange of the junction piece is balanced and positioned typically in a central location, with the first and second fixtures being movable independently of this third fixture.  
         [0019]     The invention also contemplates a system for interconnecting a series of elongate frame members to form a closed frame. In this system adjacent ends of adjoining frame members are engaged by use of the aforesaid apparatus. The frame member can be a rectangular frame, a set of apparatuses aforesaid being provided at each of the four corners of the frame.  
         [0020]     The framing members need not be assembled at right angles, but can in fact be connected at any selected angle in the range 90° to 15°. The angles of adjoining frame members with respect to the junction piece can also be different. Nor is it essential that the framing members be straight, but on the contrary, one or more of the framing members may be longitudinally curved.  
         [0021]     The system for interconnecting the frame members can be used to assemble those members around an inner panel prior to the frame members being welded together to form a complete assembly with the panel. The panel can be of any desired composition such as a sheet of glass or rigid plastics material, an insulating glazing unit, a multi-cavity sheet extrusion, or the like.  
         [0022]     The invention further provides a frame comprising a plurality of elongate frame members, adjacent ends of pairs of said members being interconnected through an interposed junction piece, wherein said frame members and said junction piece are each composed at least in part of a thermoplastic resin, wherein each said junction piece is secured to a pair of adjacent frame members by vibratory welded bonds on opposite sides of said junction piece, and wherein said junction piece has a planar flange that extends at an angle with respect to each said frame member.  
         [0023]     Preferably each hollow profile has a peripheral wall that provides a surface for welding to the planar flange. The hollow profile of the frame members can be subdivided into two or more cavities.  
         [0024]     Preferably the planar flange has a thickness in the range of 2 mm to 12 mm and preferably 3 mm to 6 mm.  
         [0025]     The flat surfaces of the planar flange may incorporate a textured surface finish to improve the build-up of friction generated heat.  
         [0026]     The frame members are preferably composed of glass fiber reinforced thermoplastic material, such as polyvinyl chloride. The frame members can have decorative coatings or finishes incorporated on their outer surfaces.  
         [0027]     The junction piece may preferably carry integral legs that extend from opposite sides of the planar flange, the legs being sized to engage longitudinally within the hollow interiors of the adjacent frame members. The integral legs of the junction piece may incorporate each an integral spring centering device. Furthermore the hollow frame profile members can be fixed to the legs of the junction pieces by ultrasonic spot welding at locations spaced from the planar flange.  
         [0028]     Preferably the ends of the framing profiles are miter cut to provide the desired corner angle of the frame, e.g. a miter cut at 45° to provide a 90° corner. The miter cut ends of the framing profiles may be formed with a so-called dado cut (open sided groove) and a pressure plate can be applied on the miter cut ends of the front face of the framing profile during the welding process to prevent the appearance of this front face being marred by any welding flash.  
         [0029]     The junction piece can incorporate devices such as traps, grooves or welding beads for locating or receiving plastic flash generated during the vibratory welding process.  
         [0030]     There are three preferred applications for the vibration corner welding process, namely: (i) where frame members are assembled around an insulating glass unit and where silicone sealant is applied in gaps between the assembled frame and the insulating glass unit; (ii) where glazing sheets are directly adhered to the sides of a frame assembly using silicone sealant, and (iii) where an assembled frame is located between spaced glazing sheets. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]     The following is a description by way of example of certain embodiments of the present invention, reference being made to the accompanying drawings, in which:  
         [0032]      FIGS. 1A and 1B  are elevation views of a frame corner assembly fabricated from square profile, glass fiber filled PVC extrusions and welded at the corner using conventional hot plate welding technology.  
         [0033]      FIG. 2  is a vertical cross section taken on the line  1 - 1  in  FIG. 1  through a corner assembly.  
         [0034]      FIG. 3  is an elevation view of the test fixture for the thermoplastic corner test as specified in the North American Fenestration Standard (NAFS-1).  
         [0035]      FIG. 4  is an exploded perspective detail of a frame corner assembly incorporating a removable tab on the outer side edge where the thermoplastic extrusions are vibration welded at the corners to a diagonal corner web  
         [0036]      FIG. 5  is a horizontal cross section of a frame corner assembly where the thermoplastic extrusions are vibration welded to a diagonal planar flange junction piece incorporating a removable tab on the outer side edge.  
         [0037]      FIG. 6A  is a perspective view of a single corner vibration welding apparatus.  
         [0038]      FIG. 6B  is a schematic diagram of the control system for a single corner friction welding apparatus.  
         [0039]      FIG. 7A  is a plan view of a single corner, vibration welding apparatus with the extrusions installed in the fixtures prior to the welding process.  
         [0040]      FIG. 7B  is a view similar to  FIG. 7A  showing the single corner vibration welding apparatus during the welding process.  
         [0041]      FIG. 8A  is an exploded perspective view and  FIG. 8B  is a perspective view of a vibration welded corner frame assembly incorporating a junction piece with a planar flange and a removable tab on the bottom edge.  
         [0042]      FIG. 9A  is a cross section detail of a planar flange web incorporating flash traps.  
         [0043]      FIG. 9B  is a cross section detail of a planar flange web incorporating welding beads.  
         [0044]      FIG. 10  is a cross section detail of the moveable fixtures that hold the framing profiles in position during the vibration welding process.  
         [0045]      FIG. 11  is a perspective view of a junction piece with a planar flange and a removable T-shaped tab on the outer side edge.  
         [0046]      FIG. 12A  is a perspective detail of a junction piece with a planar flange and incorporating a removable tab with a double set of L-shaped slots on the back edge.  
         [0047]      FIG. 12B  is an exploded top elevation view of a junction piece holding fixture and a planar flange junction piece web as shown in  FIG. 12A .  
         [0048]      FIG. 12C  is a vertical cross section of the junction piece holding fixture with a planar flange junction piece as shown in  FIG. 12B .  
         [0049]      FIG. 13  is a perspective view of a corner web with a removable tab on the bottom edge.  
         [0050]      FIG. 14A  is a top plan view of a junction piece fixture incorporating a separate pressure strip device.  
         [0051]      FIG. 14B  is a vertical cross section detail of a corner web fixture incorporating a separate pressure strip device.  
         [0052]      FIG. 15A  is a cross section plan view detail of a frame corner assembly where the thermoplastic plastic extrusions are vibration welded at the corner using a corner key with a diagonal web and integral legs.  
         [0053]      FIG. 15B  is a cross section detail of the frame corner assembly as shown in  FIG. 15A  where the plastic framing profile is ultrasonically spot welded to the integral legs of the corner key.  
         [0054]      FIG. 15C  is a cross section and elevation detail of the plastic framing profile and corner key as shown in  FIG. 15A .  
         [0055]      FIG. 16  is a fragmentary plan view of vibration welding apparatus showing that the framing profiles can be assembled at varying angles to the planar flange junction piece.  
         [0056]      FIG. 17A  is an elevation view of a round top window frame.  
         [0057]      FIG. 17B  is a cross section detail of a butt joint assembly between a straight and curved framing profile.  
         [0058]      FIG. 18  is an exploded perspective view of a vibration welded corner frame assembly incorporating a junction piece with a planar flange and a top held removable tab.  
         [0059]      FIGS. 19A and 19B  are elevation views of a vertical four head vibration welding apparatus featuring two stage frame assembly.  
         [0060]      FIG. 20  is an elevation view of a vertical four head vibration welding apparatus where all four corners are simultaneously welded.  
         [0061]      FIG. 21A  is an elevation view of a composite channel sash window panel with the thermoplastic framing profiles assembled using vibration corner welding.  
         [0062]      FIG. 21B  is a vertical cross section detail taken on a line  21 A- 21 A in  FIG. 21A  of a composite channel window panel incorporating a double glazed insulating unit.  
         [0063]      FIG. 22  is an exploded perspective view of a composite channel frame being assembled around an insulating glass unit using vibration corner welding.  
         [0064]      FIG. 23B  is a perspective view of a corner assembly of a composite channel window incorporating different size framing profiles and assembled using vibration corner welding.  
         [0065]      FIG. 24A  is a perspective view of a vibration welded composite channel frame assembly where the framing profiles incorporate a single I-shaped cavity and thin solid frame profile walls for supporting the insulating glass unit.  
         [0066]      FIG. 24B  is an exploded top view of the corner frame assembly shown in  FIG. 24A .  
         [0067]      FIG. 25A  is an elevation view of an insulating glass panel with a rigid thermoplastic spacer frame assembled using vibration corner welding.  
         [0068]      FIG. 25B  is a vertical cross section detail taken on a line  25 A- 25 A in  FIG. 25A  of the insulating glass panel incorporating a rigid thermoplastic spacer frame.  
         [0069]      FIG. 26A  is an elevation view of a sealed frame window panel where the outer glazing sheets are directly adhered to the frame assembly.  
         [0070]      FIG. 26B  is a vertical cross section detail taken on a line  26 A- 26 A in  FIG. 26A  of a sealed frame window panel as shown in  FIG. 26A .  
         [0071]      FIGS. 27A and 27B  are front and side elevation views of a corner end of a framing profile specifically fabricated for friction corner welding of sealed frame panels.  
         [0072]      FIG. 28  is an exploded perspective detail of a corner frame assembly for a sealed frame window panel as shown in  FIG. 26A .  
         [0073]      FIGS. 29A  to  29 E are details of the production steps involved in the sealed frame corner assembly using a combination of friction welding and ultrasonic spot welding techniques.  
         [0074]      FIG. 30  is a perspective view of a junction piece with a removable tab incorporating insert holes for engagement by insert pins that form part of the junction piece holding fixture.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0075]     Referring to the drawings  FIGS. 1A and 1B  show side and front elevations of a frame corner assembly  31  fabricated from square hollow profile, glass fiber filled PVC extrusions  32  and  33 . The miter cut corner ends  34  of the frame members  32  and  33  are welded together using conventional hot plate equipment. One major drawback of hot plate welding is that a large quantity of plastic flash  35  is created at the weld line  36 . This plastic flash  35  has to be mechanically removed and this process often involves removing a shallow groove at the weld line  36 . As a result of this mechanical removal process, the structural performance of the corner weld can be quite significantly reduced.  
         [0076]      FIG. 2  shows a vertical cross section on a line  1 B- 1 B through he frame corner assembly  31  where the miter cut ends  34  of the frame members  32  and  33  are welded together at the perimeter wall edge. As previously described this process creates plastic flash  35  that has to be mechanically removed from the profile exterior.  
         [0077]     In North America, the structural performance of thermoplastic corner welds are evaluated according to the North American Fenestration Standard (NAFS-1) test procedure. As shown in  FIG. 3 , the test procedure involves attaching a welded frame corner assembly  31  to a support  39  with clamps  40  and  41 . The bottom clamp  41  is located 100 mm above the top edge  42  of the lower frame profile  33 . A point load L  44  is gradually applied to the lower frame profile  33  with this load  44  being located at a distance of 360 mm from the front side edge  45  of the upper profile  32 . The pass/fail test criterion is that when loaded to failure, the break shall not extend along the entire weld line  36 .  
         [0078]     Using conventional hot plate welding technology, corner weld test samples as shown in  FIG. 2  were fabricated from 30 percent glass fiber filled PVC extrusions. The samples were tested according to NAFS-1 procedure and the samples failed with the break extending fully along the weld line  36 . The main reason that the fiber filled material failed the NAFS test procedure is that the weld strength is typically no higher than the base matrix polymer and as a result, because the 30 percent glass fiber filled profiles are stronger and stiffer, the joint is the weak link in the frame assembly.  
         [0079]     As described in detail with reference to  FIGS. 4-30 , one of the main purpose of this invention is to provide a corner frame assembly method where the test samples fabricated from 30 percent glass fiber filled PVC extrusions, consistently pass the NAFS-1 Thermoplastic Corner Weld test procedure.  
         [0080]      FIG. 4  shows an exploded perspective view of corner frame assembly where the miter cut ends  34  of thermoplastic framing member  32  and  33  are vibration welded to opposite sides of a junction piece  47  incorporating a planar flange  48  and a removable tab  49 . The junction piece  47  is made from the same base polymer as the thermoplastic framing members  32  and  33 . The planar flange  48  incorporates a rough or textured surface and because this surface treatment accelerates the generation of friction heat, the weld cycle time is substantially reduced. The wall thickness of the planar flange  48  can vary between 2 mm to 12 mm with the preferred range being 3 to 5 mm. The removable tab  49  is thicker than the planar flange  48  and this provides for increased strength and stiffness. After the welding process is complete, the removable tab  49  is cut off using a shear press or similar device. Because the vibration welding does not contaminate the plastic weld material, this removable tab can be recycled and the plastic resin reused.  
         [0081]      FIG. 5  shows a horizontal cross section through the fabricated corner frame assembly from hollow plastic profiles  32  and  33 . Because the framing members  32  and  33  are vibration welded to either side of the junction piece  47 , the structural loads at each of the two welds is reduced accordingly. In addition, the planar flange  48  provides for diagonal corner bracing, further increasing the structural performance of the frame assembly.  
         [0082]     A removable tab  49  that forms an extension of the planar flange  48  is located on the outer side back of the junction piece  47 . During the vibration welding process, this tab  49  is firmly held in a holding fixture  50  linked to the vibratory head  52  of the special vibration welding apparatus  51  as described in  FIGS. 6A, 6B  and  7 A,  7 B.  
         [0083]     A corner test sample was fabricated using the same hollow square profile PVC extrusions with 30 percent glass content as the samples that had been previously made using conventional hot plate welding equipment. The profile samples were welded to the planar flange using the special vibration welding techniques but unlike the hot plate welded test samples, these vibration welded test samples passed the NAFS-1 Thermoplastic Corner Weld test procedure.  
         [0084]     As shown in  FIG. 5 , the vibration welding process generally results in the plastic framing profiles  32  and  33  being embedded in the planar flange  48 . Although it is desirable that the planar flange is made from the same resin-based material as the framing profiles, one option is for the junction piece to be made from a stiffer plastic material (e.g. glass fiber filled material) so that the profiles are not excessively embedded within the planar flange.  
         [0085]      FIG. 6A  shows a top perspective view of a prototype single corner vibration welding apparatus  51 . The apparatus consists of five main components:  
         [0086]     1. Vibratory Head  
         [0087]     A linear vibratory head  52  that incorporates a top plate  53  which is vibrates back and forth very rapidly in a predetermined plane.  
         [0088]     2. Junction Piece Holding Fixture  
         [0089]     A junction piece holding fixture  50  is directly attached to the top plate  53  and firmly holds the planar flange junction piece  48  in position.  
         [0090]     3. Moveable Framing Fixtures  
         [0091]     Two moveable framing fixtures  55  and  56  incorporate clamping devices  60  that firmly hold the framing profiles in position. The movement of the framing fixtures  55  and  56  is operated through a variety of means including: electrical servo motors, pneumatic and hydraulic devices.  
         [0092]     4. Control Systems  
         [0093]     A control system  46  that regulates the various operating parameters of the vibration welding apparatus including: weld time, hold time, joint pressure, amplitude, frequency and voltage. The control system is located in a protective housing and is linked to an operator interface  64 .  
         [0094]     5. Machine Frame  
         [0095]     A machine frame  65  provides the structure that supports the other components.  
         [0096]     The vibratory head  53  can move in either a linear or orbital manner. With linear vibration welding, the vibratory head moves back and forth very rapidly in a predetermined plane. While with orbital vibration, the vibratory head continuously rotates in a circular operation. As a continuous process, orbital vibration offers some major advantages including: reduced time, less energy, less weld amplitude, reduced clearance and better flash control. At present, orbital vibration is somewhat less reliable because the continuous circular motion is driven by an electrical motor and so only linear vibration welding is illustrated in the following figures. However, it can be appreciated by those skilled-in-the-art that orbital vibration welding can also be substituted for many of these corner welding applications and specifically, the process offers advantages where a planar flange junction piece is used.  
         [0097]      FIG. 7A  shows a plan view of a single corner, vibration welding apparatus  51  in an open position. The linear vibration welding apparatus  51  features a vibratory head  52  that linearly moves back and forth in a predetermined plane. The vibratory head  52  is similar to the vibratory heads used on commercially available linear vibration welders such as the Branson Mini Welder, but unlike these commercially available products, the vibratory head is turned upside down as this allows for more flexible and easy positioning of the framing members  32  and  33  during the frame assembly process. A flat plate  53  is bolted to the top surface of the vibratory head  52 . As with standard vibration welders, the vibratory head is bolted to a separate heavy cast iron support (not shown) and isolated from the cast iron support structure (not shown) using rubber mounts. This cast iron support structure is in turn bolted to a machine frame  65  that positions the vibratory head  52  at a convenient working height.  
         [0098]     Flat plate metal sheets  54  are bolted to the top surface of the machine frame  65  but this top working surface is separated apart from the vibratory head  52  so that a minimum of vibratory movement is transferred to the machine frame  65 . Moveable profile fixtures  55  and  56  are supported on guide rails  57  directly attached to the top table plate  54  and these fixtures hold the framing profiles extrusions  32  and  33  in position. The moveable profile fixtures  55  and  56  move over the vibratory head  52  but there is no direct contact except where the framing profiles  32  and  33  contact the junction piece  47 . The moveable fixtures also allow for the miter cut ends  34  of the framing profiles  32  and  33  to be positioned parallel to the planar flange  48  of the junction piece  47 .  
         [0099]     Each moveable profile fixture  55  and  56  consists of a horizontal flat plate  58 , a support member  59  that is attached to the horizontal plate  58  and a clamping fixture  60  that firmly holds the profiles  32  and  33  against the support member  59 . A front clamp  60  is positioned adjacent to the side edge  61  of the flat plate  58  and to ensure that the profile  33  is firmly held in position, the miter cut profiles  32  and  33  only extend 2 or 3 mm beyond the side edge  61 . It is also important that both the profiles extend the same distance from the two clamping fixtures.  
         [0100]     To provide for a right angled joint connection (i.e. 90°), the vertical support members  59  are positioned at a 45° angle to side edge  61 . However for special framing shapes, the angular position a of the support member  59  can be adjusted as required by means of a pivot point  62  and an attachment device  63 . A fixed holding fixture  50  for the junction piece  47  is located so that the planar flange of the junction piece is in a balanced central position. The holding fixture  50  which is directly attached to the top plate  53  of the vibratory head  52 , firmly holds the removable tab  49  of the junction piece  47  in position.  
         [0101]      FIG. 7B  shows a plan view of the vibration welding equipment in operation. The miter cut ends  34  of the profile extrusions  32  and  33  are pressured against the planar flange  48  of the junction piece  47 . As required, the angular displacement of the profile fixtures  55  and  56  can be adjusted so that all four joint surfaces are parallel with each other.  
         [0102]     In operation, friction heat is generated at the two joint interfaces between the parallel surfaces of the miter cut ends  34  of the framing profiles  32  and  33  and the planar flange  48  of the junction piece  47 . By vibrating the junction piece  47  back and forth and by simultaneously pressuring the framing profiles  31  and  32  against the planar flange  48  of the junction piece  47 , friction heat is generated at the two joint interfaces. When a molten state is reached at the two joint interfaces  66  and  67 , the vibration is stopped and the perpendicular pressure P is then maintained briefly while the molten plastic solidifies to form two welded joints  66  and  67  on either side of the planar flange  48 . In order to provide for even weld strength, essentially the same perpendicular engagement force has to be simultaneously applied to each side of the junction piece  47   
         [0103]     In the vibration welding process, if excessive pressure is applied after the surface plastic has been melted, the melted plastic can be pushed away from the joint line resulting in a poor structural bond. By carefully controlling the engagement force or pressure of the framing profiles on the junction piece, this joint bond problem can be avoided. After the desired degree of melting of the materials at the joint line has been achieved, the engagement force is reduced to a level where the melted material remains molten in position between the ends of the framing profiles.  
         [0104]     In friction welding glass fiber filled profiles, one of the reasons for reduced weld strength is that the glass fibers align along the weld line, perpendicular to the applied engagement force or pressure. This weld zone is typically very narrow varying from 40 to 100 microns. By carefully controlling and optimizing the welding parameters and particularly the applied pressure, a wide weld zone can be created so that some of the glass fibers are oriented away from the weld line and cross the weld interface. As a result, higher weld strengths can be achieved for the glass-fiber filled profiles.  
         [0105]     Using the prototype corner welding apparatus, a series of experiments have been carried out and these experiments have shown that satisfactory structural welds can be achieved by optimizing the different welding parameters through quite a wide range of different parameter values. For example, maximum applied pressure can be reduced if amplitude is increased, or both maximum applied pressure and amplitude can be reduced if weld-time is increased. Particularly to reduce the amount of plastic flash that is produced, our experiments have also shown that is preferable to use a higher frequency and a lower amplitude. Generally, the different welding parameters can be varied through the following values although for each application, there is a need to establish a particular set of welding parameters.  
                                                       Maximum applied pressure   6 kN           Weld time   2-12 seconds           Weld amplitude   0.4 mm to 3 mm           Weld frequency   50 to 500 Hz                      
 
         [0106]     Generally for a particular application, the vibratory corner welding process is controlled by the weld time that is determined for a specified weld amplitude, frequency and maximum applied pressure or engagement force. It should be noted that weld time is defined as the duration of the operation of the vibratory head.  
         [0107]      FIG. 6B  is a schematic diagram of the control system  46  for the single corner vibration welding apparatus  51 . The control system  46  consists of a central controller  84  which is protected within metal housing and linked to an operating interface  45 . The controller  84  controls the operation of five main components: (i) vibratory head  55 , (ii) clamping mechanism  239  and (iii) pressuring mechanism  240  of the first moveable profile fixture  55  and (iv) the clamping mechanism  241  and (v) pressuring mechanism  242  of the second moveable profile fixture  56 . Through an input/output information feed, the operations of these five components can be coordinated and controlled.  
         [0108]     Using the prototype single corner vibration corner equipment as described in  FIGS. 6A, 6B ,  7 A and  7 B, corner frame profile assemblies have been successfully produced from a wide variety of different plastic materials, including: polyvinyl chloride (PVC); composite glass fiber filled PVC; cellular foam PVC; composite wood fiber filled PVC and thermoplastic pultrusions. For all assemblies, it is desirable that the planar flange junction piece is made from essentially the same base resin as the framing profiles. A series of alternative designs for the corner web have also been tested and our experiments have shown that satisfactory welds can be produced even with a planar flange thickness of less than 1.5 mm.  
         [0109]      FIGS. 8A and 8B  show an exploded perspective view of a vibration welded corner frame assembly  31  incorporating a junction piece  47  with a planar flange  48  incorporating a removable tab  49  on the bottom edge. In contrast to the side held junction piece, one advantage of the tab on the bottom edge is that the junction pieces are easier to load into the holding fixture.  
         [0110]     For simple corner web designs, the junction pieces can be die cut from plastic sheet material. Alternatively, the junction pieces can be injected molded and this has the advantage that various design features can be incorporated into the junction piece that essentially eliminate the need for plastic flash removal.  FIGS. 9A and 9B  show two alternative joint designs that essentially eliminate the need for mechanical flash removal. In  FIG. 9A , two hollow-thermoplastic profiles  32  and  33  are longitudinally joined together using a junction piece  47  incorporating a planar flange  48 . The junction piece  47  incorporates flash traps or melt recesses  69  on either side of a central bead  70 . During the vibration welding process, plastic flows into the flash traps  69  creating double parting lines  71 .  
         [0111]     As shown in  FIG. 9B , where the aesthetic requirements are more demanding, the plastic profiles ends  72  can incorporate a dado cut  73 . The flat cut ends  75  of the profiles  32  and  33  overlap the planar flange  48  that incorporates welding beads  74 . During the vibration welding process, plastic flows inwards around the ends of the junction piece  47  and the two flat cut ends  75  almost touch, creating a single thin parting line. As previously noted, the main advantages of using flash traps and welding beads is that the plastic flash is contained during the welding process and does not have to be mechanically removed from the surface of the plastic extrusions. As a result, it is feasible for decorative surface finishes  76  to be incorporated on the plastic extrusions  32  and  33  because there is no mechanical flash removal, these surface finishes  76  are not damaged during the welding process. A further advantage of weld beads and flash traps is that by not having to remove melted plastic flash material, joint weld strength can also be increased. Although as shown in  FIG. 9B , a dato cut is incorporated into the framing profile, it can be appreciated by those skilled-in-the-art, that welding beads can be incorporated into the joint design without the need for dato cuts.  
         [0112]     For the vibration welding equipment shown in  FIGS. 6A, 6B  and  7 A,  7 B, the framing profiles are held firmly in position by means of a front clamp  60 . For more complex profile shapes, special custom fixtures have to be used and where there is a need for different framing profiles to be welded on the same production line, it is necessary for these custom clamps to be changed over. As a result, there can be production slow downs and delays which means that the productivity advantages of vibration corner welding may not be realized.  
         [0113]     To eliminate this need for special custom fixtures,  FIG. 10  shows a cross section detail of an adjustable clamp  60  for holding the plastic framing profile  77  firmly in position. A vertical support member  59  is attached to the moveable horizontal plate  58 . The framing profile  77  is held firmly in position by means of a double set of flat metal strips  78  and  79  with each strip  81  incorporating a special gripping tip  82 . The first set of strips  78  slide into position and assume the general profile shape of the front face  80  of the framing profile  77  so that the profile  77  is held against the vertical support member  59 . The second set of flat strips  79  then slide into position and assume the general profile shape of the side face  83  of the framing profile  77  so that the framing profile  77  is held also against the horizontal plate  58 . Each set of strips incorporate a locking system (not shown) that locks the strips into position.  
         [0114]      FIG. 11  shows a perspective detail of the junction piece holding fixture  50  for the single corner vibration welding equipment  51 . The junction piece holding fixture  50  is mechanically attached to the top plate  53  of the vibratory head  52  (not shown). Because the junction piece holding fixture  50  is vibrated back and forth very rapidly, the stresses or shock level on the fixture are very high and it has been estimated that these stresses are in excess of 100 G-forces. As a result, mechanical pressure devices to hold the corner key in position are not suitable as these pressure devices can not withstand the continual vibration.  
         [0115]     As shown in  FIG. 11 , one way of eliminating mechanical pressure devices is for the removable tab  49  of the junction piece  47  to incorporate a T-shaped profile  85  and for the holding fixture  50  to also incorporate a complementary T-shaped insert hole  86 . The junction piece  47  is slid into position and the T-shaped profile  85  is held firmly in position by means of metal spring attachments (not shown).  
         [0116]      FIG. 12  illustrates an alternative corner key holding system that also incorporates no moving parts.  
         [0117]      FIG. 12A  shows a perspective detail of junction piece  47  incorporate a planar flange  48  and a removable tab  49 . The back edge  87  of the removable tab  49  incorporates a double set of L-shaped slots  88 .  
         [0118]      FIG. 12B  shows a top view of a junction piece holding fixture  50  and a planar flange junction piece  47  prior to installation of the junction piece within the holding fixture. The junction piece holding fixture  50  incorporates a narrow slot  89  and the width of this slot  89  is marginally larger than the width of the removable tab  49 . Two circular metal pegs  90  span across the narrow slot  89 .  
         [0119]      FIG. 12C  shows a cross section view of the junction piece holding fixture  50  prior to installation of the junction piece. In the corner frame assembly process, the junction piece  47  is first moved horizontally across so that the two circular pegs  90  are engaged within the double set of L-shaped slots  88 . The junction piece is then dropped down into its final position where the circular pegs  90  are contained within the circular shaped toe  91  of the L-shaped slots  88 . Compared to the T-shaped junction piece shown in  FIG. 11 , the main advantage of the double L-shaped slots is that the junction pieces use less material and so can be manufactured at a lower cost.  
         [0120]      FIG. 13  shows an exploded perspective view of a junction piece  47  with a planar flange  48  and a removable tab  49  on the bottom edge. The removable tab  49  incorporates double vertical slots  92  that correspond to double circular pegs incorporated into junction piece fixture (not shown). Compared to the side held holding system shown in  FIG. 12 , the main advantage is that the junction pieces are easier to load into the bottom held holding system.  
         [0121]      FIG. 30  shows a second alternative junction piece holding system that also incorporates no moving parts. The junction piece  47  incorporates a planar flange  48  and a removable tab  49 . Two insert holes  96  and  97  are incorporated into the removable tab  49  of the junction piece  47 . Complementary insert pins  98  and  99  are incorporated into junction piece holding fixture  50  that is attached to the top plate  53  of the vibratory head. When the two pins  98  and  99  are inserted into the two holes  96  and  97 , the junction piece is held firmly in position during the vibration welding process.  
         [0122]     Rather than incorporating flash traps and welding beads, an alternative method for controlling plastic flash as shown in  FIG. 14  is to apply a pressure strip device to the weld joint during the vibration welding process.  
         [0123]      FIG. 14A  shows a top plan detail of the corner web fixture incorporating a separate pressure strip device  95  featuring a non-stick coating such as Teflon on the contact surface of the pressure strip  95 . The profile extrusions  32  and  33  are held in position by the moveable framing fixtures  55  and  56 . A pressure strip device  95  is attached to a separate support structure  96  and this support structure is isolated from the vibratory head  52 .  
         [0124]      FIG. 14B  shows a vertical cross section detail of the single corner vibration welding equipment  51  incorporating a separate pressure strip device  95  and a bottom-held planar flange junction piece  48 . During the vibration welding process, downward pressure is directed on the weld line between the framing profiles  32  and  33  and as a result, the plastic flow generated during the welding process is directed inwards and away from the weld line between the two profiles.  
         [0125]     As shown in previous figures, the junction piece  47  consists of a planar flange  48  with a removable tab  49 . For certain framing applications, this planar flange configuration does not provide for sufficient structural support and there is a need for additional corner re-enforcement. As shown in  FIG. 15 , this can be achieved by the junction piece or corner key  100  incorporating integral legs  101 .  
         [0126]      FIGS. 15A and 15B  show a cut out cross section plan view of a corner frame assembly  31  fabricated from square profile glass fiber filled PVC profile extrusions  32  and  33  and where the profiles  32  and  33  are welded at using a junction piece or L-shaped corner key  100  incorporating integral legs  101 .  
         [0127]     As shown in  FIG. 15A , the integral legs  101  of the corner key  100  incorporates an integral spring centering device  102  that simplifies frame assembly. The planar flange  48  of the corner key  100  is first vibration welded to the miter cut ends of the profiles  32  and  33 . Because of the need to accommodate the vibration movement back and forth, the legs  101  only loosely fit within the profile.  
         [0128]     As shown in  FIG. 15B  in order to provide for additional support, the plastic framing extrusions are ultrasonically spot welded to the legs of the corner key  100 . A double tip welding head is typically used creating spot welds  106  and  107 . Because the legs only loosely fit within the profile, the ultrasonic welding process allows the plastic to flow in the gap between the corner key legs and the profile extrusions creating an extra strong welded spot bond and reduced material flow on the exterior surface. Because of their complex profile shape, the corner keys  100  are typically injected molded and have to be manufactured from essentially the same base resin material as the extruded profiles  32  and  33 .  
         [0129]     One of the main advantages of using ultrasonic spot welding is that it is an assembly technique that joins two similar thermoplastic components at localized points with no preformed hole or energy director. In operation, the spot welding tips pass through the frame profile wall and the molten plastic displaced is shaped by a raised cavity in the tip (not shown) forming a neat, raised ring on the surface. Simultaneously, energy is released at the interface producing frictional heat. The tip then penetrates the corner key, displacing molten plastic material between the two surfaces and after the plastic has solidified, this forms a permanent structural bond between the framing profiles and the corner key legs.  
         [0130]      FIG. 15C  shows a vertical cross-section through the hollow profile  33 . The integral legs  101  of the corner key  100  consist of a rigid flat bar  103  with a central positioning fin  104 . The profile extrusion  33  incorporates a half circular indentation and this allows the positioning fin  104  to be centrally located.  
         [0131]      FIG. 16  shows a fragmentary plan of vibratory head  52  of the single corner friction corner welding apparatus  51  showing framing angle options.  
         [0132]     A junction piece  47  is centrally located and extruded profiles  32  and  33  are positioned against the vertical support members (not shown) and the angular displacement D of these support members can be varied from 90° to 15° and this allows for special shape frames to be manufactured.  
         [0133]      FIG. 17A  shows an elevation view of a round top window frame  108 . The straight framing profiles  109 ,  110 ,  111  are miter cut and vibration welded at the bottom corners  113  and  114  using planar flange junction pieces  48 . At the butt joints  115  and  116  between straight framing profiles  109  and  111  and the round top profile  112 , the profiles are straight cut and vibration welded together using special junction pieces  117 .  
         [0134]      FIG. 17B  shows a cross section detail of the butt joint  115  between the straight framing profile  111  and round top or curved framing profile  112 . The junction piece  117  incorporates legs that feature an integral spring centering device that simplifies the assembly of the window frame.  
         [0135]      FIG. 18  shows an exploded perspective view of a corner frame assembly where two framing profiles  32  and  33  are vibration welded to a junction piece  47  incorporating a planar flange and with a removable tab located on the top edge  119  of the planar flange  48 . To provide for simplified handling at the framing profiles, the junction piece corner key fixture is typically attached to a flat plate located on the top surface of the vibratory head. However, the position of the vibratory head can be reversed so that the junction piece  47  is held from above and particularly for frame-and-panel assemblies, this reversed head position offers the advantage that both the panel and the final assembled unit can be more easily moved in-and-out of the vibration welding apparatus.  
         [0136]     Although frame assemblies can be manufactured using a single corner welder, it is more productive if two or more corners are welded simultaneously.  FIG. 19A  shows a front elevation view of a vertical four head vibration welder equipment  120 . As with conventional hot plate welding equipment, the four head welding equipment  120  consists of a rectangular structural frame  121  with leg supports  122  and  123 . The four welding heads  130 , 131 ,  132  and  134  are attached to two vertical bridge supports  124  and  125  that span between the top beam  126  and bottom beam  127  of the structural frame  121 . The first vertical bridge support  124  is fixed in position while the second bridge support  125  is moveable and is driven by a servo motor on a cog track located on the bottom beam  127  of the structural frame  121 . The top end  129  of the moveable bridge  125  is supported by a guide rail  128  located on the top beam  126  of the structural frame  121 .  
         [0137]     A first set of vibration welding heads  130  and  133  are attached to the first bridge support  124  that is fixed in position and a second set of vibration welding heads  131  and  132  are attached to the second moveable bridge support  125 . Each set of vibration welders are operated by a electro servo motor driven ball screw that in combination with special control devices allow the vertical position of each head to be individually controlled so that in operation, all four heads can move up and down either simultaneously or independently towards a central horizontal datum line  154 . After the four heads  130 ,  131 .  132  and  133  have moved to their initial start location, the four framing profiles  134 ,  135 ,  136  and  137  are loaded into position as well as the four junction pieces  138 , 139 , 140  and  141 .  
         [0138]     In contrast to a conventional four point welder where all four corners are welded simultaneously, the preferred operating strategy for friction welding is a two stage process. As shown in  FIG. 19A , two diagonally opposite corners  150  and  152  are first welded together. For each corner weld, the process is essentially the same as with a single corner vibration welder. Both sets of framing profiles  134 ,  137  and  135 , 136  are independently pressurized against the two diagonally opposite corner keys  138  and  140 . In addition, only the moveable frame clamping devices, immediately adjacent to the corner keys  138  and  140  are in operation. After the welding process is complete, the corner keys  138  and  140  have to be released and by incorporating as part of the vibratory welding head a tab removal shear press or a similar device (not shown), this allows for this release process to be carried out very efficiently.  
         [0139]     As shown in  FIG. 19B , the next step is for the other set of diagonally opposite corners to be welded together. The bottom head  133  on the first vertical beam is fixed in position while both the top two heads  130  and  131  move downwards while simultaneously the second bridge support  125  moves sideways. During this second stage process, only the moveable frame clamping devices immediately adjacent to the corner keys  139  and  141  are in operation. After the second set of diagonally opposite corners  151  and  153  are welded, the assembled frame is then unloaded.  
         [0140]     Because the friction welding process is so fast (3 to 6 seconds), this two stage process does not significantly increase cycle time and compared with simultaneously welding all four corners, the key advantage is that the required movement and control of the heads is greatly simplified. For the four head welder, the controllers for the individual heads form part of a coordinated control system (not shown) that controls all four heads as well as the operation of the other mechanized components of the automated four point welder.  
         [0141]     For a conventional four head, hot plate welder, the overall cycle time is about 2 minutes and this overall cycle time includes: profile loading, corner welding, cool down and frame unloading. In comparison, the estimated overall cycle time for the two-stage vibration welding process is less than 30 seconds and so this represents a significant increase in productivity. To further improve productivity, one option is to incorporate an automated mechanical feed (not shown) for installing the junction pieces in the corner holding fixtures.  
         [0142]     As shown in  FIG. 20 , it is technically feasible to simultaneously weld all four corners  150 , 151 ,  152  and  153  in one operation. All four vibration welding heads  130 ,  132 , 133  and  134  incorporate an additional servo motor  156  that allows each head to move fractionally as the plastic material is melted during the vibration welding process. As a result, the position of the heads can be fractionally adjusted in varying directions so that at four all corners, perpendicular pressure is simultaneously applied by the four framing profiles  134 , 135 ,  136  and  137  to the four corner keys  150 ,  151 ,  152  and  153 . However because the head movements involved are so small and so complex, the control system for this simultaneous four headed welding operation is complex and requires very sophisticated software. Although  FIGS. 18, 19  and  20  show vertical four head vibration corner welder, it can be appreciated by those skilled-in-the-art that the bridge supports can span horizontally on a table support.  
         [0143]     Although vibration corner can generally be used to join together extruded plastic profile extrusions, the improved assembly method offers particular advantages for fenestration applications. In addition to the production of conventional windows and doors, the improved assembly method provides for the development of new types of fenestration products. To illustrate the performance advantages of vibration corner welding, FIGS.  21  to  31  show three examples of these new types of fenestration products, namely: 1. composite channel window panels, 2. glass panel units and 3. sealed frame window panels.  
         [0144]     Compared to the simple rectangular frame assemblies illustrated in previous figures, these new types of fenestration products incorporate complex profile shapes, but it should be noted that the basic component joint design does not change and the planar flange junction piece can be configured to correspond to the miter joint contour of these more complex profiles shapes.  
         [0145]      FIG. 21A  shows an elevation view of a composite channel window panel  158  consisting of a conventional sealed double glazed unit  159  and a rectangular sash frame  160  that is assembled around the sealed glazing unit  159  using vibration corner welding.  
         [0146]      FIG. 21B  shows a cross section detail on a line  21 A- 21 A of the composite channel window panel  158 . The sealed double glazing unit  159  consists of two glazing sheets  161  and  162  and incorporates a conventional perimeter seal  163  with the specific example shown being an inner barrier seal  164  of desiccant filled polyisobutylene (TPS) and an outer structural seal  165  of polysulphide sealant. The sealed glazing unit  159  is supported on conventional hard rubber glazing blocks  166  and the glazing channel  167  is conventionally drained. After the multi-cavity hollow plastic frame has been assembled and welded at the corners, two silicone sealant beads  169  and  170  are applied in the gaps between the glazing unit  159  and the channel frame profile  168 . Preferably, the window frame profile is made from glass fiber filled PVC and this has the advantage that because of the combined stiffness of glass-and-frame assembly, the overall frame profile size can be reduced when compared to conventional PVC window profiles.  
         [0147]      FIG. 22  shows an exploded perspective corner detail of a composite channel window panel  158 . The channel-shaped framing profiles  171  and  172  are assembled around the insulating glazing unit  159  and the framing profiles  171  and  172  are then joined and sealed at the corners using vibration corner welding. One key feature is that the junction piece  47  incorporates a removable plastic web  49  that is located on the outer side of the frame and is held in the corner web holding fixture attached to the vibratory head of the friction welding equipment. This has the advantage that the frame can be assembled around the insulating glass unit and the corners then welded and sealed. As a result, by eliminating the need to separately install the insulating glass unit  169 , there are significant material and labor cost savings.  
         [0148]     With conventional hot plate welding, in order for the thin wall profile walls to be welded together at the corners, the framing profiles have to be essentially the same size and shape. However with vibration corner welding, by using a common corner web, different profile sizes and shapes can be structurally joined together. For example as shown in  FIG. 23 , the bottom framing profile  173  is larger and incorporates a deep hardware channel  175  while the side framing profile  174  is smaller and there is no hardware channel. In addition, with conventional hot plate welding, only 45° miter cut corners can be used, while with a friction welding and a corner key web, it is feasible to join together framing profiles with different miter cut angled corners (i.e. 60° and 30°).  
         [0149]     It should be noted that when joining together different size profiles using friction corner welding, it is necessary for the two moveable framing fixtures to apply different engagement forces so that when taking into account the different profile sizes, essentially the same pressure is being applied on either side of the web.  
         [0150]     Although the examples given in FIGS.  21  to  24  show examples of a window framing profile being assembled around an insulating glass unit, it can be appreciated by those skilled-in-the-art that the same production process can also be used to fabricate a wide range of frame-and-panel products including: picture frames; mirrors; partitions; shower doors and cupboard doors.  
         [0151]      FIGS. 24A and 24B  show a perspective and top plan view of a welded composite channel frame assembly where the framing profiles  176  and  177  incorporate a single I-shaped cavity  178  and where the thin supporting profile walls  179  for the insulating glass unit are solid. The main advantage of this narrow composite channel profile is that the overall width of the framing profile is reduced and as a result, there are material and cost savings. One drawback of this narrow channel profile is that with a full section corner web, it is difficult to achieve a consistent corner weld because the legs of the channel-shaped corner web are so thin.  
         [0152]     One option is for the corner web to only extend to the top profile wall  181  of the I-shaped cavity  178  and to incorporate a notch  182  in the miter cut corners of the framing profiles  176  and  177 . As a result, while the bottom part of the profiles  183  is sealed and welded at the corners, the miter cut solid profile walls  184  only butt together. However because the vibration welding process can be closely controlled, the open gap  185  between the two miter cut profiles  176  and  177  can be kept to a minimum.  
         [0153]      FIG. 25A  shows an elevation view of a sealed double glazed panel  159  incorporating a rigid thermoplastic spacer frame  186  that is welded and sealed at the corners using vibration corner welding.  
         [0154]      FIG. 25B  shows a cross section detail on a line  25 A- 25 A of the perimeter edge of the double glazed panel. The spacer frame  186  is made from an open channel, rigid thermoplastic framing profiles  187  that are vibration welded at the corners to planar flange junction pieces  47  made from essentially the same thermoplastic resin as the spacer profile. To minimize differential expansion between the glazing sheets  161  and  162  and the spacer frame  186 , the thermoplastic spacer profiles are made from glass fiber re-enforced thermoplastic extrusions or continuous glass fiber re-enforced pultrusions. After the spacer frame  186  has been assembled, desiccant-filled polyisobutylene sealant is applied to the inner surface  188  of the spacer frame  186  creating a continuous barrier seal. After the panel has been assembled, double beads  190  and  191  of structural thermosetting sealant are applied between the spacer frame  186  and the two glazing sheets  161  and  162 .  
         [0155]     For insulating glass panels, the main advantage of using vibration corner welding is that there is a continuous, single wall barrier seal made from rigid thermoplastic material. As a result, the back face  192  of the spacer frame can incorporate a variety of profile features including attachment devices. In addition without damaging the integrity of the barrier seal, other thermoplastic parts (e.g. gas fill patches) can also be welded to the back face  192  of the spacer frame  186 .  
         [0156]      FIG. 26A  shows an elevation view of a sealed frame, triple glazed sash window panel incorporating a perimeter sash frame  194  with vibration welded corners.  
         [0157]      FIG. 26B  shows a cross section detail on a line  26 A and  26 A of a triple glazed, sealed frame window panel  193 . The panel consists of two glazing outer sheets  161  and  162  that overlap the perimeter sash frame  194  and are adhered to the frame with thermosetting structural sealant  195 . The inner center glazing sheet  196  is supported by the perimeter frame  194 .  
         [0158]     The perimeter frame  194  is assembled from glass-fiber filled, hollow thermoplastic profiles  197  which are joined and sealed at the corners using vibration corner welding. The thermoplastic profiles incorporate glass fiber fill and as previously noted this provides for increased strength and rigidity as well as reduced thermal expansion. Compared to conventional window assembly, the main advantage of sealed frame glazing unit is that through composite structural action, the required size of the sash profiles  197  can be significantly reduced resulting in improved energy efficiency and material cost reductions.  
         [0159]     With composite structural action, the sealed frame panel performs in a similar manner to a stressed skin sandwich panel where the perimeter edges of the two glazing sheets  161  and  162  are respectively in compression and tension and so instead of the panel performing as two independent glazing sheets, the two sheets  161 , 162  act together as a structural unit.  
         [0160]     The glazing sheets  161  and  162  are structurally adhered to the plastic frame profiles  197  with structural thermosetting sealant  195  and for long term durability, silicone sealant is the preferred material. For enhanced composite structural performance, a high modulus silicone sealant is required with the thickness of sealant being preferably less than 3 mm. To provide for increased panel stiffness, both the bottom edges  198  and perimeter side edges  199  of the glazing sheets  161  and  162  are adhered to L-shaped seats  200  on either side of the perimeter frame profiles  197 . To allow glazing sheets  161  and  162  to bow in and out with changes in temperature and pressure, the side edge contact length is kept to a minimum with 10 mm being the typical length required.  
         [0161]     A third center glazing sheet  196  is located between the two outer glazing sheets  161  and  162  and this glazing sheet is similar in shape but smaller in size than the outer two glazing sheets. For improved thermal performance, the width of the cavity spaces  201  and  202  between the glazing sheets  161 ,  196  and  162  is typically between 9 and 18 mm. For improved energy efficiency, a low-e coating  203  can also be applied to one or more of the glass cavity surfaces of the window panel  193 . In addition, the cavity spaces  161  and  162  can incorporate a low conductive gas such as argon or krypton.  
         [0162]     To provide for long term gas retention as well as maintaining the integrity of the perimeter edge seal, there is a need for a continuous perimeter edge seal between the outer glazing sheets. Various edge seal configuration sand sealant materials can be used to provide this continuous barrier seal. One option as shown in  FIG. 26B  is to apply low permeable sealant material  204  to the front face  205  and front side edges  206  of the perimeter frame  194 . To accommodate glass bowing and movement, the sealant material must be flexible and because of its low temperature performance, polyisobutylene is the preferred material. To remove moisture vapor from the glazing cavity spaces  201  and  202 , the low permeable sealant incorporates desiccant fill material with the preferred material combination being 85 percent 3A molecular sieve and 15 percent silica gel.  
         [0163]     The rigid frame profiles  197  can be made from many alternative plastic materials produced using various processes. One preferred material is glass fiber-filled polyvinyl chloride (PVC) that is extruded to the required profile shape. One suitable product is Fiberloc 80530 that features a 30 percent glass fiber fill and is produced by PolyOne Inc. of Cleveland Ohio. The co-efficient of thermal expansion of the 30 percent, glass fiber filled material is 18×10 −6  cm/cm/° C. and this compares to the thermal coefficient of glass which is 9×10 −6  cm/cm/° C. For very large panel sizes, the thermal expansion of the plastic profiles can be further reduced by reinforcing the frame profile walls  207  and  208  adjacent to the outer glass sheets  161  and  162  with continuous unidirectional glass fiber strips (not shown).  
         [0164]     Instead of fiber glass reinforced PVC, the frame profiles  197  can be made from various other alternative plastic materials, including: thermoplastic fiber glass pultrusions, glass fiber reinforced engineering structural plastic foam extrusions and high draw oriented thermoplastic extrusions. Because the plastic profiles are firmly bonded to the glazing sheets and expand outwards from the mid points of the perimeter frame, maximum stress due to the differential expansion between the plastic profiles and the glass sheets occurs at the corners. Particularly with glass fiber filled profiles, because the corner welds are typically only as strong as the un-reinforced plastic, the corner welds can be a potential weak point in the frame assembly. To provide for increased strength and rigidity and to also reduce stress on the corner welds, the preferred assembly method is to join the plastic profiles together at the corners using a combination of friction corner welding and ultrasonic spot bonding and this production method has previously been described in  FIGS. 15A and 15B .  
         [0165]      FIGS. 27A and 27B  show a front elevation ( FIG. 27A ) and a side elevation ( FIG. 27B ) view of the diagonal cut end  209  of the framing profile for a triple glazed sealed sash window panel. By removing the frame profile material, a 3 to 4 mm deep channel  210  is formed in the diagonal cut end of the profile  209  creating plastic side ribs  211  and  212 . The dotted line  212  on the side elevation of the diagonal cut end indicates the depth of the channel  210 .  
         [0166]      FIG. 28  shows an exploded perspective detail of the corner frame assembly for a triple glazed, sealed frame window panel  193 . The two framing profiles  213  and  214  are joined together by means of special corner keys incorporating a planar flange web  215  and integral legs  216 . To provide for simplified frame assembly, the integral legs incorporate a self centering spring device.  
         [0167]     As previously shown in  FIGS. 27A and 27B , by removing the frame profile material, a channel can be formed in the miter cut ends  217  and  218  of the framing profiles  213  and  214  so that the top side rib surfaces  220  and  221  overlap the diagonal center flange  215  of the corner key  217 . During the friction welding process, the profile ends except for the top side ribs  220  and  221  are pressured against the center flange  215 . Because plastic flash is only generated at the interface between the profiles ends  222  and  223  and the corner key flange  215 , a clean parting line is created between the two top side ribs  220  and  221  of the framing profiles  213  and  214 .  
         [0168]      FIGS. 29A  to  29 E show the production steps involved in manufacturing a single, vibration-welded, sealed-frame corner assembly.  
         [0169]     As shown in  FIG. 29A , the sealed frame corner assembly consists of two framing profiles  213  and  214  and a special L-shaped corner key  219  with a diagonal center flange  215  and a removable tab  224 . A channel is formed in the miter cut ends of the framing profiles  213  and  214  so that the top side ribs  220  and  221  of the framing profiles overlap the diagonal center flange  215  of the corner key  219 .  
         [0170]     As shown in  FIGS. 29B and 29C , the two legs  225  and  226  of the L-shaped corner key  219  are loosely fitted into the two framing profiles and the corner assembly is placed in the vibration corner welding apparatus. The removable tab  224  incorporates a special arrow-head profile  227  that fits into a complementary shaped insert hole  228  within the corner key fixture  229 . The framing profiles  213  and  214  are held firmly in position by means of front clamping devices  230  and  231  that are attached to the moveable framing fixtures  232  and  233  of the vibration welding apparatus (not shown).  
         [0171]     As shown in  FIGS. 29C and 29D , the two profiles are pressured using perpendicular force against the contact surfaces of  234  and  235  of the corner key  219  and friction is created by rapidly moving the corner key  219  back and forth. During the friction welding process, as the two profiles  213  and  214  are pressured against the corner key flange  215 , plastic flash flows to either side of the contact surface. Because relatively limited flash is produced, the flash does not extend into joint line between the two diagonal cut ends  236  of the framing profiles and so as a result, a clean parting line  237  is created between the framing profiles.  
         [0172]     After the friction welding process is complete and as shown in  FIG. 29E , the tab  224  is mechanically removed from the L-shaped corner key  219 . The final step in the production process is to bond the interior profile walls to the L-shaped corner keys using ultrasonic spot welding  238 .