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.
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.
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:
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.
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.
First, a configuration of the press molding apparatus 1 according to a first embodiment will be described with reference to
As shown in
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
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
As shown in
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
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
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
As shown in
Next, a method of controlling the blank holding force exerted by the die cushions 42 and 43 will be described with reference to
As shown in
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.
A configuration of a press molding apparatus 2 according to a second embodiment will be described with reference to
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.
A configuration of a press molding apparatus 3 according to a third embodiment will be described with reference to
As shown in
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.
Number | Date | Country | Kind |
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2017-178751 | Sep 2017 | JP | national |