Abstract:
An infrared light source focuses infrared energy onto a work surface through the open end of a concentrator. The open end of the concentrator includes an elastomeric seal for sealably coupling the end of the concentrator directly to a work piece. Pneumatic pressure is applied through the concentrator and the seal to urge the work pieces together during the heating process to complete the weld. The method of infrared (IR) welding includes the steps of applying concentrated IR energy to at least one thermoplastic member while simultaneously applying pneumatic pressure to the work pieces for welding one member to another.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a thermoplastic welding process and apparatus in which infrared energy is employed as a heat source and pneumatic pressure is used to force one member against another for welding. 
     There exists a variety of welding techniques for attaching two thermoplastic materials during the manufacture of articles, such as automobile interior panels and the like. Such methods and apparatus include hot plate welding, hot air jet welding, laser welding, and ultrasonic welding. In recent years, the use of infrared welding, such as represented by U.S. Pat. No. 7,006,763, has been employed and represents an improved, relatively inexpensive and easily serviceable system for providing multiple welds coupling one thermoplastic part to another. In such a system, infrared energy from, for example, a halogen light source is focused on a work piece through a compound parabolic concentrator (CPC) or Winston cone and, subsequently, pressure is applied by mechanical means, such as an anvil or punch, for completing the welding process. Cooling air may be supplied for cooling the lamp and work piece. Although such a system provides an improved heat staking or infrared welding of thermoplastic materials, it still requires the use of movable mechanical arms for staking the work pieces together for completing the welding process after the infrared heating cycle. 
     There remains a need, therefore, for an improved method and apparatus for infrared welding of thermoplastic materials which does not employ mechanical staking or punching devices for completion of the welding process. 
     SUMMARY OF THE INVENTION 
     The system of the present invention satisfies this need by providing an infrared light source which focuses infrared energy onto a work surface through the open end of a reflector. The open end of the reflector includes an elastomeric seal for sealably coupling the end of the reflector directly to a work piece. Pneumatic pressure is applied through the reflector and the seal to urge the work pieces together during the heating process to complete the weld. In a preferred embodiment, the reflector is a compound parabolic concentrator (CPC) or a Winston cone. 
     The method of infrared (IR) welding of the present invention includes the steps of applying concentrated IR energy to thermoplastic members while simultaneously applying pneumatic pressure to the work pieces for welding one member to another. With such a system and method, therefore, there is no need for separate mechanical anvils, punches or other mechanical feature to press the work pieces together. 
     The systems and methods of the preferred embodiments of the present invention, therefore, include a source of infrared energy including a concentrator having an open end facing a work piece, a seal extending between the open end of the concentrator and sealably engaging the work piece, and a supply of pneumatic pressure for pressurizing the interior space of the concentrator and urging the work pieces together while infrared energy is applied for completing the weld. The preferred methods embodying the present invention include the steps of sealing an infrared source of light to a work piece, applying infrared energy to the work pieces and applying pneumatic pressure to the work pieces through the source of infrared energy to urge the work pieces together during the thermoplastic welding of them. 
     These and other features, objects and advantages of the present invention will become apparent upon reading the following description thereof together with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front elevational view of an infrared welding apparatus of the present invention; 
         FIG. 2  is a left side elevational view of the apparatus shown in  FIG. 1 ; 
         FIG. 3  is a vertical cross-sectional view of the apparatus shown in  FIG. 1 ; 
         FIG. 4  is an enlarged cross-sectional view of the concentrator and seal of the apparatus as shown also in  FIG. 3 ; and 
         FIG. 5  is a cross-sectional view illustrating the method of operation of the apparatus shown in  FIGS. 1-4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring initially to  FIG. 5 , there is shown a substrate  10  to which a work piece or thermoplastic part  12  is to be welded. One of the members  10  or  12  is made of a polymeric thermoplastic material which can be heated and fused utilizing infrared energy from a source  14 , such as a halogen lamp within the welding apparatus  20  of the present invention. Thus, one of the materials  10  or  12  may be polypropylene, polyethylene, polyvinylchloride, or a combination of such materials which may be employed for various parts, such as for automotive or other applications, including visors, door panels, headliners with thermoplastic crush absorbing panel members or the like, in which it is desired to secure one member to another without the need for separate mechanical fasteners. 
     As best seen in  FIGS. 1-4 , molding apparatus  20  includes a cylindrical body  22  with a recess  24  for mounting the body to a vertically movable actuator  60  ( FIG. 5 ) in a conventional manner, such that the welding apparatus  20  can be moved from a raised position spaced from the work piece  12  to the welding position shown in  FIG. 5 . In the welding position, the lower surface  36  ( FIG. 4 ) of an elastomeric seal  30  positioned at the end of a concentrator  26  surrounds the circular or other shaped opening  27  of the concentrator  26  and is in contact with and sealably engages the work piece  12 . The welding apparatus  20  includes a bulb socket  38  for receiving the infrared energy producing bulb  14 , such as a 100 watt halogen lamp. A supply conductor  16  for electrical energy is coupled to the bulb socket  38  in a conventional manner through the housing  22  to supply electrical operating energy to the bulb. Housing  22  sealably receives a reflector  34  by O-ring  37 . Reflector  34  surrounds the bulb  14  and has a parabolic surface  35  which collimates the IR rays. The concentrator directs the collimated rays downwardly through the open lower exit end  27  of the concentrator and opening  32  in the seal  30 . Concentrator  26  is a non-image-forming offset parabolic reflector similar to that described in detail in U.S. Pat. No. 7,006,763, the disclosure of which is incorporated herein by reference. The pattern of radiant energy projected by concentrator  26  onto area  15  ( FIG. 5 ) is an annular pattern. Concentrator  26  is coupled to housing  22  by opposed bayonet twist lock mounting slots and posts  40 ,  42 , as seen in  FIG. 2 , to provide easy access for replacement of bulb  14  as necessary. O-ring seal  45  seals concentrator  26  to housing  22 . 
     Coupled to housing  22  by means of a supply conduit  52  ( FIGS. 1 and 2 ) for pressurized air from a suitable source, such as a compressor, air tank, or the like. Pressurized air from the source extends through a channel  28  in seat plate  50  ( FIGS. 3 and 4 ) and downwardly through aperture  25  in the socket  38  and into the center area  29  of concentrator  26 . The seal  30 , which surrounds and is mounted to concentrator  26 , as best seen in  FIG. 4 , by a plurality of ridges and channels  31  and  33 , respectively, conforming to corresponding channels and ridges  21  and  23  in concentrator  26  for sealably snap-fitting the elastomeric seal onto the lower end of concentrator  26 . Seal  30  has an annular surface  36  in the embodiment shown which surrounds the work piece  12  in the area  15  ( FIG. 5 ) being welded. In the embodiment shown, area  15  is generally circular, although other geometries can also be employed depending on the geometry of the work piece involved. 
     As seen in  FIG. 5 , the welding apparatus  20  is mounted to an actuator arm  60  which moves upwardly and downwardly, as indicated by arrow A in  FIG. 5 , between a non-contacting position and the welding position shown in  FIG. 5 . In an assembly environment, an array of welding units  20  may be mounted on a single platen in a pattern which conforms to the desired weld pattern between the work piece and the substrate to which the work piece is to be welded. 
     In one embodiment of the invention, the pressure applied between the surface  36  of the seal and the work piece  12  by arm  60  was approximately 10 to 40 pounds to effectively seal the concentrator  26  to the work piece  12 . The hold time was from about 2 to about 20 seconds with pneumatic pressure from conduit  52  at a pressure of from about 10 to about 80 pounds per square inch (PSI), depending upon the geometry of the work piece in relation to the substrate. Subsequent to the heating and holding time, the cooling time of from about 2 to about 20 seconds is achieved by moving the welding apparatus  20  about ⅛ inch from the surface  12  of the work piece and providing a cooling air flow of from about 1 to about 5 cubic feet per minute for a time sufficient to harden the molten weld area. Typically, the work piece and substrate are heated to a temperature of about 500° F. during the heat applying step by applying sufficient infrared energy from source  14  to the welding area  15  during the heating step. By supplying air pressure during the heating step of from about 10 to about 80 PSI, the pneumatic pressure (when seal  30  sealably engages surface  15  of the work piece  12 ) adds to the clamping pressure from arm  60  to effectively press the work piece  12  into the melted substrate  10  for the fusion/welding process. Only one of the members  10 ,  12  need be a thermoplastic material, although in some applications both members will be thermoplastic. The elastomeric material employed for the seal  30  is selected to withstand the temperatures involved and may, for example, be a urethane or other suitable polymeric seal which is capable of withstanding the temperatures involved in the welding process and provide an effective seal between the concentrator  26  and work piece  12  during the welding process. 
     The control of actuator arm  60  and the application of pneumatic pressure to conduit  52  as well as power applied by conductor  16  to lamp  14  is achieved by conventional electro-pneumatic devices, such as valves and cylinders, and electrical control circuits known to those skilled in the art. The pressures applied and the holding time will vary depending on the thickness of the work piece, their material including color, and other well known factors to those in the infrared welding art. 
     It will become apparent to those skilled in the art that various modifications to the preferred embodiment of the invention as described herein can be made without departing from the spirit or scope of the invention as defined by the appended claims.