JP7485951B2 - Manufacturing method of crankshaft - Google Patents

Description

The present disclosure relates to a method for manufacturing a crankshaft, and more specifically, to a method for manufacturing a crankshaft that includes a journal, a pin that is eccentrically disposed relative to the journal, an arm that connects the journal and the pin, and a counterweight that is integrally formed with the arm.

For example, reciprocating engines mounted on automobiles, motorcycles, agricultural machinery, ships, etc., are equipped with a crankshaft to convert the reciprocating motion of pistons caused by fuel combustion into rotational motion. The crankshaft includes multiple journals, multiple pins, and multiple arms. The journal is the main shaft part of the crankshaft and rotates around its central axis. The pins are arranged eccentrically with respect to the journals and are connected to the pistons via connecting rods. An arm is arranged between each of the journals and pins, and the arms connect adjacent journals and pins. At least some of the multiple arms included in the crankshaft may be provided with counterweights.

Crankshafts are generally manufactured by die forging or casting. For example, when high strength and high rigidity are required for the crankshaft, die forging is often used as a manufacturing method for the crankshaft. When manufacturing a crankshaft by die forging, a preforming process, a die forging process, and a deburring process are carried out in that order. In addition, if necessary, a shaping process is carried out after the deburring process.

The preforming process usually includes a roll forming process and a bending process. In the preforming process, a heated billet is rolled and bent to obtain a rough surface as an intermediate material. In the roll forming process, the billet is rolled and squeezed using, for example, a grooved roll, to distribute the volume of the billet in the axial direction to obtain a rolled rough surface. In the bending process, the rolled rough surface is partially pressed down in a direction perpendicular to the axial direction. This distributes the volume of the rolled rough surface in the axial direction to form a bent rough surface.

The die forging process that follows the preforming process includes a rough forging process and a finish forging process. In the rough forging process, the bent rough material is forged using a pair of upper and lower dies to obtain a rough forged material. The rough forged material is shaped into the approximate shape of the final product, the crankshaft. In the finish forging process, the rough forged material is forged using a pair of upper and lower dies to obtain a finish forged material. The finish forged material is shaped into a shape that matches the final product, the crankshaft. In the rough forging process and finish forging process, material flows out between the parting surfaces of the dies, and burrs are formed around the rough forged material and the finish forged material.

In the burr removal process, for example, the burred finished forged material is held between a pair of dies and the burrs are punched out with a blade die. This removes the burrs from the finished forged material, resulting in a burr-free forged material. In the subsequent shaping process, the necessary areas of the burr-free forged material are pressed down, and the forged material is corrected to the finished dimensions and shape.

Various proposals have been made in the past regarding methods for manufacturing crankshafts by die forging. For example, Patent Documents 1 and 2 propose a method for manufacturing a crankshaft that includes a first preforming step and a second preforming step.

In the manufacturing method of Patent Document 1, an initial rough is formed from a billet in a first preforming process, and then a final rough is formed from the initial rough in a second preforming process. In the first preforming process, the parts of the billet that will become journals and the parts that will become pins are pressed down to form multiple flat sections. In the second preforming process, the wide direction of the flat sections formed in the first preforming process is set as the pressing direction, and the parts of the initial rough that will become journals are pressed down. In the second preforming process, the wide direction of the flat sections is set as the eccentric direction, and the parts of the initial rough that will become pins are eccentric. In the subsequent finish forging process, the final rough obtained in the second preforming process is formed into the finishing dimensions of the crankshaft by die forging.

The manufacturing method of Patent Document 2 includes a final preforming step in addition to the first and second preforming steps. In this final preforming step, the portion of the rough area obtained in the second preforming step that will become the counterweight and the portion that will become the crank arm integral with the counterweight are pressed down in the axial direction. This reduces the thickness of these portions to the thickness of the finished dimensions.

International Publication No. 2019/039199 International Publication No. 2018/056135

When manufacturing a crankshaft by die forging, a preforming process is carried out to obtain a rough surface, and then the rough surface is subjected to a die forging process. In the die forging process, a pair of dies is used to form a forging material having a shape that substantially matches the shape of the crankshaft from the rough surface. If the shape of the rough surface is significantly different from the shape of the forging material, that is, if the shape of the rough surface is far removed from the shape of the crankshaft, it is difficult to stably position the rough surface on the dies in the die forging process. If the positioning of the rough surface is unstable, defects are likely to occur in the forging material formed from the rough surface.

Patent Documents 1 and 2 state that the first preforming step and the second preforming step promote the axial volume distribution of the material, and a final rough shape close to the shape of the crankshaft can be obtained. However, these patent documents do not mention the volume distribution in the direction perpendicular to the axial direction, particularly in the longitudinal direction of the portion that will become the counterweighted arm. In order to give the rough shape a shape closer to the crankshaft and improve the stability of the rough shape in the die forging step, it is preferable to perform the volume distribution of the material more precisely in the preforming step.

The objective of this disclosure is to provide a method for manufacturing a crankshaft that allows for more precise volumetric distribution of material during the preforming process.

The manufacturing method according to the present disclosure is a method for manufacturing a crankshaft. The crankshaft includes a journal, a pin, an arm, and a counterweight. The pin is disposed eccentrically with respect to the journal. The arm connects the journal and the pin. The counterweight is formed integrally with the arm. The manufacturing method includes a first preforming step of obtaining a first rough surface from a billet, a second preforming step of obtaining a second rough surface from the first rough surface, and a third preforming step of obtaining a third rough surface from the second rough surface.

In the first preforming process, a pair of first dies are used to press down the portions of the billet corresponding to the journal and the pin in a direction perpendicular to the axial direction of the billet, thereby reducing the cross-sectional area of the portions corresponding to the journal and the pin, and forming each of these portions into a flat shape. Also, in the first preforming process, the portion of the billet corresponding to the crank web, which is composed of an arm and a counterweight, is pressed down by the pair of first dies so that the length of the portion corresponding to the arm in the pressing direction of the first dies is shorter than the length of the portion corresponding to the counterweight.

In the second preforming process, a pair of second dies are used to press down the portion of the first roughness that corresponds to the journal, with the pressing direction being perpendicular to the pressing direction of the first die and the axial direction of the first roughness. In the second preforming process, an eccentric die is used to make the portion of the first roughness that corresponds to the pin eccentric relative to the portion that corresponds to the journal, with the eccentric direction being parallel to the pressing direction of the second die. Furthermore, in the second preforming process, the portion of the first roughness that corresponds to the crank web is supported by the pair of second dies so that the length of the portion that corresponds to the arm in the pressing direction of the first die is maintained shorter than the length of the portion that corresponds to the counterweight.

In the third preforming process, a third mold is used to reduce the thickness of the portion of the second roughness that corresponds to the crank web by pressing down the portion in the axial direction of the second roughness.

The crankshaft manufacturing method disclosed herein allows for more precise volume distribution of material during the preforming process.

FIG. 1 is a side view that typically illustrates a crankshaft manufactured by a manufacturing method according to an embodiment. FIG. 2 is a cross-sectional view taken along line II-II of FIG. FIG. 3A is a side view that illustrates a billet used in the manufacturing method according to the embodiment. FIG. 3B is a side view that illustrates a first rough base material that is an intermediate material in the manufacturing method according to the embodiment. FIG. 3C is a side view that illustrates a second rough base material that is an intermediate material in the manufacturing method according to the embodiment. FIG. 3D is a side view that illustrates a second rough base material that is an intermediate material in the manufacturing method according to the embodiment. FIG. 4A is a schematic diagram for explaining a first preforming step included in the manufacturing method according to the embodiment. FIG. 4B is another schematic diagram for explaining the first preforming step. FIG. 5A is a cross-sectional view taken along line VA-VA of FIG. 4A. FIG. 5B is a cross-sectional view taken along line VB-VB of FIG. 4B. FIG. 6A is a cross-sectional view taken along the line VIA-VIA in FIG. 4A. FIG. 6B is a cross-sectional view taken along line VIB-VIB of FIG. 4B. FIG. 7A is a cross-sectional view taken along line VIIA-VIIA of FIG. 4A. FIG. 7B is a cross-sectional view taken along line VIIB-VIIB of FIG. 4B. FIG. 8A is a schematic diagram for explaining a second preforming step included in the manufacturing method according to the embodiment. FIG. 8B is another schematic diagram for explaining the second preforming step. FIG. 8C is yet another schematic diagram for explaining the second preforming step. FIG. 9A is a cross-sectional view taken along line IXA-IXA of FIG. 8A. FIG. 9B is a cross-sectional view taken along line IXB-IXB of FIG. 8C. FIG. 10A is a cross-sectional view taken along the line XA-XA of FIG. 8A. FIG. 10B is a cross-sectional view taken along line XB-XB of FIG. 8C. FIG. 11A is a cross-sectional view taken along the line XIA-XIA of FIG. 8A. FIG. 11B is a cross-sectional view taken along line XIB-XIB of FIG. 8C. FIG. 12A is a schematic diagram for explaining a third preforming step included in the manufacturing method according to the embodiment. FIG. 12B is another schematic diagram for explaining the third preforming step. FIG. 12C is yet another schematic diagram for explaining the third preforming step. FIG. 13A is a schematic cross-sectional view of FIG. 12B taken along a horizontal plane. FIG. 13B is a schematic cross-sectional view of FIG. 12C taken along a horizontal plane. FIG. 14 is a vertical sectional view of a press device that can be used in the third preforming step. FIG. 15 is a cross-sectional view of the press apparatus shown in FIG. FIG. 16A is a cross-sectional view of a portion of the second preform subjected to the third preforming step, the portion corresponding to the crank web. FIG. 16B is a cross-sectional view of a portion of the third preform formed in the third preforming step, the portion corresponding to the crank web. FIG. 17 is a diagram illustrating a crank web of a forged material formed in the die forging process after the third preforming process. FIG. 18 is a side view that illustrates a crankshaft to be manufactured in a modified example of the manufacturing method according to the embodiment. FIG. 19 is a vertical cross-sectional view that illustrates a mold used in the first preforming step in the modified example of the manufacturing method according to the embodiment. FIG. 20 is a vertical cross-sectional view that illustrates a mold used in the second preforming step in the modified example of the manufacturing method according to the embodiment. FIG. 21 is a vertical cross-sectional view that illustrates a mold used in the third preforming step in the modified example of the manufacturing method according to the embodiment.

The manufacturing method according to the first configuration is a method for manufacturing a crankshaft. The crankshaft includes a journal, a pin, an arm, and a counterweight. The pin is eccentrically disposed with respect to the journal. The arm connects the journal and the pin. The counterweight is formed integrally with the arm. The manufacturing method includes a first preforming step for obtaining a first rough surface from a billet, a second preforming step for obtaining a second rough surface from the first rough surface, and a third preforming step for obtaining a third rough surface from the second rough surface.

In the first preforming process, a pair of first dies are used to press down the portions of the billet corresponding to the journal and the pin in a direction perpendicular to the axial direction of the billet, thereby reducing the cross-sectional area of the portions corresponding to the journal and the pin, and forming each of these portions into a flat shape. Also, in the first preforming process, the portion of the billet corresponding to the crank web, which is composed of an arm and a counterweight, is pressed down by the pair of first dies so that the length of the portion corresponding to the arm in the pressing direction of the first dies is shorter than the length of the portion corresponding to the counterweight.

In the second preforming process, a pair of second dies are used to press down the portion of the first roughness that corresponds to the journal, with the pressing direction being perpendicular to the pressing direction of the first die and the axial direction of the first roughness. In the second preforming process, an eccentric die is used to make the portion of the first roughness that corresponds to the pin eccentric relative to the portion that corresponds to the journal, with the eccentric direction being parallel to the pressing direction of the second die. Furthermore, in the second preforming process, the portion of the first roughness that corresponds to the crank web is supported by the pair of second dies so that the length of the portion that corresponds to the arm in the pressing direction of the first die is maintained shorter than the length of the portion that corresponds to the counterweight.

In the third preforming process, a third mold is used to reduce the thickness of the portion of the second roughness that corresponds to the crank web by pressing down the portion in the axial direction of the second roughness.

In the crank web, which is composed of an arm and a counterweight, of the forged material obtained in the die forging process, the volume is usually distributed in the longitudinal direction. That is, in the crank web of the forged material, the volume of the counterweight side is large and the volume of the arm side is small. Therefore, in the manufacturing method of the crankshaft according to the first configuration, a rough surface reflecting this volume distribution is formed in advance in the preforming process, which is a process before the die forging process. Specifically, in the first preforming process in which a first rough surface is obtained from the billet, a portion of the billet corresponding to the crank web is pressed down by a pair of first dies. In the first preforming process, the portion of the billet corresponding to the crank web is pressed down so that the length of the portion corresponding to the arm in the pressing direction of the first dies is shorter than the length of the portion corresponding to the counterweight according to the volume distribution of the crank web of the forged material. In the first preforming process, the portion of the billet corresponding to the journal and the portion corresponding to the pin are pressed down by a pair of first dies and formed into a flat shape. This allows excess material to flow from the area corresponding to the journal and the area corresponding to the pin into the area corresponding to the crank web, and also distributes the volume in the axial direction.

In the second preforming process to obtain the second rough from the first rough, the pair of second dies press down the portion of the first rough obtained in the first preforming process that corresponds to the journal, and the eccentric die eccentrically displaces the portion of the first rough that corresponds to the pin. At this time, the volume distribution performed in the first preforming process is substantially maintained in the portion of the first rough that corresponds to the crank web. That is, in the second preforming process, the portion of the second rough that corresponds to the crank web is supported by the pair of second dies so that the length of the portion that corresponds to the arm in the pressing direction of the first die is maintained shorter than the length of the portion that corresponds to the counterweight. In addition, in the second preforming process, surplus material flows into the portion that corresponds to the crank web from the portion that corresponds to the journal and the portion that corresponds to the pin due to the pressing down of the portion that corresponds to the journal and the eccentricity of the portion that corresponds to the pin. Therefore, further volume distribution in the axial direction is performed.

Thus, according to the manufacturing method of the first configuration, not only is axial volume distribution performed for the portion corresponding to the journal, the portion corresponding to the pin, and the portion corresponding to the crank web in the first and second preforming steps, but volume distribution is also performed in the portion corresponding to the crank web such that the volume of the portion corresponding to the counterweight is large and the volume of the portion corresponding to the arm is small. Therefore, more precise volume distribution of material can be performed in the preforming step.

In the second rough part obtained through the first and second preforming steps, the volume of the part corresponding to the crank web is distributed so that the part corresponding to the counterweight has a large volume and the part corresponding to the arm has a small volume. Therefore, in the third preforming step following the first and second preforming steps, the material is less likely to be trapped at the parting surface of the third mold. Therefore, in the third preforming step, it is possible to give a relatively free shape to the part corresponding to the crank web.

In the third preforming step, it is preferable to use a third mold to constrain the outer periphery of the portion of the second roughness that corresponds to the crank web, and to form that portion into a shape that corresponds to the finished shape of the crank web (second configuration).

In the die forging process after the third preforming process, a forged material that roughly matches the finished shape of the crankshaft is formed. Therefore, in the second configuration, in the third preforming process, the outer periphery of the portion of the second roughness obtained in the second preforming process that corresponds to the crank web is constrained by the third die, and this portion is formed into a shape that corresponds to the finished shape of the crank web. This makes it possible to make the shape of the third roughness obtained in the third preforming process closer to the shape of the forged material, i.e., the shape of the die used in the die forging process. Therefore, in the die forging process, the third roughness can be stably arranged on the die, and the occurrence of defects in the forged material can be suppressed. It is also possible to improve the forming accuracy of the forged material.

In the crank web of the forged material and the final crankshaft, the width of the counterweight is greater than the width of the arm. The crank web may have a constricted portion between the arm and the counterweight. Furthermore, the crank web may have a hollowed-out portion. In the second configuration, the portion of the third rough ground corresponding to the crank web is formed into a shape corresponding to the finished shape of such a crank web. This makes it possible to reduce the amount of surplus material that flows out of the die when die forging the portion of the third rough ground corresponding to the crank web in the die forging process after the third preforming process. Therefore, the amount of burrs can be reduced in the die forging process, and the material yield can be improved. The material yield is the ratio (percentage) of the volume of the crankshaft (final product) to the volume of the billet.

In the second preforming process, the amount of eccentricity of the portion corresponding to the pin is preferably 40% or less of the amount of eccentricity of the finished dimensions of the pin (third configuration).

In the third configuration, in the second preforming process, the amount of eccentricity in the area corresponding to the pin is limited to 40% or less of the amount of eccentricity in the finished dimensions of the pin. This makes it easier for material to flow from the area corresponding to the pin to the area corresponding to the crank web in the second preforming process. This promotes volume distribution in the direction perpendicular to the axial direction in the area corresponding to the crank web.

Embodiments of the present disclosure will be described below with reference to the drawings. In each drawing, the same or equivalent components are given the same reference numerals, and the same description will not be repeated.

[Configuration of crankshaft]
Fig. 1 is a side view showing a crankshaft 10 manufactured by the manufacturing method according to this embodiment. The crankshaft 10 shown in Fig. 1 is a crankshaft mounted on a four-cylinder engine. The crankshaft 10 includes a plurality of journals J1 to J5, a plurality of pins P1 to P4, a plurality of arms A1 to A8, and a plurality of counterweights W.

The first journal J1 to the fifth journal J5 each have a roughly cylindrical shape with X1 as the central axis. The first journal J1 to the fifth journal J5 are arranged in this order along the direction in which the central axis X1 extends (axial direction) and form the main shaft portion of the crankshaft 10. The first journal J1 is connected to the front Fr. The fifth journal J5 is connected to the flange Fl. Hereinafter, when there is no need to particularly distinguish between the four journals J1 to J4, they will be collectively referred to as journal J.

The first pin P1 to the fourth pin P4 are each roughly cylindrical and are arranged alternately with the journal J in the axial direction. However, each of the first pin P1 to the fourth pin P4 is eccentric with respect to the journal J. The first pin P1 to the fourth pin P4 are arranged around the central axis X1 with a predetermined phase difference. In this embodiment, the first pin P1 and the fourth pin P4, and the second pin P2 and the third pin P3 are arranged around the central axis X1 with a phase difference of 180°. Hereinafter, when there is no need to particularly distinguish between the four pins P1 to P4, they will be collectively referred to as pins P.

Each of the first arm A1 to the eighth arm A8 is disposed between the journal J and the pin P in the axial direction. The first arm A1 to the eighth arm A8 each connect the journal J and the pin P.

The first arm A1 is disposed between the first journal J1 and the first pin P1, and connects the first journal J1 and the first pin P1. The second arm A2 is disposed between the first pin P1 and the second journal J2, and connects the first pin P1 and the second journal J2. The third arm A3 is disposed between the second journal J2 and the second pin P2, and connects the second journal J2 and the second pin P2. The fourth arm A4 is disposed between the second pin P2 and the third journal J3, and connects the second pin P2 and the third journal J3. The fifth arm A5 is disposed between the third journal J3 and the third pin P3, and connects the third journal J3 and the third pin P3. The sixth arm A6 is disposed between the third pin P3 and the fourth journal J4, and connects the third pin P3 and the fourth journal J4. The seventh arm A7 is disposed between the fourth journal J4 and the fourth pin P4, and connects the fourth journal J4 and the fourth pin P4. The eighth arm A8 is disposed between the fourth pin P4 and the fifth journal J5, and connects the fourth pin P4 and the fifth journal J5.

Each of the first arm A1 to the eighth arm A8 is provided with a counterweight W. Each of the counterweights W is formed integrally with one of the arms A1 to A8. The first arm A1 to the eighth arm A8 with the counterweight W are also referred to as the first crank web Cw1 to the eighth crank web Cw8, respectively, and when there is no need to particularly distinguish between the crank webs Cw1 to Cw8, they are collectively referred to as the crank web Cw. Also, when there is no need to particularly distinguish between the eight arms A1 to A8, they are collectively referred to as the arms A.

Figure 2 is a cross-sectional view taken along line II-II of Figure 1, and shows the crank web Cw as viewed from the pin P side. Referring to Figure 2, the width Bw of the counterweight W is greater than the width Ba of the arm A. Compared to the arm A, the counterweight W protrudes outward in the width direction from the center plane of the crank web Cw. The center plane of the crank web Cw is a plane that includes the center axis X1 of the journal J and the center axis X2 of the pin P. The width direction of the crank web Cw is the direction perpendicular to this center plane. The direction parallel to the center plane of the crank web Cw is called the longitudinal direction of the crank web Cw.

[Manufacturing method of crankshaft]
Next, a description will be given of a method for manufacturing the crankshaft 10 configured as described above. The method for manufacturing the crankshaft 10 includes a first preforming step, a second preforming step, and a third preforming step.

Figures 3A to 3D are diagrams that show the materials or formed products in each preforming step. When manufacturing the crankshaft 10, the billet 11 shown in Figure 3A is usually used as the starting material. The cross section (transverse section) perpendicular to the axial direction of the billet 11 has a circular or angular shape. The area of the transverse section of the billet 11 is substantially constant over its entire length. In the first preforming step, the rough surface 12 shown in Figure 3B is obtained from the billet 11 as the first intermediate material. In the second preforming step, the rough surface 13 shown in Figure 3C is obtained from the rough surface 12 obtained in the first preforming step as the second intermediate material. In the third preforming step, the rough surface 14 shown in Figure 3D is obtained from the rough surface 13 obtained in the second preforming step as the third intermediate material. Each step will be specifically described below.

(First preforming step)
4A and 4B are schematic diagrams for explaining the first preforming step. In Fig. 4A and 4B, the central axis of the billet 11 and the rough part 12 is denoted by the same reference symbol X1 as the central axis of the journal J. In the first preforming step, the billet 11 is pressed down using a pair of dies 21 and 22. The dies 21 and 22 can be attached to a general press device. In the example of this embodiment, the die 21 is an upper die, and the die 22 is a lower die used together with the die 21.

As shown in FIG. 4A, when the first preforming step is started, the billet 11 is placed between the die 21 and the die 22 with the die 21 raised and separated from the die 22. The billet 11 is placed on the die 22, which is the lower die. When the die 21 is lowered, the dies 21 and 22 press the billet 11 down in a direction perpendicular to its axial direction. As shown in FIG. 4B, the die 21 is brought to the bottom dead center, whereby the billet 11 is formed into the rough 12. Thereafter, the die 21 is raised, and the formed rough 12 is removed from the dies 21 and 22.

Figures 5A and 5B are cross-sectional views taken along lines VA-VA and VB-VB in Figure 4A and 4B, respectively. Figures 5A and 5B show cross-sections of the portion of the billet 11 or the rough land 12 that corresponds to the journal J. The portion that corresponds to the journal J is the portion that will become the journal J when each material is finally formed into the crankshaft 10. Hereinafter, each portion of each material that corresponds to the journal J is referred to as the journal-equivalent portion JA. Note that in order to make it easier to understand the positional relationship of each portion of the material, the central axis X1 of the journal J is also shown in Figures 5A and 5B, as well as Figures 6A, 6B, 7A, and 7B described below.

Referring to FIG. 5A, the journal equivalent portion JA of the billet 11 is placed at a position corresponding to the journal processing portion 21a provided on the die 21 and the journal processing portion 22a provided on the die 22 at the start of the first preforming step. The journal processing portion 21a of the die 21 has a concave shape capable of accommodating the journal equivalent portion JA of the billet 11. The journal processing portion 22a of the die 22 faces the journal processing portion 21a of the die 21 and has a shallower concave shape than the journal processing portion 21a. The journal processing portion 22a is formed on the tip surface of a protrusion provided on the die 22. However, contrary to this embodiment, the journal processing portion 22a of the die 22 may have a concave shape capable of accommodating the billet 11 in a cross-sectional view, and the die 21 may have a protrusion having a shallow concave journal processing portion 21a.

As shown in FIG. 5A, at the start of the first preforming step, the journal equivalent portion JA is placed on the journal processing portion 22a of the die 22. By lowering the die 21 toward the die 22, the journal equivalent portion JA is accommodated in the journal processing portion 21a of the die 21. As shown in FIG. 5B, by further lowering the die 21, the journal equivalent portion JA is pressed down by the journal processing portions 21a and 22a. In the process of lowering the die 21, the journal processing portion 22a of the die 22 enters the journal processing portion 21a of the die 21, and the opening of the journal processing portion 21a of the die 21 is blocked by the journal processing portion 22a of the die 22 to form a closed cross section. As a result, in the first preforming step, it is possible to suppress the generation of burrs when the journal equivalent portion JA is pressed down, and the material yield can be improved.

In the first preforming process, the dies 21 and 22 are used to press down the journal equivalent portion JA in a direction perpendicular to the axial direction of the billet 11, thereby reducing the cross-sectional area of the journal equivalent portion JA and forming the journal equivalent portion JA into a flat shape. In the first preforming process, all of the journal equivalent portions JA included in the billet 11 are processed in the same manner. In the rough form 12 after the first preforming process, the journal equivalent portion JA has a cross section whose dimension in the pressing direction by the dies 21 and 22 is small and whose dimension in the direction perpendicular to the pressing direction is large. In the rough form 12, the cross section of the journal equivalent portion JA has, for example, an elliptical or oval shape.

Figures 6A and 6B are respectively a VIA-VIA cross-sectional view of Figure 4A and a VIB-VIB cross-sectional view of Figure 4B. Figures 6A and 6B show cross sections of the portion of the billet 11 or the rough surface 12 that corresponds to the pin P. The portion that corresponds to the pin P is the portion that will become the pin P when each material is finally formed into the crankshaft 10. Hereinafter, each portion of each material that corresponds to the pin P will be referred to as the pin-equivalent portion PA.

Referring to FIG. 6A, the pin-equivalent portion PA of the billet 11 is disposed at a position corresponding to the pin processing portion 21b provided in the die 21 and the pin processing portion 22b provided in the die 22 during the first preforming step. The pin processing portion 21b of the die 21 has a concave shape capable of accommodating the pin-equivalent portion PA of the billet 11. The pin processing portion 22b of the die 22 faces the pin processing portion 21b of the die 21 and has a shallower concave shape than the pin processing portion 21b. The pin processing portion 22b is formed on the tip surface of a protrusion provided in the die 22. However, contrary to this embodiment, the pin processing portion 22b of the die 22 may have a concave shape capable of accommodating the billet 11 in a cross-sectional view, and the die 21 may have a protrusion having a shallow concave pin processing portion 21b.

As shown in FIG. 6A, by lowering the die 21 toward the die 22, the pin equivalent portion PA is accommodated in the pin processing portion 21b of the die 21. As shown in FIG. 6B, by further lowering the die 21, the pin equivalent portion PA is pressed down by the pin processing portions 21b and 22b of the die 21 and 22. In the process of lowering the die 21, the pin processing portion 22b of the die 22 enters the pin processing portion 21b of the die 21, and the opening of the pin processing portion 21b of the die 21 is blocked by the pin processing portion 22b of the die 22 to form a closed cross section. This makes it possible to suppress the generation of burrs when the pin equivalent portion PA is pressed down in the first preforming process, and improves the material yield.

In the first preforming step, the pin-equivalent portion PA is pressed down in a direction perpendicular to the axial direction of the billet 11 using the dies 21 and 22, thereby reducing the cross-sectional area of the pin-equivalent portion PA and forming the pin-equivalent portion PA into a flat shape. In the first preforming step, all the pin-equivalent portions PA included in the billet 11 are processed in the same manner. In the rough 12 after the first preforming step, the pin-equivalent portion PA has a cross section whose dimension in the pressing direction by the dies 21 and 22 is small and whose dimension in the direction perpendicular to the pressing direction is large. In the rough 12, the cross section of the pin-equivalent portion PA has, for example, an elliptical or oval shape. The cross section of the pin-equivalent portion PA may have the same shape or dimensions as the cross section of the journal-equivalent portion JA, or may have a different shape or dimensions.

Figures 7A and 7B are cross-sectional views taken along lines VIIA-VIIA in Figure 4A and VIIB-VIIB in Figure 4B, respectively. Figures 7A and 7B show cross-sections of the portion of the billet 11 or the rough area 12 that corresponds to the crank web Cw. The portion that corresponds to the crank web Cw is the portion that will become the crank web Cw when each material is finally formed into the crankshaft 10. Hereinafter, each portion of each material that corresponds to the crank web Cw will be referred to as the web-equivalent portion CA.

Referring to FIG. 7A, during the first preforming process, the web-corresponding portion CA of the billet 11 is positioned at a position corresponding to the web processing portion 21c provided on the die 21 and the web processing portion 22c provided on the die 22.

The web processing section 21c in one of the molds 21 includes an arm processing section 211c and a weight processing section 212c. The arm processing section 211c processes a portion (arm equivalent portion) AA of the billet 11 that corresponds to the arm A, which is a part of the crank web Cw. The weight processing section 212c processes a portion (weight equivalent portion) WA of the billet 11 that corresponds to the counterweight W that is integrally provided on the arm A. The arm processing section 211c and the weight processing section 212c each have a concave shape. Each of the arm processing section 211c and the weight processing section 212c is, for example, a concave curved surface formed on the lower surface of the mold 21. However, the weight processing section 212c is deeper than the arm processing section 211c.

The web processing section 22c in the other die 22 includes an arm processing section 221c and a weight processing section 222c. The arm processing section 221c, together with the arm processing section 211c of the die 21, is a section that processes the arm equivalent section AA of the billet 11. The weight processing section 222c, together with the weight processing section 212c of the die 21, is a section that processes the weight equivalent section WA of the billet 11. The arm processing section 221c and the weight processing section 222c each have a concave shape. Each of the arm processing section 221c and the weight processing section 222c is, for example, a concave curved surface formed on the lower surface of the die 22. However, the weight processing section 222c is deeper than the arm processing section 221c. In this embodiment, the web processing portion 22c of the mold 22 has a shape that is substantially symmetrical to the web processing portion 21c of the mold 21 with respect to a horizontal plane that includes the central axis X1 of the journal equivalent portion JA.

As shown in FIG. 7A, at the start of the first preforming step, the web corresponding portion CA is placed on the web processing portion 22c of the mold 22. As shown in FIG. 7B, by lowering the mold 21 toward the mold 22, the web corresponding portion CA is pressed down between the web processing portion 21c of the mold 21 and the web processing portion 22c of the mold 22. The pressing direction by the web processing portions 21c, 22c roughly coincides with the width direction of the crank web Cw.

In the first preforming process, the length (width) La of the arm equivalent part AA in the pressing direction of the dies 21 and 22 becomes shorter than the length (width) Lw of the weight equivalent part WA by pressing down with the dies 21 and 22. More specifically, the arm equivalent part AA is pressed down by the shallow concave arm processing parts 211c and 221c to reduce its cross-sectional area. The arm equivalent part AA is molded along the arm processing parts 211c and 221c. As the cross-sectional area of the arm equivalent part AA decreases, material flows from the arm equivalent part AA side to the deeply concave weight processing parts 212c and 222c. In addition, as the cross-sectional areas of the journal equivalent part JA and the pin equivalent part PA adjacent to the web equivalent part CA decrease, material flows from the journal equivalent part JA and the pin equivalent part PA to the weight processing parts 212c and 222c. As a result, the volume of the weight equivalent part WA becomes larger than the volume of the arm equivalent part AA. The weight equivalent portion WA is molded along the weight processing portions 212c and 222c.

In the first preforming step, all web-corresponding portions CA included in the billet 11 are processed in the same manner. However, the processing is reversed by 180° between the portions corresponding to the crank webs Cw1, CW2, Cw7, and Cw8 and the portions corresponding to the crank webs Cw3 to Cw6.

(Second preforming step)
8A to 8C are schematic diagrams for explaining the second preforming step. Referring to FIG. 8A, in the second preforming step, a pair of dies 31 and 32 are used to press down the journal-corresponding portions JA of the rough base 12 obtained in the first preforming step. In addition, in the second preforming step, a plurality of eccentric dies 41 and 42 are used to perform eccentricity of the pin-corresponding portions PA of the rough base 12.

The dies 31 and 32 can be attached to a press machine. In this embodiment, the die 31 is an upper die, and the die 32 is a lower die used together with the die 31. The multiple eccentric dies 41 are members for eccentrically moving the portion (first pin equivalent) PA1 corresponding to the first pin P1 and the portion (fourth pin equivalent) PA4 corresponding to the fourth pin P4 in the rough surface 12. Each of the eccentric dies 41 is configured to be able to rise and fall independently of the die 31. The multiple eccentric dies 42 are members for eccentrically moving the portion (second pin equivalent) PA2 corresponding to the second pin P2 and the portion (third pin equivalent) PA3 corresponding to the third pin P3 in the rough surface 12. Each of the eccentric dies 42 is configured to be able to rise and fall independently of the die 32.

In this embodiment, the eccentric dies 41, 42 are controlled to rise and fall independently of the dies 31, 32 by a die cushion 51 with a cushioning function. The dies 31, 32 are each supported by a bolster base 52 via the die cushion 51. The eccentric dies 41, 42 are each supported by the bolster base 52 via a pin base 53.

As shown in FIG. 8A, when starting the second preforming process, the rough work 12 is placed between the die 31 and the die 32 with the die 31 raised and separated from the die 32. The rough work 12 is placed on the die 32, which is the lower die. In the initial state, the lower end of each eccentric die 41 is placed at a height equal to or higher than the pressing surface of the die 31 and does not protrude downward from the pressing surface. In addition, each eccentric die 42 is placed at a height equal to or lower than the pressing surface of the die 32 and does not protrude upward from the pressing surface. Therefore, when the rough work 12 is placed on the die 32, the posture of the rough work 12 is kept substantially horizontal.

The rough material 12 is placed between the dies 31 and 32 in a position rotated 90° about the axis from the state at the end of the first preforming process. As a result, the pressing direction by the dies 31 and 32 is substantially perpendicular to both the pressing direction in the first preforming process and the axial direction of the rough material 12.

Referring to FIG. 8B, the die 31 is lowered, and the dies 31 and 32 press down the rough land 12. After the dies 31 and 32 start pressing down, the eccentric dies 41 and 42 perform eccentricity. For example, by setting the die cushion 51, the eccentric dies 41 and 42 can be brought into contact with the rough land 12 after the dies 31 and 32 have come into contact with the rough land 12. That is, when the dies 31 and 32 start pressing down the rough land 12, the cushioning function of each die cushion 51 causes each eccentric die 41 to start protruding from the die 31, and each eccentric die 42 to start protruding from the die 32.

In this way, by starting the eccentricity by the eccentric dies 41 and 42 after starting the pressing by the dies 31 and 32, the eccentricity can be performed while the rough land 12 is restrained by the dies 31 and 32. Therefore, the movement of the rough land 12 during the eccentricity can be suppressed, and each eccentric die 41 and 42 can be prevented from pressing down inappropriate parts of the rough land 12, that is, parts other than the pin-corresponding parts PA to PA4. As a result, it is possible to suppress the occurrence of underfill in the second preforming process. In addition, before the pressing down by the dies 31 and 32 is started, a bending moment with the eccentric die 42 as the fulcrum and the eccentric die 41 as the force point is not generated in the rough land 12, and the rough land 12 does not bend due to the bending moment. Therefore, the dies 31 and 32 can press down the parts of the rough land 12 other than the pin-corresponding parts PA to PA4 substantially evenly. The eccentricity caused by the eccentric dies 41, 42 may start after the pressing by the dies 31, 32 starts and before the die 31 reaches the bottom dead center, or it may start after the die 31 reaches the bottom dead center.

Referring to FIG. 8C, when each eccentric die 41 protrudes a predetermined amount from the die 31, the eccentricity of the first pin corresponding portion PA1 and the fourth pin corresponding portion PA4 of the rough land 12 is completed. When each eccentric die 42 protrudes a predetermined amount from the die 32, the eccentricity of the second pin corresponding portion PA2 and the third pin corresponding portion PA3 of the rough land 12 is completed. In the second preforming process, the pin corresponding portions PA1 and PA4 and the pin corresponding portions PA2 and PA3 are eccentric in opposite directions. The eccentricity direction of each eccentric die 41 and 42 is substantially parallel to the pressing direction of the dies 31 and 32.

For example, the amount of eccentricity of the pin equivalent parts PA1 to PA4 in the second preforming process is 60% or less of the amount of eccentricity of the finished dimensions of the pins P1 to P4, respectively. Also, for example, the amount of eccentricity of the pin equivalent parts PA1 to PA4 in the second preforming process is 20% or more of the amount of eccentricity of the finished dimensions of the pins P1 to P4, respectively. It is preferable that the amount of eccentricity of the pin equivalent parts PA1 to PA4 in the second preforming process is 40% or less of the finished dimensions of the pins P1 to P4, respectively. Most preferably, the amount of eccentricity of the pin equivalent parts PA1 to PA4 in the second preforming process is substantially 40% of the finished dimensions of the pins P1 to P4, respectively.

The rough material 12 is pressed down by the dies 31 and 32 and eccentrically moved by the eccentric dies 41 and 42 to produce the rough material 13. The rough material 13 is removed from the dies 31 and 32 and is then subjected to the third preforming process.

Figures 9A and 9B are cross-sectional views taken along the lines IXA-IXA in Figure 8A and IXB-IXB in Figure 8C, respectively. Figures 9A and 9B show cross-sections of the journal-equivalent portion JA of the rough land 12 or rough land 13.

Referring to FIG. 9A, the journal equivalent portion JA of the rough land 12 is placed at a position corresponding to the journal processing portion 31a provided on the mold 31 and the journal processing portion 32a provided on the mold 32 at the start of the second preforming process. The journal processing portion 31a of the mold 31 has a concave shape capable of accommodating the journal equivalent portion JA of the rough land 12. The journal processing portion 32a of the mold 32 faces the journal processing portion 31a of the mold 31 and has a shallower concave shape than the journal processing portion 31a. The journal processing portion 32a is formed on the tip surface of a protrusion provided on the mold 32. However, contrary to this embodiment, the journal processing portion 32a of the mold 32 may have a concave shape capable of accommodating the rough land 12 in a cross-sectional view, and a protrusion having a shallow concave journal processing portion 31a may be formed on the mold 31.

As shown in Figure 9A, at the start of the second preforming process, the journal equivalent portion JA is disposed between the journal processing portions 31a, 32a so that its major axis direction (major axis direction in the case of an ellipse) in cross-sectional view is the pressing direction of the dies 31, 32. As shown in Figure 9B, in the second preforming process, the die 31 is lowered toward the die 32, whereby the journal equivalent portion JA is pressed down by the journal processing portions 31a, 32a, thereby reducing the cross-sectional area of the flattened journal equivalent portion JA.

As the die 31 descends, the journal processing portion 32a of the die 32 enters the journal processing portion 31a of the die 31, and the opening of the journal processing portion 31a of the die 31 is blocked by the journal processing portion 32a of the die 32, forming a closed cross section. This makes it possible to suppress the generation of burrs when the journal equivalent portion JA is pressed down in the second preforming process, thereby improving material yield. In the second preforming process, all journal equivalent portions JA included in the rough area 12 are processed in the same way.

Figures 10A and 10B are cross-sectional views taken along lines XA-XA in Figure 8A and XB-XB in Figure 8C, respectively. Figures 10A and 10B show a cross section of the fourth pin-equivalent portion PA4 of the rough land 12 or 13.

Referring to FIG. 10A, the fourth pin equivalent portion PA4 of the rough surface 12 is placed at a position corresponding to the pin processing portion 41b provided on the eccentric mold 41 and the pin processing portion 32b provided on the mold 32 during the second preforming process. The pin processing portion 41b of the eccentric mold 41 and the pin processing portion 32b of the mold 32 each have a concave shape and face each other. In the second preforming process, the flattened fourth pin equivalent portion PA4 is placed between the pin processing portion 41b of the eccentric mold 41 and the pin processing portion 32b of the mold 32 so that its major axis direction (major axis direction in the case of an ellipse) is the eccentric direction of the eccentric mold 41 in a cross-sectional view.

As shown in Figures 10A and 10B, after pressing by the dies 31 and 32 begins, eccentricity by the eccentric die 41 begins. The eccentric die 41 descends toward the fourth pin equivalent portion PA4. As the eccentric die 41 descends, the fourth pin equivalent portion PA4 is pressed down by the pin processing portion 41b and becomes eccentric downward. In the second preforming process, the first pin equivalent portion PA1 of the rough area 12 is processed by the corresponding eccentric die 41 in the same manner as the fourth pin equivalent portion PA4.

In the second preforming step, the second pin corresponding portion PA2 and the third pin corresponding portion PA3 of the rough surface 12 are eccentric in the opposite direction to the first pin corresponding portion PA1 and the fourth pin corresponding portion PA4 by the corresponding eccentric dies 42. After the pressing by the dies 31 and 32 starts, each eccentric die 42 rises toward the second pin corresponding portion PA2 or the third pin corresponding portion PA3, eccentricating the corresponding portion upward. Although not shown, each eccentric die 42 and the portion of the die 31 corresponding to the eccentric die 42 have a configuration that is upside down from the eccentric die 41 and the pin processing portion 32b of the die 32 (FIGS. 10A and 10B).

Figures 11A and 11B are cross-sectional views taken along lines XIA-XIA in Figure 8A and XIB-XIB in Figure 8C, respectively. Figures 11A and 11B show a cross section of the web-equivalent portion CA of the rough land 12 or 13. The pressing direction of the web-equivalent portion CA by the dies 31 and 32 roughly coincides with the longitudinal direction of the crank web Cw.

11A and 11B show an example of a portion (seventh web equivalent portion) CA7 corresponding to the seventh crank web Cw7 among the multiple web equivalent portions CA included in the rough land 12 or the rough land 13. Referring to FIG. 11A, the seventh web equivalent portion CA7 of the rough land 12 is placed in a web processing portion provided in one of the molds 31, 32 during the second preforming step. In the example shown in FIG. 11A and 11B, the web processing portion 32c is provided in the mold 32, which is the lower mold.

11A, the web processing portion 32c has a concave shape. The web processing portion 32c is formed in a shape corresponding to the seventh arm A7 with the counterweight W. The web processing portion 32c has an arm processing portion 321c corresponding to the seventh arm A7 and a weight processing portion 322c corresponding to the counterweight W. The weight processing portion 322c is disposed above the arm processing portion 321c. In a cross-sectional view of the mold 32, the width of the weight processing portion 322c is larger than the width of the arm processing portion 321c. The width of the weight processing portion 322c increases as it moves away from the bottom surface of the web processing portion 32c. For example, both side surfaces of the weight processing portion 322c are inclined surfaces that move away from each other as they go upward. Both side surfaces of the arm processing portion 321c are substantially parallel to the pressing direction by the molds 31 and 32. However, the shapes of the arm processing portion 321c and the weight processing portion 322c are not limited to the examples in this embodiment. The bottom surface of the web processing portion 32c has, for example, an arc shape in a cross-sectional view of the mold 32. The height of the bottom surface of the web processing portion 32c is, for example, substantially equal to the height of the lower end of the fourth pin equivalent portion PA4 (FIG. 10B) after eccentricity.

As shown in FIG. 11A, in the second preforming step, the seventh web equivalent portion CA7 of the rough ground 12 is placed in the web processing portion 32c, and the die 31 is lowered toward the die 32. As shown in FIG. 11B, when the die 31 reaches the bottom dead center, the die 31 closes the web processing portion 32c to form a space S. In this space S, material flows from the journal equivalent portion JA and the fourth pin equivalent portion PA4 adjacent to the seventh web equivalent portion CA7 as the cross-sectional areas of the journal equivalent portion JA and the fourth pin equivalent portion PA4 decrease. However, during the second preforming step, the seventh web equivalent portion CA7 is supported by the die 31, 32 so that the length (width) Baa of the portion corresponding to the seventh arm in the pressing direction of the die 21, 22 in the first preforming step is maintained shorter than the length (width) Bwa of the portion corresponding to the counterweight W.

Specifically, in the space S, the material flows mainly toward the wider weight processing section 322c. Meanwhile, some material also flows toward the narrower arm processing section 321c, filling the arm processing section 321c with material. As a result, in the seventh web corresponding section CA7, the volume of the material is distributed such that the volume of the section corresponding to the counterweight W is large and the volume of the section corresponding to the seventh arm A7 is small. As shown in FIG. 11B, even after the second preforming process, the width Baa of the section corresponding to the seventh arm A7 remains shorter than the width Bwa of the section corresponding to the counterweight W.

The portions of the rough land 12 that correspond to the crank webs Cw1, CW2, and Cw8 are processed in the same manner as the seventh web corresponding portion CA7. The portions of the rough land 12 that correspond to the crank webs Cw3 to Cw6 are processed upside down compared to the seventh web corresponding portion CA7.

(Third preforming step)
12A to 12C are schematic diagrams for explaining the third preforming step. FIG. 13A and FIG. 13B are schematic diagrams showing cross sections of FIG. 12A and FIG. 12B cut on a horizontal plane, respectively. As shown in FIG. 12A to FIG. 12C, in the third preforming step, a mold 60 is used to press down each web-corresponding portion CA of the rough ground 13 obtained in the second preforming step from the axial direction of the rough ground 13, thereby reducing the thickness of the corresponding portion. In addition, in the third preforming step, a mold 60 is used to eccentrically displace each pin-corresponding portion PA of the rough ground 13 in a horizontal direction substantially perpendicular to the axial direction of the rough ground 13.

The die 60 can be attached to a press device. Figures 14 and 15 are schematic diagrams showing an example of a press device 80 to which the die 60 can be attached. Figure 14 is a cross-sectional view (longitudinal cross-sectional view) of the press device 80 cut along a vertical plane including the central axis of the rough land 13, and Figure 15 is a cross-sectional view (transverse cross-sectional view) of the press device 80 cut along a plane perpendicular to the central axis of the rough land 13. First, the configuration of the press device 80 used in the third preforming step will be described with reference to Figures 14 and 15.

As shown in FIG. 14, the press device 80 includes a plate 81, a bolster base 82, a die cushion cylinder 83, a die cushion base 84, a hydraulic cylinder 85, and a wedge 86. The plate 81 includes an upper plate 811 and a lower plate 812. The bolster base 82 includes an upper bolster base 821 and a lower bolster base 822.

The upper plate 811 supports the upper bolster base 821. The die cushion base 84 is supported by the upper bolster base 821 via a die cushion cylinder 83. The upper plate 811 moves up and down with the operation of a ram (not shown). As the upper plate 811 moves up and down, the upper bolster base 821 and the die cushion base 84 move up and down. The lower bolster base 822 is disposed on the lower plate 812.

The mold 60 includes an upper mold 61 and a lower mold 62. The upper mold 61 is supported by a die cushion base 84. The upper mold 61 moves up and down in accordance with the up and down movement of the die cushion base 84. The lower mold 62 is disposed on a lower bolster base 822.

The upper mold 61 includes a retaining mold 611 and a number of eccentric molds 612. The lower mold 62 includes a retaining mold 621 and a number of eccentric molds 622.

The retaining dies 611 and 621 are mainly used to retain the part of the rough ground 13 that corresponds to the journal J. The retaining dies 611 include a fixed retaining die 611a, two movable retaining dies 611b, a front side retaining die 611c, and a flange side retaining die 611d. In the axial direction of the rough ground 13, an eccentric die 612 is arranged between the fixed retaining die 611a and one of the movable retaining dies 611b, and between the fixed retaining die 611a and the other movable retaining die 611b. In addition, an eccentric die 612 is also arranged between one of the movable retaining dies 611b and the front side retaining die 611c, and between the other movable retaining die 611b and the flange side retaining die 611d. The fixed retaining die 611a is immovable in the axial direction of the rough ground 13. The movable retaining mold 611b, the front side retaining mold 611c, the flange side retaining mold 611d, and the eccentric mold 612 are movable in the axial direction of the rough surface 13.

The retaining mold 621 includes a fixed retaining mold 621a, two movable retaining molds 621b, a front side retaining mold 621c, and a flange side retaining mold 621d. The fixed retaining mold 621a, the movable retaining mold 621b, the front side retaining mold 621c, and the flange side retaining mold 621d are provided facing the fixed retaining mold 611a, the movable retaining mold 611b, the front side retaining mold 611c, and the flange side retaining mold 611d on the upper mold 61 side, respectively. In addition, the eccentric molds 622 are provided facing each of the eccentric molds 612 on the upper mold 61 side. The fixed retaining mold 621a is not movable in the axial direction of the rough base 13. The movable retaining mold 621b, the front side retaining mold 621c, the flange side retaining mold 621d, and the eccentric mold 622 are movable in the axial direction of the rough base 13.

Hydraulic cylinders 85 are provided on both sides of the mold 60 in the axial direction of the rough surface 13. Each hydraulic cylinder 85 is extendable in the axial direction of the rough surface 13. When the hydraulic cylinders 85 extend, the movable holding dies 611b, 621b, the front side holding dies 611c, 621c, the flange side holding dies 611d, 621d, and the eccentric dies 612, 622 move, respectively, and approach the fixed holding dies 611a, 621a.

The wedges 86 are used to move the eccentric dies 612, 622 in a horizontal direction perpendicular to the axial direction of the rough land 13. The wedges 86 are provided on both sides of the rough land 13 in a horizontal direction perpendicular to the axial direction of the rough land 13. As shown in FIG. 15, each of the wedges 86 is supported by the upper bolster base 821 in the press device 80. However, the wedges 86 are provided so as to penetrate the die cushion base 84. Therefore, the wedges 86 move independently of the die cushion base 84. That is, the wedges 86 can be moved up and down relative to the die cushion base 84 by the expansion and contraction of the die cushion cylinder 83 that supports the die cushion base 84. Each wedge 86 has an inclined surface 861.

One end of the eccentric dies 612, 622 contacts the wedge receiving members 871, 872, respectively. The wedge receiving members 871, 872 have inclined surfaces 871a, 872a, respectively, corresponding to the inclined surface 861 of the wedge 86. The inclined surfaces 871a, 872a are provided on the surfaces of the wedge receiving members 871, 872 opposite the eccentric dies 612, 622. The inclined surface 861 of the wedge 86 slides on the inclined surfaces 871a, 872a of the wedge receiving members 871, 872, causing the wedge receiving members 871, 872 and each of the eccentric dies 612, 622 to move along the eccentric direction.

Returning to Figures 12A to 12C, the third preforming step performed using the mold 60 and press device 80 configured in this manner will be described. In Figures 12A to 12C, components or related parts of the press device 80 are shown in cross section taken along a vertical plane. Some of the components of the press device 80 have been omitted from Figures 12A to 12C.

Referring to FIG. 12A, when starting the third preforming process, the upper die 61 is raised together with the die cushion base 84, and in a state separated from the lower die 62, the rough material 13 obtained in the second preforming process is placed between the upper die 61 and the lower die 62. The rough material 13 is placed on the lower die 62. At this stage, the fixed holding dies 611a, 621a, the movable holding dies 611b, 621b, the front side holding dies 611c, 621c, the flange side holding dies 611d, 621d, and the eccentric dies 612, 622 are arranged at intervals from each other in the axial direction of the rough material 13.

Next, the upper die 61 is lowered together with the die cushion base 84, and the holding dies 611 and 621 hold the portions of the rough land 13 corresponding to the journals J by sandwiching them vertically. As shown in FIG. 12B, the portion of the rough land 13 corresponding to the third journal J3 (third journal portion) JA3 is held by the fixed holding dies 611a and 621a. The portion of the rough land 13 corresponding to the second journal J2 (second journal portion) JA2 is held by one of the movable holding dies 611b and 621b. The portion of the rough land 13 corresponding to the fourth journal J4 (fourth journal portion) JA4 is held by the other movable holding dies 611b and 621b. The portion of the rough land 13 corresponding to the first journal J1 (first journal portion) JA1 is held by the front side holding dies 611c and 621c. Of the rough area 13, the portion (fifth journal equivalent portion) JA5 corresponding to the fifth journal J5 is held by the flange side holding dies 611d and 621d.

In this state, as shown in FIG. 12C, each web-equivalent portion CA of the rough ground 13 is pressed down from the axial direction. That is, by driving and extending each hydraulic cylinder 85 (FIG. 14), the front side holding molds 611c, 621c and the flange side holding molds 611d, 621d are moved in the axial direction of the rough ground 13 so that they approach each other. As the front side holding molds 611c, 621c and the flange side holding molds 611d, 621d move, the movable holding molds 611b, 621b and the eccentric molds 612, 622 also move in the axial direction of the rough ground 13. The front side holding molds 611c, 621c, the flange side holding molds 611d, 621d, the movable holding molds 611b, 621b, and the eccentric molds 612, 622 move until the adjacent molds abut against each other. As a result, the thickness of each web-equivalent portion CA of the rough ground 13 is reduced. The thickness of each web-equivalent portion CA is reduced, for example, to the finished dimension thickness of the crank web Cw.

As shown in Figures 13A and 13B, the pin equivalent parts PA1 to PA4 are decentered while the journal equivalent parts JA1 to JA4 of the rough surface 13 are held by the holding dies 611 and 621. In Figures 13A and 13B, the components of the press device 80 or related parts are shown in cross section cut along the parting surface of the die 60. Some of the components of the press device 80 are omitted in Figures 13A and 13B.

When the upper plate 811 is lowered while the journal equivalent parts JA1 to JA4 of the rough land 13 are held by the holding dies 611, 621, the die cushion cylinder 83 contracts and the wedge 86 descends relative to the die cushion base 84 (FIG. 15). As a result, as shown in FIGS. 13A and 13B, the wedge receiving member 872 on the lower die 62 side moves in the eccentric direction of the corresponding pin equivalent parts PA1 to PA4. The wedge receiving member 871 on the upper die 61 side also moves in the eccentric direction of the corresponding pin equivalent parts PA1 to PA4. The eccentric direction at this time is substantially perpendicular to both the holding direction of the rough land 13 by the holding dies 611, 621 and the axial direction of the rough land 13.

As the wedge receiving members 871, 872 move, the eccentric dies 612, 622 move in the eccentric direction. Each of the eccentric dies 612, 622 horizontally eccentricates the corresponding pin-equivalent portion PA1 to PA4 of the rough base 13. In the third preforming process, the first pin-equivalent portion PA1 and the fourth pin-equivalent portion PA4 of the rough base 13 are eccentric in the opposite direction to the second pin-equivalent portion PA2 and the third pin-equivalent portion PA3.

At the completion of the eccentricity by the eccentric dies 612, 622, it is preferable that the amount of eccentricity of each pin equivalent portion PA1 to PA4 is at least 60% of the amount of eccentricity of the finished dimension of the pin P. Most preferably, at the completion of the eccentricity, the amount of eccentricity of each pin equivalent portion PA1 to PA4 is 100% of the amount of eccentricity of the finished dimension of the pin P. The eccentricity by the eccentric dies 612, 622 may be completed before the axial pressing by the retaining dies 611, 621 and the eccentric dies 612, 622 is completed, or it may be completed after the axial pressing is completed.

In the third preforming step, the web-corresponding portion CA of the rough area 13 is also compressed. Figures 16A and 16B are cross-sectional views of the web-corresponding portion CA, showing the cross-sectional shapes before and after molding in the third preforming step, respectively.

As shown in FIG. 16A, the portion of the mold 60 facing the web corresponding portion CA is engraved with a shape corresponding to the finished shape of the crank web Cw. For example, the portion of the upper mold 61 facing the web corresponding portion CA has an arm processing portion 613 and a weight processing portion 614. The portion of the lower mold 62 facing the web corresponding portion CA has an arm processing portion 623 and a weight processing portion 624.

The arm processing parts 613, 623 are parts of the web corresponding part CA that process the part that corresponds to the arm A. The weight processing parts 614, 624 are parts of the web corresponding part CA that process the part that corresponds to the counterweight W. The arm processing parts 613, 623 and the weight processing parts 614, 624 each have a concave shape. However, the weight processing parts 614, 624 are slightly deeper than the arm processing parts 613, 623. At the boundary between the arm processing parts 613, 623 and the weight processing parts 614, 624, a part that protrudes toward the rough ground 13 is formed in correspondence with the narrowed part of the crank web Cw.

As shown in Figures 16A and 16B, in the third preforming step, the web corresponding portion CA is formed by the arm processing portions 613, 623 and the weight processing portions 614, 624. The web corresponding portion CA is formed, for example, into a shape corresponding to the finished shape of the crank web Cw while its outer periphery is restrained by the arm processing portions 613, 623 and the weight processing portions 614, 624. The shape corresponding to the finished shape of the crank web Cw is a shape that is the same as or similar to the finished shape of the crank web Cw.

The rough material 13 is processed by the die 60 to produce the rough material 14. After the third preforming step is completed, the rough material 14 is removed from the die 60. The rough material 14 is then subjected to a die forging step. That is, the rough material 14 is subjected to rough striking and finish striking to obtain a forged material with burrs. The forged material is then subjected to a burr removal step. After that, a shaping step is performed as necessary to produce the crankshaft 10 (Figure 1) as the final product.

[effect]
Fig. 17 is a schematic diagram showing a rough forged material or a finish forged material 20 of a crankshaft to be mounted on a four-cylinder engine, an eight-cylinder engine, or the like. As shown in Fig. 17, in the forged material 20 obtained in the die forging process, the volume distribution in the longitudinal direction of the crank web Cw is such that the volume on the arm A side is small and the volume on the counterweight W side is large. That is, in the crank web Cw of the forged material 20, the width of the arm A is large and the width of the counterweight W is small. The crank web Cw of the forged material 20 has a shape that roughly matches the finished shape of the crank web Cw in the final crankshaft 10.

In the manufacturing method according to the present embodiment, the volume distribution of the crank web Cw in the forging material 20 in the longitudinal direction is taken into consideration, and a preforming process, which is a process prior to the die forging process, is carried out. That is, in the first preforming process in which the rough 12 is obtained from the billet 11 as the starting material, each portion of the billet 11 corresponding to the crank web Cw is pressed down. Each portion (web-equivalent portion) CA of the billet 11 corresponding to the crank web Cw is pressed down so that the length in the pressing direction of the dies 21, 22 is small at the portion (arm-equivalent portion) AA corresponding to the arm A and large at the portion (weight-equivalent portion) WA corresponding to the counterweight W. That is, in the first preforming process, the volume distribution is performed in each web-equivalent portion CA of the billet 11 according to the crank web Cw of the forging material 20.

Furthermore, in the first preforming process, the portion of the billet 11 that corresponds to the journal J (journal equivalent portion) JA and the portion that corresponds to the pin P (pin equivalent portion) PA are pressed down by the dies 21, 22, and these portions are formed into a flat shape. As a result, excess material flows from the journal equivalent portion JA and the pin equivalent portion PA to the web equivalent portion CA. Therefore, the volume is also distributed in the axial direction between the journal equivalent portion JA, the pin equivalent portion PA, and the web equivalent portion CA.

In the second preforming process following the first preforming process, a pair of dies 31, 32 press down each journal equivalent portion JA of the rough land 12 obtained in the first preforming process. In addition, the eccentric dies 41, 42 make each pin equivalent portion PA of the rough land 12 eccentric. In the second preforming process, the volume distribution performed in the first preforming process is maintained for each web equivalent portion CA. That is, even after the second preforming process is completed, the width Baa of the arm equivalent portion AA is maintained shorter than the width Bwa of the weight equivalent portion WA in the web equivalent portion CA of the rough land 13.

In the second preforming process, as each journal-equivalent portion JA is pressed down and each pin-equivalent portion PA is eccentric, excess material flows from the journal-equivalent portion JA and the pin-equivalent portion PA to each web-equivalent portion CA. This allows the axial volume distribution to progress between the journal-equivalent portion JA, the pin-equivalent portion PA, and the web-equivalent portion CA.

In this way, according to the manufacturing method of this embodiment, not only is the material volume-distributed in the axial direction during the preforming process, but the volume-distributed in the longitudinal direction of the crank web Cw is also carried out. This makes it possible to achieve more precise volume distribution during the preforming process.

Of the dies 31 and 32 used in the second preforming process, the lower die 32 has a web processing section 32c that accommodates the web equivalent part CA of the rough ground 12. The web processing section 32c includes an arm processing section 321c and a weight processing section 322c that is wider than the arm processing section 321c. Since a relatively large space exists on the weight processing section 322c side in the web processing section 32c, the material that flows into the web processing section 32c from the journal equivalent part JA and the pin equivalent part PA mainly flows to the weight processing section 322c side. As a result, the volume of the weight equivalent part WA can be further increased in the web equivalent part CA of the rough ground 13 formed in the second preforming process. Therefore, in the web equivalent part CA, the weight equivalent part WA can be protruded outward from the arm equivalent part AA. As a result, it is possible to suppress the occurrence of underfill of the counterweight W in the die forging process. In addition, the shape of each web equivalent portion CA can be made closer to the shape of the crank web Cw of the forging material 20.

In the second preforming step, it is preferable to limit the amount of eccentricity of each pin equivalent part PA so that the pin equivalent part PA does not protrude outward beyond the adjacent web equivalent part CA in a direction substantially parallel to the pressing direction of the dies 31 and 32. For example, the amount of eccentricity of each pin equivalent part PA is limited to 40% or less of the amount of eccentricity of the finished dimension of the pin P in the final crankshaft 10. This makes it easier for material to flow from the pin equivalent part PA into the web processing part 32c in which the web equivalent part CA is located in the second preforming step. Therefore, in the second preforming step, material can be more distributed to the web equivalent part CA, making it easier to shape the web equivalent part CA. For example, if the amount of material flowing from the pin equivalent part PA into the web processing part 32c increases, the amount of material flowing toward the wide weight processing part 322c also increases, so that the protrusion of the weight equivalent part WA can be further promoted. Therefore, the shape of each web equivalent part CA can be made closer to the shape of the crank web Cw of the forged material 20.

In the manufacturing method according to this embodiment, the volume distribution of the material is precisely performed in the first preforming step and the second preforming step. Therefore, in the third preforming step, the outer periphery of the web-equivalent portion CA can be constrained and molded while preventing the material from being caught between the parting surfaces of the holding dies 611 and 621.

In the third preforming step, the outer periphery of the web-equivalent part CA is constrained by the die 60, and the web-equivalent part CA can be formed into a shape corresponding to the finished shape of the crank web Cw. For example, in the third preforming step, the web-equivalent part CA can be formed by the upper die 61 and the lower die 62 that reflect the finished shape of the counterweight W. Also, for example, the forging material 20 shown in FIG. 17 has a constricted part at the boundary between the arm A and the counterweight W that is integral with the arm A. In the third preforming step, the shape of this constricted part can be reflected in the upper die 61 and the lower die 62 to form the web-equivalent part CA. Alternatively, if a hollow part exists on the surface of the crank web Cw on the pin P side in the forging material 20, in the third preforming step, the shape of this hollow part can be reflected in the upper die 61 and the lower die 62 to form the web-equivalent part CA. Thus, the shape of each web-equivalent part CA can be made even closer to the shape of the crank web Cw of the forging material 20.

By making the shape of each web equivalent portion CA closer to the shape of the crank web Cw of the forging material 20, the posture of the rough land 14 is stabilized when the rough land 14 is placed in the die forging mold in the die forging process. This allows the rough land 14 to be stably die forged, and the occurrence of defects in the forging material 20 can be suppressed.

Also, by making the shape of each web equivalent part CA similar to the shape of the crank web Cw in advance, the amount of burrs generated in the die forging process can be reduced, and material yield can be improved. Furthermore, by making the shape of each web equivalent part CA similar to the shape of the crank web Cw, the forming accuracy in the die forging process can also be improved.

Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

In the above embodiment, an example was described in which the eccentric dies 41, 42 are raised and lowered independently of the dies 31, 32 in the second preforming step, and are controlled by the die cushion 51. However, a control mechanism other than the die cushion 51 can also be used. For example, the eccentric dies 41, 42 may be raised and lowered independently of the dies 31, 32 by a hydraulic cylinder.

In the above embodiment, an example was described in which the pin equivalent parts PA are decentered in the third preforming process. However, it is not necessary to decenter each pin equivalent part PA in the third preforming process. For example, if the amount of eccentricity of each pin equivalent part PA reaches 60% of the amount of eccentricity of the finished dimension of the pin P before the third preforming process is started, the eccentricity of the pin equivalent parts PA in the third preforming process can be omitted. Also, it is possible to only decenter some of the pin equivalent parts PA among the multiple pin equivalent parts PA in the third preforming process.

In the above embodiment, a method for manufacturing a crankshaft 10 to be mounted on a four-cylinder engine has been described. The crankshaft 10 manufactured in the above embodiment is a four-cylinder, eight-counterweight crankshaft. That is, in the above embodiment, counterweights W are integrally provided on all of the arms A included in the crankshaft 10. However, it is also possible to provide counterweights W integrally on only some of the arms A included in the crankshaft 10.

For example, by using the shapes of the dies used in the first to third preforming steps, it is possible to manufacture the 4-cylinder, 4-counterweight crankshaft 10A shown in FIG. 18. In the crankshaft 10A, the first arm A1, the fourth arm A4, the fifth arm A5, and the eighth arm A8 are integrally provided with counterweights W, while the second arm A2, the third arm A3, the sixth arm A6, and the seventh arm A7 are not provided with counterweights W. Examples of the dies used to manufacture this crankshaft 10A are shown in FIGS. 19 to 21.

Figure 19 is a diagram illustrating the dies 21A and 22A used in the first preforming step in manufacturing the crankshaft 10A. As with the dies 21 and 22 in the above embodiment, the dies 21A and 22A press down the parts of the billet 11 corresponding to the first arm A1, the fourth arm A4, the fifth arm A5, and the eighth arm A8 with the counterweight W so that the width La on the arm A side is shorter than the width Lw on the counterweight W side (Figures 7A and 7B). On the other hand, the dies 21A and 22A process the parts of the billet 11 corresponding to the second arm A2, the third arm A3, the sixth arm A6, and the seventh arm A7 without the counterweight W in the same way as the journal corresponding part JA (Figures 5A and 5B).

20 is a diagram illustrating the molds 31A and 32A used in the second preforming step in the manufacture of the crankshaft 10A. The molds 21A and 22A, like the molds 31 and 32 in the above embodiment, support the portions of the rough surface 12 obtained in the first preforming step corresponding to the first arm A1, the fourth arm A4, the fifth arm A5, and the eighth arm A8 with the counterweight W, so that the width of the arm A side is maintained shorter than the width of the counterweight W side. That is, in the first arm A1, the fourth arm A4, the fifth arm A5, and the eighth arm A8 with the counterweight W, the width Baa of the arm A side is maintained shorter than the width Bwa of the counterweight W side even after the second preforming step (FIGS. 11A and 11B). On the other hand, the portions of the rough surface 12 corresponding to the second arm A2, the third arm A3, the sixth arm A6, and the seventh arm A7, which do not have the counterweight W, are machined by the dies 31A and 32A in the same manner as the journal portion JA (FIGS. 9A and 9B). Alternatively, the portions corresponding to the second arm A2, the third arm A3, the sixth arm A6, and the seventh arm A7 do not need to be pressed down by the dies 31A and 32A.

21 is a diagram illustrating a mold 60A used in the third preforming step in the manufacture of the crankshaft 10A. The mold 60A includes an upper mold 61A and a lower mold 62A. As with the upper mold 61 and the lower mold 62 in the above embodiment, the upper mold 61A and the lower mold 62A can mold the rough surface 13 obtained in the second preforming step into a shape corresponding to the finished shape of the crank web Cw while constraining the outer periphery of the parts corresponding to the first arm A1 with the counterweight W, the fourth arm A4, the fifth arm A5, and the eighth arm A8. That is, the upper mold 61A and the lower mold 62A can have the arm processing parts 613, 623 and the weight processing parts 614, 624 similar to the upper mold 61 and the lower mold 62, respectively (FIGS. 16A and 16B).

On the other hand, the upper die 61A and the lower die 62A do not substantially press down the portions of the rough surface 13 corresponding to the second arm A2, the third arm A3, the sixth arm A6, and the seventh arm A7 that do not have the counterweight W. In other words, the outer periphery of each portion of the rough surface 13 corresponding to the second arm A2, the third arm A3, the sixth arm A6, and the seventh arm A7 is not restrained by the upper die 61A and the lower die 62A during the third preforming step.

In this way, the manufacturing method according to the present disclosure can be applied to various crankshafts regardless of the number of arms A having counterweights W. For example, the manufacturing method according to the present disclosure can be applied to crankshafts mounted on eight-cylinder engines.

10, 10A: Crankshaft J, J1 to J5: Journal P, P1 to P4: Pin A, A1 to A8: Arm W: Counterweight Cw, Cw1 to Cw8: Crank web 11: Billet 12: First die 13: Second die 14: Third die 21, 22, 21A, 22A: First die 31, 32, 31A, 32A: Second die 41, 42: Eccentric die 60, 60A: Third die

Claims (3)

A manufacturing method of a crankshaft including a journal, a pin disposed eccentrically with respect to the journal, an arm connecting the journal and the pin, and a counterweight formed integrally with the arm, comprising:
a first preforming step of obtaining a first rough shape from the billet;
A second preforming step of obtaining a second rough base from the first rough base;
A third preforming step of obtaining a third rough base from the second rough base;
Equipped with
In the first preforming step, a pair of first dies are used to press down the portions of the billet corresponding to the journal and the portions of the pin in a direction perpendicular to the axial direction of the billet, thereby reducing the cross-sectional areas of the portions corresponding to the journal and the portions corresponding to the pin to form the portions into flat shapes, and a portion of the billet corresponding to a crank web constituted by the arm and the counterweight is pressed down by the pair of first dies such that the length of the portion corresponding to the arm in the pressing direction of the first dies is shorter than the length of the portion corresponding to the counterweight,
In the second preforming step, a pair of second dies are used to press down a portion of the first roughness corresponding to the journal in a pressing direction perpendicular to the pressing direction of the first die and the axial direction of the first roughness, and an eccentric die is used to eccentrically displace a portion of the first roughness corresponding to the pin relative to a portion of the first roughness corresponding to the journal in an eccentric direction parallel to the pressing direction of the second die, and a portion of the first roughness corresponding to the crank web is supported by the pair of second dies so that a length of a portion of the first roughness corresponding to the arm in the pressing direction of the first die is maintained shorter than a length of a portion of the first roughness corresponding to the counterweight,
In the third pre-forming step, a third mold is used to press down a portion of the second rough sheet corresponding to the crank web in the axial direction of the second rough sheet, thereby reducing a thickness of the portion. The method according to claim 1,
In the third pre-forming step, the outer periphery of a portion of the second roughness corresponding to the crank web is constrained by the third mold, and the portion is formed into a shape corresponding to a finished shape of the crank web. The method according to claim 1 or 2,
a manufacturing method in which, in the second preforming step, an amount of eccentricity of the portion corresponding to the pin is 40% or less of an amount of eccentricity of a finished dimension of the pin.

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