JP2019166538A - Method for manufacturing forging crank shaft - Google Patents

Abstract

To provide a method for a forging crank shaft which enables the molding of a precisely-shaped forging crank shaft and an improvement in material yield.SOLUTION: A first preliminary molding process includes: a step of forming a plurality of flat parts; and a step of, after starting draft with a first metal mold, using a second metal mold to make a part serving as a first pin part and a part serving as a third pin part eccentric in opposite directions to each other, a part serving as a fourth pin part in the same direction as the part serving as the third pin part, and a part serving as a sixth pin part in the same direction as the part serving as the first pin part. In a secondary preliminary molding process, a pair of third metal molds are used to draft the parts serving as a plurality of flat parts and the first-sixth pin parts with the width direction of the flat parts turned in the draft direction. A final preform keeps the thickness of parts serving as a plurality of crank arm parts equal to the thickness of a finished size.SELECTED DRAWING: Figure 7C

Description

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

  In a reciprocating engine such as an automobile, a motorcycle, an agricultural machine, or a ship, a crankshaft is indispensable for converting the reciprocating motion of a piston into a rotational motion to extract power. The crankshaft can be manufactured by die forging or casting. In particular, when high strength and high rigidity are required for the crankshaft, a crankshaft manufactured by die forging (hereinafter also referred to as “forged crankshaft”) is frequently used.

  FIG. 1A to FIG. 1C are schematic views showing examples of the shape of a general forged crankshaft. Among these drawings, FIG. 1A is an overall view, FIG. 1B is a cross-sectional view taken along the line IB-IB of FIG. 1A, and FIG. 1C is a view showing a phase of a pin portion. In the example shown in FIG. 1B, typically, one crank arm portion A1, a counterweight portion W1 integral with the crank arm portion A1, and a pin portion P1 and a journal portion J1 connected to the crank arm portion A1 are shown.

  A forged crankshaft 11 shown in FIGS. 1A to 1C is a forged crankshaft of a 6-cylinder-8 counterweight mounted on a 6-cylinder engine. The forged crankshaft 11 includes seven journal portions J1 to J7, six pin portions P1 to P6, a front portion Fr, a flange portion Fl, and 12 crank arm portions (hereinafter also referred to as “arm portions”). A1 to A12. The arm portions A1 to A12 connect the journal portions J1 to J7 and the pin portions P1 to P6, respectively. Further, some of the twelve arm portions A1 to A12 are integrally provided with counterweight portions (hereinafter also referred to as “weight portions”) W1 to W8. Specifically, the first arm part A1, the second arm part A2, the fifth arm part A5, the sixth arm part A6, the seventh arm part A7, the eighth arm part A8, the eleventh arm part A11, and the twelfth arm. Part A12 is integrally provided with weight parts W1, W2, W3, W4, W5, W6, W7 and W8, respectively. The third arm portion A3, the fourth arm portion A4, the ninth arm portion A9, and the tenth arm portion A10 do not include a weight portion, and the shape thereof is an oval shape.

  A front portion Fr is provided at the front end of the forged crankshaft 11 in the axial direction, and a flange portion Fl is provided at the rear end. The front part Fr is connected to the first first journal part J1, and the flange part Fl is connected to the last seventh journal part J7.

  Hereinafter, when the journal portions J1 to J7, the pin portions P1 to P6, the arm portions A1 to A12, and the weight portions W1 to W8 are collectively referred to, the reference numerals are “J” for the journal portion and “P” for the pin portion. Also, “A” for the arm portion and “W” for the weight portion. Further, the arm part A and the weight part W integrated with the arm part A are collectively referred to as a “web”.

  As shown in FIG. 1C, the six pin portions P <b> 1 to P <b> 6 are arranged so as to be shifted by 120 ° with respect to the journal portion J. That is, the first pin portion P1 is disposed at the first position L1, the sixth pin portion P6 is disposed at the sixth position L6, and the first position L1 and the sixth position L6 are in phase. The second pin portion P2 is disposed at the second position L2, the fifth pin portion P5 is disposed at the fifth position L5, and the second position L2 and the fifth position L5 are in phase. The third pin portion P3 is disposed at the third position L3, the fourth pin portion P4 is disposed at the fourth position L4, and the third position L3 and the fourth position L4 are in phase. The phase angle between the first position L1, the second position L2, and the third position L3 is 120 °. The journal portion, the pin portion, and the arm portion are symmetrical with respect to the fourth journal portion J4 (see FIG. 1A).

  As shown in FIG. 1B, the width Bw of the weight portion W is larger than the width Ba of the arm portion A. For this reason, the weight part W protrudes largely from the arm part center plane (surface including the center axis of the pin part P and the center axis of the journal part J).

  When manufacturing a forged crankshaft having such a shape, a billet is generally used as a starting material. The cross section perpendicular to the longitudinal direction of the billet, that is, the cross section, is round or square. The area of the cross section is constant over the entire length of the billet. In the present specification, the “cross section” means a section perpendicular to the longitudinal direction of each billet or each later-described wasteland or the axial direction of the forged crankshaft. The “longitudinal section” means a section parallel to the longitudinal direction or the axial direction thereof. The area of the cross section is also simply referred to as “cross-sectional area”. A forged crankshaft is manufactured by going through a preforming step, a die forging step, and a deburring step in that order. If necessary, a shaping process is performed after the deburring process. Usually, the preforming process includes a roll forming process and a bending process. The die forging process includes a roughing process and a finishing process.

  2A to 2F are schematic views for explaining a manufacturing process of a conventional general forged crankshaft. Of these figures, FIG. 2A shows a billet. FIG. 2B shows a roll wasteland. FIG. 2C shows a bent wasteland. FIG. 2D shows the rough forging. FIG. 2E shows the finished forging. FIG. 2F shows a forged crankshaft. 2A to 2F show a series of steps in manufacturing the forged crankshaft 11 shown in FIGS. 1A to 1C.

  A method for manufacturing the forged crankshaft 11 will be described with reference to FIGS. First, after a billet 12 having a predetermined length as shown in FIG. 2A is heated by a heating furnace, roll forming and bending are performed in that order in a preliminary forming step. In roll forming, for example, the billet 12 is rolled and squeezed using a perforated roll. Thereby, the volume of the billet 12 is distributed in the axial direction, and the roll wasteland 13 as an intermediate material is obtained (see FIG. 2B). Next, in bending, the roll wasteland 13 is partially pressed down from the direction perpendicular to the axial direction. Thereby, the volume of the roll wasteland 13 is distributed and the bending wasteland 14 which is the further intermediate material is obtained (refer FIG. 2C).

  Subsequently, in the roughing process, the rough forged material 15 is obtained by forging the bent rough ground 14 up and down using a pair of molds (see FIG. 2D). The rough forged material 15 is formed with an approximate shape of a forged crankshaft (final product). Further, in the finish punching process, the rough forging material 15 is forged using a pair of dies up and down to obtain the finished forging material 16 (see FIG. 2E). The finished forged material 16 is shaped to match the forged crankshaft of the final product. At the time of roughing and finishing, surplus material flows out from between the mold splitting faces of the molds facing each other, and the surplus material becomes burr B. For this reason, the burr B is largely attached around the rough forged material 15 and the finished forged material 16.

  In the deburring process, for example, the burrs B are punched out with a cutter tool in a state where the finished forged material 16 with burrs is held between a pair of molds. Thereby, the burr | flash B is removed from the finish forging material 16, and a burr-free forging material is obtained. The forged material without burrs has substantially the same shape as the forged crankshaft 11 shown in FIG. 2F.

  In the shaping process, the burrs-free forging material is slightly crushed from above and below with a mold to correct the burrs-free forging material to the dimensional shape of the final product. Here, the key points of the burr-free forging material are, for example, the shaft portion such as the journal portion J, the pin portion P, the front portion Fr, the flange portion Fl, the arm portion A, and the weight portion W. Thus, the forged crankshaft 11 is manufactured. When manufacturing a forged crankshaft with 6 cylinders to 8 counterweights, a twisting process may be added after the deburring process in order to adjust the pin arrangement angle (120 ° phase angle). .

  The manufacturing process shown in FIGS. 2A to 2F is applicable not only to the forged crankshaft of 6 cylinders-8 pieces counterweight shown in FIGS. 1A to 1C but also to the forged crankshaft of 6 cylinders to 12 pieces counterweight.

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

  Further, the waste land obtained by the preforming is formed on the forged crankshaft in a die forging process which is a subsequent process. In order to obtain a forged crankshaft with a precise shape, it is necessary to form a rough ground with a precise shape in the preforming process.

  For example, Japanese Laid-Open Patent Publication No. 2001-105087 (Patent Document 1), Japanese Laid-Open Patent Publication No. 2-255240 (Patent Document 2), Japanese Laid-Open Patent Publication No. 62-244545 (Patent Document 3). And JP-A-59-45051 (Patent Document 4). Patent Document 1 discloses a preforming method using a pair of upper mold and lower mold. In the preforming method, when the rod-shaped workpiece is squeezed between the upper mold and the lower mold, a part of the workpiece is stretched and a part continuous with the part is offset with respect to the axis. Thereby, in patent document 1, since extending and bending can be implemented simultaneously, it is supposed that capital investment can be reduced.

  The preforming method of Patent Document 2 uses a 4-pass high-speed roll facility instead of the conventional 2-pass roll forming. In the preforming method, the cross-sectional area of the roll wasteland is determined according to the distribution of the cross-sectional areas of the weight part, the arm part, and the journal part of the forged crankshaft (final product). Thereby, in patent document 2, it is supposed that a material yield can be improved.

  In the preforming method of Patent Document 3, a volume of a part of the billet is distributed in the axial direction and the radial direction of the billet by rolling. A forged crankshaft is obtained by die forging the volume-distributed billet. Thereby, in patent document 3, it is supposed that a material yield can be improved.

  In the manufacturing method of Patent Document 4, a billet is formed on a forged crankshaft by one-time die forging using a pair of upper die, lower die, and punch. In the die forging process, first, a region to be a journal portion and a region to be a pin portion of the billet are reduced by a punch that operates separately. The volume of the billet is distributed by the reduction. Thereafter, die forging is performed by the upper die and the lower die. That is, preforming and die forging can be performed in one step. Thereby, in patent document 4, it is supposed that the forged crankshaft of complicated shape can be efficiently manufactured with a single installation.

JP 2001-105087 A JP-A-2-255240 JP 62-244545 A JP 59-45051 A

  In the production of a forged crankshaft, as described above, it is desired to reduce the formation of burrs and improve the material yield. In addition, it is desired to form a rough ground having a precise shape in the preforming step. In the preforming method described in Patent Document 1, the volume distribution of the billet and the eccentricity of the portion to be the pin portion (hereinafter also referred to as “pin equivalent portion”) can be performed to some extent.

  However, the eccentricity and volume distribution of the pin-corresponding portion are insufficient, and a large burr is formed with the shaping of the pin portion in the die forging in the subsequent process. Further, in the preforming method of Patent Document 1, the distribution of the volume of the portion that becomes the weight portion and the volume of the portion that becomes the arm portion integrally including the weight portion in the portion that becomes the web has not been studied. Therefore, in the die forging process, which is a subsequent process, the material is insufficiently filled at the weight part that largely protrudes from the center surface of the arm part, and a lack of thickness is likely to occur. In order to prevent the lack of weight in the weight portion, it is only necessary to increase the excess volume in the wasteland. However, in this case, the material yield decreases. Hereinafter, the portion that becomes the weight portion is also referred to as a “weight equivalent portion”. A portion serving as an arm portion (excluding the weight portion) integrally including the weight portion is also referred to as an “arm equivalent portion”. The weight equivalent part and the arm equivalent part are collectively referred to as “web equivalent part”.

  The preforming method of Patent Document 2 cannot decenter the pin equivalent portion. This is because of roll forming. For this reason, a large burr is formed when the pin portion is formed by die forging in a subsequent process. Further, in the preforming method of Patent Document 2, volume distribution between the weight equivalent part and the arm equivalent part cannot be performed in the web equivalent part. This is because of roll forming. For this reason, in the subsequent die forging process, the material filling of the weight portion becomes insufficient. As a result, lack of meat is likely to occur.

  In the preforming method of Patent Document 3, a facility for performing rolling is required. 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 die forging are performed with a single facility, it is not possible to perform preforming that greatly deforms the billet. Therefore, it is difficult to improve the material yield with the manufacturing method of Patent Document 4.

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

  The manufacturing method of the forged crankshaft of the present embodiment includes seven journal parts serving as rotation centers, a first position, a second position, and a third position that are eccentric with respect to the journal part and have a phase angle of 120 °. It is a manufacturing method of a forged crankshaft comprising six pin portions respectively disposed at a fourth position, a fifth position, and a sixth position, and a plurality of crank arm portions that connect the journal portion and the pin portion.

The forged crankshaft manufacturing method of the present embodiment includes a first preliminary forming step for obtaining an initial wasteland from a billet, a second preliminary forming step for obtaining a final wasteland from the initial wasteland, and forging the final wasteland by at least one die forging. And a finishing forging process for forming the finished dimensions of the crankshaft.
The first pre-forming step uses a pair of first molds, and a portion that becomes a plurality of journal portions by reducing a portion that becomes a plurality of journal portions of the billet from a direction perpendicular to the axial direction of the billet. Forming a plurality of flat portions by reducing the cross-sectional area of the first mold, and after starting the reduction by the first mold, the second mold is used to set the direction perpendicular to the billet axial direction to the first position The portion to be the first pin portion disposed at the position and the portion to be the third pin portion disposed at the third position are decentered in opposite directions, and the portion to be the fourth pin portion disposed at the fourth position is Eccentric in the same direction as the part to be the 3 pin part, eccentric to the part to be the sixth pin part arranged at the sixth position in the same direction as the part to be the first pin part, the part to be the first pin part, The part to be the third pin part, the part to be the fourth pin part, and the sixth pin Sites to be part eccentricity finished dimensions eccentricity (√3) / 2 equal to or than to include a step of reducing.
In the second pre-forming step, a pair of third dies are used, the flat portions are arranged in the second position, the plurality of flat portions, the portions serving as the first pin portions, with the width direction of the flat portions being the downward direction. The part to be, the part to be the third pin part, the part to be the fourth pin part, the part to be the fifth pin part arranged at the fifth position, and the part to be the sixth pin part are reduced.
In the final wasteland, the thicknesses of the portions serving as the plurality of crank arm portions are the same as the thicknesses of the finished dimensions.

  The forged crankshaft manufacturing method according to the embodiment of the present invention can obtain the final wasteland in which the volume distribution in the axial direction is promoted by the first preforming step and the second preforming step. Further, in the final wasteland, the volume of the part that becomes the journal part, the volume of the part that becomes the pin part, and the volume of the part that becomes the arm part are appropriately distributed. The shape of the forged crankshaft can be formed from the final waste land by the finish forging process. Thus, the material yield can be improved. Further, according to the present invention, it is possible to form a precisely shaped rough ground by the first pre-forming step and the second pre-forming step. Therefore, a forged crankshaft with a precise shape can be manufactured.

FIG. 1A is an overall view schematically showing a shape example of a general forged crankshaft. 1B is a cross-sectional view taken along the line IB-IB in FIG. 1A. FIG. 1C is a diagram showing the phase of the pin portion of the forged crankshaft of FIG. 1A. FIG. 2A is a schematic view showing a billet in a conventional manufacturing process. FIG. 2B is a schematic diagram illustrating a roll wasteland in a conventional manufacturing process. FIG. 2C is a schematic diagram showing a bent wasteland in a conventional manufacturing process. FIG. 2D is a schematic diagram showing a rough forged material in a conventional manufacturing process. FIG. 2E is a schematic diagram showing a finished forged material in a conventional manufacturing process. FIG. 2F is a schematic diagram showing a forged crankshaft in a conventional manufacturing process. FIG. 3A is a schematic diagram showing a billet in the manufacturing process example of the present embodiment. FIG. 3B is a schematic diagram illustrating an initial wasteland in the manufacturing process example of the present embodiment. FIG. 3C is a schematic diagram illustrating a final wasteland in the manufacturing process example of the present embodiment. FIG. 3D is a schematic diagram illustrating a finish forged material in the manufacturing process example of the present embodiment. FIG. 3E is a schematic view showing a forged crankshaft in the manufacturing process example of the present embodiment. FIG. 4 is a longitudinal sectional view showing a case where the first preforming step is performed with one mold. FIG. 5 is a longitudinal sectional view showing a first mold and a second mold of the present embodiment. FIG. 6 is a longitudinal sectional view showing a first mold and a second mold of the present embodiment different from FIG. FIG. 7A is a longitudinal cross-sectional view schematically showing a situation at the start of the flat part forming step in the example of the processing flow of the first preforming step. FIG. 7B is a longitudinal cross-sectional view schematically showing a situation at the end of the flat part forming step in the example of the processing flow of the first preforming step. FIG. 7C is a longitudinal cross-sectional view schematically showing a situation at the end of the eccentric step in the processing flow example of the first preforming step. FIG. 8A is a transverse cross-sectional view showing a portion that becomes 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 that becomes 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 that becomes an arm portion at the start of a flat portion forming step in the example of the processing flow of the first preforming step. FIG. 9B is a transverse cross-sectional view showing a portion that becomes an arm portion at the end of the flat portion forming step in the processing flow example of the first preforming step. FIG. 10A is a cross-sectional view showing a portion that becomes a pin portion arranged at the third position at the start of the eccentric step in the example of the processing flow of the first preforming step. FIG. 10B is a cross-sectional view showing a portion that becomes a pin portion that is disposed at the third position at the end of the eccentric step in the processing flow example of the first preforming step. FIG. 11A is a transverse cross-sectional view showing a portion to be a pin portion arranged at the second position at the start of the flat portion forming step in the processing flow example of the first preforming step. FIG. 11B is a cross-sectional view showing a portion to be a pin portion arranged at the second position at the end of the flat portion forming step in the processing flow example of the first preforming step. FIG. 12 is a schematic diagram showing the amount of eccentricity of the first pin equivalent portion and the third pin equivalent portion. FIG. 13A is a longitudinal sectional view schematically showing a situation at the start of rolling in the example of the processing flow of the second preforming step. FIG. 13B is a longitudinal cross-sectional view schematically showing a situation at the end of rolling in the example of the processing flow in the second preforming step. FIG. 14A is a cross-sectional view showing a portion that becomes a journal portion at the start of rolling in the example of the processing flow in the second preforming step. FIG. 14B is a cross-sectional view showing a portion that becomes a journal portion at the end of reduction in the processing flow example of the second preforming step. FIG. 15A is a transverse cross-sectional view showing an arm-corresponding portion at the start of rolling in the example of the processing flow of the second preforming step. FIG. 15B is a transverse cross-sectional view showing an arm-corresponding portion at the end of rolling in the example of the processing flow of the second preforming step. FIG. 16A is a cross-sectional view showing a portion that becomes a pin portion arranged at the second position at the start of rolling in the example of the processing flow of the second preforming step. FIG. 16B is a cross-sectional view showing a portion that becomes a pin portion arranged at the second position at the end of the rolling reduction in the example of the processing flow of the second preforming step. FIG. 17A is a cross-sectional view showing a portion to be a pin portion arranged at the third position at the start of reduction in the processing flow example of the second preforming step. FIG. 17B is a cross-sectional view showing a portion to be a pin portion arranged at the third position at the end of reduction in the processing flow example of the second preforming step.

  The manufacturing method of the forged crankshaft of the present embodiment includes seven journal parts serving as rotation centers, a first position, a second position, and a third position that are eccentric with respect to the journal part and have a phase angle of 120 °. It is a manufacturing method of a forged crankshaft comprising six pin portions respectively disposed at a fourth position, a fifth position, and a sixth position, and a plurality of crank arm portions that connect the journal portion and the pin portion.

The forged crankshaft manufacturing method of the present embodiment includes a first preliminary forming step for obtaining an initial wasteland from a billet, a second preliminary forming step for obtaining a final wasteland from the initial wasteland, and forging the final wasteland by at least one die forging. And a finishing forging process for forming the finished dimensions of the crankshaft.
The first pre-forming step uses a pair of first molds, and a portion that becomes a plurality of journal portions by reducing a portion that becomes a plurality of journal portions of the billet from a direction perpendicular to the axial direction of the billet. Forming a plurality of flat portions by reducing the cross-sectional area of the first mold, and after starting the reduction by the first mold, the second mold is used to set the direction perpendicular to the billet axial direction to the first position The portion to be the first pin portion disposed at the position and the portion to be the third pin portion disposed at the third position are decentered in opposite directions, and the portion to be the fourth pin portion disposed at the fourth position is Eccentric in the same direction as the part to be the 3 pin part, eccentric to the part to be the sixth pin part arranged at the sixth position in the same direction as the part to be the first pin part, the part to be the first pin part, The part to be the third pin part, the part to be the fourth pin part, and the sixth pin Sites to be part eccentricity finished dimensions eccentricity (√3) / 2 equal to or than to include a step of reducing.
In the second pre-forming step, a pair of third dies are used, the flat portions are arranged in the second position, the plurality of flat portions, the portions serving as the first pin portions, with the width direction of the flat portions being the downward direction. The part to be, the part to be the third pin part, the part to be the fourth pin part, the part to be the fifth pin part arranged at the fifth position, and the part to be the sixth pin part are reduced.
In the final wasteland, the thicknesses of the portions serving as the plurality of crank arm portions are the same as the thicknesses of the finished dimensions.

  According to the manufacturing method of the present embodiment, it is possible to obtain the final wasteland in which the volume distribution in the axial direction is promoted by the first preforming step and the second preforming step. Further, in the final wasteland, the volume of the part that becomes the journal part, the volume of the part that becomes the pin part, and the volume of the part that becomes the arm part are appropriately distributed. Therefore, the final waste land having a shape close to the shape of the forged crankshaft can be obtained also in the second preforming step. And the shape of a forge crankshaft can be modeled from the final waste land by a finish forging process. Thus, the material yield can be improved.

  In the first pre-molding step, the second mold, which is moved separately from the first mold for reducing the part to be the journal part, is the part to be the first pin part, the part to be the third pin part, the fourth pin The part to be the part and the part to be the sixth pin part are eccentric. If the first mold is integrated with the second mold, the part that becomes the first pin part, the part that becomes the third pin part, the part that becomes the fourth pin part, and the part that becomes the part that becomes the sixth pin part However, it protrudes from the part which compresses the site | part used as a journal part. Therefore, if molding is started, only the portion that becomes the pin portion is eccentric, and the billet is likely to be bent. However, if the second mold is moved separately from the first mold, the part that becomes the first pin part, the part that becomes the third pin part, the part that becomes the fourth pin part, and the part that becomes the sixth pin part The second mold to be decentered can be prevented from protruding beyond the portion that lowers the portion that becomes the journal portion. For this reason, the billet is difficult to bend during the eccentricity of the part to be the first pin part, the part to be the third pin part, the part to be the fourth pin part, and the part to be the sixth pin part. As a result, the billet is crushed at a predetermined position of the first mold, so that it is difficult for a lack of thickness or the like to occur in the initial wasteland after the tumbling.

  Preferably, in the first pre-molding step, after the reduction by the pair of first molds is completed, the first pin part, the third pin part, and the fourth pin part are formed by the second mold. The eccentricity of the part and the part to be the sixth pin part is started.

  Below, the manufacturing method of the forged crankshaft of this embodiment is demonstrated, referring drawings.

1. Manufacturing Process Example A forged crankshaft targeted by the manufacturing method according to the present embodiment includes seven journal portions J serving as a rotation center, six pin portions P eccentric with respect to the journal portion J, journal portions J, and pin portions. A plurality of arm portions A connecting P. In the following, the pin portion arranged at the first position L1 is the first pin portion, the pin portion arranged at the second position L2 is the second pin portion, and the pin portion arranged at the third position L3 is the third pin portion. The pin portion arranged at the fourth position L4 is also called a fourth pin portion, the pin portion arranged at the fifth position L5 is also called a fifth pin portion, and the pin portion arranged at the sixth position L6 is also called a sixth pin portion. . For example, a forged crankshaft of a 6 cylinder-8 counterweight shown in FIGS. 1A to 1C is a manufacturing object.

  The manufacturing method of this embodiment includes a first preforming step, a second preforming step, and a finish forging step. A deburring process may be added as a subsequent process of the finish forging process. Moreover, you may add a shaping process after a deburring process as needed. Adjustment of the arrangement angle of the pin portion can be performed in the finish forging process. Alternatively, a twisting process may be added after the deburring process, and the pin portion arrangement angle may be adjusted in this twisting process. These series of steps are performed hot.

  3A to 3E are schematic views for explaining an example of a manufacturing process of the forged crankshaft of the present embodiment. Of these figures, FIG. 3A shows a billet. FIG. 3B shows the initial wasteland. FIG. 3C shows the final wasteland. FIG. 3D shows the finished forging. FIG. 3E shows a forged crankshaft. 3A to 3E show a series of steps in manufacturing the forged crankshaft 11 having the shape shown in FIGS. 1A to 1C. The diagrams on the left side of FIGS. 3B to 3E are front views. 3B to 3E are diagrams showing the position of the portion PA1 that is the first pin portion relative to the center of the portion that is the journal portion (hereinafter also referred to as “journal equivalent portion”), and the portion PA2 that is the second pin portion. The position, the position of the part PA3 to be the third pin part, the position of the part PA4 to be the fourth pin part, the position of the part PA5 to be the fifth pin part, and the position of the part PA6 to be the sixth pin part are shown. Further, in the following, the portion to be the first pin portion is the portion corresponding to the first pin, the portion to be the second pin portion is the portion corresponding to the second pin, the portion to be the third pin portion is the portion corresponding to the third pin, and the fourth pin The part to be a part is also called a fourth pin equivalent part, the part to be the fifth pin part is also called a fifth pin equivalent part, and the part to be the sixth pin part is also called a sixth pin equivalent part. 3B and 3C, the first position L1 to the sixth position L6 of the pin portion of the forged crankshaft, which is the final product, are indicated by a two-dot chain line.

  The first preforming process includes a flat part forming process and an eccentric process. In the flat part forming step, the parts to be the plurality of journal parts of the billet 22 are reduced using a pair of first molds. The reduction direction at that time is a direction perpendicular to the axial direction of the billet 22. Thereby, seven journal equivalent parts are crushed among billets 22, and a cross-sectional area reduces in those parts. Along with this, a plurality of flat portions 23 a are formed in the billet 22. The flat portion 23a is formed at a position corresponding to the journal.

  In the eccentric process, after the start of the reduction by the first mold, the second mold is used and the first pin portion disposed at the first position (the first pin equivalent portion) and the third position are disposed. The part (3rd pin equivalent part) used as the 3rd pin part is decentered in the mutually opposite direction. The eccentric direction at that time is a direction perpendicular to the axial direction of the billet 22. Further, the portion (fourth pin equivalent portion) that becomes the fourth pin portion is eccentric in the same direction as the third pin equivalent portion. A part to be the sixth pin part (sixth pin equivalent part) is eccentric in the same direction as the first pin equivalent part. The eccentric amounts of the first pin equivalent portion, the third pin equivalent portion, the fourth pin equivalent portion, and the sixth pin equivalent portion are equal to or smaller than (√3) / 2 of the eccentric amount of the finished dimension. As a result, an initial wasteland in which the volume is distributed and the first pin equivalent portion, the third pin equivalent portion, the fourth pin equivalent portion, and the sixth pin equivalent portion are eccentric is obtained.

  In the second preforming step, the initial wasteland 23 is reduced using a third mold. The reduction direction at that time is the width direction of the flat portion. That is, in the second pre-forming step, the initial waste land 23 obtained in the first pre-forming step is rotated 90 ° around the axial direction and then reduced. Thereby, the final wasteland 24 in which the approximate shape of the forged crankshaft is formed is obtained.

  In the final wasteland 24, the eccentric direction of the first pin equivalent part PA1 and the eccentric direction of the third pin equivalent part PA3 are opposite to each other. That is, the phase angle between the first pin equivalent part PA1 and the third pin equivalent part PA3 is 180 °. The journal equivalent part, the pin equivalent part, and the arm equivalent part are symmetrical with respect to the fourth journal equivalent part. Therefore, in the final wasteland 24, the eccentric direction of the fourth pin equivalent part PA4 is the same as the eccentric direction of the third pin equivalent part PA3. The eccentric direction of the sixth pin equivalent part PA6 is the same as the eccentric direction of the first pin equivalent part PA1. Further, in the final wasteland 24, the axial thickness t1 (see FIG. 3C) of the arm-corresponding portion is the same as the finished dimension thickness t0 (see FIG. 3E). The finished dimension thickness t0 means the axial thickness of the arm portion of the forged crankshaft (final product).

  In the finish forging process, the final wasteland 24 is formed to the finished dimensions of the forged crankshaft by die forging. Specifically, a pair of upper and lower molds are used. The final wasteland 24 is disposed on the lower mold in such a posture that the first pin equivalent part PA1, the third pin equivalent part PA3, the fourth pin equivalent part PA4, and the sixth pin equivalent part PA6 are arranged in a horizontal plane. . Then, forging is performed by lowering the upper die. Further, in the finish forging step, a portion (second pin equivalent portion) to be the second pin portion arranged at the second position and a portion (fifth pin equivalent portion) to be the fifth pin portion arranged at the fifth position. Eccentric. The forging reduction direction is the eccentric direction of the second pin equivalent part PA2 and the fifth pin equivalent part PA5. Thereby, the burr | flash B is formed with the outflow of surplus material, and the finish forging material 25 with a burr | flash is obtained (refer FIG. 3D). The finished forged material 25 is shaped to match the forged crankshaft of the final product. Since the approximate shape of the forged crankshaft is formed on the final wasteland 24, the formation of burrs B can be minimized in the finish forging process. The finishing forging process may be performed once or divided into a plurality of times.

  In the deburring process, for example, the burrs B are punched out by a cutter tool in a state where the finished forged material 25 with burrs is held between a pair of molds. Thereby, the burrs B are removed from the finish forged material 25. As a result, a forged crankshaft 11 (final product) is obtained.

2. First and second molds used in the first preforming step In the first preforming step of the present embodiment, the reduction of the journal equivalent portion, the first pin equivalent portion, the third pin equivalent portion, the fourth pin The eccentricity of the corresponding portion and the sixth pin corresponding portion is performed. The reduction of the journal equivalent portion and the eccentricity of the first pin equivalent portion, the third pin equivalent portion, the fourth pin equivalent portion, and the sixth pin equivalent portion are performed by separate molds.

  If the reduction of the journal equivalent part and the eccentricity of the first pin equivalent part, the third pin equivalent part, the fourth pin equivalent part and the sixth pin equivalent part are performed with one mold, the following problems may occur. There is.

  FIG. 4 is a longitudinal sectional view showing a case where the first preforming step is performed with one mold. Referring to FIG. 4, billet 22 is arranged on first lower mold 42 in a state where first upper mold 41 and first lower mold 42 are separated from each other. As described above, in the first preforming step, the first pin equivalent portion, the third pin equivalent portion, the fourth pin equivalent portion, and the sixth pin equivalent portion are eccentric. The two pin machining portions 42h of the first lower mold 42 for machining the first pin equivalent portion and the sixth pin equivalent portion of the billet 22 protrude from the lower die journal machining portion 42a. Therefore, when the initial wasteland 23 is disposed on the first lower mold 42, the billet 22 is supported at two points by the two pin processing portions 42h. In addition, the two pin processing portions 41h of the first upper mold 41 that process the third pin corresponding portion and the fourth pin corresponding portion of the billet 22 are more of the billet 22 than the two pin processing portions 42h of the first lower mold 42. Located on the center side. In this state, when the first mold 40 lowers the billet 22, the billet 22 is moved to the billet 22 with the two pin processed portions 42h of the first lower mold 42 as fulcrums and the two pin processed portions 41h of the first upper mold 41 as the power points. A load is applied. As a result, a bending moment acts on the billet 22. If the bending moment acting on the billet 22 is excessively large, the billet 22 is curved. When the first upper mold 41 reaches the bottom dead center in a state where the billet 22 is curved, the position of the billet 22 where the first mold 40 is crushed shifts from the planned position. In other words, a situation may occur in which the pin processed portion reduces the web equivalent portion of the billet 22. For this reason, lack of meat 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 longitudinal sectional view showing a first mold and a 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 two second upper molds 51 and two second lower molds 52. The two second upper molds 51 respectively decenter the third pin equivalent part and the fourth pin equivalent part. The two second lower molds 52 respectively decenter the first pin equivalent portion and the sixth pin equivalent portion. The two second upper molds 51 and the two second lower molds 52 can be moved up and down independently of the first mold 40. Before the billet 22 is reduced, the two second lower dies 52 are disposed at the same height as or below the lower die journal processing portion 42a. The two second upper dies 51 are arranged at the same height or above the upper die journal processing portion 41a. That is, the two second upper molds 51 and the two second lower molds 52 are not protruded from the upper mold journal processing part 41a and the lower mold journal processing part 42a. Therefore, even if the billet 22 is arranged on the first lower mold 42 before the start of the reduction, the billet 22 is kept substantially horizontal.

  Further, after the start of the reduction of the journal equivalent portion by the journal processing portions 41a and 42a of the first die 40, the first pin equivalent portion, the third pin equivalent portion, the fourth pin equivalent portion and the sixth pin by the second die 50 are provided. Equivalent eccentricity is started. Therefore, the journal equivalent portion of the billet 22 is squeezed by the journal processing portions 41a and 42a during the eccentricity of the first pin equivalent portion, the third pin equivalent portion, the fourth pin equivalent portion, and the sixth pin equivalent portion. In other words, the journal equivalent portion of the billet 22 is restrained by the journal processing portions 41a and 42a.

  In short, the two second upper molds 51 and the two second lower molds 52 are moved up and down independently, and the journal equivalent part of the billet 22 is the first pin equivalent part, the third pin equivalent part, and the fourth pin equivalent part. And the billet 22 is moved in the axial direction during the eccentricity of the first pin equivalent portion, the third pin equivalent portion, the fourth pin equivalent portion and the sixth pin equivalent portion. Difficult to move. Since the billet 22 is crushed at a predetermined position of the first mold 40, the initial waste land 23 after the pulverization is less likely to be thin.

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

  A case where the control mechanism is a 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 buffer function. The two second upper molds 51 and the two second lower molds 52 are supported by the bolster base 82 via the pin base 83. When the first mold 40 starts to reduce the billet 22, the two second lower molds 52 begin to protrude from the first lower mold 42 due to the cushioning function of the die cushion 81, and the two second upper molds 51 are first upper. Begins protruding from the mold 41. After the journal processing portions 41a and 42a come into contact with the journal equivalent portion of the billet 22, the two second lower molds 52 and the two second upper dies 51 are the first pin equivalent portion, the third pin equivalent portion of the billet 22, The die cushion 81 is set so as to come into contact with the fourth pin equivalent portion and the sixth pin equivalent portion. As a result, the first pin equivalent portion, the third pin equivalent portion, the fourth pin equivalent portion, and the sixth pin equivalent portion of the billet 22 are eccentric after the start of the reduction of the journal equivalent portion.

  FIG. 6 is a longitudinal sectional view showing a first mold and a second mold of the present embodiment different from FIG. The 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 two second upper molds 51 and the two second lower molds 52. The two second upper molds 51 and the two second lower molds 52 are supported by the bolster base 82 via hydraulic cylinders 84. When the first mold 40 starts to reduce the billet 22, the hydraulic cylinder 84 is activated, the two second lower molds 52 start to protrude from the first lower mold 42, and the two second upper molds 51 are the first upper molds. Begins protruding from 41. After the journal processing portions 41a and 42a come into contact with the journal equivalent portion of the billet 22, the two second lower molds 52 and the two second upper dies 51 are the first pin equivalent portion, the third pin equivalent portion of the billet 22, The hydraulic cylinder 84 is set so as to contact the fourth pin equivalent portion and the sixth pin equivalent portion. As a result, the first pin equivalent portion, the third pin equivalent portion, the fourth pin equivalent portion, and the sixth pin equivalent portion of the billet 22 are eccentric after the start of the reduction of the journal equivalent portion.

  Whether the control mechanism is a die cushion or a hydraulic cylinder, the timing at which the two second lower molds 52 protrude from the first lower mold 42 and the two second upper molds 51 from the first upper mold 41 The projecting timing is set as appropriate. That is, the first pin equivalent portion, the third pin equivalent portion, the fourth pin equivalent portion, and the sixth pin equivalent portion of the billet 22 may be eccentric from the start of the reduction of the journal equivalent portion to the completion of the reduction. The first pin equivalent portion, the third pin equivalent portion, the fourth pin equivalent portion, and the sixth pin equivalent portion may be eccentric after completion of the reduction of the journal equivalent portion.

3. Processing Flow Example of First Preliminary Forming Process FIGS. 7A to 11B are schematic diagrams illustrating a processing flow example of the first pre-forming process. Among these drawings, FIG. 7A is a longitudinal sectional view showing the situation at the start of the flat part forming process, FIG. 7B is a longitudinal sectional view showing the situation at the end of the flat part forming process, and FIG. 7C is the end of the eccentric process. It is a longitudinal cross-sectional view which shows the condition of time. Since the 1st metal mold 40 and the 2nd metal mold 50 are symmetrical with respect to the position which processes the 4th journal equivalent part, about the 1st metal mold 40 and the 2nd metal mold 50, about the shape of the half explain. In addition, the processing of the fourth pin equivalent portion is the same as the third pin equivalent portion, the fifth pin equivalent portion is the same as the second pin equivalent portion, and the sixth pin equivalent portion is equivalent to the first pin. Is the same as the department. Therefore, in the following, description of the fourth pin equivalent portion, the fifth pin equivalent portion, and the sixth pin equivalent portion is omitted.

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

  9A and 9B are cross-sectional views showing the arm equivalent portion. Among these figures, FIG. 9A shows the situation at the start of the flat part forming process, and FIG. 9B shows the situation at the end of the flat part forming process. 9A is a sectional view taken along the line IXA-IXA in FIG. 7A, and FIG. 9B is a sectional view taken along the line IXB-IXB in FIG. 7C.

  10A and 10B are cross-sectional views showing a portion corresponding to the third pin. Among these figures, FIG. 10A shows the situation at the start of the eccentric process, and FIG. 10B shows the situation at the end of the eccentric process. 10A is a cross-sectional view taken along the line XA-XA in FIG. 7A, and FIG. 10B is a cross-sectional view taken along the line XB-XB in FIG. 7C.

  11A and 11B are cross-sectional views showing a portion corresponding to the second pin. Among these figures, FIG. 11A shows the situation at the start of the flat part forming process, and FIG. 11B shows the situation at the end of the flat part forming process. 11A is a sectional view taken along the line XIA-XIA in FIG. 7A, and FIG. 11B is a sectional view taken along the line XIB-XIB in FIG. 7C.

  10A and 10B show the second mold 50, and FIGS. 8A to 9B, FIG. 11A and FIG. 11B show the pair of first molds 40 at the top and bottom. In order to facilitate understanding of the situation, in FIGS. 8A to 11B, the axial center position C of the journal equivalent portion is indicated by a black circle. In FIG. 8B, FIG. 9B, FIG. 10B, and FIG. 11B, the first upper mold 41, the first lower mold 42, and the billet 22 at the start of the flat part forming process are shown together with two-dot chain lines. 10A and 10B, the second upper mold 51 and the billet 22 at the start of the eccentric process are shown together with a two-dot chain line. The pair of first dies 40 includes journal processing portions 41 a and 42 a that come into contact with the journal equivalent portion of the billet 22.

  The second upper mold 51 of the second mold 50 is concave as shown by a thick line in FIG. 10A and can accommodate the third pin equivalent portion of the billet 22. The second lower mold 52 (see FIG. 5) has a configuration in which the upper and lower sides of the second upper mold 51 are inverted.

  As shown by a thick line in FIG. 8A, the journal processing section includes an upper mold journal processing section 41a provided in the first upper mold 41 and a lower mold journal processing section 42a provided in the first lower mold 42. The upper die journal processing portion 41 a is concave and can accommodate the journal equivalent portion of the billet 22. The lower mold journal processing portion 42a is provided on the tip surface of the convex portion. In addition, there is no restriction | limiting in particular which of the upper type | mold journal processing part 41a and the lower type | mold journal processing part 42a is made into concave shape. In other words, the lower journal processing portion 42a may have a concave shape that can accommodate the journal equivalent portion of the billet 22.

  As shown in FIG. 9A, the arm equivalent portion does not contact the first upper mold 41. Therefore, the arm equivalent part of the billet 22 is not actively processed in the first preforming step. However, as the journal equivalent portion, the first pin equivalent portion, and the third pin equivalent portion are processed, the cross-sectional shape of the arm equivalent portion changes.

  The second upper mold 51 for processing the third pin equivalent portion is concave as shown by a thick line in FIG. 10A and can accommodate the third pin equivalent portion of the billet 22. The second lower mold 52 that processes the first pin equivalent portion is simply inverted upside down from the second upper die 51 that processes the third pin equivalent portion, and thus the description thereof is omitted.

  The portion corresponding to the second pin does not contact the first upper mold 41 and the first lower mold 42 as shown in FIG. 11A. Therefore, in the first preforming step, the portion corresponding to the second pin of the billet 22 is not actively processed. However, as the journal equivalent portion, the first pin equivalent portion, and the third pin equivalent portion are processed, the cross-sectional shape changes.

  In the first preforming step, the billet 22 is placed between the first upper mold 41 and the first lower mold 42 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. To place. At that time, the reduction direction is a direction perpendicular to the axial direction of the billet 22.

  From this state, the first upper mold 41 is lowered. Then, as shown in FIG. 8A, the journal equivalent part of the billet 22 is accommodated in the upper journal processing part 41 a of the first upper mold 41.

  When the first upper die 41 is further lowered, a closed cross section is formed by the upper die journaling portion 41a and the lower die journaling portion 42a. In this state, when the first upper die 41 is further lowered to reach the bottom dead center, as shown in FIG. 8B, the journal of the billet 22 inside the upper die journaling portion 41a and the lower die journaling portion 42a. Corresponding parts are reduced. In this way, the journal equivalent portion of the billet 22 is squeezed by the first mold 40. As a result, the cross-sectional area of the journal equivalent portion is reduced, and the flat portion 23a is formed. Along with this, the surplus material flows in the axial direction and flows into the arm-corresponding portion, and the volume distribution proceeds.

  In the cross section of the flat portion 23a, the width Bf in the direction perpendicular to the reduction direction may be larger than the thickness ta in the reduction direction. For example, the cross-sectional shape of the flat portion 23a is elliptical or oval (see FIG. 8B).

  After the pressing by the first mold 40 is started, the second lower mold 52 and the second upper mold 51 of the second mold 50 decenter the first pin equivalent part and the third pin equivalent part. Both the first pin equivalent portion and the third pin equivalent portion are eccentric along the reduction direction of the first mold 40. However, the eccentric direction of the first pin equivalent portion is opposite to the eccentric direction of the third pin equivalent portion. The eccentric amount of the first pin equivalent portion and the third pin equivalent portion is equal to or smaller than (√3) / 2 of the eccentric amount of the finished dimension. On the other hand, the portion corresponding to the second pin is not eccentric.

  FIG. 12 is a schematic diagram showing the amount of eccentricity of the first pin equivalent portion and the third pin equivalent portion. FIG. 12 is a view as seen from the axial direction of the forged crankshaft. The phase difference between the first position L1 where the first pin portion of the forged crankshaft of the three-cylinder engine is arranged and the third position L3 where the third pin portion is arranged is 120 °. However, the phase difference between the position of the first pin equivalent part PA1 and the position of the third pin equivalent part PA3 of the initial waste land 23 obtained in the first preforming step is 180 °. Therefore, the first pin equivalent portion is further decentered with respect to the axial position C of the journal equivalent portion after the first preforming step. Thereby, in the forged crankshaft which is the final product, the phase difference between the first position L1 and the third position L3 is 120 °.

  The eccentric amount (finished dimension) of the first pin portion is a distance DL between the center of the first position L1 and the axis C of the journal portion. Therefore, assuming a right triangle composed of the axial center position C of the journal part, the center of the position of the first pin equivalent part PA1, and the center of the first position L1, the eccentricity DL1 of the first pin equivalent part in the eccentric process is The eccentric amount DL of the first pin portion is equal to or smaller than (√3) / 2. If the eccentric amount DL1 of the first pin equivalent portion is larger than (√3) / 2 of the eccentric amount DL of the first pin portion, the first pin equivalent portion is eccentric to the first position L1 in the subsequent finish forging step. It is difficult. This is because the portion corresponding to the first pin must be decentered to the first position L1 along a direction that is not parallel to the reduction direction (the left-right direction in FIG. 12). If the eccentric amount DL1 of the portion corresponding to the first pin is smaller than (√3) / 2 of the eccentric amount DL of the first pin portion, the subsequent finish forging process is performed a plurality of times. For example, in the first finish forging step, the eccentric amount DL1 of the portion corresponding to the first pin is eccentric to (√3) / 2 of the eccentric amount DL of the first pin portion. In the second finish forging step, the position of the first pin equivalent part PA1 is decentered to the first position L1. The same applies to the portion corresponding to the third pin.

  After completion of the reduction by the first mold 40 and the eccentricity by the second mold 50, 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 first pin equivalent portion and the third pin equivalent portion can be eccentric. Further, the volume can be distributed in the axial direction by flowing the material from the journal equivalent portion to the arm equivalent portion. As a result, the material yield can be improved. Moreover, when an arm part contains a weight part, it can suppress that a thin part arises in a weight part. Further, the second upper mold 51 and the second lower mold 52 of the second mold 50 are moved up and down independently, and the journal equivalent part of the billet 22 is squeezed before the pin equivalent part, thereby causing the pin The billet is difficult to tilt during the eccentricity of the corresponding part. Thereby, since the volume-distributed billet is crushed at a predetermined position of the first mold 40, lack of thickness or the like hardly occurs in the final wasteland after the squeezing.

  With reference to FIG. 7C, the above description has been given of the case where the first pin equivalent portion of the billet is eccentric by the second lower mold 52 and the third pin equivalent portion is eccentric by the second upper die 51. However, these top and bottom may be reversed. That is, the first pin equivalent part may be eccentric by the second upper mold, and the third pin equivalent part may be eccentric by the second lower mold.

4). Example of Processing Flow in Second Preliminary Forming Process FIGS. 13A to 17B are schematic diagrams illustrating an example of a processing flow in the second preliminary forming process. Among these drawings, FIG. 13A is a longitudinal sectional view showing a situation at the start of the reduction, and FIG. 13B is a longitudinal sectional view showing a situation at the end of the reduction. Since the mold is symmetrical with respect to the position where the fourth journal equivalent portion is processed, FIGS. 13A and 13B show a half of the mold.

  14A and 14B are cross-sectional views showing journal equivalent portions. Of these figures, FIG. 14A shows the situation at the start of the reduction, and FIG. 14B shows the situation at the end of the reduction. 14A is a XIVA-XIVA sectional view of FIG. 13A, and FIG. 14B is a XIVB-XIVB sectional view of FIG. 13B.

  15A and 15B are cross-sectional views showing the arm equivalent portion. Among these figures, FIG. 15A shows the situation at the start of the reduction, and FIG. 15B shows the situation at the end of the reduction. 15A is an XVA-XVA sectional view of FIG. 13A and FIG. 15B is an XVB-XVB sectional view of FIG. 13B.

  16A and 16B are cross-sectional views showing a portion corresponding to the second pin. Among these figures, FIG. 16A shows the situation at the start of the reduction, and FIG. 16B shows the situation at the end of the reduction. 16A is a sectional view taken along the line XVIA-XVIA in FIG. 13A, and FIG. 16B is a sectional view taken along the line XVIB-XVIB in FIG. 13B.

  17A and 17B are cross-sectional views showing a portion corresponding to the third pin. Of these figures, FIG. 17A shows the situation at the start of reduction, and FIG. 17B shows the situation at the end of reduction. 17A is a cross-sectional view taken along the line XVIIA-XVIIA in FIG. 13A, and FIG. 17B is a cross-sectional view taken along the line XVIIB-XVIIB in FIG. 13B.

  In FIG. 14A-FIG. 17B, the initial wasteland 23 obtained at the above-mentioned 1st preforming process and a pair of 3rd metal mold | die 30 are shown up and down. 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. 14A to 17B, the axial center position C of the journal equivalent portion is indicated by a black circle, and in FIG. 14B, FIG. 15B, FIG. 16B and FIG. The third upper mold 31, the third lower mold 32, and the initial wasteland 23 at the time are written together with a two-dot chain line. The pair of third dies 30 includes a pin processing portion that contacts the pin equivalent portion, a journal processing portion that contacts the journal equivalent portion, and an arm processing portion that contacts the arm equivalent portion.

  As shown by a thick line in FIG. 14A, the journal processing section includes an upper mold journal processing section 31a provided in the third upper mold 31 and a lower mold journal processing section 32a provided in the third lower mold 32. The upper die journal processing portion 31a and the lower die journal processing portion 32a are concave and can accommodate a journal equivalent portion of the initial wasteland 23.

  As shown by a thick line in FIG. 15A, the arm processing unit includes an upper mold processing unit 31 c provided in the third upper mold 31 and a lower mold arm processing unit 32 c provided in the third lower mold 32. As shown by a thick line in FIG. 15A, the cross-sectional shape of the arm processing part is that the upper arm processing part 31c and the lower arm processing part 32c are concave as a whole.

  When the arm portion of the forged crankshaft includes a weight portion, the lower mold arm processing portion 32c has a weight processing portion 32e that comes into contact with a portion (weight equivalent portion) that becomes the weight portion. The weight processed portion 32e is located at the end of the concave lower arm processed portion 32c opposite to the eccentric direction of the pin equivalent portion. The opening width Bp of the weight processed portion 32e becomes wider in the direction opposite to the eccentric direction of the pin equivalent portion. For example, as shown in FIG. 15A, the weight processed portion 32e has inclined surfaces on both side surfaces in the rolling direction.

  In the second preforming step, the axial thickness t1 of the arm-corresponding portion is made the same as the finished dimension thickness t0 (see FIGS. 3C and 3E). For this reason, the lengths in the axial direction of the upper mold arm machining section 31c and the lower mold arm machining section 32c are the same as the thicknesses of the finished dimensions of the arm sections.

  As shown by a thick line in FIG. 16A, the pin processing portion that processes the second pin equivalent portion includes an upper die processing portion 31f provided in the third upper die 31 and a lower die pin provided in the third lower die 32. It consists of a processing part 32f. The upper die pin machining portion 31f and the lower die pin machining portion 32f are concave and can accommodate the third pin equivalent portion of the initial wasteland 23.

  The pin processed portion that comes into contact with the third pin equivalent portion is provided at a position corresponding to the third pin equivalent portion. As shown by a thick line in FIG. 17A, the pin processing portion of the third mold 30 that contacts the third pin equivalent portion includes an upper die processing portion 31 b provided in the third upper die 31, and a third lower die 32. The lower die pin processing portion 32b is provided. The upper die pin machining portion 31 b and the lower die pin machining portion 32 b are concave and can accommodate the third pin equivalent portion of the initial wasteland 23.

  In the second pre-molding step, the initial waste land 23 is moved between the third upper mold 31 and the third lower mold 32 with the third upper mold 31 raised and the third upper mold 31 and the third lower mold 32 separated. Place between. At that time, the initial wasteland 23 is rotated 90 ° around the axis from the state at the end of the first pre-forming step so that the width direction of the flat portion 23a (the major axis direction in the case of an ellipse) is the reduction direction. Be placed. When the third upper mold 31 is lowered from this state, as shown in FIG. 16A, the second pin equivalent portion of the initial waste land 23 is accommodated in the concave upper mold pin processing portion 31f. The same applies to the first and third pin equivalent portions. As shown in FIG. 14A, the journal equivalent portion is accommodated in the concave upper-type journal processing portion 31a. When the third upper mold 31 is further lowered, the initial wasteland 23 is pressed down by the third mold 30. For this reason, the cross-sectional areas of the first to third pin equivalent portions and the journal equivalent portion are reduced.

  After completion of the reduction by the third mold 30, the third upper mold 31 is raised, and the processed initial wasteland 23 (final wasteland 24) is taken out.

  By adopting such a processing flow example, as the cross-sectional areas of the pin equivalent part and the journal equivalent part decrease by reducing the pin equivalent part and the journal equivalent part, the material of the pin equivalent part and the journal equivalent part becomes It moves in the axial direction of the initial wasteland 23. Thereby, the material flows into the arm equivalent portion between the pin equivalent portion and the journal equivalent portion. As a result, the final wasteland 24 in which the volume is distributed in the axial direction can be obtained.

  Further, in the process of lowering the third upper mold 31, the opening of the concave upper pin processing portion 31f is closed by the lower mold pin processing portion 32f, and the upper mold pin processing portion 31f and the lower mold pin processing portion 32f A closed cross section is formed (see FIGS. 16A and 16B). Further, the opening of the concave upper journal processing portion 31a is closed by the lower mold journal processing portion 32a, and a closed cross section is formed by the upper die journal processing portion 31a and the lower mold journal processing portion 32a (FIG. 14A and FIG. 14B). Thereby, no burr is 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.

  In the second preforming step, burr formation may be prevented by partially reducing the journal equivalent portion by the journal processing portion. Moreover, burr formation may be prevented by partially reducing the pin-corresponding portion by the pin processing portion.

  In the second preforming step, the arm-corresponding portion does not have to be reduced by the third mold 30 from the viewpoint of promoting the axial distribution of the volume.

5. Preferred Amount, etc. The amount by which the first and third pin equivalent portions are eccentric by the first preforming step, that is, the eccentric amount Eb (mm) of the first and third pin equivalent portions of the initial rough land 23 is the eccentric amount of the finished dimension. It is preferable to be equal to or smaller than (√3) / 2 of E0 (mm). The above embodiment shows a case where the eccentric amount Eb of the first and third pin equivalent portions is the same as (√3) / 2 of the eccentric amount E0 of the finished dimension. However, from the viewpoint of ensuring the material fullness of the engraving portion for the pin portion, the eccentric amount Eb of the first and third pin equivalent portions of the initial rough land 23 is the ratio of the finished dimension to the eccentric amount E0 (Eb / (( (√3) / 2 × E0)) and preferably (1.0−Dp / 2 / ((√3) / 2 × E0)) or more. Here, Dp means the diameter of the pin part of the finished dimension (the diameter of the pin part of the forged crankshaft). From the same viewpoint, the cross-sectional area Spb (mm ² ) of the first and third pin equivalent portions of the initial wasteland 23 is the ratio ((Spb) / Sp0) to the cross-sectional area Sp0 (mm ² ) of the pin portion of the forged crankshaft. Therefore, it is preferably 0.7 or more and 1.5 or less, more preferably 0.75 or more and 1.1 or less.

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

  The present invention can be effectively used for manufacturing a forged crankshaft to be mounted on a 6-cylinder reciprocating engine.

DESCRIPTION OF SYMBOLS 11 Forging crankshaft 22 Billet 23 Initial wasteland 23a Flat part 24 Final wasteland 25 Finish forging material 30 3rd metal mold 31 3rd upper mold 32 3rd lower mold 40 1st metal mold 41 1st upper mold 42 1st lower mold 50 Second mold 51 Second upper mold 52 Second lower mold A, A1 to A12 Crank arm part J, J1 to J7 Journal part P, P1 to P6 Pin part W, W1 to W8 Counterweight part PA, PA1 to PA6 pin Equivalent part B Bali

Claims (2)

Seven journal parts serving as rotation centers, and a first position, a second position, a third position, a fourth position, a fifth position, and a sixth position that are eccentric with respect to the journal part and have a phase angle of 120 ° A forged crankshaft manufacturing method comprising: 6 pin portions respectively disposed on a plurality of crank arm portions connecting the journal portion and the pin portion;
The manufacturing method is
A first preforming step of obtaining initial wasteland from the billet;
A second preforming step for obtaining a final wasteland from the initial wasteland;
A final forging step of forming the final waste land into a final dimension of the forged crankshaft by at least one die forging,
The first pre-forming step uses a pair of first molds, and reduces the plurality of journal portions of the billet from a direction perpendicular to the axial direction of the billet. A step of forming a plurality of flat portions by reducing a cross-sectional area of a portion to be a journal portion, and after starting the reduction by the first die, a second die is used, and a direction perpendicular to the axial direction of the billet is set. The part to be the first pin part arranged at the first position in the eccentric direction and the part to be the third pin part arranged at the third position are eccentric in opposite directions to be arranged at the fourth position. The part that becomes the fourth pin part is eccentric in the same direction as the part that becomes the third pin part, and the part that becomes the sixth pin part arranged at the sixth position is the same as the part that becomes the first pin part The part which becomes eccentric in the direction and becomes the first pin part The eccentricity of the part to be the third pin part, the part to be the fourth pin part, and the part to be the sixth pin part is equal to or smaller than (√3) / 2 of the eccentricity of the finishing dimension. Including the steps of:
In the second pre-forming step, a pair of third molds are used, and the flat portions are arranged at the second position, the portions serving as the flat portions and the first pin portions, with the width direction of the flat portions being the reduction direction. A portion to be the second pin portion, a portion to be the third pin portion, a portion to be the fourth pin portion, a portion to be the fifth pin portion disposed at the fifth position, and the sixth pin portion Down the area,
The final waste land is a method for manufacturing a forged crankshaft, wherein a thickness of a portion serving as the plurality of crank arm portions is the same as a thickness of a finished dimension. A method for producing a forged crankshaft according to claim 1,
In the first pre-molding step, after the reduction by the pair of first dies is completed, the portion that becomes the first pin portion, the portion that becomes the third pin portion, and the fourth pin by the second die A method for manufacturing a forged crankshaft, wherein eccentricity of a part to be a part and a part to be the sixth pin part is started.

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