JP3778988B2 - Nozzle temperature control method for injection molding machine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a nozzle temperature control method for an injection molding machine.
[0002]
[Prior art]
In the set-up work to start the injection molding work, with the injection cylinder retracted and sprue broken, power is supplied to the heater and nozzle heater of the injection cylinder to wait for the temperature to rise, and then a purge work is performed. It is common to start the injection molding operation by adjusting the state of the injection cylinder, nozzle and molten resin, and bringing the nozzle into contact with the sprue of the mold. Of course, it is possible to raise the temperature of the injection cylinder or nozzle while keeping the nozzle in contact with the mold, but the time required for the temperature rise becomes extremely long, the start of the purge operation is delayed, and the nose during the temperature rise Such operations are generally not performed because there is a risk of sagging and the resin entering the mold.
[0003]
As a result, a significant temperature difference occurs between the sprue portion of the mold and the nozzle of the injection cylinder at the initial stage of starting the continuous molding operation, that is, the stage where the nozzle of the injection cylinder has just been touched to the mold.
[0004]
If the continuous molding operation is continued as it is, the mold gradually absorbs heat from the nozzle, and finally, the temperature of the sprue part of the mold and the temperature of the nozzle reach a thermal equilibrium state, so that the stable molding operation can be performed. In the stage until the thermal equilibrium state is reached, that is, the stage where the heat of the nozzle is taken away by the mold, the temperature at the tip of the nozzle decreases considerably, and the molten resin solidifies. In many cases, this causes a problem such as nozzle clogging and makes molding impossible.
[0005]
In such a case, at the initial stage of the continuous molding operation, the temperature rise target value of the nozzle is set to a high value by manual operation, and the temperature at the nozzle tip is prevented from being lowered while observing the state. Usually, measures such as returning the nozzle temperature increase target value to a predetermined set value are taken, but if such a manual operation is performed, there is a problem that the operator cannot be separated from the injection molding machine during that time.
[0006]
Therefore, conventionally, with respect to such a problem, the nozzle is divided into a plurality of temperature control regions, and a nozzle heater is provided for each region to control the temperature of each region individually (Japanese Utility Model Publication No. 5-12020). In Japanese Patent Publication No. 7-108544 and Japanese Patent Publication No. 7-108545), the number of heater windings is made denser than the base side, and heat is mainly supplied to the nozzle tip. However, the former method has a complicated structure and is expensive, and the latter method has a problem that the temperature at the nozzle tip becomes higher than necessary even after reaching a temperature at which continuous molding is possible.
[0007]
In addition, an injection molding machine has been proposed that adjusts the amount of heat supplied to the nozzle depending on whether the nozzle is in a nozzle touch state or a sprue break state, and prevents nose sagging caused by an increase in nozzle temperature during the sprue break. However, this is for stabilizing the nozzle temperature during the continuous molding operation after achieving thermal equilibrium, and not for stabilizing the injection molding operation before achieving thermal equilibrium.
[0008]
As a result, no matter which method is applied, it is difficult to stabilize the nozzle tip temperature before achieving thermal equilibrium, and in particular, the difference between the nozzle temperature immediately after the start of continuous molding operation and the temperature of the sprue part of the mold. In a state where the temperature of the sprue portion is low and the heat at the nozzle tip is strongly absorbed by the mold side, the temperature of the molten resin flowing through the nozzle and sprue and flowing into the mold There is also a problem such as a temporary rise and a relative temperature drop as a reaction thereof, and it is very difficult to stabilize the temperature at the tip of the cylinder.
[0009]
A method of providing temperature detection means such as a thermocouple at the tip of the nozzle to perform PID (proportional, integral, derivative) control and ON / OFF control of the nozzle heater is also conceivable, but as shown in FIG. Since the portion 100a is reduced in diameter by a considerably large taper so as to be in close contact with the hollow portion on the sprue 101 side, it is difficult to wind the nozzle heater 102 around this portion, and the thermocouple 103 is attached to this portion. It is also difficult to bury. As a result, the thermocouple 103 and the nozzle heater 102 must be provided at a position that is considerably shifted from the tip 100a of the nozzle 100 toward the base 100b, and the nozzle 100 is separated from the portion (tip 100a) where the temperature is actually desired. Sufficient temperature control cannot be performed only by relying on the thermocouple 103 provided at the position.
[0010]
Further, compared to the base 100b side of the nozzle 100 that is in direct contact with the injection cylinder and stores a certain amount of heat, the tip 100a side that absorbs heat by the sprue 101 of the mold is caused by the flow of molten resin or the like. Needless to say, the thermocouple 103 provided on the base 100b side of the nozzle 100 is directly used as the temperature detecting means for the tip 100a, from the above viewpoint. It is impossible to use as.
[0011]
Further, the target temperature is quickly reached with respect to a temperature change caused by heating due to the flow of molten resin at the time of injection or rapid cooling of the nozzle by a mold, that is, a temperature change occurring within a relatively short time such as one molding cycle. In order to improve the response as described above, the proportional band of the P (proportional) operation may be narrowed. However, if the proportional band is narrowed, overshooting or hunting may be caused. Therefore, the proportional band must be increased, and as a result, the ON / OFF control of the nozzle heater is started when the temperature deviation (difference between the target temperature and the detected temperature) is considerably large, and the responsiveness deteriorates. .
[0012]
[Problems to be solved by the invention]
The object of the present invention is that the temperature of the nozzle tip is extremely lowered even in the initial stage of the continuous molding operation where the thermal equilibrium between the mold temperature and the nozzle temperature is not achieved, and nozzle clogging does not occur, An object of the present invention is to provide a nozzle temperature control method for an injection molding machine that can stably maintain the temperature at the tip of a nozzle even with respect to a temperature change caused by the flow of a resin during one molding cycle.
[0013]
[Means for Solving the Problems]
The graph shown by the solid line in FIG. 1 is a concept in which temperature changes that occur in each part around the nozzle 100 when the temperature control of the nozzle 100 is performed by normal PID control are sampled at two time points immediately before and immediately after the injection. It is shown as an example. The horizontal axis indicates the position in the injection axis direction, and the vertical axis indicates the temperature of the nozzle 100 and each part of the mold (not shown) at each position in the injection axis direction. Sampling was performed immediately after the start of the continuous molding operation, that is, when there is a large temperature difference between the temperature of the nozzle 100 and the mold body and the sprue 101.
[0014]
As shown in FIG. 1, the temperature is high on the base 100b side of the nozzle 100 across the tip 100a of the nozzle 100 and is stable regardless of the position in the injection axis direction, and the tip 100a of the nozzle 100 is sandwiched. On the other hand, the temperature is low on the mold side and is stable regardless of the position in the injection axis direction, whereas the temperature at the tip portion 100a of the nozzle 100 is increased from the most advanced portion toward the large diameter portion. Is rising rapidly.
[0015]
The reason why the temperature on the base 100b side of the nozzle 100 is high and stable is that the heat of the nozzle heater 102 is directly transferred and stored in the nozzle body having a certain diameter and a large heat capacity (volume). Further, the temperature on the mold side is low and stable because the heat capacity (volume) of the mold itself is extremely large. Naturally, the tip portion 100a of the nozzle 100 does not have the nozzle heater 102 for stabilizing the temperature, and the heat capacity (volume) is small, so that the temperature in this portion 100a varies significantly depending on the position in the injection axis direction. . This phenomenon is exactly the same whether it is just before injection or just after injection.
[0016]
On the other hand, when only the portion of the tip portion 100a of the nozzle 100 is viewed, as is clear from FIG. 1, there is a significant difference in temperature between immediately before the start of injection and immediately after the completion of injection. As described above, in the state where the temperature of the sprue portion is low and the heat of the nozzle tip 100a is strongly absorbed by the mold side, the melt flowing into the mold through the nozzle 100 and the sprue 101 is melted. This is because a temporary increase in temperature caused by the resin and a relative decrease in temperature as a reaction thereof occur. That is, immediately after the completion of injection, the temperature of the nozzle 100 and the sprue 101 rises by absorbing the heat of the high-temperature molten resin that has flowed into the mold through the nozzle 100 and the sprue 101 in the immediately preceding injection operation. While cooling, weighing, mold opening, ejecting, and mold closing operations are performed, the heat of the nozzle 100 and the sprue 101 and the resin therein is cooled by the mold and the outside air, and the nozzle 100 and the sprue immediately before the start of the next injection. This means that the temperature of 101 becomes the lowest, and there is a high possibility that problems such as nozzle clogging will occur at this stage. Here, the term “injection” includes an injection process and a pressure holding process when the resin filling operation is divided into an injection process and a pressure holding process.
[0017]
Further, when the temperature change during one molding cycle is observed only for the tip portion 100a of the nozzle 100 when the normal PID control is performed, a temperature change as shown by a solid line in FIG. 2 is detected qualitatively. As shown in FIG. 2, the temperature of the tip 100a of the nozzle 100 is the highest immediately after the completion of injection, that is, at the stage before completion of pressure holding / measurement, and also immediately before the start of injection, that is, completion of mold closing. / Lowest at the stage before injection starts. When the injection is started, the temperature of the tip portion 100a gradually increases and reaches the maximum value immediately after the completion of the injection, and the cooling starts immediately from this point and reaches the minimum value immediately before the start of the next injection. Become.
[0018]
Naturally, the temperature of the nozzle 100 is PID-controlled, but as described above, the temperature is relatively stable on the base 100b side of the nozzle 100, and the temperature change of the tip 100a is not reflected on the thermocouple 103. There is a problem that the period of the temperature change is relatively short and it is difficult to follow the PID control. As a result, a temperature change as shown by a solid line in FIG. 2 occurs at the nozzle tip 100a.
[0019]
Therefore, the present invention detects a state variable of the injection molding machine that can estimate the temperature of the nozzle tip, and if this detected value is outside the set allowable range indicating a decrease in the nozzle tip temperature, it is maintained from the time when the mold closing starts. The above-mentioned object is achieved by increasing the energization time of the nozzle heater only during the desired setting section set within the section where the pressure completion time is the limit to prevent the temperature of the nozzle tip from decreasing. The reason why the energization time of the nozzle heater is not increased during measurement is to maintain the gate seal when the pressure holding is completed, and the reason that the energization time of the nozzle heater is not increased during mold opening is to prevent the occurrence of sag. is there.
[0020]
The state variables that estimate the nozzle tip temperature include the maximum injection pressure, the injection pressure after a predetermined time has elapsed after the start of injection, the temperature of the nozzle base when mold opening is completed, the number of shots and the elapsed time after the start of continuous molding operation, etc. When applying the maximum injection pressure or the injection pressure after a predetermined time has elapsed after the start of injection as the state variable, if the state variable exceeds the set allowable range indicating a decrease in the nozzle tip temperature, When applying the temperature of the nozzle base at the time of mold opening completion, the number of shots after the start of continuous molding operation and the elapsed time, the state variable of the nozzle tip is below the set allowable range indicating a decrease in the nozzle tip temperature. Judge as temperature drop.
[0021]
Further, at least one detection value is selected from state variables such as maximum injection pressure, injection pressure after a predetermined time has elapsed after the start of injection, temperature of the nozzle base when mold opening is completed, the number of shots after the start of continuous molding operation, and elapsed time. It may be determined that the temperature of the nozzle tip is lowered when the temperature is outside the allowable setting range indicating the drop of the nozzle tip temperature.
[0022]
As already stated, the nozzle heater can be energized at all times except during weighing or during mold opening. However, the difference in mold size and molding conditions, that is, when normal PID control is performed. In order to adjust the energization time of the nozzle heater according to the change characteristics of the nozzle tip temperature in one molding cycle, the time interval from the time after a predetermined time has elapsed after the mold closing has started until the predetermined time has elapsed since the start of injection, depending on the setting of the timer The time interval to increase the energization time of the nozzle heater can be set.
[0023]
Further, when a predetermined time elapses after the mold closing starts or when the mold closing is completed, the energization time of the nozzle heater is increased. When the predetermined time elapses after the start of injection or when the pressure holding is completed, the PID control of the nozzle heater is resumed. Even if there is a time variation in the processing of each process in the molding cycle, the effect of forced heating by increasing the energization time of the nozzle heater and the prevention of nasal sagging due to inadvertent heating during weighing and mold opening are simultaneously performed I was able to achieve it.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 3 is a block diagram showing a main part of an electric injection molding machine 30 according to an embodiment to which the present invention is applied. In FIG. 3, reference numeral 33 is a fixed platen, 32 is a movable platen, 39 is an injection cylinder, 38 is a screw, and the injection cylinder 39 is provided with a band heater 34 and a thermocouple 37 as temperature detecting means. Yes. A plurality of sets of band heaters 34 and thermocouples 37 are provided in the injection axis direction to individually control the temperature of each part of the injection cylinder 39, and the nozzle heater 102 and the thermocouple 103 are similarly provided to the nozzle 100 at the tip of the injection cylinder 39. ing. The structure of the nozzle 100 and the nozzle heater 102 and their peripheral parts is exactly the same as the conventional example shown in FIG. In FIG. 3, only the temperature controller 43 that performs PID control of the temperature of the nozzle heater 102 of the nozzle 100 is shown, but a similar temperature controller is separately provided for the band heater 34 and the thermocouple 37 of each part of the injection cylinder 39. Has been.
[0025]
The movable platen 32 is moved along a tie bar (not shown) through a drive conversion device 31 constituted by a ball nut & screw, a toggle mechanism, and the like by the shaft output of the mold clamping servomotor M1. The screw 38 is moved in the axial direction by a drive conversion device 41 constituted by a ball nut & screw, a boss & serration, and the like, and an injection servo motor M2, while being constituted by a gear mechanism 42 and a metering rotation servo motor M3. By the driving mechanism, rotational movement for metering and kneading is performed independently of movement in the axial direction. Reference numeral 50 denotes a mold attached to the fixed platen 33 and the movable platen 32.
[0026]
The control device 10 for driving and controlling the injection molding machine includes a CNC CPU 25 that is a numerical control microprocessor, a PMC CPU 18 that is a programmable machine controller microprocessor, a servo CPU 20 that is a servo control microprocessor, and an injection maintenance unit. It has a pressure monitoring CPU 17 for performing processing such as sampling of pressure and screw back pressure, etc., and information can be transmitted between each microprocessor by selecting mutual input / output via the bus 22. Yes.
[0027]
The PMC CPU 18 is connected with a ROM 13 storing a sequence program for controlling the sequence operation of the injection molding machine and a RAM 14 used for temporary storage of calculation data. The CNC CPU 25 controls the injection molding machine as a whole. A ROM 27 storing a program to be executed and a RAM 28 used for temporary storage of calculation data are connected.
[0028]
Each of the servo CPU 20 and the pressure monitor CPU 17 includes a ROM 21 storing a control program dedicated to servo control, a RAM 19 used for temporary storage of data, a ROM 11 storing a control program relating to a molding data sampling process, and the like. A RAM 12 used for temporary storage is connected.
[0029]
The servo CPU 20 is connected to a servo amplifier 15 that drives a servo motor for each axis for ejector (not shown), mold clamping, injection, screw rotation, etc., based on a command from the CPU 20. Outputs from the pulse coder P1 provided in the mold clamping servo motor M1, the pulse coder P2 provided in the injection servo motor M2, and the like are fed back to the servo CPU 20, and calculated by the servo CPU 20 based on the feedback pulse from the pulse coder P1. The current position and current speed of the screw 38 calculated based on the current position of the movable platen 32 and the feedback pulse from the pulse coder P2 are stored in the current position storage register and the current speed storage register of the RAM 19, respectively. Yes.
[0030]
The pressure monitoring CPU 17 performs sampling processing of the injection holding pressure and the screw back pressure via the pressure detector 40 and the A / D converter 16 provided at the base of the screw 38.
[0031]
The non-volatile memory 24 stores molding conditions (injection holding pressure conditions, metering conditions, temperatures of each part of the nozzle 100 and the injection cylinder 39, etc.) and various set values, parameters, macro variables, and the like in the conventional manner. This is a memory for storing molding data. Further, in this embodiment, an allowable maximum value A of the maximum injection pressure which is an allowable range of the state variable of the injection molding machine, and an allowable maximum of injection pressure after a predetermined time has elapsed after the start of injection. Each set value is stored as a value B, an allowable minimum value C of the nozzle base temperature when the mold opening is completed, and an allowable minimum value D of the number of shots after the start of the continuous molding operation. Further, a set time t1 for starting the normal ON control of the nozzle heater 102 and a set time t2 for rounding up the normal ON control and returning to the normal PID control are also stored in the nonvolatile memory 24. Yes.
[0032]
A manual data input device 29 with a display is connected to the bus 22 via a CRT display circuit 26, and various setting screens, data input operations, and the like are performed by various function keys, numeric keys, cursor movement keys, and the like. Yes.
[0033]
Then, the PMC CPU 18 performs sequence control of each axis of the injection molding machine, while the CNC CPU 25 distributes pulses to the servo motors of each axis based on the control program of the ROM 27, and the servo CPU 20 controls each axis. Based on the pulse-distributed movement command and the position feedback signal and speed feedback signal detected by the detectors such as pulse coders P1 and P2, position loop control, speed loop control, current loop control, etc. Servo control is performed and so-called digital servo processing is executed.
[0034]
The temperature control of each part of the injection cylinder 39 and the nozzle 100 by the band heater 34 and the nozzle heater 102 is performed for each temperature controller 43 via the input / output circuit 23 by the actual temperature of each part fed back by the thermocouples 37 and 103 and the CPU 18 for PMC. Based on the relationship with the set target temperature of the non-volatile memory 24 to be set, the temperature controller 43 performs PID feedback control, which is realized in the same manner as in the prior art. Further, the actual temperatures of the injection cylinder 39 and the nozzle 100 detected by the thermocouples 37 and 103 of each unit are read into the PMC CPU 18 via the input / output circuit 23. Among these, the temperature regulator 43 of the nozzle 100 can always turn on the energization state of the nozzle heater 102 by the normally ON signal input from the PMC 18 regardless of the set target temperature and the detected temperature at that time. It is configured.
[0035]
4 and 5 are flow charts showing the outline of the temperature control process for one molding cycle by the PMC CPU 18, which is repeatedly executed together with the sequence control of each axis of the injection molding machine by the PMC CPU 18. FIG.
[0036]
4 and FIG. 5, the steps of each process are shown continuously along the time series in which they are executed. In practice, however, in the same manner as the sequence control of each axis of the injection molding machine, each step is performed at predetermined intervals. The process is repeatedly executed, and does not mean that the PMC CPU 18 does not execute other processes including the sequence control of each axis while the process of each step is in a standby state. For example, if a time corresponding to one processing cycle elapses during the process of waiting for the mold closing start in step S3, the PMC CPU 18 executes the process that was executed when this process was rounded up, that is, in this case Then, the process of step S3 is stored as the first process to be executed in the next process cycle, and in the next process cycle, the processes of step S1 and step S2 are not executed and the process is restarted from the determination process of step S3. .
[0037]
Therefore, first, the PMC CPU 18 that has started the temperature control process of the first molding cycle in the continuous molding operation initializes the value of the shot number counter S to 0 (step S1), and stores the execution of the normally ON control of the nozzle heater 102. A forced heating flag F is set (step S2). That is, the forced heating flag F is set from the beginning based on the assumption that a large temperature difference has already occurred between the nozzle 100 and the mold at the start of the continuous molding operation. Since the continuous molding operation is performed subsequent to the temperature increase or purge operation of the injection cylinder 39 or the nozzle 100, the normal PDI performed from the time when the temperature increase of the injection cylinder 39 or the nozzle 100 is started at this time. The temperature control of the nozzle 100 and the cylinder 39 by the control is continuously performed.
[0038]
Next, the PMC CPU 18 determines whether or not the mold closing sequence is started (step S3). If the mold closing sequence is not started, the PMC CPU 18 stands by. As already mentioned, this does not mean waiting within the same processing cycle. Next, when the mold closing sequence is started, the PMC CPU 18 determines whether or not the forced heating flag F is set (step S4), but the flag F is set at the present stage immediately after the start of continuous molding. Therefore, the PMC CPU 18 sets the set value t1 to the timer T1 for measuring the elapsed time after the mold closing start and starts measuring time (step S5). As already described, this set value t1 is a set value for determining how many seconds after the start of the mold closing operation to start the normal ON control of the nozzle heater 102, and is optimal depending on the difference in the size of the mold and molding conditions. There is a value.
[0039]
The PMC CPU 18 that has started measuring the elapsed time after the start of mold closing waits until the timer T1 finishes measuring the set value t1 (step S6) or until the mold closing sequence is completed (step S7). . If the mold closing sequence is completed before the timer T1 finishes measuring the set value t1, the normal ON command is output to the temperature controller 43 of the nozzle heater 102 simultaneously with the completion of the mold closing sequence. When continuous heating is started (step S8), and the timer T1 completes timing of the set value t1 before the mold closing sequence is completed, a normal ON command is sent to the temperature controller 43 of the nozzle heater 102 simultaneously with completion of timing. Is output to start continuous heating of the nozzle 100 (step S9), and the completion of the mold closing sequence is awaited (step S10).
[0040]
Next, the PMC CPU 18 determines whether or not the injection sequence is started (step S11). If the injection sequence is not started, the PMC CPU 18 waits as it is, and when the start of the injection sequence is confirmed, A set value t2 is set in a timer T2 that measures the elapsed time after the start of injection, and time measurement is started (step S12). This set value t2 is a set value for deciding how many seconds after the start of the injection operation the normal ON control of the nozzle heater 102 is terminated and the normal PID control is started. Like the set value t1, the size of the mold is set. There are optimum values depending on the difference in the molding conditions.
[0041]
The PMC CPU 18 that has started measuring the elapsed time after the start of injection waits until the timer T2 completes timing of the set value t2 (step S13) or the pressure holding sequence is completed (step S14). If the pressure holding sequence is completed before the timer T2 finishes measuring the set value t2, the PID control restart command is output to the temperature controller 43 of the nozzle heater 102 simultaneously with the completion of the pressure holding sequence. Is switched to normal PID control (step S15), and when the timer T2 completes timing of the set value t2 before the pressure holding sequence is completed, the temperature control of the nozzle heater 102 is performed simultaneously with the completion of timing. Is switched to normal PID control (step S16), and the completion of the pressure holding sequence is awaited (step S17).
[0042]
Even if the setting value t2 is set to a long value by mistake, the normal ON control of the nozzle heater 102 is forcibly terminated at the same time as the pressure holding is completed and returns to the normal PID control. There will be no problem that the gate seal is broken by excessive heating. Further, even if the set value t1 is set to be long by mistake, the normal ON control of the nozzle heater 102 is forcibly started when the mold closing sequence is completed. The normally ON control of the nozzle heater 102 can be performed at least for t2 seconds from completion of mold closing, or from completion of mold closing to completion of pressure holding. Of course, it is desirable to perform optimum temperature control by adjusting the set values t1 and t2.
[0043]
As already described, the set values t1 and t2 have optimum values due to differences in the size of the mold, molding conditions, and the like. For example, as shown in FIG. 2, the temperature of the tip 100a of the nozzle 100 sets the set target value. It is desirable to set so that the temperature drop of the tip 100a during the mold closing and injection operations is as small as possible without overshoot. It can be said that a setting that can obtain a temperature change as indicated by dots in FIG. 2 is optimal.
[0044]
After that, the PMC CPU 18 stands by until one molding cycle sequence, that is, the mold opening operation is completed (step S18), and during this time, another task process by the PMC CPU 18 includes weighing, mold opening, ejection, and the like. The drive control of the shaft is performed.
[0045]
When the sequence operation of one molding cycle is completed, the PMC CPU 18 refers to the sampling file of the injection holding pressure, detects the maximum injection pressure in the molding cycle, and temporarily stores it in the register P (step S19). From the sampling file, the injection pressure corresponding to the time after the set predetermined time has elapsed after the start of injection (pressure judgment point) is temporarily stored in the register R (step S20), and the nozzle detected by the thermocouple 103 is further detected. The current temperature of 100 (large-diameter portion), that is, the temperature of the nozzle 100 when the mold opening is completed is temporarily recorded in the register N (step S21), the value of the shot number counter S is incremented by 1, and the number of shots of continuous molding work Is updated (step S22).
[0046]
Next, the PMC CPU 18 determines whether or not the maximum injection pressure P detected in this molding cycle exceeds the allowable maximum value A of the maximum injection pressure (step S23), or the injection pressure R after a predetermined time has elapsed after the start of injection. Whether the allowable maximum value B of the injection pressure is exceeded (step S24), and whether the temperature N of the nozzle 100 at the time of mold opening completion is lower than the allowable minimum value C of the nozzle temperature at the time of mold opening completion (step S25) It is determined whether or not the current shot number S is below the allowable minimum value D of the number of shots (step S26). If one of the determination results is true, the forced heating flag F is set (step S28). ) Only when all the determination results are false, the forced heating flag F is reset (step S27).
[0047]
That is, when the maximum injection pressure P exceeds the allowable maximum value A of the maximum injection pressure, and when the injection pressure R after the set predetermined time has elapsed after the start of injection exceeds the allowable maximum value B of the injection pressure, This is evidence that the temperature of the molten resin, that is, the temperature of the tip 100a of the nozzle 100 has decreased and the viscosity of the resin has increased, and that the nozzle 100 needs to be forcibly heated.
[0048]
Further, when the current shot number S is below the allowable minimum value D of the shot number, it is indicated that the heat of the nozzle 100 is strongly drawn to the mold side immediately after the start of continuous molding. Therefore, in normal PID control, a large temperature change as shown in FIG. 1 may occur between the nozzle tip temperature immediately before the start of injection and the nozzle tip temperature immediately after the completion of injection, which is eliminated. Therefore, it is necessary to perform forced heating shown in the present embodiment. In this case, in short, since it is only necessary to know the elapsed time after the start of continuous molding, instead of comparing the number of shots S with the allowable minimum value D of the number of shots, the elapsed time after the start of continuous molding (state measured by a timer) Variable) and allowable minimum elapsed time (set value) may be used.
[0049]
The same applies to the case where the temperature N of the nozzle 100 at the completion of mold opening is lower than the allowable minimum value C. That is, the temperature of the nozzle 100 is abnormally lowered at present, that is, the heat of the nozzle 100 is gold. Since it means that it is in a state immediately after the start of continuous molding that is strongly sucked to the mold side, it is necessary to forcibly heat the nozzle 100 as described above. In addition, although there has been a technical idea for performing feedback control by detecting the nozzle temperature with a thermocouple provided on the base side of the nozzle 100, this embodiment is detected by a thermocouple provided on the base side of the nozzle 100. It is estimated that there is a large temperature difference between the mold and the nozzle 100 due to a decrease in the temperature, and the nozzle heater 102 is forced to heat without performing normal PID control by the normal ON control. The configuration differs from that of the feedback control. In this embodiment, there is no temperature target value at the time of normal ON control.
[0050]
As a result, the forced heating flag F is reset only when the determination results in steps S23 to S26 are all false and the temperature stability of the nozzle tip is guaranteed, and in other cases, the forced heating flag is reset. This means that the setup state of F is maintained.
[0051]
Next, the PMC CPU 18 determines whether or not the necessary molding operation has been completed, that is, whether or not the value of the shot number counter S has reached the target value (step S29), and the value of the shot number counter S is determined. If the value of the shot number counter S has not reached the target value, the processing from step S3 is repeated.
[0052]
When repeating the continuous molding operation, if the forced heating flag F is reset in the immediately preceding molding cycle, the determination result in step S4 is false, which means that the tip temperature of the nozzle 100 is stable. The processing of step S5 to step S17 is not executed, the temperature control of the nozzle heater 102 is performed by the normal PDI control started in the processing of step S16 of the immediately preceding molding cycle, and the forced heating flag F is set. If so, the processing from step S5 to step S17 is executed in exactly the same manner as described above, and always-on forced heating control is performed instead of PID control.
[0053]
On the other hand, since the process of step S18 thru | or step S29 is implemented for every molding cycle irrespective of whether the forced heating flag F is reset, it is a case where the forced heating flag F is once reset. However, if one of the determination results in steps S23 to S26 becomes true and a change in the state variable corresponding to the abnormal nozzle tip temperature is detected, the forced heating flag F is set again. The forced heating by the normally ON control of the nozzle heater 102 is performed.
[0054]
Therefore, during the continuous molding operation, damage such as breakage of the core of the mold occurs, the molding operation is interrupted, the nozzle 100 is retracted from the mold, and the repairing operation is performed. Even in such a case, the temperature of the nozzle tip can be stabilized by the above-described temperature control process, as in the case of starting the continuous molding operation.
[0055]
【The invention's effect】
According to the present invention, even at the initial stage of the continuous molding operation where the thermal equilibrium between the mold temperature and the nozzle temperature has not been achieved, the temperature of the nozzle tip is extremely reduced and nozzle clogging does not occur, The temperature at the nozzle tip can be stably maintained even with respect to a temperature change or the like caused by a resin flow during one molding cycle.
[0056]
In addition, since the timer energizing time increase section for preventing the temperature drop at the nozzle tip is set by the timer, the heating characteristics of the nozzle can be adjusted according to the characteristics of the mold and molding conditions.
[0057]
Even if the timer is set by mistake, if the holding pressure is completed, the increase control of the energization time of the nozzle heater is forcibly terminated and normal PID control is resumed. It is possible to prevent the occurrence of sagging at the time of seal breakage, weighing and mold opening.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a structure around a nozzle in an injection molding machine, and a graph showing temperature variations in the vicinity of the nozzle.
FIG. 2 is a graph showing the temperature change at the nozzle tip in normal PID control and the temperature change at the nozzle tip when one embodiment of the present invention is applied.
FIG. 3 is a block diagram showing a main part of an electric injection molding machine according to an embodiment to which the method of the present invention is applied.
FIG. 4 is a flowchart showing an outline of a temperature control process according to an embodiment to which the method of the present invention is applied.
FIG. 5 is a continuation of the flowchart showing the outline of the temperature control process.
[Explanation of symbols]
10 Control device
11 ROM
12 RAM
13 ROM
14 RAM
15 Servo amplifier
16 A / D converter
17 CPU for pressure monitoring
18 CPU for PMC
19 RAM
20 Servo CPU
21 ROM
22 Bus
23 I / O circuit
24 Nonvolatile memory
25 CPU for CNC
26 CRT display circuit
27 ROM
28 RAM
29 Manual data input device with display
30 Electric injection molding machine
31 Drive conversion device
32 Movable platen
33 Fixed platen
34 Band heater
37 Thermocouple
38 screw
39 Injection cylinder
40 Pressure detector
41 Drive converter
42 Gear mechanism
43 Temperature controller
50 mold
100 nozzles
100a Tip
100b base
101 sprue
102 Nozzle heater
103 thermocouple
Servo motor for M1 mold clamping
M2 servo motor for injection
M3 Servo motor for metering rotation
P1 pulse coder
P2 pulse coder

Claims (8)

In a nozzle temperature control method of an injection molding machine that detects the temperature of a nozzle and performs PID control so that the detected temperature matches a set temperature to control ON / OFF of the nozzle heater , If the value of the state variable is detected and the detected value is outside the allowable setting range that indicates a decrease in the nozzle tip temperature, the setting interval set within the interval from the mold closing start time to the pressure holding completion time limit A nozzle temperature control method for an injection molding machine, wherein the energization time of the nozzle heater is increased only during the period. The nozzle temperature control method for an injection molding machine according to claim 1, wherein the state variable is a maximum injection pressure. The nozzle temperature control method for an injection molding machine according to claim 1, wherein the state variable is an injection pressure after a predetermined time has elapsed after the start of injection. The nozzle temperature control method for an injection molding machine according to claim 1, wherein the state variable is a temperature of a nozzle base when mold opening is completed. 2. The nozzle temperature control method for an injection molding machine according to claim 1, wherein the state variable is the number of shots after the start of a continuous molding operation. The state variables are the maximum injection pressure, the injection pressure after a predetermined time has elapsed after the start of injection, the nozzle detection temperature at the completion of mold opening, and the number of shots after the start of continuous molding operation, of which at least one detection value is the nozzle tip temperature. When it is out of a setting allowable range indicating a decrease, the energization time of the nozzle heater is increased only during a setting section set within a section having a limit from the mold closing start time to the pressure holding completion time. The nozzle temperature control method for an injection molding machine according to claim 1. The time interval from the time after a predetermined time elapses after the start of mold closing to the elapse of a predetermined time after the start of injection is set as the set interval according to the setting of the timer. The nozzle temperature control method of the injection molding machine as described in the item. When a predetermined time elapses after the mold closing starts or when the mold closing is completed, the energization of the nozzle heater is always turned on, and when the predetermined time elapses after the start of injection or when the pressure holding is completed, the PID control is resumed. The nozzle temperature control method for an injection molding machine according to any one of claims 1 to 6.

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