Molding method and injection molding machine for molded products

Abstract

To provide a molding method capable of molding a high-quality molded article regardless of a shape of a molded article.SOLUTION: A pair of metal mold (15, 16) is provided with a core (36), and driving is run by core pressing force means (5, 38). Then, the method includes an injection step of injecting an injection material to the pair of metal mold (15, 16), a mold platen clamping step of clamping the metal mold (15, 16) by driving a clamping apparatus (2) after completion of the injection step or in parallel with the injection step and a core compression step of pressing the core (36) by the core pressing force means (5, 38).SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a molding method for molding a molded product by injection molding and an injection molding machine.

Background Art

[0002] There are various molding methods for molding a molded product by an injection molding machine equipped with a mold clamping device and an injection device, and the compression molding method is one of them. The compression molding method is a method for preventing phenomena such as sink marks from occurring due to thermal shrinkage as the injection material injected into the cavity of the mold cools and solidifies. For example, there is a compression molding method by platen compression. In this compression molding method, the mold is clamped so as to have a small mold clamping force, or is slightly opened, and the injection material is injected into the cavity. Subsequently, the platen is driven to apply a mold clamping force to the mold. Thereby, even if thermal shrinkage occurs due to cooling, sink marks can be prevented and a molded product with excellent transferability can be obtained.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

[0004] As a compression molding method, for example, as described in Patent Document 1, there is also a compression molding method by core compression in which a core is provided in the mold and the core is driven. The core in the mold can be driven, for example, by an ejector rod of an ejector device. The mold is clamped and the injection material is injected into the cavity. Subsequently, the core is driven to compress the injection material. Then, even if thermal shrinkage of the injection material occurs, the volume in the cavity can be reduced to prevent sink marks and the like.

Summary of the Invention

Problems to be Solved by the Invention

[0005] Both die compression and core compression can prevent sink marks and produce molded products with excellent transferability. However, depending on the shape of the molded product, for example, if there is a mixture of thin-walled and thick-walled sections, it is difficult to prevent sink marks using either method, which presents a challenge.

[0006] This disclosure provides a molding method and an injection molding machine capable of molding high-quality molded products.

[0007] Other challenges and novel features will become apparent from the description and accompanying drawings in this specification. [Means for solving the problem]

[0008] This disclosure provides a pair of molds with cores, which are driven by a core pressing means. The invention also includes an injection process in which injection material is injected into the pair of molds, and after the completion of the injection process. to, or After the start of the injection process In parallel with the injection process hand, The molding method comprises a mold clamping step in which a mold clamping device is driven to clamp the mold, and a core compression step in which a core is pressed by a core pressing means. [Effects of the Invention]

[0009] This disclosure makes it possible to prevent sink marks and obtain high-quality molded products. [Brief explanation of the drawing]

[0010] [Figure 1] This is a front view showing the injection molding machine according to this embodiment. [Figure 2] This is a front cross-sectional view showing a part of the injection molding machine according to this embodiment and a mold according to this embodiment. [Figure 3] This is a flowchart illustrating the molding method according to this embodiment. [Figure 4A] This is a front cross-sectional view showing a part of the injection molding machine according to this embodiment and a mold according to this embodiment. [Figure 4B] This is a front cross-sectional view showing a part of the injection molding machine according to this embodiment and a mold according to this embodiment. [Figure 5A] This is a time chart showing each step when the molding method according to this embodiment is implemented. [Figure 5B] This is a time chart showing each step when the molding method according to this embodiment is implemented. [Modes for carrying out the invention]

[0011] The following describes specific embodiments in detail with reference to the drawings. However, the embodiments are not limited to those described below. For clarity, the following descriptions and drawings have been simplified as appropriate. In each drawing, the same elements are denoted by the same reference numerals, and redundant explanations have been omitted where necessary. Also, hatching has been omitted in some parts of the drawings to avoid clutter.

[0012] This embodiment will be described. <Injection molding machine> The injection molding machine 1 according to this embodiment, as shown in Figure 1, comprises a toggle-type mold clamping device 2 and an injection device 3. The mold clamping device 2 is equipped with an ejector device 5. The injection molding machine 1 is equipped with a control device 4, and the mold clamping device 2, the injection device 3, and the ejector device 5 are controlled by the control device 4.

[0013] <Mold clamping device> The clamping device 2 includes a fixed platen 7 fixed to the bed B, a movable platen 8 provided slidably on the bed B, and a clamping housing 9. The fixed platen 7 and the clamping housing 9 are connected by a plurality of tie bars 11, 11, …, and the movable platen 8 is slidable between the fixed platen 7 and the clamping housing 9. A clamping mechanism, that is, a toggle mechanism 13 in this embodiment, is provided between the clamping housing 9 and the movable platen 8. The fixed platen 7 and the movable platen 8 are provided with a pair of molds, a fixed-side mold 15 and a movable-side mold 16, which will be described later. The toggle mechanism 13 is provided with a crosshead 14. When the crosshead 14 is driven, the toggle mechanism 13 flexes and the molds 15, 16 are opened and closed. An ejector device 5 is provided on the movable platen 8 of such a clamping device 2.

[0014] <Injection device> The injection device 3 includes a heating cylinder 19, a screw 20 provided in the heating cylinder 19, and a screw driving device 22. The heating cylinder 19 is supported by the screw driving device 22, and the screw 20 is driven in the rotational direction and the axial direction by the screw driving device 22. The heating cylinder 19 is provided with a hopper 23 and an injection nozzle 24. When the heating cylinder 19 is heated, injection material is supplied from the hopper 23 and the screw 20 is rotated, the injection material melts and is metered. When the screw 20 is driven in the axial direction by the screw driving device 22, the injection material can be injected into the molds 15, 16.

[0015] <Mold> The fixed-side mold 15 and the movable-side mold 16 according to this embodiment will be described. As shown in FIG. 2, the fixed-side mold 15 has a relatively large and shallow recess 26 formed in its parting line. The fixed-side mold 15 is provided with a sprue 27, and the injection nozzle 24 of the injection device 3 touches it. The sprue 27 communicates with a gate 30 that opens into the recess 26 via a runner 28, and the injection material is injected.

[0016] On the movable mold 16, a trapezoidal convex portion 33 with a wide area and a relatively low height is formed on its parting line. This convex portion 33 is adapted to be inserted into the concave portion 26 of the fixed mold 15. A concave portion 34 is formed in a part of the convex portion 33 with a predetermined depth. A core 36 is inserted into this concave portion 34. This core 36 is driven by core pressing means and pressed toward the parting line side. That is, a cavity is configured by the concave portion 26 of the fixed mold 15, the convex portion 33 of the movable mold 16, and the core 36 of the concave portion 34. In the present embodiment, the core pressing means is the ejector device 5 (see FIG. 1), and the core 36 is driven by an ejector rod 38 provided in the ejector device 5.

[0017] <Forming method> The forming method according to the present embodiment is a so-called compression molding method in which an injection material is injected into the cavity of the molds 15 and 16 and then compressed, either subsequently or in parallel, for molding. The forming method according to the present embodiment is characterized in that both compression methods, namely so-called platen compression in which the mold clamping device 2 is driven to apply a mold clamping force and so-called core compression in which the core 36 is driven, are carried out.

[0018] Hereinafter, the forming method according to the present embodiment will be described. As shown in FIG. 3, the mold closing / mold clamping process is started (step S01). That is, the control device 4 drives the crosshead 14 in the mold closing direction in the mold clamping device 2 (see FIG. 1). Note that the platen compression to be carried out later is a kind of mold clamping, and it can also be regarded as continuously carrying out the mold closing / mold clamping process after step S01. In FIG. 3, this step S01 only defines the start of the mold closing / mold clamping process.

[0019] Next, the control device 4 executes step S02 to check whether the injection start conditions are met. The control device 4 is configured with multiple setting data related to mold closing and clamping for controlling the clamping device 2, and multiple setting data related to injection and holding pressure for controlling the injection device 3, and these setting data are controlled in relation to each other. For example, in the clamping device 2, when the position of the crosshead 14, i.e., the crosshead position, reaches a predetermined position and the pair of molds 15 and 16 touch, resulting in a mold-closed state, or when the pair of molds 15 and 16 approach each other to a predetermined mold opening amount, the mold closing is temporarily stopped. Then injection is started, and so on, as set by multiple setting data. And injection is set to drive the screw 20 at a predetermined screw speed, etc.

[0020] Thus, the conditions for initiating injection are defined by multiple setting data. Alternatively, they can be defined by a single setting data. Although the control device 4 does not have a specific setting data called "injection start conditions," the control device 4 determines whether to start the injection process based on whether the conditions defined by one or more setting data are met, so for convenience, this specification will refer to them as "injection start conditions." In step S02, if the control device 4 determines that the injection start conditions are met, it proceeds to step S03. If it determines that the conditions are not met, it repeats step S02.

[0021] The control device 4 starts the injection process in step S03, that is, it drives the screw 20 at the set screw speed. The injection process can be controlled in various ways by setting multiple setting data. For example, it can be controlled with only one screw speed, or it can be divided into multiple stages and controlled sequentially with multiple different screw speeds. The timing of the completion of the injection process can also be controlled in various ways. In other words, the injection process may be completed before the mold compression, which will be explained later, starts, or it may be continued for a while after it has started until it is completed. In other words, the completion of the injection process can also be set by one or more setting data, so there are various patterns. In Figure 3, step S03 only specifies the start of the injection process.

[0022] Figure 4A shows how the injection material is injected into the cavity 40 within the molds 15 and 16 during the injection process. In the example shown in Figure 4A, the molds 15 and 16 are closed, meaning they are touching each other to the extent that no clamping force is generated, and the injection process is started when the conditions for initiating injection are met. The injection process is completed when the cavity 40 is filled with the injection material. The injection material filling the cavity 40 is thicker near the recess 34 but thinner in other areas.

[0023] Next, the control device 4 executes step S04 shown in Figure 3 to check whether the mold compression start condition is met. Similar to the injection start condition, the control device 4 does not have specific setting data for the mold compression start condition. However, the condition for whether or not mold compression can be started is formed by one or more setting data set in the control device 4. The control device 4 checks whether or not the mold compression start condition is met in step S04. If the mold compression start condition is met, the device proceeds to step S05. If it is not met, step S04 is repeated.

[0024] In step S05, the control device 4 starts mold plate compression. That is, it drives the crosshead 14 to push the movable platen 8 toward the fixed platen 7. This increases the clamping force in the molds 15 and 16. For mold plate compression, one or more setting data can be used to perform compression in one stage or multiple stages. By performing mold plate compression, the injection material filled in the cavity 40 is compressed, preventing sink marks, especially in thin-walled areas.

[0025] The control device 4 executes step S06. The control device 4 has a predetermined crosshead position set by the engineer as one of the setting data. The predetermined crosshead position is a condition for performing core compression, which will be explained next. It is the setting data that determines that core compression can be performed when the crosshead 14 reaches this position. The predetermined crosshead position is the mold touch position, which is the crosshead position where molds 15 and 16 close together with almost no clamping force, or a crosshead position of a size smaller than that. This ensures that molds 15 and 16 are reliably closed. In step S06, the control device 4 determines whether the crosshead 14 has reached the predetermined crosshead position. If it has, it proceeds to step S07; otherwise, it repeats step S06.

[0026] In step S07, the control device 4 starts core compression. Specifically, it drives the ejector device 5 (see Figure 1) to press the core 36 with the ejector rod 38. This prevents sink marks in the injection material in the recess 34. In other words, sink marks are prevented in the thick-walled sections.

[0027] Figure 4B shows the simultaneous execution of mold plate compression and core compression. Specifically, the movable platen 8 is driven toward the fixed platen 7, increasing the clamping force in the molds 15 and 16, and the core 36 is driven via the ejector rod 38. By performing mold plate compression and core compression, sink marks are properly prevented in both thin-walled and thick-walled sections. Therefore, high-quality molded products can be obtained.

[0028] By the way, in the flowchart of Figure 3, there is only one condition for starting core compression, namely whether or not the crosshead 14 has reached the specified crosshead position. However, one of the conditions for starting core compression is that mold plate compression has started. In the flowchart of Figure 3, step S06 is executed after mold plate compression has started in step S05, so one of the conditions for starting core compression, that mold plate compression has started, has already been met.

[0029] Thus, there are actually two conditions for initiating core compression, and these conditions are in place to prevent damage to the ejector rod 38, core 36, and molds 15 and 16. For example, if core compression is started before molds 15 and 16 are in the closed position, or before mold plate compression is started, a large force will act on the ejector rod 38 via the core 36, potentially damaging molds 15 and 16, etc. To prevent such dangers, two conditions are set for initiating core compression. Although one of the conditions for initiating core compression is that the injection process has started, this is not a problem. This is because mold plate compression should be performed after the injection process has started, so confirming the start of mold plate compression inevitably guarantees that the injection process has started.

[0030] Figures 5A and 5B show time charts indicating the timing of each process when the molding method according to this embodiment is performed with various setting data. In the example shown in Figure 5A, the specified crosshead position set in the control device 4 (see Figure 1) is set to a crosshead position where the mold is closed and no clamping force is generated. The injection process is also set to start after the mold is closed. In the example shown in Figure 5A, the crosshead 14 (see Figure 1) reaches the specified crosshead position simultaneously with the mold closing. In other words, one of the conditions for starting core compression is met.

[0031] As shown in Figure 5A, the injection and holding pressure process begins shortly after, followed by the first stage of mold compression. The first stage of core compression begins simultaneously with the first stage of mold compression because the other condition for the start of core compression, the start of mold compression, has been met. In other words, both conditions have been met. In the example shown in Figure 5A, mold compression is performed in two stages, and core compression is also performed in two stages. After the completion of the injection and holding pressure process, the molded product is obtained after cooling.

[0032] In the example shown in Figure 5B, the control device 4 (see Figure 1) is set to a specified crosshead position where a certain amount of clamping force is generated. The injection process is set to start before the molds 15 and 16 are closed, that is, when they are open to a predetermined amount. In the example shown in Figure 5B, the injection and holding pressure process starts before the mold is closed. After a while, mold plate compression starts. This satisfies one condition for starting core compression. Eventually, the crosshead 14 (see Figure 1) reaches the specified crosshead position. At this point, another condition for starting core compression is met, and the first stage of core compression begins. In this example, there is only one stage of mold plate compression, and core compression consists of two stages. Once the injection material has cooled, a molded product is obtained.

[0033] <Modification of the embodiment> This embodiment is subject to various modifications. For example, the core pressing means for driving the core 36 (see Figure 2) was described as an ejector device 5 (see Figure 1). However, the core pressing means can also be configured using a piston cylinder unit or other devices. Furthermore, although it was described as having only one core 36 in the movable mold 16, two or more cores may be provided, or the core 36 may be provided in the fixed mold 15. When multiple cores are provided, each core may be driven independently by different core pressing means.

[0034] The mold clamping device 2 of the injection molding machine 1 according to this embodiment is a toggle-type mold clamping device, but a direct-pressure type mold clamping device may also be used. In this case as well, in order to prevent damage to the molds 15, 16, etc., it is preferable that the conditions for starting core compression be the same as in this embodiment, namely that the molds 15, 16 are closed and that mold plate compression has started.

[0035] The present invention has been described in detail above based on embodiments, but it goes without saying that the present invention is not limited to the embodiments already described, and various modifications are possible without departing from the spirit of the invention. The multiple examples described above can also be implemented in combination as appropriate. [Explanation of Symbols]

[0036] 1 Injection molding machine 2 Mold clamping device 3. Injection device 4. Control device 5 Ejector device 7 Fixed panel 8. Movable plate 9. Clamping housing 11 Tie bar 13 Toggle mechanism 14 Crosshead 15 Fixed mold 16 Movable mold 19 Heating cylinder 20 Screw 22 Screw drive mechanism 23 Hopper 24 Injection nozzle 26 Recessed 27 Sprue 28 Runner 30 Gate 33 Convex portion 34 Recess 36 cores, 38 ejector rods 40 Cavity B Bed

Claims

1. A clamping device equipped with mold plates that open and close relative to each other, An injection device for injecting injection material, A molding method for forming a molded product using a pair of molds provided on the aforementioned mold plate, The pair of molds are provided with a core that is driven by a core pressing means. The molding method includes an injection step of injecting injection material into the pair of molds, After the completion of the injection process, or after the start of the injection process and in parallel with the injection process, a mold clamping process is performed in which the mold clamping device is driven to clamp the pair of molds. A method for molding a molded product, comprising a core compression step of pressing the core with the core pressing means.

2. The method for molding a molded article according to claim 1, wherein the core compression step is performed simultaneously with or after the start of the mold clamping step.

3. The method for molding a molded article according to claim 2, wherein the core compression step is performed after the mold closing of the pair of molds.

4. The mold clamping device is configured to open and close the mold using a toggle mechanism equipped with a crosshead. The molding method for a molded product according to claim 3, wherein the closing of the pair of molds is determined by whether or not the crosshead position of the crosshead has reached a predetermined crosshead position, and the predetermined crosshead position is a predetermined crosshead position that is below the mold touch position, which is the crosshead position when the pair of molds touch each other.

5. The method for molding a molded article according to any one of claims 1 to 4, wherein the core pressing means comprises an ejector device and drives the core with an ejector rod of the ejector device.

6. The molding method for a molded article according to any one of claims 1 to 4, wherein the injection step is performed after the mold closing of the pair of molds.

7. The molding method for a molded article according to any one of claims 1 to 4, wherein the injection step is started before the mold closing of the pair of molds.

8. A clamping device equipped with mold plates that open and close relative to each other, An injection device for injecting injection material, A pair of molds provided on the aforementioned mold plate, A control device is provided, The pair of molds are provided with a core that is driven by a core pressing means. The control device includes an injection process for injecting injection material into the pair of molds, After the completion of the injection process, or after the start of the injection process and in parallel with the injection process, a mold clamping process is performed in which the mold clamping device is driven to clamp the pair of molds. An injection molding machine that performs a core compression step of pressing the core with the core pressing means to form a molded product.

9. The injection molding machine according to claim 8, wherein the control device performs the core compression step simultaneously with or after the start of the mold clamping step.

10. The injection molding machine according to claim 9, wherein the control device performs the core compression step after the mold closing of the pair of molds.

11. The mold clamping device is configured to open and close the mold using a toggle mechanism equipped with a crosshead. The injection molding machine according to claim 10, wherein the control device determines whether the pair of molds are closed based on whether the crosshead position of the crosshead has reached a predetermined crosshead position, and the predetermined crosshead position is a preset crosshead position that is below the mold touch position, which is the crosshead position when the pair of molds touch each other.

12. The injection molding machine according to any one of claims 8 to 11, wherein the injection molding machine is equipped with an ejector device, and the core pressing means is made of the ejector device and drives the core with an ejector rod.

13. The injection molding machine according to any one of claims 8 to 11, wherein the control device performs the injection process after the mold closing of the pair of molds.

14. The injection molding machine according to any one of claims 8 to 11, wherein the control device starts the injection process before the molds of the pair of molds are closed.

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