Casting method

Abstract

To provide a casting method capable of effectively preventing a shrinkage cavity defect of a product.SOLUTION: A casting method for obtaining a cast product by pouring a molten metal into a mold includes a step of grasping a shrinkage cavity defect occurrence prediction part in which the occurrence of a shrinkage cavity defect is predicted by solidification analysis simulation for analyzing the solidification state of the molten metal when the molten metal is poured into a mold to be cast in the presence of a riser, a step of forming a member having a shape and a size capable of covering the shrinkage cavity defect occurrence prediction part by lamination molding, a step of arranging the member formed by lamination molding so as to cover the shrinkage cavity defect occurrence prediction part at a position corresponding to the shrinkage cavity defect occurrence prediction part in an actual casting mold in which the actual casting is performed, and a step of pouring the molten metal into the actual casting mold, and casting the arranged member to obtain the cast product.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a casting method suitable for producing castings prone to shrinkage cavity defects. [Background technology]

[0002] Castings are produced by pouring molten metal into a mold, but shrinkage defects occur in the product due to solidification and shrinkage of the molten metal. In order to prevent such shrinkage defects, it is common to provide a riser to supply molten metal to the product part of the casting (see, for example, paragraph 0002 of Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2023-25999 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when casting a complex product, it is difficult to determine the location where shrinkage cavities will occur, and even if a feeder is provided, there are cases where molten metal cannot be supplied to the required location, making it difficult to sufficiently suppress shrinkage cavities. Also, although it has been considered to determine in advance the locations where shrinkage cavities are likely to occur and take measures to ensure that molten metal is supplied sufficiently to those locations, depending on the location, it may be difficult to supply molten metal even if a feeder is provided.

[0005] Therefore, an object of the present invention is to provide a casting method that can effectively prevent shrinkage cavity defects in products. [Means for solving the problem]

[0006] The present invention provides the following means (1) to (4).

[0007] (1) A casting method for obtaining a casting by pouring molten metal into a mold, a step of grasping shrinkage cavity defect occurrence predicted areas where shrinkage cavity defects are predicted to occur by a solidification analysis simulation that analyzes the solidification state of the molten metal when the molten metal is poured into a mold to be cast in the presence of a feeder; forming a member having a shape and size capable of covering the shrinkage cavity defect occurrence predicted portion by additive manufacturing; a step of arranging the member at a position corresponding to the shrinkage cavity defect occurrence predicted portion in an actual mold for actual casting so as to cover the shrinkage cavity defect; a step of pouring molten metal into the solid mold, inserting the member, and obtaining a casting; A casting method comprising the steps of:

[0008] (2) The step of grasping the shrinkage cavity defect occurrence predicted portion includes: The casting method according to (1), characterized in that a time to reach a flow limit solid fraction at each position in the mold is obtained by the solidification analysis simulation, and the shrinkage cavity defect occurrence prediction portion is grasped from the time to reach a flow limit solid fraction.

[0009] (3) The casting method according to (2), characterized in that a solidification delay portion, which exists in a portion away from the feeder and in which the time to reach the flow limit solid phase fraction is relatively long and solidification is delayed, is set as the shrinkage cavity defect occurrence prediction portion.

[0010] (4) The casting method according to any one of (1) to (3), wherein, when the shrinkage cavity occurrence predicted portion is separated into two or more portions, the member has a structure in which two or more portions corresponding to the two or more portions of the shrinkage cavity occurrence predicted portion are connected by a connecting portion. [Effects of the Invention]

[0011] According to the present invention, shrinkage cavity defect prediction areas where shrinkage cavity defects are predicted to occur are identified by solidification analysis simulation, a member corresponding to the shrinkage cavity defect prediction area is formed by additive manufacturing, and the member formed by additive manufacturing is placed at a corresponding position in an actual mold and cast-in, thereby making it possible to effectively prevent shrinkage cavity defects in the product. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a vertical cross-sectional view schematically showing a general mold used in casting. [Figure 2] FIG. 1 is a cross-sectional view schematically showing a general mold used in casting. [Figure 3] 1 is a flowchart illustrating a casting method according to an embodiment of the present invention. [Figure 4] FIG. 2 is a longitudinal cross-sectional view schematically illustrating a state in which an additive manufacturing member is placed in the mold illustrated in FIG. 1 and molten metal is poured into the mold to cast-in the additive manufacturing member. [Figure 5] FIG. 10 is a diagram showing the results of determining the time to reach the flow limit solid fraction for a part of a casting by solidification analysis simulation. [Figure 6] 6(a) is a diagram showing the time to reach the flow limit solid fraction of the α cross section (as viewed from the α arrow) in FIG. 5, and FIG. 6(b) is a diagram showing the time to reach the flow limit solid fraction of the β cross section (as viewed from the β arrow) in FIG. 5. [Figure 7] 5. (a) shows the volume filling rate of the α cross section (as viewed from the α arrow) in FIG. 5, and (b) shows the volume filling rate of the β cross section (as viewed from the β arrow) in FIG. [Figure 8] 10A and 10B are diagrams showing a state in which an additively manufactured component having a shape and size capable of covering an area where shrinkage cavities are predicted to occur is placed at a position corresponding to the area where shrinkage cavities are predicted to occur, where (a) is a perspective view of the additively manufactured component placed in a casting and the additively manufactured component itself, and (b) is a β-sectional view thereof. [Figure 9] This figure shows a comparison of the time to reach the flow limit solid fraction when a solidification analysis simulation is performed with and without an additive manufacturing component, and corresponds to the β cross section of the casting. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a schematic longitudinal cross-sectional view of a typical mold used in casting, and FIG. 2 is its transverse cross-sectional view. Mold 1 has a casting space S shaped to correspond to the casting to be obtained and functions to solidify the molten metal poured into it. Mold 1 consists of an upper mold 1a and a lower mold 1b. Note that for convenience, the shape of the casting space S is depicted as a simple rectangular parallelepiped in FIGS. 1 and 2, but in reality, it has a complex shape depending on the product. A feeder space 2 connected to the casting space S is provided above the upper mold 1a. Mold 1 (upper mold 1a) is also provided with a sprue 3 through which molten metal is poured. A horizontal runner 4 is connected to sprue 3, surrounding space S. Multiple molten metal inlet ports 5 are provided to connect runner 4 to space S.

[0014] Molten metal supplied to a gate 3 is fed into space S of the mold 1 via a runner 4 and a molten metal inlet 5, and casting is performed. The molten metal is supplied to the feeder space 2 in addition to the casting space S, and the molten metal supplied to the feeder space 2 functions as a feeder that replenishes the molten metal to prevent shrinkage cavities caused by solidification shrinkage of the molten metal.

[0015] However, when a complex product is cast, it is difficult to grasp the location where shrinkage cavities will occur, and even if a feeder head is provided, there are cases where molten metal cannot be supplied sufficiently to the required location. Furthermore, although the location where shrinkage cavities are likely to occur is grasped in advance by simulation, if the molten metal loses fluidity before reaching the location where shrinkage cavities are likely to occur, the molten metal will not be supplied to the location where shrinkage cavities are likely to occur, making it difficult to effectively prevent shrinkage cavities.

[0016] Therefore, in this embodiment, when a molten metal is poured into a mold to obtain a casting, shrinkage cavities that may occur even in the presence of a feeder are effectively prevented.

[0017] A casting method according to one embodiment of the present invention that effectively prevents such shrinkage cavity defects will now be described. Fig. 3 is a flowchart showing the casting method according to one embodiment of the present invention.

[0018] First, a shrinkage cavity occurrence prediction area where the occurrence of shrinkage cavities is predicted is identified by a solidification analysis simulation that analyzes the solidification state of molten metal when the molten metal is poured into a mold to be cast in the presence of a feeder (step ST1).

[0019] The solidification analysis simulation in this case analyzes the solidification process of the molten metal when it is supplied and poured into the actual mold where the casting will be performed. Various solidification analysis simulations during casting have been studied in the past, and can be performed using existing software.

[0020] The shrinkage cavity defect occurrence prediction area is grasped by solidification analysis simulation, for example, by determining the flow limit solid fraction arrival time at each position in the mold by solidification analysis simulation and using this flow limit solid fraction arrival time.

[0021] The time to reach the limit of solid fraction flow refers to the time required to reach the solid fraction at which the liquid phase flow is inhibited, and the smaller this value, the shorter the time it takes for the liquid phase fluidity to be inhibited. Conversely, if this value is large, the molten metal will remain in a state of fluidity for a long time.

[0022] Shrinkage cavities can be suppressed by supplying molten metal from the feeder. However, when casting a complex shape, there may be a solidification retardation zone away from the feeder where the time to reach the flow limit solid fraction is relatively long and solidification is delayed. When such a solidification retardation zone exists, the zone between the feeder and the solidification retardation zone reaches the flow limit solid fraction first, making it difficult for molten metal to be supplied to the solidification retardation zone that has not yet reached the flow limit solid fraction, even if solidification shrinkage occurs. Therefore, shrinkage cavities are predicted to occur in such a solidification retardation zone. Therefore, when a solidification retardation zone away from the feeder is detected by solidification analysis simulation, the solidification retardation zone can be recognized as a shrinkage cavity occurrence prediction zone.

[0023] Next, a member having a shape and size capable of covering the predicted shrinkage cavity defect occurrence area is formed by additive manufacturing (step ST2). This member (hereinafter also referred to as an additively manufactured member) is placed in the actual mold so as to correspond to the shrinkage cavity defect predicted portion, as described below, and has a shape and size that will include the entire shrinkage cavity defect predicted portion when placed. The additively manufactured member is desirably designed to have a shape and structure that makes it easy to place in the actual mold. When the shrinkage cavity defect predicted portion is present in two or more separate parts, the additively manufactured member may have a structure in which two or more parts corresponding to the two or more parts of the shrinkage cavity defect predicted portion are connected by a connecting portion. This makes it easy to place in the actual mold even when it has two or more separate parts.

[0024] Additive manufacturing is a technology in which a laser or electron beam is applied to powder typically formed in layers to melt and solidify it, and this process is repeated to build up the desired shape. Additive manufacturing allows for extremely fast cooling rates during melting and solidification, exceeding 3000°C / sec, which is not possible when cooling using a conventional mold, resulting in fine parts with extremely few defects. In addition, additive manufacturing can produce parts exactly as designed using a 3D printer or other device, so it can also handle complex shapes.

[0025] Powders used in additive manufacturing can be gas atomized powder or water atomized powder. Gas atomized powder is formed by dropping molten metal and spraying an inert gas (e.g., Ar gas) from a nozzle onto the dropped molten metal to form powder, while water atomized powder is formed by spraying water onto the dropped molten metal to form powder.

[0026] Next, an additively manufactured member formed by additive manufacturing is placed at a position corresponding to the predicted shrinkage cavity defect occurrence area in the actual mold where casting will be performed so as to cover the predicted shrinkage cavity defect occurrence area (step ST3). The actual mold used in this case is the same mold as the mold used in the solidification analysis simulation in step ST1, and its basic structure is exemplified by the one schematically shown in FIGS.

[0027] As described above, the additively manufactured member has a shape and size that allows it to cover the predicted shrinkage cavity defect area. Therefore, by placing the additively manufactured member in the actual mold at a position corresponding to the predicted shrinkage cavity defect area so as to cover the predicted shrinkage cavity defect area, the predicted shrinkage cavity defect area can be covered by the additively manufactured member.

[0028] Next, molten metal is poured into the actual mold, and the additive manufacturing member is cast-in to obtain a casting (step ST4). The casting material is not particularly limited as long as it is made of a metal material, and various materials such as iron-based materials and aluminum materials can be used. One example of an iron-based material is a steel casting, such as a steel casting for a welded structure. From the viewpoint of obtaining a casting with a uniform material, it is preferable that the molten metal and the additive manufacturing member are made of the same material.

[0029] The casting process will be described schematically. Figure 4 is a longitudinal cross-sectional view showing the state in which an AM component is placed in the mold shown in Figure 1 and molten metal is poured into it to encase the AM component. For convenience, Figure 4, like Figure 1, depicts the shape of the pouring space S as a simple rectangular parallelepiped. As shown in Figure 4, molten metal L is poured into the mold 1, in which the AM component 6 is placed, via the sprue 3, runner 4, and molten metal inlet 5, to encase the AM component 6. In Figure 4, reference numeral 7 denotes a feeder filled in the feeder space 2. As described above, the feeder 7 serves to supply molten metal L to the pouring space S. The AM component 6 is positioned so as to correspond to the area where shrinkage cavities are predicted to occur. When the molten metal L poured into the mold 1 solidifies, it is integrated with the AM component 6 to produce a casting. The casting is then removed by removing the mold 1.

[0030] As described above, in this embodiment, the predicted shrinkage cavity defect occurrence area is identified using a solidification analysis simulation, and an additively manufactured member is placed in the part of the mold corresponding to the predicted shrinkage cavity defect occurrence area and cast-in. However, since additively manufactured members essentially have almost no defects, shrinkage cavities can be effectively prevented by placing the additively manufactured member so that it covers the predicted shrinkage cavity defect occurrence area. Furthermore, since additive manufacturing can form members of any shape as designed, even if the part where shrinkage cavities are predicted has a complex shape, it is easy to create a member of a corresponding shape and size.

[0031] In addition, by placing the additively manufactured component within the mold, it also functions as a chiller within the mold, and the cooling of the molten metal by the additively manufactured component further promotes directional solidification, further increasing the effectiveness of preventing casting defects such as shrinkage cavities.

[0032] Next, the results of actually determining the time to reach the flow limit solid fraction by solidification analysis simulation and identifying the predicted areas for shrinkage cavity occurrence will be described.

[0033] Figure 5 shows the results of solidification analysis simulation to determine the time to reach the flow limit solid fraction for a portion of a casting. Figure 6(a) shows the time to reach the flow limit solid fraction for the α cross section (as viewed by the α arrow) in Figure 5, and Figure 6(b) shows the time to reach the flow limit solid fraction for the β cross section (as viewed by the β arrow) in Figure 5. Although Figures 5 and 6 are shown in grayscale, they are actually color images.

[0034] As shown in Figure 5, the casting used in the solidification analysis simulation has a complex shape with ribs and hollowed holes, and multiple feeders are installed on its upper surface. In these figures, both long and short flow limit times are indicated in light gray. However, in reality, the flow limit times are long at the feeder, exceeding 650 seconds, while the flow limit times for the majority of the product are short, at less than 100 seconds. However, the areas marked with circles in Figures 5 and 6 have flow limit times of approximately 300–600 seconds, longer than the rest of the product. In other words, the areas marked with circles have a longer flow limit time than the areas between the feeder and the circle, while the area between the feeder and the circle reaches the flow limit in a shorter time (see the area surrounded by the dashed line in Figure 6(a)). Therefore, the areas marked with circles are areas where molten metal supply from the feeder is cut off, and shrinkage cavities are predicted to occur.

[0035] Figure 7(a) shows the volume fill factor of the α cross section (as viewed by the α arrow) in Figure 5, and (b) shows the volume fill factor of the β cross section (as viewed by the β arrow) in Figure 5. Figure 7 is also shown in grayscale, but it is actually a color image. As shown in Figure 7, the area marked with a circle, where shrinkage cavities are predicted to occur, is predicted to have a low volume fill factor, confirming that shrinkage cavities will occur in the area marked with a circle.

[0036] 8A and 8B are diagrams showing the state in which an additively manufactured component having a shape and size sufficient to cover the predicted shrinkage cavity area is placed in a position corresponding to the predicted shrinkage cavity area. (a) is a perspective view of the additively manufactured component placed in the casting and the additively manufactured component itself, and (b) is a β-sectional view of the additively manufactured component. As shown in FIG. 8A, the additively manufactured component 6 has a structure in which two separate portions 6a are connected by a connecting portion 6b so as to correspond to the two separate portions of the predicted shrinkage cavity area. The additively manufactured component 6 in this example has a thin edge design to make it easier to integrate with the cast portion.

[0037] Figure 9 shows a comparison of the time to reach the flow limit solid fraction when a solidification analysis simulation is performed with and without an additively manufactured component. Similar to Figure 6(b), this figure corresponds to the β cross section of the cast product. When no additively manufactured component is provided, as shown in (b), areas where shrinkage cavities are predicted to occur are visible, whereas when an additively manufactured component is provided, as shown in (a), the predicted areas are eliminated. This confirms the effectiveness of providing an additively manufactured component.

[0038] It should be noted that the above-described embodiments are merely illustrative and should not be considered limiting, and may be omitted, substituted, or modified in various ways without departing from the spirit of the present invention.

[0039] For example, grasping the shrinkage cavity defect occurrence prediction portion by solidification analysis simulation is not limited to the above embodiment. Furthermore, the shapes of the mold and the cast product are merely examples, and various shapes can be used. [Explanation of symbols]

[0040] 1; Mold 1a; Upper mold 1b; lower mold 2. Feeder space 3; Sprue 4; Yudo 5: Molten metal inlet 6: Additive manufacturing components 7. Riser L: molten metal S: Casting space

Claims

1. A casting method for obtaining a casting product by pouring molten metal into a mold, comprising the steps of: a step of grasping shrinkage cavity defect occurrence predicted areas where shrinkage cavity defects are predicted to occur by a solidification analysis simulation that analyzes the solidification state of the molten metal when the molten metal is poured into a mold to be cast in the presence of a feeder; forming a member having a shape and size capable of covering the shrinkage cavity defect occurrence predicted portion by additive manufacturing; a step of arranging the member at a position corresponding to the shrinkage cavity defect occurrence predicted portion in an actual mold for actual casting so as to cover the shrinkage cavity defect; a step of pouring molten metal into the solid mold, inserting the member, and obtaining a casting; A casting method comprising the steps of:

2. The step of grasping a shrinkage cavity defect occurrence predicted portion includes:

2. The casting method according to claim 1, wherein a time to reach a flow limit solid fraction at each position in the mold is calculated by the solidification analysis simulation, and the shrinkage cavity defect occurrence prediction portion is determined from the time to reach a flow limit solid fraction.

3. The casting method according to claim 2, characterized in that the shrinkage cavity defect occurrence prediction portion is a solidification delay portion which exists in a portion away from the feeder head and in which solidification is delayed due to a relatively long time to reach the flow limit solid phase fraction.

4. 4. The casting method according to claim 1, wherein, when the shrinkage cavity defect occurrence predicted portion is present in two or more separated portions, the member has a structure in which two or more portions corresponding to the two or more portions of the shrinkage cavity defect occurrence predicted portion are connected by a connecting portion.

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