A method for machining prefabricated fracture grooves for the expansion fracture process of castings with bearing holes

Abstract

This application belongs to the field of expansion fracture technology and discloses a method for processing a pre-fabricated fracture groove for expansion fracture of castings with bearing holes. The method includes the following steps: processing chills according to the technical parameters of the casting with bearing holes; processing a core according to the bearing hole dimensions of the casting; installing the chills into the core, and positioning the core at the bearing hole position in the casting mold; pouring molten cast iron into the casting mold, and allowing it to cool and solidify naturally to form a pre-fabricated fracture groove. By installing and fixing the chills and core into the casting mold for casting, sequential solidification and asynchronous cooling are achieved under the action of the core and chills. As the cooling process proceeds, tensile stress is generated at the last cooled part, ultimately forming a pre-fabricated fracture groove when the inner wall of the bearing hole of the casting solidifies at this point. The pre-fabricated fracture groove is completed simultaneously during part casting, simplifying the production process, requiring only the processing of chills and cores, and reducing production costs.

Description

Technical Field

[0001] This invention relates to the field of expansion fracture technology, and in particular to a method for processing prefabricated fracture grooves for expansion fracture of castings with bearing holes. Background Technology

[0002] For cast parts with bearing holes, such as engine connecting rods, engine housings, and gearbox housings, assembly requirements necessitate separating the bearing holes into two parts: a cover and a body. Furthermore, the roundness of the bearing hole formed by the assembled cover and body must be of high precision, and the mating surface of the cover and body must be able to withstand lateral shear forces.

[0003] In existing technologies, most parts of this type employ a fracture expansion process. This process utilizes controlled brittle fracture to achieve controlled separation of the structure at a predetermined location. After natural fracture separation, the brittle fracture surface exhibits extremely high meshing accuracy, enabling the bearing hole to achieve extremely high roundness accuracy after the cover and body are assembled. This allows for high-precision assembly of the bearing hole and shaft, and the interlocking mating surfaces meet the requirement of the cover and body mating surfaces having a certain shear force resistance. To ensure low-stress brittle fracture of the bearing hole at the predetermined location during the fracture expansion process, a prestressed groove needs to be machined at the pre-fracture position inside the bearing hole; this prestressed groove is called a pre-fractured groove. However, currently, the pre-fractured groove in the fracture expansion process in the industry is basically processed using laser machining, resulting in high production costs. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for machining a prefabricated fracture groove in the expansion fracture process of castings with bearing holes.

[0005] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a method for processing a pre-fabricated fracture groove for the expansion fracture process of a casting with bearing holes, comprising the following steps:

[0006] S1: Machining chills according to the technical parameters of castings with bearing holes;

[0007] S2: Machining the core according to the bearing hole dimensions of the casting with bearing holes;

[0008] S3: Install the chill into the core, and install the core into the bearing hole position in the casting mold and position it.

[0009] S4: Pour the molten cast iron into a casting mold, and allow it to cool and solidify naturally to form a prefabricated pyrolysis tank.

[0010] By adopting the above technical solution, chills and cores are machined according to the technical parameters of the casting with bearing holes. Then, the chills and cores are installed and fixed into the casting mold for casting. During solidification, the bearing hole portion of the casting achieves sequential solidification and asynchronous cooling under the action of the core and chills. That is, the part of the bearing hole in contact with the chills solidifies first, and the part not in contact with the chills solidifies later, resulting in asynchronous cooling. As the cooling process continues, tensile stress is generated in the last cooled part, ultimately causing casting cracks to form on the inner wall of the bearing hole when it solidifies. These casting cracks are the pre-formed cracking grooves. The pre-formed cracking grooves formed in this way are completed simultaneously during part casting, simplifying the production process. Only the chills and cores need to be machined, reducing production costs.

[0011] Furthermore, the chill includes a central shaft, on which two fan-shaped iron blocks are symmetrically arranged, with V-shaped grooves formed on the adjacent sides of the two fan-shaped iron blocks.

[0012] By adopting the above technical solution, the chill is set as two symmetrically arranged fan-shaped iron blocks, so that the overall size of the chill is smaller than the size of the bearing hole of the casting with bearing hole, thereby causing the casting with bearing hole to solidify sequentially and cool asynchronously during cooling.

[0013] Furthermore, the thickness of the fan-shaped iron block is consistent with the depth of the bearing hole in the casting with bearing hole.

[0014] By adopting the above technical solution, the thickness of the fan-shaped iron block is set to be consistent with the depth of the bearing hole in the casting with bearing hole, ensuring that the bearing hole in the casting with bearing hole solidifies synchronously in its depth direction.

[0015] Furthermore, the core is a cylinder with a radius consistent with the outer ring radius of the fan-shaped iron block, and a hollow clamping cavity is provided inside for placing chills. A V-shaped protrusion is provided on the outer wall of the core corresponding to the middle of the V-shaped groove opening.

[0016] By adopting the above technical solution, a hollow cavity is set inside the core to facilitate the contact and fit between the chill and the core. A V-shaped ridge protrudes outward on the outer wall of the core corresponding to the V-shaped groove opening of the chill. This allows the core outer wall portion corresponding to the V-shaped groove of the chill to gradually cool from both sides towards the V-shaped ridge position when the casting with bearing holes cools at different times. This position is the last place where the solidification and shrinkage of the inner wall of the bearing hole in the casting with bearing holes occurs. Under the constraint of the positions on both sides where the cooling and shrinkage have been completed, tensile stress is generated at the convex end of the V-shaped ridge, which ultimately causes the inner wall of the bearing hole in the casting with bearing holes to form casting cracks when it solidifies at this point.

[0017] Furthermore, the included angle between the two sides of the V-shaped protrusion is 60°, and the distance from its protrusion to the outer wall of the core is 1mm.

[0018] By adopting the above technical solution, the V-shaped protrusion is set with an included angle of 60° and a thickness of 1mm, which facilitates the generation of macroscopic grooves at this position to cause stress concentration effect. This is used to intensify the tensile stress generated at the protrusion end of the V-shaped protrusion during the solidification of the casting with bearing hole, thereby causing casting cracks at the protrusion end of the V-shaped protrusion.

[0019] Furthermore, the protruding end of the V-shaped convex strip and the connection end with the outer wall of the core are both rounded.

[0020] By adopting the above technical solution, the protruding end of the V-shaped convex strip and the connection end with the outer wall of the core are set as arc transitions to avoid sharp protrusions forming in the above-mentioned parts when the casting with bearing hole solidifies.

[0021] Furthermore, in step S3, the core is positioned such that the surfaces of the two V-shaped protrusions on the core are perpendicular to the bolt holes of the casting with bearing holes.

[0022] By adopting the above technical solution, the surfaces of the two V-shaped protrusions on the core are perpendicular to the bolt holes of the casting with bearing holes, thereby making the prefabricated cracking grooves on both sides located in the middle of the bearing holes.

[0023] In summary, the present invention has the following beneficial effects:

[0024] 1. In this application, chills and cores are machined according to the technical parameters of the casting with bearing holes. The chills and cores are then installed and fixed into the casting mold for casting. During solidification, the bearing hole portion of the casting with bearing holes undergoes sequential solidification and asynchronous cooling under the action of the core and chills. Specifically, the portion of the bearing hole in contact with the chills solidifies first, while the portion not in contact with the chills solidifies later, resulting in asynchronous cooling. As the cooling process continues, tensile stress is generated in the last cooled portion, ultimately causing a casting crack to form on the inner wall of the bearing hole when it solidifies. This casting crack is the pre-formed cracking groove. This method of forming the pre-formed cracking groove is completed simultaneously during part casting, simplifying the production process. Only the chills and cores need to be machined, reducing production costs.

[0025] 2. In this application, a V-shaped protrusion is provided on the outer wall of the middle part of the V-shaped groove opening of the core, so that when the casting with bearing hole is cooled in different stages, the outer wall of the core corresponding to the V-shaped groove of the chill gradually cools from both sides to the middle V-shaped protrusion position. This position is the last place where the solidification shrinkage of the inner wall of the bearing hole of the casting with bearing hole occurs. Under the constraint of the positions on both sides that have completed cooling and shrinkage, tensile stress is generated at the protruding end of the V-shaped protrusion, which ultimately causes the inner wall of the bearing hole of the casting with bearing hole to form a casting crack when it solidifies at this point. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the overall structure of the core with chills according to an embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram of the overall structure of the chill in an embodiment of the present invention;

[0028] Figure 3 This is a cross-sectional structural diagram of the casting process in an embodiment of the present invention.

[0029] In the diagram: 10. Chill; 11. Central shaft; 12. Fan-shaped annular iron block; 13. V-groove; 20. Core; 21. V-shaped protrusion. Detailed Implementation

[0030] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0031] like Figure 1-3 As shown in the embodiment of this application, a method for processing a prefabricated fracture groove for the expansion fracture process of a casting with bearing holes is disclosed, including a chill 10 and a core 20. The chill 10 includes a central shaft 11 and two fan-shaped annular iron blocks 12. The two fan-shaped annular iron blocks 12 are symmetrically arranged on the shaft of the central shaft 11, and the inner rings of the two fan-shaped annular iron blocks 12 are in contact with the central shaft 11 to ensure good thermal conductivity. V-shaped grooves 13 are formed on the adjacent sides of the two fan-shaped annular iron blocks 12. The V-shaped grooves 13 are used to cooperate with the core 20, so that the bearing hole part of the casting with bearing holes contacts the chill 10 and the part contacts the core 20, thereby producing the effect of sequential solidification and asynchronous cooling. The core 20 is a cylindrical sand core with a radius consistent with the outer ring radius of the fan-shaped annular iron blocks 12 and a length consistent with the length of the central shaft 11. A hollow cavity is provided inside for placing the chill 10, which facilitates the placement of the chill 10 into the core 20 and ensures the contact between the chill 10 and the core 20. A V-shaped protrusion 21 is provided on the outer wall of the V-shaped groove 13 opening corresponding to the core 20, protruding outward. The V-shaped protrusion 21 should not be too large, the included angle between its two sides is 60°, and the distance from its protrusion point to the outer wall of the core 20 is 1mm. During processing, the protrusion point end of the V-shaped protrusion 21 and the connection end with the outer wall of the core 20 are both rounded.

[0032] A method for machining a pre-fabricated fracture groove for the expansion fracture process of a casting with a bearing hole includes the following steps:

[0033] S1: The chill 10 is machined according to the technical parameters of the casting with bearing holes. The outer radius of the fan-shaped annular iron block 12 of the chill 10 is consistent with the radius of the bearing hole of the casting with bearing holes to ensure that the bearing hole part of the casting with bearing holes contacts the chill 10 during casting; the thickness of the fan-shaped annular iron block 12 is consistent with the depth of the bearing hole of the casting with bearing holes to ensure that the bearing hole of the casting with bearing holes solidifies synchronously in its depth direction. When the casting with bearing holes has multiple bearing holes, multiple sets of fan-shaped annular iron blocks 12 can be arranged according to the specific situation to meet the machining requirements of multiple bearing holes.

[0034] S2: Machining core 20 according to the bearing hole dimensions of the casting with bearing hole. The radius of core 20 is consistent with the radius of the bearing hole in the casting with bearing hole, and it is used to place at the bearing hole position in the casting mold for forming the inner cavity of the bearing hole.

[0035] S3: Install the chill 10 into the core 20 to obtain the core 20 with the chill 10 inside. Then, install the core 20 with the chill 10 inside into the bearing hole position in the casting model and position it. During positioning, align the two V-shaped protrusions 21 on the core 20 with the bolt holes of the casting with bearing holes, and align the two fan-shaped iron blocks 12 on the chill 10 with the bearing hole positions, thereby positioning the core 20 in both the circumferential and axial directions. This ensures that the two V-shaped protrusions 21 are located in the middle of the bearing holes of the casting with bearing holes. The resulting pre-fabricated fracture groove, under the expansion fracture process, forms a fracture surface perpendicular to the bolt holes of the casting with bearing holes, thus ensuring the roundness accuracy of the cover and body and the shear force requirements of the mating surface after installation.

[0036] S4: The molten cast iron is poured into the casting mold and allowed to cool and solidify naturally to form a pre-fabricated cracking groove. Under the action of the core 20 and the chill 10, the upper and lower parts of the bearing hole of the casting with bearing hole are in direct contact with the fan-shaped iron block 12, and the left and right parts are in contact with the sand core part of the core 20, thus resulting in sequential solidification and asynchronous cooling during cooling and solidification. In other words, the bearing hole of the casting with bearing hole solidifies first at the part that contacts the fan-shaped iron block 12, and then solidifies later at the part that does not contact the fan-shaped iron block 12. At the part of the casting with bearing hole that does not contact the fan-shaped iron block 12, that is, at the sand core position of the core 20 corresponding to the V-groove 13 of the chill 10, the upper and lower sides are close to the fan-shaped iron block 12, and the middle part is far away from the fan-shaped iron block 12. Solidification occurs gradually from the sides to the middle. When solidification reaches the middle position, this position is the last place where the solidification shrinkage of the inner wall of the bearing hole of the casting with bearing hole occurs. This results in asynchronous cooling at this position. Due to the shrinkage compensation effect of the later cooled part on the earlier cooled part, shrinkage cavities or shrinkage defects will be generated at the last cooled position. Furthermore, due to the asynchronous shrinkage caused by asynchronous cooling, tensile stress will be generated at the last cooled position. Furthermore, a V-shaped protrusion 21 is provided on the outer wall of the V-shaped groove 13 opening corresponding to the core 20, protruding outwards. This V-shaped protrusion 21 is positioned at the final solidification shrinkage location of the bearing hole in the casting, creating a macro-groove that induces stress concentration. This intensifies the tensile stress generated at the protruding end of the V-shaped protrusion 21 during solidification, thus stretching the material in that area. The combined effect of defects, tensile stress, and stress concentration generates a casting crack at the final solidification shrinkage location. This crack propagates perpendicular to the tensile stress direction, the cooling gradient direction, and the desired pre-formed cracking groove, thus forming a pre-formed cracking groove. This pre-formed cracking groove is created simultaneously during the casting of the bearing hole casting, simplifying the production process. It eliminates the need for pre-casting followed by laser processing; only the chill 10 and core 20 need to be processed. Furthermore, the chill 10 and core 20 can be reused for the same type of bearing hole casting, reducing production costs.

[0037] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for machining a pre-fabricated fracture groove in the expansion fracture process of a casting with a bearing hole, characterized in that, Includes the following steps: S1: Machining chills (10) according to the technical parameters of the casting with bearing holes; S2: Machining a core (20) according to the bearing hole size of the casting with bearing hole; S3: Install the chill (10) into the core (20), and install the core (20) into the bearing hole position in the casting model and position it; S4: Pour the molten cast iron into a casting mold, and allow it to cool and solidify naturally to form a prefabricated pyrolysis tank. The chill (10) includes a central shaft (11), on which two fan-shaped annular iron blocks (12) are symmetrically arranged, and the adjacent sides of the two fan-shaped annular iron blocks (12) form a V-shaped groove (13). The core (20) is a cylinder with a radius consistent with the outer ring radius of the fan-shaped iron block (12). It has a hollow cavity for placing chills (10). A V-shaped protrusion (21) is provided on the outer wall of the core (20) corresponding to the middle of the V-shaped groove (13) opening.

2. The method for machining a pre-fabricated fracture groove for the expansion fracture process of a casting with bearing holes according to claim 1, characterized in that: The thickness of the fan-shaped iron block (12) is consistent with the depth of the bearing hole of the casting with bearing hole.

3. The method for machining a pre-fabricated fracture groove for the expansion fracture process of a casting with bearing holes according to claim 1, characterized in that: The included angle between the two sides of the V-shaped protrusion (21) is 60°, and the distance from its protrusion to the outer wall of the core (20) is 1mm.

4. The method for machining a pre-fabricated fracture groove for the expansion fracture process of a casting with bearing holes according to claim 3, characterized in that: The protruding end of the V-shaped protrusion (21) and the connection end with the outer wall of the core (20) are both rounded.

5. The method for machining a pre-fabricated fracture groove for the expansion fracture process of a casting with bearing holes according to claim 4, characterized in that: In step S3, the core (20) is positioned such that the surfaces of the two V-shaped protrusions (21) on the core (20) are perpendicular to the bolt holes of the casting with bearing holes.

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