JP2016215234A - Manufacturing method of forged crank shaft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a forged crank shaft integrally having a weight part which reduces the weight of the crank shaft without largely increasing manufacturing steps.SOLUTION: A manufacturing method of a forged crank shaft comprises: a mold forging step obtaining a forged material with burrs in which a shape of a crank shaft is formed and also excess thickness parts (Ea, Eb) protruding from end parts (Wa, Wb) to a width direction is formed at either one or both of end parts (Wa, Wb) of a weight part W in a protruding width direction; a deburring step obtaining the forged material without burrs by removing burrs from the forged material with burrs; and a bending step in which a pair of first metal molds 10 presses down a forged material 30 without burrs when screw-down direction is the width direction to bend the excess thickness parts (Ea, Eb) so that thickness is increased at the end parts (Wa, Wb) where the excess thickness parts (Ea, Eb) protrudes.SELECTED DRAWING: Figure 6A

Description

  The present invention relates to a method of manufacturing a crankshaft by hot forging.

  In reciprocating engines such as automobiles, motorcycles, agricultural machines, and ships, a crankshaft is indispensable for converting the reciprocating motion of a piston into a rotational motion to extract power. The crankshaft can be manufactured by die forging or casting. In particular, when high strength and high rigidity are required for a crankshaft, a crankshaft manufactured by die forging (hereinafter also referred to as “forged crankshaft”) is frequently used because of excellent characteristics.

  Generally, a forged crankshaft is made from a billet, and the billet has a round or square cross section and a constant cross-sectional area over the entire length. In the manufacturing process of a forged crankshaft, a preforming process, a die forging process, a deburring process, and a shaping process are provided in that order. Usually, the preforming process includes roll forming and bending processes, and the die forging process includes roughing and finishing processes.

  FIG. 1A to FIG. 1F are schematic views for explaining a manufacturing process of a conventional general forged crankshaft. FIG. 1A shows a billet, FIG. 1B shows a roll waste, FIG. 1C shows a bending waste, FIG. 1D shows a rough forged material, FIG. 1E shows a finished forged material, and FIG. 1F shows a forged crankshaft.

  The crankshaft 1 illustrated in FIG. 1F includes five journal portions J1 to J5, four pin portions P1 to P4, a front portion Fr, a flange portion Fl, and eight crank arm portions (hereinafter simply referred to as “arm portions”). (Also called) 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 crankshaft 1 has counterweight portions (hereinafter also simply referred to as “weight portions”) W1 to W8 in all eight arm portions A1 to A8. Such a crankshaft 1 shown in FIG. 1F is mounted on a 4-cylinder engine and is a 4-cylinder-8-counterweight crankshaft.

  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. Also, “A” for the arm portion and “W” for the weight portion.

  In the manufacturing method shown in FIGS. 1A to 1F, the forged crankshaft 1 is manufactured as follows. First, a billet 2 having a predetermined length as shown in FIG. 1A is heated by a heating furnace (for example, an induction heating furnace or a gas atmosphere heating furnace), and then roll forming is performed. In the roll forming step, for example, the billet 2 is rolled and squeezed using a perforated roll to distribute the volume in the longitudinal direction and form the roll waste land 3 as an intermediate material (see FIG. 1B). Next, in the bending step, the roll wasteland 3 is partially crushed from a direction perpendicular to the longitudinal direction. Thereby, the volume of the roll wasteland 3 is allocated and the bending wasteland 4 which is the further intermediate material is shape | molded (refer FIG. 1C).

  Subsequently, in the roughing process, the rough forged material 5 is obtained by press-forging the bent rough ground 4 up and down using a pair of molds (see FIG. 1D). The rough forged material 5 is formed with the approximate shape of the crankshaft (final product). Further, in the finish punching process, the rough forging material 5 is press-forged using a pair of upper and lower molds to obtain the finished forging material 6 (see FIG. 1E). The finished forged material 6 has a shape that matches the crankshaft of the final product. At the time of roughing and finishing, surplus material flows out as burrs from between the split surfaces of the molds facing each other. For this reason, the rough forged material 5 and the finished forged material 6 both have large burrs B around the formed crankshaft.

  In the deburring process, for example, the burr B is punched and removed with a blade mold in a state where the finished forged material 6 with burr is held between a pair of molds. Thereby, a burr-free forged material is obtained, and the burr-free forged material has substantially the same shape as the forged crankshaft 1 shown in FIG. 1F.

  In the shaping process, the burrs-free forging material is slightly crushed from above and below with a mold to correct the burrs-free forging material to the dimensional shape of the final product. Here, the key points of the burr-free forging material include, for example, the shaft portion such as the journal portion J, the pin portion P, the front portion Fr, the flange portion Fl, the arm portion A, and the weight portion W. Thus, the forged crankshaft 1 is manufactured.

  The manufacturing process shown in FIGS. 1A to 1F is applicable not only to the crankshaft of the 4-cylinder-8-counterweight shown in FIG. 1F but also to various crankshafts. For example, the present invention can be applied to a crankshaft of a 4-cylinder-4 counterweight. In the case of a four-cylinder-four-counterweight crankshaft, a weight portion W is integrally provided in a part of the eight arm portions A. In addition, the manufacturing process is the same for crankshafts mounted on 3-cylinder engines, in-line 6-cylinder engines, V-type 6-cylinder engines, 8-cylinder engines, and the like. In addition, when adjustment of the arrangement angle of a pin part is required, a twist process is added after a deburring process.

  In recent years, in particular, reciprocating engines for automobiles are required to be lighter in order to improve fuel efficiency. For this reason, the demand for weight reduction is also increasing in the crankshaft mounted on the reciprocating engine. To reduce the weight of the forged crankshaft, it is effective to thicken the outer peripheral portion (arc portion) in the fan-shaped weight portion. Patent Documents 1 and 2 are related arts related to thickening of the outer peripheral portion of the weight portion.

  2A and 2B are schematic views showing the shape of the weight portion of the crankshaft described in Patent Document 1, FIG. 2A shows the journal portion side surface, and FIG. 2B shows the side surface. 2A and 2B, one weight portion and an arm portion integrated with the weight portion are extracted from the crankshaft, and the shape of the remaining crankshaft is omitted. 2B is a projection view from the direction indicated by the broken-line arrow in FIG. 2A.

  As shown in FIG. 2A, the weight portion W has, for example, a fan shape centered on the axis (rotation center) of the journal portion J, and includes a surface including the axis of the journal portion J and the axis of the pin portion P. It spreads at a predetermined angle on both sides of C (hereinafter also referred to as “weight portion center plane”). For this reason, the weight part W protrudes in the both sides of the width direction (refer the arrow which gave the hatching of FIG. 2A), respectively.

  In such a fan-shaped weight portion W, in Patent Document 1, a convex portion Wz that protrudes in the thickness direction of the weight portion W (axial direction of the crankshaft) is provided on the outer periphery of the journal portion side surface of the weight portion W. It has been proposed. If the outer peripheral side (arc side) of the weight portion W is made thicker in this way, the outer peripheral side has a distance from the axis (rotation center) of the journal portion J, so the center of gravity radius of the weight portion W increases. . Accordingly, a portion of the weight portion W close to the axis (rotation center) of the journal portion J can be thinned. For this reason, the mass of the weight part W can be reduced and, as a result, a forged crankshaft can be reduced in weight.

  The convex portion Wz has a thickness or a length along the eccentric direction of the pin portion that is constant in the reduction direction (width direction of the weight portion) or becomes smaller as the distance from the center surface of the weight portion increases. This is to prevent the die-drawing gradient from being reversed and to allow the forging material to be taken out from the mold.

  In Patent Document 2, it is proposed that the crankshaft is composed of a main body in which a portion other than the weight portion is integrally formed, a weight portion formed separately from the main body, and a connecting member that connects the main body and the weight portion. Has been. According to such a crankshaft proposed in Patent Document 2, since the weight portion is formed separately, the design freedom of the weight portion can be improved and the weight can be reduced.

JP, 2015-10642, A JP 2009-197979 A

  As described above, to reduce the weight of the forged crankshaft, it is effective to thicken the outer peripheral portion (arc portion) of the weight portion as described in Patent Document 1. However, since it is necessary to prevent the mold drawing gradient from being reversed, the outer peripheral portion (arc portion) of the weight portion and the journal portion side of the weight portion (the portion close to the axis (rotation center) of the journal portion J) ) Is thickened. For this reason, further reduction in weight has been desired.

  Moreover, in the crankshaft described in the above-mentioned patent document 2, it is necessary to manufacture a weight part separately from the main body. For this reason, in addition to the increase in the number of parts to be manufactured, a process for connecting the main body and the weight part is required, and as a result, the manufacturing process is greatly increased and the manufacturing cost is remarkably increased.

  An object of the present invention is to provide a forged crankshaft manufacturing method capable of reducing the weight of a forged crankshaft integrally having a weight portion without significantly increasing the number of manufacturing steps.

  A method of manufacturing a forged crankshaft according to an embodiment of the present invention includes a journal part serving as a rotation center, a pin part eccentric with respect to the journal part, a crank arm part connecting the journal part and the pin part, A forged crankshaft manufacturing method having a counterweight portion provided integrally with a crank arm portion.

  The manufacturing method includes die forging, the shape of the forged crankshaft, and one or both of the both ends in the width direction in which the counterweight portion protrudes among the counterweight portions, from the end portion to the width direction. A die forging step for obtaining a forged material with a burr formed with a surplus portion protruding along the burr, a burr removing step for obtaining a forged material without a burr by removing the burr from the forged material with a burr, and A bending step of bending the surplus portion with the pair of first molds with the width direction being the down direction, bending the surplus portion, and increasing the thickness at the end portion where the surplus portion protrudes; ,including.

  In the bending step, the surplus portion may be bent toward the surface of the counterweight portion on the pin portion side.

  In the die forging step, as the surplus portion, a first surplus portion is formed with the thickness direction position of the counterweight portion closer to the surface of the pin portion side, and the thickness direction position is defined on the journal portion side. The second surplus portion may be formed closer to the surface. In this case, in the bending step, the first surplus portion is bent toward the surface of the counterweight portion on the pin portion side by reducing the burr-free forging material with the first mold, and The second surplus portion is bent toward the surface of the counterweight portion on the journal portion side.

  In the bending step, the surplus portion may be bent toward the surface of the counterweight portion on the journal portion side.

  In the bending step, a region of the surface of the counterweight portion on the side where the surplus portion is bent is held by pressing the second mold, at least excluding the end portion from which the surplus portion protrudes. Is preferred. In this case, in the bending step, the second mold is moved in the downward direction of the first mold following the reduction of the first mold, and the second mold is pushed to the counterweight portion. It is preferable to maintain the contact position at a fixed position.

  The bending step is preferably performed in a shaping step of correcting the shape of the crankshaft by reduction using a mold.

  In the forging crankshaft manufacturing method of the present invention, a surplus portion protruding from the end portion in the width direction of the weight portion is formed in the die forging step, and the surplus portion is bent in the folding step to increase the thickness at the end portion of the weight portion. increase. Accordingly, a portion of the weight portion that is close to the axis of the journal portion can be thinned, and as a result, the forged crankshaft can be reduced in weight. Moreover, since the weight part is provided integrally with the arm part, it is not necessary to form the weight part separately from the main body and to connect the weight part to the main body. For this reason, it can prevent that a manufacturing process increases significantly and manufacturing cost increases remarkably.

FIG. 1A shows a billet in a manufacturing process of a conventional forged crankshaft. FIG. 1B shows a rough roll in the manufacturing process of a conventional forged crankshaft. FIG. 1C shows the bending wasteland in the manufacturing process of the conventional forged crankshaft. FIG. 1D shows a rough forged material in a manufacturing process of a conventional forged crankshaft. FIG. 1E shows a finished forged material in a manufacturing process of a conventional forged crankshaft. FIG. 1F shows a forged crankshaft in a conventional forged crankshaft manufacturing process. FIG. 2A is a schematic diagram showing the shape of the weight part of the crankshaft described in Patent Document 1, and shows the journal part side surface. FIG. 2B is a diagram illustrating a side surface of the weight portion of FIG. 2A. FIG. 3A is a schematic diagram showing the shape of the weight portion of the crankshaft targeted by the first embodiment, and shows the pin portion side surface. FIG. 3B is a diagram illustrating a side surface of the weight portion of FIG. 3A. 3C is a cross-sectional view taken along the line II of FIG. 3A. FIG. 4A is a schematic diagram illustrating the shape of the weight portion before bending in the first embodiment, and is a diagram illustrating the surface of the pin portion side. FIG. 4B is a diagram illustrating a side surface of the weight portion of FIG. 4A. 4C is a cross-sectional view taken along the line II-II in FIG. 4A. FIG. 5A is a schematic diagram showing the surface of the weight part on the pin part side, and shows the time when the second mold is pressed in the processing flow example of the bending process of the first embodiment. FIG. 5B is a schematic diagram illustrating the pin portion side surface of the weight portion, and illustrates the end of the rolling in the example of the processing flow in the bending process of the first embodiment. FIG. 6A is a cross-sectional view of the weight portion, and shows the time when the second mold is pressed in the processing flow example of the bending process of the first embodiment. FIG. 6B is a cross-sectional view of the weight portion, and shows the end of rolling in the example of the processing flow in the bending process of the first embodiment. FIG. 7A is a schematic diagram showing the shape of the weight portion of the crankshaft targeted by the second embodiment, and shows the pin portion side surface. FIG. 7B is a diagram illustrating a side surface of the weight portion of FIG. 7A. FIG. 7C is a diagram showing a journal side surface of the weight part of FIG. 7A. FIG. 7D is a cross-sectional view taken along the line III-III in FIG. 7A. FIG. 8A is a schematic diagram illustrating the shape of the weight portion before bending in the second embodiment, and is a diagram illustrating the surface on the pin portion side. FIG. 8B is a diagram illustrating a side surface of the weight portion of FIG. 8A. FIG. 8C is a diagram showing a journal side surface of the weight part of FIG. 8A. 8D is a cross-sectional view taken along the line IV-IV in FIG. 8A. FIG. 9A is a cross-sectional view of the weight portion, and shows the time when the second mold is pressed in the processing flow example of the bending process of the second embodiment. FIG. 9B is a cross-sectional view of the weight portion, and shows the end of the rolling in the example of the processing flow in the bending process of the second embodiment. FIG. 10A is a schematic diagram illustrating the shape of the weight portion of the crankshaft targeted by the third embodiment, and is a diagram illustrating the surface on the journal portion side. FIG. 10B is a diagram illustrating a side surface of the weight portion of FIG. 10A. FIG. 10C is a VV cross-sectional view of FIG. 10A. FIG. 11A is a schematic diagram illustrating the shape of the weight portion before bending in the third embodiment, and is a diagram illustrating the surface on the journal portion side. FIG. 11B is a diagram illustrating a side surface of the weight portion in FIG. 11A. FIG. 11C is a cross-sectional view taken along the line VI-VI in FIG. 11A. FIG. 12A is a cross-sectional view of the weight portion, and shows the time when the second mold is pressed in the example of the processing flow in the bending process of the third embodiment. FIG. 12B is a cross-sectional view of the weight portion, and shows the end of the rolling in the example of the processing flow in the bending process of the third embodiment.

  The forged crankshaft targeted by the present invention includes a journal portion serving as a rotation center, a pin portion eccentric to the journal portion, an arm portion connecting the journal portion and the pin portion, and a weight provided integrally with the arm portion. Part. The weight portion may be provided on all the arm portions or a part of the arm portions.

  The present invention targeting such a forged crankshaft can employ, for example, the first to third embodiments. In each of the first to third embodiments, the end portion in the width direction is thickened among the weight portions, but the direction (side) in which the end portion projects is different with the thickening. Hereinafter, first to third embodiments will be described with reference to the drawings. In the description of the second embodiment and the third embodiment, the description of the parts common to the first embodiment is omitted as appropriate.

1. First Embodiment [Shape of Crankshaft]
3A to 3C are schematic views showing the shape of the weight portion of the crankshaft targeted by the first embodiment. FIG. 3A is a view showing the pin portion side surface, FIG. 3B is a view showing the side surface, and FIG. FIG. 3A to 3C, the fan-shaped weight part and the arm part integrated with the weight part are extracted from the bent (final product) crankshaft, and the remaining crankshaft shapes are shown. Is omitted. FIG. 3B is a projection view from the direction indicated by the broken-line arrow in FIG.

  As shown in FIGS. 3A to 3C, the crankshaft targeted by the first embodiment is such that both end portions (Wa, Wb) of the weight portion W are thicker than portions around the journal portion J of the weight portion W. It projects to the pin part P side along the direction and is thick. As shown in the figure, the end portions (Wa, Wb) of the weight portion W include a top portion having the largest width among the weight portions W and a peripheral portion thereof. Since the weight portion W spreads on both sides of the weight portion center plane C, the two end portions (Wa, Wb) are located on both sides of the weight portion center plane C, respectively. In the present invention, the width direction of the weight portion W means a direction in which the weight portion W (top portion) protrudes. For example, as shown by a hatched arrow in FIG. The vertical direction.

  In the crankshaft targeted by the first embodiment, the end portions (Wa, Wb) of the weight portion W are thickened, and the end portions (Wa, Wb) are the axis (rotation) of the journal portion J. Center) and distance. Thereby, since the gravity center radius of the weight part W becomes large, the site | part close | similar to the axial center (rotation center) of the journal part J among the weight parts W can be thinned. For this reason, the mass of a weight part can be reduced and, as a result, a forged crankshaft can be reduced in weight.

[Shape before bending]
4A to 4C are schematic views showing the shape of the weight portion before bending in the first embodiment, FIG. 4A is a view showing a pin portion side surface, FIG. 4B is a view showing a side surface, and FIG. It is II sectional drawing. 4A to 4C, one weight portion and an arm portion integrated with the weight portion are extracted from the shape of the crankshaft, and the shape of the remaining crankshaft is omitted. 4B is a projection view from the direction indicated by the broken-line arrow in FIG. 4A.

  As shown in FIGS. 4A to 4C, the weight portion W before bending differs from the weight portion after bending in the shape of the surface of the pin portion P side of both end portions (Wa, Wb), and in addition, the surplus portion (Ea , Eb). That is, the weight part W before bending matches the shape of the weight part after bending except for the shape of the pin part side surface of both ends (Wa, Wb) and the surplus part (Ea, Eb). Since the shape of the surface of the pin portion P side of both end portions (Wa, Wb) is different, the thickness of both end portions (Wa, Wb) before bending is the thickness of the inner region Wc of both end portions (one end portion Wa and The thickness between the other ends Wb) or smaller than the thickness of the inner region Wc at both ends.

  The surplus portions (Ea, Eb) protrude from both end portions (Wa, Wb) of the weight portion W along the width direction of the weight portion W, respectively. The surplus portions (Ea, Eb) protrude from the side surface of the weight portion W surrounded by the two-dot chain line in FIG. 4B, in other words, from the side surfaces of both end portions (Wa, Wb). In the surplus portions (Ea, Eb) shown in the same drawing, the position of the weight portion in the thickness direction is arranged closer to the surface of the pin portion P side of the side surfaces of both end portions (Wa, Wb). That is, the surplus portions (Ea, Eb) are disposed near the surface of the weight portion on the side to be bent.

  In the present invention, the surplus portions (Ea, Eb) are not portions that flow out as burrs but mean portions that protrude from the side surface position of the weight portion after bending.

[Production method]
The first embodiment includes a die forging process, a deburring process, and a bending process in that order. As a pre-process of the die forging process, for example, a preforming process can be provided. Moreover, a shaping process can be provided as a post process of a bending process, for example. Moreover, a bending process can also be implemented in a shaping process. In addition, when adjustment of the arrangement angle of a pin part is required, a twist process is added between the deburring process and the shaping process. All of these steps are performed in a series of heat.

  The preforming process can be constituted by, for example, a roll forming process and a bending process. In the roll forming process and the bending process, the volume of the billet (raw material) is distributed and the bending waste is formed.

  In the die forging process, a forged material with burrs in which the shape of the crankshaft is formed is obtained. In the forged material with burrs, the shapes of the journal portion J, the pin portion P, and the arm portion A as shown in FIGS. 4A to 4C are formed, and surplus portions (Ea, Eb) are formed. . The die forging process for obtaining such a forged material with burrs can be configured by providing a roughing process and a finishing process in that order.

  The die cutting gradient in the die forging step does not become a reverse gradient at any of the portions corresponding to the both end portions (Wa, Wb) and the surplus portions (Ea, Eb). For this reason, both rough and finish die forging can be performed without any trouble, and a forged material with burrs can be obtained.

  In the deburring step, for example, the burrs are removed from the forged material while the forged material with burrs is held between a pair of molds. Thereby, a burr-free forging material can be obtained.

  In the bending step, the obtained burr-free forging material is reduced with a pair of first dies. At that time, the surplus portion is bent toward the surface of the weight portion on the pin portion side to increase the thickness of both end portions of the weight portion. The processing flow of the bending process will be described later.

  In the shaping process, the burr-free forging material is crushed with a pair of molds and corrected to the dimensional shape of the final product. In addition, when adjustment of the arrangement angle of a pin part is required, the arrangement angle of a pin part is adjusted in a twist process. With such a process, the forged crankshaft manufacturing method of the present embodiment obtains a forged crankshaft.

[Bending process]
FIG. 5A to FIG. 6B are schematic diagrams illustrating an example of a processing flow in a bending process. 5A and 5B show the pin portion side surface of the weight portion, FIG. 5A shows when the second mold is pressed, and FIG. 5B shows the end of the reduction. 5A and 5B show the forged material 30 without burrs and the pair of first molds 10 at the top and bottom, and the second mold 22 is not shown for easy understanding of the drawings.

  6A and 6B are cross-sectional views of the weight portion. FIG. 6A shows a state where the second mold is pressed, and FIG. In the figure, a forged material 30 without burrs, a pair of first molds 10 and a second mold 22 are shown.

  In the bending process, a pair of first molds 10 are used. The first mold 10 includes an upper mold 11 and a lower mold 12, and a mold engraving portion is engraved on each of the upper mold 11 and the lower mold 12. A part of the final product shape of the crankshaft is reflected in the mold engraving portion. Specifically, in order to bend the surplus portion, the shape of both end portions of the weight portion is reflected in the mold engraving portion. Moreover, the site | part which contributes to bending of the surplus part in the type | mold engraving part inclines so that the surplus part may be guided toward the pin part side surface.

  However, as shown in FIGS. 6A and 6B, in the first mold 10, the portions corresponding to the inner regions Wc at both ends of the portions corresponding to the pin portion P-side surface of the weight portion are opened. As shown in the figure, the second mold 22 may be accommodated in the open portion. A mold engraving portion is engraved in the second mold 22, and the shape of the inner region Wc at both ends of the surface of the weight portion on the pin portion P side is reflected in the mold engraving portion.

  The part corresponding to the surface of the weight part W on the journal part J side may be held by the mold engraving part of the first mold 10 as shown in FIGS. 6A and 6B. Alternatively, it may not be held by the mold engraving portion of the first mold 10.

  The second mold 22 is independent of the first mold 10 and can be moved forward and backward so as to come into contact with or separate from the surface of the weight part on the pin part P side. The forward / backward movement of the second mold 22 is executed by a hydraulic cylinder or the like connected to the second mold 22. Such a second mold 22 is preferably movable along the reduction direction of the first mold 10. The second mold 22 can be moved in the down direction by using appropriate means such as a spring or a hydraulic cylinder separately from the drive source for the forward and backward movement. In this case, the second mold 22 may be configured such that only the second mold 22 itself can move up and down, or may be configured to move up and down integrally with a hydraulic cylinder or the like that gives the advancing and retreating movement of the second mold 22. .

  An example of a processing flow in the bending process using the first mold 10 and the second mold 22 will be described. First, the upper mold 11 and the lower mold 12 of the first mold 10 are separated from each other, and the forged material 30 after removing the burr is disposed between the upper mold 11 and the lower mold 12 in this state.

  Next, when the second mold 22 is used, the second mold 22 is advanced and pressed against the surface of the weight part W on the pin part P side, as shown in FIG. 6A. Thereby, the pin part P side surface of the weight part W is held by the second mold 22. However, the 2nd metal mold | die 22 is not pressed about the area | region of both ends (Wa, Wb) among the pin part P side surfaces of the weight part W (refer FIG. 6A). This is because if the mold is pressed and held in that region, it becomes impossible to increase the thickness at both end portions (Wa, Wb) of the weight portion by bending the surplus portions (Ea, Eb). In addition, when providing a surplus part in one edge part (Wa, Wb), you may press the 2nd metal mold | die 22 to the edge part which does not provide a surplus part.

  In this state, the first mold 10 is moved so that the upper mold 11 and the lower mold 12 are close to each other, and more specifically, the upper mold 11 is lowered to the bottom dead center. As a result, the burr-free forging material 30 is reduced by the first mold 10. During the reduction, as shown in FIG. 6B, both surplus portions (Ea, Eb) are bent toward the pin portion P side surface of the weight portion W along the mold engraving portion of the first mold 10. Project to the pin part P side. As a result, the thickness of both end portions (Wa, Wb) of the weight portion increases.

  Subsequently, the upper mold 11 and the lower mold 12 of the first mold are separated from each other, and more specifically, the upper mold 11 is raised to the top dead center. When the second mold is used, the second mold is retracted and retracted before the upper mold 11 and the lower mold 12 are separated. In a state where the upper die 11 and the lower die 12 are separated from each other, the bent burred forging material is carried out.

  Such a first embodiment can provide a crankshaft in which the end portions (Wa, Wb) of the weight portion W are thickened. Thereby, since the center of gravity radius of the weight portion is increased, the portion near the axis of the journal portion J in the weight portion can be thinned, and as a result, the forged crankshaft can be reduced in weight.

  The first embodiment includes a die forging step and a deburring step, as in a conventional general manufacturing method. In the bending step, the forged material without burrs is pressed down by the pair of first dies to bend the surplus portion and increase the thickness at the end where the surplus portion protrudes. For this reason, the bending process can utilize the press machine conventionally used frequently. Therefore, it can carry out simply using the conventional manufacturing equipment.

  In the first embodiment, since the end of the weight portion is thickened by bending, it is not necessary to form the weight portion separately from the main body and to connect the weight portion to the main body. For this reason, it can prevent that a manufacturing process increases significantly and manufacturing cost increases remarkably.

2. Second Embodiment [Shape of Crankshaft]
7A to 7D are schematic views showing the shape of the weight portion of the crankshaft targeted by the second embodiment, FIG. 7A is a view showing the pin portion side surface, FIG. 7B is a view showing the side surface, and FIG. FIG. 7D is a cross-sectional view taken along the line III-III. 7B is a projection view from the direction indicated by the broken line arrow in FIG. 7A, and FIG. 7C is a projection view from the direction indicated by the broken line arrow in FIG. 7B.

  As shown in FIG. 7A to FIG. 7D, the crankshaft targeted by the second embodiment is such that both end portions (Wa, Wb) of the weight portion W are included in the weight portion W as in the first embodiment. Compared with the area around the journal part J, it is thicker. The crankshaft targeted by the second embodiment is different from the first embodiment in that both end portions (Wa, Wb) of the weight portion W are thicker not only on the pin portion P side but also on the journal portion J side. Overhang along the direction. As in the first embodiment, the crankshaft targeted by the second embodiment can reduce the thickness of the portion near the axis of the journal portion J in the weight portion W, thereby reducing the weight of the forged crankshaft. Can be

[Shape before bending]
8A to 8D are schematic views showing the shape of the weight part before bending in the second embodiment, FIG. 8A is a view showing the pin part side surface, FIG. 8B is a view showing the side surface, and FIG. 8C is a journal part. The figure which shows a side surface and FIG. 8D are IV-IV sectional drawings.

  As shown in FIGS. 8A to 8D, the weight part W before bending in the second embodiment is similar to the weight part after bending in the second embodiment, as compared with the weight part after bending, pin portions P at both ends (Wa, Wb). The shape of the side surface is different, and additionally, it is different in that it has two extra portions (Ea, Eb) arranged closer to the surface of the pin portion P side. Furthermore, the weight part W before bending of the second embodiment is different in the shape of the journal part J side surface of both end parts (Wa, Wb), and has two surplus parts arranged near the journal part J side surface ( Ec, Ed).

  Such a weight part W before bending includes the shape of the surface on the pin part P side of both end parts (Wa, Wb), the shape of the journal part J side surface of both end parts (Wa, Wb), and the surplus part (Ea , Eb, Ec, Ed), it matches the shape of the weight part after bending. The thickness of both ends (Wa, Wb) before bending is the same as the thickness inside the both ends (Wa, Wb) or thinner than the thickness inside the both ends (Wa, Wb).

  Further, the surplus portions (Ea, Eb) disposed near the surface of the pin portion P side and the surplus portions (Ec, Ed) disposed near the surface of the journal portion J are both of the weight portion W. It protrudes from both end portions (Wa, Wb) of the weight portion W along the width direction. Those surplus portions (Ea, Eb, Ec, Ed) are all the regions surrounded by the two-dot chain line in FIG. 8B in the side surface of the weight portion W, in other words, the end portions (Wa, Wb). Projects from the side. The surplus portions (Ea, Eb) disposed near the surface of the pin portion P side and the surplus portions (Ec, Ed) disposed near the surface of the journal portion J side are arranged side by side in the thickness direction of the weight portion. Is done.

[Production method]
The second embodiment can employ the same manufacturing process as that of the first embodiment. In the die forging process of the second embodiment, a forged material with a burr in which the shape of the crankshaft is formed is obtained. In the forged material with a burr, a surplus portion disposed near the surface of the pin portion P side ( In addition to Ea, Eb), surplus portions (Ec, Ed) arranged near the surface of the journal portion J are formed. In the bending step, not only the surplus portions (Ea, Eb) arranged near the pin portion P side surface are bent toward the pin portion P side of the weight portion W, but also the surplus portions arranged near the journal portion J side surface. The meat portions (Ec, Ed) are bent toward the journal portion J side of the weight portion W. Thereby, the thickness of the both ends (Wa, Wb) of the weight part W is increased. The processing flow of the bending process will be described later.

[Bending process]
9A and 9B are cross-sectional views of the weight portion schematically showing an example of a processing flow in the bending process of the second embodiment. FIG. 9A shows a state in which the second mold is pressed, and FIG. Each is shown. The figure shows a forged material 30 without burr, a pair of first molds 10, a second mold 22 for holding the surface of the weight part W on the pin part P side, and the journal part J side of the weight part W. The 2nd metal mold | die 23 for hold | maintaining the surface is shown.

  A part of the final product shape of the crankshaft is reflected in the mold engraving portions of the upper mold 11 and the lower mold 12. Specifically, in order to bend the surplus portions (Ea, Eb) arranged near the pin portion P side surface and the surplus portions (Ec, Ed) arranged near the journal portion J side surface, the weight portion The shapes of both end portions (Wa, Wb) of W are reflected in the mold engraving portion. Moreover, the part which contributes to bending of the surplus part (Ea, Eb) arrange | positioned near the pin part P side surface among the mold engraving parts guides the surplus part toward the pin part P side surface. So as to be inclined. In addition, in the mold engraving portion, the portion that contributes to the bending of the surplus portion (Ec, Ed) arranged near the surface of the journal portion J side is guided toward the surplus portion of the journal portion J side surface. Inclined to do.

  However, as shown in FIGS. 9A and 9B, the first mold 10 of the second embodiment has both ends of the portion corresponding to the surface of the weight part at the pin portion P side, as in the first embodiment. The site | part corresponding to the inner side area | region Wc of a part (Wa, Wb) is open | released. Similarly to the first embodiment, the opening part may house the second mold 22 that holds the surface of the weight part on the pin part P side.

  In addition, the first mold 10 of the second embodiment is different from the first embodiment described above, in the region corresponding to the journal portion J side surface of the weight portion W, the inner region of both end portions (Wa, Wb). The part corresponding to Wd is open. A second mold 23 that holds the surface of the weight part W on the journal part J side may be accommodated in the open part. A mold engraving portion is engraved in the second mold 23, and the shape of the inner region of both end portions of the surface of the weight portion W on the journal portion J side is reflected in the mold engraving portion. Each of the second molds (22, 23) is independent from the first mold 10 and can be moved back and forth so as to come into contact with or separate from each surface of the weight portion. Further, it is preferable that the second molds (22, 23) are movable along the rolling-down direction of the first mold 10.

  An example of the processing flow of the bending process using such a first mold 10 and the second mold (22, 23) will be described. First, the upper mold 11 and the lower mold 12 of the first mold 10 are separated from each other, and the forged material 30 after removing the burr is disposed between the upper mold 11 and the lower mold 12 in this state.

  Next, when the second mold (22, 23) is used, the second mold (22, 23) is advanced and pressed against each surface of the weight part W, as shown in FIG. Each surface is held by a second mold (22, 23). However, the second mold is not pressed against the region of both end portions (Wa, Wb) in the pin portion P side surface and the journal portion J side surface of the weight portion W (see FIG. 9A). This is because if the second mold (22, 23) is pressed against the region and held, it becomes impossible to increase the thickness at both ends of the weight portion by bending the surplus portion.

  In this state, the burr-free forging material 30 is reduced by the first mold 10. During the reduction, as in the first embodiment, the surplus portions (Ea, Eb) near the surface of the pin portion P side are moved along the mold engraving portion of the first mold 10 to the pin portion P side of the weight portion W. Bend toward the surface and project to the pin part P side. In the second embodiment, the surplus portions (Ec, Ed) near the journal portion J side surface are further bent along the mold engraving portion of the first mold 10 toward the journal portion J side surface of the weight portion W. Project to the journal part J side. As a result, the thickness of both end portions (Wa, Wb) of the weight portion increases.

  Subsequently, the upper die 11 and the lower die 12 of the first mold are separated from each other, and the burr-free forging material that has been bent is carried out. When the second mold (22, 23) is used, the second mold (22, 23) is retracted and retracted before the upper mold 11 and the lower mold 12 are separated.

  Such a second embodiment can provide a crankshaft in which the end portions (Wa, Wb) of the weight portion W are thickened, as in the first embodiment. Thereby, a forged crankshaft can be reduced in weight. Moreover, it can carry out simply using the conventional manufacturing equipment. Furthermore, it is possible to prevent a significant increase in manufacturing process and a significant increase in manufacturing cost.

3. Third Embodiment [Crank Shaft Shape]
10A to 10C are schematic views showing the shape of the weight portion of the crankshaft targeted by the third embodiment, FIG. 10A is a view showing the journal portion side surface, FIG. 10B is a view showing the side surface, and FIG. Is a VV cross-sectional view.

  As shown in FIGS. 10A to 10C, the crankshaft targeted by the third embodiment is such that both end portions (Wa, Wb) of the weight portion W are within the weight portion, as in the first embodiment. It is thicker than the area around the journal. In the crankshaft targeted by the third embodiment, both end portions (Wa, Wb) of the weight portion W project along the thickness direction on the opposite side of the first embodiment, that is, on the journal portion J side. . The crankshaft targeted by the third embodiment can reduce the thickness of the portion near the axial center of the journal portion J in the weight portion, as in the first embodiment, thereby reducing the weight of the forged crankshaft. it can.

[Shape before bending]
FIG. 11A to FIG. 11C are schematic views showing the shape of the weight part before bending in the third embodiment, FIG. 11A is a view showing the journal part side surface, FIG. 11B is a view showing the side face, and FIG. It is VI sectional drawing.

  As shown in FIGS. 11A to 11C, the weight part W before folding of the third embodiment is different from the weight part after folding in that the shape of the journal part J side surface of both end parts (Wa, Wb) is different. This also differs in that it has two surplus portions (Ec, Ed) arranged near the surface of the journal portion J side.

  The weight part W before bending matches the shape of the weight part after bending except for the shape of the journal part J side surface of both ends (Wa, Wb) and the surplus part (Ec, Ed). To do. The thicknesses of both end portions (Wa, Wb) before bending are the same as the thicknesses of the inner regions Wd at both ends, or are thinner than the thicknesses of the inner regions Wd at both ends. Further, the surplus portions (Ec, Ed) protrude from both end portions (Wa, Wb) of the weight portion W along the width direction of the weight portion W, respectively. The surplus portions (Ec, Ed) protrude from the side surface of the weight portion W surrounded by the two-dot chain line in FIG. 11B, in other words, from the side surfaces of both end portions (Wa, Wb).

[Production method]
The third embodiment can employ the same manufacturing process as that of the first embodiment described above. In the die forging process of the third embodiment, a forged material with a burr in which the shape of the crankshaft is formed is obtained. In the forged material with a burr, a surplus portion disposed near the surface of the pin portion P side ( Instead of Ea, Eb), surplus portions (Ec, Ed) arranged near the surface of the journal portion J side are formed. In the bending step, the surplus portions (Ec, Ed) are bent toward the opposite side of the first embodiment, specifically, toward the journal portion J side surface of the weight portion W. Thereby, the thickness of the both ends (Wa, Wb) of the weight part W is increased. The processing flow of the bending process will be described later.

[Bending process]
12A and 12B are cross-sectional views of the weight portion schematically showing an example of a processing flow in the bending process of the third embodiment. FIG. 12A shows when the second mold is pressed, and FIG. Each is shown. 12A and 12B show a burr-free forged material 30, a pair of first molds 10, and a second mold 23 for holding the surface of the weight part W on the journal part J side.

  A part of the final product shape of the crankshaft is reflected in the mold engraving portions of the upper mold 11 and the lower mold 12. Specifically, in order to bend the surplus portions (Ec, Ed), the shapes of both end portions (Wa, Wb) of the weight portion W are reflected in the mold engraving portion. Moreover, the part which contributes to bending of the surplus part (Ec, Ed) in the mold engraving part is inclined so as to guide the surplus part (Ec, Ed) toward the journal part J side surface. .

  However, as shown in FIGS. 12A and 12B, the first mold 10 of the third embodiment differs from the first embodiment described above in that both ends of the portion corresponding to the journal portion J-side surface of the weight portion W are both ends. The site | part corresponding to the inner side area | region Wd of a part (Wa, Wb) is open | released. In this open part, you may accommodate the 2nd metal mold | die 23 holding the journal part J side surface of a weight part. A mold engraving portion is engraved in the second mold 23, and the shape of the inner region Wd of both end portions (Wa, Wb) in the journal portion J side surface of the weight portion W is included in the mold engraving portion. Is reflected. The second mold 23 is independent of the first mold 10 and can be moved back and forth so as to come into contact with or separate from the journal portion J side surface of the weight portion. It is preferable that the second mold 23 is movable along the reduction direction of the first mold 10.

  The part corresponding to the surface of the weight part W on the pin part P side may be held by the mold engraving part of the first mold 10 as shown in FIGS. 12A and 12B. Alternatively, it may not be held by the mold engraving portion of the first mold 10.

  An example of the processing flow of the bending process using the first mold 10 and the second mold 23 will be described. First, the upper mold 11 and the lower mold 12 of the first mold 10 are separated from each other, and the forged material 30 after removing the burr is disposed between the upper mold 11 and the lower mold 12 in this state.

  Next, when the second mold 23 is used, the second mold 23 is advanced and pressed against the journal part J side surface of the weight part W, as shown in FIG. Is held by the second mold 23. However, the 2nd metal mold | die 23 is not pressed against the area | region of both ends (Wa, Wb) among the journal part J side surfaces of the weight part W (refer FIG. 12A). If the second mold 23 is pressed and held in that region, it becomes impossible to increase the thickness at both end portions (Wa, Wb) of the weight portion W by bending the surplus portions (Ec, Ed). is there.

  In this state, the forged material 30 without burrs is reduced by the first die 10, and the surplus portions (Ec, Ed) are bent along the die engraving portion of the first die 10. The bending direction is the opposite side of the first embodiment described above, and specifically, the surplus portion is bent toward the journal portion J side surface of the weight portion W so as to project to the journal portion J side. As a result, the thickness increases at both end portions (Wa, Wb) of the weight portion.

  Subsequently, the upper die 11 and the lower die 12 of the first mold are separated from each other, and the burr-free forging material that has been bent is carried out. When the second mold 23 is used, the second mold 23 is retracted and retracted before the upper mold 11 and the lower mold 12 are separated from each other.

  In the third embodiment, a crankshaft in which the end portions (Wa, Wb) of the weight portion W are thickened can be obtained as in the first embodiment. Thereby, a forged crankshaft can be reduced in weight. Moreover, it can carry out simply using the conventional manufacturing equipment. Furthermore, it is possible to prevent a significant increase in manufacturing process and a significant increase in manufacturing cost.

  In the method for manufacturing a forged crankshaft of the present invention, the end of the weight portion may project to either the pin portion side or the journal portion side along the thickness direction, or may project to both. That is, any of the first to third embodiments can be adopted. Moreover, you may vary the side (direction) which protrudes in both ends (Wa, Wb). For example, it is possible to adopt a form in which one end portion projects to the pin portion side along the thickness direction and the other end portion projects to the journal portion side along the thickness direction. From the viewpoint of improving the balance of the crankshaft, it is preferable that the end portions (Wa, Wb) of the weight portion protrude toward the pin portion side in the thickness direction as in the first embodiment. Thereby, the distance of the axial direction of the crankshaft from the gravity center of a pin part to the gravity center of a weight part becomes short, and the balance of a crankshaft improves.

  From the viewpoint of reducing the weight of the crankshaft, it is preferable that the end portions (Wa, Wb) of the weight portion protrude along the thickness direction on both the pin portion side and the journal portion side as in the second embodiment. Thereby, while being able to thicken an edge part (Wa, Wb), the site | part close | similar to the axial center of the journal part J among weight parts can be made thinner. As a result, the forged crankshaft can be further reduced in weight.

  In each of the first to third embodiments, the area of the weight part on the side where the surplus part is bent is excluded by pressing the second mold at least the region excluding the end part from which the surplus part protrudes. It is preferable to hold. Thereby, the surface shape of the weight part can be finished precisely. Note that the second mold only holds the surface of the weight part and does not push in, so that the force required to press the second mold is small.

  When the second mold is used in the bending process, the second mold is moved in the direction of the first mold following the reduction of the first mold, and the pressing position of the second mold against the weight portion is set. It is preferable to maintain a certain position. Thereby, the surface shape of the weight part can be finished more precisely.

  In any of the first to third embodiments, it is preferable that the bending step is performed in a shaping step of correcting the shape of the crankshaft by reduction using a mold. Thereby, the manufacturing process similar to the past can be employed. In this case, the shapes of the arm portion, the journal portion, and the pin portion are also reflected in the mold engraving portions of the pair of first molds. Further, when the forged material without burr is reduced with the first die, the surplus portion is bent and the shape of the crankshaft is corrected to obtain the final product shape.

  In the first to third embodiments, the surplus portions (Ea, Eb, Ec, Ed) are provided on both end portions (Wa, Wb) of the weight portion W, and both end portions are thickened. A surplus portion may be provided on one of both end portions (Wa, Wb) of the portion W, and only the end portion from which the surplus portion protrudes may be thickened. For example, in a crankshaft mounted on a V6 engine, the shape of the arm portion A (including the weight portion W) is asymmetric with respect to the weight portion center plane C. In such a case, the shape and range may be asymmetrical at both end portions (Wa, Wb) of the weight portion W.

  In the first to third embodiments, the surplus portions (Ea, Eb, Ec, Ed) are formed so as to protrude from both end portions (Wa, Wb) of the weight portion W along the width direction of the weight portion W, respectively. To do. At that time, it is preferable that the surplus portions (Ea, Eb, Ec, Ed) are arranged near the surface of the weight portion on the side where the surplus portions are bent, in the thickness direction of the weight portion W. Thereby, it is possible to easily perform bending deformation in a predetermined direction, it is possible to suppress deformation other than the end portion during bending, and in addition, it is possible to reduce the processing load.

  In the first to third embodiments, when the forged material without burr is reduced in the bending process, the weight portion is retained by holding a part or all of the pin portion P and the journal portion J of the forged material 30 without burr. It is preferable to adopt a posture in which the width direction is the reduction direction. Thereby, the surplus part (Ea, Eb, Ec, Ed) can be bent stably. In this case, the pair of first dies 10 is provided with an open portion for accommodating a holding die (not shown) for holding the burr-free forging material 30. The holding die holds the burr-free forging material 30 movably in the reduction direction in order to perform the reduction of the burr-free forging material 30 with the first die without any trouble. The movement is realized by, for example, a coil spring or a hydraulic cylinder.

  When the end portions (Wa, Wb) project along the thickness direction toward the pin portion P as in the first and second embodiments, the thickness tp (mm) of the end portion (Wa, Wb) of the weight portion W ) Is thickened, and the pin-side surface at the end exceeds the position of the pin thrust surface (not shown), there is a risk of interference with other members during use. For this reason, it is preferable to set the thickness tp (mm) of the end portions (Wa, Wb) of the weight portion W so that the pin portion side surface of the end portion does not exceed the position of the pin thrust surface. Here, the pin thrust surface is a portion that is provided on the surface of the arm portion on the pin portion side and restricts the movement of the connecting rod in the thrust direction.

  Further, when the end portions (Wa, Wb) project along the thickness direction toward the journal J portion as in the second and third embodiments, the thickness tp of the end portions (Wa, Wb) of the weight portion W If the thickness of (mm) is increased and the journal side surface at the end exceeds the position of the journal thrust surface (not shown), there is a possibility of interference with other members during use. For this reason, it is preferable to set the thickness tp (mm) of the end portions (Wa, Wb) of the weight portion W so that the journal side surface of the end portion does not exceed the position of the journal thrust surface. Here, the journal thrust surface is provided on the journal portion side surface of the arm portion and restricts the movement of the crankshaft in the thrust direction with respect to the engine body.

  The width bp (mm, see FIG. 3A) of the end portions (Wa, Wb) to be thickened is a ratio (bp / ba) to the width ba (mm, see FIG. 3A) of the weight portion W, and is 25% or less. Is preferred. If the width ba of the weight portion W exceeds 25%, the effect of reducing the weight may be reduced. More preferably, it is 15% or less. On the other hand, in order to make the thickened end portions (Wa, Wb) function more significantly, the lower limit of the width ba of the weight portion W is preferably 2% or more.

  In 1st-3rd embodiment, you may combine the technique which thickens the outer peripheral part (arc part) of a weight part. Specifically, in the crankshaft shown in FIGS. 2A and 2B, the end of the weight portion may be further thickened.

  The present invention can be effectively used for manufacturing a forged crankshaft mounted on a reciprocating engine.

1: Forged crankshaft, J, J1-J5: Journal part, P, P1-P4: Pin part,
Fr: front part, Fl: flange part, A, A1 to A8: crank arm part,
W, W1 to W8: counterweight portion, Wa, Wb: end portions in the width direction of the weight portion,
Wc: Inner region of both ends of the weight side pin portion side surface,
Wd: Inner region of both ends of the journal portion side surface of the weight portion,
Ea, Eb: surplus portion arranged near the pin side surface,
Ec, Ed: surplus part arranged near the journal part side surface,
10: first mold, 11: upper mold, 12: lower mold, 22, 23: second mold,
30: Forged material without burr

Claims (7)

A journal part serving as a rotation center; a pin part eccentric to the journal part; a crank arm part connecting the journal part and the pin part; and a counterweight part provided integrally with the crank arm part. A method for manufacturing a forged crankshaft, comprising:
The manufacturing method is
By die forging, together with the shape of the forged crankshaft, one or both of the counterweight portions projecting from the end portion along the width direction at both or both ends in the width direction where the counterweight portion protrudes. A die forging process to obtain a forged material with a burr in which the surplus portion is formed;
By removing burrs from the forged material with burrs, a deburring step for obtaining a burrs-free forged material,
A bending step of bending the surplus portion by bending the forged material without burrs with a pair of first molds with the width direction as the down direction, and increasing the thickness at the end portion where the surplus portion protrudes. And a method for producing a forged crankshaft. In the manufacturing method of the forged crankshaft of Claim 1,
In the bending step, the surplus portion is bent toward the surface of the counterweight portion on the side of the pin portion. In the manufacturing method of the forged crankshaft of Claim 1,
In the die forging step, as the surplus portion, a first surplus portion is formed with the thickness direction position of the counterweight portion closer to the surface of the pin portion side, and the thickness direction position is defined on the journal portion side. Mold the second surplus part closer to the surface,
In the bending step, the first surplus portion is bent toward the surface of the counterweight portion on the pin portion side by reducing the burr-free forging material with the first die, and the second surplus portion A method for producing a forged crankshaft, wherein a meat part is bent toward a surface of the counterweight part on the journal part side. In the manufacturing method of the forged crankshaft of Claim 1,
In the bending step, the surplus portion is bent toward the journal portion side surface of the counterweight portion. In the manufacturing method of the forged crankshaft of any one of Claims 1-4,
In the bending step, a region of the surface of the counterweight portion on the side where the surplus portion is bent is held by pressing the second mold, at least excluding the end portion from which the surplus portion protrudes. , Manufacturing method of forged crankshaft. In the manufacturing method of the forge crankshaft of Claim 5,
In the bending step, the second mold is moved in the downward direction of the first mold following the reduction of the first mold, and the pressing position of the second mold to the counterweight portion is set. A method of manufacturing a forged crankshaft that maintains a fixed position. In the manufacturing method of the forged crankshaft of any one of Claims 1-6,
The forging crankshaft manufacturing method, wherein the bending step is performed in a shaping step of correcting the shape of the crankshaft by reduction using a mold.

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