JP6958721B2 - Forged crank shaft manufacturing method - Google Patents

Description

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

In reciprocating engines of automobiles, motorcycles, agricultural machines, ships, etc., a crank shaft is indispensable for converting the reciprocating motion of a piston into a rotary motion to extract power. The crank shaft can be manufactured by die forging or casting. In particular, when high strength and high rigidity are required for a crank shaft, a crank shaft manufactured by die forging (hereinafter, also referred to as "forged crank shaft") is often used.

1A and 1B are schematic views showing a shape example of a general forged crank shaft. Of these figures, FIG. 1A is an overall view and FIG. 1B is a cross-sectional view taken along the line IB-IB. In the example shown in FIG. 1B, one crank arm portion A7, a counter weight portion W7 integrated with the crank arm portion A7, a pin portion P4 connected to the crank arm portion A7, and a journal portion J4 are typically shown.

The forged crank shaft 11 shown in FIGS. 1A and 1B is a forged crank shaft having a 4-cylinder-8 counterweight mounted on a 4-cylinder engine. The forged crank shaft 11 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, also referred to as "arm portions"). A1 to A8 are provided. The arm portions A1 to A8 connect the journal portions J1 to J5 and the pin portions P1 to P4, respectively. Further, the eight (all) arm portions A1 to A8 integrally include counterweight portions (hereinafter, also referred to as “weight portions”) W1 to W8. A front portion Fr is provided at the front end of the forged crank shaft 11 in the axial direction, and a flange portion Fl is provided at the rear end. The front portion Fr is connected to the first journal portion J1 at the beginning, and the flange portion Fl is connected to the fifth journal portion J5 at the end.

In the following, when the journal parts J1 to J5, the pin parts P1 to P4, the arm parts A1 to A8, and the weight parts W1 to W8 are collectively referred to, the reference numerals are "J" for the journal part and "P" for the pin part. , "A" in the arm part and "W" in the weight part. Further, the arm portion A and the weight portion W integrated with the arm portion A are collectively referred to as a “web”.

As shown in FIG. 1B, the width Bw of the weight portion W is larger than the width Ba of the arm portion A. Therefore, the weight portion W greatly protrudes from the central surface of the arm portion (the surface including the central axis of the pin portion P and the central axis of the journal portion J).

When manufacturing a forged crank shaft having such a shape, a billet is generally used as a starting material. The cross section perpendicular to the longitudinal direction of the billet, i.e. the cross section, is round or square. The area of its cross section is constant over the entire length of the billet. In the present specification, the "cross section" means a cross section having a normal in the longitudinal direction of the billet or each wasteland described later, or the axial direction of the forged crank shaft. The "vertical cross section" means a cross section parallel to the longitudinal direction of the billet or each rough terrain described later, or the axial direction of the forged crank shaft and parallel to the vertical direction. Further, the area of the cross section is also simply referred to as "cross-sectional area". The forged crank shaft is manufactured by going through a preforming step, a mold forging step, and a deburring step in that order. In addition, if necessary, a shaping process is performed after the deburring process. Usually, the preforming step includes each step of roll forming and bending. The mold forging process includes roughing and finishing.

2A to 2F are schematic views for explaining a manufacturing process of a conventional general forged crank shaft. Of these figures, FIG. 2A shows a billet. FIG. 2B shows a roll wasteland. FIG. 2C shows a bent wasteland. FIG. 2D shows a rough forged material. FIG. 2E shows a finish forged material. FIG. 2F shows a forged crank shaft. 2A to 2F show a series of steps in the case of manufacturing the forged crank shaft 11 having the shapes shown in FIGS. 1A and 1B.

A method for manufacturing the forged crank shaft 11 will be described with reference to FIGS. 2A to 2F. First, a billet 12 having a predetermined length as shown in FIG. 2A is heated by a heating furnace, and then roll forming and bending are performed in this order in a preforming step. In roll forming, for example, the billet 12 is rolled and squeezed using a hole-shaped roll. As a result, the volume of the billet 12 is distributed in the axial direction to obtain the roll wasteland 13 which is an intermediate material (see FIG. 2B). Next, in bending, the roll wasteland 13 is partially pressed from a direction perpendicular to the axial direction. As a result, the volume of the roll wasteland 13 is distributed to obtain a bending wasteland 14 which is a further intermediate material (see FIG. 2C).

Subsequently, in the roughing step, the rough forged material 15 is obtained by forging the bent rough ground 14 up and down using a pair of dies (see FIG. 2D). The rough forged material 15 is formed with an approximate shape of a forged crank shaft (final product). Further, in the finish casting step, the rough forged material 15 is forged up and down using a pair of dies to obtain the finished forged material 16 (see FIG. 2E). The finish forged material 16 is formed with a shape that matches the forged crank shaft of the final product. During these roughing and finishing casting steps, surplus material flows out from between the mold split surfaces of the dies facing each other, and the surplus material becomes burr B. Therefore, both the rough forged material 15 and the finished forged material 16 have large burrs B around them.

In the deburring step, for example, the burr B is punched out by the blade mold while the finish forging material 16 with burrs is sandwiched and held by a pair of dies. As a result, the burr B is removed from the finish forging material 16, and a burr-free forging material is obtained. The burr-free forged material has substantially the same shape as the forged crank shaft 11 shown in FIG. 2F.

In the shaping process, the key points of the burr-free forging material are slightly pressed down with a mold from above and below, and the burr-free forging material is corrected to the dimensions and shape of the final product. Here, the key points of the burr-free forged material are, for example, shaft portions such as a journal portion J, a pin portion P, a front portion Fr, a flange portion Fl, and the arm portion A and a weight portion W. In this way, the forged crank shaft 11 is manufactured.

The manufacturing process shown in FIGS. 2A to 2F is not limited to the forged crank shaft of the 4-cylinder-8 counterweight shown in FIGS. 1A and 1B, and can be applied to various forged crank shafts. For example, it can be applied to a forged crank shaft having 4 cylinders and 4 counterweights.

In the case of a forged crank shaft having four cylinders and four counterweights, some of the eight arm portions A1 to A8 are integrally provided with a weight portion W. For example, the first arm portion A1 at the head, the eighth arm portion A8 at the rear end, and the two central arm portions (fourth arm portion A4 and fifth arm portion A5) integrally have a weight portion W. Further, the remaining arm portions, specifically, the second, third, sixth and seventh arm portions (A2, A3, A6 and A7) do not have a weight portion and have an oval shape. Become.

In addition, the manufacturing process is the same for forged crank shafts mounted on 3-cylinder engines, in-line 6-cylinder engines, V-type 6-cylinder engines, 8-cylinder engines, and the like. If it is necessary to adjust the arrangement angle of the pin portion, a twisting step is added after the deburring step.

The main purpose of the preforming process is to distribute the volume of billets. By allocating the volume of billets in the preforming process, the formation of burrs can be reduced in the mold forging process in the subsequent process, and the material yield can be improved. Here, the material yield means the ratio (percentage) of the volume of the forged crank shaft (final product) to the volume of the billet.

In addition, the wasteland obtained by preforming is formed into a forged crank shaft in a subsequent die forging process. In order to obtain a forged crank shaft with a precise shape, it is necessary to mold a rough ground with a precise shape in the preforming process.

Techniques for manufacturing a forged crank shaft include, for example, Japanese Patent Application Laid-Open No. 2001-105087 (Patent Document 1), Japanese Patent Application Laid-Open No. 2-255240 (Patent Document 2), and Japanese Patent Application Laid-Open No. 62-245454 (Patent Document 3). And Japanese Patent Application Laid-Open No. 59-45051 (Patent Document 4). Patent Document 1 discloses a premolding method using a pair of upper and lower dies. In the preforming method, when the rod-shaped workpiece is pressed down by the upper die and the lower die, a part of the workpiece is extended in the axial direction and a part of the workpiece is offset with respect to the axial center. As a result, Patent Document 1 states that capital investment can be reduced because stretching and bending can be performed at the same time.

The preforming method of Patent Document 2 uses a 4-pass high-speed roll facility instead of the conventional 2-pass roll facility. In the preforming method, the cross-sectional area of the rolled wasteland is determined according to the distribution of the cross-sectional areas of the weight portion, the arm portion and the journal portion of the forged crank shaft (final product). As a result, Patent Document 2 states that the material yield can be improved.

In the preforming method of Patent Document 3, a part of the volume of the billet is distributed in the axial direction and the radial direction of the billet by rolling. A forged crank shaft is obtained by forging a volume-distributed billet. As a result, Patent Document 3 states that the material yield can be improved.

In the manufacturing method of Patent Document 4, the billet is formed into a forged crank shaft by one-time die forging using a pair of upper die, lower die and punch. In the mold forging process, first, the area of the billet that becomes the journal part and the area that becomes the pin part are pressed by punches that operate separately. The volume of the billet is distributed by the reduction. After that, mold forging is carried out by the upper mold and the lower mold. That is, preforming and mold forging can be performed in one step. As a result, Patent Document 4 states that a forged crank shaft having a complicated shape can be efficiently manufactured with a single facility.

Japanese Unexamined Patent Publication No. 2001-105087 Japanese Unexamined Patent Publication No. 2-255240 Japanese Unexamined Patent Publication No. 62-24545 JP-A-59-45051

In the manufacture of forged crank shafts, as described above, it is desired to reduce the formation of burrs and improve the material yield. In the preforming method described in Patent Document 1, the volume of billets can be distributed and offset to some extent.

However, in the preforming method of Patent Document 1, the distribution of the volume of the portion serving as the weight portion and the volume of the portion serving as the arm portion integrally including the weight portion has not been examined in the portion to be the web. Therefore, in the mold forging process of the subsequent process, the weight portion that greatly overhangs from the central surface of the arm portion has insufficient material filling property, and a meat shortage is likely to occur. In order to prevent the weight portion from being depleted, it is simply necessary to increase the excess volume in the wasteland. However, in this case, the material yield is reduced. Hereinafter, the portion that becomes the weight portion is also referred to as a “weight equivalent portion”. The part that becomes the arm part (excluding the weight part) that integrally includes the weight part is also called the "arm equivalent part". The weight-equivalent part and the arm-equivalent part are collectively referred to as the "web-equivalent part".

In the preforming method of Patent Document 2, the volume of the weight-corresponding portion and the arm-corresponding portion cannot be distributed in the web-corresponding portion. This is because it is rolled. Therefore, in the mold forging process of the subsequent process, the filling property of the material of the weight portion becomes insufficient. As a result, meat loss is likely to occur.

The preforming method of Patent Document 3 requires equipment for performing rolling. Therefore, the equipment cost is high, and it is difficult to improve the production efficiency.

In the manufacturing method of Patent Document 4, since preforming and mold forging are performed with a single facility, preforming that greatly deforms the billet cannot be performed. Therefore, it is difficult to improve the material yield by the manufacturing method of Patent Document 4.

An object of the present invention is to provide a method for manufacturing a forged crank shaft capable of forming a forged crank shaft having a precise shape and improving a material yield.

A method for manufacturing a forged crank shaft according to an embodiment of the present invention is a forged crank including a journal portion serving as a center of rotation, a pin portion eccentric with respect to the journal portion, and a crank arm portion connecting the journal portion and the pin portion. This is a method for manufacturing a shaft.

The manufacturing method of the forged crank shaft includes a first preforming step of obtaining the initial wasteland from the billet, a second preforming step of obtaining the intermediate wasteland from the initial wasteland, a final preforming step of obtaining the final wasteland from the intermediate wasteland, and mold forging. Includes a finish forging process, which forms the final wasteland to the finish dimensions of the forged crank shaft. The first preforming step includes a flat portion forming step and an eccentric step. In the flat portion forming step, a pair of first molds is used to reduce the portion to be the journal portion of the billet from the direction perpendicular to the axial direction of the billet. As a result, the cross-sectional area of the portion to be the journal portion is reduced to form a flat portion. In the eccentric step, after the reduction by the first mold is started, the second mold is used to eccentric the portion to be the pin portion with the direction perpendicular to the axial direction of the billet as the eccentric direction. In the second preforming step, a pair of third dies are used to reduce the width direction of the flat portion to the pin portion of the initial wasteland and the flat portion. As a result, the thickness of a part or all of the portion to be the crank arm portion becomes larger than the thickness of the finished dimension. In the final preforming step, the fourth mold is used to reduce the intermediate wasteland from the same direction as in the second preforming step, and further, the portion to be the crank arm portion is reduced from the axial direction of the intermediate wasteland. As a result, the thickness of the portion to be the crank arm portion is reduced to the thickness of the finishing dimension while maintaining the amount of eccentricity of the portion to be the pin portion.

In the method for manufacturing a forged crank shaft according to the embodiment of the present invention, it is possible to obtain an intermediate wasteland in which axial volume distribution is promoted by the first preforming step and the second preforming step without forming burrs. can. Further, in the intermediate wasteland, the volume of the portion serving as the journal portion, the volume of the portion serving as the pin portion, and the volume of the portion serving as the arm portion are appropriately distributed. Therefore, even in the final preforming step, it is possible to obtain a final wasteland having a shape close to the shape of the forged crank shaft with almost no burrs formed. Then, by the finish forging process, the shape of the forged crank shaft can be formed from the final wasteland. From these, the material yield can be improved. Further, according to the present invention, a wasteland having a precise shape can be formed by the first preforming step and the second preforming step. Therefore, a forged crank shaft having a precise shape can be manufactured.

FIG. 1A is a schematic view showing an example of the overall shape of a general forged crank shaft. FIG. 1B is a cross-sectional view taken along the line IB-IB of FIG. 1A. FIG. 2A is a schematic view showing billets in a conventional manufacturing process. FIG. 2B is a schematic view showing a roll wasteland in a conventional manufacturing process. FIG. 2C is a schematic view showing a bent wasteland in a conventional manufacturing process. FIG. 2D is a schematic view showing a rough forged material in a conventional manufacturing process. FIG. 2E is a schematic view showing a finish forged material in a conventional manufacturing process. FIG. 2F is a schematic view showing a forged crank shaft in a conventional manufacturing process. FIG. 3A is a schematic view showing billets in the manufacturing process example of the present embodiment. FIG. 3B is a schematic view showing an initial wasteland in the manufacturing process example of the present embodiment. FIG. 3C is a schematic view showing an intermediate wasteland in the manufacturing process example of the present embodiment. FIG. 3D is a schematic view showing the final wasteland in the manufacturing process example of the present embodiment. FIG. 3E is a schematic view showing a finish forged material in the manufacturing process example of the present embodiment. FIG. 3F is a schematic view showing a forged crank shaft in the manufacturing process example of the present embodiment. FIG. 4 is a vertical cross-sectional view showing a case where the first preforming step is carried out with one mold. FIG. 5 is a vertical cross-sectional view showing the first mold and the second mold of the present embodiment. FIG. 6 is a vertical cross-sectional view showing a first mold and a second mold of the present embodiment, which are different from those of FIG. FIG. 7A is a cross-sectional view showing a situation at the start of the flat portion forming step in the processing flow example of the first preforming step. FIG. 7B is a cross-sectional view showing a situation at the end of the flat portion forming step in the processing flow example of the first preforming step. FIG. 7C is a cross-sectional view showing a situation at the end of the eccentric process in the processing flow example of the first preforming process. FIG. 8A is a cross-sectional view showing a portion to be a journal portion at the start of the flat portion forming step in the processing flow example of the first preforming step. FIG. 8B is a cross-sectional view showing a portion to be a journal portion at the end of the flat portion forming step in the processing flow example of the first preforming step. FIG. 9A is a cross-sectional view showing a portion to be a pin portion at the start of the eccentric process in the processing flow example of the first preforming process. FIG. 9B is a cross-sectional view showing a portion to be a pin portion at the end of the eccentric step in the processing flow example of the first preforming step. FIG. 10A is a cross-sectional view showing a portion to be an arm portion at the start of the flat portion forming step in the processing flow example of the first preforming step. FIG. 10B is a cross-sectional view showing a portion to be an arm portion at the end of the flat portion forming step in the processing flow example of the first preforming step. FIG. 11A is a vertical cross-sectional view schematically showing a situation before reduction in a processing flow example of the second preforming step. FIG. 11B is a vertical cross-sectional view schematically showing a situation at the end of reduction in a processing flow example of the second preforming step. FIG. 12A is a cross-sectional view showing a portion to be a journal portion before reduction in the processing flow example of the second preforming step. FIG. 12B is a cross-sectional view showing a portion to be a journal portion at the end of reduction in the processing flow example of the second preforming step. FIG. 13A is a cross-sectional view showing a portion to be a pin portion before reduction in the processing flow example of the second preforming step. FIG. 13B is a cross-sectional view showing a portion to be a pin portion at the end of reduction in the processing flow example of the second preforming step. FIG. 14A is a cross-sectional view showing an arm corresponding portion before reduction in the processing flow example of the second preforming step. FIG. 14B is a cross-sectional view showing an arm corresponding portion at the end of reduction in the processing flow example of the second preforming step. FIG. 15A is a vertical cross-sectional view schematically showing a state before reduction of a processing flow example of the final preforming step. FIG. 15B is a vertical cross-sectional view schematically showing a situation when the upper die reaches the bottom dead center in the processing flow example of the final preforming step. FIG. 15C is a vertical cross-sectional view schematically showing a situation at the end of axial movement in a processing flow example of the final preforming step. FIG. 16A is a cross-sectional view schematically showing a state before reduction of a processing flow example of the final preforming step. FIG. 16B is a cross-sectional view schematically showing a situation when the upper die reaches the bottom dead center in the processing flow example of the final preforming step. FIG. 16C is a cross-sectional view schematically showing a situation at the end of axial movement in a processing flow example of the final preforming step. FIG. 17 is a schematic view showing the posture of the intermediate wasteland in the final premolding step and the mold clamping direction by the upper and lower molds, and is a view of the intermediate wasteland viewed from the axial direction.

The method for manufacturing a forged crank shaft according to an embodiment of the present invention is a method for manufacturing a forged crank shaft including a journal portion, a pin portion, and a crank arm portion. The journal section is the center of rotation. The pin portion is eccentric with respect to the journal portion. The crank arm section connects the journal section and the pin section.

The method for manufacturing a forged crank shaft includes a first preforming step, a second preforming step, a final preforming step, and a finish forging step. The first preforming step obtains the initial wasteland from the billet. The second preforming step obtains an intermediate wasteland from the initial wasteland. The final preforming step obtains the final wasteland from the intermediate wasteland. In the finish forging process, the final wasteland is formed to the finish dimensions of the forged crank shaft by die forging.

The first preforming step includes a flat portion forming step and an eccentric step. In the flat portion forming step, a pair of first molds is used to reduce the portion to be the journal portion of the billet from the direction perpendicular to the axial direction of the billet. As a result, the cross-sectional area of the portion to be the journal portion is reduced to form a flat portion. In the eccentric step, after the reduction by the first mold is started, the second mold is used to eccentric the portion to be the pin portion with the direction perpendicular to the axial direction of the billet as the eccentric direction.

In the second preforming step, a pair of third dies are used to reduce the width direction of the flat portion to the pin portion of the initial wasteland and the flat portion. As a result, the thickness of a part or all of the portion to be the crank arm portion becomes larger than the thickness of the finished dimension.

In the final preforming step, the fourth mold is used to reduce the intermediate wasteland from the same direction as in the second preforming step, and further, the portion to be the crank arm portion is reduced from the axial direction of the intermediate wasteland. As a result, the thickness of the portion to be the crank arm portion is reduced to the thickness of the finishing dimension while maintaining the amount of eccentricity of the portion to be the pin portion.

According to the manufacturing method of the present embodiment, the intermediate wasteland in which the axial volume distribution is promoted can be obtained without forming burrs by the first preforming step and the second preforming step. Further, in the intermediate wasteland, the volume of the portion serving as the journal portion, the volume of the portion serving as the pin portion, and the volume of the portion serving as the arm portion are appropriately distributed. Therefore, even in the final preforming step, it is possible to obtain a final wasteland having a shape close to the shape of the forged crank shaft with almost no burrs formed. Then, by the finish forging process, the shape of the forged crank shaft can be formed from the final wasteland. From these, the material yield can be improved. Further, in the first preforming step, the reduction of the portion to be the journal portion and the reduction of the portion to be the pin portion are performed by separate molds. Therefore, since the portion to be the journal portion is restrained by the first mold during the eccentricity of the portion to be the pin portion, it is possible to form a wasteland having a precise shape. As a result, a forged crank shaft having a precise shape can be manufactured.

Preferably, in the first preforming step, after the reduction by the pair of first molds is completed, the eccentricity of the portion to be the pin portion by the second mold is started.

In the first preforming step, the amount of eccentricity of the portion to be the pin portion may be the same as or smaller than the amount of eccentricity of the finishing dimension.

Preferably, the portion to be the crank arm portion other than the portion to be the partial crank arm portion includes a portion to be a counterweight portion of the forged crank shaft. Then, in the second preforming step, the thickness of the part that becomes the crank arm portion including the portion that becomes the counterweight portion becomes larger than the thickness of the finishing dimension, and the thickness of the portion that becomes a part of the crank arm portion is the finishing dimension. The thickness.

The method for manufacturing the forged crank shaft of the present embodiment will be described below with reference to the drawings.

1. 1. Manufacturing process example The forged crank shaft targeted by the manufacturing method of the present embodiment includes a journal portion J that is the center of rotation, a pin portion P that is eccentric with respect to the journal portion J, and an arm that connects the journal portion J and the pin portion P. A part A is provided. The forged crank shaft may include a plurality of journal portions J, a plurality of pin portions P, and a plurality of arm portions A. The forged crank shaft may include a plurality of weight portions W. One weight portion is integrally provided on one arm portion. For example, the forged crank shaft 11 of the 4-cylinder-8 counterweight shown in FIGS. 1A and 1B is a manufacturing target. In the case of a forged crank shaft having a 4-cylinder-8 counterweight, all of the plurality of arm portions A are integrally provided with a weight portion W. Forged crank shafts with 4-cylinder-4 counterweights mentioned above are also manufactured. In the case of a forged crank shaft having four cylinders and four counterweights, a part of the plurality of arm portions A is integrally provided with a weight portion W. The shape of the arm portion without the weight portion is oval.

The manufacturing method of the present embodiment includes a first preforming step, a second preforming step, a final preforming step, and a finish forging step. A deburring step may be added as a post-step of the finish forging step. Further, if necessary, a shaping step may be added after the deburring step. If it is necessary to adjust the arrangement angle of the pin portion, a twisting step may be added after the deburring step. These series of steps are carried out hot.

3A to 3F are schematic views for explaining a manufacturing process example of the forged crank shaft of the present embodiment. Of these figures, FIG. 3A shows a billet. FIG. 3B shows the initial wasteland. FIG. 3C shows an intermediate wasteland. FIG. 3D shows the final wasteland. FIG. 3E shows a finish forged material. FIG. 3F shows a forged crank shaft. 3A to 3F show a series of steps in the case of manufacturing the forged crank shaft 11 having the shape shown in FIG. 1.

The first preforming step includes a flat portion forming step and an eccentric step. In the flat portion forming step, a pair of first dies are used to reduce the cross-sectional area at a plurality of portions (hereinafter, also referred to as “journal-corresponding portions”) serving as journal portions of the billet 22 to be processed. Along with this, a plurality of flat portions 23a are formed on the billet. The flat portion 23a is formed at a position corresponding to the journal. As shown in FIG. 8B described later, the flat portion 23a has a width Bf in the direction perpendicular to the reduction direction larger than the thickness ta in the reduction direction. In the eccentric step, a second mold 50 that operates separately from the first mold 40 is used to eccentric a plurality of portions (hereinafter, also referred to as “pin corresponding portions”) that are pin portions of the billet 22. The eccentric direction of the pin corresponding portion is a direction perpendicular to the axial direction of the billet, that is, a reduction direction of the first mold and the second mold. In this way, the initial wasteland 23 whose volume is distributed is obtained.

In the second preforming step, in order to further distribute the volume, a mold different from that in the first preforming step is used to reduce the initial wasteland 23. The reduction direction at that time is the width direction of the flat portion 23a. That is, in the second preforming step, the initial wasteland 23 obtained in the first preforming step is rotated by 90 ° in the axial direction and then reduced. As a result, an intermediate wasteland 24 without burrs can be obtained. In the intermediate wasteland 24, the axial thickness t1 (see FIG. 3C) of the arm corresponding portion is larger than the thickness t0 (see FIG. 3F) of the finishing dimension. The thickness t0 of the finishing dimension means the axial thickness of the arm portion of the forged crank shaft (final product). Further, the amount of eccentricity of the pin corresponding portion of the intermediate wasteland 24 is the same as or smaller than the amount of eccentricity of the finishing dimension. The eccentricity of the finished dimension means the eccentricity of the pin portion of the forged crank shaft. The details of the second preforming step will be described later.

In the final preforming step, the intermediate wasteland 24 is pressed down from the same direction as the second preforming step using the fourth mold. Further, the arm corresponding portion of the intermediate wasteland 24 is reduced from the axial direction of the intermediate wasteland 24. As a result, the thickness of the arm corresponding portion is reduced to the thickness of the finishing dimension while maintaining the eccentricity of the pin corresponding portion. As a result, a final wasteland 25 in which the approximate shape of the forged crank shaft is formed is obtained. The amount of eccentricity of the pin corresponding portion of the final wasteland 25 is the same as the amount of eccentricity of the pin corresponding portion of the intermediate wasteland 24, and is equal to or smaller than the amount of eccentricity of the finishing dimension.

In the finish forging step, the final wasteland 25 is formed to the finish dimensions of the forged crank shaft by die forging, as in the conventional finish casting step described above. Specifically, a pair of upper and lower molds are used. The final wasteland 25 is arranged on the lower mold in such a posture that the pin corresponding portions are lined up in the horizontal plane. Then, forging is carried out by lowering the upper mold. As a result, burrs B are formed as the surplus material flows out, and the finished forged material 26 with burrs is obtained. The finish forged material 26 is formed with a shape that matches the forged crank shaft of the final product. Since the approximate shape of the forged crank shaft is formed on the final wasteland 25, the formation of burrs B can be minimized when forging the final wasteland 25 in the finish forging step.

In the deburring step, for example, the burr B is punched out by the blade die while the finish forged material 26 with the burr is sandwiched and held by the pair of dies. As a result, the burr B is removed from the finish forged material 26. As a result, the forged crank shaft 21 (final product) is obtained.

2. First mold and second mold used in the first preforming step In the first preforming step of the present embodiment, the reduction of the journal corresponding portion and the eccentricity of the pin corresponding portion are carried out. The reduction of the journal equivalent and the eccentricity of the pin equivalent are carried out by a separate mold.

If the reduction of the journal equivalent portion and the eccentricity of the pin equivalent portion are carried out with one mold, the following problems may occur.

FIG. 4 is a vertical cross-sectional view showing a case where the first preforming step is carried out with one mold. With reference to FIG. 4, the billet 22 is arranged on the first lower mold 42 with the first upper mold 41 and the first lower mold 42 separated from each other. As described above, in the first preforming step, the pin corresponding portion is eccentric. The lower mold pin processing portion 42b of the first lower mold 42 for processing the pin corresponding portion of the billet 22 protrudes from the lower mold journal processing portion 42a. Therefore, when the billet 22 is arranged on the first lower mold 42, the billet 22 is supported at two points by the two lower mold pin processing portions 42b. Further, the upper die pin processing portion 41b of the first upper die 41 is arranged closer to the end portion side of the billet 22 than the lower die pin processing portion 42b. In this state, when the first mold 40 presses down the billet 22, a bending moment acts on the billet 22 with the lower die pin processing portion 42b as a fulcrum and the upper die pin processing portion 41b as a force point. If the bending moment acting on the billet 22 is excessively large, the billet 22 will bend. When the first upper mold 41 reaches the bottom dead center while the billet 22 is curved, the position of the billet 22 that the first mold 40 presses down deviates from the planned position. That is, a situation may occur in which the pin-processed portion of the first mold 40 presses down the arm-corresponding portion of the billet 22. Therefore, meat shortage or the like may occur in the initial wasteland after the reduction. In order to prevent this, two molds are used in the first preforming step of the present embodiment.

FIG. 5 is a vertical cross-sectional view showing the first mold and the second mold of the present embodiment. With reference to FIG. 5, the manufacturing apparatus of the present embodiment includes a first mold 40 and a second mold 50. The first mold 40 includes a first upper mold 41 and a first lower mold 42. The second mold 50 includes a second upper mold 51 and a second lower mold 52. In the case of a forged crank shaft of a 4-cylinder engine, the second die 50 includes two second upper dies 51 and two second lower dies 52. The second upper mold 51 and the second lower mold 52 can be raised and lowered independently of the first mold 40. Before the billet 22 is reduced, the second lower mold 52 is arranged at the same height or lower than the lower journal processing portion 42a, and the second upper mold 51 is arranged at the same height or above the upper journal processing portion 41a. ing. That is, the second lower die 52 and the second upper die 51 do not protrude more than the lower die journal processing section 42a and the upper die journal processing section 41a. Therefore, even if the billet 22 is arranged on the first lower mold 42 before the start of reduction, the billet 22 is not supported by the second lower mold 52. The billet 22 is supported by a plurality of lower die journal processing portions 42a. The area where the plurality of lower die journal processing portions 42a support the billet 22 is larger than the area where the second lower die 52 supports the billet. The same applies to the first upper mold 41 and the second upper mold 51. In this state, when the first mold 40 presses down the billet 22, the journal corresponding portion is evenly pressed down. That is, the bending moment is unlikely to act on the billet 22.

Further, after the upper mold journal processing portion 41a and the lower mold journal processing portion 42a of the first mold 40 start reducing the journal corresponding portion of the billet 22, the second upper mold 51 and the second lower mold 52 of the second mold 50 The eccentricity of the pin corresponding portion of the billet 22 is started. Therefore, during the eccentricity of the pin corresponding portion, the journal corresponding portion of the billet 22 is pressed down by the upper die journal processing portion 41a and the lower die journal processing portion 42a. That is, the journal corresponding portion of the billet 22 is constrained by the upper journal processing portion 41a and the lower journal processing portion 42a. Therefore, the billet 22 is difficult to move during the eccentricity of the pin corresponding portion, and the pin corresponding portion can be eccentric in a stable state.

Further, the eccentricity of the pin corresponding portion by the second mold 50 is performed with respect to the billet 22. Therefore, the pin corresponding portion or the arm corresponding portion is less likely to be scratched by the second mold 50. Specifically, it is assumed that the eccentricity of the pin corresponding portion by the second mold 50 is performed on the preformed (some volume-distributed) wasteland. Since the pin portion and the arm portion are formed to some extent in the preformed wasteland, if the preformed wasteland is misaligned with the first lower mold 42, the second mold 50 becomes an area other than the pin corresponding portion. There is a possibility of contact. In this case, there is a possibility that a defect may remain in the arm corresponding portion or the like. However, according to the manufacturing method of the present embodiment, the eccentricity of the pin corresponding portion by the second mold 50 is performed with respect to the billet 22. Since the billet 22 is not preformed, according to the manufacturing method of the present embodiment, defects such as when the pin corresponding portion of the preformed wasteland is eccentric are unlikely to occur.

In short, the second upper mold 51 and the second lower mold 52 move up and down independently, and the journal equivalent portion of the billet 22 is pressed down prior to the pin equivalent portion, so that the pin equivalent portion is eccentric. The billet 22 is difficult to bend. As a result, the billet 22 is pressed down at a predetermined position of the first mold 40, so that thinning or the like is unlikely to occur in the initial wasteland after the reduction. Further, since the pin corresponding portion is eccentric to the billet instead of the preformed wasteland, the pin corresponding portion or the arm corresponding portion is less likely to be scratched.

The configurations of the first mold 40 and the second mold 50 will be described. The second mold 50 includes a control mechanism for independently raising and lowering the second upper mold 51 and the second lower mold 52. The control mechanism is, for example, a die cushion or a hydraulic cylinder.

A case where the control mechanism is the die cushion 81 will be described with reference to FIG. The first lower mold 42 is supported by the bolster base 82 via the die cushion 81. The die cushion 81 has a cushioning function. The second lower mold 52 is supported by the bolster base 82 via the pin base 83. When the first lower mold 42 begins to press down the billet 22, the second lower mold 52 begins to protrude from the first lower mold 42 due to the cushioning function of the die cushion 81. The die cushion 81 is set so that the second lower mold 52 comes into contact with the pin corresponding portion of the billet 22 after the upper die journal processing portion 41a and the lower die journal processing portion 42a come into contact with the journal corresponding portion of the billet 22. .. The same applies to the first upper mold 41 and the second upper mold 51. As a result, the pin corresponding portion of the billet 22 is eccentric after the start of reduction of the journal corresponding portion.

FIG. 6 is a vertical cross-sectional view showing the first mold and the second mold of the present embodiment, which are different from those of FIG. A case where the control mechanism is a hydraulic cylinder 84 will be described with reference to FIG. The hydraulic cylinder 84 can raise and lower the second lower mold 52. The second lower mold 52 is supported by the bolster base 82 via the hydraulic cylinder 84. When the first lower mold 42 begins to press down the billet 22, the hydraulic cylinder 84 operates, and the second lower mold 52 begins to protrude from the first lower mold 42. The hydraulic cylinder 84 is set so that the second lower mold 52 comes into contact with the pin corresponding portion of the billet 22 after the upper die journal processing portion 41a and the lower die journal processing portion 42a come into contact with the journal corresponding portion of the billet 22. .. The same applies to the first upper mold 41 and the second upper mold 51. As a result, the pin corresponding portion of the billet 22 is eccentric after the start of reduction of the journal corresponding portion.

Regardless of whether the control mechanism is a die cushion or a hydraulic cylinder, the timing at which the second lower mold 52 protrudes from the first lower mold 42 is appropriately set. The same applies to the first upper mold 41 and the second upper mold 51. That is, the pin corresponding portion may be eccentric from the start of reduction of the journal corresponding portion to the completion of reduction. The pin equivalent may be eccentric after the journal equivalent has been reduced.

3. 3. Example of Processing Flow of First Preforming Step FIGS. 7A to 10B are schematic views showing an example of processing flow of the first preforming process. Of these figures, FIG. 7A is a vertical cross-sectional view showing a situation at the start of the flat portion forming process, FIG. 7B is a vertical cross-sectional view showing a situation at the end of the flat portion forming process, and FIG. 7C is an eccentric step. It is a vertical cross-sectional view which shows the situation at the time of the end.

8A and 8B are cross-sectional views showing a journal corresponding portion. Of these figures, FIG. 8A shows the situation at the start of the flat portion forming process, and FIG. 8B shows the situation at the end of the flat portion forming process. 8A is a sectional view taken along line VIIIA-VIIIA of FIG. 7A, and FIG. 8B is a sectional view taken along line VIIIB-VIIIB of FIG. 7C.

9A and 9B are cross-sectional views showing a pin corresponding portion. Of these figures, FIG. 9A shows the situation at the start of the eccentric process, and FIG. 9B shows the situation at the end of the eccentric process. 9A is a cross-sectional view of IXA-IXA of FIG. 7A, and FIG. 9B is a cross-sectional view of IXB-IXB of FIG. 7C. 9A and 9B show the billet 22 and the second mold 50.

10A and 10B are cross-sectional views showing an arm corresponding portion. Of these figures, FIG. 10A shows the situation at the start of the flat portion forming process, and FIG. 10B shows the situation at the end of the flat portion forming process. 10A is a cross-sectional view of XA-XA of FIG. 7A, and FIG. 10B is a cross-sectional view of XB-XB of FIG. 7C.

In order to facilitate understanding of the situation, in FIGS. 8B, 9B and 10B, the first mold 40 or the second mold 50 and the billet 22 at the start of reduction are shown together by a chain double-dashed line, and the journal corresponding portion is shown. The axial center position C of is indicated by a black circle.

With reference to FIG. 7A, the pair of first molds 40 includes an upper die journal processing section 41a and a lower die journal machining section 42a that come into contact with the journal corresponding portion. The pair of first molds 40 includes an upper mold processing portion 41c and a lower mold processing portion 42c that come into contact with the arm corresponding portion of the billet 22. One second upper mold 51 is in contact with the part to be the first pin part (corresponding part to the first pin), and the other second upper mold 51 is in contact with the part to be the fourth pin part (corresponding part to the fourth pin). Contact. One second lower mold 52 is in contact with the part to be the second pin part (corresponding part to the second pin), and the other second lower mold 52 is to be in contact with the part to be the third pin part (corresponding part to the third pin). Contact.

In the present embodiment, as shown in FIGS. 7A to 7C, a case where all of the plurality of pin corresponding portions are eccentric is shown, but the method for manufacturing the crank shaft of the present embodiment is not limited to this. In the method for manufacturing a crank shaft of the present embodiment, one pin corresponding portion may be eccentric in the first preforming step, or two or more pin corresponding portions may be eccentric. The pin equivalent portion that was not eccentric in the first preforming step may be eccentric by a well-known method in the subsequent step.

The journal processing section includes an upper die journal machining section 41a and a lower die journal machining section 42a, as shown by a thick line in FIG. 8A. The upper die journal processing section 41a is provided on the first upper die 41. The lower die journal processing section 42a is provided on the first lower die 42. The upper journal processing portion 41a has a concave shape and can accommodate the entire journal corresponding portion of the billet 22. The lower die journal processing portion 42a is provided on the tip surface of the convex portion. It should be noted that there is no particular limitation as to which of the upper die journal processing section 41a and the lower die journal processing section 42a has a concave shape. That is, the lower journal processing portion may have a concave shape capable of accommodating the entire journal corresponding portion of the billet.

As shown by the thick line in FIG. 9A, the second upper mold 51 of the second mold 50 has a concave shape and can accommodate the entire pin corresponding portion of the billet 22. The second lower mold 52 has a configuration that is upside down from the second upper mold 51.

In the first preforming step, as shown in FIG. 7A, the billet 22 is referred to as the first upper mold 41 in a state where the first upper mold 41 is raised and the first upper mold 41 and the first lower mold 42 are separated from each other. It is arranged between the first lower mold 42.

From this state, the first upper mold 41 is lowered. Then, as shown in FIG. 8A, the journal corresponding portion of the billet 22 is housed in the concave upper journal processing portion 41a. As shown in FIG. 9A, the pin corresponding portion of the billet 22 is housed in the second upper mold 51.

When the first upper die 41 is further lowered, a closed cross section is formed by the upper die journal processing section 41a and the lower die journal processing section 42a. In this state, when the first upper die 41 is further lowered to reach the bottom dead center, the entire journal corresponding portion inside the upper die journal processing section 41a and the lower die journal processing section 42a is reduced. In this way, the journal-corresponding portion of the billet 22 is pressed down by the first mold 40, and as a result, the cross-sectional area of the journal-corresponding portion is reduced and the flat portion 23a is formed. Along with this, the surplus material in the journal equivalent portion flows in the axial direction and flows into the arm equivalent portion, and the volume distribution proceeds.

With reference to FIGS. 9A and 9B, after the reduction by the first mold 40 is started, preferably after the reduction is completed, the second upper mold 51 and the second lower mold 52 of the second mold 50 correspond to the pins. Eccentric part. The center of gravity of the pin corresponding portion moves in the eccentric direction of the pin portion (see the hatched arrow in FIG. 1B). Then, the eccentricity of the pin corresponding portion becomes the same as the eccentricity of the finishing dimension. However, the amount of eccentricity of the pin corresponding portion is not limited to this. The amount of eccentricity of the pin corresponding portion may be smaller than the amount of eccentricity of the finishing dimension. In this case, in the finish forging process, the amount of eccentricity of the pin corresponding portion is defined as the amount of eccentricity of the finish dimension.

As shown by a thick line in FIG. 10A, the cross-sectional shape of the arm processed portion is concave in the upper die processed portion 41c and the lower die arm processed portion 42c. In the first preforming step, the arm portion is not positively processed. Therefore, even if the first upper die 41 reaches the bottom dead center, the upper die arm processing portion 41c does not come into contact with the arm corresponding portion of the billet 22.

After the reduction by the first mold 40 is completed, the first upper mold 41 and the second upper mold 51 are raised, and the processed billet 22 (initial wasteland 23) is taken out.

According to the first preforming step, the material flows from the journal corresponding portion to the arm corresponding portion. As a result, the volume can be appropriately distributed in the axial direction. As a result, it is possible to prevent the arm portion from being deficient in the post-process. Further, the second upper mold 51 and the second lower mold 52 of the second mold 50 move up and down independently, and the journal equivalent portion of the billet is pressed down in advance of the pin equivalent portion, thereby corresponding to the pin. The billet 22 is unlikely to bend during the eccentricity of the portion. As a result, the volume-distributed billet 22 is pressed down at a predetermined position of the first mold 40, so that the initial wasteland after the reduction is less likely to be deficient.

4. Example of Processing Flow of Second Preforming Step FIGS. 11A to 14B are schematic views showing an example of processing flow of the second preforming process. Of these figures, FIG. 11A is a vertical sectional view showing a situation before reduction, and FIG. 11B is a vertical sectional view showing a situation at the end of reduction.

12A and 12B are cross-sectional views showing a journal corresponding portion. Of these figures, FIG. 12A shows the situation before the reduction, and FIG. 12B shows the situation at the end of the reduction. 12A is a cross-sectional view taken along the line XIIA-XIIA of FIG. 11A, and FIG. 12B is a cross-sectional view taken along the line XIIB-XIIB of FIG. 11B.

13A and 13B are cross-sectional views showing pin corresponding portions. Of these figures, FIG. 13A shows the situation before the reduction, and FIG. 13B shows the situation at the end of the reduction. 13A is a cross-sectional view of XIIIA-XIIIA of FIG. 11A, and FIG. 13B is a cross-sectional view of XIIIB-XIIIB of FIG. 11B.

14A and 14B are cross-sectional views showing an arm corresponding portion. Of these figures, FIG. 14A shows the situation before the reduction, and FIG. 14B shows the situation at the end of the reduction. 14A is a cross-sectional view of XIVA-XIVA of FIG. 11A, and FIG. 14B is a cross-sectional view of XIVB-XIVB of FIG. 11B.

11A to 14B show an initial wasteland 23 and a pair of upper and lower third molds 30. The third mold 30 includes a third upper mold 31 and a third lower mold 32. In order to facilitate understanding of the situation, in FIGS. 12B, 13B and 14B, the third upper mold 31, the third lower mold 32 and the initial wasteland 23 before reduction are shown together by a two-dot chain line, and the journal corresponding part is shown. The axial center position C of is indicated by a black circle. The pair of third dies 30 include a pin processing portion that comes into contact with the pin corresponding portion and a journal processing portion that comes into contact with the journal corresponding portion.

The journal processing section includes an upper die journal machining section 31a and a lower die journal machining section 32a, as shown by a thick line in FIG. 12A. The upper die journal processing section 31a is provided on the third upper die 31. The lower die journal processing section 32a is provided on the third lower die 32. The upper die journal processing section 31a and the lower die journal processing section 32a are concave and can accommodate a journal equivalent portion in the initial wasteland.

As shown by a thick line in FIG. 13A, the pin processing portion includes an upper die pin processing portion 31b and a lower die pin processing portion 32b. The upper die pin processing portion 31b is provided on the third upper die 31. The lower mold pin processing portion 32b is provided on the third lower mold 32. The upper die pin processing portion 31b and the lower die pin processing portion 32b are concave and can accommodate the pin corresponding portion of the initial wasteland.

When the arm portion of the forged crank shaft includes a weight portion, the upper die arm processing portion 31c and the lower die arm processing portion 32c are weight-processed so as to come into contact with a portion (weight corresponding portion) to be a weight portion, as shown in FIG. 14A. It has a part 32e. The weight processing portion 32e is located at an end portion of the concave lower arm processing portion 32c opposite to the eccentric direction of the pin corresponding portion. The opening width Bp (see FIG. 14B) of the weight processing portion 32e becomes wider in the direction opposite to the eccentric direction of the pin corresponding portion. For example, as shown in FIG. 14A, both side surfaces of the weight processing portion 32e in the reduction direction are inclined surfaces.

In the second preforming step, as described above, the thickness of the arm corresponding portion is made larger than the thickness of the finishing dimension. Therefore, the axial lengths of the upper die processing portion 31c and the lower die arm processing portion 32c are larger than the thickness of the finished dimension of the arm portion.

In the second preforming step, as shown in FIG. 11A, the initial wasteland 23 is moved to the third upper mold 31 with the third upper mold 31 raised and the third upper mold 31 and the third lower mold 32 separated from each other. It is arranged between the third lower mold 32 and the third lower mold 32. At that time, the initial wasteland 23 is arranged in a posture rotated by 90 ° around the axis from the state at the end of the first preforming step so that the width direction of the flat portion (the major axis direction in the case of an ellipse) is the rolling direction. Will be done.

From this state, the third upper mold 31 is lowered. Then, as shown in FIG. 13B, a closed cross section is formed by the upper die pin processing portion 31b and the lower die pin processing portion 32b. Further, as shown in FIG. 12B, a closed cross section is formed by the upper die journal processing section 31a and the lower die journal processing section 32a. In this state, when the third upper die 31 is further lowered to reach the bottom dead center, the pin corresponding portions inside the upper die pin processing portion 31b and the lower die pin processing portion 32b are reduced. Further, the entire flat portion inside the upper die journal processing section 31a and the lower die journal processing section 32a is reduced. As a result, the cross-sectional area is reduced in the journal corresponding portion and the pin corresponding portion. Along with this, the surplus material flows in the axial direction and flows into the arm corresponding portion, and the volume distribution proceeds.

Further, according to the processing flow examples shown in FIGS. 11A to 14B, in the process of lowering the third upper mold 31, the opening of the concave upper mold pin processing portion 31b is closed by the lower mold pin processing portion 32b. A closed cross section is formed by the upper die pin processing portion 31b and the lower die pin processing portion 32b. Further, the opening of the concave upper journal processing portion 31a is closed by the lower journal processing portion 32a, and the closed cross section is formed by the upper journal processing portion 31a and the lower journal processing portion 32a. As a result, burrs are not formed between the third upper mold 31 and the third lower mold 32. Therefore, the material yield can be improved and the axial distribution of the volume can be promoted.

When a pair of third dies are used in the second preforming step, the arm corresponding portion does not have to be pressed down by the third dies from the viewpoint of promoting the axial distribution of the volume. Further, in order to adjust the shape (dimensions) of the arm corresponding portion, the arm corresponding portion may be partially reduced by the third mold (see FIGS. 14A and 14B).

After the reduction by the third mold 30 is completed, the third upper mold 31 is raised and the processed initial wasteland 23 (intermediate wasteland 24) is taken out. In the intermediate wasteland thus obtained, the thickness of the arm corresponding portion is larger than the thickness of the finishing dimension.

The method for manufacturing a forged crank shaft of the present embodiment includes the second preforming step described above. However, it is possible to omit the second preforming step. For example, after the completion of the first preforming step, the initial wasteland may be formed into the final wasteland in the final preforming step described later. However, when the second preforming step is omitted, the initial wasteland is greatly deformed, so that the final formed wasteland is likely to be flawed. Therefore, from the viewpoint of suppressing defects, it is better to carry out the second preforming step.

5. Examples of Processing Flows in the Final Preforming Steps FIGS. 15A to 15C are vertical cross-sectional views schematically showing examples of processing flows in the final preforming process. Of these figures, FIG. 15A shows the situation before reduction. FIG. 15B shows the situation when the upper die reaches the bottom dead center. FIG. 15C shows the situation at the end of the axial movement. 16A to 16C are cross-sectional views schematically showing a processing flow example of the final preforming step. Of these figures, FIG. 16A shows the situation before reduction. FIG. 16B shows the situation when the upper die reaches the bottom dead center. FIG. 16C shows the situation at the end of the axial movement. FIG. 17 is a schematic view showing the posture of the intermediate wasteland in the final premolding step and the mold clamping direction by the upper and lower molds, and is a view of the intermediate wasteland viewed from the axial direction. 15A to 15C show an intermediate wasteland 24 obtained in the above-mentioned second preforming step, a pair of upper and lower fourth molds 90, an upper plate 92, and a lower plate 93. 16A to 16C show the intermediate wasteland 24, the fourth lower mold 70, and the lower plate 93. In FIG. 16A, the intermediate wasteland 24 is shown by a broken line to facilitate understanding of the drawings.

The fourth mold 90 includes a fourth upper mold 60 and a fourth lower mold 70. The fourth upper mold 60 is supported on the upper plate 92. The upper plate 92 moves up and down with the operation of the ram (not shown) of the press machine. The fourth lower mold 70 is supported on the lower plate 93. The lower plate 93 is fixed to the base of the press machine (not shown).

The fourth upper die 60 and the fourth lower die 70 are divided into a plurality of members in order to reduce the arm corresponding portion from the axial direction of the intermediate wasteland 24. The members constituting the fourth upper mold 60 and the fourth lower mold 70 are arranged side by side along the axial direction of the intermediate wasteland 24. The fourth upper mold 60 and the fourth lower mold 70 include fixed journal type members 61 and 71, a plurality of movable journal type members 62 and 72, and a plurality of pin type members 63 and 73, respectively.

The fixed journal type members 61 and 71 are arranged at positions in the intermediate wasteland 24 including a central journal corresponding portion (a portion serving as a third journal portion) and an arm corresponding portion connected to the journal corresponding portion. The fixed journal type members 61 and 71 are immovable with respect to the upper plate 92 and the lower plate 93.

The movable journal type members 62 and 72 are the journal corresponding parts (parts serving as the first, second, fourth and fifth journal parts) other than the center in the intermediate wasteland 24, and the arm corresponding parts connected to the journal corresponding parts. It is placed at each position including. The movable journal type members 62 and 72 at the front end are also present at the positions of the front portions. The movable journal type members 62 and 72 at the rear end are also present at the positions of the flanges. The movable journal type members 62 and 72 are movable on the upper plate 92 and the lower plate 93 in the axial direction of the intermediate wasteland 24 and in the direction toward the fixed journal type members 61 and 71.

The pin-shaped members 63 and 73 are arranged at positions corresponding to the pins in the intermediate wasteland 24, respectively. The pin-shaped members 63 and 73 are movable on the upper plate 92 and the lower plate 93 in the axial direction of the intermediate wasteland 24 and in the direction toward the fixed journal-shaped members 61 and 71. The pin-shaped members 63 and 73 are immovable with respect to the upper plate 92 and the lower plate 93 in a direction other than the axial direction thereof.

The fourth upper mold 60 and the fourth lower mold 70 made of such members are formed with mold engraving portions (see reference numerals 61a, 62a, 63a, 71a, 72a and 73a in FIG. 15A, respectively). The engraved part reflects the approximate shape of the forged crank shaft (final product).

In the final preforming step, as shown in FIG. 15A, the intermediate wasteland 24 is arranged between the fourth upper mold 60 and the fourth lower mold 70 in a state where the fourth upper mold 60 is raised. At that time, the intermediate wasteland 24 is arranged so that the pin corresponding portions are lined up in the horizontal plane (see FIG. 17). From this state, the fourth upper mold 60 is lowered. Then, the intermediate wasteland 24 is compressed by the fourth upper mold 60 and the fourth lower mold 70 from the direction perpendicular to the axial direction of the intermediate wasteland 24 (horizontal direction in FIGS. 15A to 15C). As a result, the journal corresponding portion and the pin corresponding portion of the intermediate wasteland 24 are reduced, and the approximate shape of the journal portion and the pin portion is formed.

Further, as shown in FIGS. 16A to 16C, the movable journal type members 62 and 72 and the pin type members 63 and 73 are moved in the axial direction of the intermediate wasteland 24 toward the fixed journal type members 61 and 71. Let me. This movement can be achieved, for example, by a wedge mechanism or a hydraulic cylinder.

As the movable journal type members 62 and 72 and the pin type members 63 and 73 move in the axial direction, the arm corresponding portion of the intermediate wasteland 24 is reduced in the axial direction of the intermediate wasteland 24. As a result, the thickness of the arm corresponding portion is reduced to the thickness of the finishing dimension, and the approximate shape of the arm portion and the weight portion is formed. At that time, the pin corresponding portion does not move in the eccentric direction. That is, the eccentricity of the pin corresponding portion is maintained the same as the eccentricity of the finishing dimension.

After the reduction by the fourth mold 90 is completed, the fourth upper mold 60 is raised and the processed intermediate wasteland 24 (final wasteland) is taken out.

According to such a final preforming step, since the arm corresponding portion is reduced in the axial direction, the material filling property is improved in the arm portion (when the forged crank shaft includes the weight portion, the arm portion and the weight portion). It is possible to suppress the occurrence of meat shortage. Further, since the material of the arm portion is excellently filled, the final wasteland can be obtained with almost no burrs. Since this final wasteland is used, the formation of burrs can be minimized even in the finish forging process. As a result, the material yield can be improved. Since the finish forging process is a well-known mold forging process, detailed description thereof will be omitted.

6. Preferred Embodiment With reference to FIG. 5, when the crank arm portion of the crank shaft has a counterweight portion, the second upper die 51 is at a higher position than the upper die journal processing portion 41a before processing the billet 22. The second lower mold 52 is preferably at a position lower than the lower mold journal processing portion 42a. The reason for this is as follows.

With reference to FIG. 7B, as described above, in the first preforming step, the journal corresponding portion is pressed by the upper die journal processing portion 41a and the lower die journal processing portion 42a prior to the eccentricity of the pin corresponding portion. .. When the journal corresponding portion is compressed, the material of the billet 22 flows into the arm corresponding portion and the pin corresponding portion. At this time, if the second upper die 51 is located above the upper die journal processing portion 41a, a space is formed between the second upper die 51 and the billet 22. Therefore, the material from the journal corresponding portion can smoothly flow into this space without being disturbed by the second upper mold 51. Therefore, in the first preforming step, it becomes easier to distribute the volume, and it is easy to secure the material corresponding to the volume of the counterweight portion. The same applies to the second lower mold 52.

With reference to FIG. 5, when the crank arm portion of the crank shaft does not have a counterweight portion, the second upper die 51 has the same height as the upper die journal machining portion 41a before machining the billet 22. Preferably, the second lower mold 52 has the same height as the lower mold journal processing portion 42a. The reason for this is as follows.

With reference to FIG. 7B, since the crank arm portion without the counterweight portion has a small volume, the volume distribution in the preforming step can be smaller than that in the case of the crank arm portion having the counterweight portion. If the second upper die 51 is located at the same height as the upper die journal processing portion 41a, no space is formed between the second upper die 51 and the billet 22. Therefore, it becomes difficult for the material from the journal equivalent portion to smoothly flow into this space. Therefore, it is possible to prevent the material from flowing excessively from the journal corresponding portion.

From the viewpoint of improving the material filling property of the weight portion in the post-process, in the second preforming step, the thickness t1 (mm) of the arm corresponding portion of the intermediate wasteland is a ratio (t1 / t0) to the finishing dimension t0 (mm). Therefore, it is preferably 1.1 or more, and more preferably 1.5 or more. On the other hand, if the ratio (t1 / t0) exceeds 3.5, the bulge deformation region on the material surface becomes large, and the dimensional accuracy of the outer circumference of the arm portion may decrease. Therefore, the ratio (t1 / t0) is preferably 3.5 or less.

When the forged crank shaft includes a weight part, the cross-sectional area Sw2 (mm ² ) of the web equivalent part of the intermediate wasteland is The ratio (Sw2 / Sw0) of the forged crank shaft (final product) to the cross-sectional area Sw0 (mm ^{2) of the web is preferably 0.3 to 0.9.} From the same viewpoint, the cross-sectional area Sw1 (mm ² ) of the web equivalent portion of the initial wasteland is 0.2 (Sw1 / Sw0) as a ratio (Sw1 / Sw0) of the forged crank shaft (final product) to the web cross-sectional area Sw0 (mm ^2). It is preferably ~ 0.8. Here, the cross-sectional area Sw1 of the web-corresponding portion is the total of the cross-sectional area of the arm-corresponding portion and the cross-sectional area of the weight-corresponding portion. Further, the cross-sectional area Sw0 of the web is the total of the cross-sectional area of the weight portion and the cross-sectional area of the arm portion integrally provided by the weight portion.

From the viewpoint of reducing burrs formed in the post-process, the cross-sectional area Sj2 (mm ² ) of the journal corresponding part of the intermediate wasteland is the ratio (of the forged crank shaft (final product) to the cross-sectional area Sj0 (mm ^{2) of the journal part.} Sj2 / Sj0), preferably 1.0 to 1.9. From the same viewpoint, the cross-sectional area Sj1 (mm ² ) of the journal corresponding part of the initial wasteland is the ratio (Sj1 / Sj0) of the forged crank shaft (final product) to the cross-sectional area Sj0 (mm ^{2), which is 1.2 to 1.} It is preferably 9.9.

From the viewpoint of reducing burrs formed in the post-process, the cross-sectional area Sp2 (mm ^{2 ) of the pin equivalent portion of the intermediate wasteland is the ratio of the cross-sectional area Sp0 (mm 2} ) of the pin portion of the forged crank shaft (final product) to the cross-sectional area Sp0 (mm 2). Sp2 / Sp0), preferably 0.7 to 1.9. From the same viewpoint, the cross-sectional area Sp1 (mm ² ) of the pin equivalent portion of the initial wasteland is a ratio (Sp1 / Sp0) to ^{the cross-sectional area Sp0 (mm 2} ) of the pin portion of the forged crank shaft (final product). It is preferably 9 to 1.9.

In addition, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the spirit of the present invention. In the above description, the case where all the arm corresponding portions include the weight portion has been described. However, the method for manufacturing the forged crank shaft of the present embodiment is not limited to this case. For example, some arm-corresponding parts of a plurality of arm-corresponding parts may include a weight-corresponding part, and other arm-corresponding parts may not include a weight-corresponding part (eg, 4-cylinder-4 counterweights). Forged crank shaft). In this case, after the completion of the second preforming step, the thickness of a part of the arm corresponding part including the weight corresponding part is larger than the thickness of the finishing dimension, and the thickness of the arm corresponding part not including the weight corresponding part is the finishing dimension. It is preferably the same as the thickness. Since the arm corresponding part (that is, the web corresponding part) including the weight corresponding part has a large volume, it is necessary to collect the material before the final preforming process. On the other hand, since the volume of the arm corresponding part that does not include the weight corresponding part is small, it is not necessary to collect so much material. Therefore, the yield is further suppressed by reducing the amount of material collected in the arm corresponding portion that does not include the weight corresponding portion.

INDUSTRIAL APPLICABILITY The present invention can be effectively used for manufacturing a forged crank shaft mounted on a reciprocating engine.

11 Forged crank shaft 22 Billet 23 Initial rough terrain 23a Flat part 24 Intermediate rough terrain 25 Final rough terrain 26 Finished forged material 30 3rd die 40 1st die 50 2nd die 90 4th die A, A1 to A8 Crank arm J, J1 to J5 Journal part P, P1 to P4 Pin part W, W1 to W8 Counterweight part B Bali

Claims (4)

A method for manufacturing a forged crank shaft including a journal portion serving as a center of rotation, a pin portion eccentric with respect to the journal portion, and a crank arm portion connecting the journal portion and the pin portion.
The manufacturing method is
The first pre-molding process to obtain the initial wasteland from the billet,
A second preforming step of obtaining an intermediate wasteland from the initial wasteland, and
The final preforming step of obtaining the final wasteland from the intermediate wasteland, and
Includes a finish forging step of forming the final wasteland to the finish dimensions of the forged crank shaft by die forging.
In the first preforming step, a pair of first dies are used to reduce the portion of the billet to be the journal portion from a direction perpendicular to the axial direction of the billet, thereby causing the portion to be the journal portion. After starting the step of reducing the cross-sectional area to form a flat portion and the reduction by the first mold, the second mold is used to make the direction perpendicular to the axial direction of the billet eccentric to the pin portion. Including the process of eccentricity of the part
In the second preforming step, the pair of third dies are used to reduce the width direction of the flat portion to reduce the pin portion of the initial wasteland and the flat portion. The thickness of a part or all of the part that becomes the crank arm part becomes larger than the thickness of the finishing dimension.
In the final preforming step, the fourth mold is used to reduce the intermediate rough ground from the same direction as the second preforming step, and further, the portion to be the crank arm portion is reduced from the axial direction of the intermediate rough ground. A method for manufacturing a forged crank shaft, which reduces the thickness of the portion to be the crank arm portion to the thickness of the finishing dimension while maintaining the amount of eccentricity of the portion to be the pin portion. The method for manufacturing a forged crank shaft according to claim 1.
A method for manufacturing a forged crank shaft, wherein in the first preforming step, after the reduction by the pair of first dies is completed, the eccentricity of the portion to be the pin portion by the second die is started. The method for manufacturing a forged crank shaft according to claim 1 or 2.
A method for manufacturing a forged crank shaft, wherein in the first preforming step, the amount of eccentricity of the portion to be the pin portion is the same as or smaller than the amount of eccentricity of the finishing dimension. The method for manufacturing a forged crank shaft according to any one of claims 1 to 3.
The portion that becomes the crank arm portion other than the portion that becomes the partial crank arm portion includes the portion that becomes the counterweight portion of the forged crank shaft.
In the second preforming step, the thickness of the portion to be the crank arm portion including the portion to be the counterweight portion is larger than the thickness of the finish dimension, and the thickness of the portion to be the partial crank arm portion is the finish dimension. A method of manufacturing a forged crank shaft, which is the thickness of.

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