Press forming apparatus and press forming method

Abstract

A press forming apparatus includes: a punch; a blank holder disposed adjacent to the punch; a die being a counterpart of the punch; and a pad disposed to face the punch. The punch has a tip surface, an outside surface, and a stepped surface having shapes corresponding to a web portion, vertical wall portions, and a flange portion of a product, respectively. When the punch and the die are relatively moved in a pressing direction in a state where a middle portion in a width direction of a workpiece is sandwiched by the pad and punch and an outer peripheral portion in the width direction of the workpiece is bound by the blank holder and the die, the workpiece's outer peripheral portion in the width direction gets out from between the blank holder and the die, and the flange portion is shaped by the die and the punch's stepped surface.

Claims

1. A press forming apparatus forming a product by drawing a planar workpiece made of metal, the product having a web portion, a first vertical wall portion extending toward one side of the web portion, a second vertical wall portion extending toward the other side of the web portion, at least one of a first flange portion further extending from the first vertical wall portion in at least a part of a longitudinal direction and a second flange portion further extending from the second vertical wall portion in at least a part of the longitudinal direction, the press forming apparatus comprising: a punch; a blank holder disposed adjacent to the punch and slidable in a pressing direction; a die being a counterpart of the punch; and a pad disposed to face the punch and slidable in the pressing direction, wherein the punch has a tip surface, an outside surface, and a stepped surface having shapes corresponding to the web portion, the vertical wall portions, and the at least one of the first and second flange portions of the product, respectively, wherein the punch, the blank holder, the die and the pad are configured such that as a result that the punch and the die are relatively moved in the pressing direction in a state where a middle portion in a width direction of the workpiece is sandwiched by the pad and the punch and directly opposing surfaces of an outer peripheral portion in the width direction of the workpiece are pressed by the blank holder and the die, the outer peripheral portion in the width direction of the workpiece gets out from between the blank holder and the die and the at least one of the first and second flange portions is shaped by the die and the stepped surface of the punch, and wherein the punch, the blank holder, the die and the pad are configured such that the outer peripheral portion in the width direction of the workpiece gets out from between the blank holder and the die when the position of the punch in relation to the die is in a position of 20 to 99% from a processing start position of drawing of the workpiece to a processing end position.

2. The press forming apparatus according to claim 1, comprising a block to keep an interval so that an interval between the blank holder and the die may not become equal to or less than a predetermined interval.

3. The press forming apparatus according to claim 2, wherein the predetermined interval g satisfies t0.5gt1.5, with a plate thickness of the workpiece before drawing the workpiece being t.

4. The press forming apparatus according to claim 1, wherein the die has a recessed portion, and wherein the punch, the blank holder, the die and the pad are configured such that as a result that the punch and the die are relatively moved in the pressing direction in a state where the middle portion in the width direction of the workpiece is sandwiched by the pad and the punch, and the outer peripheral portion in the width direction of the workpiece is bound by the blank holder and the die, the workpiece is pushed into the recessed portion of the die together with the punch, thereby subjecting the workpiece to drawing, and the vertical wall portions are shaped by the outside surface of the punch and the die, the outer peripheral portion in the width direction of the workpiece gets out from between the blank holder and the die and the at least one of the first and second flange portions is shaped by the die and the stepped surface of the punch.

5. A press forming method to form a product by drawing a planar workpiece made of metal, the product having a web portion, a first vertical wall portion extending toward one side of the web portion, a second vertical wall portion extending toward the other side of the web portion, at least one of a first flange portion further extending from the first vertical wall portion in at least a part of a longitudinal direction and a second flange portion further extending from the second vertical wall portion in at least a part of the longitudinal direction, by using a press forming apparatus which includes a punch, a blank holder disposed adjacent to the punch and slidable in a pressing direction, a die being a counterpart of the punch, and a pad disposed to face the punch and slidable in the pressing direction, wherein the punch has a tip surface, an outside surface, and a stepped surface having shapes corresponding to the web portion, the vertical wall portions, and the at least one of the first and second flange portions of the product, respectively, the press forming method comprising: sandwiching a middle portion in a width direction of the workpiece with the pad and the punch and pressing directly opposing surfaces of an outer peripheral portion in the width direction of the workpiece with the blank holder and the die; making the outer peripheral portion in the width direction of the workpiece get out from between the blank holder and the die by relatively moving the punch and the die in the pressing direction; shaping the web portion and the vertical wall portions, and the at least one of the first and second flange portions by the die and the stepped surface of the punch; after shaping the web portion, the vertical wall portions, and the at least one of the first and second flange portions, relatively moving and separating the punch and the die; and making the outer peripheral portion in the width direction of the workpiece get out from between the blank holder and the die when the punch in relation to the die is in a position of 20 to 99% from a processing start position of drawing of the workpiece to a processing end position.

6. The press forming method according to claim 5, wherein the die has a recessed portion, and wherein in a step of shaping the web portion and the vertical wall portions, and the at least one of the first and second flange portions, making the workpiece to be pushed into the recessed portion of the die together with the punch thereby subject the workpiece to drawing by relatively moving the punch and the die in the pressing direction, and making the vertical wall portions to be shaped by the outside surface of the punch and the die by relatively moving the punch and the die in the pressing direction, and after making the outer peripheral portion in the width direction of the workpiece get out from between the blank holder and the die by relatively moving the punch and the die in the pressing direction, shaping the web portion and the vertical wall portions, and the at least one of the first and second flange portions by the die and the stepped surface of the punch.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1A is a schematic view showing an example of a product with a hat-shaped cross section, and is a side view;

(2) FIG. 1B is a schematic view showing the example the product with the hat-shaped cross section, and is a I-I cross-sectional view of FIG. 1A;

(3) FIG. 2A is a schematic view showing an example of a product with a hat-shaped cross section, and is a side view;

(4) FIG. 2B is a schematic view showing the example of the product with the hat-shaped cross section, and is a II-II cross-sectional view of FIG. 2A;

(5) FIG. 3A is a schematic view showing an example of a product with a hat-shaped cross section, and is a plan view;

(6) FIG. 3B is a schematic view showing the example the product with the hat-shaped cross section, and is a cross-sectional view of FIG. 3A;

(7) FIG. 4A is a cross-sectional view at a time of sandwiching and binding a workpiece, the cross-sectional view schematically showing a processing flow of a case of using a pad together with a blank holder in press forming;

(8) FIG. 4B is a cross-sectional view at a time of pushing, the cross-sectional view schematically showing the processing flow of the case of using the pad together with the blank holder in press forming;

(9) FIG. 4C is a cross-sectional view at a time of starting of separating operation of a punch and a die after a bottom dead center is reached, the cross-sectional view schematically showing the processing flow of the case of using the pad together with the blank holder in press forming;

(10) FIG. 5 is a cross-sectional view schematically showing a time of sandwiching and binding a workpiece in press forming using a die constituted with a plurality of components;

(11) FIG. 6A is a cross-sectional view at a time of sandwiching and binding a workpiece, the cross-sectional view schematically showing a processing flow by a press forming apparatus and a press forming method according to an embodiment;

(12) FIG. 6B is a cross-sectional view at a time of pushing, the cross-sectional view schematically showing the processing flow by the press forming apparatus and the press forming method according to the embodiment;

(13) FIG. 6C is a cross-sectional view at a time that the workpiece gets out in press forming, the cross-sectional view schematically showing the processing flow by the press forming apparatus and the press forming method according to the embodiment;

(14) FIG. 6D is a cross-sectional view at a time that an upper forming tool reaches a bottom dead center, the cross-sectional view schematically showing the processing flow by the press forming apparatus and the press forming method according to the embodiment;

(15) FIG. 7 is a cross-sectional view at another position corresponding to FIG. 6A; and

(16) FIG. 8 is a plan view showing an example in which a workpiece remains in a blank holder side and a forming variation occurs.

DESCRIPTION OF EMBODIMENTS

(17) Hereinafter, an embodiment for implementing the present invention will be described with reference to the attached drawing.

(18) FIG. 6A to FIG. 6D are cross-sectional views schematically showing a processing flow by a press forming apparatus and a press forming method according to the embodiment to which the present invention is applied. FIG. 6A shows a time of sandwiching and binding a workpiece, FIG. 6B shows a time of pushing, FIG. 6C shows a time that the workpiece gets out in press forming, and FIG. 6D shows a time that an upper forming tool reaches a bottom dead center, respectively.

(19) In this embodiment, description is carried out by using an example of press forming to form a product in which a web portion 10a is provided with an inclination (see FIG. 1A and FIG. 1B) but a cross-sectional shape is symmetric.

(20) Note that FIG. 7 shows a cross-sectional view at another position corresponding to FIG. 6A. FIG. 6A and FIG. 7A show cases of different timings, and first as shown in FIG. 7, a tall punch pushes the workpiece 50 into a recessed portion of a die 41, and thereafter, as shown in FIG. 6A, a short punch 31 pushes the workpiece 50 into the recessed portion of the die 41. Thereby, it becomes possible to provide the inclination in the web portion 10a.

(21) FIG. 6A to FIG. 6D show a case where the web portion 10a, vertical wall portions 10b, and flange portions 10c are formed in the workpiece when the upper forming tool is lowered from a top dead center to the bottom dead center. In this embodiment, the same reference numeral is given to a component corresponding to a component of the press forming apparatus described in FIG. 4A to FIG. 4C, and description is carried out focusing on differences from FIG. 4A to FIG. 4C.

(22) FIG. 6A to FIG. 6D show the workpiece 50 and a metal forming tool 20 which the press forming apparatus has. In the metal forming tool 20, an upper forming tool 40 is constituted with the die 41 and a pad 42 disposed to face the punch 31, and a lower forming tool 30 is constituted with the punch 31 and blank holders 32 disposed adjacent to the punch 31.

(23) Here, in the lower forming tool 30, a boundary position between the punch 31 and the blank holder 32 is positioned outside the recessed portion of the die 41. More specifically, the punch 31 has a tip surface 31a with a shape corresponding to the web portion 10a and an outside surface 31b with a shape corresponding to the vertical wall portions 10b, and in addition, stepped surfaces 31c with shapes corresponding to the flange portions 10c.

(24) Thereby, in a process of forming the flange portions 10c, the vertical wall portions 10b, and the web portion 10a by relatively moving the punch 31 and the die 41, outer peripheral portions in a width direction of the workpiece 50 get out from between the blank holder 32 and the die 41. This phenomenon is caused by binding lengths L of the workpiece 50 becoming shorter as a result that the workpiece 50 bound by the blank holders 32 and the die 41 is pushed into the recessed portion of the die 41 together with the punch 31 as press forming progresses. Since the outer peripheral portions in the width direction of the workpiece 50 get out from between the blank holders 32 and the die 41 as described above, the flange portions 10c are shaped in the workpiece 50 by the die 41 and the stepped surfaces 31c of the punch.

(25) A processing flow of the press forming method using such a press forming apparatus will be described.

(26) For press forming, a planar workpiece 50 made of metal is disposed between the die 41 and the punch 31.

(27) In the above state, the workpiece 50 is pressed to the punch 31 by the pad 42, and as shown in FIG. 6A, a middle portion in a width direction of the workpiece 50 is sandwiched by the pad 42 and the punch 31.

(28) Further, the workpiece 50 is pressed to the die 41 by the blank holders 32, and outer peripheral portions in the width direction of the workpiece 50 are bound by the blank holders 32 and the die 41.

(29) It suffices that timings of sandwiching of the middle portion by the pad 42 and the punch 31 and binding of the outer peripheral portions by the blank holder 32 and the die 41 are set properly in correspondence with a shape or the like of a product, similarly to in a conventional method.

(30) Then, the punch 31 and the die 41 are relatively moved to push the workpiece 50 together with the punch 31 into the recessed portion of the die 41, applying drawing to the workpiece 50, so that press forming is carried out. In a forming process thereof, as shown in FIG. 6B, the workpiece 50 is pushed into the recessed portion of the die 41 together with the punch 31, binding lengths L of the workpiece 50 become shorter, and, before long, the outer peripheral portions in the width direction of the workpiece 50 sequentially get out from between the blank holders 32 and the die 41, as shown in FIG. 6C.

(31) After the outer peripheral portions are made to get out from between the blank holders 32 and the die 41, the punch 31 and the die 41 are further moved relatively, whereby the web portion 10a is shaped by the tip surface 31a of the punch and the pad 42, and the vertical wall portions 10b are shaped by the outside surface 31b of the punch and the die 41. Further, the flange portions 10c are shaped by the stepped surfaces 31c of the punch and the die 41. When the upper forming tool reaches the bottom dead center, as shown in FIG. 6D, the tip surface 31a of the punch 31 and the pad 42 abut on (touch) the web portion 10a formed in the workpiece 50, the outside surface 31b of the punch 31 and the die 41 abut on the vertical wall portions 10b, and the stepped surfaces 31c of the punch 31 and the die 41 abut on the flange portions 10c.

(32) After the upper forming tool reaches the bottom dead center, the punch 31 and the die 41 are relatively moved and separated. In the press forming apparatus and the press forming method according to the embodiment, the shaped flange portions 10c of the workpiece 50 abut on the stepped surfaces 31c of the punch and the die 41 without abutting on the blank holders 32. Therefore, the flange portions 10c of the workpiece 50 having been press formed are not pressed by the blank holders 32, and thus the workpiece 50 can be prevented from being deformed when the punch 31 and the die 41 are separated.

(33) As described above, the press forming apparatus and the press forming method according to the embodiment can prevent the press formed workpiece from being deformed at a time of separation, without using a locking mechanism. Accordingly, there do not occur a problem that a productivity is reduced, a problem that a structure of a metal forming tool or a pressing apparatus becomes complex, and a problem that an equipment cost or a maintenance cost increases, due to the locking mechanism. Further, the press forming apparatus and the press forming method according to the embodiment is also applicable to a pressing apparatus which does not have a locking mechanism.

(34) In the press forming apparatus and press forming method according to the embodiment, as described above, the outer peripheral portions in the width direction of the workpiece 50 are made to get out from between the blank holders 32 and the die 41 sequentially in the forming process, but there is an apprehension that at that time a forming variation occurs when the workpiece 50 remaining in a blank holder 32 side is pressed by a strong pressure. For example, if one of the outer peripheral portions in the width direction of the workpiece 50 positioned in both sides of the recessed portion of the die 41 gets out from the blank holder 32 side and the other remains in the blank holder 32 side, the workpiece 50 remaining in the blank holder 32 side is pressed by a strong pressure. Thereby, there are an apprehension that a material inflow amount of the flange portion 10c or the vertical wall portion 10b in the side where the outer peripheral portion remains becomes smaller or an apprehension that the workpiece 50 is deviated in the web portion 10a in the side where the outer peripheral portion remains. There is an apprehension that shapes of products obtained as above vary. For example, in FIG. 8, dotted lines 81 indicating a positional boundary between the punch 31 and the blank holder 32, there is shown a state where an outer peripheral portion in the left side in the drawing gets out first, an outer peripheral portion in the right side remains in the blank holder 32 side, and a material gathers in the right side.

(35) In order to prevent the above, it is preferable to have a mechanism to keep an interval so that an interval between the blank holder 32 and the die 41 does not become equal to or less than a predetermined interval. In other words, it is preferable to have a mechanism to keep the intervals between the blank holders 32 and the die 41 in a state where the outer peripheral portions in the width direction of the workpiece 50 are bound, in a state where the outer peripheral portions get out of the blank holder 32. Such a mechanism to keep the intervals between the blank holders 32 and the die 41 can be materialized by disposing distance blocks 21 between the die 41 and the blank holders 32, for example. Thereby, even in a state where a part of the outer peripheral portion in the width direction of the workpiece 50 gets out from between the blank holder 32 and the die 41, the workpiece 50 remaining in the blank holder 32 side can be suppressed from being pressed by a strong pressure more than necessary since the distance blocks 21 intervene between the blank holders 32 and the die 41.

(36) It suffices that the distance block 21 is disposed so that the interval between the blank holder 32 and the die 41 is about a plate thickness of the workpiece 50 before a processing in the state where the workpiece 50 gets out, to make a forming variation small. Making the interval between the blank holder 32 and the die 41 be about the plate thickness of the workpiece 50 before the processing means that with the plate thickness (mm) of the workpiece 50 before the processing being t and the interval (unit: mm, see FIG. 6C) between the blank holder 32 and the die 41 in the state where the workpiece 50 has got out being g, the interval g is set to satisfy t0.5gt1.5.

(37) In drawing, it is preferable to bind the outer peripheral portion in the width direction of the workpiece 50 at a desired binding force by the blank holder 32 and the die 41, and g=t1.0 is preferable. However, considering diverse varieties (a plate thickness variety, a characteristic variety, a material set position variety, slide due to a temperature variety, a metal forming tool shape variety, and so on) or partial thickening, depending on a component shape or the like (change of a component height, an inclination), it is sometimes better to suppress the forming variety due to partial uneven contact caused by diverse varieties, even by somewhat alleviating binding and making the binding force be about t1.0gt1.5. On the other hand, when g>t1.5 is satisfied, the binding force to the workpiece 50 becomes small, to cause a wrinkle or the like.

(38) In the press forming apparatus and press forming method of the present invention, the position where the outer peripheral portion in the width direction of the workpiece gets out in the forming process is preferable to be a position of 20 to 99% from a processing start position, and is more preferable to be a position of 50% to 98%.

(39) Here, when a metal forming tool by which press forming is carried out as a result that an upper forming tool moves from a top dead center to a bottom dead center is used as a metal forming tool, for example, the processing start position means a position of the upper forming tool at which position the upper forming tool comes in contact with the workpiece and a processing starts, and a processing end position means the bottom dead center. Further, the position of 98% from the processing start position means a position where a distance (mm) from the processing start position to the upper forming tool becomes 98% of a distance (mm) from the processing start position to the bottom dead center.

(40) In the forming process, when the position where the outer peripheral portion in the width direction of the workpiece gets out is too close to the processing start position, a sufficient effect of drawing cannot be exhibited, and thus there is an apprehension that a wrinkle is formed in the vertical wall portion, for example. In order to prevent the above, the position where the workpiece gets out in the forming process is preferable to be made far from the processing start position to the extent that a forming defect such as a wrinkle does not occur, and more specifically, the position is preferable to be equal to or more than 20% from the processing start position and is more preferable to be equal to or more than 50%.

(41) On the other hand, in the forming process, when the position where the outer peripheral portion in the width direction of the workpiece gets out is too far from the processing start position, there is an apprehension that a part of the workpiece does not get out of the blank holder due to processing varieties. In this case, when separating the punch and the die, there is a possibility that the press formed workpiece is pressed by the blank holder and deformed, leading to a product defect. Thus, the position where the workpiece gets out in the forming process is preferable to be equal to or less than 99% from the processing start position, and is more preferable to be equal to or less than 98%.

(42) The position where the outer peripheral portion in the width direction of the workpiece gets out in the forming process can be adjusted by changing a distance d from an inside surface of the blank holder 32 to an inside surface 41a of the die 41. The distance d from the inside surface of the blank holder 32 to the inside surface 41a of the die 41 may be properly changed in correspondence with a required width of the flange portion 10c or an elastic recovery amount after forming (spring-back amount). For example, as shown in FIG. 1B, when a width w of a flange portion 10c required of a formed portion is 20 mm and a height h of the vertical wall portion 10b is 100 mm, and a high-strength steel plate of 1.4 mm in plate thickness and of 590 MPa class is used as the workpiece 50, it suffices that the distance d from the inside surface of the blank holder 32 to the inside surface 41a of the die 41 is set to be about 27 mm.

(43) Hereinabove, the present invention is described with various embodiments, but the present invention is not limited only to these embodiments and modification or the like is possible within the scope of the present invention.

(44) In the embodiment, as the metal forming tool, the metal forming tool the upper forming tool of which is constituted with the die and the pad and the lower forming tool of which is constituted with the punch and the blank holder is used, but the press forming apparatus and press forming method of the present invention is not limited to the embodiment using the aforementioned metal forming tool. In other words, it is possible to adopt an embodiment which uses a metal forming tool an upper forming tool of which is constituted with a punch and a blank holder and a lower forming tool of which is constituted with a die and a pad, as a metal forming tool.

(45) Further, though the embodiment is described in which the web portion 10a, the vertical wall portions 10b, and the flange portions 10c are press formed in the workpiece when the upper forming tool is lowered from the top dead center to the bottom dead center, in the press forming apparatus and the press forming method of the present invention, it suffices that the punch and the die are relatively moved in the pressing direction, and the present invention is not limited to the aforementioned embodiment.

(46) In this embodiment, though an example which uses the pad 42 abutting on the entire of the web portion 10a to be formed as the pad is described, an embodiment which uses a pad abutting on a part of a web portion 10a to be formed can be adopted. Further, the die is not limited to the die constituted with a single member as shown in FIG. 6A to FIG. 6D, and the die constituted with the plurality of members as shown in FIG. 5 can be adopted.

(47) The press forming apparatus and press forming method of the present invention is not limitedly applicable to the product with the hat-shaped cross section, but also is applicable to a case of press forming a product in which a flange portion 10c is provided only in one side. In this case, as shown in FIG. 6A to FIG. 6D, it is possible to use the punch 31 which has the stepped surfaces 31c in both sides, but it is also possible to use a punch which has a stepped surface only in a side where the flange portion 10c is provided. Further, even in a case of application to the product with the hat-shaped cross section, application is possible not only in a case where the flange portion 10c is provided throughout the entire length in the longitudinal direction but also in a case where the flange portion 10c is provided in a part of the longitudinal direction.

INDUSTRIAL APPLICABILITY

(48) A press forming apparatus and a press forming method of the present invention enable press forming using a pad together with a blank holder at a high productivity and at a suppressed equipment cost. Therefore, application of the press forming apparatus and the press forming method of the present invention to manufacturing of a framework component with a hat-shaped cross-section of an automobile can substantially contribute to improvement of formability and cost reduction of a component difficult to form.