JP2023041084A - injection molding method - Google Patents

Abstract

To provide an injection molding method capable of securing a stable injection resin amount regardless of an opening and closing operation of a backflow prevention device for a screw.SOLUTION: An injection molding method equipped with a backflow prevention device at a tip of a screw 11, storing a plasticized molten resin material in an injection cylinder 21 in front of the screw 11 in a metering process, and injection filling the resin material into a mold cavity 53 in an injection process, includes an operation determination mode for determining an opening and closing operation of the backflow prevention device. In the operation determination mode, an injection pressure of the injection process is a measured waveform, and when the measured waveform is within a range of preset upper and lower limits relative to the reference waveform, the opening and closing operation of the backflow prevention device is determined normal, and when a pressure rise start position of the measured waveform is retarded from a preset allowable position relative to the reference waveform, a first abnormal determination of the opening and closing operation of the backflow prevention device is made and first correction processing is performed.SELECTED DRAWING: Figure 4

Description

The present invention is injection molding in which a backflow prevention device is provided at the tip of the screw, the plasticized and melted resin material is stored in the injection cylinder in front of the screw in the metering process, and the resin material is injected and filled into the mold cavity in the injection process. Regarding the method.

Injection molding using an injection molding machine first supplies a resin material into an injection cylinder using a material supply device. The supplied resin material is plasticized by shear heat generated by the rotating motion of the screw having a helical flight and the amount of heat generated by the heater or the like provided in the injection cylinder. stored within (referred to as weighing resin). As the resin to be measured is stored, the screw moves backward, and at a predetermined retracted position, the screw stops rotating and the screw position is held (measuring step). A resistive force is applied to the backward movement of the screw to adjust the melt-kneadability of the stored molding material (referred to as back pressure control).

Next, the screw is moved forward to inject and fill the measured resin into the mold cavity (injection step). After holding pressure filling (holding pressure process) to compensate for solidification shrinkage due to cooling and solidification of weighed resin in the molten state, and cooling and holding (cooling process) in the mold cavity, the mold is opened and the molded product is taken out 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 provided with a backflow prevention device in which a flow path through which the plasticized molten resin passes is formed. In the measuring process, the flow pressure of the molten resin that is rotationally transported pushes the backflow prevention device forward, opening the flow path and storing the measured resin at the tip of the screw. Further, in the injection process, the screw advances and the backflow prevention device abuts against the screw to close the flow path, thereby preventing the backflow of the measured resin to the rear side of the screw. In particular, in the injection process, if the closure of the flow path is ambiguous, the amount of metered resin filled into the mold cavity (referred to as injection filling amount) will fluctuate. Molding defects such as welds, voids, product deformation, and product shorts occur frequently, hindering the stabilization of product quality. Moreover, if these molding defects cannot be improved, the injection molding must be interrupted and the screw-related parts including the backflow prevention device must be replaced, resulting in a significant drop in productivity. For this reason, many proposals have been made to prevent backflow of the metered resin (referred to as resin backflow) in the injection process by accurately grasping the operating state of opening and closing of the flow path of the backflow prevention device.

For example, as shown in Patent Document 1, after the weighing process, the molten resin on the tip side of the screw is pressurized to close the check valve (pressurization operation), and in this state, the screw is retracted to pour out the stored molten resin. Make the pressure equal to atmospheric pressure (depressurization operation). It is said that the amount of injected resin can be stabilized by performing the injection process with the initial screw advance position as the reference position. In addition, as shown in Patent Document 2, after the weighing process, the molten resin on the screw tip side is pressurized (screw moves forward) while the nozzle and the mold are in contact, and then the molten resin on the screw tip side is pressurized. Pull out (screw retracts). It is said that resin backflow in the injection process can be prevented by obtaining a correction value from the metering completion position and the pressurization stop position or depressurization stop position and correcting the injection speed switching point in the injection process.

In addition, as shown in Patent Document 3, the backflow of the 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 space at the tip of the nozzle due to the suck back operation are added. An injection reference point is set ahead of the injection start position. In the injection process, the forward movement of the screw is temporarily stopped at the injection reference point. It is said that this eliminates 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 part including the backflow prevention device. Furthermore, after the completion of metering, the back pressure is lowered (screw retreats), the passage is forcibly closed in the pre-injection process (screw advances), the back pressure is lowered (screw retreats), and the screw retreats. It is supposed that the weighing completion position is corrected from the stop position of the This is said to improve the measurement accuracy.

Further, as shown in Patent Document 5, the screw is moved forward after the completion of metering, and the pressure of the molten resin on the tip side of the screw is made higher than the metering back pressure to close the flow path of the backflow prevention device. After that, the screw is reversely rotated to lower the pressure on the rear side of the anti-backflow device, and the screw is further retracted. According to this, the flow path of the backflow prevention device can be kept closed until the injection process is started.

JP-A-3-230930 JP-A-4-250016 JP-A-7-214617 JP-A-2002-18923 JP 2007-253388 A

Here, the backflow prevention device is generally of the check ring type in which the flow path is opened and closed by advancing back and forth in the screw axial direction. A backflow prevention device is used. Therefore, in Patent Document 1, the non-return ring is in the forward channel open position after the metering is completed. In the pressurizing operation after the metering process, the screw advances toward the non-return ring on the front and abuts to close 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 point that the backflow of the molten resin at this time is not expected and the possibility that the backflow may fluctuate. In addition, the depressurization operation is supposed to be such that the screw retreats 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 non-return ring to close the flow path disappears in the middle of the depressurization operation, and as a result, the non-return ring separates from the screw retraction operation and the flow path is closed. The road becomes half-finished. In other words, in Patent Document 1, the closed flow path of the backflow prevention device cannot be maintained from the completion of the metering process to the start of the injection process, and there is concern about the backflow of the molten resin even in the injection process. Further, it is said that defects such as threading can be prevented without using a shut-off valve. Furthermore, the pressurization and depressurization of the molten resin after the weighing process releases volatile gas and the like contained in the molten resin, and there is great concern about molding defects due to entrainment of the gas.

Moreover, since Patent Document 2 is also a non-return ring type backflow prevention device, the same problem as in Patent Document 1 is likely to occur. In addition, since the nozzle and the mold are in contact with each other, it is possible to avoid molding defects such as stringiness, but the mold cannot be opened and the molded product cannot be taken out until the correction operation after the weighing process is completed. , productivity improvement by shortening the molding cycle cannot be expected.

Also, in Patent Document 3, there is concern about the same problem as in Patent Document 1. Furthermore, the backflow of molten resin is calculated from the dimensions of the screw part including the backflow prevention device, etc., and does not indicate the backflow in actual injection molding. In other words, the elements of injection molding that are greatly related to the backflow of the molten resin, such as aging of the backflow prevention device, the type and viscosity of the molten resin, the melting temperature, and the conditions for the injection speed, are completely ignored. reliability is questionable. In addition, the nozzle section, which is in a high-temperature and high-pressure environment, requires means for measuring the void amount at the tip of the nozzle, and there are great concerns about the measurement accuracy and service life of this measuring means. Furthermore, in a suck-back operation after weighing that causes a gap at the tip of the nozzle, the resin pressure in front of the screw becomes negative, and air is sucked in from the tip of the nozzle, resulting in molding defects such as air entrainment. Furthermore, the pressure difference before and after the backflow prevention device increases, and the non-return 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 measured resin amount fluctuates greatly.

Further, in Patent Document 4, since the correction value is obtained from the dimensions of the screw part including the backflow prevention device, there is concern about the same problem as in Patent Document 3, and further, the same problem as in Patent Document 1. . In addition, for example, means for opening and closing the flow path of the molten resin, such as a shut-off valve and a mold valve gate, are always required on the front side of the nozzle. Without these measures, during the pre-injection process where the non-return ring is forcibly closed, molten resin leaks from the nozzle, resulting in fluctuations in the metered resin amount, poor stringiness, and unexpected filling of the mold cavity. Molding defects such as (defective dripping) always occur.

Furthermore, in Patent Document 5, all the problems listed in Patent Documents 1 to 4 are concerned. Also, it is added that the screw is reversely rotated. Due to this reverse rotation of the screw, the molten resin in the screw flows back to a large extent. In the weighing process of the next shot, there is a high probability that the weighing resin cannot be stored accurately, resulting in a weighing operation failure. In this case, the injection molding is interrupted and large-scale maintenance work such as screw cleaning is required.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an injection molding method capable of securing a stable amount of injected resin regardless of the opening/closing operation of a backflow prevention device for a screw.

The injection molding method of the present invention is
In an injection molding method in which a backflow prevention device is provided at the tip of a screw, a plasticized and melted resin material is stored in an injection cylinder in front of the screw in a weighing process, and the resin material is injected and filled into a mold cavity in an injection process. ,
An operation determination mode for determining 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 the range of the upper and lower limits set in advance with respect to the reference waveform, the open/close operation of the backflow prevention device is determined to be normal. , when the pressure rise start position of the measured waveform is delayed from the preset allowable position with respect to the reference waveform, it is determined as a first abnormality determination of the opening and closing operation of the backflow prevention device, and a first correction process is performed. characterized by

In the injection molding method of the present invention,
In the first correction process, the injection start position of the injection process and the distance of the screw to the pressure increase start position are set as the first correction distance, the injection speed at the start of injection of the injection process is set as the correction speed, and the In the metering step, the metering step is started based on a preset metering control pattern, and after the screw reaches the metering completion position, the rotation of the screw is stopped, and the first correction distance is set at the correction speed. It is preferable that the screw is retracted in a non-rotational manner and stopped at a position where the non-rotational retraction is completed.

Further, in the injection molding method of the present invention,
In the first correction process, the screw is advanced at a preset speed from the non-rotational retraction completion position, and after the screw position reaches the metering completion position, the injection control pattern is set in advance. Preferably, the injection process is started.

Further, in the injection molding method of the present invention,
In the operation determination mode, when the pressure rise start position of the measured waveform is delayed from the allowable position and the pressure return position of the measured waveform is outside a preset monitoring range with respect to the reference waveform, the It is preferable that the second abnormality determination of the opening/closing operation of the backflow prevention device is performed, and the second correction processing is performed.

Furthermore, in the injection molding method of the present invention,
In the second correction process, the distance of the screw from the injection start position of the injection process to the pressure recovery position is set as a second correction distance, and the second correction distance is added to the measurement completion position to correct the measurement completion. In the measuring process, the measuring process is started based on a preset measuring control pattern, and after the screw reaches the measuring completion correction position, the rotation of the screw is stopped and the first correction is performed. The screw is retracted non-rotationally at the corrected speed, and stopped at the completion position of the non-rotational retraction. It is preferable that after the screw position is advanced and the screw position reaches the metering completion correction position, the injection process is started based on a preset injection control pattern.

Further, in the injection molding method of the present invention,
In the operation determination mode, when the pressure rise start position of the measured waveform is delayed from the allowable position and the injection pressure of the measured waveform does not return to the injection pressure of the reference waveform, the opening and closing operation of the backflow prevention device It is preferable that, as the third abnormality determination, a third correction process is performed to issue an alarm to recommend replacement work of parts related to the injection device including the backflow prevention device.

According to the present invention, it is possible to provide an injection molding method capable of securing a stable amount of injected resin regardless of the opening/closing operation of the backflow prevention device for the screw.

1 is a conceptual diagram of an injection molding machine according to an embodiment of the present invention; FIG. FIG. 10 illustrates the operation of the anti-backflow device during the weighing process; It is a figure which shows the operation|movement abnormality of a backflow prevention apparatus. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the flow of the whole injection molding method which concerns on embodiment of this invention. It is a figure showing an injection pressure waveform concerning a 1st embodiment of the present invention. It is a flow chart showing the injection molding method concerning a 1st embodiment of the present invention. It is a figure which shows the injection pressure waveform based on 2nd Embodiment of this invention. It is a flow diagram showing an injection molding method according to a second embodiment of the present invention. It is a figure which shows the injection pressure waveform based on 3rd Embodiment of this invention.

Preferred embodiments for carrying out the present invention will be described below with reference to the drawings. In addition, the following embodiments do not limit the invention according to each claim. In addition, not all combinations of features described in the embodiments are essential for the solutions of the inventions according to the respective claims. In addition, in this embodiment, the scale 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. 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 the present invention is not limited to this. The injection molding machine 100 shown in FIG. 1 includes an injection device 10 , an injection drive section 30 , an injection control section 40 and an injection mold 50 .

In the injection molding die 50, a fixed die 51 and a movable die 52 are supported by a die clamping device (not shown), and the movable die 52 moves forward and backward with respect to the fixed die 51 by the die clamping device. Here, regarding the motion of the movable mold 52, the motion of approaching the fixed mold 51 is defined as the mold closing motion, and the motion of moving away from the fixed mold 51 is defined as the mold opening motion. In addition, the mold touch point is the position where the fixed mold 51 and the movable mold 52 abut during the mold closing operation, the mold clamping operation is the movement in the mold closing operation direction from the mold touch point, and the completion position of the mold clamping operation is The mold clamping limit and the operation from the mold clamping limit to the mold touch point are defined as the step-down operation. A mold cavity 53 is formed within the range of the mold clamping limit from the mold touch point. The stationary mold 51 is also provided with a gate 54 for filling the mold cavity 53 with a resin material.

The injection device 10 includes a cylindrical injection cylinder 21 and a screw 11 that is arranged in the injection cylinder 21 and that rotates about an axis and moves forward and backward in the axial direction. A resin molded product is obtained by injecting and filling the resin material toward the mold cavity 53 by the injection device 10 .

A plurality of heaters 24 are arranged on the outer peripheral surface of the injection cylinder 21 at predetermined intervals, and the temperature of the heaters 24 is controlled by a temperature control device (not shown) to manage the injection cylinder 21 at a predetermined temperature. The temperature control by the heater 24 is used for preheating the supplied resin material, applying heat to the resin material during plasticization, and controlling the temperature of the plasticized molten resin in the weighing process, which will be described later. The tip of the injection cylinder 21 is provided with a cylinder head 22 having a conical inner wall surface and a nozzle 23 . When injection-filling the resin material into the mold cavity 53, the nozzle and the gate 54 in the fixed mold 51 are connected. A material hopper 25 is provided behind the injection cylinder 21, and the resin material is supplied from the material hopper 25 into the injection cylinder 21 by a material supply device or the like (not shown).

The screw 11 is disposed in the injection cylinder 21 so as to be movable back and forth, and the injection drive section 30 and the rear end portion of the screw 11 are connected. The injection drive unit 30 is operated based on the control command from the injection control unit 40 to adjust the rotation and forward/backward movement of the screw 11 . Here, regarding the motion of the screw 11, the direction closer to the mold cavity 53 is defined as forward F, the forward motion F is forward motion, the direction away from the mold cavity 53 is backward B, and the backward motion B is backward motion. .

Further, the screw 11 is provided with a helical flight 12 extending from the rear B to the front F. The helical direction and angle of the flight 12 are set so that the resin material supplied from the material hopper 25 can be rotationally transported forward F with respect to the rotation direction of the screw 11 by the injection drive unit 30 . As shown in FIG. 1, the flights 12 are arranged in a single row at a constant interval and at a constant angle, but the arrangement is not limited to this. It can also be an array of Alternatively, a plurality of flights 12 may be arranged only in a partial range of the screw 11 .

Further, the screw 11 has a cylindrical shape whose diameter increases stepwise from the rear B to the front F. That is, the volume of the gap between the screw 11 and the injection cylinder 21 is reduced stepwise from the rear B to the front F, for example, the transport zone (FZ), the compression zone (CZ), and the melting zone (MZ). Set like this. As a result, the resin material supplied from the material hopper 25 is forwardly transported by the rotational motion of the screw 11 and the flight 12, and due to the reduction in volume, compression action and shear heat generation act on the resin material. Due to the synergistic effect, the melted resin is gradually melted (referred to as plasticization), the 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 (referred to as metering resin). As the amount of resin to be measured increases, the screw 11 retreats to the rear B side, stops rotating at a predetermined retreated position, and holds the stopped position (referred to as a metering process). The melt-kneadability of the molding material is adjusted by restricting the backward movement of the screw 11 (referred to as back pressure control). In the injection process, the screw 11 is advanced to inject and fill the mold cavity 53 with the measured resin.

Here, as a resin material used for injection molding, for example, in automobile interior parts, a thermoplastic resin such as polypropylene (PP) resin or polyethylene (PE) resin is added with a coloring agent such as black, red, or blue. It is common to adjust the color tone of the part. In addition, plasticizers that give flexibility to thermoplastic resins, nucleating agents and clarifying agents that control the degree of crystallinity in crystalline resins, flame retardants that suppress combustion, and antistatic agents that suppress static electricity. , lubricants that improve fluidity and releasability, weathering agents and UV deterioration inhibitors that suppress deterioration due to ultraviolet rays, and reinforcing agents such as glass fibers and carbon fibers. In addition, general-purpose resins such as polypropylene (PP) resin and polyethylene (PE) resin, engineering resins such as polyamide (PA) resin and polycarbonate (PC) resin, polyphenylene sulfide (PPS) resin and polyether ether ketone (PEEK) resin, etc. A thermoplastic resin such as a super engineering resin is selected as appropriate. A combination of thermoplastic resin and additives is called a resin material. Thermosetting resins such as phenol (PF) resins and melanin (MF) resins may be used instead of thermoplastic resins.

[Backflow prevention device]
Next, a backflow prevention device incorporated in the tip portion of the screw 11 will be described with reference to FIG. 1 and FIGS. 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. The operation abnormality of the backflow prevention device is shown. As shown in FIG. 1, the backflow prevention device has a rear seat 13, a ring-shaped non-return ring 14 having a flow path R through which the resin material passes, and a screw head 15 arranged from the screw 11 toward the front F. , the non-return ring 14 is of a non-rotating type that does not interlock with the rotation of the screw 11 . In the present invention, without being limited to this, for example, a non-return ring and a part of the screw head 15 are fitted, and the non-return ring rotates in conjunction with the rotation of the screw 11. can be Further, instead of the reverse shilling 14, a reverse flow 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 weighing process, the resin material plasticized by the rotational motion of the screw 11 flows to the front B side. Due to this flow of the resin material, the non-return ring 14 is pressed against the screw head 15 on the front side F, and the flow path R is opened. The resin material passes through this flow path R and flows into the injection cylinder 21 on the front side F of the screw head 15 to obtain a metered amount of resin. MF in the figure indicates the flow direction of the resin material. As the amount of resin to be measured increases, the screw 11 moves backward while maintaining the flow path R in an open state. SF in the drawing indicates the operating direction of the screw 11 . By restricting the backward movement of the screw 11 (back pressure control), the melt-kneading state of the weighed resin is adjusted, and as a result, the weighed resin having the resin pressure P2 is obtained. At this time, if the resin pressure P1 of the resin material on the rearward B side of the check ring 14 is P1>P2, the check ring 14 is pushed forward by this pressure difference, and the passage R is maintained open. be done.

Next, as shown in FIG. 2(b), the rotation of the screw 11 is stopped to complete the weighing process. Here, by stopping the rotation of the screw 11, the flow of the resin material to the front side F stops, and the resin pressure P1 on the rear side B of the check ring 14 becomes close to zero. As a result, the pressure difference across the check ring 14 reverses (P1<P2). Due to this reversal of the pressure difference, the check ring 14 is pressed against the rear seat 13 on the rearward B side, and the flow path R is closed. GF in the drawing indicates the operating direction of the non-return ring 14 . Until the flow path R is closed, the metered resin flows backward through the flow path R toward the screw 11 (referred to as resin backflow). The amount of is also stable. As a result, the amount of metered resin is set to allow for the amount of stable resin backflow.

In the injection process, as shown in FIG. 3(a), the screw 11 moves forward while the flow path R is closed, and the measured resin on the front side F of the screw head 15 flows toward the nozzle 22, and the metal is injected. Injection filling into the mold cavity 53 . Due to the stability of the operation of the check ring 14 (stable amount of backflow of resin) and the closure of the flow path R, the injection filling amount filled in the mold cavity 53 is ensured with high accuracy, and high molding quality is achieved. Realize stable production. However, in an actual molding site, a phenomenon often occurs in which the injection filling amount of the molding material fluctuates and the molding quality is unstable. The reason why this phenomenon occurs will be described with reference to FIG.

For example, long injection molding operations inevitably cause damage to the check ring 14, such as wear, deformation, and scratches. In addition, the inner wall surface of the injection cylinder 21 also suffers similar damage. Furthermore, the resin material adhering to the check ring 14 and the inner wall surface of the injection cylinder 21 deteriorates and accumulates as retained resin. As a result, the operation of the check ring 14 after the completion of the metering process becomes slow, and the time until the flow path R is closed varies. As a result, a phenomenon occurs in which the state of the resin backflow fluctuates and the amount of the metered resin fluctuates. Further, as shown in FIG. 3(b), when the check ring 14 stops halfway and the flow path R is opened, the resin backflow continues until the pressure difference disappears (P2≈P1), and the metered resin is discharged. Amounts vary greatly. Furthermore, even in the injection process, the resin backflow fluctuates until the open flow path R is closed. Moreover, the closing timing of the flow path R also fluctuates. Due to these fluctuations, the amount of injection filling fluctuates greatly, making it very difficult to ensure stable molding quality.

Moreover, the states shown in FIGS. 2 and 3 were also confirmed by a visualization device that allows observation of the inside of the injection cylinder 21 . Therefore, it is thought that injection and filling of the resin material into the mold cavity 53 can be stabilized by taking measures to accurately detect and improve the state shown in FIG. We propose an injection molding method. Such an idea is not suggested in the prior art at all.

[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. First, the fixed mold 51 and the movable mold 52 are clamped to form the mold cavity 53 (mold clamping step). Next, the injection process is started. In the injection process, the injection control unit 40 operates the injection drive unit 30 to move the screw 11 forward based on the injection control pattern of the injection speed and injection pressure set in advance, and the measured resin is injected into the mold cavity 53. Injection filling (injection operation). When the position S of the screw 11 reaches the injection and holding pressure switching position VP, through a holding pressure step for compensating for solidification shrinkage due to cooling and solidification of the weighed resin injected and filled, and a cooling step for cooling and solidifying in the mold cavity 53, The mold is opened and the cooled and solidified product is removed from the mold cavity.

Simultaneously with the start of the injection process, the operation determination mode for determining the operation of the check ring 14 and the open/closed state of the flow path R is started, and the injection pressure waveform (referred to as the measured waveform) in the injection process is acquired by the injection control unit 40. and perform waveform evaluation. When this measured waveform is evaluated to be within the allowable range with respect to the preset reference waveform, the operation of the check ring 14 and the opening/closing state of the flow path R are determined to be normal, and the stable operation of injection molding can be performed. Guaranteed. If the measured waveform and the reference waveform are different, proceed to the next step. First, if the only difference between the measured waveform and the reference waveform is the delay in the injection pressure rise timing from the start of injection, it is assumed that a slight abnormality has occurred in the operation of the check ring 14 and the closed state of the flow path R. , the injection control unit 40 issues a first abnormality determination and performs a first correction process.

A delay in injection pressure rise is confirmed, and furthermore, evaluation is made as to whether or not the delayed injection pressure has returned to the injection pressure set value of the injection control pattern. In the case of the first abnormality determination, the return timing of the injection pressure is within the monitoring range described later. If the return timing is later than the monitoring range, the injection control unit 40 issues a second abnormality determination, assuming that there is a moderate abnormality in the operation of the check ring 14 and the closed state of the flow path R. Perform correction processing. Further, when the injection pressure cannot be restored, the injection control unit 40 judges that there is a serious abnormality in the parts of the injection device 10 including the check ring 14 and the injection cylinder 21, and makes a third abnormality determination, for example, issues an alarm. A third correction process is performed to recommend that maintenance work be performed.

[Injection molding method of 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. FIG. 5 shows the 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. FIG. 6 is a flowchart of the first correction process subsequent to the first abnormality determination shown in FIG. For the injection pressure, for example, a pressure sensor may be 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 determine the injection pressure. Alternatively, in the hydraulic injection driving section 30, the injection pressure may be calculated from the supplied hydraulic pressure, and in the electric injection driving section 30, the injection pressure may be calculated from the drive torque of the electric motor. 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 as the injection pressure. It is assumed that the injection molding operation will be interrupted due to leakage or failure of the pressure sensor.

First, as shown in FIG. 5A, the screw 11 is advanced from the injection start position SS (measurement completion position KE) toward the injection holding pressure switching position VP to inject the measured resin into the mold cavity 53. let it fill. The injection control pattern at that time is assumed to be a reference waveform K indicated by a solid line. Also, the upper limit value H and the lower limit value L at which non-defective products can be obtained are indicated by dashed lines. The upper limit value H and the lower limit value L may be obtained from past injection molding results, or may be calculated using a resin flow analysis tool. Waveform evaluation is performed by superimposing the measured waveform NG1 on this reference waveform K. FIG. The rise of the injection pressure of the measured waveform NG1 is delayed, the rise start position PR deviates from the allowable position SK calculated from the upper limit value H and the lower limit value L of the reference waveform K (PR>SK), and the measured waveform NG1 When the injection pressure returns to the reference waveform K and the return position PF is within the monitoring range KH (KH≧PF), the first abnormality determination is made and the first correction process is performed.

In the first correction process, as shown in FIG. 6, a first correction distance SB1 and a correction speed SV1 are obtained. For the first correction distance SB1, the injection pressure increase start position PR of the measured waveform shown in FIG. 5(a) is set in the injection control unit 40 (SB1=PR). Also, the metering completion correction position KH1 is set in the injection control unit 40 by adding the ascending start position SB1 to the metering completion position KE. The metering completion correction position KH1 becomes the injection start correction position SH1 for the next shot. As the correction speed SV1, the injection control unit 40 sets the injection speed V1 at the start of injection of the reference waveform shown in FIG. 5A (SV1=V1). These setting results are shown in FIG.

Next, as shown in FIG. 6, a weighing process and an injection operation are performed based on the setting result of FIG. 5(b). First, in the weighing process, the weighing operation is performed based on a preset weighing control pattern without changing the weighing conditions such as the number of revolutions of the screw 11 and back pressure control. When the position S of the screw 11 reaches the metering completion position KE, the rotation of the screw 11 is stopped. Immediately thereafter, the screw 11 is retracted to the metering completion correction position KH1 at the retraction speed of the correction speed SV1 without rotation and stopped. The stop position of this retraction becomes the injection start correction position SH1 of the subsequent injection operation. As a result, the check ring 14 is positioned on the screw head 15 side, and the flow path R is open, but the pressure difference before and after the check ring 14 disappears (P1=P2), and the back flow of the resin can be reliably stopped. can. Further, even if the reverse shilling 14 is caught on the inner wall surface of the injection cylinder 21 due to wear scars, retained resin, etc., and the reverse shilling operation is slow, the backward movement of the screw 11 will prevent the reverse shilling from being caught. Anything that would unravel and block the operation of the inverse shilling 14 can be reliably eliminated. Furthermore, excessive retraction of the screw 11 causes the resin pressure P2 on the front side F of the reverse silling 14 to become a negative pressure, causing the resin material on the screw 11 side to leak out to the front side F of the screw head 15, resulting in the amount of resin to be measured. may be excessively increased. 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 seat 13 come into contact with each other to ensure that the passage R is closed. After the passage R is closed, the resin pressure P2 on the front side F of the check ring 14 is increased, and at the metering completion position KE, the resin pressure is returned to the back pressure controlled resin pressure shown in the original metering process. Therefore, in the injection process after the weighing completion position KE, the injection process, the injection holding pressure switching, the holding pressure process, the cooling process, and the mold opening/product ejection process can proceed without changing the preset injection control pattern. The advancing speed of the screw to the metering completion position KE is set to a speed that does not flip the check ring 14 when the rear seat 13 and the check ring 14 come into contact with each other. Alternatively, the correction speed SV1 (=injection speed V1) may be the forward speed so that the forward movement of the screw 11 before and after the metering completion position KE is smoothly taken over. As a result, even if an abnormality occurs in the operation of the non-return ring 14 and the closed state of the flow path R during the operation of injection molding and a molding defect occurs, the abnormality can be detected immediately, and appropriate correction processing can be performed. By doing so, anomalies can be avoided. As a result, it is possible to return to good product molding from the injection molding of the next shot, and it is possible to minimize the loss.

[Injection molding method of the second embodiment]
Next, an injection molding method according to a second embodiment of the present invention will be described with reference to FIGS. 7 and 8. FIG. As in FIG. 5, FIG. 7 shows the 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. FIG. 8 is a flowchart of second correction processing following the second abnormality determination shown in FIG. In addition, description is omitted about the part which overlaps with 1st Embodiment.

First, as shown in FIG. 7(a), the injection pressure rise start position PR of the measured waveform NG2 is delayed and deviates from the allowable position SK (PR>SK), and the injection pressure of the measured waveform NG2 reaches the reference waveform K. , and when the return position PF is outside the monitoring range KH (KH<PF), the second abnormality determination is performed and the second correction process is performed. In the second correction process, as shown in FIG. 8, a first correction distance SB1 and a correction speed SV1 are obtained in the same manner as in the first correction process. (KE+QF). The weighing completion position KE2 after this offset is set. This second correction distance QF sets the return position PF of the injection pressure of the measured waveform shown in FIG. 7A in the injection control unit 40 (QF=PF). Also, the first correction distance SB1 is added to the metering completion position KE2 (KE2+SB1) and set in the injection control unit 40 as the metering completion correction position KH2. The metering completion correction position KH2 becomes the injection start correction position SH2 for the next shot. These setting results are shown in FIG.

Next, as shown in FIG. 8, the weighing process and the injection operation are performed based on the setting result shown in FIG. 7(b). First, in the weighing process, only the switching position of each control among the weighing conditions such as the rotational speed of the screw 11 and back pressure control is changed based on the weighing 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 of the screw 11 is stopped. Immediately thereafter, the screw 11 is retracted to the metering completion correction position KH2 at the retraction speed of the correction speed SV1 without rotation and stopped. The stop position of this retraction becomes the injection start correction position SH2 of the subsequent injection operation. Thereby, an improvement effect similar to that of the first embodiment is obtained. Furthermore, due to the offset of the screw 11 toward the rear B side, the state of contact between the check ring 14 and the inner wall surface of the injection cylinder 21 and the volume state of the retained resin change, and the operation of the check ring 14 and the opening/closing state of the flow path R change. is expected to improve. The area of the injection cylinder 21 that is not routinely used in injection molding has less wear damage and less residual resin. If the offset metering completion correction position KH2 falls within this range, the degree of improvement is expected to increase further.

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. In the course of this forward movement, the passage R is closed and the pressure of the metered resin is adjusted, as in the first embodiment. In the injection process after the metering completion position KE2, the injection process is performed based on the injection control pattern in which the switching position of each control is changed, similar to the change of the metering conditions. The position after the injection/holding pressure switching position VP is the same as in the first embodiment. Thereby, an improvement effect similar to that of the first embodiment is obtained. In addition, the restoration of stable injection molding production can be expected to extend the life of 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 where there is little wear damage and residual resin, for example, it is possible to avoid foreign matter defects due to peeling of the residual resin. In addition, it is possible to prevent long-term production stoppages due to unexpected troubles by taking advance measures such as arranging replacement parts for the injection device 10 such as the non-return ring 14 in response to the second abnormality determination.

[Injection molding method of the third embodiment]
Next, an injection molding method according to a third embodiment of the invention will be described with reference to FIG. FIG. 9, like FIGS. 5 and 7, shows the 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. In addition, description is omitted about the part which overlaps with 1st Embodiment and 2nd Embodiment.

First, as shown in FIG. 9(a), the injection pressure rise start position PR of the measured waveform NG3 is delayed and deviates from the allowable position SK (PR>SK), and the injection pressure of the measured waveform NG3 is the reference waveform K. A third abnormality determination is made when the state does not return to the normal state, and a third correction process is performed. Note that even if the first correction process is performed, the injection pressure of the measured waveform NG3 does not return to the reference waveform K, or as shown in FIG. 9B, even if the second correction process is performed, the measured waveform NG3 If the injection pressure does not return to the reference waveform K, the third abnormality determination is made and the 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, for example, that the check ring 14 or the inner wall surface of the injection cylinder 21 is worn, deformed, scratched, or accumulated in accumulated resin. This is because the function of opening and closing the flow path R does not work properly, resulting in a serious abnormal condition. That is, the third abnormality determination suggests that stable injection molding production cannot be continued. Therefore, in the third correction process, it is recommended to issue a warning, interrupt the injection molding operation, and perform maintenance work such as replacement of parts of the injection device 10 that affect the weighing process and the injection process, such as the check ring 14. . As a result, it is possible to prevent a large number of defective molded products from being generated, and by performing maintenance work at an appropriate timing, it is possible to quickly restore stable injection molding production and ensure high production efficiency.

[effect]
In this way, from the injection pressure waveform during the injection process, the quality of the injection molding is most affected from the completion of the weighing process to the injection process. Accurate degree of resin backflow can be achieved. Further, accurate correction processing can be performed in the weighing process for the next shot following the injection process. As a result, the occurrence of defective products can be minimized, and stable operation of injection molding of high-quality molded products can be provided. In addition, the states of parts related to the injection device, including the backflow prevention device, which affect the quality of injection molding, are classified into three stages, and appropriate correction processing is performed according to each classification. As a result, interruption of injection molding operation due to unexpected trouble can be avoided, and injection molding operation with high production efficiency can be provided.

Although the preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the ranges described in the above-described embodiments. Various modifications or improvements can be added to the above embodiments.

REFERENCE SIGNS LIST 100 injection molding machine 10 injection device 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 section 40 injection control section 50 injection mold 51 fixed mold 52 Movable mold 53 Mold cavity 54 Gate F Front B Rear A Region R Flow path MF Flow direction of molding material SF Operating direction of screw GF Operating direction of check ring P1 Resin pressure on B side behind check ring P2 Reverse Resin pressure on the front F side of the retaining ring S Screw position VP Injection holding pressure switching position SS Injection start position SH1, SH2 Injection start correction position KE, KE2 Metering completion position KH1, KH2 Metering completion correction position K Reference waveform H Upper limit L Lower limit Value NG1, NG2, NG3 Measurement waveform PR Rise start position PF Return position SK Allowable position KH Monitoring range SB1 First correction distance QF Second correction distance SV1 Correction speed V1 Injection speed

Claims (6)

In an injection molding method in which a backflow prevention device is provided at the tip of a screw, a plasticized and melted resin material is stored in an injection cylinder in front of the screw in a weighing process, and the resin material is injected and filled into a mold cavity in an injection process. ,
An operation determination mode for determining 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 the range of the upper and lower limits set in advance with respect to the reference waveform, the open/close operation of the backflow prevention device is determined to be normal. , when the pressure rise start position of the measured waveform is delayed from the preset allowable position with respect to the reference waveform, it is determined as a first abnormality determination of the opening and closing operation of the backflow prevention device, and a first correction process is performed. An injection molding method characterized by: In the first correction process, the injection start position of the injection process and the distance of the screw to the pressure increase start position are set as the first correction distance, the injection speed at the start of injection of the injection process is set as the correction speed, and the In the metering step, the metering step is started based on a preset metering control pattern, and after the screw reaches the metering completion position, the rotation of the screw is stopped, and the first correction distance is set at the correction speed. 2. The injection molding method according to claim 1, wherein the screw is non-rotationally retracted and the screw is stopped at a position where the non-rotational retraction is completed. In the first correction process, the screw is advanced at a preset speed from the non-rotational retraction completion position, and after the screw position reaches the metering completion position, the injection control pattern is set in advance. 3. The injection molding method according to claim 1 or 2, wherein an injection process is started. In the operation determination mode, when the pressure rise start position of the measured waveform is delayed from the allowable position and the pressure return position of the measured waveform is outside a preset monitoring range with respect to the reference waveform, the 4. The injection molding method according to any one of claims 1 to 3, wherein a second correction process is performed as a second abnormality determination of the opening/closing operation of the backflow prevention device. In the second correction process, the distance of the screw from the injection start position of the injection process to the pressure recovery position is set as a second correction distance, and the second correction distance is added to the measurement completion position to correct the measurement completion. In the measuring process, the measuring process is started based on a preset measuring control pattern, and after the screw reaches the measuring completion correction position, the rotation of the screw is stopped and the first correction is performed. The screw is retracted non-rotationally at the corrected speed, and stopped at the completion position of the non-rotational retraction. 5. The injection molding method according to claim 4, wherein after the screw is advanced and the screw position reaches the metering completion correction position, the injection process is started based on a preset injection control pattern. In the operation determination mode, when the pressure rise start position of the measured waveform is delayed from the allowable position and the injection pressure of the measured waveform does not return to the injection pressure of the reference waveform, the opening and closing operation of the backflow prevention device 6. The injection molding method according to claim 4 or 5, wherein the third abnormality determination is performed, and a third correction process is performed to generate an alarm recommending replacement work of parts related to the injection device including the backflow prevention device.

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