Abstract:
The present invention relates to a process for forming a variable gauge metal sheet into a desired shape, said process comprising: providing a variable gauge metal sheet having a first surface and a second surface, the metal sheet having a thickness measured at any point on the metal sheet as the distance between the first surface and the second surface, the thickness of the metal sheet being different over a first portion of the sheet than over a second portion of the sheet, and forming said metal sheet into a first desired shape by bending the metal sheet about a first fold line, said first fold line extending through both the first portion and the second portion, to bring segments of the first surface of the metal sheet on either side of the first fold line into increased opposition with each other, wherein said bending of the metal sheet is effected by holding the metal sheet on a first clamped side of the first fold line secured between a first clamping die and a second clamping die while applying forces to the second surface of the metal sheet on a second moved side of the first fold line, wherein the first clamping die has a first engagement surface which engages the first surface of the metal sheet and is a complementary mirror image to a surface contour of the first surface of the metal sheet that it engages, wherein the second clamping die has a second engagement surface which engages the second surface of the metal sheet and is a complementary mirror image to a surface contour of the second surface of the metal sheet that it engages.

Description:
SCOPE OF THE INVENTION  
       [0001]     The present invention relates to manufacturing metal components. More specifically, the present invention relates to a process for forming a variable gauge metal sheet into a metal component having a desired shape  
       BACKGROUND OF THE INVENTION  
       [0002]     It is known to use blank metal sheets to manufacture various types of metal components. Such blank metal sheets are bent and formed into the desired shape. The bending of a metal sheet comprises plastically deforming the metal and changing its shape. The metal is stressed beyond the yield strength, but below the ultimate tensile strength so as to not break the metal sheet into pieces. For example, in tube making, blank metal sheets are bent so as to form hollow beams. As another example, metal sheets are bent to form various automotive parts, such as tie bars in the radiator support assembly.  
         [0003]     In prior art, the bending or folding of metal sheets is accomplished by the use of press brakes. A typical prior art press brake comprises: (i) a moveable upper tool called a punch or ram; and (ii) a stationary lower tool called a die. The die has a V-shaped opening on its upper surface. A metal sheet is placed flat on the upper surface of the die over the V-shaped opening. The punch is moved downwards along a vertical axis to push down against the metal sheet and presses the metal sheet into the V-shaped opening. As a result of this downward pressure from the punch, the metal sheet is bent into a desired shape, a V-shaped bend.  
         [0004]     Several problems arise when attempting to bend blank metal sheets by using a press brake. First, when the moveable punch presses the metal sheet down into the V-shaped opening, there is significant rubbing and sliding between the surface of the metal sheet and both the surfaces of the moveable punch and the stationary die, and this often results in shoulder marks or scratches on the surface of the metal sheet. Therefore, refinishing is required after the bending procedure.  
         [0005]     Alternatively, the surface damage caused by press brake tooling can be reduced using urethane tooling or polymer die inserts. However, such provisions increase the cost of manufacturing.  
         [0006]     Further, as the moveable punch is released from the bent metal sheet, there is a tendency for the metal sheet to lose some of its bent shape. This problem is known in the art as “springback”. The amount of springback depends on several factors including the type of material, thickness, grain and temper. Springback is known to be very pronounced when the metal sheet comprises high-strength steel and aluminum alloy. Generally, the springback ranges from about 5 to 10 degrees.  
         [0007]     In an effort to reduce the problem of springback, press brakes are often designed to bend the metal sheet to a greater angle than desired, thus taking the springback into account. However, this requires the carrying out of complex calculations to predict the degree of springback. Further, because there are so many factors involved in determining the amount of springback, including material, thickness, grain and temper, it is very difficult to accurately predict. Moreover, the costs and labour time required to make the necessary adjustments to the press brake, including the size and shape of the punch, the size and shape of the V-shaped opening in the die, and the downward pressure of the punch, are high.  
         [0008]     For many metal components, it is desirable to form the metal component from a variable gauge metal sheet, or a metal sheet having a varying thickness profile. Such variable gauge metal sheets have the advantage of being able to form components which are lighter in weight because the sheet is thinner in areas which will be subjected to a lesser load than the load applied to thicker areas of the sheet. Also, less metal material is required to form the metal component. By selectively varying the thickness profile of the metal sheet, the function of the component can be optimized. Further, the varied thickness profile of the metal sheet offers greater possibilities for form design.  
         [0009]     However, the bending of variable gauge metal sheets runs into the same problems as the bending of regular metal sheets which are mentioned above. Further, the bending of variable gauge metal sheets is even more difficult because it is more complicated to bend such metal sheets along a straight fold line where the thickness of the metal sheet varies along said fold line.  
         [0010]     As mentioned above, the amount of springback varies according to the thickness of the metal sheet being bent. Therefore, where a metal sheet has a variable thickness profile, and the metal sheet is bent along a fold line where the thickness of the metal sheet varies along said fold line, the amount of springback will also vary along the fold line. This results in the metal sheet having a warped shape, with a greater amount of springback on one side of the metal sheet than the other. Further, it is difficult to design a press brake which takes into account springback when the amount of springback varies along the fold line. In this case, the amount of springback must be predicted at every point along the fold line.  
       SUMMARY OF THE INVENTION  
       [0011]     It is an object of the present invention to provide a process for forming a variable gauge metal sheet into a desired shape.  
         [0012]     It is a further object of the present invention to form metal components of lightweight construction.  
         [0013]     A further object of the present invention is to form metal components having a variable thickness which is adapted to the respective load to which the component is to be subjected.  
         [0014]     A further object of the present invention is to form a variable gauge metal sheet into a desired shape without scratching or marking the surface of the metal sheet.  
         [0015]     A further object of the present invention is to form a variable gauge metal sheet into a desired shape with less springback.  
         [0016]     A further object of the present invention is to provide a process for forming a variable gauge metal sheet into a desired shape which is relatively inexpensive and does not require significant tooling maintenance.  
         [0017]     Accordingly, in one aspect, the present invention provides a process for forming a variable gauge metal sheet into a desired shape, said process comprising: providing a variable gauge metal sheet having a first surface and a second surface, the metal sheet having a thickness measured at any point on the metal sheet as the distance between the first surface and the second surface, the thickness of the metal sheet being different over a first portion of the sheet than over a second portion of the sheet, and forming said metal sheet into a first desired shape by bending the metal sheet about a first fold line, said first fold line extending through both the first portion and the second portion, to bring segments of the first surface of the metal sheet on either side of the first fold line into increased opposition with each other, wherein said bending of the metal sheet is effected by holding the metal sheet on a first clamped side of the first fold line secured between a first clamping die and a second clamping die while applying forces to the second surface of the metal sheet on a second moved side of the first fold line, wherein the first clamping die has a first engagement surface which engages the first surface of the metal sheet and is a complementary mirror image to a surface contour of the first surface of the metal sheet that it engages, wherein the second clamping die has a second engagement surface which engages the second surface of the metal sheet and is a complementary mirror image to a surface contour of the second surface of the metal sheet that it engages.  
         [0018]     Preferably, the bending of the metal sheet about the first fold line urges the first surface of the metal sheet on the second moved side of the first fold line into a first stationary die block, said first stationary die block having a first engagement surface which engages the first surface of the metal sheet and is a complementary mirror image to the surface contour of the first surface of the metal sheet into which it is urged.  
         [0019]     It is also preferred that a second moving die block is moved into engagement with the second surface of the metal sheet on the second moved side of the first fold line to urge the first surface of the metal sheet on the second moved side of the first fold line into the first stationary die block, the second moving die block having a second engagement surface which engages the second surface of the metal sheet and is a complementary mirror image to the surface contour of the second surface of the metal sheet into which it is urged.  
         [0020]     The first fold line can lie in the second surface of the metal sheet spaced away from the first surface of the metal sheet and the bending about the first fold line is effected by a method selected from the group consisting of wing bending and tangent bending.  
         [0021]     In a preferred embodiment, the first fold line extends along the metal sheet from a first end of the metal sheet to a second end of the metal sheet, with a central plane intermediate the ends of the metal sheet and normal to the first fold line, the thickness of the metal sheet being substantially symmetrical along the central plane.  
         [0022]     The process of the present invention can further comprise forming said metal sheet into a second desired shape by bending the metal sheet about a second fold line, the second fold line extending through the first portion and the second portion to bring segments of the first surface of the metal sheet on either side of the second fold line into increased opposition with each other. The bending of the metal sheet about the second fold line is effected by holding the metal sheet on a first clamped side of the second fold line secured between a third clamping die and a fourth clamping die while applying forces to the second surface of the metal sheet on a second moved side of the second fold line. The third clamping die has a first engagement surface which engages the first surface of the metal sheet and is a complementary mirror image to the surface contour of the first surface of the metal sheet that it engages. Also, the fourth clamping die has a second engagement surface which engages the second surface of the metal sheet and is a complementary mirror image to the surface contour of the second surface of the metal sheet that it engages.  
         [0023]     Preferably, the process of the present invention further comprises forming said metal sheet into a third desired shape by bending the metal sheet about a third fold line. The third fold line extends through both the first portion and the second portion and the bending about the third fold line brings segments of the first surface of the metal sheet on either side of the third fold line into increased opposition with each other. The metal sheet is held on a first clamped side of the third fold line secured between a fifth clamping die and a sixth clamping die while forces are applied to the second surface of the metal sheet on a second moved side of the third fold line. It is preferred that the fifth clamping die have a first engagement surface which engages the first surface of the metal sheet and is a complementary mirror image to the surface contour of the first surface of the metal sheet that it engages, while the sixth clamping die has a second engagement surface which engages the second surface of the metal sheet and is a complementary mirror image to the surface contour of the second surface of the metal sheet that it engages.  
         [0024]     The metal sheet can be formed into the desired shape by wing bending. In wing bending, a metal sheet is secured by two clamping dies: one clamping die on top of the metal sheet; and one clamping die below the metal sheet. A moving die, which is called the wing, is moved into engagement with the bottom surface of the metal sheet at a location away from the two clamping dies. The metal sheet is bent about a fold line along the metal sheet. The moving die or wing rotates about an axis which is parallel to fold line, thus pushing against the bottom surface of the metal sheet and bending the metal sheet about the fold line up into the desired shape.  
         [0025]     Advantageously, the process of the present invention produces a metal component having a lightweight construction.  
         [0026]     Further, the metal component formed by the process of the present invention has a variable thickness which is adapted to the respective load to which the component is to be subjected.  
         [0027]     The bending of the variable gauge metal sheet in the process of the present invention puts stress across the whole width of the metal sheet along the fold line and thus, results in less, if any, scratching and marking.  
         [0028]     The process of the present invention surprisingly reduces the amount of springback compared to the use of prior art press brakes, particularly for high strength metal sheets such as high strength steel.  
         [0029]     Further, where the first fold line extends along the metal sheet from a first end of the metal sheet to a second end of the metal sheet, with a central plane intermediate the ends of the metal sheet and normal to the first fold line, and the thickness of the metal sheet is substantially symmetrical along the central plane, any springback which occurs will be in an amount that is equal on each side of the central plane.  
         [0030]     The process of the present invention is relatively inexpensive. For example, the tooling in press brakes are expensive to manufacture because of complex features such as the stationary die with a customized V-shaped opening. Further, press brakes are generally manually operated and often require two operators to bend larger metal sheets. In contrast, in the process of the present invention, only one operator is required, thus potentially cutting labour time in half  
         [0031]     Further, there is less tooling maintenance involved because there is no taping or waxing as required in maintaining a press brake.  
         [0032]     Advantageously, the varied thickness profile of the sheet metal offers greater possibilities for the form design.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]     Further aspects and advantages will become apparent from the following description taken together with the accompanying drawings in which:  
         [0034]      FIG. 1  is a perspective view of a variable gauge metal sheet, a first clamping die, a second clamping die and a second moving die block to be used in accordance with a first embodiment of the present invention;  
         [0035]      FIG. 2  is a cross-sectional view of the variable gauge metal sheet, the first clamping die and the second clamping die of  FIG. 1 , wherein the first clamping die has not yet come into contact with the metal sheet;  
         [0036]      FIG. 3  is a cross-sectional view of the variable gauge metal sheet, the first clamping die and the second clamping die of  FIG. 1 , wherein the metal sheet is secured between the first clamping die and the second clamping die;  
         [0037]      FIG. 4  is a side view of the variable gauge metal sheet, of  FIG. 1 , wherein the metal sheet is secured between the first clamping die and the second clamping die, and the second moving die block is moved into engagement with the metal sheet;  
         [0038]      FIG. 5  is a side view of the variable gauge metal sheet of  FIG. 4 , wherein the second moving die block pushes up against the metal sheet to bend the metal sheet about a first fold line;  
         [0039]      FIG. 6  is a side view of the variable gauge metal sheet of  FIG. 5 , wherein the metal sheet has been bent about the first fold line such as to urge the metal sheet into a first stationary die block, thus forming a first desired shape;  
         [0040]      FIG. 7  is a side view of the variable gauge metal sheet of  FIG. 6 , wherein the metal sheet is secured between a third clamping die, and a fourth clamping die and a fourth moving die block is moved into engagement with the metal sheet;  
         [0041]      FIG. 8  is a side view of the variable gauge metal sheet of  FIG. 7 , wherein the fourth moving die block pushes up against the metal sheet to bend the metal sheet about a second fold line;  
         [0042]      FIG. 9  is a side view of the variable gauge metal sheet of  FIG. 8 , wherein the metal sheet has been bent about the second fold line such as to urge the metal sheet into a third stationary die block, thus forming a second desired shape;  
         [0043]      FIG. 10  is a side view of the variable gauge metal sheet of  FIG. 9 , wherein the metal sheet is secured between a fifth clamping die, and a sixth clamping die and a sixth moving die block is brought into engagement with the metal sheet;  
         [0044]      FIG. 11  is a side view of the variable gauge metal sheet of  FIG. 10 , wherein the sixth moving die block pushes up against the metal sheet to bend the metal sheet about a third fold line;  
         [0045]      FIG. 12  is a side view of the variable gauge metal sheet of  FIG. 11 , wherein the metal sheet has been bent about the third fold line, thus forming a third desired shape;  
         [0046]      FIG. 13  is a side view of the variable gauge metal sheet that has been formed into a third desired shape;  
         [0047]      FIG. 14  is a perspective view of  FIG. 13 , wherein the variable gauge metal sheet that has been formed into the third desired shape;  
         [0048]      FIG. 15  is a perspective view of a variable gauge metal sheet, a first clamping die, a second clamping die and a second moving die block to be used in accordance with a second embodiment of the present invention;  
         [0049]      FIG. 16  is a perspective view of a variable gauge metal sheet to be used in accordance with a third embodiment of the present invention;  
         [0050]      FIG. 17  is a perspective view of a radiator support assembly including an upper tie bar that has been formed into the desired shape by the process of the present invention;  
         [0051]      FIG. 18  is an isolated perspective view of the upper tie bar of  FIG. 17 ;  
         [0052]      FIG. 19  is an edge view of the tie bar of  FIG. 18 ;  
         [0053]      FIG. 20  is a top view of the tie bar of  FIG. 18 ; and  
         [0054]      FIG. 21  is a cross-sectional view of the tie bar of  FIG. 20  along section line A-A. 
     
    
       [0055]     Throughout all the drawings and the disclosure, similar parts are indicated by the same reference numerals.  
       DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0056]      FIG. 1  illustrates a variable gauge metal sheet  10  to be shaped by a process in accordance with a first preferred embodiment of the present invention. The variable gauge metal sheet  10  has a first surface  12  and a second surface  14 . In this first preferred embodiment, as shown in  FIG. 2 , the first surface  12  is non-planar, while the second surface  14  is planar.  
         [0057]     The variable gauge metal sheet  10  has a thickness measured at any point on the metal sheet  10  as the distance between the first surface  12  and the second surface  14 . As can be seen in  FIG. 1 , the thickness of the metal sheet  10  is greater at a first portion  16  than at a second portion  18 .  FIG. 1  also shows a first fold line  28  which extends through both the first portion  16  and the second portion  18 .  
         [0058]     As shown in  FIG. 2 , a longitudinal central plane  500  is normal to the first fold line  28  and divides the metal sheet  10  into two halves. In this preferred embodiment, the thickness of the metal sheet  10  is symmetrical along the central plane  500 .  
         [0059]     In the process of the present invention, the variable gauge metal sheet  10  is bent into a first desired shape. The metal sheet  10  is secured between a first clamping die  20  and a second clamping die  22 , as shown in FIGS.  1  to  3 . The first clamping die  20  has a first engagement surface  24  which engages the first surface  12  of the metal sheet  10  and is a complementary mirror image to the surface contour of the first surface  12  of the metal sheet  10  that it engages. Similarly, the second clamping die  22  has a second engagement surface  26  which engages the second surface  14  of the metal sheet  10  and is a complementary mirror image to the surface contour of the second surface  14  of the metal sheet  10  that it engages.  
         [0060]     FIGS.  4  to  6  illustrate forming the metal sheet  10  into a first desired shape. The metal sheet is bent about a first fold line  28 , wherein the first fold line  28  extends through both the first portion  16  and the second portion  18  of the metal sheet  10 . On either side of the first fold line  28  is a first clamped side  110  and a second moved side  112 .  
         [0061]     In this preferred embodiment, the first clamping die  20  also acts as a first stationary die block  20 . As shown in  FIG. 4 , a second moving die block  30  is moved into engagement with the second surface  14  of the metal sheet  10  on the second moved side  112  of the first fold line  28 . The second moving die block  30  has a second engagement surface  32  which engages the second surface  14  of the metal sheet  10  and is a complementary mirror image to the surface contour of the second surface  14  of the metal sheet  10  into which it is urged.  
         [0062]     As shown in  FIG. 5 , the second moving die block  30  pushes up against the second surface  14  of the metal sheet  10  to bend the metal sheet  10  about the first fold line  28  such as to bring segments of the first surface  12  of the metal sheet  10  on either side of the first fold line  28  into increased opposition with each other.  
         [0063]     As shown in  FIG. 6 , the bending of the metal sheet  10  about the first fold line  28  urges the first surface  12  of the metal sheet  10  on the second moved side  112  of the first fold line  28  into the first stationary die block  20 . The first stationary die block  20  has a first engagement surface  34  which engages the first surface  12  of the metal sheet  10  and is a complementary mirror image to the surface contour of the first surface  12  of the metal sheet  10 .  
         [0064]     FIGS.  7  to  9  illustrate forming the metal sheet  10  into a second desired shape. The metal sheet  10  is bent about a second fold line  36  in a manner similar to the above-mentioned bending about the first fold line  28 . The second fold line  36  extends through both the first portion  16  and the second portion  18  of the metal sheet  10 . On either side of the second fold line  36  is a first clamped side  114  and a second moved side  116 .  
         [0065]     The metal sheet  10  is held on the first clamped side of the second fold line  36  between a third clamping die  38  and a fourth clamping die  40 . The third clamping die  38  has a first engagement surface  42  which engages the first surface  12  of the metal sheet  10  and is a complementary mirror image to the surface contour of the first surface  12  of the metal sheet  10  that it engages. The fourth clamping die  40  has a second engagement surface  44  which engages the second surface  14  of the metal sheet  10  and is a complementary mirror image to the surface contour of the second surface  14  of the metal sheet  10  that it engages.  
         [0066]     In this preferred embodiment, the third clamping die  38  also acts as a third stationary die block  38 . As shown in  FIG. 7 , a fourth moving die block  46  is moved into engagement with the second surface  14  of the metal sheet  10  on the second moved side  116  of the second fold line  36 . The fourth moving die block  46  has a second engagement surface  48  which engages the second surface  14  of the metal sheet  10  and is a complementary mirror image to the surface contour of the second surface  14  of the metal sheet  10  into which it is urged.  
         [0067]     As shown in  FIG. 8 , the fourth moving die block  46  pushes up against the second surface  14  of the metal sheet  10  to bend the metal sheet  10  about the second fold line  36  such as to bring segments of the first surface  12  of the metal sheet  10  on either side of the second fold line  36  into increased opposition with each other.  
         [0068]     As shown in  FIG. 9 , the bending of the metal sheet  10  about the second fold line  36  urges the first surface  12  of the metal sheet  10  on the second moved side  116  of the second fold line  36  into the third stationary die block  38 . The third stationary die block  38  has a first engagement surface  50  which engages the first surface  12  of the metal sheet  10  and is a complementary mirror image to the surface contour of the first surface  12  of the metal sheet  10 .  
         [0069]     FIGS.  10  to  12  illustrate forming the metal sheet  10  into a third desired shape by bending the metal sheet  10  about a third fold line  52 . The third fold line  52  extends through both the first portion  16  and the second portion  18  of the metal sheet  10 . On either side of the third fold line  52  is a first clamped side  118  and a second moved side  120 .  
         [0070]     The metal sheet  10  is held on the first clamped side of the third fold line  52  between a fifth clamping die  54  and a sixth clamping die  56 . The fifth clamping die  54  has a first engagement surface  58  which engages the first surface  12  of the metal sheet  10  and is a complementary mirror image to the surface contour of the first surface  12  of the metal sheet  10  that it engages. The sixth clamping die  56  has a second engagement surface  60  which engages the second surface  14  of the metal sheet  10  and is a complementary mirror image to the surface contour of the second surface  14  of the metal sheet  10  that it engages.  
         [0071]     As shown in  FIG. 10 , a sixth moving die block  62  is moved into engagement with the second surface  14  of the metal sheet  10  on the second moved side  120  of the third fold line  52  to urge the first surface  12  of the metal sheet  10  on the second moved side of the third fold line  52 . The sixth moving die block  62  has a second engagement surface  64  which engages the second surface  14  of the metal sheet  10  and is a complementary mirror image to the surface contour of the second surface  14  of the metal sheet  10  into which it is urged.  
         [0072]     As shown in  FIG. 11 , the sixth moving die block  62  pushes up against the second surface  14  of the metal sheet  10  to bring segments of the first surface  12  of the metal sheet  10  on either side of the third fold line  52  into increased opposition with each other.  
         [0073]     As shown in  FIG. 12 , the metal sheet  10  is bent about the third fold line  52  until a 90° angle is formed and the edge  68  of the metal sheet  10  contacts the first surface of the metal sheet  10  on the first clamped side  118  of the third fold line  52 . The bending of the metal sheet  10  about the third fold line  52  urges the first surface  12  of the metal sheet  10  on the second moved side  120  of the third fold line  52  into the fifth stationary die block  54 . The fifth stationary die block  54  has a first engagement surface  66  which engages the first surface  12  of the metal sheet  10  and is a complementary mirror image to the surface contour of the first surface  12  of the metal sheet  10 .  
         [0074]      FIGS. 13 and 14  illustrate the third desired shape, wherein the metal sheet  10  is bent about the first fold line  28 , the second fold line  36  and the third fold line  54  at 90° angles. The edge  68  of the metal sheet  10  can be joined to the first surface  12  of the metal sheet  10  on the first clamped side  188  of the third fold line  52  by welding, preferably laser welding. As a result, a hollow tube having a variable thickness is formed.  
         [0075]      FIG. 15  illustrates a variable gauge metal sheet  210  to be shaped by a process in accordance with a second preferred embodiment of the present invention. The variable gauge metal sheet  210  has a first surface  212  and a second surface  214 . In contrast to the first preferred embodiment described above and shown in  FIG. 1 , in this second preferred embodiment shown in  FIG. 15 , the first surface  212  is planar, while the second surface  214  is non-planar.  
         [0076]     The variable gauge metal sheet  210  has a thickness measured at any point on the metal sheet  210  as the distance between the first surface  212  and the second surface  214 . As can be seen in  FIG. 15 , the thickness of the metal sheet  210  is smaller at a first portion  216  than at a second portion  218 .  
         [0077]     In this second preferred embodiment, the variable gauge metal sheet  210  is bent into a first desired shape. The metal sheet  10  is secured between a first clamping die  220  and a second clamping die  222 . The first clamping die  220  has a first engagement surface  224  which engages the first surface  212  of the metal sheet  210  and is a complementary mirror image to the surface contour of the first surface  212  of the metal sheet  210  that it engages. Similarly, the second clamping die  222  has a second engagement surface  226  which engages the second surface  214  of the metal sheet  210  and is a complementary mirror image to the surface contour of the second surface  214  of the metal sheet  210  that it engages.  
         [0078]     In this preferred embodiment, the first clamping die  220  also acts as a first stationary die block  220 . A second moving die block  230  engages the second surface  214  of the metal sheet  210 . The second moving die block  230  has a second engagement surface  232  which engages the second surface  214  of the metal sheet  210  and is a complementary mirror image to the surface contour of the second surface  214  of the metal sheet  210  into which it is urged. The second moving die block  230  pushes up against the second surface  214  of the metal sheet  210  to bend the metal sheet  210  about the first fold line  228 . The bending of the metal sheet  210  about the first fold line  228  urges the first surface  212  of the metal sheet  210  into the first stationary die block  220 . The first stationary die block  220  has a first engagement surface  234  which engages the first surface  212  of the metal sheet  210  and is a complementary mirror image to the surface contour of the first surface  212  of the metal sheet  210 . In this second preferred embodiment, both surfaces  212  and  234  are planar.  
         [0079]      FIG. 16  illustrates a variable gauge metal sheet  310  to be shaped by a process in accordance with a third embodiment of the present invention. The variable gauge metal sheet  310  has a first surface  312  and a second surface  314 . In contrast to the first and second preferred embodiments described above and shown in  FIGS. 1 and 15 , in this third preferred embodiment shown in  FIG. 16 , both the first surface  312  and the second surface  314  are non-planar.  
         [0080]     The variable gauge metal sheet  310  has a thickness measured at any point on the metal sheet  310  as the distance between the first surface  212  and the second surface  214 . As can be seen in  FIG. 16 , the thickness of the metal sheet  310  is greater at a first portion  316  than at a second portion  318 .  
         [0081]     The variable gauge metal sheet  310  of the third preferred embodiment is bend about first fold line  328  by a process similar to those described in the first and second preferred embodiments. As with the first and second preferred embodiments, the die blocks used in the process of the third preferred embodiments have engagement surfaces which are complementary mirror images of the first surface  312  or the second surface  314  of the metal sheet  310 .  
         [0082]     The process of the present invention can be used in a wide variety of applications where blank metal sheets are used to manufacture metal components. For example, metal sheets can be bent by the process of the present invention to form various automobile components. The process of the present invention is particularly useful for forming ties bars in a radiator support assembly.  
         [0083]      FIG. 17  illustrates a radiator support assembly  500  for an automobile. The radiator support assembly  500  is typically located in front of the automobile engine and behind the radiator grille. This radiator support assembly  500  serves as a metal frame to support the radiator which is a device where hot engine coolant is circulated and cooled. In addition to the radiator, the radiator support assembly  500  also holds other vehicle parts such as the condenser, horn, headlights, grille and hood latch.  
         [0084]     The radiator support assembly  500  comprises an upper tie bar  400 , a lower tie bar  510 , inner posts  512  and  514 , outer posts  516  and  518 , a cross brace  520 , a hood latch mounting bracket  522  and a hood latch support bracket  524 . The upper tie bar  400  and the lower tie bar  510  make up the upper and lower support structures of the support assembly  500 . Inner posts  512  and  514  and outer posts  516  and  518  join the upper tie bar  400  and the lower tie bar  510 . The radiator is to be held in place and protected between the upper tie bar  400  and the lower tie bar  510 .  
         [0085]     The radiator support assembly  500  is important in protecting and stabilizing the radiator, and therefore, must be durable. Generally, the radiator suppot assembly  500  comprises steel. At the same time, it is desirable for the radiator support assembly  500  to be of lightweight construction, for example to increase fuel economy of the automobile. Thus, it is desirable to form components of the radiator support assembly  500  from variable gauge metal sheets where possible.  
         [0086]     As shown in FIGS.  18  to  21 , the upper tie bar  400  has a middle portion  410  and two end portions  412  and  414 . The two end portions  412  and  414  are the portions of the upper tie bar  400  which are joined to the lower tie bar  510  by the inner posts  512  and  514  and the outer posts  516  and  518 . Therefore, the end portions  412  and  414  of the upper tie bar  400  will be subjected to a greater load than the middle portion  410  of the upper tie bar  400 . As such, in order to reduce the weight of the upper tie bar  400 , the middle portion  410  can be designed to be thinner than the end portions  412  and  414 .  
         [0087]      FIG. 18  illustrates an upper tie bar  400  for a radiator support assembly which has been formed by the process of the present invention.  FIG. 19  shows an edge view of the tie bar  400  of  FIG. 18 . This edge view illustrates that the tie bar  400  has been bent across all of middle portion  410  and end portions  412  and  414 .  
         [0088]      FIG. 21  illustrates a cross-sectional view of the top view of  FIG. 20  along section line A-A. The thickness of the tie bar  400  is greater at the end portions  412  and  414  that at the middle portion  410 . The variable thickness profile of the tie bar  400  is designed such that the thinner middle portion  410  is subjected to a lesser load than the load applied to the thicker end portions  412  and  414 . This is desirable because the tie bar  400  is lighter in weight than a tie bar which lacks a variable thickness profile. Furthermore, less metal material is required to form tie bar  400  than a tie bar which lacks a variable thickness profile.  
         [0089]     By using the process of the present invention, the tie bar  400  can be bent into the desired shape along a straight fold line, wherein the fold line extends across the middle portion  410  and the end portions  414 , without scratching or marking the surface of the tie bar  400 .  
         [0090]     Although this disclosure has described and illustrated preferred embodiments of the present invention, it is to be understood that the present invention is not restricted to these particular embodiments. Rather, the present invention includes all embodiments which are functional or mechanical equivalents of the specific embodiments and features that have been described and illustrated herein. Many modifications and variations will now occur to those skilled in the art. For a definition of the present invention, reference is made to the following claims.