JP2006289480A - Press forming method and metal mold used for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase accuracy of an angle between a longitudinal wall and a flange and increase degree of flatness of the flange when forming a hat type molding. <P>SOLUTION: A final molding 12 with a hat type cross is press-formed of a metallic blank material 10 by the press forming method. The metal die is provided with a top surface 13, left and right side walls 14, taper parts 16 extended from lower ends of the side walls, and flanges 15 extended from lower ends of the taper parts. A first step S1 for forming an intermediate molding 11 with a hat cross section deeper than the final molding 12 is carried out and a second step S2 for obtaining a hat type cross section of the final molding with is carried out by reshaping the taper parts 16 and the flanges 15 of the obtained intermediate molding 11 into flat flanges 17 in sequence by the press forming method. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a press molding method and a mold used therefor. More specifically, the present invention relates to a method of press-molding a cross-section hat-shaped molded product obtained by drawing or bending a metal plate in plan view by drawing (drawing bending), and a die and a die used in the method.

JP 2004-195535 A JP 2004-314132 A Japanese Patent Laid-Open No. 2004-174551 Nippon Steel Technical Report No. 378 (2003), pages 25-29

  Although reducing the weight of automobiles and improving collision safety are conflicting issues, in recent years, the adoption ratio of high-tensile steel plates for automobile body panels has increased as a means to solve this problem. On the other hand, press forming of high-strength steel plate has higher yield point stress and less elongation than normal steel plate, so it has low shape freezing property to the mold shape, and repeated trial and error on the mold production surface. It takes a lot of man-hours and costs. This is thought to be mainly due to the large influence of the springback phenomenon accompanying press molding.

  In the current technology, the method of dealing with this phenomenon assumes a springback amount in advance, mold making with this change amount in advance, or manufacturing a mold according to the product shape, and correcting the springback amount after a try. Yes. For this reason, several mold corrections are required before obtaining a desired shape. Moreover, when shape | molding in a cross-sectional hat type | mold, the flatness of a flange part is impaired.

  In Patent Document 1, when a metal plate is formed into a U-shaped or L-shaped cross-section, the spring back is alleviated by once bending over to a desired bending angle after being once bent over a desired bending angle. A method is disclosed. According to this method, even when it is bent along a bending line that is curved along the longitudinal direction, twisting can be prevented and molding accuracy is improved. That is, the bending stress of the vertical wall once overbended is bent back to release the residual stress, thereby reducing the spring back (outward warping) of the vertical wall with respect to the top plate.

  In Patent Document 2, when a molded product having a hat-shaped cross section is press-molded, a gap is formed between the base portion of the punch and the die to cause an overrun phenomenon in the metal plate, and the punch that is doubled up and down is used. Among them, a forming method is disclosed in which a metal plate after overrun is bent back with a lower punch. This method is also a method of reducing the residual stress when the vertical wall is drawn, making the vertical wall angle with respect to the top plate accurate, and reducing warpage.

  On the other hand, Patent Document 3 discloses a method for forming a hat-shaped cross-sectional component that reduces warping of a vertical wall by drawing by using a punch that does not use a blank holder and finally bending a flange portion. Yes. This method is, so to speak, a mixed type of drawing and bending.

  Non-Patent Document 1 details the generation mechanism of springback, and refers to the tension control of the vertical wall by overrun similar to Patent Document 2. Further, it is disclosed to perform fixed pressing, to use variable bead molding at the same time, and to apply the cusp at the time of die cutting as coining at the time of fixed pressing.

  None of the conventional molding methods can correct the angle between the top plate and the vertical wall or reduce the warp of the vertical wall. is there. Also, the flatness of the flange is insufficient. An object of the present invention is to increase the accuracy of the angle between the vertical wall and the flange, particularly when forming a hat-shaped molded product that is curved in the longitudinal direction. Furthermore, this invention makes it a technical subject to raise the flatness of a flange.

  The press molding method of the present invention is a final molding of a hat-shaped cross section comprising a metal plate, a top surface, left and right side walls extending downward from both ends of the top surface, and left and right flanges extending from the lower ends of the side walls. A method of press-molding a product, comprising a top surface, left and right side walls, a tapered portion extending from the lower end of the side wall, and a flange extending from the lower end of the tapered portion, a hat cross section deeper than the final molded product A first step of forming an intermediate molded product having a shape and a second step of re-molding the tapered portion and the flange of the obtained intermediate molded product into a flat flange to obtain a hat-shaped cross-sectional shape of the molded product are sequentially performed. It is characterized by that. “Making deeper than the final molded product in the first step” means that an appropriate depth is determined according to the material and thickness of the blank material, and the shape (height and width) of the final molded product. In the embodiment described later, it is molded 5 mm deep.

  The final molded product is preferably one in which at least one of the left and right side walls is curved or bent along the longitudinal direction. The bending and bending include the case of branching in a T shape and the case of crossing in an X shape. Further, the metal plate is preferably a high-tensile steel plate having a tensile strength of 590 to 1470 MPa and a thickness of 0.5 to 3.0 mm.

  The die of the present invention is a die used in the first step of the press molding method described above, and an inclined surface that forms the tapered portion is formed at the die entrance, and the inclined surface and the vertical surface that forms the side wall. Are smoothly connected by a convex curved surface, and the inclined surface and the lower surface forming the flange are smoothly connected by a convex curved surface.

  Furthermore, in the press molding method of the present invention, such a die, a punch having an outer surface shape for forming the top surface, the left and right side walls, and the left and right tapered surfaces of the intermediate molded product, and the taper of the punch It is more preferable to perform the first step using blank holders arranged on the left and right sides outside the surface.

  The mold of the present invention is a mold used in the second step of the above-described press molding method, and includes a die corresponding to the final molded product, a punch, and holders arranged on the left and right of the punch. It is characterized in that cusps are left on the surface of the face or holder. The direction of the cusp is preferably substantially perpendicular to the folding line.

  In the press molding method of the present invention, molding is performed deeper than the desired final molded product in the first step, and molding is performed to the desired final molded product depth in the second step. That is, the taper surface and the flange formed in the first step are re-formed into a flat flange again in the second step. Therefore, the portion along the boundary between the side wall and the taper portion of the intermediate molded product formed at a predetermined taper angle in the first step is forcibly bent to 90 degrees or near in the second step, and the taper is formed. The part is bent back flat, and the boundary between the taper part and the flange is also bent back flat. And since the residual stress is released by such reverse bending back processing, the spring back of the flange is suppressed, and the angle between the flange and the side wall becomes accurate.

  Furthermore, in the second step, the taper portion and the flange portion of the intermediate molded product are reformed into a flat flange portion, so that the side wall itself is hardly bent back. Therefore, processing is smooth.

  When at least one of the left and right side walls of the final molded product is curved or bent along the longitudinal direction, the flat plate material is narrowed down to the side wall having an arcuate cross section in the first step, and The part is narrowed down to a substantially conical tapered portion. At the same time, the outer peripheral portion of the plate material becomes a flange while expanding and contracting in the circumferential direction and the radial direction, that is, in the surface direction of the plate material. And in a 2nd process, since a flange is forcedly expanded outward, it expands-contracts in a surface direction in the opposite direction to a 1st process. Accordingly, the residual stress is further released, and the spring back of the flange is suppressed. Further, in the second step, the flange is plastically deformed in the opposite direction to that in the first step, so that the yield stress is reduced by the Baudinger effect. Therefore, the applied pressure in the second step can be reduced and bending back processing becomes easy.

  When the metal plate is a high strength steel plate having a tensile strength of 590 to 1470 MPa and a thickness of 0.5 to 3.0 mm, the residual stress is particularly reduced, the angle between the side wall and the flange becomes accurate, and the shape freezing property is high. Become.

  Since the die of the present invention includes an inclined surface that forms a tapered portion at the die entrance, a tapered surface that continues from the plate material to the side wall can be formed in the first step of the molding method. Furthermore, since it has a convex curved surface that smoothly connects the inclined surface and the vertical surface that forms the side wall, and a convex curved surface that smoothly connects the inclined surface and the lateral surface that forms the flange, the material inflow resistance is reduced. Can be reduced. In particular, the size of the inclined surface is selected from the viewpoint of shape freezing properties, but the convex curved surfaces provided at the upper and lower ends of the inclined surface are the dimensions of the inclined surface so that the material inflow resistance is appropriate. You can choose your own. Therefore, the material inflow resistance can be made appropriate while improving the shape freezing property.

  In the first step of the press molding method of the present invention, a die having an inclined surface at the die entrance described above, and an outer surface shape for forming the top surface, the left and right side walls, and the left and right tapered surfaces of the intermediate molded product. In the case where the punch is provided and the blank holders arranged on the left and right sides outside the tapered surface of the punch are used, there is a gap between the inclined surface of the punch and the inclined surface of the die during the molding. Therefore, the metal plate that enters the die along the inclined surface of the die is not pinched so as to be in close contact with the inclined surface, and has a somewhat rounded shape. Then, the inclined surfaces are determined and pressed at the bottom dead center of the press, whereby a tapered portion is formed. For this reason, the material can smoothly flow into the die during molding in the middle.

  In the mold of the present invention, since cusps are left on the surface of the die face or the holder, a coining effect can be obtained at the time of final pressing at the time of reshaping. Thereby, the rounded surface formed in the drawing process or the bending process can be removed, and a flat flange surface can be formed.

  When the direction of the cusp is substantially perpendicular to the bend line, the material tends to flow in the direction in which the bending is returned while enhancing the flatness of the flange by the coining effect.

  Next, an embodiment of a press molding method of the present invention and a mold used therefor will be described with reference to the drawings. FIG. 1 is a process diagram showing an embodiment of the press molding method of the present invention, FIG. 2a is a plan view showing an example of a molded product molded by the press molding method of the present invention together with a blank material, and FIG. FIG. 3 is a perspective view showing the molded product of FIG. 2 together with a blank material, FIG. 4 is a process diagram of the main part of the press molding method of FIG. 1, and FIGS. 5a and 5b are first steps of the molding method of the present invention. FIG. 6 is a cross-sectional view showing an embodiment of a mold related to the mold and an operating state cross-sectional view, FIG. 6 is an enlarged cross-sectional view showing a main part of the molding method using the mold shown in FIG. 5a, and FIG. Sectional drawing which shows one Embodiment of the metal mold | die in connection with the 2nd process of a shaping | molding method before and behind shaping | molding, FIG. 8a is sectional drawing which shows the metal mold | die of a reference example, FIG. 8b is principal part process drawing using the metal mold | die, FIG. 9 is a perspective view of a main part showing another embodiment of a mold relating to the second step of the molding method of the present invention, 10a and 10b are plan views showing other examples of molded products to which the molding method of the present invention can be applied, respectively. FIG. 11 is a graph showing a comparison between the molding method of the present invention and the molding method of the reference example. is there.

  The forming method shown in FIG. 1 includes a first step S1 in which a blank 10 obtained by punching a flat metal plate into a predetermined shape is drawn or bent into a cross-sectional hat-shaped intermediate formed product 11, and the obtained intermediate formed product. 11 includes a second step S2 for re-molding 11 into a final molded product 12. Here, the “hat type” is a shape including a top surface 13, left and right side walls 14 extending downward from the left and right ends of the top surface, and flanges 15 and 17 extending outward from the lower ends of the side walls 14. It is. Actually, processes such as a trimming process and a drilling process are added as necessary after the second process.

  As shown in FIG. 2a, the blank 10 has a substantially "<" shape that is curved or bent in the middle. The intermediate molded product and the final molded product have a hat-shaped cross section as shown in FIG. It becomes a continuous form with substantially the same cross-sectional shape in the axial direction while being curved. The material of the blank material 10 is not particularly limited, but in order to effectively utilize the advantage of preventing the spring back according to the present invention, the spring back is large in normal processing such as a high-tensile steel plate having a tensile strength of 590 to 1470 MPa, aluminum or the like. Is preferred. The plate | board thickness of the blank material 10 is about 0.5-3.0 mm, for example.

  In the prior art, the drawing depth in the drawing process or the bending depth in the bending process is set to be the same as the final molded product dimension, and the amount of deformation due to springback is corrected in the remolding process to obtain the final molded product dimension. However, in the molding method of FIG. 1, the drawing depth in the first step S1 is formed to be about 3 to 6 mm deeper than the final molded product 12, and is bent back to the final molded product size in the re-molding process. ing. The height A1 of the intermediate molded product obtained in the first step S1 is about 3 to 6 mm higher than the height A2 of the final molded product 12 in the second step S2 (A1> A2), and the width B1 is that of the final molded product 12. It is narrower than the width B2 (B1 <B2).

  In the embodiment of FIG. 1, a tapered portion 16 is interposed between the side wall 14 of the intermediate molded product 11 and the flange 15 in order to cover the amount of bending return. That is, when bending back in the second step S2, the side wall 14 cannot be bent back, so the taper portion 16 is provided to realize the bending back processing. In the second step S <b> 2, the taper portion 16 and the flange 15 are bent back to extend flatly to obtain the flange 17 of the final molded product 12.

  In that case, as shown in FIG. 4, the length a of the taper portion 16 of the intermediate molded product 11, the length b of the flange 15, the transition region of the side wall 14 and the taper portion 16, and the transition region of the taper portion 16 and the flange 15. The total sum of the circumferential lengths e of each round is substantially equal to the sum of the length d of the flange 17 of the final molded product 12 and the circumferential length (c × π / 2) of the transition region of the side wall 14 and the flange 17. Become. As a result, the product height is lowered by the height of the tapered portion 16. In addition to the substantially flat tapered surface, the tapered portion 16 includes a substantially conical surface in a portion that is curved in a plan view like the curved portion 18 in FIG. 2A. .

  The curved portion 18 protruding in an arc shape outwardly of the blank 10 in FIG. 2a is compressed in the circumferential direction while being extended in the radial direction in the first step S1, and compressed in the radial direction in the second step S2. While being stretched in the circumferential direction. For example, the range of the arcuate outer peripheral edge (a0-b0) is temporarily compressed to (a1-b1) in the first step S1. And when it bends back in 2nd process S2, it is extended to the range of (a2-b2). Such deformation is the same not only for the flange 15 of FIG. 1 but also for the tapered portion 16 and the side wall 14. As described above, since the direction of plastic deformation in the first step and the plastic deformation in the second step are opposite in the bending portion 18, the internal stress remaining in the first step is released in the second step. .

  Further, since the deformation directions are opposite in the first step and the second step, there is an advantage that the yield stress in the second step is lowered by the Baudinger effect and the formability is improved. This advantage is particularly effective in the processing of high-tensile steel sheets with high yield stress.

  Note that the bending direction 19 that is concave outward in the upper side of FIG. 2a is also reverse in the direction of deformation, but is stretched in the circumferential direction in the first step S1, compressed in the radial direction, and the second step. In S2, it is compressed in the circumferential direction and stretched in the radial direction. Therefore, as in the case of convex outward, the direction of plastic deformation is reversed between the first step and the second step, and the internal stress remaining in the first step is released in the second step. Accordingly, the spring back based on the residual stress is reduced, and the molding accuracy of the flange 17 of the final molded product 12 is increased.

  Next, an embodiment of a mold for performing the molding method of FIG. 1 will be described with reference to FIGS. These molds are also the molds of the present invention. The mold set 20 in the first step shown in FIGS. 5 a and 5 b is composed of a die 21 that is an upper mold, a punch 22 that is a lower mold, and a blank holder (wrinkle presser) 23.

  As shown in FIG. 5 a, a concave groove 24 corresponding to the intermediate molded product 11 is formed on the lower surface of the die 21. When the molded product is curved or bent halfway as shown in FIG. 2, the concave groove 24 is also curved or bent halfway. In addition, an inclined surface (C surface) 25 is formed at the entrance portion of the die 21 instead of a general round surface shape in the die entrance shape of the drawing step, and upper and lower corners are connected by convex curved surfaces 26 and 27, respectively. It has a shape. The angle of the inclined surface 25 is usually 45 degrees, but may be in the range of 30 to 60 degrees.

  The height h and the width w of the inclined surface 25 are determined by the amount of bending back in the second step (reforming step), but are usually about 3 to 6 mm. The radius of the curved surface connecting the corners is about 1 to 3 mm. The material of the die 21 may be the same as that of the prior art, and surface treatment such as PVD (physical vapor deposition) may be applied as a countermeasure against abrasion and baking as in the prior art.

  In the prior art, since the die entrance shape of the drawing process is easy to design and machine, a rounded surface is generally adopted (see FIG. 8a). By the way, in order to carry out the bending back, which is a feature of the present invention, the setting of the bending back amount is important. This bending back amount is determined by the height of the die entrance shape, that is, the curvature radius in the case of a curved surface. . This is because the amount larger than the height of the die entrance shape cannot be bent back because the side wall (vertical wall portion) 14 of the product exists. On the other hand, the dimension setting of the radius surface of the die entrance shape determines the resistance when the material flows in.

  However, the radius of the rounded surface determined by the inflow resistance of the material is generally different from the radius of the rounded surface determined by the amount necessary for bending back. For this reason, there is a conflicting problem that if one is made an appropriate radius, the other radius cannot be made appropriate. In the present invention, the die entrance shape is an inclined surface having the most appropriate size in view of the necessary amount of bend back, and the material inflow resistance is formed at the boundary between the inclined surface and the side wall and between the inclined surface and the lower surface. From this point of view, by forming a convex curved surface having the most appropriate radius, both of the above conflicting conditions were successfully satisfied.

  As shown in FIG. 5 a, a rounded surface 32 similar to the conventional one is formed at the boundary between the inner surface 30 and the inner bottom surface 31 of the groove 24. The radius r1 of the rounded surface 32 is about 2 to 5 mm larger than the radius (r2 in FIG. 7) of the rounded surface of the final molded product. The distance between the left and right inner surfaces 30 is equal to the distance between the outer surfaces of the left and right side walls 14 of the final molded product. The dimension between the inner bottom surface 31 and the lower surface (die face) 33 of the die is the same as the dimension obtained by subtracting the plate thickness from the height of the intermediate molded product 11 (A1 in FIG. 1). Although not shown, a conventionally known knockout mechanism such as a knockout pin is provided on the inner bottom surface 31 of the die.

  The punch 22 has a contour or a cross-sectional shape corresponding to the inner surface of the intermediate molded product 11, and includes a top surface 35, left and right side surfaces 36, and a tapered surface 37 continuing from these side surfaces. An outer surface 38 facing the inner surface of the blank holder 23 with a slight gap extends from the lower end of the tapered surface 37. A relief surface 39 is formed below the outer surface 38. The top surface 35 and the side surface 36 are connected by a smooth convex surface 40. The side surface 36 and the tapered surface 37 are also connected by a smooth concave surface 41 having a small radius. The material of the punch 22 may be the same as that of the conventional one, and surface treatment such as PVD may be performed as in the conventional case.

  In the conventional drawing process, for example, as shown in FIG. 8a, the boundary between the punch 72 and the blank holder 74 is generally set at the base of the product flange 17, but in the mold of the first process in FIG. In order to reliably generate this, the punch 22 is also provided with a tapered surface 37 in accordance with the inclined surface 25 of the die 21, and the boundary thereof is shifted to the outside of the tapered surface 37. Even if the inclined surface 25 is attached only to the die 21, the workpiece does not conform to the inclined surface in the drawing process, and the blank material 10 flows in a curved shape as shown in FIG. When the drawing is completed, the die 21 and the punch 22 are pressed to generate a predetermined tapered surface shape.

  As shown in FIG. 5a, the blank holder 23 is a thick plate-like member surrounding the punch 22, and is held up and down with respect to the punch 22 and is directed upward by a die cushion via a cushion pin (not shown). Is being energized. However, the rising end of the blank holder 23 is regulated so that the upper surface 46 stops at a position slightly higher than the top surface 35 of the punch 22. This rising end may be the rising end of the die cushion.

  The blank holder 10 is sandwiched between the upper surface 46 and the lower surface 33 of the die (see FIG. 6) to provide resistance to the inflow of the material. The blank holder 23 is provided with a space 47 into which the punch 22 is inserted, and the distance between the left and right inner surfaces 48 of the space 47 is set to be a size that fits with the outer surface 38 of the punch (see FIG. 5b). A relief surface 49 is formed below the inner surface 48. Since the inner surface 48 is dimensioned so as to substantially fit with the outer surface 38 of the punch, a gap 50 corresponding to the width of the tapered surface 37 is formed between the inner surface 48 and the side surface 36 of the punch.

  To perform the first step, the die 21 of the mold set 20 is attached to a press slide, and the punch 22 is fixed to the press bolster. The blank holder 23 is held by the die cushion as described above. When the slide is at the top dead center, as shown in FIG. 5 a, the die 21 is raised, and the blank holder 23 is also raised to a position substantially flush with the punch 22. In this state, the blank material 10 is placed on the blank holder 23 and the slide is lowered. During the lowering, as shown in FIG. 6, the die 21 and the blank holder 23 sandwich the periphery of the blank material 10, and the blank material 10 is pressed against the surface of the punch 22 at the die entrance and bent while being squeezed.

  At that time, the inclined surface 25 of the die is separated from the tapered surface 37 of the punch and does not sandwich the blank material 10. Therefore, the blank material 10 does not adhere to the inclined surface 25 and is bent while being gently curved from the lower convex curved surface 27 to the upper convex curved surface 26, and then the inner side surface 30 of the die and the side surface 36 of the punch. It is extended to be flat again. Each part of the blank material is processed into the side wall 14 of the intermediate molded product while receiving such bending and extending in order. In that case, it is bent smoothly by adjusting the bending radius of the bent portion. In addition, the residual stress is less than when the drawing bending process is suddenly performed using the mold in the second step. Further, the blank material 10 is strongly sandwiched between the lower surface 33 of the die and the blank holder 23, and the resistance of the material flow is appropriately maintained by the convex curved surface 27 at the lower end of the inclined surface 25, so that wrinkles and cracks are maintained. Can be prevented.

  When the slide of the press comes to the bottom dead center, as shown in FIG. 5b, the corresponding portion of the blank 10 is clamped by the inclined surface 25 of the die and the tapered surface 37 of the punch. The taper portion 16 having a linear cross section is formed at a desired inclination angle as in one step S1. At the bottom dead center, the top surface 35 of the punch and the inner bottom surface 31 of the die sandwich the center portion of the blank 10, and a desired round surface is formed on the top surface 13 of the intermediate molded product and the corner portion 51 of the side wall 14. The

  The mold set 52 in the second step shown in FIG. 7 includes a die 54 having a small-diameter curved surface 53 at the die entrance, a punch 43 having a contour corresponding to the inner shape of the final molded product, and a periphery of the punch. And a holder 44 to be arranged. The punch and the holder 44 are usually formed separately, but may be integrally formed. The blank holder used in the first step is not adopted. The inner bottom surface 55 and the inner side surface 56 of the die are connected by a rounded surface 57 corresponding to the outer surface shape of the final molded product having a smaller diameter (radius r2) than that in the first step. Since the height of the punch 43 is adjusted to the height of the final molded product, it is lower than the height of the intermediate molded product 11.

  When the intermediate molded product 11 is put on the punch of the mold set 52 in the second step and the slide is lowered, the lower surface 60 near the entrance of the die 54 near the bottom dead center closes the upper end of the tapered portion 16 of the intermediate molded product 11. Start pressing toward the holder 44. At that time, since there is a gap between the lower surface 60 of the die and the holder 44, the taper portion 16 expands while sliding outward. Similarly, the flange 15 of the intermediate molded product 11 extends outward. Then, it continues to descend while pressing down the taper portion 16 on the lower surface 60 of the die, and so-called pressing is performed at the bottom dead center as shown in the lower side of FIG. As a result, the corner portions of the side wall 14 and the flange 15 are re-formed with a desired bending radius, and a new flange 17 is obtained. The difference S between the flange width of the intermediate molded product 11 and the flange width of the final molded product 12 shown in FIG.

  At the time of pressing, the top surface 13 of the molded product is sandwiched between the inner bottom surface 55 of the die and the top surface 62 of the punch, and the bending radius between the top surface 13 and the side wall 14 is reset to a desired dimension. Mold. Thereby, the final molded product 12 with less spring back is obtained.

  FIG. 8a shows a die for the first step as a reference example, which does not give an inclined surface to the punch and die. The die 64 of the mold set 63 of this reference example has a curved surface 65 without an inclined surface formed at the entrance. The punch 72 is not formed with a tapered surface like the punch 22 of FIG. 5B and is fitted to the blank holder 74. FIG. 8 b shows a case where bending back is performed in the second step from the intermediate molded product 67 having the rounded portion 66 formed by the curved surface 65. The sum of the circumference (a × π / 2) of the rounded portion 66 of the intermediate molded product 67 and the length b of the flange 68 is the length d of the flange 70 of the final molded product 69 and the transition region of the side wall 71 and the flange 70. Is equal to the sum of the circumference (c × π / 2). Therefore, it is possible to perform bending back processing.

  However, as described above, in order to make the flow resistance of the material appropriate, the radius of curvature is considerably small, and it is difficult to provide a sufficient difference in height between the intermediate molded product 67 and the final molded product 69 necessary for the bending back process. . In addition, since the concave or tapered surface corresponding to the curved surface 65 is not formed on the punch 72, the bending radius is not accurately formed. Furthermore, since it is difficult to return the bending fold of the bending radius to a flat shape, a large spring back of the flange 70 occurs when the bending is returned in the second step.

  FIG. 9 shows another embodiment of the punch and holder used in the second step. The punch 73 is substantially the same as in the case of FIG. 7, but a cusp 75 that is a cutting mark at the time of machining is intentionally left on the surface of the blank holder 74. The pitch p of the cusp 75 depends on the feed width of a tool used for cutting, for example, a ball end mill. The direction of the cusp 75 is preferably along the direction in which the material is bent back. In this embodiment, the cusp 75 is perpendicular to the fold line.

  When the cusp 75 is left as described above, the bending wrinkles in the first step can be removed by the coining effect, as in the case of flattening correction such as a seven-point smoothing (star strike), and a flat flange surface can be formed. Can be formed. In the case of FIG. 9, the cusp remains in the blank holder 74, but the cusp may remain on the lower surface (die face) of the die or may be formed on both.

  In the case of FIGS. 2a, 2b, and 3, the molded product is bent in the middle, but the press molding method of the present invention can be applied to a substantially straight molded product, and in that case as well, a spring is applied to some extent. The shape freezing property can be increased by suppressing the back. However, a molded product that is curved or bent halfway is more effective than a straight molded product. Further, the molding method of the present invention has a planar shape in which straight lines or curves are combined, such as a molded product 76 having a substantially T-shaped planar shape shown in FIG. 10a and a molded product 77 having a substantially X-shaped planar shape shown in FIG. 10b. It can also be applied to molded products. In the case of these molded products 76 and 77, the shape freezing property is high because the side wall includes a portion 78 that is curved or bent outwardly in a concave shape.

  In the above embodiment, the die is fixed to the slide of the press and the punch is fixed to the bolster. However, if an appropriate die cushion is used, the die can be fixed to the bolster and the punch can be fixed to the slide.

Next, effects of the present invention will be described with reference to examples and reference examples.
[Example 1]
A high-tensile steel plate with a thickness of 1.0 mm and a tensile strength of 980 MPa is punched into the shape shown in FIG. 2a (width 250 to 400 mm, length 900 mm along the center line), and 5 mm deeper than the final molded product with the mold shown in FIG. Drawing was performed in one step, and then re-molding was performed using the mold shown in FIG. A die having the cusp of FIG. 9 was used for the punch-side flange reshaping surface. The angle of the inclined surface of the die of the mold used in the first step was 45 degrees, the width w and the height h were 4 mm, and the radius of the curved surfaces above and below the inclined surface was 2 mm. The maximum height of the final molded product is 50 mm, and the maximum distance between the outer surfaces of the side walls is 90 mm.

[Example 2]
The first step and the second step were performed using the same blank material as in Example 1 except that a high-tensile steel plate having a tensile strength of 590 MPa was used.
[Reference Example 1]
The same blank material as in Example 1 was subjected to hat bending molding (first step) using the mold shown in FIG. 8a and re-molded (second step) using the mold shown in FIG. There is no cusp on the punched flange forming surface.
[Reference Example 2]
The same blank material as in Example 2 was subjected to hat bending using the mold shown in FIG. 8a, and re-formed using the mold shown in FIG.

  In order to measure the spring back, the products molded in Examples 1 and 2 and Reference Examples 1 and 2 were placed on a surface plate, and the height of the lift of the flange surface from the surface plate was measured with a height gauge. The measurement results in these cases are shown in Table 1 and the graph of FIG.

  As is clear from Table 1 and FIG. 11, it can be seen that the springback amounts of Examples 1 and 2 are as small as about 1/2 of Reference Examples 1 and 2, respectively.

It is process drawing which shows one Embodiment of the press molding method of this invention. Fig. 2a is a plan view showing an example of a molded product molded by the press molding method of the present invention together with a blank material, and Fig. 2b is an end view of the molded product. It is a perspective view which shows the molded article of FIG. 2 with a blank material. It is a principal part process drawing of the press molding method of FIG. 5a and 5b are a sectional view and an operational state sectional view showing an embodiment of a mold relating to the first step of the molding method of the present invention, respectively. It is principal part sectional drawing which shows the state in the middle of shaping | molding of the shaping | molding method using the metal mold | die of FIG. 5a. It is sectional drawing which shows one Embodiment of the metal mold | die in connection with the 2nd process of the shaping | molding method of this invention before and behind shaping | molding. FIG. 8A is a cross-sectional view showing a mold of a reference example, and FIG. 8B is a main process diagram using the mold. It is a principal part perspective view which shows other embodiment of the metal mold | die in connection with the 2nd process of the shaping | molding method of this invention. 10a and 10b are plan views showing other examples of molded products to which the molding method of the present invention can be applied, respectively. It is a graph which compares and shows the shaping | molding method of this invention, and the shaping | molding method of a reference example.

Explanation of symbols

S1 1st process S2 2nd process 10 Blank material 11 Intermediate molded product 12 Final molded product 13 Top surface 14 Side wall 15 Flange A1 Height of intermediate molded product A2 Height of final molded product 16 Taper part 17 Flange 18 of final molded product Outwardly convex curved portion 19 Outwardly concave curved portion 20 Mold set 21 Die 22 Punch 23 Blank holder 24 Die groove 25 Die inclined surface 26, 27 Die convex curved surface h Die inclined surface Height w Width of die inclined surface 30 Die inner surface 31 Die inner bottom surface 32 Die radius surface r1, r2 R radius radius 33 Die lower surface 35 Punch top surface 36 Punch side surface 37 Punch taper surface 38 Punch outer surface 39 Punch flank 40 Punch convex surface 41 Punch concave surface 43 Second step punch 44 Holder 46 Blank holder top surface 47 Blank holder Blank space 48 Blank holder inner surface 49 Relief surface 50 Gap 51 Corner portion 52 Second step mold set 53 Curved surface 54 Second step die 55 Die inner bottom surface 56 Inner side surface 57 Round surface 60 Die lower surface 62 Punch Top surface 63 Mold set 64 Die 65 Curved surface 66 Round portion 67 Intermediate molded product 68 Flange 69 Final molded product 70 Flange 71 Side wall 72 Punch 74 Blank holder 75 Cusp p Cusp pitch

Claims (7)

This is a method of press-molding a metal plate from a top surface, left and right side walls extending downward from both ends of the top surface, and a hat-shaped cross-sectional final product having left and right flanges extending from the lower ends of the side walls. And
A first molding formed into an intermediate molded product having a hat cross-sectional shape deeper than the final molded product, comprising a top surface, left and right side walls, a tapered portion extending from the lower end of the side wall, and a flange extending from the lower end of the tapered portion. Process,
A press molding method in which the taper portion and the flange of the obtained intermediate molded product are re-molded into a flat flange to sequentially perform the second step of obtaining the hat-shaped cross-sectional shape of the final molded product.   The press molding method according to claim 1, wherein at least one of the left and right side walls of the final molded product is curved or bent along the longitudinal direction.   The press forming method according to claim 1, wherein the metal plate is a high-tensile steel plate having a tensile strength of 590 to 1470 MPa and a thickness of 0.5 to 3.0 mm. A die used in the first step of the press molding method of claim 1,
An inclined surface that forms the tapered portion is formed at the die entrance, and the inclined surface and the vertical surface that forms the side wall are smoothly connected by a convex curved surface, and the inclined surface and a lower surface that forms a flange are formed. Die smoothly connected by convex curved surfaces.   A die according to claim 4, a punch having an outer surface shape for forming a top surface, left and right side walls and left and right tapered surfaces of the intermediate molded product, and left and right outside the tapered surface of the punch. The press molding method according to claim 1, wherein the first step is performed using a blank holder.   A die used in the second step of the press molding method according to claim 1, comprising a die corresponding to a final molded product, a punch, and holders arranged on the left and right of the punch. Mold with cusps on the surface. The mold according to claim 6, wherein the direction of the cusp is substantially perpendicular to the folding line.

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