JP7666255B2 - Injection Molding Method - Google Patents

Description

The present invention relates to an injection molding method in which a backflow prevention device is provided at the tip of the screw, plasticized and molten resin material is stored in an injection cylinder in front of the screw during the metering process, and the resin material is injected to fill the mold cavity during the injection process.

In injection molding using an injection molding machine, first, resin material is supplied into the injection cylinder using a material supply device. The supplied resin material is plasticized and turned into molten resin by shear heat generated by the rotational movement of the screw with a spiral flight and heat from a heater or the like installed in the injection cylinder, and is then rotated and transported to the tip of the screw and stored in the injection cylinder (called metered resin). As the metered resin is stored, the screw retreats, and the screw's rotation stops at a specified retreat position to maintain the screw position (metering process). Resistance is applied to the retreating movement of the screw to adjust the melting and mixing properties of the stored molding material (called back pressure control).

Next, the screw is advanced to inject and fill the measured resin into the mold cavity (injection process). After pressure-holding filling (pressure-holding process) to compensate for solidification shrinkage that accompanies cooling and solidification of the molten measured resin, and cooling and holding in the mold cavity (cooling process), the mold is opened and the molded product is removed from the mold cavity. This series of molding operations is repeated until the required number of molded products is obtained.

Here, the tip of the screw is equipped with a backflow prevention device that has a flow path through which the plasticized molten resin passes. In the metering process, the backflow prevention device is pressed forward by the flow pressure of the molten resin being rotated and transported, opening the flow path and storing the metered resin at the tip of the screw. In the injection process, the screw moves forward, the backflow prevention device comes into contact with the screw, closing the flow path and preventing the metered resin from flowing back to the rear of the screw. In particular, if the closure of the flow path is unclear in the injection process, the amount of metered resin filled into the mold cavity (called the injection filling amount) fluctuates, and molding defects such as product weight fluctuation, poor surface firmness, poor transfer, welds, voids, product deformation, and product shorts occur frequently, hindering the stabilization of product quality. In addition, if these molding defects cannot be improved, injection molding must be stopped and parts related to the screw, including the backflow prevention device, must be replaced, resulting in a significant decrease in productivity. To this end, many proposals have been made to accurately grasp the operating state of the backflow prevention device's flow passage opening and closing, and to prevent the backflow of metered resin (called resin backflow) during the injection process.

For example, as shown in Patent Document 1, after the metering process, the molten resin at the tip of the screw is pressurized to close the check valve (pressurizing operation), and in that state the screw is moved backward to make the pressure of the stored molten resin equal to atmospheric pressure (depressurizing operation). It is said that the amount of injected resin can be stabilized by performing the injection process with the initial forward position of the screw as the reference position. Also, as shown in Patent Document 2, after the metering process, with the nozzle and the mold in contact, the molten resin at the tip of the screw is pressurized (the screw moves forward), and then the molten resin at the tip of the screw is depressurized (the screw moves backward). It is said that resin backflow during the injection process can be prevented by calculating a correction value from the metering completion position and the pressurization stop position or the depressurization stop position, and correcting the injection speed switching point during the injection process.

As shown in Patent Document 3, an injection reference point is set forward of the injection start position by the screw stroke amount, which is the sum of the amount of backflow of molten resin due to the delay in closing the flow path of the backflow prevention device at the start of injection and the amount of gap at the tip of the nozzle due to the suck-back operation. In the injection process, the forward movement of the screw is stopped once at the injection reference point. This is said to eliminate the gap at the tip of the nozzle. Furthermore, as shown in Patent Document 4, the metering completion position is calculated from the dimensions of the screw parts including the backflow prevention device. Furthermore, after metering is completed, the back pressure is reduced (the screw moves backward), the flow path is forcibly closed in the pre-injection process (the screw moves forward), and then the back pressure is reduced (the screw moves backward), and the metering completion position is corrected from the stop position of the screw's backward movement. This is said to improve metering accuracy.

As shown in Patent Document 5, after metering is complete, the screw is advanced and the pressure of the molten resin at the tip of the screw is increased above the metering back pressure, closing the flow path of the backflow prevention device. The screw is then reversed to reduce the pressure behind the backflow prevention device, and the screw is then retreated. This allows the flow path of the backflow prevention device to remain closed until the start of the injection process.

Japanese Patent Application Publication No. 3-230930 Japanese Patent Application Publication No. 4-250016 Japanese Patent Application Publication No. 7-214617 JP 2002-18923 A JP 2007-253388 A

Here, the backflow prevention device is generally a backflow prevention ring type in which the flow path is opened and closed by moving the screw forward and backward in the axial direction, and this backflow prevention ring type device is also used in Patent Documents 1 to 5. Therefore, in Patent Document 1, when metering is completed, the backflow prevention ring is in the front flow path open position. In the pressurizing operation after the metering process, the screw advances toward the front backflow prevention ring, which abuts and closes the flow path. The flow path is closed and the pressure of the molten resin in front of the screw increases. In other words, until the flow path is closed, the molten resin flows back through the flow path to the rear side of the screw as the screw advances. There is no consideration at all about the fact that the amount of backflow of the molten resin at this time is not expected and that the amount of backflow may vary. In addition, the depressurization operation is said to be performed by retreating the screw, and the pressure of the molten resin in front of the screw becomes almost zero. This means that the resin pressure required to press the backflow prevention ring to close the flow path disappears halfway through the depressurization operation, and as a result, the backflow prevention ring moves away from the screw retreat operation, and the flow path becomes incomplete. In other words, in Patent Document 1, the flow path of the backflow prevention device cannot be kept closed between the completion of the metering process and the start of the injection process, and there is a concern that the molten resin may backflow during the injection process. In addition, although it is said that defects such as stringing can be prevented without using a shutoff valve, defects such as stringing inevitably occur due to the increase in pressure caused by the pressurizing operation after the metering process. Furthermore, the pressurization and depressurization of the molten resin after the metering process causes volatile gases contained in the molten resin to dissipate, and there is a great concern that molding defects may occur due to gas entrapment.

In addition, since Patent Document 2 also uses a backflow prevention device of the non-return ring type, there are concerns about the same problems as in Patent Document 1. Furthermore, since the nozzle and the mold are in contact with each other, molding defects such as stringiness can be avoided, but the mold cannot be opened to remove the molded product until the correction operation after the metering process is completed, so productivity improvement by shortening the molding cycle cannot be expected.

In addition, in Patent Document 3, the same problem as in Patent Document 1 is a concern. Furthermore, the backflow amount of molten resin is calculated from the dimensions of the screw parts including the backflow prevention device, and does not indicate the backflow amount in actual injection molding. In other words, the elements of injection molding that are greatly related to the backflow of molten resin, such as the aging of the backflow prevention device, the type and melt viscosity of the molten resin, the melt temperature, and the injection speed conditions, are completely ignored, and the reliability of the calculated resin backflow amount is doubtful. In addition, a means for measuring the amount of voids at the nozzle tip is required for the nozzle part, which is in a high-temperature and high-pressure environment, and the measurement accuracy and life of this measuring means are of great concern. Furthermore, in the suck-back operation after metering to the extent that voids are generated at the nozzle tip, the resin pressure in front of the screw becomes negative, and air is sucked in from the nozzle tip, which causes molding defects such as air entrapment. Furthermore, the pressure difference before and after the backflow prevention device becomes large, and the check ring is opened by the suck-back operation, so the molten resin flows from the rear side of the screw to the front side of the screw, and the metered resin amount fluctuates greatly.

In addition, in Patent Document 4, the correction value is calculated from the dimensions of the screw parts including the backflow prevention device, so there are concerns about problems similar to those in Patent Document 3, and furthermore, there are concerns about problems similar to those in Patent Document 1. In addition, for example, a means for opening and closing the flow path of the molten resin, such as a shutoff valve or a mold valve gate, is always required forward of the nozzle. Without these means, molten resin will leak from the nozzle during the pre-injection process in which the check ring is forcibly closed, and molding defects such as fluctuations in the metered resin amount, poor stringing, and unexpected filling into the mold cavity (dripping defects) will always occur.

Furthermore, in Patent Document 5, all of the problems listed in Patent Documents 1 to 4 are of concern. Also, the screw is rotated in reverse. This reverse rotation of the screw causes the molten resin in the screw to flow backwards significantly, and if, for example, the solid resin in the solid transport area (also called the transport zone) of the screw mixes with the molten resin that has flowed backwards, the screw's rotational transport capacity is greatly reduced, and there is a high probability that a metering malfunction will occur in which the metered resin cannot be stored accurately in the metering process of the next shot. In this case, injection molding must be stopped and extensive maintenance work such as cleaning the screw will be required.

The present invention aims to provide an injection molding method that can ensure a stable amount of injected resin regardless of the opening and closing operation of the screw backflow prevention device.

The injection molding method of the present invention comprises the steps of:
1. An injection molding method comprising the steps of: providing a backflow prevention device at the tip of a screw; storing a plasticized and molten resin material in an injection cylinder in front of the screw in a metering step; and injecting and filling the resin material into a mold cavity in an injection step;
An operation determination mode for determining an opening/closing operation of the backflow prevention device,
The operation judgment mode is characterized in that the injection pressure of the injection process is treated as a measured waveform, and when the measured waveform is within a range of upper and lower limits set in advance with respect to a reference waveform, the opening and closing operation of the backflow prevention device is judged to be normal, and when the start position of the pressure rise of the measured waveform is delayed beyond a preset allowable position with respect to the reference waveform, a first abnormality is judged to be present in the opening and closing operation of the backflow prevention device, and a first correction process is performed.

In the injection molding method of the present invention,
It is preferable that the first correction process sets the distance of the screw from the injection start position of the injection process to the pressure rise start position as a first correction distance, sets the injection speed at the start of injection of the injection process as a correction speed, and in the metering process, starts the metering process based on a preset metering control pattern, stops the rotation of the screw after the screw reaches a metering completion position, causes the screw to retract without rotation at the correction speed for the first correction distance, and stops the screw at the completion position of the retraction without rotation.

In addition, in the injection molding method of the present invention,
It is preferable that the first correction process comprises advancing the screw at a preset speed from the completion position of the non-rotational retreat, and after the screw position reaches the metering completion position, starting the injection process based on a preset injection control pattern.

In addition, in the injection molding method of the present invention,
In the operation judgment mode, if the pressure rise start position of the measured waveform is delayed compared to the allowable position, and further, the pressure recovery position of the measured waveform is outside a predetermined monitoring range for the reference waveform, it is preferable to judge this as a second abnormality in the opening and closing operation of the backflow prevention device and perform a second correction process.

Furthermore, in the injection molding method of the present invention,
It is preferable that the second correction process defines a distance of the screw from the injection start position of the injection process to the pressure return position as a second correction distance, and determines a metering completion correction position by adding the second correction distance to the metering completion position, and in the metering process, starts the metering process based on a preset metering control pattern, and after the screw reaches the metering completion correction position, stops the rotation of the screw, moves the screw back without rotation at the correction speed for the first correction distance, and stops the screw at the completion position of the non-rotational retraction, and in the injection process, moves the screw forward from the completion position of the non-rotational retraction at a preset speed, and after the screw position reaches the metering completion correction position, starts the injection process based on the preset injection control pattern.

In addition, in the injection molding method of the present invention,
In the operation determination mode, when the pressure rise start position of the measured waveform lags behind the allowable position and further the injection pressure of the measured waveform does not return to the injection pressure of the reference waveform, it is preferable to perform a third correction process which determines that there is a third abnormality in the opening and closing operation of the backflow prevention device and issues an alarm recommending replacement work of parts related to the injection device including the backflow prevention device.

The present invention provides an injection molding method that can ensure a stable amount of injected resin regardless of the opening and closing operation of the screw backflow prevention device.

1 is a conceptual diagram of an injection molding machine according to an embodiment of the present invention. 13A-13D illustrate the operation of the backflow prevention device during the metering process. 11A and 11B are diagrams illustrating an operational abnormality of a backflow prevention device. 1 is a diagram showing an overall flow of an injection molding method according to an embodiment of the present invention. FIG. 4 is a diagram showing an injection pressure waveform according to the first embodiment of the present invention. FIG. 1 is a flow diagram showing an injection molding method according to a first embodiment of the present invention. FIG. 11 is a diagram showing an injection pressure waveform according to a second embodiment of the present invention. FIG. 5 is a flow diagram showing an injection molding method according to a second embodiment of the present invention. FIG. 13 is a diagram showing an injection pressure waveform according to a third embodiment of the present invention.

Below, preferred embodiments for carrying out the present invention will be described with reference to the drawings. Note that the following embodiments do not limit the inventions according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solutions of the inventions according to the claims. Furthermore, in the present embodiments, the scales and dimensions of each component may be exaggerated, and some components may be omitted.

[Injection molding machine]
First, an injection molding machine according to an embodiment of the present invention will be described with reference to Fig. 1. In the following description, the injection molding machine according to the embodiment of the present invention is based on a horizontal injection molding machine, but is not limited to this. The injection molding machine 100 shown in Fig. 1 includes an injection device 10, an injection drive unit 30, an injection control unit 40, and an injection mold 50.

In the injection mold 50, the fixed mold 51 and the movable mold 52 are supported by a clamping device (not shown), and the movable mold 52 can move forward and backward relative to the fixed mold 51 by the clamping device. Here, the operation of the movable mold 52 is defined as the operation of approaching the fixed mold 51 as the mold closing operation, and the operation of moving away from the fixed mold 51 as the mold opening operation. In addition, the position where the fixed mold 51 and the movable mold 52 come into contact during the mold closing operation is defined as the mold touch point, the operation from the mold touch point in the mold closing operation direction is defined as the mold clamping operation, the completion position of the mold clamping operation is defined as the mold clamping limit, and the operation from the mold clamping limit to the mold touch point is defined as the pressure reduction operation. A mold cavity 53 is formed within the range from the mold touch point to the mold clamping limit. In addition, the fixed mold 51 is provided with a gate 54 that fills the mold cavity 53 with resin material.

The injection device 10 includes a cylindrical injection cylinder 21 and a screw 11 that is disposed within the injection cylinder 21 and rotates about its axis and moves back and forth in the axial direction. The injection device 10 injects and fills the mold cavity 53 with resin material to obtain a resin molded product.

The injection cylinder 21 has a plurality of heaters 24 arranged at a predetermined interval on its outer periphery, and the heaters 24 are temperature-controlled by a temperature control device (not shown) to maintain the injection cylinder 21 at a predetermined temperature. The temperature control by the heaters 24 is used in the metering process described below to preheat the supplied resin material, to impart heat to the resin material during plasticization, and to control the temperature of the plasticized molten resin. The tip of the injection cylinder 21 is equipped with a cylinder head 22 having a conical inner wall surface and a nozzle 23. When injecting and filling the resin material into the mold cavity 53, the nozzle is connected to the gate 54 in the fixed mold 51. In addition, a material hopper 25 is provided behind the injection cylinder 21, and the resin material is supplied from the material hopper 25 to the injection cylinder 21 by a material supply device (not shown) or the like.

The screw 11 is disposed within the injection cylinder 21 so that it can freely move forward and backward, and the rear end of the screw 11 is connected to the injection drive unit 30. The injection drive unit 30 is operated based on control commands from the injection control unit 40 to adjust the rotational movement and forward and backward movement of the screw 11. Here, with regard to the movement of the screw 11, the direction closer to the mold cavity 53 is defined as forward F, movement toward forward F is defined as forward movement, the direction away from the mold cavity 53 is defined as backward B, and movement toward backward B is defined as backward movement.

The screw 11 is also provided with a spiral flight 12 that runs from the rear B to the front F. The spiral direction and angle of the flight 12 are set so that the resin material supplied from the material hopper 25 can be rotated and transported to the front F relative to the direction of rotation of the screw 11 by the injection drive unit 30. As shown in FIG. 1, the flight 12 is arranged in a single line at a fixed interval and angle, but is not limited to this. For example, the interval and angle may be variable, or multiple lines may be arranged. Alternatively, the flights 12 may be arranged in multiple lines only in a portion of the screw 11.

The screw 11 is cylindrical in shape, with the diameter gradually increasing from the rear B to the front F. In other words, the volume of the gap between the screw 11 and the injection cylinder 21 is set to gradually decrease from the rear B to the front F, for example, as a transport zone (FZ), a compression zone (CZ), and a melting zone (MZ). As a result, the resin material supplied from the material hopper 25 is transported forward by the rotational action of the screw 11 and the flight 12, and the compression action and shear heat act on the resin material due to the reduction in volume, and the resin material is gradually melted (called plasticization) by the synergistic effect of the heat applied from the heater 24, and molten resin is generated toward the front F of the screw 11, and the molten resin is stored in the front F of the screw 11 (called metered resin). As the metered resin increases, the screw 11 retreats to the rear B side, stops rotating at a predetermined retreat position, and holds the stopped position (called the metering process). The backward movement of the screw 11 is restricted to adjust the melting and mixing properties of the molding material (called back pressure control). In the injection process, the screw 11 is advanced to inject and fill the metered resin into the mold cavity 53.

Here, as the resin material used in injection molding, for example, in the case of automobile interior parts, it is common to add colorants such as black, red, and blue to thermoplastic resins such as polypropylene (PP) resin and polyethylene (PE) resin to adjust the color tone of the parts. In addition, various additives such as plasticizers that give flexibility to thermoplastic resins, nucleating agents and clarifying agents that control the crystallinity of crystalline resins, flame retardants that suppress combustion, antistatic agents that suppress static electricity, lubricants that improve fluidity and releasability, weathering agents and ultraviolet degradation inhibitors that suppress deterioration due to ultraviolet rays, and reinforcing agents such as glass fibers and carbon fibers are appropriately selected. In addition, thermoplastic resins such as general-purpose resins such as polypropylene (PP) resin and polyethylene (PE) resin, engineering resins such as polyamide (PA) resin and polycarbonate (PC) resin, and super engineering resins such as polyphenylene sulfide (PPS) resin and polyether ether ketone (PEEK) resin are appropriately selected. Thermoplastic resins and additives are collectively called resin materials. Instead of a thermoplastic resin, a thermosetting resin such as phenol (PF) resin or melamine (MF) resin may be used.

[Backflow prevention device]
Next, the backflow prevention device incorporated in the tip of the screw 11 will be described with reference to FIG. 1 and FIG. 2 and FIG. 3 which are enlarged views of the area A enclosed by the dashed line in FIG. 1. FIG. 1 shows the arrangement of the backflow prevention device, FIG. 2 shows the operation of the backflow prevention device during the metering process, and FIG. 3 shows the operation of the backflow prevention device during the injection process and the operation abnormality of the backflow prevention device within the range from the metering process to the injection process. As shown in FIG. 1, the backflow prevention device is arranged from the screw 11 toward the front F, a rear seat 13, a ring-shaped backflow prevention ring 14 having a flow path R through which the resin material passes, and a screw head 15, and the backflow prevention ring 14 is a non-rotating type that does not rotate with the rotational movement of the screw 11. Note that the present invention is not limited to this, and may be, for example, a rotating type in which a part of the backflow prevention ring and the screw head 15 are fitted together, and the backflow prevention ring also rotates with the rotational movement of the screw 11. Also, instead of the backflow prevention ring 14, a backflow prevention device in which a slidable ball is incorporated in the flow path may be used.

First, as shown in FIG. 2(a), in the metering process, the resin material plasticized by the rotational motion of the screw 11 flows to the front B side. This flow of the resin material presses the non-return ring 14 against the screw head 15 on the front F side, opening the flow path R. The resin material flows through this flow path R into the injection cylinder 21 on the front F side of the screw head 15 to obtain the metered resin. MF in the figure indicates the flow direction of the resin material. As the metered resin increases, the screw 11 moves backward while maintaining the open state of the flow path R. SF in the figure indicates the movement direction of the screw 11. The backward movement of the screw 11 is restricted (back pressure control) to adjust the melting and kneading state of the metered resin, and as a result, the metered resin with a resin pressure P2 is obtained. At this time, if the resin pressure of the resin material on the rear B side of the non-return ring 14 is P1, P1>P2, and this pressure difference presses the non-return ring 14 to the front F side, maintaining the opening of the flow path R.

Next, as shown in FIG. 2(b), the rotation of the screw 11 is stopped to complete the metering process. Here, by stopping the rotation of the screw 11, the flow of the resin material to the forward F side is stopped, and the resin pressure P1 on the rear B side of the non-return ring 14 becomes close to zero. As a result, the pressure difference before and after the non-return ring 14 is reversed (P1<P2). This reversal of the pressure difference presses the non-return ring 14 against the rear sheet 13 on the rear B side, and the flow path R is closed. GF in the figure indicates the operating direction of the non-return ring 14. Note that until the flow path R is closed, the metered resin flows back through the flow path R to the screw 11 side (called resin backflow), but if the operation of the non-return ring 14 is stable, the amount of this resin backflow is also stable. As a result, the amount of metered resin is set in anticipation of the stable amount of resin backflow.

As shown in FIG. 3(a), in the injection process, the screw 11 moves forward with the flow path R closed, and the metered resin on the front F side of the screw head 15 flows toward the nozzle 22 and is injected and filled into the mold cavity 53. Due to the stability of the operation of the non-return ring 14 (stable amount of resin backflow) and the closure of the flow path R, the injection filling amount filled into the mold cavity 53 is ensured with high precision, realizing stable production of high quality molding. However, in actual molding sites, the injection filling amount of the molding material fluctuates, and the molding quality is often unstable. The reason for this phenomenon will be explained using FIG. 3(b).

For example, the backflow prevention ring 14 is inevitably damaged by wear, deformation, scratches, etc. due to a long-term injection molding operation. The inner wall surface of the injection cylinder 21 is also inevitably damaged in the same way. Furthermore, the resin material attached to the backflow prevention ring 14 and the inner wall surface of the injection cylinder 21 deteriorates and accumulates as retained resin. Due to these, the operation of the backflow prevention ring 14 after the metering process is completed becomes slow, and the time until the flow path R closes varies. As a result, the state of the resin backflow varies, and the amount of metered resin varies. Also, as shown in FIG. 3(b), when the backflow prevention ring 14 stops midway and the flow path R becomes open, the resin backflow continues until the pressure difference disappears (P2 ≒ P1), and the amount of metered resin varies greatly. Furthermore, even in the injection process, the resin backflow varies until the open flow path R closes. The timing of closing the flow path R also varies. Due to these fluctuations, the amount of injection filling varies greatly, making it very difficult to ensure the stabilization of molding quality.

The state shown in Figures 2 and 3 was also confirmed using a visualization device that was created to observe the inside of the injection cylinder 21. We therefore believe that by taking measures to accurately detect and improve the state shown in Figure 3(b), it is possible to stabilize the injection and filling of the resin material into the mold cavity 53, and we propose the injection molding method described below. Note that this idea has not been suggested at all in the prior art.

[Overall flow of injection molding method]
Next, the overall flow of the injection molding method according to the embodiment of the present invention will be described with reference to FIG. 4. First, the fixed mold 51 and the movable mold 52 are clamped to form a mold cavity 53 (mold clamping process). Next, the injection process is started. In the injection process, based on a preset injection control pattern of injection speed and injection pressure, the injection control unit 40 operates the injection drive unit 30 to move the screw 11 forward to inject and fill the measured resin into the mold cavity 53 (injection operation). When the position S of the screw 11 reaches the injection pressure holding switching position VP, the injection process goes through a pressure holding process to compensate for solidification shrinkage caused by cooling and solidifying the injected and filled measured resin, and a cooling process to cool and solidify the resin in the mold cavity 53, and then the mold is opened and the cooled and solidified molded product is taken out from the mold cavity.

At the same time as the injection process starts, an operation judgment mode is started to judge the operation of the backflow prevention ring 14 and the open/closed state of the flow path R, and the injection pressure waveform (referred to as the measured waveform) of the injection process is acquired by the injection control unit 40 and the waveform is evaluated. If this measured waveform is evaluated to be within an allowable range for a preset reference waveform, the operation of the backflow prevention ring 14 and the open/closed state of the flow path R are judged to be normal, and stable operation of the injection molding is guaranteed. If the measured waveform and the reference waveform differ, proceed to the next step. First, if the difference between the measured waveform and the reference waveform is only a delay in the timing of the rise in injection pressure from the start of injection, the injection control unit 40 judges that a minor abnormality has occurred in the operation of the backflow prevention ring 14 and the closed state of the flow path R, and transmits a first abnormality judgment and performs a first correction process.

The delay in the increase in injection pressure is confirmed, and furthermore, an evaluation is made as to whether the delayed injection pressure has returned to the injection pressure set value of the injection control pattern. In the case of a first abnormality judgment, the timing of the return of the injection pressure is within a monitoring range described below. If this return timing is delayed beyond the monitoring range, it is determined that a moderate abnormality has occurred in the operation of the check ring 14 and the closure state of the flow path R, and the injection control unit 40 issues a second abnormality judgment and performs a second correction process. Furthermore, if the injection pressure cannot be restored, it is determined that a serious abnormality has occurred in the components of the injection device 10, including the check ring 14 and the injection cylinder 21, and the injection control unit 40 judges that a third abnormality has occurred, and performs a third correction process, for example, issuing an alarm and recommending the performance of maintenance work.

[Injection molding method according to the first embodiment]
Next, the injection molding method according to the first embodiment of the present invention will be described with reference to Figs. 4 and 5. Fig. 5 shows the injection pressure waveform during the injection process with the position S of the screw 11 on the horizontal axis and the injection pressure on the vertical axis. Fig. 6 is a flow chart of the first correction process following the first abnormality judgment shown in Fig. 4. Here, the injection pressure may be, for example, a pressure sensor attached to the injection drive unit 30 on the rear B side of the screw 11 to detect the resin pressure received by the screw and use it as the injection pressure. Alternatively, in the hydraulically driven injection drive unit 30, the injection pressure may be calculated from the pressure of the hydraulic pressure to be supplied, and in the electrically driven injection drive unit 30, the injection pressure may be calculated from the driving torque of the electric motor. Note that a pressure sensor may be attached to the injection cylinder 21, the cylinder head 22, or the nozzle 23 to directly detect the resin pressure and use it as the injection pressure, but since the pressure sensor is attached to a high-temperature and high-pressure portion, it is expected that the injection molding operation will be interrupted due to leakage of the metered resin from the attachment portion or failure of the pressure sensor, so care must be taken.

First, as shown in Figure 5 (a), the screw 11 is advanced from the injection start position SS (metering completion position KE) toward the injection pressure holding switch position VP to inject and fill the metered resin into the mold cavity 53. The injection control pattern at this time is the reference waveform K shown by the solid line. The upper limit value H and lower limit value L that can obtain a good molded product are shown by the dashed lines. The upper limit value H and lower limit value L may be obtained from past injection molding results, or may be calculated using a resin flow analysis tool. The measured waveform NG1 is superimposed on this reference waveform K to perform waveform evaluation. If the rise in the injection pressure of the measured waveform NG1 is delayed and the start position PR of the rise is outside the allowable position SK calculated from the upper limit H and lower limit L of the reference waveform K (PR>SK), and the injection pressure of the measured waveform NG1 returns to the reference waveform K and the return position PF is within the monitoring range KH (KH≧PF), a first abnormality is determined and a first correction process is performed.

The first correction process, as shown in FIG. 6, determines the first correction distance SB1 and the correction speed SV1. The first correction distance SB1 is set in the injection control unit 40 to the rise start position PR of the injection pressure of the measured waveform shown in FIG. 5(a) (SB1=PR). In addition, the rise start position SB1 is added to the metering completion position KE to set the metering completion correction position KH1 in the injection control unit 40. The metering completion correction position KH1 becomes the injection start correction position SH1 for the next shot. The correction speed SV1 is set in the injection control unit 40 to the injection speed V1 at the start of injection of the reference waveform shown in FIG. 5(a) (SV1=V1). The results of these settings are shown in FIG. 5(b).

Next, based on the setting results of FIG. 5(b), the metering process and injection operation are performed as shown in FIG. 6. First, the metering process performs the metering operation based on a preset metering control pattern without changing the metering conditions such as the rotation speed and back pressure control of the screw 11. When the position S of the screw 11 reaches the metering completion position KE, the rotation operation of the screw 11 is stopped. Then, immediately, the screw 11 is retracted without rotation at the retraction speed of the correction speed SV1 to the metering completion correction position KH1 and stopped. The stop position of this retraction becomes the injection start correction position SH1 of the subsequent injection operation. As a result, the non-return ring 14 is located on the screw head 15 side, and the flow path R is open, but the pressure difference before and after the non-return ring 14 is eliminated (P1 = P2), and the resin backflow can be reliably stopped. In addition, even if the reverse cylinder 14 is caught on the inner wall surface of the injection cylinder 21 due to wear scratches or retained resin, causing the reverse cylinder to move slowly, the backward movement of the screw 11 can reliably remove the catch and block the movement of the reverse cylinder 14. Furthermore, excessive backward movement of the screw 11 can cause a problem in that the resin pressure P2 on the front F side of the reverse cylinder 14 becomes negative pressure, causing the resin material on the screw 11 side to leak out to the front F side of the screw head 15, resulting in an excessive increase in the amount of metered resin. This problem can be reliably prevented by setting the first correction distance SB1.

In the injection operation, the screw 11 is advanced at a predetermined speed until the position S of the screw 11 reaches the metering completion position KE. During this forward movement, the non-return ring 14 and the rear sheet 13 come into contact with each other, ensuring the closure of the flow path R. After the flow path R is closed, the resin pressure P2 on the front F side of the non-return ring 14 is increased, and at the metering completion position KE, the resin pressure is restored to the back pressure control resin pressure shown in the original metering process. Therefore, the injection process after the metering completion position KE can proceed with the injection process, injection pressure holding switching, pressure holding process, cooling process, and mold opening/product removal process without changing the previously set injection control pattern. The forward speed of the screw up to the metering completion position KE is set to a speed at which the non-return ring 14 is not bounced off when the rear sheet 13 and the non-return ring 14 come into contact with each other. Alternatively, the correction speed SV1 (= injection speed V1) may be set as the forward speed so that the forward movement of the screw 11 before and after the metering completion position KE can be smoothly continued. This allows the abnormality to be detected immediately and the appropriate correction process to be carried out to avoid the abnormality even if an abnormality suddenly occurs in the operation of the check ring 14 and the closure state of the flow path R during injection molding operation, causing a molding defect. As a result, it is possible to return to molding a good product from the next injection molding shot, and losses can be minimized.

[Injection molding method according to the second embodiment]
Next, an injection molding method according to a second embodiment of the present invention will be described with reference to Fig. 7 and Fig. 8. Fig. 7 shows an injection pressure waveform during the injection process, with the horizontal axis representing the position S of the screw 11 and the vertical axis representing the injection pressure, similar to Fig. 5. Fig. 8 is a flow chart of the second correction process following the second abnormality determination shown in Fig. 4. Note that the description of the parts that overlap with the first embodiment will be omitted.

First, as shown in FIG. 7(a), if the injection pressure of the measured waveform NG2 starts to rise late and deviates from the allowable position SK (PR>SK), and the injection pressure of the measured waveform NG2 returns to the reference waveform K and its return position PF is outside the monitoring range KH (KH<PF), a second abnormality is determined and a second correction process is performed. As shown in FIG. 8, the second correction process obtains a first correction distance SB1 and a correction speed SV1 similar to those of the first correction process, and further obtains a second correction distance QF that offsets the metering completion position KE to the rear B side (KE+QF). The metering completion position after this offset is KE2. This second correction distance QF is set to the return position PF of the injection pressure of the measured waveform shown in FIG. 7(a) in the injection control unit 40 (QF=PF). In addition, the first correction distance SB1 is added to the metering completion position KE2 (KE2+SB1) and set as the metering completion correction position KH2 in the injection control unit 40. The metering completion correction position KH2 becomes the injection start correction position SH2 for the next shot. These setting results are shown in FIG. 7(b).

Next, based on the setting results of FIG. 7(b), the metering process and the injection operation are performed as shown in FIG. 8. First, in the metering process, only the switching position of each control among the metering conditions such as the rotation speed of the screw 11 and back pressure control is changed based on the metering completion position KE2 after the offset. The metering operation is performed based on the changed metering conditions, and when the position S of the screw 11 reaches the metering completion position KE2, the rotation operation of the screw 11 is stopped. Thereafter, the screw 11 is immediately retreated without rotation to the metering completion correction position KH2 at the retreat speed of the correction speed SV1 and stopped. The stop position of this retreat becomes the injection start correction position SH2 of the subsequent injection operation. This provides the same improvement effect as the first embodiment. Furthermore, the offset of the screw 11 to the rear B side changes the contact state between the check ring 14 and the inner wall surface of the injection cylinder 21 and the volume state of the retained resin, and it is expected that the operation of the check ring 14 and the opening and closing state of the flow path R will be improved. The area of the injection cylinder 21 that is not used on a daily basis in injection molding has little wear damage or residual resin. If the offset measurement completion correction position KH2 falls within this range, the possibility of improvement will be even higher.

In the injection process, the screw 11 is advanced at a predetermined speed until the position S of the screw 11 reaches the metering completion position KE2. During this forward movement, the flow path R is closed and the pressure of the metered resin is adjusted, as in the first embodiment. The injection process after the metering completion position KE2 is performed based on an injection control pattern in which the switching positions of each control are changed, as in the case of changing the metering conditions. The injection pressure holding switching position VP and after are the same as in the first embodiment. This provides the same improvement effect as in the first embodiment. In addition, the return to stable production of injection molding can be expected to extend the life of the parts of the injection device 10, including the non-return ring 14. Furthermore, if the metering completion correction position KH2 falls within the range of the injection cylinder 21 with little wear damage or retained resin, for example, foreign matter defects due to peeling of retained resin can be avoided. In addition, by taking preemptive measures such as arranging for replacement parts of the injection device 10, such as the non-return ring 14, upon receiving the second abnormality judgment, long-term production stoppages due to unexpected trouble can be avoided.

[Injection molding method according to the third embodiment]
Next, an injection molding method according to a third embodiment of the present invention will be described with reference to Fig. 9. Like Fig. 5 and Fig. 7, Fig. 9 shows an injection pressure waveform during the injection process with the horizontal axis representing the position S of the screw 11 and the vertical axis representing the injection pressure. Note that descriptions of points that overlap with the first and second embodiments will be omitted.

First, as shown in Fig. 9(a), if the injection pressure of the measured waveform NG3 starts to rise late and deviates from the allowable position SK (PR>SK), and the injection pressure of the measured waveform NG3 does not return to the reference waveform K, a third abnormality is determined and a third correction process is performed. Note that if the injection pressure of the measured waveform NG3 does not return to the reference waveform K even after the first correction process is performed, or if the injection pressure of the measured waveform NG3 does not return to the reference waveform K even after the second correction process is performed, as shown in Fig. 9(b), a third abnormality is determined and a third correction process is performed.

Here, the reason why the injection pressure of the measured waveform NG3 cannot return to the reference waveform K is that, for example, the inside wall surface of the non-return ring 14 and the injection cylinder 21 is significantly deteriorated due to wear, deformation, scratches, accumulation of retained resin, etc., resulting in a serious abnormality in which the opening and closing function of the flow path R does not function normally. In other words, the third abnormality judgment suggests that stable production of injection molding cannot be continued. Therefore, the third correction process issues an alarm, suspends the injection molding operation, and recommends performing maintenance work to replace parts of the injection device 10 that affect the metering process and injection process, such as the non-return ring 14. This makes it possible to prevent the production of a large number of defective molded products, and by performing maintenance work at the appropriate time, stable production of injection molding can be quickly restored, ensuring high production efficiency.

[effect]
In this way, from the injection pressure waveform during the injection process, it is possible to accurately detect the pass/fail state of the backflow prevention device during the range from the completion of the metering process to the injection process, which has the greatest effect on the quality of the injection molding, and to accurately detect the degree of resin backflow. In addition, an appropriate correction process can be performed in the metering process of the next shot following the injection process. As a result, it is possible to minimize the occurrence of defective products and provide stable operation of injection molding of high-quality molded products. In addition, the state of the related parts of the injection device, including the backflow prevention device, which affect the quality of the injection molding, is classified into three stages, and appropriate correction process is performed according to each classification. This makes it possible to avoid interruption of the injection molding operation due to unexpected trouble, and to provide injection molding operation with high production efficiency.

The above describes a preferred embodiment of the present invention, but the technical scope of the present invention is not limited to the scope described in the above embodiment. Various modifications and improvements can be made to the above embodiment.

REFERENCE SIGNS LIST 100 Injection molding machine 10 Injection unit 11 Screw 12 Flight 13 Rear seat 14 Check ring 15 Screw head 21 Injection cylinder 22 Cylinder head 23 Nozzle 24 Heater 25 Material hopper 30 Injection drive unit 40 Injection control unit 50 Injection molding die 51 Fixed die 52 Movable die 53 Die cavity 54 Gate F Forward B Rear A Region R Flow path MF Flow direction of molding material SF Direction of screw movement GF Direction of check ring movement P1 Resin pressure on the B side rear of the check ring P2 Resin pressure on the F side forward of the check ring S Screw position VP Injection pressure hold switching position SS Injection start position SH1, SH2 Injection start correction position KE, KE2 Metering completion position KH1, KH2 Measurement completion correction position K Reference waveform H Upper limit value L Lower limit value NG1, NG2, NG3 Measurement waveform PR Rising start position PF Return position SK Permissible position KH Monitoring range SB1 First correction distance QF Second correction distance SV1 Correction speed V1 Injection speed

Claims (5)

1. An injection molding method comprising the steps of: providing a backflow prevention device at the tip of a screw; storing a plasticized and molten resin material in an injection cylinder in front of the screw in a metering step; and injecting and filling the resin material into a mold cavity in an injection step;
An operation determination mode for determining an opening/closing operation of the backflow prevention device,
In the operation determination mode, the injection pressure in the injection process is used as a measured waveform, and when the measured waveform is within a range of upper and lower limits set in advance with respect to a reference waveform, the opening and closing operation of the backflow prevention device is determined to be normal, and when the pressure rise start position of the measured waveform is delayed beyond a preset allowable position with respect to the reference waveform, the opening and closing operation of the backflow prevention device is determined to be a first abnormality, and a first correction process is performed.
the first correction process defines a distance of the screw from the injection start position of the injection process to the pressure rise start position as a first correction distance, and defines an injection speed at the start of injection of the injection process as a correction speed, and in the metering process, the metering process is started based on a preset metering control pattern, and after the screw reaches a metering completion position, the rotational operation of the screw is stopped, the screw is moved back without rotation at the correction speed for the first correction distance, and the screw is stopped at a completion position of the non-rotational retraction .
2. The injection molding method according to claim 1, wherein the first correction process advances the screw at a preset speed from the completion position of the non-rotational retreat, and after the position of the screw reaches the metering completion position, starts the injection process based on a preset injection control pattern.
In the operation determination mode, the pressure rise start position of the measurement waveform is delayed from the allowable position, and further,
When the pressure recovery position of the measured waveform is within a preset monitoring range with respect to the reference waveform, the first abnormality is determined to be in the opening and closing operation of the backflow prevention device, and the first correction process is performed.
3. The injection molding method according to claim 1, wherein when the pressure recovery position of the measured waveform is outside a preset monitoring range with respect to the reference waveform, a second abnormality is judged to be present in the opening and closing operation of the backflow prevention device, and a second correction process is performed.
4. The injection molding method according to claim 3, wherein the second correction process defines a distance of the screw from an injection start position of the injection process to the pressure return position as a second correction distance, and determines a metering completion correction position by adding the second correction distance to the metering completion position, and in the metering process, the metering process is started based on a preset metering control pattern, and after the screw reaches the metering completion correction position, the rotation of the screw is stopped, the screw is non-rotatingly retracted at the correction speed for the first correction distance, and the screw is stopped at the completion position of the non-rotating retraction, and in the injection process, the screw is advanced from the completion position of the non-rotating retraction at a preset speed, and after the position of the screw reaches the metering completion correction position, the injection process is started based on the preset injection control pattern.
5. The injection molding method according to claim 3, wherein in the operation determination mode, when the pressure rise start position of the measured waveform lags behind the allowable position and further the injection pressure of the measured waveform does not return to the injection pressure of the reference waveform, a third abnormality is determined to be present in the opening and closing operation of the backflow prevention device, and a third correction process is performed to issue an alarm recommending replacement work of parts related to the injection device including the backflow prevention device.

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