PRESS-FORMING DIE
A press-forming die (1) includes a die (2) having a die corner (21), which follows along an inward-facing corner (41) of a blank sheet (4), and a punch (3) having a punch corner (31). A corner groove (6) extends along a portion of the punch corner at which leading surfaces (33) and a side surface (34) intersect in a relative stroke direction (X) of the punch. The corner groove is shaped such that its groove width (W) decreases in the stroke direction and converges at a punch corner center (C1). A shoulder radius (Rps) of punch shoulders (3S), which are portions along which the corner groove and the leading surfaces intersect with the side surface, a sheet thickness (t) of the blank sheet (4), and a flange length (Ls) at both ends of the inward-facing corner preferably satisfy the relationship t≦Rps≦Ls.
This application claims priority to Japanese patent application no. 2016-158812 filed on Aug. 12, 2016, the contents of which are fully incorporated herein by reference.
TECHNICAL FIELDThe present invention relates to a press-forming die for forming a stretch flange along an edge of an inward-facing corner of a metal plate.
BACKGROUND ARTIn recent years, aluminum alloy sheets have come to be used in automotive parts to reduce the weight of the chassis. When a flange is to be formed on an automotive part, e.g., along an opening for holding a glass window of a sunroof, generally speaking, a longitudinal-wall-shaped flange that extends around a rectangular hole is press-formed according to a rectangular burring process. The flange is formed by first cutting or punching a rectangular hole in an aluminum alloy sheet, and then bending the peripheral edge portion (hole edge part) of the rectangular hole in a punch-advance direction by pushing a rectangular punch, which is larger than the rectangular hole, through the rectangular hole.
However, this known flange-forming technique forms inferior stretch flanges on aluminum alloy sheets as compared to stretch flanges that are formed on mild (low carbon) steel sheets using this known technique. Therefore, cracks have tended to occur when a curved stretch flange is formed at a corner of an aluminum alloy sheet using this known technique. For example, although uncomplicated (i.e. straight) flanges can be reliably formed along the straight edges of the rectangular hole by simply bending the straight edges in the advancing direction of the punch, when stretch flanges are formed at the corners, they must be bent (curved) while also being stretched in a direction perpendicular to the advancing direction of the punch. Consequently, to avoid cracks in the curved stretch flanges of aluminum alloy sheets, design freedoms for the corner radius, the flange length, etc. at the corners have been restricted in the past.
In view of this problem, various techniques have been studied for preventing cracks in the stretch flange of an aluminum alloy sheet during press forming. For example, Japanese Laid-open Patent Publication 2015-139783 discloses a method that comprises: a specifying step that specifies the position of the flange, which is to be deformed by stretching it beyond a preset amount, as a maximum stretch-flange deformed part; and a pre-deforming step, which forms a pre-deformed part that is deformed in a sheet-thickness direction relative to both sides or one side of the specified maximum stretch-flange deformed part. Thereafter, a flange-forming step, which is the final forming step, is performed after the formation of the pre-deformed part.
SUMMARY OF THE INVENTIONNevertheless, the above-mentioned JP 2015-139783 describes a method in which the pre-deformed part should be greatly deformed on a sheet-edge side in the pre-deforming step, and the amount of increase in a cross-sectional line length in the pre-deforming step should be set to a value that is less than the amount of increase in a cross-sectional line length of the press-formed article. However, a specific method for forming the pre-deformed part is not disclosed in JP 2015-139783. In addition, multiple steps, such as the pre-deforming step and the final forming step, are necessary in this known method, which is disadvantageous from the viewpoint of equipment costs and productivity. Furthermore, because an aluminum alloy sheet is more difficult to press-form than a steel sheet is, the above-described known method is problematic in that the desired forming process cannot be suitably performed.
It is an object of the present teachings to provide a press-forming die and a press-forming method that are capable of press-forming, in one step, a high-quality stretch flange having an inward-facing corner flange and side flanges on both sides thereof.
In view of this background information, disclosed herein is a shape for an improved press-forming die, by which the inward-facing corner flange, which is created in conjunction with the forming of the stretch flange, and the side flanges on both sides of the inward-facing corner flange can be press-formed in one step. Also disclosed herein is a preferred relationship between the shoulder radius of punch shoulders and a blank (e.g., an aluminum alloy or steel sheet, which will be referred to as a “blank sheet” herein).
In another aspect of the present teachings, a press-forming die is disclosed that is capable of press forming a blank sheet having an inward-facing corner to form a corner flange, which rises from an inner edge of the inward-facing corner, and first and second side flanges, which respectively extend from opposite sides of the corner flange. The press-forming die preferably comprises:
a die having a die corner shaped to form the corner flange and first and second die sides shaped to respectively form the first and second side flanges; and
a punch having a punch corner and first and second punch sides that respectively cooperate with the die corner and the first and second die sides to form the corner flange, the first side flange and the second side flange;
wherein the punch corner has a corner groove extending along a portion at which leading surfaces of the punch and a side surface of the punch intersect in a stroke direction of the punch; and
the corner groove is shaped such that its groove width decreases in a direction moving away from the leading surfaces in the stroke direction and converges at a punch corner center on the side surface.
Because the corner groove is provided in the punch corner of the press forming die, when the punch moves (advances) relative to the die, the first and second side flanges are first press-formed by the first and second punch sides moving past the first and second die sides. Because punch shoulders of the corner groove are shaped such that the groove width decreases the direction moving away from the leading surfaces in the stroke direction and the groove width converges (becomes zero) at the punch corner center, the corner flange is initially press-formed starting from its outer sides that are adjacent to the first and second side flanges. That is, on both sides of the center of the inward-facing corner (i.e. the blank corner center), both ends of the punch shoulders first make contact with the blank sheet, and the range of the punch shoulders that makes contact with the blank sheet gradually increases towards the blank corner center as the press forming progresses.
Accordingly, when the punch advances while stretching the inner edge of the inward-facing corner of the blank sheet and both sides thereof, the portion of the blank sheet at the blank corner center is initially not press-formed. Subsequently, as the groove width of the corner groove that is contacting and press-forming the inward-facing corner decreases, the press-forming range of the punch increases inwardly towards the blank center such that the blank corner center is press-formed last. In this sequence of the manufacturing process, the inward-facing corner of the blank sheet rises into the corner flange shape in a satisfactory manner and the inward-facing corner is bent in the moving (advancing) direction of the punch initially starting from the side flange sides until ultimately reaching the blank corner center.
As a result, localization of strain is suppressed (reduced or minimized) and cracks in the stretch flange can be prevented. As a result, a flange (in particular, a curved flange) that rises from the inner edge of the inward-facing corner can be press-formed in one step and, moreover, a high quality product can be manufactured with high productivity.
In one embodiment of the above-described press-forming die, a shoulder radius Rgs of groove shoulders, which are portions along which the corner groove and the leading surfaces intersect, and a shoulder radius Rps of punch shoulders, which are portions along which the corner groove and the leading surfaces intersect with the side surface, preferably satisfy the relationships Rps≦Rgs and Rgs≦30 mm. In such an embodiment, while the press-forming range from the side flanges towards the corner flange is widening (increasing) during the press-forming operation, the effect of suppressing (reducing) an increase in strain at both ends of the corner groove also increases.
In another embodiment of the present teachings, the positions at which the above-mentioned punch shoulders and the groove shoulders intersect on the leading surfaces are preferably at the boundaries of the punch corner with the adjacent punch sides on the side surface of the punch, or on the outer sides thereof (with reference to the blank corner center). In such an embodiment, by suitably selecting the shoulder radius Rgs, a groove depth D, and the like, the effect of suppressing (reducing, minimizing) localization of strain increases. It is noted that the boundaries of the punch corner with the adjacent punch sides include the round end positions, which constitute both ends of the punch corner, and positions in the vicinity thereof.
The ratio D/W of the corner groove, which is the ratio of the groove depth D in the stroke direction to the groove width W at the leading surfaces, is preferably larger than 0.25. In such an embodiment, localization of strain is suppressed (reduced, minimized) and the effect of reducing maximum principal strain is further increased.
In another embodiment of the present teachings, the corner groove preferably has a shape of a pair of opposing inclined surfaces. For example, the corner groove can have a V-groove shape as will be described below in further detail.
The present press-forming die can be utilized to bend various kinds of metal sheets as the blank sheet provided with the inward-facing corner according to the present teachings. In particular, superior or optimal results can be obtained when bending an aluminum alloy sheet or a steel sheet to press-form one or more corner (curved) stretch flanges.
First EmbodimentA first embodiment of a press-forming die 1 according to the present teachings will now be explained with reference to the drawings.
As shown in
The die 2 has a round die corner 21, which follows along the round inward-facing corner 41. A pair of (first and second) straight die sides 22 extends from the die corner 21 and follow along the pair of straight side parts 42. In addition, the punch 3 has a punch corner 31 and a pair of (first and second) punch sides 32, which cooperate (interact) with the die corner 21 and the pair of (first and second) die sides 22, respectively. When the punch 3 of the press-forming die 1 moves (advances) upwardly relative to the die 2, with the direction perpendicular to the sheet surface of the blank sheet 4 serving as the stroke direction X (i.e., the up-down direction in the figures), the inward-facing corner 41 and the adjacent side parts 42 of the blank sheet 4 are press-formed into the desired flange shape. Although each of the side parts 42 is straight-shaped in the present embodiment, they may have another shape. For example, at least a portion of the side parts 42 may have a curved-side shape. This applies likewise to the die sides 22 and the punch sides 32.
It is noted that the press-forming die 1 forms the flange F, which has at least one corner flange Fc, on the blank sheet 4, and the blank sheet 4 (prior to press-forming) has at least one inward-facing corner 41.
As shown in
In
In addition, the block-shaped punch 3 is sized to slide into the rectangular tubular hole 2A and is movable relative to the rectangular tubular hole 2A in the stroke direction X. The punch corner 31 of the punch 3 has an outward-facing corner shape, and is disposed opposite the die corner 21. The punch sides 32 are disposed so as to oppose the die sides 22. The die shoulders 2S on the die sides 22 on both sides of the die corner 21 respectively cooperate with the punch shoulders 3S. The shoulder radius of the die shoulders 2S is constant, as will be further discussed below.
A blank holder 5, on which the blank sheet 4 is mounted, is provided downward of the die 2 and is vertically movable. Prior to the press-forming, as shown in
As shown in
Ls=(Lc/2)×√{square root over (√2)}.
The corner flange Fc and the side flanges Fs (e.g., refer to the lower image in
As was noted above, the blank sheet 4 optionally may be composed of, for example, an aluminum alloy sheet or a steel sheet, such as a mild (low carbon) steel sheet. Aluminum alloy sheets are more effective for reducing weight than steel sheets. In addition, because aluminum alloy sheets are generally inferior to mild steel sheets in terms of stretch flange formability, the effect produced by using the press-forming techniques of the present teachings on aluminum alloy sheets is relatively large. Accordingly, a flange F having a relatively large height can be press-formed on an aluminum alloy sheet while suppressing (minimizing) strain. The die 2 and the punch 3 of the press-forming die 1 can be composed (made) of, for example, any well-known steel material typically used for casting metal dies.
As shown in
In the up-down direction between the cross section at which the corner groove 6 disappears into the end surface on the side opposite the leading surfaces 33 and the bottom surface of the punch 3, the punch 3 has a rounded rectangular outer shape (see e.g.,
The shoulder radius Rps of the punch shoulders 3S is preferably set such that the relationship t≦Rps≦Ls is satisfied, in which t is the sheet thickness of the blank sheet 4, and Ls is the flange length at both ends of the inward-facing corner 41 (see
In addition, the shoulder radius Rgs of the groove shoulders 6S, which are the portions along which the corner groove 6 and the leading surfaces 33 intersect, and the shoulder radius Rps preferably satisfy the relationship Rps≦Rgs. In addition, it is preferable that Rgs≦30 mm. In such an embodiment, as the press-forming range widens from the side flanges Fs towards (and ultimately to) the corner flange Fc during the press-forming operation, the effect of suppressing (reducing or minimizing) an increase in strain in the blank sheet 4 proximal to both ends of the corner groove 6 increases. In the present embodiment, for example, the shoulder radius Rps of the punch shoulders 3S, the shoulder radius Rgs of the groove shoulders 6S, and a valley radius Rgv of the groove-valley 6V are all equal (i.e., Rps=Rgs=Rgv).
In addition, the leading surfaces 33, along which the punch shoulders 3S and the groove shoulders 6S intersect, are preferably positioned at, or on the outer side of, the boundaries between the punch corner 31 and the punch sides 32 on the side surface 34. In this regard, the boundaries include the round ends C2, C3, which are the boundary positions, and positions in the vicinity thereof. That is, connecting parts S1, S2 (see
As was noted above, the connecting parts S1, S2 of the groove shoulders 6S are positioned outwardly of the round ends C2, C3 in the present embodiment. Thus, as shown in
In the corner groove 6 as shown in
The first embodiment described an example in which the shoulder radius Rps of the punch shoulders 3S and the shoulder radius Rgs of the groove shoulders 6S are the same size. However,
Other structural elements are the same as in the first embodiment and are assigned the same symbols and reference numbers, and explanations thereof are therefore omitted. This applies likewise to the subsequent embodiments disclosed in this specification. It is noted that, in the first and second embodiments, the corner groove 6 may be formed in the leading surfaces 33 of the punch 3 continuously with a not-shown punch corner 31 that is located on the side opposite the punch corner 31 in the diagonal direction. This applies likewise to the two corner grooves 6 of the punch 3 in the other diagonal direction.
In addition, as another exemplary shape shown in
The first embodiment described an example in which the groove depth D of the corner groove 6 in the stroke direction X is larger than 50% of the groove width W at the leading surfaces 33. However,
Alternatively,
Next, a representative, non-limiting method of press-forming a blank sheet 4 using a press-forming die 1 according to the first embodiment will be explained.
As shown in
As shown in the lower image in
In this representative, non-limiting embodiment of the present teachings, as shown by arrows in
On the other hand, if the present press-forming method is applied to, for example, an opening for an automobile sunroof or the like, the corner flange Fc formed at the opening is preferably smaller than the corner radius R and larger than the flange length L. Consequently, there is a concern that cracks will be created by press-forming the stretch flange, and consequently it is required that strain produced by press-forming the stretch flange be maximally reduced in the corner flange Fc. This is regarded as important, especially for an aluminum alloy sheet that has poor stretch flange forming properties.
To address this potential problem, the punch 3 shown in
Next, in working examples in which the corner flanges Fc were press-formed at the four inward-facing corners 41 of the blank sheet 4 using a press-forming die 1 having the above configuration, the effect of suppressing (reducing or minimizing) the generation of strain in the corner flanges Fc was evaluated.
Working Examples 1-23The blank sheet 4 was an aluminum alloy sheet (a 6000-series aluminum alloy) having a thickness of 1.2 mm. The corner radius Rc of the corner flanges Fc after press-forming was 70 mm, and the flange length Lc after press-forming was 16 mm at the blank corner center 41C. The flange length Ls at both ends of the inward-facing corner 41, which are the round ends C2, C3, and at the side parts 42 was 11.3 mm (i.e., 8√{square root over ( )}2 mm=11.3 mm). As shown in Table 1, in the punch 3, the shoulder radius Rps of the punch shoulders 3S and the shoulder radius Rgs of the groove shoulders 6S were varied in the range of 2-10 mm while setting the shoulder radius Rps equal to the shoulder radius Rgs in all examples. It is noted that the valley radius Rgv of the groove-valley part 6V was set equal to the shoulder radius Rps. In addition, the ratio W/W0 of the groove width W at the leading surfaces 33 of the corner groove 6 to the maximum (uppermost) width W0 of the punch corner 31 was set in the range of 1-1.5. The incline angle α of the inclined surfaces 61, 62 (see bottom image in
According to the press forming method shown in
For the purpose of comparison, the blank sheet 4 was press-formed using the same method as in the above-described working examples 1-23, except that the shape of the punch 3 was modified. More specifically, the punch for comparison had the same shape as that of the punch 3 of the first embodiment, except that it had no corner groove 6. The configuration of the press-forming die 1, except that of the punch, was the same, the maximum principal strain ε1 at the time that the flange F was formed in the blank sheet 4 was derived, and the results are provided in Table 1.
Comparative Examples 2-4For the purpose of comparison, the shape of the punch 3 of working example 1 was modified such that the shoulder radius Rps of the punch shoulders 3S was 14 mm, and the blank sheet 4 was press-formed according to the same method. In this case, the relationships shoulder radius Rps=shoulder radius Rgs and valley radius Rgv=shoulder radius Rps were set, and the ratio W/W0 of the groove width W to the width W0 of the punch corner 31 was set in the range of 1-1.5. Likewise, the maximum principal strain ε1 at the time that the flange F was formed on the blank sheet 4 was derived, and the results are provided in Table 1.
As shown in Table 1, in the comparative example 1 in which the punch 3 did not have the corner groove 6, the maximum principal strain ε1 was 0.233. In contrast, in working examples 1-23, in which the punch 3 had the corner groove 6, the maximum principal strain ε1 was smaller, namely in the range of 0.177-0.224. In addition, in the comparative examples 2-4, in which the shoulder radius Rps of the punch shoulders 3S was larger than the flange length Ls, the maximum principal strain ε1 was 0.240-0.245 and larger than that in comparative example 1. Based on the above results, it was determined that, when the relationship t≦Rps≦Ls is satisfied for the shoulder radius Rps of the punch shoulders 3S with respect to the sheet thickness t of the blank sheet 4 and the flange length Ls at both ends of the inward-facing corner 41, satisfactory results can be obtained.
Working Examples 24-27As shown in Table 2, the shape of the punch 3 of working example 2 was varied such that the shoulder radius Rgs of the groove shoulders was in the range of 2-30 mm. In working examples 24-27, the relationship valley radius Rgv=shoulder radius Rps was maintained. The blank sheet 4 was press-formed according to the same method as described above for working examples 1-23, the maximum principal strain ε1 at the time when the flange F was formed on the blank sheet 4 was derived, and the results are provided in Table 2.
Working Examples 28-38As shown in Table 2, the shape of the punch 3 of working example 1 was varied such that the shoulder radius Rps of the punch shoulders 3S was in the range of 2-10 mm and the ratio W/W0 of the groove width W to the width W0 of the punch corner 31 was set to 0.9 or 1.1. In working examples 28-38, the relationships shoulder radii Rps=Rgs and valley radius Rgv=shoulder radius Rps were maintained. The press-forming of the blank sheet 4 was performed according to the same method as described above for working examples 1-23, the maximum principal strain ε1 at the time that the flange F was formed on the blank sheet 4 was derived, and the results are provided in Table 2.
As shown in Table 2, even in the examples in which the relationship of the shoulder radius Rgs of the groove shoulders 6S with respect to the shoulder radius Rps of the punch shoulders 3S was Rps≦Rgs, and Rgs≦30 mm, equivalent results could be obtained. In addition, even if the ratio W/W0 was 0.9 or 1.1, equivalent results could be obtained.
In
The punch shoulders 3S are connected to the straight sides 35 of the leading surfaces 33 and first make contact with the blank sheet 4 at the punch sides 32, which are positions where strain is relatively small. In this case, because the shoulder radius Rps of the punch shoulders 3S is set comparatively small within a range larger than the sheet thickness t, the side flanges Fs rise quickly. In addition, because the groove width W of the corner groove 6 is larger than the width W0, the punch shoulders 3S of the punch corner 31 do not make contact with the inward-facing corner 41 of the blank sheet 4 at the start of the press-forming. Consequently, while stretching is suppressed (minimized or even prevented) at the inward-facing corner 41, the press-forming range migrates inwardly towards the blank corner center 41C of the inward-facing corner 41.
When the punch 3 further rises (i.e., stroke length=48 mm, 80 mm), the groove width W of the corner groove 6 (as viewed at the level of the blank sheet 4) progressively becomes smaller. As a result, the range of contact of the blank sheet 4 with the punch shoulders 3S widens (increases or converges) towards the inward-facing corner 41, and the corner flange Fc progressively rises. When the corner flange Fc rises to the position at which the lower ends of the punch shoulders 3S are exposed at the blank corner center 41C (i.e., stroke length=122 mm), the press-forming of the corner flange Fc is complete.
After the corner flange Fc has been completely raised at the round ends C2, C3 (i.e., stroke length=80 mm), the V-shaped shoulders 3S of the punch 3 approach the blank sheet 4 at the blank corner center 41C. Subsequently, as the punch 3 rises further (i.e., stroke length=122 mm), the V-shaped punch shoulders 3S raise the blank sheet 4 at the inward-facing corner 41, and thereby the press-forming of the corner flange Fc is complete.
Thus, because the punch corner 31 of the punch 3 has the corner groove 6, which varies in size in the stroke direction X (i.e. it narrows or tapers downwardly in the figures), it becomes possible to control the timing at which contact is made with the peripheral edge portion of the blank sheet 4, as well as the timing at which the peripheral edge portion of the blank sheet 4 rises and assumes the flange shape. Specifically, the punch shoulders 3S first raise the side flanges Fs on the outer side of the punch corner 31; next, the round ends C2, C3, which are the boundaries of the punch sides 32, and the vicinities thereof contact the blank sheet 4, and the range of contact widens (increases) toward the blank corner center 41C. In conventional punch configurations that do not have the corner groove 6 (e.g., refer to the left image in
In contrast, because the punch 3 according to the present teachings has the corner groove 6 (e.g., refer to the right image in
Although the above-described embodiments explained representative examples of the present teachings in which four of the corner flanges Fc are formed along a rectangular hole having four inward-facing corners 41, the press forming die 1 may be designed to press form at least one inward-facing corner 41. In such embodiments, the blank sheet 4 is not limited to having a hole shape opening such as a rectangular hole. Instead, the opening may have, e.g., one or two or more of the inward-facing corners 41, each having a shape that is curved in the longitudinal direction.
In addition, although the above-described embodiments explained representative examples of forming, at the inward-facing corner provided in the glass opening for an automobile sunroof, the corner flange Fc that rises from the inner edge of the inward-facing corner, the present teachings are not limited thereto. The press forming dies 1 and the press-forming methods, which use the press forming dies 1, of the present teachings can be readily adapted to an opening provided in any of a variety of parts for a vehicle or for other than a vehicle.
Additional embodiments of the present teachings include, but are not limited to:
1. A press-forming die (1) capable of forming, on a blank sheet (4) having an inward-facing corner (41), a corner flange (Fc), which rises from an inner edge (43) of the inward-facing corner (41), and a pair of side flanges (Fs), which extend from both sides of the corner flange (Fc), the press-forming die (1) comprising:
a die (2) having a die corner (21), which follows along the inward-facing corner (41) of the blank sheet (4), and a pair of die sides (22), which follows along a pair of side parts (42) of the blank sheet (4); and
a punch (3) having a punch corner (31) and a pair of punch sides (32) that respectively cooperate with the die corner (21) and the pair of die sides (22);
wherein the punch corner (31) has a corner groove (6) extending along a portion at which leading surfaces (33) and a side surface (34) intersect in a stroke direction (X) of the punch (3);
the corner groove (6) has a shape such that its groove width (W) decreases in a direction moving away from the leading surfaces (33) in the stroke direction (X) and converges at a punch corner center (C1); and
a shoulder radius (Rps) of punch shoulders (35), which are portions along which the corner groove (6) and the leading surfaces (33) intersect with the side surface (34), a sheet thickness (t) of the blank sheet (4), and a flange length (Ls) of the blank sheet (4) at both ends of the inward-facing corner (41) satisfy the relationship t≦Rps≦Ls.
2. The press-forming die (1) according to the above embodiment 1, wherein a shoulder radius (Rgs) of groove shoulders (6S), which are portions along which the corner groove (6) and the leading surfaces (33) intersect, and the shoulder radius (Rps) satisfy the relationships Rps≦Rgs and Rgs≦30 mm.
3. The press-forming die (1) according to the above embodiment 1 or 2, wherein the positions on the leading surfaces (33), at which the punch shoulders (35) and the groove shoulders (6S) intersect, are boundaries on the side surface (34) between the punch corner (31) and the punch sides (32), or outer sides thereof.
4. The press-forming die (1) according to any one of the above embodiments 1-3, wherein a ratio D/W of a groove depth (D) of the corner groove (6) in the stroke direction (X) to a groove width (W) of the corner groove (6) at the leading surfaces (33) is larger than 0.25.
5. The press-forming die (1) according to any one of the above embodiments 1-4, wherein the corner groove (6) has a pair of inclined surfaces (61, 62) that surround the blank corner center (41C).
6. The press-forming die (1) according to any one of the above embodiments 1-5, wherein the blank sheet (4) is composed of an aluminum alloy sheet or a steel sheet.
Representative, non-limiting examples of the present invention were described above in detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Furthermore, each of the additional features and teachings disclosed above and below may be utilized separately or in conjunction with other features and teachings to provide improved press-forming dies as well as methods of manufacturing and using the same.
Moreover, combinations of features and steps disclosed in the above detailed description, as well as in the experimental examples, may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the invention. Furthermore, various features of the above-described representative examples, as well as the various independent and dependent claims below, may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings.
All features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter, independent of the compositions of the features in the embodiments and/or the claims. In addition, all value ranges or indications of groups of entities are intended to disclose every possible intermediate value or intermediate entity for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter.
EXPLANATION OF THE REFERENCE NUMBERS
- 1 Press forming die
- 2 Die
- 21 Die corner
- 2S Die shoulder
- 3 Punch
- 31 Punch corner
- 3S Punch shoulder
- 4 Blank sheet
- 41 Inward-facing corner
- 5 Blank holder
- 6 Corner groove
- 6S Groove shoulder
- Fc Corner flange
- Fs Side flange
Claims
1. A press-forming die configured to press-form at least a region around an inward-facing corner of a blank sheet to form, on the blank sheet, a curved corner flange that rises from an inner edge of the inward-facing corner, and first and second side flanges that respectively extend from opposite sides of the corner flange, the press-forming die comprising:
- a die having a curved die corner shaped to form the curved corner flange and first and second die sides configured to respectively form the first and second side flanges; and
- a punch having a curved punch corner and first and second punch sides that are configured to respectively cooperate with the curved die corner and the first and second die sides;
- wherein a corner groove is defined in the curved punch corner and extends along a portion of the punch at which leading surfaces and a side surface of the punch intersect in a stroke direction of the punch; and
- the corner groove is shaped such that its groove width decreases in a direction moving away from the leading surfaces in the stroke direction and converges at a punch corner center on the side surface of the punch.
2. The press-forming die according to claim 1, wherein:
- groove shoulders extend along intersections of the corner groove and the leading surfaces, the groove shoulders having a shoulder radius Rgs,
- punch shoulders extend along an intersection of the corner groove and the side surface and along intersections of the leading surfaces and the side surface, the punch shoulders having a shoulder radius Rps, and
- the relationships Rps≦Rgs and Rgs≦30 mm are satisfied.
3. The press-forming die according to claim 2, wherein intersections of the punch shoulders and the groove shoulders on the leading surfaces are at or outside of boundaries of the punch corner with the first and second punch sides on the side surface of the punch.
4. The press-forming die according to claim 3, wherein a ratio D/W of a groove depth D of the corner groove in the stroke direction to a groove width W of the corner groove at the leading surfaces is larger than 0.25.
5. The press-forming die according to claim 4, wherein the corner groove is formed by first and second inclined surfaces that respectively extend from the leading surfaces and converge along a diagonal line intersecting a center point of the punch corner.
6. The press-forming die according to claim 1, wherein the die has four of said die corner, and the punch has four of said punch corner.
7. The press-forming die according to claim 1, wherein a ratio D/W of a groove depth D of the corner groove in the stroke direction to a groove width W of the corner groove at the leading surfaces is larger than 0.25.
8. The press-forming die according to claim 1, wherein the corner groove is formed by first and second inclined surfaces that respectively extend from the leading surfaces and converge along a diagonal line intersecting a center point of the punch corner.
9. The press-forming die according to claim 8, wherein the first and second inclined surfaces respectively extend from the leading surfaces at an angle within the range of 30°-60°.
10. The press-forming die according to claim 1, wherein the corner groove is V-shaped.
11. A method for forming, on a blank sheet having an inward-facing corner, a curved corner flange that rises from an inner edge of the inward-facing corner, and first and second side flanges that respectively extend from opposite sides of the corner flange, the method comprising:
- placing the blank sheet between a die and a punch of a press-forming die; and
- advancing the punch relative to the die and thereby bending the curved corner flange and the first and second side flanges,
- wherein:
- the die has a curved die corner and first and second die sides,
- the punch has a curved punch corner and first and second punch sides,
- the curved die corner and curved punch corner form the curved corner flange on the blank sheet,
- the first and second die sides and the first and second punch sides respectively form the first and second side flanges on the blank sheet,
- a corner groove is defined in the curved punch corner and extends along a portion of the punch at which leading surfaces and a side surface of the punch intersect in a stroke direction of the punch, and
- the corner groove is shaped such that its groove width decreases in a direction moving away from the leading surfaces in the stroke direction and converges at a punch corner center on the side surface of the punch.
12. The method according to claim 11, wherein, as the punch advances relative to the die, the corner groove causes the first and second side flanges to be bent before the curved corner flange is bent.
13. The method according to claim 12, wherein, as the punch advances relative to the die, the corner groove causes outer edges of the curved corner flange to be bent before a center portion of the curved corner flange is bent.
14. The method according to claim 13, wherein:
- punch shoulders extend along an intersection of the corner groove and the side surface and along intersections of the leading surfaces and the side surface, the punch shoulders having a shoulder radius Rps,
- the blank sheet has a sheet thickness t,
- the blank sheet has a flange length Ls at both ends of the inward-facing corner, and
- the relationship t≦Rps≦Ls is satisfied.
15. The method according to claim 14, wherein:
- groove shoulders extend along intersections of the corner groove and the leading surfaces, the groove shoulders having a shoulder radius Rgs, and
- the relationships Rps≦Rgs and Rgs≦30 mm are satisfied.
16. The method according to claim 15, wherein intersections of the punch shoulders and the groove shoulders on the leading surfaces are at or outside of boundaries of the punch corner with the first and second punch sides on the side surface of the punch.
17. The method according to claim 16, wherein a ratio D/W of a groove depth D of the corner groove in the stroke direction to a groove width W of the corner groove at the leading surfaces is larger than 0.25.
18. The method according to claim 17, wherein the corner groove is formed by first and second inclined surfaces that respectively extend from the leading surfaces and converge along a diagonal line intersecting a center point of the side surface of the punch corner.
19. The method according to claim 18, wherein the first and second inclined surfaces respectively extend from the leading surfaces at an angle within the range of 30°-60°.
20. The method according to claim 19, wherein the blank sheet is composed of an aluminum alloy.
Type: Application
Filed: Jul 11, 2017
Publication Date: Feb 15, 2018
Inventors: Yoichi UENO (Aichi), Yutaka YAMADA (Aichi)
Application Number: 15/646,353