JPH0847956A - Injection control method of injection molding machine - Google Patents

Abstract

PURPOSE:To shorten a molding cycle time and prevent generation of flash by detecting an injection start limit time when a difference obtained by subtracting a run out quantity of a moving platen from a stretch of a tie bar exceeds an allowable value and setting an injection start time where the difference does not exceed the allowable value. CONSTITUTION:A screw 2 in an injection cylinder 1 is driven by an injecting servo motor Ms in the direction of injection shaft and rotated by a screw rotating servo motor Mr for measuring. On the other hand, a moving platen 6 mounted slidably on a tie bar 9 to which a stationary platen 7 and a rear platen 5 are fixed is driven by a mold clamping servo motor Mc. The motors Ms, Mr, and Mc are driven by a control device 11. In this case, when a difference obtained by subtracting a run out quantity of the moving platen 6 from a stretch of the tie bar 9 at the same point in time exceeds an allowable value even a single value, an injection start time at this time is detected as an injection start limit time, so that an injection start time where the entire difference does not exceed the allowable value is set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection control method for an injection molding machine.

[0002]

2. Description of the Related Art An injection control method has been already known in which a mold clamping operation and an injection operation are performed in duplicate for the purpose of speeding up cycle time and improving degassing. This method facilitates degassing in the mold cavity by starting the injection operation during the mold clamping operation to prevent product burning, and part of the injection operation is performed in parallel with the mold clamping operation. Although it is intended to shorten the molding cycle time as a whole, if the injection operation is started too early, the mold clamping force will be weak and the mold will open more than necessary, causing burrs on the product. There is a risk that it will occur.

[0003]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an injection molding machine capable of appropriately setting an injection start time capable of shortening a molding cycle time as much as possible in a range where burr does not occur. To provide an injection control method of

[0004]

According to the present invention, an injection molding operation is performed while advancing the injection start time successively, and the extension of the tie bar and the feeding amount of the moving platen generated during the mold clamping operation are sequentially synchronized for each molding cycle. If the difference between the extension of the tie bar at the same time point minus the moving out amount of the moving platen exceeds the allowable value, the injection start time at that time is detected as the injection start limit time, and the On the basis of the above, the object was achieved by obtaining an injection start time in the vicinity of the injection start limit time in which all of the differences do not exceed the allowable values and setting this as the injection start time. Also, instead of the difference obtained by subtracting the feeding amount of the moving platen generated during the mold clamping operation from the extension of the tie bar,
The same purpose is achieved by using the difference obtained by subtracting the distance between the rear platen and the moving platen from the distance between the rear platen and the stationary platen.

Further, the injection molding operation is performed while advancing the injection start time sequentially, and the mold opening force acting on the injection molding die by the mold clamping force and the injection operation given to the injection molding die by the mold clamping operation in each molding cycle. The force and the force are sequentially synchronized, and if any point at which the mold opening force exceeds the mold clamping force is detected, the injection start time at that time is detected as the injection start limit time, and based on the injection start limit time. Further, the same object as above was achieved by setting the injection start time at which the mold opening force does not exceed the mold clamping force in the vicinity of the injection start limit time as the injection start time.

Further, the mold clamping force applied to the injection molding die by the mold clamping operation and the mold opening force acting on the injection molding die by the injection operation are on the same time axis corresponding to the elapsed time of each operation. Display the graph, move the mold opening force or the mold clamping force graph along the time axis to find the limit position where the mold opening force graph does not interfere with the mold clamping force graph, and from the limit position,
The same purpose was achieved by obtaining and setting the injection start time.

[0007]

[Function] The injection molding operation is performed while advancing the injection start time sequentially, and the difference between the extension of the tie bar minus the feeding amount of the moving platen generated during the mold clamping operation for each molding cycle, or the distance between the rear platen and the stationary platen. Then, the difference obtained by subtracting the distance between the rear platen and the moving platen is sequentially obtained, and it is determined whether or not the difference is within the allowable value range. The difference between the extension of the tie bar and the feeding amount of the moving platen generated during the mold clamping operation is the substantial mold opening amount. Therefore, by setting the allowable value to an appropriate value, the mold opening force generated by the injection pressure slightly exceeds the mold clamping force at that time, and the gas between the fixed side mold and the movable side mold is increased. It is possible to detect the injection start limit time when an appropriate gap suitable for extraction is formed. The appropriate allowable value here is the mold opening amount required for degassing in the case of performing the discrimination work using the difference obtained by subtracting the feeding amount of the moving platen from the extension of the tie bar,
Further, in the case of performing the discrimination work by using the difference obtained by subtracting the distance between the rear platen and the moving platen from the distance between the rear platen and the stationary platen, it is a value obtained by adding the mold thickness to the mold opening amount required for degassing. . Since burr may occur if the mold is opened more than necessary during the injection operation, the final injection start time should be based on the injection start limit time so that all of the differences do not exceed the allowable values. Set to. As a result, the limit amount of mold opening is kept within the allowable value, and the mold clamping operation and the injection operation are performed in an overlapping manner within the range in which the occurrence of burrs is prevented, and the molding cycle time is also shortened. It If it is not necessary to open the mold for degassing, an approximate value of zero or an approximate value of the mold thickness is set as the allowable value to detect the injection start limit time, and the mold opening force generated by the injection pressure is the mold opening force. Set the injection start time immediately before the clamping force is exceeded to prevent mold opening.

When setting the injection start time immediately before the occurrence of mold opening, the mold clamping force applied to the injection mold by the mold clamping operation and the mold opening force acting on the injection mold by the injection operation are set. The same object can be achieved by sequentially and synchronously comparing and detecting the injection start time when the time when the mold opening force exceeds the mold clamping force is detected as the injection start limit time.

Further, the mold clamping force applied to the injection molding die by the mold clamping operation and the mold opening force acting on the injection molding die by the injection operation are sampled to obtain the same time corresponding to the elapsed time of each operation. Display the graph on the axis and move the graph of mold opening force or mold clamping force along the time axis to find the limit position where the graph of mold opening force does not interfere with the graph of mold clamping force and set the injection start time. But the same is true.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a main part of a toggle type electric injection molding machine to which an injection control method according to the present invention is applied. Reference numeral 1 is an injection cylinder of the injection molding machine, and reference numeral 2 is a screw. The screw 2 is a servo motor M for injection.
It is driven in the injection axis direction by s, and is metered and rotated by a screw rotation servomotor Mr via a power transmission mechanism 3 including a timing belt, a toothed pulley, and the like. A pressure detector 4 for detecting a resin reaction force acting in the axial direction of the screw 2 is provided at the base of the screw 2 to detect the injection holding pressure in the injection holding process and the screw back pressure in the measuring and kneading process. It has become so.
Further, the injection servomotor Ms is provided with a pulse coder Ps for detecting the position and moving speed of the screw 2, and the screw rotation servomotor Mr is provided with a pulse coder P for detecting the rotation speed of the screw 2.
r is deployed.

A stationary platen 7 is fixed to the base of the injection molding machine, and a moving platen 6 slidably attached to a tie bar 9 that fastens the stationary platen 7 and the rear platen 5 is a rear platen 5.
It is driven by a mold clamping servomotor Mc arranged on the side via a drive device 8 including a ball screw and a toggle mechanism. The mold clamping servomotor Mc is provided with a pulse coder Pc for position and speed detection. Further, the rear platen 5 is provided with a mold thickness adjusting mechanism (not shown) so that the mold can be opened and closed at an optimum position according to the thicknesses of the movable mold attached to the moving platen 6 and the fixed mold attached to the stationary platen 7. And the mold clamping operation can be performed. The position control regarding the moving platen 6 is performed in the same manner as the conventional method based on the crosshead position of the toggle mechanism in the drive device 8, that is, the rotation amount of the mold clamping servomotor Mc. The arithmetic processing for obtaining the substantial position of the moving platen 6 based on the crosshead position of the toggle mechanism is already known in Japanese Patent Application Laid-Open No. 62-160219, etc., and the description thereof will be omitted. In the present embodiment, it is assumed that the substantial position of the moving platen 6 is immediately obtained based on the position feedback signal from the pulse coder Pc.

Further, the tie bar 9 is provided with a strain gauge 10 for detecting the extension of the tie bar 9.
Tie bar 9 proportional to the total length of the
The total elongation and the tie bar tension generated in proportion to the elongation of the tie bar 9 are detected. The processes of detecting the elongation of the elastic body using the strain gauge and obtaining the tension from the elongation of the elastic body are all in the category of the conventional technique, and therefore will not be particularly described. The tie bar tension mentioned here is the force with which the rear platen 5 is attracted to the stationary platen 7 by the four tie bars 9 arranged in parallel, and is not the tension generated in one tie bar 9.

The control unit 11 of the injection molding machine includes a CNC CPU 17 which is a numerical control microprocessor, a PMC CPU 16 which is a programmable machine controller microprocessor, a servo CPU 18 which is a servo control microprocessor, and It has a monitor CPU 33 for performing sampling processing of injection holding pressure and screw back pressure via the A / D converter 34,
Information can be transmitted between the microprocessors by selecting mutual input / output via the bus 28. Furthermore, the output from the strain gauge 10 is input to the monitor CPU 33 via the A / D converter 34, and is read by the PMC CPU 16 as necessary.

The PMC CPU 16 is connected to a ROM 20 storing a sequence program for controlling the sequence operation of the injection molding machine and a RAM 23 used for temporary storage of operation data, and the CNC CPU 17 is connected.
A ROM 21 that stores a program for controlling each axis of the injection molding machine and a RAM 27 that is used for temporary storage of operation data are connected to the. The non-volatile memory 26 connected to the CNC CPU 17 is a molding data storage memory for storing molding conditions and various set values, parameters, macro variables, etc. relating to the injection molding work, and injection performed in duplicate with mold clamping. The allowable value and the like used for control are also stored in the non-volatile memory 26.

Each of the servo CPU 18 and the monitoring CPU 33 has a ROM 22 storing a control program dedicated to servo control, a RAM 24 used for temporary storage of data, and a control program relating to sampling processing for obtaining pressure data and the like. ROM that stores
31 and a RAM 32 used for temporary storage of data are connected. Further, the servo CPU 18 has the CPU 1
Servo amplifier 1 that drives servo motors for each axis for mold clamping, screw rotation, injection, etc. based on commands from 8
2 to 14 are connected via a servo interface 15. Further, each of the outputs from the pulse coders Pc, Pr, Ps provided in the servo motors of the respective axes is fed back to the servo CPU 18 via the servo interface 15, and the cross head position calculated by the servo CPU 18 based on the feedback pulse of the pulse coder. The current position of the screw 2 and the values such as its moving speed and rotation speed are successively updated and stored in the RAM 24 as current values. It should be noted that although FIG. 1 omits the description of the ejector shaft servo motor and its pulse coder and servo amplifier for performing the mold release work of the product, these elements are injection molding machine and its control in the same manner as in the conventional art. Equipped on the device 11.

The input / output circuit 29 is an input / output interface for receiving a signal from a limit switch provided on each part of the injection molding machine or a control panel, or transmitting various commands to peripheral equipment of the injection molding machine. In addition, the communication interface 30 is an input / output interface for performing data transmission with a host computer or a cell controller. Manual data input device with display 19
Is connected to the bus 28 via the CRT display circuit 25 so that a monitor display screen, a function menu can be selected and various data can be input. A numeric keypad for inputting numerical data, various function keys and the like are provided. It is provided.

With the above configuration, the CNC CPU 17 distributes pulses to the servo motors of the respective axes based on the control program of the ROM 21 and various set values, and the servo CPU 18 issues the pulse distributed movement commands to the respective axes. Based on the position feedback signal and velocity feedback signal detected by a detector such as a pulse coder and a pulse coder, servo control such as position loop control, velocity loop control and current loop control is performed in the same manner as in the past, so-called digital servo processing. To execute.

Next, one embodiment of the injection control method according to the present invention will be described with reference to the flow charts of FIGS. 2 to 6 showing the outline of the “injection start time setting process” executed by the PMC CPU 16 when obtaining the injection start time. An example will be described. In this embodiment, the injection molding operation is performed while sequentially advancing the injection start time, and the injection start limit time is detected based on the difference between the extension of the tie bar 9 and the feeding amount of the moving platen 6 which occurs during the mold clamping operation. Further, it is an embodiment in which the injection start time is automatically set on the basis of the injection start limit time, and the working principle of the detection of the injection start limit time is that the mold that acts on the mold by the injection operation during the mold clamping operation. When the opening force exceeds the actual mold clamping force acting at that time, a mold opening occurs between the fixed side mold and the movable side mold, and even if the moving platen 6 is not fed out, the tie bar 9 The point is that the increase in elongation occurs. The final injection start time is set as a waiting time from the start of the mold clamping operation to the start of the injection operation.

Therefore, the PMC CPU 16 which has started the "injection start time setting process" for obtaining the injection start time.
First, the settable maximum value allowed by the system is set in the standby time storage register t1 that stores the standby time from the start of the mold clamping operation to the start of the injection operation (step S1), and the standby time initial setting completion flag F1 and injection are set. The start time setting completion flag F3 is reset (step S2), and the CNC
A mold closing start command is output to the CPU 17 for use (step S
3) Based on the clamp conditions such as the mold closing speed set in the non-volatile memory 26 by the CPU 17, the servomotor Mc for clamping of the injection molding machine in the molding start standby state of the completion of the measurement and the mold opening is performed. The driving is started, and the mold closing operation of the moving platen 6 is started (step S
3). Hereinafter, the PMC CPU 16 is the servo CPU 18
The current position A of the moving platen 6 is sequentially detected via the, and the process waits until the current position A of the moving platen 6 reaches the mold touch position set as the clamp condition in the non-volatile memory 26 (step S4, step S4). S5). The mold touch position is a position where the movable side mold attached to the moving platen 6 starts contact with the fixed side mold attached to the stationary platen 7, and in short, the operation of the moving platen 6 is in an unloaded state. This is the position where the mold closing operation is shifted to the mold clamping operation for extending the tie bar 9. The die touch position is obtained in advance when the die is attached and is stored in the non-volatile memory 26.

When the moving platen 6 has moved and its current position A has reached the mold touch position in the discrimination processing of step S5, the PMC CPU 1
6 resets the elapsed time measuring timer T and restarts it to start measuring the elapsed time after the start of the mold clamping operation (step S6), and the moving platen 6 reaches the lockup completion position (step S7). Alternatively, until the arrival of the elapsed time measuring timer T at t1 is detected (step S8), the determination process of steps S7 and S8 is repeatedly executed and stands by. At this stage, since the maximum value that can be set in the standby time storage register t1 is set, the mold lock-up must be completed first, and the PMC CPU 16 immediately after confirming the completion of the lock-up. The driving of the mold clamping servomotor Mc is stopped (step S9). In this way, the moving platen 6 is extended to the position corresponding to the mold clamping force set as the clamping condition in the non-volatile memory 26, and the lockup of the mold is completed. Elongation corresponding to the force is generated, and the movable side mold and the fixed side mold are strongly pressed by the tension of the tie bar 9 corresponding to the set mold clamping force.

The PMC CPU 16 which has stopped driving the mold clamping servomotor Mc then determines whether or not the standby time initial setting completion flag F1 is set (step S10). At this stage, since the flag F1 is in the reset state, the PMC CPU 16 waits for the current value of the elapsed time measuring timer T, that is, the value of the required time T required from the start of the mold clamping operation to the completion of the mold clamping operation. The injection start waiting time is set in the time storage register t1 as an initial value (step S11), and the waiting time initial setting completion flag F1 is set (step S12).

Next, the PMC CPU 16 outputs an injection start command to the CNC CPU 17 (step S1).
3) The CPU 17 starts driving the injection servomotor Ms based on the injection speed, the maximum injection pressure, etc. set in the nonvolatile memory 26 as the injection condition,
The screw 2 is advanced to start the injection operation. That is, the injection start timing in the first injection molding operation is irrelevant to the value of the standby time storage register t1, and is started when the mold clamping operation is completed.

Then, the C for PMC which has started the injection operation
The PU 16 determines whether or not the injection start time setting completion flag F3, which means that the setting of the injection time has been completed, is set (step S14), but since the flag F3 is in the reset state at this stage, the PMC CPU 16 The mold opening amount excess flag F2 is reset (step S21), and thereafter, until the completion of the injection and pressure holding operation is detected (step S30), the extension Δx1 of the tie bar 9 and the feeding amount Δx2 of the moving platen 6 are set. The difference Δx is detected every predetermined period, and at each time of the injection and pressure-holding operations, it is determined whether or not the difference Δx exceeds the range of the allowable value ε stored in the nonvolatile memory 26 in advance. The process will be repeatedly executed (the processes of steps S22 to S31). As is clear from the above explanation,
In the processing of steps S22 to S31, when the injection start time is gradually advanced, the mold opening amount Δx is the allowable value ε.
It is the "limit time detection process" for obtaining the first injection start time that exceeds the above, that is, the injection start limit time, and is the main part of the "injection start time setting process".

Therefore, the PMC CPU 16 which has started the "limit time detection process" first reads the output of the strain gauge 10 via the monitor CPU 33, and determines the extension of the strain gauge 10 determined by this output according to the total length of the tie bar 9. The expansion Δx1 from the natural length of the tie bar 9 is obtained by multiplying the determined coefficient (step S22), the current position A of the moving platen 6 is read via the servo CPU 18 (step S23), and the moving platen after the mold clamping operation is started. 6 is calculated (step S24), and based on these values, the difference Δx is calculated by subtracting the expansion amount Δx2 of the moving platen 6 from the expansion Δx1 of the tie bar 9 (step S25). In this embodiment, the position of the moving platen 6 is defined by a position on a number line whose origin is the lock-up completion position of the moving platen 6 and whose positive direction is the direction in which the moving platen 6 separates from the stationary platen 7. Therefore, after the mold clamping operation is started (= after the die is touched), the mold touch position is always greater than the current position A, and the feeding amount Δx2 of the moving platen 6 after the mold clamping operation is started is Δx2 = metal. Mold touch position-A> 0.

Next, the PMC CPU 16 causes the difference Δ
The value of x is the allowable value ε stored in the non-volatile memory 26.
Is larger than the value of (step S26),
Only when Δx exceeds ε, the mold opening amount excess flag F
2 is set (step S27). However, if it is limited to the first injection operation, the injection operation is started after the mold clamping operation is completely completed and the mold is locked up, so that the mold has a clamping force suitable for the injection molding die. As long as the injection molding machine is properly selected, the mold opening force generated by the injection pressure is not defeated by the mold clamping force to cause the mold opening, and the phenomenon of Δx> ε does not occur. In short, the state in which the extension Δx1 of the tie bar 9 is equal to the feeding amount Δx2 of the moving platen 6 is maintained.

PM for which the determination processing in step S26 has been executed
Next, the CPU 16 for C determines whether or not the moving platen 6 has reached the lockup completion position (step S28), but as described above, if it is limited to the first injection molding operation, it is completely completed. Since the injection operation is started after the mold clamping operation is completed and the mold is locked up, the determination result of step S28 is inevitably true and P
The MC CPU 16 outputs a drive stop command to the mold clamping servomotor Mc (step S29). Regarding the first injection molding operation, since the drive stop command has already been output to the mold clamping servomotor Mc in the process of step S9, the process of step S29 has no special meaning. Next, the CPU 16 for PMC is the CPU 1 for CNC.
It is determined whether or not the injection and pressure-holding operations under the control of 7 are completed (step S30), but if these operations are not completed, sampling of the expansion Δx1 of the tie bar 9 and the delivery amount Δx2 of the moving platen 6 are performed. The process waits for a predetermined minute time set to be suitable for (step S31), and thereafter, in the same manner as described above, until the completion of the injection and pressure holding operation is confirmed in the process of step S30. The "limit time detection process" of S31 is repeatedly executed.

When it is detected in the determination processing in step S30 that the injection and pressure-holding operations under the control of the CNC CPU 17 have been completed while the "limit time detection processing" is repeatedly executed, the PMC CPU 16 determines Whether or not the opening amount excess flag F2 is set, that is, due to the above-mentioned "limit time detection process" that is performed over the entire period of the injection and pressure-holding operations, Δx> ε and the mold is opened more than necessary. It is determined whether or not the time point at which is generated is detected (step S32). As described above, regarding the first injection molding operation, Δx> ε and the mold opening amount excess flag F2 is not set, and the determination result of step S32 is inevitably true. Therefore, PMC CPU
16 advances the injection start time by decrementing the value of the waiting time storage register t1 by a predetermined step width Δt to shorten the set value of the waiting time (step S33),
Cooling and measuring process similar to the conventional process (step S1)
8) and the process of the mold opening and the product protruding process (step S19).

The PMC CPU 16 that has completed the processing of one molding cycle in this manner determines whether or not a continuous molding stop command by an operator's operation is input from the operation panel of the injection molding machine main body or the manual data input device 19 with a display. It is determined (step S20), and if there is no request to stop molding, the process returns to step S3 and the sequence control of the next injection molding operation is started.

Also regarding the second and subsequent injection molding operations,
The processing from step S3 to step S6 is exactly the same as above. However, the waiting time of the waiting time storage register t1 by the processing of step S11 and step S33 that has already been executed in the first processing is Δt compared with the time required from the start of the mold clamping operation to the completion of the mold clamping operation. Since the setting is made shorter, the value of the elapsed time measuring timer T reaches the waiting time t1 at the stage before the mold clamping operation is completed and the mold is locked up in the second and subsequent injection molding operations. The determination result of S8 becomes true, and immediately thereafter, the injection operation is started (step S13). That is, the injection start time is advanced by Δt compared to the time of the previous injection molding operation, and as a result, part of the mold clamping operation and the injection operation is performed in duplicate.

At this stage, since the injection start time setting completion flag F3 is in the reset state (step S14), P
After resetting the mold opening amount excess flag F2 (step S21), the MC CPU 16 repeats the "limit time detection process" of steps S22 to S31 over the entire period of the injection and pressure holding operations in the same manner as described above. Will be executed. Then, in the "limit time detection process", if the time point where Δx> ε is not detected over the entire period of the injection and the pressure-holding operation, as in the above, the mold opening amount excess flag F
2 is not set, and if even one time point where Δx> ε is detected, the mold opening amount excess flag F2 is set. It should be noted that as a result of the value of the elapsed time measuring timer T reaching the waiting time t1 and the processing of step S9 not being executed before the mold is locked up, the stopping of the mold clamping servomotor Mc results in "limit time. This is executed in the process of step S29 in the "detection process".

If the mold opening amount excess flag F2 is not set at the time when the injection and pressure holding operations are completed (step S32), the PMC CPU 16 performs the same process as the standby time set value t1. Is further advanced by Δt (step S33), and steps S18 to S2
The process up to 0 is executed, the process returns to step S3 again, and the sequence control of the next injection molding operation is started.

Hereinafter, until the time point Δx> ε is detected in the “limit time detection process” or the input of the continuous molding stop command is detected, the PMC CPU 16 is
While advancing the waiting time t1 for setting the injection start time by Δt, step S3 to step S6, step S
7 to step S8, step S13 to step S14,
The processes of steps S21 to S33 and steps S18 to S20 are repeatedly executed in exactly the same manner as described above.

FIG. 8 is a conceptual diagram showing an example of changes in the mold clamping force caused by the mold clamping operation and changes in the mold opening force caused by the injection operation on the same time axis. Of course, the rising time from zero mold clamping force corresponds to the starting time of mold clamping operation, and the rising time from zero mold opening force corresponds to the starting time of injection operation.

In the present embodiment, since the first injection operation is started after the completion of the mold clamping operation, the mold opening force does not exceed the mold clamping force at any time during the first injection operation. , The tie bar 9 does not actually grow,
There is no case where Δx> ε. This is the state of FIG. 8a, and at this stage, the waiting time storage register t1 stores the time required for the mold clamping operation (step S11).
reference).

Then, when the value of the waiting time t1 is gradually advanced from this state and the injection molding operation is repeatedly executed while overlapping the injection operation with the mold clamping operation, as shown in the state of FIG. There is a possibility that the mold opening force at a certain point during operation exceeds the mold clamping force and Δx> ε. Here, “the mold opening force exceeds the mold clamping force and there is a possibility that Δx> ε” occurs, which means that the phenomenon of Δx> ε immediately occurs even if the mold opening force exceeds the mold clamping force. Because it is not limited. If ε is set to zero or a value in the vicinity thereof, Δx> ε immediately after the mold opening force exceeds the mold clamping force and the tie bar 9 slightly expands, and the mold opening amount excess flag F2 is set. However, on the other hand, if ε is set as a value of the mold opening amount required for degassing or a value in the vicinity thereof, the overshoot amount of the mold opening force with respect to the mold clamping force becomes Δx> ε is established for the first time when the tie bar 9 in the locked-up state is stretched and reaches a value sufficient to further extend by ε.
Here, the mold opening amount excess flag F2 is set for the first time (see steps S26 and S27). Naturally, when ε is set as zero or a value close to it, the purpose is to completely prevent mold opening, and when ε is set to a value higher than that, the mold is positively set within the allowable value ε. The purpose is to open and degas.
In any case, there is always a stage where Δx> ε, and the value of the waiting time t1 at that time is exactly the injection start limit time.

Step S in the second and subsequent injection molding operations
The PMC CPU 16 that repeatedly executes the processes of 3 to step S6, step S7 to step S8, step S13 to step S14, step S21 to step S33, and step S18 to step S20 is the same as the step S26 of the “limit time detection process”. Δx> ε in the discrimination process
When it is first confirmed that it has become, the mold opening amount excess flag F2 is set (step S27), and at the stage when it is confirmed that the injection and pressure-holding operations have been completed (step S3).
0), through the determination processing of step S32, step S34
Process shifts to. The value stored in the standby time storage register t1 at this point is the injection start limit time as described above, and is the critical standby time when Δx> ε. Since the injection operation in the molding cycle in which the injection start limit time is detected has already been executed with the injection start limit time as the standby time, the phenomenon of Δx> ε actually occurs, and burrs are generated in the product. There is also a possibility. Therefore, the PMC CPU 16 displays a warning on the manual data input device with display 19 that there is a risk of burrs, and further increments the current value of the standby time t1 by a step width of Δt to obtain a phenomenon of Δx> ε. The standby time immediately before the occurrence of is generated, this value is reset in the standby time storage register t1 (step S34), and the injection start time setting completion flag F3 is set (step S35). That is, the waiting time t1 set in step S34, that is, Δx> ε
The waiting time t1 immediately before the occurrence of the phenomenon is the minimum injection start waiting time without the risk of burr generation, and is the final set value.

As a result of the injection start time setting completion flag F3 being set, in subsequent injection molding operations, step S2 is performed.
Until the "limit time detection process" of 2 to step S31 is all non-executed and the input of the continuous molding stop command is detected (step S20), the PMC CPU 16 finally sets the set value t1. In short, the injection start time t1
The mold clamping operation and the injection operation are overlapped on the basis of the value of step S3 to step S6, step S7 to step S
8, step S13 to step S14, step S15
~ Each process of step S20 will be repeatedly performed. The processing of steps S15 to S17 is for detecting the lockup during the injection operation to stop the driving of the mold clamping servomotor Mc, and is not executed when the injection start time setting completion flag F3 is set. It is an alternative process of the processes of steps S28 to S30.

In this way, as a result of the injection molding operation being repeated while overlapping the mold clamping operation with the injection operation in accordance with the minimum injection start time t1 in which burrs do not occur, the molding cycle time is shortened. In addition, since the mold clamping force is not defeated by the mold opening force to cause unnecessary mold opening, the occurrence of burrs is prevented. As already explained, changing the setting of ε may completely prevent the mold opening during the injection operation, or it may be possible to positively perform the mold opening to some extent to perform the degassing. Good.

Although one embodiment has been described above, Δx
It is a problem related to the allowable value ε and the step size Δt that burrs may occur in the product molded at the critical point where> ε. Therefore, in the case where gas is vented by positively opening the mold to some extent, the allowable value ε
Set the value of to be smaller than the desired mold opening amount,
Alternatively, the burr can be easily eliminated by setting the step width of Δt small. If the allowable value ε is set smaller than the desired mold opening amount, Δ
Even if the step size of t is large to some extent, the maximum value of the mold opening amount caused by the injection operation executed in the injection start limit time does not exceed the desired mold opening amount, and
This is because if the step size of Δt is small, the increase in the mold opening amount caused by the shortening of the Δt time can be substantially ignored.
Similarly, even in the case of completely preventing the mold opening during the injection operation, it is possible to substantially prevent the mold opening by setting the step width of Δt small. Of course, in this case, it is not necessary to intentionally execute the process of step S34. However, since it is virtually impossible that the value of Δx1−Δx2 becomes less than or equal to zero, the allowable value ε in the case of completely preventing the mold opening during the injection operation.
It makes no sense to set the value of to be less than zero.

Further, in order to obtain the substantial mold opening amount Δx, it is not always necessary to use the extension Δx1 of the tie bar 9 and the feeding amount Δx2 of the moving platen 6 after the start of the mold clamping operation, and the structure of the injection molding machine and the machine coordinates. Depending on how the system origin is defined, the distance between the rear platen 5 and the stationary platen 7 and the rear platen 5-moving platen 6
The value of Δx may be obtained based on the distance. In this case, the value of Δx is obtained as a value obtained by subtracting the distance between the rear platen 5 and the moving platen 6 and the mold thickness from the distance between the rear platen 5 and the stationary platen 7.
Naturally, if the allowable value ε is set as a value including the mold thickness,
The value obtained by subtracting the distance between the rear platen 5 and the moving platen 6 from the distance between the rear platen 5 and the stationary platen 7 is compared with ε. In any case, since the presence or absence of elongation generated in the tie bar 9 by a force other than the mold clamping force or the presence or absence of inadvertent mold opening is detected, the substantial processing content is the same as that of the first embodiment. It is almost the same. Of course, as in the above-described embodiment, by changing the setting of ε, it is possible to completely prevent the mold opening during the injection operation, or to positively perform the mold opening to some extent to perform the degassing. It is possible.

Furthermore, it is possible to detect the presence or absence of mold opening due to the injection operation without using the substantial mold opening amount Δx. Let Ft be the mold clamping force applied to the injection molding die by the mold clamping operation, Ts be the mold opening force acting on the injection molding die in association with the injection operation, and Fr be the overall tension acting on the tie bar 9. The relational expression of = FT + Ts holds. It is necessary to compare the magnitude relationship between the mold clamping force FT and the mold opening force Ts in order to judge whether or not the mold will be opened in the injection molding die, but in the injection molding machine having the toggle type mold clamping mechanism. It is not always easy to directly obtain the mold clamping force FT by detecting the drive current of the mold clamping servomotor Mc from the viewpoint of the complexity of the link mechanism (the direct pressure type mold clamping mechanism). It's easy). On the other hand, the mold opening force Ts is the drive current of the injection servomotor Ms or the pressure detector 4
Can be easily obtained based on the output from the strain gauge 10 and the projected area of the mold cavity, and the tension Fr can be easily obtained based on the output from the strain gauge 10. Therefore,
Solving the above relational expression for FT, FT = Fr-Ts
And as a result, Fr-Ts> Ts, that is, Fr> 2
If the condition of Ts is satisfied, the mold clamping force FT exceeds the mold opening force Ts, and the mold opening does not occur.

Therefore, it is possible to replace the processing of steps S22 to S27 in the "limit time detection processing" of the first embodiment with the processing of steps S36 to S40 of FIG. In this case, CP for PMC
U16 reads the drive current I of the injection servomotor Ms via the servo CPU 18 (step S36), and based on this value, the reduction ratio of the power transmission mechanism interposed between the injection servomotor Ms and the screw 2 and the screw 2 To obtain a mold opening force Ts by multiplying it by a coefficient k1 determined by the cross-sectional area of the mold and the projected area of the mold cavity (step S37),
Further, the output of the strain gauge 10 is read via the monitor CPU 33, and the tension Fr acting on the tie bar 9 is calculated by multiplying the elongation of the strain gauge 10 determined by this output by a coefficient determined by the total length of the tie bar 9 and the elastic modulus. After obtaining (step S38), the magnitude relation between Fr and 2Ts is compared (step S39). Naturally, Fr> 2Ts (FT
> Ts), mold opening does not occur, and Fr ≦ 2T
If s, the mold opening occurs, so the mold opening amount excess flag F2 is set only when Fr ≦ 2Ts (step S40). The same result can be obtained by reading the output from the pressure detector 4 instead of the drive current of the injection servomotor Ms in the process of step S36. Needless to say, at this time, the value of the coefficient k1 used in the process of step S37 is a value determined by the cross-sectional area of the screw 2, the projected area of the mold cavity, and the like, and is adjusted according to the drive current I. The value is different from the coefficient k1 described above. Further, even when the substantial mold opening amount Δx is not used, the mold opening during the injection operation can be completely prevented or the mold opening can be prevented to some extent as in the first several embodiments described above. It is also possible to positively perform the gas removal. That is,
The allowable value ε ', which allows the mold opening force to exceed the mold clamping force, is set, and Fr-2Ts>-in the process of step S39.
By performing the ε'discrimination process, it is possible to positively perform the mold opening and perform the degassing. However, as in the first embodiment, the actual mold opening amount Δx is set. Since the discrimination process is not performed by comparing with the allowable value ε of, it is difficult to guarantee the actual size of the mold opening itself. Therefore, if it is necessary to set a precise mold opening amount, the mold opening force and the mold clamping force corresponding to the desired mold opening amount Δx are based on the desired mold opening amount Δx, the elastic modulus of the tie bar 9, and the like. It is necessary to obtain the difference ε'in advance and to set that value as the allowable value ε '.

In each of the embodiments described above, the final injection start time is automatically set based on the injection start limit time obtained in the "limit time detection process". S34 in "time setting process"
Alternatively, the value of the injection standby time storage register t1 at that time may be displayed on the display-equipped manual data input device 19 instead of executing the above process. in this case,
The PMC CPU 16 determines steps S3 to S6, S7 to S8, S13 to S14, and S based on the value of the injection start limit time t1.
Since each process of 15 to step S20 is repeatedly executed, the operator manually gradually changes the value of the injection standby time storage register t1 during this period, checking the presence or absence of burrs in the product, and the like. The injection start time of is calculated.

In each of the above-described embodiments, the injection start time is gradually advanced to repeatedly execute the injection molding operation, and the substantial mold opening amount and the mold opening force are obtained each time and compared with the allowable value. By detecting the injection start time limit by this, based on this injection start time limit, it was to set a more suitable injection start time by automatic or manual operation,
It is also possible to detect the injection start limit time without repeatedly performing the injection molding operation.

In this case, the injection molding machine is made to perform only the mold clamping operation, and the mold clamping force FT acting on the injection molding mold during that period is obtained.
Is sampled at a predetermined sampling cycle, and the mold clamping force FT acting at each time point is stored in a file of the non-volatile memory 26 in correspondence with the elapsed time after the start of the mold clamping operation. Similarly, the injection operation is performed on the mold in the lockup completed state, the mold opening force Ts that acts during that period is sampled at a predetermined sampling cycle, and the mold opening force Ts that acts at each time point is injected. The file is stored in the non-volatile memory 26 in correspondence with the elapsed time after the start of the operation.

The clamping force applied to the injection molding die by the clamping operation is FT, the mold opening force acting on the injection molding die with the injection operation is Ts, and the total tension acting on the tie bar 9 is Fr. For example, the point where the relational expression of Fr = FT + Ts is established has already been described. However, in the case where only the mold clamping operation is independently executed as in this embodiment, the value of Ts is always zero, so Fr = The relationship of FT is established, and the value of the mold clamping force FT at each time point is the same as the value of the tension Fr calculated based on the output from the strain gauge 10. Further, in the case of a direct pressure type injection molding machine, the mold clamping force FT at each time may be obtained from the drive current of the mold clamping servomotor Mc. Regarding the mold opening force Ts, as described above, the drive current of the injection servomotor Ms or the pressure detector 4
It can be easily obtained based on the output from the and the projected area of the mold cavity.

Therefore, for example, the PMC CPU 16 causes the PMC CPU 16 to perform the above-described sampling processing at every predetermined sampling period τ, and the result is stored in a file of the nonvolatile memory 26 as shown in FIG. Note that FIG.
Then, the mold clamping force FT i and the mold opening force T corresponding to the elapsed time i τ
Although si is stored, this does not mean that mold clamping and injection are performed at the same time. Until you get tired
The mold clamping force at the elapsed time iτ after the start of the mold clamping operation in the independently performed mold clamping operation becomes FT i, and in the injection operation executed in the lockup completed state, at the time iτ after the injection operation starts. It merely indicates that the mold opening force is Tsi. The sampling of these data can be obtained in one molding cycle by starting the injection operation after the completion of the mold clamping operation.

Therefore, the operator uses the graphic function of the manual data input device 19 with a display to
As shown in FIG. 8, these sampling data are displayed graphically on the same time axis. Then, the manual data input device 19 with a display is operated to open the mold opening force Ts.
Or the mold clamping force FT graph is shifted along the time axis so that the graph of the mold opening force Ts and the graph of the mold clamping force FT intersect at one point, for example, the state shown in b of FIG. To detect. The time corresponding to the distance between the start points of each graph in this state is the waiting time from the start of mold clamping to the start of injection, that is, the value corresponding to the injection start limit time in each of the above-described embodiments.

Therefore, for example, if this value or more is set as it is as the injection start time, it is possible to perform the molding operation such that substantial mold opening does not occur during the injection operation. The injection start limit time detected in this way is the actual mold opening amount Δx as in the first embodiment.
Is not obtained by comparing the mold opening tolerance value ε with
After all, it is difficult to obtain a desired mold opening amount only by determining the injection start time with reference to the graph. Therefore, if it is necessary to set a strict mold opening amount for degassing or the like, once set the injection start limit time to the injection start time t1.
After that, the steps S3 to S6, step S7 to step S8, step S13 to step S14, step S15 to step S20 are repeatedly executed by the method as described above, and the operator waits for injection during this time. It is necessary to manually and gradually change the value of the time storage register t1 to obtain the optimum injection start time while confirming the presence or absence of burrs in the product.

[0050]

According to the injection control method of the present invention, the injection molding operation is performed while sequentially advancing the injection start time, and the substantial mold opening amount, or the mold clamping force and the mold opening force are large or small for each molding cycle. By determining the relationship, the critical injection start time at which mold opening occurs more than necessary can be reliably detected as the injection start limit time, and an appropriate injection start time can be set based on this injection start limit time. Even when it is necessary to overlap the mold clamping operation and the injection operation to perform the injection molding work in a short cycle time, it is possible to prevent the accident such as the occurrence of burrs by inadvertently advancing the injection start time. . In addition, the mold clamping force applied to the injection mold by the mold clamping operation and the mold opening force acting on the injection mold by the injection operation are displayed graphically on the same time axis corresponding to the elapsed time of each operation. , The mold opening force or mold clamping force graph is moved along the time axis to obtain the limit position where the mold opening force graph does not interfere with the mold clamping force graph, so that the injection start limit time is reliably detected. Since the proper injection start time is set based on the injection start limit time, even if it is necessary to overlap the mold clamping operation and the injection operation and perform injection molding work in a short cycle time, careless injection is performed. Accidents such as burrs occurring earlier than before can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing a main part of a toggle electric injection molding machine of an embodiment to which an injection control method according to the present invention is applied.

FIG. 2 is a flowchart showing an injection start time setting process in the embodiment.

FIG. 3 is a continuation of the flowchart showing the injection start time setting process.

FIG. 4 is a continuation of the flowchart showing the injection start time setting process.

FIG. 5 is a continuation of the flowchart showing the injection start time setting process (limit time detection process).

FIG. 6 is a continuation of the flowchart showing the injection start time setting process.

FIG. 7 is a flowchart showing a main part of a time limit detection process of another embodiment.

FIG. 8 is a conceptual diagram showing, on the same time axis, an example of changes in the mold clamping force caused by the mold clamping operation and changes in the mold opening force caused by the injection operation.

FIG. 9 is a conceptual diagram of a file that stores changes in mold clamping force and changes in mold opening force corresponding to respective elapsed times.

[Explanation of symbols]

 5 Rear platen 6 Moving platen 7 Stationary platen 9 Tie bar 10 Strain gauge 11 Controller 16 CPU for PMC 19 Manual data input device with display 26 Non-volatile memory

Claims (4)

[Claims] 1. An injection molding operation is performed while advancing the injection start time, and the elongation of the tie bar and the amount of the moving platen fed out during the mold clamping operation are sequentially obtained in synchronization with each molding cycle, and the tie bar at the same time point is obtained. If even one difference obtained by subtracting the moving-out amount of the moving platen from the elongation of the value exceeds the allowable value, the injection start time at that time is detected as the injection start limit time, and the injection start limit time is determined based on the injection start limit time. An injection control method for an injection molding machine, wherein an injection start time in which all of the differences do not exceed an allowable value is obtained in the vicinity of, and this is set as the injection start time. 2. The injection molding operation is performed while advancing the injection start time, and the distance between the rear platen and the stationary platen and the distance between the rear platen and the moving platen during the mold clamping operation are sequentially obtained in synchronization with each other in the same molding cycle. If the difference between the distance between the rear platen and the stationary platen at the point in time minus the distance between the rear platen and the moving platen exceeds the allowable value, the injection start time at that time is detected as the injection start limit time, and based on the injection start limit time. An injection control method for an injection molding machine, wherein an injection start time in which all of the differences do not exceed an allowable value is obtained in the vicinity of the injection start limit time, and this is set as the injection start time. 3. A mold opening for causing an injection molding operation to be performed while advancing the injection start time sequentially, and for each molding cycle, the mold clamping force applied to the injection molding mold by the mold clamping operation and the injection operation by the injection operation. The force and the force are sequentially synchronized, and if any point at which the mold opening force exceeds the mold clamping force is detected, the injection start time at that time is detected as the injection start limit time, and based on the injection start limit time. The injection control method of the injection molding machine, wherein the injection start time at which the mold opening force does not exceed the mold clamping force in the vicinity of the injection start limit time is set as the injection start time. 4. The mold clamping force applied to the injection mold by the mold clamping operation and the mold opening force acting on the injection mold by the injection operation on the same time axis corresponding to the elapsed time of each operation. Display the graph, move the graph of mold opening force or mold clamping force along the time axis, find the limit position where the graph of mold opening force does not interfere with the graph of mold clamping force, and determine the injection start time from the limit position. An injection control method for an injection molding machine, which is obtained and set.