JP7406085B2 - Crankshaft manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing a crankshaft.

For example, a reciprocating engine installed in an automobile includes a crankshaft to convert reciprocating motion of a piston caused by combustion of fuel into rotational motion. The crankshaft has a journal, a pin, and an arm. The journal, pin, and arm are also referred to as a crank journal, crank pin, and crank arm, respectively. The journal is the main shaft of the crankshaft and rotates around its axis. The pin is arranged eccentrically with respect to the journal and is connected to the piston via a connecting rod. The arm connects the journal and the pin.

The crankshaft can be manufactured by die forging. For example, when manufacturing a crankshaft by die forging, a heated billet is first preformed to obtain a rough surface. Next, die forging (rough forging and finishing forging) is performed to form a finished forged product with burrs from the rough ground. This finished forged product is deburred. Thereafter, necessary parts (eg, journals, pins) of the finished forged product without burrs are pressed, and the finished forged product is shaped into the dimensions and shape of the final product.

Conventionally, various proposals have been made regarding the manufacturing process of crankshafts. For example, International Publication No. 2010/110133 (Patent Document 1) proposes a method of forming a hole in a pin in a finishing punching process. In Patent Document 1, the rough material (preformed product) is formed to be smaller than the cavity of a metal mold (forging mold) used for finishing punching. Therefore, a clearance exists between the preform and the mold when the preform is placed in the mold in the finishing stamping process. This clearance is filled with material by inserting a punch into the pin of the preform. According to Patent Document 1, since a hole is formed in the pin by inserting a punch, it is possible to reduce the weight of the crankshaft. Further, since forging is performed by filling the closed space of the mold with material, the dimensional accuracy of the crankshaft can be improved.

Japanese Unexamined Patent Publication No. 2006-247730 (Patent Document 2) proposes a method of correcting a counterweight provided on an arm. In Patent Document 2, a finish forged product without burrs is twisted in a twisting process, and bent is corrected in a restriking process. Thereafter, an intermediate jig is inserted between adjacent counterweights with the pin in between, and the counterweights are pressurized and restrained from both sides by a pressure jig, thereby correcting the shape of the counterweights.

Japanese Unexamined Patent Publication No. 2012-97888 (Patent Document 3) proposes a method of joining a counterweight to an arm of a crankshaft body. In Patent Document 3, the crankshaft body and the counterweight are each formed by cold forging. The counterweight is joined to the arm by welding and plastic fastening. According to Patent Document 3, even if the welded joint is destroyed, the counterweight can be prevented from separating from the arm by the plastically fastened joint.

International Publication No. 2010/110133 Japanese Patent Application Publication No. 2006-247730 JP2012-97888A

In a crankshaft, a counterweight is a weight that maintains rotational balance of the crankshaft. Therefore, from the viewpoint of ensuring the moment of the counterweight, it is preferable that the center of gravity of the counterweight is located far from the rotation axis of the crankshaft.

In Patent Document 3, the counterweight is molded separately from the arm. In contrast, in Patent Documents 1 and 2, the counterweight is molded integrally with the arm. In this case, in the finish punching process, a mold is used that divides the arm and counterweight into two along the vertical axis. In order to make it easier to remove the finished forging from the die, the surface of the counterweight is given a draft angle.

By providing the surface of the counterweight with a draft angle, the thickness of the end portions of the counterweight in the width direction is smaller than the thickness of the center portion of the counterweight in the width direction. In other words, due to the draft during die forging, the weight of the widthwise ends of the counterweight is small. For this reason, the center of gravity of the counterweight tends to be closer to the rotation axis of the crankshaft.

One way to move the center of gravity of the counterweight away from the rotation axis of the crankshaft is to increase the width of the counterweight. However, in this case, the counterweight increases in weight and the crankshaft also increases in weight. Increasing the weight of the crankshaft is undesirable from the viewpoint of improving fuel efficiency and reducing weight of automobiles equipped with reciprocating engines.

In short, the counterweight is required to have a sufficient moment and be lightweight.

One object of the present invention is to provide a method of manufacturing a crankshaft that can reduce the weight of the counterweight while ensuring the moment of the counterweight.

A method for manufacturing a crankshaft according to an embodiment of the present invention includes a step (a), a step (b), and a step (c). In step (a), a finished forged product with burrs is formed by die forging. This finished forged product has a journal, a pin, an arm, a counterweight, and an extra wall portion. The pin is eccentric relative to the journal. The arm connects the journal and the pin. A counterweight is connected to the arm. The surplus portion projects outward in the longitudinal direction of the counterweight from the widthwise end of the counterweight. In step (b), burrs are removed from the finished forged product. In step (c), the finished forged product from which burrs have been removed is shaped. In step (c), a pair of metal molds are used to roll down the excess wall portion along the longitudinal direction of the counterweight and press the journal. As a result, the bending of the finished forged product is corrected while allowing the material of the excess thickness to flow into the end of the counterweight.

According to the crankshaft manufacturing method according to the embodiment of the present invention, it is possible to reduce the weight of the counterweight while ensuring the moment of the counterweight.

FIG. 1 is a side view of a finished forged product obtained through steps (a) and (b) in the crankshaft manufacturing method according to the present embodiment. FIG. 2 is a front view of a crank web included in the finish forging shown in FIG. 1. FIG. 3 is a bottom view of the crank web shown in FIG. 2. FIG. 4 is a schematic diagram of a processing device used in step (c) in the crankshaft manufacturing method according to the present embodiment. FIG. 5 is a bottom view of an upper mold that constitutes a mold included in the processing apparatus shown in FIG. 4. FIG. FIG. 6 is a top view of a lower mold that constitutes a mold included in the processing apparatus shown in FIG. 4. FIG. 7 is a cross-sectional view of the mold along line VII-VII in FIGS. 5 and 6. FIG. 8A is a schematic diagram for explaining the operation of the processing device in step (c). FIG. 8B is another schematic diagram for explaining the operation of the processing device in step (c). FIG. 9 is a schematic diagram for explaining how the excess thickness is rolled down by the mold in step (c). FIG. 10 is a cross-sectional view taken along line XX in FIG. FIG. 11 is a rear view of the crank web after step (c). FIG. 12 is a bottom view of the crank web shown in FIG. 11. FIG. 13 is a bottom view of an upper mold that constitutes a mold included in a processing device in a crankshaft manufacturing method according to Modification 1 of the present embodiment. FIG. 14 is a top view of a lower mold that constitutes a mold included in a processing device in a crankshaft manufacturing method according to Modification 1 of the present embodiment. FIG. 15 is a schematic diagram for explaining how the excess thickness is rolled down by the mold shown in FIGS. 13 and 14. FIG. 16 is a bottom view of an upper mold that constitutes a mold included in a processing device in a crankshaft manufacturing method according to Modification 2 of the present embodiment. FIG. 17 is a top view of a lower mold that constitutes a mold included in a processing device in a crankshaft manufacturing method according to modification 2 of the present embodiment. FIG. 18 is a schematic diagram for explaining how the excess thickness is rolled down by the mold shown in FIGS. 16 and 17. FIG. 19 is a schematic diagram of a processing device used in step (c) in the crankshaft manufacturing method according to Modification 3 of the present embodiment.

Embodiments of the present invention will be described below. In the following description, embodiments of the present invention will be described using examples, but the present invention is not limited to the examples described below. Although specific numerical values and specific materials may be illustrated in the following description, the present invention is not limited to those examples.

The method for manufacturing a crankshaft according to the present embodiment includes a step (a), a step (b), and a step (c). In step (a), a finished forged product with burrs is formed by die forging. This finished forged product has a journal, a pin, an arm, a counterweight, and an extra wall portion. The pin is eccentric relative to the journal. The arm connects the journal and the pin. A counterweight is connected to the arm. The surplus portion projects outward in the longitudinal direction of the counterweight from the widthwise end of the counterweight. In step (b), burrs are removed from the finished forged product. In step (c), the finished forged product from which burrs have been removed is shaped. In step (c), a pair of metal molds are used to roll down the excess wall portion along the longitudinal direction of the counterweight and press the journal. Thereby, the bending of the finished forged product is corrected while the material of the excess wall portion flows into the end of the counterweight (first configuration).

In the first configuration, in the burr-free finish forged product obtained through steps (a) and (b), due to the draft during die forging, the ends of the counterweight in the width direction The thickness is smaller than the thickness of the central portion of the counterweight in the width direction. This finished forged product is shaped in step (c). At this time, the excess thickness protruding from the end of the counterweight is pressed down by the mold, and the material of the excess thickness flows into the end of the counterweight. As a result, the end of the counterweight swells in the direction of the rotation axis, increasing its thickness. In another aspect, the thickness of the counterweight is made uniform. In this case, the center of gravity of the counterweight moves away from the rotation axis of the crankshaft, and the moment of the counterweight around the rotation axis increases. That is, in the crankshaft manufactured by the manufacturing method of the first configuration, the weight of the counterweight is smaller if the moment is about the same, compared to the crankshaft manufactured by general die forging. Therefore, according to the first configuration, the weight of the counterweight can be reduced while ensuring the moment of the counterweight.

In the manufacturing method of the first configuration, preferably, the mold cavity includes a first plane facing the pin-side surface of the counterweight. In step (c), the end of the counterweight into which the material has flowed comes into contact with the first plane (second configuration).

The end of the counterweight tends to deform toward the pin side due to the reduction of the excess thickness by the mold. According to the second configuration, in step (c), the deformation of the end portion of the counterweight toward the pin side is limited by the first plane. Therefore, dimensional accuracy is improved.

In the manufacturing method of the second configuration, preferably the mold cavity includes a second plane facing the journal side surface of the counterweight. In step (c), the end of the counterweight into which the material has flowed comes into contact with the second plane (third configuration).

According to the third configuration, in step (c), the deformation of the end portion of the counterweight toward the journal side is further restricted by the second plane. Therefore, dimensional accuracy is further improved.

A specific example of the method for manufacturing a crankshaft according to this embodiment will be described below with reference to the drawings. In each figure, the same or equivalent components are designated by the same reference numerals, and the same description will not be repeated.

[Crankshaft manufacturing method]
The method for manufacturing a crankshaft according to this embodiment is typically a method for manufacturing a crankshaft by hot forging. The crankshaft manufacturing method according to the present embodiment includes a step (a) of forming a finished forged crankshaft with burrs, a step (b) of removing burrs from the finished forging, and a finishing step from which the burrs are removed. and (c) shaping the forged product. Each step will be explained below.

Step (a) and step (b)
In the method for manufacturing a crankshaft according to the present embodiment, first, in step (a), a finished forged product with burrs is formed. This finished forged product is formed by general die forging. That is, after a heated billet is preformed to obtain a rough area, die forging (rough punching and finishing punching) is performed on the rough blank to form a finished forged product with burrs. Thereafter, in step (b), the finished forged product is deburred to obtain a finished forged product without burrs.

FIG. 1 is a side view schematically showing a finished forged product 10 after deburring. The finished forged product 10 has almost the same dimensions and shape as the final product, the crankshaft. The finished forged product 10 includes a plurality of journals 11, a plurality of pins 12, a plurality of arms 13, and a plurality of counterweights 14. The finished forged product 10 further has an extra wall portion 18, which will be described later. FIG. 1 illustrates a finished forged product 10 of a crankshaft for a four-cylinder engine. However, the crankshaft manufactured by the manufacturing method of this embodiment is not limited to a crankshaft for a four-cylinder engine.

Each of the plurality of journals 11 has a substantially cylindrical shape with the central axis X1 of the finished forged product 10 as the axis. The central axis X1 becomes the rotation axis X1 of the crankshaft manufactured from the finished forged product 10. The journals 11 are arranged along the rotation axis X1 and constitute a main shaft portion of the crankshaft.

Each of the plurality of pins 12 has a substantially cylindrical shape and is eccentric with respect to the journal 11. That is, the plurality of pins 12 are arranged around the rotation axis X1 with a predetermined phase difference. In this embodiment, the pins 12 located at both ends in the direction of the rotation axis X1 have a phase difference of 180° from the two central pins 12.

Each of the arms 13 is arranged between the journal 11 and the pin 12 in the direction of the rotation axis X1. Arm 13 connects journal 11 and pin 12. The arm 13 has surfaces 131 and 132 that intersect with the rotation axis X1 direction. Of the surfaces 131 and 132, one surface 131 is connected to the journal 11, and the other surface 132 is connected to the pin 12. In this embodiment, eight arms 13 lined up in the direction of the rotation axis X1 are referred to as first to eighth arms 13a to 13h in order from the front 16 side to the flange 17 side to distinguish them as necessary.

Each of the counterweights 14 is molded integrally with the arm 13. If necessary, each of the counterweights 14 of the first to eighth arms 13a to 13h will be referred to as first to eighth counterweights 14a to 14h to distinguish them. In this embodiment, all the arms 13 integrally include a counterweight 14. However, the counterweight 14 may be provided only on some of the arms 13. The shapes of each counterweight 14 may be the same or different.

The counterweight 14 has surfaces 141 and 142 that intersect with the rotation axis X1 direction. One surface 141 is continuous with the surface 131 of the arm 13 on the journal 11 side. The other surface 142 is continuous with the surface 132 of the arm 13 on the pin 12 side.

The integrally molded arm 13 and counterweight 14 are commonly referred to as a crank web 15. FIG. 2 is a diagram of the crank web 15 viewed from the journal 11 side. FIG. 3 is a diagram of the crank web 15 viewed from the counterweight 14 side. In FIG. 2, the shape of the crankshaft, which is the final product, is shown by a two-dot chain line.

Referring to FIG. 2, in this specification, for convenience of explanation, the surface of the arm 13, the counterweight 14, and the crank web 15 on the journal 11 side is sometimes referred to as the front surface, and the surface on the pin 12 side is sometimes referred to as the rear surface. In the crank web 15, an axis perpendicular to the central axis X2 of the pin 12 and the rotational axis X1 is defined as a vertical axis Z. The direction in which the vertical axis Z extends is the longitudinal direction, and the direction perpendicular to the vertical axis Z and the rotation axis X1 is the width direction. In the longitudinal direction, the arm 13 side is called the top, the counterweight 14 side is called the bottom, and both sides in the width direction are sometimes called the left and right sides. Further, with respect to the longitudinal direction of the counterweight 14, the pin 12 side (upper side) is sometimes called the inside, and the opposite side (lower side) is sometimes called the outside. Further, with respect to the width direction of the counterweight, the vertical axis Z side is sometimes called the inside, and the opposite side is sometimes called the outside.

The counterweight 14 shown in FIG. 2 widens downward from the arm 13. The counterweight 14 has a generally fan shape when viewed from the front. That is, the counterweight 14 mainly has an outer surface 143a, an end surface 143b, and an inner surface 143c. The outer surface 143a has, for example, an arc shape when viewed from the front. The inner surface 143c is connected to the side surface of the arm 13. The end surface 143b smoothly connects the outer surface 143a and the inner surface 143c. The end side surface 143b may be a flat surface or a convex curved surface.

Excess portions 18 protrude outward in the longitudinal direction from both ends 14s of the counterweight 14 in the width direction. That is, the extra wall portion 18 is provided near the end side surface 143b of the outer surface 143a of the counterweight 14. The extra wall portion 18 is molded integrally with the counterweight 14.

In this embodiment, extra thickness portions 18 are provided at both ends 14s of the counterweight 14, respectively. However, the extra wall portion 18 may be provided only on one of both ends 14s of the counterweight 14. Moreover, the excess portion 18 may be provided on all the counterweights 14 or only on some of the counterweights 14.

Referring to FIG. 3, surfaces 141 and 142 of counterweight 14 are provided with a draft angle. Typically, the draft angle is a minimum of 1.0°. This is to make it easier to take out the finished forged product from the die during die forging in step (a). Therefore, the surfaces 141 and 142 of the counterweight 14 are each inclined downward from the center in the width direction toward the left and right. Therefore, the thickness of the counterweight 14 (dimension in the direction of the rotation axis X1) is large at the central portion in the width direction and small at both end portions 14s in the width direction.

Process (c)
In step (c), the finished forged product 10 without burrs is shaped. More specifically, the counterweight 14 having draft slopes on the surfaces 141 and 142 is processed by pressing down the excess wall portion 18 . Furthermore, by pressing each journal 11, the bending of the finished forged product 10 is corrected.

First, a device for shaping a burr-free finish forged product 10 will be described with reference to FIG. 4. FIG. 4 is a schematic diagram of the processing device 20 used in step (c).

In FIG. 4, the finish forged product 10 processed by the processing device 20 is indicated by a chain double-dashed line. In FIG. 4, the finished forged product 10 is arranged in the processing device 20 so that the third to sixth counterweights 14c to 14f are positioned upward and the remaining counterweights 14 are positioned downward. That is, when the finished forged product 10 is placed in the processing device 20, the longitudinal direction of the counterweight 14 coincides with the vertical direction (vertical direction) of the processing device 20, and the width direction of the counterweight 14 coincides with the vertical direction of the processing device 20. Matches the depth direction (horizontal direction).

The processing device 20 is, for example, a press machine. The processing device 20 includes a slide 21a, a bed 21b, mold holders 22a and 22b, and a mold 23.

The slide 21a supports the mold holder 22a from above. The slide 21a is configured to be movable up and down along a guide (not shown). The slide 21a can be driven by a mechanical, hydraulic, or hydraulic drive mechanism, for example. Bed 21b supports mold holder 22b from below. The basic structure of the slide 21a, bed 21b, and mold holders 22a and 22b is the same as that of a slide, bed, and mold holder in a known press machine. Therefore, in this embodiment, detailed explanations regarding these will be omitted.

The mold 23 shapes the finish forged product 10 into the shape and dimensions of the final product. For this purpose, the mold 23 has a cavity that corresponds to the shape and dimensions of the final product.

The mold 23 has an upper mold 23a and a lower mold 23b. That is, the mold 23 consists of a pair. The upper mold 23a is attached to the lower surface of the mold holder 22a. The lower mold 23b is attached to the upper surface of the mold holder 22b.

FIG. 5 is a bottom view of the upper mold 23a that constitutes the mold 23. FIG. 6 is a top view of the lower mold 23b that constitutes the mold 23. FIG. 7 is a cross-sectional view of the mold 23 taken along line VII-VII in FIGS. 5 and 6. FIG. 7 shows a cavity forming the contour of the crank web 15 in front view. In FIG. 7, the shape of the crankshaft, which is the final product, is shown by a two-dot chain line.

As shown in FIG. 5, the upper mold 23a has a cavity that opens on the lower surface. As shown in FIG. 6, the lower mold 23b has a cavity open to the upper surface. When the upper mold 23a and the lower mold 23b come into contact, the cavity of the upper mold 23a and the cavity of the lower mold 23b form a cavity corresponding to the shape and dimensions of the crankshaft of the final product.

Referring to FIG. 5, the cavity of upper mold 23a includes a journal bottom surface 231. As shown in FIG. The journal bottom surface 231 is arranged at a position corresponding to the journal 11. The journal bottom surface 231 has a semi-cylindrical shape that corresponds to the shape and dimensions of the final product journal. In this embodiment, the cavity of the upper mold 23a includes a pin bottom surface 232. The pin bottom surface 232 is arranged at a position corresponding to the pin 12. The pin bottom surface 232 has a semi-cylindrical shape that corresponds to the shape and dimensions of the final product pin. The cavity of the lower mold 23b shown in FIG. 6 also includes a similar journal bottom surface 231 and pin bottom surface 232.

Furthermore, referring to FIG. 5, the cavity of upper mold 23a includes a first plane 233. As shown in FIG. In the cavity of the upper die 23a, the first plane 233 is arranged at a position corresponding to the surface 142 of the upwardly facing counterweight 14 on the pin 12 side. When the upper die 23a and the lower die 23b come into contact, the first plane 233 faces the surface 142 of the upwardly facing counterweight 14 on the pin 12 side. The first plane 233 is a plane perpendicular to the central axis X1 of the finished forged product 10. The plane perpendicular to the central axis X1 of the finished forged product 10 is not only a strictly perpendicular plane to the central axis X1 of the finished forged product 10, but also a small slope of 0.5° or less with respect to the perpendicular plane. Including tilted surfaces. That is, the first plane 233 is not provided with a large slope corresponding to the draft of the finished forging 10. In another aspect, the first plane 233 is a flat wall surface. The cavity of the lower die 23b shown in FIG. 6 also includes a similar first plane 233. However, in the cavity of the lower mold 23b, the first plane 233 is arranged at a position corresponding to the surface 142 of the downward counterweight 14 on the pin 12 side.

Furthermore, referring to FIG. 5, the cavity of upper mold 23a includes a second plane 234. As shown in FIG. In the cavity of the upper mold 23a, the second plane 234 is arranged at a position corresponding to the surface 141 of the upwardly facing counterweight 14 on the journal 11 side. When the upper die 23a and the lower die 23b come into contact, the second plane 234 faces the journal 11 side surface 141 of the upward counterweight 14. The second plane 234 is a plane perpendicular to the central axis X1 of the finished forged product 10. That is, the second plane 234 is not provided with a slope corresponding to the draft of the finished forging 10. In another aspect, second plane 234 is a flat wall surface. The cavity of the lower die 23b shown in FIG. 6 also includes a similar second plane 234. However, in the cavity of the lower die 23b, the second plane 234 is arranged at a position corresponding to the surface 141 of the downward counterweight 14 on the journal 11 side.

Referring to FIG. 7, the cavity of mold 23 includes a counterweight bottom surface 235. The counterweight bottom surface 235 is arranged at a position corresponding to the counterweight 14. The counterweight bottom surface 235 has a shape and dimensions that correspond to the shape and dimensions of the final product counterweight. More specifically, the counterweight bottom surface 235 has an outer bottom surface 235a, an end side bottom surface 235b, and an inner bottom surface 235c. The shape and dimensions of the outer bottom surface 235a match the shape and dimensions of the outer surface 143a of the counterweight 14. The shape and dimensions of the end side bottom surface 235b match the shape and dimensions of the end side surface 143b of the counterweight 14. The shape and dimensions of the inner bottom surface 235c match the shape and dimensions of the inner surface 143c of the counterweight 14.

In the cavity of the upper mold 23a, the outer bottom surface 235a is arranged at a position corresponding to the outer surface 143a of the counterweight 14 facing upward. The end side bottom surface 235b is arranged at a position corresponding to the end side surface 143b of the counterweight 14 facing upward. On the other hand, the inner bottom surface 235c is arranged at a position corresponding to the inner surface 143c of the counterweight 14 facing downward.

In the cavity of the lower mold 23b, the outer bottom surface 235a is arranged at a position corresponding to the outer surface 143a of the counterweight 14 facing downward. The end side bottom surface 235b is arranged at a position corresponding to the end side surface 143b of the counterweight 14 facing downward. On the other hand, the inner bottom surface 235c is arranged at a position corresponding to the inner surface 143c of the counterweight 14 facing upward.

Next, with reference to FIGS. 8A to 10, a method for shaping a burr-free finish forged product 10 using the processing device 20 will be described. 8A to 10 are schematic diagrams for explaining the operation of the processing device 20 when shaping the finished forged product 10 in step (c).

As shown in FIG. 8A, first, the finish forged product 10 without burrs is placed in the processing device 20. The finished forged product 10 is placed on the cavity of the lower die 23b. At this time, the counterweight 14 is positioned above or below the central axis X1. That is, the longitudinal direction of the counterweight 14 is located in the up-down direction (vertical direction).

In the example of FIG. 8A, the third to sixth counterweights 14c to 14f are positioned above the central axis X1. The remaining counterweight 14 is positioned below the central axis X1.

After placing the finished forged product 10 in the processing device 20, the slide 21a is lowered. As a result, as shown in FIG. 8B, the upper mold 23a descends and contacts the lower mold 23b, and the mold 23 is closed. That is, the mold 23 forms a cavity that corresponds to the shape and dimensions of the crankshaft of the final product. At this time, the journal 11 of the finished forged product 10 is pressed along the longitudinal direction of the counterweight 14 by the journal bottom surface 231. Further, the pin 12 of the finished forged product 10 is pressed by the pin bottom surface 232. As a result, the bending of the finished forged product 10 is corrected.

Further, when the mold 23 is closed, the counterweight 14 of the finished forged product 10 is rolled down along the longitudinal direction of the counterweight 14 by the counterweight bottom surface 235 of the mold 23. Strictly speaking, the extra wall portion 18 of the finished forged product 10 is rolled down. At this time, as the upper mold 23a descends, the extra wall portion 18 is pressed down, and then the journal 11 is pressed.

9 and 10 are schematic diagrams for explaining how the excess thickness portion 18 is rolled down by the mold 23. FIG. 9 and 10 show the state after processing. FIG. 10 is a cross-sectional view taken along line XX in FIG. In FIG. 9, the surplus portion 18 before processing is shown by a two-dot chain line.

Referring to FIG. 9, as the upper die 23a descends, the outer bottom surface 235a of the counterweight bottom surface 235 comes into contact with the excess thickness portion 18, and lowers the excess thickness portion 18. At this time, pressure is applied to the extra wall portion 18 from the outer bottom surface 235a toward the counterweight 14. The inner side surface 143c of the counterweight 14 is restrained by the inner bottom surface 235c of the mold 23, and the end side surface 143b of the counterweight 14 is restrained by the end side bottom surface 235b of the mold 23. As a result, the material of the surplus portion 18 flows toward the counterweight 14 and flows into the end portion 14s of the counterweight 14 (see the arrow in FIG. 9). As a result, as shown in FIG. 10, the end portion 14s of the counterweight 14 bulges in the direction of the rotation axis X1, and the end portion 14s of the counterweight 14 becomes thicker. That is, the thickness of the counterweight 14 is made uniform.

At this time, the end portion 14s of the counterweight 14 that bulges in the direction of the rotation axis X1 contacts the first plane 233. As a result, the first plane 233 limits the bulging deformation of the end portion 14s toward the pin 12 side. That is, excessive bulging deformation of the end portion 14s is suppressed. Therefore, the dimensional accuracy of the surface 142 of the counterweight 14 on the pin 12 side is ensured.

Further, the end portion 14s of the counterweight 14 that bulges in the direction of the rotation axis X1 contacts the second plane 234. As a result, the second plane 234 limits the bulging deformation of the end portion 14s toward the journal 11 side. That is, excessive bulging deformation of the end portion 14s is suppressed. Therefore, the dimensional accuracy of the surface 141 of the counterweight 14 on the journal 11 side is ensured.

After the mold 23 is closed in this manner, the mold holder 22a is raised together with the slide 21a, and the upper mold 23a is separated from the lower mold 23b. Thereafter, the finished forged product 10 is taken out from the processing device 20. This completes the shaping of the finished forged product 10 in step (c).

11 and 12 are a rear view and a bottom view, respectively, of the crank web 15 after step (c). Referring to FIGS. 11 and 12, the end portion 14s of the counterweight 14 is bulged in the direction of the rotation axis X1. That is, at the end portion 14s of the counterweight 14, there is no draft slope from the surfaces 141 and 142 on the journal 11 side and the pin 12 side, respectively, and the thickness is increased. From another point of view, the end portion 14s of the counterweight 14 is thickened.

[Effects of this embodiment]
In the crankshaft manufacturing method according to the present embodiment, the finished forged product 10 after removing burrs is shaped. At this time, the excess wall portion 18 protruding from the end portion 14s of the counterweight 14 is rolled down by the mold 23. As a result, the material of the excess wall portion 18 flows into the end portion 14s of the counterweight 14, and the end portion 14s of the counterweight 14 is thickened. In this case, the center of gravity of the counterweight 14 moves away from the rotation axis X1, and the moment of the counterweight 14 around the rotation axis X1 increases. Therefore, it is possible to secure a desired moment without increasing the weight of the counterweight 14, and it is possible to both secure the moment and reduce the weight of the counterweight 14.

[Modification 1 of this embodiment]
A method for manufacturing a crankshaft according to modification example 1 of the present embodiment will be described with reference to FIGS. 13 to 15. 13 and 14 are schematic diagrams of a mold 23 included in the processing device 20 used in step (c). FIG. 13 shows a bottom view of the upper die 23a. FIG. 14 shows a top view of the lower mold 23b. FIG. 15 is a schematic diagram for explaining how the excess thickness portion 18 is rolled down by the mold 23. FIG. 15 shows the state after processing.

As shown in FIG. 13, the cavity of the upper mold 23a includes a journal bottom surface 231, a pin bottom surface 232, a first plane 233, and a counterweight bottom surface 235 (outer bottom surface 235a, end side bottom surface 235b, and inner bottom surface 235c). However, in the cavity of the upper die 23a, a position corresponding to the surface 141 of the counterweight 14 on the journal 11 side is open and largely recessed. In another aspect, a wall surface like the second plane is not provided. The cavity of the lower mold 23b shown in FIG. 14 is also similar to the cavity of the upper mold 23a.

Referring to FIG. 15, in step (c), when the extra wall portion 18 is pressed down by the mold 23, the end portion 14s of the counterweight 14 freely swells toward the journal 11 side in the direction of the rotation axis X1. Even in this case, the end portion 14s of the counterweight 14 is made thicker. That is, the thickness of the counterweight 14 is made uniform.

[Modification 2 of this embodiment]
A method for manufacturing a crankshaft according to a second modification of the present embodiment will be described with reference to FIGS. 16 to 18. 16 and 17 are schematic diagrams of the mold 23 included in the processing device 20 used in step (c). FIG. 16 shows a bottom view of the upper die 23a. FIG. 17 shows a top view of the lower mold 23b. FIG. 18 is a schematic diagram for explaining how the excess thickness portion 18 is rolled down by the mold 23. FIG. 18 shows the state after processing.

As shown in FIG. 16, the cavity of the upper die 23a includes a journal bottom surface 231, a pin bottom surface 232, and a counterweight bottom surface 235 (outer bottom surface 235a, end side bottom surface 235b, and inner bottom surface 235c). However, in the cavity of the upper die 23a, a position corresponding to the surface 141 of the counterweight 14 on the journal 11 side is open and largely recessed. Furthermore, in the cavity of the upper mold 23a, a position corresponding to the surface 142 of the counterweight 14 on the pin 12 side is open and largely recessed. In another aspect, walls such as the first plane and the second plane are not provided. The cavity of the lower mold 23b shown in FIG. 17 is also similar to the cavity of the upper mold 23a.

Referring to FIG. 18, in step (c), when the excess wall portion 18 is pressed down by the mold 23, the end portion 14s of the counterweight 14 is freely moved toward the journal 11 side and the pin 12 side in the rotation axis X1 direction. Inflates. Even in this case, the end portion 14s of the counterweight 14 is made thicker. That is, the thickness of the counterweight 14 is made uniform.

[Modification 3 of this embodiment]
With reference to FIG. 19, a method for manufacturing a crankshaft according to modification example 3 of the present embodiment will be described. FIG. 19 is a schematic diagram of the processing device 20 used in step (c). In FIG. 19, the finish forged product 10 processed by the processing device 20 is indicated by a two-dot chain line.

As shown in FIG. 19, the cavity of the upper mold 23a includes a journal bottom surface 231 and a pin bottom surface 232. However, in the cavity of the upper mold 23a, a position corresponding to between two arms 13 connected to the same pin 12 among the arms 13 integral with the upward counterweight 14 is open. From another point of view, no pin bottom surface is provided at a position corresponding to the pin 12 connected to the arm 13 integral with the upward counterweight 14.

The cavity of the lower mold 23b also includes a similar journal bottom surface 231 and pin bottom surface 232. However, in the cavity of the lower mold 23b, a position corresponding to between two arms 13 connected to the same pin 12 among the arms 13 integrated with the downward counterweight 14 is open. From another point of view, no pin bottom surface is provided at a position corresponding to the pin 12 connected to the arm 13 integral with the downward counterweight 14.

In the step (c) using the mold 23 (processing device 20) shown in FIG. 19, the excess wall portion 18 of the finished forged product 10 is rolled down by the mold 23 in the same manner as described above. Further, the journal 11 of the finished forged product 10 is pressed by the journal bottom surface 231. In this case, the finishing forged product 10 is not pressed against the pin 12, but the bending of the finished forged product 10 is corrected by pressing the journal 11.

In addition, it goes without saying that the present invention is not limited to the above-described embodiments, and that various changes can be made without departing from the spirit of the present invention.

10: Finished forged product 11: Journal 12: Pin 13: Arm 14: Counterweight 14s: End 143a: Outer surface 143b: End surface 143c: Inner surface 15: Crank web 18: Extra thickness 20: Processing device 23: Gold Mold 23a: Upper mold 23b: Lower mold 231: Journal bottom surface 232: Pin bottom surface 233: First plane 234: Second plane 235: Counterweight bottom surface 235a: Outside bottom surface 235b: End side bottom surface 235c: Inside bottom surface

Claims (1)

A method for manufacturing a crankshaft, the method comprising:
(a) A step of forming a finish forged product with burrs by die forging, the finish forging including a journal, a pin eccentric to the journal, an arm connecting the journal and the pin, and the a step of comprising: a counterweight connected to an arm; and an excess portion protruding outward in the longitudinal direction of the counterweight from an end in the width direction of the counterweight;
(b) removing the burr from the finish forging;
(c) a step of shaping the finished forged product from which the burr has been removed, using a pair of dies to reduce the excess wall portion along the longitudinal direction of the counterweight and to remove the journal; straightening the bending of the finished forged product while causing the material of the excess thickness to flow into the end of the counterweight by pressing ;
The cavity of the mold faces the pin-side surface of the counterweight, faces a first plane perpendicular to the central axis of the finished forging, and faces the journal-side surface of the counterweight; a second plane perpendicular to the central axis of the finished forging;
In the step (c), the end portion of the counterweight into which the material has flowed is in contact with the first plane and the second plane .

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