Abstract:
Disclosed is a method of forming metallic composite structures The method utilizes superplastic and quickplastic formation methodologies in conjunction with the use of appended engineered metallic foams to provide a energy absorbing materials.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a method of making metallic composite structures and more specifically, a method for forming metallic composite panels having an interior metallic foam core.  
       BACKGROUND OF THE INVENTION  
       [0002]     A useful method for metal sheet forming is provided in “quickplastic” or “superplastic” (“quick plastic” or “super plastic”) forming approaches (QPF or SPF) in which sheet metal is formed into a complex shape in a single-sided forming tool using gas pressure to provide the forming force to transform the sheet metal into a form. In this regard, metal sheets such as aluminum are heated and then formed into shapes using gas pressure. The technology allows complex shapes to be formed from materials otherwise difficult to form to the complex shape. Details in these methods are presented in commonly assigned U.S. Pat. No. 5,974,847 for a “Superplastic Forming Process” issued to Fredrick I. Saunders, et al., on Nov. 2, 1999, and U.S. Pat. No. 6,253,588 for “Quick Plastic Forming Of Aluminum Alloy Sheet Metal” issued to Moinuddin S. Rashid, et al., on Jul. 3, 2001, which are herein incorporated by reference.  
         [0003]     In a number of products, such as energy absorbing structures used in transportation vehicles, it would be desirable to form a metal foam portion attached to a formed sheet metal structure so as to form a lightweight compactable structure. The compactable structure would deform at predetermined stress levels when subjected to an impact. Formation of such structures to date has not been feasible due to the cost of formation of the foam portion which needs to be shaped prior to the attachment to the shaped sheet metal. Furthermore, adherence of the shaped foam portion to the shaped sheet metal requires use of an adhesive. The adhesive provides a bond in the composite (between the foam portion and the metal sheet) which has its own properties, thus establishing at least three discrete domains of properties within the composite. The interfacial properties of the adhesive may significantly complicate the design of structures using these materials.  
         [0004]     What is needed is a unified and straightforward approach for providing a complex composite structure of a formed metal sheet with a metal foam substrate. Preferably, the composite structure could be formed at low cost in such a manner that the foam does not require significant processing of the foam in the attachment step. The present invention is directed to fulfilling these needs.  
       SUMMARY OF THE INVENTION  
       [0005]     Disclosed is a method for forming a bi-phase metallic composite structure of metallic foam fused to a metal sheet by (a) placing the metallic sheet between a die and a platen. The metallic sheet is subjected to stretch forming by use of differential gas pressure, where the die has a forming surface defining a cavity between the forming surface; (b) adjusting the temperature of the metallic sheet to between a superplastic-forming temperature and a melting temperature of the metallic sheet; (c) applying gas pressure to the sandwich panel to stretch the metal sheet into conformity with the die forming surface; and (d) coupling of metallic foam core to the deformed metallic sheet.  
         [0006]     In a further embodiment of the present, the platen has a die with a panel shaping surface opposite the cavity of the first die. Prior to blow-forming with gas pressure, the sheet metal panel material is drawn into the cavity by the shaping surface as the dies close together.  
         [0007]     In yet a further embodiment, the above operations are preceded by the positioning of a metal foam core adjacent to the metal sheet. The metal sheet and foam core are heated to a forming temperature sufficient to bring the metallic sheet to its super plastic forming temperature prior to forming.  
         [0008]     In yet another embodiment of the present invention, a method for forming foams, and one-sided or two-side sandwiched foam composite structures is disclosed, by (a) placing the foam or sandwiched composite structure between two sections or parts of a die or forming tool and a movable platen between a die open position and a die closed position in which the die and the platen sealingly engage the periphery of the foam or sandwich panel. The die is configured to provide blow forming of foam or a composite sandwich panel by use of differential gas pressure. The die has a forming surface defining a cavity between the forming surface and the foam; (b) adjusting the temperature of the foam or foam sandwich panel to the super plastic forming temperature range; (c) moving the die and platen to their closed position such that the die engages the periphery of the foam or sandwich composite panel; and (d) applying gas pressure to the panel to conform the foam or the sandwiched panel with the die or tool forming surface.  
         [0009]     In a further embodiment, the tool lid has a panel shaping surface (preformer, prebender, or stuffer) opposite the cavity of the first half or forming area. Prior to blow-forming with gas or air, the foam or sandwiched composite panel is forced into the cavity by the shaping surface as the die halves close together. In yet a further embodiment, a section of foam is placed between the die forming half and a metallic sheet. [In this case, the foam does not extend to the edges of the panel, so it is not locked by the seal beads when the die is closed]. The foam is positioned in a location in which greater energy absorption is required. The metallic sheet forms on top and around the foam piece, locking it in the required position, creating a foam reinforcement where needed and in just one forming operation.  
         [0010]     The invention provides a basis for producing complex, tough, and “stiff” structures via an essentially single economic forming operation with commensurate benefits in providing low weight composites. Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
         [0012]      FIG. 1  presents a cross sectional view of a planar sandwich panel;  
         [0013]      FIG. 2  shows a planar sandwich panel with the cross section of  FIG. 1  placed between first and second die members in a die open position;  
         [0014]      FIG. 3  shows the dies of  FIG. 2  in a die closed position with a drawn sandwich panel in the cavity formed between the first and second die members;  
         [0015]      FIG. 4  shows a formed composite made by quick plastic forming of the drawn sandwich panel of  FIG. 3 ; and  
         [0016]      FIGS. 5 and 6  shows the formation of a composite structure according to one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
         [0018]     The preferred embodiments involve using superplastic (SPF) or quickplastic (QPF) (“quick plastic” or “super plastic”) forming technology approaches in forming a metallic composite structure. In this regard, a planar metal sheet capable of quick-plastic formation is used in the SPF or QPF procedure. During the SPF or QPF process, the temperature of the planar metal sheet is increased so that it is between the super plastic forming temperature and the melting temperature. The sheet metal  102  is deformed using SPF or QPF procedures to form a three dimensional formed metal sheet. The formation of the composite structure occurs either during or after the SPF or QPF of the sheet metal. In this regard, the formation of the metallic composite occurs when a metallic foam layer  106  is coupled to the formed metallic sheet.  
         [0019]     The coupling of the metallic foam  106  to the formed metal sheet is accomplished using one of several methodologies. It is envisioned that the metallic foam substrate  106  can be coupled to a quick-plastically formed sheet metal after the plastic deformation of the metal sheet  102 . This coupling can be completed by using adhesives or brazing materials which are deposited between the deformed metallic sheet  102  and the foam substrate  106 . Additionally, the deformed sheet metal can be formed so as to have a pair of locking interface surfaces which can be elastically deformed so as to engage pair of sculpted surfaces on the foam material.  
         [0020]     The metallic foam substrate  106  can also be coupled to the metallic sheet  102  during the super-plastic or quick plastic formation process. In this process the foam material  106  can be coupled to the metal sheet  102  or between a pair of sheets during the structure&#39;s formation in the SPF or QPF process. The foam substrate  106  can be sculpted prior to forming, and inserted into a quick plastic formation die with the undeformed sheet metal. During the formation of the composite structure, the sheet metal  102  can be deformed about the sculpted foam  106 . This deformation can provide a pair of interface surfaces which engage a corresponding pair of surfaces on the foam substrate  106 .  
         [0021]     Alternatively, the shape of the foam substructure  106  can be altered or modified during the SPF-QPF processing. While preprocessing of the foam substrate  106  can occur, a portion of the forming or deformation of the foam substrate  106  can take place during the SPF-QPF processing of the sheet metal  102 . When the composite structure is formed, the foam substrate  106  can be adhered to the sheet metal  102  by fusion or with the use of brazing material disposed in the construction. In this regard, it is envisioned that the coupling of the foam substrate  106  to the sheet metal  102  can additionally occur by the mechanical interaction with deformed sheet metal surfaces. This fusion coupling eliminates the need for application of an adhesive when manufacturing the panel. Additionally, the use of a fused junction also eliminates the need for managing properties respective to a bonding layer in the composite between the foam portion and the metal sheet during QPF or SPF execution.  
         [0022]     Lastly, the foam substrate  106  can be bonded to the sheet-metal prior to the SPF-QPF process. In this regard, a composite panel  100  formed of a laminate sheet of metallic foam  106  with a single sheet of metal  102  or a sheet metal sandwich is provided. By way of non-limiting example, a method for producing metallic foam composite structure using foam panel or sandwich structure is now described. Briefly referring to  FIG. 1 , a cross-sectional view of a composite panel  100  shows a first sheet  102 , and a foam section  106  with the foam section  106  fused to each of the first sheet  102 . Preferably, sheet  102  is a metallic sheet of superplasticly formable alloy (for example, without limitation, aluminum AA5083). It is envisioned however that the material can additionally be super plastic grade alloys such as titanium, magnesium, steel, or any other type of material capable of SPF or QPF formation. The metallic foam is preferably high purity aluminum alloy reinforced with a low volume fraction of (˜1 micron) ceramic particles. It is envisioned however that the material can additionally be super plastic grade titanium, magnesium, steel, or any other type of material foams and sandwiched foams capable of SPF or QPF formation. The materials chosen for the sandwich panel and the design of the panel are, therefore, defined so that the temperature of the panel environment at the time when QPF or SPF is initiated will enable the metal sheet and the metallic foam section to all have individual temperatures between their respective super plastic temperatures and melting temperatures.  
         [0023]     In one embodiment, the composite panel  100  is formed when a metal foam core is positioned against a surface of the first metal sheet  102 . Optionally, the second metal sheet  104  is positioned against the other side of the foam core. In one embodiment of the present invention, the composite panel  100  is preformed and is subsequently heated at the time of further processing so that the temperature of the panel is such that each of the first metal sheet  102 , the metallic foam  106 , and the second metal sheet  104  in the composite panel  100  has a respective temperature between the superplastic-forming temperature and the melting temperature.  
         [0024]     Turning now to  FIG. 2 , a sandwich panel  106  (having a cross section such as shown in  FIG. 1 ) is placed between first die member  208  and second die member  212  in die open position. A cavity  210  is defined between forming surface  214  of die member  208  and first metal sheet  102  of panel  100  when die  208  moves to rest against panel  202 . First die member  208  is attached to platen  204  and the second die member is attached to platen  206 . The temperature of panel  202  is adjusted so that each of the first metal sheet  102 , the metallic foam  106 , and the second metal sheet  104  in panel  100  is at the blow temperature for the material.  
         [0025]     Turning now to  FIG. 3 , die members  208  and  212  of  FIG. 2  are depicted in die closed position with the formed sandwich panel  302  in cavity  210 . After full closure of die member  208 , panel  302 , and platen  206 , pressurized air or gas, such as nitrogen or argon, is admitted against the second metal sheet  104  of heated drawn panel  302  through a suitable gas passage (not shown) in platen  206  and/or preform  212 . Concurrently, gas, in one embodiment, is vented from cavity  210  through vent passages (not shown) of die member  208  or platen  204 . Die member  208  and platen  206  grip drawn panel  302  in gas-tight sealing lockbead (not shown) engagement so that suitable gas pressure is maintained on the sandwich material until obtaining full compliance with the forming surfaces  214  of die member  208 .  
         [0026]     This high pressure blow-forming operation was conducted by gradually increasing the argon pressure to over a period of several minutes. The pressure was then relieved, the dies opened and a completed component was removed. The pan formed completely without splits or significant cavitation.  
         [0027]     At the conclusion of blow-forming, that is when panel  302  has been made to fully comply with the forming surfaces  214  of die member  208 , the die member  208  and platen  206  open so that the resulting composite structure may be withdrawn and cooled.  FIG. 4  shows one embodiment of a composite structure  400  made according to the above described method. In one embodiment, composite structure  400  is cooled below the super plastic temperature of all of shaped first sheet  102 , second sheet  104 , and foam section  106  before die member  208  and platen  206  open so that composite structure  400  will not distort after removal from die member  208  and platen  206 .  
         [0028]      FIGS. 5 and 6  shows the formation of a composite structure  408  according to one embodiment of the present invention. The metallic foam material  406  can also be coupled to the metallic sheet  402  during the super-plastic or quick plastic formation process. In this process the foam material  406  can be coupled to the metal sheet  402  or between a pair of sheets during the structure&#39;s formation in the SPF or QPF process. The foam substrate  406  can be sculpted prior to forming, and inserted into a quick plastic formation die  212  with the undeformed sheet metal  402 . During the formation of the composite structure  408 , the sheet metal  402  can be deformed about the sculpted foam  406 . This deformation can provide a pair of interface surfaces  410  and  412  which engage a corresponding pair of surfaces  414  and  416  on the foam substrate  406 .  
         [0029]     Alternatively, the shape of the foam substrate  406  can be deformed during the SPF-QPF processing. While preprocessing of the foam substrate  406  can occur, a portion of the forming or deformation of the foam substrate  406  can take place during the SPF-QPF processing of the sheet metal  402 . When the composite structure is formed, the foam can be adhered to the sheet metal  402  by fusion or with the use of brazing material disposed in the construction. In this regard, it is envisioned that the coupling of the foam substrate  406  to the sheet metal  402  can additionally occur by the mechanical interaction with deformed sheet metal surfaces  410  and  412 .  
         [0030]     As described herein, superplastic and quickplastic fabrication of one-sided and two-sided sandwiched metallic sheet  100  and foam composites into composites with curvatures provides a unified operation for making composite structures of complex shape sheet with attached metal foam where the foam portion is fused into the metal sheet. The economic forming operation enables manufacture of low weight metal-sheet/metal-foam composites having good impact absorption properties. In this regard, the technology provides a path for enabling the production of ultra-stiff, lightweight panels for automobile body structures and closures. The foam sandwich as formed provides significant stiffness in the manufactured part and, as described, is conveniently and economically formed in a single die or forming tool.  
         [0031]     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.