JP2016022514A - Manufacturing method of forged crank shaft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method capable of easily providing a forged crank shaft whose weight is reduced and rigidity is secured at the same time.SOLUTION: A forged crank shaft comprises: a journal part J to be a center of rotation; a pin part P eccentric with respect to the journal part J; and a crank arm part A connecting the journal part J and the pin part P to each other and having a recess As on a surface of a journal part J side. A manufacturing method of the forged crank shaft includes: a die-forging process of obtaining a forged material 32 having the journal part J, the pin part P and the crank arm part A by using a pair of first metallic dies from a material 31: and a deburring process of removing a burr from the forged material obtained in the die-forging process. The material 31 is a billet or a rough raw material obtained by applying preforming to the billet. In the die-forging process, the recess As is formed by making the material 31 abut on a second metallic die 20 by drafting the material 31 by the first metallic dies in a state of arranging the second metallic die 20 at a position for forming the recess.SELECTED DRAWING: Figure 7

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, and a ship, a crankshaft is indispensable for converting the reciprocating motion of a piston into a rotational motion to extract power. Crankshafts are roughly classified into those manufactured by die forging and those manufactured by casting. In particular, when high strength and high rigidity are required, the former forged crankshaft having excellent characteristics is often used.

  In general, a forged crankshaft is manufactured by using a billet having a round or square cross-section and a constant cross-sectional area over the entire length as raw materials, and sequentially performing steps of preforming, die forging, deburring, and shaping. Usually, the preforming process includes roll forming and bending processes, and the die forging process includes roughing and finishing processes.

  FIG. 1 is a schematic diagram for explaining a manufacturing process of a conventional general forged crankshaft. A crankshaft 1 (see FIG. 1 (f)) illustrated in the figure is mounted on a 4-cylinder engine and is a crankshaft of a 4-cylinder-8-counterweight. The crankshaft 1 has five journal portions J1 to J5, four pin portions P1 to P4, a front portion Fr, a flange portion Fl, and eight crank arms that connect the journal portions J1 to J5 and the pin portions P1 to P4, respectively. Part (hereinafter also simply referred to as “arm part”) A1 to A8. The crankshaft 1 has counterweight portions (hereinafter also simply referred to as “weight portions”) W1 to W8 in all eight arm portions A1 to A8.

  Hereinafter, when the journal portions J1 to J5, the pin portions P1 to P4, the arm portions A1 to A8, and the weight portions W1 to W8 are collectively referred to, the reference numerals are “J” for the journal portion and “P” for the pin portion. Also, “A” for the arm portion and “W” for the weight portion. The pin portion P and a pair of arm portions A (including the weight portion W) connected to the pin portion P are collectively referred to as “slow”.

  In the manufacturing method shown in FIG. 1, the forged crankshaft 1 is manufactured as follows. First, the billet 2 shown in FIG. 1A cut in advance to a predetermined length is heated by an induction heating furnace or a gas atmosphere heating furnace, and then roll forming is performed. In the roll forming step, for example, the billet 2 is rolled with a perforated roll and the volume thereof is distributed in the longitudinal direction while squeezing, thereby forming the roll waste land 3 as an intermediate material (see FIG. 1B). Next, in the bending process, the roll rough ground 3 obtained by roll forming is partially pressed down from the direction perpendicular to the longitudinal direction to distribute the volume thereof, and the bent rough ground 4 as a further intermediate material is formed. (See FIG. 1 (c)).

  Subsequently, in the roughing process, the bent rough ground 4 obtained by bending is press-forged using a pair of upper and lower molds, and a forged material 5 in which the approximate shape of the crankshaft (final product) is formed is formed. (See FIG. 1 (d)). Furthermore, in the finish punching process, the rough forging material 5 obtained by roughing is provided, and the rough forging material 5 is press-forged using a pair of upper and lower dies, and a shape that matches the crankshaft of the final product is formed. The forged material 6 thus formed is formed (see FIG. 1 (e)). At the time of roughing and finishing, surplus material flows out as burrs from between the mold split surfaces of the molds facing each other. For this reason, the rough forged material 5 and the finished forged material 6 both have large burrs (5a, 6a) around the shaped crankshaft.

  In the deburring process, the forged material 6 with the burr 6a obtained by finish punching is held by a die from above and below, and the burr 6a is punched and removed by a blade mold. Thereby, as shown in FIG.1 (f), the forge crankshaft 1 is obtained. In the shaping process, the key points of the forged crankshaft 1 from which burrs have been removed are slightly pressed down from above and below with a mold to correct the dimensional shape of the final product. Here, the essential parts of the crankshaft 1 correspond to, for example, a shaft portion such as the journal portion J, the pin portion P, the front portion Fr, the flange portion Fl, and the arm portion A and the weight portion W. Thus, the forged crankshaft 1 is manufactured.

  The manufacturing process shown in FIG. 1 is applicable not only to the crankshaft of the 4-cylinder-8-counterweight shown in FIG. 1 (f) but also to various crankshafts. For example, the present invention can be applied to a crankshaft of a 4-cylinder-4 counterweight. Here, in the crankshaft of the four-cylinder / four-piece counterweight, among the eight arm portions A, the weight portion W is provided in a part of the arms. For example, the weight part W is provided in the first first arm part A1, the last eighth arm part A8, and the central two arm parts (fourth arm part A4, fifth arm part A5). In addition, the manufacturing process is the same for crankshafts mounted on 3-cylinder engines, in-line 6-cylinder engines, V-type 6-cylinder engines, 8-cylinder engines, and the like. In addition, when adjustment of the arrangement angle of a pin part is required, a twist process is added after a deburring process.

  In recent years, in particular, reciprocating engines for automobiles are required to be lighter in order to improve fuel efficiency. For this reason, the crankshaft, which is a basic part of a reciprocating engine, is also required to be lighter. Examples of conventional techniques for reducing the weight of a forged crankshaft include the following.

  Patent Documents 1 and 2 describe an arm part in which a hole is formed on the surface on the journal part side, and also describe a method of manufacturing a crankshaft having this arm part. The hole part of the arm part is formed on a straight line connecting the axis center of the journal part and the axis part of the pin part (hereinafter also referred to as “arm part center line”), and is deeply recessed toward the pin part. In the arm part described in the same document, the volume of the hole part is reduced in weight. The weight reduction of the arm portion leads to a reduction in the weight of the weight portion paired with the arm portion, which in turn leads to a weight reduction of the entire forged crankshaft. Further, since the arm portion disclosed in the same document is maintained thick at both side portions in the vicinity of the pin portion sandwiching the arm portion center line, rigidity (torsional rigidity and bending rigidity) is also ensured.

  In this way, if the surface of the arm part on the journal part side is provided with a dent while maintaining the thickness of both side parts of the arm part, it is possible to reduce the weight and ensure the rigidity at the same time.

  However, it is difficult to manufacture a forged crankshaft having such a uniquely shaped arm portion by a conventional manufacturing method. In the die forging process, if a dent is to be formed on the surface of the arm portion, the die drawing gradient of the die at the dent portion becomes a reverse gradient, and there is a situation in which the molded forging material cannot be removed from the die. .

  In order to cope with such a situation, in the manufacturing methods described in Patent Documents 1 and 2, in the die forging process, the arm portion is formed small without forming a recess on the surface of the arm portion. Further, after the deburring step, a punch is pushed into the surface of the arm portion, and a dent is formed by the trace of the punch.

JP 2012-7726 A JP 2010-230027 gazette

  Certainly, according to the manufacturing methods described in Patent Documents 1 and 2, it is possible to form a dent on the surface of the arm portion on the journal portion side while maintaining a large thickness on both sides of the arm portion. . Thereby, the forged crankshaft which aimed at weight reduction and rigidity ensuring simultaneously can be manufactured.

  However, in this manufacturing method, in order to form a dent on the surface of the arm portion, the punch is strongly pressed into the surface of the arm portion to deform the entire arm portion, so that a great force is required to push the punch. For this reason, a special equipment configuration for applying a great force to the punch is required, and consideration is also required for the durability of the punch.

  The objective of this invention is providing the manufacturing method of the forge crankshaft which can obtain the forge crankshaft which aimed at weight reduction and rigidity ensuring simultaneously easily.

  In the method for manufacturing a forged crankshaft according to the embodiment of the present invention, the forged crankshaft includes a journal part serving as a rotation center, a pin part eccentric with respect to the journal part, the journal part and the pin part, and And a crank arm portion having a dent on the surface of the journal portion side. The manufacturing method is obtained by a die forging step, which uses a pair of first molds to obtain a forging material including the journal portion, the pin portion, and the crank arm portion, and the die forging step. And a deburring process for removing burrs from the forged material. The material is a billet or a rough material obtained by preforming a billet. In the die forging step, in a state where the second mold is disposed at a position where the dent is formed, the material is squeezed by the first mold and brought into contact with the second mold, thereby forming the dent. Mold.

  In the above manufacturing method, it is preferable that the second mold has a guide groove, and the burrs flowing out during the die forging process are guided by the guide groove.

  In the manufacturing method described above, it is preferable to move the second mold in the reduction direction so that the second mold is positioned at the center between the pair of first molds in the reduction process of the die forging step. .

  In the above manufacturing method, the crank arm portion of the forged crankshaft is thicker in a range from both side portions near the pin portion to the top portion in the eccentric direction of the pin portion than the thickness of the recessed portion. be able to.

  According to the present invention, in the die forging step, the material is squeezed by the pair of first dies in a state where the second dies are arranged at positions where the dents on the journal portion side surface of the arm portion are formed. Thereby, in the forged crankshaft obtained, it becomes possible to form a dent in the surface of the arm part on the journal part side while maintaining the thickness of both side parts of the arm part thick. For this reason, in the obtained forged crankshaft, weight reduction and rigidity ensuring can be achieved simultaneously. Further, since the second die is used, die forging can be performed without hindrance, and the formation of the recess of the arm portion can be easily performed without requiring a great deal of force.

FIG. 1 is a schematic diagram for explaining a manufacturing process of a conventional general forged crankshaft. 2A and 2B are schematic views showing the shape of the arm portion of the crankshaft of the first configuration example targeted by the present invention, where FIG. 2A is a perspective view and FIG. 2B is a view from the journal portion side. FIG. 4C is a top view, and FIG. 4D is a cross-sectional view taken along line AA. FIG. 3 is a schematic diagram showing the shape of the arm portion of the crankshaft of the second configuration example targeted by the present invention. FIG. 3 (a) is a front view when viewed from the journal portion side, and FIG. 3 (b). Is a top view. FIG. 4 is a schematic view showing a material shape before forging in the present invention, where FIG. 4A is a perspective view, FIG. 4B is a front view, and FIG. 4C is a top view. FIG. 5 is a schematic diagram showing the shape of the material (forged material) after forging in the present invention, where FIG. 5 (a) is a perspective view, FIG. 5 (b) is a front view, and FIG. 5 (c) is a top view. It is. FIG. 6 is a front view schematically showing the operation of the first die in the die forging step of the present invention, where FIG. 6 (a) is at the initial stage of punching, FIG. 6 (b) is at the middle stage of punching, FIG. 3C shows the end of stamping. FIG. 7 is a top view schematically showing the arrangement of the second mold in the die forging step of the present invention, where FIG. 7 (a) shows the initial stage of punching, and FIG. 7 (b) shows the end of punching. Each is shown.

  Below, the manufacturing method of the forge crankshaft of this invention is demonstrated, referring drawings.

  The method for manufacturing a forged crankshaft of the present invention includes a die forging step and a deburring step. A pre-forming step may be provided as a pre-step of the die forging step. Further, a finish forging step may be provided between the die forging step and the deburring step. Each process of pre-forming, die forging, finish forging and deburring is performed hot.

1. The shape of the crankshaft The forged crankshaft targeted by the present invention is a journal part that is the center of rotation, a pin part that is eccentric to the journal part, the journal part and the pin part are connected, and the surface on the journal part side And a crank arm portion having a recess. As such a forged crankshaft, the forged crankshaft of the first configuration example shown in FIG. 2 and the forged crankshaft of the second configuration example shown in FIG. 3 can be adopted.

  In the first configuration example and the second configuration example, the shape of the arm portion is different. Specifically, in the first configuration example, as shown in FIG. 2, the thickness is increased at both side portions (Aa, Ab) of the arm portion. On the other hand, in the second configuration example, as shown in FIG. 3, the range from the both side portions (Aa, Ab) of the arm portion to the top portion Ac (hereinafter also referred to as “pin top portion”) in the eccentric direction of the pin portion. Increase the thickness.

  2A and 2B are schematic views showing the shape of the arm portion of the crankshaft of the first configuration example targeted by the present invention, where FIG. 2A is a perspective view and FIG. 2B is a view from the journal portion side. FIG. 4C is a top view, and FIG. 4D is a cross-sectional view taken along line AA. In the figure, one of the crankshaft arm portions (including the weight portion) is representatively extracted, and the remaining crankshaft arm portions are omitted. Moreover, the crankshaft shown in the figure is in a state after deburring and shows the shape of the final product.

  As shown in the drawing, the arm portion A of the first configuration example has a dent in the region As inside the both side portions (Aa, Ab) in the vicinity of the pin portion P on the surface on the journal portion J side. On the other hand, both side parts (Aa, Ab) swell to the journal part J side, and the thickness of these both side parts (Aa, Ab) is thick compared with the thickness of a dent.

  In the arm portion A of the first configuration example as described above, the thickness of both side portions (Aa, Ab) is maintained thick, and a recess is formed on the surface on the journal portion J side. For this reason, the forged crankshaft by this invention can achieve weight reduction by the dent of the arm part A. FIG. In addition, it is possible to ensure rigidity by maintaining the thickness of both side portions (Aa, Ab) of the arm portion A.

  FIG. 3 is a schematic diagram showing the shape of the arm portion of the crankshaft of the second configuration example targeted by the present invention. FIG. 3 (a) is a front view when viewed from the journal portion side, and FIG. 3 (b). Is a top view. In the figure, one of the crankshaft arm portions (including the weight portion) is representatively extracted, and the remaining crankshaft arm portions are omitted. Moreover, the crankshaft shown in the figure is in a state after deburring and shows the shape of the final product.

  In the arm portion A of the second configuration example, as shown in the figure, a recess is formed in the region As inside the both side portions (Aa, Ab) of the surface on the journal portion J side as in the first configuration example. Have Moreover, the thickness of both side parts (Aa, Ab) is thick compared with the thickness of a dent. Furthermore, the arm part of the second configuration example is thick even in a continuous range from both side parts (Aa, Ab) to the pin top part Ac in addition to the both side parts (Aa, Ab).

  In the arm portion A of the second configuration example as described above, the thickness in the range from the both side portions (Aa, Ab) to the pin top portion Ac is continuously maintained thick, and a dent is formed on the surface on the journal portion J side. Has been. For this reason, the forged crankshaft according to the second configuration example can be reduced in weight by the recess of the arm portion A. In addition, it is possible to ensure rigidity by maintaining the thickness of both side portions (Aa, Ab) of the arm portion A.

  Here, stress concentration tends to occur in the pin fillet portion, which is a joint between the pin portion P and the arm portion A. For this reason, the pin fillet portion is often subjected to quenching by high frequency induction heating for the purpose of improving fatigue strength. At this time, since the pin top portion Ac of the arm portion A is adjacent to the pin fillet portion to which quenching is performed, there is a possibility that a crack will occur if a certain thickness is not ensured. The forged crankshaft according to the second configuration example has excellent resistance to fire cracking because the pin top portion Ac of the arm portion A is thick when quenching is applied to the pin fillet portion.

2. As described above, the method for manufacturing a forged crankshaft of the present invention includes a die forging step and a deburring step, and further includes a pre-forming step and a finish forging step as necessary. All of these steps are performed in a series of heat. When adjustment of the arrangement angle of the pin portion is necessary, a twisting process is provided as a subsequent process of the deburring process.

  The method for manufacturing a forged crankshaft of the present invention uses a billet or a rough material obtained by preforming a billet. When a rough material is used as a material, a preforming step is provided.

  For the preforming step, a step similar to the conventional manufacturing method shown in FIG. 1 can be adopted. For example, a rough material is obtained by performing a roll forming process and a bending process in that order.

  In the die forging step, a forged material is obtained from a material (billet or rough material) using a pair of first dies in the same manner as in the conventional die forging step. In the die forging step of the present invention, a second die is further used. The obtained forged material (the material after die forging) is similar to the forged crankshaft shown in FIG. 2 or FIG. 3 and includes a journal part J serving as a rotation center and a pin part P eccentric with respect to the journal part J. The arm part A which connects the journal part J and the pin part P is provided. The arm part A has a dent on the surface on the journal part J side. This die forging step will be described with reference to the case where the thickness is increased at both side portions (Aa, Ab) of the arm portion as in the first configuration example shown in FIG.

  FIG. 4 is a schematic view showing a material shape before forging in the present invention, where FIG. 4A is a perspective view, FIG. 4B is a front view, and FIG. 4C is a top view. The figure shows a billet 31 which is a material, and the billet 31 has a round cross section.

  FIG. 5 is a schematic diagram showing the shape of the material (forged material) after forging in the present invention, where FIG. 5 (a) is a perspective view, FIG. 5 (b) is a front view, and FIG. 5 (c) is a top view. It is. The forged material 32 shown in the figure has the same shape of the arm portion A as in the first configuration example shown in FIG. Specifically, in the arm portion A, the thickness of both side portions (Aa, Ab) is maintained thick, and a recess is formed on the surface on the journal portion J side.

  FIG. 6 is a front view schematically showing the operation of the first die in the die forging step of the present invention, where FIG. 6 (a) is at the initial stage of punching, FIG. 6 (b) is at the middle stage of punching, FIG. 3C shows the end of stamping. In the figure, a material before forging (billet, symbol: 31), a material after forging (forging material, symbol: 32), a pair of first mold 10 and a second mold 20 at the top and bottom. Show. Further, only the second mold 20 is shown by a cross-sectional shape at the center in the width direction of the guide groove 20a.

  FIG. 7 is a top view schematically showing the arrangement of the second mold in the die forging step of the present invention, where FIG. 7 (a) shows the initial stage of punching, and FIG. 7 (b) shows the end of punching. Each is shown. In the figure, the material before forging (billet, symbol: 31), the material after forging (forging material, symbol: 32), and the second mold 20 are shown, and the pair of first molds 10 is omitted. To do.

  The first mold 10 is composed of an upper mold 11 and a lower mold 12 that are paired up and down, and a mold engraving portion is engraved in the upper mold 11 and the lower mold 12. In the mold engraving portion, the shape of the portion of the crankshaft shape shown in FIG. 2 excluding the region where the second mold 20 abuts is reflected. In the first mold 10 shown in the figure, the shape of the arm portion A excluding the journal portion J, the pin portion P, and the recess of the region As is reflected in the mold engraving portion.

  Since the upper mold 11 and the lower mold 12 of the first mold 10 accommodate the second mold 20, a portion corresponding to the recess of the arm part A is widely opened.

  A mold engraving portion is engraved in the second mold 20, and at least the shape of the recess of the arm portion A is reflected in the mold engraving portion. The 2nd metal mold | die 20 can be moved forwards or backwards so that it may contact or separate with respect to the dent of the arm part surface. The forward / backward movement of the second mold 20 is performed by a hydraulic cylinder or the like connected to the second mold 20.

  In addition, the second mold 20 is movable in the down direction while being positioned at the center between the pair of the first mold 10, specifically, the center between the upper mold 11 and the lower mold 12 (in FIG. 6). It can move up and down). The mechanism for moving the second mold 20 in this way is, for example, a holder (not shown) that holds the second mold 20, and the lower mold 12 and the holder are connected while the holder can be moved up and down. The first elastic body (for example, a spring, not shown) and the second elastic body (for example, a spring, not shown) can be configured. The second elastic body is provided with one end connected to the upper mold 11 and the other end being in contact with the holder.

  In such a configuration, in the initial state where the upper mold 11 and the lower mold 12 are sufficiently separated and the other end of the second elastic body is not in contact with the holder, the distance between the holder and the lower mold 12 is kept constant. Is done. When the upper mold 11 approaches the lower mold 12 and the second mold 20 is positioned at the center between the upper mold 11 and the lower mold 12, the other end of the second elastic body comes into contact with the holder. When the upper mold 11 further approaches the lower mold 12, the first elastic body and the second elastic body start to be compressed, and the second mold 20 is lowered together with the holder accordingly. At this time, since the amount of contraction of the first elastic body and the second elastic body is adjusted to be the same, the second mold 20 is lowered in a state where it is located at the center between the upper mold 11 and the lower mold 12. To do.

  The die forging process using the first die 10 and the second die 20 is performed as follows. First, the material 31 is placed on the mold engraving portion of the lower mold 12 in a state where the upper mold 11 and the lower mold 12 of the first mold 10 are sufficiently separated from each other. At this time, in order to facilitate placement of the material 31, the second mold 20 is in a retracted state.

  Then, the 2nd metal mold | die 20 is advanced, and as shown to Fig.7 (a), the 2nd metal mold | die 20 is arrange | positioned in the position which shape | molds the dent of the area | region As. In other words, the 2nd metal mold | die 20 is arrange | positioned in the position of the dent of the arm part A after die forging. At that time, there is a gap between the material 31 and the second mold 20. Further, the position of the second mold 20 in the reduction direction is not the center between the pair of first molds 10 but a predetermined distance from the lower mold 12.

  When the upper mold 11 is moved toward the lower mold 12 in this state, as shown in FIG. 6 (b), the upper mold 11 has the second mold 20 positioned in the reduction direction of the first mold 10. It reaches the position that becomes the center state between the pair. At that time, the position of the second mold 20 in the reduction direction is maintained at a position at a predetermined distance from the lower mold 12.

  When the upper mold 11 is further moved toward the lower mold 12 from the state shown in FIG. 6B, the second mold 20 starts moving in the rolling direction, and the second mold 20 is the same as the first mold 10. Move so that it is centered between the pair. More specifically, when a mechanism constituted by the above-described holder, the first elastic body, and the second elastic body is employed, the second elastic body abuts on the second mold 20 and the first elastic body And the second elastic body start to compress. Accordingly, the second mold 20 is lowered. Since the amount of shrinkage of the first elastic body and the second elastic body is always adjusted to be the same when the second mold 20 is lowered, the second mold 20 includes the upper mold 11 and the lower mold 12. It descends in a state where it is always located in the middle of the center. Almost simultaneously with the start of the movement of the second mold 20 in the reduction direction, the reduction of the material 31 by the first mold 10 is started.

  The upper die 11 is further moved so that the upper die 11 reaches the reduction end position (see FIG. 5C), and the second die 20 is moved between the pair of the first die 10 according to the movement of the upper die 11. Move so that it is located in the center of By the movement of the second mold 20, the relative positional relationship between the material 31 and the second mold 20 in the rolling direction is maintained. Further, as the upper die 11 reaches the reduction end position, the reduction of the material 31 ends.

  In the process from the start of the reduction to the end, the material 31 is reduced and deformed. Thereby, the forged material 32 is obtained, and the forged material 32 is shaped to correspond to the mold engraving portions of the upper mold 11 and the lower mold 12. Specifically, the journal portion J and the pin portion P are formed on the forged material 32. Further, both side portions (Aa, Ab) of the arm portion A are formed by the mold engraving portion of the first mold 10, and the thickness of the both side portions (Aa, Ab) can be maintained at the same level as the conventional crankshaft. With the shaping by this reduction, the material overhangs and a burr 32 a is formed on the forged material 32.

  Moreover, in this invention, the 2nd metal mold | die 20 is arrange | positioned in the position which shape | molds the dent of the arm part A. FIG. For this reason, as the material (31, 32) is squeezed and overhangs, the surface of the material (31, 32) comes into contact with the second mold 20 and the material (31, 32) becomes the second mold 20 Shaped into a shape corresponding to the mold engraving part. Thereby, the dent of the arm part A is shape | molded by material (31, 32).

  As described above, according to the present invention, it is possible to form a dent on the surface of the arm portion A on the journal portion J side while maintaining the thickness of both side portions (Aa, Ab) of the arm portion A thick. For this reason, this invention can manufacture the forge crankshaft which aimed at weight reduction and rigidity ensuring simultaneously.

  After completing the reduction by the first mold 10, the second mold 20 is retracted and retracted from the surface of the arm part A on the journal part J side, and then the upper mold 11 of the first mold 10 is moved to the lower mold. 12 apart. In this state, the material 32 (forged material) is taken out. The mold engraving part of the second mold 20 for forming the dent of the arm part A has a reverse mold slope, but is retracted by advancing and retreating, so that the material 32 (forging material) is taken out. Can do. For this reason, die forging can be performed without any problem.

  Subsequently, in the deburring process, the burrs are punched and removed from the forged material with burrs to obtain a crankshaft. At that time, the main shapes (for example, the arm part A, the journal part J, and the pin part P) formed on the forged material are also maintained in the forged material (obtained crankshaft) after deburring.

  As described above, according to the present invention, it is possible to form a dent on the surface of the arm portion A on the journal portion J side while maintaining the thickness of both side portions (Aa, Ab) of the arm portion A thick. For this reason, this invention can manufacture the forge crankshaft which aimed at weight reduction and rigidity ensuring simultaneously.

  In the mold forging step, the recess of the arm portion A is formed by bringing the second mold into contact with the material. However, it is only necessary to hold the second mold, and it is not necessary to push the second mold into the material. Therefore, the force for holding the second mold is small, and the present invention does not require a great force and can be easily performed.

  In the present invention, since the shape is formed while forming burrs in the die forging step, the burrs may enter the gap between the first mold 10 (upper mold 11 and lower mold 12) and the second mold 20. . In this case, the first mold 10 and the second mold 20 may be damaged. Moreover, there is a possibility that the advance / retreat movement of the second mold 20 is hindered and the operation is stopped.

  In order to prevent these, it is preferable that the second mold 20 has a guide groove 20a, and guides the burr 32a that flows out during the die forging process by the guide groove 20a. For example, in the second mold 20 shown in FIGS. 6 and 7, a guide groove 20 a having a predetermined width is provided around a portion located in the center between the upper mold 11 and the lower mold 12 of the first mold 10. . By providing the guide groove 20a in this manner, the burr formed in the material does not enter the gap between the first mold 10 (upper mold 11 and lower mold 12) and the second mold 20, and the guide groove 20a. Be guided to.

  What is necessary is just to set suitably the shape and dimension of the guide groove 20a according to the magnitude | size of the burr | flash formed. For example, the cross-sectional shape of the guide groove 20a can be rectangular, trapezoidal, or semicircular.

  In the present invention, in the reduction process of the die forging process, it is preferable to move the second mold 20 in the reduction direction so that the second mold 20 is positioned at the center between the pair of first molds 10. Thereby, the 2nd metal mold | die 20 can be reliably arrange | positioned in the position which shape | molds a dent in a rolling process, and the processing precision of a dent shape can be improved. As the mechanism for positioning the second mold 20 in the center between the pair of the first molds 10, for example, the above-described mechanism can be adopted. Specifically, it can be constituted by a holder, a first elastic body, and a second elastic body.

  In the above description of the die forging step, the first configuration example has been described, but the present invention can also be applied to the forged crankshaft according to the second configuration example. In this case, the mold engraving portion of the first mold and the mold engraving portion of the second mold may be changed so as to conform to the shape of the forged crankshaft.

  The present invention has a high degree of freedom in designing the concave shape. Specifically, in the first configuration example and the second configuration example, the recess in the region As of the arm portion A has a spherical shape with a convex bottom surface shape, but in the present invention, the bottom shape of the recess has various shapes. Can be processed. For example, it can be a concave spherical shape, a concave V shape, a concave conical surface shape, or a planar shape. Here, the concave V-shape specifically means that the bottom surface of the recess has an inclined surface extending from the center line of the arm portion to both sides, and the inclined surface moves away from the center line of the arm portion. The shape is such that the depth of the recess is shallow.

  Further, in the first configuration example and the second configuration example, both side portions (Aa, Ab) and the pin top portion Ac are thick, and the width of the thick portion is substantially constant. In other words, in the first configuration example and the second configuration example, the contour shape of the dent portion when viewed from the journal portion side is along the contour shape of both side portions (Aa, Ab) of the arm portion A and the pin top portion Ac. Shape. In the present invention, the contour shape of the recess when viewed from the journal portion side can be various shapes. For example, a circular shape, a semicircular shape, an elliptical shape other than the shapes shown in FIGS. Also, it can be rectangular.

  Here, the shape of both side parts (Aa, Ab) can also be made into arbitrary shapes. For example, the thickness t1 (see FIG. 2C) of both side portions (Aa, Ab) may be increased or decreased as necessary, for example, undulated. Further, the width w1 (see FIG. 2B) of both side portions (Aa, Ab) is not limited to a substantially constant case, and the thickness may be appropriately changed in order to satisfy performance such as rigidity.

  A finish forging step may be provided between the die forging step and the deburring step. Below, the case where a finish forge process is provided is demonstrated.

  In the case of providing the finish forging step, in the die forging step, a forging material in which the approximate shape of the crankshaft (final product) is shaped is formed. However, about the area | region shape | molded by the type | mold engraving part of a 2nd metal mold | die, for example, the dent of the arm part A, the shape of a final product is modeled in a forging material at a die forging process. Further, the forged material has a surplus volume in order to form a finished shape while forming burrs in the finish forging process.

  In the finish forging step, a pair of third dies are used to obtain a finished forged material in which the shape of the crankshaft (final product) is formed and burrs are provided. At that time, in order to maintain the shape of the recess of the arm portion A, the fourth mold is pressed against the recess of the arm portion A.

  Similar to the first mold described above, the third mold is engraved with a mold engraving portion, and the mold engraving section includes the fourth mold among the shapes of the crankshafts shown in FIGS. The shape of the portion excluding the region where the mold abuts is reflected. Moreover, since the 3rd metal mold | die accommodates a 4th metal mold | die, the site | part corresponding to the dent of the arm part A is open | released largely.

  As in the second mold described above, the fourth mold is engraved with a mold engraving section having a shape corresponding to at least the recess of the arm section A. The fourth mold can be moved back and forth so as to be in contact with or separated from the journal part J side surface of the arm part A. In addition, the fourth mold is movable in the reduction direction so as to be located at the center between the upper mold and the lower mold of the third mold.

  The finish forging process using such a 3rd metal mold | die and a 4th metal mold | die is performed as follows. First, the forging material is stored in the lower mold engraving portion in a state where the upper mold and the lower mold of the third mold are separated from each other. At that time, the fourth mold is in a retracted (retracted) state.

  Subsequently, the fourth mold is advanced, and the fourth mold is pressed against the recess of the arm part A. In this state, the upper mold of the third mold is moved toward the lower mold. Thus, the forging material is reduced, and the shape corresponding to the upper and lower mold engraving portions, that is, the shape of the final product is formed into the forging material. On the other hand, since the fourth mold is pressed against the dent of the arm portion A, the shape thereof is restrained and held.

  Here, it is preferable to provide a guide groove in the fourth mold as in the second mold. Thereby, when the burr | flash was formed along the 2nd metal mold | die forging process, it becomes possible to advance a 4th metal mold | die, accommodating a burr | flash in the guide groove of a 4th metal mold | die.

  After completing the reduction with the third die, the fourth die is retracted and retracted from the arm part A, and then the upper die of the third die is separated from the lower die, and the forging material (finish forging material) Take out. The mold engraving part of the fourth mold for holding the dent of the arm part A has a reverse mold slope, but is retracted by advancing and retreating, so that the forging material (finish forging material) is taken out. Can do. For this reason, die forging can be performed without any problem.

  Subsequently, in the deburring process, the crankshaft is obtained by punching and removing the burrs from the finished forged material with burrs. At that time, the main shapes (for example, the arm part A, the journal part J, and the pin part P) formed on the finished forged material are maintained even in the finished forged material (obtained crankshaft) after deburring.

  By providing such a finish forging step, it is possible to improve dimensional accuracy in the production of a forged crankshaft that simultaneously achieves weight reduction and rigidity. Moreover, since the dent of an arm part is restrained by pressing a 4th metal mold | die to the dent of an arm part, the shape is stabilized. Although the fourth mold is pressed against the surface of the arm part A, since the fourth mold is not pushed further, the force for holding the fourth mold may be small. For this reason, the finishing forging process does not require a great deal of force and can be performed easily.

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

1: Forged crankshaft, J, J1-J5: Journal part, P, P1-P4: Pin part,
Fr: front part, Fl: flange part, A, A1 to A8: crank arm part,
W, W1-W8: Counterweight part, Aa, Ab: Side part of arm part,
Ac: Pin top part of the arm part,
As: Inner region of both side portions on the journal side surface of the arm portion,
10: first mold, 11: upper mold, 12: lower mold, 20: second mold,
20a: guide groove, 31: material (billet) before die forging,
32: Material after die forging (forged material), 32a: Burr

Claims (4)

A method for manufacturing a forged crankshaft, comprising:
The forged crankshaft is a journal part serving as a rotation center;
A pin part eccentric to the journal part,
A crank arm part that connects the journal part and the pin part, and has a depression on the surface of the journal part side,
The manufacturing method includes:
A die forging step of obtaining a forging material comprising the journal portion, the pin portion, and the crank arm portion from a material using a pair of first dies,
A burr removing step for removing burrs from the forged material obtained in the die forging step,
The material is a billet or a rough material obtained by preforming a billet,
In the die forging step, in a state where the second mold is disposed at a position where the dent is formed, the material is squeezed by the first mold and brought into contact with the second mold, thereby forming the dent. A method for manufacturing a forged crankshaft. In the manufacturing method of the forged crankshaft of Claim 1,
The method for manufacturing a forged crankshaft, wherein the second die has a guide groove, and the burr that flows out in a rolling process of the die forging step is guided by the guide groove. In the manufacturing method of the forged crankshaft of Claim 1 or 2,
A method for producing a forged crankshaft, wherein the second die is moved in the reduction direction so that the second die is positioned at the center between the pair of first die in the reduction process of the die forging step. In the manufacturing method of the forged crankshaft in any one of Claims 1-3,
The forged crankshaft manufacturing method, wherein the crank arm portion of the forged crankshaft is thicker in a range from both side portions near the pin portion to a top portion in the eccentric direction of the pin portion than the thickness of the recess.

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