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 or a ship, a crankshaft is indispensable in order to take out power by converting reciprocating motion of a piston into rotary motion. 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 to 1C are schematic views showing an example of the shape of a general forged crankshaft. Among these drawings, FIG. 1A is an overall view, FIG. 1B is a cross-sectional view taken along the line IB-IB of FIG. 1A, and FIG. 1C is a view showing the phase of the pin portion. In the example shown in FIG. 1B, typically, one crank arm portion A1, a counterweight portion W1 integral with the crank arm portion A1, a pin portion P1 and a journal portion J1 connected to the crank arm portion A1 are shown.
[0004]
　The forged crankshaft 11 shown in FIGS. 1A to 1C is a forged crankshaft with three cylinders and four counter weights mounted on a three cylinder engine. The forged crankshaft 11 includes four journal parts J1 to J4, three pin parts P1 to P3, a front part Fr, a flange part Fl, and six crank arm parts (hereinafter also referred to as “arm parts”). A1 to A6. The arm portions A1 to A6 connect the journal portions J1 to J4 and the pin portions P1 to P3, respectively. Further, some of the six arm portions A1 to A6 are integrally provided with counterweight portions (hereinafter, also referred to as “weight portions”) W1 to W4. Specifically, the first arm portion A1, the second arm portion A2, the fifth arm portion A5, and the sixth arm portion A6 integrally include weight portions W1, W2, W3, and W4, respectively. The third arm portion A3 and the fourth arm portion A4 do not include weight portions, and their shapes are oval.
[0005]
　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 fourth journal portion J4.
[0006]
　Hereinafter, when the journal portions J1 to J4, the pin portions P1 to P3, the arm portions A1 to A6, and the weight portions W1 to W4 are collectively referred to, the reference numerals are "J" for the journal portion and "P" for the pin portion. , "A" for the arm part, and "W" for the weight part. Further, the arm portion A and the weight portion W integrated with the arm portion A are collectively referred to as “web”.
[0007]
　As shown in FIG. 1C, the three pin portions P1 to P3 are arranged so as to be offset by 120° about the journal portion J as a center. That is, the first, second, and third pin portions P1, P2, and P3 are arranged at the first position L1, the second position L2, and the third position L3, respectively. The mutual phase angle of the first position L1, the second position L2, and the third position L3 is 120°.
[0008]
　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 protrudes from the central surface of the arm portion A (the surface including the central axis of the pin portion P and the central axis of the journal portion J).
[0009]
　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 a roll forming step and a bending and striking step. The die forging process includes a roughing process and a finishing process.
[0010]
　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 shown in FIGS. 1A to 1C.
[0011]
　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).
[0012]
　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 forged material 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. For this reason, burrs B are largely attached around the rough forged material 15 and the finish forged material 16.
[0013]
　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.
[0014]
　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. When manufacturing a forged crankshaft with three cylinders and four counterweights, a twisting step may be added after the deburring step in order to adjust the arrangement angle of the pin portion (phase angle of 120°). ..
[0015]
　The manufacturing process shown in FIGS. 2A to 2F can be applied not only to the forged crankshaft of three cylinders and four counter weights shown in FIGS. 1A to 1C but also to the forged crankshaft of three cylinders and six counter weights.
[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, it is possible to distribute the volume of the billet and perform eccentricity of a portion that will be a pin portion (hereinafter, also referred to as a “pin equivalent portion”) to some extent.
[0024]
　However, the eccentricity of the pin-equivalent portion and the distribution of the volume are insufficient, and a large burr is formed in the post-process die forging along with the shaping of the pin portion. Further, 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, the portion corresponding to the pin cannot be eccentric. This is because roll forming is used. Therefore, large burrs are formed when the pin portion is formed by the die forging in the subsequent step. Further, in the preforming method of Patent Document 2, it is not possible to perform volume distribution between the weight corresponding portion and the arm corresponding portion in the web corresponding portion. 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 method for manufacturing a forged crankshaft according to the present embodiment includes four journal portions that are rotation centers and a first position, a second position, and a third position that are eccentric to the journal portion and have a phase angle of 120°. It is a method of manufacturing a forged crankshaft including three pin portions that are respectively arranged and a plurality of crank arm portions that connect the journal portion and the pin portions.
[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, a pair of first molds are used, and the pin portion and the journal portion of the billet are pressed down from the direction perpendicular to the axial direction of the billet, thereby The cross-sectional area of ​​the flat portion is reduced to form a plurality of flat portions, and the portion of the flat portion that is the second pin portion that is arranged at the second position is eccentric, and the eccentric amount of the portion that is the second pin portion is reduced. Make it equal to or smaller than the amount of eccentricity in the finished dimension.
　In the second preforming step, a pair of second molds are used, and a step of reducing the width direction of the flat portion to reduce a plurality of journal portions is performed. Using a 3 mold, with the width direction of the flat portion being eccentric, the portion serving as the first pin portion disposed at the first position and the portion serving as the third pin portion disposed at the third position are in opposite directions. Eccentricity, and making the amount of eccentricity of the portions that will become the first and third pin portions equal to or smaller than (√3)/2 of the amount of eccentricity of the finished dimension.
　The final wasteland has a plurality of crank arm portions that have the same thickness as the finished thickness.
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 with a precise shape can be manufactured.
Brief description of the drawings
[0032]
FIG. 1A is an overall view schematically showing a shape example of a general forged crankshaft.
FIG. 1B is a cross-sectional view taken along the line IB-IB of FIG. 1A.
1C] FIG. 1C is a diagram showing a phase of a pin portion of the forged crankshaft 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] FIG. 4A is a vertical cross-sectional view schematically showing a situation at the start of reduction in a processing flow example of a first preforming step.
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 pin portion arranged at a second position at the start of reduction in the processing flow example of the first preforming step.
[FIG. 5B] FIG. 5B is a cross-sectional view showing a portion to be a pin portion arranged at the second position at the end of the reduction in the working flow example of the first preforming step.
6A] FIG. 6A is a transverse cross-sectional view showing a portion to be a journal portion at the start of reduction in the processing flow example of the first preforming step.
[FIG. 6B] FIG. 6B 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. 7A is a transverse cross-sectional view showing an arm-corresponding portion at the start of reduction in the processing flow example of the first preforming step.
FIG. 7B is a cross-sectional view showing an arm-corresponding portion at the end of the 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 second mold and a third mold of the present embodiment.
FIG. 10 is a vertical cross-sectional view showing a second mold and a third mold of the present embodiment, which are different from FIG. 9.
FIG. 11A is a vertical cross-sectional view schematically showing a situation at the start of the rolling process in the example of the processing flow of the second preforming process.
[FIG. 11B] FIG. 11B is a vertical cross-sectional view schematically 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 schematically showing a situation at the end of the eccentric process in the processing flow example of the second preforming process.
FIG. 12A is a transverse cross-sectional view showing a portion to be a pin portion arranged at the third position at the start of the eccentric process in the processing flow example of the second preforming process.
FIG. 12B is a cross-sectional view showing a portion that will be a pin portion arranged at the third position at the end of the eccentric step in the processing flow example of the second preforming step.
FIG. 13A is a transverse cross-sectional view showing a portion to be a pin portion arranged at the second position at the start of the rolling-down step in the working flow example of the second preforming step.
[FIG. 13B] FIG. 13B is a cross-sectional view showing a portion to be a pin portion arranged at the second position 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 will be a journal portion at the start of the rolling-down step in the working flow example of the second preforming step.
FIG. 14B is a transverse cross-sectional view showing a portion to be a journal portion at the end of the rolling-down step in the working flow example of the second preforming step.
FIG. 15A is a transverse cross-sectional view showing a portion which will be an arm portion at the start of the rolling-down step in the working flow example of the second preforming step.
FIG. 15B is a cross-sectional view showing a portion that will be an arm portion at the end of the rolling-down step in the working flow example of the second preforming step.
FIG. 16 is a schematic diagram showing the eccentric amounts of the first pin-corresponding part and the third pin-corresponding part.
MODE FOR CARRYING OUT THE INVENTION
[0033]
　The method for manufacturing a forged crankshaft according to the present embodiment includes four journal portions that are rotation centers and a first position, a second position, and a third position that are eccentric to the journal portion and have a phase angle of 120°. It is a method of manufacturing a forged crankshaft including three pin portions that are respectively arranged and a plurality of crank arm portions that connect the journal portion and the pin portions.
[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, a pair of first molds are used, and the pin portion and the journal portion of the billet are pressed down from the direction perpendicular to the axial direction of the billet, thereby The cross-sectional area of ​​the flat portion is reduced to form a plurality of flat portions, and the portion of the flat portion that is the second pin portion that is arranged at the second position is eccentric, and the eccentric amount of the portion that is the second pin portion is reduced. Make it equal to or smaller than the amount of eccentricity in the finished dimension.
　In the second preforming step, a pair of second molds are used, and a step of reducing the width direction of the flat portion to reduce a plurality of journal portions is performed. Using a 3 mold, with the width direction of the flat portion being eccentric, the portion serving as the first pin portion disposed at the first position and the portion serving as the third pin portion disposed at the third position are in opposite directions. Eccentricity, and making the amount of eccentricity of the portions that will become the first and third pin portions equal to or smaller than (√3)/2 of the amount of eccentricity of the finished dimension.
　The final wasteland has a plurality of crank arm portions that have the same thickness as the finished thickness.
[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 third die, which is separate from the second die for pressing down the portion to be the journal portion, decenters the portion to be the first pin portion and the portion to be the third pin portion. If the second die is integrated with the third die, the portion that decenters the portion that becomes the first pin portion and the portion that becomes the third pin portion projects more than the portion that presses down the portion that becomes the journal portion. Therefore, if the initial wasteland is arranged in the second die that is integral with the third die, the initial wasteland tends to incline. However, if the third mold is moved separately from the second mold, the third mold for eccentricizing the portion serving as the first pin portion and the portion serving as the third pin portion is pressed down at the portion serving as the journal portion. It is possible that it does not protrude beyond the part. Therefore, even if the initial wasteland is arranged on the second mold, the initial wasteland is unlikely to tilt. Since the volume-distributed initial wasteland is rolled down at a predetermined position of the second mold, it is unlikely that a thin wall or the like will occur in the final wasteland after rolling down. 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.
[0037]
　Preferably, in the second preforming step, after the reduction by the pair of second molds is completed, the eccentricity of the part serving as the first pin part and the part serving as the third pin part by the third mold is started.
[0038]
　Below, the manufacturing method of the forged crankshaft of this embodiment is demonstrated, referring drawings.
[0039]
1. Manufacturing Process Example
　The forged crankshaft targeted by the manufacturing method of the present embodiment has four journal parts J which are rotation centers, three pin parts P which are eccentric to the journal part J, the journal part J and the pin part. And a plurality of arm portions A connecting P. The three pin portions P1, P2, and P3 are arranged at the first position L1, the second position L2, and the third position L3, respectively. Hereinafter, the pin portion arranged at the first position L1 is also referred to as the first pin portion P1. The pin portion arranged at the second position L2 is also referred to as a second pin portion P2. The pin portion arranged at the third position L3 is also referred to as a third pin portion P3. The mutual phase angle of the first position L1, the second position L2, and the third position L3 is 120°. For example, the forged crankshaft of the three-cylinder/four-piece counterweight shown in FIGS. 1A to 1C is an object to be manufactured.
[0040]
　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. The arrangement angle of the pin portion can be adjusted in the finish forging step. Alternatively, a twisting step may be added after the deburring step, and the arrangement angle of the pin portion may be adjusted in this twisting step. These series of steps are carried out hot.
[0041]
　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 FIGS. 1A to 1C. The views on the left side of FIGS. 3B and 3C are front views. The drawings on the right side of FIGS. 3B and 3C show the portions serving as the first, second, and third pin portions (hereinafter, referred to as “first pin”) with respect to the center of the portion serving as the journal portion (hereinafter, also referred to as “journal equivalent portion”). Corresponding parts", "second pin equivalent parts" and "third pin equivalent parts") PA1, PA2 and PA3 are shown. The views on the left side of FIGS. 3D and 3E are plan views. The drawings on the right side of FIGS. 3D and 3E show the positions of the first, second and third pin portions P1, P2 and P3 with respect to the center of the journal portion. Further, in the drawings on the right side of FIGS. 3B and 3C, the first position L1 to the third position L3 of the pin portion of the forged crankshaft which is the final product are shown by imaginary lines.
[0042]
　In the first preforming step, the billet 22 is pressed down using the first die. The rolling direction at that time is a direction perpendicular to the axial direction of the billet 22. As a result, three pin-corresponding portions and four journal-corresponding portions of the billet 22 are crushed and the cross-sectional area is reduced at those portions. Along with this, a plurality of flat portions 23a are formed on the billet 22. The flat portion 23a is formed at the position of the pin-corresponding portion and the journal-corresponding portion.
[0043]
　In the first preforming step, the second pin-corresponding portion PA2 of the flat portion 23a is eccentric along the rolling direction. By thus narrowing down the pin-corresponding part and the journal-corresponding part, the initial wasteland 23 having a distributed volume can be obtained. Here, the amount of eccentricity of the portion corresponding to the second pin of the initial waste land 23 is equal to or smaller than the amount of eccentricity of the finished dimension. The eccentricity of the finished size means the eccentricity of the pin portion of the forged crankshaft. The first preforming step can be performed, for example, according to a processing flow example described later.
[0044]
　The second preforming step includes a rolling down step and an eccentric step.
[0045]
　In the rolling-down process, the pair of second molds are used to roll down the portions of the initial wasteland 23 that will be the plurality of journal portions. The rolling direction at that time is the width direction of the flat portion. That is, the rolling-down direction is a direction perpendicular to the eccentric direction of the second pin-corresponding portion PA2. More specifically, in the second preforming step, the initial roughened land 23 obtained in the first preforming step is rotated by 90° and then rolled down.
[0046]
　In the eccentric process, after starting the reduction by the second mold, the third mold is used to arrange the first pin portion to be arranged at the first position (first pin corresponding portion) and the third position. The part to be the third pin part (the part corresponding to the third pin) is eccentric to the opposite directions. The eccentric direction at that time is the width direction of the flat portion. The amount of eccentricity of the first and third pin portions is equal to or smaller than (√3)/2 of the amount of eccentricity of the finished dimension. As a result, the final waste land 24 in which the approximate shape of the forged crankshaft is formed is obtained.
[0047]
　In the final wasteland 24, the eccentric direction of the first pin-corresponding portion PA1 and the eccentric direction of the third pin-corresponding portion PA3 are opposite to each other. That is, in the final wasteland 24, the phase angle between the first pin corresponding portion PA1 and the second pin corresponding portion PA2 is 90°. The phase angle between the third pin-corresponding portion PA3 and the second pin-corresponding portion PA2 is 90°. Further, the phase angle between the first-pin equivalent part PA1 and the third-pin equivalent part PA3 is 180°. Further, 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). Details of the second preforming step will be described later.
[0048]
　In the finish forging step, the final rough land 24 is formed into the finished dimensions of the forged crankshaft by die forging. Specifically, a pair of upper and lower molds is used. The final wasteland 24 is arranged on the lower die in such a posture that the first and third pin corresponding portions PA1 and PA3 are arranged in a horizontal plane. Then, forging is performed by lowering the upper die. That is, the rolling direction of the forging is the eccentric direction of the second pin equivalent portion PA2. 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 in the finish forging step. The finish forging step may be performed once or may be divided into a plurality of times.
[0049]
　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.
[0050]
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 drawings, FIG. 4A is a vertical cross-sectional view showing the situation at the start of the reduction, and FIG. 4B is a vertical cross-sectional view showing the situation at the end of the reduction.
[0051]
　FIG. 5A and FIG. 5B are cross-sectional views showing a portion (a portion corresponding to the second pin) that is a pin portion arranged at the second position. Of these figures, FIG. 5A shows the situation at the start of 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.
[0052]
　6A and 6B are cross-sectional views showing a journal-corresponding portion. Of these figures, FIG. 6A shows the situation at the start of 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.
[0053]
　7A and 7B are cross-sectional views showing the arm-corresponding portion. Of these figures, FIG. 7A shows the situation at the start of 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.
[0054]
　4A to 7B show a billet 22 (or an initial waste land 23) having a round cross section and a pair of upper and lower first molds 30. The first mold 30 includes a first upper mold 31 and a first lower mold 32. To facilitate understanding of the situation, in FIGS. 5A to 7B, the shaft center position C of the journal-corresponding portion is shown by a black circle. In FIG. 5B, FIG. 6B and FIG. 7B, the first upper mold 31, the first lower mold 32 and the billet 22 at the start of reduction are also shown by a chain double-dashed line. The pair of first molds 30 each include a pin processing portion that abuts the pin corresponding portion and a journal processing portion that abuts the journal corresponding portion.
[0055]
　As shown by the thick line in FIG. 5A, the pin processing section includes an upper die pin processing section 31b provided on the first upper die 31 and a lower die pin processing section 32b provided on the first lower die 32. The upper die pin processing portion 31b has a concave shape and can accommodate the billet 22. 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.
[0056]
　The pin processed portion that abuts the first and third pin-corresponding portions is the same as the pin processed portion that abuts the second pin-corresponding portion as shown in FIGS. 5A and 5B. However, the position of the pin-processed portion that abuts the first and third pin-equivalent portions in the rolling direction is different from the position of the pin-processed portion that abuts the second pin-equivalent portion (see FIGS. 4A and 4B).
[0057]
　As shown by the thick line in FIG. 6A, the journal processing section includes an upper mold journal processing section 31 a provided on the first upper mold 31 and a lower mold journal processing section 32 a provided on the first lower mold 32. The upper journal processing portion 31a has a concave shape and can accommodate the billet 22. 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 die journal machining portion 31a and the lower die journal machining portion 32a is concave. That is, the lower mold journal processing portion 32a may be concave so as to accommodate the billet.
[0058]
　In the first preforming step, the billet 22 is placed between the first upper die 31 and the first lower die 32 in a state where the first upper die 31 is raised and the first upper die 31 and the first lower die 32 are separated from each other. To place. When the first upper die 31 is lowered from this state, as shown in FIG. 5A, the pin-corresponding portion of the billet 22 is housed in the concave upper die pin processing portion 31b. Further, as shown in FIG. 6A, the journal-corresponding portion is accommodated in the concave upper journal processing portion 31a. When the first upper die 31 is further lowered, the billet 22 is pressed down by the upper die pin machining portion 31b and the lower die pin machining portion 32b, and the upper die journal machining portion 31a and the lower die journal machining portion 32a. Therefore, the cross-sectional area of ​​the pin-corresponding part and the journal-corresponding part is reduced. As a result, the flat portion 23a as shown in FIGS. 5B and 6B is formed.
[0059]
　As shown in FIG. 4A, the position of the pin-processed portion of the pin-processed portion and the journal-processed portion that contacts the second pin-corresponding portion is the position of the pin-processed portion that contacts the first and third pin-corresponding portions. Different from Therefore, the portion corresponding to the second pin is eccentric along the rolling direction while deforming. The eccentricity of the portion corresponding to the second pin is equal to or smaller than the eccentricity of the finished dimension. After the completion of the reduction by the first mold 30, the first upper mold 31 is raised and the processed billet 22 (initial waste land 23) is taken out.
[0060]
　If such a processing flow example is adopted, as the cross-sectional area of ​​the pin-corresponding portion and the journal-corresponding portion is reduced by pressing down the pin-corresponding portion and the journal-corresponding portion, the material of the pin-corresponding portion and the journal-corresponding portion becomes It moves in the axial direction of the billet 22. 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 the initial wasteland 23 whose volume is distributed in the axial direction.
[0061]
　Further, in the process of lowering the first upper die 31, the opening of the concave upper die pin machining portion 31b is closed by the lower die pin machining portion 32b, and the upper die pin machining portion 31b and the lower die pin machining portion 32b are used. A closed cross section is formed (see Figures 5A and 5B). 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 (FIG. 6A and FIG. 6A and FIG. 6B). Thereby, no burr is formed between the first upper mold 31 and the first lower mold 32. Therefore, the material yield can be improved and the volume distribution in the axial direction can be promoted.
[0062]
　In the first preforming step, as will be described later, 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.
[0063]
　In the first preforming step, the arm-corresponding portion does not have to be pressed down by the first mold from the viewpoint of promoting the distribution of the volume in the axial direction.
[0064]
　In the cross section of the flat portion 23a, the width Bf in the direction perpendicular to the rolling direction may be larger than the thickness ta in the rolling direction. For example, the cross-sectional shape of the flat portion 23a is elliptical or oval (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.
[0065]
3. Second die and third die used in the second preforming step In the second preforming step of the
　present embodiment, the rolling of the journal corresponding portion and the eccentricity of the first and third pin corresponding portions are performed. The reduction of the journal-equivalent portion and the eccentricity of the first and third pin-equivalent portions are performed by separate molds.
[0066]
　If the pressing of the journal-corresponding portion and the eccentricity of the first and third pin-corresponding portions are performed by one die, the following problems may occur.
[0067]
　FIG. 8 is a vertical cross-sectional view showing a case where the second preforming step is performed with one die. With reference to FIG. 8, the initial waste land 23 is arranged on the second lower mold 42 in a state where the second upper mold 41 and the second lower mold 42 are separated from each other. As described above, in the second preforming step, the first pin corresponding part and the third pin corresponding part are eccentric. The pin processing portion 42h of the second lower die 42 that processes the portion corresponding to the first pin of the initial waste land 23 projects more than the lower die journal processing portion 42a. Therefore, when the initial waste land 23 is arranged on the second lower mold 42, the initial waste land 23 is easily inclined. In this state, when the second mold 40 rolls down the initial waste land 23, the initial waste land 23 is inclined, so that the initial waste land 23 is likely to move in the axial direction. When the initial waste land 23 moves during the rolling reduction, the position of the initial waste land 23 to which the second mold 40 rolls is displaced from the planned position. That is, a situation may occur in which the pin processing portion of the second 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.
[0068]
　FIG. 9 is a vertical cross-sectional view showing the second mold and the third mold of this embodiment. With reference to FIG. 9, the manufacturing apparatus of this embodiment includes a second mold 40 and a third mold 50. The third mold 50 includes a third upper mold 51 and a third lower mold 52. The third upper mold 51 causes the third pin-corresponding portion to be eccentric. The third lower mold 52 causes the portion corresponding to the first pin to be eccentric. The third upper mold 51 and the third lower mold 52 can be raised and lowered independently of the second mold 40. Before the reduction of the initial waste land 23, the third lower die 52 is arranged at the same height as or below the lower die journal machining portion 42a. Further, the third upper die 51 is arranged at the same height as or above the upper die journal processing portion 41a. That is, the third upper mold 51 and the third lower mold 52 do not protrude beyond the upper journal processing portion 41a and the lower journal processing portion 42a. Therefore, even if the initial waste land 23 is arranged on the second lower mold 42 before the start of reduction, the initial waste land 23 is kept substantially horizontal.
[0069]
　In addition, the eccentricity of the initial wasteland 23 by the third die 50 is started after the reduction of the initial wasteland 23 by the journal processing portions 41a and 42a of the second die 40 is started. Therefore, during eccentricity of the third and first pin-corresponding portions, the journal-processing portions 41a and 42a press down the journal-corresponding portions of the initial waste land 23. That is, the journal-corresponding portion of the initial wasteland 23 is restrained by the journal processing portions 41a and 42a. Therefore, the initial wasteland 23 is unlikely to be tilted during the eccentricity of the pin-corresponding portion, and is pressed down at a predetermined position.
[0070]
　In short, the third upper mold 51 and the third lower mold 52 are independently moved up and down, and the journal-corresponding portion of the initial waste land 23 is pressed down prior to the third and first pin-corresponding portions, so that It is difficult for the initial wasteland 23 to move in the axial direction during the eccentricity of the portion corresponding to the first pin. Since the volume-distributed initial waste land 23 is rolled down at a predetermined position of the second mold 40, it is unlikely that a thin wall or the like will occur in the final waste land after rolling down.
[0071]
　The configurations of the second mold 40 and the third mold 50 will be described. The third mold 50 includes a control mechanism for moving up and down the third upper mold 51 and the third lower mold 52 independently. The control mechanism is, for example, a die cushion or a hydraulic cylinder.
[0072]
　A case where the control mechanism is the die cushion 81 will be described with reference to FIG. 9. The second lower mold 42 is supported by the bolster base 82 via the die cushion 81. The die cushion 81 has a cushioning function. The third upper mold 51 and the third lower mold 52 are supported by the bolster base 82 via the pin base 83. When the second mold 40 starts rolling down the initial waste 23, the buffer function of the die cushion 81 causes the third lower mold 52 to start protruding from the second lower mold 42 and the third upper mold 51 to move from the second upper mold 41. Start to stick out. After the journal processing parts 41a and 42a contact the journal corresponding part of the initial waste land 23, the third lower mold 52 and the third upper mold 51 contact the first pin corresponding part and the third pin corresponding part of the initial waste land 23. The die cushion 81 is set as described above. As a result, the portion corresponding to the first pin and the portion corresponding to the third pin of the initial wasteland 23 are eccentric after the start of the reduction of the portion corresponding to the journal.
[0073]
　FIG. 10 is a vertical cross-sectional view showing a second mold and a third mold of the present embodiment different from FIG. 9. 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 third upper mold 51 and the third lower mold 52. The third upper mold 51 and the third lower mold 52 are supported by the bolster base 82 via a hydraulic cylinder 84. When the second mold 40 starts rolling down the initial waste 23, the hydraulic cylinder 84 operates, the third lower mold 52 begins to project from the second lower mold 42, and the third upper mold 51 projects from the second upper mold 41. start. After the journal machining parts 41a and 42a contact the journal corresponding part of the initial waste land 23, the hydraulic pressure is applied so that the third lower mold 52 and the third upper mold 51 contact the first and third pin corresponding parts of the initial waste land 23. The cylinder 84 is set. As a result, the portion corresponding to the first pin and the portion corresponding to the third pin of the initial wasteland 23 are eccentric after the start of rolling down the portion corresponding to the journal.
[0074]
　Whether the control mechanism is a die cushion or a hydraulic cylinder, the timing when the third lower mold 52 projects from the second lower mold 42 and the timing when the third upper mold 51 projects from the second upper mold 41 are It is set appropriately. That is, the first and third pin-corresponding portions of the initial wasteland 23 may be eccentric between the start of reduction of the journal-corresponding portions and the completion of the reduction. The portions corresponding to the first and third pins may be eccentric after the completion of rolling down the portions corresponding to the journal.
[0075]
　By performing the eccentricity of the portions corresponding to the first and third pins 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 first and third pins is reduced. That is, the cross-sectional area of ​​the first and third pin corresponding portions of the initial waste land 23 is smaller than the cross-sectional area of ​​the first and third pin corresponding portions of the billet. Therefore, the eccentricity of the first and third pin-corresponding portions of the initial wasteland 23 is better than the eccentricity of the first and third pin-corresponding portions of the billet. Small area and little extra material. 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 portions corresponding to the first and third pins is performed in the second preforming step.
[0076]
4. Example of Processing Flow of Second Preforming Step
　FIGS. 11A to 15B are schematic diagrams showing an example of processing flow of the second preforming step. Among 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 shows the situation at the end of the eccentric process. It is a longitudinal section shown.
[0077]
　12A and 12B are cross-sectional views showing a portion corresponding to the third pin. Of these figures, FIG. 12A shows the situation at the start of the eccentric process, and FIG. 12B shows the situation at the end of the eccentric 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.
[0078]
　13A and 13B are cross-sectional views showing a portion corresponding to the second pin. 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.
[0079]
　14A and 14B are cross-sectional views showing a journal-corresponding portion. Of these figures, FIG. 14A shows the situation at the start of the reduction process, and FIG. 14B shows the situation at the end of the reduction 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.
[0080]
　15A and 15B are cross-sectional views showing the arm equivalent part. Of these figures, FIG. 15A shows the situation at the start of the reduction process, and FIG. 15B shows the situation at the end of the reduction process. 15A is a sectional view taken along the line XVA-XVA of FIG. 11A, and FIG. 15B is a sectional view taken along the line XVB-XVB of FIG. 11C.
[0081]
　12A to 15B show the initial rough land 23 obtained in the first preforming step described above. 12A and 12B show a third mold 50, and FIGS. 13A to 15B show a pair of upper and lower second molds 40. The second mold 40 includes a second upper mold 41 and a second lower mold 42. To facilitate understanding of the situation, in FIGS. 12A to 15B, the shaft center position C of the journal-corresponding portion is indicated by a black circle. Further, in FIG. 12B, the second lower mold 42 and the third mold 50 at the start of the rolling-down process are also shown by a chain double-dashed line, and in FIGS. 13B, 14B and 15B, the second upper mold 41 and the second lower mold are shown. 42 is also indicated by a chain double-dashed line. The pair of second molds 40 includes pin processing portions 41f and 42f that contact the second pin corresponding portion of the initial waste land 23, journal processing portions 41a and 42a that contact the journal corresponding portion, and an arm that contacts the arm corresponding portion. The processing parts 41c and 42c are provided.
[0082]
　The pin processed portion that comes into contact with the second pin-corresponding portion of the second mold 40 is provided at a position corresponding to the second pin-corresponding portion. The pin-processed portion of the second mold 40 that abuts against the second pin-corresponding portion is, as shown by a thick line in FIG. The lower die pin processing portion 42f provided in the. The lower die pin machining portion 42f of the second lower die 42 has a concave shape and can accommodate the initial waste land 23. The upper die pin machining portion 41f of the second upper die 41 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 41f and the lower die pin machining portion 42f of the second die 40 is concave. That is, the upper die pin machining portion 41f of the second upper die 41 may be concave so as to accommodate the initial wasteland.
[0083]
　The third upper mold 51 of the third mold 50 is concave as shown by the thick line in FIG. 12A, and can accommodate the flat portion 23a of the initial waste land 23. The third lower mold 52 (see FIG. 9) has a configuration in which the third upper mold 51 is turned upside down.
[0084]
　As shown by the thick line in FIG. 14A, the journal processing section includes an upper mold journal processing section 41 a provided on the second upper mold 41 and a lower mold journal processing section 42 a provided on the second lower mold 42. The upper mold journal processing portion 41a has a concave shape and can accommodate the flat portion 23a 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 42a may have a concave shape capable of accommodating the flat portion of the initial wasteland.
[0085]
　As shown by the thick line in FIG. 15A, the arm processing section includes an upper die arm processing section 41c provided on the second upper die 41 and a lower die arm processing section 42c provided on the second lower die 42. As shown by the thick line in FIG. 15A, the cross section of the arm processing portion has one of the upper die arm processing portion 41c and the lower die arm processing portion 42c that is generally concave. For example, as shown in FIG. 15A, the lower die arm processing portion 42c is generally concave, and the other upper die arm processing portion 41c is planar. It should be noted that which of the upper die arm processing portion 41c and the lower die arm processing portion 42c is made concave can be appropriately set depending on the shape of the forged crankshaft.
[0086]
　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. 15A, both sides of the weight processing portion 42e are inclined surfaces.
[0087]
　In the second preforming step, the axial thickness t1 of the arm-corresponding portion is made equal to the finished thickness t0 (see FIGS. 3C and 3E). 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.
[0088]
　In the second preforming step, the initial waste land 23 is separated from the second upper mold 41 and the second lower mold 42 in a state where the second upper mold 41 is raised and the second upper mold 41 and the second lower mold 42 are separated from each other. Place in between. At that time, the initial roughened land 23 is arranged in a posture rotated by 90° around the axis from the state at the end of the first preforming step so that the flat part has a width direction (longitudinal direction in the case of an ellipse) being a pressing direction. To be done. Therefore, the rolling direction of the second mold 40 is perpendicular to the eccentric direction of the second pin equivalent portion.
[0089]
　From this state, the second upper mold 41 is lowered. Then, as shown in FIGS. 13A and 14A, the flat portion of the initial waste land 23 is accommodated in the pin processing portion 42f of the second lower die 42 and the upper die processing portion 41a of the second upper die 41. When the arm portion includes the weight portion, as shown in FIG. 15A, the arm-corresponding portion does not contact the bottom surface of the lower die arm processing portion 42c, and most of the arm-corresponding portion is included in the lower die arm processing portion 42c. Is placed in the weight processing part 42e.
[0090]
　When the second upper die 41 is further lowered, a closed cross section is formed by the upper die journal processing portion 41a and the lower die journal processing portion 42a. In this state, when the second upper die 41 is further lowered to reach the bottom dead center, as shown in FIG. 14B, the flat portion 23a inside the upper die journal machining portion 41a and the lower die journal machining portion 42a is removed. Be suppressed. Further, as shown in FIG. 13B, the flat part 23a inside the upper die pin machining portion 41f of the second upper die 41 and the lower die pin machining portion 42f of the second lower die 42 is pressed down. In this way, the flat portion 23a of the initial waste land 23 is pressed down by the second mold, and as a result, the cross-sectional area of ​​the journal-corresponding portion and the second pin-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.
[0091]
　After starting the reduction by the second die 40, the third lower die 52 and the third upper die 51 of the third die 50 eccentric the portion corresponding to the first pin and the portion corresponding to the third pin. Both the first pin-corresponding part and the third pin-corresponding part are eccentric along the pressing direction of the second mold 40. However, the eccentric direction of the portion corresponding to the first pin is opposite to the eccentric direction of the portion corresponding to the third pin. The eccentricity of the first pin-corresponding part and the third pin-corresponding part is equal to or smaller than (√3)/2 of the eccentricity of the finished dimension. On the other hand, the portion corresponding to the second pin is located in the direction perpendicular to the pressing direction of the second mold 40 and is not eccentric. Therefore, the amount of eccentricity of the portion corresponding to the second pin remains the same as or smaller than the amount of eccentricity of the finished dimension.
[0092]
　FIG. 16 is a schematic diagram showing the amount of eccentricity of the portion corresponding to the first pin and the portion corresponding to the third pin. FIG. 16 is a view seen from the axial direction of the forged crankshaft. Referring to FIG. 16, the phase difference between the first position L1 where the first pin portion of the forged crankshaft of the three-cylinder engine is arranged and the second position L2 where the second pin portion is arranged is 120°. However, the phase difference between the position PA1 of the portion corresponding to the first pin and the position PA2 of the portion corresponding to the second pin in the final wasteland obtained in the second preforming step is 90°. Therefore, after the second preforming step, the portion corresponding to the first pin is further eccentric with respect to the axial center position C of the portion corresponding to the journal. As a result, in the forged crankshaft which is the final product, the phase difference between the first position L1 and the second position L2 is 120°.
[0093]
　The amount of eccentricity (finishing dimension) of the first pin portion is the distance E0 between the center of the first position L1 and the axis C of the journal portion. Therefore, if a right-angled triangle consisting of the axial center C of the journal portion, the center of the position of the first pin corresponding portion PA1 and the center of the first position L1 is hypothesized, the eccentric amount Eb of the first pin corresponding portion PA1 in the eccentric step is assumed. Is equal to or smaller than (√3)/2 of the eccentricity amount E0 of the first pin portion. If the eccentricity Eb of the portion corresponding to the first pin is larger than (√3)/2 of the eccentricity E0 of the first pin portion, eccentric the portion corresponding to the first pin to the first position L1 in the subsequent finish forging step. It is difficult. This is because the first pin-corresponding portion must be eccentric to the first position L1 along a direction that is not parallel to the rolling direction (the left-right direction in FIG. 16). When the eccentricity amount Eb of the portion corresponding to the first pin is smaller than (√3)/2 of the eccentricity amount E0 of the first pin portion, the subsequent finish forging step is performed multiple times. For example, in the first finish forging step, the eccentricity Eb of the portion corresponding to the first pin is eccentric to (√3)/2 of the eccentricity E0 of the first pin. In the second finish forging step, the position of the first pin corresponding portion PA1 is eccentric to the first position L1. The same applies to the portion corresponding to the third pin.
[0094]
　After the reduction by the second mold 40 and the eccentricity by the third mold 50 are completed, the second upper mold 41 and the third upper mold 51 are raised 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.
[0095]
　According to the second preforming step, the first pin-corresponding portion and the third pin-corresponding portion can be eccentric. Further, the volume can be distributed in the axial direction by causing the material to flow from the portion corresponding to the second pin and the portion corresponding to the journal to the portion corresponding to the arm. As a result, the material yield can be improved. 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 third upper die 51 and the third lower die 52 of the third die 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, so that the pin It is difficult for the initial wasteland to tilt during eccentricity of the corresponding part. As a result, the volume-distributed initial wasteland is rolled down at a predetermined position of the second mold, and thus it is unlikely that a thin wall or the like will occur in the final wasteland after rolling down.
[0096]
5. Preferred embodiment, etc.
　The amount of eccentricity of the second pin corresponding portion by the first preforming step (mm), that is, the eccentricity Ea (mm) of the second pin corresponding portion of the initial rough land 23 (final rough land 24) is the eccentricity of the finish dimension. It is preferable to be 20% or more of the amount (the amount of eccentricity of the portion corresponding to the pin of the forged crankshaft) E0 (mm). It is more preferably 50% or more of the eccentricity amount E0 of the finished size, and most preferably 100% of the eccentricity amount E0 of the finished size. When the eccentricity amount Ea of the second pin-corresponding portion is smaller than the eccentricity amount E0 of the finish dimension, it is necessary to further eccentricize the second pin-corresponding portion by finish forging. Therefore, flaws may occur. In the above embodiment, the case where the eccentricity amount Ea of the second pin corresponding portion is the same as the eccentricity amount E0 of the finished dimension (100%) is shown.
[0097]
　The amount of eccentricity of the first and third pin-corresponding portions in the second preforming step, that is, the eccentricity Eb (mm) of the first and third pin-corresponding portions of the final wasteland 24 is the eccentricity amount E0 (mm) of the finishing dimension. It is preferable that it is equal to or smaller than (√3)/2 of ). In the above embodiment, the eccentricity amount Eb of the first and third pin-corresponding portions is the same as (√3)/2 of the eccentricity amount E0 of the finished dimension. However, from the viewpoint of ensuring the material filling of the engraving portion for the pin portion, the eccentricity Eb of the first and third pin corresponding portions of the final wasteland 24 is the ratio (Eb/(( √3)/2×E0)), and preferably (1.0−Dp/2/((√3)/2×E0)) or more. Here, Dp means the diameter of the pin portion of the finished dimension (the diameter of the pin portion of the forged crankshaft). From the same viewpoint, the cross-sectional area Spb (mm 2 ) of the first and third pin-corresponding portions of the final wasteland 24 is the ratio ((Spb)/Sp0) to the cross-sectional area Sp0 (mm 2 ) of the pin portion of the forged crankshaft. Therefore, it is preferably 0.7 or more and 1.5 or less, and more preferably 0.75 or more and 1.1 or less.
[0098]
　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.
Industrial availability
[0099]
　INDUSTRIAL APPLICABILITY The present invention can be effectively used for manufacturing a forged crankshaft mounted on a three-cylinder reciprocating engine.
Explanation of symbols
[0100]
　11 Forged crankshaft
　22 Billet
　23 Initial rough land
　23a Flat portion
　24 Final rough land
　25 Finishing forged material
　30 First die
　31 First upper die
　31a First die upper die journaling portion
　31b First die upper die pin machining Part
　32 First lower mold
　32a First mold lower mold journal machining part
　32b First mold lower mold pin machining part
　40 Second mold
　41 Second upper mold
　41a Second mold upper mold journal machining part
　41c Upper die arm machining portion
　41f of second die Upper die pin machining portion
　42 of second die
　42 Lower die 42a Lower die journal machining portion
　42c of second die Lower die arm machining portion
　42e of second die Weight Processed part
　42f Lower die pin processed part
　42h of second mold
　50 Pin processed part 50 of second lower mold Third mold
　51 Third upper mold
　52 3rd lower mold
　A, A1 to A6 Crank arm part
　J, J1 to J4 Journal part
　P, P1 to P3 pin part
　W, W1 to W4 Counter weight part
　PA, PA1 to PA3 pin equivalent part
　B Vari
The scope of the claims
[Claim 1]
　Four journal parts which are rotation centers, three pin parts which are eccentric to the journal part and are respectively arranged at a first position, a second position and a third position having a phase angle of 120°; A method for manufacturing a forged crankshaft comprising a journal portion and a plurality of crank arm portions connecting the pin portion, the
　method 　comprising: a
　first preforming step for obtaining an initial rough land from a billet;
A second preforming step of obtaining a rough land, and
　a finish forging step of shaping the final rough land to a finish dimension of the forged crankshaft by at least one die forging, and
　the first preforming step comprises a pair of first (1) Using a die, by pressing down the part that becomes the pin part and the part that becomes the journal part of the billet from the direction perpendicular to the axial direction of the billet, the cross-sectional area of ​​each part is reduced. While forming a plurality of flat portions, the portion of the flat portion that becomes the second pin portion arranged at the second position is eccentric, and the eccentric amount of the portion that becomes the second pin portion is finished. The eccentricity is equal to or smaller than the eccentricity, and in
　the second preforming step, a pair of second molds are used to reduce the width direction of the flat portion to the plurality of journal portions. After the step of rolling down and the rolling down by the second die, a third die is used to form a first pin portion arranged at the first position with the width direction of the flat portion being eccentric. The portion serving as the third pin portion arranged at the third position is eccentric to the opposite directions, and the eccentricity amount of the portions serving as the first and third pin portions is (√3)/2 of the eccentricity amount of the finish dimension. The same as or smaller than,
　The final wasteland is a method for manufacturing a forged crankshaft, in which the thickness of the portions that become the plurality of crank arm portions is the same as the thickness of the finished 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 second molds is completed, the first pin portion is formed by the third mold. Method for manufacturing a forged crankshaft, in which eccentricity of a portion to be formed and a portion to be the third pin portion is started.