Mold structure and casting method for castings

Abstract

To provide a mold structure and a casting method which can manufacture a casting including a portion with high strength and a portion with a thin wall while suppressing both of breakage of a sand mold and occurrence of burr.SOLUTION: In a mold structure which comprises a sand mold and a metal mold sectioning a cavity between itself and the sand mold, and casts an article by introducing a molten metal into the cavity, a protruding part protruding toward a metal mold-side mating face is provided on an end part at one side in a second direction of a sand mold-side mating face of the sand mold opposing, in a first direction, to the metal mold-side mating face which is a part of an outer peripheral surface of the metal mold, and a separation distance in the first direction between the protruding part and the metal mold-side mating face is set to be smaller than a separation distance in the first direction between a portion other than the protruding part of the sand mold-side mating face and the metal mold-side mating face.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a mold structure and a method for casting a casting.

Background Art

[0002] Conventionally, in the production of a cylinder head of a vehicle engine or the like, consideration has been given to using a mold apparatus that combines a metal mold and a sand mold. For example, in Patent Document 1, a metal mold is used for a lower mold that forms the lower surface of a cylinder head including the ceiling surface of a combustion chamber, and a sand mold is used above, and molten metal is introduced into a cavity partitioned between these lower mold and upper mold to cast the cylinder head. In this apparatus, the molten metal forming the lower surface of the cylinder head can be rapidly cooled by the metal mold to realize a high-strength lower surface of the cylinder head, and the temperature drop of the molten metal forming each part of the cylinder head other than the lower surface can be suppressed to achieve thinning.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a mold is configured by combining a metal mold and a sand mold as in Patent Document 1, while high strength and thinning can be achieved as described above, there is a risk that the sand mold may break due to the different thermal expansion amounts of the metal mold and the sand mold. Specifically, depending on the shape and dimensions of the metal mold and the sand mold, when high-temperature molten metal is introduced into the cavity partitioned by the metal mold and the sand mold, the thermal expansion amount of the metal mold may become excessive with respect to the thermal expansion amount of the sand mold, and the metal mold may collide with the opposing sand mold and break it. Here, as a configuration for avoiding the collision between the metal mold and the sand mold, it is conceivable to increase the gap between them. However, if the gap is simply increased, excessive molten metal will easily enter this gap, making it easy to generate burrs.

[0005] This invention has been made in view of the above circumstances, and aims to provide a mold structure and casting method that can produce castings including high-strength and thin-walled parts while suppressing both cracking and burr formation in the sand mold. [Means for solving the problem]

[0006] To solve the above problems, the present invention provides a mold structure for casting an article by introducing molten metal into the cavity, comprising a sand mold and a mold that partitions a cavity between the sand mold and the mold, wherein the sand mold comprises a mold-side mating surface which is a part of the outer circumferential surface of the mold and a sand mold-side mating surface which faces a predetermined first direction, the sand mold-side mating surface and the mold-side mating surface are arranged to communicate with the cavity and partition a gap extending from the cavity in a second direction intersecting the first direction, and with respect to the second direction, the cavity side is one side and the opposite side is the other side. With respect to the first direction, the side of the mold mating surface is considered one side and the opposite side is considered the other side. When this happens, the end of the sand mold side mating surface on one side in the second direction It exhibits a stepped shape such that one side of the second direction is located closer to one side of the first direction. , The protruding portion, which is one side of the stepped portion of the sand mold mating surface in the second direction, is relative to the other side of the stepped portion in the second direction. Protruding toward the mold side mating surface It takes on a shape The separation distance in the first direction between the protruding portion and the mold-side mating surface is set to a dimension smaller than the separation distance in the first direction between the portion of the sand mold-side mating surface excluding the protruding portion and the mold-side mating surface.

[0007] With this configuration, molten metal is introduced into the cavity formed by the sand mold and the die to produce a casting, thereby achieving high strength and thin walls for the casting. Moreover, in this configuration, a projection is provided at the cavity-side end of the sand mold mating surface, which faces the die-side mating surface (a part of the outer surface of the die) with a gap between them, and the projection is set to the smallest of the available distances between the sand mold mating surface and the die-side mating surface. As a result, both cracking of the sand mold and the generation of burrs can be suppressed.

[0008] Specifically, by reducing the distance in the first direction between the protrusion provided at the end of the cavity and the mating surface on the mold side, the molten metal introduced into the cavity is prevented from flowing into the gap between the sand mold mating surface and the mold mating surface. This suppresses the generation of burrs caused by molten metal entering the gap. Moreover, the protrusion has a shape that protrudes toward the mating surface on the mold side. Therefore, although the mold expands due to the small distance, it comes into contact with the protrusion, and this contact can cause only the protrusion or the vicinity of the protrusion to collapse, preventing cracks from occurring in the entire sand mold.

[0009] In the above configuration, preferably ,before The side mating surface of the sand mold is the protruding department The mold side mating surface comprises a first extension on the mold side extending to the other side in the second direction, and a second extension on the mold side extending from the other end of the first extension on the mold side in the second direction to the other side in the first direction, wherein the mold side mating surface comprises a first extension on the mold side extending along the second direction opposite to the protrusion and the first extension on the mold side, and a second extension on the mold side extending from the other end of the first extension on the mold side in the second direction to the other side in the first direction (Claim 2).

[0010] With this configuration, the sand generated by the collapse of the protrusions can be stored in the space partitioned by the first extension on the sand mold side, the first extension on the mold side, and the second extension on the mold side, preventing molten metal from flowing downstream from these spaces, i.e., into the gap between the second extension on the sand mold side and the second extension on the mold side. Therefore, the generation of burrs can be prevented more reliably.

[0011] In the above configuration, preferably, the sand mold side mating surface includes a sand mold side third extension extending from the other end of the sand mold side second extension in the first direction to the other side in the second direction, and the mold side mating surface includes a mold side third extension extending from the other end of the mold side second extension in the first direction to the other side in the second direction, and the distance between the sand mold side third extension and the mold side third extension in the first direction is set to be smaller than the distance between the sand mold side first extension and the mold side first extension in the first direction (Claim 3).

[0012] With this configuration, the gap between the sand mold mating surface and the mold mating surface is a passage that bends at least twice, and the distance between the third extension on the sand mold side and the third extension on the mold side is made relatively small, thereby reducing the amount of molten metal passing through the gap. In addition, by making the distance between the first extension on the sand mold side and the first extension on the mold side relatively large, sand generated by the collapse of the protrusion can be stored between them, while preventing pressure from being applied from the mold to the sand mold through the stored sand.

[0013] In the above configuration, preferably, the protruding portion is configured such that its strength is reduced when molten metal is introduced into the cavity (Claim 4).

[0014] With this configuration, when molten metal is introduced into the cavity and the mold expands due to heat, the protrusions can be more reliably destroyed, and both cracking and burr formation in the sand mold can be reliably prevented.

[0015] A specific configuration in which the strength of the protrusion is reduced when molten metal is introduced into the cavity is such that the thickness of the protrusion in the second direction is such that the minimum temperature of the protrusion is equal to or greater than the temperature at which the strength of the sand mold is reduced when molten metal is introduced into the cavity (Claim 5).

[0016] The present invention also provides a casting method including a mold assembly step of combining the sand mold and the metal mold so as to partition the cavity, a pouring step of pouring molten metal into the cavity to form a casting corresponding to the cavity, a mold opening step of separating the sand mold and the metal mold with the casting left on the sand mold side, and a casting removal step of breaking the sand mold to take out the casting (Claim 6).

[0017] According to this method, as described above, it is possible to manufacture a thin-walled casting while suppressing both the cracking of the sand mold and the generation of burrs.

Effects of the Invention

[0018] As described above, according to the mold structure and casting method of the present invention, it is possible to manufacture a casting including a high-strength portion and a thin-walled portion while suppressing both the cracking of the sand mold and the generation of burrs.

Brief Description of the Drawings

[0019] [Figure 1] It is a top view showing a schematic configuration of a casting apparatus. [Figure 2] It is a sectional view taken along line II-II of FIG. 1. [Figure 3] It is a sectional view taken along line III-III of FIG. 1. [Figure 4] It is a view showing an enlarged IV portion of FIG. 3. [Figure 5] It is a graph showing the relationship between the temperature and strength of the sand mold. [Figure 6] It is a graph showing the relationship between the thickness and temperature of the sand mold. [Figure 7] It is a flowchart showing the procedure for casting a cylinder head. [Figure 8] It is a view corresponding to FIG. 4, where (a) is a view before the metal mold thermally expands, and (b) is a view after the metal mold thermally expands.

Modes for Carrying Out the Invention

[0020] (1) Overall Configuration of the Mold Figure 1 is a schematic top view showing a mold 1 to which a mold structure according to an embodiment of the present invention is applied. Figure 2 is a cross-sectional view taken along line II-II of Figure 1, and Figure 3 is a cross-sectional view taken along line III-III of Figure 1.

[0021] The mold 1 according to this embodiment is used for casting the cylinder head E of an engine. More specifically, the mold 1 is used for casting the cylinder head E of a straight-six reciprocating engine in which six cylinders are arranged in a row. The bottom surface of the cylinder head E has a ceiling surface E2 of the combustion chamber E1, and the combustion chamber E1 of the engine is partitioned by the cylinder head E, a separately manufactured cylinder block, and a piston. The cylinder head E also has an intake port E3, an exhaust port E4, and a water jacket E5 formed therein. In the following description of the mold 1, the vertical direction in Figure 2, which is the direction in which the cylinder head E to be cast is aligned when connected to the cylinder block, will be referred to as the vertical direction, with the cylinder head E side being the top and the opposite side being the bottom. The left-right direction in Figure 3, which is the direction in which the combustion chamber E1 is aligned, will be referred to as the left-right direction. The direction perpendicular to the vertical direction and the left-right direction will be referred to as the engine width direction.

[0022] The mold 1 comprises a sand mold 10 and a metal mold 30.

[0023] The sand mold 10 contains multiple cores that are themselves sand molds, and these multiple cores 11 to 21 are combined to form a single sand mold 10 as a whole. Specifically, the sand mold 10 has a frame-shaped base core 11 disposed at the lower end of the sand mold 10, an upper core 21 disposed at the upper end of the sand mold 10, an intake port core 12 for forming the intake port E3, an exhaust port core 13 for forming the exhaust port E4, a water jacket core 14 for forming the water jacket E5, and so on. The sand mold 10, that is, each core 11 to 21, is made of sand that has been solidified into a predetermined shape by resin.

[0024] The mold 30 is a metal component for forming the bottom surface (lower surface) of the cylinder head E, including the ceiling surface E2 of the combustion chamber E1. The mold 30 has a roughly rectangular parallelepiped shape that extends in the left-right direction. The upper surface of the mold 30 is provided with a plurality of protrusions 31 that are arranged at equal intervals in the left-right direction and project upward. The ceiling surface E2 of the combustion chamber E1 is formed by the upper surfaces of these protrusions 31. As described above, in this embodiment, the cylinder head E of a 6-cylinder engine is cast using the mold 1, and the mold 30 has six protrusions 31.

[0025] Each core 11-21 and the mold 30 are combined such that the cavity C into which the molten metal is introduced and which forms the cylinder head E is partitioned between each core 11-21 and the mold 30, thereby forming a single mold 1. As described above, the ceiling surface E2 of the combustion chamber E1 is formed on the bottom surface, or lower surface, of the cylinder head E. Therefore, as shown in Figure 3, the mold 30 that forms the ceiling surface E2 is positioned at the lower end of the mold 1. Reference numeral 50 in Figure 3, etc., indicates a base that supports the mold 1.

[0026] The upper core 21, which is positioned at the upper end of the sand mold 10, that is, at the upper end of the mold 1, is provided with a sprue 21A that communicates with the cavity C and allows molten metal to be introduced into the cavity C. Molten metal is introduced into the cavity C through this sprue 21A. In this embodiment, an aluminum cylinder head E is cast using the mold 1, and molten aluminum alloy is introduced into the cavity C.

[0027] (2) Detailed structure of the mold Next, the characteristic structure of the present invention among the structure of mold 1 will be described. In the following description, the left-right direction corresponds to the "first direction" in the claim, and in that direction, "left side" corresponds to the "mold side mating surface side" and "one side" in the claim, and "right side" corresponds to the "other side" in the claim. Also, the up-down direction corresponds to the "second direction" in the claim, and in that direction, "upper side" corresponds to the "cavity side" and "one side" in the claim, and "lower side" corresponds to the "other side".

[0028] The base core 11 has inner circumferential surfaces 70 that are opposite to both left and right sides 50 of the mold 30 in the left-right direction. In other words, the base core 11 and the mold 30 are assembled such that the inner circumferential surfaces 70 of the base core 11 and the outer circumferential surfaces 50 of the mold 30 are opposite to each other in the left-right direction. Specifically, as described above, the base core 11 has a frame shape, and a fitting portion 11A that fits with the mold 30 is defined in the center of the base core 11. The mold 30 is inserted into the center of the base core 11 from below and assembled to fit with it. Thus, when the mold 1 is completed, a portion of the inner circumferential surface 70 of the base core 11 will be opposite to both left and right sides 50 of the mold 30 in the left-right direction.

[0029] Figure 4 is an enlarged view of the area shown in IV of Figure 3, and shows an enlarged view of the area around the right outer surface 51 of the mold 30 and the inner circumferential surface 70 of the base core 11 that is opposite it. Hereafter, the right outer surface 51 of the mold 30 will be referred to as the mold-side mating surface 51, and the inner circumferential surface 71 of the base core 11 that is opposite it will be referred to as the sand mold-side mating surface 71.

[0030] As shown in Figure 4, the mold-side mating surface 51 and the sand mold-side mating surface 71 are spaced apart in the left-right direction (before molten metal is introduced), and a gap X is defined between them. This gap X communicates with the cavity C at its upper end and extends downward from the cavity C.

[0031] The upper end of the sand mold side mating surface 71 has a stepped shape, with the upper part being positioned further to the left, and the upper end of the sand mold side mating surface 71 is provided with a projection 72 that protrudes to the left, that is, toward the mold side mating surface 51. Furthermore, the sand mold side mating surface 71 extends downward from the base end of the projection 72 toward the sand mold side First extension part 73 It has.

[0032] The sand mold side mating surface 71 also exhibits a stepped shape in the portion extending from the sand mold side first extension portion 73, and has a sand mold side second extension portion 74 extending to the right from the lower end of the sand mold side first extension portion 73, a sand mold side third extension portion 75 extending downward from the right end of the sand mold side second extension portion 74, and a sand mold side fourth extension portion 76 extending to the right from the lower end of the sand mold side third extension portion 75. The lower end of the sand mold side first extension portion 73 corresponds to the "other end in the second direction of the sand mold side first extension portion" in the claim, and the right end of the sand mold side second extension portion 74 corresponds to the "other end in the first direction of the sand mold side second extension portion." do.

[0033] Similar to the sand mold side mating surface 71, the mold side mating surface 51 also has a stepped shape. Specifically, the mold side mating surface 51 has a mold side first extension 52 extending downward from its upper end, a mold side second extension 53 extending to the right from the lower end of the mold side first extension 52, a mold side third extension 54 extending downward from the right end of the mold side second extension 53, and a mold side fourth extension 55 extending to the right from the lower end of the mold side third extension 54. The lower end of the mold side first extension 52 corresponds to the "other end in the second direction of the mold side first extension" in the claim, and the right end of the mold side second extension 53 corresponds to the "other end in the first direction of the mold side second extension".

[0034] The mold-side first extension 52 faces the protruding portion 72 and the sand-type first extension 73 in the left-right direction. Here, the mold-side first extension 52 extends almost straight in the vertical direction. In contrast, the protruding portion 72 protrudes to the left relative to the sand-type first extension 73. Thus, the left-right separation distance R1 between the mold-side first extension 52, i.e., the mold-side mating surface 51, and the protruding portion 72 is set to be smaller than the left-right separation distance R2 between the mold-side first extension 52, i.e., the mold-side mating surface 51, and the sand-type first extension 73. Hereafter, the left-right separation distance R1 between the mold-side first extension 52 and the protruding portion 72 will be referred to as the first separation distance R1, and the left-right separation distance R2 between the mold-side first extension 52 and the sand-type first extension 73 will be referred to as the second separation distance R2.

[0035] The first separation distance R1 is set to a dimension smaller than the reference distance R0, and the second separation distance R2 is set to a dimension approximately twice the reference distance R0. The reference distance is the amount of thermal expansion of the mold 30 in the rightward direction when molten metal is introduced into the cavity C. Specifically, when molten metal is introduced into the cavity C, the mold 30 expands thermally. As described above, the mold 30 has a roughly rectangular parallelepiped shape that is long in the left-right direction. Therefore, the mold 30 expands significantly in the left-right direction. The reference distance R0 is half the amount of thermal expansion of the mold 30 in the left-right direction (the difference in the left-right dimensions of the mold 30 after thermal expansion and the mold 30 before thermal expansion).

[0036] The mold-side second extension 53 extends to the right, passing below the protrusion 72 and along the sand-type second extension 74. The mold-side second extension 53 and the sand-type second extension 74 are slightly separated in the vertical direction. For example, the vertical separation distance between these second extensions 53 and 74 is smaller than the first separation distance R1. The horizontal dimension of the mold-side second extension 53 is sufficiently larger than the second separation distance R2, and the horizontal separation distance R3 (hereinafter referred to as the third separation distance R3 as appropriate) between the mold-side first extension 52 and the sand-type third extension 75, which face each other horizontally through the gap between the second extensions 53 and 74, is sufficiently larger than the second separation distance R2.

[0037] The mold-side third extension 54 extends vertically at a position spaced to the left of the sand-type third extension 75, and faces the sand-type third extension 75 in the left-right direction. The left-right separation distance R4 (hereinafter referred to as the fourth separation distance R4 as appropriate) between the mold-side third extension 54 and the sand-type third extension 75 is set to be greater than the first separation distance R1 and smaller than the second separation distance R2. The fourth separation distance R4 is set to be slightly larger than the above-mentioned reference distance R0.

[0038] The mold-side fourth extension 55 extends horizontally along the sand-type fourth extension 76. The mold-side fourth extension 55 and the sand-type fourth extension 76 are slightly separated vertically. For example, the vertical separation distance between these fourth extensions 55 and 76 is the same as the vertical separation distance between the second extensions 53 and 74. The mold-side fourth extension 55 is interrupted midway along the sand-type fourth extension 76, and the gap X opens to the outside at the right end of the mold-side fourth extension 55.

[0039] Here, as described above, the first separation distance R1 is smaller than any of the second separation distance R2, the third separation distance R3, and the fourth separation distance R4. The first separation distance R1, that is, the lateral separation distance R1 between the mold-side first extension 52 and the projection 72, is smaller than the lateral separation distance between the sand mold-side mating surface 71 excluding the projection 72 and the mold-side mating surface 51.

[0040] The protruding portion 72 is the part that collides with the mold 30 and collapses when molten metal is introduced into the cavity C, as will be described later. The protruding portion 72 is prone to collapse because it protrudes towards the mold 30, but in this embodiment, the thickness (vertical dimension) d1 of the protruding portion 72 is further set to a dimension that makes it prone to collapse.

[0041] This will be explained in detail using Figures 5 and 6. Figure 5 is a graph showing the relationship between the temperature of a test sand mold formed with the same composition as the sand mold 10 used in casting mold 1 and the strength (Young's modulus) of the test sand mold. Figure 6 is a graph showing the relationship between the thickness of the sand mold and the minimum temperature of the sand mold. Specifically, it is a graph showing the relationship between the thickness of the test sand mold in which a cavity has been formed and the minimum temperature of the test sand mold immediately after the introduction of molten metal into the cavity is completed.

[0042] As shown in Figure 5, the strength of a sand mold decreases as its temperature increases. Furthermore, the strength of a sand mold decreases sharply when its temperature exceeds a predetermined limit temperature T1. This is because, above the limit temperature T1, the resin contained in the sand mold softens and carbonizes, causing the sand particles, which were held together by the resin, to break apart.

[0043] As shown in Figure 6, the greater the thickness of the sand mold, the lower the minimum temperature of the sand mold (the lowest temperature of the sand mold immediately after the introduction of molten metal into the cavity is complete). In other words, as the thickness of the sand mold increases, the distance between the cavity and the part of the sand mold furthest from the cavity increases, which suppresses the temperature rise of that part immediately after the introduction of molten metal into the cavity is complete, and thus the minimum temperature of this part becomes lower.

[0044] Based on the above findings, the thickness d1 of the protrusion 72 is set to a thickness such that the lowest temperature of the protrusion 72 immediately after the introduction of molten metal into the cavity is equal to or greater than the limit temperature T1. In this embodiment, the thickness d1 of the protrusion 72 is set to the same value as the thickness d1 at which the lowest temperature reaches the limit temperature T1. In other words, the thickness d1 of the protrusion 72 is set to the upper limit of the thickness at which almost the entire protrusion 72 reaches the limit temperature T1 immediately after the introduction of molten metal into the cavity C is completed. As a result, the strength of the protrusion 72 decreases rapidly immediately after the introduction of molten metal into the cavity C is completed, and it collapses more easily. Note that the thickness d1 of the protrusion 72 may be set to a dimension smaller than the thickness d1 at which the lowest temperature reaches the limit temperature T1. However, if the thickness d1 of the protrusion 72 is made excessively small, there is a risk that the strength of the protrusion 72 before the introduction of molten metal into the cavity C will not be sufficiently ensured. Furthermore, if the thickness d1 of the protrusion 72 is made excessively small, molten metal may leak to the downstream portion of the protrusion 72 in the direction of molten metal flow (between the mold-side first extension 52 and the sand-type first extension 73), and this molten metal may solidify before the mold 30 undergoes thermal expansion, potentially eliminating the expansion space for the mold 30. In contrast, in this embodiment, as described above, the thickness d1 of the protrusion 72 is set to the upper limit of the thickness, ensuring the strength of the protrusion 72 before molten metal is introduced into the cavity C, and preventing premature introduction of molten metal to the downstream portion of the protrusion 72.

[0045] (3) Casting method Next, a casting method using the mold 1 described above, specifically a method for casting an aluminum cylinder head E using the mold 1, will be explained. Figure 7 is a flowchart showing the procedure for casting the cylinder head E.

[0046] First, a preparation process is carried out to prepare the sand mold 10, which is made up of multiple cores 11 to 21, and the mold 30, which is made up of multiple cores 11 to 21 (Step S1).

[0047] Next, a mold assembly process is carried out to assemble the mold 1 by combining the sand mold 10 and the mold 30 (step S2). In the mold assembly process, as described above, the sand mold 10 and the mold 30 are combined such that the mold-side mating surface 51 of the mold 30 and the sand mold-side mating surface 71 face each other in the left-right direction, and a gap X communicating with the cavity C is defined between them.

[0048] Next, a casting process is carried out in which molten aluminum is introduced into the cavity C from the sprue 21A and the cavity C is filled with molten metal (step S3). In this embodiment, the mold 1 is positioned in the opposite position to the position shown in Figure 2 in the vertical direction, that is, the upper core 21 is located at the lower end of the mold 1 and the mold 30 is located at the upper end of the mold 1, and molten metal is filled into the cavity C. After that, the mold 1 is inverted vertically to the same position as the position shown in Figure 2.

[0049] Next, a mold opening process is performed to remove the mold 30 from the casting mold 1 (step S4). The mold opening process is performed after the mold 30 has cooled and the part formed by the mold 30, i.e., the bottom surface of the cylinder head E, has solidified. Thus, even after the mold 30 is removed, the molten metal is retained inside the formed cylinder head E bottom surface and the sand mold 10.

[0050] Next, a quenching process is performed to cool the bottom surface of the solidified cylinder head E and the molten metal held in the sand mold 10 (step S5). In this embodiment, first, cooling water is sprayed onto the bottom surface of the cylinder head E to quench it, and then cooling water is sprayed onto the side of the sand mold 10 opposite to the bottom surface of the cylinder head E in the vertical direction.

[0051] Finally, the sand mold 10 is dried, the dried sand mold 10 is broken, and the sand is removed from the cavity C to remove the manufactured casting, i.e., the cylinder head E, in a casting removal process (step S6).

[0052] (4) Effects, etc. As described above, in the mold 1 according to the above embodiment, the sand mold 10 and the metal mold 30 are combined to partition the cavity C, and the cylinder head E is cast by introducing molten metal into the cavity C. Furthermore, the lower surface of the cylinder head E, including the ceiling surface E2 of the combustion chamber E1, is formed by the metal mold 30. Therefore, it is possible to cast a cylinder head E that has a high-strength ceiling surface E2 of the combustion chamber E1 while having thin walls in each part.

[0053] Furthermore, a projection 72 is provided at the upper end of the sand mold side mating surface 71 of the base core 11, which is the sand mold 10, that is, at the end of the gap X on the cavity C side, projecting toward the mold side mating surface 51. This projection 72 is located at the upper end of the sand mold side mating surface 71 of the base core 11, which is the sand mold 10, that is, at the end of the gap X on the cavity C side. In addition, the lateral separation distance R1 between the projection 72 and the mold side mating surface 51, that is, the separation distance R1 in the direction in which the sand mold side mating surface 71 and the mold side mating surface 51 face each other, is set to the smallest dimension among the lateral separation distances R1 to R4 between these mating surfaces 51 and 71. Therefore, according to the above embodiment of the mold 1, the above effects of the combination of the mold 30 and the sand mold 10 can be obtained while suppressing cracking of the sand mold 10 (base core 11) and also suppressing the generation of burrs.

[0054] Let's explain this in detail using Figure 8. Figure 8 corresponds to Figure 4, with Figure 8(a) showing the mold 30 before thermal expansion and Figure 8(b) showing the mold 30 after thermal expansion.

[0055] As described above, a gap X communicating with the cavity C is defined between the mold-side mating surface 51 and the sand mold-side mating surface 71. Therefore, when molten metal is introduced into the cavity C, the molten metal in the cavity C enters this gap X, as indicated by arrow Y10. If the left-right dimension of this gap X is large, a large amount of molten metal will enter the gap X, causing burrs to form. In contrast, in the above embodiment, a projection 72 is provided at the cavity C side end of the sand mold-side mating surface 71, projecting toward the mold-side mating surface 51, thereby keeping the left-right dimension R1 of the molten metal inlet portion from the cavity C to the gap X small. Therefore, according to the above embodiment, the amount of molten metal entering the gap X can be kept small, and the generation of burrs can be suppressed.

[0056] Here, unlike the above embodiment, even if the left-right dimension of the entire gap X is simply reduced, the intrusion of molten metal into the gap X is suppressed. However, since the mold 30 has a larger coefficient of thermal expansion than the base core 11, i.e., the sand mold 10, when molten metal is introduced into the cavity C, the mold 30 expands more thermally than the base core 11, and as shown by arrow Y1, the mold-side mating surface 51 approaches the sand mold-side mating surface 71. Therefore, if a configuration with a reduced left-right dimension of the entire gap X is adopted, the entire mold-side mating surface 51 collides with the sand mold-side mating surface 71, and as a result of applying load over a wide area of ​​the base core 11, the base core 11 breaks.

[0057] In contrast, in the above embodiment, as described above, the protruding portion 72 has a shape that protrudes toward the mold-side mating surface 51, has a small thickness d1 and is easily broken, and the lateral separation distance R1 between the protruding portion 72 and the mold-side mating surface 51 is smaller than the lateral separation distances R2, R3, and R4 between the portion of the sand mold-side mating surface 71 excluding the protruding portion 72 and the mold-side mating surface 51. Therefore, as shown in Figure 8(b), when the mold 30 undergoes thermal expansion, the mold-side mating surface 51 can be made to collide only with the protruding portion 72, and this collision can destroy the protruding portion 72, thereby preventing force from being applied from the mold 30 to other parts of the base core 11. Accordingly, according to the above embodiment, it is possible to prevent the entire base core 11 from breaking.

[0058] Furthermore, in the above embodiment, the sand mold side mating surface 71 is provided with a sand mold side first extension 73 extending downward from the base end of the protrusion 72, and a sand mold side second extension 74 extending to the right from the lower end of the sand mold side first extension 73. In addition, the mold side mating surface 51 is provided with a mold side first extension 52 extending vertically opposite to the protrusion 72 and the sand mold side first extension 73, and a mold side second extension 53 extending to the right from the lower end of the mold side first extension 52. As a result, a space X2 is defined below the protrusion 72, partitioned by the sand mold side first extension 73, the mold side first extension 52, and the mold side second extension 53. Therefore, as shown in Figure 8(b), the sand S generated by the collapse of the protrusion 72 can be stored in the space X2, thereby sealing the gap between the sand mold side second extension 74 and the mold side second extension 53. Consequently, it is possible to prevent molten metal from passing through these second extensions 53 and 74 and entering further downstream of the gap X, thereby more reliably suppressing the generation of burrs.

[0059] Furthermore, in the above embodiment, the sand mold side mating surface 71 is further provided with a third sand mold side extension 75 extending downward from the right end of the second sand mold side extension 74. Also, the mold side mating surface 51 is provided with a third mold side extension 54 extending downward from the right end of the second mold side extension 53. With this configuration, the gap X is made into a passage that bends at least twice. Therefore, it is possible to suppress molten metal from entering the downstream side of the gap X, and the generation of burrs can be suppressed even more reliably. In addition, the lateral separation distance R4 between the third sand mold side extension 75 and the third mold side extension 54 is set to be smaller than the lateral separation distance R2 between the first sand mold side extension 73 and the first mold side extension 52. Therefore, it is possible to suppress molten metal from entering between the third extension portion 75 on the sand mold side and the third extension portion 54 on the mold side, and to ensure a lateral separation distance of the space X2, thereby preventing pressure from being applied from the mold 30 to the base core 11 through the sand S generated by the collapse of the protrusion portion 72 within the space X2.

[0060] Furthermore, in the above embodiment, as described above, the thickness d1 of the protrusion 72 is set to the same value as the thickness d1 at which the lowest temperature of the protrusion 72 immediately after the introduction of molten metal into the cavity C is the limit temperature T1, that is, the temperature at which the strength of the protrusion 72 decreases. Therefore, when the mold 30 expands due to the introduction of molten metal into the cavity C, the protrusion 72 can be reliably destroyed by collision with the mold 30. Thus, it is possible to prevent the entire base core 11 from breaking due to collision with the mold 30.

[0061] (5) Variant In the above embodiment, a case was described in which a projection 72 is provided on the inner circumferential surface 70 of the base core 11 facing the right outer surface 51 of the mold 30, but the location on which the projection 72 is provided is not limited to this. Also, the core on which the projection 72 is provided is not limited to the base core 11. Furthermore, the configuration according to the above embodiment may be applied to a mold for casting articles other than cylinder heads E. Also, the thickness of the projection 72 is not limited to the above. [Explanation of symbols]

[0062] 1. Mold 10 Sand molds 11 Base core (sand mold) 30 molds 51 Mold side mating surface 52 Mold side first extension part 53 Mold side second extension part 54 Mold side third extension part 71 Sand mold side mating surface 72 Protrusion 73 Sand mold side first extension part 74 Sand mold side second extension part 75 Sand mold side third extension part C Cavity X Gap

Claims

1. A mold structure comprising a sand mold and a mold that partitions a cavity between the sand mold, wherein an article is cast by introducing molten metal into the cavity, The sand mold comprises a mold-side mating surface which is a part of the outer circumferential surface of the mold and a sand mold-side mating surface which faces the mold in a predetermined first direction. The sand mold side mating surface and the mold side mating surface are arranged to communicate with the cavity and to define a gap extending from the cavity in a second direction intersecting the first direction. When, in the second direction, the cavity side is considered one side and the opposite side the other side, and in the first direction, the mold side mating surface is considered one side and the opposite side the other side, The end of the sand mold side mating surface on one side in the second direction has a stepped shape such that the side on the second direction is located closer to the side in the first direction. The protruding portion of the stepped portion of the sand mold side mating surface, which is one side in the second direction, has a shape that protrudes toward the mold side mating surface relative to the other side of the stepped portion in the second direction. A mold structure characterized in that the distance between the protruding portion and the mold-side mating surface in the first direction is set to be smaller than the distance between the portion of the sand mold-side mating surface excluding the protruding portion and the mold-side mating surface in the first direction.

2. In the mold structure described in claim 1, The sand mold side mating surface comprises a sand mold side first extension portion extending from the protruding portion to the other side in the second direction, and a sand mold side second extension portion extending from the other end of the sand mold side first extension portion in the second direction to the other side in the first direction. The mold structure is characterized in that the mold-side mating surface comprises a mold-side first extension portion extending along the second direction opposite to the protruding portion and the sand mold-side first extension portion, and a mold-side second extension portion extending from the other end of the mold-side first extension portion in the second direction to the other side in the first direction.

3. In the mold structure according to claim 2, The sand mold side mating surface includes a sand mold side third extension extending from the other end in the first direction of the sand mold side second extension to the other side in the second direction, The mold-side mating surface includes a mold-side third extension extending from the other end of the mold-side second extension in the first direction to the other side in the second direction, A mold structure characterized in that the distance between the third extension on the sand mold side and the third extension on the mold side in the first direction is set to be smaller than the distance between the first extension on the sand mold side and the first extension on the mold side in the first direction.

4. In the mold structure described in claim 1, The mold structure is characterized in that the protruding portion is configured such that its strength is reduced when molten metal is introduced into the cavity.

5. In the mold structure according to claim 4, The mold structure is characterized in that the thickness of the protrusion in the second direction is set such that the minimum temperature of the protrusion when molten metal is introduced into the cavity is equal to or greater than the temperature at which the strength of the sand mold decreases.

6. A casting method for casting an article using a mold structure according to any one of claims 1 to 5, A mold assembly step of combining the sand mold and the mold so as to partition the cavity, A casting process in which molten metal is poured into the cavity to form a casting corresponding to the cavity. and, A mold opening step in which the sand mold and the mold are separated while the casting remains on the sand mold side, A casting method characterized by including a casting removal step of breaking the sand mold and removing the casting.

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