Heat sink and method for manufacturing the same

Abstract

To provide a heat sink having a structure in which pin fin heights can be easily made uniform, and a method for continuously manufacturing the heat sink with pin fin heights uniform over a long period of time.SOLUTION: A heat sink 1 includes a plate-like base portion 2, and a plurality of pin fins 3 provided on one surface of the base portion 2, and each of the plurality of pin fins is spaced apart in a first direction and a second direction perpendicular to the first direction, and in at least one of the first direction and the second direction, the cross-sectional area of the pin fins positioned on the outer side is smaller than the cross-sectional area of the pin fins on the center side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a heat sink and a method for manufacturing a heat sink. [Background technology]

[0002] A known heat sink has a structure including a plate-shaped base and multiple pin fins on one surface of the base. Forging is a known method for manufacturing a heat sink with this structure. One known forging method involves placing a metal material, which is the raw material for the heat sink, on a die with multiple holes and using a punch to press the metal material toward the die, thereby stretching the metal material toward the periphery of the die to form the base and causing the metal material to flow into each of the multiple holes to form the pin fins. Known die forging methods include the burr removal method (also known as the semi-closed method) and the closed method. The burr removal method involves providing a gap between the punch and the die, allowing any metal material that does not flow into the multiple holes to flow out through the gap. The closed method involves sealing the metal material between the punch and the die without providing a gap between them.

[0003] To manufacture a heat sink with uniform pin fin height using a forging method, it is necessary to uniformly fill the multiple holes in the die with metal material. However, with the deburring method, the holes located in the center of the die tend to be more easily filled with metal material, while the holes located on the periphery tend to be less easily filled with metal material. In the forging method, once the holes located in the center of the die are filled with metal material, the punch is no longer able to pressurize the metal material, preventing it from flowing into the holes on the periphery. For this reason, a method for manufacturing a heat sink that can uniformly fill multiple holes in the die with metal material using the deburring method to form pin fins with uniform height has been investigated. As a method for uniformly filling multiple holes in the die using the deburring method, it has been studied to increase the inflow resistance of the metal material in holes located near the center of the die compared to holes located on the outer sides (Patent Document 1). Patent Document 1 describes a method for increasing the inflow resistance of the metal material in holes located near the center of the die by providing irregularities on the surface of the inlet (shoulder) of the metal material in the holes located near the center of the die. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-228618 Summary of the Invention [Problem to be solved by the invention]

[0005] The method of providing irregularities on the surface of the metal inlet of the hole located near the center of the die has the risk that the irregularities will wear away with long-term continuous use of the die, making the metal inlet smoother and reducing the inflow resistance of the metal in the hole, making it difficult to continuously manufacture heat sinks with uniform pin fin heights over a long period of time.

[0006] This invention has been made in consideration of the above-mentioned circumstances, and aims to provide a heat sink with a structure that makes it easy to make the pin fin height uniform, and a method that can continuously manufacture heat sinks with uniform pin fin height over a long period of time. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides the following means.

[0008] (1) A heat sink comprising a plate-shaped base portion and a plurality of pin fins provided on one surface of the base portion, wherein the pin fins are arranged at intervals in a first direction and a second direction perpendicular to the first direction, and wherein the cross-sectional area of ​​the pin fins located on the outer side is smaller than the cross-sectional area of ​​the pin fins located in the center in at least one of the first direction and the second direction.

[0009] (2) The heat sink according to (1) above, wherein the cross-sectional area of ​​the pin fins located on the outer side is smaller than the cross-sectional area of ​​the pin fins located on the central side in both the first direction and the second direction.

[0010] (3) The heat sink according to (1) or (2) above, wherein the pin fins are arranged so that the center-to-center distances between adjacent pin fins are the same.

[0011] (4) The heat sink according to any one of (1) to (3) above, wherein the cross-sectional area of ​​the pin fins decreases stepwise from the pin fins located at the center toward the pin fins located at the outer periphery.

[0012] (5) The heat sink according to any one of (1) to (3) above, wherein the cross-sectional area of ​​the pin fins decreases continuously from the pin fins located at the center toward the pin fins located at the outer periphery.

[0013] (6) The heat sink according to any one of (1) to (5) above, wherein the cross-sectional shapes of the pin fins are similar to each other.

[0014] (7) The heat sink according to any one of (1) to (6) above, wherein each of the pin fins has a circular cross-sectional shape.

[0015] (8) The heat sink according to any one of (1) to (7) above, which is a forged product.

[0016] (9) A method for manufacturing a heat sink, comprising the steps of: preparing a die having a plurality of holes, the holes being spaced apart in a first direction and a second direction perpendicular to the first direction, and in which the cross-sectional area of ​​the holes located on the outer side is smaller than the cross-sectional area of ​​the holes located on the central side in at least one of the first direction and the second direction; and placing a metal material on the central side of the die in the first direction and the second direction, and applying pressure to the metal material toward the die, thereby stretching the metal material in the outer circumferential direction of the die and flowing into the holes. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a heat sink having a structure that makes it easy to make the pin fin height uniform, and a method for continuously manufacturing heat sinks with uniform pin fin height over a long period of time. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a perspective view of a heat sink according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of the heat sink shown in FIG. [Figure 3] 1 is a cross-sectional view of a forging device that can be used in the heat sink manufacturing method of the present embodiment. [Figure 4] FIG. 2 is a conceptual diagram showing the diameter of the hole formed in the die used in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, a heat sink and a method for manufacturing a heat sink according to an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. The drawings used in the following description may show characteristic parts enlarged for the sake of clarity, and the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate changes can be made within the scope of the present invention.

[0020] [heat sink] FIG. 1 is a perspective view of a heat sink according to a first embodiment of the present invention, and FIG. 2 is a plan view of the heat sink shown in FIG. As shown in FIGS. 1 and 2, the heat sink 1 of this embodiment includes a plate-shaped base portion 2 and a plurality of pin fins 3 provided on one surface of the base portion 2.

[0021] The base portion 2 is the part that serves as the foundation for the pin fins 3. There are no particular restrictions on the shape of the base portion 2. The planar shape of the base portion 2 may be, for example, a rounded shape such as a circle or an oval, or a polygonal shape such as a quadrangle (rectangle or square), hexagon, or octagon. The thickness of the base portion 2 may be, for example, in the range of 0.5 mm to 20 mm. The surface of the base portion 2 facing the pin fins 3 is preferably flat. The surface of the base portion 2 opposite the pin fin 3 side may be flat or may have a step. For example, the surface of the base portion 2 opposite the pin fin 3 side may have a convex or concave portion in the center.

[0022] Each of the multiple pin fins 3 extends in a direction (Z direction) perpendicular to the surface of the base portion 2. The multiple pin fins 3 are arranged at intervals in a first direction (X direction, also referred to as row direction) along the surface of the base portion 2 and in a second direction (Y direction, also referred to as column direction) perpendicular to the first direction. In this embodiment, 11 pin fins 3 are arranged in the first direction, and 10 pin fins 3 are arranged in the second direction. The multiple pin fins 3 are arranged in a staggered pattern, alternately offset in the first direction.

[0023] The pin fins 3 arranged in the second direction are arranged so that the cross-sectional area of ​​the pin fins 3 located on the outer side is smaller than the cross-sectional area of ​​the pin fins 3 located in the center. Furthermore, the largest cross-sectional area of ​​the multiple pin fins 3 arranged in the second direction is smaller on the outer side than on the center side in the first direction. That is, in both the first and second directions, the cross-sectional area of ​​the pin fins 3 located on the outer side is smaller than the cross-sectional area of ​​the pin fins 3 located in the center. In this specification, unless otherwise specified, the "cross-section of the pin fin 3" refers to the surface that appears when the pin fin 3 is cut along the surface of the base portion 2, and the "cross-sectional area of ​​the pin fin 3" refers to the area of ​​that cross-section. Among the multiple pin fins 3, the one with the largest cross-sectional area has a cross-sectional area of, for example, 1 mm 2 More than 30mm 2 The ratio of the cross-sectional area of ​​the central pin fin 3 to the outer pin fin 3 adjacent to the inner pin fin 3 may be within the range of 70 / 100 to 90 / 100. The ratio of the diameter of the central pin fin 3 to the outer pin fin 3 adjacent to the inner pin fin 3 may be within the range of 85 / 100 to 95 / 100. For example, if the cross-sectional shape of the pin fins 3 is circular, the pin fin with the largest cross-sectional area may have a diameter within the range of 1 mm to 6 mm. The ratio of the cross-sectional area of ​​the central pin fin 3 to the outer pin fin 3 adjacent to the inner pin fin 3 may be within the range of 85 / 100 to 95 / 100.

[0024] The change in the cross-sectional area of ​​the pin fins 3 may be either stepwise or continuous. "Stepwise" means that the cross-sectional area of ​​the pin fins 3 decreases at intervals of several pin fins 3 (for example, 2 to 3 pin fins) from the pin fin 3 located in the center toward the outside. "Continuously" means that the cross-sectional area of ​​the pin fins 3 decreases one by one from the center toward the outside. The cross-sectional area of ​​the pin fins 3 may have portions that change stepwise and portions that change continuously.

[0025] The multiple pin fins 3 are configured so that one pin fin 3 is adjacent to a maximum of six pin fins 3. Adjacent pin fins 3 are arranged so that the center-to-center distance is the same. The center-to-center distance is the distance between the centers of the cross sections of the pin fins 3. For example, the distance L between pin fin 3a and pin fin 3b is ab and the distance L between pin fin 3a and pin fin 3c ac and the distance L between pin fin 3a and pin fin 3d ad are the same (see FIG. 2). The center-to-center distance is, for example, within a range of 1.2 to 2 times the diameter of the pin fin with the largest cross-sectional area. The center-to-center distance may be, for example, within a range of 1.2 mm to 10 mm.

[0026] It is preferable that the cross-sectional shapes of the multiple pin fins 3 are similar to each other. There are no limitations on the cross-sectional shape of the pin fins 3. The cross-sectional shape of the pin fins 3 may be a rounded shape such as an oval, a polygonal shape such as a quadrangle (rectangle, square, diamond), hexagon, or octagon, or an irregular shape such as a wing shape.

[0027] The pin fins 3 may all have the same height. The height of the pin fins 3 may be, for example, within the range of 3 mm to 10 mm.

[0028] The heat sink 1 can be made of aluminum, aluminum alloy, copper, copper alloy, iron, iron alloy, etc. However, the material of the heat sink 1 is not limited to these metals and alloys, and various metal materials used as heat sink materials can be used.

[0029] [Heat sink manufacturing method] The method for manufacturing a heat sink according to the present embodiment includes a step of preparing a die and a step of pressing a metal material against the die. The pressing step can be performed using a forging device.

[0030] The die prepared in the preparation step has multiple holes. Pin fins of the heat sink are formed by pouring a metal material into the multiple holes. Therefore, the multiple holes in the die are positioned to correspond to the pin fins of the heat sink to be manufactured. That is, the multiple holes in the die are arranged at intervals in a first direction and a second direction perpendicular to the first direction, and are formed so that the cross-sectional area of ​​the holes located on the outer side is smaller than the cross-sectional area of ​​the holes located in the center in at least one of the first and second directions.

[0031] FIG. 3 is a cross-sectional view of a forging device that can be used in the method for manufacturing a heat sink of this embodiment. As shown in Fig. 3, a forging device 10 has a punch 11, a die 12, and a die holder 14. A metal material 100, which is the material of the heat sink, is placed between the punch 11 and the die 12. A gap 21 is provided between the punch 11 and the die 12 to allow unnecessary metal material 100 to flow out, making it possible to use a deburring method.

[0032] The punch 11 presses the metal material 100 toward the die 12. The die 12 is the die prepared in the preparation step. The die 12 has a plurality of holes 13a, 13b, and 13c. The holes 13a, 13b, and 13c are arranged so that the cross-sectional area of ​​the holes located on the outer side is smaller than the cross-sectional area of ​​the holes located in the center. In other words, the cross-sectional area of ​​the hole 13c is the largest, the cross-sectional area of ​​the hole 13b is the next largest, and the cross-sectional area of ​​the hole 13a is the smallest.

[0033] The die holder 14 has an anvil 15, knock pins 18, a knockout plate 19, and an ejector 20. The anvil 15 has a bottom plate 16 and a cylindrical die support 17 arranged around the bottom plate 16. The bottom plate 16 has an opening in its center through which the ejector 20 is inserted. The knock pins 18 are inserted into multiple holes 13a, 13b, and 13c in the die 12. The knock pins 18 are supported by the knockout plate 19. The knockout plate 19 is arranged above the bottom plate 16 and the ejector 20. The ejector 20 is movable in the vertical direction. As the ejector 20 moves in the vertical direction, the knock pins 18 move in the vertical direction via the knockout plate 19.

[0034] The heat sink is manufactured using the forging device 10 as follows. First, the die 12 is placed on the die support 17 of the die holder 14. Next, the knock pins 18 are inserted into the holes 13a, 13b, and 13c of the die 12 and pushed in until they come into contact with the knockout plate 19. Next, the position of the knockout plate 19 is adjusted to set the position of the upper end of the knock pin 18, i.e., the depth of the holes 13a, 13b, and 13c.

[0035] Next, the metallic material 100 is placed at the center of the die 12 (the center in the first and second directions). There are no limitations on the shape of the metallic material 100 as long as it can be accommodated in the cavity of the die 12. The metallic material 100 may be in the shape of a rectangular plate (hexahedron), a circular plate, or an irregular shape. It is preferable that the metallic material 100 has a shape similar to the shape of the cavity of the die 12 to prevent misalignment within the cavity. The metallic material 100 may also be chamfered. The metallic material 100 may be cut from a rolled material by trimming or machining. The metallic material 100 may also be produced by cutting or cutting a flat or round extruded material or a rectangular or round continuously cast rod. The metallic material 100 may be annealed (O-treated) to improve ductility. The metallic material 100 may also be subjected to a lubrication treatment in which a lubricant is applied to the surface.

[0036] Next, a punch 11 is used to pressurize the metal material 100 toward the die 12. The pressure stretches the metal material 100 toward the periphery of the die 12 and causes it to flow into the holes 13a, 13b, and 13c. The forging device 10 is a burr-removing forging device, and has a gap between the punch 11 and the die 12 that allows unwanted metal material to flow outward. In this burr-removing forging device, the pressure causes the metal material 100 to flow more easily toward the periphery of the die 12, making it less likely for the metal material 100 to flow into the holes from the center to the periphery of the die 12. The holes 13a, 13b, and 13c of the die 12 have smaller cross-sectional areas from the inside to the outside, so that the amount of metal material 100 that can be filled therein decreases. Therefore, even though the amount of metal material 100 flowing in decreases from the inside to the outside, the filling rate of the metal material 100 in the holes 13a, 13b, and 13c remains the same. This allows pin fins of uniform height to be formed.

[0037] During forging, the metal material 100 may be heated. For example, if the metal material 100 is aluminum or an aluminum alloy, the metal material 100 may be heated to a temperature of 400° C. or higher and 600° C. or lower. Alternatively, the metal material 100 may be forged (cold forged) without being heated.

[0038] After the heat sink having multiple pin fins has been formed by forging, the ejector 20 is moved upward to move the knock pins 18 upward via the knockout plate 19, thereby pushing the pin fins of the heat sink, thereby removing the heat sink from the die 12.

[0039] The heat sink 1 of this embodiment, configured as described above, is structured such that the cross-sectional areas of the pin fins 3 located on the outer side are smaller than those of the pin fins 3 located in the center in both the first direction (row direction) and the second direction (column direction). In other words, the volume of the pin fins 3 per unit space is smaller on the outer side than on the center. This structure allows for a smaller amount of metal material to be filled into the outer holes of the die during manufacturing of the heat sink 1 of this embodiment. Therefore, even if the metal material easily flows into the holes on the center side of the die but not into the outer holes, the metal material can be filled uniformly throughout the holes, making it easier to achieve uniform pin fin heights. Furthermore, because the volume of the pin fins 3 per unit space is smaller on the outer side than on the center, the heat sink 1 of this embodiment easily dissipates heat from the center of the heat sink 1 to the outside.

[0040] Furthermore, in the heat sink 1 of this embodiment, the multiple pin fins 3 are arranged so that the center-to-center distance between adjacent pin fins 3 is the same, and therefore the cross-sectional area of ​​the pin fins 3 located on the outside is smaller than the cross-sectional area of ​​the pin fins 3 located in the center, resulting in a structure in which the volume of the pin fins 3 per unit space is smaller on the outside than on the center.

[0041] In the heat sink 1 of this embodiment, if the cross-sectional area of ​​the pin fins gradually decreases from the pin fins 3 located in the center to the pin fins 3 located on the outside, there will be multiple pin fins 3 with the same cross-sectional area, and the knock pin 18 can be shared, making it easier to manage the forging device 10.

[0042] In the heat sink 1 of this embodiment, if the cross-sectional area of ​​the pin fins becomes continuously smaller from the pin fins 3 located in the center toward the pin fins 3 located on the outside, heat from the center is more likely to be released more evenly toward the outside.

[0043] If the cross-sectional shapes of the multiple pin fins are similar to each other, when cooling water is flowed between the pin fins 3, the cooling water tends to flow evenly and the flow of the cooling water is easy to adjust, so the pin fins 3 can be cooled more evenly.

[0044] The die 12 used in the heat sink manufacturing method of this embodiment has multiple holes 13a, 13b, and 13c, with the central hole 13c having the largest cross-sectional area and the outer holes 13a having the smallest cross-sectional area, allowing the metal material 100 to be uniformly filled throughout the holes. Therefore, the heat sink manufacturing method of this embodiment makes it possible to manufacture heat sinks with uniform pin fin height. Furthermore, because the die 12 has no irregularities on its surface, it is less likely to wear out over long periods of continuous use. Therefore, the heat sink manufacturing method of this embodiment makes it possible to continuously manufacture heat sinks with uniform pin fin height over a long period of time. In particular, when the cross-sectional shape of the holes in the die 12 is circular (i.e., when the cross-sectional shape of each of the multiple pin fins 3 of the heat sink 1 is circular), local stress concentration is less likely to occur in the holes in the die 12 even when a high load is applied during forging to manufacture the heat sink 1. Therefore, the die 12 is less likely to break over a long period of time, making it possible to continuously manufacture heat sinks with uniform pin fin height over an even longer period of time.

[0045] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as set forth in the claims.

[0046] For example, in the heat sink 1 of this embodiment, the pin fins 3 are arranged in a staggered pattern, alternately offset in the first direction, but the arrangement of the pin fins 3 is not limited to this. For example, the pin fins 3 may be arranged in parallel. Furthermore, in the heat sink 1 of this embodiment, the cross-sectional area of ​​the pin fins 3 located on the outer side is smaller than the cross-sectional area of ​​the pin fins 3 located on the central side in both the first and second directions. However, the cross-sectional area of ​​the pin fins 3 located on the outer side may be smaller than the cross-sectional area of ​​the pin fins 3 located on the central side in at least one of the first and second directions.

[0047] Although the heat sink 1 of this embodiment is a forged product, it may also be a cast product. In the case of a cast product, molten metal material is supplied to the center of the die 12 and is stretched toward the periphery of the die 12 while flowing into the holes 13a, 13b, and 13c. Furthermore, the heat sink 1 of this embodiment may also be produced by cutting or laser processing. [Example]

[0048] [Example 1] A die was prepared with 10 holes in the row direction and 11 holes in the column direction, arranged in a staggered pattern. The cross-sectional shape of the holes was circular. The center-to-center distance between adjacent holes was 3 mm, and the hole depth was 7 mm. Figure 4 shows the diameters of the holes formed in the die. In Figure 4, the numbers in the squares indicate the diameters of the holes (unit: mm). The diameter of the hole located at the 6th column (6th from the left in the X direction) x 5th row (5th from the top in the Y direction) is 2.00 mm. The diameters of the 10 holes in the 6th column are largest at the hole in the 5th row, and decrease successively by 0.9 times as they move outward in the row direction (X direction). The diameters of the 11 holes in the 5th row are largest at the hole in the 6th column, and decrease successively by 0.9 times as they move outward in the column direction (Y direction). Furthermore, the diameters also decrease successively by 0.9 times in the diagonal direction from the hole located at the 6th column x 5th row. In other words, the diameters of the holes formed in the die decrease radially from the hole located at the 6th column x 5th row.

[0049] Using the above die, a heat sink was manufactured by forging. The die was placed on a die holder. Next, a cubic aluminum alloy material (A6063) measuring 40 mm in length, 40 mm in width, and 20 mm in thickness was placed as the metal material at the center of the column and row directions of the die. Next, a punch was used to pressurize the metal material toward the die and forge it. A water-soluble lubricant had been applied to the punch and die in advance. The die temperature was 200°C, and the metal material temperature was 450°C. The punch press speed was 200 mm / sec.

[0050] When the height of the pin fins formed in the central hole reached 7 mm, the forging was stopped and the formed heat sink was removed from the die. After the resulting heat sink was allowed to cool to room temperature, the height of the pin fins on the outermost periphery of the heat sink was measured. The result was that the minimum height of the outermost pin fins was 6.98 mm, which was essentially the same as the height of the central pin fins (7 mm).

[0051] [Comparative Example 1] A die was prepared by forming 10 holes in the row direction and 11 holes in the column direction in an aluminum alloy material, all with a diameter of 1.3 mm. A heat sink was then manufactured by forging in the same manner as in Example 1, except for using this die. The height of the pin fins on the outermost periphery of the heat sink was measured. As a result, the minimum height of the pin fins on the outermost periphery was 3.66 mm, which was approximately 2.34 mm higher than the height of the central pin fin (7 mm). [Explanation of symbols]

[0052] 1 heat sink 2 Base 3, 3a, 3b, 3c pin fins 10 Forging equipment 11 Punch 12 dice 13a, 13b, 13c holes 14 Die holder 15 Anvil 16 Bottom plate 17 Die support 18 Knock pin 19 Knockout Plate 20 Ejector 21 Gap 100 Metal materials

Claims

1. The device includes a plate-shaped base portion and a plurality of pin fins provided on one surface of the base portion, The plurality of pin fins are arranged at intervals in a first direction and a second direction perpendicular to the first direction, In at least one of the first direction and the second direction, the cross-sectional area of ​​the pin fins located on the outer side is smaller than the cross-sectional area of ​​the pin fins located on the central side, Pin fins with smaller cross-sectional areas are arranged radially from the pin fin located in the center. This heat sink is characterized in that a plurality of pin fins having the same cross-sectional area are arranged in a hexagonal shape so as to surround the pin fin located at the center, and a plurality of pin fins having smaller cross-sectional areas are arranged in hexagonal and heptagonal shapes on the outside of the arrangement.

2. The heat sink according to claim 1 , wherein the cross-sectional areas of the pin fins located on the outer side are smaller than the cross-sectional areas of the pin fins located on the central side in both the first direction and the second direction.

3. The heat sink according to claim 1 or 2, wherein the plurality of pin fins are arranged such that the center-to-center distances between adjacent pin fins are the same.

4. 4. The heat sink according to claim 1, wherein the cross-sectional area of ​​the pin fins decreases stepwise from the pin fins located at the center toward the pin fins located at the outer sides.

5. 4. The heat sink according to claim 1, wherein the cross-sectional area of ​​the pin fins decreases continuously from the pin fins located at the center toward the pin fins located at the outer periphery.

6. 6. The heat sink according to claim 1, wherein the cross-sectional shapes of the plurality of pin fins are similar to each other.

7. 7. The heat sink according to claim 1, wherein each of the pin fins has a circular cross section.

8. The heat sink according to any one of claims 1 to 7, which is a forged product.

9. A method for manufacturing a heat sink according to any one of claims 1 to 8, comprising: preparing a die having a plurality of holes, the holes being spaced apart in a first direction and a second direction perpendicular to the first direction, and the cross-sectional area of ​​the holes located on the outer side being smaller than the cross-sectional area of ​​the holes located on the central side in at least one of the first direction and the second direction; A method for manufacturing a heat sink, comprising the steps of: placing a metal material on the center side of the die in the first direction and the second direction; and pressing the metal material toward the die, thereby stretching the metal material in the outer circumferential direction of the die and causing it to flow into the holes.

Images