Abstract:
The present invention provides a method and device for inductively heating a first and second surface to form a closure assembly. A method contemplated by the present invention includes spacing an upper die from a lower die for receipt of the first surface and the second surface configured in an overlying orientation, securing one end of the first surface to an end of the second surface and compressing the first surface toward the second surface to form a compressed arrangement which is inductively heated into a closure assembly.

Description:
FIELD OF THE INVENTION 
     This invention relates to a welding assembly and a method for welding a plurality of panels. More specifically, the present invention relates to an induction welding assembly and method for induction welding closure panels related to automobiles. 
     BACKGROUND OF THE INVENTION 
     Automobile manufacturing utilizes multiple techniques for joining together multiple surfaces having relatively large cross sectional areas. In some instances, these surfaces have varying cross-sections or may be fabricated using materials of different thicknesses or shapes. 
     Some methods of joining these surfaces may utilize mechanical fasteners. However, mechanical fasteners may generate concerns over time allowing the surfaces to become disjoined. Another method of joining surfaces include welding using resistance, laser, plasma or seam welding techniques. In a typical welding application, plural surfaces are overlapped and mechanically fixed in place using clamps for example. A heat source, such as an electrode is placed near the overlapped surface and approaches the overlapped surfaces. As the heat source is position near the overlapped surfaces, the temperature of the region affected by the heat source quickly raises generally forming a liquid. The heat source then progresses along the overlapped surface until the desired weld is achieved. Upon completion of the weld, the heat source is removed from the surface, which is then cooled. In this way a weld joint may be created for joining two or more surfaces together. The traditional welding heat source presents several disadvantages including safety concerns related to the excess heat and inconsistent and incomplete welds. It would be beneficial, therefore, to provide an induction device, generating a thermal effect on the joined surfaces within a narrow zone to avoid any excess heat or unsafe working environments. 
     However, traditional welding techniques provide for irregular points of stress and require excess after-welding preparation to remove any unwanted edges or surfaces. Some welding techniques may not extend along the perimeter of the joined surfaces allowing for undesired Rat Holes. Others use a flanging or hemming operation to join the surface perimeters but allow for variations in the perimeter surfaces. However, these operations may require excess material which require additional time and resources for removal. Also, some welding techniques simply are too impractical or expensive for a manufacturing process which requires consistent movement along the manufacturing line. 
     Some of the aforementioned welding techniques may provide for one or more of the following problems like, “Rat Holes” or filiform corrosion due to the migration of water to the inner radius of a hemmed surface. Additionally, using the overlapping or seam welding process may allow for a hem flange which may require additional time and resources for removing any unwanted hems or seams. Some processes utilize an adhesive or temporary weld to temporarily secure the welded surfaces prior to being welding or during shipping and assembly operations. As a result of using the adhesive, a curing process may be necessary after the welding is accomplished and after which a sealant may be required. Using a temporary weld may further contribute to any delays or excess costs. These problems and excessive operations may contribute to delays and increased costs during the manufacturing process. 
     In addition to the concerns previously identified, the flanging, adhesive bonding and the hemming processes traditionally employed in the automobile manufacturing process may further present packaging limitations, which may be required to allow for an area to apply the adhesive, an area to hem the flange or an area to apply the hold-down fixture of the hemmer. It may be beneficial to remove the excess material, if an alternative welding process were utilized. Additionally, by removing any excess material an enhanced package design may be utilized for transporting the joined surfaces providing additional benefits. Utilizing an alternative welding process may also allow for improved stiffness and rigidity of the welded surface and allow for flanges having shorter dimensions. 
     Finally, by allowing for an improved welding process which provides for the joining of surfaces along a perimeter, the finished product may have improved characteristics through sharper radii such as reduced dimensional variation and enhanced design freedom. In addition, as previously described, utilizing an alternative welding process may render several manufacturing operations unnecessary, including the die flanging operation, the hemming operation, the application of hem adhesive, the need for after-hem sealer, induction curing of the hem adhesive and in-process welds for temporarily securing surfaces during transfer from the assembly process to the finishing processes. 
     It therefore would be beneficial to provide a superior quality, high productivity and economical welding apparatus which provides at least some of the aforementioned advantages, whereby materials with different thickness and/or different surfaces may be welded while shaping the joined surfaces. 
     SUMMARY OF THE INVENTION 
     The present invention reduces the difficulties and disadvantages of the prior art by providing a method and device for inductive welding a generally planar first surface to a generally planar second surface having sufficient cross section to form a closure assembly, the method including the steps of spacing an upper die from a lower die for receipt of the first surface and the second surface configured in an overlying orientation, securing an end of the first surface to an end of the second surface between said upper and lower dies, compressing the first surface toward the second surface at said upper die and said lower die to form an end-to-end compressed first and second surface arrangement and inductively heating said end-to-end compressed first and second surface arrangement to form the closure assembly. The present invention also includes an inductive welding device addressing the difficulties and disadvantages of the prior art comprising a first arm operably separated from a second arm, said first arm associated with an upper die and said second arm associated with a lower die, said upper die adapted for receiving a first surface and said lower die adapted for receiving a second surface, said first surface overlying said second surface and an induction coil associated with one of said upper and lower dies and adapted for inductively heating said received first and second surfaces forming a closure assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a semi-schematic perspective view illustrating an induction welding assembly. 
         FIG. 1B  is a semi-schematic perspective view illustrating an inducting welding assembly of  FIG. 1A  in receipt of the end-to-end first and second surface arrangement. 
         FIG. 2  is a semi-schematic perspective view of the induction welding assembly of  FIG. 1A  in receipt of a first and second surface. 
         FIG. 3  is a semi-schematic perspective view of the induction welding assembly of  FIG. 1A . 
         FIG. 4  is a semi-schematic perspective view of the induction welding assembly of  FIG. 1A  forming a closure assembly. 
         FIG. 5  is a semi-schematic perspective view of an upper die associated with the induction welding assembly of  FIG. 1A . 
         FIG. 6  is a semi-schematic perspective view of an alternative induction welding assembly in receipt of the first and second surfaces. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
     In general, the present invention provides an induction welding device generally referred to herein by reference numeral  10 , which is adapted for forming a closure assembly  20  from a first and second generally planar surfaces  2 ,  4  having a sufficient cross section to form the closure assembly  20 . Generally, the induction welding device  10  includes a first arm  34  and a second arm  36 , the first arm  34  being associated with an upper die  14  and the second arm  36  associated with a lower die  12 . At least one induction coil  32  is also associated with at least one of the upper and lower dies  14 ,  12  and as illustrated in  FIG. 1A  is associated with the upper die  14 . In addition, in practice one or both the first and second arms  34 ,  36  may be movable between a disengaged position to an engaged position with at least one of the upper and lower dies  14 ,  12  being in electromagnetic communication with the first and second surfaces  2 ,  4 . 
     Although the upper and lower dies  14 ,  12  may be fabricated from a variety of materials, having a variety of configurations, in general a portion of the upper and lower dies  14 ,  12  associated with the induction coil is electrically insulated to sufficiently limit the passage of electrical current. The upper and lower dies  14 ,  12  are suitably positioned along a support member (not shown) for receiving the first and second surface  2 ,  4  which are to be joined. The first and second surfaces  2 ,  4  may include sheet metal body panels adapted for use in an automobile application, although other surfaces may be utilized by the present invention. In addition, first and second surfaces  2 ,  4  may be of varying dimensions, thicknesses or surfaces and placed within the induction welding device  10  at varying angles with respect to the upper and lower dies  14 ,  12 . Generally, the first and second surfaces  2 ,  4  will have a dimension greater than the receiving surface of the upper and lower dies  14 ,  12 , which may be greater than 12″ inches. The receiving surface associated with the upper die  14  is illustrated in  FIG. 1A  as an arcuate receiver or laid-out flange  16 . The receiving surface associated with the lower die  12  is illustrated in  FIG. 1A  as a passageway  26 . Although, the illustrated first and second surfaces  2 ,  4  are generally greater than 12″, the induction welding device  10  may be configured for use in joining smaller or equal dimensioned surfaces with the same or similar thicknesses or outer surface. 
     The upper and lower dies  14 ,  12  are generally affixed to the first and second arms  34 ,  36  associated with the induction welding device  10 , however, removable dies may also be used in association with the induction welding device  10 , the dies being replaceable as desired with alternatively configured die or die with alternative properties. The upper die receiver  16  and lower die receiver  26  respectively associated with the upper and lower dies  14 ,  12  are configured with a oppositely positioned shaping member which may or may not be complementary configured with respect to each other. Generally, both the arcuate receiver  16  and passageway  26  are arcuate and adapted for presenting a shaped end  38  illustrated in  FIG. 3  of the closure assembly  20 . 
     At least one of the first and second arms  34 ,  36  is moveable between the engaged and disengaged position, with the first and second arms  34 ,  36  being proximate to each other in the engaged position and separated a distance from each other in the disengaged position. Although, the distances between the first and second arms  34 ,  36  may vary, in general the first and second arms  34 ,  36  may vary between about 10 inches and about 36 inches apart during transition between the engaged and disengaged positions. 
     As previously described and illustrated, the induction coil  32  is generally associated with the upper die  14  and as illustrated in  FIG. 2  is positioned near the arcuate receiver  16  associated with the upper die  14 . In operation, the induction coil  32  is positioned near the lower die  12  in the engaged position with the first and second surfaces  2 ,  4  positioned therebetween and the induction coil  32  is generally spaced a distance from the lower die  12  in the disengaged position. 
     During the welding process, the induction coil  32  is electro-magnetically energized to allow the coil  32  to provide for induction heating. Generally, a current is passed through the induction coil  32  with a high-frequency power supply causing it to generate a magnetic field. The magnetic field in turn may create an opposing magnetic field within the first and second surfaces  2 ,  4  and generally at the interface between the first and second surfaces  2 ,  4 . The opposing magnetic fields may generate eddy currents within the first and second surfaces  2 ,  4  that may ultimately dissipate heat energy. The frequency of the power supply is sufficiently controlled to provide an accurate penetration depth in order to focus the heat energy created by the eddy currents to concentrate heat at this interface between the first and second surfaces  2 ,  4 . Thereby presenting the heating source for welding the nearby first and second surfaces  2 ,  4 . The induction coil  32  and the high-frequency magnetic field are electrically distinct from the upper die  14 . 
     The induction coil  32  may be fabricated using copper or brass tubing which is water-cooled during operation to prevent overheating or melting of the coil  32 . The coil  32  is generally mounted within an insulative material such as, but not limited to, a urethane material that provides rigidity and durability. These insulative materials are generally known in the industry and may vary accordingly. Design of the induction coil  32  may include “field shapers” for directing the magnetic field away from the induction coil  32  towards the first and second surfaces  2 ,  4 . Optionally, a “flux” material may be applied to the contact surfaces between the first and second surfaces  2 ,  4 , to promote welding of the closure assembly  20 . 
       FIG. 4  illustrates the induction welding device  10  in the engaged position, the induction coil  32  being generally positioned adjacent to and above the received first and second surfaces  2 ,  4  which are arranged in an overlapping manner, with the end of the first surface  2  associated with an end of the second surfaces  4 . Additionally, the passageway  26  associated with the lower die  12  may be angled to receive one of the first or second surfaces  2 ,  4  in an orientation rotated from or towards the upper die  14 . Alternatively, the induction coil  32  may be associated with the lower die  12  or both the lower and upper dies  12 ,  14 . The induction coil is illustrated in the process of welding first and second surfaces  2 ,  4 . 
     The distance between the surface of the induction coil  32  and the nearby first and second surfaces  2 ,  4 , is preferably minimal, because the induction welding efficiencies degenerates by the square of the distance separating the induction coil  32  from the first and second surfaces  2 ,  4 . In practice the distance may range between a few tenths of inches and up to a few inches. As Illustrated in  FIG. 5 , within the upper die  14 , the induction coil  32  is sized and shaped to surround the perimeter of the upper die  14  such that when the induction coil is activated  32 , a weld is formed around the outer periphery of the joined surfaces. Power to the induction coil  32  may be regulated based upon the desired heating temperature for the particular welding application. 
     In operation, the upper die  14  is spaced from the lower die  12  and the first and second surfaces  2 ,  4  are secured in an end-to-end orientation with an end of the first surface  2  being secured to an end of the second surface  4 . Optionally, the first and second surfaces  2 ,  4  may be angularly oriented. The first and second surfaces  2 ,  4  are generally positioned between the upper and lower dies  14 ,  12  according to the master gage datums.  FIG. 2 , illustrates the upper and lower dies  14 ,  12  in receipt of the first and second surfaces  2 ,  4  arranged in an overlying end-to-end orientation with the first surface  2  extending towards the arcuate receiver  16  and the second surface  4  extending along the passageway  26  towards the obliquely orientated lip  28 . As the upper and lower dies  14 ,  12  transition from the disengaged position towards the engaged position, the first surface  2  is compressed towards the second surface  4  forming an overlying end-to-end compressed first and second surface arrangement  30  illustrated in  FIG. 1B . Optionally, either the first, second or both dies  14 ,  12  may be configured with a specific orientation to present a closure assembly  20  having a desired shaped. If present, the arcuate receiver (also referred to as a laid-out flange)  16  may angularly receive one of the first and second surfaces  2 ,  4 . 
     Optionally, the wall structure  24  and the obliquely orientated lip  28  associated with the lower die  12  may present a deforming region for shaping the closure assembly  20  so that it has the attractive surface edge  38 . Additionally, the upper die  14  may have a complimentary configuration according to the deforming region. Alternatively, the deforming region may be associated with either or both the upper and/or lower die  14 ,  12 . During the welding process previously described, the induction coil  32  in association with the deforming region may present the shaped surface edge  38  extending from the closure assembly  20 . The deforming region may have a variety of configurations for shaping the closure assembly  20  including extending upwardly from the lower die  12  towards the upper die  14  presenting the aesthetically shaped end  38  with the second surface  4  adjacent to the first surface  2 . In this manner an alternatively configured closure assembly  120  is illustrated in  FIG. 6 . This configuration may provide a variety of closure assembly  20  configurations depending on the desired shaped surface. 
     After receiving the first and second surface  2 ,  4 , the induction coil  32 , may be activated with the high-frequency magnetic field, electrically powered to allow the induction coil  32  to heat. While the induction coil  32  may have a variety of configurations and orientations, generally, the induction coil  32  illustrated in  FIG. 5  is orientated along the perimeter of the upper die  14  to provide for an induction weld along at least a portion of the first and second surface  2 ,  4 . 
     As the induction coil  32  heats, the temperature of the upper and lower surfaces  2 ,  4  raises. Once the upper and lower surfaces  2 ,  4  reach the desired temperature, the induction welding device  10  may transition towards the engaged position with the upper die  14  directed towards the lower die  12 , the first and second surfaces  2 ,  4 , positioned therebetween in the end-to-end arrangement. Upon contact with the first and/or second surfaces  2 ,  4 , the upper die  14  may press the first and second surfaces  2 ,  4  together with sufficient force to allow for intimate contact between the upper and lower dies  14 ,  12  to form the end-to-end compressed first and second surface arrangement  30 . 
     As best illustrated in  FIG. 4 , with sufficient time and heat, the upper and lower dies  14 ,  12  may present a weld connection along the perimeter of the end-to-end compressed first and second surface arrangement  30 , forming the closure assembly  20 . The induction coil  32  may be raised or lowered onto the first and second surfaces  2 ,  4  by moving the first, second or both arms  34 ,  36  connected to the movable upper and/or lower die  14 ,  12 . The first, second or both arms&#39;  34 ,  36  movement may be controlled mechanically, hydraulically or electrically depending on the desired operation. 
     The induction coil  32  may be fabricated from a number of materials, including, as previously indicated, copper or brass tubing that is water cooled. Although, the first and second surfaces  2 ,  4  are illustrated in the end-to-end configuration, other configurations are possible for use with the induction welding device  10 . 
     Optionally, as illustrated in  FIG. 6 , a liquid may be circulated through a tube  140  associated with a lower die  112  and/or an upper die  114  to help cool the upper and lower dies  114 ,  112  and ensure that any heat transferred during the energizing of an induction coil  132  will not negatively impact the surface quality of the welded closure assembly  120 . In addition, fabricating portions of support members associated with the inductive weld assembly  110  from non-conductive materials, including non-magnetic material may prevent further overheating. 
     Generally, as illustrated in  FIG. 1B , the first and second arms  34 ,  36  associated with the upper and lower dies  14 ,  12  and associated upper and lower dies  14 ,  12  are illustrated with a generally planar configuration. The upper die  14  generally has a boss region  22  presenting the arcuate receiver  16  which is generally adapted for receiving the first surface  2  while preventing unwanted movement as the upper and lower die  14 ,  12  move towards each other. The lower die  12  has a wall structure  24  presenting the passageway  26  with the obliquely oriented lip  28  extending upwardly therefrom into the passageway  26 . In the illustrated configuration, the obliquely oriented lip  28  is generally adapted to receive the second surface  4 , preventing unwanted movement of the first and second surfaces  2 ,  4  while allowing for an angular orientation of the second surface  4  with respect to the first surface  2 . Alternatively, the upper and lower dies  14 ,  12  may be configured using a variety of shapes including regular and irregular shapes for joining the first and second surfaces  2 ,  4  to inductively heat and form the closure assembly  20 . The lower die  12 , being adapted to receive the second surface  4  may further be configured to present a shaped weld associated with the closure assembly  20  such as, but not limited to, a jewel-effect which may be presented by configuring the lower die  12  with a small radius of around 1.5 mm. 
     While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described methods, compositions and techniques that fall within the spirit and scope of the invention as set forth in the appended claims.