Patent Publication Number: US-2012025412-A1

Title: Integral cooling fixture addendum for panels formed in metal forming process

Description:
TECHNICAL FIELD 
     The field to which the disclosure generally relates includes metal forming processes, and more particularly to an integral cooling fixture addendum for a panel formed in a metal forming process. 
     BACKGROUND 
     In high temperature metal forming processes such as quick plastic forming (“QPF”) and super plastic forming (“SPF”), metal sheets are formed into product shapes in high temperature forming tools. The formed sheets are removed from the forming tools and placed on a cooling fixture by a robot or dedicated gantry for the initial portion of the time that it takes for the panel to return to room temperature. The formed panel is malleable and easily distorted at its high temperature immediately after removal from the forming process. The cooling fixture is designed to ensure that the formed panel maintains its formed shape during the time that it cools from the high forming temperature to a temperature slightly higher than room temperature. 
     SUMMARY OF EXEMPLARY EMBODIMENTS OF THE INVENTION 
     The exemplary embodiments use a particular shaping of the addendum contours of a formed panel to provide the functionality of a cooling fixture. 
     Other exemplary embodiments of the invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while disclosing exemplary embodiments 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 
       Exemplary embodiments of the invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1A  illustrates an automotive lift gate panel coupled to a forming tool according to the prior art; 
         FIG. 1B  is a cross-sectional view of the lift gate panel of  FIG. 1A  taken along line  1 B- 1 B that has been coupled to a cooling fixture according to the prior art; 
         FIG. 2  is a logic flow diagram disclosing the methodology for forming a formed part in accordance with one exemplary embodiment; 
         FIG. 3A  illustrates an automotive lift gate panel according to one exemplary embodiment coupled onto a flat surface for cooling; 
         FIG. 3B  is a cross-sectional view of the lift gate panel of  FIG. 3A  taken along line  3 A- 3 A; 
         FIG. 4A  illustrates an automotive lift gate panel according to another exemplary embodiment coupled onto a flat surface for cooling; and 
         FIG. 4B  is a cross-sectional view of the lift gate panel of  FIG. 4A  taken along line  4 A- 4 A. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following description of the embodiment(s) is merely exemplary (illustrative) in nature and is in no way intended to limit the invention, its application, or uses. Thus, the following description describes a lift gate panel as one exemplary example of a formed metal sheet that utilizes the novel principles described herein. 
       FIG. 1A  shows an automotive lift gate panel  20  after forming on a high temperature forming tool, here a typical quick plastic forming (QPF) tool  14 , in which the panel  20  has been formed downward over a male product definition  15 . The perimeter area  22  of the formed panel  20  is an addendum portion having an addendum surface  24  that follows the seal bead area of the forming tool. 
     An addendum portion refers to any portion on a molded part (i.e. part formed on the high temperature forming tool) that does not form a portion of the finished molded part after trimming. In other words, the addendum portion is a portion of the molded part that is removed by trimming. An addendum surface, by implication, is the surface of the addendum portion that is also removed. 
     Referring back to  FIG. 1A , the panel  20  surfaces transition downward from the perimeter addendum surface  24  along a transition area  26  to form a low area or trough  28  around a window frame portion  30  and a license plate portion  32  including a license plate pocket  33 , with the inner transitional surfaces  34  defining another addendum surface from the trough  28  to the window frame portion  30  and the license plate portion  32 . Internal to the window frame portion  30  is another section of window addendum material  36  that is typically left in a simple shape that would follow the gradual contours of the surrounding window opening of the window frame portion  30 . 
       FIG. 1B  shows a cross section of the formed panel  20  removed from the forming tool  14  ( FIG. 1A ) and placed on a cooling fixture  38  in accordance with a conventional method for cooling the formed panel  20 . The cooling fixture  38  includes a base plate  21  having one or more stands  23  extending therefrom each including a cooling fixture pad  25 . The cooling fixture  38  is designed to ensure that the formed panel  20  maintains its formed shape during the time that it cools from the high forming temperature to a temperature wherein the formed part is not easily distorted. Such distortion can occur in many different ways. First, the panel  20  may contract as it cools. If the panel  20  is overly constricted from movement, panel distortion may occur. In addition, if large areas of the panel  20  are not properly supported, the effects of gravity can distort the panel  20  at high temperatures. Further, high gravitational (“G”) forces from accelerated movement or impact during high temperature removal from the forming tool and placement onto the cooling fixture  38  may also result in panel distortion. 
     As shown in  FIG. 1B , the cooling fixture pads  25  therefore contacts the formed panel  20  along portions of the formed panel  20  wherein shape stiffness at elevated temperatures is insufficient to allow the formed part to maintain its shape against the forces of gravity. As shown herein, the formed panel  20  therefore contacts the cooling fixture pads  25  along a portion of its bottom surface  37 . In the embodiment shown in  FIG. 1B , the cooling fixture pads  25  contacts the bottom surface  37  along the window frame portion  30  and the license plate portion  33 . However, in other alternative embodiments, the cooling fixture pads  25  could contact the bottom surface  37  of the panel  20  at alternative locations such that the panel portion cools substantially or completely without distortion. 
     After the panel  20  cools, post-formation processing may be performed to remove the addendum surfaces constituting the perimeter addendum surface  24 , the transition area  26 , the inner transitional area  34  and the window addendum area  36 . To accomplish this, first, the molded panel  20  is removed from the cooling fixture  40 . Next, the perimeter addendum surface  24 , the transition area  26 , the inner transitional area  34  and the window addendum area  36  are trimmed with dies in a stamping press, or alternatively trimmed with a laser head on a robotic arm, depending upon the complexity of the trimming desired. The remaining portions of the molded part after trimming in general define the panel portion and herein define the lift gate  31  that may be further post-processed and eventually coupled to the rear of an automobile. 
     The exemplary embodiments described herein modify the shaping of the addendum contours of the formed panel to provide the functionality of the cooling fixture as the formed panel is placed on any flat, level surface. With proper design of this concept, the high temperature formed panels may be placed directly on the transfer conveyor which typically is a continuous flat surface expanding the length and width of the formed panel and allowed to cool without the need for a cooling fixture. In addition, the exemplary embodiments may allow smaller blank sizes (i.e. parts utilizing less addendum material that is subsequently removed) and hence better material utilization. 
     Referring now to  FIG. 2 , a logic flow diagram for forming a shaped metal panel according to one exemplary method, as well as two separate exemplary embodiments illustrating lift gate panels formed in accordance with the method of  FIG. 2 , as shown in  FIGS. 3A-B  and  4 A-B, are illustrated. 
     Referring first to  FIG. 2 , and beginning with Step  100 , an overall shape for the panel to be formed, as well as a determination of the materials used to form the panel, as well as a determination of the high temperature forming tools and molding parameters used to form the panel, may be first determined. Two conventional high temperature forming tools that may be used by the exemplary embodiments herein to form a high temperature panel are the so-called quick plastic forming tool, or QPF tool (such as  14  shown in  FIG. 1A ), and the superplastic forming tool, or SPF tool (not shown). 
     Quick plastic forming generally represents a process in which a relatively thin sheet metal workpiece is forced into conformance with a forming surface of a forming tool by a pressurized gas. Suitable sheet metal workpieces utilized in such a hot blow forming process are generally only about a millimeter to a few millimeters in thickness and are composed of materials capable of undergoing high deformation (sometimes superplastic deformation) such as aluminum and magnesium alloys. 
     Superplastic forming typically includes the steps of heating a sheet of material to a point in which superplastic deformation is possible, clamping the material within a sealed die and then using gas pressure to force the material to stretch and take the shape of a forming surface located in the die cavity. Controlling the gas pressure during the forming process controls the deformation rate of the material and maintains superplasticity at the elevated temperature. 
     Next, in Step  110 , a determination may be made as to the location of any distortion points after formation of the panel and after removal from the forming tool are determined. This may be accomplished by first forming a panel in a high temperature forming tool, removing the panel from the forming tool, and placing the panel onto a flat and level surface. The panel may then be allowed to cool a temperature below its deformation point (i.e. the deformation point is where the panel is easily distorted due to panel constriction, the forces of gravity or during tool extraction) of the material formed. The cooled panel may then be inspected to determine any points of distortion. 
     In Step  120 , an addendum location may be determined that is associated with each of the points of distortion. The addendum location may be a location wherein the introduction of addendum material is thought to prevent the localized deformation of the panel during the cooling process after high temperature formation. 
     In Step  130 , the high temperature molding tool may be modified to include these addendum locations. For a QPF forming tool or SPF forming tool, the shape of the metal part to be formed with the respective tool may be modified by size or shape to include these one or more addendum portions. 
     In Step  140 , a high temperature part may be formed within the high temperature forming tool, the high temperature part including the panel portion and the one or more addendum portions. 
     In Step  150 , the high temperature part may then be cooled on a flat surface and visually inspected to determine whether any more distortion points in the panel portion are present. If no distortion points are present, proceed to Step  160 , otherwise revert to Step  120  to determine one or more additional, or modified, addendum locations sufficient to substantially prevent distortion in the panel portion. 
     In Step  160 , the addendum portions may be removed from the panel portions of the high temperature part by trimming or some other conventional process to form the panel. The panel portion, such as, but not limited to, a lift gate panel  31 ,  52  disclosed below in  FIGS. 3A-B  and  4 A-B, may then be post-processed and used as a portion of a vehicle body. 
     Two exemplary embodiments of lift gate panels that utilize this concept, formed in a manner similar to the lift gate panel  20  of  FIG. 1A , are illustrated below in  FIGS. 3A-B  and  4 A-B. 
       FIG. 3A  illustrates a lift gate panel  40  after forming on high temperature molding apparatus such as a QPF tool in accordance with one exemplary embodiment of the present invention in which the panel  40  may have also been formed downward over a male product definition. In  FIG. 3A , the lift gate panel  40  has been removed and placed upon a flat surface  59 . The perimeter area  48  of the formed panel  40  may be an addendum portion having an addendum surface  50  that follows the seal bead area of the forming tool. The addendum surface  50  of the panel  40  may transition downward from the perimeter area  48  through a transition area  47  to a low area or trough  45  that forms a plane (shown in  FIG. 3B  as  49 ). Inboard of the planar trough  45 , the panel  40  may transition upward through a transition area  43  to the window frame portion  41  and to the license plate portion  42  including a license plate pocket  53 . Internal to the window frame portion  41  may be a perimeter portion  44  and a window opening addendum  46 . The perimeter portion  44  internal to the window frame portion  41  may transition downward to allow the center portion of the window opening addendum  46  to form a plane (shown in  FIG. 3B  as  51 ). The plane  51  internal to the window opening addendum  46  may be coincident with the plane  49  formed by the perimeter trough  45 . 
       FIG. 3B  show a cross section of the formed part  40  removed from the forming tool and placed on a flat surface  59  without the use of a cooling fixture. The formed part  40  may contact the flat surface  59  on the bottom surface  55  of the planar trough surface  45 . In addition, the bottom surface  57  of the window opening addendum  46  may also contact the flat surface  59 . The bottom surface  55  and the bottom surface  57  define a plane  61  therefore that may be parallel with planes  49  and  51 , respectively. 
       FIG. 3B  also shows that the addendum transition area  43  and the addendum perimeter portion  44  may support the window frame portion  41  and to the license plate portion  42  from the interface of the flat surface  59  and the bottom surfaces  55 ,  57 , therein substantially preventing or minimizing distortion of the window frame portion  41  and license plate portion  42  as the formed part  40  cools. 
     After the formed part  40  is cooled on the flat surface  59  to a temperature by which the formed part is no longer significantly malleable, the addendum portions may be removed. In the exemplary embodiment provided in  FIGS. 3A and 3B , a laser head on a robotic arm may be used to trim the transition area  43 , the perimeter portion  44 , the window opening addendum  46 , the transition area  47 , and the perimeter area  48 . The remaining panel portions after trimming therein may define the lift gate  52  that may be further post-processed and eventually coupled to the rear of an automobile. 
       FIG. 4A  illustrates an alternative configuration of a similar automotive lift gate formed panel  60  that may have been formed upward into a QPF tool having a female forming product definition (not shown) with a flat binder surface. Here, and in  FIG. 4B , the panel  60  has been placed on a flat surface  59 . This exemplary embodiment may allow for smaller formed panels  60  and hence better material utilization. 
     The formed panel  60  may include a perimeter addendum area  62  defining a planar surface (shown as  66  in  FIG. 4B ). The panel  60  may be continued inboard through a non-planer, transitional addendum portion  64  to a window frame portion  68  and to a license plate portion  70  having a license plate pocket  71 . Internal to the window frame portion  68  may be a perimeter addendum portion  72  that transitions downward to a center addendum portion  74  which forms a plane (shown as  76  in  FIG. 4B ). The plane  76  may be coincident with the perimeter planar surface  66 . 
       FIG. 4B  shows a cross-section of the formed part  60  removed from the forming tool and placed onto the flat surface  59  without the use of a cooling fixture. The formed part  60  may contact the flat surface on the bottom surface  80  of the perimeter addendum area  62  and along the bottom surface  82  of the center addendum portion  74 . The bottom surface  80  and the bottom surface  82  may define a plane  84  that may be parallel with planes  66  and  76 , respectively. 
       FIG. 4B  also shows that the transitional addendum portion  64  and the perimeter addendum portion  72  may support the window frame portion  68  and license plate portion  70  from the interface of the flat surface  59  and the bottom surfaces  80 ,  82  as the formed part  60  cools, therein substantially preventing or minimizing distortion of the window frame portion  68  and the license plate portion  70 . 
     After the formed part  60  may be cooled on the flat surface  59 , the addendum portions may be removed. In the exemplary embodiment provided in  FIG. 3A , a laser head on a robotic arm may trim the perimeter addendum area  62 , the transitional addendum portion  64 , the perimeter the perimeter addendum portion  72  and the center addendum portion  74 . The remaining portions after trimming may therefore define the lift gate  90  that may be further post-processed and eventually coupled to the rear of an automobile. 
     By utilizing concepts described herein, reduced investment costs may be realized, as the cost of cooling fixtures may be eliminated. Further, reduced costs may also be realized by removing the manpower machinery required to transfer a molded part such as a lift gate to and from the cooling fixture. In production situations, the flat surfaces  59  described in  FIGS. 3B and 4B , respectively, may be the initial portions of transfer conveyors that transport the formed panel  40  or  60  for further processing, including transporting to a location wherein the addendum pieces may be trimmed to form the panels  52 ,  90 , which may result in further costs savings. 
     While the above described concepts are directed to the formation of a lift gate panel, the concepts described herein may be utilized to form any type of panel formed in a high temperature forming tool that conventionally uses a cooling fixture with which to support the malleable metal part as it is cooled to its final shape. Also, additional features may be incorporated into a lift gate panel using the concepts described herein but not illustrated in  FIGS. 1-4 , including, for example, lift gate panels having lighting recesses. 
     The above description of embodiments of the invention is merely exemplary in nature and, thus, variations thereof are not to be regarded as a departure from the spirit and scope of the invention.