Molded product manufacturing method and transfer press device

Abstract

To reduce a press load when an annular workpiece is pressed so that its cross sectional shape is formed into a desired shape.SOLUTION: A manufacturing method of a formed part includes: a preparation step where an annular workpiece 99 formed of a metal is placed in a recessed part 11a of a recessed die 11; and a forming step where a protruding die 12 presses the workpiece 99 to form the workpiece 99 into an annular formed part 100. In the preparation step, the workpiece 99 is disposed in the recessed part 11a in a state that a gap is formed at least one of between an inner peripheral surface 11n of the recessed part 11a of the recessed die 11 and the workpiece 99 and between an outer peripheral surface 11g of the recessed part 11a of the recessed die 11 and the workpiece 99.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a molded product and a transfer press device used in the manufacturing method. [Background technology]

[0002] For example, cylindrical rotating parts such as bearing races, gears, and wheels have irregular cross-sectional shapes such as recesses, protrusions, and tapers depending on their functions. Cylindrical parts having shapes according to their functions require a certain degree of shape accuracy. Conventionally, to obtain cylindrical parts of a desired shape, machining such as cutting is performed on workpieces such as steel pipes, round bars, and billets.

[0003] For example, in Patent Publication No. 4562810 (Patent Document 1), a prewheel obtained by forming and forging a composite billet of an aluminum billet and a magnesium billet is subjected to machining processes such as spinning, drilling, cutting, and milling in the finishing process. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4562810 Summary of the Invention [Problem to be solved by the invention]

[0005] When mass-producing cylindrical parts with shapes suited to their functions, machining can cause problems with yield and takt time loss due to cutting. Furthermore, if it is necessary to introduce machinery for machining, manufacturing costs can become an issue.

[0006] The inventors investigated replacing machining with press forming in the process of imparting a non-circular cross-sectional shape to a cylindrical part. As a result of their investigation, they discovered that, considering mass production, it is preferable to use coining, in which an annular workpiece is compressed in a mold to form a shape corresponding to the mold. This allows for the production of an annular molded product with a desired cross-sectional shape. However, coining requires a larger press load than drawing, hole-expanding drawing, or other processes.

[0007] Therefore, the present application discloses a method for manufacturing a formed product and a transfer press device that can reduce the press load when press-forming an annular workpiece into a desired cross-sectional shape. [Means for solving the problem]

[0008] A method for manufacturing a molded product according to an embodiment of the present invention includes a preparation step of placing a workpiece formed of an annular metal in a recess of a concave mold having a recess including an annular bottom surface, an outer circumferential surface extending from an outer circumferential edge of the bottom surface, and an inner circumferential surface extending from an inner circumferential edge of the bottom surface, and a molding step of pressing the workpiece placed in the recess in the press direction with a convex mold including a top surface facing the bottom surface of the recess and protruding into the recess of the concave mold to form the workpiece into a shape corresponding to the top surface of the convex mold and the bottom surface of the concave mold, thereby forming an annular molded product. In the preparation step, the workpiece is placed in the recess with a gap between the inner circumferential surface of the recess of the concave mold and the workpiece, or between the outer circumferential surface of the recess of the concave mold and the workpiece. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to reduce the press load when press-forming an annular workpiece into a desired cross-sectional shape. [Brief explanation of the drawings]

[0010] [Figure 1]FIG. 1 is a diagram for explaining the method for producing a molded product in this embodiment. [Figure 2] FIG. 2 is a cross-sectional view for explaining the relationship between the dimensions of the formed product before and after the hole expansion and drawing process. [Figure 3] FIG. 3 is a diagram showing an example of a hole expanding and drawing process using hole expanding and drawing processing. [Figure 4] FIG. 4 is a cross-sectional view showing a modified example of an annular formed product formed in the forming step and a modified example of a tubular formed product formed in the hole expanding and drawing step. [Figure 5] FIG. 5 is a cross-sectional view showing another modified example of the annular molded product formed in the molding step and the tubular molded product formed in the hole expanding and drawing step. [Figure 6] FIG. 6 is a diagram showing an example of the configuration of a transfer press device in this embodiment. [Figure 7] FIG. 7 is a diagram showing the arrangement of the workpiece relative to the die in the test. [Figure 8] FIG. 8 is a graph showing the test results of the press load. [Figure 9] FIG. 9 is a graph showing the relationship between the central diameter ratio and the press load in the test and the FEM analysis. DETAILED DESCRIPTION OF THE INVENTION

[0011] When manufacturing cylindrical parts (tubular parts) using a press process, a plate-shaped blank with a through hole is drawn to form it into a cylindrical shape. To further impart a non-circular cross-sectional shape to the formed cylindrical product, machining such as cutting can be performed after the drawing process. Through extensive research, the inventors came up with the idea of ​​imparting a non-circular cross-sectional shape to a plate-shaped blank before drawing. They discovered that by drawing a plate-shaped blank with a non-circular cross-sectional shape already imparted to it into a cylindrical shape, the cross-sectional shape of the formed cylindrical product after drawing can be made into a desired shape. After further research, the inventors discovered that coining is suitable from the perspective of mass production for imparting a non-circular cross-sectional shape to a plate-shaped blank before drawing. Coining is a compression process in which high pressure is applied to a workpiece to form it into a desired shape. The large press load generated by coining can lead to an increase in the size of the press and a shortened mold life.

[0012] Therefore, the inventors investigated a pressing method for minimizing the forming load during press forming to impart a non-circular cross-sectional shape to an annular workpiece. After extensive investigation, they arrived at a method that actively utilizes plastic flow. Specifically, they came up with the idea of ​​placing the annular workpiece in an annular recess of a concave mold as an initial position, and providing a gap on either the inner or outer circumferential surface of the recess, or both. By pressing the annular workpiece placed in the recess of the concave mold with a convex mold in this way, an annular molded product having a desired cross-sectional shape can be obtained while reducing the press load. The following embodiments are based on this finding.

[0013] A method for manufacturing a molded product according to an embodiment of the present invention includes a preparation step of placing a workpiece formed of an annular metal in a recess of a concave mold having a recess including an annular bottom surface, an outer circumferential surface extending from an outer circumferential edge of the bottom surface, and an inner circumferential surface extending from an inner circumferential edge of the bottom surface, and a molding step of pressing the workpiece placed in the recess in the press direction with a convex mold including a top surface facing the bottom surface of the recess and protruding into the recess of the concave mold to form the workpiece into a shape corresponding to the top surface of the convex mold and the bottom surface of the concave mold, thereby forming an annular molded product. In the preparation step, the workpiece is placed in the recess with a gap between the inner circumferential surface of the recess of the concave mold and the workpiece, or between the outer circumferential surface of the recess of the concave mold and the workpiece.

[0014] According to the above manufacturing method, an annular workpiece is placed in the annular recess of the concave mold with a radial gap. When the workpiece is pressed against the convex mold, it is formed into a shape corresponding to the concave and convex molds. In this case, forming is possible with a lower press load than when no gap is provided. This is believed to be because the provision of the gap allows for appropriate plastic flow during the forming process. Furthermore, the concave mold has a recess including an annular bottom surface, inner peripheral surface, and outer peripheral surface. Because the annular workpiece is placed in this recess and pressed, the shape of the formed product does not significantly deviate from the target shape. Therefore, the desired cross-sectional shape can be imparted to the annular workpiece while reducing the press load. In other words, the press load required to press-form the cross-sectional shape of the annular workpiece into the desired shape can be reduced.

[0015] The annular workpiece before forming may be, for example, a plate-shaped blank (first blank) having an upper surface, a lower surface, and a hole penetrating from the upper surface to the lower surface. The annular formed product obtained in the forming step may also be a plate-shaped blank (second blank) having an upper surface, a lower surface, and a hole penetrating from the upper surface to the lower surface. For example, the shape of the upper surface of this second blank corresponds to the shape of the top surface of the convex mold, and the shape of the lower surface of the second blank corresponds to the shape of the bottom surface of the concave mold.

[0016] The outer peripheral edge and the inner peripheral edge of the bottom surface of the recess of the concave mold may be circular when viewed from the pressing direction, thereby making it possible to make the distribution of stress and deformation of the workpiece during the forming process more uniform in the circumferential direction.

[0017] In the preparation step, the radial length of the gap may be uniform over the entire circumferential direction. This allows the distribution of stress and deformation in the workpiece during the forming process to be closer to uniform over the circumferential direction. Note that the embodiment in which the radial length of the gap is uniform over the entire circumferential direction includes not only a case in which the radial length of the gap is strictly the same over the circumferential direction, but also a case in which there is an error in the radial length of the gap to the extent that it can be considered uniform in the behavior of the workpiece during forming.

[0018] The annular molded product formed in the molding step may have a thickness that varies in the radial direction. The annular molded product having a non-circular cross-sectional shape with a thickness that varies in the radial direction can be further subjected to, for example, drawing to form a tubular molded product having a desired cross-sectional shape.

[0019] The annular molded product formed in the molding step may have a thickness that increases radially inward. When an annular molded product having such a non-circular cross-sectional shape is formed into a tubular molded product by, for example, hole expansion and drawing, the wall thickness of the tubular molded product can be made nearly uniform.

[0020] In the preparation step, the radial length of a gap between the workpiece placed in the recess and the inner circumferential surface of the recess may be shorter than or equal to the radial length of a gap between the workpiece and the outer circumferential surface of the recess, thereby efficiently reducing the press load during forming.

[0021] In the preparation step, the workpiece may be placed in contact with either the inner circumferential surface or the outer circumferential surface of the recess, which makes it easier to position the workpiece in the recess mold.

[0022] In the forming step, the workpiece may be in contact with at least one of the inner circumferential surface and the outer circumferential surface of the recess when the convex mold is at bottom dead center with respect to the concave mold. By performing press forming in this manner, it is possible to further reduce the difference between the shape of the annular molded product and the target shape.

[0023] For example, in the forming process, the workpiece may be formed so that it contacts the outer peripheral surface of the recess but not the inner peripheral surface when the convex mold is at bottom dead center relative to the concave mold. Alternatively, the workpiece may be formed so that it contacts the inner peripheral surface of the recess but not the outer peripheral surface when the convex mold is at bottom dead center. In these cases, the press load can be efficiently reduced and the formed product can approach the target shape. Also, in the forming process, the workpiece may be formed so that it contacts both the outer peripheral surface and the inner peripheral surface of the recess when the convex mold is at bottom dead center relative to the concave mold. In this case, the press load can be reduced while further reducing the difference between the shape of the formed product and the target shape. In particular, the shape accuracy of the annular formed product after press forming is high not only on the axial end faces but also on the inner and outer peripheral surfaces.

[0024] In other words, in the forming process, when the convex mold is at bottom dead center with respect to the concave mold, there may be a gap between the workpiece and at least one of the inner circumferential surface or the outer circumferential surface of the concave portion. This allows for further reduction in press load. For example, when shape accuracy is required for the axial end surface of an annular molded product after press forming, but not for the inner circumferential surface or the outer circumferential surface, the required shape accuracy can be achieved without excessive press load.

[0025] The method for manufacturing the molded product may further include a hole expansion and drawing process in which the annular molded product formed in the molding process is formed into a tubular shape by hole expansion and drawing. In the hole expansion and drawing process, the outer diameter surface of the annular molded product becomes one axial end face of the tubular molded product by the hole expansion and drawing process, and the inner diameter surface of the annular molded product becomes the other axial end face of the tubular molded product by the hole expansion and drawing process.

[0026] In this case, the cross-sectional shape of the annular molded product formed in the molding process is reflected in the cross-sectional shape of the wall of the tubular molded product formed in the subsequent hole expansion and drawing process. Therefore, for example, a tubular molded product having a desired cross-sectional shape, such as a tubular molded product having an irregular cross-sectional shape, can be manufactured by the pressing process. Therefore, in the manufacture of molded products, the machining process can be omitted or reduced.

[0027] In this specification, "annular molded product" and "tubular molded product" are different terms used to distinguish between a molded product before hole expansion and drawing and a molded product after hole expansion and drawing. The difference between the terms "annular molded product" and "tubular molded product" is only whether the molded product is before hole expansion and drawing or after hole expansion and drawing. Other than this, it does not mean a difference in the characteristics of the molded product.

[0028] In the above manufacturing method, in the forming step, an outer diameter thickness (t0_out) of the outer diameter surface of the annular formed product before the hole expansion and drawing may be formed so as to have a first correlation with a target value of the wall thickness (a_up) of the one end face of the tubular formed product. Furthermore, an inner diameter thickness (t0_in) of the inner diameter surface of the annular formed product before the hole expansion and drawing may be set so as to have a second correlation with a target value of the wall thickness (a_down) of the other end face of the tubular formed product.

[0029] This allows the outer diameter plate thickness (t0_out) and inner diameter plate thickness (t0_in) of the annular formed product to be set independently based on the correlation with the corresponding target wall thickness. This allows the plate thickness to be set taking into account the difference in stress and strain transformation between the inner diameter side and the outer diameter side during hole expansion and drawing. Therefore, the wall thickness of the tubular formed product after hole expansion and drawing can be made closer to the target. As a result, tubular formed products of the target shape can be manufactured with high precision.

[0030] The first correlation and the second correlation may be different from each other. Both the first correlation and the second correlation may be a relationship in which the wall thickness of the tubular molded product after the hole expansion and drawing is expressed as a linear function of the plate thickness of the annular molded product before the hole expansion and drawing. In this case, the slope of the linear function representing the first correlation may be larger than the slope of the linear function representing the second correlation.

[0031] The annular molded product formed in the molding process may be plate-shaped having an upper surface, a lower surface, a hole penetrating from the upper surface to the lower surface, and a depression formed in one of the upper and lower surfaces. In this case, in the hole expansion and drawing process, one of the upper and lower surfaces of the annular molded product before the hole expansion and drawing process may be formed into the inner surface of the tubular molded product by the hole expansion and drawing process, and the other of the upper and lower surfaces of the annular molded product before the hole expansion and drawing process may be formed into the outer surface of the tubular molded product by the hole expansion and drawing process. Furthermore, the depression of the annular molded product before the hole expansion and drawing process may be formed into a recess on the inner surface of the tubular molded product by the hole expansion and drawing process.

[0032] In the hole expansion and drawing process described above, the inventors have discovered that there is a correlation between the position of the depression in the annular molded product before the hole expansion and drawing process and the position of the recess in the tubular molded product after the process. Therefore, in the above method, it is possible to control the position of the recess in the tubular molded product after the process by the position of the recess in the annular molded product before the hole expansion and drawing process. As a result, a tubular molded product of the desired shape can be manufactured with high accuracy.

[0033] A transfer press apparatus according to an embodiment of the present invention includes a bolster, a slide movable relative to the bolster in the pressing direction, and a plurality of dies. Each of the plurality of dies includes a lower die attached to the bolster and an upper die attached to the slide. A first die, one of the plurality of dies, is a coining die for coining and includes a concave die serving as the lower die and a convex die serving as the upper die. The concave die has a recess including an annular bottom surface, an outer circumferential surface extending from an outer circumferential end of the bottom surface, and an inner circumferential surface extending from an inner circumferential end of the bottom surface. The convex die includes a top surface facing the bottom surface of the recess in the pressing direction and protruding into the recess of the concave die.

[0034] In the above configuration, one of the multiple dies is a coining die, which includes a concave die with an annular recess and a convex portion. Therefore, by placing a workpiece formed of an annular metal in the concave portion and pressing it with the convex portion, an annular molded product having a shape corresponding to the coining die can be obtained. Furthermore, the workpiece can be placed in the concave portion with a gap between the inner circumferential surface of the concave portion and the workpiece or between the outer circumferential surface of the concave portion and the workpiece. This allows the workpiece to be molded into a desired shape while reducing the press load compared to when there is no gap. In other words, the press load required when coining the cross-sectional shape of the annular workpiece into a desired shape can be reduced. Furthermore, the difference between the coining load applied by the coining die and the press-molding load applied by other dies can be reduced. In other words, uneven press loads (unbalanced loads) among the multiple dies can be alleviated. This simplifies the configuration of the transfer press device.

[0035] The coining die may be located upstream of the multiple dies. In this case, an annular molded product coined by the coining die can be molded with another die to obtain a molded product of a desired shape. This makes it possible to manufacture, for example, a tubular molded product having a non-circular cross section by a press process. Furthermore, in a configuration in which a coining die that applies a relatively large load is located upstream, unbalanced loads can be alleviated.

[0036] In a transfer press, a workpiece (material to be processed) is transported sequentially through a plurality of dies and pressed. The plurality of dies are arranged in a line in the transport direction of the workpiece. In a configuration in which a coining die is arranged upstream of the plurality of dies, the coining die is arranged upstream of the central die in the transport direction among the plurality of dies. The transfer press may also have a transport mechanism that transports the workpiece sequentially through the plurality of dies.

[0037] Hereinafter, a method for manufacturing a molded product according to an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and the description of those parts will not be repeated. Furthermore, the dimensions of the components in each drawing do not faithfully represent the actual dimensions of the components and the dimensional ratios of each component.

[0038] (Embodiment) FIG. 1 is a diagram illustrating a method for manufacturing a molded product in this embodiment. The manufacturing method in this embodiment includes a preparation step, a molding step, and a hole expansion and drawing step. The upper part of FIG. 1 illustrates the preparation step, the middle part illustrates the molding step, and the lower part illustrates the hole expansion and drawing step. In the example shown in FIG. 1, in the preparation step, an annular workpiece 99 is placed in the recess 11a of the concave mold 11. In the molding step, the workpiece 99 placed in the recess 11a of the concave mold 11 is pressed by the convex mold 12 and molded into an annular molded product 100. In the hole expansion and drawing step, the annular molded product 100 is molded by hole expansion and drawing to form a tubular molded product 110. Each step will be described in detail below.

[0039] [Preparation process] The upper part of Figure 1 shows a perspective view of an annular workpiece 99 and a cross-sectional view of the workpiece 99 placed in a mold. This cross-sectional view shows a cross-section on a plane that passes through the center of the hole 1 in the workpiece 99 and is parallel to the plate thickness direction (axial direction). This is also the case for the cross-sectional views in the middle and bottom parts of Figure 1. In Figure 1, the dashed dotted line C1 indicates the central axes of the workpiece 99 and the recess 11a of the recessed mold 11. In Figure 1, the workpiece 99 and the recess 11a are arranged coaxially.

[0040] In the example shown in FIG. 1 , the annular workpiece 99 is plate-shaped and has an upper surface 2, a lower surface 3, and a hole 1 that penetrates from the upper surface 2 to the lower surface 3. When viewed from above (viewed in the thickness direction), the workpiece 99 has a shape that has the hole 1 in the center and spreads radially from the hole 1. The workpiece 99 can also be said to have a doughnut shape. In this example, the workpiece 99 is a circular plate with the hole 1 in the center. The maximum radial dimension of the workpiece 99 is greater than the thickness.

[0041] The concave mold 11 in which the workpiece 99 is placed has a recess 11a. The recess 11a includes an annular bottom surface 11b, an outer peripheral surface 11g extending from the outer peripheral end of the bottom surface 11b, and an inner peripheral surface 11n extending from the inner peripheral end of the bottom surface 11b. The outer peripheral surface 11g extends in the pressing direction from the outer peripheral end of the bottom surface 11b. The inner peripheral surface 11n extends in the pressing direction from the inner peripheral end of the bottom surface 11b. The outer peripheral surface 11g and the inner peripheral surface 11n face each other in the radial direction. The outer peripheral surface 11g and the inner peripheral surface 11n are inclined with respect to the bottom surface 11b. In the example of FIG. 1, the outer peripheral surface 11g and the inner peripheral surface 11n are perpendicular to the bottom surface 11b. Note that at least one of the outer peripheral surface 11g or the inner peripheral surface 11n does not have to be perpendicular to the bottom surface 11b. 1, the outer and inner edges of the bottom surface 11b of the recess 11a of the recessed mold 11 are concentric circles when viewed from the pressing direction. The pressing direction is the direction in which the protruding mold 12 moves relative to the recessed mold 11 during press molding.

[0042] The shape of the recess 11a of the concave mold 11 corresponds to the target shape of the annular molded product. In the example shown in FIG. 1, the bottom surface 11b of the concave mold 11 is flat, but the bottom surface 11b may have irregularities or a slope. In the example shown in FIG. 1, the inner peripheral surface 11n and the outer peripheral surface 11g of the concave mold 11 are perpendicular to the bottom surface 11b, but at least one of the inner peripheral surface 11n or the outer peripheral surface 11g does not have to be perpendicular to the bottom surface 11b. For example, at least one of the inner peripheral surface 11n or the outer peripheral surface 11g may be inclined with respect to a plane perpendicular to the bottom surface 11b, or may have irregularities on its surface.

[0043] In the preparation step, the workpiece 99 is placed in the recess 11a with a gap between the inner circumferential surface 11n of the recess 11a and the workpiece 99 or between the outer circumferential surface 11g of the recess 11a and the workpiece 99. By providing such a gap, the workpiece 99 is more likely to undergo plastic flow when pressed by the convex mold 12. The range of plastic flow is also limited mainly by the outer circumferential surface 11g and inner circumferential surface 11n of the recess 11a. This makes it possible to form the annular workpiece 99 into a desired shape while reducing the press load when the annular workpiece 99 is placed between the concave mold 11a and the convex mold 12 and press-molded.

[0044] 1, the inner and outer peripheral surfaces of the workpiece 99 and the inner and outer peripheral surfaces 11n and 11g of the recess 11a are all concentric circles when viewed from the axial direction (pressing direction). In this case, the radial length of the gap between the workpiece 99 placed in the recess 11a and the recess 11a is uniform throughout the entire circumferential direction.

[0045] In the example shown in FIG. 1, there are gaps both between the inner peripheral surface 11n of the recess 11a and the workpiece 99, and between the outer peripheral surface 11g of the recess 11a and the workpiece 99. This increases the degree of plastic flow of the workpiece during molding. This increases the effect of reducing the press load. Alternatively, the workpiece 99 may be placed in contact with either the inner peripheral surface 11n or the outer peripheral surface 11g of the recess 11a. This also achieves the effect of reducing the press load. This also makes it easier to position the workpiece 99 in the recess 11a.

[0046] As an example, the radial length sn of the gap between the workpiece 99 placed in the recess 11a and the inner peripheral surface 11n of the recess 11a may be shorter than or equal to the radial length sg of the gap between the workpiece 99 and the outer peripheral surface 11g of the recess 11a (sn≦sg). This allows for efficient reduction of the press load during forming. This effect is particularly pronounced when forming a workpiece 99 with a uniform radial thickness into a shape in which the thickness increases radially inward, as shown in FIG. 1.

[0047] The workpiece center diameter is calculated by (r1 + r2) / 2, where r1 is the radius of the inner periphery of the workpiece 99 and r2 is the radius of the outer periphery. The die center diameter is calculated by (R1 + R2) / 2, where R1 is the radius of the inner periphery of the recess 11a of the concave mold 11 and R2 is the radius of the outer periphery of the recess 11a of the concave mold 11. As an example, the workpiece 99 may be placed in the recess 11a so that the value obtained by dividing the workpiece center diameter by the die center diameter, i.e., the value (r1 + r2) / (R1 + R2) (center diameter ratio), is 1.1 or less. This makes it easier to achieve the effect of reducing the press load. Furthermore, the workpiece 99 may be placed in the recess 11a so that the value (r1 + r2) / (R1 + R2) is less than 1.0. This further enhances the effect of reducing the press load.

[0048] [Molding process] The middle part of Figure 1 shows a perspective view of an annular molded product 100 molded in the molding process and a cross-sectional view of the mold and molded product 100 at the bottom dead center of the molding process. In the example shown in Figure 1, the convex mold 12 includes a top surface 12a that faces the bottom surface 11b of the recess 11a of the recessed mold 11 in the pressing direction. The convex mold 12 has a shape that protrudes toward the recess 11a of the recessed mold 11. The convex mold 12 has a shape that allows it to be inserted into the recess 11a of the recessed mold 11. When viewed from the pressing direction, the top surface 12a of the convex mold 12 overlaps the area of ​​the recess 11a. When viewed from the pressing direction, the top surface 12a of the convex mold 12 is annular and has a shape that corresponds to the recess 11a. At the bottom dead center, the convex mold 12 is inserted partway into the recess 11a of the recessed mold 11.

[0049] In the forming process, the convex mold 12 presses the workpiece 99 placed in the concave mold 11 in the press direction. As a result, the workpiece 99 is formed into a shape corresponding to the top surface 12a of the convex mold 12 and the bottom surface 11b of the concave mold 11, becoming an annular molded product 100. At the bottom dead center, the workpiece 99 is compressed between the top surface 12a of the convex mold 12 and the bottom surface 11b of the concave mold 11 while in contact with these top surface 12a and bottom surface 11b. As a result, the shape of the workpiece 99 is frozen between the convex mold 12 and the concave mold 11. The shape of the workpiece 99 when compressed by the top surface 12a and bottom surface 11b at the bottom dead center becomes the shape of the molded product 100. The molded product 100 maintains that shape after being released from the convex mold 12 and the concave mold 11.

[0050] As described above, in the forming process of this example, a coining process is performed in which the workpiece is compressed with a die at the bottom dead center to form a shape that corresponds to the die. Coining is a compression process in which high pressure is applied to the workpiece. Therefore, in coining, a large press load is applied to the workpiece, which can increase the shape precision of the formed product.

[0051] The convex mold 12 and the concave mold 11 are dies attached to a press device. The press device may be configured, for example, to fix the concave mold 11 and move the convex mold 12 in the pressing direction. Alternatively, the press device may be configured to fix the convex mold 12 and move the concave mold 11, or to move both the convex mold 12 and the concave mold 11.

[0052] In the example shown in FIG. 1 , at bottom dead center, the molded product 100 (workpiece) is in contact with both the inner circumferential surface 11n and the outer circumferential surface 11g of the recess 11a. In this case, the inner circumferential surface 11n and the outer circumferential surface 11g restrict radial deformation of the workpiece during the molding process. This prevents the molded product 100 from significantly deviating from the target shape. Alternatively, the molded product 100 (workpiece) may be molded so that it is in contact with at least one of the inner circumferential surface 11n or the outer circumferential surface 11g of the recess 11a at bottom dead center. If the workpiece 99 comes into contact with the inner circumferential surface 11n or the outer circumferential surface 11g before the convex mold 12 reaches bottom dead center, it is believed that the normal stress in the workpiece 99 increases after contact. This increase in normal stress increases the required press load. Therefore, from the perspective of reducing the press load, it is preferable to shorten the time the workpiece 99 is in contact with the inner circumferential surface 11n or the outer circumferential surface 11g during molding. From this perspective, the molded product 100 (workpiece) may be molded so that it does not come into contact with at least one of the inner circumferential surface 11n or the outer circumferential surface 11g at the bottom dead center. The position of the molded product 100 relative to the recess 11a at the bottom dead center can be adjusted by the shape of the recess 11a and the arrangement of the workpiece 99 in the recess 11a before molding. For example, if high shape accuracy is required for the molded product 100 in the plate thickness direction (axial direction) but high shape accuracy in the radial direction is not required, adjustment may be made so that a gap is generated between the molded product 100 (workpiece) and at least one of the inner circumferential surface 11n or the outer circumferential surface 11g at the bottom dead center. This prevents the press load from becoming excessive relative to the required shape accuracy.

[0053] In the example shown in Fig. 1, an annular molded product 100 formed in a molding process has a shape in which the thickness varies in the radial direction. In this example, the radial thickness distribution of the molded product 100 can be adjusted by coining. As an example, as shown in Fig. 1, the molded product 100 formed in the molding process can be shaped so that the thickness increases radially toward the inner periphery. This allows the wall thicknesses at both axial ends of a tubular molded product 110 obtained by hole-expanding and drawing the annular molded product 100, as described below, to be made nearly uniform.

[0054] The outer side of the annular molded product 100 is the outer diameter surface 4, and the inner side of the molded product 100, i.e., the inner surface of the hole 1, is the inner diameter surface 5. In the example of Figure 1, the axial dimension of the outer diameter surface 4 (outer diameter plate thickness) is smaller than the axial dimension of the inner diameter surface 5 (inner diameter plate thickness). The plate thickness of the annular molded product 100 is thickest at the inner diameter surface 5 and becomes thinner as it moves from the inner diameter surface 5 to the outer diameter surface 4. The upper surface 2 is inclined with respect to the plate thickness direction. The lower surface 3 is perpendicular to the plate thickness direction.

[0055] [Hole expansion and drawing process] The lower part of Fig. 1 shows a perspective view and a cross-sectional view of a tubular molded product 110 formed in the hole expansion and drawing process. In the hole expansion and drawing process, the annular molded product 100 formed in the forming process is formed into a tubular shape by hole expansion and drawing to form the tubular molded product 110. In the example of Fig. 1, the axial dimension of the tubular molded product 110 is greater than the wall thickness.

[0056] After the hole expansion and drawing process, the outer diameter surface 4 of the annular molded product 100 becomes one end surface 6 of the tubular molded product 110. After the hole expansion and drawing process, the inner diameter surface 5 of the annular molded product 100 becomes the other end surface 7 of the tubular molded product 110. After the hole expansion and drawing process, the upper surface 2 of the annular molded product 100 becomes the inner peripheral surface 8 of the tubular molded product 110. After the hole expansion and drawing process, the lower surface 3 of the annular molded product 100 becomes the outer peripheral surface 9 of the tubular molded product 110.

[0057] The hole expansion drawing process includes a step of placing an annular molded product 100 between a punch and a die, and pressing the punch and die by bringing them relatively close to each other. The punch has a convex portion with a diameter larger than the diameter of the hole 1. The die has a concave portion with a diameter smaller than the outer diameter of the annular molded product 100. The convex portion of the punch presses the upper surface 2 of the annular molded product 100, and the concave portion of the die presses the lower surface 3 of the annular molded product 100. As the hole 1 is expanded by the punch, the annular molded product 100 is caught between the punch and the die and deformed.

[0058] The forming process by hole expansion and drawing may include, for example, an intermediate forming process in which the tapered surfaces of a punch and die having a predetermined taper are pressed against the upper surface 2 and the lower surface 3 of the annular formed product 100 to perform hole expansion and drawing, thereby obtaining a truncated conical intermediate formed product, and a process in which the intermediate formed product is pressed by inserting a punch from the large diameter side of the intermediate formed product using a punch and die having a smaller taper angle than the punch and die used in the intermediate forming process, with the small diameter side of the intermediate formed product positioned on the die side, thereby performing further hole expansion and drawing. In the intermediate forming process, drawing may be performed multiple times by changing the angle between the tapered surfaces of the punch and die and the processing direction. Specific examples of hole expansion and drawing will be described later.

[0059] FIG. 2 is a cross-sectional view illustrating the dimensional relationship between an annular molded product 100 before hole expansion and drawing and a tubular molded product 110 after hole expansion and drawing. The thickness t0_out of the outer diameter portion of the annular molded product 100 is smaller (thinner) than the thickness t0_in of the inner diameter portion. In the annular molded product 100, the outer diameter thickness t0_out at the outer diameter surface 4 is set based on a first correlation with a target value of the wall thickness a_up at one end portion including one end face 6 of the tubular molded product 110. The inner diameter thickness t0_in at the inner diameter surface 5 of the annular molded product 100 is set based on a second correlation with a target value of the wall thickness a_down at the other end portion including the other end face 7 of the tubular molded product 110.

[0060] The first correlation and the second correlation are different from each other. The first correlation can be, for example, a relationship in which the wall thickness a_up at one end of the tubular molded product 110 is expressed by a linear function of the thickness t0_out of the outer diameter portion. The second correlation can be, for example, a relationship in which the wall thickness a_down at the other end of the tubular molded product 110 is expressed by a linear function of the thickness t0_in of the outer diameter portion. In this case, for example, the slope K1 of the linear function representing the first correlation is larger than the slope K2 of the linear function representing the second correlation. These correlations were discovered by the inventors. As an example, the slope K1 may be 1.19≦K1≦1.55, and the slope K2 may be 0.63≦K2≦0.83.

[0061] <Example of hole expansion and drawing process using hole expansion and drawing processing> 3A and 3B are diagrams illustrating an example of a hole expansion and drawing process using hole expansion and drawing. As shown in Fig. 3A, in the first hole expansion and drawing process in the intermediate forming process, a punch 10A1 and a die 20A1 having a predetermined taper are used to press the entire surfaces of an annular metal disk molded product 100 to perform hole expansion and drawing, thereby obtaining an intermediate molded product 100A1.

[0062] The angles formed by the tapered surfaces of the punch 10A1 and the die 20A1 with respect to the machining direction are θp1 and θd1, respectively. For example, θp1=θd1.

[0063] As shown in Figure 3(b), in the second hole expansion and drawing process in the intermediate molding process, the entire both sides of the intermediate molded product 100A1 are pressed with a punch 10A2 and a die 20A2 mold with a predetermined taper to perform hole expansion and drawing, thereby obtaining the intermediate molded product 100A2.

[0064] The tapered surfaces of the punch 10A2 and the die 20A2 form angles θp2 and θd2 with the machining direction, respectively. As an example, θp2 = θd2 can be set. The angles θp2 and θd2 formed with the machining direction of the tapered surfaces of the punch 10A2 and the die 20A2 used in the second hole expansion drawing are set to be smaller than the angles θp1 and θd1 ​​formed with the machining direction of the tapered surfaces of the punch 10A1 and the die 20A1 used in the first hole expansion drawing.

[0065] As shown in FIG. 3(c), in the final forming step, the intermediate molded product 100A2 is further subjected to hole expansion and drawing using a punch 10B and a die 20B that can form a cylindrical rotating part of a desired shape, thereby obtaining a cylindrical rotating part 100B. In this embodiment, to obtain a tubular molded product having an inner diameter D1' and an outer diameter D2', the punch 10B has a cylindrical shape with an outer diameter D1', and the die 20B has an annular shape with an inner diameter D2'. Note that the cylindrical rotating part 100B is an example of a tubular molded product.

[0066] The example of the forming process by hole expansion and drawing is not limited to the example shown in Fig. 3. In Fig. 3, hole expansion and drawing is performed multiple times using multiple sets of different dies and punches. The hole expansion and drawing may be performed once, or four or more times.

[0067] In this embodiment, an annular workpiece 99 is coined to form an annular molded product 100, and the annular molded product 100 is then formed into a tubular molded product 110 by hole expansion and drawing. The coining process allows the shape of the annular molded product 100 to be controlled to values ​​based on the target dimensions of the tubular molded product 110. This eliminates or reduces the need for further cutting the tubular molded product 110 to form the desired shape after the hole expansion and drawing process. Furthermore, in the molding process of the annular molded product 100, the workpiece 99, which is placed with a gap in the recess 11a of the recessed mold 11, is pressed with the convex mold 12 to perform compression molding. This reduces the press load while forming the molded product 100 with high precision. This allows the annular molded product 100 and the tubular molded product 110 to be manufactured using processes suitable for mass production.

[0068] The annular molded product 100 and the tubular molded product 110 that can be manufactured by the manufacturing method of this embodiment are not limited to the above examples. By adjusting the shapes of the concave mold 11 and the convex mold 12 to correspond to the target shape of the annular molded product 100, it is possible to manufacture annular molded products 100 of various shapes. Furthermore, by adjusting the shapes of the concave mold 11, the convex mold 12, and the mold used in the hole expansion and drawing process to correspond to the target shape of the tubular molded product 110, it is possible to manufacture a variety of tubular molded products 110.

[0069] FIG. 4 is a cross-sectional view showing modified examples of an annular molded product 100 formed in a molding process and a tubular molded product 110 formed in a hole expanding and drawing process. In the example shown in FIG. 4, a depression 2a is formed in the upper surface 2 of the annular molded product 100. The depression 2a is a groove that surrounds the entire periphery of the hole 1. The depression 2a is a groove with a curved cross section. The cross-sectional shape of the depression 2a may or may not be a circular arc. When viewed from above, the depression 2a is formed concentrically with the hole 1. For example, in the molding process, the annular molded product 100 shown in FIG. 4 can be manufactured by using a convex mold 12 whose top surface 12a is shaped in a convex shape corresponding to the depression 2a.

[0070] A tubular molded product 110 shown in FIG. 4 is obtained by subjecting an annular molded product 100 to hole expansion and drawing. The depression 2a on the upper surface 2 of the annular molded product 100 becomes a depression 8a on the inner circumferential surface 8 of the tubular molded product 110 after hole expansion and drawing. The depression 8a on the inner circumferential surface 8 of the tubular molded product 110 is formed over the entire circumference of the inner circumferential surface 8 in a portion of the axial direction. The cross section of the depression 8a is curved. The cross section of the depression 8a may or may not be a circular arc. The shape of the depression 8a can be adjusted by adjusting the shape of the depression 2a on the upper surface 2 of the annular molded product 100.

[0071] The distance a0_out from the deepest point C0 of the recess 2a on the upper surface 2 of the annular molded product 100 before the hole expansion and drawing process to the outer diameter surface 4 is smaller than the distance a0_in from the deepest point C0 of the recess 2a to the inner diameter surface 5. The position of the recess 2a is set to have a third correlation with the target position of the recess 8a of the tubular molded product 110 after the hole expansion and drawing process. Specifically, the ratio a0_out / a0_in of the distance a0_in from the deepest point C0 of the recess of the annular molded product 100 before the process to the inner diameter surface 5 and the distance a0_out from the deepest point C0 of the recess 2a to the outer diameter surface 4 of the annular molded product 100 is set to have a third correlation with the target value of the ratio h_up / h_down of the distance h_up from the deepest point C of the recess 8a on the inner circumferential surface 8 of the tubular molded product to one end surface 6 and the distance h_down from the deepest point of the recess to the other end surface 7. The third correlation can be, for example, a relationship in which the ratio h_up / h_down of the recesses after processing is expressed by a linear function of the ratio a0_out / a0_in of the recesses before the hole expansion and drawing processing.

[0072] The third correlation is expressed, for example, by the following formula. The relational expression between the ratio a0_out / a0_in of the recess before the hole expansion and drawing process and the ratio h_up / h_down of the recess after the process is expressed by, for example, the following expression. h_up / h_down=1.17×a0_out / a0_in + B (B is a constant) In this case, the slope is expected to vary within the range of 1.17±0.12. In other words, the correlation range can be 1.05×a0_out / a0_in + B to 1.29×a0_out / a0_in + B. The ratio a0_out / a0_in of the recess before the hole expansion and drawing process can be determined by substituting the target value of the ratio h_up / h_down of the recess after the process into h_up / h_down in the following formula. (h_up / h_down)= K3×(a0_out / a0_in)+ B 1.05≦K3≦1.29

[0073] Here, B can be a value according to the conditions. The value of B can be determined, for example, by conducting the following preliminary analysis or preliminary experiment. An annular molded product before processing, having given values ​​of a0_out_0 and a0_in_0, is subjected to the hole-expanding drawing process of this embodiment, and the values ​​of h_up_0 and h_down_0 of the resulting tubular molded product are measured or analyzed. B can be determined by substituting these values ​​into B = (h_up_0 / h_down_0) - K3 × (a0_out_0 / a0_in_0).

[0074] As described above, according to this embodiment, by using the third correlation, it is possible to calculate the position of the depression in the annular molded product that is required to form the desired recess 8a in the tubular molded product 110 after processing. This makes it possible to manufacture a tubular molded product with a recess formed in a desired position by hole expansion and drawing. Therefore, the process of cutting the tubular molded product to form the recess after processing can be omitted or reduced.

[0075] In the example shown in Fig. 4, the wall thickness a_up at one end of the tubular molded product 110 is increased, and the wall thickness a_down at the other end is decreased. In a cross section of the tubular molded product 110 passing through the axis C2, the outer peripheral surface 9 and the inner peripheral surface 8 form a non-parallel trapezoid. This is because, as shown in Fig. 4, the outer diameter thickness t0_out and the inner diameter thickness t0_in of the annular molded product 100 are equal. Therefore, by combining this with the embodiment shown in Fig. 2 and adjusting the outer diameter thickness t0_out and the inner diameter thickness t0_in of the annular molded product 100, the wall thickness of the tubular molded product 110 can be made closer to uniform.

[0076] That is, the first correlation may be used to set the thickness t0_out of the outer diameter portion of the annular molded product 100, the second correlation may be used to set the thickness t0_in of the inner diameter portion of the annular molded product 100, and further the third correlation may be used to set the ratio a0_out / a0_in indicating the position of the depression in the annular molded product 100. This makes it possible to bring the wall thickness a_up at one end of the tubular molded product 110, the wall thickness a_down at the other end, and the ratio h_up_0 / h_down_0 indicating the position of the depression 8a closer to target values.

[0077] In this case, for example, as shown in FIG. 5, in the annular molded product 100, the plate thickness t0_out of the outer diameter portion is smaller than the plate thickness t0_in of the inner diameter portion (t0_out < t0_in), and the ratio a0_out / a0_in of the recesses can be set to be smaller than 1 ((a0_out / a0_in) < 1). Thereby, the plate thickness of the tubular molded product 110 becomes closer to being uniform in the axial direction, and the deviation of the deepest point of the concave portion 8a from the center in the axial direction can be reduced. The tubular molded product 110 shown in FIG. 5 has a substantially uniform wall thickness in the axial direction, and the wall thickness a_up at one end and the wall thickness a_down at the other end are substantially the same.

[0078] As the material of the workpiece 99, for example, steel, aluminum, copper, nickel, titanium, an alloy containing at least one of these, or other metals can be used. Further, as the material of the workpiece 99 other than metal, for example, a resin such as CFRTP (Carbon Fiber Reinforced Thermo Plastics) may be used.

[0079] In the above embodiment, the workpiece 99 and the molded product 100 are annular, and the tubular molded product 110 is cylindrical. The workpiece 99 and the molded product 100 have a plate thickness smaller than the dimension in the radial direction. The shapes of the workpiece 99, the annular molded product 100, and the tubular molded product 110 are not limited to these. In these, the shapes of the outer edge and the edge of the hole in plan view may be a flattened circle or an ellipse in addition to the case of a perfect circle. Further, as an example, the shapes of the outer edge and the edge of the hole viewed from the axial direction of the workpiece 99, the annular molded product 100, and the tubular molded product 110 may be polygonal. In this case, the tubular molded product has a tube with a polygonal cross-section in a plane perpendicular to the axis. The number of corners of the polygon may be increased to make the plan view shapes of the outer edge and the edge of the hole of the workpiece 99, the annular molded product 100, and the tubular molded product 110 closer to a circular shape.

[0080] [Transfer Press Device] FIG. 6 is a diagram showing an example of the configuration of a transfer press used to manufacture a molded product in this embodiment. The transfer press shown in FIG. 6 includes a frame 50, a bolster 30, a slide 40, multiple dies 20a-20e, a drive unit 60, and a transport mechanism 70. The slide 40 is movable relative to the bolster 30 in the pressing direction. The bolster 30 and the slide 40 are attached to the frame 50. The drive unit 60 reciprocates the slide 40 in the pressing direction relative to the bolster 30. The drive unit 60 includes a power source such as a hydraulic cylinder or a motor. The drive unit 60 is fixed to the frame 50. The transport mechanism 70 transports the workpiece to the pressing positions of the multiple dies 20a-20e in sequence. The transfer press is equipped with multiple independent dies 20a-20e. The multiple dies 20a-20e are arranged side by side along the direction in which the workpiece is transported by the transport mechanism 70.

[0081] Each of the multiple molds 20a to 20e has a lower mold attached to a bolster 30 and an upper mold attached to a slide 40. The multiple molds 20a, 20b, 20c, 20d, and 20e are arranged in this order from the upstream side in the conveying direction.

[0082] The die 20a located at the most upstream position is a die for punching. An annular workpiece 99 is punched out from a flat blank 98 by pressing using the die 20a.

[0083] The second die 20b from the upstream is a coining die. The lower die 22b of the die 20b is the concave die 11 shown in FIG.

[0084] The third die 20c from the upstream is a die used to obtain an intermediate formed product 100A1 by the first hole expansion and drawing in the intermediate forming step shown in Fig. 3(a). The lower die 22c of the die 20c is the die 20A1 in Fig. 3(a), and the upper die 21c of the die 20c is the punch 10A1 in Fig. 3(a).

[0085] The fourth die 20d from the upstream is a die used to obtain an intermediate formed product 100A2 by the second hole expansion and drawing process in the intermediate forming step shown in Fig. 3(b). The lower die 22d of the die 20d is the die 20A2 in Fig. 3(b), and the upper die 21d of the die 20d is the punch 10A2 in Fig. 3(b).

[0086] The fifth die 20e from the upstream is a die used to obtain the cylindrical rotary part 100B, i.e., the tubular formed product 110, by hole expansion and drawing in the final forming step shown in Fig. 3(c). The lower die 22e of the die 20e is the die 20B in Fig. 3(c), and the upper die 21e of the die 20e is the punch 10B in Fig. 3(c).

[0087] One die 20b of the multiple dies 20a to 20e of the transfer press device is a coining die for coining. Multiple dies 20c to 20e for hole expansion and drawing are arranged downstream of the coining die. In this way, both a coining die and a drawing die are provided in one press device. The press load for coining is larger than the press load for drawing. In the manufacturing method of this embodiment, it is possible to obtain an annular molded product 100 with high shape accuracy by coining while reducing the press load in the coining process. Therefore, the unbalanced load of the transfer press device can be alleviated.

[0088] In the example shown in FIG. 6, among the multiple dies 20a to 20e, die 20b, which is a coining die, is located upstream in the conveying direction. In this example, the coining die, which has a larger press load than the other dies, is located upstream and off-center in the conveying direction. In this embodiment, the press load imposed by the coining die can be reduced, so even if the coining die is located off-center in the conveying direction, the uneven load can be alleviated. Therefore, the configuration for equalizing the loads of the multiple dies 20a to 20e can be omitted or reduced. As a result, the configuration of the transfer press device can be simplified.

[0089] This embodiment can be suitably applied to, for example, the production of annular or tubular molded products such as bearing raceways, although this is not limited thereto. For example, the production method or transfer press apparatus of this embodiment can be applied to the production of annular or tubular molded products such as the outer races of rolling bearings and bushings of plain bearings. Alternatively, this embodiment can be applied to the production of annular and tubular molded products with irregular cross-sectional shapes (such as recesses, protrusions, or tapers) used in automobile bushings and oil pump parts.

[0090] <Test Results> Fig. 7 is a diagram showing the arrangement of a workpiece 99 relative to the dies (concave die 11 and convex die 12) in the test. Each of the workpieces under conditions A to F shown in Fig. 7 was subjected to coining using the concave die 11 and the convex die 12, with the arrangement shown in Fig. 7 as the initial position.

[0091] Under condition A, the initial position is the position where the outer peripheral surface of the workpiece contacts the outer peripheral surface 11g of the concave recess 11a. The central diameter of the workpiece is located radially outward of the center of gravity of the annular molded product after coining. The position of the center of gravity of the annular molded product after coining was determined by calculation. Under condition C, the initial position is the position where the center of gravity of the annular molded product after coining coincides with the central diameter of the workpiece. Under condition B, the initial position is the position where the central diameter of the workpiece lies between the positions of the central diameter under condition A and the central diameter under condition C, and is radially outward of the center of gravity of the annular molded product after coining. Under condition E, the initial position is the position where the inner peripheral surface of the workpiece contacts the inner peripheral surface of the concave recess, and the central diameter of the workpiece is radially inward of the center of gravity of the annular molded product after coining. Condition D sets the initial position as a position where the center diameter of the workpiece lies between the center diameter positions of conditions C and E and is located on the inner diameter side of the center of gravity of the annular molded product after coining. Condition F sets the initial position as a position where the inner peripheral surface 11n of the recess 11a of the concave mold 11 contacts the inner peripheral surface of the workpiece and the outer peripheral surface 11g of the recess 11a contacts the outer peripheral surface of the workpiece.

[0092] For each of conditions A to F, the annular molded product obtained by coining was formed into a tubular molded product by hole expansion and drawing. The press load during coining using a concave die 11 and a convex die 12 was measured. The load was measured at a position 0.125 mm before the bottom dead center of the press stroke. The sizes of the processed products under conditions A to F were adjusted so that the volume was constant.

[0093] The dimensions and median diameter ratios of the workpieces under test conditions A to F are as shown in Table 1 below. [Table 1]

[0094] The prototype conditions for the annular molded products used in the test are as shown in Table 2 below. As shown in Table 2 below, tests were conducted on annular molded products made using each of Material 1, Material 2, and Material 3. For Material 1, an actual molded product was made. For Materials 2 and 3, FEM analysis was performed. Material 1 was a hot-dip galvanized steel sheet with a base material of ordinary cold-rolled steel sheet. The mechanical properties of Material 1 were a yield point of 330 MPa, a tensile strength of 425 MPa, and a total elongation of 33%. The thickness of Material 1 was 6 mm. The mechanical properties of Materials 2 and 3 were the same as those of Material 1. The thickness of Material 2 was 9 mm. The thickness of Material 3 was 3 mm. The mechanical properties and thickness of Materials 2 and 3 were set as parameters for the FEM analysis. [Table 2]

[0095] The conditions for the hole expansion and drawing process are as follows: Drawing die diameter Φ42mm, lubricant: same as above, press machine: 200 ton mechanical press, press speed: same as above

[0096] The values ​​of the median diameter and median diameter ratio of the recesses of the workpiece and the mold (concave mold) were calculated as follows. Workpiece center diameter = (workpiece inner diameter + workpiece outer diameter) / 2=(r1+r2) / 2 Mold center diameter = (recess inner diameter + recess outer diameter) / 2 = (R1 + R2) / 2 Center diameter ratio = Center diameter of workpiece / Center diameter of recess = ((r1+r2) / 2) / ((R1+R2) / 2) =(r1+r2) / (R1+R2)

[0097] Fig. 8 is a graph showing the press load in the coining process using the concave die 11 and the convex die 12 for each of the conditions A to F shown in Fig. 7. Fig. 9 is a graph showing the relationship between the median diameter ratio and the press load in this test and the FEM analysis.

[0098] The results shown in FIG. 8 reveal that the press load is lower when press-forming is performed in an initial state where there is a gap between the workpiece and at least one of the outer peripheral surface 11g and inner peripheral surface 11n of the recess 11a of the mold 11 (condition F), compared to the press load when press-forming is performed in an initial state where the workpiece is constrained by both the outer peripheral surface 11g and inner peripheral surface 11n of the recess 11a (conditions A to E). Furthermore, the load tends to be lower when the workpiece 99 is closer to the inner peripheral side in the initial position. In particular, the load decreases sharply at condition C. This indicates that the load can be efficiently reduced by positioning the central diameter of the workpiece in the initial position at the same position as or closer to the inner diameter of the center of gravity of the annular molded product after coining.

[0099] The results shown in Figure 9 show that the load can be reduced efficiently when the median diameter ratio is 1.1 or less. In particular, the degree of load reduction is greater when the median diameter ratio is less than 1.0. [Explanation of symbols]

[0100] 11 Concave 11a Recess 11b Bottom surface of recess 11g Outer surface of recess 11n Inner surface of recess 12 Convex 12a Top surface 99 Workpiece 100 Annular molding 110 Tubular moldings

Claims

1. a preparation step of placing a workpiece formed of an annular metal in a recess of a concave mold having a recess including an annular bottom surface, an outer peripheral surface extending from an outer peripheral end of the bottom surface, and an inner peripheral surface extending from an inner peripheral end of the bottom surface; a molding step in which the workpiece placed in the recess is pressed in the press direction by a convex mold that includes a top surface facing the bottom surface of the recess in the press direction and that protrudes into the recess of the concave mold, thereby molding the workpiece into a shape corresponding to the top surface of the convex mold and the bottom surface of the concave mold to form an annular molded product, In the preparation step, the workpiece is placed in the recess of the concave mold in a state where there is a gap between the inner peripheral surface of the recess of the concave mold and the workpiece or between the outer peripheral surface of the recess of the concave mold and the workpiece, and the workpiece is placed so that the central diameter of the workpiece is at the same position as or closer to the inner diameter than the center of gravity of the annular molded product after coining; A method for manufacturing a molded product, wherein the central diameter of the workpiece is a value calculated from the radius r1 of the inner peripheral edge and the radius r2 of the outer peripheral edge of the workpiece by (r1 + r2) / 2.

2. A method for producing the molded article according to claim 1, A method for manufacturing a molded product, wherein the outer peripheral edge and the inner peripheral edge of the bottom surface of the recess of the concave mold are circular when viewed from the pressing direction.

3. A method for producing the molded product according to claim 2, A method for manufacturing a molded product, wherein in the preparation step, the radial length of the gap is uniform throughout the entire circumferential direction.

4. A method for producing a molded article according to any one of claims 1 to 3, The method for manufacturing a molded product, wherein the annular molded product formed in the molding step has a thickness that varies in the radial direction.

5. A method for producing a molded product according to claim 4, The method for manufacturing a molded product, wherein the annular molded product formed in the molding step has a thickness that increases radially inward.

6. A method for producing a molded article according to any one of claims 1 to 5, A method for manufacturing a molded product, wherein in the preparation process, the radial length of a gap between the workpiece placed in the recess and the inner surface of the recess is shorter than or equal to the radial length of a gap between the workpiece and the outer surface of the recess.

7. A method for producing a molded article according to any one of claims 1 to 6, A method for manufacturing a molded product, wherein in the preparation step, the workpiece is placed in contact with either the inner surface or the outer surface of the recess.

8. A method for producing a molded article according to any one of claims 1 to 7, A method for manufacturing a molded product, wherein in the molding process, the workpiece contacts at least one of the inner surface or the outer surface of the recess when the convex mold is at bottom dead center with respect to the concave mold.

9. A method for producing a molded article according to any one of claims 1 to 8, The annular molded product formed in the molding step is further formed into a tubular molded product by hole expansion and drawing. In the hole expansion and drawing process, the outer diameter surface of the annular molded product becomes one end surface in the axial direction of the tubular molded product by the hole expansion and drawing process, and the inner diameter surface of the annular molded product becomes the other end surface in the axial direction of the tubular molded product by the hole expansion and drawing process. A method for manufacturing a molded product.

10. Bolster and a slide that is movable relative to the bolster in a pressing direction; a plurality of molds; each of the plurality of molds has a lower mold attached to the bolster and an upper mold attached to the slide; One of the plurality of dies is a coining die for coining processing, and has a concave die which is the lower die and a convex die which is the upper die, the concave mold has a recess including an annular bottom surface, an outer circumferential surface extending from an outer circumferential end of the bottom surface, and an inner circumferential surface extending from an inner circumferential end of the bottom surface, the convex mold includes a top surface that faces the bottom surface of the concave portion in the pressing direction and protrudes relative to the concave portion of the concave mold, The plurality of dies include a drawing die that performs hole expansion and drawing on the annular molded product formed by the coining die.

11. 11. The transfer press apparatus according to claim 10, The coining die is disposed upstream of the plurality of dies.

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