Method, apparatus, and program for predicting the fiber orientation distribution of short fiber reinforced resins

Abstract

This invention provides a method for predicting the fiber orientation distribution of short-fiber reinforced resins, which enables structural analysis that simply considers the fiber orientation of the resin without performing flow analysis. [Solution] A method for predicting the orientation distribution of fibers contained in an injection-molded product of short fiber-reinforced resin having a skin layer and a core layer by simulation, comprising: an analysis model creation step of creating an analysis model for a virtual object using CAE analysis software based on the finite element method (S1); a step of performing a transient thermal analysis based on thermal analysis conditions including information on the gate position where the resin is injected, and predicting the flow direction of the resin from the heat flow direction obtained by the transient thermal analysis (S2, S3, S4); and a fiber orientation tensor calculation step of expressing the degree of flow direction orientation of the skin layer and the core layer with an algebraic relation, and calculating a fiber orientation tensor indicating the orientation state of the fibers by performing an algebraic operation based on the algebraic relation (S5).

Description

Technical Field

[0005]

[0001] This invention relates to a method, apparatus, and program for predicting the fiber orientation distribution of short fiber reinforced resin.

Background Art

[0002] Short fiber reinforced resin has a better balance of strength and cost than solid materials and is cheaper than long fiber resin, so it has attracted much attention. Short fiber reinforced resin products are made by injection molding, and the strength of the products varies depending on the injection conditions.

[0003] Generally, the mechanical performance of a product can be determined by its shape and material. However, since resin has anisotropy in the flow direction, its mechanical properties such as elastic modulus and strength are different in the flow direction and the direction perpendicular to it. In particular, in short fiber reinforced resin, the influence on the mechanical properties in the flow direction is large, and for the structural design of short fiber reinforced resin products, structural analysis considering the flow direction is essential.

[0004] In order to grasp this flow state, for example, as described in Non-Patent Document 1 below, it is common to perform a flow analysis.

Prior Art Documents

Non-Patent Documents

[0006] However, methods like the one described in Non-Patent Document 1 require mapping the flow direction from the flow analysis results to the structural analysis because the software and mesh used for the flow analysis and structural analysis are different. This necessitates new mapping software, which in turn increases the time required for the mapping process.

[0007] Furthermore, in order to perform highly accurate flow analysis using methods such as those described in Non-Patent Document 1, information on the molding machine is necessary. However, in many cases, the design and molding departments for short-fiber reinforced resin products are separate, or the companies involved are different entities, making it difficult to obtain molding machine data during the design phase. Moreover, because the process involves design, mold ordering, and prototyping, the influence of the fiber flow direction cannot be considered during the design phase.

[0008] The present invention aims to solve the above-mentioned problems and provide a method, apparatus, and program for predicting the fiber orientation distribution of short-fiber reinforced resins that enable structural analysis that simply considers the fiber orientation of the resin without performing flow analysis. [Means for solving the problem]

[0009] To solve the above-mentioned problems, one aspect of the method for predicting the fiber orientation distribution of a short fiber reinforced resin according to the present invention is: A method for predicting the orientation distribution of fibers contained in an injection-molded product of short fiber-reinforced resin having a skin layer and a core layer by simulation, The process involves creating an analysis model for a virtual object using CAE analysis software based on the finite element method, and A step of performing a transient thermal analysis based on thermal analysis conditions including information on the gate position where the resin is injected, and predicting the flow direction of the resin from the heat flow direction obtained by the transient thermal analysis, A fiber orientation tensor calculation step involves expressing the degree of flow direction orientation of the skin layer and the core layer using an algebraic relation, and calculating a fiber orientation tensor indicating the orientation state of the fibers by performing algebraic calculations based on the algebraic relation; It is equipped with.

[0010] According to one embodiment of the above method, the flow direction of the resin is predicted by thermal analysis, and the orientation state of the fibers is predicted by algebraic calculations, thereby simplifying the coordination between the fiber orientation state analysis and structural analysis processes in short-fiber reinforced resins.

[0011] Furthermore, according to another embodiment of the above method, When the center of the thickness direction of the injection-molded product is taken as the origin and the coordinates in the thickness direction are represented by the X-axis, and the degree of orientation coinciding with the flow direction of the resin is set to 1, and the degree of orientation coinciding with the direction perpendicular to the flow direction is set to 0, and the degree of orientation is represented by the Y-axis with the point where the degree of orientation is 0 as the origin, the algebraic relation can be represented by a V-shaped straight line with the origin as its vertex.

[0012] According to this embodiment, there is no need to solve the differential equation for fiber orientation as in the conventional method, and the orientation state of the fibers is predicted by algebraic calculations, so the amount of computation and computation time are drastically reduced.

[0013] Furthermore, according to another embodiment of the above method, The thermal analysis conditions include setting the entire system to a predetermined temperature and setting the gate position to a temperature higher than the predetermined temperature.

[0014] According to this embodiment, it is not necessary to predict the flow direction by fluid analysis as in the conventional method. Instead, the flow direction is predicted by thermal analysis based on limited information such as gate position information, so the amount of computation and computation time are drastically reduced.

[0015] The above method can be implemented as a device for predicting the fiber orientation distribution of short fiber-reinforced resins, and also as a program for predicting the fiber orientation distribution of short fiber-reinforced resins. [Effects of the Invention]

[0016] According to the present invention, it is possible to predict the fiber orientation distribution of a short fiber reinforced resin without performing fluid analysis, so that it is possible to simplify the process cooperation between the prediction of the fiber orientation distribution and the structural analysis. As a result, the amount of calculation and the calculation time can be significantly reduced, and at the design stage, highly accurate structural analysis considering the fiber orientation can be performed.

Brief Description of the Drawings

[0017] [Figure 1] FIG. 8 is a diagram showing a schematic configuration of a fiber orientation distribution prediction device for a short fiber reinforced resin according to an embodiment of the present invention. [Figure 2] FIG. 11 is a diagram showing a functional block of a fiber orientation distribution prediction device for a short fiber reinforced resin according to an embodiment of the present invention. [Figure 3] FIG. 14 is a flowchart showing the flow of the flow direction prediction process and the fiber orientation prediction process of a short fiber reinforced resin according to an embodiment of the present invention. [Figure 4] FIG. 17 is a diagram showing an example of a prediction result of the fiber orientation distribution using conventional fluid analysis. [Figure 5] FIG. 20 is a diagram showing an example of an algebraic relational expression used in the fiber orientation prediction process in the present embodiment. [Figure 6] FIG. 23 is a diagram showing the result of verifying the accuracy difference between the method of the present embodiment and the conventional method. [Figure 7] FIG. 26 is a diagram for explaining a method of verifying the accuracy difference between the method of the present embodiment and the conventional method.

Mode for Carrying Out the Invention

[0018] Hereinafter, a fiber orientation distribution prediction device for a short fiber reinforced resin according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a fiber orientation distribution prediction device 100 for a short fiber reinforced resin according to the present embodiment. As shown in FIG. 1, the fiber orientation distribution prediction device 100 for a short fiber reinforced resin according to the present embodiment includes a central processing unit 1, a display device 2, a storage device 3, an input device 4, and an output device 5.

[0019] The central processing unit 1 is a device such as a personal computer capable of executing programs, and includes a CPU and memory. The display device 2 is a device such as a liquid crystal display capable of displaying characters and images. The storage device 3 is a device such as an HDD (Hard Disk Drive) capable of storing programs and data, and an external database server may also be used. The program of the present invention is stored in the storage device 3. The input device 4 is a device such as a keyboard that allows the user to input data or instructions. The output device 5 is a device such as a printer capable of outputting characters and images.

[0020] Figure 2 shows a functional block that operates when the central processing unit 1 executes the program of the present invention. As shown in Figure 2, the central processing unit 1 functions as a control unit 10. The control unit 10 also functions as an analysis model creation unit 11, a thermal analysis condition setting unit 12, a thermal analysis unit 13, and a fiber direction tensor calculation unit 14, according to the program of the present invention.

[0021] The analysis model creation unit 11 creates an analysis model for a virtual object corresponding to a short fiber reinforced resin molded product. The analysis model is created using CAE analysis software based on the finite element method. The analysis model is, for example, an analysis model obtained by dividing shape data, such as 3D CAD data defining the product shape of the short fiber reinforced resin, into multiple minute elements called a mesh. The analysis model creation unit 11 stores the created analysis model in the storage device 3.

[0022] The thermal analysis condition setting unit 12 sets the thermal analysis conditions necessary for the thermal analysis performed by the thermal analysis unit 13. Details of the thermal analysis conditions will be described later.

[0023] The thermal analysis unit 13 performs a heat transfer analysis based on the thermal analysis conditions set by the thermal analysis condition setting unit 12, and makes a simplified prediction of the flow direction of the short fiber reinforced resin from the heat flow direction obtained from the heat transfer analysis. The thermal analysis unit 13 stores the data on the flow direction of the short fiber reinforced resin obtained as a result of the analysis in the storage device 3. Details of the thermal analysis processing by the thermal analysis unit 13 will be described later.

[0024] The fiber orientation tensor calculation unit 14 uses an algebraic relation that represents the degree of flow direction orientation of the skin layer and core layer of the short fiber reinforced resin molded product, and calculates a fiber orientation tensor that indicates the orientation state of the fibers in the short fiber reinforced resin by performing algebraic calculations based on this algebraic relation. Details of the processing by the fiber orientation tensor calculation unit 14 will be described later.

[0025] (Predictive processing of fiber orientation in short fiber reinforced resins) Next, the fiber orientation prediction process for the short fiber reinforced resin in this embodiment will be explained with reference to Figures 3 to 5.

[0026] In this embodiment, first, the analysis model creation unit 11 creates an analysis mesh as an analysis model for a virtual object corresponding to a short fiber reinforced resin molded product (Figure 3: Step S1). The analysis mesh is created using CAE analysis software based on the finite element method. The analysis mesh is a model obtained by dividing shape data, such as 3D CAD data defining the product shape of the short fiber reinforced resin, into a plurality of minute elements called a mesh. This analysis mesh can be used as a mesh for structural analysis, and in this embodiment, since the fiber orientation is reflected in this analysis mesh, the work of mapping the resin flow direction to the structural analysis is unnecessary.

[0027] Next, the thermal analysis conditions necessary for the thermal analysis process are set by the thermal analysis condition setting unit 12 (Figure 3: Step S2). These thermal analysis conditions include information on the gate position, which is information on where the resin is injected. The mesh size, the temperature of all nodes, and the temperature of the nodes corresponding to the gate position are also included in these thermal analysis conditions.

[0028] Next, the thermal analysis unit 13 performs thermal analysis (Figure 3: Step S3). In this embodiment, the flow direction of the resin is predicted not by conventional flow analysis, but by substituting it with heat transfer analysis. In other words, the flow direction of the resin is simply predicted from the heat flow direction obtained by the heat transfer analysis, making it possible to perform a structural analysis method that sets anisotropic physical properties based on the flow direction.

[0029] Specifically, the thermal analysis unit 13 sets all nodes to a certain temperature and performs a transient thermal analysis by applying a higher temperature to the nodes corresponding to the gate positions. This allows the direction of heat flow, i.e., the heat flux vector, to be obtained. Conventional flow direction prediction using fluid analysis requires flow control information input to the molding machine and takes approximately 30 minutes to 1 hour to calculate. However, the thermal analysis method in this embodiment only uses information about the gate positions and takes only a few seconds to calculate.

[0030] It should be noted that predicting the flow direction of resin using heat transfer analysis is a known method (for example, "Prediction of Flow Direction and Structural Analysis of Fiber-Reinforced Resins," Hiroo Sakamoto, Tomoko Baba, and Fumio Aoki, Mitsubishi Electric Technical Journal, Vol. 85, No. 7, 2011).

[0031] Next, the fiber orientation tensor calculation unit 14 obtains the heat flux vector as a result of the processing by the thermal analysis unit 13 (Figure 3: step S4), and performs the fiber orientation tensor calculation process (Figure 3: step S5).

[0032] Short fiber reinforced resin molded products are formed by rapidly filling the thin-walled portion of a parallel plate with molten resin containing short fibers. During this injection molding filling process, fiber-oriented layers are formed in the thickness direction, with a core layer between skin layers. The fibers are oriented in the flow direction in the skin layer and perpendicular to the flow direction in the core layer. Thus, the resin exhibits anisotropy in the flow direction, and its mechanical properties, such as elastic modulus and strength, differ in the flow direction and perpendicular to it. In particular, the influence of the flow direction on the mechanical properties is significant in short fiber reinforced resins, making structural analysis considering the flow direction essential for the structural design of short fiber reinforced resin products.

[0033] Traditionally, the prediction of such fiber orientation distribution has been performed using flow analysis. Figure 4 shows the results of predicting the fiber orientation distribution using flow analysis. In the example in Figure 4, the origin is set at the center of the thickness direction of the injection-molded product, and the coordinates in the thickness direction are represented by the X-axis. The degree of orientation is represented by the Y-axis. The degree of orientation is set to 1 if it coincides with the flow direction of the resin, and to 0 if it coincides with a direction perpendicular to the flow direction.

[0034] As can be seen from Figure 4, the orientation in the flow direction is stronger in the skin layer, i.e., the plate surface, while the orientation perpendicular to the flow direction is stronger in the core layer, i.e., the center of the plate. The fiber orientation distribution has a significant impact on mechanical properties and therefore needs to be predicted with high accuracy, but conventional methods using flow analysis have several problems.

[0035] First, because the software and meshes used for fluid analysis and structural analysis are different, it is necessary to map the flow direction from the fluid analysis results to the structural analysis. This requires new mapping software, and the mapping process itself is very time-consuming.

[0036] Furthermore, while high-precision flow analysis requires information about the molding machine, in many cases, the design and molding departments for short-fiber reinforced resin products are separate, or they are separate companies, making it difficult to obtain molding machine data during the design phase. Moreover, because the process involves design, mold ordering, and prototyping, the influence of fiber flow direction cannot be considered during the design stage.

[0037] Therefore, the inventors focused on the following points. (1) The bending stiffness of short fiber reinforced resin products is mostly determined by the orientation of the surface, and if the orientation of the surface can be predicted, the bending strength can be predicted to a certain extent. (2) The degree of orientation is a dimensionless quantity, and the tendency is roughly the same for all resins and fibers. (3) While it may not be possible to predict strengths other than bending strength with high accuracy, this is not a major problem as the purpose of using short-fiber reinforced resin is to ensure bending strength in the first place.

[0038] In this embodiment, based on the above concept, the degree of flow direction orientation of the skin layer and core layer is expressed by an algebraic relation, and a fiber orientation tensor indicating the orientation state of the fibers is calculated by performing algebraic operations based on this algebraic relation (Figure 3: Step S5).

[0039] Figure 5 shows an example of the aforementioned algebraic relation. In the example shown in Figure 5, the degree of orientation is simply approximated by a V-shaped straight line. That is, the heat flux vector is obtained as a result of processing in the thermal analysis unit 13 (Figure 3: step S4), and the fiber orientation tensor is calculated by performing algebraic calculations using the algebraic relation shown in Figure 5 from this flow direction (Figure 3: step S5).

[0040] Conventional methods using fluid analysis require the solver to solve differential equations for fiber orientation at each location, resulting in a very large computational load. However, this embodiment only requires algebraic operations, drastically reducing the computational load and computation time. For example, while conventional methods using fluid analysis required about an hour for calculation, this embodiment can be completed in just a few minutes. Furthermore, conventional methods required conducting basic tests to identify model constants included in the differential equations for fiber orientation, but this embodiment does not require basic tests because it has no parameters.

[0041] As described above, after calculating the fiber orientation tensor, structural analysis is performed. However, with the method of this embodiment, the mesh used for calculating the fiber orientation tensor and the mesh used for structural analysis are the same, which simplifies the process coordination.

[0042] In contrast, with conventional methods using fluid analysis, the meshes used for fluid analysis and structural analysis are different. This requires software to map the flow direction from the fluid analysis results to the structural analysis, and this mapping process is extremely time-consuming.

[0043] However, according to this embodiment, software for mapping flow direction to structural analysis is not required, making it possible to significantly reduce working time.

[0044] Furthermore, according to this embodiment, since there is no need to perform flow analysis, information on the molding machine is also unnecessary, and highly accurate structural analysis that takes into account the influence of the fiber flow direction can be performed from the design stage.

[0045] (Verification of accuracy differences) Next, the results of verifying the accuracy difference between the method of this embodiment and the conventional method will be explained with reference to Figures 6 and 7. In this verification, as shown in Figure 7, the bending reaction force in the simulation model 30 of the short fiber reinforced resin product was calculated when the plunger 20 was pressed down in the direction of the arrow in Figure 7.

[0046] The results are shown in Figure 6. In Figure 6, the horizontal axis represents the stroke of the plunger 20, and the vertical axis represents the bending reaction force. Solid line A and dotted line B represent examples using the conventional method, where the flow direction is predicted using fluid analysis, mapped using mapping software, and then structural analysis is performed. The only difference between solid line A and solid line B is the difference in conditions.

[0047] The solid line C represents an example in this embodiment where the flow direction is predicted by thermal analysis, the fiber orientation is predicted using that flow direction and algebraic calculations, and then structural analysis is performed. The dotted line D represents an example where, although a modeling called a shell is used as in this embodiment, the thickness is set to zero and structural analysis is performed using a conventional method.

[0048] As shown in Figure 6, in this embodiment, the accuracy of the method deteriorates as the stroke of the plunger 20 increases compared to the conventional method. However, when the stroke of the plunger 20 is shallow, that is, close to the plate surface, the bending reaction force can be calculated with very high accuracy.

[0049] As described above, this embodiment allows for structural analysis that simply considers the fiber orientation of short-fiber reinforced resin without performing flow analysis, thus simplifying the process linkage from fiber orientation prediction to structural analysis. Furthermore, since this embodiment does not perform flow analysis, it eliminates the need for mapping software to connect flow analysis software and structural analysis software, as required in conventional methods, and thus significantly reduces working time. Moreover, since this embodiment does not perform flow analysis, information on the molding machine is unnecessary, allowing for high-precision structural analysis that simply considers the fiber orientation of short-fiber reinforced resin from the design stage. Therefore, it is possible to perform high-precision structural analysis that simply considers the fiber orientation of short-fiber reinforced resin easily and at low cost.

[0050] (modified version) In the embodiments described above, an embodiment in which an analysis model is created within the fiber orientation distribution prediction device 100 for short fiber reinforced resin has been described, but the present invention is not limited to this embodiment. The analysis model may be created outside the fiber orientation distribution prediction device 100 for short fiber reinforced resin, and transmitted or output to the fiber orientation distribution prediction device 100 for short fiber reinforced resin via a network or the like, and received or input by the fiber orientation distribution prediction device 100 for short fiber reinforced resin. Furthermore, by utilizing this embodiment to perform comprehensive predictions regarding gate positions and the number of gates, it is possible to optimize the gate arrangement to meet the desired strength requirements. This allows product designers to instruct mass production personnel not only on the product shape but also on the gate positions, thereby reducing rework in mold design.

[0051] The short-fiber-reinforced resin fiber orientation distribution prediction program according to the above embodiment can be provided in a form stored on a computer-readable recording medium and installed on a computer. The recording medium is, for example, a non-transitory recording medium, such as an optical recording medium like a CD-ROM, but can include any known form of recording medium such as a semiconductor recording medium or a magnetic recording medium. It is also possible to provide the above program in the form of distribution via a communication network and install it on a computer.

[0052] The above describes a method, apparatus, and program for predicting the fiber orientation distribution of a short-fiber-reinforced resin according to embodiments of the present invention. However, the present invention is not limited thereto, and various modifications are possible without departing from the spirit of the invention. [Explanation of symbols]

[0053] 1 central processing unit 2 Display device 3 Storage device 4 Input devices 5. Output device 10 Control Unit 11. Analysis Model Creation Department 12. Thermal Analysis Condition Setting Section 13 Thermal Analysis Department 14. Fiber Direction Tensor Calculation Unit 100 Short fiber reinforced resin fiber orientation distribution prediction device

Claims

1. A method for predicting the orientation distribution of fibers contained in an injection-molded product of short fiber-reinforced resin having a skin layer and a core layer by simulation, The process involves creating an analysis model for a virtual object using CAE analysis software based on the finite element method, and A step of performing a transient thermal analysis based on thermal analysis conditions including information on the gate position where the resin is injected, and predicting the flow direction of the resin from the heat flow direction obtained by the transient thermal analysis, A fiber orientation tensor calculation step involves expressing the degree of flow direction orientation of the skin layer and the core layer using an algebraic relation, and calculating a fiber orientation tensor indicating the orientation state of the fibers by performing algebraic calculations based on the algebraic relation; A method for predicting the fiber orientation distribution of a short fiber reinforced resin, comprising the following features.

2. When the center of the thickness direction of the injection-molded product is taken as the origin and the coordinates in the thickness direction are represented by the X-axis, and the degree of orientation coinciding with the flow direction of the resin is set to 1, and the degree of orientation coinciding with the direction perpendicular to the flow direction is set to 0, and the degree of orientation is represented by the Y-axis with the point where the degree of orientation is 0 as the origin, the algebraic relation can be represented by a V-shaped straight line with the origin as its vertex. A method for predicting the fiber orientation distribution of a short fiber reinforced resin according to claim 1.

3. The thermal analysis conditions include setting the entire system to a predetermined temperature and setting the gate position to a temperature higher than the predetermined temperature. A method for predicting the fiber orientation distribution of a short fiber reinforced resin according to claim 1 or claim 2.

4. An apparatus for predicting the orientation distribution of fibers contained in an injection-molded product of short fiber-reinforced resin having a skin layer and a core layer, by simulation, An analysis model creation unit that creates an analysis model for a virtual object using CAE analysis software based on the finite element method, A thermal analysis unit performs a transient thermal analysis based on thermal analysis conditions including information on the gate position where the resin is injected, and predicts the flow direction of the resin from the heat flow direction obtained by the transient thermal analysis. A fiber orientation tensor calculation unit calculates a fiber orientation tensor indicating the orientation state of the fibers by expressing the degree of flow direction orientation of the skin layer and the core layer using an algebraic relation and performing algebraic calculations based on the algebraic relation, A device for predicting the fiber orientation distribution of short fiber-reinforced resins, equipped with the necessary components.

5. When the center of the thickness direction of the injection-molded product is taken as the origin and the coordinates in the thickness direction are represented by the X-axis, and the degree of orientation coinciding with the flow direction of the resin is set to 1, and the degree of orientation coinciding with the direction perpendicular to the flow direction is set to 0, and the degree of orientation is represented by the Y-axis with the point where the degree of orientation is 0 as the origin, the algebraic relation can be represented by a V-shaped straight line with the origin as its vertex. The device for predicting the fiber orientation distribution of a short fiber reinforced resin according to claim 4.

6. The thermal analysis conditions include setting the entire system to a predetermined temperature and setting the gate position to a temperature higher than the predetermined temperature. A device for predicting the fiber orientation distribution of a short fiber-reinforced resin according to claim 4 or claim 5.

7. A program that causes a computer to perform a simulation to predict the orientation distribution of fibers contained in an injection-molded product of short fiber-reinforced resin having a skin layer and a core layer, wherein the program causes the computer to: The process involves creating an analysis model for a virtual object using CAE analysis software based on the finite element method, and A step of performing a transient thermal analysis based on thermal analysis conditions including information on the gate position where the resin is injected, and predicting the flow direction of the resin from the heat flow direction obtained by the transient thermal analysis, A fiber orientation tensor calculation step involves expressing the degree of flow direction orientation of the skin layer and the core layer using an algebraic relation, and calculating a fiber orientation tensor indicating the orientation state of the fibers by performing algebraic calculations based on the algebraic relation; A program for predicting the fiber orientation distribution of short-fiber reinforced resins.

8. When the center of the thickness direction of the injection-molded product is taken as the origin and the coordinates in the thickness direction are represented by the X-axis, and the degree of orientation coinciding with the flow direction of the resin is set to 1, and the degree of orientation coinciding with the direction perpendicular to the flow direction is set to 0, and the degree of orientation is represented by the Y-axis with the point where the degree of orientation is 0 as the origin, the algebraic relation can be represented by a V-shaped straight line with the origin as its vertex. A program for predicting the fiber orientation distribution of a short fiber reinforced resin according to claim 7.

9. The thermal analysis conditions include setting the entire system to a predetermined temperature and setting the gate position to a temperature higher than the predetermined temperature. A program for predicting the fiber orientation distribution of a short fiber-reinforced resin according to claim 7 or claim 8.

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