Injection molding method

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

[Technical field]

[0001] The present invention relates to an injection molding method in which a backflow prevention device is provided at the tip of a screw, plasticized and molten resin material is stored in an injection cylinder in front of the screw in a metering process, and the resin material is injected to fill a mold cavity in an injection process.

[0002] In injection molding using an injection molding machine, first, a 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 motion of a screw with a spiral flight and heat from a heater or the like provided 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 moves backwards, and the rotational motion of the screw is stopped at a predetermined backward position to maintain the screw position (metering process). Resistance is applied to the backward motion of the screw to adjust the melting and mixing properties of the stored molding material (called back pressure control).

[0003] Next, the screw is moved forward to inject and fill the mold cavity with the measured resin (injection process). The molten resin is filled under pressure (pressure holding process) to compensate for the solidification shrinkage that occurs as it cools and solidifies, and the mold cavity is cooled and held (cooling process), after which 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.

[0004] Here, the tip of the screw is provided with a backflow prevention device with 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 advances, 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 side 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, for example, fluctuations in product weight, 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, it is necessary to stop injection molding and replace parts related to the screw, including the backflow prevention device, which significantly reduces productivity. For this reason, many proposals have been made to accurately grasp the operating state of opening and closing the flow passage of a backflow prevention device and to prevent the backflow of the metered resin (called resin backflow) during the injection process.

[0005] 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 the backflow of resin in 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 switching point of the injection speed in the injection process.

[0006] Also, as shown in Patent Document 3, an injection reference point is provided forward of the injection start position by the screw stroke amount obtained by adding the amount of backflow of molten resin due to the delay in closing the flow passage of the backflow prevention device at the start of injection and the amount of void 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 void 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 the metering is completed, the back pressure is reduced (the screw moves backward), the flow passage 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 the metering accuracy.

[0007] Also, as shown in Patent Document 5, after metering is completed, the screw is advanced and the pressure of the molten resin at the tip of the screw is increased above the metering back pressure to close the flow path of the backflow prevention device. After that, the screw is 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 be kept closed until the start of the injection process. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 3-230930 [Patent Document 2] Japanese Patent Application Publication No. 4-250016 [Patent Document 3] Japanese Patent Application Publication No. 7-214617 [Patent Document 4] JP 2002-18923 A [Patent Document 5] JP 2007-253388 A Summary of the Invention [Problem to be solved by the invention]

[0009] Here, the backflow prevention device is generally a backflow prevention ring type in which the flow path is opened and closed by moving forward and backward in the screw axial direction, and this backflow prevention device of the backflow prevention ring type is also used in Patent Documents 1 to 5. Therefore, in Patent Document 1, the backflow prevention ring is in the front flow path opening position when metering is completed. In the pressurizing operation after the metering process, the screw advances toward the front backflow prevention ring, and the flow path is closed when it comes into contact with it. 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 is in an incomplete state. In other words, in Patent Document 1, the flow path of the backflow prevention device cannot be kept closed from the completion of the metering process to the start of the injection process, and there is a concern of backflow of the molten resin even in the injection process. Also, 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 pressure rise caused by the pressurizing operation after the metering process. Furthermore, there is a great concern that volatile gases contained in the molten resin will dissipate due to the pressurization and depressurization of the molten resin after the metering process, resulting in molding defects due to gas entrapment.

[0010] In addition, since Patent Document 2 also uses a backflow prevention device of the check ring type, there are concerns about the same problems as in Patent Document 1. Although molding defects such as stringiness can be avoided because the nozzle and the mold are in contact with each other, the mold cannot be opened to remove the molded product until the correction operation after the metering process is completed, and therefore productivity improvement by shortening the molding cycle cannot be expected.

[0011] In addition, the same problem as in Patent Document 1 is a concern in Patent Document 3. Furthermore, the backflow amount of the 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 the 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 entrainment. 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.

[0012] 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 necessarily required forward of the nozzle. Without these means, the molten resin will leak from the nozzle in the pre-injection process in which the check ring is forcibly closed, and molding defects such as fluctuations in the metered resin amount, stringing defects, and unexpected filling into the mold cavity (sagging defects) will inevitably occur.

[0013] 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 the solid resin in the solid transport area (also called the transport zone) of the screw and the molten resin that has flowed backwards mix, 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 is required.

[0014] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to provide an injection molding method that can ensure a stable amount of injected resin regardless of the opening and closing operation of a backflow prevention device for the screw. [Means for solving the problem]

[0015] 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 predetermined upper and lower limits relative 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 in the measured waveform is delayed beyond a predetermined allowable position relative 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.

[0016] 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.

[0017] 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.

[0018] 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 preset monitoring range for the reference waveform, it is preferable that 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.

[0019] 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 backlash, and in the injection process, moves the screw forward from the completion position of the non-rotational backlash 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.

[0020] 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 a third abnormality has occurred 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. Effect of the Invention

[0021] According to the present invention, it is possible to provide an injection molding method that can ensure a stable amount of injected resin regardless of the opening and closing operation of a backflow prevention device for the screw. [Brief description of the drawings]

[0022] [Figure 1] 1 is a conceptual diagram of an injection molding machine according to an embodiment of the present invention. [Diagram 2] 13A-13D illustrate the operation of the backflow prevention device during the metering process. [Diagram 3] 11A and 11B are diagrams illustrating an operational abnormality of a backflow prevention device. [Figure 4] 1 is a diagram showing an overall flow of an injection molding method according to an embodiment of the present invention. [Diagram 5]FIG. 3 is a diagram showing an injection pressure waveform according to the first embodiment of the present invention. [Figure 6] FIG. 1 is a flow diagram showing an injection molding method according to a first embodiment of the present invention. [Figure 7] FIG. 11 is a diagram showing an injection pressure waveform according to a second embodiment of the present invention. [Figure 8] FIG. 5 is a flow diagram showing an injection molding method according to a second embodiment of the present invention. [Figure 9] FIG. 11 is a diagram showing an injection pressure waveform according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Preferred embodiments for carrying out the present invention will be described below 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 means of solving the problems 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.

[0024] [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.

[0025] In the injection mold 50, the fixed mold 51 and the movable mold 52 are supported by a mold clamping device (not shown), and the movable mold 52 is movable forward and backward relative to the fixed mold 51 by the mold clamping device. Here, with regard to the operation of the movable mold 52, the operation of approaching the fixed mold 51 is defined as a mold closing operation, and the operation of moving away from the fixed mold 51 is defined as a 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 a mold touch point, the operation from the mold touch point in the mold closing operation direction is defined as a mold clamping operation, the completion position of the mold clamping operation is defined as a mold clamping limit, and the operation from the mold clamping limit to the mold touch point is defined as a pressure reducing 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 for filling the mold cavity 53 with a resin material.

[0026] The injection device 10 includes a cylindrical injection cylinder 21 and a screw 11 that is disposed inside 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 a resin material into a mold cavity 53 to obtain a resin molded product.

[0027] The injection cylinder 21 has a plurality of heaters 24 arranged at a predetermined interval on its outer circumferential surface, and the heaters 24 are 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 for preheating the supplied resin material, imparting heat to the resin material during plasticization, and controlling the temperature of the plasticized molten resin in the metering process 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 the resin material is injected and filled into the mold cavity 53, the nozzle is connected to a 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.

[0028] The screw 11 is disposed in the injection cylinder 21 so as to be able to 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 a control command from the injection control unit 40 to adjust the rotational movement and forward and backward movement of the screw 11. Here, regarding the movement of the screw 11, the direction closer to the mold cavity 53 is defined as the forward F, the movement toward the forward F is defined as the forward movement, the direction away from the mold cavity 53 is defined as the backward B, and the movement toward the backward B is defined as the backward movement.

[0029] 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 with respect 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 constant interval and a constant 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.

[0030] The screw 11 is cylindrical in shape with a diameter that increases stepwise 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 decrease stepwise 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 resin material is compressed and heated by shear due to the reduction in volume, and is melted stepwise (referred to as plasticization) by the synergistic effect of the heat provided by 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 (referred to as metered resin). As the amount of metered resin increases, the screw 11 retreats to the rear B side, stops rotating at a predetermined retreat position, and holds the stopped position (referred to as a metering process). The melting and kneading properties of the molding material are adjusted by restricting the backward movement of the screw 11 (this is called back pressure control). In the injection process, the screw 11 is advanced to inject and fill the measured resin into the mold cavity 53.

[0031] 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 referred to as resin materials. In addition, instead of thermoplastic resins, thermosetting resins such as phenol (PF) resin and melamine (MF) resin may be used.

[0032] [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, with 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.

[0033] 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. Due to this flow of the resin material, the non-return ring 14 is pressed against the screw head 15 on the front F side, and the flow path R is opened. 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 due to this pressure difference, the non-return ring 14 is pressed forward F side, and the flow path R is maintained open.

[0034] Next, as shown in Fig. 2(b), the rotational movement of the screw 11 is stopped to complete the metering process. Here, due to the stop of the rotational movement of the screw 11, the flow of the resin material toward the front F side stops, and the resin pressure P1 on the rear B side from 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 B-side rear seat 13, and the flow path R is closed. GF in the figure indicates the operating direction of the check ring 14. Until the flow path R is closed, the metered resin flows backward through the flow path R toward the screw 11 side (referred to as resin backflow). However, if the operation of the check ring 14 is stable, the amount of this resin backflow also becomes stable. As a result, the amount of the metered resin is set in anticipation of a stable amount of resin backflow.

[0035] In the injection process, as shown in Fig. 3(a), with the flow path R closed, the screw 11 moves forward, and the metered resin on the front F side of the screw head 15 flows in the direction of the nozzle 22 and is injection-molded into the mold cavity 53. Due to the stability of the operation of the check ring 14 (stability of the amount of resin backflow) and the closing of the flow path R, the injection molding amount filled into the mold cavity 53 is ensured with high precision, realizing stable production of high-quality molding quality. However, in actual molding sites, there are many occurrences of the phenomenon that the injection molding amount of the molding material fluctuates and the molding quality is not stable. The reason for this phenomenon will be explained with reference to Fig. 3(b).

[0036] For example, the backflow prevention ring 14 inevitably suffers damage such as wear, deformation, and scratches due to a long-term injection molding operation. The inner wall surface of the injection cylinder 21 also inevitably suffers similar damage. 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 completion of the metering process 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 the metered resin varies. Furthermore, as shown in FIG. 3(b), when the backflow prevention ring 14 stops midway and the flow path R opens, the resin backflow continues until the pressure difference disappears (P2 ≒ P1), and the amount of the metered resin varies greatly. Furthermore, even in the injection process, the resin backflow varies until the open flow path R closes. The closing timing of the flow path R also varies. Due to these variations, the amount of injection filling varies greatly, making it very difficult to ensure the stabilization of molding quality.

[0037] In addition, a visualization device capable of observing the inside of injection cylinder 21 was created, and the states shown in Figures 2 and 3 were also confirmed using this visualization device. Therefore, we believe that by taking measures to accurately detect and improve the state shown in Figure 3(b), we can stabilize the injection and filling of resin material into mold cavity 53, and we propose the injection molding method described below. Note that such an idea has not been suggested at all in the prior art.

[0038] [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 the mold cavity 53 (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 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.

[0039] At the same time as the start of the injection process, an operation determination mode is started to determine the operation of the check ring 14 and the open / closed state of the flow path R, and the injection pressure waveform (referred to as a measured waveform) during 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 check ring 14 and the open / closed state of the flow path R are determined to be normal, and stable operation of the injection molding is guaranteed. If the measured waveform and the reference waveform differ, the process proceeds 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 the injection pressure from the start of injection, the injection control unit 40 determines that a minor abnormality has occurred in the operation of the check ring 14 and the closed state of the flow path R, and transmits a first abnormality determination and performs a first correction process.

[0040] A delay in the increase in injection pressure is confirmed, and further, an 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 a first abnormality judgment, the timing of the return of the injection pressure is within a monitoring range described later. 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 closed state of the flow path R, and the injection control unit 40 issues a second abnormality judgment and performs a second correction process. On the other hand, if the injection pressure cannot be restored, it is determined that a serious abnormality has occurred in the parts 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, by issuing an alarm and recommending the execution of maintenance work.

[0041] [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 FIG. 4 and FIG. 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.

[0042] First, as shown in FIG. 5(a), the screw 11 is advanced from the injection start position SS (measurement completion position KE) toward the injection pressure holding switching position VP to inject and fill the mold cavity 53 with the metered resin. The injection control pattern at that time is the reference waveform K shown by the solid line. The upper limit value H and the lower limit value L that can obtain a good molding are shown by the broken line. The upper limit value H and the lower limit value L may be obtained from past injection molding results or calculated using a resin flow analysis tool. The measurement waveform NG1 is superimposed on this reference waveform K to perform waveform evaluation. When the rise of the injection pressure of the measurement waveform NG1 is delayed and the rise start position PR is out of 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 injection pressure of the measurement waveform NG1 returns to the reference waveform K and the return position PF is within the monitoring range KH (KH≧PF), it is determined as the first abnormality and the first correction process is performed.

[0043] In the first correction process, as shown in Fig. 6, a first correction distance SB1 and a correction speed SV1 are obtained. 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 measurement 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 a metering completion correction position KH1 in the injection control unit 40. The metering completion correction position KH1 becomes the injection start correction position SH1 of 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). These setting results are shown in Fig. 5(b).

[0044] Next, based on the setting result of FIG. 5(b), the metering process and the injection operation are performed as shown in FIG. 6. First, in the metering process, the metering operation is performed based on a preset metering control pattern without changing the metering conditions such as the rotation speed of the screw 11 and back pressure control. When the position S of the screw 11 reaches the metering completion position KE, the rotation operation of the screw 11 is stopped. Immediately after that, the screw 11 is moved back 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. 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 caught part that would prevent the reverse cylinder 14 from moving. 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 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.

[0045] 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, 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 indicated in the original metering process. Therefore, in the injection process after the metering completion position KE, the injection process, the injection pressure holding switch, the pressure holding process, the cooling process, and the mold opening / product removal process can be carried out without changing the injection control pattern set in advance. The forward movement 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 repelled when the rear seat 13 comes into contact with the non-return ring 14. Alternatively, the correction speed SV1 (=injection speed V1) may be set as the forward movement speed in order to smoothly take over the forward movement of the screw 11 before and after the metering completion position KE. As a result, even if an abnormality suddenly occurs during injection molding in the operation of the check ring 14 and the closure state of the flow path R, causing molding defects, the abnormality can be detected immediately and the abnormality can be avoided by taking appropriate corrective action. As a result, it is possible to return to molding a good product from the next injection molding shot, and losses can be minimized.

[0046] [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 explanations of parts that overlap with the first embodiment will be omitted.

[0047] First, as shown in FIG. 7(a), when the start position PR of the increase in injection pressure of the measurement waveform NG2 is delayed, deviates from the allowable position SK (PR>SK), and the injection pressure of the measurement waveform NG2 returns to the reference waveform K and the return position PF thereof is outside the monitoring range KH (KH<PF), it is determined as a second abnormality 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 for offsetting the metering completion position KE backward to the B side (KE+QF). This is set as the metering completion position KE2 after the offset. This second correction distance QF is set in the injection control unit 40 as the return position PF of the injection pressure of the measurement waveform shown in FIG. 7(a) (QF=PF). Further, the first correction distance SB1 is added to the metering completion position KE2 (KE2+SB1), and it is 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. 7(b).

[0048] Next, based on the setting results in FIG. 7(b), as shown in FIG. 8, a metering process and an injection operation are performed. First, in the metering process, based on the metering completion position KE2 after the offset, 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. A metering operation is performed based on the changed metering conditions. When the position S of the screw 11 reaches the metering completion position KE2, the rotation operation of the screw 11 is stopped. Then, immediately, the screw 11 is retracted without rotation to the metering completion correction position KH2 at the retraction speed of the correction speed SV1 and stopped. The stop position of this retraction becomes the injection start correction position SH2 of the subsequent injection operation. Thereby, the same improvement effect as in the first embodiment is obtained. Further, due to the offset of the screw 11 to the B side, 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 change, and improvement in the operation of the check ring 14 and the opening / closing state of the flow path R is expected. In the range of the injection cylinder 21 that is not routinely used in injection molding, there is less wear damage and retained resin. If the offset metering completion correction position KH2 falls within this range, the expected degree of improvement is further increased.

[0049] 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 process of this advancement, 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 the 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 the 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, it is possible to avoid long-term production stoppage due to unexpected trouble.

[0050] [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. 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, similar to Figs. 5 and 7. Note that descriptions of points that overlap with the first and second embodiments will be omitted.

[0051] First, as shown in Fig. 9(a), if the rise start position PR of the injection pressure 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 does not return to the reference waveform K, it is determined as the third abnormality and the 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), it is determined as the third abnormality and the third correction process is performed.

[0052] 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 check 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 function of opening and closing 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 check ring 14. This makes it possible to prevent the generation of a large number of defective molded products, and also makes it possible to quickly restore stable production of injection molding by performing maintenance work at an appropriate time, thereby ensuring high production efficiency.

[0053] [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, appropriate correction processing 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 processing 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.

[0054] Although the preferred embodiments of the present invention have been described above, the technical scope of the present invention is not limited to the scope described in the above-mentioned embodiments. Various modifications and improvements can be made to the above-mentioned embodiments. [Explanation of symbols]

[0055] 100 injection molding machine 10 Injection device 11 Screw 12 flights 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 section 50 Injection mould 51 Fixed mold 52 Movable mold 53 Mold Cavity 54 Gate F forward B Back Area A R flow path MF Flow direction of molding material SF Screw movement direction GF non-return ring operation direction P1 Resin pressure on the rear side B of the check ring P2 Resin pressure on the F side forward of the check ring S Screw position VP Injection pressure changeover position SS injection start position SH1, SH2 Injection start correction position KE, KE2 Weighing completion position KH1, KH2 Weighing completion correction position K reference waveform H Upper limit L Lower limit NG1, NG2, NG3 measurement waveform PR ascent start position PF Return position SK allowable position KH Monitoring Range SB1 1st correction distance QF Second correction distance SV1 correction speed V1 injection speed

Claims

1. 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. 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.

3. 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. 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. 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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