Hot forged product manufacturing method

Abstract

To provide a hot forged product manufacturing method that can place a forging blank at a correct position on a pressing surface of a lower die.SOLUTION: According to this method, a forging blank is hot forged by using a metal mold for hot forging in which an upper die has a convex pressing surface, a lower die has a concave pressing surface, and the pressing surface of the lower die has a knock-out face at a middle position. When the forging blank is placed on the pressing surface of the lower die, firstly, the forging blank is placed on the knock-out face projected from the pressing surface of the lower die, and thereafter, the knock-out face is lowered together with the forging blank, and is accommodated in the pressing surface of the lower die.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a hot forged product. [Background technology]

[0002] In recent years, the demand for hot die forged products for medium to large aircraft has grown significantly. Among these forged products, for example, the turbine disks and cone shafts of aircraft jet engines are made of nickel alloys or titanium alloys and can be as large as over one meter in diameter. To manufacture these large forged products, the deformation load during hot die forging requires an extremely large pressing force.

[0003] In addition to the above-mentioned aircraft jet engines, such large forged products also include gas turbine disks for power generation. When producing such large forged products from a forged material with high deformation resistance, a hot forging die is used in which the pressing surfaces of the upper and lower dies for shaping the forged material face each other in the pressing direction of the forged material. Examples of such hot forging dies include split dies with a cylindrical die piece attached to the center of the pressing surface (Patent Document 1). Some hot forging dies have this cylindrical die piece functioning as part of the pressing surface during hot forging and as a knockout pin for removing the forged product from the die after hot forging is completed (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2013 / 147154 Brochure [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-91597 Summary of the Invention [Problem to be solved by the invention]

[0005] When a hot forged product has a bowl shape, such as the cone shaft, the hot forging die used to manufacture it also has a pressing surface corresponding to the bowl shape. For example, the upper die has a convex pressing surface, and the lower die has a concave pressing surface. In this case, when placing the forging material on the pressing surface of the lower die, it is not easy to place the forging material in the correct position on the pressing surface of the lower die because the pressing surface of the lower die is recessed. Furthermore, if the forging material falls while being placed on the pressing surface of the lower die, the impact not only causes the above-mentioned positional deviation, but may also damage the knockout surface (knockout mechanism) located in the center of the pressing surface of the lower die. An object of the present invention is to provide a method for manufacturing a hot forged product in which the pressing surface of a lower die is concave and has a knockout surface at its center, and the forging material can be placed in the "correct position." [Means for solving the problem]

[0006] That is, the present invention is a method for manufacturing a hot forged product, in which a convex pressing surface of an upper die and a concave pressing surface of a lower die are opposed to each other in the pressing direction of a forging material, and the forging material is placed on the pressing surface of the lower die and pressed with the pressing surface of the upper die to form the forging material, at the center of the pressing surface of the lower die, to obtain a bowl-shaped forged product, When the forging material is placed on the pressing surface of the lower die, the knockout surface is raised in the pressing direction to protrude from the pressing surface of the lower die, the forging material is placed on the knockout surface protruding from the pressing surface, and when the forging material is placed on the knockout surface, the height of the knockout surface is such that the forging material does not come into contact with the pressing surface of the lower die, This is a method for manufacturing a hot forged product, in which the knockout surface on which the forging material is placed is lowered and placed onto the pressing surface of the lower die, thereby placing the forging material on the pressing surface of the lower die.

[0007] The present invention also provides a method for manufacturing a hot forged product, wherein when the knockout surface on which the forging material is placed is lowered and placed on the pressing surface of the lower die, at least a portion of the knockout surface does not come into contact with the forging material. [Effects of the Invention]

[0008] According to the present invention, when hot forging a forging material, the forging material can be placed in the "correct position" on the pressing surface of the lower die. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional schematic view showing an example of a conventional hot forging die. [Figure 2] 1 is a cross-sectional schematic view showing an example of a hot forging die according to the present invention. [Figure 3] FIG. 1 is a diagram showing an example of a series of steps for producing a hot forged product according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below with reference to the drawings, with each component being explained separately, but the present invention is not limited to the embodiments explained below.

[0011] (1) The present invention "uses a hot forging die in which the convex pressing surface of the upper die and the concave pressing surface of the lower die face each other in the pressing direction of the forging material." An example of such a hot forging die is shown in FIG. 1. FIG. 1 is a schematic cross-sectional view of a hot forging die 0, the peripheral shape of which is circular, taken along a line passing through its center. The upper die 1 has a convex pressing surface 1S, and the lower die 2 has a concave pressing surface 2S, enabling a forging material 3 to be formed into a bowl-shaped forging 4. In other words, the "convex pressing surface" of the upper die and the "concave pressing surface" of the lower die according to the present invention refer to a relationship between their shapes in which the peripheral edges of the pressing surfaces are "raised." Due to this relationship, the peripheral edges of the formed forging also have a raised bowl shape (or a deep dish shape). The shapes of the pressing surfaces of the upper and lower dies other than the peripheral edges are arbitrary. However, the effects of the present invention can be achieved by ensuring that the horizontal position of the pressing surface of the lower die other than the peripheral edge is at least lower than the highest horizontal point of the peripheral edge (which is exclusively the horizontal position of the very edge of the peripheral edge). The term "hot forging" as used herein includes hot or isothermal die forging, press forging, hot die forging, and the like.

[0012] (2) In the present invention, the hot forging die of (1) above has a knockout surface at the center of the pressing surface of the lower die, which is movable in the pressing direction. First, the knockout is a die component that typically waits inside the lower die while the forging material is being formed (during hot forging), and moves in the pressing direction toward the upper die after forming (after hot forging), thereby releasing the hot-forged forged product from the lower die. The tip of this knockout is called the knockout surface, and in the present invention, this knockout surface constitutes part of the pressing surface of the lower die (i.e., the central position). An example of such a lower die is shown in a cross-sectional schematic diagram in Figure 2. The lower die 2 in Figure 2 has a substantially cylindrical knockout 5 installed in its center. After hot forging is completed, the knockout 5 moves upward, releasing the forged product 4 from the lower die 2. During hot forging, the knockout surface 5S functions as part of the pressing surface (design surface) 2S. This allows the desired shape of the forged product to be obtained even at the position where the knockout surface 5S is located on part of the pressing surface 2S.

[0013] As described above, the present invention is a method for manufacturing a hot forged product, in which a forging material placed on the pressing surface of a lower die is pressed against the pressing surface of an upper die using the hot forging dies described above in (1) and (2) to obtain a bowl-shaped forged product. The process of placing the forging material on the pressing surface of the lower die is as follows:

[0014] (3) In the present invention, when placing a forging material on the pressing surface of the lower die, first, "the knockout surface is raised in the pressing direction to protrude from the pressing surface of the lower die, and the forging material is placed on the knockout surface protruding from the pressing surface." The height of the protruding knockout surface at this time is "a height at which the forging material does not come into contact with the pressing surface of the lower die." Conventionally, when placing a forging material on the press surface of the lower die, the material, heated to the hot forging temperature, is grasped by, for example, a lifting jig and transported "directly" to the position of the press surface of the lower die. However, if the press surface of the lower die is concave, the jig may interfere with the periphery of the press surface when the forging material approaches the press surface of the lower die. This may cause the forging material to be separated from the jig before the lower surface of the forging material lands on the press surface of the lower die, resulting in the forging material being placed at a position other than the correct position on the press surface of the lower die. Furthermore, if the forging material is roughly bowl-shaped depending on the shape of the desired forged product, the position that the jig can grasp is limited. If the jig does not grasp the material tightly enough, the forging material may fall during placement, and the impact may damage the knockout of the lower die.

[0015] FIG. 3 illustrates a series of steps in the method for manufacturing a hot forged product of the present invention. In FIG. 3, only one side of the hot forging die 0 is shown, symmetrically about the center line, in a cross-sectional schematic diagram of the hot forging die 0. First, in FIG. 3(A), during the process of placing the forging material 3 on the pressing surface 2S of the lower die 2, when the forging material 3 is transported to the lower die 2, the knockout 5, which is a die component used to release the hot forged product from the lower die, is raised in advance so that the knockout surface 5S, located at the center of the pressing surface 2S of the lower die 2, protrudes upward from the pressing surface 2S of the lower die 2. The transported forging material 3 is then placed on the knockout surface 5S protruding from the pressing surface 2S. By ensuring that the height of the knockout surface 5S is such that the forging material 3 does not come into contact with the pressing surface 2S of the lower die 2, problems such as the jig interfering with the peripheral edge of the pressing surface and the forging material falling can be reduced.

[0016] (4) Next, the present invention "places the forging material on the pressing surface of the lower die by lowering the knockout surface on which the forging material is placed in (3) above and placing it on the pressing surface of the lower die." Then, after placing the transported forging material 3 on the knockout surface 5S that has been raised in advance, as shown in Figure 3(B), the knockout surface 5S is lowered together with the forging material 3 to return it to its original position on the pressing surface 2S of the lower die 2, thereby completing the process of placing the forging material 3 on the pressing surface 2S of the lower die 2. In this way, by picking up the forging material from the pressing surface of the lower die before the bottom surface of the forging material lands on the pressing surface of the lower die, it is possible to place the forging material in the correct position on the pressing surface of the lower die while minimizing damage to the knockout of the lower die. 3(C) and 3(D), the forging material 3 placed on the pressing surface 2S of the lower die 2 is pressed and formed by the pressing surface 1S of the upper die 1, to obtain a bowl-shaped forged product 4. After the hot forging is completed, the knockout 5 is raised as shown in FIG. 3(E), thereby releasing the forged product 4 from the lower die 2. In this way, a forged product 4 having the desired shape can be produced, and the forged product 4 can be smoothly released from the lower die 2.

[0017] (5) In the present invention, preferably, when the knockout surface on which the forging material is placed is lowered and placed on the pressing surface of the lower die in the above (4), "at least a part of the knockout surface does not come into contact with the forging material." While a knockout is essentially a die component used to release a forged product from a lower die after hot forging, in the present invention, the knockout surface also functions as part of the pressing surface of the lower die during hot forging. Furthermore, the knockout according to the present invention also functions as a so-called center pin, which "solely" supports the forging material heated to the hot forging temperature before hot forging, and therefore must maintain strength. However, the knockout surface is exposed to high temperatures more frequently than other parts of the die, and so deformation may occur.

[0018] Therefore, in the present invention, it is preferable to reduce the contact area between the knockout surface and the forging material, from the time when the knockout surface carrying the forging material heated to the hot forging temperature is lowered and placed on the pressing surface of the lower die, until the hot forging starts (i.e., the state shown in FIG. 3(B)), thereby reducing the frequency with which the knockout surface is exposed to high temperatures. This reduces the temperature load on the knockout surface and the possibility of deformation. Furthermore, if the thermal expansion of the knockout can be suppressed, an appropriate clearance can be maintained between the knockout and the lower die, which is also effective in ensuring smooth vertical movement of the knockout.

[0019] The hot forging die used in the present invention can be made of a hot forging die steel or a nickel-based superalloy for all or part of its components, including the knockout. In this case, it is economical to use a cheaper hot forging die steel. The hot work die steel is, for example, specified in JIS-G4404. Its typical composition ranges are, in mass%, C: 0.25 to 0.5%, N: more than 0 to 0.03%, Si: more than 0 to 1.2%, Mn: more than 0 to 0.9%, Al: 0 to 0.5%, P: 0 to 0.03%, S: 0 to 0.01%, V: 0 to 2.1%, Cr: 0.8 to 5.5%, Ni: 0 to 4.3%, Cu: 0 to 0.3%, Mo: 0 to 3.0%, W: 0 to 9.5%, Co: 0 to 4.5%, with the balance being Fe and impurities.

[0020] The above-mentioned nickel-based superalloy is, for example, an alloy equivalent to Udimet 520 (Udimet is a registered trademark of Special Metals), an alloy equivalent to Udimet 720, an alloy equivalent to Waspaloy, an alloy equivalent to Alloy 718, etc. In particular, it is preferable to manufacture the knockout body and its knockout surface from the above-mentioned nickel-based superalloy, since high-temperature strength can be imparted to them.

[0021] In the method for manufacturing a hot forged product of the present invention, nickel alloys such as Udimet 520-equivalent alloys, Udimet 720-equivalent alloys, Waspaloy-equivalent alloys, and Alloy 718-equivalent alloys, which contain intermetallic compounds such as Al, Ti, and Nb, can be used as the forging material. [Example]

[0022] A hot forging die 0 having the cross-sectional shape shown in Figure 2 was prepared, in which a convex pressing surface 1S of an upper die 1 and a concave pressing surface 2S of a lower die 2 face each other in the pressing direction of a forging material 3, and a knockout surface 5S movable in the pressing direction is located at the center of the pressing surface 2S of the lower die 2. The upper die 1 and the lower die 2 were made of SKD61 according to JIS-G4404. The knockout surface 5S was formed by overlay welding an alloy equivalent to Udimet 520 to the knockout surface of a knockout 5 body made of an alloy equivalent to Alloy 718. Then, the above-mentioned hot forging die 0 was assembled into a 50,000-ton press, and then, following the series of steps shown in Figures 3(A) to (E), a forging material 3 (made of an alloy equivalent to Alloy 718) placed on the pressing surface 2S of the lower die 2 was pressed and formed with the pressing surface 1S of the upper die 1 to obtain a bowl-shaped forged product 4, thereby carrying out a method for manufacturing a hot forged product.

[0023] First, the knockout 5 was raised so that the knockout surface 5S located at the center of the pressing surface 2S of the lower die 2 protruded upward from the pressing surface 2S of the lower die 2. Then, the transported forging material 3 was placed on this knockout surface 5S protruding from the pressing surface 2S. At this time, the height of the knockout surface 5S was sufficient so that the forging material 3 would not come into contact with the pressing surface 2S of the lower die 2 when placed on the knockout surface 5S. Therefore, the jig holding the forging material 3 did not interfere with the peripheral portion of the pressing surface 2S of the lower die 2, and the forging material 3 could be placed on the knockout surface 5S without falling.

[0024] Next, the knockout surface 5S on which the forging material 3 was placed was lowered together with the forging material 3 to return it to its original position on the pressing surface 2S of the lower die 2, and it was confirmed that the forging material 3 was in the correct position on the pressing surface 2S of the lower die 2. It was also confirmed that in this state, there was a portion of the knockout surface 5S that was not in contact with the forging material 3. The forging material 3, properly placed on the pressing surface 2S of the lower die 2, was pressed and formed by the pressing surface 1S of the upper die 1, obtaining a bowl-shaped forged product 4, and the hot forging was completed. The knockout surface 5S was then raised, allowing the forged product 4 to be smoothly released from the lower die 2. The obtained forged product 4 had the desired shape, and no deformation or damage was found in the knockout 5, including the knockout surface 5S. [Explanation of symbols]

[0025] 0 Hot forging dies 1 Upper mold 1S Pressing surface 2 Lower mold 2S pressing surface 3 Forging materials 4 Forgings 5 Knockout 5S Knockout Side

Claims

1. A method for manufacturing a hot forged product, in which a convex pressing surface of an upper die and a concave pressing surface of a lower die are opposed to each other in the pressing direction of a forging material, and a knockout surface that is movable in the pressing direction is provided at the center of the pressing surface of the lower die, and a forging material placed on the pressing surface of the lower die is pressed and formed with the pressing surface of the upper die to obtain a bowl-shaped forged product, when the forging material is placed on the pressing surface of the lower die, the knockout surface is raised in the pressing direction to protrude from the pressing surface of the lower die, the forging material is placed on the knockout surface protruding from the pressing surface, and when the forging material is placed on the knockout surface, the height of the knockout surface is such that the forging material does not come into contact with the pressing surface of the lower die, A method for manufacturing a hot forged product, characterized in that the knockout surface on which the forging material is placed is lowered and placed onto the pressing surface of the lower die, thereby placing the forging material on the pressing surface of the lower die.

2. 2. The method for manufacturing a hot forged product according to claim 1, wherein when the knockout surface on which the forging material is placed is lowered and placed on the pressing surface of the lower die, at least a portion of the knockout surface does not come into contact with the forging material.

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