A method of forging a three-cylinder crankshaft

Abstract

The present application relates to a kind of forging method of three-cylinder crankshaft, belong to engine parts manufacturing field.It includes: S1: heating to work temperature to bar stock;S2: using press bending die to press bend second connecting rod neck;S3: using connecting rod neck pre-pressing die to first connecting rod neck and third connecting rod neck are pre-pressed;S4: using balance block pre-pressing die to first connecting rod neck balance block and third connecting rod neck balance block are pre-pressed;S5: using final forging die to the product obtained in step S4 is final forged;S6: to the product obtained in step S5 is trimmed.The present application is favorable to reduce the amount of material flow to connecting rod neck surface in the process of crankshaft forging bar stock core portion, to improve the overall quality and use strength of crankshaft.

Description

Technical Field

[0001] This invention relates to the field of engine component manufacturing, and more particularly to a forging method for a three-cylinder crankshaft. Background Technology

[0002] As a crucial component of an engine, the crankshaft operates under complex and variable conditions, requiring excellent comprehensive mechanical properties such as rigidity, strength, and toughness. Its production primarily involves forging; however, while the forming technology for non-quenched and tempered steel crankshafts is relatively mature, production and application defects still exist. Currently, due to the high amount of impurities and inclusions in the initial crankshaft bar stock, under specific or complex operating conditions (such as engines for miniature mining trucks), non-quenched and tempered steel crankshaft forgings are prone to excessively large and unevenly distributed grain sizes during actual production. This leads to application defects such as fatigue damage and connecting rod journal fracture on the connecting rod journal surface during crankshaft operation. Therefore, exploring crankshaft forming processes to improve its overall performance is of great significance. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a forging method for a three-cylinder crankshaft, which reduces the amount of core material of the bar stock flowing to the surface of the connecting rod journal during the forging process, thereby improving the overall quality and strength of the crankshaft.

[0004] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A forging method for a three-cylinder crankshaft, comprising: S1: Heat the bar stock to the working temperature; S2: Use a bending die to bend the second connecting rod neck; S3: Pre-compress the first and third connecting rod necks using a connecting rod neck pre-compression mold; S4: Use the balance block pre-compression mold to pre-compress the first connecting rod neck balance block and the third connecting rod neck balance block; S5: Use the final forging die to perform final forging on the product obtained in step S4; S6: Trim the edges of the product obtained in step S5.

[0005] The beneficial effects of this invention are as follows: Compared with the existing process of bending-pre-forging-final forging, this invention uses pre-pressing to replace pre-forging, avoiding the one-time forming of the first connecting rod, the third connecting rod neck, the first connecting rod neck balance block, and the third connecting rod neck balance block. This reduces the amount of core material of the bar stock flowing to the surface of the connecting rod neck during crankshaft forming, thereby improving the overall quality and strength of the crankshaft and reducing the probability of application defects such as fatigue damage and connecting rod neck fracture on the surface of the connecting rod neck caused by crankshaft operation.

[0006] Based on the above technical solution, the present invention can be further improved as follows.

[0007] Furthermore, in step S1, the operating temperature is 1055-1199℃.

[0008] The beneficial effect of adopting the above-mentioned further scheme is that it is conducive to heating the bar stock into a molten state, making the bar stock fluid, thereby facilitating the plasticization of the bar stock.

[0009] Furthermore, in step S3, when the connecting rod neck pre-compression mold pre-compresses the first connecting rod neck and the third connecting rod neck, the first connecting rod neck, the third connecting rod neck and the second connecting rod neck are pre-compressed by being offset by 120 degrees in each other in the circumferential direction, and the second connecting rod neck is disposed between the first connecting rod neck and the third connecting rod neck.

[0010] The beneficial effect of adopting the above-mentioned further solution is that the first connecting rod neck, the third connecting rod neck, and the second connecting rod neck are staggered by 120 degrees in the circumferential direction, which helps to ensure that the preload of the connecting rod neck meets the product manufacturing requirements.

[0011] Furthermore, in step S3, the connecting rod neck pre-compression mold presses the first connecting rod neck and the third connecting rod neck down to a position greater than the target depth, so that the core material of the bar stock is far away from the target depth position.

[0012] The beneficial effect of adopting the above-mentioned further solution is that it helps to press the core material of the bar stock to a greater distance below the parting surface of the mold, thereby making the core material of the bar stock farther away from the connecting rod neck surface.

[0013] Furthermore, in step S4, when the balance block pre-compression mold pre-compresses the first connecting rod neck balance block and the third connecting rod neck balance block, the core material of the bar stock located far from the target depth position is squeezed by the balance block pre-compression mold to form flash, so as to reduce the amount of the core material of the bar stock flowing to the surface of the first connecting rod neck and the third connecting rod neck.

[0014] The beneficial effects of adopting the above-mentioned further solution are: the core material of the bar stock is extruded by the pre-compression die of the balance block to form flash, which helps to extrude the core material of the bar stock in the form of flash, thereby reducing the amount of core material of the bar stock flowing to the surface of the first connecting rod neck and the third connecting rod neck, thereby improving the overall quality and service strength of the crankshaft.

[0015] Furthermore, in step S6, the flash containing the core material of the bar stock generated in step S4 is removed.

[0016] The beneficial effect of adopting the above-mentioned further solution is that it is advantageous to obtain a product blank with a smaller amount of core material on the surface of the connecting rod neck by cutting the edges.

[0017] Furthermore, the connecting rod neck preloading mold consists of a connecting rod neck preloading upper mold and a connecting rod neck preloading lower mold. After the connecting rod neck preloading upper mold and the connecting rod neck preloading lower mold are closed, they are adapted to the first connecting rod neck and the third connecting rod neck. The balance block preloading mold consists of a balance block preloading upper mold and a balance block preloading lower mold. After the balance block preloading upper mold and the balance block preloading lower mold are closed, they are adapted to the first connecting rod neck and the first connecting rod neck balance block or to the third connecting rod neck and the third connecting rod neck balance block.

[0018] The beneficial effects of adopting the above-mentioned further solution are: the upper and lower pre-compression dies of the connecting rod neck are conducive to the initial compression of the first and third connecting rod necks, thereby facilitating the extrusion of the core material of the bar stock by the upper and lower pre-compression dies of the balance block to form flash, and the upper and lower pre-compression dies of the balance block are conducive to the shaping of the balance blocks of the first and third connecting rod necks.

[0019] Furthermore, the upper connecting rod neck preloading die includes: a main body for the upper connecting rod neck preloading die, a first connecting rod neck preloading protrusion, and a third connecting rod neck preloading protrusion. Both the first and third connecting rod neck preloading protrusions are arc-shaped protrusions disposed on the upper connecting rod neck preloading die body, and their height is greater than the target depth of the first and third connecting rod necks. The lower connecting rod neck preloading die includes: a connecting rod neck preloading base, a lower connecting rod neck preloading die body, a first connecting rod neck preloading groove, a third connecting rod neck preloading groove, and a second connecting rod. The connecting rod neck pre-compression lower die body is disposed on the connecting rod neck pre-compression base. The first connecting rod neck pre-compression groove, the third connecting rod neck pre-compression groove, and the second connecting rod neck limiting groove are all arc-shaped grooves disposed on the connecting rod neck pre-compression lower die body. The first connecting rod neck pre-compression groove and the third connecting rod neck pre-compression groove correspond one-to-one with the first connecting rod neck pre-compression protrusion and the third connecting rod neck pre-compression protrusion, and the second connecting rod neck limiting groove is adapted to the second connecting rod neck obtained in step S2.

[0020] The beneficial effects of adopting the above-mentioned further solution are: the pre-compression protrusion of the first connecting rod neck and the pre-compression protrusion of the third connecting rod neck, as well as the pre-compression groove of the first connecting rod neck and the pre-compression groove of the third connecting rod neck, are conducive to forming a pressing area for the first connecting rod neck and the third connecting rod neck, while the limiting groove of the second connecting rod neck is conducive to providing a placement space for the already shaped second connecting rod neck when pressing down the first connecting rod neck and the third connecting rod neck.

[0021] Furthermore, the upper pre-compression mold for the balance block includes: a main body for the upper pre-compression mold for the balance block, two grooves for the upper pre-compression mold for the balance block, and a limiting groove for the connecting rod neck of the upper pre-compression mold for the pre-compression mold. Both the grooves for the upper pre-compression mold for the balance block and the limiting groove for the connecting rod neck of the upper pre-compression mold for the pre-compression mold are arc-shaped grooves on the main body of the upper pre-compression mold for the balance block. The two ends of the limiting groove for the connecting rod neck of the upper pre-compression mold for the pre-compression mold are connected to the two grooves for the upper pre-compression mold for the balance block. The lower pre-compression mold for the balance block includes: a main body for the lower pre-compression mold for the balance block, two grooves for the lower pre-compression mold for the balance block, and a limiting groove for the connecting rod neck of the lower pre-compression mold for the pre-compression mold. Both the grooves for the lower pre-compression mold for the balance block and the limiting groove for the connecting rod neck of the lower pre-compression mold for the pre-compression mold are arc-shaped grooves on the main body of the lower pre-compression mold for the balance block. The two ends of the limiting groove for the connecting rod neck of the lower pre-compression mold for the pre-compression mold are connected to the two grooves for the lower pre-compression mold for the balance block.

[0022] The beneficial effects of adopting the above-mentioned further solution are: on the one hand, it is conducive to forming the plastic space of the balance block and connecting rod neck after mold closing; on the other hand, the other planar areas on the upper mold body and the lower mold body of the balance block pre-pressing are conducive to extruding the core material of the bar stock to form flash. Attached Figure Description

[0023] Figure 1 A process flow diagram provided for an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a three-cylinder crankshaft provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the connecting rod neck preload upper mold structure provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the connecting rod neck preload lower mold structure provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the balance block pre-compression upper mold structure provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of the pre-compression lower mold structure of the balance block provided in an embodiment of the present invention.

[0024] The attached diagram lists the components represented by each number as follows: 1. Second connecting rod neck; 2. First connecting rod neck; 3. Third connecting rod neck; 4. First connecting rod neck balance block; 5. Third connecting rod neck balance block; 6. Connecting rod neck preload die; 7. Balance block preload die; 61. Connecting rod neck preload upper die; 62. Connecting rod neck preload lower die; 71. Balance block preload upper die; 72. Balance block preload lower die; 611. Connecting rod neck preload upper die body; 612. First connecting rod neck preload protrusion; 613. Third connecting rod neck preload protrusion; 621. Connecting rod neck preload base; 622. Connecting rod neck preload lower die body; 623. First connecting rod neck preload groove; 624. Third connecting rod neck preload groove; 625. Second connecting rod neck limiting groove; 711. Balance block preload upper die body; 712. Balance block preload upper die groove; 713. Preload upper die connecting rod neck limiting groove; 721. Balance block preload lower die body; 722. Balance block preload lower die groove; 723. Preload lower die connecting rod neck limiting groove. Detailed Implementation

[0025] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0026] like Figure 1 As shown, a forging method for a three-cylinder crankshaft includes: S1: Heat the bar stock to the working temperature; S2: Use a bending die to bend the second connecting rod neck 1; S3: Pre-compress the first connecting rod neck 2 and the third connecting rod neck 3 using the connecting rod neck pre-compression mold 6; S4: Use the balance block pre-compression mold 7 to pre-compress the first connecting rod neck balance block 4 and the third connecting rod neck balance block 5; S5: Use the final forging die to perform final forging on the product obtained in step S4; S6: Trim the edges of the product obtained in step S5.

[0027] It should be noted that the structure of the bending die in the technical solution of the present invention is the same as that in the prior art, so the structure of the bending die is not described in this application.

[0028] The beneficial effects of this invention are as follows: Compared with the existing technology of bending-pre-forging-final forging process, this invention uses pre-pressing to replace pre-forging, avoiding the one-time forming of the first connecting rod 2, the third connecting rod neck 3, the first connecting rod neck balance block 4, and the third connecting rod neck balance block 5. This reduces the amount of core material of the bar stock flowing to the surface of the connecting rod neck during the crankshaft forming process, thereby improving the overall quality and strength of the crankshaft and reducing the probability of application defects such as fatigue damage and connecting rod neck fracture on the surface of the connecting rod neck caused by crankshaft operation.

[0029] Preferably, in step S1, the operating temperature is 1055-1199℃.

[0030] The advantages of adopting the above preferred scheme are: it is beneficial to heat the bar stock to a molten state, making the bar stock fluid, thereby facilitating the plasticization of the bar stock.

[0031] Preferably, in step S3, when the connecting rod neck pre-compression mold 6 pre-compresses the first connecting rod neck 2 and the third connecting rod neck 3, the first connecting rod neck 2, the third connecting rod neck 3 and the second connecting rod neck 1 are pre-compressed in pairs with a 120-degree offset in the circumferential direction, and the second connecting rod neck 1 is disposed between the first connecting rod neck 2 and the third connecting rod neck 3.

[0032] The advantages of adopting the above preferred scheme are: the first connecting rod neck, the third connecting rod neck, and the second connecting rod neck are staggered by 120 degrees in the circumferential direction, which helps to ensure that the preload of the connecting rod neck meets the product manufacturing requirements.

[0033] Preferably, in step S3, the connecting rod neck pre-compression mold 6 presses down the first connecting rod neck 2 and the third connecting rod neck 3 to a position greater than the target depth, so that the core material of the bar stock is far away from the target depth position.

[0034] The advantages of adopting the above preferred scheme are: it helps to press the core material of the bar stock to a greater distance below the parting surface of the mold, thereby making the core material of the bar stock farther away from the connecting rod neck surface.

[0035] Preferably, in step S4, when the balance block pre-compression mold 7 pre-compresses the first connecting rod neck balance block 4 and the third connecting rod neck balance block 5, the core material of the bar stock located far from the target depth is squeezed by the balance block pre-compression mold 7 to form flash, so as to reduce the amount of the core material of the bar stock flowing to the surface of the first connecting rod neck 2 and the third connecting rod neck 3.

[0036] The beneficial effects of adopting the above-mentioned preferred solution are: the core material of the bar stock is extruded by the pre-compression die of the balance block to form flash, which helps to extrude the core material of the bar stock in the form of flash, thereby reducing the amount of core material of the bar stock flowing to the surface of the first connecting rod neck and the third connecting rod neck, and thus improving the overall quality and service strength of the crankshaft.

[0037] It should be noted that the structure of the final forging die in the technical solution of this invention is the same as that in the prior art, so the structure of the final forging die is not described in this application.

[0038] Preferably, in step S6, the flash of the core material containing the bar generated in step S4 is removed.

[0039] The advantages of adopting the above preferred scheme are: it is beneficial to obtain a product blank with a smaller amount of core material on the surface of the connecting rod neck by cutting the edges.

[0040] Preferred, such as Figures 3 to 6 As shown, the connecting rod neck preloading mold 6 consists of a connecting rod neck preloading upper mold 61 and a connecting rod neck preloading lower mold 62. After the connecting rod neck preloading upper mold 61 and the connecting rod neck preloading lower mold 62 are closed, they are adapted to the first connecting rod neck 2 and the third connecting rod neck 3. The balance block preloading mold 7 consists of a balance block preloading upper mold 71 and a balance block preloading lower mold 72. After the balance block preloading upper mold 71 and the balance block preloading lower mold 72 are closed, they are adapted to the first connecting rod neck 2 and the first connecting rod neck balance block 4 or to the third connecting rod neck 3 and the third connecting rod neck balance block 5.

[0041] The advantages of adopting the above-mentioned preferred solution are: the upper and lower pre-compression dies of the connecting rod neck are conducive to the initial compression of the first and third connecting rod necks, thereby facilitating the extrusion of the core material of the bar stock by the upper and lower pre-compression dies of the balance block to form flash, and the upper and lower pre-compression dies of the balance block are conducive to the shaping of the balance blocks of the first and third connecting rod necks.

[0042] Preferred, such as Figure 3 and Figure 4 As shown, the connecting rod neck preload upper die 61 includes: a connecting rod neck preload upper die body 611, a first connecting rod neck preload protrusion 612, and a third connecting rod neck preload protrusion 613. The first connecting rod neck preload protrusion 612 and the third connecting rod neck preload protrusion 613 are both arc-shaped protrusions provided on the connecting rod neck preload upper die body 611, and their height is greater than the target depth of the first connecting rod neck 2 and the third connecting rod neck 3. The connecting rod neck preload lower die 62 includes: a connecting rod neck preload base 621, a connecting rod neck preload lower die body 622, a first connecting rod neck preload groove 623, a third connecting rod neck preload groove 624, and a second connecting rod neck preload groove 624. The limiting groove 625 is provided on the connecting rod neck pre-compression lower mold body 622. The first connecting rod neck pre-compression groove 623, the third connecting rod neck pre-compression groove 624 and the second connecting rod neck limiting groove 625 are all arc-shaped grooves provided on the connecting rod neck pre-compression lower mold body 622. The first connecting rod neck pre-compression groove 623 and the third connecting rod neck pre-compression groove 624 correspond one-to-one with the first connecting rod neck pre-compression protrusion 612 and the third connecting rod neck pre-compression protrusion 613. The second connecting rod neck limiting groove 625 is adapted to the second connecting rod neck 1 obtained in step S2.

[0043] The advantages of adopting the above preferred solution are: the pre-compression protrusion of the first connecting rod neck and the pre-compression protrusion of the third connecting rod neck, as well as the pre-compression groove of the first connecting rod neck and the pre-compression groove of the third connecting rod neck, are conducive to forming a pressing area for the first connecting rod neck and the third connecting rod neck, while the limiting groove of the second connecting rod neck is conducive to providing a placement space for the already shaped second connecting rod neck when pressing down the first connecting rod neck and the third connecting rod neck.

[0044] Preferred, such as Figure 5 and Figure 6 As shown, the balance block pre-pressing upper die 71 includes: a balance block pre-pressing upper die body 711, two balance block pre-pressing upper die grooves 712, and a pre-pressing upper die connecting rod neck limiting groove 713. Both the balance block pre-pressing upper die grooves 712 and the pre-pressing upper die connecting rod neck limiting groove 713 are arc-shaped groove structures provided on the balance block pre-pressing upper die body 711. The two ends of the pre-pressing upper die connecting rod neck limiting groove 713 are connected one-to-one with the two balance block pre-pressing upper die grooves 712. The pre-compression mold 72 for the balance block includes: a pre-compression mold body 721, two pre-compression mold grooves 722, and a connecting rod neck limiting groove 723. The pre-compression mold grooves 722 and the connecting rod neck limiting groove 723 are arc-shaped groove structures provided on the pre-compression mold body 721. The two ends of the connecting rod neck limiting groove 723 are connected to the two pre-compression mold grooves 722.

[0045] The advantages of adopting the above-mentioned preferred solution are: on the one hand, it is beneficial to form the plastic space of the balance block and connecting rod neck after the mold is closed; on the other hand, the other planar areas on the balance block pre-pressing upper mold body 711 and balance block pre-pressing lower mold body 721 are beneficial to extruding the core material of the bar stock to form flash.

[0046] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0047] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0048] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0049] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0050] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0051] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A forging method for a three-cylinder crankshaft, characterized in that, include: S1: Heat the bar stock to the working temperature; S2: Use a bending die to bend the second connecting rod neck (1); S3: The first connecting rod neck (2) and the third connecting rod neck (3) are pre-compressed using the connecting rod neck pre-compressing mold (6); the connecting rod neck pre-compressing mold (6) presses the first connecting rod neck (2) and the third connecting rod neck (3) down to a position greater than the target depth, so that the core material of the bar stock is far away from the target depth position; S4: The first connecting rod neck balance block (4) and the third connecting rod neck balance block (5) are pre-compressed using the balance block pre-compressing mold (7); when the balance block pre-compressing mold (7) pre-compresses the first connecting rod neck balance block (4) and the third connecting rod neck balance block (5), the core material of the bar stock located far from the target depth position is squeezed by the balance block pre-compressing mold (7) to form flash, so as to reduce the amount of the core material of the bar stock flowing to the surface of the first connecting rod neck (2) and the third connecting rod neck (3); S5: Use the final forging die to perform final forging on the product obtained in step S4; S6: Trim the edges of the product obtained in step S5.

2. The forging method for a three-cylinder crankshaft according to claim 1, characterized in that, In step S1, the operating temperature is 1055-1199℃.

3. The forging method for a three-cylinder crankshaft according to claim 1, characterized in that, In step S3, when the connecting rod neck pre-compression mold (6) pre-compresses the first connecting rod neck (2) and the third connecting rod neck (3), the first connecting rod neck (2), the third connecting rod neck (3) and the second connecting rod neck (1) are pre-compressed in pairs with a circumferential offset of 120 degrees, and the second connecting rod neck (1) is located between the first connecting rod neck (2) and the third connecting rod neck (3).

4. The forging method for a three-cylinder crankshaft according to claim 1, characterized in that, In step S6, the flash of the core material containing the bar stock generated in step S4 is removed.

5. The forging method for a three-cylinder crankshaft according to claim 1, characterized in that, The connecting rod neck preloading mold (6) is composed of a connecting rod neck preloading upper mold (61) and a connecting rod neck preloading lower mold (62). After the connecting rod neck preloading upper mold (61) and the connecting rod neck preloading lower mold (62) are closed, they are adapted to the first connecting rod neck (2) and the third connecting rod neck (3). The balance block pre-compression mold (7) is composed of a balance block pre-compression upper mold (71) and a balance block pre-compression lower mold (72). After the balance block pre-compression upper mold (71) and the balance block pre-compression lower mold (72) are closed, they are adapted to the first connecting rod neck (2) and the first connecting rod neck balance block (4) or to the third connecting rod neck (3) and the third connecting rod neck balance block (5).

6. The forging method for a three-cylinder crankshaft according to claim 5, characterized in that, The connecting rod neck preload upper die (61) includes: a connecting rod neck preload upper die body (611), a first connecting rod neck preload protrusion (612) and a third connecting rod neck preload protrusion (613). The first connecting rod neck preload protrusion (612) and the third connecting rod neck preload protrusion (613) are both arc-shaped protrusions provided on the connecting rod neck preload upper die body (611), and their height is greater than the target depth of the first connecting rod neck (2) and the third connecting rod neck (3). The connecting rod neck preload lower die (62) includes: a connecting rod neck preload base (621), a connecting rod neck preload lower die body (622), a first connecting rod neck preload groove (623), a third connecting rod neck preload groove (624), and a second connecting rod neck limiting groove (625). The connecting rod neck preload lower die body (622) is disposed on the connecting rod neck preload base (621), and the first connecting rod neck preload groove (623) and the third connecting rod neck preload groove (624) are... Both the first and second connecting rod neck limiting grooves (625) are arc-shaped grooves provided on the connecting rod neck pre-compression lower mold body (622). The first connecting rod neck pre-compression groove (623) and the third connecting rod neck pre-compression groove (624) correspond one-to-one with the first connecting rod neck pre-compression protrusion (612) and the third connecting rod neck pre-compression protrusion (613). The second connecting rod neck limiting groove (625) is adapted to the second connecting rod neck (1) obtained in step S2.

7. The forging method for a three-cylinder crankshaft according to claim 5, characterized in that, The balance block pre-pressing upper mold (71) includes: a balance block pre-pressing upper mold body (711), two balance block pre-pressing upper mold grooves (712), and a pre-pressing upper mold connecting rod neck limiting groove (713). The balance block pre-pressing upper mold grooves (712) and the pre-pressing upper mold connecting rod neck limiting groove (713) are both arc-shaped groove structures provided on the balance block pre-pressing upper mold body (711). The two ends of the pre-pressing upper mold connecting rod neck limiting groove (713) are connected to the two balance block pre-pressing upper mold grooves (712) one by one. The pre-compression mold (72) for the balance block includes: a pre-compression mold body (721), two pre-compression mold grooves (722), and a connecting rod neck limiting groove (723). The pre-compression mold grooves (722) and the connecting rod neck limiting grooves (723) are arc-shaped groove structures provided on the pre-compression mold body (721). The two ends of the connecting rod neck limiting groove (723) are connected to the two pre-compression mold grooves (722).

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