JP2018069627A - Injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection molding machine capable of decreasing variation in the weight of molded articles between shots.SOLUTION: Provided is an injection molding machine which includes: a cylinder for heating a molding material; a nozzle provided at a front end part of the cylinder; an injection member provided inside the cylinder to be movable back and forth; a drive source for moving the injection member back and forth; a pressure detector for detecting a pressure transmitted between the drive source and the injection member; and a controller for controlling the drive source on the basis of a detection result of the pressure detector. The controller controls the drive source on the basis of the detection result of the pressure detector detected between start of a loading step and rise of an internal pressure of the nozzle.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an injection molding machine.

  The controller of the injection molding machine described in Patent Document 1 controls the servo motor for injection so that the screw forward speed becomes a predetermined set speed in the injection process, and the screw position has reached the V / P switching position. At the time, the injection process is switched to the pressure holding process. In the pressure holding process, the injection servo motor is controlled so that the resin pressure at the front end of the screw is maintained at the pressure setting pressure. A load cell is used to detect the resin pressure in the pressure holding process.

JP 2011-183705 A

  Conventionally, the injection motor is controlled based on the detected value of the load cell in the pressure holding process, but the weight of the molded product sometimes varies between shots.

  The present invention has been made in view of the above problems, and a main object of the present invention is to provide an injection molding machine that can reduce variation in the weight of a molded product between shots.

In order to solve the above problems, according to one aspect of the present invention,
A cylinder for heating the molding material;
A nozzle provided at a front end of the cylinder;
An injection member disposed in the cylinder so as to freely advance and retract;
A drive source for advancing and retracting the injection member;
A pressure detector for detecting a pressure transmitted between the drive source and the injection member;
A control device for controlling the drive source based on the detection result of the pressure detector,
The control device controls the drive source based on a detection result of the pressure detector detected from a start of advance of the injection member in the filling process to a rise of the internal pressure of the nozzle. Is provided.

  According to one aspect of the present invention, there is provided an injection molding machine that can reduce variation in the weight of a molded product between shots.

It is a figure which shows the state at the time of the mold clamping of the injection molding machine by one Embodiment. It is a figure which shows the time change of the detected value of the pressure detector in the filling process by one Embodiment, or the detected value of a nozzle pressure detector.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a state during mold clamping of an injection molding machine according to an embodiment. As shown in FIG. 1, the injection molding machine includes a mold clamping device 10, an injection device 40, and a control device 90. Hereinafter, the description will be made assuming that the moving direction of the screw 43 at the time of filling (left direction in FIG. 1) is the front, and the moving direction of the screw 43 at the time of weighing (right direction in FIG. 1) is the rear.

  The mold clamping apparatus 10 performs mold closing, mold clamping, and mold opening of the mold apparatus 30. The mold apparatus 30 includes a fixed mold 32 and a movable mold 33. The mold clamping device 10 includes a fixed platen 12 to which a fixed mold 32 is attached and a movable platen 13 to which a movable mold 33 is attached. The mold clamping apparatus 10 performs mold closing, mold clamping, and mold opening of the mold apparatus 30 by moving the movable platen 13 with respect to the fixed platen 12.

  A cavity space 34 is formed between the movable mold 33 and the fixed mold 32 during mold clamping, and the injection device 40 fills the cavity space 34 with a liquid molding material. A molded product is obtained by solidifying the filled molding material. A plurality of cavity spaces 34 may be provided, and in this case, a plurality of molded products can be obtained simultaneously. The molded product is taken out from the mold apparatus 30 after the mold is opened.

  The injection device 40 is installed on a slide base Sb that can move forward and backward with respect to the frame Fr, and can move forward and backward with respect to the mold device 30. The injection apparatus 40 is touched by the mold apparatus 30 and fills the cavity space 34 in the mold apparatus 30 with the molding material. The injection device 40 includes, for example, a cylinder 41, a nozzle 42, a screw 43, a cooler 44, a metering motor 45, an injection motor 46, a pressure detector 47, a heater 48, and a temperature detector 49.

  The cylinder 41 heats the molding material supplied to the inside from the supply port 41a. The supply port 41 a is formed at the rear part of the cylinder 41. A cooler 44 such as a water-cooled cylinder is provided on the outer periphery of the rear portion of the cylinder 41. In front of the cooler 44, a heater 48 such as a band heater and a temperature detector 49 are provided on the outer periphery of the cylinder 41.

  The cylinder 41 is divided into a plurality of zones in the axial direction of the cylinder 41 (left and right direction in FIG. 1). A heater 48 and a temperature detector 49 are provided in each zone. For each zone, the control device 90 controls the heater 48 so that the temperature detected by the temperature detector 49 becomes the set temperature.

  The nozzle 42 is provided at the front end of the cylinder 41 and is pressed against the mold apparatus 30. A heater 48 and a temperature detector 49 are provided on the outer periphery of the nozzle 42. The control device 90 controls the heater 48 so that the detected temperature of the nozzle 42 becomes the set temperature.

  The screw 43 is disposed in the cylinder 41 so as to be rotatable and movable back and forth. When the screw 43 is rotated, the molding material is fed forward along the spiral groove of the screw 43. The molding material is gradually melted by the heat from the cylinder 41 while being fed forward. As the liquid molding material is fed to the front of the screw 43 and accumulated in the front portion of the cylinder 41, the screw 43 is retracted. Thereafter, when the screw 43 is advanced, the liquid molding material accumulated in front of the screw 43 is injected from the nozzle 42 and filled in the mold apparatus 30. The screw 43 corresponds to the injection member described in the claims.

  The weighing motor 45 rotates the screw 43. The drive source for rotating the screw 43 is not limited to the metering motor 45, and may be a hydraulic pump, for example.

  The injection motor 46 moves the screw 43 back and forth. Between the injection motor 46 and the screw 43, a motion conversion mechanism for converting the rotational motion of the injection motor 46 into the linear motion of the screw 43 is provided. The motion conversion mechanism includes, for example, a screw shaft and a screw nut that is screwed onto the screw shaft. A ball, a roller, or the like may be provided between the screw shaft and the screw nut. The drive source for moving the screw 43 back and forth is not limited to the injection motor 46, and may be a hydraulic cylinder, for example.

  The pressure detector 47 detects the pressure transmitted between the injection motor 46 and the screw 43. The pressure detector 47 is provided in a force transmission path between the injection motor 46 and the screw 43 and detects the pressure acting on the pressure detector 47.

  The pressure detector 47 sends a signal indicating the detection result to the control device 90. The detection result of the pressure detector 47 is used for control and monitoring of the pressure received by the screw 43 from the molding material, the back pressure against the screw 43, and the pressure acting on the molding material from the screw 43.

  As illustrated in FIG. 1, the control device 90 includes a CPU (Central Processing Unit) 91, a storage medium 92 such as a memory, an input interface 93, and an output interface 94. The control device 90 controls the mold clamping device 10 and the injection device 40 by causing the CPU 91 to execute a program stored in the storage medium 92. Further, the control device 90 receives a signal from the outside through the input interface 93 and transmits a signal through the output interface 94 to the outside. The control device 90 controls a filling process, a pressure holding process, a weighing process, and the like.

  In the filling step, the injection motor 46 is driven to advance the screw 43 at a set speed, and the liquid molding material accumulated in front of the screw 43 is filled into the cavity space 34 in the mold apparatus 30. The position and speed of the screw 43 are detected using, for example, the encoder 46a of the injection motor 46. The encoder 46 a detects the rotation of the injection motor 46 and sends a signal indicating the detection result to the control device 90. When the position of the screw 43 reaches the set position, switching from the filling process to the pressure holding process (so-called V / P switching) is performed. The set speed of the screw 43 may be changed according to the position and time of the screw 43.

  In addition, after the position of the screw 43 reaches the set position in the filling process, the screw 43 may be temporarily stopped at the set position, and then V / P switching may be performed. Immediately before the V / P switching, instead of stopping the screw 43, the screw 43 may be moved forward or backward at a slow speed.

  In the pressure-holding step, the injection motor 46 is driven to push the screw 43 forward, and the pressure of the molding material at the front end of the screw 43 (hereinafter also referred to as “pressure-holding pressure”) is maintained at a set pressure, The molding material remaining on is pressed toward the mold apparatus 30. Insufficient molding material due to cooling shrinkage in the mold apparatus 30 can be replenished. The holding pressure is detected using a pressure detector 47, for example. The pressure detector 47 sends a signal indicating the detection result to the control device 90. The set value of the holding pressure may be changed according to the elapsed time from the start of the holding process.

  In the pressure holding process, the molding material in the cavity space 34 in the mold apparatus 30 is gradually cooled, and when the pressure holding process is completed, the inlet of the cavity space 34 is closed with the solidified molding material. This state is called a gate seal, and backflow of the molding material from the cavity space 34 is prevented. After the pressure holding process, the cooling process is started. In the cooling process, the molding material in the cavity space 34 is solidified. In order to shorten the molding cycle, a metering step may be performed during the cooling step.

  In the metering step, the metering motor 45 is driven to rotate the screw 43 at a set rotational speed, and the molding material is fed forward along the spiral groove of the screw 43. Along with this, the molding material is gradually melted. As the liquid molding material is fed to the front of the screw 43 and accumulated in the front portion of the cylinder 41, the screw 43 is retracted. The number of rotations of the screw 43 is detected by using, for example, an encoder 45a of the measuring motor 45. The encoder 45a sends a signal indicating the detection result to the control device 90.

  In the measuring step, the set back pressure may be applied to the screw 43 by driving the injection motor 46 in order to limit the rapid retreat of the screw 43. The back pressure with respect to the screw 43 is detected using a pressure detector 47, for example. The pressure detector 47 sends a signal indicating the detection result to the control device 90. When the screw 43 is retracted to the set position and a predetermined amount of molding material is accumulated in front of the screw 43, the measuring process is completed.

  FIG. 2 is a diagram illustrating temporal changes in the detection value of the pressure detector and the detection value of the nozzle pressure detector in the filling process according to the embodiment. In FIG. 2, the horizontal axis indicates the elapsed time from the start of the filling process, and the vertical axis indicates the pressure. In FIG. 2, the solid line represents the time change of the detection value of the pressure detector 47, and the broken line represents the time change of the detection value of the nozzle pressure detector 51.

  The nozzle pressure detector 51 detects the internal pressure of the nozzle 42. As shown in FIG. 1, the flow path inside the nozzle 42 may have a tapered hole with a gradually decreasing inner diameter and a straight hole with a constant inner diameter in this order from the rear side toward the front side. . In this case, the nozzle pressure detector 51 detects the internal pressure of the straight hole. When the flow path inside the nozzle 42 has a plurality of sets of tapered holes and straight holes, the nozzle pressure detector 51 may detect the internal pressure of the straight hole closest to the cylinder 41 among the plurality of straight holes.

  As shown in FIG. 2, when the filling process is started and the advancement of the screw 43 is started, the advancement speed of the screw 43 is accelerated from zero to the set speed and maintained at the set speed. The advancement of the screw 43 causes resistance and mechanical resistance from the molding material accumulated in front of the screw 43, and the detection value of the pressure detector 47 rises from zero. Thereafter, when the molding material in the cylinder 41 is pushed forward from the cylinder 41 and flows into the nozzle 42, the detection value of the nozzle pressure detector 51 rises from zero. Thus, there is a time difference between the start of the filling process and the rise of the internal pressure of the nozzle 42.

  The detection value of the pressure detector 47 detected between the start of the filling process and the rise of the internal pressure of the nozzle 42 represents the movement resistance of the screw 43. The movement resistance of the screw 43 includes both resistance from the molding material accumulated in front of the screw 43 and mechanical resistance. The mechanical resistance includes, for example, sliding resistance of a motion conversion mechanism that converts the rotational motion of the injection motor 46 into linear motion of the screw 43, sliding resistance between the cylinder 41 and the screw 43, and the like. The greater the detected value of the pressure detector 47 detected between the start of the filling process and the rise of the internal pressure of the nozzle 42, the greater the movement resistance of the screw 43.

  By the way, the movement resistance of the screw 43 may vary between shots. For example, when the temperature of the molding material varies, the viscosity of the molding material varies, so that the movement resistance of the screw 43 varies. Further, when the temperature of the motion conversion mechanism varies, the viscosity of the lubricant for the motion conversion mechanism varies, and thus the movement resistance of the screw 43 varies. Further, if the temperature of the cylinder 41 varies, the inner diameter of the cylinder 41 varies, so that the movement resistance of the screw 43 varies. As the movement resistance of the screw 43 increases, the molding material accumulated in front of the screw 43 is less likely to flow into the mold apparatus 30.

  Therefore, the control device 90 of the present embodiment reduces the variation in the weight of the molded product due to the variation in the movement resistance of the screw 43, so that the pressure detected between the start of the filling process and the rise of the internal pressure of the nozzle 42 is detected. Based on the detection value of the detector 47, the injection motor 46 is controlled. Thereby, the control of the injection motor 46 can be corrected based on the movement resistance of the screw 43, and the weight variation of the molded product between shots can be reduced.

  The detection value of the pressure detector 47 used for correcting the control of the injection motor 46 is acquired from the start of the filling process to the rise of the internal pressure of the nozzle 42. The detection value of the pressure detector 47 acquired after the internal pressure of the nozzle 42 rises is not used. This is because after the rising of the internal pressure of the nozzle 42, a flow resistance is newly generated due to the flow of the molding material from the cylinder 41 to the narrower nozzle 42.

  The detection value of the pressure detector 47 used for correcting the control of the injection motor 46 may be acquired from the start of the filling process to the rise of the internal pressure of the nozzle 42. Although the time slot | zone acquired is not specifically limited, For example, the following time slot | zones are mentioned.

  The detection value of the pressure detector 47 used for correcting the control of the injection motor 46 is from time t1 when the acceleration of the screw 43 ends and the forward speed reaches the set speed to time t4 when the internal pressure of the nozzle 42 rises. It may be acquired in between, or may be acquired while the forward speed of the screw 43 is constant. This is because during the acceleration of the screw 43, noise included in the detection value of the pressure detector 47 increases due to fluctuations in mechanical resistance.

  Between the time t1 when the forward speed of the screw 43 reaches the set speed and the time t4 when the internal pressure of the nozzle 42 rises, the time period during which the detection value of the pressure detector 47 is stable (for example, the time from time t2 to time t4) Obi). The detection value of the pressure detector 47 in this time zone may be used as a value representing the movement resistance of the screw 43.

  Since the time t4 when the internal pressure of the nozzle 42 rises may vary between shots, the pressure detector 47 between time t2 and time t3 (time t3 is later than time t2 and earlier than time t4). May be used as a value representing the movement resistance of the screw 43.

  After the measurement at time t2, time t3, time t4, and the like, if the measurement data is stored in the storage medium 92, the nozzle pressure detector 51 becomes unnecessary and may be removed from the nozzle 42. That is, the nozzle pressure detector 51 may not be attached to the injection molding machine. Manufacturing costs and maintenance costs can be reduced. The times t2, t3, t4, etc. may be obtained by simulation using fluid analysis software.

  The detection value of the pressure detector 47 used for correcting the control of the injection motor 46 may be any of a waveform pattern, an average value, a representative value, and the like.

  For example, the control device 90 performs injection in the pressure-holding process performed subsequent to the filling process based on the detection value of the pressure detector 47 detected between the start of the filling process and the rise of the internal pressure of the nozzle 42. The motor 46 is controlled. According to the movement resistance of the screw 43, the control of the injection motor 46 in the pressure holding process can be corrected.

  The correction in the pressure holding process may include, for example, (1) correction of the pressure holding pressure. (1) Holding pressure correction: (1A) Correction of holding pressure setting value, (1B) Correction of holding pressure detection value, (1C) Holding pressure setting value and holding pressure detection value Or (1D) correction of the current command calculated from the deviation. The current command is calculated by, for example, PID calculation or PI calculation.

  As the movement resistance of the screw 43 increases, the molding material accumulated in front of the screw 43 is less likely to flow into the mold apparatus 30. Therefore, the control apparatus 90 corrects the holding pressure to a large value, and the mold apparatus 30. Helps the flow of molding material into the interior. Thereby, the weight variation of a molded article can be suppressed.

  The holding pressure may be corrected as a whole from the start of the holding process to the end of the holding process, or may be corrected in a part in between. For example, when multistage holding pressure is performed, the set values of the holding pressures in at least some stages may be corrected. Here, the multistage holding pressure means a holding pressure process in which the set value of the holding pressure is changed stepwise from the start of the holding process to the end of the holding process.

  The correction in the pressure holding process may include (2) correction of the time from the start of the pressure holding process to the end of the pressure holding process (hereinafter also simply referred to as “pressure holding time”). As the movement resistance of the screw 43 increases, the molding material accumulated in front of the screw 43 is less likely to flow into the mold device 30, so the control device 90 corrects the pressure holding time to a longer value. Thereby, the weight variation of a molded article can be suppressed. When multistage holding pressure is performed, the control device 90 may correct the time length of some stages or the time length of all stages.

  The correction in the pressure holding process is (3) the time for switching the set value of the pressure holding pressure between the start of the pressure holding process and the end of the pressure holding process (hereinafter also simply referred to as “multistage switching time”). Corrections may be included. Similar to the case of correcting the pressure holding time, the weight variation of the molded product can be suppressed by correcting the multistage switching time.

  When correcting the multistage switching time, the control device 90 may keep the pressure holding time constant without correcting the molding cycle so as not to change. In this case, since the molding material accumulated in front of the screw 43 is less likely to flow into the mold apparatus 30 as the movement resistance of the screw 43 is larger, the time length of the time zone in which the set value of the holding pressure is relatively large The time length is corrected to a long value, and the time length of the time zone in which the set value of the holding pressure is relatively small is corrected to a short value. Thereby, the weight variation of a molded product can be suppressed, without changing a shaping | molding cycle.

  The control device 90 may also correct the pressure holding time when correcting the multistage switching time.

  At least one of the above (1) correction of holding pressure, (2) correction of holding pressure, and (3) correction of multistage switching time may be performed, and a plurality of corrections are performed in combination. May be. The combination is not particularly limited.

  The control device 90 performs the nozzle correction from the start of the filling process in order to perform at least one correction among (1) correction of holding pressure, (2) correction of holding pressure, and (3) correction of multistage switching time. The detection value of the pressure detector 47 detected until the rising of the internal pressure 42 and a reference value set in advance may be used.

  When the detected value of the pressure detector 47 detected from the start of the filling process to the rise of the internal pressure of the nozzle 42 is larger than the reference value, the movement resistance of the screw 43 is relatively large, and the molding material is the mold device. 30 is relatively difficult to flow into. In this case, the control device 90 corrects the holding pressure to a large value. In this case, the control device 90 may correct the pressure holding time to a long value, and may similarly correct the multistage switching time.

  On the other hand, when the detected value of the pressure detector 47 detected between the start of the filling process and the rise of the internal pressure of the nozzle 42 is smaller than the reference value, the movement resistance of the screw 43 is relatively small, and the molding material is gold. It is relatively easy to flow into the mold apparatus 30. In this case, the control device 90 corrects the holding pressure to a small value. In this case, the control device 90 may correct the pressure holding time to a short value, and may similarly correct the multistage switching time.

  It should be noted that the control device 90 of the present embodiment is a storage device that is performed following the filling process based on the detection value of the pressure detector 47 detected between the start of the filling process and the rise of the internal pressure of the nozzle 42. Although the pressure process is controlled, the filling process may be controlled. The control of the injection motor 46 in the filling process can be corrected according to the movement resistance of the screw 43.

  For example, the control device 90 controls the screw 43 in the filling process so that the detection value of the pressure detector 47 detected between the start of the filling process and the rise of the internal pressure of the nozzle 42 becomes the reference value. The forward speed may be corrected.

  The forward speed is corrected by (A) correcting the forward speed setting value, (B) correcting the forward speed detection value, (C) correcting the deviation between the forward speed setting value and the forward speed detection value, (D ) Any correction of the current command calculated from the deviation may be used. The current command is calculated by, for example, PID calculation or PI calculation.

  The control device 90 may activate an output device that outputs an alarm based on the detection value of the pressure detector 47 detected between the start of the filling process and the rise of the internal pressure of the nozzle 42. As the output device, an image display device, a warning light, a buzzer, or the like is used.

  The alarm is output, for example, when the difference between the detected value of the pressure detector 47 detected between the start of the filling process and the rise of the internal pressure of the nozzle 42 and the reference position is outside the allowable range. With the output of the alarm, the control device 90 may interrupt the molding operation of the injection molding machine, but does not have to interrupt it.

  The embodiments of the injection molding machine have been described above, but the present invention is not limited to the above embodiments and the like, and various modifications are possible within the scope of the gist of the present invention described in the claims. Improvements are possible.

  For example, the injection device 40 of the above embodiment is an inline screw method, but may be a pre-plastic method. A pre-plastic injection device supplies a molding material melted in a plasticizing cylinder to the injection cylinder, and injects the molding material from the injection cylinder into a mold device. In the plasticizing cylinder, a screw is rotatably or rotatably and reciprocally disposed, and in the injection cylinder, a plunger is reciprocally disposed. In this case, the plunger corresponds to the injection member recited in the claims, and the injection device has a drive source such as an electric motor or a hydraulic cylinder that moves the plunger back and forth.

40 Injection Device 41 Cylinder 42 Nozzle 43 Screw (Injection Member)
45 Weighing motor 46 Injection motor (drive source)
47 Pressure detector 51 Nozzle pressure detector 90 Control device

Claims (3)

A cylinder for heating the molding material;
A nozzle provided at a front end of the cylinder;
An injection member disposed in the cylinder so as to freely advance and retract;
A drive source for advancing and retracting the injection member;
A pressure detector for detecting a pressure transmitted between the drive source and the injection member;
A control device for controlling the drive source based on the detection result of the pressure detector,
The said control apparatus is an injection molding machine which controls the said drive source based on the detection result of the said pressure detector detected from the advance start of a filling process to the rise of the internal pressure of the said nozzle.   The control device is configured to perform the pressure holding step performed after the filling step based on a detection result of the pressure detector detected from a start of advancement of the filling step to a rise of the internal pressure of the nozzle. The injection molding machine according to claim 1, wherein the drive source is controlled.   The control device controls the driving source in the filling step based on a detection result of the pressure detector detected from a start of advancement of the filling step to a rise of an internal pressure of the nozzle. Item 3. The injection molding machine according to Item 1 or 2.

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