Injection molding machine and injection molding method

Abstract

To provide an injection molding technology capable of suppressing occurrence of stringiness.SOLUTION: There is provided an injection molding machine, comprising: a cylinder 121 that has a nozzle 127 at a tip thereof and moves between an injection position where the nozzle 127 is connected to a cavity 12 of a mold device 10 and a standby position away from the mold device 10; a screw 123 capable of moving back and forth and rotating within the cylinder 121; and a control device 150. The control device 150 starts a movement of the cylinder 121 from the injection position to the standby position after starting a backward movement of the screw 123 or a rotation movement of the screw 123 in a direction to move the molding material to an opposite side of the nozzle.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] Conventionally, as shown in Patent Document 1, an injection molding apparatus that injects a molding material such as a thermoplastic resin from a nozzle into a mold apparatus is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the injection molding machine described in Patent Document 1, the nozzle is separated from the mold apparatus for each molding cycle. In this case, when the nozzle is separated from the mold apparatus, there is a possibility that stringing of the molding material may occur between the nozzle and the mold apparatus.

[0005] The present invention has been made in such a situation, and an exemplary object of one aspect thereof is to provide an injection molding technique capable of suppressing the occurrence of stringing.

Means for Solving the Problems

[0006] To solve the above problems, an injection molding machine according to an aspect of the present invention includes a cylinder having a nozzle at its tip, the cylinder moving between an injection position where the nozzle communicates with the cavity of the mold apparatus and a standby position where the cylinder is separated from the mold apparatus, a screw that can advance, retreat, and rotate within the cylinder, and a control device. The control device starts the movement of the cylinder from the injection position to the standby position after starting the retreat of the screw or the rotation of the screw in a direction to move the molding material toward the anti-nozzle side.

[0007] Another aspect of the present invention is an injection molding method. This method uses an injection molding machine comprising a cylinder having a nozzle at its tip and moving between an injection position where the nozzle communicates with the cavity of the mold device and a standby position spaced apart from the mold device, and a screw that can move forward and backward and rotate within the cylinder. The injection molding method includes starting the screw in a direction to move the screw backward or toward the side opposite to the nozzle of the molding material, and starting the movement of the cylinder from the injection position to the standby position after the start of the backward movement or rotation of the screw.

[0008] Any combination of the above components, or those obtained by mutually substituting the components and expressions of the present invention between methods, apparatuses, systems, etc., is also effective as an aspect of the present invention.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide an injection molding technique capable of suppressing the occurrence of wire drawing.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0011] Hereinafter, the same or equivalent components, members, and steps shown in each drawing are denoted by the same reference numerals, and redundant descriptions are omitted as appropriate. In addition, the dimensions of the members in each drawing are enlarged or reduced as appropriate for easy understanding. Also, some members that are not important in explaining the embodiments in each drawing are shown with omission.

[0012] FIG. 1 is a diagram showing the overall configuration of an injection molding machine 100 according to an embodiment. The injection molding machine 100 includes a clamping device 110 that closes, clamps, and opens a mold device, an injection device 120 that injects a molding material into the mold device, an ejector device 130 that ejects a molded product from the mold device 10, a take-out device 140 that takes out the molded product from the mold device 10, and a control device 150 that integrally controls the entire injection molding machine 100. The control device 150 can be configured by a general-purpose computer. The injection molding machine 100 is an injection molding machine that separates the nozzle of the cylinder of the injection device 120 from the mold device for each molding cycle. The injection molding machine 100 may be, for example, a rotary injection molding machine.

[0013] FIGS. 2 and 3 are cross-sectional views showing the cylinder 121 and its periphery. The cylinder 121 is in the injection position in FIG. 2 and in the standby position in FIG. 3. The mold device 10 is clamped in FIG. 2 and opened in FIG. 3.

[0014] The clamping device 110 is a vertical type in which the clamping direction is the vertical direction, and includes an upper platen 112 and a lower platen (not shown) provided at a distance below the upper platen 112. Note that the clamping device 110 may be a horizontal type in which the clamping direction is the horizontal direction.

[0015] The upper platen 112 is fixed to a frame (not shown). The lower platen is driven by a drive unit (not shown) controlled by the control device 150 and moves up and down with respect to the upper platen 112. Thereby, the mold device 10 is closed, clamped, and opened. Note that the lower platen may be fixed to the frame and the upper platen 112 may move up and down with respect to the lower platen.

[0016] The injection device 120 is of the vertical type with the axial direction of the cylinder 121 being the vertical direction, and is arranged above the upper platen 112. Note that the injection device 120 may be of the horizontal type with the axial direction of the cylinder 121 being the horizontal direction. Also, the mold clamping device 110 combined with the vertical injection device 120 may be of the vertical type or the horizontal type. Similarly, the mold clamping device 110 combined with the horizontal injection device 120 may be of the horizontal type or the vertical type.

[0017] The injection device 120 includes a cylinder 121, a screw 123, and a pressure sensor 124. The cylinder 121 includes a cylinder body 126 and a nozzle 127.

[0018] The cylinder body 126 is a cylindrical member with the axial direction being the vertical direction. A nozzle 127 is connected to the tip (lower end) of the cylinder body 126. A screw 123 is accommodated in the cylinder body 126. A solid molding material is supplied to the cylinder body 126 from a supply port (not shown). The molding material is, for example, a pellet-shaped thermoplastic resin.

[0019] The cylinder 121 is driven by a drive unit (not shown) controlled by the control device 150 to move between the injection position (the position in Fig. 1) and the standby position (the position in Fig. 2).

[0020] The injection position is the position where the molding material is injected into the mold device 10. Specifically, the injection position is the position where the nozzle 127 touches the mold device 10 through the through hole 112a provided in the upper platen 112, and the nozzle 127, and thus the cylinder 121, communicates with the cavity 12 of the mold device 10.

[0021] The standby position is a position above the injection position and where the nozzle 127 is separated from the mold device 10.

[0022] The nozzle 127 is connected to the tip (lower end) of the cylinder body 126. In this embodiment, the nozzle 127 is a shut-off nozzle and can open and close the ejection port 122a at the tip according to the control by the control device 150. The ejection port 122a is closed in FIG. 1 and open in FIG. 2.

[0023] The pressure sensor 124 detects the internal pressure of the nozzle 127 at a predetermined cycle. Each time the pressure sensor 124 detects the pressure, for example, it transmits the detected internal pressure data to the control device 150.

[0024] The screw 123 is housed inside the cylinder body 126. The screw 123 is driven by a drive unit (not shown) and can rotate inside the cylinder body 126. Further, the screw 123 is driven by another drive unit (not shown) and can move forward and backward inside the cylinder body 126, that is, it can move forward and backward. Forward movement means that the screw 123 moves toward the nozzle 127 side, that is, the lower side. Backward movement means that the screw 123 moves to the side opposite to the nozzle 127 side, that is, the anti-nozzle side, that is, the upper side.

[0025] By rotating or moving forward and backward the screw 123 inside the cylinder body 126, metering, injection (filling), and pressure holding are executed.

[0026] In metering, by rotating the screw 123 in a predetermined rotation direction (hereinafter referred to as "forward rotation"), the molding material is sent toward the nozzle side along the spiral groove of the screw 123. Along with this, the molding material is gradually melted. As the liquid molding material is sent to the tip side (nozzle 127 side) of the screw 123 and the molding material accumulates at the tip of the cylinder 121, the screw 123 moves backward.

[0027] In injection, by moving the screw 123 forward, the liquid molding material is ejected (pushed out) from the nozzle 127 into the mold device 10 and fills the cavity 12 of the mold device 10.

[0028] During the holding pressure stage, the screw 123 is further advanced to push the molding material remaining in the cylinder 121 towards the mold device 10.

[0029] The control device 150 controls, with respect to the injection device 120, the rotation and the forward and backward movement of the screw 123 within the cylinder body 126, and the movement of the cylinder 121 between the injection position and the standby position.

[0030] In particular, when the cylinder 121 moves from the injection position after the holding pressure to the standby position, the control device 150 lowers the internal pressure of the nozzle 127 and then starts the movement of the cylinder 121 in order to suppress the drawing of the molding material between the nozzle 127 and the mold device 10. Specifically, the control device 150 lowers the internal pressure of the nozzle 127 by retracting the screw 123, that is, by performing suck-back. As a modification, the control device 150 may lower the internal pressure of the nozzle 127 by rotating the screw 123 in the direction of moving the molding material toward the anti-nozzle side (hereinafter referred to as "reverse rotation"), that is, by rotating the screw 123 in the direction opposite to that during metering.

[0031] The above is the basic configuration of the injection molding machine 100. Subsequently, its operation will be described.

[0032] FIG. 4 is a flowchart for explaining the operation during molding of the injection molding machine 100. It is assumed that the mold clamping of the mold device 10 and the metering of the molding material are completed before the process of FIG. 4. The process of FIG. 4 is repeatedly executed.

[0033] The control device 150 moves the cylinder 121 to the injection position (S10). As a result, the nozzle 127 touches the mold device 10, and the nozzle 127 and thus the cylinder 121 communicate with the cavity 12 of the mold device 10.

[0034] The control device 150 opens the nozzle 127 (S12). The control device 150 injects the molding material from the nozzle 127 into the mold device 10 by advancing the screw 123 (S14). The control device 150 performs pressure holding by further advancing the screw 123 (S16).

[0035] The control device 150 starts the retreat of the screw 123, that is, the suck-back (S18). As a result, the internal pressure of the nozzle 127 starts to drop.

[0036] The control device 150 moves the cylinder 121 from the injection position to the standby position (S20). That is, after the internal pressure of the nozzle 127 starts to drop due to the start of the suck-back in S18, the cylinder 121 is moved from the injection position to the standby position.

[0037] For example, the control device 150 may move the cylinder 121 from the injection position to the standby position when the suck-back started in S18 is completed.

[0038] For example, the control device 150 may move the cylinder 121 from the injection position to the standby position when the internal pressure of the nozzle 127 detected by the pressure sensor 124 drops below a predetermined threshold pressure. The threshold pressure is an internal pressure at which thread pulling is unlikely to occur and may be determined based on experiments, simulations, knowledge, etc. The threshold pressure is, for example, 5 MPa.

[0039] For example, the control device 150 may move the cylinder 121 from the injection position to the standby position when a predetermined threshold time has elapsed since the start of the suck-back in S18. The predetermined threshold time may be the time when the internal pressure of the nozzle 127 becomes below the above-mentioned threshold pressure. In this case, the time when the internal pressure of the nozzle 127 becomes below the above-mentioned threshold pressure may be specified by experiments or the like.

[0040] The control device 150 performs mold clamping / unclamping and pressure reduction on the mold device 10 (S22). Thereby, the reverse flow of the molding material from the mold device 10 can be prevented. Note that the mold device 10 may be mold clamped / unclamped before the movement of the cylinder 121 in S20. For example, the mold device 10 may be mold clamped / unclamped immediately before the suck-back in S18. Also, the mold device 10 may be mold clamped / unclamped after the subsequent closing of the nozzle 127 in S24.

[0041] The control device 150 closes the nozzle 127 (S24). That is, the nozzle 127 is closed after reducing the internal pressure of the nozzle 127. If the nozzle 127 is closed before reducing the internal pressure of the nozzle 127, gas is less likely to come out from the injection port 122a, and thus it is difficult for the internal pressure of the nozzle 127 to decrease. The control device 150 may close the internal pressure of the nozzle 127 at an arbitrary timing after the start of the suck-back in S18. For example, the nozzle 127 may be closed before the movement of the cylinder 121 in S22. For example, the nozzle 127 may be closed during the suck-back in S18. However, it is preferable to close the nozzle 127 after the internal pressure of the nozzle 127 has decreased, for example, after the completion of the suck-back. This is because the internal pressure of the nozzle 127 is more likely to decrease in that case.

[0042] The control device 150 starts metering (S26).

[0043] In the above example, the movement of the cylinder 121 in S20 is executed before starting the metering in S26. However, as long as the timing is such that the internal pressure of the nozzle 127 is lower than at least the completion of the pressure holding in S16, the movement of the cylinder 121 in S20 may be executed after starting the metering in S26. Similarly, in the above example, the closing of the nozzle 127 in S24 is executed before starting the metering in S26. However, as long as the timing is such that the internal pressure of the nozzle 127 is lower than at least the completion of the pressure holding in S16, the closing of the nozzle 127 in S24 may be executed after starting the metering in S26. However, since the internal pressure of the nozzle 127 starts to rise when metering starts, as shown in the processing flow of FIG. 4, it is preferable to execute the movement of the cylinder 121 in S20 and the closing of the nozzle 127 in S24 before starting the metering in S26.

[0044] The inventors conducted a simulation to confirm the effects achieved by the embodiments. Specifically, the change in the internal pressure of the nozzle 127 was simulated for four cases where the order of the steps differed from each other. FIGS. 5(a) to (d) are diagrams showing the simulation. In FIGS. 5(a) to (d), the horizontal axis represents time, and the vertical axis represents the internal pressure of the nozzle 127.

[0045] In FIG. 5(a), although the cylinder 121 is retracted, that is, the cylinder 121 is moved from the injection position to the standby position, after the completion of the suck-back, metering is performed before retracting the cylinder 121. Therefore, the internal pressure of the nozzle 127 when retracting the cylinder 121 is high. In this case, the risk of thread pulling is high.

[0046] In FIGS. 5(b) to (d), the cylinder 121 is retracted after the completion of the suck-back and before the start of metering. Therefore, the internal pressure of the nozzle 127 when retracting the cylinder 121 is low. In this case, the risk of thread pulling is low.

[0047] In addition, in FIG. 5(c), the mold clamping and releasing pressure of the mold device 10 is performed immediately before the suck-back. Further, in FIG. 5(d), the mold clamping and releasing pressure of the mold device 10 is performed immediately after the retraction of the cylinder 121. In any case, in FIGS. 5(c) and (c), the mold clamping and releasing pressure of the mold device 10 is performed before closing the nozzle 127 to lower the internal pressure of the mold device 10. Therefore, in FIGS. 5(c) and (d), the internal pressure of the nozzle 127 is more likely to decrease. Therefore, in FIGS. 5(c) and (d), the risk of thread pulling is even lower.

[0048] From FIGS. 5(a) to (d), it can be seen that by retracting the cylinder 121 after the start of the suck-back and preferably before the start of metering, the risk of thread pulling can be reduced, and by performing the mold clamping and releasing pressure of the mold device 10 before closing the nozzle 127, the risk of thread pulling can be further reduced.

[0049] Next, the effects of the present embodiment will be described. According to the present embodiment, since the internal pressure of the nozzle 127 is lowered and then the cylinder 121 is moved from the injection position to the standby position, it is difficult for the molding material to leak from the nozzle 127, and thus the occurrence of stringing can be suppressed. Preferably, the cylinder 121 is moved before the start of metering. In this case, the occurrence of stringing can be more reliably suppressed. Also, when the internal pressure of the nozzle 127 detected by the pressure sensor 124 drops below a predetermined threshold pressure, the cylinder 121 may be moved. In this case, the occurrence of stringing can be more reliably suppressed. Further, when a predetermined threshold time has elapsed since the start of suck-back, the cylinder 121 may be moved. In this case, if the threshold time is appropriately set, the occurrence of stringing can be more reliably suppressed.

[0050] Also, according to the present embodiment, the nozzle 127 is a shut-off nozzle, and the nozzle 127 is closed after the internal pressure of the nozzle 127 is lowered. Thereby, it is possible to avoid the internal pressure of the nozzle 127 from being difficult to decrease. On the other hand, by closing the nozzle 127, an effect that the molding material is less likely to leak even if metering is started during the movement of the cylinder 121 can be obtained. That is, it is possible to shorten the cycle time.

[0051] As described above, the present invention has been described based on the embodiments. It should be understood by those skilled in the art that these embodiments are illustrative, and various modifications are possible for each combination of these constituent elements and each processing process, and such modifications are also within the scope of the present invention. Hereinafter, modifications will be described.

[0052] Any combination of the above-described embodiments and modifications is also useful as an embodiment of the present invention. The new embodiment resulting from the combination has the effects of the combined embodiments and modifications. It should also be understood by those skilled in the art that the functions to be achieved by each constituent element described in the claims are realized by a single one of the constituent elements shown in the embodiments and modifications or by the cooperation thereof.

Explanation of Reference Numerals

[0053] 10 Mold device, 100 Injection molding machine, 123 Screw, 127 Nozzle, 150 Control device.

Claims

1. A cylinder having a nozzle at its tip, the nozzle moving between an injection position communicating with the cavity of a mold device and a standby position spaced apart from the mold device, A screw that can move forward and backward and rotate within the cylinder, A control device, Comprising, The control device starts moving the cylinder from the injection position to the standby position after starting the backward movement of the screw or the rotation of the screw in a direction to move the molding material toward the anti-nozzle side. An injection molding machine.

2. The injection molding machine according to claim 1, wherein the control device starts moving the cylinder before starting metering.

3. Comprising a pressure sensor for detecting the internal pressure of the nozzle, The injection molding machine according to claim 1, wherein the control device starts moving the cylinder when the internal pressure of the nozzle detected by the pressure sensor drops below a predetermined threshold pressure.

4. The injection molding machine according to claim 1, wherein the control device starts moving the cylinder after a lapse of a predetermined threshold time from the start of the backward movement or the rotation of the screw.

5. The nozzle is a shut-off nozzle, The injection molding machine according to claim 1, wherein the control device closes the shut-off nozzle after starting the backward movement or the rotation of the screw.

6. An injection molding method using an injection molding machine comprising a cylinder having a nozzle at its tip, the nozzle moving between an injection position communicating with the cavity of a mold device and a standby position spaced apart from the mold device, and a screw that can move forward and backward and rotate within the cylinder, Starting the rotation of the screw in a direction to move the screw backward or in a direction to move the molding material toward the anti-nozzle side, After starting the backward movement or the rotation of the screw, starting the movement of the cylinder from the injection position to the standby position, An injection molding method comprising.

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