Apparatus and method for predicting the location of shrinkage cavities in castings

Abstract

This invention provides a device and method for predicting the location of shrinkage cavities in castings, thereby increasing the options for preventing shrinkage cavities in castings. [Solution] The present disclosure relates to a device for predicting the location of shrinkage cavities in a casting made by pouring molten metal into a mold, and includes: a measurement point setting unit for setting a plurality of measurement points P on the casting; a molten metal supply limit solid phase ratio arrival time calculation unit for calculating the molten metal supply limit solid phase ratio arrival time T, which is the time until the molten metal reaches a solid phase ratio at which it can no longer flow; a solidification path setting unit for setting a solidification path R of the casting by connecting the measurement points P selected based on the molten metal supply limit solid phase ratio arrival time T; a surface distance calculation unit for calculating the distance D from each measurement point P to the surface of the casting closest to the measurement point P on the solidification path R; and a molten metal supply interruption location identification unit for identifying a molten metal supply interruption location P1 that interrupts the supply of molten metal during solidification of the casting based on the distance D to the surface of the casting.

Description

Technical Field

[0001] The present disclosure relates to an apparatus and method for predicting the occurrence position of shrinkage cavities in cast products.

Background Art

[0002] Patent Document 1 discloses a method for predicting the occurrence position of shrinkage cavities in a cast product manufactured by injecting molten metal into a mold. For each internal point in the cast product, after obtaining the radius value of a virtual inscribed sphere, the range of internal points where the radius value is larger than the reference radius value is obtained, thereby identifying the sites where shrinkage cavities are likely to occur.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Thinning can be considered as a countermeasure for sites where shrinkage cavities are likely to occur, but there are cases where thinning is not possible depending on the performance required for the cast product. Therefore, various options are required for countermeasures for sites where shrinkage cavities are likely to occur. The present disclosure solves such problems and provides an apparatus and method for predicting the occurrence position of shrinkage cavities in a cast product that can increase the options for countermeasures against shrinkage cavities in the cast product.

Means for Solving the Problems

[0005] This disclosure relates to an apparatus for predicting the location of shrinkage cavities in a casting made by pouring molten metal into a mold, and includes: a measurement point setting unit for setting a plurality of measurement points on the casting; a molten metal supply limit solid phase ratio arrival time calculation unit for calculating the time until the molten metal reaches a solid phase ratio at which it is no longer possible to flow the molten metal for each measurement point; a solidification path setting unit for setting a solidification path of the casting by connecting the measurement points selected based on the molten metal supply limit solid phase ratio arrival time; a surface distance calculation unit for calculating the distance from each measurement point to the surface of the casting closest to the measurement point; and a molten metal supply interruption location identification unit for identifying a molten metal supply interruption location that interrupts the supply of molten metal during solidification based on the distance to the surface of the casting. This configuration increases the options for preventing shrinkage cavities in castings.

[0006] This disclosure relates to a method for predicting the location of shrinkage cavities in a casting made by pouring molten metal into a mold, comprising the steps of: setting a plurality of measurement points on the casting; calculating the time to reach the molten metal replenishment limit solid phase ratio, which is the time until the molten metal reaches a solid phase ratio at which it can no longer flow, for each of the measurement points; setting a solidification path for the casting by connecting the measurement points selected based on the time to reach the molten metal replenishment limit solid phase ratio; calculating the distance from each measurement point in the solidification path to the nearest surface of the casting; and identifying a molten metal replenishment interruption point that interrupts the replenishment of molten metal during solidification based on the distance to the surface of the casting. This configuration increases the options for preventing shrinkage cavities in castings. [Effects of the Invention]

[0007] This disclosure provides a device and method for predicting the location of shrinkage cavities in castings, which can increase the options for countermeasures against shrinkage cavities in castings. [Brief explanation of the drawing]

[0008] [Figure 1] This is a perspective cross-sectional view of a cylinder head, showing the location of shrinkage cavities. [Figure 2]Figure 1 is a partial cross-sectional view of the cylinder head as seen from the direction indicated by II. [Figure 3] This is a block diagram of a device for predicting the location of shrinkage cavities according to an embodiment. [Figure 4] This is an explanatory diagram of the shrinkage cavity location prediction method according to an embodiment. (a) Shows the state in which molten metal is being filled into the cavity. (b) Shows the state in which the filling of the cavity with molten metal is completed. (c) Shows the state in which solidification of the molten metal has begun. (d) Shows the state in which solidification of the molten metal has progressed and molten metal supply has been cut off. [Figure 5] This flowchart shows an example of a method for predicting the location of shrinkage cavities according to an embodiment. [Figure 6] Figure 1 shows an example of the solidification path and the time required to reach the molten metal supply limit for a cylinder head. [Figure 7] This graph shows the relationship between the time it takes to reach the molten metal supply limit solid fraction and the surface distance at each measurement point along the solidification path. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure will be described below with reference to Figures 1 to 7. Figure 1 is a perspective cross-sectional view of a cylinder head used to predict the location of shrinkage cavities. Figure 2 is a partial cross-sectional view of the cylinder head shown in Figure 1, viewed from the direction indicated by II. Figure 3 is a block diagram showing a shrinkage cavity location prediction device according to an embodiment. Figure 4 is an explanatory diagram of a shrinkage cavity location prediction method according to an embodiment. (a) Shows the state in which molten metal is being filled into the cavity. (b) Shows the state in which the filling of the cavity with molten metal is complete. (c) Shows the state in which solidification of the molten metal has begun. (d) Shows the state in which solidification of the molten metal has progressed and molten metal supply has been cut off. Figure 5 is a flowchart showing an example of a shrinkage cavity location prediction method according to an embodiment. Figure 6 is a diagram showing an example of the solidification path and the time it takes to reach the molten metal supply limit solid fraction of the cylinder head used to predict the location of shrinkage cavities. Figure 7 is a graph showing the relationship between the time it takes to reach the molten metal supply limit solid fraction of the measurement point in the solidification path and the surface distance.

[0010] Figures 1 and 2 illustrate the cylinder head 10 used to predict the location of shrinkage cavities. The cylinder head 10 is a cylinder head for an inline four-cylinder engine with four combustion chambers and is made of aluminum alloy. The cylinder head 10 is a casting made by pouring molten aluminum into a mold containing a core. Note that the casting method for predicting the location of shrinkage cavities is not limited to engine cylinder heads but can be applied to various other castings.

[0011] The cylinder head 10 is cast using a low-pressure casting method. However, other casting methods such as gravity casting, tilting casting, and die casting are also acceptable. For the molten aluminum, for example, an aluminum alloy with added magnesium or copper (e.g., ADC1) is used. However, it is not limited to aluminum alloys; magnesium alloys, zinc alloys, copper alloys, etc., may also be used. Molds such as metal molds or sand molds are used.

[0012] The sprue 15, through which molten aluminum is injected into the cavity formed in the mold, is located below the cylinder head 10 (shown by a dashed line in Figure 2). The molten aluminum injected from the sprue 15 fills the cavity formed in the mold from the bottom to the top (from the bottom to the top of the cylinder head 10 as shown in Figure 2).

[0013] Next, the casting cavity location prediction device 20 according to the embodiment will be described using Figure 3. The casting cavity location prediction device 20 comprises an input device 21, a storage device 22, a calculation device 23, and an output device 24.

[0014] The input device 21 consists of a keyboard, mouse, etc., and is used to input information such as the shape and dimensions of the cylinder head 10, the temperature and material of the mold, the temperature and material of the molten aluminum, and the casting conditions.

[0015] The memory device 22 is composed of a RAM (Random Access Memory), a ROM (Read Only Memory), etc., and stores information input from the input device 21, an arithmetic program related to the method for predicting the occurrence position of shrinkage cavities in cast products, etc.

[0016] The arithmetic device 23 is composed of a CPU (Central Processing Unit), etc., and executes an arithmetic program related to the method for predicting the occurrence position of shrinkage cavities in cast products stored in the memory device 22.

[0017] The output device 24 is composed of a display, etc., and outputs the result of executing the arithmetic program by the arithmetic device 23.

[0018] Subsequently, the concept of the method for predicting the occurrence position of shrinkage cavities in cast products according to the embodiment will be described using FIG. 4. The cavity 30 of the mold shown in FIG. 4 has an elongated plate shape, and a constriction 31 with a reduced width in the width direction is formed at the central portion in the length direction. Molten metal obtained by melting an aluminum alloy is injected into the cavity 30 by the low-pressure casting method. The pouring gate 35 for injecting the molten metal into the cavity 30 is provided below the cavity 30.

[0019] First, as shown in FIG. 4(a), the molten metal 33 is injected into the cavity 30 from the pouring gate 35 at a predetermined pressure, so that the lower part of the cavity 30 is filled with the molten metal 33.

[0020] Subsequently, as shown in FIG. 4(b), when the molten metal 33 reaches the portion of the cavity 30 farthest from the pouring gate 35, the filling of the molten metal 33 into the cavity 30 is completed.

[0021] Subsequently, as shown in FIG. 4(c), the solidification 34 of the molten metal starts. The solidification 34 of the molten metal starts from the molten metal portion away from the pouring gate 35 and from the outer peripheral side of the cavity 30. When the molten metal is solidified 34, the aluminum metal shrinks. Although a space is generated in the cavity 30 due to the shrinkage of the aluminum alloy, since the molten metal 33 is replenished from the pouring gate 35, no space that causes shrinkage cavities occurs.

[0022] Next, as shown in Figure 4(d), as the solidification of the molten metal 34 progresses, a portion of the constriction 31 solidifies along its entire width. On the other hand, there is still unsolidified molten metal 33 remaining in the cavity 32, which is further from the sprue 35 than the constriction 31. Since the molten metal 33 remaining in the cavity 32 is not connected to the sprue 35, no more molten metal 33 is supplied. As a result, shrinkage cavities occur in the region of the cavity 32 where molten metal 33 remains.

[0023] Thus, if there is a point (for example, the constriction 31 shown in Figure 4) that breaks the connection between the molten metal 33 and the sprue 35 before the molten metal solidifies, shrinkage cavities will occur. In other words, by identifying the point where the connection between the molten metal and the sprue is broken and the supply of molten metal is cut off (hereinafter referred to as the molten metal supply interruption point), the location of shrinkage cavities can be predicted.

[0024] Next, we will explain the method for predicting the location of shrinkage cavities in castings using the casting cavity location prediction device 20 with reference to Figures 5 to 7. Figure 5 is a flowchart showing an example of the method for predicting the location of shrinkage cavities performed by the casting cavity location prediction device 20.

[0025] In step S1, information such as the shape and dimensions of the cylinder head 10, which is used to predict the location of shrinkage cavities, is obtained from the storage device 22. The information about the cylinder head 10 is obtained by the information acquisition unit of the arithmetic unit 23.

[0026] In step S2, multiple measurement points P are set on the cylinder head 10. The measurement points P are set in the measurement point setting unit of the calculation unit 23. As shown in Figure 6, the measurement points P are set at the center of each of the approximately cubic spaces obtained by dividing the 3D model of the cylinder head 10 three-dimensionally at a predetermined pitch. Note that only a portion of the measurement points P are shown in Figure 6. The size of the pitch can be set arbitrarily. Also, the spaces obtained by the division can be set to various shapes other than cubes.

[0027] In step S3, the time to reach the molten metal replenishment limit solid fraction T is calculated for each measurement point P, which is the time until the molten aluminum reaches a solid fraction that can no longer flow. The calculation of the time to reach the molten metal replenishment limit solid fraction T is performed by the calculation unit of the calculation device 23. The time to reach the molten metal replenishment limit solid fraction T is calculated based on the temperature of the molten aluminum poured into the mold, the temperature of the mold, the distance from the sprue 15, etc. The solid fraction at which the molten aluminum can no longer flow is, for example, 0.6 to 0.7. As shown in Figure 6, the time to reach the molten metal replenishment limit solid fraction T becomes shorter the further away from the sprue 15 is. That is, the further away from the sprue 15 is, the faster the solidification rate of the molten aluminum becomes, and the shorter the time until the molten aluminum reaches a solid fraction that can no longer flow is.

[0028] In step S4, the solidification path R of the cylinder head 10 is set by connecting measurement points P selected based on the time T to reach the molten metal replenishment limit solid phase ratio. The setting of the solidification path R of the cylinder head 10 is performed by the solidification path setting unit of the calculation unit 23. As shown in Figure 6, the solidification path R of the cylinder head 10 is the path connecting the measurement point P (start point) with the shortest time T to reach the molten metal replenishment limit solid phase ratio and the measurement point P (end point) closest to the sprue 15, and the solidification sequence of the molten aluminum is shown by the line.

[0029] The solidification path R of the cylinder head 10 is set by selecting measurement points P according to the following rules. First, as shown in Figure 6, the measurement point P with the shortest time T to reach the molten metal replenishment limit solid phase ratio calculated in step S3 is set as the starting point. In Figure 6, the time T to reach the molten metal replenishment limit solid phase ratio calculated for each measurement point P is divided into 7 groups according to the length of time. Therefore, in Figure 6, there are multiple measurement points P with the shortest time T to reach the molten metal replenishment limit solid phase ratio, but in reality, the time T to reach the molten metal replenishment limit solid phase ratio differs for each measurement point P, and the measurement point P with the shortest time T to reach the molten metal replenishment limit solid phase ratio is set as the starting point.

[0030] Next, among the measurement points P adjacent to the starting point, if there is a measurement point P where the time to reach the molten metal replenishment limit solid phase ratio T is longer than the time to reach the molten metal replenishment limit solid phase ratio T at the starting point, that measurement point P is selected. The length of the time to reach the molten metal replenishment limit solid phase ratio T is compared among the seven groups shown in Figure 6. If there are multiple measurement points P where the time to reach the molten metal replenishment limit solid phase ratio T is longer, the measurement point P directly below (positive Z-axis direction in Figure 6) is selected. If there is no measurement point P where the time to reach the molten metal replenishment limit solid phase ratio T is longer, a measurement point P directly below or closer to the sprue 15 is selected. Based on these rules, measurement points P are selected up to the measurement point P closest to the sprue 15 (endpoint). Once measurement points P have been selected up to the end point, the solidification path R of the cylinder head 10 can be set by connecting the starting point and the end point with the selected measurement points P. Note that the way the measurement points P are connected between the starting point and the end point may be changed as appropriate.

[0031] In step S5, the distance D from each measurement point P in the solidification path R to the nearest surface of the cylinder head 10 is calculated. In other words, in step S5, the distance D from each measurement point P in the solidification path R to the nearest surface of the mold (including the core) is calculated. The calculation of the distance D from each measurement point P in the solidification path R to the nearest surface of the cylinder head 10 is performed by the surface distance calculation unit of the calculation device 23. The shorter the distance D to the surface of the cylinder head 10, the shorter the distance to the mold, and the faster the molten aluminum solidifies.

[0032] In step S6, a graph is created showing the relationship between the time T to reach the molten metal replenishment limit solid fraction and the distance D to the cylinder head surface for each measurement point P in the solidification path R. The graph showing the relationship between the time T to reach the molten metal replenishment limit solid fraction and the distance D to the cylinder head surface is created by the graph creation unit of the calculation unit 23. As shown in Figure 7, a graph is created showing the relationship between the time T to reach the molten metal replenishment limit solid fraction and the distance D to the cylinder head surface for each measurement point P in the solidification path R.

[0033] In step S7, based on the time T to reach the molten metal replenishment limit solid fraction and the distance D to the cylinder head surface, a molten metal replenishment cutoff point P1 is identified, which cuts off the supply of molten aluminum during solidification. The identification of the molten metal replenishment cutoff point P1 is performed by the molten metal replenishment cutoff point identification unit of the calculation unit 23. Specifically, based on the graph created in step S6, the measurement point P where the distance D to the cylinder head surface and the time T to reach the molten metal replenishment limit solid fraction are close together is designated as the molten metal replenishment cutoff point P1 (circled area in Figure 7). The degree of proximity required to be designated as the molten metal replenishment cutoff point P1 is set appropriately according to the time T to reach the molten metal replenishment limit solid fraction, the molten aluminum temperature, the mold temperature, casting conditions, etc. Note that a measurement point P where the distance D to the cylinder head surface is smaller than a predetermined threshold may also be designated as the molten metal replenishment cutoff point P1.

[0034] Figure 2 shows the molten metal supply interruption site P1 identified by the casting shrinkage cavity location prediction device 20. The occurrence of shrinkage cavities is predicted in the cylinder head 11 on the side of the cylinder head 11 that is further away from the sprue 15 than the molten metal supply interruption site P1. As a measure to suppress the occurrence of shrinkage cavities, it is conceivable to increase the thickness of the area around the molten metal supply interruption site P1 to increase the distance between the molten metal supply interruption site P1 and the surface of the cylinder head 10. By increasing the thickness of the area around the molten metal supply interruption site P1, the connection between the molten aluminum and the sprue 15 will not be severed before the molten aluminum solidifies in the cylinder head 11 on the side of the cylinder head 11 that is further away from the sprue 15 than the molten metal supply interruption site P1, and the supply of molten aluminum from the sprue 15 can be maintained.

[0035] Another measure to suppress the occurrence of shrinkage cavities is to thin the wall of the cylinder head 11 on the side away from the sprue 15 from the molten metal supply cutoff point P1. By thinning the wall, the molten aluminum can solidify before the connection between the molten aluminum and the sprue 15 is cut off at the molten metal supply cutoff point P1.

[0036] This disclosure sets a solidification path for a casting and identifies molten metal supply interruption points based on the distance from each measurement point to the nearest casting surface. By identifying these molten metal supply interruption points, the location of shrinkage cavities can be predicted. Furthermore, as a countermeasure against shrinkage cavities, shrinkage cavities can be suppressed not only by thinning the wall thickness of the shrinkage cavity areas but also by thickening the wall thickness of the molten metal supply interruption points. In other words, the options for countermeasures against shrinkage cavities in castings can be increased.

[0037] This disclosure is not limited to the embodiments described above, and may be modified as appropriate without departing from its spirit. [Explanation of symbols]

[0038] 10. Cylinder head 15...Spring Outlet 20. Device for predicting the location of shrinkage cavities in castings. P1... Molten metal supply interruption point

Claims

1. A device for predicting the location of shrinkage cavities in a casting made by pouring molten metal into a mold, A measurement point setting unit for setting multiple measurement points on the casting, A molten metal replenishment limit solid fraction arrival time calculation unit calculates the time until the molten metal reaches a solid fraction at each of the aforementioned measurement points, which is the time until the molten metal reaches a solid fraction at which it can no longer flow. A solidification path setting unit sets the solidification path of the casting by connecting the measurement points selected based on the time to reach the molten metal supply limit solid phase ratio, A surface distance calculation unit that calculates the distance from each measurement point in the solidification path to the surface of the casting closest to the measurement point, Includes a molten metal supply interruption location identification unit that identifies a molten metal supply interruption location that interrupts the supply of molten metal during solidification based on the distance to the surface of the casting, A device for predicting the location of shrinkage cavities in castings.

2. A method for predicting the location of shrinkage cavities in a casting made by pouring molten metal into a mold, The process of setting multiple measurement points on the casting, A step of calculating the time to reach the molten metal supply limit solid fraction, which is the time until the molten metal reaches a solid fraction that can no longer flow at each of the aforementioned measurement points, A step of setting the solidification path of the casting by connecting the measurement points selected based on the time to reach the molten metal supply limit solid phase ratio, A step of calculating the distance from each measurement point in the solidification path to the surface of the casting that is closest to the measurement point, The process includes identifying a molten metal supply interruption point that interrupts the supply of molten metal during solidification, based on the distance to the surface of the casting, A method for predicting the location of shrinkage cavities in castings.

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