Patent Application
20240198405
The present invention relates to a press forming method, and more particularly, to a press forming method in which flange portions of a pre-unbending press forming part, which has a hat-shaped cross section, is unbent to form, by press forming, a press formed part having a high forming height as side wall portions.
Many automotive parts are manufactured by press-forming a metal sheet. In recent years, in order to achieve both weight reduction of an automotive body and collision safety, metal sheets having higher strength are adopted as automotive parts. Examples of press formed parts press-formed as such automotive parts include a press formed part 120 having a U-shaped cross section (
The press formed part 120 having the U-shaped cross section as illustrated in
These press formed parts are manufactured by crash forming (bend forming) or deep drawing (draw forming) and are mainly used as reinforcing members of automobiles, and therefore metal sheets having high strength are used. However, as the strength of a metal sheet is higher, indices indicating formability such as ductility or stretch-flangeability of the material also decrease. For this reason, in particular, in press forming in which a U-shape press formed part having a curved portion concavely curved along a longitudinal direction, such as a substantial L-shape or a substantial T-shape in a top view, is the target shape, side wall portions in the curved portion are likely to result in stretch flange deformation to cause fractures. Furthermore, in a press formed part that is curved in a concave shape along the longitudinal direction and has a hat-shaped cross section, flange portions in the curved portions are pulled in a direction along the curve, which is likely to cause fractures in the flange portions. In addition, as a reaction force for forming the side wall portions curved in the concave shape, a top portion or punch shoulder parts in the curved portion are deformed to shrink in a direction along the curve, and thus wrinkles are likely to be generated.
Meanwhile, in press forming of a press formed part having a U-shaped cross section or a hat-shaped cross section having a curved portion convexly curved along the longitudinal direction in a top view, side wall portions or flange portions in the curved portion are compressed in a direction along the curve to result in shrinkage flanging, and thus wrinkles tend to be easily generated in the side wall portions. In addition, with a reaction force of forming the side wall portions that are convexly curved, the punch shoulder parts are pulled outward along the curve, and thus fractures are likely to be generated.
Therefore, among press formed parts having a U-shaped cross section or a hat-shaped cross section curved in a concave shape or a convex shape in a top view, particularly press formed parts having long side wall portions and a high forming height are generally press-formed in a plurality of steps in order to alleviate tensile stress or compressive stress generated in the press forming process and to prevent generation of fractures or wrinkles.
For example, in a case where the press formed part 120 having the U-shaped cross section illustrated in
Similarly, also in a case where the press formed part 130 having the hat-shaped cross section illustrated in
However, the flange portions 115 are not sufficiently unbent to be flat when the flange portions 115 are unbent in the second forming step, and for example, as illustrated in
With such bending crease portions 127 or 141 remaining, there are cases where resistance spot welding is difficult as illustrated in
In response to such a problem, there is proposed technology of straightening a bending crease portion that remains when a side wall portion having been subjected to a bending process is flattened. For example, Patent Literature 1 discloses technology for straightening a bending crease by, using a punch having three first projection parts arranged side by side at predetermined intervals and a die (die) having two second projection parts arranged so as to face two recessed forming spaces between the three first projection parts, pressing the punch toward the die side in a state where the central first projection part of the three first projection parts abuts from a projecting side of the bending crease and imparting local small deformation to the bending crease by the first projection parts of the punch and the second projection parts of the die.
However, the technology disclosed in Patent Literature 1 uses a special device for straightening a bending crease generated in a press formed part, and another additional step to straighten the bending crease is required in addition to the forming step of the press formed part, which posed a problem of a decrease in the productivity.
The present invention has been made in view of the above problem, and an object of the present invention is to provide a press forming method capable of reducing the size of the bending crease remaining in side wall portions of a press formed part obtained by unbending flange portions of the pre-unbending press formed part having a hat-shaped cross section to form the side wall portions without requiring a step of straightening the bending crease using a special device.
A press forming method according to the present invention is a method for a press formed part in which a pre-unbending press formed part having a hat-shaped cross section is unbent at flange portions using a punch and a die to form side wall portions, the pre-unbending press formed part including: a top portion; the side wall portions continuous from the top portion and inclined with respect to a press forming direction; and the flange portions continuous from the side wall portions via die shoulder parts, wherein the punch includes a top forming surface portion configured to form a top portion of the press formed part having a same shape as a shape of the top portion of the pre-unbending press formed part; and side-wall forming surface portions configured to form the side wall portions, each of the side-wall forming surface portions includes: a punch side first sloped surface portion that is continuous from and inclined outward from the top forming surface portion, the punch side first sloped surface portion having an inclination angle with respect to the press forming direction equal to an inclination angle of a side wall portion of the pre-unbending press formed part; and a punch side second sloped surface portion that is continuous from a lower end of the punch side first sloped surface portion and inclined inward from the punch side first sloped surface portion, the punch side first sloped surface portion and the punch side second sloped surface portion making a chevron shape convex outward, a punch side ridge line portion being formed at a connection portion of the punch side first sloped surface portion and the punch side second sloped surface portion, and the die includes flange unbending portions configured to unbend the flange portions of the pre-unbending press formed part placed on the punch, the press forming method including: placing the pre-unbending press formed part on the punch; relatively moving the die toward the punch; and unbending the flange portions by the flange unbending portions while the punch side ridge line portions are brought into contact with inner surface sides of the side wall portions to form the side wall portions of the press formed part.
The die may have an inner surface shape maintaining a clearance parallel to an outer surface of the punch.
The punch side ridge line portion may be formed at a position satisfying the following inequality:
h
1
−R
1(1−sin α)−R1/2≤h2≤h1−R1(1−sin α)+2πR1(90−α)/360+R1/2
In the present invention, when flange portions of a pre-unbending press formed part having a hat-shaped cross section are unbent to form side wall portions by using a punch, having punch side first sloped surface portions, punch side second sloped surface portions, and punch side ridge line portions, and a die having flange unbending portions, the flange portions are unbent by the flange unbending portions of the die while the punch side ridge line portions are brought into contact with inner surface sides of the side wall portions in the pre-unbending press formed part, whereby the size of the bending crease portion can be reduced without adding a step by a special device, and productivity can be improved.
Prior to describing a press forming method according to an embodiment of the present invention, studies on a bending crease generation mechanism and a method for reducing a bending crease will be described as a background leading to the present invention.
The present inventors have studied, using a tool of press forming 40 including a punch 41 and a die 43 as illustrated in
Illustrated in
When a flange unbending portion 43b of the die 43 comes into contact with a flange portion 115 of the pre-unbending press formed part 110 to start unbending, as illustrated in
At this point, since a gap (d1 in
Therefore, a reaction force accompanying unbending deformation of the die shoulder part 119 is applied to the side wall portion 113 and the flange portion 115 adjacent to the die shoulder part 119, and plastic bending deformation is applied in a direction opposite to the protruding shape, protruding toward the punch 41, in the die shoulder part 119. Here, regions where plastic bending deformation occurs on the side wall portion 113 side and the flange portion 115 side adjacent to the die shoulder part 119 are referred to as a side wall-side plastic bending deformation region 113a and a flange-side plastic bending deformation region 115a, respectively.
At the position of the bottom dead center of forming, as illustrated in
Here, a value (%) obtained by dividing the difference between the gap d2, which is the distance in the vertical direction between the punch side side-wall forming surface portion 41a and the die-side side wall forming surface portion 43a at the position of the bottom dead center of forming (
At the position of the bottom dead center of forming (
However, springback occurs as illustrated in
As illustrated in
Based on the above study on the mechanism in which the bending crease portion 127 is generated in the side wall portion 123 of the press formed part 120 obtained by unbending the flange portion 115 of the pre-unbending press formed part 110, the inventors further studied a method of reducing the size (bending crease height) of the bending crease portion 127 generated in the press formed part 120.
Here, as an index for quantitatively evaluating the size of the bending crease portion 127, as illustrated in
As illustrated in
Therefore, on the basis of the result of press forming simulation, the range in which the side wall-side portion receiving plastic bending deformation 127b and the flange-side portion receiving plastic bending deformation 127c occur was intensively studied. As a result, it has been found that both the side wall-side portion receiving plastic bending deformation 127b and the flange-side portion receiving plastic bending deformation 127c become wider as a bend radius R1 of the die shoulder part 119 of the pre-unbending press formed part 110 is larger and have a size of about ½ of the bend radius R1 of the die shoulder part 119.
Based on these findings, the inventors have intensively studied a method for reducing the bending crease height of the bending crease portion 127. As a result, it has been found that when the flange portion 115 of the pre-unbending press formed part 110 is unbent, the bending crease height can be reduced by bending the region where the bending crease portion 127 occurs to the side opposite to the bending crease portion 127. The present invention has been completed on the basis of the above study, and the structure thereof will be described below.
In the press forming method according to the embodiment of the present invention, as illustrated in
In the pre-unbending press formed part 110, a punch shoulder part 117 connecting the top portion 111 and a side wall portion 113 and a die shoulder part 119 connecting the side wall portion 113 and a flange portion 115 are formed.
Meanwhile, in the press formed part 120, a punch shoulder part 125 connecting a top portion 121 and a side wall portion 123 is formed. Here, the top portion 121 and the punch shoulder part 125 have the same shape as that of the top portion 111 and the punch shoulder part 117 of the pre-unbending press formed part 110, respectively. Furthermore, an inclination angle α of the side wall portion 113 of the pre-unbending press formed part 110 with respect to the press forming direction is equal to an inclination angle α of the side wall portion 123 of the press formed part 120.
As illustrated in
The top forming surface portion 11e forms the top portion 121 having the same shape as the top portion 111 of the pre-unbending press formed part 110.
A punch side side-wall forming surface portion 11a forms a side wall portion 113 of the pre-unbending press formed part 110 and has a punch side first sloped surface portion 11b, a punch side second sloped surface portion 11c, and a punch side ridge line portion 11d as illustrated in
As illustrated in
As illustrated in
As illustrated in
As illustrated in
The die-side side wall forming surface portion 13a forms the side wall portion 113 of the pre-unbending press formed part 110 in cooperation with the punch side side-wall forming surface portion 11a and has a die-side first sloped surface portion 13b and a die-side second sloped surface portion 13c as illustrated in
As illustrated in
As illustrated in
A flange unbending portion 13d is continuous from the die-side second sloped surface portion 13c and abuts on and unbend the flange portion 115 of the pre-unbending press formed part 110 placed on the punch 11. In the present embodiment, as illustrated in
Then, the pre-unbending press formed part 110 is placed on the punch 11, the die 13 is moved relatively toward the punch 11, and the entire or a part of the flange portions 115 is unbent by the flange unbending portions 13d of the die 13 while the punch side ridge line portions 11d of the punch 11 are in contact with the inner surface of the side wall portions 113 to form the side wall portions 123 of the press formed part 120. At this point, the top portion 121 is formed in the same shape as that of the top portion 111 of the pre-unbending press formed part 110.
As illustrated in
Then, as illustrated in
Next, the reason why the size of the bending crease portion 127 generated in the side wall portion 123 of the press formed part 120 can be reduced by the press forming method according to the present embodiment will be described.
A in
B in
A bending crease height hc in the surface shape profile C is the maximum value (hc in
As described above, according to the press forming method of the present embodiment, the flange portion 115 is unbent while the punch side ridge line portion 11d is brought into contact with the region (between the boundary 127d and the boundary 127e in
Comparing the surface shape profiles of the bending crease portion 127 in the case of using the punch 11 (see
Furthermore, in a case where the position at which the punch side ridge line portion 11d of the punch 11 abuts is set to the side of the side wall portion 113 or on the side of the flange portion 115, which is outside of the region where the bending crease portion 127 occurs, as illustrated in
From the results of
A length l1 (see
l
1=2πR1×(90°−α)/360° Equation (1)
In addition, a length l2 of the side wall-side plastic bending deformation region 113a in the side wall portion 113 of the pre-unbending press formed part 110 and a length l3 of the flange-side plastic bending deformation region 115a in the flange portion 115 are approximately ½ of the bend radius R1 of the die shoulder part 119 of the pre-unbending press formed part 110 as described above regarding the bending crease generation mechanism and thus are given by Equations (2) and (3).
l
2
=R
1×½ Equation (2)
l
3
=R
1×½ Equation (3)
From these, the length of the region where the bending crease portion 127 occurs can be calculated as the total value of the length l1 of the die shoulder part 119, the length l2 of the side wall-side plastic bending deformation region 113a, and the length l3 of the flange-side plastic bending deformation region 115a of the pre-unbending press formed part 110.
For example, in a case where the bend radius R1 of the die shoulder part 119 is 5 mm and the inclination angle α with respect to the press forming direction of the side wall portion 113 of the pre-unbending press formed part 110 is 3°, the length l1 of the die shoulder part 119 is 7.6 mm from Equation (1), and the length l2 of the side wall-side plastic bending deformation region 113a and the length l3 of the flange-side plastic bending deformation region 115a are both 2.5 mm from Equations (2) and (3). In this case, the length of the region where the bending crease portion 127 occurs in the pre-unbending press formed part 110 is given by the sum of these values, which is 12.6 mm (=7.6 mm+2.5 mm+2.5 m).
Let the inclination angle of the punch side first sloped surface portion 11b be the same as the inclination angle α of the side wall portion 113 of the pre-unbending press formed part 110, and let the forming height of the pre-unbending press formed part 110 be h1, then a distance hd from the top forming surface portion 11e in the press forming direction at the boundary between the die shoulder part 119 and the side wall-side plastic bending deformation region 113a is given, from the geometrical relationship illustrated in
h
d
=h
1
−R
1·(1−sin α) Equation (4).
h
s
=h
1
−R
1·(1−sin α)−R1×½ Equation (5)
h
e
=h
1
−R
1·(1−sin α)+2πR1×(90°−α)/360°+R1×½ Equation (6)
Therefore, let h2 be a distance from the top forming surface portion 11e in the press forming direction of the punch side ridge line portion 11d (see
h
1
−R
1(1−sin α)−R1/2≤h2≤h1−R1(1−sin α)+2πR1(90−α)/360+R1/2 Inequality (7)
Here, h2 represents a distance (mm) in the press forming direction from the top forming surface portion 11e of the punch 11 to the punch side ridge line portion 11d, h1 represents a forming height (mm) of the pre-unbending press formed part 110 (see
As can be seen from
From
However, in a case where the inclination angle β of the punch side second sloped surface portion 11c is made larger than the inclination angle α of the punch side first sloped surface portion 11b, the punch side second sloped surface portion 11c is closer to the top forming surface portion 11e than the punch side ridge line portion 11d is. Therefore, in a case where the die 13 of the tool of press forming 10 is relatively moved in parallel to the press forming direction, the gap in the vertical direction between the punch side second sloped surface portion 11c and the die-side second sloped surface portion 13c at the position of the bottom dead center of forming becomes wide, and the flange portion 115 to be unbent cannot be sufficiently restrained, and thus the effect of reducing the bending crease height of the bending crease portion 127 is also saturated.
Therefore, in the case where the die 13 is relatively moved in parallel to the press forming direction toward the punch 11, the inclination angle β of the punch side second sloped surface portion 11c is only required to be less than or equal to the inclination angle α of the punch side first sloped surface portion 11b (0<β≤α).
However, in a case of performing insert bending using the tool of press forming 10 including a mechanism in which the die 13 is inclined with respect to the press forming direction and moves toward the punch 11, there is no upper limit as described above for the inclination angle β of the punch side second sloped surface portion 11c, and the inclination angle β may be set as appropriate.
When the press formed part 120 is released from the tool of press forming 10 after the press-forming, the side wall portion 123 formed by unbending the flange portion 115 springs back to be convex toward the punch 11 (see
However, the springback amount of the side wall portion 123 after the release is affected by various factors such as the cross sectional shape and the shape in the longitudinal direction of the press formed part 120, the tensile strength and the sheet thickness of a metal sheet used for a blank 100, and the distribution of the residual stress or strain generated in the press formed part 120, and thus the springback amount cannot be uniformly determined. Therefore, the springback amount of the side wall portion 123 is preferably obtained in advance by numerical simulation by a finite element method or a preliminary experiment.
In addition, the die 13 preferably has an inner surface shape maintaining a clearance parallel to the outer surface of the punch 11. Here, the inner surface shape of the die 13 refers to the shapes of the die-side first sloped surface portion 13b and the die-side second sloped surface portion 13c. Incidentally, the outer surface of the punch 11 refers to the shapes of the punch side first sloped surface portion 11b and the punch side second sloped surface portion 11c. It is further preferable that the die-side first sloped surface portion 13b of the die 13 is inclined at the inclination angle α with respect to the press forming direction and is parallel to the punch side first sloped surface portion 11b and that the die-side second sloped surface portion 13c is inclined at the inclination angle β toward the punch 11 with respect to the die-side first sloped surface portion 13b and is parallel to the punch side second sloped surface portion 11c.
Then, at the position of the bottom dead center of forming where the die 13 is moved relatively and in parallel with the press forming direction to approach the punch 11, the die-side first sloped surface portion 13b and the die-side second sloped surface portion 13c are preferably provided in such a manner as to face the punch side first sloped surface portion 11b and the punch side second sloped surface portion 11c with distances in the vertical direction thereto having a predetermined gap. This is because, as in the state of the position of the bottom dead center of forming illustrated in
Here, in the tool of press forming 10 illustrated in
In a case where the clearance is less than 0%, so-called “ironing” occurs, and abnormal sliding wear of a sliding surface or a flaw called “galling” may occur, which is not preferable. Alternatively, in a case where the clearance exceeds 50%, a space where the blank can move freely is generated, thereby making it difficult for the effect of the present invention to be exerted, which is not preferable.
In particular, in a case where a metal sheet
having a tensile strength exceeding a 1600 MPa-class or a thickness of more than 3.6 mm, which is likely to cause “galling” between the tool of press forming and the blank, is used as the blank, it is important to appropriately adjust the clearance.
Note that the description of the press forming method according to the present embodiment relates to the case of press-forming the press formed part 120 having the U-shaped cross section in which the entire flange portions 115 of the pre-unbending press formed part 110 having the hat-shaped cross section are unbent to form parts of the side wall portions 123. However, as illustrated in
Furthermore, in the invention, in a case where the press formed part curved along the longitudinal direction in a top view is the target shape, it is possible to suppress fractures due to stretch flange forming or wrinkles due to shrink flange forming in the curved press formed part in addition to reducing the size (bending crease height) of the bending crease portion remaining in the side wall portions of the press formed part.
In the present embodiment, the die 13 includes the die-side first sloped surface portion 13b and the die-side second sloped surface portion 13c parallel to the punch side first sloped surface portion 11b and the punch side second sloped surface portion 11c, respectively, and compresses the side wall portions 113 of the pre-unbending press formed part 110 in cooperation with the punch side first sloped surface portion 11b and the punch side second sloped surface portion 11c.
However, the present invention is not limited to one in which the die 13 includes the die-side first sloped surface portion 13b and the die-side second sloped surface portion 13c parallel to the punch side first sloped surface portion 11b and the punch side second sloped surface portion 11c, respectively. The side wall portions may be formed in such a manner as to extend along the punch side first sloped surface portion and the punch side second sloped surface portion by unbending the flange portion while bringing the punch side ridge line portion into contact with the inner surface sides of the side wall portions.
In addition, the present invention is not limited to one including only one step of unbending the flange portions of the pre-unbending press formed part having the hat-shaped cross section prepared in advance but also includes one in which a press formed part having the target shape is press-formed in two steps of a first forming step of press-forming the pre-unbending press formed part having the hat-shaped cross section and a second forming step of unbending the flange portions of the pre-unbending press formed part to form the side wall portions.
Note that, in a case where a press formed part to be formed by the invention is an automotive part, examples of the type of the automotive part include frame components such as an A pillar, a B pillar, a roof rail, a side rail, a front side member, a rear side member, and a cross member for which a high-strength metal sheet is used.
In Example 1, press forming simulation was performed for each of a first forming step of press-forming the pre-unbending press formed part 110 having the hat-shaped cross section illustrated in
In the first forming step, a metal sheet having a sheet thickness of 1.2 mm and a tensile strength of 1180 MPa-class was used as a blank 100, and the pre-unbending press formed part 110 having the top portion 111, the side wall portions 113, and the flange portions 115 illustrated in
The target shape of the pre-unbending press formed part 110 was a shape having a forming height h of 50 mm, a length lT of the top portion 111 of 50 mm, an inclination angle α of the side wall portions 113 of 3°, a width WF of the flange portions 115 of 50 mm, and a bend radius of the punch shoulder part 117 and a bend radius of the die shoulder part 119 of 10 mm each. The dimensions of the punch and the die used in the first forming step were set so as to correspond to the target shape of the pre-unbending press formed part.
In the subsequent second forming step, as illustrated in
The target shape of the press formed part 120 was set to be the same as that of the pre-unbending press formed part 110 in terms of the length of the top portion 121 and the bend radius of the punch shoulder parts 125.
Regarding the dimensions of the tool of press forming 10, the width of the top forming surface portion 11e of the punch 11 was 50 mm, and the punch side first sloped surface portion 11b and the die-side first sloped surface portion 13b were both inclined at an inclination angle of 3° which is equal to the inclination angle α of the side wall portions 113 of the pre-unbending press formed part 110.
In addition, the distance h2 of the punch side ridge line portion 11d from the top forming surface portion 11e was 50 mm, the inclination angle of the punch side first sloped surface portion 11b was α=3°, the inclination angle of the punch side second sloped surface portion 11c with respect to the punch side first sloped surface portion 11b was β=0 to 3°, the bend radius of the die shoulder part 119 was 10 mm, and the clearance between the punch side first sloped surface portion 11b and the die-side first sloped surface portion 13b and the clearance between the punch side second sloped surface portion 11c and the die-side second sloped surface portion 13c at the bottom dead center of forming were both set to 3% of the sheet thickness of the blank 100.
Then, the bending crease height of a bending crease portion 127 generated in a side wall portion 123 of the press formed part 120 formed in the second forming step was calculated. Incidentally, the bending crease height was set to the maximum value of the distance to the surface of the bending crease portion 127 in a direction perpendicular to the side wall portion 123.
In Example 1, as described below, the press forming simulation was performed by changing the inclination angle β of the punch side second sloped surface portion 11c and the position of the punch side ridge line portion 11d of the punch 11 used for press forming the press formed part 120, and the effect of reducing the bending crease height was examined.
In the present example, first, the inclination angle β of the punch side second sloped surface portion 11c of the punch 11 used in the second forming step was changed, and the bending crease height of the bending crease portion was examined.
Examples in which the inclination angle of the punch side second sloped surface portion 11c inward from the punch side first sloped surface portion 11b was set to β=1°, 2°, and 3° within a range of less than or equal to the inclination angle α (=3°) outward from the press forming direction of the punch side first sloped surface portion 11b were set as Example 1-1, Example 1-2, and Example 1-3, respectively, and the bending crease height of a bending crease portion 127 was obtained. In addition, for comparison, an example in which the press formed part 120 in which the flange portions 115 of the pre-unbending press formed part 110 were unbent to be formed into parts of the side wall portions 123 was press-formed using the conventional tool of press forming 40 illustrated in
Table 1 shows results of the bending crease height of the press formed parts 120 in Example 1-1 to Example 1-4 and Comparative Example 1.
The bending crease height in Comparative Example 1 was 1.72 mm. Meanwhile, the bending crease heights in Example 1-1, Example 1-2, and Example 1-3 were 1.24 mm, 1.35 mm, and 1.52 mm, respectively, which were all smaller than that of Comparative Example 1. This showed that the bending crease height of the bending crease portion 127 can be reduced by using the punch 11 including the punch side ridge line portion 11d.
Furthermore, from the results of Examples 1-1 to 1-3, it was shown that the effect of reducing the bending crease height is increased by increasing the inclination angle β of the punch side second sloped surface portion 11c. This is because the deformation of bending the die shoulder parts 119 in the reverse direction is promoted when the flange portions of the pre-unbending press formed part 110 is unbent.
Note that press forming simulation was also performed for a case where the inclination angle β of the punch side second sloped surface portion 11c was set to 4° which is larger than the inclination angle α of the punch side first sloped surface portion 11b.
In this case, even in a case where the inclination angle of the punch side second sloped surface portion 11c is larger than the inclination angle α of the punch side first sloped surface portion 11b, the flange portions of the pre-unbending press formed part 110 can be unbent to press-form the press formed part 120 by making the die 13 movable also in the horizontal direction to perform insert bending toward the punch 11.
Next, press forming simulation was performed for cases where the position of the punch side ridge line portion 11d of the punch 11 used in the second forming step was changed within the preferred range of the present invention, and the bending crease height of a bending crease portion was obtained.
Here, Examples in which the inclination angle of the punch side second sloped surface portion 11c inward from the punch side first sloped surface portion 11b direction was set to β=3° within a range of less than or equal to the inclination angle α outward from the press forming direction of the punch side first sloped surface portion 11b were set as Example 2-1, Example 2-2, and Example 2-3.
Table 2 shows results of the bending crease height of the press formed parts 120 in Example 2-1 to Example 2-5 and Comparative Example 1 described above.
In Example 2-1, the position of the punch side ridge line portion 11d is set within the preferred range of the present invention. The position of the punch side ridge line portion 11d is set to be within the range of the side wall-side plastic bending deformation region 113a in Example 2-1, within the range of the die shoulder part 119 in Example 2-2, and within the range of the flange-side plastic bending deformation region 115a in Example 2-3. The bending crease heights in Example 2-1, Example 2-2, and Example 2-3 were 1.24 mm, 1.23 mm, and 1.24 mm, respectively, and were greatly smaller as compared with the bending crease height in Comparative Example 1.
In Example 2-4 and Example 2-5, the position of the punch side ridge line portion 11d is set outside the preferred range of the present invention, and the punch side ridge line portion 11d is set on the side of the punch shoulder part 117 with respect to the side wall-side plastic bending deformation region 113a in Example 2-4 and on the distal end side of the flange portion 115 with respect to the flange-side plastic bending deformation region 115a in Example 2-5. The bending crease heights in Example 2-4 and Example 2-5 were each 1.45 mm, which was smaller than the bending crease height in Comparative Example 1 but larger than those in Example 2-1 to Example 2-3.
In Example 2, press forming simulation was performed for each of the first forming step of press-forming the pre-unbending press formed part 110 having the hat-shaped cross section illustrated in
In the press forming simulation, similarly to Example 1 described above, the press formed part 130 having the hat-shaped cross section obtained by press-forming was set as Example 3, in which a tool of press forming (not illustrated) including a punch having punch side first sloped surface portions, punch side second sloped surface portions, and punch side ridge line portions and a die having flange unbending portions is used to unbend parts of the flange portions 115 of the pre-unbending press formed part 110 on the side of the side wall portions 113 to be formed into the side wall portions 133, and portions of the flange portions 115 on a side opposite to the side wall portions 113 are obtained as the flange portions 135.
The target shape of the press formed part 130 was set to a shape having a forming height of H=80 mm and a width of the flange portion 135 of WF=20 mm. Incidentally, the punch used for the press forming of the press formed part 130 was set to have an inclination angle of the punch side first sloped surface portion of α=3° and an inclination angle of the punch side second sloped surface portion of β=3°. Other conditions regarding the target shape of the press formed part 130 and dimensions of the tool of press forming were similar to those of Example 1 described above.
Moreover, in Example 2, the press formed part 130 obtained by press-forming by unbending the flange portions 115 of the pre-unbending press formed part 110 using the conventional tool of press forming 40 was set as Comparative Example 2.
Then, for each of Example 3 and Comparative Example 2, the bending crease height of the bending crease portion 141 remaining in the side wall portion 133 of the press formed part 130 having the hat-shaped cross section was obtained. The bending crease height was obtained in a similar manner to that of the above-described embodiment (see
The bending crease height in Comparative Example 2 was 1.71 mm. Meanwhile, the bending crease height in Example 3 was 1.24 mm, which was smaller than that in Comparative Example 2. As a result, it was shown that the bending crease height of the bending crease portion 141 can be reduced according to the press forming method of the present invention even in a case where the press formed part 130 having the hat-shaped cross section is set as the target shape.
According to the present invention, it is possible to provide a press forming method capable of reducing the size of a bending crease remaining in side wall portions of a press formed part obtained by unbending flange portions of the pre-unbending press formed part having a hat-shaped cross section to form the side wall portions without requiring a step of straightening the bending crease using a special device.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-080775 | May 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/005594 | 2/14/2022 | WO |
