JP7620195B2 - Manufacturing method for punched molded products - Google Patents

Description

The present invention relates to a method for manufacturing punch-molded products.

Stamped steel sheets may be used for various sliding parts such as pole parking lots for automobiles and slider parts for industrial machinery. In stamped products used as sliding parts, the end faces (punched surfaces) may become the sliding parts, so it is preferable that the end faces are also smooth. Since the shear surface is smoother than the fracture surface, if the end faces of the stamped product have a high shear surface ratio, machining after stamping can be simplified or omitted.

JP 2015-14062 A discloses an opposed die shearing device and opposed die shearing method that can improve the yield of high-precision products by minimizing the occurrence of scratches and sagging. Specifically, this opposed die shearing method includes a first step of moving a second die relative to the first die so that the second die approaches the first die, and cutting the workpiece with the first and second dies while leaving a portion of the workpiece, and a second step of moving a first punch and a second punch relative to the first and second dies after the first step, and cutting the uncut portion of the workpiece to separate the product from the workpiece.

JP 2015-14062 A

Even if the opposed die shear processing method described in JP 2015-14062 A is used, depending on the shape of the molded product, it may not be possible to obtain an end face with a high shear surface ratio.

The objective of the present invention is to provide a method for manufacturing punch-molded products that can produce punch-molded products with end faces having a high shear surface ratio.

A method for manufacturing a punch-molded product according to one embodiment of the present invention is a method for manufacturing a punch-molded product, which uses a processing device equipped with a first die and a second die to manufacture a molded product from a blank material, and each of the first die and the second die has a hole having the same contour as the contour of the molded product and a protrusion formed along the contour of the hole, and the first die and the second die are arranged so that the protrusion of the first die and the protrusion of the second die face each other across the blank material, and the first die and the second die are brought close to each other to form grooves in the blank material. The groove machining process forms a groove portion, the protrusion portion having a flat surface perpendicular to the direction of movement of the first die and the second die, the distance between the outline of the hole and the outer edge of the flat surface on a plane in which the hole and the flat surface are viewed perpendicular to the flat surface is defined as the cutting edge length a, the ratio t0/a of the thickness t0 of the blank material to the cutting edge length a is 2.5 or less, the total amount of movement of the first die and the second die in the groove machining process is defined as the stroke S, and the ratio S/t0 of the stroke S to the thickness t0 of the blank material is 0.4 or more.

The present invention provides punched molded products with end faces that have a high shear surface ratio.

FIG. 1 is a cross-sectional view showing a schematic configuration and operation of a processing device. FIG. 2 is a cross-sectional view showing a schematic configuration and operation of the processing device. FIG. 3 is a cross-sectional view showing a schematic configuration and operation of the processing device. FIG. 4 is an enlarged cross-sectional view showing the vicinity of the protrusion of the first die. FIG. 5 is a plan view of the first die as viewed in a direction perpendicular to the flat surface. FIG. 6 is a diagram showing the shape and stress distribution of the blank piece at the start of the groove machining process and at the end of the groove machining process. FIG. 7 is a schematic diagram showing a method for measuring the blank R. FIG. 8 is a diagram showing the shape of the blank piece at each stage of the groove machining process. FIG. 9 is a diagram showing the shape and stress distribution of the blank at various times during the separation process. FIG. 10 is a diagram showing the shape and stress distribution of the blank material at each point in the separation process when a model is used in which the radius of curvature R of the groove corners is 1.0 mm, 2.0 mm, and 3.0 mm. FIG. 11 is a photograph of the cut surface. FIG. 12 is a graph showing the ratio of sagging surfaces, shear surfaces, and fracture surfaces in the punched surface. FIG. 13 is a cross-sectional view that typically illustrates a sagging surface, a shear surface, and a fracture surface. FIG. 14 is a diagram showing the shape and stress distribution of a blank piece at the start of the groove machining process and at the end of the groove machining process, in the case of a material different from that in FIG. FIG. 15 shows the shape and stress distribution of the blank at various times during the separation process for a material different from that shown in FIG. FIG. 16 is a diagram showing the shape and stress distribution of the blank piece at the completion of the groove machining process when the cutting edge length a is changed. FIG. 17 is a graph showing the relationship between t0/a and blank R. FIG. 18 is a graph showing the relationship between t0/a and the shear surface ratio. FIG. 19 is a graph showing the relationship between the ratio S/t0 of the stroke S to the thickness t0 of the blank and the blank R. FIG. 20 is a graph showing the relationship between S/t0 and the shear surface ratio.

The following describes in detail an embodiment of the present invention with reference to the drawings. The same or corresponding parts in the drawings are given the same reference numerals and their description will not be repeated. The dimensional ratios between the components shown in each drawing do not necessarily represent the actual dimensional ratios.

[Overall configuration]
An overview of a method for manufacturing a punch-formed product according to an embodiment of the present invention will be described with reference to Figures 1 to 3. Figures 1 to 3 are cross-sectional views that typically show the configuration and operation of a processing device 1 used in this embodiment. In the manufacturing method according to this embodiment, a molded product 15 (Figure 3) is manufactured from a blank 10 using the processing device 1.

The blank material 10 is a metal plate having a predetermined thickness t0. The planar shape of the blank material 10 may be circular, rectangular, or any other shape.

The thickness t0 of the blank material 10 is, for example, 0.1 to 50 mm, but is not limited to this. The method for manufacturing a punch-molded product according to this embodiment is particularly effective when the thickness t0 of the blank material 10 is thick. The lower limit of the thickness t0 is preferably 5 mm, more preferably 8 mm, and even more preferably 10 mm.

The processing device 1 includes a first die 20, a second die 30, a first punch 40, and a second punch 50.

The first die 20 has a hole 20a having the same contour as the contour of the molded product 15 (Figure 3) and a protrusion 21 formed along the contour of the hole 20a.

The second die 30, like the first die 20, has a hole 30a having the same contour as the contour of the molded product 15 (Figure 3), and a protrusion 31 formed along the contour of the hole 30a.

The contour shape of the molded product 15 (Figure 3), i.e., the contour shape of holes 20a and 30a, may be circular, rectangular, or any other shape.

In this embodiment, protrusions 21 and 31 have the same shape and dimensions. Details of protrusions 21 and 31 will be described later.

The first punch 40 is positioned inside the hole 20a of the first die 20. The first punch 40 has a flat surface 41 that contacts the blank 10. It is preferable that the planar shape of the flat surface 41 is the same as the planar shape of the molded product 15.

The second punch 50 is positioned inside the hole 30a of the second die 30. Like the first punch 40, the second punch 50 has a flat surface 51 that contacts the blank 10. It is preferable that the planar shape of the flat surface 51 is the same as the planar shape of the molded product 15.

The manufacturing method for punched molded products according to this embodiment includes a groove processing step and a separation step, which are described below.

First, as shown in FIG. 1, the first die 20 and the second die 30 are arranged so that the protrusions 21 of the first die 20 and the protrusions 31 of the second die 30 face each other across the blank material 10. From this state, as shown in FIG. 2, the first die 20 and the second die 30 are brought close to each other to form grooves 11 in the blank material 10 (groove processing process).

This groove machining process can be performed, for example, by moving the first die 20 and the second die 30 toward the blank material 10 while the blank material 10 is clamped between the first punch 40 and the second punch 50. At this time, both the first die 20 and the second die 30 may be moved toward the blank material 10, or one may be fixed and the other moved toward the blank material 10. Hereinafter, the total movement amount of the first die 20 and the second die 30 in the groove machining process is referred to as the stroke S. A groove portion 11 having a thickness d = t0 - S is formed in the blank material 10 by the groove machining process. The preferred range of the stroke S will be described later.

Next, as shown in FIG. 3, while the blank 10 is sandwiched between the first die 20 and the second die 30, the first punch 40 and the second punch 50 are moved to separate the molded product 15 from the blank 10 (separation process).

Through the above steps, a molded product 15 is produced from the blank material 10.

[Configuration of protrusions 21 and 31]
Next, a detailed description will be given of the configurations of the protrusions 21 and 31. As described above, in this embodiment, the protrusions 21 and 31 have the same shape and dimensions. Therefore, the protrusions 21 will be described below.

Figure 4 is an enlarged cross-sectional view showing the vicinity of the protrusion 21 of the first die 20. The protrusion 21 has a flat surface 211 that is perpendicular to the direction of movement (z direction) of the first die 20 and the second die 30 during the groove machining process.

Here, the distance between the contour of the hole 20a and the outer edge of the flat surface 211 on a plane in which the hole 20a and the flat surface 211 are viewed from a direction perpendicular to the flat surface 211 is defined as the cutting edge length a. In other words, the cutting edge length a is the distance between the contour of the hole 20a and the outer edge of the flat surface 211 when the hole 20a and the flat surface 211 are projected onto a plane (xy plane) parallel to the flat surface 211.

Figure 5 is a plan view (xy plan view) of the first die 20 viewed from a direction perpendicular to the flat surface 211 (z direction). Figure 5 illustrates, as an example, a case in which the contour C1 of the hole 20a is circular. On the plane of Figure 5, the distance between the contour C1 of the hole 20a and the outer edge C2 of the flat surface 211 is the cutting edge length a. More specifically, the cutting edge length a is the distance between an arbitrary point P1 on the contour C1 and the point P2 on the outer edge C2 that is closest to point P1. In other words, the cutting edge length a is the shortest distance between the contour C1 and the outer edge C2.

In FIG. 5, the hole 20a has a circular contour, but the hole 20a may have any shape. Even if the hole 20a has any shape, the cutting edge length a can be calculated in the same manner as above.

In the manufacturing method of punch-formed products according to this embodiment, the ratio t0/a of the thickness t0 of the blank material 10 to the blade bottom length a is set to 2.5 or less. By setting t0/a to 2.5 or less, it is possible to obtain a molded product 15 having an end face (punched surface) with a high shear surface ratio.

[Regarding t0/a]
Hereinafter, the reason why the shear surface ratio can be increased by setting t0/a to 2.5 or less will be explained together with the analysis results by the finite element method (FEM) and the experimental results.

FEM analysis was performed simulating the situation of manufacturing a disk-shaped molded product 15 with a diameter of 45.0 mm from a disk-shaped blank material 10 with a diameter of 90.2 mm in accordance with the manufacturing method of the punch-molded product according to this embodiment. The solver used was MSC.MARC. A two-dimensional axisymmetric model was used, with a mesh size of 0.5 mm x 0.5 mm and a minimum mesh size after remeshing of 0.02 mm x 0.02 mm. The friction coefficient was 0.1 (Coulomb friction). A stress-strain curve equivalent to carbon steel material S45C for machine structures was used for the analysis.

The cutting edge length a was fixed at 3.8 mm, and the thickness t0 of the blank 10 was changed to 11 mm, 6 mm, and 3 mm, and the shape and stress distribution after processing were analyzed. The radius of curvature of the portion adjacent to the hole 20a of the flat surface 211 (portion 211a in Figure 4) was set to 1.0 mm. The dimensions of the second die 30 were the same as those of the first die 20.

In the groove processing step, the first die 20 and the second die 30 were each moved symmetrically toward the blank material 10 while a constant load of 12.3 kN was applied to the blank material 10 from the flat surface 41 of the first punch 40 and the flat surface 51 of the second punch 50. The stroke S was set to 2/3 of the thickness t0 of the blank material 10 (S/t0=2/3). That is, when the thickness t0 was 11 mm, the first die 20 and the second die 30 were each moved 3.67 mm, for a total of 7.33 mm. Similarly, when the thickness t0 was 6 mm, the first die 20 and the second die 30 were moved 4 mm in total, and when the thickness t0 was 3 mm, the first die 20 and the second die 30 were moved 2 mm in total.

In the separation process, the first die 20 and the second die 30 were fixed, and the first punch 40 was moved while applying a constant load of 12.3 kN to the blank 10 from the flat surface 51 of the second punch 50. A clearance of 0.02 mm was set between the first punch 40 and the first die 20, and between the second punch 50 and the second die 30.

Figure 6 shows the shape and stress distribution of the blank material 10 at the start of the groove machining process and at the end of the groove machining process. The "blank R" described below was calculated from the shape of the blank material 10 at the end of the groove machining process.

Figure 7 is a schematic diagram showing a method for measuring blank R. In a cross section perpendicular to the direction in which the groove extends, a straight line L1 passing through two points at the bottom of the groove and a straight line L2 passing through two points at the vertical wall of the groove are drawn. The straight lines L1 and L2 are superimposed on the cross-sectional profile, and the points where the cross-sectional profile branches off from the straight lines L1 and L2 (R-stop points) are designated as points A and B, respectively. The normal line of the straight line L1 at point A is designated as line L1', the normal line of the straight line L2 at point B is designated as line L2', and the angle between the straight lines L1' and L2' is designated as θ. The length of the arc AB (the arc AB of a circle centered at the intersection of the straight lines L1' and L2' and passing through points A and B) is designated as ΔS, and ΔS/θ is designated as blank R.

Here, the blank R is determined from the shape of the blank material 10 obtained by FEM analysis, but it is also possible to measure the contour shape of an actual sample using a shape measuring instrument (for example, Keyence Corporation's One-Shot 3D Shape Measuring Instrument VR-3000) and measure the blank R based on the measured contour shape.

As shown in Figure 6, the blank R was 1.24 mm, 2.38 mm, and 2.65 mm when the thickness t0 was 11 mm, 6 mm, and 3 mm, respectively, and there was a tendency for the blank R to increase as t0/a became smaller.

The reason why the blank R increases as t0/a decreases is presumed to be as follows. Figure 8 is a diagram showing the shape of the blank 10 at each point in the groove processing process. When the thickness t0 is 11 mm, as shown by the arrow in Figure 8, the change in the gauge length directly below the protrusion 21 (the outermost layer of the groove 11) is small. This is thought to be due to the influence of friction between the protrusion 21 and the blank 10. In contrast, when the thickness t0 is 3 mm, the change in the gauge length is large even directly below the protrusion 21 (the outermost layer of the groove 11). From this, it is thought that the thinner the t0/a, the less the influence of friction is, and the greater the plastic flow is, which results in a larger blank R.

Figure 9 shows the shape and stress distribution of the blank 10 at each point in the separation process. As shown in Figure 9, when the thickness t0 is 11 mm, stress concentration occurs at the white circle in the figure when the first punch 40 is moved to 1/4 of the bottom dead center. When the thickness t0 is 6 mm, the stress concentration is small, and when the thickness t0 is 3 mm, no stress concentration occurs.

The presence or absence of stress concentration during the separation process is believed to be influenced by the shape of the groove 11 formed in the groove processing process. In order to verify the relationship between the shape of the groove 11 and stress concentration, FEM analysis was performed using a model in which the thickness t0 was fixed at 11 mm and the radius of curvature R of the corners of the groove 11 were set to 1.0 mm, 2.0 mm, and 3.0 mm.

Figure 10 shows the shape and stress distribution of the blank 10 at each point in the separation process when using a model in which the radius of curvature R of the corners of the groove 11 is 1.0 mm, 2.0 mm, and 3.0 mm. When the radius of curvature R is 1.0 mm, stress concentration occurs at the white circle in the figure when the first punch 40 has been moved 2.0 mm. When the radius of curvature R is 2.0 mm and 3.0 mm, no stress concentration occurs when the first punch 40 has been moved 2.0 mm. In addition, there was a tendency for the larger the radius of curvature R, the later the timing at which the stress concentration points above and below the groove 11 connect.

From these results, the mechanism by which the shear surface ratio can be increased by decreasing t0/a can be inferred as follows. As can be seen from the results of Figures 6 and 8, the smaller t0/a is, the greater the movement of material directly below the protrusion 21, promoting deformation due to compressive load. As a result, the radius of curvature of the corners of the grooves 11 of the blank 10 becomes larger. As can be seen from the results of Figures 9 and 10, the greater the radius of curvature of the corners of the grooves 11, the more stress concentration during the separation process is alleviated. In punch forming, generally, the stress concentration points on the top and bottom surfaces of the plate expand and connect to form a fracture surface. It is believed that by alleviating stress concentration during the separation process, the shear state can be continued for a longer period, allowing the shear surface ratio to be increased.

Next, punching was actually performed under the same conditions as those set in the FEM analysis described above. Figure 11 shows a photograph of the punched surface (cut end surface). Figure 12 is a graph showing the ratio of sagging surfaces, shear surfaces, and fracture surfaces on the punched surface.

Figure 13 is a cross-sectional view showing a sagging surface, a shear surface, and a fracture surface. A sagging surface is a surface that occurs at the connection between the surface of the blank material 10 and the cut surface. A shear surface is a surface with a metallic luster that occurs due to shear deformation. A fracture surface is an inconsistent surface that is mainly caused by void destruction.

As shown in Figures 11 and 12, when thickness t0 was 11 mm, fracture surfaces occurred on the punched surface. In contrast, when thickness t0 was 3 mm, no fracture surfaces occurred on the punched surface, and a punched surface with a high shear surface ratio was obtained.

The FEM analysis results and the experimental results are summarized in Table 1. In the "Judgment" column, "X" means that the shear surface ratio was less than 70%, "△" means that the shear surface ratio was 70% or more but less than 80%, and "○" means that the shear surface ratio was 80% or more.

[Influence of materials]
Next, the material was changed from S45C to high carbon chromium bearing steel SUJ2, and the same FEM analysis and experiment as above were carried out.

Figure 14 shows the shape and stress distribution of the blank material 10 at the start of the groove processing process and at the end of the groove processing process when the stress-strain curve is equivalent to SUJ2. The blank R was 1.21 mm, 2.55 mm, and 2.81 mm when the thickness t0 was 11 mm, 6 mm, and 3 mm, respectively, and as with S45C, there was a tendency for the blank R to increase as t0/a became smaller.

Figure 15 shows the shape and stress distribution of the blank 10 at each point in the separation process when the stress-strain curve is equivalent to SUJ2. When the thickness t0 is 11 mm, stress concentration occurs at the white circle in the figure when the first punch 40 is moved to 1/4 of the bottom dead center. When the thickness t0 is 6 mm, the stress concentration is small, and when the thickness t0 is 3 mm, no stress concentration occurs.

As can be seen above, even when the material was changed to SUJ2, the same trends as in the case of S45C were confirmed.

[About the blade bottom length a]
The thickness t0 of the blank 10 was fixed at 11 mm, and the cutting edge length a was changed, and the same FEM analysis and experiment as above were carried out. A stress-strain curve equivalent to S45C was used for the analysis.

Figure 16 shows the shape and stress distribution of the blank 10 at the completion of the groove machining process when the cutting edge length a is changed. The blank R was 1.24 mm, 2.26 mm, and 3.17 mm when the cutting edge length a was 3.8 mm, 7.6 mm, and 11.4 mm, respectively, and as with the case of changing t0, there was a tendency for the blank R to increase as t0/a became smaller.

Figure 17 is a graph showing the relationship between t0/a and blank R obtained from the results of Figure 6 (S45C, constant t0), Figure 14 (SUJ2, constant t0), and Figure 16 (S45C, constant a). Figure 18 is a graph showing the relationship between t0/a and shear surface ratio.

As shown in Figures 17 and 18, a strong correlation was confirmed between t0/a and blank R, and between t0/a and the shear surface ratio. Figure 18 shows that by setting t0/a to 2.5 or less, the shear surface ratio can be increased to 70% or more.

t0/a is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.0 or less. By making t0/a 1.5 or less, the shear surface ratio can be made 80% or more.

If a is too large, the area of the molded product 15 that can be removed from the blank 10 will be small. The lower limit of t0/a is preferably 0.2, and more preferably 0.5.

[About Stroke S]
The same FEM analysis and experiment as above were carried out by changing the stroke S. A stress-strain curve equivalent to S45C was used for the analysis.

Figure 19 is a graph showing the relationship between the ratio S/t0 of the stroke S to the thickness t0 of the blank material 10 and the blank R. Figure 20 is a graph showing the relationship between S/t0 and the shear surface ratio.

From Figure 20, it can be seen that if S/t0 is less than 0.4, it is difficult to increase the shear surface ratio. Therefore, S/t0 should be 0.4 or more. S/t0 is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.65 or more.

Although the embodiments of the present invention have been described above, the above-mentioned embodiments are merely examples for implementing the present invention. Therefore, the present invention is not limited to the above-mentioned embodiments, and it is possible to implement the above-mentioned embodiments by appropriately modifying them as long as they do not deviate from the spirit of the present invention.

Reference Signs List 1 Processing device 10 Blank 11 Groove 15 Molded product 20 First die 20a Hole 21 Protrusion 211 Flat surface 30 Second die 30a Hole 31 Protrusion 40 First punch 41 Flat surface 50 Second punch 51 Flat surface

Claims (1)

A method for producing a stamped molded product, comprising the steps of: producing a molded product from a metal blank using a processing device having a first die and a second die,
Each of the first die and the second die has a hole having the same contour as the contour of the molded product and a protrusion formed along the contour of the hole,
a groove processing step of arranging the first die and the second die such that a protrusion of the first die and a protrusion of the second die face each other across the blank material, and bringing the first die and the second die close to each other to form grooves in the blank material;
the protrusion has a flat surface perpendicular to a moving direction of the first die and the second die,
a distance between the contour of the hole and the outer edge of the flat surface on a plane in which the hole and the flat surface are viewed in a direction perpendicular to the flat surface is defined as a cutting edge length a;
a ratio t0/a of the thickness t0 of the blank material to the blade bottom length a is 2.5 or less;
A total amount of movement of the first die and the second die in the groove machining step is defined as a stroke S,
A method for manufacturing a punch-molded product, wherein a ratio S/t0 of the stroke S to a thickness t0 of the blank material is 0.4 or more.

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