JP6208062B2 - Crank throw forging method and crank throw manufacturing method - Google Patents

Description

  The present invention relates to a crank throw forging method, a crank throw manufacturing method, and a crank throw.

  An assembly-type large-sized crankshaft for ships and the like is manufactured by forging steel forging into parts called a crank throw and a crank journal and connecting them by shrink fitting. Therefore, the crank throw requires a high fatigue strength in the vicinity of the fillet portion.

  The fatigue strength in the vicinity of the fillet portion can be improved by forming the metal flow continuously without interruption and by preventing the ghost portion, which is an unhealthy region inside the steel ingot, from being present in the vicinity of the fillet portion.

  Therefore, a crankshaft forging method (Japanese Patent Application Laid-Open No. 2003-88933) has been proposed in which a fillet portion is processed simultaneously with forging to form a metal flow along the fillet shape. In this crankshaft forging method, the fillet part is processed simultaneously with forging, so that the center part of the steel ingot with much segregation can be prevented from approaching the product surface, and the existence of the ghost part in the vicinity of the fillet part can be suppressed. It is done.

  However, the conventional crankshaft forging method is forging the crankshaft integrally, and is difficult to apply to an assembly-type large crankshaft.

  On the other hand, a method of suppressing the generation of a ghost part by reducing the cooling rate difference during casting has been conventionally used. However, in this conventional method, it is necessary to use a small steel ingot (for example, 20 t or less) in order to reduce the cooling rate difference at the time of casting. It is difficult to manufacture. Furthermore, when producing a crank throw having a high fatigue strength, the conventional method cannot produce a plurality of crank throws from one steel ingot, resulting in poor production efficiency.

JP 2003-88933 A

  The present invention has been made on the basis of the above-described circumstances, and can improve the fatigue strength of the crank throw, and can improve the productivity of the crank throw, the crank throw manufacturing method, and the crank throw For the purpose of provision.

  The invention made to solve the above-mentioned problems is a crank throw forging method in which a crank throw for an assembled crankshaft is formed by die-forging a steel ingot, and an unhealthy region inside a wasteland taken from the steel ingot The position of the ghost part and the position of the ghost part inside the crank throw that has been die-forged into this wasteland, and based on the measurement results, Based on this relationship, the ghost in the crank throw after die insertion forging is determined from the position of the ghost part in the wasteland before die insertion forging based on this relationship. Based on the process of estimating the position of the part and the estimated position of the ghost part inside the crank throw after the die insertion forging, the ghost part is located near the fillet part of the crank throw after die insertion forging. So that it is not location, characterized in that it comprises the size of the steel ingot, the shape of the steel ingot, and determining the forging method of the position and wasteland collecting wasteland from steel ingot.

  The crank throw forging method is a relationship in which the position inside the crank throw after die insertion forging is determined from the position inside the rough ground before die forging or the position inside the steel ingot based on the measurement result of the position measurement process of the ghost part. Based on this relationship, the position of the ghost portion inside the crank throw after die insertion forging is estimated from the position of the ghost portion inside the wasteland before die insertion forging. Thereby, the forging method of the crank throw can accurately estimate the position of the ghost portion inside the crank throw after die-forging, and can extract the rough ground from which the fork can be forged with excellent fatigue strength from the steel ingot. At the same time, an appropriate forging method can be selected. Further, the crank throw obtained by the forging method of the crank throw can prevent the ghost portion from being disposed in the vicinity of the fillet portion, and thus has excellent fatigue strength. In addition, because the crank throw forging method does not need to suppress the difference in cooling rate during casting, a crank throw with excellent fatigue strength can be forged using a large steel ingot, resulting in improved productivity. To do.

The length of the wasteland corresponding to the longitudinal direction of the arm is H ₀ (mm), the length of the arm in the longitudinal direction after die insertion forging is H ₁ (mm), and the diameter of the pin shaft after die insertion forging When it is set to D (mm), it is good to forge a wasteland so that following formula (1) and formula (2) may be satisfy | filled. Thus, by setting the length of the wasteland, the length in the longitudinal direction, and the diameter of the pin shaft, it is possible to more reliably prevent the ghost portion from being disposed near the fillet portion of the crank throw after die-forging. It is possible to ensure the fatigue strength of the crank throw more reliably.
1.02 <H ₁ / H ₀ <1.25 (1)
0.23 <D / H ₁ <0.45 (2)

  Moreover, another invention made | formed in order to solve the said subject forges several crank throws from the said some wasteland by the process of extract | collecting several wastelands from one steel ingot, and the forging method of the said crank throw. A process for producing a crank throw comprising the steps.

  Since the crank throw forging method uses the crank throw forging method, it is possible to appropriately estimate the range of the wasteland collected from the steel ingot for crank throw forging, and thus forging a crank throw having excellent fatigue strength can be forged. A plurality of wasteland can be efficiently collected from one steel ingot, and productivity is improved.

  Still another invention made to solve the above problem is a crank throw manufactured by the crank throw manufacturing method. Since the crank throw is manufactured by the crank throw manufacturing method, the ghost portion does not exist in the vicinity of the fillet portion, and thus has excellent fatigue strength.

  The “ghost part” means a concentrated region of alloy elements that appear as black spots when a macro structure test is performed, and the macro structure test can be performed in accordance with JIS-G0553 (2012). it can. In addition, when it is not possible to comply with this standard depending on the steel type and size, a macrostructure test may be performed by a method according to this standard. Further, “in the vicinity of the fillet portion” means a region having a predetermined thickness from the fillet portion toward the inside of the crank throw, and this predetermined thickness range can be a distance of about 1/100 of a half stroke of the crank throw, for example. Preferably, it is 30 mm or more.

  As described above, the crank throw forging method, crank throw manufacturing method, and crank throw of the present invention can improve the fatigue strength of the crank throw and have high productivity.

(A) A schematic front view showing a steel ingot before forging for explaining a forging method of a crank throw according to an embodiment of the present invention, (b) obtained by forging the steel ingot of FIG. 1 (a). Explanatory drawing of collecting wasteland for measurement from bar material, (c) Schematic front view of wasteland sampled from bar material of FIG. 1 (b), (d) Type of wasteland sampled from bar material of FIG. 1 (b) Schematic front view of crank throw after insert forging (A) Schematic perspective view of wasteland before mold forging, (b) Schematic side view of wasteland in FIG. 2 (a), (c) Schematic along the AA line of wasteland in FIG. 2 (b) Sectional view, (d) Schematic perspective view of crank throw after die-forging, (e) Schematic side view of crank throw in FIG. 2 (d), (f) B- of crank throw in FIG. 2 (e) Schematic cross-sectional view along line B Graph showing the position change inside the wasteland before and after die-forging (A) Schematic front view of steel ingot in first forging method of crank throw, (b) Schematic perspective view of bar material in first forging method of crank throw, (c) Wasteland in first forging method of crank throw (D) A schematic front view of a wasteland after compression in the first forging method of the crank throw, (e) A schematic view showing a state in which the wasteland in the first forging method of the crank throw is inserted into a mold. Sectional drawing, (f) Typical sectional drawing which shows crank throw at the time of die insertion forging in the first forging method of crank throw (A) Schematic front view of steel ingot in second forging method of crank throw, (b) Schematic perspective view of bar material in second forging method of crank throw, (c) Wasteland in second forging method of crank throw (D) Schematic sectional view showing a state in which the rough ground in the second forging method of the crank throw is inserted into the mold, (e) Crank throw at the time of die insertion forging in the second forging method of the crank throw Schematic sectional view showing The figure which shows the flow of the forging method of the crank throw which concerns on one Embodiment of this invention. Graph showing the relationship between inclusion size and fatigue strength ratio in the ghost part

  Embodiments of a crank throw forging method, a crank throw manufacturing method, and a crank throw according to the present invention will be described below.

[Crank throw forging method]
The forging method of the crank throw is a forging method in which a crank throw for an assembly-type crankshaft is formed by forging a steel ingot. The forging method of the crank throw is a step of measuring the position of the ghost part that is an unhealthy area inside the wasteland taken from the steel ingot and the position of the ghost part inside the crank throw that is die-forged from this wasteland (ghost part) Based on the measurement results) and the above measurement results, a relationship for obtaining the corresponding position inside the crank throw after die insertion forging from the position inside the rough ground before die forging or the position inside the steel ingot is obtained. The process of estimating the position of the ghost part inside the crank throw after the die insertion forging from the position of the ghost part inside the wasteland before the die insertion forging (ghost part position estimation step), and the inside of the crank throw after the die insertion forging Based on the estimated position of the ghost part, the size of the steel ingot, the shape of the steel ingot, and the waste from the steel ingot are removed so that the ghost part is not placed near the fillet part of the crank throw after die-forging. The step of determining the position to take and the forging method of the wasteland (steel ingot condition determining step), and collecting the wasteland from the steel ingot having the size and shape determined in the steel ingot condition determining step, the steel ingot condition determining step Forging a crank throw from the wasteland using the determined wasteland forging method (forging step).

<Ghost part measurement process>
In the ghost part measuring step, the waste area is sampled from a real steel ingot, and the position of the ghost part in the waste area before and after die-forging is measured. Specifically, first, the waste material 2 is obtained from the bar material 2 of FIG. 1B obtained by forging the cast steel ingot 1 of FIG. Collect 3 And the macro structure test based on JIS-G0553 (2012) is done about the extract | collected wasteland 3, and as shown in FIG.1 (c), the position of the ghost part 5 in the wasteland 3 before this die insertion forging is measured. Further, a macro structure test was performed on the crank throw 4 after die-forging the rough ground 3 collected from the bar material 2 in FIG. 1B, and as shown in FIG. Measure the position. This measurement is similarly performed on several types of steel ingots. In addition, as shown in FIG. 4, even when it mold-forges after extract | collecting from the bar material 2 and compressing the wasteland 3, the said macro structure test should be performed only about the wasteland 3 (FIG.4 (c)) before compression. . This is because by performing the macro structure test on the wasteland 3 before compression, the compression process of the wasteland 3 can also be analyzed based on the measurement result of the macro structure test.

<Ghost part position estimation step>
In the said ghost part position estimation process, first, the reverse analysis from the wasteland 3 to the steel ingot 1 is implemented, and the state of the steel ingot 1 before forging from the position of the ghost part 5 in the wasteland 3 measured in the said ghost part measurement process. The position of the ghost part 5 at is derived. For the inverse analysis, a flow coagulation analysis or a generally known method can be used. By performing the reverse analysis on several types of steel ingots, the position of the ghost portion 5 in the steel ingot 1 can be grasped for each steel type.

  Next, the change after the die-insertion forging of the position inside the wasteland 3 immediately before being inserted into the die for die-insertion forging is obtained by analysis and compared with the change of the actual macro position measured in the ghost part measurement step. The position change was analyzed by rigid plastic finite element analysis with the temperature set to the actual forging temperature and the coefficient of friction of the Coulomb friction μ being 0.1 to 0.4 depending on the conditions. The inventors of the present invention can accurately estimate the position change inside the wasteland 3 before and after die-insertion forging by designing the conditions so that the actual metal flow measured in the ghost part measurement process matches the metal flow by analysis. confirmed.

  Moreover, you may perform the estimation of the position change inside the wasteland 3 before and after die insertion forging using an approximate expression instead of using the method by the analysis mentioned above. A method for estimating the position change inside the wasteland 3 using an approximate expression will be described below.

As shown in FIG. 2 (c) and FIG. 2 (f), the longitudinal direction of the arm 8 is the height direction, and the end surface of the crank throw 4 on the pin shaft 6 side is used as a reference in the height direction. Let α be the height position of the wasteland 3 immediately before insertion into the mold (a dimensionless number from 0 to 1). Further, the distance in the height direction (arbitrary height position) to an arbitrary position of the pin shaft 6 is defined as z with the uppermost position of the pin shaft 6 of the crank throw 4 forged by die insertion as a reference. Also, with the center in the thickness direction of the crank throw 4 forged into the mold as a reference, an arbitrary position in the thickness direction is x (mm), and the thickness of the crank throw 4 forged into the mold is multiplied by 1/2. T (mm). Further, the length of the arm 8 of the crank throw 4 forged by die insertion is H ₁ (mm), and the length of the wasteland 3 just before being inserted into the die forging die corresponding to the longitudinal direction of the arm 8. Is H ₀ (mm), and the diameter of the pin shaft 6 of the crank throw 4 forged into die is D (mm), the height position α of the wasteland 3 immediately before being inserted into the die for forging into It can represent with following formula (3). In addition, β in the following formula (3) represents an arbitrary height position z of the pin shaft 6 part as a ratio to the diameter D of the pin shaft 6 as shown in the following formula (6). A (β) in) is represented by the following formula (4) or formula (5) depending on the value of β. Therefore, the value of A (β) when 0 <β <0.01 is equal to the value of A (0.01) in the following formula (4). In FIG. 2C and FIG. 2F, the metal flow 9 is indicated by a broken line.
α = f (z, x) = {(D−z) + A (β) × (T−x)} / H ₁ (3)
When 0.01 ≦ β ≦ 1.0, A (β) = 0.2710 × β− ^0.3321 (4)
When 0 <β <0.01, A (β) = 0.2710 × ^{0.01−0.3321} (5)
β = z / D (6)

  FIG. 3 shows the relationship between β (z / D) and A (β) expressed by the above formulas (4) to (6). The broken line in FIG. 3 indicates the relationship between β and A (β) obtained by the above equations (4) to (6), and the circular plot indicates the actual measurement values. From these, it can be seen that β and A (β) represented by the above formulas (4) to (6) can be sufficiently approximated to the actual position change inside the wasteland 3. Thereby, it can be said that the position change in the wasteland 3 before and after die insertion forging can be estimated with high accuracy by the above equation (3) using the above equations (4) to (6). From FIG. 3, it can be seen that the position closer to the uppermost position of the pin shaft 6 has a larger position change inside the wasteland 3 before and after die insertion forging.

  By using the approximate expression (3), it is possible to estimate a change in position before and after die-insertion forging without performing an analysis. Therefore, the ghost part 5 inside the wasteland 3 before die-insertion forge is calculated using the above expression (3). From this position, the position of the ghost part 5 inside the crank throw 4 after die-forging can be estimated.

<Ingot condition determination process>
In the ingot condition determining step, the ghost portion 5 fillets the crank throw 4 after die insertion forging based on the estimated position of the ghost portion 5 inside the crank throw 4 after die insertion forging obtained in the ghost portion position estimation step. The size of the steel ingot for forging the crank throw 4, the shape of the steel ingot, the position where the wasteland is extracted from the steel ingot, and the method for forging the wasteland are determined so as not to be arranged near the portion 7.

  Forging methods of wasteland, a method of forging into mold after compressing wasteland collected from steel ingot (first forging method) and a method of forging into die without compressing wasteland collected from steel ingot (second forging) Method). These forging methods will be described below. In FIG. 4 for explaining the first forging method and FIG. 5 for explaining the second forging method, the direction from the bottom of the steel ingot 1 toward the head is shown by a one-dot chain line, and FIGS. The direction corresponding to this axial direction is also shown with the dashed-dotted line also about the bar material and waste land shown to each figure of f) and FIG.5 (b)-(e).

(First forging method)
The steel ingot 1 in FIG. 4 (a) is forged into the bar material 2 in FIG. 4 (b). The bar material 2 is cut perpendicularly to the axial direction by gas cutting, and a plurality of waste land 3 is collected. Next, the wasteland 3 shown in FIG. 4C is compressed in the axial direction at a rolling reduction of 40% to 70% as shown in FIG. 4D. Then, as shown in FIG. 4 (e), the compressed wasteland 3 a is inserted into the lower mold 10 so that the axial direction is perpendicular to the height direction of the crank throw 4 after forging. Finally, as shown in FIG. 4 (f), the rough land 3 a inserted into the lower mold 10 is deformed by being pushed by the upper mold 11, and the crank throw 4 is forged. As shown in FIGS. 4E and 4F, the position of the ghost portion 5 inside the wasteland 3a changes as the wasteland 3a is deformed by being pushed by the upper mold 11.

(Second forging method)
The steel ingot 1 in FIG. 5 (a) is forged into the bar material 2 in FIG. 5 (b). The bar material 2 is cut perpendicular to the axial direction by gas cutting, and a plurality of waste land 3 is collected. Next, without compressing the wasteland 3 shown in FIG. 5 (c), the axial direction is perpendicular to the height direction of the crank throw 4 after forging as shown in FIG. 5 (d). The wasteland 3 is inserted into the lower mold 10. Finally, as shown in FIG. 5 (e), the rough ground 3 inserted into the lower mold 10 is deformed by being pushed by the upper mold 11, and the crank throw 4 is forged. As shown in FIGS. 5D and 5E, the position of the ghost portion 5 inside the wasteland 3 changes as the wasteland 3 is deformed by being pushed by the upper mold 11.

<Forging process>
In the forging step, the steel ingot 1 having the size and shape determined in the steel ingot condition determining step is cast, and the wasteland 3 is sampled from the steel ingot 1 according to the sampling position determined in the steel ingot condition determining step. Then, the crank throw 4 is forged from the wasteland 3 by the wasteland forging method determined in the steel ingot condition determining step. In the forging step, the crank throw 4 is forged in accordance with the conditions determined in the steel ingot condition determining step. Therefore, the ghost portion 5 is not disposed in the vicinity of the fillet portion 7 of the forged crank throw 4, and the crank throw having high fatigue strength. 4 can be forged.

Note that when forging crank throw 4 wasteland 3 taken from a steel ingot 1 and type entering forging, the length H ₀ wasteland 3 _(mm), the longitudinal length H ₁ of the arm 8 _(mm), and It is preferable that the diameter D (mm) of the pin shaft 6 after die-forging satisfies the following formulas (1) and (2).
1.02 <H ₁ / H ₀ <1.25 (1)
0.23 <D / H ₁ <0.45 (2)

When the H ₁ / H ₀ is equal to or less than the lower limit of the formula (1), it may be difficult to forge the pin shaft 6 to have a desired diameter. On the other hand, when the above H ₁ / H ₀ is equal to or greater than the upper limit of the above formula (1), the amount of change in the position of the ghost part 5 before and after die insertion forging becomes large, and it is difficult to keep the ghost part 5 away from the vicinity of the fillet part 7 There is.

When the D / H ₁ is less than or equal to the lower limit of the above formula (2), the amount of change in the position of the ghost part 5 before and after die-insertion forging becomes large, and it may be difficult to keep the ghost part away from the vicinity of the fillet part 7. On the other hand, when the D / H ₁ is equal to or greater than the upper limit of the formula (2), there is a possibility that a crank throw having a shape suitable for an assembled crankshaft cannot be formed.

  Therefore, the ghost portion 5 is disposed in the vicinity of the fillet portion 7 of the crank throw 4 after forging by die-forging the crank throw 4 from the wasteland 3 so as to satisfy the above formulas (1) and (2). This can be reliably prevented, and the fatigue strength of the crank throw 4 can be reliably improved.

<Flow of crank forging method>
FIG. 6 shows a flow of one embodiment of the crank throw forging method. Hereinafter, this flow will be described.

  First, a shape obtained by adding machining allowance to a crank throw to be forged is determined as a target forged shape (step S1).

  Next, the volume of the target forging shape determined in step S1 is determined (step S2).

  Next, the steel type and shape of the steel ingot are determined based on the target forging shape determined in step S1 (step S3). At this time, the position of the ghost part in the inside of the steel ingot determined based on the measurement result of the macro structure test in the ghost part measurement step is grasped.

  Next, a forging method for wasteland is determined in consideration of the position of the ghost portion inside the steel ingot ascertained in step S3 (step S4). In step S3, for example, it is determined whether the first forging method or the second forging method is used as a forging method for wasteland.

  Next, the metal flow inside the crank throw after die insertion forging is estimated using the analysis of the ghost part position estimation step or the approximate expression (3) (step S5).

  After estimating the metal flow, the macro structure of the crank throw after die-forging is measured, and it is investigated whether there is a ghost part in the vicinity of the fillet part (step S6). At this time, when a ghost part exists in the fillet part vicinity, it returns to step S3 or step S4. For example, if it is determined that the ghost part cannot be moved away from the vicinity of the fillet part even if the forging method of the rough ground is changed with the shape of the crank throw at that time, the process returns to step S3 and the selection of the steel ingot is performed again. Further, when it is determined that there is a possibility that the ghost part can be moved away from the vicinity of the fillet part by changing the forging method of the wasteland, the process returns to step S4, for example, the forging method of the wasteland is changed from the second forging method to the first. Change to forging method.

  When steps S3 to S6 are repeated and it is confirmed in step S6 that there is no ghost part in the vicinity of the fillet part, the size of the steel ingot at that time, the shape of the steel ingot, the position where the wasteland is collected from the steel ingot, and The forging method of the wasteland is appropriate for forging the crank throw, the size of the steel ingot for forging the crank throw, the shape of the steel ingot, the position to collect the waste land from the steel ingot, and the forging method and determination of the waste land To do. Thereafter, the crank throw is forged using the size of the steel ingot determined here, the shape of the steel ingot, the position for collecting the waste from the steel ingot, and the method for forging the waste. In addition, if it is the same crank throw, the size of the same steel ingot, the shape of the steel ingot, the position where the wasteland is sampled from the steel ingot, and the forging method of the wasteland are used without performing the processes of steps S1 to S6 thereafter. Crank throws with excellent fatigue strength can be repeatedly forged.

[advantage]
The forging method of the crank throw is based on the relationship (the above analysis or approximate expression) for obtaining the position inside the crank throw after the corresponding die forging from the position inside the rough ground before the die fitting forging or the position inside the steel ingot. Since the position of the ghost portion inside the crank throw after die insertion forging can be estimated from the position of the ghost portion inside the waste land before die insertion forging, it is possible to appropriately collect the rough ground for forging the crank throw from the steel ingot. . Thereby, even when a large steel ingot is used, a crank throw having excellent fatigue strength can be forged.

  In addition, since the forging method of the crank throw can estimate the position of the ghost portion inside the crank throw after die-forging, it is prevented that the ghost portion is disposed in the vicinity of the fillet portion, and the crank throw having high fatigue strength is achieved. Can be forged.

[Crank throw manufacturing method]
The crank throw manufacturing method includes a step of collecting a plurality of waste lands from one steel ingot (a waste land collecting step) and a step of forging a plurality of crank throws from the plurality of waste lands by the crank throw forging method (crank Slow forging process).

<Wasteland collection process>
In the wasteland sampling step, a plurality of wastelands are sampled from a large steel ingot according to the wasteland sampling position determined in the steel ingot condition determination step.

<Crank throw forging process>
In the crank throw forging step, the crank throw is forged for each collected waste land using the crank throw forging method. Since the wasteland sampled in the wasteland sampling step is sampled from a steel ingot based on the estimated position of the ghost part inside the crank throw, there is no ghost part near the fillet part of the crank throw forged from this wasteland. Therefore, a crank throw excellent in fatigue strength can be forged from any wasteland.

[advantage]
The method of manufacturing the crank throw collects a plurality of waste areas for forging the crank throw from the steel ingot based on the estimated position of the ghost portion inside the crank throw. Crank throw can be manufactured and productivity is improved.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

[Confirmation of ghost position control]
The waste land was actually forged by the first forging method and the second forging method, and it was confirmed whether the position of the ghost portion could be controlled by the crank throw forging method. Specifically, after the crank throw was manufactured by these two forging methods, the crank throw was cut and a macro structure test was performed to confirm the position of the ghost part. And the position of the ghost part of the crank throw estimated in the said ghost part position estimation process was compared with the position of the actual ghost part.

<Confirmation result>
The crank throw ghost part position estimated by the analysis in the ghost part position estimation step and the crank throw ghost part position estimated by the approximate expression are both the crank throw parts forged by the first forging method and the second forging method. It was confirmed that it almost coincided with any position of the ghost part. Thereby, it was confirmed that the position of the ghost portion could be controlled by the crank throw forging method. In addition, this confirmation revealed the following.

  When the crank throw was forged by the first forging method that compresses wasteland before forging, the ghost part 5 could be further away from the vicinity of the fillet part 7 than when the crank throw was forged by the second forging method. Thereby, for example, in the case of a large steel ingot of about 110 t, it can be said that it is effective to use this forging method because the generation region of the ghost part is wide. However, when forging a crank throw by the first forging method, the number of steps is increased compared to the second forging method.

  On the other hand, when the ghost part 5 can be moved away from the vicinity of the fillet part 7 of the crank throw 4 after forging without compressing the wasteland 3 before die-forging, the fatigue strength is excellent by the second forging method. It can be said that a crank throw can be manufactured.

[Confirmation of influence of ghost part on fatigue strength]
Inclusions that affect the fatigue strength are present in the ghost portion, and it is said that the presence of these inclusions reduces the fatigue strength of the product. Therefore, in order to confirm the influence of inclusions on the fatigue strength, fatigue test pieces were prepared from the manufactured crank throws and subjected to fatigue tests.

  The result of this fatigue test is shown in the graph of FIG. The graph of FIG. 7 shows the relationship between √area indicating the size of inclusions and the fatigue strength ratio. Specifically, the fatigue test piece is observed with an optical microscope, and the square root of the inclusion area multiplied by the short side perpendicular to the long side is defined as the square root of the inclusion area (√area). The average value and the average fatigue strength are plotted in the graph of FIG. In addition, the vertical axis | shaft of FIG. 7 has set the average fatigue strength (MPa) in case of (root) area = 105 to 1, and has shown ratio of each average fatigue strength with respect to this intensity | strength. From this result, it can be confirmed that high fatigue strength can be obtained by avoiding the ghost part.

  As described above, the crank throw forging method, the crank throw manufacturing method, and the crank throw can improve the fatigue strength of the crank throw and have high productivity. Useful as such.

DESCRIPTION OF SYMBOLS 1 Steel ingot 2 Bar material 3 Wasteland 3a Compressed wasteland 4 Crank throw 5 Ghost part 6 Pin shaft 7 Fillet part 8 Arm 9 Metal flow 10 Lower mold 11 Upper mold

Claims (3)

A crank throw forging method for forming a crank throw for an assembled crankshaft by die-forging a steel ingot,
A step of measuring the position of the ghost part which is an unhealthy area inside the wasteland sampled from the steel ingot and the position of the ghost part inside the crank throw obtained by die-forging the wasteland,
Based on the above measurement results, a relationship for obtaining the corresponding position in the crank throw after die insertion forging from the position in the wasteland before the die insertion forging or the position in the steel ingot is obtained. Estimating the position of the ghost part inside the crank throw after die-insertion forging from the position of the ghost part inside the wasteland,
Based on the estimated position of the ghost part inside the crank throw after the above mold insertion forging, the size of the steel ingot, the shape of the steel ingot, the steel ingot so that the ghost part is not arranged near the fillet part of the crank throw after the die insertion forging A method for forging a crank throw, comprising: a step of determining a position for collecting wasteland from the ground and a forging method for wasteland. The length of the wasteland corresponding to the longitudinal direction of the arm is H ₀ (mm), the length of the arm in the longitudinal direction after die insertion forging is H ₁ (mm), and the diameter of the pin shaft after die insertion forging 2. The crank throw forging method according to claim 1, wherein when D (mm) is satisfied, the waste land is forged so as to satisfy the following formula (1) and the following formula (2).
1.02 <H ₁ / H ₀ <1.25 (1)
0.23 <D / H ₁ <0.45 (2) A process of collecting a plurality of wasteland from one steel ingot;
A method for producing a crank throw, comprising: forging a plurality of crank throws from the plurality of waste areas by the forging method of the crank throw according to claim 1 or 2.

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