Press molding method

Abstract

To suppress wrinkles of a side wall in a part that is narrowed down in a recessed shape of a blank material.SOLUTION: A press molding method for pressing a metal blank material arranged between a die and a cushion against a die by a punch, and drawing the blank material includes: a first step of drawing the blank material in the state where a magnitude of a cushion load in which a part of the blank material is sandwiched between the die and the cushion is set to be equal to or smaller than a first magnitude; a second step of drawing the blank material in the state where the magnitude of the cushion load is set at a second magnitude, after the first step; and a third step of crushing wrinkles of a part sandwiched between the die and the cushion of the blank material by setting the magnitude of the cushion load at a third magnitude, after the second step. The second magnitude is larger than the first magnitude and smaller than the third magnitude.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a press molding method. [Background technology]

[0002] Regarding a press forming method for drawing a blank material, Patent Document 1 discloses a press forming method for drawing a titanium alloy blank material by a die and a pressing member in a state where the titanium alloy blank material is placed between a die and a blank support material. The forming method of Patent Document 1 includes a step of pressing at least a part of the titanium alloy against the die using the blank support material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-59045 A Summary of the Invention [Problem to be solved by the invention]

[0004] As in Patent Document 1, by pressing the blank against the die with the blank support material, the flange of the blank can be sandwiched and pressed between the blank support material and the die, which makes it possible to eliminate wrinkles in the flange. However, there has been no sufficient consideration given to suppressing wrinkles on the side walls of the portion of the blank that is drawn into a concave shape, and there is room for improvement in the formability of the blank and the quality of the press-formed product. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms.

[0006] (1) According to one embodiment of the present disclosure, there is provided a press forming method for drawing a metal blank material arranged between a die and a cushion by pressing the blank material against the die with a punch. The press forming method includes a first step of drawing the blank material while a cushion load that sandwiches a part of the blank material between the die and the cushion is set to a first size or less, a second step of drawing the blank material while a cushion load is set to a second size after the first step, and a third step of squeezing wrinkles in a part of the blank material sandwiched between the die and the cushion by setting the cushion load to a third size after the second step. The second size is larger than the first size and smaller than the third size. In this configuration, in the second step, the blank is squeezed while being clamped with a cushion load of a second magnitude, which is larger than the first magnitude and smaller than the third magnitude, so that the sidewall of the portion of the blank that is squeezed into a concave shape is easily stretched, thereby making it possible to suppress wrinkles in the sidewall and improve the formability of the blank and the quality of the press-molded product. (2) In the above embodiment, in the first step, the cushion and the blank piece may be separated to set the cushion load to 0. With this embodiment, in the first step, cracks in the side wall of the concavely drawn portion of the blank piece can be further suppressed, and in the second step, wrinkles in the side wall can be suppressed. (3) In the above embodiment, the first step, the second step, and the third step may be performed multiple times in this order. In this embodiment, the blank can be repeatedly drawn while suppressing cracks and wrinkles in the blank, so that the blank can be drawn deeper.

[0007] The present disclosure can be realized in the form of, for example, a method for manufacturing a press-molded product, a press-molding apparatus, etc. in addition to the form of the press-molding method described above. [Brief description of the drawings]

[0008] [Figure 1]FIG. 1 is a diagram showing a schematic configuration of a press molding apparatus. [Diagram 2] 1 is a flowchart of a press molding process. [Diagram 3] 1 is a graph illustrating a press molding process. [Figure 4] FIG. 4 is an enlarged view of a portion of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A. First embodiment: Fig. 1 is a diagram showing a schematic configuration of a press forming apparatus 100 in this embodiment. The press forming apparatus 100 includes a die 30, a cushion 40, a punch 50, and a control unit 90. The press forming apparatus 100 produces a press-formed product by drawing a metal blank material M using the die 30 and the punch 50. Fig. 1 shows the state of the press forming apparatus 100 before processing of the blank material M is started.

[0010] The die 30 in this embodiment has a substantially cylindrical shape. The die 30 has an opening 31 that opens vertically downward in the horizontal center, and a peripheral portion 32 around the opening 31. In this embodiment, the opening 31 has a circular cross section. In this embodiment, the die 30 is fixed to the lower portion of the slide 20 that is configured to be movable along the vertical direction, and is configured to be movable together with the slide 20. The slide 20 is operated by the driving force of the first driving portion 21 that is driven under the control of the control portion 90. In this embodiment, the first driving portion 21 is configured by a servo motor.

[0011] The punch 50 and the cushion 40 are disposed opposite the die 30. In this embodiment, the punch 50 and the cushion 40 are disposed vertically below the die 30. The punch 50 has a shape corresponding to the shape of the opening 31, and is disposed at a position opposite the opening 31. The cushion 40 in this embodiment has a substantially annular shape, and is disposed at a position opposite the peripheral edge portion 32. The punch 50 is inserted into the annular shape of the cushion 40. The cushion 40 is operated by the driving force of the second driving unit 41 that is driven under the control of the control unit 90. In this embodiment, the second driving unit 41 is configured by a servo motor.

[0012] The control unit 90 is configured by a computer having one or more processors, a storage unit, and an input / output interface for inputting and outputting signals from and to the outside. In other embodiments, the control unit 90 may be configured by a combination of multiple circuits instead of a computer.

[0013] In this embodiment, the blank material M is made of steel and has a circular plate shape. The blank material M may be made of other metals such as titanium and copper. The blank material M is disposed between the die 30, the cushion 40, and the punch 50. The blank material M is pressed against the die 30 by the punch 50, thereby being drawn. More specifically, the blank material M is pressed against the peripheral portion 32 and into the opening 31 by the punch 50 being pressed against the die 30, and is deformed into a concave shape. This causes the blank material M to be drawn. In this embodiment, the control unit 90 moves the slide 20 downward relative to the fixed punch 50, thereby moving the die 30 downward so as to approach the punch 50, and the blank material M is pressed vertically upward by the punch 50, thereby being drawn.

[0014] In this embodiment, when the blank material M is press-formed, a portion of the blank material M is appropriately sandwiched between the die 30 and the cushion 40. More specifically, a portion of the blank material M outside the portion pressed by the punch 50 is sandwiched between the die lower surface 33, which is the lower surface of the peripheral portion 32 of the die 30, and the cushion upper surface 42, which is the upper surface of the cushion 40. The load that sandwiches the blank material M between the die 30 and the cushion 40 is sometimes referred to as the cushion load. The portion of the blank material M that is sandwiched between the die 30 and the cushion 40 is sometimes referred to as the sandwiched portion Mh.

[0015] Fig. 2 is a flowchart of the press molding process executed by the control unit 90 in this embodiment. The press molding method and the method for manufacturing a press-molded product in this embodiment are realized by executing the press molding process in Fig. 2. In this embodiment, the press molding process is started in a state in which the blank material M is placed between the die 30 and the cushion 40 and the punch 50, as shown in Fig. 1.

[0016] Fig. 3 is a graph for explaining the press molding process, in which the horizontal axis represents time, the first vertical axis represents the vertical positions of the die lower surface 33 and the cushion upper surface 42, and the second vertical axis represents the magnitude of the cushion load.

[0017] In this embodiment, the control unit 90 generates a desired cushion load by controlling the second driving unit 41 to adjust the position of the cushion 40 based on the relationship between the torque value of the servo motor of the second driving unit 41 and the cushion load in the press forming process of FIG. 2. The relationship between the torque value and the cushion load is calculated in advance based on, for example, an experiment. In another embodiment, the control unit 90 may control the position of the slide 20 or the position of the cushion 40 according to, for example, a sequence created so that a desired drawing depth and a desired cushion load are obtained at a desired timing. In addition, the control unit 90 may measure the magnitude of the cushion load generated on the cushion 40 by a load sensor (not shown) such as a load cell, and feedback control the position of the slide 20 or the position of the cushion 40, or the torque value of the servo motor of the first driving unit 21 or the second driving unit 41 with reference to the sensor value.

[0018] In step S105, the control unit 90 executes a preliminary drawing process. In the preliminary drawing process of step S105, the control unit 90 draws the blank M to a depth a with the magnitude of the cushion load set to magnitude f4. In FIG. 3, the period from time t1 to time t2 corresponds to step S105.

[0019] 3, in step S105, the control unit 90 controls the first driving unit 21 to move the slide 20 downward until the die lower surface 33 is located at position p2. Position p2 is a position that is a distance a downward from position p1, which is the vertical position of the upper surface 51 of the punch 50. In addition, while the blank material M is being squeezed, the control unit 90 controls the second driving unit 41 to move the cushion 40 downward while positioning the cushion 40 at a position where a cushion load of magnitude f4 is generated.

[0020] The magnitude f4 of the cushion load in step S105 is set to a magnitude that can suppress cracks and wrinkles in the blank material M in step S105, for example. In step S105, the greater the cushion load, the more wrinkles in the blank material M are suppressed, but the more likely cracks are to occur. In contrast, the smaller the cushion load in step S105, the more cracks in the blank material M are suppressed, but the more likely wrinkles are to occur. By suppressing cracks and wrinkles in the blank material M in step S105, the possibility of drawing the blank material M more deeply in step S105 increases, and the blank material M can be press-formed more efficiently.

[0021] As shown in FIG. 2, the blank material M is squeezed to form a flange portion Mf and a recessed portion Mr in the blank material M. The recessed portion Mr is a portion of the blank material M that is squeezed and deformed into a concave shape by the punch 50 and the die 30, and has a bottom portion Bt and a side wall Sw. The flange portion Mf is a portion of the blank material M that is outside the recessed portion Mr and is not squeezed. The side wall Sw includes a portion that extends along the pressing direction of the punch 50 and a portion near the boundary with the flange portion Mf that is deformed into a shape along the edge portion Eg of the die 30. The edge portion Eg refers to the inner end of the lower end portion of the peripheral portion 32. As the blank material M is squeezed, the flange portion Mf flows into the opening 31 of the die 30 and forms the side wall Sw of the recessed portion Mr.

[0022] In step S110, the control unit 90 executes a preliminary crease-busting process. In the preliminary crease-busting process of step S110, the control unit 90 sets the magnitude of the cushion load to magnitude f3 to bust creases in the clamped portion Mh of the blank material M. In FIG. 3, the period from time t2 to time t3 corresponds to step S110.

[0023] In this embodiment, the control unit 90 crushes wrinkles in the clamped portion Mh in step S110 without squeezing the blank material M. As shown in FIG. 3, in step S110, the control unit 90 generates a cushion load of magnitude f3 by pressing the blank material M against the die 30 with the cushion 40 while positioning the die lower surface 33 at position p2. This crushes wrinkles generated in the flange portion Mf of the blank material M in step S105, for example. The magnitude f3 of the cushion load in step S110 is determined by experiment as a magnitude of the cushion load large enough to crush wrinkles in the clamped portion Mh in step S110, for example. In this embodiment, the magnitude f3 of the cushion load is larger than the magnitude f4 of the cushion load in step S105.

[0024] In step S115, the control unit 90 executes the drawing process. In the drawing process of step S115, the control unit 90 draws the blank material M to a depth b1. The drawing process in this embodiment corresponds to the first process. The first process refers to a process of drawing the blank material M by the die 30 and the punch 50 in a state in which the magnitude of the cushion load is set to a first magnitude or less. Hereinafter, the drawing process of step S115 may also be referred to as the first process. The first magnitude is determined by experiment as, for example, a magnitude of the cushion load that is small enough to suppress cracking of the blank material M due to the drawing process in the first process. In this embodiment, in step S115, the control unit 90 draws the blank material M to a depth b1 in a state in which the magnitude of the cushion load is set to 0 by separating the cushion 40 and the blank material M.

[0025] FIG. 4 is an enlarged view of a part of FIG. 3. In FIG. 3 and FIG. 4, for example, the period from time t3 to time t4 corresponds to step S115. As shown in FIG. 3 and FIG. 4, in step S115, the control unit 90 starts the downward movement of the cushion 40 before the downward movement of the slide 20, and positions the cushion upper surface 42 below position p3. Position p3 is a position that is a distance b1 away from position p2 downward. After starting the movement of the cushion 40, the control unit 90 starts the movement of the slide 20, and moves the slide 20 downward while keeping the blank material M and the cushion 40 apart, and positions the die lower surface 33 at position p3. In this embodiment, the distance b1 is shorter than the distance a.

[0026] In this embodiment, the control unit 90 sets the magnitude of the cushion load to 0 in step S115, so that when the blank material M is squeezed, the portion that formed the flange portion Mf is more likely to flow into the opening 31 compared to when the magnitude of the cushion load is greater than 0. This makes it easier to ensure the thickness of the side wall Sw of the recess Mr of the blank material M, and suppresses cracks in the side wall Sw. On the other hand, when the magnitude of the cushion load is greater than 0 in step S115, the side wall Sw is less likely to be stretched when the blank material M is squeezed, so wrinkles are more likely to occur in the side wall Sw.

[0027] In step S120, the control unit 90 executes the stretching process. In the stretching process of step S120, the control unit 90 squeezes the blank material M by a depth b2 while the magnitude of the cushion load is set to a magnitude f2 smaller than the magnitude f4. The stretching process in this embodiment corresponds to the second process. The second process refers to a process of squeezing the blank material M while the magnitude of the cushion load is set to a second magnitude after the first process. Hereinafter, the stretching process of step S120 may also be referred to as the second process. The second magnitude is larger than the first magnitude and smaller than a third magnitude in a third process described later. In this embodiment, the magnitude f2 corresponds to the second magnitude.

[0028] 3 and 4, for example, the period from time t4 to time t5 corresponds to step S120. As shown in FIG. 3 and FIG. 4, the control unit 90 controls the position of the cushion 40 to increase the magnitude of the cushion load to a magnitude f2 while moving the slide 20 downward until the die lower surface 33 is located at position p4 in step S120 of FIG. 2. Position p4 is a position that is a distance b2 away downward from position p3. In this embodiment, distance b2 is shorter than distance b1. Also, the sum of distances b1 and b2 is shorter than distance a.

[0029] In step S120, the blank material M is drawn while being sandwiched by a cushion load larger than the first magnitude, so that, for example, the side wall Sw of the recessed portion Mr of the blank material M is more easily stretched than when the blank material M is drawn while being sandwiched by a cushion load of the first magnitude. Therefore, wrinkles on the side wall Sw of the recessed portion Mr of the blank material M are suppressed. In addition, since the magnitude f2 of the cushion load in step S120 is smaller than the magnitude f3, cracks on the side wall Sw of the recessed portion Mr of the blank material M are suppressed compared to when the blank material M is drawn while being sandwiched by a cushion load of the magnitude f3. In particular, in this embodiment, since the magnitude f2 is smaller than the magnitude f4, cracks on the blank material M in step S120 are more suppressed. Therefore, by performing steps S115 and S120, the blank material M can be drawn while suppressing cracks and wrinkles on the side wall Sw of the recessed portion Mr.

[0030] In step S125, the control unit 90 executes a wrinkle squeezing process. In the wrinkle squeezing process of step S125, the control unit 90 squeezes the wrinkles in the clamped portion Mh of the blank material M by setting the magnitude of the cushion load to a magnitude f3, as in step S110. The wrinkle squeezing process in this embodiment corresponds to the third process. The third process refers to a process of squeezing the wrinkles in the clamped portion Mh of the blank material M by setting the magnitude of the cushion load to a third magnitude greater than the second magnitude f2 after the second process. Hereinafter, the wrinkle squeezing process of step S125 may also be referred to as the third process. The third magnitude is determined by experiment, for example, as the magnitude of the cushion load large enough to squeeze the wrinkles in the clamped portion Mh in the third process. In this embodiment, the magnitude f3 corresponds to the third magnitude.

[0031] 3, for example, the period from time t5 to time t6 corresponds to step S125. In this embodiment, in step S125, the control unit 90 smoothes out wrinkles in the clamped portion Mh without squeezing the blank material M, similar to step S110. By executing step S125, for example, wrinkles that have occurred in the flange portion Mf of the blank material M in step S115 or step S120 are smoothed out.

[0032] In step S130, the control unit 90 judges whether or not the press forming is completed. When the control unit 90 judges that the press forming is not completed, the control unit 90 returns the process to step S115. When the control unit 90 judges that the press forming is completed, the control unit 90 ends the press forming process. In this embodiment, the control unit 90 judges that the press forming is completed when the slide 20 moves to the bottom dead center. As shown in FIG. 3, in this embodiment, the control unit 90 executes step S115, step S120, and step S125 in this order a total of four times until the slide 20 reaches the bottom dead center. In another embodiment, the control unit 90 may judge that the press forming is completed when, for example, the blank material M is drawn to a predetermined desired depth. In this case, the control unit 90 can calculate the depth to which the blank material M is drawn based on, for example, the distance the slide 20 moves downward in the press forming process. The moving distance of the slide 20 is calculated based on, for example, the control value of the first driving unit 21.

[0033] According to the press forming method of the present embodiment described above, the method includes a first step of squeezing the blank material M with the cushion load being equal to or less than a first magnitude, a second step of squeezing the blank material M with the cushion load being equal to a second magnitude after the first step, and a third step of squeezing the clamped portion Mh by setting the cushion load to a third magnitude after the second step. The second magnitude is larger than the first magnitude and smaller than the third magnitude. As a result, in the second step, the blank material M is squeezed while clamping a part of the blank material M with a cushion load of the second magnitude, which is larger than the first magnitude and smaller than the third magnitude, so that the side wall Sw of the recess Mr of the blank material M is easily stretched. Therefore, wrinkles in the side wall Sw can be suppressed, and the formability of the blank material M and the quality of the press-molded product can be improved.

[0034] In the present embodiment, in the first step, the cushion 40 and the blank material M are separated from each other, so that the magnitude of the cushion load is set to 0. Therefore, cracks in the side wall Sw can be further suppressed in the first step, and wrinkles in the side wall Sw can be suppressed in the second step.

[0035] In this embodiment, the first, second, and third steps are performed multiple times in this order, so that the blank material M can be repeatedly drawn while suppressing cracks and wrinkles in the blank material M, and therefore the blank material M can be drawn deeper.

[0036] B. Other embodiments: (B1) In the above embodiment, in the first step, the blank material M is squeezed in a state where the magnitude of the cushion load is set to 0 by separating the cushion 40 and the blank material M. In contrast to this, in the first step, for example, the cushion 40 and the blank material M may not be separated, and the blank material M may be squeezed in a state where the cushion 40 and the blank material M are in contact with each other. In this case, wrinkles on the side wall Sw of the recess Mr of the blank material M in the first step are suppressed compared to the case where the cushion 40 and the blank material M are separated. Also, in the first step, the magnitude of the cushion load does not have to be set to 0. In this case, wrinkles on the side wall Sw in the first step are suppressed compared to the case where the cushion load is set to 0.

[0037] (B2) In the above embodiment, in the press molding of the blank material M, the first step, the second step, and the third step are performed in this order a total of four times. In contrast, the number of times that the first step to the third step are repeated may be two or three times, or may be five or more times. The first step to the third step may each be performed only once. Also, the first step and the second step may be performed multiple times, and then the third step may be performed. In this case, for example, a series of steps in which the first step and the second step are performed multiple times and then the third step is performed once is defined as one cycle, and this cycle may be performed multiple times.

[0038] (B3) In the above embodiment, the blank material M is drawn by moving the slide 20 relative to the fixed punch 50. In contrast to this, for example, the blank material M may be drawn by moving the punch 50. Also, in the above embodiment, the blank material M is drawn by pressing the blank material M vertically upward with the punch 50, but for example, the blank material M may be drawn by pressing the blank material M vertically downward with the punch 50.

[0039] (B4) In the above embodiment, when the blank material M is press-formed, a preliminary drawing step and a preliminary crease-reducing step are performed prior to the first step. However, the preliminary drawing step and the preliminary crease-reducing step do not have to be performed prior to the first step, and for example, the first step may be performed at the beginning of press forming.

[0040] (B5) In the above embodiment, in the third step, the wrinkles in the clamped portion Mh are flattened without squeezing the blank material M. In contrast, the blank material M may be squeezed in the third step. In this case, since the blank material M can be squeezed in the third step as well, the blank material M can be press-formed more efficiently. Similarly, the blank material M may be squeezed in the preliminary squeezing step.

[0041] (B6) In the above embodiment, when the first to third steps are repeated multiple times, the drawing depth and the magnitude of the cushion load in each step may be different for each repetition. For example, in the first step performed the first time, the blank material M may be drawn to a depth b1 with the magnitude of the cushion load set to 0, and in the first step performed the second time, the blank material M may be drawn to a depth shallower than the depth b1 with the magnitude of the cushion load set to greater than 0 and less than the first magnitude.

[0042] The present disclosure is not limited to the above-mentioned embodiment, and can be realized in various configurations without departing from the spirit of the present disclosure. For example, the technical features in the embodiments corresponding to the technical features in each form described in the Summary of the Invention column can be appropriately replaced or combined in order to solve the above-mentioned problems or to achieve some or all of the above-mentioned effects. Furthermore, if the technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0043] 20...slide, 21...first drive unit, 30...die, 31...opening, 32...periphery, 33...lower surface of die, 40...cushion, 41...second drive unit, 42...upper surface of cushion, 50...punch, 51...upper surface, 90...control unit, 100...press molding device

Claims

1. A press forming method in which a metal blank material disposed between a die and a cushion is pressed against the die by a punch to perform drawing, a first step of drawing the blank in a state where a cushion load applied to a portion of the blank between the die and the cushion is set to a first value or less; a second step of squeezing the blank while maintaining the cushion load at a second magnitude after the first step; and a third step of squashing wrinkles in a portion of the blank material sandwiched between the die and the cushion by setting the magnitude of the cushion load to a third magnitude after the second step, the second magnitude is greater than the first magnitude and less than the third magnitude; In the first step, the cushion and the blank are separated from each other to squeeze the blank while the magnitude of the cushion load is set to zero. In the third step, the wrinkles are eliminated without squeezing the blank.

2. The press molding method according to claim 1, A press molding method comprising performing the first step, the second step, and the third step in this order a plurality of times.

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