Technical field
[0001]
The present invention relates to a method for producing a forged crankshaft by hot forging. More particularly, the present invention relates to a method for producing a forged crankshaft for 3-cylinder engine or six-cylinder engine by hot forging.
BACKGROUND
[0002]
Automobile, for small machines such as motorcycles and agricultural machinery is often equipped with 3-cylinder or 6-cylinder engine. 3-cylinder or forged crankshaft used in the 6-cylinder engine (hereinafter simply referred to as "crankshaft") includes four journals, of three and the pin portion, the six connecting the these journal portion and the pin portion, respectively comprising a crank arm portion (hereinafter, simply referred to as "arm") and the. The first pin portion of the front side, the second pin of the central, and a third pin portion of the side rear are arranged with a phase difference of 120 ° in the journal portion around. Of the six arm portions, four arm portions connected to the first pin portion and the third pin portion (first, second, fifth and sixth arm portions) each counterweight unit (hereinafter, simply "weight part" including also referred to) and.
[0003]
　Recently, weight reduction of the crankshaft is required to improve the fuel economy. Response to the request, it is effective to reduce the weight of the pin portion near the arm portion. By the weight of the arm is reduced, because it is possible to reduce the weight of the weight portion. Prior art to reduce the weight of the arms reduce the weight of the crankshaft is disclosed in JP 2012-7726 (Patent Document 1) and WO 2015/075934 (Patent Document 2).
[0004]
　In the technique described in Patent Document 1, forming small arm in the forging process. Further, after the burr punching step, pushing the punch to the surface of the journal portion of the arm portion. Thus, a deep hole in the surface of the arm portion is formed. Weight amount corresponding arm portion of the volume of the hole is reduced. Further, in both side portions of the pin in the vicinity of the arm portion, the thickness is maintained thick. Therefore, the rigidity of the arm portion is ensured.
[0005]
　In the technique described in Patent Document 2, forming the respective excess metal portions on both sides of the arm portion in the forging process. Further, after the burr punching step, folding the excess thickness portion to the journal portion of the arm portion by the upper and lower molds. Thus, both sides of the pin in the vicinity of the arm portion, the thickness becomes thicker. Inside the thickness of their sides becomes thinner. Therefore, the weight of the arm is reduced, the rigidity of the arm portion is ensured.
[0006]
　Thus, according to the technique described in Patent Documents 1 and 2, it is possible to produce a forged crankshaft which reduce the weight while ensuring the rigidity.
CITATION
Patent Document
[0007]
Patent Document 1: JP 2012-7726 JP
Patent Document 2: WO 2015/075934
Summary of the Invention
Problems that the Invention is to Solve
[0008]
　However, in the technique described in Patent Document 1, since the deformation of the entire arm is pushed strongly punch to the surface of the arm portion, it requires a great deal of force to push the punch. Therefore, it is necessary special equipment for applying a great force to the punch. In addition, it is necessary to consider with respect to durability of the punch.
[0009]
　Meanwhile, in the technology described in Patent Document 2, the excess thickness portion to locally protrude from it only rolling by the upper and lower molds is sufficient, not requiring a great deal of force. However, when folding the excess thickness portion, excess thickness portion first comes into contact with the lower mold. Thus, the initial step of folding the excess thickness portion, a state in which portions other than the excess thickness portion of the forged material is floated from the lower mold, the posture of the forged material becomes unstable. Therefore, a special device for stabilizing required attitude forging.
[0010]
　An object of the present invention is to provide a manufacturing method capable of producing a forged crankshaft which reduce the weight while maintaining the rigidity with a simple structure.
Means for Solving the Problems
[0011]
　Manufacturing method according to an embodiment of the present invention, each of the four journal portions, the first being arranged with a phase difference of 120 ° in the journal portion around the second and third pin portion, a journal portion and the pin portion and six crank arm portion connecting to a method for manufacturing a forged crankshaft including.
　This manufacturing method is
　a forging step of forming the finishing forging with burrs by the upper forging die and the lower forging die, targeting all or a portion of the crank arm connected to the first and third pin portion, the the pin outer circumference of the upper forging die side in the vicinity of the crank arm portion, and a forging step of forming a surplus wall portion projecting from the outer periphery,
　a burr punching step of removing burrs from the finish forged material,
　the excess thickness portion by the upper die by reduction with, it comprises a reduction step of overhang the excess thickness portion to the journal portion side.
Effect of the invention
[0012]
　According to the present invention, it is possible to produce a forged crankshaft which reduce the weight while maintaining the rigidity with a simple structure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013]
[1] Figure 1 is a schematic diagram showing an example of a forged crankshaft for 3-cylinder engine.
[2] Figure 2 (a) ~ (f) are schematic views showing an example of a manufacturing process of forging the crank shaft for 3-cylinder engine.
FIG. 3 is a sectional view showing an example of the shape of the arm portion having a excess thickness portion at the finish forged material.
[4] FIG. 4 is a cross-sectional view taken along line IV-IV of FIG.
FIG. 5 is a sectional view showing a prior reduction step conditions.
FIG. 6 is a cross-sectional view taken along line VI-VI of Figure 5.
[7] FIG. 7 is a sectional view showing the situation after reduction process.
[8] FIG. 8 is a cross-sectional view taken along the line VIII-VIII in FIG.
[9] FIG. 9 is a sectional view showing another example of the shape of the arm portion having a excess thickness portion at the finish forged material.
[10] FIG 10 is a cross-sectional view taken along line X-X in FIG.
[11] FIG. 11 is a sectional view showing a prior reduction step conditions.
[12] FIG 12 is a cross-sectional view taken along line XII-XII of Figure 11.
[13] FIG 13 is a cross-sectional view showing the situation after reduction process.
[14] FIG 14 is a cross-sectional view taken along line XIV-XIV in FIG. 13.
[15] FIG 15 is a schematic diagram showing an example of a forged crankshaft for 6-cylinder engine.
DESCRIPTION OF THE INVENTION
[0014]
　Manufacturing method according to an embodiment of the present invention is a method for producing a forged crankshaft. Forged crankshaft for 3-cylinder engine, connecting four journal portions, the first being arranged with a phase difference of 120 ° in the journal portion around the second and third pin portion, a journal portion and the pin portion, respectively including six crank arm portion. The manufacturing method of this embodiment includes a forging step, a burr punching step, a reduction step. In forging process, shaping the finish forged material with burrs by the upper forging die and the lower forging die. In this forging process, all connected to the first and third pin portion or targeting portion of the crank arm portion, the outer periphery of the upper forging die side of the pin portion vicinity of the crank arm, the excess metal protruding from the outer periphery section to form a. In Bali punching process, to remove the burrs from the finish forged material. The reduction step, by reduction of the excess thickness portion by the upper mold, thereby overhanging the excess thickness portion to the journal portion.
[0015]
　In the production method of the present embodiment, to form the excess thickness portion only in the upper forging die side forging process. Furthermore, the reduction of the excess thickness portion by the upper mold at a reduction process, thereby overhanging the excess thickness portion to the journal portion. Thus, at the side of the upper mold side of the both side portions of the pin in the vicinity of the arm portion, the thickness becomes thicker. Inner thickness of the side becomes thinner. Side of the thickness of the lower mold side is thick. Therefore, the weight of the arm is reduced, the rigidity of the arm portion is ensured. That is, it is possible to produce a forged crankshaft which reduce the weight while ensuring the rigidity. Here, excess thickness portion to the lower forging die side of the arm portion is not formed. Therefore, extensively contact with lower mold forging from the initial reduction step, the posture of the forging is stabilized. Therefore, it is unnecessary any special device for stabilizing the attitude of the forging. That is, it is possible to produce a forged crankshaft with a simple configuration.
[0016]
　In a typical example, the arm portion excess thickness portion in the forging process is formed (the arm portion excess thickness portion at a reduction process is flared in the journal portion side), four arms connected to the first and third pin portion part (first, second, fifth and sixth arm portions) are all of the. In this case, it is possible to most decrease the weight of the crankshaft. The arm portion excess thickness portion is formed by forging process can be part of the arm portions of the four arm portions connected to the first and third pin portion. That is, the arm portion excess thickness portion is formed, for example, may be only the first arm portion may be only the first and sixth arm portion.
[0017]
　In the pin portion near the arm portion, the area where excess thickness portion is formed is a region of the outer periphery of the upper forging die side of the arm portion, as long as an area including at least a portion of the side of the arm, in particular but it is not limited. Excess thickness portion may for example be formed close to the weight portion. Moreover, the excess thickness portion can be formed to near the distal end of the arm (so-called pin top portion).
[0018]
　In a typical example, reduction step is performed prior to the burr punching process.
[0019]
　In another typical example, reduction process is included in the burr punching process. In this case, there is no need to provide a reduction process as a separate step.
[0020]
　In yet another exemplary embodiment, reduction process is performed after the burr punching process. For example, if the manufacturing method of this embodiment comprises a shaping step, reduction step may be included in the shaping step. The shaping step, correcting the shape of the forging is removed burrs. If the reduction step is included in the shaping step, the the reduction step and the shaping step it is not necessary to provide a separate step.
[0021]
　The manufacturing method of this embodiment may include a pre-forming step prior to the forging step. However, the manufacturing method of this embodiment is not provided with a twisting step. In the production method of the present embodiment, because the position of the pin portion of the finishing forging (phase difference) is consistent with the position of the pin portion of the final product.
[0022]
　Usually, in the forging step in the manufacturing method of this embodiment, the journal portion side surface of the arm portions excess thickness portion is formed, the parting line between the upper forging die and the lower forging die is biased to the lower forging die side . Side of the thickness of the lower forging die side of the arm portion is thicker than the thickness of the side of the upper forging die side.
[0023]
　Manufacturing method of the present embodiment is applied to forged crankshaft for 3-cylinder or 6-cylinder engine.
[0024]
　Hereinafter, the manufacturing method of this embodiment will be described with reference to the drawings. Hereinafter, as an example, the case of manufacturing a forged crankshaft for 3-cylinder engine by the production method of the present embodiment.
[0025]
　[General shape of the crankshaft]
　FIG 1 is a schematic diagram showing an example of a forged crankshaft for 3-cylinder engine. The left side of FIG. 1 shows a plan view as taken along the crankshaft in a horizontal direction when assuming a forging process and a reduction process. On the right side of FIG. 1, showing the position of the pin portion when viewed crankshaft from the front.
[0026]
　Referring to FIG. 1, the crankshaft 1 includes four journals J1 ~ J4, and three pin portions P1 ~ P3, 6 one arm portion connecting these journals J1 ~ J4 pin portions P1 ~ P3 and respectively It includes an A1 ~ A6, the. Journals J1 ~ J4 is a rotational center of the crankshaft 1. The first pin portion P1 of the front, the third pin portion P3 of the central second pin portion P2, and the rear side of the eccentric to the journals J1 ~ J4, phase difference of 120 ° in the journal J1 ~ J4 about in are located.
[0027]
　Of the six arm portions A1 ~ A6, 4 two arm portions connected to the first pin portion P1 and the third pin portion P3 (first, second, fifth and sixth arm portions) A1, A2, A5 and A6 are each have a weight portion W1, W2, W5 and W6. Two arm portions connected to the second pin portion P2 is (third and fourth arm portions) A3 and A4 having no weight portion.
[0028]
　Below, when a generic term for the journal portion J1 ~ J4, also referred to as its sign as "J". When collectively first and third pin portion P1 and P3, also referred to the code "P". When collectively arm A1, A2, A5 and A6 having a weight portion, also referred to the code "A".
[0029]
　When assuming the forging process and reduction process, the second pin portion P2 is disposed at a position directly below the axis of the journal portion J. The first and third pin portion P1 and P3, respectively, are arranged in a position rotated 30 ° from the horizontal upwardly passing through an axis of the journal portion J.
[0030]
　Details will be described later, of the six arm portions A1 ~ A6, 4 one arm portion A connected to the first and third pin portion P (P1 and P3) (A1, A2, A5 and A6) are shown below and it has a shape. At the side of the upper mold side of the both side portions of the pin portion near P of the arm A, the thickness is thicker. The inside of the thickness of the side is thinner. The thickness of the side serving as the lower mold side is thicker to the same degree as the side that becomes the upper mold side.
[0031]
　[Crankshaft production method]
　FIG. 2 (a) ~ (f) are schematic views showing an example of a manufacturing process of forging the crank shaft for 3-cylinder engine. FIG 2 (a) ~ (f) , shows a plan view as taken along the crankshaft in a vertical direction when assuming a forging process and a reduction process. The manufacturing method of this embodiment includes a pre-forming step, and the forging step, a burr punching step, a shaping step. These series of steps is carried out in hot. Usually, the preforming step comprises a bending beating step and roll forming step. Forging step includes a rough beating process and finishing beating process.
[0032]
　Raw materials of the crankshaft in cross section is the cross-sectional area is constant billet over the entire length in the round or square. First, as shown in FIG. 2 (a), cutting the billet, to prepare the material 2 of the predetermined length. Heating the material 2 by induction heating furnace or gas heating furnace. The roll forming process, rolling the material 2 by grooved roll. Thus, as shown in FIG. 2 (b), roll wasteland 3 volume in the longitudinal direction is allocated is molded. Then, a bending beating process. The bending beating process, partially press pressure roll wasteland 3 from the longitudinal and perpendicular directions. Thus, as shown in FIG. 2 (c), longitudinally and the bending volume is distributed in a direction perpendicular wasteland 4 is molded.
[0033]
　Subsequently, the rough beating process, the wasteland 4 press forging bending using a pair of dies vertically. Thus, as shown in FIG. 2 (d), rough forging material 5 is approximate shape are shaped in a crank shaft (final product) is molded. Furthermore, the finishing beating process, forging a 5 rough forging material using a pair of molds (the upper forging die and the lower forging die) vertically. Thus, as shown in FIG. 2 (e), finishing the forging material 6 shape is shaped to conform to the crankshaft of the final product except for some shapes are formed.
[0034]
　Details will be described later, among the rough forged material 5 and six arm portions A1 ~ A6 finish forged material 6, four arm portions A (A1 connected to the first pin portion P1 and the third pin portion P3, A2, A5 and A6), that is, four arm portions a having a weight portion W, the excess thickness portion (not shown) are formed. That is, some of the shape of the arm portion A is slightly different from the shape of the arm portion A of the crankshaft of the final product. Is the approximate shape shaping the excess thickness portion is rough beating process, the shape of the excess thickness portion is completely finishing beating process.
[0035]
　When rough beating process and finishing beating process, from between the parting surface of the mold facing each other, the burr flows out. Therefore, the rough forging 5 and finishing forging 6 with burrs 5a and 6a are around the shaped crank shaft.
[0036]
　The burr punching process, while maintaining a mold finishing forging 6 with burrs 6a from above and below, punching burrs 6a by blade type. Thus, as shown in FIG. 2 (f), the crank shaft 1 having a shape that matches the crankshaft of the final product except for the shape of the part described above is obtained.
[0037]
　The shaping step, the crankshaft 1 of the key points of the removal of the burrs, for example, the shaft portion such journal J and pin portions P1 ~ P3, and the arm portion A and the weight portion W, slightly rolling a die from above and below, to correct the size and shape of the final product. The shaft portion is reduction in shaping step includes a front portion Fr connected to the first journal portion J1 of the front, and also a flange portion Fl connected to the fourth journal portion J4 of the rear side. The shaping step may be corrected by rolling the third and fourth arm portions A3 and A4 having no weight portion W. In the present embodiment, in the shaping step, the excess thickness portion is pressure. In this manner, the crankshaft 1 of the final product is produced.
[0038]
　Formation of excess metal portion and reduction]
　FIG. 3 is a sectional view showing an example of the shape of the arm portion having a excess thickness portion at the finish forged material. Arm unit shown in FIG. 3 representatively shows a shape of the first arm portion A1 that connects the first pin portion P1 and a first journal portion J1. That is, the cross-section shown in FIG. 3 corresponds to a cross section along line III-III in FIG. 2 (e). Figure 4 is a cross-sectional view taken along line IV-IV of FIG.
[0039]
　5 to 8 are cross-sectional views for explaining the situation of reduction steps. Of these figures, FIGS. 5 and 6 show a state before reduction step, 7 and 8 show a state after the reduction step. Also, the cross-section shown in FIG. 5 and FIG. 7 is consistent with the cross-section shown in FIG. 3. The cross-section shown in FIG. 6 corresponds to a cross section along line VI-VI of Figure 5. The cross-section shown in FIG. 8 corresponds to a cross section along line VIII-VIII in FIG. That is, the cross-section shown in FIG. 6 and 8, consistent with the cross section shown in FIG.
[0040]
　As described above, the finish forged material is molded by the upper forging die and the lower forging die forging process (finishing beating process). In the finishing forging shaped by the forging process, the second pin portion P2 is disposed at a position directly below the axis of the journal portion J. Referring to FIG. 3, the first pin portion P1 is disposed at a position 30 ° rotated upward from the horizontal line passing through the axis of the journal portion J. On the other hand, the third pin portion P3, the first pin portion P1 with respect to a line passing through the centers of the second pin portion of the journal portion J are arranged at positions symmetrical.
[0041]
　As shown in FIG. 3, the surface of the first journal portion J1 of the first arm portion A1, (corresponding to the position of the burr) parting line L between the upper forging die and the lower forging die is lower forging die side biased to. Therefore, as shown in FIG. 4, the thickness of the side Ab lower forging machine side of the first arm portion A1 is thicker than the thickness of the side Aa of the upper forging die side. This is because stamped gradient exists.
[0042]
　Further, as shown in FIGS. 3 and 4, the first pin portion P1 near the first arm portion A1, the excess thickness portion Ac is formed on the outer periphery of the upper forging die side of the first arm portion A1. In the axial direction of the journal portion, the excess thickness portion Ac is formed in a part of the side Aa on forging machine side of the first arm portion A1. If the excess thickness portion Ac is Rarere provided in a part of the side Aa, when pressure is excess thickness portions Ac as described later, it tends to bend the crushed easily or journal portion side excess thickness portion Ac. The excess metal portion Ac protrudes upward from the outer periphery side Aa on forging machine side of the first arm portion A1. The amount of protrusion of the excess thickness portion Ac is not particularly limited. However, the amount of protrusion of the excess thickness portion Ac is if too large, the mass of the crankshaft is increased. Therefore, the amount of protrusion of the excess thickness portion Ac is the mass of the crank shaft, is appropriately set in consideration of the rigidity of the arm portion A. The outer periphery of the lower forging machine side of the first arm portion A1 is not formed excess thickness portion. The upper forging die and the lower forging die, are such types engraving unit shape reflecting the first arm portion A1 is engraved. Type draft of mold sculpture section is not a reverse gradient. Therefore, there is no problem in stamping finish forged material.
[0043]
　Finishing forging such forms are removed burrs in Bali punching process. Burrs were removed forging is correct geometry by the upper and lower molds in the shaping process. At this time, the excess thickness part Ac are also under pressure.
[0044]
　As shown in FIGS. 5-8, shaping step (reduction step) the upper mold 11 and the lower mold 12, it is used. Shaping step, a second pin portion P2 similar to the forging step in a state arranged at a position directly below the axis of the journal portion J, for reduction of the forging material. The upper mold 11 and the lower mold 12 are engraved the type engraved portion of a shape corresponding to the posture of such forging. For example, in a mold engraved portions of the upper mold 11, the shape corresponding to the outer periphery of the upper mold side of the first arm portion A1 is consistent with the shape of the final product. Similarly, in the mold engraved portion of the lower mold 12, the shape corresponding to the outer periphery of the lower mold side of the first arm portion A1 is consistent with the shape of the final product.
[0045]
　The shaping step, first, forging without burrs are accommodated in a mold engraved portion of the lower die 12. At this time, as shown in FIGS. 5 and 6, the first arm portion A1 extensively contact with mold engraved portion of the lower die 12. The lower mold 12 side of the first arm portion A1 is because not formed excess thickness portion. Accordingly, the posture of the first arm portion A1, i.e. the posture of the forging is stabilized.
[0046]
　Then, the upper die 11 is lowered. Thus, the shaft portion of the forging material is pressure. Together with this, the mold engraved portion of the upper die 11 is brought into contact with the excess thickness portion Ac, to pressure as it is excess thickness portion Ac. Thus, as shown in FIGS. 7 and 8, the excess thickness portion Ac is deformed as or bent as crushed, it overhangs the first journal portion J1 side. As a result, the thickness of the upper mold 11 side portion Aa of the first arm portion A1 becomes thick. Since no deformation inner portion of the side Aa, the thickness of that part is thinner. Since the side Ab of the lower mold 12 side is not deformed, the thickness of the side Ab is made in advance thicker. For example, the thickness of the side Ab of the lower die 12 side is a side about the same after reduction of the upper mold 11 side.
[0047]
　[Other embodiments]
　Fig. 9 is a sectional view showing another example of the shape of the arm portion having a excess thickness portion at the finish forged material. Figure 10 is a cross-sectional view taken along line X-X in FIG. Arm unit shown in FIG. 9 and FIG. 10 is a modification of the arm unit shown in FIGS. 3 and 4 described above. 11 to 14 are sectional views for explaining the situation of reduction process with respect to the arm unit shown in FIGS. 9 and 10. Of these figures, FIG. 11 shows the situation before reduction process. Figure 12 shows a cross section along line XII-XII of Figure 11. Figure 13 shows the situation after the reduction step. Figure 14 shows a cross section along line XIV-XIV in FIG. 13.
[0048]
　As shown in FIGS. 9 and 10, the arm portion A of the finishing forging, has a shape shown below. The journal portion J-side surface of the pin portion near P of the arm A, step along the parting line L is formed. That is, the area above the forging die side including the side Aa and the excess thickness portion Ac of the arm portion A is recessed than the area of ​​the lower forging die side including the side Ab of the arm A. Thus, the thickness of the side Ab lower forging die side is thicker. On the other hand, the thickness of the arm portion A of the upper forging die side (including the side Aa) is made significantly thinner than the thickness of the side Ab lower forging die side.
[0049]
　Finishing forging such forms are removed burrs by burr punching process. Thereafter, excess metal portion Ac of the forging material is reduction by shaping step (reduction step) shown in FIGS. 11 to 14. Shaping process shown in FIGS. 11 to 14 are similar to the shaping step described with reference to FIGS. 5 to 8. Thus, as shown in FIG. 14, the thickness of the side Aa of the upper mold 11 side of the arm portion A is increased. The thickness of the side Ab of the lower mold 12 side of the arm portion A is thicker than the thickness of the side Aa of the upper mold 11 side. Portion of the thickness between the side Aa and side Ab of the arm A is remarkably thin.
[0050]
　Others The invention is not limited to the above embodiments, without departing from the scope of the present invention, various modifications are possible. For example, in some cases preforming step is omitted. Sometimes rough beating step is omitted. Sometimes shaping step is omitted. If the shaping step is omitted, may be performed under a pressure of excess thickness portion is provided separately and step before the burr punching process. It may be carried out under a pressure of surplus meat section in Bali punching process. It may be carried out under a pressure of excess thickness portion is provided separately with step after the burr punching process.
[0051]
　It is also possible to pressure at the desired complete when the excess thickness portion of the shape can be formed in the rough beating process, beating finishing excess thickness portion formed by rough beating process step. In that case, without reduction in finishing beating process the excess thickness portion formed by rough beating process may be reduction in the finishing beating subsequent step.
[0052]
　In the above description has described the case of manufacturing a crankshaft for 3-cylinder engine. However, the manufacturing method of this embodiment is also applicable to a crank shaft for 6-cylinder engine.
[0053]
　Figure 15 is a schematic view showing an example of a forging crankshaft 6-cylinder engine. The Figure 15 shows a plan view as taken along the crankshaft in a vertical direction when assuming a forging process and a reduction process. Referring to FIG. 15, the fourth pin portion P4 corresponds to the third pin portion P3, the fifth pin portion P5 corresponds to the second pin portion P2, the sixth pin portion P6 corresponds to the first pin portion P1 to. That is, forged crankshaft for 6-cylinder engine, a shape that is symmetrically arranged forging crankshaft for two three-cylinder engine with respect to the journal J4. Therefore, to the production of forged crankshaft for such six-cylinder engine, it is naturally applicable manufacturing method of this embodiment.
Industrial Applicability
[0054]
　The present invention can be effectively utilized in the production of forged crankshaft used in the three-cylinder engine or six-cylinder engine.
DESCRIPTION OF SYMBOLS
[0055]
　　1 forged crankshaft
　　J1 ~ J4 journal portions
　　P1 ~ P3 pin
　　A1 ~ A6 crank arm portion
　　W1 ~ W6 counterweight portion
　　side of Aa on forging die side
　　side of Ab lower forging die side
　　Ac excess thickness portions
　　L parting line
　　11 the upper mold
　　12 lower mold

The scope of the claims
[Requested item 1]
　Four journal portions, the first, second and third pin portion, and the journal portion and the pin portion and six crank arm portion connecting each arranged with a phase difference of 120 ° in the journal portion around a method of manufacturing a forged crankshaft comprising,
　a forging step of forming the finishing forging with burrs by the upper forging die and the lower forging die, the whole or a part connected to the first and third pin portion a crank arm portion of interest, the outer periphery of the upper forging die side of the pin in the vicinity of the crank arm portion, and a forging step of forming a surplus wall portion projecting from the outer periphery,
　removing burrs from the finishing forging material burr punching a step, which
　by reduction of the excess thickness portions by the upper mold, and a reduction step of overhang the excess thickness portions in the journal portion, the production method of the forged crankshaft.
[Requested item 2]
　A method of manufacturing a forged crankshaft according to claim 1,
　wherein the burr punching the reduction step is performed prior to step, the manufacturing method of the forged crankshaft.
[Requested item 3]
　A method of manufacturing a forged crankshaft according to claim 1,
　wherein the reduction step is included in the burr punching step, the production method of the forged crankshaft.
[Requested item 4]
　A method of manufacturing a forged crankshaft according to claim 1,
　wherein the reduction step after the burr punching steps are performed, the production method of the forged crankshaft.
[Requested item 5]
　A method of manufacturing a forged crankshaft according to claim 4,
　comprising a shaping step of correcting the shape of the forging is removed burr,
　the reduction step is included in the shaping step, the production method of the forged crankshaft .
[Requested item 6]
　A method of manufacturing a forged crankshaft according to any one of claims 1 to 5,
　in the forging process, in the journal portion surface of the crank arm where the excess thickness portions are formed, the the upper forging die parting line are biased to the lower forging die side between the lower forging die, the lower forging die side portion of the thickness of the crank arm portion, a side portion of the upper forging die side It is thicker than the thickness of the method of manufacturing a forged crankshaft.
[Requested item 7]
　A method of manufacturing a forged crankshaft according to any one of claims 1 to 6,
　wherein the forged crankshaft 3 is for cylinder engine, the production method of the forged crankshaft.
[Requested item 8]
　A method of manufacturing a forged crankshaft according to any one of claims 1 to 6,
　wherein the forged crankshaft is for 6-cylinder engine, the production method of the forged crankshaft.