阅读说明：本技术 冲压成型方法 (Press molding method ) 是由 澄川智史 于 2019-12-27 设计创作，主要内容包括：本发明的冲压成型方法用于成型冲压成型品(1),冲压成型品(1)呈具有顶板部(3)、纵壁部(5)及凸缘部(7)的截面帽形状,并具有凸状弯曲部位(11),该凸状弯曲部位(11)是在侧面观察时沿着长边方向向高度方向凸状地弯曲而形成的,冲压成型方法包括：第一成型工序,冲压成型出中间成型品(21),中间成型品(21)形成有顶板等效部(23)和包含呈沿着长边方向扭曲的形状的扭曲纵壁部(25a)的纵壁等效部(25),并具有凸状弯曲等效部位(31)；以及第二成型工序,将中间成型品(21)冲压成型为目标形状的冲压成型品(1),上述第一成型工序中的扭曲纵壁部(25a)以与顶板等效部(23)形成的角度在端部侧比在凸状弯曲等效部位(31)的长边方向的中央大的方式扭曲。(A press-forming method of the present invention is a press-forming method for forming a press-formed article (1), the press-formed article (1) having a hat-shaped cross section including a top plate portion (3), a vertical wall portion (5), and a flange portion (7), and having a convex bending portion (11), the convex bending portion (11) being formed by bending convexly in a height direction along a longitudinal direction when viewed from a side surface, the press-forming method including: a first molding step of press-molding an intermediate molded article (21), the intermediate molded article (21) having a ceiling equivalent portion (23) and a vertical wall equivalent portion (25) including a twisted vertical wall portion (25a) twisted in the longitudinal direction, and having a convex bending equivalent portion (31); and a second molding step of press-molding the intermediate molded article (21) into a press-molded article (1) having a desired shape, wherein the twisted vertical wall section (25a) in the first molding step is twisted so that an angle formed with the ceiling equivalent section (23) is larger at the end section side than at the center in the longitudinal direction of the convex bending equivalent section (31).)

1. A press-forming method for forming a press-formed product having a cross-sectional hat shape with a top plate portion, a vertical wall portion continuous from the top plate portion, and a flange portion continuous from the vertical wall portion, and having a convex-shaped bent portion formed by bending the top plate portion and/or the flange portion convexly in a height direction along a longitudinal direction when viewed from a side surface,

the press molding method is characterized by comprising:

a first molding step of press-molding an intermediate molded article having a ceiling equivalent portion corresponding to the ceiling portion and a vertical wall equivalent portion corresponding to the vertical wall portion and including a twisted vertical wall portion twisted in a longitudinal direction, and having a convex bending equivalent portion corresponding to the convex bending portion; and

a second molding step of press-molding the intermediate molded product into the press-molded product,

the twisted vertical wall portion in the first molding step is twisted so that an angle formed with the ceiling equivalent portion is larger at an end portion side than at a center in a longitudinal direction of the convex bending equivalent portion.

2. The press-forming method according to claim 1,

the twisted vertical wall portion in the first molding step is set so that a twist amount T obtained from the following equation is in a range of 10 DEG to 20 DEG,

T＝Δθ×(H/L)

wherein the content of the first and second substances,

Δ θ: angle difference (═ theta-₂-θ₁)；

θ₁: an angle (°) formed by the twisted vertical wall portion at the center in the longitudinal direction of the convex bending equivalent portion and the top plate equivalent portion;

θ₂: an angle (°) formed by the twisted vertical wall portion and the ceiling equivalent portion at the end in the longitudinal direction of the twisted vertical wall portion;

h: a vertical wall height (mm) of the twisted vertical wall portion;

l: the longitudinal length (mm) of the twisted vertical wall portion is longer.

Technical Field

The present invention relates to a press forming method, and more particularly to a press forming method for a press formed product having a hat-shaped cross section (hat-shaped cross section) having a top plate portion (web section), a side wall portion (side wall section), and a flange portion (flange section) and being curved convexly in a height direction along a longitudinal direction when viewed from a side surface.

Background

Press forming is a method of transferring the shape of a die by pressing a metal material (metal sheet) such as a steel sheet with a die (press forming). In particular, most of automobile parts (automotive parts) are manufactured by press molding. Recently, from the viewpoint of weight reduction of automobile bodies, there is an increasing tendency to use high-strength steel sheets (high-strength steel sheets) for automobile body parts. However, as the characteristics of steel sheets and other metal materials, there is a tendency that ductility (elongation) is poor when strength is increased, and molding defects such as fracture (fracture) and wrinkles (wrikles) are often generated in press molding of high-strength steel sheets, which is a problem.

Among the frame members of the automobile body, curved members (curved parts) having a sharply curved shape such as front side frames (front side frames) and rear side frames (rear side frames) are difficult to mold because they are likely to be broken or wrinkled when they are manufactured by press molding. Recently, automobile companies and component companies have made studies on the application of high-strength steel sheets to the manufacture of these curved parts in order to further reduce the weight of automobile bodies, and it has become a problem how to perform press forming while preventing cracking and wrinkling.

Some techniques have been proposed so far for press-molding a bent member while suppressing cracking and wrinkling. For example, patent document 1 discloses the following technique: in press forming of an L-shaped member (L-shaped part) which is bent in a plan view, a material is slid on a bottom surface of a male die (punch) by a forming force (forming load) for forming a flange and a vertical wall, thereby preventing wrinkles of the bottom of the male die and cracks of the flange.

Patent document 2 proposes the following method: in a member bent in the vertical direction, a blank (blank) is subjected to drawing forming (drawing forming) while a punch bottom of the blank is pressed in a plate thickness direction by a pusher plate (pad), thereby preventing out-of-plane deformation (out-of-plane deformation) and suppressing wrinkles.

Patent document 3 discloses the following technique: in press forming of a bending press member having a hat-shaped cross section bent in a longitudinal direction, a bending portion (folding portion) is added to an end portion in a width direction of a blank by preliminary forming (preforming), and the bending press member is press formed in a state where the bending portion is left, thereby suppressing generation of wrinkles in a flange portion. According to this technique, since the bending portion to be added to the widthwise end portion of the material in the preliminary molding increases the rigidity (stiffness) of the widthwise end portion, and the resistance (resistance) to the force contracting in the longitudinal direction is increased, even if the force contracting in the longitudinal direction is applied by the excess material (process metal) due to the bent shape, the generation of wrinkles in the flange portion can be suppressed.

Further, some techniques for press-molding a bent member by adding a bead for the purpose of suppressing the occurrence of cracks and wrinkles have been proposed. Patent document 4 discloses the following technique: when the material is press formed in one step into a shape having a curvature (curvature) in a plan view of the end portion of the material and a flange surface below the vertical wall surface in a side view, the vertical wall surface is provided with a convex rib and the flange surface immediately below the convex rib, thereby suppressing the occurrence of wrinkles in the material forming portion.

Patent document 1: japanese patent No. 5168429

Patent document 2: japanese patent No. 5733475

Patent document 3: japanese patent No. 5965159

Patent document 4: japanese patent laid-open publication No. 2010-115674

However, in the technique disclosed in patent document 1, when the punch bottom has a shape such as a seat surface (mounted surface), or when the punch bottom has a closed shape such as a bag shape, the material cannot be moved greatly, and therefore, there are limitations on the members that can be used.

In the technique disclosed in patent document 2, molding is performed using a blank holder and a pusher plate at the same time, and when the molded product is removed from the mold, if the blank holder or the pusher plate is kept in a pressurized state, the molded product is pressed and deformed, and therefore a locking mechanism (locking structure) for preventing movement is required. However, a press machine (press machine) equipped with this mechanism is not common and therefore has poor versatility.

In the technique disclosed in patent document 3, the bent shape of the flange portion needs to be formed flat in the next step, but a bending mark (curl) may remain. In particular, in the case of automobile parts, the flange is often a joint surface (surface for joining) to another part, and high surface accuracy is required, and therefore care must be taken when applying the molding method.

The technique disclosed in patent document 4 has a problem that the rib added to prevent the generation of wrinkles and cracks remains as it is when the press working is performed in one step.

Disclosure of Invention

The present invention has been made to solve the above-described problems, and an object thereof is to provide a press forming method capable of press forming a press-formed product having a cross-sectional hat shape having a top plate portion, a vertical wall portion, and a flange portion and curved in a convex shape in a height direction along a longitudinal direction into a good shape so as to suppress cracking and wrinkling.

A press-forming method according to the present invention is a press-forming method for forming a press-formed product having a hat-shaped cross section including a top plate portion, a vertical wall portion continuous from the top plate portion, and a flange portion continuous from the vertical wall portion, and having a convex bending portion formed by bending the top plate portion and/or the flange portion in a convex manner in a height direction along a longitudinal direction when viewed from a side surface, the press-forming method including: a first molding step of press-molding an intermediate molded product (deformed part) having a top plate equivalent portion (a joint correcting to web) corresponding to the top plate portion and a vertical wall equivalent portion (a joint correcting to side wall) corresponding to the vertical wall portion and including a twisted vertical wall portion (a twisted side wall) having a shape twisted in a longitudinal direction, and having a convex bending equivalent portion (a joint bending to bending curve) corresponding to the convex bending portion (a convex bending portion); and a second forming step of press-forming the intermediate formed product into the press-formed product, wherein the twisted vertical wall portion in the first forming step is twisted so that an angle formed with the ceiling equivalent portion is larger on an end portion side than at a center in a longitudinal direction of the convex bending equivalent portion.

The twisted vertical wall portion in the first molding step may be set so that a twist amount T obtained from the following expression is in a range of 10 ° to 20 °,

T＝Δθ×(H/L)

wherein the content of the first and second substances,

Δ θ: angle difference (═ theta-₂-θ₁)；

θ₁: an angle (°) formed by the twisted vertical wall portion at the center in the longitudinal direction of the convex bending equivalent portion and the top plate equivalent portion;

θ₂: an angle (°) formed by the twisted vertical wall portion and the ceiling equivalent portion at the end in the longitudinal direction of the twisted vertical wall portion;

h: a vertical wall height (mm) of the twisted vertical wall portion;

l: the longitudinal length (mm) of the twisted vertical wall portion is longer.

According to the present invention, shear deformation (shear deformation) can be generated in the twisted vertical wall portion, and the press-formed product can be press-formed into a good shape so as to suppress the occurrence of cracks and wrinkles.

Drawings

Fig. 1 is a view for explaining an intermediate molded article obtained by press molding in the press molding method according to the embodiment of the present invention and a target press molded article (a-1 is a perspective view of the intermediate molded article, (a-2) is a view showing a cross section of a center of a convex bent portion in the intermediate molded article and a cross section of an end portion in a longitudinal direction in a superimposed manner, and (b) is a perspective view of the press molded article).

Fig. 2 is a view (a is a perspective view, (b) is a plan view, and (c) is a side view) illustrating a press-molded article to be molded in the present invention.

Fig. 3 is a cross-sectional view perpendicular to the longitudinal direction of a press-molded article to be molded in the present invention.

Fig. 4 is a diagram illustrating the movement of a material and the portions of the press-formed product where tensile deformation (compressive deformation) and compressive deformation (compressive deformation) occur when the press-formed product to be molded in the present invention is press-formed by a conventional press-forming method.

Fig. 5 is a diagram illustrating the movement of the material when the vertical wall portion is press-formed so as to be shear-deformed in the process of completing the present invention.

Fig. 6 is a view (a is a perspective view, (b) is a plan view, and (c) is a side view) illustrating an intermediate molded product press-molded in the first molding step of the press-molding method according to the embodiment of the present invention.

Fig. 7 is a diagram showing in-plane shear deformation (in-plane shear deformation) in the twisted vertical wall portion of an intermediate molded product which is press-molded by the press-molding method according to the embodiment of the present invention.

Fig. 8 is a diagram showing the vertical wall height and the longitudinal direction length of the twisted vertical wall portion of the intermediate molded product obtained by press molding by the press molding method according to the embodiment of the present invention, which indicates the amount of twist.

Fig. 9 is a view showing a case where the vertical wall height of the twisted vertical wall portion of the intermediate molded product press-molded by the press-molding method according to the embodiment of the present invention is changed ((a) is a perspective view, (b) is a plan view, and (c) is a side view).

Fig. 10 is a view showing a case where the longitudinal direction length of the twisted vertical wall portion of the intermediate molded product press-molded by the press-molding method according to the embodiment of the present invention is changed (where (a) is a perspective view, (b) is a plan view, and (c) is a side view).

Fig. 11 is a view showing an intermediate molded article having a twisted vertical wall portion of a curved surface shape which is twisted in a reverse direction to the twisted vertical wall portion of the intermediate molded article press-molded by the press-molding method according to the embodiment of the present invention ((a) is a perspective view, (b) is a plan view, and (c) is a side view).

Fig. 12 is a view showing in-plane shear deformation in the twisted vertical wall portion that is twisted in the opposite direction to the twisted vertical wall portion of the intermediate molded product press-molded by the press-molding method according to the embodiment of the present invention.

Fig. 13 is a view showing another example of an intermediate molded article press-molded by the press-molding method according to the embodiment of the present invention (where (a) is a perspective view, (b) is a plan view, and (c) is a side view).

Fig. 14 shows another example of the press-molded article to be molded in the present invention ((a) only the top plate portion is curved in a convex manner, and (b) only the flange portion is curved in a convex manner).

Fig. 15 is a diagram illustrating drawing and shape forming (crash forming) applied to the press forming method according to the embodiment of the present invention, (where (a), (b) are drawing and (c) and (d) are shape forming).

Fig. 16 is a diagram illustrating a cross-sectional shape perpendicular to the longitudinal direction of the press-molded product to be molded in this example.

FIG. 17 is a view showing a cross-sectional shape perpendicular to the longitudinal direction of the twisted vertical wall portion of the intermediate molded product obtained by press molding in the present example ((a): a center of convex curvature and (b): an end portion in the longitudinal direction).

Detailed Description

Before the press-forming method according to the embodiment of the present invention is explained, the press-formed product to be formed in the present invention, the cause of the occurrence of cracks and wrinkles when the press-formed product is press-formed, and the process of completing the present invention will be explained. In the present embodiment, the height direction of the press-formed article coincides with the press-forming direction of the press-formed article.

< Press Molding >

As shown as an example in fig. 2 and 3, the press-formed product 1 to be molded in the present invention has a cross-sectional hat shape having a top plate portion 3, a vertical wall portion 5 continuous from the top plate portion 3, and a flange portion 7 continuous from the vertical wall portion 5, and has a convex bent portion 11 formed by bending the top plate portion 3 and the flange portion 7 in a convex manner in the height direction along the longitudinal direction when viewed from the side (fig. 2 (c)), and linear portions 13 extending linearly are provided on both sides in the longitudinal direction of the convex bent portion 11. Here, the convex curved portion 11 is curved convexly in the height direction along the longitudinal direction, meaning that the center of a circular arc curved convexly is located on the flange portion 7 side in a side view.

Fig. 4 shows the movement of the material during press molding when the press molded article 1 is viewed from the side. In the process of press-forming a blank (metal plate), the blank is bent at a punch shoulder arc (punch corner) 4 between the top plate 3 and the vertical wall 5, and the material moves in a direction (direction of an arrow in fig. 4) orthogonal to a bending ridge (ridge) of the punch shoulder arc 4.

Therefore, in the convex bent portion 11, the material in the flange portion 7 is concentrated to shorten the length in the longitudinal direction, while the length in the longitudinal direction of the top plate 3 is lengthened, thereby generating a difference in the length of the line between the top plate 3 and the flange portion 7 in the longitudinal direction. This makes it easy for the top plate 3 to be subjected to tensile deformation and thus to be broken, and makes it easy for the flange 7 to be subjected to compressive deformation and thus to be wrinkled.

Accordingly, in order to suppress the occurrence of cracks and wrinkles when the press-formed product 1 is press-formed, it is considered important to reduce the difference in the length of the line in the longitudinal direction between the top plate 3 and the flange 7 by changing the movement of the material during the press-forming process so that the tensile deformation and the compression deformation do not occur in the top plate 3 and the flange 7 in the convex bent portion 11.

Therefore, it is considered that the top plate 3 and the flange 7 in the convex bending portion 11 are preferably press-formed without a difference in the longitudinal line length therebetween. Fig. 5 shows the movement of the material in an ideal state. In order to prevent a difference in the length of the top plate 3 and the flange 7 in the longitudinal direction, as shown in fig. 5, it is necessary to cause shear deformation in a portion of the blank corresponding to the vertical wall portion 5 (hereinafter referred to as "vertical wall equivalent portion") and move the material in the same direction as the press forming direction. However, in press forming, basically, the die is moved only in the vertical direction, and the material of the vertical wall equivalent portion is not easily subjected to in-plane shear deformation by the limited movement of the die.

The inventors have repeatedly and seriously studied a method of causing the material to generate in-plane shear deformation. As a result, it has been found that the vertical wall equivalent portion in the blank can be subjected to in-plane shear deformation by press-forming the vertical wall equivalent portion into a curved surface shape that is twisted out of plane along the longitudinal direction. The present invention has been made based on the above-described studies, and a press molding method according to an embodiment of the present invention will be described below.

< Press Molding method >

The press-molding method of the present embodiment is a method of press-molding the press-molded article 1 illustrated in fig. 1 (b) and 2 into a target shape, and includes a first molding step of preforming a blank into an intermediate molded article 21 (fig. 1 (a-1), (a-2)), and a second molding step of press-molding the intermediate molded article 21 into the press-molded article 1 of the target shape. The material used in the press molding method of the present invention may be not only a steel sheet but also a plastic material of a thin sheet (sheet), and examples thereof include aluminum alloy sheet (aluminum alloy sheet), magnesium alloy sheet (magnesium alloy sheet), titanium alloy sheet (titanium alloy sheet), and resin sheet (plastic sheet). The material strength (material strength) of the blank is not particularly limited.

First Forming Process

The first molding step is a step of preforming the blank into an intermediate molded article 21 ((a-1) of fig. 1 and (a-2) of fig. 1).

As shown in fig. 1 (a-1), the intermediate formed article 21 has a cross-sectional hat shape having a top plate equivalent portion 23 corresponding to the top plate portion 3 of the press-formed article 1, a vertical wall equivalent portion 25 corresponding to the vertical wall portion 5 of the press-formed article 1 and including a twisted vertical wall portion 25a having a curved surface shape twisted in the longitudinal direction with respect to the vertical wall portion 5, and a flange equivalent portion 27 corresponding to the flange portion 7 of the press-formed article 1, and has a convex bending equivalent portion 31 corresponding to the convex bending portion 11 of the press-formed article 1 and a straight line equivalent portion 33 corresponding to the straight line portion 13.

In the intermediate molded article 21, the twisted vertical wall portion 25a is formed over the entire length of the vertical wall equivalent portion 25 in the longitudinal direction. Fig. 1 (a-2) shows the shape of the cross section orthogonal to the longitudinal direction of the intermediate molded product 21 at the center in the longitudinal direction of the convex bending equivalent portion 31 (hereinafter referred to as "convex bending center") and at the end in the longitudinal direction of the twisted vertical wall portion 25a (hereinafter referred to as "longitudinal end"). For convenience of explanation, the sectional shape shown in fig. 1 (a-2) shows the position of the flange equivalent part 27 in the height direction in alignment.

As shown in fig. 1 (a-2), the vertical wall portion 25a is twisted at an angle θ at the long side direction end portion with the angle formed with the ceiling equivalent portion 23 being taken as θ₂Angle theta at the center of the biconvex curve₁The large way is distorted. Then, along with the twisting, the angle θ formed by the twisted vertical wall portion 25a and the ceiling equivalent portion 23 continuously changes along the longitudinal direction.

In the present embodiment, as shown in fig. 1, the top plate equivalent portion 23 of the intermediate formed product 21 has the same shape as the top plate portion 3 (fig. 2) of the press-formed product 1. In contrast, as shown in fig. 1, the flange equivalent portion 27 of the intermediate molded article 21 is continuous with the vertical wall equivalent portion 25 including the twisted vertical wall portion 25a, which is a shape different from the shape of the vertical wall portion 5, and therefore, as shown in fig. 6 (b) and 6 (c), has a shape different from that of the flange portion 7 of the press-molded article 1 (fig. 2 (b) and 2 (c)) in plan view and side view.

In addition, the angle formed by the ceiling equivalent portion 23 and the twisted vertical wall portion 25a of the intermediate molded article 21 is the end (θ) in the longitudinal direction₂) Specific convex curved center (theta)₁) Large (see (a-2) of fig. 1). Therefore, the height of the intermediate molded article 21 in the height direction is not constant along the longitudinal direction, but is different from the height of the press-molded article 1 in the height direction.

Further, the ridge length of the land portion 24 (fig. 6) between the ceiling equivalent portion 23 and the vertical wall equivalent portion 25 of the intermediate molded product 21 or the ridge length of the land portion (die corner portion)26 (fig. 6) between the vertical wall equivalent portion 25 and the flange equivalent portion 27 is also different from the ridge lengths of the land portion 4 and the land portion 6 (fig. 2) of the press-formed product 1.

For example, when the top plate equivalent portion 23 is formed in the same shape as the top plate portion 3 of the press-formed product 1 of the target shape, the ridge length of the punch shoulder arc portion 24 is the same as that of the press-formed product 1, but the ridge length of the die shoulder arc portion 26 is different from that of the press-formed product 1. In the case where the flange equivalent portion 27 is formed in the same shape as the flange portion 7 of the press-formed product 1 of the target shape, the ridge length of the punch shoulder arc portion 24 is different from that of the press-formed product 1 even if the ridge length of the die shoulder arc portion 26 is formed in the same shape as that of the press-formed product 1.

Second Forming Process

The second molding step is a step of press-molding the intermediate molded article 21 (fig. 1 (a-1) and fig. 1 (a-2)) into a press-molded article 1 (fig. 1 (b)) having a desired shape. In the second molding step, the vertical wall equivalent portion 25 including the twisted vertical wall portion 25a whose angle with the ceiling equivalent portion 23 changes in the longitudinal direction is molded into the vertical wall portion 5 of the target shape. The flange equivalent portion 27 is formed into the flange portion 7 having a desired shape.

Reason why cracking and wrinkling can be suppressed

Next, the reason why a press-formed product that is convexly curved in the height direction along the longitudinal direction when viewed from the side can be press-formed by the press-forming method of the present embodiment so as to suppress cracking and wrinkling will be described.

In the first molding step, as shown in fig. 1, a twisted vertical wall portion 25a having a curved surface shape twisted out-of-plane along the longitudinal direction is formed in the vertical wall equivalent portion 25 corresponding to the vertical wall portion 5 of the press-molded product 1. As described above, when a material (blank) is formed into a curved surface shape that twists out of plane, the material undergoes in-plane shear deformation in addition to out-of-plane shear deformation, as shown in fig. 7.

Thereby, the movement of the material toward the center in the longitudinal direction of the flange equivalent portion 27 in the convex bending equivalent portion 31 is suppressed, and the movement of the material toward the end portion side in the longitudinal direction in the top plate equivalent portion 23 is also suppressed. Therefore, in the twisted vertical wall portion 25a, as shown in fig. 5, the difference in the linear length between the linear length in the longitudinal direction of the roof equivalent portion 23 and the linear length in the longitudinal direction of the flange equivalent portion 27 is small. As a result, in the second molding step, when the intermediate molded article 21 is press-molded into the press-molded article 1 having the desired shape, the top plate portion 3 is prevented from being broken, and the flange portion 7 is prevented from being wrinkled.

Preferable range of the amount of twist of the twisted vertical wall portion

As shown in fig. 7, the press-forming method of the present invention suppresses cracking in the top plate portion 3 and wrinkles in the flange portion 7 of the target press-formed product 1 (fig. 2) by generating in-plane shear deformation in the twisted vertical wall portion 25a in the first forming step.

Here, the magnitude of the in-plane shear deformation in the twisted vertical wall portion 25a depends on the degree of twisting of the twisted vertical wall portion 25 a. In the present invention, the degree of twisting of the twisted vertical wall portion 25a can be expressed by the angle change and the aspect ratio of the twisted vertical wall portion 25 a.

The angle change of the twisted vertical wall portion 25a is an angle θ at the center of convex curvature (center in the longitudinal direction of the convex curvature equivalent portion 31) of the angle formed by the twisted vertical wall portion 25a and the roof equivalent portion 23₁And an angle theta at the end in the longitudinal direction (the end in the longitudinal direction of the twisted vertical wall portion 25a)₂The angular difference Δ θ is obtained (see (a-2) of fig. 1).

As shown in fig. 8, the aspect ratio (aspect ratio) of the twisted vertical wall portion 25a is derived from the ratio H/L of the vertical wall height H to the longitudinal direction length L of the twisted vertical wall portion 25 a. Here, the vertical wall height H and the longitudinal length L of the twisted vertical wall portion are formed in the height and the longitudinal length in the direction orthogonal to the longitudinal direction in the plane of the twisted vertical wall portion 25 a.

The amount of twist T (°) is obtained from the following formula (1).

T＝Δθ×(H/L)＝(θ₂-θ₁)×(H/L) (1)

From the equation (1), it can be seen that in order to change the amount of distortion T, (1) the angle θ formed by the distortion vertical wall portion 25a at the center of the convex curve and the ceiling equivalent portion 23 is changed₁And (2) an angle θ formed by the twisted longitudinal wall portion 25a at the end in the longitudinal direction and the ceiling equivalent portion 23₂The vertical wall height H of the twisted vertical wall portion 25a (3) and the longitudinal length L of the twisted vertical wall portion 25a (4) may be set.

Fig. 9 shows an example of the intermediate molded article 41 in which the height H of the twisted vertical wall portion 25a is changed, and fig. 10 shows an example of the intermediate molded article 61 in which the longitudinal length L of the twisted vertical wall portion 25a is changed.

The intermediate molded article 21 shown in fig. 1 and 6 is formed with a twisted vertical wall portion 25a over the entire length in the longitudinal direction. On the other hand, in the intermediate molded article 61 shown in fig. 10, the longitudinal length L of the twisted vertical wall portion 65a is shorter than the longitudinal length of the vertical wall portion 5 of the press-molded article 1. In the intermediate molded article 61, an angle θ formed by the twisted vertical wall portion 65a at the end in the longitudinal direction and the ceiling equivalent portion 63₂The angle at the end in the longitudinal direction of the vertical wall portion 65a is merely distorted, not the end in the longitudinal direction of the entire intermediate molded article 61.

In addition, as described above, the angle θ formed between the twisted vertical wall portion 25a of the intermediate molded product 21 press-formed in the first molding step and the ceiling equivalent portion 23 needs to be set to the angle at the end in the longitudinal direction₂Angle theta at the center of the biconvex curve₁Is large. For example, as shown in FIG. 11, the angle θ at the end in the longitudinal direction is made₂Angle theta at the center of the biconvex curve₁When small, as shown in fig. 12, the in-plane shear deformation of the twisted vertical wall portion 25a is reversed from that of the twisted vertical wall portion 25a shown in fig. 7. Therefore, even if the intermediate molded product 81 is press-molded into the press-molded product 1 having a desired shape, the difference in the length of the line in the longitudinal direction between the top plate 3 and the flange 7 cannot be reduced, and the effect of suppressing cracking and wrinkling cannot be obtained.

In addition, the amount of distortion T suitable for suppressing cracking and wrinkling was investigated by simulation based on Finite Element Method (FEM). As a result, it was found that if the twist amount T is set in the range of 10 ° to 20 °, both cracking and wrinkling are preferably suppressed. When the twist amount T is less than 10 °, in some cases, the in-plane shear deformation of the twisted vertical wall portion 25a is insufficient. When the twist amount T exceeds 20 °, the twisted vertical wall portion 25a may be subjected to excessive shear deformation in the first molding step, and shear wrinkles (shear wrinkles) may occur in the vertical wall equivalent portion.

The aspect ratio H/L of the twisted vertical wall portion 25a may be obtained using the vertical wall height H at the center of the longitudinal length of the twisted vertical wall portion 25a (the middle position between the center of the convex curve and the longitudinal end) and the longitudinal length L at the center of the vertical wall height.

Intermediate molded article and shape of Press molded article

In the above description, the top plate equivalent portion of each of the intermediate molded article 21 (fig. 1 and 6), the intermediate molded article 41 (fig. 9), and the intermediate molded article 61 (fig. 10) has the same shape as the top plate portion having the target shape, and the flange equivalent portion has a shape different from the flange portion 7 having the target shape.

That is, in the present invention, as in the intermediate molded article 101 shown in fig. 13, the flange equivalent portion 107 may be formed in the same shape as the flange portion 7 (fig. 2) having the target shape, and the top plate equivalent portion 103 may be formed in a shape different from the top plate portion 3 having the target shape.

Even in such an intermediate molded article 101, if the angle θ formed by the twisted vertical wall portion 105a at the end in the longitudinal direction and the ceiling equivalent portion 103 is large, the intermediate molded article can be easily formed₂An angle theta formed by the twisted vertical wall part 105a at the center of the convex curve and the ceiling equivalent part 103₁When the diameter is large, the twisted vertical wall portion 105a formed in the vertical wall equivalent portion 105 is also subjected to in-plane shear deformation as shown in fig. 7 and is press-formed. Therefore, in the press-formed product 1 in which the intermediate formed product 101 is press-formed into a desired shape, both the cracking of the top plate portion 3 and the wrinkling of the flange portion 7 can be suppressed.

However, as shown in fig. 6, if the top plate equivalent portion 23 of the intermediate formed product 21 has the same shape as the top plate portion 3 having the target shape, the intermediate formed product 21 can be stably press-formed without looseness (wobbble) when the intermediate formed product 21 is placed on the punch of the die used in the second forming step, and therefore, it is preferable to form the intermediate formed product 21 in which the top plate equivalent portion 23 having the same shape as the top plate portion 3 having the target shape is formed.

In addition, although both the top plate portion 3 and the flange portion 7 of the press-formed product 1 to be molded are curved in a convex manner in the height direction along the longitudinal direction in the above description, as shown in fig. 14, the press-formed product 121 in which only the top plate portion 123 is curved in a convex manner and the press-formed product 141 in which only the flange portion 147 is curved in a convex manner may be formed as objects to be molded in the present invention.

The above description is directed to a case where a press-formed product having a constant radius of curvature in the longitudinal direction at the convex curved portion 11, such as the press-formed product 1 illustrated in fig. 2, is to be molded. That is, in the present invention, a press-formed product in which a plurality of convex curved portions having different radii of curvature are connected may be used as a molding target.

In this case, for each convex curved portion having a constant radius of curvature, the twisted vertical wall portion in the convex curved portion may have a curved surface shape twisted from the center in the longitudinal direction of the convex curved portion toward the end portion side. In each of the convex curved portions, the angle formed by the roof equivalent portion and the twisted vertical wall portion at the end in the longitudinal direction of the twisted vertical wall portion of the convex curved portion may be larger than the angle formed by the roof equivalent portion and the twisted vertical wall portion at the center in the longitudinal direction of the convex curved portion.

Further, the press-formed product 1 to be molded in the present embodiment has the linear portions 13 on both sides in the longitudinal direction of the convex bent portion 11, but the present invention may be applied to a press-formed product having a linear portion on one side in the longitudinal direction of the convex bent portion, or a press-formed product having only the convex bent portion.

In addition, the angle formed by the top plate 3 and the vertical wall 5 of the press-formed product 1 illustrated in FIG. 2 is constant along the longitudinal direction,that is, as shown in fig. 3, the angle θ at the center of the convex curve (the center in the longitudinal direction of the convex curved portion 11) of the press-formed product 1_1,0An angle theta with the end in the longitudinal direction (the end in the longitudinal direction of the longitudinal wall portion 5)_2,0Are equal. That is, in the present invention, the angle formed by the top plate and the vertical wall portion changes along the longitudinal direction, that is, the vertical wall portion is formed into a curved surface shape that is twisted along the longitudinal direction.

In this case, the twisted longitudinal wall portion of the intermediate molded product may be formed into a curved surface shape twisted further in the longitudinal direction than the longitudinal wall portion of the target shape by making an angle difference between an angle at the end in the longitudinal direction of the twisted longitudinal wall portion of the intermediate molded product and an angle at the center in the longitudinal direction of the convex bending equivalent portion larger than an angle difference between an angle at the center in the longitudinal direction of the convex bending portion (convex bending center) and an angle at the end in the longitudinal direction (longitudinal direction end) of the longitudinal wall portion of the target shape press-molded product.

For example, the angle formed by the ceiling equivalent portion and the twisted vertical wall portion at the convexly curved center of the intermediate molded product may be set to the angle formed by the ceiling portion and the vertical wall portion at the convexly curved center of the target shape, and the angle formed by the ceiling equivalent portion and the twisted vertical wall portion at the end portions in the longitudinal direction of the intermediate molded product may be set to be larger than the angle formed by the ceiling portion and the vertical wall portion at the end portions in the longitudinal direction of the target shape.

About pressing method

Even if the twisted vertical wall portion 25a is formed in the first molding step and the in-plane shear deformation occurs as described above, the flange equivalent portion 27 may be subjected to compression deformation and wrinkles may occur. In this case, as shown in fig. 15 (a) and 15 (b), the first forming step is preferably drawing in which the blank 201 is press-formed while sandwiching the end portion thereof with the blank holder 215 and the die 211. On the other hand, in the second molding step, the intermediate molded article 203 is bent at the punch shoulder arc portion 24 between the ceiling equivalent portion 23 and the vertical wall equivalent portion 25, and the twisted vertical wall portion of the intermediate molded article 203 is molded into a vertical wall portion of a desired shape. Therefore, as shown in fig. 15 (c) and 15 (d), the second molding step may be a shape molding step of press-molding the intermediate molded article 203 by sandwiching the intermediate molded article between the female die 221 and the male die 223. That is, if there is a fear that wrinkles may occur in the flange portion of the press-formed product 205 which is press-formed in the second forming step, the second forming step may be performed by drawing.

In the drawing and the shape forming, a pusher plate (not shown) paired with the punch 213 (fig. 15 a, 15 b) or the punch 223 (fig. 15 c, 15 d) may be inserted into the die 211 (fig. 15 a, 15 b) or the die 221 (fig. 15 c, 15 d) to press the portion 201a (see fig. 15 a) of the blank 201 corresponding to the top plate equivalent portion 203a of the intermediate formed product 203 in the first forming step and to press the top plate equivalent portion 203a (see fig. 15 c) of the intermediate formed product 203 in the second forming step.

Examples

The following description will explain the operation and effects of the press forming method according to the present invention, since a specific press forming experiment is performed.

In the press forming experiment, as shown in fig. 2, the press formed product 1 was set as a forming target, and the press formed product 1 had a cross-sectional hat shape having the top plate portion 3, the vertical wall portion 5, and the flange portion, and had a convex bent portion 11 formed by bending the top plate portion 3 and the flange portion 7 in a convex manner in the height direction along the longitudinal direction in a side view, and straight portions 13 extending to both sides in the longitudinal direction.

As shown in fig. 16, the dimensions of the press-formed product 1 were such that the width of the top plate 3 was 60mm, the vertical wall height of the vertical wall portion 5 was 70mm, the width of the flange portion 7 was 20mm, and the angle formed by the top plate 3 and the vertical wall portion 5 was 80 °. The length in the longitudinal direction was 385mm, the curvature radius of the curve of the convex curved portion 11 was R150mm, and the angle θ on the acute angle side among the angles formed by the top plate 3 and the press forming direction in the straight line equivalent portion 33 in the side view was set to₀Set to 70. In addition, materials for press forming were used in the experimentsA steel sheet having a thickness of 1.2mm and a tensile strength of 1180MPa was used.

Here, the pressing method in the first forming step is drawing (see fig. 15 (a) and 15 (b)), and the pressing method in the second forming step is shape forming (see fig. 15 (c) and 15 (d)). Here, in the first step, the nip load (load) was 20 tonf.

As shown in fig. 6, the first forming step forms the ceiling equivalent portion 23, the vertical wall equivalent portion 25 including the twisted vertical wall portion 25a twisted in the longitudinal direction, and the flange equivalent portion 27, and press-forms the intermediate formed product 21 having the convex bending equivalent portion 31. Here, the twisted vertical wall portion 25a has a longitudinal length L of 250mm and a vertical wall height H of 70mm (see fig. 8).

Fig. 17 shows a cross-sectional shape of the intermediate molded article 21. In the present embodiment, the angle θ formed with the ceiling equivalent part 23 at the end in the longitudinal direction of the vertical wall part 25a (fig. 17 (b)) is to be twisted₂An angle θ formed between the ceiling equivalent portion 23 and the twisted vertical wall portion 25a at the center (fig. 17 (a)) in the longitudinal direction of the convex bending equivalent portion 31₁The large example is set as the present invention example. Then, by changing these two angles θ₁And angle theta₂And the angle difference Δ θ (═ θ)₂-θ₁) The intermediate formed product 21 was press-formed in the first forming step and press-formed into a target shape in the second forming step, and the press-formability was evaluated by the presence or absence of cracks and wrinkles in the obtained press-formed product 1.

For the evaluation of the fracture, the value was "x" in the case of fracture, the value was "Δ" in the case of no fracture but a portion with a narrow width due to the reduction in the sheet thickness, and the value was "o" in the case of no fracture at all and a portion with a narrow width. For the evaluation of wrinkles, the evaluation was "x" in the case of significant wrinkles, "Δ" in the case of minute wrinkles, and "o" in the case of no wrinkles at all.

In the present embodiment, an example in which the press-formed article 1 is press-formed by one step of shape forming or drawing forming and an example in which the press-formed article 1 is press-formed by two steps of the first forming step and the second forming step, and the vertical wall equivalent portion 25 of the intermediate formed article 21 press-formed in the first forming step is not a curved surface shape twisted in the longitudinal direction are taken as conventional examples.

Further, the angle θ formed by the ceiling equivalent portion 23 and the twisted vertical wall portion 25a of the intermediate formed article 21 press-formed in the first forming step is an angle θ formed by the press-formed article 1 press-formed in the first forming step and the second forming step in both steps₁And theta₂Examples that deviate from the scope of the present invention are set as comparative examples.

Further, the press-molded articles of the conventional examples and comparative examples were also evaluated for the presence or absence of cracks and wrinkles in the same manner as in the present invention examples. Table 1 shows the press forming conditions and the results of the evaluation of press formability.

[ Table 1]

TABLE 1

In Table 1, the convex curvature center angle θ₁The angle formed by the ceiling equivalent part 23 and the twisted vertical wall part 25a at the center in the longitudinal direction of the convex bending equivalent part 31 of the intermediate molded article 21 is shown in fig. 17 (a)), and the longitudinal end angle θ₂Is an angle formed by the ceiling equivalent portion 23 at the end portion in the longitudinal direction of the twisted vertical wall portion 25a and the twisted vertical wall portion 25a (or the vertical wall equivalent portion 25) (fig. 17 (b)). The angular difference Δ θ, the longitudinal length L, and the vertical wall height H are values obtained in the same manner as in the above-described embodiment, and the twist amount T is a value obtained by substituting the angular difference Δ θ, the longitudinal length L, and the vertical wall height H into the above-described equation (1).

In table 1, conventional examples 3 to 5, comparative examples 2 to 4, and present invention examples 1 to 13 are collectively shown under the same condition of the angular difference Δ θ. In addition, conventional example 1 is an example in which a press-molded article 1 is molded by one step of shape molding. In addition, in conventional example 2, the press-formed product 1 is formed by a single drawing step, and the angle formed by the top plate 3 and the vertical wall 5 is 100 ° which is a target shape.

In conventional example 1, although no crack was found in the top plate 3, wrinkles were generated in the flange 7. In conventional example 2, although no wrinkles were found in the flange portion 7, the top plate portion 3 was broken.

In conventional examples 3 to 5, the center angle θ of the convex curve is determined by₁Angle theta with end in the longitudinal direction₂Since the angle difference Δ θ of (3) is 0, the intermediate formed product 21 cannot be press-formed by applying in-plane shear deformation to the vertical wall equivalent part 25. Therefore, in the press-formed product 1 in which the intermediate formed product 21 is press-formed into a desired shape, a difference in the length of the line in the longitudinal direction between the top plate 3 and the flange portion 7 occurs, and both the crack in the top plate 3 and the wrinkle in the flange portion 7 cannot be suppressed at the same time.

In comparative examples 1 to 4, the angle θ of the end in the longitudinal direction₂Central angle theta of curvature than convex₁Small so that the angular difference Δ θ is negative. Therefore, in the first molding step, the convex bending center angle θ₁Angle theta with end in the longitudinal direction₂The twisted vertical wall portion 25a is formed by in-plane shear deformation, but the direction of the in-plane shear deformation is opposite to the direction of the shear deformation in the twisted vertical wall portion of the present example (see fig. 12), and therefore the difference in the longitudinal line length between the top plate equivalent portion 23 and the flange equivalent portion 27 is not reduced. As a result, in the target-shaped press-formed product 1, both the crack in the top plate portion 3 and the wrinkle in the flange portion 7 cannot be suppressed at the same time.

In invention examples 1 to 13, the end angle θ in the longitudinal direction₂Central angle theta of curvature than convex₁Large so that the angle difference Delta theta is positive and the angle theta is equal to the convex bending center angle theta₁The angle theta of the end in the longitudinal direction₂The longitudinal length L and the vertical wall height H of the twisted vertical wall portion 25a were changed.

Table 1 shows inventive examples 1 to 4(Δ θ is 20 °), inventive examples 5 to 7(Δ θ is 20 °) andθ ═ 40 °), inventive examples 8 to 9(Δ θ ═ 60 °), inventive example 10(Δ θ ═ 80 °), and convex bend central angle θ₁Inventive example 11(θ) having an angle smaller than the angle (100 °) formed between the top plate 3 and the vertical wall 5 of the target shape₁95 °), and any of invention example 12(L is 125mm) and invention example 13(H is 35mm) in which the longitudinal direction length L and the vertical wall height H of the twisted vertical wall portion 25a were changed, can be press-formed into a press-formed product while suppressing both cracking and wrinkling.

This is considered to be because the intermediate molded article 21 of invention examples 1 to 13 is molded by the in-plane shear deformation of the twisted vertical wall portion 25a shown in fig. 7, and thus the difference in the length of the line between the top plate portion 3 and the flange portion 7 in the longitudinal direction is reduced. In inventive examples 5 to 7(T ═ 11.2 °), inventive examples 8 to 9(T ═ 16.8 °), and inventive examples 11(T ═ 12.6 °), in which the twist amount T was within the preferable range of the present invention (10 ° to 20 °), no cracking and no wrinkles were observed at all in the press-molded article 1, and good results were obtained.

As described above, according to the press-forming method of the present invention, it was confirmed that a press-formed product having a hat-shaped cross section which is convexly curved in the height direction along the longitudinal direction when viewed from the side can be press-formed so as to suppress both cracking and wrinkling.

Industrial applicability of the invention

According to the present invention, it is possible to provide a press-forming method capable of press-forming a press-formed product having a cross-sectional hat shape including a top plate portion, a vertical wall portion, and a flange portion and curved in a convex shape in a height direction along a longitudinal direction into a good shape so as to suppress cracking and wrinkling.

Description of the reference numerals

1 … press-formed article; 3 … top plate; 4 … convex die shoulder arc part; 5 … longitudinal wall portions; 6 … concave die shoulder arc part; 7 … flange portion; 11 … convex bending part; 13 … straight line portion; 21 … intermediate molded article; 23 … roof equivalent; 24 … convex die shoulder arc; 25 … longitudinal wall equivalent; 25a … twisting the vertical wall portion; 26 … concave die shoulder arc part; 27 … flange equivalent; 31 … convex curve equivalent; 33 … straight line equivalent; 41 … intermediate molded article; 43 … roof equivalent; 45 … longitudinal wall equivalent; 45a … twisted vertical wall portions; 47 … flange portion; 51 … convex curve equivalent; 53 … straight line equivalent; 61 … intermediate molded article; 63 … roof equivalent; 65 … longitudinal wall equivalent; 65a … twisted vertical wall parts; 67 … flange portion; 71 … convex curve equivalent; 73 … straight line equivalent; 81 … intermediate molded article; 83 … top plate equivalent; 85 … longitudinal wall equivalent; 85a … twisted vertical wall part; 87 … flange portion; 91 … convex bending equivalent part; 93 … straight line equivalent; 101 … intermediate molded article; 103 … top plate equivalent; 105 … longitudinal wall equivalent; 105a … twisted vertical wall parts; 107 … flange equivalent; 111 … convex bending equivalent part; 113 … straight line equivalent; 121 … press-formed article; 123 … top plate; 125 … longitudinal wall portions; 127 … flange portion; 131 … convex bending part; 133 … straight line; 141 … press-molded article; 143 … top panel; 145 … longitudinal wall portions; 147 … flange portion; 151 … convex curved portion; 153 … straight line portion; 201 … blank; part 201a …; 203 … intermediate molded article; 203a … top plate equivalent; 205 … press-formed article; 211 … concave die; 213 … male die; 215 … swage ring; 221 … die; 223 … male die.