JP2006247684A - Method, apparatus and program for simulating die-casting, and recording medium for recording the program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for simulating a die-casting with which rippled surface defect developed caused by solidification of molten material on the way of filling-up, can further surely be presumed. <P>SOLUTION: This method is performed through the following processes, that is; a pre-treating process S100 containing a factor-making step S101 for dividing the shape of a mold into fine factors by positioning on the coordinate axes, and a factor-defining step S102 for defining the mold factors and cavity factors; a filling-up heat conduction analyzing process S200 containing a filling-up heat conduction analyzing step S201 for performing a filling-up range analysis to respective cavity factors and also, calculating the temperature in the molten material filling-up factors and a solid-phase ratio calculating step S202 for calculating the solid-phase ratio of the molten metal material; and an evaluating process S300 containing a solid-phase thickness calculating step S301 for calculating the solid-phase thickness as the thickness in the cavity factors which continuously becomes the solid-phase 1 from the inner wall surface in the mold factors at the completing time of the filling-up, and a surface-defect developing evaluating step S302 for presuming the development of the surface defect from the solid-phase thickness. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a die casting simulation capable of accurately predicting surface defects that may occur in a casting obtained by die casting (hereinafter simply referred to as die casting).

For example, in the case of producing a casting (molded product) made of an aluminum alloy or the like, there is a die casting that is a method of pressurizing and filling a molten metal material (hereinafter, appropriately referred to as a molten metal material or simply a molten material) into a mold. It is used a lot.
Problems in castings obtained by die casting include sinkhole defects, entrainment defects such as air, defective hot water defects, surface defects, and the like. Among these, there is a surface defect as one of the particularly serious defects.

  In die casting, a casting is produced by applying a large casting pressure of 20 to 80 MPa. However, depending on casting conditions, surface defects (wrinkles) showing wrinkle-like shapes are generated in each part of the casting surface. In order to eliminate such surface defects, the shape of the molded product (casting), molding method (runner, gate, overflow), injection conditions (low speed, switching timing, high speed, etc.), mold temperature control, etc. are optimized. There is a need to.

  However, since a molded article manufactured by die casting usually has a three-dimensionally complicated shape and is thin, the flow of the molten material and the solidification phenomenon are extremely complicated and short-time phenomena. For this reason, the coagulation phenomenon or the like cannot theoretically be accurately clarified, and therefore it is not easy to find an appropriate condition. Moreover, it is not easy to systematically analyze surface defects experimentally, and the current situation is that trial and error are repeated.

By the way, in recent years, with the improvement of computer computing power, the range of application of a technique for analyzing the behavior of a molten material when filling the mold with the molten material in a die using a computer, that is, a so-called die casting simulation has been expanded.
The conventional die casting simulation aims to deepen the understanding of the flow of the molten material and the solidification behavior accompanying the flow, and is expected as a useful means for searching for appropriate die casting conditions.

  Many conventional die casting simulation methods perform simultaneous analysis of the flow of molten material and solidification, but those that analyze solidification behavior after filling have also been developed. For example, the method for analyzing solidification of molten metal disclosed in Patent Document 1 divides a mold into microelements in the solidification analysis, and analyzes heat conduction and solute movement for each microelement.

Further, internal defects at the time of filling a molten metal have also been developed. For example, a casting defect prediction method using numerical analysis disclosed in Patent Document 2 divides a mold into minute elements, and each minute element is divided. Then, the molten metal temperature, molten metal pressure and gas pressure are obtained every predetermined time, and it is predicted that vacancies (shrinkage defects) will be generated at a site where the gas pressure is higher than the molten metal pressure.
However, the analysis at the time of filling and solidification in the conventional die casting simulation is mainly for predicting internal defects, and a method for measuring the occurrence of surface defects has not been developed yet.

JP-A-10-34320 JP-A-8-257741

  The present invention has been made in view of such conventional problems, and a die casting simulation method that can more accurately estimate the surface defects of the wrinkle generated due to solidification of the molten material during filling, The present invention intends to provide the apparatus, the program thereof, and a recording medium on which the program is recorded.

The first invention is a die casting simulation method for predicting at least the occurrence of surface defects in the casting when performing die casting to obtain a casting having a desired shape by pressurizing and solidifying a molten metal material into a mold. There,
An element creating step of positioning the shape of the mold used for forming the molten metal material on a coordinate system and dividing the space of the coordinate system into a plurality of microelements;
For each of the microelements, a preprocessing step including a mold element when positioned in the mold region of the mold and an element defining step that defines a cavity element when positioned in the cavity region of the mold;
For each of the cavity elements, a filling region analysis for analyzing the filling state of the molten metal material over time is performed, and the molten material filling element that is the cavity element filled with the molten metal material is filled with the molten material. The heat transfer between the elements and between the molten material filling element and the mold element is analyzed over time based on the respective heat transfer coefficients, and the temperature of the molten material filling element is calculated over time. Filling heat transfer analysis step;
A solid phase ratio calculating step for calculating, over time, a solid phase ratio of the molten metal material in the molten material filling element according to the calculated temperature of the molten material filling element, ,
A solid phase thickness calculating step of calculating a solid phase thickness which is a thickness of the cavity element having a solid phase ratio of 1 continuously from an inner wall surface of the mold element when filling is completed;
A die casting simulation method comprising: an evaluation step including a surface defect occurrence evaluation step for predicting the occurrence of surface defects from the solid phase thickness (Claim 1).

  In the die casting simulation method of the present invention, at least the pretreatment step and the filling heat transfer analysis step, and the evaluation step including the solid phase thickness calculation step and the surface defect occurrence evaluation step Do. This makes it possible to predict the occurrence of surface defects that could not be analyzed conventionally.

  That is, as a result of intensive research conducted by the present inventors for the purpose of solving the above-mentioned problems, in the conventional die casting simulation method, the solidification state during filling is analyzed, but the thickness of the solid phase on the surface in contact with the mold is It was found that the calculation was not performed, and therefore, it was not possible to fully grasp the influence of the solid phase that ultimately prevented the casting from adhering to the mold at the casting pressure. It has also been found that the occurrence of surface defects concentrates on the portion where the solid phase thickness is thick. If the solid phase is thick, it becomes difficult to rapidly cool the solid phase by mechanically deforming it with the casting pressure and bringing it into close contact with the mold, thereby generating water wrinkles. In this invention, the said evaluation process which can evaluate this point was added positively.

  Specifically, the solid phase ratio of each element accompanying the filling is calculated by the solid phase ratio calculating step of the filling heat transfer analysis step. Then, in the solid phase thickness calculation step of the evaluation step, the solid phase thickness, which is the thickness of the cavity element having a solid phase ratio of 1 continuously from the inner wall surface of the mold element when filling is completed, is calculated. . That is, the thickness of the skin portion solidified on the surface of the molten metal material in the cavity immediately after filling is calculated. Then, by performing the surface defect occurrence evaluation step using the solid phase thickness, it becomes possible to make a determination that could not be made conventionally.

  Therefore, according to the die-casting simulation method of the present invention, it is possible to more accurately estimate the surface defects that are caused by the melting of the molten material during solidification.

A second invention is a die casting simulation program for causing a computer to execute the die casting simulation method of the first invention.
A third invention resides in a computer-readable storage medium storing the die casting simulation program of the second invention.
According to a fourth aspect of the present invention, there is provided a die casting simulation apparatus comprising a computer configured to execute the die casting simulation method according to the first aspect of the present invention.

  In any of these second to fourth inventions, the above-described die casting simulation can be performed using them, and as described above, it is possible to predict the occurrence of surface defects that could not be analyzed conventionally.

  In the first invention, as described above, a packed heat transfer analysis including at least a pretreatment process including the element creating step and the element defining step, the filling heat transfer analyzing step, and the solid phase ratio calculating step. A process and an evaluation process including the solid phase thickness calculation step and the surface defect occurrence evaluation step are performed. These will be further described below.

<Pretreatment process>
The pre-processing step includes (1) an element creation step and (2) an element definition step, and is a step of preparing model data for a mold and preparing for a filling heat transfer analysis step described later.
(1) Element creation step The element creation step is a step in which a template (mold) that is the object of the present die casting simulation method is positioned on a coordinate system, and a space on the coordinate system is divided into a plurality of minute elements made of a polyhedron. . That is, this is a step of subdividing the space on the coordinate system into microelements for analysis.
Any coordinate system can be selected. In this space on the coordinate system, microelements are formed with a size as required.

  As a method of dividing into minute elements, a method of dividing with small elements of orthogonal hexahedron as used in the finite difference method, and a relatively polyhedral shape according to the shape of the casting mold as in the finite element method. There are methods that can be changed. The finite difference method is advantageous in that it can be easily divided into small elements and the analysis is mathematically simple.

In addition, it is not necessary to define minute elements in the entire coordinate system space, and it is necessary in a filling heat transfer analysis process described later such as a necessary part (such as a cavity region into which molten material is injected and a mold region in contact therewith). It is sufficient to define it within a range that includes a minimum of (part). However, in order to analyze the mold temperature and the like more accurately, it is preferable to create a microelement so as to include the entire mold region. The accuracy of analysis can be improved if the size of the minute element to be created is as small as possible, but more analysis time is required.
In addition, it is preferable to employ a size of minute elements that can sufficiently reproduce the structure of the mold. Therefore, the size of the minute element can be appropriately determined from the required accuracy, the fundamental constraint of simulation, the analysis time, and the like. Note that the size of the microelements does not have to be the same for all portions, and the size can be changed depending on the analysis site. For example, in a thin part of a die-cast product, it is preferable to locally set a small element size to improve analysis accuracy.

  By the way, in order to position the mold on the coordinate system, the shape of the mold needs to be converted into numerical data such as a CAD data model. The method for converting the shape of the mold into numerical data is not particularly limited. For example, the shape of the mold may be designed from the beginning by CAD, or the shape of the prototype may be digitized by some method such as a three-dimensional scanner. . Here, when the numerical value data of the type is created by CAD, it is necessary to read the type data created by CAD or the like and extract the outer shape data of the type. A known method can be used for the method. Further, the CAD data may be used as it is in this method. In this step, a die-cast product (cast) that is die-cast instead of the mold can be positioned on the coordinate system.

(2) Element definition step In the element definition step, each of the microelements defined in the element creation step is defined as a mold element when positioned in the mold area of the mold and positioned in the cavity area of the mold. Is a step of defining model data by defining a cavity element. That is, it is a step of defining the attributes of each microelement for a later-described filling heat transfer analysis step and constructing the shape of the mold on the coordinate system with the microelements.
Note that this step is a step that is performed after the microelements are defined in the above-described element creation step. However, this step is not necessarily performed after all the microelements are defined, and one or more microelements are defined. It is also possible to repeat this step every time and then repeat the element creation step.

Here, the “mold area” of the mold is an area where the mold itself is formed and the molten material does not flow. The “cavity area” of the mold is the flow of the molten material and finally the molded product (casting). Each means a region that is a portion where is formed.
Specifically, a method for defining each microelement as a mold element and a cavity element is not particularly limited, and a known method can be adopted. An example will be described below with reference to FIGS.

FIG. 1 shows an enlarged view of the shape of the mold and a part of the microelements. In addition, this figure shows a mold and minute elements on a two-dimensional view for convenience of description and explanation, and the following explanation is also based on a two-dimensional figure, but the essence is not different from a three-dimensional one.
As shown in FIG. 1, orthogonal coordinates are adopted as coordinates, and a square minute element 1 on the coordinate system (the shape is not particularly limited to a square. In addition, when applied to three dimensions, a rectangular parallelepiped.・ Cubes and other polyhedrons of arbitrary shape can be exemplified as element shapes, and so on. Further, the boundary line K of the model data of the mold is positioned on the coordinates.

  As shown in FIGS. 1 and 2, when the position of the center of gravity 2 of each microelement 1 exists in the mold area S1 (shaded portion) of the mold, the microelement 1 is defined as a mold element, and the boundary line If it exists in the cavity region S2, which is a region surrounded by K, the microelement is defined as a cavity element. FIG. 2 shows a state in which each microelement 1 is defined as a mold element and a cavity element. In FIG. 2, the center of gravity 2 existing in the mold region S1 is represented by a white circle, and the center of gravity 2 present in the cavity region S2 is represented by a black circle. In addition, although handling of the microelement which does not correspond to any of mold area | region S1 and cavity area | region S2 is not specifically limited, It is preferable to prescribe | regulate so that it may not become a computational load.

<Filling heat transfer analysis process>
The filling heat transfer analysis step performs (1) a filling heat transfer analysis step and (2) a solid phase ratio calculation step.
In the filling heat transfer analysis step, it is preferable to set a reference time. That is, as the analysis progresses, the reference time is advanced little by little, and the behavior of the molten material in the mold can be analyzed by applying each step based on the reference time. Therefore, in the filling heat transfer analysis step, the analysis is performed based on an arbitrary time set in the filling heat transfer analysis step regardless of the progress of real time. And it is not indispensable that each step always analyzes at the same frequency with respect to the time passage set in the filling heat transfer analysis process. For example, the time intervals for performing these steps can all be the same interval, or can be different intervals.

(1) Filling heat transfer analysis step In the filling heat transfer analysis step, the filling region analysis is performed and the temperature of the molten material filling element is calculated over time.
First, in the filling region analysis, the filling state of the molten metal material is analyzed over time for each of the cavity elements. That is, the physical behavior of the injected molten metal material in the mold is analyzed for every minute element and every minute time. And the microelement with which the molten metal material was filled is handled as a molten material filling element.
There is no particular limitation on the basic method for analysis of molten metal filling. For example, known techniques and conventional techniques such as VOF (Volume of Fluid), SOLA, FAN, and improved methods thereof can be applied.

Further, for the molten material filling element, the heat transfer between the molten material filling elements and between the molten material filling element and the mold element is analyzed over time based on the respective heat transfer coefficients. The temperature of each of the molten material filling elements is calculated over time.
The heat transfer analysis is performed not only between the molten material filling elements but also over time between the molten material filling element and the outermost surface of the casting mold (that is, the mold element in contact with the cavity element). calculate.

  In the heat transfer analysis step, the heat transfer between each element is based on the heat transfer coefficient set in each model at a time interval set so that the calculation does not diverge and the calculation is completed within the allowable time. To calculate. The heat transfer analysis method performed in the filling heat transfer analysis step is not particularly limited. For example, a calculation method such as using the differential method and the ADI method in combination with unsteady heat conduction analysis in consideration of heat advection and latent heat. Can be used to calculate the heat conduction for each element.

(2) Solid phase ratio calculation step The solid phase ratio calculation step calculates the solid phase ratio of the molten material filled in the molten material filling element based on the temperature of the molten material filling element calculated in the filling heat transfer analysis step. To do. The solid phase ratio is represented by a numerical value between 0 and 1 when the state in which all of the molten metal material in the molten material filling element is solidified is 1, and when the state is all in the molten state, and the intermediate state is 0. The solid phase ratio can be calculated from a phase diagram or the like, or can be calculated by a theoretical formula or approximate formula such as a Seil formula. Here, the solid phase ratio is a concept that includes not only the solid phase ratio itself but also parameters related to the solid phase ratio, and is calculated using the liquid phase ratio, temperature, etc., which are parameters related to the solid phase ratio. You can go. The liquid phase ratio is a value obtained by subtracting the solid phase ratio from 1. When temperature is used as a parameter related to the solid phase ratio, the temperature above the temperature at which all become liquid phase and the temperature below at which all becomes solid phase are treated in the same manner.

<Evaluation process>
In the evaluation process, (1) a solid phase thickness calculation step and (2) a surface defect occurrence evaluation step are performed.
(1) Solid phase thickness calculation step The solid phase thickness calculation step is a solid phase thickness that is the thickness of the cavity element that has a solid phase ratio of 1 continuously from the inner wall surface of the mold element when filling is completed. Is a step of calculating. As described above, the solid phase thickness indicates the thickness of the skin portion solidified on the surface of the molten metal material in the cavity immediately after filling. This step is performed immediately after completion of filling.

Usually, since the molten metal material is deprived of heat from the wall surface in contact with the mold and solidified, the solid phase ratio is increased from the cavity element adjacent to the inner wall surface (cavity surface) of the mold. The element having a solid phase ratio of 1 is located on the inner wall surface side of the mold. An element having a solid phase ratio of less than 1 exists inside the element having a solid phase ratio of 1.
By obtaining the distance from the inner wall surface of the mold (mold element) to the element having the solid phase ratio <1, the solid phase thickness at which the solid phase ratio is 1 can be obtained. The solid phase thickness of the element having a solid phase ratio <1 adjacent to the final element when the solid phase ratio is continuously 1 from the inner wall surface is obtained from the element volume, the solid phase ratio, and the area of the adjacent portion. Can do.
The sum of the thicknesses of the elements having a solid phase ratio of 1 and the sum of the solid phase thicknesses in the elements having a solid phase ratio of <1 adjacent to the final element is obtained as the solid phase thickness. . When the element adjacent to the inner wall surface has a solid phase ratio <1, the solid phase thickness is a value determined by the element volume, the solid phase ratio, and the area of the adjacent part.

  Examples of the calculation formula for obtaining the solid phase thickness include the following.

Where L: solid phase thickness, n: number of elements with solid phase ratio = 1 continuously from the inner wall surface, V _{n + 1} : n + 1-th element volume from wall surface, fs _{n + 1} : n + 1 from wall surface The solid phase ratio of the n th element, S _{n + 1} : the area of the n + 1 th element from the wall surface in contact with the n th element, L _m : the length of the m th element from the wall surface.

(2) Surface defect occurrence evaluation step The surface defect occurrence evaluation step is a step of predicting the occurrence of surface defects from the obtained solid phase thickness.
Specifically, whether or not the obtained solid phase thickness is thicker than a predetermined reference thickness is performed in each part, and it can be predicted that surface defects will occur in the thick part. Further, in determining this standard, more accurate evaluation can be performed by changing the standard value according to actual casting conditions such as casting pressure.

  In this surface defect occurrence evaluation step, it is preferable to predict that a surface defect will occur at a location where the solid phase thickness is 0.4 mm or more. As shown in the examples described later, it is possible to obtain high accuracy by predicting that a surface defect is generated at a location of 0.4 mm or more in at least the die casting simulation method of the present invention.

Further, the surface defect generation evaluation step may predict that a surface defect is generated at a location where the solid phase thickness is 0.1 × e ^{0.0297 × P} mm (where P is a casting pressure (MPa)) or more. More preferred (Claim 3). That is, in the normal case, as described above, it is possible to evaluate with one fixed reference value. However, for example, when the actual surface defect occurrence state changes under casting pressure conditions, the evaluation standard assumes that It is preferable to reflect the casting pressure currently being performed. One example is the above calculation formula. In this way, by setting different standards depending on the casting pressure, it is possible to perform an analysis that is closer to actuality. In the process up to the solid phase thickness calculation step, it is not particularly necessary to use casting pressure for analysis.

  In the die casting simulation method of the present invention, it is optimal that the molten metal material to be analyzed is an alloy exhibiting skin-generating solidification in which a solidified phase is formed from the skin side during solidification (Claim 3). . Among die casting alloys, there are more types that are more likely to solidify from the inside than alloys that exhibit skin-generating solidification as described above, in which case surface defects are less likely to occur. On the other hand, the alloy showing the skin formation type solidification is likely to cause surface defects in die casting, and therefore, the use of the method of the present invention is particularly effective.

  Specifically, the molten metal material is preferably an Al—Si based aluminum alloy having a Si content of 8 to 14 mass%. The Al—Si-based aluminum alloy having the specific Si content particularly has a high incidence of surface defects due to die casting. Therefore, the use of the above-described die casting simulation method of the present invention is very effective.

Example 1
A die casting simulation method and apparatus according to an embodiment of the present invention will be described with reference to FIGS.
The die casting simulation apparatus 1 of this example is an apparatus having a computer 10 provided with means for executing each analysis step as shown in FIG. An input device 11 such as a keyboard and a storage medium reading device and an output device 12 such as a display and a printer are connected to the computer 10.

  The means that can be executed by the computer 10 is means for executing each step in a die casting simulation method to be described later. Specifically, the element creation step execution means 21, the element definition step execution means 22, and the filling heat transfer analysis step. An execution unit 23, a solid phase ratio calculation step execution unit 24, a solid phase thickness calculation step execution unit 25, and a surface defect occurrence evaluation step execution unit 26 are included. These execution means read and execute what is created as a die casting simulation program for causing a computer to execute a die casting simulation method to be described later.

As shown in FIG. 3, the die casting simulation method of the present example includes a pretreatment process S100 including an element creation step S101 and an element definition step S102, a filling heat transfer analysis step S201, and a solid phase ratio calculation step S202. This is a method of performing an evaluation step S300 including a thermal analysis step S200, a solid phase thickness calculation step S301, and a surface defect occurrence evaluation step S302.
This will be described in further detail below.

In this example, model data of a mold is created by CAD, and die casting simulation is performed using the model data.
(1) Pretreatment process S100
An orthogonal coordinate system was adopted as the coordinate system. The shape of the casting mold is created as CAD data. In order to simplify the description, a two-dimensional description represented by x and y is shown in FIG. The following description in two dimensions can be simply extended to three dimensions.
First, CAD data is arranged on a two-dimensional coordinate system. Then, the coordinate system is divided into minute elements in the x and y axis directions (element creation step S101).

  Next, an element in which the position of the center of gravity of the minute element 1 is located in the casting mold area S1 of the CAD data is defined as a mold element 1a, and an element located in the cavity area S2 is defined as a cavity element 1b (element definition step S102). Further, the heat transfer coefficients between the cavity elements 1b, between the mold elements 1a, and between the cavity element 1b and the mold element 1a are set to appropriate values in advance.

  As shown in FIG. 3, in the casting mold of this example, the gate G into which the molten metal is injected is arranged on the right side of the drawing, and the vent hole V for discharging the air in the cavity region S2 is arranged on the left side. . As described above, each square represents the microelement 1, and the bold line K of the boundary line of the microelement 1 represents the CAD data of the template.

(2) Filling heat transfer analysis step S200
In the filling heat transfer analysis step S200, a filling heat transfer analysis step S201 for performing the filling region analysis and calculating the temperature of the molten material filling element over time, and the solid phase ratio of the molten metal material in the molten material filling element over time are performed. The solid phase ratio calculating step S202 is calculated. Each analysis is performed at each minute time interval set according to the progress of time in the simulation.

  In the filling region analysis, the filling ratio of the molten metal for the cavity element is sequentially calculated at predetermined time intervals. The filling region analysis proceeds by the finite difference method. After a predetermined time from the start of injection, several cavity elements are filled with the molten metal material, and when the time further advances, the cavity element filled with the molten metal material is changed. It will increase. In the heat transfer analysis performed together with this, the temperature of each microelement (molten material filling element) filled with the molten metal is analyzed by an unsteady heat conduction calculation method (filling heat transfer analysis step S201).

  In the solid phase ratio calculating step S202, the solid phase ratio is calculated for each of the molten material filling elements based on the calculated temperature. The solid phase ratio is calculated by applying the temperature of each molten material filling element to the Seil's equation. This solid phase ratio calculation step S202 is performed at the same minute time interval as the filling heat transfer analysis step S201 as a predetermined time interval. The filling heat transfer analysis step S201 and the solid phase ratio calculation step S202 are repeated until filling is completed. Then, after confirming that the filling is completed in step S209, the process proceeds to the evaluation step S300.

(3) Evaluation process S300
In the evaluation step S300, first, a solid phase thickness calculation step S301 is performed. This step is performed immediately after the filling of the molten metal into the cavity is completed based on the result of the above-described filling heat transfer analysis step S200.

In the solid phase thickness calculation step S301, first, a region where an element having a solid phase ratio exceeding 0 is detected in the cavity element adjacent to the mold element.
Next, when the solid phase ratio fs of the detected element is 0 <fs <1, the element is set as a Cs element, and only the solid phase thickness Lc in the element is equal to the solid phase thickness in the portion. Become. As a calculation formula at this time, the solid phase thickness Lc = (element volume × solid phase ratio) / (area of the surface in contact with the mold element) can be adopted.

On the other hand, among the elements in the cavity element adjacent to the mold element, those having a solid phase ratio of 1 in the region where the solid phase ratio is detected to exceed 0 are recognized as quasi-type elements, and the elements The solid phase thickness Lj is calculated by the following formula: Lj = (element volume) / (area of the surface in contact with the mold element).
Next, when the solid phase ratio of the cavity element adjacent to the quasi-type element in the thickness direction is 1, this element is also a quasi-type element, and the solid phase thickness Lj is Lj = (element volume) / (Area of the surface in contact with the above-mentioned quasi-type element) Hereinafter, as long as the solid phase ratio of the element in contact with the thickness direction is 1, the thickness Lj of each element is calculated with the same calculation formula.
When the cavity element adjacent in the thickness direction to the quasi-type element is the Cs element described above, the solid phase thickness Lc is expressed as Lc = (element volume × solid phase ratio) / (the above The area of the surface in contact with the quasi-type element is calculated using a calculation formula.

The sum of the solid phase thickness Lj of all quasi-type elements (ΣLj) and the solid phase thickness Lc of the Cs element, that is, ΣLj + Lc, among the elements that are sequentially in contact with the mold element in the thickness direction, that is, ΣLj + Lc The phase thickness is L.
The solid phase thickness L of the element having a solid phase ratio of 0 is naturally 0.

Next, a surface defect occurrence evaluation step S302 is performed. In this step, evaluation is performed from the solid phase thickness L obtained for each cavity element adjacent to the mold element.
For example, when the solid phase thickness exceeds 0.4 mm, the surface defect generating element is used. The standard of 0.4 mm can be changed according to the actual casting conditions and the material of the molten metal material.
In any case, for all the cavity elements adjacent to the mold element, if the total solid phase thickness L in the thickness direction exceeds the reference value, the cavity element is identified and distinguished from the others, The distribution in which surface defects occur can be expressed on a computer. Specifically, it is possible to output the image of a casting (molded product) to be drawn by a technique such as painting a portion where a surface defect occurs with a predetermined mark. It is also possible to output only coordinate data, not an image.

(Example 2)
This example shows a specific example of the result of simulation using the method of the first embodiment.
First, in this example, in order to evaluate the effectiveness of the simulation, a die casting mold was actually manufactured, a casting 8 having the shape shown in FIG. 6 was actually manufactured, and surface defects were observed. The casting 8 has a flat plate shape, to which a molten metal injection pressurizing portion 81, a runner portion 82, and a gate portion 83 are connected.

  As casting pressure, two kinds of conditions of 30 MPa and 65 MPa were used. The material was ADC12 alloy. Other main conditions were injection temperature: 640 ° C., low speed: 0.3 m / s, and high speed: 1.5 m / s. The low speed and the high speed mean the forward speed of a pressurizing plunger (not shown) used for injecting the molten metal material. In this example, a two-stage injection method is adopted in which the speed is initially set to the condition of the low speed and then switched to the condition of the high speed in the middle.

  And the surface of the obtained casting 8 was observed, the surface defect (hot water wrinkle) generating part 9 was specified, and the result was shown to Fig.7 (a) (b). (A) of the figure is manufactured with a casting pressure of 30 MPa, and (b) of the figure is manufactured with a casting pressure of 65 MPa. Moreover, these figures show the observed surface defect (water bath) generating portion 9.

  Next, the die casting simulation method shown in Example 1 was performed. In this example, it is assumed that the flat casting 8 shown in FIG. 6 is made, and a model in which the molten metal injection pressurizing portion 81, the runner portion 82, and the gate portion 83 are also part of the casting is assumed. And the part which encloses these was made into the casting_mold | template part, the shape was created as CAD data, and pre-processing process S100 mentioned above was performed.

In addition, in the surface defect occurrence evaluation step S302 of the evaluation step S300 after the filling heat transfer analysis step S200 is performed, first, the reference value is set to 0.4 mm, and the solid phase thickness L is set to 0.4 mm or more. It was predicted that surface defects would occur. In this case, the simulation does not consider the casting pressure at all.
The result is shown in FIG. As shown in the figure, the simulation result output shows a portion 5 where surface defects may occur on the surface of the image of the casting 8.
As can be seen from the comparison between FIG. 8 and FIG. 7 described above, it can be seen that the simulation results this time are in good agreement with the casting pressure of 65 MPa shown in FIG. On the other hand, as compared with the case of the casting pressure of 30 MPa in FIG.

Next, in this example, the die casting simulation was performed again. In the surface defect occurrence evaluation step S302 of the evaluation step S300, the reference value for the determination was set to 0.1 × e ^{0.0297 × P} mm. And as a value of casting pressure P, 30 MPa was used.
The simulation result is shown in FIG. This figure shows a portion 5 where surface defects may occur on the surface of the image of the casting 8 as in the case of FIG.
As can be seen from the comparison between FIG. 9 and FIG. 7 described above, it can be seen that the simulation result of this time is in good agreement with the case of the casting pressure of 30 MPa shown in FIG.

Explanatory drawing which shows an example of the element creation method in this invention. Explanatory drawing which shows an example of the element definition method in this invention. FIG. 3 is a flowchart showing a die casting simulation method in the first embodiment. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram illustrating a configuration of a die casting simulation apparatus in Embodiment 1. Explanatory drawing which shows the element creation result in Example 1. FIG. The perspective view which shows the casting actually produced in Example 2. FIG. In Example 2, (a) Explanatory view showing the generation distribution of surface defects in a casting produced under a casting pressure of 30 MPa, (b) Explanatory view showing the occurrence distribution of surface defects in a casting produced under a casting pressure of 65 MPa. . FIG. 9 is an explanatory diagram showing a first simulation result in Example 2. Explanatory drawing which shows the 2nd simulation result in Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Die-casting simulation apparatus 10 Computer 21 Element creation step execution means 22 Element definition step execution means 23 Filling heat transfer analysis step execution means 24 Solid phase ratio calculation step execution means 25 Solid phase thickness calculation step and execution means 26 Surface defect generation evaluation step Execution means S100 Preprocessing step S101 Element creation step S102 Element definition step S200 Filling heat transfer analysis step S201 Filling heat transfer analysis step S202 Solid phase ratio calculation step S300 Evaluation step S301 Solid thickness calculation step S302 Surface defect occurrence evaluation step

Claims (8)

A die casting simulation method for predicting at least the occurrence of surface defects occurring in the casting when performing die casting to obtain a casting having a desired shape by pressurizing and solidifying a molten metal material into a mold,
An element creating step of positioning the shape of the mold used for forming the molten metal material on a coordinate system and dividing the space of the coordinate system into a plurality of microelements;
For each of the microelements, a preprocessing step including a mold element when positioned in the mold region of the mold and an element defining step that defines a cavity element when positioned in the cavity region of the mold;
For each of the cavity elements, a filling region analysis for analyzing the filling state of the molten metal material over time is performed, and the molten material filling element that is the cavity element filled with the molten metal material is filled with the molten material. The heat transfer between the elements and between the molten material filling element and the mold element is analyzed over time based on the respective heat transfer coefficients, and the temperature of the molten material filling element is calculated over time. Filling heat transfer analysis step;
A solid phase ratio calculating step for calculating, over time, a solid phase ratio of the molten metal material in the molten material filling element according to the calculated temperature of the molten material filling element, ,
A solid phase thickness calculating step of calculating a solid phase thickness that is a thickness of the cavity element that is continuously at a solid phase ratio of 1 from an inner wall surface of the mold element when filling is completed;
A die casting simulation method comprising: an evaluation step including a surface defect occurrence evaluation step for predicting the occurrence of surface defects from the solid phase thickness.   2. The die casting simulation method according to claim 1, wherein the surface defect occurrence evaluation step predicts that a surface defect is generated at a location where the solid phase thickness is 0.4 mm or more. ^3. The surface defect occurrence evaluation step according to claim 1, wherein the surface defect occurrence evaluation step predicts that a surface defect occurs at a location where the solid phase thickness is 0.1 × e ^{0.0297 × P} mm (where P is a casting pressure (MPa)) or more. A die casting simulation method characterized by:   The die casting simulation method according to any one of claims 1 to 3, wherein the molten metal material to be analyzed is an alloy exhibiting skin-generating solidification in which a solidified phase is formed from the skin side during solidification. .   5. The die casting simulation method according to claim 4, wherein the molten metal material is an Al—Si based aluminum alloy having a Si content of 8 to 14 mass%.   A die casting simulation program for causing a computer to execute the die casting simulation method according to any one of claims 1 to 5.   A computer-readable storage medium on which the die casting simulation program according to claim 6 is recorded.   A die-casting simulation apparatus comprising a computer configured to execute the die-casting simulation method according to claim 1.

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