Injection molding machine and injection molding method

Abstract

To provide a screw-in plunger type injection molding machine that adjusts a flow rate and a pressure of a resin while metering a resin material.SOLUTION: An injection molding machine includes: a cylindrical barrel having a heater on its outer periphery and storing a molten resin inside; a cylindrical plunger including a heater on its outer periphery and a screw that moves back and forth inside the barrel to send the molten resin to the barrel, melting the resin material inside and injecting the molten resin stored inside the barrel by moving back and forth inside the barrel; a mechanism for controllably moving the plunger forward and backward relative to the barrel; and a mechanism for controllably moving the screw forward and backward relative to the plunger.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an injection molding machine and an injection molding method.

Background Art

[0002] In order to plasticize and inject molten resin at an appropriate pressure, the pressure in the plunger is monitored. The electric injection device of Patent Document 1 uses an electric motor 54 as a drive source to move the plunger forward and backward, supplies a resin material into the injection chamber, and moves the plunger backward while applying back pressure to the resin material with the plunger, thereby filling and metering the injection material into the injection chamber. A pressure sensor is provided at the tip of the plunger in a state where it moves backward integrally with the plunger, and the controller controls the driving torque of the electric motor in the backward direction of the plunger so that the detected pressure by the pressure sensor becomes an appropriate set back pressure.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the injection molding machine of the above document is not a device using a screw plunger type injection molding machine. Further, the injection molding machine of the above document is not a device for adjusting pressure during metering. Therefore, an object of the present disclosure is to provide a screw plunger type injection molding machine that adjusts the flow rate and pressure of resin during metering of the resin material.

Means for Solving the Problems

[0005] The injection molding machine of the present disclosure is a cylindrical barrel having a heater on the outer periphery and storing molten resin inside, A cylindrical plunger comprises a heater on its outer circumference and a screw that moves back and forth inside to send the molten resin to the barrel, which melts the resin material inside and moves back and forth inside the barrel to inject the molten resin stored inside the barrel, A mechanism for controlling the forward and backward movement of the plunger relative to the barrel, The injection molding machine comprises a mechanism for controllably moving the screw back and forth relative to the plunger.

[0006] The above configuration provides a screw-in plunger type injection molding machine that adjusts the flow rate and pressure of the resin material during metering.

[0007] The injection molding machine of this disclosure is The mechanism that controls the forward and backward movement of the screw relative to the plunger is characterized in that it is a motor.

[0008] With the above configuration, it is possible to control the mechanism that moves the screw back and forth relative to the plunger.

[0009] The injection molding machine of this disclosure is The mechanism for controllably moving the screw forward and backward relative to the plunger is characterized by being a hydraulic cylinder with a braking mechanism.

[0010] With the above configuration, it is possible to control the mechanism that moves the screw back and forth relative to the plunger.

[0011] The injection molding machine of this disclosure is The mechanism for controllably moving the screw back and forth relative to the plunger is characterized by being a screw length variable cylinder.

[0012] With the above configuration, it is possible to control the mechanism that moves the screw back and forth relative to the plunger.

[0013] The injection molding method of this disclosure is A cylindrical barrel with a heater on its outer circumference and a container for storing molten resin inside, A cylindrical plunger comprises a heater on its outer circumference and a screw that moves back and forth inside to send the molten resin to the barrel, which melts the resin material inside and moves back and forth inside the barrel to inject the molten resin stored inside the barrel, A mechanism for controlling the forward and backward movement of the plunger relative to the barrel, A method for injection molding a resin material using an injection molding machine equipped with, This injection molding method involves adjusting the flow rate and pressure of the molten resin passing through the tip of the screw by adjusting the opening of the screw check while measuring the resin material.

[0014] The above configuration provides a method for adjusting the flow rate and pressure of resin material during metering in a screw-in plunger type injection molding machine. [Effects of the Invention]

[0015] This disclosure provides a screw-in plunger type injection molding machine that adjusts the flow rate and pressure of resin material during metering. [Brief explanation of the drawing]

[0016] [Figure 1] This diagram shows a schematic of an injection molding apparatus according to an embodiment, and a schematic diagram showing the opening degree of the screw check. [Figure 2] This is a schematic diagram of three types of screw check mechanisms according to the embodiment. [Modes for carrying out the invention]

[0017] Embodiment Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the invention according to the claims is not limited to the following embodiments. Also, not all of the configurations described in the embodiments are essential as means for solving the problems. For the sake of clarity of explanation, the following description and drawings have been appropriately omitted and simplified. In each drawing, the same reference numerals are assigned to the same elements, and duplicate explanations are omitted as necessary.

[0018] (Description of an injection molding apparatus according to an embodiment) FIG. 1 is a schematic view of an injection molding apparatus according to an embodiment and a schematic view showing the opening degree of a screw check. FIG. 2 is a schematic view of three types of screw check mechanisms according to an embodiment. The injection molding apparatus according to the embodiment will be described while referring to FIGS. 1 and 2. The injection molding apparatus according to the embodiment is an injection molding apparatus that injects molten resin into a mold.

[0019] As shown in FIG. 1, the injection molding machine 100 includes a barrel 101, a plunger 104, a screw 106, a hopper 108, a screw check mechanism 110, and a screw rotation motor 111.

[0020] The barrel 101 has a cylindrical shape. A heater 102 is provided on the outer circumference of the cylindrical shape of the barrel 101. Molten resin 103 is stored inside the cylindrical shape of the barrel 101. Due to the heating of the heater 102, the molten resin 103 maintains a molten state. Inside the barrel 101, a plunger 104 having an outer diameter along the inner circumference of the cylindrical shape of the barrel 101 is disposed. The molten resin 103 stored inside the barrel 101 is injected to the outside by the forward and backward movement of the plunger 104 with respect to the barrel 101. Therefore, a mechanism 109 for advancing and retreating the plunger with respect to the barrel controllably is installed. Controllable means that not only the forward and backward movement can be controlled but also it is possible to stop and hold. The mechanism 109 for advancing and retreating the plunger with respect to the barrel uses, for example, a motor mechanism.

[0021] The plunger 104 has a cylindrical shape. A heater 105 is provided on the outer circumference of the cylindrical plunger 104. Inside the plunger 104, there is resin material 107 supplied from the hopper 108 and molten resin 103 formed by melting the resin material 107. As the resin material 107 moves from the supply source in the hopper 108 to the tip of the plunger 104, it is heated and melted using the heater 105 to become molten resin 103. Inside the plunger 104, a screw 106 is positioned to rotate and apply shear force to the resin material 107 while advancing and melting it.

[0022] The screw 106 is rotated by a screw rotation motor 111 and a pulley or reduction gear.

[0023] The purpose of controlling the molten resin pressure in the barrel during the metering operation is to indirectly control the molten resin pressure flowing around the screw in the plunger, thereby appropriately controlling the shear heat generated in the molten resin due to the rotation of the screw.

[0024] The molten resin pressure inside the barrel may be changed for purposes other than controlling the plasticizing back pressure, such as degassing or adding fiber material. However, changing the molten resin pressure during the metering operation would affect the plasticizing back pressure, making it impossible to change the molten resin pressure during that time. Therefore, if the molten resin pressure inside the barrel needs to be changed for purposes other than controlling the plasticizing back pressure, this operation must be performed outside of the metering operation, leading to increased cycle time and decreased productivity.

[0025] Due to its structure, a small amount of resin leaks from the plunger sliding part, and the amount of leakage is proportional to the molten resin pressure inside the barrel and time. During the metering operation, increasing the molten resin pressure inside the barrel in order to increase the molten resin pressure inside the plunger increases the amount of resin leakage from the barrel and the plunger sliding part.

[0026] Therefore, the screw-in plunger type injection molding machine of this disclosure is equipped with a screw check mechanism 110, which is a mechanism that controls the forward and backward movement of the screw relative to the plunger.

[0027] As shown in the lower part of Figure 1, the screw check mechanism 110 can control the screw relative to the tip of the plunger to fully closed, intermediate, and fully open positions. In other words, the screw check mechanism 110 can control the forward, backward, and stop movements within the plunger 104.

[0028] By fully closing the screw check mechanism 110, the flow rate can be set to zero and the resin pressure to maximum. By fully opening the screw check mechanism 110, the flow rate can be set to maximum and the resin pressure to minimum. By taking an intermediate position between fully closed and fully open, the opening degree of the screw check can be adjusted during the metering operation to provide feedback control of the flow rate and resin pressure of the resin passing through the screw tip. Furthermore, an injection molding method is provided in which the flow rate and pressure of the molten resin passing through the screw tip are adjusted by the opening degree of the screw check during the metering of the resin material.

[0029] As shown in Figure 2(a), the screw check mechanism 110 can use a motor 201 that moves the screw back and forth relative to the plunger 104. The screw check mechanism 110 can be implemented using a motor 201, a ball screw, or a similar actuator that moves the screw back and forth.

[0030] As shown in Figure 2(b), the screw check mechanism 110 can use a hydraulic cylinder 202 with a brake mechanism.

[0031] As shown in Figure 2(c), the screw check mechanism 110 can use a screw length variable cylinder 203.

[0032] During the weighing operation, the resin material 107 introduced from the hopper 108 into the plunger 104 is gradually melted and propelled forward by the screw 106. During this time, the resin material 107 is heated and melted not only by heat transfer from the heater 105 installed inside or around the plunger wall, but also by shear heat generated by friction between the rotating screw 106 and the resin material 107.

[0033] For example, if the screw rotation speed is increased to shorten the weighing operation time, the amount of heat received by the resin material 107 may be insufficient, resulting in a defect called unmelted resin. To prevent this, one method is to increase the shear heat generated between the screw 106 and the resin material 107 by increasing the molten resin pressure inside the plunger 104.

[0034] There is a correlation between the pressure, viscosity, and shear heat generation of molten resin. Increasing the molten resin pressure increases both the viscosity and the shear heat generation of the screw and resin material. Therefore, intentionally increasing the molten resin pressure is often used to prevent unmelted resin.

[0035] On the other hand, the feed rate of the molten resin, mainly provided by the screw rotation, decreases due to the conservation of energy, as it is converted into thermal energy through shearing. Therefore, excessive pressure not only increases the metering time but also causes new quality defects, such as decomposition of the resin due to excessive heat input to the molten resin.

[0036] By appropriately controlling the molten resin pressure within the plunger 104, it is possible to achieve both melt quality and a smooth molding cycle.

[0037] (Description of pressure control according to the embodiment) During the metering operation, the molten resin 103 inside the plunger 104 passes through a hole at the tip of the plunger 104, which becomes the screw check mechanism 110, and is stored inside the barrel 101. At this time, the flow path width of the screw check is smaller than that of the others, and pressure loss occurs as it passes through.

[0038] If P1 is the molten resin pressure in barrel 101, P2 is the molten resin pressure in plunger 104, and P3 is the pressure loss in the screw check section, then the following relationship must hold for the molten resin 103 in plunger 104 to flow into barrel 101. P1+P3 <P2

[0039] In related screw-in plunger type injection molding machines, since P3 is constant, P2 is controlled by controlling P1.

[0040] The technology disclosed herein allows control of P2 by controlling P3. According to the Darcy-Weisbach equation, the pressure loss in a pipe is inversely correlated with the flow path cross-sectional area. Therefore, by narrowing the opening of the screw check and restricting the flow path through which the molten resin 103 can pass, P3 increases. Conversely, by widening the opening of the screw check and widening the flow path through which the molten resin 103 can pass, P3 decreases.

[0041] Therefore, by controlling P3, the value of P2 can be freely changed even during the weighing operation.

[0042] It should be noted that the present invention is not limited to the embodiments described above, and can be modified as appropriate without departing from the spirit of the invention. [Explanation of symbols]

[0043] 100 Injection molding machine, 101 Barrel, 102 Heater, 103 Molten resin, 104 Plunger, 105 Heater, 106 Screw, 107 Resin material, 108 Hopper, 109 Mechanism for moving the plunger back and forth relative to the barrel, 110 Screw check mechanism, 111 Motor for screw rotation, 201 Motor for moving the screw back and forth, 202 Hydraulic cylinder with brake mechanism, 203 Screw length variable cylinder

Claims

1. A cylindrical barrel with a heater on its outer circumference and a container for storing molten resin inside, A cylindrical plunger comprises a heater on its outer circumference and a screw that moves back and forth inside to send the molten resin to the barrel, which melts the resin material inside and moves back and forth inside the barrel to inject the molten resin stored inside the barrel, A mechanism for controlling the forward and backward movement of the plunger relative to the barrel, It comprises a screw check mechanism that controls the forward and backward movement of the screw relative to the plunger, During the weighing of the resin material, the flow rate and pressure of the molten resin passing through the tip of the screw are adjusted by the opening of the screw check. An injection molding machine that increases the molten resin pressure in the plunger when increasing the screw rotation speed to increase the feed rate in order to shorten the time required for the metering operation of the aforementioned resin material.

2. The injection molding machine according to claim 1, wherein the screw check mechanism is a motor.

3. The injection molding machine according to claim 1, wherein the screw check mechanism is a hydraulic cylinder with a brake mechanism.

4. A cylindrical barrel with a heater on its outer circumference and a container for storing molten resin inside, A cylindrical plunger comprises a heater on its outer circumference and a screw that moves back and forth inside to send the molten resin to the barrel, which melts the resin material inside and moves back and forth inside the barrel to inject the molten resin stored inside the barrel, A mechanism for controlling the forward and backward movement of the plunger relative to the barrel, A method for injection molding a resin material using an injection molding machine equipped with, During the weighing of the resin material, the flow rate and pressure of the molten resin passing through the tip of the screw are adjusted by the opening of the screw check. An injection molding method in which, when increasing the screw rotation speed to increase the feed rate in order to shorten the time of the metering operation of the resin material, the molten resin pressure in the plunger is increased.

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