Patent Publication Number: US-7222416-B2

Title: Edge bending apparatus

Description:
TECHNICAL FIELD 
   The present invention relates an edge bending technique suitable for use in manufacture of vehicle hoods. 
   BACKGROUND ART 
   Edge bending is an essential technique for the manufacture of automobiles, particularly their bonnets or hoods. A typical example of such hoods is shown in top plan in  FIG. 14  hereof. The example hood has a cross section as shown in  FIG. 15  hereof. 
   As shown in  FIG. 14 , the hood  100  includes a stiffener member  101  covered with a skin member  102 , and edges of the skin member  102  are folded back around edges of the stiffener member  101  so that the skin member  102  and stiffener member  101  are secured with each other into an integral unit. 
   Discussion will be made next as to typical steps in a conventional method of manufacture of the hood  100  with reference to (a) to (c) of  FIG. 16  hereof. 
   In a first step shown in section (a) of  FIG. 16 , there are first provided a skin member  102  having been formed by bending or drawing a blank into a predetermined shape and then bending edges  103  and  104  about 90 degrees, and a stiffener member  101  similarly formed by bending or drawing. Then, the stiffener  101  turned upside down is placed on the skin member  102  also held upside down. 
   In the next step shown in section (b) of  FIG. 16 , the edges  103  and  104  of the skin member  102  are bent inwardly; the edge bending is also called “hemming”. 
   Section (c) of  FIG. 16  shows the hood  100  having undergone the edge bending or hemming operations. Turning this hood  100  upside down can provide the hood  100  of  FIG. 15 . 
   As examples of the hemming technique, there are known an “entire-peripheral-edge bending apparatus” disclosed in Japanese Utility Model Laid-Open Publication No. HEI-4-134225 ({circle around (1)} publication) and an “entire-peripheral-edge hemming method for a panel having a line” disclosed in Japanese Patent Laid-Open Publication No. HEI-4-351227 ({circle around (2)} publication). 
   In  FIG. 3  of the {circle around (1)} publication, a peripheral flange portion  2   a  (the same reference numerals as appearing in the above-mentioned publications are used here for convenience of description of the background art) is bent, by a pre-hemming punch  18  movable in a left-and-right direction of the figure, to cover an end edge portion  3   a.    
   In the {circle around (2)} publication, as shown in  FIGS. 3 to 5  thereof, a pre-hemming punch  9  is pivotally mounted on a pivot shaft  11 , and a flange portion  2   a  of an outer panel is bent by moving a cam-driver punch  15  downward to thereby cause the pre-hemming punch  9  to pivot about the pivot shaft  11 . 
   With the hemming technique disclosed in the {circle around (1)} publication, there has to be provided a means for pushing the pre-hemming punch  18  in the horizontal direction. Generally, the pushing means converts a vertical operating force of a cam-driver punch moving downward, similarly to the cam-driver punch  15  in the {circle around (2)} publication, into a horizontal force via a pivot member and cam. 
   However, as evident from  FIG. 4  in the {circle around (2)} publication, the operating force conversion requires a plurality of intermediary component parts. Further, with the hemming technique disclosed in the {circle around (2)} publication, the pivot shaft  11  wears with long time use, as a result of which too much looseness or play would be produced between the component parts. Thus, the pre-hemming punch  9  tends to be positioned inaccurately, which would adversely affect the finishing accuracy of products. 
   DISCLOSURE OF THE INVENTION 
   In view of the foregoing, it is an object of the present invention to provide a technique which permits accurate hemming without using a cam and cam driver. 
   To accomplish the above object, the present invention provides an edge bending method which comprises the steps of: installing a first hemming mold unit and a second hemming mold unit in a single pressing machine in parallel; causing the first hemming mold unit to perform partial bending of an edge of a workpiece; transferring the workpiece, having undergone the partial bending, to the second hemming mold unit thorough a first workpiece transfer section and a second workpiece transfer section; and causing the second hemming mold unit to perform remaining bending of the edge of the workpiece, whereby predetermined bending of the edge of the workpiece is completed within the single pressing machine. 
   The necessary bending of the workpiece edge is performed only by downward movement of upper molds. To achieve this, the edge bending of the workpiece is performed through at least two bending stages, the initial bending stage by the first hemming mold unit and the second bending stage by the second hemming mold unit. In this way, the necessary edge bending is carried out step by step via the plurality of hemming mold units. 
   According to the present invention, the workpiece is placed directly on the upper molds with no intervening cam and cam driver. Thus, there is no need to worry about occurrence of undue looseness or play between the elements, and it is possible to maintain a good finishing accuracy of products over a long period of time. 
   In addition, because no intervening cam and cam driver is employed, the edge bending apparatus can be greatly simplified in construction. 
   The present invention also provides an edge bending apparatus which comprises: a first hemming mold unit for bending an edge of a workpiece halfway through a predetermined full bending angle; and a second hemming mold unit for further bending the edge of the workpiece from the halfway angle to the predetermined full bending angle, the first hemming mold unit and the second hemming mold unit being installed in a same pressing machine in parallel. 
   The necessary bending of the workpiece edge is performed only by downward movement of upper molds. To achieve this, the edge bending of the workpiece is performed through at least two bending stages, the initial bending stage by the first hemming mold unit and the second bending stage by the second hemming mold unit. In this way, the necessary edge bending is carried out step by step via the plurality of hemming mold units. 
   According to the present invention, the workpiece is placed directly on the upper molds with no intervening cam and cam driver. Thus, there is no need to worry about occurrence of undue looseness or play between the elements, and it is possible to maintain a good finishing accuracy of products over a long period of time. 
   In addition, because no intervening cam and cam driver is employed, the edge bending apparatus can be greatly simplified in construction. 
   The edge bending apparatus of the invention may further comprise: a first workpiece transfer section movable upward and downward through a lower mold of the first hemming mold unit for placing a workpiece on the first hemming mold unit or feeding a workpiece to the first hemming mold unit; a second workpiece transfer section movable upward and downward through a lower mold of the second hemming mold unit for placing the workpiece on the second hemming mold unit or feeding the workpiece to the second hemming mold unit; and an intermediate workpiece transfer section disposed between the first workpiece transfer section and the second workpiece transfer section for supporting thereon the workpiece to be transferred horizontally from the first workpiece transfer section to the second workpiece transfer section. 
   In the present invention, horizontal transfer of the workpiece within the single pressing machine is absolutely essential. Thus, there are provided the first, second and intermediate workpiece transfer sections for effecting the horizontal transfer of the workpiece. 
   Further, in the present invention, the first, second and intermediate workpiece transfer sections each include rollers provided to project above an upper surface thereof in such a manner that the workpiece can be easily transferred horizontally on the rollers through manual operation by a human operator. 
   Although the first, second and intermediate workpiece transfer sections may be driven using a motor or cylinder as a driving source to horizontally transfer the workpiece, the present invention is arranged to horizontally transfer the workpiece by placing the workpiece on the rollers, provided to project above the upper surface of the workpiece transfer sections, so that the workpiece can be easily transferred manually by a human operator. Thus, the first, second and intermediate workpiece transfer sections can be considerably reduced in size and cost. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Certain preferred embodiments of the present invention will be described in detail below, by way of example only, with reference to the accompanying drawings, in which: 
       FIG. 1  is a sectional view of an edge bending apparatus in accordance with the present invention; 
       FIG. 2  is a view seen in a direction of a  2 — 2  arrow of  FIG. 1 ; 
       FIG. 3  is a view of the edge bending apparatus seen in a direction of arrow “ 3 ” of  FIG. 2 ; 
       FIG. 4  is a view of the edge bending apparatus seen in a direction of arrow “ 4 ” of  FIG. 2 ; 
       FIG. 5  is a view of the edge bending apparatus seen in a direction of a  5 — 5  arrow of  FIG. 2 ; 
       FIG. 6  is a view explanatory of a first sequence of operations performed by the edge bending apparatus of the present invention; 
       FIG. 7  is a view explanatory of a second sequence of operations performed by the edge bending apparatus of the present invention; 
       FIG. 8  is a view explanatory of a third sequence of operations performed by the edge bending apparatus of the present invention; 
       FIG. 9  is a view explanatory of how a first hemming mold unit of the invention works; 
       FIG. 10  is a view explanatory of a fourth sequence of operations performed by the edge bending apparatus of the present invention; 
       FIG. 11  is a view explanatory of a fifth sequence of operations performed by the edge bending apparatus of the present invention; 
       FIG. 12  is a view explanatory of a sixth sequence of operations performed by the edge bending apparatus of the present invention; 
       FIG. 13  is a view explanatory of how a second hemming mold unit of the invention works; 
       FIG. 14  is a plan view of a hood; 
       FIG. 15  is a sectional view of the hood taken along line  15 — 15  of  FIG. 14 ; and 
       FIG. 16  is a view explanatory of a conventionally-known method for manufacturing the hood. 
   

   BEST MODE FOR CARRYING OUT THE INVENTION 
   Now, a detailed description will be made about embodiments of the present invention, with reference to the accompanying drawings. 
     FIG. 1  is a sectional view of an edge bending apparatus in accordance with the present invention. The edge bending apparatus  10  generally comprises first and second hemming mold units  20  and  30  integrally connected with each other in a left-and-right (horizontal) direction of the figure. Specifically, the first hemming mold unit  20  includes a first lower mold  22  having a peripheral support surface  21  for supporting thereon a peripheral edge of a workpiece (not shown in the figure), and a first upper mold  24  vertically movable toward and away from the first lower mold  22  and having a bending blade  23  for bending the peripheral edge of the workpiece to halfway through a predetermined full bending angle. The first hemming mold unit  20  also includes a hanging frame  27  attached, via bolts  26 , to a cross beam  25  of the first upper mold  24  in such a manner that the hanging frame  27  can move vertically relative to the cross beam  25 , workpiece retainers  28  fixed to the hanging frame  27 , and positioning pins  29 . 
   Similarly, the second hemming mold unit  30  includes a second lower mold  32  having a peripheral support surface  31  for supporting thereon the peripheral edge of the workpiece, and a second upper mold  34  vertically movable toward and away from the second lower mold  32  and having a bending blade  33  for further bending the peripheral edge of the workpiece from the halfway angle to the predetermined full bending angle. The second hemming mold unit  30  also includes a hanging frame  37  attached, via bolts  36 , to a cross beam  35  of the second upper mold  34  in such a manner that the hanging frame  37  can move vertically relative to the cross beam  35 , workpiece holders  38  fixed to the hanging frame  37 , and positioning pins  39 . 
   The first lower mold  22  has a central space, in which are accommodated a first workpiece transfer section  40  (to be later described in detail in relation to  FIG. 4 ), and a combination of upper and lower level switches  41  and  42  and level sensing rod  43  for monitoring a level of the first workpiece transfer section  40 . When a first lateral projection  44  on the level sensing rod  43  contacts the upper level switch  41 , it can be seen that the first workpiece transfer section  40  is currently at an upper level, i.e. a position for lifting up the workpiece off the first lower mold  22 . Further, when a second lateral projection  45  on the level sensing rod  43  contacts the lower level switch  42 , it can be seen that the first workpiece transfer section  40  is currently at a lower level, i.e. a standby position. 
   Similarly, the second lower mold  32  has a central space, in which are accommodated a second workpiece transfer section  50 , and a combination of upper and lower level switches  41  and  42  and level sensing rod  43  for monitoring a level of the second workpiece transfer section  50 . When a first lateral projection  44  on the level sensing rod  43  contacts the upper level switch  41 , it can be seen that the second workpiece transfer section  50  is currently at an upper level, i.e. a position for lifting up the workpiece off the second lower mold  32 . Further, when a second lateral projection  45  on the level sensing rod  43  contacts the lower level switch  42 , it can be seen that the second workpiece transfer section  50  is currently at a lower level, i.e. a standby position. 
   That is, the second workpiece transfer section  50  is constructed similarly to the first workpiece transfer section  40 . 
   In addition, the edge bending apparatus  10  includes an intermediate workpiece transfer section  60  disposed between the first and second lower molds  22  and  32 , and this intermediate workpiece transfer section  60  includes rollers  61  and a bracket  62  rotatably supporting thereon the rollers  61 . 
   The edge bending apparatus  10  further includes a front workpiece transfer section  70  disposed forward of (in the figure, to the right of) the first lower mold  22  (remotely from the second lower mold  32 ), and this front workpiece transfer section  70  includes rollers  61  and a bracket  62  rotatably supporting thereon the rollers  61 . 
     FIG. 2  is a view of the edge bending apparatus  10  seen in a direction of the  2 — 2  arrow of  FIG. 1 . The first workpiece transfer section  40  is accommodated in the central space of the first lower mold  22  having the peripheral support surface  21 , and similarly the second workpiece transfer section  50  is accommodated in the central space of the second lower mold  32  having the peripheral support surface  31 . The front workpiece transfer section  70  and intermediate workpiece transfer section  60  are disposed forward and rearward of the first lower mold  22 . 
   Further, on each of the first and second lower molds  22  and  32 , there are provided a workpiece stopper  80  generally in the shape of a crossing gate, a workpiece detecting sensor  89 , and a workpiece guide  88 . 
     FIG. 3  is a view of the edge bending apparatus  10  seen in a direction of arrow “ 3 ” of  FIG. 2 . Each of the workpiece stopper  80  in the crossing gate shape includes an L-shaped arm  83  that is pivotally connected via a pin  82  to a base  81 , and a retaining plate  84  fastened via bolts  85  to the distal end of the L-shaped arm  83 ; a resilient plate  86 , such as a rubber plate, is secured to the distal end of the retaining plate  84 . The L-shaped arm  83  is reciprocatively pivotable, via a cylinder  87  mounted on the base  81 , between a solid-line position and an imaginary-line position. 
   The imaginary lines in  FIG. 3  denote a standby position where the workpiece stopper  80  does not hinder horizontal movement of the workpiece, while the solid lines denote a stopping position where the workpiece stopper  80  abuts against the workpiece and thereby blocks the horizontal movement of the workpiece. 
   Referring back to  FIG. 2 , as the not-shown workpiece is transferred horizontally to the first workpiece transfer section  40  via the front workpiece transfer section  70 , the workpiece comes into contact with the resilient plate  86  of the workpiece stopper  80  so that it can be positioned at a predetermined place. 
   Similarly, as the workpiece is transferred horizontally to the second workpiece transfer section  50  via the intermediate workpiece transfer section  60 , the workpiece comes into contact with the resilient plate  86  of the workpiece stopper  80  so that it can be positioned at a predetermined place. 
     FIG. 4  is a view of the edge bending apparatus  10  seen in a direction of arrow “ 4 ” of  FIG. 2 . As shown, each of the workpiece detecting sensors  89 , specifically in the form of a proximity switch or opto-electronic switch, is provided, near the corresponding peripheral support surface  21  or  31 , for detecting presence/absence of a workpiece denoted in imaginary line. 
   Reference numeral  90  represents upper mold guiding pieces that are provided around the outer periphery of the first and second lower molds  22  and  32  as appropriate. 
     FIG. 5  is a view of the edge bending apparatus  10  seen in a direction of the  5 — 5  arrow of  FIG. 2 . As shown, the second workpiece transfer section  50  includes a base plate  51 , a lifting/lowering cylinder  52  connected to the base plate  51 , and guide bars  53  provided, along opposite sides of the lifting/lowering cylinder  52 , for sliding movement through the base plate  51 . The second workpiece transfer section  50  also includes a lifting/lowering plate  55  connected to a piston rod  54  of the cylinder  52 , a frame member  56  coupled to the lifting/lowering plate  55 , and rollers  61  attached to the frame  56 . As shown in  FIG. 2 , the frame  56  has a rectangular shape, and a plurality of rollers  61  (in the illustrated example, a total of eight rollers  61 , four on each of the left and right sides) are attached to the frame  56 , so as to provide a greater workpiece-carrying area. 
   The first workpiece transfer section  40  is constructed in the same manner as the second workpiece transfer section  50 , and thus the construction of the first workpiece transfer section  40  will not be described in detail here to avoid unnecessary duplication. 
   Referring back to  FIG. 5 , the lifting/lowering plate  55 , frame  56  and rollers  61  can be together raised to the position denoted by imaginary lines. Namely, the imaginary-line position is a lifted-up position of these elements, while the solid-line position is a standby position of these elements. 
   Next, a description will be made about behavior of the edge bending apparatus  10  arranged in the above-described manner. 
     FIG. 6  is a view explanatory of a first or initial sequence of operations performed by the edge bending apparatus of the present invention. First workpiece  93 , comprising a skin member  91  and stiffener member  92 , is transferred horizontally to the first hemming mold unit  20  via the front workpiece transfer section  70  and first workpiece transfer section  40  while the first and second upper molds  24  and  34  are held in the upper standby position. 
     FIG. 7  is a view explanatory of a second sequence of operations performed by the edge bending apparatus of the present invention. Here, the first and second workpiece transfer sections  40  and  50  are lowered to the standby position, so that the first workpiece  93  is placed on the first lower mold  22 . 
   After that, the first and second upper molds  24  and  34  are lowered to a predetermined position (slightly above a bottom dead center). Thus, the positioning pins  29  extending from the hanging frame  27  fit into positioning holes  94  of the stiffener member  92 , so that the stiffener member  92  can be positioned at a predetermined place. Immediately after that, the workpiece retainers  28  retain the stiffener member  92 . 
   In this state, the first and second upper molds  24  and  34  are lowered further. Although the hanging frame  27  can not be lowered any further at this time, the downward movement of the first and second upper molds  24  and  34  is never hindered because the bolts  26  extend through the cross beam  25 . 
     FIG. 8  is a view explanatory of a third sequence of operations performed by the edge bending apparatus of the present invention. Here, edges  95  of the skin member  91  are both bent about half of the predetermined full bending angle by means of the bending blades  23  of the first upper mold  24 ; this partial bending of the edges will be later detailed in relation to a next figure. Note that the operational sequences of  FIGS. 6 to 8  may be carried out in a successive manner with no substantial intervening break. 
   (a) and (b) of  FIG. 9  are views explanatory of how the first hemming mold unit works in the present invention. 
   As shown in (a), the first upper mold  24  is lowered toward the first work piece  93  currently placed on the first lower mold  22 ; note that the edges  95  of the first work piece  93  has already been bent about 90 degrees in the previous step. 
   Then, as shown in (b), the edges  95  of the first work piece  93  is further bent to about half the predetermined full bending angle via the bending blades  23  as the first upper mold  24  is lowered toward the first work piece  93 . 
     FIG. 10  is a view explanatory of a fourth sequence of operations performed by the edge bending apparatus of the present invention. The first workpiece  93 , having so far been located below the first upper mold  24 , is transferred horizontally to below the second upper mold  34  as indicated by arrow {circle around (1)} while the first and second upper molds  24  and  34  are held in the upper standby position. At this time, the horizontal transfer of the first workpiece  93  is greatly facilitated by the rollers  61  of the first workpiece transfer section lifted up to the upper level position, intermediate workpiece transfer section  60  and second workpiece transfer section also lifted up to the upper level position. 
   Now that the space below the first upper mold  24  has been emptied, a next or second workpiece  96  (which is of exactly the same type as the first workpiece  93  but referred to here by a different name just for convenience of description) is transferred to below the first upper mold  24  as indicated by arrow {circle around (2)} by means of the front workpiece transfer section  70  and first workpiece transfer section  40 . 
   Namely, by this time, the first workpiece  93  has been appropriately set in the second hemming mold unit  30 , and the second workpiece  96  has been appropriately set in the first hemming mold unit  20 . 
     FIG. 11  is a view explanatory of a fifth sequence of operations performed by the edge bending apparatus of the present invention. Here, the first and second workpiece transfer sections  40  and  50  are lowered to the standby position, so that the first workpiece  93  is placed on the second lower mold  32  and the second workpiece  96  is placed on the first lower mold  22 . 
   After that, the first and second upper molds  24  and  34  are lowered to a predetermined position (slightly above a bottom dead center). Thus, the positioning pins  29  extending from the hanging frame  27  fit into positioning holes  94  of the stiffener member  92 , so that the stiffener member  92  can be positioned at a predetermined place. Immediately after that, the workpiece retainers  28  retain the stiffener member  92 . 
   In this state, the first and second upper molds  24  and  34  are lowered further. Although the hanging frame  27  is not lowered any further at this time, the downward movement of the first and second upper molds  24  and  34  is never hindered because the bolts  26  extend through the cross beam  25 . 
     FIG. 12  is a view explanatory of a sixth sequence of operations performed by the edge bending apparatus of the present invention. Here, the edges  95  of the skin member  91  are further bent to the predetermined full angle via the bending blades  33  of the second upper mold  34 . This complete bending of the edges  95  will be later detailed in relation to a next figure. Note that the operational sequences of  FIGS. 10 to 12  may be carried out in a successive manner with no substantial intervening break. 
   In parallel with the bending of the edges  95  by the bending blades  33  of the second upper mold  34 , the first hemming mold  20  performs preliminary bending of the second workpiece  96  in the same manner as already described earlier in relation to  FIGS. 6 to 8 . 
   (a) and (b) of  FIG. 13  are views explanatory of how the second hemming mold unit works in the present invention. 
   As shown in (a), the second upper mold  34  is lowered toward the first work piece  93  currently placed on the second lower mold  32 . 
   Then, as shown in (b), the edges  95  of the first work piece  93  is further bent to the predetermined full bending angle via the bending blades  33  as the second upper mold  34  is lowered toward the first work piece  93 . 
   It should be obvious that the workpieces  93 ,  96  can be completely bent at their edges, i.e. hemmed, in a successive fashion by repeating the operation sequences of  FIGS. 10–12 . Namely, in the present invention, a plurality of hemming mold units, including at least the above-described first and second hemming mold units  20  and  30 , are installed in a single pressing machine (not shown), a workpiece  93 ,  96  is subjected to partial (preliminary) edge-bending or hemming by the first hemming mold unit  20 , the workpiece having thus been partially bent is transferred to the second hemming mold unit  30 , and then the workpiece are subjected to the remaining hemming by the second hemming mold unit  30  to ultimately assume the full bending angle; that is, the present invention is characterized by completing the necessary hemming of the workpiece within the single pressing machine. 
   According to the edge bending method of the present invention, the workpiece is placed directly on the upper molds with no intervening cam and cam driver. Thus, there is no need to worry about occurrence of undue looseness or play, and it is possible to maintain a good finishing accuracy of products over a long period of time. In addition, because no intervening cam and cam driver is employed, the present invention accomplishes the superior advantageous result that the edge bending apparatus can be greatly simplified in construction. 
   Further, in the present invention, a so-called robot may be used to feed a workpiece to the first hemming mold unit and horizontally transfer the workpiece from the first hemming mold unit to the second hemming mold unit. However, in the edge bending apparatus provided with the first, second and intermediate workpiece transfer sections as described above, the workpiece can be fed to the first hemming mold unit and transferred from the first hemming mold unit to the second first hemming mold unit without requiring use of such an expensive robot. As a consequence, costs of the edge bending apparatus can be reduced to a considerable degree. 
   Further, although the first, second and intermediate workpiece transfer sections may be driven using a motor or cylinder as a driving source to horizontally transfer the workpiece, the present invention is arranged to horizontally transfer the workpiece by placing the workpiece on the rollers, provided to project above the upper surface of the workpiece transfer sections, so that the workpiece can be easily transferred on the rollers manually by a human operator. Thus, the first, second and intermediate workpiece transfer sections can be considerably reduced in size and cost. 
   Whereas the embodiment of the present invention has been described as installing two hemming mold units in a single pressing machine, three or more hemming mold units may be installed in the pressing machine. If it is necessary for each of the hemming mold units to bend the workpiece by a reduced angle, the increased number of the hemming mold units will be more effective. 
   Although the embodiment has been described as connecting together the left and right upper or lower molds, separate molds may be mounted on a common board called a die set and this die set with the molds may be installed in the pressing machine. 
   Furthermore, any types of workpieces, such as a hood, trunk lid, door and sun roof, which require hemming may be handled by the present invention. 
   INDUSTRIAL APPLICABILITY 
   The inventive edge bending method can be employed in the manufacture of automobiles, particularly their hoods, and is useful in that it permits edge bending in a single pressing machine.