Press forming method of metal plate

Abstract

To provide a press forming method for a metal plate, capable of preventing generation of cracks.SOLUTION: A press forming method for a metal plate comprises: a first stage in which a metal plate is arranged between a die and a punch, and a portion of the metal plate is made to be held between and by the die and a die cushion pad; and a second stage in which the metal plate is formed by making the die and punch relative approach each other while applying a die cushion force to the metal plate with the die cushion. The press forming method for a metal plate employs the following: in the second stage, if a relative average speed of the die and the punch from an initial position of the punch up to an intermediate position A before coming into contact with the metal plate is specified as a first speed, and a relative average speed of the die and the punch from the immediate position A up to a bottom death point is specified as a second speed, the second speed is made to be lower than the first speed, and a halt step to temporarily halt the punch and the die is performed at least once during a period from a contact position where the punch comes into contact with the metal plate to the bottom death point.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for press forming a metal plate.

Background Art

[0002] In various fields such as automobiles, home appliances, furniture, and miscellaneous goods, press-formed products (hereinafter referred to as press-formed articles) are used. A press-formed article is usually obtained by stretching or drawing a metal plate sandwiched between the peripheral portion of a die and a die cushion pad (also referred to as a blank holder or a wrinkle presser) between the forming recess of the die and the forming protrusion of the punch, and plastically deforming the metal plate into a desired shape. By performing such press forming, members having complex shapes can be efficiently mass-produced.

[0003] However, among metal plates, a metal plate with high yield strength has the characteristic that it is difficult to perform press forming because of its high hardness. In particular, when performing deep drawing forming or square tube forming with a large amount of deformation, there is a risk of cracks occurring in the press-formed article.

[0004] Patent Document 1 describes a press forming method in which, in order to efficiently perform deep drawing forming, a steel plate as a workpiece is disposed between a die having a forming recess and a punch having a forming protrusion, and when drawing the steel plate held by the blank holder and the die by relatively moving the die and the punch in the approaching direction, the processing speed, which is the time change rate of the relative movement amount of the die and the punch, is changed from the pre-stage processing speed, which is the processing speed before the shift point, to the post-stage processing speed, which is the processing speed after the shift point and is greater than the pre-stage processing speed, at the shift point where the relative movement amount reaches a predetermined value. Further, FIG. 2A of Patent Document 1 shows the relationship between the stroke amount of the punch and time when step motion forming is performed so that the average processing speed is substantially the same as that of linear motion forming, and further, FIG. 2C suggests that when the step motion forming shown in FIG. 2A is applied to deep drawing forming, the sheet thickness reduction rate is smaller than that of linear motion forming.

Prior Art Documents

Patent Documents

[0005] Patent Document 1 Japanese Patent Application Laid-Open No. 2016-221536 Summary of the Invention Problems to be Solved by the Invention

[0006] However, even when step motion forming is performed such that the average processing speed is substantially the same as that of linear motion forming with respect to a blank material made of a metal plate as described in Patent Document 1, cracks may occur in the press-formed product after forming.

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide a press forming method for a metal plate capable of preventing the occurrence of cracks. Means for Solving the Problems

[0008] In order to solve the above problems, the present invention employs the following configuration. [1] A first step of disposing a metal plate between a die and a punch and sandwiching a part of the metal plate with the die and a die cushion pad; A second step of forming the metal plate by relatively approaching the die and the punch while applying a die cushion force to the metal plate by the die cushion pad, wherein in the second step, when the relative average speed of the die and the punch from the initial position of the punch to an intermediate position before contacting the metal plate is defined as a first speed and the relative average speed of the die and the punch from the intermediate position to the bottom dead center is defined as a second speed, the second speed is set to be lower than the first speed, and at least two or more stop steps of temporarily stopping the punch and the die are performed between the contact position where the punch contacts the metal plate and the bottom dead center. In the second step, when the relative average speed of the die and the punch from the initial position of the punch to an intermediate position before contacting the metal plate is defined as a first speed and the relative average speed of the die and the punch from the intermediate position to the bottom dead center is defined as a second speed, the second speed is set to be lower than the first speed, and at least two or more stop steps of temporarily stopping the punch and the die are performed between the contact position where the punch contacts the metal plate and the bottom dead center. A method for press-forming a metal plate, wherein when the ironing force applied to the metal plate by the ironing pad is defined as a first ironing force from the start to the first stop step, a second ironing force from the first stop step to the last stop step, and a third ironing force after the last stop step, the second ironing force is made smaller than the first ironing force and the third ironing force. [2] A first step of disposing the metal plate between a die and a punch and sandwiching a part of the metal plate with the die and the ironing pad; A second step of forming the metal plate by relatively approaching the die and the punch while applying an ironing force to the metal plate by the ironing pad. In the second step, when the relative average speed of the die and the punch from the initial position of the punch to an intermediate position before contacting the metal plate is defined as a first speed, and the relative average speed of the die and the punch from the intermediate position to the bottom dead center is defined as a second speed, the second speed is made lower than the first speed, and at least one stop step of temporarily stopping the punch and the die is performed between the contact position where the punch contacts the metal plate and the bottom dead center; A method for press-forming a metal plate, wherein when the position of the punch when the forming load of the punch shows a maximum value is defined as the maximum load position, the first stop step is performed when the punch reaches a range from the maximum load position to a position where the forming load becomes 80% of the maximum value. [3] A first step of disposing the metal plate between a die and a punch and sandwiching a part of the metal plate with the die and the ironing pad; A second step of forming the metal plate by relatively approaching the die and the punch while applying an ironing force to the metal plate by the ironing pad. In the second step, During the period from the contact position where the punch contacts the metal plate to the bottom dead center, at least two or more stop steps of temporarily stopping the punch and the die are performed, and When the cushioning force of the metal plate by the die cushion pad is defined as the first cushioning force up to the first stop step, the second cushioning force from the first stop step to the last stop step, and the third cushioning force after the last stop step, the second cushioning force is made smaller than the first cushioning force and the third cushioning force. A method for press-forming a metal plate. [4] When the position of the punch when the forming load of the punch shows the maximum value is defined as the maximum load position, when the punch reaches the range from the maximum load position to the position where the forming load becomes 80% of the maximum value, the first stop step is performed. The method for press-forming a metal plate according to [1] or [3]. [5] When the punch reaches a position 5 to 10 mm away from the bottom dead center, the last stop step is performed. The method for press-forming a metal plate according to [1] or [3]. [6] The second speed is a speed of 40% or more and 70% or less with respect to the first speed. The method for press-forming a metal plate according to [1]. [7] The intermediate position is a position 10 mm to 20 mm away from the contact position. The method for press-forming a metal plate according to [1]. [8] The stop time in the stop step is in the range of 0.2 to 1.0 seconds. The method for press-forming a metal plate according to [1] or [3]. [9] The second cushioning force is in the range of 0.1 to 0.5 times the first cushioning force or the third cushioning force. The method for press-forming a metal plate according to [1] or [3].

[10] A first step of disposing a metal plate between a die and a punch and sandwiching a part of the metal plate with the die and a die cushion pad, and A second step of forming the metal plate by relatively approaching the die and the punch while applying a cushioning force to the metal plate by the die cushion pad. In the second stage, When the relative average speed of the die and the punch from the initial position of the punch to the intermediate position immediately before contacting the metal plate is defined as the first speed, and the relative average speed of the die and the punch from the intermediate position to the bottom dead center is defined as the second speed, the second speed is set to be lower than the first speed, and during the period from the contact position where the punch contacts the metal plate to the bottom dead center, the stop step of temporarily stopping the punch and the die is performed at least once or more. A method for press-forming a metal plate, wherein the last stop step is performed when the punch reaches a position 5 to 10 mm away from the bottom dead center.

[11] A first stage of disposing a metal plate between a die and a punch and sandwiching a part of the metal plate with the die and a die cushion pad; A second stage of forming the metal plate by relatively approaching the die and the punch while applying a cushioning force to the metal plate by the die cushion pad; In the second stage, When the relative average speed of the die and the punch from the initial position of the punch to the intermediate position immediately before contacting the metal plate is defined as the first speed, and the relative average speed of the die and the punch from the intermediate position to the bottom dead center is defined as the second speed, the second speed is set to be lower than the first speed, and during the period from the contact position where the punch contacts the metal plate to the bottom dead center, the stop step of temporarily stopping the punch and the die is performed at least once or more. A method for press-forming a metal plate, wherein the stop time in the stop step is in the range of 0.2 to 1.0 seconds.

[12] A first stage of disposing a metal plate between a die and a punch and sandwiching a part of the metal plate with the die and a die cushion pad; A second stage of forming the metal plate by relatively approaching the die and the punch while applying a cushioning force to the metal plate by the die cushion pad; In the second stage, When the relative average speed of the die and the punch from the initial position of the punch to the intermediate position immediately before contacting the metal plate is defined as the first speed, and the relative average speed of the die and the punch from the intermediate position to the bottom dead center is defined as the second speed, the second speed is set lower than the first speed, and during the period from the contact position where the punch contacts the metal plate to the bottom dead center, at least 2 one stop step of temporarily stopping the punch and the die is performed When the diking force on the metal plate by the diking pad is defined as the first diking force from the start to the first stop step, the second diking force from the first stop step to the last stop step, and the third diking force after the last stop step, The metal plate press forming method, wherein the second die cushion force is in the range of 0.1 to 0.5 times that of the first die cushion force or the third die cushion force.

Advantages of the Invention

[0009] According to the invention described in [1] above, in the second stage, the first speed is set until before the punch contacts the metal plate, and then the speed is decelerated to the second speed which is lower than the first speed until the punch reaches the bottom dead center, so that the impact applied to the metal plate when the punch contacts the metal plate is reduced. Also, by providing at least one stop step during the period from the contact position where the punch contacts the metal plate to the bottom dead center, when the stop step ends and the punch and the die are moved again, the strain in the metal plate being formed is dispersed, thereby suppressing the fracture of the material due to strain concentration. Furthermore, by setting the relative speed of the punch and the die before and after the stop step to the second speed which is lower than the first speed, the speed control of the punch and the die during the forming of the metal plate becomes easy, and the strain concentration in the metal plate being formed can be prevented. As described above, by suppressing the impact on the metal plate, dispersing the strain in the metal plate being formed, and preventing strain concentration, cracking of the press-formed product can be prevented. Also, in the second stage, by setting the relative speed of the punch and the die before the punch contacts the metal plate to the first speed which is higher than the second speed, an increase in the forming time due to the provision of the stop step can be suppressed, and the overall forming time can be shortened.

[0010] According to the invention described in [2] above, by making the first cushioning force before the first stop step higher than the second cushioning force, the formability of the metal plate by the punch in the initial stage of forming can be enhanced. Also, by making the second cushioning force between the first stop step and the last stop step smaller than the cushioning forces (the first and third cushioning forces) before the first stop step and after the last stop step, the inflow of material between the punch and the die in the middle stage of forming is promoted. As a result, excessive thickness reduction of the metal plate during forming can be prevented, the strain can be more dispersed, the breakage of the material due to the concentration of strain can be suppressed, and cracking of the press-formed product can be prevented. Furthermore, by making the third cushioning force after the stop step higher than the second cushioning force, the formability of the metal plate by the punch and the die in the later stage of forming can be enhanced. Thereby, a press-formed product having the desired shape and no cracks can be obtained.

[0011] According to the invention described in [3] above, in the second stage, by providing at least two or more stop steps between the contact position where the punch contacts the metal plate and the bottom dead center, when the stop steps are completed and the punch and the die are moved again, the dispersion of strain in the metal plate during forming is achieved. As a result, the breakage of the material due to the concentration of strain is suppressed, and cracking of the press-formed product can be prevented. Also, by making the first cushioning force before the first stop step higher than the second cushioning force, the formability of the metal plate by the punch in the initial stage of forming can be enhanced. Furthermore, by making the second cushioning force between the first stop step and the last stop step smaller than the cushioning forces (the first and third cushioning forces) before the first stop step and after the last stop step, the inflow of material between the punch and the die in the middle stage of forming is promoted. As a result, excessive thickness reduction of the metal plate during forming can be prevented, the strain can be more dispersed, and the breakage of the material due to the concentration of strain is suppressed. Also, by making the third cushioning force after the stop step higher than the second cushioning force, the formability of the metal plate by the punch and die in the latter stage of forming can be enhanced. As described above, a press-formed product having a desired shape and no cracks can be obtained.

[0012] According to the invention described in [4] above, when the punch reaches the range from the maximum load position to the position where the forming load becomes 80% of the maximum value, by performing the first stop step, it is possible to shift to the stop step after the forming of the metal plate by the punch in the initial stage of forming is almost completed. As a result, the strain dispersion effect on the metal plate being formed during the stop step can be further enhanced, and a press-formed product with a desired shape can be manufactured while preventing cracks.

[0013] According to the invention described in [5] above, when the punch reaches a position 5 to 10 mm away from the bottom dead center, the last stop step is performed, and by changing the cushioning force to the third cushioning force at that time, the formability of the metal plate by the punch and die in the latter stage of forming can be further enhanced.

[0014] According to the invention described in [6] above, by setting the second speed to be 40% or more and 70% or less of the first speed, the speed control of the punch and die during the forming of the metal plate becomes easier, and the concentration of strain in the metal plate being formed can be prevented.

[0015] According to the invention described in [7] above, by setting the intermediate position to a position 10 mm to 20 mm away from the contact position, the relative speed of the punch and die can be surely reduced to the second speed before the punch contacts the metal plate.

[0016] According to the invention described in [8] above, by setting the stop time in the stop step to be in the range of 0.2 to 1.0 seconds, when the punch and die are moved again after the stop step, the dispersion of strain in the metal plate can be more surely achieved.

[0017] According to the invention described in [9] above, by setting the second cushioning force in the range of 0.1 to 0.5 times the first cushioning force and the third cushioning force, the inflow of the material between the punch and the die during molding can be ensured, excessive reduction in plate thickness can be suppressed, and breakage of the material can be prevented.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0019] Hereinafter, a press molding method for a metal plate according to an embodiment of the present invention will be described. The press molding method of the present embodiment is a press molding method using a punch, a die, and a wrinkle presser, and is particularly preferably applied to deep drawing molding or square tube drawing molding.

[0020] Figure 1 shows an example of a molded product that can be molded by the molding method of the present embodiment. The molded product 2 shown in Fig. 1 is manufactured by subjecting the metal sheet 1 to square tube drawing. The molded product 2 has a rectangular bottom surface portion 21, a flange portion 22, and four vertical wall portions 23 connecting the bottom surface portion 21 and the flange portion 22. A first bending portion 1b (punch shoulder) is provided between the bottom surface portion 21 and the vertical wall portion 23, and a second bending portion 1c (die shoulder) is provided between the vertical wall portion 23 and the flange portion 22. The distance between the bottom surface portion 21 and the flange portion 22, that is, the height d of the vertical wall portion 23, is a height corresponding to the distance from the contact position described later to the bottom dead center position D.

[0021] The molded product 2 shown in Fig. 1 can be used, for example, for automotive parts. Further, the molded product 2 can also be used for exterior panels of home appliances and kitchen appliances. When the molded product 2 is used for these applications, it is not limited to the shape shown in Fig. 1, and the bottom surface portion 21, the flange portion 22, and the vertical wall portion 23 may be appropriately deformed.

[0022] The material of the metal sheet 1 is not particularly limited, and examples of the material include steel, stainless steel, titanium or titanium alloy, aluminum or aluminum alloy, copper or copper alloy, etc. In the present embodiment, it is preferably applied to a metal sheet having relatively high yield strength. As an example of such a metal sheet, a ferritic-austenitic duplex stainless steel sheet can be exemplified.

[0023] Next, an example of a press molding machine suitably used in the molding method of the present embodiment will be described. Figs. 2 and 3 are process diagrams showing the basic procedures of the press molding method of the present embodiment. The press molding machine 30 shown in Fig. 2(a) is a so-called servo press machine, and includes a die 31, a punch 32, and a die cushion pad 33. The die cushion pad 33 is generally also called a blank holder or a wrinkle suppressor. The press molding machine 30 improves the moldability of the molded product 2 by sandwiching a part 1a of the steel sheet 1 between the peripheral edge of the die 31 and the die cushion pad 33 during press molding.

[0024] A servo motor (not shown) is connected to the die 31 in the press molding machine 30 as a drive source. By using a servo motor as the drive source of the die 31, the slide motion by the die 31 and the punch 32 can be freely controlled. In this case, the press molding machine 30 operates with the punch 32 as the fixed side and the die 31 and the die cushion pad 33 as the movable side.

[0025] Note that the press molding machine 30 applicable to this embodiment is not limited to the above, and the punch 32 may be the movable side and the die 31 and the die cushion pad 33 may be the fixed side. In this case, a servo motor may be used as the drive source of the punch 32 and the die cushion pad 33, respectively. Further, the punch 32, the die 31, and the die cushion pad 33 may be configured to be movable, respectively. In this case, a servo motor may be used as the drive source of the punch 32, the die 31, and the die cushion pad 33, respectively.

[0026] In the press molding machine 30 according to this embodiment, in the order along the relative movement direction of the punch 32 with respect to the die 31, the initial position of the punch, the intermediate position A on the die 31 side from the initial position, the contact position where the punch 32 first contacts the metal plate 1, the first stop position B, the second stop position C, and the bottom dead center position D of the punch 32 are set, respectively. The initial position and the contact position of the punch 32 are determined by the structure of the press molding machine 30. Further, the intermediate position A, the first stop position B, the second stop position C, and the bottom dead center position D are determined by the relationships described below.

[0027] First, the initial position of the punch 32 is the relative position of the punch 32 with respect to the die 31 in the state where the punch 32 waits before the start of press molding. Specifically, as shown in Fig. 2(a), it is a position separated from the die 31.

[0028] The contact position is the relative position of the punch 32 with respect to the die 31 when the punch 32 first contacts the metal plate 1. In FIGS. 2 and 3, the contact position is at the same height as the upper surface 31a of the die 31. Also, the contact position is the position where the metal plate 1 before forming is first fixed by the die 31 and the cushion pad 33.

[0029] The intermediate position A is the position where the relative average speed of the punch 32 and the die 31 is changed from the first speed to the second speed, and is set at a position 10 mm to 20 mm away from the contact position toward the initial position side.

[0030] The first stop position B is a position determined based on the position (maximum load position) where the forming load of the punch 32 during forming shows the maximum value, and is the relative position of the punch 32 with respect to the die 31 when the punch 32 reaches the range from beyond the maximum load position to the position where the forming load becomes 80%, preferably 90%, of the maximum value. The first stop position B is determined by at least the material, thickness, and mechanical properties (strength, elongation, etc.) of the metal plate 1, the cushioning force by the cushion pad 33, and the shapes and sizes of the die 31 and the punch 32. As a method for determining the first stop position B, the forming load applied to the punch 32 during press forming may be measured and determined each time press forming is performed, or press forming may be experimentally performed on the metal plate 1 in advance, and it may be determined based on the maximum load position of the punch 32 at that time.

[0031] The second stop position C is set at a position 5 to 10 mm away from the bottom dead center position D of the punch 32 toward the initial position side.

[0032] The bottom dead center position D of the punch is arbitrarily determined according to the target shape of the molded product 2. As shown in FIG. 1, when the forming height of the molded product 2 is d, the bottom dead center position D in FIGS. 2 and 3 is set at a position separated by a distance corresponding to the forming height d from the contact position (located at the upper surface 31a of the die 31).

[0033] (First Embodiment) Next, the press forming method of the first embodiment will be described. The press forming method of this embodiment includes a first step of installing a metal plate 1 on a press forming machine 30, and a second step of forming the metal plate 1 by relatively approaching a die 31 and a punch 32 while applying a cushioning force to the metal plate 1 by a cushion pad 33. In the second step, the relative average speed of the die 31 and the punch 32 from the initial position to the intermediate position A is defined as the first speed, the relative average speed of the die 31 and the punch 32 from the intermediate position A to the bottom dead center position D is defined as a second speed lower than the first speed, and further, a stop step of temporarily stopping the punch 32 and the die 31 is performed at a first stop position B and a second stop position C while the punch 31 is moving from the contact position to the bottom dead center position D. However, the stop step may be performed only at the first stop position B.

[0034] Hereinafter, the press forming method of this embodiment will be described in detail with reference to FIGS. 2 to 4. FIG. 4 is a graph showing the relationship between the relative position of the punch with respect to the bottom dead center and time.

[0035] (First step) In the first step, as shown in FIG. 2(a), the metal plate 1 is disposed between the die 31 and the punch 32, the metal plate 1 is placed on the upper surface 31a of the die 31, and further, a part 1a of the metal plate is restrained by the cushion pad 33. At this time, the punch 31 is at the initial position. Depending on the press forming machine 30, the initial position is, for example, a position about 100 to 200 mm away from the position where the metal plate 1 is installed.

[0036] (Second step) Next, in the second step, the metal plate 1 is formed by relatively approaching the die 31 and the punch 32 while applying a cushioning force to the metal plate 1 by the cushion pad 33. In this embodiment, the cushioning force is made constant from the start to the end of the forming. Specifically, while the metal plate 1 is restrained by the cushion pad 33, the metal plate 1 is lifted together with the die 31 and the cushion pad 33 to approach the punch 32, and the forming is performed while deforming the metal plate 1 by the die 31 and the punch 32. The cushioning force is not particularly limited, and may be set, for example, in the range of 10 to 100 kN.

[0037] In the second stage, as shown in FIGS. 2(a) and 2(b), while the steel plate 1 is constrained by the cushion pad 33, the die 31 and the punch 32 are relatively approximated at the first speed V1 until the position of the tip 32a of the punch 32 reaches the intermediate position A from the initial position. In FIG. 4, the initial position corresponds to the position where the punch position on the vertical axis of FIG. 4 is 200 mm. Also, the intermediate position A corresponds to the position where the punch position in FIG. 4 is 55 mm. The movement of the punch 32 relative to the die 31 during the stroke from the initial position to the intermediate position A may be a so-called crank motion. The first speed V1 is the relative average speed of the punch 31 with respect to the die 31 between the initial position and the intermediate position A.

[0038] The first speed V1 is preferably in the range of, for example, 100 mm / s to 200 mm / s. By setting the first speed V1 to 100 mm / s or more, the time (hereinafter referred to as the forming time) until the punch 32 reaches the bottom dead center position D from the initial position and returns to the initial position again can be shortened. Also, by setting the first speed V1 to 200 mm / s or less, the relative speed of the punch 32 with respect to the die 31 can be surely decelerated from the first speed V1 to the second speed V2 when the punch 32 reaches the intermediate position A.

[0039] When the first speed V1 is expressed in strokes per minute (spm), which is an index of how many reciprocations the punch can make in one minute between the initial position and the bottom dead center, it is a speed corresponding to 15 to 30 spm.

[0040] Also, in the second stage, as shown in FIGS. 2(b) to 3(c), while the position of the tip 32a of the punch 32 moves from the intermediate position A to the bottom dead center position D, the die 31 and the punch 32 are relatively approximated at the second speed V2. The bottom dead center position D in FIG. 4 corresponds to the position where the punch position on the vertical axis of FIG. 4 is 0 mm. The movement of the die 31 and the punch 32 during the stroke from the intermediate position A to the bottom dead center position D may be a so-called crank motion. The second speed V2 is the relative average speed of the punch 32 with respect to the die 31 between the intermediate position A and the bottom dead center position D. However, the stop time of the intermediate stop step is not included in the calculation of the second speed V2.

[0041] The second speed V2 is preferably in the range of, for example, 65 mm / s to 130 mm / s. By setting the second speed V2 to 65 mm / s or more, an increase in the molding time can be prevented. Also, by setting the second speed V2 to 130 mm / s or less, it is possible to prevent strain from concentrating on a specific portion of the metal plate 1. Further, the second speed V2 is preferably set to a speed that is 40% or more and 70% or less of the first speed V1. By setting the second speed V2 within this range, the speed control of the punch 32 and the die 31 during the molding of the metal plate 1 becomes easier. Also, the second speed V2 corresponds to a speed of 10 to 20 strokes per minute (spm) when expressed in strokes per minute.

[0042] The operation of the punch 32 according to this embodiment is a crank motion at the first speed V1 from the initial position to the intermediate position A, a crank motion at the second speed V2 from the intermediate position A to the bottom dead center position D, and further a crank motion at the first speed V1 from the bottom dead center position D after the molding is completed back to the initial position, and operates as a so-called link motion as a whole. In FIG. 4, for reference, a crank motion at a constant speed is illustrated by a dotted line for comparison with the link motion of the punch 32 according to this embodiment.

[0043] In the second stage, as shown in FIG. 2(c), from the time when the tip 32a of the punch 32 contacts the metal plate 1 at the contact position, the forming of the metal plate 1 is started. Then, as shown in FIG. 3(a), until the tip 32a of the punch 32 reaches the first stop position B from the contact position, the metal plate 1 is mainly bent and deformed by the punch 32, and the first bending portion 1b, which is the punch shoulder portion, is formed. In the initial stage of forming from FIG. 2(c) to FIG. 3(a), the bottom surface portion 21 and the first bending portion 1b of the molded product 2 are formed. The forming load of the punch 32 in the initial stage of forming shows the maximum value.

[0044] Next, in the second stage, as shown in FIG. 3(a), when the tip 32a of the punch 32 reaches the first stop position B, a stop step of temporarily stopping the operations of the die 31 and the punch 32 is performed. In FIG. 4, the first stop position B corresponds to the position where the punch position on the vertical axis of FIG. 4 is 35 mm. The stop time is in the range of 0.2 to 1.0 seconds. After the stop time has elapsed, the operations of the die 31 and the punch 32 are resumed. By setting the stop time to 0.2 seconds or more, the dispersion effect of the strain becomes sufficient, and by setting the stop time to 1.0 seconds or less, the forming time can be shortened. The stop step may be performed only once at the first stop position B.

[0045] As described above, the first stop position B is determined based on the position where the forming load of the punch 32 during the forming of the metal plate 1 shows the maximum value. The first stop position B is the relative position of the punch 32 with respect to the die 31 when the punch 32 reaches the range from beyond the maximum load position to the position where the forming load becomes 80%, preferably 90% of the maximum value. By performing the stop step at the first stop position B, the dispersion of the strain in the metal plate 1 can be achieved.

[0046] Note that Fig. 7 shows an example of the change in the forming load of the punch 32 during the forming of the metal plate 1. On the horizontal axis (forming height) of Fig. 7, the contact position where the punch 32 contacts the metal plate 1 is set as 0 mm, and the position of the bottom dead center is set as 55 mm. In the example shown in Fig. 7, since the forming load shows the maximum value at a forming height of 17 mm, this position is defined as the maximum load position, and the first stop position B may be set in the range from this position until the forming load reaches 80%, preferably 90%, of the maximum value. In practice, the press forming may be actually performed on the metal plate 1 to measure the change in the forming load of the punch, and the first stop position B may be set based on the result.

[0047] Next, in the second stage, as shown in Fig. 3(b), when the tip 32a of the punch 32 reaches the second stop position C, a stop step of temporarily stopping the operations of the die 31 and the punch 32 is performed again. The stop step may be performed only once at the first stop position B, or may be performed for the second time at the second stop position C. In Fig. 4, the second stop position C corresponds to the position where the punch position on the vertical axis of Fig. 4 is 5 mm. The stop time is in the range of 0.2 to 1.0 seconds. After the stop time has elapsed, the operations of the die 31 and the punch 32 are resumed. By setting the stop time to 0.2 seconds or more, the dispersion effect of the strain becomes sufficient, and by setting the stop time to 1.0 seconds or less, the forming time can be shortened.

[0048] As described above, the second stop position C is set at a position 5 to 10 mm away from the bottom dead center position D of the punch 32 toward the initial position side. By performing the stop step again at the second stop position C, it becomes possible to further achieve the dispersion of the strain in the metal plate 1. That is, in the middle stage of forming from the first stop step to the last stop step, mainly tensile deformation is applied to the metal plate 1, and the part corresponding to the vertical wall portion 23 of the formed product 1 is formed. In this middle stage of forming, strain tends to concentrate on the curved side portion where the vertical wall portions 23 are joined, particularly the curved side portion near the punch shoulder. However, by providing two or more stop steps, the dispersion of the strain is achieved, thereby avoiding the breakage of the material during forming.

[0049] The stop step is preferably provided at least once, more preferably two or more times, in order to effectively achieve the dispersion of strain in the metal plate 1. If the stop step is not performed, the dispersion of strain in the metal plate 1 will be insufficient, and there is a risk that the material will break during forming or the strength will decrease due to a reduction in plate thickness.

[0050] The stop step is not particularly limited as long as it is performed one or more times, and it may be performed twice, three times, or four times. When providing the stop step three or more times, it is effective for achieving strain dispersion to perform the stop step further between the first stop position B and the second stop position C.

[0051] Next, as shown in FIG. 3(c), until the tip 32a of the punch 32 reaches the bottom dead center position D, the die 31 and the die cushion pad 33 are relatively approached to the punch 32 to complete the forming.

[0052] In the latter stage of forming from the last stop step (the second stop position C) until the punch 32 reaches the bottom dead center position D, bending deformation is performed at the die shoulder of the metal plate 1 to form the second bent portion 1c. Further, when forming the second bent portion 1c, since a part 1a of the metal plate 1 is sandwiched and constrained between the upper surface 31a of the die 31 and the die cushion pad 33, the generation of wrinkles at the portion corresponding to the flange portion 22 of the formed product 2 is suppressed.

[0053] In order to obtain such an effect, it is preferable to set the second stop position C where the last stop step is performed at a position 5 to 10 mm away from the bottom dead center position D of the punch 32 toward the initial position side. By setting the second stop position C at a position 5 mm or more away from the bottom dead center position D of the punch 32 toward the initial position side, it is possible to surely form the second bent portion 1c and suppress the generation of wrinkles in the flange portion 22. Further, by setting the second stop position C at a position within 10 mm from the bottom dead center position D of the punch 32 toward the initial position side, the interval between the first stop position B and the second stop position C can be widened, and the strain dispersion in the metal plate 1 can be surely achieved.

[0054] As described above, according to the present embodiment, in the second stage, the first speed is used until the punch 32 contacts the metal plate 1, and then the speed is decelerated to a second speed lower than the first speed until the punch 32 reaches the bottom dead center position D, so that the impact applied to the metal plate 1 when the punch 32 contacts the metal plate 1 is reduced. Also, by providing at least one or more stop steps between the contact position where the punch 32 contacts the metal plate 1 and the bottom dead center position D, when the stop step ends and the punch 32 and the die 31 are moved again, the strain in the metal plate 1 during forming is dispersed, thereby suppressing the breakage of the material due to strain concentration. Furthermore, by setting the relative speed of the punch 32 and the die 31 before and after the stop step to a second speed lower than the first speed, the speed control of the punch 32 and the die 31 during the forming of the metal plate 1 becomes easy, and the strain concentration in the metal plate 1 during forming can be prevented. As described above, by suppressing the impact on the metal plate 1, dispersing the strain in the metal plate 1 during forming, and preventing strain concentration, the breakage of the material during forming can be suppressed, and cracking of the press-formed product 2 can be prevented. Also, in the second stage, by setting the relative speed of the punch 32 and the die 31 before the punch 32 contacts the metal plate 1 to a first speed higher than the second speed, an increase in the forming time due to the provision of the stop step can be suppressed, and the overall forming time can be shortened.

[0055] Also, according to the present embodiment, when the punch 32 reaches the range from exceeding the maximum load position to the position where the forming load becomes 80% of the maximum value, by performing the first stop step, it is possible to shift to the stop step after the forming of the metal plate 1 by the punch 32 in the initial stage of forming is almost completed. Thereby, the strain dispersion effect on the metal plate 1 during forming by the stop step can be further enhanced, and a press-formed product 2 having a desired shape can be manufactured while preventing cracking.

[0056] Moreover, according to the present embodiment, by setting the second speed to be 40% or more and 70% or less of the first speed, the speed control of the punch 32 and the die 31 during the forming of the metal plate 1 becomes easier, and the concentration of strain in the metal plate 1 during forming can be prevented.

[0057] Moreover, according to the present embodiment, by setting the intermediate position A to be a position 10 mm to 20 mm away from the contact position, the relative speed between the punch 32 and the die 1 can be surely reduced to the second speed before the punch 32 contacts the metal plate 1.

[0058] Moreover, according to the present embodiment, by setting the stop time in the stop step to be in the range of 0.2 to 1.0 seconds, when the punch and the die are moved again after the stop step, the dispersion of strain in the metal plate can be more surely achieved.

[0059] (Second Embodiment) Next, the second embodiment will be described. In the press forming method of the aforementioned first embodiment, the cushion force from the start to the end of forming is constant. However, in the press forming method of the present embodiment, during the press forming in the second stage, two or more stop steps are provided, and the cushion force is changed in each stop step. Since the operations other than the control of the cushion force are the same as those in the first embodiment, in the present embodiment, the control of the cushion force will be described, and other descriptions will be omitted.

[0060] FIG. 5 is a diagram for explaining the press forming method of the present embodiment, and shows a graph of the relationship between the relative position of the punch with respect to the bottom dead center, the cushion force, and time. FIG. 5 is enlarged in the vertical axis direction compared to FIG. 4 in order to facilitate the understanding of the relationship between the relative position of the punch and the cushion force. That is, in FIG. 4, the maximum value of the vertical axis is 200 mm, but in FIG. 5, it is set to 80 mm. Also, in FIG. 5, the illustration of the initial position is omitted.

[0061] In this embodiment, as shown in FIG. 5, the cushioning force of the cushion pad 33 on the metal plate 1 is defined as the first cushioning force from the initial step to the first stop step, the second cushioning force smaller than the first cushioning force from the first stop step to the last stop step, and the third cushioning force larger than the second cushioning force after the last stop step. In this way, the second cushioning force is made smaller than the first cushioning force and the third cushioning force.

[0062] More specifically, as shown in FIGS. 2(a) to 3(a), the cushioning force when the relative position of the punch 32 with respect to the die 31 reaches from the initial position to the first stop position B is defined as the first cushioning force, the cushioning force when reaching from the first stop position B to the second stop position C is defined as the second cushioning force, and the cushioning force when reaching from the second stop position C to the bottom dead center position D is defined as the third cushioning force. After the relative position of the punch 32 with respect to the die 31 reaches the bottom dead center position D, the restraint by the cushion pad 33 may be released.

[0063] The first cushioning force and the third cushioning force may be set, for example, in the range of 10 to 100 kN. The first cushioning force and the third cushioning force may be the same, or either one may be made smaller. Also, the second cushioning force is preferably in the range of 0.1 to 0.5 times the first cushioning force or the third cushioning force. For example, the second cushioning force may be in the range of 5 to 50 kN.

[0064] The change from the first cushioning force to the second cushioning force is preferably made during the first stop step, and the change from the second cushioning force to the third cushioning force is preferably made during the last stop step. If the change in the cushioning force is made at a time other than the stop step, the restraint of the metal sheet 1 during forming becomes unstable and there is a concern about the generation of wrinkles. Therefore, it is advisable to change the cushioning force during the stop step. Also, by changing the cushioning force in the first stop step and the last stop step, the section for maintaining the second cushioning force can be widened, and the inflow of the material can be further promoted. In this case, the stop time of the stop step is more preferably 0.5 seconds or more.

[0065] According to the present embodiment, by making the first cushioning force before the first stop step higher than the second cushioning force, the formability of the punch shoulder portion (the first bending portion 1b) of the metal sheet 1 by the punch 32 in the initial stage of forming can be enhanced. Also, by making the second cushioning force between the first stop step and the last stop step smaller than the cushioning forces (the first and third cushioning forces) before the first stop step and after the last stop step, the inflow of the material between the punch 32 and the die 31 in the middle stage of forming is promoted. As a result, excessive reduction in the plate thickness of the vertical wall portion of the metal sheet 1 during forming can be prevented, the strain can be more dispersed, the breakage of the material due to the concentration of the strain can be suppressed, and the cracking of the press-formed product can be prevented. Furthermore, by making the third cushioning force after the last stop step higher than the second cushioning force, the formability of the die shoulder portion (the second bending portion 1c) and the flange portion 22 of the metal sheet 1 by the punch 32 and the die 31 in the final stage of forming can be enhanced. Thereby, a formed product 2 having the desired shape and no cracks can be obtained.

[0066] Further, according to the present embodiment, when the punch 32 reaches the second stop position C which is 5 to 10 mm away from the bottom dead center position D, the final stop step is performed, and at this time, by changing the cushioning force to the third cushioning force, the formability of the die shoulder (second bending portion 1c) and the flange portion 22 of the metal plate 1 by the punch 32 and the die 31 in the latter stage of forming can be further enhanced.

[0067] (Third Embodiment) Next, the third embodiment will be described. In the press forming method of the foregoing second embodiment, while changing the relative average speed of the die 31 and the punch 32 from the first speed to the second speed at the intermediate position A, the cushioning force was changed. However, in the press forming method of the present embodiment, the cushioning force is changed without changing the relative average speed of the die 31 and the punch 32 at the intermediate position A. Since the operations other than the control of the relative speed of the die 31 and the punch 32 are the same as those in the second embodiment, in the present embodiment, the control of the relative average speed of the die 31 and the punch 32 will be described, and other descriptions will be omitted.

[0068] FIG. 6 is a diagram for explaining the press forming method of the present embodiment, and shows in a graph the relationship between the relative position of the punch with respect to the bottom dead center, the cushioning force, and time. As shown in FIG. 6, the operation of the punch 32 according to the present embodiment operates at a so-called crank motion without changing the relative average speed from the initial position to the intermediate position A and the relative average speed from the intermediate position A to the bottom dead center position D. Then, after defining the first stop position B and the second stop position C, the cushioning force is controlled in the same manner as in the case of the second embodiment.

[0069] According to the present embodiment, similar to the second embodiment, in the second stage, by providing at least two or more stop steps between the contact position A where the punch 32 contacts the metal plate 1 and the bottom dead center position D, when the stop step ends and the punch 32 and the die 31 are moved again, the dispersion of the strain in the metal plate 1 being formed is achieved. Thereby, the breakage of the material due to the concentration of the strain is suppressed, and the cracking of the press formed product can be prevented. Furthermore, by making the first cushioning force before the first stop step higher than the second cushioning force, the formability of the metal plate 1 by the punch 32 in the initial stage of forming can be enhanced. Furthermore, by making the second cushioning force between the first stop step and the last stop step smaller than the cushioning forces (the first and third cushioning forces) before the first stop step and after the last stop step, the inflow of the material between the punch 32 and the die 31 in the middle stage of forming is promoted. As a result, excessive thickness reduction of the metal plate 1 during forming can be prevented, the strain can be more dispersed, and breakage of the material due to strain concentration is suppressed. Also, by making the third cushioning force after the stop step higher than the second cushioning force, the formability of the metal plate 1 by the punch 32 and the die 31 in the final stage of forming can be enhanced. As described above, a press-formed product having a desired shape and no cracks can be obtained.

Example

[0070] Hereinafter, the present invention will be described in more detail with reference to examples. Under the conditions shown in Table 1A, press forming of a metal plate was performed. The metal plate was a two-phase stainless steel thin plate (NSSC2120 manufactured by Nippon Steel & Sumitomo Metal Corporation) with a size of 170 mm square and a thickness of 1.0 mm. The press-formed product had the shape shown in FIG. 1, with the size of the bottom surface portion being 70 mm in length × 70 mm in width, the height of the vertical wall portion being 50 mm, and the width of the flange portion being 10 mm.

[0071]

Table 1A

[0072] In Table 1A, in Test Examples 1 and 10, the operation of the punch was a so-called link motion in which the speed was changed from the first speed to the second speed at an intermediate position, the cushioning force was kept constant, and the stop step was performed 4 times in Test Example 1 and 2 times in Test Example 10. The position of the stop step was the height position when the height of the bottom dead center was 0 mm.

[0073] In Test Examples 2, 3, 6 to 8, and 11, the operation of the punch was set as a so-called link motion, and the cushioning force was changed as shown in Table 1A. The change in the cushioning force was carried out at the first stop step and the last stop step.

[0074] In Test Example 4, the operation of the punch was set as a so-called crank motion, and the cushioning force was kept constant.

[0075] In Test Example 5, the operation of the punch was set as a so-called link motion, and the cushioning force was kept constant.

[0076] In Test Example 9, the operation of the punch was set as a so-called link motion, and the cushioning force was changed as shown in Table 1A. The change in the cushioning force was carried out at the first stop step and the last stop step. The stop step had a stop time of 0 seconds. That is, substantially no stop step was provided, and the cushioning force was changed at positions 35 mm and 5 mm from the bottom dead center.

[0077] In Test Examples 1 to 3 and 7 to 11 except Test Example 6, the position of the first stop step was set as the position at a height of 35 mm from the bottom dead center. This position was within the range from the position exceeding the maximum load position to the position where the forming load became 80% of the maximum value when the position of the punch where the forming load of the punch showed the maximum value was defined as the maximum load position.

[0078] Also, the intermediate position, which is the position where the speed is changed from the first speed to the second speed, was set at a position 15 mm away from the contact position.

[0079] The evaluation method was determined by visual inspection for the presence or absence of cracks. For the visual evaluation, the condition where cracks were observed was marked as ×, and the condition without cracks was marked as ○ or ◎. Furthermore, for the test examples where no cracks occurred, the thickness reduction rate at the location near the vertical wall portion of the first bending portion (punch shoulder portion) between the bottom surface portion and the vertical wall portion was measured. Those with a thickness reduction rate of less than 5% with respect to the thickness of the blank metal plate were evaluated as ◎, and those with a thickness reduction rate of 5% or more were evaluated as ○. The results are shown in Table 1B.

[0080]

Table 1B

[0081] In Test Example 1, since the size of the dicking force was constant, the evaluation was ○.

[0082] In Test Examples 2 and 3, since the press forming was performed under the most favorable conditions, the evaluation was ◎.

[0083] In Test Examples 4 and 5, since the pressing was performed under conditions outside the scope of the present invention, the evaluation was ×.

[0084] In Test Example 6, when the position of the first stop step was outside the range from the position where the forming load of the punch reached the maximum value (the maximum load position) to the position where the forming load became 80% of the maximum value, the evaluation was ○ because it was performed at a position outside this range.

[0085] In Test Example 7, since the final stop step was performed when the punch reached a position 15 mm away from the bottom dead center, the evaluation was ○.

[0086] In Test Example 8, since the second speed was not in the range of 40% or more and 70% or less of the first speed, the evaluation was ○.

[0087] In Test Example 9, since the dicking force was changed without substantially performing a stop step, the evaluation became ×.

[0088] In Test Example 10, since the size of the dicking force was constant, the evaluation was ○.

[0089] In Test Example 11, since the size of the second dicking force was outside the range of 0.1 to 0.5 times that of the first dicking force and the third dicking force, the evaluation was ○.

Explanation of Reference Signs

[0090] 1…Metal plate, 31…Die, 32…Punch, 33…Die cushion pad, A…Intermediate position, D…Bottom dead center position (bottom dead center).

Claims

1. A first step of disposing a metal plate between a die and a punch and sandwiching a part of the metal plate with the die and a cushion pad; A second step of forming the metal plate by relatively approaching the die and the punch while applying a cushioning force to the metal plate by the cushion pad, and in the second step, when the relative average speed of the die and the punch from the initial position of the punch to an intermediate position immediately before contacting the metal plate is defined as a first speed, and the relative average speed of the die and the punch from the intermediate position to the bottom dead center is defined as a second speed, the second speed is set lower than the first speed, and at least two or more stop steps of temporarily stopping the punch and the die are performed between the contact position where the punch contacts the metal plate and the bottom dead center, A press forming method of a metal plate, wherein when the cushioning force applied to the metal plate by the cushion pad is defined as a first cushioning force until the first stop step, a second cushioning force from the first stop step to the last stop step, and a third cushioning force after the last stop step, the second cushioning force is made smaller than the first cushioning force and the third cushioning force.

2. A first step of disposing a metal plate between a die and a punch and sandwiching a part of the metal plate with the die and a cushion pad; A second step of forming the metal plate by relatively approaching the die and the punch while applying a cushioning force to the metal plate by the cushion pad, and in the second step, when the relative average speed of the die and the punch from the initial position of the punch to an intermediate position immediately before contacting the metal plate is defined as a first speed, and the relative average speed of the die and the punch from the intermediate position to the bottom dead center is defined as a second speed, the second speed is set lower than the first speed, and at least one or more stop steps of temporarily stopping the punch and the die are performed between the contact position where the punch contacts the metal plate and the bottom dead center. A method for press-forming a metal plate, wherein when the position of the punch when the forming load of the punch shows a maximum value is defined as the maximum load position, when the punch reaches a range from beyond the maximum load position to the position where the forming load becomes 80% of the maximum value, a first stop step is performed.

3. A first step of disposing a metal plate between a die and a punch and sandwiching a part of the metal plate with the die and a die cushion pad; A second step of forming the metal plate by relatively approaching the die and the punch while applying a cushion force to the metal plate by the die cushion pad, the method comprising: In the second step, At least two or more stop steps of temporarily stopping the punch and the die are performed between the contact position where the punch contacts the metal plate and the bottom dead center, and When the cushion force applied to the metal plate by the die cushion pad is defined as a first cushion force from the start to the first stop step, a second cushion force from the first stop step to the last stop step, and a third cushion force after the last stop step, the second cushion force is made smaller than the first cushion force and the third cushion force. A method for press-forming a metal plate.

4. The method for press-forming a metal plate according to claim 1 or claim 3, wherein when the position of the punch when the forming load of the punch shows a maximum value is defined as the maximum load position, when the punch reaches a range from beyond the maximum load position to the position where the forming load becomes 80% of the maximum value, a first stop step is performed.

5. The method for press-forming a metal plate according to claim 1 or claim 3, wherein when the punch reaches a position 5 to 10 mm away from the bottom dead center, a last stop step is performed.

6. The method for press-forming a metal plate according to claim 1, wherein the second speed is 40% or more and 70% or less of the first speed.

7. The method for press-forming a metal plate according to claim 1, wherein the intermediate position is a position 10 mm to 20 mm away from the contact position.

8. The method for press-forming a metal plate according to claim 1 or claim 3, wherein the stop time in the stop step is in the range of 0.2 to 1.0 seconds.

9. The method for press-forming a metal plate according to claim 1 or claim 3, wherein the second cushioning force is in the range of 0.1 to 0.5 times the first cushioning force or the third cushioning force.

10. A first step of disposing a metal plate between a die and a punch and sandwiching a part of the metal plate with the die and a cushion pad; A second step of forming the metal plate by relatively approaching the die and the punch while applying a cushioning force to the metal plate with the cushion pad, comprising: In the second step, When the relative average speed of the die and the punch from the initial position of the punch to an intermediate position immediately before contacting the metal plate is defined as a first speed, and the relative average speed of the die and the punch from the intermediate position to the bottom dead center is defined as a second speed, the second speed is set to be lower than the first speed, and at least one stop step of temporarily stopping the punch and the die is performed between the contact position where the punch contacts the metal plate and the bottom dead center; A method for press-forming a metal plate, wherein the last stop step is performed when the punch reaches a position 5 to 10 mm away from the bottom dead center.

11. A first step of disposing a metal plate between a die and a punch and sandwiching a part of the metal plate with the die and a cushion pad; A second step of forming the metal plate by relatively approaching the die and the punch while applying a cushioning force to the metal plate with the cushion pad, comprising: In the second step, When the relative average speed of the die and the punch from the initial position of the punch to an intermediate position immediately before contacting the metal plate is defined as a first speed, and the relative average speed of the die and the punch from the intermediate position to the bottom dead center is defined as a second speed, the second speed is set to be lower than the first speed, and at least one stop step of temporarily stopping the punch and the die is performed between the contact position where the punch contacts the metal plate and the bottom dead center; A method for press-forming a metal plate, wherein the stop time in the stop step is in the range of 0.2 to 1.0 second.

12. A first step of disposing a metal plate between a die and a punch and sandwiching a part of the metal plate with the die and a cushion pad; A second step of forming the metal plate by relatively approaching the die and the punch while applying a dicing force to the metal plate by the dicing pad, In the second step, When the relative average speed of the die and the punch from the initial position of the punch to an intermediate position immediately before contacting the metal plate is defined as a first speed, and the relative average speed of the die and the punch from the intermediate position to the bottom dead center is defined as a second speed, the second speed is set to be lower than the first speed, and at least two or more stop steps of temporarily stopping the punch and the die are performed between the contact position where the punch contacts the metal plate and the bottom dead center, A press forming method for a metal plate, wherein when the dicing force on the metal plate by the dicing pad is defined as a first dicing force until the first stop step, as a second dicing force from the first stop step to the last stop step, and as a third dicing force after the last stop step, the second dicing force is in the range of 0.1 to 0.5 times the first dicing force or the third dicing force.

Images