Injection molding machine

Abstract

To provide an injection molding machine that can perform injection molding with a thin mold. [Solution] The injection molding machine comprises a mold clamping device that opens and closes the mold and clamps the mold, an injection device that injects molten resin, and a control device. The mold has a cavity which is a space corresponding to the shape of the molded product, a cold runner through which the molten resin supplied to the cavity passes, and a nozzle passage which allows the tip of the nozzle that injects the molten resin to reach the cold runner. The injection device comprises a nozzle that injects molten resin, a nozzle touch motor that moves the nozzle back and forth between a separated position away from the mold and a nozzle touch position where the tip reaches the cold runner, and a position sensor that detects the position of the nozzle tip. The control device controls the nozzle touch motor based on the position of the nozzle tip detected by the position sensor so that the nozzle moving forward from the separated position passes through the nozzle passage and stops at the nozzle touch position.

Description

Technical Field

[0001] The present invention relates to an injection molding machine that injects molten resin into a mold to form a molded product.

Background Art

[0002] Conventionally, an injection molding machine including a mold clamping device that opens and closes a mold and clamps it, and an injection device that injects molten resin into a cavity of the clamped mold is known. Among such injection molding machines, there is one that moves a nozzle for injecting molten resin back and forth between a separated position separated from the mold and a nozzle touch position touching the mold (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] [[ID=�8]] However, in a conventional injection molding machine, as shown in FIG. 6(B), when the nozzle abuts against the movable mold and stops moving (the pulse signal from the rotary encoder stops being output continuously for a predetermined time), the nozzle touch motor is stopped.

[0005] Therefore, since the nozzle is strongly pressed against the mold, it is common to provide a sprue bush in the mold to receive the load applied from the nozzle. As a result, the thickness of the mold increases, and the cold runner, which is the passage of the molten resin reaching the cavity, also becomes longer. Consequently, there is a problem that the amount of resin to be discarded increases.

[0006] This invention was made to solve the problems of the prior art, and its objective is to provide an injection molding machine that can perform injection molding with a thinner mold. [Means for solving the problem]

[0007] To solve the above problems, the present invention provides an injection molding machine comprising a mold clamping device for opening and closing a mold and clamping the mold, an injection device for injecting molten resin, and a control device for controlling the operation of the mold clamping device and the injection device, wherein the mold has a cavity which is a space corresponding to the shape of the molded product, a cold runner through which the molten resin supplied to the cavity passes, and a nozzle passage which allows the tip of the nozzle for injecting the molten resin to reach the cold runner, the injection device comprises the nozzle for injecting the molten resin, a nozzle touch motor which moves the nozzle back and forth between a separated position away from the mold and a nozzle touch position where the tip reaches the cold runner, and a position sensor which detects the position of the tip of the nozzle, and the control device controls the nozzle touch motor based on the position of the tip of the nozzle detected by the position sensor such that the nozzle moving forward from the separated position passes through the nozzle passage and stops at the nozzle touch position. [Effects of the Invention]

[0008] According to the present invention, an injection molding machine capable of performing injection molding with a reduced mold thickness can be obtained. [Brief explanation of the drawing]

[0009] [Figure 1] This is a front view of the injection molding machine according to this embodiment. [Figure 2] This is a hardware block diagram of an injection molding machine. [Figure 3] This is a flowchart of the injection control process. [Figure 4] This figure shows the state of the mold during steps S11 to S16. [Figure 5]This figure shows the state of the mold during steps S17 to S21. [Figure 6] This figure shows the nozzle's forward speed during steps S12 to S16. [Modes for carrying out the invention]

[0010] The injection molding machine 10 according to the present invention will be described below with reference to the drawings. The embodiments of the present invention described below are merely examples of how the present invention can be implemented, and do not limit the scope of the present invention to the scope described in the embodiments. Therefore, the present invention can be implemented by making various modifications to the embodiments.

[0011] Figure 1 is a front view of the injection molding machine 10 according to this embodiment. Figure 2 is a hardware block diagram of the injection molding machine 10. The injection molding machine 10 is a device that injects molten resin into a mold 21 to form a molded product M. The injection molding machine 10 according to this embodiment is a so-called "vertical type". As shown in Figures 1 and 2, the injection molding machine 10 mainly comprises a mold clamping device 20, an injection device 30, a display input device 40, and a control device 50.

[0012] The mold clamping device 20 opens and closes the mold 21 and clamps it. Specifically, the mold clamping device 20 mainly comprises a fixed die plate 23 that supports the fixed side mold 22, a movable die plate 25 that supports the movable side mold 24 directly above the fixed side mold 22, and a mold opening / closing motor 61 that moves the movable die plate 25 in the vertical direction.

[0013] The mold opening / closing motor 61 is a servo motor that moves the movable die plate 25 in the vertical direction. The driving force of the mold opening / closing motor 61 is transmitted to the movable die plate 25, for example, through a toggle link mechanism (not shown). As shown in Figure 1, when the movable die plate 25 rises, the fixed mold 22 and the movable mold 24 separate. On the other hand, when the movable die plate 25 lowers, the fixed mold 22 and the movable mold 24 come into contact, forming a cavity 21a inside the mold 21. Then, when further downward pressure is applied to the movable die plate 25, the fixed mold 22 and the movable mold 24 are clamped together.

[0014] As shown in Figure 4(C), a cavity 21a is formed inside the clamped mold 21. The cavity 21a is a space corresponding to the shape of the molded product M. In addition, a cold runner 21b and a nozzle passage 21c are formed in the movable mold 24. Note that the cold runner 21b and nozzle passage 21c are not limited to being formed in the movable mold 24, but may also be formed in the fixed mold 22.

[0015] The cold runner 21b is a passage through which the molten resin supplied to the cavity 21a passes. The nozzle passage 21c is a passage that allows the tip of the nozzle 36, which injects the molten resin, to reach the cold runner 21b. When the fixed mold 22 and the movable mold 24 are clamped together, the end of the cold runner 21b communicates with the cavity 21a. The nozzle passage 21c extends downward from the upper surface of the fixed mold 22. The lower end of the nozzle passage 21c also communicates with the cold runner 21b. As a result, the molten resin injected from the nozzle 36 that enters the nozzle passage 21c passes through the cold runner 21b and fills the cavity 21a.

[0016] The mold clamping device 20 also includes an ejector pin 26 (see FIGS. 4 and 5) and an ejector motor 62 (see FIG. 2). The ejector pin 26 is supported by the fixed mold 22 so as to be able to project and retract with respect to the cavity 21a. The ejector motor 62 is a servo motor that causes the ejector pin 26 to project and retract with respect to the cavity 21a. As shown in FIG. 5(A), when the cavity 21a is filled with molten resin, the ejector pin 26 is immersed in the fixed mold 22. Also, as shown in FIG. 5(C), after the molded product M is molded in the cavity 21a, when the ejector pin 26 projects into the cavity 21a, the molded product M is taken out of the cavity 21a.

[0017] The injection device 30 plasticizes, measures, and injects the resin supplied from a hopper (not shown). The injection device 30 according to the present embodiment is disposed above the mold clamping device 20. The injection device 30 according to the present embodiment mainly includes a heating cylinder 31, a screw 32, a nozzle touch motor 63, a metering motor 64, and an injection motor 65.

[0018] The heating cylinder 31 is a cylindrical member extending in the vertical direction. A nozzle hole 36a of a nozzle 36 for injecting molten resin is formed at the tip (lower end) of the heating cylinder 31, and a supply port (not shown) for receiving the supply of resin from the hopper is formed on the base end (upper end) side. And a linear internal space from the supply port to the nozzle 36 is formed inside the heating cylinder 31. Also, a band heater (not shown) for heating the heating cylinder 31 is attached to the outer peripheral surface of the heating cylinder 31.

[0019] The nozzle touch motor 63 is a servo motor that moves (advances and retreats) the injection device 30 (nozzle 36) in the vertical direction. The injection device 30 moves in the vertical direction between a separated position (FIG. 4(A)) and a nozzle touch position (FIG. 4(C)) when the driving force of the nozzle touch motor 63 is transmitted through a driving force transmission mechanism (not shown). In this specification, the movement of the nozzle 36 in the direction approaching the mold 21 (downward) is expressed as "advance", and the movement of the nozzle 36 in the direction away from the mold 21 (upward) is expressed as "retreat".

[0020] The separation position is the position where the tip of the nozzle 36 is separated from the mold 21. The nozzle touch position is the position where the tip of the nozzle 36 reaches the cold runner 21b through the nozzle passage 21c. That is, the separation position is a position above the nozzle touch position (a position away from the mold 21). Also, a deceleration start position is set between the separation position and the nozzle touch position.

[0021] The separation position is a predetermined position. The nozzle touch position is a position input by the operator through the display input device 40 according to the dimensions of the mold 21 (more specifically, the movable mold 24). The deceleration start position may have a fixed relative position with the nozzle touch position or may be input by the operator through the display input device 40.

[0022] A rotary encoder 66 is provided for the nozzle touch motor 63. The rotary encoder 66 outputs a pulse signal to the control device 50 as the nozzle touch motor 63 rotates. The control device 50 identifies the position of the tip of the nozzle 36 by integrating the pulse signal output from the rotary encoder 66. That is, the rotary encoder 66 is an example of a position sensor that detects the position of the tip of the nozzle 36. However, the specific example of the position sensor is not limited to the rotary encoder 66.

[0023] The control device 50 may, for example, add the pulse signal output from the rotary encoder 66 to the integrated value when rotating the nozzle touch motor 63 in a direction to bring the nozzle 36 closer to the nozzle touch position. On the other hand, the control device 50 may subtract the pulse signal output from the rotary encoder 66 from the integrated value when rotating the nozzle touch motor 63 in a direction to bring the nozzle 36 closer to the separation position.

[0024] The screw 32 is a long, rod-shaped member with a helical groove formed on its outer circumference. The screw 32 is housed in the internal space of the heating cylinder 31 in a state where it can move forward and backward and rotate. The metering motor 64 is a servo motor that rotates the screw 32 within the heating cylinder 31. The injection motor 65 is a servo motor that moves the screw 32 forward and backward within the heating cylinder 31. The injection device 30 performs metering and injection operations by moving the screw 32 forward and backward or rotating it within the heating cylinder 31.

[0025] The metering operation involves rotating the screw 32 to meter a predetermined amount of molten resin into the tip side (nozzle 36 side) of the heating cylinder 31. At this time, the resin supplied to the heating cylinder 31 is plasticized by the frictional heat and shear heat generated between the heating cylinder 31 and the screw 32, as well as the heat generated by the band heater. The molten resin also moves along the helical groove of the screw 32 towards the tip side of the heating cylinder 31 and accumulates at the tip side of the heating cylinder 31. As a result, the screw 32 retracts while rotating inside the heating cylinder 31.

[0026] The injection operation involves advancing the screw 32 to inject the molten resin, which has been metered at the tip of the heating cylinder 31, through the nozzle 36 at the nozzle touch position. As a result, the molten resin injected from the nozzle 36 fills the cavity 21a of the mold 21.

[0027] The display input device 40 is a user interface that includes a display (display device) for displaying various information to be notified to the operator, and buttons, switches, dials (input devices) for receiving operations from the operator. The display input device 40 may also include a touch panel (input device) superimposed on the display. For example, the display input device 40 receives operations from the operator to input the nozzle touch position and operations from the operator to instruct the molding of the molded product M, and outputs operation signals corresponding to the received operations to the control device 50.

[0028] As shown in Figure 2, the control device 50 comprises a CPU (Central Processing Unit) 51 and memory 52. ​​The memory 52 is composed of, for example, ROM (Read Only Memory), RAM (Random Access Memory), HDD (Hard Disk Drive), or a combination thereof. The control device 50 performs the processing described later by having the CPU 51 read and execute program code stored in the ROM or HDD. RAM is used as a work area when the CPU 51 executes the program.

[0029] However, the specific configuration of the control device 50 is not limited to this and may be implemented using hardware such as an ASIC (Application Specific Integrated Circuit) or FPGA (Field-Programmable Gate Array).

[0030] The control device 50 controls the operation of the entire injection molding machine 10. The control device 50 controls each motor 61 to 65 based on the operation signals output from the display input device 40 and the pulse signals output from the rotary encoder 66. Although rotary encoders are also installed on motors 61, 62, 64, and 65 other than the nozzle touch motor 63, their illustration and description are omitted in this specification.

[0031] [Injection control processing] Figure 3 is a flowchart of the injection control process. Figure 4 shows the state of the mold 21 at S11 to S16 in Figure 3. Figure 5 shows the state of the mold 21 at S17 to S21 in Figure 3. Figure 6 shows the forward speed of the nozzle 36 at S12 to S16 in Figure 3. The injection control process is the process of molding a molded product M by injecting molten resin into the cavity 21a of the mold 21. The control device 50 executes the injection control process shown in Figure 3 in response to the input of a molding instruction for a molded product M being input to the display input device 40.

[0032] At the start of the injection control process, as shown in Figure 4(A), the mold 21 is open, there is no molded product M in the cavity 21a, the ejector pin 26 is retracted into the fixed mold 22, the nozzle 36 is in a separated position, and a predetermined amount of molten resin is metered to the tip side of the heating cylinder 31.

[0033] First, the control device 50 closes and clamps the mold 21 by rotating the mold opening / closing motor 61 (S11). As a result, the cavity 21a and the cold runner 21b are connected, as shown in Figure 4(B).

[0034] Next, the control device 60 controls the nozzle touch motor 63 (S12-S15) so that the nozzle 36, moving forward from the separated position, passes through the nozzle passage 21c and stops at the nozzle touch position, based on the position of the tip of the nozzle 36 detected by the pulse signal of the rotary encoder 66. As a result, the tip of the nozzle 36 passes through the nozzle passage 21c and reaches the cold runner 21b, as shown in Figure 4(C).

[0035] As shown in Figure 6(A), the section between the separation position and the nozzle touch position can be divided into an acceleration section, a constant speed section, and a deceleration section. The acceleration section is the section in which the injection device 30 moves forward while accelerating. The constant speed section is the section in which the injection device 30 moves forward at a constant speed. The deceleration section is the section in which the injection device 30 moves forward while decelerating. The acceleration section and the constant speed section are the sections on the separation position side of the deceleration start position. Also, the acceleration section is the section on the separation position side of the constant speed section. On the other hand, the deceleration section is the section on the nozzle touch position side of the deceleration start position.

[0036] At the start of step S12, the tip of the nozzle 36 is stopped at the separated position (forward speed = 0). The control device 60 then controls the nozzle touch motor 63 so that the injection device 30 (nozzle 36) accelerates to a predetermined forward speed by the time the tip of the nozzle 36 reaches the deceleration start position (S12). For example, as shown in Figure 6(A), the control device 60 accelerates the nozzle 36 to a predetermined forward speed in the acceleration section and moves the nozzle 36 forward at a constant speed in the constant speed section. As another example, the constant speed section may be omitted, and the control device may be controlled so that the nozzle 36 reaches a predetermined forward speed at the timing when the tip of the nozzle 36 reaches the deceleration start position. Furthermore, although Figure 6(A) illustrates an example of acceleration at a constant acceleration, the progression of the forward speed is not limited to this.

[0037] Next, when the tip of the nozzle 36 reaches the deceleration start position (S13: Yes), the control device 60 decelerates the forward speed of the injection device 30 (nozzle 36) in the deceleration section (S14) so ​​that the tip of the nozzle 36 stops at the nozzle touch position. The progression of the forward speed from the deceleration start position to the nozzle touch position is not particularly limited, but for example, it may be a constant deceleration as shown by the solid line in Figure 6(A), or the deceleration may be gradually reduced as shown by the dashed line in Figure 6(A). As a result, the load that the nozzle 36, which stops at the nozzle touch position, places on the mold 21 becomes an extremely small value.

[0038] Next, after the tip of the nozzle 36 stops at the nozzle touch position (S15: Yes), the control device 60 further rotates the nozzle touch motor 63 by a predetermined number of rotations to push the nozzle 36 into the movable mold 24 (S16). The predetermined number of rotations is the number of rotations required to eliminate play in the drive force transmission mechanism (for example, belt slack, play between gears, etc.). As a result, although the load that the nozzle 36 places on the mold 21 is greater than before step S16 is executed, it is still sufficiently small compared to the conventional method.

[0039] Next, the control device 50 rotates the injection motor 65 to advance the screw 32 within the heating cylinder 31 (S17). As a result, the molten resin metered in the area in front of the screw 32 within the heating cylinder 31 is injected from the nozzle 36 through the cold runner 21b into the cavity 21a. Consequently, as shown in Figure 5(A), the cavity 21a and the cold runner 21b are filled with molten resin.

[0040] Next, the control device 50 rotates the screw 32 inside the heating cylinder 31 by rotating the metering motor 64 (S18). As a result, the resin supplied to the heating cylinder 31 through the hopper is plasticized, and the molten resin to be injected next is metered into the space in front of the screw 32 inside the heating cylinder 31. The screw 32 also retracts inside the heating cylinder 31.

[0041] Next, the control device 50 waits to execute the process from step S20 onward until the cooling time has elapsed (S19: No) after the molten resin has been injected into the cavity 21a. The cooling time is the time it takes for the molten resin in the cavity 21a and the cold runner 21b to solidify, and is input, for example, through the display input device 40. As a result, the cavity 21a and the cold runner 21b cool and solidify. Meanwhile, the molten resin in the nozzle 36 is maintained in a molten state by the heat of the band heater of the heating cylinder 31.

[0042] Next, after the cooling time has elapsed (S19: Yes), the control device 50 rotates the nozzle touch motor 63 to retract the injection device 30 (nozzle 36) to the separated position, and rotates the mold opening / closing motor 61 to open the mold 21 (S20). As a result, the injection device 30 and the movable mold 24 rise, as shown in Figure 5(B).

[0043] Next, the control device 50 rotates the ejector motor 62 to make the ejector pin 26 protrude (S21). As a result, as shown in Figure 5(C), the molded product M and the resin solidified in the cold runner 21b (hereinafter referred to as "runner resin R") are separated from the mold 21. Note that although the mold 21 is shown in a simplified manner in Figures 4 and 5, in reality the runner resin R in the cold runner 21b is configured in a shape that allows it to be separated from the mold 21. Furthermore, the control device 60 causes the robot arm to take out the molded product M that has been separated from the mold 21.

[0044] [Effects of the Embodiment] According to the above embodiment, since the tip of the nozzle 36 directly reaches the cold runner 21b, the sprue bush can be omitted. Furthermore, since the resin inside the nozzle 36 that has entered the nozzle passage 21c is continuously heated by the band heater that heats the heating cylinder 31, there is no need to provide a heater for heating the resin in the mold 21. As a result, it becomes possible to make the mold 21 (especially the movable side mold 24) thinner.

[0045] Furthermore, according to the above embodiment, the nozzle touch motor 63 is actively controlled so that the tip of the nozzle 36 stops at the nozzle touch position. This makes it possible to significantly reduce the load applied from the nozzle 36 to the mold 21 compared to the conventional method in which the nozzle touch motor 63 is kept rotating until the tip of the nozzle 36 contacts the mold. As a result, injection molding can be achieved even with a thin mold 21.

[0046] Furthermore, according to the above embodiment, a deceleration start position is set between the separation position and the nozzle touch position to gradually reduce the rotational speed of the nozzle touch motor 63. This makes it possible to precisely stop the tip of the nozzle 36 at the nozzle touch position. As a result, the load applied from the nozzle 36 to the mold 21 can be minimized, making the mold 21 thinner.

[0047] Furthermore, according to the above embodiment, after the tip of the nozzle 36 stops at the nozzle touch position, the nozzle touch motor 63 is rotated further by the number of rotations necessary to eliminate the play in the drive force transmission mechanism, thereby enabling precise positioning of the tip of the nozzle 36. This stabilizes the quality of the molded product M.

[0048] Furthermore, according to the above embodiment, as the mold 21 becomes thinner, the cold runner 21b also becomes shorter. As a result, the volume of the runner resin R decreases, which reduces the cooling time and shortens the cycle time of the injection molding machine 10, as well as reducing the amount of waste resin (i.e., runner resin R).

[0049] Furthermore, according to the above embodiment, since the nozzle touch position is input to the operator via the display input device 40, the tip of the nozzle 36 can be stopped at an appropriate position even when the mold 21 is replaced. However, the control device 50 is not limited to acquiring the nozzle touch position via the display input device 40, and may also acquire the nozzle touch position corresponding to the mold 21 from a server (not shown) or the mold 21 itself.

[0050] [Differentiation] Furthermore, the injection molding machine 10 to which the present invention can be applied is not limited to the vertical type shown in Figure 1, but may also be a so-called "horizontal type" in which the clamping device 20 and the injection device 30 are arranged horizontally. [Explanation of Symbols]

[0051] 10…Injection molding machine, 20…Clamping device, 21…Mold, 21a…Cavity, 21b…Cold runner, 21c…Nozzle passage, 22…Fixed mold, 23…Fixed die plate, 24…Movable mold, 25…Movable die plate, 26…Eject pin, 30…Injection device, 31…Heating cylinder, 32…Screw, 33…Conveyor, 36…Nozzle, 36a…Nozzle hole, 40…Display input device, 50…Control device, 51…CPU, 52…Memory, 60…Control device, 61…Mold opening / closing motor, 62…Eject motor, 63…Nozzle touch motor, 64…Measuring motor, 65…Injection motor, 66…Rotary encoder

Claims

1. In an injection molding machine comprising a mold clamping device for opening and closing a mold and clamping the mold, an injection device for injecting molten resin, and a control device for controlling the operation of the mold clamping device and the injection device, The aforementioned mold includes, The cavity is a space that corresponds to the shape of the molded product, A cold runner through which the molten resin supplied to the cavity passes, A nozzle passage is formed that allows the tip of the nozzle for injecting the molten resin to reach the cold runner. The injection device is, The nozzle for injecting the molten resin, A nozzle touch motor moves the nozzle back and forth between a separated position, where it is separated from the mold, and a nozzle touch position, where its tip reaches the cold runner. The system includes a position sensor for detecting the position of the tip of the nozzle, The injection molding machine is characterized in that the control device controls the nozzle touch motor based on the position of the nozzle tip detected by the position sensor, such that the nozzle, moving forward from the separated position, passes through the nozzle passage and stops at the nozzle touch position.

2. In the injection molding machine according to claim 1, Between the aforementioned separation position and the nozzle touch position, a deceleration start position is set. The control device is characterized by reducing the forward speed of the nozzle from the deceleration start position so that the nozzle stops at the nozzle touch position.

3. In the injection molding machine according to claim 2, The control device is characterized in that, after the tip of the nozzle stops at the nozzle touch position, it further rotates the nozzle touch motor by a predetermined number of rotations.

4. In the injection molding machine according to claim 1, The device includes an input device to which the nozzle touch position is input, The control device is characterized by stopping the nozzle at the nozzle touch position when the input device is stopped.

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