Molding method and injection molding machine

Abstract

To provide a molding method capable of appropriately molding a molded product without dripping.SOLUTION: A molding method includes: a plug forming step S1; a pre-pressurization step S3; and an injection nozzle heating step S4. The plug forming step S1 forms a plug (37) in an injection nozzle (22) to prevent dripping. In the pre-pressurization step S3, a screw (17) is driven under pressure control at a specified pressure, and the presence or absence of forward movement of the screw (17) is monitored. In the injection nozzle heating step S4, the injection nozzle (22) is heated while the injection nozzle (22) is kept in contact with a mold (28). Then, when the forward movement of the screw (17) is detected, the system switches to an injection operation in which the screw (17) is driven by position control.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a molding method for molding a molded product by injecting an injection material into a mold, and to an injection molding machine. [Background technology]

[0002] An injection molding machine is equipped with a mold clamping device and an injection device. The mold is clamped by the mold clamping device, and the screw in the injection device is rotated to melt and measure the injection material. Once the measurement is complete, the screw is driven axially, i.e., the material is injected. The injection material fills the cavity formed in the mold. After the injection material has solidified, the mold is opened to obtain a molded product. Resin materials are widely used as injection materials, but as described in Patent Document 1, non-ferrous metals such as magnesium alloys are also used. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-279728 Summary of the Invention [Problem to be solved by the invention]

[0004] Injection materials used in injection molding vary in physical properties, but some have low viscosities when melted. Such injection materials are prone to leaking from the injection nozzle at the tip of the injection device, a phenomenon known as "snot." To prevent this, the temperature of the injection material at the tip of the injection nozzle can be lowered to form a so-called plug. This method temporarily prevents sniffing by using a plug, and then heats the injection nozzle during injection to melt the plug. However, accurately timing the melting of the plug is difficult. In particular, for injection materials whose viscosity changes significantly with even a slight change in temperature, the viscosity drops rapidly, making it virtually impossible to predict the timing of melting. This can lead to leakage of the injection material before the injection operation, resulting in molding defects.

[0005] The present disclosure provides a molding method and an injection molding machine that can prevent dripping and reliably inject an injection material into a mold.

[0006] Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0007] The molding method of the present disclosure includes a plug forming step, a pre-pressurizing step, and an injection nozzle heating step. The plug forming step is performed by forming a plug in the injection nozzle. Injection nozzle tip The pre-pressurizing step drives the screw under pressure control to pressurize the injection material to a specified pressure, while monitoring whether the screw is moving forward. The injection nozzle heating step heats the injection nozzle while it is in contact with the mold. The molding method of the present disclosure performs the pre-pressurizing step and the injection nozzle heating step in parallel, and when forward movement of the screw is detected, switches to injection operation in which the screw is driven under position control. [Effects of the Invention]

[0008] The present disclosure can prevent dripping and can reliably inject injection material into a mold. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a front view showing a vertical injection molding machine according to an embodiment of the present invention. [Figure 2A] 1 is a front cross-sectional view showing a part of an injection device and a mold according to the present embodiment. [Figure 2B] 1 is a front cross-sectional view showing a part of an injection device and a mold according to the present embodiment. [Figure 2C] 1 is a front cross-sectional view showing a part of an injection device and a mold according to the present embodiment. [Figure 2D] 1 is a front cross-sectional view showing a part of an injection device and a mold according to the present embodiment. [Figure 2E] 1 is a front cross-sectional view showing a part of an injection device and a mold according to the present embodiment. [Figure 2F] 1 is a front cross-sectional view showing a part of an injection device and a mold according to the present embodiment. [Figure 2G] 1 is a front cross-sectional view showing a part of an injection device and a mold according to the present embodiment. [Figure 3] 3 is a flowchart of a molding method according to the present embodiment. [Figure 4] 10 is a flowchart of a molding method according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Specific embodiments will be described in detail below with reference to the drawings. However, the present invention is not limited to the following embodiments. For clarity of explanation, the following description and drawings have been simplified as appropriate. In each drawing, the same elements are given the same reference numerals, and duplicate explanations are omitted as necessary. Furthermore, hatching has been omitted in some areas to avoid cluttering the drawings.

[0011] The present embodiment will be described. <Vertical injection molding machine> As shown in FIG. 1, the vertical injection molding machine 1 according to this embodiment includes a mold clamping device 2, an injection device 3 provided above the mold clamping device 2, and a controller 4 for controlling these.

[0012] <Mold clamping device> The mold clamping unit 2 includes a fixed platen 9 fixed to the housing 7, an upper movable platen 10 provided above the fixed platen 9, and a lower movable platen (not shown) provided within the housing 7. The upper movable platen 10 and the lower movable platen are connected by three tie bars 12, 12, ..., and when a mold clamping mechanism (not shown) provided between the lower movable platen and the fixed platen 9 is driven, the upper movable platen 10 is driven up and down. The mold clamping unit 2 is provided with a turntable 14, although it is not an essential component. The turntable 14 is provided above the fixed platen 9 and is capable of rotating 180 degrees around a single central tie bar 12, i.e., of rotating inverted.

[0013] <Injection device> The injection unit 3 is provided on the upper movable platen 10 of the mold clamping unit 2. The injection unit 3 includes a heating cylinder 16, a screw 17 provided within the heating cylinder 16, a drive mechanism 19 that drives the screw 17, and an elevator 20 that raises and lowers the entire injection unit 3. An injection nozzle 22 is provided at the tip of the heating cylinder 16. As shown in FIG. 2A, the heating cylinder 16 and the injection nozzle 22 are provided with a heating cylinder band heater 23 and an injection nozzle heater 24, respectively. The heating cylinder 16 and the injection nozzle 22 are provided with a heating cylinder temperature sensor 25 and an injection nozzle temperature sensor 26, each of which is a thermocouple. Although FIG. 2A shows only one heating cylinder band heater 23 and one heating cylinder temperature sensor 25, multiple sensors are provided on the heating cylinder 16.

[0014] The heating cylinder 16 and injection nozzle 22 are heated by the heating cylinder band heater 23 and injection nozzle heater 24, while temperatures are detected by the heating cylinder temperature sensor 25 and injection nozzle temperature sensor 26. When the screw 17 is rotated, the injection material is melted and measured. When the screw 17 is driven axially, the molten injection material is injected. While resin can also be used as the injection material, in this embodiment, a non-ferrous metal such as tin or a magnesium alloy is used. In other words, the vertical injection molding machine 1 according to this embodiment is a metal injection molding machine.

[0015] <controller> The controller 4 of the vertical injection molding machine 1 according to this embodiment stores a plurality of programs for carrying out the molding method according to this embodiment. Specifically, these are a pre-pressurization control means, an injection nozzle heating control means, and a pre-heating control means. When carrying out the molding method according to this embodiment, these control means respectively carry out a pre-pressurization step, an injection nozzle heating step, and a pre-heating step, and the specific control contents will be explained later.

[0016] <Mold> In the mold clamping apparatus 2 according to this embodiment, a lower mold 27 is provided on the turntable 14, and an upper mold 28 is provided on the upper movable platen 10. As shown in FIG. 2A, the lower mold 27 has a protrusion 30 formed thereon that protrudes from the center of the parting line. The upper mold 28 has a recess 31 formed thereon in the center of the parting line, and a sprue 32 is connected to the recess 31. When the lower mold 27 and the upper mold 28 are clamped together, a cavity 34 is formed by the protrusion 30 and the recess 31, as shown in FIG. 2A.

[0017] <Method for molding a molded product according to the present embodiment> A molding method for a molded product according to this embodiment will now be described. As shown in Figure 3, the molding method according to this embodiment begins with a plug molding process in step S1. As shown in Figure 2A, the injection nozzle 22 is brought into contact with the upper mold 28, and the output of the injection nozzle heater 24 is suppressed. This causes the temperature of the tip of the injection nozzle 22 to be cooled by the lower temperature of the upper mold 28. The injection material 36 in a molten state within the heating cylinder 16 and the injection nozzle 22 solidifies at the tip of the injection nozzle 22, forming a plug 37. This prevents the injection material from leaking from the tip of the injection nozzle 22, resulting in dripping.

[0018] Next, as shown in Fig. 3, a metering step is carried out in step S2. As shown in Fig. 2B, the screw 17 is rotated to melt the injection material. The molten injection material is then sent forward by the screw 17. Because the outlet of the injection nozzle 22 is closed by the plug 37, the screw 17 retreats, i.e., moves up. In other words, the injection material is metered.

[0019] Once metering is complete, the pre-pressurization step is started in step S3 as shown in Fig. 3. In the pre-pressurization step, the screw 17 is driven by pressure control as shown in Fig. 2C to pressurize the injection material to a specified pressure, which is a predetermined pressure preset in the controller 4. This specified pressure is sufficiently smaller than the injection pressure in the injection step, but is set to a pressure such that the molten injection material would be extruded from the injection nozzle 22 if the plug 37 were not present. With the specified pressure applied in this manner, the controller 4 begins monitoring the advancement of the screw 17, i.e., the change in the screw position.

[0020] While the pre-pressurization step continues, the injection nozzle heating step is started in step S4 as shown in Figure 3. In the injection nozzle heating step, the injection nozzle 22 is heated by the injection nozzle heater 24 to melt the plug 37. At this time, the temperature of the injection nozzle 22 detected by the injection nozzle temperature sensor 26 is controlled to be higher than the melting temperature of the injection material.

[0021] In this way, the pre-pressurization process and the injection nozzle heating process are carried out in parallel, and the presence or absence of forward movement of the screw 17 is monitored as shown in step S5 in Figure 3. The presence or absence of forward movement can be determined by whether or not the screw position has exceeded a specified length preset in the controller 4. In other words, the presence or absence of forward movement is determined by the magnitude of change in the position of the screw 17. Alternatively, it may be determined by whether or not the change exceeds a specified length within a specified time. In this case, the presence or absence of forward movement is determined by the magnitude of the speed of the screw 17. If forward movement of the screw 17 is not detected, the process is repeated in step S6 as shown in Figure 3. In other words, the pre-pressurization process and the injection nozzle heating process are continued.

[0022] Eventually, the temperature of the injection nozzle 22 rises, and the plug 37 shown in FIG. 2C melts. Then, as shown in FIG. 2D, injection material leaks from the tip of the injection nozzle 22. The screw 17 advances by the amount of the leaked material. In step S5 shown in FIG. 3, the forward movement of the screw 17 is detected. The controller then executes the injection molding process in step S7. Specifically, the pre-pressurization process is stopped, and the drive of the screw 17 is switched from pressure control to position control. The controller 4 drives the screw 17 at a preset injection speed. Then, as shown in FIG. 2E, the cavity 34 is filled with the injection material 36. Since the injection molding process begins upon detection of the forward movement of the screw 17, the molten injection material flows through the sprue 32 without solidifying, ensuring that it is reliably inserted into the cavity 34. This prevents molding defects.

[0023] If necessary, pressure dwelling is performed to prevent sink marks. After pressure dwelling is complete, the output of the injection nozzle heater 24 is reduced to lower the temperature of the injection nozzle 22. Because the temperature of the molds 27 and 28 is lower than that of the injection nozzle 22, the injected material 36 in the cavity 34 solidifies. Figure 2F shows a molded product 40 that has solidified in the cavity 34. As the molded product 40 solidifies, a plug 37 is formed at the tip of the injection nozzle 22. This prevents the molten injected material 36 from leaking out of the injection nozzle 22. Note that the injection nozzle 22 may be forcibly cooled using an air jet or the like to form the plug 37.

[0024] In either case, since the plug 37 is formed in the injection molding step S7, there is no need to perform the plug forming step S1 in the next molding cycle. When the molds 27 and 28 are opened, a molded product 40 is obtained, as shown in FIG. 2G. The injection molding step S7 is then completed. As shown in FIG. 3, the next molding cycle is repeated. That is, the process proceeds to the measurement step of step S2.

[0025] <Molding method according to the second embodiment> This embodiment can be modified in various ways. For example, the molding method can be modified. A modified molding method according to a second embodiment will be described. As shown in FIG. 4, the molding method according to the second embodiment also performs a plug molding process in step S1, followed by a weighing process in step S2. The processing after the weighing process is different from that of the first embodiment. That is, in the molding method according to the second embodiment, a preheating process is performed in step S10. In the preheating process, the injection nozzle 22 is first separated from the upper mold 28. While the injection nozzle 22 is separated from the upper mold 28, the injection nozzle 22 is heated by the injection nozzle heater 24. When the injection nozzle 22 is separated from the upper mold 28, heat is not conducted to the upper mold 28, allowing for rapid heating. However, in this preheating process, the plug 37 is heated to a degree that does not melt.

[0026] Next, the injection nozzle heating step is started in step S4. That is, the injection nozzle 22 is brought into contact with the upper mold 28. Then, the injection nozzle 22 is heated by the injection nozzle heater 24. Next, the pre-pressurizing step is started in step S3. That is, as described in the first embodiment, the screw 17 is driven by pressure control to pressurize the injection material to a specified pressure that is a predetermined pressure that is preset in the controller 4. In the first embodiment, as shown in FIG. 3, the pre-pressurizing step is started in step S3, and then the injection nozzle heating step is started in step S4. However, in the molding method according to the second embodiment, the order of steps S3 and S4 is reversed. Either step S3 or step S4 may be performed first, or they may be performed simultaneously.

[0027] In the molding method according to the second embodiment, the forward movement of the screw 17 is also monitored in step S5, and if there is no forward movement, processing continues in step S6. If forward movement is detected, the injection molding process already described is carried out in step S7. Molding is then carried out in the same manner. In the molding method according to the second embodiment, the injection nozzle 22 is preheated in the preheating step S10, thereby shortening the heating time.

[0028] <Other Variations> In this embodiment, the vertical injection molding machine 1 has been described as a metal injection molding machine. However, the molding method according to this embodiment can also be implemented with a vertical injection molding machine that uses resin as the injection material. Furthermore, the molding method according to this embodiment can also be implemented with a horizontal injection molding machine, not just the vertical injection molding machine 1. [Example]

[0029] Tin has a melting point of approximately 232°C, transitions rapidly from solid to liquid near its melting point, and has low viscosity in the liquid state. In other words, it is an injection material that tends to drip. Furthermore, the vertical injection molding machine 1 is prone to dripping because the opening of the injection nozzle 22 faces downward. Therefore, molding a molded product using tin as the injection material and the vertical injection molding machine 1 is generally difficult. Therefore, an experiment was conducted using the vertical injection molding machine 1 of this embodiment, tin as the injection material, and the molding method of this embodiment. This was to confirm that molded products could be properly molded using the molding method of this embodiment.

[0030] Experimental Method: Molding was performed using the molding method according to this embodiment shown in Figure 3. In the metering step S2, the temperatures of the heating cylinder 16 (see Figure 2A) and the injection nozzle 22 were set to 260°C and 220°C, respectively. In the pre-pressurizing step, a specified pressure of 5 MPa was adopted, and pressure control was performed by driving the screw 17 so that this pressure was applied to the injection material. Note that before the pre-pressurizing step can begin, it is necessary that a plug 37 is reliably formed in the injection nozzle 22. Therefore, to confirm that the plug 37 has been formed, the screw position of the screw 17 was monitored every 0.5 seconds, and the pre-pressurizing step was then performed after confirming that the screw 17 had not moved by 0.01 mm or more.

[0031] In the injection nozzle heating step, the injection nozzle 22 was heated to 310°C while the temperature was detected by the injection nozzle temperature sensor 26. The forward movement of the screw 17 was monitored every 0.05 seconds, and if the screw position changed by more than 0.3 mm, it was determined that the screw had advanced. In the injection molding step S7, the speed of the screw 17, i.e., the injection speed, was set to 70 mm / s, and the holding pressure was set to 10 MPa.

[0032] Test Results: The molding cycle was repeated using the molding method according to this embodiment, but no dripping occurred and no molding defects occurred. In other words, the molding method according to this embodiment was able to properly mold molded products, even though it used tin, an injection material that is difficult to mold, and a vertical injection molding machine 1.

[0033] The invention made by the inventor has been specifically described above based on the embodiments, but it goes without saying that the present invention is not limited to the above-described embodiments and various modifications are possible without departing from the spirit of the invention. The multiple examples described above can also be implemented in appropriate combinations. [Explanation of symbols]

[0034] 1 Vertical injection molding machine 2 Mold clamping device 3 Injection unit 4 Controller 7 Housing 9 Fixed board 10 Upper movable platen 12 Tie bar 14 Turntable 16 Heating cylinder 17 Screw 19 Drive mechanism 20 lifting device 22 injection nozzle 23 Heating cylinder band heater 24 Injection nozzle heater 25 Heating cylinder temperature sensor 26 Injection nozzle temperature sensor 27 Lower mold 28 Upper mold 30 Convex portion 31 Concave portion 32 sprue 34 cavity 36 Injection material 37 Plug 40 Molded products

Claims

1. a heating cylinder having an injection nozzle at its tip; a screw placed in the heating cylinder, The molding method includes a plug forming step of forming a plug in the injection nozzle to close the tip of the injection nozzle; a pre-pressurizing step of driving the screw under pressure control to pressurize the injection material to a specified pressure and monitoring whether the screw is moving forward; an injection nozzle heating step of heating the injection nozzle while the injection nozzle is in contact with the mold, The molding method comprises carrying out the preliminary pressurization step and the injection nozzle heating step in parallel, and when forward movement of the screw is detected, switching to an injection operation in which the screw is driven by position control to mold a molded product.

2. 2. The molding method according to claim 1, wherein the specified pressure is a pressure such that the advancement of the screw is prevented when the plug is present and the screw advances when the plug melts.

3. 3. The molding method according to claim 1, wherein the injection material is a non-ferrous metal.

4. 4. The molding method according to claim 3, wherein the non-ferrous metal is tin.

5. 5. The molding method according to claim 1, wherein the injection molding machine is a vertical injection molding machine.

6. 6. The molding method according to claim 1, wherein the forward movement of the screw is detected by determining whether the screw position has changed beyond a specified length.

7. 7. The molding method according to claim 1, wherein the injection nozzle heating step measures the temperature of the injection nozzle and controls it to a target temperature.

8. the molding method includes a preheating step carried out prior to the injection nozzle heating step, the preheating step is a step of heating the injection nozzle while separating the injection nozzle from the mold, 8. The molding method according to claim 1, wherein the preheating step is completed before the plug melts, and the injection nozzle is brought into contact with the mold, and the process proceeds to the injection nozzle heating step.

9. a mold clamping device that clamps the mold; an injection device that injects an injection material; a controller; The injection device includes a heating cylinder having an injection nozzle at its tip; a screw contained in the heating cylinder, The controller is provided with a preliminary pressurization control means and an injection nozzle heating control means, the pre-pressurization control means is a control means that, when a plug is formed in the injection nozzle and the tip of the injection nozzle is closed, drives the screw by pressure control to pressurize the injection material to a specified pressure, and monitors whether the screw is moving forward or not; the injection nozzle heating control means is a control means for heating the injection nozzle while the injection nozzle is in contact with a mold, the controller operates the pre-pressurization control means and the injection nozzle heating control means in parallel, and when forward movement of the screw is detected, the controller switches to an injection operation in which the screw is driven by position control.

10. 10. The injection molding machine according to claim 9, wherein the specified pressure is a pressure such that the advancement of the screw is prevented when the plug is present and the screw advances when the plug is melted.

11. 11. The injection molding machine according to claim 9 or 10, wherein the injection material is a non-ferrous metal.

12. 12. The injection molding machine of claim 11, wherein the non-ferrous metal is tin.

13. The injection molding machine according to any one of claims 9 to 12, wherein the injection molding machine is a vertical injection molding machine.

14. 14. The injection molding machine according to claim 9, wherein the forward movement of the screw is detected based on whether or not the screw position has changed beyond a specified length.

15. 15. The injection molding machine according to claim 9, wherein the injection nozzle heating control means measures the temperature of the injection nozzle and controls it to a target temperature.

16. the controller includes a preheating control means that is executed prior to the injection nozzle heating control means, the preheating control means is a control means for heating the injection nozzle while separating the injection nozzle from the mold, 16. The injection molding machine according to claim 9, wherein the preheating control means is completed before the plug melts, the injection nozzle is brought into contact with the mold, and the injection nozzle heating control means is started.

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