Manufacturing method for castings

Abstract

To provide a method for manufacturing castings that can reduce the occurrence of defects in castings and improve dimensional accuracy. [Solution] A method for manufacturing a casting that will be used as the material for a mold comprises a mold fitting step of joining a first mold and a second mold, and a pouring step of pouring molten metal into the cavity formed between the first mold and the second mold, and before the mold fitting step, a placement step of placing a block consisting of a model that will be destroyed upon contact with the molten metal and a refractory material that adheres closely to the model with a part of the model exposed, into at least one of the first mold and the second mold such that a part of the model is exposed in the cavity.

Description

【Technical Field】 【0001】 The present invention relates to a method for manufacturing a casting that serves as a mold material. 【Background Art】 【0002】 Regarding the technology for manufacturing a casting that serves as a mold material, the prior art disclosed in Patent Document 1 is as follows: After creating a mold in the same shape as the casting using a material that disappears when contacted by molten metal, the mold is buried in casting sand, molten metal is poured into the mold, and the cavity formed by the disappearance of the mold is filled with molten metal to manufacture the casting. 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 International Publication No. 2008 / 050555 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 In the prior art, since the mold has the same size as the casting, if the mold is buried in casting sand in a deformed state, the dimensional accuracy of the casting will decrease. In addition, when a mold of the same size as the casting disappears, a large amount of gas is generated, and the generated gas may cause defects in the casting. 【0005】 The present invention has been made to solve this problem, and an object thereof is to provide a method for manufacturing a casting that can reduce the occurrence of defects and improve dimensional accuracy. 【Means for Solving the Problems】 【0006】 A first embodiment for achieving this objective is a method for manufacturing a casting that will be used as the material for a mold, comprising a mold fitting step of joining a first mold and a second mold, and a pouring step of pouring molten metal into the cavity formed between the first mold and the second mold, wherein, prior to the mold fitting step, a block comprising a model that will be destroyed upon contact with the molten metal and a refractory material that adheres closely to the model with a portion of the model exposed is placed in at least one of the first mold and the second mold such that a portion of the model is exposed in the cavity. 【0007】 In a second embodiment, the refractory material is foundry sand mixed with a binder, as in the first embodiment. 【0008】 A third embodiment is the first or second embodiment, wherein at least one of the first mold and the second mold is provided with a bottomed hole leading to a cavity, and the block is placed in the hole during the placement process. 【0009】 A fourth aspect is the third aspect, in which the block includes a bottom surface facing the bottom of the hole, a top surface located opposite the bottom surface, and four sides connecting the bottom surface and the top surface, with the model and refractory material exposed on two opposing sides of the sides. 【0010】 A fifth aspect is the third aspect, wherein the block includes a bottom surface facing the bottom of the hole, a top surface located opposite the bottom surface, and a side surface connecting the bottom surface and the top surface, and the model has an undercut portion where the inclination of the top surface with respect to the vertical is large, and the block has refractory material in close contact with the undercut portion. [Effects of the Invention] 【0011】 According to the present invention, a block consisting of a model that disappears upon contact with molten metal and a refractory material that adheres closely to the model with a portion of the model exposed is placed in at least one of a first mold and a second mold such that a portion of the model is exposed in the cavity. Then, molten metal is poured into the cavity created between the first mold and the second mold, so that the space created by the disappearance of the model and the cavity are filled with molten metal, and the molten metal solidifies to form a casting. The volume of the model is part of the volume of the casting, and furthermore, since the model is supported by the first or second mold and the refractory material, deformation of the model and gas generation can be reduced compared to the case where a model of the same size as the casting is buried in the casting sand. Therefore, the occurrence of defects in the casting can be reduced and dimensional accuracy can be improved. [Brief explanation of the drawing] 【0012】 [Figure 1] (a) is a plan view of the casting in one embodiment, (b) is a perspective view of the raised portion, and (c) is a cross-sectional view of the raised portion along the line Ic-Ic in Figure 1(b). [Figure 2] (a) is a perspective view of a clip that is insert-molded into a seat pad, and (b) is a cross-sectional view of the seat pad including the clip. [Figure 3] (a) is a cross-sectional view of the mold, (b) is an enlarged cross-sectional view of the part of the mold shown in IIIb of Figure 3(a), and (c) is a cross-sectional view of the mold into which molten metal has been poured. [Figure 4] (a) is a perspective view of the model, and (b) is a perspective view of the block in the first embodiment. [Figure 5] Figure 3(a) is a cross-sectional view of the mold along the VV line. [Figure 6] (a) is a perspective view of the block in the second embodiment, (b) is a cross-sectional view of the mold in which the block is placed, and (c) is a perspective view of the mold. [Figure 7] (a) is a cross-sectional view of the mold in which the blocks are arranged in the third embodiment, and (b) is a perspective view of the mold. [Modes for carrying out the invention] 【0013】 Preferred embodiments of the present invention will be described below with reference to the drawings. Figure 1(a) is a plan view of a casting 10 in one embodiment. The casting 10 is a mold material used for mold molding of a foam made of synthetic resin. Figure 1(a) shows the lower mold which forms the design surface of the foam. When the raw material is foamed in the mold cavity formed by combining the upper mold (not shown) and the lower mold, the surface of the foam appears as an inverted version of the molded surfaces 11 of the upper and lower molds. 【0014】 An example of the foam material is a seat pad 30 (described later) made of soft polyurethane foam. Examples of uses for the seat pad 30 include a seat cushion to support the user's buttocks, a seat back used as a backrest for the user, an armrest for a sofa or chair, and a footrest. For decoration or to enhance user comfort, a cover (not shown) made of woven or knitted fabric or leather may be placed over the seat pad 30. 【0015】 The casting 10 includes a molding surface 11 for forming the design surface of the foam, a raised portion 12 on which a part of the molding surface 11 is raised in a striated manner, and a flange 13 that protrudes around the entire circumference of the molding surface 11. The raised portion 12 creates grooves on the design surface of the foam necessary for suspending the surface layer (not shown). The raised portion 12 is provided with a plurality of recesses 14. 【0016】 A mold is formed by processing or attaching to the casting 10, as needed, seals to prevent leakage of foam raw materials, vent slits and vent holes to discharge gases generated during molding, and temperature control piping (none of which are shown) to adjust the temperature. The flange of the upper mold (not shown) is joined to the flange 13 to create a cavity. 【0017】 FIG. 1(b) is a perspective view of the raised portion 12. FIG. 1(b) shows the vicinity of the recess 14 in the raised portion 12. The raised portion 12 includes two side surfaces 15 extending along the raised portion 12 and a top surface 16 adjacent to the side surfaces 15. A plurality of recesses 14 are provided from the side surface 15 to the top surface 16 at the ridge where the side surface 15 and the top surface 16 intersect. The recesses 14 are provided at opposite portions of the side surface 15 so that two form a pair. By forming the paired recesses 14 in the raised portion 12, the wall portions 17 appear. Two wall portions 17 are arranged side by side in the direction in which the raised portion 12 extends. 【0018】 FIG. 1(c) is a cross-sectional view of the raised portion 12 taken along line Ic-Ic of FIG. 1(b). The wall portion 17 includes a base 18, a first portion 19 adjacent to the base 18 in the height direction, and a second portion 20 adjacent to the first portion 19 in the height direction. The apex of the second portion 20 is a part of the top surface 16 of the raised portion 12. The thickness of the first portion 19 (the dimension in the left-right direction in FIG. 1(c)) is larger than the thickness of the base 18, and the thickness of the second portion 20 is smaller than the thickness of the first portion 19. Due to the relationship between the thickness of the base 18 and the thickness of the first portion 19, there is an undercut portion 21 in which the inclination of the wall portion 17 with respect to the height direction of the raised portion 12 increases from the base 18 to the first portion 19. 【0019】 FIG. 2(a) is a perspective view of the clip 32 insert-molded into the sheet pad 30. The clip 32 is a member made of synthetic resin. The clip 32 includes a substrate 33, a pair of leg portions 34 protruding from the center in the width direction of the substrate 33, and a pair of claws 35 protruding from the tips of the leg portions 34 so as to approach each other. The leg portions 34 are provided such that the distance between them facing each other widens. Two sets of leg portions 34 are arranged side by side on one substrate 33. 【0020】 Figure 2(b) is a cross-sectional view of the sheet pad 30 including the clip 32. Figure 2(b) shows the vicinity of the groove 31 in the sheet pad 30. The clip 32 is embedded in the sheet pad 30 such that the leg portion 34 protrudes from the bottom of the groove 31 of the sheet pad 30. The clip 32 is provided to suspend a part of the skin (not shown) covering the sheet pad 30 into the groove 31. The leg portion 34 present in the groove 31 hooks and fixes the component attached to the skin with the claw 35. 【0021】 When forming the sheet pad 30, the wall portion 17 of the raised portion 12 (see Figure 1(c)) is placed between the leg portions 34 of the clip 32 until the claw 35 of the clip 32 catches on the undercut portion 21 of the wall portion 17, and then the clip 32 is fixed to the raised portion 12. After that, the raw material is foamed in the cavity of the mold. As a result, the shape of the raised portion 12 is inverted to become the groove 31 and appears in the sheet pad 30, and a sheet pad 30 with the leg portions 34 of the clip 32 provided at the bottom of the groove 31 is obtained. 【0022】 Figure 3(a) is a cross-sectional view of the mold 40 used for forming the casting 10. The mold 40 includes a first mold 41 and a second mold 42. The first mold 41 and the second mold 42 are exemplified as being made of casting sand kneaded with a binder. The casting sand is exemplified by ceramic artificial sand, natural sand, silica sand, chromite sand, zircon sand, and the binder is exemplified by an alkali phenol resin for ester curing, but there is no limitation on the materials of the molds 41, 42, the casting sand, and the binder. 【0023】 The mold 40 has a cavity 43 formed by combining the first mold 41 and the second mold 42, which is made in the shape of the casting 10 (see Figure 1(a)). The cavity 43 includes a cavity 44 for forming the flange 13 of the casting 10 and a cavity 45 for forming the raised portion 12. The cavity 45 is provided on the mating surface 41a (the surface where the second mold 42 is mated) of the first mold 41. The sprue 46 provided in the second mold 42 is connected to the cavity 43. The molten metal is poured from the sprue 46 into the cavity 43, and the casting 10 is cast. The metal constituting the molten metal is exemplified by aluminum and aluminum alloys. 【0024】 Figure 3(b) is a cross-sectional view of the first mold 41, enlarged from the portion indicated by IIIb in Figure 3(a). The first mold 41 is provided with a hole 47 that connects to a cavity 45. A block 50 that fits into the hole 47 is placed in the first mold 41. The block 50 is a component for forming the raised portion 12 (see Figure 1(c)). 【0025】 Figure 4(a) is a perspective view of a model 51, which is part of block 50. Model 51 is made of a material that disappears upon contact with molten metal (e.g., expanded polystyrene). The shape and size of model 51 are the same as the shape and size of the recessed portion 14 of the raised portion 12 (see Figure 1(b)) (near the top surface 16 of a part of the raised portion 12 in the height direction). 【0026】 Model 51 includes a rectangular plate-shaped base 52, two first protrusions 53 projecting in the same direction from two ends on the long side of the base 52, a second protrusion 54 spaced apart from the first protrusions 53 and provided between them, and two wall portions 55 connecting the first protrusions 53 and the second protrusions 54. The heights of the first protrusions 53, the second protrusions 54, and the wall portions 55 are the same. The thickness of the first protrusions 53 and the second protrusions 54 (width of model 51) is equal to the thickness between the sides 15 of the raised portion 12 (see Figure 1(c)). The thickness of the first protrusions 53 and the second protrusions 54 is the same along the entire height of model 51. Since the thickness of the wall portions 55 is smaller than the thickness of the first protrusions 53 and the second protrusions 54, the wall portions 55 create a recess in model 51. 【0027】 Let's return to Figure 3(b) for explanation. The wall portion 55 includes a base 56, a first portion 57 adjacent to the base 56 in the height direction, and a second portion 58 adjacent to the first portion 57 in the height direction. The thickness of the first portion 57 (dimensions on the left and right in Figure 3(b)) is greater than the thickness of the base 56, and the thickness of the second portion 58 is less than the thickness of the first portion 57. Due to the relationship between the thickness of the base 56 and the thickness of the first portion 57, the wall portion 55 has an undercut portion 59 from the base 56 to the first portion 57, where the inclination of the wall portion 55 with respect to the height direction is greater. 【0028】 Figure 4(b) is a perspective view of block 50. Block 50 consists of a model 51 and a refractory material 60 that adheres closely to the model 51. The refractory material 60 has fire resistance, meaning it will not burn or melt even if it comes into contact with molten metal, at least until the molten metal solidifies. Firing sand mixed with a binder is preferable for the refractory material 60. This is because the firing sand mixed with a binder flows according to the shape of the surface of the model 51, and solidifies with the firing sand filling the depressions in the model 51, allowing the block 50 to be made into any simple shape. In this embodiment, the refractory material 60 adheres closely to the first protrusion 53, the second protrusion 54, and the wall portion 55. The refractory material 60 also adheres closely to the undercut portion 59 of the wall portion 55 (see Figure 3(b)). 【0029】 In this embodiment, the shape of block 50 is a rectangular prism (cuboid) including a rectangular base 61, a rectangular top 62, and four side surfaces 63 connecting the base 61 and the top 62. The base 61 of block 50 is made of refractory material 60, and the top 62 is made of model 51. On one of the two opposing side surfaces 63a and 63b of block 50, model 51 and refractory material 60 are visible, and on the other two opposing side surfaces 63c and 63d, model 51 and refractory material 60 are also visible. Block 50 does not have any undercuts on the side surfaces 63 that increase the inclination of the base 61 with respect to the vertical direction. In this embodiment, the cross-sectional area of ​​the side surfaces 63 is the same throughout the entire area between the base 61 and the top 62. 【0030】 Figure 5 is a cross-sectional view of the mold 40 along the VV line in Figure 3(a). The hole 47 provided in the first mold 41 is connected to the cavity 45, and the block 50 fits snugly into the hole 47. In this embodiment, the hole 47 expands the cavity 45, and the block 50 closes the hole 47. The bottom surface 61 of the block 50 fitted into the hole 47 faces the bottom 48 of the hole 47. The height of the block 50 (distance between the bottom surface 61 and the top surface 62) is exemplified to range from 2 / 5 to 1 times the depth of the cavity 45 (distance between the bottom 48 of the hole 47 and the mating surface 41a). The length of the side surface 63 of the block 50 (left and right dimensions in Figure 5) is the same along the entire height of the block 50. The boundary between the model 51 and the refractory material 60 is located at the boundary between the hole 47 and the cavity 43, and the portion of the side surface 63 of the block 50 in which the model 51 is visible is visible in the cavity 43. 【0031】 Let's return to Figure 3(b) for explanation. The bottom surface 61 of block 50 is in contact with the bottom 48 of hole 47, so the top surface 62 of block 50 is exposed in the cavity 45. Two of the side surfaces 63 of block 50, 63a and 63b, are in contact with the first mold 41. Two of the side surfaces 63 of block 50, 63c and 63d, are exposed in the cavity 45. The width of the side surfaces 63 of block 50 (the left and right dimensions in Figure 3(b)) is the same along the entire height of block 50. 【0032】 An example of a manufacturing method for the casting 10 is described below. First, a block made of synthetic resin such as rigid urethane is processed using an NC machine tool to create a mold to which the clip 32 can be attached. Then, a model 51 is made using a mold that reflects the model, and a block 50 is made by pressing refractory material 60 onto the model 51. Next, a prototype is made using a mold that is the same shape and size as the seat pad 30, with additional space for placing the block 50. The prototype with the block 50 placed on it is inverted to create a first mold 41 and a second mold 42. When removing the mold from the first mold 41, which was made by inverting the prototype, the block 50 removed from the mold can be placed in the first mold 41 (placement step). 【0033】 Alternatively, a prototype with a designated space for block 50 can be used to create the first mold 41 and the second mold 42 by placing an object of the same shape and size as block 50 on the prototype and then inverting it. In the placement process, block 50 is fitted into a hole 47 provided in the first mold 41, and block 50 is placed in the first mold 41. Next, in the mold fitting process, the first mold 41 and the second mold 42 are joined together, creating a cavity 43 between the first mold 41 and the second mold 42. In the pouring process, molten metal is poured into the cavity 43 from the sprue 46 of the second mold 42. 【0034】 Figure 3(c) is a cross-sectional view of the mold 40 into which molten metal has been poured. The model 51 (see Figure 3(b)) disappears upon contact with the molten metal, so a raised portion 12 reflecting the shape of the first mold 41 and the refractory material 60 is created on the casting 10. After casting, the first mold 41, the second mold 42, and the refractory material 60 are broken down using a vibrator, hammer, etc., and the casting 10 is removed. After cleaning the surface of the casting 10 by shot blasting, etc., a seal is processed or attached to the casting 10 as needed to obtain a mold for forming the sheet pad 30. 【0035】 When insert molding the clip 32 using a mold equipped with a part to which the clip 32 is attached, if the raw material for the sheet pad 30 gets into the gap between the part and the mold, or if the part comes off the mold after repeated molding, the mold needs to be repaired. However, since the recess 14 of the casting 10 is part of the raised part 12, raw material does not penetrate, and the frequency of repairs to the casting 10 can be reduced. In addition, the volume of the model 51 is part of the volume of the casting 10, and the model 51 is supported by the first mold 41 and the refractory material 60. Therefore, compared to the case where a model of the same size as the casting 10 is buried in the casting sand, deformation of the model 51 can be reduced, and the generation of gas when the model 51 disappears can be reduced. Consequently, the occurrence of defects in the casting 10 can be reduced and dimensional accuracy can be improved. 【0036】 Since the height of the model 51 is lower than the height of the raised portion 12, the amount of gas generated when the model 51 in contact with the molten metal disappears can be reduced compared to the case where the height of the model 51 is the same as the height of the raised portion 12. 【0037】 In the placement process, the block 50 is fitted into a hole 47 provided in the first mold 41, making it easier to position the block 50 at a specified location in the first mold 41. Furthermore, it is possible to ensure the accuracy of positioning the block 50 in the first mold 41. 【0038】 Because block 50 does not have an undercut portion on its side surface 63 that would cause a large inclination of the bottom surface 61 relative to the vertical, block 50 can be easily placed in the cavity 45 or hole 47. Model 51 has an undercut portion 59 on the top surface 62 of block 50 that would cause a large inclination of the top surface 62 relative to the vertical, but block 50 is made so that there is no undercut portion on the top surface 62 that would cause a large inclination of the top surface 62 relative to the vertical, as the refractory material 60 adheres closely to the undercut portion 59 of model 51. Since model 51 disappears upon contact with the molten metal, a casting 10 including the undercut portion 21 can be manufactured. 【0039】 Figure 6(a) is a perspective view of block 70 in the second embodiment. Block 70 consists of a model 51 and a refractory material 60 that is in close contact with the model 51, and is a rectangular prism including a rectangular base 71, a rectangular top 72, and four sides 73 connecting the base 71 and the top 72. The model 51 and the refractory material 60 are visible on the base 71 and the top 72. The distance between the base 71 and the top 72 (height of block 70) is equal to the height of the model 51. 【0040】 On one of the two opposing sides 73a and 73b of the side 73 of block 70, only the refractory material 60 is visible, while on the other two opposing sides 73c and 73d of the side 73, both the model 51 and the refractory material 60 are visible. The distance between the two sides 73a and 73b of block 70 (the width of block 70) is greater than the width of model 51 by the thickness of the refractory material 60 attached to model 51. 【0041】 Figure 6(b) is a cross-sectional view of the mold 40 (first mold 41) in which the block 70 is placed. Figure 6(c) is a perspective view of the first mold 41. As shown in Figure 6(c), a hole 47 leading to a cavity 45 is provided in the mating surface 41a of the first mold 41. The hole 47 expands the width of the cavity 45, and the refractory material 60 of the block 70 is placed inside the hole 47. The position of the hole 47, that is, the position in which the block 70 is placed, can be easily confirmed from the mating surface 41a of the first mold 41. 【0042】 As shown in Figure 6(b), the bottom surface 71 of block 70 is in contact with the bottom 48 of hole 47, and the top surface 72 of block 70 is at the same height as the mating surface 41a of the first mold 41. The model 51 is visible on the top surface 72 of block 70, and as the molten metal comes into contact with it and the model 51 disappears, a raised portion 12 is created in the casting 10 that reflects the shape of the first mold 41 and the refractory material 60. 【0043】 Figure 7(a) is a cross-sectional view of the mold 40 (first mold 41) in which the block 80 in the third embodiment is placed. The block 80 consists of a model 51 and a refractory material 60 that is in close contact with the model 51, and includes a rectangular bottom surface 81 and a stepped top surface 82. The model 51 and the refractory material 60 are visible on the bottom surface 81 and the top surface 82. The width of the block 80 (the distance between two opposing side surfaces 83a and 83b) is greater than the width of the model 51 by the thickness of the refractory material 60 attached to the model 51. 【0044】 The bottom surface 81 of block 80 is in contact with the bottom 48 of hole 47, and the portion of the top surface 82 of block 80 that is made of refractory material 60 is at the same height as the mating surface 41a of the first mold 41. The model 51 is visible on the top surface 82 of block 80, and as the molten metal comes into contact with it and the model 51 disappears, a raised portion 12 is created in the casting 10 that reflects the shape of the first mold 41 and the refractory material 60. 【0045】 Figure 7(b) is a perspective view of the first mold 41 in which the block 80 is placed. The mating surface 41a of the first mold 41 is provided with a hole 47 that connects to a cavity 45. The hole 47 widens the width of the cavity 45, and since the refractory material 60 of the block 80 is placed inside the hole 47, the position of the hole 47, i.e., the position in which the block 80 is placed, can be easily confirmed from the mating surface 41a of the first mold 41. 【0046】 Although the present invention has been described above based on embodiments, it can be easily inferred that the present invention is not limited in any way to the above embodiments, and that various improvements and modifications are possible without departing from the spirit of the present invention. 【0047】 In this embodiment, we have described a case where the base 52 of the model 51 is rectangular and the blocks 50 and 70 are rectangular prisms (rectangular prisms) including the rectangular vertices 62 and 72, but this is not necessarily the only case. The shapes of the model 51 and the blocks 50 and 70 are set appropriately according to the shape of the part of the casting 10. For example, it is certainly possible to make the blocks 50 and 70 into polygonal prisms or cylinders other than rectangular prisms, where the cross-sectional area is the same from the base 61 and 71 of the blocks 50 and 70 to the vertices 62 and 72. It is also certainly possible to make the blocks 50 and 70 into cones, frustocones, pyramids, or truncated pyramids, etc., where the cross-sectional area decreases as it approaches the base 61 and 71 of the blocks 50 and 70, or into a shape that combines a part with the same cross-sectional area and a part with a smaller cross-sectional area. 【0048】 In the embodiment, a case was described in which the casting 10 (material for the lower mold) is cast using blocks 50, 70, and 80, including a model 51 for creating a shape identical to the raised portion 12 to which the clip 32 is attached, but the invention is not necessarily limited to this. The model 51 may be identical in shape to parts other than the raised portion 12 to which the clip 32 is attached. Examples of other parts include protrusions for fixing backing material such as nonwoven fabric that reinforces the back surface of the sheet pad 30, and protrusions for fixing elastic bodies such as foam or three-dimensional mesh structures that become part of the sheet pad 30. In these cases, by placing the blocks in the second mold 42, protrusions (raised portions) for fixing backing material and elastic bodies can be provided in the casting that will become the material for the upper mold. [Explanation of symbols] 【0049】 10 Castings 41 First mold 42. Second mold 45 Cavity 47 holes 48 bottom 50, 70, 80 blocks 51 Model 59 Undercut section 60 Refractories 61, 71, 81 Base 62,72,82 Top surface 63, 73, 83 Side view

Claims

[Claim 1] A method for manufacturing castings that will be used as the material for a mold, A mold fitting process in which the first mold and the second mold are joined together, The process includes a pouring step in which molten metal is poured into the cavity formed between the first mold and the second mold, Before the aforementioned mold matching process, A method for manufacturing a casting, comprising a placement step of placing a block, which consists of a model that is destroyed upon contact with the molten metal and a refractory material that adheres closely to the model with a portion of the model exposed, into at least one of the first mold and the second mold such that a portion of the model is exposed in the cavity. [Claim 2] The method for manufacturing a casting according to claim 1, wherein the refractory material is foundry sand mixed with a binder. [Claim 3] At least one of the first mold and the second mold is provided with a bottomed hole that leads to the cavity. The method for manufacturing a casting according to claim 1 or 2, wherein the block is fitted into the hole in the arrangement step. [Claim 4] The block includes a bottom surface facing the bottom of the hole, a top surface located opposite the bottom surface, and four sides connecting the bottom surface and the top surface. The method for manufacturing a casting according to claim 3, wherein the model and the refractory material are visible on two opposing sides of the aforementioned side surfaces. [Claim 5] The block includes a bottom surface facing the bottom of the hole, a top surface located opposite the bottom surface, and a side surface connecting the bottom surface and the top surface. The aforementioned model has an undercut portion in which the inclination of the top surface with respect to the vertical direction is large, The method for manufacturing a casting according to claim 3, wherein the block has the refractory material in close contact with the undercut portion.

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