JP6906926B2 - Injection molding machine - Google Patents

Description

The present invention relates to an injection molding machine.

The controller of the injection molding machine described in Patent Document 1 controls an injection servomotor so that the forward speed of the screw becomes a predetermined set speed in the injection process, and the position of the screw reaches the V / P switching position. At that point, the injection process is switched to the pressure holding process, and in the pressure holding process, the injection servomotor is controlled so that the resin pressure at the front end of the screw is maintained at the holding pressure set pressure.

Japanese Unexamined Patent Publication No. 2011-183705

In the pressure holding step, the molding material remaining in the cylinder is pushed forward by the screw, the pressure of the molding material at the front end portion of the screw is maintained at a set pressure, and the molding material remaining in the cylinder is pushed toward the mold apparatus. The shortage of molding material due to cooling shrinkage in the mold device can be replenished.

By the way, the molding material remaining in the cylinder at the end of the pressure holding process is filled in the mold apparatus at the next shot. Therefore, the larger the amount of the molding material remaining in the cylinder at the end of the pressure holding process, the larger the amount of the molding material having a long residence time in the cylinder. A molding material having a long residence time is likely to be deteriorated by heat, which may cause deterioration of the quality of the molded product. Therefore, we want to reduce the amount of molding material remaining in the cylinder at the end of the pressure holding process as much as possible.

However, the amount of the molding material remaining in the cylinder may be insufficient in the pressure holding process due to the backflow of the molding material or the like. When the screw advances and exceeds the cushion position in the pressure holding process, the amount of molding material remaining in the cylinder is insufficient, so that the control device interrupts the pressure holding process.

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 capable of suppressing interruption of the pressure holding process due to insufficient amount of molding material remaining in the cylinder in the pressure holding process. do.

In order to solve the above problems, according to one aspect of the present invention,
A cylinder that heats the molding material and
A screw that is arranged inside the cylinder so that it can move forward and backward and rotate freely.
A control device for controlling the advance / retreat and rotation of the screw is provided.
The control device monitors the position of the screw in the pressure holding step, and based on the position of the screw, retracts the screw to a predetermined position to reduce the pressure of the molding material at the front end portion of the screw, and then continues. An injection molding machine is provided that moves the screw forward and backward at the predetermined position and rotates the screw.

According to one aspect of the present invention, there is provided an injection molding machine capable of suppressing interruption of the pressure holding process due to insufficient amount of molding material remaining in the cylinder in the pressure holding process.

It is a figure which shows the state at the time of mold clamping of the injection molding machine by one Embodiment. It is a flowchart which shows the processing of the control apparatus by one Embodiment.

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

FIG. 1 is a diagram showing a state at the time of mold clamping of an injection molding machine according to one 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 moving direction of the screw 43 at the time of filling (left direction in FIG. 1) will be described as the front, and the moving direction of the screw 43 at the time of weighing (right direction in FIG. 1) will be described as the rear.

The mold clamping device 10 closes, clamps, and opens the mold of the mold apparatus 30. The mold device 30 includes a fixed mold 32 and a movable mold 33. The mold clamping device 10 has a fixed platen 12 to which the fixed mold 32 is attached and a movable platen 13 to which the movable mold 33 is attached. The mold clamping device 10 closes, molds, and opens the mold device 30 by moving the movable platen 13 with respect to the fixed platen 12.

At the time of mold clamping, a cavity space 34 is formed between the movable mold 33 and the fixed mold 32, 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. The number of cavity spaces 34 may be plural, in which case a plurality of molded articles can be obtained at the same time. 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 device 40 is touched by the mold device 30, and fills the cavity space 34 in the mold device 30 with a molding material. The injection device 40 includes, for example, a cylinder 41, a nozzle 42, a screw 43, a cooler 44, a measuring motor 45, an injection motor 46, a pressure detector 47, a heater 48, a temperature detector 49, and the like.

The cylinder 41 heats the molding material supplied internally from the supply port 41a. The supply port 41a is formed at the rear portion 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. A heater 48 such as a band heater and a temperature detector 49 are provided on the outer periphery of the cylinder 41 in front of the cooler 44.

The cylinder 41 is divided into a plurality of zones in the axial direction of the cylinder 41 (left-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 detection temperature of the temperature detector 49 reaches the set temperature.

The nozzle 42 is provided at the front end of the cylinder 41 and is pressed against the mold device 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 reaches the set temperature.

The screw 43 is rotatably and rotatably arranged in the cylinder 41. 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 of the cylinder 41, the screw 43 is retracted. After that, when the screw 43 is advanced, the liquid molding material accumulated in front of the screw 43 is ejected from the nozzle 42 and filled in the mold device 30.

A backflow prevention ring 51 is attached to the front portion of the screw 43 so as to be able to advance and retreat. When the screw 43 is advanced, the backflow prevention ring 51 is pushed backward by the pressure of the molding material in front of the screw 43 and retracts to a closed position that blocks the flow path of the molding material. As a result, the molding material accumulated in the front of the screw 43 is prevented from flowing backward. On the other hand, when the screw 43 is rotated, the backflow prevention ring 51 is pushed forward by the pressure of the molding material sent forward along the spiral groove of the screw 43 to open the flow path of the molding material. Move forward to. As a result, the molding material is sent to the front of the screw 43. The backflow prevention ring 51 may be either a co-rotation type that rotates with the screw 43 or a non-co-rotation type that does not rotate with the screw 43.

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, for example, a hydraulic pump.

The injection motor 46 advances and retreats the screw 43. Between the injection motor 46 and the screw 43, a motion conversion mechanism or the like for converting the rotational motion of the injection motor 46 into the linear motion of the screw 43 is provided. The motion conversion mechanism has, for example, a screw shaft and a screw nut screwed onto the screw shaft. A ball, roller, or the like may be provided between the screw shaft and the screw nut. The drive source for advancing and retreating the screw 43 is not limited to the injection motor 46, and may be, for example, a hydraulic cylinder.

The pressure detector 47 detects the pressure transmitted between the injection motor 46 and the screw 43. The pressure detector 47 is provided in the 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 controlling and monitoring the pressure received by the screw 43 from the molding material, the back pressure on the screw 43, the pressure acting on the molding material from the screw 43, and the like.

As shown 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 the program stored in the storage medium 92. Further, the control device 90 receives a signal from the outside at the input interface 93 and transmits the signal to the outside at the output interface 94. The control device 90 controls a filling process, a pressure holding process, a measuring 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 in the cavity space 34 in the mold apparatus 30. The position and speed of the screw 43 are detected by using, for example, the encoder 46a of the injection motor 46. The encoder 46a 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.

After the position of the screw 43 reaches the set position in the filling step, 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 to keep the pressure of the molding material at the front end of the screw 43 (hereinafter, also referred to as “pressure holding pressure”) at a set pressure, and inside the cylinder 41. The molding material remaining in the mold device 30 is pushed toward the mold device 30. The shortage of molding material due to cooling shrinkage in the mold apparatus 30 can be replenished. The holding pressure is detected using, for example, a pressure detector 47. 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 pressure step and the like.

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

In the weighing step, the weighing motor 45 is driven to rotate the screw 43 at a set rotation 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 of the cylinder 41, the screw 43 is retracted. The rotation speed of the screw 43 is detected by using, for example, the encoder 45a of the measuring motor 45. The encoder 45a sends a signal indicating the detection result to the control device 90.

In the weighing step, the injection motor 46 may be driven to apply a set back pressure to the screw 43 in order to limit the sudden retreat of the screw 43. The back pressure on the screw 43 is detected using, for example, a pressure detector 47. The pressure detector 47 sends a signal indicating the detection result to the control device 90. When the screw 43 retracts to the set position and a predetermined amount of molding material is accumulated in front of the screw 43, the weighing process is completed.

By the way, the molding material remaining in the cylinder 41 at the end of the pressure holding process is filled in the mold apparatus 30 in the next shot. Therefore, the larger the amount of the molding material remaining in the cylinder 41 at the end of the pressure holding step, the larger the amount of the molding material having a long residence time in the cylinder 41. A molding material having a long residence time is likely to be deteriorated by heat, which may cause deterioration of the quality of the molded product. Therefore, it is desired to reduce the amount of molding material remaining in the cylinder 41 at the end of the pressure holding process as much as possible. However, the amount of the molding material remaining in the cylinder 41 may be insufficient in the pressure holding step due to the backflow of the molding material (for example, the seal leakage of the backflow prevention ring 51).

Therefore, the control device 90 of the present embodiment monitors the position of the screw 43 in the pressure holding step, and rotates the screw 43 based on the position of the screw 43. As a result, the molding material is sent to the front of the screw 43, so that interruption of the pressure holding process due to insufficient amount of the molding material remaining in the cylinder 41 in the pressure holding process can be suppressed.

FIG. 2 is a flowchart showing the processing of the control device according to the embodiment. The processing after step S101 shown in FIG. 2 is started when the start condition of the pressure holding step is satisfied. The start condition of the pressure holding process is, for example, that the screw 43 has reached the V / P switching position.

In step S101, with the rotation of the screw 43 stopped, the screw 43 is pressed forward so that the holding pressure becomes the set pressure. As a result, when the molding material is replenished from the cylinder 41 to the mold device 30, the screw 43 advances, so that the control device 90 performs step S102. As described above, the set pressure of the molding material at the front end portion of the screw 43 may be changed according to the elapsed time from the start of the pressure holding process and the like.

In step S102, it is checked whether or not the position of the screw 43 is behind the set position. The position of the screw 43 is detected by, for example, the encoder 46a of the injection motor 46. The position of the screw 43 can also be calculated from a current command to the injection motor 46 or the like. The set position is optimized in advance by a test or the like and stored in the storage medium 92. As the set position, for example, the cushion position conventionally set in the pressure holding process may be used. However, the set position may be a position behind the cushion position.

If the position of the screw 43 is at the set position or is ahead of the set position in step S102 (steps S102, No), the amount of molding material remaining in the cylinder 41 is insufficient, so that the control device 90 steps. Perform S103. In step S103, the screw 43 is rotated to feed the molding material in front of the screw 43. The rotation speed and rotation time of the screw 43 may be set in advance, and may be appropriately corrected based on the position of the screw 43, the detection value of the pressure detector 47, and the like. When the amount of molding material remaining in front of the screw 43 in the cylinder 41 is restored to a predetermined amount, the control device 90 proceeds to step S104.

On the other hand, when the position of the screw 43 is behind the set position in step S102 (step S102, Yes), the amount of the molding material remaining in the cylinder 41 is sufficient, so the process proceeds to step S104.

In step S104, it is checked whether or not the end condition of the pressure holding process is satisfied. The end condition of the pressure holding process is, for example, that the elapsed time from the start of the pressure holding process has reached the set time.

If the end condition of the pressure holding step is not satisfied in step S104 (step S104, No), the control device 90 returns to step S101 and continues the processing after step S101.

On the other hand, when the end condition of the pressure holding process is satisfied in step S104 (step S104, Yes), the control device 90 ends the current process. After the pressure holding process is completed, a cooling process and the like are performed.

Next, the above step S103 will be described in more detail. The step S103 is performed when the position of the screw 43 is the set position or is ahead of the set position in the step S102 (step S102, No). In step S103, the control device 90 performs, for example, the following process (1) or the following process (2).

(1) The control device 90 moves the screw 43 forward and backward at a predetermined position and rotates the screw 43. When the screw 43 is rotated, the molding material is fed forward along the spiral groove of the screw 43. When the backflow prevention ring 51 is pushed forward by the pressure of the molding material sent forward and moves from the closed position to the open position, the molding material is sent to the front of the screw 43.

For example, the control device 90 advances and stops the screw 43 and rotates the screw 43 at a set position or a position where it is detected that the position of the screw 43 is ahead of the set position. Further advancement of the screw 43 can be prevented, and the molding material can be fed in front of the screw 43.

Further, when the control device 90 detects that the position of the screw 43 is in front of the set position or the set position, the screw 43 may be retracted to a predetermined position to reduce the holding pressure. Subsequently, the control device 90 moves the screw 43 forward and backward at a predetermined position and rotates the screw 43. By reducing the holding pressure, the resistance to move the backflow prevention ring from the closed position to the open position can be reduced, and the molding material can be easily fed to the front of the screw 43.

The control device 90 may release the holding of the holding pressure at the set pressure while the screw 43 is moved back and forth and stopped at a predetermined position. The control device 90 may perform the holding of the holding pressure at the set pressure again after sufficiently feeding the molding material in front of the screw 43.

In order to move the screw 43 forward and backward at a predetermined position, the control device 90 may create a current command for the injection motor 46 so that the electric angles of each phase of the injection motor 46 are fixed, or the rotation of the injection motor 46. You may activate the braking device to stop. As the braking device, for example, an electromagnetic brake or the like is used.

(2) The control device 90 pushes the screw 43 forward to hold the holding pressure at the set pressure and rotates the screw 43. As a result, the molding material can be sent to the front of the screw 43 while controlling the pressure for pushing the molding material remaining in the cylinder 41 toward the mold device 30.

For example, the control device 90 holds the holding pressure and rotates the screw 43 at the set pressure when it detects that the position of the screw 43 is the set position or the position ahead of the set position. It is possible to prevent a decrease in the pressure for pushing the molding material remaining in the cylinder 41 toward the mold apparatus 30.

Further, when the control device 90 detects that the position of the screw 43 is in front of the set position or the set position, the holding pressure may be reduced from the first set pressure to the second set pressure. The first set pressure is the set pressure at the time when it is detected that the position of the screw 43 is the set position or ahead of the set position. Subsequently, the control device 90 pushes the screw 43 forward to hold the holding pressure at the second set pressure, and rotates the screw 43. By reducing the holding pressure from the first set pressure to the second set pressure, the resistance to move the backflow prevention ring from the closed position to the open position can be reduced, and the molding material can be easily fed to the front of the screw 43.

The control device 90 monitors the position of the screw 43 while maintaining the holding pressure at the set pressure and rotating the screw 43, and when the screw 43 retracts to a predetermined position, the rotation of the screw 43 may be stopped. This is because the fact that the screw 43 retracts to a predetermined position means that the amount of the molding material in front of the screw 43 is restored to a predetermined amount in the cylinder 41.

The control device 90 monitors the position of the screw 43 while maintaining the holding pressure at the set pressure and rotating the screw 43, and when the screw 43 advances further, the rotation speed of the screw 43 may be increased. By increasing the rotation speed of the screw 43, the flow rate of the molding material sent to the front of the screw 43 can be increased, and the advance of the screw 43 can be suppressed.

If the screw 43 can be further advanced while rotating the screw 43, the set position may be a position behind the cushion position.

The control device 90 monitors the position of the screw 43 while holding the holding pressure at the set pressure and rotating the screw 43, and the screw 43 advances further than the set position to reach the cushion position or exceeds the cushion position. Then, the pressure holding process may be interrupted.

Further, the control device 90 monitors the position of the screw 43 while holding the holding pressure at the set pressure and rotating the screw 43, and further advances the screw 43 from the set position to reach a predetermined position or a predetermined position. When the above is exceeded, the advance / retreat of the screw 43 may be stopped and the screw 43 may be rotated. In this case, the control device 90 will perform both the process (1) and the process (2). When both the process (1) and the process (2) are performed, the order is not particularly limited, and either process may come first.

Although the embodiment of the injection molding machine has been described above, the present invention is not limited to the above-described embodiment and the like, and various modifications and modifications are made within the scope of the gist of the present invention described in the claims. It can be improved.

For example, the backflow prevention ring 51 of the above embodiment retracts due to the pressure of the molding material in front of the screw 43 and advances by the pressure of the molding material sent forward along the spiral groove of the screw 43. Not limited to this. The injection device 40 may have a drive source for advancing and retreating the backflow prevention ring 51 between the open position and the closed position.

40 Injection device 41 Cylinder 42 Nozzle 43 Screw 45 Weighing motor 46 Injection motor 47 Pressure detector 90 Control device

Claims (3)

A cylinder that heats the molding material and
A screw that is arranged inside the cylinder so that it can move forward and backward and rotate freely.
A control device for controlling the advance / retreat and rotation of the screw is provided.
The control device monitors the position of the screw in the pressure holding step, and based on the position of the screw, retracts the screw to a predetermined position to reduce the pressure of the molding material at the front end portion of the screw, and then continues. An injection molding machine that moves the screw forward and backward at the predetermined position and rotates the screw. The control device monitors the position of the screw in the pressure holding step, pushes the screw forward based on the position of the screw, and holds the pressure of the molding material at the front end portion of the screw at a set pressure. , rotating the screw, injection molding machine according to claim 1. The control device monitors the position of the screw in the pressure holding step, and reduces the pressure of the molding material at the front end portion of the screw from the first set pressure to the second set pressure based on the position of the screw. followed holds the pressure in the second set pressure, rotating the screw, injection molding machine according to claim 1 or claim 2.

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