Method for controlling injection molding machine and method for manufacturing injection molded article

Abstract

A control method for an injection molding machine for forming an injection molded article by injecting a molten resin in a cylinder into a mold, in which an injection molded article evaluated as a qualified product in advance is used as a reference product, and in a primary injection molding process of the reference product, the injection molded article is subjected to injection molding in the mold. A peak pressure in a mold, and a pressure reduction time from an injection start time to a time at which the pressure in the mold drops to zero, or a pressure integral value from the injection start time to a time at which the pressure in the mold drops to zero, are acquired. And adjusting the temperature of the charging barrel so that the peak pressure in the mold becomes the peak pressure in the mold of the reference product, and adjusting the temperature in the mold so that the pressure reduction time or the pressure integral value becomes the pressure reduction time or the pressure integral value of the reference product.

Description

TECHNICAL FIELD

[0001] The present application relates to a control method of an injection molding machine and a manufacturing method of an injection molded product. BACKGROUND

[0002] In an injection molding process using a thermoplastic resin, although the size and quality of a molded product are stabilized by adjusting the packing and packing time, when the viscosity and solidification speed, etc. vary depending on the quality of the resin material, the pressure in the mold (mold internal pressure) at the time of injection molding varies. Therefore, a molded product having a deviation in physical properties, size, and appearance, etc. is produced, which causes a problem in the quality of the product. As a countermeasure against the variation in the mold internal pressure due to the deviation (viscosity, solidification speed, etc.) in the quality of the resin material, the prior art has adopted a method of feeding back the pressure in the mold and reflecting it to the screw advance pressure. That is, the control of the mold internal pressure is achieved by detecting the mold internal pressure by a mold internal pressure sensor and correcting the error by reflecting it to the screw advance pressure.

[0003] Furthermore, in Patent Literature 1, an injection molding pressure holding control device is described, which divides the control mode of injection molding pressure holding into an early stage and a later stage, the early stage is pressure control based on the mold internal pressure, and the later stage is switched to pressure control based on the oil pressure in the injection cylinder, and has a function of being able to continue pressure control. In Patent Literature 2, a mold internal resin pressure control method of an injection molding machine is described, which provides a strain gauge for detecting the strain of the mold near the resin flow passage of the mold for injection molding or in the cavity, and a mold internal pressure control unit which converts the strain of the mold into the resin pressure in the mold and controls the resin pressure, and controls the resin pressure in the mold by the mold internal pressure control unit by measuring the strain of the mold from the injection of the molten resin into the cavity until it is cooled and solidified, within a range of a necessary and sufficient mold internal resin pressure set in advance, thereby performing injection molding.

[0004] Prior Art Documents

[0005] Patent Literature

[0006] Patent Literature 1: Japanese Patent Application Laid-Open No. 62-261419

[0007] Patent Literature 2: Japanese Patent Application Laid-Open No. 8-112842 SUMMARY

[0008] Problems to be Solved by the Invention

[0009] However, the control method based on the above-mentioned correction of the mold internal pressure assumes no temperature variation, and when temperature variation occurs, there is a problem that the quality of the injection molded product is deviated.

[0010] The present invention was made in view of the above-mentioned problems in the prior art, and its object is to provide a control method for an injection molding machine that can adjust the deviation of the injection molded article caused by the quality of the resin material even when temperature changes occur, and to provide a method for manufacturing resin molded articles by using the control method of the injection molding machine to obtain the injection molded article.

[0011] Solution for solving the problem

[0012] One aspect of the present invention that solves the aforementioned problems is as follows.

[0013] (1) A control method for an injection molding machine, which forms an injection-molded article by injecting molten resin from a barrel into a mold, wherein,

[0014] Using a pre-assessed, qualified injection-molded product as a reference, during a single injection molding process of the reference product, the peak pressure within the mold and the pressure drop time from the start of injection to the moment the pressure within the mold drops to zero, or the integral pressure value from the start of injection to the moment the pressure within the mold drops to zero, are obtained.

[0015] In the injection molding process of manufacturing the target product, the barrel temperature is adjusted so that the peak pressure in the mold becomes the peak pressure in the mold of the reference product, and the temperature in the mold is adjusted so that the pressure drop time or the pressure integral value becomes the pressure drop time or pressure integral value of the reference product.

[0016] (2) According to the control method of the injection molding machine described in (1) above, in the injection molding process of manufacturing the target product, when the peak pressure in the mold is greater than the peak pressure in the mold of the reference product, the barrel temperature is reduced, and when it is less than the peak pressure in the mold of the reference product, the barrel temperature is increased.

[0017] (3) According to the control method of the injection molding machine described in (1) or (2) above, wherein, during the injection molding process of manufacturing the target product, when the pressure reduction time in the mold is longer than the pressure reduction time in the mold of the reference product, the mold temperature is reduced, and when it is shorter than the pressure reduction time in the mold of the reference product, the mold temperature is increased.

[0018] (4) The control method of the injection molding machine according to any one of (1) to (3) above, wherein, during the injection molding process of manufacturing the target product, when the pressure integral value in the mold is greater than the pressure integral value in the mold of the reference product, the mold temperature is reduced, and when it is less than the pressure integral value in the mold of the reference product, the mold temperature is increased.

[0019] (5) A method for manufacturing an injection molded article, wherein the injection molding machine is controlled by the control method of the injection molding machine described in any one of (1) to (4) above to manufacture the injection molded article.

[0020] Invention Effects

[0021] According to the present invention, a control method for an injection molding machine can be provided, which can adjust the deviation of the injection molded article caused by the quality of the resin material even in the event of temperature fluctuations, and a method for manufacturing a resin molded article by using the control method of the injection molding machine to obtain the injection molded article is also provided. Attached Figure Description

[0022] Figure 1 This is a graph (main curve) showing the pressure change over time within the mold during injection molding.

[0023] Figure 2 This is a diagram showing the location for measuring the dimensions of the dumbbell-shaped sample piece formed by injection molding in the embodiment.

[0024] Figure 3 This is a graph showing the dimensions at positions a, b, and c of dumbbell-shaped specimens obtained by injection molding with two resins of different melt viscosities under the same conditions.

[0025] Figure 4 A graph showing the dimensions at positions a, b, and c of the dumbbell-shaped sample obtained in Example 1-1.

[0026] Figure 5 A graph showing the dimensions at positions a, b, and c of the dumbbell-shaped sample pieces obtained in Examples 1-2.

[0027] Figure 6 A graph showing the dimensions at positions a, b, and c of the dumbbell-shaped specimen obtained in Comparative Example 1-1.

[0028] Figure 7 A graph showing the dimensions at positions a, b, and c of the dumbbell-shaped specimens obtained in Comparative Examples 1-2.

[0029] Figure 8 A graph showing the dimensions at positions a, b, and c of the dumbbell-shaped specimen obtained in Comparative Example 3. Detailed Implementation

[0030] <Control Methods for Injection Molding Machines>

[0031] The control method for the injection molding machine in this embodiment is a method for controlling an injection molding machine that forms an injection-molded article by injecting molten resin in the barrel into a mold. Furthermore, using an injection-molded article that has been evaluated as a qualified product as a reference product, during one injection molding process of the reference product, the peak pressure in the mold and the pressure reduction time or the integral pressure value from the start of injection to the moment when the pressure in the mold drops to zero are obtained. Next, during the injection molding process for manufacturing the target article, the barrel temperature is adjusted so that the peak pressure in the mold becomes the peak pressure in the mold of the reference product, and the mold temperature is adjusted so that the pressure reduction time or the integral pressure value becomes the pressure reduction time or the integral pressure value of the reference product.

[0032] In the control method of the injection molding machine of this embodiment, injection molded products with minimal dimensional changes and appearance defects, and rated as good, are pre-defined as qualified products and designated as reference products. Furthermore, when injection molding the reference product, the peak pressure in the mold during a single injection molding process and the depressurization time or pressure integral value from the start of injection to the moment the pressure in the mold drops to zero are obtained. By setting the peak pressure, depressurization time, or pressure integral value in the mold during the injection molding process of the reference product in the injection molding process of manufacturing the target product, qualified products can be obtained. Therefore, during the injection molding process of manufacturing the target product, the barrel temperature is adjusted so that the peak pressure in the mold becomes the peak pressure of the reference product, and the mold temperature is adjusted so that the depressurization time or pressure integral value becomes the depressurization time or pressure integral value of the reference product. Through this control of the injection molding machine, even in the event of temperature fluctuations, deviations in the quality of the injection molded products, especially dimensional changes and appearance defects, can be suppressed.

[0033] In the control method of the injection molding machine of this embodiment, firstly, an injection molded product that has been evaluated as a qualified product is determined as a reference product. Here, "qualified product" refers to an injection molded product with fewer dimensional changes and appearance defects, and possessing the desired properties. Regarding qualified products, by performing a single injection molding or preferably multiple injection moldings in advance, the injection molded product with the best quality or the product with the desired quality can be determined.

[0034] Next, during a single injection molding process of the reference product, the peak pressure within the mold and the pressure drop time from the start of injection to the moment the pressure within the mold drops to zero, or the integral pressure value from the start of injection to the moment the pressure within the mold drops to zero, are obtained. For this, see the example shown below. Figure 1 The main curve in the diagram will be used for illustration. Figure 1This represents the change in mold pressure over time during a single injection molding process. The solid line is the master curve for the reference product, and the dashed line is the master curve for injection molding using a resin material with a higher melt viscosity than the reference product. Furthermore, the horizontal axis represents time, and the vertical axis represents the pressure within the mold. Figure 1 As shown, the pressure reaches its maximum in region A of the circle. That is, this maximum pressure is the peak pressure. Then, the pressure decreases and eventually drops to zero. The "pressure drop time" is the time from the start of injection molding until the pressure in the mold drops to zero. Figure 1 In the process, starting from the moment of injection (0 seconds), the peak pressure is reached in about 3 seconds, and the pressure drops to zero in about 25 seconds. Therefore, the pressure drop time is about 25 seconds.

[0035] On the other hand, the "pressure integral value" is the time integral value of the pressure from the start of injection molding until the pressure inside the mold drops to zero. Figure 1 The area in the middle is the region enclosed by the main curve and the horizontal axis (the straight line with pressure = 0 MPa).

[0036] In addition, the "injection start time" in the pressure reduction time and pressure integral value refers to the moment when the resin material begins to be injected into the mold in the injection molding machine.

[0037] As described above, in this embodiment, the peak pressure and depressurization time or pressure integral value within the mold of the reference product are obtained in advance.

[0038] The target product is manufactured by injection molding using the peak pressure and depressurization time or pressure integral value in the mold of the reference product obtained in the above manner. Specifically, the barrel temperature is adjusted so that the peak pressure in the mold becomes the peak pressure in the mold of the reference product, and the temperature in the mold is adjusted so that the depressurization time or pressure integral value becomes the depressurization time or pressure integral value of the reference product. That is, the change in pressure in the mold caused by the deviation of the resin material is calibrated by the barrel temperature and the temperature in the mold to make it equivalent to the reference product. More specifically, (1) the change in peak pressure in the mold caused by the change in the melt viscosity of the resin material is calibrated by the barrel temperature, and (2) the change in depressurization time or pressure integral value in the mold caused by the change in the curing speed of the resin material is calibrated by the mold temperature. The following will explain (1) and (2).

[0039] (1) Peak pressure variation in the mold caused by changes in the melt viscosity of the resin material

[0040] Factors affecting pressure variations within the mold include resin material quality deviations and external disturbances (mold temperature, barrel temperature, etc.). Furthermore, the "melt viscosity," a characteristic of the resin material, is calibrated using "barrel temperature." That is, the pressure value obtained from the injection molding machine's sensors is fed back, and the barrel temperature is adjusted to ensure that the peak pressure within the mold is the same as that of a qualified quality reference product.

[0041] For example, when the peak pressure in the mold during the injection molding process of the target product is greater than the peak pressure in the mold of the reference product, the barrel temperature is lowered. Conversely, when it is lower than the peak pressure in the mold of the reference product, the barrel temperature is raised. Moreover, the barrel temperature can be adjusted using temperature regulation, PID control, etc., as described in the embodiments below.

[0042] (2) Changes in pressure drop time or pressure integral value within the mold caused by variations in the curing rate of the resin material.

[0043] As mentioned above, factors affecting pressure variations within the mold include resin material quality deviations and external interference. One characteristic of the resin material, the "curing speed," is calibrated using the "mold temperature." That is, the mold temperature is adjusted so that the pressure reduction time or pressure integral value within the mold is the same as that of a qualified quality reference product.

[0044] For example, when the depressurization time in the mold during the injection molding process of the target product is longer than the depressurization time in the mold of the reference product, the mold temperature decreases. Conversely, when the depressurization time is shorter than that in the mold of the reference product, the mold temperature increases.

[0045] Similarly, when the integral pressure value inside the mold during the injection molding process of the target product is greater than the integral pressure value inside the mold of the reference product, the mold temperature is lowered. Conversely, when it is less than the integral pressure value inside the mold of the reference product, the mold temperature is raised. Moreover, the mold temperature can be adjusted using temperature regulation, PID control, etc., as described in the embodiments below.

[0046] In the injection molding process of manufacturing the target product, the time points at which the peak pressure and depressurization time or pressure integral value in the mold are set to the values ​​of the reference product can be performed in any injection cycle (shot). For example, it can be set using values ​​every 5 injection cycles or every 10 injection cycles.

[0047] The mold temperature and barrel temperature are controlled within the injection molding machine as follows: First, the deviation between the output value (peak pressure and depressurization time or pressure integral value) detected by the pressure sensor installed in the mold and the pre-acquired reference value (peak pressure and depressurization time or pressure integral value) of the reference sample is determined. Next, the mold temperature and barrel temperature are adjusted to reduce the deviation between the measured output value (peak pressure and depressurization time or pressure integral value) and the reference value (target value) of the master curve of the reference sample.

[0048] Furthermore, the above control can be executed via sequence control of a PLC (Programmable Logic Controller) located outside the injection molding machine. Specifically, calibration based on barrel and mold temperatures is performed by sending signals from the PLC to the injection molding machine. In the signal transmission from the PLC to the injection molding machine, for example, the difference between the measured peak pressure and a reference value can be used to adjust the barrel and mold temperatures according to a program.

[0049] In the control method of the injection molding machine of this embodiment, the resin material used for injection molding is not particularly limited as long as it is a thermoplastic resin, and various thermoplastic resins can be used.

[0050] <Manufacturing Method of Injection Molded Articles>

[0051] The injection molding manufacturing method of this embodiment manufactures injection molded articles by controlling the injection molding machine using the above-described injection molding machine control method. Therefore, even in the event of temperature fluctuations, deviations in the injection molded articles caused by the quality of the resin material can be adjusted, thereby enabling the manufacture of injection molded articles with minimal quality deviations.

[0052] Example

[0053] The following examples will be used to illustrate this embodiment in more detail, but this embodiment is not limited to the following examples.

[0054] Manufacturing of Injection Molded Products

[0055] Using resin materials 1 and 2 with different melt viscosities, injection molding was performed under the following molding conditions to obtain dumbbell-shaped sample pieces (sample type: 1A).

[0056] Resin Material 1: Polyplastics Plastics Co., Ltd., polyacetal resin (DURACON (registered trademark) (standard sample (MI = 9g / 10 minutes))

[0057] Resin Material 2: Polyplastics Plastics Co., Ltd., polyacetal resin (DURACON (registered trademark) (high flowability (MI = 14g / 10 minutes))

[0058] (Molding conditions)

[0059] Barrel temperature: 200℃

[0060] Mold temperature: 80℃

[0061] Injection speed: 17mm / second

[0062] Holding pressure: 80MPa

[0063] Injection holding time: 30 seconds

[0064] Cooldown: 10 seconds

[0065] Sampling period: 1 / 1000 second

[0066] In addition, during injection molding, a pressure sensor (manufactured by Futaba Electronics Industry Co., Ltd., pressure sensor SSE) is used. This is used to monitor the pressure inside the mold.

[0067] The state of the mold and dumbbell-shaped sample piece during injection molding is shown in the figure. Figure 2 .like Figure 2 As shown, molten resin flows into the mold 10 from the gate 12, reaching the other end and forming a dumbbell-shaped sample piece 14. Inside the mold 10, the width at any position a, b, and c is 10 mm, and the distance between positions a, b, and c is 30 mm.

[0068] The widths at positions a, b, and c of dumbbell-shaped specimens molded using resin material 1 (hereinafter referred to as "reference specimens") and dumbbell-shaped specimens molded using resin material 2 (hereinafter referred to as "high-flow specimens") are measured. The measurement results are shown below. Figure 3 .exist Figure 3 In the diagram, the dashed line represents the measurement results of the reference sample, and the solid line represents the measurement results of the high-flow-rate sample. Figures 4 to 8 The same applies to China.

[0069] On the other hand, for reference products, they are manufactured according to the pressure changes during injection molding. Figure 1 Using the same master curve, we can calculate the peak pressure in the mold and the pressure integral value from the start of injection until the pressure in the mold drops to zero.

[0070] like Figure 3 As shown, the reference sample and the high-flow-rate sample deviate in width at positions a, b, and c. This can be attributed to the fact that the high-flow-rate sample has a lower melt viscosity compared to the reference sample, resulting in higher pressure and therefore larger dimensions.

[0071] As mentioned above, when two resins with different melt viscosities are injection molded in the same manner, a deviation in width will occur. Therefore, in order to reduce such dimensional deviations, in the following embodiments, injection molding is performed by controlling the injection molding machine. Specifically, the injection molding machine is controlled to bring the dimensions of the high-flow product closer to those of the reference product. That is, the reference product is evaluated as a qualified product, and the peak pressure in the mold during a single injection molding process of the reference product and the pressure integral value from the start of injection to the moment the pressure drops to zero are obtained. Based on these values, control is performed to bring the high-flow product closer to the dimensions of the reference product.

[0072] [Example 1-1]

[0073] Dumbbell-shaped sample pieces were obtained in the same manner as described in "Preparation of Injection-Molded Articles" above. However, during the injection molding process of the high-flow-rate article, the barrel temperature was adjusted to determine the peak pressure within the mold during the injection molding of the reference article. Furthermore, the mold temperature was adjusted to determine the pressure integral value from the start of injection molding until the pressure dropped to zero during the injection molding of the reference article. The widths at positions a, b, and c of the dumbbell-shaped sample pieces for both the reference article and the high-flow-rate article were measured. The measurement results are shown below. Figure 4 .like Figure 4 As shown, the deviation of the width of the dumbbell-shaped sample pieces at positions a, b, and c in both the reference sample and the high-flow sample is suppressed.

[0074] [Examples 1-2]

[0075] For both the reference sample and the high-flow-rate sample, the mold temperature was set to 5°C higher. Otherwise, dumbbell-shaped sample pieces for both the reference sample and the high-flow-rate sample were obtained in the same manner as in Examples 1-1. Furthermore, the widths of the dumbbell-shaped sample pieces at positions a, b, and c for both the reference sample and the high-flow-rate sample were measured. The measurement results are shown below. Figure 5 .like Figure 5 As shown, in both the reference product and the high-flow product, the width deviations at positions a, b, and c of the dumbbell-shaped sample piece are suppressed. That is, it can be seen that even with temperature variations, the width deviations at positions a, b, and c of the dumbbell-shaped sample piece in both the reference product and the high-flow product are suppressed. Furthermore, in Examples 1-1 and 1-2, it can be confirmed that the appearance of the injection-molded articles is identical for both the reference product and the high-flow product.

[0076] [Comparative Example 1-1]

[0077] Dumbbell-shaped sample pieces were obtained in the same manner as described in "Preparation of Injection-Molded Articles" above. However, during the injection molding process of the high-flow product, adjustments were made to ensure that the peak pressure within the mold was equivalent to that of the reference product during injection molding. Furthermore, the widths of the dumbbell-shaped sample pieces at positions a, b, and c were measured for both the reference product and the high-flow product. The measurement results are shown below. Figure 6 .like Figure 6 As shown, in both the reference sample and the high-flow sample, the deviation of the width at positions a, b, and c of the dumbbell-shaped sample piece was suppressed.

[0078] [Comparative Examples 1-2]

[0079] For both the reference sample and the high-flow-rate sample, the mold temperature was set to 5°C higher. Otherwise, dumbbell-shaped sample pieces were obtained for both the reference sample and the high-flow-rate sample using the same method as in Comparative Example 1-1. The widths of the dumbbell-shaped sample pieces at positions a, b, and c were measured for both the reference sample and the high-flow-rate sample. The measurement results are shown below. Figure 7 .like Figure 7 As shown, the reference sample and the high-flow sample exhibit width deviations at positions a, b, and c. That is, in Comparative Example 1-1, the width deviation of the dumbbell-shaped sample piece was suppressed; conversely, in Comparative Example 1-2, the width deviation was not suppressed due to the increase in mold temperature. In other words, when the mold temperature fluctuates, adjusting only the peak pressure within the mold leads to deviations in the quality of the molded product.

[0080] [Comparative Example 3]

[0081] For high-flow products, the integral pressure value from the start of injection molding to the moment the pressure drops to zero was measured without adjusting the mold temperature to make it a reference product. Otherwise, dumbbell-shaped sample pieces for both the reference product and the high-flow product were obtained in the same manner as in Examples 1-2. That is, during the injection molding of the high-flow product, only the barrel temperature was controlled. Furthermore, the widths of the dumbbell-shaped sample pieces at positions a, b, and c for both the reference product and the high-flow product were measured. The measurement results are shown in… Figure 8 .like Figure 8 As shown, the reference product and the high-flow product deviate in width at positions a, b, and c. Based on this result, it is clear that temperature control is required for both the mold and the barrel.

[0082] (1) Dimensional changes

[0083] For the dumbbell-shaped sample pieces injection molded in each embodiment and comparative example, the dimensions at positions a to c were measured. A maximum difference of less than 0.005 mm from the reference sample was rated as good, and a difference exceeding 0.005 mm was rated as poor. The evaluation results are shown in Table 1.

[0084] [Table 1]

[0085] Temperature variation Dimensional change Example 1-1 No Good Example 1-2 Yes Good Comparative Example 1-1 No Good Comparative Example 1-2 Yes Poor Comparative Example 3 Yes Poor

[0086] As shown in Table 1, in Examples 1-1 to 1-2, each evaluation result was good, and even when the mold temperature changed, the deviation of the injection molded product caused by the quality of the resin material could be adjusted. In contrast, in Comparative Examples 1-1 to 1-2, good evaluation results were obtained when there was no temperature change, but became unsatisfactory when temperature change occurred.

[0087] On the other hand, it can be seen that in Comparative Example 3 where the mold temperature was not adjusted, a good evaluation result was not obtained. Therefore, in order to adjust the deviation of the injection molded product caused by the quality of the resin material, it is necessary to adjust both the mold temperature and the barrel temperature.

[0088] Label Explanation

[0089] 10 molds

[0090] 12. Gate

[0091] 14. Dumbbell-shaped sample pieces.

Claims

1. A control method for an injection molding machine, which forms an injection-molded article by injecting molten resin in a barrel into a mold, characterized in that, Using a pre-assessed, qualified injection-molded product as a reference, during a single injection molding process of the reference product, the peak pressure within the mold and the pressure drop time from the start of injection to the moment the pressure within the mold drops to zero, or the integral pressure value from the start of injection to the moment the pressure within the mold drops to zero, are obtained. In the injection molding process of manufacturing the target product, the barrel temperature is adjusted so that the peak pressure in the mold becomes the peak pressure in the mold of the reference product, and the temperature in the mold is adjusted so that the pressure drop time or the pressure integral value becomes the pressure drop time or pressure integral value of the reference product.

2. The control method for an injection molding machine according to claim 1, characterized in that, During the injection molding process of manufacturing the target product, when the peak pressure in the mold is greater than the peak pressure in the mold of the reference product, the barrel temperature decreases; when it is less than the peak pressure in the mold of the reference product, the barrel temperature increases.

3. The control method for an injection molding machine according to claim 1 or 2, characterized in that, During the injection molding process of manufacturing the target product, when the pressure reduction time in the mold is longer than the pressure reduction time in the mold of the reference product, the mold temperature is lowered; when it is shorter than the pressure reduction time in the mold of the reference product, the mold temperature is raised.

4. The control method for an injection molding machine according to claim 1 or 2, characterized in that, During the injection molding process of manufacturing the target product, when the pressure integral value inside the mold is greater than the pressure integral value inside the mold of the reference product, the mold temperature is reduced; when it is less than the pressure integral value inside the mold of the reference product, the mold temperature is increased.

5. A method for manufacturing an injection-molded article, characterized in that, Injection-molded articles are manufactured by controlling the injection molding machine using the control method of the injection molding machine as described in claim 1 or 2.

Images