JP5217928B2 - Press working method and press molded body - Google Patents

Description

  The present invention relates to a method of pressing an end portion of a material such as a thin steel plate into a curved shape without using a blank holder, and a press-molded body formed by this method. In the present specification, press working means bending and drawing.

  In the manufacturing process of industrial products typified by automobile parts, parts of various shapes (press-formed bodies) are manufactured by a press-forming method using a thin steel plate or the like as a raw material. Most of them are formed by bending or drawing an end portion of a flat plate-like material. In that case, there is not much problem when the press-formed body is processed along a straight line, but when the ridgeline of processing is a curve, that is, when bending into a shape having a curvature when viewed in plan As shown in FIG. 1, the line length D1 before molding of the end portion of the material does not match the line length D2 after molding. For this reason, when D1> D2, wrinkles and buckling are likely to occur, which lowers the molding quality. In FIG. 1, 1 is the upper surface of the material, 2 is the vertical wall surface, and 3 is the flange surface. The flange surface is also called a face surface.

  Suppression of wrinkles that occur in the material forming part due to press molding is a long-standing problem. For example, in Patent Document 1 and Patent Document 2, a material is fixed to suppress wrinkles when performing drawing by press. It has been proposed to suppress the material inflow during the molding process by providing an uneven bead on the blank holder and imparting an uneven shape to the face surface of the press-formed body.

However, since the techniques of Patent Document 1 and Patent Document 2 are both provided with beads in the blank holder, they cannot be applied when the blank holder is not used. In addition, if a blank holder is provided with a bead to suppress the inflow of the material, large expansion and contraction of the material will be allowed, and the amount of strain of the material will increase, and consequently residual tensile and compressive stress will work according to this amount of strain. As a result, the spring back after press molding becomes large, and the dimensional accuracy of the press-molded body decreases. Furthermore, there is a drawback in that the material requires a surplus portion of the wrinkle holding portion, and the yield of the material is reduced accordingly.
Japanese Patent Laid-Open No. 2004-9107 JP 2007-245188 A

  Therefore, the object of the present invention is to solve the above-mentioned conventional problems and effectively suppress wrinkling and buckling of the material forming portion when pressing into a shape having a curvature when the end portion of the material is viewed in plan. A technology that can improve the dimensional accuracy by suppressing residual tensile / compressive stress, and can improve the yield of the material without the need to provide a surplus portion of the wrinkle holding portion in the material. Is to provide.

The press working method of the present invention made to solve the above-mentioned problem is that the central part of a flat plate-like material is supported by a pad, has a curvature when viewed in plan, and has a side view. Sometimes, in the processing method of pressing into a shape having a flange surface below the vertical wall surface, a convex bead protruding in a convex shape is applied to the vertical wall surface, and the flange surface directly below the flange surface crosses the flange surface and extends from the flange surface. By providing a concave bead recessed in a concave shape, wrinkle generation in the material molded portion is suppressed.

  As described in claim 3, the sum of the line lengths of the longitudinal cross sections of the convex beads and the concave beads is La, and the line length of the longitudinal cross section of the corresponding portion before applying these beads is Lb. When the value obtained by dividing the difference between La and Lb by Lb is within the critical elongation limit for each material strength, the line length D2 of the cross section of the concave bead, and the line length D1 of the corresponding part of the material before press forming In this case, it is preferable that the value obtained by dividing the difference between D2 and D1 by D1 is within the breaking limit elongation for each material strength.

Further, the press-formed body of the present invention made to solve the above problems has a curvature when the end of the flat plate-like material is viewed in plan, and a flange surface below the vertical wall when viewed from the side. A press-molded body processed into a shape having a convex bead protruding in a convex shape on the vertical wall surface, and the flange surface directly below it is transverse to the flange surface and recessed from the flange surface into a concave shape. A concave bead is provided.

  As described in claim 4, the sum of the line lengths of the longitudinal cross-sections of the convex beads and the concave beads is La, and the line length of the vertical cross-section of the corresponding part before applying these beads is Lb. When the value obtained by dividing the difference between La and Lb by Lb is within the breaking limit elongation for each material strength, the line length D2 of the cross section of the concave bead, and the line length D1 before press forming of the corresponding part of the material In this case, the value obtained by dividing the difference between D2 and D1 by D1 is preferably within the breaking limit elongation for each material strength.

  According to the present invention, by forming an uneven bead on the vertical wall surface of the press-formed body that has been pressed and the flange surface directly below, the wire length in the material stage in both the longitudinal direction and the longitudinal direction, The line length of the corresponding part of the press-formed body can be made substantially equal. As a result, generation of wrinkles during press working can be suppressed. Unlike the prior art in which a bead is provided in a blank holder, the present invention does not give a large stretch or shrinkage to a material, and therefore, the residual tensile / compressive stress of a press-formed product can be suppressed and dimensional accuracy can be improved. Further, in the present invention, since it is not necessary to provide a surplus portion of the wrinkle holding portion in the material, the yield of the material can be improved.

  In particular, if these bead shapes have the dimensions described in claims 2 and 4, the material is hardly stretched or shrunk, and therefore more preferable results in the effect of preventing wrinkle generation and the effect of improving dimensional accuracy. Can be obtained.

Preferred embodiments of the present invention are shown below.
In the present embodiment, as shown in FIG. 2, the center portion of the material is supported by the pad 4 and has a curvature when the end portion of the material is viewed in plan using a press mold not provided with a blank holder. The shape is press-molded by the bending blade 5. 6 is a punch. In FIG. 2, the material is placed on the upper surface of the punch 6 and pressed by the pad 4, and a pair of bending blades 5 are lowered on both sides of the punch 6 so that the ends on both sides of the material are the outer shape of the punch 6. Bend along. In this specification, in order to make the explanation easy to understand, the upper and lower relations are described on the assumption that the material is set on the upper surface of the punch 6 and bent as shown in FIG. As is obvious, it is possible to invert the top and bottom of FIG. 2 and to lower the punch 6 toward the inside of the bending blade 5. In addition, if the blank holder 7 shown with the broken line in FIG. 2 is added, a drawing process can be performed.

  As shown in FIGS. 3 and 4, the press-molded body has a flange surface 3 below the vertical wall surface 2 when viewed from the side. In the present invention, the press-molded body projects in a convex shape on the vertical wall surface 2 of the press-molded body. By providing the convex bead 10 and also by providing the concave bead 20 recessed in a concave shape on the flange surface 3 immediately below, the line length in the material stage and the line length of the corresponding part of the press-formed body The difference is reduced or preferably zero. The shape of these beads will be described in detail below. However, as shown in FIG. 3, the shape of the bead is gently protruding from the vertical wall surface 2 or the shape of protruding from the vertical wall surface 2 as shown in FIG. It is good.

  5 and 6 are an enlarged perspective view of the bead shown in FIG. 3 and a central longitudinal sectional view thereof. In these drawings, A is the vertical wall reference surface (same as the vertical wall surface 2) of the press-formed body, B is the flange surface reference surface (same as the flange surface 3), and C is the surface of the central overhanging portion 11 of the convex bead 10. , D is the central surface of the concave bead 20. As is apparent from FIG. 6, the convex bead 10 projects from the vertical wall surface 2 into a convex shape, and the concave bead 20 is recessed from the flange surface 3 into a concave shape. Note that both side surfaces 12 of the central overhanging portion 11 are inclined surfaces toward the vertical wall surface 2, and both side surfaces 21 of the concave bead 20 are inclined surfaces toward the flange surface 3.

  7 and 8 are an enlarged perspective view of the bead shown in FIG. 4 and a central longitudinal sectional view thereof. Also in these drawings, A is a vertical wall reference surface (same as the vertical wall surface 2), B is a flange surface reference surface (same as the flange surface 3), C is the surface of the convex bead 10, and D is concave. It is the center part surface of the bead 20. The difference is in whether the surface C of the convex bead 10 is a flat slope or a stepped slope, but it protrudes from the vertical wall surface 2 into a convex shape, and the flange surface 3 is recessed in a concave shape. It is common.

  In the present invention, by forming the convex bead 10 and the concave bead 20 on the press-molded body, the line length in the material stage and the corresponding portion of the press-molded body in both the longitudinal direction and the longitudinal direction are determined. Reduce the difference from the line length to zero or suppress wrinkles. In order to sufficiently exhibit this effect, it is desirable to determine the bead shape so as to satisfy the following conditions.

  9, L1 is a longitudinal wall section line length before beading, L2 is a sectional line length of a flange surface before beading, and L3 is a section of a longitudinal wall convex portion of the bead forming portion. Line length L4 is a cross-sectional line length of the flange surface of the bead forming portion. L1 + L2 ≦ L3 + L4 is set because there is a possibility that wrinkles occur when the line length of the corresponding portion of the press-molded body becomes smaller than the line length in the material stage. However, if the difference between L3 + L4 and L1 + L2 becomes too large, the material may break, so {(L3 + L4) − (L1 + L2)} / (L1 + L2) ≦ εe. Here, εe is the breaking limit elongation for each material strength. Most preferably, L1 + L2 = L3 + L4.

  FIG. 9 is an explanation of the longitudinal line length, but it is necessary to reduce the difference between the longitudinal length and the corresponding line length of the press-formed body in the longitudinal direction. For this reason, as shown in FIG. 10, D2−D1 ≧ 0, where D1 is the longitudinal length of the material end before molding, and D2 is the longitudinal length of the material end after molding. However, as in the case of FIG. 9, (D2-D1) / D1 ≦ εe. In the present invention, the concave bead 20 is formed to increase the longitudinal length of the end portion of the material after molding, thereby satisfying the above relationship.

  By forming a bead that satisfies the above-described conditions, wrinkles can be reliably prevented from occurring even when the end of the material is bent into a curved shape using a press mold that does not include a blank holder. . Hereinafter, a specific method of determining the size of each bead will be described with reference to FIGS. 11 and 12.

First, a line length difference Δ1 between the end portions of the material before and after forming is calculated geometrically. Next, considering the relationship with other parts and other production technology requirements, the bead number N and the bead width outer diameter W are determined, and the line length absorption amount δ1 (the difference in the line length that can be absorbed by one bead) Is determined. (Δ1 = Δ1 / N). This δ1 is a starting value for obtaining the size shown below. When determining the size of the concave bead 20, as shown in FIG. 11, the one-side opening amount C of the concave bead is determined in consideration of the bead width outer diameter dimension W and the slope angle θ. Here, θ is selected on the condition that any surface constituting the bead does not become a negative angle, and θ is 40 ° to 60 ° for the same condition on any surface. θ = cos ⁻¹ (C / E). However, a relationship of E = C + 0.5 × δ1 is established between the hypotenuse length E and the line length absorption amount δ1, and at this time, the bead depth T is T = C · tan θ. Here, C, E, and T are determined based on the known θ and δl.

Next, a method for determining the size of the convex bead 10 will be described with reference to FIG. First, the depth F of the cross section is F = L1 × (L2) from the vertical wall cross section line length L1 before flange application, the flange cross section line length L2, the cross section line length L4 of the flange surface at the bead forming portion, and the concave bead depth T. -L4) / (L1 + T). Further, the section line length L4 of the flange surface at the bead forming portion is L4 = L1 + L2-L3 = L1 + L2- (L1 ² + F ² ) using the condition that the section line length before and after the bead application is equal (L1 + L2 = L3 + L4). ^It is expressed as ^0.5 × (L1 + T) / L1. Here, F and L4 can be determined based on the known L1 and L2 and T determined as described above. Next, the one-side opening amount G of the convex bead 10 can be determined from the geometric relationship between the depth F and the hypotenuse length K by the equation G = (F ² −0.25δ1 ² ) / δ1. A relationship of K = G + 0.5 × δ1 is established between the hypotenuse length K and the line length absorption amount δ1 of the convex bead 10, and K is determined based on G determined as described above and the known δl. it can. In the bead forming portion, the longitudinal wall convex section cross-sectional line length L3 is L3 = (L1 ² + F ²⁾ from the longitudinal wall sectional length L1 before the bead application, the sectional depth F of the convex bead 10, and the depth T of the concave bead. ) It can be approximately determined by the formula ^0.5 × (L1 + T) / L1. In this way, a bead shape with no line length difference before and after molding can be determined. For actual shape generation, three-dimensional CAD software is used, and dimensions of each part are determined so as to approximate the above-described geometric conditions.

  The shape of the bead to be imparted to the press-formed body has been described above. However, the punch 6 that determines the inner surface shape of the press-formed body and the bending blade 5 that bends the material between the punch 6 have these convexities. Needless to say, it is provided with a concavo-convex structure for providing the bead 10 and the concave bead 20.

  In the above-described embodiment, the projected cross-sectional shape of the convex bead 10 viewed from the top view direction is a shape protruding in a trapezoidal shape, and the projected cross-sectional shape of the concave bead 20 viewed from the front view direction is a shape recessed in a trapezoidal shape. It is. However, the projected cross-sectional shapes of the convex bead 10 and the concave bead 20 may be triangular or quadrangular, and the projected cross-sectional shapes of the convex bead 10 and the concave bead 20 may be triangular or quadrangular. Needless to say, it is included in the scope of the invention. Hereinafter, the difference between these three types of projected cross-sectional shapes will be briefly described.

FIG. 21 schematically shows these three types of cross-sectional shapes. When the protrusion amount is a and the width on one side is b1, the line length (difference between the bead surface line length and the line length without the bead) formed by forming the bead is 2a for the quadrangle, and c−b = ^{(a 2 -b 2) 1/2 -b} , the triangle becomes ^{(a 2 -b 2) 1/2 -b1} . Here, b is the length of the base of a right triangle formed on both sides in the case of a trapezoid, and c is the length of the hypotenuse. In this way, if only the line length that can be earned by simply forming a bead is compared, the quadrangle is maximized, and the line length that can be earned decreases when the corner of the square is dropped like a trapezoid or a triangle. However, in consideration of press formability, an area that cannot be pressed with a quadrangle is generated, whereas a trapezoid or a triangle can be pressed, and a trapezoid is preferable overall.

  Next, considering the ease of wrinkling of the bead shape with reference to FIG. 22, there is a property that thickening, that is, wrinkling, tends to occur at the apexes where the broken lines concentrate in the bead shape. In addition, the smaller the angle of each vertex, the larger the amount of bending, and the tendency to increase the thickness, that is, wrinkles. For example, as shown in FIG. 22, when comparing a trapezoid having the same line length with a triangle, the trapezoid has two vertices, and the angle at one vertex is an obtuse angle, so the amount of bending is small. . On the other hand, in the case of a triangle, it can be considered that the two vertices of the trapezoid overlap each other, and the angle at the vertices becomes an acute angle and the amount of bending increases. As a result, wrinkles are less likely to occur because the trapezoid has a smaller thickness increase, and the wrinkles are more likely to be concentrated in the triangle. For the above reasons, as shown in the embodiment, the projected cross-sectional shapes of the convex beads 10 and the concave beads 20 are best trapezoidal. However, as shown in FIG. 23, the overhanging portion can be constituted by a sine function or a quadratic curve instead of the trapezoid.

  In order to evaluate the workability (wrinkles and cracks) of a press-formed body, the sheet thickness reduction rate before and after material processing is used on site. The inventors actually repeated the pressing of the steel sheet, and for each material strength level, investigated that there is no wrinkle / crack if it is a press-formed body that fits within a certain range of sheet thickness reduction rate, and the following numerical values are used as evaluation indices. Using. For example, in the case of a material having a strength level of 270 MPa, there is no wrinkle / crack if the press-molded body falls within a plate thickness reduction rate of ± 20%. In the case of a 590 MPa class material, there is no wrinkle / crack in the range of −15% to 17%, and there is no wrinkle / crack in the range of −8% to 12% at 980 MPa or more. Wrinkles occur when the lower limit is exceeded, and cracks occur when the upper limit is exceeded. The following examples will be described using the above evaluation indices.

(Example 1) The flat steel plate shown in FIG. 13 was bent so that the material end line length D1 before forming was 247 mm and the material end line length D2 after forming was 217 mm. The bending is a bending along an arc having a vertical wall surface with a radius of curvature of 400 mmR and a flange surface tip with a radius of curvature of 568 mmR. Since the line length difference is 30 mm, three beads are provided as shown in FIG. 14, and the line length absorption per bead is about 10 mm. When each bead was formed into the shape and size shown in FIG. 15, bending forming without any wrinkles could be performed. In the case where no bead was provided, wrinkles were formed on the flange surface. The press-formed body of FIG. 15 was obtained by using a 980 MPa material, and the sheet thickness reduction rate was −7% at the minimum and 10% at the maximum, which was within the standard range. When the bead was not provided, the plate thickness reduction rate was -13% minimum, which was lower than the reference lower limit value -8%, and wrinkles were generated.

(Example 2) When bending was performed under the same conditions as in Example 1, the shape and size of the three beads were changed as shown in FIG. In this case, the amount of overhang of the upper part of the vertical wall surface increases, and the absorbable line length can be increased as compared with the bead of the first embodiment. Also in this example, no wrinkles were generated in the press-formed body. In this case, the thickness reduction rate of the 980 MPa material was -5% at the minimum and 11% at the maximum, which was within the reference range of the index.

(Example 3) The flat steel plate shown in FIG. 17 was bent so that the material end line length D1 before forming was 253 mm and the material end line length D2 after forming was 243 mm. The bending is a bending along an arc having a vertical wall surface with a radius of curvature of 400 mmR and a flange surface tip with a radius of curvature of 890 mmR. Since the line length difference is 10 mm, three beads were provided to make the line length absorption amount 4 mm. The bending process was performed using a press apparatus having a structure shown in FIG. 18, and the punch 6 and the die (corresponding to the bending blade 5 in FIG. 2) were provided with an uneven structure corresponding to the bead. The shape and size of the bead is as shown in FIG. 19, and a press-molded body having no wrinkles could be obtained by one bending. In this case, the thickness reduction rate of the 980 MPa material was a minimum of −3% and a maximum of 8%, which was within the reference range indicated by the index. In the case where no beads were provided, wrinkles were formed on the flange surface exceeding the reference value.

(Example 4) When bending was performed under the same conditions as in Example 3, bending was performed in two stages. The bend shape for pre-bending was as shown in FIG. 20 by numerical simulation, and the bead shape for the second bending was the same as FIG. Even by such two-stage bending, a press-molded body having no wrinkles could be obtained. In this case, the thickness reduction rate of the 980 MPa material was -6% at the minimum and 7% at the maximum, which was within the reference range of the index.

It is a perspective view explaining the edge part line length difference of the raw material before and behind shaping | molding. It is explanatory drawing of the bending method of this invention. It is a perspective view which shows the press molding of this invention. It is a perspective view which shows the press molding of this invention. FIG. 4 is an enlarged perspective view of the bead shown in FIG. 3. FIG. 4 is a central longitudinal sectional view of the bead shown in FIG. 3. FIG. 5 is an enlarged perspective view of the bead shown in FIG. 4. FIG. 5 is a central longitudinal sectional view of the bead shown in FIG. 4. It is explanatory drawing of a preferable bead shape. It is a perspective view explaining the edge part line length difference of a longitudinal direction. It is explanatory drawing of the specific determination method of the size of a concave bead. It is explanatory drawing of the specific determination method of the size of a convex bead. It is a perspective view which shows the bending shape of Example 1. FIG. 1 is a perspective view showing a press-formed body of Example 1. FIG. It is explanatory drawing of the bead shape of Example 1. FIG. It is explanatory drawing of the bead shape of Example 2. FIG. It is a perspective view which shows the bending shape in Example 3. FIG. It is explanatory drawing of the bending method in Example 3. FIG. It is explanatory drawing of the bead shape in Example 3. FIG. It is explanatory drawing of the bead shape for the pre-bending in Example 4. FIG. It is explanatory drawing with the relationship between bead shape and line length. It is explanatory drawing with the relationship between bead shape and wrinkle easiness. It is explanatory drawing which shows the modification of a bead shape.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Upper surface of raw material 2 Vertical wall surface 3 Flange surface 4 Pad 5 Bending blade 6 Punch 7 Blank holder 10 Convex bead 11 Center overhang part 12 Both side surface 20 Concave bead 21 Both side surface

Claims (4)

In the processing method of supporting the center portion of the flat plate material with a pad, having a curvature when the end portion of the material is viewed in plan, and pressing into a shape having a flange surface below the vertical wall surface when viewed from the side, A convex bead that protrudes in a convex shape is applied to the vertical wall surface, and a concave bead that is recessed from the flange surface into a concave shape is applied to the flange surface immediately below the flange surface. A press working method characterized by suppressing generation of wrinkles. A press-molded body processed into a shape having a curvature when viewed from the end of a flat plate material and having a flange surface below the vertical wall when viewed from the side, and projecting into a convex shape on the vertical wall A press-molded product, wherein a convex bead is provided , and a concave bead that is recessed from the flange surface into a concave shape is applied to a flange surface immediately below the convex bead.   When the sum of the lengths of the longitudinal cross sections of the convex beads and the concave beads is La, and the length of the vertical cross section of the corresponding portion before applying these beads is Lb, the difference between La and Lb is Lb. The difference between D2 and D1 is defined as D1 when the value obtained by dividing the value is within the breaking limit elongation for each material strength, the line length D2 of the transverse cross section of the concave bead, and the line length D1 of the corresponding part of the material before press molding. The press working method according to claim 1, wherein the value divided by is within the breaking limit elongation for each material strength.   When the sum of the lengths of the longitudinal cross sections of the convex beads and the concave beads is La, and the length of the vertical cross section of the corresponding portion before applying these beads is Lb, the difference between La and Lb is Lb. When the divided value is within the breaking limit elongation for each material strength, and is the line length D2 of the transverse cross section of the concave bead and the line length D1 of the corresponding part of the material before press molding, the difference between D2 and D1 is The press-formed product according to claim 2, wherein the value divided by D1 is within the breaking limit elongation for each material strength.

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