JP2016215227A - 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 forged crank shaft and an excess thickness part Ea protruding from an outer peripheral surface Wa of a weight part W to a fan-shaped radial direction are formed by a die-forging; a deburring step obtaining a forged material 40 without burrs by removing burrs from the forged material with burrs; and a bending step in which a first metal mold 11 is moved from the outer peripheral surface Wa side to a journal part J side to bend the excess thickness part Ea by pressing the first metal mold 11 against the excess thickness part Ea so that thickness is increased at an edge part Wb of the outer peripheral surface in the weight part W.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 of billet. The billet has a round or square cross section and a constant cross-sectional area over its 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 four-cylinder engine.

  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 can be applied to various crankshafts as well as the 4-cylinder-8-piece counterweight crankshaft as shown in FIG. 1F. For example, the present invention can be applied to a crankshaft of a 4-cylinder-4 counterweight. In the crankshaft of the four-cylinder / four-piece counterweight, the 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 peripheral portion of the outer peripheral surface among the fan-shaped weight portions. Patent Documents 1 and 2 are related arts related to thickening of the peripheral portion of the outer peripheral surface.

  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 W and an arm portion A that is integral with the weight portion W 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”).

  In Patent Document 1, it is proposed to provide a convex portion Wz around the outer peripheral surface Wa of the weight portion W, and the convex portion Wz extends from the surface of the weight portion W on the journal portion J side in the thickness direction of the weight portion W ( It protrudes in the axial direction of the crankshaft. If the peripheral portion of the outer peripheral surface Wa of the weight portion W is thickened by providing such a convex portion Wz, the peripheral portion of the outer peripheral surface Wa has a distance from the axis (rotation center) of the journal portion J. Therefore, the center of gravity radius of the weight portion W is increased. Accordingly, the peripheral portion of the journal portion J in the weight portion W 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 of the weight portion has a thickness or a length along the eccentric direction of the pin portion that is constant in the reduction direction (the width direction of the weight portion, see the hatched arrow in FIG. 2A), or the weight portion center plane C It gets smaller as you move away from it. This is to prevent the die-drawing gradient from being reversed in the die forging step and to allow the forging material to be taken out from the die.

  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 peripheral portion of the outer peripheral surface Wa of the weight portion as shown in FIGS. 2A and 2B. Here, when the peripheral portion of the outer peripheral surface Wa of the weight portion is thickened, the inner peripheral side region Wc (FIG. 2A) of the edge portion is compared with the edge portion Wb of the outer peripheral surface (outside the two-dot chain line in FIG. 2A). (Inside the two-dot chain line) has a small contribution to improving the balance ratio (enlarging the center of gravity radius) and hinders weight reduction. In the crankshaft described in Patent Document 1, since it is necessary to prevent the mold drawing gradient from being reversed, the portion sandwiched between the outer peripheral surface Wa of the weight portion and the straight line Wy extending in the width direction. Is thickened. As a result, in the weight portion of the crankshaft described in Patent Document 1, the inner peripheral side region Wc of the edge portion of the outer peripheral surface must be thickened. For this reason, it has been desired to further reduce the weight by thickening only the portion that greatly contributes to improving the balance ratio, that is, the edge Wb of the outer peripheral surface.

  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, the number of parts to be manufactured is increased and a step of connecting the main body and the weight portion is required. As a result, the manufacturing process is greatly increased and the manufacturing cost is remarkably increased.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a forged crankshaft manufacturing method capable of obtaining a forged crankshaft with reduced weight without greatly increasing the number of manufacturing steps in a forged crankshaft having an integral weight portion. It is in.

  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, It is a manufacturing method of the forge crankshaft which has a fan-shaped counterweight part provided integrally with a crank arm part.

  The manufacturing method obtains a forged material with a burr formed by die forging, together with the shape of the forged crankshaft and a surplus portion protruding from the outer peripheral surface of the counterweight portion along the radial direction of the fan shape. A die forging step, a deburring step of removing a burr from the forged material with burrs, and obtaining a burr-free forged material, and moving the first die from the outer peripheral surface side toward the journal part side. And bending the surplus part by pressing the first mold against the surplus part and increasing the thickness at the edge of the outer peripheral surface of the counterweight part.

  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, by moving the first mold, the first surplus portion is bent toward the surface of the counterweight portion on the pin portion side, and the second surplus portion is The counterweight portion is bent toward the surface of 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, it is preferable that at least a region excluding the edge of the outer peripheral surface of the surface of the counterweight portion on the side where the surplus portion is bent is held by pressing the second mold.

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

  In the forging crankshaft manufacturing method of the present invention, a surplus portion protruding from the outer peripheral surface of the weight portion is formed in the die forging step, and the surplus portion is bent by the first mold in the bending step, and the outer periphery of the weight portion is formed. Increase the thickness at the edge of the surface. Thereby, the other part of the weight 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. 3B is a cross-sectional view taken along the line II of FIG. 3A. FIG. 4A is a schematic diagram showing the shape of the weight part before bending in the first embodiment, and shows the pin part side surface. 4B 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 showing the pin portion side surface of the weight portion, and shows the end of the bending in the example of the processing flow of the bending step 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 bending in the example of the processing flow of 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 view showing the journal side surface of the weight part of FIG. 7A. 7C is a cross-sectional view taken along the line III-III in FIG. 7A. FIG. 8A is a schematic diagram showing the shape of the weight part before bending in the second embodiment, and shows the pin part side surface. FIG. 8B is a diagram showing a journal side surface of the weight part of FIG. 8A. 8C 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 bending in the processing flow example of 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. 10B 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. 11B 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 bending 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 edge of the outer peripheral surface of the weight portion is thickened, but the direction (side) in which the edge of the outer peripheral surface protrudes is different with the increase in thickness. 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 and 3B are schematic views showing the shape of the weight part of the crankshaft targeted by the first embodiment, FIG. 3A is a view showing the surface of the pin part side, and FIG. 3B is a cross-sectional view taken along II (weight) FIG. 3A and 3B, the fan-shaped weight part W and the arm part A integrated with the weight part W are extracted from the bent crankshaft (final product), and the remaining cranks are shown. The shape of the shaft is omitted.

  As shown in FIG. 3A and FIG. 3B, the weight portion W of the crankshaft targeted by the first embodiment is such that the edge Wb of the outer peripheral surface is pinned in the thickness direction as compared with the peripheral portion of the journal portion J. Projects to the part P side and is thick. As shown in FIG. 3A, the edge Wb of the outer peripheral surface of the weight portion W is shaped along the outer peripheral surface Wa of the weight portion W, and has a predetermined length from the outer peripheral surface Wa to the inner peripheral side (journal portion J side). Spread with.

  In the crankshaft targeted by the first embodiment, the edge portion Wb of the outer peripheral surface of the weight portion W is thickened, and the edge portion Wb of the outer peripheral surface is the axis (rotation center) of the journal portion J. And there is a distance. Further, the edge Wb of the outer peripheral surface has a shape along the outer peripheral surface Wa of the weight portion W, and the inner peripheral side region Wc of the edge Wb of the outer peripheral surface is made like the crankshaft described in Patent Document 1 described above. Not included. That is, the inner peripheral region Wc is not thickened. As a result, the center of gravity radius of the weight portion W is increased, so that other portions of the weight portion W, for example, the peripheral portion of the journal portion J and the inner peripheral side region Wc of the edge portion Wb of the outer peripheral surface 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 and 4B are schematic views showing the shape of the weight part before bending in the first embodiment, FIG. 4A is a view showing a pin part side surface, and FIG. 4B is a sectional view taken along line II-II. 4A and 4B, one weight portion W and the arm portion A integrated with the weight portion W are extracted from the shape of the crankshaft, and the remaining crankshaft shapes are omitted.

  As shown in FIG. 4A and FIG. 4B, the weight portion W before bending differs from the weight portion after bending in the shape of the surface on the pin portion P side of the edge portion Wb of the outer peripheral surface, and additionally, the surplus portion Ea is formed. It also differs in having it. That is, the weight part W before bending matches the shape of the weight part after bending except for the shape of the surface of the outer peripheral edge Wb on the pin part P side and the surplus part Ea. Since the shape of the surface of the pin portion P side at the edge Wb of the outer peripheral surface is different, the thickness of the edge Wb before bending is thinner than the thickness of the edge Wb after bending.

  The surplus part Ea protrudes from the outer peripheral surface Wa of the weight part W along the fan-shaped radial direction. Further, in the surplus portion Ea shown in the figure, the position of the weight portion in the thickness direction is arranged closer to the pin portion P side surface of the outer peripheral surface Wa. That is, the surplus portion Ea is disposed near the surface of the weight portion on the side to be bent.

  In the present invention, the surplus portion Ea means not a portion that flows out as burrs but a portion that protrudes from the position of the outer peripheral surface Wa 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 and 4B are formed, and the surplus portion Ea is 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 edge Wb and the surplus portion Ea of the outer peripheral surface of the weight portion W. 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 first mold is pressed against the surplus part by moving the first mold from the outer peripheral surface side of the weight part toward the journal part side. Thereby, the surplus part is bent toward the pin part side surface of the weight part, and the thickness is increased at the edge of the outer peripheral surface of the weight part. An example of the processing flow in 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 bending. 5A and 5B show the forged material 40 without burrs, the first mold 10 pressed against the surplus portion Ea, and a pair of holding molds 30 at the top and bottom to facilitate understanding of the drawings. Therefore, the second mold 21 that holds the surface of the weight part W on the pin part P side is omitted.

  6A and 6B are cross-sectional views of the weight portion in the center plane of the weight portion, FIG. 6A shows the time when the second mold is pressed, and FIG. 6B shows the time when the bending is finished. In the figure, a forged material 40 without burrs, a first mold 11 and a second mold 21 holding the surface of the weight part W on the pin part P side are shown. Thus, the pair of holding molds 30 is omitted.

  In the bending step, the first mold 11 is used to bend the surplus portion Ea. The first mold 11 is engraved with a mold engraving portion. 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 Ea, the shape of the outer peripheral surface Wa of the weight portion W is reflected in the mold engraving portion. Moreover, the site | part which contributes to bending of the surplus part Ea among the type | mold engraving parts inclines so that the surplus part Ea may be guided toward the pin part P side surface.

  Such a first mold 11 can move back and forth from the outer peripheral surface Wa side of the weight portion W toward the journal portion J side. The forward / backward movement of the first mold 11 can be realized, for example, by connecting a hydraulic cylinder to the first mold 11. In this case, the first mold 11 may be moved along the eccentric direction of the pin portion P in accordance with the operation of the hydraulic cylinder (see the thick arrow in FIG. 5A). Further, the first mold 11 may be U-shaped along the outer peripheral surface Wa of the weight portion W.

  In the example of the processing flow shown in the figure, the burr-free forging material 40 is held by a pair of holding dies 30 at the top and bottom during bending. The holding mold 30 includes an upper mold 31 and a lower mold 32. On the upper mold 31 and the lower mold 32, a mold engraving portion is engraved. A part of the shape of the crankshaft is reflected in the mold engraving portion. For example, the shape of the pin part P, the journal part J, and the arm part A is reflected in the mold engraving part. Further, the shape around the journal portion J in the weight portion W may be reflected in the mold engraving portion. In the holding mold 30, the portion corresponding to the outer peripheral surface Wa of the weight portion W is opened so that the surplus portion can be bent by the first mold 11.

  Further, the mold engraving portion of the holding mold 30 does not reflect the shape of the inner peripheral side region Wc of the outer peripheral surface portion of the surface of the weight portion W on the pin portion P side. A part corresponding to the inner peripheral side region Wc of the part Wb is opened. This is to prevent the die-cutting gradient from becoming a reverse gradient. A second mold 21 as shown in FIGS. 6A and 6B may be disposed in the opening. A mold engraving portion is engraved in the second mold 21, and the shape of the inner peripheral region Wc is reflected in the mold engraving portion on the pin portion P side surface of the weight portion W.

  The second mold 21 is independent of the first mold 11 and the holding mold 30 and can be moved forward and backward so as to come into contact with or separate from the surface of the weight part W on the pin part P side. The forward / backward movement of the second mold 21 is executed by a hydraulic cylinder or the like connected to the second mold 21.

  An example of the processing flow of the bending process using such a first mold 11, the second mold 21, and the holding mold 30 will be described. First, the upper mold 31 and the lower mold 32 of the holding mold 30 are separated from each other, and the forged material 40 after removing the burr is disposed between the upper mold 31 and the lower mold 32 in this state. In this state, the upper mold 31 and the lower mold 32 of the holding mold 30 are moved so as to approach each other, and more specifically, the upper mold 31 is lowered to the bottom dead center. Thereby, the burr-free forging 40 is sandwiched and held between the upper die 31 and the lower die 32.

  Next, when the second mold 21 is used, the second mold 21 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 21. However, the 2nd metal mold | die 21 is not pressed about the area | region of the edge Wb of an outer peripheral surface 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 the edge Wb of the outer peripheral surface of the weight portion by bending the surplus portion Ea.

  Subsequently, as shown in FIGS. 5B and 6B, the first mold 11 is moved (advanced) from the outer peripheral surface Wa side of the weight part W toward the journal part J side. As a result, the surplus portion Ea is bent along the mold engraving portion of the first mold 11 toward the pin portion P side surface of the weight portion W so as to project to the pin portion P side. As a result, the thickness increases at the edge Wb of the outer peripheral surface of the weight portion. Since the surplus portion Ea is bent by the first mold 11, the force required for the first mold 11 to advance is smaller than that for punching by mold forging or punching.

  Subsequently, the first mold 11 is retracted and retracted. When the second mold 21 is used, the second mold 21 is also retracted and retracted. Then, the upper mold 31 and the lower mold 32 of the holding mold 30 are separated from each other, and more specifically, the upper mold 31 is raised to the top dead center. In a state where the upper die 31 and the lower die 32 are separated from each other, the bent burred forging material is carried out.

  Such a first embodiment can provide a crankshaft in which the edge portion Wb of the outer peripheral surface of the weight portion W is thickened. Thereby, since the center-of-gravity radius of a weight part becomes large, the other site | part of the weight part W can be thinned, As a result, a forged crankshaft can be reduced in weight.

  In the first embodiment, since the edge Wb of the outer peripheral surface of the weight portion is thickened by bending, it is not necessary to form the weight portion separately from the main body and 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 7C 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, and FIG. 7B is a view showing the journal portion side surface. FIG. 7C is a sectional view taken along line III-III.

  As shown in FIGS. 7A to 7C, the weight portion W of the crankshaft targeted by the second embodiment is such that the outer peripheral edge Wb is the peripheral portion of the journal portion J, as in the first embodiment. Is thicker than The weight portion W of the crankshaft targeted by the second embodiment is different from the first embodiment in that the outer peripheral edge Wb is not only in the pin portion P side but also in the journal portion J side in the thickness direction. Overhang along. In the crankshaft according to the second embodiment having such a weight portion W, the other portions of the weight portion W can be thinned, and the forged crankshaft can be reduced in weight, as in the first embodiment.

[Shape before bending]
8A to 8C are schematic views showing the shape of the weight part before bending in the second embodiment, FIG. 8A is a view showing the surface on the pin part side, FIG. 8B is a view showing the surface on the journal part side, and FIG. Fig. 4 is a sectional view taken along line IV-IV.

  As shown in FIGS. 8A to 8C, 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, on the pin part P side at the edge Wb of the outer peripheral surface. The shape of the surface is different, and in addition, there is a difference in having a surplus portion Ea arranged near the surface of the pin portion P side. Furthermore, the weight part W before bending of the second embodiment has a different shape on the surface of the journal part J side at the edge part Wb of the outer peripheral surface, and has a surplus part Eb arranged closer to the surface of the journal part J side. It is different.

  Such a weight part W before bending includes the shape of the surface of the pin part P side at the edge Wb of the outer peripheral surface, the shape of the surface of the journal part J side of the edge Wb of the outer peripheral surface, and the surplus parts (Ea, Eb Except for), it matches the shape of the weight part after bending. The thickness of the edge Wb of the outer peripheral surface before bending is smaller than the thickness of the edge of the outer peripheral surface after bending.

  Further, the surplus part Ea disposed near the pin P side surface and the surplus part Eb disposed near the journal part J side surface both have a fan-shaped diameter from the outer peripheral surface Wa of the weight part W. Project along the direction. The surplus part Ea arranged near the surface of the pin part P side and the surplus part Eb arranged near the surface of the journal part J side are arranged side by side in the thickness direction of the weight part W.

[Production method]
The second embodiment can employ the same manufacturing process as that of the first embodiment. In the die forging step of the second embodiment, a forged material with burrs in which the shape of the crankshaft is formed is obtained. In the forged material with burrs, the surplus portion Ea disposed closer to the surface of the pin portion P side. Not only that, the surplus portion Eb disposed near the surface of the journal portion J side is formed. In the bending step, the surplus portion Ea disposed near the surface of the pin portion P side is not only bent toward the pin portion P side of the weight portion W, but the surplus portion Eb disposed near the surface of the journal portion J side. Bend toward the journal portion J side of the weight portion W. Thereby, the thickness is increased at the edge Wb of the outer peripheral surface of the weight part W. An example of the processing flow in 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 the time when the second mold is pressed, and FIG. Each is shown. This figure is a cross-sectional view in the center plane of the weight portion. In the figure, the forged material 40 without burrs, the first die 11, the second die 21 holding the pin portion P side surface of the weight portion W, and the journal portion J side surface of the weight portion W are held. The second mold 22 is shown, and the holding mold is not shown in order to facilitate understanding of the drawing.

  A part of the final product shape of the crankshaft is reflected in the mold engraving portion of the first mold 11. Specifically, in order to bend the surplus portion Ea disposed near the surface of the pin portion P side and the surplus portion Eb disposed near the surface of the journal portion J side, the shape of the outer peripheral surface Wa of the weight portion W is This is reflected in the mold carving department. Moreover, the part which contributes to the bending of the surplus part Ea arrange | positioned near the pin part P side surface among mold engraving parts inclines so that the surplus part Ea may be guided toward the pin part P side surface. doing. In addition, the portion of the mold engraving portion that contributes to the bending of the surplus portion Eb arranged near the surface of the journal portion J side guides the surplus portion Eb toward the surface of the journal portion J side. Inclined. Such a first mold 11 can move back and forth from the outer peripheral surface Wa side of the weight portion W toward the journal portion J side.

  In the example of the processing flow shown in the figure, as in the first embodiment, the forged material 40 without burrs is held by a pair of holding dies (not shown) at the time of bending. A mold engraving portion is engraved in the upper mold and the lower mold of the holding mold, and a part of the shape of the crankshaft is reflected in the mold engraving section.

  As in the first embodiment, the holding mold according to the second embodiment allows the surplus portions (Ea, Eb) to be bent by the first die 11, so that the outer peripheral surface Wa of the weight portion W can be bent. The corresponding part is open. Also, the shape engraving portion of the holding mold does not reflect the shape of the inner peripheral side region Wc of the edge portion Wb in the surface of the pin portion P side of the weight portion W, and the edge portion Wb of the outer peripheral surface is not reflected. A part corresponding to the inner peripheral side region Wc is opened. A second mold 21 as shown in the figure may be disposed in the open part, and the pin part side surface of the weight part W may be held by the second mold 21.

  In addition, unlike the first embodiment described above, the mold engraving portion of the holding mold of the second embodiment includes the inner peripheral side region Wc of the edge portion Wb in the journal portion J side surface of the weight portion W. The portion corresponding to the inner peripheral side region Wc of the edge Wb of the outer peripheral surface is also opened without reflecting the shape. This is to prevent the die-cutting gradient from becoming a reverse gradient. A second mold 22 as shown in the figure may be disposed in the open part, and the journal part side surface of the weight part W may be held by the second mold 22. A mold engraving portion is engraved in the second mold 22, and the shape of the inner peripheral side region Wc of the outer peripheral edge Wb in the journal portion J side surface of the weight portion is formed in the mold engraving portion. It is reflected.

  Each of the second molds (21, 22) is independent from the first mold 11 and the holding mold, and can be moved forward and backward so as to come into contact with or separate from each surface of the weight portion. is there.

  An example of a processing flow of a bending process using such a first mold 11, a second mold (21, 22) and a holding mold will be described. First, the upper mold and the lower mold of the holding mold are separated from each other, and the forged material 40 after removing the burrs is disposed between the upper mold and the lower mold in that state. In this state, the upper mold and the lower mold of the holding mold are moved close to each other, and the burr-free forging material 40 is held between the upper mold and the lower mold.

  Next, when the second mold (21, 22) is used, the second mold (21, 22) is advanced and pressed against each surface of the weight part W as shown in FIG. Each surface is held by the second mold (21, 22). However, the second mold (21, 22) is not pressed against the region of the edge Wb of the outer peripheral surface of the surface of the weight portion W on the pin portion P side and the surface of the journal portion J (see FIG. 9A). When the second mold (21, 22) is pressed against and held in the region, it becomes impossible to increase the thickness at the edge Wb of the outer peripheral surface of the weight portion by bending the surplus portions (Ea, Eb). Because.

  In this state, the first mold 11 is moved (advanced) from the outer peripheral surface Wa side of the weight portion W toward the journal portion J side. Thus, as in the first embodiment, the surplus portion Ea near the surface of the pin portion P side is bent along the mold engraving portion of the first mold 11 toward the surface of the weight portion W on the pin portion P side, and the pin Project to the part P side. In the second embodiment, the surplus portion Eb near the surface of the journal portion J side is further bent along the mold engraving portion of the first mold 11 toward the surface of the journal portion J of the weight portion W, and the journal portion J side Overhang. As a result, the thickness increases at the edge Wb of the outer peripheral surface of the weight portion.

  Subsequently, the first mold 11 is retracted and retracted. When the second mold (21, 22) is used, the second mold (21, 22) is also retracted and retracted. Then, after the upper mold and the lower mold of the holding mold are separated from each other, the bent burr-free forging material is carried out.

  Such a second embodiment can provide a crankshaft in which the edge Wb of the outer peripheral surface of the weight portion W is thickened, as in the first embodiment. Thereby, a forged crankshaft can be reduced in weight. Moreover, it can prevent that a manufacturing process increases significantly and manufacturing cost increases remarkably.

3. Third Embodiment [Crank Shaft Shape]
10A and 10B 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, and FIG. 10B is a VV sectional view. .

  As shown in FIGS. 10A and 10B, the weight portion W of the crankshaft targeted by the third embodiment is such that the outer peripheral edge Wb is the peripheral portion of the journal portion J, as in the first embodiment. Is thicker than In the weight portion W of the crankshaft targeted by the third embodiment, the edge portion Wb of the outer peripheral surface projects in the thickness direction on the opposite side of the first embodiment, that is, on the journal portion J side. In the crankshaft according to the third embodiment having such a weight portion W, the other portions of the weight portion W can be thinned and the forged crankshaft can be reduced in weight as in the first embodiment.

[Shape before bending]
11A and 11B 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, and FIG. 11B is a VI-VI cross-sectional view.

  As shown in FIGS. 11A and 11B, the weight portion W before folding in the third embodiment is different from the weight portion after folding in the shape of the journal portion J side surface at the edge Wb of the outer peripheral surface. It also differs in that it has a surplus portion Eb. The weight part W before bending matches the shape of the weight part after bending except for the shape of the surface on the journal part J side at the edge Wb of the outer peripheral surface and the surplus part Eb. The thickness of the edge Wb of the outer peripheral surface before bending is thinner than the thickness of the edge Wb of the outer peripheral surface after bending.

  The surplus portion Eb protrudes from the outer peripheral surface Wa of the weight portion W along the fan-shaped radial direction. Further, in the surplus portion Eb shown in the drawing, the position of the weight portion in the thickness direction is disposed closer to the journal portion J-side surface of the outer peripheral surface Wa.

[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 burrs in which the shape of the crankshaft is formed is obtained. In the forged material with burrs, the surplus portion Ea disposed near the surface of the pin portion P side is obtained. Instead, the surplus part Eb arranged near the surface of the journal part J is formed. In the bending step, the surplus portion Eb is 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 edge Wb of the outer peripheral surface of the weight part W is increased. An example of the processing flow in 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 the processing flow of the bending process of the third embodiment. FIG. 12A shows the time when the second mold is pressed, and FIG. Each is shown. This figure is a cross-sectional view in the center plane of the weight portion. 12A and 12B show the burr-free forging material 40, the first die 11, and the second die 22 that holds the surface of the weight portion W on the journal portion J side to facilitate understanding of the drawings. Therefore, illustration of the holding mold is omitted.

  A part of the final product shape of the crankshaft is reflected in the mold engraving portion of the first mold 11. Specifically, in order to bend the surplus portion Eb, the shape of the outer peripheral surface Wa of the weight portion W is reflected in the mold engraving portion. Moreover, the part which contributes to bending of the surplus part Eb in the mold engraving part is inclined so as to guide the surplus part Eb toward the journal part J side surface.

  In the processing flow example of the third embodiment, as in the first embodiment, the burr-free forging 40 is held by a pair of holding dies at the top and bottom during bending. A mold engraving portion is engraved in the upper mold and the lower mold of the holding mold, and a part of the shape of the crankshaft is reflected in the mold engraving section. In this holding mold, the portion corresponding to the outer peripheral surface Wa of the weight part W is opened so that the surplus part Eb can be bent by the first mold 11.

  Further, the shape engraving portion of the holding mold does not reflect the shape of the inner peripheral side region Wc of the edge portion Wb in the journal portion J side surface of the weight portion W, and the edge portion Wb of the outer peripheral surface is not reflected. A part corresponding to the inner peripheral side region Wc is opened. A second mold 22 as shown in the figure may be disposed in the open portion. A mold engraving portion is engraved in the second mold 22, and the shape of the inner peripheral side region Wc of the outer peripheral edge Wb among the journal portion J side surfaces of the weight portion W is included in the mold engraving portion. Is reflected. The second mold 22 is independent of the first mold 11 and the holding mold 30, and can move forward and backward so as to come into contact with or separate from the journal part J side surface of the weight part W.

  An example of a processing flow of a bending process using such a first mold 11, a second mold 22, and a holding mold will be described. First, the upper mold and the lower mold of the holding mold are separated from each other, and the forged material 40 after removing the burrs is disposed between the upper mold and the lower mold in that state. In this state, the upper mold and the lower mold of the holding mold are moved close to each other, and the burr-free forging material 40 is held between the upper mold and the lower mold.

  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 journal part J side as shown in FIG. 12A. As a result, the journal part J 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 the edge Wb of an outer peripheral surface among the journal part J side surfaces of the weight part W (refer FIG. 12A). This is because if the second mold 22 is pressed and held in that region, it becomes impossible to increase the thickness at the edge Wb of the outer peripheral surface of the weight portion W by bending the surplus portion Eb.

  In this state, the first mold 11 is moved (advanced) from the outer peripheral surface Wa side of the weight portion W toward the journal portion J side. Thereby, the surplus portion Eb is bent along the mold engraving portion of the first mold 11 as in the first embodiment. However, in the third embodiment, the surplus portion Eb is bent toward the journal portion J side surface of the weight portion W, more specifically, on the opposite side of the first embodiment, and is projected to the journal portion J side. . As a result, the thickness increases at the edge Wb of the outer peripheral surface of the weight portion.

  Subsequently, the first mold 11 is retracted and retracted. When the second mold 22 is used, the second mold 22 is also retracted and retracted. Then, after the upper mold and the lower mold of the holding mold are separated from each other, the bent burr-free forging material is carried out.

  Such a third embodiment can provide a crankshaft in which the edge Wb of the outer peripheral surface of the weight portion W is thickened, as in the first embodiment. Thereby, a forged crankshaft can be reduced in weight. Moreover, it can prevent that a manufacturing process increases significantly and manufacturing cost increases remarkably.

  In the manufacturing method of the forged crankshaft of the present invention, the edge Wb of the outer peripheral surface of the weight part may project to either the pin part P side or the journal part J side along the thickness direction. Also good. That is, any of the first to third embodiments can be adopted. From the viewpoint of improving the balance of the crankshaft, it is preferable that the edge Wb of the outer peripheral surface of the weight portion protrudes in the thickness direction toward the pin portion P as in the first embodiment. Thereby, the distance in the axial direction of the crankshaft from the center of gravity of the pin part P to the center of gravity of the weight part W is shortened, and the balance of the crankshaft is improved.

  From the viewpoint of weight reduction of the crankshaft, it is preferable that the edge portion Wb of the outer peripheral surface of the weight portion protrudes along the thickness direction on both the pin portion P side and the journal portion J side as in the second embodiment. . As a result, the edge Wb of the outer peripheral surface can be made thicker, and other parts of the weight part W can be made thinner. As a result, the forged crankshaft can be further reduced in weight.

  In the first to third embodiments, in the surface of the weight portion W on the side where the surplus portions (Ea, Eb) are bent, the region excluding at least the edge Wb of the outer peripheral surface is defined as the second mold (21, It is preferable to hold by the pressing of 22). Thereby, the surface shape of the weight part W can be finished precisely. Note that the second mold (21, 22) only holds the surface of the weight portion W and does not push in, so that the force required to press the second mold (21, 22) is small.

  In 1st-3rd embodiment, it is preferable to implement a bending process by the shaping process which corrects the shape of a crankshaft by the reduction using a metal mold | die. Thereby, the manufacturing process similar to the past can be employed. In this case, a pair of shaping dies may be used instead of the pair of holding dies. The pair of shaping molds can be composed of an upper mold and a lower mold, and a mold engraving portion is engraved in each of the upper mold and the lower mold. A part of the final product shape of the crankshaft is reflected in the mold engraving part. Specifically, the mold engraving part includes the arm part A, the journal part J, the pin part P, the weight part W, and the flange part Fl. The shape of the front part Fr and the like is reflected. In addition, the shaping mold is provided with an open portion for placing the first mold 11 and the second mold (21, 22) in the same manner as the holding mold described above.

  When such a shaping mold is used, the following processing flow can be adopted. First, the upper mold and the lower mold of the shaping mold are separated from each other, and the forged material after removing the burr is placed between the upper mold and the lower mold in that state. In this state, the upper mold and the lower mold of the shaping mold are moved so as to approach each other, and the burr-free forging material 40 is pressed down between the upper mold and the lower mold. At that time, the shape of the crankshaft is corrected to obtain the final product shape except for the edge portion Wb of the outer peripheral surface of the weight portion W. Next, when the second mold (21, 22) is used, the second mold (21, 22) is advanced. Then, the 1st metal mold | die 11 is advanced and a surplus part is bent. Subsequently, the first mold 11 is retracted and retracted. When the second mold (21, 22) is used, the second mold (21, 22) is also retracted and retracted. Then, after the upper mold and the lower mold of the shaping mold are separated from each other, the burr-free forged material that has been bent and shaped is carried out.

  In the first to third embodiments, the surplus portions (Ea, Eb) are formed so as to protrude from the outer peripheral surface of the weight portion along the fan-shaped radial direction. At this time, it is preferable that the surplus portions (Ea, Eb) are arranged near the surface of the weight portion W on the side where the surplus portions (Ea, Eb) are bent. Thereby, bending deformation in a predetermined direction can be easily performed, deformation other than the edge Wb of the outer peripheral surface can be suppressed during bending, and in addition, a processing load can be reduced.

  As in the first and second embodiments, the edge Wb of the outer peripheral surface may protrude toward the pin portion P along the thickness direction. In this case, the thickness tp (mm, see FIG. 3B) of the edge Wb of the outer peripheral surface of the weight portion W is increased, and the pin portion P side surface of the edge Wb of the outer peripheral surface is the position of the pin thrust surface (not shown). Exceeding this may cause interference with other members during use. For this reason, it is preferable to set the thickness tp (mm) of the edge Wb of the outer peripheral surface of the weight part W so that the pin side surface of the edge Wb of the outer peripheral surface 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, as in the second and third embodiments, the edge Wb of the outer peripheral surface sometimes protrudes along the thickness direction toward the journal J portion. In this case, when the thickness tp (mm) of the edge Wb of the outer peripheral surface of the weight part W is increased and the journal part J side surface of the outer peripheral edge Wb exceeds the position of the journal 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 edge Wb of the outer peripheral surface of the weight W so that the journal side surface of the edge Wb of the outer peripheral surface 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.

  From the viewpoint of promoting weight reduction, the length L1 (mm, see FIG. 3A) of the edge portion Wb is a ratio (L1 / L2) to the length L2 (mm) of the weight portion W in the radial direction. % Or more is preferable, and 3% or more is more preferable. On the other hand, when L1 exceeds 50% in the ratio (L1 / L2), the periphery of the journal portion J of the weight portion W is included in the edge portion Wb, and there is a concern that weight reduction may be hindered. For this reason, it is preferable to set it as 50% or less, and 35% or less is more preferable. Here, the radial length L2 of the weight portion W is the difference between the radius R1 (mm, see FIG. 3A) of the outer peripheral surface Wa of the weight portion and the radius R2 (mm, see FIG. 3A) of the journal portion (R1−R2). ).

  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 edge portion of the outer peripheral surface of the weight portion may be further thickened.

  In the first to third embodiments, the edge portion Wb is thickened in the entire circumferential range of the outer peripheral surface Wa, that is, in a range from one top portion of the weight portion W to the other top portion. Such a form is suitable for a crankshaft in which the shape of the arm part A (including the weight part W) is symmetrical with respect to the weight part center plane C. Here, the top portion of the weight portion W is a portion that protrudes most in the width direction.

  The edge Wb may be thickened at a part in the circumferential direction of the outer peripheral surface Wa. Such a configuration is suitable for a crankshaft in which the shape of the arm portion A (including the weight portion W) is asymmetric with respect to the weight portion center plane C, for example, a crankshaft mounted on a V6 engine. The range in which the edge Wb of the outer peripheral surface is thickened can be changed by appropriately adjusting the circumferential range in which the surplus portions (Ea, Eb) are formed.

  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 part, Wa: outer peripheral surface of weight part,
Wb: edge part of outer peripheral surface of weight part, Wc: inner peripheral side area of edge part,
Ea, Eb: surplus part, 11: first mold, 21, 22: second mold,
30: Die for holding, 31: Upper die, 32: Lower die, 40: Forging material without burr

Claims (6)

A journal part serving as a center of rotation; a pin part eccentric to the journal part; a crank arm part connecting the journal part and the pin part; and a fan-shaped counterweight part provided integrally with the crank arm part; A forged crankshaft manufacturing method comprising:
The manufacturing method is
A die forging step for obtaining a forged material with a burr formed by die forging, together with the shape of the forged crankshaft, the surplus portion protruding from the outer peripheral surface of the counterweight portion along the radial direction of the fan shape,
By removing burrs from the forged material with burrs, a deburring step for obtaining a burrs-free forged material,
By moving the first mold from the outer peripheral surface side toward the journal portion side, the first mold is pressed against the surplus portion to bend the surplus portion, and the outer peripheral surface of the counterweight portion And a bending step of increasing the thickness at the edge of the 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, by moving the first mold, the first surplus portion is bent toward the surface of the counterweight portion on the pin portion side, and the second surplus portion is moved to the counterweight. Forging a crankshaft, wherein the forging crankshaft is bent toward the surface of the journal portion side of the portion. 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,
Forging crankshaft, wherein in the bending step, a region excluding at least an edge of the outer peripheral surface of the surface of the counterweight portion on the side where the surplus portion is bent is held by pressing a second mold. Manufacturing method. In the manufacturing method of the forged crankshaft of any one of Claims 1-5,
The method of manufacturing a forged crankshaft, wherein the bending step is performed in a shaping step of correcting the shape of the crankshaft by reduction using a pair of molds.

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