PRESS MOLDING METHOD AND PRESS MOLDING APPARATUS

Abstract

The present disclosure is applied to a press molding method for press-molding a workpiece by a press die composed of an upper die and a lower die while holding the workpiece by a die cushion. The press molding method according to the present disclosure includes pressing process, in which a press position at which the workpiece is pressed by the press die is gradually lowered while repeatedly pressing and releasing the workpiece by the press die a plurality of times until the press position reaches a bottom dead center, wherein in the pressing process, a holding force for holding the workpiece by the die cushion is controlled separately from a press molding force for press-molding the workpiece by the press die.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese patent application No. 2017-178751, filed on Sep. 19, 2017, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

The present disclosure relates to a press molding method and a press molding apparatus.

A method of sandwiching and press-molding a metal plate, which is a workpiece, by an upper die and a lower die in the vertical direction is often used to mold automobile parts and the like (see, for example, Japanese Unexamined Patent Application Publication No. 2005-199318).

In the press molding method described in Japanese Unexamined Patent Application Publication No. 2005-199318, in order to prevent the metal plate from cracking, after a punch (the lower die) is first brought into contact with the metal plate and the molding is started, an operation of temporarily releasing the punch from the metal plate and molding the metal plate again using the punch and a die (the upper die) is performed at least one or more times until the punch reaches an end of a stroke and the molding is completed.

In addition, in the press molding method disclosed in Japanese Unexamined Patent Application Publication No. 2005-199318, the metal plate is molded while it is being sandwiched between a blank holder (a die cushion) and a die in order to prevent the metal plate from wrinkling.

SUMMARY

However, the press molding method disclosed in Japanese Unexamined Patent Application Publication 2005-199318 does not adjust a blank holding force exerted by the blank holding. Therefore, even when the workpiece can be prevented from cracking, it may not be prevented from wrinkling, which leads to a problem that it is not possible to both prevent the workpiece from cracking and to prevent the workpiece from wrinkling.

The present disclosure has been made to solve the above-mentioned problem. The present disclosure aims to provide a press molding method and a press molding apparatus capable of both preventing a workpiece from cracking and preventing the workpiece from wrinkling.

An example aspect of the present disclosure is a press molding method for press-molding a workpiece by a press die composed of an upper die and a lower die while holding the workpiece by a die cushion. The press molding method includes pressing process, in which a press position at which the workpiece is pressed by the press die is gradually lowered while repeatedly pressing and releasing the workpiece by the press die a plurality of times until the press position reaches a bottom dead center. In the pressing process, a holding force for holding the workpiece by the die cushion is controlled separately from a press molding force for press-molding the workpiece by the press die.

An example aspect of the present disclosure is press molding apparatus including a press die composed of an upper die and a lower die and a die cushion, configured to press-mold a workpiece by the press die while holding the workpiece by the die cushion, and configured to execute pressing process, in which a press position at which the workpiece is pressed by the press die is gradually lowered while repeatedly pressing and releasing the workpiece by the press die a plurality of times until the press position reaches a bottom dead center. The press molding apparatus includes:

• • a first control unit configured to control, in the pressing process, a press molding force for press-molding the workpiece by the press die; and
  • a second control unit configured to control, in the pressing process, a holding force for holding the workpiece by the die cushion separately from the press molding force controlled by the first control unit.

The above example aspects achieve an effect of providing a press molding method and a press molding apparatus capable of both effectively preventing a workpiece from cracking and effectively preventing the workpiece from wrinkling.

The above and other objects, features and advantages of the present disclosure will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present disclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing a configuration example of a press molding apparatus according to a first embodiment;

FIG. 2 is a view showing an example of a press molding method according to related art;

FIG. 3 is a view showing an example of the press molding method according to the first embodiment;

FIG. 4 is a view showing an example of movements of a lower surface of an upper die and blank holding surfaces during a molding process by the press molding method according to the first embodiment;

FIG. 5 is a view showing an example of a stress-strain diagram estimated for a metal plate being molded by the press molding method according to the first embodiment;

FIG. 6 is a view showing a configuration example of a press molding apparatus according to a second embodiment; and

FIG. 7 is a view showing a configuration example of a press molding apparatus according to a third embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The same or corresponding elements are denoted by the same signs throughout the drawings, and repeated descriptions will be omitted as necessary for the sake of clarity.

(1) First Embodiment

First, a configuration of the press molding apparatus 1 according to a first embodiment will be described with reference to FIG. 1. FIG. 1 is a view showing a configuration example of a press molding apparatus 1 according to the first embodiment.

As shown in FIG. 1, the press molding apparatus 1 according to the first embodiment includes an upper die 10, a lower die 20, a slide 30, a die cushion apparatus 40, a slide motion controller 50, a cushion motion controller 60, and a synchronization control unit 70.

In the upper die 10, a projection is formed at a center on a lower surface side, and in the lower die 20, a recess corresponding to the projection of the upper die 10 is formed at a center on an upper surface side. The upper die 10 and the lower die 20 are disposed on the upper and lower sides, respectively, in such a way that the projection of the upper die 10 and the recess of the lower die 20 face each other. The upper die 10 and the lower die 20, which constitute a press die, sandwich a metal plate W, which is a workpiece, in a vertical direction and press-mold (draw) the metal plate W into a hat-shape.

Regarding the slide 30, the upper die 10 is fixed to a lower surface thereof. The slide 30 is driven by a servo motor or a hydraulic servo (not shown) to be elevated or lowered. Thus, the upper die 10 is elevated or lowered together with the slide 30 while the upper die 10 is fixed to the lower surface of the slide 30. The position of the lower die 20 is fixed. When the slide 30 is lowered, a press molding force for pressing the metal plate W in the vertical direction is generated by the upper die 10 and the lower die 20.

The die cushion apparatus 40 is provided for the purpose of effectively preventing the metal plate W from wrinkling when the metal plate W is being press-molded. The die cushion apparatus 40 includes a die cushion main body 41 that is driven by the servo motor or the hydraulic servo (not shown) to be elevated or lowered. The die cushion main body 41 is disposed below the lower die 20. The die cushion apparatus 40 includes die cushions 42 extending upward from an upper surface of the die cushion main body 41 and disposed along outer walls of the lower die 20. The recess of the lower die 20 penetrates vertically. The die cushion apparatus 40 includes a die cushion 43 extending upward from the upper surface of the die cushion main body 41 and inserted into the recess of the lower die 20. When the die cushion main body 41 is elevated, a holding force (hereinafter referred to as a blank holding force) for sandwiching and holding the metal plate W in the vertical direction between the upper die 10 and the die cushions 42 and 43 is generated by the die cushions 42 and 43.

During the press-molding of the metal plate W, the press molding force is generated by the upper die 10 and the lower die 20 to press-mold the metal plate W while the blank holding force is being generated by the die cushions 42 and 43 to hold the metal plate W.

The slide motion controller 50 is a first control unit that controls the operation for elevating and lowering the slide 30 (the upper die 10). When the slide 30 (the upper die 10) is elevated or lowered, the position of the lower surface of the upper die 10 changes, and the press molding force exerted on the metal plate W changes. Therefore, by controlling the operation for elevating and lowering the slide 30 (the upper die 10), it is possible to control the press molding force exerted on the metal plate W.

The cushion motion controller 60 is a second control unit that controls the operation for elevating and lowering the die cushion main body 41. When the die cushion main body 41 is elevated or lowered, the positions of the upper surfaces of the die cushions 42 and 43 (i.e., the positions of the blank holding surfaces) change, and the blank holding force exerted on the metal plate W changes. Therefore, by controlling the operation for elevating and lowering the die cushion main body 41, it is possible to control the blank holding force exerted on the metal plate W.

The synchronization control unit 70 controls a timing of the operation for elevating and lowering the die cushion main body 41 controlled by the cushion motion controller 60 so that it is synchronized with a timing of the operation for elevating and lowering the slide 30 (the upper die 10) controlled by the slide motion controller 50. For example, the synchronization control unit 70 performs synchronization control such as starting to elevate the die cushion main body 41 at the timing when the slide 30 (the upper die 10) starts to be lowered.

As described above, in the first embodiment, control on the press molding force exerted by the upper die 10 and the lower die 20, which is performed by the slide motion controller 50, and control on the blank holding force exerted by the die cushions 42 and 43, which is performed by the cushion motion controller 60, are separately performed. However, as mentioned above, the timings of the control on the press molding force and the control on the blank holding force are synchronized by the synchronization control unit 70.

Next, a press molding method according to the first embodiment will be compared with the press molding method according to the related art.

First, a press molding method according to the related art will be described with reference to FIG. 2. FIG. 2 is a view showing an example of the press molding method according to the related art. As shown in FIG. 2, the upper die 10 is lowered from an initial position, and the press molding force is generated by the upper die 10 and the lower die 20 to press the metal plate W (processes P91, P92, and P93). At this time, the die cushions 42 and 43 are elevated from the initial position, and the blank holding force is generated by the die cushions 42 and 43 to hold the metal plate W. In this way, the metal plate W is pressed by the upper die 10 and the lower die 20 while the metal plate W is being held by the die cushions 42 and 43. After that, the upper die 10 is further lowered so that a press position at which the metal plate W is pressed reaches a press bottom dead center (a process P94).

From the process P92 onward, the metal plate W is pressed by the upper die 10 and the lower die 20 at all times. Thus, the amount of inflow of the material of the metal plate W flowing into a vertical wall part of the recess of the lower die 20 becomes insufficient, and the metal plate W may crack at the vertical wall part.

Next, the press molding method according to the first embodiment will be described with reference to FIG. 3. FIG. 3 is a view showing an example of the press molding method according to the first embodiment.

As shown in FIG. 3, first processes P1 to P3 are similar to the processes P91 to P93 according to the related art, respectively.

However, in the subsequent process P4, the upper die 10 is elevated. Then, the pressing on the metal plate W by the upper die 10 and the lower die 20 is released, and the material of the metal plate W flows into the vertical wall part. This effectively prevents the metal plate W from cracking at the vertical wall part.

Then, in the subsequent process P5, the upper die 10 is lowered again. Thus, the metal plate W is pressed by the upper die 10 and the lower die 20. At this time, the press position at which the metal plate W is pressed is lower than the press position when the upper die 10 was lowered last time.

After that, the processes P4 and P5 are repeated until the press position of the metal plate W reaches the press bottom dead center (process P6).

In this way, in the first embodiment, the press position of the metal plate W is gradually lowered to the press bottom dead center while the metal plate W is repeatedly pressed and released by the upper die 10 and the lower die 20. When the upper die 10 is lowered, the amount of inflow of the material of the metal plate W flowing into the vertical wall part of the lower die 20 becomes insufficient, and the metal plate W may crack at the vertical wall part. However, in the first embodiment, the upper die 10 is elevated, and the material of the metal plate W is made to flow into the vertical wall part of the lower die 20 before the metal plate W starts to crack due to the lowering of the upper die 10. This effectively prevents the metal plate W from cracking at the vertical wall part.

In the first embodiment, the control on the blank holding force exerted by the die cushions 42 and 43 is performed separately from the control on the press molding force exerted by the upper die 10 and the lower die 20. Therefore, for example, in the situation where the metal plate W is less prone to wrinkling but is prone to cracking, the blank holding force can be reduced to increase the amount of inflow of the material of the metal plate W flowing into the vertical wall part of the lower die 20. This more effectively prevents the metal plate W from cracking. On the contrary, in the situation where the metal plate W is less prone to cracking but is prone to wrinkling, the blank holding force can be increased to effectively prevent the metal plate W from wrinkling. Thus, it is possible to both effectively prevent the metal plate W from cracking and to effectively prevent the metal plate W from wrinkling.

Next, a method of controlling the blank holding force exerted by the die cushions 42 and 43 and the press molding force exerted by the upper die 10 and the lower die 20 will be described in detail with reference to FIG. 4. FIG. 4 is a view showing an example of movement of the lower surface of the upper die 10 and the blank holding surfaces (the upper surfaces of the die cushions 42 and 43) while the metal plate W is molded by the press molding method according to the first embodiment. In FIG. 4, the horizontal axis represents time [second], and the vertical axis represents a stroke [mm] indicating a distance from the press bottom dead center. Further, FIG. 4 shows a state in which the processes P4 and P5 of FIG. 3 are repeated.

First, a method of controlling press molding force exerted by the upper die 10 and the lower die 20 will be described with reference to FIG. 4. As shown in FIG. 4, the upper die 10 is elevated by T1 [mm] in the process P4 and lowered by T2 (T2>T1) [mm] in the process P5. Thus, when the processes P4 and P5 are performed once, the upper die 10 is lowered by T2−T1 [mm]. By repeating these processes P4 and P5 a plurality of times, the upper die 10 is gradually lowered, and consequently the press position of the metal plate W can be gradually lowered, so that the metal plate W is gradually molded.

As described above, when the upper die 10 is lowered, the amount of inflow of the material of the metal plate W flowing into the vertical wall part of the lower die 20 becomes insufficient, and the metal plate W may crack at the vertical wall part. However, in the first embodiment, the upper die 10 is elevated in the process P4 before the metal plate W starts to crack so that the material of the metal plate W flows into the vertical wall part of the lower die 20, and then the upper die 10 is lowered again in the process P5. This effectively prevents the metal plate W from cracking at the vertical wall part of the lower die 20. The effect of preventing the metal plate W from cracking improves as the amount of molding of the metal plate W (corresponding to T2−T1) becomes finer.

Further, since the metal plate W is gradually molded, the molding load applied by the upper die 10 can also be reduced. Moreover, since the metal plate W is gradually molded, it is possible to prevent spring back from occurring at a part of the metal plate W molded near a shoulder part of the lower die 20. This improves accuracy fixability.

Next, the principle by which the press molding method according to the first embodiment can effectively prevent the crack from occurring will be described with reference to FIG. 5. FIG. 5 is a view showing an example of a stress-strain diagram estimated for the metal plate W in the process of it being molded by the press molding method according to the first embodiment. In FIG. 5, the horizontal axis represents strain ε, and the vertical axis represents stress σ. In addition, X1 and X2 shown in FIG. 5 represent states of the metal plate W at X1 and X2 in FIG. 4, respectively.

As shown in FIG. 5, while the state of the metal plate W is X1, when the upper die 10 is elevated in the process P4, the stress applied to the metal plate W at the vertical wall part of the lower die 20 is reduced, and a region of the vertical wall part shrinks by an amount of elastic deformation. Then, the material of the metal plate W flows into the vertical wall part. Next, when the upper die 10 is lowered in the process P5, the stress applied to the metal plate W at the vertical wall part of the lower die 20 is increased. Thus, the region of the vertical wall part extends by an amount of the elastic deformation, so that the region of the vertical wall part plasticizes to the state of X2, in which the state of deformation progresses more than it is at the original state of X1. In this way, every time the processes P4 and P5 are repeated, the material of the metal plate W flows into the vertical wall part of the lower die 20 and the strain of the metal plate W progresses.

Next, a method of controlling the blank holding force exerted by the die cushions 42 and 43 will be described with reference to FIG. 4. In the first embodiment, the control on the blank holding force exerted by the die cushions 42 and 43 is performed separately from the control on the press molding force exerted by the upper die 10 and the lower die 20. FIG. 4 shows two patterns, patterns 1 and 2, regarding the method of controlling the blank holding force exerted by the die cushions 42 and 43.

As shown in FIG. 4, the pattern 1 is a pattern in which the metal plate W is pressed at all times by the die cushions 42 and 43 while the processes P4 and P5 are repeated. Specifically, the blank holding surfaces are moved in the same manner as that of the lower surface of the upper die 10 so that the distance between the blank holding surfaces and the lower surface of the upper die 10 is always constant, that is, so that the blank holding force is always constant and large. The pattern 1 is a pattern that is used, for example, in a situation where the metal plate W is less prone to cracking but is prone to wrinkling. The pattern 1 can increase the blank holding force to effectively prevent the metal plate W from wrinkling.

On the other hand, in the pattern 2, while the processes P4 and P5 are being repeated, the state in which the metal plate W is pressed by the die cushions 42 and 43 and the state in which the pressing by the die cushions 42 and 43 is released are repeated. Specifically, in the process P5, the distance between the blank holding surfaces and the lower surface of the upper die 10 is increased at the timing when the lowering of the upper die 10 is completed to thereby reduce the blank holding force, so that the pressing on the metal plate W by the die cushions 42 and 43 is released. Moreover, in the process P5, the distance between the blank holding surfaces and the lower surface of the upper die 10 is reduced while the upper die 10 is being lowered to thereby increase the blank holding force, so that the die cushions 42 and 43 press the metal plate W again. However, the pattern 2 is not limited to this, and may be a pattern that reduces the blank holding force at all times. The pattern 2 is a pattern used, for example, in a situation where the metal plate W is less prone to wrinkling but is prone to cracking. The pattern 2 reduces the blank holding force to allow the material of the metal plate W to flow into the vertical wall part of the lower die 20, thereby making it possible to effectively prevent the metal plate W from cracking.

As described above, in the first embodiment, the control on the blank holding force exerted by the die cushions 42 and 43 is performed separately from the control on the press molding force exerted by the upper die 10 and the lower die 20. Therefore, for example, in the method of controlling the blank holding force, the pattern 1 can be used in a situation where the metal plate W is less prone to cracking but is prone to wrinkling, while the pattern 2 can be used in a situation where the metal plate W is less prone to wrinkling but is prone to cracking. Thus, it is possible to both effectively prevent the metal plate W from cracking and to effectively prevent the metal plate W from wrinkling.

In the pattern 2, when the pressing of the metal plate W by the die cushions 42 and 43 is released, in a predetermined number of times of the releasing out of a plurality of times of the releasing, the metal plate W may be in contact with both of the upper die 10 and the die cushions 42 and 43, and in a remaining number of times of the releasing out of the plurality of times of the releasing, the metal plate W may be separated from at least one of the upper die 10 and the die cushions 42 and 43. The state in which the metal plate W is in contact with both of the upper die 10 and the die cushions 42 and 43 and the state in which the metal plate W is separated from at least one of the upper die 10 and the die cushions 42 and 43 can transition to either state, for example, by adjusting the distance between the blank holding surfaces and the lower surface of the upper die 10, namely, the blank holding force. For example, in a situation where the metal plate W is less prone to wrinkling but is prone to cracking, control may be performed in such a way that the metal plate W is separated from at least one of the upper die 10 and the die cushions 42 and 43, and the blank holding is not performed. Further, in a situation where the metal plate W is prone to wrinkling and cracking, control may be performed in such a way that the metal plate W is in contact with both of the upper die 10 and the die cushions 42 and 43, and the blank holding is performed by a small blank holding force. Thus, it is possible to both effectively prevent the metal plate W from cracking and to effectively prevent the metal plate W from wrinkling more accurately.

(2) Second Embodiment

A configuration of a press molding apparatus 2 according to a second embodiment will be described with reference to FIG. 6. FIG. 6 is a view showing a configuration example of the press molding apparatus 2 according to the second embodiment. As shown in FIG. 6, the press molding apparatus 2 according to the second embodiment differs from the press molding apparatus 1 according to the first embodiment in that the press molding apparatus 2 further includes a state monitoring controller 80 in addition to the components included the press molding apparatus 1 according to the first embodiment. The configuration of the second embodiment other than the state monitoring controller 80 is the same as that of the first embodiment.

The state monitoring controller 80 monitors at least one of an equipment state of the press molding apparatus 2 (e.g., a temperature and a molding load applied by the upper die 10), a material state of the metal plate W (e.g., the amount of inflow of the material of the metal plate W flowing into the vertical wall part of the lower die 20), or die states of the upper die 10 and the lower die 20 (e.g., an amount of wear of the upper die 10 and the lower die 20 and the number of shots of the upper die 10).

For example, regarding the equipment state, the temperature can be monitored using a temperature sensor or the like, and the load applied to the upper die 10 can be monitored using a load sensor or the like attached to, for example, the slide 30. Regarding the material state, the amount of inflow of the material of the metal plate W can be monitored by, for example, detecting displacement of the metal plate W by a laser displacement meter. Regarding the die state, the amount of wear of the upper die 10 and the lower die 20 can be monitored by, for example, detecting the size of the gap between the upper die 10 and the lower die 20, and the number of shots of the upper die 10 can be monitored by, for example, measuring the number of times the upper die 10 is elevated and lowered.

In the second embodiment, the slide motion controller 50 controls the operation for elevating and lowering the slide 30 (the upper die 10), namely, the press molding force exerted on the metal plate W, based on at least one of the equipment state of the press molding apparatus 2, the material state of the metal plate W, and the die state of the upper die 10 and the lower die 20, which have been monitored by the state monitoring controller 80.

For example, when the slide motion controller 50 determines that the amount of inflow of the material of the metal plate W flowing into the vertical wall part of the lower die 20 is large based on the material state of the metal plate W, the slide motion controller 50 controls the press molding force so that it is large. By doing so, the number of times the upper die 10 is elevated and lowered can be reduced, and thus the productivity can be improved. On the contrary, when the slide motion controller 50 determines that the amount of inflow of the material of the metal plate W flowing into the vertical wall part of the lower die 20 is small, the slide motion controller 50 controls the press molding force so that it is small. By doing so, the stress applied to the metal plate W at the vertical wall part of the lower die 20 can be reduced, thereby making it possible to effectively prevent the metal plate W from cracking at the vertical wall part.

In addition, when the slide motion controller 50 determines that the molding load applied by the upper die 10 is small based on the equipment state of the press molding apparatus 2, the slide motion controller 50 controls the press molding force so that it is large. By doing so, the number of times the upper die 10 is elevated and lowered can be reduced, and thus the productivity can be improved. On the contrary, when the slide motion controller 50 determines that the molding load applied by the upper die 10 is large, the slide motion controller 50 controls the press molding force so that it is small. By doing so, the stress applied to the metal plate W at the vertical wall part of the lower die 20 can be reduced, thereby making it possible to effectively prevent the metal plate W from cracking at the vertical wall part.

(3) Third Embodiment

A configuration of a press molding apparatus 3 according to a third embodiment will be described with reference to FIG. 7. FIG. 7 is a view showing a configuration example of the press molding apparatus 3 according to the third embodiment.

As shown in FIG. 7, the press molding apparatus 3 according to the third embodiment differs from the press molding apparatus 1 according to the first embodiment in that the press molding apparatus 3 includes an upper die 11 and a lower die 21 instead of the upper die 10 and the lower die 20, includes die cushions 44 and 45 instead of the die cushions 42 and 43, and further includes members 46 and 47, an actuator controller 90, and actuators 91 to 95 in addition to the components included in the press molding apparatus 1 according to the first embodiment. The configurations of the third embodiment other than the components described above are the same as those of the first embodiment.

The upper die 11 and the lower die 21 differ from the upper die 10 and the lower die 20 according to the first embodiment in that a projection is formed at a center on an upper surface side of the lower die 21, and a recess, corresponding to the projection of the lower die 21, is formed at a center on a lower surface side of the upper die 11.

The die cushions 44 and 45 differ from the die cushions 42 and 43 according to the first embodiment in that the die cushions 44 and 45 are provided on the upper die 11 side. In the third embodiment, the members 46 and 47 provided on the lower die 21 side are elevated and lowered in accordance with the operation for elevating and lowering the die cushion main body 41. The die cushion 44 sandwiches and holds the metal plate W with the lower die 21 in the vertical direction, while the die cushion 45 sandwiches and holds the metal plate W with the member 47 in the vertical direction. Further, in the third embodiment, the lower die 21 is also elevated and lowered in accordance with the operation for elevating and lowering the die cushion main body 41.

The actuator 91 is disposed inside the upper die 11. The actuator 91 changes the die shape of the upper die 11 in a direction to expand or contract it in the horizontal direction of the drawing. The actuator 92 is disposed outside the upper die 11. The actuator 92 changes the die shape of the upper die 11 in a direction to expand or contract it in the horizontal direction of the drawing.

The actuator 93 is disposed inside the lower die 21. The actuator 93 changes the die shape of the lower die 21 in a direction to expand or contract in the horizontal direction of the drawing. The actuator 94 is disposed outside the lower die 21. The actuator 94 changes the die shape of the lower die 21 in the direction to expand or contract in the horizontal direction of the drawing.

The actuator controller 90 determines the press position of the metal plate W based on the operation for elevating and lowering the slide 30 (the upper die 10) controlled by the slide motion controller 50, and controls the actuators 91 to 95 based on the press position of the metal plate W.

For example, the slide motion controller 50 controls the actuator 91, 92, 93, and 94 so that the die shapes of the upper die 11 and the lower die 21 contract in the horizontal direction of the drawing as the press position of the metal plate W is gradually lowered.

As described above, in the third embodiment, not only the blank holding force exerted by the die cushions 44 and 45 can be controlled, but also the die shapes of the upper die 11 and the lower die 21 can be controlled based on the operation for elevating and lowering the slide 30 (the upper die 10).

Note that the present disclosure is not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit of the present disclosure. For example, although the second and third embodiments have been separately described, the second and third embodiments may be combined.

From the disclosure thus described, it will be obvious that the embodiments of the disclosure may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.

Claims

1. A press molding method for press-molding a workpiece by a press die composed of an upper die and a lower die while holding the workpiece by a die cushion, the press molding method comprising pressing process, in which a press position at which the workpiece is pressed by the press die is gradually lowered while repeatedly pressing and releasing the workpiece by the press die a plurality of times until the press position reaches a bottom dead center, wherein in the pressing process, a holding force for holding the workpiece by the die cushion is controlled separately from a press molding force for press-molding the workpiece by the press die.

2. The press molding method according to claim 1, wherein in the pressing process, holding and releasing of the workpiece by the die cushion are repeated a plurality of times.

3. The press molding method according to claim 2, wherein when the workpiece is released from the die cushion, in a predetermined number of times of the releasing out of a plurality of times of the releasing, the workpiece is in contact with both of the press die and the die cushion, and in a remaining number of times of the releasing out of the plurality of times of the releasing, the workpiece is separated from at least one of the press die and the die cushion.

4. The press molding method according to claim 1, wherein in the pressing process, at least one of an equipment state of a press molding apparatus, a material state of the workpiece, and a die state of the press die is monitored, andthe press molding force is controlled based on at least one of the equipment state of the press molding apparatus, the material state of the workpiece, and the die state of the press die.

5. The press molding method according to claim 1, wherein in the pressing process, a die shape of the upper die and a die shape of the lower die are changed based on the press position.

6. A press molding apparatus comprising a press die composed of an upper die and a lower die and a die cushion, configured to press-mold a workpiece by the press die while holding the workpiece by the die cushion, and configured to execute pressing process, in which a press position at which the workpiece is pressed by the press die is gradually lowered while repeatedly pressing and releasing the workpiece by the press die a plurality of times until the press position reaches a bottom dead center, the press molding apparatus comprising: a first control unit configured to control, in the pressing process, a press molding force for press-molding the workpiece by the press die; anda second control unit configured to control, in the pressing process, a holding force for holding the workpiece by the die cushion separately from the press molding force controlled by the first control unit.