Sand mold design support device and sand mold design support method

Abstract

To provide a sand mold designing support device a sand mold designing support method capable of solving a problem of insufficient strength of the sand mold before production of a mold and installation of a facility, so as to contribute to cost reduction and lead-time reduction.SOLUTION: A sand mold designing support device includes an acquisition unit for acquiring shape information indicating a shape of a sand mold or a shape of a mold corresponding to the sand mold, a storage unit, and a control device. The control device calculates molding pressures at a plurality of positions of a contact surface between the sand mold and the mold by using information on squeeze pressure to be applied to a molding device and shape information, and obtains a molding pressure ratio indicating the molding pressure to the squeeze pressure for each position. A relational formula between strength of the sand mold and the molding pressure ratio is preliminarily stored in the storage device. The control device determines a lower limit value of the molding pressure ratio necessary for molding the sand mold on the basis of the relational formula stored in the storage unit and strength required for the sand mold, and notifies a user of instructions for urging the user to change the shape of the sand mold until the minimum value of the molding pressure ratio exceeds the lower limit value.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a sand mold design support device and a sand mold design support method. [Background technology]

[0002] In sand casting, sand is pressed against a model of the product to transfer the shape and form a sand mold, molten metal is poured into the sand mold, and after the molten metal solidifies, the sand mold is dismantled to obtain the cast product. In sand casting, if the sand mold collapses when the molten metal is poured and sand gets mixed into the product, it can cause defects, so the sand mold needs to have a certain degree of strength. However, when the sand mold is made by transferring the shape of the model, it is difficult to fill the convex parts of the sand mold or the parts corresponding to the concave parts (pockets) of the model with sand, and the strength of the sand mold is easily reduced.

[0003] Equipment for improving the sand mold strength of such difficult-to-fill areas is disclosed in Japanese Patent No. 3271740 (Patent Document 1) and Japanese Patent No. 3595320 (Patent Document 2). The techniques disclosed in Patent Document 1 and Patent Document 2 both involve adding a local pressurizing mechanism to existing equipment, which increases equipment costs and maintenance costs. For this reason, the addition of such equipment should be kept to a minimum. However, these patent documents do not disclose whether or not a local pressurizing mechanism needs to be installed, or standards for its placement.

[0004] Therefore, in the technology disclosed in Patent Document 1 and Patent Document 2, it is not possible to consider the necessity of a local pressure mechanism before making a pattern for casting, and weak parts are only identified during the trial production. It takes a long time to make a pattern and install the equipment. In the technology disclosed in Patent Document 1 and Patent Document 2, the equipment to deal with weak parts is installed and adjusted after the sand mold trial production, which leads to an increase in the lead time for launching a new product.

[0005] Thus, in the shape design stage before the start of prototype production, a method for estimating the strength of the sand mold is required. For example, as shown in "Analysis of Stress Distribution in Mold during Squeezing Molding" (Non-Patent Document 1), a method for estimating the strength of the sand mold has been proposed at the academic research level.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0007]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, since the method of Non-Patent Document 1 assumes a sliding surface with the sand mold as a two-dimensional shape and integrates the stress acting on the sliding surface, it is necessary to manually set the sliding surface every time the shape is changed. Therefore, it is difficult to automate the calculation in the technology disclosed in Non-Patent Document 1.

[0009] The present disclosure has been made to solve such problems, and its object is to eliminate the strength shortage of the sand mold before model production and equipment installation by obtaining the part with low sand mold strength from the molding pressure ratio, and to provide a sand mold design support device and a sand mold design support method that can contribute to cost reduction and lead time reduction.

Means for Solving the Problems

[0010] A design support apparatus according to an aspect of the present disclosure includes an acquisition unit that acquires shape information representing the shape of a sand mold or a mold corresponding to the sand mold, a storage unit, and a control device. The control device calculates the molding pressure at a plurality of positions on the contact surface between the sand mold and the mold by using the finite volume method, using the information on the squeeze pressure applied to the molding apparatus and the shape information, and obtains a molding pressure ratio representing the molding pressure with respect to the squeeze pressure for each position. In the storage unit, a relational expression between the strength of the sand mold and the molding pressure ratio is stored in advance. The control device determines a lower limit value of the molding pressure ratio required for molding the sand mold from the relational expression stored in the storage unit and the strength required for the sand mold, and notifies the user of an instruction to prompt a change in the shape of the sand mold until the minimum value of the molding pressure ratio exceeds the lower limit value.

[0011] A design support apparatus according to an aspect of the present disclosure includes an acquisition unit that acquires shape information representing the shape of a sand mold or a mold corresponding to the sand mold, a storage unit, and a control device. The control device acquires area information regarding the bottom area and the side area of the sand mold or the mold based on the shape information, calculates the molding pressure on the contact surface between the sand mold and the mold by using the information on the squeeze pressure applied to the molding apparatus and the ratio of the bottom area to the side area, and obtains a molding pressure ratio representing the molding pressure with respect to the squeeze pressure. In the storage unit, a relational expression between the strength of the sand mold and the molding pressure ratio is stored in advance. The control device determines a lower limit value of the molding pressure ratio required for molding the sand mold from the relational expression stored in the storage unit and the strength required for the sand mold, and notifies the user of an instruction to prompt a change in the shape of the sand mold until the molding pressure ratio exceeds the lower limit value.

[0012] A design support method according to an aspect of the present disclosure includes a step of acquiring shape information representing the shape of a sand mold or a mold corresponding to the sand mold, a step of calculating the molding pressure at a plurality of positions on the contact surface between the sand mold and the mold by using the finite volume method, using the information on the squeeze pressure applied to the molding apparatus and the shape information, a step of obtaining a molding pressure ratio representing the molding pressure with respect to the squeeze pressure for each position, a step of determining a lower limit value of the molding pressure ratio required for molding the sand mold from the relational expression between the strength of the sand mold and the molding pressure ratio and the strength required for the sand mold, and a step of notifying the user of an instruction to prompt a change in the shape of the sand mold until the minimum value of the molding pressure ratio exceeds the lower limit value.

[0013] A design support method according to one aspect of the present disclosure includes: obtaining shape information representing the shape of a sand mold or a pattern corresponding to the sand mold; obtaining area information regarding the bottom area and the side area of the sand mold or the pattern based on the shape information; calculating a molding pressure on the contact surface between the sand mold and the pattern using information on the squeeze pressure applied to the molding device and the ratio of the bottom area to the side area; obtaining a molding pressure ratio representing the molding pressure with respect to the squeeze pressure; determining a lower limit value of the molding pressure ratio required for molding the sand mold from the relational expression between the strength of the sand mold and the molding pressure ratio; and notifying the user of an instruction to prompt a change in the shape of the sand mold until the molding pressure ratio exceeds the lower limit value.

Advantages of the Invention

[0014] According to the present disclosure, by obtaining a portion with low sand mold strength from the molding pressure ratio, it is possible to eliminate insufficient strength of the sand mold before pattern making and equipment installation, contributing to cost reduction and lead time reduction.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Best Mode for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the embodiments described below, when referring to the number, amount, etc., unless otherwise specified, the scope of the present disclosure is not necessarily limited to the number, amount, etc. The same parts and corresponding parts are given the same reference numerals, and duplicate explanations may not be repeated. It is initially planned to use the configurations in the embodiments in appropriate combinations.

[0017] Embodiment 1. FIG. 1 is a diagram for explaining the outline of sand casting in Embodiment 1. The sand casting process 100 includes a kneading process shown in FIG. 1(A), a molding process shown in FIG. 1(B), and a pouring process shown in FIG. 1(C). The kneading process shown in FIG. 1(A) is a process of putting sand 102 and bentonite 103 into a kneader 101 and kneading them together with water.

[0018] The molding process shown in FIG. 1(B) is to put a product model (hereinafter referred to as a model) 10 into the area surrounded by a sand mold frame 104, an upper frame 105, and a lower frame 106, and fill it with casting sand created by the kneader 101 on top of it. The sand mold 13 created from the casting sand includes an upper sand mold 11 and a lower sand mold 12. In the molding process, the shape of the model 10 is transferred to the sand mold 13 (upper sand mold 11 and lower sand mold 12) by uniformly pressing the surface of the upper frame 105 from the upper part of the upper frame 105 by a cylinder device equipped with a piston rod (not shown).

[0019] Here, in the molding process of creating the mold 13 including the upper mold 11 and the lower mold 12, among the compressive stresses acting inside the mold, that is, within the powder layer, the direction of the maximum principal stress (the direction in which the pressure during molding propagates) is indicated by an arrow in Fig. 1(B). Hereinafter, it is assumed that the direction of the maximum principal stress is always perpendicular to the surface to which the pressure is applied. The surface of the mold frame 104 that contacts the mold is a surface perpendicular to the upper surface of the upper frame 105, which is the surface to which the pressure is applied, and is parallel to the direction of the maximum principal stress. On the other hand, the surface of the mold 10 has a surface parallel to and a surface perpendicular to the surface to which the pressure is applied.

[0020] In the pouring process shown in Fig. 1(C), the molten metal 108, which is the molten metal from the ladle 107, is poured into the space formed in the gap of the mold 13 formed by combining the upper mold 11 and the lower mold 12. Thereafter, in the mold removal process (not shown), after the molten metal 108 solidifies, the mold 13 composed of the upper mold 11 and the lower mold 12 is disassembled to take out the product. After the product is taken out, the mold 13 is crushed and reused.

[0021] Fig. 2 is a block diagram showing the configuration of the mold design support device. The design support device 200 includes a control device 20, an acquisition unit 24, a display unit 25, and an input unit 26. The control device 20 includes a CPU (Central Processing Unit) 21, a memory 22 (ROM (Read Only Memory) and RAM (Random Access Memory)), an I / O (Input / Output Port) 23 for inputting and outputting various signals, and the like. The control device 20 is connected to the acquisition unit 24, the display unit 25, and the input unit 26 via the I / O 23. The memory 22 functions as a storage unit.

[0022] The CPU 11 expands and executes the program stored in the ROM in the RAM or the like. The program stored in the ROM is a program in which the processing procedure of the control device 20 is described. The control device 20 executes the control of each device according to these programs. This control is not limited to software processing, and it is also possible to process it with dedicated hardware (electronic circuit).

[0023] The acquisition unit 24 acquires the drawings used during model production or design information such as 3D-CAD. The design information includes the shape data of the sand mold 13 or the shape data of the model 10. The design information also includes the shape data regarding the bottom area and the side area of the convex portion of the sand mold 13. The acquisition unit 24 also acquires the shape data after the user has modified the design information. The acquisition unit 24 may acquire the measurement data of a measuring device (not shown). Here, the measuring device is preferably composed of any one of a light-sectioning three-dimensional scanner, a pattern projection type three-dimensional scanner, and a TOF type three-dimensional scanner. Regardless of the method, the measuring device may be any device that can measure the shape of the convex portion where the sand mold strength is most likely to decrease in the sand mold 13.

[0024] Instead of the measurement results from the measuring device, the results of manually measuring the depth and width of the convex portion where the sand mold strength is most likely to decrease in the sand mold 13 with a caliper or the like may be adopted. Here, the convex portion of the sand mold 13 is molded by transferring the shape of the concave portion of the model 10. Therefore, the measurement of the convex portion of the sand mold 13 may be replaced with the measurement of the concave portion of the model 10.

[0025] The display unit 25 is a device such as a liquid crystal monitor that displays various information based on the signal output from the control device 20. The input unit 26 receives the input of the value after the design change and inputs a signal to the control device 20. The input unit 26 is a device that receives the operation of the user, such as a keyboard, for example.

[0026] Even when manufacturing products of the same shape, the defect rate of the products varies depending on the equipment configuration of the molding device for molding the sand mold or the properties of the sand used. Therefore, in order to newly design a molding device, it is necessary to set design criteria based on the information of the existing molding device. Hereinafter, a method for designing the shape of a sand mold, which is one of the design criteria, will be described.

[0027] Each step of the method for designing the sand mold shape will be described. FIG. 3 is a flowchart showing the sand mold design process. The sand mold design process is a process executed by the CPU 21 of the control device 20 that executes various processes. Hereinafter, each step in the flowchart executed by the CPU 21 will be simply denoted as "S".

[0028] The CPU 21 acquires information on the sand mold shape in S1. The CPU 21 acquires, for example, the shape data of the sand mold 13 based on the design information transmitted from the acquisition unit 24. Hereinafter, the process executed by the CPU 21 using the shape data of the sand mold 13 will be described. Note that the CPU 21 may acquire the shape data of the model 10 based on the design information transmitted from the acquisition unit 24. The CPU 21 may execute the following process using the shape data of the model 10.

[0029] Next, the CPU 21 identifies, in S2, the part where the strength of the sand mold is likely to decrease. At the part where the strength of the sand mold is likely to decrease, the molding pressure ratio P / P0 representing the molding pressure with respect to the squeeze pressure applied to the molding device is the smallest. Therefore, identifying the part where the strength of the sand mold is likely to decrease is the same as identifying the value of the part where the molding pressure ratio P / P0 shows the minimum value. Here, P0 [MPa] is the squeeze pressure of the molding device, and P [MPa] is the molding pressure at the contact surface where the model 10 and the sand mold 13 are in contact. The squeeze pressure P0 varies depending on the configuration and settings of the molding device. In contrast, the molding pressure ratio P / P0 is less affected by the equipment and is determined by the sand mold shape or the model shape.

[0030] The CPU 21 calculates the molding pressure P using the shape data representing the shape of the mold 13 acquired from the acquisition unit 24 or the shape data representing the shape of the model 10, and obtains the molding pressure ratio P / P0. Regarding the calculation method of the molding pressure ratio P / P0, a numerical analysis method in the finite volume method can be used. By the above method, the CPU 21 can predict the molding pressure P at the contact surface where the model 10 and the mold 13 come into contact from the squeeze pressure P0 set during molding. The molding pressure P is closely related to the density or strength of the mold 13. Here, the pressure distribution in the mold is not uniform and varies depending on the location. However, the location where the pressure is lowest is considered to be a factor in defect occurrence. Therefore, for one mold 13 or one model 10, the molding pressure ratios P / P0 at a plurality of locations are calculated, and the smallest value may be used as the evaluation value of the molding pressure ratio P / P0 at the strength insufficient part.

[0031] Next, the CPU 21 determines the lower limit value of the molding pressure ratio in S3. The lower limit value of the molding pressure ratio is determined using the relational expression between the measured value of the mold strength of the existing molding apparatus and the molding pressure ratio, as will be described later. Hereinafter, the lower limit value of the molding pressure ratio obtained in this way is also referred to as the estimated molding pressure ratio.

[0032] Next, the CPU 21 determines in S4 whether the minimum value of the molding pressure ratios P / P0 at a plurality of positions exceeds the estimated molding pressure ratio which is the lower limit value. When the CPU 21 determines that the minimum value of the molding pressure ratio P / P0 exceeds the estimated molding pressure ratio (YES in S4), since there is no strength deficiency in the mold 13, it notifies that there is no need to change the design shape (S5) and ends the process. Specifically, the CPU 21 transmits a signal for displaying on the display unit 25 a notification instructing the user that there is no need to change the design shape of the mold.

[0033] When the CPU 21 determines that the minimum value of the molding pressure ratio P / P0 is less than or equal to the estimated molding pressure ratio (NO in S4), since there is insufficient strength in the mold 13, it issues a notification instructing that it is necessary to change the design shape (S6). Specifically, the CPU 21 transmits a signal for displaying on the display unit 25 a notification instructing the user to prompt a change in the design shape of the mold. The CPU 21 waits until it receives the shape data after the user modifies the design information of the mold 13.

[0034] When the CPU 21 receives the value of the shape data after the design change in S7, it returns the process to S1. In the processes after S1, based on information representing the shape of the mold 13 newly obtained from the changed shape data, processes such as calculating the molding pressure ratio P / P0 are repeated. The CPU 21 notifies the user of an instruction to prompt a change in the shape of the mold as shown in S6 until the minimum value of the molding pressure ratio P / P0 exceeds the lower limit value. As a result, it becomes possible to predict the mold strength and design a shape that is less likely to produce parts where the mold strength is likely to decrease without actually manufacturing the model 10 and molding the mold 13 multiple times for trial production.

[0035] (Regarding the calculation method of the molding pressure ratio by the finite volume method) The method for calculating the molding pressure ratio P / P0 by numerical calculation using the finite volume method executed in S2 will be specifically described. FIG. 4 is a diagram for explaining the outline of the numerical calculation method using the finite volume method. Consider a minute region with a width Δx, depth Δy, and height Δz inside the mold 13. It is assumed that the molding pressure is applied from the plane z = 0 and propagates in the positive z-axis direction. Let the coordinates inside the minute region be (x, y, z) = (x1, y1, z1), the internal pressure be P1, and the balance of the inflow and outflow of the pressure in the minute region be taken. The pressure is assumed to propagate (also referred to as advection) in the positive z-axis direction. In the x and y directions, the pressure is assumed to propagate according to the pressure difference with the adjacent regions.

[0036] Here, let the pressure transfer rate from region x = x0 to x = x1 be ΔP(0→1), the pressure transfer rate from region x = x1 to x = x0 be ΔP(1→0), the pressure transfer rate from region x = x1 to x = x2 be ΔP(1→2), and the pressure transfer rate from region x = x2 to x = x1 be ΔP(2→1). First, ignoring the pressure propagation in the y direction and taking the pressure balance, we get equations (1) to (5).

[0037]

Number

[0038]

Number

[0039]

Number

[0040]

Number

[0041]

Number

[0042] Here, α[m] is a parameter indicating the pressure transfer ratio between adjacent cells and has a unit of length. Expanding and organizing these equations gives equation (6).

[0043]

Number

[0044] Similarly, adding the pressure balance in the y direction gives equation (7).

[0045]

Number

[0046] As a boundary condition, P0 = P1 = 0 is given on the model surface. By sequentially calculating P1 from z = 0 in the positive z-axis direction, the modeling pressure at that point can be estimated. Furthermore, by arranging the above formula (7), it becomes formula (8).

[0047]

Number

[0048] From here, when taking the limit where Δx, Δy, and Δz are 0, it becomes formula (9), which is a second-order partial differential equation same as the diffusion equation.

[0049]

Number

[0050] Next, consider the balance of the cells in contact with the wall (model surface). A certain cell is in contact with the model surface, the surface area of the contacting surface is S [m 2 , the friction coefficient between the mold and the model is β, and when taking the pressure balance, it becomes formula (10).

[0051]

Number

[0052] When arranging this, it becomes formula (11).

[0053]

Number

[0054] When adding formula (8) and formula (11), it becomes formula (12).

[0055]

Number

[0056] The CPU 21 executes a program for sequentially calculating the formula (12). The mesh used in the finite volume method uses an orthogonal grid, and the convergence condition (αΔz / (Δx) 2 <0.5 and αΔz / (Δy) 2 <0.5). Then, assuming that the squeeze pressure at z = 0 is P0, the pressure distribution is calculated by the Jacobi method, and the molding pressure P on the mold surface is calculated. Thus, the molding pressure ratio P / P0 representing the molding pressure P with respect to the squeeze pressure P0 can be obtained.

[0057] Here, it does not matter which method is used to solve the formula (9) or the formula (12) by numerical analysis. In the calculation program, either a structured grid or an unstructured grid may be used. For the solution method of the partial differential equation, either an explicit method or an implicit method may be used. Alternatively, for the solution method of the partial differential equation, after giving the formula (11) as a boundary condition using a partial differential equation solver (for example, MATLAB (registered trademark), OpenFOAM (registered trademark), etc.), the formula (9) may be directly calculated.

[0058] In this way, by using the finite volume method to calculate the molding pressure P at each position of the contact surface, the molding pressure ratio P / P0 at each position of the contact surface can be obtained. Since the molding pressure ratio P / P0 is an index that depends only on the mold shape, it can be calculated even when the molding device to be used is not determined, and the design change can be considered. Furthermore, according to the above various formulas, for a mold having a complicated shape in the three-dimensional direction, the calculation for obtaining the molding pressure ratio P / P0 can be automated.

[0059] (Regarding various parameters) In the above equation, it is assumed that the direction of the largest component (maximum principal stress) among the compressive stresses acting inside the sand mold, that is, within the powder layer, is the vertical direction. In reality, it is known that the direction of the maximum principal stress changes to an oblique direction depending on the shape of the mold and the like. Ideally, it is necessary to calculate the stress balance within the cell, determine the direction of the maximum principal stress, and take the pressure balance in the horizontal and vertical directions accordingly. To do this, it is necessary to obtain the converged value of the pressure by iterative calculation in both the horizontal and vertical directions, which results in an excessive computational load. In this method, by assuming the direction of the maximum principal stress to be the vertical direction and regarding the pressure propagation in the vertical direction as advection in a single direction, the iterative calculation in the vertical direction is made unnecessary, and the computational load is reduced by performing iterative calculation only in the horizontal direction.

[0060] Here, the diffusion coefficient α represents the amount of pressure change per 1 [m] in the vertical direction (the above z direction) when the second-order derivative of the pressure in the horizontal direction (the above x, y directions) is 1 [Pa / m 2 . Based on the measured values according to the sand properties, parameter fitting is performed, and α is set to a value of about 0.02 to 0.1 [m].

[0061] Thus, the above calculation method first sets the parameter of α, and once the parameter is determined, it can be calculated in the same way for any sand mold shape. Therefore, the above calculation method facilitates the automation of the calculation by completing the parameter setting once.

[0062] (Regarding the determination of the lower limit value of the molding pressure ratio) As an example of a method for calculating the lower limit value of the molding pressure ratio, a method using existing mold strength standards is shown. First, the mold strength of sand molds manufactured by each model of an existing molding apparatus is measured, and by comparing it with the calculated molding pressure ratio P / P0, a relational expression between the mold strength and the molding pressure ratio is derived. Fig. 5 is a graph showing the relationship between the measured value of the mold strength and the molding pressure ratio. As shown in Fig. 5, strength measurements were taken at multiple locations for each of the sand molds manufactured by models A, B, C, and D. Here, when measuring multiple sand molds, it is necessary to keep the molding conditions (settings of the molding apparatus and sand mixing conditions) the same. From this, the regression equation [mold strength] = 3.21 - 5.31(1 - [molding pressure ratio] 3 ) was obtained.

[0063] In the regression equation shown by the dashed line in Fig. 5, the mold strength standard is set to 0.5 [kgf / cm 2 . As shown in Fig. 5, the estimated molding pressure ratio corresponding to 0.5 [kgf / cm 2 is 0.20. This 0.20 is determined as the lower limit value of the molding pressure ratio.

[0064] (Regarding reflection on the designed shape) When the minimum value among the molding pressure ratios P / P0 at multiple positions is lower than the estimated molding pressure ratio that is the lower limit value, the user changes the designed shape. Specifically, in order to ensure the mold strength, the user changes the mold shape by lowering the height or widening the width of the mold convex part. As a result, it is no longer necessary to repeat trial production and correction for reducing casting defects as in the past, and before actually manufacturing the model and molding the sand mold, the mold strength can be predicted and a shape that is less likely to cause a mold strength neck part can be designed.

[0065] In addition, when it is difficult to change the shape of the sand mold due to product function or casting technology issues, in addition to changing the parting surface between the upper mold and the lower mold, the strength neck part may be replaced with a core using a high-strength self-hardening sand mold. This makes it possible to correct the sand mold strength neck part without changing the sand mold shape. For example, when changing the parting surface, the position where the strength is likely to decrease should be set to a position around the center of the upper mold and the lower mold. This makes it less likely for the sand mold to collapse and less likely for casting defects to occur. Even if the sand mold strength is still insufficient, the strength neck part can be eliminated by replacing it with a high-strength core created in a separate process.

[0066] Here, when the strength cannot be satisfied by changing the design shape or the parting surface, and it is difficult to introduce a core, prior consideration may be given to modifying the equipment of the molding device (such as installing a local pressurizing mechanism). By predicting the molding pressure in advance before making the mold in this way, appropriate measures such as shape changes and equipment modifications can be considered in advance, contributing to cost reduction and lead time reduction. It can also contribute to reducing the defect rate of sand molds manufactured by existing molding devices. For various changes, those that can be easily changed during production and shape changes with little change in casting quality should be implemented first.

[0067] An example of reflecting the actual design shape will be described. FIG. 6 is a diagram showing an example of a cast product. The cast product 30 includes a product part 1 and a riser part. Usually, when manufacturing a cast product, in addition to the product part 1, a part called a riser is also cast. The riser part includes a sprue 2, a runner 3, a push riser 4, a dam break 5, and a dam 6.

[0068] The product part 1 is the part that imitates the finally formed product shape. The sprue 2 is the part for pouring the molten metal. The runner 3 is the part that rectifies the flow of the molten metal and floats and separates the impurities contained in the molten metal. The riser 4 is the part installed to compensate for the solidification shrinkage of the molten metal and suppress casting defects. The knockout 5 is the part for separating the product part 1 and the riser 4 by applying an external force after solidification is completed. The weir 6 is the part connecting the riser and the product part.

[0069] In order to cast the shape of the casting 30, as shown in FIG. 1, the sand mold 13 is molded separately into the upper sand mold 11 and the lower sand mold 12. FIG. 7 is the shape data 31 showing an example of the upper sand mold 11. The design support device 200 performs numerical calculations using the shape data 31 corresponding to the shape of the pattern 10.

[0070] FIG. 8 is a diagram showing the calculation result 41 of the molding pressure ratio in the sand mold shape before improvement. As shown in FIG. 8, the calculation result 41 of the molding pressure ratio P / P0 corresponding to the shape data 31 is displayed on the display unit 25. As shown in FIG. 8, the peripheral part 42 of the part 43 showing the weir 6 has a low molding pressure ratio P / P0 and is a value below the estimated molding pressure ratio 0.2 set as the minimum value.

[0071] The weir 6 is the part where the flow velocity of the molten metal is the fastest and the sand mold is likely to collapse. For this reason, the user needs to take countermeasures. The user changed the shape data 31 to increase the distance between the riser 4 and the product part 1 and lower the height of the riser 4. FIG. 9 is a diagram showing the calculation result 51 of the molding pressure ratio in the sand mold shape after improvement. As shown in FIG. 9, the calculation result 51 of the molding pressure ratio P / P0 corresponding to the changed shape data 31 is displayed on the display unit 25. As shown in FIG. 9, the peripheral part 52 of the part 53 showing the weir 6 has risen above the estimated molding pressure ratio 0.2. In the calculation result 51, the region below the estimated molding pressure ratio 0.2 has disappeared. As a result, the calculation result 51 is estimated to be less likely to cause the collapse of the sand mold.

[0072] Embodiment 2. In the above-described Embodiment 1, a method of calculating the molding pressure using the finite volume method was explained. In Embodiment 2, a method of calculating the molding pressure ratio using a simple approximation formula will be explained. Regarding a sand mold convex portion having a simple shape such as a rectangular parallelepiped or a cylinder, it is possible to derive a molding pressure ratio using a simple approximation formula without performing sequential calculations. The calculation method is shown below. As a simple shape, consider a cylinder or a rectangular parallelepiped having a height H, a bottom area S1, and a side area S2. In the shape of the sand mold convex portion, it is assumed that the pressure distribution in the internal lateral direction can be ignored. When the pressure on the mold surface is P wall When taking the pressure balance in the height direction (z direction), Equation (13) is obtained.

[0073]

Equation

[0074] When this is rearranged, Equation (14) is obtained.

[0075]

Equation

[0076] Taking the limit where Δz is 0 from here, Equation (15) is obtained.

[0077]

Equation

[0078] As a boundary condition, the squeeze pressure at the upper end of the sand mold is set to P0. That is, when P = P0 is given at z = 0, the general solution of Equation (15) is Equation (16).

[0079]

Equation

[0080] When the pressure on the mold surface is set to 0 (when P wall = 0), the pressure at the bottom of the pocket-shaped recess with a depth of H is Equation (17).

[0081] [Number]

[0082] As shown in formula (17), the molding pressure ratio P / P0 of the simple shape part of the sand mold is obtained by the ratio of the bottom area to the side area. In this way, from the actual sand mold, the shape of the mold, or the design information, the part where pressure is most difficult to propagate in the sand mold, that is, the shape of the convex part with a narrow horizontal width and a high vertical height, is read, information regarding the bottom area and the side area is acquired, and by inputting it into formula (17), the molding pressure ratio P / P0 can be calculated. For example, when the pocket has a cylindrical shape with a bottom radius r [m] and a depth L [m], the bottom area S1 = πr 2 , S2 = 2πrL, so formula (18) can be derived. The molding pressure ratio P / P0 obtained by the ratio of the bottom area to the side area is obtained assuming that the pressure at one point is the same across the entire surface.

[0083] [Number]

[0084] (Regarding various parameters) The friction coefficient β between the wall surface and the sand mold strictly changes depending on the direction of the maximum principal stress. When the direction of the maximum principal stress is parallel to the wall surface, it is expressed as β = μk using the internal friction coefficient μ of the sand and the Rankine coefficient k. When the direction of the maximum principal stress is perpendicular to the wall surface, β = 1.0. Using the measured results of the sand mold pressure or the sand mold strength, parameter fitting was performed so that the sand mold strength can be predicted even for different mold shapes. As a result, for the friction coefficient β with a sand mold frame that has a simple shape and can be regarded as parallel to the direction of the maximum principal stress, a value of about 0.12 to 0.16 is set. For the friction coefficient β of the mold surface with a complex shape and where the direction of the maximum principal stress also easily changes, a value of about 0.4 to 0.8 is set. Thereby, the actual sand mold strength can be reproduced well.

[0085] Thus, the above calculation method first sets the parameter of β, and once the parameter is determined, it can be calculated in the same way for any sand mold shape. Therefore, the above calculation method facilitates the automation of calculation by completing the parameter setting once.

[0086] <Modification Example> A method of calculating the lower limit value of the molding pressure ratio from the defective rate will be described. When there is no strength standard for the sand mold, or when it is difficult to measure the actual strength of the sand mold, the lower limit value may be calculated using the statistical information of the defective rate of the sand mold. First, the molding pressure ratio is calculated from the design information of the sand mold by the method described above. Here, the pressure distribution in the sand mold is not uniform and varies depending on the part, but the part with the lowest pressure is considered to be the cause of defective generation, so the minimum value of the molding pressure ratio P / P0 is used. The molding pressure ratios P / P0 in a plurality of molding devices are obtained, and a relational expression between the molding pressure ratio and the defective rate is derived from the defective rates of the sand molds manufactured by each molding device. This relational expression may be linear or polynomial approximation.

[0087] This relational expression should have higher accuracy in the region with a high defective rate. Therefore, it is desirable to derive the relational expression using only the molding devices with a relatively high defective rate to a certain extent. For example, since the defective rate in a foundry is generally about 3 - 5%, the molding devices with a defective rate of less than 3% are excluded, and the relational expression is derived by narrowing down to the molding devices with a defective rate of 3% or more, so that a more accurate relational expression can be obtained. From the obtained relational expression, the lower limit value of the molding pressure ratio P / P0 is obtained. The setting of the lower limit value varies depending on the casting process. As an example of the setting method, since the defective rate in a foundry is about 3 - 5%, the estimated molding pressure ratio corresponding to a defective rate of 5% may be determined as the lower limit value.

[0088] <Summary> The present disclosure relates to a design support device 200 for a sand mold 13 in sand mold casting using a molding device. The design support device 200 includes an acquisition unit 24 that acquires shape data representing the shape of the sand mold 13 or the mold 10 corresponding to the sand mold 13, a memory 22, and a CPU 21 (control device 20). The CPU 21 calculates the molding pressure P at a plurality of positions on the contact surface between the sand mold 13 and the mold 10 by the finite volume method using the information on the squeeze pressure P0 applied to the molding device and the shape data, and for each position, obtains a molding pressure ratio P / P0 representing the molding pressure P with respect to the squeeze pressure P0. In the memory 22, a relational expression between the strength of the sand mold 13 and the molding pressure ratio P / P0 is stored in advance. The CPU 21 determines a lower limit value of the molding pressure ratio P / P0 required for molding the sand mold 13 from the relational expression stored in the memory 22 and the strength required for the sand mold 13, and notifies the user of an instruction to prompt a change in the shape of the sand mold 13 until the minimum value of the molding pressure ratio P / P0 exceeds the lower limit value.

[0089] The present disclosure relates to a design support device 200 for a sand mold 13 in sand mold casting using a molding device. The design support device 200 includes an acquisition unit 24 that acquires shape data representing the shape of the sand mold 13 or the mold 10 corresponding to the sand mold 13, a memory 22, and a CPU 21. Based on the shape data, the CPU 21 acquires area data regarding the bottom area and the side area of the sand mold 13 or the mold 10, and calculates the molding pressure P on the contact surface between the sand mold 13 and the mold 10 using the information on the squeeze pressure P0 applied to the molding device and the ratio of the bottom area to the side area, and obtains a molding pressure ratio P / P0 representing the molding pressure P with respect to the squeeze pressure P0. In the memory 22, a relational expression between the strength of the sand mold 13 and the molding pressure ratio P / P0 is stored in advance. The CPU 21 determines a lower limit value of the molding pressure ratio P / P0 required for molding the sand mold 13 from the relational expression stored in the memory 22 and the strength required for the sand mold 13, and notifies the user of an instruction to prompt a change in the shape of the sand mold 13 until the molding pressure ratio P / P0 exceeds the lower limit value.

[0090] The present disclosure relates to a method for assisting in the design of a sand mold 13 in sand casting using a molding apparatus. The method for assisting in the design of the sand mold 13 includes: a step of acquiring shape data representing the shape of the sand mold 13 or a pattern 10 corresponding to the sand mold 13; a step of calculating a molding pressure P at a plurality of positions on the contact surface between the sand mold 13 and the pattern 10 by the finite volume method using information on a squeeze pressure P0 applied to the molding apparatus and the shape data; a step of obtaining a molding pressure ratio P / P0 representing the molding pressure P with respect to the squeeze pressure P0 for each position; a step of determining a lower limit value of the molding pressure ratio P / P0 required for molding the sand mold 13 from a relational expression between the strength of the sand mold 13 and the molding pressure ratio P / P0 and the strength required for the sand mold 13; and a step of notifying the user of an instruction to prompt a change in the shape of the sand mold 13 until the minimum value of the molding pressure ratio P / P0 exceeds the lower limit value.

[0091] The present disclosure relates to a method for assisting in the design of a sand mold 13 in sand casting using a molding apparatus. The method for assisting in the design of the sand mold 13 includes: a step of acquiring shape data representing the shape of the sand mold 13 or a pattern 10 corresponding to the sand mold 13; a step of acquiring area data regarding the bottom area and the side area of the sand mold 13 or the pattern 10 based on the shape data; a step of calculating a molding pressure P on the contact surface between the sand mold 13 and the pattern 10 using information on a squeeze pressure P0 applied to the molding apparatus and the ratio of the bottom area to the side area; a step of obtaining a molding pressure ratio P / P0 representing the molding pressure P with respect to the squeeze pressure P0; a step of determining a lower limit value of the molding pressure ratio P / P0 required for molding the sand mold 13 from a relational expression between the strength of the sand mold 13 and the molding pressure ratio P / P0 and the strength required for the sand mold 13; and a step of notifying the user of an instruction to prompt a change in the shape of the sand mold 13 until the molding pressure ratio P / P0 exceeds the lower limit value.

[0092] The sand mold 13 design support apparatus 200 and the sand mold 13 design support method according to the present embodiment have the above-described configuration, and can contribute to cost reduction and lead time reduction by calculating the molding pressure ratio P / P0 before pattern production and equipment installation.

[0093] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the description of the above embodiments but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Explanation of Signs

[0094] 1 Product section, 2 Hot water outlet, 3 Hot water passage, 4 Pressurized hot water, 5 Weir fold, 6 Weir, 10 Mold, 11 Upper sand mold, 12 Lower sand mold, 13 Sand mold, 20 Control device, 22 Memory, 24 Acquisition section, 25 Display section, 26 Input section, 30 Cast product, 31 Shape data, 41, 51 Calculation results, 42, 52 Peripheral parts, 43, 53 Parts, 100 Sand casting process, 101 Kneader, 102 Sand, 103 Bentonite, 104 Sand mold frame, 105 Upper frame, 106 Lower frame, 107 Pot, 108 Molten metal, 200 Design support device.

Claims

1. A sand mold design support device in sand mold casting using a molding device, wherein the design support device comprises: an acquisition unit that acquires shape information representing the shape of the sand mold or a mold corresponding to the sand mold; a storage unit; and a control device, wherein the control device: calculates molding pressures at a plurality of positions on a contact surface between the sand mold and the mold by a finite volume method using information on a squeeze pressure applied to the molding device and the shape information, and obtains a molding pressure ratio representing the molding pressure with respect to the squeeze pressure for each position; a relational expression between the strength of the sand mold and the molding pressure ratio is stored in advance in the storage unit; and the control device: determines a lower limit value of the molding pressure ratio required for molding the sand mold from the relational expression stored in the storage unit and the strength required for the sand mold; A sand mold design support device that notifies a user of an instruction to prompt a change in the shape of the sand mold until a minimum value of the molding pressure ratio exceeds the lower limit value.

2. A sand mold design support device in sand mold casting using a molding device, wherein the design support device comprises: an acquisition unit that acquires shape information representing the shape of the sand mold or a mold corresponding to the sand mold; a storage unit; and a control device, wherein the control device: acquires area information regarding a bottom area and a side area of the sand mold or the mold at a position where pressure propagation of the sand mold is difficult to propagate based on the shape information; calculates a molding pressure on a contact surface between the sand mold and the mold using information on a squeeze pressure applied to the molding device and a ratio of the bottom area to the side area, and obtains a molding pressure ratio representing the molding pressure with respect to the squeeze pressure; a relational expression between the strength of the sand mold and the molding pressure ratio is stored in advance in the storage unit; and the control device: determines a lower limit value of the molding pressure ratio required for molding the sand mold from the relational expression stored in the storage unit and the strength required for the sand mold; A sand mold design support device that notifies a user of an instruction to prompt a change in the shape of the sand mold until the molding pressure ratio exceeds the lower limit value.

3. A sand mold design support method in sand mold casting using a molding device, the method comprising the steps of: acquiring shape information representing the shape of the sand mold or a mold corresponding to the sand mold; calculating molding pressures at a plurality of positions on a contact surface between the sand mold and the mold by a finite volume method using information on a squeeze pressure applied to the molding device and the shape information; For each position, a step of obtaining a molding pressure ratio representing the molding pressure with respect to the squeeze pressure; A step of determining a lower limit value of the molding pressure ratio required for molding the sand mold from a relational expression between the strength of the sand mold and the molding pressure ratio and the strength required for the sand mold; A method for assisting in the design of a sand mold, including a step of notifying the user of an instruction to prompt a change in the shape of the sand mold until the minimum value of the molding pressure ratio exceeds the lower limit value.

4. A method for assisting in the design of a sand mold in sand casting using a molding apparatus, A step of obtaining shape information representing the shape of the sand mold or a model corresponding to the sand mold; A step of obtaining area information regarding the bottom area and the side area of the sand mold or the model based on the shape information; A step of calculating the molding pressure of the contact surface between the sand mold and the model using information on the squeeze pressure applied to the molding apparatus and the ratio of the bottom area to the side area; A step of obtaining a molding pressure ratio representing the molding pressure with respect to the squeeze pressure; A step of determining a lower limit value of the molding pressure ratio required for molding the sand mold from a relational expression between the strength of the sand mold and the molding pressure ratio and the strength required for the sand mold; A method for assisting in the design of a sand mold, including a step of notifying the user of an instruction to prompt a change in the shape of the sand mold until the molding pressure ratio exceeds the lower limit value.

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