JPWO2013002363A1 - Press forming method - Google Patents

Abstract

This press molding method is a press molding method that uses a multi-axis press device that operates a plurality of shafts independently, and extrudes the bottom of the concave portion of the material in which the concave portion is formed to stretch the hollow shaft. A first step of setting the material in a concave mold; and defining the recess of the material by the first tool so that an end surface of the cylindrical side wall is formed in the axial direction of the first tool. And a second step of pressing and molding the bottom of the material at a second speed Vb in the axial direction of the second tool with a second tool at the same time as pressing into the first tool at a first speed Vi. In the second step, Vb / Vi, which is a ratio of the second speed Vb to the first speed Vi, is controlled in a range of 0.7 to 1.5.

Description

The present invention relates to a material press-molding method.
This application claims priority on June 30, 2011 based on Japanese Patent Application No. 2011-145903 for which it applied to Japan, and uses the content here.

  As a method of forming a cylindrical container having a constant diameter with a bottom and a multistage cylindrical product having stepped parts with different diameters, a method of further drawing a cup-shaped intermediate material is widely used. Yes. For example, Non-Patent Document 1 discloses a redrawing method in which an intermediate material formed into a cup shape from a disk-shaped material in a first step is drawn again in a second step.

  In this processing method, a punch that penetrates the inside of the wrinkle presser is held while the cup-shaped intermediate material formed in the first step is sandwiched between the wrinkle presser that is a cylindrical tool inserted in the inner surface of the cup. A cylindrical protrusion is formed on the bottom of the cup-shaped intermediate material by pushing it into the annular inner surface of the die. In such a molding method, the inflow of the material from the cup-shaped intermediate material between the punch and the cylindrical inner surface of the die becomes insufficient, and molding defects such as material breakage at the corner of the punch tip are likely to occur. There was a problem.

  With respect to such a problem, in Patent Document 1 and Patent Document 2, there is a method for preventing molding defects caused by material breakage or the like by positively pushing a cup into a cylindrical inner surface of a die using divided dies. Presented. Patent documents 3 and 4 are disclosed as related technologies.

Japanese Unexamined Patent Publication No. 8-150426 Japanese Unexamined Patent Publication No. 2002-113528 Japanese Laid-Open Patent Publication No. 8-141662 Japanese Patent Laid-Open No. 6-210363

Shuji Nagata, Jun Yanagimoto: Plastic processing understood from the foundation, (1999), p.195, Corona

  However, among the drawing methods described above, the method disclosed in Patent Document 1 is a molding method using hydraulic pressure, and thus the structure of the mold becomes complicated. Furthermore, since the direction of pushing the cup into the inner surface of the die is opposite to the pushing direction of the punch, there are many cases where the cup cannot be pushed in sufficiently.

  In the method disclosed in Patent Document 2, when the bottom portion of the intermediate material formed into a cup shape is drawn with a movable punch, it is inserted into the inner surface of the side wall surface that is arranged so as to sandwich the side wall. The tool and a movable tool arranged outside the outer wall surface are brought into sliding contact with the intermediate material in accordance with the movable punch. Thus, the material on the side wall of the intermediate material is positively fed into the inner surface of the die to prevent material breakage at the punch tip corner of the molded product. However, since it is common that a gap is provided between the side wall surface of the actual cup-shaped intermediate material and the tool for clamping the side wall from the inner and outer surfaces, it is intended. In many cases, the material cannot be sufficiently fed into the inner surface of the die on the side wall of the intermediate material. In addition, since the die is divided, there is a problem that cracks are likely to occur at the square portions at the end of the contact surface with the die material.

  In Patent Document 3, a thickening process using a coining process or an axial compression process is added in the middle of the molding process in order to make the product thickness more uniform after the drawing process, and the thickness is reduced by drawing. A method of increasing the thickness of the portion to be produced is disclosed. However, this method has a problem that productivity is lowered and manufacturing cost is increased because the number of steps of simply increasing the thickness is increased by one step. In addition, this method is a method of performing thickening molding after drawing for the purpose of improving the thickness accuracy of the molded product. That is, with this method, it is difficult to prevent molding defects due to material breakage or the like in the drawing processing that is the object of the present invention.

  For example, in Patent Document 4, after checking the correspondence between the portion where the thickness is reduced after molding and the position of the material in advance, the material portion corresponding to the portion where the thickness is reduced after drawing is compared with other portions. In other words, a method of drawing a material that has been machined so as to be relatively thick is disclosed. However, in such a method, it is necessary to process all materials to be molded into predetermined dimensions and shapes by machining such as cutting and grinding, leading to an increase in cost and a decrease in production efficiency. There is.

  The present invention provides a drawing method for the above-described problem, which does not easily cause cracking of a material during molding without using a split die that easily causes die cracking or a hydraulic pressure that complicates a mold structure. For the purpose.

In order to solve the above problems and achieve the object, the present invention employs the following means.
(1) A press molding method according to an aspect of the present invention uses a multi-axis press device that operates a plurality of shafts independently, and extrudes the bottom of the recess of the material in which the recess is formed to provide a hollow shaft. A first forming step of setting the material in a concave mold; and an end surface of a side wall forming a cylindrical shape by defining the recess of the material by a first tool. Is pushed in the axial direction of the first tool at the first speed Vi, and at the same time, the bottom of the material is extruded in the axial direction of the second tool by the second tool at the second speed Vb. And in the second step, Vb / Vi, which is a ratio of the second speed Vb to the first speed Vi, is controlled within a range of 0.7 to 1.5. .

(2) In the press molding method according to (1) above, in the second step, the material is wrinkled by the third tool provided between the first tool and the second tool. The thickness of the material before the second step is t, the gap s1 between the outer peripheral surface of the material and the inner peripheral surface of the concave mold, and the inner peripheral surface of the material and the third The following conditional expression (a) may be satisfied, where s is the total sum of the gaps s2 with the outer peripheral surface of the tool.
0.02 × t ≦ s ≦ 0.3 × t (a)

  By applying the present invention, the material can be stably drawn without causing cracks.

It is sectional drawing which showed the example of the metal mold | die used for this embodiment. It is sectional drawing which showed the example of the metal mold | die used for this embodiment. It is sectional drawing which showed the example of the metal mold | die used for this embodiment. It is a schematic diagram explaining the crack in the punch tip corner | angular part which is a problem which this embodiment tends to improve. It is a figure which shows the state before a raw material fills the metal mold | die of this embodiment. It is a figure which shows the state after a raw material fills the metal mold | die of this embodiment.

  Details of the press molding method according to the present embodiment will be described below with reference to the drawings. In this embodiment, a cup-shaped material 6 is used as a material in which a recess is formed, and the cup-shaped material 6 is molded. FIG. 1A to FIG. 1C are schematic views of a mold (press mold) 100 of a multi-axis press apparatus used in the present embodiment. The mold 100 shown in FIGS. 1A to 1C is used by being installed at a predetermined position of the multi-axis press apparatus having a plurality of axes that can be independently operated as described above. A cylindrical punch 1 that pushes out the inner bottom of the punch 1 and a cylindrical presser 2 that covers the periphery of the punch 1 and has a wrinkle presser 2 that presses the inner surface of the cup-shaped material 6 on its outer peripheral surface during the molding process. The punch 1 is a rod-like punch that pushes the inner bottom portion of a cup-shaped material 6 disposed on the set side (upper side of the sheet) of a die 4 (described later) to the material discharge side (lower side of the sheet) of the die 4. In the press molding method according to the present embodiment, the bottom portion of the cup-shaped material 6 is extruded and stretched into a hollow shaft by the above-described multi-axis press apparatus.

The outer diameter of the material used is preferably 20 mm to 300 mm. If the outer diameter is less than 20 mm, it is difficult to extrude the bottom of the cup-shaped material 6 and to draw it into a hollow shaft. On the other hand, if the outer diameter is more than 300 mm, the mold becomes large and the molding load increases, so that a practical press molding becomes difficult, for example, a large press is required. More desirably, it is 50 mm to 120 mm.
The plate thickness (wall thickness) of the material is desirably 1.5 mm to 15 mm. If it is less than 1.5 mm, it will be difficult to push the side wall end face of the material, and if it exceeds 15 mm, it will be difficult to form a cup-shaped intermediate material. More desirably, it is 2 mm to 12 mm.

The mold 100 used in the present embodiment has an outer peripheral punch 3 that is an annular cylindrical shaft that surrounds the periphery of the wrinkle presser 2. The outer peripheral punch 3 has a protrusion 3 a that pushes the upper edge of the opening of the cup-shaped material 6 disposed on the material set side of the die 4 into the material discharge side of the die 4. Further, the mold 100 of the present embodiment is a substantially ring-shaped die 4 that presses the material 6 with the punch 1 that descends while pressing the bottom of the cup-shaped material 6 to finish it into a predetermined dimensional shape. And a counter punch 5 that is inserted into the inner surface of the cylindrical die 4 and presses the bottom surface of the material with the punch 1.
The mold 100 includes a convex mold and a concave mold. The convex mold includes a punch 1, a wrinkle presser 2 and an outer peripheral punch 3, and the concave mold includes a die 4 and a counter punch 5.

  In addition, the multi-axis press device of this embodiment has a drive mechanism (not shown) that can control the movement of the punch 1, the wrinkle presser 2, the outer peripheral punch 3, and the counter punch 5 independently. The movement of each part of the mold 100 is controlled by a press machine not shown in the present embodiment so as to form the material 6 into a predetermined size and shape.

  Next, the behavior of each part in the press molding method using the mold 100 shown in FIGS. 1A to 1C will be described. First, the punch 1, the wrinkle presser 2, and the outer peripheral punch 3 are raised to a height sufficient to insert the cup-shaped material 6 between the die 4 by the control of the drive mechanism of the press. In this state, the cup-shaped material 6 is set (set) on the upper surface of the die 4 so that the central axis of the inner periphery of the die 4 substantially coincides with the central axis. Thereafter, the punch 1, the wrinkle presser 2, and the outer peripheral punch 3 are integrated and lowered while being controlled by the drive mechanism of the press. When the wrinkle presser 2 and the punch 1 are in contact with the bottom surface of the material 6 and the outer peripheral punch 3 is in contact with the upper edge surface of the cup-shaped material 6, the above-described lowering operation is stopped (see FIG. 1A).

  At this time, simultaneously with the movement of these tools, the counter punch 5 rises along the inner surface of the cylindrical die 4. When the counter punch 5 comes into contact with the bottom surface of the material 6, the above-described ascending operation stops (see FIG. 1A). The cup-shaped material 6 is pressed between the crease presser 2 and the die 4 and between the punch 1 and the counter punch 5 and fixed in the die 4 with the operation of each part of the mold so far completed.

  From the state in which the cup-shaped material 6 is fixed in the die 4 as described above, the bottom of the material 6 is pushed out while the punch 1 is lowered while the wrinkle presser 2 is stopped. Further, the counter punch 5 is lowered in accordance with the movement of the punch 1. By this operation, a cylindrical projection having a diameter smaller than the outer diameter of the material 6 is formed on the bottom of the cup-shaped material 6 (see FIG. 1B). During this molding, the outer peripheral punch 3 descends in response to the lowering of the punch 1, so that the upper edge surface of the opening of the material 6 is pressed to flow the material 6 into the mold 100, that is, the die 4 and the counter punch 5, and the region between the punch 1, the wrinkle presser 2 and the outer peripheral punch 3, and prompts the inflow to the material discharge side (see FIGS. 1B and 1C). By this operation, the material is prevented from being broken at the corners of the punch tip as shown in FIG.

  When the outer peripheral punch 3 is lowered, the ratio of the lowering speed Vi to the lowering speed Vb of the punch 1 is Vb / Vi = 0.7 to 1.5 in order to prevent breakage of the material at the corner of the punch tip. Control to be within range. The lowering speed Vi of the outer peripheral punch 3 with respect to the lowering speed Vb of the punch 1 is important for preventing the breakage of the raw material at the shoulder of the punch tip of the raw material 6 during molding for the following reason. In the press molding method according to the present embodiment, the material is ruptured by pressing the upper edge of the cup-shaped material 6 using the outer peripheral punch 3 during molding to promote the inflow of the material into the mold 100. Without forming, it can be molded stably. Therefore, when the descending speed ratio between the outer peripheral punch 3 and the punch 1 is not appropriate, a sufficient inflow effect of the material 6 into the mold 100 cannot be obtained, and for example, a fracture as shown in FIG. 2 may occur. is there. The reason why the sufficient inflow effect of the material 6 into the mold 100 is not obtained is that between the cup-shaped material 6 and the die 4 installed at a predetermined position of the die 4 before molding and the material 6 are wrinkled. The influence of the gap provided between the presser 2 is conceivable.

  The reason why the above-described inflow effect cannot be obtained will be described with reference to FIGS. 3A and 3B. FIG. 3A shows a state in which the punch 1, the wrinkle presser 2 and the outer peripheral punch 3 are in contact with the material 6 set on the material setting side of the die 4 (however, the pressing force applied to the material 6 is negligible) It is assumed that the force is weak. FIG. 3B is a diagram illustrating a state after the material 6 is filled in the mold 100.

  Here, the behavior of the multi-axis press apparatus when changing from the state of FIG. 3A to the state of FIG. 3B will be described. As shown in FIG. 3A, when the material 6 is set in the mold 100, horizontal gaps are formed between the material 6 and the wrinkle presser 2 and between the material 6 and the die 4. When the upper edge of the material 6 is pressed by the outer peripheral punch 3 from this state, the upper end portion of the material 6 is subjected to compressive stress by the pressing of the outer peripheral punch 3. As the stress propagates, the material 6 is distorted, and the shape of the material 6 changes so as to fill the gap during setting. After that, the state shown in FIG. 3B is reached, and the entire surface of the outer wall of the material 6 and the inner wall of the mold 100 are in contact, that is, the inside of the mold 100 is filled with the material 6.

  The reason why a gap is provided between the material 6 and the crease presser 2 and the die 4 when the material 6 is installed (set) will be described. This gap is provided to enable and facilitate the installation of the material 6 at a predetermined position inside the mold 100. If there is no gap between the material 6 and the die 4, when the material 6 is set in the mold 100, the material 6 and the die 4 are in a fitted state before being placed in a predetermined position. 6 may not be able to be pushed. Accordingly, the material 6 cannot be moved to a predetermined position in the mold 100 and installed. In addition, when the material 6 that can no longer be moved is forcibly moved, problems such as wrinkling of the material 6 or the mold 100 may occur.

  On the other hand, the gap between the material 6 and the wrinkle presser 2 facilitates the insertion of the wrinkle presser 2 into the inner surface of the cup-shaped material 6 at the start of molding, and between the wrinkle presser 2 and the material 6. It is provided for the purpose of preventing wrinkles.

  In the state where the gap as described above is provided between each part of the mold and the material 6, when the punch 1 is lowered while pressing the upper edge of the cup-shaped material 6 with the outer peripheral punch 3, the drawing is performed. Depending on the ratio of the lowering speed of the outer punch 3 and the lowering speed of the punch 1, the inside of the mold 100 of the material 6 due to the pressing of the upper edge of the material 6 of the outer punch 3 in the press forming method according to the present embodiment. In some cases, the material 6 may be broken without sufficiently obtaining an inflow effect. This is because the lowering speed of the outer peripheral punch 3 and the lowering of the punch 1 are lowered when the upper edge of the raw material 6 is pressed by the outer peripheral punch 3 with a gap between the raw material 6 and the tool such as the die 4 and the wrinkle presser 2. Depending on the value of the speed ratio, the effect of pressing is not the promotion of the inflow of the material 6 into the mold 100, which is the object of the present embodiment, but the gap between the material 6 and the die 4 and the wrinkle presser 2 etc. This is because the effect of pressing by the outer peripheral punch 3 does not sufficiently contribute to preventing the material 6 from being broken.

  In the press molding method according to the present embodiment, in order to prevent such a problem, when the outer peripheral punch 3 is lowered, the lowering speed is controlled to an appropriate value. That is, in the press molding method according to the present embodiment, the lowering speed Vi of the outer peripheral punch 3 is controlled so as to be in the range of Vb / Vi = 0.7 to 1.5 in a ratio with the lowering speed Vb of the punch 1. . By setting Vb / Vi within the above range, it is possible to perform molding without causing breakage of the material while sufficiently securing the effect of inflow of the material 6 into the die 4 by the pressing of the outer peripheral punch 3.

  When the ratio Vb / Vi between the lowering speed Vi of the outer peripheral punch 3 and the lowering speed Vb of the punch is more than 1.5, the lowering speed of the punch 1 is excessive with respect to the lowering speed of the outer peripheral punch 3, and The feed amount of the material 6 into the mold 100 by the outer peripheral punch 3 is insufficient, and the material breakage at the corner of the tip of the punch 1 cannot be sufficiently prevented.

  Further, when Vb / Vi is less than 0.7, the pressing of the material 6 by the outer peripheral punch 3 becomes excessive, and there are problems in manufacturing the product such as burrs between the outer peripheral punch 3 and the die 4. The above range does not depend on whether the material is filled in the mold 100 or not.

  Here, in the state illustrated in FIG. 3A, that is, in a state before pressing the upper edge of the material 6 by the outer peripheral punch 3, the thickness of the material 6 is formed between the material 6 and the die 4. A gap (horizontal gap) is defined as s1, and a gap (horizontal gap) formed between the material 6 and the wrinkle presser 2 is defined as s2. When the sum of s1 and s2 is s, 0.02 × t ≦ s ≦ 0.3 × t is preferably satisfied. When the plate thickness t and the total sum s of the gaps satisfy the above conditions, the effect of defining the speed ratio between the lowering speed Vi of the outer peripheral punch 3 and the lowering speed Vb of the punch as described above can be obtained more reliably. Can do. Even when the total sum s of the gaps is not in the above-described range, breakage and burrs do not occur, and the molding can be completed. However, if the total sum s of the gaps is smaller than 0.02t, the wrinkle presser 2 cannot be smoothly inserted into the inner surface of the cup-shaped material 6 installed in the mold 100 before molding, and the material 6 A dent wrinkle may arise in an upper edge surface, or a part of side wall may become thin. When the total sum s of the gaps exceeds 0.3 t, the gap is excessive, and after the wrinkle presser 2 is inserted, when the upper edge of the cup-shaped material 6 starts to be pressed by the outer peripheral punch 3, the side wall of the material 6 is bent. May occur and shape defects may occur in the molded product. Therefore, when high forming accuracy is required, the total sum s of the gaps preferably satisfies 0.02 × t ≦ s ≦ 0.3 × t.

For determining whether or not the material 6 is filled in the mold, pre-molding is performed with the same material and setting conditions of the multi-axis press device. For example, the control position of each part of the mold and the degree of filling of the material inside the mold It is sufficient to determine whether the material is full or not at the position of the mold based on the relationship. More specifically, an experiment for terminating molding in the middle of molding is performed under a plurality of different conditions (Vb / Vi conditions), and the stroke of the punch 1 from the start of driving of the multi-axis press device to the end of molding under each condition. Record the amount. And by measuring the shape of the cross-section of the molded material, grasping the full state of the material from the relationship with the mold shape obtained from the mold drawing in which the detailed dimensions and shape of the mold are described, The timing for changing the speed ratio can be experimentally determined in advance using the stroke amount of the punch 1 from the start of driving.
A method other than the above may be used to determine whether the material 6 is filled in the mold. For example, when the material 6 fills the mold, the load on the outer peripheral punch 3 increases. Therefore, a load meter may be attached to the outer peripheral punch 3, and the presence or absence of fullness may be determined by a change in load.

(Example 1)
Using a multi-axis press machine shown in FIGS. 1A to 1C, a cup-shaped material of carbon steel having an outer diameter of φ90 mm × thickness of 2 mm × height of 30 mm, a cup having an outer diameter of φ50 mm at a room temperature of 2 mm. Molded into. In this molding, the ratio between the lowering speed Vi of the outer peripheral punch 3 and the lowering speed Vb of the punch in both cases before and after the material confirmed by the preforming is filled into the mold (before and after filling). The multi-axis press apparatus was set so that Vb / Vi had the same value. Table 1 shows the relationship between the speed ratio Vb / Vi and the molding result in this molding.

  When the speed ratio Vb / Vi was in the range of 0.7 to 1.5, the molding could be completed without causing breakage or burrs in the material. On the other hand, when the speed ratio Vb / Vi is smaller than 0.7, a burr that becomes a problem in product manufacture occurs in the material. When the speed ratio Vb / Vi was larger than 1.5, the molding was interrupted because the material being molded was broken.

(Example 2)
Using the multi-axis press shown in FIGS. 1A to 1C, an aluminum cup-shaped material having an outer diameter of 120 mm, a wall thickness of 5 mm, and a height of 40 mm is used. Molded into. In this molding, the ratio Vb / Vi between the lowering speed Vi of the outer peripheral punch 3 and the lowering speed Vb of the punch is different between before and after filling the inside of the mold confirmed by the preliminary molding. A multi-axis press was set up. Table 2 shows the relationship between the speed ratio Vb / Vi of the multi-axis press machine and the molding result in this molding.

  When the speed ratio Vb / Vi was in the range of 0.7 to 1.5 in both cases before and after filling, the molding could be completed without causing breakage or burrs in the material. On the other hand, when the speed ratio Vb / Vi becomes a value smaller than 0.7 in any case before and after the filling, the material has a burr that becomes a problem in manufacturing the product. Moreover, when the speed ratio Vb / Vi was a value greater than 1.5 in either case before and after filling, the forming was interrupted because the material being formed was broken.

Example 3
Further, by using the multi-axis press apparatus shown in FIGS. 1A to 1C, a cup-shaped material made of carbon steel having an outer diameter of φ80 mm × thickness of 5 mm × height of 45 mm remains at a thickness of 5 mm, and a cup having an outer diameter of φ45 mm Molded at room temperature. Table 3 shows the relationship between the total s of the gaps between the material 6 and the die 4 and the wrinkle presser 2 in this molding, and the molding results.

  In the state shown in FIG. 3A, the gaps in Table 3 are the total thickness s of gaps (horizontal gaps) formed between the material 6, the die 4 and the wrinkle presser 2, and the plate thickness dimension of the material 6. The value divided by t.

When the speed ratio Vb / Vi was in the range of 0.7 to 1.5 in both cases before and after filling, the molding could be completed without causing breakage or burrs in the material. On the other hand, when the speed ratio Vb / Vi becomes a value smaller than 0.7 in any case before and after the filling, the material has a burr that becomes a problem in manufacturing the product. Moreover, when the speed ratio Vb / Vi was a value greater than 1.5 in either case before and after filling, the forming was interrupted because the material being formed was broken.
If the total gap s is smaller than 0.02 times the thickness of the material, a wrinkle presser insertion failure occurs. If the gap is larger than 0.3 times the thickness of the material 6, the side wall of the material 6 Bending occurred. On the other hand, when the total gap s is in the range between 0.02 and 0.3 times the plate thickness t of the material, such insertion failure of the wrinkle presser and bending of the material side wall may occur. Therefore, it was possible to perform molding with higher accuracy.

  In the press molding of the present invention, the material can be stably drawn without causing cracks. Therefore, the utility value of the industry is high.

1 Punch 2 Wrinkle presser 3 Peripheral punch 3a Protrusion 4 Die (concave die)
5 Counter punch 6 Material

In order to solve the above problems and achieve the object, the present invention employs the following means.
(1) A press molding method according to an aspect of the present invention includes:
A press molding method for extruding a bottom of the recess of a material having a recess and drawing it into a hollow shaft using a multi-axis press device that operates a plurality of shafts independently. A first step of setting in a mold; a first tool for axially pushing an end surface of a cylindrical side wall defining the recess of the material ; and the bottom of the material as a shaft Lowering the first to third tools together using a second tool for pushing in a direction and a third tool arranged between the first tool and the second tool is, the third tool is pressed against the bottom, while stopping the said third tool, by the first tool, the end surface of the side wall of the material in the axial direction of the first tool simultaneously pushed at a first speed Vi, by the second tool, the bottom of the material A second step of extruding and forming at a second speed Vb in the axial direction of the second tool, wherein the ratio of the second speed Vb to the first speed Vi in the second step Vb / Vi is controlled within a range of 0.7 to 1.5.

(2) In the press molding method according to (1) above, in the second step, the material is wrinkled by the third tool provided between the first tool and the second tool. A thickness t of the material before the second step, a horizontal gap s1 between the outer peripheral surface of the material and the inner peripheral surface of the concave mold, and the inner peripheral surface of the material The following conditional expression (a) may be satisfied, where s is the sum of the horizontal gaps s2 with the outer peripheral surface of the third tool.
0.02 × t ≦ s ≦ 0.3 × t (a)

Claims (2)

Using a multi-axis press device that independently operates a plurality of shafts, a press molding method that extrudes the bottom of the recess of the material in which the recess is formed and stretches it into a hollow shaft,
A first step of setting the material in a concave mold;
The first tool pushes the end face of the side wall of the material defining the recess into the cylindrical shape at the first speed Vi in the axial direction of the first tool, and at the same time by the second tool. A second step of extruding and forming the bottom of the material in the axial direction of the second tool at a second speed Vb;
With
In the second step, Vb / Vi which is a ratio of the second speed Vb to the first speed Vi is controlled in a range of 0.7 to 1.5. In the second step, the material is also creased simultaneously by a third tool provided between the first tool and the second tool;
Before the second step,
The thickness of the material is t,
When s is the sum of the gap s1 between the outer circumferential surface of the material and the inner circumferential surface of the concave mold and the gap s2 between the inner circumferential surface of the material and the outer circumferential surface of the third tool,
The following conditional expression (1) is satisfied;
The press molding method according to claim 1.
0.02 × t ≦ s ≦ 0.3 × t (1)

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