JPH10128818A - Weldline length-estimating method for molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for estimating easily and surely the difference in weldline length of a molded product generated by used resin materials or molding conditions. SOLUTION: In the weldline length estimating method, the flow association angle or the flow confluence angle of molten resin is computed, and the computed flow association angle or the flow confluence angle is compared with a reference value, from which a weldline generation estimating section is selected, and the part having the 'exponent' bing more than set values measured preliminarily for each of resins is defined as weldline. Further the above-referred 'exponent' is converted into the correction disappearance reference angle by using the function found preliminarily, and the correction disappearance reference angle is compared with the flow association angle or flow confluence angle to determine the positions of weldlines.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for predicting the length of a weld line in a molded product by flow analysis.

[0002]

2. Description of the Related Art Plastic molded products obtained by injection molding of resins and the like are widely used for home electric appliances, OA equipment and the like, but these products often require high appearance. One of the things that impairs the appearance is the weld line, and the position of occurrence is a problem in relation to the design surface.

When the resin flows from two different directions, the weld line is formed at the junction, but the entire area of the junction does not necessarily become the weld line. If the downstream side is sufficiently downstream with respect to the resin flow direction, there is a case where the weld does not become a problem in appearance even at the junction.
Whether or not a weld line is generated at the junction is determined by the angle between the flow fronts when the resins merge, that is, the flow association angle. It has been experimentally confirmed by Yokoi of the Institute of Industrial Science, the University of Tokyo that the flow association angle when the resin actually flows in the mold cavity is related to the presence or absence of weld lines. It is described in the Proceedings of the Japan Society of Molding and Processing. Since the flow association angle increases toward the downstream,
This value is an index of the length of the weld line.

On the other hand, as a method of estimating the length of a weld line, a conventional method of injection molding C using a computer has been known.
There is a flow analysis of AE. This is a method in which, for example, a flow association angle based on a flow vector calculated at each element or each node is used and is used as a judgment criterion for a weld line length or strength prediction.
No. 6,086,045.

However, in flow analysis software, a part of a calculation term indicating a flow pattern of a resin is usually used in a simplified form. Therefore, a flow vector calculated by flow analysis, that is, a flow pattern, is The flow pattern is slightly different from the flow pattern when the resin actually flows in the mold cavity, and this tendency is particularly strong near the resin merging portion. Therefore, a method based on only the calculated flow vector, for example, based on the flow association angle as a criterion, has sometimes been insufficient for predicting the weld line.
For example, even when the length of a weld line is clearly different in an actual molded product due to a difference in resin material or molding conditions, the difference does not clearly appear on a flow analysis.

If the flow pattern of the actual resin is to be reproduced more accurately in the analysis without simplifying the calculation formula, the flow analysis software itself must be recreated from the ground up, and the flow analysis software must be redesigned from the viewpoint of time and cost. Is not preferred. Also, the program itself becomes enormous, and is not practical in terms of calculation speed and calculation stability.

[0007]

SUMMARY OF THE INVENTION In view of such circumstances, an object of the present invention is to provide a method for easily and reliably estimating a difference in weld line length of a molded product due to a resin material or molding conditions. I do.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the value of the "power index" that changes depending on the resin, the shear rate and the temperature, and the conditions under which the weld line disappears. It has been experimentally found that there is a correlation between the above, and by using this, it is possible to accurately predict the length of a weld line, thereby completing the present invention.

That is, the present invention provides a flow analysis step of performing a flow analysis of a molten resin with respect to the shape of a molded article and calculating a flow association angle or a flow confluence angle of the molten resin, and wherein the calculated flow association angle is smaller than a set value. Or a step of selecting an expected weld line occurrence portion for selecting a region of the molded article in which the calculated flow merging angle is larger than a set value, and calculating a “power index” for the shear rate of the shear viscosity in the selected region. A process for calculating an "exponent index" and a process for determining a weld line in which the calculated "exponent index" is equal to or higher than a reference value previously measured for each resin as a weld line. It relates to a line length prediction method.

Further, according to the present invention, through the above-mentioned flow analysis step, weld line occurrence predicting part selecting step and "power index" calculating step, the calculated power exponent is corrected and eliminated using a function which has been obtained in advance. The corrected vanishing reference angle replacing step to be replaced with the reference angle, and the weld line of the weld line is compared by comparing the flow association angle or the flow merging angle calculated in the flow analyzing step with the corrected vanishing reference angle calculated in the correcting vanishing reference angle replacing step. The present invention relates to a method for estimating a weld line length of a molded article, comprising a weld line determining step of determining a position.

Hereinafter, the present invention will be described in detail. Generally, in the flow analysis process, initial data such as molded product shape data, resin injection point, injection resin temperature, mold temperature, injection flow rate, injection time, resin melt viscosity, etc. are input in advance, and the resin flow state is calculated using a computer. I do. As a method of discretization in analysis, FEM (finite element method), FDM (difference method), B
A known method such as EM (Boundary Element Method) can be used, but FEM (Finite Element Method) is most preferable because of its wide range of application. As a means for dividing the shape of the molded product into each element, a generally available mesh generator can be used. This flow analysis step can be performed using a known simulation program.

FIG. 1 is a conceptual diagram of the flow merging angle in the present invention.
FIG. 2 shows a conceptual diagram of the flow association angle. The flow merging angle is
When the resins flow from two different directions and merge as shown by α in FIG. 1, the angle is formed by the two flow directions. The flow association angle is the angle formed by the flow fronts when the resins flow from two different directions and merge as shown by θ in FIG. 2, and generally is the complement of the flow merge angle.

In the present invention, the flow analysis of the molten resin is performed on the shape of the molded product, and the flow association angle or the flow merging angle of the molten resin is calculated. Next, a region of the molded article in which the calculated flow association angle is smaller than an arbitrarily set value or in which the calculated flow merge angle is larger than the set value is selected, and this is set as a weld line occurrence predicting unit.

The "power index" in the present invention will be described. Assuming that the shear rate is γ, the logarithmic value of the shear rate is γL, the shear viscosity is η, the logarithmic value of the shear viscosity is ηL, the temperature is T, and the “power index” is n, n is defined as the slope of ηL with respect to γL. You. That is, η = C × γ ⁿ and the logarithmic value of C is CL, CL is the ηL intercept in γL. However, in this case, n is usually a negative number because it takes a value between -1 and 0. Therefore, in the present invention, n
, That is, N where N = n + 1 can be used as a "power exponent". In this case, N is usually a positive number between 0 and 1, making it easier to handle. Since N and n are defined as described above, the form of a function of η, γ, T for each resin, ie, N (or n + 1)
= F (η, γ, T). In the following description, N will be used for explanation.

The inventors of the present invention have conducted intensive studies, and have found that the value of the “power index” that changes depending on the resin, the shear rate and the temperature,
It has been experimentally found that there is a correlation between the position where the weld line disappears, that is, the weld line length. From this, the “exponent index” when the weld line disappears for each resin, that is, the “exponent index” of the weld disappearance
Can be set. FIG. 3 shows an example of the relationship between the weld line length and the weld disappearance “power index”. On the other hand, the “exponent index” at each element or each node of the weld occurrence prediction unit obtained in the “exponent index” calculation step is:
It has been confirmed by the verification analysis performed by the present inventors that when the joined resins flow in parallel in the downstream direction, they tend to become smaller toward the downstream. Therefore, by comparing each calculated “exponent index” with the weld disappearance “exponent index”, a portion larger than the weld disappearance “exponent index” can be defined as a weld line position. As described above, the "power index" is a value that changes depending on the type of resin, shear rate, temperature, etc. By introducing the "power index", it is possible to evaluate the weld line length due to differences in resin type and molding conditions. Become.

The corrected vanishing reference angle in the present invention will be described. The corrected vanishing reference angle has a meaning of “an angle obtained by correcting a calculated flow association angle (or flow confluence angle) using a“ power index ””. Therefore, the introduction of the corrected vanishing reference angle makes it possible to more accurately predict the weld line length due to the difference in resin type and molding conditions. The present inventors have confirmed by a verification experiment that there is a correlation between the corrected disappearance reference angle and the “power index”, and found that the function can be formed by the following method. Therefore, using this function, the “exponent index” distribution calculated in the previous process can be converted to the corrected vanishing reference angle distribution.

A method of converting the corrected vanishing reference angle into a function will be described. The procedure is shown below. Injection molding is actually performed to obtain a molded product with a weld line. Simulation is performed by flow analysis under the same cavity shape, resin type, and molding conditions as when actually injection-molded, to obtain a flow association angle (or flow confluence angle) distribution and a "power index" distribution. The flow association angle (or flow confluence angle) and "power exponent" in the analysis at the same point as the weld line vanishing point of the actual molded article are extracted. These values will be referred to as a corrected vanishing reference angle and a vanishing “power index”, respectively. The same as above is performed for various product shapes, resin types and molding conditions, and the corrected disappearance reference angle disappears.
Function. Corrected vanishing reference angle and vanishing "power index" extracted in the above procedure
Is shown in FIG. It can be seen that there is a correlation between the corrected vanishing reference angle and the vanishing “exponent exponent”, which can be functioned.

The “exponent index” distribution in the weld line occurrence predicting section obtained in the “exponent index” calculation step can be replaced with a corrected vanishing reference angle distribution using this function. By comparing the replaced corrected disappearance reference angle distribution with the flow association angle distribution or the flow confluence angle distribution calculated in the flow analysis step, the flow association angle is smaller than the corrected disappearance reference angle, or the flow confluence angle is A portion larger than the corrected vanishing reference angle can be defined as a weld line.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described more specifically below with reference to the flowcharts of FIGS. 5, 6, and 7 showing an embodiment of the present invention, and FIG. 8 showing a comparative example. In the following example, the shape (long side 220 mm × short side 120 mm) shown in FIG.
X 30 mm x 30 mm on a 2.5 mm thick square plate at a position 30 mm behind the flow direction of the molten resin from the film gate
In this case, the prediction method of the present invention is applied to an injection-molded product (having an opening of 0.2 mm), and a weld line is generated behind the opening in the flow direction of the molten resin.

Further, in order to show the validity of the prediction method of the present invention, a molded article was obtained by actually performing injection molding under the same conditions as in the example, and the weld line length was measured and compared with the predicted value. The molding machine used for the injection molding and the method for measuring the weld line length of the obtained molded product are as follows. 1) Injection molding machine All-rounder 320-210-75 manufactured by Ahburg
0 was used. 2) Weld line length measurement method The weld line depth of the obtained molded product was measured using a contact type surface roughness meter (Surfcom 570A manufactured by Tokyo Seimitsu Co., Ltd., stylus 1 μm).
The measurement was performed by scanning the needle in the direction perpendicular to the weld line in R). This weld line depth measurement is shown in FIG.
0.5m backward from the opening shown in the resin flow direction
The process was repeated at m intervals until the depth became 1 μm or less. The distance from the opening when the depth became 1 μm or less was defined as the weld line length of the molded article.

Example 1 The resin used was H of Denkastyrol manufactured by Denki Kagaku Kogyo KK
RM-2, molding conditions: resin temperature 210 ° C., injection rate 4
Assuming that the temperature was 2 cm ³ / sec and the mold temperature was 40 ° C., the predicted value and the actually measured value were obtained.

First, the flow analysis step will be described with reference to the flowchart shown in FIG. In the flow analysis process, molded product shape data using a known simulation program,
Initial data such as a resin injection point, injection resin temperature, mold temperature, injection flow rate, injection time, and melt viscosity of the resin are input in advance, and flow analysis is performed using a computer. In this flow analysis step, the temperature T, shear rate γ, viscosity η, flow vector, and the like at each element or each node are calculated, and the flow association angle θ or the flow merge angle α is calculated from the flow vector.

Next, a description will be given of a step of selecting a predicted portion of a weld line occurrence. In this step, the flow association angle θ calculated in the flow analysis step is smaller than a set value θs,
Alternatively, an element or a node where the calculated flow merging angle α is larger than the set value αs is selected. θs and αs can be arbitrarily set within a range where the selected element or node does not become too small or too large. In this embodiment, θs is 16
When the angle was set to 5 degrees, the nodes in the circles and circles shown in FIG. 9 were selected. As described above, the element or the node of the junction is roughly selected in this step, but this is not necessarily the weld line. That is, the portion ● is a weld line finally determined by the present invention as described later, and the portion consisting of both the portion and the portion ○ is selected as a weld line occurrence predicting portion.
If this step is omitted, a part clearly different from the junction may be determined as a weld line.
Also, by narrowing down the calculation range in this process,
The calculation cost in the subsequent steps can be reduced.

Next, the "power index" calculation step will be described. In this step, a "power index" N at each element or each node selected in the weld line occurrence predicting part selecting step is calculated. This N is obtained by calculating η, γ, T at each element or each node obtained in the flow analysis step by N =
By applying the function to f (η, γ, T), it is possible to calculate at each element or each node selected in the weld line occurrence predicting part selecting step. The function of N = f (η, γ, T) used at this time is obtained by measuring the shear viscosity of the resin to be used when the shear rate and the temperature are changed using a commercially available known capillary rheometer or the like. The data is obtained in advance by mathematical processing and stored in a database.

In this example, the resin used was Denkastyrol HRM-2 manufactured by Denki Kagaku Kogyo Co., Ltd.
OSAND twin capillary rheometer RH7
And shear rates of 1500, 750, 375, 18 at 190 ° C., 210 ° C. and 230 ° C.
The shear viscosities at 0, 90, 30, 15, and 6 / sec were measured. The logarithmic value γL of the shear rate, the logarithmic value ηL of the shear viscosity, and the temperature T at each measurement point were mathematically approximated to a cubic quadratic function.

[0026]

(Equation 1)

This was partially differentiated with respect to γL, and 1 was added to obtain a function represented by the following equation (2).

[0028]

(Equation 2)

When n is used as the "power exponent", a function represented by the following equation 3 is used.

[0030]

(Equation 3)

The function of Equation 2 above was used in the "power index" calculation step. As a result, the "exponent index" as shown in FIG.
An N distribution was obtained.

Next, the weld line determination step will be described. In this step, a part where the “exponent index” obtained by the “exponent index” calculation step at each element or each node of the weld line occurrence prediction unit is equal to or more than a certain reference value is defined as a weld line. The reference value, the weld disappearance “power index” NL, which has been obtained in advance by the present inventors through a verification experiment, has a correlation between the condition under which the weld line disappears, specifically, the weld length. There is. Therefore, by comparing each calculated “power index” with the weld disappearance “power index”, a portion larger than the weld disappearance “power index” can be defined as a weld line. As a result of applying the weld loss “exponent index” NL = 0.20 in the resin HRM-2 used in the present example to the present example, the nodes indicated by ● in FIG. 10 were selected. Therefore, this portion can be predicted as a weld line. ● The length when the portions are connected by a straight line is defined as the predicted length, and the values are shown in Table 1. Table 1 also shows the actual weld line length of the injection molded product as an actually measured value. It can be seen that the predicted value is good.

[0033]

[Table 1]

As shown in Table 1, when the resin used in the above was QF of Denka ABS manufactured by Denki Kagaku Kogyo KK, the resin used was HRM-2, and the injection rate under the molding conditions was 63 cm ³ / sec. For the case, the predicted value and the measured value of the weld line length were obtained in the same manner as described above. Table 1 shows the results. It can be seen that the predicted value is good even if the resin or molding conditions are changed.

Example 2 The resin used was H of Denkastyrol manufactured by Denki Kagaku Kogyo KK
RM-2, molding conditions: resin temperature 210 ° C., injection rate 4
Assuming that the temperature was 2 cm ³ / sec and the mold temperature was 40 ° C., the predicted value and the measured value were obtained.

Use the flowchart shown in FIG. The flow analysis step, the weld line occurrence prediction part selection step, and the “power index” calculation step were performed in the same manner as in Example 1.

The correction vanishing reference angle replacing step will be described. In this step, the “exponent index” distribution in the weld line occurrence prediction section obtained in the “exponent index” calculation step is replaced with the corrected disappearance reference angle distribution. For this replacement, a function obtained in advance by a verification experiment is used.

Next, the weld line determination step will be described. In this step, the corrected disappearance reference angle distribution in the weld line occurrence prediction section obtained in the corrected disappearance reference angle replacement step is compared with the flow association angle distribution or the flow merging angle distribution obtained in the flow analysis step. Thus, the weld line length is determined. A position where the flow association angle is smaller than the corrected disappearance reference angle or a position where the flow merge angle is larger than the corrected disappearance reference angle is defined as a weld line position. FIG. 12 also shows the corrected vanishing reference angle distribution and the flow association angle distribution in this embodiment. In this case, the weld line position can be predicted up to a point where the flow association angle is smaller than the corrected disappearance reference angle. The distance from the opening to the point where the flow association angle is smaller than the corrected disappearance reference angle is defined as the predicted length, and the value is shown in Table 1. Table 1 also shows the actual weld line length of the injection molded product as an actually measured value. It can be seen that the predicted value is good.

As shown in Table 1, the resins used were HRM-3 and HRM- of Denkastyrol manufactured by Denki Kagaku Kogyo KK
5. For the case of using HI-SQ, QF of Denka ABS, and the case of using HRM-2 of Denkastyrol and setting the injection rate under the molding conditions to 63 cm ³ / sec, the predicted values of the weld line length and The measured values were determined. Table 1 shows the results. It can be seen that the predicted value is good even if the resin or molding conditions are changed.

Example 3 The resin used was H of Denkastyrol manufactured by Denki Kagaku Kogyo KK
RM-2, molding conditions: resin temperature 210 ° C., injection rate 4
Assuming that the temperature was 2 cm ³ / sec and the mold temperature was 40 ° C., the predicted value and the actually measured value were obtained.

Use the flowchart shown in FIG. The flow analysis step was performed in the same manner as in Example 2 except that the flow merging angle α was calculated instead of calculating the flow association angle θ from the flow vector in Example 2. In the present embodiment, in the weld line occurrence predicting part selecting step, an element or a node where the flow merging angle α calculated in the flow analyzing step is larger than the reference value αs is selected. αs can be set arbitrarily within a range in which the number of selected elements or nodes does not become too small or too large. In this embodiment, αs is set to 15 degrees. The “power index” calculation step was performed in the same manner as in Example 2. The corrected vanishing reference angle replacement step was performed in the same manner as in Example 2. However, the corrected vanishing reference angle in the present embodiment is a function of the flow merging angle. In the case of the present embodiment, the weld line determination step determines the length of the weld line by comparing each flow merging angle and the corrected vanishing reference angle in the weld line occurrence predicting section. The distance from the opening to the point where the flow merging angle is larger than the corrected vanishing reference angle is defined as the predicted length, and the value is shown in Table 1. Table 1 also shows the actual weld line length of the injection molded product as an actually measured value. It can be seen that the predicted value is good.

Comparative Example 1 As a comparative example, there is a method as shown in the flowchart of FIG.
In the case of FIG. 8, since the value used in the calculation result is only the flow vector, the difference in the weld line length due to the resin type and the molding conditions cannot be clearly evaluated. This is because when the molten resin actually flows in the mold, the flow pattern changes depending on the resin type and the molding conditions, especially in the vicinity of the confluence, whereas the flow vector calculated by the flow analysis and eventually the flow pattern This is because the difference does not appear clearly.

[0043]

According to the method for estimating the length of a weld line according to the present invention, the position at which a weld line is generated in an injection-molded article or the like is determined.
Differences due to resin materials or molding conditions can be easily and reliably predicted. Therefore, it is possible to reduce costs by reducing the number of mold prototypes and the development period associated therewith.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a flow merging angle.

FIG. 2 is an explanatory diagram of a flow association angle.

FIG. 3 is a graph showing an example of the relationship between weld disappearance “exponent index” and weld line length.

FIG. 4 is a graph showing a relationship between a weld disappearance “power index” and a corrected disappearance reference angle.

FIG. 5 is a flowchart of a prediction method according to the first embodiment of the present invention.

FIG. 6 is a flowchart of a prediction method according to a second embodiment of the present invention.

FIG. 7 is a flowchart of a prediction method according to a third embodiment of the present invention.

FIG. 8 is a flowchart of a prediction method showing Comparative Example 1 of the present invention.

FIG. 9 is a plan view showing the shape of a molded product used in an example of the present invention.

FIG. 10 is an explanatory diagram of a result of selecting a predicted weld line occurrence part and a result of predicting a weld line in the example of the present invention.

FIG. 11 is a graph showing a “power index” distribution in the example of the present invention.

FIG. 12 is a graph showing a flow association angle distribution and a corrected disappearance reference angle distribution in an example of the present invention.

[Explanation of symbols]

 α Flow confluence angle θ Flow association angle N “Power exponent” β Correction vanishing reference angle

Claims (2)

[Claims] 1. A flow analysis step of performing a flow analysis of a molten resin on a shape of a molded product and calculating a flow association angle or a flow confluence angle of the molten resin, and the calculated flow association angle is smaller than a set value, or A step of selecting a weld line occurrence predicting portion for selecting a region of the molded article in which the calculated flow merging angle is larger than a set value; and a “power exponent” for calculating a “power exponent” for the shear rate of the shear viscosity in the selected region. A weld line length of a molded article, comprising: a calculation step; and a weld line determination step of defining a place where the calculated “exponent index” is equal to or more than a reference value previously measured for each resin as a weld line. Forecasting method. 2. A corrected extinction reference angle obtained by using a function in which a calculated “exponent index” is obtained through a flow analysis step, a predicted occurrence part selecting step, and a “exponent index” calculating step according to claim 1. Correction vanishing reference angle replacement step to replace the, the position of the weld line by comparing the flow association angle or flow merging angle calculated in the flow analysis step and the correction vanishing reference angle calculated in the correction vanishing reference angle replacement step. A method for estimating a weld line length of a molded article, comprising a step of determining a weld line to be determined.