Patent Publication Number: US-9421597-B2

Title: Press-work method and bottomed container

Description:
TECHNICAL FIELD 
     The present invention relates to a press-work method of thickening an inclined portion rising from a bottom surface portion of a bottomed container, and to a bottomed container manufactured by the same. 
     BACKGROUND ART 
     With reference to  FIG. 1A  and  FIG. 1B , as a method of thickening a vertical wall of a bottomed container, a method in which a disk-shaped workpiece is formed into a bottomed container  11  by deep drawing, and an end surface  11   b  of the bottomed container is pushed by a pushing punch  14  while a bottomed container bottom surface  11   a  is sandwiched by a die  12  and a pressing punch  13 , to thereby thicken a vertical wall  11   c  of the bottomed container has been conventionally in general use. In this method, however, being constrained only weakly, the vertical wall portion of the bottomed container buckles during the thickening, so that folding  11   d  occurs. This has made it difficult to realize a large thickening ratio (sheet thickness after the thickening/original sheet thickness) exceeding 1.3. 
     For example, Patent Literature 1 discloses a thickening press-work method in which a pressing punch and an upsetting punch are provided, and between an upper end portion and a bottom inner portion of a workpiece, a gap is reserved between the pressing punch and a die, and an upper surface of the end portion of the workpiece is pressed by the upsetting punch. However, in the method of Patent Literature 1, folding may also occur because buckling occurs in the gap during the thickening. 
     Therefore, there has been proposed a method to overcome the drawbacks of the above-described thickening methods, in the manufacture of a pulley piston for continuously variable transmission of an automobile, as described in Non Patent Literature 1. This forming method is capable of preventing folding ascribable to buckling because a portion to be thickened is thickened by pushing an end portion of a cup in a state where a constraint surface of a material is increased by providing a corner portion in the portion to be thickened. However, since a gap of the portion to be thickened is geometrically decided by constraint by the shape of a mold and the movement of the mold, a maximum thickening ratio that can be achieved in one forming is about 1.5. Further, before this process, it is necessary to form a bottomed cylindrical container by deep drawing or the like, and totally two processes are required. 
     Further, Patent Literature 2 proposes a method in which a press-worked workpiece which has an end wall, a bent portion bent from an outer periphery of the end wall toward one side, and a cylindrical portion provided to continue from the bent portion is used, the workpiece is clamped by a clamp punch adapted to an inner surface of the workpiece, a clamp die adapted to an outer surface of the end wall, and a thickness-increase guide die fitted to an outer peripheral surface of the clamp die so as to be swingable in an axial direction and adapted to outer peripheral surfaces of the bent portion and the cylindrical portion, a thickness-increasing punch is inserted in space formed between the clamp punch and the thickness-increase guide die to apply an axial-direction compression load to the cylindrical portion, thereby thickening the bent portion, and the thickness-increase guide die is retracted from the clamp die according to the thickening. 
     Further, Patent Literature 3 proposes a structure in which a knockout for receiving a body portion of a workpiece, a plate presser for pressing an area up to the middle of a rising portion rising obliquely outward from the body portion, a thickness-increasing punch for pressing a tip of the rising portion, and a die for receiving the rising portion are provided, and the die is movable in an axial direction relatively to the knockout and the thickness-increasing punch. In the process of crushing the rising portion by pressing the tip of the rising portion by the thickness-increasing punch, the die is pressed by the rising portion which is in the course of being thickened without being pushed by the thickness-increasing punch, to move relatively to the knockout, so that a gap between the plate presser and the die which sandwich the rising portion widens. 
     However, the methods of Patent Literatures 2, 3 also require the forming of a bottomed cylindrical container by deep drawing or the like, and thus require totally two processes. Further, a cutting process is sometimes required because a large step occurs in a boundary between a thickened portion and a non-thickened portion. Further, an achievable thickening ratio is not mentioned. 
     Further, in the structure in which the die is divided and part thereof is moved, in Patent Literature 2, for example, a force in a direction perpendicular to an inclined portion (2 b  in Patent Literature 2) acts on the thickness-increase guide die at the time of the thickening. Since this force acts in such a direction as to make the thickness-increase guide die separate from the clamp die (outward in a diameter direction), a gap occurs in a boundary between the clamp die and the thickness-increase guide die, which may cause a burr. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Laid-open Patent Publication No. 2001-47175 
     Patent Literature 2: Japanese Laid-open Patent Publication No. 2010-247199 
     Patent Literature 3: Japanese Laid-open Patent Publication No. 2009-248092 
     Non-Patent Literature 
     Non Patent Literature 1: “Automotive Engineering”, Automotive Engineers of Japan Inc., 1996, Vol. 50, No 12, p. 31-37 
     SUMMARY OF INVENTION 
     Technical Problem 
     The present invention was made in order to solve the above-described conventional drawbacks and its main object is to make it possible to avoid folding due to buckling to achieve thickening with a thickening ratio of 1.5 times or more in a press-work. Its another object is to make it possible to manufacture a bottomed container having a smooth shape without a large step in a boundary between a thickened portion and a non-thickened portion. Its another object is to make it possible to manufacture a bottomed container whose inclined portion is thickened, from a disk-shaped workpiece by a press-work having one process. 
     Solution to Problem 
     The gist of the present invention that is to achieve the aforesaid objects is as follows. 
     [1] A press-work method using a press mold which includes an inner punch, an intermediate punch disposed along an outer periphery of the inner punch and having an intermediate punch inclined portion at a leading end, an outer punch disposed along an outer periphery of the intermediate punch, and a die having a die inclined portion facing the intermediate punch inclined portion, central axes of all of which are disposed coaxially, the method including a thickening step of, while constraining a bottom portion of a bottomed container by the inner punch and the die, pressing an end portion of the bottomed container by the outer punch and moving the intermediate punch in a direction opposite a direction in which the outer punch is pressed, to thereby thicken a bottomed container inclined portion of the bottomed container sandwiched by the intermediate punch inclined portion and the die inclined portion. 
     [2] A press-work method using a press mold which includes an inner punch having an inner punch flat portion and an inner punch inclined portion at a leading end, an intermediate punch disposed along an outer periphery of the inner punch and having an intermediate punch inclined portion at a leading end, an outer punch disposed along an outer periphery of the intermediate punch, and a die having a die inclined portion disposed to face the intermediate punch inclined portion, central axes of all of which are disposed coaxially, the inner punch inclined portion being formed at an end portion, of the leading end of the inner punch, on a side adjacent to the intermediate punch inclined portion, the method including: 
     an outer punch pressing step of, while constraining a bottom portion of a bottomed container by the inner punch flat portion and the die, pressing an end portion of the bottomed container by the outer punch to thereby bring a bottomed container inclined portion, of the bottomed container, which extends along the inner punch inclined portion and the intermediate punch inclined portion, into contact with the die inclined portion; 
     an intermediate punch pressing step of pressing the intermediate punch in a direction of the die against the bottomed container which is brought into contact with the die inclined portion in the outer punch pressing step, to bring the intermediate punch inclined portion into contact with the bottomed container inclined portion; and 
     a thickening step of pressing the outer punch against the bottomed container which is brought into contact with the intermediate punch inclined portion in the intermediate punch pressing step, and moving the intermediate punch in a direction opposite a direction in which the outer punch is pressed, to thereby thicken the bottomed container inclined portion. 
     [3] The press-work method according to [1], including, before the thickening step, a forming step of pressing a disk-shaped workpiece into the die by the inner punch and the intermediate punch to form the bottomed container in which the bottomed container inclined portion is formed at a position sandwiched by the intermediate punch inclined portion and the die inclined portion. 
     [4] The press-work method according to [2], including, before the outer punch pressing step, a forming step of pressing a disk-shaped workpiece into the die by the inner punch and the intermediate punch to form the bottomed container in which the bottomed container inclined portion is formed at a position sandwiched by the inner punch inclined portion and the intermediate punch inclined portion, and the die inclined portion. 
     [5] The bottomed container manufactured by the press-work method according to [1], wherein a thickening ratio of a thickness of the bottomed container inclined portion is 1.5 times or more. 
     [6] The bottomed container manufactured by the press-work method according to [2], wherein a thickening ratio of a thickness of the bottomed container inclined portion is 1.5 times or more. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to avoid folding due to buckling to achieve thickening with a thickening ratio of 1.5 times or more. 
     Further, it is possible to manufacture a bottomed container having a smooth shape without a large step in a boundary between a thickened portion and a non-thickened portion. 
     Furthermore, it is possible to manufacture a bottomed container whose inclined portion is thickened, from a disk-shaped workpiece by a press-work having one process. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a cross-sectional view illustrating a conventional thickening work. 
         FIG. 1B  is a cross-sectional view illustrating the conventional thickening work. 
         FIG. 2  is a cross-sectional view illustrating a state before deep drawing in a press-work method according to a first embodiment. 
         FIG. 3  is a cross-sectional view illustrating a state after the deep drawing in the press-work method according to the first embodiment. 
         FIG. 4  is a cross-sectional view illustrating a state in the middle of thickening in the press-work method according to the first embodiment. 
         FIG. 5  is a cross-sectional view illustrating a state after the thickening in the press-work method according to the first embodiment. 
         FIG. 6  is a cross-sectional view illustrating a state before deep drawing in a press-work method according to a second embodiment. 
         FIG. 7  is a cross-sectional view illustrating a state after the deep drawing in the press-work method according to the second embodiment. 
         FIG. 8  is a cross-sectional view illustrating a state where an inclined portion of a die is brought into contact with an inclined portion of a bottomed container in the press-work method according to the second embodiment. 
         FIG. 9  is a cross-sectional view illustrating a state where an inclined portion of an intermediate punch is brought into contact with the inclined portion of the bottomed container in the press-work method according to the second embodiment. 
         FIG. 10  is a cross-sectional view illustrating a state in the middle of thickening in the press-work method according to the second embodiment. 
         FIG. 11  is a cross-sectional view illustrating a state after the thickening in the press-work method according to the second embodiment. 
         FIG. 12  is a cross-sectional view illustrating a comparative example of the second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, modes for carrying out the present invention will be described with reference to the attached drawings. 
     As a result of studious studies, the present inventor has found out that, by performing deep drawing by using an inner punch, an intermediate punch disposed along an outer periphery of the inner punch, and a die, central axes of all of which are coaxially disposed, to form a bottomed container, and subsequently, while constraining a workpiece, performing thickening by gradually increasing a gap between the intermediate punch and the die when an end surface of the bottomed container is pressed by the outer punch, it is possible to perform the thickening with a thickening ratio of 1.5 times or more by a press-work having one process while avoiding folding due to buckling. 
     (First Embodiment) 
       FIG. 2  is a cross-sectional view illustrating a state before deep drawing is executed. As illustrated in  FIG. 2 , a press mold includes an inner punch  23 , an intermediate punch  24  disposed along an outer periphery of the inner punch  23 , an outer punch  25  disposed along an outer periphery of the intermediate punch  24 , a knockout  26 , and a die  27  disposed along an outer periphery of the knockout  26 , central axes of all of which are coaxially disposed. The inner punch  23  is disposed to face the knockout  26  and the die  27 , and the intermediate punch  24  and the outer punch  25  are disposed to face the die  27 . 
     The inner punch  23  has a columnar shape, and is of a movable type capable of moving up and down by a not-illustrated drive source of a mechanical type (hydraulic or servo motor, or the like). 
     The intermediate punch  24  has a cylindrical shape, and on its surface that comes into contact with a portion to be thickened of a workpiece (that is, on a lower end portion (leading end) of the intermediate punch  24 ), an intermediate punch inclined portion  24   a  is formed. This intermediate punch inclined portion  24   a  is inclined in an obliquely upward direction from an inner punch  23  side toward an outer punch  25  side. The intermediate punch  24  is of a movable type capable of moving up and down by a not-illustrated mechanical drive source. 
     The outer punch  25  has a cylindrical shape and is of a movable type capable of moving up and down by a not-illustrated mechanical drive source. 
     The knockout  26  has a columnar shape, is intended to detach a formed product from the mold, and is of a movable type capable of moving up and down by a not-illustrated mechanical drive source. 
     The die  27  is of a fixed type, has a substantially concave shape, and has, at a center portion, a hole allowing the knockout  26  to be inserted therein. Further, in the die  27 , a die inclined portion  27   a  is formed, and this die inclined portion  27   a  is disposed to face the intermediate punch inclined portion  24   a.    
     In this embodiment, by executing the following forming step and thickening step, the workpiece  21  was press-worked. As the workpiece  21 , a disk-shaped high-tensile steel sheet (SAPH590) having a 240 mm outside diameter and a 4 mm sheet thickness was used. 
     The workpiece  21  is placed on the die  27  and is subjected to the deep drawing by pressing the inner punch  23  and the intermediate punch  24 , whereby a bottomed container  22  in which a bottomed container inclined portion  22   a  is formed at a position sandwiched by the intermediate punch inclined portion  24   a  and the die inclined portion  27   a  is formed as illustrated in  FIG. 3  (forming step). 
     In the state illustrated in  FIG. 3 , a bottom portion of the bottomed container  22  is constrained by the inner punch  23  and the die  27 . 
     Subsequently, as illustrated in  FIG. 4  and  FIG. 5 , an end surface of the bottomed container  22  formed in the forming step is pressed by the outer punch  25 , and the intermediate punch  24  is moved upward. Consequently, a gap between the intermediate punch inclined portion  24   a  and the die inclined portion  27   a  gradually becomes larger, which makes it possible to perform the thickening while suppressing buckling by sandwiching the bottomed container inclined portion  22   a  by the intermediate punch inclined portion  24   a  and the die inclined portion  27   a  (thickening step). The cross-sectional views in  FIG. 4  and  FIG. 5  illustrate states in the middle of the thickening and after the thickening respectively. 
     After the thickening step, the inner punch  23 , the intermediate punch  24 , the outer punch  25 , and the knockout  26  are moved upward, and the bottomed container  22  is detached from the die  27 . A sheet thickness of the bottomed container inclined portion  22   a  is 6.9 mm, and thus the thickness can be increased to 1.73 times an original sheet thickness of 4 mm without any occurrence of folding due to buckling. 
     Further, at the time of the thickening, a force in a direction perpendicular to the intermediate punch inclined portion  24   a  acts on the intermediate punch  24 , but since this force acts in such a direction as to press the intermediate punch  24  against the inner punch  23  (inward in a diameter direction (center direction)), there occurs no gap in a boundary between the inner punch  23  and the intermediate punch  24  and a burr is not generated. 
     (Second Embodiment) 
     In a second embodiment, a bottomed container having a smooth shape without a large step in a boundary between a thickened portion and a non-thickened portion is manufactured. 
       FIG. 6  is a cross-sectional view illustrating a state before deep drawing is executed. As illustrated in  FIG. 6 , a press mold includes an inner punch  33 , an intermediate punch  34  disposed along an outer periphery of the inner punch  33 , an outer punch  35  disposed along an outer periphery of the intermediate punch  34 , a knockout  36 , and a die  37  disposed along an outer periphery of the knockout  36 , central axes  30  of all of which are coaxially disposed. The inner punch  33  is disposed to face the knockout  36  and the die  37 , and the intermediate punch  34  and the outer punch  35  are disposed to face the die  37 . 
     The inner punch  33  has a columnar shape, and on its leading end, an inner punch inclined portion  33   a  and an inner punch flat portion  33   b  are formed. The inner punch inclined portion  33   a  is formed on a peripheral edge portion of the leading end, that is, on an end portion on a side adjacent to an intermediate punch inclined portion  34   a , and the inner punch flat portion  33   b  is formed around the central axis  30 . The inner punch inclined portion  33   a  is inclined in an obliquely upward direction from a central axis  30  side toward an intermediate punch  34  side. The inner punch flat portion  33   b  extends in a horizontal direction perpendicular to the central axis  30 . The inner punch  33  is of a movable type capable of moving up and down by a not-illustrated mechanical drive source. 
     The intermediate punch  34  has a cylindrical shape, and on its surface that comes into contact with a portion to be thickened of a workpiece (that is, on a lower end portion (leading end) of the intermediate punch  34 ), the intermediate punch inclined portion  34   a  is formed. This intermediate punch inclined portion  34   a  is inclined in an obliquely upward direction from an inner punch  33  side toward an outer punch  35  side. The intermediate punch  34  is of a movable type capable of moving up and down by a not-illustrated mechanical drive source. 
     Here, when a height of an end portion of the inner punch inclined portion  33   a  on a side more distant from the central axis  30  and a height of an end portion of the intermediate punch inclined portion  34   a  on a side closer to the central axis  30  are equal, that is, in the state illustrate in  FIG. 6 , the inner punch inclined portion  33   a  and the intermediate punch inclined portion  34   a  form a smooth curve. 
     The outer punch  35  has a cylindrical shape and is of a movable type capable of moving up and down by a not-illustrated mechanical drive source. 
     The knockout  36  has a columnar shape, is intended to detach a formed product from the mold, and is of a movable type capable of moving up and down by a not-illustrated mechanical drive source. 
     The die  37  is of a fixed type, has a substantially concave shape, and has, at a center portion, a hole allowing the knockout  36  to be inserted therein. In the die  37 , a die inclined portion  37   a  is formed, and this die inclined portion  37   a  is disposed to face the inner punch inclined portion  33   a  and the intermediate punch inclined portion  34   a.    
     In this embodiment, by executing the following forming step, outer punch pressing step, intermediate punch pressing step, and thickening step, the workpiece  31  was press-worked. As the workpiece  31 , a disk-shaped high-tensile steel sheet (SAPH590) having a  224  outside diameter and a 4 mm sheet thickness was used. 
     The workpiece  31  is placed on the die  37 , and is subjected to the deep drawing by pressing the inner punch  33  and the intermediate punch  34 , whereby a bottomed container  32  in which a bottomed container inclined portion  32   a  is formed at a position sandwiched by the inner punch inclined portion  33   a  and the intermediate punch inclined portion  34   a , and the die inclined portion  37   a  is formed as illustrated in  FIG. 7  (forming step). 
     In the state illustrated in  FIG. 7 , a bottom portion of the bottomed container  32  is constrained by the inner punch flat portion  33   b  of the inner punch  33  and the die  37 . 
     Subsequently, an end surface of the bottomed container  32  formed in the forming step is pressed by the outer punch  35 , whereby the bottomed container inclined portion  32   a  extending along the inner punch inclined portion  33   a  and the intermediate punch inclined portion  34   a  is brought into contact with the die inclined portion  37   a  as illustrated in  FIG. 8  (outer punch pressing step). 
     Subsequently, the intermediate punch  34  is moved downward toward the bottomed container  32  which is brought into contact with the die  37  in the outer punch pressing step (the intermediate punch  34  is pressed toward the die  37 ), whereby the intermediate punch inclined portion  34   a  is brought into contact with the bottomed container inclined portion  32   a  as illustrated in  FIG. 9  (intermediate punch pressing step). 
     Subsequently, as illustrated in  FIG. 10  and  FIG. 11 , an end surface of the bottomed container  32  is pressed by the outer punch  35 , and the intermediate punch  34  is moved upward. Consequently, a gap between the intermediate punch inclined portion  34   a  and the die inclined portion  37   a  gradually becomes larger, which makes it possible to perform the thickening while suppressing buckling by sandwiching the bottomed container inclined portion  32   a  by the intermediate punch inclined portion  34   a  and the die inclined portion  37   a  (thickening step). The cross-sectional views in  FIG. 10  and  FIG. 11  illustrate states in the middle of the thickening and after the thickening respectively. 
     After the thickening step, the inner punch  33 , the intermediate punch  34 , the outer punch  35 , and the knockout  36  are moved upward, and the bottomed container  32  is detached from the die  37 . A sheet thickness of the bottomed container inclined portion  32   a  is 8 mm, and thus the thickness can be increased to twice an original sheet thickness of 4 mm without any occurrence of folding due to buckling. Further, a smooth shape is achieved without any large step in a boundary between a thickened portion and a non-thickened portion. 
     Further, at the time of the thickening, a force in a direction perpendicular to the intermediate punch inclined portion  34   a  acts on the intermediate punch  34 , but since this force acts in such a direction as to press the intermediate punch  34  against the inner punch  33  (inward in a diameter direction (center direction)), there occurs no gap in a boundary between the inner punch  33  and the intermediate punch  34  and a burr is not generated. 
     Here, in the state illustrated in  FIG. 7 , if the end portion of the bottomed container  32  is pressed by the outer punch  35  without the intermediate punch  34  abutting on the bottomed container  32 , the bottomed container inclined portion  32   a  is not sufficiently constrained, and accordingly, buckling occurs in the bottomed container inclined portion  32   a  as illustrated in  FIG. 12 . Therefore, by executing the thickening process by the outer punch  35  while constraining the bottomed container inclined portion  32   a  by sandwiching it by the intermediate punch  34  and the die  37 , it is possible to suppress the buckling in the bottomed container inclined portion  32   a.    
     In the above-described examples, an angle made by the bottomed container inclined portions  22   a,    32   a  and the horizontal direction is 45°, but it is desirably not less than 20° nor more than 70°. This is because, if the angle made by the bottomed container inclined portion  22   a ,  32   a  and the horizontal direction is less than 20°, a flow of a material from bottomed container vertical wall portions  22   b ,  32   b  to the bottomed container inclined portions  22   a ,  32   a  becomes worse, and a load required for the forming becomes large. Further, this is because, if the angle made by the bottomed container inclined portions  22   a ,  32   a  and the horizontal direction is over 70°, a contact length of the workpieces  21 ,  31  and the mold becomes long, and accordingly a frictional force becomes large, so that a load required for the forming becomes large. Note that the bottomed container vertical wall portions  22   b ,  32   b  mean portions of the bottomed containers  22 ,  32  on a side closer to the outer punches  25 ,  35  than the bottomed container inclined portions  22   a ,  32   a.    
     Hitherto, the present invention has been described together with various embodiments, but the present invention is not limited only to these embodiments, and changes and so on can be made within the scope of the present invention. 
     In the above-described examples, SAPH590 is used as the workpiece, but it is not limited to an iron-based material, but an aluminum-based metal, a titanium-based metal, or the like is usable. 
     Further, in the above-described embodiments, the examples where the bottomed container whose inclined portion is thickened is manufactured from the disk-shaped workpiece by the press-work having one process, but the present invention is also applicable to a press-work whose thickening target is a bottomed container having an inclined portion which is formed in a separate process, that is, to a press-work whose starting state is  FIG. 3  or  FIG. 7 . 
     INDUSTRIAL APPLICABILITY 
     The present invention is usable for thickening an inclined portion rising from a bottom surface portion of a bottomed container.