JP2009233881A - Injection molding process analysis method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a process analysis method remarkably improving entire whole accuracy of the injection molding simulation, by accurately considering flow/solidifying characteristics of resin. <P>SOLUTION: In the flow analysis in the injection molding process of resin materials, the effect of solidifying due to the progress of crystallization by application of pressure during flowing and stopping of the flow of the resin materials, is taken into account, and a temperature of stopping the flow of the resin materials is assumed as the crystallization temperature Ts at pressurizing time. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for improving the prediction accuracy of resin flow / solidification behavior particularly in a resin injection molding process.

In the flow process, assuming the Hele-Show flow in hydrodynamics, the Navier-Stokes equation is predicted by using a 2.5D thin shell element or a 3D element to predict the filling pattern, pressure, short shot, mold clamping Predicts problems in injection molding such as force and weld line generation. With respect to processes from filling to holding pressure, cooling, and mold release in resin injection molding, resin molding simulation methods as described in Patent Document 1 and Non-Patent Document 1 are known. In addition, there are Patent Document 2 and Non-Patent Document 2 as related documents.
JP 09-150443 A Special table 2003-510202 gazette The Japan Society for Technology of Plasticity "Flow Analysis-Plastic Molding" Corona Corporation 2004 RT Fenner, “Practical Finite Element Method” Science 1980

  As described above, the conventional technology has insufficient prediction accuracy of filling pressure, and in addition to short shot, mold clamping force, and weld line generation, pressure distribution in pressure holding process and cooling process based on flow analysis results This affects the prediction results such as temperature distribution, fiber orientation distribution, shrinkage, etc., which causes poor warpage deformation analysis accuracy. Therefore, regardless of whether it is a prototype or a mass-produced product, there is a strong demand from the plastics industry to increase the accuracy of simulation prediction in the injection molding process. An object of the present invention is to significantly improve the overall accuracy of the injection molding simulation by accurately considering the flow and solidification characteristics of the resin.

  In the present invention, in order to remarkably improve the accuracy of the injection molding simulation, the effect of the crystallization progressing by the application of pressure during the flow and the flow stopping and solidifying is considered in the simulation.

  That is, the present invention is an injection molding process analysis method characterized in that, in the flow analysis in a resin material injection molding process, the temperature at which the resin material stops flowing is the crystallization temperature Ts during pressurization.

  INDUSTRIAL APPLICABILITY The present invention enables accurate analysis of resin flow in an injection molding process, and is particularly effective in improving accuracy such as short shot prediction, filling pattern of products having thin-walled portions, and shrinkage rate prediction. . As a result, it is possible to reduce the cost of trial production, the cost of correcting the product mold, the shortening of the delivery time, and the improvement of the product quality.

  Details of the present invention will be described below.

  According to Non-Patent Document 1, the Navier-Stokes equation is simplified as follows by approximation that omits the convection term.

  On the other hand, the heat conduction equation is derived from the energy conservation law and the Fourier heat conduction law, and the temperature is obtained. From this temperature, etc., the viscosity used in equation (4) is obtained, and the pressure is obtained.

  Furthermore, when the fibrous filler is contained, the time dependency of the speed in each element is obtained from the calculation result, and the fiber orientation state is calculated from the result. Mechanical anisotropy such as material anisotropy for each element, shrinkage anisotropy, and elastic modulus is required from the fiber orientation state.

  The above is the calculation method mainly in the flow process. In the flow process, the density change does not largely affect the calculation of the filling pattern or the like in most cases, but in the pressure holding process, the density change is mainly large. Therefore, the pressure equation expressed by the equation (4) is changed to the following equation (6) to calculate.

  Using this equation, the pressure change and density change are calculated until the end of cooling, and the shrinkage rate of each element is obtained.

  Next, linear structure calculation is performed to calculate the displacement, that is, the amount of deformation after contraction. Although the shrinkage after cooling is determined for each element, the elements are not balanced. Therefore, structural calculation is performed to obtain the shrinkage rate and deformation of the entire molded product from the individual shrinkage rates. Here, the basic concept of linear structure calculation will be explained. First, the stress / strain equation is composed of a stress-strain equation, a strain-displacement equation, and a force balance equation. The stress-strain formula is expressed by the following formulas (7) and (8).

Here, ε is strain, E is Young's modulus σ is stress, ν is Poisson's ratio γ is shear strain, τ is shear stress, G is shear rigidity, and lowercase letters x, y, and z are coordinate components. Further, y and z components such as εy and εz are also expressed in the same manner as the above formulas (7) and (8), but formulas for these are omitted. Next, the strain-displacement formula is expressed by the following formulas (9) to (11).

Here, u, v, and w indicate x, y, and z components of displacement, respectively. Furthermore, the equation of force balance can be expressed by equation (12), where X is the x component of the external force.

When the equations (7) to (12) are discretized and further integrated according to the principle of virtual work, the following stiffness equation (13) relating to elements is obtained.

Here, [K] is an elastic stiffness matrix, {d} is a nodal displacement, and {f} is a nodal force. Finally, the stiffness equation (13) for the elements is overlapped for all the elements to obtain the stiffness equation for the entire system. This is a set of simultaneous linear equations, and by calculating the inverse matrix of [K], the amount of contraction and deformation of the entire molded product can be determined by converting the nodal displacement. A detailed calculation method in the above structural analysis is well known in Non-Patent Document 2 and the like, and can be calculated using commercially available software, and thus detailed description thereof is omitted.

  The above is the case where a 2.5-dimensional thin shell structural element is used. The case where a three-dimensional element is used is shown below. Patent Document 1 discloses a method for obtaining a pressure and the like by using the flow conductance shown as S in equations (4) and (5) and calculating using the following equation (14).

  However, this is a simplified calculation, and more specifically, as shown in Non-Patent Document 1, it is calculated using a continuous equation, Navier-Stokes equation, and energy conservation equation. Other formulas can be calculated in the same way even if the dimension is expanded.

  When a numerical analysis is actually performed in the flow / holding process, it is necessary to discretize a continuous calculation area as in the above-described structural calculation and convert the governing differential equation into an algebraic equation. As a discretization method, methods such as a difference method, a variational method, a finite element method, and a control volume method are known, and these methods can be appropriately selected and used. Also, the influence of inertia, the influence of gravity, etc. omitted above can be taken into consideration.

  In the above method, the temperature calculation based on the heat conduction equation is coupled simultaneously with the calculation of the pressure and the progress of filling. In order to increase the calculation accuracy, it is necessary to consider the temperature dependence of the viscosity in the temperature calculation and the influence of the solidified region due to cooling. As the filling progresses and time elapses, the resin is cooled. Since the resin does not flow in the solidified region, it is necessary to calculate by specifying the molten region. The temperature is used as a reference for dividing the melting / solidifying region, and the name as the temperature divided into the solidifying region and the melting region is hereinafter referred to as a flow stop temperature. The flow stop temperature is generally also referred to as a no-flow temperature, a solidification temperature, a solidification temperature, a transition temperature, and a solid-liquid transition temperature.

  In the conventional technology, in order to consider the solidification region, when using a 2.5-dimensional element, or in the method described in Patent Document 1, calculation is performed by reducing the wall thickness by calculating the flow conductance with the solidification of the resin. . In these cases, the flow stop temperature is calculated by fixing the flow stop temperature without considering the pressure during flow. Actually, the flow stop temperature depends on the pressure, and since the solidified state in the cavity depends on the pressure, the amount of decrease in the wall thickness is underestimated, and as a result, the filling pattern, temperature, pressure, and the like are different from actual ones. In the present invention, since the flow stop temperature is determined in consideration of the pressure change during the flow, the prediction accuracy is higher than that in the prior art.

  On the other hand, in the method described in Patent Document 2, in order to consider the solidified layer as a non-flowing region, the viscosity of all contacts constituting the element is calculated for each element, and the element is calculated from the temperature result obtained by heat conduction analysis. It is divided into a solidified region and a melted region, the average viscosity of the melted region is obtained, and the pressure is calculated using the average viscosity. At that time, no consideration is given to the solidification temperature used when determining the solidified region and the molten region. It became clear that the analysis accuracy in the flow and pressure holding process is improved by considering that the flow stop temperature depends on the pressure.

  The flow stop temperature at the time of pressure application can be measured with a PVT (pressure-volume-temperature) measuring device or a viscometer described in ISO-11443.

  The flow stop temperature at pressure P determined by flow analysis is

Approximate as More precisely, it may be compared with the crystallization temperature data under various pressures, and the flow stop temperature can be expressed as a high-order function of the pressure P. Since it has accuracy, Equation (15) considering reduction of calculation load is useful in engineering. Specific calculation methods that take these effects into consideration, and measurement examples of b6 and Ts ₀ are shown in Examples.

  Embodiments according to the present invention will be described below with reference to the drawings.

  FIG. 1 is a flowchart showing the entire analysis processing procedure. First, shape definition and mesh division (element division) are performed (step S1). In the process of step S1, the shape is defined by a CAD system or the like. Use the CAD interface to capture the shape, or create the shape using a CAD system, and the shape of the molded product to be analyzed, and the resin flow path from the tip of the nozzle of the molding machine such as the runner and gate to the cavity Define. After that, an element division preprocessor performs element division such as a finite element method to create a model for analysis. If it is expected to depend heavily on the cooling conditions in the mold, the mold cooling pipe, mold outer wall, insert frame, etc. are defined in shape and divided into elements such as the finite element method. Add.

  After this, the physical property data (viscosity, specific volume, thermal conductivity, specific heat, etc.) of the resin and mold taking into account the temperature dependence for the analysis, molding conditions (injection speed, resin temperature, holding pressure value, holding pressure) Time), analysis conditions, boundary conditions for warp deformation analysis are defined, and input data for analysis is created (step S2).

  If it is expected that the cooling state is strongly dependent on the cooling state in the mold, a cooling analysis (step) is performed to calculate mainly the temperature distribution in the mold based on the input data created in step S2 as necessary. S3) is performed.

  Based on the input data created in step S2 or by adding the temperature distribution in the mold obtained in step S3 to the input data, the process in which the resin fills the mold and the subsequent holding pressure cooling process Flow analysis including the mold is performed (step S4), and analysis results such as pressure and temperature are obtained.

  The fiber orientation is calculated from the result obtained in step S4 (step S5). From this result, the elastic modulus, Poisson's ratio, and shrinkage are calculated and used as input conditions for the structure calculation (step S6). Then, linear structure calculation is performed to obtain the deformation amount (step S7). Thereby, a residual stress, a deformation amount after warping deformation, and a shape after deformation are obtained.

  FIG. 2 is a flowchart showing in detail the analysis processing procedure from step S2 to step S4. In step S2-1, the viscosity is measured with a capillary according to the method described in ISO-11443. Furthermore, the function approximation of the viscosity is performed from the viscosity data (step S2-2). For this function, the Cross-WLF formula, the Cross formula, etc. are generally used. Based on the set boundary conditions, the Navier-Stokes equation is simplified and discretized, and the filling stage is calculated. At the same time, heat transfer calculation is added to consider heat generation due to shearing and solidification during flow (step S4-1). As a condition for stopping the flow, the temperature of the equation (15) is used, the portion below that temperature is treated as a solid, and the cross-sectional area or the melting region is changed with respect to the thickness, that is, the filling direction (step S4- 2). It is repeatedly calculated until the filling analysis calculation end condition is satisfied (step S4-3). The condition for completing the filling analysis calculation is that all the resin flow fronts reach a temperature at which they do not flow, or that the entire cavity is filled with resin. After the calculation is completed, the filling pattern, temperature, pressure, and other results are recorded (step S4-4) and optionally output.

  Hereinafter, although concretely demonstrated based on an Example, these Examples do not restrict | limit this invention.

  The shape of the test piece used is an 80 mm square flat plate and a disk-shaped flat plate. The element division model shape used for the calculation is shown in FIGS.

In the analysis of the present embodiment, the structural analysis is performed subsequent to the flow analysis. Therefore, boundary conditions for structural analysis such as constraint conditions are added in advance when performing shape definition and mesh division.
Resin material: Unfilled polybutylene terephthalate resin and reinforced polybutylene terephthalate resin containing 30% by weight of glass fiber
80mm square flat plate mold and molding condition shape: cavity 80mm long, 80mm wide, 2mm thick
Gate size width 4mm, thickness 2mm (side gate)
Resin temperature: 260 ℃
Mold temperature: 60 ℃
Injection flow rate: 25cm ³ / s
Holding pressure: PBT 30MPa PBT / GF 60MPa
Holding pressure time: 15 seconds Cooling time: 10 seconds Disk-shaped flat plate Mold and molding condition shape: Cavity diameter 80mm, thickness 3-0.5mm
Gate size φ1.2mm (Center pin gate)
Resin temperature: 260 ℃
Mold temperature: 60 ℃
Injection flow rate: 1.54cm ³ / s
-PVT apparatus A PVT test system manufactured by Toyo Seiki Seisakusho Co., Ltd. is used to measure the inflection point temperature of the specific volume when the temperature is lowered under a constant pressure. After melting an unfilled polybutylene terephthalate resin at 260 ° C., the temperature dependence of the volume is measured under a cooling condition under a pressure of 2 levels or more. The results are shown in FIG. From the temperature dependence of the inflection point shown in FIG. 6, Ts ₀ and b6 are obtained by the method of least squares using the relationship of equation (15). As a result, Ts ₀ is 224 ° C. and b6 is 0.38 (° C./MPa). Since this method is easy to control the temperature, a highly accurate measurement result can be obtained.

-Melt viscosity measuring device The flow stop pressure at the time of pressure change at a constant temperature is measured using a capillograph 1C manufactured by Toyo Seiki Seisakusho Co., Ltd. according to the method described in ISO-11443. Unfilled polybutylene terephthalate resin is used, the cylinder temperature is set to 240 ° C., 250 ° C., 260 ° C., and the die dimensions are L = 20 mm and D = 1 mm. The measurement results are shown in FIG. At 240 ° C., when the shear rate is 2432 (1 / s) or more, the pressure continues to increase during the measurement, but the flow stop pressure at the shear rate 2432 (1 / s) is 41 MPa. Further, the inflection point is obtained based on the flow stop pressure obtained at a temperature of two or more levels, and the pressure dependence of the transition temperature is obtained by the least square method applied to the equation (15). As a result, Ts ₀ is 224 ° C. and b6 is 0.38 (° C./MPa). This method has an advantage that the measurement time can be shortened as compared with the case where the PVT apparatus is used. Further, since the generated gas component during measurement can be eliminated, it is suitable for a material that generates gas due to thermal degradation or the like.

-Shrinkage The shrinkage was measured at 23 ° C. and 50% RH for 24 hours after molding, and the flow direction and the direction perpendicular to the flow were measured with a three-dimensional dimension measuring machine. From the mold dimensions at room temperature and the actual dimensions, the mold shrinkage rate (%) is calculated as (mold dimension-product dimension) / mold dimension x 100.

Example 1
Using the equation (15), analysis is performed with b6 = 0.38 (° C./MPa). The gate seal time based on the analysis is a time during which the maximum temperature in the gate element is equal to or lower than the temperature of equation (15). This gate seal time determination method is the same in the following comparative examples and examples. The contraction rate is obtained from the displacement of the node at the same position as the actual measurement.

Comparative Example 1
Under the same conditions as in Example 1, B6 = 0 in the equation (15).

Example 2
Similar to Example 1, the case where 30% glass fiber filled polybutylene terephthalate resin is used is shown. b6 = 0.38 (℃ / MPa).

Comparative Example 2
Under the same conditions as in Example 2, b6 = 0 is set in equation (15).

  The results are shown in Table 1.

Example 3
Using equation (15), b6 = 0.38 (° C./MPa). The determination of short shot in the analysis is made when the nozzle pressure reaches the maximum injection pressure of the molding machine before full filling. FIG. 8 shows an actual filling area, and FIG. 9 shows a filling area in the third embodiment.

Comparative Example 3
This is a case where b6 = 0 in the equation (15) under the same conditions as in the third embodiment. FIG. 10 shows the filling region in Comparative Example 3.

Example 4
A case where the resin is a polybutylene terephthalate resin filled with 30% glass fiber is shown in the case of Example 1. b6 = 0.38 (° C./MPa). FIG. 11 shows an actual filling region, and FIG. 12 shows a filling region in Example 4.

Comparative Example 4
This is a case where b6 = 0 in the equation (15) under the same conditions as in the second embodiment. FIG. 13 shows the filling region in Comparative Example 4.

  The results are shown in Table 2.

It is a flowchart which shows the whole analysis processing procedure. It is a flowchart which shows in detail the analysis processing procedure from step S2 to step S4. It is the element division | segmentation model shape (flat plate) used for calculation. It is an element division model shape (disk) used for calculation. It is a graph which shows the temperature dependence of the volume of unfilled polybutylene terephthalate resin. It is a graph which shows the temperature dependence of the inflection point of unfilled polybutylene terephthalate resin. It is a graph which shows the shear rate dependence of the viscosity of unfilled polybutylene terephthalate resin. It is a figure which shows the actual filling area | region of a disk shaped flat plate (unfilled polybutylene terephthalate resin). It is a figure which shows the filling area | region in Example 3 of a disk shaped flat plate (unfilled polybutylene terephthalate resin). It is a figure which shows the filling area | region in the comparative example 3 of a disk shaped flat plate (unfilled polybutylene terephthalate resin). It is a figure which shows the actual filling area | region of a disk shaped flat plate (glass fiber containing polybutylene terephthalate resin). It is a figure which shows the filling area | region in Example 4 of a disk shaped flat plate (glass fiber containing polybutylene terephthalate resin). It is a figure which shows the filling area | region in the comparative example 4 of a disk shaped flat plate (glass fiber containing polybutylene terephthalate resin).

Claims (5)

In the flow analysis in the injection molding process of a resin material, the temperature at which the resin material stops flowing is set as a crystallization temperature Ts during pressurization obtained by the following formula: an injection molding process analysis method.

Ts ₀ : Crystallization temperature of resin material at normal pressure (° C)
P: Pressure applied to resin material by flow analysis (MPa)
b6: Pressure dependence coefficient of crystallization temperature (MPa / ° C) The injection molding process according to claim 1, wherein the pressure dependency coefficient b6 of the crystallization temperature is obtained by measuring an inflection point temperature of a specific volume when the temperature is lowered under a constant pressure at a pressure of two or more levels. analysis method. The injection molding process analysis method according to claim 1, wherein the pressure dependency coefficient b6 of the crystallization temperature is obtained by measuring a flow stop pressure at a temperature of two or more levels when the pressure changes at a constant temperature. A method for analyzing a filling pattern of a resin material into a cavity when the resin material is injection-molded, wherein the injection molding process analysis method according to any one of claims 1 to 3 is used. A dimension and deformation analysis method for a molded product obtained by injection molding of a resin material, wherein the injection molding process analysis method according to any one of claims 1 to 3 is used.

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