JP7366327B1 - How to find gate seal time - Google Patents

Abstract

The flow analysis method for injection molding using thermoplastic resin consists of the steps of creating a flow analysis model that divides the injection molded product into multiple elements, setting the injection molding conditions, and determining the flow under the molding conditions. The analysis includes the step of obtaining the time from the injection start time until the temperature at the center of the gate of the flow analysis model reaches the flow stop temperature as a gate seal time.

Description

The present disclosure relates to determining molding conditions and gate seal time in resin molding simulation.

Injection molding is a method of obtaining molded products by heating and melting thermoplastic resin, injecting it into a mold, and then cooling and solidifying it, and is widely used because of its excellent productivity. To obtain stable molded products, it is necessary to set molding conditions according to the resin used, product shape, mold structure, and injection molding machine. If the molding conditions are not appropriate, the dimensions, weight, warpage, and This causes quality problems such as changes in the tendency of deformation. Therefore, at the molding site, optimization is performed by implementing a huge number of molding conditions in order to obtain the optimal molding conditions. On the other hand, in flow analysis using CAE (Computer Aided Engineering), it is possible to calculate temperature and pressure fluctuations in the injection molding process by giving the resin temperature, mold temperature, and injection speed. It is used for warpage/deformation analysis that takes into account the orientation of filler material, and for predicting filling patterns, and flow analysis is being used to shorten the time from product design to the start of mass production.

Here, a gate seal is one of the indicators for obtaining a stable injection molded product. Gate sealing is a phenomenon in which the resin in the gate portion solidifies and stops flowing, and the time during which the resin in the gate portion solidifies and stops flowing is called gate sealing time. If holding pressure is stopped before the gate sealing time, molten resin will flow back into the injection molding machine through the gate, resulting in incomplete filling and weight loss. On the other hand, even if holding pressure is stopped after the gate sealing time, the gate is solidified, so the resin will not flow back, and a stable injection molded product can be obtained, so this is an indicator that must be measured at molding sites.

Gate sealing time is taken into account when estimating flow patterns, warpage, and deformation through flow analysis, but parameters related to heat calculations are not sufficiently valid, especially when predicting the occurrence of sink marks or voids, and the actual molded product is There was a discrepancy, and an analysis method to accurately determine the gate seal time was required. Therefore, when actually molding is performed under the molding conditions used in the analysis, the results may differ from the analytical results due to incomplete filling, warping, sink marks, etc. due to the lack of gate sealing. An analytical method was needed.

International publication WO2018/135443

An object of the present invention is to calculate the gate sealing time, that is, the time required for the temperature at the center of the gate to reach the flow stop temperature, by flow analysis using CAE or the like. The calculated gate sealing time can be used to optimize the molding conditions.

As a result of extensive research in view of the above circumstances, the present inventors have discovered a method for determining gate sealing time from temperature data and pressure data obtained through flow analysis, and have completed the contents of the present disclosure. I ended up doing it.

More specifically, the present disclosure includes the following aspects.
[1] A flow analysis method for injection molding using thermoplastic resin,
a step of creating a flow analysis model that divides the injection molded product into multiple elements;
a step of setting molding conditions for injection molding;
A flow analysis method comprising the step of obtaining, as a gate seal time, a time from injection start time until the temperature at the center of the gate of the flow analysis model reaches a flow stop temperature in the flow analysis under the molding conditions.

[2] The flow analysis method according to [1], further comprising the step of obtaining the weight of the injection molded product at the gate seal time in the flow analysis under the molding conditions.

[3] In the step of obtaining the weight of the injection molded product, the weight of the injection molded product is obtained based on the PVT data of the thermoplastic resin measured in advance from the temperature distribution and pressure distribution calculated by the flow analysis. The flow analysis method according to [2].

[4] Gate seal time t2 and injection molded product under molding condition c2, where the weight of the injection molded product has changed such that the weight of the injection molded product is greater than that under molding condition c1, compared to gate seal time t1 and injection molded product weight w1 under molding condition c1. Weight w2, gate sealing time t3 and injection molded product weight w3 under molding condition c3, which is changed so that the weight of the injection molded product does not decrease compared to molding condition c2, always satisfy w1<w2=w3. The flow analysis method according to [2] or [3], wherein the gate sealing time t2 when doing so is the gate sealing time at which the maximum weight of the injection molded product is obtained.

[5] The flow analysis method according to [4], wherein the gate sealing time t2 is the minimum gate sealing time at which the maximum weight of the injection molded product is obtained when t2<t3 is always satisfied.

[6] The method according to [4], wherein the change in molding conditions changes any one or more of injection speed, holding pressure, and holding pressure time while keeping cylinder temperature and mold temperature constant. Flow analysis method.

[7] The flow according to [6], wherein the cylinder temperature or mold temperature is arbitrarily changed and then kept constant, the minimum gate seal time is calculated, and the shortest minimum gate seal time is selected from among them. analysis method.

[8] Any one of [1] to [7], wherein the flow stop temperature is an inflection point when cooling at a cooling rate within the range of 1 ° C / min to 50 ° C / min in specific heat measurement. The flow analysis method described in item (1) above.

[9] The flow analysis method according to any one of [1] to [8], wherein a value measured according to ISO 22007-6 is used as the thermal conductivity among the resin data used in the flow analysis.

[10] A computer-readable storage medium that stores a program that causes a computer to execute the flow analysis method according to any one of [1] to [9].

FIG. 1 is a flowchart illustrating an example of a method for determining molding conditions and minimum gate seal time according to an embodiment. FIG. 2 is a diagram showing an example of PVT data of thermoplastic resin.

Embodiments of the present disclosure will be described below. Note that the present disclosure is not limited to the following embodiments.

(Method of determining gate seal time)
An example of the method for determining the gate seal time according to this embodiment will be described in detail with reference to FIG. 1.
As shown in the flowchart of FIG. 1, an example of the method for determining the gate sealing time according to the present embodiment is a flow analysis method, which includes creating a flow analysis model (S1), setting molding conditions (S2), and determining the gate seal time. Includes acquisition of seal time (S3). An example of a method for determining the gate seal time is to obtain the weight of the molded product (S4), determine whether the obtained weight is the maximum (S5), and determine whether the obtained gate seal time is the minimum (S6). ) to obtain maximum injection molded part weight and minimum gate seal time.

(Creation of flow analysis model (S1))
In the step (S1) of creating a flow analysis model in which the injection molded product is divided into a plurality of elements, the shape of the injection molded product is divided into minute three-dimensional elements to create a model necessary for executing the simulation. For example, the shape of the injection molded product (this can be the designed shape of the injection molded product, the shape of the mold, etc.) is calculated by a computer using three-dimensional shape measurement or a CAD (Computer Aided Design) system. take in. Next, the shape imported into the computer is divided into a plurality of three-dimensional elements using an element division preprocessor or the like to create a flow analysis model.

(Setting molding conditions (S2))
In the step (S2) of setting molding conditions for performing flow analysis, the created flow analysis model is used to set molding conditions for performing flow analysis (simulation) of injection molding.
The molding conditions include setting the position and size of the injection port (gate) for the molding material (thermoplastic resin) in the mold. The molding conditions further include any one or more of cylinder temperature, mold temperature, injection speed, holding pressure, and holding pressure time.
In addition, in order to obtain the maximum weight of the injection molded product and the minimum gate sealing time, it is necessary to change the injection molding temperature by changing one or more of the cylinder temperature, mold temperature, injection speed, holding pressure, and holding pressure time. It can be selected based on the analysis results of molded product weight and gate sealing time. In addition, based on the analysis results of the injection molded product weight and gate sealing time obtained by fixing one or more of the molding conditions excluding the holding time and varying the others depending on the purpose, the maximum The injection molded part weight and minimum gate seal time may be selected. For example, when performing an analysis to obtain an injection molded product with emphasis on appearance, the cylinder temperature and mold temperature are fixed at the upper limit temperature of the resin to be analyzed, and the holding time is varied to increase the weight of the injection molded product and the gate seal time. can be analyzed. In addition, when performing analysis for the purpose of shortening cycle time, fix the cylinder temperature and mold temperature to the lower limit temperature of the resin to be analyzed, fix the injection speed to the maximum injection speed of the injection molding machine, and set the pressure holding time to the maximum injection speed of the injection molding machine. It is possible to analyze the injection molded product weight and gate seal time by changing it.
That is, some of the cylinder temperature, mold temperature, injection speed, holding pressure, and holding pressure time may be fixed without being changed.

(Acquisition of gate seal time (S3))
In the step (S3) of obtaining the gate seal time, a flow analysis of injection molding is executed using the created flow analysis model and the set molding conditions. Through flow analysis, the temperature and pressure of each element of the flow analysis model in the process of injecting and molding the molding material is calculated.
When performing flow analysis, physical property values (also referred to as "resin data") of the molding material (thermoplastic resin) used in injection molding are input. The physical property values used for flow analysis include data representing the relationship between pressure, volume, and temperature (hereinafter referred to as "PVT data". See Figure 2 for an example), thermal conductivity data, specific heat data, etc. be.
Common methods for obtaining thermal conductivity include the hot disk method and laser flash method, but the AC steady method is suitable for measuring materials with excellent heat insulation properties such as thermoplastic resins. (ISO22007-6) is preferred.

Through the flow analysis, the gate sealing time for the set molding conditions is obtained as the time from the injection start time until the temperature at the center of the gate of the flow analysis model reaches the flow stop temperature. If there are multiple gates, choose the one with the thickest wall.
In addition, in obtaining the gate seal time (S3), the flow stop temperature is the inflection point when cooling at a cooling rate within the range of 1°C per minute to 50°C per minute in the specific heat measurement of the thermoplastic resin. It can be done. For example, as shown in Table 1, when the cooling rate of the thermoplastic resin is changed to 2°C/min, 10°C/min, and 30°C/min, the gate sealing time obtained by flow analysis is 24.2 seconds. , 25.2 seconds, and 26.2 seconds. These gate sealing times are not significantly different from the actually measured value of 26.0 seconds, indicating that relatively accurate gate sealing times can be obtained within the above cooling rate range.

In obtaining the gate sealing times shown in Table 1, Duracon (registered trademark) POM M90-44 (unfilled material) manufactured by Polyplastics Co., Ltd. was used as the thermoplastic resin for the actual molded product. The molding conditions were a resin (cylinder) temperature of 205° C., a mold temperature of 40° C., a holding pressure of 50 MPa, and a holding pressure time of 35 seconds. Further, the specific heat of the thermoplastic resin was measured by a differential scanning calorimeter (DSC), and the thermal conductivity was determined by the steady-current alternating current method (ISO22007-6) described above. For the flow analysis, Moldflow (registered trademark) Insight 2019.0.5 (three-dimensional solid model) build 20180921.0959_C70L71 manufactured by Autodesk was used.

(Obtaining the weight of the molded product (S4))
In the step (S4) of obtaining the weight of the injection molded product, the weight of the injection molded product is obtained from the temperature and pressure of each element calculated in step (S3).
To obtain the weight of the injection molded product, use the temperature and pressure of each element during the gate sealing time when the temperature at the center of the gate reaches the flow stop temperature.

More specifically, first, the temperature distribution and pressure distribution of the injection molded product in the mold are calculated from the temperature and pressure of each element calculated by flow analysis.
To calculate the weight of the injection molded product, data ("PVT data") representing the relationship between the pressure, volume, and temperature of the molding material (thermoplastic resin) obtained in advance is used. In particular, PVT data is the relationship between temperature T and specific volume with pressure P kept constant.
Figure 2 shows PVT data for certain molding materials. The horizontal axis is temperature (unit: °C), and the vertical axis is the reciprocal of density, that is, specific volume (unit: cm ³ /g). What is shown in FIG. 2 is the relationship between temperature and specific volume when the pressure (P) is 50 MPa.
Figure 2 shows that the specific volume of the thermoplastic resin at a temperature of 40°C is approximately 0.70 cm ³ /g, and when the temperature of the thermoplastic resin is 200°C, the specific volume is approximately 0.82 cm ³ /g. ing.
By applying the data to the temperature distribution and pressure distribution data obtained through flow analysis, the mass per unit volume (reciprocal of specific volume) of each element can be determined.
The mass of each element can be calculated by dividing the volume of each element by the specific volume (multiplying by the density), so by adding them up for all elements, the weight of the injection molded product can be calculated.

(Determination of whether the acquired weight is the maximum (S5))
In the step (S5) of determining whether the weight of the injection molded product is the maximum, it is determined whether the weight (S4) calculated under the set molding conditions is the maximum.
To determine whether the weight is the maximum, it is recommended to first determine whether the weight of the injection molded product is at an extreme value, as known by the differential method. In other words, it is preferable to first determine whether or not the change in the weight w of the injection molded product obtained when the molding condition c is slightly changed is approximately zero for the weight w of the injection molded product under a certain molding condition c. Furthermore, regarding the weight w of the injection molded product obtained in this way, it is good to confirm that the weight of the injection molded product decreases significantly if the molding conditions c are changed significantly to some extent.
In step (S5), if it is determined that the weight calculated under the set molding conditions is the maximum ("Yes" under S5 in FIG. 1), it is determined whether the obtained gate sealing time is the minimum or not. The process advances to a step of determining (S6).
In step (S5), if it is determined that the weight calculated under the set molding conditions is not the maximum ("No" next to S5 in FIG. 1), step (S2) of setting molding conditions for flow analysis. Go back to and set different molding conditions. Under these different molding conditions, the gate seal time is obtained (S3) and the weight of the resin molded product is obtained (S4), and it is determined whether the obtained weight is the maximum (S5).
In addition, in this method, "different molding conditions" can be defined as molding conditions (new molding conditions) that are changed not slightly but rather significantly from the molding conditions previously used for flow analysis.

(Determination of whether the acquired gate seal time is the minimum (S6))
In the step (S6) of determining whether the acquired gate sealing time is the minimum, it is determined whether the gate sealing time (S3) calculated under the set molding conditions is the minimum.
To determine whether the time is the minimum, it is preferable to first determine whether the gate seal time has reached an extreme value, as in step (S5). That is, it is preferable to first determine whether or not the change in gate seal time t obtained when molding condition c is slightly changed with respect to gate seal time t under a certain molding condition c becomes approximately zero. Furthermore, regarding the gate sealing time t obtained in this way, it is good to confirm that if the molding condition c is changed significantly to some extent, the gate sealing time increases significantly.
In step (S6), if it is determined that the gate sealing time calculated under the set molding conditions is the minimum ("Yes" under S6 in FIG. 1), the gate sealing time so determined is and the molding conditions are set as the minimum gate sealing time and the molding conditions that provide it (S7).
In step (S6), if the gate sealing time calculated under the set molding conditions is not determined to be the minimum ("No" next to S6 in FIG. 1), the step (S6) of setting molding conditions for performing flow analysis ( Return to S2) and set different molding conditions. Under these different molding conditions, the gate seal time is obtained (S3) and the weight of the resin molded product is obtained (S4), and it is determined whether the obtained weight is the maximum (S5). It is determined whether the time is the minimum (S6).
In other words, at the end of the method (S7), the molding conditions are set (S2), the gate seal time is obtained (S3), and the molded product is The weight acquisition (S4) will be repeated.

Note that the determination as to whether the acquired weight is the maximum (S5) and the determination as to whether the acquired gate sealing time is the minimum (S6) can be performed at the same time. That is, only when the obtained weight is the maximum and the obtained gate seal time is the minimum, the molding conditions and the minimum gate seal time are determined (S7), and otherwise the molding conditions are set (S2). It is good to return to .

The minimum gate sealing time and the molding conditions that provide it can be determined as follows.

First, it is assumed that the gate seal time t1 and the injection molded product weight w1 are obtained by flow analysis for the molding condition c1.
It is assumed that the molding condition c2 has changed so that the weight of the injection molded product is greater than that under the molding condition c1.
For example, compared to molding condition c1, molding condition c2 may increase the weight of the injection molded product by appropriately adjusting the holding pressure and pressure holding time.
Assume that the gate sealing time t2 and the injection molded product weight w2 are obtained by flow analysis for the molding condition c2.
It is assumed that the molding condition c3 is changed so that the weight of the injection molded product does not decrease compared to the molding condition c2. Trends that increase the weight of injection molded products include increasing the holding time, increasing the holding pressure, and increasing the injection speed. If the cylinder temperature or mold temperature is extremely low, the weight may be reduced due to lack of fluidity, so in that region it may be possible to increase the weight by increasing the cylinder temperature or mold temperature, but the If the cylinder temperature or mold temperature is further increased when filling properties have been obtained, the density may decrease due to thermal expansion of the resin, and the weight of the injection molded product may decrease, so the temperature was changed. Care must be taken when considering the weight of the injection molded product.
Assume that the gate sealing time t3 and the injection molded product weight w3 are obtained by flow analysis for the molding condition c3. Since the molding condition c3 is changed so that the weight of the injection molded product does not decrease compared to the molding condition c2, w3 is greater than or equal to w2 (w3≧w2).

Molding condition c2 gives the maximum weight of the injection molded product, which means that even if c3 is changed so that the weight of the injection molded product does not decrease compared to molding condition c2 (that is, even if w3≧w2) This means that the weight remains unchanged (that is, w3=w2). Therefore, it is important to ensure that the weight of the injection molded product satisfies w1<w2=w3.

Note that "always w1<w2=w3" simply means that the weight of the injection molded product is at its maximum at the time of w2, and the gate sealing time t2 under molding condition c2 is not necessarily the minimum. This means that it is not the gate seal time of . This means that the weight of the injection molded product is stable at its maximum value.

Furthermore, since molding conditions c2 and molding conditions c3 both give the maximum weight (w2=w3) of the injection molded product, it is difficult to determine which molding condition c2 or molding condition c3 gives the minimum gate sealing time from the viewpoint of productivity. It is desirable to make a determination (step (S6)).
The molding condition c3 is changed so that the weight of the injection molded product does not decrease compared to the molding condition c2 (that is, w3≧w2), and the gate sealing time is often in the relationship of t2<t3. , if t3<t2, replace the molding condition c2 (and w2, t2 at that time) with the molding condition c3 (and w3, t3 at that time) so that the relationship w2=w3 and t2<t3. Then, the molding conditions are further changed so that w1 < w2 = w3 and t2 < t3, and the minimum gate sealing time t2 and molding condition c2 that yield the maximum weight of the injection molded product are determined. You may obtain .

Regarding the weight of the injection molded product under the molding conditions c1, c2, and c3, it can be understood more specifically that "w1<w2=w3 and always t2<t3" holds true from the following example.
For example, suppose that when the holding force is increased as the molding condition c2 compared to the molding condition c1, the injection molded product weight w2 becomes slightly larger than the injection molded product weight w1. If the injection molded product weight w3 remains the same as the injection molded product weight w2 even if the holding pressure is further increased as the molding condition c3 compared to the molding condition c2, this means that w1<w2=w3.
Here, it is assumed that as molding condition c3, the cylinder temperature is lowered and the holding pressure is increased compared to molding condition c2. In that case, when the holding force is increased without changing the cylinder temperature, or when both the cylinder temperature and the holding force are increased, the injection molded product weight w3 will still be greater than the injection molded product weight w2 (w1<w2<w3). Therefore, it cannot be said that such molding conditions c1, c2, and c3 always satisfy w1<w2=w3.
In other words, the requirement "w1<w2=w3" is satisfied only when the molding conditions c2 and c3 are such that the resin is filled to the point where no more resin can enter.

In determining the minimum gate seal time and the molding conditions that provide it, as mentioned above, some of the cylinder temperature, mold temperature, injection speed, holding pressure, and holding pressure time are changed as the molding conditions change. It may be fixed without being changed.
In particular, any one or more of the injection speed, holding pressure, and holding pressure time can be changed while keeping the cylinder temperature and mold temperature constant.
Furthermore, after calculating the minimum gate sealing time while keeping the cylinder temperature or mold temperature constant after changing the cylinder temperature or the mold temperature arbitrarily, the shortest minimum gate sealing time may be selected from among them.

The present disclosure provides a method for determining gate seal time of an injection molded article by flow analysis. Thereby, the molding conditions can be optimized using the calculated gate sealing time.
The present disclosure further provides a method for determining the minimum gate seal time that is stable at maximum product weight.
This method allows you to find the optimal molding conditions through simulation, so you can efficiently optimize molding condition parameters (temperature, speed, pressure, etc.) even in molding sites where there are no skilled workers with sufficient skills. becomes possible.
Overall, it is possible to reduce the time required for molding or to reduce material loss (environmentally friendly) that occurs by the number of molding shots required to find the optimal molding conditions in actual molding. In actual molding, if the physical properties of the resin used or the control of the molding machine differ from the analytical molding conditions, or if the analytical molding conditions cause problems such as appearance or mold release, the analytical molding conditions may be modified and implemented as long as the problem can be solved.

The present disclosure is not limited to the above-described embodiments, but also includes various modifications in which components are added, deleted, or converted to the above-described configuration. Moreover, each embodiment can be combined in various ways.
In particular, the present disclosure should not be construed as limited to the embodiments or examples described above with respect to shape, material, or conditions.

Furthermore, the present disclosure also includes a program for causing one or more processors to execute a method for determining molding conditions and gate seal time in a resin molding simulation according to the present disclosure. The program may be provided recorded on a computer-readable non-transitory storage medium.

Claims (9)

A flow analysis method for injection molding using thermoplastic resin,
a step of creating a flow analysis model that divides the injection molded product into multiple elements;
a step of setting molding conditions for injection molding;
In the flow analysis under the molding conditions, obtaining the time from the injection start time until the temperature at the center of the gate of the flow analysis model reaches a flow stop temperature as a gate seal time ;
A flow analysis method comprising the step of calculating the weight of the injection molded product from the temperature and pressure of each of the plurality of elements during the gate sealing time in the flow analysis under the molding conditions. In the step of calculating the weight of the injection molded product, the weight of the injection molded product is calculated based on PVT data of the thermoplastic resin measured in advance from the temperature distribution and pressure distribution calculated by the flow analysis. Flow analysis method according to item 1 . Gate seal time t2 and injection molded product weight w2 under molding condition c2, which has changed so that the weight of the injection molded product is increased compared to molding condition c1, compared to gate seal time t1 and injection molded product weight w1 under molding condition c1, In addition, the gate sealing time t3 and the injection molded product weight w3 under molding condition c3, which were changed so that the weight of the injection molded product did not decrease compared to molding condition c2, were made sure to satisfy w1<w2=w3. 3. The flow analysis method according to claim 1 , wherein the gate sealing time t2 is the gate sealing time at which the maximum weight of the injection molded product is obtained. 4. The flow analysis method according to claim 3 , wherein the gate sealing time t2 is the minimum gate sealing time at which the maximum weight of the injection molded product is obtained when t2 < t3. 4. The flow analysis method according to claim 3 , wherein the change in molding conditions is to change any one or more of injection speed, holding pressure, and holding pressure time while keeping cylinder temperature and mold temperature constant. . 6. The flow analysis method according to claim 5 , wherein after calculating the minimum gate seal time while keeping the cylinder temperature or the mold temperature constant after arbitrarily changing the cylinder temperature or the mold temperature, the shortest minimum gate seal time is selected from among the minimum gate seal times. 2. The flow analysis method according to claim 1 , wherein the flow stop temperature is an inflection point when cooling is performed at a cooling rate within a range of 1° C./min to 50° C./min in specific heat measurement. 2. The flow analysis method according to claim 1 , wherein a value measured according to ISO 22007-6 is used as thermal conductivity among the resin data used in the flow analysis. A computer-readable storage medium storing a program for causing a computer to execute the flow analysis method according to claim 1.

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