Patent Grant
10603707
This invention relates to a press-forming method for a component having a hat-shaped or U-shaped cross-section and curved in a widthwise direction along with a longitudinal direction, and more particularly to a press-forming method suppressing generations of cracks due to stretch flanging deformation and wrinkles due to shrink flanging deformation. Also, the invention relates to a component manufactured by using the press-forming method as a press-formed product having a hat-shaped or U-shaped cross section and curved in a widthwise direction along with a longitudinal direction.
A higher-strength metal sheet has been recently demanded in order to establish collision safety of an automobile and weight reduction of an automobile body. However, as the tensile strength is increased, the metal sheet tends to decrease a ductility largely associated with a press formability. To this end, there is a tendency that bend forming (bending) or draw forming (drawing) is frequently used instead of bulging in which a ductility of a raw material largely affects the formability.
In the drawing, a blank of a metal sheet as a material to be formed into a component is first mounted onto a punch and a blank holder. A die is moved downward from above the blank to hold the blank between the die and the blank holder, and then the blank is curved by crowding the punch into the die to apply a proper tension to the blank. In this case, a material (a part of the blank) is largely drawn into a gap between the punch and the die to form a vertical wall portion of a component because the blank is held between the die and the blank holder. Therefore, the formation of the vertical wall portion becomes easy even in a material having a poor ductility. Also, since an out-of-plane deformation of the blank (wrinkling) is suppressed by the die and the blank holder, tension applied to the material drawn into the gap for the formation of the vertical wall portion is easily adjusted and hence there is a merit that a component of a complicated form can be easily formed.
On the other hand, when the component of a complicated form is manufactured by the drawing, there is an issue that cracks or wrinkles are generated at an end part of the blank in a position corresponding to a flange portion, which is likely to become a problem particularly in the manufacture of a component PT having a curved portion C curved in a widthwise direction along with a longitudinal direction and straight side portions S connecting to the both ends of the curved portion C as shown by a perspective view in
When the top portion T, vertical wall portions W, flange portions F and the like of the component PT are curved in the widthwise direction of the component PT along with the longitudinal direction of the component PT as shown in
As a method for suppressing the wrinkles due to the shrink flanging deformation is known a method of dispersing the shrink flanging deformation as described in Patent Document 1. As a method for suppressing the cracks due to the stretch flanging deformation are known a method of dispersing the stretch flanging deformation as described in Patent Document 2 and a method of mitigating the stretch flanging deformation by moving the material of the top portion toward the vertical wall portion.
Patent Document 1: JP-A-2010-227995
Patent Document 2: JP-A-2014-039957
Patent Document 3: WO2014/106932 A1
As the strength of the metal sheet becomes higher, stress caused with respect to the deformation amount is increased, and hence stress exceeding the buckling strength of the metal sheet is easily caused to generate larger wrinkles. Also, as the strength of the metal sheet becomes higher, the wrinkle strength is increased, so that the method of dispersing the wrinkles as described in Patent Document 1 cannot be said to be a sufficient countermeasure. Further, the ductility in the end part of the blank is decreased in the higher-strength metal sheet, so that the prevention of cracks by the dispersion of stretch flanging deformation as described in Patent Document 2 is critical.
When the high-strength metal sheet is press-formed into a component curved in the widthwise direction along with the longitudinal direction as mentioned above, it is necessary to mitigate the generation of shrink flanging deformation and stretch flanging deformation themselves in order to suppress wrinkles due to the shrink flanging deformation and cracks due to the stretch flanging deformation. However, when the material is improperly moved, shape defects such as winkles and so on are caused in another site such as the top portion or the like, so that it is necessary to move the material without causing excess and deficiency thereof in the whole of the component.
The press-forming method according to the invention advantageously solving the above problem is a method for press-forming a component having a hat-shaped or U-shaped cross section and comprising a curved portion curved in a widthwise direction along with a longitudinal direction and straight side portions connecting to the both ends of the curved portion from a sheet-shaped blank, characterized in that the blank is drawn to a hat-shaped or U-shaped cross section through a hat-shaped cross-sectional form comprising a top portion, vertical wall portions connecting at their upper end parts to both end parts of the top portion through fillet portions, and flange portions connecting at their internal end parts to the lower end parts of the vertical wall portions through fillet portions, and
a material movement in the flange portion of the curved portion is caused in the drawing to mitigate tensile deformation or compression deformation in the circumferential direction generated in the flange portion of the curved portion.
In the press-forming method according to the invention, in order to cause the material movement in the flange portion of the curved portion for mitigating the circumferential tensile deformation or compression deformation generated in the flange portion of the curved portion, it is preferable to set a balance position of the material flowed in the straight side portion to the vertical wall portion on the side of the stretch flanging deformation in the curved portion or the fillet portion between the vertical wall portion and the flange portion and to increase the material flowed from the side of the shrink flanging deformation in the straight side portions to an extent exceeding the top portion (material movement pattern MA).
In the press-forming method according to the invention, in order to cause the material movement in the flange portion of the curved portion for mitigating the circumferential tensile deformation or compression deformation generated in the flange portion of the curved portion, it is preferable to set a balance position of the material flowed in the curved portion to the vertical wall portion on the side of the shrink flanging deformation or the fillet portion between the vertical wall portion and the flange portion and to suppress the material flowed from the side of the shrink flanging portion in the curved portion and increase the material flowed from the side of the stretch flanging deformation to an extent exceeding the top portion (material movement pattern MB).
A method of manufacturing a component according to the invention is characterized in that a sheet-shaped blank is drawn into a component of a preliminary shape having a hat-shaped or U-shaped cross section and curved in a widthwise direction along with a longitudinal direction by using the aforementioned press-forming method according to the invention, and the component of the preliminary shape is subjected to at least one of a restriking for rendering a bending radius of the fillet portions into a predetermined radius and a trimming for rendering a contour shape thereof into a predetermined shape to manufacture a component having a hat-shaped or U-shaped cross section and curved in a widthwise along with a longitudinal direction.
The component according to the invention is a component having a hat-shaped or U-shaped cross section and curved in a widthwise direction along with a longitudinal direction, characterized in that a sheet-shaped blank is drawn by using the aforementioned press-forming method according to the invention and formed into a predetermined shape by using at least one of a restriking for rendering a bending radius of the fillet portions into a predetermined radius and a trimming for rendering a contour shape thereof.
In the press-forming method according to the invention, when a component having a hat-shaped or U-shaped cross section and comprising a curved portion curved in a widthwise direction along with a longitudinal direction and straight side portions connecting to the both ends of the curved portion is press-formed from a sheet-shaped blank, the blank is subjected to a drawing into a hat-shaped or U-shaped cross section through a hat-shaped cross-sectional form comprising a top portion, vertical wall portions connecting at their upper end parts to both end parts of the top portion through fillet portions, and flange portions connecting at their internal end parts to the lower end parts of the vertical wall portions through fillet portions, and a material movement is caused in the flange portion of the curved portion for mitigating a tensile deformation or a compression deformation in a circumferential direction generated in the flange portion of the curved portion, so that one or both of the generation of winkles due to the shrink flanging deformation and the generation of cracks due to the stretch flanging deformation can be suppressed.
In the press-forming method according to the invention, it is preferable to use a metal sheet having a tensile strength of 440-1470 MPa as a blank. In this case, it is possible to suppress one or both of the occurrence of wrinkles due to the shrink flanging deformation and the occurrence of cracks due to the stretch flanging deformation in the press-forming of a component made of a high-strength metal sheet.
An embodiment of the invention will be described in detail by means of an example with reference to the drawings. When a sheet-shaped blank is drawn into a component as shown in
This is due to the fact that the die set is designed so as to cause a balance of tension in the top portion P. When the material passes through a shoulder portion of a punch 2 forming a punch shoulder fillet portion P (portions having bending radii R1 and R2) and a shoulder portion of a die member 4 forming a die shoulder fillet portion D (portions having bending radii R3 and R4), respectively, as the punch shoulder fillet portion P (R surface portion) is shown on the left side of
Also, the material is subjected to a friction resistance from the shoulder portion of the punch 2 at a position of contacting the punch shoulder fillet portion P with the punch shoulder. The material passing through a portion forming the flange portion F or a portion forming the vertical wall portion W is subjected to an inflow resistance DR due to a friction caused by contacting with any one of the blank holder 1, the punch 2, and the die member 4 as shown in
The inventors have got an idea that the material can be moved so as to mitigate the cracks due to the stretch flanging deformation and/or the wrinkles due to the shrink flanging deformation by changing the tension balance position X and made studies thereon. As a result, it has been found out that the balance position X can be freely determined by defining the shape of the die set and/or the friction resistance so that F1 and F2 are equal, wherein F1 is a total amount of the resistances on one hand with respect to a certain point and F2 is a total amount of resistances on the other hand.
In the drawing method according to the embodiment, when a component having a hat-shaped or U-shaped cross section and comprising a curved portion C curved in a widthwise direction along with a longitudinal direction and straight side portions S connecting to the both ends of the curved portion as shown in
Further, the balance position X is moved toward the vertical wall portion W by using a method of decreasing an inflow resistance at the F2 side on the right side of
On the other hand, as the method of increasing the inflow resistance at the F1 side, there are a method wherein beads and/or embosses (not shown) formed in the blank holder 1 and/or the die member 4, i.e. beads and/or embosses formed in the flange portion F at the F1 side on the left side of
The reason why the bending radius is preferable to be set to 1.1-10 times is due to the fact that when it is less than 1.1 times, the difference of the resistances is so small and it is difficult to move the balance position X, while when it is more than 10 times, the deformation amount of the material is increased in the restriking from the fillet portion of a preliminary shape into the fillet portion of a predetermined shape, so that the shortage in the ductility of the material is caused to increase the possibility of causing cracks.
When a component of a preliminary shape is press-formed in the drawing method according to the aforementioned embodiment by making the bending radius in the shoulder portions of the punch 2 and/or the die member 4 larger than that of a component of a predetermined shape, the component of the preliminary shape is re-struck by bending or drawing to make the bending radius in the fillet portions P and/or the fillet portions D of the component smaller, whereby a component provided with fillet portions having a predetermined radius can be manufactured.
If a predetermined contour shape cannot be obtained by the drawing or the subsequent restriking, it is possible to manufacture a component having the predetermined contour shape by conducting a trimming for rendering the contour shape into the predetermined shape after or together with the restriking.
The balance position X can be determined by conducting an experiment of the drawing or a numerical analysis by a finite element method in the target component. Since the influence by the bending⋅unbending resistance is larger than the influence by the friction resistance or the shrinking resistance in the flange portion F, the shape of the component may be simply determined so that the bending⋅unbending resistance counterbalances at the vertical wall portion W or the flange portion F.
The bending⋅unbending resistance Fb can be calculated from the following formula using yield strength σe and thickness t of the material and bending radius R:
Fb=σe×t/(2*(0.5*t+R))
As a result of finding the above method for determining the balance position X, the inventors could find a method of generating an ideal material movement for suppressing one or both of the stretch flanging deformation and shrink flanging deformation as shown in
In this method, the material movement pattern MA is caused at least by determining the balance position X in the vertical wall portion W on the side of the stretch flanging deformation EF or in the fillet portion between the vertical wall W and the flange portion F at the straight side portions S connecting to the both ends of the curved portion C in the middle part of the vertical wall portion W curved in a widthwise direction of a component to be formed. Moreover, it is preferable that the material movement pattern MB is caused by determining the balance position X in the vertical wall portion W on the side of the shrink flanging deformation CF or in the fillet portion between the vertical wall portion W and the flange portion F at the curved portion C of the middle part.
In the usual drawing, when the material flowed from the flange portion F is suppressed, the forming at the shoulder portions of the punch 2 or the shoulder portions of the die member 4 becomes difficult. In this embodiment, however, the forming at the shoulder portions of the punch 2 and the shoulder portions of the die member 4 are mitigated because the material flowed from the top portion T is caused.
In the material movement pattern MA, since the material movement is increased in the flange portion F, the vertical wall portion W, and the punch shoulder fillet portion P on the side of shrink flanging deformation CF shown on the left side of
In the material movement pattern MB, the material in the flange portion F, the vertical wall portion W, and the top portion T on the side of the stretch flanging deformation EF shown on the right side of
According to the press-forming method of this embodiment, not only a component having a hat-shaped cross section and curved in a widthwise direction but also a component having a U-shaped cross section and curved in a widthwise direction can be formed by using all the material located in the flange portion F for forming the vertical wall portion W.
It is preferable that a metal sheet as a raw material for the blank has a tensile strength of 440-1470 MPa. Since a metal sheet having a tensile strength of less than 440 MPa is excellent in the ductility and drawability, it is less in the merit using the drawing method of this embodiment. On the other hand, since a metal sheet having a tensile strength exceeding 1470 MPa is poor in the ductility, cracks are easily caused at the shoulder portions of the punch 2 and/or the shoulder portions of the die member 4 which are not targeted in the drawing method of this embodiment, so that the drawing of the component may be difficult.
Table 1 shows various specifications of steel sheets of 270, 440, 980, 1180, and 1470 MPa grade. Table 2 shows results examined on comparative examples of the conventional method and examples of the method according to this embodiment in components having a hat-shaped cross section shown in
In order to change the balance position X, the radius of the fillet portion is set to a value as shown in Table 3 at the curved portion C and in Table 4 at the straight side portions S connecting to the curved portion, respectively. Here, the radius of the fillet portion in the punch shoulder and the die shoulder is R1 and R3 on the side near to the shrink flanging deformation CF, and R2 and R4 on the side near to the stretch flanging deformation EF, respectively. A round bead having a bending radius of 8 mm is used as a bead.
When the material movement pattern MA is caused by using the shrink flanging deformation CF in the above examination, there is used a shape of a component wherein additional curved portions AC causing shrink flange deformation CF are further connected to the straight side portions S as shown in
The conventional method is a usual drawing wherein the balance position X is on the top portion T. The evaluation of the formed products is performed visually wherein winkles and cracks generated in the flange portion are evaluated by three stages ∘, Δ and x based on standards shown in Table 5 and Table 6, respectively.
As a result of the above examination, the 270 MPa grade steel sheet can be formed without generating wrinkles or cracks by either one of the conventional drawing method and the drawing method according to this embodiment. In the case of using the steel sheets of not less than 440 MPa, predominant cracks and wrinkles are generated in the conventional drawing method, whereas the generation of cracks and wrinkles can be prevented in the drawing method according to this embodiment.
Although the above is described with reference to the illustrated examples, the invention is not limited to the above examples and can be properly changed within a scope disclosed in the claims. For example, the die set used in the drawing may have a structure that the right and left shoulder portions and the concave portion of the die member 4 are made of different members instead of the structure shown in
According to the press-forming method of the invention, the method of manufacturing a component by using the press-forming method, and the component manufactured by using the press-forming method, when a component having a hat-shaped or U-shaped cross section and comprising a curved portion curved in a widthwise direction along with a longitudinal direction and straight side portions connecting to the both ends of the curved portion is press-formed from a sheet-shaped blank, the drawing is performed so as to have a hat-shaped or U-shaped cross section through a hat-shaped cross-sectional form comprising a top portion, vertical wall portions connecting at their upper end parts to both end parts of the top portion through fillet portions and flange portions connecting at their internal end parts thereof to the lower end parts of the vertical wall portions through fillet portions, and the material movement toward the flange portions of the curved portion is caused in the drawing to mitigate tensile deformation in the circumferential direction or compression deformation in the circumferential direction generated in the flange portion of the curved portion, whereby one or both of the generation of winkles due to the shrink flanging deformation and the generation of cracks due to the stretch flanging deformation can be suppressed.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/JP2015/060113 | Mar 2015 | WO | international |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/052555 | 1/29/2016 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2016/157976 | 10/6/2016 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 9266162 | Tanaka | Feb 2016 | B2 |
| 20130239645 | Tanaka et al. | Sep 2013 | A1 |
| 20150336619 | Tanaka et al. | Nov 2015 | A1 |
| 20170028455 | Fujii | Feb 2017 | A1 |
| Number | Date | Country |
|---|---|---|
| S59-076625 | May 1984 | JP |
| H05-44322 | Jun 1993 | JP |
| 2005-186154 | Jul 2005 | JP |
| 2007-190588 | Aug 2007 | JP |
| 2009-262168 | Nov 2009 | JP |
| 2010-064138 | Mar 2010 | JP |
| 2010-227995 | Oct 2010 | JP |
| 2013-27912 | Feb 2013 | JP |
| 2014-039957 | Mar 2014 | JP |
| 2014-240078 | Dec 2014 | JP |
| 2015-186154 | Oct 2015 | JP |
| 2012070623 | May 2012 | WO |
| 2014106932 | Jul 2014 | WO |
| Entry |
|---|
| Translation; JP 2007-190588A, Aug. 2007. |
| Aug. 28, 2018 Office Action issued in Chinese Patent Application No. 201680017285.7. |
| Mar. 22, 2016 Search Report issued in International Patent Application No. PCT/JP2016/052555. |
| Jun. 29, 2017 Office Action issued in Japanese Patent Application No. 2016-524546. |
| Mar. 27, 2018 Search Report issued in European Patent Application No. 16771860.0. |
| Apr. 29, 2019 Office Action issued in Chinese Applicatio No. 201680017285.7. |
| Oct. 22, 2018 Office Action issued in Korean Patent Application No. 2017-7026798. |
| Number | Date | Country | |
|---|---|---|---|
| 20180085811 A1 | Mar 2018 | US |
