Progressive area forging method

Abstract

Disclosed is a progressive area forging method including: a first forging step of press-forming a central region of one surface of a preform placed on a concave bed using a first die, such that a first protrusion is formed on a central region of the other surface of the preform; and a second forging step of press-forming a peripheral region of the one surface of the press-formed preform using a second die, such that the one surface of the preform is formed to be flat.

Description

CROSS REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority to Korea Patent Application No. 10-2025-0038817, filed Mar. 26, 2025, the entire contents of which is incorporated herein for all purposes by this reference.FIELD

[0002] The present disclosure relates to a progressive area forging method, and more particularly, to a progressive area forging method that calculates a pressable cross-sectional area according to a limited press load capacity and a flow stress of a material to derive specifications of a plurality of dies, and that progressively performs press forming from a central portion toward a peripheral portion of a preform using the plurality of dies, thereby manufacturing a formed product of a superalloy material through multiple forging stages.BACKGROUND

[0003] A gas turbine is a rotary heat engine that operates a turbine using high-temperature, high-pressure combustion gas, and generally includes a compressor, a combustor, and a turbine. The turbine is composed of components such as a disk and blades.

[0004] Conventionally, a turbine disk has been entirely formed by a single-die forging method, which requires a high forging load. Accordingly, manufacturing a turbine disk using a high-capacity press results in high cost and a long production time. In contrast, a turbine disk formed by a rotary forging process fails to meet the required quality standards.

[0005] Here, the turbine disk is manufactured from a superalloy material. Since a superalloy exhibits a flow stress at high temperatures that is several times higher than that of ordinary carbon steel, forming a product by die forging requires a press having an extremely high load capacity, far exceeding that used for carbon steel, thereby causing technical difficulties.

[0006] In particular, a turbine disk for a large gas turbine is made of a Ni-based superalloy and has a large forged size, thereby requiring a forging press having a capacity of 50,000 tons or more. When a superalloy is forged using a hammer forging method with a high strain rate, it is difficult to obtain high-quality products due to the occurrence of cracks, deformation heat, and other defects during forging. Therefore, the superalloy must be forged using a press.

[0007] Accordingly, there is a need for a die and a forging method that can reduce cost and manufacturing time compared to conventional processes and enable the manufacture of medium to large-sized forged products made of a superalloy material using a press having a relatively low load capacity.

[0008] In addition, there is a need to determine specifications of a plurality of dies based on an applicable pressable cross-sectional area is applied, taking into account the limited load capacity of the press and the stable flow stress of the superalloy material during hot forging.SUMMARY

[0009] An object of the present disclosure is to provide a progressive area forging method that calculates a pressable cross-sectional area based on a limited press load capacity and a flow stress of a material to determine specifications of a plurality of dies, and that progressively performs press forming from a central portion toward a peripheral portion of a preform using the plurality of dies, thereby manufacturing a formed product of a superalloy material through multiple forging stages.

[0010] The technical problem to be achieved by the present disclosure is not limited to the above-mentioned technical problem, and other technical problems that are not mentioned will be clearly understood by ordinary-skilled persons in the art to which the present disclosure pertains from the following description.

[0011] One embodiment is a progressive area forging method including: a first forging step of press-forming a central region of one surface of a preform placed on a concave bed using a first die, such that a first protrusion is formed on a central region of the opposite surface of the preform; and a second forging step of press-forming a peripheral region of the one surface of the press-formed preform using a second die, such that the one surface of the preform is formed to be flat.

[0012] According to an embodiment, the progressive area forging method further includes a third forging step of press-forming the one surface of the preform using a third die, such that a second protrusion is formed in a central region of the one surface of the preform.

[0013] According to an embodiment, the progressive area forging method further includes a fourth forging step of press-forming a peripheral region of the one surface of the preform using the second die while maintaining the second protrusion, such that a third protrusion is formed in a peripheral region of the opposite surface of the preform.

[0014] According to an embodiment, the progressive area forging method further includes a fifth forging step of press-forming an edge region of the one surface of the preform using a fourth die, such that a fourth protrusion is formed to surround the second protrusion and to have a lower height than the second protrusion.

[0015] According to an embodiment, the first die has a cylindrical shape, and the concave bed includes a first concave portion and a second concave portion, and wherein the first concave portion is formed at a central portion of the concave bed to be recessed in a pressing direction by at least a bottom area of the first die, and the second concave portion is formed around the first concave portion to be recessed to a shallower depth than the first concave portion.

[0016] According to an embodiment, in the first forging step, the first protrusion may be formed to protrude by a volume corresponding to a space of the first concave portion.

[0017] According to an embodiment, an outer diameter of the second die is larger than an outer diameter of the first die, a central portion of the second die is hollow and penetrated therethrough, and an inner diameter of the second die is equal to or smaller than a diameter of the first concave portion and is concentrically aligned therewith.

[0018] According to an embodiment, an outer diameter of the third die is smaller than the outer diameter of the second die, a central portion of the third die is hollow and penetrated therethrough, and an inner diameter of the third die is formed to be identical to the inner diameter of the second die.

[0019] According to an embodiment, in the fourth forging step, a press-formed region may include a region press-formed in the third forging step and may be larger than the region press-formed in the third forging step.

[0020] According to an embodiment, in the fourth forging step, the third protrusion is formed to protrude by a volume corresponding to a space of the second concave portion, and a diameter of the third protrusion may be larger than a diameter of the fourth protrusion.

[0021] According to an embodiment, an outer diameter of the fourth die is larger than the outer diameters of the first die, the second die, and the third die, a central portion of the fourth die is hollow and penetrated therethrough, and an inner diameter of the fourth die may be larger than the outer diameters of the first die and the third die and smaller than the outer diameter of the second die.

[0022] According to an embodiment, the progressive area forging method further includes, prior to the first forging step, an upsetting step of compressing a billet placed on a flat bed by a press to form the billet into the preform.

[0023] According to an embodiment, the first die, the second die, the third die, and the fourth die are pressed by the press, and a load capacity of the press may be set to 160 MN to 180 MN.

[0024] According to an embodiment, in the upsetting step, the billet is heated to 1000° C. to 1100° C. before being compressed by the press, the preform is reheated to 1000° C. to 1100° C. after the upsetting step and before the first forging step, and the preform may be reheated to 1000° C. to 1100° C. after the second forging step and before the third forging step.

[0025] According to an embodiment, a formed product manufactured through the first forging step to the fifth forging step is a turbine disk of a gas turbine formed of a superalloy material, and the turbine disk may be formed to have a diameter of 1600 mm to 1800 mm.

[0026] According to an embodiment, the first die, the second die, the third die, and the fourth die have chamfered or rounded edge portions that contact the preform, thereby preventing stress concentration.

[0027] According to an embodiment, the first protrusion and the second protrusion are symmetrical with respect to a center line of the formed product, and the third protrusion and the fourth protrusion may also be symmetrical with respect to the center line of the formed product.

[0028] According to an embodiment, cross-sectional areas of the first die, the second die, the third die, and the fourth die may be calculated and set based on at least one of a load capacity of the press, a type of the preform material, and a flow stress according to a heating temperature.

[0029] According to an embodiment, the cross-sectional areas of the first die, the second die, the third die, and the fourth die may be set to a value obtained by dividing a maximum load capacity of the press by a strain rate and the flow stress.

[0030] According to an embodiment, an inner diameter of any one of the first die, the second die, the third die, and the fourth die is set to be smaller than a maximum outer diameter of a previous die, such that press-formed regions overlap each other.

[0031] According to the present disclosure, specifications of a plurality of dies can be determined by calculating a pressable cross-sectional area based on a press load capacity limited to a range of 160 MN to 180 MN and a flow stress of a superalloy material. The cross-sectional areas of the plurality of dies that contact the preform may be set to be less than or equal to a predetermined area. Accordingly, a formed product having a target shape and made of a superalloy material can be manufactured even using a press with aa limited load capacity.

[0032] By using the plurality of dies and employing free forging and hot forging methods, and by progressively press-forming the preform from the central portion toward the peripheral portion in divided areas, uniform forming and stable flow stress of the superalloy material can be secured.

[0033] Even when the formed product is manufactured through multiple forging steps using a press with relatively low load capacity, the formed product can satisfy required quality characteristics. The required quality characteristics refer to an effective strain, flow stress, and amount of deformation of the formed product that meet predetermined standards.

[0034] Each forging step can be completed in less than one minute, thereby reducing production cost and manufacturing time, and enabling the production of high-quality, medium to large-sized turbine disks made of a superalloy with a press with a low load capacity.

[0035] The effects of the present disclosure are not limited to the above-described effects and other effects which are not described herein may be derived by those skilled in the art from the following description of the embodiments of the present disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0037] FIG. 1 is a perspective view of a power-generation gas turbine and an enlarged cross-sectional view of its interior.

[0038] FIG. 2 is a flowchart schematically illustrating an overall procedure of a progressive area forging method according to one embodiment of the present disclosure.

[0039] FIGS. 3A and 3B are diagrams illustrating a process of an upsetting step according to one embodiment.

[0040] FIGS. 4A and 4B are diagrams illustrating a result of the upsetting step according to one embodiment.

[0041] FIGS. 5A and 5B are diagrams illustrating a process of the first forging step according to one embodiment.

[0042] FIGS. 6A and 6B are diagrams illustrating a result of the first forging step according to one embodiment.

[0043] FIGS. 7A and 7B are diagrams illustrating a process of the second forging step according to one embodiment.

[0044] FIGS. 8A and 8B are diagrams illustrating a result of the second forging step according to one embodiment.

[0045] FIGS. 9A and 9B are diagrams illustrating a process of the third forging step according to one embodiment.

[0046] FIGS. 10A and 10B are diagrams illustrating a result of the third forging step according to one embodiment.

[0047] FIGS. 11A and 11B are diagrams illustrating a process of the fourth forging step according to one embodiment.

[0048] FIGS. 12A and 12B are diagrams illustrating a result of the fourth forging step according to one embodiment.

[0049] FIGS. 13A and 13B are diagrams illustrating a process of the fifth forging step according to one embodiment.

[0050] FIGS. 14A and 14B are diagrams illustrating a result of the fifth forging step according to one embodiment.

[0051] FIG. 15 is a perspective view of a concave bed according to one embodiment.

[0052] FIG. 16 is a cross-sectional view of the concave bed taken along line X-X′ of FIG. 15.

[0053] FIG. 17 is a diagram illustrating a formed product according to one embodiment.

[0054] FIG. 18 is a diagram illustrating a turbine disk obtained by machining the formed product of FIG. 17.

[0055] FIGS. 19A and 19B are graphs illustrating flow stresses analyzed according to temperature and strain rate for calculating cross-sectional areas of a plurality of dies used in the progressive area forging method according to one embodiment.

[0056] The drawings attached to the present specification illustrate a preferred embodiment of the present disclosure and serve to further facilitate understanding of the technical idea of the present disclosure in conjunction with the detailed description of the disclosure. Accordingly, the present disclosure should not be construed as being limited to the matters shown in these drawings.DETAILED DESCRIPTION

[0057] Hereinafter, a preferrable embodiment with respect to a progressive area forging method according to the present disclosure will be described with reference to accompanying drawings.

[0058] Further, terms described below are defined in consideration of the functions of one or more exemplary embodiments, and may have different meanings according to the intention of a user or operator or the convention. Furthermore, the exemplary embodiments described below are not intended to limit the scope of the present disclosure but merely to exemplify configurational elements defined in the claims.

[0059] In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification. Throughout the specification, when a certain portion “includes” or “comprises” a certain component, this indicates that other components are not excluded and may be further included unless otherwise noted.

[0060] In the present specification, regarding an element represented as a “unit” or a “module”, two or more elements may be combined into one element or one element may be divided into two or more elements according to subdivided functions. In addition, each element described hereinafter may additionally perform some or all of functions performed by another element, in addition to main functions of itself, and some of the main functions of each element may be performed entirely by another component.

[0061] Referring first to FIGS. 1 to 4, a progressive area forging method 1 according to one embodiment of the present disclosure will be described.

[0062] The progressive area forging method 1 according to one embodiment of the present disclosure broadly includes an upsetting step U, a first process R1, and a second process R2. The first process R1 includes a first forging step S1, a second forging step S2, and a third forging step S3. The second process R2 includes a fourth forging step S4 and a fifth forging step S5. Through the progressive area forging method 1, a preform 10 can be manufactured into a formed product 20. However, the present disclosure is not limited thereto. In some embodiments, the progressive area forging method 1 may include only the first process R1. In such case, the first process R1 may include only the first forging step S1 and the second forging step S2.

[0063] In the upper portion of FIG. 1, a perspective view of a power-generation gas turbine is illustrated, and in the lower portion, an enlarged internal cross-sectional view taken along line A-A′ of the upper portion is illustrated. In the lower portion of FIG. 1, a compressor, a combustor, and a turbine are arranged sequentially from left to right. The turbine portion includes a first stage, a second stage, a third stage, and a fourth stage from the left to right. A formed product 20 manufactured by the progressive area forging method 1 can be machined and used as turbine disks T for stages 1 to 4.

[0064] Referring to FIGS. 2 to 17, the progressive area forging method 1 according to one embodiment of the present disclosure will be described in detail.

[0065] In the first process R1, a preform 10 mounted on a concave bed 500 is press-formed using a first die 100, a second die 200, and a third die 300, such that a first protrusion 11 and a second protrusion 12 are formed in the central portion of the preform 10. Subsequently, after the first process R1, in the second process R2, the preform 10 is press-formed by the second die 200 and a fourth die 400, such that a third protrusion 13 and a fourth protrusion 14 are formed in the peripheral portion of the preform 10.

[0066] FIGS. 3A and 3B illustrate a process of the upsetting step U. FIG. 3A shows the billet B before compression, and FIG. 3B shows the billet B after being formed into the preform 10. The upsetting step U is performed prior to the first forging step S1. In this upsetting step U, the billet B mounted on a flat bed F is compressed by a flat die P attached to the lower portion of a press to form the preform 10.

[0067] FIGS. 4A and 4B illustrate a result of the upsetting step U. FIG. 4A shows a perspective view of a structural analysis result of the preform 10, and FIG. 4B shows a cross-sectional view of the structural analysis result of the preform 10. As shown in FIG. 4B, stress is concentrated inside the preform 10, causing internal non-uniformity, which may lead to cracking. Accordingly, by performing a plurality of forging steps S1, S2, S3, S4, and S5, internal uniformity and stable flow stress can be ensured.

[0068] FIGS. 5A and 5B illustrate a process of the first forging step S1. FIG. 5A is a side view of the preform 10 being press-formed by the first die 100, and FIG. 5B is a perspective view thereof. As shown in FIGS. 5A and 5B, the first die 100 may be formed in a cylindrical shape. The preform 10 is mounted on a concave bed 500 and press-formed by the first die 100. During the press-forming, the central axes of the preform 10, the first die 100, and the concave bed 500 are aligned.

[0069] FIGS. 6A and 6B illustrate a result of the first forging step S1. FIG. 6A is a perspective view of the preform 10 after being press-formed by the first die 100, and FIG. 6B is a cross-sectional view. In the first forging step S1, a central portion of one side of the preform 10 mounted on the concave bed 500 is press-formed by the first die 100. When press-formed, a first protrusion 11 can be formed in the central portion of the opposite side of the preform 10. Here, one side of the preform 10 refers to the upper side, and the opposite side refers to the lower side.

[0070] Specifically, as shown in FIGS. 6A, 6B, 15, and 16, the concave bed 500 may include a first concave portion 501 and a second concave portion 502. The first concave portion 501 may be formed in the central portion of the concave bed 500 such that it is recessed in the press direction to a depth corresponding to at least the bottom area of the first die 100. The second concave portion 502 may be formed around the first concave portion 501 such that a high step d1 is defined between the first concave portion and the second concave portion 502. That is, the second concave portion 502 is recessed to a shallower depth than the first concave portion 501. Further, the second concave portion 502 is lower than the top surface of the concave bed 500 and may be formed with a low step d2 relative to the top surface of the concave bed 500. Accordingly, in the first forging step S1, the first protrusion 11 may be formed so as to protrude by a volume corresponding to the first concave portion 501.

[0071] The press direction, throughout the specification, refers to a vertical direction in which the press is lowed to press the preform.

[0072] FIGS. 7A and 7B illustrate a process of the second forging step S2. FIG. 7A is a side view of the preform 10 being press-formed by the second die 200, and FIG. 7B is a perspective view thereof. FIGS. 8A and 8B illustrate a result of the second forging step S2. FIG. 8A is a perspective view of the preform 10 after being press-formed by the second die 200, and FIG. 8B is a cross-sectional view.

[0073] As shown in FIGS. 6A, 6B, 7A, 7B, 8A and 8B, in the second forging step S2, a peripheral region of the central portion of one side of the preform 10 press-formed in the first forging step S1 can be press-formed by the second die 200. As a result, one side of the preform 10 can be formed flat.

[0074] Further, the outer diameter of the second die 200 is larger than that of the first die 100, and its central portion may be hollow and penetrated therethrough. That is, the second die 200 may be formed in an annular shape. The inner diameter of the second die 200 may be equal to or smaller than the diameter of the first concave portion 501 and concentrically aligned therewith. The region press-formed by the second die 200 partially overlaps with the region press-formed by the first die 100 to prevent burr formation.

[0075] FIGS. 9A and 9B illustrate a process of the third forging step S3. FIG. 9A is a side view of the preform 10 being press-formed by the third die 300, and FIG. 9B is a perspective view thereof. FIGS. 10A and 10B illustrate a result of the third forging step S3. FIG. 10A is a perspective view of the preform 10 after being press-formed by the third die 300, and FIG. 10B is a cross-sectional view.

[0076] As shown in FIGS. 8A, 8B, 9A, 9B, 10A, and 10B, in the third forging step S3, one side of the preform 10 can be press-formed by the third die 300. As a result, a second protrusion 12 can be formed in the central region of one side of the preform 10. Here, the outer diameter of the third die 300 may be smaller than the outer diameter of the second die 200, and its central portion may be hollow and penetrated therethrough. That is, the third die 300 may be formed in an annular shape. The inner diameter of the third die 300 may be equal to the inner diameter of the second die 200, which will be described in connection with the fourth forging step S4.

[0077] FIGS. 11A and 11B illustrate a process of the fourth forging step S4. FIG. 11A is a side view of the preform 10 being press-formed by the second die 200, and FIG. 11B is a perspective view thereof. FIGS. 12A and 12B illustrate a result of the fourth forging step S4. FIG. 12A is a perspective view of the preform 10 after being press-formed by the second die 200, and FIG. 12B is a cross-sectional view.

[0078] As shown in FIGS. 10A, 10B, 11A, 11B, 12A, and 12B, in the fourth forging step S4, a peripheral region of one side of the preform 10 can be press-formed by the second die 200 while maintaining the second protrusion 12. The region press-formed in the fourth forging step S4 may include the region press-formed in the third forging step S3 and may be larger.

[0079] Further, the inner diameter of the third die 300 may be formed equal to that of the second die 200. In the fourth forging step S4, to prevent the central hollow portion of the second die 200 from affecting the second protrusion 12, the inner diameter of the second die 200 may be equal to or greater than the inner diameter of the third die 300.

[0080] After the fourth forging step S4, a third protrusion 13 can be formed on a peripheral region of the opposite side of the preform 10. Referring again to FIGS. 15 to 17, the third protrusion 13 may protrude by the amount of the second concave portion 502. Further, the diameter of the third protrusion 13 may be larger than the diameter of the fourth protrusion 14.

[0081] FIGS. 13A and 13B illustrate a process of the fifth forging step S5. FIG. 13A is a side view of the preform 10 being press-formed by the fourth die 400, and FIG. 13B is a perspective view thereof. FIGS. 14A and 14B illustrate a result of the fifth forging step S5. FIG. 14A is a perspective view of the preform 10 after being press-formed by the fourth die 400, and FIG. 14B is a cross-sectional view.

[0082] Referring again to FIGS. 5A to 17, in the fifth forging step S5, an edge region of one side of the preform 10 can be press-formed by the fourth die 400. The outer diameter of the fourth die 400 may be larger than the outer diameters of the first die 100, the second die 200, and the third die 300, and the central portion of the fourth die 400 may be hollow and penetrated therethrough. The inner diameter of the fourth die 400 may be larger than the outer diameters of the first die 100 and the third die 300 and smaller than the outer diameter of the second die 200. Through the fifth forging step S5, a fourth protrusion 14 can be formed surrounding the second protrusion 12, with a height lower than that of the second protrusion 12 to provide a step d2.

[0083] The preform 20 produced through the progressive regional forging method 1 is shown in FIG. 17. Referring to the structure of the preform 20, the first protrusion 11 and the second protrusion 12 may be formed symmetrically with respect to the centerline C-C′ of the preform 20. Likewise, the third protrusion 13 and the fourth protrusion 14 may also be symmetrical with respect to the centerline C-C′. It is preferable that such symmetry be considered in proportion, as dimensions may vary.

[0084] FIG. 18 illustrates a turbine disk T obtained by machining the preform 20 shown in FIG. 17. In FIG. 18, the turbine disk T is formed by cutting and machining the outer surface of the preform 20, and the dimensional difference between the preform 20 of FIG. 17 and the turbine disk T of FIG. 18 is minimal. The preform 20 is formed of a superalloy material and constitutes a turbine disk T for a gas turbine, wherein the turbine disk T may have a diameter ranging from 1600 mm to 1800 mm.

[0085] FIGS. 19A and 19B illustrate a graph analyzing the flow stress according to temperature and strain rate, for calculating cross-sectional areas of the plurality of dies 100, 200, 300, 400 used in the progressive regional forging method 1.

[0086] Referring to FIGS. 2 to 19, according to the progressive regional forging method 1, the preform 10 can be press-formed such that a plurality of steps d1, d2 are formed, by gradually increasing the press-formed area in a radial direction from the center of the preform 10.

[0087] The flat die P, the first die 100, the second die 200, the third die 300, and the fourth die 400 used for press forming are pressed by a press, wherein the press may have a load capacity set in the range of 160 MN to 180 MN. In addition, edges of the first die 100, the second die 200, the third die 300, and the fourth die 400 that contact the preform 10 may be chamfered or rounded to prevent stress concentration.

[0088] In the upsetting step U, the billet B may be heated to a temperature in the range of 1000° C. to 1100° C. prior to being compressed by the press. After the upsetting step U and before the first forging step S1, the preform 10 may be reheated to a temperature in the range of 1000° C. to 1100° C. After the second forging step S2 and before the third forging step S3, the preform 10 may also be reheated to a temperature in the range of 1000° C. to 1100° C.

[0089] The time required for each step of the progressive regional forging method 1 is approximately as follows: the upsetting step U takes about 58 seconds; the first forging step S1 takes about 7.7 seconds; the second forging step S2 takes about 5.6 seconds; the third forging step S3 takes about 4.1 seconds; the fourth forging step S4 takes about 3.3 seconds; and the fifth forging step S5 takes about 4.4 seconds.

[0090] The cross-sectional areas of the first die 100, the second die 200, the third die 300, and the fourth die 400 may be calculated and determined based on at least one of the press load capacity, the material type of the preform 10, and the flow stress according to the heating temperature. Here, the cross-sectional areas of the first die 100, the second die 200, the third die 300, and the fourth die 400 refer to the areas of horizontally cut surfaces that contact the preform 10.

[0091] The cross-sectional areas of the first die 100, the second die 200, the third die 300, and the fourth die 400 may be set to values obtained by dividing a maximum load capacity of the press by a strain rate and the flow stress. In addition, an inner diameter of any one of the first die 100, the second die 200, the third die 300, and the fourth die 400 may be set smaller than the maximum outer diameter of the preceding die so that the forged regions overlap.

[0092] The cross-sectional areas of the plurality of dies 100, 200, 300, 400 used in the progressive regional forging method 1 may be calculated by analyzing the flow stress of the material according to temperature and strain rate. Referring to the graphs of FIGS. 19A and 19B, when forging an IN706 superalloy material with a press having a load capacity of 170 MN, the maximum allowable cross-sectional area can be calculated to be approximately 1.06 m2.

[0093] Specifically, at a forging temperature of 1000° C., the flow stress of the IN706 material according to strain rate is shown in the graph of FIGS. 19A and 19B. FIG. 19A indicates that, at a forging temperature of 1000° C. and a strain rate of 0.01 / sec, the flow stress is calculated to be 150 MPa. FIG. 19B indicates that, at a forging temperature of 1000° C. and a strain rate of 0.1 / sec, the flow stress is calculated to be 240 MPa.

[0094] Based on a press having a load capacity of 170 MN, the initial strain rate of IN706 is calculated to be 0.011 / sec. When the press speed is set to 17 mm / sec and the initial upsetting height is set to 1,500 mm, the strain rate is calculated to be 0.011 / sec. Referring to the graph of FIGS. 19A and 19B, the flow stress corresponding to a strain rate of 0.011 / sec is approximately 160 MPa.

[0095] Therefore, according to the pressure equation, the calculation is established as: 170 MN / Area=160 MPa (160 N / mm2 ). Solving the equation, the cross-sectional area is calculated to be approximately 1.06 m2. Accordingly, the cross-sectional areas of the first die 100, the second die 200, the third die 300, and the fourth die 400 may each be set to be equal to or less than approximately 1.06 m2. In other words, the cross-sectional areas of the plurality of dies 100, 200, 300, 400 may be determined by taking into account the load capacity of the press and the flow stress of the material.

[0096] Accordingly, according to the progressive regional forging method 1 of an embodiment of the present disclosure, the specifications of a plurality of dies 100, 200, 300, 400 can be determined by calculating the depressible cross-sectional area based on the press load capacity, which is limited within a range of 160 MN to 180 MN, and the flow stress of the superalloy material. The cross-sectional areas of the plurality of dies 100, 200, 300, 400 in contact with the preform 10 may be set to be equal to or less than a predetermined area. Accordingly, even with a press having a limited load capacity, a forged product having a target shape made of a superalloy material can be produced.

[0097] Furthermore, by using the plurality of dies 100, 200, 300, 400 in combination with free forging and hot forging, and progressively depressing the preform 10 from the central portion toward the peripheral portion in increments of partial areas, uniform forging and stable flow stress of the superalloy material can be ensured.

[0098] Moreover, even when the forging is carried out through a plurality of forging steps S1, S2, S3, S4, S5 using a press with a relatively low load capacity, the forged product 20 can satisfy the required quality characteristics. The required quality characteristics refer to effective strain, flow stress, and deformation amount of the forged product 20 that meet predetermined standards. Accordingly, high-quality medium to large turbine disks made of a superalloy can be manufactured using a press with a relatively low load capacity.

[0099] In addition, the processing time for each forging step S1, S2, S3, S4, S5 can be minimized to less than one minute, thereby reducing production costs and shortening the manufacturing period of the forged product 20.

[0100] The present disclosure is not limited to the above-described specific embodiments and descriptions, and various modifications may be made by those skilled in the art without departing from the gist of the present disclosure claimed in the claims. Such variations are within the protection scope of the present disclosure.REFERENCE NUMERALS1: progressive area forging method

[0102] U: upsetting step

[0103] P: flat die

[0104] F: flat bed

[0105] B: billet

[0106] S1: first forging step

[0107] S2: second forging step

[0108] S3: third forging step

[0109] S4: fourth forging step

[0110] S5: fifth forging step

[0111] 10: preform

[0112] 11: first protrusion

[0113] 12: second protrusion

[0114] 13: third protrusion

[0115] 14: fourth protrusion

[0116] 20: formed product

[0117] 100: first die

[0118] 200: second die

[0119] 300: third die

[0120] 400: fourth die

[0121] 500: concave bed

[0122] 501: first concave portion

[0123] 502: second concave portion

[0124] d1: high step

[0125] d2: low step

[0126] T: turbine disk

Examples

Embodiment Construction

[0057]Hereinafter, a preferrable embodiment with respect to a progressive area forging method according to the present disclosure will be described with reference to accompanying drawings.

[0058]Further, terms described below are defined in consideration of the functions of one or more exemplary embodiments, and may have different meanings according to the intention of a user or operator or the convention. Furthermore, the exemplary embodiments described below are not intended to limit the scope of the present disclosure but merely to exemplify configurational elements defined in the claims.

[0059]In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification. Throughout the specification, when a certain portion “includes” or “comprises” a certain component, this indicates that other components are not excluded and may be further included unless otherwise no...

CROSS REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority to Korea Patent Application No. 10-2025-0038817, filed Mar. 26, 2025, the entire contents of which is incorporated herein for all purposes by this reference.FIELD

[0002] The present disclosure relates to a progressive area forging method, and more particularly, to a progressive area forging method that calculates a pressable cross-sectional area according to a limited press load capacity and a flow stress of a material to derive specifications of a plurality of dies, and that progressively performs press forming from a central portion toward a peripheral portion of a preform using the plurality of dies, thereby manufacturing a formed product of a superalloy material through multiple forging stages.BACKGROUND

[0003] A gas turbine is a rotary heat engine that operates a turbine using high-temperature, high-pressure combustion gas, and generally includes a compressor, a combustor, and a turbine. The turbine is composed of components such as a disk and blades.

[0004] Conventionally, a turbine disk has been entirely formed by a single-die forging method, which requires a high forging load. Accordingly, manufacturing a turbine disk using a high-capacity press results in high cost and a long production time. In contrast, a turbine disk formed by a rotary forging process fails to meet the required quality standards.

[0005] Here, the turbine disk is manufactured from a superalloy material. Since a superalloy exhibits a flow stress at high temperatures that is several times higher than that of ordinary carbon steel, forming a product by die forging requires a press having an extremely high load capacity, far exceeding that used for carbon steel, thereby causing technical difficulties.

[0006] In particular, a turbine disk for a large gas turbine is made of a Ni-based superalloy and has a large forged size, thereby requiring a forging press having a capacity of 50,000 tons or more. When a superalloy is forged using a hammer forging method with a high strain rate, it is difficult to obtain high-quality products due to the occurrence of cracks, deformation heat, and other defects during forging. Therefore, the superalloy must be forged using a press.

[0007] Accordingly, there is a need for a die and a forging method that can reduce cost and manufacturing time compared to conventional processes and enable the manufacture of medium to large-sized forged products made of a superalloy material using a press having a relatively low load capacity.

[0008] In addition, there is a need to determine specifications of a plurality of dies based on an applicable pressable cross-sectional area is applied, taking into account the limited load capacity of the press and the stable flow stress of the superalloy material during hot forging.SUMMARY

[0009] An object of the present disclosure is to provide a progressive area forging method that calculates a pressable cross-sectional area based on a limited press load capacity and a flow stress of a material to determine specifications of a plurality of dies, and that progressively performs press forming from a central portion toward a peripheral portion of a preform using the plurality of dies, thereby manufacturing a formed product of a superalloy material through multiple forging stages.

[0010] The technical problem to be achieved by the present disclosure is not limited to the above-mentioned technical problem, and other technical problems that are not mentioned will be clearly understood by ordinary-skilled persons in the art to which the present disclosure pertains from the following description.

[0011] One embodiment is a progressive area forging method including: a first forging step of press-forming a central region of one surface of a preform placed on a concave bed using a first die, such that a first protrusion is formed on a central region of the opposite surface of the preform; and a second forging step of press-forming a peripheral region of the one surface of the press-formed preform using a second die, such that the one surface of the preform is formed to be flat.

[0012] According to an embodiment, the progressive area forging method further includes a third forging step of press-forming the one surface of the preform using a third die, such that a second protrusion is formed in a central region of the one surface of the preform.

[0013] According to an embodiment, the progressive area forging method further includes a fourth forging step of press-forming a peripheral region of the one surface of the preform using the second die while maintaining the second protrusion, such that a third protrusion is formed in a peripheral region of the opposite surface of the preform.

[0014] According to an embodiment, the progressive area forging method further includes a fifth forging step of press-forming an edge region of the one surface of the preform using a fourth die, such that a fourth protrusion is formed to surround the second protrusion and to have a lower height than the second protrusion.

[0015] According to an embodiment, the first die has a cylindrical shape, and the concave bed includes a first concave portion and a second concave portion, and wherein the first concave portion is formed at a central portion of the concave bed to be recessed in a pressing direction by at least a bottom area of the first die, and the second concave portion is formed around the first concave portion to be recessed to a shallower depth than the first concave portion.

[0016] According to an embodiment, in the first forging step, the first protrusion may be formed to protrude by a volume corresponding to a space of the first concave portion.

[0017] According to an embodiment, an outer diameter of the second die is larger than an outer diameter of the first die, a central portion of the second die is hollow and penetrated therethrough, and an inner diameter of the second die is equal to or smaller than a diameter of the first concave portion and is concentrically aligned therewith.

[0018] According to an embodiment, an outer diameter of the third die is smaller than the outer diameter of the second die, a central portion of the third die is hollow and penetrated therethrough, and an inner diameter of the third die is formed to be identical to the inner diameter of the second die.

[0019] According to an embodiment, in the fourth forging step, a press-formed region may include a region press-formed in the third forging step and may be larger than the region press-formed in the third forging step.

[0020] According to an embodiment, in the fourth forging step, the third protrusion is formed to protrude by a volume corresponding to a space of the second concave portion, and a diameter of the third protrusion may be larger than a diameter of the fourth protrusion.

[0021] According to an embodiment, an outer diameter of the fourth die is larger than the outer diameters of the first die, the second die, and the third die, a central portion of the fourth die is hollow and penetrated therethrough, and an inner diameter of the fourth die may be larger than the outer diameters of the first die and the third die and smaller than the outer diameter of the second die.

[0022] According to an embodiment, the progressive area forging method further includes, prior to the first forging step, an upsetting step of compressing a billet placed on a flat bed by a press to form the billet into the preform.

[0023] According to an embodiment, the first die, the second die, the third die, and the fourth die are pressed by the press, and a load capacity of the press may be set to 160 MN to 180 MN.

[0024] According to an embodiment, in the upsetting step, the billet is heated to 1000° C. to 1100° C. before being compressed by the press, the preform is reheated to 1000° C. to 1100° C. after the upsetting step and before the first forging step, and the preform may be reheated to 1000° C. to 1100° C. after the second forging step and before the third forging step.

[0025] According to an embodiment, a formed product manufactured through the first forging step to the fifth forging step is a turbine disk of a gas turbine formed of a superalloy material, and the turbine disk may be formed to have a diameter of 1600 mm to 1800 mm.

[0026] According to an embodiment, the first die, the second die, the third die, and the fourth die have chamfered or rounded edge portions that contact the preform, thereby preventing stress concentration.

[0027] According to an embodiment, the first protrusion and the second protrusion are symmetrical with respect to a center line of the formed product, and the third protrusion and the fourth protrusion may also be symmetrical with respect to the center line of the formed product.

[0028] According to an embodiment, cross-sectional areas of the first die, the second die, the third die, and the fourth die may be calculated and set based on at least one of a load capacity of the press, a type of the preform material, and a flow stress according to a heating temperature.

[0029] According to an embodiment, the cross-sectional areas of the first die, the second die, the third die, and the fourth die may be set to a value obtained by dividing a maximum load capacity of the press by a strain rate and the flow stress.

[0030] According to an embodiment, an inner diameter of any one of the first die, the second die, the third die, and the fourth die is set to be smaller than a maximum outer diameter of a previous die, such that press-formed regions overlap each other.

[0031] According to the present disclosure, specifications of a plurality of dies can be determined by calculating a pressable cross-sectional area based on a press load capacity limited to a range of 160 MN to 180 MN and a flow stress of a superalloy material. The cross-sectional areas of the plurality of dies that contact the preform may be set to be less than or equal to a predetermined area. Accordingly, a formed product having a target shape and made of a superalloy material can be manufactured even using a press with aa limited load capacity.

[0032] By using the plurality of dies and employing free forging and hot forging methods, and by progressively press-forming the preform from the central portion toward the peripheral portion in divided areas, uniform forming and stable flow stress of the superalloy material can be secured.

[0033] Even when the formed product is manufactured through multiple forging steps using a press with relatively low load capacity, the formed product can satisfy required quality characteristics. The required quality characteristics refer to an effective strain, flow stress, and amount of deformation of the formed product that meet predetermined standards.

[0034] Each forging step can be completed in less than one minute, thereby reducing production cost and manufacturing time, and enabling the production of high-quality, medium to large-sized turbine disks made of a superalloy with a press with a low load capacity.

[0035] The effects of the present disclosure are not limited to the above-described effects and other effects which are not described herein may be derived by those skilled in the art from the following description of the embodiments of the present disclosure.BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0037] FIG. 1 is a perspective view of a power-generation gas turbine and an enlarged cross-sectional view of its interior.

[0038] FIG. 2 is a flowchart schematically illustrating an overall procedure of a progressive area forging method according to one embodiment of the present disclosure.

[0039] FIGS. 3A and 3B are diagrams illustrating a process of an upsetting step according to one embodiment.

[0040] FIGS. 4A and 4B are diagrams illustrating a result of the upsetting step according to one embodiment.

[0041] FIGS. 5A and 5B are diagrams illustrating a process of the first forging step according to one embodiment.

[0042] FIGS. 6A and 6B are diagrams illustrating a result of the first forging step according to one embodiment.

[0043] FIGS. 7A and 7B are diagrams illustrating a process of the second forging step according to one embodiment.

[0044] FIGS. 8A and 8B are diagrams illustrating a result of the second forging step according to one embodiment.

[0045] FIGS. 9A and 9B are diagrams illustrating a process of the third forging step according to one embodiment.

[0046] FIGS. 10A and 10B are diagrams illustrating a result of the third forging step according to one embodiment.

[0047] FIGS. 11A and 11B are diagrams illustrating a process of the fourth forging step according to one embodiment.

[0048] FIGS. 12A and 12B are diagrams illustrating a result of the fourth forging step according to one embodiment.

[0049] FIGS. 13A and 13B are diagrams illustrating a process of the fifth forging step according to one embodiment.

[0050] FIGS. 14A and 14B are diagrams illustrating a result of the fifth forging step according to one embodiment.

[0051] FIG. 15 is a perspective view of a concave bed according to one embodiment.

[0052] FIG. 16 is a cross-sectional view of the concave bed taken along line X-X′ of FIG. 15.

[0053] FIG. 17 is a diagram illustrating a formed product according to one embodiment.

[0054] FIG. 18 is a diagram illustrating a turbine disk obtained by machining the formed product of FIG. 17.

[0055] FIGS. 19A and 19B are graphs illustrating flow stresses analyzed according to temperature and strain rate for calculating cross-sectional areas of a plurality of dies used in the progressive area forging method according to one embodiment.

[0056] The drawings attached to the present specification illustrate a preferred embodiment of the present disclosure and serve to further facilitate understanding of the technical idea of the present disclosure in conjunction with the detailed description of the disclosure. Accordingly, the present disclosure should not be construed as being limited to the matters shown in these drawings.DETAILED DESCRIPTION

[0057] Hereinafter, a preferrable embodiment with respect to a progressive area forging method according to the present disclosure will be described with reference to accompanying drawings.

[0058] Further, terms described below are defined in consideration of the functions of one or more exemplary embodiments, and may have different meanings according to the intention of a user or operator or the convention. Furthermore, the exemplary embodiments described below are not intended to limit the scope of the present disclosure but merely to exemplify configurational elements defined in the claims.

[0059] In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification. Throughout the specification, when a certain portion “includes” or “comprises” a certain component, this indicates that other components are not excluded and may be further included unless otherwise noted.

[0060] In the present specification, regarding an element represented as a “unit” or a “module”, two or more elements may be combined into one element or one element may be divided into two or more elements according to subdivided functions. In addition, each element described hereinafter may additionally perform some or all of functions performed by another element, in addition to main functions of itself, and some of the main functions of each element may be performed entirely by another component.

[0061] Referring first to FIGS. 1 to 4, a progressive area forging method 1 according to one embodiment of the present disclosure will be described.

[0062] The progressive area forging method 1 according to one embodiment of the present disclosure broadly includes an upsetting step U, a first process R1, and a second process R2. The first process R1 includes a first forging step S1, a second forging step S2, and a third forging step S3. The second process R2 includes a fourth forging step S4 and a fifth forging step S5. Through the progressive area forging method 1, a preform 10 can be manufactured into a formed product 20. However, the present disclosure is not limited thereto. In some embodiments, the progressive area forging method 1 may include only the first process R1. In such case, the first process R1 may include only the first forging step S1 and the second forging step S2.

[0063] In the upper portion of FIG. 1, a perspective view of a power-generation gas turbine is illustrated, and in the lower portion, an enlarged internal cross-sectional view taken along line A-A′ of the upper portion is illustrated. In the lower portion of FIG. 1, a compressor, a combustor, and a turbine are arranged sequentially from left to right. The turbine portion includes a first stage, a second stage, a third stage, and a fourth stage from the left to right. A formed product 20 manufactured by the progressive area forging method 1 can be machined and used as turbine disks T for stages 1 to 4.

[0064] Referring to FIGS. 2 to 17, the progressive area forging method 1 according to one embodiment of the present disclosure will be described in detail.

[0065] In the first process R1, a preform 10 mounted on a concave bed 500 is press-formed using a first die 100, a second die 200, and a third die 300, such that a first protrusion 11 and a second protrusion 12 are formed in the central portion of the preform 10. Subsequently, after the first process R1, in the second process R2, the preform 10 is press-formed by the second die 200 and a fourth die 400, such that a third protrusion 13 and a fourth protrusion 14 are formed in the peripheral portion of the preform 10.

[0066] FIGS. 3A and 3B illustrate a process of the upsetting step U. FIG. 3A shows the billet B before compression, and FIG. 3B shows the billet B after being formed into the preform 10. The upsetting step U is performed prior to the first forging step S1. In this upsetting step U, the billet B mounted on a flat bed F is compressed by a flat die P attached to the lower portion of a press to form the preform 10.

[0067] FIGS. 4A and 4B illustrate a result of the upsetting step U. FIG. 4A shows a perspective view of a structural analysis result of the preform 10, and FIG. 4B shows a cross-sectional view of the structural analysis result of the preform 10. As shown in FIG. 4B, stress is concentrated inside the preform 10, causing internal non-uniformity, which may lead to cracking. Accordingly, by performing a plurality of forging steps S1, S2, S3, S4, and S5, internal uniformity and stable flow stress can be ensured.

[0068] FIGS. 5A and 5B illustrate a process of the first forging step S1. FIG. 5A is a side view of the preform 10 being press-formed by the first die 100, and FIG. 5B is a perspective view thereof. As shown in FIGS. 5A and 5B, the first die 100 may be formed in a cylindrical shape. The preform 10 is mounted on a concave bed 500 and press-formed by the first die 100. During the press-forming, the central axes of the preform 10, the first die 100, and the concave bed 500 are aligned.

[0069] FIGS. 6A and 6B illustrate a result of the first forging step S1. FIG. 6A is a perspective view of the preform 10 after being press-formed by the first die 100, and FIG. 6B is a cross-sectional view. In the first forging step S1, a central portion of one side of the preform 10 mounted on the concave bed 500 is press-formed by the first die 100. When press-formed, a first protrusion 11 can be formed in the central portion of the opposite side of the preform 10. Here, one side of the preform 10 refers to the upper side, and the opposite side refers to the lower side.

[0070] Specifically, as shown in FIGS. 6A, 6B, 15, and 16, the concave bed 500 may include a first concave portion 501 and a second concave portion 502. The first concave portion 501 may be formed in the central portion of the concave bed 500 such that it is recessed in the press direction to a depth corresponding to at least the bottom area of the first die 100. The second concave portion 502 may be formed around the first concave portion 501 such that a high step d1 is defined between the first concave portion and the second concave portion 502. That is, the second concave portion 502 is recessed to a shallower depth than the first concave portion 501. Further, the second concave portion 502 is lower than the top surface of the concave bed 500 and may be formed with a low step d2 relative to the top surface of the concave bed 500. Accordingly, in the first forging step S1, the first protrusion 11 may be formed so as to protrude by a volume corresponding to the first concave portion 501.

[0071] The press direction, throughout the specification, refers to a vertical direction in which the press is lowed to press the preform.

[0072] FIGS. 7A and 7B illustrate a process of the second forging step S2. FIG. 7A is a side view of the preform 10 being press-formed by the second die 200, and FIG. 7B is a perspective view thereof. FIGS. 8A and 8B illustrate a result of the second forging step S2. FIG. 8A is a perspective view of the preform 10 after being press-formed by the second die 200, and FIG. 8B is a cross-sectional view.

[0073] As shown in FIGS. 6A, 6B, 7A, 7B, 8A and 8B, in the second forging step S2, a peripheral region of the central portion of one side of the preform 10 press-formed in the first forging step S1 can be press-formed by the second die 200. As a result, one side of the preform 10 can be formed flat.

[0074] Further, the outer diameter of the second die 200 is larger than that of the first die 100, and its central portion may be hollow and penetrated therethrough. That is, the second die 200 may be formed in an annular shape. The inner diameter of the second die 200 may be equal to or smaller than the diameter of the first concave portion 501 and concentrically aligned therewith. The region press-formed by the second die 200 partially overlaps with the region press-formed by the first die 100 to prevent burr formation.

[0075] FIGS. 9A and 9B illustrate a process of the third forging step S3. FIG. 9A is a side view of the preform 10 being press-formed by the third die 300, and FIG. 9B is a perspective view thereof. FIGS. 10A and 10B illustrate a result of the third forging step S3. FIG. 10A is a perspective view of the preform 10 after being press-formed by the third die 300, and FIG. 10B is a cross-sectional view.

[0076] As shown in FIGS. 8A, 8B, 9A, 9B, 10A, and 10B, in the third forging step S3, one side of the preform 10 can be press-formed by the third die 300. As a result, a second protrusion 12 can be formed in the central region of one side of the preform 10. Here, the outer diameter of the third die 300 may be smaller than the outer diameter of the second die 200, and its central portion may be hollow and penetrated therethrough. That is, the third die 300 may be formed in an annular shape. The inner diameter of the third die 300 may be equal to the inner diameter of the second die 200, which will be described in connection with the fourth forging step S4.

[0077] FIGS. 11A and 11B illustrate a process of the fourth forging step S4. FIG. 11A is a side view of the preform 10 being press-formed by the second die 200, and FIG. 11B is a perspective view thereof. FIGS. 12A and 12B illustrate a result of the fourth forging step S4. FIG. 12A is a perspective view of the preform 10 after being press-formed by the second die 200, and FIG. 12B is a cross-sectional view.

[0078] As shown in FIGS. 10A, 10B, 11A, 11B, 12A, and 12B, in the fourth forging step S4, a peripheral region of one side of the preform 10 can be press-formed by the second die 200 while maintaining the second protrusion 12. The region press-formed in the fourth forging step S4 may include the region press-formed in the third forging step S3 and may be larger.

[0079] Further, the inner diameter of the third die 300 may be formed equal to that of the second die 200. In the fourth forging step S4, to prevent the central hollow portion of the second die 200 from affecting the second protrusion 12, the inner diameter of the second die 200 may be equal to or greater than the inner diameter of the third die 300.

[0080] After the fourth forging step S4, a third protrusion 13 can be formed on a peripheral region of the opposite side of the preform 10. Referring again to FIGS. 15 to 17, the third protrusion 13 may protrude by the amount of the second concave portion 502. Further, the diameter of the third protrusion 13 may be larger than the diameter of the fourth protrusion 14.

[0081] FIGS. 13A and 13B illustrate a process of the fifth forging step S5. FIG. 13A is a side view of the preform 10 being press-formed by the fourth die 400, and FIG. 13B is a perspective view thereof. FIGS. 14A and 14B illustrate a result of the fifth forging step S5. FIG. 14A is a perspective view of the preform 10 after being press-formed by the fourth die 400, and FIG. 14B is a cross-sectional view.

[0082] Referring again to FIGS. 5A to 17, in the fifth forging step S5, an edge region of one side of the preform 10 can be press-formed by the fourth die 400. The outer diameter of the fourth die 400 may be larger than the outer diameters of the first die 100, the second die 200, and the third die 300, and the central portion of the fourth die 400 may be hollow and penetrated therethrough. The inner diameter of the fourth die 400 may be larger than the outer diameters of the first die 100 and the third die 300 and smaller than the outer diameter of the second die 200. Through the fifth forging step S5, a fourth protrusion 14 can be formed surrounding the second protrusion 12, with a height lower than that of the second protrusion 12 to provide a step d2.

[0083] The preform 20 produced through the progressive regional forging method 1 is shown in FIG. 17. Referring to the structure of the preform 20, the first protrusion 11 and the second protrusion 12 may be formed symmetrically with respect to the centerline C-C′ of the preform 20. Likewise, the third protrusion 13 and the fourth protrusion 14 may also be symmetrical with respect to the centerline C-C′. It is preferable that such symmetry be considered in proportion, as dimensions may vary.

[0084] FIG. 18 illustrates a turbine disk T obtained by machining the preform 20 shown in FIG. 17. In FIG. 18, the turbine disk T is formed by cutting and machining the outer surface of the preform 20, and the dimensional difference between the preform 20 of FIG. 17 and the turbine disk T of FIG. 18 is minimal. The preform 20 is formed of a superalloy material and constitutes a turbine disk T for a gas turbine, wherein the turbine disk T may have a diameter ranging from 1600 mm to 1800 mm.

[0085] FIGS. 19A and 19B illustrate a graph analyzing the flow stress according to temperature and strain rate, for calculating cross-sectional areas of the plurality of dies 100, 200, 300, 400 used in the progressive regional forging method 1.

[0086] Referring to FIGS. 2 to 19, according to the progressive regional forging method 1, the preform 10 can be press-formed such that a plurality of steps d1, d2 are formed, by gradually increasing the press-formed area in a radial direction from the center of the preform 10.

[0087] The flat die P, the first die 100, the second die 200, the third die 300, and the fourth die 400 used for press forming are pressed by a press, wherein the press may have a load capacity set in the range of 160 MN to 180 MN. In addition, edges of the first die 100, the second die 200, the third die 300, and the fourth die 400 that contact the preform 10 may be chamfered or rounded to prevent stress concentration.

[0088] In the upsetting step U, the billet B may be heated to a temperature in the range of 1000° C. to 1100° C. prior to being compressed by the press. After the upsetting step U and before the first forging step S1, the preform 10 may be reheated to a temperature in the range of 1000° C. to 1100° C. After the second forging step S2 and before the third forging step S3, the preform 10 may also be reheated to a temperature in the range of 1000° C. to 1100° C.

[0089] The time required for each step of the progressive regional forging method 1 is approximately as follows: the upsetting step U takes about 58 seconds; the first forging step S1 takes about 7.7 seconds; the second forging step S2 takes about 5.6 seconds; the third forging step S3 takes about 4.1 seconds; the fourth forging step S4 takes about 3.3 seconds; and the fifth forging step S5 takes about 4.4 seconds.

[0090] The cross-sectional areas of the first die 100, the second die 200, the third die 300, and the fourth die 400 may be calculated and determined based on at least one of the press load capacity, the material type of the preform 10, and the flow stress according to the heating temperature. Here, the cross-sectional areas of the first die 100, the second die 200, the third die 300, and the fourth die 400 refer to the areas of horizontally cut surfaces that contact the preform 10.

[0091] The cross-sectional areas of the first die 100, the second die 200, the third die 300, and the fourth die 400 may be set to values obtained by dividing a maximum load capacity of the press by a strain rate and the flow stress. In addition, an inner diameter of any one of the first die 100, the second die 200, the third die 300, and the fourth die 400 may be set smaller than the maximum outer diameter of the preceding die so that the forged regions overlap.

[0092] The cross-sectional areas of the plurality of dies 100, 200, 300, 400 used in the progressive regional forging method 1 may be calculated by analyzing the flow stress of the material according to temperature and strain rate. Referring to the graphs of FIGS. 19A and 19B, when forging an IN706 superalloy material with a press having a load capacity of 170 MN, the maximum allowable cross-sectional area can be calculated to be approximately 1.06 m2.

[0093] Specifically, at a forging temperature of 1000° C., the flow stress of the IN706 material according to strain rate is shown in the graph of FIGS. 19A and 19B. FIG. 19A indicates that, at a forging temperature of 1000° C. and a strain rate of 0.01 / sec, the flow stress is calculated to be 150 MPa. FIG. 19B indicates that, at a forging temperature of 1000° C. and a strain rate of 0.1 / sec, the flow stress is calculated to be 240 MPa.

[0094] Based on a press having a load capacity of 170 MN, the initial strain rate of IN706 is calculated to be 0.011 / sec. When the press speed is set to 17 mm / sec and the initial upsetting height is set to 1,500 mm, the strain rate is calculated to be 0.011 / sec. Referring to the graph of FIGS. 19A and 19B, the flow stress corresponding to a strain rate of 0.011 / sec is approximately 160 MPa.

[0095] Therefore, according to the pressure equation, the calculation is established as: 170 MN / Area=160 MPa (160 N / mm2 ). Solving the equation, the cross-sectional area is calculated to be approximately 1.06 m2. Accordingly, the cross-sectional areas of the first die 100, the second die 200, the third die 300, and the fourth die 400 may each be set to be equal to or less than approximately 1.06 m2. In other words, the cross-sectional areas of the plurality of dies 100, 200, 300, 400 may be determined by taking into account the load capacity of the press and the flow stress of the material.

[0096] Accordingly, according to the progressive regional forging method 1 of an embodiment of the present disclosure, the specifications of a plurality of dies 100, 200, 300, 400 can be determined by calculating the depressible cross-sectional area based on the press load capacity, which is limited within a range of 160 MN to 180 MN, and the flow stress of the superalloy material. The cross-sectional areas of the plurality of dies 100, 200, 300, 400 in contact with the preform 10 may be set to be equal to or less than a predetermined area. Accordingly, even with a press having a limited load capacity, a forged product having a target shape made of a superalloy material can be produced.

[0097] Furthermore, by using the plurality of dies 100, 200, 300, 400 in combination with free forging and hot forging, and progressively depressing the preform 10 from the central portion toward the peripheral portion in increments of partial areas, uniform forging and stable flow stress of the superalloy material can be ensured.

[0098] Moreover, even when the forging is carried out through a plurality of forging steps S1, S2, S3, S4, S5 using a press with a relatively low load capacity, the forged product 20 can satisfy the required quality characteristics. The required quality characteristics refer to effective strain, flow stress, and deformation amount of the forged product 20 that meet predetermined standards. Accordingly, high-quality medium to large turbine disks made of a superalloy can be manufactured using a press with a relatively low load capacity.

[0099] In addition, the processing time for each forging step S1, S2, S3, S4, S5 can be minimized to less than one minute, thereby reducing production costs and shortening the manufacturing period of the forged product 20.

[0100] The present disclosure is not limited to the above-described specific embodiments and descriptions, and various modifications may be made by those skilled in the art without departing from the gist of the present disclosure claimed in the claims. Such variations are within the protection scope of the present disclosure.REFERENCE NUMERALS1: progressive area forging method

[0102] U: upsetting step

[0103] P: flat die

[0104] F: flat bed

[0105] B: billet

[0106] S1: first forging step

[0107] S2: second forging step

[0108] S3: third forging step

[0109] S4: fourth forging step

[0110] S5: fifth forging step

[0111] 10: preform

[0112] 11: first protrusion

[0113] 12: second protrusion

[0114] 13: third protrusion

[0115] 14: fourth protrusion

[0116] 20: formed product

[0117] 100: first die

[0118] 200: second die

[0119] 300: third die

[0120] 400: fourth die

[0121] 500: concave bed

[0122] 501: first concave portion

[0123] 502: second concave portion

[0124] d1: high step

[0125] d2: low step

[0126] T: turbine disk

Examples

Embodiment Construction

[0057]Hereinafter, a preferrable embodiment with respect to a progressive area forging method according to the present disclosure will be described with reference to accompanying drawings.

[0058]Further, terms described below are defined in consideration of the functions of one or more exemplary embodiments, and may have different meanings according to the intention of a user or operator or the convention. Furthermore, the exemplary embodiments described below are not intended to limit the scope of the present disclosure but merely to exemplify configurational elements defined in the claims.

[0059]In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification. Throughout the specification, when a certain portion “includes” or “comprises” a certain component, this indicates that other components are not excluded and may be further included unless otherwise no...

Claims

1. A progressive area forging method comprising:a first forging step of press-forming a central region of one surface of a preform placed on a concave bed using a first die, such that a first protrusion is formed on a central region of an opposite surface of the preform; anda second forging step of press-forming a peripheral region of the one surface of the press-formed preform using a second die, such that the one surface of the preform is formed to be flat.

2. The progressive area forging method according to claim 1, further comprising:a third forging step of press-forming the one surface of the preform using a third die, such that a second protrusion is formed in a central region of the one surface of the preform.

3. The progressive area forging method according to claim 2, further comprising:a fourth forging step of press-forming a peripheral region of the one surface of the preform using the second die while maintaining the second protrusion, such that a third protrusion is formed in a peripheral region of the opposite surface of the preform.

4. The progressive area forging method according to claim 3, further comprising:a fifth forging step of press-forming an edge region of the one surface of the preform using a fourth die, such that a fourth protrusion is formed to surround the second protrusion and to have a lower height than the second protrusion.

5. The progressive area forging method according to claim 1,wherein the first die has a cylindrical shape, and the concave bed includes a first concave portion and a second concave portion, andwherein the first concave portion is formed at a central portion of the concave bed to be recessed in a pressing direction by at least a bottom area of the first die, and the second concave portion is formed around the first concave portion to be recessed to a shallower depth than the first concave portion.

6. The progressive area forging method according to claim 5,wherein in the first forging step, the first protrusion is formed to protrude by a volume corresponding to a space of the first concave portion.

7. The progressive area forging method according to claim 5,wherein an outer diameter of the second die is larger than an outer diameter of the first die, a central portion of the second die is hollow and penetrated therethrough, andwherein an inner diameter of the second die is equal to or smaller than a diameter of the first concave portion and is concentrically aligned therewith.

8. The progressive area forging method according to claim 2,wherein an outer diameter of the third die is smaller than the outer diameter of the second die, a central portion of the third die is hollow and penetrated therethrough, andwherein an inner diameter of the third die is formed to be identical to the inner diameter of the second die.

9. The progressive area forging method according to claim 3,wherein in the fourth forging step, a press-formed region includes a region press-formed in the third forging step and is larger than the region press-formed in the third forging step.

10. The progressive area forging method according to claim 4,wherein in the fourth forging step, the third protrusion is formed to protrude by a volume corresponding to a space of the second concave portion, andwherein a diameter of the third protrusion is larger than a diameter of the fourth protrusion.

11. The progressive area forging method according to claim 4,wherein an outer diameter of the fourth die is larger than the outer diameters of the first die, the second die, and the third die, a central portion of the fourth die is hollow and penetrated therethrough, andwherein an inner diameter of the fourth die is larger than the outer diameters of the first die and the third die and smaller than the outer diameter of the second die.

12. The progressive area forging method according to claim 4, further comprising:prior to the first forging step, an upsetting step of compressing a billet placed on a flat bed by a press to form the billet into the preform.

13. The progressive area forging method according to claim 12,wherein the first die, the second die, the third die, and the fourth die are pressed by the press, and a load capacity of the press is set to 160 MN to 180 MN.

14. The progressive area forging method according to claim 12,wherein in the upsetting step, the billet is heated to 1000° C. to 1100° C. before being compressed by the press, the preform is reheated to 1000° C. to 1100° C. after the upsetting step and before the first forging step, and the preform is reheated to 1000° C. to 1100° C. after the second forging step and before the third forging step.

15. The progressive area forging method according to claim 4,wherein a formed product manufactured through the first forging step to the fifth forging step is a turbine disk of a gas turbine formed of a superalloy material, and the turbine disk is formed to have a diameter of 1600 mm to 1800 mm.

16. The progressive area forging method according to claim 4,wherein the first die, the second die, the third die, and the fourth die have chamfered or rounded edge portions that contact the preform, thereby preventing stress concentration.

17. The progressive area forging method according to claim 4,wherein the first protrusion and the second protrusion are symmetrical with respect to a center line of the formed product, and the third protrusion and the fourth protrusion are also symmetrical with respect to the center line of the formed product.

18. The progressive area forging method according to claim 12,wherein cross-sectional areas of the first die, the second die, the third die, and the fourth die are calculated and set based on at least one of a load capacity of the press, a type of the preform material, and a flow stress according to a heating temperature.

19. The progressive area forging method according to claim 18,wherein the cross-sectional areas of the first die, the second die, the third die, and the fourth die are set to a value obtained by dividing a maximum load capacity of the press by a strain rate and the flow stress.

20. The progressive area forging method according to claim 4,wherein an inner diameter of any one of the first die, the second die, the third die, and the fourth die is set to be smaller than a maximum outer diameter of a previous die, such that press-formed regions overlap each other.

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