Abstract:
A method of reinforcing a part formed from a sheet metal panel that has a predetermined area that requires reinforcement by forming a grid pattern of V-shaped channels in the predetermined area. The grid pattern may be formed by wire electrodes in an electro-hydraulic forming tool having a one-sided die. Alternatively, the grid pattern may be formed by a plurality of electrodes that are arranged in an array that is aligned in at least two directions on the opposite side of the part from the one-sided die.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    The invention was made with Government support under Contract No. DE-FG36-08GO18128. The Government has certain rights to the invention. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to a method of manufacturing an integral reinforcement for a part, such as a structural component of a vehicle, and to the integral reinforcement grid made according to the method. 
       BACKGROUND 
       [0003]    Sheet metal stamping and spot welding are the traditional technologies used to form interior and exterior panels for vehicles and other durable goods. Sheet metal stamping processes for making automotive panels include blanking, drawing, trimming and flanging. In addition to this traditional sequence of stamping operations, a restrike operation or secondary trimming operation may be involved. This method of manufacturing was employed to make parts from mild steel for decades. 
         [0004]    New fuel economy standards require car designers to use lighter and stronger materials such as Advanced High Strength Steels (“AHSS”)/Ultra High Strength Steels (“UHSS”) and Aluminum alloys. AHSS/UHSS save weight by reducing the material thickness that is compensated for by the increased strength of the replacement materials. However, design and gauge selection of many interior panels and structural parts are driven by bending and torsion stiffness. 
         [0005]    Simple replacement of mild steels with thinner higher strength steels degrades the elastic bending and torsion performance characteristics of parts made by the higher strength materials. These performance characteristics of high strength materials are the major roadblocks that limit implementation of AHSS and UHSS in the automotive industry. Insufficient bending stiffness of stamped panels made of AHSS and UHSS steels also works against broad adoption of these materials in other durable goods. 
         [0006]    One proposed solution that is currently being implemented is patching portions of the parts with over laid patches in local areas where the stamped blank has insufficient stiffness. For example, a hot stamped patch of Boron steel may be applied to a portion of a B-pillar reinforcement. In another example, a patch of high strength material may be bonded by polyurethane to a portion of a roof panel for reinforcing the roof. Providing a patch of the high strength materials adds weight to the vehicle and reduces the advantages offered by the adoption of high strength materials. 
         [0007]    The problem of insufficient stiffness of stamped panels that have a design driven by elastic bending requirements and torsional stiffness is addressed by this disclosure. The lack of elastic stiffness results in the use of blanks that have an increased gauge that is counterproductive to weight savings. 
         [0008]    The above problems and other problems are addressed by this disclosure as summarized below. 
       SUMMARY 
       [0009]    According to one aspect of this disclosure, reinforcing sharp V-shaped ribs are integrally formed on stamped panels by adding an additional manufacturing operation of electro-hydraulic forming ribs or a grid on parts made of AHSS/UHSS. 
         [0010]    The reinforcement is formed as narrow sharp channels in localized areas. The panel is first formed to the desired major curvature and then is subjected to an advanced forming process, such as electro-hydraulic forming (“EHF”), that increases the amount of strain that can be applied to the part without fracturing. 
         [0011]    According to one aspect of this disclosure as it relates to a method of reinforcing a part, the method comprises forming a metal panel into a three dimensional shape that includes a predetermined area requiring reinforcement, and forming a grid pattern including a plurality of grooves in the area requiring reinforcement. 
         [0012]    According to other aspects of the method, the step of forming a grid pattern may further comprise electro-hydraulically forming the grid pattern against a one-sided die by discharging at least one electrode in a fluid, wherein the fluid is contained in a vessel contacts the area requiring reinforcement. Alternatively, an electro-magnetic forming tool may be used to form the V-shaped grooves instead of electro-hydraulic forming the grooves. The step of forming a grid pattern may further comprise forming a grid of V-shaped cross-section grooves that includes a first set of parallel grooves extending in a first direction and a second set of parallel grooves that extend in a second direction, and wherein the first and second sets of grooves intersect at a predetermined angle. The predetermined angle may be approximately a right angle. 
         [0013]    According to another aspect of this disclosure, the step of forming the grid pattern may further comprise placing the predetermined area between an electro-hydraulic chamber and a one-sided die. The electro-hydraulic chamber includes a first plurality of wire electrodes that extend in a first direction. A stored electrical charge is discharged through the wires to form a first set of the plurality of grooves into a sharp V-shaped cross-section. The predetermined area may then be placed between the electro-hydraulic chamber and the one-sided die. A second plurality of wire electrodes that extend across the electro-hydraulic chamber in a second direction that is different than the first direction. A stored electrical charge is discharged through the wires to form a second set of the plurality of grooves into a sharp V-shaped cross-section with the first and second sets of grooves intersecting at a predetermined angle. 
         [0014]    According to an alternative embodiment of this disclosure, the step of forming the grid pattern may further comprise placing the predetermined area of the panel over an array of electrodes that are aligned in a first direction and that are aligned in a second direction, wherein the first direction and the second directions intersect. The plurality of electrodes are discharged to form a first plurality of channels in the first direction and a second plurality of channels that extend in a second direction. 
         [0015]    The electrodes are connected to a source of stored electrical power having a first polarity, and the panel is connected to the source of stored electrical power having a second polarity that is opposite the first polarity. 
         [0016]    According to another aspect of this disclosure, a part is disclosed that comprises a metal panel that is formed into an intermediate part shape that includes a predetermined area requiring reinforcement. A plurality of intersecting V-shaped channels are formed in the metal panel at the area requiring reinforcement. A first set of the V-shaped channels are disposed to resist deformation in a first direction and a second set of V-shaped channels are disposed to resist deformation in a second direction, wherein the first and second directions are different. 
         [0017]    According to other aspects of this disclosure as it relates to the part, the V-shaped channels may terminate in a protruding portion that is a sharp edge. The V-shaped channels may form a grid pattern that reinforces a predetermined area of the part in at least two different directions. The grid pattern may be an array of channels that intersect at right angles. Alternatively, the grid pattern may be an array of parallel channels that intersect at acute and oblique angles. The first set of V-shaped channels may be parallel to each other, and the second set of V-shaped channels may be parallel to each other. The channels may also be oriented in a non-parallel orientation that is aligned to counter a bending moment in the part. 
         [0018]    According to other aspects of this disclosure as it relates to a system for reinforcing a part formed from a metal panel, the system may include a first forming tool that forms the metal panel into an intermediate three dimensional part shape that includes a predetermined area that requires added strength. A second forming tool forms a plurality of channels into the predetermined area in a grid pattern after the first forming tool forms the part shape that reinforces the predetermined area in at least two directions. 
         [0019]    According to other aspects of the system, the second forming tool may be an electro-hydraulic forming tool that has a one-sided die. The electro-hydraulic forming tool may include a first plurality of wire electrodes that are parallel to each other and extend in a first direction and a second plurality of wire electrodes that are parallel to each other and extend in a second direction. Alternatively, the electro-hydraulic forming tool may include a plurality of electrodes that are aligned in a first direction and a plurality of electrodes that are aligned in a second direction. The first direction and the second directions intersect. The electrodes are discharged to form a first plurality of channels that extend in the first direction and a second plurality of channels that extend in the second direction. 
         [0020]    The above aspects and other aspects of this disclosure will be explained in greater detail below with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a perspective view of a compartment pan, or floor pan, of a vehicle that includes a predetermined area that is integrally reinforced with a grid pattern of sharp edged ribs; 
           [0022]      FIG. 2  is a diagrammatic cross-sectional view showing an electro-hydraulic forming chamber that may be used to form the integral reinforcement grid in a part such as the compartment pan shown in  FIG. 1  or other parts that require reinforcement; 
           [0023]      FIG. 3  is a cross-sectional view taken along the line  3 - 3  in  FIG. 1  through a portion of a panel having an integral reinforcement grid; 
           [0024]      FIG. 4  is a diagrammatic view of an electrode wire electro-hydraulic forming tool that is shown ready to form the ribs of the integral reinforcement grid that extend in one direction; 
           [0025]      FIG. 5  is a perspective view of a panel including the integrally formed grid of reinforcement ribs; 
           [0026]      FIG. 6  is a diagrammatic view of an electro-hydraulic forming tool that includes electrodes disposed at the intersection of the ribs forming grid of integral reinforcement ribs; and 
           [0027]      FIG. 7  is a diagrammatic view of an electro-hydraulic forming tool illustrating ribs aligned in a non-parallel fashion. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    A detailed description of the illustrated embodiments of the present invention is provided below. The disclosed embodiments are examples of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale. Some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed in this application are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art how to practice the invention. 
         [0029]    A grid pattern of intersecting grooves  10  is illustrated that is formed on a selected portion  12  of a floor pan  16  for a vehicle (as shown in  FIG. 1 ). 
         [0030]    Referring to  FIG. 2 , an electro-hydraulic forming tool  18  is illustrated that includes a one-sided die  20 . The one-sided die  20  includes a plurality of V-shaped grooves  22  that are parallel and extend in one direction across all or part of the one-sided die  20 . A fluid chamber  24  is defined by a lower tool  26 . The fluid chamber  24  contains a fluid  28 , such as water or an aqueous solution including a rust inhibitor. As shown, four wires  30  extend across the chamber  24  and are aligned with the grooves  22  formed in the upper die  20  on the opposite side of a blank  32 , or work piece. 
         [0031]    In operation, the cavity  24  and the lower tool  26  is filled with a fluid  28 . The electrode wires  30  are assembled to the lower tool  26  to extend across the cavity  24 . The electrode wires  30  are connected to a source of stored energy, such as a bank of capacitors (not shown) that provide a pulse of current that is discharged through the electrode wires  30  to create a shockwave below the blank  32 . The shockwave is transmitted through the fluid and causes the work piece  32  to conform to the grooves  22  in the upper die  20 . 
         [0032]    Referring to  FIG. 3  a cross-section of the ribs in the floor pan  16  are shown. The ribs are V-shaped and are formed with a relatively sharp distal edge that has a slightly arcuate shape due to the limits of forming the metal part in a die. The interior radius of the rib is less than 0.5 t, wherein “t” is the thickness of the metal. 
         [0033]    Referring to  FIG. 4 , five wires are shown in a bottom plan view extending across the fluid chamber  24 . The grooves  22  are illustrated to be in the background of the wires  30 . It can be seen that the wires  30  are substantially centered relative to the grooves  22 . The wires  30  are on the lower side of the work piece  32 . The grooves  22  and the upper die  20  are shown to be aligned with the wires  30 . A second set of grooves  36  extend perpendicular to the grooves  22 . No wires are shown to be aligned with the grooves  36  because the groove pattern is formed by a first step of firing the wires that are opposite the grooves  22 . After the first step is completed, wires (not shown) are installed to extend perpendicularly relative to the wires  30  and in alignment with the grooves  36 . 
         [0034]    Referring to  FIG. 5 , a section of the grid pattern reinforcement is shown to include a first set of V-channels  40  that are perpendicular to channels  42 . The channels  40 ,  42  terminate in a sharp apex  44 . The apex  44  preferably has an interior radius of less than 0.5 t, wherein “t” is the thickness of the metal. A sharp edged channel provides a superior reinforcement to a channel having a rounded edge. The base edges  46  of the channels  40  and  42  form a sharp edge with the body  48  of the panel. 
         [0035]    Referring to  FIG. 6 , an alternative embodiment of an electro-hydraulic forming tool is shown in which thirty electrodes  50  are shown that are provided on the lower side of the panel  32 . The electrodes  50  are immersed in the fluid  28 . The electrodes  50  are aligned with the intersections of a plurality of grooves  52  extending vertically in the one sided die  20 , as shown in  FIG. 6 , and grooves  54  that extend horizontally in the one sided die  20 , as shown in  FIG. 6 . It should be understood that the terms “vertically” and “horizontally” as used with reference to  FIG. 6  refer to the direction that they extend on that page and to not limit the orientation of the grooves  52  and  54  in the die or the orientation of the V-shaped channels  40  and  42  that are formed in the panel. 
         [0036]    In operation, the panel is placed on the lower tool that is provided with the plurality of electrodes  50 . The electrodes  50  are submerged in the fluid  28  on the opposite side of the panel  32  from the grooves  52  and  54  in the one sided die  20 . The electrodes  50  are connected to a source of stored electrical current, such as a bank of capacitors. The electrodes  50  are discharged below the surface of the liquid  28  to create a shockwave that flows through the fluid  28  and forms the panel  32  into the grooves  52  and  54  of the one-sided die  20 . 
         [0037]    Referring to  FIG. 7 , an alternative pattern of V-shaped reinforcing ribs is illustrated on a panel  60 . The panel  60  includes a set of non-parallel vertical ribs  62  and a set of non-parallel horizontal ribs  64 . The ribs may also be curved or otherwise non-linear depending upon the nature and direction of the reinforcement that is desired in the finished panel  60 . 
         [0038]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.