Specification
Title of invention: Method of manufacturing forged crankshaft
Technical field
[0001]
　The present invention relates to a method for manufacturing a crankshaft by hot forging.
Background technology
[0002]
　In a reciprocating engine of an automobile, a motorcycle, an agricultural machine, a ship, or the like, a crankshaft is indispensable for converting reciprocating motion of a piston into rotary motion and extracting power. The crankshaft can be manufactured by die forging or casting. In particular, when high strength and high rigidity are required for the crankshaft, a crankshaft manufactured by die forging (hereinafter, also referred to as “forged crankshaft”) is often used.
[0003]
　1A and 1B are schematic views showing an example of the overall shape of a general forged crankshaft. Of these drawings, FIG. 1A is an overall view and FIG. 1B is a cross-sectional view taken along the line IB-IB of FIG. 1A. In the example shown in FIG. 1B, typically, one crank arm portion A7, a counter weight portion W7 integrated with the crank arm portion A7, a pin portion P4 and a journal portion J4 connected to the crank arm portion A7 are shown.
[0004]
　The forged crankshaft 11 shown in FIGS. 1A and 1B is a four-cylinder-8-piece counterweight forged crankshaft mounted on a four-cylinder engine. The forged crankshaft 11 includes five journal parts J1 to J5, four pin parts P1 to P4, a front part Fr, a flange part Fl, and eight crank arm parts (hereinafter also referred to as “arm parts”). A1 to A8. The arm portions A1 to A8 connect the journal portions J1 to J5 and the pin portions P1 to P4, respectively. The eight (all) arm portions A1 to A8 are integrally provided with counterweight portions (hereinafter, also referred to as “weight portions”) W1 to W8. A front portion Fr is provided at the front end of the forged crankshaft 11 in the axial direction, and a flange portion Fl is provided at the rear end. The front portion Fr is connected to the leading first journal portion J1 and the flange portion Fl is connected to the trailing fifth journal portion J5.
[0005]
　Hereinafter, when the journal portions J1 to J5, the pin portions P1 to P4, the arm portions A1 to A8, and the weight portions W1 to W8 are collectively referred to, the reference numerals are "J" for the journal portion and "P" for the pin portion. , "A" for the arm and "W" for the weight. Further, the arm portion A and the weight portion W integrated with the arm portion A are collectively referred to as “web”.
[0006]
　As shown in FIG. 1B, the width Bw of the weight portion W is larger than the width Ba of the arm portion A. Therefore, the weight portion W largely projects from the center surface of the arm portion (the surface including the central axis of the pin portion P and the central axis of the journal portion J).
[0007]
　When manufacturing a forged crankshaft having such a shape, a billet is generally used as a starting material. The cross section perpendicular to the longitudinal direction of the billet, ie the cross section, is round or prismatic. The area of ​​its cross section is constant over the entire length of the billet. In the present specification, the “transverse cross section” means a cross section perpendicular to the longitudinal direction of the billet or each rough land described later or the axial direction of the forged crankshaft. "Longitudinal section" means a section parallel to its longitudinal direction or its axial direction. In addition, the area of ​​the cross section is also simply referred to as "cross-sectional area". The forged crankshaft is manufactured by sequentially performing a preforming step, a die forging step, and a deburring step. If necessary, a shaping process is performed after the deburring process. Usually, the preforming step includes roll forming and bending. The die forging step includes each step of roughing and finishing.
[0008]
　2A to 2F are schematic views for explaining a manufacturing process of a conventional general forged crankshaft. Of these figures, FIG. 2A shows a billet. FIG. 2B shows a roll wasteland. FIG. 2C shows a bent wasteland. FIG. 2D shows a rough forged material. FIG. 2E shows a finish forging. FIG. 2F shows a forged crankshaft. 2A to 2F show a series of steps for manufacturing the forged crankshaft 11 having the shape shown in FIGS. 1A and 1B.
[0009]
　A method for manufacturing the forged crankshaft 11 will be described with reference to FIGS. 2A to 2F. First, a billet 12 having a predetermined length as shown in FIG. 2A is heated by a heating furnace, and then roll forming and bending are performed in that order in a preforming step. In roll forming, the billet 12 is rolled and squeezed using, for example, a hole-type roll. Thereby, the volume of the billet 12 is distributed in the axial direction, and the roll waste 13 which is an intermediate material is obtained (see FIG. 2B). Next, in bending, the roll waste 13 is partially pressed down from the direction perpendicular to the axial direction. Thereby, the volume of the roll waste 13 is distributed, and the bending waste 14 which is a further intermediate material is obtained (see FIG. 2C).
[0010]
　Subsequently, in the roughing step, the rough forged material 15 is obtained by forging the bending waste 14 up and down using a pair of dies (see FIG. 2D). The rough forged material 15 has a rough shape of a forged crankshaft (final product). Further, in the finish forging step, the rough forged material 15 is forged by using a pair of dies up and down to obtain a finished forged material 16 (see FIG. 2E). The finish forging 16 has a shape that matches the forged crankshaft of the final product. During the roughing and finishing, the surplus material flows out between the mold splitting surfaces of the dies facing each other, and the surplus material becomes the burr B. Therefore, both the rough forged material 15 and the finish forged material 16 have large burrs B around them.
[0011]
　In the deburring step, for example, the burr B is punched out by the blade die while the finish forging material 16 with the burr is sandwiched and held by the pair of dies. As a result, the burr B is removed from the finish forged material 16 and a burr-free forged material is obtained. The burr-free forged material has substantially the same shape as the forged crankshaft 11 shown in FIG. 2F.
[0012]
　In the shaping step, the key points of the burr-free forging material are slightly pressed down from above and below by a die to correct the burr-free forging material into the final product dimension and shape. Here, the important points of the burr-free forged material are, for example, the shaft portion such as the journal portion J, the pin portion P, the front portion Fr, the flange portion Fl, and the arm portion A and the weight portion W. In this way, the forged crankshaft 11 is manufactured.
[0013]
　The manufacturing process shown in FIGS. 2A to 2F can be applied not only to the forged crankshaft of the 4-cylinder-8-piece counterweight shown in FIGS. 1A and 1B, but also to various forged crankshafts. For example, it can be applied to a forged crankshaft with four cylinders and four counter weights.
[0014]
　In the case of a forged crankshaft with four cylinders and four counter weights, some of the eight arm sections A1 to A8 are integrally provided with a weight section W. For example, the first arm portion A1 at the head, the eighth arm portion A8 at the tail and the two central arm portions (the fourth arm portion A4 and the fifth arm portion A5) integrally have the weight portion W. The remaining arm portions, specifically, the second, third, sixth, and seventh arm portions (A2, A3, A6, and A7) do not include weight portions, and their shapes are oval. Become.
[0015]
　In addition, the manufacturing process is the same for a forged crankshaft mounted on a 3-cylinder engine, an in-line 6-cylinder engine, a V-type 6-cylinder engine, an 8-cylinder engine, or the like. If the arrangement angle of the pin portion needs to be adjusted, a twisting step is added after the deburring step.
[0016]
　The main purpose of the preforming process is to distribute the billet volume. By distributing the volume of the billet in the preforming step, it is possible to reduce the formation of burrs in the die forging step which is a post step and improve the material yield. Here, the material yield means the ratio (percentage) of the volume of the forged crankshaft (final product) to the volume of the billet.
[0017]
　In addition, the rough land obtained by the preforming is formed into a forged crankshaft in a die forging process which is a post process. In order to obtain a precisely shaped forged crankshaft, it is necessary to form a precisely shaped waste land in the preforming process.
[0018]
　Techniques for manufacturing a forged crankshaft are disclosed in, for example, Japanese Patent Laid-Open No. 2001-105087 (Patent Document 1), Japanese Patent Laid-Open No. 2-255240 (Patent Document 2), and Japanese Patent Laid-Open No. 62-244545 (Patent Document 3). And JP-A-59-45051 (Patent Document 4). Patent Document 1 discloses a preforming method using a pair of an upper mold and a lower mold. In the preforming method, when the rod-shaped workpiece is pressed by the upper die and the lower die, a part of the workpiece is extended and a portion continuous with the part is offset with respect to the axial center. As a result, in Patent Document 1, since the elongation and the bending can be performed at the same time, the facility investment can be reduced.
[0019]
　The preforming method of Patent Document 2 uses 4-pass high-speed roll equipment instead of the conventional 2-pass roll forming. In the preforming method, the cross-section area of ​​the roll waste is determined according to the distribution of the cross-section areas of the weight portion, arm portion and journal portion of the forged crankshaft (final product). As a result, in Patent Document 2, the material yield can be improved.
[0020]
　In the preforming method of Patent Document 3, a part of the volume of the billet is distributed in the axial direction and the radial direction of the billet by rolling. A forged crankshaft is obtained by die forging the volume-distributed billet. Thereby, in Patent Document 3, the material yield can be improved.
[0021]
　In the manufacturing method of Patent Document 4, the billet is formed into a forged crankshaft by one-time die forging using a pair of an upper die, a lower die and a punch. In the die forging step, first, the region of the billet, which becomes the journal part, and the region of the pin part, are pressed down by a punch that operates separately. The volume of the billet is distributed by the reduction. After that, die forging is performed by the upper die and the lower die. That is, preforming and die forging can be performed in one step. As a result, Patent Document 4 states that a forged crankshaft having a complicated shape can be efficiently manufactured with a single facility.
Prior art documents
Patent literature
[0022]
Patent Document 1: Japanese Patent Laid-Open No. 2001-105087
Patent Document 2: Japanese Patent Laid-Open No. 2-255240 Japanese Patent
Document 3: Japanese Patent Laid-Open No. 62-244545 Japanese
Patent Document 4: Japanese Patent Laid-Open No. 59-45051
Summary of the invention
Problems to be Solved by the Invention
[0023]
　In the manufacture of forged crankshafts, it is desired to reduce the formation of burrs and improve the material yield as described above. In addition, it is desired to form a precisely shaped waste land in the preforming step. In the preforming method described in Patent Document 1, the volume distribution and offset of the billet can be performed to some extent.
[0024]
　However, in the preforming method of Patent Document 1, the distribution of the volume of the portion serving as the weight portion and the volume of the portion serving as the arm portion integrally including the weight portion in the portion serving as the web is not considered. Therefore, in the die forging process which is a post-process, the weight portion that largely protrudes from the center surface of the arm portion has insufficient material filling, and is likely to have a thin wall. In order to prevent the lack of thickness of the weight portion, it is convenient to increase the surplus volume in the wasteland. However, in this case, the material yield is reduced. Below, the part which becomes a weight part is also called a "weight equivalent part." A portion that is an arm portion (excluding the weight portion) integrally including the weight portion is also referred to as an “arm equivalent portion”. The weight-equivalent part and the arm-equivalent part are collectively referred to as “web-equivalent part”.
[0025]
　In the preforming method of Patent Document 2, it is not possible to perform volume distribution between the weight equivalent part and the arm equivalent part in the web equivalent part. This is because roll forming is used. Therefore, in the die forging step which is a post-step, the material of the weight portion is insufficiently filled. As a result, lack of meat is likely to occur.
[0026]
　The preforming method of Patent Document 3 requires equipment for rolling. Therefore, the equipment cost is high and it is difficult to improve the production efficiency.
[0027]
　In the manufacturing method of Patent Document 4, since the preforming and die forging are performed by a single facility, the preforming that significantly deforms the billet cannot be performed. Therefore, it is difficult to improve the material yield with the manufacturing method of Patent Document 4.
[0028]
　An object of the present invention is to provide a method for manufacturing a forged crankshaft that can form a forged crankshaft with a precise shape and that can improve the material yield.
Means for solving the problem
[0029]
　The manufacturing method of the forged crankshaft of the present embodiment includes a plurality of journal portions that are rotation centers, a plurality of pin portions that are eccentric with respect to the journal portions, and a plurality of crank arm portions that connect the journal portions and the pin portions. It is a manufacturing method of a forged crankshaft provided.
[0030]
　The method for manufacturing a forged crankshaft according to the present embodiment includes a first preforming step for obtaining an initial wasteland from a billet, a second preforming step for obtaining a final wasteland from the initial wasteland, and a final wasteland forging by at least one die forging. A finish forging step of forming into a finish dimension of the crankshaft.
　In the first preforming step, the pin portion and the journal portion of the billet are pressed down in a direction perpendicular to the axial direction of the billet to reduce the cross-sectional area of ​​each portion and reduce Form a flat portion.
　In the second preforming step, a pair of first molds are used, and a step of reducing the width direction of the flat portion to a plurality of journal parts is performed. And a step of making the width direction of the flat portion eccentric to eccentric the portions that will become the plurality of pin portions, using two molds.
　In the final wasteland, the thickness of the portion that becomes the plurality of crank arm portions is the same as the thickness of the finish dimension.
Effect of the invention
[0031]
　In the method for manufacturing a forged crankshaft according to the embodiment of the present invention, the first preforming step and the second preforming step can provide a final wasteland in which the distribution of axial volume is promoted. Further, in the final wasteland, the volume of the portion that becomes the journal portion, the volume of the portion that becomes the pin portion, and the volume of the portion that becomes the arm portion are appropriately distributed. By the finish forging process, the shape of the forged crankshaft can be formed from the final waste land. From these, the material yield can be improved. Further, according to the present invention, it is possible to form a precisely shaped rough land by the first preforming step and the second preforming step. Therefore, a forged crankshaft having a precise shape can be formed.
Brief description of the drawings
[0032]
FIG. 1A is a schematic view showing an example of the overall shape of a general forged crankshaft.
FIG. 1B is a cross-sectional view taken along the line IB-IB of FIG. 1A.
FIG. 2A is a schematic diagram showing a billet in a conventional manufacturing process.
[FIG. 2B] FIG. 2B is a schematic view showing a roll waste in a conventional manufacturing process.
FIG. 2C is a schematic diagram showing a bent wasteland in a conventional manufacturing process.
FIG. 2D is a schematic view showing a rough forged material in a conventional manufacturing process.
FIG. 2E is a schematic diagram showing a finish forged material in a conventional manufacturing process.
FIG. 2F is a schematic diagram showing a forged crankshaft in a conventional manufacturing process.
FIG. 3A is a schematic view showing a billet in the manufacturing process example of the present embodiment.
FIG. 3B is a schematic diagram showing an initial wasteland in the manufacturing process example of the present embodiment.
FIG. 3C is a schematic diagram showing a final waste land in the example of the manufacturing process of the present embodiment.
[FIG. 3D] FIG. 3D is a schematic view showing a finish forged material in the manufacturing process example of the present embodiment.
FIG. 3E is a schematic diagram showing a forged crankshaft in the manufacturing process example of the present embodiment.
FIG. 4A is a vertical cross-sectional view schematically showing a situation before reduction in a processing flow example of a first preforming step.
[FIG. 4B] FIG. 4B is a vertical cross-sectional view schematically showing a situation at the end of reduction in the processing flow example of the first preforming step.
[FIG. 5A] FIG. 5A is a cross-sectional view showing a portion to be a journal portion before reduction in a processing flow example of a first preforming step.
[FIG. 5B] FIG. 5B is a cross-sectional view showing a portion to be a journal portion at the end of reduction in the processing flow example of the first preforming step.
FIG. 6A is a transverse cross-sectional view showing a portion to be a pin portion before reduction in a processing flow example of the first preforming step.
[FIG. 6B] FIG. 6B is a cross-sectional view showing a portion to be a pin portion at the end of reduction in the processing flow example of the first preforming step.
FIG. 7A is a transverse cross-sectional view showing an arm-corresponding portion before reduction in a processing flow example of the first preforming step.
[FIG. 7B] FIG. 7B is a cross-sectional view showing an arm-corresponding portion at the end of reduction in the processing flow example of the first preforming step.
FIG. 8 is a vertical cross-sectional view showing a case where the second preforming step is performed with one die.
FIG. 9 is a vertical cross-sectional view showing a first mold and a second mold of the present embodiment.
FIG. 10 is a vertical cross-sectional view showing a first mold and a second mold of the present embodiment different from FIG. 9.
FIG. 11A is a vertical cross-sectional view showing a situation at the start of the rolling process in the example of the processing flow of the second preforming process.
FIG. 11B is a vertical cross-sectional view showing a situation at the end of the rolling-down step in the processing flow example of the second preforming step.
FIG. 11C is a vertical cross-sectional view showing a situation at the end of the eccentric process in the processing flow example of the second preforming process.
FIG. 12A is a cross-sectional view showing a portion that will be an arm portion at the start of the rolling-down step in the processing flow example of the second preforming step.
FIG. 12B is a cross-sectional view showing a portion that will be an arm portion at the end of the rolling-down step in the processing flow example of the second preforming step.
FIG. 13A is a cross-sectional view showing a portion that will be a journal portion at the start of the rolling step in the processing flow example of the second preforming step.
[FIG. 13B] FIG. 13B is a cross-sectional view showing a portion which will be a journal portion at the end of the rolling-down step in the working flow example of the second preforming step.
FIG. 14A is a transverse cross-sectional view showing a portion that serves as a pin portion at the start of the eccentric step in the processing flow example of the second preforming step.
FIG. 14B is a transverse cross-sectional view showing a portion which will be a pin portion at the end of the eccentric process in the processing flow example of the second preforming process.
MODE FOR CARRYING OUT THE INVENTION
[0033]
　The manufacturing method of the forged crankshaft of the present embodiment includes a plurality of journal portions that are rotation centers, a plurality of pin portions that are eccentric with respect to the journal portions, and a plurality of crank arm portions that connect the journal portions and the pin portions. It is a manufacturing method of a forged crankshaft provided.
[0034]
　The method for manufacturing a forged crankshaft according to the present embodiment includes a first preforming step for obtaining an initial wasteland from a billet, a second preforming step for obtaining a final wasteland from the initial wasteland, and a final wasteland forging by at least one die forging. A finish forging step of forming into a finish dimension of the crankshaft.
　In the first preforming step, the pin portion and the journal portion of the billet are pressed down in a direction perpendicular to the axial direction of the billet to reduce the cross-sectional area of ​​each portion and reduce Form a flat portion.
　In the second preforming step, a pair of first molds are used, and a step of reducing the width direction of the flat portion to a plurality of journal parts is performed. And a step of making the width direction of the flat portion eccentric to eccentric the portions that will become the plurality of pin portions, using two molds.
　In the final wasteland, the thickness of the portion that becomes the plurality of crank arm portions is the same as the thickness of the finish dimension.
[0035]
　According to the manufacturing method of the present embodiment, it is possible to obtain the final wasteland in which the distribution of the volume in the axial direction is promoted by the first preforming step and the second preforming step. Further, the final wasteland has a shape close to the shape of the forged crankshaft because the volume of the portion that becomes the journal portion, the volume of the portion that becomes the pin portion, and the volume of the portion that becomes the arm portion are appropriately distributed. .. Then, by the finish forging step, the shape of the forged crankshaft can be formed from the final waste land. From these, the material yield can be improved.
[0036]
　Further, in the second preforming step, the second die, which is separate from the first die that presses down the portion that becomes the journal portion, decenters the portion that becomes the pin portion. If the first die is integrated with the second die, the portion that eccentrically forms the pin portion will protrude more than the portion that presses down the journal portion. Therefore, when the molding is started, only the portion to be the pin portion is eccentric, and the initial wasteland is likely to be curved. However, if the second mold moves separately from the first mold, it is possible to prevent the second mold, which eccentrically forms the pin portion, from projecting more than the portion that compresses the journal portion. Therefore, even if the molding is started, first, the part to be the journal part is pressed down, and after the part to be the journal part is pressed down, the part to be the pin part can be eccentric. Therefore, the initial wasteland is unlikely to bend during the eccentricity of the pin portion. Since the volume-distributed initial wasteland is rolled down at a predetermined position of the first mold, it is unlikely that a thin wall or the like will occur in the final wasteland after rolling down.
[0037]
　Preferably, in the second preforming step, after the reduction by the pair of first molds is completed, the eccentricity of the portions forming the plurality of pin portions by the second mold is started.
[0038]
　Preferably, the amount of eccentricity of the pin portion is equal to or smaller than the amount of eccentricity of the finished dimension.
[0039]
　Below, the manufacturing method of the forged crankshaft of this embodiment is demonstrated, referring drawings.
[0040]
1. Manufacturing Process Example
　The forged crankshaft targeted by the manufacturing method of the present embodiment has a plurality of journal portions J serving as rotation centers, a plurality of pin portions P eccentric to the journal portion J, a journal portion J and a pin portion. And a plurality of arm portions A connecting P. For example, the forged crankshaft of the 4-cylinder-8-piece counterweight shown in FIGS. 1A and 1B is an object to be manufactured. In the case of a forged crankshaft with four cylinders and eight counter weights, all of the plurality of arm portions A are integrally provided with weight portions W. The aforementioned forged crankshafts of 4 cylinders and 4 counter weights are also manufactured. In the case of a forged crankshaft with four cylinders and four counter weights, a part of the plurality of arm portions A integrally includes a weight portion W. Moreover, not all the arm portions A may include the weight portion W. The shape of the arm portion without the weight portion is an elliptical shape. In addition, that the arm portion is provided with the weight portion "integrally" means that the arm portion and the weight portion are not separate parts, but both are molded from one billet.
[0041]
　The manufacturing method of this embodiment includes a first preforming step, a second preforming step, and a finish forging step. A deburring step may be added as a step after the finish forging step. Moreover, you may add a shaping process after a deburring process as needed. When the arrangement angle of the pin portion needs to be adjusted, a twisting step may be added after the deburring step. These series of steps are carried out hot.
[0042]
　3A to 3E are schematic diagrams for explaining an example of a manufacturing process of the forged crankshaft of the present embodiment. Of these figures, FIG. 3A shows a billet. FIG. 3B shows the initial wasteland. FIG. 3C shows the final wasteland. Figure 3D shows the finish forging. FIG. 3E shows a forged crankshaft. 3A to 3E show a series of steps for manufacturing the forged crankshaft 11 having the shape shown in FIG. 1A.
[0043]
　In the first preforming step, in the billet 22 that is the material to be processed, a plurality of portions serving as pin portions (hereinafter, also referred to as “pin equivalent portions”) and a plurality of portions serving as journal portions (hereinafter referred to as “journal equivalent portions”). (Also referred to as "part"). Along with this, a plurality of flat portions 23a are formed on the billet. The flat portion 23a is formed at the position of the pin-corresponding portion and the journal-corresponding portion. As shown in FIGS. 5B and 6B described later, the flat portion 23a has a width Bf in the direction perpendicular to the rolling direction larger than the thickness ta in the rolling direction. In this way, the initial wasteland 23 in which the volume is distributed is obtained. In the first preforming step, for example, a reduce roll or a cross roll can be used. Further, the first preforming step can also be performed according to an example of a processing flow using a third mold described later.
[0044]
　The second preforming step includes a rolling down step and an eccentric step. In the rolling down step, the journal-corresponding portion of the initial waste land 23 is rolled down using the pair of first molds. In the eccentric process, after starting the reduction by the first mold, the second mold is used to eccentric the portion corresponding to the pin. In the second preforming step, the rolling direction and the eccentric direction are the width direction of the flat portion 23a. That is, in the second preforming step, the initial waste 23 obtained in the first preforming step is rotated by 90° and then rolled down. As a result, the final waste land 24 in which the approximate shape of the forged crankshaft is formed is obtained. In the final wasteland 24, the axial thickness t1 (see FIG. 3C) of the arm equivalent portion is the same as the finished thickness t0 (see FIG. 3E). The finished thickness t0 means the axial thickness of the arm portion of the forged crankshaft (final product). Further, the eccentric amount of the pin corresponding portion of the final waste land 24 is the same as or smaller than the eccentric amount of the finished dimension. The eccentricity of the finished size means the eccentricity of the pin portion of the forged crankshaft. Details of the second preforming step will be described later.
[0045]
　In the finish forging step, the final roughened land 24 is formed into the final dimension of the forged crankshaft by die forging, similarly to the above-described conventional finish forging step. Specifically, a pair of upper and lower molds is used. The final waste land 24 is arranged on the lower mold in such a posture that the corresponding pins are arranged in a horizontal plane. Then, forging is performed by lowering the upper die. Thereby, the burr B is formed along with the outflow of the surplus material, and the finish forged material 25 with the burr is obtained (see FIG. 3D). The finish forged material 25 has a shape that matches the forged crankshaft of the final product. Since the approximate shape of the forged crankshaft is formed on the final waste land 24, it is possible to minimize the formation of the burr B when the final waste land 24 is forged in the finish forging step. The finish forging step may be performed once or may be divided into a plurality of times.
[0046]
　In the deburring step, for example, the burr B is punched out by the tool die while the finishing forged material 25 with the burr is sandwiched and held by the pair of dies. Thereby, the burr B is removed from the finish forged material 25. As a result, the forged crankshaft 11 (final product) is obtained.
[0047]
2. Example of Processing Flow of First Preforming Step
　FIGS. 4A to 7B are schematic diagrams showing an example of processing flow of the first preforming step. Of these figures, FIG. 4A is a vertical cross-sectional view showing the situation before reduction, and FIG. 4B is a vertical cross-sectional view showing the situation at the end of reduction.
[0048]
　5A and 5B are cross-sectional views showing a journal-corresponding portion. Of these figures, FIG. 5A shows the situation before reduction, and FIG. 5B shows the situation at the end of reduction. 5A is a sectional view taken along the line VA-VA of FIG. 4A, and FIG. 5B is a sectional view taken along the line VB-VB of FIG. 4B.
[0049]
　6A and 6B are cross-sectional views showing a portion corresponding to the pin. Of these figures, FIG. 6A shows the situation before reduction, and FIG. 6B shows the situation at the end of reduction. 6A is a sectional view taken along the line VIA-VIA of FIG. 4A, and FIG. 6B is a sectional view taken along the line VIB-VIB of FIG. 4B.
[0050]
　7A and 7B are cross-sectional views showing the arm-corresponding portion. Of these figures, FIG. 7A shows the situation before reduction, and FIG. 7B shows the situation at the end of reduction. 7A is a VIIA-VIIA sectional view of FIG. 4A, and FIG. 7B is a VIIB-VIIB sectional view of FIG. 4B.
[0051]
　4A to 7B show a billet 22 having a round cross section and a pair of upper and lower third molds 30. The third mold 30 includes a third upper mold 31 and a third lower mold 32. In order to facilitate understanding of the situation, in FIG. 5B, FIG. 6B, and FIG. 7B, the third upper mold 31, the third lower mold 32, and the billet 22 before reduction are also shown by a chain double-dashed line, and The shaft center position C is shown by a black circle. The pair of third molds 30 includes a pin processing portion that abuts the pin corresponding portion and a journal processing portion that abuts the journal corresponding portion.
[0052]
　As shown by the thick line in FIG. 5A, the journal processing section includes an upper mold journal processing section 31a and a lower mold journal processing section 32a. The upper die journal processing section 31 a is provided on the third upper die 31. The lower die journal processing section 32 a is provided on the third lower die 32. The upper mold journal processing portion 31a has a concave shape and can accommodate a billet. The lower mold journal processing portion 32a is provided on the tip surface of the convex portion. It should be noted that there is no particular limitation as to which of the upper mold journal processing portion 31a and the lower mold journal processing portion 32a has a concave shape. That is, the lower mold journal processing portion 32a may be concave so as to accommodate the billet.
[0053]
　As shown by the thick line in FIG. 6A, the pin processing portion includes an upper die processing portion 31b and a lower die processing portion 32b. The upper die pin processing portion 31b is provided on the third upper die 31. The lower die pin processing portion 32b is provided on the third lower die 32. The upper die pin processing portion 31b has a concave shape and can accommodate a billet. The lower die pin processing portion 32b is provided on the tip surface of the convex portion. It should be noted that there is no particular limitation as to which of the upper die pin machining portion 31b and the lower die pin machining portion 32b is concave. That is, the lower die pin processing portion 32b may be concave so as to accommodate the billet.
[0054]
　In the first preforming step, as shown in FIG. 4A, the billet 22 is moved to the third upper mold 31 while the third upper mold 31 is raised to separate the third upper mold 31 and the third lower mold 32 from each other. It is arranged between the third lower molds 32. When the third upper die 31 is lowered from this state, the pin-corresponding portion of the billet 22 is accommodated in the concave upper die-pin machining portion 31b (see FIG. 6A), and the journal-corresponding portion is concave upper-journal machining portion. 31a (see FIG. 5A). When the third upper die 31 is further lowered, the billet is pressed by the upper die pin processing portion 31b and the lower die pin processing portion 32b, and the upper die journal processing portion 31a and the lower die journal processing portion 32a. The cross-sectional area is reduced. As a result, the flat portion 23a as shown in FIGS. 5B and 6B is formed. In the cross section of the flat portion 23a, the width Bf is larger than the thickness ta (see FIGS. 5B and 6B). The width Bf and the thickness ta of the flat portion 23a may be different between the journal-corresponding portion and the pin-corresponding portion. After the completion of the reduction by the third mold 30, the third upper mold 31 is lifted and the processed billet 22 (initial waste land 23) is taken out.
[0055]
　If such a processing flow example is adopted, the material moves in the axial direction of the billet as the pin-corresponding portion and the journal-corresponding portion are pressed down. As a result, the material flows into the arm-corresponding portion between the pin-corresponding portion and the journal-corresponding portion. As a result, it is possible to obtain an initial wasteland having a volume distributed in the axial direction.
[0056]
　Further, according to the processing flow example shown in FIGS. 4A to 7B, in the process of lowering the third upper mold 31, the opening of the concave upper mold pin processed portion 31b is closed by the lower mold pin processed portion 32b, A closed cross section is formed by the upper die pin machining portion 31b and the lower die pin machining portion 32b. Further, the opening of the concave upper mold journal processing portion 31a is closed by the lower mold journal processing portion 32a, and a closed cross section is formed by the upper mold journal processing portion 31a and the lower mold journal processing portion 32a. Thereby, no burr is formed between the third upper mold 31 and the third lower mold 32. Therefore, the material yield can be improved and the volume distribution in the axial direction can be promoted.
[0057]
　When a pair of third molds is used in the first preforming step, the arm-corresponding part does not have to be pressed down by the third mold from the viewpoint of promoting the distribution of the volume in the axial direction (see FIGS. 7A and 7B). .. Further, in order to adjust the shape (dimension) of the arm-corresponding portion, the arm-corresponding portion may be partially pressed down by the third mold.
[0058]
3. First Mold and Second Mold Used in Second Preforming Step In the second preforming step of the
　present embodiment, the rolling of the journal corresponding portion and the eccentricity of the pin corresponding portion are performed. The reduction of the journal-equivalent portion and the eccentricity of the pin-equivalent portion are performed by separate molds.
[0059]
　If the pressing of the journal-corresponding portion and the eccentricity of the pin-corresponding portion are carried out by one die, the following problems may occur.
[0060]
　FIG. 8 is a vertical cross-sectional view showing a case where the second preforming step is performed with one die. Referring to FIG. 8, the initial waste land 23 is arranged on the first lower mold 42 in a state where the first upper mold 41 and the first lower mold 42 are separated from each other. As described above, in the second preforming step, the pin corresponding portion is eccentric. The lower die pin machining portion 42b of the first lower die 42 for machining the pin corresponding portion of the initial waste land 23 projects more than the lower die journal machining portion 42a. Therefore, when the initial waste land 23 is arranged on the first lower die 42, the initial waste land 23 is supported at two points by the two lower die pinning portions 42b. Further, the upper die pin machining portion 41b of the first upper die 41 is arranged closer to the end portion side of the initial waste land 23 than the lower die pin machining portion 42b. In this state, when the first mold 40 rolls down the initial waste land 23, a load is applied to the initial waste land 23 with the lower die pin machining portion 42b as a fulcrum and the upper die pin machining portion 41b as a force point. As a result, a bending moment acts on the initial wasteland 23. If the bending moment acting on the initial wasteland 23 is excessively large, the initial wasteland 23 will bend. When the first upper die 41 reaches the bottom dead center in the state where the initial waste land 23 is curved, the position of the initial waste land 23 where the first die 40 is pressed is displaced from the planned position. That is, a situation may occur in which the pin processing portion of the first mold 40 rolls down the arm-corresponding portion of the initial waste land 23. As a result, flesh and the like may occur in the final wasteland after reduction. In order to prevent this, two molds are used in the second preforming step of this embodiment.
[0061]
　FIG. 9 is a vertical cross-sectional view showing the first mold and the second mold of this embodiment. With reference to FIG. 9, the manufacturing apparatus of the present embodiment includes a first mold 40 and a second mold 50. The second mold 50 includes a second upper mold 51 and a second lower mold 52. In the case of a forged crankshaft of a four-cylinder engine, the second mold 50 includes two second upper molds 51 and two second lower molds 52. The second upper mold 51 and the second lower mold 52 can be raised and lowered independently of the first mold 40. Before the reduction of the initial waste land 23, the second lower mold 52 is arranged at the same height as or below the lower journal processing section 42a, and the second upper mold 51 is arranged at the same height as or above the upper journal processing section 41a. Has been done. That is, the second lower mold 52 and the second upper mold 51 do not project beyond the lower mold journal processing portion 42a and the upper mold journal processing portion 41a. Therefore, even if the initial waste land 23 is arranged on the first lower die 42 before the reduction is started, the initial waste land 23 is not supported by the second lower die 52. The initial waste land 23 is supported by a plurality of lower mold journal processing portions 42a. The area where the plurality of lower die journal processing portions 42a support the initial wasteland 23 is larger than the area where the second lower die 52 supports the initial wasteland. The same applies to the first upper mold 41 and the second upper mold 51. In this state, when the first mold 40 rolls down the initial wasteland 23, the journal-equivalent portion is evenly rolled down. That is, it is difficult for the load to be applied to the pin-corresponding portion of the initial waste land 23. Therefore, the bending moment is unlikely to act on the initial wasteland 23.
[0062]
　Further, after the reduction of the initial rough land 23 by the lower journal processing portion 42a of the first mold 40, the eccentricity of the pin corresponding portion of the initial rough land 23 by the second lower mold 52 of the second mold 50 is started. After the start of the reduction of the initial rough land 23 by the upper mold journal processing portion 41a of the first mold 40, the eccentricity of the pin corresponding portion of the initial rough ground 23 by the second upper mold 51 of the second mold 50 is started. Therefore, the eccentric portion of the pin-corresponding portion is pressed down by the upper die journal machining portion 41a and the lower die journal machining portion 42a. That is, the journal-corresponding portion of the initial waste land 23 is constrained by the upper die journal machining section 41a and the lower die journal machining section 42a. Therefore, the initial wasteland 23 is difficult to move during the eccentricity of the pin-corresponding portion, and is pressed down at a predetermined position.
[0063]
　In short, the second upper mold 51 and the second lower mold 52 are independently moved up and down, and the journal-corresponding portion of the initial wasteland 23 is pressed down prior to the pin-corresponding portion. It is difficult for the initial wasteland 23 to bend. Since the volume-distributed initial rough land 23 is rolled down at a predetermined position of the first mold 40, it is less likely that a thin wall or the like will occur in the final rough land after rolling down.
[0064]
　The configurations of the first mold 40 and the second mold 50 will be described. The second mold 50 includes a control mechanism for moving up and down the second upper mold 51 and the second lower mold 52 independently. The control mechanism is, for example, a die cushion or a hydraulic cylinder.
[0065]
　A case where the control mechanism is the die cushion 81 will be described with reference to FIG. 9. The first lower mold 42 is supported by the bolster base 82 via the die cushion 81. The die cushion 81 has a cushioning function. The second lower mold 52 is supported by the bolster base 82 via the pin base 83. When the first lower mold 42 starts to roll down the initial waste 23, the buffer function of the die cushion 81 causes the second lower mold 52 to start protruding from the first lower mold 42. The die cushion 81 is set so that the second lower mold 52 contacts the pin corresponding part of the initial waste land 23 after the upper mold journal processing part 41a and the lower mold journal processing part 42a contact the journal corresponding part of the initial waste land 23. To be done. The same applies to the first upper mold 41 and the second upper mold 51. As a result, the pin-corresponding portion of the initial waste land 23 is eccentric after the start of rolling down the journal-corresponding portion.
[0066]
　FIG. 10 is a vertical cross-sectional view showing a first mold and a second mold of this embodiment, which are different from FIG. A case where the control mechanism is the hydraulic cylinder 84 will be described with reference to FIG. 10. The hydraulic cylinder 84 can raise and lower the second lower mold 52. The second lower mold 52 is supported by the bolster base 82 via a hydraulic cylinder 84. When the first lower mold 42 begins to roll down the initial waste 23, the hydraulic cylinder 84 operates and the second lower mold 52 begins to project from the first lower mold 42. The hydraulic cylinder 84 is set so that the second lower mold 52 contacts the pin corresponding part of the initial waste land 23 after the upper mold journal processing part 41a and the lower mold journal processing part 42a contact the journal corresponding part of the initial waste land 23. To be done. The same applies to the first upper mold 41 and the second upper mold 51. As a result, the pin-corresponding portion of the initial waste land 23 is eccentric after the start of rolling down the journal-corresponding portion.
[0067]
　Regardless of whether the control mechanism is a die cushion or a hydraulic cylinder, the timing at which the second lower mold 52 projects from the first lower mold 42 is set appropriately. The same applies to the first upper mold 41 and the second upper mold 51. That is, the pin-corresponding portion may be eccentric between the start of the rolling of the journal-corresponding portion and the completion of the rolling. The pin-corresponding portion may be eccentric after completion of the reduction of the journal-corresponding portion.
[0068]
　By performing the eccentricity of the pin-corresponding portion in the second preforming step instead of the first preforming step, the following advantages can be obtained. In the first preforming step, the cross-sectional area of ​​the billet corresponding to the pin is reduced. That is, the cross-sectional area of ​​the pin corresponding part of the initial waste land 23 is smaller than the cross-sectional area of ​​the pin corresponding part of the billet. Therefore, when the pin corresponding part of the initial waste land 23 is eccentric, the cross-sectional area of ​​the pin corresponding part after eccentricity is smaller and the surplus material is smaller than when the pin corresponding part of the billet is eccentric. If the surplus material is small, the amount of burrs after the finishing forging process in the post process is small and the yield is good. Therefore, in the manufacturing method of the present embodiment, in order to improve the yield, the eccentricity of the pin corresponding portion is performed in the second preforming step.
[0069]
4. Example of Processing Flow of Second Preforming Step
　FIGS. 11A to 14B are schematic diagrams showing an example of processing flow of the second preforming step. Of these drawings, FIG. 11A is a vertical cross-sectional view showing the situation at the start of the rolling-down process, FIG. 11B is a vertical cross-sectional view showing the situation at the end of the rolling-down process, and FIG. 11C is the situation at the end of the eccentric process. FIG.
[0070]
　FIG. 12A and FIG. 12B are cross-sectional views showing a portion corresponding to the arm. Of these figures, FIG. 12A shows the situation at the start of the reduction process, and FIG. 12B shows the situation at the end of the reduction process. 12A is a sectional view taken along the line XIIA-XIIA of FIG. 11A, and FIG. 12B is a sectional view taken along the line XIIB-XIIB of FIG. 11C.
[0071]
　13A and 13B are cross-sectional views showing a journal-corresponding portion. Of these figures, FIG. 13A shows the situation at the start of the reduction process, and FIG. 13B shows the situation at the end of the reduction process. 13A is a sectional view taken along the line XIIIA-XIIIA of FIG. 11A, and FIG. 13B is a sectional view taken along the line XIIIB-XIIIB of FIG. 11C.
[0072]
　14A and 14B are cross-sectional views showing a portion corresponding to the pin. Of these figures, FIG. 14A shows the situation at the start of the eccentric process, and FIG. 14B shows the situation at the end of the eccentric process. 14A is a sectional view taken along the line XIVA-XIVA of FIG. 11A, and FIG. 14B is a sectional view taken along the line XIVB-XIVB of FIG. 11C.
[0073]
　11A to 13B show the initial waste land 23 obtained in the above-described first preforming step and the pair of first molds 40 in the upper and lower directions. 14A and 14B show the initial wasteland 23 and the second mold 50. The first mold 40 includes a first upper mold 41 and a first lower mold 42. In order to facilitate understanding of the situation, in FIGS. 12B and 13B, the first upper mold 41, the first lower mold 42, and the initial waste land 23 at the start of reduction are also shown by a chain double-dashed line, and the axis of the journal equivalent part is also shown. The center position C is indicated by a black circle. In FIG. 14B, the second upper die 51 and the initial waste land 23 at the start of reduction are also shown by a chain double-dashed line, and the axial center position C of the journal-corresponding portion is shown by a black circle. The pair of first molds 40 includes an upper die arm processing portion 41c and a lower die arm processing portion 42c that abut the arm corresponding portion of the initial waste land 23, and an upper die journal processing portion 41a and a lower die that abut the journal corresponding portion. The journal processing unit 42a is provided. The second mold 50 includes a second upper mold 51 and a second lower mold 52. One of the second upper molds 51 is in contact with a portion serving as the first pin portion (a portion corresponding to the first pin), and the other second upper mold 51 is a portion serving as a fourth pin portion (a portion corresponding to the fourth pin). Abut. One of the second lower molds 52 is in contact with a portion serving as a second pin portion (a portion corresponding to the second pin), and the other second lower mold 52 is a portion serving as a third pin portion (a portion corresponding to the third pin). Abut.
[0074]
　Regarding the cross-sectional shape of the arm processing portion, as shown by the thick line in FIG. 12A, the lower die arm processing portion 42c is concave. The upper die arm processing part 41c is planar. It should be noted that which of the upper die arm processing portion and the lower die arm processing portion is to be concave can be appropriately set according to the shape of the forged crankshaft.
[0075]
　When the arm portion of the forged crankshaft includes a weight portion, the lower die arm processing portion 42c has a weight processing portion 42e that comes into contact with a portion (weight equivalent portion) to be the weight portion. The weight processing portion 42e is located on the opening side of the concave lower die arm processing portion 42c. The opening width Bp of the weight processing portion 42e becomes wider as it goes away from the bottom surface of the concave lower die processing portion 42c. For example, as shown in FIG. 12A, both sides of the weight processing portion 42e are inclined surfaces.
[0076]
　In the second preforming step, as described above, the thickness of the arm-corresponding part is made equal to the thickness of the finished dimension. Therefore, the axial lengths of the upper die arm processing portion 41c and the lower die arm processing portion 42c are the same as the finished thickness of the arm portion.
[0077]
　As shown by the thick line in FIG. 13A, the journal processing section includes an upper mold journal processing section 41a and a lower mold journal processing section 42a. The upper die journal processing section 41 a is provided on the first upper die 41. The lower die journal processing section 42 a is provided on the first lower die 42. The upper mold journal processing portion 41a is concave and can accommodate the entire flat portion of the initial waste land 23. The lower mold journal processing portion 42a is provided on the tip surface of the convex portion. It should be noted that there is no particular limitation as to which of the upper die journal machining portion 41a and the lower die journal machining portion 42a is concave. That is, the lower journal processing portion may have a concave shape capable of accommodating the entire flat portion of the initial wasteland.
[0078]
　The second upper mold 51 of the second mold 50 has a concave shape as shown by a thick line in FIG. 14A and can accommodate the entire flat portion of the initial waste land 23. The second lower mold has a configuration in which the second upper mold 51 is turned upside down.
[0079]
　In the second preforming step, as shown in FIG. 11A, the first upper mold 41 is lifted to separate the first upper mold 41 and the first lower mold 42 from each other, and the initial waste land 23 is removed from the first upper mold 41. And the first lower mold 42. At that time, the initial rough land 23 was rotated about the axis by 90° from the state at the end of the first preforming step so that the width direction (the major axis direction in the case of an ellipse) of the flat portion was the rolling direction and the eccentric direction. Arranged in a posture.
[0080]
　From this state, the first upper mold 41 of the first mold 40 is lowered. Then, as shown in FIGS. 13A and 14A, the flat portion of the initial waste land 23 is accommodated in the concave upper mold journal processing portion 41 a and the second upper mold 51. At that time, as shown in FIG. 12A, the arm equivalent portion does not contact the bottom surface of the lower die arm machining portion 42c, and most of the arm equivalent portion is inside the weight machining portion 42e of the lower die arm machining portion 42c. Is located in.
[0081]
　When the first upper mold 41 is further lowered, a closed cross section is formed by the upper mold journal processing portion 41a and the lower mold journal processing portion 42a. In this state, when the first upper die 41 is further lowered to reach the bottom dead center, the entire flat portions inside the upper die journal machining portion 41a and the lower die journal machining portion 42a are pressed down. In this way, the flat portion of the initial waste land 23 is pressed by the first mold 40, and as a result, the cross-sectional area of ​​the journal-corresponding portion is reduced. Along with this, the surplus material flows in the axial direction and flows into the arm-corresponding portion, and the volume distribution proceeds.
[0082]
　After the reduction by the first mold 40 is started, preferably after the reduction is completed, the second upper mold 51 and the second lower mold 52 of the second mold 50 decenter the pin corresponding portions. The center of gravity of the portion corresponding to the pin moves in the eccentric direction of the pin portion (see the hatched arrow in FIG. 1B). The eccentricity of the pin-corresponding part is the same as the eccentricity of the finished dimension. However, the amount of eccentricity of the portion corresponding to the pin is not limited to this. The eccentric amount of the pin corresponding portion may be smaller than the eccentric amount of the finished dimension. In this case, in the finish forging step, the eccentric amount of the pin-corresponding portion is set as the eccentric amount of the finish dimension.
[0083]
　After the completion of the reduction by the first die 40, the first upper die 41 and the second upper die 51 are lifted to take out the processed initial waste land 23 (final waste land 24). In the final wasteland 24 thus obtained, the thickness of the arm-corresponding part is the same as the finished thickness.
[0084]
　According to the second preforming step, the material flows from the pin-corresponding portion and the journal-corresponding portion to the arm-corresponding portion. Thereby, the volume can be distributed in the axial direction. Further, in the arm-corresponding portion, the material flows inside the arm processing portions 41c and 42c, the width becomes narrower on the concave bottom side, and becomes wider on the concave opening side. Therefore, the volume is properly distributed in the arm-corresponding portion. As a result, it is possible to suppress the occurrence of wall thinning in the arm portion in the finish forging step which is a post-step. Further, it is possible to reduce the surplus material provided in the arm-corresponding part, and improve the material yield. Further, when the arm portion includes the weight portion, it is possible to suppress the occurrence of lack of thickness in the weight portion. Further, the second upper mold 51 and the second lower mold 52 of the second mold 50 are independently moved up and down, and the journal-corresponding portion of the initial waste land 23 is pressed down prior to the pin-corresponding portion. It is difficult for the initial wasteland 23 to bend during the eccentricity of the portion corresponding to the pin. As a result, the volume-distributed initial waste 23 is pressed down at a predetermined position of the first mold 40, so that the final waste after the reduction is unlikely to suffer from wall thickness or the like, and a final waste having a precise shape can be obtained.
[0085]
　According to the manufacturing method of the present embodiment, a final waste land can be obtained by the above-described first preforming step and second preforming step. Therefore, the material yield can be improved.
[0086]
　Furthermore, according to the manufacturing method of the present embodiment, the distribution of the volume in the axial direction can be promoted by the first preforming step and the second preforming step. That is, the cross-sectional area of ​​the pin-corresponding part and the journal-corresponding part can be reduced, and the cross-sectional area of ​​the arm-corresponding part can be increased. Since the final rough land on which the rough shape of the forged crankshaft is shaped is used, the formation of burrs can be minimized even in the finish forging step. With these, the material yield can be improved.
[0087]
5. Volume distribution in the arm-corresponding part The volume distribution in the arm-corresponding part in
　the second preforming step is adjusted by appropriately changing the shapes of the arm processing parts 41c, 42c according to the shape of the forged crankshaft (final product). You can For example, the opening width of the arm processing section may be changed, or the arm processing section may be an inclined surface.
[0088]
6. Preferred Embodiments
　As described above, in the second preforming step, when forming the arm-corresponding part, the upper part of the upper-die journaling part 41a acts as a partition that restricts the axial flow of the material. In order to increase this effect, it is important to narrow the opening width (Bj: see FIG. 13A) in the concave upper mold journal processing portion 41a. On the other hand, if the opening width Bj of the recessed upper journal processing portion is too narrow, the load increases in the subsequent process.
[0089]
　From these, the opening width Bj (mm) of the concave upper die journaled portion is 0.5 to 1.5 as a ratio to the diameter Dj (mm) of the journal portion of the forged crankshaft (final product). preferable.
[0090]
　In the above-mentioned first preforming step, the third die 30 is used to reduce the entire circumference of the billet. A state where a closed cross section is formed by the upper mold journal processing portion 31a and the lower mold journal processing portion 32a and a closed cross section is formed by the upper mold pin processing portion 31b and the lower mold pin processing portion 32b during the reduction. And This can prevent burr formation. Burr formation may be prevented by partially rolling down the journal-corresponding portion by the journal processing portion. Further, the formation of burrs may be prevented by partially rolling down the portion corresponding to the pin by the pin processing portion.
[0091]
　In addition, it goes without saying that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, even in the case of manufacturing a forged crankshaft (for example, a forged crankshaft with four cylinders and four counter weights) including an elliptical arm portion that does not include a weight portion, the first embodiment of the above embodiment The preforming step, the second preforming step, and the finish forging step can be applied.
Industrial availability
[0092]
　INDUSTRIAL APPLICABILITY The present invention can be effectively used for manufacturing a forged crankshaft mounted on a reciprocating engine.
Explanation of symbols
[0093]
　11 Forged crankshaft
　22 Billet
　23 Initial rough land
　23a Flat portion
　24 Final rough land
　25 Finish forged material
　30 Third die
　31 Third upper die
　31a Third die upper die journaling portion
　31b Third die upper die pin machining Part
　32 Third lower mold
　32a Lower mold journal machining part
　32b of third mold Lower pin machining part
　40 of third mold 40 First mold
　41 First upper mold
　41a Upper mold journal machining part
　41b of first mold First die upper die pin machining portion
　41c First die upper die arm machining portion
　42 First lower die
　42a First die lower die journal machining portion
　42b First die lower die pin machining portion
　42c 1 Mold Lower Mold Processing Section
　42e Weight Processing Section
　50 Second Mold
　51 Second Upper Mold
　52 Second Lower Mold
　A, A1 to A8 Crank arm part
　J, J1 to J5 Journal part
　P, P1 to P4 Pin part
　W, W1 to W8 Counterweight part
　B Burr
The scope of the claims
[Claim 1]
　A method for manufacturing a forged crankshaft, comprising: a plurality of journal portions that are rotation centers; a plurality of pin portions that are eccentric to the journal portion; and a plurality of crank arm portions that connect the journal portions and the pin portions. In the
　manufacturing method, a
　first preforming step for obtaining an initial wasteland from a billet, a
　second preforming step for obtaining a final wasteland from the initial wasteland, and a
　forging crankshaft for the final wasteland by at least one die forging. And a finish forging step of forming to a finish dimension of, in
　the first preforming step, a portion of the billet that becomes the pin portion and a portion that becomes the journal portion are perpendicular to the axial direction of the billet. By reducing the cross-sectional area of ​​each portion to form a plurality of flat portions, and in
　the second preforming step, a pair of first molds are used to change the width direction of the flat portions. After the step of pressing down the parts to be the plurality of journal parts in the pressing down direction and starting the pressing down by the first mold, a second mold is used and the width direction of the flat part is made eccentric to And a step of eccentricizing a portion to be a pin portion,
　wherein the final rough land has a thickness of a portion to be the plurality of crank arm portions that is the same as a thickness of a finish dimension.
[Claim 2]
　The method for manufacturing a forged crankshaft according to claim 1,
　wherein, in the second preforming step, after the reduction by the pair of first molds is completed, the plurality of pin portions formed by the second mold are Method of manufacturing a forged crankshaft, which starts eccentricity of the part.
[Claim 3]
　The method for manufacturing a forged crankshaft according to claim 1 or 2,
　wherein the eccentricity of the pin portion is the same as or smaller than the eccentricity of the finished dimension. Method.