Injection molding machine control method and method of manufacturing injection molded product

Abstract

To provide a method for controlling an injection molding machine that can reduce filling variation of multiple cavities in a multi-cavity mold.SOLUTION: In a method for controlling an injection molding machine equipped with a multi-cavity mold having a plurality of cavities, a pressure profile indicating time variation of pressure in all of the plurality of cavities is measured, a pressure profile X indicating time variation of pressure in a reference cavity is obtained in advance from a plurality of pressure profiles, and the filling volume of each of the cavities is adjusted so that the time variation of the pressure in the plurality of cavities matches the pressure profile X in the injection molding of a product to be manufactured.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a control method for an injection molding machine and a manufacturing method for an injection molded product. [Background technology]

[0002] Injection molding using thermoplastic resins is used in a wide range of fields as a manufacturing method that can mass-produce parts with complex shapes. In particular, injection molding using a "multiple-cavity mold" with multiple cavities in one mold is widely used because it can achieve high productivity and cost reduction. By using a multi-cavity mold, multiple products can be produced with a single injection molding, which greatly improves production efficiency and reduces the repetition of the same work, making it possible to reduce processing costs. In addition, injection molding using a multi-cavity mold improves yields compared to using a single-cavity mold, which also leads to reduced material costs.

[0003] On the other hand, in injection molding using a multi-cavity mold, the adjustment of the filling variation among multiple cavities is an important issue. However, even if the length of the runner to each cavity is made equal, the filling balance is lost due to the flow inertia caused by the different flow lengths of the inner and outer circumferences, and there is a concern that this will cause variation in product quality and a decrease in yield. Known methods for adjusting the amount of resin filled into each cavity in a multi-cavity mold include, for example, adjusting the gate size or runner size. In these methods, adjustments are made by finding the optimal balance of the filling amount while visually checking for short shots and checking the weight. However, there are problems in that errors are large when determining the filling of each cavity visually, and it takes time to determine by checking the weight because accurate weight cannot be measured until the molded product reaches room temperature. Therefore, technologies are known that solve such problems and eliminate filling variations among multiple cavities (see Patent Documents 1 and 2).

[0004] Patent Document 1 describes a method for eliminating the variation between cavities by changing the flow path cross-sectional area of ​​at least one of the runners that communicate with each cavity, thereby generating a difference in the pressure transmission of the molten resin in the runner to the cavities. Patent Document 2 describes a method for switching from an injection operation to a pressure-holding operation based on the resin pressure in the mold, calculating a pressure loss value by subtracting the resin pressure in the mold from the resin pressure in the injection cylinder, and correcting a target pressure value for pressure-holding based on the pressure loss value and a reference pressure loss value. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-433 [Patent Document 2] Patent No. 7209512 Summary of the Invention [Problem to be solved by the invention]

[0006] The techniques described in the above Patent Documents 1 and 2 focus on the pressure value inside the mold, and do not take into account the pressure during the solidification process.

[0007] The present invention has been made in consideration of the above-mentioned problems in the conventional art, and an object of the present invention is to provide a control method for an injection molding machine that can reduce variations in resin filling in multiple cavities of a multi-cavity mold, and a manufacturing method for a resin molded product that obtains an injection molded product by utilizing the control method for the injection molding machine. [Means for solving the problem]

[0008] One aspect of the present invention that solves the above problems is as follows. (1) A method for controlling an injection molding machine equipped with a multi-cavity mold having a plurality of cavities, comprising the steps of: measuring pressure profiles indicating a change in pressure over time in all of the plurality of cavities; and obtaining a pressure profile X indicating a change in pressure over time in a reference cavity from the plurality of pressure profiles; A control method for an injection molding machine, comprising: adjusting a time change in pressure in each of a plurality of cavities during injection molding of an article to be manufactured such that the time change in pressure in the plurality of cavities coincides with the pressure profile X.

[0009] (2) A control method for an injection molding machine as described in (1) above, wherein the multi-cavity mold has a cold runner structure including multiple cold runners, and during injection molding of the product to be manufactured, the change in pressure over time in each of the multiple cavities is adjusted by adjusting the flow rate of resin in the cold runner for each of the multiple cavities.

[0010] (3) The injection molding machine includes a mechanism for adjusting the flow rate of resin in the cold runners by changing the angle of an adjuster, and a motor equipped with a position detector for changing the angle of the adjuster; The control method for an injection molding machine according to (2) above, wherein the flow rates of resin in the multiple cold runners are adjusted by adjusting the angles of the adjusters using the motors.

[0011] (4) A method for controlling an injection molding machine as described in (1) above, wherein the multi-cavity mold has a hot runner structure including a plurality of hot runners, and during injection molding of the product to be manufactured, the change in pressure over time in each of the plurality of cavities is adjusted by adjusting the heating temperature of each of a plurality of nozzles for injecting resin into each of the plurality of cavities.

[0012] (5) The method for controlling an injection molding machine according to (4) above, wherein the heating of the plurality of nozzles is performed by electromagnetic induction heating.

[0013] (6) A method for producing an injection-molded product, comprising controlling an injection molding machine by the method for controlling an injection molding machine according to any one of (1) to (5) above to produce an injection-molded product. Effect of the Invention

[0014] According to the present invention, it is possible to provide a control method for an injection molding machine that can reduce variations in resin filling in multiple cavities of a multi-cavity mold, and a manufacturing method for a resin molded product that obtains an injection molded product by utilizing the control method for the injection molding machine. [Brief description of the drawings]

[0015] [Figure 1] FIG. 2 is a schematic diagram showing an arrangement of multiple cavities in a multi-cavity mold. [Diagram 2] FIG. 13 is a graph illustrating a pressure profile showing the change in pressure over time in multiple cavities. [Diagram 3] FIG. 13 shows (A) a plurality of cavities, (B) an adjuster, and (C) a state in which the adjuster is adjusted with a hex wrench. [Figure 4] FIG. 1 is a system diagram showing the system configuration for controlling the heating temperature of a cavity in a hot runner by a PLC. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] <Injection molding machine control method> The control method for an injection molding machine of this embodiment is a control method for an injection molding machine equipped with a multi-cavity mold having multiple cavities. Then, pressure profiles showing the time change of pressure in all of the multiple cavities are measured, and a pressure profile X showing the time change of pressure in a reference cavity is obtained in advance from the multiple pressure profiles. Furthermore, in injection molding of a product to be manufactured, the time change of pressure in each of the multiple cavities is adjusted so that the time change of pressure in the multiple cavities matches the pressure profile X.

[0017] The injection molding machine used in the control method for an injection molding machine of this embodiment is an injection molding machine equipped with a multi-cavity mold having multiple cavities.

[0018] In the control method of the injection molding machine of this embodiment, a pressure profile (hereinafter, simply referred to as "pressure profile") showing the change in pressure over time in all of the multiple cavities is measured, and a pressure profile X showing the change in pressure over time in a reference cavity is obtained in advance from the multiple pressure profiles. The pressure profile showing the change in pressure over time in the reference cavity that is the basis of the pressure profile X can be appropriately determined so that the resin filling variation is at a level that satisfies the user, such as no resin filling variation between each cavity or a small resin filling variation. Then, in the next and subsequent injection moldings, the pressure of each cavity is adjusted so that it matches the acquired pressure profile X, thereby bringing the variation in the resin filling amount in all of the multiple cavities into a desired range. Therefore, in this embodiment, in the injection molding of the product to be manufactured, the pressure of each cavity is adjusted so that it matches the previously acquired pressure profile X, thereby reducing the variation in the resin filling amount in all of the multiple cavities. In addition, the thermoplastic resin to be the target of the control method of the injection molding machine of the present embodiment is not particularly limited. In addition, in this specification, the expression "filling amount of resin" means the filling amount of a thermoplastic resin or a resin composition containing a thermoplastic resin. The control method for the injection molding machine according to this embodiment will be described in detail below.

[0019] In this embodiment, first, pressure profiles indicating the change over time of the pressure in all of the multiple cavities are measured, and a pressure profile X indicating the change over time of the pressure in a reference cavity is obtained from the multiple pressure profiles. Fig. 1 shows a schematic diagram of the arrangement of multiple cavities in a multi-cavity mold. In Fig. 1, eight cavities 12 to 26 are connected to a runner 30 via a gate (not shown), and molten resin or resin composition is introduced into each cavity via a sprue 32, the runner 30, and the gate. Each cavity is provided with a pressure sensor, and the pressure in each cavity over time is measured. That is, the pressure in each cavity can be measured from the start of injection molding until the pressure at the end of injection molding becomes zero.

[0020] Here, the pressure profile in the cavity that is the basis of the pressure profile X can be appropriately determined so that the resin filling variation is satisfactory to the user, for example, when there is no resin filling variation between multiple cavities or when the resin filling variation is small, as described above. For example, in one injection molding, the pressure profile can be set to the average of the pressure profiles in the cavities with the same resin filling amount among multiple cavities, the average of the pressure profiles in all cavities, or the median of the pressure profiles in the cavities with the same resin filling amount among multiple cavities. Also, in multiple injection moldings, the pressure profile in the cavity with the smallest resin filling variation can be set as the pressure profile X.

[0021] A specific example of the pressure profile is shown in FIG. 2. In FIG. 2, the horizontal axis indicates time (sec) and the vertical axis indicates pressure (MPa). The solid line indicates a pressure profile in which the variation in the amount of resin filled in a plurality of cavities is within a desired range, that is, a pressure profile X indicating the time change in the pressure in the reference cavity. The dashed line indicates a pressure profile in which the variation is not within a desired range. As shown in FIG. 2, the pressure profile indicates the time change in the pressure in a plurality of cavities, which is highest immediately after the mold is clamped, decreases as the resin solidifies, and finally becomes zero. As shown in FIG. 2, the waveforms of the solid line and the dashed line do not match, so as described later, the pressure profile of each cavity is adjusted so that the injection molding with the dashed line pressure profile matches the solid line pressure profile X.

[0022] Next, in the injection molding of the product to be manufactured, the filling pressure of each of the multiple cavities is adjusted so that the time change of the pressure in the multiple cavities matches the pressure profile X obtained as described above. As described above, the variation in the filling amount can be adjusted by performing the injection molding of the product to be manufactured so that the time change of the pressure in the multiple cavities matches the pressure profile X. If the pressure tends to be lower than the pressure profile X, the filling pressure is increased, and conversely, if the pressure tends to be higher than the pressure profile X, the filling pressure is decreased. In such an adjustment of the resin filling pressure, the preferred form differs depending on whether the multi-cavity mold has a cold runner structure or a hot runner, and each will be described below. In this embodiment, it is preferable that the pressure changes over time in the multiple cavities completely match the pressure profile X, but it is not necessary to completely match them. For example, it is not necessary to completely match them within a range where the filling variations in the multiple cavities are tolerable, and some deviation is acceptable.

[0023] When a multi-cavity mold has a cold runner structure including a plurality of cold runners, the time change of pressure in each of the plurality of cavities during injection molding of the product to be manufactured can be adjusted by adjusting the flow rate of resin in the cold runner for each of the plurality of cavities. Such flow rate adjustment of the resin in the cold runner can be performed by adjusting an adjuster. FIG. 3 shows a schematic diagram of adjustment of an adjuster in a runner near the entrance of a plurality of cavities 12 to 26. The area enclosed by square in FIG. 3(A) is an area 40 where an adjuster in a runner near the entrance of the cavity is present, and an adjuster 42 that can be adjusted with a hexagonal wrench is provided as shown in FIG. 3(B), and FIG. 3(C) shows how the adjuster 42 is adjusted with a hexagonal wrench 44. For example, when the pressure profile during injection molding of the product to be manufactured tends to be lower than the desired pressure profile, the adjuster 42 is adjusted to increase the flow rate of resin. In the opposite case, adjust the adjuster 42 to reduce the flow rate of the resin.

[0024] In FIG. 3, a manual adjustment is shown in which the adjuster on the runner near the entrance of the cavity is adjusted with a hexagonal wrench, but the angle of the adjuster can also be set to be electrically adjusted with a servo motor or the like. Such a configuration eliminates the need for manual adjustment and allows for automation. For example, an injection molding machine is provided with a mechanism for adjusting the flow rate of resin in multiple runners by changing the angle of the adjuster, and a motor equipped with a position detector that changes the angle of the adjuster. The flow rate of resin in multiple runners is then adjusted by adjusting the angle of the adjuster with the motor.

[0025] On the other hand, when a multi-cavity mold has a hot runner structure including a plurality of hot runners, the time change in pressure in each of the plurality of cavities during injection molding of the product to be manufactured can be achieved by adjusting the heating temperature of each of the plurality of nozzles for injecting resin into each of the plurality of cavities. FIG. 4 shows a system configuration for adjusting the heating temperature of the cavities in a mold 50. The mold 50 is electrically connected to an in-mold pressure sensor 54 for measuring the in-mold pressure and a temperature controller 56 for controlling the hot runner tip temperature. The in-mold pressure sensor 54 and the temperature controller 56 are electrically connected to a PLC (programmable logic controller) 52. When the temperature controller 56 increases the hot runner tip temperature, the resin flow rate increases, and when the temperature controller 56 decreases the temperature, the resin flow rate decreases. In such a configuration, the PLC 52 can be set to recognize the in-mold pressure measured by the in-mold pressure sensor 54, and adjust the temperature controller 56 to match the desired pressure profile to control the hot runner tip temperature. Furthermore, with this configuration, the pressure changes over time within the multiple cavities can be automatically controlled to match a desired pressure profile.

[0026] The heating method in the hot runner may be any of the internal heating method, external heating method, and gate method (open gate method, valve gate method). As the heating means, heating by electromagnetic induction heating is preferred because it allows high temperature increase and decrease rates.

[0027] <Manufacturing method of injection molded products> The method for manufacturing an injection-molded product according to the present embodiment controls an injection molding machine by the above-described method for controlling an injection molding machine according to the present embodiment to manufacture an injection-molded product. Therefore, even when a large number of injection-molded products are manufactured, it is possible to obtain injection-molded products with little variation, stable strength, and improved dimensional accuracy. EXAMPLES

[0028] The present embodiment will be described in more detail below with reference to examples, but the present embodiment is not limited to the following examples.

[0029] (Advance preparation 1) A multi-cavity mold having eight cavities capable of molding a disk-shaped molded product with a diameter of 10 mm was prepared. This multi-cavity mold had a cold runner structure, and was equipped with a mechanism for adjusting the flow rate of the resin of the eight cold runners by changing the angle of the adjuster, and a motor equipped with a position detector for changing the angle of the adjuster. Each cavity of the multi-cavity mold was equipped with a pressure sensor, making it possible to measure the pressure over time. Then, the multi-cavity mold was mounted on an injection molding machine, and injection molding was performed using polyacetal resin (Duracon (registered trademark)) manufactured by Polyplastics Co., Ltd. as the resin. At that time, a pressure profile showing the time change in pressure in all eight cavities was measured. After injection molding, the diameters of the disk-shaped molded products obtained from the eight cavities were measured using an image measuring device VR-6000 manufactured by Keyence Corporation. The cavity from which a disk-shaped molded product with a median diameter was obtained was designated as the "reference cavity." The pressure profile showing the change in pressure over time in the "reference cavity" was designated as pressure profile X1.

[0030] [Example 1] In the same manner as in preparation 1, a multi-cavity mold was used to obtain a disk-shaped molded product by injection molding. However, injection molding was performed while adjusting the resin flow rate by automatically adjusting the adjuster with a motor so as to obtain the pressure profile X1 obtained in preparation 1. Then, the diameter of the disk-shaped molded product in each cavity was measured. The measurement results are shown in Table 1.

[0031] [Comparative Example 1] Except for not performing the automatic adjustment using the adjuster, injection molding was performed in the same manner as in Example 1, and the diameter of the disk-shaped molded product was measured. The measurement results are shown in Table 1.

[0032] (Preparation 2) A multi-cavity mold having eight cavities capable of molding a disk-shaped molded product with a diameter of 10 mm was prepared. This multi-cavity mold has a hot runner structure, and the heating temperature of each of the eight nozzles for injecting resin into each of the eight cavities can be adjusted. In addition, each cavity of the multi-cavity mold is equipped with a pressure sensor, making it possible to measure the pressure over time. Then, the multi-cavity mold was mounted on an injection molding machine, and injection molding was performed using polyacetal resin (Duracon (registered trademark)) manufactured by Polyplastics Co., Ltd. as the resin. At that time, a pressure profile showing the time change of the pressure in all eight cavities was measured. After injection molding, the diameters of the disk-shaped molded products obtained by the eight cavities were measured. The cavity from which the disk-shaped molded product with the median diameter was obtained was designated as the "reference cavity". Then, the pressure profile showing the time change of the pressure in the "reference cavity" was designated as pressure profile X2.

[0033] [Example 2] As in preparation 2, a multi-cavity mold was used to obtain a disk-shaped molded product by injection molding. However, the nozzle temperature was adjusted to obtain the pressure profile X2 obtained in preparation 2. The diameter of the disk-shaped molded product in each cavity was then measured. The measurement results are shown in Table 1.

[0034] [Comparative Example 2] Injection molding was carried out in the same manner as in Example 2, except that the nozzle temperature was not adjusted, and the diameter of the disk-shaped molded product was measured. The measurement results are shown in Table 1.

[0035] [Example 3] In the same manner as in advance preparation 1, the above multi-cavity mold was used to obtain a disk-shaped molded product by injection molding. However, injection molding was performed while adjusting the resin flow rate by automatically adjusting the adjuster with a motor so as to obtain the pressure profile X1 obtained in advance preparation 1. The molded product together with the runner was then removed from the multi-cavity mold, and a tensile load was applied to the disk-shaped molded product and the runner, and the load at which they broke was obtained as the tensile breaking load. The measurement results are shown in Table 1. All of the molded products broke at the locations corresponding to the gates.

[0036] [Comparative Example 3] Injection molding was performed in the same manner as in Example 3, except that the resin flow rate was not adjusted by automatically adjusting the adjuster, and the tensile breaking load was measured. The measurement results are shown in Table 1. In Comparative Example 3, like Example 3, all molded products broke at the location corresponding to the gate.

[0037] [Table 1]

[0038] It can be seen from Table 1 that, compared with Comparative Examples 1 to 3, each of Examples 1 to 3 has reduced variations among the eight cavities. [Explanation of symbols]

[0039] 10 Multiple Cavities 12~26 Cavity 30 Runner 32 sprues

Claims

1. A method for controlling an injection molding machine equipped with a multi-cavity mold having a plurality of cavities, comprising the steps of: measuring pressure profiles indicating a change in pressure over time in all of the plurality of cavities; and obtaining a pressure profile X indicating a change in pressure over time in a reference cavity from the plurality of pressure profiles in advance; A control method for an injection molding machine, comprising: adjusting a time change in pressure in each of a plurality of cavities so that the time change in pressure in the plurality of cavities coincides with the pressure profile X during injection molding of an article to be manufactured.

2. 2. The control method for an injection molding machine according to claim 1, wherein the multi-cavity mold has a cold runner structure including a plurality of cold runners, and during injection molding of the product to be manufactured, adjustment of the change in pressure over time in each of the plurality of cavities is performed by adjusting the flow rate of resin in the cold runner for each of the plurality of cavities.

3. the injection molding machine includes a mechanism for adjusting the flow rate of resin in the cold runners by changing the angle of an adjuster, and a motor equipped with a position detector for changing the angle of the adjuster; 3. The method for controlling an injection molding machine according to claim 2, wherein the flow rates of the resin in the plurality of cold runners are adjusted by adjusting angles of the adjusters using the motors.

4. 2. The method for controlling an injection molding machine according to claim 1, wherein the multi-cavity mold has a hot runner structure including a plurality of hot runners, and during injection molding of the product to be manufactured, adjustment of the change in pressure over time in each of the plurality of cavities is performed by adjusting the heating temperature of each of a plurality of nozzles for injecting resin into each of the plurality of cavities.

5. The method for controlling an injection molding machine according to claim 4 , wherein the heating of the plurality of nozzles is performed by electromagnetic induction heating.

6. A method for producing an injection molded product, comprising controlling an injection molding machine by the method for controlling an injection molding machine according to claim 1 or 2 to produce an injection molded product.

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