JP4537441B2 - Control method of injection molding machine - Google Patents

Description

  The present invention relates to a method for controlling an injection molding machine.

  It is known that an injection pressure profile in a filling / holding process is a large factor that determines the accuracy of a molded product in injection molding. In the case of a thin-walled molded product, a molding failure phenomenon such as short, sink, burr, warp, etc. occurs due to the difference in injection pressure before and after V / P switching (switching from injection process to pressure holding process). In particular, overfilling, which is the cause of burrs, is also a direct cause of mold breakage and is a molding defect phenomenon that is most hated.

  Molding conditions for avoiding the above-described defective phenomenon include V / P switching position setting, injection speed setting, holding pressure setting, etc., but each setting affects each other in a complicated manner, so that good molding is achieved. To find the conditions, even an expert needs very complicated work.

  On the other hand, even if the V / P switching is performed using the detection value of the mold internal pressure sensor installed in the mold (so-called mold internal pressure V / P switching), the holding pressure setting after the V / P switching is determined. It's not easy.

  FIG. 3 shows the behavior of the screw speed, gate pressure, screw position, and injection pressure in the conventional injection / holding process. Normally, the pressure holding process is controlled by setting the pressure and time.

  However, the behavior of the resin in the mold cavity is, for example, an increase in volume that occurs when the resin compressed by the gate or the like is released in the cavity. The pressure in the pressure-holding process (the pressure in the screw head) was changed. However, there is little influence on the resin in the cavity due to the flow volume in the nozzle from the screw head to the cavity, the volume of the resin in the spool and the runner.

  On the other hand, the following injection molding methods have been proposed. When the screw advances and reaches the set position after the injection process starts, the screw is stopped at the set position for the set time. Alternatively, after the injection process starts, when the pressure in the injection cylinder reaches the set pressure, the screw is stopped at the position at the time when the pressure is reached (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 7-299850 (second page, FIG. 3)

  However, in the method as described above, since the screw position and the pressure in the injection cylinder are likely to vary for each molding cycle, it is difficult to stably mold an accurate molded product.

  Accordingly, an object of the present invention is to provide a method for controlling an injection molding machine that can improve the accuracy of a molded product.

According to the control method of the injection molding machine of the present invention, the screw is advanced to start filling the resin mold cavity into the cavity, and the screw position of the screw is maintained before the resin is filled in the cavity. , after filling the inside of said cavity, characterized that you transition to the pressure-holding process.

  Furthermore, in the control method according to the present invention, the screw position maintaining time is 0.5 (sec) or less.

  According to the present invention, an accurate molded product can be stably molded.

  It can be said that the control method according to the present invention is a molding method utilizing the characteristics of the molten resin (compressibility as an elastic body), which will be described later.

  FIG. 1 shows a schematic configuration of a hydraulic injection molding machine to which the present invention is applied. On the hydraulic injection device side, the screw 12 in the heating cylinder 20 is driven by the screw driving cylinder 11 via an injection shaft (not shown). That is, the screw 12 can be moved forward, backward, and stopped by controlling the inflow and outflow of the hydraulic oil to the screw driving cylinder 11 by the cylinder driving servo valve 13. The cylinder drive servo valve 13 switches a hydraulic path between the screw drive cylinder 11, the hydraulic source 14, and the hydraulic oil tank 15. Injection pressure sensors 16 and 17 are provided in the hydraulic piping, and a screw position sensor 18 is provided in a movable portion that moves integrally with the screw 12.

  On the other hand, on the mold clamping device side, a fixed mold 22 is attached to the fixed platen 21, and a movable mold 24 is attached to the movable platen 23. In this embodiment, in order to detect the mold internal pressure of the mold, a mold internal pressure sensor 25 is provided on the cavity surface of the mold. The mold internal pressure sensor may be provided in the runner portion or the gate, and the pressure detected in either case is referred to as mold internal pressure.

  In this control method, a control device (not shown) receives detection signals from various sensors such as the injection pressure sensors 16 and 17, the screw position sensor 18 and the mold pressure sensor 25, and controls the cylinder drive servo valve 13 to perform the following. The control method is executed.

  Next, the control operation by this control method will be described. In the following, only the control operation portion related to the present invention will be mainly described in the molding operation per cycle.

  In the control method according to the present embodiment, after the injection process starts, when the pressure obtained by the mold internal pressure sensor 25 installed in the mold reaches a preset pressure (hereinafter referred to as screw position control start mold internal pressure) Screw position control is performed to maintain the screw at the current screw position, and after a preset screw position control time has elapsed, the process proceeds to a conventional pressure holding process. That is, in this control method, it can be said that there is no conventional V / P switching.

  FIG. 2 shows the behavior of the screw speed, in-mold pressure, screw position, and injection pressure in the molding operation including the injection step, screw position control step, and pressure holding step when the present invention is applied. Here, the used resin shows a high compressibility characteristic in the molten state, and the mold pressure sensor is shown in the case where it is arranged in the runner portion. Therefore, the in-mold pressure shown in FIG. 2 indicates the pressure in the runner portion.

  After the filling process based on the detection signals of the injection pressure sensors 16 and 17 is reached, when the pressure in the runner reaches a mold internal pressure (screw position control start mold internal pressure) set just before the resin fills the cavity. By controlling the screw position using the detection signals of the screw position sensor 18 and the mold internal pressure sensor 25, the screw position at that time can be maintained and overfilling in the cavity can be prevented, and the distance from the gate in the cavity can be increased. It is possible to prevent the occurrence of burrs occurring at the locations. In other words, in a state where the position of the screw is maintained, the resin is just filled in the cavity and is full.

  Thereafter, when a preset time elapses, the screw position control is released, that is, the screw position is released, and the process proceeds to the pressure holding process by the pressure control based on the detection signals of the injection pressure sensors 16 and 17 again. Although the screw may be temporarily retracted due to the shift to the pressure-holding step, the injection pressure is kept constant by the action of the pressure-holding step of applying a predetermined pressure in the mold by pressure control.

  For the in-mold pressure for starting the screw position holding and the time until the position holding is maintained and the pressure holding process is started, the values obtained when a good molded product is obtained in the molding conditions are adopted. . Further, the screw position control time is usually a value of 0.5 (sec) or less in the case of a thin molded product.

  As described above, when the in-mold pressure sensor is used for screw position control, the variation in the in-mold pressure for each molding cycle is small, so that a highly accurate molded product can be stably molded.

  Needless to say, the present invention is applicable not only to the hydraulic injection molding machine as described with reference to FIG. 1 but also to an electric injection molding machine.

1 shows a schematic configuration of a hydraulic injection molding machine to which the present invention is applied. The behavior of screw speed, in-mold pressure, screw position, and injection pressure in a molding operation including an injection process, a screw position control process, and a pressure holding process when the present invention is applied is shown. The behavior of screw speed, gate pressure, screw position, and injection pressure in the conventional injection / holding process is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Screw drive cylinder 12 Screw 13 Cylinder drive servo valve 14 Hydraulic source 15 Hydraulic oil tank 16, 17 Injection pressure sensor 18 Screw position sensor 20 Heating cylinder 21 Fixed platen 22 Fixed mold 23 Movable platen 24 Movable mold 25 Internal pressure Sensor

Claims (2)

Advance the screw to start filling the resin mold cavity,
From just before the resin is filled in the cavity, maintaining the screw position of the screw, after filling the inside of the cavity, a control method of an injection molding machine, characterized that you transition to the pressure-holding process. The control method according to claim 1 , wherein the screw position maintaining time is 0.5 (sec) or less.

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