Patent Application
20180104735
The present invention relates to a press-working apparatus, a press-working method, and a press-molded product, and particularly relates to a press-working apparatus and a press-working method for obtaining a molded product including a U-shaped portion in a cross-section, and a press-molded product obtained by such an apparatus or method.
Long channel materials and hat-shaped materials molded by press working are generally used as, for example, structural parts of vehicles and the like. High strength is required of structural parts of vehicles in order to ensure crash safety, vehicle body rigidity, etc. In addition, axisymmetric cup-shaped materials similarly molded by press working are generally used as, for example, rotation members such as drums and hubs in transmissions of vehicles. High strength is required of rotation members as well in order to withstand transmitted torque.
The channel materials and hat-shaped materials and the cup-shaped materials described above all include a U-shaped portion in a cross-section. The U-shaped portion includes a wall, a bottom, and a punch-nose between the wall and the bottom. In the case where strength is required of a member as described above, the sheet thickness of the member needs to be ensured sufficiently in this U-shaped portion. Hence, as described in Patent Literature 1, for example, a technology of making the distance between a die and a punch larger than the sheet thickness of a work in press working, and pushing in an end of a wall after formation of the outline of a U-shaped portion, thereby increasing the sheet thickness of (thickening) the entire U-shaped portion including a punch-nose has been known.
Patent Literature 1: JP 2009-208149A
In the conventional technology described above, when the end of the wall is pushed in, a material is caused to flow between the wall and the bottom to thicken the entire U-shaped portion. Therefore, it is necessary to make the outside of the punch-nose have a shape with curvature and make the curvature radius large to some extent, which limits design. In addition, since the U-shaped portion is entirely thickened, it is difficult to perform working to thicken only the punch-nose to a desired sheet thickness, for example.
Hence, the present invention has been made in view of the above problems, and an object of the present invention is to provide a novel and improved press-working apparatus, press-working method, and press-molded product that enable flexible molding of a punch-nose in press working for obtaining a molded product including a U-shaped portion in a cross-section.
According to an aspect of the present invention in order to achieve the above-mentioned object, there is provided a press-working apparatus configured to provide a molded product by performing press working on a work, the molded product including, in a cross-section, a U-shaped portion including a bottom, a wall, and a punch-nose between the bottom and the wall, the press-working apparatus including: a die in which a recessed portion to receive the U-shaped portion is formed; a first punch that sandwiches a central area of the bottom with a bottom surface of the recessed portion; and a second punch that is pushed into the recessed portion later than the first punch, to restrain the wall between the second punch and a side surface of the recessed portion, and sandwich the work with the bottom surface to mold a peripheral area of the bottom and the punch-nose. A sandwiching width of the first punch that sandwiches the central area of the bottom and a setback amount of the second punch from the first punch in a push-in direction are set on the basis of a target sheet thickness of the punch-nose.
In the press-working apparatus, the work may have a flat plate shape at the time of starting the press working, and the first punch and the second punch may push the flat-plate-shaped work into the recessed portion while maintaining a state where the second punch is set back relative to the first punch by first pressing, to mold the wall and the central area of the bottom.
The second punch may be pushed into the recessed portion by second press working, to sandwich the work with the bottom surface to mold the peripheral area of the bottom and the punch-nose.
The sandwiching width of the first punch and the setback amount of the second punch may be set in a manner that a cross-sectional area of a tapered portion between the central area of the bottom and the wall, which is molded by first press working, coincides with a cross-sectional area of a ridge portion of the molded product in which the punch-nose has the target sheet thickness, which is molded by second press working.
For example, the sandwiching width of the first punch and the setback amount of the second punch may be set to satisfy Formula (A) below.
[Math. 1]
√{square root over ((H12+W12))}×t=(Rp+t)2−¼πRp2 (A)
Here, H1 is the setback amount of the second punch, W1 is a length of the tapered portion in a width direction, Rp is a curvature radius of an inside of the punch-nose, and t is a sheet thickness of the work.
In the press-working apparatus, the molded product may be a long member in which the U-shaped portion forms a channel shape, or may be an axisymmetric member in which the U-shaped portion forms a cup shape. The punch-nose may be molded to have a larger sheet thickness than the wall and the bottom. An outside of the punch-nose may be molded to be substantially right-angled.
The press-working apparatus may further include a third punch that abuts against an end surface of the wall on an opposite side to the punch-nose, and is pressed toward the bottom surface after molding of the punch-nose.
According to another aspect of the present invention in order to achieve the above-mentioned object, there is provided a press-working method configured to provide a molded product by performing press working on a work, the molded product including, in a cross-section, a U-shaped portion including a bottom, a wall, and a punch-nose between the bottom and the wall, the press-working method including: a first press-working step of a first punch sandwiching a central area of the bottom with a bottom surface of a recessed portion of a die; and a second press-working step of a second punch being pushed into the recessed portion of the die later than the first punch, to restrain the wall between the second punch and a side surface of the recessed portion, and sandwich the work with the bottom surface to mold a peripheral area of the bottom and the punch-nose. A sandwiching width of the first punch that sandwiches the central area of the bottom and a setback amount of the second punch from the first punch in a push-in direction are set on the basis of a target sheet thickness of the punch-nose.
The work may have a flat plate shape at the time of starting the press working, and in the first press-working step, the first punch and the second punch may push the flat-plate-shaped work into the recessed portion while maintaining a state where the second punch is set back relative to the first punch, to mold the wall and the central area of the bottom.
In the second press-working step, the second punch may be pushed into the recessed portion, to sandwich the work with the bottom surface to mold the peripheral area of the bottom and the punch-nose.
The sandwiching width of the first punch and the setback amount of the second punch may be set in a manner that a cross-sectional area of a tapered portion between the central area of the bottom and the wall, which is molded by first press working, coincides with a cross-sectional area of a ridge portion of the molded product in which the punch-nose has the target sheet thickness, which is molded by second press working.
For example, the sandwiching width of the first punch and the setback amount of the second punch may be set to satisfy Formula (B) below.
[Math. 2]
√{square root over ((H12+W12))}×t=(Rp+t)2−¼πRp2 (B)
Here, H1 is the setback amount of the second punch, W1 is a length of the tapered portion in a width direction, Rp is a curvature radius of an inside of the punch-nose, and t is a sheet thickness of the work.
The press-working method may include a heating step of heating the work to a predetermined temperature before the first press-working step.
Furthermore, the press-working method may further include a receiving step of causing the recessed portion formed in the die to receive the U-shaped portion of the molded product before the first press-working step.
The press-working method may further include an additional molding step of, using the molded product including, in a cross-section, the U-shaped portion including the bottom, the wall, and the punch-nose as a second work, molding a second molded product by pushing in an end surface of the wall of the second work by a fifth punch in a state where the bottom of the second work is sandwiched by a second die and a fourth punch. The additional molding step may use a second press-working apparatus including the second die that has a shape corresponding to a shape of the second molded product, has a recessed portion to accommodate the second work, and supports at least the bottom of the second work, the fourth punch that sandwiches the bottom of the second work with the second die, and the fifth punch that pushes in the end surface of the wall of the second work to mold the second molded product.
Here, the recessed portion of the second die of the second press-working apparatus may be formed in a manner that a length between surfaces corresponding to the wall of the second work is larger than a length between outer surfaces of the wall of the second work, and in the additional molding step, the wall of the second work may be thickened by pushing in the end surface of the wall of the second work by the fifth punch in a state where the bottom of the second work is sandwiched by the second die and the fourth punch.
Alternatively, a portion of the second die of the second press-working apparatus that supports the bottom of the second work may include a fixed die that supports a central area and a movable die that supports an end and is movable in an extension direction of the wall, and in the additional molding step, a vertical wall extended portion extended from the wall may be formed by moving the movable die by pushing in the end surface of the wall of the second work by the fifth punch in a state where the bottom of the second work is sandwiched by the second die and the fourth punch.
In a portion of the second die of the second press-working apparatus that supports the wall of the second work, a step portion recessed in a direction going away from the wall may be formed at a position corresponding to the bottom of the second work, and in the additional molding step, a ceiling extended portion extended from the bottom may be formed by pushing in the end surface of the wall of the second work by the fifth punch in a state where the bottom of the second work is sandwiched by the second die and the fourth punch.
According to still another aspect of the present invention in order to achieve the above-mentioned object, there is provided a press-molded product molded by performing press working on a work, the press-molded product including, in a cross-section, a U-shaped portion including a bottom, a wall, and a punch-nose between the bottom and the wall. The punch-nose has a larger sheet thickness than the wall and the bottom. According to still another aspect of the present invention, there is provided a press-molded product molded by performing press working on a work, the press-molded product including, in a cross-section, a U-shaped portion including a bottom, a wall, and a punch-nose between the bottom and the wall. An outside of the punch-nose is substantially right-angled.
Here, a curvature radius R1 of an inside of the punch-nose, a curvature radius R2 of an outside of the punch-nose, and a sheet thickness t of the bottom and the wall of the work may satisfy a relation of Formula (C) below,
R2≤R1+t (C)
A hardness of the punch-nose of the press-molded product may be higher than a hardness of the work.
For example, the hardness of the punch-nose of the press-molded product may be 1.5 times or more as much as the hardness of the work.
The bottom of the press-molded product may include a central area, and a peripheral area between the central area and the punch-nose, the peripheral area being an area within a predetermined distance from the punch-nose, and a hardness of a boundary portion between the central area and the peripheral area may be higher than a hardness of the work and lower than a hardness of the punch-nose.
Here, the predetermined distance from the punch-nose may be decided on the basis of a sheet thickness of the work and a curvature radius of an inside of the punch-nose.
The central area of the bottom of the press-molded product may be an area molded by first press working, and the peripheral area of the bottom of the press-molded product may be an area molded by second press working after the first press working.
A sheet thickness of the wall of the press-molded product may be larger than a sheet thickness of the bottom.
The press-molded product may further include a vertical wall extended portion obtained by extending the wall.
Alternatively, the press-molded product may further include a ceiling extended portion obtained by extending the bottom.
As described above, the present invention enables flexible molding of a punch-nose in press working for obtaining a molded product including a U-shaped portion in a cross-section.
Hereinafter, (a) preferred embodiment(s) of the present invention will be described in detail with reference to the appended drawings. In this specification and the appended drawings, structural elements that have substantially the same function and structure are denoted with the same reference numerals in the drawings, and repeated explanation of these structural elements is omitted in some cases.
As illustrated in
After the start of press working, when the punch 140 is pressed toward the bottom surface of the recessed portion 126 (first pressing), the cushion 128 shrinks first, and the movable die 124 is pushed into the recessed portion 126 while sandwiching the center of the work 10 with the inside movable punch 146. At this point in time, the cushions 148 and 150 do not shrink; thus, the punch 140 is pushed into the recessed portion 126 in a state where the positional relation in which the outside movable punch 144 is set back relative to the inside movable punch 146 is maintained. In other words, the outside movable punch 144 is pushed into the recessed portion 126 later than the inside movable punch 146.
As illustrated in
Here, in the present embodiment, the wall 12 is restrained between the outside movable punch 144 and the side surface 130 of the recessed portion 126. In other words, in the press-working apparatus 100, the outside movable punch 144 is designed in a manner that its distance from the side surface 130 substantially coincides with the sheet thickness of the work 10. In addition, at the point in time when the movable die 124 pushed in by the inside movable punch 146 hits the bottom of the recessed portion 126, a tapered portion 16 is formed between the bottom 14a and the wall 12, because the outside movable punch 144 is pushed into the recessed portion 126 later than the inside movable punch 146.
As illustrated in
As illustrated in
In the press-working apparatus 100 to perform working on the work 10 in this manner, working is performed in a manner that the length of the tapered portion 16 formed by the first pressing is greater than the total length of the peripheral area 14b of the bottom and the punch-nose 18; thus, the punch-nose 18 is molded to have a larger sheet thickness than the wall 12 and the bottom 14. Hence, it is necessary to appropriately set the sandwiching width of the upper surface of the inside movable punch 146 that sandwiches the central area 14a of the bottom 14 of the work 10, and the setback amount of the outside movable punch 144 from the inside movable punch 146 in the push-in direction, which determine the length of the tapered portion 16. Specifically, in order for the punch-nose 18 to be molded to have a larger sheet thickness than the wall 12 and the bottom 14, the amount of the work that constitutes the tapered portion 16 is equal to or more than the amount of the work that is needed for the punch-nose 18 to have a target sheet thickness. That is, if a cross-sectional area of the tapered portion 16 is equal to or more than a cross-sectional area of a portion including the punch-nose 18 (corresponding to a ridge portion described later) that is formed from the tapered portion 16, the punch-nose 18 can have the target sheet thickness or more.
First, the cross-sectional area of the portion including the punch-nose 18 that is formed from the tapered portion 16 is calculated in the following manner. For description,
As illustrated in
A cross-sectional area SA of the ridge portion illustrated in
[Math. 3]
S
A=¼{π(Rp+t)2−πRp2} (1)
In the case of making the outside of the punch-nose 18 right-angled, a cross-sectional area SB of the ridge portion of the work 10 is expressed by Formula (2) below.
[Math. 4]
S
B=(Rp+t)2−¼πRp2 (2)
Meanwhile, a cross-sectional area ST of the tapered portion 16 is expressed by Formula (3) below, where the length of the tapered portion 16 in the push-in direction is denoted by H1 and the length of the tapered portion 16 in the width direction is denoted by W1 as illustrated in
[Math. 5]
S
T=√{square root over ((H12+W12))}×t (3)
According to the above description, if the cross-sectional area ST of the tapered portion 16 is at least equal to or more than the cross-sectional area SA expressed in Formula (1) above, the sheet thickness of the punch-nose 18 does not decrease from the sheet thickness of the work 10. In addition, to make the outside of the punch-nose 18 substantially right-angled, the cross-sectional area ST of the tapered portion 16 is made equal to the cross-sectional area SB expressed in Formula (2) above. In this manner, the cross-sectional area ST of the tapered portion 16 may be set in accordance with the target sheet thickness of the punch-nose 18.
In the press-working apparatus 100, the length H1 of the tapered portion 16 in the push-in direction, which determines the cross-sectional area ST of the tapered portion 16, corresponds to the setback amount of the outside movable punch 144 from the inside movable punch 146 in the push-in direction of the press-working apparatus 100. In addition, the length W1 of the tapered portion 16 in the width direction, which determines the cross-sectional area ST of the tapered portion 16, corresponds to ½ of a difference between the width of the recessed portion 126 of the fixed die 122 and the width of the upper surface of the inside movable punch 146. The width of the upper surface of the inside movable punch 146 is the sandwiching width to sandwich the central area 14a of the bottom 14. The width of the recessed portion 126 of the fixed die 122 is decided as a size of a molded product; hence, the length W1 of the tapered portion 16 in the width direction is adjusted in accordance with the width of the upper surface of the inside movable punch 146.
Therefore, the cross-sectional area ST of the tapered portion 16 can be set to a predetermined size by adjusting the setback amount of the outside movable punch 144 from the inside movable punch 146 in the push-in direction of the press-working apparatus 100 and the width of the upper surface of the inside movable punch 146 (i.e., the sandwiching width). Hence, the cross-sectional area ST of the tapered portion 16 is decided on the basis of the target sheet thickness of the punch-nose 18, and the press-working apparatus 100 is configured in a manner that the tapered portion 16 having the decided cross-sectional area ST is obtained; thus, a molded product in which the punch-nose 18 is thickened can be obtained.
As already described, in the conventional technology, a material is caused to flow between the wall and the bottom by making the outside of the punch-nose have a large curvature radius, to thicken the entire U-shaped portion in a cross-section. In this case, if the outside of the punch-nose has a small curvature radius, flow of the material is inhibited, which causes flaws such as a fold mark. In contrast, in the present embodiment, after the wall 12 and the central area of the bottom 14 are molded, the outside movable punch 144 crushes the tapered portion 16 to mold the punch-nose 18; thus, flow of material does not occur between the wall 12 and the bottom 14, and accordingly it is possible to make the outside of the punch-nose 18 have a small curvature radius or make the outside of the punch-nose 18 substantially right-angled.
As described above, in the example illustrated in
As a specific example, in the case where the sheet thickness t of the wall 12 and the bottom 14 of the work 10 is 5 mm, the curvature radius R2 of the outside of the punch-nose 18 is set to 0.5 mm (10% of the sheet thickness t), and the curvature radius R1 of the inside is set to 7.5 mm (1.5 times the sheet thickness t); thus, press working can be performed without causing flaws. Note that since the outside of the punch-nose 18 can be right-angled as in the example illustrated in
On the other hand, in the example illustrated in
In addition, in a work molded by the press-working apparatus according to the present embodiment, a punch-nose is harder than other portions. As an example,
The thickness before press working of the work of this example was 1.6 mm, and a hardness (hereinafter also referred to as “material hardness”) HV0 thereof was 85. A tapered portion formed by the first press working had a length in the width direction of 10 mm and a length in the push-in direction of 10 mm. Then, after the punch-nose and a peripheral area of the bottom were molded by the second press working, hardness at a position of 200 μm in the thickness direction from the outer surface of the work was measured every 1 mm from the punch-nose toward the wall and the bottom.
The plastic strain distribution shown in
As shown in
More specifically, the bottom at the position away from the punch-nose by the predetermined distance corresponds to a bottom-side end area of the tapered portion, which is adjacent to a portion sandwiched by the inside movable punch in the recessed portion of the die by the first press working. The central area of the bottom is sandwiched by the first press working and therefore substantially maintains the hardness of the material hardness HV0, whereas the bottom-side end area of the tapered portion is not sandwiched by the first press working. Therefore, it is presumed that work hardening is caused in the bottom-side end area of the tapered portion by the second press working performed after the first press working. Consequently, the work molded by the press-working apparatus according to the present embodiment has the hardness distribution shown in
For comparison, if a punch-nose is molded by performing press working once, for example, stress is concentrated on the punch-nose, and plastic strain occurs only in the punch-nose. In contrast, when the punch-nose is molded by multi-step press working as in the press-working apparatus according to the present embodiment, the central area of the bottom can substantially maintain the hardness of the material hardness HV0 in the first press working, and furthermore, a load in the second press working after the first press working can be easily dispersed throughout the tapered portion molded in the first press working. This suppresses concentration of stress on the punch-nose molded from the tapered portion, and also reduces a load in molding the punch-nose and the peripheral area of the bottom from the tapered portion.
Although the work of this example is a 270 MPa-grade steel sheet and is soft steel with high work hardenability, also a steel sheet with low work hardenability, such as a high-tensile steel sheet, similarly exhibits a tendency of hardness being high in the punch-nose and in the bottom at a position away from the punch-nose by a predetermined distance. In this case, a rate of increase in hardness in the tapered portion and in the bottom at the position away from the punch-nose by the predetermined distance is lower than that in soft steel as in this example. Specifically, the hardness in the punch-nose is approximately 1.5 times the material hardness HV0, and the hardness in the bottom at the position away from the punch-nose by the predetermined distance is approximately 1.1 times the material hardness HV0.
On the other hand, an axisymmetric-shaped molded product 60 illustrated in the example of
The molded products 50 and 60 described above both are molded products that are molded by press working and include a U-shaped portion in a cross-section. These molded products exhibit, for example, a characteristic of a punch-nose of the
U-shaped portion being thickened or the outside of the punch-nose being substantially right-angled, as described above. Note that, although details will be described later, particularly in the case where the molded product has a cup shape, thinning may occur in the punch-nose in a step of molding the U-shaped portion in the cross-section. When thinning is suppressed by applying the present embodiment in such a case, the curvature radius of the outside of the punch-nose of the molded product may be equal to or smaller than the sum of the curvature radius of the inside and the sheet thickness.
After this, when the punch 140 is further pressed toward the bottom surface 132, the inside of the punch-nose 18 is expanded by the outside movable punch 144; thus, the wall 12 is pushed out upward. At this time, the fixed punch 142 is pushed up by the end surface 19 of the wall 12 to be set back with respect to the outside movable punch 144. In other words, in the present modification example, the action of the fixed punch 142 with respect to the end surface 19 is opposite to that in the example illustrated in
In the present modification example, the length of the tapered portion 16 is adjusted by setting a difference in position between the outside movable punch 144 and the inside movable punch 146 at the time of starting press working (the initial length of the cushion 150), for example, and the outside of the punch-nose 18 is molded to be substantially right-angled, without performing additional pressing by the fixed punch 142 as in the example illustrated in
In the first embodiment of the present invention described above, in press-working of the work 10 using the press-working apparatus 100, the outside movable punch 144 is pushed into the recessed portion 126 later than the inside movable punch 146; thus, the tapered portion 16 is formed between the wall 12 and the bottom 14a. Since the length of the tapered portion 16 is greater than the total length of the peripheral area 14b of the bottom and the punch-nose 18 that are finally formed, by molding the punch-nose 18 by expanding the tapered portion 16, the punch-nose 18 can be thickened without causing material to flow between the wall 12 and the bottom 14. Therefore, in the present embodiment, it is possible to make the outside of the punch-nose 18 have a small curvature radius as compared with a conventional technology or make the outside of the punch-nose 18 substantially right-angled. In addition, it is possible to thicken only the punch-nose 18 without thickening the wall 12 and the bottom 14.
In the press-working apparatus 100 according to the present embodiment, in a series of pressing steps of pushing in the punch 140, the action of the cushion 150 causes the outside movable punch 144 to be pushed into the recessed portion 126 later than the inside movable punch 146. This allows flexible molding of the punch-nose 18. Accordingly, the press-working apparatus 100 may be uniaxial, and there is no need for a multi-axial press-working apparatus in which a plurality of portions of a punch are pressed independently of each other.
Although press working is started from a state where the work 10 has a flat plate shape as illustrated in
As another modification example of the first embodiment of the present invention, for example, a corner surface may be formed between a side surface and a bottom surface in a recessed portion formed in a die. By molding a work along this corner surface, the outside of a punch-nose between a wall and a bottom can be worked precisely into a shape with curvature. Hereinafter, description will be given on press-molding in a case where the outside of the punch-nose is provided with curvature. Note that other points are similar to those in the first embodiment, and therefore repeated explanation is omitted.
As illustrated in
After the start of press working, when the punch 140 is pressed toward the bottom surface of the recessed portion 226, the cushion 228 shrinks first, and the movable die 224 is pushed into the recessed portion 226 while sandwiching the center of the work 20 with the inside movable punch 146. As in the first embodiment, the punch 140 is pushed into the recessed portion 126 in a state where the positional relation in which the outside movable punch 144 is set back relative to the inside movable punch 146 is maintained. Accordingly, the outside movable punch 144 is pushed into the recessed portion 226 later than the inside movable punch 146.
As illustrated in
Here, as a difference from the first embodiment, in the present embodiment, a corner surface 234 with curvature is present between a bottom surface 232 and the side surface 230 of the recessed portion 226. The bottom surface 232 is formed by the movable die 224 that has hit the bottom, and the side surface 230 and the corner surface 234 are formed by the fixed die 222. Accordingly, in the present embodiment, an outer dimension of the movable die 224 is smaller than an inner dimension of the recessed portion 226 by a dimension of the corner surface 234. Also in the present embodiment, a tapered portion 26 is formed by the outside movable punch 144 being pushed into the recessed portion 226 later than the inside movable punch 146; the tapered portion 26 is not in contact with the corner surface 234.
As illustrated in
Also in the present embodiment, it is apparent from
A molded product molded by the press-working apparatus 200 according to the present embodiment has the same characteristic as the molded product in the first embodiment, except that, in a cross-section, the outside of a punch-nose is molded into a shape with curvature as described above. In other words, a molded product of the present embodiment exhibits a characteristic of a punch-nose being thickened as in the example illustrated in
In addition, the shape of a molded product in the present embodiment may be a long shape (in which a U-shaped portion forms a channel shape) as illustrated in
In the other modification example of the first embodiment of the present invention described above, in press-working of the work 20 using the press-working apparatus 200, the outside movable punch 144 is pushed into the recessed portion 226 later than the inside movable punch 146, and thus the tapered portion 26 is formed, as in the first embodiment. Since the length of the tapered portion 26 is greater than the total length of the bottom 24b and the punch-nose 28 that are finally formed, by molding the punch-nose 28 by expanding the tapered portion 26, the punch-nose 28 can be thickened without causing material to flow between the wall 22 and the bottom 24. In the present embodiment, since the corner surface 234 is formed in the recessed portion 226, the outside of the punch-nose 28 can be stably molded into a shape with curvature; since there is no need to cause a material to flow between the wall 22 and the bottom 24 as described above, the curvature radius of the outside of the punch-nose 28, which is determined by the corner surface 234, can be made smaller than that in a conventional technology, for example. Also in the present embodiment, the press-working apparatus 200 may be uniaxial as in the first embodiment.
Also in the present embodiment, press working in the press-working apparatus 200 is not necessarily started from a state where the work 20 has a flat plate shape as illustrated in
Next, a second embodiment of the present invention is described. In the present embodiment, so-called deep drawing is performed to obtain an axisymmetric-shaped molded product that includes a cup shape formed by a U-shaped portion in a cross-section. In the following description, deep drawing according to the present embodiment and advantages thereof are described in comparison with deep drawing according to a conventional technology. Note that as already described, the first embodiment can also be applied to deep drawing for obtaining an axisymmetric-shaped molded product that includes a cup shape. In other words, even without additional description, a configuration similar to that in the first embodiment can be adopted in the deep drawing in the present embodiment. Similarly, in the case of applying the first embodiment to deep drawing, a configuration similar to that in the present embodiment can be adopted.
In the conventional technology, a punch-nose 98 between a wall 92 and a bottom 94 is simply bent by a shoulder portion 952 of the punch 940; thus, a difference in perimeter between the outside and the inside makes the punch-nose 98 have a smaller sheet thickness than the wall 92 and the bottom 94 (the punch-nose 98 is thinned). Such thinning is significant in the case where the curvature radius of the inside of the punch-nose 98 is made small in a cross-section, for example. The occurrence of thinning in the punch-nose 98 is generally unpreferable, because higher strength is required of the punch-nose 98 rather than the wall 92 and the bottom 94 in some cases.
In deep drawing in the present embodiment, the above-described problem of thinning of a punch-nose in the conventional technology is improved.
As illustrated in
After the start of press working, when the punch 340 is pressed toward the bottom surface of the recessed portion 126, the cushion 128 shrinks first, and the movable die 124 is pushed into the recessed portion 126. At this point in time, the cushion 350 does not shrink; thus, the punch 340 is pushed into the recessed portion 126 in a state where the positional relation in which the fixed punch 344 is set back relative to the movable punch 346 is maintained. In other words, the fixed punch 344 is pushed into the recessed portion 126 later than the movable punch 346. At this time, the blank holder 360 restrains a peripheral portion of the work 30 between the blank holder 360 and an upper surface of the fixed die 122, to suppress occurrence of a wrinkle. Note that such a blank holder may be provided similarly in performing deep drawing in the configuration of the first embodiment, for example.
As illustrated in
As illustrated in
As a specific example, in the present embodiment, in the case where the wall 32 and the bottom 34 of the work 30 have a sheet thickness of 2 mm, deep drawing can be performed using the press-working apparatus 300 in a manner that the sheet thickness of the punch-nose 38 is maintained at 2 mm. Note that in the same case, in deep drawing according to a conventional technology, the sheet thickness of a punch-nose decreased to 1.57 mm.
In the second embodiment of the present invention described above, in deep drawing of the work 30 using the press-working apparatus 300, the fixed punch 344 is pushed into the recessed portion 126 later than the movable punch 346, and thus the tapered portion 36 is formed between the wall 32 and the bottom 34a. By molding the punch-nose 38 by expanding the tapered portion 36, thinning of the punch-nose 38 can be suppressed, as in the first embodiment. Also in the present embodiment, the press-working apparatus 300 may be uniaxial as in the first embodiment.
Also in the present embodiment, press working in the press-working apparatus 300 is not necessarily started from a state where the work 30 has a flat plate shape as illustrated in
Note that in the first embodiment, the first punch that sandwiches the central area of the bottom and the second punch that molds the peripheral area of the bottom and the punch-nose while restraining the wall are both provided as a movable punch, but in the present embodiment, the second punch is a fixed punch. In addition, in the present embodiment, the third punch that abuts against the end surface of the wall is not provided, unlike in the first embodiment. Also in the first embodiment, it is possible to similarly adopt a configuration in which the third punch is not provided and the second punch is a fixed punch.
In addition, described in the present embodiment is suppression of thinning of a punch-nose in deep drawing, but similar thinning of a punch-nose may occur also in bending for obtaining a long molded product. Accordingly, also in bending, the configuration of the present embodiment may be adopted to suppress thinning of a punch-nose (i.e., the punch-nose is not necessarily thickened).
Next, a third embodiment of the present invention is described. In the present embodiment, an additional molding step is added in which a molded product molded by a method in the first embodiment or the second embodiment (hereinafter also simply referred to as the “above embodiment”) is further subjected to press working, and thus a molded product in which a wall is thicker than a bottom is molded. By press-molding a molded product with a thickened wall using a molded product molded by the above embodiment, the wall can be thickened without overlap of inner corner surfaces. Hereinafter, assuming the use of a molded product molded by the above embodiment, description will be given on the additional molding step of thickening the wall.
As illustrated in
The die 420 has a recessed portion 430 that accommodates the work 40. The shape of the recessed portion 430 is formed to correspond to the shape of a molded product to be produced using the work 40. Consequently, a length of the recessed portion 430 in an opposing direction of a wall 42 of the work 40 is greater than a length between opposing outer surfaces of the wall 42. The work 40 is placed in the recessed portion 430 with an opening side of the cup shape facing the punch 440 side, in a manner that a space corresponding to thickening to be caused by the press working is present on the outside of the wall 42 of the work 40, in a state where the work 40 is accommodated in the recessed portion 430.
On the other hand, the movable punch 444 of the punch 440 has a shape corresponding to the cup shape of the work 40. The movable punch 444 is inserted from the opening of the work 40, and is placed in a manner that its lower surface and side surface are in contact with the inner surface (i.e., a bottom surface 432 and a side surface 434) of the cup shape of the work 40. At this time, the movable punch 444 presses the work 40 by a cushion 446 linked to the fixed punch 442, and sandwiches a bottom 44 of the work 40 with the bottom surface 432 of the recessed portion 430 of the die 420. In addition, the fixed punch 442 abuts against an end surface 49 of the wall 42 of the work 40.
When press working by the press-working apparatus 400 is started, the cushion 446 provided between the fixed punch 442 and the movable punch 444 shrinks, and the fixed punch 442 moves toward the bottom surface 432 of the recessed portion 430, as illustrated in
Here, a molded product molded according to the present embodiment is obtained by performing press working using the press-working apparatus 400 on a molded product in which the outside of a punch-nose has a small curvature radius or is substantially right-angled, which is molded according to the above embodiment. If the outside of a punch-nose of a work has a large curvature radius and the punch-nose has a small sheet thickness, when the press-working apparatus 400 presses an end of a wall, a material of the wall and a bottom flows, and flaws such as a fold mark occur on the inside of the punch-nose. The fold mark portion is a portion where inner surfaces of the wall and the bottom contact and overlap each other, and the wall and the bottom are likely to be released from the overlap to open; thus, strength decreases as compared with other portions. In addition, the fold mark portion may cause fatigue breakdown.
In contrast, in the case where a molded product including, in a cross-section, a U-shaped portion in which the outside of the punch-nose has a small curvature radius or is substantially right-angled is used as a work as in the present embodiment, a material of the punch-nose 48 flows in a state where the bottom 44 of the work 40 is sandwiched by the bottom surface 432 of the recessed portion 430 and a lower surface of the movable punch 444, and a space between the punch-nose 48 and the bottom surface 432 and the side surface 434 of the recessed portion 430 is filled. Consequently, it is possible to make the outside of the punch-nose 48 have a small curvature radius or be substantially right-angled like before press working, without causing a fold mark on the inside of the punch-nose 48.
In the third embodiment of the present invention described above, in press-working of the work 40 using the press-working apparatus 400, a molded product including, in a cross-section, a U-shaped portion in which the outside of the punch-nose has a small curvature radius or is substantially right-angled, which is molded in the above embodiment, is used as the work 40. Then, the press-working apparatus 400 applies a load to the end surface 49 of the wall 42 in a state where the bottom 44 of the work 40 is sandwiched; thus, the wall 42 can be thickened without causing a material to flow between the wall 42 and the bottom 44. In addition, it is possible to make the outside of the punch-nose 48 have a small curvature radius as compared with a conventional technology or make the outside of the punch-nose 48 substantially right-angled; thus, the punch-nose 48 after molding can also be thickened.
Next, a fourth embodiment of the present invention is described. In the present embodiment, an additional molding step is added in which a molded product molded by a method in the first embodiment or the second embodiment is further subjected to press working, and thus a molded product in which a wall is extended with respect to a bottom is molded. By press-molding a molded product in which a wall is extended with respect to a bottom using a molded product molded by the above embodiment, the wall can be extruded without overlap of inner corner surfaces, and the wall can be extended. Hereinafter, assuming the use of a molded product molded by the above embodiment, description will be given on the additional molding step of extending the wall.
As illustrated in
In the die 520, the vertical wall fixed die 522, the ceiling fixed die 523, and the movable die 524 form a recessed portion that accommodates the work 40. The vertical wall fixed die 522 supports the wall 42 of the work 40, and the ceiling fixed die 523 and the movable die 524 support the bottom 44 of the work 40. As illustrated in
On the other hand, the movable punch 544 of the punch 540 has a shape corresponding to the cup shape of the work 40. The movable punch 544 is inserted from the opening of the work 40, and is placed in a manner that its lower surface and side surface are in contact with the inner surface (i.e., a bottom surface and a side surface) of the cup shape of the work 40. At this time, the movable punch 544 that is linked to the fixed punch 542 by a cushion 546 presses the work 40, and sandwiches the bottom 44 of the work 40 with the ceiling fixed die 523. In addition, the fixed punch 542 abuts against the end surface 49 of the wall 42 of the work 40. In the initial state, the work 40 is not deformed by the fixed punch 542 abutting against the end surface 49 of the wall 42 of the work 40.
When press working by the press-working apparatus 500 is started, the cushion 546 provided between the fixed punch 542 and the movable punch 544 shrinks, and the fixed punch 542 moves toward the bottom surface of the recessed portion, as illustrated in
At this time, the work 40 after press working has a first inner punch-nose 48a inside the recessed portion, and a second inner punch-nose 48b formed by the vertical wall extended portion 46 obtained by extending the wall 42 and the bottom 44. As in the third embodiment, a molded product molded according to the present embodiment is obtained by performing press working using the press-working apparatus 500 on a molded product in which the outside of a punch-nose has a small curvature radius or is substantially right-angled, which is molded according to the first embodiment or the second embodiment. If the outside of a punch-nose of a work has a large curvature radius and the punch-nose has a small sheet thickness, when the press-working apparatus 500 presses an end of a wall, a material of the wall and a bottom flows, and flaws such as a fold mark occur in the first inner punch-nose 48a. The fold mark portion has lower strength than other portions, and may cause fatigue breakdown.
In contrast, in the case where a molded product including, in a cross-section, a U-shaped portion in which the outside of the punch-nose has a small curvature radius or is substantially right-angled is used as a work as in the present embodiment, a material of the punch-nose 48 flows while pushing down the movable die 524, in a state where the bottom 44 of the work 40 is sandwiched by the bottom surface of the recessed portion and a lower surface of the movable punch 544. Consequently, a fold mark does not occur on the inside of the punch-nose 48. In addition, in the second inner punch-nose 48b, as in the first inner punch-nose 48a, it is desirable to provide the inside of the punch-nose 48 with some curvature radius (not close to zero) in terms of avoiding stress concentration on the punch-nose 48. For example, the second inner punch-nose 48b may be provided with substantially the same curvature radius as the first inner punch-nose 48a.
In the fourth embodiment of the present invention described above, in press-working of the work 40 using the press-working apparatus 500, a molded product including, in a cross-section, a U-shaped portion in which the outside of the punch-nose has a small curvature radius or is substantially right-angled, which is molded in the above embodiment, is used as the work 40. Then, the press-working apparatus 500 applies a load to the end surface 49 of the wall 42 in a state where the central area 523a of the bottom 44 of the work 40 is sandwiched. Thus, the wall 42 can be extended without causing a material to flow between the wall 42 and the bottom 44, and a fold mark does not occur in the first inner punch-nose 48a.
Next, a fifth embodiment of the present invention is described. In the present embodiment, an additional molding step is added in which a molded product molded by a method in the first embodiment or the second embodiment is further subjected to press working, and thus a molded product with an extended bottom is molded. By press-molding a molded product with an extended bottom using a molded product molded by the above embodiment, the bottom can be extruded without overlap of inner corner surfaces, and the bottom can be extended. Hereinafter, assuming the use of a molded product molded by the above embodiment, description will be given on the additional molding step of extending the bottom.
As illustrated in
In the die 620, the vertical wall fixed die 622 and the ceiling fixed die 623 form a recessed portion that accommodates the work 40. The vertical wall fixed die 522 supports an area other than a portion where the bottom 44 is to be extended, of the wall 42 of the work 40. In addition, in a portion of the vertical wall fixed die 622 that corresponds to an area of the portion where the bottom 44 is to be extended, a step portion 622a depressed in a direction going away from the wall 42 of the work 40 is formed to correspond to the shape of a ceiling extended portion 47 to be formed. By installing the vertical wall fixed die 622 on the ceiling fixed die 623, a space 632 corresponding to the shape of the ceiling extended portion 47 is formed by the step portion 622a of the vertical wall fixed die 622 and the ceiling fixed die 623. The work 40 placed in the recessed portion of the die 620 is in a state where a partial area of the wall 42 and the bottom 44 are supported, as illustrated in
On the other hand, the movable punch 644 of the punch 640 has a shape corresponding to the cup shape of the work 40. The movable punch 644 is inserted from the opening of the work 40, and is placed in a manner that its lower surface and side surface are in contact with the inner surface (i.e., a bottom surface and a side surface) of the cup shape of the work 40. At this time, the movable punch 644 presses the work 40 by a cushion 646 linked to the fixed punch 642, and sandwiches the bottom 44 of the work 40 with the ceiling fixed die 623. In addition, the fixed punch 642 abuts against the end surface 49 of the wall 42 of the work 40. In the initial state, the work 40 is not deformed by the fixed punch 642 abutting against the end surface 49 of the wall 42 of the work 40.
When press working by the press-working apparatus 600 is started, the cushion 646 provided between the fixed punch 642 and the movable punch 644 shrinks, and the fixed punch 642 moves toward the bottom surface of the recessed portion, as illustrated in
As in the third and fourth embodiments, a molded product molded according to the present embodiment is obtained by performing press working using the press-working apparatus 600 on a molded product in which the outside of a punch-nose has a small curvature radius or is substantially right-angled, which is molded according to the first embodiment or the second embodiment. If the outside of a punch-nose of a work has a large curvature radius and the punch-nose has a small sheet thickness, when the press-working apparatus 600 presses an end of a wall, a material of the wall and a bottom flows, and flaws such as a fold mark occur inside the punch-nose 48. The fold mark portion has lower strength than other portions, and may cause fatigue breakdown.
In contrast, in the case where a molded product including, in a cross-section, a U-shaped portion in which the outside of the punch-nose has a small curvature radius or is substantially right-angled is used as a work as in the present embodiment, a material of the punch-nose 48 flows in a state where the bottom 44 of the work 40 is sandwiched by the bottom surface of the recessed portion and a lower surface of the movable punch 644, and the space 632 is filled. Consequently, a fold mark does not occur in the first inner punch-nose 48a formed by the inner surface of the wall 42 and the bottom 44. Note that by the formation of the ceiling extended portion 47 obtained by extending the bottom 44, a third inner punch-nose 48c is formed by the outer surface of the wall 42 and the ceiling extended portion 47. In the third inner punch-nose 48c, as in the first inner punch-nose 48a, it is desirable to provide the inside of the punch-nose 48 with some curvature radius (not close to zero) in terms of avoiding stress concentration on the punch-nose 48. For example, the third inner punch-nose 48c may be provided with substantially the same curvature radius as the first inner punch-nose 48a.
In the fifth embodiment of the present invention described above, in press-working of the work 40 using the press-working apparatus 600, a molded product including, in a cross-section, a U-shaped portion in which the outside of the punch-nose has a small curvature radius or is substantially right-angled, which is molded in the above embodiment, is used as the work 40. Then, the press-working apparatus 600 applies a load to the end surface 49 of the wall 42 in a state where the bottom 44 of the work 40 is sandwiched. Thus, the bottom 44 can be extended without causing a material to flow between the wall 42 and the bottom 44, and a fold mark does not occur in the first inner punch-nose 48a.
According to the first and second embodiments of the present invention described above, in press working of a work using a press-working apparatus, a tapered portion is formed between a wall and a bottom, and then a punch-nose is molded by expanding the tapered portion. Thus, the punch-nose can be thickened without causing a material to flow between the wall and the bottom. Therefore, it is possible to make the outside of the punch-nose have a small curvature radius as compared with a conventional technology or make the outside of the punch-nose substantially right-angled. In addition, according to the first and second embodiments of the present invention, the outside of the punch-nose is not molded to have a small curvature radius or be substantially right-angled from a flat plate in one step, but the shape of the outside of the punch-nose is molded by stepwise push-in; thus, press molding can be performed with a smaller load than that in a conventional technology. Consequently, even press molding of a steel material with high strength can be performed without causing a crack or the like in molding. Note that materials that can be molded by a press-molding method according to the first and second embodiments of the present invention include aluminum and the like, in addition to steel.
Moreover, according to the third to fifth embodiments of the present invention, a molded product in which the outside of a punch-nose has a small curvature radius or is substantially right-angled, which is molded by a press-molding apparatus of the first embodiment or the second embodiment, is used as a second work, and press working is further performed to form a molded product with another shape. Since the molded product in which the outside of the punch-nose has a small curvature radius or is substantially right-angled is used as the second work, flaws such as a fold mark can be prevented from occurring on the inside of the punch-nose when thickening of the wall or extension of the wall or the bottom is performed by press working.
Furthermore, molded products molded by a press-molding apparatus of the third to fifth embodiments of the present invention have complicated shapes, and generally have been formed by connecting a plurality of parts by welding or the like. However, a molded product with a complicated shape can be produced as one part by combining press molding using a press-molding apparatus of the first embodiment or the second embodiment and press molding using a press-molding apparatus of the third to fifth embodiments. This can reduce the number of parts and reduce the weight of a part, and also can cut production cost.
A crash test was performed to evaluate shock absorption performance of a press-molded product molded by a press-working apparatus of the present invention. In the present example, a three-point bending test was performed on a press-molded product with a channel shape having a U-shaped portion, in which a flange portion extending from a wall was formed, and shock absorption performance was evaluated on the basis of absorption energy per unit volume. The test was performed on five press-molded products having different shapes of punch-noses. A 980 MPa-grade steel sheet was used as a work. The press-molded product to be tested was molded using a press-working apparatus obtained by configuring the press-working apparatus 100 described in the first embodiment in a manner that a flange portion can be molded in addition.
Here,
First, in starting press working, the flat-plate-shaped work 10 is sandwiched by the movable punch 744 and the inside movable die 724 (STEP 1). Then, the die 720 is pushed in to the punch 740 side until the outside movable die 726 abuts against the fixed punch 742, a wall is restrained, between a projection 742a of the fixed punch 742 and the outside movable die 726, and a central area of a bottom is molded by the movable punch 744 and the inside movable die 724 (STEP 2). At this time, a tapered portion is formed between the central area of the bottom and the wall. In addition, a portion of the work 10 that is sandwiched by the outside movable die 726 and the fixed punch 742 becomes a flange portion.
After that, when the die 720 is further pushed in to the punch 740 side, the cushion 750 shrinks and the movable punch 744 abuts against the fixed punch 742. At this time, an end surface of the movable punch 744 is flush with an end surface of the projection 742a of the fixed punch 742. By bringing about this state, a peripheral area of the bottom and a punch-nose are molded. In this manner, the movable punch 744 is pushed in later than the fixed punch 742; thus, the punch-nose is thickened.
In the present example, the press-molded product 80 with the shape illustrated in
As illustrated in
Moreover, in addition to having the punch-nose whose sheet thickness is increased from a sheet thickness of the work, the press-molded products of Tests 2 to 5 used in the present example have a work-hardened area in the bottom and the punch-nose, as illustrated in
The preferred embodiment(s) of the present invention has/have been described above with reference to the accompanying drawings, whilst the present invention is not limited to the above examples. A person skilled in the art may find various alterations and modifications within the scope of the appended claims, and it should be understood that they will naturally come under the technical scope of the present invention.
Although a steel sheet is given as an example of a work in the above embodiments, the present invention is not limited to this example. For example, as a work to be subjected to working by a press-working apparatus, a metal sheet of iron, aluminum, titanium, stainless steel, etc., a composite material (metal-resin, different types of metal), and carbon fibers can also be used. Furthermore, the present invention is also applicable to hot stamping of performing press working in state where a work is heated to a predetermined temperature to be softened. In this case, a press-working apparatus and a press-working method of the present invention are applied to and performed in press working after heating of the work. Also in a press-molded product molded by hot stamping, a punch-nose of a U-shaped portion is thickened. In addition, a press-molded product molded by the press-working apparatus can be used for not only cars or car parts, for example, but also various vehicles, general machines, home electrical appliances, shipping, etc.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-091190 | Apr 2015 | JP | national |
| 2016-088085 | Apr 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/063341 | 4/28/2016 | WO | 00 |
