JP4571163B2 - Suckback amount setting method and injection molding machine - Google Patents

Description

  The present invention relates to a suck back amount setting method and an injection molding machine capable of automatically setting an appropriate suck back amount in an injection molding machine.

  Injection molding advances the screw and injects resin from the nozzle into the mold, forming the molded product by a pressure-holding process that applies a predetermined pressure to the resin in the mold, and rotating the screw, In addition, it can be divided into a metering step in which a predetermined amount of resin is metered into the cylinder by moving backward while applying a predetermined back pressure. After the metering process is finished, a predetermined pressure is generated in the resin in the cylinder. Therefore, the screw is retracted by a predetermined amount to reduce the resin pressure in the cylinder so that the resin in the cylinder does not leak from the nozzle. A suck back process is performed. The purpose of the suck-back process is to reduce the pressure in the cylinder as described above. However, if the screw is retracted too much, air may be engulfed into the nozzle, causing bubbles to be mixed in the molded product and causing problems. For this reason, it is desirable that the optimum amount of suckback is set such that the pressure in the cylinder is sufficiently reduced and the screw does not retreat excessively.

For this reason, a method of retracting the screw by a predetermined movement amount, a method of retracting the screw for a predetermined time, or the like has been adopted (see Patent Document 1). In order to obtain the amount of backward movement of the screw for suckback, the relationship between the resin pressure displayed on the screen of the injection molding machine and the position of the screw is displayed, and the operator can determine the optimal amount of screw movement while viewing this display screen. A method for obtaining and setting has been conventionally employed.
In order to obtain a more suitable suckback process, a pressure sensor for detecting the resin pressure in the cylinder is provided, and the screw is detected until the resin pressure detected by the pressure sensor becomes zero or below a certain threshold value. A suckback method for retreating is known (see Patent Documents 1 to 5).

JP-A-6-71705 No. 5-3295 Japanese Patent Publication No. 4-60810 Japanese Patent Publication No. 5-34135 Japanese Utility Model Publication No. 5-47624

However, in the method of obtaining the optimum screw movement amount while observing the waveform of the resin pressure with respect to the screw position, the operator moves the screw backward movement amount for sucking back while reading the graph displayed on the screen of the injection molding machine ( It was necessary to set a suckback amount), which was troublesome.
On the other hand, the suckback method in which the screw is automatically retracted until the resin pressure reaches a predetermined amount has a problem that the position at which the suckback process is completed varies in each molding cycle, and the subsequent injection process becomes unstable. It was.
It is desirable that the screw backward movement amount (suckback amount) in the suck back process is the same movement amount for each molding cycle, and it is desirable that the optimum movement amount can be easily set.
Accordingly, an object of the present invention is to provide a suck back amount setting method and an injection molding machine that can easily and uniformly set a uniform suck back amount for each molding cycle.

The invention according to claim 1 is a suck back amount setting method in a suck back process of an injection molding machine, wherein the injection molding machine has a pressure sensor for detecting a resin pressure in a cylinder, and a position of a screw in an injection direction. A position detecting means for detecting and a display device are provided, and after completion of the weighing process, the screw is moved backward, and the resin pressure detected by the pressure sensor based on the screw position detected by the detecting means is less than a predetermined set value. The amount of screw backward movement until reaching the value of the screw is obtained, the value of the amount of backward movement of the screw is displayed on the screen of the display device, and the displayed amount of backward movement of the screw is set as the suckback amount. The suck back process is controlled by the sucked back amount. Further, if the resin pressure does not reach the set predetermined value before the screw backward movement amount reaches a predetermined value set in advance as a limit value of the suck back amount, a display indicating that the suck back amount is not detected is displayed. It is displayed on the device .

The inventions according to claims 2 and 3 comprise means for controlling the rotational drive of the screw and means for controlling the drive of the screw in the injection direction. After the screw is rotated and the molten resin is metered, the screw is retracted. An injection molding machine that performs suck back, a position detection means for detecting the position of the screw in the injection direction, a pressure sensor for detecting the resin pressure in the cylinder, and after completion of the weighing process, the screw is moved backward, Based on the screw position obtained by the position detection means, the screw reverse movement amount when the resin pressure detected by the pressure sensor reaches a preset predetermined value or less is obtained, and the obtained screw reverse movement amount is automatically set as the suck back amount. set, when the suck-back amount is set, and a control means for controlling the suck-back process in the suck-back amount, and a display device, the control hand If the resin pressure does not fall below the set predetermined value before the screw backward movement amount reaches a predetermined value set in advance as a limit value of the suck back amount, a display indicating that no suck back amount has been detected is displayed. This is an injection molding machine to which the suck back amount setting method according to claim 1 is applied. Further, as the suck back amount to be set, the control means obtains an average value from the plurality of screw backward movement amounts, and sets this average value as the suck back amount .

  The amount of screw retreat movement at which the resin pressure reaches a set pressure (for example, 0 atm) is obtained and set as a suck back amount. Thereafter, the suck back process is controlled by this set suck back amount. The suck back amount is controlled with a uniform suck back amount for each molding cycle, and stable molding can be performed.

First, the principle and operation of the present invention will be described.
1 to 3 are explanatory diagrams for explaining the principle and operation of the present invention. 1 to 3, the horizontal axis indicates the time from the start of screw retraction in the suck back process, and the vertical axis indicates the detected resin pressure in the cylinder and the amount of screw retreat movement.
As shown in FIGS. 1 to 3, during the measuring process, the screw rotates and the resin is melted and kneaded, and a predetermined back pressure is applied to the screw in the axial direction to measure the resin. . Therefore, the resin pressure during the measurement process is kept constant by the set back pressure, and the screw moves backward when the resin pressure becomes equal to or higher than the set back pressure, and the amount of backward movement increases with the passage of time.

  Then, when the screw reaches the measuring point and the measuring process is finished, the rotation of the screw is stopped, the suck back process is started, and the screw is moved backward. The resin pressure decreases due to the screw retreat. The resin pressure in the cylinder changes depending on the amount of screw backward movement (suckback amount) in this suckback process.

In the example shown in FIG. 1, the sackback amount (screw backward movement amount) is appropriate, and the resin pressure is set at the pressure reduction judgment pressure (example in FIG. 1) at the time when the sackback process is completed (when the screw backward movement is stopped). , And the timing at which the screw stops moving backward and the set pressure reduction judgment pressure (0 atm) is the same.
On the other hand, as shown in FIG. 2, if the suckback amount (screw backward movement amount) is small, the resin pressure has not reached the target set pressure reduction judgment pressure (0 atmospheric pressure) when the screw backward movement is stopped. In this state, a phenomenon that the molten resin leaks from the nozzle tip occurs.
Furthermore, as shown in FIG. 3, when the screw moves backward despite the large suck back amount (screw backward movement amount) and the resin pressure reaches 0 atm, air is sucked from the nozzle tip. As a result, air is injected into the mold at the time of injection, causing bubbles to be mixed into the molded product.

  As described above, in the suck back process, it is desirable to stop the backward movement of the screw when the set pressure reduction judgment pressure (0 atm) is reached. That is, it is desirable that the suck back amount (screw backward movement amount) is set as the backward movement amount at which the resin pressure reaches a set pressure reduction determination pressure (for example, 0 atm). Moreover, it is desirable that this suck back amount be constant for each molding cycle.

  Therefore, according to the present invention, the reverse movement amount at which the resin pressure reaches the set pressure reduction judgment pressure (0 atm) is set as the suck back amount, and after the setting, the suck back process is controlled by the set suck back amount. did.

FIG. 4 is a principal block diagram of an embodiment of the present invention.
A nozzle 9 is attached to the tip of the cylinder 7 in which the screw 1 is inserted, and a hopper 15 for supplying resin pellets into the cylinder 7 is attached to the rear end of the cylinder 7. The screw 1 is rotationally driven via a transmission mechanism 12 by a screw rotating servo motor 10 as rotational driving means for rotationally driving the screw 1. Further, an injection servo motor 11 as an axial driving means for driving the screw 1 in the axial direction causes the screw 1 to move in the axial direction by a transmission mechanism 13 and a conversion mechanism 14 that converts the rotational motion of the ball screw / nut or the like into linear motion. It is configured to drive and control injection and back pressure. Position / speed detectors 16 and 17 for detecting the rotational position and speed of the servo motor 10 for rotating the screw and the servo motor 11 for injection are mounted. The position / speed detector detects the rotational speed of the screw 1 and the screw. The position 1 (position in the screw axis direction) and the moving speed (injection speed) can be detected. Further, a pressure sensor 18 such as a load cell for detecting the pressure from the molten resin in the cylinder 7 applied to the screw 1 is provided.

  A control device 20 for controlling the injection molding machine is connected to a CNC CPU 22 which is a numerical control microprocessor, a PMC CPU 21 which is a programmable machine controller microprocessor, and a servo CPU 25 which is a servo control microprocessor via a bus 36. ing.

  A ROM 26 storing a sequence program for controlling the sequence operation of the injection molding machine and a RAM 27 used for temporary storage of calculation data are connected to the PMC CPU 21, and a program for controlling the injection molding machine as a whole is connected to the CNC CPU 22. A stored ROM 28 and a RAM 29 used for temporary storage of calculation data are connected.

  The servo CPU 25 is connected to a ROM 31 that stores a control program dedicated to servo control that performs processing of a position loop, a speed loop, and a current loop, and a RAM 32 that is used for temporary storage of data. Further, the servo CPU 25 is connected to a servo amplifier 34 for the screw rotating servo motor 10 and a servo amplifier 35 for the injection servo motor 11 based on a command from the CPU 25. Are attached with position / speed detectors 16 and 17, respectively, and outputs from the position / speed detectors 16 and 17 are fed back to the servo CPU 25. The servo CPU 25 is positioned based on a movement command to each axis (screw rotation servomotor 10 or injection servomotor 11) commanded from the CNC CPU 22 and detection positions and speeds fed back from the position / speed detectors 16 and 17. In addition to performing speed feedback control, current feedback control is also executed to drive and control the servo motors 10 and 11 via the servo amplifiers 34 and 35, respectively. A current value register is provided for storing the rotational positions of the screw rotation servomotor 10 and the injection servomotor 11 fed back from the position / velocity detectors 16 and 17, and depending on the rotational positions of the servomotors 10 and 11, respectively. The rotational position of the screw 1 and the axial position (injection position) can be detected.

The servo CPU 25 receives a detection resin pressure (resin pressure applied to the screw 1) obtained by converting the detection signal from the pressure sensor 18 into a digital signal by the A / D converter 33.
A servo motor and servo amplifier for driving the mold clamping mechanism and the ejector mechanism are also provided, but these are not directly related to the present invention and are omitted in FIG.
An input device 30 with a display device composed of a liquid crystal or a CRT is connected to a bus 36 via a display circuit 24. Further, a molding data storage RAM 23 composed of a non-volatile memory is also connected to the bus 36, and the molding data storage RAM 23 stores molding conditions, various set values, parameters, macro variables, etc. relating to the injection molding operation.

With the above configuration, the PMC CPU 21 controls the sequence operation of the entire injection molding machine, and the CNC CPU 22 instructs the servo motor of each axis to move based on the operating program stored in the ROM 28 and the molding conditions stored in the molding data storage RAM 23. Servo CPU 25 detects the movement command distributed to each axis (servo motor of each drive axis such as screw rotation servomotor 10 and injection servomotor 11) and a position / speed detector. Based on the position and speed feedback signals, servo control such as position loop control, speed loop control, and current loop control is performed in the same manner as in the past, and so-called digital servo processing is executed.
The configuration described above is the same as the control device of the conventional electric injection molding machine. The difference from the conventional control device is that the processing of the suck back process is different, and the software for performing the processing stored in the ROM 28 is different. Is different.

FIG. 5 is a flowchart showing a processing algorithm of a suck back process executed by the CNC CPU 22 including the suck back amount setting method in the first mode of the present embodiment.
In this first mode, after the metering step is completed, the screw 1 is retracted, and the value (numerical value) of the reverse movement amount at which the resin pressure reaches the set decompression judgment pressure (0 atm) is obtained and displayed on the display device. However, after the suck back amount is set based on this display, the suck back step is executed with the set suck back amount.

  A predetermined value D is set in advance as a limit amount of the suck back amount. When the suck back process is started, first, it is determined whether or not the suck back amount setting completion flag F is set to “1” (step a1). The suck back amount setting completion flag F is set to “0” when molding conditions are set for molding a molded product, and is initially “0”. Next, a screw position (axial position) S1 is obtained and stored from a current value register that stores the rotational position of the injection servomotor 11 obtained from the position / speed detector 17 based on feedback (step a2). Further, a predetermined set value D indicating the limit of the suck back amount set in the obtained screw position S1 is added to obtain the screw retreat limit position SL (step a3).

  Then, the injection servo motor 11 is driven via the servo CPU 25 to start the backward movement of the screw 1, and the suck back is started (step a4). Next, the screw position Sr is read (step a5), and it is determined whether the screw position Sr has reached or exceeded the screw retraction limit position SL obtained in step a3 (step a6). That is, it is determined whether or not the backward movement amount of the screw 1 has reached a set predetermined amount D or more indicating the set limit of the suck back amount. If the screw backward limit position SL is not reached, the servo CPU 25, A / D converter The pressure from the molten resin in the cylinder 7 detected by the pressure sensor 18 is read via 33 (step a7), and the pressure reduction judgment pressure at which the pressure is set (for example, a pressure close to 0 atm such as 1.0 MPa) It is determined whether or not (step a8).

If the read pressure has not reached the set pressure reduction determination pressure or less, the process returns to step a4 and the processes of steps a4 to a8 are repeated.
When the read pressure is equal to or lower than the set pressure reduction judgment pressure, the backward movement of the screw is stopped (suck back is stopped) (step a9), the screw position S2 at this time is read (step a10), and the screw position S2 is changed to step a2. The screw position S1 read in step S1 is subtracted, and the reverse movement amount from the screw reverse movement start (suck back start) to the screw reverse movement stop (suck back stop) is obtained as a suck back amount SB, and the value of this suck back amount SB ( (Numerical value) is displayed on the display screen of the display device / input device 30, and the completion of suck back amount detection is displayed by lighting a lamp or the like (step a11).

On the other hand, when the screw 1 exceeds the screw retreat limit position SL before the resin pressure read in step a7 reaches the set pressure reduction judgment pressure (step a6), the retreat movement of the screw is stopped (step a12). The incomplete suckback amount detection is displayed by a lamp or the like (step a13).
Hereinafter, when the suck back amount SB is obtained during the suck back process in each molding cycle and the suck back amount SB is obtained, the value of the suck back amount SB is displayed. Is displayed. If the display indicating that the suckback amount detection is not completed continues, the molding condition is adjusted, or a predetermined value set as the limit amount of the suckback amount is adjusted.

  Thus, when the suck back amount SB is obtained and the value is displayed, the operator reads the displayed value and sets it as the suck back amount SB. When the suck back amount SB is set, the suck back amount setting completion flag F is set to “1”. Therefore, in the subsequent suckback process, since the suckback amount setting completion flag F is determined to be “1” in step a1, the process proceeds to step a14, the screw position S1 is read and stored, and the backward movement of the screw is started. (Start of suck back) (step a15), the screw position Sr is read, and the read screw position Sr becomes equal to or greater than the value (S1 + SB) obtained by adding the set suck back amount SB to the screw position S1 read in step a14. If Sr ≧ (S1 + SB) is not satisfied, the process returns to step a15 and the processes of steps a15 to a17 are repeated. Then, when the screw position Sr becomes a value of (S1 + SB) and the screw 1 moves backward by the set suckback amount SB, the backward movement of the screw is stopped (step a18), and the process of this suckback process is ended.

  As described above, the screw backward movement amount that reaches the decompression determination pressure at which the resin pressure is set is obtained as the suck back amount SB, and the suck back process after the suck back amount SB is set is a set constant amount. This is controlled by the backward movement of the screw by the suck back amount SB. As a result, an appropriate suckback amount SB in which the screw reverse stop position and the decompression completion position coincide with each other as shown in FIG. 1 is set, and thereafter, the suckback process is controlled with this constant suckback amount SB. Prevents variations in suckback amount.

FIG. 6 is a flowchart showing a processing algorithm of a suck back process executed by the CNC CPU 22 including the suck back amount setting method in the second mode of the present embodiment.
In the first aspect described above, the operator sets the obtained suckback amount SB. In the second aspect, the control apparatus 20 automatically sets the suckback amount SB.

The difference between the second mode and the first mode is that the process of step a11 in the first mode is only changed to step a11 ′ in the second mode, and the other processes are the same as the first mode. Same as embodiment.
In the suck back process, the screw 1 starts to move backward, and the amount of backward movement is obtained from the screw backward movement position at the time when the detected resin pressure reaches the set pressure reduction judgment pressure or less, and this is set as the suck back amount SB. It is the same as the first embodiment. In the second embodiment, the obtained suckback amount SB is automatically set as the suckback amount, and the suckback amount setting completion flag F is set to “1” (step a11 ′). At this time, it is displayed by a lamp or the like indicating completion of suck back setting.
After the suckback amount SB is set in this way, the processing of steps a1 and a14 to a18 is executed as in the first embodiment, and the suckback processing of the screw backward movement by this suckback amount SB is executed. Will be.

  When obtaining the suck back amount SB, a plurality of suck back amounts SB may be obtained and an average value thereof may be obtained and set. For example, the processing of steps a1 to a10 is performed, then the suckback amount is obtained, the suckback amount is accumulated, the counter is counted up, and when the counter reaches the set value, the accumulated value of the suckback amount Is divided by the counter value to obtain an average value, and the average value of the suck back amount is displayed as the suck back amount SB in the first mode, and is automatically set as the suck back amount in the second mode. This is what you need to do.

It is explanatory drawing for demonstrating the principle of this invention, an effect | action, and is explanatory drawing when the time of pressure reduction completion and the time of screw backward movement stop correspond in a suck back process. It is explanatory drawing for demonstrating the principle of this invention, an effect | action, and is an explanatory view of the state in which the resin pressure in a cylinder remains, when a screw backward movement stop is carried out at a suck back process. It is explanatory drawing for demonstrating the principle of this invention, an effect | action, and is explanatory drawing when a screw moves backward and stops although decompression is completed by the suck back process. It is a principal part block diagram of one Embodiment of this invention. It is a flowchart which shows the processing algorithm of the suck back process including the suck back amount setting method of the 1st aspect in the embodiment. It is a flowchart which shows the processing algorithm of the suck back process including the suck back amount setting method of the 2nd aspect in the embodiment.

Explanation of symbols

1 Screw 7 Cylinder 10 Screw Servo Motor 11 Injection Servo Motor 16, 17 Position / Speed Detector 18 Pressure Sensor 20 Controller

Claims (3)

A suck back amount setting method in a suck back process of an injection molding machine, wherein the injection molding machine includes a pressure sensor that detects a resin pressure in a cylinder, a position detection unit that detects a position of a screw in an injection direction, and a display. An amount of screw retraction until the resin pressure detected by the pressure sensor reaches a predetermined value or less based on the screw position detected by the detection means after completion of the weighing process. The screw backward movement amount is displayed on the screen of the display device, and the displayed screw backward movement amount is set as the suckback amount. After this setting, the suckback amount is set at the set suckback amount. so as to control the process, before the screw retreat movement amount reaches the predetermined value set in advance as a limit value of the suck-back amount, the resin pressure is the set If it does not reach the predetermined value or less, suck-back amount setting method a display of the suck back amount undetected and be displayed on the display device. An injection molding machine that includes a means for rotationally driving a screw and a means for controlling the drive of the screw in the injection direction, and performs a suck back for retreating the screw after the screw is rotated and the molten resin is metered. And
Position detection means for detecting the position of the screw in the injection direction, pressure sensor for detecting the resin pressure in the cylinder, and after completion of the metering process, the screw is moved backward, and the above-mentioned position detection means is used to determine When the resin pressure detected by the pressure sensor reaches the set predetermined value or less, the screw backward movement amount is obtained, the obtained screw backward movement amount is automatically set as the suck back amount, and when the suck back amount is set, Control means for controlling the suck back process with the suck back amount, and a display device, the control means, before the screw backward movement amount reaches a predetermined value preset as a limit value of the suck back amount, When the resin pressure does not reach the set predetermined value or less, a display indicating that the suck back amount is not detected is displayed on the display device. Molding machine out. The injection molding machine according to claim 2, wherein the control means obtains an average value from the plurality of screw backward movement amounts and sets the average as a suck back amount.

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