JP6186113B2 - Injection molding machine - Google Patents

Description

  The present invention relates to an injection molding machine.

  The injection molding machine includes an injection device that injects molten resin into a mold apparatus. The mold apparatus includes a fixed mold and a movable mold, and a cavity space is formed between the fixed mold and the movable mold when the mold is clamped. The injection device measures the molten resin in a cylinder, and fills the cavity space in the mold apparatus with the measured molten resin. The resin cooled and solidified in the cavity space is taken out as a molded product after the mold is opened (see, for example, Patent Document 1).

International Publication No. 2005/068155

  The melting speed of the resin material may vary due to variations in the particle size of the resin material. For this reason, the molding becomes unstable, and the quality of the molded product may be deteriorated.

  The present invention has been made in view of the above problems, and an object thereof is to provide an injection molding machine having excellent molding stability.

In order to solve the above problems, an injection molding machine according to an aspect of the present invention is provided.
A screw that fills the mold by measuring and injecting the molten resin in the cylinder;
A weighing motor for rotating the screw;
A detector for detecting the rotational torque of the weighing motor;
A drive unit for moving the screw in the axial direction;
A control unit for controlling the measuring motor and the moving drive unit,
The control unit adjusts a filling amount by the screw by adjusting a setting value related to the control of the moving drive unit in the injection / holding step based on a detection value of the detector in a measuring step. .

An injection molding machine according to another aspect of the present invention is
A screw for measuring molten resin in a measuring cylinder;
A weighing motor for rotating the screw;
A detector for detecting the rotational torque of the weighing motor;
An injection cylinder for receiving the molten resin measured in the measuring cylinder;
A plunger that injects molten resin in the injection cylinder and fills the mold;
A driving unit for moving the plunger in the axial direction;
A control unit for controlling the measuring motor and the moving drive unit,
The control unit adjusts a filling amount by the plunger by adjusting a setting value related to the control of the driving unit for movement in the injection / holding step based on a detection value of the detector in a measuring step. .

  According to the present invention, an injection molding machine excellent in molding stability is provided.

It is a figure which shows the mold clamping apparatus of the injection molding machine by one Embodiment of this invention. It is a figure which shows the injection apparatus of the injection molding machine by one Embodiment of this invention. It is a figure which shows the time change of the various parameters which show the state of the injection molding machine by one Embodiment. It is a schematic diagram which shows the time change of the rotational torque of the motor for measurement by one Embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In each of the drawings, the same or corresponding components are denoted by the same or corresponding reference numerals, and description thereof will be omitted.

(Clamping device)
FIG. 1 is a view showing a mold clamping device of an injection molding machine according to an embodiment of the present invention. FIG. 1 shows a state of mold clamping. In the description of the mold clamping device, the moving direction of the movable platen when closing the mold will be referred to as the front, and the moving direction of the movable platen when opening the mold will be described as the rear.

  The injection molding machine 10 includes a frame 11, a fixed platen 12 fixed to the frame 11, and a toggle support 15 that is movable with respect to the frame 11 at a predetermined distance between the fixed platen 12 and the frame 11. Is provided. A plurality of (for example, four) tie bars 16 are installed between the fixed platen 12 and the toggle support 15.

  The injection molding machine 10 further includes a movable platen 13 that is disposed so as to face the fixed platen 12 and that can be moved back and forth (moved in the left-right direction in the drawing) along the tie bar 16. A movable mold 33 is attached to a surface of the movable platen 13 facing the fixed platen 12, and a fixed mold 32 is attached to a surface of the fixed platen 12 facing the movable platen 13. The fixed mold 32 and the movable mold 33 constitute a mold apparatus 30.

  The injection molding machine 10 includes a toggle mechanism 20 disposed between the movable platen 13 and the toggle support 15, a mold clamping motor 26 that operates the toggle mechanism 20, and rotational movement generated by the mold clamping motor 26. A ball screw mechanism 27 is further provided as a transmission mechanism that converts the motion into a linear motion and transmits it to the toggle mechanism 20. The fixed platen 12, the movable platen 13, the toggle support 15, the toggle mechanism 20, the mold clamping motor 26, and the like constitute a mold clamping device.

  The toggle mechanism 20 includes a crosshead 24 that is movable back and forth in a direction parallel to the mold opening / closing direction, a second toggle lever 23 that is swingably attached to the crosshead 24, and a first that is swingably attached to the toggle support 15. A toggle lever 21 and a toggle arm 22 that is swingably attached to the movable platen 13 are provided. Between the first toggle lever 21 and the second toggle lever 23 and between the first toggle lever 21 and the toggle arm 22 are linked. The toggle mechanism 20 is a so-called inner winding 5-node double toggle mechanism, and has a vertically symmetrical configuration.

  The ball screw mechanism 27 includes, for example, a ball screw nut 27a fixed to the cross head 24 and a ball screw shaft 27b screwed to the ball screw nut 27a. The ball screw shaft 27b is rotatably supported with respect to the toggle support 15. When the output shaft of the mold clamping motor 26 rotates, the ball screw shaft 27b rotates and the ball screw nut 27a advances and retreats, so that the cross head 24 advances and retreats.

  When the toggle mechanism 20 is operated by driving the mold clamping motor 26 in the forward direction and advancing the cross head 24 as a driven member, the movable platen 13 is advanced and the mold is closed.

  When the mold clamping motor 26 is further driven in the forward direction, the toggle mechanism 20 generates a mold clamping force obtained by multiplying the propulsive force of the mold clamping motor 26 by the toggle magnification. A mold clamping force sensor 17 is attached to a tie bar 16 that extends according to the mold clamping force. The mold clamping force sensor 17 detects the mold clamping force every predetermined time by detecting distortion (elongation) of the tie bar 16. The detected mold clamping force is sequentially input to the control unit 80. A cavity space C is formed between the fixed mold 32 and the movable mold 33 in the clamped state. The cavity space C is filled with molten resin and solidified to form a molded product.

  Subsequently, when the mold clamping motor 26 is driven in the reverse direction, the cross head 24 is moved backward, and the toggle mechanism 20 is operated, the movable platen 13 is moved backward to perform mold opening. Thereafter, by operating the electric ejector device, the molded product is ejected from the movable mold 33.

  The mold clamping device of this embodiment uses the toggle mechanism 20 to generate the mold clamping force. However, without using the toggle mechanism 20, the driving force generated by the mold clamping motor 26 is directly applied to the mold clamping force. May be transmitted to the movable platen 13. Further, the propulsive force generated by the mold clamping cylinder may be directly transmitted to the movable platen 13 as a mold clamping force. Further, the mold may be opened and closed by a linear motor, and the mold may be clamped by an electromagnet, and the system of the mold clamping device is not limited.

(Injection device)
FIG. 2 is a view showing an injection apparatus of an injection molding machine according to an embodiment of the present invention. In the description of the injection device, unlike the description of the mold clamping device, the resin injection direction is assumed to be the front and the direction opposite to the resin injection direction is assumed to be the rear.

  The injection molding machine 10 further includes an injection device 40 that injects the resin melted in the heating cylinder 42 from the nozzle 41 and fills the cavity space C in the mold device 30. The injection device 40 includes an injection motor (movement drive unit) 43. The rotation of the injection motor 43 is transmitted to the ball screw shaft 44. A ball screw nut 45 that moves forward and backward by the rotation of the ball screw shaft 44 is fixed to a pressure plate 46. The pressure plate 46 is movable along guide bars 47 and 48 fixed to a base frame (not shown). The forward / backward movement of the pressure plate 46 is transmitted to the screw 52 via a bearing 49, a resin pressure detector (for example, load cell) 50, and an injection shaft 51. The screw 52 is disposed in the heating cylinder 42 so as to be rotatable and movable in the axial direction. A hopper 53 for resin supply is provided at the rear portion of the heating cylinder 42. The rotation movement of the metering motor 55 is transmitted to the injection shaft 51 via a connecting member 54 such as a belt or a pulley. That is, when the injection shaft 51 is rotationally driven by the metering motor 55, the screw 52 rotates.

  In the weighing step, the weighing motor 55 is driven to rotate the screw 52, and the resin pellet supplied to the rear end portion of the screw 52 is sent to the front of the screw 52. In this process, the resin pellets are softened and melted. Since the molten resin is stored in front of the screw 52, the screw 52 moves backward. In the injection process (also referred to as a filling process), the injection motor 43 is driven to advance the screw 52 and push the molten resin to inject from the nozzle 41. The molten resin is pushed into the cavity space C through the sprue S, the runner R, the gate G and the like shown in FIG. The force with which the screw 52 pushes the molten resin is detected as a reaction force by the resin pressure detector 50. That is, the resin pressure applied to the screw 52 (resin injection pressure) is detected. The detected resin pressure is input to the control unit 80. In addition, since the resin is thermally contracted by cooling in the cavity space C, the resin pressure (resin injection pressure) applied to the screw 52 is maintained at a predetermined pressure in the pressure-holding process in order to replenish the heat-shrinkable resin. It is.

  A position detector 57 that detects the position of the screw 52 is attached to the pressure plate 46. A detection signal from the position detector 57 is input to the control unit 80. The detection signal of the position detector 57 may also be used to detect the moving speed of the screw 52.

  Each of the injection motor 43 and the metering motor 55 may be a servo motor, and includes encoders 43a and 55a for detecting the rotation speed. The rotation speeds detected by the encoders 43a and 55a are respectively input to the control unit 80. The controller 80 feedback-controls the injection motor 43 and the metering motor 55 based on the detection results of the encoders 43a and 55a.

  The control unit 80 is configured by a microcomputer or the like, and includes, for example, a CPU, a ROM for storing control programs, a readable / writable RAM for storing calculation results, a timer, a counter, an input interface, an output interface, and the like. Have.

(Time change of various parameters indicating the state of the injection molding machine)
FIG. 3 is a diagram illustrating a change over time of actual values of various parameters indicating the state of the injection molding machine according to the embodiment. In FIG. 3, the horizontal axis represents time, and the vertical axis represents the screw position, the screw forward speed (resin injection speed), and the screw pressure (resin injection pressure). In FIG. 3, for convenience of explanation, the screw stop time (t3−t1) is illustrated to be longer than the actual time. The injection molding machine 10 is a mold closing process for closing the mold apparatus 30 and a mold clamping process for tightening the mold apparatus 30. An injection process for controlling the injection speed of the resin, a pressure holding process for controlling the injection pressure of the resin, a cooling process for solidifying the resin in the mold apparatus 30 after the pressure holding process, and a resin for the next molded product are measured. A metering process, a mold opening process for opening the mold apparatus 30, and an ejecting process for projecting a molded product from the mold apparatus 30 after the mold opening are performed. The injection molding machine repeatedly manufactures a molded product by repeatedly performing these steps. FIG. 3 shows temporal changes of various parameters in the injection process, the pressure holding process, the cooling process, and the metering process.

  The injection process is performed after the mold clamping process. In the injection process, the injection motor 43 is driven to advance the screw 52. The screw 52 pushes the molten resin and injects it from the nozzle 41. The molten resin flows into the cavity space C through the sprue S, the runner R, the gate G, and the like formed in the mold apparatus 30.

  In the injection process, current is supplied to the injection motor 43 so that the forward speed of the screw 52 becomes a set value. The set value of the screw speed may be changed stepwise as the screw position advances. For example, when the detection value of the position detector 57 reaches the set value, the set value of the screw speed is changed.

  In order to change the setting value of the screw speed, a timer that measures the time from the start of the injection process (time t0) may be used instead of the position detector 57. Since the screw position and time are in a correspondence relationship, the same is true regardless of which setting value of the screw speed is changed.

  The set value of the screw speed may be substantially 0 (zero) at time t1 before the pressure holding process starts. The screw 52 is rapidly decelerated, and the screw 52 stops at time t2. When the screw 52 is stopped, the screw position hardly changes. Therefore, instead of monitoring the detection value of the position detector 57, the control unit 80 measures the elapsed time from the screw stop setting start time t1 with a timer.

  Here, “the screw stops” includes not only that the screw 52 is completely stopped, but also that the screw 52 moves forward at a very low speed and that the screw 52 moves back at a low speed. When the screw 52 retreats at a slow speed, the screw 52 temporarily stops before the retreat at a slow speed.

  When the screw 52 stops at time t2, the flow front of the resin does not reach the end of the cavity space C. While the screw 52 is stopped, the flow front of the resin advances with the compressive force applied to the resin during injection. Since the screw 52 is stopped, the resin gradually decelerates due to the flow resistance.

  Switching from the injection process to the pressure holding process is called V / P switching. The V / P switching is performed at time t3 when the time from the screw stop setting start time t1 reaches the set value. When the screw stop is not performed after the injection process is started and before the pressure holding process is started, the V / P switching is performed when the detection value of the position detector 57 reaches the set value or the time from the start of the injection process. This is performed when the measured value of the timer that measures the value reaches the set value.

  When the resin is cooled in the cavity space C, the resin is thermally contracted. In order to replenish the resin for heat shrinkage, the resin pressure applied to the screw 52 (resin injection pressure) is maintained at a predetermined pressure in the pressure holding step. A current is supplied to the injection motor 43 so that the detection value of the resin pressure detector 50 becomes a set value. The set value of the injection pressure of the resin in the pressure holding process may change stepwise with time. In the pressure holding process, since the change in the screw position is small, the time from the V / P switching is measured by the timer of the control unit 80.

  At time t4 when the time from the V / P switching reaches the set time, the set value of the injection pressure of the resin is returned to substantially 0 (zero), and the pressure holding process is completed. When the pressure holding process is completed, the gate G which is the entrance of the cavity space C is closed with the solidified resin. This state is called a gate seal, and the injection pressure of the resin is not transmitted to the cavity space C, and the backflow of the resin from the cavity space C is prevented.

  After completion of the pressure holding process, a cooling process for solidifying the resin in the cavity space C is performed. In the cooling process, in the state where the supply of the resin to the cavity space C is cut off, the resin shrinks in the cavity space C due to cooling. The cooling of the resin also proceeds in the injection process and the pressure holding process, and the resin surface is solidified when the pressure holding process is completed.

  The measurement process is performed after the pressure holding process is completed. The metering process may be performed during the cooling process to shorten the molding cycle. In the weighing step, the weighing motor 55 is driven to rotate the screw 52, and the resin pellet supplied to the rear end portion of the screw 52 is sent to the front of the screw 52. In this process, the resin pellets are softened and melted. Since the molten resin is stored in front of the screw 52, the screw 52 moves backward. When the screw 52 moves backward by a predetermined distance and a predetermined amount of molten resin is accumulated in front of the screw 52, the rotation of the screw 52 is stopped.

  In the measuring step, a current is supplied to the measuring motor 55 so that the rotational speed of the screw 52 becomes a set value, and a rotational torque corresponding to the supplied current is generated. For example, a current sensor 58 is used as a detector for detecting the rotational torque of the weighing motor 55. The current sensor 58 detects a current supplied to the metering motor 55. The detection value of the current sensor 58 is supplied to the control unit 80 and converted into the rotational torque of the metering motor 55. The rotational torque of the metering motor 55 includes the rotational torque of the screw 52 and the shearing torque of the resin.

  FIG. 4 is a schematic diagram showing a change over time of the rotational torque of the metering motor according to the embodiment.

  Since the screw 52 is started at the start of the weighing process, the rotational torque of the weighing motor 55 increases as shown in FIG. When the number of rotations of the screw 52 reaches a set value, the rotational torque of the metering motor 55 becomes small and stabilizes before long.

  By the way, the melting speed of the resin material may vary from shot to shot (one cycle) due to variations in the particle size of the resin material. The more resin that begins to melt, the higher the viscosity of the molten resin and the higher the rotational torque of the metering motor 55. Also, the more resin that begins to melt, the more voids and the lower the resin density. Therefore, the density of the molten resin measured in the heating cylinder 42 and the rotational torque of the metering motor 55 are correlated.

  The control unit 80 adjusts a setting value related to the control of the injection motor 43 based on the detected rotational torque of the metering motor 55. The filling amount (injection amount) of the molten resin can be adjusted according to the density of the molten resin measured in the heating cylinder 42, and the molten resin filled in the mold apparatus 30 in the injection / holding process can be adjusted. The weight can be kept constant.

  For adjusting the molding conditions, the rotational torque of the metering motor 55 when the rotational speed of the metering motor 55 becomes a set value and is stabilized may be used. For example, the average value of the rotational torque after a set time (for example, half of the measurement time T) has elapsed since the start of the measurement process is used. Note that an integral value of the rotational torque can be used instead of the average value of the rotational torque.

  The set value adjusted by the control unit 80 includes (1) the time from the start of the injection process to the start of the pressure holding process (t3-t0), or the screw position at the start of the pressure holding process. When the pressure holding process start time t3 becomes earlier, the screw movement distance up to time t3 becomes shorter and the filling amount of the molten resin becomes smaller. On the other hand, when the pressure holding process start time t3 is delayed, the screw moving distance up to time t3 is increased, and the amount of filling of the molten resin is increased.

  When the screw 52 stops in the injection process, the setting value adjusted by the control unit 80 is, for example, (2) the time from the start of the injection process to the start of setting of the screw stop (t1-t0), or at the start of setting of the screw stop. It may be a screw position. When the screw stop setting start time t1 becomes earlier, the screw movement distance up to time t1 becomes shorter and the amount of molten resin charged becomes smaller. On the other hand, when the screw stop setting start time t1 is delayed, the screw movement distance up to time t1 is increased, and the filling amount of the molten resin is increased.

  Further, the set value adjusted by the control unit 80 includes (3) a pressure holding time (t4-t3) from the start to the end of the pressure holding process. When the pressure holding time is shortened, the screw moving distance is shortened and the filling amount of the molten resin is decreased. On the other hand, when the pressure holding time becomes longer, the screw moving distance becomes longer and the filling amount of the molten resin becomes larger.

  Further, the set value adjusted by the control unit 80 includes (4) a resin pressure (resin injection pressure) applied to the screw 52 in the pressure holding step. Since the pressure holding process is a process for replenishing thermal shrinkage due to cooling of the resin, when the pressure holding is lowered, the filling amount of the molten resin is reduced. On the other hand, when the holding pressure increases, the filling amount of the molten resin increases. When the set value of the injection pressure of the resin changes stepwise with time, at least one set value may be adjusted.

  The setting value adjusted by the control unit 80 only needs to include at least one of the setting values (1) to (4), and the combination thereof is free.

  When the detected rotational torque of the metering motor 55 exceeds the upper limit value of the preset range, the control unit 80 increases the set values (1) to (4) above the preset reference value. Moreover, the control part 80 makes the setting value of said (1)-(4) smaller than the preset reference value, when the detected rotational torque of the motor 55 for weighing is smaller than the lower limit of the said range. . The amount of change of each set value is determined in advance and may be a constant amount or may be an amount proportional to the amount of deviation of the detected rotational torque of the metering motor 55 from the above range. The reference value is set by a user, for example.

  On the other hand, when the detected rotational torque of the metering motor 55 is within the above range, the control unit 80 does not change the set values (1) to (4) and keeps the preset reference values. . An excessive setting change can be prevented by providing a width between the upper limit value and the lower limit value.

  The adjustment of the set value by the control unit 80 may be performed every measurement, or may be performed in response to a user request. The user's request is input by the input unit 94 (see FIG. 2) such as a keyboard and transmitted to the control unit 80. The user's request may be made when the particle size distribution or average particle size of the resin material changes, for example, when the lot of the resin pellet changes or when the mixing ratio of the resin pellet and the recycled material changes.

  The rotational torque of the metering motor 55 is recorded on a recording medium such as a RAM and is read out as necessary. The rotational torque of the weighing motor 55 is recorded on the recording medium in association with the ID information of the molded product.

  The injection molding machine 10 may further include a display unit 92 (see FIG. 2) that displays the rotational torque of the metering motor 55 that is used for adjusting molding conditions in the injection / holding process. The user can confirm the stability of the density of the molten resin measured in the heating cylinder 42.

  The display unit 92 includes a display, for example, and displays an image of the rotational torque of the weighing motor 55 in response to a user request under the control of the control unit 80. The user request is input through the input unit 94 and transmitted to the control unit 80. The display unit 92 outputs the molded product ID information and the rotational torque of the weighing motor 55 in association with each other.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications and substitutions may be made within the scope of the gist of the present invention described in the claims. Is possible.

  For example, the injection device 40 of the above embodiment is a screw inline method in which the screw 52 for measuring the resin and injecting the resin is disposed in the heating cylinder 42, but may be a screw pre-pull method. The screw pre-pull type injection device includes a screw that measures the molten resin in the measuring cylinder, an injection cylinder that receives the molten resin measured in the measuring cylinder, and a plunger that injects the molten resin in the injection cylinder and fills the mold. With.

  Moreover, the setting value which the control apparatus 80 adjusts is not restricted to the setting value of said (1)-(4). In the case of setting values other than the above (1) to (4), the magnitude of the rotational torque of the metering motor 55 and the magnitude of the change of the setting value may be reversed. That is, when the rotational torque of the metering motor 55 exceeds the preset upper limit value of the predetermined range, the set value related to the control of the injection motor 43 may be reduced. Further, when the rotational torque of the metering motor 55 is smaller than a preset lower limit value of a predetermined range, the set value related to the control of the injection motor 43 may be increased.

  Moreover, in the said embodiment, although the setting value of the rotation speed of the screw 52 is constant irrespective of a screw position, it may be changed in steps as the screw 52 retreats. For example, when the detection value of the position detector 57 reaches a set value, the set value of the rotational speed of the screw 52 is changed. In this case, the rotational torque of the metering motor 55 when the screw 52 rotates at the changed set value and the rotational torque is stabilized may be used for adjusting the molding conditions.

  In the above embodiment, a rotary motor is used as the moving drive unit that moves the screw 52 in the axial direction. However, a linear motor or a fluid pressure cylinder may be used, and the configuration of the moving drive unit is particularly limited. Not.

DESCRIPTION OF SYMBOLS 10 Injection molding machine 12 Fixed platen 13 Movable platen 30 Mold apparatus 32 Fixed mold 33 Movable mold 42 Heating cylinder (cylinder)
43 Injection motor (drive unit for movement)
52 Screw 55 Weighing motor 58 Current sensor (detector)
80 Control unit

Claims (8)

A screw that fills the mold by measuring and injecting the molten resin in the cylinder;
A weighing motor for rotating the screw;
A detector for detecting the rotational torque of the weighing motor;
A drive unit for moving the screw in the axial direction;
A control unit for controlling the measuring motor and the moving drive unit,
The control unit adjusts a filling amount by the screw by adjusting a setting value related to the control of the moving drive unit in the injection / holding step based on a detection value of the detector in a measuring step. An injection molding machine characterized by that. A screw for measuring molten resin in a measuring cylinder;
A weighing motor for rotating the screw;
A detector for detecting the rotational torque of the weighing motor;
An injection cylinder for receiving the molten resin measured in the measuring cylinder;
A plunger that injects molten resin in the injection cylinder and fills the mold;
A driving unit for moving the plunger in the axial direction;
A control unit for controlling the measuring motor and the moving drive unit,
The control unit adjusts a filling amount by the plunger by adjusting a setting value related to the control of the driving unit for movement in the injection / holding step based on a detection value of the detector in a measuring step. An injection molding machine characterized by that. The set value related to the control of the moving drive unit, the time from the injection process start to start the pressure-holding process, or to claim 1 or 2 including the location of the member to be moved by the moving drive unit at the start of the pressure holding process The injection molding machine described. The control unit stops the member moved by the driving unit for movement after the injection process starts and before the pressure holding process starts,
Set value related to the control of the moving drive unit are both from the injection process start time until start of setting of the stop of the member, or of claims 1 to 3 including the position of the member in the setting at the time of starting of stopping the member or an injection molding machine according to item 1. The injection molding machine according to any one of claims 1 to 4 , wherein the set value related to the control of the moving drive unit includes a pressure holding time from a start to a finish of the pressure holding process. The injection molding machine according to any one of claims 1 to 5 , wherein the set value related to the control of the moving drive unit includes a resin pressure acting on a member moved by the moving drive unit in a pressure holding process. The controller is
When the detection value of the detector exceeds the upper limit value of the predetermined range, the set value related to the control of the drive unit for movement is made larger than a preset reference value,
If the detected value of the detector is smaller than the lower limit of the predetermined range, to any one of claims 1 to 6, smaller than a preset reference value the setting value related to the control of the moving drive unit The injection molding machine described. The injection molding machine according to any one of claims 1 to 7 , further comprising a display unit that displays a detection value of the detector used for the adjustment by the control unit.

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