JP2007245469A - Method for controlling injection moulding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for controlling an injection molding machine which can prevent drooling by a simple composition without increasing costs and obtain a molding stably. <P>SOLUTION: The method includes a process in which a pressure not generating drooling based on an experienced value is inputted as a set pressure in a threshold value setting part 16, a process for storing a pressure waveform in an injection process and molding conditions in an operation processing part 14, and a sack back amount change process in which on the basis of a load cell 6 and the measured value of an encoder 13, a sack back/nozzle part temperature control part 15 changes a sack back amount one by one from the sack back amount of the molding conditions based on the pressure waveform stored in the operation processing part 14. When a pressure detected by the load cell 6 in the sack back amount change process reaches the set pressure, continuous molding is carried out in a sack back amount to be the set pressure. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for controlling an injection molding machine that can prevent drooling.

  In the conventional technology, as a general process for producing a molded product, after the injection and pressure holding process, there is a sucking back process after the weighing (plasticizing) process during the cooling process in order to solidify the molded product and shorten the cycle. It is done. Here, FIG. 4 shows a schematic configuration diagram of an example of a conventional injection apparatus control system, and FIG. 5 shows an example of a pressure waveform graph in conventional suckback control and nozzle part temperature control. In the suck back process in the injection molding, the process controller 101 can arbitrarily set the reverse speed and the reverse position, and the set signal is sent from the servo amplifier unit 102 to the injection servo motor 103 to be sent to the timing belt 104, the ball screw A screw 108 that is rotatably inserted into the cylinder 107 is controlled via 105. The screw 108 can be slightly retracted without rotating, thereby reducing the resin pressure at the screw tip.

  The position of the suck back process (the position where the screw 108 is retracted) is sent to the monitor screen of the process controller 101 via the encoder 113, and the resin pressure at the screw tip after the suck back is sent to the monitor screen of the process controller 101 via the load cell 106. Has been.

  On the other hand, the resin supplied from the hopper 112 falls into the screw groove when the rotation of the screw 108 starts and is transferred toward the nozzle 109. In this transfer process, the resin is compressed and melted and stored at the tip of the screw 108 in accordance with the mass of the molded product. The amount of heat necessary for this melting is supplied from the kneading heat generated by the screw 108 and the band heater 110 attached to the outer periphery of the cylinder 107.

  In the conventional injection molding as described above, the molten resin leaks from the nozzle 109 hole because the resin pressure is released to the nozzle side when the mold is opened (not shown) due to the above-mentioned resin pressure at the tip of the screw. The phenomenon Drooling 111 has occurred.

Conventionally, according to Patent Document 1, Patent Document 2, Patent Document 3, etc., a method of quickly controlling the temperature of the nozzle portion by using a heat insulating layer or a small heat adjusting portion at the nozzle tip portion, and the nozzle tip hole is completely completed with a needle Each of the above-described combinations is disclosed, such as a method for covering up and a method of subdividing temperature control of the nozzle portion and feedback control of the temperature of the tip portion to perform optimum temperature management.
JP 2003-266505 A JP 2002-283413 A Japanese Patent Laid-Open No. 10-109344

  However, disposing a plurality of heaters and sensors increases the manufacturing cost significantly. Further, in the case of a sealing method using a mechanical needle nozzle, there may be a problem of pressure loss or material change at the time of injection due to the resistance of the needle, and black spots due to carbide in the blind spot depending on the shape of the needle.

  For this reason, most of the open nozzles (open type) provided as standard in injection molding machines occupy. As countermeasures for drooling in open nozzles, the suck-back process and temperature control of the nozzle part, which are provided as standard in injection molding machines, were mainly carried out by the trial and error method. However, since the operator (molding engineer) can arbitrarily adjust the temperature control of the suck back process and the nozzle part, whether or not each set value is optimal has not been studied. This led to defective molded products. In the conventional system, 1. 1. It took a considerable amount of time to stabilize the molded product. 2. Molding defects occurred due to environmental changes such as room temperature and mold temperature. In addition, when a defect occurs, problems such as the fact that the operator is taking measures every time may occur.

  Accordingly, an object of the present invention is to provide a method for controlling an injection molding machine that can prevent drooling with a simple configuration and can stably obtain a molded product without causing an increase in cost. And

  In order to achieve the above object, a method for controlling an injection molding machine according to the present invention includes a process controller that receives a signal from an injection molding machine and controls the operation of the injection molding machine, and an arithmetic process connected to the process controller. Part, sackback / nozzle part temperature control part that sequentially changes the suckback amount and nozzle temperature, a load cell that measures the resin pressure, an encoder that measures the position of the screw, and pressure and temperature in the molding process In the control method of the injection molding machine having the threshold value setting unit for setting the threshold value, a step of inputting a pressure at which drooling based on experience values does not occur into the threshold value setting unit as a set pressure, and an injection processing step in the arithmetic processing unit Based on the process of memorizing the pressure waveform and molding conditions in A suck back amount changing step in which the suck back amount changing step for sequentially changing the suck back amount from the suck back amount of the molding condition based on the pressure waveform stored in the arithmetic processing unit is included in the suck back amount changing step. When the pressure detected by the load cell reaches the set pressure, continuous molding is performed with a suck back amount that becomes the set pressure.

  The control method of the present invention automatically adjusts the suck back amount so that the set pressure can be obtained by inputting a pressure value that can prevent drooling to the threshold setting unit as the set pressure. Since this control is performed by a function that is provided as standard in the injection molding machine, drooling can be automatically prevented without increasing the cost.

  Further, the control method of the injection molding machine of the present invention, when the predetermined pressure is not reached in the suck back amount changing step, the nozzle temperature is calculated from the nozzle temperature of the molding condition based on the pressure waveform stored in the arithmetic processing unit. A nozzle temperature changing step that sequentially changes may be included, and when the pressure detected by the load cell in the nozzle temperature changing step reaches a set pressure, continuous molding may be performed at the nozzle temperature that becomes the set pressure. In this case, even when the drooling cannot be prevented only by adjusting the suck back amount, the set pressure is obtained by adjusting the nozzle temperature, and the drooling can be automatically prevented from occurring.

  According to the present invention, the occurrence of drooling can be automatically prevented by the standard equipment of the injection molding machine.

  A configuration diagram of a control system of the injection molding machine of the present embodiment is shown in FIG.

  The injection device of the electric injection molding machine includes a cylinder 7, an open nozzle-shaped nozzle 9 provided at the tip of the cylinder 7, a screw 8 inserted into the cylinder 7 so as to be able to rotate and move forward and backward, and one end of the screw 8. Furthermore, a load cell 6 that measures the distortion due to the reaction force of the screw 8 at the time of injection as an injection pressure, a ball screw 5 that moves the screw 8 in the axial direction, and an injection servo motor 3 that rotates the ball screw 5 via the timing belt 4 And a control unit 17 including a process controller 1 that controls the injection servomotor 3 based on a signal from the load cell 6 and a signal from an encoder 13 provided in the injection servomotor 3.

  In addition to the process controller 1, the control unit 17 includes an arithmetic processing unit 14, a suck-back / nozzle unit temperature control unit 15, and a threshold setting unit 16 connected to the process controller 1.

  The suck back / nozzle part temperature control unit 15 performs control for sequentially changing the suck back amount and control for sequentially changing the temperature of the nozzle part.

  The threshold setting unit 16 sets the number of times of suck back control, the amount of change of suck back amount, the number of shots of nozzle temperature control, the amount of change of nozzle temperature, etc. Has the function to set. These values are input when the pressure and temperature at which a good product is formed without drooling or stringing are known as experience values, or past similar data is set.

  The arithmetic processing unit 14 stores the current suck back position, the set temperature of the nozzle 9 part, and the pressure waveform during the injection process (see FIG. 2).

  In an injection molding machine with such a structure, as a general process for producing a molded product, a measurement (plasticization) process is performed during the cooling process for the purpose of solidifying the molded product and shortening the cycle after the injection pressure holding process. A post-suckback process is performed. In this suck back process, as shown in FIG. 1, the process controller 1 can arbitrarily set the reverse speed and the reverse position, and the set signal is sent from the servo amplifier 2 to the injection servo motor 3. A screw 8 that is rotatably inserted into the cylinder 7 is controlled via a timing belt 4 and a ball screw 5. The screw 8 is slightly retracted without rotating so that the resin pressure at the screw tip can be lowered. The position of the suck back process (position where the screw 8 is retracted) is sent to the monitor screen of the process controller 1 via the encoder 13 and the resin pressure at the screw tip after the suck back is sent via the load cell 6 for display. Has been.

  On the other hand, the resin supplied from the hopper 12 falls into the groove of the screw 8 when the rotation of the screw 8 starts and is transferred in the direction of the nozzle 9. In this transfer process, the resin is compressed and melted and stored on the tip side of the screw 8 in accordance with the mass of the molded product. The amount of heat necessary for this melting is supplied from the kneading heat generated by the screw 8 and the band heater 10 attached to the outer periphery of the cylinder 7.

  The molten resin is injected into a mold (not shown) by the injection molding machine having the above-described configuration, and after cooling, the mold is opened and the molded product is taken out. When the mold is opened, the tip of the above-described screw 8 is opened. Due to the resin pressure, the resin pressure is released to the nozzle 9 side, so that drooling of the phenomenon that the molten resin leaks from the hole of the nozzle 9 has occurred. The control method of the present embodiment eliminates such drooling by using the standard equipment of the injection molding machine.

  Here, an example of a pressure waveform (injection waveform) during the injection process is shown in FIG.

  In the pressure waveform shown in FIG. 2, a local pressure peak having a maximum pressure value of 40 MPa is seen 0.1 seconds after the start of injection. The pressure value α is a pressure value when the molten resin passes through the nozzle gate, and is a value generated because the molten resin is solidified (a skin layer is formed) at the tip of the nozzle portion. As the molten resin solidifies, drooling from the nozzle can be prevented. If the pressure value α when passing through the nozzle is too high, optimal injection control cannot be performed, and a good molded product cannot be obtained. Therefore, it is necessary to control the pressure value α when passing through the nozzle to be within a range not exceeding the optimum upper limit value obtained from the experience of the operator. Therefore, in the correction of the suck back amount and the nozzle tip temperature, which will be described later, the upper limit monitoring pressure value is input to the threshold setting unit 16 so that the pressure value α does not exceed the upper limit value taking the quality of the molded product into consideration. Perform quality control of molded products.

  Hereinafter, details of control for preventing drooling of the present embodiment will be described with reference to a flowchart shown in FIG.

  First, for example, “lower limit pressure = 30 MPa”, “upper pressure = 40 MPa”, and “time = 0.1 sec” are input and set in the threshold setting unit 16 as the passing pressure value and time of the nozzle gate (step S1). In addition, when the numerical value when a good product is molded is known, the numerical value to be input may be input in advance.

  Next, the operator starts molding based on normal molding conditions (step S2).

  Generally, when the molding is started, when the mold is brought into contact with the mold (not shown), the temperature of the nozzle 9 is drastically lowered because the mold temperature is usually lower than the temperature of the nozzle 9 and is over by nozzle temperature control such as PID control. It becomes a mechanism that stabilizes when a certain time elapses by repeatedly shooting and undershooting. For this reason, check whether drooling has occurred, in particular, to automatically correct drooling on molded parts due to disturbances such as a certain period of molding start and fluctuations in mold temperature. (Step S3). The confirmation of the occurrence of drooling is performed, for example, when the remaining amount of the molten resin in the nozzle decreases due to drooling, the screw 8 moves forward, and the movement of the screw 8 is detected by the encoder 13 to the arithmetic processing unit 14. To determine whether drooling has occurred.

  Here, if drooling does not occur, continuous molding is performed under the current molding conditions (step S11).

  On the other hand, if drooling has occurred, the current suckback position, nozzle part temperature, and pressure waveform are stored in the arithmetic processing part 14 (step S4).

  Subsequently, it is confirmed whether the nozzle gate position can be determined from the pressure waveform stored in the arithmetic processing unit 14 (step S4). In other words, when the pressure value stored in the arithmetic processing unit 14 is larger than the lower limit value set by the threshold setting unit 16, the arithmetic processing unit 14 determines that the nozzle gate position has been confirmed. The nozzle gate position is a position where the resin is solidified. When the pressure value stored in the arithmetic processing unit 14 is smaller than the lower limit value and the nozzle gate position cannot be confirmed, the suck back / nozzle temperature control unit 15 starts suck back automatic control (step S6). For example, when the current suck back position setting value is 3.0 mm, the suck back position setting value is gradually increased to 3.1 mm, 3.2 mm,. Along with this, the passage pressure of the resin at the nozzle gate position becomes higher. At this time, each suckback amount is stored in the arithmetic processing unit 14 (step S7). Accordingly, the set value of the process controller 1 is also automatically converted via the arithmetic processing unit 14.

  Next, the arithmetic processing unit 14 determines whether or not the pressure value detected by the load cell 6 has reached the set upper limit value (step S8). If it reaches the upper limit value, it means that the value when the good product was molded is reached, so the control by the suck back / nozzle temperature control unit 15 is stopped, and after checking whether drooling has occurred or not, continuous molding (Step S11).

  On the other hand, if only the suck back amount is changed by the automatic suck back control, the skin layer is not formed by lowering the nozzle temperature when the resin passage pressure at the nozzle gate position does not reach the upper limit value and the skin layer is not formed. In order to form the nozzle, automatic nozzle temperature control is started (step S9). With the nozzle part temperature automatic control, the set temperature of the nozzle part is gradually lowered from the current set value to 0.1 ° C, 0.2 ° C ··· for each molding shot, and this temperature is calculated. It is stored in the processing unit 14 (step S10). The set temperature of the nozzle part lowered in steps and the actually measured value at that time are automatically converted to the set value of the process controller 1 via the arithmetic processing part 14 and the molding is repeated.

  Similarly, the arithmetic processing unit 14 determines whether or not the pressure value detected by the load cell 6 has reached the set upper limit value (step S8). If it reaches the upper limit value, it means that the value when the good product was molded is reached, so the control by the suck back / nozzle temperature control unit 15 is stopped, and after checking whether drooling has occurred or not, continuous molding (Step S11).

  For example, the threshold setting unit 16 sets the number of suck back control shots as “number of times of suck back control”, “change amount of suck back amount”, “number of shots of nozzle temperature control”, and “change amount of nozzle temperature”. Assume that “20 shots”, the gradually increasing suck back amount “0.1 mm”, the nozzle temperature control shot count “10 shots”, and the gradually decreasing temperature amount “C” are input as “1 ° C.”. In this case, in the above automatic suck back control and automatic nozzle temperature control, molding is first performed under the condition “Max value = 2 mm” where the suck back amount is gradually increased by the number of shots, and then the nozzle temperature is gradually increased by the number of shots. Continuous molding is repeated under the condition “Max value = 10 ° C.” lowered to

  As described above, the suck-back / nozzle temperature controller 15 optimizes the position of the suck-back and the nozzle temperature, thereby generating a skin layer of the molten resin in the nozzle and preventing drooling. In addition, since the pressure upper limit value and time are set based on the quality of the molded product (“pressure = 40 MPa”, “time = 0.1 sec” in the case of the above example) Defects can be reduced.

Further, according to the present embodiment, the following molding defects are improved by automatically controlling the position of the suck back and the temperature of the nozzle portion from the actual injection waveform and correcting each setting based on the normal molding conditions. be able to.
1. It is possible to prevent drooling by using the standard function of an injection molding machine without arranging a plurality of heaters and sensors.
2. In preventing drooling by mechanical seals of needles such as needle nozzles, resin color changeability including pressure loss during injection is poor, and depending on the structure, there will be problems such as wear and contamination, but this embodiment Since the open nozzle that is a standard equipment of the injection molding machine is used, there is no problem inherent to the needle nozzle.
3. Drooling can be prevented by using the standard equipment of the injection molding machine without prompt control of the nozzle temperature and feedback control of the actual temperature.
4). Even if a disturbance occurs during molding, particularly a change in room temperature or mold temperature, defective molding due to disturbance or the like can be minimized by automatically correcting the position of the suckback and the temperature of the nozzle portion.
5). Even if sudden molding defects occur during automatic operation, automatic correction can be performed, so that molding defects can be minimized.
6). Since the upper limit pressure when passing through the nozzle is set based on the quality of the molded product, the reduction of molding defects can be minimized.
7). By forming the skin layer on the molten resin in the nozzle, the amount of resin stored at the screw tip can be stabilized, and the weight variation of the molded product can be minimized.

  In addition, this embodiment can prevent not only drooling but also stringing. In this case, an experience value that does not cause stringing is input as the set value to be input to the threshold setting unit 16.

It is a schematic block diagram of an example of the control system of the injection device of the present invention. It is an example of the pressure waveform graph in the suck back control and nozzle part temperature control of this invention. It is an example of the flowchart of the suck back nozzle part temperature automatic control method of this invention. It is a schematic block diagram of an example of the control system of the conventional injection device. It is an example of the pressure waveform graph in the conventional suck back control and nozzle part temperature control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Process controller 2 Servo amplifier part 3 Injection servo motor 4 Timing belt 5 Ball screw 6 Load cell 7 Cylinder 8 Screw 9 Nozzle 10 Band heater 12 Hopper 13 Encoder 14 Arithmetic processing part 15 Suck back nozzle part temperature control part 16 Threshold setting part 17 Control Part

Claims (2)

A signal from the injection molding machine is input, a process controller (1) for controlling the operation of the injection molding machine, an arithmetic processing unit (14) connected to the process controller (1), and a suck back amount Suckback / nozzle temperature controller (15) for sequentially changing the nozzle temperature, a load cell (6) for measuring the resin pressure, an encoder (13) for measuring the position of the screw (8), and molding In a control method of an injection molding machine having a threshold setting unit (16) for setting threshold values of pressure and temperature in the process,
Inputting a pressure at which drooling based on experience values does not occur as a set pressure into the threshold setting unit (16);
Storing the pressure waveform and molding conditions in the injection process in the arithmetic processing unit (14);
Based on the measurement values of the load cell (6) and the encoder (13), the suck back / nozzle temperature controller (15) sucks back molding conditions based on the pressure waveform stored in the arithmetic processor (14). A suck back amount changing step for sequentially changing the suck back amount from the amount,
An injection molding machine characterized in that, when the pressure detected by the load cell (6) in the suck back amount changing step reaches the set pressure, continuous molding is performed at a suck back amount that becomes the set pressure. Control method. A nozzle temperature changing step of sequentially changing the nozzle temperature from the nozzle temperature of the molding condition based on the pressure waveform stored in the arithmetic processing unit (14) when the set pressure is not reached in the suck back amount changing step; Including
The injection molding machine according to claim 1, wherein when the pressure detected by the load cell (6) in the nozzle temperature changing step reaches the set pressure, continuous molding is performed at the nozzle temperature that becomes the set pressure. Control method.

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