Patent Publication Number: US-2021170466-A1

Title: Determining the bend deduction of a sheet metal workpiece to be bent

Description:
The invention relates to a method for estimating a shortening length of a sheet metal workpiece which is bent about n bending axes and by n bending angles alpha, wherein the bent sheet metal workpiece comprises n+1 limbs extending along a straight extension line and n curved regions which are produced by bending the sheet metal workpiece and extend between two adjacent limbs. 
     The letter n stands for a natural number; i.e. n=1, 2, 3, 4 . . . . 
     A difficulty in bending a sheet metal strip about a bending axis consists in selecting the original length of the sheet metal strip such that the bent sheet metal strip has defined dimensions. During the bending operation, according to the standard teaching, depending on the workpiece to be bent, compression occurs on the inside of the curvature area, while the material on the outside of the curvature area is subject to stretching. The extent of compression and stretching of the workpieces on the inside and on the outside of the curvature is hard to predict due to the plurality of the influencing factors. 
     DE112012000792 suggest a method for determining the original dimensions of a sheet metal workpiece prior to bending into a sheet metal construction, said method being based on the determination of a length H 3  and the determination of angles. When looking at the bent workpiece as a triangle, the length H 3  essentially corresponds to the height of the triangle. 
     The method according to the invention differs from the method disclosed in DE112012000792 in that it can be carried out without the determination of the length H 3  and without the determination of the angles and can thus be carried out in a simple manner. 
     EP1398094 relates to a method for determining the arm length of a bending part in a bending device. However, in EP1398094 there is no indication of the determination of the shortening lengths as are part of the method according to the invention. EP1398094 is in particular limited to the determination of one arm length only. 
     EP2683504 describes a method for dynamic correction of a bending angle of a sheet metal material on a panel bender machine. The method described therein is inter alia based on the determination of the nominal bending angle and the distance of the bending punch from the bent sheet metal, after the bending punch has been brought back into a retracted position. The method that will be described below goes without the determination of these parameters. 
     DE10009074 relates to a method for air bending or swivel bending of a workpieces as well as a device for determining the position of a workpiece leg during bending. In DE10009074, there is no indication of a determination of the lengths and distances and the calculation of the shortening as described in the method according to the invention. 
     DE10163956 describes a method and a device for measuring lengths on a workpiece deformed by bending. In DE10163956, there is no indication of the calculation of the shortenings as described in the method according to the invention. 
     The methods according to the prior art are generally not easy to perform. It is the object of the present invention to overcome the shortcomings of the prior art for determining the shortening of a sheet metal workpiece taking place as a result of a bending process about a bending axis. 
     The invention discussed below in particular faces the object of being able to determine the shortening occurring when a sheet metal workpiece is bent in a method that is as simple as possible and with an exactness that is as high as possible in the sense of an estimation. With the aid of the method according to the invention, it should in particular be simple to determine changes in the bending behavior of a plurality of sheet metal workpieces to be bent, in particular the behavior of a plurality of the sheet metal workpiece to be bent in view of the shortening taking place. 
     This object is achieved by means of a method according to the claims. 
     The method according to the invention is mainly, but not in a limited manner, directed towards sheet metal workpieces having a thickness that remains constant over the surface of extent of the sheet metal workpiece. This does not preclude that the thickness can vary for example within the range of the boundaries defined by relevant standards. 
     The method according to the invention is mainly directed towards bent sheet metal workpieces which are produced by means of a die bending tool by cold bending. The bent sheet metal workpieces can be produced considering DIN6935. 
     The estimation of the shortening resulting from bending a sheet metal workpiece about a bending axis can take place by the determination of a tangent shortening, the method for tangent shortening comprising the following steps:
         determining the original length L 0  of the sheet metal strip prior to bending of the sheet metal workpiece,   determining the intersection of the straight extension lines of adjacent limbs or of straight lines parallel to the straight extension lines, said straight lines running at the surfaces of the limbs facing away from the respective bending axis,   determining the i distances A 1 , A 2  between the intersections and the free ends of the limbs and optionally if n&gt;2 determining the j distances B 1  between the intersections,   determining a tangent shortening T according to the formula:       

     
       
         
           
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     A sheet metal workpiece with n=1 bending axes comprises two limbs and a curved region extending between the limbs. Thus, merely the distances A 1  and A 2  can be determined. 
     A sheet metal workpiece with n=2 bending axes comprises three limbs and two curved regions extending between two adjacent limbs. Thus, two distances A 1 , A 2  and one distance B 1  can be determined. 
     The number of distances A that can be determined and the number of distances B that can be determined are predefined by the geometric givens. 
     The estimation of the shortening resulting from bending a sheet metal workpiece about a bending axis can take place by the determination of an edge shortening, the method for tangent shortening comprising the following steps:
         determining the original length L 0  of the sheet metal strip prior to bending of the sheet metal workpiece,   determining k edge lengths C of the bent sheet metal workpiece, said edge lengths C each indicating a distance from a free end of a limb to a tangent point to be measured in parallel to the straight extension line of the limb, at which tangent point a tangent normal to the first straight extension line is tangent to the curved region,   optionally 1 edge lengths D of the bent sheet metal workpiece, said edge lengths D indicating a distance from a tangent point to a further tangent point to be measured in parallel to the straight extension line of the limb, at which tangent points tangents normal to the straight extension lines are tangent to the curved region,   calculating the edge shortening length K according to the following formula:       

     
       
         
           
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     A sheet metal workpiece with n=1 bending axes comprises two limbs and a curved region extending between the limbs. Thus, merely the distances C 1  and C 2  can be determined. 
     A sheet metal workpiece with n=2 bending axes comprises three limbs and two curved regions extending between two adjacent limbs. Thus, two distances C 1 , C 2  and one distance D 1  can be determined. 
     The number of distances C that can be determined and the number of distances D that can be determined are predefined by the geometric givens. 
     The presently disclosed invention also relates to a device for determining an edge shortening length of a sheet metal workpiece, said device comprising a first measuring element surface and a second measuring element surface, wherein the first measuring element surface and the second measuring element surface are placed at a right angle to each other. 
     The measuring element surfaces are designed such that the surface of the limbs of the sheet metal tool can be placed against the measuring element surfaces and the edge lengths of the sheet metal tool can be determined by determination of a distance of the free end of the sheet metal tool from the intersection of the measuring element surfaces. 
     Such a device according to the invention can comprise contacting measuring device and/or contactless measuring devices for the determination of the distances of the free end from the intersection of the measuring element surfaces. 
     The second measuring element surface, by means of which second measuring element surface the limb is brought into contact with the edge length to be determined, can have a length L 2  that is smaller than the edge length C to be determined. This formation allows for determination of the edge length C by overhang measure. 
     For the purpose of better understanding of the invention, it will be elucidated in more detail by means of the figures below. 
    
    
     
       These show in a respectively very simplified schematic representation: 
         FIG. 1  the geometric proportions of a sheet metal workpiece bent about a bending axis having a bending angle alpha&lt;90° for determining edge shortening; 
         FIG. 2  the geometric proportions of a sheet metal workpiece bent about a bending axis having a bending angle 90&lt;alpha&lt;1800 for determining edge shortening; 
         FIG. 3  the geometric proportions of a sheet metal workpiece bent about two bending axes having a bending angle 90&lt;alpha&lt;180° for determining edge shortening; 
         FIG. 4  the geometric proportions of a sheet metal workpiece bent about a bending axis having a bending angle alpha&lt;90° for determining tangent shortening; 
         FIG. 5  a measuring device for determining the tangent shortening; 
         FIG. 6  the geometric proportions of a sheet metal workpiece bent about two bending axes having two bending angles alpha&lt;90° for determining tangent shortening; 
         FIG. 7  possibilities for determining the tangent shortening; 
         FIG. 8  the determination of the tangent shortening of a multiply bent sheet metal workpiece. 
     
    
    
     First of all, it is to be noted that in the different embodiments described, equal parts are provided with equal reference numbers and/or equal component designations, where the disclosures contained in the entire description may be analogously transferred to equal parts with equal reference numbers and/or equal component designations. Moreover, the specifications of location, such as at the top, at the bottom, at the side, chosen in the description refer to the directly described and depicted figure and in case of a change of position, these specifications of location are to be analogously transferred to the new position. For the sake of clarity, not all elements are provided with reference numbers in all figures. 
       FIG. 1  and  FIG. 2  illustrate the lengths and distances to be determined on a sheet metal workpiece  1 , said sheet metal workpiece  1  having been bent about a bending axis  2  by a bending angle alpha. The determination of the tangent shortening T mentioned in the description of  FIG. 1  and  FIG. 2  as a method according to the invention for estimating a shortening occurring during bending of a sheet metal workpiece about a bending axis  2  oriented so as to be normal to the image plane of  FIG. 1  and  FIG. 2  is possible for all bending angles alpha&lt;180°.  FIG. 1  shows a sheet metal workpiece  1  bent about a bending axis  2  with a bending angle alpha&lt;90° and  FIG. 1  shows a sheet metal workpiece  1  bent about a bending axis  2  with a bending angle 90°&lt;alpha&lt;180°. 
     The sheet metal workpieces  1  shown in  FIG. 1  and  FIG. 2  each have a bending axis  2 , such that n=1. 
     The bent bending workpieces  1  shown in  FIG. 1  and in  FIG. 2  each comprise a first limb  3 , said first limb  3  extending along a first straight extension line  4 , a second limb  5 , said second limb  5  extending along a second straight extension line  6 , and a curved region  7  extending between the first limb  3  and the second limb  5 . The respective transition between the limbs  3 ,  4  and the curved region  7  is geometrically defined by the extension of the limbs  3 ,  4  and the polygonal extension of the curved region  7 , wherein the first transition point  14  between the first limb  3  and the curved region  7  as well as the second transition point  15  between the second limb  5  and the curved region  7  are hard to determine on the sheet metal workpiece  1 . 
     The curved region  6  has a polygonal shape, wherein the first limb  3  and/or the second straight extension line  4  and the second limb  5  and/or the second straight extension line  5  are each tangential to the end points of the curved region  7 . 
     The person skilled in the art is capable of determining the original length L 0  of the sheet metal workpiece prior to bending, which is not shown in any figure, of the sheet metal workpiece  1  about the bending axis  2  using measuring methods according to the prior art. The original length L 0  is defined as the length that can be measured between the free ends  12 ,  13  of the sheet metal workpiece  1 . 
     The person skilled in the art determines the intersection S additionally marked by a circle between a first straight line  8  and a second straight line  9 , the first straight line  8  and the second straight line  9  being parallel straight lines to the first straight extension line  4  and/or to the second straight extension line  6 . The first straight line  8  is the straight line parallel to the first straight extension line  4 , said first straight line  8  being a tangent to the outer first surface  10  of the first limb  3 . The second straight line  9  is the straight line parallel to the second straight extension line  6 , said second straight line  9  being a tangent to the outer second surface  11  of the second limb  5 . 
     The intersection S can be determined such that a first measuring element is placed against the outer first surface  10  and a second measuring element is placed against the outer second surface  11 . The measuring elements placed against the outer surfaces with their edges placed against the surfaces extend congruently with the first straight line  8  and/or with the second straight line. 
     After the determination of the intersection S, the person skilled in the art is capable of determining the lengths A 1  and A 2  entered in  FIG. 1 . According to the definition, length A 1  is the length measured between the free first end  12  of the first limb  3  and the intersection S. According to the definition, length A 2  is the length measured between the free second end  13  of the second limb  5 . 
     The person skilled in the art determines the tangent shortening T from the measured original length L 0  of the sheet metal workpiece with the aid of the length A 1  and the length A 2  according to the formula T=L 0 −A 1 −A 2 . 
     The method according to the invention for estimating the shortening of a sheet metal workpiece can also be applied to a bent sheet metal workpiece comprising n limbs.  FIG. 3  illustrates an application of the method according to the invention to a sheet metal workpiece  1  comprising a first limb  3 , a second limb  5 , a third limb  24 . A first curved region  7  extends between the first limb  3  and the second limb  5  and a second curved region  25  extends between the second limb  5  and the third limb  24 . The first curved region  7  is produced by bending of the sheet metal workpiece  1  about a first bending axis  2  and the second curved region  25  is produced by bending of the sheet metal workpiece  1  about a second bending axis  26 .  FIG. 3  relates to the special case that the sheet metal workpiece  1  during bending about the first bending axis  2  and during bending about the second bending axis  26  is respectively bent by a bending angle alpha. 
     The first limb  3  extends along a first straight extension line  4 , the second limb  5  and the third limb  24  extend along a second straight extension line  6  and/or along a third straight extension line  27 . 
     The person skilled in the art determines the first intersection S 1  as an intersection of the first straight line  8  with the second straight line  9 . The intersections S 1  and S 2  are additionally marked by a circle in  FIG. 3 . The first straight line  8  extends in the first surface  10  of the first limb  3 , said first surface  10  facing away from the first bending axis  2  and being parallel to the first straight extension line  4 . The second straight line  9  runs in the second surface  11  of the second limb  5 , said second surface  11  facing away from the first bending axis  2  and being parallel to the second straight extension line. 
     Then, the intersection S 2  as an intersection of the third straight line  28  with the fourth straight line  29  is determined. The third straight line  28  extends in the third surface  30  of the second limb  5  facing away from the second bending axis  26  and is parallel to the second extension axis  6 . The fourth straight line  29  runs in the fourth surface  31  of the third limb  24 , said fourth surface  31  being the surface of the third limb  24  that faces away from the second bending axis  26  and being parallel to the third straight extension line  27 . 
     The person skilled in the art lastly determines the distance A 1  as the distance between the first free end  12  of the sheet metal workpiece  1  and the first intersection S 1 , the distance A 2  as the distance between the second end  13  of the sheet metal workpiece  1  and the second intersection S 2  and the distance B 1  between the intersections S 1  and S 2 . The mentioned distances are measured in parallel to the first straight extension line  3  and/or to the second straight extension line  6  and/or to the third straight extension line  27 . The distance A 1  is parallel to the first extension line  4 , the distance A 2  is parallel to the third extension line  27  and the distance B 1  is parallel to the second extension line  6 . 
     The person skilled in the art calculates the tangent shortening defined by the disclosure of the invention by T=L 0 −A 1 −A 2 −B 1 . 
       FIG. 4  illustrates the lengths and distances to be determined on a sheet metal workpiece  1 , the sheet metal workpiece  1  having been bent about a bending axis  2  by a bending angle alpha in order to determine the edge shortening K; the edge shortening can be determined after bending of a sheet metal workpiece about a bending axis  2  and by a bending angle smaller than or equal to 90°. 
     The person skilled in the art is capable of measuring the original length L 0  of the undeformed sheet metal workpiece  1  which is shown in no figure. The original length L 0  is the length that can be measured between the free ends  12 ,  13  of the undeformed sheet metal piece  1 . 
     The sheet metal workpiece  1  bent about a bending axis  2  oriented normal to the image plane of  FIG. 4  comprises a first limb  3 , said first limb extending along a first straight extension line  4 , a second limb  5  extending along a second straight extension line  6  and a polygonal curved region  7  extending between the limbs  3 ,  4 . The straight extension lines  4 ,  5  form the tangents to the curved region  7 . 
     The straight extension lines  4 ,  5  contact the curved region  7  at a first transition point  14  and/or at a second transition point  15 , which transition points  14 ,  15  are geometrically clearly defined, but are difficult to determine on the bent sheet metal workpiece  1 . 
     The person skilled in the art determines the first tangent point  16 , at which first tangent point  16 , a straight line oriented normal with respect to the first straight extension line  4  forms a first tangent  18  to the curved region  7 . Moreover, the second tangent point  17  can be determined, at which second tangent point  17 , a straight line oriented normal with respect to the second straight extension line  6  forms a second tangent  19  to the curved region  7 . The tangent points  16 ,  17  are additionally marked by circles. 
     A first edge length C 1  can be measured on the bent sheet metal workpiece, said first edge length C 1  being defined as the distance between the first free end  12  and the first tangent point  16 , the distance being parallel to the first straight extension line  4 . In like manner, a second edge length C 2  on the bent sheet metal workpiece  1  can be determined, which second edge length C 2  can be measured as the distance to be measured in parallel to the second straight extension line  6  between the second free end  13  and the second tangent point  17 . 
     The first edge length C 1 , for example, can be measured in a very simple manner using a caliper. For this purpose, the inner edges of the outer measuring jaws for external dimensions of objects are placed against the first free end  12  and against the outer surface of the curvature  7  and the edge of the bar of the caliper facing the outer jaws is placed against the first surface  10 . By placing the edge of the bar of the caliper against the first surface, the first tangent point  16  is determined and the first edge length C 1  is measured. 
     In like manner, the second edge length C 2  is determined by placing the inner edges of the outer measuring jaws against the second free end  13  and against the outer surface of the curvature  7  and placing the edge of the bar of the caliper facing the outer measuring jaws against the first surface  11 . 
     Finally, the person skilled in the art is capable of estimating the shortening of the sheet metal workpiece  1  occurring due to bending of the sheet metal workpiece  1  about the bending axis  2  and by an angle alpha&lt;90° by calculating the edge shortening. The edge shortening can be calculated by means of the formula K=L−C 1 −C 2 . 
       FIG. 4  illustrates the special case of a bending angle alpha=90°. In analogy to the figure descriptions above for  FIG. 1  to  FIG. 3 , the person skilled in the art is able to determine the intersection S as an intersection of the first straight line  8  and the second straight line  9 . In this regard, the construction operations described in sufficient detail above are to be applied. The intersection S is additionally marked by a circle in  FIG. 4 . The distance A 1  and the distance A 2  also are to be determined analogously to the description above, with the person skilled in the art recognizing that in the special case of a bending angle alpha=90° shown in  FIG. 4 , A 1 =C 1  and A 2 =C 2  apply. It further applies to the special case of alpha=90° L 0 −C 1 −C 2 =K=T=L 0 −A 1 −A 2 . 
       FIG. 5  illustrates a further method for determining the edge lengths C 1 , C 2  on a bent sheet metal workpiece  1  having a bending angle alpha smaller than or equal to 90°. 
     The measuring arrangement comprises a first measuring element  20  and a second measuring element  21  having a first measuring element surface  22  and/or a second measuring element surface  23 . The measuring element surfaces  22 ,  23  are arranged at an angle of 90° with respect to one another. The second measuring element surface  23  has a known length L 2 . 
     The measuring elements  20 ,  21  can be parts of a bending machine. 
     The bent sheet metal workpiece  1  is placed against the measuring surface  22 ,  23  with its outer surface. For determining the first edge length C 1 , the first surface  10  contacts the second measuring element surface  23  and the outer surface of the curved region  7  contacts the first measuring element surface  22 . 
       FIG. 5  shows a sheet metal workpiece  1  having a bending angle alpha equal to 80°. The first measuring element surface  22  contacts the outer surface of the curved region  7  the first measuring element surface  22 . 
     Since the length L 2  is known, the person skilled in the art is capable of determining the first edge length C 1  by determining the overhang measure L 1 . The measure L 1  can for example be determined by means of contactless measuring methods. 
     For determining the second edge length C 2 , the person skilled in the art places the bent sheet metal workpiece  1  with the second surface  11  against the second measuring element surface  23  and with the outer surface of the curved region  7  against the first measuring element surface  22 , to hence, in turn, determine the second edge length B via measuring the overhang measure L 1 . The process of determining the second edge length C 2  is not shown in  FIG. 5 . 
       FIG. 6  illustrates the method for estimating the shortening of a sheet metal workpiece  1  bent about two bending axes  2 ,  26  comprising a first bending angle alpha smaller than or equal to 900 and a second bending angle smaller than or equal to 90°. 
     The sheet metal workpiece  1  comprises a first limb  3 , a second limb  5  and a third limb  24 , said limbs  3 ,  5 ,  24  extending along straight extension lines  4 ,  6 ,  27 . The first limb  3  and the second limb  5  are separated by the first curved region  7 . The second limb  5  and the third limb  25  are separated by the second curved region  25 . 
     For measuring the first edge length C 1 , the person skilled in the art places the edges of the bar of a caliper (not shown in  FIG. 6 ) against the first surface  10  of the first limb  3 , said first surface  10  being the surface of the first limb  3  facing away from the first bending axis  2 . The person skilled in the art further places the inner edge of an outer measuring jaw against the first free end  12  and an inner of the other outer measuring jaw against the first curved region  7 . By placing the bar against the first surface  10 , the inner edge of the other outer measuring jaw contacts the first curved region  7  at the first tangent point  16 . 
     The determination of the second edge length C 2  is carried out in like manner, wherein the edge of the bar of the caliper (not shown in  FIG. 6 ) is placed against the second surface  11  of the third limb  24 . The inner edges of the outer measuring jaw in turn contact the second free end  13  of the sheet metal workpiece  1  and the second tangent point  17 . 
     For determining the edge length D 1 , the edge of the bar of the caliper (not shown in  FIG. 6 ) is placed against the third surface  30  of the second limb  5  and the inner edges of the outer measuring jaw are placed against the first curved region  7  and against the second curved region  25 . 
     The person skilled in the art calculates the edge shortening of the sheet metal workpiece  1  as a result of bending of the sheet metal workpiece  1  about the first bending axis  2  and about the second bending axis  26  by means of the formula K=L-C 1 -C 2 -D 1 . 
     In the description to  FIG. 6 , the construction of the tangents et cetera is not described in such detail as in the figure descriptions above, to illustrate, also by means of the written description, how easily the method according to the invention can be carried out. 
       FIG. 7  in addition to  FIG. 5  illustrates how the sheet metal workpieces  1  shortened as a result of bending and shown in exemplary shapes can be measured using the method according to the invention such that the shortening can be estimated. As was initially elucidated in the description of  FIG. 5  above, the bent sheet metal workpiece  1  is placed in the measuring device formed by the first measuring element  20  and the second measuring element  21  such that the sheet metal workpiece  1  contacts the measuring device and a free end  12  can be measured. 
     The tangent shortening is determined for each of the sheet metal workpieces  1  shown in  FIG. 7 . 
     By means of  FIG. 8 , it is explained how, by measuring the free end, the shortening of a sheet metal workpiece  1  bent about a first bending axis  2  and about a second bending axis  26  is estimated by application of the method according to the invention. The sheet metal workpiece  1  comprises a first limb  3  extending along a first straight extension line  4 , a second limb  5  extending along a second straight extension line  6  and a third limb  24  extending along a third straight extension line  27 . The sheet metal workpiece  1  comprises a first curved region  7  extending between the first limb  3  and the second limb  5  and a second curved region  25  extending between the second limb  5  and the third limb  24 . The first curved region  7  and the second curved region  25  are produced by bending of the sheet metal workpiece  1  about a first bending axis  2  and/or about a second bending axis  26  by a bending angle alpha. The bent sheet metal workpiece  1  shown in  FIG. 8  thus has two equal bending angles. 
     The bent sheet metal workpiece  1  is placed in a measuring device comprising a first measuring element surface  22  and a second measuring element surface  23  with its first end  12  for measurement. For the sake of clarity merely the measuring element surfaces  22 ,  23 , which are arranged at a right angle with respect to one another, are shown in  FIG. 8 . 
     The sheet metal workpiece  1  with its first end  12  contacts the second measuring element surface  23  and with its first surface  10  contacts the first measuring element surface  22 , whereby the sheet metal workpiece  1  is also oriented towards the measuring device. 
     The second end  13  of the sheet metal workpiece  1  is measure applying contactless and/or contacting measuring methods according to the prior art, wherein in particular the distance a and the distance b to the first measuring element surface  22  and/or to the second measuring element surface  23  is/are determined. 
     The person skilled in the art hence known the distance a and the distance b as well as the bending angle alpha as well as the sheet metal thickness s. 
     It therefore applies due to the geometric relations, which the person skilled in the art can read from  FIG. 8 : 
     
       
         
           
             
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                              
                             
                               ( 
                               
                                 α 
                                 2 
                               
                               ) 
                             
                           
                         
                       
                       ) 
                     
                   
                 
               
             
           
         
       
       
         
           
             T 
             = 
             
               
                 L 
                  
                 0 
               
               - 
               
                 ( 
                 
                   
                     
                       b 
                       
                         s 
                          
                         i 
                          
                         
                           n 
                            
                           
                             ( 
                             α 
                             ) 
                           
                         
                       
                     
                     · 
                     
                       ( 
                       
                         1 
                         - 
                         
                           cos 
                            
                           
                             ( 
                             α 
                             ) 
                           
                         
                       
                       ) 
                     
                   
                   + 
                   
                     2 
                     · 
                     s 
                     · 
                     
                       tan 
                        
                       
                         ( 
                         
                           α 
                           2 
                         
                         ) 
                       
                     
                   
                   + 
                   a 
                 
                 ) 
               
             
           
         
       
     
     The exemplary embodiments show possible embodiment variants of the method according to the invention, and it should be noted in this respect that the invention is not restricted to these particular illustrated embodiment variants of it, but that rather also various combinations of the individual embodiment variants are possible and that this possibility of variation owing to the teaching for technical action provided by the present invention lies within the ability of the person skilled in the art in this technical field. The person skilled in the art does not have to exercise an inventive step for this. 
     The scope of protection is determined by the claims. However, the description and the drawings are to be adduced for construing the claims. Individual features or feature combinations from the different exemplary embodiments shown and described may represent independent inventive solutions. The object underlying the independent inventive solutions may be gathered from the description. 
     All methods for determining distances can also be supplemented or replaced by other methods in accordance with the prior art and/or by the application of known teaching. 
     Finally, as a matter of form, it should be noted that for ease of understanding of the structure, elements are partially not depicted to scale and/or are enlarged and/or are reduced in size. 
     
       
         
           
               
             
               
                   
               
               
                 List of reference numbers 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                  1  
                 sheet metal workpiece  
               
               
                  2  
                 (first) bending axis  
               
               
                  3  
                 first limb  
               
               
                  4  
                 first straight extension line  
               
               
                  5  
                 second limb  
               
               
                  6  
                 second straight extension line  
               
               
                  7  
                 first curved region  
               
               
                  8  
                 first straight line  
               
               
                  9  
                 second straight line  
               
               
                 10  
                 first surface  
               
               
                 11  
                 second surface  
               
               
                 12  
                 first end  
               
               
                 13  
                 second end  
               
               
                 14  
                 first transition point  
               
               
                 15  
                 second transition point  
               
               
                 16  
                 first tangent point  
               
               
                 17  
                 second tangent point  
               
               
                 18  
                 first tangent  
               
               
                 19  
                 second tangent  
               
               
                 20  
                 first measuring element  
               
               
                 21  
                 second measuring element  
               
               
                 22  
                 first measuring element surface  
               
               
                 23  
                 second measuring element surface  
               
               
                 24  
                 third limb  
               
               
                 25  
                 second curved region  
               
               
                 26  
                 second bending axis  
               
               
                 27  
                 third extension axis  
               
               
                 28  
                 third straight line  
               
               
                 29  
                 fourth straight line  
               
               
                 30  
                 third surface  
               
               
                 31  
                 fourth surface  
               
               
                 S  
                 intersection  
               
               
                 A i    
                 distance  
               
               
                 B j    
                 distance  
               
               
                 C k    
                 distance  
               
               
                 D l    
                 distance