Method for manufacturing neutron member and casting method

Abstract

To provide a core member used by filling filled sand into a hollow part and capable of preventing the deformation and breakage of a mold at sufficient strength while securing high gas permeability, a core member production method and a core member casting method.SOLUTION: A core member 100 for casting is formed by molding sand used for the molding of a mold produced using an additional production device and a binder hardened by joining the particles of the molding sand each other, and has a hollow structure provided with a hole 120 to form into an injection port of the filled sand. In this way, the core member 100 can be used as a core by filling filled sand into a hollow part. Then, when casting is performed using the filled sand having the average particle diameter larger than that of the molding sand, a gap between the particles of the filled sand is made large to improve the gas permeability of the core. Also, a gas generated during the casting can be released to the outside. Further, since the filled sand is filled into the hollow part to be used, the deformation and breakage of the core can be prevented.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a core member used for creating a cavity when casting a casting having a cavity, a method for manufacturing the same, and a casting method.

Background Art

[0002] As a core used for creating a cavity in a casting, shell cores are widely used. A shell core is formed by pouring a mixed material of a binder and sand into a heated mold and hardening the binder by heat. Therefore, the hardened portion is mainly near the surface, and the shell core can be obtained by discharging the unhardened sand inside.

[0003] Shell cores are usually made to have a hollow structure for reducing the raw materials used and for gas venting during casting. Therefore, the strength of the shell core is generally designed to be higher than that of the main mold commonly used. There are also known such shell cores that are filled with shell sand in the hollow part of the hollow structure during use (see Patent Documents 1 and 2).

[0004] On the other hand, in recent years, molds produced by a laminated 3D printer have become widespread. Generally used molds are obtained by transferring a wooden mold or a metal mold that is a prototype. However, such molds must necessarily undergo a mold removal operation, and the wooden mold and the metal mold need to have a shape that can be removed (see Patent Document 3).

[0005] In contrast, a mold by a laminated 3D printer is obtained by hardening only the necessary parts in the sand laid to a certain thickness and sequentially laminating them, so that the operation of mold removal does not occur. Therefore, even a mold having a shape such as an inverse gradient can be easily manufactured.

[0006] Among molds, cores often have complex shapes, and when making such cores with molds, they often have to be made in multiple parts. When the number of divisions increases not only in the cores but also in the main mold, the dimensional accuracy decreases. However, in the case of a laminated 3D printer, there is no limitation in shape, and even for complex shapes, there is no need for division. Therefore, laminated 3D printers are increasingly being used to make cores.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, the cores and main molds produced by laminated 3D printers have lower air permeability compared to general sand molds, and gas defects are likely to occur in castings. Laminated 3D printers cannot lay any casting sand. The laid thickness must be constant, and its surface must be flat.

[0009] In order to obtain such a layered body, the material for the laminated 3D printer is specially adjusted. The mold obtained with such a material tends to have a higher bulk specific gravity and is inferior in air permeability compared to a general mold with the same average particle size.

[0010] As a countermeasure against gas defects, in the case of the main mold, it is possible to change to a plan with vent holes formed or to reduce the wall thickness. However, in the case of cores, it is difficult to adopt such methods. Also, it is conceivable to form a hollow part in the core and have a structure in which gas is discharged from there, but if there is not enough strength, deformation or breakage of the core may occur during casting.

[0011] The present invention has been made in view of such circumstances, and provides a core member that is used by filling hollow portions with filling sand, can prevent deformation and breakage of a mold with sufficient strength while ensuring high air permeability, a method for manufacturing the same, and a casting method.

Means for Solving the Problems

[0012] Upper In order to achieve the above object, the present invention takes the following means. That is, A method for manufacturing a core member for casting, comprising a series of steps of spreading molding sand used for molding a mold to a uniform thickness and injecting a binder into the molding sand to cure the molding sand, and repeating the series of steps to fabricate the core member using an additive manufacturing apparatus. The core member has a hollow structure provided with a hole that also serves as an inlet for filling sand, an outlet for the uncured molding sand, and a vent for gas generated during casting. The thickness of the wall portion forming the hollow structure is 2 mm to 10 mm, the angle of repose of the filling sand is 25° to 41°, and the average particle size of the filling sand is 98 μm to 350 μm It is characterized by the following.

[0013] In this way, the core member can be used as a core by filling the hollow portion with filling sand. If casting is performed using filling sand having a larger average particle size than the molding sand, the gaps between the particles of the filling sand become larger, and the air permeability of the core can be improved. In addition, the gas generated during casting can be released to the outside through the holes. Further, since the filling sand is filled in the hollow portion and used, deformation and breakage of the core can be prevented.

[0014] Middle In the core member, the holes are formed in the ledge portion This This facilitates the injection of the filling sand and the handling of the core.

[0015] Middle In the core member, the thickness of the wall portion forming the hollow structure is 5 mm or more and 10 mm or less This As described above, when the thickness of the wall portion is 5 mm or more, the risk of breakage as a mold can be kept low and sufficient strength can be maintained. In addition, when the thickness of the wall portion is 10 mm or less, sufficient air permeability can be ensured.

[0016] Middle In the method for manufacturing the core member Among them A series of steps including a step of spreading the molding sand to a predetermined thickness and a step of injecting and curing the binder to a predetermined portion to be a formed body are repeated to form the formed body using an additive manufacturing apparatus This Thereby, even for a core having a complex shape, dimensional accuracy can be maintained high without being divided into multiple parts.

[0017] The casting method of the present invention Related to the method for manufacturing a core member is a casting method using a core member having a hollow structure provided with a hole that also serves as an inlet for filling sand, an outlet for the unhardened molding sand, and a vent for gas generated during casting. The method includes the steps of installing the core member in the master mold so that the hole is disposed outside the master mold, filling the hollow portion of the core member with the filling sand having a larger average particle size than the molding sand to form a mold, injecting molten metal into the mold, and removing the casting produced in the mold.

[0018] This increases the gaps between the particles of the filling sand, improves the air permeability, and allows gas to escape from the gaps between the particles of the filling sand during casting. Even with complex cores, sufficient air permeability can be maintained, and gas defects in the casting can be reduced.

[0019] Casting In the casting method, the angle of repose of the filling sand is 40° or less This This evenly fills the hollow portion of the core member with the filling sand, reduces filling unevenness, and can prevent deformation of the core due to the pressure of the molten metal. When the filling sand has high fluidity, it is likely to spread evenly in the hollow portion.

[0020] Casting In the casting method, the average particle size of the filling sand is 3 times or more the average particle size of the molding sand This This can further improve the air permeability of the core.

[0021] Casting In the casting method, the average particle size of the filling sand is 100 μm or more and 350 μm or less Filling By setting the average particle size of the filling sand to 100 μm or more, the air permeability of the core can be improved. Also, by setting the average particle size of the filling sand to 350 μm or less, the surface unevenness caused by the filling sand can be reduced, and the shape transferred to the casting can be smoothed.

[0022] Casting In the casting method, the filling sand does not contain a binder ThisAccordingly, it is possible to prevent the binder from becoming a gas generation source due to the heat of the molten metal.

Advantages of the Invention

[0023] According to the present invention, the filling sand is filled into the hollow portion and used, and it is possible to prevent deformation and breakage of the mold with sufficient strength while ensuring high air permeability.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0025] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0026] [Core Member] FIG. 1 is a perspective view showing a core member 100. The core member 100 for casting is formed of molding sand and a binder and has a hollow structure. The molding sand is sand used for molding a mold by a 3D printer (additive manufacturing apparatus). The binder binds and cures the particles of the molding sand.

[0027] In the example shown in FIG. 1, the core member 100 realizes a hollow structure by a wall portion 110 formed of molding sand and a binder, and is formed in a cylindrical shape with both ends sealed. Details of the molding sand and the binder will be described later.

[0028] The wall portion 110 is provided with a hole 120 that serves as an inlet for the filling sand. The size of the hole 120 is not particularly limited and is appropriately set according to the shape of the core to be produced. The hole 120 is preferably formed in the cope portion. Thereby, the molten metal does not flow into the hole 120, and the generated gas can be discharged to the outside of the system. As a result, sufficient air permeability can be maintained even for complex cores, and gas defects in the casting can be reduced. In addition, it becomes easier to inject the filling sand and handle the core. Note that the cope portion is the end portion of the core that is supported by the main mold and extends outside the main mold. The main mold refers to a mold for forming the outer shape of the casting.

[0029] The wall portion 110 of the core member 100 is preferably thin. The gas generated during casting is generated not only from the molten metal but also from the core. When a test piece based on JIS Z 2601 is produced from the material used for the core using a laminated type 3D printer and the air permeability of the test piece is measured, it is less than 50. Thus, the core produced by the laminated type 3D printer has low air permeability.

[0030] From the above viewpoints, the thickness of the wall portion 110 of the core member 100 is preferably 10 mm or less. By having the thickness of the wall portion 110 be 10 mm or less, sufficient air permeability can be ensured. The thickness of the wall portion 110 forming the hollow structure is preferably 5 mm or more. By having the thickness of the wall portion 110 be 5 mm or more, the risk of breakage as a mold can be kept low and sufficient strength can be maintained. The thickness of the wall portion 110 is more preferably 2 mm or more. If it is less than 2 mm, the risk of breakage increases when handling the core member 100, so the practical lower limit is 2 mm.

[0031] [Manufacturing method of core member] (Overall process) The manufacturing method of the core member 100 configured as described above will be described. The core member 100 is preferably manufactured using a laminated type 3D printer (additive manufacturing apparatus). A commercially available binder jet type 3D printer can be used as the 3D printer.

[0032] The data of the core member 100 input into the 3D printer is not left in the shape of the cavity of the casting, but is designed to have a hollow structure while maintaining the outer shape, and a part is open by forming holes 120. Through these holes 120, the gas generated during casting can be released. Also, the holes 120 serve as outlets for the uncured molding sand and become inlets for the filling sand after the discharge. Note that the hollow structure refers to a structure made up of a wall portion and a hollow portion, and the hollow portion refers to the space itself surrounded by the wall portion (excluding the wall portion).

[0033] In this way, by using a 3D printer, a series of steps of spreading sand evenly to a certain thickness and spraying and curing a binder on a predetermined portion that becomes the shaped body are repeated to form the shaped body. As a result, even for cores with complex shapes, high dimensional accuracy can be maintained without multi-segmentation. Details of the molding material will be described later.

[0034] When the shaping is completed, in the formed laminate, the cured shaped body (for example, the core member 100) is in a state of being buried in the uncured sand. By removing the uncured sand from the laminate, the shaped body is taken out. When the shaped body is hollow, even if the surrounding uncured sand is removed, uncured sand remains in the hollow portion. By providing holes 120 in the wall portion 110 that forms the hollow structure of the core member 100, the uncured sand can be discharged from these holes 120.

[0035] (Molding Material) For the molding sand, a dedicated sand for laminated 3D printers is used. Commercially available dedicated sands can be appropriately selected and used. Examples of commercially available dedicated sands include, for example, original materials of 3D printers and TCaST (registered trademark, manufactured by Taiheiyo Cement Corporation). The dedicated sand can be selected, for example, taking into account the heat resistance according to the melting temperature of the metal to be cast. Furthermore, commercially available dedicated sands can be modified and used as molding sand. The average particle size of the molding sand is preferably 60 μm or more and 150 μm or less, and more preferably about 100 μm.

[0036] [Casting Method] (Overall Process) A casting method using the above-mentioned core member 100 will be described. FIG. 2 is a perspective view showing the upper mold 210, the lower mold 220, and the core member 100. The upper mold 210 and the lower mold 220 are main molds formed in a box shape when mated, and grooves are provided on the mating surface so that the core members 100 are arranged at equal intervals.

[0037] During casting, first, the core member 100 is installed in the lower mold 220. At this time, the core member 100 is arranged so that the flange portion protrudes from the lower mold 220. Then, the upper mold 210 is mated with the lower mold 220, and the inside of the upper mold 210 and the lower mold 220 is closed to assemble the mold. A hole 120 is provided in the flange portion of the core member 100, and filling sand can be injected into the core member 100 even after mating. By filling the hollow portion with the filling sand through the hole 120, the core member 100 can be used as a core.

[0038] By filling the hollow portion of the core member 100 with filling sand, it is possible to prevent the core from deforming or being damaged by the pressure of the molten metal during casting. It is preferable not to add a binder such as that used in a general mold to the filling sand. Thereby, it is possible to avoid the binder becoming a gas generation source due to the heat of the molten metal. Details of the filling sand will be described later.

[0039] Once the mold is prepared, the molten metal is poured into the mold. A molten metal inlet 212 is opened in the wall portion 211 of the upper mold 210. The inlet 212 is preferably provided at a position where there is no core member 100 directly below. During casting, the core is surrounded by the molten metal and receives the pressure of the molten metal. Therefore, if the core has a hollow structure, deformation or damage of the core will occur. If it deforms, a casting of a predetermined dimension cannot be obtained, and if it is damaged, a hollow portion of the casting cannot be formed. Therefore, the hollow portion is filled with filling sand.

[0040] Then, the molten metal is cooled and the casting produced in the mold is taken out. At this time, the mold is disassembled. FIG. 3 is a perspective view showing the produced casting 300. The casting 300 is formed in a rectangular parallelepiped shape, and five cylindrical holes passing through from the front to the back are formed at equal intervals.

[0041] (Filling sand) The filling sand can be selected from commonly used casting sands. As the filling sand, for example, silica sand, zircon sand, chromite sand, olivine sand, alumina sand, artificial sand (ceramic-based), and a mixture of these sands can be used. The sand used for the filling sand is not particularly limited and can be selected from the perspective of heat resistance according to the metal to be cast.

[0042] It is preferable that the permeability of the filling sand is high so that the gas generated from the molten metal or the core member is discharged outside the core. Specifically, it is preferable that the permeability of the filling sand is higher than that of the core member. As the particle size of the sand increases, the gap between the sands becomes larger and the permeability improves. Therefore, it is preferable that the average particle size of the filling sand is larger than the average particle size of the molding sand. When filling the filling sand, if the filling sand with a larger average particle size than the molding sand is used, the gap between the particles of the filling sand becomes larger, and the permeability of the core can be improved. It is preferable that the average particle size of the filling sand is 3 times or more the average particle size of the molding sand. Thereby, the permeability of the core can be further improved.

[0043] On the other hand, in order to trace the surface shape of the core onto the casting, it is desirable to use the maximum average particle size of the filling sand as 3 times the average particle size of the molding sand as a guideline. The core receives the pressure of the molten metal. Although the core member 100 is hardened, its strength decreases and its deformability increases due to the heat of the molten metal. Therefore, the core member 100 is likely to follow the unevenness of the filling sand at the interface between the core member 100 and the filling sand. Since the surface of the core is transferred to the surface of the casting, it is not preferable that the average particle size of the filling sand becomes larger than the average particle size of the sand of the core member 100 and the unevenness of the surface of the core becomes too large. However, when the geometric tolerance required for the cast surface portion where the core is transferred is not strict, there is no need to be particular about the average particle size of the filling sand.

[0044] Since the filling sand needs to be evenly filled in the hollow part of the core, it is preferably highly fluid. If the filling sand is not evenly filled and there are filling irregularities, the core is likely to be deformed by the pressure of the molten metal. When the amount of deformation increases, the dimensions of the hollow part of the casting deviate from the predetermined values. From this perspective, the angle of repose of the filling sand is preferably 45° or less, more preferably 40° or less. Also, the angle of repose of the filling sand is preferably 25° or more. This is because the air permeability can be improved during filling when it is 25° or more.

[0045] The average particle size of the filling sand is preferably 100 μm or more and 350 μm or less. By setting the average particle size of the filling sand to 100 μm or more, the air permeability of the core can be improved. Also, by setting the average particle size of the filling sand to 350 μm or less, the surface unevenness due to the filling sand can be reduced, and the shape transferred to the casting can be smoothed. It is preferable that no binder is contained between the particles of the filling sand. This can avoid the binder becoming a gas generation source due to the heat of the molten metal.

[0046] [Examples] Following the above method, a core member was fabricated and casting was performed. CJP660 (manufactured by 3D SYSTEMS) was used as the 3D printer. TCaST (manufactured by Taiheiyo Cement Corporation, average particle size is 100 μm) was used as the molding sand.

[0047] First, a hollow core member having the shape shown in FIG. 1 was fabricated. Samples Nos. 1 to 20 of core members with a diameter of φ40 × 250 mm and a wall thickness (thickness of the wall part) as shown in Table 1 were molded. At the end, the uncured sand was discharged, and a hole with a diameter of φ20 was provided as the injection port for the filling sand. [Table 1]

[0048] As the main mold, an upper mold and a lower mold having the shape shown in FIG. 2 were fabricated by a 3D printer in the same manner as the core member. The injection port of the filling sand was oriented upward, and the core member was placed between the upper mold and the lower mold. When the upper mold and the lower mold were combined, the overall external dimensions of the main mold were width 430 mm × depth 200 mm × height 70 mm.

[0049] A heating sleeve (not shown) serving as a sprue was installed at the molten metal inlet on the upper surface of the upper mold. A 10 kg weight was placed on the upper mold so that the upper mold would not be lifted by the pressure of the molten metal during pouring. As the filling sand, silica sand with a purity of 99.8% or more, whose angle of repose and average particle size were adjusted as shown in the table, was used.

[0050] The average particle size was measured using a laser diffraction type particle size distribution analyzer with D50 as the average particle diameter. The average particle size was measured using MT3300EXII (manufactured by MicrotracBEL) as the particle size distribution analyzer. The angle of repose was measured using a Powder Tester PT-X (manufactured by Hosokawa Micron). FCD450 was poured as molten metal from the heating sleeve. The molten metal was cooled, the mold was broken, and the part of the heating sleeve was cut. The obtained casting had the appearance shown in Fig. 3.

[0051] Fig. 4 is a perspective view showing the cut surface of the casting. The casting was cut at the position of the dotted line (passing through the center of the hole in the cylinder). Fig. 5 is a perspective view showing the cut casting. The appearance after cutting is as shown in Fig. 5. The performance of the core member was evaluated by observing the surface of the hole at the cut part 310.

[0052] The performance was evaluated by the defects of the casting and the surface roughness of the surface of the casting at the part 310 shown in Fig. 4. Regarding the defects, the presence or absence of common defects occurring in the casting was confirmed. Regarding the surface roughness, it was evaluated based on an Alasa standard piece manufactured by Nippon Metal Electroforming Co., Ltd.

[0053] For Sample Nos. 1 to 10, no surface defects were observed and the maximum height of the surface roughness was 35 s or less, so they were evaluated as "OK". For Sample Nos. 12 and 13, the occurrence of insertion defects was observed, so they were evaluated as "NG". Since the angle of repose of the filling sand was large, there were places where the filling sand was not sufficiently filled in the hollow part of the core member, and cracks entered the core member from there due to the pressure of the molten metal, and the molten metal invaded the cracks, resulting in insertion defects.

[0054] Samples No. 15 to 17 showed the occurrence of gas defects and were evaluated as "NG". Since the particle size of the filling sand was small, the gas discharge was insufficient, resulting in gas defects in the casting. Sample No. 18 showed the occurrence of gas defects and was evaluated as "NG". Although the gas discharge ability was sufficient based on the angle of repose and particle size of the internal sand, the thickness of the core member was as thick as 12 mm, so the amount of gas generated from the outside was large, resulting in gas defects in the casting.

[0055] Sample No. 19 showed the occurrence of insertion defects and was evaluated as "NG". Since there was no filling sand, the strength could not be ensured, cracks occurred in the core due to the pressure of the molten metal, and the molten metal invaded into the hollow part of the core, resulting in defects.

[0056] Sample No. 20 had a thin wall thickness of the core member and was damaged when taken out from the 3D printer, so it was evaluated as "NG". Samples No. 11 and 14 had a rougher surface roughness than the OK samples but were evaluated as "OK depending on the application". Specifically, the average particle size of the filling sand was more than three times the average particle size of the molding sand used for the core member, and undulations were observed on the casting surface. Thus, although the surface roughness was inferior to that of the OK samples, it may be recognized as "OK" as long as it is limited to products for specific applications. For example, it is fully possible to apply it to mechanical parts that transfer fluids or powders that do not require such high transfer accuracy for specific applications.

[0057] The evaluation of Samples No. 1 to 20 is related to the characteristics of the filling sand. Figure 5 is a graph plotting the samples in relation to the angle of repose and average particle size of the filling sand. In Figure 5, ● indicates samples evaluated as "OK", ▲ indicates samples evaluated as "OK depending on the application", and × indicates samples evaluated as "NG". It was confirmed that the angle of repose is preferably 40° or less, but even when it exceeds 40°, it may be evaluated as "OK" if the average particle size is 300 μm or less. Also, it was confirmed that the condition for avoiding an "NG" evaluation is that the average particle size is generally 100 μm or more.

Explanation of Symbols

[0058] 100 Core member 110 (Wall of the core member) 120 holes 210 upper mold 211 (wall of the upper mold) 212 injection port 220 lower mold 300 casting 310 (part of the casting)

Claims

Claim 1 A method for manufacturing a core member for casting, comprising: a step of spreading molding sand used for molding a mold to a uniform thickness; a step of spraying a binder onto the molding sand to cure the molding sand, and repeating a series of these steps to produce the core member using an additive manufacturing apparatus; wherein the core member: has a hollow structure provided with a hole that also serves as an inlet for filling sand, an outlet for the uncured molding sand, and a vent for gas generated during casting; is characterized in that the thickness of the wall portion forming the hollow structure is 2 mm to 10 mm, the angle of repose of the filling sand is 25° to 41°, and the average particle diameter of the filling sand is 98 μm to 350 μm.

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