Abstract:
Unitary closure panels for automotive vehicles may be formed to have regions of different materials by a spray casting process. Separate sprays of different materials, for example two different metal alloys, are applied to touching regions of a spray application surface. The separate sprays may be applied sequentially or simultaneously to the forming surface to coat the respective regions so that the regions are contiguous or overlapping and a unitary body is formed. The spray formed body may be compressed and trimmed between facing surfaces to form a vehicle closure panel of specified outline, curvature, thickness, and porosity.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/978,801, titled “Spray Cast Mixed-Material Structural Members”, filed Oct. 10, 2007. 
    
    
     TECHNICAL FIELD 
     This disclosure pertains to making vehicle body or closure panels with contiguous or overlapping surface regions formed of two or more different materials. More specifically, this disclosure pertains to the use of spray casting of different materials for making such mixed-material vehicle closure panels. 
     BACKGROUND OF THE INVENTION 
     There is a continuing need to reduce weight of automotive vehicle components in order to reduce fuel consumption of passenger and commercial vehicles. Some vehicle components may have one portion that could be formed of a relatively light weight material and another portion that requires a stronger but heavier material. An example of such components include vehicle closure panels such as an inner or outer door panel, deck lid panel, tailgate panel, hood panel, or quarter panel. A major portion of the panel might be formed of a light weight reinforced polymer composition or a low density metal such as an aluminum alloy or a magnesium alloy. And contiguous edge portions of the panel, where hinges or latching mechanisms are attached, could be made of a stronger material such as a steel alloy. However, the manufacture of such mixed material panels have required complex and expensive processing. 
     This disclosure provides a spray casting based practice for the manufacture of mixed-material vehicle closure panels. 
     SUMMARY OF THE INVENTION 
     This invention is applicable generally to vehicle closure panels that may be formed by spraying and accumulating atomized drops of a molten material in a body on a collecting surface. Two or more sprays are used to form a panel having two touching regions, contiguous or overlapping, of different materials. 
     Sometimes the spray collecting surface is a forming surface (like a mold or die surface) shaped to form a side of the panel. In another embodiment the spray collecting surface may be a metal stamping or a polymer shape to which a higher strength material is sprayed to locally strengthen specific areas of the metal stamping or polymer shape. In one embodiment, molten metal or polymer melt is prepared under suitable conditions and placed in a tundish for the spray casting operation. This is done for each material to be sprayed. A controlled stream of each liquid material is drained from a tundish, or other holding vessel, and the liquid stream is suitably atomized into droplets of desired size. Atomization may be obtained, for example, by impacting the falling material stream with radially inwardly directed jets from a surrounding annular stream of atomizing gas, such as nitrogen. In other embodiments, known metal spraying techniques other than the molten metal spray may be used to achieve a desired outcome. 
     Each of the spray processes is controlled so that the drops accumulate and solidify on the collecting/forming surface to form a body region with minimal porosity consistent with the properties of the sprayed liquid. Such spray casting permits portions of different thicknesses to be formed in the spray cast area on the forming surface. In forming automotive body panels, the sprayed material may be, for example, a metal such as a ferrous alloy, an aluminum alloy, or a magnesium alloy. In another example, the sprayed material may be a thermoplastic or uncured thermosetting polymeric composition such as polyethylene, polypropylene, polyamide, polyurethane, or the like. The separate spray streams may be applied to the forming surface simultaneously or sequentially. The separate spray streams may be joined along edges, or the material spray may overlap all or portions of the previous layer. The temperature of the forming surface is suitably controlled for accumulation of the sprayed drops ultimately in a solid mass of desired porosity (or non-porous condition) and local thickness over the spray area. Each spraying operation (processing parameters such as melt temperature, temperature of atomizing gas, ambient temperature, spray distance, and temperature of the substrate or forming surface) is suitably controlled to manage the partial or complete solidification of the sprayed material before, or as, it impacts the collecting surface. 
     Reinforcement of a sprayed panel may be obtained, for example, by placing a mat of reinforcing fibers (such as steel wool, glass fibers, ceramic fibers, or any combination thereof) on the spray receiving surface and infiltrating the mat with the liquid spray. Or reinforcement within the sprayed body may be attained by including reinforcing particles (including short fibers) in the spray droplets. 
     After the sprayed material has accumulated on the receiving surface to a desired shape it will, in many embodiments, be a precursor of the desired vehicle body panel member. The spray cast precursor body panel may be further consolidated, shaped, trimmed or the like to a more finished formed closure panel by a compacting step such as hot isostatic pressing, die pressing, die trimming, or the like. The spray collecting surface may be used to shape a side(s) of the closure panel or the solidified panel member may be removed from the collecting surface for shaping, trimming, etc. In many embodiments of the invention, the spraying and any subsequent shaping step may be conducted in a closed chamber with a protective atmosphere, such as an atmosphere of argon or nitrogen. 
     In many embodiments of the invention two or more materials are sprayed, simultaneously or sequentially, on the forming surface to form a unitary closure panel having a first region of one material such as an aluminum alloy and a second region of a second material such as a steel alloy. In one embodiment, an edge of the second region is touching and joined to an edge of the first region. In another embodiment, the two materials may be layered so that the second or subsequent layers may overlap all or a portion of the preceding sprayed layer. Separate melts of the two materials may be prepared in separate vessels in one or more melting chambers. The respective molten materials are maintained in atmospheres that protect desired properties of the respective melts. 
     In an embodiment of the invention, the structure of a closure panel to be manufactured is analyzed to identify two or more distinct regions that may advantageously be made of metallic or polymeric materials having different properties. A gathering or forming surface is then prepared to shape a side of the body panel to be formed. The forming surface may be preheated to enhance agglomeration and continuity of the sprayed material. The sprays of the different materials are then directed to the respective distinct regions of the forming surface with sufficient overlapping or merging of the different materials to form a unitary panel. The regions of overlapping materials may be heat treated to enhance their joining and properties. In another embodiment a thin coating of a metal alloy interlayer may be deposited over at least a portion of the first material, and the second material may be deposited over at least a portion of the interlayer, to enable a well bonded corrosion-resistant transition between the two base materials. 
     It is contemplated that this spray practice of different materials may be used to form two-material vehicle closure panels. Such vehicle closure panels may include door panels, hood panels, tailgate panels, deck lid panels, or quarter panels. Vehicle doors are often made by separately forming complementary inner and outer door panels. Each panel is often made of a shaped sheet material to define a vehicle closure member and a window opening. The panels are ultimately attached to each other (e.g., adhesively bonded or hemmed and welded) around the perimeter of matching peripheral edges. The attached panels define a space between them for a window, window closure hardware, wiring, door closure and locking components, and the like. The assembled closure member is attached on one side to a vehicle body structure. In accordance with an embodiment of this invention, a door inner panel, for example, may be formed of a major sheet area of a light weight material such as an aluminum alloy or magnesium alloy and a smaller, but stronger hinge area or door closure area of a steel alloy. In another embodiment, the inner panel may be made of a major sheet area of a polymeric (or fiber reinforced polymer) and a metal alloy hinge or closure area. 
     Other embodiments and advantages of the invention will be apparent from more detailed descriptions of preferred embodiments and references to the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a two-material door inner panel according to one embodiment of the invention. 
         FIG. 2  illustrates a cross-sectional view of a portion of two-material door inner panel according to one embodiment of the invention. 
         FIG. 3  illustrates a cross-sectional view of a portion of a two-material door inner panel according to one embodiment of the invention. 
         FIG. 4  is a schematic view, in vertical arrangement, of a melt crucible and a tundish in a vacuum melt chamber. An atomizer for a stream of molten material is in a separate atmosphere-controlled chamber below the melt chamber and the atomized stream falls onto a forming surface. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     This invention provides a method for forming unitary vehicle closure panels having a first region of a first material and an adjacent and touching, or an at least partially overlapping, second region of a second material. Such vehicle closure panels are usually stamped from a sheet material and hinges or the like are attached to the formed panel. This invention provides a method of forming integrally bonded panel portions and hinge or latch portions of different materials. The panel portion may be composed of a light weight material, while the hinge or latch portion may be composed of a heavier and stronger material. Thus, the vehicle closure panels of the invention may be lighter than known closure panels while still providing the necessary strength for a particular application in the vehicle. 
     In various embodiments, the vehicle closure panel may be, but is not limited to, a door inner panel, door outer panel, tailgate panel, hood panel, deck lid panel, or quarter panels. A spray cast method is used to form at least one of the two regions. The first and second regions may be formed of different metal compositions, of different polymer compositions, or of a metal composition and a polymer composition. The first and second regions may be side-by-side or at least partially overlapping. 
     In one embodiment of the invention, a generally sheet type vehicle closure panel is formed. For example, the closure panel may be an inner door panel  10  for an automotive vehicle, as illustrated in  FIG. 1 . In this example, a first region or major panel area  12  of the inner door panel will be formed of spray cast aluminum alloy and a second region or smaller hinge or latch attachment area  14  will be formed of a carbon steel alloy. The inner door panel  10  is basically a curved, three-dimensional, door surface layer structure of shaped sheet material with a window opening  16  in its upper region and openings  18  in the lower part of the panel for driver or passenger activated door and window closure mechanisms, speakers, or access to other components. In the example of  FIG. 1 , the panel area  12  is formed of a spray cast aluminum alloy and the attachment area  14  is formed of spray cast carbon steel. The areas  12  and  14  are touching side-by-side. The inner door panel  10  is shaped to fit against and be attached to a complementary door outer panel (not shown). Both panels may be curved for the shape of the vehicle body to which they are hinged and latched. Various electrical and mechanical window and door closure components may be assembled between the inner and outer panels in vehicle manufacture. 
       FIG. 2  shows a cross-sectional view of region A in  FIG. 1 . In the embodiment shown in  FIG. 2 , the areas  12  and  14  touch in an overlapping region  17 . In another embodiment (not shown), a thin coating of a metal alloy interlayer may be located in the overlapping region  17  between the area  12  and the area  14 .  FIG. 3  also shows a cross-sectional view of region A in  FIG. 1 . In the embodiment shown in  FIG. 3 , the areas  12  and  14  touch side-by-side and the areas  12  and  14  include a reinforcing material  19 , for example a porous wire mat, onto which the spray cast alloy was sprayed. The reinforcing material  19  may be located where the areas  12  and  14  touch and may extend for some distance into the areas  12  and  14 . 
       FIG. 4  illustrates an exemplary spray casting apparatus  20 . Such apparatus  20  comprises an upper chamber  22  (optionally closable for atmospheric control) in which a melt of metal alloy or polymer is prepared for spray casting onto a forming surface or mold die cavity  24  in the shape of, for example, the door inner panel  10 . In another embodiment, the surface may be a metal stamping or a polymer shape that has the minimum thickness and minimum strength properties of the desired vehicle closure panel. A higher strength material is sprayed over portions of the metal stamping or polymer shape to locally strengthen those areas. Referring again to  FIG. 4 , depending on the composition of a specified metal alloy or polymer the upper chamber  22  may be adapted to accommodate vacuum melting, or melting in a protective gaseous atmosphere, of the sprayable composition. When a suitable melt has been prepared, molten metal (or polymer material) may be drained from a melt crucible  26  into a tundish  28  for melt spraying. The melt crucible  26  and tundish  28  may be located in the upper chamber  22 . In this embodiment, spray castable material then flows down into a lower chamber  30  in which spray casting onto the forming surface  24  for the inner door panel  10  (or other part) or onto a collecting surface provides a precursor shape for the part to be formed. The lower chamber  30  may be under vacuum or in a protective gaseous atmosphere depending on the particular materials being used. 
     As the spray castable material is released from the tundish  28  it is atomized in atomizer  32  and sprayed as droplets in a suitable pattern onto the part forming surface. Atomization may be accomplished by impingement of an inert gas against the stream dropping from the tundish  28 . 
     There are other processing variables that may be managed in the spray casting operation. For example, the temperature of the molten material, the size range of the spray droplets, the distance of the spray path, the nature and temperature of the atomization medium, and the temperature of the surface on which the spray accumulates are variables that may be considered in an effort to accumulate a suitable thickness of sprayed material on a forming surface. The material droplets/particles may be solid, partly solid and partly liquid, or liquid when they impact the forming surface or previously deposited material. In other embodiments, any suitable known metal spraying technique may be used to form the first and second region of a vehicle closure panel. 
     In many embodiments of the invention, there will be two separate spray steps of the type described above. A first material spray stage will form, for example, the aluminum alloy panel area  12  and a second spray cast stage will provide the steel hinge attachment area  14 . The spray patterns will be controlled so that there will be continuity and suitable attachment of the two contiguous material regions of the formed part. In one embodiment of the invention the forming surface  24  may be first positioned for a first spray casting stage and then moved into position for a second spray stage. 
     In another embodiment, the first spray step will form a first panel area, and the second spray step will form a second panel area or layer overlapping all or portions of the first panel area. In another embodiment, a very thin interlayer is formed over at least a portion of the first panel area, and then the second spray step forms a layer overlapping all or portions of the interlayer. The interlayer may function as a corrosion-resistant transition between the two sprayed materials. The interlayer may be composed of any suitable brazing alloy composition. 
     After the spray casting has been completed, the forming surface  24  carrying the two sprayed material areas  12 ,  14  may be removed from the lower spray chamber  30 . The sprayed materials may be subjected to further thermal processing or thermo-mechanical processing. In general, it may be helpful to use an opposing, complementary forming tool or surface to compact the layer(s) of the two sprayed materials against the original forming surface. Such processing consolidates the sprayed material to a desired density, local thicknesses, local curvature, and edges of the sprayed body may be trimmed or the like to bring the spray cast precursor body to (or close to) finished dimensions. Thus, a vehicle closure panel such as a curved, generally rectangular, vehicle inner door panel is formed in a few processing steps with connected and/or at least partially overlapping regions of different metals (or polymer materials). Such a panel may, for example, have a length and width of about 1 meter and a thickness of approximately 1 mm to 4 mm. 
     In some spray casting steps it may be useful to include particles or short fibers of reinforcing material in the metal droplets. The particles or fibers may include steel wool, glass fibers, ceramic fibers, or any combination thereof. In other embodiments it may be useful to place a reinforcing porous wire mat or the like in the forming surface and fill the reinforcing object with sprayed liquid droplets. The reinforcing mat may include reinforcing fibers such as steel wool, glass fibers, ceramic fibers, or any combination thereof. 
     Thus, it is seen that many vehicle closure panels having contiguous or overlapping regions of different materials may be formed by the disclosed spray cast processes. 
     Practices of the invention have been shown by examples that are presented as illustrations and not limitations of the invention.