JPH0785128A - Injection molding resin molded product design method - Google Patents

Abstract

(57) [Abstract] [Purpose] To facilitate the optimization of molding conditions such as the protruding pin position or the number of pins so as not to cause deformation when releasing a resin molded product in injection molding. [Structure] The shape of a resin molded product is divided into a plurality of minute elements, and the contraction strain at the time of releasing the resin molded product from the mold is obtained for each of these minute elements. The reaction force R generated on the surface of the mold against the contraction of the resin is calculated from the constraint conditions of the mold, and the frictional force F of the mold surface is calculated from the reaction force R. A method for designing an injection-molded resin molded product, in which the position or the number of ejection pins at the time of release is set based on the distribution and size of the molded product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for designing a resin molded product by injection molding, and more particularly to a method for designing a resin molded product for optimizing a protrusion condition at the time of releasing after injection molding.

[0002]

2. Description of the Related Art In the injection molding of a resin product, a resin material is melt-injected into a mold, held and cooled to be solidified, and then, after the mold is opened, the resin molded product is extruded by an ejector pin to be separated from the mold. I am trying. Shrinkage occurs in the resin molded product during the process of cooling and solidification in the mold, and since the normal resin molded product has a complicated three-dimensional shape such as a rib structure and a box structure, shrinkage occurs in the mold. At this time, the resin-molded product is constrained by the mold to generate a frictional force with the surface of the mold.

Therefore, when the resin molded product is released from the mold, it is necessary to apply an external force that opposes this frictional force by the ejection pin. However, when the rigidity of the resin molded product is insufficient with respect to the external force generated by the protrusion pin, the molded product is deformed, resulting in defective molding. Therefore, optimizing the protruding pin position and the like in injection molding has become an important issue in the design of resin molded products.

Heretofore, such setting of the ejecting pin position and the like has been carried out by a technique in which an experienced die designer finds an appropriate ejecting condition while repeatedly correcting a trial die according to an empirical rule from a product drawing. It was As a result, the number of mold trials is increased and the product development period is extended, resulting in a very high development cost. On the other hand, as a method of predicting molding defects that occur in the injection molding process of resin products using computer simulation methods and optimizing product design, mold design, molding conditions, etc. The finite element method, boundary element method, difference method, FAN method,
There is a proposal to analyze the injection molding process from injection filling to pressure holding, cooling, shrinkage, and room temperature equilibrium by numerical analysis techniques such as the control volume method.

However, the conventional computer simulation method is generally a simple method of determining the temperature distribution of each part of the molded product during the cooling process of the resin and determining the conditions such as the protruding position from the temperature distribution. Molding defects such as warp deformation of the product can be predicted, but since the external force applied to the molded product by the ejection pin at the time of mold release is not taken into consideration, there is a defect that the obtained ejection pin position and ejection force are not accurate.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to easily attain appropriate molding conditions such as a protruding pin position or the number of pins so as not to cause deformation at the time of releasing a resin molded product in injection molding. To provide a designing method.

[0007]

According to the present invention for achieving the above object, the shape of a resin molded product is divided into a plurality of minute elements, and each of these minute elements is released from the mold. The shrinkage strain at the time point is obtained, and the reaction force R generated on the surface of the die against the shrinkage of the resin is obtained from the shrinkage strain of each minute element and the constraint condition by the die, and the die is obtained from the reaction force R. The surface frictional force F is obtained, and the position or the number of the ejection pins at the time of release is set from the distribution and size of the frictional force F with respect to the resin molded product.

Further, in the present invention, at least one of the restraint condition corresponding to the frictional force F, the load corresponding to the frictional force F, the rigidity corresponding to the frictional force F, and the ejection load of the ejection pin is used to determine the resin molded product. Deformation, stress and strain that occur in the resin molded product when the
It is also possible to set the shape such as the wall thickness of the resin molded product or the molding conditions such as the protrusion time based on the stress and strain.

Further, in the present invention, the deformation, stress, and strain generated in the resin molded product at the time of protrusion of the resin molded product are obtained, and further the contraction and deformation state up to the room temperature equilibrium state are obtained, and these deformation and stress are obtained. It is also possible to set the shape such as the wall thickness of the resin molded product based on the strain, shrinkage and deformation state. In the practice of the present invention, the shrinkage distortion of the resin molded product, the reaction force R generated on the mold surface, the deformation, stress and strain generated in the resin molded product when the resin molded product is ejected, and the room temperature equilibrium of this resin molded product The finite element method,
Boundary element method, difference method, FAN method, control volume method, and other numerical analysis methods can be easily used by making full use of a computer.

More specifically, it is preferable to adopt the steps described below. First, the shape of the resin molded product to be injection molded is divided into a plurality of minute elements, and the shrinkage strain at the time of mold release after injection molding of the resin molded product is calculated for each of these minute elements by the numerical analysis method described above. Seek by
(Step 1). In this step 1, if the molding conditions are input to the computer together with the physical properties of the resin, the filling, holding, cooling, and shrinkage analysis of injection molding are sequentially executed for each minute element by the numerical analysis method described above, and inside the mold. The shrinkage strain after solidification of the minute element portion is obtained.

Next, the shrinkage strain for each minute element thus obtained and the constraint condition by the mold are input to the computer (step 2). Then, the reaction force R generated on the surface of the mold against the contraction of the resin is obtained by the above-mentioned numerical analysis method based on the shrinkage strain and the constraint condition by the mold (step 3). And, from this reaction force R, the friction force F
Then, by calculating the sum of the frictional forces F acting in the protruding direction, the total protruding force can be made equal (step 4).

From the evaluation of the distribution and size of the frictional force F thus obtained for each minute element with respect to the entire resin molded product, the protruding position or the number of the protruding pins is set from the portion where the frictional force F is large. be able to. In the present invention, either the constraint condition corresponding to the frictional force F, the load corresponding to the frictional force F, or the rigidity corresponding to the frictional force F is input to the computer (step 5), and the protrusion load is also input to the computer. After inputting (step 6) and obtaining the deformation, stress, and strain generated in the resin molded product at the time of protrusion by the above-mentioned numerical analysis method from these data (step 7), based on these deformation, stress, and strain, As the shape of the resin molded product, it is possible to appropriately set the wall thickness of the portion that is greatly deformed by the protrusion and reinforce the ribs, and thereby to reduce the cycle time by shortening the protrusion time.

Deformation, stress, and strain generated in the resin molded product at the time of the above-mentioned protrusion are inputted into the computer with the constraint conditions acting on the contact portion between the resin and the mold at the time of mold release, and the sum of the frictional force F at the protrusion position. It can be easily obtained by inputting the forced displacement loads enough to generate reaction forces equal to to the computer and numerically analyzing these. These are subjected to, for example, graphic processing to be displayed in modified views, contour lines, and graphs.

Further, in the present invention, the above-mentioned numerical analysis method is applied to the shrinkage and deformation state of the entire resin molded product up to the room temperature equilibrium state, with the deformation, stress, and strain states occurring in the resin molded product at the time of the above-mentioned protrusion as initial conditions. If it is determined by (step 8), the design of the shape of the resin molded product can be made more appropriate by evaluating these deformation, stress, strain state and contraction, deformation state.

In the present invention, the reaction force R
When the frictional force F is calculated from, the frictional force F can be generally expressed as F = H (R) as a function of the reaction force R. For example, in the simplest case, the friction coefficient K to F
= K × R. The distribution of the frictional force F may be graphically processed to display contour lines or graphs.

Further, in step 5, for example, a constraint condition is set in a portion where the frictional force F acts in the protruding direction, and in step 7, a releasing force exceeding the frictional force F is generated when the analysis at the time of protruding is performed. It is conceivable to remove the constraint condition and continue the analysis. These may be graphically processed to display contour lines or graphs. Also,
As the ejection load input in step 6, for example, a method in which a forced displacement amount is given to the ejection pin position and analysis is performed until all the constraint conditions are satisfied by the above-described method, or the constraint conditions obtained in step 5 are not changed, A method is considered in which the amount of forced displacement is given to the position of the protruding pin, the analysis in step 7 is performed, and the amount of forced displacement is increased until the total sum of the protruding forces generated on the protruding pin becomes equal to the total frictional force F acting in the protruding direction. To be

It is possible to optimize the ejection pin arrangement, ejection force, ejection time, etc. from the numerical values obtained by the above arithmetic processing and the outputs obtained by performing graphic processing on the numerical values.

[0018]

EXAMPLES Hereinafter, a method for designing a resin molded article of the present invention will be described with reference to the examples shown in the drawings. FIG. 1 is a flowchart showing the procedure according to the present invention, and steps 1 to 8 of this flowchart are as described above. Here, the ejection condition when the box-shaped resin molded product shown in FIG. 2 is injection-molded will be described.

First, as shown in FIG. 2, a resin molded product 10
The entire shape of is divided into a plurality of minute elements 20. Then, input molding conditions such as injection pressure, injection temperature, mold temperature, etc. of the injection molding into the computer, and physical properties such as viscosity and thermal conductivity of the resin material, and fill analysis, holding pressure analysis, cooling analysis of the injection molding. By performing the shrinkage rate analysis, the thermal shrinkage strain generated in each minute element 20 inside the mold is calculated.
(Step 1).

FIG. 3 is a conceptual diagram in which the contracted state of the resin molded product in the case where there is no restraint by the die is shown by a solid line S, and when restrained by the die is shown by a broken line S '. Since the resin molded product 10 actually has a binding force by a mold and is formed as shown by a broken line S ′, the resin molded product 10 is
Generates a reaction force R due to a so-called hugging force that comes into close contact with the surface of the mold. Therefore, in step 2, step 1
The reaction force generated on the mold surface by performing the heat shrinkage structural analysis in step 3 by inputting the constraint condition in the direction of the normal to the mold surface with the heat shrinkage strain obtained in step 3 as the initial strain load. Find R.

Next, in step 4, assuming that the friction coefficient K for the reaction force R is 0.3, for example, the friction force F between the mold surface and the resin can be obtained as F = 0.3R. it can. By calculating this frictional force F for each minute element 20, the distribution of the entire resin molded product can be obtained. For example, if the direction of the arrow X in FIG. 4 is the protruding direction, the reaction force R is generated in the direction perpendicular to the direction X of the arrow A.
The portion (hatched portion) is the portion that generates the frictional force F that opposes the protrusion. The effective position of the ejector pin can be examined by the frictional force F generated in the A portion. Here, for example, point B in the figure is set as the position of the protruding pin. Further, for example, the total sum of the frictional forces F acting on the part A is calculated,
This can be the total ejection force or the release force.

Next, in order to simulate the protrusion at the time of mold opening, a constraint condition for the portion A, for example, is input in step 5, and in step 6, the forced displacement ΔZ is set at the point B of the protrusion pin, for example ΔZ = Enter as 1.
Subsequently, in step 7, a structural analysis is performed from the constraint condition and the forced displacement, and the total sum of reaction forces generated at the position of the protruding pin is obtained. ΔZ is adjusted so that the total of the reaction forces becomes equal to the total of the frictional forces described above, and the structural analysis is performed again to obtain the stress, strain, and deformation amount generated when the resin molded product is ejected.

FIG. 5 is an enlarged conceptual view showing the deformed state of the resin molded product. From this, the protruding deformation can be evaluated, and the cooling time or the like for obtaining the rigidity required to suppress the deformation can be evaluated. Initialize the obtained deformation, stress, and strain states as described above, and then enter the amount of heat shrinkage after release in step 8 to perform shrinkage analysis and determine the shape of the molded product in the room temperature changed state. Ask. From this, it is possible to predict shrinkage and warpage deformation in consideration of protrusion deformation, and it becomes possible to study the design to optimize the rib reinforcement and wall thickness of the product.

Although the case of the box-shaped resin molded product has been described above, the present invention is not limited to this embodiment, and other three-dimensional three-dimensionally shaped resin molded products can be used. Applicable.

[0025]

As described above, according to the present invention, it is possible to predict the frictional force between the resin surface and the mold surface that occurs when the resin molded product is ejected at the time of releasing the mold. Can be optimized, and further, the shape of the resin molded product such as ribs and wall thickness can be optimized. Moreover, since it can be performed more easily than the conventional method in which the trial die is repeatedly modified according to the rule of thumb, the development cost can be reduced by shortening the product development period and reducing the number of die trials. .

[Brief description of drawings]

1 is a flow chart showing the procedure for carrying out the method of the present invention.

FIG. 2 is a conceptual diagram showing a state in which the box-shaped resin molded product is divided into minute elements when the present invention is applied to the box-shaped resin molded product.

FIG. 3 is a conceptual diagram showing a comparison between the box-shaped resin molded product shown in FIG. 2 assuming that there is no mold and the case where there is a mold.

FIG. 4 is a conceptual diagram showing a portion of the box-shaped resin molded product shown in FIG. 2 where a frictional force is generated with respect to mold release.

FIG. 5 is a conceptual diagram exaggeratedly showing a state in which the box-shaped resin molded product shown in FIG. 2 is deformed by a protrusion pin at the time of release.

[Explanation of symbols]

10 Box-shaped resin molded product 20 Minute element S Shape of box-shaped resin molded product assuming that there is no mold S'Shape of box-shaped resin molded product constrained by mold X Protrusion direction A Action of frictional force Part B protruding pin position

Claims (3)

[Claims] 1. The shape of a resin molded product is divided into a plurality of minute elements, and the shrinkage strain at the time of releasing the resin molded product from the mold is determined for each of these minute elements, and the shrinkage for each minute element is calculated. From the strain and the restraint conditions by the mold, the reaction force R generated on the mold surface against the contraction of the resin is determined, and the frictional force F of the mold surface is determined from the reaction force R. A method for designing an injection-molded resin-molded product, wherein the position or the number of ejection pins at the time of release is set based on the distribution and size of the resin-molded product. 2. At least one of a restraint condition corresponding to the frictional force F, a load corresponding to the frictional force F, and a rigidity corresponding to the frictional force F, and a protrusion load of the protrusion pin when the resin molded product is ejected. The deformation, stress, and strain generated in the resin molded product are obtained, and the molding conditions such as the shape such as the wall thickness of the resin molded product or the protrusion time are set based on these deformation, stress, and strain. Injection molding resin molded product design method. 3. The deformation, stress and strain generated in the resin molded product when the resin molded product is ejected are obtained, and further the contraction and the deformation state until reaching the room temperature equilibrium state are obtained, and these deformation, stress and strain are calculated. The method for designing an injection-molded resin-molded product according to claim 2, wherein the shape such as the wall thickness of the resin-molded product is set based on the contracted or deformed state.